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Bärtling, Yves, Dietrich Hoppe, and Uwe Hampel. "Preliminary investigations on high energy electron beam tomography." Forschungszentrum Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-64330.
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In computed tomography (CT) cross-sectional images of the attenuation distribution within a slice are created by scanning radiographic projections of an object with a rotating X-ray source detector compound and subsequent reconstruction of the images from these projection data on a computer. CT can be made very fast by employing a scanned electron beam instead of a mechanically moving X-ray source.
Now this principle was extended towards high-energy electron beam tomography with an electrostatic accelerator. Therefore a dedicated experimental campaign was planned and carried out at the Budker Insitute of Nuclear Physics (BINP), Novosibirsk. There we investigated the capabilities of BINP’s accelerators as an electron beam generating and scanning unit of a potential high-energy electron beam tomography device. The setup based on a 1 MeV ELV-6 (BINP) electron accelerator and a single detector.
Besides tomographic measurements with different phantoms, further experiments were carried out concerning the focal spot size and repeat accuracy of the electron beam as well as the detector’s response time and signal to noise ratio.
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Bärtling, Yves, Dietrich Hoppe, and Uwe Hampel. "Preliminary investigations on high energy electron beam tomography." Forschungszentrum Dresden-Rossendorf, 2010. https://hzdr.qucosa.de/id/qucosa%3A22134.
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In computed tomography (CT) cross-sectional images of the attenuation distribution within a slice are created by scanning radiographic projections of an object with a rotating X-ray source detector compound and subsequent reconstruction of the images from these projection data on a computer. CT can be made very fast by employing a scanned electron beam instead of a mechanically moving X-ray source.
Now this principle was extended towards high-energy electron beam tomography with an electrostatic accelerator. Therefore a dedicated experimental campaign was planned and carried out at the Budker Insitute of Nuclear Physics (BINP), Novosibirsk. There we investigated the capabilities of BINP’s accelerators as an electron beam generating and scanning unit of a potential high-energy electron beam tomography device. The setup based on a 1 MeV ELV-6 (BINP) electron accelerator and a single detector.
Besides tomographic measurements with different phantoms, further experiments were carried out concerning the focal spot size and repeat accuracy of the electron beam as well as the detector’s response time and signal to noise ratio.
3
Suard, Mathieu. "Characterization and optimization of lattice structures made by Electron Beam Melting." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI055/document.
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Le récent développement de la Fabrication Additive de pièces métalliques permet d'élaborer directement des structures à partir de modèles 3D. En particulier, la technologie "Electron Beam Melting" (EBM) permet la fusion sélective, couche par couche, de poudres métalliques. Elle autorise la réalisation de géométries très complexes mais apporte de nouvelles contraintes de fabrication.Ce travail se concentre sur la caractérisation géométrique et mécanique de structures treillis produites par cette méthode. Les pièces fabriquées sont comparées au design initial à travers des caractérisations par tomographie aux rayons X. Les propriétés mécaniques sont testées en compression uni-axiale. Pour les poutres de faibles épaisseur, la différence entre la structure numérique et celle fabriquée devient significative. Les écarts au design initial se traduisent pour chaque poutre par un concept de matière mécaniquement efficace. D'un point de vue modélisation, ce concept est pris en compte en remplaçant la poutre fabriquée par un cylindre avec un diamètre mécaniquement équivalent. Ce diamètre équivalent est utilisé dans des simulations et optimisations "réalistes" intégrant ainsi les contraintes de fabrication de la technologie EBM.Différentes stratégies sont aussi proposées pour réduire la proportion de volume "inefficace" et améliorer le contrôle de la taille des poutres, soit en jouant sur les paramètres procédé et les stratégies de fusion, soit en effectuant des post-traitementsThe recent development of Additive Manufacturing for the fabrication of metallic parts allows structures to be directly manufactured from 3D models. In particular, the "Electron Beam Melting" (EBM) technology is a suitable process which selectively melts a powder bed layer by layer. It can build very complex geometries but brings new limitations that have to be quantified.This work focuses on the structural and mechanical characterization of lattice structures produced by such technology. The structural characterization mainly rely on X-ray tomography whereas mechanical properties are assessed by uni-axial compression. The geometry and related properties of the fabricated structures are compared with the designed ones. For small strut size, the difference between the designed structure and the produced one is large enough to impact the desired mechanical properties. The concept of mechanical efficient volume is introduced. For the purpose of simulation, this concept is taken into account by replacing the struts by a cylinder with a textit{mechanical equivalent diameter}. After validation, it has been used into "realistic" simulation and optimization procedures, thus taking into account the process constraints.Post-treatments (Chemical Etching and Electro-Chemical Polishing) were applied on lattice structures to get rid of the inefficient matter by decreasing the surface roughness. The control of the size of the fabricated struts was improved by tuning the process strategies and parameters
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Tammas-Williams, Samuel. "XCT analysis of the defect distribution and its effect on the static and dynamic mechanical properties in Ti-6Al-4V components manufactured by electron beam additive manufacture." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/xct-analysis-of-the-defect-distribution-and-its-effect-on-the-static-and-dynamic-mechanical-properties-in-ti6al4v-components-manufactured-by-electron-beam-additive-manufacture(cb034391-b61f-4e16-91cd-7ad3c9ec6312).html.
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Selective electron beam melting (SEBM) is a promising powder bed Additive Manufacturing technique for near-net-shape manufacture of high-value titanium components. An extensive research program has been carried out to characterise in 3D the size, volume fraction, and spatial distribution of the pores in model samples, using X-ray computed tomography (XCT), and correlate them to the SEBM process variables. The average volume fraction of the pores (97.5 %) where fatigue cracks would initiate based on the relative stress intensity factor of all the pores. In contrast, crack growth was found to be insensitive to porosity, which was attributed to the much higher stress concentration generated by the crack in comparison to the pores. Some crack diversion was associated with the local microstructure, with prior β grain boundaries often coincident with crack diversion.
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Glasser, Francis. "Méthodes de détection de rayonnement X pulsé pour la tomographie par transmission avec accélérateur linéaire." Grenoble 1, 1988. http://www.theses.fr/1988GRE10081.
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Etude du comportement de semi-conducteurs et d'un scintillateur comme convertisseurs de photons x en signal mesurable. Application a la tomographie industrielle utilisant un accelerateur lineaire en vue du controle non destructif d'objets denses et volumineux
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PEREIRA, LILIAN N. "Uso de diodos epitaxiais de Si em dosimetria de fótons." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10581.
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Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Lepinay, Kevin. "Développement et applications de la tomographie chimique par spectroscopie EDX." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0124/document.
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Cette thèse porte sur l’évaluation des techniques pour la tomographie chimique par STEM EDX : mise au point des procédures expérimentales, traitement des données, reconstruction des volumes, analyse de la qualité des résultats obtenus et évaluation de la complexité globale. Les performances très limitées de l’analyse STEM EDX font que peu d’études, jusqu’à aujourd’hui, se sont portées sur cette technique. Cependant, les avancées très notables procurées par les nouveaux détecteurs ‘SDD’ ainsi que les sources électroniques X-FEG haute brillance, rendant l’analyse STEM EDX 2D très rapide, ont relancé la possibilité de la tomographie chimique ; la technique demande toutefois à être mise au point et évaluée (performances et complexité). Nous avons travaillé sur un microscope Tecnai Osiris permettant d’acquérir des cartographies chimiques EDX de centaines de milliers de pixels avec une résolution de l’ordre du nanomètre en quelques minutes. Nous avons choisi de préparer par FIB des échantillons en forme de pointe et d’utiliser un porte-objet permettant une exploration angulaire de 180° sans ombrage. Puis, à l’aide d’échantillons modèles (billes de SiO2 dans une résine), nous avons évalué les déformations d’échantillon par l’irradiation du faisceau électronique. Ceci nous a permis de proposer une méthode pour limiter cet effet par déposition d’une couche de 20 nm de chrome. Des simulations d’images ont permis d’évaluer les logiciels et méthodes de reconstruction. La méthodologie de chaque étape d’une analyse de tomographie STEM EDX a ensuite été expliquée, et l’intérêt de la technique démontré grâce à la comparaison de l’analyse 2D et 3D d’un transistor FDSOI 28 nm. La qualité des reconstructions (rapport signal-sur-bruit, résolution spatiale) a été évaluée en fonction des paramètres expérimentaux à l’aide de simulations et d’expériences. Une résolution de 4 nm est démontrée grâce à l’analyse d’une mire et d’un transistor « gate all around ». Pour ce même transistor, la possibilité et l’intérêt d’analyse de défaillance à l’échelle nanométrique est prouvée. Une analyse d’un défaut de grille d’une SRAM ou de trous dans un pilier en cuivre permettent d’expliquer l’intérêt d’une combinaison d’un volume HAADF (morphologie et résolution < 4 nm) et du volume EDX (information chimique). La conclusion est que cette technique, qui reste encore à améliorer du point de vue de sa simplicité, montre déjà son utilité pour l’analyse et la mise au point des technologies avancées (nœud 20 nm et après)This thesis focuses on the evaluation of the STEM EDX chemical tomography technique: development of experimental procedures, data processing and volumes reconstruction, quality analysis of the results and evaluation of the overall complexity. Until now, STEM EDX analysis performances were very limited, so only few studies about this technique have been realized. However, very significant progress procured by the new SDD detectors as well as by the high brightness electronic sources (X-FEG), making the STEM EDX 2D analysis very fast, have revived the possibility of the chemical tomography, although the technique has to be developed and evaluated (performance and complexity). We have worked on a Tecnai Osiris which acquires EDX chemical mapping of hundreds of thousands of pixels with resolution of one nanometer and in a few minutes. We chose to prepare the rod-shaped samples by FIB and use a sample holder allowing an angle of exploration of 180° without shadowing effects. Then, using model samples (SiO2 balls in resin), we evaluated the sample deformation due to the electron beam irradiation. This allowed us to propose a method to reduce this effect by depositing a 20 nm chromium layer. Images simulations were used to evaluate the software and the reconstruction methods. The methodology of each step of the STEM EDX tomography analysis is then explained and the technique interest is demonstrated by comparing the 2D and the 3D analysis of a transistor 28 nm FDSOI. The quality of the reconstructions (signal-to-noise ratio, spatial resolution) was evaluated, in function of experimental parameters, using simulations and experiments. A resolution of 4 nm is demonstrated through the analysis of a test pattern and a "gate all around” transistor. For the same transistor, the possibility and the interest of a failure analysis at the nanoscale is proven. Analyses of a SRAM gate fail or of the holes in a copper pillar explain the benefits of a combination between a HAADF volume (morphology and resolution < 4 nm) and an EDX volume (chemical information). To conclude, this technique, which still needs to be improved in terms of simplicity, is already showing its usefulness for the analysis and the development of advanced technologies (20nm node and beyond)
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Gong, Hao. "A Scheme for Ultra-Fast Computed Tomography Based on Stationary Multi-Beam X-ray Sources." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/75054.
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The current cardiac computed tomography (CT) technology is mainly limited by motion blurring and radiation dose. The conceptual multi-source interior CT scheme has provided a potential solution to reduce motion artifacts and radiation exposure. This dissertation work conducted multi-facet investigations on a novel multi-source interior CT architecture (G. Cao, et. al, IEEE Access, 2014;2:1263-71) which employs distributed stationary multi-beam Carbon-nanotube (CNT) X-ray sources and simultaneously operates multiple source-detector chains to improve temporal resolution. The collimation based interior CT is integrated in each imaging chain, to suppress radiation dose. The central thesis statement is: Compared to conventional CT design, this distributed source array based multi-source interior CT architecture shall provide ultra-fast CT scan of region-of-interest (ROI) inside body with comparable image quality at lower radiation dose. Comprehensive studies were conducted to separately investigate three critical aspects of multi-source interior CT: interior CT mode, X-ray scattering, and scatter correction methods. First, a single CNT X-ray source based interior micro-CT was constructed to serve as a down-scaled experimental verification platform for interior CT mode. Interior CT mode demonstrated comparable contrast-noise-ratio (CNR) and image structural similarity to the standard global CT mode, while inducing a significant radiation dose reduction (< 83.9%). Second, the data acquisition of multi-source interior CT was demonstrated at clinical geometry, via numerical simulation and physical experiments. The simultaneously operated source-detector chains induced significant X-ray forward / cross scattering and thus caused severe CNR reduction (< 68.5%) and CT number error (< 1122 HU). To address the scatter artifacts, a stationary beam-stopper-array (BSA) based and a source-trigger-sequence (STS) based scatter correction methods were proposed to enable the online scatter measurement / correction with further radiation dose reduction (< 50%). Moreover, a deterministic physics model was also developed to iteratively remove the scatter-artifacts in the multi-source interior CT, without the need for modifications in imaging hardware or protocols. The three proposed scatter correction methods improved CNR (< 94.0%) and suppressed CT number error (< 48 HU). With the dedicated scatter correction methods, the multi-source interior CT could provide ROI-oriented imaging with acceptable image quality at significantly reduced radiation dose.Ph. D.
