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      Articles written in Pramana – Journal of Physics

    • Crystallographic and magnetic phase transition in TlMnCl3

      R Vijayaraghavan M D Karkhanavala S D Damle L C Gupta U R K Rao

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      The results of our NMR, EPR and magnetic susceptibility measurements in the paramagnetic state of TlMnCl3 are reported here. The NMR paramagnetic shift of thallium is found to be small but positive. Mn2+ EPR line is exchange narrowed. The susceptibility measurements indicate an antiferromagnetic transition. The heat of crystallographic phase transition ΔH, in TlMnCl3 has been measured using differential scanning calorimetry. The crystallographic phase transition appears to be first order and ΔH is unusually low viz. 10 cal mole−1. In the case of KMnF3 ΔH, which is reported here for the first time, is determined to be 2 cal mole−1.

    • ESR study of exchange coupled pairs in copper diethyldithiocarbamate

      R Kumari Cowsik R Srinivasan

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      ESR investigations on exchange coupled pairs of Cu ions in single crystals of Cu(dtc)2, isomorphously diluted with the corresponding diamagnetic zinc salt, are reported. The spin Hamiltonian parameters for the coupled species (S=1) are:g=2.1025,g+=2.031,A=75.1×10−4 cm−1,B=14.8×10−4,D=276.0×10−4 cm−1 andE=46.7×10−4 cm−1. While theg andA tensors show tetragonal symmetry, the zeor-field splitting tensor is rhombic and has principal axes different from those of theg andA tensors. Intensity measurements made down to 4.2 K indicate that the exchange is ferromagnetic with |FFF| ∼ 10 cm−1. Direct dipole-dipole interaction appears to be the major contribution to the zero-field splitting. A calculation on the distributed point dipole model shows that dipolar interaction is considerably modified by the high covalency of the Cu-S bond and accounts for the rhombic nature of the tensor. The possible exchange mechanisms in Cu(dtc)2—direct exchange and superexchange through the bridging sulphurs—are discussed.

    • Structure determination of Ls-threonine by neutron diffraction

      M Ramanadham S K Sikka R Chidambaram

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      The structure of the aminoacid, Ls-threonine [NH3+ CH(CHOHCH3)COO], space groupP212121,a=13.630(5),b=7.753(1),c=5.162(2) Å,z=4, has been determined from neutron diffraction data using direct methods. The intensities of 1148 neutron Bragg reflections were measured from a single crystal. The structural parameters were refined by the method of least squares using anisotropic temperature factors. The finalR(F2) is 0.068. The structure was also refined from the x-ray data of Shoemakeret al (1950J. Am. Chem. Soc.72 2328); there is good agreement between the two sets of heavy atom parameters. The parameters of hydrogen atoms are of course more precisely determined in our neutron study. The molecular conformation and the hydrogen bonding scheme are discussed. Weighted average values of bond distances and angles from 14 aminoacid structures with ionized carboxylic groups studied by neutron diffraction at Brookheven and Trombay are also presented.

    • Coexistence curve and rectilinear diameter in the critical liquid system carbon disulphide+nitromethane

      E S R Gopal R Ramachandra P Chandra Sekhar

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      The phase boundary of the binary liquid system CS2+CH3NO2 is studied over nearly six decades in reduced temperature 3×10−6<ε=(TCT)/TC<2×10−1 and over the composition range 8-98 mole % of CS2. The critical parameters areTC=335.132K andxC=57.34 mole % of CS2. A single critical exponentβ=0.315±0.004 fits the observations over the entire range with no indication ofβ increasing to the classical value of 1/2 far away fromTC. The diameter of the coexistence curve shows a rectilinear behaviour only far away fromTC. NearTC, the deviation ΔX from the rectilinear law seems to fit a curve of the form ΔX=fε7/8 exp (−h), the derivative of which has a singularity like that of specific heat. An ambiguity in the analysis of the data in terms of mole fractions and volume fractions is pointed out. It is also suggested that the curvature of the diameter may be much weaker in a liquid-gas system and hence might have escaped detection.

    • The filamentary structure of the sunspot magnetic fields

      R Pratap

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      The filamentary structure of the magnetic fields as well as the coherent radiations that emanate from a sunspot are explained considering solar burst as a non-equilibrium process. Methods of irreversible statistical mechanics have been applied to the problem of an electron gas in a constant magnetic field to explain the above features. We have obtained the non-equilibrium distribution function in the self-consistent field approximation. The dielectric function, we obtained, is a function of time, besides being a function of frequency and wavevector. We have thus taken the non-linearity of the system as well. This theory explains many features of stria bursts, chain bursts as well as the type III bursts. This also accounts for the bunching of the magnetic field lines as a consequence of quantisation of flux in the Landau sense.

    • Analysis of proton-carbon inelastic cross sections measured in satellite experiment and upper limit on primary cosmic ray deuteron flux in the energy range 20 to 600 GeV

      Som N Ganguli R Raghavan A Subramanian

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      An analysis has been made of the experimental results of Akimovet al on the inelastic cross sections of proton on proton and carbon targets in the energy range 20 to 600 GeV obtained from artificial earth satellites. It is found that an upper limit of 4% at 95% confidence level can be set on the fraction of deuterons relative to the flux of protons in the primary cosmic radiation at energies in the range 20 to 60 GeV. There is an indication for a rise of (29±7) mb in the inelastic cross section of proton against carbon in the energy range of 200 to 600 GeV over and above what is expected from Glauber’s theory. If this rise has to be interpreted as due to contamination from cosmic ray deuterons, the fraction of deuterons relative to protons needed is (15±4)% in this energy region.

    • Analysis of cosmic ray data on nucleon-nucleus collisions and its implication on high energy behaviour of nucleon-nucleon total cross section

      Som N Ganguli R Raghavan A Subramanian

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      From existing cosmic ray measurements of theinelastic collision cross sections of nucleons on nuclei of carbon, iron and lead in the range of energies 102 to 104 GeV as well as the measurements of cross sections on air nuclei in the extensive air shower (EAS) regions (105 to 108 GeV), we conclude that the Glauber multiple scattering theory is adequate to account for the data. Recent suggestion of Maor and Nussinov to parametrize the nucleon-nucleon total cross section with a component growing proportional to ln2E (E is the incident energy) is at variance with the EAS data. However the data are consistent with a nucleon-nucleon total cross section rising no faster than lnE in these energy regions.

    • Crystal field effects on the saturation magnetic moment of Sm3+ ion in ferronagnetic samarium compounds

      S K Malik R Vijayaraghavan

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      The effects of cubic crystal fields on the saturation magnetic moment of Sm3+ ion in ferromagnetic compounds have been investigated. In samarium compounds with magnetic elements, the exchange fieldHex acting on Sm3+ ion is taken to be proportional to the sublattice magnetization of the magnetic element, while in compounds with nonmagnetic elementsHex is taken to be proportional to the spin average of the Sm3+ ion and is determined self-consistently. In both types of compoundsHex is assumed to be along [001] direction. The saturation magnetic moment is calculated by taking into account the admixture of excited (J=7/2 andJ=9/2) levels into the ground (J=5/2) level of Sm3+ ion by crystal fields and exchange fields. It is shown that depending upon the strength, the crystal fields quench or enhance the magnetic moment from the free ion value, and in some cases force Sm3+ ion to behave effectively like an (L+S) ion rather than an (LS)ion. The crystal fields may have important bearing on the performance of samarium compounds as permanent magnet materials.

    • Frequency distribution function and critical points for phonons in graphite

      R Ramani K K Mani

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      A molecular force field for the study of the dynamics of graphite has been reported earlier (Mani and Ramani 1974). In the present paper we present calculations of the single phonon density of states and the lattice specific heat. Most of the peaks in the frequency distribution function have been identified and classified using symmetry-required critical points. The validity of the force field used has also been discussed.

    • Chiral constraints in dual models

      R Ramachandran

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      An attempt is made to see how much of chiral symmetry is contained in dual models for pseudoscalar mesons. The chiral constraints are found to be contained in dual models as either dynamical restriction or kinematical factors. At the phenomenological level there is no serious inconsistency.

    • Orbit of the spectroscopic binary b Persei

      R Rajamohan M Parthasarathy

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      New spectroscopic orbital elements have been derived for the close binary system b Persei. The period is improved to 1.527360 days. Earlier observations by Cannon (1914), Harper (1930) and Heard (1938) have been reanalysed and the reality of the variations in the orbital elements is established. The change inω indicates an aspidal motion period of about 60 years. Changes in some of the orbital elements may be due to the distortion of the radial velocity curve by gas streams present in the system. In view of the flaring radio emission detected from this system and the variations of the orbital elements, we believe that the close binary system b Persei is in an active mass transfer phase.

    • Photoelectric photometry of the open cluster NGC 1778

      U C Joshi R Sagar P Pandey

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      PhotoelectricU, B, V magnitudes and colours for 48 stars in the open cluster NGC 1778 have been determined. The colour excess is$$0_ \cdot ^m 34$$, distance to the cluster 1062 pc, and apparent diameter of the cluster 4.5 minutes of arc. The age is estimated at 1.6×108 years.

    • The C (2Π)→X(2Σ+) transition in thermal emission spectra of the diatomic alkaline earth bromides) transition in thermal emission spectra of the diatomic alkaline earth bromides

      M M Joshi R Gopal

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      The extensive thermal emission spectrum attributed to the diatomic bromides of calcium, strontium and barium has been observed in the visible region at temperatures about 2200–2400° C, using a vacuum graphite furnace. Many new bands,viz., 141 in CaBr, 53 in SrBr and 68 in BaBr, have been recorded and classified. The vibrational constants agree with those determined by earlier workers and involved the ground state in each case. The transition C→X apears in each molecule and consists of two equally intense systems,viz., C1→X and C2→X. The general spectroscopic features of the C→X systems of the bromides of the II A sub group of the periodic table have been compared. They exhibit a close structural similarity and furnish a good example of homologous spectra. The system C→X in all these molecules arises from a C2π−X2Σ+ transition where the2π state appears to be intermediate between Hund’s cases (a) and (b).

    • Equation of state and temperature variation of the bulk modulus of the alkaline earth fluorides

      R Srinivasan V Ramachandran

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      The isotherms for the alkaline earth fluorides (CaF2, SrF2 and BaF2) have been computed using the expression for the total free energy of a crystal in the quasiharmonic approximation. The theoretical points for SrF2 and BaF2 have been compared with the points derived from Bridgman’s experimental relation.

      The temperature variation of the isothermal bulk modulus of the alkaline earth fluorides has been worked out on the basis of Axe’s shell model. The theoretica points are compared with the points obtained from the temperature variation of the elastic constants data. It is found that the vibrational contribution to the temperature variation of the elastic constants in these crystals is significant.

    • Images of an incoherent annulus in the presence of transverse sinusoidal vibrations

      K Singh R Rattan

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      The diffraction image of an incoherent bright annular test object is obtained by using Fourier transform method. The effect of transverse sinusoidal vibrations has been studied and results are given in graphical form for various sizes of the object. It is observed that in certain cases the presence of vibrations completely distorts the object. Hence a detailed analysis of image intensity distribution should prove useful in aerial reconnaissance work and performance evaluation tests.

    • Studies in molecular structure, symmetry and conformation—Part XIV. Crystal and molecular structure of L-isoleucine hydrochloride monohydrate form II

      K I Varughese R Srinivasan

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      The crystal structure of a new form of L-isoleucine hydrochloride monohydrate C6H13O2NHClH2O (termed form II) has been determined using three-dimensional photographic data. This differs conformationally from the hydrochloride derivative (termed form I, Trommel and Bijvoet 1954) reported earlier. The crystal belongs to the orthorhombic space group P212121 with cell dimensions,a=5.87±0.01,b=24.77±0.02 andc=6.85±0.01 Å and four molecules per cell,ρobs=1.240 g/cm3,ρcal=1.238 g/cm3,µ for CuKa=32.6 cm−1.

    • Determination of imaginary components of anomalous scattering of some elements from experimental data

      S S Rajan R Srinivasan

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      Using the Bijvoet difference data reported in the literature for four compounds,viz./it, zinc sulphide, L-α-glyceryl phosphoryl ethanolamine monohydrate, 1-β-arabinofurinosyl cytosine hydrochloride and lithium aluminium oxide, the anomalous dispersion components Δf″ of the stronger anomalous scatterer in each case is calculated accepting the theoretical values for the lighter anomalous scatterers. For MoKα radiation the values turn out to be Δf″zn=1.470 (85), and for CuKα Δf″P=0.430 (25) Δf″C1=0.715 (18) and Δf″A1=0.264 (21).

    • Site symmetry and internal strains

      R Srinivasan G Lakshmi

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      The determination of the internal strains on the coupling parameter approach becomes very involved particularly when the number of atoms per unit cell is very large. It is shown in this paper that a knowledge of the site symmetry of the atoms helps one in determining the number of non-vanishing internal strain coefficients easily. The internal strain coefficients of two symmetry connected atoms can also be related. Examples are shown to illustrate these ideas.

    • Dielectric properties of 4′-n-alkyl-4-cyanobiphenyls in their nematic phases

      B R Ratna R Shashidhar

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      The principal dielectric constants of the pentyl to octyl derivatives of 4′-n-alkyl-4-cyanobiphenyl have been measured as functions of temperature in their nematic and isotropic phases. All the compounds exhibit a strong positive dielectric anisotropy due to the presence of a large dipole moment along the major molecular axis. The principal dielectric constantsε andε as well as the anisotropy Δε decrease with increasing alkyl chain length. The experimental value of$$\bar \in = \frac{1}{3}$$ (ε+2ε) decreases with decreasing temperature, and is throughout less than the extrapolated isotropic value, in conformity with the model of antiferroelectric short range order proposed by Madhusudana and Chandrasekhar.

    • Nuclear quadrupole resonance studies of209Bi in Bi4(GeO4)3 and Bi4(SiO4)3

      K V Gopalakrishnan L C Gupta R Vijayaraghavan

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      Nuclear quadrupole resonance (NQR) of209Bi has been studied in Bi4 (GeO4)3 and Bi4 (SiO4)3 using a wide band coherence-controlled superregenerative oscillator-detector. All the four allowed (ΔMI=±1) transitions are observed. In both cases the electric field gradient (EFG) tensor is axially symmetric (η=0.0). The quadrupole coupling constante2qQ is measured to be 490.8±1 MHz and 470.4±1 MHz respectively. It is pointed out that the purely ionic model is inadequate to understand these results. With the available experimental accuracy and the strength of the applied electric field (∼ 6 KV/cm), no field-induced effects on the NQR spectrum could be observed in the case of Bi4 (SiO4)3.

    • A spectroscopic study of the Scorpio-Centaurus association

      R Rajamohan

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      Rotational velocities as well as hydrogen and helium line intensities of one hundred and twelve members of the Scorpio-Centaurus association have been derived. For stars withMv<0·0, the distribution of rotational velocities of both the upper Scorpius subgroup and the upper Centaurus -Lupus subgroup are similar and closely resemble those of the field stars. Stars withMv>0·0, all of which are found in the dense upper Scorpius region, rotate much faster than their counter-parts amongst field stars, the Pleiades and Alpha-Persei cluster members.

      The measured equivalent width ofHγ for 77 stars provide a distance modulus of 6·0 ± 0·09 magnitudes for the association. Evolutionary effects in the derived hydrogen line intensities are found between the two subgroups. The hydrogen-line intensities at all spectral types in the upper Centaurus-Lupus subgroup are systematically smaller than those of members in the upper Scorpius subgroup.

      Analysis of high dispersion spectra of five members of the association yield a helium abundance ofNHe/NH=0·096 ± 0·004. Along with data available in the literature, the mean helium abundance of thirteen stars of this association is found to be 0·098 ± 0·004 by number. For the two main subgroups of this association, we derive a value of 0·105 ± 0·001 for the upper Centaurus-Lupus group from three stars and 0·096 ± 0·005 for the upper Scorpius group from ten stars.

      Within the capabilities of our present methods, there seems to be no difference between the two subgroups as far as rotational velocities and initial helium abundance are concerned, a fact that must be borne in mind in the interpretation of the difference found between the two subgroups from photoelectric photometry.

    • Electron momentum distributions and compton profiles of some molecules with FSGO model

      S R Gadre R Ramaswamy P T Narasimhan

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      The electron momentum distributions and the Compton profiles (within the impulse approximation) of H2, LiH, methane, water, acetylene, ethylene, ethane cyclopropane and cyclobutane have been calculated using the floating spherical Gaussian orbital (FSGO) wavefunctions. The agreement of the single-FSGO Compton profiles with the corresponding experimental or the Hartree-Fock (HF-SCF) theoretical ones is fairly good in most of the cases examined. The advantages and drawbacks of using the FSGO model for the calculation of Compton profiles are discussed.

    • The asteroidal belt and Kirkwood gaps—I. A statistical study

      R Pratap

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      In this paper we have made a spectral analysis study of matter distribution in the asteroidal belt. We have Fourier analysed this distribution and obtained the autocorrelation and power spectrum, and have identified the ratios from the resonance theory. We have shown that the Kirkwood gaps cannot be satisfactorily interpreted as due to mere resonance between the asteroid and Jupiter orbital motions. We propose that they may be regarded as a consequence of density waves generated in the gas dise in the ecliptic plane in the neighbourhood of the Sun. We have also shown that the process is non-Marcovian and hence cannot be subjected to a hydrodynamical analysis.

    • The asteroidal belt and Kirkwood gaps—II. Kinematical theory

      R Pratap

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      We have developed a kinematical theory for the asteroidal belt and Kirkwood gaps from the point of view of stellar dynamics. We have generated the potential that would produce these gaps and have made a spectral analysis study. We have shown that these gaps could be due to spiral tubes of matter in the ecliptic plane as a consequence of differential rotation and spatial interference of density waves. We have also shown that this mechanism could account for depletion of matter from this region.

    • ESR study of exchange coupled pairs in copper diethyldithiocarbamate—explanation of the low temperature hyperfine anomaly

      CV Manjunath Kumari Santosh R Srinivasan

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      A study of the hyperfine interaction in the ESR of Cu-Cu pairs in single crystals of copper diethyldithiocarbamate as a function of temperature has shown distinct differences in the hyperfine structure in the two fine structure transitions at 20 K, the spectrum not having the same hyperfine intensity pattern in the low field fine structure transition in contrast to that of the high field transition. The details of the structure of both the fine structure transitions in the 20 K spectrum have now been explained by recognizing the fact that the mixing of the nuclear spin states caused by the anisotropic hyperfine interaction affects the electron spin states | + 1 > and | −> differently. This has incidentally led to a determination of the sign ofD confirming the earlier model. The anomalous hyperfine structure is found to become symmetric at 77 K and 300 K. It is proposed that the reason for this lies in the dynamics of spin-lattice interaction which limits the lifetime of the spin states in each of the electronic levels | − 1 >, | 0 > and | + 1 > The estimate of spin-lattice relaxation time agrees with those indicated from other studies. The model proposed here for the hyperfine interaction of pairs in the electronic triplet state is of general validity.

    • Dual charged solution in curved space-time

      R Ramachandran V M Raval

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      A dual charged solution carrying both electric and magnetic charge is formulated in SU(2) × U(1) gauge theory without making use of the topological characteristics of Higgs fields. When Dirac quantisation condition is imposed, two consequences follow: (i) Weinberg angle is restricted to the value sin2θ = 1/2 and (ii) the solution cannot have fractional electric change, but must have integer items the basic electric charge of the theory. The infinity inherent in the theory is removed at the classical level by the use of gravitational effects by obtaining the same solution in the curved space-time. The resultant metric is of Reissner-Nordström form.

    • An on-line TDC-312 computer-controlled neutron diffractometer

      A Sequeira S N Momin H Rajagopal J N Soni R Chidambaram Dilip Kumar A Ramana Rao V M Gopu

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      The design and fabrication of an indigenous on-line computer controlled four-circle neutron diffractometer at the CIRUS reactor in Trombay are described. The diffractometer has an 18 in dia full-circle crystal-orienter which is sturdy enough to carry a cryostat. Three crystal orientation angles χ, φ and ω and the detector angle 2θ can be set to an accuracy of 0·01°. The four angle shafts are driven through precision worm-gears by SCR-controlled DC motors and their instantaneous positions sensed by optical digitizers. The diffractometer is interfaced to an ECIL TDC-312 computer system consisting of the CPU with 4K-memory, ASR-35 teletype, X-Y plotter and the digital input/output system (DIOS). The DIOS which operates under program control is a real-time peripheral device used to exchange information in digital form between the computer and the diffractometer. A software package consisting of over 40 useroriented teletype commands has been developed for on-line control and automatic data-acquisition.

    • Computer simulation of back sputtering and ion penetration into polycrystalline targets

      R Shanta

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      In the present work computer simultations of the back sputtering of low energy neon ions with low impact parameter and the penetration of the same for higher values of the impact parameter have been performed. Initial ion energies in the range 100 to 500 eV and impact parameters in the range 0<p⩽0.61 Å have been used. Assuming a binary collision model and for the interatomic potential the Leibfried-Oen matching potential, we compute the complete collision cascade. For Ne+-Cu interaction, the sputtering threshold energy is found to be 125 eV and the sputtering yield increases with the ion energy. The sputtering yield versus ion energy is plotted and is found to agree well with experiment. It is seen that the back scattering is confined to small impact parameters justifying the use of the binary collision model.

    • An angular momentum expansion of energy and structure of high spin states

      M Satpathy R Sahu A Ansari L Satpathy

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      A new angular momentum expansion of level energies of ground-state band of even-even nuclei has been obtained which is found to converge rapidly even for the most back-bending nuclei. Attempts have been made to interpret the parameters and calculate them microscopically. It is found that nuclear structure in the forward bending region is quite different compared to that in the back-bending region.

    • A polarised neutron study of magnetic moment density in Cu2MnAl

      V C Rakhecha R Chakravarthy N S Satya Murthy

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      A polarised neutron study of the ferromagnetic Heusler alloy Cu2Mn0.863Al1.057 has been made. It has been concluded that the magnetic moment density is primarily situated on the Mn ions. On assigning the Mn-moment value, the observed magnetic form factor is found to be in good agreement with the Mn2+ free ion form factor calculated by Watson and Freeman. A slight asphericity has been observed in the moment density. It is estimated that there are about 3% excess 3d-electrons in the Eg states compared to spherical distribution. There is evidence of a very small positive polarisation of the Cu atoms. No appreciable conduction electron polarisation is found.

    • On the alleged equivalence of certain field theories

      R Rajaraman

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      We critically examine some recent claims that certain field theories with and without boson kinetic energy terms are equivalent. We point out that the crucial element in these claims is the finiteness or otherwise of the boson wavefunction renormalisation constant. We show that when this constant is finite, the equivalence proof offered in the literature fails in a direct way. When the constant is divergent, the claimed equivalence is only a consequence of improper use of divergent quantities.

    • An automated high precision calorimeter for the temperature range 200K–400K. Part 1: Design and performance

      I S Williams R Street E S R Gopal

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      A fully automated calorimeter has been designed and tested over the temperature range 200K–400K. The system may be used for measurements with an absolute accuracy of 0.2% of samples of approximate mass 50g and thermal capacity 15 JK−1. The temperature of the sample is determined by a quartz crystal thermometer of resolution 100 µK which is not in direct thermal contact with the sample. The performance of the system is illustrated by results obtained on high purity copper, distilled water and K2PbCu(NO2)6 which exhibits very sharp first order phase transitions at about 273.4K and 281.8K.

    • The resolution of a paradox which arises in the elementary discharge theory of an ion source

      R Jones

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      It is shown that the inclusion of a small amount of primary ionisation makes the solution to the discharge equilibrium problem single valued.

    • Characteristics of high energy interactions I. High energy gamma-ray spectra near the top of the atmosphere

      R Hasan A K Agrawal M S Swami

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      An emulsion chamber was used to study the characteristics of high energy nuclear interactions from the production spectra ofγ-rays. The emulsion chamber, which comprised of two parts, namely the detector and the graphite producer unit, was exposed to cosmic rays for about 7 hr at an atmospheric depth of 10 g cm−2 at Hyderabad (geomagnetic latitude 7·6°N). 720 electromagnetic cascades due toγ-rays were recorded in the detector. These cascades were classified into three groups; (a)γ-rays from nuclear interactions in the detector (b)γ-rays from nuclear interactions in the producer unit and (c)γ-rays of atmospheric origin. The energies of the cascades were determined using photometric method. The spectra ofγ-rays from groups (a) and (c) were determined and compared with similar spectra obtained at greater atmospheric depths. The spectra were found to obey a power law. The spectrum ofγ-rays of atmospheric origin was found to steepen at high energies,Er>2200 GeV.

    • Characteristics of high energy interactions II. Production spectra of Gamma-rays in graphite

      A K Agrawal R Hasan M S Swami

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      Twenty high energy nuclear interactions produced in the graphite units of an emulsion chamber were recorded. The emulsion chamber was exposed to cosmic rays at an atmospheric depth of 10 g cm−2 for about 7 hr over Hyderabad, India. Fourteen interactions which radiated energyΣ Er⩾1000 GeV in the form ofγ-rays were analysed in detail. The median energy 〈Σ Er〉 of the interactions was 1600 GeV. Results concerning the multiplicity, the transverse and longitudinal momentum distributions, and the fractional energy distribution ofγ-rays in these interactions are presented. The average transverse momentum ofπ0—mesons <ptπ0> is found to increase very slowly with the primary energyE0 and it can be approximated by the function <ptπ0>=0·238E00.06.

    • On the colour contribution to effective weak vertex in broken colour gauge theories

      R Ramachandran

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      Treating the breaking of colour symmetry via the mixing between the colour gluons and weak bosons (a la Rajasekaran and Roy) it is observed that the colour contribution to the effective weak vertex of a quark at zero momentum transfer is zero uptoO(α).

    • Output characteristics of a 400 MW Nd:glass laser system

      R Bhatnagar P D Gupta B S Narayan M Anwar B L Gupta D D Bhawalkar

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      The paper discusses the performance characteristics of a Nd: glass laser system designed for laser produced plasma studies. It consists of aQ-switched oscillator followed by two amplifier stages. The output behaviour of the oscillator, i.e. laser pulse duration, peak power and optimum coupling, has been studied and is in good agreement with theory. Gain characteristics of amplifiers were obtained as a function of various parameters. Energies in excess of 7 J with pulse durations as small as 18 nsec were obtained giving rise to 400 MW peak power.

    • Molecular packing for planar molecules

      Y T Thathachari R Kamalam R Srinivasan

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      The crystal packing of five planar molecules is considered in this paper. Each unit cell contains two non-equivalent molecules whose planes are inclined to each other. It is shown that the angle of inclination between the planes is completely determined by a simple geometrical criterion. A simple sequential arrangement of the four molecules defining the elementary parallelopiped of which the entire crystal is built leads to various configurations from which the one which has the least interaction energy can be picked out. Using a crude Lennard-Jones potential for the non-bonded interaction and a hard sphere model for the atoms, one can compute the crystal structure from the minimum energy criterion and this is found to be in fair agreement with the observed structure. This simple sequential packing with some modifications can provide an useful model for calculating the radial distribution function in amorphous solids involving planar groups.

    • Adjustment of the ion energy distribution in double plasma and other synthesized plasma devices

      R Jones

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      The parallel ion energy distribution of a synthesized plasma can be readily controlled via plasma potential gradients in the ion source chamber(s). Alternatively, layers of electrically biased metal filaments can introduce an isotropic ion heating.

    • Effect of correlations on nuclear muon capture

      R Parthasarathy Y R Waghmare

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      The process μ+12C→12B+vμ is studied using the modified Hartree Fock wavefunction obtained with the unitary-model-operator-approach starting from the realistic hardcore nucleon-nucleon interaction, with the aim of testing the wavefunctions and obtaining a numerical value for the induced pseudoscalar coupling constant (gP). These observables, namely, the partial capture rate to the12B(1+; g.s), its recoil nuclear polarisation and the total capture rate, which exhaust the available experimental data in the above process have been calculated and compared with the other theoretical and experimental results.

