Search results for "Geometria"

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.

Ricci-flow based conformal mapping of the proximal femur to identify exercise loading effects.

2018

AbstractThe causal relationship between habitual loading and adaptive response in bone morphology is commonly explored by analysing the spatial distribution of mechanically relevant features. In this study, 3D distribution of features in the proximal femur of 91 female athletes (5 exercise loading groups representing habitual loading) is contrasted with 20 controls. A femur specific Ricci-flow based conformal mapping procedure was developed for establishing correspondence among the periosteal surfaces. The procedure leverages the invariance of the conformal mapping method to isometric shape differences to align surfaces in the 2D parametric domain, to produce dense correspondences across an…

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.

Projective Architecture

2009

Sbacchi indaga su quale sia stata la reale influenza della nozione di "proiezione" nell'ambito della progettazione architettonica a partire da Guarini. Per fare ciò vengono presi in considerazione i concetti di luce e ombra così come quelli di linea astratta, piano, sezione, geometria proiettiva e prospettiva. Michele Sbacchi investigates the real influence of the notion of projection on architectural design before and during the age of Guarini. He takes into consideration concepts such as light and shadow, abstract line, plane, section, projective geometry and perspective. To do this he looks at the ideas of Gregorius Saint Vincent, Alberti, Guarini, Desargues and de l’Orme, among others.