1,720,989 research outputs found
On The Slope of Fibred Surfaces
No full textWe give an asymptotically sharp lower bound for the slope λ(f) of a fibration f : S → B, where S is a surface and B is a curve, if there exists an involution on the general fibre F of f. We also construct a new lower bound of λ(f) depending increasingly on the irregularity of S; as an application of this new bound we have a criteria to control the existence of other fibrations on S
Slopes of trigonal fibred surfaces and of higher dimensional fibrations
No full textWe prove a sharp lower bound for the slope of trigonal fibrations of even genus and general Maroni invariant using a method of Cornalba-Harris
Higher-dimensional Clifford-Severi equalities
Get PDFLet X be a smooth complex projective variety, a: X → A a morphism to an abelian variety such that pic0(A) injects into pic0(X) and let L be a line bundle on X; denote by ha0(X,L) the minimum of h0(X,LS - a-α) for α Pic0(A). The so-called Clifford-Severi inequalities have been proven in [M. A. Barja, Generalized Clifford-Severi inequality and the volume of irregular varieties, Duke Math. J. 164(3) (2015) 541-568; M. A. Barja, R. Pardini and L. Stoppino, Linear systems on irregular varieties, J. Inst. Math. Jussieu (2019) 1-39; doi:10.1017/S1474748019000069]; in particular, for any L there is a lower bound for the volume given by: vol(L) ≥ n!ha0(X,L), and, if KX - L is pseudoeffective, vol(L) ≥ 2n!ha0(X,L). In this paper, we characterize varieties and line bundles for which the above Clifford-Severi inequalities are equalities
Stability and singularities of relative hypersurfaces
Get PDFWe study relative hypersurfaces over curves, and prove an instability
condition for the fibres. This gives an upper bound on the log canonical
threshold of the relative hypersurface. We compare these results with the
information that can be derived from Nakayama's Zariski decomposition of
effective divisors on relative projective bundles.Comment: 26 pages, 1 figure, revised version with minor change
On the topological index of irregular surfaces
No full textWe study the topological index of some irregular surfaces that we call generalized Lagrangian. We show that under certain hypotheses on the base locus of the Lagrangian system the topological index is non-negative. For the minimal surfaces of general type with q=4 and p_g=5 we prove the same statement without any hypotheses. Some similar results for higher dimensional varieties are given
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
Linear stability of projected canonical curves, with applications to the slope of fibred surfaces
Get PDFLet f : S → B be a non locally trivial relatively minimal fibred surface. We prove a lower bound for the slope of f depending increasingly from the relative irregularity of f and the Clifford index of the general fibres
LINEAR SYSTEMS on IRREGULAR VARIETIES
Get PDFLet be a normal complex projective variety, a subvariety of dimension (possibly) and a morphism to an abelian variety such that injects into; let be a line bundle on and a general element.We introduce two new ingredients for the study of linear systems on. First of all, we show the existence of a factorization of the map, called the eventual map of on, which controls the behavior of the linear systems, asymptotically with respect to the pullbacks to the connected étale covers induced by the -th multiplication map of.Second, we define the so-called continuous rank function, where is the pullback of an ample divisor of. This function extends to a continuous function of, which is differentiable except possibly at countably many points; when we compute the left derivative explicitly.As an application, we give quick short proofs of a wide range of new Clifford-Severi inequalities, i.e., geographical bounds of the form where depends on several geometrical properties of, or
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
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