Tesis sobre el tema "Microstructure (physique) – Imagerie spectroscopique"
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Armanni, Thibaut. "Étude de nouveaux alliages de titane pour applications aéronautiques hautes températures". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0342.
Texto completoImproving the high-temperature resistance of titanium alloys is a major challenge for the aerospace industry. Exceeding the current limit of 550°C in aircraft engines requires finding the best compromise between good oxidation resistance and good mechanical properties. Near-alpha alloys consisting mainly of a compact hexagonal phase are the best candidates. Unfortunately, they are sensitive to cold creep-fatigue, known as the dwell effect. In this context, our work aims to achieve two main objectives. Firstly, to contribute to the design of new near-alpha alloys based on machine learning, supported by extensive mechanical testing, at both ambient and high temperatures. Secondly, to gain a better understanding of the effect of chemical composition, particularly silicon content, on the microstructure and mechanical behaviour. Our approach was based on multi-scale microstructure study of selected alloys using a combination of different microscopy techniques. We examined the influence of a variation in silicon content using a combination of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). We showed that silicide precipitation occurs above a certain silicon content. We demonstrated the limitations of two-dimensional analysis, and used an alternative technique combining ion beam cutting (FIB) with SEM observation to reconstruct the 3D microstructure. This approach enabled us to analyze and quantify the shapes, sizes and spatial distributions of the silicides. Finally, we carried out tensile tests at different strain rates as well as creep tests under various conditions to better understand how silicon addition improves the behaviour of near-alpha alloys
Richard, Alain. "Outils pour la spectroscopie en champ proche optique : application à l'imagerie hyperspectrale". Paris 11, 2001. http://www.theses.fr/2001PA112338.
Texto completoOptical studies of single nanoobjects imply the development of tools allowing a high spatial selection and of high optical sensitivity. I have implemented a set-up dedicated to such studies, by combining scanning near-field optical microscopy and fluorescence or Raman spectroscopy. The analysis of single nanoobject properties is derived from hyperspectral optical imaging. Both the total intensity of the emitted signal and its spectrum are recorded at each location of the probed sample area. For that purpose, I have built specific devices, among which an original all electric sensor to measure distances in the nanometer range. It is based on shear force principle. The movement of the sample is obtained with a 50 micronmeters dynamical range flat scanner including piezoelectric tubes. An optical sensor, that I have developed, controls the scanner displacement in order to compensate the scan for the near-field region. . .
Lagrange, Jean-François. "Etude spectroscopique et imagerie rapide d'une plume d'ablation laser obtenue à partir de cibles céramiques d'oxydes complexes (CaCu3Ti4O12 et BaxSr1-xTiO3)". Phd thesis, Université François Rabelais - Tours, 2010. http://tel.archives-ouvertes.fr/tel-00951389.
Texto completoReinhart, Guillaume. "Dynamique de formation de la microstructure de solidification d' alliages métalliques : caractérisation par imagerie synchrotron". Aix-Marseille 3, 2006. http://www.theses.fr/2006AIX30039.
Texto completoWe studied in situ and real-time the directional solidification of thin samples of binary alloys and a quasicrystal using both X-ray radiography and topography techniques. On Al-3. 5wt%Ni non-refined alloys, we studied the formation of the initial state and the solidification front morphology (cellular then dendritic growth). Mechanical strains wer highlighted. The Columnar to Equiaxed Transition was studied on Al-3. 5wt%Ni refined alloys. We described the blocking of the columnar front and the following equiaxed growth regime. The refining particles efficiency reaches a limit. An analysis of the microstructure morphology was performed. The study of the i-AlPdMn quasicrystal shows the growth of faceted dodecahedral grains. Thermosolutal convection effects were highlighted. Strain visualisation shows a strong deformation of grains. The apparition of porosity was observed during fusion of grains
Nguyen, Thanh Tung. "Modeling of complex microcracking in cement based materials by combining numerical simulations based on a phase-field method and experimental 3D imaging". Thesis, Paris Est, 2015. http://www.theses.fr/2015PESC1152/document.
