Abstract Light scattering diagnostics of turbid media containing both structural and dynamic inhomogeneities is currently of significant importance. One of the important directions in modern light scattering diagnostics is the development of methods for probing biological media with visible- and near-infrared radiation allowing for visualization of the biotissue structure. Optical methods for studying the biotissue structure and characterization of its optical properties are very promising and have been rapidly developing during the past decade. The present work is aimed at improving and discovering new potentials of currently existing methods of laser diagnostics of biological tissues containing both structural and dynamic inhomogeneities. In particular, the feasibilities of spatially resolved reflectometry and time-of-flight techniques for the problem of noninvasive determination of glucose level in human blood and tissues were examined both numerically and experimentally. The relative sensitivities of these methods to changes in glucose level were estimated. Time-of-flight technique was found to be more sensitive. The possibilities of Doppler optical coherence tomography for imaging of dynamic inhomogeneities with high resolution were considered. This technique was applied for the first time for the imaging of complex autowave cellular motility and cytoplasm shuttle flow in the slime mold Physarum polycephalum. The effect of multiple scattering on the accuracy of the measured flow velocity profiles for the case of single flow and for the case of the flow embedded into the static medium with strong scattering was studied. It was shown that this effect causes significant distortion to the measured flow velocity profiles and it is necessary to take this into account while making quantitative measurements of flow velocities.

Abstract This thesis deals with the developing of fibre-optic instruments for monitoring the health of civil engineering and composite structures. A number of sensors have been tested for use with different road structures, concrete bridges, fibre reinforced polymer (FRP) containers and other composite specimens, the interrogation methods being mainly based on measuring optical power and time-of-flight (TOF). The main focus is on the development of a fibre-optic TOF measurement system and its applications, but different sensing needs and fibre-optic measurement systems are also reviewed, with the emphasis on commercial devices. Deformation in a road structure was studied with microbending sensors of gauge-length about 10 cm and a commercial optical time domain reflectometer (OTDR) in a quasi-distributed fashion. The responses of the optical fibre sensors during the one-year measurement period were similar in shape to those obtained with commercial strain gauges but the absolute measurement values typically deviated by several tens of per cent. Low dynamic range, crosstalk and poor signal-to-noise ratio proved to be the main problem when measuring several successive sensors with an OTDR. In another road investigation, microbending and speckle sensors were found useful for providing on/off-type information for traffic control applications. FRP composite containers were investigated with the focus on developing a continuous monitoring system for improving yield and quality by evaluating the state of cure during the manufacturing process and for assessing damage, e.g. delaminations, during service life. Standard multi-mode and single mode fibres with a typical length of a few hundreds of metres were embedded inside the walls of containers during the normal manufacturing process, and the measurements were carried out using an optical through-power technique and an OTDR. This largely empirical investigation revealed that the coating material and its thickness have an effect on loading sensitivity and on the applicability of the method for cure monitoring. The measurement data also indicated that the end-of-curing process and the location of external damage can be determined with a distributed optical fibre sensor and an OTDR. Several versions of a pulsed time-of-flight measurement system were developed for interrogating sensor arrays consisting of multiple long gauge-length sensors. The early versions based on commercial electronics were capable of producing relevant measurement data with a reasonable precision, but they suffered especially from poor spatial resolution, low sampling rate and long-term drift. The high precision TOF system developed in this thesis is capable of measuring time delays between a number of wideband reflectors, such as connectors or fibre Bragg gratings (FBG), along a fibre path with a precision of about 280 fs (rms-value) and a spatial resolution of about 3 ns (0.30 m) in a measurement time of 25 milliseconds. By using a fibre loop sensor with a reference fibre, a strain precision below 1 με and a measurement frequency of 4 Hz can be achieved. The system has proved comparable in performance to a commercial FBG interrogation system in monitoring the behaviour of a bridge deck, while the fact that it allows static and dynamic measurements with a number of long gauge-length sensors, also embedded in FRP composite material, makes this TOF device unique relative to other measurement systems.

