550 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
Giant magnetic enhancement in Fe/Pd films and its influence on the magnetic interlayer coupling
The magnetic properties of thin Pd fcc(001) films with embedded monolayers of
Fe are investigated by means of first principles density functional theory. The
induced spin polarization in Pd is calculated and analyzed in terms of quantum
interference within the Fe/Pd/Fe bilayer system. An investigation of the
magnetic enhancement effects on the spin polarization is carried out and its
consequences for the magnetic interlayer coupling are discussed. In contrast to
{\it e.g.} the Co/Cu fcc(001) system we find a large effect on the magnetic
interlayer coupling due to magnetic enhancement in the spacer material. In the
case of a single embedded Fe monolayer we find aninduced Pd magnetization
decaying with distance from the magnetic layer as ~ with
. For the bilayer system we find a giant magnetic
enhancement (GME) that oscillates strongly due to interference effects. This
results in a strongly modified magnetic interlayer coupling, both in phase and
magnitude, which may not be described in the pure
Ruderman-Kittel-Kasuya-Yoshida (RKKY) picture. No anti-ferromagnetic coupling
was found and by comparison with magnetically constrained calculations we show
that the overall ferromagnetic coupling can be understood from the strong
polarization of the Pd spacer
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
Ab initio linear scaling response theory: Electric polarizability by perturbed projection
A linear scaling method for calculation of the static {\em ab inito} response
within self-consistent field theory is developed and applied to calculation of
the static electric polarizability. The method is based on density matrix
perturbation theory [Niklasson and Challacombe, cond-mat/0311591], obtaining
response functions directly via a perturbative approach to spectral projection.
The accuracy and efficiency of the linear scaling method is demonstrated for a
series of three-dimensional water clusters at the RHF/6-31G** level of theory.
Locality of the response under a global electric field perturbation is
numerically demonstrated by approximate exponential decay of derivative density
matrix elements.Comment: 4.25 pages in PRL format, 2 figure
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
Venture capital as a mean of innovation financing in conditions of investment climate volatility in Ukraine
The energy conversion efficiency of a conventional pn junction solar cell decreases as the temperature increases, and this may eventually lead to failures in the photovoltaic system, especially if it uses concentrated solar radiation. In this work, we show that spectrally selective reflector (SSR) surfaces can be important for reducing the heat buildup on passively cooled solar cells. We outline a computational scheme for optimizing DC magnetron-sputtered TiO(2):Nb-based SSRs tailored for silicon solar cells and find good agreement of the reflectance with an experimental realization of the optimal SSR. A figure of merit for SSRs has also been derived and applied to the experimental data
Диагностика сердечной недостаточности с сохраненной систолической функцией левого желудочка у пациентов с артериальной гипертензией
КАРДИОЛОГИЯГИПЕРТЕНЗИЯСЕРДЕЧНАЯ НЕДОСТАТОЧНОСТЬ ЗАСТОЙНАЯ /ДИАГНОСТИКАИНСТРУКЦИИ ПО ПРИМЕНЕНИ
Analysis of mesoscale effects in high-shear granulation through a computational fluid dynamics-population balance coupled compartment model
There is a need for mesoscale resolution and coupling between flow-field information and the evolution of particle properties in high-shear granulation. We have developed a modelling framework that compartmentalizes the high-shear granulation process based on relevant process parameters in time and space. The model comprises a coupled-flow-field and population-balance solver and is used to resolve and analyze the effects of mesoscales on the evolution of particle properties. A Diosna high-shear mixer was modelled with microcrystalline cellulose powder as the granulation material. An analysis of the flow-field solution and compartmentalization allows for a resolution of the stress and collision peak at the impeller blades. Different compartmentalizations showed the importance of resolving the impeller region, for aggregating systems and systems with breakage. An independent study investigated the time evolution of the flow field by changing the particle properties in three discrete steps that represent powder mixing, the initial granulation stage mixing and the late stage granular mixing. The results of the temporal resolution study show clear changes in collision behavior, especially from powder to granular mixing, which indicates the importance of resolving mesoscale phenomena in time and space
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