Volume 7, Issue 4
October 1976, pages 223-290
pp 223-235 October 1976 Liquids
The paper discusses the theory of Couette flow of a nematic liquid crystal. The apparent viscosity, orientation and velocity profiles are computed forp-azoxyanisole as functions of shear rate and magnetic field for symmetric and asymmetric molecular alignments at the boundaries and for different relative radii of the cylinders. For symmetric homeotropic boundary condition an azimuthal field exhibits a threshold analogous to a Freedericksz transition. An expression is also derived for the Freedericksz threshold in the hydrostatic case.
pp 236-244 October 1976 Solids
We present a comparison of high-temperature three-phonon resistivities from the relaxation time methods due to Klemens, Callaway, and Debye, and the variational method due to Leibfried and Schlömann. All the calculations are based upon the same choice of anharmonic crystal potential; and hence the results are suitable for comparison on quantitative basis. We find that the resistivities in increasing order of magnitude come from the methods due to Klemens, Callaway Debye, and Leibfried and Schlömann respectively.
pp 245-249 October 1976 Solids
The measurements of electrical conductivity (σ) from 300 to 1200 K and dielectric constant (ε′) from 4·2 to 1200 K of A-type Nd2O2 pellets are reported here. Electrical conductivity (σ) data can be explained in terms of impurity. The dielectric constant (ε′) increases slowly up to 500 K as is expected for ionic solids. The increase ofε′ becomes much faster above 500 K, which is attributed to space charge polarization of thermally generated charge carriers.
pp 250-254 October 1976 Solids
A series of copper doped sulpho-selenide binary solid solutions, giving electroluminescent emission, right from green to red, has been prepared using ZnS and ZnSe in varying proportions. The behaviour of such polycrystalline samples was studied by usual methods in audio-frequency range. While the hydrogen ion acted as the main donor impurity in the entire series, its comparative study was made with chlorine coactivated samples. As regards the electroluminescent emission, while in the case of hydrogen coactivation, it is the transition from donor levels to the copper level that predominates, Cl-coactivation favoured direct transition from conduction band to same fundamental copper level. On frequency variation while the samples with ZnS-ZnSe composition showed marked peak shifts in their respective emission bands, no such effect could be observed in samples with single base.
pp 255-265 October 1976 Solids
This theoretical study summarizes ionic and electronic processes in AgBr crystals and the influence of its results on photographic process. It deals with the importance of surface generated interstitials which Gurney and Mott left untouched because of the non-availability of sufficient data at that time. The magnitude of various parameters,e.g., mean intra-electron-ion distance in a latent image site, the rate of neutralization of Ag+ ion with trapped electron and capture cross-section for combination of Ag+ ion with the trapped electron, etc. (as desired for understanding the theory of photographic process) are calculated at different temperatures. The results when used in our earlier papers (Singh and Sharma, 1974 and 1975, and Singh 1975) for calculating charged particle track characteristics theoretically were found to give good agreement with the published experimental data (Della Corteet al 1953 and Dyer and Hechman 1967). A model for the mechanism of latent image formation (silver speck) is discussed.
pp 266-276 October 1976 Statistical Physics
Electrical resistance measurements are reported on the binary liquid mixtures CS2 + CH3CN and CS2 + CH3NO2 with special reference to the critical region. Impurity conduction seems to be the dominant mechanism for charge transport. For the liquid mixture filled at the critical composition, the resistance of the system aboveTc follows the relationR=Rc−A(T−Tc)b withb=0·6±0·1. BelowTc the conductivities of the two phases obey a relation σ2−σ1=B(Tc−T)β with β=0·34±0·02, the exponent of the transport coefficient being the same as the exponent of the order parameter, an equilibrium property.
pp 277-286 October 1976 Nuclear And Particle Physics
It is shown that the ΔCh=ΔS decays of a baryon sextuplet, triplet and singlet of SU (3), into meson and baryon, can provide simple tests of the iscspin and SU (3) transformation properties of the ΔCh=ΔS non-leptonic interaction in the Glashow Iliopoulos-Maiani scheme.
pp 287-290 October 1976 Nuclear And Particle Physics
Total cross-section forπ+, using the high energy approximation, have been calculated for12C and32S at various energies around the (3, 3) resonance in the free pion-nucleon system. It is observed that the shift in energy of the position of the maximum in the pion-nucleus cross-section with respect to that in the free pion-nucleon system depends sensitively on the shape of the nuclear density. Using the realistic density it is further found that the shift due to the off-shell behaviour of the pion-nucleon scattering amplitude is very small. This observation is different from that reported in the literature by other authors.
Volume 93 | Issue 5
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