Étude expérimentale et numérique des processus de dévolatilisation et d'oxydation du charbon pulvérisé à fort gradient de chauffe sous air et sous atmosphères enrichies en oxygène

La place du charbon dans le mix énergétique mondial actuel et à venir est importante, notamment dans le domaine de la production d’électricité. Un enjeu énergétique et environnemental crucial à l’heure actuelle est de soutenir le besoin croissant en énergie électrique, tout en limitant les rejets de CO2. Le développement de la combustion du charbon pulvérisé sous des atmosphères favorisant la capture du CO2 à l’échelle industrielle est une façon d’atteindre ce but. L’étude proposée a ainsi pour objectif de contribuer à la compréhension des modifications des processus physico-chimiques de combustion du charbon pulvérisé induites par un changement d’atmosphère d’oxydation. Plus précisément, la dévolatilisation et l’oxydation des composés dévolatilisés ont été étudiées sous air, sous air enrichi en oxygène et sous oxycombustion en ayant recours à une approche de modélisation par réseaux de réacteurs chimiques. Dans la première partie de cette thèse, des modèles cinétiques de dévolatilisation empirique et structurel ont été considérés. Leurs prédictions ont été comparées à des mesures expérimentales effectuées sous atmosphère inerte, sous air et sous atmosphères enrichies en oxygène en ayant recours à un dispositif de laboratoire reproduisant des gradients de chauffe industriels. Cette étude a mis en évidence que l’atmosphère de combustion n’influençait qu’indirectement la dévolatilisation dans les conditions étudiées via la modification des transferts thermiques en direction des particules. Cette analyse a de plus permis de sélectionner le modèle de dévolatilisation à deux réactions compétitives ainsi que le modèle Chemical Percolation Devolatilization (CPD) qui ont ensuite été implémentés dans le réseau de réacteurs. La deuxième partie de cette thèse a consisté à modéliser, avec ANSYS FLUENT, la dynamique des écoulements dans la chambre de combustion du banc d’essais. Ces résultats numériques ont permis, dans la troisième partie de la thèse, de déterminer les propriétés des réacteurs du réseau telles que leur taille et les transferts de masse et d’énergie se produisant entre eux. L’approche de modélisation par réseau de réacteurs a en outre permis de considérer une cinétique chimique détaillée comprenant 190 espèces impliquées dans 869 réactions. Les simulations opérées ont permis d’étudier finement les processus d’oxydation des composés dévolatilisés incluant des espèces azotées et soufrées ainsi que des goudrons et notamment d’expliquer les modifications observes au niveau des concentrations en CO, NO, SO2 et en précurseurs de suies lors du changement d’atmosphère de combustion. Cette analyse des chemins réactionnels a notamment mis en évidence que, sous oxycombustion, l’augmentation de la concentration de CO observée est due à une oxydation accrue des goudrons et à une production accrue de HCO tandis que la formation de NO par des chemins alternatifs comme HCN→NCO→HNCO→HNO→NO s’est avérée favorisée

Intervertebral disc cells as competent phagocytes in vitro: implications for cell death in disc degeneration

INTRODUCTION: Apoptosis has been reported to occur in the intervertebral disc. Elsewhere in the body, apoptotic cells are cleared from the system via phagocytosis by committed phagocytes such as macrophages, reducing the chance of subsequent inflammation. These cells, however, are not normally present in the disc. We investigated whether disc cells themselves can be induced to become phagocytic and so have the ability to ingest and remove apoptotic disc cells, minimising the damage to their environment. METHOD: Bovine nucleus pulposus cells from caudal intervertebral discs were grown in culture and exposed to both latex particles (which are ingested by committed phagocytes) and apoptotic cells. Their response was monitored via microscopy, including both fluorescent and video microscopy, and compared with that seen by cell lines of monocytes/macrophages (THP-1 and J774 cells), considered to be committed phagocytes, in addition to a nonmacrophage cell line (L929 fibroblasts). Immunostaining for the monocyte/macrophage marker, CD68, was also carried out. RESULTS: Disc cells were able to ingest latex beads at least as efficiently, if not more so, than phagocytic THP-1 and J774 cells. Disc cells ingested a greater number of beads per cell than the committed phagocytes in a similar time scale. In addition, disc cells were able to ingest apoptotic cells when cocultured in monolayer with a UV-treated population of HeLa cells. Apoptotic disc cells, in turn, were able to stimulate phagocytosis by the committed macrophages. CD68 immunostaining was strong for THP-1 cells but negligible for disc cells, even those that had ingested beads. CONCLUSION: In this study, we have shown that intervertebral disc cells are capable of behaving as competent phagocytes (that is, ingesting latex beads) and apoptotic cells. In terms of number of particles, they ingest more than the monocyte/macrophage cells, possibly due to their greater size. The fact that disc cells clearly can undergo phagocytosis has implications for the intervertebral disc in vivo. Here, where cell death is reported to be common yet there is normally no easy access to a macrophage population, the endogenous disc cells may be encouraged to undergo phagocytosis (for example, of neighbouring cells within cell clusters)

Mechanistic implications of the active species involved in the oxidation of hydrocarbons by iron complexes of pyrazine-2-carboxylic acid

The reactivity towards H2O2 of the complexes [Fe(pca)2(py)2]·py (1) and Na2{[Fe(pca3)]2O}·2H2O·CH3CN (2) (where pca− is pyrazine-2-carboxylate) and their catalytic activity in the oxidation of hydrocarbons is reported. Addition of H2O2 to 1 results in the formation of a dinuclear Fe(III)–(µ-O)–Fe(III) species characterized spectroscopically and by cyclic voltammetry. By contrast, treatment of 2 with H2O2 results in the formation of mononuclear iron(II) complexes, [Fe(pca)2(solvent)2]. The experimental results indicate that the catalytic activity of the starting complexes 1 and 2 is strongly dependent on the species formed in solution.

