Secant spaces and Clifford's theorem
Sectional invariants of scroll over a smooth projective variety
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.
Sieve methods for varieties over finite fields and arithmetic schemes
Classical sieve methods of analytic number theory have recently been adapted to a geometric setting. In the new setting, the primes are replaced by the closed points of a variety over a finite field or more generally of a scheme of finite type over . We will present the method and some of the surprising results that have been proved using it. For instance, the probability that a plane curve over is smooth is asymptotically as its degree tends to infinity. Much of this paper is an exposition...
Singularités imposables en position générale à une hypersurface projective
Singularities on complete algebraic varieties
We prove that any finite set of n-dimensional isolated algebraic singularities can be afforded on a simply connected projective variety.
Smooth curves on a cone which pass through its vertex.
Smooth Enriques surfaces in P4 and exceptional bundles.
Smooth non-special surfaces of P4.
Some defective secant varieties to osculating varieties of Veronese surfaces.
We consider the k-osculating varietiesOk,d to the Veronese d?uple embeddings of P2. By studying the Hilbert function of certain zero-dimensional schemes Y ⊂ P2, we find the dimension of Osk,d, the (s?1)th secant varieties of Ok,d, for 3 ≤ s ≤ 6 and s = 9, and we determine whether those secant varieties are defective or not.
Some intrinsic and extrinsic characterizations of the projective space
Some invariant theory among quasi-projectives
Some topological conditions for projective algebraic manifolds with degenerate dual varieties: connections with -bundles
Si illustrano alcune relazioni tra le varietà proiettive complesse con duale degenere, le varietà la cui topologia si riflette in quella della sezione iperpiana in misura maggiore dell'ordinario e le varietà fibrate in spazi lineari su di una curva.
Special effect varieties in higher dimension.
Here we introduce the concept of special effect varieties in higher dimension and we generalize to Pn, n ≥ 3, the two conjectures given in [2] for the planar case. Finally, we propose some examples on the product of projective spaces and we show how these results fit with the ones of Catalisano, Geramita and Gimigliano.
Stability of pencils of plane quartic curves
In questa nota si danno dei criteri per la stabilità di fasci di quartiche piane.
Stupeň inverznej krivky v projektívnom priestore Lagrangeových-Sylvestrových polynómov
Subvarieties of Segre varieties and trisecant lines.
Sui sistemi lineari di cuadriche riducibili ed irriducibili a jacobiana identicamente nulla.
Sulla caratteristica della jacobiana dei sistemi lineari irriducibili di quadriche
Sulla trasversalità di due superfici in
Siano una curva ridotta ed irriducibile, ed un sistema minimale di generatori dell'ideale omogeneo . Nel § 2 determiniamo una condizione necessaria e sufficiente perché due superfici , , aventi equazioni ,