Axisymmetric Stationary Solutions as Harmonic Maps

We present a method for generating exact solutions of Einstein equations in vacuum using harmonic maps, when the spacetime possesses two commutating Killing vectors. This method consists in writing the axisymmetric stationry Einstein equations in vacuum as a harmonic map which belongs to the group SL(2,R), and decomposing it in its harmonic "submaps". This method provides a natural classification of the solutions in classes (Weil's class, Lewis' class etc).Comment: 17 TeX pages, one table,( CINVESTAV- preprint 12/93

Generation of Closed Timelike Curves with Rotating Superconductors

The spacetime metric around a rotating SuperConductive Ring (SCR) is deduced from the gravitomagnetic London moment in rotating superconductors. It is shown that theoretically it is possible to generate Closed Timelike Curves (CTC) with rotating SCRs. The possibility to use these CTC's to travel in time as initially idealized by G\"{o}del is investigated. It is shown however, that from a technology and experimental point of view these ideas are impossible to implement in the present context.Comment: 9 pages. Submitted to Classical and Quantum Gravit

Nonequilibrium charge dynamics of light-driven rings threaded by a magnetic flux

We study theoretically the charge polarization and the charge current dynamics of a mesoscopic ring driven by short asymmetric electromagnetic pulses and threaded by an external static magnetic flux. It is shown that the pulse-induced charge polarization and the associated light-emission is controllable by tuning the external magnetic flux. Applying two mutually perpendicular pulses triggers a charge current in the ring. The interplay between this nonequilibrium and the persistent currents is investigated and the conditions under which the pulses stop the persistent current are identified.Comment: 6 pages, 2 figures; submitted to EP

Oscillatons revisited

In this paper, we study some interesting properties of a spherically symmetric oscillating soliton star made of a real time-dependent scalar field which is called an oscillaton. The known final configuration of an oscillaton consists of a stationary stage in which the scalar field and the metric coefficients oscillate in time if the scalar potential is quadratic. The differential equations that arise in the simplest approximation, that of coherent scalar oscillations, are presented for a quadratic scalar potential. This allows us to take a closer look at the interesting properties of these oscillating objects. The leading terms of the solutions considering a quartic and a cosh scalar potentials are worked in the so called stationary limit procedure. This procedure reveals the form in which oscillatons and boson stars may be related and useful information about oscillatons is obtained from the known results of boson stars. Oscillatons could compete with boson stars as interesting astrophysical objects, since they would be predicted by scalar field dark matter models.Comment: 10 pages REVTeX, 10 eps figures. Updated files to match version published in Classical and Quantum Gravit

O preconceito linguístico no ciberespaço: a discriminação, os agentes e as especificidades

Imergir no ciberespaço é defrontar-se com a síntese do humano. A complexidade das relações que se estabelecem no espaço virtual abriga problemáticas que dificilmente podem ser identificadas sem um olhar minucioso. Objetivando investigar o preconceito linguístico e trabalhá-lo amplamente, foi esse o espaço que escolhemos para ser locus de busca de ocorrências do referido fenômeno. Este trabalho se inscreve na Sociolinguística e trata-se da análise dos perfis dos agentes da discriminação linguística no espaço virtual divididos entre três redes sociais, Twitter, Orkut e Facebook e das manifestações discriminatórias por eles produzidas. Aferindo a complexidade e a multiplicidade de processos que constituem o preconceito linguístico e seus sujeitos, percebemos a dimensão que assume a postura discriminatória quando suas manifestações são reproduzidas no ciberespaço. Adentrando um território ainda inexplorado, haja vista que não há nenhuma pesquisa precedente semelhante a esta, descobrimos um preconceito plural que surge e ganha anuência em um espaço que, pensado para a democracia, revela-se reduto também de processos segregacionistas, que vitimam sujeitos que, devido ao uso considerado errado que fazem da língua portuguesa, são subjugados e repudiados, formando uma nova massa de indivíduos, que denominamos, neste trabalho, de excluídos sócio-digitais. Amparados em teorias da comunicação como as de McLuhan (1969) e Lévy (1996-1999) e em trabalhos linguísticos e sociolinguísticos como os de Gnerre (1991), Bortoni-Ricardo (2004), Pagotto (2004), Scherre (2005) e Mollica (2007), caracterizamos o ciberespaço e explanamos o preconceito linguístico nele encontrado, ressaltando as implicaturas do locus na produção da mensagem que nosso elenco de agentes do preconceito linguístico produz e veicula. Os resultados logrados indicam, dentre outros, que os agentes do preconceito linguístico são majoritariamente sujeitos do sexo feminino, concentrados nos níveis mais altos de escolaridade e pertencentes às faixas etárias que compreendem os indivíduos jovens e adultos jovens

Exact inflationary solutions

We present a new class of exact inflationary solutions for the evolution of a universe with spatial curvature, filled with a perfect fluid, a scalar field with potential $V_{\pm}(\phi)=\lambda(\phi^2\pm\delta^2)^2$ and a cosmological constant $\Lambda$. With the $V_+(\phi)$ potential and a negative cosmological constant, the scale factor experiments a graceful exit. We give a brief discussion about the physical meaning of the solutions.Comment: 10 pages, revtex file, 6 figures included with epsf. To be published in IJMP-

Quintessence and Scalar Dark Matter in the Universe

Continuing with previous works, we present a cosmological model in which dark matter and dark energy are modeled by scalar fields $\Phi$ and $\Psi$, respectively, endowed with the scalar potentials $V(\Phi)=V_{o}[ \cosh {(\lambda \sqrt{\kappa_{o}}\Phi)}-1]$ and $\tilde{V}(\Psi)=\tilde{V_{o}}[ \sinh {(\alpha \sqrt{\kappa_{o}}\Psi)}] ^{\beta}$. This model contains 95% of scalar field. We obtain that the scalar dark matter mass is $m_{\Phi}\sim 10^{-26}eV.$ The solution obtained allows us to recover the success of the standard CDM. The implications on the formation of structure are reviewed. We obtain that the minimal cutoff radio for this model is $r_{c}\sim 1.2 kpc.$Comment: 4 pages REVTeX, 3 eps color figures. Minor changes and references updated. To appear in Classical and Quantum Gravity as a Letter to the Editor. More information at http://www.fis.cinvestav.mx/~siddh/PHI

Efeito do armazenamento na qualidade de sementes de linhagens de sorgo.

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