12,849 research outputs found
A theoretical study of heterojunction and graded band gap type solar cells
The work performed concentrated on including multisun effects, high temperature effects, and electron irradiation effects into the computer analysis program for heterojunction and graded bandgap solar cells. These objectives were accomplished and the program is now available for such calculations
Analysis of supersonic conical flows
Method of characteristics analytical technique for flow predictions of supersonic cross flows over conical bodie
Modelling the Extreme X-ray Spectrum of IRAS 13224-3809
The extreme NLS1 galaxy IRAS 13224-3809 shows significant variability,
frequency depended time lags, and strong Fe K line and Fe L features in the
long 2011 XMM-Newton observation. In this work we study the spectral properties
of IRAS 13224-3809 in detail, and carry out a series of analyses to probe the
nature of the source, focusing in particular on the spectral variability
exhibited. The RGS spectrum shows no obvious signatures of absorption by
partially ionised material (warm absorbers). We fit the 0.3-10.0 keV spectra
with a model that includes relativistic reflection from the inner accretion
disc, a standard powerlaw AGN continuum, and a low-temperature (~0.1 keV)
blackbody, which may originate in the accretion disc, either as direct or
reprocessed thermal emission. We find that the reflection model explains the
time-averaged spectrum well, and we also undertake flux-resolved and
time-resolved spectral analyses, which provide evidence of gravitational
light-bending effects. Additionally, the temperature and flux of the blackbody
component are found to follow the relation expected for simple
thermal blackbody emission from a constant emitting area, indicating a physical
origin for this component.Comment: 12 pages, 7 figures, accepted for publication in MNRA
Hybrid functionals within the all-electron FLAPW method: implementation and applications of PBE0
We present an efficient implementation of the PBE0 hybrid functional within
the full-potential linearized augmented-plane-wave (FLAPW) method. The
Hartree-Fock exchange term, which is a central ingredient of hybrid
functionals, gives rise to a computationally expensive nonlocal potential in
the one-particle Schroedinger equation. The matrix elements of this exchange
potential are calculated with the help of an auxiliary basis that is
constructed from products of FLAPW basis functions. By representing the Coulomb
interaction in this basis the nonlocal exchange term becomes a Brillouin-zone
(BZ) sum over vector-matrix-vector products. We show that the Coulomb matrix
can be made sparse by a suitable unitary transformation of the auxiliary basis,
which accelerates the computation of the vector-matrix-vector products
considerably. Additionally, we exploit spatial and time-reversal symmetry to
identify the nonvanishing exchange matrix elements in advance and to restrict
the k summations for the nonlocal potential to an irreducible set of k points.
Favorable convergence of the self-consistent-field cycle is achieved by a
nested density-only and density-matrix iteration scheme. We discuss the
convergence with respect to the parameters of our numerical scheme and show
results for a variety of semiconductors and insulators, including oxide
materials, where the PBE0 hybrid functional improves the band gaps and the
description of localized states in comparison with the PBE functional.
Furthermore, we find that in contrast to conventional local
exchange-correlation functionals ferromagnetic EuO is correctly predicted to be
a semiconductor.Comment: 15 pages, 6 figures, 2 table
Evolutionary L∞ identification and model reduction for robust control
An evolutionary approach for modern robust control oriented system identification and model reduction in the frequency domain is proposed. The technique provides both an optimized nominal model and a 'worst-case' additive or multiplicative uncertainty bounding function which is compatible with robust control design methodologies. In addition, the evolutionary approach is applicable to both continuous- and discrete-time systems without the need for linear parametrization or a confined problem domain for deterministic convex optimization. The proposed method is validated against a laboratory multiple-input multiple-output (MIMO) test rig and benchmark problems, which show a higher fitting accuracy and provides a tighter L�¢���� error bound than existing methods in the literature do
Dynamic Resonance Effects in the Statistical Distributions of Asteroids and Comets
Some principles in the distribution of Centaurs and the "Scattered Disk"
objects, as well as the Kuiper belt objects for its semi-major axes,
eccentricities and inclinations of the orbits have been investigated. It has
been established, that more than a half from them move on the resonant orbits
and that is what has been predicted earlier. The divergence of the maximum in
the observable distribution of the objects of the Kuiper belt for the
semi-major axes with an exact orbital resonance has been interpreted.Comment: 7 pages, 5 figures, 1 table. International Conference "100 years
since Tunguska phenomenon: Past, present and future", (June 26-28, 2008.
Russia, Moscow), International Conference "Modern problems of astronomy"
(August 12-18, 2007, Ukraine, Odessa
Northern and Western Corn Rootworms in Minnesota
The occurrence and population changes of the northern corn rootworm, Diabrotica longicornis (Say), and the western corn rootworm, D. virgifera LeConte, were reviewed on the basis of information assembled at the Department of Agriculture of the State of Minnesota; and the Department of Entomology, Fisheries, and Wildlife and the Extension Entomologist\u27s Office of the University of Minnesota.
The review shows no record of the northern species in Minnesota before 1899, but it appeared between 1899 and 1915. Populations were probably very law until 1932. Sporadic infestations were reported between 1932 and l 953. Progressive increase in infestation from 1954 paralleled an increase in continuous planting of corn. The western species reached Minnesota in 196 l. By 1968 it was found in practically all counties where the northern species was found . There was no displacement of the northern species by the western in Minnesota, as happened in some other localities
Trends and Variation in End-of-Life Care for Medicare Beneficiaries With Severe Chronic Illness
Provides an updated analysis of regional and hospital variations in end-of-life care for Medicare beneficiaries with chronic illnesses, including percentage of hospital deaths, days in intensive care units, and physician labor per patient
Improved detectivity of pyroelectric detectors
High detectivity single-element SBN pyroelectric detectors were fabricated. The theory and technology developments related to improved detector performance were identified and formulated. Improved methods of material characterization, thinning, mounting, blackening and amplifier matching are discussed. Detectors with detectivities of 1.3 x 10 to the 9th power square root of Hz/watt at 1 Hz are reported. Factors limiting performance and recommendations for future work are discussed
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