247 research outputs found
The Quantum Refrigerator: The quest for absolute zero
The scaling of the optimal cooling power of a reciprocating quantum
refrigerator is sought as a function of the cold bath temperature as . The working medium consists of noninteracting particles in a harmonic
potential. Two closed-form solutions of the refrigeration cycle are analyzed,
and compared to a numerical optimization scheme, focusing on cooling toward
zero temperature. The optimal cycle is characterized by linear relations
between the heat extracted from the cold bath, the energy level spacing of the
working medium and the temperature. The scaling of the optimal cooling rate is
found to be proportional to giving a dynamical interpretation to
the third law of thermodynamics
Low temperature Thermodynamics in the Context of Dissipative Diamagnetism
We revisit here the effect of quantum dissipation on the much - studied
problem of Landau diamagnetism, and analyze the results in the light of the
third law of thermodynamics. The case of an additional parabolic potential is
separately assessed. We find that dissipation arising from strong coupling of
the system to its environment qualitatively alters the low-temperature
thermodynamic attributes such as the entropy and the specific heat
Electronic thermal transport in strongly correlated multilayered nanostructures
The formalism for a linear-response many-body treatment of the electronic
contributions to thermal transport is developed for multilayered
nanostructures. By properly determining the local heat-current operator, it is
possible to show that the Jonson-Mahan theorem for the bulk can be extended to
inhomogeneous problems, so the various thermal-transport coefficient integrands
are related by powers of frequency (including all effects of vertex corrections
when appropriate). We illustrate how to use this formalism by showing how it
applies to measurements of the Peltier effect, the Seebeck effect, and the
thermal conductance.Comment: 17 pages, 4 figures, submitted to Phys. Rev.
Notes on the Third Law of Thermodynamics.I
We analyze some aspects of the third law of thermodynamics. We first review
both the entropic version (N) and the unattainability version (U) and the
relation occurring between them. Then, we heuristically interpret (N) as a
continuity boundary condition for thermodynamics at the boundary T=0 of the
thermodynamic domain. On a rigorous mathematical footing, we discuss the third
law both in Carath\'eodory's approach and in Gibbs' one. Carath\'eodory's
approach is fundamental in order to understand the nature of the surface T=0.
In fact, in this approach, under suitable mathematical conditions, T=0 appears
as a leaf of the foliation of the thermodynamic manifold associated with the
non-singular integrable Pfaffian form . Being a leaf, it cannot
intersect any other leaf const. of the foliation. We show that (N) is
equivalent to the requirement that T=0 is a leaf. In Gibbs' approach, the
peculiar nature of T=0 appears to be less evident because the existence of the
entropy is a postulate; nevertheless, it is still possible to conclude that the
lowest value of the entropy has to belong to the boundary of the convex set
where the function is defined.Comment: 29 pages, 2 figures; RevTex fil
Diffuse-Charge Dynamics in Electrochemical Systems
The response of a model micro-electrochemical system to a time-dependent
applied voltage is analyzed. The article begins with a fresh historical review
including electrochemistry, colloidal science, and microfluidics. The model
problem consists of a symmetric binary electrolyte between parallel-plate,
blocking electrodes which suddenly apply a voltage. Compact Stern layers on the
electrodes are also taken into account. The Nernst-Planck-Poisson equations are
first linearized and solved by Laplace transforms for small voltages, and
numerical solutions are obtained for large voltages. The ``weakly nonlinear''
limit of thin double layers is then analyzed by matched asymptotic expansions
in the small parameter , where is the
screening length and the electrode separation. At leading order, the system
initially behaves like an RC circuit with a response time of
(not ), where is the ionic diffusivity, but nonlinearity
violates this common picture and introduce multiple time scales. The charging
process slows down, and neutral-salt adsorption by the diffuse part of the
double layer couples to bulk diffusion at the time scale, . In the
``strongly nonlinear'' regime (controlled by a dimensionless parameter
resembling the Dukhin number), this effect produces bulk concentration
gradients, and, at very large voltages, transient space charge. The article
concludes with an overview of more general situations involving surface
conduction, multi-component electrolytes, and Faradaic processes.Comment: 10 figs, 26 pages (double-column), 141 reference
Cosmological Dark Energy: Prospects for a Dynamical Theory
We present an approach to the problem of vacuum energy in cosmology, based on
dynamical screening of Lambda on the horizon scale. We review first the
physical basis of vacuum energy as a phenomenon connected with macroscopic
boundary conditions, and the origin of the idea of its screening by particle
creation and vacuum polarization effects. We discuss next the relevance of the
quantum trace anomaly to this issue. The trace anomaly implies additional terms
in the low energy effective theory of gravity, which amounts to a non-trivial
modification of the classical Einstein theory, fully consistent with the
Equivalence Principle. We show that the new dynamical degrees of freedom the
anomaly contains provide a natural mechanism for relaxing Lambda to zero on
cosmological scales. We consider possible signatures of the restoration of
conformal invariance predicted by the fluctuations of these new scalar degrees
of freedom on the spectrum and statistics of the CMB, in light of the latest
bounds from WMAP. Finally we assess the prospects for a new cosmological model
in which the dark energy adjusts itself dynamically to the cosmological horizon
boundary, and therefore remains naturally of order H^2 at all times without
fine tuning.Comment: 50 pages, Invited Contribution to New Journal of Physics Focus Issue
on Dark Energ
Movement and Fluctuations of the Vacuum
Quantum fields possess zero-point or vacuum fluctuations which induce
mechanical effects, namely generalised Casimir forces, on any scatterer.
