1,720,985 research outputs found
Sulla razionalità dei piani doppi e tripli ciclici
No full textRiassunto della tesi di dottorato, con omonimo titolo, difesa con esito positivo all'Università di Roma "La Sapienza" il 26/03/199
Rivestimenti del piano. Sulla razionalità dei piani doppi e tripli ciclici
No full textLo studio dei rivestimenti doppi del piano inizia agli albori della geometria algebrica moderna. Anche Enriques dava un ruolo centrale allo studio di queste superfici, come testimoniano molti lavori suoi e dei suoi allievi, per l'importanza cruciale che hanno nella classificazione delle superfici algebriche. La presente opera illustra in modo ampio e dettagliato le proprietà dei rivestimenti doppi e tripli del piano, in particolare di quelli che sono superfici razionali
On the representation of Enriques surfaces as double planes
No full textIn this paper we give a short proof of the well-known representation of Enriques surfaces as double planes, by using the properties of the adjoint linear system to the branch curve
On rational and ruled double planes
No full textFollowing the ideas of Castelnuovo and Enriques, we classify the birational equivalence classes of double planes which are rational or ruled surfaces. In order to do this, we prove that the vanishing of the m-adjoint linear system to the branch curve of the canonical resolution of a double plane, for m ≥ 2, is a necessary and sufficient condition for the ruledness of the double plane
On degenerations of plane Cremona transformations
No full textThis article studies the possible degenerations of Cremona transforma- tions of the plane of some degree into maps of smaller degree
Surfaces of general type with vanishing geometric genus from double planes
Full text linkWe show how to construct some old and new surfaces of general typewith vanishing geometric genus from double planes,by computing explicit equations of their branch curves
On the classification of numerical Godeaux surfaces with an involution
No full textReport on a work in progress, with M. Mendes Lopes, about the classification of numerical Godeaux surfaces (i.e. minimal algebraic surfaces of general type with vanishing geometric genus and bi-genus equal to 2) with an automorphism of order 2
On Cremona contractibility
No full textWe give a constructive proof of a classical theorem which determines irreducible plane curves that are contractible to a point by a Cremona transformation. The problem of characterizing Cremona contractible (not necessarily irreducible) hypersurfaces in a projective space is in general widely open: we report on the only known result about reducible plane curves consisting of two components, due to litaka, and we discuss a couple of examples concerning plane curves with more components. Finally, we prove that all varieties of codimension at least two in a projective space are Cremona contractible to a point
On Double Planes with Kodaira Dimension Zero
No full textIn this paper we report on a work in progress about the classification of birational equivalence classes of double planes which are surfaces of Kodaira dimension zero, namely K3, Enriques and bielliptic surfaces
Even sets of four nodes on rational surfaces
No full textWe describe smooth rational projective algebraic surfaces X, over an
algebraically closed field of characteristic different from 2, having an even set of
four disjoint (-2)-curves, i.e. such that the sum of the four curves is divisible by
2 in the Picard group of X
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