538 research outputs found
Quantum Thermodynamic Cycles and quantum heat engines
In order to describe quantum heat engines, here we systematically study
isothermal and isochoric processes for quantum thermodynamic cycles. Based on
these results the quantum versions of both the Carnot heat engine and the Otto
heat engine are defined without ambiguities. We also study the properties of
quantum Carnot and Otto heat engines in comparison with their classical
counterparts. Relations and mappings between these two quantum heat engines are
also investigated by considering their respective quantum thermodynamic
processes. In addition, we discuss the role of Maxwell's demon in quantum
thermodynamic cycles. We find that there is no violation of the second law,
even in the existence of such a demon, when the demon is included correctly as
part of the working substance of the heat engine.Comment: 17 pages, 9 figures, 4 table
Current fluctuations in a single tunnel junction
We study noise spectra of currents through a tunnel junction in weak
tunneling limit. We introduce effective capacitance to take into account the
interaction effect and explicitly incorporate the electromagnetic environment
of the junction into the formulation. We study the effect of charging energy
and macroscopic environment on noise spectra. We calculate current fluctuations
at tunneling barrier and fluctuations measured at leads. It is shown that two
fluctuations have different noise spectra and the relation between them is
nontrivial. We provide an explanation for the origin of the difference.
Experimental implications are discussed.Comment: 25 pages, Revtex 3.
Remarks on Shannon's Statistical Inference and the Second Law in Quantum Statistical Mechanics
We comment on a formulation of quantum statistical mechanics, which
incorporates the statistical inference of Shannon.
Our basic idea is to distinguish the dynamical entropy of von Neumann, , in terms of the density matrix ,
and the statistical amount of uncertainty of Shannon, , with in the representation where the total
energy and particle numbers are diagonal. These quantities satisfy the
inequality . We propose to interprete Shannon's statistical inference
as specifying the {\em initial conditions} of the system in terms of . A
definition of macroscopic observables which are characterized by intrinsic time
scales is given, and a quantum mechanical condition on the system, which
ensures equilibrium, is discussed on the basis of time averaging.
An interesting analogy of the change of entroy with the running coupling in
renormalization group is noted. A salient feature of our approach is that the
distinction between statistical aspects and dynamical aspects of quantum
statistical mechanics is very transparent.Comment: 16 pages. Minor refinement in the statements in the previous version.
This version has been published in Journal of Phys. Soc. Jpn. 71 (2002) 6
Kondo-lattice model: Application to the temperature-dependent electronic structure of EuO(100) films
We present calculations for the temperature-dependent electronic structure
and magnetic properties of thin ferromagnetic EuO films. The treatment is based
on a combination of a multiband-Kondo lattice model with first-principles
TB-LMTO band structure calculations. The method avoids the problem of
double-counting of relevant interactions and takes into account the correct
symmetry of the atomic orbitals. We discuss the temperature-dependent
electronic structures of EuO(100) films in terms of quasiparticle densities of
states and quasiparticle band structures. The Curie temperature T_C of the EuO
films turns out to be strongly thickness-dependent, starting from a very low
value = 15K for the monolayer and reaching the bulk value at about 25 layers
Interaction Properties of the Periodic and Step-like Solutions of the Double-Sine-Gordon Equation
The periodic and step-like solutions of the double-Sine-Gordon equation are
investigated, with different initial conditions and for various values of the
potential parameter . We plot energy and force diagrams, as functions
of the inter-soliton distance for such solutions. This allows us to consider
our system as an interacting many-body system in 1+1 dimension. We therefore
plot state diagrams (pressure vs. average density) for step-like as well as
periodic solutions. Step-like solutions are shown to behave similarly to their
counterparts in the Sine-Gordon system. However, periodic solutions show a
fundamentally different behavior as the parameter is increased. We
show that two distinct phases of periodic solutions exist which exhibit
manifestly different behavior. Response functions for these phases are shown to
behave differently, joining at an apparent phase transition point.Comment: 17pages, 15 figure
The postulates of gravitational thermodynamics
