964 research outputs found
Lovelock-Lifshitz Black Holes
In this paper, we investigate the existence of Lifshitz solutions in Lovelock
gravity, both in vacuum and in the presence of a massive vector field. We show
that the Lovelock terms can support the Lifshitz solution provided the
constants of the theory are suitably chosen. We obtain an exact black hole
solution with Lifshitz asymptotics of any scaling parameter in both
Gauss-Bonnet and in pure 3rd order Lovelock gravity. If matter is added in the
form of a massive vector field, we also show that Lifshitz solutions in
Lovelock gravity exist; these can be regarded as corrections to Einstein
gravity coupled to this form of matter. For this form of matter we numerically
obtain a broad range of charged black hole solutions with Lifshitz asymptotics,
for either sign of the cosmological constant. We find that these asymptotic
Lifshitz solutions are more sensitive to corrections induced by Lovelock
gravity than are their asymptotic AdS counterparts. We also consider the
thermodynamics of the black hole solutions and show that the temperature of
large black holes with curved horizons is proportional to where is
the critical exponent; this relationship holds for black branes of any size. As
is the case for asymptotic AdS black holes, we find that an extreme black hole
exists only for the case of horizons with negative curvature. We also find that
these Lovelock-Lifshitz black holes have no unstable phase, in contrast to the
Lovelock-AdS case. We also present a class of rotating Lovelock-Lifshitz black
holes with Ricci-flat horizons.Comment: 26 pages, 10 figures, a few references added, typo fixed and some
comments have been adde
Black-hole dynamics in BHT massive gravity
Using an exact Vaidya-type null-dust solution, we study the area and entropy
laws for dynamical black holes defined by a future outer trapping horizon in
(2+1)-dimensional Bergshoeff-Hohm-Townsend (BHT) massive gravity. We consider
the theory admitting a degenerate (anti-)de Sitter vacuum and pure BHT gravity.
It is shown that, while the area of a black hole decreases by the injection of
a null dust with positive energy density in several cases, the Wald-Kodama
dynamical entropy always increases.Comment: 7 pages, 1 figur
Spatially homogeneous Lifshitz black holes in five dimensional higher derivative gravity
We consider spatially homogeneous Lifshitz black hole solutions in five
dimensional higher derivative gravity theories, which can be possible near
horizon geometries of some systems that are interesting in the framework of
gauge/gravity duality. We show the solutions belonging to the nine Bianchi
classes in the pure R^2 gravity. We find that these black holes have zero
entropy at non-zero temperatures and this property is the same as the case of
BTZ black holes in new massive gravity at the critical point. In the most
general quadratic curvature gravity theories, we find new solutions in Bianchi
Type I and Type IX cases.Comment: 15 pages, no figure; v2, refs added, version to appear in JHE
Pathologies in Asymptotically Lifshitz Spacetimes
There has been significant interest in the last several years in studying
possible gravitational duals, known as Lifshitz spacetimes, to anisotropically
scaling field theories by adding matter to distort the asymptotics of an AdS
spacetime. We point out that putative ground state for the most heavily studied
example of such a spacetime, that with a flat spatial section, suffers from a
naked singularity and further point out this singularity is not resolvable by
any known stringy effect. We review the reasons one might worry that
asymptotically Lifshitz spacetimes are unstable and employ the initial data
problem to study the stability of such systems. Rather surprisingly this
question, and even the initial value problem itself, for these spacetimes turns
out to generically not be well-posed. A generic normalizable state will evolve
in such a way to violate Lifshitz asymptotics in finite time. Conversely,
enforcing the desired asymptotics at all times puts strong restrictions not
just on the metric and fields in the asymptotic region but in the deep interior
as well. Generically, even perturbations of the matter field of compact support
are not compatible with the desired asymptotics.Comment: 36 pages, 1 figure, v2: Enhanced discussion of singularity, including
relationship to Gubser's conjecture and singularity in RG flow solution, plus
minor clarification
Absence of p300 induces cellular phenotypic changes characteristic of epithelial to mesenchyme transition
p300 is a transcriptional cofactor and prototype histone acetyltransferase involved in regulating multiple cellular processes. We generated p300 deficient (p300−) cells from the colon carcinoma cell line HCT116 by gene targeting. Comparison of epithelial and mesenchymal proteins in p300− with parental HCT116 cells showed that a number of genes involved in cell and extracellular matrix interactions, typical of ‘epithelial to mesenchyme transition' were differentially regulated at both the RNA and protein level. p300− cells were found to have aggressive ‘cancer' phenotypes, with loss of cell–cell adhesion, defects in cell–matrix adhesion and increased migration through collagen and matrigel. Although migration was shown to be metalloproteinase mediated, these cells actually showed a downregulation or no change in the level of key metalloproteinases, indicating that changes in cellular adhesion properties can be critical for cellular mobility
Boundary Conditions and Unitarity: the Maxwell-Chern-Simons System in AdS_3/CFT_2
We consider the holography of the Abelian Maxwell-Chern-Simons (MCS) system
in Lorentzian three-dimensional asymptotically-AdS spacetimes, and discuss a
broad class of boundary conditions consistent with conservation of the
symplectic structure. As is well-known, the MCS theory contains a massive
