1,220 research outputs found
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
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
X - Ray Flares and Their Connection With Prompt Emission in GRBs
We use a wavelet technique to investigate the time variations in the light
curves from a sample of GRBs detected by Fermi and Swift. We focus primarily on
the behavior of the flaring region of Swift-XRT light curves in order to
explore connections between variability time scales and pulse parameters (such
as rise and decay times, widths, strengths, and separation distributions) and
spectral lags. Tight correlations between some of these temporal features
suggest a common origin for the production of X-ray flares and the prompt
emission.Comment: 7th Huntsville Gamma-Ray Burst Symposium, GRB 2013: paper 15 in eConf
Proceedings C130414
Bluetongue virus infection creates light averse Culicoides vectors and serious errors in transmission risk estimates.
BackgroundPathogen manipulation of host behavior can greatly impact vector-borne disease transmission, but almost no attention has been paid to how it affects disease surveillance. Bluetongue virus (BTV), transmitted by Culicoides biting midges, is a serious disease of ruminant livestock that can cause high morbidity and mortality and significant economic losses. Worldwide, the majority of surveillance for Culicoides to assess BTV transmission risk is done using UV-light traps. Here we show that field infection rates of BTV are significantly lower in midge vectors collected using traps baited with UV light versus a host cue (CO2).MethodsWe collected Culicoides sonorensis midges in suction traps baited with CO2, UV-light, or CO2 + UV on three dairies in southern California to assess differences in the resulting estimated infection rates from these collections. Pools of midges were tested for BTV by qRT-PCR, and maximum likelihood estimates of infection rate were calculated by trap. Infection rate estimates were also calculated by trapping site within a dairy. Colonized C. sonorensis were orally infected with BTV, and infection of the structures of the compound eye was examined using structured illumination microscopy.ResultsUV traps failed entirely to detect virus both early and late in the transmission season, and underestimated virus prevalence by as much as 8.5-fold. CO2 + UV traps also had significantly lower infection rates than CO2-only traps, suggesting that light may repel infected vectors. We found very high virus levels in the eyes of infected midges, possibly causing altered vision or light perception. Collecting location also greatly impacts our perception of virus activity.ConclusionsBecause the majority of global vector surveillance for bluetongue uses only light-trapping, transmission risk estimates based on these collections are likely severely understated. Where national surveillance programs exist, alternatives to light-trapping should be considered. More broadly, disseminated infections of many arboviruses include infections in vectors' eyes and nervous tissues, and this may be causing unanticipated behavioral effects. Field demonstrations of pathogen-induced changes in vector behavior are quite rare, but should be studied in more systems to accurately predict vector-borne disease transmission
Modelling the moistening of the free troposphere during the northwestward progression of Indian monsoon onset
Understanding and prediction of the Indian monsoon onset is of paramount importance for agricultural planning that affects food production and the gross domestic product of the country. A recent observational study suggests that the progression of the Indian monsoon onset in a northwestward direction, which is perpendicular to the mean flow, is reinforced by the moistening of the free troposphere by pre-monsoon showers and wetting of the land surface. As the onset progresses, the mid-tropospheric dry layer is thought to be constantly moistened from below by detrainment from shallow cumulus and congestus clouds from the southeast. The dry layer becomes much shallower towards southeast India, making the profile closer to moist adiabatic, providing favourable conditions for deep cumulus convection. Increased moistening of the free troposphere thereby pushes the northern limit of moist convection to move northwestwards. Here we examine the representation of this process in hindcast simulations from the fully coupled atmosphere-ocean seasonal forecast system of the UK Met Office, GloSea5. The model effectively captures the mid-level dry air intrusion from the northwest which suppresses convection over the northwestern parts of India. We also show that detrainment from shallow convection, measured by moisture tendencies around the freezing level, acts to saturate the free troposphere ahead of the monsoon onset, eroding the dry-layer from the southeast. This work suggests that initialized coupled models are capable of simulating dynamic and thermodynamic processes inherent in monsoon progression during the onset
Use of bacterial ureolysis for improved gelation of silica sol in rock grouting
Low pH silica-based grouts suitable for penetrating fine aperture fractures are increasingly being developed for use in engineering applications. Silica sol has an initial low viscosity and mixing with an accelerator destabilises the suspension producing a gel. The influence of sodium, calcium and ammonium chloride accelerators on gel time, rate of gelation and shear strength of the resulting gel were investigated in this study. For the first time the potential use of bacterial ureolysis as an accelerator for the destabilisation of silica sol was also explored. This study demonstrates that bacterial ureolysis can be used to control the gelation of silica sol. The rate of ureolysis increases with increasing bacterial density, resulting in faster gel times and higher rates of gelation. In addition, for grouts with similar gel times, using bacterial ureolysis to induce destabilisation results in a higher rate of gelation, a higher final shear strength and a more uniform gel than direct addition of the corresponding chemical accelerator. These results suggest that bacterial ureolysis could potentially be used in rock grouting to achieve long gel times and hence greater penetration, while also maintaining sufficiently rapid gelation to minimise issues related to fingering and erosion of the fresh grout
The Hurst Exponent of Fermi GRBs
Using a wavelet decomposition technique, we have extracted the Hurst exponent
for a sample of 46 long and 22 short Gamma-ray bursts (GRBs) detected by the
Gamma-ray Burst Monitor (GBM) aboard the Fermi satellite. This exponent is a
scaling parameter that provides a measure of long-range behavior in a time
series. The mean Hurst exponent for the short GRBs is significantly smaller
than that for the long GRBs. The separation may serve as an unbiased criterion
for distinguishing short and long GRBs.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
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