Membrane patterned by pulsed laser micromachining for proton exchange membrane fuel cell with sputtered ultra-low catalyst loadings

International audienceProton exchange membranes were nano-and micro-patterned on their cathode side by pressing them against stainless steel molds previously irradiated by a Ti:Sapphire femtosecond laser. The membranes were associated to ultra-low loaded thin catalytic layers (25 µgPt cm-2) prepared by plasma magnetron sputtering. The Pt catalyst was sputtered either on the membrane or on the porous electrode. The fuel cell performance in dry conditions were found to be highly dependent on the morphology of the membrane surface. When nanometric ripples covered by a Pt catalyst were introduced on the surface of the membrane, the fuel cell outperformed the conventional one with a flat membrane. By combining nano-and micro-patterns (nanometric ripples and 11-24 µm deep craters), the performance of the cells was clearly enhanced. The maximum power density achieved by the fuel cell was multiplied by a factor of 3.6 (at 50 °C and 3 bars): 438 mW cm-2 vs 122 mW cm-2. This improvement is due to high catalyst utilization with a high membrane conductivity. When Pt is sputtered on the porous electrode (and not on the membrane), the contribution of the patterned membrane to the fuel cell efficiency was less significant, except in the presence of nanometric ripples. This result suggests that the patterning of the membrane must be consistent with the way the catalyst is synthesized, on the membrane or on the porous electrode

Investigation of pulsed laser induced dewetting in nanoscopic metal films

Hydrodynamic pattern formation (PF) and dewetting resulting from pulsed laser induced melting of nanoscopic metal films have been used to create spatially ordered metal nanoparticle arrays with monomodal size distribution on SiO_{\text{2}}/Si substrates. PF was investigated for film thickness h\leq7 nm < laser absorption depth \sim11 nm and different sets of laser parameters, including energy density E and the irradiation time, as measured by the number of pulses n. PF was only observed to occur for E\geq E_{m}, where E_{m} denotes the h-dependent threshold energy required to melt the film. Even at such small length scales, theoretical predictions for E_{m} obtained from a continuum-level lumped parameter heat transfer model for the film temperature, coupled with the 1-D transient heat equation for the substrate phase, were consistent with experimental observations provided that the thickness dependence of the reflectivity of the metal-substrate bilayer was incorporated into the analysis. The spacing between the nanoparticles and the particle diameter were found to increase as h^{2} and h^{5/3} respectively, which is consistent with the predictions of the thin film hydrodynamic (TFH) dewetting theory. These results suggest that fast thermal processing can lead to novel pattern formation, including quenching of a wide range of length scales and morphologies.Comment: 36 pages, 11 figures, 1 tabl

Direct measurements of the energy flux due to chemical reactions at the surface of a silicon sample interacting with a SF6 plasma

Energy exchanges due to chemical reactions between a silicon surface and a SF6 plasma were directly measured using a heat flux microsensor (HFM). The energy flux evolution was compared with those obtained when only few reactions occur at the surface to show the part of chemical reactions. At 800 W, the measured energy flux due to chemical reactions is estimated at about 7 W.cm\^{-2} against 0.4 W.cm\^{-2} for ion bombardment and other contributions. Time evolution of the HFM signal is also studied. The molar enthalpy of the reaction giving SiF4 molecules was evaluated and is consistent with values given in literature.Comment: 3 page

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

A neural approach for inducing multilingual resources and natural language processing tools for low-resource languages

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Metallic thin films heated by pulsed lasers. Numerical simulation of the thermal field and the melting kinetics

This modeling is especially applied to the pulsed laser induced heating and melting of a metallic film deposited on a substrate. Study of the thermal field over a surface is usually performed by considering the assumption of ‘semi-infinite medium’. However, a thin film deposited on a rough substrate surface induces bad thermal contacts commonly known as ‘thermal contact resistance’. This interfacial thermal resistance affects the melting kinetics mainly when the film thickness (Z) is small comparatively to the heat diffusion length (Z$_T$). In this work the heat conduction equation and related boundary conditions are resolved by using the implicit finite differences method. The heat source (i.e. the laser intensity) is treated as a surface boundary layer. The thermal contact resistance is introduced in the computation procedure when the heat wave propagation reaches the thin film/substrate interface. It is then possible to calculate the critical temperatures and the melting threshold fluence for high and low contact resistance values. Under these conditions, the temperature profile and melting depth are plotted considering different thickness.. Finally, for 750 mJ/cm² excimer laser fluence and 0.1 cm²/s thin film apparent diffusivity results show that for Z/Z$_T$ higher than 0.5, there is no sensitive effect of the thermal contact resistance on the melting kinetics

