8,210 research outputs found
Cartographic research in EREP programme for small scale mapping
There are no author-identified significant results in this report
Exploring the use of Controlled English for communication with ACT-R agents
Research is being undertaken into sense-making by collaborative agents, based upon a cognitive framework of human behaviour, ACT-R, together with communication between the agents. We explore the use of Controlled English for this purpos
Conductivity in a disordered one-dimensional system of interacting fermions
Dynamical conductivity in a disordered one-dimensional model of interacting
fermions is studied numerically at high temperatures and in the
weak-interaction regime in order to find a signature of many-body localization
and vanishing d.c. transport coefficients. On the contrary, we find in the
regime of moderately strong local disorder that the d.c. conductivity sigma0
scales linearly with the interaction strength while being exponentially
dependent on the disorder. According to the behavior of the charge stiffness
evaluated at the fixed number of particles, the absence of the many-body
localization seems related to an increase of the effective localization length
with the interaction.Comment: 4 pages, 5 figures, submitted to PR
Universal model for exoergic bimolecular reactions and inelastic processes
From a rigorous multichannel quantum-defect formulation of bimolecular
processes, we derive a fully quantal and analytic model for the total rate of
exoergic bimolecular reactions and/or inelastic processes that is applicable
over a wide range of temperatures including the ultracold regime. The theory
establishes a connection between the ultracold chemistry and the regular
chemistry by showing that the same theory that gives the quantum threshold
behavior agrees with the classical Gorin model at higher temperatures. In
between, it predicts that the rates for identical bosonic molecules and
distinguishable molecules would first decrease with temperature outside of the
Wigner threshold region, before rising after a minimum is reached.Comment: 5 pages, 1 figur
PROTECTING RIPENING SWEET CORN FROM BLACKBIRDS IN IDAHO WITH 4-AMINOPYRIDINE
Chemicals recently have been used to reduce bird damage in a variety of crops. One such chemical, 4-aminopyridine (4AP), first reported for this use by Goodhue, et al. (1964), was tested by De Grazio, et al. (1971, 1972) and was shown to be a safe, economical, and effective chemical for reducing blackbird damage to ripening field corn. Blackbirds ingesting 4AP emit distress cries and perform aerial displays that frighten other members of the flock from the field. An advantage of this method of reducing damage is that usually less than one percent of the blackbird flock ingest baits and become affected (De Grazio, et al., 1972). A logical extension for the use of 4AP would be in preventing blackbird damage to ripening sweet corn. On 27 June 1974, the Environmental Protection Agency granted a permit (No. 11649-EXP-3G) to test the effectiveness of Avitrol FC Corn Chops-991 (cracked corn treated with 3 percent 4AP and diluted with untreated cracked corn at a 1:99 ratio) in reducing blackbird damage to this crop. This paper reports the results of a study conducted in 1974 to evaluate aerially-broadcast 4AP baits to protect ripening sweet-corn fields from blackbirds. I am indebted to L. Baer and D. Stohr of American Fine Food, Inc., of Payette, Idaho, for providing data on field locations and history of bird damage, and to the many landowners who allowed me to use their fields. I acknowledge field assistance given by R. L. Martinez (Bureau of Plant Industry, Philippines), A. Ouattara (FAO trainee), and R. N. Smith (U.S. Fish and Wildlife Service). I thank coworkers of the Denver Wildlife Research Center--J. E. Peterson for analysis of the sweet-corn samples for 4AP residues; J. F. Besser and J. L. Guarino for assistance in planning this study; and A. H. Jones for review of the manuscript
Doping Dependence of Polaron Hopping Energies in La(1-x)Ca(x)MnO(3) (0<= x<= 0.15)
Measurements of the low-frequency (f<= 100 kHz) permittivity at T<= 160 K and
dc resistivity (T<= 430 K) are reported for La(1-x)Ca(x)MnO(3) (0<= x<= 0.15).
Static dielectric constants are determined from the low-T limiting behavior of
the permittivity. The estimated polarizability for bound holes ~ 10^{-22}
cm^{-3} implies a radius comparable to the interatomic spacing, consistent with
the small polaron picture established from prior transport studies near room
temperature and above on nearby compositions. Relaxation peaks in the
dielectric loss associated with charge-carrier hopping yield activation
energies in good agreement with low-T hopping energies determined from
variable-range hopping fits of the dc resistivity. The doping dependence of
these energies suggests that the orthorhombic, canted antiferromagnetic ground
state tends toward an insulator-metal transition that is not realized due to
the formation of the ferromagnetic insulating state near Mn(4+) concentration ~
0.13.Comment: PRB in press, 5 pages, 6 figure
Wave functions in the neighborhood of a toroidal surface; hard vs. soft constraint
The curvature potential arising from confining a particle initially in
three-dimensional space onto a curved surface is normally derived in the hard
constraint limit, with the degree of freedom normal to the
surface. In this work the hard constraint is relaxed, and eigenvalues and wave
functions are numerically determined for a particle confined to a thin layer in
the neighborhood of a toroidal surface. The hard constraint and finite layer
(or soft constraint) quantities are comparable, but both differ markedly from
those of the corresponding two dimensional system, indicating that the
curvature potential continues to influence the dynamics when the particle is
confined to a finite layer. This effect is potentially of consequence to the
modelling of curved nanostructures.Comment: 4 pages, no fig
Theory of Anisotropic Hopping Transport due to Spiral Correlations in the Spin-Glass Phase of Underdoped Cuprates
We study the in-plane resistivity anisotropy in the spin-glass phase of the
high- cuprates, on the basis of holes moving in a spiral spin
background. This picture follows from analysis of the extended model with
Coulomb impurities. In the variable-range hopping regime the resistivity
anisotropy is found to have a maximum value of around 90%, and it decreases
with temperature, in excellent agreement with experiments in
LaSrCuO. In our approach the transport anisotropy is due to the
non-collinearity of the spiral spin state, rather than an intrinsic tendency of
the charges to self-organize.Comment: 5 pages, 4 figures; expanded versio
Insulator-metal-insulator transition and selective spectral weight transfer in a disordered strongly correlated system
We investigate the metal insulator transitions at finite temperature for the
Hubbard model with diagonal alloy disorder. We solve the dynamical mean field
theory equations with the non crossing approximation and we use the coherent
potential approximation to handle disorder. The excitation spectrum is given
for various correlation strength and disorder. Two successive metal
insulator transitions are observed at integer filling values as is
increased. An important selective transfer of spectral weight arises upon
doping. The strong influence of the temperature on the low energy dynamics is
studied in details.Comment: submitted to Phys. Rev.
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