Volume 30, Issue 5
May 1988, pages 1-442
pp 1- May 1988 Rapid Communications
Indications of superconductivity in the 200–300K range in the Bi-Ca-Sr-Cu-O system
C N R Rao R A Mohan Ram L Ganapathi R Vijayaraghavan
Some of the Bi-Ca-Sr-Cu-O compositions show indications of onset of superconductivity in the 200–300 K region, possibly due to the intergrowth of different layered sequences.
pp 371-374 May 1988 General Relativity
Circular orbits of an electron around a proton in Schwarzschild geometry
The energy of an electron in circular orbits around a proton in Schwarzschild geometry has been investigated and is found to be red shifted. The electrical dipole moment of such a system is also estimated.
pp 375-385 May 1988 Nuclear Physics
Non-statistical structures in^{12}C(^{15}N,^{4}He)^{23}Na reaction
The data on theϑ_{lab}=7° excitation functions of^{12}C(^{15}N,^{4}He)^{23}Na reaction betweenE_{cm}=9.42 and 17.33 MeV for 28 states upto an excitation energy of 8.940 MeV in^{23}Na have been subjected to statistical analysis. In addition to statistical fluctuations, the results of the analysis indicate the existence of non-statistical structures atE_{cm}=10.66, 10.93, 11.38, 12.62, 13.16, 15.32 and 16.18 MeV.
pp 387-405 May 1988 Molecular Physics
The minimax technique in relativistic Hartree-Fock calculations
Using the set of trial spinors$$\left\{ {N_i \left( {_{\hat \Omega _i u_i }^{u_i } } \right), i = 1, \ldots , N} \right\}$$ and the Dirac-Coulomb Hamiltonian (H_{DC}) we discuss the role of the minimax theorem in relativistic Hartree-Fock calculations. In principle, the minimax theorem guarantees the occurrence of an upper bound. We also consider a scaling of the functionsu_{i} and discuss the condition to derive the relativistic hypervirial theorem; the variational procedure represented by the condition serves as an example of the minimax technique. Single zeta calculations onH_{2}^{+},H_{2} and He are analysed. The effect of enlarging the basis is investigated for the He atom. The “upper bound” obtained by usingcoherent basis spinors differs from the result of the (random) linear variation using the kinetically balanced basis set by an amount which is at most of orderc^{−4}. Use of thecoherent basis set is advocated.
pp 407-417 May 1988 Condensed Matter Physics
Solid solutions of CsCl-Br in different molal concentrations were prepared and X-ray diffractograms taken. The integrated intensities of the Bragg peaks have been estimated and structure factors were obtained. The crystal lattice in each of these solid solution samples is made up of a random distribution of Cs^{+}, Cl^{−} and Br^{−} ions depending upon the molal concentration. A pseudo-atom model has been proposed in which the Cs^{+} ions occupy (000) position and a pseudo-atom occupies (1/2 1/2 1/2) position. The presence of incoherence scattering in these solid solutions has been considered by applying the necessary correction to the atomic scattering factors. The integrated intensities have been analysed and the temperature variation of the Debye-Waller factors of the metal (Cs^{+}) ion and the pseudo ion (CB^{−}) have been estimated.
pp 419-421 May 1988 Condensed Matter Physics
Specific heat of YBa_{2}Cu_{3}O_{7−x} from 4.2 to 60 K
N Sankar V Sankaranarayanan R Srinivasan G Rangarajan G V Subba Rao
The specific heat of superconducting oxide compound, YBa_{2}Cu_{3}O_{7 −x}, is studied using a quasi-adiabatic calorimeter from 4.2 to 60 K. The analysis of the specific heat data below 15 K gives a value of 17 mJ/mole K^{2} for the electronic heat capacity coefficient. The value ofθ_{D}(0) is determined to be 397±8 K. The variation ofθ_{D} with temperature was calculated in the temperature range 4.2 to 60 K.
pp 423-428 May 1988 Condensed Matter Physics
Lattice dynamics of MgSiO_{3} perovskite
Narayani Choudhury S L Chaplot K R Rao Subrata Ghose
A lattice dynamical study of the geophysically important mineral MgSiO_{3} in its orthorhombic perovskite phase, with space group Pnma (D_{2h}^{16}) has been carried out using a rigid ion model, with the potential consisting of Coulombic and short-ranged interactions. With the help of program DISPR, the ionic charges and radii were optimized using the equilibrium conditions. The resulting potential model is employed to predict the elastic constants and the phonon dispersion relations. The computed long wavelength optic modes are in good agreement with the corresponding experimental Raman and infrared active bands. The phonon density of states has been obtained and is used to evaluate the specific heat, the mean square displacements and thermal parameters of atoms.
pp 429-433 May 1988 Condensed Matter Physics
Threshold pump strain for parametric amplification inn-indium antimonide
Phenomenological approach has been used to determine the threshold pump strain by assuming that at this strain the pump generates an electric field for which the drift velocity of the carriers equals the sound velocity. Numerical values obtained forn-InSb have been compared with similar studies which are based on Boltzmann transport approach.
pp 435-442 May 1988 Condensed Matter Physics
Mass enhancement factor for Pd and Pt
We report calculations of the mass enhancement factors for Pd and Pt by comparing the physical quantities using the interpolation scheme band structure, with the corresponding experimental data. Our results are compared with other theoretical calculations.
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