27,614 research outputs found
Building a Sample of Distant Clusters of Galaxies
Candidate clusters of galaxies drawn from the sample identified from the
moderately deep I-band data of the ESO Imaging Survey (EIS), have been used for
follow-up optical/infrared imaging and spectroscopic observations. The
observations were conducted to assess the nature of these candidates over a
large range of redshifts. Currently, 163 EIS candidates have (V-I) colors, 15
have (I-K) and 65 cluster fields have been observed spectroscopically. From a
preliminary analysis of these data, we find that > 65% of the candidates
studied show strong evidence of being real physical associations, over the
redshift range 0.2<z<1.1. The evidence in some cases comes directly from
spectroscopic measurements, in others indirectly from the detection of
overdensities of objects with either the same color or the same photometric
redshift, or from a combination of color and spectroscopic information.
Preliminary results also suggest that the redshift derived from the
matched-filter algorithm is a reasonable measure of the cluster's redshift,
possibly overestimating it by Delta z ~0.1, at least for systems at z<0.7.
Overdensities of red objects have been detected in over 100 candidates, 38 of
which with estimated redshifts >0.6, and six candidates in the interval
0.45<z<0.81 have either been identified directly from measured redshifts or
have been confirmed by the measurement of at least one redshift for galaxies
located along a red-sequence typical of cluster early-type galaxies. Lastly,
five candidates among those already observed in the infrared have (I-Ks) colors
consistent with them being in the redshift interval 0.8<z<1.1. The sample of
"confirmed" clusters, already the largest of its kind in the southern
hemisphere, will be further enlarged by ongoing observations.Comment: To appear in "Large Scale Structure in the X-ray Universe", ed. M.
Plionis and I. Georgantopoulos (Paris: Editions Frontieres), in pres
Análise comparativa do meio físico e socioeconômico de três municípios com parques florestais: Araponga, Caparaó e São Roque de Minas - MG.
O meio físico, a localização geográfica, e a história de ocupação de um município contribuem na sua socioeconomia. Do mesmo modo, limitações físicas naturais resultam em pouca alteração antrópica, protegendo áreas que podem vir a ser transformadas em unidades de conservação, sob leis de proteção ambiental. Estas áreas, como por exemplo, parques florestais, apresentam potencial turístico, como uma alternativa socioeconômica. Este trabalho é uma análise comparativa de informações municipais socioeconômicas, históricas e do meio físico, com o objetivo de investigar uma possível influência de parques florestais na socioeconomia de municípios do Estado de Minas Gerais que contém grande parte de suas áreas com topografia acidentada e altitude elevada. Foram selecionados os municípios de Araponga, com o Parque Estadual da Serra do Brigadeiro, recém criado em 1996; Caparaó, com o Parque Nacional de Caparaó, criado em 1962; e São Roque de Minas, com o Parque Nacional da Serra da Canastra, criado em 1972. São Roque de Minas e Caparaó são Municípios tradicionalmente incluídos na rede turística, o que pode vir a ocorrer com Araponga futuramente. Os resultados mostram que os municípios de Araponga e Caparaó apresentam restrição topográfica, enquanto que as maiores limitações de São Roque são devidas ao solo. Historicamente, a formação de Araponga é semelhante a de Caparaó, em ocupação. Com relação a localização geográfica, Araponga está melhor situada que São Roque de Minas em distância dos grandes centros, mas as condições de acesso são similares. Considerando a socioeconomia, Araponga tem maiores índices de analfabetismo, evasão populacional, menor ICM, menores salários, e pior distribuição de renda. Enfocando o turismo em Caparaó e São Roque de Minas, as taxas de visitação atingiram 28.613 pessoas para o ano de 1999 em Caparaó, correspondendo a mais de 400% da população, e 3.000 pessoas/ano em São Roque de Minas (IBAMA, 1993), que corresponde a 52% da população. Embora não conclusivo, indica-se, pelas informações levantadas, que as piores condições socioeconômicas de Araponga em relação a Caparaó se devam à situação geográfica e a contribuição turística na economia de Caparaó. Já São Roque de Minas tem melhor desenvolvimento que Araponga e Caparaó devido à origem histórica e maior porção de terras menos acidentadas, refletindo na economia pecuária. A contribuição pelo turismo neste município é ainda modesta.bitstream/CNPS-2010/14880/1/doc-71-municipios-mg.pd
Fast Community Identification by Hierarchical Growth
A new method for community identification is proposed which is founded on the
analysis of successive neighborhoods, reached through hierarchical growth from
a starting vertex, and on the definition of communities as a subgraph whose
number of inner connections is larger than outer connections. In order to
determine the precision and speed of the method, it is compared with one of the
most popular community identification approaches, namely Girvan and Newman's
algorithm. Although the hierarchical growth method is not as precise as Girvan
and Newman's method, it is potentially faster than most community finding
algorithms.Comment: 6 pages, 5 figure
PAIRWISE VELOCITIES OF GALAXIES IN THE CFA AND SSRS2 REDSHIFT SURVEYS
(compressed version) We combine the CfA Redshift Survey (CfA2) and the
Southern Sky Redshift Survey (SSRS2) to estimate the pairwise velocity
