Black soliton in a quasi-one-dimensional trapped fermion-fermion mixture

Employing a time dependent mean-field-hydrodynamic model we study the generation of black solitons in a degenerate fermion-fermion mixture in a cigar-shaped geometry using variational and numerical solutions. The black soliton is found to be the first stationary vibrational excitation of the system and is considered to be a nonlinear continuation of the vibrational excitation of the harmonic oscillator state. We illustrate the stationary nature of the black soliton, by studying different perturbations on it after its formation.

Quantum toy model for black-hole backreaction

We propose a simple quantum field theoretical toy model for black-hole evaporation and study the backreaction of Hawking radiation onto the classical background. It turns out that the horizon is also pushed back in this situation (i.e., the interior region shrinks) though this backreaction is not caused by energy conservation but by momentum balance. The effective heat capacity and induced entropy variation can have both signs-depending on the parameters of the model.

Semiclassical approach to black hole absorption of electromagnetic radiation emitted by a rotating charge

We consider an electric charge, minimally coupled to the Maxwell field, rotating around a Schwarzschild black hole. We investigate how much of the radiation emitted from the swirling charge is absorbed by the black hole and show that most of the photons escape to infinity. For this purpose we use the Gupta-Bleuler quantization of the electromagnetic field in the modified Feynman gauge developed in the context of quantum field theory in Schwarzschild spacetime. We obtain that the two photon polarizations contribute quite differently to the emitted power. In addition, we discuss the accurateness of the results obtained in a full general relativistic approach in comparison with the ones obtained when the electric charge is assumed to be orbiting a massive object due to a Newtonian force.

Overspinning a nearly extreme charged black hole via a quantum tunneling process

We examine a nearly extreme macroscopic Reissner-Nordstrom black hole in the context of semiclassical gravity. The absorption rate associated with the quantum tunneling process of scalar particles whereby this black hole can acquire enough angular momentum to violate the weak cosmic-censorship conjecture is shown to be nonzero.

Black hole entropy associated with the supersymmetric sigma model

By means of an identity that equates the elliptic genus partition function of a supersymmetric sigma model on the N-fold symmetric product (SX)-X-N of X ((SX)-X-N=X-N/S-N, where S-N is the symmetric group of N elements) to the partition function of a second-quantized string theory, we derive the asymptotic expansion of the partition function as well as the asymptotic for the degeneracy of spectrum in string theory. The asymptotic expansion for the state counting reproduces the logarithmic correction to the black hole entropy.

Scaler radiation emitted from a source rotating around a black hole

We analyse the scalar radiation emitted from a source rotating around a Schwarzschild black hole using the framework of quantum held theory at the tree level. We show that for relativistic circular orbits the emitted power is about 20-30% smaller than what would be obtained in Minkowski spacetime. We also show that most of the emitted energy escapes to infinity. Our formalism can readily be adapted to investigate similar processes.

Connection between UHECR's and supermassive relic particles

One of the models proposed for the origin of ultra high energy cosmic rays (UHECR's) suggests that these events are the decay products of relic superheavy metastable particles, which we call S particles. These particles can be produced in the reheating period following the inflationary epoch of the early Universe. We study this possibility and obtain constraints on some parameters such as the lifetime and direct couplings of the X-particle to the inflaton field from the requirement that they are responsible for the observed UHECR flux.

Absorption cross section of canonical acoustic holes

We compute numerically the absorption cross section of a canonical acoustic hole for sound waves with arbitrary frequencies. Our outputs are in full agreement with the expected low- and high-frequency limits.

Black-hole back-reaction - a toy model

Using a kink of arbitrary shape as a toy model for a black hole ( horizon), we study the back-reaction of the evaporation process and find that the horizon is always pushed back ( as in the gravitational case). The associated heat capacity and entropy variation, on the other hand, can be positive or negative, depending on the parameters.

Scalar radiation emitted from a rotating source around a Reissner-Nordstrom black hole

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Black hole partition function using the hybrid formalism of superstrings

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Black and green pigments based on chromium-cobalt spinels

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

First report of black rot of Colocasia esculenta caused by Ceratocystis fimbriata in Brazil

Ceratocystis fimbriata foi encontrado em tubérculos de inhame (Colocasia esculenta), apresentando lesões escuras, pouco profundas, contendo estruturas de reprodução do fungo, cuja coloração variava do cinza ao negro. As amostras foram coletadas em supermercados, quitandas e varejões nos Estados de São Paulo, Rio de Janeiro, Bahia, Rondônia e Distrito Federal que, na maioria dos casos, comercializavam inhame produzido no Estado de São Paulo. Os sintomas de podridão negra indicam se tratar de uma doença de pós-colheita. Seqüências de rDNA indicam que os isolados de Colocasia sp. pertencem ao clado da America Latina do complexo C. fimbriata, embora esses isolados sejam mais agressivos em pseudo-pecíolos de C. esculenta do que os isolados de Ficus carica e Mangifera indica.

Electric charge rotating around a black hole

We consider an electric charge rotating around a Schwarzschild black hole. We compute, using quantum field theory in curved spacetime at the tree level, the power emitted by the rotating charge minimally coupled to the Maxwell field. We also compute how much of the radiation emitted by the swirling charge is absorbed by the black hole.

Observation of initial clinical manifestations and repercussions from the treatment of 314 human injuries caused by black sea urchins (Echinometra lucunter) on the southeastern Brazilian coast

INTRODUÇÃO: Os acidentes causados por ouriços-do-mar são as ocorrências por animais marinhos mais comuns no país. O ouriço-do-mar preto (Echinometra lucunter) é a espécie que mais causa ferimentos em banhistas. MÉTODOS: Este trabalho registrou e estudou 314 agravos com ênfase nas manifestações clínicas iniciais observadas e suas implicações na terapêutica recomendada. RESULTADOS: Todos os acidentes foram causados pelo ouriço-do-mar preto e aconteceram em banhistas. As lesões e a dor foram associadas ao trauma causado pela penetração das espículas (não ocorreu inflamação ou dor imediata sem pressão sobre os pontos comprometidos). As complicações deste tipo de acidente, incluindo infecções e granulomas de corpo estranho, estão associadas com a permanência das espículas nos ferimentos. CONCLUSÕES: Foi confirmado o fato do acidente causado por esta espécie ser o mais comum no Brasil e apresentar caráter traumático, sendo a principal recomendação a retirada precoce dos espinhos para prevenção de complicações tardias como as infecções e formação de granulomas de corpo estranho.