A knowledge-based approach for the extraction of machining features from solid models

Computer understanding of machining features such as holes and pockets is essential for bridging the communication gap between Computer Aided Design and Computer Aided Manufacture. This thesis describes a prototype machining feature extraction system that is implemented by integrating the VAX-OPS5 rule-based artificial intelligence environment with the PADL-2 solid modeller. Specification of original stock and finished part geometry within the solid modeller is followed by determination of the nominal surface boundary of the corresponding cavity volume model by means of Boolean subtraction and boundary evaluation. The boundary model of the cavity volume is managed by using winged-edge and frame-based data structures. Machining features are extracted using two methods : (1) automatic feature recognition, and (2) machine learning of features for subsequent recognition. [Continues.

Surface Patterns On Single Cells: A Consequence Of A Phase Transition To Modulated Phases

Patterns are ubiquitous in the world around us, and we have only begun to scratch the surface of understanding their complexity and formation. In this thesis, we draw inspiration from rigid, extracellular surface patterns found on single living cells in many taxa and try to understand if there is a common thread in their pattern formation mechanisms that can be described by a single physical formalism. Pollen grains, butterfly wing scales, and deep-sea protists called phaeodarians all have beautifully ornate and varied hard surface structures that are likely patterned by the deposition of some soft organic matrix originating inside of the cell. We focus on pollen grain surfaces because of their remarkable geometric variety that is well documented. We find, through our own electron microscopy and careful histological techniques, that the patterns arise due to a phase separation of a transient polysaccharide material mechanically coupled to the underlying elastic cell membrane. We then show that the entire evolved diversity of patterns can be recapitulated by exploring both the equilibrium states and the dynamics of a modified Landau-Ginzburg model of phase transitions to modulated phases. We observe the surprising fact that only ~10% of extant species exhibit patterns that reach equilibrium. Furthermore, we find that although these patterns have evolved many times in seed plants, they are not, on average, selected for. The remaining 90% of pollen grain surfaces resemble arrested intermediate states of the phase transition process. We then document the pattern formation process in butterfly wing scales and show that a transient, spatially periodic surface material sits between the global surface features of the scales (the ridges). We postulate that the phase transition of this material may also contribute to the regular patterns on wing scale cells. We finally image the full three-dimensional features of geodesic phaeodarians tests using x-ray-computed tomography

AUSTENITIC STAINLESS STEELS FOR FUTURE NUCLEAR FUEL CLADDINGS

Nuclear power systems have been under continuous development since the first nuclear power plant started operation in 1954. They are categorized into different generations, with each new generation having significant technological advances over the previous one. The worldwide effort to develop the next generation of nuclear reactors was defined at the Generation IV International Forum (GIF) in 2000. Six types of design were proposed, including supercritical water cooled reactor (SCWR). Materials in this reactor will be exposed to more severe environments than the current generation of reactors to assure higher efficiency in energy production and the current materials used for fuel cladding need to be improved or new materials should be developed. In this thesis, the behavior of two existing nuclear materials, stainless steels 310S and 316L was investigated, under conditions approximating the nuclear reactor environment. An environment with dynamic loop of supercritical water (SCW) was used to test the performance of the alloys and the oxides formed were analyzed. Oxidation of the alloys in air was also performed for comparison. It was found that although both alloys showed good oxidation resistance in air at 600ºC, stainless steel 310S has better resistance in SCW environment compared to stainless steel 316L. A thin protective oxide layer of Mn2CrO4 spinel delays oxidation in alloy 310S. In order to improve the oxidation resistance of 310S and 316L stainless steels, thermo-mechanical processing (TMP) was applied to modify their microstructures. The deformation and annealing texture of the as-received and processed samples were investigated by means of X-ray diffraction (XRD) and orientation imaging microscopy (OIM). Different rolling paths and different deformation levels before annealing were used to produce samples of different grain size with similar texture and samples of similar grain size with different textures. Subsequently, the oxidation resistance of thermo-mechanically processed 316L and 310S samples in SCW was studied. It was found that the oxidation resistance of stainless steels 316L and 310S can be improved up to four and five times, respectively, by decreasing the grain size below a critical value of 3 µm. It was demonstrated that samples with smaller grain size provided higher fraction of grain boundaries for fast diffusion of chromium to reach the surface and compensate losses due to dissolution of chromium in the oxidation media. External oxide layers formed on as-received and thermo-mechanically processed stainless steel 316L samples was characterized to establish possible correlation between orientation of the substrate and oxide grains. Micro and macro textures of the substrate and the oxide layers were examined and the results showed that the texture of substrate did not affect the texture of magnetite (Fe3O4) in the upper oxide layer. In addition, the texture of magnetite did not affect the texture of hematite (Fe2O3) on samples where hematite was an additional oxide phase. The strong texture of both oxides was explained with surface free energy minimization and strain energy minimization theory. This means that the texture of both oxides is dictated by a competition between their surface and strain energies

