7,746 research outputs found
Simulating spatial variability of cereal yields from historical yield maps and satellite imagery
[Abstract]: The management of spatial variability of crop yields relies on the availability of affordable and accurate spatial data. Yield maps are a direct measure of the crop yields, however, costs and difficulties in collection and processing to generate yield maps results in poor availability of such data in Australia. In this study, we used historical mid-season normalised difference vegetation index (NDVI), generated from Landsat imagery over 4 years. Using linear regression model, the NDVI was compared to the actual yield map from a 257 ha paddock. The difference between actual and predicted yield showed that 77% and 93% of the paddock area had an error of <20% and <30%, respectively. The linear model obtained in the paddock was used to simulate crop yield for an adjoining paddock of 162 ha. On an average of 4 years, the difference between actual and simulated yield showed that 87% of the paddock had an error of <20%. However, this error varied from season to season. Paddock area with <20% error increased exponentially with decreasing in-crop rainfall between anthesis and crop maturity. Furthermore, the error in simulating crop yield also varied with the soil constraints. Paddock zones with high concentrations of subsoil chloride and surface soil exchangeable sodium percentage generally had higher percent of error in simulating crop yields. Satellite imagery consistently over-predicted cereal yields in areas with subsoil constraints, possibly due to chloride-induced water stress during grain filling. The simulated yield mapping methodology offers an opportunity to identify within-field spatial variability using satellite imagery as a surrogate measure of biomass. However, the ability to successfully simulate crop yields at farm scale or regional scale requires wider evaluation across different soil types and climatic conditions
The hyperon mean free paths in the relativistic mean field
The - and -hyperon mean free paths in nuclei are firstly
calculated in the relativistic mean field (RMF) theory. The real parts of the
optical potential are derived from the RMF approach, while the imaginary parts
are obtained from those of nucleons with the relations:
and . With the
assumption, the depth of the imaginary potential for is
3.5 MeV, and for is 7 MeV at
low incident energy. We find that, the hyperon mean free path decreases with
the increase of the hyperon incident energies, from 200 MeV to 800 MeV; and in
the interior of the nuclei, the mean free path is about fm for
, and about fm for , depending on the hyperon
incident energy.Comment: 5 figures, 6 page
Understanding the critical role of boundary conditions in meso-scale finite element simulation of braided composites
A reasonable boundary condition for the meso-scale finite element (FE) simulation of textile composites is necessary for model validation against experiments, which is sometimes over-simplified for saving computation time. This paper examines the influence of boundary conditions on the global stressâstrain response and deformation pattern, as well as the local damage and failure characters, through systematically comparison studies of numerical results against experimental results under different loading conditions. The results suggest that reasonable application of periodic boundary conditions can effectively improve the calculation efficiency, and the employment of symmetric boundary conditions along the loading direction will cause the undesired strain concentration and premature damage at the loading edges of the model. Besides, extra constraints along the thickness direction may restrain the normal out-of-plane deformation of the braided composites and thereby cause an overestimation of the transverse strengths. Graphical abstract: [Figure not available: see fulltext.]
A Bogomol`nyi equation for intersecting domain walls
We argue that the Wess-Zumino model with quartic superpotential admits static
solutions in which three domain walls intersect at a junction. We derive an
energy bound for such junctions and show that configurations saturating it
preserve 1/4 supersymmetry.Comment: 4 pages revtex. No figures. Revised version to appear in Physical
Review Letters includes discussion of the supersymmetry algebr
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Osteocyte dysfunction promotes osteoarthritis through MMP13-dependent suppression of subchondral bone homeostasis.
