Worm algorithms for classical statistical models

We show that high-temperature expansions may serve as a basis for the novel approach to efficient Monte Carlo simulations. "Worm" algorithms utilize the idea of updating closed path configurations (produced by high-temperature expansions) through the motion of end points of a disconnected path. An amazing result is that local, Metropolis-type schemes may have dynamical critical exponents close to zero (i.e., their efficiency is comparable to the best cluster methods). We demonstrate this by calculating finite size scaling of the autocorrelation time for various (six) universality classes.Comment: 4 pages, latex, 2 figure

Nonequilibrium relaxation of the two-dimensional Ising model: Series-expansion and Monte Carlo studies

We study the critical relaxation of the two-dimensional Ising model from a fully ordered configuration by series expansion in time t and by Monte Carlo simulation. Both the magnetization (m) and energy series are obtained up to 12-th order. An accurate estimate from series analysis for the dynamical critical exponent z is difficult but compatible with 2.2. We also use Monte Carlo simulation to determine an effective exponent, z_eff(t) = - {1/8} d ln t /d ln m, directly from a ratio of three-spin correlation to m. Extrapolation to t = infinity leads to an estimate z = 2.169 +/- 0.003.Comment: 9 pages including 2 figure

Influence of through-flow on linear pattern formation properties in binary mixture convection

We investigate how a horizontal plane Poiseuille shear flow changes linear convection properties in binary fluid layers heated from below. The full linear field equations are solved with a shooting method for realistic top and bottom boundary conditions. Through-flow induced changes of the bifurcation thresholds (stability boundaries) for different types of convective solutions are deter- mined in the control parameter space spanned by Rayleigh number, Soret coupling (positive as well as negative), and through-flow Reynolds number. We elucidate the through-flow induced lifting of the Hopf symmetry degeneracy of left and right traveling waves in mixtures with negative Soret coupling. Finally we determine with a saddle point analysis of the complex dispersion relation of the field equations over the complex wave number plane the borders between absolute and convective instabilities for different types of perturbations in comparison with the appropriate Ginzburg-Landau amplitude equation approximation. PACS:47.20.-k,47.20.Bp, 47.15.-x,47.54.+rComment: 19 pages, 15 Postscript figure

New Dynamic Monte Carlo Renormalization Group Method

The dynamical critical exponent of the two-dimensional spin-flip Ising model is evaluated by a Monte Carlo renormalization group method involving a transformation in time. The results agree very well with a finite-size scaling analysis performed on the same data. The value of $z = 2.13 \pm 0.01$ is obtained, which is consistent with most recent estimates

The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: Analysis of potential systematics

We analyze the density field of galaxies observed by the Sloan Digital Sky Survey (SDSS)-III Baryon Oscillation Spectroscopic Survey (BOSS) included in the SDSS Data Release Nine (DR9). DR9 includes spectroscopic redshifts for over 400,000 galaxies spread over a footprint of 3,275 deg^2. We identify, characterize, and mitigate the impact of sources of systematic uncertainty on large-scale clustering measurements, both for angular moments of the redshift-space correlation function and the spherically averaged power spectrum, P(k), in order to ensure that robust cosmological constraints will be obtained from these data. A correlation between the projected density of stars and the higher redshift (0.43 < z < 0.7) galaxy sample (the `CMASS' sample) due to imaging systematics imparts a systematic error that is larger than the statistical error of the clustering measurements at scales s > 120h^-1Mpc or k < 0.01hMpc^-1. We find that these errors can be ameliorated by weighting galaxies based on their surface brightness and the local stellar density. We use mock galaxy catalogs that simulate the CMASS selection function to determine that randomly selecting galaxy redshifts in order to simulate the radial selection function of a random sample imparts the least systematic error on correlation function measurements and that this systematic error is negligible for the spherically averaged correlation function. The methods we recommend for the calculation of clustering measurements using the CMASS sample are adopted in companion papers that locate the position of the baryon acoustic oscillation feature (Anderson et al. 2012), constrain cosmological models using the full shape of the correlation function (Sanchez et al. 2012), and measure the rate of structure growth (Reid et al. 2012). (abridged)Comment: Matches version accepted by MNRAS. Clarifications and references have been added. See companion papers that share the "The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey:" titl

Publisher Correction: Primary functional brain connections associated with melancholic major depressive disorder and modulation by antidepressants

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Oxytocin's neurochemical effects in the medial prefrontal cortex underlie recovery of task-specific brain activity in autism: a randomized controlled trial

