242 research outputs found
Asymptotically Lifshitz wormholes and black holes for Lovelock gravity in vacuum
Static asymptotically Lifshitz wormholes and black holes in vacuum are shown
to exist for a class of Lovelock theories in d=2n+1>7 dimensions, selected by
requiring that all but one of their n maximally symmetric vacua are AdS of
radius l and degenerate. The wormhole geometry is regular everywhere and
connects two Lifshitz spacetimes with a nontrivial geometry at the boundary.
The dynamical exponent z is determined by the quotient of the curvature radii
of the maximally symmetric vacua according to n(z^2-1)+1=(l/L)^2, where L
corresponds to the curvature radius of the nondegenerate vacuum. Light signals
are able to connect both asymptotic regions in finite time, and the
gravitational field pulls towards a fixed surface located at some arbitrary
proper distance to the neck. The asymptotically Lifshitz black hole possesses
the same dynamical exponent and a fixed Hawking temperature given by T=z/(2^z
pi l). Further analytic solutions, including pure Lifshitz spacetimes with a
nontrivial geometry at the spacelike boundary, and wormholes that interpolate
between asymptotically Lifshitz spacetimes with different dynamical exponents
are also found.Comment: 19 pages, 1 figur
A boundary stress tensor for higher-derivative gravity in AdS and Lifshitz backgrounds
We investigate the Brown-York stress tensor for curvature-squared theories.
This requires a generalized Gibbons-Hawking term in order to establish a
well-posed variational principle, which is achieved in a universal way by
reducing the number of derivatives through the introduction of an auxiliary
tensor field. We examine the boundary stress tensor thus defined for the
special case of `massive gravity' in three dimensions, which augments the
Einstein-Hilbert term by a particular curvature-squared term. It is shown that
one obtains finite results for physical parameters on AdS upon adding a
`boundary cosmological constant' as a counterterm, which vanishes at the
so-called chiral point. We derive known and new results, like the value of the
central charges or the mass of black hole solutions, thereby confirming our
prescription for the computation of the stress tensor. Finally, we inspect
recently constructed Lifshitz vacua and a new black hole solution that is
asymptotically Lifshitz, and we propose a novel and covariant counterterm for
this case.Comment: 25 pages, 1 figure; v2: minor corrections, references added, to
appear in JHE
Field theories with anisotropic scaling in 2D, solitons and the microscopic entropy of asymptotically Lifshitz black holes
Field theories with anisotropic scaling in 1+1 dimensions are considered. It
is shown that the isomorphism between Lifshitz algebras with dynamical
exponents z and 1/z naturally leads to a duality between low and high
temperature regimes. Assuming the existence of gap in the spectrum, this
duality allows to obtain a precise formula for the asymptotic growth of the
number of states with a fixed energy which depends on z and the energy of the
ground state, and reduces to the Cardy formula for z=1. The holographic
realization of the duality can be naturally inferred from the fact that
Euclidean Lifshitz spaces in three dimensions with dynamical exponents and
characteristic lengths given by z, l, and 1/z, l/z, respectively, are
diffeomorphic. The semiclassical entropy of black holes with Lifshitz
asymptotics can then be recovered from the generalization of Cardy formula,
where the ground state corresponds to a soliton. An explicit example is
provided by the existence of a purely gravitational soliton solution for BHT
massive gravity, which precisely has the required energy that reproduces the
entropy of the analytic asymptotically Lifshitz black hole with z=3.
Remarkably, neither the asymptotic symmetries nor central charges were
explicitly used in order to obtain these results.Comment: 17 pages, no figures, references corrected and update
Sublittoral soft bottom communities and diversity of Mejillones Bay in northern Chile (Humboldt Current upwelling system)
The macrozoobenthos of Mejillones Bay (23°S; Humboldt Current) was quantitatively investigated over a 7-year period from austral summer 1995/1996 to winter 2002. About 78 van Veen grab samples taken at six stations (5, 10, 20 m depth) provided the basis for the analysis of the distribution of 60 species and 28 families of benthic invertebrates, as well as of their abundance and biomass. Mean abundance (2,119 individuals m-2) was in the same order compared to a previous investigation; mean biomass (966 g formalin wet mass m-2), however, exceeded prior estimations mainly due to the dominance of the bivalve Aulacomya ater. About 43% of the taxa inhabited the complete depth range. Mean taxonomic Shannon diversity (H', Log e) was 1.54 ± 0.58 with a maximum at 20 m (1.95 ± 0.33); evenness increased with depth. The fauna was numerically dominated by carnivorous gastropods, polychaetes and crustaceans (48%). About 15% of the species were suspensivorous, 13% sedimentivorous, 11% detritivorous, 7% omnivorous and 6% herbivorous. Cluster analyses showed a significant difference between the shallow and the deeper stations. Gammarid amphipods and the polychaete family Nephtyidae characterized the 5-mzone, the molluscs Aulacomya ater, Mitrella unifasciata and gammarids the intermediate zone, while the gastropod Nassarius gayi and the polychaete family Nereidae were most prominent at the deeper stations. The communities of the three depth zones did not appear to be limited by hypoxia during non-El Niño conditions. Therefore, no typical change in community structure occurred during El Niño 1997–1998, in contrast to what was observed for deeper faunal assemblages and hypoxic bays elsewhere in the coastal Humboldt Current system