The successful revival of three-dimensional (3D) cinema has generated a great deal of interest in 3D video. However, contemporary eyewear-assisted displaying technologies are not well suited for the less restricted scenarios outside movie theaters. The next generation of 3D displays, autostereoscopic multiview displays, overcome the restrictions of traditional stereoscopic 3D and can provide an important boost for 3D television (3DTV). Then again, such displays require scene depth information in order to reduce the amount of necessary input data. Acquiring this information is quite complex and challenging, thus restricting content creators and limiting the amount of available 3D video content. Nonetheless, without broad and innovative 3D television programs, even next-generation 3DTV will lack customer appeal. Therefore simplified 3D video content generation is essential for the medium's success. This dissertation surveys the advantages and limitations of contemporary 3D video acquisition. Based on these findings, a combination of dedicated depth sensors, so-called Time-of-Flight (ToF) cameras, and video cameras, is investigated with the aim of simplifying 3D video content generation. The concept of Time-of-Flight sensor fusion is analyzed in order to identify suitable courses of action for high quality 3D video acquisition. In order to overcome the main drawback of current Time-of-Flight technology, namely the high sensor noise and low spatial resolution, a weighted optimization approach for Time-of-Flight super-resolution is proposed. This approach incorporates video texture, measurement noise and temporal information for high quality 3D video acquisition from a single video plus Time-of-Flight camera combination. Objective evaluations show benefits with respect to state-of-the-art depth upsampling solutions. Subjective visual quality assessment confirms the objective results, with a significant increase in viewer preference by a factor of four. Furthermore, the presented super-resolution approach can be applied to other applications, such as depth video compression, providing bit rate savings of approximately 10 percent compared to competing depth upsampling solutions. The work presented in this dissertation has been published in two scientific journals and five peer-reviewed conference proceedings.  In conclusion, Time-of-Flight sensor fusion can help to simplify 3D video content generation, consequently supporting a larger variety of available content. Thus, this dissertation provides important inputs towards broad and innovative 3D video content, hopefully contributing to the future success of next-generation 3DTV.

La fission nucléaire est un phénomène complexe dont tous les mécanismes ne sont pas entièrement compris. Dans le cadre d'une coopération internationale, le CEA/DAM/DIF étudie les spectres en énergie des neutrons prompts émis lors de la fission induite par des neutrons rapides, et plus particulièrement la zone à basse énergie de ces spectres (<1 MeV). Ce travail de thèse a consisté à optimiser un dispositif expérimental de mesure de neutrons prompts de fission. Dans un premier temps, de nouveaux détecteurs de fission ont été développés. Nous en rapportons ici la conception et étudions leurs performances en termes de discrimination alpha-fission, de résolution en temps et de distorsion sur le spectre mesuré. Le second axe de développement abordé au cours de cette thèse est celui de la détection des neutrons. Plusieurs types de détecteurs ont été comparés (discrimination neutron-gamma, efficacité de détection), en vue d'optimiser la détection des neutrons de basse énergie (<1 MeV). Ce mémoire présente les résultats de ces études. Enfin, le dispositif expérimental ainsi optimisé est utilisé pour mesurer le spectre en énergie des neutrons prompts émis lors de la fission induite par neutrons de l' ²³⁸UU. Après avoir présenté la méthode utilisée pour l'analyse des données, les résultats obtenus sont interprétés en termes de modèles et d'évaluations. / The nuclear fission is a complex phenomenon whose mechanisms are not fully understood. Within the framework of an international cooperation, the CEA/DAM/DIF is taking part in the study of prompt fission neutron energy spectra from fast neutron induced fission, focusing on the low energy domain of these spectra (<1 MeV). This PhD was dedicated to the optimization of the experimental setup. New fission detectors were developed. We report on their conception and their performances in terms of alpha-fission discrimination, timing resolution and distortion on the measured spectrum. In a second step, several neutron detectors were studied (neutron-gamma discrimination, detection efficiency), so as to optimize the detection of low energy neutrons (<1 MeV). In the present document, we report on the results of this comparative study. Finally, the optimized experimental setup was used to measure prompt fission neutron energy spectra for the fast-neutron induced fission of ²³⁸U. After detailing the data analysis method, the results are interpreted in terms of models and evaluations.

