14,232 research outputs found
SPH simulations of the chemical evolution of bulges
We have implemented a chemical evolution model on the parallel AP3M+SPH DEVA
code which we use to perform high resolution simulations of spiral galaxy
formation. It includes feedback by SNII and SNIa using the Qij matrix
formalism. We also include a diffusion mechanism that spreads newly introduced
metals. The gas cooling rate depends on its specific composition. We study the
stellar populations of the resulting bulges finding a potential scenario where
they seem to be composed of two populations: an old, metal poor,
-enriched population, formed in a multiclump scenario at the beginning
of the simulation and a younger one, formed by slow accretion of satellites or
gas, possibly from the disk due to instabilities.Comment: 2 pages, 3 figures. Proceedings of IAUS 245 "Formation and Evolution
of Galaxy Bulges
The role of magnetoplasmons in Casimir force calculations
In this paper we review the role of magneto plasmon polaritons in the Casimir
force calculations. By applying an external constant magnetic field a strong
optical anisotropy is induced on two parallel slabs reducing the reflectivity
and thus the Casimir force. As the external magnetic field increases, the
Casimir force decreases. Thus, with an an external magnetic field the Casimir
force can be controlled.The calculations are done in the Voigt configuration
where the magnetic field is parallel to the slabs. In this configuration the
reflection coefficients for TE and TM modes do not show mode conversion.Comment: contribution to QFEXT09, Norman, Oklahoma 200
How was the Hubble sequence 6 Gyrs ago?
The way galaxies assemble their mass to form the well-defined Hubble sequence
is amongst the most debated topic in modern cosmology. One difficulty is to
link distant galaxies to those at present epoch. We aim at establishing how
were the galaxies of the Hubble sequence, 6 Gyrs ago. We intend to derive a
past Hubble sequence that can be causally linked to the present-day one. We
selected samples of nearby galaxies from the SDSS and of distant galaxies from
the GOODS survey. We verified that each sample is representative of galaxies.
We further showed that the observational conditions necessary to retrieve their
morphological classification are similar in an unbiased way. Morphological
analysis has been done in an identical way for all galaxies in the two samples.
We found an absence of number evolution for elliptical and lenticular galaxies,
which strikingly contrasts with the strong evolution of spiral and peculiar
galaxies. Spiral galaxies were 2.3 times less abundant in the past, that is
exactly compensated by the strong decrease by a factor 5 of peculiar galaxies.
It strongly suggests that more than half of the present-day spirals had
peculiar morphologies, 6 Gyrs ago, and this has to be accounted by any scenario
of galactic disk evolution and formation. The past Hubble sequence can be used
to test these scenarios as well as to test evolution of fundamental planes for
spirals and bulges.Comment: Version accepted by Astronomy and Astrophysics, October 21 2009.
Including low resolution images. 11 pages, 8 figure
Quaternary glacial evolution in the Central Cantabrian Mountains (Northern Spain)
Peer reviewedPostprin
Clustering in complex networks. II. Percolation properties
The percolation properties of clustered networks are analyzed in detail. In
the case of weak clustering, we present an analytical approach that allows to
find the critical threshold and the size of the giant component. Numerical
simulations confirm the accuracy of our results. In more general terms, we show
that weak clustering hinders the onset of the giant component whereas strong
clustering favors its appearance. This is a direct consequence of the
differences in the -core structure of the networks, which are found to be
totally different depending on the level of clustering. An empirical analysis
of a real social network confirms our predictions.Comment: Updated reference lis
Stüben, P.E. (2022). Weevils of Macaronesia. Canary Islands, Madeira, Azores (Coleoptera: Curculionoidea). Curculio Institute: Mönchengladbach, 783 pp.
Amateur naturalists at the beginning of their pursuit of the discovery of Coleoptera biodiversity are usually fascinated by the beauty of buprestids (jewel beetles), of Cerambycids (longhorn beetles) or even of Carabids and Cicindelids (ground and tiger beetles) due to their conspicuous and often glossy iridescent metallic colours. Weevils do not normally fall into this selection and to most people they are known as pests of food products. In Portuguese common language they are known under the name of “gorgulhos”. However, the weevils are probably the most diverse group in the animal and plant kingdoms with over 60,000 described species (Oberprieler et al. 2007). […].info:eu-repo/semantics/publishedVersio
Percolation and Epidemic Thresholds in Clustered Networks
We develop a theoretical approach to percolation in random clustered
networks. We find that, although clustering in scale-free networks can strongly
affect some percolation properties, such as the size and the resilience of the
giant connected component, it cannot restore a finite percolation threshold. In
turn, this implies the absence of an epidemic threshold in this class of
networks extending, thus, this result to a wide variety of real scale-free
networks which shows a high level of transitivity. Our findings are in good
agreement with numerical simulations.Comment: 4 Pages and 3 Figures. Final version to appear in PR
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