13,708 research outputs found
Free energy surfaces from nonequilibrium processes without work measurement
Recent developments in statistical mechanics have allowed the estimation of
equilibrium free energies from the statistics of work measurements during
processes that drive the system out of equilibrium. Here a different class of
processes is considered, wherein the system is prepared and released from a
nonequilibrium state, and no external work is involved during its observation.
For such ``clamp-and-release'' processes, a simple strategy for the estimation
of equilibrium free energies is offered. The method is illustrated with
numerical simulations, and analyzed in the context of tethered single-molecule
experiments.Comment: 15 pages, 3 figures (1 color); accepted to J. Chem. Phy
Matching pre-equilibrium dynamics and viscous hydrodynamics
We demonstrate how to match pre-equilibrium dynamics of a 0+1 dimensional
quark gluon plasma to 2nd-order viscous hydrodynamical evolution. The matching
allows us to specify the initial values of the energy density and shear tensor
at the initial time of hydrodynamical evolution as a function of the lifetime
of the pre-equilibrium period. We compare two models for the pre-equilibrium
quark-gluon plasma, longitudinal free streaming and collisionally-broadened
longitudinal expansion, and present analytic formulas which can be used to fix
the necessary components of the energy-momentum tensor. The resulting dynamical
models can be used to assess the effect of pre-equilibrium dynamics on
quark-gluon plasma observables. Additionally, we investigate the dependence of
entropy production on pre-equilibrium dynamics and discuss the limitations of
the standard definitions of the non-equilibrium entropy.Comment: 24 pages, 5 figures,v2: minor modifications and updated references.
Accepted for publication in Phys. Rev.
Covariant statistical mechanics and the stress-energy tensor
After recapitulating the covariant formalism of equilibrium statistical
mechanics in special relativity and extending it to the case of a non-vanishing
spin tensor, we show that the relativistic stress-energy tensor at
thermodynamical equilibrium can be obtained from a functional derivative of the
partition function with respect to the inverse temperature four-vector \beta.
For usual thermodynamical equilibrium, the stress-energy tensor turns out to be
the derivative of the relativistic thermodynamic potential current with respect
to the four-vector \beta, i.e. T^{\mu \nu} = - \partial \Phi^\mu/\partial
\beta_\nu. This formula establishes a relation between stress-energy tensor and
entropy current at equilibrium possibly extendable to non-equilibrium
hydrodynamics.Comment: 4 pages. Final version accepted for publication in Phys. Rev. Let
Relativistic Nucleus-Nucleus Collisions: Zone of Reactions and Space-Time Structure of a Fireball
A zone of reactions is determined and then exploited as a tool in studying
the space-time structure of an interacting system formed in a collision of
relativistic nuclei. The time dependence of the reaction rates integrated over
spatial coordinates is also considered. Evaluations are made with the help of
the microscopic transport model UrQMD. The relation of the boundaries of
different zones of reactions and the hypersurfaces of sharp chemical and
kinetic freeze-outs is discussed.Comment: 6 pages, 5 figure
Diffusion of multiple species with excluded-volume effects
Stochastic models of diffusion with excluded-volume effects are used to model
many biological and physical systems at a discrete level. The average
properties of the population may be described by a continuum model based on
partial differential equations. In this paper we consider multiple interacting
subpopulations/species and study how the inter-species competition emerges at
the population level. Each individual is described as a finite-size hard core
interacting particle undergoing Brownian motion. The link between the discrete
stochastic equations of motion and the continuum model is considered
systematically using the method of matched asymptotic expansions. The system
for two species leads to a nonlinear cross-diffusion system for each
subpopulation, which captures the enhancement of the effective diffusion rate
due to excluded-volume interactions between particles of the same species, and
the diminishment due to particles of the other species. This model can explain
two alternative notions of the diffusion coefficient that are often confounded,
namely collective diffusion and self-diffusion. Simulations of the discrete
system show good agreement with the analytic results
Momentum of an electromagnetic wave in dielectric media
Almost a hundred years ago, two different expressions were proposed for the
energy--momentum tensor of an electromagnetic wave in a dielectric. Minkowski's
tensor predicted an increase in the linear momentum of the wave on entering a
dielectric medium, whereas Abraham's tensor predicted its decrease. Theoretical
arguments were advanced in favour of both sides, and experiments proved
incapable of distinguishing between the two. Yet more forms were proposed, each
with their advocates who considered the form that they were proposing to be the
one true tensor. This paper reviews the debate and its eventual conclusion:
that no electromagnetic wave energy--momentum tensor is complete on its own.
