1,721,042 research outputs found
Varieties connected by chains of lines
No full textIn this paper we give for any integer a numerical criterion ensuring the existence of a chain of length of lines through two general points of an irreducible variety , involving the degrees and the number of homogeneous polynomials defining . We show that our criterion is sharp.1681616
Instanton bundles on the flag variety F(0,1,2)
No full textInstanton bundles on P3 have been at the core of the research in Algebraic Geometry during the last thirty years. Motivated by the recent extension of their definition to other Fano threefolds of Picard number one, we develop the theory of instanton bundles on the complete flag variety F := F(0, 1, 2) of point-lines on P2. After giving for them two different monadic presentations, we use it to show that the moduli space MIF (k) of instanton bundles of charge k is a geometric GIT quotient and the open subspace MIs(k) ⇢ MIF (k) of stable instanton bundles has a generically smooth component of dim 8k −3. Finally we study their locus of jumping conics
‘t Hooft bundles on the complete flag threefold and moduli spaces of instantons
Get PDFIn this work we study the moduli spaces of instanton bundles on the flag twistor space . We stratify them in terms of the minimal twist supporting global sections and we introduce the notion of (special) 't Hooft bundle on . In particular we prove that there exist -stable 't Hooft bundles for each admissible charge . We completely describe the geometric structure of the moduli space of (special) 't Hooft bundles for arbitrary charge . Along the way to reach these goals, we describe the possible structures of multiple curves supported on some rational curves in as well as the family of del Pezzo surfaces realized as hyperplane sections of . Finally we investigate the splitting behavior of 't Hooft bundles when restricted to conics
Dante Alive. Essays on a Cultural Icon
Get PDFObra ressenyada: Ciabattoni, Francesco ; Marchesi, Simone (eds,). "Dante Alive : essays on a Cultural Icon". New York e Londra : Routledge, 2023
Classification of the invariants of foliations by curves of low degree on the three-dimensional projective space
Get PDFWe study foliations by curves on the three-dimensional projective space with no isolated singularities, which is equivalent to assuming that the conormal sheaf is locally free. We provide a classification of the topological and algebraic invariants of the conormal sheaves and singular schemes for such foliations by curves, up to degree 3. In particular, we prove that foliations by curves of degree 1 or 2 are contained in a pencil of planes or are Legendrian, and are given by the complete intersection of two codimension one distributions. Furthermore, we prove that the conormal sheaf of a foliation by curves of degree 3 with reduced singular scheme either splits as a sum of line bundles or is an instanton bundle. For degree larger than 3, we focus on two classes of foliations by curves, namely Legendrian foliations and those whose conormal sheaf is a twisted null-correlation bundle. We give characterizations of such foliations, describe their singular schemes and their moduli spaces
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
- …
