• Volume 65, Issue 3

      September 2005,   pages  359-546

    • The incompatibility between local hidden variable theories and the fundamental conservation laws

      C S Unnikrishnan

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      I discuss in detail the result that the Bell’s inequalities derived in the context of local hidden variable theories for discrete quantized observables can be satisfied only if a fundamental conservation law is violated on the average. This result shows that such theories are physically nonviable, and makes the demarcating criteria of the Bell’s inequalities redundant. I show that a unique correlation function can be derived from the validity of the conservation law alone and this coincides with the quantum mechanical correlation function. Thus, any theory with a different correlation function, like any local hidden variable theory, is incompatible with the fundamental conservation laws and space-time symmetries. The results are discussed in the context of two-particle singlet and triplet states, GHZ states, and two-particle double slit interferometry. Some observations on quantum entropy, entanglement, and nonlocality are also discussed.

    • Chiral soliton model vs. pentaquark structure for Θ(1540)

      R Ramachandran

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      The exotic baryon Θ+(1540 MeV) is visualized as an expected (iso) rotational excitation in the chiral soliton model. It is also argued as a pentaquark baryon state in a constituent quark model with strong diquark correlations. I contrast these two points of view; observe the similarities and differences between the two pictures. Collective excitation, the characteristic of chiral soliton model, points toward small mixing of representations in the wake ofSU (3) breaking. In contrast, constituent quark models prefer near ‘ideal’ mixing, similar to ω-φ mixing.

    • A correspondence between IBA-1 and IBA-2 models and electromagnetic transitions in the decay of some erbium isotopes

      Harun Resşit Yazar Ihsan Uluer

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      The interacting boson approximation IBA-1 model space, in which neutron and proton degrees of freedom are not distinguished, can be considered as a subspace of the IBA-2 model space. Using the microscopic background of the IBA-2 model, a correspondence can be established between IBA-1 and IBA-2 model space. Since the space of the IBA-1 model can be regarded as a subspace of the IBA-2 model there is a unique way to ‘Project’ the operators of the IBA-2 model onto those of IBA-1. This projection can be carried out using theF-spin formalism. In the IBA-2 model, the lowest states are indeed fully symmetric, and using the calculations with the help of this projection, we explore the energy levels and the electric quadrupole transition probabilitiesB(E2; {ie393-01}) and γ-ray E2/M1 mixing ratios for selected transitions of162, 164, 166, 168, 170Er. Owing to admixtures of non-fully-symmetric states in IBA-2, we renormalized the parameters (ε) and (κ). This is the first time we show that this projection can be applied to some heavier isotopes and the results obtained for162, 164, 166, 168, 170Er isotopes are reasonably in good agreement with the previous experimental values.

    • Laser frequency stabilization and large detuning by Doppler-free dichroic lock technique: Application to atom cooling

      V B Tiwari S R Mishra H S Rawat S Singh S P Ram S C Mehendale

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      We present results of a study of frequency stabilization of a diode laser (λ = 780 nm) using the Doppler-free dichroic lock (DFDL) technique and its use for laser cooling of atoms. Quantitative measurements of frequency stability were performed and the Allan variance was found to be 6.9 × 1011 for an averaging time of 10 s. The frequency-stabilized diode laser was used to obtain the trapping beams for a magneto-optic trap (MOT) for Rb atoms. Using the DFDL technique, the laser frequency could be locked over a wide range and this enabled measurement of detuning dependence of the number and temperature of cold atoms using a relatively simple experimental set-up.

    • Scattering of light by a periodic structure in the presence of randomness IV. Limit of detection by curve fitting

      S Chatterjee V C Vani

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      In the context of scattering of light, we determine the extent of randomness within which a hidden periodic part can still be detected. The detection is carried out using a technique called the extended matched filtering, first introduced by us in this context. The earlier prediction, before our technique was introduced, had placed the limit of detection, by intensity measurements alone, at (r0/Λ) ∼ 0.33, where r0 is the coherence length of light for scattering by the rough part of the surface and Λ is the wavelength of the periodic part of the surface. In our earlier works we have shown that by intensity measurements alone, the limit of detection can be taken to a much lower value of (r0/Λ), when the extended matched filtering method is employed. In this paper we follow the extended matched filtering method, and try to reach the lowest possible value of detection in (r0/Λ) by fitting the data to a polynomial. It is concluded by our numerical work that the lowest possible limit for detection from intensity measurements alone is (r0/Λ) = 0.11.