      As far as the partial capture rate is concerned the use of the unitary-model operator approach wave functions for12C withb=2.09 fm and Cohen-Kurath wave function for12B(1+; g.s) reduces the pure shell model capture rate by about 30%. The effect of strong configuration mixing in the ground state of12C in taken into account by introducing a scale factor ξ similar to the ‘amplitude reduction factor’ of Donnelly and Walecka. With this ξ the agreement with the experiment both for the partial capture rate and the beta decay ‘ft’ value is found to be satisfactory.

      The12B(1+; g.s) recoil polarisation is found to be insensitive to the use of the unitary-model-operator-approach wave functions. When compared with the experimental data, we obtaingP=(14.9±1.9)gA.

      The total capture rate is found to be sensitive to the use of the unitary-modeloperator-approach wave functions which contain the effect of nucleon-nucleon short range correlations and we obtain a satisfactory agreement with the experiment for16O and12C, thereby revealing the importance of the effect of such correlations in the total capture rate studies.

    • A decomposition theorem for SU(n) and its application to CP-violation through quark mass diagonalisation

      P P Divakaran R Ramachandran

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      It is proved that the groupG=SU(n) has a decompositionG=FCF whereF is a maximal abelian subgroup andC is an (n − 1)2 parameter subset of matrices. The result is applied to the problem of absorbing the maximum possible number of phases in the mass-diagonalising matrix of the charged weak current into the quark fields; i.e., of determining the exact number of CP-violating phases for arbitrary number of generations. The inadequacies of the usual way of solving this problem are discussed. Then=3 case is worked out in detail as an example of the constructive procedure furnished by the proof of the decomposition theorem.

    • A method for constructing radial wave packets with application to target distortion in electron-atom collisions

      R Lal S K Joshi

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      It has been shown that an analysis of radial stationary state wave functions of a particle in terms of their loops leads to such continuous, single-valued and finite functions which represent a practically convenient form of the radial wave packets of that particle at various positions. The radial wave packets have been used to investigate target distortion in electron-atom collisions. The distortion of the target is defined in terms of quantum-mechanical probabilities given by the wave packets. A closed expression which depends upon the position of the colliding electron, is obtained for the potential energy of the target in the field of the colliding electron.

    • Quantum beats from channeling relativistic electrons

      R Lal S K Joshi

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      Possibility has been explored of periodic time variation of intensity (quanturn beats) of radiation emitted from relativistic electrons channeling along the 〈110〉 axis of a crystal of f.c.c. (diamond) lattice structure.

    • Electrical transport properties of CuWO4

      R Bharati R Shanker R A Singh

      More Details Abstract Fulltext PDF

      The temperature dependence of the electrical conductivity, thermoelectric power and dielectric constant of the antiferromagnetic CuWO4 have been studied in the temperature range 300–1000 K. The conductivity results can be summarised by the equations σI=6.31 × 10−3 exp (−0.29 eV/kT) ohm−1 cm−1 in the temperature range 300–600 K and σII=3.16 × 105 exp (−1.48 eV/kT) ohm−1 cm−1 between 600 K and 1000 K. The thermoelectric power can be expressed byθ=[− 1.25 (103/T) + 3.9] mV/K. Initially dielectric constant increases slowly but for high temperatures its increase is fast.

    • Relativistic star clusters with high central redshift

      M C Durgapal P S Rawat R Banerji

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      Collisionless star clusters in dynamical equilibrium are of current interest in general relativity and astrophysics. A step-function distribution is chosen for star clusters. The corresponding equation of state is analogous to a Fermi-gas equation. These clusters are found to be pulsationally unstable for a central redshift ofZc ⩾ 0·54. Further, a model of clusters is developed in which the core has an extremely relativistic equation of state. These structures are unstable forZc ⩾ 2·55 when we use Chandrasekhar’s technique to study their pulsational stability.

    • Fusion reactor start-up by RF cavity mode heating of a gas

      R Jones

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      The application of high power microwaves to a gas-filled resonant cavity may be an ideal way to start up Tokamak, mirror or other thermonuclear reactors. RF coupling problems are avoided by input of microwave power prior to wave cut-off.

    • Coherent bremsstrahlung from relativistic channelled positrons

      R Lal S K Joshi

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      Poor beam collimation leads to overcompensation of suppression of coherent bremsstrahlung in the axial channelling case. This fact has been used to study the effect of beam divergence on the radiation emitted by relativistic (axially) channelled positrons. It has been found that due to beam divergence in the experiment of Alguard and co-workers in which radiation of 56 MeV positrons channelling along 〈110〉 rows of a silicon crystal is observed, coherent bremsstrahlung becomes an important contributing factor to the high frequency part of the observed spectrum.

    • Magnetic moment distributions and form factors in ferromagnetic nickel-ruthenium alloys

      R Chakravarthy L Madhav Rao N S Satya Murthy

      More Details Abstract Fulltext PDF

      Using polarised neutrons, the full three-dimensional magnetic structure amplitudes in the Ni1−c Ruc single crystals forc = 0·027, 0·033 and 0·046 were measured. Moment density maps in various portions of the Wigner-Seitz cell were obtained. It is seen from these maps that unlike Ni-based alloys with 3d impurities, the introduction of Ru to the Ni matrix produces extensive perturbations in the diffuse moment density, giving rise to a netpositive diffuse moment which tends to increase with Ru concentration. The asphericity of the host moment at first increases and then decreases with increasing Ru content. Another significant outcome of the present study is the evidence for the reversal of the sign of the Ru moment, from negative to positive, obtained by comparing the shape of the spherical site form factors of the three-alloy concentrations with the Ni spherical form factor itself. The sign reversal of the impurity moment is confirmed by the form factor analyses. Strong local environmental effects seem to play a major role in this alloy system.

    • New band systems of NiBr molecule in visible region

      R Gopal M M Joshi

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      Thermal emission spectrum of NiBr molecule excited by vacuum graphite tube furnace revealed the existence of ten new band sub-systems in the region λλ 5540-4720 Å which were attributed toAX,BX,CX andDX transitions. Vibrational analysis was carried out for each of the systems mentioned above.A2 Δ has been suggested as the ground state of NiBr molecule with an electronic interval of about 533 cm−1. Transitions responsible for NiBr spectrum appear to be of the type2π–2Δ and2Δ–2Δ.

    • The ‘time of occurrence’ in quantum mechanics

      M D Srinivas R Vijayalakshmi

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      Apart from serving as a parameter in describing the evolution of a system, time appears also as an observable property of a system in experiments where one measures ‘the time of occurrence’ of an event associated with the system. However, while the observables normally encountered in quantum theory (and characterized by self-adjoint operators or projection-valued measures) correspond to instantaneous measurements, a time of occurrence measurement involves continuous observations being performed on the system to monitor when the event occurs. It is argued that a time of occurrence observable should be represented by a positive-operator-valued measure on the interval over which the experiment is carried out. It is shown that while the requirement of time-translation invariance and the spectral condition rule out the possibility of a self-adjoint time operator (Pauli’s theorem), they do allow for time of occurrence observables to be represented by suitable positive-operator-valued measures. It is also shown that the uncertainty in the time of occurrence of an event satisfies the time-energy uncertainty relation as a consequence of the time-translation invariance, only if the time of occurrence experiment is performed on the entire time axis.

    • A statistical model of the discotic mesophase

      R Locqueneux

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      The evaluation of the thermodynamic properties of an ideal discotic mesophase needs the determination of a partition function, that depends upon two basic types of energy storage, translational and rotational. Here, we suppose we can substitute for the complex effective intermolecular potential, different mean potentials acting on each individual molecule. The defining assumptions for a discotic mesophase include the stipulations, first—that each simple disk-like molecule is, during most of the time, confined to a cell, secondly—that each molecule has an external rotation which is more or less hindered by a periodic potential. The cells are stacked in columns and the columns form a regular hexagonal array, each molecule moves in a cell as in an infinite potential well due to the neighbouring molecules.

      This model has allowed the general formulation of the mesophase-free energy. From this, we obtain the form of the coefficient of isothermal compressibility when the external rotations of the molecules are hindered and the vibrational energy is weak.

    • Chemical ordering in As-Se glasses: X-ray absorption edge and XPES studies

      K J Rao R Mohan P R Sarode M S Hegde

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      X-ray absorption edge and X-ray photoelectron spectroscopic studies of As-Se glasses seem to support a chemical ordering model.

    • The radio frequency conductivity of some aliphatic alcohols at different temperatures

      R Ghosh I R A Chaudhury

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      Activation energies for viscous flow and conductivity are computed from experimental values of RF conductivity (frequency 400 kHz) at different temperatures for eight polar liquids. It is observed that for aliphatic alcohols the activation energy for conductivity is greater than that for viscous flow. However, their ratio is slightly greater than unity and is different for different alcohols whereas for nonassociating polar liquids the ratio is almost equal to unity. The dependence of conductivity on viscosity for the liquid alcohols does not follow the Walden’s law but can be well represented by Adamczewskis relation.

    • An analysis of energetic cosmic ray interactions in graphite

      R Hasan M S Swami

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      Fifty two high energy cosmic ray interactions in graphite have been analysed. The analysis strongly suggests that some of the characteristics of high energy interactions are dependent on the total transverse momentum,Σpt, of allγ-rays in an interaction. Out of the 52 events analysed, 29 haveΣpt⩽2.5 GeV/c and the rest haveΣpt>2.5 GeV/c; the former are called smallpt events while the latter are designated as largept events. For these two types of events, the characteristics investigated are: (a) fractional energy distribution ofγ-rays, (b) the invariant mass ofγ-rays and (c) the energy distribution ofγ-rays in the emission system.

    • The B-A system of CP molecule

      R Tripathi S B Rai K N Upadhya

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      The B-A system of CP molecule has been reinvestigated. The rotational structures in the (0, 0) and (1, 1) bands have been photographed in the second order of a 10.6 m grating with 25µ slit width. The molecular constants have been determined using a weighted least squares fit computer program. It is found that the spin-splitting constant in the B-state is negative and not positive as reported by previous workers. An accurate value ofα in the A-state could be determined. The present analysis also suggests that the spin-splitting constant in the ground state of CP should be positive, hence the assignment of theR1 andR2 orP1 andP2 branches in the B-X system of CP by Barwaldet al should be interchanged.

    • Localized modes of ammonium ion in KCl lattice

      R Kesavamoorthy V Umadevi Debendranath Sahoo

      More Details Abstract Fulltext PDF

      Following the standard Green’s functions matrix partitioning technique, the force constant changes needed to explain the translational (6.8 THz) and torsional (10.1 THz) modes occurring in the KCl:NH4+ system are calculated. Three different defect site symmetries are considered for the ammonium ion impurity. These are (i)Oh, in which the ammonium ion is a free rotor, (ii)Td, in which it is a hindered rotor and (iii)C4v, in which it rotates freely about a N - H ... Cl axis and librates around the other two crystallographic axes.Oh defect symmetry explains only the translational mode, while in the other two symmetries both the modes are explained with reasonable changes in the force constants. It is also shown that the same set of force constant changes explains the local modes in the deuterated sample as well.

    • Isospin violations in largePT pion inclusive processes in perturbative quantum chromodynamics

      H S Mani M Noman M Rafat R Ramachandran

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      We investigate the asymmetries arising due to electromagnetic interactions in largePT pion inclusive processes. The hardqcd processes that contribute to such asymmetries areq+gq+γ,q+qg+γ etc. which are suspected to be substantial, as indicated by theqcd predictions for a significant and increasingγ/πo ratio at largePT. We calculate the expected isospin related asymmetries and propose tests that might detect them. Our estimates indicate that the effects are much smaller than may be naively expected. We also observe a remarkable scaling of asymmetries in the variablePT/(s)1/2.

    • Neutral particle modelling assumptions: Theory and experiment

      R Jones

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      The neutral particle recycling models that have been used to date in numerical plasma confinement simulations are by no means equivalent but may lead, instead, to divergent results. As a consequence of this confinement studies based on individual neutral assumptions must be received with a healthy degree of scepticism.

      We go on to compare experimental observations of the time development of plasma density, temperature, and neutral pressure made in an electrostatic surface trap with numerical plasma simulations incorporating a number of alternative neutral models.

    • Radiative decays of charged leptons in arbitrary order

      P P Divakaran R Ramachandran

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      In radiative decays of charged leptons induced by non-degenerate neutrino masses and consequent lepton flavour-mixing, the dominant suppression factor at the 1-loop level is (Σ ma2)/mW2,ma being the mass of theath neutrino. We show that this suppression factor is presentin all orders in a class of models including the standard model.

    • A Mössbauer study of hyperfine interaction in the systems CoxMn3−xyFeyO4 and NixMn3−xyFeyO4

      V K Singh R Chandra S Lokanathan

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      A Mössbauer study of systems CoxMn3−xyFeyO4 and NixMn3−xyFeyO4 for values ofx=0·1, 0·5, 1·0 andy ranging from 0·1 to 2·0 in steps of 0·2 have been made. At room temperature samples fory values ranging in between 0·1 to 0·5 exhibit paramagnetic behaviour while all spectra for values ofy between 0·6 to 0·8 show relaxation effects. Well-defined hyperfine Zeeman spectra are observed for all the samples withy>0·8 and resolved in two sextets corresponding to octahedral and tetrahedral site symmetries and a central doublet probably due to the presence of super-paramagnetic particles in the system. The hyperfine field at57Fe nucleus reduces with decreasing iron cobalt and nickel concentration. These observations have been explained in terms of site preference of cations and exchange interactions.

    • An AC magnetic susceptibility bridge and cryostat for the temperature range 2–300 K

      R Ranganathan G Rangarajan

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      A mutual inductance bridge to measure low frequency magnetic susceptibilities of magnetic materials has been constructed. Salient features of the bridge, which uses a variable mutual inductance simulated using operational amplifiers, the cryostat and the coil assembly are described in this paper. The apparatus has been employed for accurate measurement of superconducting transition temperatures and for sensitive detection of magnetic ordering transitions in liquid helium and liquid nitrogen temperature ranges respectively. The bridge has been calibrated to determine the static susceptibility of magnetic materials as a function of temperature.

    • Integral energy spectrum of primary cosmic rays at high energies

      R Hasan S C Arora D Hans M S Swami

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      The integral energy spectrum of primary cosmic rays has been obtained. In the energy range (2.4×103−1.1×105 GeV), the spectrum of all nuclei is consistent with a power law of indexγ=1.55±0.06 and the flux of all nuclei is:N(⩾E0)⋍(5.1±1.8)×10−1×E0−1.55 particles/cm2 sterad. sec., whereE0 is in GeV. The spectrum of primaryα-particles in the energy range (4.4×103−4.8×104) GeV is also consistent with a power law of indexγ=1.71±0.12 and the flux is:N(⩾E0)=(4.2±1.4)×10−1×E0−1.71, particles per cm2 sterad. sec, whereE0 is in GeV.

    • Temperature variation of the Debye-Waller factors of Ba++ and F ions in BaF2 powder by x-ray diffraction

      R Srinivasan K S Girirajan

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      The temperature variation of the Debye-Waller factors of Ba++ and F ions in BaF2 powder has been studied using x-ray powder diffraction over the temperature range 77°–298°K. A continuous flow cryostat has been specially fabricated for this purpose for the YPC 50 NM powder diffractometer available in the department. The Debye-Waller factors of Ba++ and F between room temperature and 879°K have been measured using single crystal neutron diffraction by Cooperet al. Theoretical lattice dynamics shell model calculations using a 7-parameter model in a quasiharmonic approximation have been done over a temperature range 77° to 879°K. The theoretical values have been compared with the present x-ray measurements and the single crystal neutron diffraction values and the results are discussed.

    • Ion source scaling laws

      R Jones

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      Simple theory and basic plasma physics experiments are used to deduce scaling laws for ion source discharges.

    • Strong coupling expansion in the massive Thirring model

      R Banerjee

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      A strong coupling expansion of the Green functions in the massive Thirring model is formulated. Expressions obtained for the fundamental fermion mass and theβ function agree with the known qualitative features of these physical quantities.

    • Electron beam fusion, energy compression, and the absolute instability

      R Jones

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      Absolute electron beam-plasma instability is suggested as a means of energy compression for pellet and liner inertial confinement fusion systems.

    • Generalized pencils of rays in statistical wave optics

      R Simon

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      The recently introduced generalized pencil of Sudarshan which gives an exact ray picture of wave optics is analysed in some situations of interest to wave optics. A relationship between ray dispersion and statistical inhomogeneity of the field is obtained. A paraxial approximation which preserves the rectilinear propagation character of the generalized pencils is presented. Under this approximation the pencils can be computed directly from the field conditions on a plane, without the necessity to compute the cross-spectral density function in the entire space as an intermediate quantity. The paraxial results are illustrated with examples. The pencils are shown to exhibit an interesting scaling behaviour in the far-zone. This scaling leads to a natural generalization of the Fraunhofer range criterion and of the classical van Cittert-Zernike theorem to planar sources of arbitrary state of coherence. The recently derived results of radiometry with partially coherent sources are shown to be simple consequences of this scaling.

    • Theoretical calculation of electron-impact resonance excitation of alkali atoms

      C S Singh R Srivastava D K Rai

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      Total cross-section for electron impact excitation of the resonance levels in Li, Na and K are calculated using the method due to Crothers and McCarroll. The results are compared with other available theoretical and experimental data.

    • A search for superheavy nuclei tracks in extraterrestrial olivine crystals

      J S Yadav A P Sharma G N Flerov V O Perelygin S G Stetsenko P Pellas C Perron R Antanasijevich B Jakupi Y Todorovich

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      A study is made for the search of superheavy nuclei in Marjalahti, Eagle Station and in other pallasite olivines. The olivine crystals are calibrated for heavy ion track lengths by using heavy ion beams from cyclotrons. The calibration for ultra heavy ions which are presently not available with sufficient energy to produce volume tracks in olivine crystals, is based on Katz and Kobetich model of track formation. The length spectrum of volume tracks, revealed by puncturing them with focussed Nd-glass laser beam, is measured and the abundances of different nuclei groups are calculated. Partial annealing has been used at 430°C for 32 hr which eliminates the interfering tracks due to nuclei of atomic numberS ≤ 50. During the scanning 4 cm3 olivine crystals, about 360 long tracks of uranium group as well as two very long tracks have been found. If these tracks belong to superheavy nuclei, the relative abundance of super heavies is found to be 6 × 10−11 in galactic cosmic rays.

    • Spin structure of nucleon

      R Ramachandran

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      The quark spin content of the nucleons is subjected to constraints implied by sum rules due to global approximate chiral symmetries and perturbativeqcd effects. The model, so obtained, has a large polarisation residing in the flavour singlet constituents of hadron. Predictions for the expected longitudinal and transverse spin asymmetries in deep inelastic lepton-nucleon scattering are made on the basis of the standard form of the electromagnetic and charged weak currents.

    • Laser excited fluorescence of Na2

      K S Chandrasekhar S D Sharma T K Balasubramanian R D’Souza R Bhatnagar

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      Fluorescence was excited in theB1ΓuX1Σg+ system of Na2, using the 488 and 514.5 nm radiations from a cw Ar+ laser. The fluorescence was monitored through a double monochromator employing photoelectronic detection. In the spectrum resulting from the 488 nm excitation, apart from a large number of fluorescence series, a previously unreported series could be identified. On either side of all the members of the strongest series a large number of collisional satellites were observed and assigned.

    • Measurement ofL-shell photoelectric cross-sections in lower intermediateZ elements at 6 keV

      N Singh R Mittal K L Allawadhi B S Sood

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      L-shell photoelectric cross-sections have been measured at 6 keV for eight elements in the range 40⩽Z⩽53. The measurements agree with theoretical calculations.

    • Fusion-fission angular distributions: A new probe of fast fission fractionation in nucleus-nucleus collisions

      S S Kapoor V S Ramamurthy R Ramanna

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      Fragment angular distributions in heavy ion-induced fission reactions have been analysed in terms of a two component model—fission following compound nucleus formation and fast fission events. It is seen that, contrary to the general assumption, fast fission competes with compound nucleus fission even when the composite system is formed with a spin less than the rotating liquid drop model limit for vanishing fission barrier.

    • Studies on the valence state of Ce and Eu in some new boron and silicon containing rare earth intermetallic compounds

      S K Malik S K Dhar R Vijayaraghavan

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      Compounds of the formula RPd3Bx (R=rare earth with 0⩽x⩽1) and RPd3Six (R=La, Ce, Eu with 0⩽x⩽0.3) can be prepared by alloying boron or silicon with parent RPd3 compounds. Addition of boron (silicon) does not change the structure but results in lattice expansion. The valence state of Ce in CePd3 and that of Eu in EuPd3 is strongly influenced by boron and silicon. Ce is known to be in a valence fluctuating state in CePd3 while Eu is trivalent (J=0) in EuPd3. The increase in the lattice parameter as a function of boron concentration is observed to be larger in CePd3Bx and EuPd3Bx compared to that in other RPd3Bx alloys giving the first indication of the change in the valence state of Ce and Eu. This is confirmed from susceptibility measurements. With the addition of boron, susceptibility increases and the effective paramagnetic moments approach the values corresponding to Ce3+ (J=5/2, μeff=2.54 μB) and Eu2+ (J=7/2, μeff=7.94 μB) in the two alloy systems CePd3Bx and EuPd3Bx respectively. In the case of europium alloys,151Eu Mössbauer studies point out the importance of near-neighbour environment effects. Further, in EuPd3B, where all the europium ions are crystallographically equivalent, a single Mössbauer line, with an isomer shift characteristic of europium ions in valence-fluctuating state, is observed at 300 K. However, at 88 K the Mössbauer absorption splits into two lines corresponding to europium ions in two valence states,e.g. divalent- and trivalent-like. Such a behaviour indicates thermally-induced charge ordering of europium ions. Addition of silicon to CePd3, like boron, results in unusual lattice expansion and changes the valency of cerium towards 3+. the valence change is further corroborated by susceptibility measurements. In EuPd3Six alloys, susceptibility and Mössbauer studies indicate that in the limiting single phase alloy EuPd3Si0.25 the europium ions are on the verge of valence instability. Susceptibility results on CeRh3Bx alloys are also presented.

    • The crystal fields inα-alums—A high pressure magnetic resonance study

      Shantanu Sinha R Srinivasan

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      The origin of the crystal field and its variation with temperature in severalα-alums have been studied bynmr of27Al andepr of Cr3+ at high hydrostatic pressures and low temperatures. The results lead to an explanation of the anomalous temperature variation of the axial crystal field at the trivalent ion site. The mechanism of the phase transition in ammonium alum is also explained. A correlation between the axial crystal field as determined bynmr (e2qQ/h) and that determined byepr (D) has been obtained.

    • Muon capture by16O—using a microscopic theory of particle-hole states

      V N Sridhar R Parthasarathy Y R Waghmare

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      The partial capture rates for the process,μ +16O (g·s) →16N (2, 1, 0, 3) +vμ have been calculated using the particle-hole wavefunctions obtained using self-consistent procedure. In deriving these wavefunctions, the effectiveN-N interaction has been constructed from the bare Hamada-Johnston interaction. The terms in the muon capture Hamiltonian that depend on the momentum of the capturing proton have been included and their importance in 0+ → 0 transition is exhibited. The agreement with the available experimental data is good. The need to incorporate meson exchange effects in 0+ → 0 transition is pointed out.

    • Reanalysis of polarised neutron data on NiRu using projection operator formalism

      R Chakravarthy L Madhav Rao

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      Projection operator formalism has been applied to analyse magnetic structure amplitudes in Ni1−xRux (x=0·027, 0·033 and 0·046) alloys. This method is suitable for metals and alloys as it does not assume any free ion form factor. A new prescription has been discussed for the local site moment and diffuse moment in this frame work. The results of the present analysis are compared with those obtained using form factor analysis.

    • Automation of the direct current comparator resistance bridge

      R Aidun R Caton Sigurds Arajs

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      The direct current comparator resistance bridge, Model 9975, manufactured by Guildline Instruments, Inc., which permits electrical resistance measurements up to eight digits, has been fully automated. Details of this automation are described in this paper. The performance of the automated bridge is demonstrated with applications to electrical resistivity studies on some metallic alloys.

    • Temperature dependence of79BrNQR frequency in cadmium strontium, barium, zinc, magnesium and nickel bromates

      S Ramaprabhu R Valli K V S Rama Rao

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      The79Br quadrupole resonance in cadmium, strontium, barium, zinc, magnesium and nickel bromates is studied in the range 77 to 305 K. The temperature dependence of the resonance frequencies in these systems has been analysed on the basis of the torsional motion of the BrO3 groups. The torsional frequency and its temperature behaviour have been analysed.

    • Absorption spectrum of the HCCO radical

      S L N G Krishnamachari R Venkatasubramanian

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      In the flash-photolysis of oxazole and isoxazole, new transient absorption bands are observed in the region 3080–3670 A. Vibrational analysis of these bands showed that they can be arranged into two electronic systems with their origin bands at 3333.60 A and 3367.01 A. Based on the experimental conditions under which the bands are produced and on the analysis of their vibrational and gross-rotational structure, these bands are assigned to a new carrier, the HCCO free radical.

    • Electron transport in Chevrel phase superconductors, Cu1.8Mo6S8−ySey, 0⩽y⩽8 and Cu1.8Mo6S8−yTey, 0⩽y⩽4—Fit to Cote-Meisel theory

      V Sankaranarayanan G Rangarajan R Srinivasan

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      Normal state electrical resistivity of the Chevrel phase compounds of the type Cu1.8Mo6S8−ySey, 0⩽y⩽8 and Cu1.8Mo6S8−yTey, 0⩽y⩽4 is analysed on the basis of the generalized diffraction model which incorporates a postulate on electron-phonon interaction,viz phonons with wavelength exceeding the electron mean-free path are ineffective electron scatterers. Fit obtained by this model was found to be superior to other models based on the interbands-d scattering of electrons.

    • Infrared studies on ion irradiated quartz

      A K Sood V Umadevi R Kesavamoorthy G Venkataraman

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      Damage produced inα- and fused quartz bombarded with low energy (∼ 100 keV) D+, He+ and Ar+ ions, has been studied by observing the changes in their spectrum. Besides bulk reflectivity, the attenuated total reflection spectrum has also been studied, the latter with a view to obtaining the surface polariton frequencies. It is observed that for the same fluence, the changes following D+ irradiation are much higher compared to that for Ar+ irradiation. The variation of the surface polariton frequency inα-quartz with the damage energy deposited has the same trend as observed earlier for refractive index. Some annealing studies have also been performed in argon-irradiated samples. These studies indicate that whereas in fused quartz the damaged layer recovers completely, inα-quartz there is a residual amorphization even after annealing. A two-layer model is proposed which gives a reasonable simulation of the observedir properties.

    • Probing proton spin structure through hadronic reactions

      M Rafat R Ramachandran

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      Inclusive and semi-inclusive photon producing polarized proton reactions have been employed to probe the spin structure of the proton. Combinations of cross-sections are suggested which may measure valence quarks polarization and gluon polarization in the proton separately. The general formalism is used to predict numerical results using a model of spin structure based on Altarelli-Parisi equations.

    • Quantum supersymmetric generalisation of Bogomolnyi bounds

      R Rajaraman

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      We review here classical Bogomolnyi bounds, and their generalisation to supersymmetric quantum field theories by Witten and Olive. We also summarise some recent work by several people on whether such bounds are saturated in the quantised theory.

    • Bethe-Salpeter dynamics for two-photon processes

      A N Mitra N Nimai Singh R Ramanathan

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      Recent experimental data on single hadron production by two-photon beams inpetra andpep have provided a unique opportunity for testing specific models of confinement through a study of one of their cleanest predictionsviz the γγ →H amplitudes. Motivated by this new facility, aqcd-oriented Bethe-Salpeter model of harmonic confinement, which has already been found to describe rather well several classes of hadronic data (from mass spectra to electromagnetic and pionic couplings), is now employed for a detailed comparison of its predictions onP → γγ andT → γγ couplings with the data. The agreement is quite good for all cases except one (η → γγ).

