1,328 research outputs found
Supernovae and Positron Annihilation
Radioactive nuclei, especially those created in SN explosion, have long been
suggested to be important contributors of galactic positrons. In this paper we
describe the findings of three independent OSSE/SMM/TGRS studies of positron
annihilation radiation, demonstrating that the three studies are largely in
agreement as to the distribution of galactic annihilation radiation. We then
assess the predicted yields and distributions of SN-synthesized radionuclei,
determining that they are marginally compatible with the findings of the
annihilation radiation studies.Comment: 7 pages, accepted for publication in New Astronomy Reviews (Astronomy
with Radioactivites III
Asymptotically cylindrical 7-manifolds of holonomy G_2 with applications to compact irreducible G_2-manifolds
We construct examples of exponentially asymptotically cylindrical Riemannian
7-manifolds with holonomy group equal to G_2. To our knowledge, these are the
first such examples. We also obtain exponentially asymptotically cylindrical
coassociative calibrated submanifolds. Finally, we apply our results to show
that one of the compact G_2-manifolds constructed by Joyce by desingularisation
of a flat orbifold T^7/\Gamma can be deformed to one of the compact
G_2-manifolds obtainable as a generalized connected sum of two exponentially
asymptotically cylindrical SU(3)-manifolds via the method given by the first
author (math.DG/0012189).Comment: 36 pages; v2: corrected trivial typos; v3: some arguments corrected
and improved; v4: a number of improvements on presentation, paritularly in
sections 4 and 6, including an added picture
A feasibility study of metabolic phenotyping of dried blood spot specimens in rural Chinese women exposed to household air pollution
Background
Exposure–response studies and policy evaluations of household air pollution (HAP) are limited by current methods of exposure assessment which are expensive and burdensome to participants.
Methods
We collected 152 dried blood spot (DBS) specimens during the heating and non-heating seasons from 53 women who regularly used biomass-burning stoves for cooking and heating. Participants were enrolled in a longitudinal study in China. Untargeted metabolic phenotyping of DBS were generated using ultra-high performance liquid chromatography coupled with mass spectrometry to exemplify measurement precision and assessment for feasibility to detect exposure to HAP, evaluated by season (high pollution vs. low pollution) and measured personal exposure to fine particulate matter <2.5 μm diameters (PM2.5) and black carbon (BC) in the 48-h prior to collecting the DBS specimen.
Results
Metabolites e.g., amino acids, acyl-carnitines, lyso-phosphorylcholines, sphinganine, and choline were detected in the DBS specimens. Our approach is capable of detecting the differences in personal exposure to HAP whilst showing high analytical reproducibility, coefficient of variance (CV) <15%, meeting the U.S. Food and Drug Administration criteria.
Conclusions
Our results provide a proof of principle that high-resolution metabolic phenotypic data can be generated using a simple DBS extraction method thus suitable for exposure studies in remote, low-resource settings where the collection of serum and plasma is logistically challenging or infeasible. The analytical run time (19 min/specimen) is similar to most global phenotyping methods and therefore suitable for large-scale application
Non-Abelian dynamics and heavy multiquarks, Steiner-tree confinement in hadron spectroscopy
A brief review is first presented of attempts to predict stable multiquark
states within current models of hadron spectroscopy. Then a model combining
flip-flop and connected Steiner trees is introduced and shown to lead to stable
multiquarks, in particular for some configurations involving several heavy
quarks and bearing exotic quantum numbers.Comment: 8 pages, 5 figures, Invited talk at the 21st European Conference on
Few-Body Problems in Physics, Salamanca, Spain, August 29th--September 3rd,
2010, to appear in the Proceedings, ed.~A.~Valcarce et al., to appear in
Few-Body Syste
Alternatively spliced isoforms of TRIP8b differentially control h channel trafficking and function
Anisotropic dark energy stars
A model of compact object coupled to inhomogeneous anisotropic dark energy is
studied. It is assumed a variable dark energy that suffers a phase transition
at a critical density. The anisotropic Lambda-Tolman-Oppenheimer-Volkoff
equations are integrated to know the structure of these objects. The anisotropy
is concentrated on a thin shell where the phase transition takes place, while
the rest of the star remains isotropic. The family of solutions obtained
depends on the coupling parameter between the dark energy and the fermion
