5,493 research outputs found
Copper toxicity mechanisms in algal systems and isolated chloroplasts
Imperial Users onl
The shock reprocessing model of electron acceleration in impulsive solar flares
We propose a new two-stage model for acceleration of electrons in solar
flares. In the first stage, electrons are accelerated stochastically in a
post-reconnection turbulent downflow. The second stage is the reprocessing of a
subset of these electrons as they pass through a weakly compressive fast shock
above the apex of the closed flare loop on their way to the chromosphere. We
call this the "shock reprocessing" model. The model reproduces the energy
dependent arrival time delays observed for both the pulsed and smooth
components of impulsive solar flare x-rays with physically reasonable
parameters for the downflow region. The model also predicts an emission site
above the loop-top, as seen in the Masuda flare. The loop-top source
distinguishes the shock reprocessing model from previous models. The model
makes testable predictions for the energy dependence of footpoint pulse
strengths and the location and spectrum of the loop-top emission, and can
account for the observed soft-hard-soft trend in the spectral evolution of
footpoint emission. Our model highlights the concept that reconnection is an
acceleration environment rather than a single process. Which combination of
processes operate may depend on the initial conditions that determine, for
example, whether the reconnection downflow is turbulent. The shock reprocessing
model comprises one such combination.Comment: submitted to MNRA
A sparse representation of gravitational waves from precessing compact binaries
Many relevant applications in gravitational wave physics share a significant
common problem: the seven-dimensional parameter space of gravitational
waveforms from precessing compact binary inspirals and coalescences is large
enough to prohibit covering the space of waveforms with sufficient density. We
find that by using the reduced basis method together with a parametrization of
waveforms based on their phase and precession, we can construct ultra-compact
yet high-accuracy representations of this large space. As a demonstration, we
show that less than judiciously chosen precessing inspiral waveforms are
needed for cycles, mass ratios from to and spin magnitudes . In fact, using only the first reduced basis waveforms yields a
maximum mismatch of over the whole range of considered parameters. We
test whether the parameters selected from the inspiral regime result in an
accurate reduced basis when including merger and ringdown; we find that this is
indeed the case in the context of a non-precessing effective-one-body model.
This evidence suggests that as few as numerical simulations of
binary black hole coalescences may accurately represent the seven-dimensional
parameter space of precession waveforms for the considered ranges.Comment: 5 pages, 3 figures. The parameters selected for the basis of
precessing waveforms can be found in the source file
Black Male Student-Athletes and Racial Inequities in NCAA Division I College Sports
The purpose of this report is to make transparent racial inequities in NCAA Division I college sports. Specifically, the authors offer a four-year analysis of Black men's representation on football and basketball teams versus their representation in the undergraduate student body on each campus. The report concludes with recommendations for the NCAA and commissioners of the six major sports conferences, college and university leaders, coaches and athletics directors, journalists, and Black male student-athletes and their families
Distinguishing Solar Flare Types by Differences in Reconnection Regions
Observations show that magnetic reconnection and its slow shocks occur in
solar flares. The basic magnetic structures are similar for long duration event
(LDE) flares and faster compact impulsive (CI) flares, but the former require
less non-thermal electrons than the latter. Slow shocks can produce the
required non-thermal electron spectrum for CI flares by Fermi acceleration if
electrons are injected with large enough energies to resonate with scattering
waves. The dissipation region may provide the injection electrons, so the
overall number of non-thermal electrons reaching the footpoints would depend on
the size of the dissipation region and its distance from the chromosphere. In
this picture, the LDE flares have converging inflows toward a dissipation
region that spans a smaller overall length fraction than for CI flares. Bright
loop-top X-ray spots in some CI flares can be attributed to particle trapping
at fast shocks in the downstream flow, the presence of which is determined by
the angle of the inflow field and velocity to the slow shocks.Comment: 15 pages TeX and 2 .eps figures, accepted to Ap.J.Let
Common hazards and their mitigating measures in work zones: A qualitative study of worker perceptions
Road construction and maintenance activities present challenges for ensuring the safety of workers and the traveling public alike. Hazards in work zones are typically studied using historical crash records but the current study took a qualitative approach by interviewing 66 workers from various work zones in Queensland, Australia. This supplemented and enhanced the limited available data regarding the frequency and nature of work zone crashes in Australia, provided worker insights into contributing factors, and assessed their opinions on the likely effectiveness of current or future approaches to hazard mitigation. Workers may not be aware of objective data regarding effectiveness, but their attitudes and consequent levels of compliance can influence both the likelihood of implementation and the outcomes of safety measures. Despite the potential importance of worker perceptions, they have not been studied comprehensively to date, and thus this study fills a significant gap in the literature. Excessive vehicle speeds, driver distraction and aggression towards roadworkers, working in wet weather, at night and close to traffic stream were among the most common hazards noted by workers. The safety measures perceived to be most effective included police presence, active enforcement, and improving driver awareness and education about work zones. Worker perceptions differed according to their level of exposure to hazards
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