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Lifton, Joseph J. "The influence of scatter and beam hardening in X-ray computed tomography for dimensional metrology." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/378342/.
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This thesis is concerned with the use of X-ray computed tomography (CT) for making dimensional measurements. Scattered radiation and beam hardening are two phenomena that are well-known to severely degrade the quality of cone-beam CT data; however, the impact they have on dimensional measurements is not well understood. The aim of this work is to better understand how scatter and beam hardening influence dimensional measurements. The influence that scattered radiation and beam hardening have on internal and external dimensional measurements is investigated for two surface determination methods: the ISO50 method and a local gradient-based method. The work includes both experiment and simulation. The influence of scatter is assessed through the use of source collimation and the beam stop array scatter correction method, whilst the influence of beam hardening is assessed using spectrum pre-filtration. The simulation makes use of empirically derived X-ray spectra and scatter signals; good agreement between measured and simulated data is seen. The results show the presence of scatter and beam hardening decreases the measured size of internal features and increases the measured size of external features. This effect is seen for both surface determination methods, with the local method being more robust for outer features. The ISO50 surface determination method fails to give the ‘correct’ surface position for both inner and outer features in the presence of scatter and/or beam hardening. For the local surface determination method, scatter and beam hardening change the turning point of the edge gradient, this being the property by which surface points are defined for the local method; it is therefore through this change in turning point that scatter and beam hardening influence dimensional measurements.
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Bhatia, Navnina. "Scattering correction in cone beam tomography using continuously thickness-adapted kernels." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI092.
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La tomodensitométrie intégrant une source de rayons X à faisceau divergent et un détecteur grand champ est une technique bien connue dans le domaine de la tomographie industrielle. La nature des matériaux et les épaisseurs traversées conduisent inévitablement à la génération de rayonnement diffusé. Ce dernier est généré par l’objet mais également par le détecteur. La présence de rayonnement parasite conduit à ne plus respecter l’hypothèse de la loi de Beer-Lambert. Par conséquent, on voit apparaitre sur les coupes tomographiques des artefacts de reconstruction comme des streaks, des effets ventouses ou des valeurs d’atténuation linéaire erronée. Par conséquence, on retrouve dans la littérature de nombreuses méthodes de correction du diffusé. Ce travail vise à mettre en point et tester une méthode originale de correction du diffusé. Le premier chapitre de cette étude, dresse un état de l’art de la plupart des méthodes de corrections existantes. Nous proposons, dans le deuxième chapitre, une évolution de la méthode de superposition des noyaux de convolution (Scatter Kernel Superposition). Notre méthode repose sur une description continue des noyaux en fonction de l’épaisseur traversée. Dans cette méthode, les noyaux de diffusion sont paramétrés analytiquement sur toute la plage d'épaisseur. Le procédé a été testé pour des objets à la fois mono-matériaux et poly-matériaux, ainsi que sur des données expérimentales et simulées. Nous montrons dans le troisième chapitre l’importance de la contribution du diffusé détecteur dans la qualité de l’image reconstruite. Mais également l’importance de décrire les noyaux de convolution à l'aide d'un modèle à quatre gaussienne. Les résultats obtenus à partir de données expérimentales prouvent que la correction du diffusé de l'objet seul ne suffit pas pour obtenir une image de reconstruite sans artefacts. Afin de disposer d’une meilleur modélisation du diffusé du détecteur, nous décrivons, dans le dernier chapitre, une méthode basée sur la combinaison de données expérimentales et simulées permettant d’améliorer l’estimation des noyaux de diffuséAdvanced Cone Beam Computed Tomography (CBCT) typically uses a divergent conebeam source and a large area detector. As a result, there an inevitable increase in the size area of illumination causing an increase in the intensity of X-ray scatter signal, both from the object and the detector. This leads to the violation of prime assumption of reconstruction process which is based on straight line integrals path followed by the photons. Consequently scatter artifacts appear in the reconstruction images as steaks, cupping effect and thus produce wrong reconstruction values. Due to the severity of the reconstruction artifact caused by scatter, many scatter corrections methods have been adopted in literature. The first part of this study, reviews most of the existing scatter correction methods. The effect of scattering becomes more prominent and challenging in case of X-ray source of high energy which is used in industrial Non Destructive Testing (NDT), due to higher scatter to primary ratio (SPR). Therefore, in this study, we propose a continuously thickness-adapted deconvolution approach based on improvements in the Scatter Kernel Superposition (SKS) method. In this method, the scatter kernels are analytically parameterized over the whole thickness range of the object under study to better sample the amplitude and shape of kernels with respect to the thickness. The method is tested for both homogeneous and heterogeneous objects as well as simulated and experimental data. Another important aspect of this study is the comprehensive evaluation of contribution of the detector scatter performed using continuous method by separating the contribution of scatter due to the object and the detector. This is performed by modeling the scatter kernels using a four-Gaussian model. In the first approach, we performed this evaluation based on simulation of kernels from Monte Carlo simulations and the corrections are performed on typical industrial experimental data. The results obtained prove that the scatter correction only due to the object is not sufficient to obtain reconstruction image, free from artifacts, as the detector also scatters considerably. In order to prove this point experimentally and to have a better modeling of the detector, we describe a method based on combination of experiments and simulations to calculate the scatter kernels. The results obtained also prove, the contribution of the detector scattering becomes important and the PSF of the detector is not constant as considered in the studies so far, but it varies to a great extend with the energy spectrum
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Vroome, Kyle M. "Anterior alveolar bone changes following premolar extractions : a cone beam computed tomography evaluation /." Oklahoma City : [s.n.], 2009.
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Wheatland, Jonathan Antony Thomas. "Characterising the multi-scale properties of flocculated sediment by X-ray and focused ion beam nano-tomography." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/25984.
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The hydrodynamic behaviour of fine suspended aqueous sediments, and stability of the bedforms they create once settled, are governed by the physical properties (e.g., size, shape, porosity and density) of the flocculated particles in suspension (flocs). Consequently, accurate prediction of the transport and fate of sediments and of the nutrients and pollutants they carry depends on our ability to characterise aqueous flocs. Current research primarily focuses on characterising flocs based on their external gross-scale (>1 μm) properties (e.g., gross morphology, size and settling velocity) using in situ techniques such as photography and videography. Whilst these techniques provide valuable information regarding the outward behaviour of flocculated sediment (i.e. transport and settling), difficulties associated with extracting 3D geometries from 2D projections raises concerns regarding their accuracy and key parameters such as density can only be estimated. In addition, they neglect to inform on the internal micro- and nano-scale structure of flocs, responsible for much of their behaviour and development. Transmission electron microscope (TEM) and environmental electron microscope may be used to obtain nano-scale information in, essentially, 2D but there is a large scale gap between this information and the macro-scale of optical techniques. To address this issue this study uses 3D tomographic imaging over a range of spatial scales. Whilst commonly used in materials science and the life sciences, correlative tomography has yet to be applied in the environmental sciences. Threading together 3D Xray micro-computed tomography (X-ray μCT) and focused ion beam nano-tomography (FIBnt) with 2D TEM makes material characterisation from the centimetre to nanometre-scale possible. Here, this correlative imaging strategy is combined with a non-destructive stabilisation procedure and applied to the investigation of flocculated estuarine sediment, enabling the multi length-scale properties of flocs to be accurately described for the first time. This work has demonstrated that delicate aqueous flocs can be successfully stabilised via a resin embedding process and contrasted for both electron microscopy and X-ray tomography imaging. The 3D information obtained can be correlated across all length-scales from nm to mm revealing new information about the structure and morphology of flocs. A new system of characterising floc structure can be defined based on the association of particles and their stability in the structure rather than simply their size. This new model refutes the postulate that floc structures are fractal in nature.
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Olsen, Justin Todd. "Buccal plate changes following rapid versus slow palatal expansion : a cone beam comuted tomography study /." Oklahoma City : [s.n.], 2009.
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Wils, Patricia. "Tomographie par rayons X : correction des artefacts liés à la chaîne d'acquisition." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00708545.
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L'imagerie cone-beam computed tomography (CBCT) est une méthodologie de contrôle non destructif permettant l'obtention d'images volumiques d'un objet. Le système d'acquisition se compose d'un tube à rayons X et d'un détecteur plan numérique. La recherche développée dans ce manuscrit se déroule dans le contexte industriel. L'objet est placé sur une platine de rotation et une séquence d'images 2D est acquise. Un algorithme de reconstruction procure des données volumiques de l'atténuation de l'objet. Ces informations permettent de réaliser une étude métrologique et de valider ou non la conformité de la pièce imagée. La qualité de l'image 3D est dégradée par différents artefacts inhérents à la plateforme d'acquisition. L'objectif de cette thèse est de mettre au point une méthode de correction adaptée à une plateforme de micro-tomographie par rayons X d'objets manufacturés poly-matériaux. Le premier chapitre décrit les bases de la physique et de l'algorithmie propres à la technique d'imagerie CBCT par rayons X ainsi que les différents artefacts nuisant à la qualité de l'image finale. Le travail présenté ici se concentre sur deux types d'artefacts en particulier: les rayonnements secondaires issus de l'objet et du détecteur et le durcissement de faisceau. Le second chapitre présente un état de l'art des méthodes visant à corriger le rayonnement secondaire. Afin de quantifier le rayonnement secondaire, un outil de simulation basé sur des techniques de Monte Carlo hybride est développé. Il permet de caractériser le système d'acquisition installé au laboratoire de façon réaliste. Le troisième chapitre détaille la mise en place et la validation de cet outil. Les calculs Monte Carlo étant particulièrement prohibitifs en terme de temps de calcul, des techniques d'optimisation et d'accélération sont décrites. Le comportement du détecteur est étudié avec attention et il s'avère qu'une représentation 2D suffit pour modéliser le rayonnement secondaire. Le modèle de simulation permet une reproduction fidèle des projections acquises avec le système réel. Enfin, le dernier chapitre présente la méthodologie de correction que nous proposons. Une première reconstruction bruitée de l'objet imagé est segmentée afin d'obtenir un modèle voxélisé en densités et en matériaux. L'environnement de simulation fournit alors les projections associées à ce volume. Le volume est corrigé de façon itérative. Des résultats de correction d'images tomographiques expérimentales sont présentés dans le cas d'un objet mono-matériaux et d'un objet poly-matériaux. Notre routine de correction réduit les artefacts de cupping et améliore la description du volume reconstruit.
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Slater, Thomas Jack Alfred. "Three dimensional chemical analysis of nanoparticles using energy dispersive X-ray spectroscopy." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/three-dimensional-chemical-analysis-of-nanoparticles-using-energy-dispersive-xray-spectroscopy(3eb607a2-eb03-4d45-b9eb-71b0ca45c2db).html.
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The aim of this thesis is to investigate the methodology of three dimensional chemical imaging of nanoparticles through the use of scanning transmission electron microscope (STEM) – energy dispersive X-ray (EDX) spectroscopy. In this thesis, an absorption correction factor is derived for spherical nanoparticles that can correct X-ray absorption effects. Quantification of EDX spectra of nanoparticles usually neglects X-ray absorption within the nanoparticle but may lead to erroneous results, thus an absorption correction is important for accurate compositional quantification. The absorption correction presented is verified through comparison with experimental data of Au X-ray peaks in spherical Au nanoparticles and is found to agree excellently. This absorption correction allows accurate compositional quantification of large ( > 100 nm) particles with STEM-EDX.Three dimensional chemical mapping is achievable through the use of EDX spectroscopy with electron tomography. Here, the methodology of STEM-EDX tomography is fully explored, with a focus on how to avoid artefacts introduced through detector shadowing and low counts per pixel. A varied-time acquisition scheme is proposed to correct for detector shadowing that is shown to provide a more constant intensity over a series of projections, allowing a higher fidelity reconstruction. The STEM-EDX tomography methodology presented is applied to the study of AgAu nanoparticles synthesized by the galvanic replacement reaction. The elemental distribution as a function of the composition of the as-synthesized nanoparticles is characterised and a reversal in the element segregated to the surface of the nanoparticles is found. The composition at which the reversal takes place is shown to correlate with a peak in the catalytic yield of a three component coupling reaction. It is hypothesized that a continuous Au surface results in the optimum catalytic conditions for the reaction studied, which guides the use of galvanically prepared AgAu nanoparticles as catalysts.
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Patel, Neepa. "A cone-beam computerized tomography evaluation of anterior root resorption comparing SureSmile® and conventional edgewise treatments." Oklahoma City : [s.n.], 2009.
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Flay, Nadia. "An investigation of the factors associated with the X-ray tube and their influence on dimensional measurement in micro-focus cane-beam industrial X-ray computed tomography systems." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/414010/.
