3,276 research outputs found
Positive Analysis of Invasive Species Control as a Dynamic Spatial Process
This paper models control of invasive buffelgrass (Pennisetum ciliare), a fire-prone African bunchgrass spreading rapidly across the southern Arizona desert as a spatial dynamic process. Buffelgrass spreads over a gridded landscape. Weed carrying capacity, treatment costs, and damages vary over grid cells. Damage from buffelgrass depends on its spatial distribution in relation to valued resources. We conduct positive analysis of recommended heuristic strategies for buffelgrass control, evaluating their ability to prevent weed establishment and to reduce damage indices over time. The high dimensionality of the problem makes full dynamic optimization intractable. However, two heuristic strategies – potential damage weighting and consecutive year treatment – perform well in terms of percent damage reduction relative to no treatment and to static optimization. Results also suggest specific recommendations for deployment of rapid rapid-response teams to prevent invasions in new areas. The long-run population size and spatial distribution of buffelgrass is sensitive to priority weights for protection of different resources. Land managers with different priorities may pursue quite different control strategies, which may pose a challenge for coordinating control across jurisdictions.invasive species, integer programming, Crop Production/Industries, Environmental Economics and Policy, Q57, Q58,
Wide range optical studies on transparent SWNT films
We present transmission spectra from the far infrared through the ultraviolet region on
freestanding SWNT films at temperatures between 40 and 300 K. Several interesting features are
observed in the low-frequency part of the spectrum: the Drude-like frequency dependence of the
metallic tubes as well as a (sample-dependent) peak in the conductivity around 0.01 eV. We also
studied the accidental nitrate doping of the SWNT samples during purification by nitric acid. Asprepared
purified samples exhibit increased metallic absorption and decreased interband transitions;
these features disappear on heating in vacuum
A PC computer program minimix for the calculation of the stability constans of MqLpLp´, type mixed or the mixture of MqLp and MqLp´ complexes from spectrophotometric measurements
Submicron plasticity: yield stress, dislocation avalanches, and velocity distribution
The existence of a well defined yield stress, where a macroscopic piece of
crystal begins to plastically flow, has been one of the basic observations of
materials science. In contrast to macroscopic samples, in micro- and
nanocrystals the strain accumulates in distinct, unpredictable bursts, which
makes controlled plastic forming rather difficult. Here we study by simulation,
in two and three dimensions, plastic deformation of submicron objects under
increasing stress. We show that, while the stress-strain relation of individual
samples exhibits jumps, its average and mean deviation still specify a
well-defined critical stress, which we identify with the jamming-flowing
transition. The statistical background of this phenomenon is analyzed through
the velocity distribution of short dislocation segments, revealing a universal
cubic decay and an appearance of a shoulder due to dislocation avalanches. Our
results can help to understand the jamming-flowing transition exhibited by a
series of various physical systems.Comment: 5 page
Universal Pion Freeze-out Phase-Space Density
Results on the pion freeze-out phase-space density in sulphur-nucleus, Pb-Pb
and pion-proton collisions at CERN-SPS are presented. All heavy-ion reactions
are consistent with the thermal Bose-Einstein distrtibution f=1/(exp(E/T)-1) at
T~120 MeV, modified for expansion. Pion-proton data are also consistent with f,
but at T~180 MeV.Comment: 1 page, 1 figure; 98' report for GSI-Darmstad
Nonequilibrium phase transition in a driven Potts model with friction
We consider magnetic friction between two systems of -state Potts spins
which are moving along their boundaries with a relative constant velocity .
Due to the interaction between the surface spins there is a permanent energy
flow and the system is in a steady state which is far from equilibrium. The
problem is treated analytically in the limit (in one dimension, as
well as in two dimensions for large- values) and for and finite by
Monte Carlo simulations in two dimensions. Exotic nonequilibrium phase
transitions take place, the properties of which depend on the type of phase
transition in equilibrium. When this latter transition is of first order, a
sequence of second- and first-order nonequilibrium transitions can be observed
when the interaction is varied.Comment: 13 pages, 9 figures, one journal reference adde
Estimation of regional differences in wind erosion sensitivity in Hungary
In Hungary, wind erosion is one of the most serious natural hazards. Spatial
and temporal variation in the factors that determine the location and
intensity of wind erosion damage are not well known, nor are the regional
and local sensitivities to erosion. Because of methodological challenges, no
multi-factor, regional wind erosion sensitivity map is available for
Hungary. The aim of this study was to develop a method to estimate the
regional differences in wind erosion sensitivity and exposure in Hungary.
Wind erosion sensitivity was modelled using the key factors of soil
sensitivity, vegetation cover and wind erodibility as proxies. These factors
were first estimated separately by factor sensitivity maps and later
combined by fuzzy logic into a regional-scale wind erosion sensitivity map.
Large areas were evaluated by using publicly available data sets of remotely
sensed vegetation information, soil maps and meteorological data on wind
speed. The resulting estimates were verified by field studies and examining
the economic losses from wind erosion as compensated by the state insurance
company. The spatial resolution of the resulting sensitivity map is suitable
for regional applications, as identifying sensitive areas is the foundation
for diverse land development control measures and implementing management
activities
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