    • Phenomenology of the Pokaranpne experiment

      R Chidambaram S K Sikka Satish C Gupta

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      The phenomenology of the Pokaranpne experiment (yield - 12 kiloton oftnt) conducted in a shale-sandstone rock, 107 meters underground, is described with the aid of computations using a one-dimensional spherical symmetric rock mechanics computer code developed by the authors. The calculated values of cavity radius, spall velocity and extent of rock fracturing are in good agreement with the observed values. The principal mechanism for crater formation at Pokaran was spall and the relatively smaller crater dimensions and non-venting of radioactivity gases were due to lower kinetic energy transferred to the shale-sandstone rock.

    • Defect structure studies using positron annihilation spectroscopy

      R Krishnan D D Upadhyaya

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      The positron annihilation method is a new addition to the range of sensitive complementary nuclear techniques available for materials’ research. The preferential sensitivity of positrons towards micro-defect domains which are not assessable by other techniques makes it an attractive tool for many materials science problems. The present paper is intended as a brief introduction on the principle of measurements and its potential is exemplified with the help of results on some metallic and ceramic systems.

    • X-ray photoelectron spectroscopy for surface film analysis in corrosion research

      P K Chauhan H S Gadiyar R Krishnan

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      Surface films on metals and alloys often protect them from reaction with the environment, and hence a knowledge of their protective properties and composition could be invaluable for predicting their corrosion behaviour. XPS (x-ray photoelectron spectroscopy) could provide a quantitative analysis of the chemical composition, the nature of valence states and elemental distribution within the surface films.

      The present paper reviews the potential of this technique in corrosion studies. A brief review of the work done on the passivation of iron and iron-chromium alloys and on the inhibition studies on copper base alloys has been given. A few examples of investigations carried out at authors’ laboratory are also included. An attempt has been made to establish a correlation between the compositions of the films formed and corrosion behaviour of carbon steel in 10.5 pH lithium hydroxide solution and of Cu-Ni alloys and sacrificial Al-Zn-Sn alloys in synthetic sea-water.

    • On the classical solution of SO(3) gauge theory and ’t Hooft-Polyakov monopole

      R Parthasarathy T S Santhanam K H Mariwalla

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      It is shown that the ansatz for the asymptotic (r → ∞) gauge fields used by ’t Hooft in the study of monopoles in SO(3) electroweak theory is not unique.

    • Pre-equilibrium emission effect in (n, p) reaction cross-sections at 14.8 MeV

      J P Gupta H D Bhardwaj R Prasad

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      The influence of pre-equilibrium emission on (n, p) reaction cross-sections at 14.8 MeV has been studied. Cross-sections for (n, p) reactions have been measured by the activation technique at 14.8 .1; 0.5 MeV neutron energy. The experimental cross-section values have been compared with the calculated values at 14.8 MeV with and without considering the pre-equilibrium emission. Equilibrium calculations have been performed according to the statistical model of Hauser and Feshbach while the hybrid model has been used to include the pre-equilibrium contribution. Pre-equilibrium emission has been considered only in the first emission step. The comparison of experimental and calculated values clearly indicates the presence of pre-equilibrium emission.

    • Polarised raman and infrared spectra and vibrational analysis forα-naphthylamine

      R Shanker R A Yadav I S Singh O N Singh

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      The Raman spectrum of polycrystalline α-naphthylamine was recorded in the region 100–4000 cm−1. Polarisation measurements were made in CS2 and CHCl3 solutions. The infrared spectrum was recorded in nujol mull in the region 200–4000 cm−1. The resolution was better than 2 cm−1 and the accuracy of the measurements was within ± 2 cm−1 for all the spectra. Vibrational assignments have been proposed for the observed frequencies. Out of the 54 normal modes of vibrations, 51 modes could be observed experimentally.

    • Classical solitons with no quantum counterparts and their supersymmetric revival

      R K Kaul R Rajaraman

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      We demonstrate the phenomenon stated in the title, using for illustration a two-dimensional scalar-field model with a triple-well potential {fx837-1}. At the classical level, this system supports static topological solitons with finite energy. Upon quantisation, however, these solitons develop infinite energy, which cannot be renormalised away. Thus this quantised model has no soliton sector, even though classical solitons exist. Finally when the model is extended supersymmetrically by adding a Majorana field, finiteness of the soliton energy is recovered.

    • Pressure studies on two discotic liquid crystals

      V N Raja R Shashidhar S Chandrasekhár R E Boehm D E Martire

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      Pressure-temperature diagrams have been studied for two discotic compounds, hexa-n-octyloxytriphenylene and hexa-n-decanoyloxytriphenylene, both of which exhibit the columnar (D) phase at atmospheric pressure. Two interesting results, common to both compounds, have been obtained: (a) in contrast to what is usually observed in liquid crystals of rod-like molecules, the columnar-isotropic (D-I) transition, which is enantiotropic at atmospheric pressure, becomes monotropic at high pressures; (b) dT/dP ≈ 0 for theD-I transition, implying that despite the drastic change in the molecular order at this transition, the associated volume change is extremely small.

    • High pressure phase transitions in organic solids I:α → β transition in resorcinol

      Surinder M Sharma V Vijayakumar S K Sikka R Chidambaram

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      An experimental program has been started to study polymorphic phase transitions under pressure in organic solids using the Be gasketing technique developed by us. This allows us to obtain x-ray diffraction patterns of low symmetry organic solids with high resolution, employing CuKα radiation. The first organic solid studied is α-resorcinol. At 0.5 GPa, it transforms to its high temperature and denser modification, β-resorcinol. The transformation mechanism is discussed with the help of molecular packing calculations.

    • Determination of force fields for two conformers of nitromethane bycndo/Force method

      R Brakaspathy A Jothi Surjit Singh

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      cndo/Force method is used to evaluate the redundancy free internal valence force fields for two conformers of nitromethane. The initial force field is set up by taking the interaction and bending force constants from this method and transferring the stretching force constants from the force fields of chemically related molecules. The final force field is obtained by refining the initial force field using vibrational frequencies of isotopic speciesviz CH3NO2, CD3NO2, CH315NO2 and CH3N18O2. The final force field thus obtained is reasonable on the basis of frequency fit and potential energy distribution. The barrier to internal rotation is found to be 0.048 kcal mol−1.

    • Improved condition for the absence of bound states and converging analytic bounds to critical screening parameter

      R Dutt D Singh Y P Varshni

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      Converging lower bound to the critical screening parameterDc associated with the ground state of a two-particle system interacting through a cut-off Coulomb potential is obtained analytically using an improved condition for the absence of bound states. The predicted numerical result for the lower bound is found to be within 10−3% of the exact result. On the other hand, a multi-parameter variational approach yields a tight upper bound, within 0.54% of the exact result. It is shown that the critical screening parameter for the exciteds-states can also be determined in an approximate way. We obtainDcms ≈ [0.764435n−2+0.617737n−3]−1 wheren is the principal quantum number. The predictedDc for various quantum states (n=1 to 8) are in good agreement with the values obtained numerically by Singh and Varshni.

    • Spectral asymmetry of Dirac Hamiltonian in a five-dimensional Kaluza-Klein theory

      R Parthasarathy V Srinivasan

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      It is shown that the fermion number in a five-dimensional Kaluza-Klein theory (M4×S1) in which the fermion is interacting with a monopole field, is quantized in units of (ϕR)2 where the scalar ϕ is asymptotically constant andR is the radius of S1.

    • Ionization states of cosmic rays:Anuradha (IONS) experiment in Spacelab-3

      S Biswas R Chakraborti R Cowsik N Durgaprasad P J Kajarekar R K Singh M N Vahia J S Yadav N Dutt J N Goswami D Lal H S Mazumdar D V Subhedar M K Padmanabhan

      More Details Abstract Fulltext PDF

      The measurements of the ionization states, composition, energy spectra and spatial distribution of heavy ions of helium to iron of energies 10–100 MeV/amu in the anomalous cosmic rays are of major importance in understanding their origin which is unknown at present.Anuradha (IONS) cosmic ray experiment in Spacelab-3 was designed to determine the above properties in near earth space and this had a highly successful flight and operations aboard the shuttle Challenger at an orbital altitude of 352 km during 29 April to 6 May 1985. The instrument employs solid state nuclear track detectors (CR-39) of high sensitivity and large collecting area of about 800 cm2 and determines the arrival time information of particles with active elements. Experimental methods, flight operations and preliminary results are briefly described. Initial results indicate that relatively high fluxes of low energy cosmic ray α-particles, oxygen group and heavier ions were obtained. The flight period corresponded to that of quiet Sun and the level of solar activity was close to solar minimum. It is estimated that about 10,000 events of low energy cosmic ray alpha particles with time annotation are recorded in the detector together with similar number of events of oxygen and heavier ions of low energy cosmic rays.

    • The thorium cycle for fast breeder reactors

      R Ramanna S M Lee

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      The role that could be played by liquid metal-cooled fast breeder reactors (LMFBRs) in the utilization of India’s considerable thorium resources is reviewed in this article. Distinct advantages of thorium-based fuels over plutonium-uranium fuels in LMFBRs pertain to a more favourable coolant voiding reactivity coefficient and better fuel element irradiation stability. The poorer breeding capability of thorium-fuelled fast reactors can in principle be overcome by improved core design and development of advanced fuel concepts. The technical feasibility of such advanced thorium fuels and core designs must be established by sustained research and development. It is also necessary to efficiently close the thorium fuel cycle of fast breeder reactors by appropriate development of the fuel reprocessing and refabrication stages. The Fast Breeder Test Reactor (FBTR) at Kalpakkam is expected to be an important tool for development of thorium fuel and fuel cycle technology. A quick look at the economics of the thorium cycle for fast reactors, vis-a-vis the more conventional uranium cycle indicates only a small and acceptable cost disadvantage on account of the need for remote fabrication of recycled thorium fuel.

    • Spin fluctuation effects in substituted CeRu2Si2 and YbPd2Si2 alloys

      A M Umarji C Godart L C Gupta R Vijayaraghavan

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      Effects of chemical substitution in CeRu2Si2, a well-studied heavy fermion system and YbPd2Si2 have been investigated through magnetic susceptibility and x-ray diffraction in the systems CeRuxSi2, CeRu2−xOsxSi2, CeRu2Si2−xGex and YbPd2Si2−xGex. Replacing silicon by germanium generates normal chemical pressure effect, namely, Ce and Yb atoms in CeRu2Si2 and YbPd2Si2 became more and less magnetic respectively. With increasing Ge concentration, CeRu2Si2−xGex exhibits larger susceptibility at low temperature, goes to an antiferromagnetic state and finally becomes ferromagnetic. In YbPd2Si2−xGex, increasing Ge concentration drives Yb atoms to more divalent state. Electronic effects are more pronounced in CeRu2−xOsxSi2 though CeRu2Si2 and CeOs2Si2 have very nearly the same lattice parameters. It is conjectured that CeRu2Si2−xGex may be the first Ce-based heavy fermion having a magnetic ground state.

    • Switching behaviour of unijunction transistor in the presence of magnetic field

      S L Agrawal R Swami

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      The influence of magnetic field on some switching parameters (turn-on time, turn-off time and amplitude of the current pulse appearing at base 1 terminal) of a unijunction transistor has been theoretically and experimentally investigated. The various switching parameters are shown to be governed by the magneto-concentration effect.

    • High pressure phase transitions in organic solids II: X-ray diffraction study ofp-dichlorobenzene at high pressures

      Hema Sankaran Surinder M Sharma S K Sikka R Chidambaram

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      X-ray diffraction experiments onp-dichlorobenzene at high pressures show a transition at ∼ 0.3 GPa, to a new phase, the diffraction pattern of which cannot be indexed on the anticipated low temperature monoclinic crystal structure. We have instead found an orthorhombic cell, very closely related to the low temperature monoclinic cell, for this new phase. This structure, which also occurs inp-diiodobenzene at ambient conditions, has cell constantsa =14.02,b = 6.06,c = 7.41Å andZ = 4. The space group is Pbca. This new phase has a non-β herring-bone structure, in contrast with the initialα phase which has aβ-structure with ribbon-like arrangement of molecules, with Cl-Cl contacts of ∼ 4A between adjacent molecules. This implies that with pressure the halogen-halogen interaction in this compound plays a less dominant role in crystal engineering.

    • Some remarks on the finiteness of soliton mass

      R K Kaul R Rajaraman

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      Some subtleties regarding regularizations in computing the soliton energy of degenerate systems are discussed.

    • Design studies of a 100 MeV proton linear accelerator

      P Singh R Mythili M G Betigeri

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      Design details of a 100 MeV proton linear accelerator (Alvarez system) operating at a resonating frequency of 400 MHz have been studied. Increase in the linac operating frequency has become feasible with the possibility of injecting protons from a radio frequency quadrupole accelerator with energies higher than the conventional pre-injectors. Various electrical parameters of such a system have been calculated and compared with the existing linac injectors operating at 200 MHz.

    • Theoretical studies on magnetic superconductors

      R Jagadish K P Sinha

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      The discovery of magnetic superconductors has posed the problem of the coexistence of two kinds of orders (magnetic and superconducting) in some temperature intervals in these systems. New microscopic mechanisms developed by us to explain the coexistence and reentrant behaviour are reported. The mechanism for antiferromagnetic superconductors which shows enhancement of superconductivity below the magnetic transition is found relevant for rare-earth systems having less than half-filled f-atomic shells. The theory will be compared with the experimental results of SmRh4B4 system. A phenomenological treatment based on a generalized Ginzburg-Landau approach will also be presented to explain the anomalous behaviour of the second critical field in some antiferromagnetic superconductors.

      These magnetic superconductors provide two kinds of Bose fields, namely, phonons and magnons which interact with each other and also with the conduction electrons. Theoretical studies of the effects of the excitations of these modes on superconducting pairing and magnetic ordering in these systems will be discussed.

    • Nuclear magnetic resonance studies in rare earth ternary phosphides

      R Vijayaraghavan

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      The results of31P Knight shift (KS) and spin-lattice relaxation time (T1) measurements in the temperature interval 4.2–300 K are reported for the compounds RENi2P2(RE=Ce, Eu, Yb) in order to understand the nature of the ground state in these compounds. KS results conclusively establish that all these compounds exhibit non-magnetic ground states. The temperature dependence of spin-fluctuation temperature (Tsf) in each case is estimated from the measured data. For EuNi2P2 the values ofTsf above 77 K qualitatively agree with those obtained from Mössbauer and susceptibility data employing ionic interconfigurational fluctuation model, but disagree at lower temperatures.

    • Shock Hugoniot calculations and melting in Pb

      B K Godwal S K Sikka R Chidambaram

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      Shock Hugoniot calculations are carried out for lead (Pb) using both solid and liquid state theories. The Hugoniots in solid and liquid cases are in mutual agreement within the experimental uncertainties. However, the shock temperatures are quite different as computed from solid and liquid state theories. This fact can perhaps be used to detect melting along the shock Hugoniot provided the shock temperatures are accurately measured.

    • Enhancement of thermopower in the highTc superconductor YBa2Cu3O7 and related compounds

      R Srinivasan V Sankaranarayanan N P Raju S Natarajan U V Varadaraju G V Subba Rao

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      The absolute thermopower of single phase YBa2Cu3O7 and Y0.8Er0.2Ba2Cu3O7 has been measured in the range 250 K to the superconducting transition temperature. It is found that these compounds show a large enhancement of thermopower in the range 150 K down toTc. This enhancement shows a steep exponential drop as the temperature increases from the transition temperature. The temperature variation of the enhancement is too steep to be accounted for by electron-phonon or electron-local structural excitation mechanisms.

    • Fluctuations in12C+24Mg elastic and inelastic scattering

      B Ghosh R Singh

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      The data on the ϑc.m.=180° excitation functions of12C+24Mg,12C* (4.43 MeV)+24Mg and12C+24Mg*(1.36 MeV) from 12.27 to 22.80 MeV, 16.53 to 27.47 MeV, and 11.33 to 26.40 MeV(c.m.) respectively have been subjected to statistical analysis. The effect of averaging interval, employed for data reduction, on the coherence widths as obtained from the autocorrelation function has been studied. The fluctuating features of the cross-sections turn out to be consistent with the statistical model expectations.

    • Synergism in electron gas in crossed fields

      R Pratap

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      An electron gas in crossed electric and magnetic fields of arbitrary strength is considered in the framework of nonequilibrium statistical mechanics. It is known that more than one independent frequency existing in a system, which are of comparable magnitude, can generate coherent synergic radiation. In the present system three independent frequencies exist: viz the synchrotron frequency due to the magnetic field, the hopping frequency due to the electric field, and the plasma frequency. It is shown that all these can combine to generate a new synergic coherent radiation. The results also show the possibility of interpreting the quantum nature of Hall conductance as due to density function alone. Besides these, the solution admits the Schubnikov-de Haas oscillation of the electrical conductivity due to change in the fields.

    • Optical birefringence and order parameter of three nematogens

      M Mitra S Paul R Paul

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      Results of the measurement of refractive indices and densities of three nematic liquid crystals at different temperatures are reported. The molecular polarizabilities have been calculated from refractive indices using both the Vuks’ and the Neugebauer’s relations. The orientational order parameters are determined from the polarizability values. The variation of order parameter with temperature for these compounds shows a reasonably good agreement with Maier and Saupe theory except near the clearing points where the experimental values are less than those obtained from the theory. The possible reasons for this have been discussed.

    • Force field calculations of acetonitrile using CNDO/force method

      R Brakaspathy Surjit Singh

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      The redundancy-free internal valence force field (RFIVFF) of acetonitrile is reported using CNDO/force method. The initial force field is set up by taking the interaction and bending force constants from CNDO force field and transferring stretching force constants from the force fields of chemically related molecules. The final force field is obtained by refining the initial force field using vibrational harmonic frequencies of CH3CN,13CH3CN, CH313CN, CH3C15N, CD3CN and CD313CN. The final force field thus obtained is found to be excellent on the basis of frequency fit and potential energy distribution.

    • Specific heat anomaly in the 90 K superconductor HoBa2Cu3O7−y

      B K Basu S M Pattalwar R N Dixit S Y Shete A K Rajarajan L C Gupta R Vijayaraghavan

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      We report here the results of our heat capacityCp measurements on a monophasic material HoBa2Cu3O7−y. ΔCp/Tc, the jump inCp at the superconducting transition temperature (=91 K) of the material is measured to be 31 mJ/mol-K2.

    • Indications of superconductivity in the 200–300K range in the Bi-Ca-Sr-Cu-O system

      C N R Rao R A Mohan Ram L Ganapathi R Vijayaraghavan

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      Some of the Bi-Ca-Sr-Cu-O compositions show indications of onset of superconductivity in the 200–300 K region, possibly due to the intergrowth of different layered sequences.

    • Non-statistical structures in12C(15N,4He)23Na reaction

      R Singh

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      The data on theϑlab=7° excitation functions of12C(15N,4He)23Na reaction betweenEcm=9.42 and 17.33 MeV for 28 states upto an excitation energy of 8.940 MeV in23Na have been subjected to statistical analysis. In addition to statistical fluctuations, the results of the analysis indicate the existence of non-statistical structures atEcm=10.66, 10.93, 11.38, 12.62, 13.16, 15.32 and 16.18 MeV.

    • Specific heat of YBa2Cu3O7−x from 4.2 to 60 K

      N Sankar V Sankaranarayanan R Srinivasan G Rangarajan G V Subba Rao

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      The specific heat of superconducting oxide compound, YBa2Cu3O7 −x, is studied using a quasi-adiabatic calorimeter from 4.2 to 60 K. The analysis of the specific heat data below 15 K gives a value of 17 mJ/mole K2 for the electronic heat capacity coefficient. The value ofθD(0) is determined to be 397±8 K. The variation ofθD with temperature was calculated in the temperature range 4.2 to 60 K.

    • Orthorhombic structure: a necessity in superconducting 1-2-3 compounds

      R Prakash O Prakash N S Tavare

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      X-ray and resistivity measurements on YBa2Cu3O7−δ(1-2-3) samples show that for the same but low oxygen concentration,δ⋍0·55, no superconducting transition down to 4·2 K is observed for the tetragonal phase samples while the orthorhombic phase shows aTc ∼ 31 K. The effect of oxygen concentration onTc is isolated.Tc=91±1 K has, however, been observed continuously for the normal oxygen annealed samples,δ⋍0·07. The experimental results suggest strongly the necessity of the 1-2-3 compound to be in the orthorhombic phase for the superconducting mechanism to be operative.

    • Non-thermal rotational and vibrational excitation of CN produced in the flash photolysis of thiazole

      R Venkatasubramanian S L N G Krishnamachari

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      In the flash photolysis of thiazole at low pressure without any diluent, the 0–0, 1–1 and 0–1 bands of the CN violet system were observed in absorption; the 0–0 band at 3883·4 Å showed a high rotational excitation corresponding to a temperature of ⋍2000 K. The addition of argon makes the NCS bands appear with good intensity and at the same time relaxes the CN rotationally and vibrationally. These observations suggest that highly excited NCS is initially formed in the photodecomposition of thiazole which acted as a precursor to the rotationally and vibrationally excited CN radical. This paper deals with studies on the effect of argon on the relative intensities of CN and NCS and on the non-thermal rotational and vibrational intensity distribution of the CN violet system. The mechanism of formation of rotationally unrelaxed CN in the flash photolysis of thiazole has been proposed.

    • Measurement and analysis of excitation functions for alpha-induced reactions in copper

      H D Bhardwaj A K Gautam R Prasad

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      Excitation functions for the production of68Ga,67Ga,66Ga,65Ga +65Zn and61Cu fromα-induced reactions in natural copper have been measured in the energy range ≈ 10–40 MeV using the stacked foil technique. A stack of nine copper foils was irradiated by a 40 MeVα-beam. Theγ-rays emitted from the irradiated samples were recorded. Excitation functions have also been calculated theoretically using a statistical model with and without the inclusion of pre-equilibrium emission of particles. Pre-equilibrium component simulated by exciton model shows that the inclusion of pre-equilibrium emission gives better agreement between experimental and theoretical excitation functions. Pre-equilibrium fraction depends on the incident energy and the target mass number.

    • Γ andX bandgap hydrostatic deformation potentials for epitaxial In0.52Al0.48As on InP(001)

      R People A Jayaraman K W Wecht S K Alexander A Y Cho D L Sivco

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      The pressure dependence of the direct and indirect bandgap of epitaxial In0.52Al0.48As on InP(001) substrate has been measured using photoluminescence up to 92 kbar hydrostatic pressure. The bandgap changes from Γ toX at an applied pressure of ∼ 43 kbar. Hydrostatic deformation potentials for both the Γ andX bandgaps are deduced, after correcting for the elastic constant (bulk modulus) mismatch between the epilayer and the substrate. For the epilayer we obtain$$(\Xi _d + \tfrac{1}{3}\Xi _u - a) as - (6 \cdot 92 + 0 \cdot 3) eV$$ and+(2.81±0.15)eV for the Γ andX bandgaps respectively. From the pressure dependence of the normalized Γ-bandgap photoluminescence intensity a Γ-X lifetime ratio, (τΓX), of 4.1×10−3 is deduced.

    • On the nature of the dhcp to fcc transition under pressure in Pr and Pr-Th alloys

      V Vijayakumar B K Godwal S K Sikka R Chidambaram

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      The results of electrical resistance (R), thermoelectric power (TEP) and X-ray diffraction measurements on praseodymium (Pr) and its alloys with thorium under pressure are reported. The maximum inR vsP curve exhibited by Pr persists only in the dhcp phase of PrTh alloy. X-ray measurements confirmed that in the alloys also the maximum inR vsP curve is due to the dhcp → fcc transition. Thus the behaviour of Pr and Pr-Th alloys is different from that of La and its alloys with Ce and Th where the maximum in theR vsP curve is electronic in origin and is exhibited by the dhcp, fcc and dist fcc phases.

    • Superconductivity in layered nickel oxides

      C N R Rao A K Ganguli R Nagarajan

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      Likely presence of superconductivity in layered nickelates of K2NiF4 structure is pointed out.

    • A satellite-borne experiment to study the fifth force

      R Cowsik N Krishnan S Unnikrishnan S N Tandon P Saraswat

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      An experiment with a satellite-borne torsion balance capable of measuring the fifth force which couples to baryon number or lepton number with a strengtr gravity and range ~ 109 cm is described.

    • Structure of nuclei in the regionA = 70

      R Sahu S P Pandya

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      The structure of the selenium nuclei in the regionA = 70 is studied using our deformed configuration mixing (DCM) shell model based on Hartree-Fock states. An effective interaction given by Kuo and modified by Bhatt is used. An attempt is made to understand the coexistence of shapes in selenium nuclei.

    • Gribov ambiguity in gauge theories

      R Parthasarathy

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      Gribov ambiguity in gauge field theories is discussed and it is shown that such an ambiguity exists even for Abelian theories in covariant gauge at finite temperature. Both geometric and algebraic proofs are presented. In view of the importance of non-perturbative methods, some special gauges are given in which such ambiguities do not exist or are not relevant. The significance of these in the study of confinement in QCD is pointed out.

    • Criterion for a unique non-relativistic quark model

      R Nag S N Mukherjee S Sanyal

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      We have calculated the mean square charge radii of the neutron and proton, and compared them with the experimental values, to construct a unique non-relativistic quark potential model. It is shown for the first time that, contrary to general belief, it is possible to reproduce simultaneously the baryon mass spectrum and the electromagnetic sizes of neutron and proton using a single potential model. It was found necessary to add admixtures of excited states of the nucleon in the unperturbed ground state wavefunctions.

    • Hamilton’s theory of turns and a new geometrical representation for polarization optics

      R Simon N Mukunda ECG Sudarshan

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      Hamilton’s theory of turns for the group SU(2) is exploited to develop a new geometrical representation for polarization optics. While pure polarization states are represented by points on the Poincaré sphere, linear intensity preserving optical systems are represented by great circle arcs on another sphere. Composition of systems, and their action on polarization states, are both reduced to geometrical operations. Several synthesis problems, especially in relation to the Pancharatnam-Berry-Aharonov-Anandan geometrical phase, are clarified with the new representation. The general relation between the geometrical phase, and the solid angle on the Poincaré sphere, is established.

    • Nucleon exchange mechanism of mass asymmetry relaxation in fission and other binary nuclear reactions

      V S Ramamurthy R Ramanna

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      Mass asymmetry relaxation as manifested in fission and heavy ion-induced binary reactions is reviewed. In fission, the dynamics is characteristic of a fully damped case and is well described by a stochastic theory. In heavy ion deep inelastic collisions and quasi-fission, on the other hand, the relaxation is incomplete giving rise to the possibility of studying its time evolution.

    • An analysis of the mass formulae forS- andP-wave mesons

      V Gupta R Kögerler

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      Mass regularities forS- andP-wave mesons and relations between their masses are discussed. A detailed analysis is given forS-wave mesons which extends the investigations onP-wave mesons reported earlier. Masses for theS- andP-states of all interesting$$q\bar q$$-systems (including toponium states) are predicted. Partial understanding of the mass formulae is obtained within a general potential model approach. Scaling arguments are presented which support the empirical scaling behaviour found for the expectation values determining the spin-splittings in the potential picture.

    • Synergism in electron gas in crossed fields. II degenerate 3DEG—hall conductance

      R Pratap J Sreekumar

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      A microscopic many body correlation dynamics has been worked out for a 3DEG in degenerate state far removed from equilibrium, placed in crossed electric and magnetic fields of arbitrary strength. It is shown that linear electric field case gives only σ12, even though the response function retains all the nonlinear effects in the system. The nonanalytic behaviour of the response function is explicitly shown. The quantisation of Hall current comes out as a direct consequence both for odd and even filling factors, and this is due to an exact evaluation of the dynamics in the self consistent field case. Radiated energy for this system is also calculated. A comparison of the present results with those obtained based on Kubo formalism has brought out the incompatability of using external fields as ordering parameters in any expansion scheme. A further new result is the nonanalytic property of the response function obtained in the present formulation.

