208 research outputs found
Connection between horizons and algebraic type
We study connections between both event and quasilocal horizons and the
algebraic type of the Weyl tensor. The relation regarding spacelike future
outer trapping horizon is analysed in four dimensions using double-null
foliation.Comment: 4 pages, to appear in Proceedings of Spanish relativity meeting 201
Charged AdS Black Holes and Catastrophic Holography
We compute the properties of a class of charged black holes in anti-de Sitter
space-time, in diverse dimensions. These black holes are solutions of
consistent Einstein-Maxwell truncations of gauged supergravities, which are
shown to arise from the inclusion of rotation in the transverse space. We
uncover rich thermodynamic phase structures for these systems, which display
classic critical phenomena, including structures isomorphic to the van der
Waals-Maxwell liquid-gas system. In that case, the phases are controlled by the
universal `cusp' and `swallowtail' shapes familiar from catastrophe theory. All
of the thermodynamics is consistent with field theory interpretations via
holography, where the dual field theories can sometimes be found on the world
volumes of coincident rotating branes.Comment: 19 pages, revtex, psfig, 6 multicomponent figures, typos, references
and a few remarks have been repaired, and adde
Strong Cosmic Censorship and Causality Violation
We investigate the instability of the Cauchy horizon caused by causality
violation in the compact vacuum universe with the topology , which Moncrief and Isenberg considered. We show that if
the occurrence of curvature singularities are restricted to the boundary of
causality violating region, the whole segments of the boundary become curvature
singularities. This implies that the strong cosmic censorship holds in the
spatially compact vacuum space-time in the case of the causality violation.
This also suggests that causality violation cannot occur for a compact
universe.Comment: corrected version, 8 pages, one eps figure is include
Surface-Gravity Inequalities and Generic Conditions for Strong Cosmic Censorship
Transforming Penrose's intuitive picture of a strong cosmic censorship
principle, that generically forbids the appearance of locally naked space-time
singularities, into a formal mathematical proof, remains at present, one of the
most outstanding unsolved mathematical problems from the theory of
gravitational collapse. Part of the difficulty lies in the fact that we do not
possess yet a clear-cut understanding of the hypothesis needed for the
establishment of some sort of strong cosmic censorship theorem. What we have is
a selected list of solutions, which at first sight seem to go against cosmic
censorship, but at the end they fail in some way. However, the space of
solutions of Einstein's field equations is vast. In this article, we plan to
increase one's intuition by establishing a link between certain inequalities
for Cauchy-horizon stability and a set of generic conditions, such as a
reasonable equation of state--which determines whether the space-time is
asymptotically flat or not, an energy condition, and an hypothesis over the
class of metrics on which Einstein's field equations ought to be solved to
ensure strong cosmic censorship inside black-holes. With these tools in hand we
examine the Cauchy-horizon stability of the theory created by Born and
Infeld--whose action principle has been used as a prototype in superstring
theory, and the singularity-free Bardeen's black-hole model.Comment: 6 pages, 2 figures(type eps), REVTeX
Pair of accelerated black holes in a de Sitter background: the dS C-metric
Following the work of Kinnersley and Walker for flat spacetimes, we have
analyzed the anti-de Sitter C-metric in a previous paper. In the de Sitter
case, Podolsky and Griffiths have established that the de Sitter C-metric (dS
C-metric) found by Plebanski and Demianski describes a pair of accelerated
black holes in the dS background with the acceleration being provided (in
addition to the cosmological constant) by a strut that pushes away the two
black holes or, alternatively, by a string that pulls them. We extend their
analysis mainly in four directions. First, we draw the Carter-Penrose diagrams
of the massless uncharged dS C-metric, of the massive uncharged dS C-metric and
of the massive charged dS C-metric. These diagrams allow us to clearly identify
the presence of two dS black holes and to conclude that they cannot interact
gravitationally. Second, we revisit the embedding of the dS C-metric in the 5D
Minkowski spacetime and we represent the motion of the dS C-metric origin in
the dS 4-hyperboloid as well as the localization of the strut. Third, we
comment on the physical properties of the strut that connects the two black
holes. Finally, we find the range of parameters that correspond to non-extreme
black holes, extreme black holes, and naked particles.Comment: 11 pages, 11 figures (RevTeX4). Published version: references adde
Impacts of dietary calcium, phytate, and phytase on inositol hexakisphosphate degradation and inositol phosphate release in different segments of digestive tract of broilers
A total of 720 straight-run Heritage
56 M Ă— fast feathering Cobb 500F broiler chickens was
fed from 11 to 13 d of age to determine the impacts
of dietary calcium (Ca), phytate phosphorus (PP), and
phytase concentrations on inositol phosphate (IP3–6)
profile in different digestive tract (GI) segments. The
experiment was a 2 Ă— 2 Ă— 3 randomized block design
with 2 Ca (0.7 and 1.0%) and 2 PP (0.23 and 0.34%)
concentrations and 3 doses of Buttiauxella sp. phytase
(0, 500, and 1,000 FTU/kg). The experiment was replicated
in time (block) with 3 replicates per treatment
(Trt) of 10 birds per block. Concentrations of IP3–6 in
the crop, proventriculus (Prov) plus (+) gizzard (Giz),
and distal ileum, as well as the ileal IP6 and P disappearance
were determined at 13 d of age. The detrimental
impact of Ca on IP6 and P disappearance was
observed only in the ileum, where 11% reduction in both
IP6 and P disappearance was seen when Ca increased from 0.7 to 1.0% (P < 0.05). Higher IP5 and IP6 concentrations
were seen in both the crop and Prov+Giz
at 0.34% PP as compared to birds fed to 0.23% PP
diets, regardless of Ca or phytase (P < 0.05), whereas
IP3 and IP4 concentrations were not affected by PP
(P > 0.05). Inclusion of phytase, at both 500 and 1,000
FTU/kg, resulted in lower IP6 and the accumulation of
lower IP ester (IP3–5) concentrations in all GI segments
(P < 0.05). Improved IP6 and P disappearance was seen
as a result of phytase inclusion, despite the degree of
improvement affected by PP (P < 0.05). On average,
5.5 and 6.7 times improvement in IP6 was observed
with 500 and 1,000 FTU phytase/kg inclusion, respectively,
resulting in 41 and 64% greater P digestibility,
respectively. In conclusion, phytase can effectively degrade
IP6 to lower esters and increase P utilization.
