Displaying similar documents to “On the dimension of the adjoint linear system for threefolds”

Threefolds with nef anticanonical bundles.

Thomas Peternell, Fernando Serrano (1998)

Collectanea Mathematica

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In this paper we study the global structure of projective threefolds X whose anticanonical bundle -KX is nef.

Seshadri positive submanifolds of polarized manifolds

Lucian Bădescu, Mauro Beltrametti (2013)

Open Mathematics

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Let Y be a submanifold of dimension y of a polarized complex manifold (X, A) of dimension k ≥ 2, with 1 ≤ y ≤ k−1. We define and study two positivity conditions on Y in (X, A), called Seshadri A-bigness and (a stronger one) Seshadri A-ampleness. In this way we get a natural generalization of the theory initiated by Paoletti in [Paoletti R., Seshadri positive curves in a smooth projective 3-fold, Atti Accad. Naz. Lincei Cl. Sci. Fis. Mat. Natur. Rend. Lincei (9) Mat. Appl., 1996, 6(4),...

Subsheaves of the cotangent bundle

Paolo Cascini (2006)

Open Mathematics

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For any smooth projective variety, we study a birational invariant, defined by Campana which depends on the Kodaira dimension of the subsheaves of the cotangent bundle of the variety and its exterior powers. We provide new bounds for a related invariant in any dimension and in particular we show that it is equal to the Kodaira dimension of the variety, in dimension up to 4, if this is not negative.

Contractions of smooth varieties. II. Computations and applications

Marco Andreatta, Jarosław A. Wiśniewski (1998)

Bollettino dell'Unione Matematica Italiana

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Una contrazione su una varietà proiettiva liscia X è data da una mappa φ : X → Z propria, suriettiva e a fibre connesse in una varietà irriducibile normale Z . La contrazione si dice di Fano-Mori se inoltre - K X è φ -ampio. Nel lavoro, naturale seguito e completamento delle ricerche introdotte in [A-W3], si studiano diversi aspetti delle contrazioni di Fano-Mori attraverso esempi (capitolo 1) e teoremi di struttura (capitoli 3 e 4). Si discutono anche alcune applicazioni allo studio di morfismi birazionali...

On the structure of linked 3-folds.

Aldo Biancofiore, Maria Lucia Fania (2001)

Revista Matemática Complutense

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The structure of 3-folds in P which are generally linked via a complete intersection (f,f,f) to 3-folds in P of degree d ≤ 5 is determined. We also give three new examples of smooth 3-folds in P of degree 11 and genus 9. These examples are obtained via liaison. The first two are 3-folds linked via a complete intersection (2,3,3) to 3-folds in P of degree 7: (i) the hyperquadric fibration over P and (ii) the scroll over P. The third example is Pfaffian linked to a 3-dimensional quadric...

Effective nonvanishing, effective global generation

Mark Andrea A. De Cataldo (1998)

Annales de l'institut Fourier

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We prove a multiple-points higher-jets nonvanishing theorem by the use of local Seshadri constants. Applications are given to effectivity problems such as constructing rational and birational maps into Grassmannians, and the global generation of vector bundles.