1,618 research outputs found
Black holes and neutron stars in the generalized tensor-vector-scalar theory
Bekenstein's Tensor-Vector-Scalar (TeVeS) theory has had considerable success
as a relativistic theory of Modified Newtonian Dynamics (MoND). However, recent
work suggests that the dynamics of the theory are fundamentally flawed and
numerous authors have subsequently begun to consider a generalization of TeVeS
where the vector field is given by an Einstein-Aether action. Herein, I develop
strong-field solutions of the generalized TeVeS theory, in particular exploring
neutron stars as well as neutral and charged black holes. I find that the
solutions are identical to the neutron star and black hole solutions of the
original TeVeS theory, given a mapping between the parameters of the two
theories, and hence provide constraints on these values of the coupling
constants. I discuss the consequences of these results in detail including the
stability of such spacetimes as well as generalizations to more complicated
geometries.Comment: Accepted for publication in Physical Review
Mapping the Universe Expansion: Enabling percent-level measurements of the Hubble Constant with a single binary neutron-star merger detection
The joint observation of the gravitational-wave and electromagnetic signal from the binary neutron-star merger GW170817 allowed for a new independent measurement of the Hubble constant , albeit with an uncertainty of about 15\% at 1. Observations of similar sources with a network of future detectors will allow for more precise measurements of . These, however, are currently largely limited by the intrinsic degeneracy between the luminosity distance and the inclination of the source in the gravitational-wave signal. We show that the higher-order modes in gravitational waves can be used to break this degeneracy in astrophysical parameter estimation in both the inspiral and post-merger phases of a neutron star merger. We show that for systems at distances similar to GW170817, this method enables percent-level measurements of with a single detection. This would permit the study of time variations and spatial anisotropies of with unprecedented precision. We investigate how different network configurations affect measurements of , and discuss the implications in terms of science drivers for the proposed 2.5- and third-generation gravitational-wave detectors. Finally, we show that the precision of measured with these future observatories will be solely limited by redshift measurements of electromagnetic counterparts
Induction of DR\IA antigens in human liver allografts: An immunocytochemical and clinicopathologic analysis of twenty failed grafts
Twenty failed human liver allograft specimens obtained at the time of retransplantation procedures were studied using a panel of monoclonal antibodies (T11, T4, T8, NK, B1, OKM1, OKM5, Ia, DR). A clinicopathologic analysis was used to distinguish between graft failures secondary to rejection (n=10) and those due, at least in part, to other causes (n=10). T lymphocytes constituted the major infiltrating cellular population in the liver in rejection cases, but significant numbers of B cells and monocytes/macrophages were present also. Following transplantation, but not before, the bile duct epithelium, as well as portal and central vein and hepatic artery endothelium expressed DR/Ia antigens. These structures are preferential targets of the rejection reaction. The selective destruction of bile ducts in livers undergoing rejection was manifested in these patients by striking elevations of serum gamma glutamyl transpeptidase (GGTP) activity, a marker of biliary epithelial damage. The induced expression of DR/Ia antigens on structures targeted for immune destruction may be an important event in the pathogenesis of liver allograft rejection. © 1985 by The Williams and Wilkins Co
Pleiotropy of FRIGIDA enhances the potential for multivariate adaptation.
An evolutionary response to selection requires genetic variation; however, even if it exists, then the genetic details of the variation can constrain adaptation. In the simplest case, unlinked loci and uncorrelated phenotypes respond directly to multivariate selection and permit unrestricted paths to adaptive peaks. By contrast, 'antagonistic' pleiotropic loci may constrain adaptation by affecting variation of many traits and limiting the direction of trait correlations to vectors that are not favoured by selection. However, certain pleiotropic configurations may improve the conditions for adaptive evolution. Here, we present evidence that the Arabidopsis thaliana gene FRI (FRIGIDA) exhibits 'adaptive' pleiotropy, producing trait correlations along an axis that results in two adaptive strategies. Derived, low expression FRI alleles confer a 'drought escape' strategy owing to fast growth, low water use efficiency and early flowering. By contrast, a dehydration avoidance strategy is conferred by the ancestral phenotype of late flowering, slow growth and efficient water use during photosynthesis. The dehydration avoidant phenotype was recovered when genotypes with null FRI alleles were transformed with functional alleles. Our findings indicate that the well-documented effects of FRI on phenology result from differences in physiology, not only a simple developmental switch
Gravitational-Wave Cosmology across 29 Decades in Frequency
