2,274 research outputs found
Influence of external magnetic fields on growth of alloy nanoclusters
Kinetic Monte Carlo simulations are performed to study the influence of
external magnetic fields on the growth of magnetic fcc binary alloy
nanoclusters with perpendicular magnetic anisotropy. The underlying kinetic
model is designed to describe essential structural and magnetic properties of
CoPt_3-type clusters grown on a weakly interacting substrate through molecular
beam epitaxy. The results suggest that perpendicular magnetic anisotropy can be
enhanced when the field is applied during growth. For equilibrium bulk systems
a significant shift of the onset temperature for L1_2 ordering is found, in
agreement with predictions from Landau theory. Stronger field induced effects
can be expected for magnetic fcc-alloys undergoing L1_0 ordering.Comment: 10 pages, 3 figure
Transmission, reflection and localization in a random medium with absorption or gain
We study reflection and transmission of waves in a random tight-binding
system with absorption or gain for weak disorder, using a scattering matrix
formalism. Our aim is to discuss analytically the effects of absorption or gain
on the statistics of wave transport. Treating the effects of absorption or gain
exactly in the limit of no disorder, allows us to identify short- and long
lengths regimes relative to absorption- or gain lengths, where the effects of
absorption/gain on statistical properties are essentially different. In the
long-lengths regime we find that a weak absorption or a weak gain induce
identical statistical corrections in the inverse localization length, but lead
to different corrections in the mean reflection coefficient. In contrast, a
strong absorption or a strong gain strongly suppress the effect of disorder in
identical ways (to leading order), both in the localization length and in the
mean reflection coefficient.Comment: Important revisions and expansion caused by a crucial property of
$\hat Q
Elementary School Math Instruction: Can Reading Specialist Assist?
While experts in the field of reading increasingly agree on the importance of direct instruction in vocabulary building, professionals in the field of elementary school mathematics tend to emphasize the use of concrete, manipulative materials and informal math language development over direct, specific instruction in technical terms or verbalizations of concepts. Today\u27s elementary classroom teachers find contradictory recommendations when they seek to make decisions about teaching the meanings of technical words in their mathematics classes. This article presents a discussion of the contradictions and some suggestions for practical resolution of disagreements, which will enable school reading specialists to provide both background and practical help to classroom teachers
Management of the Rice Tungro Virus Vector \u3ci\u3eNephotettix virescens\u3c/i\u3e (Homoptera: Cicadellidae) with Controlled-Release Formulations of Carbofuran
Field trials were conducted in lowland flooded rice in the Philippines to evaluate a number of carbofuran controlled-release formulations in comparison with commercial formulations. The test formulations were based on a biodegradable matrix of pine kraft lignin and were used as granules of different sizes and also in the form of small strips. The release rates were assessed under field conditions by bioassaying rice plants in the field, using adult rice green leafhopper, Nephotettix virescens Distant. The lignin formulations with a high level of active ingredient (15–45% by weight) gave as good or better control than the commercial 3% granules in tests based on three application techniques: broadcast into the floodwater, soil incorporation, and root zone injection. The improvements in control levels of green leafhoppers were most marked with soil incorporation and root zone application. The best lignin-based formulation reduced levels of tungro virus infection from 23% for a conventional flowable carbofuran formulation to 1.0% at an application rate of 0.5 kg (AI)/ha. At the same rate, the grain yield was increased from 3.56 t/ha to 5.5 t/ha, using the controlled-released formulation
Factors Affecting Insecticide-Induced Resurgence of the Brown Planthopper, \u3ci\u3eNilaparvata lugens\u3c/i\u3e on Rice
Resurgence of the brown planthopper, Nilaparvata lugens (Stål) on rice was induced by applications of decamethrin, methyl parathion, and diazinon. Differential mortality of predators and hoppers did not appear to be the primary factor for resurgence. Hoppers appeared to be attracted to methyl parathion and decamethrin treated plants because of plant growth. Improved plant growth, however, did not compensate for the increased feeding of the insecticide-treated hopper population, and plants treated with resurgence-causing insecticides succumbed to feeding injury earlier than untreated plants. Population increases were due in part to stimulation of reproduction of the hopper, either by contact action of the insecticides or through increased plant growth. Reduction in the length of the nymphal stage and increased adult longevity resulting in a shortened life cycle and longer oviposition period, respectively, were additional factors contributing to resurgence
Influence of adatom interactions on second layer nucleation
We develop a theory for the inclusion of adatom interactions in second layer
nucleation occurring in epitaxial growth. The interactions considered are due
to ring barriers between pairs of adatoms and binding energies of unstable
clusters. The theory is based on a master equation, which describes the time
development of microscopic states that are specified by cluster configurations
on top of an island. The transition rates are derived by scaling arguments and
tested against kinetic Monte-Carlo simulations. As an application we reanalyze
experiments to determine the step edge barrier for Ag/Pt(111).Comment: 4 pages, 4 figure
Enhanced Transmission Through Disordered Potential Barrier
Effect of weak disorder on tunneling through a potential barrier is studied
analytically. A diagrammatic approach based on the specific behavior of
subbarrier wave functions is developed. The problem is shown to be equivalent
to that of tunneling through rectangular barriers with Gaussian distributed
heights. The distribution function for the transmission coefficient is
derived, and statistical moments \left are calculated. The
surprising result is that in average disorder increases both tunneling
conductance and resistance.Comment: 10 pages, REVTeX 3.0, 2 figures available upon reques
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