However, the efficacy of phytase can be affected by diet
Ca and PP concentrations.The Butti-auxella Axtra (R) PHY and partial financial support from Danisco Animal Nutrition, DuPont Industrial Bio-sciences.http://ps.oxfordjournals.orgam2018Animal and Wildlife Science
Biomarker-guided sequential targeted therapies to overcome therapy resistance in rapidly evolving highly aggressive mammary tumors
Combinatorial targeted therapies are more effective in treating cancer by blocking by-pass mechanisms or inducing synthetic lethality. However, their clinical application is hampered by resistance and toxicity. To meet this important challenge, we developed and tested a novel concept of biomarker-guided sequential applications of various targeted therapies using ErbB2-overexpressing/PTEN-low, highly aggressive breast cancer as our model. Strikingly, sustained activation of ErbB2 and downstream pathways drives trastuzumab resistance in both PTEN-low/trastuzumab-resistant breast cancers from patients and mammary tumors with intratumoral heterogeneity from genetically-engineered mice. Although lapatinib initially inhibited trastuzumab-resistant mouse tumors, tumors by-passed the inhibition by activating the PI3K/mTOR signaling network as shown by the quantitative protein arrays. Interestingly, activation of the mTOR pathway was also observed in neoadjuvant lapatinib-treated patients manifesting lapatinib resistance. Trastuzumab + lapatinib resistance was effectively overcome by sequential application of a PI3K/mTOR dual kinase inhibitor (BEZ235) with no significant toxicity. However, our p-RTK array analysis demonstrated that BEZ235 treatment led to increased ErbB2 expression and phosphorylation in genetically-engineered mouse tumors and in 3-D, but not 2-D, culture, leading to BEZ235 resistance. Mechanistically, we identified ErbB2 protein stabilization and activation as a novel mechanism of BEZ235 resistance, which was reversed by subsequent treatment with lapatinib + BEZ235 combination. Remarkably, this sequential application of targeted therapies guided by biomarker changes in the tumors rapidly evolving resistance doubled the life-span of mice bearing exceedingly aggressive tumors. This fundamentally novel approach of using targeted therapies in a sequential order can effectively target and reprogram the signaling networks in cancers evolving resistance during treatment. © 2014 IBCB, SIBS, CAS All rights reserved
Domain Wall Spacetimes: Instability of Cosmological Event and Cauchy Horizons
The stability of cosmological event and Cauchy horizons of spacetimes
associated with plane symmetric domain walls are studied. It is found that both
horizons are not stable against perturbations of null fluids and massless
scalar fields; they are turned into curvature singularities. These
singularities are light-like and strong in the sense that both the tidal forces
and distortions acting on test particles become unbounded when theses
singularities are approached.Comment: Latex, 3 figures not included in the text but available upon reques
The Similarity Hypothesis in General Relativity
Self-similar models are important in general relativity and other fundamental
theories. In this paper we shall discuss the ``similarity hypothesis'', which
asserts that under a variety of physical circumstances solutions of these
theories will naturally evolve to a self-similar form. We will find there is
good evidence for this in the context of both spatially homogenous and
inhomogeneous cosmological models, although in some cases the self-similar
model is only an intermediate attractor. There are also a wide variety of
situations, including critical pheneomena, in which spherically symmetric
models tend towards self-similarity. However, this does not happen in all cases
and it is it is important to understand the prerequisites for the conjecture.Comment: to be submitted to Gen. Rel. Gra
Driven to excess? Linking calling, character and the (mis)behaviour of marketers
We are presently at a point of unique circumstantial convergence where recession, an increased emphasis on business ethics, and marketer’s reluctance to accept shifting social agendas have combined to identify the need for a new approach to marketing. Using concepts from the human resources, marketing and psychology literatures, and especially Erich Fromm’s ideas concerning economic character, this paper posits that marketers – as a professional community – are driven to promote consumerist outcomes; victims of an automaton amalgam of calling and character. The analysis suggests the vulnerability of both marketer and consumer are mutually reinforcing and that we need, somehow, to break this damaging cycle of dependence. We know little, however, about how marketers think and feel about their discipline, so this paper also promotes an agenda for marketer behaviour research, as a countervailing balance to a currently disproportionate focus on the consumer
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