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Search Results: 1 - 10 of 120044 matches for " T. Becker "
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Das nasse Kind
Becker T
Journal für Urologie und Urogyn?kologie , 2006,
Kryptorchismus, Hydrozele, Varikozele: Diagnostik und Therapie
Becker T
Journal für Urologie und Urogyn?kologie , 2009,
NMR properties of a one-dimesional Cu-O model
T. Becker,M. Gabay,T. Giamarchi
Physics , 2000, DOI: 10.1103/PhysRevB.62.12489
Abstract: We obtain the Knight shifts and the relaxation rates related to the Fermi contact interaction term for a one-dimensional Cu-O model using bosonization technique. We consider the small interaction limit at half-filling and away from half-filling. In this framework we predict that the antiferromagnetic contribution to the relaxation rate of the nuclear oxygen spin is completely suppressed even away from half-filling, when the temperature is low enough. In the strong interaction limit at half-filling we compute the effective Fermi contact interaction performing a Gutzwiller projection. Both limits suggest that the one-dimensional versions of the Mila-Rice and of the Shastry scenarios of transferred hyperfine couplings which were proposed to explain the NMR measurements for High-T_c cuprates fail in a one-dimensional situation.
M. De Becker,M. Filho,T. Harries
Revista mexicana de astronomía y astrofísica , 2010,
Prospects for the study of dust making Wolf-Rayet binaries with the VLTI-Spectro-Imager (VSI)
M. De Becker,M. Filho,T. Harries
Physics , 2009,
Abstract: In response to ESO's call for proposals for second generation instruments for the Very Large Telescope Interferometer (VLTI), a consortium is currently developing the VLTI-Spectro-Imager (VSI). In the context of the Phase A study, a science group has prepared a science case taking advantage of the expected performances of VSI. Among several science topics, the case of dust making Wolf-Rayet binaries producing the so-called pinwheel nebulae has been considered. Here, we review the main specifications of VSI, and we provide preliminary results expected to illustrate the imaging capabilities of VSI, and the interest for the study of pinwheel nebulae similar to those formed close to well-known systems such as WR98a and WR104.
Dynamics of a stochastically driven running sandpile
T. Becker,H. de Vries,B. Eckhardt
Physics , 1994, DOI: 10.1007/BF01208378
Abstract: We analyze in detail a one-dimensional stochastically driven running sandpile. The dynamics shows three different phases, depending on the on-site relaxation rate and stochastic driving rate. Two phases are characterized by the presence of travelling waves. The third shows algebraic relaxation.
Renormalization approach to many-particle systems
K. W. Becker,A. Huebsch,T. Sommer
Physics , 2002, DOI: 10.1103/PhysRevB.66.235115
Abstract: This paper presents a renormalization approach to many-particle systems. By starting from a bare Hamiltonian ${\cal H}= {\cal H}_0 +{\cal H}_1$ with an unperturbed part ${\cal H}_0$ and a perturbation ${\cal H}_1$,we define an effective Hamiltonian which has a band-diagonal shape with respect to the eigenbasis of ${\cal H}_0$. This means that all transition matrix elements are suppressed which have energy differences larger than a given cutoff $\lambda$ that is smaller than the cutoff $\Lambda$ of the original Hamiltonian. This property resembles a recent flow equation approach on the basis of continuous unitary transformations. For demonstration of the method we discuss an exact solvable model, as well as the Anderson-lattice model where the well-known quasiparticle behavior of heavy fermions is derived.
X-ray Counterparts of Millisecond Pulsars in Globular Clusters
W. Becker,H. H. Huang,T. Prinz
Physics , 2010,
Abstract: We have systematically studied the X-ray emission properties of globular cluster millisecond pulsars in order to evaluate their spectral properties and luminosities in a uniform way. Cross-correlating the radio timing positions of the cluster pulsars with the high resolution Chandra images revealed 31 X-ray counterparts identified in nine different globular cluster systems, including those in 47 Tuc. Timing analysis has been performed for all sources corresponding to the temporal resolution available in the archival Chandra data. Making use of unpublished data on M28, M4 and NGC 6752 allowed us to obtain further constraints for the millisecond pulsar counterparts located in these clusters. Counting rate and energy flux upper limits were computed for those 36 pulsars for which no X-ray counterparts could be detected. Comparing the X-ray and radio pulse profiles of PSR J1821-2452 in M28 and the 47 Tuc pulsars PSR J0024-7204D,O,R indicated some correspondence between both wavebands. The X-ray efficiency of the globular cluster millisecond pulsars was found to be in good agreement with the efficiency Lx ~ 10^-3 Edot observed in Galactic field rotation-powered pulsars. Millisecond pulsars in the galactic plane and in globular clusters appear to show no distinct differences in their X-ray emission properties.
Current fluctuations in boundary driven diffusive systems in different dimensions: a numerical study
T. Becker,K. Nelissen,B. Cleuren
Physics , 2015, DOI: 10.1088/1367-2630/17/5/055023
Abstract: We use kinetic Monte Carlo simulations to investigate current fluctuations in boundary driven generalized exclusion processes, in different dimensions. Simulation results are in full agreement with predictions based on the additivity principle and the macroscopic fluctuation theory. The current statistics are independent of the shape of the contacts with the reservoirs, provided they are macroscopic in size. In general, the current distribution depends on the spatial dimension. For the special cases of the symmetric simple exclusion process and the zero-range process, the current statistics are the same for all spatial dimensions.
Subduction to the lower mantle – a comparison between geodynamic and tomographic models
B. Steinberger, T. H. Torsvik,T. W. Becker
Solid Earth (SE) & Discussions (SED) , 2012, DOI: 10.5194/se-3-415-2012
Abstract: It is generally believed that subduction of lithospheric slabs is a major contribution to thermal heterogeneity in Earth's entire mantle and provides a main driving force for mantle flow. Mantle structure can, on the one hand, be inferred from plate tectonic models of subduction history and geodynamic models of mantle flow. On the other hand, seismic tomography models provide important information on mantle heterogeneity. Yet, the two kinds of models are only similar on the largest (1000 s of km) scales and are quite different in their detailed structure. Here, we provide a quantitative assessment how good a fit can be currently achieved with a simple viscous flow geodynamic model. The discrepancy between geodynamic and tomography models can indicate where further model refinement could possibly yield an improved fit. Our geodynamical model is based on 300 Myr of subduction history inferred from a global plate reconstruction. Density anomalies are inserted into the upper mantle beneath subduction zones, and flow and advection of these anomalies is calculated with a spherical harmonic code for a radial viscosity structure constrained by mineral physics and surface observations. Model viscosities in the upper mantle beneath the lithosphere are ~1020 Pas, and viscosity increases to ~1023 Pas in the lower mantle above D". Comparison with tomography models is assessed in terms of correlation, both overall and as a function of depth and spherical harmonic degree. We find that, compared to previous geodynamic and tomography models, correlation is improved, presumably because of advances in both plate reconstructions and mantle flow computations. However, high correlation is still limited to lowest spherical harmonic degrees. An important ingredient to achieve high correlation – in particular at spherical harmonic degree two – is a basal chemical layer. Subduction shapes this layer into two rather stable hot but chemically dense "piles", corresponding to the Pacific and African Large Low Shear Velocity Provinces. Visual comparison along cross sections indicates that sinking speeds in the geodynamic model are somewhat too fast, and should be 2 ± 0.8 cm yr 1 to achieve a better fit.
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