Dynamics of a Driven Single Flux Line in Superconductors

We study the low temperature dynamics of a single flux line in a bulk type-II superconductor, driven by a surface current, both near and above the onset of an instability which sets in at a critical driving. We found that above the critical driving, the velocity profile of the flux line develops a discontinuity.Comment: 10 pages with 4 figures, REVTE

The Several Guises of the BRST Symmetry

We present several forms in which the BRST transformations of QCD in covariant gauges can be cast. They can be non-local and even not manifestly covariant. These transformations may be obtained in the path integral formalism by non standard integrations in the ghost sector or by performing changes of ghost variables which leave the action and the path integral measure invariant. For different changes of ghost variables in the BRST and anti-BRST transformations these two transformations no longer anticommute.Comment: 3 pages, revte

Driven Depinning in Anisotropic Media

We show that the critical behavior of a driven interface, depinned from quenched random impurities, depends on the isotropy of the medium. In anisotropic media the interface is pinned by a bounding (conducting) surface characteristic of a model of mixed diodes and resistors. Different universality classes describe depinning along a hard and a generic direction. The exponents in the latter (tilted) case are highly anisotropic, and obtained exactly by a mapping to growing surfaces. Various scaling relations are proposed in the former case which explain a number of recent numerical observations.Comment: 4 pages with 2 postscript figures appended, REVTe

Avalanches and Correlations in Driven Interface Depinning

We study the critical behavior of a driven interface in a medium with random pinning forces by analyzing spatial and temporal correlations in a lattice model recently proposed by Sneppen [Phys. Rev. Lett. {\bf 69}, 3539 (1992)]. The static and dynamic behavior of the model is related to the properties of directed percolation. We show that, due to the interplay of local and global growth rules, the usual method of dynamical scaling has to be modified. We separate the local from the global part of the dynamics by defining a train of causal growth events, or "avalanche", which can be ascribed a well-defined dynamical exponent $z_{loc} = 1 + \zeta_c \simeq 1.63$ where $\zeta_c$ is the roughness exponent of the interface. We observe that the avalanche size distribution obeys a power-law decay with an exponent $\kappa \simeq 1.25$.Comment: 7 pages, (5 figures available upon request), REVTeX, RUB-TP3-93-0

Thermo-mechanical behaviour of a compacted swelling clay

Compacted unsaturated swelling clay is often considered as a possible buffer material for deep nuclear waste disposal. An isotropic cell permitting simultaneous control of suction, temperature and pressure was used to study the thermo-mechanical behaviour of this clay. Tests were performed at total suctions ranging from 9 to 110 MPa, temperature from 25 to 80 degrees C, isotropic pressure from 0.1 to 60 MPa. It was observed that heating at constant suction and pressure induces either swelling or contraction. The results from compression tests at constant suction and temperature evidenced that at lower suction, the yield pressure was lower, the elastic compressibility parameter and the plastic compressibility parameter were higher. On the other hand, at a similar suction, the yield pressure was slightly influenced by the temperature; and the compressibility parameters were insensitive to temperature changes. The thermal hardening phenomenon was equally evidenced by following a thermo-mechanical path of loading-heating-cooling-reloading

Sr2+ binding to the Ca2+ binding site of the synaptotagmin 1 C2B domain triggers fast exocytosis without stimulating SNARE interactions

Sr2+ triggers neurotransmitter release similar to Ca2+, but less efficiently. We now show that in synaptotagmin 1 knockout mice, the fast component of both Ca2+- and Sr2+-induced release is selectively impaired, suggesting that both cations partly act by binding to synaptotagmin 1. Both the C(2)A and the C2B domain of synaptotagmin 1 bind Ca2+ in phospholipid complexes, but only the C2B domain forms Sr2+/phospholipid complexes; therefore, Sr2+ binding to the C2B domain is sufficient to trigger fast release, although with decreased efficacy. Ca2+ induces binding of the synaptotagmin C, domains to SNARE proteins, whereas Sr2+ even at high concentrations does not. Thus, triggering of the fast component of release by Sr2+ as a Ca2+ agonist involves the formation of synaptotagmin/ phospholipid complexes, but does not require stimulated SNARE binding

Singularities and Avalanches in Interface Growth with Quenched Disorder

A simple model for an interface moving in a disordered medium is presented. The model exhibits a transition between the two universality classes of interface growth phenomena. Using this model, it is shown that the application of constraints to the local slopes of the interface produces avalanches of growth, that become relevant in the vicinity of the depinning transition. The study of these avalanches reveals a singular behavior that explains a recently observed singularity in the equation of motion of the interface.Comment: 4 pages. REVTEX. 4 figs available on request from [email protected]

Intermedin attenuates LPS-induced inflammation in the rat testis

First reported as a vasoactive peptide in the cardiovascular system, intermedin (IMD), also known as adrenomedullin 2 (ADM2), is a hormone with multiple potent roles, including its antioxidant action on the pulmonary, central nervous, cardiovascular and renal systems. Though IMD may play certain roles in trophoblast cell invasion, early embryonic development and cumulus cell-oocyte interaction, the role of IMD in the male reproductive system has yet to be investigated. This paper reports our findings on the gene expression of IMD, its receptor components and its protein localization in the testes. In a rat model, bacterial lippolysaccharide (LPS) induced atypical orchitis, and LPS treatment upregulated the expression of IMD and one of its receptor component proteins, i.e. receptor activity modifying protein 2 (RAMP2). IMD decreased both plasma and testicular levels of reactive oxygen species (ROS) production, attenuated the increase in the gene expression of the proinflammatory cytokines tumor necrosis factor alpha (TNFα), interleukin 6 (IL6) and interleukin 1 beta (IL1β), rescued spermatogenesis, and prevented the decrease in plasma testosterone levels caused by LPS. The restorative effect of IMD on steroidogenesis was also observed in hydrogen peroxide-treated rat primary Leydig cells culture. Our results indicate IMD plays an important protective role in spermatogenesis and steroidogenesis, suggesting therapeutic potential for IMD in pathological conditions such as orchitis.published_or_final_versio

Vortex avalanches and self organized criticality in superconducting niobium

In 1993 Tang proposed [1] that vortex avalanches should produce a self organized critical state in superconductors, but conclusive evidence for this has heretofore been lacking. In the present paper, we report extensive micro-Hall probe data from the vortex dynamics in superconducting niobium, where a broad distribution of avalanche sizes scaling as a power-law for more than two decades is found. The measurements are combined with magneto-optical imaging, and show that over a widely varying magnetic landscape the scaling behaviour does not change, hence establishing that the dynamics of superconducting vortices is a SOC phenomenon.Comment: 3 pages + 4 figures, a reference added, citation typos fixe