共查询到20条相似文献,搜索用时 15 毫秒
1.
C. Soulé 《Advances in Mathematics》2005,198(1):107-127
Atiyah and Hirzebruch gave examples of even degree torsion classes in the singular cohomology of a smooth complex projective manifold, which are not Poincaré dual to an algebraic cycle. We notice that the order of these classes must be small compared to the dimension of the manifold. However, building upon a construction of Kollár, one can provide such examples with arbitrary high prime order, the dimension being fixed. This method also provides examples of torsion algebraic cycles, which are non trivial in the Griffiths group, and lie in a arbitrary high level of the H. Saito filtration on Chow groups. 相似文献
2.
On the one hand, for a general Calabi–Yau complete intersection X, we establish a decomposition, up to rational equivalence, of the small diagonal in X×X×X, from which we deduce that any decomposable 0-cycle of degree 0 is in fact rationally equivalent to 0, up to torsion. On the other hand, we find a similar decomposition of the smallest diagonal in a higher power of a hypersurface, which provides us an analogous result on the multiplicative structure of its Chow ring. 相似文献
3.
For a smooth irreducible complete algebraic curveC the “gaps” are the integersn such that every linear series of degreen has at least a base point. The Lüroth semigroup SC of a curveC is the subsemigroup ofN whose elements are not gaps. In this paper we deal with irreducible smooth curves of type (a, b) on a smooth quadricQ. The main result is an algorithm by which we can say if some integer λ∈N is a gap or is in SC. In the general case there are integers λ which are undecidable. For curves such as complete intersection, arithmetically
Cohen-Macaulay or Buchsbaum, we are able to describe explicitly “intervals” of gaps and “intervals” of integers which belong
to SC. For particular cases we can completely determine SC, by giving just the type of the curve (in particular the degree and the genus).
Work done with financial support of M.U.R.S.T. while the authors were members of G.N.S.A.G.A. of C.N.R. 相似文献
4.
The purpose of this paper is to construct non-trivial elements in the Abel–Jacobi kernels in any codimension by specializing correspondences with non-trivial Hodge-theoretical invariants at points with different transcendence degrees over a subfield in C. 相似文献
5.
Reza Akhtar 《Journal of Pure and Applied Algebra》2005,196(1):21-37
Let A be an abelian variety over a field k. We consider
CH0(A) as a ring under Pontryagin product and relate powers of the ideal
I⊆CH0(A) of degree zero elements to powers of the algebraic equivalence relation. We also consider a filtration
F0⊇F1⊇… on the Chow groups of varieties of the form
T×kA (defined using Pontryagin products on
A×kA considered as an A-scheme via projection on the first factor) and prove that
Fr coincides with the r-fold product
(F1)*r as adequate equivalence relations on the category of all such varieties. 相似文献
6.
Eric Katz 《Expositiones Mathematicae》2009,27(1):1-36
We give an introduction to Tropical Geometry and prove some results in tropical intersection theory. The first part of this paper is an introduction to tropical geometry aimed at researchers in Algebraic Geometry from the point of view of degenerations of varieties using projective not-necessarily-normal toric varieties. The second part is a foundational account of tropical intersection theory with proofs of some new theorems relating it to classical intersection theory. 相似文献
7.
Boris Khesin 《Topology》2004,43(5):1231-1246
We prove an analogue of the de Rham theorem for polar homology; that the polar homology HPq(X) of a smooth projective variety X is isomorphic to its Hn,n−q Dolbeault cohomology group. This analogue can be regarded as a geometric complexification where arbitrary (sub)manifolds are replaced by complex (sub)manifolds and de Rham's operator d is replaced by Dolbeault's . 相似文献
8.
9.
Yoshiaki Fukuma 《Journal of Pure and Applied Algebra》2007,209(1):99-117
Let (X,L) be a polarized manifold of dimension n. In this paper, for any integer i with 0≤i≤n we introduce the notion of the ith sectional invariant of (X,L). We define the ith sectional Euler number ei(X,L), the ith sectional Betti number bi(X,L), and the ith sectional Hodge number of type (j,i−j) of (X,L) and we will study some properties of these. 相似文献
10.
Partially supported by Science Project Geometry of Algebraic Varieties, n. 0-198-SC1, and by fundings from M.U.R.S.T. and G.N.S.A.G.A. (C.N.R.), Italy 相似文献
11.
Tails of correlation mixtures of elliptical copulas 总被引:1,自引:0,他引:1
Correlation mixtures of elliptical copulas arise when the correlation parameter is driven itself by a latent random process. For such copulas, both penultimate and asymptotic tail dependence are much larger than for ordinary elliptical copulas with the same unconditional correlation. Furthermore, for Gaussian and Student t-copulas, tail dependence at sub-asymptotic levels is generally larger than in the limit, which can have serious consequences for estimation and evaluation of extreme risk. Finally, although correlation mixtures of Gaussian copulas inherit the property of asymptotic independence, at the same time they fall in the newly defined category of near asymptotic dependence. The consequences of these findings for modeling are assessed by means of a simulation study and a case study involving financial time series. 相似文献
12.
