1,528 research outputs found
NGC 4337: an over-looked old cluster in the inner disc of the Milky Way
Galactic open clusters do not survive long in the high density regions of the
inner Galactic disc. Inside the solar ring only 11 open clusters are known with
ages older than one Gyr. We show here, basing on deep, high-quality photometry,
that NGC 4337, contrary to earlier findings, is indeed an old open cluster. The
cluster is located very close to the conspicuous star cluster Trumpler 20, as
well mis-classified in the past, and that has received so much attention in
recent years. NGC 4337 shows a significant clump of He-burning stars which was
not detected previously. Its beautiful color-magnitude diagram is strikingly
similar to the one of the classical old open clusters IC 4651, NGC 752, and NGC
3680, and this suggests similar age and composition. A spectroscopic study is
much needed to confirm our findings. This, in turn, would also allow us to
better define the inner disc radial abundance gradient and its temporal
evolution.To this aim, a list of clump star candidates is provided.Comment: 5 pages, 4 eps figures, in press as MNRAS Lette
The thickening of the thin disk in the third Galactic quadrant
In the third Galactic quadrant (180 < l < 270) of the Milky Way, the Galactic
thin disk exhibits a significant warp ---shown both by gas and young stars---
bending down a few kpc below the formal Galactic plane (b=0). This warp shows
its maximum at 240, in the direction of the Canis Major constellation. In a
series of papers we have traced the detailed structure of this region using
open star clusters, putting particular emphasis on the spiral structure of the
outer disk. We noticed a conspicuous accumulation of young star clusters within
2-3 kpc from the Sun and close to b=0, that we interpreted as the continuation
of the Local (Orion) arm towards the outer disk. While most clusters (and young
stars in their background) follow closely the warp of the disk, our decade-old
survey of the spiral structure of this region led us to identify three
clusters, Haffner~18(1 and 2) and Haffner~19, which remain very close to b=0
and lie at distances (4.5, 8.0, and 6.4 kpc) where most of the material is
already significantly warped. Here we report on a search for clusters that
share the same properties as Haffner~18 and 19, and investigate the possible
reasons for such an unexpected occurrence. We present UBVRI photometry of
5~young clusters, namely NGC~2345, NGC~2374, Trumpler~9, Haffner~20, and
Haffner~21, which also lie close to the formal Galactic plane. With the
exception of Haffner~20, in the background of these clusters we detected young
stars that appear close to b=0, and are located at distances up to 8 kpc from
the Sun, thus deviating significantly from the warp. These populations define a
structure that distributes over almost the entire third Galactic quadrant. We
discuss this structure in the context of a possible thin disk flaring, in full
similarity with the Galactic thick disk.Comment: 53 pages, 12 eps figures, in press in the Astronomical Journa
Semantic enrichment of knowledge sources supported by domain ontologies
This thesis introduces a novel conceptual framework to support the creation of knowledge representations based on enriched Semantic Vectors, using the classical vector space model approach extended with ontological support. One of the primary research challenges addressed here relates to the process of formalization and representation of document contents, where most existing approaches are limited and only take into account the explicit, word-based information in the document. This research explores how traditional knowledge representations can be enriched through incorporation of implicit information derived from the complex relationships (semantic associations) modelled by domain ontologies with the addition of information presented in documents. The relevant achievements pursued by this thesis are the following: (i) conceptualization of a model that enables the semantic enrichment of knowledge sources supported by domain experts; (ii) development of a method for extending the traditional vector space, using domain ontologies; (iii) development of a method to support ontology learning, based on the discovery of new ontological relations expressed in non-structured information sources; (iv) development of a process to evaluate the semantic enrichment; (v) implementation of a proof-of-concept, named SENSE (Semantic Enrichment kNowledge SourcEs), which enables to validate the ideas established under the scope of this thesis; (vi) publication of several scientific articles and the support to 4 master dissertations carried out by the department of Electrical and Computer Engineering from FCT/UNL. It is worth mentioning that the work developed under the semantic referential covered by this thesis has reused relevant achievements within the scope of research European projects, in order to address approaches which are considered scientifically sound and coherent and avoid “reinventing the wheel”.European research projects - CoSpaces (IST-5-034245), CRESCENDO (FP7-234344) and MobiS (FP7-318452
Not Can I, But Should I: Analyzing the Pre-existing conditions surrounding successful third party intervention into intrastate conflicts
Defense Analysis Poste
Integrating metalloporphycenes into p-type NiO-based dye-sensitized solar cells
In the current work, we have explored a novel synthetic route towards metalated porphycenes and their use in p-type NiO-based dye-sensitized solar cells. Particular emphasis is placed on the influence that the relative positioning of the anchoring group exerts on the DSSC performance
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