80 research outputs found
Entropy production in systems with unidirectional transitions
The entropy production is one of the most essential features for systems
operating out of equilibrium. The formulation for discrete-state systems goes
back to the celebrated Schnakenberg's work and hitherto can be carried out when
for each transition between two states also the reverse one is allowed.
Nevertheless, several physical systems may exhibit a mixture of both
unidirectional and bidirectional transitions, and how to properly define the
entropy production in this case is still an open question. Here, we present a
solution to such a challenging problem. The average entropy production can be
consistently defined, employing a mapping that preserves the average fluxes,
and its physical interpretation is provided. We describe a class of stochastic
systems composed of unidirectional links forming cycles and detailed-balanced
bidirectional links, showing that they behave in a pseudo-deterministic
fashion. This approach is applied to a system with time-dependent stochastic
resetting. Our framework is consistent with thermodynamics and leads to some
intriguing observations on the relation between the arrow of time and the
average entropy production for resetting events.Comment: (Accepted for publication in Physical Review Research
Powerful ordered collective heat engines
We introduce a class of stochastic engines in which the regime of units
operating synchronously can boost the performance. Our approach encompasses a
minimal setup composed of interacting units placed in contact with two
thermal baths and subjected to a constant driving worksource. The interplay
between unit synchronization and interaction leads to an efficiency at maximum
power between the Carnot, , and the Curzon-Ahlborn bound,
. Moreover, these limits can be respectively saturated maximizing
the efficiency, and by simultaneous optimization of power and efficiency. We
show that the interplay between Ising-like interactions and a collective
ordered regime is crucial to operate as a heat engine. The main system features
are investigated by means of a linear analysis near equilibrium, and developing
an effective discrete-state model that captures the effects of the synchronous
phase. The present framework paves the way for the building of promising
nonequilibrium thermal machines based on ordered structures.Comment: Improved main text and supplemental material. Some figures and new
analysis were performe
New features of the phase transition to superconducting state in thin films
The Halperin-Lubensky-Ma (HLM) effect of a fluctuation-induced change of the
order of phase transition in thin films of type I superconductors with
relatively small Ginzburg-Landau number is considered. Numerical data
for the free energy, the order parameter jump, the latent heat, and the
specific heat of W, Al and In are presented to reveal the influence of film
thickness and material parameters on the properties of the phase transition. We
demonstrate for the first time that in contrast to the usual notion the HLM
effect occurs in the most distinct way in superconducting films with high
critical magnetic field rather than in materials with small .
The possibility for an experimental observation of the fluctuation change of
the order of superconducting phase transition in superconducting films is
discussed.Comment: 11 pages, MikTexTeX, 3 fig, 2 Tables, corrected some typos, Submitted
J.Phys:Cond Ma
Metamagnetic Quantum Criticality in Sr3Ru2O7
We consider the metamagnetic transition in the bilayer ruthenate, , and use this to motivate a renormalization group treatment of a zero-temperature quantum-critical end-point. We summarize the results of mean field theory and give a pedagogical derivation of the renormalization-group equations. These are then solved to yield numerical results for the susceptibility, the specific heat and the resistivity exponent which can be compared with measured data on to provide a powerful test for the standard framework of metallic quantum criticality. The observed approach to the critical point is well-described by our theory explaining a number of unusual features of experimental data. The puzzling behaviour very near to the critical point itself, though, is not accounted for by this, or any other theory with a Fermi surface
Neisseria gonorrhoeae Infection Induces Altered Amphiregulin Processing and Release
Adhesion of the human pathogen Neisseria gonorrhoeae has established effects on the host cell and evokes a variety of cellular events including growth factor activation. In the present study we report that infection with N. gonorrhoeae causes altered amphiregulin processing and release in human epithelial cells. Amphiregulin is a well-studied growth factor with functions in various cell processes and is upregulated in different forms cancer and proliferative diseases. The protein is prototypically cleaved on the cell surface in response to external stimuli. We demonstrate that upon infection, a massive upregulation of amphiregulin mRNA is seen. The protein changes its subcellular distribution and is also alternatively cleaved at the plasma membrane, which results in augmented release of an infection-specific 36 kDa amphiregulin product from the surface of human cervical epithelial cells. Further, using antibodies directed against different domains of the protein we could determine the impact of infection on pro-peptide processing. In summary, we present data showing that the infection of N. gonorrhoeae causes an alternative amphiregulin processing, subcellular distribution and release in human epithelial cervical cells that likely contribute to the predisposition cellular abnormalities and anti-apoptotic features of N. gonorrhoeae infections
Intracellular expression of Tat alters mitochondrial functions in T cells: a potential mechanism to understand mitochondrial damage during HIV-1 replication
HIV-1 replication results in mitochondrial damage that is enhanced during antiretroviral therapy (ART).
