共查询到20条相似文献,搜索用时 15 毫秒
1.
Lucio Guerra 《manuscripta mathematica》1999,98(1):1-8
We provide a general estimate for the number of irreducible components of a Chow variety, the variety that parametrizes algebraic
cycles of given dimension and degree contained in a projective variety. The result is then applied to obtain an upper bound
for the finite number of surfaces of general type that are images of a fixed surface.
Received: 29 January 1998 / Revised version: 24 June 1998 相似文献
2.
Christopher D. Hacon 《Mathematische Zeitschrift》2000,235(4):717-726
The purpose of this paper is to give two applications of Fourier transforms and generic vanishing theorems:
– we give a cohomological characterization of principal polarizations
– we prove that if X an abelian variety and a polarization of type (1, ...,1,2), then a general pair is log canonical.
Received 14 May, 1999 / Published online September 14, 2000 相似文献
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Jörg Jahnel 《manuscripta mathematica》1998,96(4):421-442
Let X be an arithmetic variety and L be an element of the Néron-Severi group of its generic fiber X
K
. Then there are only finitely many line bundles on X, generically belonging to L, such that the degrees of on the irreducible components of the special fibers of X and the height of are bounded. The concept of a height used here is recalled. Several elementary properties of this height are proven.
Received: 9 March 1996 相似文献
7.
We show that the set of the homogeneous saturated ideals with given initial ideal in a fixed term-ordering is locally closed
in the Hilbert scheme, and that it is affine if the initial ideal is saturated. Then, Hilbert schemes can be stratified using
these subschemes. We investigate the behaviour of this stratification with respect to some properties of the closed points.
As application, we describe the singular locus of the component of Hilb4
z
+1
ℙ4 containing the ACM curves of degree 4.
Received: 30 November 1998 / Revised version: 16 September 1999 相似文献
8.
Stephan Endraß 《manuscripta mathematica》1999,99(3):341-358
For a double solid V→ℙ3> branched over a surface B⊂ℙ3(ℂ) with only ordinary nodes as singularities, we give a set of generators of the divisor class group in terms of contact surfaces of B with only superisolated singularities in the nodes of B. As an application we give a condition when H
* (˜V , ℤ) has no 2-torsion. All possible cases are listed if B is a quartic. Furthermore we give a new lower bound for the dimension of the code of B.
Received: 16 November 1998 相似文献
9.
Daisuke Matsushita 《Mathematische Annalen》2001,321(4):755-773
We classify singular fibres over general points of the discriminant locus of projective Lagrangian fibrations over 4-dimensional
holomorphic symplectic manifolds. The singular fibre F is the following either one: F is isomorphic to the product of an elliptic curve and a Kodaira singular fibre up to finite unramified covering or F is a normal crossing variety consisting of several copies of a minimal elliptic ruled surface of which the dual graph is
Dynkin diagram of type or . Moreover, we show all types of the above singular fibres actually occur.
Received: 10 March 2000 / Revised version: 29 September 2000 / Published online: 24 September 2001 相似文献
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R.V. Gurjar 《Mathematische Annalen》1997,309(2):341-357
12.
Francesco Mordasini 《manuscripta mathematica》1999,99(4):443-464
Let X be a quasi-projective scheme and ℱ a coherent sheaf of modules over X such that its non-Cohen–Macaulay locus is at most one dimensional. We use and extend the techniques of Brodmann to construct
proper birational morphisms of quasi-projective schemes f:Y→X and Cohen–Macaulay coherent sheaves of modules over Y that are isomorphic to the pull-back of ℱ away from the exceptional locus of f. Certain blow-ups of X at locally complete intersections subschemes which contain non-reduced scheme structures on the non-Cohen–Macaulay locus
of ℱ are the main part of the construction.
Received: 19 February 1998 / Revised version: 28 December 1998 相似文献
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Summary. Let be a complex polynomial of
degree with and Cauchy radius 1 about the
origin. We discuss the order of magnitude
of the minimal number such that
Previous estimates of are improved to . Some other related properties of these polynomials
are also exhibited.
Received March 3, 1993 相似文献
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Kyo Nishiyama 《Mathematische Annalen》2000,318(4):777-793
Let G be a reductive Lie group. Take a maximal compact subgroup K of G and denote their Lie algebras by and respectively. We get a Cartan decomposition . Let be the complexification of , and the complexified decomposition. The adjoint action restricted to K preserves the space , hence acts on , where denotes the complexification of K. In this paper, we consider a series of small nilpotent -orbits in which are obtained from the dual pair ([R. Howe, Transcending classical invariant theory. J. Amer. Math. Soc. 2 (1989), no. 3, 535–552]). We explain astonishing
simple structures of these nilpotent orbits using generalized null cones. For example, these orbits have a linear ordering
with respect to the closure relation, and acts on them in multiplicity-free manner. We clarify the -module structure of the regular function ring of the closure of these nilpotent orbits in detail, and prove the normality.
All these results naturally comes from the analysis on the null cone in a matrix spaceW , and the double fibration of nilpotent orbits in and . The classical invariant theory assures that the regular functions on our nilpotent orbits are coming from harmonic polynomials
on W with repspect to or . We also provide many interesting examples of multiplicity-free actions on conic algebraic varieties.
Received November 1, 1999 / Published online October 30, 2000 相似文献
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Given a rational surface singularity (S,P), we relate S-isomorphism classes of normal blowing-ups of S and properties of semifactorization for complete ideals in . This relation is understood via the natural cell decomposition of the characteristic cone P˜(X/S), where X is a desingularization of S. Received: 1 April 1998 / Revised version: 2 July 1998 相似文献
20.
Keita Tono 《manuscripta mathematica》1998,97(1):75-59
Let
and be two non-constant weighted homogeneous polynomials. Suppose that f and g are not powers of polynomials. Let p and q be two positive integers. In this paper, we calculate the fundamental group of the complement of the affine hypersurface
in . In particular, we prove that the fundamental group is determined by p and q.
Received: 29 January 1998 相似文献