Magnetic circular dichroism in the 2p4d x-ray emission of EuO

Magnetic circular dichroism is observed for ferromagnetic EuO (T C 569 K) in the b2,15 fluorescence at incident photon energies resonant with the 2p 3/2 excitation. The dichroism is dominated by exchange interac-tion between the localized 4 f electrons and the final state 4d core hole. The spectral shapes obtained by atomic multiplet calculations for the 2p4d emission show good agreement with the experimental data

Dynamic SU(2) Lattice Gauge Theory at Finite Temperature

The dynamic relaxation process for the (2+1)--dimensional SU(2) lattice gauge theory at critical temperature is investigated with Monte Carlo methods. The critical initial increase of the Polyakov loop is observed. The dynamic exponents $\theta$ and $z$ as well as the static critical exponent $\beta/\nu$ are determined from the power law behaviour of the Polyakov loop, the auto-correlation and the second moment at the early stage of the time evolution. The results are well consistent and universal short-time scaling behaviour of the dynamic system is confirmed. The values of the exponents show that the dynamic SU(2) lattice gauge theory is in the same dynamic universality class as the dynamic Ising model.Comment: 10 pages with 2 figure

Universal Short-time Behaviour of the Dynamic Fully Frustrated XY Model

With Monte Carlo methods we investigate the dynamic relaxation of the fully frustrated XY model in two dimensions below or at the Kosterlitz-Thouless phase transition temperature. Special attention is drawn to the sublattice structure of the dynamic evolution. Short-time scaling behaviour is found and universality is confirmed. The critical exponent $\theta$ is measured for different temperature and with different algorithms.Comment: 18 pages, LaTeX, 8 ps-figure

Experimentelle Untersuchung zur diagnostischen Leistungsfähigkeit digitaler Flachdetektorsysteme bei der Erkennung nicht dislozierter Rippenfrakturen

Ziel ist es, die diagnostische Leistungsfähigkeit digitaler Flachdetektorsysteme in Hinblick auf eine möglichen Dosisreduktion zu untersuchen. 100 artifiziell frakturierte und 100 unfrakturierte Schweinerippen wurden mit einem konventionellen Film-Foliensystem der Geschwindigkeitsklasse S=400, einem Speicherfoliensystem (S=400,S=800) und einem Flachdetektorsystem (S=400,S=800,S=1600,S=6400) geröntgt. Die Bewertung erfolgte anhand einer fünfstufigen Konfidenzskala, die statistische Auswertung der 4200 Einzelbeobachtungen durch eine ROC-Analyse. Es ergaben sich folgende Az-Werte: Film-Foliensystem 0,834 (S=400), Speicherfoliensystem 0,789 (S=400) und 0,729 (S=800), Flachdetektorsystem 0,879 (S=400), 0,833 (S=800), 0,765 (S=1600) und 0,576 (S=6400). Die Varianzanalyse ergab keinen signifikanten Unterschied zwischen dem Flachdetektorsystem (S=800) und dem Film-Foliensystems (S=400). Bei gleicher Strahlendosis ist der Flachdetektor dem Film-Foliensystem statistische signifikant überlegen

Dynamic Approach to the Fully Frustrated XY Model

Using Monte Carlo simulations, we systematically investigate the non-equilibrium dynamics of the chiral degree of freedom in the two-dimensional fully frustrated XY model. The critical initial increase of the staggered chiral magnetization is observed. By means of the short-time dynamics approach, we estimate the second order phase transition temperature $T_{c}$ and all the dynamic and static critical exponents $\theta$, z, $\beta$ and $\nu$.Comment: 5 pages with 6 figures include

Multiplet ligand-field theory using Wannier orbitals

We demonstrate how ab initio cluster calculations including the full Coulomb vertex can be done in the basis of the localized, generalized Wannier orbitals which describe the low-energy density functional (LDA) band structure of the infinite crystal, e.g. the transition metal 3d and oxygen 2p orbitals. The spatial extend of our 3d Wannier orbitals (orthonormalized Nth order muffin-tin orbitals) is close to that found for atomic Hartree-Fock orbitals. We define Ligand orbitals as those linear combinations of the O 2p Wannier orbitals which couple to the 3d orbitals for the chosen cluster. The use of ligand orbitals allows for a minimal Hilbert space in multiplet ligand-field theory calculations, thus reducing the computational costs substantially. The result is a fast and simple ab initio theory, which can provide useful information about local properties of correlated insulators. We compare results for NiO, MnO and SrTiO3 with x-ray absorption, inelastic x-ray scattering, and photoemission experiments. The multiplet ligand field theory parameters found by our ab initio method agree within ~10% to known experimental values

Critical exponents of the two-layer Ising model

The symmetric two-layer Ising model (TLIM) is studied by the corner transfer matrix renormalisation group method. The critical points and critical exponents are calculated. It is found that the TLIM belongs to the same universality class as the Ising model. The shift exponent is calculated to be 1.773, which is consistent with the theoretical prediction 1.75 with 1.3% deviation.Comment: 7 pages, with 10 figures include

Dynamic Approach to Weak First Order Phase Transitions

A short-time dynamic approach to weak first order phase transitions is proposed. Taking the 2-dimensional Potts models as examples, from short-time behaviour of non-equilibrium relaxational processes starting from high temperature and zero temperature states,x pseudo critical points K^{*} and K^{**} are determined. A clear difference of the values for K^{*} and K^{**} distinguishes a weak first order transition from a second order one. At the pseudo critical points, pseudo critical exponents can be estimated.Comment: 9 pages with 4 postscript figures include

Microscopic Non-Universality versus Macroscopic Universality in Algorithms for Critical Dynamics

We study relaxation processes in spin systems near criticality after a quench from a high-temperature initial state. Special attention is paid to the stage where universal behavior, with increasing order parameter emerges from an early non-universal period. We compare various algorithms, lattice types, and updating schemes and find in each case the same universal behavior at macroscopic times, despite of surprising differences during the early non-universal stages.Comment: 9 pages, 3 figures, RevTeX, submitted to Phys. Rev. Let

The evolution of social philopatry in female primates

The transition from solitary life to sociality is considered one of the major transitions in evolution. In primates, this transition is currently not well understood. Traditional verbal models appear insufficient to unravel the complex interplay of environmental and demographic factors involved in the evolution of primate sociality, and recent phylogenetic reconstructions have produced conflicting results. We therefore analyze a theoretical model for the evolution of female social philopatry that sheds new light on the question why most primates live in groups. In individual-based simulations, we study the evolution of dispersal strategies of both resident females and their offspring. The model reveals that social philopatry can evolve through kin selection, even if retention of offspring is costly in terms of within-group resource competition and provides no direct benefits. Our model supports the role of predator avoidance as a selective pressure for group-living in primates, but it also suggests that a second benefit of group-living, communal resource defense, might be required to trigger the evolution of sizable groups. Lastly, our model reveals that seemingly small differences in demographic parameters can have profound effects on primate social evolution