Reversible to Irreversible Flow Transition in Periodically Driven Vortices

We show that periodically driven superconducting vortices in the presence of quenched disorder exhibit a transition from reversible to irreversible flow under increasing vortex density or cycle period. This type of behavior has recently been observed for periodically sheared colloidal suspensions and we demonstrate that driven vortex systems exhibit remarkably similar behavior. We also provide evidence that the onset of irreversible behavior is a dynamical phase transition.Comment: 4 pages, 4 postscript figures. Version to appear in Physical Review Letter

Landscape context mediates the relationship between plant functional traits and decomposition

Aims: It has been well demonstrated that several interacting endogenous and exogenous factors influence decomposition. However, teasing apart the direct and indirect effects of these factors to predict decomposition patterns in heterogenous landscapes remains a key challenge. Methods: At 157 locations in a temperate forest, we measured decomposition of a standard substrate (filter paper) over two years, the landscape context in which decomposition took place, and the functional composition of the woody species that contributed leaf litter to the forest floor where litter bags were placed. We tested for direct and indirect effects of landscape context and direct effects of forest functional composition on decay using structural equation modelling. Results: We found that landscape context had direct effects on decay and indirect effects on decay via its influence on the functional composition of the surrounding forest. Forest functional composition also had direct effects on decay, but these effects decreased or disappeared completely over time. Moreover, community weighted mean trait values were better predictors of decay than functional dispersion of leaf traits, and leaf nitrogen content and carbon content were better predictors of decay than leaf dry matter content or leaf toughness. Conclusions: Our results highlight the importance of an integrative approach that examines the direct and indirect effects of multiple factors for understanding and predicting decomposition patterns across heterogenous landscapes

Using sports infrastructure to deliver economic and social change: Lessons for London beyond 2012

Over the last two decades, there has been a new trend emerging within sport, which has seen a shift, from investment for the sake of sport, to investment in sport for good (Sport England, 2008). In the context of the latter approach, there has been an emergence of the use of sport to address regeneration objectives, largely stemming from the belief of government and other sporting and non-sporting organizations, that it can confer a wide range of economic and social benefits to individuals and communities beyond those of a purely physical sporting nature, and can contribute positively to the revitalization of declining urban areas (BURA, 2003). This commentary will examine regeneration legacy in the context of the London Olympic Games. In particular, it will focus on the use of sports stadia as a tool for delivering economic and social change, and by drawing upon previous examples, suggest lessons London can learn to enhance regeneration legacies beyond 2012

Researching Social Networks in Action

Many communities across Canada today are challenged by conditions that approach social and economic disintegration. As agencies of the state cut back their financial support of welfare services, citizens are faced with both increasing levels of stress and fewer forms of relief provided by established institutions. For researchers, the challenges of a shrinking resource base are compounded by ongoing epistemological and methodological controversies within social science. The recent emergence of a postmodern critique of traditional social-scientific methodology arises from some profound reorientations in the philosophy and the social context of the social sciences, reorientations that are reflective of fundamental economic and political transformations. This paper describes the action-research program we have designed and implemented in response to these challenges. Starting with a small core of citizens from the community of Hespeler, Ontario, we have been using ethnographic methods to trace the networks of which these people are part and the ways in which those networks are constructed and maintained. The insights gained from this inquiry process are being used, in turn, to develop methods of strengthening local support structures, through collaborative processes of research and action. Such strengthening forms of interaction are not only desirable on their own terms. They also provide a model for restructuring relationships among research participants, and among forms of knowledge and being

Transcriptional adaptation of Mycobacterium tuberculosis within macrophages: Insights into the phagosomal environment

Little is known about the biochemical environment in phagosomes harboring an infectious agent. To assess the state of this organelle we captured the transcriptional responses of Mycobacterium tuberculosis (MTB) in macrophages from wild-type and nitric oxide (NO) synthase 2–deficient mice before and after immunologic activation. The intraphagosomal transcriptome was compared with the transcriptome of MTB in standard broth culture and during growth in diverse conditions designed to simulate features of the phagosomal environment. Genes expressed differentially as a consequence of intraphagosomal residence included an interferon � – and NO-induced response that intensifies an iron-scavenging program, converts the microbe from aerobic to anaerobic respiration, and induces a dormancy regulon. Induction of genes involved in the activation and �-oxidation of fatty acids indicated that fatty acids furnish carbon and energy. Induction of �E-dependent, sodium dodecyl sulfate–regulated genes and genes involved in mycolic acid modification pointed to damage and repair of the cell envelope. Sentinel genes within the intraphagosomal transcriptome were induced similarly by MTB in the lungs of mice. The microbial transcriptome thus served as a bioprobe of the MTB phagosomal environment

On the convergence of quadrature formulas connected with multipoint Padé-type approximants

29 pages, no figures.-- MSC2000 codes: 41A55, 41A21.MR#: MR1408352 (97e:41066)Zbl#: Zbl 0856.41027^aLet $I(F)= \int^1_{- 1} F(x)\omega(x) dx$, where $\omega$ is a complex valued integrable function. We consider quadrature formulas for $I(F)$ which are exact with respect to rational functions with prescribed poles contained in \overline{\bbfC}\backslash [- 1, 1]. Their rate of convergence is studied.The research by the first three authors (P.G.-V., M.J.P., R.O.) was partially supported by the HCM project ROLLS, under Contract CHRX-CT93-0416. Research by the fourth author (G.L.L.) was carried out while on a visit at Universidad de La Laguna. This visit was made possible by a travel grant from CDE-IMU.Publicad

Patterns of subnet usage reveal distinct scales of regulation in the transcriptional regulatory network of Escherichia coli

The set of regulatory interactions between genes, mediated by transcription factors, forms a species' transcriptional regulatory network (TRN). By comparing this network with measured gene expression data one can identify functional properties of the TRN and gain general insight into transcriptional control. We define the subnet of a node as the subgraph consisting of all nodes topologically downstream of the node, including itself. Using a large set of microarray expression data of the bacterium Escherichia coli, we find that the gene expression in different subnets exhibits a structured pattern in response to environmental changes and genotypic mutation. Subnets with less changes in their expression pattern have a higher fraction of feed-forward loop motifs and a lower fraction of small RNA targets within them. Our study implies that the TRN consists of several scales of regulatory organization: 1) subnets with more varying gene expression controlled by both transcription factors and post-transcriptional RNA regulation, and 2) subnets with less varying gene expression having more feed-forward loops and less post-transcriptional RNA regulation.Comment: 14 pages, 8 figures, to be published in PLoS Computational Biolog