90 research outputs found
Production, by co-grinding in a media mill, of porous biodegradable polylactic acid-apatite composite materials for bone tissue engineering
This paper presents the results of a study of the production of porous biodegradable composite materials by
co-grinding, followed by scaffolding. Dry powders of polylactic acid and nanocrystalline carbonated apatite,
analogous to bone mineral were co-ground in a tumbling ball mill in order to disperse the mineral filler
within the polymer. Porous scaffolds were then made by hot moulding the mixture of the two components
along with a pore-forming agent which was subsequently eliminated by washing. The mechanical resistance
of the scaffolds was evaluated in order to determine the best operating conditions to produce implants
offering optimised properties for use as bone substitutes. It was shown that 30 wt.% of filler and 70 wt.% of
pore-forming agent produce scaffolds which are sufficiently porous and resistan
Influence of Moisture on the Electrical Properties of XLPE Insulation
During their operating service, insulated power cables can be exposed to wet environment. The presence of moisture in cables surroundings may affect the properties of the used insulation material for instance, XLPE widely employed in MV and HV power cables insulation and therefore the reliability of the insulated cables. In order to examine the influence of wet aging conditions on the performances of XLPE insulated cables,samples (plates moulded from granules HFDE 4201-EC) of the same insulation material were exposed during 5600 hours to wet environment inside a cell simulating moisture. The XLPE material used in the present investigation is employed as
insulation for medium voltage (MV) cables (18 / 30 kV). This work presents the results of the effect of aging under wet conditions on the electrical properties of XLPE. The goal of this paper was to investigate the eventual degradation of XLPE insulation under humidity effect by characterization techniques. For this purpose, measurements of dielectric losses factor, relative permittivity, volume resistivity and dielectric strength were performed
An oracle based method to compute a coupled equilibrium in a model of international climate policy
This paper proposes a computational game-theoretic model for the international negotiations that should take place at the end of the period covered by the Kyoto protocol. These negotiations could lead to a self-enforcing agreement on a burden sharing scheme given the necessary global emissions limit that will be imposed when the real extent of climate change is known. The model assumes a non-cooperative behavior of the parties except for the fact that they will be collectively committed to reach a target on total cumulative emissions by the year 2050. The concept of normalized equilibrium, introduced by J.B. Rosen for concave games with coupled constraints, is used to characterize a family of dynamic equilibrium solutions in an m-player game where the agents are (groups of) countries and the payoffs are the welfare gains obtained from a Computable General Equilibrium (CGE) model. The model deals with the uncertainty about climate sensitivity by computing an S-adapted equilibrium. These equilibria are computed using an oracle-based method permitting an implicit definition of the payoffs to the different players, obtained through simulations performed with the global CGE model GEMINI-E
An Oracle method to couple climate and economic dynamics
This paper deals with an oracle method to couple economic and climate models. The approach permits a dialogue between two models pertaining to two different scientific domains, the climate module being a fully-coupled ocean-atmosphere-ice model, whereas the economic module is an adaptation of the neo-classical optimal economic growth paradigm. The paper explains how the Analytic Centre Cutting Plane Method (ACCPM) is implemented to integrate in the optimal economic growth model a constraint on climate change that is computed from the climate model runs. Several experiments show the usefulness of the approach to build new types of integrated assessment meta-model
Production par co-broyage de matériaux composites poreux biodégradables à usage orthopédique
Lâarticle prĂ©sente les rĂ©sultats dâune Ă©tude sur la production de matĂ©riaux composites poreux biodĂ©gradables par co-broyage suivi dâune mise en forme. De lâacide polylactique et une apatite nanocristalline carbonatĂ©e analogue au minĂ©ral osseux, sous forme de poudres, ont Ă©tĂ© cobroyĂ©s dans un broyeur Ă boulets afin de disperser la charge minĂ©rale dans le polymĂšre. Des implants poreux ont ensuite Ă©tĂ© rĂ©alisĂ©s en moulant Ă chaud le mĂ©lange des deux constituants et un agent porogĂšne qui a ensuite Ă©tĂ© Ă©liminĂ© par lessivage. La rĂ©sistance mĂ©canique des implants a enfin Ă©tĂ© caractĂ©risĂ©e. Il a Ă©tĂ© montrĂ© que des pourcentages de 30 % de charge et 70 % dâagent porogĂšne permettent de produire des implants suffisamment poreux et rĂ©sistants
Phosphates du Protérozoïque supérieur dans la chaßne des Dahomeyides (circa 600 Ma) de la région de Bassar (Nord-Togo, Afrique de l'Ouest)
Les phosphates de Bassar (nord du Togo) sont situés dans la partie tectonisée de la couverture du craton ouest-africain, et plus précisément dans les schistes de l'unité structurale de l'Atacora de la chaßne des Dahomeyides. Les roches phosphatées se présentent comme des intercalations d'épaisseur variables (< 30 m). Elles sont généralement constituées de pellets d'apatite plus ou moins pure et recristallisée enrobés dans une matrice essentiellement phosphatée. Ce gisement s'ajoute notamment aux indices d'Aloub Djouana et de Pagala et démontre ainsi une extension fort intéressante des phosphates précambriens dans les unités tectonisées au front des Dahomeyide
- âŠ