Diplomová práce přibližuje systémy LIDAR přímo měřící čas průletu a časově digitální převodníky určené k použití v těchto systémech. Představuje problematiku distribuce hodinových signálů napříč soubory časově digitálních převodníků v LIDAR systémech a věnuje se jednomu z nových řešení této problematiky, které je založené na injekcí zavěšených oscilátorech. Technika injekčního zavěšení oscilátorů je důkladně matematicky popsána. V programu Matlab byl vytvořen simulační model injekcí zavěšeného kruhového oscilátoru, který potvrzuje správnost uvedených analytických predikcí. Ve výrobní technologii ONK65 byl navržen injekcí zavěšený kruhový oscilátor stabilizovaný pomocí smyčky závěsu zpoždění, určený pro implementaci časově digitálního převodníku pro systém LIDAR. Navržený injekcí zavěšený kruhový oscilátor byl verifikován počítačovými simulacemi zohledňujícími vliv procesních, napěťových i teplotních variací. Oscilátor poskytuje specifikované časové rozlišení 50 pikosekund a dosahuje dvakrát nižší hodnoty fázového neklidu než ekvivalentní volnoběžný oscilátor v dané technologii.

No description available.

Des perspectives énergétiques sobres en carbone pour atténuer le changement climatique nécessitent le remplacement des combustibles fossiles par des sources produisant peu de CO2, par exemple l’énergie nucléaire. L'une des options discutées par le Forum international Gen-IV pour la prochaine génération de réacteurs nucléaires consiste à utiliser le cycle du thorium. L'isotope fissile 233U est l'un des isotopes les plus importants du cycle du thorium et est directement responsable du bilan neutronique. L'une des particularités de ce noyau est d'avoir une section efficace de capture qui est inférieure d'un ordre de grandeur à celle de fission. Cette circonstance rend très difficile la mesure de sa section efficace de capture, comme l'atteste seulement deux jeux de données à haute résolution disponibles depuis les années 1960. Dans cette thèse, une nouvelle mesure auprès de la source de neutrons n_TOF est décrite utilisant une nouvelle chambre à fission compacte insérée au centre d'un détecteur de rayons gamma, le calorimètre à absorption totale. La chambre à fission permet d’identifier et de soustraire les rayons gamma de la réaction de fission dans le but d’améliorer la précision de la section efficace de capture de 233U. La chambre à fission est conçue dans cet objectif. Son excellente performance est décrite en détail et permet d'extraire des informations sur les rayons gamma de fission. Une discussion détaillée du processus de réduction des données et des éléments clés de l’analyse, est présentée et aboutit au calcul du rapport alpha de 233U, le rapport entre la section efficace de capture et celle de fission. / A low-carbon energy outlook to mitigate the climate change requires the replacement of fossil fuel by sources with low CO2 emissions, like nuclear energy.. One of the options discussed in the Gen-IV International Forum for the the next generation of nuclear reactors is to use the thorium cycle. The fissile isotope 233U is among the most important isotopes in the thorium cycle and directly responsible for the neutron economy. One of the particularities of this nucleus is to have a capture cross section which is one order of magnitude lower than fission, making the measurement of the 233U capture cross section very challenging as indicated by only two high resolution data sets available since the 1960s. In this thesis, a new measurement at the n_TOF neutron source is described employing a novel compact fission chamber inserted in the center of the Total Absorption Calorimeter g-ray detector. The fission chamber allows to tag and subsequently subtract the gamma rays from the fission reaction aiming to improve the accuracy of the 233U capture cross section.The performance of the custom tailored fission chamber is described in detail and allows to extract information about the prompt fission g-rays. A detailed discussion of the data reduction process and the key elements in the analysis is given resulting in the calculation of the 233U-alpha-ratio, the ratio between the capture and fission cross-section.