AUSTENITIC STAINLESS STEELS FOR FUTURE NUCLEAR FUEL CLADDINGS

Nuclear power systems have been under continuous development since the first nuclear power plant started operation in 1954. They are categorized into different generations, with each new generation having significant technological advances over the previous one. The worldwide effort to develop the next generation of nuclear reactors was defined at the Generation IV International Forum (GIF) in 2000. Six types of design were proposed, including supercritical water cooled reactor (SCWR). Materials in this reactor will be exposed to more severe environments than the current generation of reactors to assure higher efficiency in energy production and the current materials used for fuel cladding need to be improved or new materials should be developed. In this thesis, the behavior of two existing nuclear materials, stainless steels 310S and 316L was investigated, under conditions approximating the nuclear reactor environment. An environment with dynamic loop of supercritical water (SCW) was used to test the performance of the alloys and the oxides formed were analyzed. Oxidation of the alloys in air was also performed for comparison. It was found that although both alloys showed good oxidation resistance in air at 600ºC, stainless steel 310S has better resistance in SCW environment compared to stainless steel 316L. A thin protective oxide layer of Mn2CrO4 spinel delays oxidation in alloy 310S. In order to improve the oxidation resistance of 310S and 316L stainless steels, thermo-mechanical processing (TMP) was applied to modify their microstructures. The deformation and annealing texture of the as-received and processed samples were investigated by means of X-ray diffraction (XRD) and orientation imaging microscopy (OIM). Different rolling paths and different deformation levels before annealing were used to produce samples of different grain size with similar texture and samples of similar grain size with different textures. Subsequently, the oxidation resistance of thermo-mechanically processed 316L and 310S samples in SCW was studied. It was found that the oxidation resistance of stainless steels 316L and 310S can be improved up to four and five times, respectively, by decreasing the grain size below a critical value of 3 µm. It was demonstrated that samples with smaller grain size provided higher fraction of grain boundaries for fast diffusion of chromium to reach the surface and compensate losses due to dissolution of chromium in the oxidation media. External oxide layers formed on as-received and thermo-mechanically processed stainless steel 316L samples was characterized to establish possible correlation between orientation of the substrate and oxide grains. Micro and macro textures of the substrate and the oxide layers were examined and the results showed that the texture of substrate did not affect the texture of magnetite (Fe3O4) in the upper oxide layer. In addition, the texture of magnetite did not affect the texture of hematite (Fe2O3) on samples where hematite was an additional oxide phase. The strong texture of both oxides was explained with surface free energy minimization and strain energy minimization theory. This means that the texture of both oxides is dictated by a competition between their surface and strain energies

