Dans le cadre de la mise au point des nouveaux réacteurs de la Génération IV, la France s'attache notamment à la conception du Very High Temperature Reactor, qui prévoit l'utilisation de matériaux devant résister à plus hautes températures et plus longtemps. Parmi les matériaux existants, AREVA a fait le choix de déterminer le comportement mécanique du Grade 91 (Fe-9Cr-1Mo-Nb-V) pour équiper les gros composants. Ces gros composants sont des structures soudées, si bien que les soudures, points faibles potentiels, doivent être étudiées. Les trois partenaires industriels (AREVA, CEA, EDF) ont lancé une étude commune en octobre 2005 avec le Centre des Matériaux sur le fluage d'un Grade 91, métal de base et joint soudé, à 500°C pour des durées d'exposition allant jusqu'à 4500 h. <br /><br /> Des essais de vieillissement thermique, de traction et de fluage à 450°C et 500°C, sur du métal de base et du joint soudé ont été réalisés. Différentes géométries d'éprouvettes de fluage de joint soudé ont été testées. Aucune évolution significative de la microstructure n'a été constatée en termes de nature et de taille de précipités et de dimension de la sous-structure par rapport à la microstructure avant essai. Peu d'endommagement par cavitation a pu être mis en évidence. Le mécanisme qui conduit à la ruine finale du matériau après fluage est de type viscoplastique à 500°C, contrairement à 625°C où l'endommagement par cavitation est la cause principale de la rupture des éprouvettes de fluage pour les temps d'exposition les plus longs.<br /><br />A partir des courbes expérimentales de fluage du métal de base et du joint soudé entier, un modèle phénoménologique de comportement de type Norton à 500°C est proposé. L'exposant de Norton du métal de base est de 19, alors que celui du joint soudé entier est de 18. Ces valeurs suggèrent la présence de contraintes internes et indiquent que le glissement des dislocations peut être le mécanisme qui contrôle la déformation par fluage. Les éprouvettes de joint soudé cassent dans le métal fondu en fluage et dans le métal de base en traction. La zone affectée thermiquement n'a pas de rôle visible dans la résistance de la structure à 500°C, du moins jusqu'à 4500 h. De ce fait, une décomposition en série du comportement en fluage du joint soudé entier peut être faite à l'aide de ceux du métal fondu et du métal de base. Connaissant le comportement du métal de base et du joint soudé entier, il est possible d'ajuster les paramètres du modèle au métal fondu. Une autre méthode d'ajustement des paramètres du métal fondu est également proposée à partir des essais sur une géométrie amincie contenant uniquement du métal fondu. Les résultats de ces modèles sont cohérents avec les données de la littérature. Ce modèle permet de prédire le temps à rupture à plus long terme, en bon accord avec des résultats du CEA, avec des outils simples de modélisation.

<p>In the last decades, high speed cutting has become an attractive technology in the wood industry. The possibility of reducing global costs in addiction with an increase in productivity, were the main reasons for the enlargement of the use of this technology. </p><p>As usual, these advantages are accompanied by disadvantages that should be carefully analyzed. If on the one hand cutting forces are reduced with increasing cutting speeds, on the other hand, the centrifugal forces affecting the tool are higher. Exposed to such high loads, there is a considerable risk of tool failure that embeds hazards for both machine and workers. </p><p>To prevent the risk of accidents and to guarantee safety in use, security standards have been implemented in industrial fields, imposing specific experimental tests, with defined procedure modes. Accordingly with these standards, the results obtained through the tests should fall inside limited ranges. The experimental tests suggested on the European Standards are intended to simulate the real working conditions of a rotating cutting tool, where extreme centrifugal forces are imposed by the high values of speed. Although their main importance, these destructive tests aren’t always practicable. It happens, for instance, with tools produced in small batch sizes, or as an ascertainment for the fail-critical speed during the development stage, or even due to physical incompatibilities between the tool and the laboratory testmachines. </p><p>The high value of weight associated with the cutting tool prototype developed and patented by Verktygs Larsson AB was an impediment to run the laboratorial tests specified by the standards, forcing the company to find a new way to assure the safety requirements of their product. </p><p>The main goal of this project was the development of an alternative method based on finite element theory to perform a safety analysis to the prototype of a wood cutter. This tool is used as a component in high speed planers. </p><p>In addiction to this primary objective, some considerations were made about other available models, with increased dimensions or even with different parameters. If there was the need, design changes could be assumed in order to guarantee that the tool reached the requisites of the safety standards. Considering an optimization effort, material changes would also be considered, to aim in the direction of reducing the tool weight and the consequent centrifugal forces.</p>

