Volume 59, Issue 3
September 2002, pages 433-552 and L553-L561
pp 433-443 September 2002
Radial oscillations of neutron stars in strong magnetic fields
VK Gupta Vinita Tuli S Singh JD Anand Ashok Goyal
The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to include strong magnetic field. It is found that magnetized neutron stars support higher maximum mass whereas the effect of magnetic field on radial stability for observed neutron star masses is minimal.
pp 445-456 September 2002
Occurrence of stable periodic modes in a pendulum with cubic damping
Dynamical systems with nonlinear damping show interesting behavior in the periodic and chaotic phases. The Froude pendulum with cubical and linear damping is a paradigm for such a system. In this work the driven Froude pendulum is studied by the harmonic balancing method; the resulting nonlinear response curves are studied further for resonance and stability of symmetric oscillations with relatively low damping. The stability analysis is carried out by transforming the system of equations to the linear Mathieu equation.
pp 457-464 September 2002
Quark mass corrections to the perturbative thrust and its effect on the determination of α_{s}
We consider the effects of quark masses to the perturbative thrust in e^{+}e^{−} annihilation. In particular we show that perturbative power corrections resulting from non-zero quark masses considerably alters the size of the non-perturbative power corrections and consequently, significantly changes the fitted value of α_{s}.
pp 465-477 September 2002
Bounds on neutrino mixing with exotic singlet neutrinos
J K Singhal Sardar Singh Ashok K Nagawat N K Sharma
We examine the effects of mixing induced non-diagonal light-heavy neutrino weak neutral currents on the amplitude for the process $$v_a \overline v _a \to ZZ$$ (with a=e, μ or τ). By imposing constraint that the amplitude should not exceed the perturbative unitarity limit at high energy $$\left( {\sqrt s = \Lambda } \right)$$, we obtain bounds on light-heavy neutrino mixing parameter sin^{2}$$\theta _L^{v_a } $$ where $$\theta _L^{v_a } $$ is the mixing angle. In the case of one heavy neutrino (mass mξ) or mass degenerate heavy neutrinos, for Λ=1 TeV, no bound is obtained for mξ<0.50 TeV. However, sin^{2}$$\theta _L^{v_a } $$≤3.8 × 10^{−6} for mξ=5 TeV and sin $$\theta _L^{v_a } $$≤6.0 × 10^{−8} for mξ=10 TeV. For Λ=∞, no constraint is obtained for mξ<0.99 TeV and sin^{2}$$\theta _L^{v_a } $$≤3.8 × 10^{−2} (for mξ=5 TeV) and sin^{2}$$\theta _L^{v_a } $$≤9.6 × 10^{−3} (for mξ=10 TeV).
pp 479-486 September 2002
Universal relation between spectroscopic constants
A universal relation between the Sutherland parameter, Δ (= k_{e}r_{e}^{/2}/2D_{e}) and the dimensionless parameter G (= 8ω_{e}x_{e}/B_{e}), has been established using 40 electronic states, which include ground as well as excited states of polar and non-polar molecules. This relation is used to predict the dissociation energy of four lowest electronic states of S_{2} molecule. The respective values for the states X^{3}Σ_{g}^{/−}, a^{1}Δ_{g}, b^{1}Σ_{g}^{/+} and B^{3}Σ_{u}^{/−} turn out to be 36557, 31431, 28247 and 13429 cm^{−1}, and are in good agreement with the experimental values. Furthermore, metastable states a^{1}Δ_{g} and b^{1}Σ_{g}^{/+} of S_{2} are shown to dissociate into ^{3}P_{1} + ^{3}P_{1} as against the dissociation of X^{3}Σ_{g}^{/−} into ^{3}P_{2} + ^{3}P_{1}. In addition, a relation between Sutherland parameter Δ and internuclear distance r_{e}, viz., Δ=2.2r_{e} has been obtained for the ground state of alkali diatomic molecules.
pp 487-496 September 2002
CO_{2} laser photoacoustic spectra and vibrational modes of heroin, morphine and narcotine
R L Prasad S N Thakur G C Bhar
Heroin, morphine and narcotine are very large molecules having 50, 40 and 53 atoms respectively. Moderately high resolution photoacoustic (PA) spectra have been recorded in 9.6 µm and 10.6 µm regions of CO_{2} laser. It is very difficult to assign the modes of vibrations for PA bands by comparison with conventional low resolution IR spectra. The ab initio quantum chemical calculations were used for determining the molecular geometries and normal mode frequencies of vibrations of these molecules for assignments of PA spectra.
