Schwinger effect for non-Abelian gauge bosons

We investigate the Schwinger effect for the gauge bosons in an unbroken non-Abelian gauge theory (e.g. the gluons of QCD). We consider both constant "color electric" fields and "color magnetic" fields as backgrounds. As in the Abelian Schwinger effect we find there is production of "gluons" for the color electric field, but no particle production for the color magnetic field case. Since the non-Abelian gauge bosons are massless there is no exponential suppression of particle production due to the mass of the electron/positron that one finds in the Abelian Schwinger effect. Despite the lack of an exponential suppression of the gluon production rate due to the masslessness of the gluons, we find that the critical field strength is even larger in the non-Abelian case as compared to the Abelian case. This is the result of the confinement phenomenon on QCD.Comment: 15 pages revtex, contribution to IF-YITP GR+HEP+Cosmo International Symposium VI Naresuan University, Thailan

Formal Modelling, Testing and Verification of HSA Memory Models using Event-B

The HSA Foundation has produced the HSA Platform System Architecture Specification that goes a long way towards addressing the need for a clear and consistent method for specifying weakly consistent memory. HSA is specified in a natural language which makes it open to multiple ambiguous interpretations and could render bugs in implementations of it in hardware and software. In this paper we present a formal model of HSA which can be used in the development and verification of both concurrent software applications as well as in the development and verification of the HSA-compliant platform itself. We use the Event-B language to build a provably correct hierarchy of models from the most abstract to a detailed refinement of HSA close to implementation level. Our memory models are general in that they represent an arbitrary number of masters, programs and instruction interleavings. We reason about such general models using refinements. Using Rodin tool we are able to model and verify an entire hierarchy of models using proofs to establish that each refinement is correct. We define an automated validation method that allows us to test baseline compliance of the model against a suite of published HSA litmus tests. Once we complete model validation we develop a coverage driven method to extract a richer set of tests from the Event-B model and a user specified coverage model. These tests are used for extensive regression testing of hardware and software systems. Our method of refinement based formal modelling, baseline compliance testing of the model and coverage driven test extraction using the single language of Event-B is a new way to address a key challenge facing the design and verification of multi-core systems.Comment: 9 pages, 10 figure

Nonlinear Hierarchical Models for Longitudinal Experimental Infection Studies

Experimental infection (EI) studies, involving the intentional inoculation of animal or human subjects with an infectious agent under controlled conditions, have a long history in infectious disease research. Longitudinal infection response data often arise in EI studies designed to demonstrate vaccine efficacy, explore disease etiology, pathogenesis and transmission, or understand the host immune response to infection. Viral loads, antibody titers, symptom scores and body temperature are a few of the outcome variables commonly studied. Longitudinal EI data are inherently nonlinear, often with single-peaked response trajectories with a common pre- and post-infection baseline. Such data are frequently analyzed with statistical methods that are inefficient and arguably inappropriate, such as repeated measures analysis of variance (RM-ANOVA). Newer statistical approaches may offer substantial gains in accuracy and precision of parameter estimation and power. We propose an alternative approach to modeling single-peaked, longitudinal EI data that incorporates recent developments in nonlinear hierarchical models and Bayesian statistics. We begin by introducing a nonlinear mixed model (NLMM) for a symmetric infection response variable. We employ a standard NLMM assuming normally distributed errors and a Gaussian mean response function. The parameters of the model correspond directly to biologically meaningful properties of the infection response, including baseline, peak intensity, time to peak and spread. Through Monte Carlo simulation studies we demonstrate that the model outperforms RM-ANOVA on most measures of parameter estimation and power. Next we generalize the symmetric NLMM to allow modeling of variables with asymmetric time course. We implement the asymmetric model as a Bayesian nonlinear hierarchical model (NLHM) and discuss advantages of the Bayesian approach. Two illustrative applications are provided. Finally we consider modeling of viral load. For several reasons, a normal-errors model is not appropriate for viral load. We propose and illustrate a Bayesian NLHM with the individual responses at each time point modeled as a Poisson random variable with the means across time points related through a Tricube mean response function. We conclude with discussion of limitations and open questions, and a brief survey of broader applications of these models

