958 research outputs found
Carbon fiber composites for cryogenic filament-wound vessels
Advanced unidirectional and bidirectional carbon fiber/epoxy resin composites were evaluated for physical and mechanical properties over a cryogenic to room temperature range for potential application to cryogenic vessels. The results showed that Courtaulds HTS carbon fiber was the superior fiber in terms of cryogenic strength properties in epoxy composites. Of the resin systems tested in ring composites, CTBN/ERLB 4617 exhibited the highest composite strengths at cryogenic temperatures, but very low interlaminar shear strengths at room temperature. Tests of unidirectional and bidirectional composite bars showed that the Epon 828/Empol 1040 resin was better at all test temperatures. Neither fatigue cycling nor thermal shock had a significant effect on composite strengths or moduli. Thermal expansion measurements gave negative values in the fiber direction and positive values in the transverse direction of the composites
Logahedra: A new weakly relational domain
Weakly relational numeric domains express restricted classes of linear inequalities that strike a balance between what can be described and what can be efficiently computed. Popular weakly relational domains such as bounded differences and octagons have found application in model checking and abstract interpretation. This paper introduces logahedra, which are more expressiveness than octagons, but less expressive than arbitrary systems of two variable per inequality constraints. Logahedra allow coefficients of inequalities to be powers of two whilst retaining many of the desirable algorithmic properties of octagons
Quantum picturalism for topological cluster-state computing
Topological quantum computing is a way of allowing precise quantum
computations to run on noisy and imperfect hardware. One implementation uses
surface codes created by forming defects in a highly-entangled cluster state.
Such a method of computing is a leading candidate for large-scale quantum
computing. However, there has been a lack of sufficiently powerful high-level
languages to describe computing in this form without resorting to single-qubit
operations, which quickly become prohibitively complex as the system size
increases. In this paper we apply the category-theoretic work of Abramsky and
Coecke to the topological cluster-state model of quantum computing to give a
high-level graphical language that enables direct translation between quantum
processes and physical patterns of measurement in a computer - a "compiler
language". We give the equivalence between the graphical and topological
information flows, and show the applicable rewrite algebra for this computing
model. We show that this gives us a native graphical language for the design
and analysis of topological quantum algorithms, and finish by discussing the
possibilities for automating this process on a large scale.Comment: 18 pages, 21 figures. Published in New J. Phys. special issue on
topological quantum computin
Novel technique for constraining r-process (n,) reaction rates
A novel technique has been developed, which will open exciting new
opportunities for studying the very neutron-rich nuclei involved in the
r-process. As a proof-of-principle, the -spectra from the -decay
of Ga have been measured with the SuN detector at the National
Superconducting Cyclotron Laboratory. The nuclear level density and
-ray strength function are extracted and used as input to
Hauser-Feshbach calculations. The present technique is shown to strongly
constrain the Ge()Ge cross section and reaction rate.Comment: 5 pages, 3 figure
The beta-Oslo method: experimentally constrained () reaction rates relevant to the -process
Unknown neutron-capture reaction rates remain a significant source of
uncertainty in state-of-the-art -process nucleosynthesis reaction network
calculations. As the -process involves highly neutron-rich nuclei for which
direct () cross-section measurements are virtually impossible,
indirect methods are called for to constrain () cross sections used
as input for the -process nuclear network. Here we discuss the newly
developed beta-Oslo method, which is capable of providing experimental input
for calculating () rates of neutron-rich nuclei. The beta-Oslo method
represents a first step towards constraining neutron-capture rates of
importance to the -process.Comment: 4 pages, 1 figure, conference proceedings Nuclei in the Cosmos XV
2018, Italy
Replication, Pathogenesis and Transmission of Pandemic (H1N1) 2009 Virus in Non-Immune Pigs
The declaration of the human influenza A pandemic (H1N1) 2009 (H1N1/09) raised important questions, including origin and host range [1,2]. Two of the three pandemics in the last century resulted in the spread of virus to pigs (H1N1, 1918; H3N2, 1968) with subsequent independent establishment and evolution within swine worldwide [3]. A key public and veterinary health consideration in the context of the evolving pandemic is whether the H1N1/09 virus could become established in pig populations [4]. We performed an infection and transmission study in pigs with A/California/07/09. In combination, clinical, pathological, modified influenza A matrix gene real time RT-PCR and viral genomic analyses have shown that infection results in the induction of clinical signs, viral pathogenesis restricted to the respiratory tract, infection dynamics consistent with endemic strains of influenza A in pigs, virus transmissibility between pigs and virus-host adaptation events. Our results demonstrate that extant H1N1/09 is fully capable of becoming established in global pig populations. We also show the roles of viral receptor specificity in both transmission and tissue tropism. Remarkably, following direct inoculation of pigs with virus quasispecies differing by amino acid substitutions in the haemagglutinin receptor-binding site, only virus with aspartic acid at position 225 (225D) was detected in nasal secretions of contact infected pigs. In contrast, in lower respiratory tract samples from directly inoculated pigs, with clearly demonstrable pulmonary pathology, there was apparent selection of a virus variant with glycine (225G). These findings provide potential clues to the existence and biological significance of viral receptor-binding variants with 225D and 225G during the 1918 pandemic [5]
