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Search Results: 1 - 10 of 19694 matches for " Stefan Simon "
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Pinning of stripes in cuprate superconductors
Simon Bogner,Stefan Scheidl
Physics , 2001, DOI: 10.1103/PhysRevB.64.054517
Abstract: We examine the effects of disorder on striped phases in high-temperature superconductors and related materials. In the presence of quenched disorder, pinning by the atomic lattice - which might give rise to commensuration effects - is irrelevant for the stripe array on large length scales. As a consequence, the stripes have divergent displacement fluctuations and topological defects are present at all temperatures. Therefore the positional order of the stripe array is short ranged, with a finite correlation length even at zero temperature. Thus lock-in phenomena can exist only as crossovers but not as transitions. In addition, this implies the glassy nature of stripes observed in recent experiments.
A New In Vitro Model to Study Cellular Responses after Thermomechanical Damage in Monolayer Cultures
Alice Hettler, Simon Werner, Stefan Eick, Stefan Laufer, Frank Weise
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0082635
Abstract: Although electrosurgical instruments are widely used in surgery to cut tissue layers or to achieve hemostasis by coagulation (electrocautery), only little information is available concerning the inflammatory or immune response towards the debris generated. Given the elevated local temperatures required for successful electrocautery, the remaining debris is likely to contain a plethora of compounds entirely novel to the intracorporal setting. A very common in vitro method to study cell migration after mechanical damage is the scratch assay, however, there is no established model for thermomechanical damage to characterise cellular reactions. In this study, we established a new in vitro model to investigate exposure to high temperature in a carefully controlled cell culture system. Heatable thermostat-controlled aluminium stamps were developed to induce local damage in primary human umbilical vein endothelial cells (HUVEC). The thermomechanical damage invoked is reproducibly locally confined, therefore allowing studies, under the same experimental conditions, of cells affected to various degrees as well as of unaffected cells. We show that the unaffected cells surrounding the thermomechanical damage zone are able to migrate into the damaged area, resulting in a complete closure of the ‘wound’ within 48 h. Initial studies have shown that there are significant morphological and biological differences in endothelial cells after thermomechanical damage compared to the mechanical damage inflicted by using the unheated stamp as a control. Accordingly, after thermomechanical damage, cell death as well as cell protection programs were activated. Mononuclear cells adhered in the area adjacent to thermomechanical damage, but not to the zone of mechanical damage. Therefore, our model can help to understand the differences in wound healing during the early phase of regeneration after thermomechanical vs. mechanical damage. Furthermore, this model lends itself to study the response of other cells, thus broadening the range of thermal injuries that can be analysed.
Jahrestagung 2012 in Aachen - Tagungsbericht [GMA Annual Conference 2012 in Aachen - Conference Report]
Simon, Melanie,Sopka, Sasa,Beckers, Stefan K.
GMS Zeitschrift für Medizinische Ausbildung , 2012, DOI: 10.3205/zma000833
Abstract:
Abundances, masses, and weak-lensing mass profiles of galaxy clusters as a function of richness and luminosity in LambdaCDM cosmologies
Stefan Hilbert,Simon D. M. White
Physics , 2009, DOI: 10.1111/j.1365-2966.2010.16310.x
Abstract: We test the concordance LCDM cosmology by comparing predictions for the mean properties of galaxy clusters to observations. We use high-resolution N-body simulations of cosmic structure formation and semi-analytic models of galaxy formation to compute the abundance, mean density profile, and mass of galaxy clusters as a function of richness and luminosity, and we compare these predictions to observations of clusters in the Sloan Digital Sky Survey (SDSS) maxBCG catalogue. We discuss the scatter in the mass-richness relation, the reconstruction of the cluster mass function from the mass-richness relation, and fits to the weak-lensing cluster mass profiles. The impact of cosmological parameters on the predictions is investigated by comparing results from galaxy models based on the Millennium Simulation (MS) and another WMAP1 simulation to those from a WMAP3 simulation. We find that the simulated weak-lensing mass profiles and the observed profiles of the SDSS maxBCG clusters agree well in shape and amplitude. The mass-richness relations in the simulations are close to the observed relation, with differences lesssim 30%. The MS and WMAP1 simulations yield cluster abundances similar to those observed, whereas abundances in the WMAP3 simulation are 2-3 times lower. The differences in cluster abundance, mass, and density amplitude between the simulations and the observations can be attributed to differences in the underlying cosmological parameters, in particular the power spectrum normalisation sigma_8. Better agreement between predictions and observations should be reached with a normalisation $0.722
SAPPORO: A way to turn your graphics cards into a GRAPE-6
Evghenii Gaburov,Stefan Harfst,Simon Portegies Zwart
Physics , 2009, DOI: 10.1016/j.newast.2009.03.002
Abstract: We present Sapporo, a library for performing high-precision gravitational N-body simulations on NVIDIA Graphical Processing Units (GPUs). Our library mimics the GRAPE-6 library, and N-body codes currently running on GRAPE-6 can switch to Sapporo by a simple relinking of the library. The precision of our library is comparable to that of GRAPE-6, even though internally the GPU hardware is limited to single precision arithmetics. This limitation is effectively overcome by emulating double precision for calculating the distance between particles. The performance loss of this operation is small (< 20%) compared to the advantage of being able to run at high precision. We tested the library using several GRAPE-6-enabled N-body codes, in particular with Starlab and phiGRAPE. We measured peak performance of 800 Gflop/s for running with 10^6 particles on a PC with four commercial G92 architecture GPUs (two GeForce 9800GX2). As a production test, we simulated a 32k Plummer model with equal mass stars well beyond core collapse. The simulation took 41 days, during which the mean performance was 113 Gflop/s. The GPU did not show any problems from running in a production environment for such an extended period of time.
