778 research outputs found
Geotechnical causes for variations in output measured from shallow buried charges
The role of the geotechnical conditions on the impulse delivered by a shallow buried charge has received much attention in recent times. As the importance of the soil in these events has become better understood, the control over the geotechnical conditions has improved. While previous work has investigated directly the role of geotechnical conditions on the magnitude of the impulse from a buried charge, the current work aims to identify how these same conditions also affect the repeatability of testing using soils. In this paper the authors draw together their work to date for a wide range of different soil types and moisture contents to investigate the variation in output from nominally identical tests. The methodology for the preparation of soil beds and the measurement of impulse is described along with the measured variations in peak and residual deflections of a target plate fixed to the impulse measurement apparatus
Projectively equivariant quantizations over the superspace
We investigate the concept of projectively equivariant quantization in the
framework of super projective geometry. When the projective superalgebra
pgl(p+1|q) is simple, our result is similar to the classical one in the purely
even case: we prove the existence and uniqueness of the quantization except in
some critical situations. When the projective superalgebra is not simple (i.e.
in the case of pgl(n|n)\not\cong sl(n|n)), we show the existence of a
one-parameter family of equivariant quantizations. We also provide explicit
formulas in terms of a generalized divergence operator acting on supersymmetric
tensor fields.Comment: 19 page
Enhancing gravitational wave astronomy with galaxy catalogues
Joint gravitational wave (GW) and electromagnetic (EM) observations, as a key
research direction in multi-messenger astronomy, will provide deep insight into
the astrophysics of a vast range of astronomical phenomena. Uncertainties in
the source sky location estimate from gravitational wave observations mean
follow-up observatories must scan large portions of the sky for a potential
companion signal. A general frame of joint GW-EM observations is presented by a
multi-messenger observational triangle. Using a Bayesian approach to
multi-messenger astronomy, we investigate the use of galaxy catalogue and host
galaxy information to reduce the sky region over which follow-up observatories
must scan, as well as study its use for improving the inclination angle
estimates for coalescing binary compact objects. We demonstrate our method
using a simulated neutron stars inspiral signal injected into simulated
Advanced detectors noise and estimate the injected signal sky location and
inclination angle using the Gravitational Wave Galaxy Catalogue. In this case
study, the top three candidates in rank have , and posterior
probability of being the host galaxy, receptively. The standard deviation of
cosine inclination angle (0.001) of the neutron stars binary using
gravitational wave-galaxy information is much smaller than that (0.02) using
only gravitational wave posterior samples.Comment: Proceedings of the Sant Cugat Forum on Astrophysics. 2014 Session on
'Gravitational Wave Astrophysics
Scientific Highlights of the HETE-2 Mission
The HETE-2 mission has been highly productive. It has observed more than 250
GRBs so far. It is currently localizing 25 - 30 GRBs per year, and has
localized 43 GRBs to date. Twenty-one of these localizations have led to the
detection of X-ray, optical, or radio afterglows, and as of now, 11 of the
bursts with afterglows have known redshifts. HETE-2 has confirmed the
connection between GRBs and Type Ic supernovae, a singular achievement and
certainly one of the scientific highlights of the mission so far. It has
provided evidence that the isotropic-equivalent energies and luminosities of
GRBs are correlated with redshift, implying that GRBs and their progenitors
evolve strongly with redshift. Both of these results have profound implications
for the nature of GRB progenitors and for the use of GRBs as a probe of
cosmology and the early universe. HETE-2 has placed severe constraints on any
X-ray or optical afterglow of a short GRB. It is also solving the mystery of
"optically dark' GRBs, and revealing the nature of X-ray flashes.Comment: 10 pages, 9 figures, to appear in proc. "The Restless High-Energy
Universe", Royal Tropical Institute, Amsterdam; revised text, added ref
Measuring spatial pressure distribution from explosives buried in dry Leighton Buzzard sand
Direct measurement of the intense loading produced by the detonation of a buried explosive is an extremely difficult task. Historically, high-fidelity measurement techniques have not been sufficiently robust to capture the extremely high pressures associated with such events, and researchers have relied on ‘global’ measurements such as the average loading acting over a particular area of interest. Recently, a large-scale experimental approach to the direct measurement of the spatial and temporal variation in loading resulting from an explosive event has been developed, which utilises Hopkinson pressure bars (HPBs) inserted through holes in a large target plate such that their faces lie flush with the loaded face. This article presents results from ten experiments conducted at 1/4 scale, using 17 HPBs to measure the spatial pressure distribution from explosives buried in dry Leighton Buzzard sand, a commonly available sand used in many geotechnical applications. Localised pressure measurements are used in conjunction with high speed video to provide a detailed examination of the physical processes occurring at the loaded face, as well allowing quantification of these effects. Example pressure–time and impulse–time traces are provided in full to allow researchers to use this data for validation of numerical modelling approaches
Short Gamma Ray Bursts as possible electromagnetic counterpart of coalescing binary systems
Coalescing binary systems, consisting of two collapsed objects, are among the
most promising sources of high frequency gravitational waves signals
detectable, in principle, by ground-based interferometers. Binary systems of
Neutron Star or Black Hole/Neutron Star mergers should also give rise to short
Gamma Ray Bursts, a subclass of Gamma Ray Bursts. Short-hard-Gamma Ray Bursts
might thus provide a powerful way to infer the merger rate of two-collapsed
object binaries. Under the hypothesis that most short Gamma Ray Bursts
originate from binaries of Neutron Star or Black Hole/Neutron Star mergers, we
outline here the possibility to associate short Gamma Ray Bursts as
electromagnetic counterpart of coalescing binary systems.Comment: 4 pages, 1 figur
Effect of tensor couplings in a relativistic Hartree approach for finite nuclei
The relativistic Hartree approach describing the bound states of both
nucleons and anti-nucleons in finite nuclei has been extended to include tensor
couplings for the - and -meson. After readjusting the parameters
of the model to the properties of spherical nuclei, the effect of
tensor-coupling terms rises the spin-orbit force by a factor of 2, while a
large effective nucleon mass sustains. The overall
nucleon spectra of shell-model states are improved evidently. The predicted
anti-nucleon spectra in the vacuum are deepened about 20 -- 30 MeV.Comment: 31 pages, 4 postscript figures include
Common and low frequency variants in MERTK are independently associated with multiple sclerosis susceptibility with discordant association dependent upon HLA-DRB1*15:01 status
Multiple Sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system. The risk of developing MS is strongly influenced by genetic predisposition, and over 100 loci have been established as associated with susceptibility. However, the biologically relevant variants underlying disease risk have not been defined for the vast majority of these loci, limiting the power of these genetic studies to define new avenues of research for the development of MS therapeutics. It is therefore crucial that candidate MS susceptibility loci are carefully investigated to identify the biological mechanism linking genetic polymorphism at a given gene to the increased chance of developing MS. MERTK has been established as an MS susceptibility gene and is part of a family of receptor tyrosine kinases known to be involved in the pathogenesis of demyelinating disease. In this study we have refined the association of MERTK with MS risk to independent signals from both common and low frequency variants. One of the associated variants was also found to be linked with increased expression of MERTK in monocytes and higher expression of MERTK was associated with either increased or decreased risk of developing MS, dependent upon HLA-DRB1*15:01 status. This discordant association potentially extended beyond MS susceptibility to alterations in disease course in established MS. This study provides clear evidence that distinct polymorphisms within MERTK are associated with MS susceptibility, one of which has the potential to alter MERTK transcription, which in turn can alter both susceptibility and disease course in MS patients
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
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