Étude du frittage non-conventionnel de céramiques de type YAG:Nd en présence d’ajout de silice

L’objectif de cette étude était de cerner l’influence du procédé de frittage non conventionnel employé pour la mise en forme des pièces (frittage SPS ou post-frittage HIP) sur l’activation des processus densifiants. Il s’avère qu’un traitement SPS des poudres initiales permet d’abaisser la température de début de frittage et conduit dans certaines conditions à des pièces translucides ou transparentes. L’influence de la silice, introduit comme ajout de frittage, et du néodyme, introduit comme dopant, est également discutée dans ce travail. Le post-frittage HIP, quant à lui, permet l’élimination de la porosité résiduelle dans les échantillons, ce qui conduit à la transparence des pièces réalisées

On Finslerized Absolute Parallelism spaces

The aim of the present paper is to construct and investigate a Finsler structure within the framework of a Generalized Absolute Parallelism space (GAP-space). The Finsler structure is obtained from the vector fields forming the parallelization of the GAP-space. The resulting space, which we refer to as a Finslerized Parallelizable space, combines within its geometric structure the simplicity of GAP-geometry and the richness of Finsler geometry, hence is potentially more suitable for applications and especially for describing physical phenomena. A study of the geometry of the two structures and their interrelation is carried out. Five connections are introduced and their torsion and curvature tensors derived. Some special Finslerized Parallelizable spaces are singled out. One of the main reasons to introduce this new space is that both Absolute Parallelism and Finsler geometries have proved effective in the formulation of physical theories, so it is worthy to try to build a more general geometric structure that would share the benefits of both geometries.Comment: Some references added and others removed, PACS2010, Typos corrected, Amendemrnts and revisions performe

Nuclear fuel cycle, with a liquid ore and fuel:toward renewable energy

To fulfill the conditions required for a nuclear renewable energy concept, one has to explore a combination of processes going from the front end of the nuclear fuel cycle to the fuel production and the energy conversion using specific fluid fuels and reactors. Extraction of uranium from a diluted fluid ore such as seawater has been studied in various countries worldwide. This extraction should be carried out parsimoniously. An extraction rate of 103 tons of U per year over centuries would not modify significantly the equilibrium concentration of uranium in the oceans (3.3 ppb). This equilibrium results from the input of 104 tons of U per year by river waters and its scavenging on the sea floor from the 1.37 × 1018 tons of water in the oceans. For a renewable uranium extraction, the use of a specific biomass material is suggested to adsorb uranium and subsequently other transition metals. The uranium loading on the biomass would be around 100 mg per kg. After contact time, the loaded material would be dried and burned (CO2 neutral) with heat conversion into electricity. The uranium ‘burning’ in a molten salt fast reactor helps to optimize the energy conversion by burning all actinide isotopes with an excellent yield for producing a maximum amount of thermal energy from fission and converting it into electricity. This optimisation can be reached by reducing the moderation and the fission product concentration in the liquid fuel/coolant. These effects can be achieved by using a maximum amount of actinides and a minimum amount of alkaline/earth alkaline elements yielding a harder neutron spectrum. Under these optimal conditions the consumption of natural uranium would be 7 tons per year and per gigawatt (GW) of produced electricity. The coupling of uranium extraction from the sea and its optimal utilisation in a molten salt fast reactor should allow nuclear energy to gain the label renewable. In addition, the amount of seawater used by a nuclear power plant to cool the last coolant fluid and the turbine would be ∼2.1 × 109 tons per year for a fast molten salt reactor, corresponding to 7 tons of natural uranium extractable per year. This practice justifies the label renewable

Polymethacrylates.Material Selection For Medical Applications:Requirements For Several Kinds of Medical Applications

This chapter reviews several cases of methacrylate-based polymers used for medical applications. The main chemicals and fillers used for elaborating biomaterials are presented, together with the main synthesis reactions. Their properties are recalled and discussed using the well-established structure-properties relationships of polymer physicochemistry. Last, the main degradation mechanisms are recalled, together with their consequences on the engineering properties of polymethacrylates, in order to predict the long-term in vivo behavior of such complex materials

Efeitos da sombra e da aspersão de água na produção de leite de vacas da raça Holandesa durante o verão - DOI: 10.4025/actascianimsci.v26i1.1961

The objectives of this study were to evaluate the effect s of natural and artificial shade and sprinkling water on the physiologic responses (rectal temperature and respiration rate), and productive (fat, protein and somatic cells) of 20 Holstein-Friesian dairy cows, during the summer. The cows were divided in two groups and submitted for two environment (sun and shade) with and without water sprinkling before and after milking. Wind speed, temperature and relative humidity, black globe temperature and milk yield were recorded daily. Rectal temperature and respiration rate were measured twice weekly on the morning and evening; milk analyzed fortnightly. Respiration rate, milk yield and somatic cell number were affected (P < 0,01) for considered meteorological factors. Rectal temperature did not affect by treatments shade supply and water sprinkling showed to be profitable to the cows.Os objetivos deste estudo foram avaliar os efeitos da sombra natural e artificial e da aspersão de água nas respostas fisiológicas (temperatura retal e frequência respiratória) e produtivas (gordura, proteína e células somáticas) de 20 vacas leiteiras da raça Holandesa, durante o verão. As vacas foram divididas em dois grupos e submetidas a dois ambientes (sol e sombra) com e sem aspersão de água antes e depois da ordenha. A velocidade do vento, temperatura e umidade relativa, temperatura do globo-negro e produção de leite foram registradas diariamente. A temperatura retal e a freqüência respiratória foram medidas duas vezes por semana de manhã e à tarde; o leite, analisado quinzenalmente. A freqüência respiratória, a produção de leite e a contagem de células somáticas foram influenciadas (p < 0,01) pelos fatores meteorológicos considerados. A temperatura retal não sofreu influência dos tratamentos. O fornecimento de sombra e a aspersão de água mostraram ser benéficas às vacas