The reality of virtual environments

In this article, the reality of virtual environment is described in detail. Highly detailed three-dimensional (3D) computer models and environments are commonly used in design, manufacturing, simulation, and entertainment. These virtual environments (VEs) are often successful at appearing realistic when time remains still, but as the mobile objects are set into motion and interact with their surroundings, the movements often appear unnatural. In many prerendered VEs used for entertainment purposes, all of the object's motions must be handmade by 3-D animators in a process that is time consuming and lacks strict realism. In other VEs such as the first generation of 3-D video games, objects are modeled by their bounding space or by a sphere that surrounds all of the 3-D model's vertices. In these cases, the motions are often quite linear, and the collision response algorithms are quite simplistic; some even revert to stopping an object's motion when it collides with the environment. These techniques are much too minimal and greatly reduce the level of realism in VEs.     

Plasma-refining process to provide solar-grade silicon

A new purification process has been developed to refine metallurgical silicon using a plasma torch blowing at the surface of the silicon to be purified. An inductive system has been designed to maintain the silicon in a liquid state, control the shape of its free surface and to provide a strong electromagnetic stirring, ensuring a rapid transfer of pollutants from the bulk liquid to its surface. A numerical model is used to control the design of the induction system and to look at its potential evolutions. It is shown that even with a reduced induction power, the stirring is sufficient to provide a very rapid mass transfer in the liquid, compared to the reaction rate at the surface (deduced from experiments). The effect of the power and frequency of the induction power is also discussed, showing that it gives the possibility to control the heating power and the shape of the surface, and even to push the liquid away from any contact with the crucible. The material provided by the refining process operating in such conditions was used to produce solar cells that reached a conversion efficiency of 12.7%     

Group VI transition metal carbides as alternatives in the hydrodechlorination of chlorofluorocarbons

The synthesis of transition metal carbides of tungsten and molybdenum has been carried out via temperature programmed reactions (TPRs) of metal oxides or passivated nitrides. Their specific chloropentafluoroethane conversion rates were at best one order of magnitude less than that of a reference Pd based catalyst. The intrinsic rates range from 4.7 to 14.7 nmol m⁻² s⁻¹ and decrease as follows: Mo₂C>WC>W₂C≈WC_1−x>MoC_1−x. The group VI carbide samples catalyse hydrodehalogenation and dehydrofluorination. WC appears to be as selective towards pentafluoroethane (HFC-125) as the Pd based catalyst. Then the selectivity decreases in the following sequence: W₂C>Mo₂C>WC_1−x>MoC_1−x. All the carbide catalysts deactivate at the early stages of the reaction. Based on the XPS results and the product distribution of the reaction, the deactivation has been mainly attributed to a site blocking phenomenon due to a strong deposit of polymeric carbon and of hydrofluorocarbon polymers. Polymerisation of detected unsaturated compounds take place on acidic sites probably generated by fluoride and/or chloride in the course of the reaction.     

Microwave radiometric imaging at 3 GHz for the exploration ofbreast tumors

A process of microwave radiometric imaging at 3 GHz permits the mapping of radiometric intensities on a square area about half a decimeter on a side. These data, translated in terms of a colored image, point out the existence of lateral temperature gradients in tissues. This system was initially used for examining large breast tumors; at present, it is also used for detecting smaller, impalpable tumors. The rules for characterizing benignancy or malignancy of small tumors which appear in a mammographic examination (X-rays) are defined. The definition of an appropriate parameter, deduced from this image processing, makes it possible to indicate benignancy or malignancy. In experiments conducted on 18 patients, all the malignant lesions had a radiometric ratio greater than 65%, while benign lesions were below 55%. However, a zone of uncertainty (between 55% and 70%) exists where it is wise not to assert malignancy or benignancy     

Influence of the reactant concentration in selective hydrogenation of 1,3-butadiene over supported gold catalysts under alkene rich conditions: A consideration of reaction mechanism

This article is about the reaction of selective hydrogenation of 1,3-butadiene performed in an excess of alkenes (propene/butadiene ratio = 100) over supported gold catalysts, so as to mimic the conditions of purification of light alkenes (C4 cuts) from the presence of impurities (highly unsaturated compounds, 1–3%). Gold was found highly selective (close to 100%, no propane or butane formation) for the hydrogenation of butadiene to butenes at 100% conversion of butadiene. The influence of the concentrations of the various reactants, i.e. hydrogen, butadiene and propene, on the rates of butadiene and propene hydrogenation was investigated, and the apparent reaction orders were deduced from the dependence of rate on partial pressure in the gas phase. The reason for the high selectivity of gold catalysts is that the reaction of hydrogenation of alkenes occurs at much higher temperature (0.1% conversion at 300°C) than that of selective hydrogenation of butadiene (100% at T <170°C). Moreover, the presence of propene has only a limited influence on the reaction of butadiene hydrogenation, while butadiene has no influence on propene hydrogenation; the two reactions of hydrogenation hardly influence each other. Hydrogen dissociation is the rate limiting step of the reaction (partial order of 0.7 and 1 with respect to H₂ for butadiene and propene hydrogenation, respectively), responsible for the low activity of gold. The catalytic properties of gold were compared to those of palladium-based catalysts, and reasons for their different behaviour were discussed.     

Catalytic reduction of nitrogen monoxide by propene in the presence of excess oxygen over gold based ceria catalyst

The catalytic reduction of nitrogen monoxide by propene in the presence of excess oxygen over gold based ceria catalyst was studied. Adsorption and temperature programmed desorption of NO/O₂ on Au/CeO₂ reveal that the catalyst adsorbs and desorbs NO over a large range of temperature. A maximum of 26% conversion of NO _x was obtained around 210 °C, with a selectivity of 50% to N₂.     

Solar cells from upgraded metallurgical grade (UMG) and plasma-purified UMG multi-crystalline silicon substrates

High impurity concentrations do not allow the direct use of upgraded metallurgical grade (UMG) Si for PV production. A newly developed prototype inductive plasma-purification system and process allowed the significant reduction of the elements B, C, O, P, Al, Ca, Fe and Ti, depending on the duration of the treatment. Based on this type of purification, it is shown that subsequent appropriate low-cost cell-processing yields homogeneously distributed energy-conversion efficiencies throughout the cast ingots. Stabilised cell efficiencies of up to 14.7% were already experimentally shown to be attainable on highly B-doped (ρ<0.1 Ω cm) 102 cm² multi-crystalline Si substrates of high purity. On plasma-purified UMG p-type 0.1–0.2 Ω cm ingots, efficiencies of up to 12.38% are reached, to be compared with about 10.12% on the same material without prior plasma treatment. Some light-induced degradation is present on processed samples, which is most likely linked to the presence of metastable boron–oxygen complexes in the material, and results in stabilised efficiencies of, respectively, 12.19% and 10.00%.