Geometrically closed rings

We develop the basic theory of geometrically closed rings as a generalisation of algebraically closed fields, on the grounds of notions coming from positive model theory and affine algebraic geometry. For this purpose we consider several connections between finitely presented rings and ultraproducts, affine varieties and definable sets, and we introduce the key notion of an arithmetic theory as a purely algebraic version of coherent logic for rings.Comment: 18 page

Advances in f-element cyanide chemistry

International audienceThis Dalton perspective gives an overview of the development of cyanide chemistry of 4f- and 5f-elements, a field which was poorly explored in contrast to the attention paid to the cyanide complexes of the d transition metals. The use of the cyanide ligand led to the discovery of mono- and polycyanide complexes which exhibit unprecedented and unexpected coordination geometries. A new type of linear metallocenes including [U(Cp*)2(CN)5]3- (Cp* = C5Me5) and the first bent actinocenes [An(Cot)2(CN)]- (An = Th, U; Cot = C8H8) were isolated. Thorocene was found to be much more reactive than uranocene since a series of sterically crowded cyanide complexes have been obtained only from [Th(Cot)2]. A series of cyanido-bridged dinuclear compounds and mononuclear mono-, bis- and tris(cyanide) complexes were prepared by addition of cyanide salts to [MN*3] (M = Ce, U) and [UN*3]+ (N* = N(SiMe3)2]. The CeIII, UIII and UIV ions were clearly differentiated in these reactions by cyanide linkage isomerism, as shown for example by the structures of the cyanide complex [UIIIN*3(CN)2]2- and of the isocyanide derivatives [CeIIIN*3(NC)2]2- and [UIVN*3(NC)]-. While the U-CN/NC coordination preference towards the UIII/UIV pair is related to the subtle balance between steric, covalent and ionic factors, DFT computations and in particular the calculated total bonding energies between the metal and the cyanide ligand allowed the observed coordination mode to be predicted. The ability of the cyanide ligand to stabilize the high oxidation states was assessed with the synthesis of UV and UVI complexes in the inorganic and organometallic series

Jeunesse périphérique en centre-ville : l’exemple de Lyon

L’article présente sous un éclairage nouveau un travail de recherche consacré aux pratiques du centre-ville des « jeunes de banlieue » de l’agglomération lyonnaise, en l’occurrence la rue de la République, principale artère piétonne de la presqu’île lyonnaise et le centre commercial de la Part-Dieu. Que font donc les adolescents des quartiers dits difficiles de l’agglomération lyonnaise lorsqu’ils ne sont pris en charge ni par l’école ni par les structures de loisir ou sportives ? Lorsqu’ils sont à la fois dehors (dans la rue, dans l’espace public) et dedans (dans le centre commercial, dans le flux de la foule) ? Pour y répondre, une méthode originale a été employée : des observations et des suivis de parcours déambulatoires les mercredis après-midi et les samedis après-midi sur plus d’une année. Il en ressort la vision d’une pratique de l’espace faite d’épreuves pour lesquelles la déambulation fait figure de ressource (faculté à ce mouvoir à sa guise pour les uns, capacité à contrôler les conduites pour les autres) et d’enjeu (rapprochements, drague, mise à distance) tant pour les filles que pour les garçons. Vus sous cet angle, les deux espaces étudiés présentent des formes relativement opposées de régulation.When peripheral youth comes down town : an example at Lyon. Thinking the city as a resource and mobility as a learning This article presents in a new perspective a research dealing with how suburbs’ youth from the « greater Lyon » practice the centre town, especially rue de la République, the main pedestrian thoroughfare of Lyon’s peninsula, and the shopping centre of La Part-Dieu. What ever do juveniles coming from the so-called difficult neighbourhoods of the greater Lyon when they are not taken in charge either by school or by leisure or sport organisations ? When they stand both outside (in the street, in public space) and inside (in the shopping centre, in the flow of the crowd). To answer those questions, an original method has been employed : observing and following their walking at random on Wednesday and Saturday afternoons over a year long. A vision then comes out : practising space as a series of tests for which strolling becomes a resource (the ability to move oneself on his own way for some, the ability to control behaviours for others) and shows what is at stake both for girls and boys (proximities, chatting up, distance keeping). Thus analysed, the two urban spaces present relatively opposed forms of regulation.Cuando los jovenes de la periferia llegan en el centro ciudad : el ejemplo de Lyon. Pensar la ciudad como un recurso y la movilidad como un aprendizaje    El artículo enfoca de cierta manera un trabajo de investigacíon dedicado a las practicas de centro de la ciudad de los jóvenes de las afueras del poblado de LYON, más precisamente la calle de La Republique, calle peatonal principal de la península de LYON, y el centro comercial de La Part Dieu¿ Que hacen los adolescentes de los barrios dichos dificiles cuando la escuela y las organisaciones de ocios o de deportivo no se hacen cargo de ellos? Cuando estan a la vez fuera (en la calle, en el espacio público) y dentro (en el centro comercial, en el flujo del gentío) ?Para responder, se ha empleado un método original : observaciones y seguimientos de los traslados de los jóvenes, los miércoles y sábados en la tarde durante más de un año.De eso resulta la visíon de una practica del espacio hecha de pruebas por las cuales la deambulacíon aparece como recursos (facultad de moverse a su modo por unos, capacidad de controlar las conductas por otros) y como lo que está en juego (acercamientos, ligar, puesta a distancia) tanto por las chicas como por los chicos.Desde este punto de vista, los dos espacios estudiados presentan formas relativamente contrarios de regulacíon