Effect of Secondary Interactions on the Fundamental Properties of Small Molecule Models of the Diiron Hydrogenase Active Site

The unique active site of [FeFe]-hydrogenase has inspired over 300 small molecule models derived from the classical organometallic complex, (μ-SRS-)[Fe(CO)3]2. However, no model complex has yet reproduced the hydrogen production capabilities of the enzyme. One reason for this is that the model complexes are not subject to the large number of second coordination sphere interactions that are present in the active site. This work represents two approaches to explore the importance of non-covalent interactions on the properties of small molecule models, (μ-SRS)[Fe(CO)3]2 and (μ-SRS[Fe(CO)2L]2, of the enzyme active site. First, a series of diiron models with additional steric bulk built into the dithiolate linker that connects the two irons were synthesized. While the electron donating ability of the dithiolate is not drastically altered, as evidenced by infrared spectroscopy, variable temperature - NMR studies show that the energy barrier for certain intramolecular dynamic processes, important in modeling the enzyme active site, is significantly lowered. Electrochemical studies on the all-CO derivatives showed no significant differences in the redox properties of the sterically bulky complexes compared to complexes without added steric bulk. For substituted complexes in which CO is replaced by strong donor ligands greater electrochemical changes were observed, with some events being more accessible by up to 230 mV. One electron oxidation of the disubstituted complexes has produced a series of rare mixed-valent FeIFeII complexes. An X-ray crystal structure of one of these complexes, (μ-SCH2C(CH3)2CH2S-)[Fe(CO)2PMe3]2PF6 shows both a semi-bridging carbonyl and an open site similar to the 2-Fe subsite in the Hox state of the enzyme active site. Another method for studying secondary interactions on the model complexes used a host-guest approach to provide an artificial protein environment. Reaction of an aryl sulfonate-containing diiron complex with natural β-cyclodextrin results in encapsulation of the model. The X-ray crystal structure of the inclusion complex, Na (μ-SCH2N(C6H4SO3-)CH2S-)[Fe(CO)3]2·2 β-cyclodextrin shows complete enclosure of the diiron model within two cyclodextrin units. Solution studies support the formation of an inclusion complex and show that the cyclodextrin is capable of producing significant redox changes to the model complex in H2O. This work has provided a new highly modifiable method for affecting change in the properties of model complexes through intermolecular interactions

Attitudes to depression and its treatment in primary care

Background Undertreatment of depression in primary care is common. Efforts to address this tend to overlook the role of patient attitudes. Our aim was to validate and describe responses to a questionnaire about attitudes to depression and its treatment in a sample with experience of moderate and severe depressive episodes. Method Cross-sectional survey of 866 individuals with a confirmed history of an ICD-10 depressive episode in the 12 months preceding interview, recruited from 7271 consecutive general practitioner (GP) attendees in 36 general practices in England and Wales. Attitudes to and beliefs about depression were assessed using a 19-item self-report questionnaire. Results Factor analysis resulted in a three-factor solution: factor 1, depression as a disabling, permanent state; factor 2, depression as a medical condition responsive to support; and factor 3, antidepressants are addictive and ineffective. Participants who received and adhered to antidepressant medication and disclosed their depression to family and friends had significantly lower scores on factors 1 and 3 but higher scores on factor 2. Conclusions People with moderate or severe depressive episodes have subtle and divergent views about this condition, its outcome, and appropriate help. Such beliefs should be considered in primary care as they may significantly impact on help seeking and adherence to treatment

Quantum gravity, the cosmological constant, and parity transformation

One of the leading issues in quantum field theory and cosmology is the mismatch between the observed and calculated values for the cosmological constant in Einstein's field equations of up to 120 orders of magnitude. In this paper, we discuss new methods to potentially bridge this chasm using the generalized uncertainty principle (GUP). We find that if quantum gravity GUP models are the solution to this puzzle, then it may require the gravitationally modified position operator undergo a parity transformation at high energies.Comment: 10 pages, revtex-4, 0 figures, published in PL