When the appropriate accompanying energy--momentum tensor for the material
medium is also considered, experimental predictions of all the various proposed
tensors will always be the same, and the preferred form is therefore
effectively a matter of personal choice.Comment: 23 pages, 3 figures, RevTeX 4. Removed erroneous factor of mu/mu_0
from Eq.(44
The economic and livelihood value of provisioning services of the Ga-Mampa wetland, South Africa
The size of the Ga-Mampa wetland (1 km2), in the Olifants River catchment in South Africa, was halved between 1996 and 2004. This jeopardizes the ecological integrity and influences the benefits people obtain from the wetland. This study therefore analysed the economic values of the provisioning services derived from the Ga-Mampa wetland and evaluated their contribution to the livelihoods of local stakeholders. Using a direct market valuation technique and based on a mix of data collection approaches that include questionnaire survey, focus group discussions, key informant interviews, field observation and measurements and collection of market prices, we estimated the economic value of the main provisioning services provided by the wetland (collection of edible plants, crop production, livestock grazing, fishing, hunting, fuel-wood, reeds and sedge collection). The results show that the contribution of the wetland to the livelihoods of local community, estimated at an annual net financial value of 35 per household and is about half of the average monthly cash income from all income sources. Crop production contributes the highest gross and net financial value, whereas sedge collection yields the highest cash income. Most of the materials harvested from the wetland are used for household subsistence and are rarely sold. In addition to their economic and livelihood value, the wetland services are also essential to sustain the social and cultural responsibilities in gift giving to neighbours and relatives. The study concludes that the local people are highly dependent on the wetland ecosystem services in many ways but that current use exceeds sustainability levels, which jeopardizes their future livelihoods. We therefore recommend that the local stakeholders be supported in identifying alternative sources of livelihoods while simultaneously developing sustainable management strategies for small wetlands such as Ga-Mampa. In addition, other ecosystem services (regulating, supporting and cultural, including recreational benefits) provided by the wetland to local and downstream stakeholders need to be further studied and economically assessed.ZONE HUMIDE;ECOSYSTEME;GESTION DE L'EAU;ANALYSE ECONOMIQUE;VALEUR NON MARCHANDE;AFRIQUE DU SUD;ECONOMIC VALUATION;LIVELIHOOD ANALYSIS;MARKET VALUATION;PROVISIONING SERVICES;WETLAND ECOSYSTEMS
Anisotropic Flow and Viscous Hydrodynamics
We report part of our recent work on viscous hydrodynamics with consistent
phase space distribution f(x,\p) for freeze out. We develop the gradient
expansion formalism based on kinetic theory, and with the constraints from the
comparison between hydrodynamics and kinetic theory, viscous corrections to
f(x,\p) can be consistently determined order by order. Then with the obtained
f(x,\p), second order viscous hydrodynamical calculations are carried out for
elliptic flow .Comment: 8 pages, 2 figures. Proceedings for the 28th Winter Workshop on
Nuclear Dynamics, Dorado Del Mar, Puerto Rico, United States Of America, 7 -
14 Apr 201
Bulk viscosity of the massive Gross-Neveu model
A calculation of the bulk viscosity for the massive Gross-Neveu model at zero
fermion chemical potential is presented in the large- limit. This model
resembles QCD in many important aspects: it is asymptotically free, has a
dynamically generated mass gap, and for zero bare fermion mass it is scale
invariant at the classical level (broken through the trace anomaly at the
quantum level). For our purposes, the introduction of a bare fermion mass is
necessary to break the integrability of the model, and thus to be able to study
momentum transport. The main motivation is, by decreasing the bare mass, to
analyze whether there is a correlation between the maximum in the trace anomaly
and a possible maximum in the bulk viscosity, as recently conjectured. After
numerical analysis, I find that there is no direct correlation between these
two quantities: the bulk viscosity of the model is a monotonously decreasing
function of the temperature. I also comment on the sum rule for the spectral
density in the bulk channel, as well as on implications of this analysis for
other systems.Comment: v2: 3->3 processes included, conclusions unchanged. Comments and
references added. Typos corrected. To appear in Phys. Rev.
Irreversible Thermodynamics in Multiscale Stochastic Dynamical Systems
This work extends the results of the recently developed theory of a rather
complete thermodynamic formalism for discrete-state, continuous-time Markov
processes with and without detailed balance. We aim at investigating the
question that whether and how the thermodynamic structure is invariant in a
multiscale stochastic system. That is, whether the relations between
thermodynamic functions of state and process variables remain unchanged when
the system is viewed at different time scales and resolutions. Our results show
that the dynamics on a fast time scale contribute an entropic term to the
"internal energy function", , for the slow dynamics. Based on the
conditional free energy , one can then treat the slow dynamics as if
the fast dynamics is nonexistent. Furthermore, we show that the free energy,
which characterizes the spontaneous organization in a system without detailed
balance, is invariant with or without the fast dynamics: The fast dynamics is
assumed to reach stationarity instantaneously on the slow time scale; they have
no effect on the system's free energy. The same can not be said for the entropy
and the internal energy, both of which contain the same contribution from the
fast dynamics. We also investigate the consequences of time-scale separation in
connection to the concepts of quasi-stationaryty and steady-adiabaticity
introduced in the phenomenological steady-state thermodynamics
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