197,605 research outputs found
Higher secant varieties of embedded in bi-degree
No full textLet denote the Segre-Veronese embedding of
via the sections of the sheaf . We study the dimensions of higher secant varieties of and we prove that there is no defective secant variety, except possibly for values of . Moreover when is multiple of , the secant variety of has the expected dimension for every
Holey Segre varieties
No full textgeneralizzando le varieta' di Segre (classiche), si introducono le varieta' di Segre "Holey", prodotto tensoriale di PG(n,q) e PG(m,q^k), fornendone una descrizione algebrica e studiandone la struttura geometrica. Inoltre, per particolari valori dei parametri, si prova che una varieta' di Segre holey ammette una partizione in varieta' di Segre classiche, e che alcune varieta' di Segre holey sono sottogeometrie non canoniche immerse in opportune varieta' di Segre
Mixed multiplicities, Segre numbers and Segre classes
No full textBased on classical results of Rees and on multivariate Hilbert polynomials, we define new mixed multiplicities of two arbitrary ideals in a local ring (A, m) and use them to express the local degrees of all varieties appearing in the Gaffney–Gassler construction of Segre cycles. We prove that the classical mixed multiplicities of m and an arbitrary ideal I, which are a special case of the new ones, are equal to the generalized Samuel multiplicities of an ideal in the Rees algebra R_I(A). This equality is used to improve a result of Jeffries, Montaño and Varbaro on the degree of the fiber cone of an ideal.
We conclude the paper with formulas (and their inverses) which express the degrees of Segre classes of subschemes of arbitrary projective varieties by generalized Samuel multiplicities or by classical mixed multiplicities. Using the mixed multiplicities of balanced rational normal scrolls, which have been computed by Hoang and Lam, we find the mixed multiplicities of all rational normal scrolls as well as their Segre classes and their generalized Samuel multiplicities
Présentation de M. Gesare Segre par M. Jules Horrent
No full textHorrent Jules. Présentation de M. Gesare Segre par M. Jules Horrent. In: Bulletin de la Classe des lettres et des sciences morales et politiques, tome 62, 1976. pp. 276-278
A characterization of the Corrado Segre variety
No full textAbstract. In this paper we give a combinatorial characterization of the Corrado Segre variety of type {n,m} in
terms of its incidence structure of points and lines
Vector field construction of Segre sets
No full textA CR generic real analytic CR manifold M carries two families of Segre varieties and conjugate Segre varieties. We observe in this article that their complexifications give rise to two families of foliations of the complexification of M which coincide with the flow foliations induced by the complexified CR (1,0) and (0,1) vector fields tangent to M. As an application, we derive a new proof of the characterization of finite type in terms of Segre sets
Montferrer de Segre a Castellciutat
No full textVista de Montferrer de Segre, poble (732 m alt) i cap del municipi de Montferrer i Castellbò (Alt Urgell), situat a la dreta del Segre. És emplaçat dalt d'un turó, prop del riu, que és continuació del de Castellciutat
Paroles d'accueil à M. C. Segre prononcées par M. Albert Henry
No full textHenry Albert. Paroles d'accueil à M. C. Segre prononcées par M. Albert Henry . In: Bulletin de la Classe des lettres et des sciences morales et politiques, tome 62, 1976. p. 275
On the Segre characteristic of a block triangular matrix
No full textAbstractConsider two complex matrices A and B of sizes n×n and m×m respectively, and let λ be an eigenvalue of both matrices. If α=(n1,n2) and β=(m1,m2) are the Segre characteristics associated with λ of A and B, respectively, and γ=(r1,r2,r3,r4) is a nonincreasing sequence of nonnegative integers, then a method for determining when γ is the Segre characteristic of the block triangular matrixM=ALOBin terms of α and β, and the structure of matrix L is presented. A completely explicit description of the Segre characteristic of M associated with λ is obtained. Using similar techniques, general cases when α, β and γ have more elements and satisfy some size restrictions are considered
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