A differential game theory approach to DC-DC buck converter control

Tribunal: Prof. Rafael Canetti, Prof. Eleonora Catsigeras (Universidad de la República), Prof. Martin Ordonez (University of British Columbia, Canadá).This thesis deals with the problem of controlling a generic synchronous buck converter against unpredictable, and possibly discontinuous, but bounded load disturbances. The problem is canonically framed as a dynamical conflict between the automatic controller in charge of the output voltage regulation and an hypothetical disturber. In particular, the conflict is regarded as a pursuit-evasion game in distance. Applying classical methods of differential game theory, the game is completely solved identifing three qualitative different cases that can take place depending on how a positive derived parameter value compares to unity. The game’s solution provides optimal strategies for the controller and the disturber which can be used, respectively, for worst-case-aware control and benchmark testing (of any control method). Furthermore, from the topography of the game’s value function, qualitative and quantitative information about the physical limits of buck converter control is gained, allowing for early design stage optimization of the converter’s LC filter towards regulation performance, regardless of the control method that might finally be selected.Esta tesis aborda el problema de controlar un convertidor sincrónico tipo buck genérico frente a perturbaciones impredecibles, y posiblemente discontinuas, pero acotadas de la corriente de carga. El problema se plantea en forma canónica como un conflicto dinámico entre el controlador automático encargado de la regulación del voltaje de salida y un perturbador hipotético. En particular, el conflicto es visto como un juego de persecusión-evasión en distancia. Aplicando métodos clásicos de la teoría de juegos diferenciales, el juego es completamente resuelto identificando tres casos cualitativamente distintos que pueden ocurrir dependiendo de si el valor de un parámetro derivado positivo es menor, igual, o mayor que uno. La solución del juego provee estrategias óptimas para el controlador y para el perturbador que pueden ser utilizadas, respectivamente, para implementar control ante el peor caso y para realizar pruebas de referencia (aplicables a cualquier método de control). Además, de la topografía de la función valor del juego, se obtiene información cualitativa y cuantitativa acerca de los límites físicos inherentes al control de convertidores tipo buck, permitiendo la optimización del filtro LC con respecto al desempeño de la regulación en las primeras etapas de diseño, aun antes de haber finalmente elegido un método de control

THE USE OF PREBIOTICS TO IMPROVE FISH HEALTH

The aim of this project was to analyse critically the potential use of prebiotics in aquaculture. Initially, the intestinal microflora of rainbow trout, raised in the aquarium facilities at CEFAS, Weymouth, was investigated using both conventional bacteriological (culture, BiOLOG) and molecular (Restriction Fragment Length Polymorphism (RFLP), 16S rRNA gene sequencing) techniques. Dominant colony types were identified as Aeromonas sobria, Carnobacterium piscicola and Clostridium gasigenes. A series of in vitro growth curve studies was carried out using a selection of intestinal bacteria and known fish pathogens, to determine the ability of intestinal bacteria to utilise the potential prebiotic candidates inulin, lactulose and lactitol. Both inhibition and stimulation of the growth of certain bacteria was noted. Inulin and lactulose were top-dressed onto commercial trout pellets at levels of 1000mg/Kg and 100mg/Kg and fed to healthy rainbow trout to determine the effect in vivo. Using Terminal Restriction Fragment Length Polymorphism (tRFLP) analysis and RFLP analysis, inulin was shown to increase the growth of Aeromonas sobria and decrease the growth of Clostridium gasigenes in comparison to samples obtained from fish fed a control diet. Prebiotic supplemented feeds were both palatable and safe. To investigate the effect of feeding an inulin-supplemented diet on the susceptibility of Rainbow trout to Yersinia ruckeri a cohabitation challenge was performed. Relative percent survival at 55% positive control mortality (RPS55) was 47%. Chi²analysis showed that differences between the controls and fish fed a diet supplemented with both 100 and 10mg inulin /Kg pellet feed were significant suggesting that inulin can improve the survival of fish coming into contact with the pathogen Yersinia ruckeri.Centre for the Environment, Fisheries and Aquaculture Science (CEFAS

Development and Characterisation of PC12 Cell Lines Allowing Inducible Expression of Prion Proteins Carrying Pathogenic Mutations

Inherited prion diseases are linked to mutations in the prion protein (PrP)p gene that are presumed to favor conversion of PrP into a neurotoxic isoform (PrpSc) Several cellular models of inherited prion diseases have been Q developed in which mutant PrP costitutively expressed acquires PrPSc-like properties but is not cytotoxic. However, the use of constitutive models does not exclude the potential toxicity of mutant PrP, as it can be speculated that only J clones resistant to PrP toxicity are selected after clonal selection. To rule out n this possibility a tetracycline-inducible (Tet-on) model was developed in this thesis, in which PrP expression is switched on after clonal selection. cDNAs encoding mouse wild-type PrP, as well as mouse PrP homologues of the human D178N (D177N/M128 and D177NA/128) and nine-octapeptide (PG14) mutations under the control of the tetracycline-responsive element, were transfected in PC12 Tet-on cells. The Tet-on system was chosen based on the lack of pleiotropic or toxic effects and because it allows a tightly regulated expression of the protein of interest. To ensure unwanted background expression of PrP in the absence of inducer, cells were co-transfected with J pTet-tTS, encoding the tet-controlled transcriptional silencer. The D177N and PG14 mutants expressed in this system displayed biochemical properties reminiscent of PrP^^, including detergent insolubility and low protease resistance. Low levels of mutant PrPs were detected on the cell surface by confocal immunofluorescence analysis compared to wild-type PrP. These mutant displayed reticular intracellular distribution, suggesting impaired delivery to the cell surface and retention in the endoplasmic reticulum (ER). Evaluation of cellular viability revealed a decrement in cell survival after 96 h of mutant PrP expression, associated with an increased number of apoptotic cells. This effect was not fully consistent and was not exacerbated by Q neuronal differentiation with NGF or by treating cells with FI2O2, tunicamycin, or by removing serum. The results presented in this thesis also demonstrate that expression of PrP does not protect PC 12 Tet-on cells from such stresses. To explore the possibility that expression of mutant PrPs triggered toxic -1 response pathways in the ER, the mRNA level of ER stress markers was measured. The results shown in this thesis indicate that, although the altered intracellular distribution of mutant PrPs suggested retention of the protein in the endoplasmic reticulum, ER stress responses were not detected

Image Analysis for the Life Sciences - Computer-assisted Tumor Diagnostics and Digital Embryomics

Current research in the life sciences involves the analysis of such a huge amount of image data that automatization is required. This thesis presents several ways how pattern recognition techniques may contribute to improved tumor diagnostics and to the elucidation of vertebrate embryonic development. Chapter 1 studies an approach for exploiting spatial context for the improved estimation of metabolite concentrations from magnetic resonance spectroscopy imaging (MRSI) data with the aim of more robust tumor detection, and compares against a novel alternative. Chapter 2 describes a software library for training, testing and validating classification algorithms that estimate tumor probability based on MRSI. It allows flexible adaptation towards changed experimental conditions, classifier comparison and quality control without need for expertise in pattern recognition. Chapter 3 studies several models for learning tumor classifiers that allow for the common unreliability of human segmentations. For the first time, models are used for this task that additionally employ the objective image information. Chapter 4 encompasses two contributions to an image analysis pipeline for automatically reconstructing zebrafish embryonic development based on time-resolved microscopy: Two approaches for nucleus segmentation are experimentally compared, and a procedure for tracking nuclei over time is presented and evaluated