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La Maladie d’Alzheimer est caractérisée par la formation de dégénérescences neurofibrillaires, constituées de protéine Tau anormalement hyperphosphorylée et agrégée. De nombreuses études traitent de possibles stratégies thérapeutiques basées sur l’inhibition de cette polymérisation, et présentent les effets bénéfiques de certaines molécules dont les polyphénols, mais les résultats obtenus jusque là, manquent de données au niveau moléculaire. Ainsi, après avoir synthétisé, une banque de polyphénols de structures différentes, et 3 peptides représentatifs de la région P de phosphorylation de Tau, c’est en suivant une stratégie combinant la RMN et la modélisation moléculaire, que nous avons évalué les paramètres dynamiques du complexe formé. Ce projet nous a apporté des informations en termes d’affinité, et de relations structure/activité et ainsi, de mieux appréhender les mécanismes d’interactions intervenant dans l’agrégation de Tau par les polyphénols. / Alzheimer's disease is characterized by the formation of neurofibrillary tangles constituted by abnormally hyperphosphorylated and aggregated Tau protein. Many studies deal with potential therapeutic strategies based on the inhibition of this polymerization, and show the beneficial effects of some molecules like polyphenols, but the obtained so far results show a lack of data at the molecular level. Thus, after the synthesis of, a library of polyphenols with different structures, and 3 representative peptides of the P2 phosphorylation Tau region, by following a strategy combining NMR and molecular modeling, we have evaluated dynamic parameters of the formed complex. This project has provided us informations in terms of affinity, and structure / activity relationships, and leading us to a better understanding of the mechanisms led to better understand the mechanisms involved in the aggregation Tau inhibition phenomena by polyphenols.

L'utilisation récente d'une voie originale de croissance cristalline basée sur les mécanismes vapeur-liquide-solide (VLS) à partir d'un bain Ge-Si a permis des améliorations importantes de la qualité cristalline des couches minces hétéroépitaxiales de SiC-3C sur substrats sur substrat α-SiC(0001). Ce travail a pour but d'approfondir les connaissances sur cette technique de croissance, d'améliorer le procédé et de déterminer les propriétés du matériau élaboré. La première partie est dédiée à la compréhension et la maîtrise des différents mécanismes impliqués dans la croissance de SiC-3C par VLS. Cela a notamment permis la détermination des paramètres limitant la taille des échantillons et la démonstration des avantages à utiliser des alliages fondus contant 50 at% de Ge au lieu de 75 at%. Une étude de la croissance latérale sur substrats patternés a donné des indications intéressantes pouvant être intégrées dans le modèle d'élimination des macles. L'incorporation intentionnelle et non intentionnelle de dopants de type n et p pendant la croissance VLS a été suivie. Pour le dopage n, nous avons démontré l'existence d'un lien clair entre l'impureté N et la stabilisation du polytype SiC-3C. En outre, nous avons réussi à abaisser le dopage résiduel n des couches en dessous de 1x1017 cm-3. Pour le dopage p, le meilleur élément n'est pas le Ga mais l'Al, même s'il doit être ajouté à un alliage de type Si-Ge pour éviter l'homoépitaxie. Enfin, ces couches ont été caractérisées optiquement et électriquement par différentes techniques. Les mesures C-V et G-V ont permis d'estimer une concentration très faible (7×109 cm-2) de charges fixes dans l'oxyde SiO2 ainsi qu'une densité d'états d'interface aussi basse que 1.2×1010 cm-2eV-1 à 0.63 eV sous la bande de conduction. Ces valeurs record sont une très bonne base pour le développement d'un composant de type MOSFET en SiC-3C / Recently, the use of an original growth approach based on vapour-liquid-solid (VLS) mechanism with Ge-Si melts has led to significant improvement of the crystalline quality of the 3C-SiC thin layers heteroepitaxially grown