S Singh
Articles written in Pramana – Journal of Physics
Volume 10 Issue 6 June 1978 pp 639-647 Fluids
Second virial coefficient for a mixture of nonspherical molecules of arbitrary symmetry
The mixture and interaction second virial coefficients of a binary gas mixture of nonspherical molecules of arbitrary symmetry have been calculated for a set of unlike force parameters which is obtained from the force parameters for like interactions by using empirical combination rules. In the calculation molecular anisotropy of very general type has been accounted. The relative contribution of each branch of interactions has been evaluated as a function of temperature. The theoretical values of interaction second virial coefficient have been compared with the experimental data of N_{2}+A, N_{2}+He, N_{2}+H_{2}, N_{2}+O_{2}, N_{2}+C_{2}H_{4}, N_{2}+C_{2}H_{6}, CO_{2}+A, CO_{2}+H_{2}, CO_{2}+N_{2}, CO_{2}+O_{2}, CO_{2}+CO, CO_{2}+C_{2}H_{4}, CO_{2}+C_{2}H_{6}, O_{2}+A and H_{2}+CO. The agreement between theory and experiment is satisfactory for all the systems. Numerical estimations of the mixture second virial coefficients as a function of temperature and composition are given for the systems CO_{2}+A, CO_{2}+H_{2}, CO_{2}+N_{2}, CO_{2}+O_{2} and CO_{2}+CO.
Volume 12 Issue 2 February 1979 pp 171-177 Atomic And Molecular Physics
Interaction second virial co-efficient of polar-quadrupolar gas mixtures
The interaction second virial coefficient of a binary polar-quadrupolar gas mixtures of non-spherical molecules of arbitrary symmetry has been calculated for a set of unlike force parameters which is obtained from the force parameters for like interactions by using empirical combination rules. In the calculation the influence of anisotropic interactions has been considered. The relative contribution of each branch of interactions has been evaluated as a function of temperature. The theoretical results have been compared with the experimental data of CH_{3}F + N_{2}, CH_{3}F + CO_{2} and CH_{3}Cl + CS_{2}. The agreement between theory and experiment is satisfactory.
Volume 20 Issue 4 April 1983 pp 347-357 Statistical Mechanics
On the virial coefficients of the equation of state of a system of non-axial molecules
A thermodynamic perturbation theory in which all angle-dependent interactions are considered as a perturbation of the central potential is applied to calculate the second and third virial coefficients of a fluid composed of non-axial molecules. The influence of a large number of anisotropic pair- and three-body non-ādditive interactions has been considered. Experimental values have been used for the dipole moment, quadrupole tensor and for anisotropic polarizability. The parameters for the central Lennard-Jones (12-6) potential have been determined from the viscosity data. The relative contribution of each branch of pair and triplet interactions has been evaluated as a function of temperature for molecules possessing both the axial- and non-axial symmetries. It has been shown that the non-axial approximation is an improvement over the axial one. Theoretical results have been compared with the experimental data of CH_{3}OH.
Volume 32 Issue 4 April 1989 pp 419-433 Nuclear Reactions
Clustering phenomena in radioactive and stable nuclei and in heavy-ion collisions
S S Malik S Singh R K Puri S Kumar Raj K Gupta
A theory for clustering formation in nuclei and in heavy-ion collisions has been worked out in terms of the quantum-mechanical fragmentation process. Treating the mass fragmentation and relative separation coordinates as weakly coupled, the spontaneous cluster-decay of radioactive nuclei has been considered as a two-step process of clustering formation and tunnelling of the confining nuclear interaction barrier. This model has also been applied to “stable” nuclei, lighter than lead. The effects of adding more and more neutrons to colliding
Volume 49 Issue 4 October 1997 pp 443-453 Research Articles
Bulk viscosity of neutron stars
V K Gupta A Wadhwa S Singh J D Anand
Viscosity of neutron stars has been a continuing area of research for many years now. Recently interest in this field has revived because of the possibility of URCA processes in neutron stars. In this paper we report calculation of the bulk viscosity of neutron stars from these processes. For this purpose we have used the
Volume 54 Issue 5 May 2000 pp 737-749 Research Articles
Bulk viscosity of strange quark matter in density dependent quark mass model
J D Anand N Chandrika Devi V K Gupta S Singh
We have studied the bulk viscosity of strange quark matter in the density dependent quark mass model (DDQM) and compared results with calculations done earlier in the MIT bag model where
Volume 59 Issue 3 September 2002 pp 433-443
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.
Volume 93 Issue 6 December 2019 Article ID 0092 Research Article
Cooling of fermionic $^{83}\rm{Kr}$ and bosonic $^{84}\rm{Kr}$ isotopes in a magneto-optical trap
Simultaneous laser cooling of two isotopes of krypton, $^{83}\rm{Kr}$ and $^{84}\rm{Kr}$, is reported here in a two-isotope magneto-optical trap (TIMOT). The number of cold metastable $^{83}\rm{Kr}$ atoms in this TIMOT is dependent on the power of the repumping laser beams used, which is maximised for our set-up by varying the powers of repumping lasers. These studies may be useful to investigate cold collisions between fermionic $^{83}\rm{Kr}$ and bosonic $^{84}\rm{Kr}$ atoms in the metastable state.
Volume 94, 2019
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