The asymmetric Exclusion Process and Brownian Excursions

We consider the totally asymmetric exclusion process (TASEP) in one dimension in its maximal current phase. We show, by an exact calculation, that the non-Gaussian part of the fluctuations of density can be described in terms of the statistical properties of a Brownian excursion. Numerical simulations indicate that the description in terms of a Brownian excursion remains valid for more general one dimensional driven systems in their maximal current phase.Comment: 23 pages, 1 figure, in latex, e-mail addresses: [email protected], [email protected], [email protected]

Nonequilibrium stationary states and equilibrium models with long range interactions

It was recently suggested by Blythe and Evans that a properly defined steady state normalisation factor can be seen as a partition function of a fictitious statistical ensemble in which the transition rates of the stochastic process play the role of fugacities. In analogy with the Lee-Yang description of phase transition of equilibrium systems, they studied the zeroes in the complex plane of the normalisation factor in order to find phase transitions in nonequilibrium steady states. We show that like for equilibrium systems, the ``densities'' associated to the rates are non-decreasing functions of the rates and therefore one can obtain the location and nature of phase transitions directly from the analytical properties of the ``densities''. We illustrate this phenomenon for the asymmetric exclusion process. We actually show that its normalisation factor coincides with an equilibrium partition function of a walk model in which the ``densities'' have a simple physical interpretation.Comment: LaTeX, 23 pages, 3 EPS figure

Strong asymmetric limit of the quasi-potential of the boundary driven weakly asymmetric exclusion process

We consider the weakly asymmetric exclusion process on a bounded interval with particles reservoirs at the endpoints. The hydrodynamic limit for the empirical density, obtained in the diffusive scaling, is given by the viscous Burgers equation with Dirichlet boundary conditions. In the case in which the bulk asymmetry is in the same direction as the drift due to the boundary reservoirs, we prove that the quasi-potential can be expressed in terms of the solution to a one-dimensional boundary value problem which has been introduced by Enaud and Derrida \cite{de}. We consider the strong asymmetric limit of the quasi-potential and recover the functional derived by Derrida, Lebowitz, and Speer \cite{DLS3} for the asymmetric exclusion process

Nonequilibrium Steady States of Matrix Product Form: A Solver's Guide

We consider the general problem of determining the steady state of stochastic nonequilibrium systems such as those that have been used to model (among other things) biological transport and traffic flow. We begin with a broad overview of this class of driven diffusive systems - which includes exclusion processes - focusing on interesting physical properties, such as shocks and phase transitions. We then turn our attention specifically to those models for which the exact distribution of microstates in the steady state can be expressed in a matrix product form. In addition to a gentle introduction to this matrix product approach, how it works and how it relates to similar constructions that arise in other physical contexts, we present a unified, pedagogical account of the various means by which the statistical mechanical calculations of macroscopic physical quantities are actually performed. We also review a number of more advanced topics, including nonequilibrium free energy functionals, the classification of exclusion processes involving multiple particle species, existence proofs of a matrix product state for a given model and more complicated variants of the matrix product state that allow various types of parallel dynamics to be handled. We conclude with a brief discussion of open problems for future research.Comment: 127 pages, 31 figures, invited topical review for J. Phys. A (uses IOP class file

The Gut-Lung Axis in Health and Respiratory Diseases: A Place for Inter-Organ and Inter-Kingdom Crosstalks.

