Les productions pampéennes ont été réorientées au cours de deux « révolutions » d'ordre productif et d'ordre technologique qui ont fait, de la Pampa humide du littoral en particulier, la principale région productrice d'oléo-protéagineux et, de l'Argentine en général, l'un des premiers exportateurs mondiaux de produits dérivés de soja et de tournesol. Après la crise du début des années 1 990, les perspectives du marché mondial et du Mercosur remotivent aujourd'hui les producteurs, qui vivent une troisième « révolution » d'ordre agro- industriel. Les premières années du XXIe siècle devraient être propices à un retour remarqué de l'Argentine dans les échanges internationaux, avec de nouveaux produits et sur de nouveaux marchés.

With a view to making highly efficient light shutters, the object of this study is to know the best structure of the liquid crystal polymer composite yielding a high extinction ratio. The main feature of this letter shows that experimental results are consistent with anomalous diffraction approach. For our demonstration, we made polymer dispersed liquid crystal (PDLC) cells having different droplet radius (a), ranging from 0.5 to 1 μm. In addition, a strong wavelength sensitivity with these radii is measured in the visible region. Beyond one micron, droplets yield higher transmission as regards both the wavelength and the optical anisotropy of the liquid crystal. These results bring forward that the most efficient PDLC films must follow the optimization relation: a(Δn)/λ=0.3, where λ is the wavelength and Δn the liquid crystal anisotropy.

For the development of reflective flat displays, polymer liquid crystal composite is a good potential challenger material. Ln order to reduce the driving voltage and to enhance the brightness of the backscattered off-state, it is necessary to understand and optimise the composite formation. Based on a suitable liquid crystal and polymer couple, we describe a model for the fabrication of polymer dispersed liquid crystal. The influence of the main parameters on the composite production is studied. We choose the case of polymerization-induced phase separation, by means of ultra violet light polymerizing monomer. This study shows how the polymerization parameters control the droplet size and the remaining monomer content, both of which play a role in back-scattering and saturation voltage. We bring to light, the strong temperature sensitivity of PDLC formation and the necessary precautions to reach the optimum performance of the chosen liquid crystal-polymer couple. As this step is essential to exploit PDLC systems, it could also be systematically used to compare then under the best conditions.

In this paper, the syntheses of two styrene-based monomers bearing either an optical active group, Dispersed Red 1, or a photocrosslinkable cinnamate group are described. The study of their copolymerizations with maleic anhydride and the characterizations of the copolymers are,given. Polymer materials with exposure to UV curing light, 254 nm, exhibit a photobleaching process. This feature can be used in the preparation of channelized wave-guide using photomask methods.

The PVCN polymer is used to obtain a localized optical waveguide with a one-step masking. Under UV irradiation, the opening of CC bonds appears and leads to a bleaching of the absorption band around 280 nm. The bleaching provides a decrease of the refractive index. This irreversible photomodification is used to draw localized waveguides by irradiation through a positive mask.

La calorimétrie différentielle à balayage est appliquée à l'étude de la polymérisation en masse du méthacrylate de méthyle et du méthacrylate de pentafluorophényle (MAPF) en présence de 2,2-azobis(2-méthylpropionitrile) (AIBN) et de peroxydicarbonate de bis(4-tertiobutylcyclohexyle). Les vitesses globales de polymérisation des deux monomères avec l'AIBN sont comparées ainsi que celles du MAPF avec les deux amorceurs. On trouve pour les enthalpies de polymérisation des deux monomères dans le domaine 50–60° des valeurs voisines de 50 kJ · mol−1.

Fatal outcome after ethanol renal ablation in child with end-stage kidneysL Garel, JL Mareschal, MF Gagnadoux, D Pariente, M Guilbert and J SauvegrainAudio Available | Share

The dynamic stiffness matrix for circular curved members of constant section has been derived for the determination of natural frequencies of continuous curved beams undergoing in-plane vibrations. An example of a two-span curved beam is given to illustrate the application of the proposed method and to show the effects of rotary inertia, shear and the central angle of the arc upon the natural frequencies of the beam.