14,527 research outputs found
Phase transition in the Jarzynski estimator of free energy differences
The transition between a regime in which thermodynamic relations apply only
to ensembles of small systems coupled to a large environment and a regime in
which they can be used to characterize individual macroscopic systems is
analyzed in terms of the change in behavior of the Jarzynski estimator of
equilibrium free energy differences from nonequilibrium work measurements.
Given a fixed number of measurements, the Jarzynski estimator is unbiased for
sufficiently small systems. In these systems, the directionality of time is
poorly defined and configurations that dominate the empirical average, but
which are in fact typical of the reverse process, are sufficiently well
sampled. As the system size increases the arrow of time becomes better defined.
The dominant atypical fluctuations become rare and eventually cannot be sampled
with the limited resources that are available. Asymptotically, only typical
work values are measured. The Jarzynski estimator becomes maximally biased and
approaches the exponential of minus the average work, which is the result that
is expected from standard macroscopic thermodynamics. In the proper scaling
limit, this regime change can be described in terms of a phase transition in
variants of the random energy model (REM). This correspondence is explicitly
demonstrated in several examples of physical interest: near-equilibrium
processes in which the work distribution is Gaussian, the sudden compression of
an ideal gas and adiabatic quasi-static volume changes in a dilute real gas.Comment: 29 pages, 5 figures, accepted for publication in Physical Review E
(2012
Rare Events and Scale--Invariant Dynamics of Perturbations in Delayed Dynamical Systems
We study the dynamics of perturbations in time delayed dynamical systems.
Using a suitable space-time coordinate transformation, we find that the time
evolution of the linearized perturbations (Lyapunov vector) can be mapped to
the linear Zhang surface growth model [Y.-C. Zhang, J. Phys. France {\bf 51},
2129 (1990)], which is known to describe surface roughening driven by power-law
distributed noise. As a consequence, Lyapunov vector dynamics is dominated by
rare random events that lead to non-Gaussian fluctuations and multiscaling
properties.Comment: Final version to appear in Phys. Rev. Lett., 4 pages, 3 eps fig
On the Kinematics of GRB980425 and its association with SN1998bw
In this paper I put forward a model in which GRB980425 is both associated
with SN1998bw and is also a standard canonical (long; ~seconds) gamma-ray
burst. Herein it is argued that if gamma-ray bursts are relativistic jets with
the fastest moving material at the core, then the range of observed jet
inclinations to the line-of-sight produces a range in the observed properties
of GRBs, i.e. the lag-luminosity relationship. In particular, if the jet
inclination is high enough, the observed emitter will move slowly enough to
render relativistic beaming ineffective, thus distinguishing the jet from
apparent isotropic emission. Thus we expect a break in the lag-luminosity
relationship. I propose that GRB980425 defines that break. The position of this
break gives important physical parameters such as the Lorentz factor
(\gamma_max ~ 1000), the jet opening angle (~1 degree), and thus the beaming
fraction (~10^-4). Estimates of burst rates are consistent with observation. If
correct, this model is evidence in favor of the collapsar mode as the
progenitor of cosmological, long gamma-ray bursts.Comment: 7 pages, including 1 figure. Submitted to ApJ Letter
Extreme Quantum Advantage for Rare-Event Sampling
We introduce a quantum algorithm for efficient biased sampling of the rare
events generated by classical memoryful stochastic processes. We show that this
quantum algorithm gives an extreme advantage over known classical biased
sampling algorithms in terms of the memory resources required. The quantum
memory advantage ranges from polynomial to exponential and when sampling the
rare equilibrium configurations of spin systems the quantum advantage diverges.Comment: 11 pages, 9 figures;
http://csc.ucdavis.edu/~cmg/compmech/pubs/eqafbs.ht
Deformed Jarzynski Equality
The well-known Jarzynski equality, often written in the form , provides a non-equilibrium means to measure
the free energy difference of a system at the same inverse
temperature based on an ensemble average of non-equilibrium work .
The accuracy of Jarzynski's measurement scheme was known to be determined by
the variance of exponential work, denoted as . However, it was recently found that can systematically diverge in both classical and quantum cases. Such
divergence will necessarily pose a challenge in the applications of Jarzynski
equality because it may dramatically reduce the efficiency in determining
. In this work, we present a deformed Jarzynski equality for both
classical and quantum non-equilibrium statistics, in efforts to reuse
experimental data that already suffers from a diverging . The main feature of our deformed Jarzynski
equality is that it connects free energies at different temperatures and it may
still work efficiently subject to a diverging . The conditions for applying our deformed Jarzynski equality may be
met in experimental and computational situations. If so, then there is no need
to redesign experimental or simulation methods. Furthermore, using the deformed
Jarzynski equality, we exemplify the distinct behaviors of classical and
quantum work fluctuations for the case of a time-dependent driven harmonic
oscillator dynamics and provide insights into the essential performance
differences between classical and quantum Jarzynski equalities.Comment: 24 pages, 1 figure, accepted version to appear in Entropy (Special
Issue on "Quantum Thermodynamics"
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