on α-SiC(0001) substrate. This work tries to deepen the knowledge of such specific growth method, to improve the process and to determine the properties of the grown material. The first part was dedicated to the understanding and mastering of the various mechanisms involved in 3C-SiC growth by VLS mechanism. This led to the determination of the parameters limiting sample size and the demonstration of the benefits of using 50 at% Ge instead of 75 at% Ge melts. A study of lateral enlargement on patterned substrates gave some interesting hints which can be integrated in the model of twin defect elimination. The incorporation of non intentional and intentional n- and p-type dopants during VLS growth was studied. For n-type doping, a clear link between N impurity and 3C polytype stability was demonstrated. Besides, high purity layers with residual n-type doping below 1x1017 cm-3 were achieved. For p-type doping, the best element was shown to be Al and not Ga, even if it has to be alloyed with Ge-Si melts to avoid homoepitaxial growth. Finally, these layers were characterised by several optical and electrical means like Raman spectroscopy, low temperature photoluminescence, deep leveltransient spectroscopy and MOS capacitors measurements. Very low concentrationsof fixed oxide charges estimated about 7×109 cm-2 and interface states densities Dit equal to 1.2×1010 cm-2eV-1at 0.63 eV below the conduction band have been achieved. These record values are a very good base toward 3C-SiC MOSFET

The detection of low-mass extra-solar planets through radial-velocity searches is currently limited by the intrinsic magnetic activity of the host stars. The correlated noise that arises from their natural radial-velocity variability can easily mimic or conceal the orbital signals of super-Earth and Earth-mass extra-solar planets. I developed an intuitive and robust data analysis framework in which the activity-induced variations are modelled with a Gaussian process that has the frequency structure of the photometric variations of the star, thus allowing me to determine precise and reliable planetary masses. I applied this technique to three recently discovered planetary systems: CoRoT-7, Kepler-78 and Kepler-10. I determined the masses of the transiting super-Earth CoRoT-7b and the small Neptune CoRoT-7c to be 4.73 ± 0.95 M⊕ and 13.56 ± 1.08 M⊕, respectively. The density of CoRoT-7b is 6.61 ± 1.72 g.cm⁻³, which is compatible with a rocky composition. I carried out Bayesian model selection to assess the nature of a previously identified signal at 9 days, and found that it is best interpreted as stellar activity. Despite the high levels of activity of its host star, I determined the mass of the Earth-sized planet Kepler-78b to be 1.76 ± 0.18 M⊕. With a density of 6.2(+1.8:-1.4) g.cm⁻³, it is also a rocky planet. I found the masses of Kepler-10b and Kepler-10c to be 3.31 ± 0.32 M⊕ and 16.25 ± 3.66 M⊕, respectively. Their densities, of 6.4(+1.1:-0.7) g.cm⁻³ and 8.1 ± 1.8 g.cm⁻³, imply that they are both of rocky composition – even the 2 Earth-radius planet Kepler-10c! In parallel, I deepened our understanding of the physical origin of stellar radial-velocity variability through the study of the Sun, which is the only star whose surface can be imaged at high resolution. I found that the full-disc magnetic flux is an excellent proxy for activity-induced radial-velocity variations; this result may become key to breaking the activity barrier in coming years. I also found that in the case of CoRoT-7, the suppression of convective blueshift leads to radial-velocity variations with an rms of 1.82 m.s⁻¹, while the modulation induced by the presence of dark spots on the rotating stellar disc has an rms of 0.46 m.s⁻¹. For the Sun, I found these contributions to be 2.22 m.s⁻¹ and 0.14 m.s⁻¹, respectively. These results suggest that for slowly rotating stars, the suppression of convective blueshift is the dominant contributor to the activity-modulated radial-velocity signal, rather than the rotational Doppler shift of the flux blocked by starspots.

