• Volume 13, Issue 3

      September 1979,   pages  205-335

    • Analysis of ultrasonic anomaly in V3Si

      S Dattagupta G Venkataraman

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      V3Si exhibits an ultrasonic anomaly when cooled well below its martensitic and superconducting transition temperatures (Tm andTc), and a magnetic field is applied on to the sample. The anomaly is thought to be due to reorientation of microdomains formed belowTm, to energetically favourable configurations. The effect disappears when the domains are stabilised in new configurations in the presence of the magnetic field. An analysis of these results is presented in this paper by relating the ultrasonic attenuation coefficient to strain fluctuations, arising here from domain reorientations. The treatment is based on a master equation for the probability matrix whose elements yield the probabilities of transitions between domain configurations, in the presence of both the magnetic field and the stress wave. Arguments for the validity of this master equation, when the oscillatory stress is weak, are given in a longish appendix. The derived results are used to analyse, in qualitative terms, the observed experimental facts. Also, new measurements are suggested which may help interpret the experimental data in a satisfactory manner.

    • Zeeman effect of NQR in 4,6-dichloropyrimidine and 6-chloro 2,4-dimethoxypyrimidine

      V S S Sastry J Ramakrishna

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      Zeeman (35Cl) NQR studies in polycrystalline samples of 4,6-dichloropyrimidine and 6 chloro 2,4 dimethoxypyrimidine show that the asymmetry at the four chemically inequivalent chlorine sites in the former is about 10%, while in the latter (one line) the asymmetry is almost zero. Using a valence-bond picture, C-Cl bonds in 4,6-dichloropyrimidine have been characterised, and the results are also compared with those in a corresponding benzene compound using a simple molecular orbital calculation. The axial symmetry of C-Cl bond in the second compound has been attributed to mesomeric effects.

    • Thermal expansion and a new phase transition in pyroelectric LiKSO4

      D P Sharma

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      Single crystal macroscopic thermal expansion coefficient measurements have been made on uniaxial lithium potassium sulphate crystal both along and normal to the six fold axis, employing Fizeau’s interferometer method. Measurements were made in the range of −120°C to 500°C. The results show that lithium potassium sulphate exhibits two major anomalies in its expansion coefficients around −95°C and 422°C respectively, the one at −95°C has been observed for the first time. The nature of dimensional changes of the crystal at the upper and lower transition points are opposite in nature. The crystal shows considerable lattice anisotropy. Megaw’s tilt concept has been invoked to explain the relative magnitudes of expansion coefficients alonga andc directions. Structural features responsible for the absence of ferroelectricity in this crystal have been pointed out.

    • A universal scaling law for hadronic reactions

      P P Divakaran

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      A master scaling law is proposed for arbitrary distributions in arbitrary hadronic processes of which all experimentally established scaling laws (and a host of others, easily deduced as occasion demands) are special cases.

    • A unified theory of weak interactions

      P P Divakaran

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      A gauge model for the weak interactions of the leptons (ve, e, μ, νμ) and the quarks (qp, qn,,qp′) is presented in which deviations from universality, such as the Cabibbo suppression, are explicitly and spontaneously generated. The gauge group is, to begin with SU(4). There are three quartets of Higgs scalars with suitable vacuum expectation values, sufficient and necessary to give masses to all gauge bosons. It turns out that this gauge group is too ‘large’ and fails to account for many observed symmetries of weak interactions, especially electron-muon symmetry. This symmetry corresponds to a discrete transformationR which is an element of SU(4). To accommodate it, the gauge group is restricted to the subgroup of SU(4) which commutes withR. There are now 7 gauge bosons, 4 charged and 3 neutral. One pair of charged bosons is necessarily heavier than the other pair (denotedW±) and two neutrals are necessarily heavier than the third (W0). The electron and the muon become massive while the neutrinos and the quark fields remain massless.

      The dominant charged weak currents coupling toW± havee-μ universality and Cabibbo universality for both of whichR-symmetry is essential—the Cabibbo angle is a simple function of the vacuum expectation values. The same symmetry ensurese-μ symmetry and the absence of flavour-changing components in the neutral currents. The currents coupling to the heavier gauge bosons break all these symmetries but these bosons can be made arbitrarily heavy and so are relevant only in the domain of ‘ultraweak’ interactions.

