Broad Histogram Method for Continuous Systems: the XY-Model

We propose a way of implementing the Broad Histogram Monte Carlo method to systems with continuous degrees of freedom, and we apply these ideas to investigate the three-dimensional XY-model with periodic boundary conditions. We have found an excellent agreement between our method and traditional Metropolis results for the energy, the magnetization, the specific heat and the magnetic susceptibility on a very large temperature range. For the calculation of these quantities in the temperature range 0.7<T<4.7 our method took less CPU time than the Metropolis simulations for 16 temperature points in that temperature range. Furthermore, it calculates the whole temperature range 1.2<T<4.7 using only 2.2 times more computer effort than the Histogram Monte Carlo method for the range 2.1<T<2.2. Our way of treatment is general, it can also be applied to other systems with continuous degrees of freedom.Comment: 23 pages, 10 Postscript figures, to be published in Int. J. Mod. Phys.

An Accreting Black Hole in the Nuclear Star Cluster of the Bulgeless Galaxy NGC 1042

We present spectroscopic evidence for a low-luminosity, low-excitation active galactic nucleus (AGN) in NGC 1042, powered by an intermediate-mass black hole. These findings are significant in that the AGN is coincident with a compact star cluster known to reside in the nucleus, thus providing an example where the two types of central mass concentration coexist. The existence of a central black hole is additionally remarkable in that NGC 1042 lacks a stellar bulge. Objects such as NGC 1042 may have an important role in testing theories for the genesis of massive black holes in galaxy nuclei, and the extent to which they are in symbiosis with the larger stellar host.Comment: 15 pages, 6 figures, accepted for publication in Ap

Coherence in scale-free networks of chaotic maps

We study fully synchronized states in scale-free networks of chaotic logistic maps as a function of both dynamical and topological parameters. Three different network topologies are considered: (i) random scale-free topology, (ii) deterministic pseudo-fractal scale-free network, and (iii) Apollonian network. For the random scale-free topology we find a coupling strength threshold beyond which full synchronization is attained. This threshold scales as $k^{-\mu}$, where $k$ is the outgoing connectivity and $\mu$ depends on the local nonlinearity. For deterministic scale-free networks coherence is observed only when the coupling strength is proportional to the neighbor connectivity. We show that the transition to coherence is of first-order and study the role of the most connected nodes in the collective dynamics of oscillators in scale-free networks.Comment: 9 pages, 8 figure

Spatial variations of the fine-structure constant in symmetron models

We investigate the variation of the fine-structure constant, {\alpha}, in symmetron models using N-body simulations in which the full spatial distribution of {\alpha} at different redshifts has been calculated. In particular, we obtain simulated sky maps for this variation, and determine its power spectrum. We find that in high-density regions of space (such as deep inside dark matter halos) the value of {\alpha} approaches the value measured on Earth. In the low-density outskirts of halos the scalar field value can approach the symmetry breaking value and leads to significantly different values of {\alpha}. If the scalar-photon coupling strength {\beta}{\gamma} is of order unity we find that the variation of {\alpha} inside dark matter halos can be of the same magnitude as the recent claims by Webb et al. of a dipole variation. Importantly, our results also show that with low-redshift symmetry breaking these models exhibit some dependence of {\alpha} on lookback time (as opposed to a pure spatial dipole) which could in principle be detected by sufficiently accurate spectroscopic measurements, such as those of ALMA and the ELT-HIRES.Comment: 11 pages, 9 figure

A Concept for Attribute-Based Authorization on D-Grid Resources

In Germany's D-Grid project numerous Grid communities are working together to provide a common overarching Grid infrastructure. The major aims of D-Grid are the integration of existing Grid deployments and their interoperability. The challenge lies in the heterogeneity of the current implementations: three Grid middleware stacks and different Virtual Organization management approaches have to be embraced to achieve the intended goals. In this article we focus oil the implementation of an attribute-based authorization infrastructure that not only leverages the well-known VO attributes but also campus attributes managed by a Shibboleth federation

An outbreak of sheep-associated malignant catarrhal fever in sows

his paper describes a case of malignant catarrhal fever in a sow herd in Belgium caused by infection with ovine herpesvirus-2 (OHV-2). The 11 affected sows had high fever and 10 of them died within 3 days after the onset of clinical disease. The most prominent macroscopic lesion was a hemorrhagic to pseudo-membranous gastritis. Histopathology revealed severe infiltration and necrosis of the gastric mucosa. Neither antimicrobial treatment nor injection with anti-inflammatory drugs ameliorated the severity of the disease. As the sows and sheep were housed in the same building with the possibility of having direct nose-to-nose contact, and as PCR testing showed that the virus found in the sows was identical to that found in the sheep, it is very likely that the infection was transmitted from the subclinically infected sheep to the sows. The present case showed that OHV-2 infection should be included in the differential diagnosis when facing problems of fever followed by death, especially when pigs are housed in close contact with sheep

Existence and stability of solitons for the nonlinear Schr\"odinger equation on hyperbolic space

We study the existence and stability of ground state solutions or solitons to a nonlinear stationary equation on hyperbolic space. The method of concentration compactness applies and shows that the results correlate strongly to those of Euclidean space.Comment: New: As noted in Banica-Duyckaerts (arXiv:1411.0846), Section 5 should read that for sufficiently large mass, sub-critical problems can be solved via energy minimization for all d \geq 2 and as a result Cazenave-Lions results can be applied in Section 6 with the same restriction. These requirements were addressed by the subsequent work with Metcalfe and Taylor in arXiv:1203.361

On the Size of Hadrons

The form factor and the mean-square radius of the pion are calculated analytically from a parametrized form of a $q\bar q$ wave function. The numerical wave function was obtained previously by solving numerically an eigenvalue equation for the pion in a particular model. The analytical formulas are of more general interest than just be valid for the pion and can be generalized to the case with unequal quark masses. Two different parametrizations are investigated. Because of the highly relativistic problem, noticable deviations from a non-relativistic formula are obtained.Comment: 14 pages, minor typos corrected, several points clarified, results unchange

Multi-order interference is generally nonzero

It is demonstrated that the third-order interference, as obtained from explicit solutions of Maxwell's equations for realistic models of three-slit devices, including an idealized version of the three-slit device used in a recent three-slit experiment with light (U. Sinha et al., Science 329, 418 (2010)), is generally nonzero. The hypothesis that the third-order interference should be zero is shown to be fatally flawed because it requires dropping the one-to-one correspondence between the symbols in the mathematical theory and the different experimental configurations.Comment: Replaced Figs. 4,5 and caption of Fig.