Performances d'une centrale à concentrateur de Fresnel de moyenne puissance sur sites Algériens

International audienceL'objectif du présent travail est de caractériser une centrale à concentrateur de Fresnel de moyenne puissance (5MWe) sur différents sites Algériens (Sahara), ces sites ont été choisis pour comparaison en déplaçant la centrale dans ces derniers, à savoir Hassi-R'mel, Tamanrasset, Béni-Abbes, et El Oued. Une modélisation théorique a permis la détermination du nombre optimum des miroirs à ne pas dépasser pour éviter les effets d'ombre, blocage et l'effet cosinus. Le nombre optimum de miroirs a été estimé à 40 miroirs. Par ailleurs, une simulation a été réalisée à l'échelle horaire : elle concerne l'ensoleillement, le système 'champ', et le système 'récepteur'. Les résultats de la simulation sont représentés en moyenne annuels. Les rendements, la production énergétique annuelle, et le coût du kWh sont évalués. En effet, le calcul du rendement diffère d'un site à un autre avec des valeurs de 15.7%, 11.8%,11.6%, et 10.4% respectivement pour les sites Tamanrasset, El Oued, Béni-Abbes, Hassi R'mel. Les performances thermiques et les résultats technico-économiques sont évalués aussi pour ces mêmes sites. Mots clés : Énergie solaire, concentrateur solaire à miroirs de Fresnel, les centrales solaires thermiques, performance, les centrales thermoélectriques

Building specialized bilingual lexicons using large-scale background knowledge

Conference of 2013 Conference on Empirical Methods in Natural Language Processing, EMNLP 2013 ; Conference Date: 18 October 2013 Through 21 October 2013; Conference Code:111413International audienceBilingual lexicons are central components of machine translation and cross-lingual information retrieval systems. Their manual construction requires strong expertise in both languages involved and is a costly process. Several automatic methods were proposed as an alternative but they often rely on resources available in a limited number of languages and their performances are still far behind the quality of manual translations. We introduce a novel approach to the creation of specific domain bilingual lexicon that relies on Wikipedia. This massively multilingual encyclopedia makes it possible to create lexicons for a large number of language pairs. Wikipedia is used to extract domains in each language, to link domains between languages and to create generic translation dictionaries. The approach is tested on four specialized domains and is compared to three state of the art approaches using two language pairs: French-English and Romanian-English. The newly introduced method compares favorably to existing methods in all configurations tested

Micro-spikes formed on mesoporous silicon by UV picosecond laser irradiation

International audienceConical spikes with sizes ranging between 0.2 and 5 µm were formed on a mesoporous silicon surface under ultraviolet picosecond laser irradiation in ambient air. Scanning electron microscopy was employed to visualize the successive steps in the formation of the spikes. On increasing the number of shots (up to 1000) at a fluence of 400 mJ/cm2, an increase in the size and an enhancement in the distribution of spikes were observed. The experimental observations revealed that the formation and the growth of these structures were mainly due to material ablation and removal mechanisms. FTIR analysis on several large (5X 5 mm2) irradiated zones showed an enhancement in the absorption coefficient mainly in the IR range from 1 to 8 µm versus the size of the microstructures

Optimization of diode pumped solid state ultraviolet laser dicing of silicon carbide chips using design of experiment methodology

International audienceThis paper investigates the laser micromachining of SiC-4H wafers with an ultraviolet (355 nm) nanosecond source. The design of experiment methodology was used to study the effect of pulse energy, number of passes, defocus, and scanning speed on scribing depth and was modeled with Design Expert (R) software. Pulse energy and scanning speed were found to have a significant effect on scribe depth (by a factor of 10 compared to defocus), while the effect of the number of passes varied with pulse energy and scanning speed. The model predicted a narrow set of processing parameters to scribe half of the wafer thickness (180/360 mu m). A more fundamental study was also conducted in order to validate literature observations on the ablation mechanism. A brief comparison between conventional blade dicing and the laser scribe-break method was performed on a 3 in. diameter wafer. It was discovered that a possible gain of gross die (number of usable chips per wafer) of 7% could be achieved which could provide a useful economic benefit