Nonlocal Conductivity in the Vortex-Liquid Regime of a Two-Dimensional Superconductor

We have simulated the time-dependent Ginzburg-Landau equation with thermal fluctuations, to study the nonlocal dc conductivity of a superconducting film. Having examined points in the phase diagram at a wide range of temperatures and fields below the mean-field upper critical field, we find a portion of the vortex-liquid regime in which the nonlocal ohmic conductivity in real space is negative over a distance several times the spacing between vortices. The effect is suppressed when driven beyond linear response. Earlier work had predicted the existence of such a regime, due to the high viscosity of a strongly-correlated vortex liquid. This behavior is clearly distinguishable from the monotonic spatial fall-off of the conductivity in the higher temperature or field regimes approaching the normal state. The possibilities for experimental study of the nonlocal transport properties are discussed.Comment: 18 pages, revtex, 6 postscript figure

Incommensuration Effects and Dynamics in Vortex Chains

We examine the motion of one-dimensional (1D) vortex matter embedded in a 2D vortex system with weak pinning using numerical simulations. We confirm the conjecture of Matsuda et al. [Science 294, 2136 (2001)] that the onset of the temperature induced motion of the chain is due to an incommensuration effect of the chain with the periodic potential created by the bulk vortices. In addition, under an applied driving force we find a two stage depinning transition, where the initial depinning of the vortex chain occurs through soliton like pulses. When an ac drive is added to the dc drive, we observe phase locking of the moving vortex chain.Comment: 4 pages, 4 postscript figure

Hall-conductivity sign change and fluctuations in amorphous Nbx_{x}Ge1−x_{1-x} films

The sign change in the Hall conductivity has been studied in thin amorphous Nb$_{1-x}$Ge$_x (x\approx$0.3) films. By changing the film thickness it is shown that the field at which the sign reversal occurs shifts to lower values (from above to below the mean-field transition field $H_{c2}$) with increasing film thickness. This effect can be understood in terms of a competition between a positive normal and a negative fluctuation contribution to the Hall conductivity.Comment: 5 pages, 4 figures, to appear in Phys. Rev.

Dynamic ordering and frustration of confined vortex rows studied by mode-locking experiments

The flow properties of confined vortex matter driven through disordered mesoscopic channels are investigated by mode locking (ML) experiments. The observed ML effects allow to trace the evolution of both the structure and the number of confined rows and their match to the channel width as function of magnetic field. From a detailed analysis of the ML behavior for the case of 3-rows we obtain ({\it i}) the pinning frequency $f_p$, ({\it ii}) the onset frequency $f_c$ for ML ($\propto$ ordering velocity) and ({\it iii}) the fraction $L_{ML}/L$ of coherently moving 3-row regions in the channel. The field dependence of these quantities shows that, at matching, where $L_{ML}$ is maximum, the pinning strength is small and the ordering velocity is low, while at mismatch, where $L_{ML}$ is small, both the pinning force and the ordering velocity are enhanced. Further, we find that $f_c \propto f_p^2$, consistent with the dynamic ordering theory of Koshelev and Vinokur. The microscopic nature of the flow and the ordering phenomena will also be discussed.Comment: 10 pages, 7 figure, submitted to PRB. Discussion has been improved and a figure has been adde

A novel guinea pig model of Chlamydia trachomatis genital tract infection

Contains fulltext : 95582.pdf (publisher's version ) (Closed access)Genital Chlamydia trachomatis infections often result in pelvic inflammatory disease and sequelae including infertility and ectopic pregnancies. In addition to the already established murine models, the development of other animal models is necessary to study the safety and efficacy of prototype vaccine candidates. The intravaginal infection of guinea pigs with C. trachomatis has been tested in three independent studies. The first two studies investigated the effect of hormonal treatment of the animals prior to infection with serovars D and E. The results showed that estradiol treatment was required for sustained infection. The third study conducted an immunization-challenge experiment to explore the feasibility of measuring protection in this guinea pig model. C. trachomatis bacteria were sampled using vaginal swabs and measured by qPCR. Using immunohistochemistry the bacteria were detected in the oviducts 19 days post-infection, indicating that the estradiol treatment resulted in ascending infection. Furthermore, immunization of guinea pigs with live EB formulated with ISCOM matrix led to reduction of cervico-vaginal shedding and diminished the severity of pathology. In this study we have developed a new guinea pig model of C. trachomatis female genital tract infection for the purpose of evaluating potential vaccine candidates