Samuel Rocha de Oliveira

Exact self‐gravitating disks and rings: A solitonic approach

The Belinsky–Zakharov version of the inverse scattering method is used to generate a large class of solutions to the vacuum Einstein equations representing uniformly accelerating and rotating disks and rings. The solutions studied are generated from a simple class of static disks and rings that can be expressed in a simple form using suitable complex functions of the usual cylindrical coordinates.

The Schenberg spherical gravitational wave detector: the first commissioning runs

Here we present a status report of the first spherical antenna project equipped with a set of parametric transducers for gravitational detection. The Mario Schenberg, as it is called, started its commissioning phase at the Physics Institute of the University of Sao Paulo, in September 2006, under the full support of FAPESP. We have been testing the three preliminary parametric transducer systems in order to prepare the detector for the next cryogenic run, when it will be calibrated. We are also developing sapphire oscillators that will replace the current ones thereby providing better performance. We also plan to install eight transducers in the near future, six of which are of the two-mode type and arranged according to the truncated icosahedron configuration. The other two, which will be placed close to the sphere equator, will be mechanically non-resonant. In doing so, we want to verify that if the Schenberg antenna can become a wideband gravitational wave detector through the use of an ultra-high sensitivity non-resonant transducer constructed using the recent achievements of nanotechnology.

Geodesics around Weyl?Bach's ring solution

We explore some of the gravitational features of a uniform infinitesimal ring both in the Newtonian potential theory and in general relativity. We use a spacetime associated with a Weyl static solution of the vacuum Einsteins equations with ring-like singularity. The Newtonian motion for a test particle in the gravitational field of the ring is studied and compared with the corresponding geodesic motion in the given spacetime. We have found a relativistic peculiar attraction: free-falling particle geodesics lead to the inner rim but never hit the ring.

Uniformly accelerated black holes

The static and stationary C metric are examined in a generic framework and their interpretations studied in some detail, especially those with two event horizons, one for the black hole and another for the acceleration. We find that (i) the spacetime of an accelerated static black hole is plagued by either conical singularities or a lack of smoothness and compactness of the black hole horizon, (ii) by using standard black hole thermodynamics we show that accelerated black holes have a higher Hawking temperature than Unruh temperature of the accelerated frame, and (iii) the usual upper bound on the product of the mass and acceleration parameters

Superposition of Weyl solutions to the Einstein equations: cosmic strings and domain walls

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TWO KERR BLACK HOLES WITH AXISYMMETRIC SPINS : HEAD-ON COLLISION AND GRAVITATIONAL RADIATION

is just a coordinate artifact. The main results are extended to accelerated rotating black holes with no significant changes.

Métodos Numéricos de Volumes Finitos aplicados em Hidrodinâmica Ideal via Octave

The solutions to the Einstein equations representing the superposition of a particle and a ring are studied. The appearance of strut-type and membrane-type singularities is analysed. These objects are compared with cosmic strings and domain walls. It is found that, unlike the usual domain walls, the membranes have null effective gravitational mass, as have struts and strings. The relationship of these membranes with walls associated with sigma-model-type field theories is indicated.

Fractal structure in the scalar λ ( φ 2 − 1 ) 2 theory

We present a semi-analytical approach to the interaction of two (originally) Kerr black holes through a head-on collision process. An expression for the rate of emission of gravitational radiation is derived from an exact solution to Einsteins field equations. The total amount of gravitational radiation emitted in the process is calculated. We find that the spin-spin interaction increases the emission of gravitational wave energy by up to 0.2% of the total rest mass. We also discuss the possibility of spin exchange between the holes.

Superposition of Weyl solutions: the equilibrium forces

Nas ultimas decadas, Metodos Numericos de Volumes Finitos vem sendo desenvolvidos, aprimorados e aplicados em sistemas de equacoes diferenciais parciais (EDP’s) hiperbolicos nao lineares dependentes do tempo [4]. As leis de conservacoes sao escritas por sistemas de EDP’s e a modelagem da maioria dos problemas em Ciencias e/ou Engenharias parte de tais leis. Em particular, um sistema que se destaca e o formado pelas equacoes de Euler que modelam o escoamento de um fluido por possuir dificuldades e desafios referentes a obtencao de solucoes numericas [3]. O carater puramente nao linear dessas equacoes possibilitam a formacao dos tres tipos de ondas elementares: ondas de choque, ondas de rarefacao e ondas de contato, que aparecem como descontinuidades na solucao das equacoes de Euler [6]. No que diz respeito a Metodos Numericos, cada um possui suas proprias propriedades que influenciam diretamente na solucao numerica tornando-os adequados ou nao dependendo da aplicacao em questao. Neste trabalho sao feitas comparacoes entre os metodos de volumes finitos aplicados as equacoes de Euler Unidimensionais, dada pelas seguintes expressoes: [...]