    • Magnetic properties of Zr doped Y9Co7

      R Ranganathan J L Tholence B V B Sarkissian

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      Detailed measurements of magnetization and ac susceptibility at low temperatures of 1% Zr-substituted Y9Co7 are presented. All results are indicative of itinerant weak ferromagnetism withTc ∼ 9.5 K. The zero-field magnetizations followT2 orT4/3 behaviour as in the Ni-substituted system. The estimated critical exponents areβ=0.38±0.03,γ=1.16±0.05. It is argued that the main effect of the non-magnetic Zr-substitution in Y9Co7 is to stabilize the ferromagnetic ordering by suppressing the ‘hopping’ of Co atoms along thec-axis sites of the hexagonal structure.

    • Phonon density of states of tetracyanoethylene from coherent inelastic neutron scattering at Dhruva reactor

      S L Chaplot R Mukhopadhyay P R Vijayaraghavan A S Deshpande K R Rao

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      Inelastic neutron scattering experiments to determine phonon density of states of coherent scattering samples of polycrystalline complex solids are generally intensity-limited and therefore are feasible only at high flux facilities. Phonon density of states of the monoclinic phase of tetracyanoethylene at 300 K, obtained using the medium resolution triple axis spectrometer at the new Indian medium flux reactor Dhruva are reported here. The raw data is converted to the “neutron weighted” phonon density of states by applying suitable corrections. Comparison made with results from a theoretical calculation based on a semirigid molecule model of lattice dynamics is fair. Results from Dhruva are also consistent with that obtained (to be published) at the high flux pulsed neutron source (ISIS) of the Rutherford Appleton Laboratory in United Kingdom.

    • Phase transformation and electrical resistivity of tetracyanoethylene under pressure

      P Ch Sahu K Govinda Rajan Mohammad Yousuf R Mukhopadhyay S L Chaplot K R Rao

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      This paper reports the phase transformation behaviour of tetracyanoethylene (TCNE) under pressure as revealed by AC electrical resistivity, its time evolution and X-ray diffraction studies. An irreversible transformation from monoclinic to cubic phase occurs at 2.1±0.1 GPa and is indicated by a sharp resistivity drop at this pressure. The time evolution of resistivity studies indicate that this transformation occurs via an intermediate phase having resistivity higher than either of the two crystalline phases. Finally, the kinetics of phase transformations obtained by time evolution of resistivity is compared with the X-ray studies on the pressure quenched TCNE.

    • Electronic structure of La2CuO4

      G Subramoniam R S Rao S Mathi Jaya R Asokamani

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      The electronic band structure of La2CuO4 is performed using self-consistent linear muffin-tin orbital method. The 17 band complex is found to arise mainly from the overlap between Cu-3d and O-2p wavefunctions. The calculated density of states at the Fermi energy (NEF), the conduction band-width and the electronic specific heat coefficient are given.

    • 1H relaxation study in (NH4)2SbF5

      B Bandyopadhyay A Ghoshray R Mukhopadhyay R M Kadam

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      1H spin-lattice relaxation rate (T1−1) has been measured using inversion recovery technique in polycrystalline (NH4)2SbF5 system in the temperature range 140–400 K. From the plot of log (M0M) againstτ, we have estimated two differentT1 corresponding to two inequivalent ammonium ions in the unit cell. Temperature-dependence ofT1 in each case exhibits features of double minima indicating the influence of different correlation times corresponding to different types of motion. Activation energies at different temperature regions have been estimated. Some features of dynamics of motion of the different groups of ions across the phase transitions have been discussed.

    • Structure factor of charged colloidal suspensions using Brownian-dynamics simulation: Comparison of Yukawa and Sogami pair potentials

      B V R Tata A K Sood R Kesavamoorthy

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      Static structure factorsS(Q) are obtained for dilute charged colloidal systems using Brownian dynamics simulation method for the widely used screened Coulomb repulsive Yukawa potential and the recently proposed Sogami pair potential. The latter potential has, in addition to the usual repulsive part, an attractive term which is necessary to understand the reentrant phase transition reported in these colloids. It is shown for the first time thatS(Q) obtained using the Sogami potential for parameters favourable for liquid-like order agrees well with that measured experimentally. Thus it appears that the Sogami potential explains features of a homogeneous liquid as well as phase separated states, whereas Yukawa potential does not.

    • Wavelength dependence of phase conjugate reflectivity in absorbing media and thermal grating studies by four wave mixing

      R Krishna Mohan B Raghavendra Prasad C K Subramanian P S Narayanan

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      The development of optical phase conjugation using thermally formed gratings in absorbing media, especially the dye solutions, has besides the high efficiencies, many other characteristics which are worthy of study. Here the wavelength dependence of phase conjugate reflectivity in relation to absorption spectrum of rhodamine-6G and rhodamine-B in water, methanol and ethanol is reported. Further the Bragg condition has been verified for the dominant diffracted beam which shows that the thermal grating behaves like an optically thick grating.

    • Analysis of the absorption mechanism during laser-metal interaction

      B S Yilbas R Davies Z Yilbas A Koc

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      The present study examines the absorption of a laser beam at different wavelengths by a partially-ionized vapour during the interaction mechanism. The applicability of the theoretical models developed is discussed in detail. The interaction of the high- and low-power intensities of a laser beam with plasma is distinguished. It is shown that different metal vapours at similar temperatures and densities have absorption depths which may differ by an order of magnitude. Even more substantial is the difference between the absorption depths of light from different lasers in common use. It is also shown that the free electron temperature becomes significantly different from the heavy particle temperature for power intensities above the critical level which is typically > 1014W/m2. The free electron velocity distribution has an isotropic part which becomes non-Maxwellian for power intensities greater than the critical power intensity.

    • Pressure-tuned resonance Raman scattering and photoluminescence studies on MBE grown bulk GaAs at theE0 gap

      A Jayaraman G A Kourouklis R People S K Sputz L Pfeiffer

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      Hydrostatic pressure has been used to tune in resonance Raman scattering (RRS) in bulk GaAs. Using a diamond anvil cell, both the photoluminescence peak (PL) and the 2 LO and LO-phonon Raman scattered intensities have been monitored, to establish RRS conditions. When theE0 gap of GaAs matchesħωS orħωL, the 2 LO and LO-phonon intensity, respectively, exhibit resonance Raman scattering maxima, at pressures determined byħωL. With 647.1 nm radiation (ħωL = 1.916 eV), a sharp and narrow resonance peak at 3.75 GPa is observed for the 2 LO-phonon. At this pressure the 2 LO-phonon goes through its maximum intensity, and falls right on top of the PL peak, revealing thatħωS(2 LO) =E0. This is the condition for “outgoing” resonance. Experiments with other excitation energies (ħωL) show, that the 2 LO resonance peak-pressure moves to higher pressure with increasingħωL, and the shift follows precisely theE0 gap. Thus, the 2 LO RRS is an excellent probe to follow theE0 gap, far beyond the Γ-X cross-over point. A brief discussion of the theoretical expression for resonance Raman cross section is given, and from this the possibility of a double resonance condition for the observed 2 LO resonance is suggested. The LO-phonon resonance occurs at a pressure whenħωLE0, but the pressure-induced transparency of the GaAs masks the true resonance profile.

    • Pressure induced amorphization of AlPO4

      Hema Sankaran Surinder M Sharma S K Sikka R Chidambaram

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      AlPO4 has been compressed to pressures of 16 GPa in a diamond anvil cell and its X-ray diffraction pattern studied by the energy-dispersive technique. The compound is observed to become amorphous at ∼ 12 GPa. This explains the loss of Raman spectrum of AlPO4 reported by Jayaraman and coworkers (1987).

    • Unusually large shift in low-temperature susceptibility peak of Fe2.8Ti0.2O4 with frequency

      C Radhakrishnamurty S D Likhite R Nagarajan

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      The temperature dependence of magnetic susceptibility,x, of titanomagnetites (Fe3−xTixO4, 0⩽x⩽0.2) at different frequencies in the range of 13 Hz to 117 kHz is reported. Whereas the position of thex-peak of Fe3O4 at 120 K shows no significant shift over this frequency range, that of Fe2.8Ti0.2O4 shifts from 70 K at 13 Hz to 115 K at 117 kHz. This seems to be the first observation of such large shift in the position of ax-peak observed at low-temperatures is attributed to the occurrence of an isotropic point (temperature at which first order anisotropy constantK1=0) associated with change in crystal structure. In such a case a shift inx-peak with frequency is not expected normally. Thus, the observed large shift in the position ofx-peak with frequency is an unusual phenomenon and some of its repercussions are discussed.

    • Spectroscopically determined electronegativity values for heavy elements

      Chintamani Mande Subha Chattopadhyay Prabodh C Deshmukh R Padma Pranawa C Deshmukh

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      A new scale of electronegativity based on X-ray spectroscopic data was earlier presented by Mande and others for the elements3Li to54Xe. The present paper reports an extension of this scale carried out for most of the heavier elements lying between55Cs and92U. The present approach is based on the physical interpretation of electronegativity of an atom as the attractive electrostatic force it exerts at a distance equal to its covalent radius. To estimate this force, experimental spectroscopic data have been employed. The merits of such an approach have been pointed out recently by Mullay and may be of interest in the context of the intimate relation found between electronegativity and superconducting transition temperature.

    • Fusion cross section for the system6Li+28Si atE ∼ 36 MeV

      S Kailas R Vandenbosch A Charlop A Garcia S Gil S J Luke B McLain D Prindle

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      The fusion cross section for the system6Li+28Si has been measured atE∼36 MeV. Combining this with the data available at lower energies, the nucleus-nucleus real potentials have been determined for a range of interaction distances.

    • An automated ac-magnetic susceptibility apparatus

      A Chakravarti R Ranganathan A K Raychaudhuri

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      We report here both hardware and software for an ac susceptibility measurement system, namely the design and construction of the cryostat, coil system, sample rod assembly and also the automation of the sample rod movement, bridge control and nulling etc with the help of an inexpensive Z-80A microprocessor via a home-made IEEE-488 interface. The variable parameters are temperature, magnitude of the rms field and frequency. An entirely new dynamic bridge nulling algorithm with continuous sample movement, which eliminates to a large extent problems related to time-dependent drifts, has been developed. We also present some experimental data collected with this system.

    • A map describing EEG activity of human brain

      Jitendra C Parikh R Pratap

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      A model of electrical activity of human brain considered as a complex dynamical system is given based on the EEG time series. The model fits the data remarkably well. The predictive ability of the model is limited to a few time steps as expected for a chaotic time series.

    • Microstructural investigations of melt grown YBa2Cu3O7

      T Rajasekharan R Gopalan T Roy

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      The results of microstructural investigations on bulk YBa2Cu3O7 prepared by melt growth process are reported.

    • Determination ofL-shell X-ray production cross-sections in holmium by 10–40 keV photons

      K S Mann K S Kahlon H S Aulakh N Singh R Mittal K L Allawadhi B S Sood

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      In an effort to resolve the existing discrepancy between experiment and theory, the cross-sections for the production ofLl,Lα,Lβ andLγ groups ofL-shell X-rays of Ho by photons of nine energies in the range 10–40 keV have been measured using an improved version of annular source double reflection geometrical set-up. Contrary to the earlier findings of Garget al that the measured values of the cross-sections are consistently higher than those calculated theoretically, the present results do not confirm this. The plausible deficiencies in the experiments of Garget al are pointed out and possible remedies to overcome them are suggested. It is concluded that the higher values obtained by Garget al are probably due to systematic errors in their method of measurement.

    • Synthesis and dielectric properties of Ba3NaRNb10O30 [R = La and Sm]

      K S Singh R Sati R N P Choudhary

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      Polycrystalline samples of Ba3NaRNb10O30 (R = La and Sm) have been prepared by high temperature solid-state reaction method. The X-ray powder diffraction technique has been used to test the formation of the compounds. Lattice parameters, space groups and basic structures of the compounds have been obtained from X-ray data. The dielectric constant has been measured as a function of frequency (100 Hz–10 kHz) and temperature (−180 to 200°C) to understand transition mechanism in these ferroelectric compounds.

    • Fermi surface characteristics and enhancement factors for tantalum

      A K Solanki R Ahuja S Auluck

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      We present calculations of the extremal areas of Fermi surface orbits in the bcc transition metal tantalum usingab initio linear muffin tin orbital method in the atomic sphere approximation. The calculations demonstrate the need to include relativistic corrections for a good representation of the Fermi surface. Self-consistent calculations are performed using various exchange-correlation potentials. The calculations indicate that Barth-Hedin-Janak exchange provides the best agreement with the experiment. Enhancement factors are also calculated using the BHJ exchange-correlation potential. These are compared with experimental results as well as with some of the available theoretical calculations.

    • Surface line and plug flow models governing laser produced vapour from metallic surfaces

      Bekir Sami Yilbas R Davies Z Yilbas A Gorur I Acar

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      In this study a line surface and plug-flow models are examined. The laser beam/target interactions present alternative explanations for the previously noted observations of vapour ejection in the bursts. The importance of choosing between these models rests in the potential difference, in estimates for fluid and vapour variables and in possible inferences for adjacent regions.

    • Debye-Waller factor of lead nitrate

      R Somashekar U D Prahllad M S Madhava

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      The X-ray Debye-Waller factors and Debye temperatures of lead nitrate single crystals taken in the powder form have been determined by measuring integrated intensities of selected Bragg reflections at different temperatures. The characteristic specific Debye temperature has been compared with the value obtained from elastic constant data.

    • Magnetization studies in niobium and YBa2Cu3O7 samples

      B V B Sarkissian A K Grover G Balakrishnan Ravi Kumar P L Paulose R Vijayaraghavan V Sankaranarayanan C K Subramanian

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      The results of experimental studies on hysteresis in magnetization, thermomagnetic history effects, anomalous variations in magnetic hysteresis curves and the decay rates of magnetization obtained under different thermomagnetic histories in specimens of conventional and high temperature superconductors are presented. The Bean’s critical state model is considered adequate to explain magnetic behaviour in conventional hard superconductors. The similarity in the general features of the results of different experiments on specimens of the two families of superconductors underscores the efficacy of the said model to understand some aspects of the macroscopic magnetic response of high temperature superconductors as well. For instance, the isothermal magnetization hysteresis loop which comprises of magnetization curves along forward (−Hmax to +Hmax) and reverse (+Hmax to −Hmax) paths define an envelop within which all isothermal magnetization data along different thermomagnetic histories lie. There exist inequality relationship between various field values identified asHpeak,HI,HII etc. in isothermal magnetization hysteresis as well as magnetic relaxation data. The entire field span of an isothermal magnetization hysteresis data set can be considered to comprise of three parts corresponding to (Mrem(H)−MFC(H)+MZFC(H)) being equal to, less than or greater than zero, whereMrem(H) are the remanent magnetization values obtained on reducing field to zero after having the specimen in different applied field (H) values. There are, however some situations amongst thermomagnetic history effects in specimens which show incomplete flux trapping on field cooling, where the critical state model has been found inadequate.

    • An automated thermoelectric power apparatus using electro-optic relays

      A Chakravarti R Ranganathan

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      We report the design and construction of a thermoelectric power apparatus using home-made electro-optic relays with Z-80A microprocessor for automatic data acquisition and control. The advantages of such relays made out of LED-LDR combinations for the measurement of ΔE and ΔT are discussed in detail.

    • Thermal conductivity of YBa2Cu3O7 from 7 K to 260 K

      T R Ravindran V Sankaranarayanan R Srinivasan

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      Thermal conductivity of YBa2Cu3O7 has been measured on samples of a few mm thickness. AboveTc thermal conductivity is found to decrease with increase in temperature, pointing towards a contribution to thermal resistivity from three-phonon Umklapp processes. BelowTc thermal conductivity increases rapidly before reaching a maximum at about 50 K and then falls towards zero at lower temperatures. The experimental set up is described and results discussed.

    • Ultra lowqa discharge experiments in the SINP tokamak

      A N Sekar Iyengar S K Majumdar J Basu R K Paul R Pal S Chowdhury

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      Operation of most tokamaks in limited byqa, the edge safety factor, which is usually about 2–3. In the SINP tokamak we have been able to obtain discharges withqa values as low as 0·8. In this paper we describe our results on the setting up processes and the MHD activity associated with these ultra lowqa discharges.

    • Covalent binding parameters and the ground state wavefunctions of vanadyl ion complexes

      B N Misra Ajitendra Narayan R Kripal

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      The Steven’s method of molecular orbitals for octahedral complexes containing transition metal ions has been used for estimating the binding parameters and interpreting theg factors of VO2+ ion in single crystals. The expressions forg factors have been given in terms ofK andK taking into account the tetragonal crystalline field and covalent binding effects. Computations show thatK should be less than 0.066 in order to fit the experimentalg values. The ground state wave function (GSWF) of VO2+ ion doped in different single crystals has been estimated using crystal field theory. The GSWF is found to be indxy state with slight admixture of the excited states$$d_{x^2 - y^2 } $$,dxz anddyz. The hyperfine interaction parameterP and Fermi contact termX have also been estimated.

    • Dielectric properties of Pb(Mg1/4Zn1/4Nb1/2)O11/4

      S Sharma R N P Choudhary R Sati

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      Polycrystalline samples of Pb(Mg1/4Zn1/4Nb1/2)O11/4 have been synthesized by high temperature columbite precursor solid state reaction technique. Using X-ray diffraction (XRD) technique, compound formation in single phase cubic structure was observed and XRD analysis provided preliminary structural data. Detailed studies of dielectric properties of the compound reveal that this compound has high dielectric constant and diffuse phase transition in a wide range of temperatures around the Curie temperature. The charge deficiency of the compound presumably gets compensated in the high temperature columbite precursor process of sample preparation which is supported by single phasic form of the material.

    • Optical mode-coupling in a ring due to a back-scatterer

      A Venugopalan Deepak Kumar R Ghosh

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      The coupling of light waves travelling clockwise and counterclockwise along an optical ring due to a back-scattering element is studied. An asymmetric mode splitting occurs as a consequence of the discontinuity suffered by the waves at the scattering point. The mode splitting shows up in an interference pattern and lends itself to an experimental verification.

    • Rotational excitations of NH4+ in (NH4)xK1−xI

      S L Narasimhan R Mukhopadhyay

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      We propose a gaussian model for the distribution of rotational tunneling lines which constitute the experimentally observed inelastic neutron scattering spectra in the range 0 to 0.6 meV from the mixed system (NH4)xK1−xI. The intensity profiles generated by this model are in remarkable agreement with the experimentally observed ones.

    • Simulation of X-ray diffraction patterns for silk fibres using paracrystalline statistics

      R Somashekar R Gopalkrishne Urs

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      Using paracrystalline statistics, we have simulated one-dimensional and three-dimensional X-ray diffraction patterns from natural silk fibres for various values of crystal size and lattice distortion parameters. This is in agreement with the experimental observation of X-ray pattern reported earlier.

    • TDPAC studies of Hf doped YBCO

      R Govindaraj M Premila Padma Gopalan K P Gopinathan

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      Time differential perturbed angular correlation measurements of the 133–482 keVγ-γ cascade of181Ta in Hf-doped YBa2Cu3O7−x are presented. The181Hf precurser nuclei are incorporated into the sample by thermal neutron irradiation. Two quadrupole interaction frequencies are observed in the as-irradiated sample:vQ1=161±10 MHz with intensityf1=75%, asymmetry parameterη1=0.32 and damping parameter Λ1=0.42, andvQ2=1108±40 MHz withf2=25%,η2=0.62, and Λ2=0.60. On annealing the sample in air at various temperaturesTa and quenching to room temperature,f1 remained nearly constant forTa<600°C andvQ1 for all annealing temperatures indicating that these are insensitive to oxygen stoichiometry. This frequency is interpreted to be due to181Hf substitutingY sites. BeyondTa=600°C,f1 increased and reached a constant value of 90% forTa=800°C. The value ofvQ2 showed a slight variation between 1086 and 1160 MHz, whilef2 remained nearly constant at 25% forTa<600°C. This component is identified to be due to181Hf substituting Cu 1 sites in the Cu-O chains of YBCO. Above 600°CvQ2 decreased and reached a value of 808 MHz beyond 750°C.

    • Critical current density of a sample of melt grown Y1.2Ba1.8Cu2.4Ox

      V Ganesan R Srinivasan R Gopalan T Rajasekaran

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      Melt grown samples of Y1.2Ba1.8Cu2.4Ox have been prepared and studied for their current carrying capacity. The composition was chosen to include Y2BaCuO5 (211) particles in the YBa2Cu3Ox (123) phase. The critical current density (Jc) of these samples was studied as a function of magnetic field using magnetization technique. The micrographic investigation shows well aligned grains in this material. The magnetic hysteresis measurements were done using a MPMS SQUID magnetometer up to the fields of 5.5 T. TheJc was estimated from the remanent magnetization using Bean model. Isothermal magnetization hysteresis loops at low fields reveal the presence of only one kind of hysteresis loops (corresponding to intragrain magnetizations). This is a valid proof that the weak links are greatly eliminated in these samples prepared by MG process. TheJc behaviour as a function of magnetic field has two components, a rapidly decaying exponential function of field and the other component that predominates at higher fields. This could be explained if we assume that the sample contains two phases of superconductors, one having a lowHc2 becoming normal at fairly medium fields of the order of a few kilogauss will act as pinning centres for the other phase having higherHc2 and hence higherJc at high fields.

    • StandardSU(5) supergravity grand unification model and predictions

      Pran Nath R Arnowitt

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      A review is given of the StandardSU(5) supergravity model. This model has passed an important check regarding unification of the electro-weak and the strong couplings using high precision LEP data. It is shown that for a significant domain of the parameter space the model also satisfies constraints on the SUSY spectrum from CDF and LEP, as well as proton stability and cosmological relic density constraints.

    • Molecular dynamics in chloronitrobenzenes using NQR data

      Shanta Sastry R Shantha Kumari R Chandramani

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      The torsional frequencies have been rigorously evalulated in the compounds 1,2,4,5-tetrachloro-3,6-dinitrobenzene and 1,3,5-trichloro-2,4-dinitrobenzene over an extended temperature range (77K–392K) using the experimental results of NQR and crystal structure data. The values have been compared with those obtained by using the X-ray thermal parameters.

    • Pre-equilibrium effects in the formation of meta stable states

      R Upadhyay Ch V Sastry R K Jain J Rama Rao

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      Isomeric yield ratios have been measured for93Nb(α, 2n)95m,gTc reaction in the energy range 25–60 MeV. The ratios were compared with theoretical values obtained by means of two models one based on compound nucleus mechanism only and the other including pre-equilibrium effects. The trend of experimental ratios is better reproduced by the latter model, although there remains some discrepancy as to the magnitude at higher energies.

    • New band system of MnSe molecule

      K N Uttam R Gopal M M Joshi

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      Thermal emission spectrum of MnSe molecule, excited in high temperature graphite furnace, has been photographed in the spectral region λλ4150–5800 Å at a reciprocal linear dispersion of 7.3 Å/mm. The study reveals the presence of two band systems viz.A–X andB–X in whichB–X is entirely new. While the systemA–X consists of 29 bands, the new systemB–X comprises of 24 single headed and red degraded bands. Vibrational analysis performed suggested that both the systems involve ground state6Σ with a vibrational frequencyωe=361.0 cm−1. Transition responsible for MnSe spectrum appears to be of the type6Σ–6Σ.

      An estimation of the ground state vibrational frequency for MnTe molecule gives rise to its value as 280 cm−1.

    • Computation of collective modes and acoustic investigations at different temperatures of vitrous silica

      R V Gopala Rao R Venkatesh

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      This paper is mainly concerned with elastic and acoustic properties of vitrous silica besides the computation of phonon frequencies. Thus the phonon frequencies of vitrous silica have been calculated assuming the electronic bulk modulus,Ke, as equal to zero. New equations have been derived to relate the pressure derivatives of second order elastic constants to the acoustic Gruneisen’s parameters using both Bhatia-Singh’s parameters and Schofield’s equations. The calculated longitudinal and transverse Gruneisen’s parameters and the predicted absorption band spectra from Nagendranath’s equation and Bhatia Singh’s parameters are in good agreement with experiment. The calculated mean acoustic mode Gruneisen’s parameter evaluated from the pressure derivative of Nagendranath’s equation is also in good agreement with experiment.

    • Even harmonics of AC susceptibility in some sintered pellets of high temperature superconductors

      A Das A Bajpai A Banerjee R Srinivasan

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      The real (χ′n) and imaginary (χ″n) parts of even harmonic susceptibility (n⩽6) are measured as a function of external DC field (Hdc) in the field increasing (H↑) and decreasing (H↑) cycle. Hysteresis is observed betweenH↑ andH↓ cycles. In theH↓ cycle, at a field,Hcomp=4·2G, bothχ′ andχ″ of all the even harmonics vanish indicating a true cancellation of fields in the intergrain region (Heff≈0) caused by the balance betweenHdc and the remanent magnetization of the grains. The position of the extrema and the zero of the various harmonics undergo a shift proportional to the remanent magnetization of the grains at that particular field.

    • Computation of collective modes and acoustic investigations at different temperatures of vitrous silica

      R V Gopala Rao R Venkatesh

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    • Giant magnetoresistance in bulk samples of LaMnO3 with varying Mn4+ content

      R Mahendiran R Mahesh A K Raychaudhuri C N R Rao

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      Magnetoresistance (MR) in bulk samples of LaMnO3 has been investigated by varying the Mn4+ content from 10 to 33 per cent by chemical means, without aliovalent doping. With the increase in Mn4+ content, the structure of LaMnO3 changes first from orthorhombic to rhombohedral and then to cubic and the material becomes increasingly ferromagnetic, exhibiting a resistivity maximum akin to an insulator-metal transition atTPeak, just below the ferromagneticTc. The magnitude of MR is highest in the cubic sample (with 33% Mn4+) around theTPeak, and negligible in the non-magnetic orthorhombic sample (12% Mn4+).

    • On singularity-free spacetimes

      Naresh Dadhich L K Patel R Tikekar

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      We consider here the metric for the singularity-free family of fluid models. The metric is unique for cylindrically symmetric space-time with metric potentials being separable functions of radial and time coordinates in the comoving coordinates. It turns out that fluid models separate out into two classes, withρµp in general butρ = 3p in particular andp =ρ. It is shown that in both the cases radial heat flow can be incorporated without disturbing the singularity-free character of the spacetime. The geodesics of the singularity-free metric are studied and the geodesic completeness is established. Several previously known solutions are derived as particular cases.

    • Vibrational analysis of NaM2OH(H2O)(MoO4)2/D2O [M=Ni, Zn]

      R Ratheesh G Suresh V U Nayar

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      The infrared and Raman spectra of NaNi2OH(H2O)(MoO4)2 and NaZn2OH (H2O)(MoO4)2 and their partially deuterated analogues are recorded and analysed on the basis of vibrations of MoO42− tetrahedra and H2O molecules. The MoO42− groups are found to be more distorted in NaNi2OH(H2O)(MoO4)2 than in the other compound. Bands indicating the presence of H3O+ ions are not observed in NaZn2OH(H2O)(MoO4)2 ruling out the possibility of the formulation of NaZn2OHO(MoO3OH)2. Hydrogen bonds of medium strength are present in both the compounds.

    • Development of an experimental facility for studying atomic-field, bremsstrahlung from keV electrons interacting with atoms and molecules

      S K Goel M J Singh R Shanker

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      A dedicated working setup for studying the process of atomic-field bremsstrahlung and its dependence on various parameters for keV electrons incident on a solid or a gaseous target has been indigenously developed. The setup consists of a high vacuum scattering chamber attached with a rotatable X-ray photon detector, a home-built high voltage electron gun with a replaceable tungsten-filament cathode, an isolated floating high voltage system, high vacuum pumping units, various signal processing electronic modules and an IBM PC/XT based 4K-multichannel analyzer. A brief description of the facility is presented. The performance of the facility has been tested by recording the bremsstrahlung spectra from 7.0 keV electrons on thin Ag, Au and 7.5 keV electrons on Hf targets; the corresponding spectra are presented and discussed. The gun can operate in the range of 0–8.0 kV accelerating voltage in the present configuration. Other feasible experiments that can be performed on the setup are also briefly mentioned.

