• Volume 41, Issue 4

      October 1993,   pages  295-399

    • Controlling of chaos by weak periodic perturbations in Duffing-van der Pol oscillator

      S Rajasekar

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      This paper investigates the possibility of controlling horseshoe and asymptotic chaos in the Duffing-van der Pol oscillator by both periodic parametric perturbation and addition of second periodic force. Using Melnikov method the effect of weak perturbations on horseshoe chaos is studied. Parametric regimes where suppression of horseshoe occurs are predicted. Analytical predictions are demonstrated through direct numerical simulations. Starting from asymptotic chaos we show the recovery of periodic motion for a range of values of amplitude and frequency of the periodic perturbations. Interestingly, suppression of chaos is found in the parametric regimes where the Melnikov function does not change sign.

    • Mathematical analysis of isobaric decay chain in alpha particle induced reactions

      S Mukherjee N L Singh J Rama Rao

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      A detailed mathematical formalism is developed from the first principles, to separate out the fractional contributions of the cross-sectionσg andσp for the production of the two isobaric precursor nuclei- grand parent and parent, respectively, to the cross-sectionσd for the formulation of the residual nucleus of interest. The analytical work of separating out such contributions gives a meaningful picture to the comparison with the theoretical predictions of hybrid model, using the initial excition numbern0 = 4(4p0h).

    • Measurement and analysis of the excitation functions for alpha particle induced reactions on niobium

      S Mukherjee M H Rashid S N Chintalapudi

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      Stacked foil activation technique and Ge(Li) gamma ray spectroscopy have been used for determining the excitation functions up to 45 MeV, of six reactions93Nb[(α, n), (α, 2n)m, (α, 2n)g, (α, 3n), (α,p3n) and (α, αn)]. Excitation functions were also calculated theoretically by means of the hybrid model with and without the inclusion of pre-equilibrium emission of particles. A general agreement was found in (α, xn) type of reactions.

    • Sub-barrier fission fragment angular distributions for the system19F+232Th

      S Kailas A Navin A Chatterjee P Singh A Saxena D M Nadkarni D C Biswas R K Choudhury S S Kapoor

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      The measurements of fission fragment angular distributions for the system19F+232Th have been extended to the sub-barrier energies of 89.3, 91.5 and 93.6 MeV. The measured anisotropies, within errors are nearly the same over this energy region. However, the deviation of the experimental values of anisotropies from that of standard statistical model predictions increases as the bombarding energy is lowered.

    • Ab-initio Hartree-Fock self-consistent-field calculations—An indigenous development of computer programs

      Sambhu N Datta

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      A set of indigenously developed computer programs for ab-initio Hartree-Fock calculations on both closed- and open-shell molecules have been described. These programs have been written for calculations using GTO basis sets. Integral formulae have been taken from Taketaet al [8]. Structures and functions of the programs have been discussed. These programs have been extensively tested. Molecular integrals over GTO basis sets have been chosen for tests and as numerical examples in this paper. Results of calculations using very accurate minimal bases have been given for methane. Time taken for these computations in a CDC Cyber 180/840 machine has been indicated. Trends in the calculations have also been illustrated by employing 4-gaussian expansions for the STO’s and by varying the basis size for LiH and BH+.

    • Ab-initio nonrelativistic and relativistic Hartree-Fock calculations for both closed- and open-shell molecules using GTO basis

      Sambhu N Datta

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      Computer programs forab-initio Hartree-Fock and Dirac-Hartree-Fock calculations on closed- and open-shell atoms and molecules have been indigenously developed. Sample results of high quality are given for Li, Be, LiH and Be2. As a byproduct of these calculations the importance of considering relativistic effects in the investigation of the elusive bound-state structure of Be2 is clearly indicated.

    • Electron impact excitation of Ni XIX using theR-matrix method

      Man Mohan M Le Dourneuf A Hibbert V M Burke

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      Collision strengths for all the transitions between the 15 lowest states of neon-like Ni XIX have been calculated for electron impact in the 80–140 Ry energy range. Configuration-interaction wavefunctions have been used to represent the target states. The standardR-matrix code has been used to calculate the lower scattering partial waves (L≤9), while a no-exchange version of the same code has been used to compute efficiently the higher partial waves (L≥10). Effective collision strengths for 105 excitation transitions between the ground state 2s22p61Se and the 142s22p53l Rydberg states are tabulated for electron temperatures in the range logT=5.40 to logT=7.00, withT expressed in °K.

    • Dynamics of immiscible radial viscous fingering: A numerical study

      Subir K Sarkar David Jasnow

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      In this paper we undertake a numerical investigation of the dynamics of the interface in the problem of immiscible radial viscous fingering in a Hele-Shaw cell when the areal flow rate is maintained constant. Comparison is made with experimental results to check if there is a need to introduce velocity-dependent boundary conditions and to incorporate the effect of thickness of the film left behind by the moving interface. Some new scaling results are suggested by the numerical data. These data, along with those available from laboratory experiments, provide support for a mean field theory for radial immiscible viscous fingering published recently [Phys. Rev. Lett.65, 2680 (1990)].

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