1,205 research outputs found
Spherically Symmetric Gravitational Collapse of General Fluids
We express Einstein's field equations for a spherically symmetric ball of
general fluid such that they are conducive to an initial value problem. We show
how the equations reduce to the Vaidya spacetime in a non-null coordinate
frame, simply by designating specific equations of state. Furthermore, this
reduces to the Schwarzschild spacetime when all matter variables vanish. We
then describe the formulation of an initial value problem, whereby a general
fluid ball with vacuum exterior is established on an initial spacelike slice.
As the system evolves, the fluid ball collapses and emanates null radiation
such that a region of Vaidya spacetime develops. Therefore, on any subsequent
spacelike slice there exists three regions; general fluid, Vaidya and
Schwarzschild, all expressed in a single coordinate patch with two
free-boundaries determined by the equations. This implies complicated matching
schemes are not required at the interfaces between the regions, instead, one
simply requires the matter variables tend to the appropriate equations of
state. We also show the reduction of the system of equations to the static
cases, and show staticity necessarily implies zero ``heat flux''. Furthermore,
the static equations include a generalization of the Tolman-Oppenheimer-Volkoff
equations for hydrostatic equilibrium to include anisotropic stresses in
general coordinates.Comment: 11 pages, 3 figures, submitted to Phys. Rev.
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ISABELLE full scale dipoles
Data are presented on the various cosine theta type magnet models constructed at BNL in the development of ring magnets for ISABELLE, a pair of intersecting 200 GeV proton accelerating storage rings. The rings are to be filled with 30 GeV protons from the AGS and then accelerated to 200 GeV. The acceleration period is a 120 sec ramp from approximately 0.5 T to 4 T. The effect of mechanical precompression on training was studied by varying the interference fit between the coil (ISA IV) and its iron shield. The results were used to optimize the mechanical design of the full-size magnet models. (auth
The Tensor-Vector-Scalar theory and its cosmology
Over the last few decades, astronomers and cosmologists have accumulated vast
amounts of data clearly demonstrating that our current theories of fundamental
particles and of gravity are inadequate to explain the observed discrepancy
between the dynamics and the distribution of the visible matter in the
Universe. The Modified Newtonian Dynamics (MOND) proposal aims at solving the
problem by postulating that Newton's second law of motion is modified for
accelerations smaller than ~10^{-10}m/s^2. This simple amendment, has had
tremendous success in explaining galactic rotation curves. However, being
non-relativistic, it cannot make firm predictions for cosmology.
A relativistic theory called Tensor-Vector-Scalar (TeVeS) has been proposed
by Bekenstein building on earlier work of Sanders which has a MOND limit for
non-relativistic systems.
In this article I give a short introduction to TeVeS theory and focus on its
predictions for cosmology as well as some non-cosmological studies.Comment: 44 pages, topical review for Classical and Quantum Gravit
Plasma metabolite profiles in children with current asthma
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146270/1/cea13183.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146270/2/cea13183_am.pd
Diaspirin-crosslinked hemoglobin reduces blood transfusion in noncardiac surgery: a multicenter, randomized, controlled, double-blinded trial.
UNLABELLED: In this randomized, prospective, double-blinded clinical trial, we sought to investigate whether diaspirin-crosslinked hemoglobin (DCLHb) can reduce the perioperative use of allogeneic blood transfusion. One-hundred-eighty-one elective surgical patients were enrolled at 19 clinical sites from 1996 to 1998. Selection criteria included anticipated transfusion of 2-4 blood units, aortic repair, and major joint or abdomino-pelvic surgery. Once a decision to transfuse had been made, patients received initially up to 3 250-mL infusions of 10% DCLHb (n = 92) or 3 U of packed red blood cells (PRBCs) (n = 89). DCLHb was infused during a 36-h perioperative window. On the day of surgery, 58 of 92 (64%; confidence interval [CI], 54%-74%) DCLHb-treated patients received no allogeneic PRBC transfusions. On Day 1, this number was 44 of 92 (48%; CI, 37%-58%) and decreased further until Day 7, when it was 21 of 92 (23%; CI, 15%-33%). During the 7-day period, 2 (1-4) units of PRBC per patient were used in the DCLHb group compared with 3 (2-4) units in the control patients (P = 0.002; medians and 25th and 75th percentiles). Mortality (4% and 3%, respectively) and incidence of suffering at least one serious adverse event (21% and 15%, respectively) were similar in DCLHb and PRBC groups. The incidence of jaundice, urinary side effects, and pancreatitis were more frequent in DCLHb patients. The study was terminated early because of safety concerns. Whereas the side-effect profile of modified hemoglobin solutions needs to be improved, our data show that hemoglobin solutions can be effective at reducing exposure to allogeneic blood for elective surgery.
IMPLICATIONS: In a randomized, double-blinded red blood cell controlled, multicenter trial, diaspirin-crosslinked hemoglobin spared allogeneic transfusion in 23% of patients undergoing elective noncardiac surgery. The observed side-effect profile indicates a need for improvement in hemoglobin development
Observational constraints on inhomogeneous cosmological models without dark energy
It has been proposed that the observed dark energy can be explained away by
the effect of large-scale nonlinear inhomogeneities. In the present paper we
discuss how observations constrain cosmological models featuring large voids.
We start by considering Copernican models, in which the observer is not
occupying a special position and homogeneity is preserved on a very large
scale. We show how these models, at least in their current realizations, are
constrained to give small, but perhaps not negligible in certain contexts,
corrections to the cosmological observables. We then examine non-Copernican
models, in which the observer is close to the center of a very large void.