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In recent years, X-ray computed tomography (XCT) has successfully entered the field of dimensional metrology. XCT offers advantages over traditional tactile and optical coordinate measuring machines because of its ability to detect both the outer and inner geometries of an object. Due to the complex nature of XCT, there are a large number of factors which can influence dimensional measurement; many of these factors are still poorly understood. The novel study of a number of influence factors associated with the X-ray tube and their influence on dimensional measurement in micro-focus cone-beam XCT systems is presented in this thesis. The influence factors investigated in this study are the positional stability of the focal spot, the off-focal radiation, the focal spot size and the focal spot shape. The necessary background information to X-ray physics, XCT technology and dimensional metrology is discussed. The analysis of these influence factors was conducted at the National Physical Laboratory using experimental and computer simulation techniques. The experimental part of this research was carried out on Nikon Metrology XT H 225 M, with simulations performed using bespoke computer codes. The results of the study show that the positional stability of the focal spot, the off-focal radiation, the focal spot size and shape can all affect dimensional measurement. It is, therefore, proposed to include these parameters as part of the future standardised X-ray tube qualification and performance verification procedures of XCT systems. The evaluation techniques developed during the study can be employed as part of these standardised procedures. In addition, based on the findings of the study a number of future areas of research are proposed.
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Ghous, Abid Petroleum Engineering Faculty of Engineering UNSW. "3D imaging and modeling of carbonate core at multiple scales." Awarded By:University of New South Wales. Petroleum Engineering, 2010. http://handle.unsw.edu.au/1959.4/44606.
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The understanding of multiphase flow properties is essential for the exploitation of hydrocarbon reserves in a reservoir; these properties in turn are dependent on the geometric properties and connectivity of the pore space. The determination of the pore size distribution in carbonate reservoirs remains challenging; carbonates exhibit complex pore structures comprising length scales from nanometers to several centimeters. A major challenge to the accurate evaluation of these reservoirs is accounting for pore scale heterogeneity on multiple scales. This is the topic of this thesis. Conventionally, this micron scale information is achieved either by building stochastic models using 2D images or by combining log and laboratory data to classify pore types and their behaviour. None of these capture the true 3D connectivity vital for flow characterisation. We present here an approach to build realistic 3D network models across a range of scales to improve property estimation through employment of X-ray micro-Computed Tomography (μCT) and Focussed Ion Beam Tomography (FIBT). The submicron, or microporous, regions are delineated through a differential imaging technique undertaken on x-ray CT providing a qualitative description of microporosity. Various 3-Phase segmentation methods are then applied for quantitative characterisation of those regions utilising the attenuation coefficient values from the 3D tomographic images. X-ray micro-CT is resolution limited and can not resolve the detailed geometrical features of the submicron pores. FIB tomography is used to image the 3D pore structure of submicron pores down to a scale of tens of nanometers. We describe the experimental development and subsequent image processing including issues and difficulties resolved at various stages. The developed methodology is implemented on cores from producing wackstone and grainstone reservoirs. Pore network models are generated to characterise the 3D interconnectivity of pores. We perform the simulations of petrophysical properties (permeability and formation resistivity) directly on the submicron scale image data. Simulated drainage capillary pressure curves are matched with the experimental data. We also present some preliminary results for the integration of multiscale pore information to build dual-scale network models. The integration of multiscale data allows one to select appropriate effective medium theories to incorporate sub-micron structure into property calculations at macro scale giving a more realistic estimation of properties.
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Schörner, Karsten [Verfasser], PETER [Akademischer Betreuer] BOENI, and Franz [Akademischer Betreuer] Pfeiffer. "Development of Methods for Scatter Artifact Correction in Industrial X-ray Cone-beam Computed Tomography / Karsten Schörner. Gutachter: Franz Pfeiffer. Betreuer: Peter Böni." München : Universitätsbibliothek der TU München, 2012. http://d-nb.info/1022885669/34.
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Pereira, João Nuno Mendes Santos. "Técnicas radiográficas em Medicina Dentária na detecção de lesões endo-perio: uma análise comparativa." Master's thesis, [s.n.], 2015. http://hdl.handle.net/10284/5046.
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Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Medicina DentáriaA área da imagiologia e da endodontia estão em completa interligação. O diagnóstico e a concretização de um plano de tratamento dependem dos achados clínicos assim como os imagiológicos. No entanto, a quantidade de técnicas imagiológicas que hoje estão à disposição do clínico e do paciente invocam a necessidade de compreender quais as vantagens na utilização dos diversos meios para o sucesso no tratamento. Foi então realizada uma pesquisa nas bases de dados online PubMed, Scielo, Science Direct e b-On, compreendida entre o ano de 1996 e 2015, tendo sido seleccionados 48 artigos e o recurso a 3 livros para a concretização do trabalho. As conclusões obtidas são de que apesar da evolução e da descoberta de novas técnicas imagiológicas, não existe nenhuma que seja nem aconselhada ou desaconselhada ou sensível a 100% para o diagnóstico das patologias e que o recurso às diversas técnicas deve ter por base certos critérios que justifiquem a sua utilização. The imaging and endodontics area are in full interconnection. The diagnoses and the implementation of a treatment plan depend on the clinical as well as imaging foundings. However, the amount of imaging techniques that is now available to the clinician and patient, cal the need to understand the advantages in the use of various means to success in treatment. It was then carried out a search in online databases PubMed, Scielo, Science Direct and b -On, between 1996 and 2015 and was selected 48 articles and the use of 3 books for completing the work. The conclusions reached are in spite of evolution and discovery of new imaging techniques, there is none that is either recommended or discouraged or sensible at 100% for the diagnosis and that the use of various techniques should be based on certain criteria that justify its use.
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Junqueira, José Luiz Cintra. "Avaliação comparativa entre as telerradiografias cefalométricas laterais convencional, digital e geradas por tomografia computadorizada por aquisição volumétrica - cone beam /." Araçatuba : [s.n.], 2007. http://hdl.handle.net/11449/104521.
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Orientador: Francisco Antonio BertozBanca: Eduardo Cesar Almada Santos
Banca: José Augusto Sproesser
Banca: Ney Soares de Araújo
Banca: Thomaz Wassal
Resumo: O objetivo nesta pesquisa foi analisar os resultados obtidos comparativamente entre as telerradiografias cefalométricas laterais convencional, digital e as geradas pela tomografia computadorizada por aquisição volumétrica Cone Beam (CBTC). Foram realizadas distintamente as três tomadas radiográficas em 35 pacientes que estavam compreendidos na faixa etária de 12 a 14 anos. Foram utilizados dois programas específicos para a realização das análises cefalométricas de Rickets, McNamara e Jarabak, sendo utilizadas medidas lineares e angulares dos traçados. Apenas no traçado de Jarabak, foram utilizadas duas medidas lineares, para todas as outras, foi usada somente uma mensuração. Quatro tipos de exames radiográficos associados aos programas de análise cefalométrica foram utilizados. Por considerar o melhor resultado nos valores obtidos, a variável de referência foi a aquisição volumétrica CBTC em norma ortogonal, sendo comparado com os outros métodos. Verificou-se que os resultados obtidos pelas medidas angulares apresentaram menor variabilidade, enquanto as medidas lineares somente no traçado cefalométrico de McNamara obteve-se similaridade das variáveis. Observou-se que as técnicas radiográficas cefalométricas laterais convencionais apresentaram as maiores discrepâncias em relação à variável de referência. As análises cefalométricas realizadas pelo mesmo programa obtiveram os melhores resultados. Concluiu-se que para a obtenção de análises cefalométricas mais fidedignas deve-se utilizar um mesmo programa de avaliação e a tecnologia digital, principalmente a aquisição volumétrica CBTC em norma ortogonal e a telerradiografia cefalométrica lateral digital.
Abstract: The aim of this research was to analyze the results obtained comparatively among digital and conventional lateral cephalometric teleradiographies and the ones generated by Cone Beam volume computerized tomography (CBCT). Three distinct radiographies were performed in 35 patients in a 12 to 14 year-old group. Two specific programs were used to perform the cephalometric analysis according to Ricketts, McNamara and Jarabak, using linear and angular measurements of tracings. Two linear measurements were used just for Jarabak's tracing, for all the others only one measurement was used. Four types of radiographic exams associated to the cephalometric analysis program were used. For considering the best result in the obtained values, the variable of reference was the volume acquisition (CBCT) being compared to the other methods. It was verified that the results obtained by angular measurements presented less variability, while the linear measurements only in McNamara's cephalometric tracing presented similarity of variables. It was observed that the conventional lateral cephalometric radiography techniques presented bigger discrepancies in relation to the variable of reference. The cephalometric analysis performed by the same evaluation program had the best results. It was concluded that in order to obtain more reliable cephalometric analysis, one should use the same evaluation program and digital technology, particularly the volume acquisition (CBCT) in octagonal norm and digital lateral cephalometric teleradiography.
Doutor
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Alpuche, Aviles Jorge Edmundo. "The Development and Validation of a First Generation X-Ray Scatter Computed Tomography Algorithm for the Reconstruction of Electron Density Breast Images Using Monte Carlo Simulation." Journal of X-ray Science and Technology, IOS Press, 2011. http://hdl.handle.net/1993/4970.
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Breast CT is a promising modality whose inherent scatter could be used to reconstruct electron density (rho_e) images. This has led us to investigate the benefits of reconstructing linear attenuation coefficient (mu) and (rho_e) images of the breast. First generation CT provides a cost-effective and simple approach to reconstruct (rho_e) images in a laboratory but is limited by the anisotropic probability of scatter, attenuation, noise and contaminating scatter (coherent and multiple scatter).
These issues were investigated using Monte Carlo (MC) simulations of a first generation breast scatter enhanced CT (B-SECT) system. A reconstruction algorithm was developed for the B-SECT system and is based on a ring of detectors which eliminates the scatter dependence on the relative position of the scattering centre. The algorithm incorporates an attenuation correction based on the (mu) image and was tested against analytical and MC simulations. MC simulations were also used to quantify the dose per scan.
The ring measures a fraction of the total single incoherent scatter which is proportional to ray integrals of (rho_e) and can be quantified even when electron binding is non negligible. The algorithm typically reconstructs accurate (rho_e) images using a single correction for attenuation but has the capability for multiple iterations if required. MC simulations show that the dose coefficients are similar to those of cone beam breast CT. Coherent and multiple scatter can not be directly related to (rho_e) and lead to capping artifacts and overestimated (rho_e) by a factor greater than 2. This issue can be addressed using empirical corrections based on the radiological path of the incident beam and result in (rho_e) images of breast soft tissue with 1% accuracy, 3% precision and a mean glandular dose of 4 mGy for a 3D scan. The reconstructed (rho_e) image was more accurate than the (rho_e) estimate derived from the (mu) image. An alternative correction based on the thickness of breast traversed by the beam provides an enhanced contrast image reflecting the breast scatter properties. These results demonstrate the feasibility of detecting small (rho_e) changes in the intact breast and shows that further experimental evaluation of this technique is warranted.
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Junqueira, José Luiz Cintra [UNESP]. "Avaliação comparativa entre as telerradiografias cefalométricas laterais convencional, digital e geradas por tomografia computadorizada por aquisição volumétrica – cone beam." Universidade Estadual Paulista (UNESP), 2007. http://hdl.handle.net/11449/104521.
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junqueira_jlc_dr_araca.pdf: 590701 bytes, checksum: 5985895fd4803a2523f4047b068089a6 (MD5)O objetivo nesta pesquisa foi analisar os resultados obtidos comparativamente entre as telerradiografias cefalométricas laterais convencional, digital e as geradas pela tomografia computadorizada por aquisição volumétrica Cone Beam (CBTC). Foram realizadas distintamente as três tomadas radiográficas em 35 pacientes que estavam compreendidos na faixa etária de 12 a 14 anos. Foram utilizados dois programas específicos para a realização das análises cefalométricas de Rickets, McNamara e Jarabak, sendo utilizadas medidas lineares e angulares dos traçados. Apenas no traçado de Jarabak, foram utilizadas duas medidas lineares, para todas as outras, foi usada somente uma mensuração. Quatro tipos de exames radiográficos associados aos programas de análise cefalométrica foram utilizados. Por considerar o melhor resultado nos valores obtidos, a variável de referência foi a aquisição volumétrica CBTC em norma ortogonal, sendo comparado com os outros métodos. Verificou-se que os resultados obtidos pelas medidas angulares apresentaram menor variabilidade, enquanto as medidas lineares somente no traçado cefalométrico de McNamara obteve-se similaridade das variáveis. Observou-se que as técnicas radiográficas cefalométricas laterais convencionais apresentaram as maiores discrepâncias em relação à variável de referência. As análises cefalométricas realizadas pelo mesmo programa obtiveram os melhores resultados. Concluiu-se que para a obtenção de análises cefalométricas mais fidedignas deve-se utilizar um mesmo programa de avaliação e a tecnologia digital, principalmente a aquisição volumétrica CBTC em norma ortogonal e a telerradiografia cefalométrica lateral digital.
