Simultaneous measurements of PIV, anisole-PLIF and OH-PLIF for investigating back-supported stratified flame propagation in lean and nonflammable mixtures

International audienceIn an effort to reduce pollutant emissions and increase energy efficiency, partially premixed combustion has been integrated into many new combustion technologies. The present study investigated lean back-supported flames in a stratified combustion regime. This strategy leads to hybrid combustion regimes, ranging between fully premixed and fully non-premixed reactants, with a large panel of flame structures and properties requiring to be characterized. Outwardly propagating flames were observed following ignition under laminar stratification conditions generated in a constant volume vessel. The quantitative analysis of the flame properties relied on simultaneous PIV measurements to obtain local flame burning velocities and stretch rates and used anisole-PLIF measurements to calculate the equivalence ratio. Simultaneous OH-PLIF measurements were used to differentiate between the burned gas boundaries and the active flame front. This differentiation was necessary to investigate the nonflammable mixture. The OH-gradient measurement proved to be suitable for distinguishing burned gas interfaces from active flame fronts. Simultaneous OH-and anisole-PLIF measurements were used to estimate the thermal flame thickness. Two flame families were investigated: in family A the flame was ignited in a lean mixture (φ=0.6) with a rich stratification; in family B the mixture in the chamber was nonflammable. In rich mixtures ignition compensated for the non-equidiffusive effects of the lean propane flame and reinforced the flame's stretch resistance. Both a flammable and a nonflammable mixture were investigated to determine the time scales of the back-supported propagation for the given stratification. The enhanced combustion regime allowed the flame to propagate with an active flame front, even in the nonflammable mixture. Combustion continued for a few milliseconds before the flame extinguished. The richer the stratification, the longer the combustion lasted in the nonflammable mixture

Modelling and optimising the marginal expansion of an existing district heating network

Although district heating networks have a key role to play in tackling greenhouse gas emissions associated with urban energy systems, little work has been carried out on district heating networks expansion in the literature. The present article develops a methodology to find the best district heating network expansion strategy under a set of given constraints. Using a mixed-integer linear programming approach, the model developed optimises the future energy centre operation by selecting the best mix of technologies to achieve a given purpose (e.g. cost savings maximisation or greenhouse gas emissions minimisation). Spatial expansion features are also considered in the methodology. Applied to a case study, the model demonstrates that depending on the optimisation performed, some building connection strategies have to be prioritised. Outputs also prove that district heating schemes' financial viability may be affected by the connection scenario chosen, highlighting the necessity of planning strategies for district heating networks. The proposed approach is highly flexible as it can be adapted to other district heating network schemes and modified to integrate more aspects and constraints

Bioavailable Trace Metals in Neurological Diseases

Medical treatment in Wilson’s disease includes chelators (d-penicillamine and trientine) or zinc salts that have to be maintain all the lifelong. This pharmacological treatment is categorised into two phases; the first being a de-coppering phase and the second a maintenance one. The best therapeutic approach remains controversial, as only a few non-controlled trials have compared these treatments. During the initial phase, progressive increase of chelators’ doses adjusted to exchangeable copper and urinary copper might help to avoid neurological deterioration. Liver transplantation is indicated in acute fulminant liver failure and decompensated cirrhosis; in cases of neurologic deterioration, it must be individually discussed. During the maintenance phase, the most important challenge is to obtain a good adherence to lifelong medical therapy. Neurodegenerative diseases that lead to a mislocalisation of iron can be caused by a culmination of localised overload (pro-oxidant siderosis) and localised deficiency (metabolic distress). A new therapeutic concept with conservative iron chelation rescues iron-overloaded neurons by scavenging labile iron and, by delivering this chelated metal to endogenous apo-transferrin, allows iron redistribution to avoid systemic loss of iron

Chelators in Iron and Copper Toxicity

Purpose of Review Chelation therapy is used for diseases causing an imbalance of iron levels (for example haemochromatosis and thalassaemia) or copper levels (for example Menkes’ and Wilson’s diseases). Currently, most pharmaceutical chelators are relatively simple but often have side effects. Some have been taken off the market. This review attempts to find theory and knowledge required to design or find better chelators. Recent Findings Recent research attempting to understand the biological mechanisms of protection against iron and copper toxicity is reviewed. Understanding of molecular mechanisms behind normal iron/copper regulation may lead to the design of more sophisticated chelators. The theory of metal ion toxicity explains why some chelators, such as EDTA, which chelate metal ions in a way which exposes the ion to the surrounding environment are shown to be unsuitable except as a means of killing cancer cells. The Lewis theory of acids and bases suggests which amino acids favour the attachment of the hard/intermediate ions Fe2+, Fe3+, Cu2+ and soft ion Cu+. Non-polar amino acids will chelate the ion in a position not in contact with the surrounding cellular environment. The conclusion is that only the soft ion binding cysteine and methionine appear as suitable chelators. Clearly, nature has developed proteins which are less restricted. Recent research on naturally produced chelators such as siderophores and phytochemicals show some promise as pharmaceuticals. Summary Although an understanding of natural mechanisms of Fe/Cu regulation continues to increase, the pharmaceutical chelators for metal overload diseases remain simple non-protein molecules. Natural and synthetic alternatives have been studied but require further research before being accepted

