613 research outputs found
Universal criterion for black hole stability
It is shown that a non-rotating macroscopic black hole with very large
horizon area can remain in stable thermal equilibrium with Hawking radiation
provided {\it its mass, as a function of horizon area, exceeds its
microcanonical entropy, i.e., its entropy when isolated, without thermal
radiation or accretion, and having a constant horizon area} (in appropriate
units). The analysis does not use properties of specific classical spacetimes,
but depends only on the plausible assumption that the mass is a function of the
horizon area for large areas.Comment: 6 pages Latex, no figures; an equation adde
Schwarzschild horizon dynamics and SU(2) Chern-Simons theory
We discuss the effect of different choices in partial gauge fixing of bulk
local Lorentz invariance, on the description of the horizon degrees of freedom
of a Schwarzschild black hole as an SU(2) Chern-Simons theory with specific
sources. A classically equivalent description in terms of an ISO(2)
Chern-Simons theory is also discussed. Further, we demonstrate that both these
descriptions can be partially gauge fixed to a horizon theory with U(1) local
gauge invariance, with the solder form sources being subject to extra
constraints in directions orthogonal to an internal vector field left invariant
by U(1) transformations. Seemingly disparate approaches on characterization of
the horizon theory for the Schwarzschild black hole (as well as spherical
Isolated Horizons in general) are thus shown to be equivalent physically.Comment: 22 pages Latex, no figures, version accepted for publication in
Physical Review
Communication Behaviour of Farmers Adopting Rice Fallow Pulse Technologies
A study was conducted to assess the communication behaviour of farmers adopting recommended rice fallow pulse crop technologies in Karaikal district. Karaikal district is a part of Union Territory of Puducherry located in the tail end of Cauvery delta zone where most of the farmers follow the rice fallow pulse crop with the availabe moisture, which fetches more income to them. The communication behaviour was studied under two dimensions viz., information source utilisation and information sharing behaviour. Correlation was worked out to assess the contribution of communication behaviour in the knowledge and adoption of rice fallow pulse technologies. In the case of regular contact, group members, neighbours and family members were the major sources of information. Information source utilization and information sharing were significant in their relationship with knowledge level of farmers whereas information sharing of farmers alone contributed positively to the adoption of technologies
Electric field driven destabilization of the insulating state in nominally pure LaMnO3
We report an electric field driven destabilization of the insulating state in
nominally pure LaMnO3 single crystal with a moderate field which leads to a
resistive state transition below 300 K. The transition is between the
insulating state in LaMnO3 and a high resistance bad metallic state that has a
temperature independent resistivity. The transition occurs at a threshold field
(Eth) which shows a steep enhancement on cooling. While at lower temperatures
the transition is sharp and involves large change in resistance but it softens
on heating and eventually absent above 280K. When the Mn4+ content is increased
by Sr substitution up to x=0.1, the observed transition though observable in
certain temperature range, softens considerably. The observation has been
explained as bias driven percolation type transition between two coexisting
phases, where the majority phase is a charge and orbitally ordered polaronic
insulating phase and the minority phase is a bad metallic phase. The mobile
fraction f of the bad metallic phase deduced from the experimental data follows
an activated kinetics with the activation energy nearly equal to 200 meV and
the prefactor fo is a strong function of the field that leads to a rapid
enhancement of f on application of field leading to the resistive state
transition. We suggest likely scenarios for such co-existing phases in
nominally pure LaMnO3 that can lead to the bias driven percolation type
transition.Comment: Accepted in JPC
Mass and charge fluctuations and black hole entropy
The effects of thermal fluctuations of the mass (horizon area) and electric
charge, on the entropy of non-rotating charged {\it macroscopic} black holes,
are analyzed using a grand canonical ensemble. Restricting to Gaussian
fluctuations around equilibrium, and assuming a power law type of relation
between the black hole mass, charge and horizon area, characterized by two real
positive indices, the grand canonical entropy is shown to acquire a logarithmic
correction with a positive coefficient proportional to the sum of the indices.
However, the root mean squared fluctuations of mass and charge relative to the
mean values of these quantities turn out to be independent of the details of
the assumed mass-area relation. We also comment on possible cancellation
between log (area) corrections arising due to {\it fixed area} quantum
spacetime fluctuations and that due to thermal fluctuations of the area and
other quantities.Comment: 8 pages revtex, no figure
Parabolic bundles on algebraic surfaces I - the Donaldson-Uhlenbeck compactification
The aim of this paper is to construct the parabolic version of the Donaldson-Uhlenbeck compactification for the moduli space of parabolic stable bundles on an algebraic surface with parabolic structures along a divisor with normal crossing singularities. We prove the non-emptiness of the moduli space of parabolic stable bundles of rank 2
Generalized Hawking-Page Phase Transition
The issue of radiant spherical black holes being in stable thermal
equilibrium with their radiation bath is reconsidered. Using a simple
equilibrium statistical mechanical analysis incorporating Gaussian thermal
fluctuations in a canonical ensemble of isolated horizons, the heat capacity is
shown to diverge at a critical value of the classical mass of the isolated
horizon, given (in Planckian units) by the {\it microcanonical} entropy
calculated using Loop Quantum Gravity. The analysis reproduces the Hawking-Page
phase transition discerned for anti-de Sitter black holes and generalizes it in
the sense that nowhere is any classical metric made use of.Comment: 9 Pages, Latex with 2 eps figure
Universal canonical black hole entropy
Non-rotating black holes in three and four dimensions are shown to possess a
canonical entropy obeying the Bekenstein-Hawking area law together with a
leading correction (for large horizon areas) given by the logarithm of the area
with a {\it universal} finite negative coefficient, provided one assumes that
the quantum black hole mass spectrum has a power law relation with the quantum
area spectrum found in Non-perturbative Canonical Quantum General Relativity.
The thermal instability associated with asymptotically flat black holes appears
in the appropriate domain for the index characterising this power law relation,
where the canonical entropy (free energy) is seen to turn complex.Comment: Revtex, 5 pages, no figures. Typos corrected and a footnote and some
references adde
Decision Analysis Methodology for remediation of Contaminated Groundwater Under the Influence of Technical and Economic Parameters
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