Activated Escape of a Self-Propelled Particle from a Metastable State.

We study the noise-driven escape of active Brownian particles (ABPs) and run-and-tumble particles (RTPs) from confining potentials. In the small noise limit, we provide an exact expression for the escape rate in terms of a variational problem in any dimension. For RTPs in one dimension, we obtain an explicit solution, including the first subleading correction. In two dimensions we solve the escape from a quadratic well for both RTPs and ABPs. In contrast to the equilibrium problem we find that the escape rate depends explicitly on the full shape of the potential barrier, and not only on its height. This leads to a host of unusual behaviors. For example, when a particle is trapped between two barriers it may preferentially escape over the higher one. Moreover, as the self-propulsion speed is varied, the escape route may discontinuously switch from one barrier to the other, leading to a dynamical phase transition.

Organic solvents impair life-traits and biomarkers in the New Zealand mudsnail Potamopyrgus antipodarum (Gray) at concentrations below OECD recommendations.

Potamopyrgus antipodarum is a gastropod mollusk proposed for use in the development of reproduction tests within the Organization for Economic Cooperation and Development (OECD). Numerous chemicals, including endocrine disrupters, are relatively water-insoluble, and water-miscible solvents are currently used for testing them. OECD recommends a maximum concentration of 100 µll(-1). As several studies highlighted effects of lower concentrations of solvents, this study assessed the effects of 20 µll(-1) acetone, ethanol, methanol and dimethylsulfoxide (DMSO) on juvenile and adult snails during 42 days. Ethanol decreased juvenile growth, while acetone increased the rate of embryonic development. All solvents increased estradiol-like levels in adult snails. DMSO only increased mRNA expression of vitellogenin-like gene, while acetone, ethanol and methanol decreased mRNA expression of three nuclear receptor (estrogen receptor-like, ecdysone-induced protein and chicken ovalbumin upstream promoter transcription factor) genes as well as of genes encoding proteins involved in genomic (prohibitin-2) and non-genomic (striatin) pathways of estrogens activity in vertebrates. This study highlights the confounding effects of low concentrations of solvents and recommends avoiding their use. Where solvent use is inevitable, their concentrations and type should be investigated for suitability for the measured endpoints prior to use in chemical testing strategies.

Equilibriumlike fluctuations in some boundary-driven open diffusive systems.

There exist some boundary-driven open systems with diffusive dynamics whose particle current fluctuations exhibit universal features that belong to the Edwards-Wilkinson universality class. We achieve this result by establishing a mapping, for the system fluctuations, to an equivalent open yet equilibrium-diffusive system. We discuss the possibility of observing dynamic phase transitions using the particle current as a control parameter.

Microarray analysis of genes with impaired insulin regulation in the skeletal muscle of type 2 diabetic patients indicates the involvement of basic helix-loop-helix domain-containing, class B, 2 protein (BHLHB2).

AIMS/HYPOTHESIS: One of the major processes by which insulin exerts its multiple biological actions is through gene expression regulation. Thus, the identification of transcription factors affected by insulin in target tissues represents an important challenge. The aim of the present study was to gain a greater insight into this issue through the identification of transcription factor genes with insulin-regulated expression in human skeletal muscle. METHODS: Using microarray analysis, we defined the sets of genes modulated during a 3 h hyperinsulinaemic-euglycaemic clamp (2 mU min(-1) kg(-1)) in the skeletal muscle of insulin-sensitive control volunteers and in moderately obese insulin-resistant type 2 diabetic patients. RESULTS: Of the 1,529 and 1,499 genes regulated during the clamp in control and diabetic volunteers, respectively, we identified 30 transcription factors with impaired insulin-regulation in type 2 diabetic patients. Analysis of the promoters of the genes encoding these factors revealed a possible contribution of the transcriptional repressor basic helix-loop-helix domain-containing, class B, 2 protein (BHLHB2), insulin regulation of which is strongly altered in the muscle of diabetic patients. Gene ontology analysis of BHLHB2 target genes, identified after BHLHB2 overexpression in human primary myotubes, demonstrated that about 10% of the genes regulated in vivo during hyperinsulinaemia are potentially under the control of this repressor. The data also suggested that BHLHB2 is situated at the crossroads of a complex transcriptional network that is able to modulate major metabolic and biological pathways in skeletal muscle, including the regulation of a cluster of genes involved in muscle development and contraction. CONCLUSIONS/INTERPRETATION: We have identified BHLHB2 as a potential novel mediator of insulin transcriptional action in human skeletal muscle.

