2,757 research outputs found
Asymptotic Normalization Coefficients for 13C+p->14N
The proton exchange reaction has been measured
at an incident energy of 162 MeV. Angular distributions were obtained for
proton transfer to the ground and low lying excited states in . Elastic
scattering of on also was measured out to the rainbow angle
region in order to find reliable optical model potentials. Asymptotic
normalization coefficients for the system have been
found for the ground state and the excited states at 2.313, 3.948, 5.106 and
5.834 MeV in . These asymptotic normalization coefficients will be used
in a determination of the S-factor for at solar
energies from a measurement of the proton transfer reaction
.Comment: 5 pages, 6 figure
Using Unmanned Aerial Vehicles for Bird Harassment on Fish Ponds
The effects of aquaculture decline on piscivorous birds in the Mississippi Delta concern catfish farmers, with possible increases in fish loss and disease transmission. Piscivorous birds quickly habituate to most current methods of harassment (loud noises and visual disturbances) leading to increased depredation and disease. Our study was designed to test the efficacy of using unmanned aerial vehicles (UAVs) to effectively control piscivorous birds at fish farms. We hypothesized that a UAV would be more efficient at reducing the number of fish-eating birds on fish ponds than current forms of harassment. We conducted pre-treatment bird surveys, harassment observations, and post-treatment surveys at each experimental unit before and after each treatment on the same treatment days on 6 study sites in the Mississippi Alluvial Valley. The results of this study indicate that UAV harassment did not reduce piscivorous bird abundance more than human harassment in a 2-year field experiment
Tests of Transfer Reaction Determinations of Astrophysical S-Factors
The reaction has been used to determine
asymptotic normalization coefficients for transitions to the ground and first
excited states of . The coefficients provide the normalization for
the tails of the overlap functions for and allow us
to calculate the S-factors for at astrophysical
energies. The calculated S-factors are compared to measurements and found to be
in very good agreement. This provides the first test of this indirect method to
determine astrophysical direct capture rates using transfer reactions. In
addition, our results yield S(0) for capture to the ground and first excited
states in , without the uncertainty associated with extrapolation from
higher energies.Comment: 6 pages, 2 figure
Correlation of Static Stress Changes and Earthquake Occurrence in
A systematic analysis is made of static Coulomb stress changes and
earthquake occurrence in the area of the North Aegean Sea, Greece, in order to assess the
prospect of using static stress changes to construct a regional earthquake likelihood
model. The earthquake data set comprises all events of magnitude M ≥ 5.2 which have
occurred since 1964. This is compared to the evolving stress field due to constant tectonic
loading and perturbations due to coseismic slip associated with major earthquakes (M ≥
6.4) over the same period. The stress was resolved for sixteen fault orientation classes,
covering the observed focal mechanisms of all earthquakes in the region. Analysis using
error diagrams shows that earthquake occurrence is better correlated with the constant
tectonic loading component of the stress field than with the total stress field changes since
1964, and that little, if any, information on earthquake occurrence is lost if only the
maximum of the tectonic loading over the fault orientation classes is considered.
Moreover, the information on earthquake occurrence is actually increased by taking the
maximum of the evolving stress field since 1964, and of its coseismic–slip component,
over the fault orientation classes. The maximum, over fault orientation classes, of linear
combinations of the tectonic loading and the evolving stress field is insignificantly better
correlated with earthquake occurrence than the maximum of the tectonic loading by itself.
