388 research outputs found
Nonmetro Recreation Counties: Their Identification and Rapid Growth
More than 80 percent of the Nation’s 285 million people now reside in metropolitan areas. Many in this vast city and suburban population are attracted to the recreational opportunities and attractions of rural areas, such as beautiful scenery, lakes, mountains, forests, and resorts. For rural communities struggling to offset job losses from farming, mining, and manufacturing, capitalizing on the recreational appeal of an area fosters economic development, attracts new residents, and retains existing population. This article outlines a method to identify nonmetro counties with high recreation development. It then examines the linkage between such development and population change, and considers its implications for the future of rural and small-town America
Bootstrapped Block Lanczos for large-dimension eigenvalue problems
The Lanczos algorithm has proven itself to be a valuable matrix eigensolver
for problems with large dimensions, up to hundreds of millions or even tens of
billions. The computational cost of using any Lanczos algorithm is dominated by
the number of sparse matrix-vector multiplications until suitable convergence
is reached. Block Lanczos replaces sparse matrix-vector multiplication with
sparse matrix-matrix multiplication, which is more efficient, but for a
randomly chosen starting block (or pivot), more multiplications are required to
reach convergence. We find that a bootstrapped pivot block, that is, an initial
block constructed from approximate eigenvectors computed in a truncated space,
leads to a dramatically reduced number of multiplications, significantly
outperforming both standard vector Lanczos and block Lanczos with a random
pivot. A key condition for speed-up is that the pivot block have a non-trivial
overlap with the final converged vectors. We implement this approach in a
configuration-interaction code for nuclear structure, and find a reduction in
time-to-solution by a factor of two or more, up to a factor of ten.Comment: 14 pages, 5 figures, 2 table
Behavior of shell-model configuration moments
An important input into reaction theory is the density of states or the level
density. Spectral distribution theory (also known as nuclear statistical
spectroscopy) characterizes the secular behavior of the density of states
through moments of the Hamiltonian. One particular approach is to partition the
model space into subspaces and find the moments in those subspaces; a
convenient choice of subspaces are spherical shell-model configurations. We
revisit these configuration moments and find, for complete
many-body spaces, the following behaviors: (a) the configuration width is
nearly constant for all configurations; (b) the configuration asymmetry or
third moment is strongly correlated with the configuration centroid; (c) the
configuration fourth moment, or excess is linearly related to the square to the
configuration asymmetry. Such universal behavior may allow for more efficient
modeling of the density of states in a shell-model framework.Comment: 12 pages, 8 figure
Uncertainty quantification of transition operators in the empirical shell model
While empirical shell model calculations have successfully described
low-lying nuclear data for decades, only recently has significant effort been
made to quantify the uncertainty in such calculations. Here we quantify the
statistical error in effective parameters for transition operators in empirical
calculations in the (--) valence space,
specifically the quenching of Gamow-Teller transitions, effective charges for
electric quadrupole (E2) transitions, and the effective orbital and spin
couplings for magnetic dipole (M1) transitions. We find the quenching factor
for Gamow-Teller transitions relative to free-space values is tightly
constrained and that the isoscalar coupling of E2 is much more tightly
constrained than the isovector coupling. For effective M1 couplings, we found
isovector components more constrained than isoscalar, but that to get any
sensible result we had to fix one of four couplings. This detailed
quantification of uncertainties, while highly empirical, nonetheless is an
important step towards interpretation of experiments
Radiolysis of water ice in the outer solar system: Sputtering and trapping of radiation products
We performed quantitative laboratory radiolysis experiments on cubic water ice between 40 and 120 K, with 200 keV protons. We measured sputtering of atoms and molecules and the trapping of radiolytic molecular species. The experiments were done at fluences corresponding to exposure of the surface of the Jovian icy satellites to their radiation environment up to thousands of years. During irradiation, O2 molecules are ejected from the ice at a rate that grows roughly exponentially with temperature; this behavior is the main reason for the temperature dependence of the total sputtering yield. O2 trapped in the ice is thermally released from the ice upon warming; the desorbed flux starts at the irradiation temperature and increases strongly above 120 K. Several peaks in the desorption spectrum, which depend on irradiation temperature, point to a complex distribution of trapping sites in the ice matrix. The yield of O2 produced by the 200 keV protons and trapped in the ice is more than 2 orders of magnitude smaller than used in recent models of Ganymede. We also found small amounts of trapped H2O2 that desorb readily above 160 K.Fil: Bahr, D.A.. University of Virginia; Estados UnidosFil: Famá, M.. University of Virginia; Estados UnidosFil: Vidal, Ricardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Baragiola, Raul Antonio. University of Virginia; Estados Unido
Benefits of greenhouse gas mitigation on the supply, management, and use of water resources in the United States
Climate change impacts on water resources in the United States are likely to be far-reaching and substantial because the water is integral to climate, and the water sector spans many parts of the economy. This paper estimates impacts and damages from five water resource-related models addressing runoff, drought risk, economics of water supply/demand, water stress, and flooding damages. The models differ in the water system assessed, spatial scale, and unit of assessment, but together provide a quantitative and descriptive richness in characterizing water sector effects that no single model can capture. The results, driven by a consistent set of greenhouse gas (GHG) emission and climate scenarios, examine uncertainty from emissions, climate sensitivity, and climate model selection. While calculating the net impact of climate change on the water sector as a whole may be impractical, broad conclusions can be drawn regarding patterns of change and benefits of GHG mitigation. Four key findings emerge: 1) GHG mitigation substantially reduces hydro-climatic impacts on the water sector; 2) GHG mitigation provides substantial national economic benefits in water resources related sectors; 3) the models show a strong signal of wetting for the Eastern US and a strong signal of drying in the Southwest; and 4) unmanaged hydrologic systems impacts show strong correlation with the change in magnitude and direction of precipitation and temperature from climate models, but managed water resource systems and regional economic systems show lower correlation with changes in climate variables due to non-linearities created by water infrastructure and the socio-economic changes in non-climate driven water demand
The uncertainties on the EFT coupling limits for direct dark matter detection experiments stemming from uncertainties of target properties
Direct detection experiments are still one of the most promising ways to
unravel the nature of dark matter. To fully understand how well these
experiments constrain the dark matter interactions with the Standard Model
particles, all the uncertainties affecting the calculations must be known. It
is especially critical now because direct detection experiments recently moved
from placing limits only on the two elementary spin independent and spin
dependent operators to the complete set of possible operators coupling dark
matter and nuclei in non-relativistic theory. In our work, we estimate the
effect of nuclear configuration-interaction uncertainties on the exclusion
bounds for one of the existing xenon-based experiments for all fifteen
operators. We find that for operator number 13 the uncertainty on
the coupling between the dark matter and nucleon can reach more than 50% for
dark matter masses between 10 and 1000 GeV. In addition, we discuss how quantum
computers can help to reduce this uncertainty.Comment: 12 pages, 6 figures; submitted to Phys. Rev. D, May 17, 202
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