639 research outputs found
Radial asymptotics of Lemaitre-Tolman-Bondi dust models
We examine the radial asymptotic behavior of spherically symmetric
Lemaitre-Tolman-Bondi dust models by looking at their covariant scalars along
radial rays, which are spacelike geodesics parametrized by proper length
, orthogonal to the 4-velocity and to the orbits of SO(3). By introducing
quasi-local scalars defined as integral functions along the rays, we obtain a
complete and covariant representation of the models, leading to an initial
value parametrization in which all scalars can be given by scaling laws
depending on two metric scale factors and two basic initial value functions.
Considering regular "open" LTB models whose space slices allow for a diverging
, we provide the conditions on the radial coordinate so that its
asymptotic limit corresponds to the limit as . The "asymptotic
state" is then defined as this limit, together with asymptotic series expansion
around it, evaluated for all metric functions, covariant scalars (local and
quasi-local) and their fluctuations. By looking at different sets of initial
conditions, we examine and classify the asymptotic states of parabolic,
hyperbolic and open elliptic models admitting a symmetry center. We show that
in the radial direction the models can be asymptotic to any one of the
following spacetimes: FLRW dust cosmologies with zero or negative spatial
curvature, sections of Minkowski flat space (including Milne's space), sections
of the Schwarzschild--Kruskal manifold or self--similar dust solutions.Comment: 44 pages (including a long appendix), 3 figures, IOP LaTeX style.
Typos corrected and an important reference added. Accepted for publication in
General Relativity and Gravitatio
Gravitational Charged Perfect Fluid Collapse in Friedmann Universe Models
This paper is devoted to study the gravitational charged perfect fluid
collapse in the Friedmann universe models with cosmological constant. For this
purpose, we assume that the electromagnetic field is so weak that it does not
introduce any distortion into the geometry of the spacetime. The results
obtained from the junction conditions between the Friedmann and the
Reissner-Nordstrm de-Sitter spacetimes are used to solve the field
equations. Further, the singularity structure and mass effects of the
collapsing system on time difference between the formation of apparent horizons
and singularity have been studied. This analysis provides the validity of
Cosmic Censorship Hypothesis. It is found that the electric field affects the
area of apparent horizons and their time of formation.Comment: 17 pages, accepted for publication in Astrophys. Space Sc
Newtonian Analysis of Gravitational Waves from Naked Singularity
Spherical dust collapse generally forms a shell focusing naked singularity at
the symmetric center. This naked singularity is massless. Further the Newtonian
gravitational potential and speed of the dust fluid elements are everywhere
much smaller than unity until the central shell focusing naked singularity
formation if an appropriate initial condition is set up. Although such a
situation is highly relativistic, the analysis by the Newtonian approximation
scheme is available even in the vicinity of the space-time singularity. This
remarkable feature makes the analysis of such singularity formation very easy.
We investigate non-spherical even-parity matter perturbations in this scheme by
complementary using numerical and semi-analytical approaches, and estimate
linear gravitational waves generated in the neighborhood of the naked
singularity by the quadrupole formula. The result shows good agreement with the
relativistic perturbation analysis recently performed by Iguchi et al. The
energy flux of the gravitational waves is finite but the space-time curvature
carried by them diverges.Comment: 23 pages, 8 figure
Minimum black hole mass from colliding Gaussian packets
We study the formation of a black hole in the collision of two Gaussian
packets. Rather than following their dynamical evolution in details, we assume
a horizon forms when the mass function for the two packets becomes larger than
half the flat areal radius, as it would occur in a spherically symmetric
geometry. This simple approximation allows us to determine the existence of a
minimum black hole mass solely related to the width of the packets. We then
comment on the possible physical implications, both in classical and quantum
physics, and models with extra spatial dimensions.Comment: 11 pages, 4 figure
The prognostic significance of low-frequency somatic mutations in metastatic cutaneous melanoma