Pushing towards the ET sensitivity using 'conventional' technology
Stefan Hild,Simon Chelkowski,Andreas Freise
Physics , 2008,
Abstract: Recently, the design study `Einstein gravitational wave Telescope' (ET) has been funded within the European FP7 framework. The ambitious goal of this project is to provide a conceptual design of a detector with a hundred times better sensitivity than currently operating instruments. It is expected that this will require the development and implementation of new technologies, which go beyond the concepts employed for the first and second detector generations. However, it is a very interesting and educational exercise to imagine a Michelson interferometer in which conventional technologies have been pushed to - or maybe beyond - their limits to reach the envisaged sensitivity for the Einstein Telescope. In this document we present a first sketchy analysis of what modifications and improvements are necessary to go, step-by-step, from second generation gravitational wave detectors to the Einstein Telescope.
Prospects of higher-order Laguerre Gauss modes in future gravitational wave detectors
Simon Chelkowski,Stefan Hild,Andreas Freise
Physics , 2009, DOI: 10.1103/PhysRevD.79.122002
Abstract: The application of higher-order Laguerre Gauss (LG) modes in large-scale gravitational wave detectors has recently been proposed. In comparison to the fundamental mode, some higher-order Laguerre Gauss modes can significantly reduce the contribution of coating Brownian noise. Using frequency domain simulations we give a detailed analysis of the longitudinal and angular control signals derived with a LG33 mode in comparison to the fundamental TEM00 mode. The performance regarding interferometric sensing and control of the LG33 mode is found to be similar, if not even better in all aspects of interest. In addition, we evaluate the sensitivity gain of the implementation of LG33 modes into the Advanced Virgo instrument. Our analysis shows that the application of the LG33 mode results in a broadband improvement of the Advanced Virgo sensitivity, increasing the potential detection rate of binary neutron star inspirals by a factor 2.1.
Delocalization in Coupled Luttinger Liquids with Impurities
Stefan Scheidl,Simon Bogner,Thorsten Emig
Physics , 2001, DOI: 10.1103/PhysRevB.65.224507
Abstract: We study effects of quenched disorder on coupled two-dimensional arrays of Luttinger liquids (LL) as a model for stripes in high-T_c compounds. In the framework of a renormalization-group analysis, we find that weak inter-LL charge-density-wave couplings are always irrelevant as opposed to the pure system. By varying either disorder strength, intra- or inter-LL interactions, the system can undergo a delocalization transition between an insulator and a novel strongly anisotropic metallic state with LL-like transport. This state is characterized by short-ranged charge-density-wave order, the superconducting order is quasi long-ranged along the stripes and short-ranged in the transversal direction.
A diophantine equation for sums of consecutive like powers
Simon Felten,Stefan Müller-Stach
Mathematics , 2013,
Abstract: We show that the diophantine equation $n^\ell+(n+1)^\ell + ...+ (n+k)^\ell=(n+k+1)^\ell+ ...+ (n+2k)^\ell$ has no solutions in positive integers $k,n \ge 1$ for all $\ell \ge 3$.
Comparison of the Gene Expression Profiles from Normal and Fgfrl1 Deficient Mouse Kidneys Reveals Downstream Targets of Fgfrl1 Signaling
Simon D. Gerber, Ruth Amann, Stefan Wyder, Beat Trueb
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0033457
Abstract: Fgfrl1 (fibroblast growth factor receptor-like 1) is a transmembrane receptor that is essential for the development of the metanephric kidney. It is expressed in all nascent nephrogenic structures and in the ureteric bud. Fgfrl1 null mice fail to develop the metanephric kidneys. Mutant kidney rudiments show a dramatic reduction of ureteric branching and a lack of mesenchymal-to-epithelial transition. Here, we compared the expression profiles of wildtype and Fgfrl1 mutant kidneys to identify genes that act downstream of Fgfrl1 signaling during the early steps of nephron formation. We detected 56 differentially expressed transcripts with 2-fold or greater reduction, among them many genes involved in Fgf, Wnt, Bmp, Notch, and Six/Eya/Dach signaling. We validated the microarray data by qPCR and whole-mount in situ hybridization and showed the expression pattern of candidate genes in normal kidneys. Some of these genes might play an important role during early nephron formation. Our study should help to define the minimal set of genes that is required to form a functional nephron.
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