La mise au point d'un modèle mécaniste permettant de simuler le fonctionnement de prairies à flore complexe est un projet ambitieux, permis par la synthèse de divers travaux de recherche en ...agronomie, zootechnie et écologie fonctionnelle. Les applications de ce type de modèle concernent la gestion des prairies, le rôle de la biodiversité pour les services écologiques des prairies et la simulation des impacts du changement climatique. Le projet DISCOVER étudie les relations entre la biodiversité et le fonctionnement de couverts prairiaux à flore complexe dans des expériences de longue durée, ce qui permet de paramétrer et d'évaluer un modèle mécaniste (GEMINI) lequel simule la dynamique des espèces végétales et ses conséquences pour la production végétale, la qualité de l'herbe et le fonctionnement du sol. Pour des plantes en compétition au sein du couvert, GEMINI calcule la capture de lumière et d'azote, ainsi que la morphologie des parties aériennes et des racines. Les effets du nombre et du type d'espèce pour la productivité de la prairie ont été simulés, en tenant compte de la plasticité de forme et de fonction des plantes. Des exemples de résultats sont donnés.
Within the framework of the 'DISCOVER' project (ANR Bio-diversity), the relationships between the bio-diversity and the functioning of pasture swards with a complex floristic composition are being studied in long-duration experiments, The data supply parameters and the means of evaluation for setting-up a mechanical model (GEMINI) that simulates the dynamics of the plant species and its consequences on the production and the quality of the herbage, and also on the workings of the soil. For the plants competing among themselves within the sward, GEMINI calculates the interception of light and of nitrogen, as well as the morphology of the above-ground parts and of the roots. The first modelling studies had borne on the simplified case of sown grass-clover associations. The present ambition of DISCOVER is to apply the model to swards with a complex floristic make-up, constituted by voluntary species, generally less well known. The effects of the number and of the type of species on the productivity of the pastures have been simulated, taking into account their plasticity of form and of function. Three examples of results are given. They concern : the role of the plasticity of leaf features in the response of grasses to nitrogen; the role of etiolation in the response of a dicotyledon to shade; and the role of the number of species and of functional groups in the productivity of the pasture. The applications of the model concern the role of bio-diversity in the ecological benefits of pastures with a complex floristic composition, and the simulation of the impacts of the climatic change.
A vacuum arc plasma source has been designed and tested for fabrication of thin films clear of droplets. In order to avoid these droplets, the source has been optimized to produce pulsed plasmas ...generated by the anode, and to screen the anodic region against the plasma streaming away from the cathode spot. We present here spectroscopic measurements and analyses carried out in order to characterize the electron population of such anode plasmas. The vacuum arc was first operated with a carbon anode of diameter 0.5 mm and an arc current of 192 A. The visible and near infrared spectra were recorded with various resolutions, in direct view of the anode spot, with an intensified CCD camera. Several dominant lines were identified as C/sup +/ and C/sup 2+/ Lines. The relative intensities corresponding to transitions between meaningful multiplets show that the local thermal equilibrium is reached, and this allows a straightforward determination of the electron temperature and of the electron density. The values are about 3.2 eV and 2.5 10/sup 17/ cm/sup -3/. The study has been extended to lower currents of 140, 92 and 65 A. The temperature and the density are regularly decreasing down to about 2 eV and 1.5 10/sup 15/ cm/sup -3/.
Two cases of acute post-traumatic renal failure in severely head injured patients are reported. An increase in intracranial pressure (ICP) was shown up by continuous monitoring during haemodialysis: ...it was more important during conventional haemodialysis than during continuous arteriovenous haemofiltration. Although this effect is well known experimentally, few cases of continuous ICP pressure monitoring have been reported in head injury patients undergoing haemodialysis. The increase in ICP is explained in the dog as a result of blood-brain differences in urea concentration and osmolality leading to an increase in cerebral spinal fluid volume and cerebral tissue swelling. If dialysis is necessary in these patients, it should be carried out early and progressively, the patient's ICP being monitored continuously.
Because the greater number of viral cervical lesions, the authors recall their cytological and pathological pictures. In 30% of the causes, they have observed relations between flat condylomas and ...cervical severe dysplasias and carcinoma in situ. But in these last lesions, the cytological characters of the viral infestations are not visuable. The relationship between condyloma and carcinoma in situ is explained by the virus modifications on the germinative cells genoma which enhance great multiplication of these cells and inhibit the epidermoid differentiation. When the virus are not very active, or the host responses sufficient, the cell differentiation and maturation permit the replication of the virus and its appearance in the cytoplasm of the superficial cells. The authors stress on the complete destruction of the viral cervical lesions and the later control of the cervix.
L'action de recherche n°8 du PGRN "Ecophysiologie de l'huître perlière #Pinctada margaritifera$ : étude de la respiration et de la filtration" aborde successivement l'activité valvaire, la ...respiration, la filtration chez l'huître perlière. Le suivi de l'activité valvaire montre un rythme nycthéméral d'ouverture : les valves sont plus ouvertes la nuit. Les mouvements valvaires sont plus nombreux et plus amples durant la journée. Un travail méthodologique important a été réalisé pour la mise au point du matériel de mesure de la respiration et de la filtration utilisable aussi bien au laboratoire que in situ à Takapoto. (Résumé d'auteur)
