4,629 research outputs found
Scaling in Gravitational Clustering, 2D and 3D Dynamics
Perturbation Theory (PT) applied to a cosmological density field with
Gaussian initial fluctuations suggests a specific hierarchy for the correlation
functions when the variance is small. In particular quantitative predictions
have been made for the moments and the shape of the one-point probability
distribution function (PDF) of the top-hat smoothed density. In this paper we
perform a series of systematic checks of these predictions against N-body
computations both in 2D and 3D with a wide range of featureless power spectra.
In agreement with previous studies, we found that the reconstructed PDF-s work
remarkably well down to very low probabilities, even when the variance
approaches unity. Our results for 2D reproduce the features for the 3D
dynamics. In particular we found that the PT predictions are more accurate for
spectra with less power on small scales. The nonlinear regime has been explored
with various tools, PDF-s, moments and Void Probability Function (VPF). These
studies have been done with unprecedented dynamical range, especially for the
2D case, allowing in particular more robust determinations of the asymptotic
behaviour of the VPF. We have also introduced a new method to determine the
moments based on the factorial moments. Results using this method and taking
into account the finite volume effects are presented.Comment: 13 pages, Latex file, 9 Postscript Figure
Environmental Dependence of the Fundamental Plane of Galaxy Clusters
Galaxy clusters approximate a planar (FP) distribution in a three-dimensional
parameter space which can be characterized by optical luminosity, half-light
radius, and X-ray luminosity. Using a high-quality catalog of cluster
redshifts, we find the nearest neighbor cluster for those common to an FP study
and the cluster catalog. Examining scatter about the FP, we find 99.2%
confidence that it is dependent on nearest neighbor distance. Our study of
X-Ray clusters finds that those with high central gas densities are
systematically closer to neighbor clusters. If we combine results here with
those of Fritsch and Buchert, we find an explanation for some of our previous
conclusions: Clusters in close proximity to other clusters are more likely to
have massive cooling flows because they are more relaxed and have higher
central gas densities.Comment: Accepted for publication in Astrophysical Journal Letters. Moderate
revisions, including more statistical analysis and discussion. Latex, 7 page
DISTRIBUIÇÃO Espacial e Temporal da Comunidade Fitoplanctônica em uma Área de Malacocultura no Município de Anchieta Es
RESUMO
O presente trabalho foi realizado na região costeira próxima da área estuarina de Anchieta, ES, em uma área de malacocultura. As amostragens foram realizadas mensalmente no período de janeiro a dezembro de 2004 em 10 (dez) pontos: Rio, 1A, 1B, 1C, 2A, 2B, 2C, 3A, 3B, 3C. Foi realizada análise quali-quantitativa da comunidade fitoplanctônica e das variáveis ambientais, tais como temperatura da água, transparência, salinidade, pH e oxigênio dissolvido. Os resultados de temperatura da água e pH pouco variaram ao longo do ano. A pluviosidade interferiu na transparência da água e, portanto, foi a variável ambiental que mais influenciou na comunidade fitoplanctônica local. As diatomáceas foram as mais representativas (em análise qualitativa e quantitativa) das Classes. Os dados de densidade foram baixos se comparados a outras regiões costeiras, mas teve uma alta diversidade e equitabilidade demonstrando que a área de estudo ainda é uma região bem preservada, com poucos impactos ambientais. Os baixos valores de densidade e biovolume indicam que os mexilhões dependem muito pouco da comunidade fitoplanctônica como alimento. Em relação às espécies potencialmente tóxicas, a Classe Bacillariophyceae novamente teve a maior representatividade no número de ocorrências dos táxons ao longo do ano. As espécies fitoplanctônicas potencialmente tóxicas ainda não promovem florações, mas deve se considerar um alerta, uma vez que a população de Anchieta lançar seus efluentes domésticos no rio Benevente ou diretamente no mar. Esta pesquisa é um sub-projeto de maricultura sustentada do Projeto RECOS Milênio, financiado pelo CNPq a partir de 2004.
