18,592 research outputs found
Dealing with Divergent Demands: Questionnaire Construction Between Longitudinal and Comparative Constraints
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.
Heavy quark damping rate in hot viscous QCD plasma
We derive an expression for the heavy quark damping rate in hot quark gluon
plasma in presence of flow. Here all the bath particles here are out of
equilibrium due to the existence of non-zero velocity gradient. The magnetic
sector shows similar infrared divergences even after hard thermal loop
corrections as one encounters in case of non-viscous plasma. We estimate the
first order correction in () for heavy quark damping rate due to the
non-zero viscosity of the QCD plasma.Comment: 19 pages, 1 figure, accepted for publication in PR
Definition and relevance of nonequilibrium intensive thermodynamic parameters
We show that intensive thermodynamic parameters associated to additive
conserved quantities can be naturally defined from a statistical approach in
far-from-equilibrium steady-state systems, under few assumptions, and without
any detailed balance requirement. It may apply, e.g., to dissipative systems
like granular gases where volume or mass is still conserved, or to systems with
periodic boundary conditions where fluxes of conserved quantities are present.
We emphasize the usefulness of this concept to characterize the coexistence of
different nonequilibrium phases, and discuss the influence of the contact
between two different systems, in relation with measurement issues.Comment: 4 pages, final versio
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
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
Dynamics and efficiency of a self-propelled, diffusiophoretic swimmer
Active diffusiophoresis - swimming through interaction with a self-generated,
neutral, solute gradient - is a paradigm for autonomous motion at the
micrometer scale. We study this propulsion mechanism within a linear response
theory. Firstly, we consider several aspects relating to the dynamics of the
swimming particle. We extend established analytical formulae to describe small
swimmers, which interact with their environment on a finite lengthscale. Solute
convection is also taken into account. Modeling of the chemical reaction
reveals a coupling between the angular distribution of reactivity on the
swimmer and the concentration field. This effect, which we term "reaction
induced concentration distortion", strongly influences the particle speed.
Building on these insights, we employ irreversible, linear thermodynamics to
formulate an energy balance. This approach highlights the importance of solute
convection for a consistent treatment of the energetics. The efficiency of
swimming is calculated numerically and approximated analytically. Finally, we
define an efficiency of transport for swimmers which are moving in random
directions. It is shown that this efficiency scales as the inverse of the
macroscopic distance over which transport is to occur.Comment: 16 pages, 11 figure
- …