This thesis describes an investigation on the blowout phenomenon in gas turbine combustors. The combustor primarily used for this study was a swirl- and dump-stabilized, atmospheric pressure device, which did not exhibit dynamic combustion instabilities. The first part of the thesis work concentrated on finding a sensing methodology to be able to predict the onset of approach of combustor blowout using optical methods. Temporary extinction-reignition events that occurred prior to blowout were found to be precursor events to blowout. A threshold based method was developed to identify these events in the time-resolved sensor output. The number and the average length of each event were found to increase as the LBO limit (fuel-air ratio) is approached. This behavior is used to predict the proximity to lean blowout. In the second part of this study, the blowout sensor was incorporated into a control system that monitored the approach of blowout and then actuated an alternate mechanism to stabilize the combustor near blowout. Enhanced stabilization was achieved by redirecting a part of the main fuel to a central preinjection pilot injection. The sensing methodology, without modification, was effective for the combustor with pilot stabilization. An event based control algorithm for controlling the combustor from blowing out was also developed in this study. The control system was proven to stabilize the combustor even when the combustor loading was rapidly changed. The final part of this study focused on understanding the physical mechanisms behind the precursor events. High speed movies of flame chemiluminescence and laser sheet scattering from oil droplets seeded into the reactants were analyzed to explain the physical processes that cause the extinction and the reignition of the combustor during a precursor event. A physical model for coupling of the fluid dynamics of vortex breakdown and combustion during precursor and blowout events is proposed. This model of blowout phenomenon, along with the sensing and control strategies developed in this study could enable the gas turbine combustor designers to design combustors with wider operability regimes. This could have significant payoffs in terms of reduction in NOx emissions from the combustor.

Alumina (Al2O3) is one of the most widely used engineering ceramic. It can be used in a wide range of applications like electrical/thermal insulation, wear resistance, structural refractories, cutting tools, abrasives, catalyst carriers and coatings. A traditional ceramic process has several steps (i.e. powder synthesis and processing, shape forming, drying, organic burnout and densification). Accessing powders with sizes in the range of a couple of micrometers down to several tens of nanometers is considered critical in attaining higher densities in the final ceramic bodies. Besides since significant shrinkage can be observed in the thermal treatment steps due to the excessive use of additives (e.g. binders, solvents and plasticizers) in the powder processing and forming steps, it is important to take remedies that would increase the solids loading in the initial mixtures. In addition, most of the conventional additives and solvents used in these steps are toxic and it is necessary to replace them with the environmentally benign aqueous-based alternatives. Alumoxanes could be used as a benign aqueous-based alternative to be used as a ceramic precursor or an agent. They are a group of compounds that have nano sized boehmite cores encapsulated with the organic groups used in its production steps. In this research work, alumoxane nano particles which can be used as precursors for nano-alumina were developed starting from aluminum trihydroxide. As a preconditioning step, grinding was applied to decrease the aluminum hydroxide particle size (&amp / #8804 / 60 &amp / #956 / m) to submicron sizes. This process was followed by the glycothermal ageing step, and organic derivative of boehmite was obtained. The amorphous particles thus obtained were further treated mechanochemically in a high energy ball mill with organic chemicals like acetic acid, methoxy acetic acid, stearic acid and L-lysine. After this step the observed sizes of the particles were as low as 10-100 nm. The effects of organic molecules used in each step were studied by FTIR spectroscopy and their effectiveness in exfoliation of hydroxide layers were identified with dynamic light scattering from processing solutions dispersed in aqueous medium. Moreover, in each step, structural analyses were carried out by XRD.

