5,592 research outputs found
An Overview of the Use of the SimSphere Soil Vegetation Atmosphere Transfer (SVAT) Model for the Study of Land-Atmosphere Interactions
Soil Vegetation Atmosphere Transfer (SVAT) models consist of deterministic mathematical representations of the physical processes involved between the land surface and the atmosphere and of their interactions, at time-steps acceptable for the study of land surface processes. The present article provides a comprehensive and systematic review of one such SVAT model suitable for use in mesoscale or boundary layer studies, originally developed by [1]. This model, which has evolved significantly both architecturally and functionally since its foundation, has been widely applied in over thirty interdisciplinary science investigations, and it is currently used as a learning resource for students in a number of educational institutes globally. The present review is also regarded as very timely, since a variation of a method using this specific SVAT model along with satellite observations is currently being considered in a scheme being developed for the operational retrieval of soil surface moisture by the US National Polar-orbiting Operational Environmental Satellite System (NPOESS), in a series of satellites that are due to be launched from 2016 onwards
Auxiliary field diffusion Monte Carlo calculations of magnetic moments of light nuclei with chiral EFT interactions
We calculate the magnetic moments of light nuclei () using the
auxiliary field diffusion Monte Carlo method and local two- and three-nucleon
forces with electromagnetic currents from chiral effective field theory. For
all nuclei under consideration, we also calculate the ground-state energies and
charge radii. We generally find a good agreement with experimental values for
all of these observables. For the electromagnetic currents, we explore the
impact of employing two different power countings, and study theoretical
uncertainties stemming from the truncation of the chiral expansion
order-by-order for select nuclei within these two approaches. We find that it
is crucial to employ consistent power countings for interactions and currents
to achieve a systematic order-by-order convergence.Comment: 7 pages, 4 figures, supplemental materia
Equilibration of quantum many-body fast neutrino flavor oscillations
Neutrino gases are expected to form in high density astrophysical
environments, and accurately modeling their flavor evolution is critical to
understanding such environments. In this work we study a simplified model of
such a dense neutrino gas in the regime for which neutrino-neutrino coherent
forward scattering is the dominant mechanism contributing to the flavor
evolution. We show evidence that the generic potential induced by this effect
is non-integrable and that the statistics of its energy level spaces are in
good agreement with the Wigner surmise. We also find that individual neutrinos
rapidly entangle with all of the others present which results in an
equilibration of the flavor content of individual neutrinos. We show that the
average neutrino flavor content can be predicted utilizing a thermodynamic
partition function. A random phase approximation to the evolution gives a
simple picture of this equilibration. In the case of neutrinos and
antineutrinos, processes like yield a rapid equilibrium satisfying in
addition to the standard lepton number conservation in regimes where
off-diagonal vacuum oscillations are small compared to interactions.Comment: 16 pages, 8 figures, 1 appendi
Mantle Sources and Geochemical Evolution of the Picture Gorge Basalt, Columbia River Basalt Group
The Columbia River Basalt Group (CRBG) is the youngest continental flood basalt province, proposed to be sourced from the deep-seated plume that currently resides underneath Yellowstone National Park. If so, the earliest erupted basalts from this province, such as those in the Picture Gorge Basalt (PGB), aid in understanding and modeling plume impingement and the subsequent evolution of basaltic volcanism. Using geochemical and isotopic data, this study explores potential mantle sources and magma evolution of the PGB. Long known geochemical signatures of the PGB include overall large ion lithophile element (LILE) enrichment and relative depletion of high field strength elements (HFSE) typical of other CRBG main-phase units. Basaltic samples of the PGB have 87Sr/86Sr ratios on the low end of the range displayed by other CRBG lavas and mantle-like δ18O values. The relatively strong enrichment of LILE and depletion of HFSE coupled with depleted isotopic signatures suggest a metasomatized upper mantle as the most likely magmatic source for the PGB. Previous geochemical