Iron platinum (FePt) has attracted growing interest because of its high Curie temperature, magneto-crystalline anisotropy and chemical stability. Nanoparticles (NPs) made of this alloy are promising candidates for a wide range of biomedical applications including magnetic separation, magnetic targeted drug delivery, hyperthermia for cancer therapy and also as magnetic resonance imaging (MRI) contrast agents. This thesis presents the synthesis, functionalization and characterization of FePt NPs along with a toxicity study and an investigation into their application as MRI contrast agents. Regarding their synthesis, different approaches have been explored including the co-reduction of Fe and Pt precursors in an aqueous media, the thermal decomposition in a conventional high-boiling solvent such as benzyl ether, and in low-melting organic salts (ionic liquids). The data revealed an inhomogeneous composition distribution of Fe and Pt between particles obtained in aqueous media, due to the iron salts hydrolysis, and a mismatch in the co-reduction kinetic of the two metal precursors. While the iron content in the NPs could be increased by using more hydrolytically stable iron precursors or stronger reducing agents, there are remaining limiting parameters which prevent further Fe content increase in NPs. In contrast, by excluding the water from the reaction system and using a Fe²⁻ iron precursor, homogenous 1:1 Fe to Pt ratio NPs can be obtained through a modified thermal decomposition pathway in benzyl ether. Based on the study of synthesis in this conventional chemical, the potential of ionic liquids (ILs) to be used as novel solvents for FePt NPs synthesis was further explored. It was then demonstrated that ionic liquids (ILs) can not only be used as a solvent for synthesis of FePt NPs, but also can provide an exciting alternative pathway to direct synthesis fct-FePt NPs. In the context of the bioapplication of FePt NPs, a family of FePt NPs was specifically designed to enhance their MRI contrast agents properties. In contrast with previous reports, this thesis demonstrates that FePt NPs can be made non-toxic and provides the first data on their cellular uptake mechanisms. A six times increase in the FePt based T₂ contrast properties compared to clinical iron oxide NPs is reported. The relationship between the MRI contrast properties and the NPs architecture is explored and rationalised as the basis for the design of NPs as enhanced MRI contrast agents. Finally, the first observations of cellular and in vivo MR imaging with FePt NPs is also reported. This study opens the way for several applications of FePt NPs such as regenerative medicine and stem cell therapy, thus providing a bio-platform to develop novel diagnostic and therapeutic agents.

<div>Defects are unavoidable, life-limiting and dominant sites of damage and subsequent failure in a material. Ni-based superalloys are commonly used in high temperature applications and inevitably found to have defects in the form of inclusions, voids and microscopic cracks which are below the resolution of standard inspection techniques. A mechanistic understanding of the role of defects in such industrially relevant bulk polycrystalline material is essential for philosophies of design and durability to follow and ensure structural integrity of components in the inevitable presence of such defects. The current understanding of defect-mediated damage, in bulk Ni superalloys, is limited by experimental techniques that can capture the local micromechanical state of the material surrounding the defect. In this work, we combine mechanical testing with in-situ, non-destructive 3-D X-ray characterization techniques to obtain rich multi-modal datasets at the microscale to interrogate complex defect-microstructure interactions and elucidate the mechanisms of failure around defects. The attenuated X-ray beam, after passage through the material, is utilized through computed micro-tomography to characterize the defects owing to its sensitivity to density differences in the material. The diffracted X-ray beam, after illuminating the material, is employed through high energy diffraction microscopy in various modes to interrogate the evolving micromechanical state around the discovered defects.