Universal cumulants of the current in diffusive systems on a ring.

We calculate exactly the first cumulants of the integrated current and of the activity (which is the total number of changes of configurations) of the symmetric simple exclusion process on a ring with periodic boundary conditions. Our results indicate that for large system sizes the large deviation functions of the current and of the activity take a universal scaling form, with the same scaling function for both quantities. This scaling function can be understood either by an analysis of Bethe ansatz equations or in terms of a theory based on fluctuating hydrodynamics or on the macroscopic fluctuation theory of Bertini, De Sole, Gabrielli, Jona-Lasinio, and Landim.

Interaction ruling animal collective behavior depends on topological rather than metric distance: evidence from a field study.

Numerical models indicate that collective animal behavior may emerge from simple local rules of interaction among the individuals. However, very little is known about the nature of such interaction, so that models and theories mostly rely on aprioristic assumptions. By reconstructing the three-dimensional positions of individual birds in airborne flocks of a few thousand members, we show that the interaction does not depend on the metric distance, as most current models and theories assume, but rather on the topological distance. In fact, we discovered that each bird interacts on average with a fixed number of neighbors (six to seven), rather than with all neighbors within a fixed metric distance. We argue that a topological interaction is indispensable to maintain a flock's cohesion against the large density changes caused by external perturbations, typically predation. We support this hypothesis by numerical simulations, showing that a topological interaction grants significantly higher cohesion of the aggregation compared with a standard metric one.

Dynamical first-order phase transition in kinetically constrained models of glasses.

We show that the dynamics of kinetically constrained models of glass formers takes place at a first-order coexistence line between active and inactive dynamical phases. We prove this by computing the large-deviation functions of suitable space-time observables, such as the number of configuration changes in a trajectory. We present analytic results for dynamic facilitated models in a mean-field approximation, and numerical results for the Fredrickson-Andersen model, the East model, and constrained lattice gases, in various dimensions. This dynamical first-order transition is generic in kinetically constrained models, and we expect it to be present in systems with fully jammed states.

Chaotic properties of systems with Markov dynamics.

We present a general approach for computing the dynamic partition function of a continuous-time Markov process. The Ruelle topological pressure is identified with the large deviation function of a physical observable. We construct for the first time a corresponding finite Kolmogorov-Sinai entropy for these processes. Then, as an example, the latter is computed for a symmetric exclusion process. We further present the first exact calculation of the topological pressure for an N-body stochastic interacting system, namely, an infinite-range Ising model endowed with spin-flip dynamics. Expressions for the Kolmogorov-Sinai and the topological entropies follow.

Quasiequilibrium during aging of the two-dimensional Edwards-Anderson model.

We test the quasiequilibrium picture of the aging dynamics--strictly valid in the asymptotic dynamical regime of aging systems--in the preasymptotic aging regime of the two-dimensional Edwards-Anderson spin glass model. We compare the fluctuation-dissipation characteristic for spin autocorrelation function and response with a corresponding one obtained for a suitably defined correlation function and its conjugated response. In agreement with the quasiequilibrium picture we find that after a short transient the two corresponding fluctuation-dissipation ratios (FDR's) coincide at equal times. Moreover we show that, as it happens for the usual FDR, the dynamic FDR at finite time coincides with the static one at finite size.

Soil surface structure effect on isoproturon and diflufenican loss in runoff.