sector dual to a vector operator in the boundary theory, and a topological
sector consisting of flat connections dual to U(1) chiral currents; the
boundary conditions we examine include double-trace deformations in these two
sectors, as well as a class of boundary conditions that mix the vector
operators with the chiral currents. We carefully study the symplectic product
of bulk modes and show that almost all such boundary conditions induce
instabilities and/or ghost excitations, consistent with violations of unitarity
bounds in the dual theory.Comment: 50+1 pages, 6 figures, PDFLaTeX; v2: added references, corrected
typo
Changes in Parasite Virulence Induced by the Disruption of a Single Member of the 235 kDa Rhoptry Protein Multigene Family of Plasmodium yoelii
Invasion of the erythrocyte by the merozoites of the malaria parasite is a
complex process involving a range of receptor-ligand interactions. Two protein
families termed Erythrocyte Binding Like (EBL) proteins and Reticulocyte Binding
Protein Homologues (RH) play an important role in host cell recognition by the
merozoite. In the rodent malaria parasite, Plasmodium yoelii,
the 235 kDa rhoptry proteins (Py235) are coded for by a multigene family and are
members of the RH. In P. yoelii Py235 as well as a single
member of EBL have been shown to be key mediators of virulence enabling the
parasite to invade a wider range of host erythrocytes. One member of Py235,
PY01365 is most abundantly transcribed in parasite
populations and the protein specifically binds to erythrocytes and is recognized
by the protective monoclonal antibody 25.77, suggesting a key role of this
particular member in virulence. Recent studies have indicated that overall
levels of Py235 expression are essential for parasite virulence. Here we show
that disruption of PY01365 in the virulent YM line directly
impacts parasite virulence. Furthermore the disruption of
PY01365 leads to a reduction in the number of schizonts
that express members of Py235 that react specifically with the mcAb 25.77.
Erythrocyte binding assays show reduced binding of Py235 to red blood cells in
the PY01365 knockout parasite as compared to YM. While our
results identify PY01365 as a mediator of parasite virulence,
they also confirm that other members of Py235 are able to substitute for
PY01365
String Theory on Warped AdS_3 and Virasoro Resonances
We investigate aspects of holographic duals to time-like warped AdS_3
space-times--which include G\"odel's universe--in string theory. Using
worldsheet techniques similar to those that have been applied to AdS_3
backgrounds, we are able to identify space-time symmetry algebras that act on
the dual boundary theory. In particular, we always find at least one Virasoro
algebra with computable central charge. Interestingly, there exists a dense set
of points in the moduli space of these models in which there is actually a
second commuting Virasoro algebra, typically with different central charge than
the first. We analyze the supersymmetry of the backgrounds, finding related
enhancements, and comment on possible interpretations of these results. We also
perform an asymptotic symmetry analysis at the level of supergravity, providing
additional support for the worldsheet analysis.Comment: 24 pages + appendice
AIDS-associated paracoccidioidomycosis in a patient with a CD4+ T-cell count of 4 cells/mm³
Ribosomal oxygenases are structurally conserved from prokaryotes to humans
2-Oxoglutarate (2OG)-dependent oxygenases have important roles in the regulation of gene expression via demethylation of N-methylated chromatin components1,2 and in the hydroxylation of transcription factors3 and splicing factor proteins4. Recently, 2OG-dependent oxygenases that catalyse hydroxylation of transfer RNA5,6,7 and ribosomal proteins8 have been shown to be important in translation relating to cellular growth, TH17-cell differentiation and translational accuracy9,10,11,12. The finding that ribosomal oxygenases (ROXs) occur in organisms ranging from prokaryotes to humans8 raises questions as to their structural and evolutionary relationships. In Escherichia coli, YcfD catalyses arginine hydroxylation in the ribosomal protein L16; in humans, MYC-induced nuclear antigen (MINA53; also known as MINA) and nucleolar protein 66 (NO66) catalyse histidine hydroxylation in the ribosomal proteins RPL27A and RPL8, respectively. The functional assignments of ROXs open therapeutic possibilities via either ROX inhibition or targeting of differentially modified ribosomes. Despite differences in the residue and protein selectivities of prokaryotic and eukaryotic ROXs, comparison of the crystal structures of E. coli YcfD and Rhodothermus marinus YcfD with those of human MINA53 and NO66 reveals highly conserved folds and novel dimerization modes defining a new structural subfamily of 2OG-dependent oxygenases. ROX structures with and without their substrates support their functional assignments as hydroxylases but not demethylases, and reveal how the subfamily has evolved to catalyse the hydroxylation of different residue side chains of ribosomal proteins. Comparison of ROX crystal structures with those of other JmjC-domain-containing hydroxylases, including the hypoxia-inducible factor asparaginyl hydroxylase FIH and histone Nε-methyl lysine demethylases, identifies branch points in 2OG-dependent oxygenase evolution and distinguishes between JmjC-containing hydroxylases and demethylases catalysing modifications of translational and transcriptional machinery. The structures reveal that new protein hydroxylation activities can evolve by changing the coordination position from which the iron-bound substrate-oxidizing species reacts. This coordination flexibility has probably contributed to the evolution of the wide range of reactions catalysed by oxygenases
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