• Volume 43, Issue 5

      November 1994,   pages  353-409

    • Sound velocity in binary liquid mixtures and the statistical mechanical theories

      J D Pandey Shikha A K Shukla Anil K Singh

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      Sound velocity in three binary liquid mixtures benzene+cyclohexane (I), cyclohexane+carbontetrachloride (II) and benzene+carbontetrachloride (III) has been measured. Significant structure and Flory — Patterson theories have been employed to evaluate ultrasonic velocity in the systems. The values are in good agreement with the experimental ones. A comparative study of significant structure theory and Flory-Patterson Theory has been made. Both the theories give satisfactory results for the three liquid mixtures.

    • Isothermal compressibility and sound velocity of binary liquid systems: Application of hard sphere models

      J D Pandey P Jain V Vyas

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      Sound velocity and density were measured in six binary liquid mixtures namely,n-heptane+toluene (I);n-heptane+n-hexane (II); toluene+n-hexane (III); cyclohexane+n-heptane (IV); cyclohexane+n-hexane (V), andn-decane+n-hexane (VI) at 298.15 K. The experimental isothermal compressibility has been evaluated from measured values of density and sound velocity. The isothermal compressibility of these mixtures has been calculated theoretically using different models for the hard sphere equation of state and also using Flory’s statistical theory. The computed values of isothermal compressibility were also compared with the experimentally evaluated values. A satisfactory agreement has been observed.

    • Transport coefficients of quasicrystals

      K Rama Mohana Rao P Hemagiri Rao

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      The transport coefficients for the nine point groups$$5(C_5 ), \bar 5(S_{10} ), \overline {10} (C_{5h} ), \overline {10} m2(D_{5h} ), 52(D_5 ), 5m(C_{5\upsilon } ), \bar 5 2m(D_{5d} ), 235(I), 2/m \bar 3 \bar 5(I_h )$$ —which represent the symmetry groups of the quasicrystals in two and three dimensions—have been evaluated and tabulated in this work, employing group-theoretical methods.

    • Phonons and periodons in IV–VI semiconductor superlattices

      Nabonita D Chowdhury Sankar P Sanyal

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      We have calculated the phonon and periodon dispersion relations in IV–VI semi-conducting bulk PbTe and SnTe and their superlattice structure. The model used here is a one-dimensional lattice which includes harmonic interactions up to second neighbours as well as on-site nonlinear electron-ion interactions at the anion site. We calculate the phonon and periodon dispersion relations in bulk and PbTe-SnTe superlattice for the transverse optic and acoustic modes using the transfer matrix method. Our analysis has predicted correct nature of the folding of acoustic and confinement of optical phonons at various frequency intervals corresponding to pass and stop bands of the superlattices.

    • Electronic contribution to electric field gradient in β-gallium

      B K Acharya N C Mohapatra

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      Electronic contribution to electric field gradient (EFG) inβ-Ga has been calculated for the first time using the band wave functions. The results show that the magnitudes of the quadrupole resonance frequency and the net EFG agree with experiment to within 7% and 2% respectively.

    • Application of laser beam deflection technique to study the diffusion process in electrolyte solutions

      Achamma Kurian C V Bindhu S S Harilal Riju C Issac V P N Nampoori C P G Vallabhan

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      A simple method based on laser beam deflection to study the variation of diffusion coefficient with concentration in a solution is presented. When a properly fanned out laser beam is passed through a rectangular cell filled with solution having concentration gradient, the emergent beam traces out a curved pattern on a screen. By taking measurements on the pattern at different concentrations, the variation of diffusion coefficient with concentration can be determined.

    • Electric field gradient in transition metal: Scandium

      B B Panigrahi N C Mohapatra

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      Corrections to results of electric field gradient (EFG) already published [Pramana — J. Phys.41, 443 (1993)] are reported. The corrected net EFG is:q=−8.01×1013 esu/cm3 against the published valueq=16.06×1013 esu/cm3. The present result agrees reasonably well with the experimental result, |qexpt|=13×1013 esu/cm3.

      Recently, a computational error is detected, which modifies the results of EFG, we have already published [1]. The error was committed mainly in the part that evaluated thep-p contribution [1] to EFG by the conduction electrons. The corrected results are summarized in table 1 which must replace the table 1 of the published work [1].

      In addition, the lattice parameters as well as the temperature were also misquoted in the previous work [1]. The right parameters are:a=6.25311 au andc=9.96509 au. The temperature at which EFG’s are calculated is 293 K instead of 11 K as reported before [1].

      The discussions and conclusions made in the published work [1] remain almost unchanged except that they now refer to the corrected numbers. Although the corrected net EFG suffers a sign reversal from the one already published [1], the agreement with experiment is still considered reasonably good because the sign of experimental EFG is not determined. The computational error however does not affect the introduction and theory section of the published work [1].

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

      R V Gopala Rao R Venkatesh

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