Elevated serum procollagen type III peptide in splanchnic and peripheral circulation of patients with inflammatory bowel disease submitted to surgery
BACKGROUND: In the hypothesis that the increased collagen metabolism in the intestinal wall of patients affected by inflammatory bowel disease (IBD) is reflected in the systemic circulation, we aimed the study to evaluate serum level of procollagen III peptide (PIIIP) in peripheral and splanchnic circulation by a commercial radioimmunoassay of patients with different histories of disease. METHODS: Twenty-seven patients, 17 with Crohn and 10 with ulcerative colitis submitted to surgery were studied. Blood samples were obtained before surgery from a peripheral vein and during surgery from the mesenteric vein draining the affected intestinal segment. Fifteen healthy age and sex matched subjects were studied to determine normal range for peripheral PIIIP. RESULTS: In IBD patients peripheral PIIIP level was significantly higher if compared with controls (5.0 ± 1.9 vs 2.7 ± 0.7 μg/l; p = 0.0001); splanchnic PIIIP level was 5.5 ± 2.6 μg/l showing a positive gradient between splanchnic and peripheral concentrations of PIIIP. No significant differences between groups nor correlations with patients' age and duration of disease were found. CONCLUSIONS: We provide evidence that the increased local collagen metabolism in active IBD is reflected also in the systemic circulation irrespective of the history of the disease, suggesting that PIIIP should be considered more appropiately as a marker of the activity phases of IBD
Photoreduction of gaseous oxidized mercury changes global atmospheric mercury speciation, transport and deposition
Anthropogenic mercury (Hg(0)) emissions oxidize to gaseous Hg(II) compounds, before deposition to Earth surface ecosystems. Atmospheric reduction of Hg(II) competes with deposition, thereby modifying the magnitude and pattern of Hg deposition. Global Hg models have postulated that Hg(II) reduction in the atmosphere occurs through aqueous-phase photoreduction that may take place in clouds. Here we report that experimental rainfall Hg(II) photoreduction rates are much slower than modelled rates. We compute absorption cross sections of Hg(II) compounds and show that fast gas-phase Hg(II) photolysis can dominate atmospheric mercury reduction and lead to a substantial increase in the modelled, global atmospheric Hg lifetime by a factor two. Models with Hg(II) photolysis show enhanced Hg(0) deposition to land, which may prolong recovery of aquatic ecosystems long after Hg emissions are lowered, due to the longer residence time of Hg in soils compared with the ocean. Fast Hg(II) photolysis substantially changes atmospheric Hg dynamics and requires further assessment at regional and local scales
Lipoprotein lipase activity and mass, apolipoprotein C-II mass and polymorphisms of apolipoproteins E and A5 in subjects with prior acute hypertriglyceridaemic pancreatitis
Journal Article; Research Support, Non-U.S. Gov't;BACKGROUND
Severe hypertriglyceridaemia due to chylomicronemia may trigger an acute pancreatitis. However, the basic underlying mechanism is usually not well understood. We decided to analyze some proteins involved in the catabolism of triglyceride-rich lipoproteins in patients with severe hypertriglyceridaemia.
METHODS
Twenty-four survivors of acute hypertriglyceridaemic pancreatitis (cases) and 31 patients with severe hypertriglyceridaemia (controls) were included. Clinical and anthropometrical data, chylomicronaemia, lipoprotein profile, postheparin lipoprotein lipase mass and activity, hepatic lipase activity, apolipoprotein C II and CIII mass, apo E and A5 polymorphisms were assessed.
RESULTS
Only five cases were found to have LPL mass and activity deficiency, all of them thin and having the first episode in childhood. No cases had apolipoprotein CII deficiency. No significant differences were found between the non-deficient LPL cases and the controls in terms of obesity, diabetes, alcohol consumption, drug therapy, gender distribution, evidence of fasting chylomicronaemia, lipid levels, LPL activity and mass, hepatic lipase activity, CII and CIII mass or apo E polymorphisms. However, the SNP S19W of apo A5 tended to be more prevalent in cases than controls (40% vs. 23%, NS).
CONCLUSION
Primary defects in LPL and C-II are rare in survivors of acute hypertriglyceridaemic pancreatitis; lipase activity measurements should be restricted to those having their first episode during childhood.Part of the studies were financed by grants
from the Swedish Research Council and from the King Gustaf V and Queen Victoria Research Fund and by grants from Grupos de Investigacion y Desarrollo Tecnologico de la Junta de Andalucia (Grupo consolidado CTS-
159).Ye
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