</div><div>Three case studies are performed with specimens made of a Ni-based superalloy specially designed and fabricated to have internal defects in the form of: (i) an inclusion, (ii) a microscopic crack, and (iii) voids. In each case, the grain scale information is investigated to reveal heterogeneity in the local micromechanical state of the material as a precursor for the onset of failure. Models and simulations based on finite element or crystal plasticity are utilized, wherever necessary, to assess the factors essential to the underlying mechanism of failure. In the first case study, the detrimental effects of an inclusion in initiating a crack upon cyclic loading is interrogated and the state of bonding, residual stresses, and geometrical stress concentrations around the inclusion are demonstrated to be of utmost importance. In the second case study, the propagation of a short fatigue crack through the microstructure is examined to reveal the crystallographic nature of crack growth through the (i) alignment of the crack plane with the most active slip system, (ii) the correlation between the crack growth rate and the maximum resolved shear stresses, and (iii) the dependence of the crack growth direction on microplasticity within grains ahead of the crack front. In the third case study, the role of voids in ductile failure under tensile loading is explored to illuminate the activation and operation of distinct mechanisms of inter-void shear and necking under the control of the local state of stress triaxiality and the local plasticity within the grains at critical sites of fracture.</div><div>In summary, a grain scale description of the micromechanical state has been unambiguously determined through experiments to examine the heterogeneity around defects in the material. It has enabled us to identify and isolate the nature of factors essential to the activation of specific mechanisms at the onset failure. The grain scale thus provides an ideal physical basis to understand the fundamentals of defect mediated damage and failure instilling trust in the predictive capabilities of models that incorporate the response of the grain structure. The generated datasets can be used to instantiate and calibrate such models at the grain level for higher fidelity. </div>

Polymer brushes are extremely versatile materials, as monomer choice allows the user to design a material with the desired physiochemical properties. Given the wide variety in monomer functionality, polymers can be fine-tuned for a specific application. In this work, polymer brushes bound to a silica support are designed and utilized to enhance performance of protein extraction and chromatographic separations. <br> The effectiveness of an analytical method is strongly affected by matrix composition, however, the presence of species other than the target analyte is usually unavoidable. An excellent technique will be able to identify and/or quantify the analyte even when its concentration is low compared with interfering molecules. Protein analysis is particularly challenging, since many proteins of clinical and scientific significance are present in complicated matrices such as plasma or cell lysates. <br>A common method to specifically separate a protein from a complicated matrix is solid phase extraction. In this method, a species (such as an antibody) with high specificity towards the target is immobilized onto a solid substrate (commonly beads or small particles for greater surface area). Next, the target is collected onto the surface, bound by the species. The solid substrate is rinsed of the liquid matrix, before elution of the target. Only the active species should interact with the analyte, and the surface should be otherwise inactive. However, nonspecific interactions lead to binding/adsorption of undesirable compounds. Therefore, an optimal substrate for protein extraction must be 1) easily and completely removable from the liquid phase, 2) have a high concentration of active sites for specific binding, and 3) exhibit low nonspecific binding. As part of this work, commercial magnetic particles were coated with a nonporous silica layer that tolerates the acid bath and silane coating necessary to attach a polymer layer. On the silane coating, a polymer layer was covalently bound; this layer contains epoxide active groups for immobilizing antibodies. These antibodies bind to the target molecule with high specificity, and low nonspecific binding. Obtained particles were evaluated for protein extraction, where antibodies as well as specifically engineered drug compounds were successfully bound to the particle surface.<br>Glycosylation influences several physiopathological processes in proteins. Glycans can act as receptors, modify protein solubility, and participate in folding conformation. Altered glycosylation is a common feature in tumorous cells. As such, many modifications in glycoproteins have been related to cancer, including increased branching of N-glycans or augmented units of sialic acid. Therefore, characterization of glycoproteins is important not only as a diagnostic tool, but also to monitor patients’ response to treatment. Furthermore, it is important in the growing field of monoclonal antibodies as drug carriers. <br>Among different methods used for glycosylation analysis, Hydrophilic Interaction Liquid Chromatography (HILIC) has showed important advantages over time-consuming digestion-MS based techniques. An adequate HILIC stationary phase can be used to rapidly differentiate glycoforms present in a sample. In the second part of this work, a polymer brush based bonded phase was developed as a HILIC stationary phase. The new polymer improved the separation of a model glycoprotein compared with a commercial HILIC column, while also exhibiting enhanced stability over a previous bonded phase synthetized in our group.<br><br>

