2,325 research outputs found
Explicit Euler method for solving time dependent Schr\H{o}dinger equation
Using an explicit Euler substitution it was obtained a system of differential
equations, which can be used to find the solution of time-dependent
1-dimentional Schr\H{o}dinger equation for a general form of the time-dependent
potential.Comment: 1 page. Accepted for publication in Phys. Rev.
Fertirrigação no cultivo protegido de hortaliças.
bitstream/item/60795/1/revista-ed-2.pd
Large and small-scale structures and the dust energy balance problem in spiral galaxies
The interstellar dust content in galaxies can be traced in extinction at
optical wavelengths, or in emission in the far-infrared. Several studies have
found that radiative transfer models that successfully explain the optical
extinction in edge-on spiral galaxies generally underestimate the observed
FIR/submm fluxes by a factor of about three. In order to investigate this
so-called dust energy balance problem, we use two Milky Way-like galaxies
produced by high-resolution hydrodynamical simulations. We create mock optical
edge-on views of these simulated galaxies (using the radiative transfer code
SKIRT), and we then fit the parameters of a basic spiral galaxy model to these
images (using the fitting code FitSKIRT). The basic model includes smooth
axisymmetric distributions along a S\'ersic bulge and exponential disc for the
stars, and a second exponential disc for the dust. We find that the dust mass
recovered by the fitted models is about three times smaller than the known dust
mass of the hydrodynamical input models. This factor is in agreement with
previous energy balance studies of real edge-on spiral galaxies. On the other
hand, fitting the same basic model to less complex input models (e.g. a smooth
exponential disc with a spiral perturbation or with random clumps), does
recover the dust mass of the input model almost perfectly. Thus it seems that
the complex asymmetries and the inhomogeneous structure of real and
hydrodynamically simulated galaxies are a lot more efficient at hiding dust
than the rather contrived geometries in typical quasi-analytical models. This
effect may help explain the discrepancy between the dust emission predicted by
radiative transfer models and the observed emission in energy balance studies
for edge-on spiral galaxies.Comment: 9 pages, 5 figures, accepted for publication in A&
Processing of Copper-Graphite-Alumina Powders by High-Energy Milling
Com o apoio RAADRI.Copper-matrix composites are versatile materials used in several electromechanical applications, but relatively low strength and thermal stability impair advanced uses. Development of robust solutions combining low wear and low electrical loss are thus paramount. This work proposes high-energy milling of copper-graphite-alumina powders: graphite is conductive and self-lubricating; alumina toils as dispersion-strengthener and grain refiner. Tailored batches with 2wt%-graphite and 2wt%-alumina were milled up to 16h in planetary ball mill and characterized by XRD, FEG-SEM/EDS, microhardness and Raman. Produced powders are nanostructured, containing graphite and alumina nanoparticles homogeneously distributed in copper. Increasing milling time results in some degree of nanographite amorphization and size decrease. Copper crystallite size and achieved hardness are affected mainly above 4 h milling. Attained results suggest that efficient dispersion of graphite and alumina nanoparticles is achieved, envisaging high conductivity, high strength and thermal stability. The copper-graphite-alumina system thus seemingly opens an opportunity window for PM processing of advanced copper composites
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