    • Estimation of parameters of gravitational waves from coalescing binaries

      R Balasubramanian B S Sathyaprakash S V Dhurandhar

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      In this paper we deal with the measurement of parameters of the gravitational wave signal emitted by a coalescing binary system of compact stars. We present the results of Monte Carlo simulations carried out for initial LIGO, incorporating the first post-Newtonian corrections to the waveform. Using the parameters so determined, we estimate the direction to the source. We stress the use of the time-of-coalescence rather than the time-of-arrival of the signal to determine the direction of the source. We show that this can considerably reduce the errors in the determination of the direction of the source.

    • The real symplectic groups in quantum mechanics and optics

      Arvind B Dutta N Mukunda R Simon

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      We present a utilitarian review of the family of matrix groups Sp(2n, ℛ), in a form suited to various applications both in optics and quantum mechanics. We contrast these groups and their geometry with the much more familiar Euclidean and unitary geometries. Both the properties of finite group elements and of the Lie algebra are studied, and special attention is paid to the so-called unitary metaplectic representation of Sp(2n, ℛ). Global decomposition theorems, interesting subgroups and their generators are described. Turning ton-mode quantum systems, we define and study their variance matrices in general states, the implications of the Heisenberg uncertainty principles, and develop a U(n)-invariant squeezing criterion. The particular properties of Wigner distributions and Gaussian pure state wavefunctions under Sp(2n, ℛ) action are delineated.

    • Effect of heavy quark symmetry on the mass difference ofB-system in minimal left right symmetric model

      A K Giri L Maharana R Mohanta

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      An estimation of the mass difference of$$B_d^0 - \bar B_d^0 $$ system with heavy quark symmetry formalism is presented. The effective Hamiltonian describing the transition$$\bar hd \leftrightarrow h\bar d$$ (whereh=b forBd0-system) is considered in a manifest left right symmetric (MLRS) model along with contribution from neutral Higgs boson. We use the spin and flavor symmetry for heavy quarks to obtain the transition matrix element 〈Bd0|ℋeff(x)|$$\bar B_d^0 $$d0〉 in terms of Isgur-Wise function. Assuming thatBd0 and$$\bar B_d^0 $$ states are at rest, we find that Isgur-Wise function turns out to be unity. However using the experimental values of ΔMK and$$\Delta M_{B_4 } $$ as input, we find thatMR=835 GeV andMH⩾2·9 TeV.

    • Composite Anderson-Newns model and density of states due to chemisorption: Quasi-chemical approximation

      R Guleria P K Ahluwalia K C Sharma

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      In this paper a variation in density of states (DOS) of the substrate due to chemisorption of hydrogen on transition metals using composite Anderson-Newns model has been investigated for different coverages in quasi-chemical approximation of Fowler and Guggenhiem, which in the limitz→∞ gives the Bragg-Williams approximation as a special case. Variation in density of states has been studied for one-dimensional periodic substrate with change in adatom interaction energy and coverage. With increase in coverage, the bonding and antibonding (B-AB) peaks are found to shift towards higher energies and at the same time relative height of the peaks also increases. The interesting feature to observe is that both approximations for a particular coverage, give split-off states with different height for both (B-AB) peaks. It particularly indicates change in B-AB states, representing amount of chemisorption, with the change in interaction energy between adatoms. At the same time bond strength is also found to decrease with interaction between adatoms.

    • Ratios ofB andD meson decay constants with heavy quark symmetry

      A K Giri L Maharana R Mohanta

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      SU(3) flavor symmetry allows the decay constantsfD1 andfD2 as well asfB1 andfB1 to be equal. But due toSU(3) flavor symmetry breaking the ratiosfB1/fB2 andfD1/fD2 are deviated from unity. We have estimated these ratios in the heavy quark effective theory and obtainedfB1/fB2=0.93,fD1/fD2=0.94 and the double ratio (fB1/fB2)/(fD1/fD2)=0.99.

    • Temperature dependent photoluminescence studies of ZnSe:I single crystals grown by chemical vapor transport

      Suruchi Anand Prabhat Verma S C Abbi K P Jain M J Tafreshi K Balakrishnan R Dhansekaran

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      The single crystal ZnSe:I sample was grown by the chemical vapor transport (CVT) method using iodine as the transporting agent. The iodine incorporates itself effectively as a donor in the lattice. The sample shows a 〈111〉 optical quality surface and has an absorption edge at 2.55 eV due to a deep impurity band nearly 0.15eV below the conduction band. The photoluminescence emission spectra of this crystal have been measured for its temperature dependence as well as for excitation energy dependence. The photoluminescence is in accordance with a donor-acceptor complex formation involving iodine activated donors and self-activated acceptors. The configuration coordinate model has been used to explain the temperature dependent changes in the peak position and the bandwidth of the emission band. The decrease in luminescence efficiency with increasing temperature is explained by using a simple model for thermal quenching. The activation energy at low temperature range (T<200K) is different from that at high temperature range (200K<T<300K).

    • Raman study of phase transition in ferroelectric Ba0.95Ca0.05TiO3

      Rekha Rao A P Roy B A Dasannacharya S Balakumar R Ilangovan P Ramasamy

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      Raman scattering investigation of phase transition in the ferroelectric Ba0.95Ca0.05TiO3 is reported. The results suggest onset of significant dynamic disorder at 105°C. This corroborates findings of recent structural study regarding large positional disorder associated with Ti and O1 atoms well below the tetragonal to cubic transition temperature (∼150°C).

    • Radiative decays of heavy mesons with heavy quark symmetry

      A K Giri L Maharana R Mohanta

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      The radiative decays of heavy mesons are considered in heavy quark symmetry formalism. Introducing the interpolating fields for the heavy mesons we obtain the transition matrix element and the corresponding decay widths in the heavy quark symmetry limits. The Isgur-Wise function present in the expression is determined by ISGW quark model. The results obtained agree reasonably well with other estimations.

    • Ratios ofB andD meson decay constants with heavy quark symmetry

      A K Giri L Maharana R Mohanta

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    • Measurement and analysis of excitation functions for alpha induced reactions on iodine and cesium

      N P M Sathik M Afzal Ansari B P Singh R Prasad

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      The excitation functions for the reactions127I(α, 2n)129Cs,127I(α, 4n)127Cs,133Cs(α, 2n)135La and133Cs(α, 4n)133La have been measured up to ≈50 MeVα-particle energy using the stacked foil activation technique. Measured excitation functions are compared with pre-equilibrium geometry dependent hybrid model calculations. It has been found that theoretical calculations using an initial exciton numbern0=4 (2p+2n+0h) give good agreement with experimental excitation functions.

    • Radiative decays of heavy baryons with heavy quark symmetry

      A K Giri L Maharana R Mohanta

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      The decay widths for the radiative decays of heavy baryons are calculated in the heavy quark effective theory. Introducing the interpolating fields for heavy baryons we obtain the transition matrix elements and the corresponding decay widths. Considering theSU(6) flavor-spin wave functions for heavy baryons, the coupling constants are calculated in the nonrelativistic quark model. Since the masses of the heavy baryons are not available, we have taken the predicted bag model masses. We find our results are quite different from that of the heavy quark bag model calculations.

    • Editors’ note

      R Nityananda H R Krishnamurthy

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    • Localized coherent structures of (2+1) dimensional generalizations of soliton systems

      M Lakshmanan R Radha

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      We briefly review the recent progress in obtaining (2+1) dimensional integrable generalizations of soliton equations in (1+1) dimensions. Then, we develop an algorithmic procedure to obtain interesting classes of solutions to these systems. In particular using a Painlevé singularity structure analysis approach, we investigate their integrability properties and obtain their appropriate Hirota bilinearized forms. We identify line solitons and from which we introduce the concept of ghost solitons, which are patently boundary effects characteristic of these (2+1) dimensional integrable systems. Generalizing these solutions, we obtain exponentially localized solutions, namely the dromions which are driven by the boundaries. We also point out the interesting possibility that while the physical field itself may not be localized, either the potential or composite fields may get localized. Finally, the possibility of generating an even wider class of localized solutions is hinted by using curved solitons.

    • Chaos in the hydrogen atom interacting with external fields

      K Ganesan R Gębarowski

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      In this review we discuss the chaotic dynamics (both classical and quantal aspects) of a simple atomic system, namely hydrogen atom interacting with time independent and time dependent external fields. These include: i) static electric field, ii) static magnetic field, iii) combined electric and magnetic fields, in parallel and perpendicular configuration, iv) instantaneous and generalized van der Waals field, v) mass anisotropy and vi) linearly and circularly polarized microwave fields.

    • Two body non-leptonic decaysB with heavy quark and chiral symmetry

      A K Giri L Maharana R Mohanta

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      We have analysed the two body non-leptonic charmed-meson decays of heavyB meson based on the factorization assumption. The transition matrix elements and the corresponding decay widths are calculated in the heavy quark and chiral symmetry limit and the Isgur-Wise function present in the expression is determined by the wave function model of Aliet al. The results obtained are quite interesting and agree reasonably well with the experimental data.

    • Some two body non-leptonicB decays and estimation offD in the heavy quark effective theory

      A K Giri R Mohanta

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      We have studied some of the two body nonleptonic decays ofB meson in the context of heavy quark effective theory using factorization hypothesis. Treatinga1 as a free parameter, we have obtained its value asa1=0.822±0.045, by correlating the experimental and predicted branching ratio for$$\bar B^0 \to D^ + \pi ^ - $$ process. With this value ofa1 the branching ratios obtained for other decay channels are in good agreement with the experiment. The decay constant ofD meson is extracted to be 280.82 MeV. Heavy quark spin symmetry has also been tested.

    • Four constant potential function of amorphous selenium and evaluation of its thermodynamic and acoustic properties

      R Venkatesh R V Gopala Rao Sumita Bandyopadhyay

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      Litov and Anderson after various considerations suggested a four constant potential function for a-Se as well as a-As2S3. Hence we also used a four constant potential function with the sole purpose of applying this potential function to obtain several acoustic, thermodynamic and other properties. We calculated several acoustic properties of a-Se like second order elastic constants (SOECs), their pressure derivatives, the longitudinal and transverse Grüneisen constant by two different methods, phonon frequencies, absorption band position through the use of Nath-Smith-Delaunay’s equation, and the thermodynamic properties like heat capacity, bulk modulus, thermal Grüneisen constant, the pressure derivative of the bulk modulus (dKT/dP=C1), the pressure derivative ofC1 which is related to Anderson-Grüneisen parameter, pressure derivative of Grüneisen constant namelyγg which is related to second Grüneisen constant, characteristics of phonon frequencies, potential energy function through the use of fitted parameters and third order elastic constants. Finally we calculatedKT at the reduced density ofρ/ρ0=1.1.KT is obtained from the potential function with the fitted parameters. In all the above cases the calculated values are found to be in good agreement with experiment wherever available. In this connection it is important to point out that we eliminated ‘C’ a constant in the potential function using the equilibrium condition as was done by Litovet al in a-Se and Gerlichet al in the case of a-As2S3 as all amorphous substances are isotropic as mentioned by several authors. We contemplate to calculate several other properties for a-Se and a-As2S3 and present them at a later stage.

    • SCORPION: A system for coincidences between recoil and projectile ions at NSC, New Delhi

      M J Singh S K Goel R Shanker D O Kataria N Madhavan P Sugathan J J Das D K Avasthi A K Sinha

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      An on-line facility to measure coincidences between the recoil ions and the scattered projectiles (SCORPION) has been designed, fabricated and commissioned at Nuclear Science Centre (NSC), New Delhi. The facility consists of a four jaw slit assembly, a time of flight (TOF) spectrometer, a parallel plate electrostatic charge analyser and a one dimensional position sensitive parallel plate avalanche counter (PPAC). Details of the design and working principles of various components and the test results obtained for the Siq+-Ar collision system are presented to highlight the performance of the system. A multiple loss of up to four electrons has been observed for 60 MeV Si4+ ions colliding with argon atoms in a single collision condition. Spectra of recoil ions detected in coincidence with a particular charge state of the scattered projectile show a bell shaped distribution as a function of the recoil charge state (r) for the electron loss events. However, the yield of recoil ions drops asr increases for the direct ionization channel. Also for electron loss, the peak of the recoil ion distribution is seen to shift to a higher recoil charge state as the number of lost electrons from the projectile increases.

    • TDPAC measurements in textured hcp samples

      R Govindaraj K P Gopinathan

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      Time differential perturbed angular correlation measurements done on the 482 keV level of181Ta probe nuclei in well annealed reference foil samples ofα-ZrHf,α-TiHf andα-Hf indicate that all probe nuclei are defect free, substitutional and experience quadrupole frequencies characteristic of these matrices. But mostly the ratio of the intensities of the harmonic components of the quadrupole frequency is never in 3:2:1, which is understood to be due to the selective orientation of microcrystallites brought out by the pre thermo-mechanical treatments on the sample. This paper illustrates as to how texturing in general could cause ambiguities in the measurements of the hyperfine interaction parameters of probe nuclei particularly in hcp foil samples with or without the association of any defects and the ways to delineate the effect of texturing.

    • Two body non-leptonic Λb decays in the largeNc limit

      A K Giri L Maharana R Mohanta

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      The two body non-leptonic Λb decays are analysed in the HQET with factorization approximation and largeNc limit. In this limit, Λb and Λc baryons can be treated as the bound states of chiral soliton and heavy meson, and consequently the Isgur-Wise function comes out in a straight forward manner. The results obtained remain well below their previously predicted upper limit.

    • Ratio of the color suppressed decays Λb→ΛJ/ψ andB0KJ/ψ

      A K Giri R Mohanta

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      Based on the factorization approximation, we have estimated the ratio of the branching fractions for the color suppressed nonleptonic decays Λb→ΛJ/ψ andB0KJ/ψ. Treating thes-quark as heavy, we have used the HQET to calculate the hadronic matrix elements. The mesonic Isgur-Wise function is calculated in the quark model whereas for the baryonic IW function we have employed the bound state soliton picture. The results obtained agree very well with the recent CDF experimental data.

    • Proton NMR in CeNiInH0.53 down to liquid helium temperature

      R Ray A Ghoshray K Ghoshray N Chatterjee

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      The NMR probe and the matching network has been designed for the1H NMR study in CeNiInH0.53 down to liquid helium temperature using Bruker MSL 100 spectrometer. NMR line-shape measurement shows the absence of any signature of proton pairing in CeNiInH0.53 down to 3.86 K, as it was observed for high hydrogen concentration. The measurement of the spin-lattice relaxation time in the temperature range 300–20K reveals that the relaxation rate is mainly governed by the Korringa-type relaxation mechanism.

    • Weak radiative decay Λb→Λγ in the heavy quark effective theory

      A K Giri R Mohanta

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      The weak radiative decay Λb→Λγ is studied in the heavy quark effective theory treatings-quark as heavy. This rare decay is induced by the short distance electromagnetic penguins. Including corrections of the order of (1/mQ), we obtain the transition matrix element and the corresponding decay width. The Isgur-Wise function is evaluated in the largeNc limit and the branching ratio obtained is 1.48×10−5.

    • Helium implanted CuHf as studied by TDPAC and positron lifetime measurements

      R Govindaraj G Venugopal Rao K P Gopinathan B Viswanathan

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      181Ta time differential perturbed angular correlation (TDPAC) and positron lifetime measurements were carried out on homogeneously α-implanted CuHf samples. TDPAC measurements indicate the trapping of vacancy clusters and helium associated defect complexes by Hf atoms. The presence of helium-vacancy complexes and helium stabilised voids has been identified by positron lifetime measurements. Further the nucleation and growth stages of helium bubbles have been identified. TDPAC and positron lifetime measurements indicate that Hf atoms act as heterogeneous nucleating centers for helium bubbles. Hf atoms are found to suppress the bubble growth in CuHf as indicated by the results of positron lifetime measurements.

    • Foreword

      P Sugathan N Madhavan AK Sinha R Singh

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    • Experimental investigations of the nuclear level density by using heavy ion reactions

      G Viesti M Lunardon D Fabris G Nebbia M Cinausero E Fioretto G Prete JB Natowitz K Hagel R Wada

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      The transition of the level density parameter aoff from the low excitation energy value aoff=A/8 MeV−1 to the Fermi gas value aFGA/15 MeV−1 was discovered a few years ago studying particle spectra evaporated from hot compound systems of A∼ 160. A number of experiments have been recently performed to confirm the earlier findings and extend the investigation to other mass regions and to higher excitation energies. Furthermore, precision coincidence experiments have been done in the lead region in which evaporation residues are tagged by low energy gammarays. Those experiments open the possibility of a detailed study of the level densities in nuclei where the shell effects are important.

    • Fusion-fission dynamics in the superheavy nucleus production

      G Giardina P D’Agostino G Fazio M Herman AI Muninov A Nasirov G Oliva R Palamara R Ruggeri

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      The fusion-fission reaction mechanism leading to the massive nucleus formation is studied. We investigate the superheavy nucleus formation in heavy-ion induced reactions by analysing the evaporation residue (ER) production in order to study the fusion dynamics and the decay properties of nuclei close to the stability island at Z=114. We consider the 61Ni+208Pb, 48Ca+238U and 48Ca+244Pu reactions that lead to the Z=110, 112 and 114 superheavy elements respectively.

      By using the dinuclear system (DNS) concept of the two interacting nuclei we calculate the quasifission-fusion competition in the entrance channel and the fission-evaporation competition along the de-excitation cascade of the compound nucleus. The dynamics of the entrance channel allows us to determine the beam energy window which is favorable to the fusion, while the dynamic evolution of the compound nucleus on the shell correction to the fission barrier and the dissipative effects influence the fission-evaporation competition in order to obtain the residue nuclei from the superheavy nucleus formation. We also calculate the τntot ratio at each step of the de-excitation cascade of the compound nucleus and we present a systematics of τntot (at first step of the cascade) for many reactions that lead to nuclei with Z=102–114.

    • Dissipative processes in light heavy ion collisions

      A Pop A Andronic I Berceanu M Duma D MoisĂ M Petrovici V Simion G Immé G Lanzanò A Pagano G Raciti R Coniglione A Del Zoppo P Piatelli P Sapienza N Colonna G d’Erasmo A Pantaleo

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      The characteristics of the dissipative processes in the collisions of light heavy ion systems at incident energies below 10 MeV/nucleon have been studied. The correlations between different experimental observables show similar trends as those known at much heavier systems and semiempirical relationships are established starting from assumptions on the nature of the microscopic mechanisms. The charge equilibration process in light systems is also studied.

    • Measurement of the ground state 2n pickup probability for 28Si+68Zn and its role in sub-barrier fusion enhancement

      Vandana Tripathi Lagy T Baby PV Madhusudhana Rao SK Hui R Singh JJ Das P Sugathan N Madhavan AK Sinha

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      The ground state and excited state transfer yields for the 2-neutron pickup channel in the 28Si+68Zn system have been measured explicitly. The recoil mass separator at the nuclear Science Centre, New Delhi was used for the measurement. A NaI(T1) detector was used for detecting the deexcitation γ’s from the transfer products. The kinematic coincidence technique was employed for the transfer measurement. Simplified coupled channels calculations show that out of all transfer channels the major contribution to the sub-barrier enhancement comes from the ground state 2 neutron pickup channel with a ground state Q-value of+1.83 MeV.

    • Inclusive and exclusive measurements in the projectile breakup of 7Li

      T Madhusoodhanan Samit Mandal MP Sathyavathiamma Ramani NG Puttaswamy TS Mudhole A Mandal DK Avasthi R Shyam SK Datta

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      The inclusive and exclusive measurements were carried out for 7Li projectile breakup on 27Al target at 48 MeV. In the inclusive data we have observed a broad peak around the beam velocity for alphas and tritons. The exclusive data for alpha-triton coincidences show good agreement with the post-form DWBA theory of breakup reactions.

    • Breakup of 8B and the 7Be(p, γ)8B reaction

      R Shyam IJ Thompson

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      The calculated rate of events in some of the existing solar neutrino detectors is directly proportional to the rate of the 7Be(p, γ)8B reaction measured in the laboratory at low energies. However, the low-energy cross sections of this reaction are quite uncertain as various measurements differ from each other by 30–40%. The Coulomb dissociation process which reverses the radiative capture by the dissociation of 8B in the Coulomb field of a target, provides an alternate way of accessing this reaction. While this method has several advantages (like large breakup cross sections and flexibility in the kinematics), the difficulties arise from the possible interference by the nuclear interactions, uncertainties in the contributions of the various multipoles and the higher order effects, which should be considered carefully. We review the progress made so far in the experimental measurements and theoretical analysis of the breakup of 8B and discuss the current status of the low-energy cross sections (or the astrophysical S-factor) of the 7Be(p, γ)8B reaction extracted therefrom. The future directions of the experimental and theoretical investigations are also suggested.

    • Multiple ionization of argon in coincidence with projectile ions in 60–120 MeV Siq+-Ar collisions

      MJ Singh DO Kataria N Madhavan P Sugathan JJ Das DK Awasthi AK Sinha R Shanker

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      A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer processes in collisions of 60–120 MeV Siq+ (q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization, electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated. The data reported on the present collision system result from a direct measurement in the considered impact energy for the first time. The total ionization cross-sections for the recoil ions are shown to scale as q1.7/Ep0.5, where Ep is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/j2 upto j = 8+. The average recoil charge state 〈j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing cross-sections σqq are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow our data for different ionization processes is reviewed and discussed.

    • Λb→Λc+a1 decay in the heavy quark effective theory

      R Mohanta AK Giri

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      Using the heavy quark approximation, we have studied the nonleptonic decay mode Λb→Λca1. We have included nonfactorizable contributions as well as factorizable ones in our analysis. The estimated branching ratio for this process is (1.4±0.1)% and the asymmetry parameter α found to be −0.8.

    • Parity of the band head at 3710 keV in 99Rh using clover detector as compton polarimeter

      R Palit HC Jain PK Joshi S Nagaraj BVT Rao SN Chintalapudi SS Ghugre

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      Clover detector has been used as a Compton polarimeter to measure the linear polarization of γ-rays produced in heavy ion fusion reaction. The polarization sensitivity of the clover detector has been measured over γ-ray energies ranging from 386 to 1368 ke V. The E1 multipolarity of the 1117 keV transition in 99Rh has been established using this polarimeter. This has resulted in the assignment of negative parity to the band head at 3710 keV in 99Rh.

    • Impact of electron irradiation on particle track etching response in polyallyl diglycol carbonate (PADC)

      R Mishra S P Tripathy A Kul Shrestha A Srivastava S Ghosh K K Dwivedi D T Khathing M Müller D Fink

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      In the present work, attempts have been made to investigate the modification in particle track etching response of polyallyl diglycol carbonate (PADC) due to impact of 2 MeV electrons. PADC samples pre-irradiated to 1, 10, 20, 40, 60, 80 and 100 Mrad doses of 2 MeV electrons were further exposed to 140 MeV28 Si beam and dose-dependent track registration properties of PADC have been studied. Etch-rate values of the PADC irradiated to 100 Mrad dose electron was found to increase by nearly 4 times that of pristine PADC. The electron irradiation has promoted chain scissioning in PADC, thereby converting the polymer into an easily etchable polymer. Moreover, the etching response and the detection efficiency were found to improve by electron irradiation. Scanning electron microscopy of etched samples further revealed the surface damage in these irradiated PADCs.

    • Quantum chromodynamics: Working group report

      Sourendu Gupta D Indumathi S Banerjee R Basu M Dittmar RV Gavai F Gelis D Ghosh Sourendu Gupta D Indumathi Asmita Mukherjee

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      This is the report of the QCD working group at WHEPP-6. Discussions and work on heavy ion collisions, polarized scattering, and collider phenomenology are reported.

    • Discussion on a possible neutrino detector located in India

      MVN Murthy Urjit A Yajnik KRS Balaji G Bhattacharyya Amol Dighe Shashikant Dugad ND Hari Dass PK Kabir Kamales Kar D Indumathi John G Learned Debasish Majumdar NK Mondal MVN Murthy SN Nayak Sandip Pakvasa Amitava Raychaudhuri RS Raghavan G Rajasekaran R Ramachandran Alak K Ray Asim K Ray Saurabh Rindani HS Sharatchandra Rahul Sinha Nita Sinha S Umasankar Urjit A Yajnik

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      We have identified some important and worthwhile physics opportunities with a possible neutrino detector located in India. Particular emphasis is placed on the geographical advantage with a stress on the complimentary aspects with respect to other neutrino detectors already in operation.

    • Non-linearity parameter B/A of binary liquid mixtures at elevated pressures

      J D Pandey J Chhabra R Dey V Sanguri R Verma

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      When sound waves of high amplitude propagate, several non-linear effects occur. Ultrasonic studies in liquid mixtures provide valuable information about structure and interaction in such systems. The present investigation comprises of theoretical evaluation of the acoustic non-linearity parameter B/A of four binary liquid mixtures using Tong and Dong equation at high pressures and T=303.15 K. Thermodynamic method has also been used to calculate the non-linearity parameter after making certain approximations.

    • Measurement of temperature fluctuations and anomalous transport in the SINP tokamak

      R Kumar S K Saha

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      Temperature fluctuations have been measured in the edge region of the SINP tokamak. We find that these fluctuations have a comparatively high level (30–40%) and a broad spectrum. The temperature fluctuations show a quite high coherence with density and potential fluctuations and contribute considerably to the anomalous particle flux.

    • Runaway electrons in the SINP tokamak

      Ramesh Narayanan A N Sekar Iyengar R Pal

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      The experimental determination of the dependance of confinement time of runaways on various discharge parameters has been presented along with the angular distribution of hard X-rays (HXrays) emitted from the torus in presence and absence of Langmuir probes.

    • Mirnov coil data analysis for tokamak ADITYA

      D Raju R Jha P K Kaw S K Mattoo Y C Saxena Aditya Team

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      The spatial and temporal structures of magnetic signal in the tokamak ADITYA is analysed using recently developed singular value decomposition (SVD) technique. The analysis technique is first tested with simulated data and then applied to the ADITYA Mirnov coil data to determine the structure of current peturbation as the discharge progresses. It is observed that during the current rise phase, current perturbation undergoes transition from m=5 poloidal structure to m=4 and then to m=3. At the time of current termination, m=2 perturbation is observed. It is observed that the mode frequency remains nearly constant (≈10 kHz) when poloidal mode structure changes from m=4 to m=2. This may be either an indication of mode coupling or a consequences of changes in the plasma electron temperature and density scale length.

    • Electron temperature (Te) measurements by Thomson scattering system

      R Rajesh B Ramesh Kumar S K Varshney Manoj Kumar Chhaya Chavda Aruna Thakkar N C Patel Ajai Kumar Aditya Team

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      Thomson scattering technique based on high power laser has already proved its superoirity in measuring the electron temperature (Te and density (ne) in fusion plasma devices like tokamaks. The method is a direct and unambiguous one, widely used for the localised and simultaneous measurements of the above parameters. In Thomson scattering experiment, the light scattered by the plasma electrons is used for the measurements. The plasma electron temperature is measured from the Doppler shifted scattered spectrum and density from the total scattered intensity. A single point Thomson scattering system involving a Q-switched ruby laser and PMTs as the detector is deployed in ADITYA tokamak to give the plasma electron parameters. The system is capable of providing the parameters Te from 30 eV to 1 keV and ne from 5 × 1012cm−3−5 × 1013cm−3. The system is also able to give the parameter profile from the plasma center (Z=0 cm) to a vertical position of Z=+22 cm to Z=−14 cm, with a spatial resolution of 1 cm on shot to shot basis. This paper discusses the initial measurements of the plasma temperature from ADITYA.

