Anisotropic self-affine properties of experimental fracture surfaces

The scaling properties of post-mortem fracture surfaces of brittle (silica glass), ductile (aluminum alloy) and quasi-brittle (mortar and wood) materials have been investigated. These surfaces, studied far from the initiation, were shown to be self-affine. However, the Hurst exponent measured along the crack direction is found to be different from the one measured along the propagation direction. More generally, a complete description of the scaling properties of these surfaces call for the use of the 2D height-height correlation function that involves three exponents zeta = 0.75, beta = 0.6 and z = 1.25 independent of the material considered as well as of the crack growth velocity. These exponents are shown to correspond to the roughness, growth and dynamic exponents respectively, as introduced in interface growth models. They are conjectured to be universal.Comment: 12 page

Nanoscale damage during fracture in silica glass

We report here atomic force microscopy experiments designed to uncover the nature of failure mechanisms occuring within the process zone at the tip of a crack propagating into a silica glass specimen under stress corrosion. The crack propagates through the growth and coalescence of nanoscale damage spots. This cavitation process is shown to be the key mechanism responsible for damage spreading within the process zone. The possible origin of the nucleation of cavities, as well as the implications on the selection of both the cavity size at coalescence and the process zone extension are finally discussed.Comment: 12 page

Les chemins de fer vicinaux de la Haute-Saône de l’extension (1878-1912) au déclin (1918-1938) : un modèle de desserte d’un département en mutation économique

Le département de la Haute-Saône doit son nom au cours supérieur de la rivière Saône qui le traverse dans sa totalité. La Saône occupe une large dépression bordée au Nord et au Sud par des plateaux d’altitude moyenne. A l’Est, leur faciès devient plus montagneux puisque la retombée méridionale des Vosges occupe toute cette façade du département qui culmine à plus de 1 200 m au ballon de Servance, tandis que le point le plus bas est, à l’extrême Ouest du département, à 191 m d’altitude où conf..

Bacterial toxins modifying the actin cytoskeleton

Numerous bacterial toxins recognize the actin cytoskeleton as a target. The clostridial binary toxins (Iota and C2 families) ADP-ribosylate the actin monomers causing the dissociation of the actin filaments. The large clostridial toxins from Clostridium difficile, Clostridium sordellii and Clostridium novyi inactivate, by glucosylation, proteins from the Rho family that regulate actin polymerization. In contrast, the cytotoxic necrotic factor from Escherichia coli activates Rho by deamidation and increases the formation of actin filaments. The enterotoxin of Bacteroides fragilis is a protease specific for E-cadherin and it promotes the reorganization of the actin cytoskeleton. The bacterial toxins that modify the actin cytoskeleton induce various cell disfunctions including changes in cell barrier permeability and disruption of intercellular junctions

Election turnout statistics in many countries: similarities, differences, and a diffusive field model for decision-making

We study in details the turnout rate statistics for 77 elections in 11 different countries. We show that the empirical results established in a previous paper for French elections appear to hold much more generally. We find in particular that the spatial correlation of turnout rates decay logarithmically with distance in all cases. This result is quantitatively reproduced by a decision model that assumes that each voter makes his mind as a result of three influence terms: one totally idiosyncratic component, one city-specific term with short-ranged fluctuations in space, and one long-ranged correlated field which propagates diffusively in space. A detailed analysis reveals several interesting features: for example, different countries have different degrees of local heterogeneities and seem to be characterized by a different propensity for individuals to conform to the cultural norm. We furthermore find clear signs of herding (i.e. strongly correlated decisions at the individual level) in some countries, but not in others.Comment: 15 pages, 9 figures, 7 table

Aging, phase ordering and conformal invariance

In a variety of systems which exhibit aging, the two-time response function scales as $R(t,s)\approx s^{-1-a} f(t/s)$. We argue that dynamical scaling can be extended towards conformal invariance, obtaining thus the explicit form of the scaling function $f$. This quantitative prediction is confirmed in several spin systems, both for $T<T_c$ (phase ordering) and $T=T_c$ (non-equilibrium critical dynamics). The 2D and 3D Ising models with Glauber dynamics are studied numerically, while exact results are available for the spherical model with a non-conserved order parameter, both for short-ranged and long-ranged interactions, as well as for the mean-field spherical spin glass.Comment: 4 pp, 2 figs. Introduction extended, Refs. added; Phys. Rev. Lett. in pres

Evidence for the effectiveness of the blood—CSF barrier in the fetal rat choroid plexus. A freeze-fracture and peroxidase diffusion study

International audienceThe blood--cerebrospinal fluid (CSF) barrier in the choroid plexus is principally constituted of apical junctional complexes between epithelial cells. The effectiveness of this barrier was studied during the fetal development in the rat. Choroid plexuses from fetuses (14th and 18th embryonic day) and newborn (1 and 6 day old) rats were examined after intravascular administration of a proteic tracer (horseradish peroxidase) and investigated by freeze-fracture. From the 14th day of fetal life, apical junctions were seen to constitute a barrier that prevents the passage of peroxidase from blood to CSF; the tight junctions were morphologically similar to those of the mature animals; the junctional fibrils appeared continuous on complementary replicas. These data suggest that, from the 14th day of fetal development, the blood--CSF barrier is both morphologically and physiologically mature

Occupation time of a renewal process coupled to a discrete Markov chain

Abstract A semi-Markov process is one that changes states in accordance with a Markov chain but takes a random amount of time between changes. We consider the generalisation to semi-Markov processes of the classical Lamperti law for the occupation time of a two-state Markov process. We provide an explicit expression in Laplace space for the distribution of an arbitrary linear combination of the occupation times in the various states of the process. We discuss several consequences of this result. In particular, we infer the limiting distribution of this quantity rescaled by time in the long-time scaling regime, as well as the finite-time corrections to its moments

Lévy statistics and laser cooling: how rare events bring atoms to rest

A 2001 graduate-level book demonstrating the application of Lévy statistics to understand laser cooling of atoms