Symmetries of vacuum therefore raise fundamental questions when confronted
with the principle of relativity of motion in vacuum. The specific case of
uniformly accelerated motion is particularly interesting, in connection with
the much debated question of the appearance of vacuum in accelerated frames.
The choice of Rindler representation, commonly used in General Relativity,
transforms vacuum fluctuations into thermal fluctuations, raising difficulties
of interpretation. In contrast, the conformal representation of uniformly
accelerated frames fits the symmetry properties of field propagation and
quantum vacuum and thus leads to extend the principle of relativity of motion
to uniform accelerations.
Mirrors moving in vacuum with a non uniform acceleration are known to
radiate. The associated radiation reaction force is directly connected to
fluctuating forces felt by motionless mirrors through fluctuation-dissipation
relations. Scatterers in vacuum undergo a quantum Brownian motion which
describes irreducible quantum fluctuations. Vacuum fluctuations impose ultimate
limitations on measurements of position in space-time, and thus challenge the
very concept of space-time localisation within a quantum framework.
For test masses greater than Planck mass, the ultimate limit in localisation
is determined by gravitational vacuum fluctuations. Not only positions in
space-time, but also geodesic distances, behave as quantum variables,
reflecting the necessary quantum nature of an underlying geometry.Comment: 17 pages, to appear in Reports on Progress in Physic
Stochastic Dynamical Structure (SDS) of Nonequilibrium Processes in the Absence of Detailed Balance. IV: Emerging of Stochastic Dynamical Equalities and Steady State Thermodynamics from Darwinian Dynamics
This is the fourth paper, the last one, on solution to the problem of absence
of detailed balance in nonequilibrium processes. It is an approach based on
another known universal dynamics: The evolutionary dynamics first conceived by
Darwin and Wallace, referring to as Darwinian dynamics in the present paper,
has been found to be universally valid in biology; The statistical mechanics
and thermodynamics, while enormously successful in physics, have been in an
awkward situation of wanting a consistent dynamical understanding; Here we
present from a formal point of view an exploration of the connection between
thermodynamics and Darwinian dynamics and a few related topics. We first show
that the stochasticity in Darwinian dynamics implies the existence temperature,
hence the canonical distribution of Boltzmann-Gibbs type. In term of relative
entropy the Second Law of thermodynamics is dynamically demonstrated without
detailed balance condition, and is valid regardless of size of the system. In
particular, the dynamical component responsible for breaking detailed balance
condition does not contribute to the change of the relative entropy. Two types
of stochastic dynamical equalities of current interest are explicitly discussed
in the present approach: One is based on Feynman-Kac formula and another is a
generalization of Einstein relation. Both are directly accessible to
experimental tests. Our demonstration indicates that Darwinian dynamics
represents logically a simple and straightforward starting point for
statistical mechanics and thermodynamics and is complementary to and consistent
with conservative dynamics that dominates the physical sciences. Present
exploration suggests the existence of a unified stochastic dynamical framework
both near and far from equilibrium.Comment: latex, 49 page
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