The aim of this research was to analyze the results obtained comparatively among digital and conventional lateral cephalometric teleradiographies and the ones generated by Cone Beam volume computerized tomography (CBCT). Three distinct radiographies were performed in 35 patients in a 12 to 14 year-old group. Two specific programs were used to perform the cephalometric analysis according to Ricketts, McNamara and Jarabak, using linear and angular measurements of tracings. Two linear measurements were used just for Jarabak’s tracing, for all the others only one measurement was used. Four types of radiographic exams associated to the cephalometric analysis program were used. For considering the best result in the obtained values, the variable of reference was the volume acquisition (CBCT) being compared to the other methods. It was verified that the results obtained by angular measurements presented less variability, while the linear measurements only in McNamara’s cephalometric tracing presented similarity of variables. It was observed that the conventional lateral cephalometric radiography techniques presented bigger discrepancies in relation to the variable of reference. The cephalometric analysis performed by the same evaluation program had the best results. It was concluded that in order to obtain more reliable cephalometric analysis, one should use the same evaluation program and digital technology, particularly the volume acquisition (CBCT) in octagonal norm and digital lateral cephalometric teleradiography.
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Moraes, Sergio Herrero [UNESP]. "Análise tomográfica Cone Beam e histológica do preparo do canal radicular com três sistemas rotatórios." Universidade Estadual Paulista (UNESP), 2010. http://hdl.handle.net/11449/101637.
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moraes_sh_dr_arafo.pdf: 695564 bytes, checksum: 9ac4357d57946680feb71b26574a149e (MD5)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
O presente estudo teve como objetivos as análise tomográfica e histológica do preparo do canal radicular com três sistemas rotatórios de NiTi: ProTaper (grupo 1), Mtwo (grupo 2) e K3 (grupo 3). Trinta e seis molares superiores foram radiografados pela técnica de tomografia cone beam (feixe cônico) antes e depois do preparo rotatório do canal mésio-vestibular. Os dentes foram pesados antes e depois do preparo para analisar a capacidade de corte dos instrumentos pela remoção de dentina. Aumento na área do canal, no alargamento do comprimento mésio-distal do canal, centralização e transporte do canal nos terços cervical, médio e apical foram analisadas nas tomografias computadorizadas transferidas para o software Canvas 11. Após o preparo dos canais radiculares as raízes foram descalcificadas, cortadas com 6 μm de espessura e coradas com hematoxilina-eosina, para exame das irregularidades das paredes de dentina do canal radicular e da presença de resíduos no canal. Para avaliar estatisticamente os resultados foi utilizado o método de variância (ANOVA).Os resultados revelaram que houve diferença estatisticamente significante entre os grupos. ProTaper removeu significativamente mais dentina do que Mtwo e K3 (p<0,05). Mtwo removeu mais do que o K3 (p<0,05). Protaper, Mtwo e K3 aumentaram significativamente a área do canal depois do preparo (p<0,05). A diferença foi significativa no terço cervical entre ProTaper e K3 (p<0,05), Mtwo e K3; terço médio entre ProTaper e K3 (p<,0,05), Mtwo e K3 (p<0,05); no terço apical entre ProTaper e K3 (p<0,05), Mtwo e K3.p<0,05). Protaper, Mtwo e K3 aumentaram significativamente o comprimento mésio-distal do canal. A diferença foi significativa entre ProTaper e K3 (p<0,05) , Mtwo e K3 nos terços cervical, médio e apical. Na avaliação da centralização do canal foi encontrada diferença significativa de desvio entre os grupos...
The key goal of the present study was the histological and tomographic analysis of the root canal preparation with three NiTi rotatory systems: ProTaper (group 1), Mtwo (group 2) e K3 (group 3). Thirty six maxillary molar teeth were radiographed with the cone beam technique before and after the mesial-buccal root canal preparation. The teeth were weighted before and after preparation to analyse dentine removal capacity of the cutting instruments. Images from computed tomography were transferred to the software Canvas 11 to allow for analysis of the increase of the root canal area, the widening of the mesial-distal distance, and the root canal centring and transport in the cervical, mesial and apical thirds. After the root canal preparation, the roots were decalcified, cut to 6 μm thickness, from the cervical third to the apical one and dyed with hematoxylin-eosin. The roots were then analysed as to irregularities in the dentine wall of the root canal, and presence of any residue. The variance method (ANOVA) was used to statistically evaluate the results, which presented statistically relevant difference amongst the groups. ProTaper removed dentine more significantly than Mtwo and K3 (p<0,05). Mtwo removed more than K3 (p<0,05). All groups presented significant increase in the area of the root canal after preparation (p<0,05), mainly in the cervical third and the apical third. Cervical third the difference was ProTaper and K3 (p<0,05), Mtwo and K3, and in the apical third the difference was ProTaper and K3 (p<0,05), Mtwo and K3 (p<0,05). Protaper, Mtwo e K3 significantly increased the mesial-distal distance... (Complete abstract click electronic access below)
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Krenkel, Martin Verfasser], Tim [Akademischer Betreuer] [Salditt, and Detlev [Akademischer Betreuer] Schild. "Cone-beam x-ray phase-contrast tomography for the observation of single cells in whole organs / Martin Krenkel. Betreuer: Tim Salditt. Gutachter: Tim Salditt ; Detlev Schild." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://d-nb.info/1078774285/34.
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Krenkel, Martin [Verfasser], Tim [Akademischer Betreuer] Salditt, and Detlev [Akademischer Betreuer] Schild. "Cone-beam x-ray phase-contrast tomography for the observation of single cells in whole organs / Martin Krenkel. Betreuer: Tim Salditt. Gutachter: Tim Salditt ; Detlev Schild." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://nbn-resolving.de/urn:nbn:de:gbv:7-11858/00-1735-0000-0023-9684-C-9.
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Moraes, Sergio Herrero. "Análise tomográfica Cone Beam e histológica do preparo do canal radicular com três sistemas rotatórios /." Araraquara : [s.n.], 2010. http://hdl.handle.net/11449/101637.
Full textAbstract:
Orientador: Marcelo GonçalvesBanca: Yara Teresinha Correa Silva Sousa
Banca: Ivaldo Gomes de Moraes
Banca: Fábio Luiz Camargo Villela Berbert
Banca: Mario Tanomaru Filho
Resumo: O presente estudo teve como objetivos as análise tomográfica e histológica do preparo do canal radicular com três sistemas rotatórios de NiTi: ProTaper (grupo 1), Mtwo (grupo 2) e K3 (grupo 3). Trinta e seis molares superiores foram radiografados pela técnica de tomografia cone beam (feixe cônico) antes e depois do preparo rotatório do canal mésio-vestibular. Os dentes foram pesados antes e depois do preparo para analisar a capacidade de corte dos instrumentos pela remoção de dentina. Aumento na área do canal, no alargamento do comprimento mésio-distal do canal, centralização e transporte do canal nos terços cervical, médio e apical foram analisadas nas tomografias computadorizadas transferidas para o software Canvas 11. Após o preparo dos canais radiculares as raízes foram descalcificadas, cortadas com 6 μm de espessura e coradas com hematoxilina-eosina, para exame das irregularidades das paredes de dentina do canal radicular e da presença de resíduos no canal. Para avaliar estatisticamente os resultados foi utilizado o método de variância (ANOVA).Os resultados revelaram que houve diferença estatisticamente significante entre os grupos. ProTaper removeu significativamente mais dentina do que Mtwo e K3 (p<0,05). Mtwo removeu mais do que o K3 (p<0,05). Protaper, Mtwo e K3 aumentaram significativamente a área do canal depois do preparo (p<0,05). A diferença foi significativa no terço cervical entre ProTaper e K3 (p<0,05), Mtwo e K3; terço médio entre ProTaper e K3 (p<,0,05), Mtwo e K3 (p<0,05); no terço apical entre ProTaper e K3 (p<0,05), Mtwo e K3.p<0,05). Protaper, Mtwo e K3 aumentaram significativamente o comprimento mésio-distal do canal. A diferença foi significativa entre ProTaper e K3 (p<0,05) , Mtwo e K3 nos terços cervical, médio e apical. Na avaliação da centralização do canal foi encontrada diferença significativa de desvio entre os grupos... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The key goal of the present study was the histological and tomographic analysis of the root canal preparation with three NiTi rotatory systems: ProTaper (group 1), Mtwo (group 2) e K3 (group 3). Thirty six maxillary molar teeth were radiographed with the cone beam technique before and after the mesial-buccal root canal preparation. The teeth were weighted before and after preparation to analyse dentine removal capacity of the cutting instruments. Images from computed tomography were transferred to the software Canvas 11 to allow for analysis of the increase of the root canal area, the widening of the mesial-distal distance, and the root canal centring and transport in the cervical, mesial and apical thirds. After the root canal preparation, the roots were decalcified, cut to 6 μm thickness, from the cervical third to the apical one and dyed with hematoxylin-eosin. The roots were then analysed as to irregularities in the dentine wall of the root canal, and presence of any residue. The variance method (ANOVA) was used to statistically evaluate the results, which presented statistically relevant difference amongst the groups. ProTaper removed dentine more significantly than Mtwo and K3 (p<0,05). Mtwo removed more than K3 (p<0,05). All groups presented significant increase in the area of the root canal after preparation (p<0,05), mainly in the cervical third and the apical third. Cervical third the difference was ProTaper and K3 (p<0,05), Mtwo and K3, and in the apical third the difference was ProTaper and K3 (p<0,05), Mtwo and K3 (p<0,05). Protaper, Mtwo e K3 significantly increased the mesial-distal distance... (Complete abstract click electronic access below)
Doutor
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Channagiri, Samartha A. "Multiscale characterization of aging mechanisms in commercial LiFePO4 battery cathodes." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1468233768.
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Malusek, Alexandr. "Calculation of scatter in cone beam CT : Steps towards a virtual tomograph." Doctoral thesis, Linköping : Department of Medical and Health Sciences, Linköping University, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11275.
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Oliveira, Matheus Lima de 1984. "Influence of anatomical location and FOV size on cone-beam computed tomography gray values = Análise da influência da localização anatômica e tamanho do FOV nos valores de cinza em imagens de tomografia computadorizada de feixe cônico." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/289200.
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Orientador: Guilherme Monteiro TosoniTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
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Resumo: O objetivo deste estudo foi avaliar a influência da região anatômica e do tamanho do FOV (field of view) nos valores de cinza em imagens de tomografia computadorizada de feixe cônico (TCFC). Soluções homogêneas de fosfato de potássio dibásico (K2HPO4) foram preparadas em sete diferentes concentrações e armazenadas separadamente em tubos de polipropileno. Um phantom de uma cabeça humana teve seis dentes extraídos - um incisivo central um primeiro prémolar e um primeiro molar da maxila e da mandíbula - e substituídos por esses tubos, que foram escaneados separadamente pelos aparelhos NewTom 3G, NewTom 5G e 3D Accuitomo 170, sob diferentes tamanhos de FOV. Em cortes axiais, valores médios de cinza foram obtidos em cinco níveis diferentes dentro de cada tubo de polipropileno e a média foi calculada. Para cada aparelho, análise de regressão linear avaliou a relação entre os valores médios de cinza e a concentração de K2HPO4 em seis regiões anatômicas, sob os diferentes FOVs. Coeficiente de determinação (R2) foi calculado. Nos três aparelhos, a correlação linear entre os valores de cinza e as concentrações de K2HPO4 variou entre as regiões anatômicas e os tamanhos de FOV (0,93 < R2 < 0,99). Desse modo, pode se concluir que a relação entre os valores de cinza em imagens de TCFC e a densidade do objeto não é uniforme por todo o arco dentário e é influenciada pelo tamanho do FOV nos três aparelhos de TCFC testados. A comparação desses valores obtidos em diferentes regiões anatômicas e com diferentes tamanhos de FOV não é confiável
Abstract: The aim of this study was to evaluate the influence of anatomical location and FOV (field of view) size in CBCT numbers. Homogeneous solutions of dipotassium phosphate (K2HPO4) were prepared at seven different concentrations and stored separately in polypropylene tubes. Six teeth were extracted from a human head phantom - the upper and lower central incisors, first premolars and first molars - and replaced by the tubes, which were scanned separately by NewTom 3G, NewTom 5G and 3D Accuitomo 170 under different FOV sizes. In axial sections, CBCT numbers were obtained at five levels within each polypropylene tube, and the average was calculated. For each CBCT unit, linear regression analysis evaluated the relationship between CBCT numbers and the concentration of K2HPO4 in six anatomical regions, under different FOVs. Coefficient of determination (R2) was calculated. Linear correlation between CBCT numbers and concentrations of K2HPO4 ranged between anatomical regions and FOV sizes (0.93 < R2 <0.99). Thus, it can be concluded that the relationship between CBCT numbers and object density is not uniform throughout the dental arch, and is influenced by the FOV size on the three CBCT units tested in this study. The comparison of CBCT numbers from different anatomical regions and with different FOV sizes is unreliable
Doutorado
Radiologia Odontologica
Doutor em Radiologia Odontológica
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Schurch, Brandt Roger. "Three-dimensional imaging and analysis of electrical trees." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/threedimensional-imaging-and-analysis-of-electrical-trees(73e032f6-3e6b-4ee9-9cc1-953a11f36cb3).html.