<p>This thesis reports on the results of investigating Fe-containing minerals in meteorites, with focus on Fe-Ni minerals and their magnetic properties, along with some synthetic Fe-Ni analogues. The New Halfa meteorite, which fell in Sudan 1994, has been studied using Mössbauer spectroscopy, X-ray diffraction, and electron microprobe analysis techniques, and classified as an ordinary L-type chondrite of petrologic type 4. Mössbauer spectra of taenite-enriched samples from the metal particles of the New Halfa (L4) and Al Kidirate (H6) meteorites identify the following γ (fcc) Fe-Ni phases: the ferromagnetic atomically ordered taenite (<i>tetrataenite</i>) with ~ 50 at % Ni, the ferromagnetic disordered taenite with ~ 50 at % Ni, the low-Ni (~ 25 at %) paramagnetic taenite (<i>antitaenite</i>). The presence of the superstructure of tetrataenite is confirmed by synchrotron X-ray diffraction.</p><p>Fe-rich γ (fcc) Fe-Ni alloys with compositions Fe₇₉Ni₂₁, Fe₇₆Ni₂₄, and Fe₇₃Ni₂₇, which serve as synthetic analogues of antitaenite, are prepared by mechanical alloying and subsequent annealing at 650 °C. The Mössbauer results indicate that these alloys are inhomogeneous and contain a high moment (HM) ferromagnetic Ni-rich phase (> 30 at % Ni) and a low moment (LM) paramagnetic Fe-rich phase, which orders antiferromagnetically at low temperature. The coexistence of these phases is attributed to phase segregation occurring on short range, probably nanometer scale, consistent with the Fe-Ni phase diagram below 400 °C where there is a miscibility gap associated with a spinodal decomposition in alloys with < 50 at % Ni.</p><p>The combined high field Mössbauer spectroscopy and SQUID magnetometry results on these alloys at room temperature indicate large induced local magnetic moments in the paramagnetic part of the sample, which increases with increasing the Ni content. The results, when compared with the high field Mössbauer results on antitaenite from the metal particle of Al Kidirate and New Halfa meteorites may be used to estimate the Ni content of antitaenite in meteorites.</p><p>High pressure ⁵⁷Fe Mössbauer spectroscopy measurements up to ~ 41 GPa have been carried out at room temperature using the diamond anvil cell (DAC) technique in order to investigate the magnetic properties of γ (fcc) ⁵⁷Fe₅₃Ni₄₇ alloy. The results indicate a pressure induced Invar effect at ~ 7 GPa and a non-magnetic or paramagnetic state above 20 GPa, demonstrating the volume dependence of the magnetic moment of γ (fcc) Fe-Ni alloys.</p>

In the last decades, high speed cutting has become an attractive technology in the wood industry. The possibility of reducing global costs in addiction with an increase in productivity, were the main reasons for the enlargement of the use of this technology. As usual, these advantages are accompanied by disadvantages that should be carefully analyzed. If on the one hand cutting forces are reduced with increasing cutting speeds, on the other hand, the centrifugal forces affecting the tool are higher. Exposed to such high loads, there is a considerable risk of tool failure that embeds hazards for both machine and workers. To prevent the risk of accidents and to guarantee safety in use, security standards have been implemented in industrial fields, imposing specific experimental tests, with defined procedure modes. Accordingly with these standards, the results obtained through the tests should fall inside limited ranges. The experimental tests suggested on the European Standards are intended to simulate the real working conditions of a rotating cutting tool, where extreme centrifugal forces are imposed by the high values of speed. Although their main importance, these destructive tests aren’t always practicable. It happens, for instance, with tools produced in small batch sizes, or as an ascertainment for the fail-critical speed during the development stage, or even due to physical incompatibilities between the tool and the laboratory testmachines. The high value of weight associated with the cutting tool prototype developed and patented by Verktygs Larsson AB was an impediment to run the laboratorial tests specified by the standards, forcing the company to find a new way to assure the safety requirements of their product. The main goal of this project was the development of an alternative method based on finite element theory to perform a safety analysis to the prototype of a wood cutter. This tool is used as a component in high speed planers. In addiction to this primary objective, some considerations were made about other available models, with increased dimensions or even with different parameters. If there was the need, design changes could be assumed in order to guarantee that the tool reached the requisites of the safety standards. Considering an optimization effort, material changes would also be considered, to aim in the direction of reducing the tool weight and the consequent centrifugal forces.