pp 497-514 September 2002
Atomic displacements in dilute alloys of Cr, Nb and Mo
Kanzaki lattice static method is used to calculate the atomic displacements due to substitutional impurities in 3d (Cr) and 4d (Nb, Mo) metals. Wills and Harrison interatomic potential is used to calculate dynamical matrix and the impurity-induced forces up to second nearest neighbors. The calculated atomic displacements for 3d, 4d and 5d impurities in Cr (V, Mn, Fe, Ni, Nb, Mo, Ta and W), Nb (V, Cr, Mn, Fe, Zr, Mo, Ta and W) and Mo (V, Cr, Mn, Fe, Zr, Nb, Ta and W) are tabulated up to 10 NN’s. The strain field due to 3d impurities is least in Cr metal while it is larger in Nb and Mo metals. For 4d and 5d impurities the strain is larger in Cr metal than in Nb and Mo hosts. Similar trend is found for relaxation energies also.
pp 515-524 September 2002
Single and double ionization of gallium by electron impact
Electron impact single and double ionization cross sections of gallium have been calculated in the binary encounter approximation using accurate expression for σ_{Δ};E including exchange and interference as given by Vriens and Hartree-Fock velocity distributions for the target electrons throughout the calculations. It is concluded that the ionization of 3d shell contributes partly to single ionization and partly to double ionization. The results so obtained show reasonably good agreement with the experimental data.
pp 525-529 September 2002
A new ultrasonic method to detect chemical additives in branded milk
S Mohanan P G Thomas Panicker Lilly Iype M Laila I Domini RG Bindu
A new ultrasonic method — thermoacoustic analysis — is reported for the detection of the added chemical preservatives in branded milk. The nature of variation and shift in the thermal response of the acoustic parameters specific acoustic impedance, adiabatic compressibility and Rao’s specific sound velocity for different samples of branded milk as compared to the chemical added pure milk are explained as due to the presence of chemicals in these branded samples.
pp 531-537 September 2002
Mössbauer studies of hyperfine fields in disordered Fe_{2}CrAl
N Lakshmi K Venugopalan J Varma
Heusler-like alloy Fe_{2}CrAl was prepared and studied. Structure determination was done by X-ray. The structure was found to conform to the B_{2} type. Magnetic hyperfine fields in this sample were studied by the Mössbauer effect. The Mössbauer spectra were recorded over a range of temperature from 40 to 296 K. The Mössbauer spectra showed the co-existence of a paramagnetic part with a magnetic hyperfine portion at all recorded temperatures. Even with the distribution in the magnetic hyperfine field, the average hyperfine field follows the (T/T_{c})^{3/2} law. The paramagnetic part of the hyperfine field is explained in terms of the clustering of Cr atoms.
pp 539-545 September 2002
Stochastic resonance and chaotic resonance in bimodal maps: A case study
G Ambika N V Sujatha K P Harikrishnan
We present the results of an extensive numerical study on the phenomenon of stochastic resonance in a bimodal cubic map. Both Gaussian random noise as well as deterministic chaos are used as input to drive the system between the basins. Our main result is that when two identical systems capable of stochastic resonance are coupled, the SNR of either system is enhanced at an optimum coupling strength. Our results may be relevant for the study of stochastic resonance in biological systems.
pp 547-552 September 2002
Linear electro-optical properties of tetragonal BaTiO_{3}
Linear optical susceptibility and clamped linear electro-optical tensor coefficients of tetragonal BaTiO_{3} are calculated using a formalism based on bond charge theory. Calculated values are in close agreement with experimental data. The covalent Ti-O bonds constituting distorted TiO_{6} octahedral groups are found to be major contributors to the electro-optic coefficients making them more sensitive than the BaO_{12} groups for these properties. Orientations of chemical bonds play an important role in determining these properties.
pp L553-L561 September 2002 Rapid Communication
Phenomenology of a realistic accelerating universe using tracker ﬁelds
We present a realistic scenario of tracking of scalar ﬁelds with varying equation of state. The astrophysical constraints on the evolution of scalar ﬁelds in the physical universe are discussed. The nucleosynthesis and the galaxy formation constraints have been used to put limits on $\Omega_{\phi}$ and estimate 𝜖 during cosmic evolution. Interpolation techniques have been applied to estimate $\epsilon\simeq 0.772$ at the present epoch. The epoch of transition from matter to quintessence dominated era and consequent onset of acceleration in cosmic expansion is calculated and taking the lower limit $\Omega^{0}_{n} = 0.2$ as estimated from $SN_{e}I_{a}$ data, it is shown that the supernova observations beyond redshift $z = 1$ would reveal deceleration in cosmic expansion.
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