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Electrical trees are micrometre-size tubular channels of degradation in high voltage polymeric insulation, a precursor to failure of electrical power plant. Hence, electrical trees critically affect the reliability of power systems and the performance of new insulation designs. Imaging laboratory-grown electrical trees has been an important tool for studying how trees develop. Commonly, electrical trees prepared in transparent or translucent polymers are imaged using traditional optical methods. Consequently, most of the analysis has been based on two-dimensional (2D) images of trees, thus, valuable information may be lost. However, electrical trees are complex interconnected structures that require a tree-dimensional (3D) approach for more complete analysis. This thesis investigates a method for imaging and analysis of electrical trees to characterise their 3D structure and provide a platform for further modelling. Laboratory created electrical trees were imaged using X-ray Computed Tomography (XCT) and Serial Block-Face Scanning Electron Microscopy (SBFSEM), 3D imaging techniques that provide sub-micrometre spatial resolution. Virtual replicas of the trees, which are the 3D geometrical models representing the real electrical trees, were generated and new indices to characterise the 3D structure of electrical trees were developed. These parameters were indicative of differences in tree growth and thus, they can be used to investigate patterns and classify the structure of electrical trees. The progression of the tree was analysed using cross-sections of the tree that are orthogonal to the growth: the number of tree channels and area covered by them were measured. The fractal dimension of the tree was calculated from the 3D model and from the 2D projections, the latter being lower for all the tree-type structures studied. Parameters from the skeleton of the tree such as number of nodes, segment length, tortuosity and branch angle were measured. Most of the mean segment lengths ranged 6-13 µm, which is in accordance to the 10µm proposed by various tree-growth models. The capabilities of XCT and SBFSEM imaging techniques were evaluated in their application to electrical trees. Bush and branch trees, including early-growth electrical trees (of length 20-40 µm), were analysed and compared using the comprehensive tool of visualisation and characterisation developed. A two-stage tree-growth experiment was conducted to analyse the progression and development of tree branches using XCT: tree channels after the second stage of growth were wider than after the first, while the fractal dimension remained the same. The capabilities of XCT and SBFSEM were tested for imaging electrical trees in optically-opaque materials such as micro and nano-filled epoxy compounds. The general structure of trees in epoxy filled up to 20 wt% micro-silica was observed using both techniques. The use of a virtual replica as the 3D geometrical model for the simulation of the electric field distribution using Finite Element Analysis (FEA) was preliminary explored. A combination of the imaging techniques is proposed for a more complete structural analysis of trees. It is believed that a great impact towards understanding electrical treeing will be achieved using the 3D technical platform developed in this thesis.
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Cadiou, François. "Étude de l'impact de la microstructure sur les propriétés effectives électriques des batteries lithium-ion." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI108.
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Cette étude porte sur la compréhension du lien existant entre l’architecture microstructurelle et les propriétés effectives de conductivité dans les électrodes des batteries Li-ion. Les batteries Li-ion sont très intéressantes pour des domaines tels que le transport électrique. En effet, elles présentent une grande densité d’énergie et de puissance ce qui en fait de bons substituts pour les moteurs thermiques. Cependant, même si elles sont maintenant assez largement utilisées dans beaucoup de domaines, il y a toujours besoin d’en optimiser les performances. Ceci passe par une meilleure compréhension de l’impact de la microstructure sur les propriétés effectives pour réduire l’écart entre théorie et pratique. L’attention est portée ici sur les électrodes positives des batteries lithium-ion. Les caractéristiques tridimensionnelles telles que la percolation des phases, leur tortuosité ou encore leurs dimensions caractéristiques ont un fort impact sur les propriétés à l'échelle macroscopique. Leur étude nécessite l’utilisation de techniques d’imagerie 3D comme la tomographie aux rayons X et la tomographie sériée par faisceau d’ions focalisés et MEB (FIB/SEM) pour obtenir des données quantitatives et en interpréter les propriétés de transport de charge. Ces volumes sont alors traités (segmentation et analyses morphologiques) et utilisés comme base pour des simulations numériques. La méthode FFT (Fast Fourrier Transform) avec opérateur de Green « discret » est choisie. Ces simulations permettent, soit de remonter aux propriétés de conduction électrique des phases, à partir de la mesure de la conductivité de l’électrode, par méthode inverse, soit de prédire la conductivité effective de l’électrode, en utilisant des propriétés mesurées expérimentalement sur les phases prises séparément. Les microstructures 3D numériques peuvent également être altérées afin de prédire l’impact, sur ses propriétés effectives, de changements de composition dans la formulation de l’électrode. De nouveaux outils consacrés à la meilleure compréhension de la relation entre microstructure, propriétés effectives et performance des batteries lithium-ion sont développésLi-ion batteries are interesting for applications such as electric vehicles. They have indeed a high energy and power density, which makes them good substitutes for internal combustion engines. However, even if they are now quite widely used in many fields, there is still a need to optimize their performance. This requires a better understanding of the impact of the electrodes microstructure on their effective properties to narrow the gap between ideal and practical performance. Three-dimensional characteristics such as the carbon additive percolation or the tortuosity of the porosity have a strong impact on the electrode charge transport properties and power performance. The use of 3D imaging techniques such as X-ray tomography and serial focused ion beam and SEM tomography (FIB/SEM) is very powerful to quantify the electrode microstructures and interpret their charge transport properties. Furthermore, by processing the reconstructed volumes, one can use them as a basis for numerical simulations. We have chosen the FFT (Fast Fourrier Transform) method with "discrete" Green operator for numerical computations. These simulations can either be used to back calculate the phase (active material or conducting additive/binder) conduction properties from macroscopic electrical measurements by inverse method, or to predict the electrode effective conductivity from the phase conductivities. The 3D numerical microstructures obtained can also be modified in order to predict the influence of compositional changes in the electrode formulation on its properties. This study sets new tools to understand better the relationships between microstructure, effective electrical properties and the performance of Li-ion battery composite electrodes
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Amante, Joseph David. "Scanning Methods as Monitoring, Verification, and Accounting tools for CO₂ Sequestration in Unconventional Gas Reservoirs." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/76047.
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Unconventional gas reservoirs in carbon dioxide sequestration activities is a relatively new and unexplored concept currently undergoing pilot scale testing. Sequestration has the potential for enhancing gas recovery while mitigating carbon dioxide to long term storage structures. Due to the extremely complex systems associated with these unconventional reservoirs, modeling becomes difficult to predict accurately. This thesis presents methods to increase the confidence of inferred parameter testing for unconventional reservoir sequestration in both seam coal bed methane wells and a shale wells. Various tests include the use of computed tomography coupled with Avizo modeling software, inductively coupled mass spectrometer fluid transport analysis, pressure transient build tests, liquid level detection, and desorption analysis coupled with cleat image analysis. Analyses of coals performed by both environmental scanning electron microscope (ESEM) and micro CT demonstrate that distributions of cleat porosity in coals are anisotropic and not correlated to the seam depth or location. ESEM is used with micro CT scanning to verify the results before and after the impregnation of the carbonic acid. The micro CT data in Avizo Fire© was used calculate an increase in cleat permeability by 25%. The increase of major flow pathways is caused by the dissolution of carbonates. Changes in the structures were observed qualitatively through ESEM and micro CT and quantitatively through Avizo and inductively coupled mass spectrometry. The results of comparative study between the cleat structures and the desorption of various seams indicate a trend in the cleat porosity and the desorption rate of the coals as well as the cleat porosity and the total gas in various seams.Master of Science
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Velasco, Solange Kobayashi. "Detecção de fraturas radiculares e alveolares em incisivos superiores de maxilas caninas maceradas por meio de radiografias periapicais digitais e tomografia computadorizada por feixe cônico." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/23/23154/tde-06032017-135604/.
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O objetivo deste trabalho foi comparar radiografias periapicais (RP) com quatro protocolos diferentes de tomografia computadorizada por feixe cônico (TCFC) para o diagnóstico de fraturas alveolares e radiculares. Oitenta incisivos superiores (40 hígidos e 40 com fratura radicular) de cães foram inseridos em 80 alvéolos anteriores (40 hígidos e 40 com fratura alveolar) de 20 maxilas caninas maceradas em posições randomizadas previamente. Cada maxila foi submetida a duas RP com diferentes angulações verticais e a quatro protocolos de TCFC com variações em kV (72 kV ou 80 kV), mA (4 mA ou 8 mA) e número de projeções (400 ou 500). As imagens obtidas foram randomizadas e analisadas por dois radiologistas odontológicos por duas vezes, com um intervalo de duas semanas entre as observações. Valores de sensibilidade, especificidade e acurácia para as análises binárias foram melhores para TCFC do que RP; fraturas radiculares apresentaram melhores resultados corretos de diagnóstico do que fraturas alveolares para RP e TCFC. Para a verificação da acurácia através da área sob a curva (ASC) de característica de operação do receptor (ROC), resultados de TCFC foram melhores do que resultados de RP; fraturas radiculares apresentaram melhores resultados corretos de diagnóstico do que fraturas alveolares para RP e TCFC. Quando a localização da fratura alveolar (porção vestibular ou porção palatina do alvéolo) ou da fratura radicular (terço cervical, médio ou apical) foi levada em consideração para a realização das análises estatísticas, os mesmos apresentaram uma discreta redução. RP com duas angulações verticais diferentes podem ser consideradas um bom método para diagnosticar fraturas radiculares. Quando não é possível diagnosticar fraturas radiculares e alveolares em RP, o próximo exame de escolha é a TCFC.The purpose of this study was to compare periapical radiograph (PR) and four different protocols of cone-beam computed tomography (CBCT) in the diagnosis of alveolar and root fractures. Eighty incisor teeth (40 higid and 40 with root fracture) from the canine species were inserted in 80 anterior alveolar sockets (40 higid sockets and 40 sockets with alveolar fracture) of 20 macerated canine maxillae in previously randomized positions. Afterwards, each maxilla was submitted to periapical radiograph in two different vertical angulation incidences, and to four different CBCT protocols, with variations in kV values (72 kV or 80 kV), mA values (4 mA or 8 mA) and number of frames (400 ou 500). The images were randomized and posteriorly analyzed by two oral and maxillofacial radiologists two times, with a two-week interval between observations. Sensitivity, specificity and accuracy values for binary analyses were better for CBCT than for PR; root fractures showed better diagnosis results than alveolar fractures for both CBCT and PR. When accuracy was calculated through area under the receiver operating characteristic (ROC) curve, CBCT showed better results than PR; root fractures showed better diagnosis results than alveolar fractures for both CBCT and PR. There was a slight reduction in value results when we considered the alveolar fracture (buccal or palatine portion of alveolus) or root fracture (cervical, median or apical third) location to perform the statistical analyses. Periapical radiograph with two different vertical angulations may be considered an accurate method to detect root fractures. When no fractures are diagnosed in PR and the patient describes pain symptoms, the subsequent exam of choice is CBCT.
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ALGARVE, FABIO J. "Caracterização dosimétrica do BeO em feixes de radiodiagnóstico convencional, mamografia e tomografia computadorizada, pelas técnicas de termoluminescência e luminescência opticamente estimulada." reponame:Repositório Institucional do IPEN, 2017. http://repositorio.ipen.br:8080/xmlui/handle/123456789/28017.
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A radiação ionizante é amplamente utilizada em diversas áreas na indústria e na medicina. No campo da medicina, a radiação ionizante é utilizada tanto para fins terapêuticos como para fins diagnósticos, abrangendo assim um grande intervalo de doses de diferentes tipos de radiações. Para certificar que a finalidade da prática esteja sendo alcançada, são necessários estudos detalhados de detectores e dispositivos que atendam aos diferentes tipos de radiações. Neste trabalho foi realizado um estudo das características dosimétricas de amostras de BeO em feixes padronizados de radiodiagnóstico convencional, mamografia e tomografia computadorizada, utilizando as técnicas de termoluminescência (TL) e luminescência opticamente estimulada (OSL) e propondo um sistema adequado para sua utilização em dosimetria de feixes. Os principais resultados obtidos foram: alta sensibilidade à luz branca durante a irradiação, boa reprodutibilidade das respostas TL e OSL (coeficientes de variação inferiores a 5%), parâmetros cinéticos correspondentes aos valores obtidos em todos os métodos testados, sem fading dentro do período estudado para ambas as técnicas. As características dosimétricas obtidas neste trabalho mostram a possibilidade de aplicação das amostras de BeO em dosimetria da radiação X, considerando os intervalos de dose empregados, pelas técnicas de TL e OSL. Assim, as amostras de BeO apresentaram sua utilização potencial para dosimetria de feixes de radiodiagnóstico convencional, mamografia e tomografia computadorizada.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
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ARATA, ANELYSE. "Degradação a baixa temperatura da Y-TZP odontológica: análise microestrutural e avaliação das propriedades mecânicas." reponame:Repositório Institucional do IPEN, 2016. http://repositorio.ipen.br:8080/xmlui/handle/123456789/27129.
