Electrical conductivity and thermal dilepton rate from quenched lattice QCD

We report on a continuum extrapolation of the vector current correlation function for light valence quarks in the deconfined phase of quenched QCD. This is achieved by performing a systematic analysis of the influence of cut-off effects on light quark meson correlators at $T\simeq 1.45 T_c$ using clover improved Wilson fermions. We discuss resulting constraints on the electrical conductivity and the thermal dilepton rate in a quark gluon plasma. In addition new results at 1.2 and 3.0 $T_c$ will be presented.Comment: 4 pages, 6 eps figures, to appear in the proceedings of Quark Matter 2011, 23-28 May 2011, Annecy, Franc

Role of nucleon resonance excitation in ϕ\phi meson photoproduction

The resonance effects are investigated in the $\phi$ meson photoproduction near threshold through a quark model approach with an effective Lagrangian. The diffractive contribution is consistently estimated by the {\it t}-channel Pomeron exchange. Another non-diffractive process, {\it t}-channel $\pi^0$ exchange is also included. The numerical result shows that the Pomeron exchange plays dominant role in the $\phi$ meson photoproduction, while the cross sections of the non-diffractive processes, i.e. {\it s}- and {\it u}-channel excitations, and {\it t}-channel $\pi^0$ exchange, are quite small. In the polarization observables, we find that large asymmetries are produced in the backward direction by the interferences from the {\it s}- and {\it u}-channel resonances, while in the forward direction, only very small asymmetries are generated. Meanwhile, we find that the effects from the $\pi^0$ exchange are generally negligible.Comment: Contribution to "2nd International Conference on Perspectives in Hadronic Physics", Trieste, ICTP, 10-14 May 1999, to appear in Few-body Syste

General Design Bayesian Generalized Linear Mixed Models

Linear mixed models are able to handle an extraordinary range of complications in regression-type analyses. Their most common use is to account for within-subject correlation in longitudinal data analysis. They are also the standard vehicle for smoothing spatial count data. However, when treated in full generality, mixed models can also handle spline-type smoothing and closely approximate kriging. This allows for nonparametric regression models (e.g., additive models and varying coefficient models) to be handled within the mixed model framework. The key is to allow the random effects design matrix to have general structure; hence our label general design. For continuous response data, particularly when Gaussianity of the response is reasonably assumed, computation is now quite mature and supported by the R, SAS and S-PLUS packages. Such is not the case for binary and count responses, where generalized linear mixed models (GLMMs) are required, but are hindered by the presence of intractable multivariate integrals. Software known to us supports special cases of the GLMM (e.g., PROC NLMIXED in SAS or glmmML in R) or relies on the sometimes crude Laplace-type approximation of integrals (e.g., the SAS macro glimmix or glmmPQL in R). This paper describes the fitting of general design generalized linear mixed models. A Bayesian approach is taken and Markov chain Monte Carlo (MCMC) is used for estimation and inference. In this generalized setting, MCMC requires sampling from nonstandard distributions. In this article, we demonstrate that the MCMC package WinBUGS facilitates sound fitting of general design Bayesian generalized linear mixed models in practice.Comment: Published at http://dx.doi.org/10.1214/088342306000000015 in the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org

Condom use and incident sexually transmitted infection after initiation of long-acting reversible contraception

Background Use of more effective contraception may lead to less condom use and increased incidence of sexually transmitted infection. Objective The objective of this study was to compare changes in condom use and incidence of sexually transmitted infection acquisition among new initiators of long-acting reversible contraceptives to those initiating non-long-acting reversible contraceptive methods. Study Design This is a secondary analysis of the Contraceptive CHOICE Project. We included 2 sample populations of 12-month continuous contraceptive users. The first included users with complete condom data (baseline, and 3, 6, and 12 months) (long-acting reversible contraceptive users: N = 2371; other methods: N = 575). The second included users with 12-month sexually transmitted infection data (long-acting reversible contraceptive users: N = 2102; other methods: N = 592). Self-reported condom use was assessed at baseline and at 3, 6, and 12 months following enrollment. Changes in condom use and incident sexually transmitted infection rates were compared using χ2 tests. Risk factors for sexually transmitted infection acquisition were identified using multivariable logistic regression. Results Few participants in either group reported consistent condom use across all survey time points and with all partners (long-acting reversible contraceptive users: 5.2%; other methods: 11.3%; P < .001). There was no difference in change of condom use at 3, 6, and 12 months compared to baseline condom use regardless of method type (P = .65). A total of 94 incident sexually transmitted infections were documented, with long-acting reversible contraceptive users accounting for a higher proportion (3.9% vs 2.0%; P = .03). Initiation of a long-acting reversible contraceptive method was associated with increased sexually transmitted infection incidence (odds ratio, 2.0; 95% confidence ratio, 1.07–3.72). Conclusion Long-acting reversible contraceptive initiators reported lower rates of consistent condom use, but did not demonstrate a change in condom use when compared to preinitiation behaviors. Long-acting reversible contraceptive users were more likely to acquire a sexually transmitted infection in the 12 months following initiation

Accurate Modelling of Left-Handed Metamaterials Using Finite-Difference Time-Domain Method with Spatial Averaging at the Boundaries

The accuracy of finite-difference time-domain (FDTD) modelling of left-handed metamaterials (LHMs) is dramatically improved by using an averaging technique along the boundaries of LHM slabs. The material frequency dispersion of LHMs is taken into account using auxiliary differential equation (ADE) based dispersive FDTD methods. The dispersive FDTD method with averaged permittivity along the material boundaries is implemented for a two-dimensional (2-D) transverse electric (TE) case. A mismatch between analytical and numerical material parameters (e.g. permittivity and permeability) introduced by the time discretisation in FDTD is demonstrated. The expression of numerical permittivity is formulated and it is suggested to use corrected permittivity in FDTD simulations in order to model LHM slabs with their desired parameters. The influence of switching time of source on the oscillation of field intensity is analysed. It is shown that there exists an optimum value which leads to fast convergence in simulations.Comment: 17 pages, 7 figures, submitted to Journal of Optics A Nanometa special issu