Turbulent spectra in real-time gauge field evolution

We investigate ultraviolet fixed points in the real-time evolution of non-Abelian gauge fields. Classical-statistical lattice simulations reveal equal-time correlation functions with a spectral index 3/2. Analytical understanding of this result is achieved by employing a 2PI- loop expansion for the quantum theory.Comment: 4 pages, 2 figures. Talk presented at SEWM 2008, August 26-29, Amsterda

Bottom-up isotropization in classical-statistical lattice gauge theory

We compute nonequilibrium dynamics for classical-statistical SU(2) pure gauge theory on a lattice. We consider anisotropic initial conditions with high occupation numbers in the transverse plane on a characteristic scale ~ Q_s. This is used to investigate the very early stages of the thermalization process in the context of heavy-ion collisions. We find Weibel or "primary" instabilities with growth rates similar to those obtained from previous treatments employing anisotropic distributions of hard modes (particles) in the weak coupling limit. We observe "secondary" growth rates for higher-momentum modes reaching substantially larger values and we analyse them in terms of resummed loop diagrams beyond the hard-loop approximation. We find that a coarse grained pressure isotropizes "bottom-up" with a characteristic inverse rate of gamma^{-1} ~ 1 - 2 fm/c for coarse graining momentum scales of p < 1 GeV choosing an initial energy density for RHIC of epsilon = 30 GeV/fm^3. The nonequilibrium spatial Wilson loop is found to exhibit an area law and to become isotropic on a similar time scale.Comment: 22 pages, 12 figures. Phys. Rev. D version, appendix on insensitivity to volume and cutoff effects adde

Out of equilibrium dynamics of coherent non-abelian gauge fields

We study out-of-equilibrium dynamics of intense non-abelian gauge fields. Generalizing the well-known Nielsen-Olesen instabilities for constant initial color-magnetic fields, we investigate the impact of temporal modulations and fluctuations in the initial conditions. This leads to a remarkable coexistence of the original Nielsen-Olesen instability and the subdominant phenomenon of parametric resonance. Taking into account that the fields may be correlated only over a limited transverse size, we model characteristic aspects of the dynamics of color flux tubes relevant in the context of heavy-ion collisions.Comment: 12 pages, 10 figures; PRD version, minor change

Anomalous Nernst effect in perpendicularly magnetised {\tau}-MnAl thin films

$\tau$-MnAl is interesting for spintronic applications as a ferromagnet with perpendicular magnetic anisotropy due to its high uniaxial magnetocrystalline anisotropy. Here we report on the anomalous Nernst effect of sputter deposited $\tau$-MnAl thin films. We demonstrate a robust anomalous Nernst effect at temperatures of 200 K and 300 K with a hysteresis similar to the anomalous Hall effect and the magnetisation of the material. The anomalous Nernst coefficient of (0.6$\pm$0.24) $\mu$V/K at 300 K is comparable to other perpendicular magnetic anisotropy thin films. Therefore $\tau$-MnAl is a promising candidate for spin-caloritronic research

Scalar Field Theory with a Non-Standard Potential

We study the phase structure of a 4D complex scalar field theory with a potential V(Phi) = | Lambda^3 / Phi - Lambda Phi |^2 at zero and at finite temperature. The model is analyzed by mean field and Monte Carlo methods. At zero temperature the theory falls in the universality class of the 4D Ising model when varying Lambda. The situation is less clear-cut for variations w.r.t. Lambda at large temperatures and variations w.r.t. temperature at a given value of Lambda. We observe temperature independence of the mass of the first excitation.Comment: 24 pages, 9 figures; version published in Phys. Rev. D 7

Dynamic contrast enhancement of paragangliomas of the head and neck: evaluation with time-resolved 2D MR projection angiography

