77 research outputs found
Monocanalicular versus bicanalicular silicone intubation for nasolacrimal duct stenosis in adults
Purpose: To compare the success rate of monocanalicular versus bicanalicular silicone intubation of incomplete nasolacrimal duct obstruction (nasolacrimal duct stenosis) in adults. Methods: In a retrospective, nonrandomized comparative case series, 48 eyes of 44 adult patients with nasolacrimal duct stenosis underwent endoscopic probing and either bicanalicular (BCI; n = 22 eyes) or monocanalicular (MCI; n = 26 eyes) nasolacrimal duct intubation under general anesthesia. "Complete success" was defined as complete disappearance of the symptoms, "partial success" as improvement with some residual symptoms, and "failure" as absence of improvement or worsening of symptoms at last follow-up. The last follow-up examination included diagnostic probing and irrigation if there was not complete success. Results: Patient ages ranged from 31 to 90 years (mean, 69; SD, 11.5). Forty-five tubes were removed 6 to 17 weeks (mean, 9.1; SD, 3) after surgery. Premature tube dislocation and removal occurred in one eye with BCI and in two eyes with MCI. Follow-up ranged from 6 to 52 months (mean, 14.9; SD, 8.4). The complete success rate was nearly the same in eyes with MCI (16/26, 61.53) and BCI (13/22, 59.09). Partial success (MCI: 8/26, 30.76; BCI: 1/22, 4.54) and failure (MCI: 2/26, 7.69; BCI: 8/22, 36.36) were, however, significantly different (p = 0.010). Complications included 3 slit puncta with BCI and 4 temporary superficial punctuate keratopathy after MCI. Conclusions: MCI had virtually the same complete success rate as BCI, a higher partial success rate than BCI, and a lower failure rate than BCI in treatment of nasolacrimal duct stenosis in adults. ©2005 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc
Further restrictions on the topology of stationary black holes in five dimensions
We place further restriction on the possible topology of stationary
asymptotically flat vacuum black holes in 5 spacetime dimensions. We prove that
the horizon manifold can be either a connected sum of Lens spaces and "handles"
, or the quotient of by certain finite groups of
isometries (with no "handles"). The resulting horizon topologies include Prism
manifolds and quotients of the Poincare homology sphere. We also show that the
topology of the domain of outer communication is a cartesian product of the
time direction with a finite connected sum of 's
and 's, minus the black hole itself. We do not assume the existence of
any Killing vector beside the asymptotically timelike one required by
definition for stationarity.Comment: LaTex, 22 pages, 9 figure
A Higher Dimensional Stationary Rotating Black Hole Must be Axisymmetric
A key result in the proof of black hole uniqueness in 4-dimensions is that a
stationary black hole that is ``rotating''--i.e., is such that the stationary
Killing field is not everywhere normal to the horizon--must be axisymmetric.
The proof of this result in 4-dimensions relies on the fact that the orbits of
the stationary Killing field on the horizon have the property that they must
return to the same null geodesic generator of the horizon after a certain
period, . This latter property follows, in turn, from the fact that the
cross-sections of the horizon are two-dimensional spheres. However, in
spacetimes of dimension greater than 4, it is no longer true that the orbits of
the stationary Killing field on the horizon must return to the same null
geodesic generator. In this paper, we prove that, nevertheless, a higher
dimensional stationary black hole that is rotating must be axisymmetric. No
assumptions are made concerning the topology of the horizon cross-sections
other than that they are compact. However, we assume that the horizon is
non-degenerate and, as in the 4-dimensional proof, that the spacetime is
analytic.Comment: 24 pages, no figures, v2: footnotes and references added, v3:
numerous minor revision
On the `Stationary Implies Axisymmetric' Theorem for Extremal Black Holes in Higher Dimensions
All known stationary black hole solutions in higher dimensions possess
additional rotational symmetries in addition to the stationary Killing field.
Also, for all known stationary solutions, the event horizon is a Killing
horizon, and the surface gravity is constant. In the case of non-degenerate
horizons (non-extremal black holes), a general theorem was previously
established [gr-qc/0605106] proving that these statements are in fact generally
true under the assumption that the spacetime is analytic, and that the metric
satisfies Einstein's equation. Here, we extend the analysis to the case of
degenerate (extremal) black holes. It is shown that the theorem still holds
true if the vector of angular velocities of the horizon satisfies a certain
"diophantine condition," which holds except for a set of measure zero.Comment: 30pp, Latex, no figure
Thermodynamic and gravitational instability on hyperbolic spaces
We study the properties of anti--de Sitter black holes with a Gauss-Bonnet
term for various horizon topologies (k=0, \pm 1) and for various dimensions,
with emphasis on the less well understood k=-1 solution. We find that the zero
temperature (and zero energy density) extremal states are the local minima of
the energy for AdS black holes with hyperbolic event horizons. The hyperbolic
AdS black hole may be stable thermodynamically if the background is defined by
an extremal solution and the extremal entropy is non-negative. We also
investigate the gravitational stability of AdS spacetimes of dimensions D>4
against linear perturbations and find that the extremal states are still the
local minima of the energy. For a spherically symmetric AdS black hole
solution, the gravitational potential is positive and bounded, with or without
the Gauss-Bonnet type corrections, while, when k=-1, a small Gauss-Bonnet
coupling, namely, \alpha << {l}^2 (where l is the curvature radius of AdS
space), is found useful to keep the potential bounded from below, as required
for stability of the extremal background.Comment: Shortened to match published (PRD) version, 18 pages, several eps
figure
Black Holes in Higher-Dimensional Gravity
These lectures review some of the recent progress in uncovering the phase
structure of black hole solutions in higher-dimensional vacuum Einstein
gravity. The two classes on which we focus are Kaluza-Klein black holes, i.e.
