Boundary value problems for the Lorentzian Dirac operator

On a compact globally hyperbolic Lorentzian spin manifold with smooth spacelike Cauchy boundary the (hyperbolic) Dirac operator is known to be Fredholm when Atiyah-Patodi-Singer boundary conditions are imposed. In this paper we investigate to what extent these boundary conditions can be replaced by more general ones and how the index then changes. There are some differences to the classical case of the elliptic Dirac operator on a Riemannian manifold with boundary.Comment: error in examples 4.10 and 4.11 correcte

Boundary value problems for the Lorentzian Dirac operator

On a compact globally hyperbolic Lorentzian spin manifold with smooth spacelike Cauchy boundary the (hyperbolic) Dirac operator is known to be Fredholm when Atiyah-Patodi-Singer boundary conditions are imposed. In this paper we investigate to what extent these boundary conditions can be replaced by more general ones and how the index then changes. There are some differences to the classical case of the elliptic Dirac operator on a Riemannian manifold with boundary.Comment: error in examples 4.10 and 4.11 correcte

Collective Dynamics Of Two-dimensional Swimming Bacteria: Experiments And Models

The physical properties of collectively swimming bacteria have been thoroughly investigated both experimentally and theoretically using simulations. While models successfully predict some aspects of the dynamics observed in experiments, both models and experiments vary in their underlying assumptions and physical conditions. Hence, it is not clear which models are appropriate for which experimental setups. Here, we study, both experimentally and using two types of models (agent-based and continuous), the statistics of two strains of Serratia marcescens, wild-type and a nontumbling strain, swimming on a two-dimensional monolayer at varying concentrations. The experimental setup allows for a direct comparison with simulation results. Both models capture some aspects of the dynamics but fail at displaying others, especially at high densities. In particular, the effect of tumbling is much more significant than mere rotational (angular) diffusion

Collective Dynamics Of Two-dimensional Swimming Bacteria: Experiments And Models

The physical properties of collectively swimming bacteria have been thoroughly investigated both experimentally and theoretically using simulations. While models successfully predict some aspects of the dynamics observed in experiments, both models and experiments vary in their underlying assumptions and physical conditions. Hence, it is not clear which models are appropriate for which experimental setups. Here, we study, both experimentally and using two types of models (agent-based and continuous), the statistics of two strains of Serratia marcescens, wild-type and a nontumbling strain, swimming on a two-dimensional monolayer at varying concentrations. The experimental setup allows for a direct comparison with simulation results. Both models capture some aspects of the dynamics but fail at displaying others, especially at high densities. In particular, the effect of tumbling is much more significant than mere rotational (angular) diffusion

Heterogeneous Bacterial Swarms with Mixed Lengths

Heterogeneous systems of active matter exhibit a range of complex emergent dynamical patterns. In particular, it is difficult to predict the properties of the mixed system based on its constituents. These considerations are particularly significant for understanding realistic bacterial swarms, which typically develop heterogeneities even when grown from a single cell. Here, mixed swarms of cells with different aspect ratios are studied both experimentally and in simulations. In contrast with previous theory, there is no macroscopic phase segregation. However, locally, long cells act as nucleation cites, around which aggregates of short, rapidly moving cells can form, resulting in enhanced swarming speeds. On the other hand, high fractions of long cells form a bottleneck for efficient swarming. Our results suggest a physical advantage for the spontaneous heterogeneity of bacterial swarm populations

Supersymmetric Monojets at the Large Hadron Collider

Supersymmetric monojets may be produced at the Large Hadron Collider by the process qg -> squark neutralino_1 -> q neutralino_1 neutralino_1, leading to a jet recoiling against missing transverse momentum. We discuss the feasibility and utility of the supersymmetric monojet signal. In particular, we examine the possible precision with which one can ascertain the neutralino_1-squark-quark coupling via the rate for monojet events. Such a coupling contains information on the composition of the neutralino_1 and helps bound dark matter direct detection cross-sections and the dark matter relic density of the neutralino_1. It also provides a check of the supersymmetric relation between gauge couplings and gaugino-quark-squark couplings.Comment: 46 pages, 10 figures. The appendix has been rewritten to correct an error that appears in all previous versions of the appendix. This error has no effect on the results in the main body of the pape

Divergence via Europeanisation: rethinking the origins of the Portuguese debt crisis

A founding myth of the euro was that profound economic convergence could be achieved across the core and periphery of Europe. Scholarship from within Comparative Political Economy (CPE) has compellingly pointed to this myth of convergence as the fundamental mistake of the euro project (Regan, “Imbalance of Capitalisms”). Economic and Monetary Union was applied across a range of incompatible varieties of capitalism with little appreciation for how difficult it would be for peripheral economies to overcome long-standing institutional stickiness. Yet, while institutional stickiness tells us much about the causes of declining competitiveness, it tells us much less about the origins of brand new patterns of debt-led growth. This article modifies this CPE account by drawing attention to the much overlooked case of Portugal. In contrast to CPE’s emphasis on institutional stickiness, this paper explores the ways in which negotiation of European integration has been generative of institutional transformation leading to debt-led growth in Portugal. By combining Europeanisation with CPE, this article shows that, far from an inability to do so, in the case of Portugal, it has been the attempt to ‘follow the rules’ of European Integration that explains its damaging patterns of debt-led growth

Perceptions of, and reactions to, environmental heat: a brief note on issues of concern in relation to occupational health

Average temperatures around the world are already increasing, and climate change projections suggest that global mean temperatures will continue to rise. As the effects, and projected effects, of climate change are becoming clearer, it is more apparent that the health effects of heat exposure will need further investigation. The risks associated with heat exposure are especially relevant to understandings of occupational health for people involved in labouring or agricultural work in low-income countries. This review is a partial look at the ways in which issues surrounding heat exposure and occupational health have been treated in some of the available literature. This literature focuses on military-related medical understandings of heat exposure as well as heat exposure in working environments. The ways that these issues have been treated throughout the literature reflect the ways in which technologies of observation are intertwined with social attitudes. The effects of heat on the health of working people, as well as identification of risk groups, will require further research in order to promote prophylactic measures as well as to add to understandings of the actual and potential consequences of climatic change