Because soil surface structure has a considerable influence on infiltration rate, the sealing process is postulated to have a significant effect on herbicide loss through runoff. We evaluated the effect of degraded soil surface structures on herbicide loss in runoff, and used the experimental data to test the uniform mixing zone concept and two-site sorption kinetics for modeling herbicide transfer to runoff. The experiments were done with simulated rainfall on 10-m2 plots in the field and 0.25-m2 plots in the laboratory after a surface application of 1.5 kg ha(-1) of isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] and 0.187 kg ha(-1) of diflufenican [2',4'-difluoro-2-(alpha,alpha,alpha-trifluoro-m-tolyloxy) nicotinanilide]. Isoproturon (IPU) and diflufenican (DFF) concentrations were very high in the first runoff (up to 60 mg L(-1) for IPU and 2 mg L(-1) for DFF) when simulated rainfall was applied 24 h after the treatment. The concentrations decreased very rapidly with total rainfall depth. Degradation of the structural state of the soil surface increased the ratio of pesticide loss to application rate from 0.3 to 10% for IPU and from 0.7 to 7.8% for DFF for a runoff depth of less than 1 mm. The structural state of the soil surface influences the rapidity at which runoff begins after the onset of rain, and the runoff coefficient at steady state. Furthermore, the development of a surface seal seems to limit the depth of soil-runoff interaction and thus influences the dynamics of herbicide mobilization. Concentrations of IPU in the runoff were satisfactorily described with a model incorporating a uniform mixing zone and two-site sorption-desorption.

Cathepsin B and N-acetyl-beta-D-glucosaminidase in human synovial cells in culture: effects of interleukin-1.

Human synovial cells were cultured in vitro and tested for the activities of two lysosomal enzymes, cathepsin B and N-acetyl-beta-D-glucosaminidase (NAGA) under various conditions. Unstimulated synovial cells display intracellular and extracellular activities of both enzymes. However, cathepsin B was secreted in a latent pepsin-activatable form, whereas NAGA was secreted in an active form. Most of the cell strains analysed secreted rather limited amounts of the enzymes (less than 25% of total activity); some strains, however were highly secretory, the secreted activity reaching up to 50% of total activity. Cells were then stimulated with human recombinant interleukin-1 alpha (rhIL-1 alpha) or beta. Only the levels of secreted NAGA were clearly increased. Results are to be interpreted in view of the role played by synovial cells and by the lysosomal enzymes they release in inflammatory joint diseases and it would be worthwhile in the future to check for secreted NAGA in various body fluids, such as the synovial fluid of the inflamed joint.

Differential effects of interleukin-1 alpha and beta on the arachidonic acid cascade in human synovial cells and chondrocytes in culture.

The effects of interleukin-1 alpha and beta were tested on the [3H]-arachidonic acid release and the prostaglandin synthesis by human cultured synovial cells and chondrocytes. Both forms of interleukin-1 stimulated the arachidonic acid release but interleukin-1 beta was more potent than IL-1 alpha. Human synovial cells and chondrocytes synthesized three types of prostaglandins upon stimulation with interleukin-1 alpha or beta: prostaglandin E2, F2 alpha and 6-keto-prostaglandin F1 alpha. Regarding the synthesis of these prostaglandins, IL-1 beta was again more potent than IL-1 alpha. A comparison between interleukin-1-stimulated synovial cells and chondrocytes revealed neither significant quantitative nor qualitative differences in both the arachidonic acid release and the prostaglandin synthesis.

Brain-tissue cysts in rats infected with the RH strain of Toxoplasma gondii.

Virulent strains of the coccidian parasite Toxoplasma gondii become attenuated so as to survive and complete their life cycle; however, it is not known whether the attenuation process is attributable to an innate cystogenic capacity of the parasite or to host-induced mechanisms. This report presents direct evidence of RH cystogenesis in non-immunised Fischer rats and subsequent attenuation of RH pathogenicity in non-immunised mice following a single passage through rats. Taken together, these preliminary observations tend to suggest that at least one mechanism of T. gondii involves intermediate host attenuation.