By-passing fluctuation theorems

Fluctuation theorems impose constraints on possible work extraction probabilities in thermodynamical processes. These constraints are stronger than the usual second law, which is concerned only with average values. Here, we show that such constraints, expressed in the form of the Jarzysnki equality, can be by-passed if one allows for the use of catalysts---additional degrees of freedom that may become correlated with the system from which work is extracted, but whose reduced state remains unchanged so that they can be re-used. This violation can be achieved both for small systems but also for macroscopic many-body systems, and leads to positive work extraction per particle with finite probability from macroscopic states in equilibrium. In addition to studying such violations for a single system, we also discuss the scenario in which many parties use the same catalyst to induce local transitions. We show that there exist catalytic processes that lead to highly correlated work distributions, expected to have implications for stochastic and quantum thermodynamics.

Stellar models: firm evidence, open questions and future developments

During this last decade our knowledge of the evolutionary properties of stars has significantly improved. This result has been achieved thanks to our improved understanding of the physical behavior of stellar matter in the thermal regimes characteristic of the different stellar mass ranges and/or evolutionary stages.This notwithstanding, the current generation of stellar models is still affected by several, not negligible, uncertainties related to our poor knowledge of some thermodynamical processes and nuclear reaction rates, as well as the efficiency of mixing processes. These drawbacks have to be properly taken into account when comparing theory with observations, to derive evolutionary properties of both resolved and unresolved stellar populations.In this paper we review the major sources of uncertainty along the main evolutionary stages, and emphasize their impact on population synthesis techniques.

Identical thermodynamical processes and the generalization of the Clausius inequality

We stress the advantages of heat and work reservoirs in the formalism of Thermodynamics and using an illustrative example show the need to reformulate the concepts of heat and work to avoid inconsistencies, namely, with regard to the Second Law. To deal with this problem, we use the concept of identical thermodynamical processes and obtain the condition for two such processes to be identical even when the system neighbourhood as a whole cannot be treated as a reservoir. The aforementioned concept is then applied to obtain a standardized definition of heat and work as well as a generalization of the well-known Clausius inequality. Finally, we return to the example given earlier to corroborate the effectiveness of our results.PACS Nos.: 05.70.–a, 44.90.+c, 65.40.Gr

Identical thermodynamical processes and entropy

Starting from the concept of identical thermodynamical processes, we treat invariance under interchange of identical processes as a symmetry. We show the conservation of entropy in reversible processes to be intimately related to this symmetry. PACS Nos.: 44.60, 65.50