Portail HAL UHA (Université de Haute-Alsace)
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Gaussian Unit-simplex Markov random fields as a fast proxy for MRF sampling
No full textMarkov random fields are classical models for Bayesian image modeling, but their sampling relies on traditionally Gibbs techniques, implying a non-negligible computational cost. On the other hand, Gaussian Markov random fields (GMRF), which are used to model continuous and spatially homogeneous variables, can benefit from highly efficient sampling techniques. In this paper, we propose a new discrete Markov field, based on a unit-simplex geometry, and coined Gaussian unit simplex Markov field (GUM). This model is specifically designed to benefit from the GMRF approach for sampling. We show that its sampling complexity is related to the GMRF sampling complexity. Numerical results show this leverages drastic improvement in the sampling time, while sharing similar empirical properties with a classical Markov random field
Synthesis of novel D–π–A-based photosensitive alkoxyamine: application of two-photon polymerization via nitroxide-mediated photopolymerization
No full textInternational audienceWe present an efficient method for surface customization using a novel D–π–A-based photosensitive alkoxyamine. The D–π–A-based chromophore group exhibits remarkable efficiency in the homolytic cleavage of the >NO–C bond enabling the production of well-defined structures through two-photon stereolithography (TPS). Furthermore, we show that surface customization can be achieved in a second step, owing to the “living” character originating from the alkoxyamine and via a Nitroxide Mediated PhotoPolymerization (NMP2) process. Additionally, we investigated how TPS-related parameters such as wavelengths and laser power influence the re-polymerization step
Vertically aligned mesoporous silica films bearing covalently bound tris(2,2-bipyridyl)ruthenium(II) redox photocatalysts
No full textInternational audienceThis work reports a strategy to prepare mesoporous silica films with preferential vertical alignment of pore channels with covalently attached tris(2,2'-bipyridyl)ruthenium(II) redox photocatalysts, i.e. [Ru(bpy)2(bpy')] 2+ (prepared from a precursor grafting agent containing 2,2'-bipyridine (bpy) and derivatized 4,4'-dimethyl-2,2'-bipyridine (bpy') units). This was achieved by the electrochemically assisted self-assembly of vertically-aligned mesoporous silica films containing varying amounts of azide groups and their subsequent derivatization by click coupling with an alkyne-bearing [Ru(bpy)2(bpy')] 2+ reagent. The effectiveness of the functionalization processes was monitored by infrared spectroscopy, indicating a best compromise reached for an azide content large enough to immobilize a high content of [Ru(bpy)2(bpy')] 2+ moieties, but not too large to avoid steric constraints and leading to lower yields of the click reaction. The structural integrity (hexagonal order and mesopore orientation) after functionalization was checked by transmission electron microscopy and grazing-incidence small-angle X-ray scattering. The films were generated on transparent indium-tin oxide electrodes and cyclic voltammetry experiments demonstrated a good electrochemical response via electron hopping between adjacent [Ru(bpy)2(bpy')] 2+ moieties immobilized in the nanochannels, which was dependent on the functionalization level and proved stable upon repetitive potential cycling as a result of their covalent attachment to the silica walls. These films also exhibit luminescence, which can be exploited for photoelectrochemical applications, e.g., detection by electrochemiluminescence or electrochemical regeneration of photocatalyst, as illustrated here from preliminary experiments.</div
Soot Particle Emissions: Formation and Suppression Mechanisms in Gas Turbines
No full textInternational audienceThis article reports on field tests devoted to the emissions of particles from gas turbines (GT) and more particularly to the formation of soot and its suppression by fuel additives. These field tests involved four heavy-duty gas turbines used as power generators and equipped with air atomization systems. These machines were running on natural gas, No. 2 distillate oil, heavy crude oil and heavy fuel oil, respectively. The GT running on natural gas produced no soot or ash and its upstream air filtration system in fact allowed lower concentrations of exhaust particles than those found in ambient air. Soot emitted when burning the three liquid fuels (No. 2 distillate; heavy crude oil; and heavy oil) was effectively reduced using fuel additives based on iron(III), cerium(III) and cerium(IV). Cerium was found to be very effective as a soot suppressant and gave rise to two surprising effects: cerium(III) performed better than cerium(IV) and a “memory effect” was observed in the presence of heat recovery boilers due to the deposition of active cerium species. All of the reported results, both regarding natural gas emissions and soot reduction, are original. A review of the soot formation mechanisms and a detailed interpretation of the test results are provided
Heat generation from swirl-stabilized aluminum-air flames
