7,549 research outputs found
Magnetic transition and polaron crossover in a two-site single polaron model including double exchange interaction
A two-site double exchange model with a single polaron is studied using a
perturbation expansion based on the modified Lang-Firsov transformation. The
antiferromagnetic to ferromagnetic transition and the crossover from small to
large polaron are investigated for different values of the antiferromagnetic
interaction () between the core spins and the hopping () of the itinerant
electron. Effect of the external magnetic field on the small to large polaron
crossover and on the polaronic kinetic energy are studied. When the magnetic
transition and the small to large polaron crossover coincide for some suitable
range of , the magnetic field has very pronounced effect on the transport.Comment: REVTEX and ps files, accepted in the European Physical Jour.
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
Kinetic market models with single commodity having price fluctuations
We study here numerically the behavior of an ideal gas like model of markets
having only one non-consumable commodity. We investigate the behavior of the
steady-state distributions of money, commodity and total wealth, as the
dynamics of trading or exchange of money and commodity proceeds, with local (in
time) fluctuations in the price of the commodity. These distributions are
studied in markets with agents having uniform and random saving factors. The
self-organizing features in money distribution are similar to the cases without
any commodity (or with consumable commodities), while the commodity
distribution shows an exponential decay. The wealth distribution shows
interesting behavior: Gamma like distribution for uniform saving propensity and
has the same power-law tail, as that of the money distribution, for a market
with agents having random saving propensity.Comment: RevTeX4, 6 pages, 5 eps figures, accepted in Eur. Phys. J.
Effect of different site energies on polaronic properties
Using the perturbation method based on a variational phonon basis obtained by
the modified Lang-Firsov (MLF) transformation, the two-site single polaron
Holstein model is studied in presence of a difference in bare site energies
(=-). The polaronic ground-state wave
function is calculated up to the fifth order of perturbation. The effect of
(acts as a site-energy disorder) on the polaron crossover,
polaronic kinetic energy, oscillator wavefuncion and polaron localization are
studied. Considering a double-exchange Holstein model with finite ,
role of disorder on the properties of the double-exchange system is also
discussed.Comment: 9 pages, 7 figures, submitted to PR
First excited state calculation using different phonon bases for the two-site Holstein model
The single-electron energy and static charge-lattice deformation correlations
have been calculated for the first excited state of a two-site Holstein model
within perturbative expansions using different standard phonon bases obtained
through Lang-Firsov (LF) transformation, LF with squeezed phonon states,
modified LF, modified LF transformation with squeezed phonon states, and also
within weak-coupling perturbation approach. Comparisons of the convergence of
the perturbative expansions for different phonon bases reveal that modified LF
approach works much better than other approaches for major range of the
coupling strength.Comment: 11 pages (REVTEX), 4 postscript figure
Relaxation in statistical many-agent economy models
We review some statistical many-agent models of economic and social systems
inspired by microscopic molecular models and discuss their stochastic
interpretation. We apply these models to wealth exchange in economics and study
how the relaxation process depends on the parameters of the system, in
particular on the saving propensities that define and diversify the agent
profiles.Comment: Revised final version. 6 pages, 5 figure
Universal canonical entropy for gravitating systems
The thermodynamics of general relativistic systems with boundary, obeying a
Hamiltonian constraint in the bulk, is argued to be determined solely by the
boundary quantum dynamics, and hence by the area spectrum. Assuming, for large
area of the boundary, (a) an area spectrum as determined by Non-perturbative
Canonical Quantum General Relativity (NCQGR), (b) an energy spectrum that bears
a power law relation to the area spectrum, (c) an area law for the leading
order microcanonicai entropy, leading thermal fluctuation corrections to the
canonical entropy are shown to be logarithmic in area with a universal
coefficient. Since the microcanonical entropy also has univeral logarithmic
corrections to the area law (from quantum spacetime fluctuations, as found
earlier) the canonical entropy then has a universal form including logarithmic
corrections to the area law. This form is shown to be independent of the index
appearing in assumption (b). The index, however, is crucial in ascertaining the
domain of validity of our approach based on thermal equilibrium.Comment: 6 pages revtex, one eps figure; based on talk delivered at the
International Conference on Gravitation and Cosmology held at Kochi, India
during 5-9 January, 200
Effect of relative humidity on the long-term operation of a single mask triple GEM chamber
The characteristic studies of a Single Mask~(SM) triple Gas Electron
Multiplier (GEM) detector are carried out using Ar/CO gas mixture in 70/30
volume ratio in continuous flow mode. A Fe X-ray source is used for this
work. The gain and energy resolution are studied from the 5.9 keV X-ray energy
spectra. After correcting the effects of temperature and pressure variation,
the effect of relative humidity on the gain and energy resolution of the
chamber is investigated. The details of the experimental setup, measurement
methods and results are presented in this article
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