The objectives of the thesis work were to study theinteraction between embedded piezoceramic transducers andcomposite structures as well as determine techniques tosimplify the Lamb waves analysis. Firstly, this studyconsidered the design of the embedded piezoceramic transducers.Secondly, the effect of the embedded transducer on thecomposite strength as well as the influence of the mechanicallyloaded composite on the characteristics of the embeddedtransducer were investigated. Finally, to simplify the analysisof such complex Lamb wave responses, two techniques weredeveloped. They were based on the wavelet technique and amodelling technique, respectively. The design of the embedded piezoceramic transducers wasimproved by reducing the stress concentrations in the compositeas well as in all components constituting the piezoceramictransducer, that is, the piezoceramic element, interconnectorand conductive adhesive. The numerical analysis showed that thethickness of the interconnector had no significant influence onthe stress state of the piezoceramic transducer. It was alsofound that a compliant conductive adhesive reduced the stressconcentration located at the edge of the piezoceramic element.The structural integrity of composites embedded with theimproved piezoceramic transducer was investigated. Theexperiments, performed in tensile and compressive staticloading, indicated that the strength of the composite was notsignificantly reduced by the embedded piezoceramic transducer.Further investigations were conducted to evaluate theperformance of the improved piezoceramic transducer used as aLamb wave generator embedded in composites subjected tomechanical loading. The tests were conducted in tensile andcompressive static loading as well as fatigue loading. Thestudy showed a large working range of the embedded piezoceramictransducer. A post processing technique based on the waveletswas further assessed in the detection of damage and in thedamage size evaluation. A new wavelet basis was developedspecially for processing the Lamb wave response. This method,focused on the wavelet coefficients from the decomposition Lambwave response, showed promising results in evaluating thedamage size. The wavelets offered a sensitive tool to detectsmall damage, compared to other detection methods, improvingthe damage detection capabilities. The other technique wasdevoted to the simplification of the generated Lamb waves bythe use of multi-element transducers. The transducers weredesigned using both a normal-mode expansion and a FE-method.This technique allowed reducing the effect of a Lamb wave modetowards another. This technique was successfully implemented ina damage detection system in composites. <b>Keywords:</b>Embedded piezoceramic, transducer, composite,structural integrity, health monitoring, damage detection, Lambwaves, wavelets, normal-mode expansion, FE-method

