• Volume 56, Issue 1

      January 2001,   pages  1-135

    • A review of the microscopic modeling of the 5-dim. black hole of HB string theory

      Spenta R Wadia

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      We review the theory of the microscopic modeling of the 5-dim. black hole of type HB string theory in terms of the D1D5 brane system. A detailed discussion of the low energy effective Lagrangian of the brane system is presented and the black hole micro-states are identified. These considerations are valid in the strong coupling regime of supergravity due to the non-renormalization of the low energy dynamics in this model. Using Maldacena duality and standard statistical mechanics methods one can account for black hole thermodynamics and calculate the absorption cross section and the Hawking radiation rates. Hence, at least in the case of this model black hole, since we can account for black hole properties within a unitary theory, there is no information paradox.

    • A plethora of strange nonchaotic attractors

      Surendra Singh Negi Ramakrishna Ramaswamy

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      We show that it is possible to devise a large class of skew-product dynamical systems which have strange nonchaotic attractors (SNAs): the dynamics is asymptotically on fractal attractors and the largest Lyapunov exponent is non-positive. Furthermore, we show that quasiperiodic forcing, which has been a hallmark of essentially all hitherto known examples of such dynamics is not necessary for the creation of SNAs.

    • Study of ΛΛ dynamics and ground state structure of low and medium mass double Λ hypernuclei

      MD Abdul Khan Tapan Kumar Das

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      We critically review the ΛΛ dynamics by examining Λ - Λ and Λ-nucleon phenomenological potentials in the study of the bound state properties of double-Λ hypernuclei ΛΛ6He, ΛΛ10Be, ΛΛ14C, ΛΛ18O, ΛΛ22Ne, ΛΛ26Mg, ΛΛ30Si, ΛΛ34S, ΛΛ38Ar, ΛΛ42Ca, ΛΛ46Ti, ΛΛ50Cr, ΛΛ54Fe, ΛΛ58Ni, ΛΛ62Zn, ΛΛ66Ge, ΛΛ70Se, ΛΛ74Kr, ΛΛ78Sr, ΛΛ82Zr, ΛΛ86Mo, ΛΛ90Ru, ΛΛ94Pd, ΛΛ98Cd, ΛΛ102Sn in the frame work of (core+Λ+Λ) three body model. An effective ΛN potential is obtained by folding the phenomenological ΛN potential into the density distribution of the core nuclei. The former two cases (i.e. ΛΛ6He and ΛΛ10Be) are revisited to justify the correctness of the present potential model. Assuming the same potential model we predicted some of the structural properties of heavier doubly Λ-hypernuclei. The hyperspherical harmonics expansion method, which is an essentially exact method has been employed for the three body system. A convergence in binding energy up to 0.15% for Kmax=20 has been achieved. In our calculation we have made no approximation in restricting the allowed l-values of the interacting pairs.

    • Measurement of στ product of solid state laser materials by an alternative method: Application to Nd3+ doped YVO4 crystal for 4F3/24I11/2 transition

      PK Mukhopadhyay Jogy George SK Sharma Rakesh Kapoor TPS Nathan

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      In this paper an alternative approach for measurement of στ product for 4F3/24I11/2 transition of Nd3+ doped YVO4 crystal is reported. In this method a microchip laser is formed by keeping a small piece of the sample in plane-plane resonator and a diode laser (808 nm) is used for pumping. The pump power induced thermal lensing effect is used to make the cavity stable. The cavity mode area is estimated by measuring the thermal lens focal length at the threshold and the average pump area is measured by Gaussian fit to the intensity profiles of the pump beam. The value of στ product of Nd:YVO4 crystal obtained by this method is within 10% of the reported values. The advantage of this method is that it is a simple method for direct measurement of στ product of laser crystals.

    • Overlapping B3Π0uX1Σg/+ and 1Π1uX1Σg/+ non-radiative characteristic of Br2 vapour in the wavelength region 505–541 nm

      Ramesh C Sharma SN Thakur

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      The vibronic vapour phase photoacoustic spectrum of Br2 in the wavelength region 505–541 nm (19796–18480 cm−1) has been recorded using microphone as well as pump-probe method. Discrete vibronic bands superimposed on a monotonically increasing continuum background towards the dissociation limit results from the overlapping B3Π0u/+X1Σg/+ and 1Π1uX1Σg/+ electronic transitions. Vibronic bands originating from υ″=0 have been used to estimate the relative rate of non-radiative relaxation as a function of the excited state B3Π0u vibrational quantum number υ′. A comparison with the optical absorption spectroscopy of Br2 leads to the identification of three broad spectral regions between 505 and 541 nm (19796 and 18480 cm−1) on the basis of different non-radiative relaxation processes.

    • Effect of radiative cooling on collapsing charged grains

      BP Pandey Vinod Krishan M Roy

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      The effect of the radiative cooling of electrons on the gravitational collapse of cold dust grains with fluctuating electric charge is investigated. We find that the radiative cooling as well as the charge fluctuations, both, enhance the growth rate of the Jeans instability. However, the Jeans length, which is zero for cold grains and nonradiative plasma, becomes finite in the presence of radiative cooling of electrons and is further enhanced due to charge fluctuations of grains resulting in an increased threshold of the spatial scale for the Jeans instability.

    • The influence of a transverse magnetic field on a subnormal glow discharge in air

      DC Jana SS Pradhan

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      In subnormal glow discharge under d.c. excitation at different pressure in a varying transverse magnetic field (0 to 30 G) some measurements have been carried out for various initial average tube currents. The voltage across the discharge increases and average tube current and residual current decreases in the magnetic field. With the help of Beckman’s expression [4] for the axial field and the electron density distribution in a transverse magnetic field the observed variation of current and voltage can be satisfactorily explained. The variation of axial electric field with transverse magnetic field can be represented to a fair degree of accuracy by the derived equation. The behaviour of residual current with magnetic field has been observed in these oscillations.

    • Quantum hysteresis loops in microscopic system: The loop area as a dynamical parameter

      Chandan Kumar Mondal SP Bhattacharyya

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      The area enclosed by hysteresis loops in a periodically forced bistable microscopic system at zero-temperature is examined by using the time dependent Hellmann-Feynman theorem and the Fourier grid Hamiltonian recipe for solving time-dependent Schrödinger equation. Effects of non-zero temperatures are explored with reference to a symmetric double well potential. The barrier crossing or, relaxation rates are shown to correlate systematically with the area of the loop. The possible use of hysteresis loop area in designing field parameters for optimal control is suggested.

    • Magnetization curves for non-elliptic cylindrical samples in a transverse field

      Debjani Karmakar KV Bhagwat

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      Using recent results for the surface current density on cylindrical surfaces of arbitrary cross-section producing uniform interior magnetic field and an assumed set of flux-fronts, solutions of Bean’s critical state model for cylindrical samples with non-elliptic cross-section are presented. Magnetization hysteresis loops for two cross-sections with different aspect ratios are obtained. A comparison with some exact results shows the limitations of this approach.

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