Lorentz-breaking effects in scalar-tensor theories of gravity

In this work, we study the effects of breaking Lorentz symmetry in scalar-tensor theories of gravity taking torsion into account. We show that a space-time with torsion interacting with a Maxwell field by means of a Chern-Simons-like term is able to explain the optical activity in syncrotron radiation emitted by cosmological distant radio sources. Without specifying the source of the dilaton-gravity, we study the dilaton-solution. We analyse the physical implications of this result in the Jordan-Fierz frame. We also analyse the effects of the Lorentz breaking in the cosmic string formation process. We obtain the solution corresponding to a cosmic string in the presence of torsion by keeping track of the effects of the Chern-Simons coupling and calculate the charge induced on this cosmic string in this framework. We also show that the resulting charged cosmic string gives us important effects concerning the background radiation.The optical activity in this case is also worked out and discussed.Comment: 10 pages, no figures, ReVTex forma

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.

Gravitation: Global Formulation and Quantum Effects

A nonintegrable phase-factor global approach to gravitation is developed by using the similarity of teleparallel gravity with electromagnetism. The phase shifts of both the COW and the gravitational Aharonov-Bohm effects are obtained. It is then shown, by considering a simple slit experiment, that in the classical limit the global approach yields the same result as the gravitational Lorentz force equation of teleparallel gravity. It represents, therefore, the quantum mechanical version of the classical description provided by the gravitational Lorentz force equation. As teleparallel gravity can be formulated independently of the equivalence principle, it will consequently require no generalization of this principle at the quantum level.Comment: Latex (IOP style), 14 pages, 3 figures. To appear in Classical and Quantum Gravit

Loop variables in the geometry of a rotating black string

In this paper we analyze in the Wilson loop context the parallel transport of vectors and spinors around a closed loop in the background space-time of a rotating black string in order to classify its global properties. We also examine particular closed orbits in this space-time and verify the Mandelstam relations.Comment: 14 pages, iopart styl

Grupos funcionais na restauração passiva de floresta ombrófila densa sob plantios de eucalipto no Parque Estadual da Serra do Mar.

Alguns estudos apontam que reflorestamentos de eucalipto podem catalisar o processo de restauração de florestas nativas, tornando o local mais propício para o estabelecimento de plântulas de árvores nativas. A fim de comprovar esta hipótese, encontra-se em andamento pesquisa que busca descrever a dinâmica de sucessão de trechos secundários de Floresta Ombrófila Densa Montana, em especial como evolui a regeneração natural sob plantios de eucalipto no Núcleo Santa Virgínia - Parque Estadual da Serra do Mar. O primeiro inventário de nativas regenerantes no sub-bosque desses talhões foi realizado em 1993 e encontra-se em andamento a remedição deste mesmo plantio. Este trabalho apresenta a avaliação dos grupos funcionais da comunidade arbórea em 1993, a fim de averiguar se houve alteração na composição e/ou proporção desses grupos no censo atual. Por meio de revisões bibliográficas, foi realizada a atualização nomenclatural e a classificação das espécies em grupos funcionais. No inventário de 1993 foram registradas 64 espécies, 42 gêneros e 25 famílias. Predominaram as secundárias tardias residentes no sub-bosque (44% das espécies e 51% dos indivíduos), em detrimento das secundárias tardias transientes, secundárias iniciais e pioneiras, o que indica possível competição com os eucaliptos ainda existentes no dossel. O predomínio do sub-bosque resultou no destaque de espécies polinizadas e dispersas por animais (Zoofilia - 89% das espécies e 97% dos indivíduos; Zoocoria - 88% e 80%)

Gravitational field around a time-like current-carrying screwed cosmic string in scalar-tensor theories

In this paper we obtain the space-time generated by a time-like current-carrying superconducting screwed cosmic string(TCSCS). This gravitational field is obtained in a modified scalar-tensor theory in the sense that torsion is taken into account. We show that this solution is comptible with a torsion field generated by the scalar field $\phi$. The analysis of gravitational effects of a TCSCS shows up that the torsion effects that appear in the physical frame of Jordan-Fierz can be described in a geometric form given by contorsion term plus a symmetric part which contains the scalar gradient. As an important application of this solution, we consider the linear perturbation method developed by Zel'dovich, investigate the accretion of cold dark matter due to the formation of wakes when a TCSCS moves with speed $v$ and discuss the role played by torsion. Our results are compared with those obtained for cosmic strings in the framework of scalar-tensor theories without taking torsion into account.Comment: 21 pages, no figures, Revised Version, presented at the "XXIV- Encontro Nacional de Fisica de Particulas e Campos ", Caxambu, MG, Brazil, to appear in Phys. Rev.

Dados climatológicos: Estação de Pacajus, 1996.

Para a pesquisa agropecuária, os dados coletados em estações climatológicas são de suma importância, uma vez que possibilitam o monitoramento do clima, bem como o leventamento dos seus efeitos sobre pragas e doenças nas culturas, a estimativa da evapotranspiração, do volume e dos turnos de irrigação, dentre muitas outras finalidades básicas.bitstream/CNPAT-2010/8976/1/Ba-002.pd