Les bétons légers, formés des fibres de bois et d’une pâte de ciment Portland, constituent une nouvelle alternative à explorer pour réduire l’impact environnemental des bâtiments. Ils sont utilisés dans la construction durable, comme des éléments secondaires, pour leurs performances thermiques, hydriques et mécaniques. Cependant, la généralisation de leur utilisation dans le bâtiment ne sera rendue possible sans résoudre certains verrous scientifiques liés à leur caractérisation et à leur formulation. Le présent travail s’inscrit dans cet objectif. Il s’agit de contribuer à la caractérisation de ces bétons légers à base des fibres de bois à travers l’expérience et la modélisation. Le module d’Young et la résistance à la rupture ont été mesurés par des tests de flexion et de compression. Un modèle numérique a été également développé pour prédire le comportement des éprouvettes en flexion et la réponse structurale des systèmes de coffrage permanent. La méthodologie numérique permet ainsi d’aider dans le choix des paramètres optimums pour une meilleure conception des panneaux de coffrage destinés à la construction. L’étude du comportement hygrothermique du matériau de construction bois-ciment a été abordée en s’appuyant sur l’expérience et la simulation. Les équations des transferts couplés de chaleur et d’humidité d’un milieu poreux ont été implémentées dans le logiciel Comsol Multiphysics®. En dernier, le modèle développé a été appliqué et validé sur plusieurs réponses dynamiques issues des tests hygrothermiques réalisés en interne. Les mesures des propriétés physico-thermique du matériau composite bois-ciment ont été ensuite intégrées dans le code Abaqus via une routine utilisateur Umatht dans l’objectif de simuler le comportement thermique à hautes températures des panneaux composites bois-ciment. Les profils des températures sont évalués et comparés à ceux des tests de carbonisation réalisés, à l’aide d’un panneau rayonnant, sur des échantillons exposés à un flux de chaleur uniforme de 6kW/m2. Les simulations montrent que le modèle développé est capable de prédire les profils de températures, la zone et la profondeur de la couche du charbon durant l’exposition au feu / Lightweight concretes made from wood fibres and Portland cement paste are a new alternative for the reduction of the environmental impact of buildings. They are used in sustainable constructions as secondary elements for their thermal, hydric and mechanical performance. However, the generalisation of their use is not possible without resolving certain scientific obstacles related to their characterisation. Hence the aim of the present work, which is to contribute towards their characterisation through experimentation and numerical simulation. The Young's modulus and tensile strength were measured through flexural and compression tests. A numerical model has also been developed to predict the behaviour of specimens under bending test as well as their structural response when used as permanent formwork. In particular, the model helps to choose the optimum parameters for a better design of the formwork system. The study of the hygrothermal behaviour of the wood-cement material was carried out using both experimental work and simulation. The equations of coupled heat and moisture transfers for a porous medium have been implemented in the Comsol Multiphysics® software. The developed model has been applied and validated on several dynamic responses resulting from hygro-thermal tests carried out in the laboratory. The obtained physico-thermal properties of the wood-cement composite material were then incorporated into the Abaqus code via a Umatht user subroutine to simulate its high temperature behavior. The temperature profiles are evaluated and compared with the charring tests performed using a radiant panel on samples exposed to a uniform heat flux of 6kW/m². The simulations show that the developed model is able to predict the temperature profiles, the area and the depth of the charred layer during fire exposure

