On this thesis work, design and construction of an up to date complete RF excitation system was intended. This excitation system is mainly based on highly efficient switching power generators and proper coupling of the power to the object plasma. This new excitation system design should answer the demands of today&#039 / s progressed CO2 lasers on various power ranges. Though it could be used by a large variety of applications including RF plasma and RF heating, on the first occasion in order to define design considerations, this system is to be exploited by RF excited fast flow and RF excited slab CO2 laser constructions.

In this thesis, control schemes for the self-excited induction generator are developed with Matlab/Simulink. Self-excited induction generator is considered as a constant voltage-constant frequency supply for an isolated load. A wind turbine is assumed to be the variable-speed drive of the induction generator. Control schemes aim to ensure a constant voltage-constant frequency operation of the induction generator in case of the variations in the wind speed and/or the load. From the general model of the self-excited induction generator, the characteristics of the system and the dynamic responses of the system in case of any disturbance are examined. Next, the control strategies are developed both for the squirrel-cage rotor induction generator and for the wound-rotor induction generator. Two control loops are necessary for constant voltage-constant frequency operation of a variable speed induction generator, one for the voltage regulation and the other for the frequency regulation. After developing the control loops, constant voltage-constant frequency operation of the self-excited induction generator is simulated with a cage type saturation adaptive induction generator, a fixed capacitor with thyristor controlled reactor (TCR) used for frequency regulation and switched external resistors connected to the stator terminals used for voltage regulation.

Development of a three dimensional (3D) HYBROT model with targeted in vivo like intact cellular circuitry in thick brain slices for multi-site stimulation and recording will provide a useful in vitro model to study neuronal dynamics at network level. In order to make this in vitro model feasible, we need to develop several associated technologies. These technologies include development of a thick organotypic brain slice culturing method, a three dimensional (3D) micro-fluidic multielectrode Neural Interface system (µNIS) and the associated electronic interfaces for stimulation and recording of/from tissue, development of targeted stimulation patterns for closed-loop interaction with a robotic body, and a deep-tissue non-invasive imaging system. To make progress towards this goal, I undertook two projects: (i) to develop a method to culture thick organotypic brain slices, and (ii) construct a multiphoton imaging system that allows long-term and deep-tissue imaging of two dimensional and three dimensional cultures. Organotypic brain slices preserve cytoarchitecture of the brain. Therefore, they make more a realistic reduced model for various network level investigations. However, current culturing methods are not successful for culturing thick brain slices due to limited supply of nutrients and oxygen to inner layers of the culture. We developed a forced-convection based perfusion method to culture viable 700µm thick brain slices. Multiphoton microscopy is ideal for imaging living 2D or 3D cultures at submicron resolution. We successfully fabricated a custom-designed high efficiency multiphoton microscope that has the desired flexibility to perform experiments using multiple technologies simultaneously. This microscope was used successfully for 3D and time-lapse imaging. Together these projects have contributed towards the progress of development of a 3D HYBROT. ----- 3D Hybrot: A hybrid system of a brain slice culture embodied with a robotic body.