Nitrite complexes of the rare earth elements

International audienceThe coordination chemistry of the nitrite anion has been investigated with rare earth elements, and the resulting complexes were structurally characterized. Among them, the first homoleptic examples of nitrite complexes of samarium, ytterbium and yttrium are described. The coordination behavior of the nitrite ion is directly controlled by the ionic radius of the metal cation. While the nitrito ligand is stable in the coordination sphere of cerium(III), it is readily reduced by SmI2

Catalytic methylation of aromatic amines with formic acid as the unique carbon and hydrogen source

International audienceA novel methodology is presented for the direct methylation of amines, using formic acid as a unique source of carbon and hydrogen. Based on ruthenium(II) catalysts, the formation of the N-CH3 group proceeds via an efficient formylation/transfer hydrogenation pathwa

First reductive dimerization of a polycyclic azine

International audienceThe tptz molecule is reduced by potassium into its anion-radical in the compound K(tptz)2 (1), whereas it is reductively coupled by SmI2 and UI3(py)4 into the bis-triazinide ligand in the dinuclear complexes [Sm2(tptz– tptz)(DMF)8][I]4·3.5DMF (2·3.5DMF) and U2I6(tptz– tptz)(MeCN)2·2MeCN (3·2MeCN) where each metal ion occupies a pentadentate N5 cavity of the [tptz–tptz]2– ligand

Scavenging of aerosol particles by rain in a cloud resolving model

International audienceWe describe a below-cloud scavenging module of aerosol particles by raindrops for use in a three-dimensional mesoscale cloud resolving model. The rate of particle removal is computed by integrating the scavenging efficiency over the aerosol particle and the drop size distributions. Here the numerical integration is performed accurately with a Gauss quadrature algorithm. The efficiency of the scavenging module is partially confirmed with experimental data. More interestingly, it is illustrated by two numerical experiments: the simulation of a forced convective circulation in a tropical cloudy boundary layer and a two-dimensional simulation of an African squall line. The results show a very selective wet removal of the aerosol particles which clearly depends on the mode radius, the width and the vertical profile of concentration. Furthermore, the squall line case shows the importance of resolving internal circulations to redistribute layers of aerosol particles in order to improve estimates of particle removal by below-cloud scavenging