Palavras-chave: fitoplâncton, toxinas, molusco
Program on Earth Observation Data Management Systems (EODMS)
An assessment was made of the needs of a group of potential users of satellite remotely sensed data (state, regional, and local agencies) involved in natural resources management in five states, and alternative data management systems to satisfy these needs are outlined. Tasks described include: (1) a comprehensive data needs analysis of state and local users; (2) the design of remote sensing-derivable information products that serve priority state and local data needs; (3) a cost and performance analysis of alternative processing centers for producing these products; (4) an assessment of the impacts of policy, regulation and government structure on implementing large-scale use of remote sensing technology in this community of users; and (5) the elaboration of alternative institutional arrangements for operational Earth Observation Data Management Systems (EODMS). It is concluded that an operational EODMS will be of most use to state, regional, and local agencies if it provides a full range of information services -- from raw data acquisition to interpretation and dissemination of final information products
Critical collapse of collisionless matter - a numerical investigation
In recent years the threshold of black hole formation in spherically
symmetric gravitational collapse has been studied for a variety of matter
models. In this paper the corresponding issue is investigated for a matter
model significantly different from those considered so far in this context. We
study the transition from dispersion to black hole formation in the collapse of
collisionless matter when the initial data is scaled. This is done by means of
a numerical code similar to those commonly used in plasma physics. The result
is that for the initial data for which the solutions were computed, most of the
matter falls into the black hole whenever a black hole is formed. This results
in a discontinuity in the mass of the black hole at the onset of black hole
formation.Comment: 22 pages, LaTeX, 7 figures (ps-files, automatically included using
psfig
Rate-dependent propagation of cardiac action potentials in a one-dimensional fiber
Action potential duration (APD) restitution, which relates APD to the
preceding diastolic interval (DI), is a useful tool for predicting the onset of
abnormal cardiac rhythms. However, it is known that different pacing protocols
lead to different APD restitution curves (RCs). This phenomenon, known as APD
rate-dependence, is a consequence of memory in the tissue. In addition to APD
restitution, conduction velocity restitution also plays an important role in
the spatiotemporal dynamics of cardiac tissue. We present new results
concerning rate-dependent restitution in the velocity of propagating action
potentials in a one-dimensional fiber. Our numerical simulations show that,
independent of the amount of memory in the tissue, waveback velocity exhibits
pronounced rate-dependence and the wavefront velocity does not. Moreover, the
discrepancy between waveback velocity RCs is most significant for small DI. We
provide an analytical explanation of these results, using a system of coupled
maps to relate the wavefront and waveback velocities. Our calculations show
that waveback velocity rate-dependence is due to APD restitution, not memory.Comment: 17 pages, 7 figure
Synthesis of 4-Piperidinoflavan
A study of the reaction of flavylium perchlorate with piperidine showed that piperidine perchlorate was formed plus two other compounds. One of these appears to be 4-piperidinoflavene which should be reducible to 4-piperidinoflavan. This compound had not been described previously, hence its synthesis was undertaken. Flavanone was prepared according to the method of Kostanecki (1). Catalytic reduction of flavanone with hydrogen and a platinum catalyst gave a 79% yield of a compound melting at 145- 147°. This corresponds to the, B-isomer of 4-hydroxyflavan originally obtained by Karrar, Yen and Reichstein (2) as the result of a titanous chloride reduction of flavanone. Mozingo and Adkins (3) also obtained this ,B-isomer by catalytic reduction of flavanone but used copper-chromium oxide at 120° and hydrogen at 100-200 atm. Treatment of the 4-hydroxyflavan with phosphorus tribromide at 0° gave a 52% yield of 4-bromoflavan. An ether solution of this bromo-compound reacted with two equivalents of piperidine to form piperidinium hydrobromide and {3-4 piperidinoflavan. Upon recrystallization from ether, colorless needles were obtained melting at 137-138° which had the correct analysis for this compound
Spherically symmetric steady states of galactic dynamics in scalar gravity
The kinetic motion of the stars of a galaxy is considered within the
framework of a relativistic scalar theory of gravitation. This model, even
though unphysical, may represent a good laboratory where to study in a
rigorous, mathematical way those problems, like the influence of the
gravitational radiation on the dynamics, which are still beyond our present
understanding of the physical model represented by the Einstein--Vlasov system.
The present paper is devoted to derive the equations of the model and to prove
the existence of spherically symmetric equilibria with finite radius.Comment: 13 pages, mistypos correcte
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