• D P Ahalpara

      Articles written in Pramana – Journal of Physics

    • The deformation producing tendency of (d3/2f7/2) empirical effective interaction

      D P Ahalpara K H Bhatt

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      The effective matrix elements in (d3/2f7/2)2 configuration have been recently defined by Erskineet al. and Sherret al. assuming shell clcsures for S32 and Ca40. We have attempted to verify whether this empirically deduced (d3/2f7/2)2 interaction permits thed3/2 shell to remain closed when nucleons are added to Ca40. It is found that the Erskine interaction gives rise to ground states of thef7/2 shell nuclei in which thed3/2 orbit is completely filled. However that interaction over-binds Ca40. If the centroid of the (d3/2)2 interaction is modified to fit the Ca40 binding energy, the ground states of Cr48 and Fe52 become deformed and thed3/2 orbit is not completely filled.

    • Shell model spectra of92Tc and93Ru

      D P Ahalpara K H Bhatt

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      Shell model calculations for the nuclei91Mo,92Tc and93Ru in the Talmi approach have been done. The ground state binding energies and the excitation spectra agree with experiment.

    • Collective bands of the positive parity states inf7/2 shell nuclei

      D P Ahalpara

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      Collective bands of the positive parity states in odd-A f7/2 shell nuclei are described in the framework of deformed Hartree-Fock theory by projecting states from lowest energy intrinsic states with (d32/−1f72/n+1) one hole configurations. In the calculation empirical (d3/2f7/2)2 effective matrix elements have been used to test the tacit assumptions of the Bansal and French model.

    • Enhanced isospin dependence of the empirical particle-hole effective interaction

      D P Ahalpara K H Bhatt

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      The separation betweenT=0 andT=1 centroids of the empirical effective interaction is fairly large for the (d32/−1f7/2)JT particle-hole interaction as compared to nearby (f7/2)2JT and (d5/2)2JT particle-particle interactions. This interesting feature of the empirical effective interaction is shown to arise as a consequence of renormalization of the effective interaction as one truncates the configuration space from (sd)−1(fp)1 to (d32/−1f7/2) and from (fp)2 and (sd)2 configurations to (f7/2)2 and (d5/2)2 respectively.

    • The collective bands of positive parity states in odd-A (fp) shell nuclei

      D P Ahalpara

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      The low-lying collective bands of positive parity states in (fp) shell nuclei are described in the deformed Hartree-Fock method by projecting states of definite angular momenta from ‘the lowest energy intrinsic states in (sd)−1 (fp)n+1 configurations. The modified Kuo-Brown effective interaction for (fp) shell and modified surface delta interaction (MSDI) for a hole in (sd) shell with a particle in (fp) shell have been used.

      The collective bands of states are in general well reproduced by the effective interactions. The excitation energies of the band head states are however off by about one MeV. The calculated magnetic moments of the band headj=3/2+ states are in reasonable agreement with experiment. Using effective chargesep=1.33e anden=0.64e we get fairly good agreement forE(2) transitions. The hinderedM(1) transition strengths are reproduced to the correct order however they are slightly higher compared to experiment.

    • Model equations from a chaotic time series

      A K Agarwal D P Ahalpara P K Kaw H R Prabhakara A Sen

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      We present a method for obtaining a set of dynamical equations for a system that exhibits a chaotic time series. The time series data is first embedded in an appropriate phase space by using the improved time delay technique of Broomhead and King (1986). Next, assuming that the flow in this space is governed by a set of coupled first order nonlinear ordinary differential equations, a least squares fitting method is employed to derive values for the various unknown coefficients. The ability of the resulting model equations to reproduce global properties like the geometry of the attractor and Lyapunov exponents is demonstrated by treating the numerical solution of a single variable of the Lorenz and Rossler systems in the chaotic regime as the test time series. The equations are found to provide good short term prediction (a few cycle times) but display large errors over large prediction time. The source of this shortcoming and some possible improvements are discussed.

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