The gut and lungs are anatomically distinct, but potential anatomic communications and complex pathways involving their respective microbiota have reinforced the existence of a gut-lung axis (GLA). Compared to the better-studied gut microbiota, the lung microbiota, only considered in recent years, represents a more discreet part of the whole microbiota associated to human hosts. While the vast majority of studies focused on the bacterial component of the microbiota in healthy and pathological conditions, recent works have highlighted the contribution of fungal and viral kingdoms at both digestive and respiratory levels. Moreover, growing evidence indicates the key role of inter-kingdom crosstalks in maintaining host homeostasis and in disease evolution. In fact, the recently emerged GLA concept involves host-microbe as well as microbe-microbe interactions, based both on localized and long-reaching effects. GLA can shape immune responses and interfere with the course of respiratory diseases. In this review, we aim to analyze how the lung and gut microbiota influence each other and may impact on respiratory diseases. Due to the limited knowledge on the human virobiota, we focused on gut and lung bacteriobiota and mycobiota, with a specific attention on inter-kingdom microbial crosstalks which are able to shape local or long-reached host responses within the GLA

J Pediatr Gastroenterol Nutr

OBJECTIVES: Cystic fibrosis-related liver disease (CFLD) can develop silently in early life and approximately 10% of children with cystic fibrosis (CF) become cirrhotic before adulthood. Clinical, biological, and ultrasound criteria used to define CFLD often reveal liver involvement at an advanced stage. The aim of this retrospective study was to assess the progression of liver stiffness measurement (LSM) in pediatric patients with CF. METHODS: The change of LSM, expressed as kPa/year and %/year, was measured using transient elastography (Fibroscan) in 82 children with CF (median age: 6.8 years, interquartile range [IQR]: 5.8). Mean time interval between the 2 LSM was 3.5 years. RESULTS: Median initial liver stiffness was 3.7 kPa (IQR: 1.3), and then progressed by 0.23 kPa/year, that is, 6%/year. The 7 patients who developed CFLD had a higher initial level of alanine aminotransferase (50 [IQR: 15] vs 30 [IQR: 18], P = 0.0001) and presented a more rapid progression of LSM (0.94 vs 0.23 kPa/year, P = 0.02). CONCLUSIONS: The present study shows that the slope of worsening of liver stiffness is greater in patients who will develop CFLD, suggesting that annual transient elastography may be useful to detect risk of severe liver disease at an earlier stage

Purification and characterization of two thermostable laccases from Pycnoporus sanguineus and potential role in degradation of endocrine disrupting chemicals

In this study, the purification and characterization of two thermostable laccases produced by Pycnoporus sanguineus CS43 (LacI and LacII) were performed. Also, their biotechnological potential was assessed through the degradation of endocrine disrupting chemicals (EDCs). Laccases were purified by ultrafiltration, ion exchange (IEX) and hydrophobic interaction chromatography achieving specific activities close to 285 U mg-1. The molecular weights of LacI and LacII, determined by SDS-electrophoresis, were 68 and 66 kDa, respectively. Both laccases showed high amino acid sequence similarity (91%) between them and high thermostability, at 50 and 60 °C (half-lives of 277.7 and 18 h for LacI, 35.8 and 2.25 h for LacII). The isoforms oxidized common laccase substrates such as 2,2′-azino-bis (3-ethylbenzthiazoline-6- sulfonate (ABTS), 2,6-dimethoxyphenol (DMP) and guaiacol at acidic pH conditions. ABTS was the most efficient substrate, showing high specificity constants of 74,816 and 36,746 mM-1 s-1 for Lac I and LacII, and Michaelis constants (Km) of 6.9 and 12.2 μM respectively at pH 3. Both purified laccases remained active at high concentrations of organic solvents (acetonitrile, ethanol and acetone), with an IC50 (v/v) of >64%, 55% and 47% for LacI, and 33%, 52% and 31% for LacII, respectively. LacI and LacII were tested to degrade EDCs, nonylphenol and triclosan, with more than 95% removal after 8 h of treatment with 100 U/L at pH 5 as determined by means of HPLC. The high thermostability, unique Michaelis-Menten kinetic parameters, and organic solvent tolerance demonstrated for the isoforms produced by P. sanguineus CS43 render them promising candidates for industrial applications. LacI exerted a higher thermal and pH stability, tolerance against inhibitors and was a more efficient catalyst for ABTS and DMP than LacII. © 2014 The Authors