1,146 research outputs found
Enabling a High Throughput Real Time Data Pipeline for a Large Radio Telescope Array with GPUs
The Murchison Widefield Array (MWA) is a next-generation radio telescope
currently under construction in the remote Western Australia Outback. Raw data
will be generated continuously at 5GiB/s, grouped into 8s cadences. This high
throughput motivates the development of on-site, real time processing and
reduction in preference to archiving, transport and off-line processing. Each
batch of 8s data must be completely reduced before the next batch arrives.
Maintaining real time operation will require a sustained performance of around
2.5TFLOP/s (including convolutions, FFTs, interpolations and matrix
multiplications). We describe a scalable heterogeneous computing pipeline
implementation, exploiting both the high computing density and FLOP-per-Watt
ratio of modern GPUs. The architecture is highly parallel within and across
nodes, with all major processing elements performed by GPUs. Necessary
scatter-gather operations along the pipeline are loosely synchronized between
the nodes hosting the GPUs. The MWA will be a frontier scientific instrument
and a pathfinder for planned peta- and exascale facilities.Comment: Version accepted by Comp. Phys. Com
Instabilities in the Flux Line Lattice of Anisotropic Superconductors
The stability of the flux line lattice has been investigated within
anisotropic London theory. This is the first full-scale investigation of
instabilities in the `chain' state. It has been found that the lattice is
stable at large fields, but that instabilities occur as the field is reduced.
The field at which these instabilities first arise, ,
depends on the anisotropy and the angle at which the
lattice is tilted away from the -axis. These instabilities initially occur
at wavevector , and the component of along the
average direction of the flux lines, , is always finite. As the
instability occurs at finite the dependence of the cutoff on is
important, and we have used a cutoff suggested by Sudb\ospace and Brandt. The
instabilities only occur for values of the anisotropy appropriate to
a material like BSCCO, and not for anisotropies more appropriate to YBCO. The
lower critical field is calculated as a function of the angle
at which the applied field is tilted away from the crystal axis. The
presence of kinks in is seen to be related to instabilities in
the equilibrium flux line structure.Comment: Extensively revised paper, with modified analysis of elastic
instabilities. Calculation of the lower critical field is included, and the
presence of kinks in is seen to be related to the elastic
instabilities. 29 pages including 16 figures, LaTeX with epsf styl
Improved Determination of the Mass of the Light Hybrid Meson From QCD Sum Rules
We calculate the next-to-leading order (NLO) -corrections to the
contributions of the condensates and in the
current-current correlator of the hybrid current
g\barq(x)\gamma_{\nu}iF_{\mu\nu}^aT^aq(x) using the external field method in
Feynman gauge. After incorporating these NLO contributions into the Laplace
sum-rules, the mass of the = light hybrid meson is recalculated
using the QCD sum rule approach. We find that the sum rules exhibit enhanced
stability when the NLO -corrections are included in the sum rule
analysis, resulting in a light hybrid meson mass of approximately 1.6
GeV.Comment: revtex4, 10 pages, 7 eps figures embedded in manuscrip
Functional maturation of isolated neural progenitor cells from the adult rat hippocampus
Although neural progenitor cells (NPCs) may provide a source of new neurons to alleviate neural trauma, little is known about their electrical properties as they differentiate. We have previously shown that single NPCs from the adult rat hippocampus can be cloned in the presence of heparan sulphate chains purified from the hippocampus, and that these cells can be pushed into a proliferative phenotype with the mitogen FGF2 [Chipperfield, H., Bedi, K.S., Cool, S.M. & Nurcombe, V. (2002) Int. J. Dev. Biol., 46, 661-670]. In this study, the active and passive electrical properties of both undifferentiated and differentiated adult hippocampal NPCs, from 0 to 12 days in vitro as single-cell preparations, were investigated. Sparsely plated, undifferentiated NPCs had a resting membrane potential of approximate to -90 mV and were electrically inexcitable. In > 70%, ATP and benzoylbenzoyl-ATP evoked an inward current and membrane depolarization, whereas acetylcholine, noradrenaline, glutamate and GABA had no detectable effect. In Fura-2-loaded undifferentiated NPCs, ATP and benzoylbenzoyl-ATP evoked a transient increase in the intracellular free Ca2+ concentration, which was dependent on extracellular Ca2+ and was inhibited reversibly by pyridoxalphosphate-6-azophenyl-2'-4'-disulphonic acid (PPADS), a P2 receptor antagonist. After differentiation, NPC-derived neurons became electrically excitable, expressing voltage-dependent TTX-sensitive Na+ channels, low- and high-voltage-activated Ca2+ channels and delayed-rectifier K+ channels. Differentiated cells also possessed functional glutamate, GABA, glycine and purinergic (P2X) receptors. Appearance of voltage-dependent and ligand-gated ion channels appears to be an important early step in the differentiation of NPCs
