12,282 research outputs found
An evaluation of the utilization of remote sensing in resource and environmental management of the Chesapeake Bay region
A nine-month study was conducted to assess the effectiveness of the NASA Wallops Chesapeake Bay Ecological Program in remote sensing. The study consisted of a follow-up investigation and information analysis of actual cases in which remote sensing was utilized by management and research personnel in the Chesapeake Bay region. The study concludes that the NASA Wallops Chesapeake Bay Ecological Program is effective, both in terms of costs and performance
Neutrinos in Cosmology and Astrophysics
We briefly review the recent developments in neutrino physics and
astrophysics which have import for frontline research in nuclear physics. These
developments, we argue, tie nuclear physics to exciting developments in
observational cosmology and astrophysics in new ways. Moreover, the behavior of
neutrinos in dense matter is itself a fundamental problem in many-body quantum
mechanics, in some ways akin to well-known issues in nuclear matter and nuclei,
and in some ways radically different, especially because of nonlinearity and
quantum de-coherence. The self-interacting neutrino gas is the only many body
system driven by the weak interactions.Comment: 7 pages, 1 figur
Modification of the Brink-Axel Hypothesis for High Temperature Nuclear Weak Interactions
We present shell model calculations of electron capture strength
distributions in A=28 nuclei and computations of the corresponding capture
rates in supernova core conditions. We find that in these nuclei the Brink-Axel
hypothesis for the distribution of Gamow-Teller strength fails at low and
moderate initial excitation energy, but may be a valid tool at high excitation.
The redistribution of GT strength at high initial excitation may affect capture
rates during collapse. If these trends which we have found in lighter nuclei
also apply for the heavier nuclei which provide the principal channels for
neutronization during stellar collapse, then there could be two implications
for supernova core electron capture physics. First, a modified Brink-Axel
hypothesis could be a valid approximation for use in collapse codes. Second,
the electron capture strength may be moved down significantly in transition
energy, which would likely have the effect of increasing the overall electron
capture rate during stellar collapse.Comment: 15 pages, 19 figure
Neutrino Pair Emission from Hot Nuclei During Stellar Collapse
We present shell-model calculations showing that residual interaction-induced
configuration mixing enhances the rate of neutral current de-excitation of
thermally excited nuclei into neutrino-antineutrino pairs. Though our
calculations reinforce the conclusions of previous studies that this process is
the dominant source of neutrino pairs near the onset of neutrino trapping
during stellar collapse, our shell-model result has the effect of increasing
the energy of these pairs, possibly altering their role in entropy transport in
supernovae.Comment: 9 pages, 8 figure
Majorana Neutrino Magnetic Moment and Neutrino Decoupling in Big Bang Nucleosynthesis
We examine the physics of the early universe when Majorana neutrinos
(electron neutrino, muon neutrino, tau neutrino) possess transition magnetic
moments. These extra couplings beyond the usual weak interaction couplings
alter the way neutrinos decouple from the plasma of electrons/positrons and
photons. We calculate how transition magnetic moment couplings modify neutrino
decoupling temperatures, and then use a full weak, strong, and electromagnetic
reaction network to compute corresponding changes in Big Bang Nucleosynthesis
abundance yields. We find that light element abundances and other cosmological
parameters are sensitive to magnetic couplings on the order of 10^{-10} Bohr
magnetons. Given the recent analysis of sub-MeV Borexino data which constrains
Majorana moments to the order of 10^{-11} Bohr magnetons or less, we find that
changes in cosmological parameters from magnetic contributions to neutrino
decoupling temperatures are below the level of upcoming precision observations.Comment: 19 pages, 9 figure
Presupernova collapse models with improved weak-interaction rates
Improved values for stellar weak interaction rates have been recently
calculated based upon a large shell model diagonalization. Using these new
rates (for both beta decay and electron capture), we have examined the
presupernova evolution of massive stars in the range 15-40 Msun. Comparing our
new models with a standard set of presupernova models by Woosley and Weaver, we
find significantly larger values for the electron-to-baryon ratio Ye at the
onset of collapse and iron core masses reduced by approximately 0.1 Msun. The
inclusion of beta-decay accounts for roughly half of the revisions, while the
other half is a consequence of the improved nuclear physics. These changes will
have important consequences for nucleosynthesis and the supernova explosion
mechanism.Comment: 4 pages, 2 figure
An Active-Sterile Neutrino Transformation Solution for r-Process Nucleosynthesis
We discuss how matter-enhanced active-sterile neutrino transformation in both
neutrino and antineutrino channels could enable the production of the rapid
neutron capture (r-process) nuclei in neutrino-heated supernova ejecta. In this
scheme the lightest sterile neutrino would be heavier than the electron
neutrino and split from it by a vacuum mass-squared difference roughly between
3 and 70 eV and vacuum mixing angle given by .Comment: 27 pages plus twelve figures. Submitted to Phys. Rev.
Light Element Synthesis in High Entropy Relativistic Flows Associated with Gamma Ray Bursts
We calculate and discuss the light element freeze-out nucleosynthesis in high
entropy winds and fireballs for broad ranges of entropy-per-baryon, dynamic
timescales characterizing relativistic expansion, and neutron-to-proton ratios.
With conditions characteristic of Gamma Ray Bursts (GRBs) we find that
deuterium production can be prodigious, with final abundance values 2H/H
approximately 2%, depending on the fireball isospin, late time dynamics, and
the effects of neutron decoupling- induced high energy non-thermal nuclear
reactions. This implies that there potentially could be detectable local
enhancements in the deuterium abundance associated with GRB events.Comment: 14 pages 3 figure
Spatial Externalities and Vector-Borne Plant Diseases: Pierce’s Disease and the Blue-Green Sharpshooter in the Napa Valley
Pierce’s Disease (PD) is a bacterial disease that can kill grapevines over a span of one to three years. In this paper, we examine and model PD and vector control decisions made at the vineyard level in the Napa Valley in an effort to understand how the pest and disease affect individual growers, and to examine spatial externality issues and potential benefits from cooperation between adjacent vineyards. The model that we created adds to the literature by (a) treating grape vines as capital stocks that take time to reach bearing age and thus cannot be immediately replaced in the event of becoming diseased. We also (b) relax the assumption of an interior solution by examining the boundaries of parameter space for which winegrape growing is profitable and thus allowing growers to abandon land if it is not. We also explore (c) the effect of changing different policy parameters, such as PD control and vine replacement costs. Finally (d) we examine the potential benefits of cooperation between growers to manage vector populations, and determine that coordinated vector control could help riparian-adjacent growers to lessen grapevine losses and land abandonment, and thus to remain profitable in times of high PD pressure.Pierce’s Disease, winegrapes, perennial crop modeling, agricultural pests and diseases, optimal control theory, Crop Production/Industries, Production Economics, Resource /Energy Economics and Policy, Q12, Q24, C61,
The Benefits and Costs of Alternative Policies for the Management of Pierce's Disease: A Case Study of the Blue-Green Sharpshooter in the Napa Valley
Replaced with revised version of poster on 07/23/10.Production Economics, Resource /Energy Economics and Policy,
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