This thesis reports on the results of investigating Fe-containing minerals in meteorites, with focus on Fe-Ni minerals and their magnetic properties, along with some synthetic Fe-Ni analogues. The New Halfa meteorite, which fell in Sudan 1994, has been studied using Mössbauer spectroscopy, X-ray diffraction, and electron microprobe analysis techniques, and classified as an ordinary L-type chondrite of petrologic type 4. Mössbauer spectra of taenite-enriched samples from the metal particles of the New Halfa (L4) and Al Kidirate (H6) meteorites identify the following γ (fcc) Fe-Ni phases: the ferromagnetic atomically ordered taenite (tetrataenite) with ~ 50 at % Ni, the ferromagnetic disordered taenite with ~ 50 at % Ni, the low-Ni (~ 25 at %) paramagnetic taenite (antitaenite). The presence of the superstructure of tetrataenite is confirmed by synchrotron X-ray diffraction. Fe-rich γ (fcc) Fe-Ni alloys with compositions Fe79Ni21, Fe76Ni24, and Fe73Ni27, which serve as synthetic analogues of antitaenite, are prepared by mechanical alloying and subsequent annealing at 650 °C. The Mössbauer results indicate that these alloys are inhomogeneous and contain a high moment (HM) ferromagnetic Ni-rich phase (&gt; 30 at % Ni) and a low moment (LM) paramagnetic Fe-rich phase, which orders antiferromagnetically at low temperature. The coexistence of these phases is attributed to phase segregation occurring on short range, probably nanometer scale, consistent with the Fe-Ni phase diagram below 400 °C where there is a miscibility gap associated with a spinodal decomposition in alloys with &lt; 50 at % Ni. The combined high field Mössbauer spectroscopy and SQUID magnetometry results on these alloys at room temperature indicate large induced local magnetic moments in the paramagnetic part of the sample, which increases with increasing the Ni content. The results, when compared with the high field Mössbauer results on antitaenite from the metal particle of Al Kidirate and New Halfa meteorites may be used to estimate the Ni content of antitaenite in meteorites. High pressure 57Fe Mössbauer spectroscopy measurements up to ~ 41 GPa have been carried out at room temperature using the diamond anvil cell (DAC) technique in order to investigate the magnetic properties of γ (fcc) 57Fe53Ni47 alloy. The results indicate a pressure induced Invar effect at ~ 7 GPa and a non-magnetic or paramagnetic state above 20 GPa, demonstrating the volume dependence of the magnetic moment of γ (fcc) Fe-Ni alloys.

QC 20100623

Protein sequence motifs are gathering more and more attention in the field of sequence analysis. The recurring patterns have the potential to determine the conformation, function and activities of the proteins. In our work, we obtained protein sequence motifs which are universally conserved across protein family boundaries. Therefore, unlike most popular motif discovering algorithms, our input dataset is extremely large. As a result, an efficient technique is essential. We use two granular computing models, Fuzzy Improved K-means (FIK) and Fuzzy Greedy K-means (FGK), in order to efficiently generate protein motif information. After that, we develop an efficient Super Granular SVM Feature Elimination model to further extract the motif information. During the motifs searching process, setting up a fixed window size in advance may simplify the computational complexity and increase the efficiency. However, due to the fixed size, our model may deliver a number of similar motifs simply shifted by some bases or including mismatches. We develop a new strategy named Positional Association Super-Rule to confront the problem of motifs generated from a fixed window size. It is a combination approach of the super-rule analysis and a novel Positional Association Rule algorithm. We use the super-rule concept to construct a Super-Rule-Tree (SRT) by a modified HHK clustering, which requires no parameter setup to identify the similarities and dissimilarities between the motifs. The positional association rule is created and applied to search similar motifs that are shifted some residues. By analyzing the motifs results generated by our approaches, we realize that these motifs are not only significant in sequence area, but also in secondary structure similarity and biochemical properties.

L'objectif de ce travail est d'évaluer l'effet de la nature du support et l'effet de promotion sur les propriétés catalytiques des catalyseurs d'HDS à base de Mo. Pour obtenir les systèmes catalytiques adéquats, nous avons appliqué la préparation par " voie acac ", qui consiste à faire réagir le promoteur sous forme de complexe acétylacétonate (de Co, Ni ou Fe) sur le sulfure de molybdène supporté (sur γ-Al2O3, SiO2, TiO2 ou ZrO2). Les différents solides obtenus ont été caractérisés par MET, IR(CO) et SPX notamment pour tenter de quantifier les phases actives, puis ils ont été testés dans les réactions d'HDS du thiophène et du 4,6-DMDBT. L'activité catalytique a pu être corrélée aux résultats de caractérisation par une nouvelle approche qui consiste à calculer l'activité apparente par site NiMoS ou CoMoS. Cette approche montre que la qualité des sites actifs CoMoS et NiMoS est la meilleure sur SiO2 et comparable sur les supports γ-Al2O3, TiO2 et ZrO2. Par la même méthode nous avons préparé de nouveaux catalyseurs de type CoNiMoS supportés, en ajoutant les promoteurs Co et Ni soit simultanément soit successivement au MoS2. Cette étude permet un fort apport expérimental aux études théoriques qui avancent l'hypothèse de différentes affinités du Co et du Ni pour les deux type de bords S-edge et Mo-edge sur γ-Al2O3 et TiO2.