Search for Global Dipole Enhancements in the HiRes-I Monocular Data above 10^{18.5} eV
Several proposed source models for Ultra-High Energy Cosmic Rays (UHECRs)
consist of dipole distributions oriented towards major astrophysical landmarks
such as the galactic center, M87, or Centaurus A. We use a comparison between
real data and simulated data to show that the HiRes-I monocular data for
energies above 10^{18.5} eV is, in fact, consistent with an isotropic source
model. We then explore methods to quantify our sensitivity to dipole source
models oriented towards the Galactic Center, M87, and Centaurus A.Comment: 17 pages, 31 figure
CD9 co-operation with syndecan-1 is required for a major staphylococcal adhesion pathway
Epithelial colonization is a critical first step in bacterial pathogenesis. Staphylococcus aureus can utilize several host factors to associate with cells, including ι5β1 integrin and heparan sulfate proteoglycans, such as the syndecans. Here, we demonstrate that a partner protein of both integrins and syndecans, the host membrane adapter protein tetraspanin CD9, is essential for syndecan-mediated staphylococcal adhesion. Fibronectin is also essential in this process, while integrins are only critical for post-adhesion entry into human epithelial cells. Treatment of epithelial cells with CD9-derived peptide or heparin caused significant reductions in staphylococcal adherence, dependent on both CD9 and syndecan-1. Exogenous fibronectin caused a CD9-dependent increase in staphylococcal adhesion, whereas blockade of β1 integrins did not affect adhesion but did reduce the subsequent internalization of adhered bacteria. CD9 disruption or deletion increased β1 integrin-mediated internalization, suggesting that CD9 coordinates sequential staphylococcal adhesion and internalization. CD9 controls staphylococcal adhesion through syndecan-1, using a mechanism that likely requires CD9-mediated syndecan organization to correctly display fibronectin at the host cell surface. We propose that CD9-derived peptides or heparin analogs could be developed as anti-adhesion treatments to inhibit the initial stages of staphylococcal pathogenesis
Age, sex, and lung volume dependence of dissolved xenonâ129 MRI gas exchange metrics
Purpose
To characterize the dependence of Xe-MRI gas transfer metrics upon age, sex, and lung volume in a group of healthy volunteers.
Methods
Sixty-five subjects with no history of chronic lung disease were assessed with 129Xe-MRI using a four-echo 3D radial spectroscopic imaging sequence and a dose of xenon titrated according to subject height that was inhaled from a lung volume of functional residual capacity (FRC). Imaging was repeated in 34 subjects at total lung capacity (TLC). Regional maps of the fractions of dissolved xenon in red blood cells (RBC), membrane (M), and airspace (Gas) were acquired at an isotropic resolution of 2âcm, from which global averages of the ratios RBC:M, RBC:Gas, and M:Gas were computed.
Results
Data from 26 males and 36 females with a median age of 43ây (range: 20â69ây) were of sufficient quality to analyze. Age (pâ=â0.0006) and sex (pâ<â0.0001) were significant predictors for RBC:M, and a linear regression showed higher values and steeper decline in males: RBC:M(Males)â=ââ0.00362âĂâAgeâ+â0.60 (pâ=â0.01, R2â=â0.25); RBC:M(Females)â=ââ0.00170âĂâAgeâ+â0.44 (pâ=â0.02, R2â=â0.15). Similarly, age and sex were significant predictors for RBC:Gas but not for M:Gas. RBC:M, M:Gas and RBC:Gas were significantly lower at TLC than at FRC (plus inhaled volume), with an average 9%, 30% and 35% decrease, respectively.
Conclusion
Expected age and sex dependence of pulmonary function concurs with 129Xe RBC:M imaging results, demonstrating that these variables must be considered when reporting Xe-MRI metrics. Xenon doses and breathing maneuvers should be controlled due to the strong dependence of Xe-MRI metrics upon lung volume
Large Extra Dimensions and Decaying KK Recurrences
We suggest the possibility that in ADD type brane-world scenarios, the higher
KK excitations of the graviton may decay to lower ones owing to a breakdown of
the conservation of extra dimensional ``momenta'' and study its implications
for astrophysics and cosmology. We give an explicit realization of this idea
with a bulk scalar field , whose nonzero KK modes acquire vacuum
expectation values. This scenario helps to avoid constraints on large extra
dimensions that come from gamma ray flux bounds in the direction of nearby
supernovae as well as those coming from diffuse cosmological gamma ray
background. It also relaxes the very stringent limits on reheat temperature of
the universe in ADD models.Comment: 16 pages, late
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