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O objetivo deste estudo foi a Y-TZP odontológica submetida ao envelhecimento hidrotérmico acelerado (EH). Especificamente: a) determinar a curva cinética de transformação de fase tetragonal para monoclínica; b) calcular a velocidade de crescimento da frente da camada transformada durante o EH; c) avaliar a relação entre a porcentagem de fase monoclínica e profundidade da transformação de fase com a resistência à flexão biaxial (FB); d) avaliar o efeito da associação do EH e fadiga na resistência à FB. Discos sinterizados (YZ- Vita YZ, LP-Lava Plus) foram submetidos ao EH a 120°C, 130°C e 150°C e analisados por difração de raios X (DRX). Uma amostra por grupo foi analisada por microscopia eletrônica de varredura (MEV) e tomografia de coerência óptica (OCT) para calcular a profundidade de transformação de fase e a velocidade da frente de transformação. Grupos de (YZ, LP e LA-Lava) foram submetidos ao EH (150°C) por (n=10): 0, 5, 25, 70 e 140 horas. Após o EH os grupos de YZ foram novamente divididos (n=10): com e sem ciclagem mecânica, todas as cerâmicas foram submetidas ao teste de flexão biaxial (ISO 6872) e análise de variância 1 fator (ANOVA) (α=0,05) para comparar os resultados. Os resultados de DRX indicam que a Y-TZP apresenta um comportamento sigmoidal de transformação de fase devido à limitação da profundidade de penetração dos raios X (~6,3 μm). As análises de MEV e OCT confirmaram o crescimento linear da frente de envelhecimento em função do tempo para todas as temperaturas. O ANOVA 1-fator demonstrou redução de 10-19% da resistência à FB após 140 horas de envelhecimento (150°C) para todas as cerâmicas, havendo correlação negativa entre profundidade da camada transformada e resistência à FB. Extrapolando os resultados de profundidade para 37°C foi calculado que a frente de transformação de fase levaria 1053 e 2104 anos para atingir a profundidade de 62,67μm e 85,55μm responsáveis pela diminuição da resistência mecânica da YZ e LP, respectivamente. A associação do EH com a ciclagem mecânica não apresentou efeitos deletérios para a YZ. O OCT foi validado como método preciso, fácil e rápido para avaliação da camada transformada e estudos de cinética.
Tese (Doutorado em Tecnologia Nuclear )
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
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Hagos, Bereket Abrha. "Microstructural and chemical behaviour of irradiated graphite waste under repository conditions." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/microstructural-and-chemical-behaviour-of-irradiated-graphite-waste-under-repository-conditions(45b519ef-2f67-4aca-9b92-94a975e12875).html.
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A procedure to evaluate the leaching properties of radionuclides from irradiated graphite waste has been developed by combining ANSI 16.1 (USA) and NEN 7345 (Netherlands) standardised diffusion leaching techniques. The ANSI 16.1 standard has been followed to the acquire the leachates and to determine the leach rate/ diffusion coefficient and NEN 7345 standard technique has been used to determine the diffusion mechanism of radionuclides. The investigation employs simulated Drigg groundwater as a leachant using semi-dynamic technique for the production of leachate specimens. From gamma spectroscopy analysis the principal radionuclides present in terms of activity were 60Co, 137Cs, 134Cs, 155Eu, 133Ba and 46Sc. The dominant radionuclides are 60Co, 134Cs and 133Ba which together account for about 91 % of the total activity. The 91 % can be broken down into 73.4 % 60Co, 9.1 % 134Cs and 8.1 % 133Ba. Analysis of total beta and total beta without tritium activity release from Magnox graphite was measured using liquid scintillating counting. Preliminary results show that there is an initial high release of activity and decreases when the leaching period increases. This may be due to the depletion of contaminants which were absorbed by the internal pore networks and the surface. During the leaching test approximately 275.33 ± 18.20 Bq of 3H and 106.26 ± 7.01 Bq of 14C was released into the leachant within 91 days. Irradiation induced damages to the nuclear graphite crystal structure have been shown to cause disruption of the bonding across the basal planes. Moreover, the closures of Mrozowski cracks have been observed in nuclear graphite, the bulk property are governed by the porosity, in particular, at the nanometre scale. Therefore, knowledge of the crystallite structure and porosity distribution is very important; as it will assist in understand the affects of irradiated damage and location and the mechanism of the leaching of radionuclides. The work reported herein contributed several key findings to the international work on graphite leaching to offer guidance leading toward obtaining leaching data in the future: (a) the effective diffusion coefficient for 14C from graphite waste has been determined. The diffusion process for 14C has two stages resulting two different values of diffusion coefficient, i.e., for the fast and slow components; (b) the controlling leaching mechanism for 3H radionuclide from graphite is shown to be surface wash–off; and for that of 14C radionuclide the initial controlling leaching mechanism is surface wash-off following by diffusion which is the major transport mechanism ; (c) The weight loss originates from the open pore structure which has been opened up by radiolytic oxidation; at the higher weight losses much of the closed porosity in the graphite has been opened. The investigation indicates that weigh loss has a major influence on the leaching of elements from the irradiated graphite; and (d) the analysis of the pores in nuclear graphite can be categorised into three types. These three types of pores are: (1) small pores narrow which are slit-shaped pores in the binder phase or matrix, (2) gas evolution pores or gas entrapment pores within the binder phase or matrix and (3) lenticular pores which are large cracks within the filler particles. It is shown in this thesis that by using tomography to study the morphology of the different pores coupled with the distribution of impurities an understanding of the role of porosity in leaching is possible.
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Heckmann, Thibaut. "Reverse engineering secure systems using physical attacks." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEE018/document.
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Avec l’arrivée des dernières générations de téléphones chiffrés (BlackBerry PGP, iPhone), l’extraction des données par les experts est une tâche de plus en plus complexe et devient un véritable défi notamment après une catastrophe aérienne ou une attaque terroriste. Dans cette thèse, nous avons développé des attaques physiques sur systèmes cryptographiques à des fins d’expertises judiciaires. Une nouvelle technique de re-brasage à basse température des composants électroniques endommagés, utilisant un mélange eutectique 42Sn/58Bi, a été développée. Nous avons exploité les propriétés physico-chimiques de colles polymères et les avons utilisées dans l’extraction de données chiffrées. Une nouvelle technique a été développée pour faciliter l’injection et la modification à haute-fréquence des données. Le prototype permet des analyses en temps réel des échanges processeur-mémoire en attaque par le milieu. Ces deux techniques sont maintenant utilisées dans des dispositifs d’attaques plus complexes de systèmes cryptographiques. Nos travaux nous ont mené à sensibiliser les colles polymères aux attaques laser par pigmentation. Ce processus permet des réparations complexes avec une précision laser de l’ordre de 15 micromètres. Cette technique est utilisable en réparations judiciaires avancées des crypto-processeurs et des mémoires. Ainsi, les techniques développées, mises bout à bout et couplées avec des dispositifs physiques (tomographie 3D aux rayons X, MEB, laser, acide fumant) ont permis de réussir des transplantations judiciaires de systèmes chiffrés en conditions dégradées et appliquées pour la première fois avec succès sur les téléphones BlackBerry chiffrés à l’aide de PGPWhen considering the latest generation of encrypted mobile devices (BlackBerry’s PGP, Apple’s iPhone), data extraction by experts is an increasingly complex task. Forensic analyses even become a real challenge following an air crash or a terrorist attack. In this thesis, we have developed physical attacks on encrypted systems for the purpose of forensic analysis. A new low-temperature re-soldering technique of damaged electronic components, using a 42Sn/58Bi eutectic mixture, has been developed. Then we have exploited the physico-chemical properties of polymer adhesives and have used them for the extraction of encrypted data. A new technique has been developed to facilitate injection and high-frequency data modification. By a man-in-the-middle attack, the prototype allows analysing, in real-time, the data exchanges between the processor and the memory. Both techniques are now used in more complex attacks of cryptographic systems. Our research has led us to successfully sensitise polymer adhesives to laser attacks by pigmentation. This process allowed complex repairs with a laser with 15 micrometres precision and has been used in advanced forensic repair of crypto-processors and memory chips. Finally, the techniques developed in this thesis, put end-to-end and coupled with physical devices (X-ray 3D tomography, laser, SEM, fuming acids), have made it possible to have successful forensic transplants of encrypted systems in degraded conditions. We have successfully applied them, for the first time, on PGP-encrypted BlackBerry mobile phone
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Spencer, Benjamin. "On-line C-arm intrinsic calibration by means of an accurate method of line detection using the radon transform." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAS044/document.
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Les ``C-arm'' sont des systémes de radiologie interventionnelle fréquemment utilisés en salle d'opération ou au lit du patient. Des images 3D des structures anatomiques internes peuvent être calculées à partir de multiples radiographies acquises sur un ``C-arm mobile'' et isocentrique décrivant une trajectoire généralement circulaire autour du patient. Pour cela, la géométrie conique d'acquisition de chaque radiographie doit être précisément connue. Malheureusement, les C-arm se déforment en général au cours de la trajectoire. De plus leur motorisation engendre des oscillations non reproductibles. Ils doivent donc être calibrés au cours de l'acquisition. Ma thèse concerne la calibration intrinsèque d'un C-arm à partir de la détection de la projection du collimateur de la source dans les radiographies.Nous avons développé une méthode de détection de la projection des bords linéaires du collimateur. Elle surpasse les méthodes classiques comme le filtre de Canny sur données simulées ou réelles. La précision que nous obtenons sur l'angle et la position (phi,s) des droites est de l'ordre de: phi{RMS}=+/- 0.0045 degrees et s{RMS}=+/- 1.67 pixels. Nous avons évalué nos méthodes et les avons comparés à des méthodes classiques de calibration dans le cadre de la reconstruction 3DMobile isocentric x-ray C-arm systems are an imaging tool used during a variety of interventional and image guided procedures. Three-dimensional images can be produced from multiple projection images of a patient or object as the C-arm rotates around the isocenter provided the C-arm geometry is known. Due to gravity affects and mechanical instabilities the C-arm source and detector geometry undergo significant non-ideal and possibly non reproducible deformation which requires a process of geometric calibration. This research investigates the use of the projection of the slightly closed x-ray tube collimator edges in the image field of view to provide the online intrinsic calibration of C-arm systems.A method of thick straight edge detection has been developed which outperforms the commonly used Canny filter edge detection technique in both simulation and real data investigations. This edge detection technique has exhibited excellent precision in detection of the edge angles and positions, (phi,s), in the presence of simulated C-arm deformation and image noise: phi{RMS} = +/- 0.0045 degrees and s{RMS} = +/- 1.67 pixels. Following this, the C-arm intrinsic calibration, by means of accurate edge detection, has been evaluated in the framework of 3D image reconstruction
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Bhattacharya, Arunodaya. "Ion irradiation effects on high purity bcc Fe and model FeCr alloys." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112398/document.
