Counting Dyons in N=8 String Theory

A recently discovered relation between 4D and 5D black holes is used to derive exact (weighted) BPS black hole degeneracies for 4D N=8 string theory from the exactly known 5D degeneracies. A direct 4D microscopic derivation in terms of weighted 4D D-brane bound state degeneracies is sketched and found to agree.Comment: 10 page

Propagação das ondas de flexão em placas compósitas

Este trabalho tem como objectivo principal o estudo experimental/numérico da propagação de ondas de flexão em estruturas laminadas tipo placa. A medição do campo de deslocamentos é efectuada por holografia TV de duplo impulso. Para o efeito foi desenvolvida uma montagem experimental utilizando um LASER de Rubi e um sistema de controlo para, com elevada precisão, gerar e registar no tempo a evolução da força de impacto. Vários registos foram efectuados para diferentes instantes de tempo em duas placas laminadas compósitas. Um programa de elementos finitos, Ansys ®, foi utilizado para, nas mesmas condições de carga e de tempo, simular numericamente a resposta das placas. Por fim, é apresentado o estudo comparativo dos resultados obtidos pelas diferentes técnicas.Os autores agradecem à Fundação para a Ciência e a Tecnologia –FCT o apoio financeiro no âmbito do projecto POCI/EME/63236/2004

Partition functions and elliptic genera from supergravity

We develop the spacetime aspects of the computation of partition functions for string/M-theory on AdS(3) xM. Subleading corrections to the semi-classical result are included systematically, laying the groundwork for comparison with CFT partition functions via the AdS(3)/CFT(2) correspondence. This leads to a better understanding of the "Farey tail" expansion of Dijkgraaf et. al. from the point of view of bulk physics. Besides clarifying various issues, we also extend the analysis to the N=2 setting with higher derivative effects included.Comment: 34 page

Digital holography using a photographic camera

In this work an experimental device for surface deformation assessment on components and structures is presented. The system is based in a holographic interferometric technique and benefits from all the advantages associated with these techniques such as: high resolution, full field, non contact and the possibility of post processing the obtained numerical data. To perform measurements the proposed device uses digital holograms recorded with a standard digital photographic camera. In order to test and validate the system proposed some experimental results are presented and discussed

Técnicas de cálculo de fase aplicadas à mecânica

Neste trabalho é realizado um estudo sobre o cálculo da distribuição espacial da fase com aplicação nas principais técnicas ópticas da Mecânica experimental: técnicas de Interferometria holográfica, Moiré interferométrico e caracterização de forma 3D. Todas estas técnicas para além de utilizarem a luz, para aceder à forma, ao deslocamento ou a deformação de objectos ou estruturas, recorrem também a métodos de cálculo de fase para melhorar a sua resolução, a qual, por sua vez, varia de técnica para técnica podendo em algumas delas ser ajustada ao problema em estudo

Massive lower gastrointestinal bleeding from idiopathic ileocolonic varix: report of a case

Dis Colon Rectum. 2006 Apr;49(4):524-6. Massive lower gastrointestinal bleeding from idiopathic ileocolonic varix: report of a case. Lopes LM, Ramada JM, Certo MG, Pereira PR, Soares JM, Ribeiro M, Areias J, Pinho C. SourceGastroenterology Department, Hospital Geral Santo António, Porto, Portugal. [email protected] Abstract Idiopathic varices of the entire colon are very rare. We report on a 64-year-old patient with massive lower gastrointestinal hemorrhage from an extensive ileocolonic varix. Diagnosis was established by colonoscopy. The patient underwent an emergency ileocolectomy with satisfactory results. This rare case shows the importance of colonoscopy in the evaluation of patients with lower gastrointestinal hemorrhage and reminds us that sometimes the diagnosis is not what we expect. Recognition of this abnormality is important because varices may be the cause of massive lower gastrointestinal hemorrhage. PMID: 16395635 [PubMed - indexed for MEDLINE

Critical points of the Black-Hole potential for homogeneous special geometries

We extend the analysis of N=2 extremal Black-Hole attractor equations to the case of special geometries based on homogeneous coset spaces. For non-BPS critical points (with non vanishing central charge) the (Bekenstein-Hawking) entropy formula is the same as for symmetric spaces, namely four times the square of the central charge evaluated at the critical point. For non homogeneous geometries the deviation from this formula is given in terms of geometrical data of special geometry in presence of a background symplectic charge vector.Comment: 17 pages, LaTeX fil

5D Attractors with Higher Derivatives

We analyze higher derivative corrections to attractor geometries in five dimensions. We find corrected AdS_3xS^2 geometries by solving the equations of motion coming from a recently constructed four-derivative supergravity action in five dimensions. The result allows us to explicitly verify a previous anomaly based derivation of the AdS_3 central charges of this theory. Also, by dimensional reduction we compare our results with those of the 4D higher derivative attractor, and find complete agreement.Comment: 18 pages, harvma

Black Hole Entropy Function and the Attractor Mechanism in Higher Derivative Gravity

We study extremal black hole solutions in D dimensions with near horizon geometry AdS_2\times S^{D-2} in higher derivative gravity coupled to other scalar, vector and anti-symmetric tensor fields. We define an entropy function by integrating the Lagrangian density over S^{D-2} for a general AdS_2\times S^{D-2} background, taking the Legendre transform of the resulting function with respect to the parameters labelling the electric fields, and multiplying the result by a factor of 2\pi. We show that the values of the scalar fields at the horizon as well as the sizes of AdS_2 and S^{D-2} are determined by extremizing this entropy function with respect to the corresponding parameters, and the entropy of the black hole is given by the value of the entropy function at this extremum. Our analysis relies on the analysis of the equations of motion and does not directly make use of supersymmetry or specific structure of the higher derivative terms.Comment: LaTeX file, 12page

AdS4 flux vacua in type II superstrings and their domain-wall solutions

We investigate the emergence of supersymmetric negative-vacuum-energy ground states in four dimensions. First, we rely on the analysis of the effective superpotential, which depends on the background fluxes of the internal manifold, or equivalently has its origin in the underlying gauged supergravity. Four-dimensional, supersymmetric anti-de Sitter vacua with all moduli stabilized appear when appropriate Ramond and Neveu--Schwarz fluxes are introduced in IIA. Geometric fluxes are not necessary. Then the whole setup is analyzed from the perspective of the sources, namely D/NS-branes or Kaluza--Klein monopoles. Orientifold planes are also required for tadpole cancellation. The solutions found in four dimensions correspond to domain walls interpolating between AdS4 and flat spacetime. The various consistency conditions (equations of motion, Bianchi identities and tadpole cancellation conditions) are always satisfied, albeit with source terms. We also speculate on the possibility of assigning (formal) entropies to AdS4 flux vacua via the corresponding dual brane systems.Comment: Acknowledgment replace