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51.
Ajoy K. Ghatak 《Zeitschrift für Physik A Hadrons and Nuclei》1969,226(5):454-462
The response of a “Lorentz gas” to a pulsed a.c. electric field and its relaxation after the cessation of this field has been studied by solving the Boltzmann's transfer equation. Explicit expressions for the electron distribution function and the current density are obtained under the assumption that the collision frequency is independent of the electron velocity. 相似文献
52.
We study the behavior of a naturally straight highly extensible elastic filament subjected to large extensional and twisting strains. We find that two different phases can coexist for a range of parameter values: the plectoneme and the solenoid. A simple theory based on a neo-Hookean model for the material of the filament and accounting for the slender geometry suffices to explain these observations, and leads to a phase diagram that is consistent with observations. Extension and relaxation experiments on these phases show the presence of large hysteresis loops and sawtooth-like force-displacement curves which are different for the plectoneme and the solenoid. 相似文献
53.
Enakshi Khular Arun Kumar Anurag Sharma I. C. Goyal A. K. Ghatak 《Optical and Quantum Electronics》1981,13(2):109-115
The refractive index profile of buried graded-index planar optical waveguides fabricated by ion migration can be described by a buried secant hyperbolic function. Using such a profile, we have obtained the exact propagation characteristics for such buried optical waveguides. We have also shown that profiles which deviate slightly from the above profile can be treated as perturbations and a first-order perturbation correction gives very accurate results. 相似文献
54.
Summary An attempt is made to study effective electron mass in quantum well wires of ternary chalcopyrite semiconductors by formulating
a new 1D dispersion relation, within the framework of thek·p formalism considering the anisotropies in the band parameters. It is found, taking quantum well wires ofn-CdGeAs2 as an example, that the effective Fermi level mass depends on the subband index due to the combined influence of crystal-field
splitting parameter and the anisotropic spinorbit splitting parameters, respectively. The masses increase with increasing
carrier degeneracy and decreasing film thickness, respectively. In addition, the well-known results for the corresponding
parabolic energy bands have been derived as special cases of the generalized formulations. 相似文献
55.
P.N. Chakrabortty R. DasguptaS.K. Dasgupta S.R. Ghosh U.R. Ghatak 《Tetrahedron》1972,28(17):4653-4665
Two new synthetic routes to a number of tetracyclic intermediates, for the total synthesis of some diterpenoids incorporating the bicyclo[3.2.1]octane moiety, are described. The syntheses of the bicyclo[3,2,1]octane derivatives begin with preparation of the hydroaromatic γ,δ-unsaturated acids 6, 15 and 17, and proceed via the α-diazomethyl ketones to the corresponding pentacyclic ketones 20, 24 and 26 by an intramolecular carbenoid insertion reaction, followed by a regiospecific acid-catalysed cleavage of the aromatic conjugated cyclopropane bond to the respective unsaturated ketones 27, 29 and 30. The second route to these unsaturated ketones involves a single step boron trifluoride etherate catalysed intramolecular alkylation in the corresponding α-diazomethyl ketones. The tetracyclic ketones 31, 34 and 35 were obtained in quantitative yields by a regiostereospecific hydrogenolytic cleavage of the aromatic conjugated cyclopropane bond in the respective pentacyclic precursors with PdC in ethanol. Under the same conditions, reduction of the styrenoid bond in the ketones 29 and 30 proceeds stereospecifically leading to 34 and 35 respectively, whereas the unsaturated ketone 27 gave a mixture of epimeric ketones 31 and 32 in a ratio of 69:31. 相似文献
56.
57.
Sobhendu K. Ghatak 《Physics letters. A》1977,62(3):168-170
A pseudospin with S=1 model for valence transition in rare-earth compounds is proposed. The saturation behaviour of the magnetic susceptibility at low temperature is shown to be the consequence of tunnelling between the two pertinent configurations of the rare-earth ion. 相似文献
58.
59.
The effect of structural disorder on the properties of a Heisenberg ferromagnet is considered within the Bethe-Peierls-Weiss approximation. It is concluded that the details of the structural disorder, and its effect on the exchange interactions between localized spins, determine the direction of change in the Curie temperature with respect to the crystalline case. 相似文献
60.
A cost-effective and eco-friendly synthesis of 2-aryl-1-arylmethyl-1H-benzimidazoles has been developed through the condensation of different aldehydes with o-phenylenediamine using alumina-sulfuric acid as a recyclable heterogeneous solid acid catalyst. Morphological properties of the catalyst have been investigated. Effect of different solvents and comparison of alumina-sulfuric acid with different acid catalysts have also been studied. A plausible mechanistic pathway has been proposed on the basis of the isotope labelling experiments where catalytic behaviour of alumina-sulfuric acid has been explained. 相似文献