modeling of the PGB utilized the composition of two high-MgO primitive dikes exposed in the northern portion of the Monument Dike swarm as parental melt. However, fractionation of these dike compositions cannot generate the compositional variability illustrated by basaltic lavas and dikes of the PGB. This study identifies a second potential parental PGB composition best represented by basaltic flows in the extended spatial distribution of the PGB. This composition also better reflects the lowest stratigraphic flows identified in the previously mapped extent of the PGB. Age data reveal that PGB lavas erupted first and throughout eruptions of main-phase CRBG units (Steens, Imnaha, Grande Ronde Basalt). Combining geochemical signals with these age data indicates cyclical patterns in the amounts of contributing mantle components. Eruption of PGB material occurred in two pulses, demonstrated by a ~0.4 Ma temporal gap in reported ages, 16.62 to 16.23 Ma. Coupling ages with observed geochemical signals, including relative elemental abundances of LILE, indicates increased influence of a more primitive, potentially plume-like source with time
Complete Analysis of Baryon Magnetic Moments in 1/N_c
We generate a complete basis of magnetic moment operators for the N_c = 3
ground-state baryons in the 1/N_c expansion, and compute and tabulate all
associated matrix elements. We then compare to previous results derived in the
literature and predict additional relations among baryon magnetic moments
holding to subleading order in 1/N_c and flavor SU(3) breaking. Finally, we
predict all unknown diagonal and transition magnetic moments to <= 0.15 mu_N
accuracy, and suggest possible experimental measurements to improve the
analysis even further.Comment: 28 pages (including 11 tables), ReVTeX. One reference and grant
acknowledgment adde
The BCS Functional for General Pair Interactions
The Bardeen-Cooper-Schrieffer (BCS) functional has recently received renewed
attention as a description of fermionic gases interacting with local pairwise
interactions. We present here a rigorous analysis of the BCS functional for
general pair interaction potentials. For both zero and positive temperature, we
show that the existence of a non-trivial solution of the nonlinear BCS gap
equation is equivalent to the existence of a negative eigenvalue of a certain
linear operator. From this we conclude the existence of a critical temperature
below which the BCS pairing wave function does not vanish identically. For
attractive potentials, we prove that the critical temperature is non-zero and
exponentially small in the strength of the potential.Comment: Revised Version. To appear in Commun. Math. Phys
A Conjecture about Hadrons
We conjecture that in the chiral limit of QCD the spectrum of hadrons is
comprised of decoupled, reducible chiral multiplets. A simple rule is developed
which identifies the chiral representations filled out by the ground-state
hadrons. Our arguments are based on the algebraic structure of superconvergence
relations derived by Weinberg from the high-energy behavior of pion-hadron
scattering amplitudes.Comment: 15 pages LaTe
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The global distribution of Bacillus anthracis and associated anthrax risk to humans, livestock and wildlife.
Bacillus anthracis is a spore-forming, Gram-positive bacterium responsible for anthrax, an acute infection that most significantly affects grazing livestock and wild ungulates, but also poses a threat to human health. The geographic extent of B. anthracis is poorly understood, despite multi-decade research on anthrax epizootic and epidemic dynamics; many countries have limited or inadequate surveillance systems, even within known endemic regions. Here, we compile a global occurrence dataset of human, livestock and wildlife anthrax outbreaks. With these records, we use boosted regression trees to produce a map of the global distribution of B. anthracis as a proxy for anthrax risk. We estimate that 1.83 billion people (95% credible interval (CI): 0.59-4.16 billion) live within regions of anthrax risk, but most of that population faces little occupational exposure. More informatively, a global total of 63.8 million poor livestock keepers (95% CI: 17.5-168.6 million) and 1.1 billion livestock (95% CI: 0.4-2.3 billion) live within vulnerable regions. Human and livestock vulnerability are both concentrated in rural rainfed systems throughout arid and temperate land across Eurasia, Africa and North America. We conclude by mapping where anthrax risk could disrupt sensitive conservation efforts for wild ungulates that coincide with anthrax-prone landscapes
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