29 research outputs found
Characterizations of Veronese and Segre varieties
We survey the known and recent characterizations of Segre varieties and Veronesea varieties
On the varieties of the second row of the split Freudenthal-Tits Magic Square
Our main aim is to provide a uniform geometric characterization of the
analogues over arbitrary fields of the four complex Severi varieties, i.e.~the
quadric Veronese varieties in 5-dimensional projective spaces, the Segre
varieties in 8-di\-men\-sional projective spaces, the line Grassmannians in
14-dimensional projective spaces, and the exceptional varieties of type
in 26-dimensional projective space. Our theorem can be
regarded as a far-reaching generalization of Mazzocca and Melone's approach to
finite quadric Veronesean varieties. This approach takes projective properties
of complex Severi varieties as smooth varieties as axioms.Comment: Small updates, will be published in Annales de l'institut Fourie
Codes and caps from orthogonal Grassmannians
In this paper we investigate linear error correcting codes and projective
caps related to the Grassmann embedding of an orthogonal
Grassmannian . In particular, we determine some of the parameters of
the codes arising from the projective system determined by
. We also study special sets of points of
which are met by any line of in at most 2 points and we
show that their image under the Grassmann embedding is a
projective cap.Comment: Keywords: Polar Grassmannian; dual polar space; embedding; error
correcting code; cap; Hadamard matrix; Sylvester construction (this is a
slightly revised version of v2, with updated bibliography
Veronese representation of projective Hjelmslev planes over some quadratic alternative algebras
We geometrically characterise the Veronese representations of ring projective planes over algebras which are analogues of the dual numbers, giving rise to projective Hjelmslev planes of level 2 coordinatised over quadratic alternative algebras. These planes are related to affine buildings of relative type Ã_2 and respective absolute type Ã_2, Ã_5 and Ẽ_6
A characterization of the finite Veronesean by intersection properties
A combinatorial characterization of the Veronese variety of all quadrics in PG(n, q) by means of its intersection properties with respect to subspaces is obtained. The result relies on a similar combinatorial result on the Veronesean of all conics in the plane PG(2, q) by Ferri, Hirschfeld and Thas, and Thas and Van Maldeghem, and a structural characterization of the quadric Veronesean by Thas and Van Maldeghem