11,083 research outputs found
Echoes of the gravitational decoupling: scalar perturbations and quasinormal modes of hairy black holes
The behavior of hairy black hole solutions, obtained by the gravitational
decoupling (GD) method, is investigated under scalar perturbations. The
quasinormal mode frequencies of such solutions are regulated by GD hair. The
numerically generated wave solutions are derived for a range of values for the
GD hairy black hole parameters, with higher-frequency modes very sensitive to
them. The results are confronted with the corresponding ones for the
Schwarzschild solution, whose deviations from it demonstrate a unique physical
identification of GD hairy black holes. The method here presented comprises the
first steps towards the obtainment of the observable signature of GD hairy
black holes at ground-based detectors, emitted from coalescing binary systems
of GD hairy black hole mergers in the ringdown phase.Comment: 15 pages, 6 figure
How the Charge Can Affect the Formation of Gravastars
In recent work we physically interpreted a special gravastar solution
characterized by a zero Schwarzschild mass. In fact, in that case, none
gravastar was formed and the shell expanded, leaving behind a de Sitter or a
Minkowski spacetime, or collapsed without forming an event horizon, originating
what we called a massive non-gravitational object. This object has two
components of non zero mass but the exterior spacetime is Minkowski or de
Sitter. One of the component is a massive thin shell and the other one is de
Sitter spacetime inside. The total mass of this object is zero Schwarzschild
mass, which characterizes an exterior vacuum spacetime. Here, we extend this
study to the case where we have a charged shell. Now, the exterior is a
Reissner-Nordstr\"om spacetime and, depending on the parameter
of the equation of state of the shell, and the charge, a
gravastar structure can be formed. We have found that the presence of the
charge contributes to the stability of the gravastar, if the charge is greater
than a critical value. Otherwise, a massive non-gravitational object is formed
for small charges.Comment: 17 pages and 7 figures, several typos corrected, accepted for
publication in JCA
Non-collinear coupling between magnetic adatoms in carbon nanotubes
The long range character of the exchange coupling between localized magnetic
moments indirectly mediated by the conduction electrons of metallic hosts often
plays a significant role in determining the magnetic order of low-dimensional
structures. In addition to this indirect coupling, here we show that the direct
exchange interaction that arises when the moments are not too far apart may
induce a non-collinear magnetic order that cannot be characterized by a
Heisenberg-like interaction between the magnetic moments. We argue that this
effect can be manipulated to control the magnetization alignment of magnetic
dimers adsorbed to the walls of carbon nanotubes.Comment: 13 pages, 5 figures, submitted to PR
Efeito de retardadores de crescimento no tamanho dos ramos da cultivar de videira festival.
Com o bjetivo de controlar o crescimento dos ramos da cultivar Festival, como resposta ao uso dos retardadores de crescimento Chlormequat e Paclobutrazol 25%, realizou-se um experimento em condições de campo em Petrolina-P
Quantitative adsorbate structure determination under catalytic reaction conditions
Current methods allow quantitative local structure determination of adsorbate geometries on surfaces in ultrahigh vacuum (UHV) but are incompatible with the higher pressures required for a steady-state catalytic reactions. Here we show that photoelectron diffraction can be used to determine the structure of the methoxy and formate reaction intermediates during the steady-state oxidation of methanol over Cu(110) by taking advantage of recent instrumental developments to allow near-ambient pressure x-ray photoelectron spectroscopy. The local methoxy site differs from that under static UHV conditions, attributed to the increased surface mobility and dynamic nature of the surface under reaction conditions
Stable Gravastars of Anisotropic Dark Energy
Dynamical models of prototype gravastars made of phantom energy are
constructed, in which an infinitely thin spherical shell of a perfect fluid
with the equation of state divides the whole spacetime
into two regions, the internal region filled with a dark energy (or phantom)
fluid, and the external Schwarzschild region. It is found that in some cases
the models represent the "bounded excursion" stable gravastars, where the thin
shell is oscillating between two finite radii, while in other cases they
collapse until the formation of black holes or normal stars. In the phase
space, the region for the "bounded excursion" gravastars is very small in
comparison to that of black holes, but not empty, as found in our previous
papers. Therefore, although the existence of gravastars can not be completely
excluded from current analysis, the opposite is not possible either, that is,
even if gravastars exist, they do not exclude the existence of black holes.Comment: 35 pages, 43 figures, added some clarifying texts and corrected some
typos, accepted for publication in JCA
Efeito de retardadores de crescimento na producao de biomassa aerea da cultivar de videira festival.
Com objetivo de observar o efeito dos retardadores de crescimento, Chlormequat e Paclobutrazol 25% aplicados após a poda (AP), sobre a quantidade de biomassa fresca e seca proveniente das plantas de videira ?Festival?, em dois ciclos de produção, realizou-se um experimento em condições de campo em Petrolina-PE
Efeito do paclobutrazol e do chlormequat na fertilidade das gemas de videiras (Vitis vinifera L.) cv. Festival.
Pondera-se que, através da aplicação de reguladores de crescimento PBZ e CCC, poder-se-ão aumentar a fertilidade das gemas das videiras da cultivar Festival, obtendo-se, em conseqüência, plantas mais produtivas.E em:
- …