dispersion of galaxies \sig12 on a scale of \sim 1 \hmpc. Both surveys are
complete to an apparent magnitude limit . Our sample includes 12,812
galaxies distributed in a volume 1.8 \times 10^6 \hmpc3. We conclude: 1) The
pairwise velocity dispersion of galaxies in the combined CfA2+SSRS2 redshift
survey is \sig12=540 \kms \pm 180 \kms. Both the estimate and the variance of
\sig12 significantly exceed the canonical values \sig12=340 \pm40 measured
by Davis \& Peebles (1983) using CfA1. 2) We derive the uncertainty in \sig12
from the variation among subsamples with volumes on the order of \hmpc3. This variation is nearly an order of magnitude larger than the
formal error, 36 \kms, derived using least-squares fits to the CfA2+SSRS2
correlation function. This variation among samples is consistent with the
conclusions of Mo \etal (1993) for a number of smaller surveys and with the
analysis of CfA1 by Zurek \etal (1994). 3) When we remove Abell clusters with
from our sample, the pairwise velocity dispersion of the remaining
galaxies drops to 295 \pm 99 \kms. Thus the dominant source of variance in
\sig12 is the shot noise contributed by dense virialized systems. 4) The
distribution of pairwise velocities is consistent with an isotropic exponential
with velocity dispersion independent of scale.Comment: 61 pages uuencoded, compressed postscript in 5 pieces. Also available
in one piece at http://www.dao.nrc.ca/DAO/SCIENCE/science.htm
The Power Spectrum of Galaxies in the Nearby Universe
We compute the power spectrum of galaxy density fluctuations in a recently
completed redshift survey of optically-selected galaxies in the southern
hemisphere (SSRS2). The amplitude and shape of the SSRS2 power spectrum are
consistent with results of the Center for Astrophysics redshift survey of the
northern hemisphere (CfA2), including the abrupt change of slope on a scale of
30-50Mpc/h; these results are reproducible for independent volumes of space and
variations are consistent with the errors estimated from mock surveys. Taken
together, the SSRS2 and CfA2 form a complete sample of 14,383 galaxies which
covers one-third of the sky. The power spectrum of this larger sample continues
to rise on scales up to ~ 200Mpc/h, with weak evidence for flattening on the
largest scales. The SSRS2+CfA2 power spectrum and the power spectrum
constraints implied by COBE are well-matched by an Omega*h ~ 0.2,
Omega+lambda_0=1 CDM model with minimal biasing of optically-selected galaxies.Comment: Accepted for publication in The Astrophysical Journal Letters, Sept.
23, 1994. 10 pages uuencoded compressed postscript, including two figures.
JHU-9410200
What are the Best Hierarchical Descriptors for Complex Networks?
This work reviews several hierarchical measurements of the topology of
complex networks and then applies feature selection concepts and methods in
order to quantify the relative importance of each measurement with respect to
the discrimination between four representative theoretical network models,
namely Erd\"{o}s-R\'enyi, Barab\'asi-Albert, Watts-Strogatz as well as a
geographical type of network. The obtained results confirmed that the four
models can be well-separated by using a combination of measurements. In
addition, the relative contribution of each considered feature for the overall
discrimination of the models was quantified in terms of the respective weights
in the canonical projection into two dimensions, with the traditional
clustering coefficient, hierarchical clustering coefficient and neighborhood
clustering coefficient resulting particularly effective. Interestingly, the
average shortest path length and hierarchical node degrees contributed little
for the separation of the four network models.Comment: 9 pages, 4 figure
An Analytical Approach to Neuronal Connectivity
This paper describes how realistic neuromorphic networks can have their
connectivity properties fully characterized in analytical fashion. By assuming
that all neurons have the same shape and are regularly distributed along the
two-dimensional orthogonal lattice with parameter , it is possible to
obtain the accurate number of connections and cycles of any length from the
autoconvolution function as well as from the respective spectral density
derived from the adjacency matrix. It is shown that neuronal shape plays an
important role in defining the spatial spread of network connections. In
addition, most such networks are characterized by the interesting phenomenon
where the connections are progressively shifted along the spatial domain where
the network is embedded. It is also shown that the number of cycles follows a
power law with their respective length. Morphological measurements for
characterization of the spatial distribution of connections, including the
adjacency matrix spectral density and the lacunarity of the connections, are
suggested. The potential of the proposed approach is illustrated with respect
to digital images of real neuronal cells.Comment: 4 pages, 6 figure
Tecnologias para redução do uso do fogo na agricultura.
A Embrapa tem realizado pesquisas e transferência de tecnologias visando à diminuição ou total eliminação do uso do fogo. O objetivo é desenvolver e validar sistemas de produção, gerar informações e resultados científicos sobre plantios que permitam o uso do solo por mais tempo, como a Integração Lavoura-Pecuária-Floresta, sistemas agroflorestais comerciais e sistemas florestais.bitstream/item/136066/1/PortalDiadeCampoLiane.pd
- …