Projective manifolds whose tangent bundles are numerically effective.
Projective Manifolds with the Same Homology as ...
Projective threefolds containing a smooth rational surface with ample normal bundle.
Quartic threefolds containing two skew double lines
Quasi-Gorenstein Fano 3-folds with isolated non-rational loci
Quasi-lines and their degenerations
In this paper we study the structure of manifolds that contain a quasi-line and give some evidence towards the fact that the irreducible components of degenerations of the quasi-line should determine the Mori cone. We show that the minimality with respect to a quasi-line yields strong restrictions on fibre space structures of the manifold.
Rank 4 vector bundles on the quintic threefold
By the results of the author and Chiantini in [3], on a general quintic threefold X⊂P 4 the minimum integer p for which there exists a positive dimensional family of irreducible rank p vector bundles on X without intermediate cohomology is at least three. In this paper we show that p≤4, by constructing series of positive dimensional families of rank 4 vector bundles on X without intermediate cohomology. The general member of such family is an indecomposable bundle from the extension class Ext 1...
Rank-two vector bundles on general quartic hypersurfaces in P4.
In this paper all non-splitting rank-two vector bundles E without intermediate cohomology on a general quartic hypersurface X in P4 are classified. In particular, the existence of some curves on a general quartic hypersurface is proved.
Rational curves on hypersurfaces
Real algebraic threefolds I. Terminal singularities.
The aim of this series of papers is to develop the theory of minimal models for real algebraic threefolds. The ultimate aim is to understand the topology of the set of real points of real algebraic threefolds. We pay special attention to 3–folds which are birational to projective space and, more generally, to 3–folds of Kodaira dimension minus infinity.present work contains the beginning steps of this program. First we classify 3–dimensional terminal singularities over any field of characteristic...
Real singular Del Pezzo surfaces and 3-folds fibred by rational curves, II
Let be a real smooth projective 3-fold fibred by rational curves such that is orientable. J. Kollár proved that a connected component of is essentially either Seifert fibred or a connected sum of lens spaces. Answering three questions of Kollár, we give sharp estimates on the number and the multiplicities of the Seifert fibres (resp. the number and the torsions of the lens spaces) when is a geometrically rational surface. When is Seifert fibred over a base orbifold , our result generalizes...
Segre-Veronese embeddings of P1 x P1 x P1 and their secant varieties.
In this paper we compute the dimension of all the sth higher secant varieties of the Segre-Veronese embeddings Yd of the product P1 × P1 × P1 in the projective space PN via divisors of multidegree d = (a,b,c) (N = (a+1)(b+1)(c+1) - 1). We find that Yd has no deficient higher secant varieties, unless d = (2,2,2) and s = 7, or d = (2h,1,1) and s = 2h + 1, with defect 1 in both cases.
Semilinear equations, the function, and generalized Gauduchon metrics
In this paper, we generalize the Gauduchon metrics on a compact complex manifold and define the functions on the space of its hermitian metrics.
Seshadri positive curves in a smooth projective -fold
A notion of positivity, called Seshadri ampleness, is introduced for a smooth curve in a polarized smooth projective -fold , whose motivation stems from some recent results concerning the gonality of space curves and the behaviour of stable bundles on under restriction to . This condition is stronger than the normality of the normal bundle and more general than being defined by a regular section of an ample rank- vector bundle. We then explore some of the properties of Seshadri-ample curves....
Simple models of quasihomogeneous projective 3-folds.
Simultaneous Resolution of Threefold Double Points.
Smooth double subvarieties on singular varieties, III
Let k be an algebraically closed field, char k = 0. Let C be an irreducible nonsingular curve such that rC = S ∩ F, r ∈ ℕ, where S and F are two surfaces and all the singularities of F are of the form , s ∈ ℕ. We prove that C can never pass through such kind of singularities of a surface, unless r = 3a, a ∈ ℕ. We study multiplicity-r structures on varieties r ∈ ℕ. Let Z be a reduced irreducible nonsingular (n-1)-dimensional variety such that rZ = X ∩ F, where X is a normal n-fold, F is a (N-1)-fold...
Some abelian threefolds with nontrivial Griffiths group
Some birational maps of Fano 3-folds
Some density results for curves with non-simple jacobians.