Black hole formation in bidimensional dilaton gravity coupled to scalar matter systems

This work deals with the formation of black hole in bidimensional dilaton gravity coupled to scalar matter fields. We investigate two scalar matter systems, one described by a sixth power potential and the other defined with two scalar fields containing up to the fourth power in the fields. The topological solutions that appear in these cases allow the formation of black holes in the corresponding dilaton gravity models.Comment: Latex, 9 pages. Published in Mod. Phys. Lett. A14 (1999) 268

Self-similar magnetoresistance of Fibonacci ultrathin magnetic films

We study numerically the magnetic properties (magnetization and magnetoresistance) of ultra-thin magnetic films (Fe/Cr) grown following the Fibonacci sequence. We use a phenomenological model which includes Zeeman, cubic anisotropy, bilinear and biquadratic exchange energies. Our physical parameters are based on experimental data recently reported, which contain biquadratic exchange coupling with magnitude comparable to the bilinear exchange coupling. When biquadratic exchange coupling is sufficiently large a striking self-similar pattern emerges.Comment: 5 pages, 5 EPS figures, REVTeX, accepted for publication in Phys. Rev.

Space-Time Description of Scalar Particle Creation by a Homogeneous Isotropic Gravitational Field

We give the generalization of the method of the space-time description of particle creation by a gravitational field for a scalar field with nonconformal coupling to the curvature. The space-time correlation function is obtained for a created pair of the quasi-particles, corresponding to a diagonal form of the instantaneous Hamiltonian. The case of an adiabatic change of the metric of homogeneous isotropic space is analyzed. We show that the created pairs of quasi-particles in de Sitter space should be interpreted as pairs of virtual particles.Comment: 7 pages, 3 figure

Embedded System for Real Color Composition in Experimental Physics

Software can be considered educational when properly contextualized in a relationship of teaching and learning. This paper describes an embedded system and an educational software developed and applied in experimental physics to real and virtual colors composition. The educational system developed allows student interaction by voice commands, which makes the assimilation process of red/green/blue (RGB) color formation concepts more didactic and playful. The application of educational software in experiments also allows to verify, in real time, the influence of programs change on the physical phenomena and stimulates the logical reasoning development and consequently the autonomy of the students, to the measure that can raise hypothesis, make modifications in the programming and take off conclusions from the practical results obtained

Relação sexual do parasitismo por Haemonchus contortus em Caprinos (Capra hircus).

A hemoncose é uma doença parasitaria importante para pecuária, sendo os ovinos e caprinos as espécies que apresentam um maior acometimento. Esta enfermidade é provocada pelo nematódeo de gênero Haemonchus sp., parasito de abomaso, medindo entre 1 a 2,5 cm. Tratase da mais patogênica das helmintoses, provocando diminuição do ganho de peso, graves anemias, edemas de mucosa gástrica diminuindo a absorção de nutrientes, edemas externos denominados ?edema de barbela?, sendo sua sintomatologia característica de hemoncose, além de provocar óbito em graves parasitoses. O objetivo deste trabalho foi descrever a fauna parasitária abomasal e a relação sexual do parasitismo por Haemonchus contortus. Foram coletadas amostras abomasais de caprinos após o abate, sendo recuperado um total de 12460 helmintos. Os animais abatidos foram observados no pré abate e pós abate. No pré abate foram observados pelos arrepiados e sem brilho além de anemias grave. Após o abate foi observado o parasitismo abomasal por H. contortus e T. axei, onde a carga parasitária do H. contortus representou mais de 98% do parasitismo, sendo a relação entre macho e fêmea equivalente, além do parasitismo observou-se lesões de mucosa provocado pela fixação do nematóide ao órgão e carcaça pálida. Sexual relationship of parasitism by Haemonchus contortus in Goats (Capra hircus). Abstract: The hemoncose is an important parasitic disease to livestock, being the species sheep and goats the most affected. This disorder is caused by the nematode Haemonchus sp. abomasal parasite, measuring 1 to 2.5 cm. This is the most pathogenic helminthes, causing reduction of weight gain, severe anemia, edema of the gastric mucosa promoting decreasing the absorption of nutrients, external swelling called "edema of dewlap", and it?s characteristic signs of hemoncose, besides causing death in severe parasitosis. The aim of this study was describe the abomasal parasite fauna and sexual parasitism with Haemonchus contortus. Abomasal samples were collected after slaughter of goats, being recovered a total of 12460 helminths. The slaughtered animals were observed before and after slaughter. Before the slaughter were observed hair bristly and opaque, beyond severe anemia. After killing was observed abomasal parasitism by H. contortus and T. axei, where the parasitic load of H. contortus was accounted for more than 98% of parasitism, being equivalent the relation between male and female, in addition of the parasitism was observed mucosal lesions caused by fixation of nematode in abomasum, and pale carcass

Thermal Casimir effect for neutrino and electromagnetic fields in closed Friedmann cosmological model

We calculate the total internal energy, total energy density and pressure, and the free energy for the neutrino and electromagnetic fields in Einstein and closed Friedmann cosmological models. The Casimir contributions to all these quantities are separated. The asymptotic expressions for both the total internal energy and free energy, and for the Casimir contributions to them are found in the limiting cases of low and high temperatures. It is shown that the neutrino field does not possess a classical limit at high temperature. As for the electromagnetic field, we demonstrate that the total internal energy has the classical contribution and the Casimir internal energy goes to the classical limit at high temperature. The respective Casimir free energy contains both linear and logarithmic terms with respect to the temperature. The total and Casimir entropies for the neutrino and electromagnetic fields at low temperature are also calculated and shown to be in agreement with the Nernst heat theorem.Comment: 23 pages, to appear in Phys. Rev.

Present status of controversies regarding the thermal Casimir force

It is well known that, beginning in 2000, the behavior of the thermal correction to the Casimir force between real metals has been hotly debated. As was shown by several research groups, the Lifshitz theory, which provides the theoretical foundation for the calculation of both the van der Waals and Casimir forces, leads to different results depending on the model of metal conductivity used. To resolve these controversies, the theoretical considerations based on the principles of thermodynamics and new experimental tests were invoked. We analyze the present status of the problem (in particular, the advantages and disadvantages of the approaches based on the surface impedance and on the Drude model dielectric function) using rigorous analytical calculations of the entropy of a fluctuating field. We also discuss the results of a new precise experiment on the determination of the Casimir pressure between two parallel plates by means of a micromechanical torsional oscillator.Comment: 14 pages, 1 figure, iopart.cls is used, to appear in J. Phys. A (special issue: Proceedings of QFEXT05, Barcelona, Sept. 5-9, 2005