Les populations néoteniques de Triturus helveticus des causses et du Bas-Languedoc I. Répartition et caractéristiques

Neoteny is common in some populations of Palmate newts Triturus helveticus of Southern France. Population samples have been collected from 117 pools, at three different seasons of the year. Percentages of neotenic individuals have been calculated for 29 of these pools where neotenic newts were found. Neoteny is not evenly distributed over the whole study area. It is more prevalent in the S.E. part of the Causse du Larzac and in the Causse de Blandas, than in the coastal plains of Languedoc. On the “ causses ” (arid limestone tablelands), neoteny only occurs among palmate newts, no neotenic individual having ever been found among the sympatric Triturus marmoratus population. Morphological differences between neotenic and normal popu lations of Triturus helveticus are described. None of them is consistent enough to allow sub-specific status to be given to the neotenic population. Breeding takes place later in the season among the Larzac population and the duration of the aquatic phase of the yearly cycle is also longer in the plateau population than among the newts of the coastal plains. All these differences, morphological as well as biological, disappear when the newts are kept in labo ratory conditions. Metamorphosis occurs normally when the progeny of both newt populations are bred in the laboratory. However mortality is much higher among the progeny of neotenic females, during their first three months of life

Les populations néoténiques de Triturus helveticus Raz. des Causses et du Bas-Languedoc. II. Ecologie

The physical, chemical, and biotic characteristics of the ponds where neotenic populations of Palmate newts are found in Sou thern France are described. The frequency of neoteny is high in permanent ponds, at an altitude ranging from 400 to 700 m, on arid limestone plateaux with a yearly rainfall of 1500-2000 mm. In such areas there are large seasonal variations of water temperature, ranging from + 1 to + 28 °C, water remaining cold (below + 15°C) for 8 to 10 months during the year. The saline content of water is low, as shown by conductivity figures (less than 200 pmhos/cm/cm2) . No iodine deficiency was ever found in the ponds of the study area. A correlation has been found between the frequency of neoteny and the water concentration in Ca, Mg and particularly K (which may account for 35-40 % of the cations) . The aridity of the area surrounding the pools can also contri bute to the selection of neotenic individuals, paedogenesis being of obvious adaptive value in such an environment

Les populations néoténiques de Triturus helveticus des Causses et du Bas-Languedoc. I. Répartition et caractéristiques

Neoteny is common in some populations of Palmate newts Triturus helveticus of Southern France. Population samples have been collected from 117 pools, at three different seasons of the year. Percentages of neotenic individuals have been calculated for 29 of these pools where neotenic newts were found. Neoteny is not evenly distributed over the whole study area. It is more prevalent in the S.E. part of the Causse du Larzac and in the Causse de Blandas, than in the coastal plains of Languedoc. On the “causses” (arid limestone tablelands), neoteny only occurs among palmate newts, no neotenic individual having ever been found among the sympatric Triturus marmoratus population. Morphological differences between neotenic and normal populations of Triturus helveticus are described. None of them is consistent enough to allow sub-specific status to be given to the neotenic population. Breeding takes place later in the season among the Larzac population and the duration of the aquatic phase of the yearly cycle is also longer in the plateau population than among the newts of the coastal plains. All these differences, morphological as well as biological, disappear when the newts are kept in laboratory conditions. Metamorphosis occurs normally when the progeny of both newt populations are bred in the laboratory. However mortality is much higher among the progeny of neotenic females, during their first three months of life.Gabrion J., Sentein P., Gabrion C. Les populations néoténiques de Triturus helveticus des Causses et du Bas-Languedoc. I. Répartition et caractéristiques. In: La Terre et La Vie, Revue d'Histoire naturelle, tome 31, n°3, 1977. pp. 489-506

Les populations néoténiques de Triturus helveticus Raz. des Causses et du Bas-Languedoc. II. Écologie

The physical, chemical, and biotic characteristics of the ponds where neotenic populations of Palmate newts are found in Southern France are described. The frequency of neoteny is high in permanent ponds, at an altitude ranging from 400 to 700 m, on arid limestone plateaux with a yearly rainfall of 1500-2000 mm. In such areas there are large seasonal variations of water temperature, ranging from + 1 to + 28°C, water remaining cold (below + 15°C) for 8 to 10 months during the year. The saline content of water is low, as shown by conductivity figures (less than 200 μmhos/cm/cm²). No iodine deficiency was ever found in the ponds of the study area. A correlation has been found between the frequency of neoteny and the water concentration in Ca, Mg and particularly K (which may account for 35-40 % of the cations). The aridity of the area surrounding the pools can also contri¬ bute to the selection of neotenic individuals, paedogenesis being of obvious adaptive value in such an environment.Gabrion J., Sentein P., Gabrion C. Les populations néoténiques de Triturus helveticus Raz. des Causses et du Bas-Languedoc. II. Écologie. In: La Terre et La Vie, Revue d'Histoire naturelle, tome 32, n°4, 1978. pp. 577-610

Influence de la stéréorégularité de poly(3-alkylthiophènes) photodopes sur la stabilité thermique de la conductivité électrique

La stéréorégularité des polymères joue un rôle clef pour la conductivité électrique des poly(3-alkylthiophènes). Différentes méthodes de synthèse ont été réalisées menant à des polymères de stéréorégularités différentes dont le comportement de la conductivité électrique a été étudié. Le photodopage des polymères a été obtenu par photodissociation de matériaux de type sels d'oniums. L'influence de différentes atmosphères et l'effet de la température sur la cinétique de dégradation ont été étudiés. Le photodopage de tels systèmes a été appliqué à la réalisation de réseaux résistifs de haute résolution par des techniques de lithographie

Cellules solaires photovoltaïques plastiques enjeux et perspectives

Après avoir détaillé le fonctionnement d'une cellule photovoltaïque plastique et les paramètres photovoltaïques permettant de caractéiser son efficacité, un état de l'art des technologies de fabrication des cellules est présenté. Des moyens d'amélioration des performances des cellules photovoltaïques organiques sont ensuite illustrés par l'étude de dispositifs développés au Laboratoire Composants Organiques (LCO) du CEA Saclay

Molecular rectification in oriented polymers

We underline the intrinsic rectifying nature of an oriented polymeric material. Orientation of the initially symmetric structure is performed through DC-field ordering of the polar molecules contained in the polymer. The internal field induced in the polymeric material is evidenced by the induction of a rectifying current-voltage characteristic. Our preparation technique opens a new route for the improvement of organic-semiconductor devices efficiency