1,720,955 research outputs found
Compattificazioni wonderful e spazi di moduli di Kontsevich di coniche
No full textIn questa tesi studiamo alcune varietà algebriche dal punto di vista della geometria birazionale. Data una varietà vogliamo descrivere tutti i suoi modelli birazionali. In generale questo è un problema molto difficile, ma per una classe speciale di varietà, chiamate Mori dream spaces, la geometria birazionale è codificata in una decomposizione in insiemi convessi del loro cono effettivo. I Mori dream spaces sono stati introdotti da Y. Hu e S. Keel e sono chiamati così poiché si comportano nel miglior modo possibile dal punto di vista del programma dei modelli minimali.
La prima parte della tesi è dedicata alla costruzione di compattificazioni wonderful di spazi di mappe lineari. Riprendiamo la costruzione, dovuta a I. Vainsencher, degli spazi delle collineazioni e delle quadriche complete di rango massimo e poi la generalizziamo a spazi di mappe lineari di qualsiasi rango. Costruiamo poi la compattificazione wonderful dello spazio delle matrici simmetriche e simplettiche.
Grazie ad un risultato di D. Luna, le varietà wonderful sono varietà sferiche e quindi Mori dream spaces. Approfittando della struttura sferica di questi spazi studiamo la loro geometria birazionale dal punto di vista della teoria di Mori e nei casi di rango di Picard basso diamo una descrizione completa della decomposizione del cono effettivo.
Nella seconda parte mettiamo in relazione le nostre nuove compattificazioni wonderful con altri spazi di moduli come gli schemi di Hilbert e gli spazi di Kontsevich di mappe stabili. Infatti, otteniamo in questo modo molti risultati sulla geometria birazionale degli spazi di moduli di Kontsevich di coniche in Grassmanniane, in Grassmanniane Lagrangiane e di mappe stabili di bi-grado (1,1) in un prodotto di due spazi proiettivi.In this thesis we study certain algebraic varieties from the point of view of birational geometry. Given a variety we want to describe all its birational models. In general, this is a very difficult problem, but for a special class of varieties, called Mori dream spaces, the birational geometry is encoded in a decomposition into convex sets of their effective cone. Mori dream spaces have been introduced by Y. Hu and S. Keel, and are named so since they behave in the best possible way from the point of view of the minimal model program.
The first part of the thesis is dedicated to the construction of wonderful compactifications of spaces of linear maps. We recall the construction, due to I. Vainsencher, of the spaces of complete collineations and quadrics of maximal rank and then we generalize it to spaces of linear maps of any rank. Then, we construct the wonderful compactification of the space of symmetric and symplectic matrices.
By a result of D. Luna, wonderful varieties are spherical and hence Mori dream spaces. So, we take advantage of the spherical structure of these spaces to study their birational geometry from the point of view of Mori theory and in the cases of small Picard rank we give a complete description of the decomposition of the effective cone.
In the second part, we relate our wonderful compactification to other moduli spaces such as Hilbert schemes and Kontsevich spaces of stable maps. In fact, we get several results on the birational geometry of Kontsevich moduli spaces of conics in Grassmannians, in Lagrangian Grassmannians and of stable maps of bi-degree (1,1) in a product of two projective spaces
Complete symplectic quadrics and Kontsevich spaces of conics in Lagrangian Grassmannians
Full text linkA wonderful compactification of an orbit under the action of a semi-simple and simply connected group is a smooth projective variety containing the orbit as a dense open subset, and where the added boundary divisor is simple normal crossing. We construct the wonderful compactification of the space of symmetric and symplectic matrices, and investigate its geometry. As an application, we describe the birational geometry of the Kontsevich spaces parametrizing conics in Lagrangian Grassmannians
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
