2,062 research outputs found
Portfolio efficiency and discount factor bounds with conditional information:An Empirical Study
Prediction of Monthly Discharge in Ungauged Catchments Under Agricultural Land Use in the Upper Ping Basin, Northern Thailand
The present paper describes a methodology proposed for surface runoff modelling in gauged and ungauged subcatchments of Northern Thailand. Gauged catchments are modelled using calibration against measured flow data, whereas streamflow in the ungauged subcatchments is simulated by a disaggregation procedure utilising measured streamflow data from a larger gauged catchment in which the ungauged subcatchment may be nested. The disaggregation technique is based on the assumption that the streamflow contribution from each subcatchment to the total catchment yield is proportional to a ratio of the catchment's area and its average slope. The Mae Chaem catchment in the Upper Ping River basin was selected as a case study for applying the approach. The model testing performed in two subcatchments, where the modelled streamflow was compared with the measured data, showed that the first pass approach algorithm provides the accuracy of 13-17% of the relative error for the monthly time step
Particle acceleration by ultra-relativistic shocks: theory and simulations
We consider the acceleration of charged particles near ultra-relativistic
shocks, with Lorentz factor Gamma_s >> 1. We present simulations of the
acceleration process and compare these with results from semi-analytical
calculations. We show that the spectrum that results from acceleration near
ultra-relativistic shocks is a power law, N(E) \propto E^{-s}, with a nearly
universal value s \approx 2.2 - 2.3 for the slope of this power law.
We confirm that the ultra-relativistic equivalent of Fermi acceleration at a
shock differs from its non-relativistic counterpart by the occurence of large
anisotropies in the distribution of the accelerated particles near the shock.
In the rest frame of the upstream fluid, particles can only outrun the shock
when their direction of motion lies within a small loss cone of opening angle
theta_c \approx 1/Gamma_s around the shock normal.
We also show that all physically plausible deflection or scattering
mechanisms can change the upstream flight direction of relativistic particles
originating from downstream by only a small amount: Delta theta ~ 1/Gamma_s.
This limits the energy change per shock crossing cycle to Delta E ~ E, except
for the first cycle where particles originate upstream. In that case the
upstream energy is boosted by a factor ~ Gamma_s^2 for those particles that are
scattered back across the shock into the upstream region.Comment: Accepted by MNRAS, 39 pages, 10 figures, uses latex macro mn.st
Chandra Observations of the Crab-like Supernova Remnant G21.5-0.9
Chandra observations of the Crab-like supernova remnant G21.5-0.9 reveal a
compact central core and spectral variations indicative of synchrotron burn-off
of higher energy electrons in the inner nebula. The central core is slightly
extended, perhaps indicating the presence of an inner wind-shock nebula
surrounding the pulsar. No pulsations are observed from the central region,
yielding an upper limit of ~40% for the pulsed fraction. A faint outer shell
may be the first evidence of the expanding ejecta and blast wave formed in the
initial explosion, indicating a composite nature for G21.5-0.9.Comment: 4 pages, 2 figures, formatted with emulateapj, submitted to ApJ
Establishing A Continuum of Care to Improve Follow-Up Rates for Survivors of Sexual Assault
Introduction. In 2011 there were over 1000 reported sexual assaults in Vermont. Current recommendations suggest that survivors of sexual assault (survivors) receive follow- up care within two weeks after an initial Sexual Assault Nurse Examiner (SANE) exam, but fewer than 15% receive documented follow-up. A published report has demonstrated increased follow-up to over 80% when appointments are scheduled prior to discharge from the emergency department (ED).https://scholarworks.uvm.edu/comphp_gallery/1082/thumbnail.jp
Particle acceleration at ultrarelativistic shocks: an eigenfunction method
We extend the eigenfunction method of computing the power-law spectrum of
particles accelerated at a relativistic shock fronts to apply to shocks of
arbitrarily high Lorentz factor. In agreement with the findings of Monte-Carlo
simulations, we find the index of the power-law distribution of accelerated
particles which undergo isotropic diffusion in angle at an ultrarelativistic,
unmagnetized shock is s=4.23 (where s=-d(ln f)/dp with f the Lorentz invariant
phase-space density and p the momentum). This corresponds to a synchrotron
index for uncooled electrons of a=0.62 (taking cooling into account a=1.12),
where a=-d(ln F)/dn, F is the radiation flux and n the frequency. We also
present an approximate analytic expression for the angular distribution of
accelerated particles, which displays the effect of particle trapping by the
shock: compared with the non-relativistic case the angular distribution is
weighted more towards the plane of the shock and away from its normal. We
investigate the sensitivity of our results to the transport properties of the
particles and the presence of a magnetic field. Shocks in which the ratio of
Poynting to kinetic energy flux upstream is not small are less compressive and
lead to larger values of .Comment: Minor additions on publicatio
Testing Hardy nonlocality proof with genuine energy-time entanglement
We show two experimental realizations of Hardy ladder test of quantum
nonlocality using energy-time correlated photons, following the scheme proposed
by A. Cabello \emph{et al.} [Phys. Rev. Lett. \textbf{102}, 040401 (2009)].
Unlike, previous energy-time Bell experiments, these tests require precise
tailored nonmaximally entangled states. One of them is equivalent to the
two-setting two-outcome Bell test requiring a minimum detection efficiency. The
reported experiments are still affected by the locality and detection
loopholes, but are free of the post-selection loophole of previous energy-time
and time-bin Bell tests.Comment: 5 pages, revtex4, 6 figure
Local context effects during emotional item directed forgetting in younger and older adults
This paper explored the differential sensitivity young and older adults exhibit to the local context of items entering memory. We examined trial-to-trial performance during an item directed forgetting task for positive, negative, and neutral (or baseline) words each cued as either to-be-remembered (TBR) or to-be-forgotten (TBF). This allowed us to focus on how variations in emotional valence (independent of arousal) and instruction (TBR vs. TBF) of the previous item (trial n-1) impacted memory for the current item (trial n) during encoding. Different from research showing impairing effects of emotional arousal, both age groups showed a memorial boost for stimuli when preceded by items high in positive or negative valence relative to those preceded by neutral items. This advantage was particularly prominent for neutral trial n items that followed emotional items suggesting that, regardless of age, neutral memories may be strengthened by a local context that is high in valence. A trending age difference also emerged with older adults showing greater sensitivity when encoding instructions changed between trial n-1 and n. Results are discussed in light of age-related theories of cognitive and emotional processing, highlighting the need to consider the dynamic, moment-to-moment fluctuations of these systems
Gamma rays and neutrinos from the Crab Nebula produced by pulsar accelerated nuclei
We investigate the consequences of the acceleration of heavy nuclei (e.g.
iron nuclei) by the Crab pulsar. Accelerated nuclei can photodisintegrate in
collisions with soft photons produced in the pulsar's outer gap, injecting
energetic neutrons which decay either inside or outside the Crab Nebula. The
protons from neutron decay inside the nebula are trapped by the Crab Nebula
magnetic field, and accumulate inside the nebula producing gamma-rays and
neutrinos in collisions with the matter in the nebula. Neutrons decaying
outside the Crab Nebula contribute to the Galactic cosmic rays. We compute the
expected fluxes of gamma-rays and neutrinos, and find that our model could
account for the observed emission at high energies and may be tested by
searching for high energy neutrinos with future neutrino telescopes currently
in the design stage.Comment: 8 pages, 4 figures, LaTeX uses revtex.sty, submitted to Phys. Rev.
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