6,242 research outputs found
Quasinormal modes of d-dimensional spherical black holes with a near extreme cosmological constant
We derive an expression for the quasinormal modes of scalar perturbations in
near extreme d-dimensional Schwarzschild-de Sitter and Reissner-Nordstrom-de
Sitter black holes. We show that, in the near extreme limit, the dynamics of
the scalar field is characterized by a Poschl-Teller effective potential. The
results are qualitatively independent of the spacetime dimension and field
mass.Comment: 5 pages, REVTeX4, version to be published in Physical Review
Gravitational quasinormal radiation of higher-dimensional black holes
We find the gravitational resonance (quasinormal) modes of the higher
dimensional Schwarzschild and Reissner-Nordstrem black holes. The effect on the
quasinormal behavior due to the presence of the term is investigated.
The QN spectrum is totally different for different signs of . In more
than four dimensions there excited three types of gravitational modes: scalar,
vector, and tensor. They produce three different quasinormal spectra, thus the
isospectrality between scalar and vector perturbations, which takes place for
D=4 Schwarzschild and Schwarzschild-de-Sitter black holes, is broken in higher
dimensions. That is the scalar-type gravitational perturbations, connected with
deformations of the black hole horizon, which damp most slowly and therefore
dominate during late time of the black hole ringing.Comment: 13 pages, 2 figures, several references are adde
Large Charge Four-Dimensional Non-Extremal N=2 Black Holes with R^2-Terms
We consider N=2 supergravity in four dimensions with small R^2 curvature
corrections. We construct large charge non-extremal black hole solutions in all
space, with either a supersymmetric or a non-supersymmetric extremal limit, and
analyze their thermodynamic properties. This generalizes some of the extremal
solutions presented in [arXiv:0902.0831]. The indexed entropy of the
non-extremal extension of the supersymmetric black hole, has the form of the
extremal entropy, with the charges replaced by a function of the charges, the
moduli at infinity and the non-extremality parameter. This is the same behavior
as in the case without R^2-terms.Comment: 13 pages. v2: stripped down to letter format, based on the background
given in [arXiv:0902.0831]. v3: up to date with CQG versio
Black Holes, Space-Filling Chains and Random Walks
Many approaches to a semiclassical description of gravity lead to an integer
black hole entropy. In four dimensions this implies that the Schwarzschild
radius obeys a formula which describes the distance covered by a Brownian
random walk. For the higher-dimensional Schwarzschild-Tangherlini black hole,
its radius relates similarly to a fractional Brownian walk. We propose a
possible microscopic explanation for these random walk structures based on
microscopic chains which fill the interior of the black hole.Comment: 18 pages, 4 figures, 2 tables; v2 and v3: minor changes and refs.
adde
Black Holes in Supergravity: the non-BPS Branch
We construct extremal, spherically symmetric black hole solutions to 4D
supergravity with charge assignments that preclude BPS-saturation. In
particular, we determine the ground state energy as a function of charges and
moduli. We find that the mass of the non-BPS black hole remains that of a
marginal bound state of four basic constituents throughout the entire moduli
space and that there is always a non-zero gap above the BPS bound.Comment: 29 pages, one appendix, no figures; v2. few comments and references
added and a missing sign included; v3. further references adde
Promoção do crescimento em mudas micropropagadas de bananeira por rizobactérias.
A micropropagação in vitro constitui uma ferramenta eficiente na obtenção de mudas sadias e homogêneas. Entretanto, a micropropagação também elimina a microbiota benéfica ao crescimento vegetativo. (Lazarovits e Nowak, 1997). A re-introdução de certos microrganismos tanto de forma individual como misturas de isolados, via tratamento de explantes, podem promover o crescimento das futuras plântulas e protegê-las contra doenças (Lazarovits e Nowak, 1997; Siddiqui e Shaukat, 2002). Rizobactérias ou PGPR (plant growth-promoting rhizobacteria) são bactérias saprófitas que vivem na rizosfera das plantas, e têm sido relacionadas com o incremento da produção agrícola como promotoras do crescimento de plantas e como agentes de biocontrole de doenças (Chen et al., 1996; Liu et al., 1995)pdf 121
Quasi-normal modes of Schwarzschild-de Sitter black holes
The low-laying frequencies of characteristic quasi-normal modes (QNM) of
Schwarzschild-de Sitter (SdS) black holes have been calculated for fields of
different spin using the 6th-order WKB approximation and the approximation by
the P\"{o}shl-Teller potential. The well-known asymptotic formula for large
is generalized here on a case of the Schwarzchild-de Sitter black hole. In the
limit of the near extreme term the results given by both methods are
in a very good agreement, and in this limit fields of different spin decay with
the same rate.Comment: 9 pages, 1 ancillary Mathematica(R) noteboo
Generic bounds on dipolar gravitational radiation from inspiralling compact binaries
Various alternative theories of gravity predict dipolar gravitational
radiation in addition to quadrupolar radiation. We show that gravitational wave
(GW) observations of inspiralling compact binaries can put interesting
constraints on the strengths of the dipole modes of GW polarizations. We put
forward a physically motivated gravitational waveform for dipole modes, in the
Fourier domain, in terms of two parameters: one which captures the relative
amplitude of the dipole mode with respect to the quadrupole mode () and
the other a dipole term in the phase (). We then use this two parameter
representation to discuss typical bounds on their values using GW measurements.
We obtain the expected bounds on the amplitude parameter and the phase
parameter for Advanced LIGO (AdvLIGO) and Einstein Telescope (ET) noise
power spectral densities using Fisher information matrix. AdvLIGO and ET may at
best bound to an accuracy of and and
to an accuracy of and respectively.Comment: Matches with the published versio
Superpotentials from flux compactifications of M-theory
In flux compactifications of M-theory a superpotential is generated whose
explicit form depends on the structure group of the 7-dimensional internal
manifold. In this note, we discuss superpotentials for the structure groups:
G_2, SU(3) or SU(2). For the G_2 case all internal fluxes have to vanish. For
SU(3) structures, the non-zero flux components entering the superpotential
describe an effective 1-dimensional model and a Chern-Simons model if there are
SU(2) structures.Comment: 10 page
Avaliação e identificação de Pseudomonas sp. e Bacillus sp. dois isolados de rizobactérias antagônicas a Radopholus similis.
As rizobactérias PGPR (plant growth-promoting rhizobacteria) são microrganismos que podem promover o desenvolvimento e crescimento de plantas e atuar no controle biológico de doenças. Bactérias dos gêneros Pseudomonas e Bacillus são amplamente conhecidas pela capacidade de atuarem no biocontrole de fitopatógenos, dentre esses, nematóides. Isso se deve, principalmente, pela produção direta de compostos tóxicos, alteração dos exsudatos radiculares ou da indução de resistência na planta hospedeira. Assim, o uso desses microrganismos como agentes de biocotnrole do Radopholus similis, causador de necroses radiculares, em bananeira, é um alternativa a ser estudada. Visando a identificação de isolados com potencial uso no controle de fitopatógenos, o emprego de técnicas moleculares torna-se uma ferramenta indispensável. Nesse sentido, a técnica de PCR (reação em cadeia da polimerase) é uma forma rápida e eficiente de caracterizar isolados promissores. Dessa forma, este estudo teve como objetivo avaliar o potencial de biocontrole in vitro das rizobactérias ao R. Similis, e identificar por meio de PCR, a prevalência dos gêneros Pseudomonas e Bacillus entre isolados pré-selecionados.PDF. 071
- …