The bioavailability of iron is limited by the solubility of Fe(III) at circumneutral pH. In the High Nutrient-Low Chlorophyll (HNLC) zones of the ocean, the natural or anthropogenic addition of iron stimulates primary productivity and consumes carbon dioxide. As a result, iron fertilization has been proposed to mitigate anthropogenic carbon emissions and lower global temperatures. The natural sources of iron to the ocean are not fully constrained and include eolian depositions as well as inputs from continental shelf sediments, rivers, hydrothermal vents, and icebergs. Regardless of their source, the effectiveness of iron additions in promoting carbon fixation depends on the presence of organic ligands either natural or produced by microorganisms that stabilize or solubilize Fe(III) at neutral pH. For example, siderophores are well known to be expressed extracellularly by prokaryotes in the photic zones of the oceans to increase the bioavailability of iron. In this dissertation, the production of iron nanoparticles is demonstrated in vent fluids from the 90 North hydrothermal system. These iron nanoparticles may either catalyze the oxidation of sulfide to thiosulfate and produce a potential electron acceptor for microbial respiration or provide a source of iron that stimulates primary production at great distances from the hydrothermal vents. In addition, dissolved iron under the form of soluble organic-Fe(III) complexes is demonstrated to constitute a significant source of iron in estuarine sediments that receive large amounts of particulate iron from flocculation and precipitation at the salinity transition of this estuary. A novel competitive ligand equilibration absorptive cathodic stripping voltammetry (CLE-ACSV) technique reveals that the speciation of iron changes from largely colloidal or particulate in the upper estuary to truly dissolved organic-Fe(III) in the lower estuary. It is also demonstrated that organic-Fe(III) complexes are produced far below the sediment-water interface, suggesting that dissimilatory iron-reducing bacteria may play an important role in their production. These complexes then diffuse across the sediment-water interface and provide a significant source of iron to the continental shelf. The mechanism of reduction of iron oxides by iron-reducing bacteria is not fully understood and presents a unique physiological problem for the organism, as the terminal reductase has to transfer electrons to a solid electron acceptor. In this dissertation, it is demonstrated for the first time using random mutagenesis that the respiration of solid Fe(III) oxides by Shewanella oneidensis, a model iron-reducing prokaryote, first proceeds through a non-reductive dissolution step involving organic ligands that are released extracellularly by the cells. These soluble complexes are then reduced by the organism to produce Fe(II) and recycle the ligand for additional solubilization. Incubations with deletion mutants of the proteins involved in the respiration of Fe(III) revealed that the type-II secretion system, which translocates proteins on the outer membrane of gram-negative bacteria, is involved in the production of organic-Fe(III) complexes by secreting an endogenous iron-solubilizing ligand or a protein involved in the biosynthesis of this ligand on the outer membrane. In addition, periplasmic decaheme cytochromes produced by Shewanella appear to be involved in the mechanism of production of the endogenous organic ligand either directly or through a sensing mechanism that controls its production. In turn, two decaheme cytochromes positioned on the outer-membrane and hypothesized to be involved in the electron transfer to the mineral surface do not appear to be involved in the solubilization mechanism, suggesting either that the cells regulate the ligand production via periplasmic sensing systems or that these cytochromes are not involved in the solubilization mechanism. Altogether this research shows the production of organic-Fe(III) complexes in sediments generates a significant flux of dissolved iron to support primary production in continental shelf waters and that these complexes may be partly produced by iron-reducing bacteria. Indeed, experiments with a model organism demonstrate dissimilatory iron reducing bacteria produce endogenous organic ligands with high iron-binding constants to non-reductively solubilize iron oxides during the anaerobic respiration of iron oxides. The organic ligand is apparently recycled several times to minimize the energy cost associated with its biosynthesis. These findings demonstrate that the solubilization of iron oxides by organic ligands may be an important, yet underappreciated process in aquatic systems.