6,998 research outputs found
Microscopic mass estimations
The quest to build a mass formula which have in it the most relevant
microscopic contributions is analyzed. Inspired in the successful Duflo-Zuker
mass description, the challenges to describe the shell closures in a more
transparent but equally powerful formalism are discussed.Comment: 14 pages, 6 figures, submitted to Journal of Physics G, Focus issue
on Open Problems in Nuclear Structure Theor
Exclusive W^+ + photon production in proton-antiproton collisions II: results
We present results for total cross sections, single and double differential
distributions and correlations between pairs of outgoing particles in the
reactions p + antip --> W^+ + photon and p + antip --> W^+ + photon + jet at
sqrt(S)=1.8 TeV. Order alpha-strong QCD corrections and leading logarithm
photon bremsstrahlung contributions are included in the MS-bar mass
factorization scheme for three experimental scenarios: 1) 2-body inclusive
production of W^+ and photon, 2) exclusive production of W^+, photon and 1 jet
and 3) exclusive production of W^+ and photon with 0 jet.
The latest CTEQ parton distribution functions, which fit the newly released
HERA data, are used in our analysis. The dependence of our results on the mass
factorization scale is used to place error bars on our predictions for the
single differential distributions and correlations.Comment: 15 pages (LateX). 50 pages of postscript figures available via ftp
anonymous from max.physics.sunysb.edu in the directory
preprints/mendoza/EXCLUSIVE_W_GAMMA_II.dir (files named fig_*.ps)
ITP-SB-93-80. ([email protected])([email protected]
Polarization and readout of coupled single spins in diamond
We study the coupling of a single nitrogen-vacancy center in diamond to a
nearby single nitrogen defect at room temperature. The magnetic dipolar
coupling leads to a splitting in the electron spin resonance frequency of the
nitrogen-vacancy center, allowing readout of the state of a single nitrogen
electron spin. At magnetic fields where the spin splitting of the two centers
is the same we observe a strong polarization of the nitrogen electron spin. The
amount of polarization can be controlled by the optical excitation power. We
combine the polarization and the readout in time-resolved pump-probe
measurements to determine the spin relaxation time of a single nitrogen
electron spin. Finally, we discuss indications for hyperfine-induced
polarization of the nitrogen nuclear spin
Relating United States Crop Land Use to Natural Resources and Climate Change
Crop production depends not only on the yield but also on the area harvested. The yield response to climate change has been widely examined, but the sensitivity of crop land use to hypothetical climate change has not been examined directly. Crop land-use regression models for estimating crop area indices (CAIs) - the percent of land used for corn, soybean, wheat, and sorghum production - are presented. Inputs to the models include available water-holding capacity of the soil, percent of land available for rain-fed agricultural production, annual precipitation, and annual temperature. The total variance of CAI explained by the models ranged from 78% for wheat to 87% for sorghum, and the root-mean-square errors ranged from 1.74% for sorghum to 4.24% for corn. The introduction of additional climatic variables to the models did not significantly improve their performance.
The crop land-use models were used to predict the CAI for every crop reporting district in the United States for the current climatic condition and for possible future climate change scenarios (various combinations of temperature and precipitation changes over a range of -3° to +6°C and -20% to +20%, respectively). The magnitude of climatic warning suggested by GCMs (GISS and GFDL) is from 3.5° to 5.9°C for regions of the United States. For this magnitude of warming, the model suggests corn and soybean production areas may decline while wheat and sorghum production areas may expand. If the warming is accompanied by a decrease in annual precipitation from 1% to 10%, then the areas used for corn and soybean production could decrease by as much as 20% and 40%, respectively. The area for sorghum and wheat under these conditions would increase by as much as 80% and 70%, respectively; the exact amount depending strongly on the change in precipitation. In general, small changes in temperature or precipitation produced larger corresponding changes (on a percentage basis) in soybean, wheat, and sorghum area than in corn area
Relating United States Crop Land Use to Natural Resources and Climate Change
Crop production depends not only on the yield but also on the area harvested. The yield response to climate change has been widely examined, but the sensitivity of crop land use to hypothetical climate change has not been examined directly. Crop land-use regression models for estimating crop area indices (CAIs) - the percent of land used for corn, soybean, wheat, and sorghum production - are presented. Inputs to the models include available water-holding capacity of the soil, percent of land available for rain-fed agricultural production, annual precipitation, and annual temperature. The total variance of CAI explained by the models ranged from 78% for wheat to 87% for sorghum, and the root-mean-square errors ranged from 1.74% for sorghum to 4.24% for corn. The introduction of additional climatic variables to the models did not significantly improve their performance.