    • Induced focusing and conversion of a Gaussian beam into an elliptic Gaussian beam

      Manoj Mishra Swapan Konar

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      We have presented an investigation of the induced focusing in Kerr media of two laser beams, the pump beam and the probe beam, which could be either Gaussian or elliptic Gaussian or a combination of the two. We have used variational formalism to derive relevant beam-width equations. Among several important findings, the finding that a very week probe beam can be guided and focused when power of both beams are well below their individual threshold for self-focusing, is a noteworthy one. It has been found that induced focusing is not possible for laser beams of any wavelength and beam radius. In case both beams are elliptic Gaussian, we have shown that when power of both beams is above a certain threshold value then the effective radius of both beams collapses and collapse distance depends on power. Moreover, it has been found that induced focusing can be employed to convert a circular Gaussian beam into an elliptic Gaussian beam.

    • The shape of an axisymmetric bubble in uniform motion

      P N Shankar

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      We consider in a frame fixed to a bubble translating with steady speedU, the inviscid, axisymmetric, irrotational motion of the liquid past it. If all speeds are normalized byU and lengths by {ie437-1}, whereT is the surface tension of the liquid-bubble interface, it can be shown that the unknown bubble shape and field depend on a single parameter {ie437-2} alone, where the pressures are the ones in the bubble and far away respectively. WhenΓ is very large the bubble is almost spherical in shape while for Γ<- Γ* ≈ -0.315, bubbles whose exteriors are simply connected do not exist. We solve the non-linear, free boundary problem for the whole range Γ* < Γ < ∞ by the use of an analytical representation for the bubble shape, a surface singularity method to compute potential flows and a generalized Newton’s method to continue inΓ. Apart from providing explicit representations for bubble shapes and detailed numerical values for the bubble parameters, we show that the classical linearized solution for largeΓ is a very good approximation, surprisingly, to as low values of Γ as 2. We also show that Miksiset al [1] is inaccurate over the whole range and in serious error for large and smallΓ. These have been corrected.

    • Molecular dynamics study of two-and three-dimensional classical fluids using double Yukawa potential

      Y Pathania P K Ahluwalia

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      We have carried out a molecular dynamics simulation of two- and three-dimensional double Yukawa fluids near the triple point. We have compared some of the static and dynamic correlation functions with those of Lennard—Jones, when parameters occurring in double Yukawa potential are chosen to fit Lennard-Jones potential. The results are in good agreement. However, when repulsive and attractive parameters occurring in double Yukawa potential are varied, we found distinct differences in static and dynamic correlation functions. We have also compared the two-dimensional correlation functions with those of three-dimensional to study the effect of dimensionality, near the triple point region.

    • Material parameters for thermoelectric performance

      M N Tripathi C M Bhandari

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      The thermoelectric performance of a thermoelement is ideally defined in terms of the so-called figure-of-meritZ = α2σ/λ, where α,σ and λ refer respectively to the Seebeck coefficient, electrical conductivity and thermal conductivity of the thermoelement material. However, there are other parameters which are fairly good indicators of a material’s thermoelectric ‘worth’. A simple yet useful performance indicator is possible with only two parameters — energy gap and lattice thermal conductivity. This indicator can outline all potentially useful thermoelectric materials. Thermal conductivity in place of lattice thermal conductivity can provide some additional information about the temperature range of operation. Yet another performance indicator may be based on the slope of α vs. ln σ plots. α plotted against ln σ shows a linear relationship in a simplified model, but shows a variation with temperature and carrier concentration. Assuming that such a relationship is true for a narrow range of temperature and carrier concentration, one can calculate the slope m of α vs. ln σ plots against temperature and carrier concentrations. A comparison between the variation ofZT and slopem suggests that such plots may be useful to identify potential thermoelectric materials.