The general principles and logical structure of a thermodynamic formalism
that incorporates strongly self-gravitating systems are presented. This
framework generalizes and simplifies the formulation of thermodynamics
developed by Callen. The definition of extensive variables, the homogeneity
properties of intensive parameters, and the fundamental problem of
gravitational thermodynamics are discussed in detail. In particular, extensive
parameters include quasilocal quantities and are naturally incorporated into a
set of basic general postulates for thermodynamics. These include additivity of
entropies (Massieu functions) and the generalized second law. Fundamental
equations are no longer homogeneous first-order functions of their extensive
variables. It is shown that the postulates lead to a formal resolution of the
fundamental problem despite non-additivity of extensive parameters and
thermodynamic potentials. Therefore, all the results of (gravitational)
thermodynamics are an outgrowth of these postulates. The origin and nature of
the differences with ordinary thermodynamics are analyzed. Consequences of the
formalism include the (spatially) inhomogeneous character of thermodynamic
equilibrium states, a reformulation of the Euler equation, and the absence of a
Gibbs-Duhem relation.Comment: 28 pages, Revtex, no figures. An important sentence and several minor
corrections included. To appear in Physical Review
On the Second Law of thermodynamics and the piston problem
The piston problem is investigated in the case where the length of the
cylinder is infinite (on both sides) and the ratio is a very small
parameter, where is the mass of one particle of the gaz and is the mass
of the piston. Introducing initial conditions such that the stochastic motion
of the piston remains in the average at the origin (no drift), it is shown that
the time evolution of the fluids, analytically derived from Liouville equation,
agrees with the Second Law of thermodynamics.
We thus have a non equilibrium microscopical model whose evolution can be
explicitly shown to obey the two laws of thermodynamics.Comment: 29 pages, 9 figures submitted to Journal of Statistical Physics
(2003
On The Phase Structure and Thermodynamic Geometry of R-Charged Black Holes
We study the phase structure and equilibrium state space geometry of
R-charged black holes in , 4 and 7 and the corresponding rotating ,
and branes. For various charge configurations of the compact black
holes in the canonical ensemble we demonstrate new liquid-gas like phase
coexistence behaviour culminating in second order critical points. The critical
exponents turn out to be the same as that of four dimensional asymptotically
AdS black holes in Einstein Maxwell theory. We further establish that the
regions of stability for R-charged black holes are, in some cases, more
constrained than is currently believed, due to properties of some of the
response coefficients. The equilibrium state space scalar curvature is
calculated for various charge configurations, both for the case of compact as
well as flat horizons and its asymptotic behaviour with temperature is
established.Comment: 1 + 33 pages, LaTeX, 25 figures. References adde
Influence Action and decoherence of hydrodynamic modes
We derive an influence action for the heat diffusion equation and from its
spectral dependence show that long wavelength hydrodynamic modes are most
readily decohered. The result is independent of the details of the microscopic
dynamics, and follows from general principles alone.Comment: 5 pages, no figure
On the nonequilibrium entropy of large and small systems
Thermodynamics makes definite predictions about the thermal behavior of
macroscopic systems in and out of equilibrium. Statistical mechanics aims to
derive this behavior from the dynamics and statistics of the atoms and
molecules making up these systems. A key element in this derivation is the
large number of microscopic degrees of freedom of macroscopic systems.
Therefore, the extension of thermodynamic concepts, such as entropy, to small
(nano) systems raises many questions. Here we shall reexamine various
definitions of entropy for nonequilibrium systems, large and small. These
include thermodynamic (hydrodynamic), Boltzmann, and Gibbs-Shannon entropies.
We shall argue that, despite its common use, the last is not an appropriate
physical entropy for such systems, either isolated or in contact with thermal
reservoirs: physical entropies should depend on the microstate of the system,
not on a subjective probability distribution. To square this point of view with
experimental results of Bechhoefer we shall argue that the Gibbs-Shannon
entropy of a nano particle in a thermal fluid should be interpreted as the
Boltzmann entropy of a dilute gas of Brownian particles in the fluid
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