1,332 research outputs found
Radiation Damage of F8 Lead Glass with 20 MeV Electrons
Using a 20 MeV linear accelerator, we investigate the effects of
electromagnetic radiation on the optical transparency of F8 lead glass.
Specifically, we measure the change in attenuation length as a function of
radiation dose. Comparing our results to similar work that utilized a proton
beam, we conclude that F8 lead glass is more susceptible to proton damage than
electron damage.Comment: 5 pages, 6 figure
Towards hardware acceleration of neuroevolution for multimedia processing applications on mobile devices
This paper addresses the problem of accelerating large artificial neural networks (ANN), whose topology and weights can evolve via the use of a genetic algorithm. The proposed digital hardware architecture is capable of processing any evolved network topology, whilst at the same time providing a good trade off between throughput, area and power consumption. The latter is vital for a longer battery life on mobile devices. The architecture uses multiple parallel arithmetic units in each processing element (PE). Memory partitioning and data caching are used to minimise the effects of PE pipeline stalling. A first order minimax polynomial approximation scheme, tuned via a genetic algorithm, is used for the activation function generator. Efficient arithmetic circuitry, which leverages modified Booth recoding, column compressors and carry save adders, is adopted throughout the design
Field corn response to nitrogen as affected by previous winter crop
Testing double cropping systems in the irrigated areas of the Pacific Northwest
led us to evaluate late-planted corn response to N fertilizer when following either a
winter cereal grown for silage or winter peas plowed down as green manure
Vanishing Gamow-Teller Transition Rate for A=14 and the Nucleon-Nucleon Interaction in the Medium
The problem of the near vanishing of the Gamow-Teller transition () in
the A=14 system between the lowest and states is
revisited. The model space is extended from the valence space to the
valence space plus all 2 excitations. The question is addressed
as to what features of the effective nucleon-nucleon interaction in the medium
are required to obtain the vanishing strength in this extended space. It
turns out that a combination of a realistic strength of the tensor force
combined with a spin-orbit interaction which is enhanced as compared to the
free interaction yields a vanishing strength. Such an interaction can be
derived from a microscopic meson exchange potential if the enhancement of the
small component of the Dirac spinors for the nucleons is taken into account.Comment: RevTex file, 7 pages, four postscript figures. submitted to Phys.
Rev. C as a brief repor
Langevin Simulation of Thermally Activated Magnetization Reversal in Nanoscale Pillars
Numerical solutions of the Landau-Lifshitz-Gilbert micromagnetic model
incorporating thermal fluctuations and dipole-dipole interactions (calculated
by the Fast Multipole Method) are presented for systems composed of nanoscale
iron pillars of dimension 9 nm x 9 nm x 150 nm. Hysteresis loops generated
under sinusoidally varying fields are obtained, while the coercive field is
estimated to be 1979 14 Oe using linear field sweeps at T=0 K. Thermal
effects are essential to the relaxation of magnetization trapped in a
metastable orientation, such as happens after a rapid reversal of an external
magnetic field less than the coercive value. The distribution of switching
times is compared to a simple analytic theory that describes reversal with
nucleation at the ends of the nanomagnets. Results are also presented for
arrays of nanomagnets oriented perpendicular to a flat substrate. Even at a
separation of 300 nm, where the field from neighboring pillars is only 1
Oe, the interactions have a significant effect on the switching of the magnets.Comment: 19 pages RevTeX, including 12 figures, clarified discussion of
numerical technique
Zone-subsoiling effects on infiltration, runoff, erosion, and yields of furrow-irrigated potatoes
Soil compaction is a problem in many Pacific Northwest fields. We hypothesized that zone subsoiling
would improve potato (Solanum tuberosum L., cv. 'Russet Burbank' ) yield or grade, increase
infiltration, and decrease bulk density, runoff, and erosion of furrow-irrigated fields, while maintaining
trafficability and irrigability of furrows. A 2 year study was established on a Portneuf silt loam
(coarse-silty, mixed, mesic Durixerollic Calciorthids). In the fall, plots were in wheat stubble (1988)
or bean stover (1989), and were either disked (10-12 cm ), chiselled (25-30 cm ), or moldboard
plowed (20-25 cm ). Fall tillages were split in spring, half of each plot receiving in-row zone subsoiling
(46 cm ) after planting potatoes. The effect of zone subsoiling on infiltration in 1989 was small because
of variation across fall tillages. In 1990, zone subsoiling increased infiltration by 10% across fall
tillages. Erosion decreased up to 278% with zone subsoiling. Zone subsoiling reduced erosion more
effectively than it increased infiltration, shown by a two- to three-fold decrease in the sediment loss
to water infiltrated ratio. Zone subsoiling increased infiltration and reduced erosion more in 1990
when the study was conducted on a slightly steeper slope with higher water application rates than in
1989. In 1989, zone subsoiling increased the yield of grade 1 tubers by 3.8 t ha-1 (4.6%), but the total
yield was not significantly increased. In 1990, zone subsoiling increased the total yield by 4.2 t ha-1
the yield of grade 1 tubers by 5.6 t ha-1 (7.7%). With zone subsoiling, the percentage of large
grade 1 market-grade tubers increased by 3.3% in 1989 and 5.7% in 1990. Zone subsoiling requires
some extra attention by the irrigator early in the season to insure uniform furrow irrigation, but it can
potentially conserve both soil and water while improving grade and yield
Growth, microstructure, and failure of crazes in glassy polymers
We report on an extensive study of craze formation in glassy polymers.