Dans les installations industrielles, des inspections régulières sont planifiées pour évaluer l’état de santé interne des composants. Si des fissures sont révélées, il est souhaitable de savoir si l’exploitation de la structure peut se poursuivre ou si un régime de fonctionnement dégradé pourrait être envisagé. En se basant sur la mécanique élastique linéaire de la rupture, les travaux présentés traitent donc dans le cas de composants fissurés de la dispersion de durée de vie résiduelle relative aux incertitudes sur les paramètres du modèle de prévision. La longueur de fissure initiale, les propriétés du matériau ainsi que les paramètres d’entrée de la loi de Paris ont été considérés comme des variables aléatoires, dont les distributions ont été déterminées expérimentalement puis ajustées par des lois statistiques adéquates. Des contrôles ultrasonores par mesure du temps de vol de l’onde diffractée – Time Of Flight Diffraction (TOFD) en anglais – et des mesures de champs obtenues par corrélation d’images numériques ont été utilisés pour quantifier la propagation d’une fissure dans une éprouvette à défaut soumise à des sollicitations cycliques uniaxiales. Les données expérimentales recueillies ont été utilisées pour initialiser les calculs et valider les résultats numériques. Les distributions de taille de fissure obtenue après un nombre donné de cycles de sollicitation et de nombre de cycles de sollicitation conduisant à une taille définie de fissure ont été obtenues par une méthode de Monte-Carlo appliquée au modèle de prévision. L’ajustement de ces distributions par de lois log-normales a fourni des outils analytiques d’estimation probabiliste de propagation de fissure. Cela a notamment permis la réalisation de cartographies de risques et l’évaluation de l’évolution de la fiabilité du composant étudié. Enfin, les effets d’une actualisation de la connaissance de la longueur de fissure au cours de la vie de ce composant en termes d’incertitude de prévision et d’extension de durée de vie résiduelle prévisionnelle ont été étudiés. En particulier, afin de limiter le coût des campagnes de contrôle non destructifs dans le cas industriel, une stratégie d’optimisation de l’actualisation de cette connaissance basée sur l’étude de fiabilité a été proposée. / In industrial plants, regular inspections are planned to assess the internal state of installations. If some cracks are revealed, it is desirable to know whether the structure can still be used or if a degraded mode of operation should be considered. Starting from a linear elastic fracture mechanics model, the work presented studied the scatter of the remaining life of such cracked parts due to the uncertainties on the parameters of the prediction model. Initial crack size, material properties and input parameters of Paris’ law have been considered as random variables and their distributions have been experimentally identified and fitted with convenient statistical laws. Time Of Flight Diffraction (TOFD) and field measurement technique based on Digital Image Correlation (DIC) were used to monitor the crack propagation initiated from a notch introduced in specimen submitted to uniaxial cyclic loading. Experimental crack length results were used to initiate computations and as a mean to validate numerical results. Both the crack lengths distributions resulting from the application of loading cycles and the distribution of the number of cycles leading to a given crack length were obtained from a Monte-Carlo method applied to the prediction model. The fit of these distributions with log-normal laws provided analytical tools to assess probabilistic crack propagation. It allowed for risk mapping and for the evaluation of the studied component’s reliability evolution. Last, the effects of an actualisation of crack length knowledge along the life of this component in terms of assessment uncertainty and predicted residual life extension has been studied. Especially, to limit the cost of non-destructive techniques inspection in industrial cases, a reliability-based strategy has been proposed for the optimisation of the crack knowledge actualisation.

No description available.

Positron emission tomography (PET) is a nuclear medicine imaging techniquethat uses radiotracers to visualize processes like metabolism and perfusion. Theradiotracer emits positrons, which collide with shell electrons of the atomsthat make up the surrounding tissue. Such a collision produces two gammarayphotons, emitted roughly 180 degrees apart [1]. PET captures thesephotons using a cylindrical arrangement of detectors. When two photons aredetected simultaneously by different detectors, it registers as a line of response(LOR). These LORs are then pre-processed into a sinogram. A mathematicalreconstruction method is used to computationally recover the 3D distribution ofthe radiotracer (activity map) from the sinogram. However, genuine LORs can becorrupted by false LORs that come from scattering, random events, and spuriousevents. Mitigating these in reconstruction algorithms is essential for improvingPET imaging accuracy and reliability.This paper explores the theoretical foundation of the Time of Flight (TOF) SingleScatter Simulation (SSS) model by Watson (2007) [2]. It also includes a Pythonimplementation of the MATLAB code associated with [2]. The model modelsCompton scattering to accurately estimate scattered photons in PET.Incorporating TOF data into the SSS model improves estimation accuracy, albeitat the cost of increased computational time. To expedite computations, thealgorithm was simplified by restricting operations to a subset of rings anddetectors and by pre-processing images through cropping and downscaling.Interpolation fills in missing data, ensuring complete estimation.The outcome of this project is a Python implementation that exhibited a strongcorrelation with the estimates obtained using the MATLAB implementation. Anotable issue arose during the comparison between the main components ofthe SSS algorithm in Python and MATLAB. The Euclidean norm between theresults from these two implementations was significant, indicating that they wereon different scales. Nevertheless, both implementations accurately predictedthe scatter in the same locations and relative magnitudes, despite the scalediscrepancy. Investigation into the discrepancy’s cause is ongoing, but theproject demonstrates the feasibility of implementing the TOF SSS algorithm inPython.