Rol de las ciudades intermedias en la copresencia de modelos de producción agropecuarios : Enseñanzas del caso de Rodez (Francia) para las problemáticas identificadas en Francia y Argentina

El objetivo de este trabajo consiste en analizar el rol de las ciudades intermedias localizadas en el corazón de espacios rurales y agropecuarios, tomando el caso de la ciudad de Rodez, en la Región Occitania, en el suroeste de Francia, en tanto caso emblemático para luego generar una reflexión metodológica en un espacio representativo de lo agropecuario a nivel mundial: la región pampeana argentina. Nuestra hipótesis es que estas ciudades intermedias en esos espacios cumplen un papel esencial en la articulación, competencia y dependencia/ complementariedad funcional con la actividad agropecuaria en su área de influencia y aún en otras escalas. Partimos de considerar que no hay espacios rurales dinámicos sin ciudades dinámicas y que este tipo de dupla produce innovaciones sociales, económicas y tecnológicas que hacen a un proyecto territorial. Para lograr este objetivo, en este trabajo se movilizan dos conceptos centrales para aprehender la ciudad y la actividad agropecuaria en una visión geográfica. Por un lado, el concepto de ciudad intermedia y, por otro, el de copresencia. El análisis demuestra la copresencia de modelos agropecuarios que operan por simultaneidad en la ciudad intermedia de Rodez y emerge así un dispositivo para el estudio de estas problemáticas que se están aplicando en otras ciudades de Francia y de la Argentina.Facultad de Ciencias Agrarias y ForestalesConsejo Nacional de Investigaciones Científicas y TécnicasInstituto Nacional de Tecnología Agropecuari

Pyrolysis of a polyvinylsilazane, polymeric precursor for silicon carbonitride : structural investigation by

Dans ce travail, nous présentons notre stratégie de caractérisation par RMN en solution et à l’état solide de précurseurs polymériques et de céramiques à base de carbonitrure de silicium. L’étude présentée concerne un polymère polyhydrogénovinylsilazane ; elle est qualitative (identification des environnements locaux de tous les atonies H, C, Si et N) et quantitative (quantification des sites et des phases en présence). Enfin, nous donnons une description d’ensemble de la formation du matériau céramique qui est constitué à 1400°C de carbonitrure de silicium et de carbone dit libre

STRUCTURAL DIAGNOSTIC OF HIGH TEMPERATURE LIQUID PHASES BY 27Al NMR

L'amélioration des procédés de soudage par plasma ou laser suppose une bonne connaissance des propriétés microscopiques du liquide constituant la zone fondue. Le développement de nouvelles sondes de résonance magnétique nucléaire permet d'atteindre cet objectif. L'analyse de la raie de résonance de 27Al dans des oxydes liquides alumineux montre un régime d'échange rapide entre des coordinences quatre, cinq et six et une dépendance de la position de cette raie en fonction de la composition du liquide.Improvements of welding processes by plasma or laser require a good knowledge of the microscopic properties of the liquid associated to the melted area. The development of new high temperature NMR probes allows to reach such a goal. In the case of alumina bearing liquids, the analysis of the 27Al resonance line shows a rapid exchange regime of Al in four, five or six fold coordination together with a dependence of the resonance line versus the liquid composition

Signal-to-noise enhancement when T

Very long experimental times are necessary in order to obtain NMR spectra when the observed nuclei present important spin-lattice relaxation times. DEFT sequence allows for reduction of acquisition time though increasing the signal to noise ratio. An analytical approach is proposed for which optimal conditions of usage has been defined for the special case of T2≪T1. To obtain full maximization it is necessary to use linear prediction. At last a 2D exchange experiment using DEFT is presented

Quantitative analysis in MAS NMR of quadrupolar nuclei

The aim of this contribution is to give some indications on how to acquire an NMR spectrum of a quadrupolar nucleus in MAS conditions in order to perform a quantitative treatment of the data. In MAS conditions, recently, a way to access to the amount of magnetization contained in "the centerband" has been presented. In this paper, it is a experimental protocol which is proposed to get the NMR signal of quadrupolar nuclei in MAS conditions, and processing it, in a way that will allow an accurate quantification of sites populations

NMR, symmetry elements, structure and phase transitions in the argyrodite family

Cu7PSe6 belongs to a family of structures known as the argyrodites. It undergoes two phases transitions. The high temperature phase has been determined by X-ray diffraction. It has a $F\overline{4}3m$ space group. Medium temperature phases have been refined using a non-harmonic technique and the space group proposed is P213. The low temperature phase had an apparent space group of $F\overline{4}3m$ also. Use of X-ray diffraction and NMR together has allowed to determine the space groups of all phases as being respectively $F\overline{4}3m$, P213 and Pmn21. Positioning of disordered coppers in the structure is therefore possible and the structure can be described by connex polyhedra of PSe3-4 and SeCux-2x. The phase transitions can be understood by an ordered motion of SeCux-2x polyhedra. If these polyhedra set in motion independently two transitions are to be observed, if they are coupled only one is observed

In situ NMR measurements under hydrothermal conditions: study of the formation of polymeric Al hydrolysis species

In order to understand the formation mechanisms of oxide frameworks prepared by the hydrothermal method, in situ NMR experiments are performed. An attempt to describe the formation of Al hydrolysis species at 400K shows the necessity of high T NMR to observe polymers and aggregated polycations. Calibration of the intensity of a reference signal versus temperature allows to extract the fraction of Al observed by NMR together with the true proportions of Al species from RT to 400 K

IDENTIFICATION OF THE SODIUM DIFFUSION MECHANISMS WITHIN THE LAYERED NA(LI)XMO2O4 SYSTEM - EFFECT OF WATER AND EXCHANGE OF SODIUM BY LITHIUM

The layered molybdates of general formula MxMo2O4(M=Li or Na) were shown to be promising cathode materials for rechargeable batteries. One of the limitations for the performance of rechargeable batteries is the kinetics of the intercalation reactions taking place at the electrode/electrolyte interfaces. This paper reviews our results concerning the understanding of the diffusion mechanisms involved during the intercalation of Na, Li, and H2O between the MoO2 layers, which form these molybdenum oxides. Electrochemical techniques, as well as ac and dc measurements, were used to evaluate the electrical properties of these materials, which were found to be related to the changes observed in the local structure, and occuring during the intercalation reaction. Study of the local structure was carried out using NMR and ESR spectroscopies, while ac and dc techniques were used to evaluate the electrical parameters