15,971 research outputs found
Enhanced hydrogen storage in Ni/Ce composite oxides
The properties of dried (but not calcined) coprecipitated nickel ceria systems have been investigated in terms of their hydrogen emission characteristics following activation in hydrogen. XRD and BET data obtained on the powders show similarities to calcined ceria but it is likely that the majority of the material produced by the coprecipitation process is largely of an amorphous nature. XPS data indicate very little nickel is present on the outermost surface of the particles. Nevertheless, the thermal analytical techniques (TGA, DSC and TPD-MS) indicate that the hydrogen has access to the catalyst present and the nickel is able to generate hydrogen species capable of interacting with the support. Both unactivated and activated materials show two hydrogen emission features, viz. low temperature and high temperature emissions (LTE and HTE, respectively) over the temperature range 50 and 500 °C. A clear effect of hydrogen interaction with the material is that the activated sample not only emits much more hydrogen than the corresponding unactivated one but also at lower temperatures. H2 dissociation occurs on the reduced catalyst surface and the spillover mechanism transfers this active hydrogen into the ceria, possibly via the formation and migration of OHâ species. The amount of hydrogen obtained (0.24 wt%) is 10Ă higher than those observed for calcined materials and would suggest that the amorphous phase plays a critical role in this process. The affiliated emissions of CO and CO2 with that of the HTE hydrogen (and consumption of water) strongly suggests a proportion of the hydrogen emission at this point arises from the water gas shift type reaction. It has not been possible from the present data to delineate between the various hydrogen storage mechanisms reported for ceria
Afferent Convergence from Divergent Sources Appears to Enhance the Spastic Patient\u27s Ability to Inhibit Antagonist Motoneurons During an Agonist Contraction
Spasticity and excessive muscular cocontraction during movement are common impairments following upper motor neuron (UMN) lesions. For example, during voluntary ankle dorsiflexion, individuals with spastic type cerebral palsy (CP) do not inhibit the antagonist triceps surae motoneuron pool
Time Dilation from Spectral Feature Age Measurements of Type Ia Supernovae
We have developed a quantitative, empirical method for estimating the age of
Type Ia supernovae (SNe Ia) from a single spectral epoch. The technique
examines the goodness of fit of spectral features as a function of the temporal
evolution of a large database of SNe Ia spectral features. When a SN Ia
spectrum with good signal-to-noise ratio over the rest frame range 3800 to 6800
A is available, the precision of a spectral feature age (SFA) is (1-sigma) ~
1.4 days. SFA estimates are made for two spectral epochs of SN 1996bj (z=0.574)
to measure the rate of aging at high redshift. In the 10.05 days which elapsed
between spectral observations, SN 1996bj aged 3.35 3.2 days, consistent
with the 6.38 days of aging expected in an expanding Universe and inconsistent
with no time dilation at the 96.4 % confidence level. The precision to which
individual features constrain the supernova age has implications for the source
of inhomogeneities among SNe Ia.Comment: 14 pages (LaTex), 7 postscript figures to Appear in the Astronomical
Journa
Multiscale Kinetic Monte-Carlo for Simulating Epitaxial Growth
We present a fast Monte-Carlo algorithm for simulating epitaxial surface
growth, based on the continuous-time Monte-Carlo algorithm of Bortz, Kalos and
Lebowitz. When simulating realistic growth regimes, much computational time is
consumed by the relatively fast dynamics of the adatoms. Continuum and
continuum-discrete hybrid methods have been developed to approach this issue;
however in many situations, the density of adatoms is too low to efficiently
and accurately simulate as a continuum. To solve the problem of fast adatom
dynamics, we allow adatoms to take larger steps, effectively reducing the
number of transitions required. We achieve nearly a factor of ten speed up, for
growth at moderate temperatures and large D/F.Comment: 7 pages, 6 figures; revised text, accepted by PR
Experimental estimates of the photon background in a potential light-by-light scattering study
High power short pulse lasers provide a promising route to study the strong field effects of the quantum vacuum, for example by direct photonâphoton scattering in the all-optical regime. Theoretical predictions based on realistic laser parameters achievable today or in the near future predict scattering of a few photons with colliding Petawatt laser pulses, requiring single photon sensitive detection schemes and very good spatio-temporal filtering and background suppression. In this article, we present experimental investigations of this photon background by employing only a single high power laser pulse tightly focused in residual gas of a vacuum chamber. The focal region was imaged onto a single-photon sensitive, time gated camera. As no detectable quantum vacuum signature was expected in our case, the setup allowed for characterization and first mitigation of background contributions. For the setup employed, scattering off surfaces of imperfect optics dominated below residual gas pressures of 1 Ă 10â4 mbar. Extrapolation of the findings to intensities relevant for photonâphoton scattering studies is discussed
On the informational content of wage offers
This article investigates signaling and screening roles of wage offers in a single-play matching model with two-sided unobservable characteristics. It generates the following predictions as matching equilibrium outcomes: (i) âgoodâ jobs offer premia if âhigh-qualityâ worker population is large; (ii) âbadâ jobs pay compensating differentials if the proportion of âgoodâ jobs to âlow-qualityâ workers is large; (iii) all firms may offer a pooling wage in markets dominated by âhigh-qualityâ workers and firms; or (iv) Greshamâs Law prevails: âgoodâ types withdraw if âbadâ types dominate the population. The screening/signaling motive thus has the potential of explaining a variety of wage patterns
The Multiple Origin of Blue Straggler Stars: Theory vs. Observations
In this chapter we review the various suggested channels for the formation
and evolution of blue straggler stars (BSSs) in different environments and
their observational predictions. These include mass transfer during binary
stellar evolution - case A/B/C and D (wind Roche-lobe overflow) mass transfer,
stellar collisions during single and binary encounters in dense stellar
cluster, and coupled dynamical and stellar evolution of triple systems. We also
explore the importance of the BSS and binary dynamics in stellar clusters. We
review the various observed properties of BSSs in different environments (halo
and bulge BSSs, BSSs in globular clusters and BSSs in old open clusters), and
compare the current observations with the theoretical predictions for BSS
formation. We try to constrain the likely progenitors and processes that play a
role in the formation of BSSs and their evolution. We find that multiple
channels of BSS formation are likely to take part in producing the observed
BSSs, and we point out the strengths and weaknesses of each the formation
channel in respect to the observational constraints. Finally we point out
directions to further explore the origin of BSS, and highlight eclipsing binary
BSSs as important observational tool.Comment: Chapter 11, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
Evaluating the effectiveness of a sodium butyrate feed additive for the control of Salmonella carriage in finishing pigs
This study aimed to investigate the effectiveness of commercially available sodium butyrate to control the shedding of Salmonella on two Irish pig farms with a history of high Salmonella seroprevalence. On both farms, pens (12-17 pigs/pen) were randomly assigned to a control (finisher feed without additives) or an acid treatment (the same feed supplemented with 0.03% sodium butyrate) for 24-26 days prior to slaughter. On Farm A, Salmonella shedding was reduced in the acid group compared to the control group at the end of the treatment period (30% vs. 57% probability of detecting Salmonella in faeces, respectively; p\u3c0.05). However no effect of treatment was observed on Farm B, which could perhaps be explained by a concomitant infection by Lawsonia intracellularis. No significant differences in Salmonella recovery rates were observed from caecal digesta or ileocaecal/mesenteric lymph nodes collected at slaughter in either of the trials. Furthermore, feed intake, weight gain and feed conversion efficiency did not differ significantly between control and treatment groups on either farm
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