    • Lie-optics, geometrical phase and nonlinear dynamics of self-focusing and soliton evolution in a plasma

      D Subbarao R Uma H Singh Kamal Goyal Sanjeev Goyal Ravinder Kumar

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      It is useful to state propagation laws for a self-focusing laser beam or a soliton in group-theoretical form to be called Lie-optical form for being able to predict self-focusing dynamics conveniently and amongst other things, the geometrical phase. It is shown that the propagation of the gaussian laser beam is governed by a rotation group in a non-absorbing medium and by the Lorentz group in an absorbing medium if the additional symmetry of paraxial propagation is imposed on the laser beam. This latter symmetry, however, needs care in its implementation because the electromagnetic wave of the laser sees a different refractive index profile than the laboratory observer in this approximation. It is explained how to estimate this non-Taylor paraxial power series approximation. The group theoretical laws so-stated are used to predict the geometrical or Berry phase of the laser beam by a technique developed by one of us elsewhere. The group-theoretical Lie-optic (or ABCD) laws are also useful in predicting the laser behavior in a more complex optical arrangement like in a laser cavity etc. The nonlinear dynamical consequences of these laws for long distance (or time) predictions are also dealt with. Ergodic dynamics of an ensemble of laser beams on the torus during absorptionless self-focusing is discussed in this context. From the point of view of new physics concepts, we introduce a stroboscopic invariant torus and a stroboscopic generating function in classical mechanics that is useful for long-distance predictions of absorptionless self-focusing.

    • Volume effect of laser produced plasma on X-ray emissions

      V K Senecha Y B S R Prasad M P Kamath A S Joshi G S Solanki A P Kulkarni S Gupta R Pareek H C Pant

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      An investigation of x-ray emission from Cu plasma produced by 1.054 µm Nd:glass laser pulses of 5 ns duration, at 2 × 1012 − 2 × 1013 W cm−2 is reported. The x-ray emission has been studied as a function of target position with respect to the laser beam focus position. It has been observed that x-ray emissions from ns duration plasma show a volume effect similar to subnanosecond plasmas. Due to this effect the x-ray yield increases when target is moved away relative to the best focal plane of the laser beam. This result supports the theoretical model of Tallents and has also been testified independently using suitably modified theoretical model for our experimental conditions. While above result is in good agreement with similar experimental results obtained for sub-nanosecond laser produced plasmas, it differs from result claiming filamentation rather than pure geometrical effect leading to x-ray enhancement for ns plasmas.

    • Scaling of x-ray emission and ion velocity in laser produced Cu plasmas

      Y B S R Prasad V K Senecha H C Pant M P Kamath G S Solanki P K Tripathi A P Kulkarni S Gupta R Pareek A S Joshi N Sreedhar Sameer Nigam C P Navathe

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      The x-ray emission from slab targets of copper irradiated by Nd:glass laser (1.054 µm, 5 and 15 ns) at intensities between 1012 and 1011W/cm2 has been studied. The x-ray emissions were monitored with the help of high quantum efficiency x-ray silicon photo diodes and vacuum photo diodes, all covered with aluminium filters of different thickness. The x-ray intensity vs the laser intensity has a scaling factor of (1.2–1.92). The relative x-ray conversion efficiency follows an empirical relationship which is in close agreement with the one reported by Babonneau et al. The ion velocities were monitored using Langmuir probes placed at different angles and radial distances from the target position. The variation of the ion velocity with the laser intensity follows a scaling of the form Φβ where β ∼0.22 which is in good agreement with the reported scaling factor values. The results on the x-ray emission from Cu plasma are reported.

    • Lie-optic matrix algorithm for computer simulation of paraxial self-focusing in a plasma

      D Subbarao R Uma Kamal Goyal Sanjeev Goyal Karuna Batra

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      Propagation algorithm for computer simulation of stationary paraxial self-focusing laser beam in a medium with saturating nonlinearity is given in Lie-optic form. Accordingly, a very natural piece-wise continuous Lie transformation that reduces to a restricted Lorentz group of the beam results. It gives rise to a matrix method for self-focusing beam propagation that is constructed and implemented. Although the results use plasma nonlinearities of saturable type, and a gaussian initial beam, these results are applicable for other media like linear optical fibers and to more general situations.

    • Microwave plasma deposition of diamond like carbon coatings

      D S Patil K Ramachandran N Venkatramani M Pandey R D’Cunha

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      The promising applications of the microwave plasmas have been appearing in the fields of chemical processes and semiconductor manufacturing. Applications include surface deposition of all types including diamond/diamond like carbon (DLC) coatings, etching of semiconductors, promotion of organic reactions, etching of polymers to improve bonding of the other materials etc. With a 2.45 GHz. 700 W, microwave induced plasma chemical vapor deposition (CVD) system set up in our laboratory we have deposited diamond like carbon coatings. The microwave plasma generation was effected using a wave guide single mode applicator. We have deposited DLC coatings on the substrates like stainless steel, Cu-Be, Cu and Si. The deposited coatings have been characterized by FTIR, Raman spectroscopy and ellipsometric techniques. The results show that we have achieved depositing ∼95% sp3 bonded carbon in the films. The films are unform with golden yellow color. The films are found to be excellent insulators. The ellipsometric measurements of optical constant on silicon substrates indicate that the films are transparent above 900 nm.

    • Minimum dissipative relaxed states in toroidal plasmas

      R Bhattacharyya MS Janaki B Dasgupta

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      Relaxation of toroidal discharges is described by the principle of minimum energy dissipation together with the constraint of conserved global helicity. The resulting Euler-Lagrange equation is solved in toroidal coordinates for an axisymmetric torus by expressing the solutions in terms of Chandrasekhar-Kendall (C-K) eigenfunctions analytically continued in the complex domain. The C-K eigenfunctions are obtained as hypergeometric functions that are solutions of scalar Helmholtz equation in toroidal coordinates in the large aspect-ratio approximation. Equilibria are constructed by assuming the current to vanish at the edge of plasma. For the m=0, n=0 (m and n are the poloidal and toroidal mode numbers respectively) relaxed states, the magnetic field, current, q (safety factor) and pressure profiles are calculated for a given value of aspect-ratio of the torus and for different values of the eigenvalue λr0. The new feature of the present model is that solutions allow for both tokamak as well as RFP-like behaviour with increase in the values of λr0, which is related directly to volt-sec in the experiment.

    • Stability-transport modeling of the SINP tokamak discharges

      S L Ahiri S Mukhopadhyay A N S Iyengar R Pal

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      A one-dimensional stability transport code has been developed to simulate the evolution of tokamak plasma discharges. Explicit finite-difference methods have been used to follow the temporal evolution of the electron temperature equation. The poloidal field diffusion equation has been solved at every time step. The effects of MHD instabilities have been incorporated by solving equations for MHD mixing and tearing modes as and when required. The code has been applied to follow the evolution of tokamak plasma discharges obtained in the Saha Institute of Nuclear Physics (SINP) tokamak. From these simulations, we have been able to identify the possible models of thermal conductivity, diffusion and impurity contents in these discharges. Effects of different MHD modes have been estimated. It has been found that in low q0 discharge m=1, n=1 and m=2, n=1 modes play major role in discharge evolution. These modes are found to result in the positive jump in the loop voltage which was also observed in the experiments. Hollow current density profile jφ and negative shear in the q profile have also been found in the rising phase of a discharge.

    • Phase stabilization in cinnarizine complexes using X-ray profile analysis

      G Nagendrappa S Subramanya Raj Urs M S Madhava R Somashekar

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      Characterization of cobalt(II), cadmium(II), copper(II) and tin(II) cinnarizine complexes have been carried out using conductivity, electronic spectra, infrared, nmr, thermogravimetric and X-ray analyses to establish the nature of phase stabilization in these materials. Also, the intrinsic strain components present in these materials during the formation have been computed using wide-angle X-ray scattering analysis. The variation of the crystallite shape ellipsoid in these materials has been discussed on the basis of Hosemann’s paracrystalline model.

    • Multifragmentation and dynamics in heavy ion collisions

      R Roy

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      A midrapidity zone formed in heavy-ion collisions has been investigated through special selections of light particles and intermediate mass fragments detected in the reaction 35Cl on 12C at 43 MeV/nucleon and the reactions 58Ni on 12C, 24Mg, and 197Au at 34.5 MeV/nucleon, and of neutron energy spectra measured in the reaction 35Cl on natTa. Properties of the observables have been examined to characterize the neck-like structure formed between the two reaction partners.

    • High spin rotational bands in 65Zn

      B Mukherjee S Muralithar RP Singh R Kumar K Rani RK Bhowmik

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      The nucleus 3065Zn was studied using the 52Cr(16O, 2pn)65Zn reaction at a beam energy of 65 MeV. The level scheme is extended up to an excitation energy of 10.57 MeV for spin-parity (41/2ħ) with several newly observed transitions placed in it.

    • High-spin structure of yrast-band in 78Kr

      PK Joshi R Palit HC Jain S Nagaraj JA Sheikh

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      Lifetime of levels up to 22+, have been measured in 78Kr and an oblate shape is assigned to the ground state using the CSM and the configuration dependent shell correction calculations. Calculations further show that 78Kr is highly γ-soft nucleus. The experimental Qt values coupled with theoretical calculations indicate an oblate shape for 78Kr at low spins and triaxial shape at higher spins

    • Structure of 72,74Se at high spin

      R Palit HC Jain PK Joshi JA Sheikh

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      Lifetimes of high spin states up to {$$I^\pi $$}=22+ in the yrast positive parity bands have been measured to investigate the shape evolution with increasing spin in 72, 74Se. The Qt values derived from these measurements indicate that prolate shape stabilizes for 72Se, while a triaxial shape develops for 74Se at higher spins. Comparison of the observed trend in Qt with spin for 72, 74Se with that of the corresponding kryptones isotones emphasizes the stability provided by N=38 prolate shell gap even at high rotational frequency.

    • Deformation effects in the 28Si+12C and 28Si+28Si reactions

      C Bhattacharya M Rousseau C Beck V Rauch R M Freeman R Nouicer F Haas O Dorvaux K Eddahbi P Papka O Stezowski S Szilner D Mahboub A Szanto de Toledo A Hachem E Martin S J Sanders

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      The possible occurrence of highly deformed configurations is investigated in the 40Ca and 56Ni di-nuclear systems as formed in the 28Si + 12C, 28Si reactions by using the properties of emitted light charged particles. Inclusive as well as exclusive data of the heavy fragments and their associated light charged particles have been collected by using the ICARE charged particle multidetector array. The data are analysed by Monte Carlo CASCADE statistical-model calculations using a consistent set of parameters with spin-dependent level densities. Significant deformation effects at high spin are observed as well as an unexpected large 8Be cluster emission of a binary nature.

    • Breakup of 42 MeV 7Li projectiles in the fields of 12C and 197Au nuclei

      Dhruba Gupta C Samanta R Kanungo P Basu Subinit Roy S Kailas A Chatterjee B J Roy K Mahata A Samant A Shrivastava

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      Inclusive cross sections of α particles and tritons from the breakup of 42 MeV 7Li by 12C and 197Au targets are presented and analysed in the framework of the Serber model. Spectral distortions due to the targets and relevant reaction mechanisms are discussed.

    • Fabrication and testing of the recoil mass spectrometer at Bombay Pelletron

      S Nagaraj H C Jain P K Joshi S D Paul R Palit H V Panchal B S Naidu A Chatterjee A Navin

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      A recoil mass spectrometer (RMS) has been designed, fabricated and installed at the 15° S beam-line of the Pelletron at TIFR. The RMS consists of a quadrupole doublet just after the target chamber followed by an ‘electrostatic deflector’, a magnetic dipole and a second electrostatic deflector. The recoils produced in the 12C + 58Ni reaction using 60 MeV 12C beam were focussed with the help of electric and magnetic fields and detected in a strip detector placed at the focal plane of the RMS. Further testing of the spectrometer to obtain mass resolution and efficiency are in progress.

    • Multiplicity distributions and charged-neutral fluctuations

      Tapan K Nayak MM Aggarwal A Agnihotri Z Ahammed ALS Angelis V Antonenko V Arefiev V Astakhov V Avdeitchikov TC Awes PVKS Baba SK Badyal A Baldine L Barabach C Barlag S Bathe B Batiounia T Bernier KB Bhalla VS Bhatia C Blume R Bock E-M Bohne D Bucher A Buijs E-J Buis H Büsching L Carlen V Chalyshev S Chattopadhyay KE Chenawi R Cherbatchev T Chujo A Claussen AC Das MP Decowski V Djordjadze P Donni I Doubovik AK Dubey MR Dutta Majumdar S Eliseev K Enosawa H Feldmann P Foka S Fokin V Frolov MS Ganti S Garpman O Gavrishchuk FJM Geurts TK Ghosh R Glasow SK Gupta B Guskov HA Gustafsson HH Gutbrod R Higuchi I Hrivanacova M Ippolitov H Kalechofsky R Kamermans K-H Kampert K Karadjev K Karpio S Kato S Kees H Kim BW Kolb I Kosarev I Koutcheryaev A Kugler P Kulinich V Kumar M Kurata K Kurita N Kuzmin I Langbein A Lebedev YY Lee H Löhner DP Mahapatra V Manko M Martin A Maximov R Mehdiyev G Mgebrichvili Y Miake D Mikhalev GC Mishra Y Miyamoto B Mohanty D Morrison DS Mukhopadhyay V Myalkovski H Naef BK Nandi SK Nayak TK Nayak S Neumaier A Nianine V Nikitine S Nikolaev S Nishimura P Nomokov J Nystrand FE Obenshain A Oskarsson I Otterlund M Pachr A Parfenov S Pavliouk T Peitzmann V Petracek F Plasil ML Purschke B Raeven J Rak R Raniwala S Raniwala VS Ramamurthy NK Rao F Retiere K Reygers G Roland L Rosselet I Roufanov JM Rubio SS Sambyal R Santo S Sato H Schlagheck H-R Schmidt G Shabratova I Sibiriak T Siemiarczuk BC Sinha N Slavine K Söderström N Solomey G Sood SP Sørensen P Stankus G Stefanek P Steinberg E Stenlund D Stüken M Sumbera T Svensson MD Trivedi A Tsvetkov C Twenhöfel L Tykarski J Urbahn NV Eijndhoven WHV Heeringen GJV Nieuwenhuizen A Vinogradov YP Viyogi A Vodopianov S Vörös MA Vos B Wyslouch K Yagi Y Yokota GR Young

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      Results from the multiplicity distributions of inclusive photons and charged particles, scaling of particle multiplicities, event-by-event multiplicity fluctuations, and charged-neutral fluctuations in 158A GeV Pb+Pb collisions are presented and discussed. A scaling of charged particle multiplicity as Npart1.07±0.05 and photos as Npart1.12±0.03 have been observed, indicating violation of naive wounded nucleon model. The analysis of localized charged-neutral fluctuation indicates a model-independent demonstration of non-statistical fluctuations in both charged particles and photons in limited azimuthal regions. However, no correlated charged-neutral fluctuations are observed.

    • First results from RHIC-PHENIX

      Tarun Kanti Ghosh K Adcox S S Adler N Ajitanand Y Akiba J Alexander L Aphecetche Y Arai S H Aronson R Averbeck T C Awes K N Barish P D Barnes J Barrette B Bassalleck S Bathe V Baublis A Bazilevsky S Belikov F G Bellaiche S T Belyaev M J Bennett Y Berdnikov S Botelho M L Brooks D S Brown N Bruner D Bucher H Buesching V Bumazhnov G Bunce J Burward-Hoy S Butsyk T A Carey P Chand J Chang W C Chang L L Chavez S Chernichenko C Y Chi J Chiba M Chiu R K Choudhury T Christ T Chujo M S Chung P Chung V Cianciolo B A Cole D G D’Enterria G David H Delagrange A Denisov A Deshpande E J Desmond O Dietzsch B V Dinesh A Drees A Durum D Dutta K Ebisu Y V Efremenko K El Chenawi H En’yo S Esumi L Ewell T Ferdousi D E Fields S L Fokin Z Fraenkel A Franz A D Frawley S-Y Fung S Garpman T K Ghosh A Glenn A L Godoi Y Goto S V Greene M Grosse Perdekamp S K Gupta W Guryn H-Å Gustafsson J S Haggerty H Hamagaki A G Hansen H Hara E P Hartouni R Hayano N Hayashi X He T K Hemmick J Heuser J C Hill D S Ho K Homma B Hong A Hoover T Ichihara K Imai M S Ippolitov M Ishihara B V Jacak W Y Jang J Jia B M Johnson S C Johnson K S Joo S Kametani J H Kang M Kann S S Kapoor S Kelly B Khachaturov A Khanzadeev J Kikuchi D J Kim H J Kim S Y Kim Y G Kim W W Kinnison E Kistenev A Kiyomichi C Klein-Boesing S Klinksiek L Kochenda D Kochetkov V Kochetkov D Koehler T Kohama A Kozlov P J Kroon K Kurita M J Kweon Y Kwon G S Kyle R Lacey J G Lajoie J Lauret A Lebedev D M Lee M J Leitch X H Li Z Li D J Lim M X Liu X Liu Z Liu C F Maguire J Mahon Y I Makdisi V I Manko Y Mao S K Mark S Markacs G Martinez M D Marx A Masaike F Matathias T Matsumoto P L McGaughey E Melnikov M Merschmeier F Messer M Messer Y Miake T E Miller A Milov S Mioduszewski R E Mischke G C Mishra J T Mitchell A K Mohanty D P Morrison J M Moss F Mühlbacher M Muniruzzaman J Murata S Nagamiya Y Nagasaka J L Nagle Y Nakada B K Nandi J Newby L Nikkinen P Nilsson S Nishimura A S Nyanin J Nystrand E O’Brien C A Ogilvie H Ohnishi I D Ojha M Ono V Onuchin A Oskarsson L Österman I Otterlund K Oyama L Paffrath A P T Palounek V S Pantuev V Papavassiliou S F Pate T Peitzmann A N Petridis C Pinkenburg R P Pisani P Pitukhin F Plasil M Pollack K Pope M L Purschke I Ravinovich K F Read K Reygers V Riabov Y Riabov M Rosati A A Rose S S Ryu N Saito A Sakaguchi T Sakaguchi H Sako T Sakuma V Samsonov T C Sangster R Santo H D Sato S Sato S Sawada B R Schlei Y Schutz V Semenov R Seto T K Shea I Shein T-A Shibata K Shigaki T Shiina Y H Shin I G Sibiriak D Silvermyr K S Sim J Simon-Gillo C P Singh V Singh M Sivertz A Soldatov R A Soltz S Sorensen P W Stankus N Starinsky P Steinberg E Stenlund A Ster S P Stoll M Sugioka T Sugitate J P Sullivan Y Sumi Z Sun M Suzuki E M Takagui A Taketani M Tamai K H Tanaka Y Tanaka E Taniguchi M J Tannenbaum J Thomas J H Thomas T L Thomas W Tian J Tojo H Torii R S Towell I Tserruya H Tsuruoka A A Tsvetkov S K Tuli H Tydesjö N Tyurin T Ushiroda H W van Hecke C Velissaris J Velkovska M Velkovsky A A Vinogradov M A Volkov A Vorobyov E Vznuzdaev H Wang Y Watanabe S N White C Witzig F K Wohn C L Woody W Xie K Yagi S Yokkaichi G R Young I E Yushmanov W A Zajc Z Zhang S Zhou

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      The PHENIX experiment consists of a large detector system located at the newly commissioned relativistic heavy ion collider (RHIC) at the Brookhaven National Laboratory. The primary goal of the PHENIX experiment is to look for signatures of the QCD prediction of a deconfined high-energy-density phase of nuclear matter quark gluon plasma. PHENIX started data taking for Au+Au collisions at √sNN=130 GeV in June 2000. The signals from the beam-beam counter (BBC) and zero degree calorimeter (ZDC) are used to determine the centrality of the collision. A Glauber model reproduces the ZDC spectrum reasonably well to determine the participants in a collision. Charged particle multiplicity distribution from the first PHENIX paper is compared with the other RHIC experiment and the CERN, SPS results. Transverse momentum of photons are measured in the electro-magnetic calorimeter (EMCal) and preliminary results are presented. Particle identification is made by a time of flight (TOF) detector and the results show clear separation of the charged hadrons from each other.

    • Meson production in p + d reactions

      H Machner M Betigeri J Bojowald A Budzanowski A Chatterjee J Ernst L Freindl D Frekers W Garske K Grewer A Hamacher J Ilieva L Jarczyk K Kilian S Kliczewski W Klimala D Kolev T Kutsarova J Lieb H Machner A Magiera H Nann L Pentchev HS Plendl D Protić B Razen P Von Rossen BJ Roy R Siudak J Smyrski RV Srikantiah A Strzałkowski R Tsenov K Zwoll

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      Total and differential cross sections for the reactions p + d3He + m0 with m=π, η and p + d3H+π+ were measured with the GEM detector at COSY for beam momenta between threshold and the maximum of the corresponding baryon resonance. For both reactions a strong forward-backward asymmetry was found. The data were compared with model calculations. The aspect of isospin symmetry breaking is studied.

    • Structure of light neutron-rich nuclei through coulomb dissociation

      U Datta Pramanik T Aumann D Cortina H Emling H Geissel M Hellström R Holzmann N Iwasa Y Leifels G Münzenberg M Rejmund C Scheidenberger K Sümmerer A Leistenschneider Th W Elze A Grünschloss S Ilievski K Boretzky J V Kratz R Kulessa E Lubkiewicz E Wajda W Walus P Reiter H Simon

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      Coulomb breakup of neutron-rich nuclei around mass A ∼ 20 has been studied experimentally using secondary beams (∼ 500–600 MeV/u) of unstable nuclei produced at GSI. The spectroscopic factor deduced for the neutron occupying s1/2 level in 15C ground state is consistent with the earlier reported value. The data analysis for Coulomb breakup of 17C shows that most of the cross section yields the 16C core in its excited state. For 17–22O, the low-lying E1 strength amounts up to about 12% of the energy weighted dipole sum rule strength depending on neutron excess. The cluster sum rule limit with 16O as a core is almost exhausted for 17,18O, while for more neutron rich isotopes the strength with respect to that limit decreases.

    • Polarization modulational instability in a birefringent optical fiber with fourth order dispersion

      R Ganapathy V C Kuriakose

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      We obtain conditions for the occurrence of polarization modulational instability in the anomalous and normal dispersion regimes for the coupled nonlinear Schrödinger equation modelling fourth order dispersion effects when the linearly polarized pump is oriented at arbitrary angles with respect to the slow and fast axes of the birefringent fiber.

    • Spatial solitons in nonlinear liquid waveguides

      R Barillé G Rivoire

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      Spatial solitons are studied in a planar waveguide filled with nonlinear liquids. Spectral and spatial measurements for different geometries and input power of the laser beam show the influence of different nonlinear effects as stimulated scatterings on the soliton propagation and in particular on the beam polarization. The stimulated scattering can be used advantageously to couple the two polarization components. This effect can lead to multiple applications in optical switching.

    • Investigations of low qa discharges in the SINP tokamak

      S Lahiri A N S Iyengar S Mukhopadhyay R Pal

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      Low edge safety factor discharges including very low qa (1<qa<2) and ultra low qa (0<qa<1) have been obtained in the SINP tokamak. It has been observed that accessibility of these discharges depends crucially on the fast rate of plasma current rise. Several interesting results in terms of different time scales like Tqa · τR etc have been obtained using a set of softwares developed at SINP. From fluctuation analysis of the external magnetic probe data it has been found that MHD instabilities m=1, n=1 and m=2, n=1 etc. play major role in the evolution of these discharges. To investigate the internal details of these discharges, an internal magnetic probe system has been developed using which current density jφ and other related parameters have been estimated. By carrying out a resistive stability analysis, evidence of the above-mentioned MHD instabilities have again been found. The physical processes lying behind the accessibility and evolution of the low qa discharges have been thoroughly investigated.

    • Development of a new experimental setup for studying collisions of keV-electrons with thick and thin targets

      RK Singh RK Mohanta R Hippler R Shanker

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      Development of a new lectron-recoil ion/photon coincidence setup for investigating some of the electron induced collision processes, such as electron bremsstrahlung, electron backscattering, innershell excitation and multiple ionization of target atoms/molecules in bombardment of electrons having energies from 2.0 keV to 30.0 keV with solid and gaseous targets is described. The new features include the use of a compact multipurpose scattering chamber, a time-of-flight spectrometer for detection of multiply charged target ions, a 45°-parallel plate electrostatic analyzer for measuring energy and angle of the ejected electrons, a room temperature high resolution Si-PIN photo diode X-ray detector for counting the collisionally induced photons, a coincidence data acquisition system consisting of a 200 MHz Pentium based 8K-multichannel analyzer and a standard network of a fast/slow coincidence electronics. In particular, the details of design, fabrication and assembly of indigenous components employed in the setup are presented. Selected experiments planned with the setup are mentioned and briefly discussed. A report on performance, optimization, efficiency, time resolution etc. of the time-of-flight (TOF) spectrometer and that of the 45°-parallel plate electrostatic analyzer (PPEA) is presented. Test spectra of electron-recoil ion coincidences, energy distribution of ejected electrons and characteristic plus non-characteristic X-ray spectrum are illustrated to exhibit the satisfactory performance of the developed setup.

    • Design and fabrication of a time-of-flight spectrometer for studies of multiple ionization of gases by charged particle impact

      RK Singh RK Mohanta MJ Singh R Hippler SK Goel R Shanker

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      A time-of-flight spectrometer has been designed and fabricated for measuring the charge state distributions of target ions produced in collisions of keV-electrons with gaseous target atoms/molecules. The design details of the spectrometer and the description of experimental procedures for optimizing various parameters are presented and discussed. The working principle of the spectrometer, its time- and mass-focussing conditions, transmissions and detection efficiency etc. are given. A few typical test runs on multiple ionization of Ne and Ar gas atoms are illustrated. These spectra are found to yield the time resolution of about 10 ns for Ar4+ ion peak in 24.0 keV e — Ar collisions while the mass resolution of the spectrometer is obtained about 10% at mass m=20.

    • Cross-phase modulational instability in an elliptical birefringent fiber with higher order nonlinearity and dispersion

      R Ganapathy VC Kuriakose

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      We obtain conditions for the occurrence of cross-phase modulational instability in the normal dispersion regime for the coupled higher order nonlinear Schrödinger equation with higher order dispersion and nonlinear terms.

    • Foreword

      R Pinto R Nagarajan

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    • Possible coexistence of superconductivity and magnetic order in NdPt2B2C

      S K Dhar A D Chinchure E Alleno C Godart L C Gupta R Nagarajan

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      Coexistence of superconductivity and magnetic order has been one of the exciting aspects of the quaternary borocarbide superconductors, So far, RNi2B2C (R=Tm, Er, Ho and Dy) are the only known magnetic superconductors in this family. Here, we present our resistivity, magnetization and heat capacity studies on NdPt2B2C (nominal composition, NdPt1.5Au0.6B2C and NdPt2.1B2.4C1.2). We find superconductivity in both samples with Tc,onset ∼ 3 K. Bulk magnetic order is found to occur below 1.7 K. We suggest that NdPt2B2C is a possible magnetic superconductor.

    • Magnetism and superconductivity in ErNi2B2C

      NJ Bancroft DMcK Paul G McIntyre CD Dewhurst R Cubitt

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      We have performed a series of neutron diffraction experiments from the magnetic order and the vortex lattice in single crystal ErNi2B2C. The incommensurate magnetic structure develops additional even harmonics below the ‘ferromagnetic’ ordering temperature, TF of 2.3 K. This feature and the existence of rods of diffuse scattering suggest the development of ferromagnetic microdomain walls. The magnetic structure is very sensitive to the application of a magnetic field with changes in modulation vector and harmonic content. Studies of the vortex lattice show the presence of a 45° reorientation transition and a distorted hexagonal to square transition as a function of applied field. Further distortions of the vortex lattice occur at TN, but no changes are seen at TF.