Depuis plus d’un siècle, la radiographie sur film est utilisée pour le contrôle non destructif (CND) de pièces industrielles. Avec l’introduction de méthodes numériques dans le domaine médical, la communauté du CND industriel a commencé à considérer également les techniques numériques alternatives au film. La radiographie numérique (en anglais Computed radiography -CR) utilisant les écrans photostimulables (en anglais imaging plate -IP) est une voie intéressante à la fois du point de vue coût et facilité d’implémentation. Le détecteur (IP) utilisé se rapproche du film car il est flexible et réutilisable. L’exposition de l’IP aux rayons X génère une image latente qui est ensuite lue et numérisée grâce à un système de balayage optique par laser. A basse énergie, les performances du système CR sont bonnes ce qui explique son utilisation importante dans le domaine médical. A haute énergie par contre, les performances du système CR se dégradent à la fois à cause de la mauvaise absorption de l’IP mais également de la présence de rayonnement diffusé par la pièce qui, étant d’énergie plus faible, est préférentiellement absorbée par l’IP. Les normes internationales préconisent l’utilisation d’écrans métalliques pour améliorer la réponse des systèmes CR à haute énergie. Néanmoins, la nature et l’épaisseur de ces écrans n’est pas clairement définie et la gamme des configurations possibles est large. La simulation est un outil utile pour prévoir les performances d’une expérience et déterminer les meilleures conditions opératoires. Les méthodes Monte Carlo sont communément admises comme étant les plus précises pour simuler les phénomènes de transport de rayonnement, et ainsi comprendre les phénomènes physiques en jeu. Cependant, le caractère probabiliste de ces méthodes implique des temps de calcul importants, voire prohibitifs pour des géométries complexes. Les méthodes déterministes au contraire, peuvent prendre en compte des géométries complexes avec des temps de calcul raisonnables, mais l’estimation du rayonnement diffusé est plus difficile. Dans ce travail de thèse, nous avons tout d’abord mené une étude de simulation Monte Carlo afin de comprendre le fonctionnement des IP avec écrans métalliques à haute énergie pour le contrôle de pièces de forte épaisseur. Nous avons notamment suivi le trajet des photons X mais également des électrons. Quelques comparaisons expérimentales ont pu être menées à l’ESRF (European Synchrotron Radiation Facility). Puis nous avons proposé une approche de simulation hybride, qui combine l'utilisation de codes déterministe et Monte Carlo pour simuler l'imagerie d'objets de forme complexe. Cette approche prend en compte la dégradation introduite par la diffusion des rayons X et la fluorescence dans l'IP ainsi que la diffusion des photons optiques dans l'IP. Les résultats de différentes configurations de simulation ont été comparés. / For over a century, film-based radiography has been used as a nondestructive testing technique for industrial inspections. With the advent of digital techniques in the medical domain, the NDT community is also considering alternative digital techniques. Computed Radiography (CR) is a cost-efficient and easy-to-implement replacement technique because it uses equipment very similar to film radiography. This technology uses flexible and reusable imaging plates (IP) as a detector to generate a latent image during x-ray exposure. With an optical scanning system, the latent image can be readout and digitized resulting in a direct digital image. CR is widely used in the medical field since it provides good performance at low energies. For industrial inspection, CR application is limited by its poor response to high energy radiation and the presence of scattering phenomena. To completely replace film radiography by such a system, its performance still needs to be improved by either finding more appropriate IPs or by optimizing operating conditions. Guidelines have been addressed in international standards to ensure a good image quality supplied by CR system, where metallic screens are recommended for the case of using high energy sources. However, the type and thickness of such a screen are not clearly defined and a large panel of possible configurations does exist. Simulation is a very useful tool to predict experimental outcomes and determine the optimal operating conditions. The Monte Carlo (MC) methods are widely accepted as the most accurate method to simulate radiation transport problems. It can give insight about physical phenomena, but due to its random nature, a large amount of computational time is required, especially for simulations involving complex geometries. Deterministic methods, on the other hand, can handle easily complex geometry, and are quite efficient. However, the estimation of scattering effects is more difficult with deterministic methods. In this thesis work, we have started with a Monte Carlo simulation study in order to investigate the physical phenomena involved in IP and in metallic screens at high energies. In particular we have studied separately the behavior of X-ray photons and electrons. Some experimental comparisons have been carried out at the European Synchrotron Radiation Facility. Then, we have proposed a hybrid simulation approach, combining the use of deterministic and Monte Carlo code, for simulating the imaging of complex shapes objects. This approach takes into account degradation introduced by X-ray scattering and fluorescence inside IP, as well as optical photons scattering during readout process. Different simulation configurations have been compared.