matter. The solutions share several features in common with the gravastar
model. There is a critical coupling parameter that gives non-singular black
hole solutions. The mass-radius relations are studied as well as the internal
structure of the compact objects. The hydrodynamic stability of the models is
analyzed using a standard test from the mass-radius relation. For each
permissible value of the coupling parameter there is a maximum mass, so the
existence of black holes is unavoidable within this model.Comment: 12 pages, 6 figures, final manuscript, Accepted for publication in
Astrophysics & Space Scienc
Near-Surface Interface Detection for Coal Mining Applications Using Bispectral Features and GPR
The use of ground penetrating radar (GPR) for detecting the presence of near-surface interfaces is a scenario of special interest to the underground coal mining industry. The problem is difficult to solve in practice because the radar echo from the near-surface interface is often dominated by unwanted components such as antenna crosstalk and ringing, ground-bounce effects, clutter, and severe attenuation. These nuisance components are also highly sensitive to subtle variations in ground conditions, rendering the application of standard signal pre-processing techniques such as background subtraction largely ineffective in the unsupervised case. As a solution to this detection problem, we develop a novel pattern recognition-based algorithm which utilizes a neural network to classify features derived from the bispectrum of 1D early time radar data. The binary classifier is used to decide between two key cases, namely whether an interface is within, for example, 5 cm of the surface or not. This go/no-go detection capability is highly valuable for underground coal mining operations, such as longwall mining, where the need to leave a remnant coal section is essential for geological stability. The classifier was trained and tested using real GPR data with ground truth measurements. The real data was acquired from a testbed with coal-clay, coal-shale and shale-clay interfaces, which represents a test mine site. We show that, unlike traditional second order correlation based methods such as matched filtering which can fail even in known conditions, the new method reliably allows the detection of interfaces using GPR to be applied in the near-surface region. In this work, we are not addressing the problem of depth estimation, rather confining ourselves to detecting an interface within a particular depth range
Space-time inhomogeneity, anisotropy and gravitational collapse
We investigate the evolution of non-adiabatic collapse of a shear-free
spherically symmetric stellar configuration with anisotropic stresses
accompanied with radial heat flux. The collapse begins from a curvature
singularity with infinite mass and size on an inhomogeneous space-time
background. The collapse is found to proceed without formation of an even
horizon to singularity when the collapsing configuration radiates all its mass
energy. The impact of inhomogeneity on various parameters of the collapsing
stellar configuration is examined in some specific space-time backgrounds.Comment: To appear in Gen. Relativ. Gra
Radiative falloff of a scalar field in a weakly curved spacetime without symmetries
We consider a massless scalar field propagating in a weakly curved spacetime
whose metric is a solution to the linearized Einstein field equations. The
spacetime is assumed to be stationary and asymptotically flat, but no other
symmetries are imposed -- the spacetime can rotate and deviate strongly from
spherical symmetry. We prove that the late-time behavior of the scalar field is
identical to what it would be in a spherically-symmetric spacetime: it decays
in time according to an inverse power-law, with a power determined by the
angular profile of the initial wave packet (Price falloff theorem). The field's
late-time dynamics is insensitive to the nonspherical aspects of the metric,
and it is governed entirely by the spacetime's total gravitational mass; other
multipole moments, and in particular the spacetime's total angular momentum, do
not enter in the description of the field's late-time behavior. This extended
formulation of Price's falloff theorem appears to be at odds with previous
studies of radiative decay in the spacetime of a Kerr black hole. We show,
however, that the contradiction is only apparent, and that it is largely an
artifact of the Boyer-Lindquist coordinates adopted in these studies.Comment: 17 pages, RevTeX
Management of Anticoagulant and Thrombolytic Agents in Deep Venous Thrombosis
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68445/2/10.1177_153857448201600101.pd
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