Texto completoAn approach combining numerical simulations and experimental techniques is developed to model complex microcracking in heterogeneous cementitious materials. The proposed numerical model allowed us to predict accurately in 3D the initiation and the propagation of microcracks at the scale of the actual microstructure of a real sample subjected to compression. Its predictions have been validated by a direct comparison with the actual crack network characterized by 3D imaging techniques. In a first part, the numerical simulation tools are developed and tested. More specifically, the phase-field method is applied to microcracking simulations in highly heterogeneous microstructures and its advantages for such simulations are discussed. Then, the technique is extended to account for interfacial cracking, possibly occurring at inclusion/matrix interfaces. In a second part, the experimental methods used and developed in this work are described. The procedures to obtain the evolution of the 3D crack network within the samples by means of X-rays computed microtomography and in-situ mechanical testing are presented. Then, we focus on the developed image processing tools based on digital volume correlation to extract with good accuracy the cracks from the grey level images. In a third part, we compare the predictions of the numerical model with experimental results obtained, first, with a model material made of expanded polystyrene beads embedded in a plaster matrix, and second, to a more complex lightweight concrete. More precisely, we use the experimental data to identify by inverse approaches the local microstructural parameters, and use the experimental displacements measured by digital volume correlation to define boundary conditions to be applied on sub-domains within the sample for the simulations. The obtained direct comparisons of 3D microcrack networks and their evolutions demonstrate the very good predictive capability of the numerical model
Lebois, Alice. "Brain microstructure mapping using quantitative and diffsusion MRI". Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01063198.
Texto completoVo, Quoc Thang. "Imagerie d'essais mécaniques sur des composites à matrice métallique : contribution expérimentale à la validation de méthodes d'homogénéisation et identification de propriétés mécaniques par phases". Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20151/document.
Texto completoThis work is focused on a matrix/inclusion metal composite. A simple method is proposed to evaluate the elastic properties of one phase while the properties of the other phase are assumed to be known. The method is based on both an inverse homogenization scheme and mechanical field's measurements by 2D digital image correlation. The originality of the approach rests on the scale studied, i.e. the microstructure scale of material: the characteristic size of the inclusions is about few tens of microns. The evaluation is performed on standard uniaxial tensile tests associated with a long-distance microscope. It allows observation of the surface of a specimen on the microstructure scale during the mechanical stress. First, the accuracy of the method is estimated on ‘perfect' mechanical fields coming from numerical simulations for four microstructures: elastic or porous single inclusions having either spherical or cylindrical shape. Second, this accuracy is estimated on real mechanical field for two simple microstructures: an elasto-plastic metallic matrix containing a single cylindrical micro void or four cylindrical micro voids arranged in a square pattern. Third, the method is used to evaluate elastic properties of inclusions with arbitrary shape in an oxidized Zircaloy-4 sample of the fuel cladding of a pressurized water reactor after an accident loss of coolant accident (LOCA). In all this study, the phases are assumed to have isotropic properties
Goutailler, Florent. "Polarisation dynamique nucléaire à basse température et fort champ magnétique pour des applications biomédicales en imagerie spectroscopique par résonance magnétique". Phd thesis, Université Claude Bernard - Lyon I, 2011. http://tel.archives-ouvertes.fr/tel-00672305.
Texto completoRan, Peipei. "Imaging and diagnostic of sub-wavelength micro-structures, from closed-form algorithms to deep learning". Electronic Thesis or Diss., université Paris-Saclay, 2020. http://www.theses.fr/2020UPASG061.
Texto completoElectromagnetic probing of a gridlike, finite set of infinitely long circular cylindrical dielectric rods affected by missing ones is investigated from time-harmonic single and multiple frequency data. Sub-wavelength distances between adjacent rods and sub-wavelength rod diameters are assumed throughout the frequency band of operation and this leads to a severe challenge due to need of super-resolution within the present micro-structure, well beyond the Rayleigh criterion. A wealth of solution methods is investigated and comprehensive numerical simulations illustrate pros and cons, completed by processing laboratory-controlled experimental data acquired on a micro-structure prototype in a microwave anechoic chamber. These methods, which differ per a priori information accounted for and consequent versatility, include time-reversal, binary-specialized contrast-source and sparsity-constrained inversions, and convolutional neural networks possibly combined with recurrent ones
Lavoie, Sébastien. "Sur l’extraction de spectres en absorption de sources ponctuelles et étendues avec SpIOMM". Thesis, Université Laval, 2014. http://www.theses.ulaval.ca/2014/30669/30669.pdf.
Texto completoInstalled at the Mont-Mégantic Observatory, the imaging Fourier transform spectrometer SpIOMM possesses a large field of view and high throughput. This places it favourably when compared to other astronomical integral field spectrometers. Until now, the work done with the instrument has been limited to the study of emission lines. The physical processes behind absorption features are also important and their study can gain from an instrument like SpIOMM. We explore SpIOMM’s capabilities for the study of absorption line spectra. Absorption lines are more sensitive to noise than their emission counterpart. A different reduction process is used. Extended sources and point sources are studied. We present spectra from stars in clusters and the galaxy M87. The analysis shows SpIOMM’s capabilities for both types of sources. The results are important since a new imaging Fourier transform spectrometer, SITELLE, is to be delivered to the Canada-France-Hawaii telescope in 2014.