Doctor of Philosophy

dissertationMammalian hosts have evolved protein "restriction factors" to combat retroviruses. TRIM5α and the related TRIMCyp protein (collectively TRIM5), are restriction factors that can potently restrict retroviruses, including HIV-1, by binding their capsids and blocking reverse transcription. Previous studies have shown that the C-terminal SPRY/CypA domains of TRIM5 proteins bind the capsids of susceptible retroviruses and that higher-order oligomerization of TRIM5 proteins apparently also contributes to capsid binding. However, the biochemical and structural details of these interactions are not fully understood. To study how TRIM5 proteins recognize capsids, we have developed new methods for expressing and purifying recombinant TRIM5 proteins. Here, we report biochemical, electron microscopic and X-ray crystallographic studies of pure recombinant TRIM5 proteins and their complexes with authentic HIV-1 core particles and in vitro-assembled mimics of the HIV-1 capsid surface. In Chapter 2, we report the expression, purification and electron crystallographic studies of a restrictive, but non-native chimeric rhesus TRIM5 protein (TRIM5-21R), and show that TRIM5-21R can spontaneously self-assemble into paracrystalline hexagonal lattices comprising 6-sided rings. Moreover, ring assembly is promoted by TRIM5-21R binding to hexagonal HIV-1 CA assemblies. In Chapter 3, we report the first crystal structure of a TRIM coiled-coil domain (from human TRIM25) as well as supporting analytical ultracentrifugation and disulfide crosslinking experiments showing that other iv TRIM coiled-coils, including TRIM5, also form antiparallel dimers that are ~170 Å long. In Chapter 4, we describe the expression and purification of 11 different mammalian TRIM5 alleles. We demonstrate that TRIM5 hexagonal assembly is a conserved property and report electron microscopic and biochemical studies showing that TRIM5 proteins form a ~35 nm-spaced, flexible hexagonal "net" on the surface of decorated HIV-1 cores and other capsid mimics. In Chapter 5, I present my ongoing attempts to crystallize and determine the structure of the TRIM5α core domains in the assembled state. Taken together, my work supports a "pattern recognition" model for capsid recognition in which TRIM5 proteins have evolved to restrict a variety of different retroviruses by cooperatively assembling flexible hexagonal nets that can bind avidly and adapt to the symmetry, hexagonal spacing and curvature of retroviral capsids

Multi-layered nanocomposite polymer latexes and films

Clay platelets and silica nanoparticles are used as Pickering stabilizers in the fabrication of hybrid armored polymer particles through a Pickering emulsion polymerization process. A variety of hydrophobic comonomers (i.e., styrene-co- (n-butyl acrylate) (Sty:BA), methyl methacrylate-co-(n-butyl acrylate) (MMA:BA)), styrene-co-(2-ethyl hexyl acrylate) (Sty:2-EHA), vinyl acetate (VAc) and vinyl pivalate (VPiv) are used as organic film forming components. Polymerization kinetics and particle size distributions were examined as a function of monomer conversion. Additionally, key mechanistic features of the polymerization process by quantitatively analyzing the concentration of silica nanoparticles in the water phase during monomer conversion by disc centrifugation are unraveled. It is also showed the crucial role of Laponite clay discs in the particle formation (nucleation) of the Pickering emulsion polymerization process. Increasing amounts of clay nanodiscs leads to smaller average particles sizes, but broader particle size distributions. Polymer films of poly(styrene-co-n-butyl acrylate) armored with Laponite clay were studied as a function of clay amount. Improvements in mechanical, thermal and surface topography provided by clay platelets are reported. In addition, advantages are shown in use of hybrid polymer particles in comparison with simple blend mixtures of polymer particles plus inorganic particles. Humidity properties of poly(styrene-co-n-butyl acrylate) films as a function of clay content are investigated. It is demonstrated that the presence of Laponite clay improves the water storage capacity of polymer films. Also water barrier properties are improved when clay platelets are applied. Finally, a versatile two step Pickering emulsion polymerization for the fabrication of core-shell particles armored with Laponite clay XLS is developed. The obtained particles contain a "hard" core and a "soft" shell armored with clay. The different in the refractive indexes between the core and shell makes these core-shell particles interesting for possible use as colloidal crystals.EThOS - Electronic Theses Online ServiceBASF AktiengesellschaftAdvantage West Midlands (AWM)European Regional Development Fund (ERDF)GBUnited Kingdo