La tomographie par rayons X ou CT pour "Computed Tomography" est un outil puissant pour caractériser et localiser les défauts internes et pour vérifier la conformité géométrique d’un objet. Contrairement au cas des applications médicales, l’objet inspecté en Contrôle Non Destructif (CND) peut être très grand et composé de matériaux de haute atténuation, auquel cas l’utilisation d’une trajectoire circulaire pour l’inspection est impossible à cause de contraintes dans l’espace. Pour cette raison, l’utilisation de bras robotisés est l’une des nouvelles tendances reconnues dans la CT, car elle autorise plus de flexibilité dans la trajectoire d’acquisition et permet donc la reconstruction 3D de régions difficilement accessibles dont la reconstruction ne pourrait pas être assurée par des systèmes de tomographie industriels classiques. Une cellule de tomographie X robotisée a été installée au CEA. La plateforme se compose de deux bras robotiques pour positionner et déplacer la source et le détecteur en vis-à-vis. Parmi les nouveaux défis posés par la tomographie robotisée, nous nous concentrons ici plus particulièrement sur la limitation de l’ouverture angulaire imposée par la configuration en raison des contraintes importantes sur le mouvement mécanique de la plateforme. Le deuxième défi majeur est la troncation des projections qui se produit lorsque l’objet est trop grand par rapport au détecteur. L’objectif principal de ce travail consiste à adapter et à optimiser des méthodes de reconstruction CT pour des trajectoires non standard. Nous étudions à la fois des algorithmes de reconstruction analytiques et itératifs. Avant d’effectuer des inspections robotiques réelles, nous comptons sur des simulations numériques pour évaluer les performances des algorithmes de reconstruction sur des configurations d’acquisition de données. Pour ce faire, nous utilisons CIVA, qui est un outil de simulation pour le CND développé au CEA et qui est capable de simuler des données de projections réalistes correspondant à des configurations d’acquisition définies par l’utilisateur. / X-ray computed tomography (CT) is a powerful tool to characterize or localize inner flaws and to verify the geometric conformity of an object. In contrast to medical applications, the scanned object in non-destructive testing (NDT) might be very large and composed of high-attenuation materials and consequently the use of a standard circular trajectory for data acquisition would be impossible due to constraints in space. For this reason, the use of robotic arms is one of the acknowledged new trends in NDT since it allows more flexibility in acquisition trajectories and therefore could be used for 3D reconstruction of hardly accessible regions that might be a major limitation of classical CT systems. A robotic X-ray inspection platform has been installed at CEA LIST. The considered system integrates two robots that move the X-ray generator and detector. Among the new challenges brought by robotic CT, we focus in this thesis more particularly on the limited access viewpoint imposed by the setup where important constraints control the mechanical motion of the platform. The second major challenge is the truncation of projections that occur when only a field-of-view (FOV) of the object is viewed by the detector. Before performing real robotic inspections, we highly rely on CT simulations to evaluate the capability of the reconstruction algorithm corresponding to a defined scanning trajectory and data acquisition configuration. For this purpose, we use CIVA which is an advanced NDT simulation platform developed at CEA and that can provide a realistic model for radiographic acquisitions and is capable of simulating the projection data corresponding to a specific CT scene defined by the user. Thus, the main objective of this thesis is to develop analytical and iterative reconstruction algorithms adapted to nonstandard trajectories and to integrate these algorithms in CIVA software as plugins of reconstruction.