    • Peak effect at microwave frequencies in swift heavy ion irradiated YBa2Cu3O7-δ thin films

      Tamalika Banerjee Avinash Bhangale D Kanjilal S P Pai R Pinto

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      The vortex dynamics at microwave frequencies in YBa2Cu3O7-δ (YBCO) films have been studied. We observe a peak in the microwave (4.88 and 9.55 GHz) surface resistance in some films in magnetic fields up to 0.8 T. This is associated with the ‘peak-effect’ phenomenon and reflects the order-disorder transformation of the flux line lattice near the transition temperature. Introduction of artificial pinning centers like columnar defects created as a result of irradiation with 200 MeV Ag ion (at a fluence of 4×1010 ions/cm2) leads to the suppression of the peak in films previously exhibiting ‘peak effect’.

    • Peak effect in surface resistance at microwave frequencies in Dy-123 thin films

      A R Bhangale T Banerjee P Raychaudhuri S S Bhagwat S P Pai J John V C Bagwe V S Shirodkar R Pinto

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      A pronounced peak in the microwave (at frequency 9.55 GHz) surface resistance, Rs vs. T plot (where T is the temperature) has been observed in epitaxial DyBa2Cu3O7−y superconducting thin films in magnetic fields (parallel to c-axis) in the range 2 to 8 kOe, and temperatures close to the superconducting transition temperature Tc(H). Our data suggest that the nature of peaks observed in the two films is different, thereby indicating different defect structures in the films.

    • Effect of swift heavy ion irradiation on surface resistance of DyBa2Cu3O7-δ thin films at microwave frequencies

      Ujwala Ail Tamalika Banerjee A R Bhangale D Kanjilal R Pinto

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      We report the observation of a propounced peak in surface resistance at microwave frequencies of 4.88 GHz and 9.55 GHz and its disappearance after irradiation with swift ions in laser ablated DyBa2Cu3O7-δ (DBCO) thin films. The measurements were carried out in zero field as well as in the presence of magnetic fields (up to 0.8 T). The films were irradiated using 90 MeV oxygen ions at Nuclear Science Centre, New Delhi at a fluence of 3×1013 ions/cm2. Introduction of point defects and extended defects after irradiation suppresses the peak at 9.55 GHz whereas no suppression is observed at 4.88 GHz. These results and the vortex dynamics in the films at microwave frequencies before and after irradiation are discussed.

    • Ferrites — what is new?

      R Ranganathan Anindita Ray

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      Ferrites, combining insulating and ferrimagnetic properties, have long been used in technology. The aim of this paper is to focus on new features in these materials. In the classical theory of ferrimagnets, Néel had predicted the unusual thermal variation of the spontaneous magnetization, such as, the disappearance of the magnetization at a temperature which was not the Curie temperature but at a point where there was compensation of the spontaneous magnetization of the two sublattices. We show experimentally that temperature (TK) in spinel oxide is different under the ZFC and FC magnetization method. To our knowledge, only limited attempt has been made to study TK as very few systems exhibit such behavior. In general, some of the ferrites have specific semiconducting properties, e.g., a very low carrier mobility. We discuss the anomalies of the magneto-resistance in ferrites that occur at order-disorder and order-order magnetic phase transition along with our ac and dc conductivity data near the spin compensation temperature. Another notable feature of the ferrites is that, upon irradiation of heavy ions, one can tune the magnetic ordering on bulk sample without destructive effects, i.e., irradiation-induced magnetization. It is interesting to note that spinel ferrite (nano) particle is an ideal small particle magnetic system as the crystal chemistry issue can be controlled, unlike pure metal particle systems where the crystal chemistry issues are basically fixed. In relevance to this, we will also discuss the future prospects, namely, the effect of irradiation on small particle magnetism, as, so far, only a limited attempt has been made in this field.

    • BiFeO3 thin films: Novel effects

      V R Palkar R Pinto

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      In this paper we report synthesis of phase-pure highly resistive magnetoelectric BiFeO3 thin films on Pt/TiO2/SiO2/Si substrate by using pulsed laser deposition technique. For the first time saturated ferroelectric hysteresis loop has been observed. It has confirmed the presence of ferroelectricity in BiFeO3 compound. The films exhibit dielectric anomaly near Neel temperature. This anomaly is related to the influence of vanishing magnetic order on the electric order. In situ domain alignment occurs during observation of the films under transmission electron microscope.

    • Size effect study in magnetoelectric BiFeO3 system

      Shwetha Shetty VR Palkar R Pinto

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      In this paper, we report for the first time finite size effects on Néel temperature (TN) of magnetoelectric BiFeO3 system. Novel wet chemical route has been developed to produce fine particles of BiFeO3 with controlled size and size distribution. Unlike other oxide systems, lattice volume contraction has been observed with decrease in particle size. The decrease in TN is co-related to unit cell volume contraction occurring with reduction in particle size.

    • Temperature hysteretic effect and its influence on colossal magnetoresistance of La0.33Nd0.33Ca0.33MnO3

      Darshan C Kundaliya Reeta Vij AA Tulapurkar U Vaidya R Pinto RG Kulkarni

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      Electrical resistance (R) measurements of a bulk La0.33Nd0.33Ca0.33MnO3 perovskite in magnetic fields up to 40 kOe have revealed anomalous temperature hysteretic effects both in 0 Oe and 20 kOe magnetic fields. The sharp peak observed in the R vs. T plot indicates the occurrence of metal-to-insulator (M-I) transition at a temperature of TMI=110 K and 140 K, for cooling and warming paths, respectively. An applied magnetic field of 20 kOe reduces the resistance and shifts TMI to 160 K and 185 K for cooling and warming, respectively. We have observed a much higher resistance in the cooling path than in the warming path leading to the hysteretic resistance ratio (Rcool/Rwarm) of 200 at 110 K and 1.8 at 160 K for 0 Oe and 20 kOe, respectively. Record values of colossal magnetoresistance (CMR) have been achieved. The CMR value reaches nearly 99% in the temperature ranges of 90 K to 140 K and 90 K to 170 K for 20 kOe and 40 kOe magnetic fields in the cooling mode, respectively. The observed unusual behavior is attributed to the co-existence of La-rich and Nd-rich domains assumed to be distributed randomly in the compound.

    • Enhanced temperature-independent magnetoresistance below the metal-insulator transition temperature of epitaxial La0.2Nd0.4Ca0.4MnO3 thin films

      Darshan C Kundaliya A A Tulapurkar J John R Pinto R G Kulkarni

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      Epitaxial La0.2Nd0.4Ca0.4MnO3 thin films have been deposited at 800°C on LaAlO3 substrate using pulsed laser deposition technique. The structural and magnetotransport properties of the films have been studied. The sharp peak in the temperature dependence of the resistance corresponding to metal-to-insulator transition (Tp) has been observed at a temperature of Tp=82 K, 97 K and 110 K for 0 Oe, 20 kOe and 40 kOe magnetic fields, respectively. The film exhibits a large nearly temperature-independent magnetoresistance around 99% in the temperature regime below Tp. The zero field-cooled (ZFC) and field-cooled (FC) magnetization data at 50 Oe shows irreversibility between the ZFC and FC close to the ferromagnetic transition temperature Tc=250 K. The ZFC temperature data of the film displays ferromagnetic behavior for higher temperature regime Tc=250 K>T>Tp=82 K, and a decrease in magnetization with decreasing temperature up to 5 K below 82 K exhibiting a sort of antiferromagnetic behavior in the low temperature regime (T<82 K=Tp=TN).

    • Modification of magnetic anisotropy in metallic glasses using high-energy ion beam irradiation

      KV Amrute UR Mhatre SK Sinha DC Kothari R Nagarajan D Kanjilal

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      Heavy ion irradiation in the electronic stopping power region induces macroscopic dimensional change in metallic glasses and introduces magnetic anisotropy in some magnetic materials. The present work is on the irradiation study of ferromagnetic metallic glasses, where both dimensional change and modification of magnetic anisotropy are expected. Magnetic anisotropy was measured using Mössbauer spectroscopy of virgin and irradiated Fe40Ni40B20 and Fe40Ni38Mo4B18 metallic glass ribbons. 90 MeV 127I beam was used for the irradiations. Irradiation doses were 5×1013 and 7.5×1013 ions/cm2. The relative intensity ratios D23 of the second and third lines of the Mössbauer spectra were measured to determine the magnetic anisotropy. The virgin samples of both the materials display in-plane magnetic anisotropy, i.e., the spins are oriented parallel to the ribbon plane. Irradiation is found to cause reduction in magnetic anisotropy. Near-complete randomization of magnetic moments is observed at high irradiation doses. Correlation is found between the residual stresses introduced by ion irradiation and the change in magnetic anisotropy.

    • Electrical transport and magnetic ordering in R2Ti3Ge4 (R=Dy, Ho and Er) compounds

      R Nirmala V Sankaranarayanan K Sethupathi AV Morozkin T Geethakumary Y Hariharan

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      New R2Ti3Ge4 (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize in the parent, Sm5Ge4-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series. The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects.

    • Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films

      SP Pai S Wanchoo SC Purandare T Banerjee PR Apte AM Narsale R Pinto

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      We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 µm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, Ic, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a Jc of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 Å). The difference in Jc indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of Jc at two different thicknesses (1800 Å and 1500 Å) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 Å. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection.

    • SQUID-based measuring systems

      MP Janawadkar R Baskaran R Nagendran K Gireesan N Harishkumar Rita Saha L S Vaidhyanathan J Jayapandian Y Hariharan TS Radhakrishnan

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      A program has been developed and initiated at the Indira Gandhi Centre for Atomic Research (IGCAR) for the utilization of SQUID sensors in various application areas. DC SQUID sensors based on Nb-AlOx-Nb Josephson junctions have been designed and developed inhouse along with associated flux-locked loop (FLL) electronics. A compact low field SQUID magnetometer insertible in a liquid helium storage dewar has also been developed inhouse and is in use. Efforts to build a high field SQUID magnetometer, SQUID-DAC system, are in progress. A planar gradiometric DC SQUID sensor for non-destructive evaluation (NDE) application to be used in relatively unshielded environment has been designed and developed. An easily portable NDE cryostat with a small lift-off distance, to be used in external locations has been designed and tested. The magnetic field produced by a given two-dimensional current density distribution is inverted using the Fourier transform technique.

    • Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

      Neeraj Khare AK Gupta UP Moharil AK Raychaudhuri SP Pai R Pinto

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      La0.67Ba0.33MnO3 (LBMO) thin film is deposited on a 36.7°C SrTiO3 bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.

    • Sensitivity of surface resistance measurement of HTS thin films by cavity resonator, dielectric resonator and microstrip line resonator

      N D Kataria Mukul Misra R Pinto

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      Microwave surface resistance (Rs) of silver-doped YBa2Cu3O7-δ (YBCO) thin film, deposited by laser ablation technique on 10 mm × 10 mm LaAlO3 substrate, has been measured by resonant techniques in the frequency range from 5 GHz to 20 GHz. The geometrical factor of the sample and the resonator has been determined theoretically by the knowledge of the electromagnetic field distribution in the resonators. The microwave surface resistance of the superconducting sample is then extracted from the measured Q value as a function of temperature. The sensitivity of the Rs measurement, that is, the relative change in the Q value with the change in the Rs value is determined for each resonator.

    • Magneto-transport properties of La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3 tunnel junction

      P Raychaudhuri C Mitra K Dorr KH Muller G Kobernik R Pinto

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      Hole-doped rare-earth manganite La0.7Ca0.3MnO3 and the electron-doped manganite La0.7Ce0.3MnO3 both show a metal-insulator transition around 250 K associated with a ferromagnetic transition and colossal magnetoresistance. In an earlier publication we have reported the rectifying characteristic of La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3 tunnel junction at room temperature, showing that it is possible to fabricate a diode out of the polaronic insulator regime of doped manganites. Here we report the magneto-transport properties of such a tunnel junction above and below the metal-insulator transition. We show, from the large positive magnetoresistance of the tunnel junction at low temperature, that La0.7Ce0.3MnO3 could be a minority spin carrier ferromagnet. The implication of this observation is discussed.

    • Direct injection of spin-polarized carriers across YBa2Cu3O7-δ-La0.3Ca0.7MnO3 interface at 77 K

      K V Upadhye K Ganesh Kumara S C Purandare S P Pai R Pinto

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      We report here injection of spin-polarized carriers from a half-metallic La0.3Ca0.7MnO3 (LCMO) colossal magnetoresistive (CMR) thin film into a high-temperature superconducting YBa2Cu3O7-δ (YBCO) thin film studied using a micro-bridge. The LCMO and YBCO films were grown on 〈100〉 LaAlO3 (LAO) substrate sequentially using pulsed laser deposition (PLD). I-V measurements carried out at 77 K show that while normal critical current, Icn, of the micro-bridge is 80 mA, the critical current, Icp, through the micro-bridge when injected from the CMR layer is 38 mA. This clearly shows that spin-polarized quasiparticles injected from the the CMR layer into the YBCO layer suppress the critical current of the superconductor via the pair-breaking phenomena.

    • Information flow due to controlled interference in entangled systems

      R Srikanth

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      We point out that controlled quantum interference corresponds to measurement in an incomplete basis and implies a nonlocal transfer of classical information. A test of whether such a generalized measurement is permissible in quantum theory is presented.

    • A modal method for finite amplitude, nonlinear sloshing

      P N Shankar R Kidambi

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      A modal method is used to calculate the two-dimensional sloshing motion of an inviscid liquid in a rectangular container. The full nonlinear problem is reduced to the solution of a system of nonlinear ordinary differential equations for the time varying coefficients in the expansions of the interface and the potential. The effects of capillarity are included in the formulation. The simplicity, generality and power of the method are exhibited not only by recovering the earlier results obtained, for example, by Penney and Price [1], Tadjbakhsh and Keller [2] and Faltinsen et al [3], but also by obtaining new and interesting results of the effects of capillarity and shallow depth, which would be difficult to obtain otherwise. For example, it is found that for the initial interface profile considered here, parasitic capillary waves, borne by the higher number wave modes, are generated for moderate capillarity but disappear for larger values of the parameter. The method can be extended to other simple geometries.

    • Mechanical design of the recirculating, terminal pumping in the lund pelletron, and experimental experience

      R Hellborg K Hākansson M Faarinen M Kiisk P Persson G Skog K Stenström

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      A recirculating terminal pumping system has been installed in the 3 MV Pelletron tandem accelerator in Lund. An extremly limited space in the high voltage terminal and the absence of electrical power in the terminal, forced us to provide a unique design for the installation and powering of the new pumps. Details of the technical design, as well as experience of the use of the new system for accelerator mass spectrometry, will be given.

    • New modifications in 15 UD pelletron at nuclear science centre

      S Chopra N S Pawar M P Singh Rakesh Kumar J Prasad V P Patel Raj Pal B Kumar S Ojha K Devarani T Nandi M Sota P Barua S Gargari R Joshi D Kanjilal SK Datta

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      The 15 UD pelletron at NSC has been operational and performed well during the last 11 years. There have been major modifications performed for upgradation of pelletron system over this period. Major upgradations which have been implemented are new resistor network system for voltage gradient, doublet to singlet unit conversion for accelerator units, turbopump based gas stripper system etc. In addition accelerator mass spectroscopy program has also been started. A new multi-cathode source, Wien filter etc. have been procured and will be added soon in the system. An overview of the most significant upgradations undertaken and other activities for the system are being reported in the present paper.

    • Beam optics optimization of a negative-ion sputter source

      F Osswald R Rebmeister

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      A negative-ion sputter source has been studied in order to increase the beam intensity delivered by the Vivitron tandem injector. The aim was to characterize the influence on the beam intensity of some factors related to the configuration of the source such as the shape of the target holder, the target surface topography and the anode/cathode voltage. The paper reports the results carried out by experimentation on a test facility and on the injector itself as well as the investigations performed with computer simulations.

    • Superconducting linear accelerator system for NSC

      P N Prakash T S Datta B P Ajith Kumar J Antony P Barua J Chacko A Choudhury G K Chadhari S Ghosh S Kar S A Krishnan Manoj Kumar Rajesh Kumar A Mandal D S Mathuria R S Meena R Mehta K K Mistri A Pandey M V Suresh Babu B K Sahu A Sarkar S S K Sonti A Rai S Venkatramanan J Zacharias R K Bhowmik A Roy

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      This paper reports the construction of a superconducting linear accelerator as a booster to the 15 UD Pelletron accelerator at Nuclear Science Centre, New Delhi. The LINAC will use superconducting niobium quarter wave resonators as the accelerating element. Construction of the linear accelerator has progressed sufficiently. Details of the entire accelerator system including the cryogenics facility, RF electronics development, facilities for fabricating niobium resonators indigenously, and present status of the project are presented.

    • First on-line test of the LINAC superbuncher at nuclear science centre

      S Ghosh R Mehta P N Prakash A Mandal G K Chaudhari S S K Sonti D S Mathuria K K Mistry A Rai S Rao P Barua A Pandey B K Sahu A Sarkar G Joshi S K Datta R K Bhowmik A Roy

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      An on-line test of the LINAC superbuncher at Nuclear Science Centre has been successfully performed. DC O7+ beam of nominal energy 92 MeV was accelerated through the superbuncher resonator, operating at a field of 4.54 MV/m. The total energy gain of the beam was measured to be 4.5 MeV. For the pulsed beam test a phase locked bunched beam of O7+ of nominal energy 92 MeV, FWHM 1.3 ns from the pre-tandem multiharmonic buncher was injected into the superbuncher. By properly adjusting the phase and amplitude of the resonator, the best FWHM of the bunched beam was measured to be 185 ps near the entrance of the first LINAC module. Fully depleted cooled surface barrier detector was used for measuring the time width. In a separate experiment the intrinsic time resolution of the same detector was measured to be 134 ps. Consequently the intrinsic time width of the bunched beam, after correcting for the detector resolution, would be 127 ps. Details of the experiment and results are presented.

    • A high resolution AMS-injector for the Pelletron in Lund

      R Hellborg S Bazhal M Faarinen K Håkansson C-E Magnusson P Persson G Skog K Stenström

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      A high resolution injector system has recently been installed at the Lund 3 MV tandem Pelletron accelerator. The new injector, designed mainly for 26Al ions, will increase the experimental potential of the Lund AMS facility considerably. High quality energy- and mass-resolution is obtained by using a 90° spherical electrostatic analyzer followed by a 90° magnetic analyzer. The injector is equipped with a high intensity sputtering source with a spherical ionizer.

      A new analytical technique for acceptance calculations as well as PC-based computational methods have been used in the design of the ion optical system of the new injector.

      Compared to our old injector system which has a magnetic analyzer with a bending angle of only 15°, the new system has a more than ten times better resolution. The beam optics of the new system is also better designed to match the accelerator acceptance. In this way the ion transmission from the ion source to the detector, for different ions of interest in our AMS programme, has been increased.

    • Single crystal EPR studies of Mn(II) doped into zinc ammonium phosphate hexahydrate (ZnNH4PO4·6H2O): A case of interstitial site for bio-mineral analogue

      H Anandalakshmi K Velavan I Sougandi R Venkatesan P Sambasiva Rao

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      Single crystal EPR studies of Mn(II)-doped zinc ammonium phosphate hexahydrate (ZnNH4PC4·6H2O) have been reinvestigated at room temperature. Single crystal rotations along the three orthogonal axes indicate that the spin Hamiltonian parameters for the interstitial site are:gxx = 1.966,gyy = 1.972,gzz = 1.976;Dxx = -12.28 mT,Dyy = -2.09 mT andDzz = 14.37 mT;Axx = 9.06 mT,Ayy = 9.06 mT andAzz = 11.09 mT;a = -0.11 mT. These parameters differ considerably from the previous report of Chand and Agarwal and indicate the orthorhombic nature of the paramagnetic impurity. The impurity is found to enter the lattice interstitially, in contrast to earlier prediction of substitutional position. The percentage covalency of the Mn-0 bond has been estimated.

    • Combined neutron and synchrotron studies of magnetic films

      Sunil K Sinha S Roy M R Fitzsimmons S Park M Dorn O Petracic I V Roshchin Zhi Pan Li X Batlle R Morales A Misra X Zhang K Chesnel J B Kortright Ivan K Schuller

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      We discuss specular reflectivity and off-specular scattering of neutrons and X-rays from magnetic films. Both these techniques are capable of providing information about the morphology of the chemical and magnetic roughness and the magnetic domain structure. The use of neutrons with polarization analysis enables the spatial distribution of different vector components of the magnetization to be determined, and the use of resonant magnetic X-ray scattering enables magnetization in a compound system to be determined element-selectively. Thus both these methods provide powerful and complementary new probes for studying magnetism at the nanoscopic level in a variety of systems such as those exhibiting exchange bias, giant magnetoresistance, spin injection, etc. We shall illustrate with an example of both techniques applied to an exchange bias system consisting of a single crystal of antiferromagnetic FeF2 capped with a ferromagnetic Co film, and discuss what has been learned about how exchange bias works in such a system.

    • Determination of thorium and uranium contents in soil samples using SSNTD’s passive method

      T A Salama U Seddik T M Dsoky A Ahmed Morsy R El-Asser

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      Thorium-to-uranium ratios have been determined in different soil samples using CR-39 and LR-115-II solid-state nuclear track detectors (SSNTDs). A calibration method based on determination of SSNTD registration sensitivity ratio for α-particles of thorium and uranium series has been developed. Thorium and uranium contents of the standard soil samples have been determined and compared with its known values. There is a good agreement between the results of this method and the values of standard samples. The method is simple, inexpensive, non-destructive and has a wide range of applications in environment, building materials and petroleum fields.

    • Bianchi type-V model with a perfect fluid and A-term

      T Singh R Chaubey

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      A self-consistent system of gravitational field with a binary mixture of perfect fluid and dark energy given by a cosmological constant has been considered in Bianchi Type-V universe. The perfect fluid is chosen to be obeying either the equation of state p=γρ with γ ε |0,1| or a van der Waals equation of state. The role of A-term in the evolution of the Bianchi Type-V universe has been studied.

    • Laser-induced breakdown spectra of Zn2 molecule in the violet region

      Subhash C Singh K S Ojha R Gopal

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      Laser-induced breakdown spectrum has been recorded in the region of 380–455 nm using second harmonics of Nd:YAG laser, computer-controlled TRIAX 320 M monochromator with a reciprocal linear dispersion 2.64 nm/mm fitted with ICCD detector. The spectrum consists of 108 bands, which are classified into four new subsystems E0u+ (1Σu+) → A1g(3Πg), J0g±\1g(3Σg+) → D1u(1Πu), F1u → A0g±(3Πg) and F1u → A2g(3Πg) along with additional bands of the known system E0u+(1Σu+) → A0g±(3Πg). The molecular constants for these systems have also been determined.

    • Working group report: Astroparticle and neutrino physics

      Raj Gandhi Subhendra Mohanty Tarun Souradeep S Agarwalla K Bhattacharya B Brahmachari R Crittenden S Goswami P Ghoshal M Lindner H S Mani S Mitra S Pascoli S Panda R Rangarajan S Ray T Roy Choudhury R Saha S Sarkar A Srivastava R Sheth S Uma Sankar U Yajnik

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      The working group on astroparticle and neutrino physics at WHEPP-9 covered a wide range of topics. The main topics were neutrino physics at INO, neutrino astronomy and recent constraints on dark energy coming from cosmological observations of large scale structure and CMB anisotropy.

    • Working group report: Flavor physics and model building

      M K Parida Nita Sinha B Adhikary B Allanach A Alok K S Babu B Brahmachari D Choudhury E J Chun P K Das A Ghosal D Hitlin W S Hou S Kumar H N Li E Ma S K Majee G Majumdar B Mishra G Mohanty S Nandi H Pas M K Parida S D Rindani J P Saha N Sahu Y Sakai S Sen C Sharma C D Sharma S Shalgar N N Singh S Uma Sankar N Sinha R Sinha F Simonetto R Srikanth R Vaidya

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      This is the report of flavor physics and model building working group at WHEPP-9. While activites in flavor physics have been mainly focused on B-physics, those in model building have been primarily devoted to neutrino physics. We present summary of working group discussions carried out during the workshop in the above fields, and also briefly review the progress made in some projects subsequently.

    • Working group report: Heavy-ion physics and quark-gluon plasma

      Munshi G Mustafa Sudhir Raniwala T Awes B Rai RS Bhalerao JG Contreras RV Gavai SK Ghosh P Jaikumar GC Mishra AP Mishra H Mishra B Mohanty J Nayak J-Y Ollitrault SC Phatak L Ramello R Ray PK Sahu AM Srivastava DK Srivastava VK Tiwari

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      This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported.

    • Working group report: Quantum chromodynamics

      V Ravindran Pankaj Agrawal Rahul Basu Satyaki Bhattacharya J Blümlein V Del Duca R Harlander D Kosower Prakash Mathews Anurag Tripathi

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      This is the report of the subgroup QCD of Working Group-4 at WHEPP-9. We present the activities that had taken place in the subgroup and report some of the partial results arrived at following the discussion at the working group meetings.

    • Cosmic no-hair conjecture in scalar-tensor theories

      T Singh R Chaubey

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      We have shown that, within the context of scalar-tensor theories, the anisotropic Bianchi-type cosmological models evolve towards de Sitter Universe. A similar result holds in the case of cosmology in Lyra manifold. Thus the analogue of cosmic no-hair theorem of Wald [1] hold in both the cases. In fact, during inflation there is no difference between scalar-tensor theories, Lyra’s manifold and general relativity (GR).

    • Modelling of the magnetic and magnetostrictive properties of high permeability Mn-Zn ferrites

      R Szewczyk

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      This paper presents the results of modelling of both magnetic and magnetostrictive properties of high permeability Mn0.51Zn0.44Fe2.05O4 ferrites. The parameters of energy-based Jiles-Atherton-Sablik (J-A-S) model were calculated for each experimental hysteresis loop on the basis of evolutionary strategies and Hook-Jevis optimization method. Finally, high conformity between experimental and modelling results was achieved. This high conformity indicates that the presented results create new opportunity of modelling of the properties of inductive components based on ferrites as well as quantitative description of magnetization process.

    • Electrospun polystyrene fibres on TiO$_2$ nanostructured film to enhance the hydrophobicity and corrosion resistance of stainless steel substrates

      Azimirad R Safa S

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      A dual layer of dip-coated TiO$_2$ film (top layer) and electrospun polystyrene (bottom layer) was coated on stainless steel (SS) substrates. The morphological and structural studies were performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their hydrophobicity and corrosion resistance were also investigated using contact angle (CA) and electrochemical corrosion tests in acidic and salt solutions, respectively. Contact angle results showed that the naturally hydrophilic TiO$_2$/SS sample (CA ∼ 66$^\deg$) turned into a superhydrophic surface (CA ∼ 148$^\deg$) when it was covered by polystyrene fibres (PS/TiO2/SS). This observation can be attributed to the intrinsic hydrophobicity of organic polystyrene fibres (due to their low surface energy) and also to the existence of trapped air bubbles between fibres. Electrochemical corrosion tests showed that the corrosion rate was substantially decreased by using a protective bilayer (PS/TiO$_2$) from 33 to 0.39 mV/y for bare SS sample and from 0.01 to 0.003 mV/y for PS/TiO$_2$/SS sample in 1 M salt and acidic solutions, respectively. The superhydrophobic protective layer forms an obstacle against ionic exchange interactions. Therefore, it slows down the breaking of the surface oxidic layer on the metal substrate and prevents the metallic surface underneath from further corrosion.

    • A physics-based potential and electric field model of a nanoscale rectangular high-K gate dielectric HEMT

      Das B Goswami R Bhowmick B

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      In this paper, we have developed a physics-based model for surface potential, channel potential, electric field and drain current for AlGaN/GaN high electron mobility transistor with high-K gate dielectric using two-dimensional Poisson equation under full depletion approximation with the inclusion of effect of polarization charges. The accuracy of the model has been verified and is found to be in good agreement with the simulated results.

