273 research outputs found
Thermodynamic constraints on fluctuation phenomena
The relationships between reversible Carnot cycles, the absence of perpetual
motion machines and the existence of a non-decreasing, globally unique entropy
function forms the starting point of many textbook presentations of the
foundations of thermodynamics. However, the thermal fluctuation phenomena
associated with statistical mechanics has been argued to restrict the domain of
validity of this basis of the second law of thermodynamics. Here we demonstrate
that fluctuation phenomena can be incorporated into the traditional
presentation, extending, rather than restricting, the domain of validity of the
phenomenologically motivated second law. Consistency conditions lead to
constraints upon the possible spectrum of thermal fluctuations. In a special
case this uniquely selects the Gibbs canonical distribution and more generally
incorporates the Tsallis distributions. No particular model of microscopic
dynamics need be assumed.Comment: 12 pages, 24 figure
Critical phenomena and thermodynamic geometry of charged Gauss-Bonnet AdS black holes
In this paper, we study the phase structure and equilibrium state space
geometry of charged topological Gauss-Bonnet black holes in -dimensional
anti-de Sitter spacetime. Several critical points are obtained in the canonical
ensemble, and the critical phenomena and critical exponents near them are
examined. We find that the phase structures and critical phenomena drastically
depend on the cosmological constant and dimensionality . The
result also shows that there exists an analogy between the black hole and the
van der Waals liquid gas system. Moreover, we explore the phase transition and
possible property of the microstructure using the state space geometry. It is
found that the Ruppeiner curvature diverges exactly at the points where the
heat capacity at constant charge of the black hole diverges. This black hole is
also found to be a multiple system, i.e., it is similar to the ideal gas of
fermions in some range of the parameters, while to the ideal gas of bosons in
another range.Comment: 17 pages, 8 figures, 3 table
Off-Diagonal Long-Range Order in Bose Liquids: Irrotational Flow and Quantization of Circulation
On the basis of gauge invariance, it is proven in an elementary and
straightforward manner, but without invoking any {\it ad hoc} assumption, that
the existence of off-diagonal long-range order in one-particle reduced density
matrix in Bose liquids implies both the irrotational flow in a simply connected
region and the quantization of circulation in a multiply connected region, the
two fundamental properties of a Bose superfluid. The origin for both is the
phase coherence of condensate wave-functions. Some relevant issues are also
addressed.Comment: Revtex, 4 pages, no figure
The Importance of Host Plant Limitation for Caterpillars of an Arctiid Moth (Platyprepia Virginalis) Varies Spatially
Spatial dynamic theories such as source–sink models frequently describe habitat-specific demographies, yet there are surprisingly few field studies that have examined how and why interacting species vary in their dynamics across multiple habitat types. We studied the spatial pattern of interaction between a chewing herbivore and its primary larval host plant in two habitat types. We found that the interaction between an arctiid caterpillar (Platyprepia virginalis) and its host (Lupinus arboreus) differed in wet vs. upland dry habitats, as did yearly population dynamics for the caterpillar. In upland sites, there was a strong positive relationship between lupine cover and the abundance of caterpillars although this relationship was not apparent in wet sites. Additionally, in wet sites, caterpillar populations were larger and less variable across years. Caterpillars appeared to exhibit source–sink dynamics, with the time-averaged finite growth rate λ \u3e 1 in wet sites (sources), λ \u3c 1 in upland dry sites (sinks), and predominant source-to-sink movement of late-instar caterpillars. Populations in upland dry sites also went locally extinct in years of low regional abundance. Emigration from wet sites could potentially explain the lack of coupling of herbivore and host plant dynamics in these sites. These results indicate that movement and other factors affecting demography are habitat-specific and have important implications for trophic control. Acknowledging such complexity makes simple models of trophic control seem overly general but may allow us to formulate more broadly applicable ecological models
Social Network Reciprocity as a Phase Transition in Evolutionary Cooperation
In Evolutionary Dynamics the understanding of cooperative phenomena in
natural and social systems has been the subject of intense research during
decades. We focus attention here on the so-called "Lattice Reciprocity"
mechanisms that enhance evolutionary survival of the cooperative phenotype in
the Prisoner's Dilemma game when the population of darwinian replicators
interact through a fixed network of social contacts. Exact results on a "Dipole
Model" are presented, along with a mean-field analysis as well as results from
extensive numerical Monte Carlo simulations. The theoretical framework used is
that of standard Statistical Mechanics of macroscopic systems, but with no
energy considerations. We illustrate the power of this perspective on social
modeling, by consistently interpreting the onset of lattice reciprocity as a
