• Volume 4, Issue 2

      February 1975,   pages  53-103

    • Residue-squaring iterative diagonalization method for perturbation problems

      P M Mathews

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      We present a new method for the evaluation of the change in eigenvalues due to a perturbation of strength λ. It is a fast converging iterative method which, at thenth step, gives results accurate to order (2n+1−1) in λ. Unlike the Rayleigh-Schrödinger perturbation theory in quantum mechanics, which becomes prohibitively cumbersome when carried to higher orders, the present method involves a routine which remains stralghtforward at all stages.

    • Partial diagonality of stress trace

      Probir Roy

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      The trace of the stress energy tensor is shown to be diagonal between two states whose total four-momenta are equal. Additional comments are made on certain matrix-elements of the time-derivative of the dilation charge.

    • Phenomenology of S and P pion-pion partial wave amplitudes

      B B Deo J K Mohapatra

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      A scheme of parametrization ofππ S andP partial wave amplitudes is proposed. Analytic, crossing and unitarity properties are rigorously satisfied. The analyticity property is made explicit by the use of a conformally mapped variable. Our expressions fit excellently with both phase shift and inelastic curves for centre of mass energy up to 1·4 GeV.

    • Scission-point distributions in LRA fission

      B Krishnarajulu G K Mehta

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      Trajectory calculations were performed using the three-point-charge model. The input parameters took values distributed over a wide range. Using experi mental distributions, each trajectory was assigned a ‘weight’; and the trajectories and their statistical ‘weights’ were used in obtaining initial distributions which in turn reproduced other experimental distributions, such as the angular distribution ofα-particles, very well. Some information about the initial distributions has been obtained. The effect of the anticorrelation, between the finalα and fragment energies, on the initial distributions has been examined.

    • The crystal structure of bis-(L-threonine) copper(II).H2O

      V Amirthalingam K V Muralidharan

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      The crystal structure of bis-(L-threonine) copper (II).H2O, Cu (C4H8NO3)2.H2O has been determined by heavy atom and Fourier methods and refined by least-squares using visually estimated three-dimensional x-ray data of 893 reflections. The blue crystals are monoclinic, space groupP21 withα=11·02,b=4·90,c=11·16Å andβ=93·5°,Z=2. The finalR is 0·10. Coordination of copper is distorted square pyramidal with ligands intrans configuration. The conformation of one of the aminoacid ligand is identical with Ls-Threonine while the other has a conformation with torsional angleχ1, 2=−74(1)°.

    • Effect of variations in peptide parameters and charges on the unperturbed dimensions of polypeptide chains

      A R Srinivasan V S R Rao

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      The net charges on various atoms of poly (l-alanine), polyglycine, poly (N-methyl-l-alanine) and poly (N-methylglycine) were computed using the MOLCAO method of Del Re forσ charges and the Hückel MO method forπ charges. The characteristic ratiosC were computed for all the above polypeptide chains, with different sets of parameters for the peptide unit. The calculated values ofC are found to be very sensitive to the input peptide geometry. The calculated value of 2·2 forC of poly (N-methylglycine) obtained with set-3 parameters (derived from a crystal structure containing prolyl residue) is closer to the experimental value of 1·8±0·2 than the value of 2·7 obtained with set 1 (Pauling-Corey parameters), suggesting that the peptide parameters of N-substituted aminoacids have close similarity to set 3 rather than to set 1. The calculated values ofC of the polypeptide chains show no correlation with the number of allowed conformations, suggesting that the ratio ofC/Cf need not always provide information about the flexibility or freedom of rotation of chain units.

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