13,412 research outputs found
Three-dimensional simulations of laser-plasma interactions at ultrahigh intensities
Three-dimensional (3D) particle-in-cell (PIC) simulations are used to
investigate the interaction of ultrahigh intensity lasers (
W/cm) with matter at overcritical densities. Intense laser pulses are
shown to penetrate up to relativistic critical density levels and to be
strongly self-focused during this process. The heat flux of the accelerated
electrons is observed to have an annular structure when the laser is tightly
focused, showing that a large fraction of fast electrons is accelerated at an
angle. These results shed light into the multi-dimensional effects present in
laser-plasma interactions of relevance to fast ignition of fusion targets and
laser-driven ion acceleration in plasmas.Comment: 2 pages, 1 figur
Verbal Collision Avoidance Messages of Varying Perceived Urgency Reduce Crashes in High Risk Scenarios
Collision Avoidance Systems (CASs) are increasingly being installed in motor vehicles. Concurrently, verbal warnings are increasingly utilized in aviation, surface transportation, and medical environments. The current driving simulation investigation examined crash avoidance behaviors in high risk driving situations and crash rate reduction as a function of exposure to different types of verbal CAS messages. CAS messages varied in presentation level (PL) and signal word. Postdrive ratings of perceived urgency, alerting effectiveness, and annoyance were also examined. The type of CAS warning presented resulted in significant differences in appropriate crash avoidance behaviors and crash rates. In the current paradigm, the most effective CAS warnings were those of moderate PU, specifically the low PU signal word “notice” presented at high PL and the high PU signal word “danger” presented at low PL. Results are discussed in terms of their implications for CAS warning design and hazard matching applicability
Species Abundance Patterns in Complex Evolutionary Dynamics
An analytic theory of species abundance patterns (SAPs) in biological
networks is presented. The theory is based on multispecies replicator dynamics
equivalent to the Lotka-Volterra equation, with diverse interspecies
interactions. Various SAPs observed in nature are derived from a single
parameter. The abundance distribution is formed like a widely observed
left-skewed lognormal distribution. As the model has a general form, the result
can be applied to similar patterns in other complex biological networks, e.g.
gene expression.Comment: 4 pages, 3 figures. Physical Review Letters, in pres
Coherent open-loop optimal control of light-harvesting dynamics
We apply theoretically open-loop quantum optimal control techniques to
provide methods for the verification of various quantum coherent transport
mechanisms in natural and artificial light-harvesting complexes under realistic
experimental constraints. We demonstrate that optimally shaped laser pulses
allow to faithfully prepare the photosystem in specified initial states (such
as localized excitation or coherent superposition, i.e. propagating and
non-propagating states) and to probe efficiently the dynamics. These results
provide a path towards the discrimination of the different transport pathways
and to the characterization of environmental properties, enhancing our
understanding of the role that coherent processes may play in biological
complexes.Comment: 12 pages, 15 figure
Top-dressing durum with nitrogen to manage protein
Non-Peer ReviewedGrain protein is an important factor in determining the quality of durum wheat (Triticum turidum L.). Durum markets pay a premium for protein content of 13% or higher. During the 1990's, the average protein content of durum produced on the Canadian prairies has been 12.5% or less, leaving a sizable proportion of the durum crop unsuitable for the premium market. The overall objective of this project is to determine the effect and relative efficiency of top-dressed N on grain protein, quality, yield, and economic return of durum wheat. Nitrogen at three rates (20,40 and 60 kg N ha-1) was top-dressed on durum at 4 growth stages; before germination (during seeding), five leaf, flag leaf and flowering. The study was done over three years at two locations (Indian Head and Swift Current, SK). Four cultivars were used. Increasing the rate of top-dressed nitrogen increased the protein content of the durum. Applying all the nitrogen at
seeding provided the most consistent increases in protein. However, when the yield potential increased during the growing season due to above normal spring and summer precipitation, protein levels in the durum seed increased when nitrogen was top-dressed during the growing season
The open cluster NGC 6520 and the nearby dark molecular cloud Barnard 86
Wide field BVI photometry and CO(10) observations are presen ted
in the region of the open cluster NGC 6520 and the dark molecular cloud
Barnard~86. From the analysis of the optical data we find that the cluster is
rather compact, with a radius of 1.00.5 arcmin, smaller than previous
estimates. The cluster age is 15050 Myr and the reddening
E=0.420.10. The distance from the Sun is estimated to be
1900100 pc, and it is larger than previous estimates. We finally derive
basic properties of the dark nebula Barnard 86 on the assumption that it lies
at the same distance of the cluster.Comment: 21 pages, 8 eps figures (a few degraded in resolution), accepted for
publication in the Astronomical Journa
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