605 research outputs found
ERTS-1 imagery of village and cultivation sites in Niger and Upper Volta
There are no author-identified significant results in this report
Earth Resources Technology Satellite-1 (ERTS-1) data and anthropology: Use of these data in carrying capacity estimates for sites in Upper Volta and Niger
The author has identified the following significant results. Repetitively derived multispectral band imagery from ERTS-1 is now available for many parts of the earth's land surface and represents major new data sources for anthropological work in habitat, land use, and settlement patterns. A completed first step test of ERTS-1 data is available in carrying capacity estimates for Mossi, Hausa, and Sonrai sites derived from: (1) field work; (2) aerial photography; and (3) ERTS-1. Data can test more than one carrying capacity formula
Ab initio calculations of response properties including electron-hole interaction
We discuss the current status of a computational approach which allows to
evaluate the dielectric matrix, and hence electronic excitations like optical
properties, including local field and excitonic effects. We introduce a recent
numerical development which greatly reduces the use of memory in such type of
calculations, and hence eliminates one of the bottlenecks for the application
to complex systems. We present recent applications of the method, focusing our
interest on insulating oxides.Comment: 11 pages, 5 figures, 1999 MRS Proceedin
Interactive multi-spectral analysis of more than one Sonrai village in Niger, West Africa
Use of LANDSAT data and an interaction system is considered for identifying and measuring small scale compact human settlements (villages) for demographic and anthropological studies. Because village components are not uniformly distributed within any one village, they apparently are multimodal, spectrally. Therefore, the functions of location and enumeration are kept separate. Measurement of a known village is compared with CCT response
Investigation of shear stress and shear flow within a partonic transport model
Starting from a classical picture of shear viscosity we construct a steady velocity gradient in the partonic cascade BAMPS. Using the Navier-Stokes-equation we calculate the shear viscosity coefficient. For elastic isotropic scatterings we find a very good agreement with the analytic values. For both elastic and inelastic scatterings with pQCD cross sections we find good agreement with previously published calculations
Ab initio calculation of excitonic effects in the optical spectra of semiconductors
An ab initio approach to the calculation of excitonic effects in the optical
absorption spectra of semiconductors and insulators is formulated. It starts
from a quasiparticle bandstructure calculation and is based on the relevant
Bethe--Salpeter equation.
An application to bulk silicon shows a substantial improvement with respect
to previous calculations in the description of the experimental spectrum, for
both peak positions and lineshape.Comment: 4 pages, 1 figur
Beyond time-dependent exact-exchange: the need for long-range correlation
In the description of the interaction between electrons beyond the classical
Hartree picture, bare exchange often yields a leading contribution. Here we
discuss its effect on optical spectra of solids, comparing three different
frameworks: time-dependent Hartree-Fock, a recently introduced combined
density-functional and Green's functions approach applied to the bare exchange
self-energy, and time-dependent exact-exchange within time-dependent
density-functional theory (TD-EXX). We show that these three approximations
give rise to identical excitonic effects in solids; these effects are
drastically overestimated for semiconductors. They are partially compensated by
the usual overestimation of the quasiparticle band gap within Hartree-Fock. The
physics that lacks in these approaches can be formulated as screening. We show
that the introduction of screening in TD-EXX indeed leads to a formulation that
is equivalent to previously proposed functionals derived from Many-Body
Perturbation Theory. It can be simulated by reducing the long-range part of the
Coulomb interaction: this produces absorption spectra of semiconductors in good
agreement with experiment.Comment: 12 pages, 3 figures, 1 tabl
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