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Les alliages binaires FeCr de structure FM (ferrito/martensitique) sont actuellement les candidats les plus prometteurs comme matériaux de structure pour les réacteurs rapides refroidis au sodium et les futurs systèmes de fusion. Cependant, l'impact de Cr sur l'évolution de la microstructure irradié dans ces matériaux n’est pas bien compris. De plus, particulièrement pour les applications de fusion, le scénario de dégâts d'irradiation devrait être compliquée en outre par la présence de grandes quantités d'hélium produit par transmutation nucléaire (~ 10 appm He / dpa). Dans ce contexte, une étude spécifique des effets de l'irradiation ionique (influence du Cr et de l’He sur l’évolution de la microstructure) a été menée à 500 ° C sur une grande variété d’alliages FeCr de haute pureté (à teneur en Cr allant de ~ 3 wt.% À 14 wt.%) ainsi que sur du Fe pur. Les irradiations ont été effectuées à l'aide ions Fe, en mode mono-faisceau et mode dual-beam (irradiation par des ions Fe et co-implantation d'He) afin de pouvoir séparer le dommage ballistique de l’implantation couplée avec de l’He. Trois différentes doses ont été étudiées: dose élevée (157 dpa, avec 17 appm He / dpa), dose intermédiaire (45 dpa, avec 57 appm He / dpa) et in situ à faible dose (0,33 dpa, avec 3030 appm He / dpa). Les expériences ont été effectuées en utilisant l'installation JANNuS triple faisceau du CEA-Saclay et la plateforme in-situ du CSNSM-Orsay. L’évolution microstructurale des échantillons est essentiellement faite par MET, SAT et par EDS en mode STEM. Les principaux résultats sont les suivants : 1) L’étude détaillée de la population des cavités dans du Fe irradié à forte dose a révélé une forte réduction du gonflement du fait de l'ajout d’He. Une réduction drastique de la taille des cavités en dépit d’une densité plus élevée a été observée. Ce comportement a été observé tout au long zone irradié, jusqu’au pic d’endommagement. 2) La microstructure de cavités a également été étudiée dans les alliages FeCr irradiés en double faisceau à forte dose, et les résultats ont été comparés à ceux obtenus dans le Fe pur. L'analyse a été effectuée à une profondeur intermédiaire de 300 à 400 nm sous la surface (pour éviter les effets des interstitiels injectés et les effets de surface), correspondant à 128 dpa, 13 appm He / dpa. L’étude par TEM a montré que l'addition de petites quantités de Cr, aussi basse que 3wt.%, est très efficace pour réduire fortement le gonflement. Une réduction drastique de la taille des cavités a été mise en évidence. Par exemple, la taille moyenne des cavités pour l’alliage Fe3% Cr est de l’ordre de 0,9 nm alors qu’elle est voisine de 6,8 nm pour le Fe pur. De plus, la variation du gonflement en fonction de la teneur en Cr n’est pas monotone et présente un maximum local à environ 9 -. 10wt% Cr. 3) Le couplage des différentes techniques d’analyse, MET classique, STEM/EDS et analyse SAT appliqué à l’étude des alliages FeCr irradiés à faible et moyenne dose révèle la présence de zones enrichies en Cr sur le plan d’habitat des boucles de dislocation. Ce phénomène est relié à un phénomène de ségrégation induite par irradiation (RIS) de Cr au voisinage du coeur des boucles de dislocation. Quand la boucle se développe sous irradiation, les zones de ségrégation ne peuvent probablement pas se redissoudre du fait de la présence d'impuretés telles que le C. Lorsque les boucles sont imagées par MET, ces zones enrichies produisent des franges de contraste au voisinage du plan de la boucle. Une estimation quantitative de cet enrichissement a été déduit par STEM / EDS et l'SAT. La teneur en Cr dans ces domaines se situe entre 23 -. 35% par EDS et 22 % par SAT, ce qui est bien en dessous de la teneur en Cr de la phase α’ riche en CrFeCr binary alloys are a simple representative of the reduced activation ferritic/martensitic (F-M) steels, which are currently the most promising candidates as structural materials for the sodium cooled fast reactors (SFR) and future fusion systems. However, the impact of Cr on the evolution of the irradiated microstructure in these materials is not well understood in these materials. Moreover, particularly for fusion applications, the radiation damage scenario is expected to be complicated further by the presence of large quantities of He produced by the nuclear transmutation (~ 10 appm He/dpa). Within this context, an elaborate ion irradiation study was performed at 500 °C on a wide variety of high purity FeCr alloys (with Cr content ranging from ~ 3 wt.% to 14 wt.%) and a bcc Fe, to probe in detail the influence of Cr and He on the evolution of microstructure. The irradiations were performed using Fe self-ions, in single beam mode and in dual beam mode (damage by Fe ions and co-implantation of He), to separate ballistic damage effect from the impact of simultaneous He injection. Three different dose ranges were studied: high dose (157 dpa, 17 appm He/dpa for the dual beam case), intermediate dose (45 dpa, 57 appm He/dpa for dual beam case) and in-situ low dose (0.33 dpa, 3030 appm He/dpa for the dual beam case). The experiments were performed at the JANNuS triple beam facility and dual beam in situ irradiation facility at CEA-Saclay and CSNSM, Orsay respectively. The microstructure was principally characterized by conventional TEM, APT and EDS in STEM mode. The main results are as follows: 1) A comparison of the cavity microstructure in high dose irradiated Fe revealed strong swelling reduction by the addition of He. It was achieved by a drastic reduction in cavity sizes and an increased number density. This behaviour was observed all along the damage depth, upto the damage peak. 2) Cavity microstrusture was also studied in the dual beam high dose irradiated FeCr alloys, and the results were compared to bcc Fe. The analysis was performed at an intermediate depth 300 – 400 nm below the surface (to avoid injected interstitial effect and surface effects), corresponding to 128 dpa, 13 appm He/dpa. TEM study revealed that the addition of small quantities of Cr, as low as 3wt.%, is highly efficient in strongly reducing void swelling. It was achieved by a drastic reduction of cavity sizes. For instance, average cavity size in Fe3%Cr was 0.9 nm as opposed to 6.8 nm in bcc Fe. Furthermore, the variation of void swelling as a function of Cr content is non-monotonic, with alocal maxima around 9 - 10wt.%Cr. 3) Coupling of conventional TEM, STEM/EDS and APT analysis on low and intermediate dose irradiated FeCr alloys revealed the presence of Cr enriched zones on the habit plane of the dislocation loops. This is expected to be due to radiation induced segregation (RIS) of Cr close to the core of the loops. As the loop grows under irradiation, the segregated areas are probably prevented from re-dissolution by impurity elements such as C. When imaged by TEM using classical diffraction contrast imaging techniques, these enriched zones produce displacement fringe contrast on the loop plane. A quantitative estimate of this enrichment was deduced by STEM/EDSand APT. The Cr content in these areas was between 23 - 35 at.% measured by EDS and 22 ± 2 at.% obtained by APT, whichis well below the Cr content of the Cr-rich α’ phase
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Matskova, Natalia. "Approche multi-échelle pour la caractérisation de l'espace poreux des réservoirs pétroliers argileux non conventionnels." Thesis, Poitiers, 2018. http://www.theses.fr/2018POIT2276.
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Les réservoirs pétroliers argileux sont caractérisés par des systèmes de pores associés à une distribution spatiale hétérogène à plusieurs échelles des phases minérales et organiques. Cette hétérogénéité nécessite une approche multi-échelle et multi-outils pour caractériser le réseau de pores. Une telle approche a été développée grâce à la sélection rigoureuse de 7 carottes issues de la formation de Vaca Muerta (Argentine), avec différentes maturations d'hydrocarbures mais des compositions minérales comparables. La tomographie RX 3D et la cartographie de la porosité par autoradiographie ont révélé les hétérogénéités à l'échelle des carottes, et permis d'identifier des zones homogènes pour le prélèvement de sous-échantillons comparables et représentatifs.Le couplage corrélatif de différentes techniques a permis d'atteindre un bilan quantitatif de la porosité / tailles de pores et pour la première fois, sur des blocs non broyées, notamment pour les expériences d'adsorption d'azote. Les résultats d’autoradiographie sont en accord avec les autres méthodes, indiquant que tous les pores sont connectés et accessibles par la résine d’imprégnation. Une diminution de la porosité totale ainsi que des tailles de pores a également été observée avec la maturation de la matière organique.Une approche innovante pour l'acquisition et le traitement de mosaïques d’images MEB a fourni des cartographies de la distribution des phases minérales et organiques à l'échelle du cm. Le couplage corrélatif avec la carte de porosité par autoradiographie des mêmes zones, a révélé les corrélations spatiales entre variations minéralogiques et de porositéGas shale reservoirs are characterized by pore systems, associated with a heterogeneous spatial distribution of mineral and organic phases at multiple scales. This high heterogeneity requires a multi-scale & multi-tool approach to characterize the pore network. Such an approach has been developed on 7 cores from the Vaca Muerta formation (Argentina), which belong to areas with various hydrocarbon maturities, but with comparable mineral compositions. 3D µtomography and quantitative 2D mapping of the connected porosity by autoradiography have been applied at the core scale, in aim to localize and analyze the spatial heterogeneities, and to identify similar homogenous areas for localizing comparable sub-samples.The correlative coupling of various techniques was applied to achieve quantitative balance of porosity and pore size distribution, from mm to nm scales on representative sub-samples and for the first time, on preserved blocks rather than crushed powders, even for nitrogen gas adsorption experiments. Results of autoradiography are in very good agreement with other total bulk porosities, indicating that all pores are connected and accessed by the 14C-MMA used for impregnation. Decreased total porosity and pore throat/body sizes were also observed as organic matter maturity increased. An innovative approach for electron microscopy images acquisition and treatment provided large mosaics, with the distribution of mineral and organic phases at the cm scale. The correlative coupling with the autoradiography porosity map of the same zone, revealed the spatial correlations between mineralogical variations and porosity
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Baimpas, Nikolaos. "'Hybrid' non-destructive imaging techniques for engineering materials applications." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:1aa00fed-34e6-4a5e-951b-c710e21ac23c.
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The combination of X-ray imaging and diffraction techniques provides a unique tool for structural and mechanical analysis of engineering components. A variety of modes can be employed in terms of the spatial resolution (length-scale), time resolution (frequency), and the nature of the physical quantity being interrogated. This thesis describes my contributions towards the development of novel X-ray “rich” imaging experimental techniques and data interpretation. The experimental findings have been validated via comparison with other experimental methods and numerical modelling. The combination of fast acquisition rate and high penetration properties of X-ray beams allows the collection of high-resolution 3-D tomographic data sets at submicron resolution during in situ deformation experiments. Digital Volume Correlation analysis tools developed in this study help understand crack propagation mechanisms in quasi-brittle materials and elasto-plastic deformation in co-sprayed composites. For the cases of crystalline specimens where the knowledge of “live” or residual elastic strain distributions is required, diffraction techniques have been advanced. Diffraction Strain Tomography (DST) allows non-destructive reconstruction of the 2-D (in-plane) variation of the out-of-plane strain component. Another diffraction modality dubbed Laue Orientation Tomography (LOT), a grain mapping approach has been proposed and developed based on the translate-rotate tomographic acquisition strategy. It allows the reconstruction of grain shape and orientation within polycrystalline samples, and provides information about intragranular lattice strain and distortion. The implications of this method have been thoroughly investigated. State-of-the-art engineering characterisation techniques evolve towards scrutinising submicron scale structural features and strain variation using the complementarity of X-ray imaging and diffraction. The first successful feasibility study is reported of in operando stress analysis in an internal combustion engine. Finally, further advancement of ‘rich’ imaging techniques is illustrated via the first successful application of Time-of-Flight Neutron Diffraction Strain (TOF-NDST) tomography for non-destructive reconstruction of the complete strain tensor using an inverse eigenstrain formulation.
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Sorel, Julien. "Tomographie électronique analytique : Automatisation du traitement de données et application aux nano-dispositifs 3D en micro-électronique." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI078.
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Ce travail porte sur l’automatisation du traitement des données de tomographie électronique analytique appliquée aux nano-dispositifs électroniques. La technique utilisée est la spectroscopie de dispersion en énergie des rayons-X en mode balayage en microscopie électronique en transmission (STEM-EDX : Scanning Transmission Electron Microscopy, Energy Dispersive X-ray spectroscopy). Si la tomographie électronique STEM-EDX a bénéficié d’avancées technologiques récentes, comme de nouvelles sources électroniques ‘X’-FEG (Field Emission Gun) et des détecteurs X sensibles, les SDD (Silicon Drift Detectors), elle reste chronophage avec une statistique de comptage souvent faible pour éviter des durées prohibitives et une dégradation de l’échantillon par irradiation électronique. L’empilement des projections STEM-EDX, acquises sous différents angles d’inclinaison, est par ailleurs très volumineux et les logiciels commerciaux actuels ne peuvent pas le traiter automatiquement et de manière optimale. Pour améliorer cette situation, nous avons développé un programme utilisant la librairie Hyperspy en langage python, dédiée au traitement de données multi-dimensionnelles. L’analyse statistique multivariée permet d’optimiser et d’automatiser le débruitage des données, la calibration des spectres et la séparation des raies d’émission X superposées pour l’obtention de reconstructions tridimensionnelles quantitatives. Une technique de reconstruction avancée, l’acquisition comprimée, a aussi été mise en œuvre, diminuant le nombre de projections sans réduire l’information 3D finale. La méthode développée a été utilisée pour l’analyse chimique 3D de quatre nanostructures issues de la microélectronique : des transistors FET multi-grilles, HEMT et GAA, et un film mince GeTe. Les échantillons ont été taillés en pointe par FIB (Focused Ion Beam: Faisceau d’ions focalisés), et les données obtenues sur un microscope Titan Themis muni d’un système à 4 détecteurs SDD. L’évaluation du programme atteste qu’il permet d’obtenir des résultats précis et fiables sur les architectures 3D étudiées. Des pistes d’améliorations sont discutées en perspective d’un futur logiciel dédié au traitement de données en tomographie électronique analytiqueThe aim of this thesis is to automate the process of hyperspectral analysis for analytical electron tomography applied to nanodevices. The work presented here is focused on datasets obtained by energy-dispersive X-ray spectroscopy in a scanning transmission electron microscope (STEM-EDX). STEM-EDX tomography has benefited greatly from recent developments in electron sources such as the ‘X’-FEG (Field Emission Gun), and multiple X-ray detector systems such as the Super-X, incorporating four SSD (Silicon Drift Detectors) detectors. The technique remains however very time-consuming, and low X-ray count rates are necessary to minimize the total acquisition time and avoid beam damage during the experiment. In addition, tomographic stacks of STEM-EDX datacubes, acquired at different tilt angles, are too large to be analyzed by commercial software packages in an optimal way. In order to automate this process, we developed a code based on Hyperspy, a Python library for multidimensional data analysis. Multivariate statistical analysis techniques were employed to optimize and automate the denoising, the energy calibration and the separation of overlapping X-ray lines, with the aim to achieve quantitative, chemically sensitive volumes. Moreover, a compressed sensing based algorithm was employed to achieve high fidelity reconstructions with undersampled tomographic datasets. The code developed during this thesis was used for the 3D chemical analysis of four microelectronic nanostructures: FinFET, HEMT and GAA transistors, and a GeTe thin film for memory device applications. The samples were prepared in a needle shape using a focused ion beam, and the data acquisitions were performed using a Titan Themis microscope equipped with a super-X EDX detector system. It is shown that the code yields 3D morphological and chemical information with high accuracy and fidelity. Ways to improve the current methodology are discussed, with future efforts aiming at developing a package dedicated to analytical electron tomography
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Ornek, Cem. "Performance characterisation of duplex stainless steel in nuclear waste storage environment." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/performance-characterisation-of-duplex-stainless-steel-in-nuclear-waste-storage-environment(4db73e9b-c87c-40a6-9778-0b823b1c499f).html.