Gusachenko, Ivan. "Microscopie par génération de second harmonique résolue en polarisation : développements théoriques et expérimentaux et application à l'imagerie de la microstructure du tendon pendant des essais mécaniques". Phd thesis, Ecole Polytechnique X, 2012. http://pastel.archives-ouvertes.fr/pastel-00910146.
Texto completoPeyrega, Charles. "Prédiction des propriétés acoustiques de matériaux fibreux hétérogènes à partir de leur microstructure 3D". Phd thesis, École Nationale Supérieure des Mines de Paris, 2010. http://pastel.archives-ouvertes.fr/pastel-00568918.
Texto completoDenis, Gauthier. "Implication des dimensions neurocognitives dans le maintien de l’effort physique au travers du rôle endossé par le cortex préfrontal et de la perspective coûts/bénéfices". Thesis, Université Côte d'Azur, 2020. http://www.theses.fr/2020COAZ4091.
Texto completoThe prefrontal cortex (PFC), usually known for its involvement in higher cognitive control, appears to be particularly involved in maintaining physical effort. While this involvement suggests the existence of a psychological component in the ability to tolerate and maintain exercise, the underlying neurocognitive mechanisms remain relatively unknown. Recent theoretical proposals speculate that exercise termination is determined by a decision-making process, controlled by the PFC. The integration and conscious evaluation of the costs (i.e., unpleasant feelings of fatigue) and benefits (e.g., rewards), associated with the physical task, would control this decision. Maintaining an effort would be facilitated when estimated benefits increase or perceived costs decrease. However, how cognitive functioning and the PFC may modulate the integration of this information to support a decision to continue exercise remains to be clarified. The level of attention given to costs and benefits could play a role in this process. In addition, the unpleasant sensations of fatigue would be limited via an inhibitory function implemented at the level of the PFC. The objective of this doctoral work was to clarify the involvement of the neurocognitive dimensions and in particular of the PFC in the integration and processing of costs and benefits likely to modulate maintaining an effort. The results of study 1 failed to reveal the involvement of the PFC through the engagement of its inhibitory cognitive function in physical endurance. However, the results of studies 2, 3 and 4 indicated that the orientation of attention, more or less directed towards the costs or the benefits, modulated the endurance performance and the activity of the regions of the PFC involved in the integration and regulation of this information. Attention focused on monetary benefits improved performance compared to a focus on the costs of the effort or a cognitive distraction task. The focus on costs and benefits led to increased activity in the anterior and inferior regions of the PFC involved in interpreting this information (study 3). In addition, performing a cognitive distraction task delayed the decision to stop the exercise and resulted in decreased inhibitory activity in prefrontal regions that may regulate exercise costs (study 2). These results suggest the ability of attention to delay exercise cessation by facilitating the conscious integration of benefits (through focusing on that information) and disrupting that of costs (through cognitive distraction). It also tends to emphasize the involvement of the PFC in the regulation of perceived costs and the processing of costs and benefits associated with endurance effort. In a relatively contradictory way, a focus on costs did not necessarily lead to an earlier cessation of the effort (compared to a cognitive distraction condition) but to an improvement in muscular endurance in individuals with the best aerobic capacities (study 4). Facilitating the conscious integration of the costs of the effort would thus prove favorable in maintaining the exercise in certain individuals. The results of this work reinforce the idea that neurocognitive processes are involved in maintaining physical effort. Identifying attentional strategies that could facilitate engaging in physical activity and exercise pursuit in different populations is an interesting research perspective, particularly in sedentary individuals for whom physical activity represents a real health issue
Bogno, Abdoul-Aziz. "Application de la radiographie X synchrotron à la caractérisation de la microstructure de solidification d'alliages métalliques". Thesis, Aix-Marseille 3, 2011. http://www.theses.fr/2011AIX30015.
Texto completoA systematic experimental study of the formation of solidification microstructures of metallic alloys (Al-Cu) was carried out by the application of synchrotron X-ray radiography. Synchrotron X-ray radiography gave access to in situ and real time observations which allowed us to quantitatively analyze the dynamical physical parameters involved in the solidification process (growth rate, solute redistribution, equiaxed grain interaction etc). It also allowed to show the influence of natural convection and gravity on these various physical parameters and consequently on the formation of the solidification microstructures. Our experimental results were compared with models predictions of the dendritic growth and the necessity of microgravity solidification experiments was evidenced. Finally series of tests were carried out on the experimental setup designed by the Swedish Space Corporation (SSC) in the framework of the project XRMON (In situ X-Ray MONitoring of advanced metallurgical processes under microgravity and terrestrial conditions) of ESA-MAP for in situ and real time solidification experiments under microgravity conditions on board a sounding rocket Maser12. Maser12 mission is scheduled for November 2011. The tests results validated the experimental setup in term of imaging and thermal behaviour
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.