static solutions with an event horizon in asymptotically flat spaces with
compact directions, and stationary solutions with an event horizon in
asymptotically flat space. Highlights include the recently constructed
multi-black hole configurations on the cylinder and thin rotating black rings
in dimensions higher than five. The phase diagram that is emerging for each of
the two classes will be discussed, including an intriguing connection that
relates the phase structure of Kaluza-Klein black holes with that of
asymptotically flat rotating black holes.Comment: latex, 49 pages, 5 figures. Lectures to appear in the proceedings of
the Fourth Aegean Summer School, Mytiline, Lesvos, Greece, September 17-22,
200
Topological Charged Black Holes in High Dimensional Spacetimes and Their Formation from Gravitational Collapse of a Type II Fluid
Topological charged black holes coupled with a cosmological constant in
spacetimes are studied, where is an Einstein
space of the form . The global structure for
the four-dimensional spacetimes with is investigated systematically.
The most general solutions that represent a Type fluid in such a high
dimensional spacetime are found, and showed that topological charged black
holes can be formed from the gravitational collapse of such a fluid. When the
spacetime is (asymptotically) self-similar, the collapse always forms black
holes for , in contrast to the case , where it can form
either balck holes or naked singularities.Comment: 14 figures, to appear in Phys. Rev.
Classical Yang-Mills Black hole hair in anti-de Sitter space
The properties of hairy black holes in Einstein–Yang–Mills (EYM) theory are reviewed, focusing on spherically symmetric solutions. In particular, in asymptotically anti-de Sitter space (adS) stable black hole hair is known to exist for frak su(2) EYM. We review recent work in which it is shown that stable hair also exists in frak su(N) EYM for arbitrary N, so that there is no upper limit on how much stable hair a black hole in adS can possess
Stability of Black Holes and Black Branes
We establish a new criterion for the dynamical stability of black holes in spacetime dimensions in general relativity with respect to axisymmetric
perturbations: Dynamical stability is equivalent to the positivity of the
canonical energy, \E, on a subspace, , of linearized solutions
that have vanishing linearized ADM mass, momentum, and angular momentum at
infinity and satisfy certain gauge conditions at the horizon. This is shown by
proving that---apart from pure gauge perturbations and perturbations towards
other stationary black holes---\E is nondegenerate on and that,
for axisymmetric perturbations, \E has positive flux properties at both
infinity and the horizon. We further show that \E is related to the second
order variations of mass, angular momentum, and horizon area by \E = \delta^2
M - \sum_A \Omega_A \delta^2 J_A - \frac{\kappa}{8\pi} \delta^2 A, thereby
establishing a close connection between dynamical stability and thermodynamic
stability. Thermodynamic instability of a family of black holes need not imply
dynamical instability because the perturbations towards other members of the
family will not, in general, have vanishing linearized ADM mass and/or angular
momentum. However, we prove that for any black brane corresponding to a
thermodynamically unstable black hole, sufficiently long wavelength
perturbations can be found with \E < 0 and vanishing linearized ADM
quantities. Thus, all black branes corresponding to thermodynmically unstable
black holes are dynamically unstable, as conjectured by Gubser and Mitra. We
also prove that positivity of \E on is equivalent to the
satisfaction of a "local Penrose inequality," thus showing that satisfaction of
this local Penrose inequality is necessary and sufficient for dynamical
stability.Comment: 54 pages, Latex, 2 figures, v2: Anzatz for momentum in proof of
Gubser-Mitra conjecture corrected; factor of 2 in symplectic form corrected;
several typos in formulas corrected; v3: revised argument concerning horizon
gauge condition on p. 10; typos corrected and several minor changes;
reference added; v4: formula (86) for \E corrected, footnote adde
An Infinite Class of Extremal Horizons in Higher Dimensions
We present a new class of near-horizon geometries which solve Einstein's
vacuum equations, including a negative cosmological constant, in all even
dimensions greater than four. Spatial sections of the horizon are inhomogeneous
S^2-bundles over any compact Kaehler-Einstein manifold. For a given base, the
solutions are parameterised by one continuous parameter (the angular momentum)
and an integer which determines the topology of the horizon. In six dimensions
the horizon topology is either S^2 x S^2 or CP^2 # -CP^2. In higher dimensions
the S^2-bundles are always non-trivial, and for a fixed base, give an infinite
number of distinct horizon topologies. Furthermore, depending on the choice of
base we can get examples of near-horizon geometries with a single rotational
symmetry (the minimal dimension for this is eight). All of our horizon
geometries are consistent with all known topology and symmetry constraints for
the horizons of asymptotically flat or globally Anti de Sitter extremal black
holes.Comment: 42 pages, latex. v2: corrected section 6.1, two references added. v3:
modified angular momentum and corrected area comparison, version to be
published in Commun. Math. Phy
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