Spin dynamics simulations of the magnetic dynamics of RbMnF3_3 and direct comparison with experiment

Spin-dynamics techniques have been used to perform large-scale simulations of the dynamic behavior of the classical Heisenberg antiferromagnet in simple cubic lattices with linear sizes $L\leq 60$. This system is widely recognized as an appropriate model for the magnetic properties of RbMnF$_3$. Time-evolutions of spin configurations were determined numerically from coupled equations of motion for individual spins using a new algorithm implemented by Krech {\it etal}, which is based on fourth-order Suzuki-Trotter decompositions of exponential operators. The dynamic structure factor was calculated from the space- and time-displaced spin-spin correlation function. The crossover from hydrodynamic to critical behavior of the dispersion curve and spin-wave half-width was studied as the temperature was increased towards the critical temperature. The dynamic critical exponent was estimated to be $z=(1.43\pm 0.03)$, which is slightly lower than the dynamic scaling prediction, but in good agreement with a recent experimental value. Direct, quantitative comparisons of both the dispersion curve and the lineshapes obtained from our simulations with very recent experimental results for RbMnF$_3$ are presented.Comment: 30 pages, RevTex, 9 figures, to appear in PR

Domain Wall Bubbles in High Energy Heavy Ion Collisions

It has been recently shown that meta-stable domain walls exist in high-density QCD ($\mu\neq 0$) as well as in QCD with large number of colors ($N_c\to\infty$), with the lifetime being exponentially long in both cases. Such metastable domain walls may exist in our world as well, especially in hot hadronic matter with temperature close to critical. In this paper we discuss what happens if a bubble made of such wall is created in heavy ion collisions, in the mixed phase between QGP and hadronic matter. We show it will further be expanded to larger volume $\sim 20 fm^3$ by the pion pressure, before it disappears, either by puncture or contraction. Both scenarios leave distinctive experimental signatures of such events, negatively affecting the interference correlations between the outgoing pions.Comment: 6 pages, 1 fi

Collapse of a semiflexible polymer in poor solvent

We investigate the dynamics and the pathways of the collapse of a single, semiflexible polymer in a poor solvent via 3-D Brownian Dynamics simulations. Earlier work indicates that the condensation of semiflexible polymers generically proceeds via a cascade through metastable racquet-shaped, long-lived intermediates towards the stable torus state. We investigate the rate of decay of uncollapsed states, analyze the preferential pathways of condensation, and describe likelihood and lifespan of the different metastable states. The simulation are performed with a bead-stiff spring model with excluded volume interaction and exponentially decaying attractive potential. The semiflexible chain collapse is studied as functions of the three relevant length scales of the phenomenon, i.e., the total chain length $L$, the persistence length $L_p$ and the condensation length $L_0 = \sqrt{k_B T L_p/u_0}$, where $u_0$ is a measure of the attractive potential per unit length. Two dimensionless ratios, $L/L_p$ and $L_0/L_p$, suffice to describe the decay rate of uncollapsed states, which appears to scale as $(L/L_p)^{1/3} (L_0/L_p)$. The condensation sequence is described in terms of the time series of the well separated energy levels associated with each metastable collapsed state. The collapsed states are described quantitatively through the spatial correlation of tangent vectors along the chain. We also compare the results obtained with a locally inextensible bead-rod chain and with a phantom bead-spring model. Finally, we show preliminary results on the effects of steady shear flow on the kinetics of collapse.Comment: 9 pages, 8 figure

Molecular dynamic simulation of a homogeneous bcc -> hcp transition

We have performed molecular dynamic simulations of a Martensitic bcc->hcp transformation in a homogeneous system. The system evolves into three Martensitic variants, sharing a common nearest neighbor vector along a bcc direction, plus an fcc region. Nucleation occurs locally, followed by subsequent growth. We monitor the time-dependent scattering S(q,t) during the transformation, and find anomalous, Brillouin zone-dependent scattering similar to that observed experimentally in a number of systems above the transformation temperature. This scattering is shown to be related to the elastic strain associated with the transformation, and is not directly related to the phonon response.Comment: 11 pages plus 8 figures (GIF format); to appear in Phys. Rev.

Thermal fluctuations of gauge fields and first order phase transitions in color superconductivity

We study the effects of thermal fluctuations of gluons and the diquark pairing field on the superconducting-to-normal state phase transition in a three-flavor color superconductor, using the Ginzburg-Landau free energy. At high baryon densities, where the system is a type I superconductor, gluonic fluctuations, which dominate over diquark fluctuations, induce a cubic term in the Ginzburg-Landau free energy, as well as large corrections to quadratic and quartic terms of the order parameter. The cubic term leads to a relatively strong first order transition, in contrast with the very weak first order transitions in metallic type I superconductors. The strength of the first order transition decreases with increasing baryon density. In addition gluonic fluctuations lower the critical temperature of the first order transition. We derive explicit formulas for the critical temperature and the discontinuity of the order parameter at the critical point. The validity of the first order transition obtained in the one-loop approximation is also examined by estimating the size of the critical region.Comment: 12 pages, 4 figures, final version published in Phys. Rev.

Interstitials, Vacancies and Dislocations in Flux-Line Lattices: A Theory of Vortex Crystals, Supersolids and Liquids

We study a three dimensional Abrikosov vortex lattice in the presence of an equilibrium concentration of vacancy, interstitial and dislocation loops. Vacancies and interstitials renormalize the long-wavelength bulk and tilt elastic moduli. Dislocation loops lead to the vanishing of the long-wavelength shear modulus. The coupling to vacancies and interstitials - which are always present in the liquid state - allows dislocations to relax stresses by climbing out of their glide plane. Surprisingly, this mechanism does not yield any further independent renormalization of the tilt and compressional moduli at long wavelengths. The long wavelength properties of the resulting state are formally identical to that of the ``flux-line hexatic'' that is a candidate ``normal'' hexatically ordered vortex liquid state.Comment: 21 RevTeX pgs, 7 eps figures uuencoded; corrected typos, published versio

RANTES/CCL5 and risk for coronary events: Results from the MONICA/KORA Augsburg case-cohort, Athero-express and CARDIoGRAM studies

Background: The chemokine RANTES (regulated on activation, normal T-cell expressed and secreted)/CCL5 is involved in the pathogenesis of cardiovascular disease in mice, whereas less is known in humans. We hypothesised that its relevance for atherosclerosis should be reflected by associations between CCL5 gene variants, RANTES serum concentrations and protein levels in atherosclerotic plaques and risk for coronary events. Methods and Findings: We conducted a case-cohort study within the population-based MONICA/KORA Augsburg studies. Baseline RANTES serum levels were measured in 363 individuals with incident coronary events and 1,908 non-cases (mean follow-up: 10.2±