Diffusion under confinement: hydrodynamic finite-size effects in simulation

We investigate finite-size effects on diffusion in confined fluids using molecular dynamics simulations and hydrodynamic calculations. Specifically, we consider a Lennard-Jones fluid in slit pores without slip at the interface and show that the use of periodic boundary conditions in the directions along the surfaces results in dramatic finite-size effects, in addition to that of the physically relevant confining length. As in the simulation of bulk fluids, these effects arise from spurious hydrodynamic interactions between periodic images and from the constraint of total momentum conservation. We derive analytical expressions for the correction to the diffusion coefficient in the limits of both elongated and flat systems, which are in excellent agreement with the molecular simulation results except for the narrowest pores, where the discreteness of the fluid particles starts to play a role. The present work implies that the diffusion coefficients for wide nanopores computed using elongated boxes suffer from finite-size artifacts which had not been previously appreciated. In addition, our analytical expression provides the correction to be applied to the simulation results for finite (possibly small) systems. It applies not only to molecular but also to all mesoscopic hydrodynamic simulations, including Lattice-Boltzmann, Multi-Particle Collision Dynamics or Dissipative Particle Dynamics, which are often used to investigate confined soft matter involving colloidal particles and polymers.Comment: 3 figures and 1 in the supplemental sectio

Comparative Biology of the Resistance to Vitamin K Antagonists: An Overview of the Resistance Mechanisms

Vitamin K antagonists (VKA) are used in human medicine as well as for the management of rodent populations. In both cases, we have to deal with inter-individual resistances. Many mechanisms of resistances are common in humans and rodents. Moreover, with the large use of vitamin K antagonist rodenticides, the resistant phenotype is overrepresented in some rodent populations. Consequently, some resistance mechanisms with a low prevalence in the human population have a higher prevalence in rodent population; thus, they can be more studied in rodents. The aim of this chapter is to cross knowledge coming from human medicine and rodent research in order to better understand each resistance mechanism. After an overview of the essential knowledge for the understanding of the VKA action, this chapter presents the different methods of VKA resistance studying and then it assesses the current knowledge on VKA resistance in humans and rodents

Credit et dynamiques economiques

La longue recession de l'economie mondiale dans les annees 1990 redonne de l'eclat aux conceptions financieres du cycle economique. La mode du cycle reel, qui avait prevalu dans le sillage de la nouvelle economie classique, a du mal a apprehender les evenements qui se sont succede depuis 1989, si tant est qu'elle ait eu une part de verite empirique. Les faillites bancaires aux Etats-Unis et dans les pays scandinaves, l'effondrement des prix des actifs patrimoniaux au Royaume-Uni et au Japon, apres leur ascension vertigineuse, peuvent difficilement etre imputes a des chocs dans les conditions reelles de production. Il paraît plus raisonnable de les rapporter aux perturbations provoquees par la liberalisation financiere a l'interieur des pays et entre les pays. Si cette hypothese minimale de travail peut etre retenue, de nombreuses questions en decoulent. La liberalisation financiere a-t-elle modifie les interactions entre la finance et l'economie ? Si modification il y a, est-elle un phenomene transitoire pendant que les comportements s'ajustent a de nouvelles regles ou un caractere permanent du nouvel environnement financier ? Une finance ouverte et liberalisee provoque-t-elle des instabilites qui se repercutent dans les ajustements macro-economiques et doivent nous apprendre a vivre avec des fluctuations reelles beaucoup plus accusees qu'on en avait l'habitude dans les trente ans qui ont suivi la deuxieme guerre mondiale ?politique monetaire; croissance

Poisoning by Anticoagulant Rodenticides in Humans and Animals: Causes and Consequences

Anticoagulant rodenticides (ARs) are a keystone of the management of rodent populations in the world. The widespread use of these molecules raises questions on exposure and intoxication risks, which define the safety of these products. Exposures and intoxications can affect humans, domestic animals and wildlife. Consequences are different for each group, from the simple issue of intoxication in humans to public health concern if farm animals are exposed. After a rapid presentation of the mechanism of action and the use of anticoagulant rodenticides, this chapter assesses the prominence of poisoning by anticoagulant rodenticides in humans, domestic animals and wildlife

