Non-equilibrium Phase-Ordering with a Global Conservation Law

In all dimensions, infinite-range Kawasaki spin exchange in a quenched Ising model leads to an asymptotic length-scale $L \sim (\rho t)^{1/2} \sim t^{1/3}$ at $T=0$ because the kinetic coefficient is renormalized by the broken-bond density, $\rho \sim L^{-1}$. For $T>0$, activated kinetics recovers the standard asymptotic growth-law, $L \sim t^{1/2}$. However, at all temperatures, infinite-range energy-transport is allowed by the spin-exchange dynamics. A better implementation of global conservation, the microcanonical Creutz algorithm, is well behaved and exhibits the standard non-conserved growth law, $L \sim t^{1/2}$, at all temperatures.Comment: 2 pages and 2 figures, uses epsf.st

Evaluation of HIV counseling and testing in ANC settings and adherence to short course antiretroviral prophylaxis for PMTCT in Francistown, Botswana

Worldwide, it is estimated that two million children are infected with HIV (USAID 2005). The vast majority of these infections are the result of mother-to-child transmission (MTCT) of the virus during pregnancy, labor, or breastfeeding. However, there are effective methods for prevention of mother-to-child transmission (PMTCT). Botswana is one of the first countries in the developing world with a national PMTCT program that uses an efficacious and complex regimen to reduce vertical transmission. At the time of this evaluation (August - December 2005), the standard of care for prevention of MTCT of HIV in Botswana included three-drug antiretroviral therapy for HIV-infected women with a CD4 count of 200 (300 mg AZT in the morning and 300 mg AZT in the evening); four weeks of AZT for their infants; single-dose maternal and infant nevirapine (NVP); and 12 months of free infant formula. Botswana's PMTCT program also provided routine HIV testing for all pregnant women during antenatal care (ANC) to identify HIV-positive women for prophylaxis or treatment. While programs often report the number of individuals beginning AZT and receiving nevirapine for PMTCT, effectiveness is dependent on the level of adherence of individuals to these regimens. To describe adherence of pregnant women to the current PMTCT regimen, the Horizons Program of the Population Council, in collaboration with the Centers for Disease Control and Prevention (CDC) and Premiere Personnel in Botswana, conducted an evaluation to describe HIV-related services provided to women during their pregnancies, document the content of post-test counseling sessions for HIV-positive pregnant women, whether HIV-positive women remembered what had been discussed, the extent of AZT adherence based on self-reports, and the operational successes and barriers to adherence to AZT for PMTCT

Breakdown of Scaling in the Nonequilibrium Critical Dynamics of the Two-Dimensional XY Model

The approach to equilibrium, from a nonequilibrium initial state, in a system at its critical point is usually described by a scaling theory with a single growing length scale, $\xi(t) \sim t^{1/z}$, where z is the dynamic exponent that governs the equilibrium dynamics. We show that, for the 2D XY model, the rate of approach to equilibrium depends on the initial condition. In particular, $\xi(t) \sim t^{1/2}$ if no free vortices are present in the initial state, while $\xi(t) \sim (t/\ln t)^{1/2}$ if free vortices are present.Comment: 4 pages, 3 figure

Persistence in systems with algebraic interaction

Persistence in coarsening 1D spin systems with a power law interaction $r^{-1-\sigma}$ is considered. Numerical studies indicate that for sufficiently large values of the interaction exponent $\sigma$ ($\sigma\geq 1/2$ in our simulations), persistence decays as an algebraic function of the length scale $L$, $P(L)\sim L^{-\theta}$. The Persistence exponent $\theta$ is found to be independent on the force exponent $\sigma$ and close to its value for the extremal ($\sigma \to \infty$) model, $\bar\theta=0.17507588...$. For smaller values of the force exponent ($\sigma< 1/2$), finite size effects prevent the system from reaching the asymptotic regime. Scaling arguments suggest that in order to avoid significant boundary effects for small $\sigma$, the system size should grow as ${[{\cal O}(1/\sigma)]}^{1/\sigma}$.Comment: 4 pages 4 figure

Comment on ``Theory of Spinodal Decomposition''

I comment on a paper by S. B. Goryachev [PRL vol 72, p.1850 (1994)] that presents a theory of non-equilibrium dynamics for scalar systems quenched into an ordered phase. Goryachev incorrectly applies only a global conservation constraint to systems with local conservation laws.Comment: 2 pages LATeX (REVTeX macros), no figures. REVISIONS --- more to the point. microscopic example added, presentation streamlined, long-range interactions mentioned, to be published in Phys. Rev. Let

Stress-free Spatial Anisotropy in Phase-Ordering

We find spatial anisotropy in the asymptotic correlations of two-dimensional Ising models under non-equilibrium phase-ordering. Anisotropy is seen for critical and off-critical quenches and both conserved and non-conserved dynamics. We argue that spatial anisotropy is generic for scalar systems (including Potts models) with an anisotropic surface tension. Correlation functions will not be universal in these systems since anisotropy will depend on, e.g., temperature, microscopic interactions and dynamics, disorder, and frustration.Comment: 4 pages, 4 figures include