Mimer le vivant pour piéger les radionucléides

International audienceLes peptides sont très utilisés en chimie médicinale car ils présentent de nombreux avantages pour des utilisations in vivo par rapport aux molécules purement synthétiques. Comme les protéines, ils sont solubles dans les fluides biologiques et leur dégradation conduit à des acides aminés bio-compatibles, ce qui limite leur toxicité. Des peptides aux séquences bien choisies peuvent mimer la structure des protéines et donc reproduire des interactions moléculaires essentielles dans le vivant, entre deux protéines ou entre des protéines et l'ADN par exemple. Mimer ces interactions permet non seulement d'étudier les mécanismes du vivant mais aussi de bloquer certaines réactions biologiques indésirables, un point crucial pour qui veut mettre au point des médicaments inhibant ces réactions. Les peptides peuvent également piéger-ou chélater-des ions métalliques. À ce titre, ils sont donc des candidats intéressants pour mettre au point des molé- Les peptides sont des molécules qui ressemblent aux protéines présentes dans les organismes vivants. Ils sont constitués des mêmes briques élémentaires-les acides aminés-, liés entre eux par des liaisons amides primaires, dites « peptidiques » (figure p. 40). Il existe 20 acides aminés naturels, qui diffèrent par la nature de leur chaîne latérale. Ces acides aminés donnent naissance à de très nombreuses combinaisons, caractérisées par la grande variété de protéines du vivant. En général, on considère que les peptides possèdent moins de 70 à 80 acides aminés quand les protéines peu-vent être beaucoup plus longues. La présence de liaisons peptidiques dans les peptides et les protéines impose des structures tridimensionnelles particulières, mainte-nues par de nombreuses liaisons hydrogène. Les plus communes sont les structures en hélice α et en feuillet β, mais il existe aussi des structures aléatoires sans réelle organisation tridimensionnelle. cules visant à éliminer des métaux toxiques de l'organisme. Ces com-posés modèles sont également des outils très utiles pour étudier les interactions des métaux avec les protéines, interactions qui sont à l'origine de nombreux processus biologiques vitaux ou néfastes. PIÈGES À MÉTAUX De nombreux ions métalliques essentiels sont efficacement piégés ou chélatés dans des sites bien définis de protéines (1). Certains interviennent ainsi directement dans des réactions chimiques ou biologiques nécessaires à la vie, à l'instar du fer de l'hémoglobine sur lequel se fixe l'oxygène lors du processus de respiration, quand d'autres sont nécessaires pour imposer des structures particulières aux protéines, comme les doigts de zinc. Tout métal, même essentiel, peut néanmoins s'avérer toxique si sa concentration excède les valeurs physiologiques. La concentration cellulaire en métaux est donc finement régulée Utilisés ou produits par les centrales électronucléaires, les actinides sont des radionucléides sans aucune fonction biologique connue et sont toxiques à la fois par leurs propriétés chimiques et radiologiques. C'est pourquoi les chimistes élaborent des molécules pour les piéger à l'intérieur de l'organisme et limiter ainsi leur toxicité en cas de contamination suite à une exposition accidentelle. Une des approches utilisées pour éliminer les actinides de l'organisme repose sur des peptides mimant le vivant

Simultaneous measurements of PIV, anisole-PLIF and OH-PLIF for investigating back-supported stratified flame propagation in lean and nonflammable mixtures

International audienceIn an effort to reduce pollutant emissions and increase energy efficiency, partially premixed combustion has been integrated into many new combustion technologies. The present study investigated lean back-supported flames in a stratified combustion regime. This strategy leads to hybrid combustion regimes, ranging between fully premixed and fully non-premixed reactants, with a large panel of flame structures and properties requiring to be characterized. Outwardly propagating flames were observed following ignition under laminar stratification conditions generated in a constant volume vessel. The quantitative analysis of the flame properties relied on simultaneous PIV measurements to obtain local flame burning velocities and stretch rates and used anisole-PLIF measurements to calculate the equivalence ratio. Simultaneous OH-PLIF measurements were used to differentiate between the burned gas boundaries and the active flame front. This differentiation was necessary to investigate the nonflammable mixture. The OH-gradient measurement proved to be suitable for distinguishing burned gas interfaces from active flame fronts. Simultaneous OH-and anisole-PLIF measurements were used to estimate the thermal flame thickness. Two flame families were investigated: in family A the flame was ignited in a lean mixture (φ=0.6) with a rich stratification; in family B the mixture in the chamber was nonflammable. In rich mixtures ignition compensated for the non-equidiffusive effects of the lean propane flame and reinforced the flame's stretch resistance. Both a flammable and a nonflammable mixture were investigated to determine the time scales of the back-supported propagation for the given stratification. The enhanced combustion regime allowed the flame to propagate with an active flame front, even in the nonflammable mixture. Combustion continued for a few milliseconds before the flame extinguished. The richer the stratification, the longer the combustion lasted in the nonflammable mixture

Production, commercialisation et consommation de pots en pierre ollaire, aspects d’une vaisselle originale à travers l’exemple du Saint-Mont

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Thermo-Mechanical Modeling of a Glacier-Permafrost System in Spitsbergen, Implications for Subglacial Hydrology

International audienceWithin the framework of climate change, a small polar glacierized watershed was monitored. Field surveys show winter discharges causing large icings. A 2D modeling approach along the main axis of the system is developed to study the evolution of the glacier-bed system. Two codes are chained (one for the glacier and one for the porous media). Results confirm that the glacier is polythermal with a cold based terminus. Its rapid retreat (20 m.a -1 ) should lead to a cold glacier within decades to a century. Simulations show that permafrost development precedes glacier retreat (thin glacier tongue with -5°C mean annual air temperatures measured at Ny Alesund) while in the mountainous part with a somewhat stable glacier position, permafrost could develop over longer times and extend deep. The unfrozen porous medium extension below the glacier will progressively reduce resulting in the disappearance of winter discharges most probably within this century