1,721,013 research outputs found
On 4-generated bundles and directly linked subcanonical curves
No full textGiven a subcanonical curve r in P3, we study conditions under which r is
directly linked to another subcanonical curve r’. We show that this happens when the rank 2 bundle E associated to r admits a surjection U: @“O+( -a,) + E, a, E Z. We give an explicit construction of such a r starting with surjection u and we prove that the numbers ai appearing in ZA are uniquely determined by E: this implies that we have at most 3 possibilities for the numerical characters of a subcanonical curve directly linked to
On some properties of rank 2 bundles on algebraic surfaces
No full textThis paper is concerned on the Moduli spaces M= M(X,c1 ,c2 ,H) of rank 2 vector bundles on a smooth projective surface X, with Chern classes c1 Pic(X), c2 in Z, stable with respect to a fixed polarization H. We prove that when c2 is large, there are bundles in M with good cohomology. Then we show that when X has Kodaira dimension >0, then M contains at least one irregular component
On the identifiability of binary Segre products
No full textWe prove that a product of m > 5 copies of P^1, embedded in the projective space P^r by the standard Segre embedding, is k-identifiable (i.e. a general point of the secant variety S^k(X) is contained in only one (k + 1)-secant k-space), for all k such that k + 1 ≤ 2m−1/m. The research that led to the present paper was partially supported by a grant of the group GNSAGA of INdAM
On some moduli spaces of rank 2 bundles over K3 surfaces
No full textThe aim of this note is to give some remark on the structure of components in the Moduli space of rank 2 bundles, with given Chern classes, over K3 surfaces
The classification of (1,k)-defective surfaces
No full textWe give the full classification of surfaces X such that the family of lines contained in a (k+1)-secant P^k to X has dimension smaller than the expected
Nodal curves and postulation of generic fat points on P^2
No full textWe study the postulation of a general union Z of fat points of P2, when
most of the connected components of Z have multiplicity 2. This problem is related to the existence of 'good' families of curves on P2 with prescribed singularities, most of them being nodes, and to the cohomology of suitable line bundles on blowing ups of th
Corrigendum to: Focal loci of families and the genus of curves on surfaces
No full textWe correct a mistake in the statement of Theorem 1.3 in [Proc. Amer. Math. Soc. 127 (1999), no. 12, 3451-3459]
Sulla proiezione piana generica di un ramo di curva
No full textSi studiano condizioni sotto le quali un ramo di curva spaziale sia equiproiettabile, cioe abbia sequenza delle molteplicita uguale alla sequenza delle molteplicità della sua proiezione generica
The cohomology of rank 2 bundles on P^2
No full textWe classify all sequences of integers that can be, up to a shift, the cohomology sequence {h 1 (E(n))} of a rank 2 bundle E on P^2. We show how some of the main invariants of the bundle can be read from the sequence
Good failures for fat points in P^2
No full textFixing numbers t,d in some numerical range, we can find configurations of double points for which the cohomology of the sheaves I_Z(t), Omega_{P^2} ensor I_Z(t) fails to be as expected exactly at level t and the failure is equal to d
- …