The onset of HIV-1 replication is regulated by viral protein Tat, a 101-residue protein codified by two exons that elongates viral transcripts. Although the first exon of Tat (aa 1â72) forms itself an active protein, the presence of the second exon (aa 73â101) results in a more competent transcriptional protein with additional functions.
Results: Mitochondrial overall functions were analyzed in Jurkat cells stably expressing full-length Tat (Tat101) or one-exon Tat (Tat72). Representative results were confirmed in PBLs transiently expressing Tat101 and in HIV-infected Jurkat cells. The intracellular expression of Tat101 induced the deregulation of metabolism and cytoskeletal proteins which remodeled the function and distribution of mitochondria. Tat101 reduced the transcription of the mtDNA,
resulting in low ATP production. The total amount of mitochondria increased likely to counteract their functional impairment. These effects were enhanced when Tat second exon was expressed.
Conclusions: Intracellular Tat altered mtDNA transcription, mitochondrial content and distribution in CD4+ T cells.
The importance of Tat second exon in non-transcriptional functions was confirmed. Tat101 may be responsible for mitochondrial dysfunctions found in HIV-1 infected patients.We greatly appreciate the secretarial assistance of Mrs Olga Palao. This work was supported by FIPSE (360924/10), Spanish Ministry of Economy and Competitiveness (SAF2010-18388), Spanish Ministry of Health (EC11- 285), AIDS Network ISCIII-RETIC (RD12/0017/0015), Instituto de Salud Carlos III, Spanish Ministry of Economy and Competitiveness (FIS PI12/00506). The work of Sara RodrĂguez-Mora is supported by a fellowship of Sara Borrell from Spanish Ministry of Economy and Competitiveness (2013). The work of MarĂa Rosa LĂłpez-Huertas is supported by a fellowship of the European Union Programme Health 2009 (CHAARM).S
Mutual Information Disentangles Interactions from Changing Environments
Real-world systems are characterized by complex interactions of their internal degrees of freedom, while living in ever-changing environments whose net effect is to act as additional couplings. Here, we introduce a paradigmatic interacting model in a switching, but unobserved, environment. We show that the limiting properties of the mutual information of the system allow for a disentangling of these two sources of couplings. Further, our approach might stand as a general method to discriminate complex internal interactions from equally complex changing environments
Entropy production in master equations and Fokker-Planck equations: facing the coarse-graining and recovering the information loss
Systems operating out of equilibrium exchange energy and matter with the environment, thus producing entropy in their surroundings. Since the entropy production depends on the current flowing throughout the system, its quantification is affected by the level of coarse-graining we adopt. In particular, it has been shown that the description of a system via a Fokker?Planck equation (FPE) lead to an underestimation of the entropy production with respect to the corresponding one in terms of microscopic transition rates. Moreover, such a correction can be derived exactly. Here we review this derivation, generalizing it when different prescriptions to derive the FPE from a Langevin equation are adopted. Then, some open problems about Gaussian transition rates and underdamped limit are discussed. In the second part of the manuscript we present a new approach to dealing with the discrepancy in entropy production due to the coarse graining by introducing enough microscopic variables to correctly estimate the entropy production within the FPE description. We show that any discrete state system can be described by making explicit the contribution of each microscopic current
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