    • Thermal expansion behaviour and phase stability of AFe$_2$As$_2$ (A=Ca, Sr and Eu) using powder diffraction technique


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      The thermal expansibilities and phase stabilities of AFe$_2$As$_2$ (A = Ca, Sr and Eu) have been investigated by powder diffraction techniques in the temperature range 5–600 K.We found the anisotropic thermal expansivities with temperature for all the compounds. The lattice parameter in the tetragonal phase (AT) of CaFe$_2$As$_2$ contracts with increasing temperature, whereas CT expands. The rate of contraction in AT is lower than the rate of expansion in CT. Other compounds show normal thermal expansion behaviour along both a- and c-axes. In-plane expansion (i.e., along the a-axis) is found to be the smallest for EuFe$_2$As$_2$ and the highest for BaFe$_2$As$_2$. However, therate of change of thermal expansivities along out-of-plane (i.e., along the c-axis) is higher as we go from Ba, Sr, Eu and Ca, respectively. Above 600 K, we notice the appearance/disappearance of certain reflections which suggest that tetragonal phase is not stable above this temperature for these compounds.

    • Shock wave propagation in soda lime glass using optical shadowgraphy


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      Propagation of shock waves in soda lime glass, which is a transparent material, has been studied using the optical shadowgraphy technique. The time-resolved shock velocity information has been obtained (1) in single shot, using the chirped pulse shadowgraphy technique, with a temporal resolution of tens of picoseconds and (2) in multiple shots, using conventional snapshot approach, with a second harmonic probe pulse. Transient shock velocities of $(5–7) \times 10^{6}$ cm/s have been obtained. The scaling of the shock velocity with intensity in the $2 \times 10^{13}–10^{14}$ W/cm$^2$ range has been obtained. The shock velocity is observed to scale with laser intensity as $I^{0.38}$. The present experiments also show the presence of ionization tracks, generated probably due to X-ray hotspots from small-scale filamentation instabilities. The results and various issues involved in these experiments are discussed

    • Structural, photoconductive, thermoelectric and activation energy measurements of $V$-doped transparent conductive $SnO_{2}$ films fabricated by spray pyrolysis technique


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      This report investigated the structural, optical and electrical properties of V-doped $SnO_{2}$ thin films deposited using spray pyrolysis technique. The $SnO_{2}$:$V$ films, with different $V$-content, were deposited on glasssubstrates at a substrate temperature of $550\deg C$ using an aqueous ethanol solution consisting of tin and vanadium chloride. X-ray diffraction studies showed that the $SnO_{2}$:$V$ films were polycrystalline only with tin oxide phasesand the preferred orientations are along (1 1 0), (1 0 1), (2 1 1) and (3 0 1) planes. Using Scherrer formula, the grain sizes were estimated to be within the range of 25--36 nm. The variation in sheet resistance and optical direct band gap are functions of vanadium doping concentration. Field emission scanning electron microscopy (FESEM) revealed the surface morphology to be very smooth, yet grainy in nature. Optical transmittance spectra of the films showed high transparency of about $\approx 69--90%$ in the visible region, decreasing with increase in $V$-doping. The direct band gap for undoped $SnO_{2}$ films was found to be 3.53 eV, while for higher V-doped films it shifted toward lower energies in the range of 3.27--3.53 eV and then increased again to 3.5 eV. The Hall effect and Seebeck studies revealed that the films exhibit n-type conductivity. The thermal activation energy, Seebeck coefficient and maximum of photosensitivity in the films were found to be in the range of 0.02--0.82 eV (in thelow-temperature range), $0.15--0.18 {\rm mV K^{−1}}$ (at $T = 350 K$) and 0.96--2.84, respectively.

    • The effect of concentration of H$_2$ physisorption on the current–voltage characteristic of armchair BN nanotubes in CNT–BNNT–CNT set


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      In this research, we have studied physisorption of hydrogen molecules on armchair boron nitride (BN) nanotube (3,3) using density functional methods and its effect on the current–voltage ($I–V$) characteristic of the nanotube as a function of concentration using Green’s function techniques. The adsorption geometries and energies, charge transfer and electron transport are calculated. It is found that H$_2$ physisorption can suppress the $I–V$ characteristic of the BN nanotube, but it has no effect on the band gap of the nanotube. As the H$_2$concentration increases, under the same applied bias voltage, the current through the BN nanotube first increases and then begins to decline. The current–voltage characteristic indicates that H$_2$ molecules can be detected by aBN-based sensor.

    • Plastic scintillator-based hodoscope for the characterization of large-area resistive plate chambers


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      A scintillator-based hodoscope is fully operational at Nuclear Physics Division, Bhabha Atomic Research Centre (NPD-BARC). It was used for characterizing the resistive plate chambers (RPCs) assembled for the RE4 upgrade for the compact muon solenoid (CMS) experiment, installed during the long shut-down (LS1) using cosmic muons. It has now been employed for R & D related to gas mixtures and glass RPCs for the Indiabased neutrino observatory (INO) and muon tomography studies. The hodoscope is equipped with gas flow lines,LV, HV and VME-based DAQ with multihit TDCs. CERN-based software was adapted, implemented and along with the cosmic trigger, was used to evaluate the functional parameters for the RPCs, such as efficiency, clustersize etc.

    • Modelling of capacitance and threshold voltage for ultrathin normally-off AlGaN/GaN MOSHEMT


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      A compact quantitative model based on oxide semiconductor interface density of states (DOS) is proposed for Al$_{0.25}$Ga$_{0.75}$N/GaN metal oxide semiconductor high electron mobility transistor (MOSHEMT). Mathematical expressions for surface potential, sheet charge concentration, gate capacitance and threshold voltage have been derived. The gate capacitance behaviour is studied in terms of capacitance–voltage (CV) characteristics. Similarly, the predicted threshold voltage ($V_T$) is analysed by varying barrier thickness and oxide thickness. The positive $V_T$ obtained for a very thin 3 nm AlGaN barrier layer enables the enhancement mode operation of the MOSHEMT. These devices, along with depletion mode devices, are basic constituents of cascode configuration in power electronic circuits. The expressions developed are used in conventional long-channel HEMT drain current equation and evaluated to obtain different DC characteristics. The obtained results are compared withexperimental data taken from literature which show good agreement and hence endorse the proposed model.

    • The properties of $C$-parameter and coupling constants


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      We present the properties of the C-parameter as an event-shape variable. We calculate the coupling constants in the perturbative and also in the non-perturbative parts of the QCD theory, using the dispersive as wellas the shape function models. By fitting the corresponding theoretical predictions to our data, we find $\alpha_{s}(M_{Z^{0}} ) = 0.117 \pm 0.014$ and $\alpha_{0}(\mu_{I} ) = 0.491 \pm 0.043$ for dispersive model and $\alpha_{ s}(M_{Z^{0}} ) = 0.124 \pm 0.015$ and $\lambda_{1} = 1.234 \pm 0.052$ for the shape function model. Our results are consistent with the world average value of $\alpha_{s}(M_{Z^{0}} ) = 0.118 \pm 0.002$. All these features are explained in the main text.

    • Factors controlling phase formation of novel Sr-based Y-type hexagonal ferrite nanoparticles


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      New Sr-based Y-type nanocrystalline hexagonal ferrites with a nominal chemical composition of Sr$_2$Mg$_2$Fe$_{12}$O$_{22}$ (Sr$_2$Y) were prepared by autocombustion from mixtures of Sr(NO$_3$)$_2$, Mg(NO$_3$ )$_2$·6H$_2$O and Fe(NO$_3$)$_3$·9H$_2$O. The newly prepared Sr$_2$Y nanocrystalline particles were characterized by powder X-ray diffraction (XRD). A well crystalline phase of Sr$_2$Y with hexagonal crystal structure was observed. Fourier transform infrared spectroscopy (FTIR) studies revealed the information about the positions of the ions and their bonds within the lattice structure of the Sr2Y. The chemical elements and their oxidation states in the Sr$_2$Y hexaferriteswere determined using X-ray photoelectron spectroscopy (XPS). The XRD, FTIR and XPS studies confirmed the formation of Sr$_2$Mg$_2$Fe$_{12}$O$_{22}$ hexaferrites. The morphology and porosity of the prepared Sr$_2$Y nanocrystalline Sr$_2$Y hexaferrite particles were studied by field emission scanning electron microscopy. The magnetic properties of Sr$_2$Y hexaferrites showed dependence on the methods of preparation conditions and calcination treatments. The values of coercivity, saturation magnetization and retentivity were in the range of 21.33–19.66 kA m$^{−1}$, 42.44–38.72 emu g$^{−1}$ and 10.05–13.19 emu g$^{−1}$ respectively.

    • Cross over of recurrence networks to random graphs and random geometric graphs


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      Recurrence networks are complex networks constructed from the time series of chaotic dynamical systems where the connection between two nodes is limited by the recurrence threshold. This condition makes the topology of every recurrence network unique with the degree distribution determined by the probability densityvariations of the representative attractor from which it is constructed. Here we numerically investigate the properties of recurrence networks from standard low-dimensional chaotic attractors using some basic network measuresand show how the recurrence networks are different from random and scale-free networks. In particular, we show that all recurrence networks can cross over to random geometric graphs by adding sufficient amount of noise tothe time series and into the classical random graphs by increasing the range of interaction to the system size. We also highlight the effectiveness of a combined plot of characteristic path length and clustering coefficient in capturing the small changes in the network characteristics.

    • Effects of electron–phonon interaction and impurity on optical properties of hexagonal-shaped quantum wires


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      We have investigated the influence of electron–phonon (e–p) interaction and hydrogenic donor impurity simultaneously on energy difference, binding energy, the linear, nonlinear and total refractive index changes and absorption coefficients of a hexagonal-shaped quantum wire. For this goal, we have used finite-elementmethod (FEM), a compact density matrix approach and an iterative procedure. It is deduced that energy difference and binding energy decrease by changing the impurity position with and without e–p interaction. The dipole matrix elements have complex behaviours in the presence of impurity with and without e–p interaction. The refractive index changes and absorption coefficients increase and shift towards lower energies by enhancing $a_1$ with central impurity. In the presence of central impurity, the absorption coefficients and refractive index changes enhance and shift toward higher energies when e–p interaction is considered.

    • The general class of Bianchi cosmological models with dark energy and variable $\Lambda$ and $G$ in viscous cosmology


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      The general class of Bianchi cosmological models with dark energy in the form of modified Chaplygin gas with variable $\Lambda$ and $G$ and bulk viscosity have been considered. We discuss three types of average scalefactor by using a special law for deceleration parameter which is linear in time with negative slope. The exact solutions to the corresponding field equations are obtained. We obtain the solution of bulk viscosity ($\xi$ ), cosmologicalconstant ($\Lambda$), gravitational parameter ($G$) and deceleration parameter ($q$) for different equations of state. The model describes an accelerating Universe for large value of time $t$ , wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.

    • The anisotropic cosmological models in $f (R, T)$ gravity with $\Lambda (T)$


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      The general class of anisotropic Bianchi cosmological models in $f(R, T)$ modified theories of gravity with $\Lambda (T)$ has been considered. This paper deals with $f(R, T)$ modified theories of gravity, where the gravitational Lagrangian is given by an arbitrary function of Ricci scalar $R$ and the trace of the stress-energy tensor $T$ has been investigated for a specific choice of $f (R,T )$ = $f_{1}(R) + f_{2}(T)$. The exact solutions to the corresponding field equations are obtained in quadrature form. We have discussed three types of solutions of the average scale factor for the general class of Bianchi cosmological models by using a special law for deceleration parameter which is linear in time with a negative slope. The solutions to the Einstein field equations are obtained for three differentphysical viable cosmologies. All physical parameters are calculated and discussed in each model.

    • Algebraic resolution of the Burgers equation with a forcing term


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      We introduce an inhomogeneous term, $f (t,x)$, into the right-hand side of the usual Burgers equation and examine the resulting equation for those functions which admit at least one Lie point symmetry. For those functions $f (t,x)$ which depend nontrivially on both $t$ and $x$, we find that there is just one symmetry. If $f$ is a function of only $x$, there are three symmetries with the algebra $sl(2,R)$. When $f$ is a function of only $t$ , there are five symmetries with the algebra $sl(2,R)\oplus_{s} 2A_1$. In all the cases, the Burgers equation is reduced to the equation for a linear oscillator with nonconstant coefficient.

    • Physics potential of the ICAL detector at the India-based Neutrino Observatory (INO)


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      The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies andpath lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial toaddress some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations.We describe the simulation framework, the neutrino interactions in the detector, and the expected responseof the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Itscharge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles.

    • Improved performance of organic light-emitting diode with vanadium pentoxide layer on the FTO surface


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      Vanadium pentoxide layer deposited on the fluorine-doped tin oxide (FTO) anode by vacuum deposition has been investigated in organic light-emitting diode (OLED).With 12nm optimal thickness of $V_{2}O_{5}$, the luminance efficiency is increased by 1.66 times compared to the single FTO-based OLED. The improvement of current efficiency implies that there is a better charge injection and better controlling of hole current. To investigate the performance of OLED by the buffer layer, $V_{2}O_{5}$ films of different thicknesses were deposited on the FTO anode and their $J–V$ and $L–V$ characteristics were studied. Further analysis was carried out by measuring sheet resistance, optical transmittance and surface morphology with the FE-SEM images. This result indicates that the $V_{2}O_{5}$ (12 nm) buffer layer is a good choice for increasing the efficiency of FTO-based OLED devices within the tunnelling region. Here the maximum value of current efficiency is found to be 2.83 cd/A.

    • Heat transfer with thermal radiation on MHD particle–fluid suspension induced by metachronal wave


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      In this article, effects of heat transfer on particle–fluid suspension induced by metachronal wave have been examined. The influence of magnetohydrodynamics (MHD) and thermal radiation are also taken into account with the help of Ohm’s law and Roseland’s approximation. The governing flow problem for Casson fluid model is based on continuity, momentum and thermal energy equation for fluid phase and particle phase. Taking the approximation of long wavelength and zero Reynolds number, the governing equations are simplified. Exact solutions are obtained for the coupled partial differential equations. The impact of all the embedding parameters is discussed with the help of graphs. In particular, velocity profile, pressure rise, temperature profile and trapping phenomena are discussed for all the emerging parameters. It is observed that while fluid parameter enhances the velocity profile, Hartmann number and particle volume fraction oppose the flow.

    • First-principle calculations of structural, electronic, optical, elastic and thermal properties of $\rm{MgXAs_{2} (X = Si, Ge)}$ compounds


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      First-principle calculations on the structural, electronic, optical, elastic and thermal properties of the chalcopyrite $\rm{MgXAs_{2} (X = Si, Ge)}$ have been performed within the density functional theory (DFT) using the full potential linearized augmented plane wave (FP-LAPW) method. The obtained equilibrium structural parameters are in good agreement with the available experimental data and theoretical results. The calculated band structures reveal a direct energy band gap for the interested compounds. The predicted band gaps using the modified Becke–Johnson(mBJ) exchange approximation are in fairly good agreement with the experimental data. The optical constants such as the dielectric function, refractive index, and the extinction coefficient are calculated and analysed. The independent elastic parameters namely, $C_{11}, C_{12}, C_{13}, C_{33}, C_{44}$ and $C_{66}$ are evaluated. The effects of temperature and pressure on some macroscopic properties of $\rm{MgSiAs_{2}}$ and $\rm{MgGeAs_{2}}$ are predicted using the quasiharmonic Debye model in which the lattice vibrations are taken into account.

    • $K^{0}_{S}$ Production from beryllium target using 120 GeV/c protons beam interactions at the MIPP experiment


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      We have measured the cross-section for the $K^{0}_{S}$ production from beryllium target using 120 GeV/c protons beam interactions at the main injector particle production (MIPP) experiment at Fermilab. The data were collected with target having a thickness of 0.94% of the nuclear interaction length. The $K^{0}_{S}$ inclusive differential cross-section in bins of momenta is presented covering momentum range from 0.4GeV/c to 30GeV/c. The measured inclusive $K^{0}_{S}$ production cross-section amounts to $39.54 \pm 1.46\delta_{stat} \pm 6.97\delta_{syst}$ mb and the value is compared with the prediction of FLUKA hadron production model.

    • Anisotropic stars obeying Chaplygin equation of state


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      In this work we provide a framework for modelling compact stars in which the interior matter distribution obeys a generalised Chaplygin equation of state. The interior geometry of the stellar object is described by a spherically symmetric line element which is simultaneously co-moving and isotropic with the exterior space–time being vacuum. We are able to integrate the Einstein field equations and present closed form solutions which adequately describe compact strange star candidates such as 4U 1538-52, PSR J1614-2230, Vela X-1 and Cen X-3 (Gangopadhyay $\it{et al, Mon. Not. R. Astron. Soc.} \bf{431}$, 3216 (2013)).

    • Quantum chemical calculations of $\rm{Cr_{2}O_{3}/SnO_{2}}$ using density functional theory method


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      Quantum chemical calculations have been employed to study the molecular effects produced by $\rm{Cr_{2}O_{3}/SnO_{2}}$ optimised structure. The theoretical parameters of the transparent conducting metal oxides were calculated using DFT/B3LYP/LANL2DZ method. The optimised bond parameters such as bond lengths, bond angles and dihedral angles were calculated using the same theory. The non-linear optical property of the title compound was calculated using first-order hyperpolarisability calculation. The calculated HOMO–LUMO analysis explains the charge transfer interaction between the molecule. In addition, MEP and Mulliken atomic charges werealso calculated and analysed.

    • Geometry of magnetic rotational (MR) band-crossing phenomenon in MR bands


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      A semiclassical (SC) approach is proposed to calculate the $B(M1)$ transition rates in the band-crossing region of two magnetic rotational (MR) bands. In the present work, a geometry is suggested for the shear blades to govern its behaviour during the band-crossing. In the crossing region, gradual alignment of two nucleons is responsible for the crossing behaviour and it must give a quantised resultant angular momentum. As an example, it is successfully implemented for the MR bands in the mass $A = 110$ and $A = 200$ regions. A good agreement of the present semiclassical calculations with the experimental values is presented and furthermore, it is seen that the present proposal is also helpful to see the core contribution in the MR phenomenon.

    • Applicability of strange nonchaoticWien-bridge oscillators for secure communication


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      In this paper, experimental realisation of synchronisation of strange nonchaotic attractor inunidirectionally coupled Wien-bridge oscillator is presented. Preliminary work of chaotic and strange nonchaotic dynamics with diode as the nonlinear element is published in J. Nonlinear Dyn. 2015, 1 (2015). In this work, two Wien-bridge oscillators are coupled at the aperiodic dynamics for application in secure communication. The dynamics of the coupled system is explored by experimental and numerical studies. Employing the simple communication masking method with aperiodic dynamics offers some advantages rather than using chaotic attractors, i.e., the range of control parameter value is smaller than the range for which the system exhibits chaotic behaviour. The performance of the system is evaluated and it is found that experimental result agrees with numerical results.

    • Investigation of nuclear quantum effect on the hydrogen bonds of ammonium dihydrogen phosphate using single-crystal neutron diffraction and theoretical modelling


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      Potassium dihydrogen phosphate (KDP) family of hydrogen-bonded crystal constitutes an important family of crystals not only because of their immense importance in the field of nonlinear optics (NLOs) but also due to the fact that hydrogen bonds of these crystals provide us with a rare opportunity to understand the fundamental nature of hydrogen bonds, such as the effect of local chemical environment on the strength of hydrogen bonds and nuclear quantum effect on strong, moderate and weak hydrogen bonds. Keeping this aim in mind, we have undertaken detailed single-crystal neutron diffraction (SCND) investigations on ammonium dihydrogen phosphate(ADP) and KDP along with their deuterated analogue crystals under ambient conditions. Fine differences in thehydrogen bonds of the above-mentioned crystals are analysed in the light of a simple diabatic two-state theoreticalmodel for hydrogen bonds. It is proposed that the presence of a partially covalent $\rm{N–H_{N}–O}$ bond in ADP has a very significant effect on its O–H bond making it highly anharmonic. It is this higher bond anharmonicity in ADPthat is most likely responsible for its larger NLO coefficient compared to KDP.

    • The possible effect of stratospheric quasi-biennial oscillation on the critical frequency of the ionospheric F2-layer


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      In this study, the coupling between the stratospheric quasi-biennial oscillation (QBO) and the critical frequency of the ionospheric F2-layer (foF2) was analysed statistically. The multiple regression model was used as a statistical tool. The model was developed by adding the sunspot number (SSN), which affects the foF2 (measured for Madras, Kodaikanal, Bogota, Manila and Tahiti) in the ionosphere at a significant level. Four different ‘Dummy’sets of data were used in the model in order to observe the effect of the direction (east–west) and the magnitude (for both directions, between 0 and 15 m/s and between 0 and 16 m/s and the largest value) of QBO. It was observed that the variations of foF2 in the range of 60–78% in the model could be explained by SSN and $\rm{SSN^{2}}$. The change of 2–13% that occurred in foF2 could be explained by the whole set of QBO. It was also observed that the effect of the direction and magnitude of QBO on foF2 differed between the stations.

    • Thermal transport of rate-type fluid impinging obliquely over a heated sheet


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      The main objective of this study is to examine the two-dimensional (2D) oblique Oldroyd-B flow on a stretching heated sheet. The flow governing problem is converted into nonlinear ordinary differential equations through proper scaling transformations. The prevailing set of equations is solved computationally with a tolerance level of $10^{−5}$. The velocity and temperature of a fluid model under consideration are portrayed to discuss the influence of all associated parameters on momentum and thermal characteristics. Heat flux at the wall has been computed numerically and analysed in a physical manner. The results obtained depict a reversed flow region for non-positive values of shear flow components once a free parameter is varied. It is noticed that heat transfer at the wall drops due to a rise in Deborah number $\beta_{1}$ as well as Biot number Bi.

    • One-dimensional nuclear design analyses of the SST-2


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      Steady State Tokamak-2 (SST-2) will be an intermediate fusion machine before Indian DEMOnstration power reactor (DEMO) development to realise the reactor technologies. It is designed for fusion gain Q = 5 andfusion power in the range of 100–300 MW. Nuclear design analyses of SST-2 machine have been carried out to support the conceptual design work. Analyses have been carried out for two breeding blanket concepts: Indian lead–lithium ceramic breeder (LLCB) and helium-cooled ceramic breeder (HCCB). The analyses assess the tritium production and radiation shielding capability of the machine referring to the engineering design parameters. In this study, one-dimensional radiation transport calculations have been performed to assess the SST-2 nuclear responses for 1 full power year (FPY) operation. Nuclear responses such as tritium breeding ratio (TBR), various radiation loads to toroidal field (TF) coil have been calculated to obtain the radial build-up of SST-2 capable of breeding tritium and satisfying the shielding requirements. The assessment has been made using the ANISEN code andFENDL 2.1 cross-section library. It is observed that the TBRs with LLCB and HCCB blankets are 0.85 and 0.94, respectively. Shielding calculations confirm that the radial build is sufficient to protect the superconducting TF coils for 1 FPY.

    • Characteristics of solar microflares as seen in soft X-ray emission


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      In this paper, we present the thermal and non-thermal characteristics of solar plasma producing microflares in 4–12 keV energy range. The X-ray spectra of 10 B-class solar microflares observed by the silicon(Si) detector (4–25 keV) on-board solar X-ray spectrometer (SOXS) mission were analysed in 4–12 keV energy range. We employed forward fitting for the spectral modelling of thermal and non-thermal components of X-ray spectra with isothermal, multithermal and single power-law functions in order to determine flare parameters. The fit results obtained from the combination of isothermal and single power-law functions yield a weighted mean value of emission measure $\rm{(EM) \approx 0.0203×10^{49}cm^{−3}}$, plasma temperature [Case (1)] $T (1) \approx 10.24$MK and non-thermal spectral index $\gamma (1) \approx 3.90$. The fit results obtained from the combination of multithermal and single power-law functions yield a weighted mean value of differential emission measure, $\rm{(DEM) \approx 0.00116 × 10^{49} cm^{−3} keV^{−1}}$, plasma temperature [Case (2)], $T (2) \approx 12.90$MK, thermal spectral index, $\delta \approx 4.06$ and non-thermal spectral index, $\gamma (2) \approx 3.81$. Further, we obtained the mean value of conduction cooling time, $\tau_{c}(T) \approx 283$ s at 11.6 MK, thermal energy, $E_{th} \approx 0.50×10^{29}$erg and thermal–non-thermal cross-over energy, $\epsilon_{th} \approx 9.23$ keV. In this analysis, the obtained results were found to be compatible with the earlier analysis carried out for the microflares through Reuven Ramety High Energy Solar Spectroscopic Imager (RHESSI), Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) and NuSTAR observations. Here, we observed that EM decreases with increasing plasma temperature $(T)$. We find that $\tau_{c}(T)$ scale with plasma temperature $(T)$ with an inverse gradient exhibits time delay characteristic of the cooling process of plasma. The correlation of $E_{th}$ and temperature $(T)$ shows moderate anticorrelation. The present analysis demonstrates the multithermal plasma model and conduction cooling process during high temperature of microflares (similar to large flares) followed by radiative cooling in post-flare.

    • Comparative study of discharge characteristics and associated film growth for post-cathode and inverted cylindrical magnetron sputtering


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      In this study, an experimental investigation of a DC cylindrical magnetron discharge for argon gas in post-cathode (i.e. direct) and hollow-cathode (i.e. inverted) configurations was carried out. The discharge properties at different externally applied magnetic fields and operating pressures were measured and compared for both the configurations. The discharge current ($I$)–voltage ($V$) characteristics obey $I \propto V^{n}$, where the value of $n$ is in the range of 3–8. The discharge current increases linearly with the magnetic field in the post-cathode configuration, whereas it saturates at higher magnetic fields in the case of inverted configuration. Measurement of plasma potential indicated a considerable anode fall in the inverted magnetron configuration, whereas a negligible anode fall and strong cathode fall were observed in the case of post-cathode configuration. The plasma density and electron temperature, measured using a double Langmuir probe, were observed to be higher in the inverted magnetron configuration. The plasma density was found to be maximum at around 3–4 cm away from the respective inner electrode in both the configurations. A clear change in surface morphology of copper thin film was observed in the case of inverted magnetron configuration, which might be due to the extra ionisation near the anode owing to the anode fall.

    • Long-time dynamics of a vertical-cavity surface-emitting laser under optical feedback


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      External optical feedback in vertical-cavity surface-emitting laser (VCSEL) is found to influence its output intensity.We studied the effect of the amount of total output polarisation feedback and polarisation-selective feedback on the output intensities of a VCSEL for a low-resolution sampling and for long temporal duration. A 40 μs resolution time-series correlation analysis is performed for different feedback conditions and the characteristicdynamics is investigated.We found a correlated fluctuation in VCSEL output for a moderate amount of total feedbackand polarised feedback. The period of such fluctuations is found to be reduced from total feedback to the polarised feedback of the system.

    • Locally rotationally symmetric Bianchi type-I cosmological model with dynamical $Lambda$ and $G$ in $f (R)$ gravity


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      In this paper, we have studied the locally rotationally symmetric (LRS) Bianchi type-I cosmological model filled with a bulk viscous cosmological fluid in $f(R)$ gravity in the presence of time-varying gravitational and cosmological constant. We have used the power-law and intermediate scenario for scale factor to obtain thesolution of the field equations. The evolution of temperature of a viscous Universe is also analysed.

    • Density functional theory of influence of methane adsorption on the electronic properties of a PbS cluster


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      The effect of methane adsorption on the electronic properties of a lead sulphide (PbS) cluster is investigated using density functional theory (DFT) when an oxygen molecule was previously adsorbed to the cluster. This paper studies how the pre-adsorption of oxygen influences the tendency of PbS cluster to adsorb $\rm{CH}_{4}$ and variations of its electronic properties due to $\rm{CH}_{4}$ adsorption. Further investigation on how these variations occur was carried out by charge transfer calculations. The discussion based on the results of this study succeeded in explaining the previously reported experimental observations.

    • Peristaltic transport of Jeffrey fluid in a rectangular duct through a porous medium under the effect of partial slip: An application to upgrade industrial sieves/filters