Cosmological measurement of neutrino mass in the presence of leptonic asymmetry
We show that even the smallest neutrino mass consistent with the
Super--Kamiokande data is relevant for cosmological models of structure
formation and cosmic microwave background (CMB) anisotropies, provided that a
relic neutrino asymmetry exists. We calculate the precision with which a 0.07
eV neutrino mass could be extracted from CMB anisotropy and large-scale
structure data by the future Planck satellite and Sloan Digital Sky Survey. We
find that such a mass can be detected, assuming a large relic neutrino
asymmetry still allowed by current experimental data. This measurement of the
absolute value of the neutrino mass would be crucial for our understanding of
neutrino models.Comment: 8 pages, 2 PS figures, version to be publishe
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Preliminary field evaluation of high efficiency steel filters
The authors have conducted an evaluation of two high efficiency steel filters in the exhaust of an uranium oxide grit blaster at the Y-12 Plant in Oak Ridge Tennessee. The filters were installed in a specially designed filter housing with a reverse air-pulse cleaning system for automatically cleaning the filters in-place. Previous tests conducted on the same filters and housing at LLNL under controlled conditions using Arizona road dust showed good cleanability with reverse air pulses. Two high efficiency steel filters, containing 64 pleated cartridge elements housed in the standard 2{prime} x 2{prime} {times} l{prime} HEPA frame, were evaluated in the filter test housing using a 1,000 cfm slip stream containing a high concentration of depleted uranium oxide dust. One filter had the pleated cartridges manufactured to the authors specifications by the Pall Corporation and the other by Memtec Corporation. Test results showed both filters had a rapid increase in pressure drop with time, and reverse air pulses could not decrease the pressure drop. The authors suspected moisture accumulation in the filters was the problem since there were heavy rains during the evaluations, and the pressure drop of the Memtec filter decreased dramatically after passing clean, dry air through the filter and after the filter sat idle for one week. Subsequent laboratory tests on a single filter cartridge confirmed that water accumulation in the filter was responsible for the increase in filter pressure drop and the inability to lower the pressure drop by reverse air pulses. No effort was made to identify the source of the water accumulation and correct the problem because the available funds were exhausted
The star pile in Abell 545
Context:Struble (1988) found what appeared to be a cD halo without cD galaxy
in the center of the galaxy cluster Abell 545. This remarkable feature has been
passed almost unnoticed for nearly twenty years.
Aims:Our goal is to review Struble's claim by providing a first (preliminary)
photometric and spectroscopic analysis of this ''star pile''.
Methods:Based on archival VLT-images and long-slit spectra obtained with
Gemini-GMOS, we describe the photometric structure and measure the redshift of
the star pile and of the central galaxy.
Results:The star pile is indeed associated with Abell 545. Its velocity is
higher by about 1300 km/s than that of the central object. The spectra indicate
an old, presumably metal-rich population. Its brightness profile is much
shallower than that of typical cD-galaxies.
Conclusions:The formation history and the dynamical status of the star pile
remain elusive, until high S/N spectra and a dynamical analysis of the galaxy
cluster itself become available. We suggest that the star pile might provide an
interesting test of the Cold Dark Matter paradigm.Comment: 6 pages, 7 figures. Accepted for publication in A&
Chemical abundance patterns in the inner Galaxy: the Scutum Red Supergiant Clusters
The location of the Scutum Red-Supergiant (RSG) clusters at the end of the
Galactic Bar makes them an excellent probe of the Galaxy's secular evolution;
while the clusters themselves are ideal testbeds in which to study the
predictions of stellar evolutionary theory. To this end, we present a study of
the RSGs' surface abundances using a combination of high-resolution H-band
spectroscopy and spectral synthesis analysis. We provide abundance measurements
for elements C, O, Si, Mg, Ti, and Fe. We find that the surface abundances of
the stars studied are consistent with CNO burning and deep, rotationally
enhanced mixing. The average a/Fe ratios of the clusters are solar, consistent
with a thin-disk population. However, we find significantly sub-solar Fe/H
ratios for each cluster, a result which strongly contradicts a simple
extrapolation of the Galactic metallicity gradient to lower Galacto-centric
distances. We suggest that a simple one-dimensional parameterization of the
Galaxy's abundance patterns is insufficient at low Galactocentric distances, as
large azimuthal variations may be present. Indeed, we show that the abundances
of O, Si and Mg are consistent with independent measurements of objects in
similar locations in the Galaxy. In combining our results with other data in
the literature, we present evidence for large-scale (~kpc) azimuthal variations
in abundances at Galacto-centric distances of 3-5kpc. While we cannot rule-out
that this observed behaviour is due to systematic offsets between different
measurement techniques, we do find evidence for similar behaviour in a study of
the barred-spiral galaxy NGC4736 which uses homogeneous methodology. We suggest
that these azimuthal abundance variations could result from the intense but
patchy star formation driven by the potential of the central bar.Comment: 13 pages, 9 figures, accepted to Ap
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