• Volume 26, Issue 5

      May 1986,   pages  379-464

    • Analysis of a nonlinear stochastic model of cooperative behaviour

      M C Valsakumar

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      A stochastic model of cooperative behaviour is analyzed with regard to its critical properties. A cumulant expansion to fourth order is used to truncate the infinite set of coupled evolution equations for the moments. Linear stability analysis is performed around all the permissible steady states. The method is shown to be incapable of reproducing the critical boundary and the nature of the phase transition. A linearization, which respects the symmetry of the potential, is proposed which reproduces all the basic features associated with the model. The dynamics predicted by this approximation is shown to agree well with the Monte-Carlo simulation of the nonlinear Langevin equation.

    • Low energy scattering data and phase shifts

      M Z Rahman Khan M Shoeb

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      We point out that at any given low energyσtot and a ratio of integrated scattering data likeF/B can, in principle, be used unambiguously to finds-andp-wave phase shifts. Thus efforts to obtain other low energy data like elastic dσ/dΩ andP/E are unnecessary. It is also indicated that the mere knowledge whetherF/B is greater than or less than unity enables us to draw important conclusions about the nature of the interaction in thep-state without performing detailed calculations. Thus a strong case is made out for obtaining much more preciseF/B data than are presently available. The discussion refers mainly to low energy ∧p scattering data.

    • Application of current algebra and partial conservation of axialvector current to kaon-proton interactions

      K Krishna Murthy M L P Rao Prathibha Nuthakki

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      A soft-pion study using current algebra and the partially conserved axial vector current (PCAC) hypothesis is made of the kaon-proton interaction processKpKp2π0. Considering both pions to be soft, the differential rate for the process is normalized to the differential rate of the corresponding process without the pions. Theoretical predictions for the ratio of cross-sections at various kaon momenta are compared with experimental results.

    • Stochastic model of nuclear levelwidth

      N Rudra P Rudra

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      We investigate here the origin of nuclear levelwidth as an effect of the coupling of particle mode and the surface vibration mode of the nucleus. This interaction is taken to be stochastic in nature, characterized by a single correlation timet0, the random nature of the interaction originating from the partition of the total hamiltonian into those of the two modes. The Redfield equation of motion for the density matrix for the particle mode is solved. The solution of the Redfield equation shows that the occupation number in any particle state decays with a time constant depending on the correlation timet0 and the quantum-mechanical matrix elements of the interaction hamiltonian. The inverse of this decay time will give the width of this level. Numerical calculations have been done for82207Pb125.

    • On the response of LR-115 plastic track detector to1020Ne-ion

      S M Farid

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      The track etch rates of1020Ne-ion in cellulose nitrate (LR-115) have been measured for different temperatures and the activation energy is determined. The experimental results show that both the track etch rate and the normalized track etch rate depend on the energy loss as well as on etching temperature. The maximum etched track length of1020Ne-ion agrees with the theoretically computed range. The experimental results show that there is no sharp threshold, at least in CN(LR-115).

    • Interaction of electromagnetic field with the OH radical: A non-perturbative approach

      Bhupat Sharma Man Mohan

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      A non-perturbative approach for the study of the interaction of a hydroxyl (OH) radical with infra-red radiation is presented. The dressed states and vibrational transition probability of OH radical are defined by a quasi-energy approach (non-perturbative).

    • Electron spin resonance and optical absorption studies on copper-doped lithium hydrazinium sulphate single crystals

      V Chandra Mouli G Sivarama Sastry

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      ESR and optical absorption studies have been carried out on Cu2+-doped lithium hydrazinium sulphate single crystals at 303 K. The spin-Hamiltonian parameters evaluated indicate a N2O2 square planar environment for Cu2+ ion in this lattice. The correlation ofESR and crystal structure data leads us to conclude that Cu2+ ion enters the lattice interstitially. Charge compensation is achieved by the release of protons. Using the optical absorption andESR data, bonding parameters and orbital reduction factors are also evaluated.

    • Dynamic response and frequency dependent local field correction for an electron gas system

      Chayanika Shah G Mukhopadhyay

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      We present here an approximate scheme to obtain the complex frequency-dependent local field correction,G (q, ω). Using the equation of motion approach we develop here a methodology from which the results obtained by earlier workers, for density-density response function of an electron gas, can be arrived at in a simple systematic manner. We study in detail an approximation made along the similar lines as Singwi and coworkers, which leads to a compact expression for a complex frequency-dependent local field correction. We give results for damping coefficient of long wavelength plasmons which depends on ImG(q, ω). The real and imaginary parts ofG(q, ω) as functions ofω for various values ofq are also calculated. The dynamic structure factorS(q, ω) is evaluated forq=1.6qF and compared with earlier theoretical and experimental results.

    • Ultrasonic absorption studies in some solutions of carboxylic-acids in dioxan

      K Srinivasa Manja A Srinivasa Rao

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      Ultrasonic absorption studies are carried out in carboxylic acid-dioxan mixtures for various concentrations at 30±0.1°C. The measured absorption is much higher than the classical absorption. The excess absorption initially increases with increase of carboxylic acid concentration, attains a maximum and then decreases with further increase in concentration. The related parameters such as volume viscosity, relaxation time and free energy difference between the two states (ΔF) have also been calculated. The results can be explained satisfactorily using Hall’s two-state model.

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