House Mice as a Real Sanitary Threat of Human and Animal Leptospirosis: Proposal for Integrated Management

International audienceLeptospirosis is a reemerging zoonosis and ranges in severity from benign to sometimes fatal. In cattle, infection may be responsible for abortion and infertility cases causing economic losses. Humans may be contaminated through direct contact with urine of infected animals or indirectly though interaction with urine-contaminated environment. Many wildlife species living close to cattle, especially commensal rodents may play a role in the transmission of leptospires. Because little is known on the epidemiology of nonmaintenance Leptospira serovars, appropriate management is still limited. On a French farm where human and cattle leptospirosis were detected, the transmission cycle was explored to propose appropriate mitigation measures. For that, commensal rodents present on the farm were trapped and their leptospires carriage was studied by molecular methods. Trapped mice were shown to carry two pathogenic Leptospira species (L. interrogans and L. kirschneri). Since these 2 serogroups were simultaneously detected in the trapped mice and in the cows of this farm, we suspected an initial Leptospira transmission from mice to cows requiring an effective management of mice on this farm. Because resistance to anticoagulant rodenticides due to Vkorc1 mutations has been largely described in rodents and first-generation anticoagulant rodenticides seemed to be inefficient in controlling mice on this farm, susceptibility of these mice to anticoagulants has been characterized by Vkorc1 sequencing. 50% of the trapped mice carried mutations in the Vkorc1 gene leading to severe resistance to first-generation anticoagulants. The management of such mice that are a real sanitary threat can be achieved only by using the most toxic second-generation anticoagulants or nonanticoagulant solutions

Carbon Dioxide in Montmorillonite Clay Hydrates: Thermodynamics, Structure, and Transport from Molecular Simulation

International audienceWe report a Monte Carlo and molecular dynamics simulations study of carbon dioxide in hydrated sodium montmorillonite, including thermodynamical, structural, and dynamical properties. In order to simulate the behavior of a clay caprock in contact with a CO2 reservoir, we consider clays in equilibrium with H2O−CO2 mixtures under conditions close to relevant ones for geological storage, namely a temperature T = 348 K, and pressures P = 25 and 125 bar, and under which two bulk phases coexist: H2O-rich liquid on the one hand and CO2-rich gas (P = 25 bar) or supercritical fluid (P = 125 bar) on the other hand. We first use grand canonical MC simulations to determine the number of stable states in clay, their composition, and the corresponding equilibrium interlayer distances. The vertical, horizontal, and radial distribution functions of the confined mixture, subsequently obtained using molecular dynamics, reveal some structural feature induced by the presence of CO2. Finally, the simulations indicate that carbon dioxide considerably influences the diffusion of mobile species in clays. We discuss these results by comparing them with those obtained for the bulk mixtures, as well as for Na-montmorillonite in equilibrium with a pure water reservoir water at the same temperature and pressure

Establishment of the Variation of Vitamin K Status According to Vkorc1 Point Mutations Using Rat Models

International audienceVitamin K is crucial for many physiological processes such as coagulation, energy metabolism, and arterial calcification prevention due to its involvement in the activation of several vitamin K-dependent proteins. During this activation, vitamin K is converted into vitamin K epoxide, which must be re-reduced by the VKORC1 enzyme. Various VKORC1 mutations have been described in humans. While these mutations have been widely associated with anticoagulant resistance, their association with a modification of vitamin K status due to a modification of the enzyme efficiency has never been considered. Using animal models with different Vkorc1 mutations receiving a standard diet or a menadione-deficient diet, we investigated this association by measuring different markers of the vitamin K status. Each mutation dramatically affected vitamin K recycling efficiency. This decrease in recycling was associated with a significant alteration of the vitamin K status, even when animals were fed a menadione-enriched diet suggesting a loss of vitamin K from the cycle due to the presence of the Vkorc1 mutation. This change in vitamin K status resulted in clinical modifications in mutated rats only when animals receive a limited vitamin K intake totally consistent with the capacity of each strain to recycle vitamin K