Volume 58, Issue 1
January 2002, pages 1-134 and L135-L145
pp 1-12 January 2002 Research Articles
Quantum cosmology in Ashtekar variables with non-minimally coupled scalar-tensor theory
Using non-minimally coupled scalar-tensor theory in homogeneous and isotropic cosmological model, quantum cosmology has been developed for Ashtekar variables. The wave function has been evaluated by solving the Wheeler-Dewitt (WD) equation and also using path integral formulation. Semi-classical limit using WKB approximation has also been discussed. Finally, the quantum Bohmian trajectories has been studied in detail.
pp 13-19 January 2002 Research Articles
Quantum Einstein’s equations and constraints algebra
In this paper we shall address this problem: Is quantum gravity constraints algebra closed and what are the quantum Einstein’s equations. We shall investigate this problem in the de-Broglie-Bohm quantum theory framework. It is shown that the constraint algebra is weakly closed and the quantum Einstein’s equations are derived.
pp 21-26 January 2002 Research Articles
Star products from commutative string theory
A boundary-state computation is performed to obtain derivative corrections to the Chern-Simons coupling between a p-brane and the RR gauge potential C^{p}−3. We work to quadratic order in the gauge field strength F, but all orders in derivatives. In a certain limit, which requires the presence of a constant B-field background, it is found that these corrections neatly sum up into the *_{2} product of (commutative) gauge fields. The result is in agreement with a recent prediction using noncommutativity.
pp 27-30 January 2002 Research Articles
Bridge between bound state and reaction effective nucleon-nucleon potentials
It has been a long standing problem to find the connection between the realistic nucleon-nucleon interaction and the interaction between two nucleons when they are embedded inside a nuclear medium, the so-called ‘effective interaction’. On the one hand various many-body approaches have been employed, while on the other hand, information is sought on the basis of static nuclear properties. Both provide partial information. An attempt is made to understand if there is an inherent link, a bridge, which connects all these informations, through the study of heavy ion fusion reactions.
pp 31-38 January 2002 Research Articles
X-ray fluorescence in some rare earth and high Z elements excited by 661.6 keV γ-rays
T Yashoda S Krishnaveni Shivalinge Gowda TK Umesh Ramakrishna Gowda
The K-shell X-ray fluorescence cross sections are determined experimentally for 10 elements such as Pb, Hg, Ir, W, Lu, Tm, Dy, Tb, Gd and Nd at excitation energy of 661.6 keV associated with γ-rays of ^{137}Cs radioisotope. The technique employed involves the measurement of total intensity of fluorescent K X-rays that follow the photoeffect absorption of a known flux of γ-rays using a well type Nal(Tl) detector. The obtained results are compared with the available theoretical values and other measured values.
pp 39-57 January 2002 Research Articles
(e, 3e) Differential cross section of He (2^{1}S) and He (2^{3}S)
Kshamata Muktavat MK Srivastava
The angular distribution of the five-fold differential cross section for the electron impact double ionization of He (2^{1}S) and He (2^{3}S) has been studied. The kinematical conditions for maxima/minima in the angular distribution for the two cases have been compared. The two-step process for the double ionization is found to contribute very little in the triplet case.
pp 59-66 January 2002 Research Articles
Operational characteristics of dual gain single cavity Nd:YVO_{4} laser
Pranab K Mukhopadhyay Jogy George S K Sharma P K Gupta T P S Nathan
Operational characteristics of a dual gain single cavity Nd:YVO_{4} laser have been investigated. With semiconductor diode laser pump power of 2 W, 800 mW output was obtained with a slope efficiency of 49%. Further, by changing the relative orientation of the two crystals the polarization characteristics of the output could be varied. In particular by keeping the two Nd:YVO_{4} crystals with their c-axes orthogonal to each other and adjusting the gain of the crystals so that both operate at approximately the same power level, completely unpolarized beams could be obtained.
pp 67-77 January 2002 Research Articles
Arti Gokhale Preeti Vyas J Panikar Y Choyal K P Maheshwari
Analytical and numerical study of the stability of sheet electron beam in periodically cusped magnetic field (PCM) is made. The beam has been considered as having diffused density profile. The conditions for beam focusing are discussed.
