Volume 56, Issue 1
January 2001, pages 1-135
pp 1-46 January 2001 Review
A review of the microscopic modeling of the 5-dim. black hole of HB string theory
We review the theory of the microscopic modeling of the 5-dim. black hole of type HB string theory in terms of the D_{1}–D_{5} 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.
pp 47-56 January 2001 Research Articles
A plethora of strange nonchaotic attractors
Surendra Singh Negi Ramakrishna Ramaswamy
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.
pp 57-76 January 2001 Research Articles
Study of ΛΛ dynamics and ground state structure of low and medium mass double Λ hypernuclei
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 _{ΛΛ}^{6}He, _{ΛΛ}^{10}Be, _{ΛΛ}^{14}C, _{ΛΛ}^{18}O, _{ΛΛ}^{22}Ne, _{ΛΛ}^{26}Mg, _{ΛΛ}^{30}Si, _{ΛΛ}^{34}S, _{ΛΛ}^{38}Ar, _{ΛΛ}^{42}Ca, _{ΛΛ}^{46}Ti, _{ΛΛ}^{50}Cr, _{ΛΛ}^{54}Fe, _{ΛΛ}^{58}Ni, _{ΛΛ}^{62}Zn, _{ΛΛ}^{66}Ge, _{ΛΛ}^{70}Se, _{ΛΛ}^{74}Kr, _{ΛΛ}^{78}Sr, _{ΛΛ}^{82}Zr, _{ΛΛ}^{86}Mo, _{ΛΛ}^{90}Ru, _{ΛΛ}^{94}Pd, _{ΛΛ}^{98}Cd, _{ΛΛ}^{102}Sn 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. _{ΛΛ}^{6}He and _{ΛΛ}^{10}Be) 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 K_{max}=20 has been achieved. In our calculation we have made no approximation in restricting the allowed l-values of the interacting pairs.
pp 77-85 January 2001 Research Articles
PK Mukhopadhyay Jogy George SK Sharma Rakesh Kapoor TPS Nathan
In this paper an alternative approach for measurement of στ product for ^{4}F_{3/2}→^{4}I_{11/2} transition of Nd^{3+} doped YVO_{4} 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:YVO_{4} 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.
pp 87-94 January 2001 Research Articles
The vibronic vapour phase photoacoustic spectrum of Br_{2} 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 B^{3}Π_{0u}^{/+} ← X^{1}Σ_{g}^{/+} and ^{1}Π_{1u} ← X^{1}Σ_{g}^{/+} 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 B^{3}Π_{0u} vibrational quantum number υ′. A comparison with the optical absorption spectroscopy of Br_{2} 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.
pp 95-105 January 2001 Research Articles
Effect of radiative cooling on collapsing charged grains
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.
pp 107-115 January 2001 Research Articles
The influence of a transverse magnetic field on a subnormal glow discharge in air
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.
pp 117-126 January 2001 Rapid Communication
Quantum hysteresis loops in microscopic system: The loop area as a dynamical parameter
Chandan Kumar Mondal SP Bhattacharyya
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.
pp 127-135 January 2001 Rapid Communication
Magnetization curves for non-elliptic cylindrical samples in a transverse field
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.
Current Issue
Volume 93 | Issue 6
December 2019
Click here for Editorial Note on CAP Mode
© 2017-2019 Indian Academy of Sciences, Bengaluru.