972 research outputs found
Strangeness contribution to the vector and axial form factors of the nucleon
The strangeness contribution to the vector and axial form factors of the
nucleon is presented for momentum transfers in the range
GeV. The results are obtained via a combined analysis of forward-scattering
parity-violating elastic asymmetry data from the and HAPPEx
experiments at Jefferson Lab, and elastic and scattering
data from Experiment 734 at Brookhaven National Laboratory. The
parity-violating asymmetries measured in elastic scattering at
forward angles establish a relationship between the strange vector form factors
and , with little sensitivity to the strange axial form factor
. On the other hand, elastic neutrino scattering at low is
dominated by the axial form factor, with still some significant sensitivity to
the vector form factors as well. The combination of the two data sets allows
the simultaneous extraction of , , and over a significant
range of for the very first time.Comment: 3 pages, 1 figure, will appear in AIP Conference Proceedings for
PANIC 200
Simulation of transient energy distributions in sub-ns streamer formation
Breakdown and streamer formation is simulated in atmospheric pressure nitrogen for a 2D planar electrode system. A PIC code with multigrid potential solver is used to simulate the evolution of the non-equilibrium ionization front on sub-nanosecond timescales. The ion and electron energy distributions are computed, accounting for the inclusion of inelastic scattering of electrons, and collisionally excited metastable production and ionization. Of particular interest is the increased production of metastable and low-energy ions and electrons when the applied field is reversed during the progress of the ionization front, giving insight into the improved species yields in nanosecond pulsed systems
An Energy-Minimization Finite-Element Approach for the Frank-Oseen Model of Nematic Liquid Crystals: Continuum and Discrete Analysis
This paper outlines an energy-minimization finite-element approach to the
computational modeling of equilibrium configurations for nematic liquid
crystals under free elastic effects. The method targets minimization of the
system free energy based on the Frank-Oseen free-energy model. Solutions to the
intermediate discretized free elastic linearizations are shown to exist
generally and are unique under certain assumptions. This requires proving
continuity, coercivity, and weak coercivity for the accompanying appropriate
bilinear forms within a mixed finite-element framework. Error analysis
demonstrates that the method constitutes a convergent scheme. Numerical
experiments are performed for problems with a range of physical parameters as
well as simple and patterned boundary conditions. The resulting algorithm
accurately handles heterogeneous constant coefficients and effectively resolves
configurations resulting from complicated boundary conditions relevant in
ongoing research.Comment: 31 pages, 3 figures, 3 table
The evolution of electron overdensities in magnetic fields
When a neutral gas impinges on a stationary magnetized plasma an enhancement in the ionization rate occurs when the neutrals exceed a threshold velocity. This is commonly known as the critical ionization velocity effect. This process has two distinct timescales: an ionâneutral collision time and electron acceleration time. We investigate the energization of an ensemble of electrons by their self-electric field in an applied magnetic field. The evolution of the electrons is simulated under different magnetic field and density conditions. It is found that electrons can be accelerated to speeds capable of electron impact ionization for certain conditions. In the magnetically dominated case the energy distribution of the excited electrons shows that typically 1% of the electron population can exceed the initial electrostatic potential associated with the unbalanced ensemble of electrons
Strange form factors of the nucleon in a two-component model
The strange form factors of the nucleon are studied in a two-component model
consisting of a three-quark intrinsic structure surrounded by a meson cloud. A
comparison with the available experimental world data from the SAMPLE, PVA4,
HAPPEX and G0 collaborations shows a good overall agreement. The strange
magnetic moment is found to be positive, 0.315 nm.Comment: 11 pages, 2 tables, 5 figures, accepted for publication in J. Phys.
G. Revised version, new figures, extra table, new results, updated reference
Flash sintering of beta-alumina solid electrolytes for sodium battery applications
The rechargeable sodium batteries, sodium sulphur (NaS) batteries and molten-salt sodium nickel chloride (Na-NiCl2) are proven commercially available systems, particularly for large-scale energy storage applications and electric vehicle applications respectively. They have attractive properties such as the use of abundant low-cost raw materials, high energy and power density, high faradaic efficiency of charge/discharge, zero self-discharge rate and proven long-term durability. Conventional manufacturing of the core component, the sodium betaâ-alumina solid electrolyte, requires a high sintering temperatures, ~ 1600 °C to achieve high density and good ceramic quality, which contributes significantly to battery cost, energy and time consumption in production. Flash sintering, a novel low-cost electrical field-assisted sintering technology, has been investigated for sintering betaâ-alumina samples in a collaboration between Lucideon Limited and Ionotec Limited. This work will describe the preliminary results on flash sintering equipment design and prototype sodium betaâ-alumina ceramics with variation of the flash-sintering process parameters, i.e. current, frequency, times (incubation, development, holding), pulse experiments, current ramp rate, the on-set furnace temperature, sample geometry (discs versus open-ended tubes), electrode materials (Ag versus Pt paints), single versus double electrode and sample homogeneity. In particular, we will report a significant step towards scale up by showing results on homogeneously-sintered, highly dense more complex geometries such as tubes and closed end tubes using refined field sintering process
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