Magnetic Resonance Imaging (MRI) is considered as a slow imaging technique. Various approaches to accelerate MRI imaging have been explored by researchers in the past decades. Earlier gradient based methods have reached the safety limit. Parallel receiving techniques achieve accelerations by reducing phase encoding steps. Among these methods, SEA Imaging achieved the highest possible acceleration by completely eliminating phase encoding. However, SEA imaging is limited to thin planar slices above the array due to the correction needed for the inherent phase cancellation caused by voxel-sized coils. A phase compensation gradient pulse is used for this correction in SEA imaging. This phase compensation is dependent on slice position and thickness as well as the orientation of the array elements, placing stringent restrictions on SEA imaging, limiting its applications. Converting the SEA system into Transmit / Receive (T/R) mode, which is the main purpose of this study, eliminates the requirement for phase compensation gradient because phase departed during transmit is refocused during receiving. Independent amplitude and phase control of RF pulse for each coil of a SEA array is achieved using a low cost scalable parallel transmit system design. The first 64-channel parallel transmitter for MRI in the world is constructed and tested. Software is also developed to control the phase and amplitude of all the 64 channels of RF excitation pulses independently through National Instruments DAQ system. The system consists of vector modulators controlled by digital controlled potentiometers, two-stage amplifiers and T/R switches on the transmit side. All these are combined with newly designed and constructed preamplifiers and the existing 64-channel parallel receivers on the receive side, leading to the only 64-channel parallel T/R system available for MRI. As a bonus, the system can be easily updated to full Transmit SENSE capability. Furthermore, simulations and images are done to synthesize transmit patterns thanks to the large channel count. Testing results show that the system is capable of 100W per channel simultaneous transmission. Using this system, transmit field can be synthesized by varying the phase and amplitude across channel without traditionally required complicated pulse sequences involving simultaneous RF and gradient fields. Curved slice excitation has conventionally been considered a difficult task for MRI, achievable only through complicated pulses sequences. Using this system and flexible array wrapped around the subject to be imaged, the system is able to excite curved slice using one shot. TR images indicate that the system is capable of high speed surface imaging at 200 frames per second following the surface of a flexible SEA array coil which has not been achieved using other methods in MRI.

Thesis (Ph.D.); Submitted to the University of California, Berkeley, CA (US); 24 Nov 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--56751" McGuire, John Andrew. USDOE Director. Office of Science. Office of Basic Energy Sciences. Materials Science and Engineering Division (US) 11/24/2004. Report is also available in paper and microfiche from NTIS.

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Ces dernières années d'importantes avancées techniques dans la manipulation des gaz atomiques ultrafroids ont ouvert la voie à la réalisation de fluides quantiques mésoscopiques de basse dimension. L'objet de cette thèse est l'étude théorique de certains systèmes mésoscopiques réalisables avec un gaz de Bose unidimensionel. Ces systèmes présentent des phénomènes quantiques intéressants, et sont potentiellement utiles en vue d'applications technologiques. Nous étudions le phénomène des courants permanents induits dans un gaz confiné sur un anneau par la rotation d'une barrière de potentiel, nous examinons la faisabilité d'un qubit fondé sur la superposition d'états de courant dans un réseau en forme d'anneau traversé par un champ de jauge et contenant un 'weak-link', ainsi que l'excitation dipolaire du gaz dans un 'split-trap' induit par le déplacement hors équilibre du potentiel externe. Dans tous ces cas, nous combinons diverses approches analytiques et numériques, qui permettent de couvrir l'ensemble des régimes d'interactions. Nous mettons en lumière un régime jusque-là inconnu, d'écrantage maximal des barrières de potentiel par le fluide, dû à une competition entre les effets des interactions et des fluctuations quantiques. Ces résultats ont des conséquences significatives sur le comportement de tels systèmes et, de ce fait, sont importants pour les réalisations en cours et à venir de dispositifs à gaz d'atomes ultrafroids. / Thanks to the experimental breakthrough of the last years in the manipulation of ultra cold atomic gases, it has become possible to realize low-dimensional and mesoscopic quantum fluids. The object of this thesis is the theoretical investigation of a few mesoscopic systems that can be realized with a one-dimensional Bose gas. These systems exhibit interesting quantum phenomena, and are potentially relevant for technological applications. We study the phenomenon of persistent currents induced by stirring the gas confined on a ring with a potential barrier, we examine the feasibility of a qubit based on the superposition of current states in a ring lattice threaded by a gauge field in the presence of a weak-link, and we investigate the dipole excitation of the gas in a split trap induced by an out-of-equilibrium displacement of the external potential. In all these cases, we apply a combination of analytical and numerical approaches that allow to cover all the interaction regimes. As a recurring theme, we disclose a so-far unknown regime of maximal screening of the barrier potential by the fluid, arising from the interplay of effects due to interactions and quantum fluctuations. These results have significant consequences for the behaviour of such systems and are important for the ongoing and future realization of ultracold atomic gases devices.

