1,492 research outputs found

    Enabling a High Throughput Real Time Data Pipeline for a Large Radio Telescope Array with GPUs

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    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

    Novel Thermal Properties of Nanostructured Materials

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    Instabilities in the Flux Line Lattice of Anisotropic Superconductors

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    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, b(ϵ,θ)b^*(\epsilon,\theta), depends on the anisotropy ϵ\epsilon and the angle θ\theta at which the lattice is tilted away from the cc-axis. These instabilities initially occur at wavevector k(ϵ,θ)k^*(\epsilon,\theta), and the component of kk^* along the average direction of the flux lines, kzk_z, is always finite. As the instability occurs at finite kzk_z the dependence of the cutoff on kzk_z is important, and we have used a cutoff suggested by Sudb\ospace and Brandt. The instabilities only occur for values of the anisotropy ϵ\epsilon appropriate to a material like BSCCO, and not for anisotropies more appropriate to YBCO. The lower critical field Hc1(ϕ)H_{c_1}(\phi) is calculated as a function of the angle ϕ\phi at which the applied field is tilted away from the crystal axis. The presence of kinks in Hc1(ϕ)H_{c_1}(\phi) 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 Hc1H_{c_1} 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 1+1^{-+} Light Hybrid Meson From QCD Sum Rules

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    We calculate the next-to-leading order (NLO) αs\alpha_s-corrections to the contributions of the condensates and 2^2 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 JPCJ^{PC}=1+1^{-+} light hybrid meson is recalculated using the QCD sum rule approach. We find that the sum rules exhibit enhanced stability when the NLO αs\alpha_s-corrections are included in the sum rule analysis, resulting in a 1+1^{-+} light hybrid meson mass of approximately 1.6 GeV.Comment: revtex4, 10 pages, 7 eps figures embedded in manuscrip

    Physics in the Real Universe: Time and Spacetime

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    The Block Universe idea, representing spacetime as a fixed whole, suggests the flow of time is an illusion: the entire universe just is, with no special meaning attached to the present time. This view is however based on time-reversible microphysical laws and does not represent macro-physical behaviour and the development of emergent complex systems, including life, which do indeed exist in the real universe. When these are taken into account, the unchanging block universe view of spacetime is best replaced by an evolving block universe which extends as time evolves, with the potential of the future continually becoming the certainty of the past. However this time evolution is not related to any preferred surfaces in spacetime; rather it is associated with the evolution of proper time along families of world linesComment: 28 pages, including 9 Figures. Major revision in response to referee comment

    Functional maturation of isolated neural progenitor cells from the adult rat hippocampus

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    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

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    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

    Effet de l’association du haricot mungo sur le rendement du mil dans le Bassin arachidier, Sénégal

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    Ce numéro est constitué d’articles issus de la seconde édition des Rencontres Francophones sur les Légumineuses (RFL2) qui s’est tenu à Toulouse (France) les 17 et 18 octobre 2018.Agricultural production in Senegal is constrained by rainfall variability, persistent droughts, and low soilfertility. These constraints have decreased pearl millet yield in Senegal. Mungbean, a short-duration andrelatively drought-tolerant grain legume, is capable of improving soil fertility and increasing cropproduction. To investigate the potential of mungbean for increasing millet yield through intercropping,field experiments were conducted during the 2017 growing season in Bambey (Senegal). Intercroppingtreatments (sole millet (T1), sole mungbean (T2), and 23% (T3), 43% (T4), 47% (T5), 62% (T6), 125% (T7)et 164% (T8) of mungbean in sole millet) were laid out in a randomized complete block design andreplicated four times. Studied parameters included millet and mungbean yield parameters and combinedyields, normalized difference vegetation index (NDVI), canopy cover, and land equivalent ratio (LER).Intercropping (millet + mungbean) did not significantly increase millet biomass or grain yield comparedto millet alone. However, grain yield, number of pods and seeds, and plant height of mungbean plantswere significantly higher in T7 and T8 compared to other treatments. Combined yields were alsosignificantly (P ≤ 0.05) higher (up to 56%) under millet – mungbean intercropping. Similarly,intercropping significantly (P ≤ 0.05) increased LER and canopy cover (62%) over millet alone but notNDVI values. Results from this first-year suggest that intercropping with mungbean could sustain milletproduction through diversification of agricultural systems.La production agricole au Sénégal est limitée par la variabilité des précipitations, les sécheressespersistantes et la faible fertilité des sols. Ces contraintes ont contribué à la baisse des rendements dumil au Sénégal. Le haricot mungo, une légumineuse à graines à cycle court et relativement tolérante àla sécheresse, est capable d'améliorer la fertilité du sol et d’augmenter la production agricole. Pourétudier le potentiel du haricot mungo à augmenter le rendement du mil, des essais ont été menéspendant la saison culturale de 2017 à Bambey (Diourbel). Les systèmes d’association (mil seul (T1),haricot mungo seul (T2) et 23% (T3), 43% (T4), 47% (T5), 62% (T6), 125% (T7) et 164% (T8) de haricotmungo en association avec le mil) ont été disposés en blocs complets randomisés et répliqués quatrefois. Les données collectées comprennent les paramètres de rendement du mil et du haricot mungo etle rendement total en grains, l'indice de végétation par différence normalisée (NDVI), le taux decouverture du sol, et le land equivalent ratio (LER). L’association du mil avec le haricot mungo n'a passignificativement augmenté la biomasse et le rendement en grains du mil par rapport au mil seul.Cependant, le rendement en grains, le nombre de gousses et de graines, et la hauteur des plants deharicot mungo ont été significativement plus élevés pour les traitements T7 et T8 par rapport aux autrestraitements. Le rendement total en grains était aussi significativement (P ≤ 0,05) plus élevé (jusqu'à56%) en association. De même, l’association des cultures a entrainé des différences significatives pourle LER et le taux de couverture du sol (62%) mais pas pour les valeurs de NDVI. Les résultats de cettepremière année suggèrent que l'association avec le haricot mungo pourrait soutenir la production de milgrâce à la diversification des systèmes agricoles

    CD9 co-operation with syndecan-1 is required for a major staphylococcal adhesion pathway

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    Epithelial colonization is a critical first step in bacterial pathogenesis. Staphylococcus aureus can utilize several host factors to associate with cells, including α5β1 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 xenon‐129 MRI gas exchange metrics

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    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 2 cm, 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 43 y (range: 20–69 y) were of sufficient quality to analyze. Age (p = 0.0006) and sex (p < 0.0001) were significant predictors for RBC:M, and a linear regression showed higher values and steeper decline in males: RBC:M(Males) = −0.00362 × Age + 0.60 (p = 0.01, R2 = 0.25); RBC:M(Females) = −0.00170 × Age + 0.44 (p = 0.02, R2 = 0.15). 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
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