19,293 research outputs found
Sedimentation of Oblate Ellipsoids at low and Moderate Reynolds numbers
In many applications to biophysics and environmental engineering,
sedimentation of non-spherical particles for example: ellipsoids, is an
important problem. In our work, we simulate the dynamics of oblate ellipsoids
under gravity. We study the settling velocity and the average orientation of
the ellipsoids as a function of volume fraction. We see that the settling
velocity shows a local maximum at the intermmediate densities unlike the
spheres. The average orientation of the ellipsoids also shows a similar local
maximum and we observe that this local maximum disappears as the Reynolds
number is increased. Also, at small volume fractions, we observe that the
oblate ellipsoids exhibit an orientational clustering effect in alignment with
gravity accompanied by strong density fluctuations. The vertical and horizontal
fluctuations of the oblate ellipsoids are small compared to that of the
spheres
An Introduction to Ontologies and Ontology Engineering
In the last decades, the use of ontologies in information systems has become more and more popular in various fields, such as web technologies, database integration, multi agent systems, natural language processing, etc. Artificial intelligent researchers have initially borrowed the word “ontology” from Philosophy, then the word spread in many scientific domain and ontologies are now used in several developments. The main goal of this chapter is to answer generic questions about ontologies, such as: Which are the different kinds of ontologies? What is the purpose of the use of ontologies in an application? Which methods can I use to build an ontology
Controlled Shock Shells and Intracluster Fusion Reactions in the Explosion of Large Clusters
The ion phase-space dynamics in the Coulomb explosion of very large ( atoms) deuterium clusters can be tailored using two consecutive
laser pulses with different intensities and an appropriate time delay. For
suitable sets of laser parameters (intensities and delay), large-scale shock
shells form during the explosion, thus highly increasing the probability of
fusion reactions within the single exploding clusters. In order to analyze the
ion dynamics and evaluate the intracluster reaction rate, a one-dimensional
theory is used, which approximately accounts for the electron expulsion from
the clusters. It is found that, for very large clusters (initial radius
100 nm), and optimal laser parameters, the intracluster fusion yield becomes
comparable to the intercluster fusion yield. The validity of the results is
confirmed with three-dimensional particle-in-cell simulations.Comment: 25 pages, 11 figures, to appear in Physical Review
Otimização da eficiência reprodutiva em caprinos e ovinos.
A eficiência reprodutiva é um dos principais fatores que interferem na eficiência produtiva de caprinos e ovinos, a exemplo do que ocorre com bovinos e bubalinos. Considerando que condições sanitárias, nutricionais e de bem-estar animal adequadas ao sistema de produção estejam sendo aplicadas, a otimização do sistema produtivo terá como principal limitante a eficiência reprodutiva do rebanho. O objetivo deste artigo foi rever os conceitos básicos de reprodução em caprinos e ovinos e como eles podem ser estrategicamente assistidos no sentido de se incrementar o potencial de produção dos animais ao longo de sua vida reprodutiva
Alguns aspectos da transferência de embriões em caprinos.
O objetivo deste artigo foi descrever de forma sucinta as etapas envolvidas na transferência de embriões em caprinos
Estratégias para o controle do ciclo estral e superovulação em ovinos e caprinos.
A caprinovinocultura está apresentando um ciclo de crescimento mundial. Este crescimento intensificou-se nas últimas décadas, sobretudo em países em desenvolvimento, detentores dos maiores rebanhos. Acompanhando esta tendência mundial, projeta-se uma multiplicação da ordem de cinco vezes o rebanho brasileiro atual para os próximos vinte anos. Serão mais de 100 e 50 milhões de cabeças de ovinos e caprinos, respectivamente. Dentro desta perspectiva, haverá ampla necessidade de se assistir a reprodução destes animais seja para permitir aumento da eficiência reprodutiva e/ou produtiva dos rebanhos, seja para multiplicação mais eficiente de genótipos superiores. O objetivo deste artigo foi rever os aspectos relacionados à fisiologia reprodutiva de ovelhas e cabras e discutir estratégias para o controle do ciclo estral e superovulação
Dynamical star-disk interaction in the young stellar system V354 Mon
The main goal of this work is to characterize the mass accretion and ejection
processes of the classical T Tauri star V354 Mon, a member of the young stellar
cluster NGC 2264. In March 2008, photometric and spectroscopic observations of
V354 Mon were obtained simultaneously with the CoRoT satellite, the 60 cm
telescope at the Observat\'orio Pico dos Dias (LNA - Brazil) equipped with a
CCD camera and Johnson/Cousins BVRI filters, and the SOPHIE \'echelle
spectrograph at the Observatoire de Haute-Provence (CNRS - France). The light
curve of V354 Mon shows periodical minima (P = 5.26 +/- 0.50 days) that vary in
depth and width at each rotational cycle. From the analysis of the photometric
and spectroscopic data, it is possible to identify correlations between the
emission line variability and the light-curve modulation of the young system,
such as the occurrence of pronounced redshifted absorption in the H_alpha line
at the epoch of minimum flux. This is evidence that during photometric minima
we see the accretion funnel projected onto the stellar photosphere in our line
of sight, implying that the hot spot coincides with the light-curve minima. We
applied models of cold and hot spots and a model of occultation by
circumstellar material to investigate the source of the observed photometric
variations. We conclude that nonuniformly distributed material in the inner
part of the circumstellar disk is the main cause of the photometric modulation,
which does not exclude the presence of hot and cold spots at the stellar
surface. It is believed that the distortion in the inner part of the disk is
created by the dynamical interaction between the stellar magnetosphere,
inclined with respect to the rotation axis, and the circumstellar disk, as also
observed in the classical T Tauri star AA Tau and predicted by
magnetohydrodynamical numerical simulations.Comment: Accepted by Astronomy and Astrophysic
Three-dimensional simulations of laser-plasma interactions at ultrahigh intensities
Three-dimensional (3D) particle-in-cell (PIC) simulations are used to
investigate the interaction of ultrahigh intensity lasers (
W/cm) with matter at overcritical densities. Intense laser pulses are
shown to penetrate up to relativistic critical density levels and to be
strongly self-focused during this process. The heat flux of the accelerated
electrons is observed to have an annular structure when the laser is tightly
focused, showing that a large fraction of fast electrons is accelerated at an
angle. These results shed light into the multi-dimensional effects present in
laser-plasma interactions of relevance to fast ignition of fusion targets and
laser-driven ion acceleration in plasmas.Comment: 2 pages, 1 figur
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