首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
《Mathematische Nachrichten》2017,290(8-9):1281-1302
By Jahnke–Peternell–Radloff and Takeuchi, almost Fano threefolds with del Pezzo fibrations were classified. Among them, there exist 10 classes such that the existence of members of these was not proved. In this paper, we construct such examples belonging to each of 10 classes.  相似文献   

2.
We study certain moduli spaces of stable vector bundles of rank 2 on cubic and quartic threefolds. In many cases under consideration, it turns out that the moduli space is complete and irreducible and a general member has vanishing intermediate cohomology. In one case, all except one component of the moduli space has such vector bundles.  相似文献   

3.
It is well known that the Sylvester matrix equation AX + XB = C has a unique solution X if and only if 0 ∉ spec(A) + spec(B). The main result of the present article are explicit formulas for the determinant of X in the case that C is one-dimensional. For diagonal matrices A, B, we reobtain a classical result by Cauchy as a special case.The formulas we obtain are a cornerstone in the asymptotic classification of multiple pole solutions to integrable systems like the sine-Gordon equation and the Toda lattice. We will provide a concise introduction to the background from soliton theory, an operator theoretic approach originating from work of Marchenko and Carl, and discuss examples for the application of the main results.  相似文献   

4.
5.
The change of zero locus of a global holomorphic 2-form on a threefold under birational transformations is investigated. It is proved that existence of 2-forms with certain conditions on their zero loci on a threefold of nonnegative Kodaira dimension limits types of terminal singularities appearing on its minimal models. As a result of the restriction on the types of terminal singularities and Reid's Riemann-Roch formula, a universal bound N is found such that the linear system NK defines a birational map from a threefold of general type admitting those 2-forms, where K is the canonical bundle of the threefold. Received March 10, 2000 / Published online October 11, 2000  相似文献   

6.
7.
We introduce the polynomial Hamiltonian and we prove that the associated Hamiltonian system is Liouville-C-integrable, but fails to be real-analytically integrable in any neighbourhood of an equilibrium point. The proof only uses power series expansions, and is elementary.  相似文献   

8.
In this paper we classify pairs (X,ℰ) with ℰ ample vector bundle of rank r on a smooth variety X of dimension n= 2r−1 such that K X + det ℰ=? x . Received: 7 April 2000  相似文献   

9.
In this paper, we investigate whether the 124 nonsingular toric Fano 4-folds admit totally nondegenerate embeddings from abelian surfaces or not. In consequence, we determine the possibilities of these embeddings, except for the remaining 18 nonsingular toric Fano 4-folds. Received: 12 July 2002  相似文献   

10.
A classification of smooth complex projective threefoldsX polarized by two very ample line bundlesL andM is given, under the assumption that two general elements of |L| and |M| intersect transversally along a smooth hyperelliptic curve.
Sunto Si fornisce una classificazione delle terne (X,L,M), doveX è una varietà algebrica proiettiva complessa liscia di dimensione 3 edL,M sono due fibrati lineari molto ampi suX, tali che l’intersezione di due elementi generici di |L| ed |M| sia una curva iperellittica.
  相似文献   

11.
In this paper, we consider the existence problem of rank one and two stable Ulrich bundles on imprimitive Fano 3-folds obtained by blowing-up one of P3, Q (smooth quadric in P4), V3 (smooth cubic in P4) or V4 (complete intersection of two quadrics in P5) along a smooth irreducible curve. We prove that the only class which admits Ulrich line bundles is the one obtained by blowing up a genus 3, degree 6 curve in P3. Also, we prove that there exist stable rank two Ulrich bundles with c1=3H on a generic member of this deformation class.  相似文献   

12.
13.
The purpose of this paper is two-fold. Firstly, we will give some parabolic-like conditions which improve the well-known angle conditions and allow further computations of the critical groups both at degenerate critical points and at infinity. As an application, we then consider the second-order Hamiltonian systems
  相似文献   

14.
This paper deals with polarized pairs , where is a nonsingular projective threefold and is a very ample line bundle on it, such that for one smooth member  | |, one has (Â)=2. A large class of pairs whose adjoint line bundle is nef and big was indirectedly studied by Beltrametti and co-workers. We add some more information, both in this general case and also when the adjoint line bundle fails to be nef and big.  相似文献   

15.
16.
The aim of this work is to contribute to the classification of projective varieties according to their representation type, providing examples of n  -dimensional varieties of wild representation type, for arbitrary n?2n?2. More precisely, we prove that all Fano blow-ups of PnPn at a finite number of points are of wild representation type exhibiting families of dimension of order r2r2 of simple (hence, indecomposable) ACM rank r   vector bundles for any r?nr?n. In the two dimensional case, the vector bundles that we construct are moreover Ulrich bundles and μ-stable with respect to certain ample divisor.  相似文献   

17.
In this paper, we improve and extend the works of Liu and Davids [Dual synchronization of chaos, Phys. Rev. E 61 (2000) 2176–2179] which only introduce the dual synchronization of 1-D discrete chaotic systems. The dual synchronization of two different 3-D continuous chaotic systems, Lorenz systems and Rössler systems, is discussed. And a sufficient condition of dual synchronization about the two different chaotic systems is obtained. Theories and numerical simulations show the possibility of dual synchronization and the effectiveness of the method.  相似文献   

18.
19.
We prove that every globally F-regular variety is log Fano. In other words, if a prime characteristic variety X is globally F-regular, then it admits an effective Q-divisor Δ such that −KX−Δ is ample and (X,Δ) has controlled (Kawamata log terminal, in fact globally F-regular) singularities. A weak form of this result can be viewed as a prime characteristic analog of de Fernex and Hacon's new point of view on Kawamata log terminal singularities in the non-Q-Gorenstein case. We also prove a converse statement in characteristic zero: every log Fano variety has globally F-regular type. Our techniques apply also to F-split varieties, which we show to satisfy a “log Calabi-Yau” condition. We also prove a Kawamata-Viehweg vanishing theorem for globally F-regular pairs.  相似文献   

20.
We construct examples of supersingular Calabi-Yau threefolds in characteristic 2 making use of the method by Schoen. Unirational Calabi-Yau threefolds of five different topological types are obtained. There are two examples with the third Betti number zero among them, and they are counted as other examples of non-liftable Calabi-Yau threefolds in characteristic 2 after the one given by Schröer.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号