共查询到20条相似文献,搜索用时 562 毫秒
1.
The topological characteristics are studied of the set of points at which the stalks of an ample Banach bundle are finite-dimensional or separable. A connection is established between the property of the stalks of a bundle to be finite-dimensional or separable with the analogous property of the stalks of the ample hull of the bundle. A new criterion is obtained for existence of the dual bundle. 相似文献
2.
Shiyu CAO 《数学年刊B辑(英文版)》2023,44(1):1-16
In this paper, the author discusses the deformations of compact complex manifolds with ample canonical bundles. It is known that a complex manifold has unobstructed deformations when it has a trivial canonical bundle or an ample anti-canonical bundle.When the complex manifold has an ample canonical bundle, the author can prove that this manifold also has unobstructed deformations under an extra condition. 相似文献
3.
We study a Seshadri constant at a general point on a rational surface whose anticanonical linear system contains a pencil. First, we describe a Seshadri constant of an ample line bundle on such a rational surface explicitly by the numerical data of the ample line bundle. Second, we classify log del Pezzo surfaces which are special in terms of the Seshadri constants of the anticanonical divisors when the anticanonical degree is between 4 and 9. 相似文献
4.
Sai-Kee Yeung 《Compositio Mathematica》2000,123(2):209-223
Let L be an ample line bundle on a Kähler manifolds of nonpositive sectional curvature with K as the canonical line bundle. We give an estimate of m such that K+mL is very ample in terms of the injectivity radius. This implies that m can be chosen arbitrarily small once we go deep enough into a tower of covering of the manifold. The same argument gives an effective Kodaira Embedding Theorem for compact Kähler manifolds in terms of sectional curvature and the injectivity radius. In case of locally Hermitian symmetric space of noncompact type or if the sectional curvature is strictly negative, we prove that K itself is very ample on a large covering of the manifold. 相似文献
5.
Krishna Hanumanthu 《Journal of Algebra》2010,323(2):526-539
We give examples of Koszul rings that arise naturally in algebraic geometry. In the first part, we prove a general result on Koszul property associated to an ample line bundle on a projective variety. Specifically, we show how Koszul property of multiples of a base point free ample line bundle depends on its Castelnuovo–Mumford regularity. In the second part, we give examples of Koszul rings that come from adjoint line bundles on minimal irregular surfaces of general type. 相似文献
6.
Indranil Biswas 《Bulletin des Sciences Mathématiques》2005,129(6):539-543
Let X be a smooth projective curve defined over an algebraically closed field of positive characteristic. We give a necessary and sufficient condition for a vector bundle over X to be ample. This generalizes a criterion given by Lange in [Math. Ann. 238 (1978) 193-202] for a rank two vector bundle over X to be ample. 相似文献
7.
We study the k-very ampleness of the adjoint bundle K S+det E associated to a k-very ample vector bundle E on an algebraic surface S. We extend the results of Beltrametti and Sommese to the vector bundle case and give the classification of the pairs (S, E) such that the preservation of k-very ampleness fails. 相似文献
8.
S Subramanian 《Proceedings Mathematical Sciences》1989,99(3):197-208
We construct a line bundle on a complex projective manifold (a general ruled variety over a curve) which is not ample, but
whose restriction to every proper subvariety is ample. This example is of interest in connection with ampleness questions
of vector bundles on varieties of dimension greater than one. The method of construction shows that a stable bundle of positive
degree on a curve is ample. The example can be used to show that there is no restriction theorem for Bogomolov stability. 相似文献
9.
Let L be an ample line bundle on a K3 surface. We give a sharp bound on n for which nL is k-jet ample.Received: 27 December 2002 相似文献
10.
Hiroyuki Terakawa 《Mathematische Nachrichten》1998,195(1):237-250
We give a numerical criterion for an ample line bundle on an abelian surface to be it-very ample for a nonnegative integer k. This result implies the equivalence of k-very ampleness and k-spannedness. We also give a complete classification of polarized abelian surfaces with k - very ample polarizations. Our results extend those of Bauer and Szemberg [BaSzl] and Ramanan [Ra]. 相似文献
11.
Jian Xiao 《中国科学 数学(英文版)》2022,65(1):51-62
Let X be a smooth projective variety of dimension n,and let E be an ample vector bundle over X.We show that any Schur class of E,lying in the cohomology group of bidegree(n-1,n-1),has a representative which is strictly positive in the sense of smooth forms.This conforms the prediction of Griffiths conjecture on the positive polynomials of Chern classes/forms of an ample vector bundle on the form level,and thus strengthens the celebrated positivity results of Fulton and Lazarsfeld(1983)for certain degrees. 相似文献
12.