Autologous chondrocyte implantation for cartilage repair: monitoring its success by magnetic resonance imaging and histology

Autologous chondrocyte implantation is being used increasingly for the treatment of cartilage defects. In spite of this, there has been a paucity of objective, standardised assessment of the outcome and quality of repair tissue formed. We have investigated patients treated with autologous chondrocyte implantation (ACI), some in conjunction with mosaicplasty, and developed objective, semiquantitative scoring schemes to monitor the repair tissue using MRI and histology. Results indicate repair tissue to be on average 2.5 mm thick. It was of varying morphology ranging from predominantly hyaline in 22% of biopsy specimens, mixed in 48%, through to predominantly fibrocartilage, in 30%, apparently improving with increasing time postgraft. Repair tissue was well integrated with the host tissue in all aspects viewed. MRI scans provide a useful assessment of properties of the whole graft area and adjacent tissue and is a noninvasive technique for long-term follow-up. It correlated with histology (P = 0.02) in patients treated with ACI alone

The Price of Safety in an Active Network

Security is a major challenge for "Active Networking," accessible programmability creates numerous opportunities for mischief. The point at which programmability is exposed, e.g., through the loading and execution of code in network elements, must therefore be carefully crafted to ensure security. The SwitchWare active networking research project has studied the architectural implications of various tradeoffs between performance and security. Namespace protection and type safety were achieved with a module loader for active networks, ALIEN, which carefully delineated boundaries for privilege and dynamic updates. ALIEN supports two extensions, the Secure Active Network Environment (SANE), and the Resource Controlled Active Network Environment (RCANE). SANE extends ALIEN's node protection model into a distributed setting, and uses a secure bootstrap to guarantee integrity of the namespace protection system. RCANE provides resource isolation between active network node users, including separate heaps and robust time-division multiplexing of the node. The SANE and RCANE systems show that convincing active network security can be achieved. This paper contributes a measurement-based analysis of the costs of such security with an analysis of each system based on both execution traces and end-to-end behavior

Criteria for choosing clinically effective glaucoma treatment: A discussion panel consensus

AbstractBackground:In the clinical management of patients at risk for or diagnosed with primary open-angle glaucoma (POAG), the aim of medical treatment is to reduce intraocular pressure (IOP) and then maintain it over time at a level that preserves both the structure and function of the optic nerve.Objective:The objective of this report was to establish a consensus on the criteria that should be used to determine the characteristics of IOP-lowering medication.Methods:Discussion was held among a panel of 12 physicians considered to be experts in glaucoma to develop a consensus on the criteria used by them to determine the characteristics of the IOP-lowering medication chosen for initial monotherapy and adjunctive treatment of ocular hypertension (OHT) or POAG. Consensus development combined available evidence and the impressions of these physicians regarding the clinical effectiveness of IOP-lowering medication for OHT and POAG. Once the panel identified the criteria, the order of priority and the relative importance of these criteria were then established in the setting of 3 risk categories (low, medium, and high) for a patient to experience significant visual disability from glaucoma over their expected life span.Results:The panel identified 5 criteria to determine the characteristics of IOP-lowering medication for OHT and POAG: IOP-lowering effect, systemic adverse events (AEs), ocular tolerability, compliance/administration, and cost of treatment. IOP-lowering effect was consistently ranked as the highest priority and cost as the lowest. The priority of compliance/administration did not vary by clinical situation. Systemic AEs and ocular tolerability were ranked as higher priorities in initial monotherapy than in adjunctive treatment and ranked lower as the risk for visual disability increased. The priority given to the criteria used to determine clinical effectiveness varied both with the risk for functional vision loss from glaucoma and whether initial monotherapy or adjunctive treatment was being considered.Conclusion:Glaucoma treatment should be assessed with regard to the need not only to lower IOP but also to minimize systemic and ocular AEs, promote patient compliance, and minimize cost. The order of priority and relative importance given to these treatment criteria will vary as part of individualizing patient care

Tris(1,10-phenanthroline)iron(II) μ-oxido-bis­[trichloridoferrate(III)]

In the title salt, [Fe(C12H8N2)3][Fe2Cl6O], the ionic components are linked into a two-dimensional supra­molecular layer by two pairs of C—H⋯Cl hydrogen bonds and π–π stacking inter­actions [centroid–centroid distances = 3.655 (4) and 3.498 (3) Å]. The salt is characterized as a mixed-valent FeII–FeIII compound, in which an FeII atom is coordinated by three phen ligands, forming a six-coordinated cationic entity and the anionic part is formed by two FeIII atoms in tetra­hedral coordination environments constructed by three chloride ions and one bridging oxide ligand. Intra­molecular C—H⋯N hydrogen bonds are observed

Heterogeneous dermatitis complaints after change in drinking water treatment: a case report

BACKGROUND: The disinfectant monochloramine minimizes the formation of potentially hazardous and regulated byproducts, and many drinking water utilities are shifting to its use. CASE PRESENTATION: After a drinking water utility serving 2.4 million people switched to monochloramine for residual disinfection, a small number of residents complained of dermatitis reactions. We interviewed 17 people about their symptoms. Skin appearance, symptoms, and exposures were heterogeneous. Five respondents had history of hives or rash that preceded the switch to monochloramine. CONCLUSION: The complaints described were heterogeneous, and many of the respondents had underlying or preexisting conditions that would offer plausible alternative explanations for their symptoms. We did not recommend further study of these complaints