18 research outputs found
Quasinormal modes for the SdS black hole : an analytical approximation scheme
Quasinormal modes for scalar field perturbations of a Schwarzschild-de Sitter
(SdS) black hole are investigated. An analytical approximation is proposed for
the problem. The quasinormal modes are evaluated for this approximate model in
the limit when black hole mass is much smaller than the radius of curvature of
the spacetime. The model mirrors some striking features observed in numerical
studies of time behaviour of scalar perturbations of the SdS black hole. In
particular, it shows the presence of two sets of modes relevant at two
different time scales, proportional to the surface gravities of the black hole
and cosmological horizons respectively. These quasinormal modes are not
complete - another feature observed in numerical studies. Refinements of this
model to yield more accurate quantitative agreement with numerical studies are
discussed. Further investigations of this model are outlined, which would
provide a valuable insight into time behaviour of perturbations in the SdS
spacetime.Comment: 12 pages, revtex, refs added and discussion expanded, version to
appear in Phys. Rev.
Quasinormal frequencies of Schwarzschild black holes in anti-de Sitter spacetimes: A complete study on the asymptotic behavior
We present a thorough analysis for the quasinormal (QN) behavior, associated
with the decay of scalar, electromagnetic and gravitational perturbations, of
Schwarzschild-anti-de Sitter black holes. As it is known the anti-de Sitter
(AdS) QN spectrum crucially depends on the relative size of the black hole to
the AdS radius. There are three different types of behavior depending on
whether the black hole is large, intermediate, or small. The results of
previous works, concerning lower overtones for large black holes, are completed
here by obtaining higher overtones for all the three black hole regimes. There
are two major conclusions that one can draw from this work: First,
asymptotically for high overtones, all the modes are evenly spaced, and this
holds for all three types of regime, large, intermediate and small black holes,
independently of l, where l is the quantum number characterizing the angular
distribution; Second, the spacing between modes is apparently universal, in
that it does not depend on the field, i.e., scalar, electromagnetic and
gravitational QN modes all have the same spacing for high overtones. We are
also able to prove why scalar and gravitational perturbations are isospectral,
asymptotically for high overtones, by introducing appropriate superpartner
potentials.Comment: 22 page
Profile of IL-2, IL-4, IL-10, IFN- ? , TNF- ? and KC-like cytokines in pregnant bitches
Avaliação dos parâmetros cardiorrespiratórios, hemogasométricos e da concentração plasmática de cortisol em bovinos submetidos à imobilização eletromagnética
From phenotype to genotype: a Bayesian solution
The study of biological systems commonly depends on inferring the state of a 'hidden' variable, such as an underlying genotype, from that of an 'observed' variable, such as an expressed phenotype. However, this cannot be achieved using traditional quantitative methods when more than one genetic mechanism exists for a single observable phenotype. Using a novel latent class Bayesian model, it is possible to infer the prevalence of different genetic elements in a population given a sample of phenotypes. As an exemplar, data comprising phenotypic resistance to six antimicrobials obtained from passive surveillance of Salmonella Typhimurium DT104 are analysed to infer the prevalence of individual resistance genes, as well as the prevalence of a genomic island known as SGI1 and its variants. Three competing models are fitted to the data and distinguished between using posterior predictive p-values to assess their ability to predict the observed number of unique phenotypes. The results suggest that several SGI1 variants circulate in a few fixed forms through the population from which our data were derived. The methods presented could be applied to other types of phenotypic data, and represent a useful and generic mechanism of inferring the genetic population structure of organism
The preparation of high-purity thorium by the magnesium reduction of thorium tetrachloride
Preregistration is hard, and worthwhile
Preregistration clarifies the distinction between planned and unplanned research by reducing unnoticed flexibility. This improves credibility of findings and calibration of uncertainty. However, making decisions before conducting analyses requires practice. During report writing, respecting both what was planned and what actually happened requires good judgment and humility in making claims.journalMultivariate analysis of psychological dat