Die Pyrolyse ausgewählter Polysiloxane und Poly(chlor)silane erzeugt meso- und mikroporöses SiC, welches als Hochtemperatur-beständiges Material für Filter, Katalysatorträger und Sensoren ein hohes Anwendungspotential besitzt. Der Pyrolyseprozess bis 1500 °C wird thermogravimetrisch und massenspektrometrisch verfolgt und die resultierenden "Bulk"-Pyrolysate mittels DRIFT-Messungen, Elementaranalyse, XRD, N2-Adsorption und FESEM charakterisiert. Zusammensetzung, Kristallinität und Poreneigenschaften des precursorabgeleiteten SiC lassen sich über die Precursorart sowie über die Pyrolysetemperatur und -dauer steuern. Die Poren entstehen je nach Precursor zwischen 1200 und 1500 °C. Im Falle von mesoporösen Pyrolysaten wird die Porenbildung in erster Linie durch die Abgabe gasförmiger Reaktionsprodukte hervorgerufen. Die Porengrößen dieser Produkte liegen zwischen 6 und 12 nm und die spezifische Oberfläche beträgt bis zu 270 m2/g. Bei den mikroporösen Pyrolysaten, gekennzeichnet durch Poren von 1,5 nm Größe und spezifischen Oberflächen bis 530 m2/g, werden die Poreneigenschaften vor allem durch den im Überschuss vorhandenen elementaren Kohlenstoff geprägt.

Source: Dissertation Abstracts International, Volume: 70-03, Section: B, page: 1574. Adviser: Elaine Symanski. Includes bibliographical references.

Dissertation (Ph.D.)--University of South Florida, 2008. / Includes vita. Includes bibliographical references.

In recent years, bio-based polymers derived from renewable resources have become increasingly important as sustainable and eco-efficient products which can replace the products based on petrochemical-derived stocks. The objective of our work was to develop novel bio-based reactive systems suitable for high performance composite materials especially epoxy systems. The most commonly used starting monomer to formulate epoxy networks is the diglycidyl ether of bisphenol A, DGEBA, derived from bisphenol A and epichlorohydrin. Bio-based epichlorohydrin is commercially available. So the challenge to obtain a fully bio-based epoxy prepolymer is to replace bisphenol A by a bio-based precursor. Another interest for replacing bisphenol A by a bio-based precursor is that bisphenol A has been known to have estrogenic properties. In this study, we studied different bio-based epoxy systems and compared them to a classical DGEBA based system using, in a first step, isophorone diamine (IPD) as conventional curing agent. Bio-based epoxy prepolymers were derived from natural sugars, sorbitol and isosorbide respectively. Sorbitol polyglycidyl ether is available commercially, while isosorbide diglycidyl ether was synthesized either via conventional epoxidation (i.e. using epichlorohydrin) or via the diallyl isosorbide intermediate. Another bio-based epoxy prepolymer was derived from cardanol and is also a commercial product. Chemical structure of the bio-based epoxy prepolymers were analyzed by different analytical methods, gelation and crosslinking reactions were studied using rheological measurements and differential scanning calorimetry, respectively. Properties of the cured networks were evaluated using dynamic mechanical analysis and thermo gravimetric analysis. Influence of the bio-based epoxy prepolymer structure on the system properties as well as the influence of the crosslinking agent structure (either derived from renewable resources or bio-based ones) was discussed. Water absorption of the bio-based networks was also studied.

Per- and polyfluoroalkyl substances are a large group of global environmental contaminants. They can be divided into two sub-groups, 1) perfluoroalkyl acids (PFAAs) and 2) so called precursors, i.e. compounds that can potentially be transformed to form PFAAs. PFAAs are today ubiquitous in wildlife and humans. Food and drinking water are assumed to be the dominant human exposure pathways for PFAAs. The main aim of this doctoral thesis was to develop highly sensitive and fully validated analytical methods for the determination of a range of PFAAs and selected precursors in dietary samples. The methods were based on liquid chromatography coupled to mass spectrometry. Samples were extracted by solvent extraction followed by a cleanup step employing solid phase extraction. The cleanup step could at the same time be used as a fractionation of ionic PFAAs and neutral precursors. Paper I and II describe the development of methods for simultaneous analysis of three groups of PFAAs including perfluoroalkyl phosphonic acids (PFPAs) in drinking water and food. Methyl piperidine was used as ion pairing agent, leading to highly sensitive analysis of PFPAs. A first screening of tap water samples and different food items revealed that human dietary exposure to PFPAs in Europe is currently not of concern. A novel method for simultaneous analysis of perfluoroalkyl carboxylic acids (PFCAs) and polyfluoroalkyl phosphate esters (PAPs) in food and packaging materials is described in paper III. Targeted food samples and their packaging were analyzed. The results showed that PAPs may contribute to human exposure to PFCAs. In paper IV temporal trends (1991-2011) of perfluorooctane sulfonic acid (PFOS) and its precursors in herring were investigated. Rapidly decreasing trends were found for precursors, whereas PFOS did not show a significant change over time. Precursors in fish may have played an important role for human exposure to PFOS in the 1990s but are probably negligible today. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p> / PERFOOD project (KBBE-227525)

