1,782 research outputs found
Three-dimensional shapelets and an automated classification scheme for dark matter haloes
We extend the two-dimensional Cartesian shapelet formalism to d-dimensions.
Concentrating on the three-dimensional case, we derive shapelet-based equations
for the mass, centroid, root-mean-square radius, and components of the
quadrupole moment and moment of inertia tensors. Using cosmological N-body
simulations as an application domain, we show that three-dimensional shapelets
can be used to replicate the complex sub-structure of dark matter halos and
demonstrate the basis of an automated classification scheme for halo shapes. We
investigate the shapelet decomposition process from an algorithmic viewpoint,
and consider opportunities for accelerating the computation of shapelet-based
representations using graphics processing units (GPUs).Comment: 19 pages, 11 figures, accepted for publication in MNRA
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.
Volumetric and anatomical MRI for hypoxic-ischemic encephalopathy: relationship to hypothermia therapy and neurosensory impairments.
OBJECTIVE: To relate volumetric magnetic resonance imaging (MRI) findings to hypothermia therapy and neurosensory impairments.
STUDY DESIGN: Newborns \u3e or =36 weeks\u27 gestation with hypoxic-ischemic encephalopathy who participated in the National Institute of Child Health and Human Development hypothermia randomized trial at our center were eligible. We determined the relationship between hypothermia treatment and usual care (control) to absolute and relative cerebral tissue volumes. Furthermore, we correlated brain volumes with death or neurosensory impairments at 18 to 22 months.
RESULT: Both treatment groups were comparable before randomization. Total brain tissue volumes did not differ in relation to treatment assignment. However, relative volumes of subcortical white matter were significantly larger in hypothermia-treated than control infants. Furthermore, relative total brain volumes correlated significantly with death or neurosensory impairments. Relative volumes of the cortical gray and subcortical white matter also correlated significantly with Bayley Scales psychomotor development index.
CONCLUSION: Selected volumetric MRI findings correlated with hypothermia therapy and neurosensory impairments. Larger studies using MRI brain volumes as a secondary outcome measure are needed
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
Epstein - Barr virus latent membrane protein 1 suppresses reporter activity through modulation of promyelocytic leukemia protein-nuclear bodies
The Epstein-Barr virus (EBV) encoded Latent Membrane Protein 1 (LMP1) has been shown to increase the expression of promyelocytic leukemia protein (PML) and the immunofluorescent intensity of promyelocytic leukemia nuclear bodies (PML NBs). PML NBs have been implicated in the modulation of transcription and the association of reporter plasmids with PML NBs has been implicated in repression of reporter activity. Additionally, repression of various reporters in the presence of LMP1 has been noted. This study demonstrates that LMP1 suppresses expression of reporter activity in a dose responsive manner and corresponds with the LMP1 induced increase in PML NB intensity. Disruption of PML NBs with arsenic trioxide or a PML siRNA restores reporter activity. These data offer an explanation for previously conflicting data on LMP1 signaling and calls attention to the possibility of false-positives and false-negatives when using reporter assays as a research tool in cells expressing LMP1
Reversible binding of platelet-derived growth factor-AA, -AB, and -BB isoforms to a similar site on the "slow" and "fast" conformations of alpha 2-macroglobulin.
The mechanism by which the platelet-derived growth factor (PDGF)-binding protein, alpha 2-macroglobulin (alpha 2M), modulates PDGF bioactivity is unknown, but could involve reversible PDGF-alpha 2M binding. Herein we report that greater than 70% of 125I-PDGF-BB or -AB complexed to alpha 2M was dissociated by SDS-denaturation followed by SDS-polyacrylamide gel electrophoresis, i.e. most of the binding was noncovalent. Reduction of the PDGF.alpha 2M complex following denaturation dissociated the cytokine from alpha 2M by greater than 90%, suggesting covalent disulfide bond formation. Approximately 50% of the growth factor was dissociated by lowering the pH from 7.5 to 4.0. 125I-PDGF-BB bound alpha 2M in a time-dependent manner (t1/2 = approximately 1 h), reaching equilibrium after 4 h. The 125I-PDGF.BB/alpha 2M complex dissociated more slowly (t1/2 = approximately 2.5 h). "Slow" and "fast" alpha 2M bound nearly equal amounts of PDGF-AB or -BB. Trypsin treatment converted PDGF-BB/alpha 2M complex to the fast conformation but did not release bound 125I-PDGF-BB. All PDGF-isoforms (AA, -AB, and -BB) competed for binding with 125I-PDGF-BB binding to slow alpha 2M and fast alpha 2M-methylamine by 65-80%. Other cytokines that bind alpha 2M (transforming growth factor-beta 1 and -beta 2, tumor necrosis factor-alpha, basic fibroblast growth factor, interleukin -1 beta, and -6) did not compete for 125I-PDGF-BB binding slow alpha 2M, but transforming growth factor-beta 1 and basic fibroblast growth factor inhibited 125I-PDGF-BB binding alpha 2M-methylamine by 30-50%. The reversible nature of the PDGF.alpha 2M complex could allow for targeted PDGF release near mesenchymal cells which possess PDGF receptors
Detection and parameter estimation of binary neutron star merger remnants
Detection and parameter estimation of binary neutron star merger remnants can shed light on the physics of hot matter at supranuclear densities. Here we develop a fast, simple model that can generate gravitational waveforms, and show it can be used for both detection and parameter estimation of post-merger remnants. The model consists of three exponentially-damped sinusoids with a linear frequency-drift term. The median fitting factors between the model waveforms and numerical-relativity simulations exceed 0.90. We detect remnants at a post-merger signal-to-noise ratio of ≥7 using a Bayes-factor detection statistic with a threshold of 3000. We can constrain the primary post-merger frequency to ±^(1.4)_(1.2)% at post-merger signal-to-noise ratios of 15 with an increase in precision to ±^(0.3)_(0.2)% for post-merger signal-to-noise ratios of 50. The tidal coupling constant can be constrained to ±⁹₁₂% at post-merger signal-to-noise ratios of 15, and ±5% at post-merger signal-to-noise ratios of 50 using a hierarchical inference model
Detection and parameter estimation of binary neutron star merger remnants
Detection and parameter estimation of binary neutron star merger remnants can
shed light on the physics of hot matter at supranuclear densities. Here we
develop a fast, simple model that can generate gravitational waveforms, and
show it can be used for both detection and parameter estimation of post-merger
remnants. The model consists of three exponentially-damped sinusoids with a
linear frequency-drift term. The median fitting factors between the model
waveforms and numerical-relativity simulations exceed 0.90. We detect remnants
at a post-merger signal-to-noise ratio of using a Bayes-factor
detection statistic with a threshold of 3000. We can constrain the primary
post-merger frequency to at post-merger signal-to-noise
ratios of 15 with an increase in precision to for
post-merger signal-to-noise ratios of 50. The tidal coupling constant can be
constrained to at post-merger signal-to-noise ratios of 15,
and at post-merger signal-to-noise ratios of 50 using a hierarchical
inference model
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
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