Background: Little is known about the prognostic significance of somatically mutated genes in metastatic melanoma (MM). We have employed a combined clinical and bioinformatics approach on tumor samples from cutaneous melanoma (SKCM) as part of The Cancer Genome Atlas project (TCGA) to identify mutated genes with potential clinical relevance. Methods: After limiting our DNA sequencing analysis to MM samples (n = 356) and to the CANCER CENSUS gene list, we filtered out mutations with low functional significance (snpEFF). We performed Cox analysis on 53 genes that were mutated in â„3% of samples, and had â„50% difference in incidence of mutations in deceased subjects versus alive subjects. Results: Four genes were potentially prognostic [RAC1, FGFR1, CARD11, CIITA; false discovery rate (FDR) 75% of the samples that exhibited corresponding DNA mutations. The low frequency, UV signature type and RNA expression of the 22 genes in MM samples were confirmed in a separate multi-institution validation cohort (n = 413). An underpowered analysis within a subset of this validation cohort with available patient follow-up (n = 224) showed that somatic mutations in SPEN and RAC1 reached borderline prognostic significance [log-rank favorable (p = 0.09) and adverse (p = 0.07), respectively]. Somatic mutations in SPEN, and to a lesser extent RAC1, were not associated with definite gene copy number or RNA expression alterations. High (>2+) nuclear plus cytoplasmic expression intensity for SPEN was associated with longer melanoma-specific overall survival (OS) compared to lower (†2+) nuclear intensity (p = 0.048). We conclude that expressed somatic mutations in infrequently mutated genes beyond the well-characterized ones (e.g., BRAF, RAS, CDKN2A, PTEN, TP53), such as RAC1 and SPEN, may have prognostic significance in MM
Talented suppliers? Strategic change and innovation in the UK aerospace industry
The 1990s marked the start of extensive re-structuring in the aerospace industry throughout the world. While the ensuing consolidation among prime contractors has been widely researched, the changes affecting the aerospace supply chain have received less attention. This study focuses on the re-structuring taking place within the supply chain of the UK aerospace industry. The findings point to extensive re-structuring. Unlike most earlier studies the lean supply model was found to be a powerful influence, with suppliers moving away from subcontractor status and instead taking on the mantle of âtalentedâ suppliers. While some of the implications of lean supply, in terms of the dynamics of innovation, were not apparent, there were modest signs of increased process innovation on the part of some suppliers
Animal welfare considerations for using large carnivores and guardian dogs as vertebrate biocontrol tools against other animals
Introducing consumptive and non-consumptive effects into food webs can have profound effects on individuals, populations and communities. This knowledge has led to the deliberate use of predation and/or fear of predation as an emerging technique for controlling wildlife. Many now advocate for the intentional use of large carnivores and livestock guardian dogs as more desirable alternatives to traditional wildlife control approaches like fencing, shooting, trapping, or poisoning. However, there has been very little consideration of the animal welfare implications of deliberately using predation as a wildlife management tool. We assess the animal welfare impacts of using dingoes, leopards and guardian dogs as biocontrol tools against wildlife in Australia and South Africa
following the âFive Domainsâ model commonly used to assess other wildlife management tools. Application of this model indicates that large carnivores and guardian dogs cause considerable lethal and non-lethal animal welfare impacts to the individual animals they are intended to control. These impacts are likely similar across different predator-prey systems, but are dependent on specific predator-prey combinations; combinations that result in short chases and quick kills will be rated as less harmful than those that result in long chases and protracted kills. Moreover, these impacts are typically rated greater than those caused by traditional wildlife control techniques. The intentional lethal and non-lethal harms caused by large carnivores and guardian dogs should not be ignored or dismissively assumed to be negligible. A greater understanding of the impacts they impose would benefit from empirical studies of the animal welfare outcomes arising from their use in different contexts
Loop Quantum Gravity: An Inside View
This is a (relatively) non -- technical summary of the status of the quantum
dynamics in Loop Quantum Gravity (LQG). We explain in detail the historical
evolution of the subject and why the results obtained so far are non --
trivial. The present text can be viewed in part as a response to an article by
Nicolai, Peeters and Zamaklar [hep-th/0501114]. We also explain why certain no
go conclusions drawn from a mathematically correct calculation in a recent
paper by Helling et al [hep-th/0409182] are physically incorrect.Comment: 58 pages, no figure
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
- âŠ