thermodynamical phase transition that, moreover, cannot be captured by a purely
mean-field approach.Comment: 10 pages. APS styl
Fourier, hyperbolic and relativistic heat transfer equations: a comparative analytical study
[EN] Parabolic heat equation based on Fourier's theory (FHE), and hyperbolic heat equation (HHE), has been used to mathematically model the temperature distributions of biological tissue during thermal ablation. However, both equations have certain theoretical limitations. The FHE assumes an infinite thermal energy propagation speed, whereas the HHE might possibly be in breach of the second law of thermodynamics. The relativistic heat equation (RHE) is a hyperbolic-like equation, whose theoretical model is based on the theory of relativity and which was designed to overcome these theoretical impediments. In this study, the three heat equations for modelling of thermal ablation of biological tissues (FHE, HHE and RHE) were solved analytically and the temperature distributions compared. We found that RHE temperature values were always lower than those of the FHE, while the HHE values were higher than the FHE, except for the early stages of heating and at points away from the electrode. Although both HHE and RHE are mathematically hyperbolic, peaks were only found in the HHE temperature profiles. The three solutions converged for infinite time or infinite distance from the electrode. The percentage differences between the FHE and the other equations were larger for higher values of thermal relaxation time in HHE.This work received financial support from the Spanish Government (Ministerio de Ciencia e Innovacion, Ref. TEC2011-27133-C02-01).López Molina, JA.; Rivera Ortun, MJ.; Berjano, E. (2014). Fourier, hyperbolic and relativistic heat transfer equations: a comparative analytical study. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences. 470:1-16. https://doi.org/10.1098/rspa.2014.0547S11647
Unraveling the Landau's consistence criterion and the meaning of interpenetration in the "Two-Fluid" Model
In this letter we show that it is possible to unravel both the physical
origin of the Landau's consistence criterion and the specific and subtle
meaning of interpenetration of the "two fluids" if one takes into account that
in the hydrodynamic regime one needs a coarse-graining in time to bring the
system into local equilibrium. That is, the fuzziness in time is relevant for
the phenomenological Landau's consistency criterion and the meaning of
interpenetration. Note also that we are not questioning the validity of the
"Two-Fluid" Model.Comment: 8 pages, affiliation added, typos corrected, final version published
in Eur. Phys. J.
Hydrodynamic modes in a trapped Bose gas above the Bose-Einstein transition
We discuss the collective modes of a trapped Bose gas in the hydrodynamic
regime where atomic collisions ensure local thermal equilibrium for the
distribution function. Starting from the conservation laws, in the linearized
limit we derive a closed equation for the velocity fluctuations in a trapped
Bose gas above the Bose-Einstein transition temperature. Explicit solutions for
a parabolic trap are given. We find that the surface modes have the same
dispersion relation as the one recently obtained by Stringari for the
oscillations of the condensate at within the Thomas-Fermi approximation.
Results are also given for the monopole ``breathing'' mode as well as for the
excitations which result from the coupling of the monopole and quadrupole
modes in an anisotropic parabolic well.Comment: 4 pages, no figure, submitted to Phys. Rev. Let
Bulk viscosity of superfluid neutron stars
The hydrodynamics, describing dynamical effects in superfluid neutron stars,
essentially differs from the standard one-fluid hydrodynamics. In particular,
we have four bulk viscosity coefficients in the theory instead of one. In this
paper we calculate these coefficients, for the first time, assuming they are
due to non-equilibrium beta-processes (such as modified or direct Urca
process). The results of our analysis are used to estimate characteristic
damping times of sound waves in superfluid neutron stars. It is demonstrated
that all four bulk viscosity coefficients lead to comparable dissipation of
sound waves and should be considered on the same footing.Comment: 11 pages, 1 figure, this version with some minor stylistic changes is
published in Phys. Rev.
The superfluid fountain effect in a Bose-Einstein condensate
We consider a simple experimental setup, based on a harmonic confinement,
where a Bose-Einstein condensate and a thermal cloud of weakly interacting
alkali atoms are trapped in two different vessels connected by a narrow
channel. Using the classical field approximation, as described in J. Phys. B
40, R1 (2007) and optimized in Phys. Rev. A 81, 013629 (2010) for an arbitrary
trapping potential, we theoretically investigate the analog of the celebrated
superfluid helium fountain effect. We show that this thermo-mechanical effect
might indeed be observed in this system. By analyzing the dynamics of the
system, we are able to identify the superfluid and normal components of the
flow as well as to distinguish the condensate fraction from the superfluid
component. We show that the superfluid component can easily flow from the
colder vessel to the hotter one while the normal component is practically
blocked in the latter.Comment: 13 pages, 11 figures, 3 table
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