Thèse Médecine Paris, 1823 numéro 32.

Ce travail de thèse porte sur la compréhension et le contrôle du procédé de croissance de films de diamant nanocristallin (DNC) par dépôt chimique en phase vapeur assisté par plasma micro-onde distribué. Deux axes de travail ont été suivis pour atteindre ces objectifs : une étude « matériau » visant à étudier les mécanismes de germination et de croissance et les caractéristiques des films de DNC élaborés ; une étude « plasma » s’intéressant au diagnostic des décharges basse pression H₂ /CH₄/CO₂ utilisées pour la croissance.Concernant le premier volet, des techniques de caractérisation ex situ, telles que la microscopie électronique à balayage, à transmission haute résolution et à force atomique, la spectroscopie Raman, la diffraction des rayons X, la réflectométrie UV-visible, et in situ, telles que l’interférométrie de réflectance laser, ont été mises en oeuvre pour étudier la densité de germination, la morphologie, la topographie, la microstructure, la pureté et la vitesse de croissance des films de DNC. L’influence de certains paramètres du procédé, tels que la pression dans l’enceinte, la position du substrat, la composition gazeuse, la température de surface, la puissance micro-onde et le prétraitement ex situ du substrat, a été étudié pour le silicium. La synthèse de DNC jusqu’à une température aussi basse que 130 °C a ainsi pu être maîtrisée. La faisabilité de la croissance à cette température sur un matériau polymère comme le polytétrafluoroéthylène (PTFE) a été démontrée. La croissance de films de DNC sur d’autres types de substrats tels que le nitrure de silicium et l'acier inoxydable a également été examinée. Concernant la deuxième partie de ce travail, le diagnostic du plasma de dépôt a été effectué par spectroscopie optique d’émission et spectroscopie d'absorption infrarouge en utilisant comme sources de rayonnement des diodes lasers accordables en longueurs d’ondes et des lasers à cascade quantique à cavité externe. L’influence des conditions expérimentales, en particulier de la puissance micro-onde et de la pression dans l’enceinte, sur la concentration du radical méthyl CH₃, précurseur de croissance du diamant, et de cinq molécules stables (CH₄, CO₂, CO, C₂H₂, C₂H₆), ainsi que sur le degré de dissociation de H₂ et les températures cinétiques, vibrationnelles et rotationnelles des espèces, a été étudiée. Le degré de dissociation élevé des précurseurs gazeux, pour une température de gaz relativement faible de quelques centaines de kelvins, indiquent que la chimie du plasma est principalement gouvernée par des processus électroniques. Le système à plasma micro-onde distribué utilisé permet cependant de produire certaines espèces de croissance et de gravure en quantité comparable aux procédés de croissance de DNC conventionnels tout en permettant le processus de synthèse à basse température. / This PhD thesis focuses on the understanding and the control of the nanocrystalline diamond (NCD) film growth process by distributed antenna array microwave plasma-assisted chemical vapor deposition. Two approaches were followed to reach these objectives: a « material » study aiming at studying the nucleation and growth mechanisms and the characteristics of the synthesized NCD films; a « plasma » study focusing on the diagnostics of H₂/CH₄/CO₂ low-pressure discharges used for NCD growth.Concerning the first part of this work, ex situ characterization techniques, such as scanning and high resolution transmission electron microscopy, atomic force microscopy, Raman spectroscopy, X-ray diffraction, UV-visible reflectometry, and in situ, such as laser reflectance interferometry, were used to study the nucleation density, morphology, topography, microstructure, purity, and growth rate of NCD films. The influence of some process parameters, such as chamber pressure, substrate position, gas composition, surface temperature, microwave power and ex situ substrate pretreatment, has been studied for silicon. The synthesis of NCD down to a substrate temperature as low as 130 °C has been thus investigated. The feasibility of NCD growth at this temperature on a polymeric material such as polytetrafluoroethylene (PTFE) has been demonstrated. The growth of NCD films on other kinds of substrates such as silicon nitride and stainless steel was also examined.Concerning the second part of this work, the diagnostics of the deposition plasma was carried out by optical emission spectroscopy and infrared absorption spectroscopy using wavelength-tunable laser diodes and external cavity quantum cascade lasers as radiation sources. The influence of the experimental conditions, in particular of the microwave power and the pressure in the chamber, on the concentration of the methyl radical CH₃, the diamond growth precursor, and of five stable molecules (CH₄, CO₂, CO, C₂H₂, C₂H₆), as well as on the degree of dissociation of H₂ and the kinetic, vibrational and rotational temperatures of the species, was studied. The high degree of dissociation of gas precursors, for a relatively low gas temperature of a few hundred degrees, indicates that the plasma chemistry is mainly governed by electronic processes. The considered distributed microwave plasma system nevertheless allows to produce some growth and etching species in amount comparable to conventional NCD growth processes, while permitting low temperature synthesis process.

