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Multiwave analysis of high-mass star forming regions
Full text linkCi sono stati notevoli sforzi per capire come si formano le stelle, sia da un punto di vista teorico che osservativo. Abbiamo raggiunto una buona comprensione di come si formano le stelle di bassa massa isolate (Klein et al. 2006). Lo scenario attualmente accettato è che le stelle di bassa massa si formano attraverso il collasso gravitazionale di un core prestellare; in seguito la formazione della sorgente prosegue con un accrescimanto dal disco che la circonda.
Estendere questa teoria ad stelle di alta massa non è banale. Le protostelle di alta massa raggiungono la sequenza principale mentre sono ancora nella fase di accrescimento principale. Quando la protostella centrale raggiunge una massa di circa 10 masse solari si innesca la fusione dell'idrogeno nel nucleo della stella e la pressione di radiazione e il vento dovrebbero impedire un'ulteriore accrescimento. Diverse teorie sono oggi proposte per permettere la formazione di oggetti di alta massa, che vengono presentate nel capitolo introduttivo, e noi cerchiamo di discriminare tra questi modelli teorici attraverso la ricostruzione della Star-Formation Hystori di ammassi stellari che si formano in regioni di formazione di alta massa. La presentazione di questo lavoro è divisa in tre sezioni.
• La prima parte presenta l'analisi del nostro campione di sorgenti e la discussione dei risultati scientifici. Questa è a sua volta divisa in tre capitoli. Nel capitolo 2 presentiamo i risultati della nostra analisi nelle bande del Vicino-InfraRosso caratterizzando le proprietà dei clusters di bassa massa; mentre nel capitolo 3, abbiamo mostriamo come ottenere le SEDS per gli oggetti di massa intermedia ed alta e come queste si confrontano con i modelli teorici. Nel Capitolo4 mettiamo insieme i risultati su tutte le lunghezze d'onda prese in esame per estrapolare le informazioni sulla storia dei clusters in fase di formazione.
• Nella seconda sezione presentiamo la struttura e le prestazioni dell' algoritmo di analisi dati da noi sviluppato.
• L'ultima sezione riassume i risultati ottenuti in questo lavoro di ricerca.There have been considerable efforts to understand how stars form from both a theoretical
and an observational point of view. We have reached a good understanding of how isolated
lowmass stars form (Klein et al. 2006). The widely accepted scenario is that low-mass
stars form by the gravitational collapse of a prestellar core followed at later stages by disk
accretion. Extending this theory to high-mass stars is not trivial. Highmass (proto-)stars
reach the zero age main sequence while still accreting. When the central protostar reaches
a mass of about 10 Msun hydrogen fusion ignites in the core and the star’s radiation pressure
and wind should prevent further accretion. Several theories are today proposed, we discuss
about them in the introduction, and we try to discriminate between these theoretical models
through the re-building of the Star-Formation Hystori of clusters formed in high-mass star
formation regions.
The presentation of this work is divided into three section.
• The first part presents the analysis of our sample and the discussion of our scientific
results, it is divided in three chapter. In the chapter 2 we presents the results of our
analysis in the Near-IR banbs to characterized the properties of low mass cluster in
our sample, while in the chapter 3 we shown the SEDs building for intermediate and
high-mass objects and the fits with theoretical models. In the chapter4 we take again
our results on all the examinated wavelengths to extrapolate the information about
the clusters star formation history.
• In the second section the structure and the performances of our data analysis algorithm
is presented.
• The last section recapitulates the results obtain in all this wor
Efficacia di un nuovo erbicida di post-emergenza su grano duro
No full textIn varie condizioni malerbologiche tipiche del litorale e delle aree interne laziali con prevalente presenza di Lolium multifl orum e Phalaris
brachystachys è stata verifi cata l’effi cacia di Hussar Maxx, nuovo formulato a base di iodosulfuron + mesosulfuro
Properties of stellar clusters around high-mass young stars
No full textContext: Twenty-six high-luminosity IRAS sources believed to be collection of stars in the early phases of high-mass star formation have been observed in the near-IR (J, H, K_s) to characterize the clustering properties of their young stellar population and compare them with those of more evolved objects (e.g., Herbig Ae/Be stars) of comparable mass. All the observed sources possess strong continuum and/or line emission in the millimeter, being therefore associated with gas and dust envelopes. Nine sources have far-IR colors characteristic of UCHII regions, while the other 17 are probably experiencing an evolutionary phase that precedes the hot-cores, as suggested by a variety of evidence collected in the past decade.
Aims: We attempt to gain insight into the initial conditions of star formation in these clusters (initial mass function [IMF], star formation history [SFH]), and to determine mean cluster ages.
Methods: For each cluster, we complete aperture photometry. We derive stellar density profiles, color-color and color-magnitude diagrams, and color (HKCF) and luminosity (KLF) functions. These two functions are compared with simulated KLFs and HKCFs from a model that generates populations of synthetic clusters starting from assumptions about the IMF, SFH, and Pre-MS evolution, and using the average properties of the observed clusters as boundary conditions (bolometric luminosity, dust distribution, infrared excess, extinction).
Results: Twenty-two sources show evidence of clustering with a stellar richness indicator that varies from a few up to several tens of objects, and a median cluster radius of 0.7 pc. A considerable number of cluster members present an infrared excess characteristic of young pre-main-sequence objects. For a subset of 9 detected clusters, we could perform a statistically significant comparison of the observed KLFs with those resulting from synthetic cluster models; for these clusters, we find that the median stellar age ranges between 2.5×105 and 5×106 years, with evidence of an age spread of the same entity within each cluster. We also find evidence that older clusters tend to be smaller in size, in agreement with our clusters being on average larger than those around relatively older Herbig Ae/Be stars. Our models allow us to explore the relationship between the mass of the most massive star in the cluster and both the cluster richness and the total stellar mass. Although these relationships are predicted by several classes of cluster formation models, their detailed analysis suggests that the properties of our modeled clusters may not be consistent with them resulting from random sampling of the IMF.
Conclusions: Our results are consistent with star formation having occurred continuously over a period of time longer than the typical crossing time
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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