1,721,842 research outputs found
New PARSEC evolutionary tracks of massive stars at low metallicity: testing canonical stellar evolution in nearby star forming dwarf galaxies
Full text linkIn this thesis I present new models of massive stars for low metallicity computed with the new code PARSEC: Padova TRieste Stellar Evolution Code. An updated version of this code, known as PARSEC V1.1, has already been released but, in the published version, the range of initial masses does not go beyond 12M . Recently, the PARSEC library of stellar evolutionary tracks has been extended with the inclusion of new models of massive stars, from 14M to 350M . The input physics is the same used in the PARSEC V1.1 version, but for the mass-loss rate which is included by considering the most recent updates in literature. In this thesis I perform a thorough comparison of the new models of massive stars with existing observational data. This is a critical and necessary step because the stellar evolution theory still contains some parameters that need to be tuned to well observed stellar samples. For this reason I focus on the low metallicity environment, Z=0.001, Z=0.004 and Z=0.0005, for which the metal poor dwarf irregular star forming galaxies, Sextans A, WLM, NGC 6822 and SagDIG, provide simple but powerful workbenches: the color-magnitude diagrams (CMDs) of their young stellar populations. From the simulations of these CMDs I draw the following conclusions: While the new models reproduce fairly well the observed CMDs of Sextans A, WLM and NGC 6822, a detailed analysis of the stellar color distributions indicates that the predicted blue loop is not hot enough in models that assume the canonical extent of overshooting from the convective regions. In the framework of a mild extended mixing during central hydrogen burning, the only way to reconcile the discrepancy is to enhance the overshooting at the base of the convective envelope (EO) during the first dredge-UP. Reproducing the features of the observed CMDs with standard values of envelope overshooting would require a metallicity significantly lower than the values measured in these galaxies. I find that the mixing scales required to reproduce the observed loops are large, EO=2HP or EO=4HP . These values are definitely larger than those derived from, e.g., the observed location of the RGB bump in low mass stars. This effect, if confirmed, would imply a strong dependence of the mixing scale below the formal Schwarzschild border, on the stellar mass or luminosity. Other quantities, such as the star formation rate and the initial mass function, are only slightly sensitive to this effect. This result is further validated in the comparison with the observed CMD of SagDIG at lower metal- licity, where I find an overshooting scale EO=2HP to best reproduce the observed loops. I also discuss the dependence of the blue loop extension on the adopted instability criterion and find that, contrary ito what stated in literature, the Schwarzschild criterion, instead of the Ledoux criterion, favours the development of blue loops. Other factors that could affect the CMD comparisons such as differential internal extinction or the presence of binary systems are found to have negligible effects on the results. I thus confirm that, in presence of core overshooting during the H-burning phase, a large envelope overshooting is needed to reproduce the main features of the central He-burning phase of intermediate- and high-mass stars
The effect of integrated microprocessor controlled knee-foot for inclined walking - a preliminary study on LiNX
No full text
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
Untargeted metabolite profiling of petal blight in field-grown Rhododendron agastum using GC-TOF-MS and UHPLC-QTOF-MS/MS
No full textDuan, Sheng-Guang, Hong, Kun, Tang, Ming, Tang, Jing, Liu, Lun-Xian, Gao, Gui-Feng, Shen, Zhi-Jun, Zhang, Xi-Min, Yi, Yin (2021): Untargeted metabolite profiling of petal blight in field-grown Rhododendron agastum using GC-TOF-MS and UHPLC-QTOF-MS/MS. Phytochemistry (112655) 184: 1-12, DOI: 10.1016/j.phytochem.2021.112655, URL: http://dx.doi.org/10.1016/j.phytochem.2021.11265
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
- …
