2,247 research outputs found
Macroscopic proof of the Jarzynski-Wojcik fluctuation theorem for heat exchange
In a recent work, Jarzynski and Wojcik (2004 Phys. Rev. Lett. 92, 230602)
have shown by using the properties of Hamiltonian dynamics and a statistical
mechanical consideration that, through contact, heat exchange between two
systems initially prepared at different temperatures obeys a fluctuation
theorem. Here, another proof is presented, in which only macroscopic
thermodynamic quantities are employed. The detailed balance condition is found
to play an essential role. As a result, the theorem is found to hold under very
general conditions.Comment: 9 pages, 0 figure
Tolman mass, generalized surface gravity, and entropy bounds
In any static spacetime the quasi-local Tolman mass contained within a volume
can be reduced to a Gauss-like surface integral involving the flux of a
suitably defined generalized surface gravity. By introducing some basic
thermodynamics and invoking the Unruh effect one can then develop elementary
bounds on the quasi-local entropy that are very similar in spirit to the
holographic bound, and closely related to entanglement entropy.Comment: V1: 4 pages. Uses revtex4-1; V2: Three references added; V3: Some
notational changes for clarity; introductory paragraph rewritten; no physics
changes. This version accepted for publication in Physical Review Letter
Gravitational energy
Observers at rest in a stationary spacetime flat at infinity can measure
small amounts of rest-mass+internal energies+kinetic energies+pressure energy
in a small volume of fluid attached to a local inertial frame. The sum of these
small amounts is the total "matter energy" for those observers. The total
mass-energy minus the matter energy is the binding gravitational energy.
Misner, Thorne and Wheeler evaluated the gravitational energy of a
spherically symmetric static spacetime. Here we show how to calculate
gravitational energy in any static and stationary spacetime for isolated
sources with a set of observers at rest.
The result of MTW is recovered and we find that electromagnetic and
gravitational 3-covariant energy densities in conformastatic spacetimes are of
opposite signs. Various examples suggest that gravitational energy is negative
in spacetimes with special symmetries or when the energy-momentum tensor
satisfies usual energy conditions.Comment: 12 pages. Accepted for publication in Class. Quantum Gra
Cosmologies with Energy Exchange
We provide a simple mathematical description of the exchange of energy
between two fluids in an expanding Friedmann universe with zero spatial
curvature. The evolution can be reduced to a single non-linear differential
equation which we solve in physically relevant cases and provide an analysis of
all the possible evolutions. Particular power-law solutions exist for the
expansion scale factor and are attractors at late times under particular
conditions. We show how a number of problems studied in the literature, such as
cosmological vacuum energy decay, particle annihilation, and the evolution of a
population of evaporating black holes, correspond to simple particular cases of
our model. In all cases we can determine the effects of the energy transfer on
the expansion scale factor. We also consider the situation in the presence of
anti-decaying fluids and so called phantom fluids which violate the dominant
energy conditions.Comment: 12 pages, 1 figur
Configurational temperature control for atomic and molecular systems
A new configurational temperature thermostat suitable for molecules with holonomic constraints is derived. This thermostat has a simple set of motion equations, can generate the canonical ensemble in both position and momentum space, acts homogeneously through the spatial
coordinates, and does not intrinsically violate the constraints. Our new configurational thermostat is
closely related to the kinetic temperature Nosé-Hoover thermostat with feedback coupled to the position variables via a term proportional to the net molecular force. We validate the thermostat by comparing equilibrium static and dynamic quantities for a fluid of n-decane molecules under
configurational and kinetic temperature control. Practical aspects concerning the implementation of the new thermostat in a molecular dynamics code and the potential applications are discussed
Planck Fluctuations, Measurement Uncertainties and the Holographic Principle
Starting from a critical analysis of recently reported surprisingly large
uncertainties in length and position measurements deduced within the framework
of quantum gravity, we embark on an investigation both of the correlation
structure of Planck scale fluctuations and the role the holographic hypothesis
is possibly playing in this context. While we prove the logical independence of
the fluctuation results and the holographic hypothesis (in contrast to some
recent statements in that direction) we show that by combining these two topics
one can draw quite strong and interesting conclusions about the fluctuation
structure and the microscopic dynamics on the Planck scale. We further argue
that these findings point to a possibly new and generalized form of quantum
statistical mechanics of strongly (anti)correlated systems of degrees of
freedom in this fundamental regime.Comment: 19 pages, Latex, no figures, some new references, to appear
ModPhysLett
Fluctuation theorem for the renormalized entropy change in the strongly nonlinear nonequilibrium regime
Generalizing a recent work [T. Taniguchi and E. G. D. Cohen, J. Stat. Phys.
