Rigidity II: non-orientable case.
Rings with many idempotents.
Robust decoupling through algebraic output feedback in manipulation systems
This paper investigates the geometric and structural characteristics involved in the control of general mechanisms and manipulation systems. These systems consist of multiple cooperating linkages that interact with a reference member of the mechanism (the “object”) by means of contacts on any available part of their links. Grasp and manipulation of an object by the human hand is taken as a paradigmatic example for this class of manipulators. Special attention is devoted to the output specification...
Secondary invariants for Frechet algebras and quasihomomorphisms.
Selmer groups and torsion zero cycles on the selfproduct of a semistable elliptic curve.
Slices and transfers.
Some algebraic aspects of quadratic forms over fields of characteristic two.
Some remarks on conjectures about cyclotomic fields and -groups of
Splitting obstructions and properties of objects in the Nil categories
We show that the objects of Bass-Farrell categories which represent 0 in the corresponding Nil groups are precisely those which are stably triangular. This extends to Waldhausen's Nil group of the amalgamated free product with index 2 factors. Applications include a description of Cappell's special UNil group and reformulations of those splitting and fibering theorems which use the Nil groups.
Stability of -algebras is not a stable property.
Stable rings generated by their units.
Stable short exact sequences and the maximal exact structure of an additive category
It was recently proved that every additive category has a unique maximal exact structure, while it remained open whether the distinguished short exact sequences of this canonical exact structure coincide with the stable short exact sequences. The question is answered by a counterexample which shows that none of the steps to construct the maximal exact structure can be dropped.
Strictification of categories weakly enriched in symmetric monoidal categories.
Strong separativity over exchange rings
An exchange ring is strongly separative provided that for all finitely generated projective right -modules and , . We prove that an exchange ring is strongly separative if and only if for any corner of , implies that there exist such that and if and only if for any corner of , implies that there exists a right invertible matrix . The dual assertions are also proved.
Structure du groupe de Grothendieck équivariant d’une courbe et modules galoisiens
Cet article est consacré à l’étude de la structure d’anneau du groupe de Grothendieck équivariant d’une courbe projective munie d’une action d’un groupe fini. On explicite cette structure en introduisant un groupe de classes de cycles à coefficients dans les caractères et une notion d’auto-intersection pour ces cycles. De ce résultat, on déduit une expression de la caractéristique d’Euler équivariante d’un -faisceau.
Structure of unitary groups over finite group rings and its application
In this paper, we determine all the normal forms of Hermitian matrices over finite group rings , where , is a commutative -group with order . Furthermore, using the normal forms of Hermitian matrices, we study the structure of unitary group over through investigating its BN-pair and order. As an application, we construct a Cartesian authentication code and compute its size parameters.
Subrings in imaginary quadratic fields which are not universal for GE₂
Sur la complétion de la -théorie équivariante
Sur la forte -moyennabilité d’un groupoïde
Sur la racine carrée de la codifférente
On présente deux résultats nouveaux concernant la racine carrée de la codifférente d’une extension faiblement ramifiée de . Le premier, relatif à sa structure galoisienne, s’inscrit dans la stratégie classique développée notamment par Fröhlich et Taylor. Le second, qui concerne le réseau entier unimodulaire associé, est prouvé à l’aide de calculs numériques portant sur des exemples intéressants.