Texto completoLi-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
Chini, Maria Rita. "Analyse des hétérogénéités de microstructure et de microtexture héritées par transformation de phase β→α dans des pièces massives en alliage Ti-10V-2Fe-3Al : influence sur la dispersion des propriétés mécaniques". Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0149.
Texto completoThe β-metastable titanium alloys such as Ti-10V-2Fe-3Al are gradually replacing α/β alloys in aeronautical applications thanks to their improved specific strength. However, their microstructures are complex and multi-scale, consisting of a β matrix (of millimetric grains) partially transformed into primary αp nodules (micrometric) and secondary αs lamellae (sub-micrometric). The final mechanical properties are very sensitive to local variations of the microstructure, which are not always fully controlled during forging of massive parts. Moreover, the β matrix, which represent 40% of the volume and whose elastic and plastic behavior is strongly anisotropic (like the α phase) complicates the understanding of the mechanisms of deformation. The first objective of this thesis was to efficiently characterize the microstructure/texture of the different constituents (β/αp/αs) and their heterogeneities within half-finished products and forged parts by using techniques of multi-scale characterization (neutron diffraction, electronic imaging coupled with image analysis and EBSD, reconstruction of high temperature microtextures β/αp). As a result the fragmentation of the β grains into subgrains, the αp macrozones, the destruction of the orientation relation between β/αp and the organization of the αs lamellae in colonies or basket weave was quantified and the differences in size of domains revealed by crystallography and by standard imaging were pointed out. The second objective is to apply this methodology to the analysis of fracture surfaces of samples exhibiting singular behavior (in tension or in fatigue) in order to characterize the microstructural configurations leading to early cracking. This analysis was mainly performed by manual polishing coupled with EBSD acquisitions but also by using 3D imaging by SEM-FIB (Focus Ion Beam) and TKD (Transmission Kikuchi Diffraction) technique on a thin foil FIB-extracted from the crack initiation site. Finally, this experimental study was completed by a micromechanical simulation on a 100% β model microstructure. The objective was to evaluate the influence of the elastic anisotropy of the β phase on the genesis of incompatibility stresses in the elastic and elasto-plastic regimes. The overall results contribute to a better understanding of the variations of mechanical properties related to the local microstructure
Lombardini, Alberto. "Nonlinear optical endoscopy with micro-structured photonic crystal fibers". Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4377.
Texto completoIn this thesis, we propose the use of a novel type of photonic crystal fiber, the Kagomé lattice hollow core fiber, for the delivery of ultra-short pulses in nonlinear endoscopy. These fibers allow undistorted pulse delivery, over a broad transmission window, with minimum background signal generated in the fiber, thanks to the propagation in a hollow-core. We solved the problem of spatial resolution, by means of a silica micro-bead inserted in the Kagomé fiber large core. We have developed a miniature imaging system, based on a piezo-electric tube scanner, an achromatic micro-lenses assembly and a specifically designed Kagomé double-clad fiber. With this system we were able to image biological tissues, in endoscope modality, activating different contrasts such as TPEF, SHG and CARS, at the distal end of the fiber, a result which finds no equal in current literature. The integration in a portable probe (4.2 mm in diameter) shows the potential of this system for future in-vivo multimodal endoscopy
Lachapelle, François-René. "Caractérisation photométrique et spectroscopique de compagnons sous-stellaires de faible masse autour d'étoiles de la région de formation Upper Scorpius". Thèse, 2013. http://hdl.handle.net/1866/10721.
Texto completoFollowing the discovery of about 2000 brown dwarfs over the past two decades, we begin to understand the physics of these objects of mass intermediate between stellar and planetary masses. Nevertheless, the atmosphere and evolution models for these low-mass objects are still struggling to reproduce their characteristics at young ages. This work presents the characterization of four sub-stellar mass (8-30 MJup) companions orbiting at large separation (300-900 AU) around young stars (5 Myr) in the Upper Scorpius formation region. New spectra (0,9-2,5 um) and new photometric measurements (YJHKsL') are presented and analyzed in order to determine the mass, effective temperature, luminosity and surface gravity of these companions, while assessing the fidelity with which the synthetic spectra from two recent atmosphere models reproduce the observed spectra.