• Volume 17, Issue 4

      October 1981,   pages  297-368

    • Electrical conductivity and stimulated thermocurrent studies in dicalcium lead propionate single crystal

      V Madhusudan S G Sathyanarayan G Sivarama Sastry

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      Electrical conductivity and stimulated thermocurrent (stc) studies are carried out in dicalcium lead propionate (dlp) in pure, Cu2+, Fe3+ and acetate doped single crystals over a temperature range of 303° to 503° K. Conductivity measurements on pure and doped single crystals ofdlp indicate that both propionate anions and metallic cations are responsible for the transition occurring at 333°K. Thermoelectric power measurements from 340° to 500°K indlp (pure) indicate that the transport charge carriers are electrons. A model for the conduction mechanism is proposed on the basis of hopping ofπ or resonating electrons of carboxyl groups through tunnel paths involving metal ions (Pb2+ and Ca2+). From activation energies estimated from conductivity andstc measurements, thestc peak indlp (Fe3+) occurring at 513°K is attributed to impurity vacancy jump mechanism.

    • Elastic scattering of electrons by helium atoms in high energy higher order Born approximation

      N S Rao H S Desai

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      The differential cross-sections forē-helium elastic scattering are calculated by using Yateshigh-energy higher order Born approximations, through 0 (KiEmphasis>−2) of the incident electron momentum, and comparisons have been made with the recent theoretical and experimental results.

    • Model for vibrational relaxation: Pure-dephasing and depopulation

      A K Sood S Dattagupta

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      The three dominant mechanisms giving major contributions to vibrational relaxation in molecular systems are (a) pure dephasing, (b) depopulation (or energy relaxation), and (c) resonant transfer. Here (c) is not considered but the effects due to thesimultaneous occurrence of (a) and (b) are treated within a stochastic model. In dealing with (a), the vibrational frequency is assumed to undergo random uncorrelated ‘jump’, due to fluctuations in the environment of the active molecule between a continuous set of values. The ensuing results are somewhat different from those of the commonly used Kubo model of vibrational dephasing, especially at long times and appear to be better suited in interpreting certain experimental data. The model is next extended to include the simultaneous occurrence of (b). The calculation leads to two important conclusions: (i) the lineshape is not just the convolution of those due to (a) and (b), and (ii) the lineshape is asymmetric, if the intermolecular interactions are not isotropic.

    • The application ofclean to crystallographic problems

      Ramesh Narayan

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      It is suggested that the radio astronomical technique of image reconstruction calledclean could be profitably used in crystallography to improve sharpened Patterson maps andE-maps. The method is here generalized to handle the symmetries which arise in crystallographic maps. Simulations on model one and two dimensional structure are presented to illustrate the power of the method.

    • $$^3 \overrightarrow {He} $$ (γ, π°)$$^3 \overrightarrow {He} $$ as the nuclear probeas the nuclear probe

      G Ramachandran R S Keshavamurthy K Venkatesh

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      The state of polarization of the recoil nucleus inγ+3He→π°+3He as well as the asymmetry in the differential cross-section when the initial3He is polarized are studied together with the differential cross-section taking into consideration theS, S′ andD-state admixtures in the nuclear wavefunctions. In view of the considerable spin dependence in the photoproduction amplitudes these observables are found to be quite sensitive to the small admixtures ofS′ andD-states in the nuclear wave-functions.

    • Convergent polynomial expansion, scaling of differential cross-section and computation of scaling functions for elastic diffraction scattering processes

      N Giri M K Parida

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      Existing data on the differential cross-section ratio at high energies for pp,$$\bar p$$p, π±p andK±p scatering have been fitted by the proposed convergent polynomial expansion to determine the unknown coefficients in the scaling function. It is found that the data are very well represented within and somewhat outside the peak regions by only four or five terms in the proposed series in terms of Laguerre polynomials.

    • Order-order transition in a macromolecular system—poly-L-proline I and II

      R C Agnihotri C Mehrotra V D Gupta Vandana Srivastava

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      Ising model formalism developed for order-disorder transition in poly-peptides has been modified for the study of order-order transition in a macromolecular system. A two-state theory is developed and applied to poly-L-proline I and II. Various transition curves for different chain lengths are obtained as a function of solvent composition. Transition curves and crossing point for a solvent system are in excellent agreement with the experimental data on poly-L-proline.

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