1,721,072 research outputs found
Young stellar clusters in the Vela D molecular cloud
No full textIt is now well established by means of direct and indirect observations that most, if not all, stars are formed in groups rather than in isolation (Clarke, Bonnell & Hillenbrand 2000). An important result that strongly constrains theories of massive star and stellar cluster formation is that the stellar density of young stellar clusters seems to depend on the mass of the most massive star in the cluster. Low-mass stars are usually found to form in loose groups with typical densities of a few stars per cubic parsec (Gomez et al. 1993), while high-mass stars are found within dense stellar clusters of up to 104 stars per cubic parsec (e.g. the Orion Nebula Cluster, Hillenbrand & Hartmann 1998). To explain this different behaviour, it has been proposed that massive stars may form with a process that is drastically different from the standard accretion picture, e.g. by coalescence of lower mass seeds in a dense cluster environment. The transition between these two modes of formation should occur in the intermediate-mass regime, namely 2 <= M/M0 <= 15
Mid-IR observations of small stellar clusters surrounding Herbig AeBe stars
No full textWe present TIMMI2 observations at 10 mu m of 12 fields centered on known Herbig AeBe (HAeBe) stars. We detected sources (in addition to the HAeBe star) in five fields, three of which are associated with early B stars. Using complementary near-IR and optical data, we estimate that the detected sources are young, embedded (AV, ~ 5-24 mag), intermediate-mass objects ( ~ 1.5-3.5 Msun). In four objects the 10 mu m emission can be accounted for by a circumstellar disk, while in 2 cases (possibly 3) there is evidence that the objects are still in an earlier stage of evolution (Class I). These results confirm the association of the early B Herbig stars with rather rich clusters, as well as their very young age. If our estimates of the stellar parameters are confirmed, this would be the largest sample so far of embedded, intermediate-mass objects available for further studies
Subcutaneous alternariosis
No full textA case of subcutaneous alternariosis caused by Alternaria alternata is reported in a 52-year-old male who underwent kidney transplantation 1 year earlier. The infection manifested as a vegetating mass about 7 cm in diameter on the right forearm. Histological examination with Grocott staining and periodic acid-Schiff diastase revealed fungal spores and hyphae with chronic granulomatous inflammation. Biopsy fragments inoculated on Sabouraud-glucose agar with chloramphenicol produced colonies which were identified as Alternaria alternata on the basis of macroscopic and microscopic character
Characterization of Narrow Band Filters for Infrared Astronomy The Brgamma and H_2 filters
No full textWe present a characterization of two narrow band filters commonly used in Infrared Astronomy. Our study mainly quantifies the effect of temperature and tilt angle on the central wavelength and width of the transmission bands of such filters. This allows to evaluate some important effects that must be taken into account to have good quality astronomical images. Effects as the limitation of the field of view and the presence of OH sky lines in the final image are quantified
The IMF and star formation history of the stellar clusters in the Vela D cloud
No full textAims.We present the results of a Near-Infrared deep photometric survey of a
sample of six embedded star clusters in the Vela-D molecular cloud,
all associated with luminous ( ) IRAS
sources. The clusters are unlikely to be older than a few 106
yrs, since all are still associated with molecular gas.Methods.We employed the fact that all clusters lie at the same distance and
were observed with the same instrumental setting to derive
their properties in a consistent way, being affected by the same
instrumental and observational biases.
We extracted the clusters' K Luminosity Functions and developed a
simple method to correct them for extinction, based on colour-magnitude
diagrams. The reliability of the method has been tested by
constructing synthetic clusters from theoretical tracks for pre-main
sequence stars and a standard Initial Mass Function.
The clusters' Initial Mass Functions have been derived from the
dereddened
K Luminosity Functions by adopting a set of pre-main sequence
evolutionary tracks and assuming coeval star formation.Results.All clusters are small ( members) and compact (radius
pc); their most massive stars are
intermediate-mass ( ) ones.
The dereddened K Luminosity Functions are likely to arise
from the same
distribution, suggesting that the selected clusters have quite
similar Initial Mass Functions and star formation histories.
The Initial Mass Functions are consistent with those
derived for field stars and clusters. Adding them
together we found that the “global” Initial Mass Function
appears steeper at the high-mass end and
exhibits a drop-off at . In fact,
a standard Initial Mass Function would
predict a star with within one of the clusters,
which is not found. Hence, either high-mass stars need larger
clusters
to be formed, or the Initial Mass Function of the single clusters is
steeper at the
high-mass end because of the physical conditions in the parental gas
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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