pp 79-89 January 2002 Research Articles
Investigations of low q_{a} discharges in the SINP tokamak
S Lahiri A N S Iyengar S Mukhopadhyay R Pal
Low edge safety factor discharges including very low q_{a} (1<q_{a}<2) and ultra low q_{a} (0<q_{a}<1) have been obtained in the SINP tokamak. It has been observed that accessibility of these discharges depends crucially on the fast rate of plasma current rise. Several interesting results in terms of different time scales like T_{q}_{a} · τ_{R} etc have been obtained using a set of softwares developed at SINP. From fluctuation analysis of the external magnetic probe data it has been found that MHD instabilities m=1, n=1 and m=2, n=1 etc. play major role in the evolution of these discharges. To investigate the internal details of these discharges, an internal magnetic probe system has been developed using which current density j_{φ} and other related parameters have been estimated. By carrying out a resistive stability analysis, evidence of the above-mentioned MHD instabilities have again been found. The physical processes lying behind the accessibility and evolution of the low q_{a} discharges have been thoroughly investigated.
pp 91-100 January 2002 Research Articles
Compton profiles of momentum distribution of conduction electrons in the orthorhombic phase of α-Ga metal at low temperature are calculated in the band model for the three crystallographic directions (100), (010), and (001). Unlike the results at room temperature, previously reported by Lengeler, Lasser and Mair, the present results show strong anisotropy in the Compton profiles with the momentum distribution along (001) direction being substantially different from the other two directions. While experimental data on Compton profiles at low temperatures are not available for comparison with theory, the resistivity data in α-Ga at low temperature strongly support this anisotropic behaviour. Besides, the electronic heat capacity constant γ available from both experiment and present calculation suggests that the conduction electron distribution at low temperature in the orthorhombic phase is markedly different from the free-electron-like-distribution at room temperature, thus lending additional support to anisotropic behaviour of Compton profiles. It would be nice to have Compton profiles data from experiment at low temperature for direct comparison with theory. It is hoped that the present work would stimulate enough interest in that direction.
pp 101-111 January 2002 Research Articles
Mithlesh Kumar Y Babu A R Dhobale R M Kadam M D Sastry
Photo-EPR measurements carried out on Nd^{3+} -doped polyvinyl alcohol (PVA) films have shown that nearly 100% reduction occurs in the intensity of EPR of Nd^{3+} under in situ copper vapor laser (CVL) illumination (510.5 nm and 578.2 nm). The kinetics of decay and recovery were investigated. Photoacoustic (PA) spectra, observed under CVL pump condition had shown that the CVL induced changes were not due to photoinduced valence change, and that the CVL pumping creates highly favorable conditions for non-equilibrium population distribution in the excited electronic states. The complete disappearance of EPR under CVL pumping is attributed either to the possible equalization of population of |+〈 and |−〈 Zeeman components, through the decay of many excited states in the presence of magnetic field or configurational changes around Nd^{3+} shifting the resonance frequency. The former appears less probable in view of the relatively slower recovery of EPR signal.
pp 113-119 January 2002 Brief Reports
Test particle trajectories near cosmic strings
Farook Rahaman Subenoy Chakraborty K Maity
We present a detailed analysis of the motion of test particle in the gravitational field of cosmic strings in different situations using the Hamilton-Jacobi (H-J) formalism. We have discussed the trajectories near static cosmic string, cosmic string in Brans-Dicke theory and cosmic string in dilaton gravity.
pp 121-126 January 2002 Brief Reports
Higher dimensional global monopole in Brans-Dicke theory
Farook Rahaman Subenoy Chakraborty Mehedi Kalam
The gravitational field of a higher dimensional global monopole in the context of Brans-Dicke theory of gravity is investigated. The space time metric and the scalar field generated by a global monopole are obtained using the weak field approximation. Finally, the geodesic of a test particle due to the gravitational field of the monopole is studied.
pp 127-134 January 2002 Brief Reports
Gravitational field of spherical domain wall in higher dimension
An exact solution of Einstein’s equations is found describing the gravitational field of a spherical domain wall with nonvanishing stress component in the direction perpendicular to the plane of the wall. Also we have studied the motion of test particle around the domain wall.
pp L135-L145 January 2002 Rapid Communication
SNO results and neutrino magnetic moment solution to the solar neutrino problem
We have analysed the solar neutrino data obtained from chlorine, gallium and Super-Kamiokande (SK) experiments (1258 days) and also the new results that came from Sudbury Neutrino Observatory (SNO) charge current (CC) and elastic scattering (ES) experiments considering that the solar neutrino deﬁcit is due to the interaction of neutrino transition magnetic moment with the solar magnetic ﬁeld. We have also analysed the moments of the spectrum of scattered electrons at SK. Another new feature in the analysis is that for the global analysis, we have replaced the spectrum by its centroid.
Current Issue
Volume 93 | Issue 6
December 2019
Click here for Editorial Note on CAP Mode
© 2017-2019 Indian Academy of Sciences, Bengaluru.