In this work, we propose an approach that allows to explore the potential pathophysiological mechanisms (at neuronal population level) of ictogenesis by combining clinical intracranial electroencephalographic (iEEG) recordings with a neural mass model. IEEG recordings from temporal lobe epilepsy (TLE) patients around seizure onset were investigated. Physiologically meaningful parameters (average synaptic gains of the excitatory, slow and fast inhibitory population, Ae, B and G) were identified during interictal to ictal transition. We analyzed the temporal evolution of four ratios, i.e. Ae/G, Ae/B, Ae/(B + G), and B/G. The excitation/inhibition ratio increased around seizure onset and decreased before seizure offset, suggesting the disturbance and restoration of balance between excitation and inhibition around seizure onset and before seizure offset, respectively. Moreover, the slow inhibition may have an earlier effect on the breakdown of excitation/inhibition balance. Results confirm the decrease in excitation/inhibition ratio upon seizure termination in human temporal lobe epilepsy, as revealed by optogenetic approaches both in vivo in animal models and in vitro. We further explored the distribution of the average synaptic gains in parameter space and their temporal evolution, i.e. the path through the model parameter space, in TLE patients. Results showed that the synaptic gain values located roughly on a plane before seizure onset, dispersed during ictal and returned when the seizure terminated. Cluster analysis was performed on seizure paths and demonstrated consistency in synaptic gain evolution across different seizures from individual patients. Furthermore, two patient groups were identified, each one corresponding to a specific synaptic gain evolution in the parameter space during a seizure. Results were validated by a bootstrapping approach based on comparison with random paths. The differences in the path revealed variations in EEG dynamics for patients despite showing an identical seizure onset pattern. Our approach may have the potential to classify the epileptic patients into subgroups based on different mechanisms revealed by subtle changes in synaptic gains and further enable more robust decisions regarding treatment strategy. The increase of excitation/inhibition ratios, i.e. Ae/G, Ae/B and Ae/(B+G), around seizure onset makes them potential cues for seizure detection. We explored the feasibility of a model based seizure detection algorithm. A simple thresholding method was employed. We evaluated the algorithm against the manual scoring of a human expert on iEEG samples from patients suffering from different types of epilepsy. Results suggest that Ae/(B+G), i.e. excitation/(slow + fast inhibition) ratio, allowed the best performance and that the algorithm best suited TLE patients. Leave-one-out cross-validation showed that the algorithm achieved 94.74% sensitivity for TLE patients. The median false positive rate was 0.16 per hour, and median detection delay was -1.0 s. Of interest, the values of the threshold determined by leave-one-out cross-validation for TLE patients were quite constant, suggesting a general excitation/inhibition balance baseline in background iEEG among TLE patients. Such a model-based seizure detection approach is of clinical interest and could also achieve good performance for other types of epilepsy provided that more appropriate model, i.e. better describe epileptic EEG waveforms for other types of epilepsy, is implemented. Altogether, this thesis contributes to the field of epilepsy research from two perspectives. Scientifically, it gives new insights into the mechanisms underlying interictal to ictal transition, and facilitates better understanding of epileptic seizures. Clinically, it provides a tool for reviewing EEG data in a more efficient and objective manner and offers an opportunity for on-demand therapeutic devices. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Fluorescence microscopy is an indispensable tool in the areas of cell biology, histology and material science as it enables non-invasive observation of specimen in their natural environment. The main advantage of fluorescence microscopy is that, it is non-invasive and capable of imaging with very high contrast and visibility. It is dynamic, sensitive and allows high selectivity. The specificity and sensitivity of antibody-conjugated probes and genetically-engineered fluorescent protein constructs allows the user to label multiple targets and the precise location of intracellular components. However, its spatial reso- lution is limited to one-quarter of the excitation wavelength (Abbe’s diffraction limit). The advent of new and sophisticated optics and availability of fluorophores has made fluorescence imaging a flourishing field. Several advanced techniques like TIRF, 4PI, STED, SIM, SPIM, PALM, fPALM, GSDIM and STORM, have enabled high resolution imaging by breaking the diffraction barrier and are a boon to medical and biological research. Invention of confocal and multi-photon microscopes have enabled observation of the specimen embedded at depth. All these advances in fluorescence microscopy have made it a much sought-after