These models can give large corrections to the observables which mimic an
accelerated FLRW model. We carefully discuss the main observables and tests
able to exclude them.Comment: 27 pages, 7 figures; invited contribution to CQG special issue
"Inhomogeneous Cosmological Models and Averaging in Cosmology". Replaced to
match the improved version accepted for publication. Appendix B and
references adde
MWA rapid follow-up of gravitational wave transients: prospects for detecting prompt radio counterparts
We present and evaluate the prospects for detecting coherent radio
counterparts to gravitational wave (GW) events using Murchison Widefield Array
(MWA) triggered observations. The MWA rapid-response system, combined with its
buffering mode ( minutes negative latency), enables us to catch any
radio signals produced from seconds prior to hours after a binary neutron star
(BNS) merger. The large field of view of the MWA ( at
120\,MHz) and its location under the high sensitivity sky region of the
LIGO-Virgo-KAGRA (LVK) detector network, forecast a high chance of being
on-target for a GW event. We consider three observing configurations for the
MWA to follow up GW BNS merger events, including a single dipole per tile, the
full array, and four sub-arrays. We then perform a population synthesis of BNS
systems to predict the radio detectable fraction of GW events using these
configurations. We find that the configuration with four sub-arrays is the best
compromise between sky coverage and sensitivity as it is capable of placing
meaningful constraints on the radio emission from 12.6\% of GW BNS detections.
Based on the timescales of four BNS merger coherent radio emission models, we
propose an observing strategy that involves triggering the buffering mode to
target coherent signals emitted prior to, during or shortly following the
merger, which is then followed by continued recording for up to three hours to
target later time post-merger emission. We expect MWA to trigger on
BNS merger events during the LVK O4 observing run, which
could potentially result in two detections of predicted coherent emission.Comment: Accepted for publication in PAS
Two New Loci for Body-Weight Regulation Identified in a Joint Analysis of Genome-Wide Association Studies for Early-Onset Extreme Obesity in French and German Study Groups
Meta-analyses of population-based genome-wide association studies (GWAS) in adults have recently led to the detection of new genetic loci for obesity. Here we aimed to discover additional obesity loci in extremely obese children and adolescents. We also investigated if these results generalize by estimating the effects of these obesity loci in adults and in population-based samples including both children and adults. We jointly analysed two GWAS of 2,258 individuals and followed-up the best, according to lowest p-values, 44 single nucleotide polymorphisms (SNP) from 21 genomic regions in 3,141 individuals. After this DISCOVERY step, we explored if the findings derived from the extremely obese children and adolescents (10 SNPs from 5 genomic regions) generalized to (i) the population level and (ii) to adults by genotyping another 31,182 individuals (GENERALIZATION step). Apart from previously identified FTO, MC4R, and TMEM18, we detected two new loci for obesity: one in SDCCAG8 (serologically defined colon cancer antigen 8 gene; p = 1.85610 x 10(-8) in the DISCOVERY step) and one between TNKS (tankyrase, TRF1-interacting ankyrin-related ADP-ribose polymerase gene) and MSRA (methionine sulfoxide reductase A gene; p = 4.84 x 10(-7)), the latter finding being limited to children and adolescents as demonstrated in the GENERALIZATION step. The odds ratios for early-onset obesity were estimated at similar to 1.10 per risk allele for both loci. Interestingly, the TNKS/MSRA locus has recently been found to be associated with adult waist circumference. In summary, we have completed a meta-analysis of two GWAS which both focus on extremely obese children and adolescents and replicated our findings in a large followed-up data set. We observed that genetic variants in or near FTO, MC4R, TMEM18, SDCCAG8, and TNKS/MSRA were robustly associated with early-onset obesity. We conclude that the currently known major common variants related to obesity overlap to a substantial degree between children and adults
Gravitational Waves From Known Pulsars: Results From The Initial Detector Era
We present the results of searches for gravitational waves from a large selection of pulsars using data from the most recent science runs (S6, VSR2 and VSR4) of the initial generation of interferometric gravitational wave detectors LIGO (Laser Interferometric Gravitational-wave Observatory) and Virgo. We do not see evidence for gravitational wave emission from any of the targeted sources but produce upper limits on the emission amplitude. We highlight the results from seven young pulsars with large spin-down luminosities. We reach within a factor of five of the canonical spin-down limit for all seven of these, whilst for the Crab and Vela pulsars we further surpass their spin-down limits. We present new or updated limits for 172 other pulsars (including both young and millisecond pulsars). Now that the detectors are undergoing major upgrades, and, for completeness, we bring together all of the most up-to-date results from all pulsars searched for during the operations of the first-generation LIGO, Virgo and GEO600 detectors. This gives a total of 195 pulsars including the most recent results described in this paper.United States National Science FoundationScience and Technology Facilities Council of the United KingdomMax-Planck-SocietyState of Niedersachsen/GermanyAustralian Research CouncilInternational Science Linkages program of the Commonwealth of AustraliaCouncil of Scientific and Industrial Research of IndiaIstituto Nazionale di Fisica Nucleare of ItalySpanish Ministerio de Economia y CompetitividadConselleria d'Economia Hisenda i Innovacio of the Govern de les Illes BalearsNetherlands Organisation for Scientific ResearchPolish Ministry of Science and Higher EducationFOCUS Programme of Foundation for Polish ScienceRoyal SocietyScottish Funding CouncilScottish Universities Physics AllianceNational Aeronautics and Space AdministrationOTKA of HungaryLyon Institute of Origins (LIO)National Research Foundation of KoreaIndustry CanadaProvince of Ontario through the Ministry of Economic Development and InnovationNational Science and Engineering Research Council CanadaCarnegie TrustLeverhulme TrustDavid and Lucile Packard FoundationResearch CorporationAlfred P. Sloan FoundationAstronom
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