Pour une utilisation durable des nappes d'eau souterraine : une approche par les incitations

La gestion d'une ressource en commun pose le problème de la surexploitation. Cette possibilité se produit lorsque l'appropriateur cherche à maximiser son profit tout en partageant le coût de son exploitation avec les autres appropriateurs. C'est le modèle de la tragédie des communs de Hardin (1968). Les solutions proposées pour dépasser ce dilemme sont la gestion centralisée de la ressource, l'instauration des droits de propriété transférable et la gestion collective. La Tunisie a opté pour ce dernier choix à travers une gestion décentralisée par les groupements à intérêt collectif (GIC). L'implémentation des règles dans une action collective articulée autour de l'exploitation d'une nappe à accès libre constitue la finalité du papier. Pour cela, nous nous proposons, dans le cadre de ce travail, la réalisation d'un diagnostic de la situation étudiée en vue de mieux appréhender son fonctionnement. Nous cherchons à effectuer une représentation sous forme de jeux du problème d'accès à la nappe et de l'allocation de la ressource, situations où se pose la question de l'implémentation des règles. La structure du Dilemme du Prisonnier est souvent utilisée pour rendre compte de l'exploitation de la ressource en commun. Nous nous gardons d'effectuer cette appréciation à priori tant qu'une observation se basant sur une méthodologie d'approche n'ait pas confirmé une structure particulière de jeu. La revue de la littérature a permis de distinguer d'autres jeux possibles permettant de rendre compte des problèmes dans une action collective. Afin d'identifier ces jeux, nous décomposerons les cas étudiés en autant d'actions possibles pertinentes. L'approche adoptée à cet effet s'inspirera de celle proposée par Ostrom : l'Institutional Analysis Developpement (IAD). Elle consiste dans la définition des variables suivantes : les acteurs participants, l'information dont ils disposent, leurs stratégies et leurs gains respectifs. Ce travail aura pour terrain d'étude la plaine de Kairouan

Internet scalability: properties and evolution

Copyright © 2008 IEEEMatthew Roughan; Steve Uhlig; Walter Willinge

Corrosion behaviour of nitrided ferritic stainless steels for use in solid oxide fuel cell devices

Plasma nitriding was applied to ferritic stainless steel substrates to improve their performances as interconnects for solid oxide fuel cell devices. The samples underwent electrical conductivity test and SEM/EDS, TEM/EDS, environmental-SEM analyses. The first stages of corrosion were recorded in-situ with the e-SEM. Nitriding is effective in limiting the undesired chromium evaporation from the steel substrates and accelerates the corrosion kinetics, but its influence of the electrical conductivity is ambiguous. No intergranular corrosion is found in the steel substrate after long time operation. Nitriding helps commercially competitive porous coating to improve chromium retention properties of metal interconnects

Unique myological changes associated with ossified fabellae: a femorofabellar ligament and systematic review of the double-headed popliteus

The fabella is a sesamoid bone embedded in the tendon of the lateral head of the gastrocnemius. It is the only bone in the human body to increase in prevalence in the last 100 years. As the fabella can serve as an origin/insertion for muscles, tendons, and/or ligaments (e.g., the oblique popliteal and fabellofibular ligaments), temporal changes in fabella prevalence could lead to temporal changes in “standard” knee anatomy. The aim of this study was to investigate unique myological changes to the posterolateral corner knee associated with ossified fabella presence and perform a systematic review to contextualize our results. Methods Thirty-three fresh frozen cadaveric knees were considered. As the knees were all used for previous experimentation, the knees were in variable levels of preservation. Those with adequate preservation were used to determine ossified fabella presence/absence. When ossified fabellae were present, unique myologies associated with the fabella were recorded. A systematic review was performed on the double-headed popliteus to investigate possible correlations between this anatomical variant and the fabella. Results Of the 33 knees, 30 preserved enough soft tissue to determine fabella presence/absence: 16/30 knees had fabellae (five cartilaginous and 11 ossified). Eight of the eleven knees with ossified fabellae retained enough soft tissue to investigate the posterolateral knee anatomy. Of these, 4/8 exhibited unique myological changes. One knee had a double-headed popliteus muscle where one head originated from the medial side of a large, bulbous fabella. A systematic review revealed double-headed popliteus muscles are rare, but individuals are 3.7 times more likely to have a fabella if they have a double-headed popliteus. Another knee had a large, thick ligament stretching from the lateral edge of the fabella to the inferoposterior edge of the lateral femoral epicondyle, deep to the lateral collateral ligament (LCL) and near the popliteal sulcus. We found no mention of such a ligament in the literature and refer to it here as the “femorofabellar ligament”. In all four knees, the plantaris and lateral gastrocnemius appeared to share a common tendinous origin, and the fabella was located at/near the junction of these muscles. In the case of the double-headed popliteus, the fabella clearly served as an origin for the plantaris. Conclusions Despite being found in an average of 36.80% of human knees, most standard anatomical models fail to account for the fabella and/or the unique myological changes associated with fabella presence. Although our sample is small, these data highlight aspects of human biological variability generally not considered when creating generalized anatomical models. Further work is needed to identify additional changes associated with ossified fabellae and the functional consequences of omitting these changes from models

Oxide-Supported IrNiO_x Core-Shell Particles as Efficient, Cost-Effective, and Stable Catalysts for Electrochemical Water Splitting

Active and highly stable oxide-supported IrNiOx core–shell catalysts for electrochemical water splitting are presented. IrNix@IrOx nanoparticles supported on high-surface-area mesoporous antimony-doped tin oxide (IrNiOx /Meso-ATO) were synthesized from bimetallic IrNix precursor alloys (PA-IrNix /Meso-ATO) using electrochemical Ni leaching and concomitant Ir oxidation. Special emphasis was placed on Ni/NiO surface segregation under thermal treatment of the PA-IrNix /Meso-ATO as well as on the surface chemical state of the particle/oxide support interface. Combining a wide array of characterization methods, we uncovered the detrimental effect of segregated NiO phases on the water splitting activity of core–shell particles. The core–shell IrNiOx /Meso-ATO catalyst displayed high water-splitting activity and unprecedented stability in acidic electrolyte providing substantial progress in the development of PEM electrolyzer anode catalysts with drastically reduced Ir loading and significantly enhanced durability