Insong Choe 《manuscripta mathematica》2001,105(4):501-506
A compact complex manifold X obtained by taking quotient of a bounded symmetric domain has an ample canonical line bundle. We prove that the dimension
of very ample pluricanonical subsystem is strictly bigger than 2n, where n is the dimension of X.
Received: 23 June 2000 / Revised version: 30 March 2001 相似文献
13.
Daisuke Matsushita 《Mathematische Annalen》2014,358(3-4):565-572
We prove that the pull back of an ample line bundle by an almost holomorphic Lagrangian fibration is nef. As an application, we show birational semi rigidity of Lagrangian fibrations. 相似文献
14.
Andreas Leopold Knutsen 《manuscripta mathematica》2001,104(2):211-237
We give necessary and sufficient conditions for a big and nef line bundle L of any degree on a K3 surface or on an Enriques surface S to be k-very ample and k-spanned. Furthermore, we give necessary and sufficient conditions for a spanned and big line bundle on a K3 surface S to be birationally k-very ample and birationally k-spanned (our definition), and relate these concepts to the Clifford index and gonality of smooth curves in |L| and the existence of a particular type of rank 2 bundles on S.
Received: 28 March 2000 / Revised version: 20 October 2000 相似文献
15.
Sola Conde Luis Eduardo; Wisniewski Jaroslaw A. 《Proceedings London Mathematical Society》2004,89(2):273-290
A line bundle over a complex projective variety is called bigand 1-ample if a large multiple of it is generated by globalsections and a morphism induced by the evaluation of the spanningsections is generically finite and has at most 1-dimensionalfibers. A vector bundle is called big and 1-ample if the relativehyperplane line bundle over its projectivisation is big and1-ample. The main theorem of the present paper asserts that any complexprojective manifold of dimension 4 or more, whose tangent bundleis big and 1-ample, is equal either to a projective space orto a smooth quadric. Since big and 1-ample bundles are almostample, the present result is yet another extension of the celebratedMori paper Projective manifolds with ample tangent bundles(Ann. of Math. 110 (1979) 593606). The proof of the theorem applies results about contractionsof complex symplectic manifolds and of manifolds whose tangentbundles are numerically effective. In the appendix we re-provethese results. 2000 Mathematics Subject Classification 14E30,14J40, 14J45, 14J50. 相似文献
16.
Sai-Kee Yeung 《Transactions of the American Mathematical Society》2001,353(4):1387-1401
We study the problem about the very ampleness of the canonical line bundle of compact locally Hermitian symmetric manifolds of non-compact type. In particular, we show that any sufficiently large unramified covering of such manifolds has very ample canonical line bundle, and give estimates on the size of the covering manifold, which is itself a locally Hermitian symmetric manifold, in terms of geometric data such as injectivity radius or degree of coverings.
17.
MANETTI Marco 《中国科学 数学(英文版)》2011,(8)
We determine the base space of the Kuranishi family of some complete intersections in the product of an abelian variety and a projective space.As a consequence,we obtain new examples of obstructed irregular surfaces with ample canonical bundle and maximal Albanese dimension. 相似文献
18.
Milena Hering 《Journal of Algebra》2010,323(4):1012-1017
We give a criterion for the section ring of an ample line bundle to be Koszul in terms of multigraded regularity. We discuss applications to adjoint bundles on toric varieties as well as to polytopal semigroup rings. 相似文献
19.
Edoardo Ballico 《Annali di Matematica Pura ed Applicata》1981,129(1):69-80
Summary
In this paper we prove that the restriction of the tangent bundle of a nonsingular quadrix Q to a subvariety X is ample if and only if X does not contain a straight line. This implies that the normal bundle of a locally complete intersection, reduced and irreducible curve C is ample if and only if C is not a straight line. The result gives information also for higher dimensional subvarieties of Q.The author is member of G.N.S.A.G.A. of C.N.R. 相似文献
20.
Jean-Pierre Demailly 《Inventiones Mathematicae》1996,124(1-3):243-261
Let be an ample line bundle
on a non singular projective
-fold .
It is first shown that
is very ample for
.
The proof develops an original idea of Y.T. Siu
and is based on a combination of the Riemann-Roch
theorem together with an
improved Noetherian induction technique for the Nadel multiplier ideal
sheaves. In the second part, an effective version of the big Matsusaka
theorem is obtained, refining an earlier version of Y.T. Siu: there is
an explicit polynomial bound
of
degree in the arguments,
such that is very ample for
. The refinement is obtained through
a new sharp upper bound for the dualizing sheaves of algebraic
varieties embedded in projective space.
Oblatum 30-I-1995 & 18-V-1995 相似文献