    • Ultrasonic studies of aluminium-substituted Bi(Pb)-2223 superconductors

      M B Solunke P U Sharma M P Pandya V K Lakhani K B Modi P Venugopal Reddy S S Shah

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      The compositional dependence of elastic properties of Al3+-substituted Bi(Pb)-2223 superconducting system with the general formula Bi1.7−x AlxPb0.3Sr2Ca2Cu3 Oy(x = 0.0, 0.1, 0.2 and 0.3) have been studied by means of ultrasonic pulse transmission (UPT) technique at 1 MHz (300 K). The elastic moduli of the specimens are computed and corrected to zero porosity. The observed variation of elastic constants with aluminium substitution has been explained on the basis of the strength of interatomic bonding. The applicability of heterogeneous metal mixture rule for estimating elastic constants and transition temperature has been tested.

    • Negative chemical pressure effects induced by Y substitution for Ca on the ‘exotic’ magnetic behavior of the spin-chain compound, Ca3Co2O6

      S Rayaprol E V Sampathkumaran

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      The magnetic behavior of a solid solution, Ca3 x Yx CO2 O6, based on the ‘exotic’ spin-chain compound, Ca3Co2O6, crystallizing in K4CdCl6-derived rhombohedral structure is investigated. Among the compositions investigated(x = 0.0, 0.3, 0.5, 0.75 and 1.0), single-phase formation persists up tox = 0.75, with the elongation of the c-axis. The present investigations reveal that the temperature at which the ‘so-called’ ‘partially disordered antiferromagnetic structure’ sets in (which occurs at 24 K for the parent compound,x = 0.0) undergoes gradual reduction with the substitution of Y for Ca, attaining the value of about 2.2 K for the nominalx = 1.0. The trend observed in this characteristic temperature is opposite to that reported under external pressure, thereby establishing that Y substitution exerts negative chemical pressure. Anomalous steps observed in the isothermal magnetization at very low temperatures (around 2 K) forx = 0.0, which have been proposed to arise from ‘quantum tunneling effects’ are found to vanish by a small substitution (x = 0.3) of Y for Ca. Systematics in AC and DC magnetic susceptibility behavior with Y substitution for Ca have also been probed. We believe that the present results involving the expansion of chain length without disrupting the magnetic chain may be useful to the overall understanding of the novel magnetism of the parent compound.

    • Theoretical study of two-element array of equilateral triangular patch microstrip antenna on ferrite substrate

      K K Verma K R Soni

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      The radiation characteristics of a two-element array of equilateral triangular patch microstrip antenna on a ferrite substrate are studied theoretically by considering the presence of bias magnetic field in the direction of propagation of electromagnetic waves. It is found that the natural modes of propagation in the direction of magnetic field are left- and right-circularly polarized waves and these modes have different propagation constants. In loss-less isotropic warm plasma, this array antenna geometry excites both electromagnetic (EM) and electroacoustic plasma (P) waves in addition to a nonradiating surface wave. In the absence of an external magnetic field, the EM- and P-waves can be decoupled into two independent modes, the electroacoustic mode is longitudinal while the electromagnetic mode is transverse. The far-zone EM-mode and P-mode radiation fields are derived using vector wave function techniques and pattern multiplication approaches. The results are obtained in both plasma medium and free space. Some important antenna parameters such as radiation conductance, directivity and quality factor are plotted for different values of plasma-to-source frequency.

    • Parity and the spin—statistics connection

      J A Morgan

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      A simple demonstration of the spin—statistics connection for general causal fields is obtained by using the parity operation to exchange spatial coordinates in the scalar product of a locally commuting field operator, evaluated at position x, with the same field operator evaluated at − x, at equal times.