Romanized Arabic and Berber detection using prediction by partial matching and dictionary methods

Conference of 13th IEEE/ACS International Conference of Computer Systems and Applications, AICCSA 2016 ; Conference Date: 29 November 2016 Through 2 December 2016; Conference Code:128291International audienceArabic is one of the Semitic languages written in Arabic script in its standard form. However, the recent rise of social media and new technologies has contributed considerably to the emergence of a new form of Arabic, namely Arabic written in Latin scripts, often called Romanized Arabic or Arabizi. While Romanized Arabic is an informal language, Berber or Tamazight uses Latin script in its standard form with some orthography differences depending on the country it is used in. Both these languages are under-resourced and unknown to the state-of-the-art language identiüers. In this paper, we present a language automatic identifier for both Romanized Arabic and Romanized Berber. We also describe the built linguistic resources (large dataset and lexicons) including a wide range of Arabic dialects (Algerian, Egyptian, Gulf, Iraqi, Levantine, Moroccan and Tunisian dialects) as well as the most popular Berber varieties (Kabyle, Tashelhit, Tarifit, Tachawit and Tamzabit). We use the Prediction by Partial Matching (PPM) and dictionary-based methods. The methods reach a macro-average F-Measure of 98.74% and 97.60% respectively

Evaluating the impact of using a domain-specific bilingual lexicon on the performance of a hybrid machine translation approach

Conference of 10th International Conference on Recent Advances in Natural Language Processing, RANLP 2015 ; Conference Date: 7 September 2015 Through 9 September 2015; Conference Code:116983International audienceThis paper describes an Example-Based Machine Translation prototype and presents an evaluation of the impact of using a domain specific vocabulary on its performance. This prototype is based on a hybrid approach which needs only monolingual texts in the target language and consists to combine translation candidates returned by a cross-language search engine with translation hypotheses provided by a finite-state transducer. The results of this combination are evaluated against a statistical language model of the target language in order to obtain the n-best translations. To measure the performance of this hybrid approach, we achieved several experiments using corpora on two domains from the European Parliament proceedings (Europarl) and the European Medicines Agency documents (Emea). The obtained results show that the proposed approach out performs the state-of-the-art Statistical Machine Translation system Moses when texts to translate are related to the specialized domain

Measurement of total phenolic content and antioxidant activity of aerial parts of medicinal plant Coronopus didymus.

Objective: To evaluate the total phenolic content and compare the antioxidant activity of various solvent extracts and fractions from the aerial parts of Coronopus didymus through various assays. Methods: Total phenolic content was determined using the Folin-Ciocalteu assay and the in vitro antioxidant activity of a number of different extracts was investigated in a dose-dependent manner with three different methods: the 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and ferric reducing antioxidant power (FRAP) assays. A flavone was isolated from the most active ethanolic extract with high antioxidant activity using size exclusion chromatography. IC50 values were calculated for the DPPH and ABTS methods. The FRAP activity was assessed in terms of μM Fe (II) equivalent. Results: The phenolic content was found to be highest in the ethanol extract (CDA Et; 47.8 mM GAE) and the lowest in the dichloromethane extract (CDA DCM; 3.13 mM GAE). The ethanol extract showed high radical scavenging activity towards DPPH and ABTS radicals with IC50 values of (7.80 × 102) and (4.32 × 102) μg/mL, respectively. The most active ethanol extract had a FRAP value of 1921.7 μM Fe (II) equivalent. The isolated flavone F10C (5,7,4′-trihydroxy-3′-methoxy flavone) was far more effective for scavenging free radicals in the DPPH and ABTS assays with IC50 of 43.8 and 0.08 μg/mL, than the standard trolox, with IC50 values of 97.5 and 21.1 μg/mL, respectively. In addition, the flavone F10C and the standard ascorbic acid had FRAP values of 1621.7 and 16 038.0 μM Fe (II) equivalents, respectively. Conclusions: The total phenolic content of extracts in decreasing order is ethanol extract (CDA Et) &gt; acetone extract (CDA ACE) &gt; phenolic extract (CDA MW) &gt; n-hexane extract (CDA nHX)&gt; chloroform extract (CDA CHL) &gt; dichloromethane extract (CDA DCM). The ordering of extracts in terms of antioxidant activity from highest to lowest is CDA Et &gt; CDA MW &gt; CDA DCM &gt; CDA CHL &gt; CDA ACE &gt; CDA nHX in DPPH, ABTS and FRAP assays. A significant relationship is found between antioxidant potential and total phenolic content, suggesting that phenolic compounds are the major contributors to the antioxidant activity of C. didymus.</p