5,885 research outputs found
Radiating Collapse with Vanishing Weyl stresses
In a recent approach in modelling a radiating relativistic star undergoing
gravitational collapse the role of the Weyl stresses was emphasised. It is
possible to generate a model which is physically reasonable by approximately
solving the junction conditions at the boundary of the star. In this paper we
demonstrate that it is possible to solve the Einstein field equations and the
junction conditions exactly. This exact solution contains the Friedmann dust
solution as a limiting case. We briefly consider the radiative transfer within
the framework of extended irreversible thermodynamics and show that
relaxational effects significantly alter the temperature profiles.Comment: 10 pages, submitted to IJMP-
On trapped surface formation in gravitational collapse II
Further to our consideration on trapped surfaces in gravitational collapse,
where pressures were allowed to be negative while satisfying weak energy
condition to avoid trapped surface formation, we discuss here several other
attempts of similar nature in this direction. Certain astrophysical aspects are
pointed out towards examining the physical realization of such a possibility in
realistic gravitational collapse
Gravitational collapse from smooth initial data with vanishing radial pressure
We study here the spherical gravitational collapse assuming initial data to
be necessarily smooth, as motivated by the requirements based on physical
reasonableness. A tangential pressure model is constructed and analyzed in
order to understand the final fate of collapse explicitly in terms of the
density and pressure parameters at the initial epoch from which the
collapsedevelops. It is seen that both black holes and naked singularities are
produced as collapse end states even when the initial data is smooth. We show
that the outcome is decided entirely in terms of the initial data, as given by
density, pressure and velocity profiles at the initial epoch, from which the
collapse evolves.Comment: 10 pages,3 figures,revtex4,Revised Versio
Socio-economic dimension of fish farming in Assam
Information on socio-economic framework of the fish farmer
community forms a benchmark for policy formulation to develop this
economically backward sector. Very few studies have been conducted on the
socio-economic aspect of fish farming. Two districts of Assam, Darrang and
Nagaon, were selected for this study where 120 respondents from each district
were selected randomly. The characteristics representing the personnel and
socio-economic attributes of the fish farmers are presented in this paper. The
socio-economic status of fish farmers has to be improved by bringing the
modern concepts of fish farming to the doorstep of farmers
Laser phase modulation approaches towards ensemble quantum computing
Selective control of decoherence is demonstrated for a multilevel system by
generalizing the instantaneous phase of any chirped pulse as individual terms
of a Taylor series expansion. In the case of a simple two-level system, all odd
terms in the series lead to population inversion while the even terms lead to
self-induced transparency. These results also hold for multiphoton transitions
that do not have any lower-order photon resonance or any intermediate virtual
state dynamics within the laser pulse-width. Such results form the basis of a
robustly implementable CNOT gate.Comment: 10 pages, 4 figures, PRL (accepted
Techno-economic viability of rice-fish culture in Assam
The economic viability of rice-fish culture practiced by the fanners of Assam in North-
Eastern part of India was evaluated using techno-economic approach. The fanners followed
extensive level farming practice using low input technology. Cobb-Douglas production
function was used to determine the input-output relationship of the system. The cost and
return evaluation shows that rice-fish culture can be a more profitable option than
monoculture of paddy
Quantum random walk : effect of quenching
We study the effect of quenching on a discrete quantum random walk by
removing a detector placed at a position abruptly at time from its
path. The results show that this may lead to an enhancement of the occurrence
probability at provided the time of removal where
scales as . The ratio of the occurrence probabilities
for a quenched walker () and free walker () shows that it
scales as at large values of independent of . On the other
hand if is fixed this ratio varies as for small . The
results are compared to the classical case. We also calculate the correlations
as functions of both time and position.Comment: 5 pages, 6 figures, accepted version in PR
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