Radiation from a D-dimensional collision of shock waves: higher order set up and perturbation theory validity

The collision of two D-dimensional, ultra-relativistic particles, described in General Relativity as Aichelberg-Sexl shock waves, is inelastic. In first order perturbation theory, the fraction of the initial centre of mass energy radiated away was recently shown to be 1/2 - 1/D. Here, we extend the formalism to higher orders in perturbation theory, and derive a general expression to extract the inelasticity, valid non-perturbatively, based on the Bondi mass loss formula. Then, to clarify why perturbation theory captures relevant physics of a strong field process in this problem, we provide one variation of the problem where the perturbative framework breaks down: the collision of ultra-relativistic charged particles. The addition of charge, and the associated repulsive nature of the source, originates an extra radiation burst, which we argue to be an artifact of the perturbative framework, veiling the relevant physics.Comment: 21 pages, 3 figures; v2: matches version to Appear in Phys. Rev.

Understanding the Forward Premium Puzzle: A Microstructure Approach

High-interest-rate currencies tend to appreciate relative to low-interest-rate currencies. We argue that adverse-selection problems between participants in foreign exchange markets can account for this 'forward premium puzzle.' The key feature of our model is that the adverse selection problem facing market makers is worse when, based on public information, a currency is expected to appreciate.

A Double Myers-Perry Black Hole in Five Dimensions

Using the inverse scattering method we construct a six-parameter family of exact, stationary, asymptotically flat solutions of the 4+1 dimensional vacuum Einstein equations, with U(1)^2 rotational symmetry. It describes the superposition of two Myers-Perry black holes, each with a single angular momentum parameter, both in the same plane. The black holes live in a background geometry which is the Euclidean C-metric with an extra flat time direction. This background possesses conical singularities in two adjacent compact regions, each corresponding to a set of fixed points of one of the U(1) actions in the Cartan sub-algebra of SO(4). We discuss several aspects of the black holes geometry, including the conical singularities arising from force imbalance, and the torsion singularity arising from torque imbalance. The double Myers-Perry solution presented herein is considerably simpler than the four dimensional double Kerr solution and might be of interest in studying spin-spin interactions in five dimensional general relativity.Comment: 23 pages, 7 figures, LaTeX. v2: minor changes, references added; version published in JHE

Vibration of the railway track-viaduct system under moving vehicles taking into account the interaction effect

Vibration of the railway track-viaduct system under moving vehicles taking into account the interaction effec

Hedging and Financial Fragilities in Fixed Exchange Rate Regimes.

Currency crises that coincide with banking crises tend to share four elements. First, governments provide guarantees to domestic and foreign bank creditors. Second, banks do not hedge their exchange rate risk. Third, there is a lending boom before the crises. Finally, when the currency/banking collapse occurs interest rates rise and there is a persistent decline in output. This paper proposes an explanation for these regularities.BANKS ; EXCHANGE RATE ; FINANCIAL MARKET

Influence of oxygen content on the antibacterial effect of Ag-O coatings deposited by magnetron sputtering

Ag and AgOx thin films were deposited by pulsed DC magnetron sputtering, for medical devices, in order to provide antibacterial properties. During the deposition process, oxygen flow, and, consequently, oxygen fraction, was varied (0â15 sccm) to understand the influence of oxygen species in the physical, chemical and structural properties of thin films. Coatings morphology was observed by scanning electron microscopy (SEM) and their nanostructure and composition were assessed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS), respectively. XRD and XPS analyses revealed that Ag thin films are composed by metallic Ag, which crystallizes in fcc-Ag phase; whereas AgOx showed a mixture of Ag2O and AgO phases for low oxygen fraction that became single AgO with the increase of oxygen fraction in the discharge. Surface wettability and surface tension of the coatings were also determined showing hydrophobic character. Halo inhibition zone tests were performed against Staphylococcus epidermidis, in order to evaluate the antibacterial behavior of coatings, and silver ion release was measured. Only AgOx presented antibacterial behavior, showing that the presence of silver oxide are the main reasons for the antibacterial effect, probably due to the increased production of ROS (Reactive Oxygen Species),making these coatings promising for medical applications.The authors acknowledgments the financial support of FCTFundação para a Ciência e Tecnologia through grant SFRH/BD/90321/2012. Also thank support by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013, and projects ERA-SIINN/0004/2013 through the “Fundo Europeu de Desenvolvimento Regional” (FEDER)

Sotalol in the Treatment of Fetal Tachyarrhythmia

A taquicardia fetal é uma situação rara, que, quando mantida coloca em risco a vida do feto. O modo de tratamento não é consensual, existindo várias modalidades farmacológicas. O objectivo deste estudo foi avaliar a eficácia e segurança do sotalol no tratamento de taquicardias fetais. Material e métodos: Estudo retrospectivo, com base nos registos de consulta e entrevista às mães dos fetos com taquicardia supraventricular, referenciados ao Serviço de Cardiologia Pediátrica do Hospital de Santa Marta, durante um período de dez anos. Resultados: Foram diagnosticados oito fetos com taquicardia supraventricular, dos quais seis foram tratados com sotalol. A idade média de gestação na apresentação foi de 30 semanas. Nenhum feto apresentava cardiopatia estrutural, em dois verificou-se hidropisia fetal e outro apresentou hidrocefalia. A taquicardia era supraventricular em todos, sendo em dois por flutter auricular. Em todos os casos, excepto um, houve conversão a ritmo sinusal, não se registando efeitos secundários nas mães nem mortalidade fetal. No período neonatal em três crianças foram registados episódios de taquicardia supraventricular paroxística. Conclusão: O sotalol mostrou-se seguro e eficaz no tratamento das taquicardias fetais, mas, dada a pequenez da amostra, outros estudos mais alargados são necessários para se tirarem conclusões válidas