14,182 research outputs found
A simulation study of Large Area Crop Inventory Experiment (LACIE) technology
The author has identified the following significant results. The LACIE performance predictor (LPP) was used to replicate LACIE phase 2 for a 15 year period, using accuracy assessment results for phase 2 error components. Results indicated that the (LPP) simulated the LACIE phase 2 procedures reasonably well. For the 15 year simulation, only 7 of the 15 production estimates were within 10 percent of the true production. The simulations indicated that the acreage estimator, based on CAMS phase 2 procedures, has a negative bias. This bias was too large to support the 90/90 criterion with the CV observed and simulated for the phase 2 production estimator. Results of this simulation study validate the theory that the acreage variance estimator in LACIE was conservative
Two-Dimensional Electrons in a Strong Magnetic Field with Disorder: Divergence of the Localization Length
Electrons on a square lattice with half a flux quantum per plaquette are
considered. An effective description for the current loops is given by a
two-dimensional Dirac theory with random mass. It is shown that the
conductivity and the localization length can be calculated from a product of
Dirac Green's functions with the {\it same} frequency. This implies that the
delocalization of electrons in a magnetic field is due to a critical point in a
phase with a spontaneously broken discrete symmetry. The estimation of the
localization length is performed for a generalized model with fermion
levels using a --expansion and the Schwarz inequality. An argument for the
existence of two Hall transition points is given in terms of percolation
theory.Comment: 10 pages, RevTeX, no figure
Interacting bosons in an optical lattice: Bose-Einstein condensates and Mott insulator
A dense Bose gas with hard-core interaction is considered in an optical
lattice. We study the phase diagram in terms of a special mean-field theory
that describes a Bose-Einstein condensate and a Mott insulator with a single
particle per lattice site for zero as well as for non-zero temperatures. We
calculate the densities, the excitation spectrum and the static structure
factor for each of these phases.Comment: 17 pages, 5 figures; 1 figure added, typos remove
Investigation into the redox behavior of bis(pentamethylcyclopentadienyl)(.mu.-.eta.1-disulfide)(.mu.-.eta.2-disulfide)diiron: an unexpected reversible .eta.1 .dblharw. .eta.2 rearrangement of a disulfur bridge
Integer Quantum Hall Effect for Lattice Fermions
A two-dimensional lattice model for non-interacting fermions in a magnetic
field with half a flux quantum per plaquette and levels per site is
considered. This is a model which exhibits the Integer Quantum Hall Effect
(IQHE) in the presence of disorder. It presents an alternative to the
continuous picture for the IQHE with Landau levels. The large limit can be
solved: two Hall transitions appear and there is an interpolating behavior
between the two Hall plateaux. Although this approach to the IQHE is different
from the traditional one with Landau levels because of different symmetries
(continuous for Landau levels and discrete here), some characteristic features
are reproduced. For instance, the slope of the Hall conductivity is infinite at
the transition points and the electronic states are delocalized only at the
transitions.Comment: 9 pages, Plain-Te
Morphological regions and oblique incidence dot formation in a model of surface sputtering
We study solid surface morphology created by off-normal ion-beam sputtering
with an atomistic, solid-on-solid model of sputter erosion. With respect to an
earlier version of the model, we extend this model with the inclusion of
lateral erosion. Using the 2-dimensional structure factor, we found an upper
bound , in the lateral straggle , for clear ripple formation.
Above this upper bound, for longitudinal straggle , we found
the possibility of dot formation (without sample rotation). Moreover, a
temporal crossover from a hole topography to ripple topography with the same
value of collision cascade parameters was found. Finally, a scaling analysis of
the roughness, using the consecutive gradient approach, yields the growth
exponents and 0.67 for two different topographic regimes.Comment: 8 pages, 14 figure
- …