technique. The first chapter provides an overview of the fundamental concepts in fluorescence imag- ing. A brief history of emergence of the field is provided in this chapter along with the evolution of different super-resolution microscopes. An introduction to the concept of fluorophores, their broad classification and their characteristics is discussed in this chap- ter. A brief explanation of different fluorescence imaging techniques and some trending techniques are introduced. This chapter provides a thorough foundation for the research work presented in the thesis. Second chapter deals with different microscopy techniques that have changed the face of biophotonics and nanoscale imaging. The resolution of optical imaging systems are dictated by the inherent property of the system, known as impulse response or more popularly “point spread function”. A basic fluorescence imaging system is presented in this chapter and introduces the concept of point spread function and resolution. The introduction of confocal microscope and multi-photon microscope brought about improved optical sectioning. 4PI microscopy technique was invented to improve the axial resolution of the optical imaging system. Using this microscopy modality, an axial resolution of upto ≈ 100nm was made possible. The basic concepts of these techniques is provided in this chapter. The chapter concludes with a discussion on some of the optical engineering techniques that aid in improved lateral and axial resolution improvements and then we proceed to take on these engineering techniques in detail in the next chapter. Introduction of spatial masks at the back aperture of the objective lens results in gen- eration of a Bessel-like beam, which enhances our ability to see deeper inside a spec- imen with reduced aberrations and improved lateral resolution. Bessel beams have non-diffracting and self-reconstructing properties which reduces the scattering while ob- serving cells embedded deep in a thick tissue. By coupling this with the 4PI super- resolution microscopy technique, multiple excitation spots can be generated along the optical axis of the two opposing high-NA objective lenses. This technique is known as multiple excitation spot optical (MESO) microscopy technique. It provides a lateral resolution improvement upto 150nm. A detailed description of the technique and a thorough analysis of the polarization properties is discussed in chapter 3. Chapters 4 and 5 bring the focus of the thesis to the main topic of research - multi- dimensional image reconstruction for fluorescence microscopy by employing the statis- tical techniques. We begin with an introduction to filtering techniques in Chapter 4 and concentrate on an edge-preserving denoising filter: Bilateral Filter for fluorescence microscopy images. Bilateral filter is a non-linear combination of two Gaussian filters, one based on proximity of two pixels and the other based on the intensity similarity of the two. These two sub-filters result in the edge-preserving capability of the filter. This technique is very popular in the field of image processing and we demonstrate the application of the technique for fluorescence microscopy images. The chapter presents a through description of the technique along with comparisons with Poisson noise mod- eling. Chapters 4 and 5 provide a detailed introduction to statistical iterative recon- struction algorithms like expectation maximization-maximum likelihood (EM-ML) and maximum a-posteriori (MAP) techniques. The main objective of an image reconstruc- tion algorithm is to recover an object from its noisy degraded images. Deconvolution methods are generally used to denoise and recover the true object. The choice of an appropriate prior function is the crux of the MAP algorithm. The remaining of chapter 5 provides an introduction to different potential functions. We show some results of the MAP algorithm in comparison with that of ML algorithm. In chapter 6, we continue the discussion on MAP reconstruction where two new potential functions are introduced and demonstrated. The first one is based on the application of Taylor series expansion on the image. The image field is considered to be analytic and hence Taylor series produces an accurate estimation of the field being reconstructed. The second half of the chapter introduces an interpolation function to approximate the value of a pixel in its neighborhood. Cubic B-splines are widely used as a basis function during interpolation and they are popular technique in computer vision and medical imaging techniques. These novel algorithms are tested on di_erent microscopy data like, confocal and 4PI. The results are shown at the _nal part of the chapter. Tagging cell organelles with uorescent probes enable their visualization and analysis non-invasively. In recent times, it is common to tag more than one organelle of interest and simultaneously observe their structures and functions. Multicolor uorescence imaging has become a key technique to study speci_c processes like pH sensing and cell metabolism with a nanoscale precision. However, this process is hindered by various problems like optical artifacts, noise, autouorescence, photobleaching