The crop land-use models were used to predict the CAI for every crop reporting district in the United States for the current climatic condition and for possible future climate change scenarios (various combinations of temperature and precipitation changes over a range of -3° to +6°C and -20% to +20%, respectively). The magnitude of climatic warning suggested by GCMs (GISS and GFDL) is from 3.5° to 5.9°C for regions of the United States. For this magnitude of warming, the model suggests corn and soybean production areas may decline while wheat and sorghum production areas may expand. If the warming is accompanied by a decrease in annual precipitation from 1% to 10%, then the areas used for corn and soybean production could decrease by as much as 20% and 40%, respectively. The area for sorghum and wheat under these conditions would increase by as much as 80% and 70%, respectively; the exact amount depending strongly on the change in precipitation. In general, small changes in temperature or precipitation produced larger corresponding changes (on a percentage basis) in soybean, wheat, and sorghum area than in corn area
Planning Complex Agro-Ecosystems: The Case of Analog Forestry
Traditional agroecosystems, aimed at maximizing the short term productivity, are characterized by
oversimplification of ecological structure and dependence on the use of external inputs. Moreover,
intensive agriculture is one of the main cause of deforestation. The main consequence of traditional
agriculture is the loss of natural ecosystems and of their precious services. Analog forestry has emerged
as a sustainable productive model able to be integrated in forest contexts, without degrading their
ecological functions. The obtained agro-ecosystem is characterized by an ecological structure similar to
the one of forest, and by the presence of several productive species in the same area. In this study we
formalize a planning problem aimed at the optimized design of an analog forest on the medium term. In
particular, besides the maximization of income, we considered both ecological (i.e., the presence of
different vertical layers and several species) and socio-economic requirements (i.e., the smoothing of
both inter- and intra-annual variability of income). We focus the analysis on the Peruvian Amazon, basing
on a species database created by ArBio, a Peruvian association which promotes the analog forestry as
tool for pursuing the conservation of forest ecosystem services. The obtained results show that the interannual
income variability, characterizing an approach of short-term maximization, can be eliminated by
adopting the gradual planting of individuals belonging to the same species. Secondly, we quantified the
economic and ecological performance of the designed analog forest under different settings of the
planning problem. The introduction of the defined ecological and socio-economic constraints affects the
economic performance on the medium term, by reducing the annual economic income up to 80%
Soil and water pollution in a banana production region in tropical Mexico
The effects of abundant Mancozeb (Mn, Zn— bisdithiocarbamate) applications (2.5 kg ha-1week-1 for 10 years) on soil and surface-, subsurface- and groundwater pollution were monitored in a banana production region of tropical Mexico. In soils, severe manganese accumulation was observed, wheras the main metabolite ethylenethiourea was near the detection limit. Surface and subsurface water was highly polluted with ethylenethiourea, the main metabolite of Mancozeb (22.5 and 4.3 lg L-1, respectively), but not with manganese. In deep ground water, no ethylenethiourea was detected. The level of pollution in the region presents a worrisome risk for aquatic life and for human health
On the Nature of Andromeda IV
Lying at a projected distance of 40' or 9 kpc from the centre of M31,
Andromeda IV is an enigmatic object first discovered during van den Bergh's
search for dwarf spheroidal companions to M31. Being bluer, more compact and
higher surface brightness than other known dwarf spheroidals, it has been
suggested that And IV is either a relatively old `star cloud' in the outer disk
of M31 or a background dwarf galaxy. We present deep HST WFPC2 observations of
And IV and the surrounding field which, along with ground-based long-slit
spectroscopy and Halpha imagery, are used to decipher the true nature of this
puzzling object. We find compelling evidence that And IV is a background galaxy
seen through the disk of M31. The moderate surface brightness (SB(V)~24), very
blue colour (V-I<~0.6), low current star formation rate (~0.001 solar mass/yr)
and low metallicity (~10% solar) reported here are consistent with And IV being
a small dwarf irregular galaxy, perhaps similar to Local Group dwarfs such as
IC 1613 and Sextans A. Although the distance to And IV is not tightly
constrained with the current dataset, various arguments suggest it lies in the
range 5<~D<~8 Mpc, placing it well outside the confines of the Local Group. It
may be associated with a loose group of galaxies, containing major members UGC
64, IC 1727 and NGC 784. We report an updated position and radial velocity for
And IV.Comment: 26 pages, LaTex with 9 figures (including 6 jpg plates). Accepted for
publication in A
The Current Status of the Distribution Range of the Western Pine Beetle, Dendroctonus brevicomis (Curculionidae: Scolytinae) in Northern Mexico
Abstract The distribution range of the western pine beetle Dendroctonus brevicomis LeConte (Coleoptera: Curculionidae) is supported only by scattered records in the northern parts of Mexico, suggesting that its populations may be marginal and rare in this region. In this study, we review the geographical distribution of D. brevicomis in northern Mexico and perform a geometric morphometric analysis of seminal rod shape to evaluate its reliability for identifying this species with respect to other members of the Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae) complex. Our results provide 30 new records, with 26 distributed in the Sierra Madre Occidental and 4 in the Sierra Madre Oriental. These records extend the known distribution range of D. brevicomis to Durango and Tamaulipas states in northern Mexico. Furthermore, we find high geographic variation in size and shape of the seminal rod, with conspicous differences among individuals from different geographical regions, namely west and east of the Great Basin and between mountain systems in Mexico.
Key words: seminal rod shape, geometric morphometry, Dendroctonus frontalis comple
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