106 research outputs found
On the relaxation to nonequilibrium steady states
The issue of relaxation has been addressed in terms of ergodic theory in the
past. However, the application of that theory to models of physical interest is
problematic, especially when dealing with relaxation to nonequilibrium steady
states. Here, we consider the relaxation of classical, thermostatted particle
systems to equilibrium as well as to nonequilibrium steady states, using
dynamical notions including decay of correlations. We show that the condition
known as {\Omega}T-mixing is necessary and sufficient to prove relaxation of
ensemble averages to steady state values. We then observe that the condition
known as weak T-mixing applied to smooth observables is sufficient for
relaxation to be independent of the initial ensemble. Lastly, weak T-mixing for
integrable functions makes relaxation independent of the ensemble member, apart
from a negligible set of members enabling the result to be applied to
observations from a single physical experiment. The results also allow us to
give a microscopic derivation of Prigogine's principle of minimum entropy
production in the linear response regime. The key to deriving these results
lies in shifting the discussion from characteristics of dynamical systems, such
as those related to metric transitivity, to physical measurements and to the
behaviour of observables. This naturally leads to the notion of physical
ergodicity.Comment: 44 pages, 1 figur
Fluctuation Theorems
Fluctuation theorems, which have been developed over the past 15 years, have
resulted in fundamental breakthroughs in our understanding of how
irreversibility emerges from reversible dynamics, and have provided new
statistical mechanical relationships for free energy changes. They describe the
statistical fluctuations in time-averaged properties of many-particle systems
such as fluids driven to nonequilibrium states, and provide some of the very
few analytical expressions that describe nonequilibrium states. Quantitative
predictions on fluctuations in small systems that are monitored over short
periods can also be made, and therefore the fluctuation theorems allow
thermodynamic concepts to be extended to apply to finite systems. For this
reason, fluctuation theorems are anticipated to play an important role in the
design of nanotechnological devices and in understanding biological processes.
These theorems, their physical significance and results for experimental and
model systems are discussed.Comment: A review, submitted to Annual Reviews in Physical Chemistry, July
2007 Acknowledgements corrected in revisio
The Glass Transition and the Jarzynski Equality
A simple model featuring a double well potential is used to represent a
liquid that is quenched from an ergodic state into a history dependent glassy
state. Issues surrounding the application of the Jarzynski Equality to glass
formation are investigated. We demonstrate that the Jarzynski Equality gives
the free energy difference between the initial state and the state we would
obtain if the glass relaxed to true thermodynamic equilibrium. We derive new
variations of the Jarzynski Equality which are relevant to the history
dependent glassy state rather than the underlying equilibrium state. It is
shown how to compute the free energy differences for the nonequilibrium history
dependent glassy state such that it remains consistent with the standard
expression for the entropy and with the second law inequality.Comment: 16 pages, 5 figure
Independence of the transient fluctuation theorem to thermostatting details
The dependence of fluctuation theorem on the precise mathematical details of thermostatting mechanism for an infinite class of fictious time reversible deterministic thermostats was analyzed. Theoretical and numerical analysis were carried out for a class of time reversible deterministic thermostats that fix various moments of the momentum distribution. In this large thermostat the transient fluctuation theorem (TFT) was found dependent of the precise moment that the thermostat fixes. The study shows that in a non-equilibrium system in contact with a thermostat and having large degrees of freedom, the transient fluctuation relation is insensitive to the details of thermostatting mechanisms
On the relationship between dissipation and the rate of spontaneous entropy production from linear irreversible thermodynamics
When systems are far from equilibrium, the temperature, the entropy and the thermodynamic entropy production are not deļ¬ned and the Gibbs entropy does not provide useful information about the physical properties of a system. Furthermore, far from equilibrium, or if the dissipative ļ¬eld changes in time, the spontaneous entropy production of linear irreversible thermodynamics becomes irrelevant. In 2000 we introduced a deļ¬nition for the dissipation function and showed that for systems of arbitrary size, arbitrarily near or far from equilibrium, the time integral of the ensemble average of this quantity can never decrease. In the low-ļ¬eld limit, its ensemble average becomes equal to the spontaneous entropy production of linear irreversible thermodynamics. We discuss how these quantities are related and why one should use dissipation rather than entropy or entropy production for non-equilibrium systems
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IRE1Ī± and IGF signaling predict resistance to an endoplasmic reticulum stress-inducing drug in glioblastoma cells.
To date current therapies of glioblastoma multiforme (GBM) are largely ineffective. The induction of apoptosis by an unresolvable unfolded protein response (UPR) represents a potential new therapeutic strategy. Here we tested 12ADT, a sarcoendoplasmic reticulum Ca2+ ATPase (SERCA) inhibitor, on a panel of unselected patient-derived neurosphere-forming cells and found that GBM cells can be distinguished into "responder" and "non-responder". By RNASeq analysis we found that the non-responder phenotype is significantly linked with the expression of UPR genes, and in particular ERN1 (IRE1) and ATF4. We also identified two additional genes selectively overexpressed among non-responders, IGFBP3 and IGFBP5. CRISPR-mediated deletion of the ERN1, IGFBP3, IGFBP5 signature genes in the U251 human GBM cell line increased responsiveness to 12ADT. Remarkably, >65% of GBM cases in The Cancer Genome Atlas express the non-responder (ERN1, IGFBP3, IGFBP5) gene signature. Thus, elevated levels of IRE1Ī± and IGFBPs predict a poor response to drugs inducing unresolvable UPR and possibly other forms of chemotherapy helping in a better stratification GBM patients
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Dissipation and the Relaxation to Equilibrium
Using the recently derived Dissipation Theorem and a corollary of the
Transient Fluctuation Theorem (TFT), namely the Second Law Inequality, we
derive the unique time independent, equilibrium phase space distribution
function for an ergodic Hamiltonian system in contact with a remote heat bath.
We prove under very general conditions that any deviation from this equilibrium
distribution breaks the time independence of the distribution. Provided
temporal correlations decay, and the system is ergodic, we show that any
nonequilibrium distribution that is an even function of the momenta, eventually
relaxes (not necessarily monotonically) to the equilibrium distribution.
Finally we prove that the negative logarithm of the microscopic partition
function is equal to the thermodynamic Helmholtz free energy divided by the
thermodynamic temperature and Boltzmann's constant. Our results complement and
extend the findings of modern ergodic theory and show the importance of
dissipation in the process of relaxation towards equilibrium.Comment: 18 pages, no figure
A Derivation of the Gibbs Equation and the Determination of Change in Gibbs Entropy from Calorimetry
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