Electrical and Electronic Engineering - Theses
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ItemThree-dimensional intensity reconstruction in single-particle experiments: a spherical symmetry approach( 2015)The ability to decipher the three-dimensional structures of biomolecules at high resolution will greatly improve our understanding of the biological machinery. To this aim, X-ray crystallography has been used by scientists for several decades with tremendous results. This imaging method however requires a crystal to be grown, and for most interesting biomolecules (proteins, viruses) this may not be possible. The single-particle experiment was proposed to address these limitations, and the recent advent of ultra-bright X-ray Free Electron Lasers (XFELs) opens a new set of opportunities in biomolecular imaging. In the single-particle experiment, thousands of diffraction patterns are recorded, where each image corresponds to an unknown, random orientation of individual copies of the biomolecule. These noisy, unoriented two-dimensional diffraction patterns need to be then assembled in three-dimensional space to form the three-dimensional intensity function, which characterizes completely the three-dimensional structure of the biomolecule. This work focuses on geometrical variations of an existing algorithm, the Expansion-Maximization-Compression (EMC) algorithm introduced by Loh and Elser. The algorithm relies upon an expec-tation-maximization method, by maximizing the likelihood of an intensity model with respect to the diffraction patterns. The contributions of this work are (i) the redefinition of the EMC algorithm in a spherical design, motivated by the intrinsic properties of the intensity function, (ii) the utilisation of an orthonormal harmonic basis on the three-dimensional ball which allows a sparse representation of the intensity function, (iii) the scaling of the EMC parameters with the desired resolution, increasing computational speed and (iv) the intensity error is analysed with respect to the EMC parameters.
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ItemNeural correlates of consciousness and communication in disorders of consciousness( 2015)It is difficult to distinguish disorders of consciousness from certain disorders of communication for vegetative and minimally conscious patients who suffer from impairment of awareness and cannot produce reliable behavioural output. This thesis reviews some previous neuroimaging studies on mental imagery and brain injured patients, and presents a functional magnetic resonance imaging (fMRI) study of five patients that seeks to extend communication with them through asking them to answer simple questions with ‘yes’, ‘no’ or ‘I don’t know’ answers by performing mental imagery tasks of ‘playing tennis’, ‘navigating the home’, ‘imagining familiar faces’, and ‘counting up from 10 by 7s’. Consideration is given to how each individual’s activation map deviates from the control group map and a quantitative method of overlap, the percent overlap metric A, to classify the deviations is proposed. Promising results were found on controls with this method to infer which imagery task had been done. The full results of three tests for each participant are reported: speech comprehension capacity, mental imagery, and question-answer. Specific brain activations were observed in the first two tests: the posterior parts of superior and middle temporal cortices for ‘sentences’ in the language test; the paraphippocampal area and premotor area for navigation, superior parietal cortex and premotor area for tennis; lateral prefrontal (BA44,45), intra-parietal sulcus, and superior parietal areas for counting; frontal orbital cortex, left Broca’s area 44, and right Broca’s area 45 for faces in the imagery test. In the question-answer test, most of tennis or navigation tasks could be identified correctly when employed while answering as measured by the metric A. Although some patients produced activations in similar areas to controls for certain tasks, only two minimally conscious patients showed significant activation changes as judged by the fMRI time series for some tasks. The activation maps observed for two patients with 1.5T MRI provide independent support to the work from other groups (at 3T) on finding patients with a disorder of consciousness who can perform mental imagery tasks, which suggests broader clinical utility for the tests presented here. Given the control participant results for the mental imagery and question-answers tasks, it should be possible to at least work with locked-in patients at 1.5T. An original contribution includes consideration of the task of mental calculation. The evidence for specific pattern for counting task is provided for a group of 11 healthy participants.
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ItemInvestigations of electro-optic sampling systems for the sensitive measurements of electric field( 2015)As the progress in integrated circuits (ICs) and antenna technology has been springing up for the last several decades, an ideal and highly sensitive characterization system for those high speed electronics is required side by side. The testing system must have larger bandwidth, less invasiveness and a very good spatial resolution. With this premise, none of us can deny the importance of electro-optic probing technique which is an anticipating method of mapping the electric field and characterization of high speed electronic and optoelectronic modules. Electro-optic sampling is the combination of Pockels eff ect and advanced laser technology and that makes it pretty fast and the best in spatial resolution. But there is a lot more to go to achieve the goals for its sensitivity. This dissertation engirds the investigations for some non-linear parameters used in electro-optic probing techniques. Those parameters can play important role in enhancing the sensitivity of the novel electro-optic sampling techniques. This includes optimal input polarization of the input laser beam which can have a noticeable impact on valuable out- put current of the detector. The very famous and the merit point of the electro-optic sampling is phase retardation which not only depends upon the applied electric fi eld of the device under test (DUT) a very good deal but also upon the rotation angle inside the electro-optic crystal and the variety of angles of incidence of the laser beam. Our investigation rivets to the dependence of phase retardation upon rotation angle and angles of incidence in order to map the three components of arbitrary electric field and to get better results. If we go further we realize some recondite issues to concentrate upon, especially for the better spatial resolution of the electro-optic sampling technique and it is essential to investigate about the other parameters like how to minimize the spot size of the laser beam on an electro-optic crystal with the response of the cavity. More and more, the factors that e ffects the spatial resolution of the electro-optic sampling techniques including the inappropriate injection of reflected beam into the fi ber and losses, attenuation coefficient due to the beam divergence at the Air/EO interface with diff erent thickness of the crystal and attenuation coefficient due to the beam divergence at the back of the crystal with different re reflections. We summed up that all these factors will be helpful further even in electro-optic tip crafting in order to minimize the size of the footprint of the tip to characterize the miniatures of the chips.
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ItemThe synchronisation relationship between fetal and maternal cardiovascular systems( 2015)During pregnancy, the fetal physiological condition is carefully checked and monitored during the foetus' development. It is well known that the health of the foetus relies heavily on the nutrient and oxygen supply. The oxygen and nutrient supply is exchanged from the maternal vessel to the fetal vascular system via maternal placenta. The hypothesis that this research is trying to prove is that there may exist a strong synchronised relationship between the maternal and fetal cardiac systems, and the relationship may also correlate to the gestation period. The focus of the research was to extract fECG and mECG using non-invasive abdominal recordings and analyse the relationship between the parameters derived from the ECG signals. The research used derived parameters from the abdominal recordings to analyse the relationship between the maternal and fetal cardiac systems. To do this the fECG and mECG signals need to be separated from multiple abdominal and thoracic signals from open online source recordings. The principle of the ECG separation was based on independent component analysis (ICA) that considers multiple component signals statistically independent to each other. The pairs of extracted fECG and mECG signals are analysed on the time scale to investigate the synchronisation relationship. Being able to extract the heart rate of fetus and the mother independently is the key to determining the existence of a synchronised relationship between the separate cardiac systems. The findings from the fECG and mECG recordings at different gestational periods is that there is a direct relationship between the mother's cardiovascular system on the foetus, it may be caused by the nutritional influence during certain gestation periods.