      The Cabibbo angleϑc itself is determined by minimising a very general class of Higgs potentials, leading to a numerical valueϑc = ±π/8, | tanϑc | = √2 − 1 (an alternative solution | tanϑc | = (√2+1) is rejected), independent of the parameters and of the precise form of the potential. This is the ‘bare’ϑc; in low energy/momentum transfer processes, this value is renormalised by the structure of the hadrons. A model is given for this renormalisation which reduces the renormalised value of | tanϑc | to about 0.2–0.3 from the bare value 0.41. Recent data on highly inelastic neutrino interactions are shown to be not inconsistent with | tanϑc | = 0.4.

    • Magnetic moments of baryons in broken SU(4)

      C P Singh Ramesh C Verma M P Khanna

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      Assuming that the anomalous magnetic moment interaction has the formaT11 +bT22 +cT44 +sTαα in SU(4), which may arise due to symmetry breaking or some other dynamical effects, we have obtained the magnetic moments and the transition moments of the ordinary and charmed baryons.

    • Analysis of two neutron (proton) transfer reaction data in the Zr-region

      S Haq Y K Gambhir

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      The spectroscopic amplitudes, form factors, angular distributions and total cross-sections for two nucleon transfer reactions in Zr-region in the zero range distorted wave Born approximation are calculated using consistent set of shell model wave functions. A single normalisation factor gives a good fit to all the two neutron transfer reaction data whereas the corresponding fit for the two-proton transfer reaction data is less satisfactory.

    • 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.

    • Scanning electron microscopic studies on different habits of gel grown doped manganese carbonate crystals

      W Franke M A Ittyachen K Mohanan Pillai

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      The effect of impurities on the growth of manganese carbonate crystals has been studied. Stereophotogrammetric analysis showed that all crystal faces have the same Miller indices$$\left\{ {10\bar 11} \right\}$$ and the peanut-shaped forms are twins with twin axis 0001.

    • Self-image (autoidolon) techniques for the realisation of optical computing type operations

      S V Pappu H R Manjunath

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      Self-images of a number of spatially periodic (e.g., gratings) and quasiperiodic (e.g., halftone picture) objects have been systematically studied. These studies indicate that self-imaging techniques could be useful in optical computing type operations. It is also established that the Rayleigh relation in the context of self-imaging is quantitatively in error.

    • Miscibility studies of disc-like molecules

      J Billard B K Sadashiva

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      The total miscibility method is applied to study the recently discovered mesophases of disc-like molecules, benzene-hexa-n-alkanoates. These compounds do not form continuous solid solutions, but are totally miscible in the liquid and mesomorphic states. The virtual mesophase-isotropic transition temperature for the hexanoate compound derived from the miscibility diagram is in excellent accord with that obtained from the previously reported pressure-temperature phase diagram. With simplifying assumptions, it is possible to predict with acceptable reliability the isobaric binary phase diagrams of any two members of the series. The real and virtual mesophase-liquid transition temperatures are linear functions of the molecular weight. On the other hand, a plot of the crystal-liquid transition temperatures versus the molecular weight exhibits a minimum. Total miscibility in the mesomorphic state is not observed for two members of different discogenic series, but the existence of different mesophase types is not proved. Lyotropic mesomorphism for a disc-like mesophase is established.

    • Density dependence of solar emission lines of carbon-like ions

      P K Raju B N Dwivedi

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      Steady state level population of 15 levels of carbon-like ions: NeV, MgVII, SiIX, and SXI have been computed as a function of electron density and temperature taking into account collisional processes and spontaneous radiative ones. Photo-excitation among the ground term levels has also been considered. Knowing the level density, line intensities have been computed as a function of electron density and temperature. This study indicates that line intensity ratios for carbon-like ions can be used as a diagnostic in the determination of these two parameters of the solar plasma. The resulting line fluxes from these ions at earth distance are compared with observation.

    • 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.

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