Systematic structural studies in metal complex chemistry

A procedure is presented for detecting geometrical preferences, deformations and interconversion pathways between different geometries for the transition metal coordination sphere ML(_n). A discrepancy index [R(_ang)(x)] was proposed initially to address the problems of dimensionality and permutation complexity in the systematic analysis of coordination sphere geometry with higher coordination numbers (n > 7). But it can also be used generally for the lower coordination numbers. A set of standard geometries for coordination numbers 2-9 are presented and the angles between the center point and each vertex for the polyhedra which are used to describe the coordination sphere geometries for coordination numbers 7-9 are idealised. These angles correspond to the metal-ligand valence angles in the coordination complex and are used as the standard values to measure the deviation of a real coordination sphere in the complex from these standard polyhedra. Geometry of each coordination sphere (ML(_7-9)) from the Cambridge Structural Database (CSD) is identified by the calculations of R(_ang)(x) values. Also the unique enumeration numbers of the ligands corresponding to each geometry can be derived over the n! ligand permutations. The different geometrical clusters and interconversion pathways from one to another are mapped in a designed two-dimensional plot. The symmetry coordinates and principal component analysis are initially applied in these higher coordination number systems. They not only map the clusters represented to those standard geometries in the different symmetric point groups but also provide and confirm the interconversion pathways between the different geometries. The other systematic study involves the analysis and correlation of the metal σ-π bond in the transition metal alkyne and alkene complexes from the CSD. Geometrical features of this specific bond are examined in the view of structure and some useful correlation between the key geometrical parameters are defined. Finally, X-ray crystal structure determinations are briefly described and the crystal structures of ten transition metal compounds in coordination numbers 4-6 are presented

