Near-surface stellar magneto-convection: simulations for the Sun and a metal-poor solar analog

We present 2D local box simulations of near-surface radiative magneto-convection with prescribed magnetic flux, carried out with the MHD version of the CO5BOLD code for the Sun and a solar-like star with a metal-poor chemical composition (metal abundances reduced by a factor 100, [M/H]=-2). The resulting magneto-hydrodynamical models can be used to study the influence of the metallicity on the properties of magnetized stellar atmospheres. A preliminary analysis indicates that the horizontal magnetic field component tends to be significantly stronger in the optically thin layers of metal-poor stellar atmospheres.Comment: Proc. IAU Symposium 259, Cosmic Magnetic Fields: from Planets, to Stars and Galaxies, K.G. Strassmeier, A.G. Kosovichev and J.E. Beckman, eds. (2009) p.23

Interaction effects and transport properties of Pt capped Co nanoparticles

We studied the magnetic and transport properties of Co nanoparticles (NPs) being capped with varying amounts of Pt. Beside field and temperature dependent magnetization measurements we performed delta-M measurements to study the magnetic interactions between the Co NPs. We observe a transition from demagnetizing towards magnetizing interactions between the particles for an increasing amount of Pt capping. Resistivity measurements show a crossover from giant magnetoresistance towards anisotropic magnetoresistance

Electrochemical characterization of nonaqueous systems for secondary battery application

Electrochemical evaluation of electrode organic electrolyte combinations for rechargeable battery system

Microtubule dynamics depart from wormlike chain model

Thermal shape fluctuations of grafted microtubules were studied using high resolution particle tracking of attached fluorescent beads. First mode relaxation times were extracted from the mean square displacement in the transverse coordinate. For microtubules shorter than 10 um, the relaxation times were found to follow an L^2 dependence instead of L^4 as expected from the standard wormlike chain model. This length dependence is shown to result from a complex length dependence of the bending stiffness which can be understood as a result of the molecular architecture of microtubules. For microtubules shorter than 5 um, high drag coefficients indicate contributions from internal friction to the fluctuation dynamics.Comment: 4 pages, 4 figures. Updated content, added reference, corrected typo

Quantum revival patterns from classical phase-space trajectories

A general semiclassical method in phase space based on the final value representation of the Wigner function is considered that bypasses caustics and the need to root-search for classical trajectories. We demonstrate its potential by applying the method to the Kerr Hamiltonian, for which the exact quantum evolution is punctuated by a sequence of intricate revival patterns. The structure of such revival patterns, lying far beyond the Ehrenfest time, is semiclassically reproduced and revealed as a consequence of constructive and destructive interferences of classical trajectories.Comment: 7 pages, 6 figure

Monte Carlo Study of Short-Range Order and Displacement Effects in Disordered CuAu

The correlation between local chemical environment and atomic displacements in disordered CuAu alloy has been studied using Monte Carlo simulations based on the effective medium theory (EMT) of metallic cohesion. These simulations correctly reproduce the chemically-specific nearest-neighbor distances in the random alloy across the entire Cu\$_x\$Au\$_{1-x}\$ concentration range. In the random equiatomic CuAu alloy, the chemically specific pair distances depend strongly on the local atomic environment (i.e. fraction of like/unlike nearest neighbors). In CuAu alloy with short-range order, the relationship between local environment and displacements remains qualitatively similar. However the increase in short-range order causes the average Cu-Au distance to decrease below the average Cu-Cu distance, as it does in the ordered CuAuI phase. Many of these trends can be understood qualitatively from the different neutral sphere radii and compressibilities of the Cu and Au atoms.Comment: 9 pages, 5 figures, 2 table

On The Evolution of Magnetic White Dwarfs

We present the first radiation magnetohydrodynamics simulations of the atmosphere of white dwarf stars. We demonstrate that convective energy transfer is seriously impeded by magnetic fields when the plasma-beta parameter, the thermal to magnetic pressure ratio, becomes smaller than unity. The critical field strength that inhibits convection in the photosphere of white dwarfs is in the range B = 1-50 kG, which is much smaller than the typical 1-1000 MG field strengths observed in magnetic white dwarfs, implying that these objects have radiative atmospheres. We have then employed evolutionary models to study the cooling process of high-field magnetic white dwarfs, where convection is entirely suppressed during the full evolution (B > 10 MG). We find that the inhibition of convection has no effect on cooling rates until the effective temperature (Teff) reaches a value of around 5500 K. In this regime, the standard convective sequences start to deviate from the ones without convection owing to the convective coupling between the outer layers and the degenerate reservoir of thermal energy. Since no magnetic white dwarfs are currently known at the low temperatures where this coupling significantly changes the evolution, effects of magnetism on cooling rates are not expected to be observed. This result contrasts with a recent suggestion that magnetic white dwarfs with Teff < 10,000 K cool significantly slower than non-magnetic degenerates.Comment: 11 pages, 12 figures, accepted for publication in the Astrophysical Journa

Physics of a microsystem starting from non-equilibrium quantum statistical mechanics

In this paper we address the problem to give a concrete support to the idea, originally stemming from Niels Bohr, that quantum mechanics must be rooted inside the physics of macroscopic systems. It is shown that, starting from the formalism of the non-equilibrium statistical operator, which is now a consolidated part of quantum statistical mechanics, particular correlations between two isolated systems can be singled out and interpreted as microsystems. In this way also a new framework is established in which questions of decoherence can be naturally addressed.Comment: 14 pages, latex, no figures, contribution to the Proceedings of the XXXIII Symposium on Mathematical Physics (Torun, Poland