Survivors of torture may have long-term physical, psychiatric and psychological sequelae. The aim of this study was to determine whether survivors of torture exhibit any psychopathology, whether they demonstrate abnormal findings on Brain Single Photon Emission Computed Tomography (SPECT) imaging, and whether correlations exist between Post Traumatic Stress Disorder (PTSD), Major Depressive Disorder (MDD), perfusion changes on Brain SPECT and Initial Self Reporting Questionnaire (SRQ8) scores. Thirty-six volunteers were recruited in a non randomised manner. Participants were assessed by a psychiatrist. The SRQ8, Impact of Event Scale – Revised (IES-R) and Montgomery Asberg Depression Rating Scale (MADRS) were administered. Participants underwent Brain SPECT imaging to assess cerebral perfusion changes. Data was analysed using Statistica 9.1. The primary psychiatric diagnoses made were PTSD, MDD or both. Participants with psychopathology had higher SRQ8, MADRS and IES-R scores. Although qualitatively, participants with psychopathology showed increased abnormal cerebral perfusion on Brain SPECT imaging, as compared to those participants without psychopathology, this could not be proven statistically. Perfusion changes were noted in the temporal cortices, parietal cortices, orbitofrontal cortices, thalami and basal ganglia. Higher SRQ8 scores were associated with higher scores on the MADRS and IES-R, and hence correlated with diagnoses of MDD and PTSD, but no direct association was noted with the visualised abnormal Brain SPECT imaging findings.

Electrochemical impedance spectroscopy (EIS) has been exploited as a rich source of Proton Exchange Membrane Fuel Cell (PEMFC) diagnostic information for many years. Several investigators have characterized different failure modes for PEMFCs using EIS and it now remains to determine how this information is to be obtained and used in a diagnostic or control algorithm for an operating PEMFC. This work utilizes the concept of impedance spectral fingerprints (ISF) to uniquely identify between failure modes in an operating PEMFC. Three well documented PEMFC failure modes, carbon monoxide (CO) poisoning, dehydration, and flooding were surveyed, modelled, and simulated in the time domain and the results were used to create a database of ISFs. The time domain simulation was realized with a fractional order differential calculus state space approach. A primary goal of this work was to develop simple and cost effective algorithms that could be included in a PEMFC on-board controller. To this end, the ISF was discretized as coarsely as possible while still retaining identifying spectral features using the Goertzel algorithm in much the same way as in dual tone multi-frequency detection in telephony. This approach generated a significant reduction in computational burden relative to the classical Fast Fourier Transform approach. The ISF database was used to diagnose simulated experimental PEMFC failures into one of five levels of failure: none (normal operation), mild, moderate, advanced, and extreme from one of the three catalogued failure modes. The described ISF recognition algorithm was shown to correctly identify failure modes to a lower limit of SNR = 1dB.

Purpose: Medical imaging systems are used to scan patients to obtain valuable information for diseases diagnosis and assisting treatment. An ideal scanner should be sensitive enough to detect any trace amount of abnormal tissue at its early stage. With the continuous development of high-tech treatment systems such as Tomotherapy (manufactured by Tomo HD), the high-resolution imaging system is favorable to reduce the damage of normal tissue due to the image guidance of Mega-voltage beam before treatment. In this study, a software approach was presented to improve image resolution without hardware upgrade of a scanner. Methodology A programming technique “Super Resolution Technique” was used and demonstrated in an example of CT. It utilized several similar images with known relative shifts between them. (They can be positional or angular shifted and taken at the same time frame as far as possible). Those images are of low resolution and can be reconstructed to form a higher resolution image. A Super Resolution program was written by MATLAB to prove the method. The experiments 1 to 4 were purely computer-based simulations and experiment 5 used a LightSpeed VCT scanner for real scans. For the computer-based experiments, a few low resolution images have been attempted and registration steps were explored for image reconstruction. A resolution target, USAF1951, was called from MATLAB and used to examine the resolving power before and after image processing based on Super Resolution algorithm. Image-image subtraction was used to compare pre-processing and post-processing images. The number of non-zero pixels was used to access the percentage of similarity. For the experiment using LightSpeed VCT scanner, a GE VCT QA phantom was used to test the performance of the technique. Result From the experiments using USAF1951, it was found that: the minimum resolvable line pairs had improved from family -1 element 6 to family 0 element 2 (2 elements improvement) after applying “Super Resolution Technique” as shown in the experiment 1. An xy directional shifting of the pre-processing images resulted in a better reconstructed image than x-axis shifting or y-axis shifting in terms of resolution, shown in the experiment 2. The experiment 3 concluded that the more the pre-processing images, the better the reconstructed image would be. The experiment 4 showed that the shifts of pre-processing images greater than the detector size could still result in a higher resolution image. The experiment 5 revealed that applying “Super Resolution Technique” to a real CT scanner could not give an obvious improvement in resolution, but the image background noise had reduced. Conclusion It was concluded that the “Super Resolution Technique” could improve the image resolution and reduce the background noise at expense of more imaging time and more dose from the additional view. In case of hardware upgrade of imaging device is not practicable, Super Resolution could help improve the image quality. / published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