The quantification of diversification benefits due to risk aggregation plays a prominent role in the (regulatory) capital management of large firms within the financial industry. However, the complexity of today’s risk landscape makes a quantifiable reduction of risk concentration a challenging task. In the present paper we discuss some of the issues that may arise. The theory of second-order regular variation and second-order subexponentiality provides the ideal methodological framework to derive second-order approximations for the risk concentration and the diversification benefit. 相似文献
13.
Yoshiaki Fukuma 《Journal of Pure and Applied Algebra》2007,211(3):609-621
Let (X,L) be a polarized manifold of dimension n defined over the field of complex numbers. In this paper, we treat the case where n=3 and 4. First we study the case of n=3 and we give an explicit lower bound for h0(KX+L) if κ(X)≥0. Moreover, we show the following: if κ(KX+L)≥0, then h0(KX+L)>0 unless κ(X)=−∞ and h1(OX)=0. This gives us a partial answer of Effective Non-vanishing Conjecture for polarized 3-folds. Next for n=4 we investigate the dimension of H0(KX+mL) for m≥2. If n=4 and κ(X)≥0, then a lower bound for h0(KX+mL) is obtained. We also consider a conjecture of Beltrametti-Sommese for 4-folds and we can prove that this conjecture is true unless κ(X)=−∞ and h1(OX)=0. Furthermore we prove the following: if (X,L) is a polarized 4-fold with κ(X)≥0 and h1(OX)>0, then h0(KX+L)>0. 相似文献
14.
Mustapha Lahyane 《Journal of Pure and Applied Algebra》2010,214(7):1217-1240
We give a numerical criterion for ensuring the finite generation of the effective monoid of the surfaces obtained by a blowing-up of the projective plane at the supports of zero dimensional subschemes assuming that these are contained in a degenerate cubic. Furthermore, this criterion also ensures the regularity of any numerically effective divisor on these surfaces. Thus the dimension of any complete linear system is computed. On the other hand, in particular and among these surfaces, we obtain ringed rational surfaces with very large Picard numbers and with only finitely many integral curves of strictly negative self-intersection. These negative integral curves except two (−1)-curves are all contained in the support of an anticanonical divisor. Thus almost all the geometry of such surfaces is concentrated in the anticanonical class. 相似文献
15.
Marco Franciosi 《Advances in Mathematics》2004,186(2):317-333
Let C be a numerically connected curve lying on a smooth algebraic surface. We show that if is an ample invertible sheaf satisfying some technical numerical hypotheses then is normally generated. As a corollary we show that the sheaf ωC⊗2 on a numerically connected curve C of arithmetic genus pa?3 is normally generated if ωC is ample and does not exist a subcurve B⊂C such that pa(B)=1=B(C−B). 相似文献
16.
Margarida Brito Ana Cristina Moreira Freitas 《Insurance: Mathematics and Economics》2008,43(2):203-208
We establish an Edgeworth expansion for an estimator of the adjustment coefficient R, directly related to the geometric-type estimator for general exponential tail coefficients, proposed in [Brito, M., Freitas, A.C.M., 2003. Limiting behaviour of a geometric-type estimator for tail indices. Insurance Math. Econom. 33, 211-226].Using the first term of the expansion, we construct improved confidence bounds for R. The accuracy of the approximation is illustrated using an example from insurance (cf. [Schultze, J., Steinebach, J., 1996. On least squares estimates of an exponential tail coefficient. Statist. Dec. 14, 353-372]). 相似文献
17.
Catalina Bolancé 《Insurance: Mathematics and Economics》2008,43(2):209-213
This paper questions the equidistribution assumption for the random effects in a frequency risk model. Two models are presented, which use parametric and nonparametric links between the variance of the random effect and frequency risk. They are estimated on a Spanish automobile insurance portfolio, for which a decreasing link is obtained. Conclusions are drawn for credibility and bonus-malus coefficients. 相似文献
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19.
Chad Schoen 《Mathematische Zeitschrift》2006,252(1):11-17
An example is given in which specialization is not injective.
Partial support by the NSF (DMS-0200012) gratefully acknowledged. 相似文献
20.
Let A be a direct limit of a direct system of Cohen–Macaulay rings. In this paper, we describe the Cohen–Macaulay property of A. Our results indicate that A is not necessarily Cohen–Macaulay. We show A is Cohen–Macaulay under various assumptions. As an application, we study Cohen–Macaulayness of non-affine normal semigroup rings. 相似文献