    • Two-neutrino double β decay of96Zr to excited 2+ state of96Mo

      J Singh R Chandra P K Raina P K Rath

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      The two-neutrino double beta decay of96Zr isotope for 0+ → 2+ transition has been studied in the PHFB model. In our earlier work, the reliability of the intrinsic wave functions of96Zr and96Mo isotopes has been established by obtaining an overall agreement between a number of theoretically calculated spectroscopic properties as well as half-lives of 2vββ decay for 0+ → 0+ transition and the available experimental data. In the present work, the half-life of 2vββ decay for 0+ ar 2+ transition T12/2v(0+2+) has been calculated using the same set of intrinsic wave functions.

    • Optical model potential of 800 MeV/c K+ meson for12C and40Ca by the method of inversion

      I Ahmad M A Abdulmomen Ghada A Hamra

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      The elastic scattering differential cross-sections of 800 MeV/c K+ mesons from12C and Ca have been analyzed using the Ericson’s parametrization for the phase shift. It is found that the parameter values obtained by our analysis are significantly different from those obtained from the closed expression for K+-nucleus amplitude derived by the strong absorption approximation. Next, using the phase shift obtained from the present analysis we calculate the K+ optical model potentials for12C and40Ca by the method of inversion. The calculated potentials are compared with the recently determined phenomenological ones.

    • Studies of linear correlation factor of dielectric polarization and excess dipolar free energies of amides in apolar solvents

      M Malathi R Sabesan S Krishn An

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      The Kirkwood-Frohlich correlation factor (g), Eyring’s parametersG and G* and the dipolar excess free energies of dilute solutions of formamide, acetamide,N-methyl acetamide,N,N-dimethyl formamide andN,N-dimethyl acetamide in 1,4-dioxan/benzene were obtained from a measurement of their static dielectric permittivities at 308 K. The fluid structure of these amides is discussed. Both in formamide and acetamide a dimeric linear chain with the individual dipoles more or less parallely oriented is preferred. InN-methyl acetamide, the antiparallel orientation of dipoles at lower concentrations turns into a parallel orientation with increase of concentration. In tertiary amides, with increase of concentration, parallel orientation of dipoles with global value ofg tending to unity is observed. The dipolar excess free energy of mixing in a given solvent is of the order primary amide > secondary amide > tertiary amide.

    • A comparative study of non-linearity parameter for binary liquid mixtures

      J D Pandey Ranjan Dey Vinay Sanguri Jyotsna Chhabra Tanuja Nautiyal

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      The present investigation comprises of theoretical evaluation of acoustic non-linearity parameter,B/A for equimolar binary mixtures, viz. chlorobenzene or 1-chloronaphthalene with a series of normal alkanes (n-Cn,n = 6, 8, 10, 12, 14, 16), and with a series of highly branched alkanes (br-Cn,n = 6, 8, 12, 16), viz. 2,2-dimethylbutane (br-C6), 2,2,4-trimethylpentane (br-C8), 2,2,4,6,6-pentamethylheptane (br-C12) and 2,2,4,4,6,8,8-heptamethylnonane (br-C16). Tong and Dong method, thermoacoustical method, Hartmann relation and Ballou relation have been employed to evaluateB/A. A comparative study ofB/A values obtained from the aforementioned methods has been made. The results are discussed on the basis of structural orientations of normal and branched alkanes.

    • Laser-induced down-conversion parameters of singly and doubly doped ZnS phosphors

      H S Bhatti Rajesh Sharma N K Verma

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      Singly and doubly doped ZnS phosphors have been synthesized using flux method. Laser-induced photoluminescence has been observed in ZnS-doped phosphors when these were excited by the pulsed UV N2 laser radiation. Due to down-conversion phenomenon, fast phosphorescence emission in the visible region is recorded in milliseconds time domain for ZnS:Mn while in the case of ZnS:Mn:killer (Fe, Co and Ni) the lifetime reduces to microseconds time domain. Experimentally observed luminescent emission parameters of excited states such as, lifetimes, trap-depth values and decay constants have been reported here at room temperature. The high efficiency and fast recombination times observed in doped ZnS phosphors make these materials very attractive for optoelectronic applications.

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