This dissertation concerns the ability of human observers to perform detection tasks in medical images that contain structured noise. We shall show that physical measures of image quality, such as signal-to-noise ratio (SNR), resolution, modulation transfer function (MTF), and contrast, do not accurately predict how well an observer can detect lesions in an image. We have found that for images with equal pixel SNR, humans can detect a low contrast object more readily in images that have a low-pass noise structure, as opposed to a high-pass noise structure. This finding is important in the comparison of images generated by a classical pinhole imaging system with images generated by a computed tomography imager. We would like to have a figure of merit that accurately predicts a physician's ability to perform perceptual tasks. That is, we want a figure of merit for imaging systems that is more than an evaluation of the physician's performance, measured using human observers and an accepted method such as receiver operating characteristic (ROC) techniques. We want a figure of merit that we can calculate without requiring lengthy observer studies. To perform this calculation, we need a model of the imaging system hardware in cascade with a verified model of the human observer. We have chosen to approach this problem by modelling the human observer as an ideal observer. Our hypothesis is that the human observer acts approximately as an ideal-observer who does not have the ability to prewhiten the noise in an image. Without this ability, the ideal observer's detection performance for even a simple task is degraded substantially in correlated noise. This is just the effect that we have found for human observers. In search of a physiological explanation for a human observer's inability to do prewhitening, we shall investigate the detection capability of the ideal observer when a frequency-selective mechanism is invoked. This mechanism corresponds to the frequency channels known to exist in the human visual system. We shall show that the presence of such a mechanism can explain the degradation of human observer performance in correlated noise.

Electrochemical impedance spectroscopy (EIS) has been exploited as a rich source of Proton Exchange Membrane Fuel Cell (PEMFC) diagnostic information for many years. Several investigators have characterized different failure modes for PEMFCs using EIS and it now remains to determine how this information is to be obtained and used in a diagnostic or control algorithm for an operating PEMFC. This work utilizes the concept of impedance spectral fingerprints (ISF) to uniquely identify between failure modes in an operating PEMFC. Three well documented PEMFC failure modes, carbon monoxide (CO) poisoning, dehydration, and flooding were surveyed, modelled, and simulated in the time domain and the results were used to create a database of ISFs. The time domain simulation was realized with a fractional order differential calculus state space approach. A primary goal of this work was to develop simple and cost effective algorithms that could be included in a PEMFC on-board controller. To this end, the ISF was discretized as coarsely as possible while still retaining identifying spectral features using the Goertzel algorithm in much the same way as in dual tone multi-frequency detection in telephony. This approach generated a significant reduction in computational burden relative to the classical Fast Fourier Transform approach. The ISF database was used to diagnose simulated experimental PEMFC failures into one of five levels of failure: none (normal operation), mild, moderate, advanced, and extreme from one of the three catalogued failure modes. The described ISF recognition algorithm was shown to correctly identify failure modes to a lower limit of SNR = 1dB.

Thesis (Ph. D., Computer Science)--University of Idaho, August 2009. / Major professor: Mark L. Manwaring. Includes bibliographical references (leaves 172-179). Also available online (PDF file) by subscription or by purchasing the individual file.

Thesis (Ph.D.)--Aberdeen University, 2008. / Title from web page (viewed on June 3, 2009). Includes bibliographical references.

Electrochemical impedance spectroscopy (EIS) has been exploited as a rich source of Proton Exchange Membrane Fuel Cell (PEMFC) diagnostic information for many years. Several investigators have characterized different failure modes for PEMFCs using EIS and it now remains to determine how this information is to be obtained and used in a diagnostic or control algorithm for an operating PEMFC. This work utilizes the concept of impedance spectral fingerprints (ISF) to uniquely identify between failure modes in an operating PEMFC. Three well documented PEMFC failure modes, carbon monoxide (CO) poisoning, dehydration, and flooding were surveyed, modelled, and simulated in the time domain and the results were used to create a database of ISFs. The time domain simulation was realized with a fractional order differential calculus state space approach. A primary goal of this work was to develop simple and cost effective algorithms that could be included in a PEMFC on-board controller. To this end, the ISF was discretized as coarsely as possible while still retaining identifying spectral features using the Goertzel algorithm in much the same way as in dual tone multi-frequency detection in telephony. This approach generated a significant reduction in computational burden relative to the classical Fast Fourier Transform approach. The ISF database was used to diagnose simulated experimental PEMFC failures into one of five levels of failure: none (normal operation), mild, moderate, advanced, and extreme from one of the three catalogued failure modes. The described ISF recognition algorithm was shown to correctly identify failure modes to a lower limit of SNR = 1dB. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate