Search results for " GEOMETRIA"
showing 10 items of 291 documents
Per una biografia scientifica di Corrado Segre
2013
Geometria elementare: dalla geometria del triangolo alla geometria dinamica
Da una decina di anni si discute sull’importanza di presentare, a fini didattici e anche per la formazione dei docenti, la geometria elementare mediante l’utilizzo di software di geometria dinamica. Ciò naturalmente si inserisce in una visione dell’insegnamento della geometria che valorizzi gli aspetti laboratoriali. Occorre comunque rilevare che il laboratorio non va visto, in questo contesto, come una serie di interventi episodici e slegati, ma come la sede naturale per affrontare aspetti che possano destare l’interesse, affiancando quelli curricolari anche attraverso percorsi storici che tocchino spunti di origini differenti, di tipo trasversale, mediante il quale gli argomenti del passa…
Picard et les géomètres italiens: histoire des deux prix Bordin
2013
Dans mon intervention je chercherai à mettre au point la question des rapports entre Picard et les géomètres algébriques italiens, en particulier Enriques, Castelnuovo et Severi, en montrant comment si, d'un côté, les thèmes de recherche se croisent, d'un autre ils ont été développés en utilisant des langages mathématiques profondément différents au point de rendre parfois impossible ou presque la compréhension réciproque. Je chercherai aussi à donner un aperçu des rapports en théorie des nombres entre Picard et Bianchi et de l'influence de Corrado Segre et Fano sur Cartan qui à son tour eut une profonde influence sur Benjamin Segre.
The structure of symplectic groups associated with a quadratic extension of fields
2003
Given a quadratic extension L/K of fields and a regular alternating space (V, f) of finite dimension over L, we determine the isometry group of a K-subspace W of V which does not split into the orthogonal sum of two proper K-subspaces, W being neither an L-space nor a K-substructure.
Some algebraic and topological properties of the nonabelian tensor product
2013
Several authors investigated the properties which are invariant under the passage from a group to its nonabelian tensor square. In the present note we study this problem from the viewpoint of the classes of groups and the methods allow us to prove a result of invariance for some geometric properties of discrete groups.
Locally compact (2, 2)-transformation groups
2010
We determine all locally compact imprimitive transformation groups acting sharply 2-transitively on a non-totally disconnected quotient space of blocks inducing on any block a sharply 2-transitive group and satisfying the following condition: if Δ1, Δ2 are two distinct blocks and Pi, Qi ∈ Δi (i = 1, 2), then there is just one element in the inertia subgroup which maps Pi onto Qi. These groups are natural generalizations of the group of affine mappings of the line over the algebra of dual numbers over the field of real or complex numbers or over the skew-field of quaternions. For imprimitive locally compact groups, our results correspond to the classical results of Kalscheuer for primitive l…
On Intrinsic Negative Curves
2023
Extension theory and the calculus of butterflies
2016
Abstract This paper provides a unified treatment of two distinct viewpoints concerning the classification of group extensions: the first uses weak monoidal functors, the second classifies extensions by means of suitable H 2 -actions. We develop our theory formally, by making explicit a connection between (non-abelian) G-torsors and fibrations. Then we apply our general framework to the classification of extensions in a semi-abelian context, by means of butterflies [1] between internal crossed modules. As a main result, we get an internal version of Dedecker's theorem on the classification of extensions of a group by a crossed module. In the semi-abelian context, Bourn's intrinsic Schreier–M…
MR 3007673 Reviewed Geiss F. The Unirationality of Hurwitz spaces of 6-gonal curves of small genus. Documenta Mathematica (2012) 17, 627--640. (Revie…
2013
Let H (d, w) be the Hurwitz space that parametrizes degree d simple coverings of the projective line with w = 2g + 2d - 2 branch points. A classic result affirms the unirationality of these spaces for d \leq 3. Successively, Arbarello and Cornalba in [E. Arbarello and M. Cornalba, Footnotes to a paper of Beniamino Segre, Math. Ann. 256 (1981), 341--362] prove that the spaces H (d, w) are unirational in the following cases: d \leq 5 and g \geq d - 1, d = 6 and 5 \leq g \leq 10 or g = 12 and d = 7 and g = 7. In this paper, the author studies the problem of unirationality over an algebraically closed field of characteristic zero when d = 6. In particular, the author proves that the spaces H (6…
On double Veronese embeddings in the Grassmannian G(1,N)
2004
We classify all the embeddings of P^n in a Grassmannian of lines G(1,N) such that the composition with Pl\"ucker is given by a linear system of quadrics of P^n.