1,363 research outputs found
Macroscopic equations for the adiabatic piston
A simplified version of a classical problem in thermodynamics -- the
adiabatic piston -- is discussed in the framework of kinetic theory. We
consider the limit of gases whose relaxation time is extremely fast so that the
gases contained on the left and right chambers of the piston are always in
equilibrium (that is the molecules are uniformly distributed and their
velocities obey the Maxwell-Boltzmann distribution) after any collision with
the piston. Then by using kinetic theory we derive the collision statistics
from which we obtain a set of ordinary differential equations for the evolution
of the macroscopic observables (namely the piston average velocity and
position, the velocity variance and the temperatures of the two compartments).
The dynamics of these equations is compared with simulations of an ideal gas
and a microscopic model of gas settled to verify the assumptions used in the
derivation. We show that the equations predict an evolution for the macroscopic
variables which catches the basic features of the problem. The results here
presented recover those derived, using a different approach, by Gruber, Pache
and Lesne in J. Stat. Phys. 108, 669 (2002) and 112, 1177 (2003).Comment: 13 pages, 7 figures (revTeX4) The paper has been completely rewritten
with new derivation and results, supplementary information can be found at
http://denali.phys.uniroma1.it/~cencini/Papers/cppv07_supplements.pd
Quantum thermodynamics with missing reference frames: Decompositions of free energy into non-increasing components
If an absolute reference frame with respect to time, position, or orientation
is missing one can only implement quantum operations which are covariant with
respect to the corresponding unitary symmetry group G. Extending observations
of Vaccaro et al., I argue that the free energy of a quantum system with
G-invariant Hamiltonian then splits up into the Holevo information of the orbit
of the state under the action of G and the free energy of its orbit average.
These two kinds of free energy cannot be converted into each other. The first
component is subadditive and the second superadditive; in the limit of
infinitely many copies only the usual free energy matters.
Refined splittings of free energy into more than two independent
(non-increasing) terms can be defined by averaging over probability measures on
G that differ from the Haar measure.
Even in the presence of a reference frame, these results provide lower bounds
on the amount of free energy that is lost after applying a covariant channel.
If the channel properly decreases one of these quantities, it decreases the
free energy necessarily at least by the same amount, since it is unable to
convert the different forms of free energies into each other.Comment: 17 pages, latex, 1 figur
Thermodynamic curvature measures interactions
Thermodynamic fluctuation theory originated with Einstein who inverted the
relation to express the number of states in terms of entropy:
. The theory's Gaussian approximation is discussed in most
statistical mechanics texts. I review work showing how to go beyond the
Gaussian approximation by adding covariance, conservation, and consistency.
This generalization leads to a fundamentally new object: the thermodynamic
Riemannian curvature scalar , a thermodynamic invariant. I argue that
is related to the correlation length and suggest that the sign of
corresponds to whether the interparticle interactions are effectively
attractive or repulsive.Comment: 29 pages, 7 figures (added reference 27
Microcanonical quantum fluctuation theorems
Previously derived expressions for the characteristic function of work
performed on a quantum system by a classical external force are generalized to
arbitrary initial states of the considered system and to Hamiltonians with
degenerate spectra. In the particular case of microcanonical initial states
explicit expressions for the characteristic function and the corresponding
probability density of work are formulated. Their classical limit as well as
their relations to the respective canonical expressions are discussed. A
fluctuation theorem is derived that expresses the ratio of probabilities of
work for a process and its time reversal to the ratio of densities of states of
the microcanonical equilibrium systems with corresponding initial and final
Hamiltonians.From this Crooks-type fluctuation theorem a relation between
entropies of different systems can be derived which does not involve the time
reversed process. This entropy-from-work theorem provides an experimentally
accessible way to measure entropies.Comment: revised and extended versio
Internal thermal noise in the LIGO test masses : a direct approach
The internal thermal noise in LIGO's test masses is analyzed by a new
technique, a direct application of the Fluctuation-Dissipation Theorem to
LIGO's readout observable, (longitudinal position of test-mass face,
weighted by laser beam's Gaussian profile). Previous analyses, which relied on
a normal-mode decomposition of the test-mass motion, were valid only if the
dissipation is uniformally distributed over the test-mass interior, and they
converged reliably to a final answer only when the beam size was a
non-negligible fraction of the test-mass cross section. This paper's direct
analysis, by contrast, can handle inhomogeneous dissipation and arbitrary beam
sizes. In the domain of validity of the previous analysis, the two methods give
the same answer for , the spectral density of thermal noise, to within
expected accuracy. The new analysis predicts that thermal noise due to
dissipation concentrated in the test mass's front face (e.g. due to mirror
coating) scales as , by contrast with homogeneous dissipation, which
scales as ( is the beam radius); so surface dissipation could
become significant for small beam sizes.Comment: 6 pages, RevTex, 1 figur
Ignorance based inference of optimality in thermodynamic processes
We derive ignorance based prior distribution to quantify incomplete
information and show its use to estimate the optimal work characteristics of a
heat engine.Comment: Latex, 10 pages, 3 figure
Isotropic, Nematic and Smectic A Phase Behaviour in a Fictitious Field
Phase behaviours of liquid crystals under external fields, conjugate to the
nematic order and smectic order, are studied within the framework of mean field
approximation developed by McMillan. It is found that phase diagrams, of
temperature vs interaction parameter of smectic A order, show several
topologically different types caused by the external fields. The influences of
the field conjugate to the smectic A phase, which is fictitious field, are
precisely discussed.Comment: To be published in J. Phys. Soc. Jpn. vol.73 No.
Entropy of Extremal Black Holes in Two Dimensions
Entropy for two dimensional extremal black holes is computed explicitly in a
finite-space formulation of the black hole thermodynamics and is shown to be
zero {\it locally}. Our results are in conformity with the recent one by
Hawking et al in four dimensions.Comment: 11 page
Calculation of the Chiral Lagrangian Coefficients
We present a systematic way to combine the global color model and the
instanton liquid model to calculate the chiral
Lagrangian coefficients. Our numerical results are in agreement well with the
experimental values.Comment: 7 pages, To appear in Chin.Phys.Lett, Year 200
Efficiency in nanostructured thermionic and thermoelectric devices
Advances in solid-state device design now allow the spectrum of transmitted
electrons in thermionic and thermoelectric devices to be engineered in ways
that were not previously possible. Here we show that the shape of the electron
energy spectrum in these devices has a significant impact on their performance.
We distinguish between traditional thermionic devices where electron momentum
is filtered in the direction of transport only and a second type, in which the
electron filtering occurs according to total electron momentum. Such 'total
momentum filtered' kr thermionic devices could potentially be implemented in,
for example, quantum dot superlattices. It is shown that whilst total momentum
filtered thermionic devices may achieve efficiency equal to the Carnot value,
traditional thermionic devices are limited to efficiency below this. Our second
main result is that the electronic efficiency of a device is not only improved
by reducing the width of the transmission filter as has previously been shown,
but also strongly depends on whether the transmission probability rises sharply
from zero to full transmission. The benefit of increasing efficiency through a
sharply rising transmission probability is that it can be achieved without
sacrificing device power, in contrast to the use of a narrow transmission
filter which can greatly reduce power. We show that devices which have a
sharply-rising transmission probability significantly outperform those which do
not and it is shown such transmission probabilities may be achieved with
practical single and multibarrier devices. Finally, we comment on the
implications of the effect the shape of the electron energy spectrum on the
efficiency of thermoelectric devices.Comment: 11 pages, 15 figure
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