Quantum fluctuations of the gravitational field in the early Universe, amplified by inflation, produce a primordial gravitational-wave background across a broad frequency band. We derive constraints on the spectrum of this gravitational radiation, and hence on theories of the early Universe, by combining experiments that cover 29 orders of magnitude in frequency. These include Planck observations of cosmic microwave background temperature and polarization power spectra and lensing, together with baryon acoustic oscillations and big bang nucleosynthesis measurements, as well as new pulsar timing array and ground-based interferometer limits. While individual experiments constrain the gravitational-wave energy density in specific frequency bands, the combination of experiments allows us to constrain cosmological parameters, including the inflationary spectral index nt and the tensor-to-scalar ratio r. Results from individual experiments include the most stringent nanohertz limit of the primordial background to date from the Parkes Pulsar Timing Array, ΩGW(f)\u3c2.3×10−10. Observations of the cosmic microwave background alone limit the gravitational-wave spectral index at 95% confidence to nt≲5 for a tensor-to-scalar ratio of r=0.11. However, the combination of all the above experiments limits nt\u3c0.36. Future Advanced LIGO observations are expected to further constrain nt\u3c0.34 by 2020. When cosmic microwave background experiments detect a nonzero r, our results will imply even more stringent constraints on nt and, hence, theories of the early Universe
Gravitational waves from Sco X-1: A comparison of search methods and prospects for detection with advanced detectors
The low-mass X-ray binary Scorpius X-1 (Sco X-1) is potentially the most
luminous source of continuous gravitational-wave radiation for interferometers
such as LIGO and Virgo. For low-mass X-ray binaries this radiation would be
sustained by active accretion of matter from its binary companion. With the
Advanced Detector Era fast approaching, work is underway to develop an array of
robust tools for maximizing the science and detection potential of Sco X-1. We
describe the plans and progress of a project designed to compare the numerous
independent search algorithms currently available. We employ a mock-data
challenge in which the search pipelines are tested for their relative
proficiencies in parameter estimation, computational efficiency, robust- ness,
and most importantly, search sensitivity. The mock-data challenge data contains
an ensemble of 50 Scorpius X-1 (Sco X-1) type signals, simulated within a
frequency band of 50-1500 Hz. Simulated detector noise was generated assuming
the expected best strain sensitivity of Advanced LIGO and Advanced VIRGO ( Hz). A distribution of signal amplitudes was then
chosen so as to allow a useful comparison of search methodologies. A factor of
2 in strain separates the quietest detected signal, at
strain, from the torque-balance limit at a spin frequency of 300 Hz, although
this limit could range from (25 Hz) to (750 Hz) depending on the unknown frequency of Sco X-1. With future
improvements to the search algorithms and using advanced detector data, our
expectations for probing below the theoretical torque-balance strain limit are
optimistic.Comment: 33 pages, 11 figure
Metabolite and Lipid Biomarkers Associated With Intraocular Pressure and Inner Retinal Morphology: ¹H NMR Spectroscopy Results From the UK Biobank
Purpose: The purpose of this study was to assess metabolites associated with intraocular pressure (IOP) and inner retina structure. / Methods: We cross-sectionally assessed 168 non-fasting plasma metabolites measured by nuclear magnetic resonance (NMR) spectroscopy with IOP (n = 28,195), macular retinal nerve fiber layer thickness (mRNFL; n = 10,584), and macular ganglion cell inner plexiform layer thickness (mGCIPL; n = 10,554) in the UK Biobank. We used multiple linear regression models adjusting for various covariates with probit-transformed metabolite levels as predictors for each outcome. Each estimate represents the difference in outcome variable per standard deviation increase in the probit-transformed metabolite values. We used the number of effective (NEF) tests and false discovery rate (FDR) to adjust for multiple comparisons for metabolites and metabolite classes, respectively. / Results: In individual metabolite analysis, multiple amino acids, especially branched-chain amino acids, were associated with lower IOP (-0.12 mm Hg; 95% confidence interval = -0.16 to -0.07; NEF = 2.7E-05). Albumin, 3 hydroxybutyrate, lactate, and several lipids were associated with higher IOP (range = 0.07 to 0.18 mm Hg, NEF = ≤ 0.039). In IOP-adjusted analyses, five HDL-related metabolites were associated with thinner mRNFL (-0.15 microns for all metabolites, NEF = ≤ 0.027), whereas five LDL-related metabolites were associated with thicker mGCIPL (range = 0.17 to 0.20 microns; NEF = ≤ 0.044). In metabolite class analysis, the lipid components of lipoproteins (cholesterol, triglycerides, etc.) were not associated with our outcomes (FDR > 0.2 for all); yet multiple lipoproteins were significantly (FDR < 0.05) associated with all outcomes. / Conclusions: Branched-chain amino acids were associated with lower IOP, HDL metabolites were associated with thinner mRNFL, and LDL metabolites were associated with thicker mGCIPL
Improving pulsar-timing solutions through dynamic pulse fitting
Precision pulsar timing is integral to the detection of the nanohertz
stochastic gravitational-wave background as well as understanding the physics
of neutron stars. Conventional pulsar timing often uses fixed time and
frequency-averaged templates to determine the pulse times of arrival, which can
lead to reduced accuracy when the pulse profile evolves over time. We
illustrate a dynamic timing method that fits each observing epoch using basis
functions. By fitting each epoch separately, we allow for the evolution of the
pulse shape epoch to epoch. We apply our method to PSR J11035403 and
demonstrate that it undergoes mode changing, making it the fourth millisecond
pulsar to exhibit such behaviour. Our method, which is able to identify and
time a single mode, yields a timing solution with a root-mean-square error of
1.343 , a factor of 1.78 improvement over template fitting on
both modes. In addition, the white-noise amplitude is reduced 4.3 times,
suggesting that fitting the full data set causes the mode changing to be
incorrectly classified as white noise. This reduction in white noise boosts the
signal-to-noise ratio of a gravitational-wave background signal for this
particular pulsar by 32%. We discuss the possible applications for this method
of timing to study pulsar magnetospheres and further improve the sensitivity of
searches for nanohertz gravitational waves.Comment: Accepted in MNRAS, 8 pages, 8 figure
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