Abstract.: Our objective was to evaluate tumor hemodynamics of paragangliomas of the head and neck. A 2D magnetic resonance projection angiography (MRPA) protocol was developed. Six patients with histologically proven paragangliomas were included in the study. The sequence protocol and data post-processing procedure were optimized in view of a high temporal resolution and maximum contrast-to-noise ratio. Image-time series of two freely orientated slabs could be obtained. Correlation analysis was performed to generate selective arterial and venous weighted angiographic images. Glomus tumors showed a rapid and intense homogeneous enhancement following the intravenous administration of contrast material. The smallest tumors investigated measured 10mm and could be visualized clearly. Time-resolved analysis of the tumor enhancement revealed an early bolus arrival within the vascular bed of the tumor and prolonged incomplete washout indicating blood pooling. The dynamic contrast enhancement of glomus tumors can be evaluated non-invasively with MRPA providing a high temporal resolution and high image quality. The characteristic contrast enhancement of glomus tumors can be helpful in the diagnostic workup of lesions that may mimic glomus tumor

Examination of the concept of degree of rate control by first-principles kinetic Monte Carlo simulations

The conceptual idea of degree of rate control (DRC) approaches is to identify the "rate limiting step" in a complex reaction network by evaluating how the overall rate of product formation changes when a small change is made in one of the kinetic parameters. We examine two definitions of this concept by applying it to first-principles kinetic Monte Carlo simulations of the CO oxidation at RuO2(110). Instead of studying experimental data we examine simulations, because in them we know the surface structure, reaction mechanism, the rate constants, the coverage of the surface and the turn-over frequency at steady state. We can test whether the insights provided by the DRC are in agreement with the results of the simulations thus avoiding the uncertainties inherent in a comparison with experiment. We find that the information provided by using the DRC is non-trivial: It could not have been obtained from the knowledge of the reaction mechanism and of the magnitude of the rate constants alone. For the simulations the DRC provides furthermore guidance as to which aspects of the reaction mechanism should be treated accurately and which can be studied by less accurate and more efficient methods. We therefore conclude that a sensitivity analysis based on the DRC is a useful tool for understanding the propagation of errors from the electronic structure calculations to the statistical simulations in first-principles kinetic Monte Carlo simulations.Comment: 27 pages including 5 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Is Micro X-ray Computer Tomography a Suitable Non-Destructive Method for the Characterisation of Dental Materials?

The aim of the study was to investigate the effect of X-rays used in micro X-ray computer tomography (µXCT) on the mechanical performance and microstructure of a variety of dental materials. Standardised bending beams (2 × 2 × 25 mm3) were forwarded to irradiation with an industrial tomograph. Using three-dimensional datasets, the porosity of the materials was quantified and flexural strength was investigated prior to and after irradiation. The thermal properties of irradiated and unirradiated materials were analysed and compared by means of differential scanning calorimetry (DSC). Single µXCT measurements led to a significant decrease in flexural strength of polycarbonate with acrylnitril-butadien-styrol (PC-ABS). No significant influence in flexural strength was identified for resin-based composites (RBCs), poly(methyl methacrylate) (PMMA), and zinc phosphate cement (HAR) after a single irradiation by measurement. However, DSC results suggest that changes in the microstructure of PMMA are possible with increasing radiation doses (multiple measurements, longer measurements, higher output power from the X-ray tube). In summary, it must be assumed that X-ray radiation during µXCT measurement at high doses can lead to changes in the structure and properties of certain polymers

The Suction Panel - xHLFC and Structural Solution for Energy Efficient Aviation

Future energy-efficient aircraft requires a further drastic reduction in drag and weight. Is it contradictory to improve both at the same time? Is it possible to design a highly efficient HLFC system to be weight-neutral? The present study, performed within the Cluster of Excellence SE2A – Sustainable and Energy-Efficient Aviation, summarizes aspects and considerations of the contributing disciplines to derive a solution for a suction-based system on short-range aircraft wings with maximum efficiency, i.e. hybrid laminar flow control application capabilities at minimum weight penalty. Several new features – novel wing design and simulation tools, the potentials of thin plies for weigth saving and the 3D-printing possibilities for ventable core structures – are investigated to achive this goal