Molecular dynamics simulations of a coarse-grained bead-spring model were
employed to investigate the molecular level processes during craze nucleation,
widening, and breakdown for a wide range of temperature, polymer chain length
, entanglement length and strength of adhesive interactions between
polymer chains. Craze widening proceeds via a fibril-drawing process at
constant drawing stress. The extension ratio is determined by the entanglement
length, and the characteristic length of stretched chain segments in the
polymer craze is . In the craze, tension is mostly carried by the
covalent backbone bonds, and the force distribution develops an exponential
tail at large tensile forces. The failure mode of crazes changes from
disentanglement to scission for , and breakdown through scission
is governed by large stress fluctuations. The simulations also reveal
inconsistencies with previous theoretical models of craze widening that were
based on continuum level hydrodynamics
Coupled virus - bacteria interactions and ecosystem function in an engineered microbial system
Viruses are thought to control bacterial abundance, affect community composition and influence ecosystem function in natural environments. Yet their dynamics have seldom been studied in engineered systems, or indeed in any system, for long periods of time. We measured virus abundance in a full-scale activated sludge plant every week for two years. Total bacteria and ammonia oxidising bacteria (AOB) abundances, bacterial community profiles, and a suite of environmental and operational parameters were also monitored. Mixed liquor virus abundance fluctuated over an order of magnitude (3.18 Ă 108 â 3.41 Ă 109 virusâs mL-1) and that variation was statistically significantly associated with total bacterial and AOB abundance, community composition, and effluent concentrations of COD and NH4+- N and thus system function. This suggests viruses play a far more important role in the dynamics of activated sludge systems than previously realised and could be one of the key factors controlling bacterial abundance, community structure and functional stability and may cause reactors to fail. These finding are based on statistical associations, not mechanistic models. Nevertheless, viral associations with abiotic factors, such as pH, make physical sense giving credence to these findings and highlighting the role that physical factors play in virus ecology. Further work is needed to identify and quantify specific bacteriophage and their hosts to enable us to develop mechanistic models of the ecology of viruses in wastewater treatment systems. However, since we have shown that viruses can be related to effluent quality and virus quantification is simple and cheap, practitioners would probably benefit from quantifying viruses now
Enhancement of low-mass dileptons in heavy-ion collisions
Using a relativistic transport model for the expansion stage of S+Au
collisions at 200 GeV/nucleon, we show that the recently observed enhancement
of low-mass dileptons by the CERES collaboration can be explained by the
decrease of vector meson masses in hot and dense hadronic matter.Comment: 12 pages, RevTeX, 3 figures available from [email protected]
Rapid cooling of magnetized neutron stars
The neutrino emissivities resulting from direct URCA processes in neutron
stars are calculated in a relativistic Dirac-Hartree approach in presence of a
magnetic field. In a quark or a hyperon matter environment, the emissivity due
to nucleon direct URCA processes is suppressed relative to that from pure
nuclear matter. In all the cases studied, the magnetic field enhances
emissivity compared to the field-free cases.Comment: 9 pages; Revtex; figure include
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