The neuropeptide oxytocin may be an effective therapeutic strategy for the currently untreatable social and communication deficits associated with autism. Our recent paper reported that oxytocin mitigated autistic behavioral deficits through the restoration of activity in the ventromedial prefrontal cortex (vmPFC), as demonstrated with functional magnetic resonance imaging (fMRI) during a socio-communication task. However, it is unknown whether oxytocin exhibited effects at the neuronal level, which was outside of the specific task examined. In the same randomized, double-blind, placebo-controlled, within-subject cross-over clinical trial in which a single dose of intranasal oxytocin (24 IU) was administered to 40 men with high-functioning autism spectrum disorder (UMIN000002241/000004393), we measured N-acetylaspartate (NAA) levels, a marker for neuronal energy demand, in the vmPFC using (1)H-magnetic resonance spectroscopy ((1)H-MRS). The differences in the NAA levels between the oxytocin and placebo sessions were associated with oxytocin-induced fMRI signal changes in the vmPFC. The oxytocin-induced increases in the fMRI signal could be predicted by the NAA differences between the oxytocin and placebo sessions (P=0.002), an effect that remained after controlling for variability in the time between the fMRI and (1)H-MRS scans (P=0.006) and the order of administration of oxytocin and placebo (P=0.001). Furthermore, path analysis showed that the NAA differences in the vmPFC triggered increases in the task-dependent fMRI signals in the vmPFC, which consequently led to improvements in the socio-communication difficulties associated with autism. The present study suggests that the beneficial effects of oxytocin are not limited to the autistic behavior elicited by our psychological task, but may generalize to other autistic behavioral problems associated with the vmPFC

Convection in Binary Fluid Mixtures. II. Localized Traveling Waves. (Physical Review E, in press)

Nonlinear, spatially localized structures of traveling convection rolls are investigated in quantitative detail as a function of Rayleigh number for two different Soret coupling strengths (separation ratios) with Lewis and Prandtl numbers characterizing ethanol-water mixtures. A finite-difference method was used to solve the full hydrodynamic field equations numerically. Structure and dynamics of these localized traveling waves (LTW) are dominated by the concentration field. Like in the spatially extended convective states ( cf. accompanying paper), the Soret-induced concentration variations strongly influence, via density changes, the buoyancy forces that drive convection. The spatio-temporal properties of this feed-back mechanism, involving boundary layers and concentration plumes, show that LTW's are strongly nonlinear states. Light intensity distributions are determined that can be observed in side-view shadowgraphs. Detailed analyses of all fields are made using colour-coded isoplots, among others. In the frame comoving with their drift velocity, LTW's display a nontrivial spatio-temporal symmetry consisting of time-translation by half an oscillation period combined with vertical reflection through the horizontal midplane of the layer. A time-averaged concentration current is driven by a phase difference between the waves of concentration and vertical velocity in the bulk of the LTW state. The associated large-scale concentration redistribution stabilizes the LTW and controls its drift velocity into the quiescent fluid by generating a buoyancy-reducing concentration "barrier" ahead of the leading LTW front. The selection of the width of the LTW's is investigated and comparisons with experiments are presented.Comment: 18 pages and 6 figures as uuencoded Postscript file (using uufiles) 1 color figure as uuencoded Postscript file, a high resolution version of the color figure (about 10MB) can be requested from [email protected] or [email protected].: (Barten)present address: PSI, CH-5232 Villigen PSI, Switzerlan

α1Proteinase Inhibitor Regulates CD4+ Lymphocyte Levels and Is Rate Limiting in HIV-1 Disease

Background: The regulation of adult stem cell migration through human hematopoietic tissue involves the chemokine CXCL12 (SDF-1) and its receptor CXCR4 (CD184). In addition, human leukocyte elastase (HLE) plays a key role. When HLE is located on the cell surface (HLE CS), it acts not as a proteinase, but as a receptor for a 1proteinase inhibitor (a 1PI, a 1antitrypsin, SerpinA1). Binding of a1PI to HLECS forms a motogenic complex. We previously demonstrated that a1PI deficiency attends HIV-1 disease and that a1PI augmentation produces increased numbers of immunocompetent circulating CD4 + lymphocytes. Herein we investigated the mechanism underlying the a 1PI deficiency that attends HIV-1 infection. Methods and Findings: Active a 1PI in HIV-1 subjects (median 17 mM, n = 35) was significantly below normal (median 36 mM, p,0.001, n = 30). In HIV-1 uninfected subjects, CD4 + lymphocytes were correlated with the combined factors a1PI, HLECS + lymphocytes, and CXCR4 + lymphocytes (r 2 = 0.91, p,0.001, n = 30), but not CXCL12. In contrast, in HIV-1 subjects with.220 CD4 cells/ml, CD4 + lymphocytes were correlated solely with active a 1PI (r 2 =0.93,p,0.0001, n = 26). The monoclonal anti-HIV-1 gp120 antibody 3F5 present in HIV-1 patient blood is shown to bind and inactivate human a 1PI. Chimpanzee a 1PI differs from human a1PI by a single amino acid within the 3F5-binding epitope. Unlike human a1PI, chimpanzee a1PI did not bind 3F5 or become depleted following HIV-1 challenge, consistent with the normal CD4 + lymphocyte levels and benign syndrome of HIV-1 infected chimpanzees. The presence of IgG-a 1PI immune complexes correlated with decreased CD4 + lymphocytes in HIV-1 subjects