2,527 research outputs found
Different regimes of Forster energy transfer between an epitaxial quantum well and a proximal monolayer of semiconductor nanocrystals
We calculate the rate of non-radiative, Forster-type energy transfer (ET)
from an excited epitaxial quantum well (QW) to a proximal monolayer of
semiconductor nanocrystal quantum dots (QDs). Different electron-hole
configurations in the QW are considered as a function of temperature and
excited electron-hole density. A comparison of the theoretically determined ET
rate and QW radiative recombination rate shows that, depending on the specific
conditions, the ET rate is comparable to or even greater than the radiative
recombination rate. Such efficient Forster ET is promising for the
implementation of ET-pumped, nanocrystal QD-based light emitting devices.Comment: 14 pages, 4 figure
Distribution of Soils by Natural Drainage Class and by Slope Class for Iowa Counties
Natural drainage class (namely, poor, imperfect, and well drained) and slope class are estimated for Iowa counties through a 2% ¼-section sample soil survey. Estimate of soil drainage class is given also by slope class. Counties vary widely in the amount of poorly drained soils. Kossuth County has 56.4% of poorly drained soils, while Allamakee has less than 1%. Land use management and conservation considerations are discussed briefly
Heterogeneous encoding of temporal stimuli in the cerebellar cortex
Local feedforward and recurrent connectivity are rife in the frontal areas of the cerebral cortex, which gives rise to rich heterogeneous dynamics observed in such areas. Recently, similar local connectivity motifs have been discovered among Purkinje and molecular layer interneurons of the cerebellar cortex, however, task-related activity in these neurons has often been associated with relatively simple facilitation and suppression dynamics. Here, we show that the rodent cerebellar cortex supports heterogeneity in task-related neuronal activity at a scale similar to the cerebral cortex. We provide a computational model that inculcates recent anatomical insights into local microcircuit motifs to show the putative basis for such heterogeneity. We also use cell-type specific chronic viral lesions to establish the involvement of cerebellar lobules in associative learning behaviors. Functional heterogeneity in neuronal profiles may not merely be the remit of the associative cerebral cortex, similar principles may be at play in subcortical areas, even those with seemingly crystalline and homogenous cytoarchitectures like the cerebellum.</p
Effect of inter-wall surface roughness correlations on optical spectra of quantum well excitons
We show that the correlation between morphological fluctuations of two
interfaces confining a quantum well strongly suppresses a contribution of
interface disorder to inhomogeneous line width of excitons. We also demonstrate
that only taking into account these correlations one can explain all the
variety of experimental data on the dependence of the line width upon thickness
of the quantum well.Comment: 13 pages, 8 figures, Revtex4, submitted to PR
Evaluation of different deployment strategies for larviciding to control malaria: a simulation study
BACKGROUND: Larviciding against malaria vectors in Africa has been limited to indoor residual spraying and insecticide-treated nets, but is increasingly being considered by some countries as a complementary strategy. However, despite progress towards improved larvicides and new tools for mapping or treating mosquito-breeding sites, little is known about the optimal deployment strategies for larviciding in different transmission and seasonality settings. METHODS: A malaria transmission model, OpenMalaria, was used to simulate varying larviciding strategies and their impact on host-seeking mosquito densities, entomological inoculation rate (EIR) and malaria prevalence. Variations in coverage, duration, frequency, and timing of larviciding were simulated for three transmission intensities and four transmission seasonality profiles. Malaria transmission was assumed to follow rainfall with a lag of one month. Theoretical sub-Saharan African settings with Anopheles gambiae as the dominant vector were chosen to explore impact. Relative reduction compared to no larviciding was predicted for each indicator during the simulated larviciding period. RESULTS: Larviciding immediately reduced the predicted host-seeking mosquito densities and EIRs to a maximum that approached or exceeded the simulated coverage. Reduction in prevalence was delayed by approximately one month. The relative reduction in prevalence was up to four times higher at low than high transmission. Reducing larviciding frequency (i.e., from every 5 to 10 days) resulted in substantial loss in effectiveness (54, 45 and 53% loss of impact for host-seeking mosquito densities, EIR and prevalence, respectively). In seasonal settings the most effective timing of larviciding was during or at the beginning of the rainy season and least impactful during the dry season, assuming larviciding deployment for four months. CONCLUSION: The results highlight the critical role of deployment strategies on the impact of larviciding. Overall, larviciding would be more effective in settings with low and seasonal transmission, and at the beginning and during the peak densities of the target species populations. For maximum impact, implementers should consider the practical ranges of coverage, duration, frequency, and timing of larviciding in their respective contexts. More operational data and improved calibration would enable models to become a practical tool to support malaria control programmes in developing larviciding strategies that account for the diversity of contexts
Excitonic effects in solids described by time-dependent density functional theory
Starting from the many-body Bethe-Salpeter equation we derive an
exchange-correlation kernel that reproduces excitonic effects in bulk
materials within time-dependent density functional theory. The resulting
accounts for both self-energy corrections and the electron-hole
interaction. It is {\em static}, {\em non-local} and has a long-range Coulomb
tail. Taking the example of bulk silicon, we show that the
divergency is crucial and can, in the case of continuum excitons, even be
sufficient for reproducing the excitonic effects and yielding excellent
agreement between the calculated and the experimental absorption spectrum.Comment: 6 pages, 1 figur
Local exchange-correlation vector potential with memory in Time-Dependent Density Functional Theory: the generalized hydrodynamics approach
Using Landau Fermi liquid theory we derive a nonlinear non-adiabatic
approximation for the exchange-correlation (xc) vector potential defined by the
xc stress tensor. The stress tensor is a local nonlinear functional of two
basic variables - the displacement vector and the second-rank tensor which
describes the evolution of momentum in a local frame moving with Eulerian
velocity. For irrotational motion and equilibrium initial state the dependence
on the tensor variable reduces to that on a metrics generated by a dynamical
deformation of the system.Comment: RevTex, 5 pages, no figures. Final version published in PR
Exact exchange-correlation potential for a time-dependent two electron system
We obtain an exact solution of the time-dependent Schroedinger equation for a
two-electron system confined to a plane by an isotropic parabolic potential
whose curvature is periodically modulated in time. From this solution we
compute the exact time-dependent exchange correlation potential v_xc which
enters the Kohn-Sham equation of time-dependent density functional theory. Our
exact result provides a benchmark against which various approximate forms for
v_xc can be compared. Finally v_xc is separated in an adiabatic and a pure
dynamical part and it is shown that, for the particular system studied, the
dynamical part is negligible.Comment: 23 pages, 6 figure
- …