Volume 18, Issue 6
June 1982, pages 461-532
pp 461-472 June 1982 Solid State Physics
Effect of phonon focussing on thermal conductivity of silicon
Thermal conductivity of a cubic crystal in the boundary scattering regime is calculated, taking into account the difference between the phonon phase and group velocities. Numerical estimates in the case of silicon indicate appreciable anisotropy in conductivity as a result of phonon focussing, its maximum value being about 90% larger than the minimum. The contributions of the individual polarization branches are found to be more strongly dependent on direction than the total conductivity. It is further observed that the angle between the phonon phase and group velocities can be sometimes as large as 10°, 24° and 18° in the case of the longitudinal and the two transverse acoustic branches, respectively.
pp 473-484 June 1982 Plasma Physics
Surface instability of a collisionless semi-infinite current carrying plasma is studied. The semi-infinite plasma bounded by a plane surface is under the influence of a high frequency (hf) field. There are two classes of surface modes. One is a normal extension of zero high frequency field and the other due entirely to the presence ofhf field. As expected, with the increase in thehf field, the growth rates of the surface instabilities decrease. There are regions defined by the electron drift velocityu where the unstable surface and bulk regions overlap. The interesting result is that unlike the bulk plasma, there is a stable region on theu-axis flanked by two unstable regions. The width of this stable region increases with the increase in the field strength.
pp 485-494 June 1982 Nuclear And Particle Physics
Photoelectric cross-sections of light elements and compounds at low photon energies
K S R Sarma K L Narasimham K Premchand S Bhuloka Reddy K Parthasaradhi V Lakshminarayana
Total photon mass attenuation coefficients in C, Al, S, Ti, B_{2}O_{3}, LiF, ZnO, Y_{2}O_{3} and H_{8}O_{2}C_{5} (perspex) are measured on a good geometry set-up using proportional counter, Si(Li) and Ge(Li) detecting systems in the energy region from 6.47 to 52.014 keV employing x-rays and gamma rays from radioactive sources. The deduced photoelectric cross-sections are found to agree with the theoretical values of Storm and Israel, Scofield and semiexperimental values of Veigele wherever available within a few percent. The photo-electric cross-sections in elements, S, Ti and Y at their respectiveK-edges obtained by extrapolation technique agree with the theoretical values of Storm and Israel and Scofield at the respectiveK-edges except in S. In the case of S both the theoretical values atK-edges are found to be underestimations, more in the case of Scofield evaluations.
pp 495-500 June 1982 Nuclear And Particle Physics
Uniqueness of the solution of the Lippmann-Schwinger equation
A few consequences of the uniqueness of the scattering wavefunction in non-break up channel are discussed.
pp 501-509 June 1982 Molecular Physics
Expressions involving vibrational frequencies, Coriolis coupling constants and masses of the atoms of the molecule that are invariant under symmetrical isotopic substitutions are derived for octahedral XY_{6} molecules following the method given by Jagannathan and others. These invariants are used to calculate the force constants, compliance constants and mean amplitudes of vibration of 13 molecules of XY_{6}-type.
pp 511-516 June 1982 Molecular Physics
A relationship between the torsional frequency (v_{10}) and the potential barrier (V_{n}) has been determined forAB_{n} type molecular system havingn-fold symmetry axis. It is found thatv_{10} varies prominently asV_{n}^{1/2},V_{n} andV_{n}^{2} in certain ranges. TheV_{n} value computed fromv_{10} andI*_{r} has been compared with that obtained from other experimental data for someAB_{n} units in different molecular-crystalline systems. Although there is in general a good agreement, in some cases the values differ significantly, perhaps due to the erroneous assignment of torsional mode and/or the large errors in theV_{n} value obtained from other experimental data.
pp 517-523 June 1982 Mathematical And Statistical Physics
A method of solution of the ornstein-zernike equation in one and three dimensions
An elegant analytic method is presented to derive a modified form of the Ornstein-Zernike equation which not only solves the statistical mechanical problem for hard rods and spheres but can be used to find solutions for arbitrary non-vanishing direct correlation functions.
pp 525-532 June 1982 Mathematical And Statistical Physics
Normal form expansion in an algebraic way
It is shown that in an algebraic approach, normal form expansion of operators, bounded or not, but densely defined on Fock space, converge weakly.
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