• Volume 34, Issue 3

      March 1990,   pages  173-257

    • Triad of homogeneous and inhomogeneous three particle Lippmann-Schwinger equations

      Suprokash Mukherjee

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      A general distribution theoretic treatment of the convergence of sequences involving wave functions show that the problem of non-uniqueness does not exist for the solutions of the Lippmann-Schwinger equation for multichannel scattering, in the eigenfunction space.

    • Stability of theS matrix pole

      G Rajasekaran S S Vasan

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      We show how the position and residue of theS matrix pole can remain stable under changes in the form of the parametrization of theS matrix elements. We also derive a relation among the shifts in the Breit-Wigner resonance parameters under the same changes and verify the relation numerically for the case of Δ(1232). Despite its stability, the pole does not provide a unique definition of the resonance because of the existence of shadow poles.

    • A relation between X-ray diffraction based liquid structure and packing coefficient

      A Mikusinska-Planner

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      A relation between the liquid structure and the molecules packing coefficient has been derived on the grounds of the experimental results of X-ray diffraction studies. The packing coefficientk was assumed to be a criterion of correctness of the structural models of 2-methyl-1-propanol and 2-methyl-2-propanol based on experimental results. This coefficient was estimated from the specific volumes of moleculesV0, volumes of elementary pseudocellsV and the number of molecules comprised into these pseudocells. The volumesV of pseudocells were estimated from the same X-ray diffraction pattern as was used for determination of the liquid structure. The determined values of the packing coefficient support the chain-like structure of associates of liquid 2-methyl-1-propanol and reject the chain-like structure for liquid 2-methyl-2-propanol.

    • Convexity of internal energy of cubic crystal deformed to orthorhombic structure

      K P Thakur R K Jha O P Thakur

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      A generalized set of strain variablesqrN, has been defined to develop the expression for a generalized set of second order and third-order elastic moduliCrsN andCrstN for a cubic crystal deformed to orthorhombic structure. The HessainCrsNδqrδqs andCrstNδqrδqsδqt (r=1, 2……6; summation convention) are calculated in the new variables and compared withG-strength andS-strength, for both positive and negative loading environment.

      The convexity of the internal energy relative to various choice of strain measure is examined considering up to third degree terms in the internal energy expression. The computational results forbcc iron is presented according to the new moduli. The stable ranges thus obtained for iron under hydrostatic compressive and tensile stresses is found to generate the classical stable range, green-stable range and stretch-stable range as the specific cases. However,bcc iron does not seem to follow any conventional stable ranges under hydrostatic compression, where the present generalized stable range is found satisfactory.

    • Anharmonic effects on lattice resonant modes of impure metallic crystals

      S K Roy N Kundu

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      The effect of lattice anharmonicity on the resonant modes of dilute impurities for Au-Cu, Au-Ag and W-Cr metallic systems are studied from the poles of the double time temperature dependent impure Green’s function of these crystals. The third order force constants used in the present work are derived assuming the systems to obey the Lennard-Jones potential. The inclusion of lattice anharmonicity has been found to increase the resonant frequency which depends upon the mass defect, force constant change parameter and the impurity concentration terms. Some interesting features about the phase shift and the change in width of the vibrational spectrum are reported at room temperature for the isotopic defects and the defects interacting with host atoms. The results are found to be in qualitative agreement with the experiments on the systems considered.

    • The Young-Hoshino pseudopotential for lithium: calculations of structure and thermodynamics

      T Das R N Joarder

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      The recently proposed Young-Hoshino model pseudopotential for lithium has been applied to the calculation of structure and thermodynamics. A slight modification of the model potential is necessary and this produces better core size and long range tail of the interionic effective pair potential than the original model.

    • Melting temperatures of some alkali halide mixed crystal systems

      D B Sirdeshmukh K G Subhadra K A Hussain

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      The melting points in the KCl-KBr, RbCl-RbBr and KBr-RbBr mixed crystal systems have been measured using the microscopic method. In all the three systems, melting points vary nonlinearly with composition, with negative deviations from linearity and maximum deviation at about the equimolar concentration. The observed composition dependence of the melting points is explained qualitatively in terms of the enhanced concentration of point defects and dislocations in mixed crystals.

    • Electrical conductivity, thermoelectric power and figure of merit of doped Bi-Sb tapes produced by melt spinning technique

      T K Dey

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      Temperature dependence of electrical conductivity and thermoelectric power are presented for In and Pb doped Bi + 8.28 at % Sb quenched tapes between 77 and 300K. The results are explained in terms of model for disordered semiconductors. Analysis of our data on electrical conductivity indicates the presence of a temperature independent part and a strongly temperature dependent part. While theT independent part originates from band conduction, theT dependent component could be understood considering the presence of localized states. Thermoelectric figure-of-merit of these tapes are also measured at 300K, which shows a large enhancement (∼40%) over that reported earlier on thin Bi-Sb films. This suggests that doped Bi-Sb quenched tapes may be considered as a candidate for material in producing economic and light weight thermoelectric devices.

    • Design and the operational characteristics of a 16 µ CF4 laser

      P K Gupta V P Singhal N S Shikarkhane S Sinha S Sasikumar U Nundy U K Chatterjee

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      The design and the operational characteristics of a CO2 laser pumped CF4 laser developed at BARC are reported. Output energies of up to 20 mJ have been obtained at 615 cm−1 with an absorbed energy conversion efficiency of 10%.

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