Scalar fields in the Lense-Thirring background with a cosmic string and Hawking radiation

We analyze the influence of the gravitational field produced by a slowly rotating black hole with a cosmic string along the axis of symmetry on a massive scalar field. Exact solutions of both angular and radial parts of the Klein-Gordon equation in this spacetime are obtained, and are given in terms of the confluent Heun functions. We emphasize the role of the presence of the cosmic string in these solutions. We also investigate the solutions in regions near and far from the event horizon. From the radial solution, we obtain the exact wave solutions near the exterior horizon of the black hole, and discuss the Hawking radiation of massive scalar particles.Comment: 6 page

Interstellar medium disruption in the Centaurus A group

We present the results of a 21 cm neutral hydrogen (HI) line detection experiment in the direction of 18 low luminosity dwarf galaxies of the Centaurus A group, using the Australia Telescope National Facility 64m Parkes Radio Telescope and the Australia Telescope Compact Array. Five dwarfs have HI masses between M_HI=4x10^5 to M_HI=2.1x10^7 Msol and 0.04<M_HI/L_B<1.81 Msol L_{sol, B}^-1. The other 13 have upper-limits between M_HI<5x10^5 and M_HI<4x10^6 Msol (M_HI}/L_B<0.24 Msol L_{sol, B}^-1). Two of the mixed-morphology dwarfs remain undetected in HI, a situation that is in contrast to that of similar Local Group and Sculptor group objects where all contain significant amounts of neutral gas. There is a discontinuity in the HI properties of Centaurus A group low luminosity dwarfs that is unobserved amongst Sculptor group dwarfs. All objects fainter than M_B=-13 have either M_HI>10^7 Msol or M_HI<10^6 Msol. This gap may be explained by the ram pressure stripping mechanism at work in this dense environment where all galaxies with M_HI<10^7 Msol have been stripped of their gas. The required intergalactic medium density to achieve this is ~10^-3 cm^-3.Comment: 7 figures, 2 table

Far Infrared Slab Lensing and Subwavelength Imaging in Crystal Quartz

We examine the possibility of using negative refraction stemming from the phonon response in an anisotropic crystal to create a simple slab lens with plane parallel sides, and show that imaging from such a lens should be possible at room temperature despite the effects of absorption that are inevitably present due to phonon damping. In particular, we consider the case of crystal quartz, a system for which experimental measurements consistent with all-angle negative refraction have already been demonstrated. Furthermore, we investigate the possibility of subwavelength imaging from such materials, and show that it should be possible for certain configurations.Comment: 12 pages, 10 figure

Hierarchical Spatial Organization of Geographical Networks

In this work we propose the use of a hirarchical extension of the polygonality index as a means to characterize and model geographical networks: each node is associated with the spatial position of the nodes, while the edges of the network are defined by progressive connectivity adjacencies. Through the analysis of such networks, while relating its topological and geometrical properties, it is possible to obtain important indications about the development dynamics of the networks under analysis. The potential of the methodology is illustrated with respect to synthetic geographical networks.Comment: 3 page, 3 figures. A wokring manuscript: suggestions welcome

Casimir energy in a small volume multiply connected static hyperbolic pre-inflationary Universe

A few years ago, Cornish, Spergel and Starkman (CSS), suggested that a multiply connected ``small'' Universe could allow for classical chaotic mixing as a pre-inflationary homogenization process. The smaller the volume, the more important the process. Also, a smaller Universe has a greater probability of being spontaneously created. Previously DeWitt, Hart and Isham (DHI) calculated the Casimir energy for static multiply connected flat space-times. Due to the interest in small volume hyperbolic Universes (e.g. CSS), we generalize the DHI calculation by making a a numerical investigation of the Casimir energy for a conformally coupled, massive scalar field in a static Universe, whose spatial sections are the Weeks manifold, the smallest Universe of negative curvature known. In spite of being a numerical calculation, our result is in fact exact. It is shown that there is spontaneous vacuum excitation of low multipolar components.Comment: accepted for publication in phys. rev.

Vortex behavior near a spin vacancy in 2D XY-magnets

The dynamical behavior of anisotropic two dimensional Heisenberg models is still a matter of controversy. The existence of a central peak at all temperatures and a rich structure of magnon peaks are not yet understood. It seems that the central peaks are related, in some way, to structures like vortices. In order to contribute to the discussion of the dynamical behavior of the model we use Monte Carlo and spin dynamics simulations as well analytical calculations to study the behavior of vortices in the presence of nonmagnetic impurities. Our simulations show that vortices are attracted and trapped by the impurities. Using this result we show that if we suppose that vortices are not very much disturbed by the presence of the impurities, then they work as an attractive potential to the vortices explaining the observed behavior in our simulations.Comment: 4 pages, 6 figure

Seismic behaviour analysis and retrofitting of a row building

Rammed earth is one of the oldest building materials in the world and is present in Portugal with a particular focus in the South of the country. The mechanical properties and the structural behavior of rammed earth constructions have been the subject of study of many researchers in the recent years. This study is part of a broader research on vernacular seismic culture in Portugal. Numerical analyzes were carried out to assess the influence of different retrofitting solutions in the behavior and seismic performance of an rammed earth building representative of the vernacular heritage of Alentejo region. Understating the structural fragilities of this type of constructions allowed determining the most appropriate retrofitting solutions.Project ‘SEISMIC-V –Vernacular Seismic Culture in Portugal’ (PTDC/ATP-AQI/3934/2012), from the Portuguese Science and Technology Foundation (FCT