A composite stress–change variable is constructed from ordering of the maximum
tectonic loading component and the maximum coseismic–slip component, in order to
optimize the correlation with earthquake occurrence. The results indicate that it would be
difficult to construct a time–varying earthquake likelihood model from the evolving stress
field that is more informative than a time–invariant model based on the constant tectonic
loading
Asymptotic normalization coefficients for 8B->7Be+p from a study of 8Li->7Li+n
Asymptotic normalization coefficients (ANCs) for 8Li->7Li+n have been
extracted from the neutron transfer reaction 13C(7Li,8Li)12C at 63 MeV. These
are related to the ANCs in 8B->7Be+p using charge symmetry. We extract ANCs for
8B that are in very good agreement with those inferred from proton transfer and
breakup experiments. We have also separated the contributions from the p_1/2
and p_3/2 components in the transfer. We find the astrophysical factor for the
7Be(p,gamma)8B reaction to be S_17(0)=17.6+/-1.7 eVb. This is the first time
that the rate of a direct capture reaction of astrophysical interest has been
determined through a measurement of the ANCs in the mirror system.Comment: 5 pages, 3 figures, 2 table
On several families of elliptic curves with arbitrary large Selmer groups
In this paper, we calculate the Selmer groups
S^{(\phi)} (E / \Q) and S^{(\hat{\varphi})} (E^{\prime} / \Q) of elliptic
curves via descent theory
(see [S, Chapter X]), in particular, we obtain that the Selmer groups of
several families of such elliptic curves can be arbitrary large.Comment: 22 page
Core handling and processing for the WAIS Divide ice-core project
On 1 December 2011 the West Antarctic Ice Sheet (WAIS) Divide ice-core project reached its final depth of 3405 m. The WAIS Divide ice core is not only the longest US ice core to date, but is also the highest-quality deep ice core, including ice from the brittle ice zone, that the US has ever recovered. The methods used at WAIS Divide to handle and log the drilled ice, the procedures used to safely retrograde the ice back to the US National Ice Core Laboratory (NICL) and the methods used to process and sample the ice at the NICL are described and discussed
Core handling and processing for the WAIS Divide ice-core project
On 1 December 2011 the West Antarctic Ice Sheet (WAIS) Divide ice-core project reached its final depth of 3405 m. The WAIS Divide ice core is not only the longest US ice core to date, but is also the highest-quality deep ice core, including ice from the brittle ice zone, that the US has ever recovered. The methods used at WAIS Divide to handle and log the drilled ice, the procedures used to safely retrograde the ice back to the US National Ice Core Laboratory (NICL) and the methods used to process and sample the ice at the NICL are described and discussed
Optical model potentials involving loosely bound p-shell nuclei around 10 MeV/A
We present the results of a search for optical model potentials for use in
the description of elastic scattering and transfer reactions involving stable
and radioactive p-shell nuclei. This was done in connection with our program to
use transfer reactions to obtain data for nuclear astrophysics, in particular
for the determination of the astrophysical S_17 factor for 7Be(p,\gamma)8B
using two (7Be,8B) proton transfer reactions. Elastic scattering was measured
using 7Li, 10B, 13C and 14N projectiles on 9Be and 13C targets at or about
E/A=10 MeV/nucleon. Woods-Saxon type optical model potentials were extracted
and are compared with potentials obtained from a microscopic double folding
model. We use these results to find optical model potentials for unstable
nuclei with emphasis on the reliability of the description they provide for
peripheral proton transfer reactions. We discuss the uncertainty introduced by
the procedure in the prediction of the DWBA cross sections for the (7Be,8B)
reactions used in extracting the astrophysical factor S_17(0).Comment: 16 pages, LaTEX file, 9 figures (PostScript files
Pseudo-prospective Evaluation of UCERF3-ETAS Forecasts During the 2019 Ridgecrest Sequence
The 2019 Ridgecrest sequence provides the first opportunity to evaluate Uniform California Earthquake Rupture Forecast v.3 with epidemic‐type aftershock sequences (UCERF3‐ETAS) in a pseudoprospective sense. For comparison, we include a version of the model without explicit faults more closely mimicking traditional ETAS models (UCERF3‐NoFaults). We evaluate the forecasts with new metrics developed within the Collaboratory for the Study of Earthquake Predictability (CSEP). The metrics consider synthetic catalogs simulated by the models rather than synoptic probability maps, thereby relaxing the Poisson assumption of previous CSEP tests. Our approach compares statistics from the synthetic catalogs directly against observations, providing a flexible approach that can account for dependencies and uncertainties encoded in the models. We find that, to the first order, both UCERF3‐ETAS and UCERF3‐NoFaults approximately capture the spatiotemporal evolution of the Ridgecrest sequence, adding to the growing body of evidence that ETAS models can be informative forecasting tools. However, we also find that both models mildly overpredict the seismicity rate, on average, aggregated over the evaluation period. More severe testing indicates the overpredictions occur too often for observations to be statistically indistinguishable from the model. Magnitude tests indicate that the models do not include enough variability in forecasted magnitude‐number distributions to match the data. Spatial tests highlight discrepancies between the forecasts and observations, but the greatest differences between the two models appear when aftershocks occur on modeled UCERF3‐ETAS faults. Therefore, any predictability associated with embedding earthquake triggering on the (modeled) fault network may only crystalize during the presumably rare sequences with aftershocks on these faults. Accounting for uncertainty in the model parameters could improve test results during future experiments.Maximilian J. Werner and Warner Marzocchi received funding from the European Union's Horizon 2020 research and innovation program (Number 821115, RISE: Real‐Time Earthquake Risk Reduction for a Resilient Europe). This research was supported by the Southern California Earthquake Center (SCEC; Contribution Number 10082). SCEC is funded by National Science Foundation (NSF) Cooperative Agreement EAR‐1600087 and the U.S. Geological Survey (USGS) Cooperative Agreement G17AC00047
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