184 research outputs found
Distorted 5-dimensional vacuum black hole
In this paper we study how the distortion generated by a static and neutral
distribution of external matter affects a 5-dimensional
Schwarzschild-Tangherlini black hole. A solution representing a particular
class of such distorted black holes admits an RxU(1)xU(1) isometry group. We
show that there exists a certain duality transformation between the black hole
horizon and a stretched singularity surfaces. The space-time near the distorted
black hole singularity has the same topology and Kasner exponents as those of a
5-dimensional Schwarzschild-Tangherlini black hole. We calculate the maximal
proper time of free fall of a test particle from the distorted black hole
horizon to its singularity and find that, depending on the distortion, it can
be less, equal to, or greater than that of a Schwarzschild-Tangherlini black
hole of the same horizon area. This implies that due to the distortion, the
singularity of a Schwarzschild-Tangherlini black hole can come close to its
horizon. A relation between the Kretschmann scalar calculated on the horizon of
a 5-dimensional static, asymmetric, distorted black hole and the trace of the
square of the Ricci tensor of the horizon surface is derived.Comment: 20 pages, 9 figure
Dynamical Horizons and their Properties
A detailed description of how black holes grow in full, non-linear general
relativity is presented. The starting point is the notion of dynamical
horizons. Expressions of fluxes of energy and angular momentum carried by
gravitational waves across these horizons are obtained. Fluxes are local and
the energy flux is positive. Change in the horizon area is related to these
fluxes. A notion of angular momentum and energy is associated with
cross-sections of the horizon and balance equations, analogous to those
obtained by Bondi and Sachs at null infinity, are derived. These in turn lead
to generalizations of the first and second laws of black hole mechanics. The
relation between dynamical horizons and their asymptotic states --the isolated
horizons-- is discussed briefly. The framework has potential applications to
numerical, mathematical, astrophysical and quantum general relativity.Comment: 44 pages, 2 figures, RevTeX4. Minor typos corrected. Final PRD
versio
Isolated Horizons: Hamiltonian Evolution and the First Law
A framework was recently introduced to generalize black hole mechanics by
replacing stationary event horizons with isolated horizons. That framework is
significantly extended. The extension is non-trivial in that not only do the
boundary conditions now allow the horizon to be distorted and rotating, but
also the subsequent analysis is based on several new ingredients. Specifically,
although the overall strategy is closely related to that in the previous work,
the dynamical variables, the action principle and the Hamiltonian framework are
all quite different. More importantly, in the non-rotating case, the first law
is shown to arise as a necessary and sufficient condition for the existence of
a consistent Hamiltonian evolution. Somewhat surprisingly, this consistency
condition in turn leads to new predictions even for static black holes. To
complement the previous work, the entire discussion is presented in terms of
tetrads and associated (real) Lorentz connections.Comment: 56 pages, 1 figure, Revtex; Final Version, to appear in PR
Time-dependent response of a zonally averaged ocean–atmosphere–sea ice model to Milankovitch forcing
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Springer-Verlag for personal use, not for redistribution. The definitive version was published in Climate Dynamics 6 (2010): 763-779, doi:10.1007/s00382-010-0790-6.An ocean-atmosphere-sea ice model is developed to explore the time-dependent
response of climate to Milankovitch forcing for the time interval 5-3 Myr BP. The ocean
component is a zonally averaged model of the circulation in five basins (Arctic, Atlantic,
Indian, Pacific, and Southern Oceans). The atmospheric component is a one-dimensional
(latitudinal) energy balance model, and the sea-ice component is a thermodynamic model.
Two numerical experiments are conducted. The first experiment does not include sea ice
and the Arctic Ocean; the second experiment does. Results from the two experiments are
used to investigate (i) the response of annual mean surface air and ocean temperatures to
Milankovitch forcing, and (ii) the role of sea ice in this response.
In both experiments, the response of air temperature is dominated by obliquity cycles
at most latitudes. On the other hand, the response of ocean temperature varies with latitude
and depth. Deep water formed between 45°N-65°N in the Atlantic Ocean mainly responds
to precession. In contrast, deep water formed south of 60°S responds to obliquity when sea
ice is not included. Sea ice acts as a time-integrator of summer insolation changes such that
annual mean sea-ice conditions mainly respond to obliquity. Thus, in the presence of sea
ice, air temperature changes over the sea ice are amplified, and temperature changes in deep
water of southern origin are suppressed since water below sea ice is kept near the freezing
point.This work was supported by an NSERC Discovery
Grant awarded to L.A.M. We also thank GEC3 for a Network Grant
Stationary Black Holes as Holographs
Smooth spacetimes possessing a (global) one-parameter group of isometries and
an associated Killing horizon in Einstein's theory of gravity are investigated.
No assumption concerning the asymptotic structure is made, thereby, the
selected spacetimes may be considered as generic distorted stationary black
holes. First, spacetimes of arbitrary dimension, , with matter
satisfying the dominant energy condition and allowing non-zero cosmological
constant are investigated. In this part complete characterisation of the
topology of the event horizon of ``distorted'' black holes is given. It is
shown that the topology of the event horizon of ``distorted'' black holes is
allowed to possess a much larger variety than that of the isolated black hole
configurations. In the second part, 4-dimensional (non-degenerate) electrovac
distorted black hole spacetimes are considered. It is shown that the spacetime
geometry and the electromagnetic field are uniquely determined in the black
hole region once the geometry of the bifurcation surface and one of the
electromagnetic potentials are specified there. Conditions guaranteeing the
same type of determinacy, in a neighbourhood of the event horizon, on the {\it
domain of outer communication} side are also investigated. In particular, they
are shown to be satisfied in the analytic case.Comment: 31 pages, LaTeX; typos corrected, new references added, to appear in
CQ
Porphyromonas gingivalis gingipains cause defective macrophage migration towards apoptotic cells and inhibit phagocytosis of primary apoptotic neutrophils:gingipains, apoptotic cell removal & inflammation
Periodontal disease is a prevalent chronic inflammatory condition characterised by an aberrant host response to a pathogenic plaque biofilm resulting in local tissue damage and frustrated healing that can result in tooth loss. Cysteine proteases (gingipains) from the key periodontal pathogen Porphyromonas gingivalis have been implicated in periodontal disease pathogenesis by inhibiting inflammation resolution and are linked with systemic chronic inflammatory conditions such as rheumatoid arthritis. Efficient clearance of apoptotic cells is essential for the resolution of inflammation and tissue restoration. Here we sought to characterise the innate immune clearance of apoptotic cells and its modulation by gingipains. We examined the capacity of gingipain-treated macrophages to migrate towards and phagocytose apoptotic cells. Lysine gingipain treatment of macrophages impaired macrophage migration towards apoptotic neutrophils. Furthermore, lysine gingipain treatment reduced surface expression levels of CD14, a key macrophage receptor for apoptotic cells, which resulted in reduced macrophage interactions with apoptotic cells. Additionally, whilst apoptotic cells and their derived secretome were shown to inhibit TNF-α induced expression by P.gingivalis LPS, we demonstrated that gingipain preparations induced a rapid inflammatory response in macrophages that was resistant to the anti-inflammatory effects of apoptotic cells or their secretome. Taken together these data indicate that P.gingivalis may promote the chronic inflammation seen in periodontal disease patients by multiple mechanisms including rapid, potent gingipain-mediated inflammation coupled with receptor cleavage leading to defective clearance of apoptotic cells and reduced anti-inflammatory responses. Thus gingipains represent a potential therapeutic target for intervention in the management of chronic periodontal disease
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