126, 1 (2006)] that was based on the Onsager-Machlup theory, a nonlinear
relaxation process is considered for a macroscopic thermodynamic quantity. It
is found that the fluctuation theorem holds in the nonlinear nonequilibrium
regime if the change of the entropy characterized by local equilibria is
appropriately renormalized. The fluctuation theorem for the ordinary entropy
change is recovered in the linear near-equilibrium case. This result suggests a
possibility that the the information-theoretic entropy of the Shannon form may
be modified in the strongly nonlinear nonequilibrium regime.Comment: 14 pages, no figures. Typos correcte
Integral Constraints On cosmological Perturbations and their Energy
We show the relation between Traschen's integral equations and the energy,
and ``position of the centre of mass'', of the matter perturbations in a
Robertson-Walker spacetime. When the perturbations are ``localised'' we get a
set of integral constraints that includes hers. We illustrate them on a simple
example.Comment: 19 pages, Tex file, submitted to Classical and Quantum Gravit
Irreversible thermodynamics of open chemical networks I: Emergent cycles and broken conservation laws
In this and a companion paper we outline a general framework for the
thermodynamic description of open chemical reaction networks, with special
regard to metabolic networks regulating cellular physiology and biochemical
functions. We first introduce closed networks "in a box", whose thermodynamics
is subjected to strict physical constraints: the mass-action law, elementarity
of processes, and detailed balance. We further digress on the role of solvents
and on the seemingly unacknowledged property of network independence of free
energy landscapes. We then open the system by assuming that the concentrations
of certain substrate species (the chemostats) are fixed, whether because
promptly regulated by the environment via contact with reservoirs, or because
nearly constant in a time window. As a result, the system is driven out of
equilibrium. A rich algebraic and topological structure ensues in the network
of internal species: Emergent irreversible cycles are associated to
nonvanishing affinities, whose symmetries are dictated by the breakage of
conservation laws. These central results are resumed in the relation between the number of fundamental affinities , that of broken
conservation laws and the number of chemostats . We decompose the
steady state entropy production rate in terms of fundamental fluxes and
affinities in the spirit of Schnakenberg's theory of network thermodynamics,
paving the way for the forthcoming treatment of the linear regime, of
efficiency and tight coupling, of free energy transduction and of thermodynamic
constraints for network reconstruction.Comment: 18 page
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Effect of reflood prediction uncertainties on LOFT cladding oxidation
The FLOOD4 and RELAP4/MOD6 computer codes, which are used to perform LOFT reflood analysis, have been compared to FLECHT-SET and Semiscale gravity feed tests to provide an evaluation of core reflood prediction techniques and an identification of phenomena important to LOFT reflood behavior. These comparisons provide a basis for estimating uncertainty in cladding temperature history during the LOFT loss-of-coolant experiments (LOCEs). The bounds on the cladding temperature response are then utilized to estimate a range of expected cladding oxidation and embrittlement which is essential for identifying special equipment needed during replacement, storage, and post-test examination of LOFT fuel modules. FLOOD4 couples the system hydraulic response with core heat transfer and steam generation. Four heat transfer correlations simulate the boiling curve and liquid entrainment, fallback and vaporization in the steam generators are modeled. FLOOD4 requires user input multipliers to specify the dispersed flow heat transfer, liquid entrainment and correlations to describe liquid fallback from the upper plenum region. The fraction of liquid vaporized in the steam generators must also be user input
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