3,726 research outputs found
Planetary nebulae in the inner Milky Way
New abundances of planetary nebulae located towards the bulge of the Galaxy
are derived based on observations made at LNA (Brazil). We present accurate
abundances of the elements He, N, S, O, Ar, and Ne for 56 PNe located towards
the galactic bulge. The data shows a good agreement with other results in the
literature, in the sense that the distribution of the abundances is similar to
those works. From the statistical analysis performed, we can suggest a
bulge-disk interface at 2.2 kpc for the intermediate mass population, marking
therefore the outer border of the bulge and inner border of the disk.Comment: 2 pages, 1 figure, uses iaus.cls, in press, IAU Symp. 265, Chemical
abundances in the Universe: Connecting the first Stars to Planets, Ed. K.
Cunha, M. Spite, B. Barbu
Planetary nebulae as probes for galactic chemical evolution
The role of planetary nebulae as probes for the galactic chemical evolution
is reviewed. Their abundances throughout the Galaxy are discussed for key
elements, in particular oxygen and other alpha elements. The abundance
distribution derived from planetary nebulae leads to the establishment of
radial abundance gradients in the galactic disk that are important constraints
to model the chemical evolution of the Galaxy. The radial gradient, well
determined for the solar neighborhood, is examined for distinct regions. For
the galactic anticenter in particular, the observational data confirm results
from galactic evolution models that point to a decreasing in the gradient slope
at large galactocentric distances. The possible time evolution of the radial
gradient is also examined comparing samples of planetary nebulae of different
ages, and the results indicate that a flattening in the gradient occurred,
which is confirmed by some galactic evolution models. The galactic bulge is
another important region whose modeling can be constrained by observational
results obtained from planetary nebulae. Results derived in the last few years
indicate that bulge nebulae have an abundance distribution similar to that of
disk objects, however with a larger dispersion.Comment: 8 pages, 6 figures, LaTeX, To be published in the Proceedings of the
IAU Symposium 234: Planetary Nebulae in Our Galaxy and Beyon
Planetary nebulae and the chemical evolution of the galactic bulge
Electron temperatures, densities, ionic and elemental abundances of helium,
nitrogen, oxygen, argon, sulfur and neon were derived for a sample of bulge
planetary nebulae, representative of its intermediate mass population. Using
these results as constraints, a model for the chemical evolution of the
galactic bulge was developed. The results indicate that the best fit is
achieved using a double-infall model, where the first one is a fast collapse of
primordial gas and the second is slower and enriched by material ejected by the
bulge itself during the first episode.Comment: 4 pages, 4 figures, to appear in the proceedings of the conference
"Planetary Nebulae as astronomical tools" held in Gdansk, Poland, jun 28/jul
02, 200
Population density and photosynthetic pigment content in symbiotic dinoflagellates in the Brazilian scleractinian coral Montastrea cavernosa (Linnaeus, 1767)
A dinâmica sazonal na densidade de células e na concentração de pigmentos fotossintetizantes das zooxantelas de Montastrea cavernosa foram analisados no período setembro/1999 a setembro/2000 nos Recifes do Picãozinho (06º42'05"/07º07'30" S e 34º48'37"/34º50'00" W), Nordeste do Brasil. Verificou-se que existe um padrão distinto entre estes parâmetros, com maior quantidade de células no período chuvoso e maior concentração de pigmentos fotossintetizantes na época de estiagem. Ambos os parâmetros apresentaram, no entanto, uma nítida redução em seus valores nos meses de maiores índices pluviométricos (junho e julho /1999). Especulamos que tal fato deve estar relacionado com o regime de chuvas que pode variar em magnitude e freqüência, afetando a qualidade ótica da água e o estado fisiológico das células.The seasonal dynamics of cell density and photosynthetic pigment contents of the zooxanthellae hosted by Montastrea cavernosa were investigated on coastal reefs off Picãozinho (06º42'05"/07º07'30"S and 34º48'37"/34º50'00" W), Northeast Brazil between September 1999 and 2000. A distinct pattern of these parameters was found: cell numbers were greater during the rainy season (autumn/winter) while photosynthetic pigments were greater during the dry season (summer). Both parameters showed drastic reductions during heavy rains (June and July 1999). We speculate that this pattern is largely influenced by the rain cycles which, owing to their magnitude and frequency, affect the water clarity and the seasonal physiological condition of the cells
Promoting health equity through social capital in deprived communities: a natural policy experiment in Trieste, Italy
Planetary nebulae and the chemical evolution of the galactic bulge: new abundances of older objects
In view of their nature, planetary nebulae have very short lifetimes, and the
chemical abundances derived so far have a natural bias favoring younger
objects. In this work, we report physical parameters and abundances for a
sample of old PNe located in the galactic bulge, based on low dispersion
spectroscopy secured at the SOAR telescope using the Goodman Spectrograph. The
new data allow us to extend our database including older, weaker objects that
are at the faint end of the planetary nebula luminosity function (PNLF). The
results show that the abundances of our sample are lower than those from our
previous work. Additionally, the average abundances of the galactic bulge do
not follow the observed trend of the radial abundance gradient in the disk.
These results are in agreement with a chemical evolution model for the Galaxy
recently developed by our group.Comment: 2 pages, 2 figures, to appear in proceedings of the IAU Symposium
283: "Planetary Nebulae: An Eye to the Future", Eds.: A. Manchado, L.
Stanghellini and D. Schoenberne
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
THE RELATIONSHIP BETWEEN FRONT CRAWL PERFORMANCE AND HYDRODYNAMICS IN YOUNG FEMALE SWIMMERS
The aim of this study was to analyse the relationship between front crawl performance and hydrodynamic variables during leg kicking. Sixteen female swimmers (9.2±0.6 years) participated in this study. The 200m front crawl performance, the 200m front crawl kicking performance and the active drag during leg kicking were measured. The velocity perturbation method was used to determine active drag. The 200m front crawl performance was significantly correlated with performance in 200m kicking (0.89), with hydrodynamic drag force during leg kicking (-0.70), and power output in kicking (-0.64). Drag coefficient was not related to the performance in 200 m front crawl. These findings underline the importance of leg kicking to performance in front crawl swimming in these ages and suggests the important role of kicking tasks during training in young swimmers
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