and leakage of uorescence from one channel to the other. Chapter 7 deals with an image reconstruction technique to obtain noise-free and distortion-less data from multiple channels when imaging a multicolor sample. This technique is easily adaptable with the existing imaging systems and has potential application in biological imaging and biophysics where multiple probes are used to tag the features of interest. The fact that the lateral resolution of an optical system is better than the axial resolution is well known. Conventional microscopes focus on cells that are very close to the cover-slip or a few microns into the specimen. However, for cells that are embedded deep in a thick sample (ex: tissues), it is di_cult to visualize them using a conventional microscope. A number of factors like, scattering, optical aberrations, mismatch of refractive index between the objective lens and the mounting medium and noise, cause distortion of the images of samples at large depths. The system PSF gets distorted due to di_raction and its shape changes rapidly at large depths. The aim of chapter 8 is to introduce a technique to reduce distortion of images acquired at depth by employing image reconstruction techniques. The key to this methodology is the modeling of PSF at large depths. Maximum likelihood technique is then employed to reduce the streaking e_ects of the PSF and removes noise from raw images. This technique enables the visualization of cells embedded at a depth of 150_m. Several biological processes within the cell occur at a rate faster than the rate of acquisition and hence vital information is missed during imaging. The recorded images of these dynamic events are corrupted by motion blur, noise and other optical aberrations. Chapter 9 deals with two techniques that address temporal resolution improvement of the uorescence imaging system. The _rst technique focuses on accelerating the data acquisition process. This includes employing the concept of time-multiplexing to acquire sequential images from a dynamic sample using two cameras and generating multiple sheets of light using a di_raction grating, resulting in multi-plane illumination. The second technique involves the use of parallel processing units to enable real-time image reconstruction of the acquired data. A multi-node GPU and CUDA architecture effciently reduce the computation time of the reconstruction algorithms. Faster implementation of iterative image reconstruction techniques can aid in low-light imaging and dynamic monitoring of rapidly moving samples in real time. Employing rapid acquisition and rapid image reconstruction aids in real-time visualization of cells and have immense potential in the _eld of microbiology and bio-mechanics. Finally, we conclude the thesis with a brief section on the contribution of the thesis and the future scope the work presented. Thank you for using www.freepdfconvert.com service! 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Les propriétés spectrales des composants fluorescents de la matière organique d’un sol naturel ont été étudiées dans les trois fractions physiques ; substances humiques, acide fulvique et acide humique, par la méthode des matrices d’excitation et d’émission de fluorescence couplée à l’algorithme Parallel Factor analysis (PARAFAC). Les modifications spectrales de ces composants ont été suivies (forme et pseudo-concentrations) en présence d’un contaminant de type hydrocarbure aromatique polycyclique (le benzo(a)pyrène (BaP), toxique et à caractère cancérigène) : (1) en faisant varier les volumes d’une solution pure de BaP dans chaque fraction de même concentration en matières organiques, (2) en faisant varier les concentrations en matière organique pour des concentrations fixes de BaP, qui ont été suivies dans le temps. Les résultats ont montré que le BaP influence d’une manière différente les fluorophores présents dans les trois fractions et ont permis de clarifier le type d’interactions avec une fraction ou l’autre. D’autre part, une discussion a été menée sur les paramètres de validation du nombre de composants pour le choix des modèles de PARAFAC. / The spectral properties of the fluorescent components of the organic matter of a natural soil were studied in the three physical fractions; humic substances, fulvic acid and humic acid, by the method of the excitation and fluorescence emission matrices coupled to the Parallel Factor Analysis (PARAFAC) algorithm. The spectral modifications of these components were studied (form and pseudo-concentrations) in the presence of a polycyclic aromatic hydrocarbon contaminant (benzo (a) pyrene (BaP), toxic and carcinogenic): (1) by varying the volumes of a pure solution of BaP in each fraction having the same concentration of organic matter, (2) by varying the concentrations of organic matter for fixed concentrations of BaP, which were followed over time. The results showed that the BaP influences the fluorophores present in the three fractions in a different way and clarified the type of interactions with one fraction or the other. On the other hand, a discussion was held on parameters for validating the number of components for the selection of PARAFAC models.