Osteoarthritis (OA), long considered a primary disorder of articular cartilage, is commonly associated with subchondral bone sclerosis. However, the cellular mechanisms responsible for changes to subchondral bone in OA, and the extent to which these changes are drivers of or a secondary reaction to cartilage degeneration, remain unclear. In knee joints from human patients with end-stage OA, we found evidence of profound defects in osteocyte function. Suppression of osteocyte perilacunar/canalicular remodeling (PLR) was most severe in the medial compartment of OA subchondral bone, with lower protease expression, diminished canalicular networks, and disorganized and hypermineralized extracellular matrix. As a step toward evaluating the causality of PLR suppression in OA, we ablated the PLR enzyme MMP13 in osteocytes while leaving chondrocytic MMP13 intact, using Cre recombinase driven by the 9.6-kb DMP1 promoter. Not only did osteocytic MMP13 deficiency suppress PLR in cortical and subchondral bone, but it also compromised cartilage. Even in the absence of injury, osteocytic MMP13 deficiency was sufficient to reduce cartilage proteoglycan content, change chondrocyte production of collagen II, aggrecan, and MMP13, and increase the incidence of cartilage lesions, consistent with early OA. Thus, in humans and mice, defects in PLR coincide with cartilage defects. Osteocyte-derived MMP13 emerges as a critical regulator of cartilage homeostasis, likely via its effects on PLR. Together, these findings implicate osteocytes in bone-cartilage crosstalk in the joint and suggest a causal role for suppressed perilacunar/canalicular remodeling in osteoarthritis
Comparison of Zn_{1-x}Mn_xTe/ZnTe multiple-quantum wells and quantum dots by below-bandgap photomodulated reflectivity
Large-area high density patterns of quantum dots with a diameter of 200 nm
have been prepared from a series of four Zn_{0.93}Mn_{0.07}Te/ZnTe multiple
quantum well structures of different well width (4 nm, 6 nm, 8 nm and 10 nm) by
electron beam lithography followed by Ar+ ion beam etching. Below-bandgap
photomodulated reflectivity spectra of the quantum dot samples and the parent
heterostructures were then recorded at 10 K and the spectra were fitted to
extract the linewidths and the energy positions of the excitonic transitions in
each sample. The fitted results are compared to calculations of the transition
energies in which the different strain states in the samples are taken into
account. We show that the main effect of the nanofabrication process is a
change in the strain state of the quantum dot samples compared to the parent
heterostructures. The quantum dot pillars turn out to be freestanding, whereas
the heterostructures are in a good approximation strained to the ZnTe lattice
constant. The lateral size of the dots is such that extra confinement effects
are not expected or observed.Comment: 23 pages, LaTeX2e (amsmath, epsfig), 7 EPS figure
Photoluminescence and photoluminescence excitation studies of lateral size effects in Zn_{1-x}Mn_xSe/ZnSe quantum disc samples of different radii
Quantum disc structures (with diameters of 200 nm and 100 nm) were prepared
from a Zn_{0.72}Mn_{0.28}Se/ZnSe single quantum well structure by electron beam
lithography followed by an etching procedure which combined dry and wet etching
techniques. The quantum disc structures and the parent structure were studied
by photoluminescence and photoluminescence excitation spectroscopy. For the
light-hole excitons in the quantum well region, shifts of the energy positions
are observed following fabrication of the discs, confirming that strain
relaxation occurs in the pillars. The light-hole exciton lines also sharpen
following disc fabrication: this is due to an interplay between strain effects
(related to dislocations) and the lateral size of the discs. A further
consequence of the small lateral sizes of the discs is that the intensity of
the donor-bound exciton emission from the disc is found to decrease with the
disc radius. These size-related effects occur before the disc radius is reduced
to dimensions necessary for lateral quantum confinement to occur but will
remain important when the discs are made small enough to be considered as
quantum dots.Comment: LaTeX2e, 13 pages, 6 figures (epsfig
Evolutionary multi-stage financial scenario tree generation
Multi-stage financial decision optimization under uncertainty depends on a
careful numerical approximation of the underlying stochastic process, which
describes the future returns of the selected assets or asset categories.
Various approaches towards an optimal generation of discrete-time,
discrete-state approximations (represented as scenario trees) have been
suggested in the literature. In this paper, a new evolutionary algorithm to
create scenario trees for multi-stage financial optimization models will be
presented. Numerical results and implementation details conclude the paper
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