5,429 research outputs found
The Three-Dimensional BTZ Black Hole as a Cylindrical System in Four-Dimensional General Relativity
It is shown how to transform the three dimensional BTZ black hole into a four
dimensional cylindrical black hole (i.e., black string) in general relativity.
This process is identical to the transformation of a point particle in three
dimensions into a straight cosmic string in four dimensions.Comment: Latex, 9 page
Gravitational collapse to toroidal, cylindrical and planar black holes
Gravitational collapse of non-spherical symmetric matter leads inevitably to
non-static external spacetimes. It is shown here that gravitational collapse of
matter with toroidal topology in a toroidal anti-de Sitter background proceeds
to form a toroidal black hole. According to the analytical model presented, the
collapsing matter absorbs energy in the form of radiation (be it scalar,
neutrinos, electromagnetic, or gravitational) from the exterior spacetime. Upon
decompactification of one or two coordinates of the torus one gets collapsing
solutions of cylindrical or planar matter onto black strings or black
membranes, respectively. The results have implications on the hoop conjecture.Comment: 6 pages, Revtex, modifications in the title and in the interpretation
of some results, to appear in Physical Review
Quasi-normal modes of toroidal, cylindrical and planar black holes in anti-de Sitter spacetimes: scalar, electromagnetic and gravitational perturbations
We study the quasi-normal modes (QNM) of scalar, electromagnetic and
gravitational perturbations of black holes in general relativity whose horizons
have toroidal, cylindrical or planar topology in an asymptotically anti-de
Sitter (AdS) spacetime. The associated quasinormal frequencies describe the
decay in time of the corresponding test field in the vicinities of the black
hole. In terms of the AdS/CFT conjecture, the inverse of the frequency is a
measure of the dynamical timescale of approach to thermal equilibrium of the
corresponding conformal field theory.Comment: Latex, 16 pages. Minor change
Pair creation of higher dimensional black holes on a de Sitter background
We study in detail the quantum process in which a pair of black holes is
created in a higher D-dimensional de Sitter (dS) background. The energy to
materialize and accelerate the pair comes from the positive cosmological
constant. The instantons that describe the process are obtained from the
Tangherlini black hole solutions. Our pair creation rates reduce to the pair
creation rate for Reissner-Nordstrom-dS solutions when D=4. Pair creation of
black holes in the dS background becomes less suppressed when the dimension of
the spacetime increases. The dS space is the only background in which we can
discuss analytically the pair creation process of higher dimensional black
holes, since the C-metric and the Ernst solutions, that describe respectively a
pair accelerated by a string and by an electromagnetic field, are not know yet
in a higher dimensional spacetime.Comment: 10 pages; 1 figure included; RexTeX4. v2: References added. Published
version. v3: Typo in equation (46) fixe
Collapsing shells of radiation in anti-de Sitter spacetimes and the hoop and cosmic censorship conjectures
Gravitational collapse of radiation in an anti-de Sitter background is
studied. For the spherical case, the collapse proceeds in much the same way as
in the Minkowski background, i.e., massless naked singularities may form for a
highly inhomogeneous collapse, violating the cosmic censorship, but not the
hoop conjecture. The toroidal, cylindrical and planar collapses can be treated
together. In these cases no naked singularity ever forms, in accordance with
the cosmic censorship. However, since the collapse proceeds to form toroidal,
cylindrical or planar black holes, the hoop conjecture in an anti-de Sitter
spacetime is violated.Comment: 4 pages, Revtex Journal: to appear in Physical Review
On the black hole limit of rotating discs and rings
Solutions to Einstein's field equations describing rotating fluid bodies in
equilibrium permit parametric (i.e. quasi-stationary) transitions to the
extreme Kerr solution (outside the horizon). This has been shown analytically
for discs of dust and numerically for ring solutions with various equations of
state. From the exterior point of view, this transition can be interpreted as a
(quasi) black hole limit. All gravitational multipole moments assume precisely
the values of an extremal Kerr black hole in the limit. In the present paper,
the way in which the black hole limit is approached is investigated in more
detail by means of a parametric Taylor series expansion of the exact solution
describing a rigidly rotating disc of dust. Combined with numerical
calculations for ring solutions our results indicate an interesting universal
behaviour of the multipole moments near the black hole limit.Comment: 18 pages, 4 figures; Dedicated to Gernot Neugebauer on the occasion
of his 70th birthda
Vitamin-D Receptor Agonist Calcitriol Reduces Calcification in Vitro Through Selective Upregulation of SLC20A2 but not SLC20A1 or XPR1
Vitamin D deficiency (hypovitaminosis D) causes osteomalacia and poor long bone mineralization. In apparent contrast, hypovitaminosis D has been reported in patients with primary brain calcifications ( Fahr\u27s disease ). We evaluated the expression of two phosphate transporters which we have found to be associated with primary brain calcification (SLC20A2, whose promoter has a predicted vitamin D receptor binding site, and XPR1), and one unassociated (SLC20A1), in an in vitro model of calcification. Expression of all three genes was significantly decreased in calcifying human bone osteosarcoma (SaOs-2) cells. Further, we confirmed that vitamin D (calcitriol) reduced calcification as measured by Alizarin Red staining. Cells incubated with calcitriol under calcifying conditions specifically maintained expression of the phosphate transporter SLC20A2 at higher levels relative to controls, by RT-qPCR. Neither SLC20A1 nor XPR1 were affected by calcitriol treatment and remained suppressed. Critically, knockdown of SLC20A2 gene and protein with CRISPR technology in SaOs2 cells significantly ablated vitamin D mediated inhibition of calcification. This study elucidates the mechanistic importance of SLC20A2 in suppressing the calcification process. It also suggests that vitamin D might be used to regulate SLC20A2 gene expression, as well as reduce brain calcification which occurs in Fahr\u27s disease and normal aging
Probabilidade de morte em bezerras Holandês X Guzerá.
Foi estudado neste experimento a mortalidade até 1 ano de 614 bezerras de 6 grupos de cruzamento holandês, como parte da avaliação de estratégias de cruzamentos.Resumo
Estimativas da diferença aditiva entre raças e da heterose para mortalidade em bezerras Holandês X Guzerá.
Como parte de um experimento de avaliação de estratégias de cruzamentos, foi estudada a mortalidade até 12 ano de 614 bezerras de 6 grupos de cruzamentos Holandês X Guzerá.Resumo
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