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The majority of UK’s intermediate level radioactive waste is currently stored in 316L and 304L austenitic stainless steel containers in interim storage facilities for permanent disposal until a geological disposal facility has become available. The structural integrity of stainless steel canisters is required to persevere against environmental degradation for up to 500 years to assure a safe storage and disposal scheme. Hitherto existing severe localised corrosion observances on real waste storage containers after 10 years of exposure to an ambient atmosphere in an in-land warehouse in Culham at Oxfordshire, however, questioned the likelihood occurrence of stress corrosion cracking that may harm the canister’s functionality during long-term storage. The more corrosion resistant duplex stainless steel grade 2205, therefore, has been started to be manufactured as a replacement for the austenitic grades. Over decades, the threshold stress corrosion cracking temperature of austenitic stainless steels has been believed to be 50-60°C, but lab- and field-based research has shown that 304L and 316L may suffer from atmospheric stress corrosion cracking at ambient temperatures. Such an issue has not been reported to occur for the 2205 duplex steel, and its atmospheric stress corrosion cracking behaviour at low temperatures (40-50°C) has been sparsely studied which requires detailed investigations in this respect. Low temperature atmospheric stress corrosion cracking investigations on 2205 duplex stainless steel formed the framework of this PhD thesis with respect to the waste storage context. Long-term surface magnesium chloride deposition exposures at 50°C and 30% relative humidity for up to 15 months exhibited the occurrence of stress corrosion cracks, showing stress corrosion susceptibility of 2205 duplex stainless steel at 50°C.The amount of cold work increased the cracking susceptibility, with bending deformation being the most critical type of deformation mode among tensile and rolling type of cold work. The orientation of the microstructure deformation direction, i.e. whether the deformation occurred in transverse or rolling direction, played vital role in corrosion and cracking behaviour, as such that bending in transverse direction showed almost 3-times larger corrosion and stress corrosion cracking propensity. Welding simulation treatments by ageing processes at 750°C and 475°C exhibited substantial influences on the corrosion properties. It was shown that sensitisation ageing at 750°C can render the material enhanced susceptible to stress corrosion cracking at even low chloride deposition densities of ≤145 µm/cm². However, it could be shown that short-term heat treatments at 475°C can decrease corrosion and stress corrosion cracking susceptibility which may be used to improve the materials performance. Mechanistic understanding of stress corrosion cracking phenomena in light of a comprehensive microstructure characterisation was the main focus of this thesis.
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Staub, Déborah. "Étude du comportement mécanique à rupture des alumines de forte porosité : Application aux supports de catalyseurs d'hydrotraitement des résidus." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0089/document.
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La présente étude porte sur le comportement mécanique de deux types de supports de catalyseurs utilisés industriellement en hydrotraitement des résidus. Ces supports extrudés, fabriqués par IFPEN, sont constitués d’alumine de transition γ avec un taux de porosité proche de 70%. La porosité du premier matériau est uniquement constituée de mésopores (< 50 nm). La porosité du second matériau est constituée de mésopores et de macropores (jusqu’à 20 µm). Les niveaux de sollicitation en service étant très peu connus, cette étude s’attache à décrire de manière précise et exhaustive le comportement mécanique de ces supports sous une large gamme de sollicitations, et à identifier les différents mécanismes de ruine possibles. L’objectif final est de mieux comprendre les relations entre les paramètres microstructuraux et les propriétés mécaniques afin d’identifier des leviers d’amélioration de la tenue mécanique des supports. Dans un premier temps, une méthodologie adaptée de caractérisation mécanique est établie. Le comportement des supports est étudié d’une part en traction, à l’aide d’essais de flexion trois points et d’écrasement diamétral, et d’autre part, en compression sous différents taux de triaxialité, à l’aide d’essais de compression uniaxiale et hydrostatique et d’essais de micro-indentation sphérique. Les différents mécanismes responsables de la ruine des supports sont identifiés au moyen de techniques d’imagerie telles que la microscopie électronique à balayage et la micro-tomographie à rayons X. En traction, le comportement est fragile avec l’amorçage de la rupture sur un défaut critique. En compression, une transition fragile / quasi-plastique du comportement est observée avec l’augmentation du taux de confinement. Cette quasi-plasticité s’exprime en particulier à travers un phénomène de densification de la macroporosité. Dans un deuxième temps, un critère de rupture est identifié pour chaque type de matériau en vue de représenter sur une même surface de charge les différents types de comportement et phénomènes physiques observés. Cette identification est réalisée en couplant les essais d’indentation sphérique à une analyse numérique. Des critères faisant intervenir la pression hydrostatique permettent de rendre compte de la forte dissymétrie du comportement des matériaux en traction et en compression. Enfin, dans un souci de se rapprocher des sollicitations subies par les supports de catalyseurs dans un réacteur en service, le comportement d’un empilement de supports est étudié en compression œdométrique. L’analyse de cet essai par tomographie à rayons X permet de déterminer les différents mécanismes de ruine intervenant au sein d’un empilement, en particulier ceux responsables de la génération de fines. Les résultats illustrent la pertinence de la caractérisation en flexion et en indentation des supports de catalyseurs seuls pour prévoir leur comportement au sein d’un empilement en compressionIn this work, we study the mechanical behaviour of two types of catalysts supports produced by IFPEN and industrially used in residues hydrotreating. Those extruded supports are made of transition γ-alumina with about 70% of porous volume. The first material’s porosity is exclusively composed of mesopores (< 50 nm). The porosity of the second material is composed of both mesopores and macropores (up to 20 µm). Because of the limited knowledge of the stress fields in embedded catalysts supports in use in a reactor, this study aims at precisely and exhaustively describing the mechanical behaviour of those supports under a wide range of stresses, and identifying the possible damage mechanisms. The final objective is to better understand the influence of microstructural parameters on the mechanical properties of the supports in order to propose some leads about how to improve their mechanical strength. First, an adequate mechanical characterization methodology is set. On one hand, the tensile mechanical behaviour of the supports is studied with three-point bending and diametrical crushing tests. On the other hand, their compressive behaviour under various triaxiality rates is characterized in uniaxial and hydrostatic compression, and by spherical micro-indentation. The different damaging mechanisms are identified by imaging techniques such as scanning electronic microscopy and X-ray micro-tomography. Under tensile stresses, the supports exhibit a brittle behaviour and fracture initiates at a critical flaw. Under compressive stresses, a brittle/quasi-plastic transition is observed with increasing the triaxiality rate. The quasi-plasticity is mainly due to the densification of the macroporosity. The second part of the study consists in identifying, for each material, a fracture criterion able to represent every types of behaviour and physical phenomena observed on the same yield surface. This identification is achieved by coupling the spherical indentation tests to a numerical analysis. Fracture criteria involving hydrostatic pressure are well suited to describe the highly dissymmetric mechanical behaviour of the materials in tension and in compression. The last part of this work aims at studying the mechanical behaviour of a stack of supports under œdometric compression in order to produce stress fields more representative of those existing within the supports stacked in a reactor. This test is analysed by X-ray tomography, which allows us to determine/acknowledge the different damaging mechanisms involved in fragments and fines generation. The results illustrate the suitability of the bending and indentation tests to characterize the mechanical properties of a single support and relate them to its mechanical behaviour in a stack of supports under compression
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Parsons, David, and David Parsons. "The production and detection of optimized low-Z linear accelerator target beams for image guidance in radiotherapy." 2012. http://hdl.handle.net/10222/15393.
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Recent work has demonstrated improvement of image quality with low atomic number (Z) linear accelerator (linac) targets and energies as low as 3.5 MV compared to a standard 6 MV therapeutic beam. In this work, the incident electron beam energy has been lowered to energies between 1.90 and 2.35 MeV. The improvement of megavoltage planar image quality with the use of carbon and aluminum linac targets has been assessed compared to a standard 6 MV therapeutic beam.
Common electronic portal imaging devices contain a 1.0 mm copper conversion plate to increase detection efficiency of a therapeutic megavoltage spectrum. When used in imaging with a photon beam generated with a low-Z target, the conversion plate attenuates a substantial proportion of photons in the diagnostic range, thereby reducing the achievable image quality. Image quality as a function of copper plate thickness has been assessed for planar imaging and cone beam computed tomography.
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Graham, Sean Alexander. "Modulation of x-ray fluence patterns in cone-beam computed tomography." 2006. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=450538&T=F.
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Rezvani, Nargol. "Iterative Reconstruction Algorithms for Polyenergetic X-ray Computerized Tomography." Thesis, 2012. http://hdl.handle.net/1807/34865.
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A reconstruction algorithm in computerized tomography is a procedure for reconstructing the attenuation coefficientscient, a real-valued function associated with the object of interest, from the measured projection data. Generally speaking, reconstruction algorithms in CT fall into two categories: direct, e.g., filtered back-projection (FBP), or iterative. In this thesis, we discuss a new fast matrix-free iterative reconstruction method based on a polyenergetic model.
While most modern x-ray CT scanners rely on the well-known filtered back-projection algorithm, the corresponding reconstructions can be corrupted by beam hardening artifacts. These artifacts arise from the unrealistic physical assumption of monoenergetic x-ray beams. In this thesis, to compensate, we use an alternative model that accounts for differential absorption of polyenergetic x-ray photons and discretize it directly. We do not assume any prior knowledge about the physical properties of the scanned object. We study and implement different solvers and nonlinear unconstrained optimization methods, such as a Newton-like method and an extension of the Levenberg-Marquardt-Fletcher algorithm. We explain how we can use the structure of the Radon matrix and the properties of FBP to make our method matrix-free and fast. Finally, we discuss how we regularize our problem by applying different regularization methods, such as Tikhonov and regularization in the 1-norm. We present numerical reconstructions based on the associated nonlinear discrete formulation incorporating various iterative optimization methods.
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Chen, Tsung-Ming, and 陳聰銘. "Analysis of CT value variation of dental cone-beam X-ray tomography." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/79515922485894084837.
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碩士中原大學
生物醫學工程研究所
100
Abstract Dental Implant has become the major treatment for the toothless patient. The alveolar bone conditions, bone quality and density, are the key points for the implant as success or not. Computer Tomography (CT) is one of the methods for diagnostic tools of dental surgery. The CT value, (Housfield unit, Hu, or CT number) is useful for clinical assessment at the quality and density of alveolar bone. Dental Cone Beam CT (Dental CBCT) has become the mainstream of the dental fields to use CT. Thus, the CT value of Dental CBCT is worth exploring in the performance of the CT value. In this study, to design some of phantoms is necessary. The phantoms will be scanned by the current machines of Dental CBCT and Multi-Detector CT (MDCT) in Taiwan. MDCT is the current CT now. The images of phantoms will be stored by DICOM format after scanned. After importing the DICOM images, the third party software, ImplantMax will read and describe the data of the CT value. The data will be analyzed and discussed via Excel X/Y Scattergram. The data of the CT numbers include air, water and aluminum material. Aluminum material is often used at radiographic analysis as bone, because the attenuation coefficient of the aluminum material for x-ray is close to the attenuation coefficient of human bone. The results show that the distribution of CT value range of Dental CBCT is wider than MDCT. The CT number of Dental CBCT is far away the real CT number of phantom material. The current Dental CBCT is not recommended to make the quantitative analysis of the CT value for alveolar bone by this study, but there is a certain value on MDCT.
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Swan, Kathryn A. "Image quality and radiation dose in cone beam computed tomography for orthodontics." 2007. http://catalog.hathitrust.org/api/volumes/oclc/166870223.html.
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