No full textInternational audienceTo limit global warming, new ways of transporting and storing energy are required. In such a context, metals are currently being considered as suitable energy carriers. In this investigation, aluminum-air flames were stabilized by a swirled-flow in a combustion chamber for heat production. Commercial Al particles were tested in various size range (from 0 to 400 µm). The total air flow rate injected varied from 5.6 (n)m3/h to 8 (n)m3/h corresponding to geometric swirl number ranging from 0.7 to 28. Self-igniting and continuous aluminum flames stopped after more than five minutes were established. Aluminum particles in the size range 0 to 36 µm were needed to ignite the flame. Indeed, no flame ignition was obtained with the 36 to 50 µm size range under these conditions. Increasing the swirl number from 7 to 14 and 28 enabled increasing the overall Al conversion rate. More than 45 % of the heat delivered by aluminum combustion was recovered in the combustion chamber which was water-cooled. Samples collected in the combustion chamber were observed by optical microscopy. Some unburnt or partly burnt aluminum particles were observed mainly for the samples collected at the inlet of the combustion chamber
Connecting the dots: Isolated trails of detected narrow rivers in multispectral images
No full textInternational audienceDetecting and monitoring rivers, specially narrow river trails hold substantial economic, societal, and cultural importance. However, segments of narrow trails of rivers may appear as isolated from remotely sensed images.In this paper, we address the problem of localization of narrow rivers in remote sensing images.As these rivers may be occluded, thin, or under-resolved, pixel-based methods might not be stable enough to ensure satisfying recovery.In this paper, we propose a two-step approach: first, we detect the main river course and larger segment through a pixel-based approach relying on the normalized difference water index. Second, after missing segments are identified, we propose to connect the dots through a Bézier curve adjustment using a dedicated greedy optimization approach.Results on synthetic and real images show the interest of the proposed approach, with respect to pixel-based alternatives
Identification des clés RH contribuant à la résilience organisationnelle – le cas d’une association en prise avec la crise sanitaire
No full textNational audienc
La production politique des paysages nucléaires : le cas de la centrale de Wylfa (Pays de Galles)
No full textInternational audienceBuilding on previous works inviting to take into account the political dimensions of industrial landscapes, this paper offers to analyze the construction of a nuclear power plant as a politics of landscape production. We focus on the case of Wylfa Nuclear Power plant, in the North of Wales. In the early 1960, its construction was presented as a technological promise of modernization for a rural area suffering from demographic and industrial decline. Simultaneously, debates over landscape preservation in the United Kingdom led to its institutionalization, translating into the 1957 Electricity Act forcing new power infrastructure to include amenity clauses. Mobilizing the renewal of materialist approaches in energy geography, our paper considers landscapes as resulting from the interrelations between materials elements, actors and ideas. Relying on fieldwork conducted at Wylfa in 2021, including observations, archival work and semi-structured interviews, we identify a series of variables, which frame the material and sensible forms of nuclear landscapes.Dans la continuité de travaux qui invitent à prendre en compte la dimension politique des paysages industriels, nous proposons d’analyser la construction d’une centrale nucléaire comme une politique de production du paysage. Pour cela, nous prenons le cas de la centrale de Wylfa, au Pays de Galles. Au début des années 1960, sa construction est présentée comme une promesse de modernisation pour une région rurale souffrant de déclin industriel. En parallèle, les débats sur la préservation des paysages se structurent au Royaume-Uni, s’institutionnalisant dans l’Electricity Act de 1957, qui est le premier texte législatif majeur à comporter une clause sur l’aménité du paysage et sa préservation. Mobilisant le renouveau matérialiste de la géographie des énergies, nous proposons de considérer les paysages comme la résultante de relations entre des éléments matériels, des acteurs et des idées. En nous reposant sur une enquête de terrain menée en 2021, alliant observation, travail d’archives et entretiens, nous identifions une série de variables (techniques, juridiques et politiques) qui conditionnent la forme d’un paysage nucléaire
Tensile Characterization of Single Plant Fibres : a Benchmark Study
No full textInternational audienceOver the past 20 years, a large number of studies have been carried out to determine the mechanicalproperties of plant fibres. Most studies focus on the use of tensile tests on elementary fibres. Despite itsadvantages, this method is also time-consuming and challenging because of the tiny size of the fibresand the many sources of uncertainty.The aim of the present benchmark study was to gain a better understanding and quantify the sources ofvariability when estimating the tensile properties of plant fibres. For that purpose, three batches of fibreswere selected: two plant fibres, i.e. combed hemp and flax fibres as well as a synthetic organic fibre, i.e.aramid fibres, for benchmark purpose. A total of approximately 1250 fibres were tested. 9 researchgroups participated in this interlaboratory exercise.Results highlight significant intra- and inter-laboratory variability. Human factors and experimentalprocedures, especially for the estimation of the fibre cross-sectional area and the tensile strain, wereidentified as the main sources of scatter in tensile properties. Post-processing procedures, particularlydetermining the starting point of the tensile test, are also crucial, involving the elimination of slacks infibre and load train
