633 research outputs found
Extinction calculations of multi-sphere polycrystalline graphitic clusters - A comparison with the 2175 AA peak and between a rigorous solution and discrete-dipole approximations
Certain dust particles in space are expected to appear as clusters of
individual grains. The morphology of these clusters could be fractal or
compact. In this paper we study the light scattering by compact and fractal
polycrystalline graphitic clusters consisting of touching identical spheres. We
compare three general methods for computing the extinction of the clusters in
the wavelength range 0.1 - 100 micron, namely, a rigorous solution (Gerardy &
Ausloos 1982) and two different discrete-dipole approximation methods --
MarCODES (Markel 1998) and DDSCAT (Draine & Flatau 1994). We consider clusters
of N = 4, 7, 8, 27,32, 49, 108 and 343 particles of radii either 10 nm or 50
nm, arranged in three different geometries: open fractal (dimension D = 1.77),
simple cubic and face-centred cubic. The rigorous solution shows that the
extinction of the fractal clusters, with N < 50 and particle radii 10 nm,
displays a peak within 2% of the location of the observed interstellar
extinction peak at ~4.6 inverse micron; the smaller the cluster, the closer its
peak gets to this value. By contrast, the peak in the extinction of the more
compact clusters lie more than 4% from 4.6 inverse micron. At short wavelengths
(0.1 - 0.5 micron), all the methods show that fractal clusters have markedly
different extinction from those of non-fractal clusters. At wavelengths > 5
micron, the rigorous solution indicates that the extinction from fractal and
compact clusters are of the same order of magnitude. It was only possible to
compute fully converged results of the rigorous solution for the smaller
clusters, due to computational limitations, however, we find that both
discrete-dipole approximation methods overestimate the computed extinction of
the smaller fractal clusters.Comment: Corrections added in accordance with suggestions by the referee. 12
pages, 12 figures. Accepted for publication in Astronomy & Astrophysic
Time-reversible Born-Oppenheimer molecular dynamics
We present a time-reversible Born-Oppenheimer molecular dynamics scheme,
based on self-consistent Hartree-Fock or density functional theory, where both
the nuclear and the electronic degrees of freedom are propagated in time. We
show how a time-reversible adiabatic propagation of the electronic degrees of
freedom is possible despite the non-linearity and incompleteness of the
self-consistent field procedure. Time-reversal symmetry excludes a systematic
long-term energy drift for a microcanonical ensemble and the number of
self-consistency cycles can be kept low (often only 2-4 cycles per nuclear time
step) thanks to a good initial guess given by the adiabatic propagation of the
electronic degrees of freedom. The time-reversible Born-Oppenheimer molecular
dynamics scheme therefore combines a low computational cost with a physically
correct time-reversible representation of the dynamics, which preserves a
detailed balance between propagation forwards and backwards in time.Comment: 4 pages, 4 figure
Density Matrix Perturbation Theory
An expansion method for perturbation of the zero temperature grand canonical
density matrix is introduced. The method achieves quadratically convergent
recursions that yield the response of the zero temperature density matrix upon
variation of the Hamiltonian. The technique allows treatment of embedded
quantum subsystems with a computational cost scaling linearly with the size of
the perturbed region, O(N_pert.), and as O(1) with the total system size. It
also allows direct computation of the density matrix response functions to any
order with linear scaling effort. Energy expressions to 4th order based on only
first and second order density matrix response are given.Comment: 4 pages, 2 figure
Modern technologies production of cheese enriched with Omega - 3 fatty acids
Thermochromic films of MgxV1-xO2 were made by reactive dc magnetron sputtering onto heated glass. The metal-insulator transition temperature decreased by similar to 3 K/at. %Mg, while the optical transmittance increased concomitantly. Specifically, the transmittance of visible light and of solar radiation was enhanced by similar to 10% when the Mg content was similar to 7 at. %. Our results point at the usefulness of these films for energy efficient fenestration
Interstellar extinction by fractal polycrystalline graphite clusters?
Certain dust particles in space are expected to appear as clusters of
individual grains. The morphology of these clusters could be fractal or
compact. To determine how these structural features would affect the
interpretation of the observed interstellar extinction peak at m,
we have calculated the extinction by compact and fractal polycrystalline
graphite clusters consisting of touching identical spheres. We compare three
general methods for computing the extinction of the clusters, namely, a
rigorous solution and two different discrete-dipole approximation methods.Comment: 4 pages, 2 figures. Proceedings for the 6'th International Conference
on Electromagnetic and Light Scattering by Non-spherical Particles, Marts
2002, Florid
Диагностика сердечной недостаточности с сохраненной систолической функцией левого желудочка у пациентов с артериальной гипертензией
КАРДИОЛОГИЯГИПЕРТЕНЗИЯСЕРДЕЧНАЯ НЕДОСТАТОЧНОСТЬ ЗАСТОЙНАЯ /ДИАГНОСТИКАИНСТРУКЦИИ ПО ПРИМЕНЕНИ
Оптимизация преподавания нормальной физиологии в медицинских вузах студентам, обучающимся на иностранном языке
ВУЗЫВЫСШИЕ УЧЕБНЫЕ ЗАВЕДЕНИЯОБРАЗОВАНИЕ МЕДИЦИНСКОЕНОРМАЛЬНАЯ ФИЗИОЛОГИЯ (ДИСЦИПЛИНА)МЕТОДИКА ПРЕПОДАВАНИЯФИЗИОЛОГИЯ /ОБУЧСТУДЕНТЫ МЕДИЦИНСКИХ УЧЕБНЫХ ЗАВЕДЕНИЙИНОСТРАННЫЕ СТУДЕНТЫОПТИМИЗАЦИЯ ПРЕПОДАВАНИ
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