Development of new probes based on carbon nanocones for near-field microscopies

La microscopie à champ proche permet l'étude topographique et des propriétés physiques (électrique, mécanique, etc.) de la surface d'un matériau à l'échelle nanométrique. Pour ce faire, l'échantillon étudié est balayé en surface par une sonde (ou pointe) dont les caractéristiques géométriques (comme le rayon de courbure de l'apex et le facteur de forme) et les propriétés physiques (mécanique, électrique etc.) doivent être adaptées pour garantir une résolution suffisante et une représentation fidèle de la surface. Cependant, les sondes actuelles présentent des limitations importantes vis-à-vis de la résolution apportée, dans les artefacts possibles d'imagerie, et dans leur adaptabilité concernant leur utilisation dans différents modes (qu'ils soient conducteurs ou non). Ces limitations sont causées principalement par le type de matériau utilisé (par exemple le silicium ou le nitrure de silicium, en standard, ou des nanotubes de carbone), ainsi que par les procédés de fabrication employés pour structurer la géométrie des sondes. Dans ce travail, nous étudions le potentiel de nanocônes de carbone (morphologie carbonée graphénique en forme de cônes à haut facteur de forme et d'apex nanométrique) pour différents modes de microscopie à champ proche. Ces nanocones présentent d'excellentes propriétés mécaniques (forte liaison C-C) et électriques. Ces derniers ont déjà été testés avec succès et brevetés en tant qu'émetteurs d'électrons pour les canons à émission de champ froid équipant les microscopes électroniques par transmission les plus performants. Ces diverses caractéristiques des nanocônes (facteur de forme, apex nanométrique, conductivité, stabilité mécanique, forte cohésion atomique) et d'autres (hydrophobicité, inertie chimique, morphologie multi-échelle micro-nano...) font qu'ils pourraient également constituer une solution prometteuse pour concevoir des sondes potentiellement supérieures aux sondes existantes, qu'elles soient standard ou plus spécifiques comme celles en nanotubes de carbone, pour divers types de microscopie à champ proche, notamment en termes de résolution spatiale et durabilité. Dans une première partie, cette thèse est dédiée à la synthèse de nanocônes de carbone individuels suivant une méthode originale de synthèse nommée ToF-CVD (Time of Flight - Chemical Vapor Deposition). Le travail révèle des mécanismes de formation complexes mettant en jeu d'une part les mécanismes de nucléation en phase hétérogène spécifiques de la CVD du carbone pyrolytique, et d'autre part des mécanismes de mouillabilité impliquant de phénomènes connus du domaine comme l'instabilité de Plateau-Rayleigh. Le montage des nanocônes sur des supports dédiés en tant que sondes pour microscopies à champ proche est ensuite réalisé, suivi par des études de caractérisation (SEM, TEM, spectroscopie RAMAN) pour évaluer leurs caractéristiques initiales du point de vue géométrique et structural et leur évolution vis-à-vis des conditions opératoires requises à la fois lors du montage et pour les différents modes de microscopie à champ proche étudiés. Dans une seconde partie, le potentiel des nanocônes de carbone en tant que sondes pour des modes de microscopie à champ proche non conducteurs comme le mode topographie (microscopie à force atomique - AFM) et le mode "Peak Force Quantitative Nano Mechanical" (PF-QNM), et pour des modes conducteurs comme pour la microscopie à effet tunnel (STM), la microscopie à force atomique conducteur (c-AFM), la microscopie à force Kelvin (KFM) est évalué. Cette évaluation est faite sur la base de (i) leurs performances ; (ii) leur durabilité ; (iii) leur versatilité. La finalité ultime est de comparer la performance des sondes-nanocônes de carbone par rapport à des sondes commerciales. Les nanocônes de carbone se révèlent être de véritables sondes multimodes avec peu d'équivalents actuels. Des améliorations sont cependant nécessaires et possibles, ce pour quoi des directions sont proposées.Near-field microscopy allows studying the topography and the physical properties (electrical, mechanical, etc.) of a material surface at nanoscale. For such a purpose, the sample surface is scanned by a probe (or tip) which geometric characteristics (such as the apex radius and the aspect ratio) and the physical properties (mechanical, electrical, etc.) must be suitable to ensure a sufficient resolution and a reliable representation of the surface. However, the current probes have significant limitations regarding the resolution, the possible imaging artifacts, as well as their ability to be used in different modes (conductive and non-conductive). These limitations are caused mainly by the type of material used (for example silicon or silicon nitride, for standard probes, or carbon nanotubes), as well as by the manufacturing processes used to structure the geometry of the probes. In this work, we study the potential of carbon nanocones (graphenic carbonaceous morphology with conical shape with high aspect ratio and nanosized apex) for different modes of near-field microscopy. These nanocones exhibit excellent mechanical (strong C-C bond) and electrical properties. They have already been successfully tested and patented as electron emitters for the cold-field-emission guns which equip the most performing transmission electron microscopes. These various characteristics of the nanocones (aspect ratio, nanosized apex, conductivity, mechanical stability, strong atomic cohesion) and others (hydrophobicity, chemical inertia, multiscale micro-nano morphology...), make that they could also constitute a promising solution for designing probes potentially superior to existing probes, either standard or more specific such as those in carbon nanotubes, for various types of near-field microscopy, in particular in terms of spatial resolution and durability. In the first part, this thesis is dedicated to the synthesis of individual carbon nanocones using an original synthesis method called ToF-CVD (Time of Flight Chemical Vapor Deposition). The work reveals complex formation mechanisms involving the heterogeneous phase nucleation mechanisms specific of the CVD deposition of pyrolytic carbon on the one hand, and well-known wetting mechanisms such the Plateau-Rayleigh instability on the other hand. The mounting of the nanocones on dedicated supports as probes for near-field microscopies is then carried out, followed by characterization studies (SEM, TEM, RAMAN spectroscopy) to assess their starting characteristics from the geometry and structure point of view, and their evolution under the operating conditions required for both the probe fabrication and for the different near-field microscopy modes studied. In a second part, the potentiality of carbon nanocones as probes for non-conductive modes such as topographic mode (atomic force microscopy - AFM) and "Peak Force Quantitative Nano Mechanical" (PF-QNM) mode, as well as for conductive modes such as scanning tunneling microscopy (STM), conductive atomic force microscopy (c-AFM), and Kelvin force microscopy (KFM) is evaluated. This evaluation is made on the basis of (i) performances; (ii) durability; (iii) versatility. The final goal is to compare the performance of the carbon nanocone probes with other commercial probes. Carbon nanocones reveal to truly be multimode probes with few existing counterparts nowadays. Improvements are needed and possible, for which directions are proposed