Zusammenfassung: Patienten mit Down Syndrom (DS, Trisomie 21) entwickeln im vierten Lebensjahrzehnt eine Neuropathologie, wie sie beim Morbus Alzheimer (AD) beobachtet wird. Im Gehirn dieser Patienten kommt es zur Ausbildung von senilen Plaques, neurofibrillären Veränderungen und zu einer Schädigung des cholinergen Systems. Als erstes Zeichen der beginnenden Veränderungen wird die erhöhte Konzentration und Akkumulation von sogenannten beta-A4-Peptiden gewertet. Diese Peptide, die auch den Hauptbestandteil der senilen Plaques darstellen, entstehen durch die Prozessierung eines größeren Proteins des Amyloidvorläuferproteins (amyloid precursor protein, APP). Beim Menschen wurde das APP-Gen auf einem distalen Segment des langen Arms des Chromosoms 21 lokalisiert. Das Homolog dieses evolutionär stark konservierten, syntenen Segmentes liegt bei der Maus auf dem Chromosom 16. Natürlich in wilden Mäusepopulationen auftretende Robertsonsche Translokationen ermöglichen es, Mäuse mit Trisomie 16 zu züchten. Mit Hilfe der Maus-Trisomie 16 sollte ein Modell etabliert werden, mit dem es unter in vivo Bedingungen möglich ist, die Auswirkungen der erhöhten APP-Gendosis auf die Ausbildung der bei DS und AD beobachteten neurodegenerativen Veränderungen zu untersuchen. Da trisomische Feten am Ende der Trächtigkeit absterben, wurden aus dem basalen Vorderhirn trisomischer und diploider Feten Transplantate gewonnen und in den Lateralventrikel adulter euploider Mäuse implantiert. Die Entwicklung der Transplantate wurde nach 1, 3, 6, 9 und 12 Monaten immunhistochemisch charakterisiert. Ein Antikörper gegen das Thymozytenantigen (Thy)-1.2 wurde, beruhend auf der unterschiedlichen Thy-1-Allel-Expression von Transplantat und Empfänger, zur Transplantatidentifikation genutzt. Mit Antikörpern gegen das neuronale Markerprotein PGP-9.5, gegen Cholinacetyltransferase, Parvalbumin und Glutamatdecarboxylase wurden Neuronen charakterisiert. Die immunologische Reaktion wurde mit Antikörpern gegen saures fibrilläres Gliaprotein, gegen das Makrophagenantigen F4/80, gegen CD3, gegen CD45/ B220 und mit Lycopersicon esculentum-Lektin untersucht. Für den APP- bzw. beta-A4-Peptidnachweis wurden ein Antikörper gegen den C-Terminus des APP und der Antikörper 4G8 eingesetzt. Zusätzlich wurde mit Hilfe von molekularbiologischen Techniken (Northern-Blot, Polymerase-Kettenreaktion) die APP-Expression in Trisomie 16-Feten untersucht. Mit immunhistochemischen und histochemischen Methoden wurde versucht, den Entwicklungstand des basalen Vorderhirns zum Zeitpunkt der Transplantatpräparation am Gestationstag 15 zu untersuchen. / Summary: Patients suffering from Down's syndrome (DS, trisomy 21) develop neuropathological abnormalities similar to Alzheimer's disease (AD) in the fourth decade of life. Amongst others, neuritic plaques, neurofibrillary abnormalities and alterations in cholinergic basal forebrain systems were observed. These sequentially occuring disturbancies are initiated by a rise in the concentration and accumulation of the beta-amyloid-peptides. The beta-amyloid-peptides are derived by proteolytic processing from a larger amyloid precursor protein (APP) and compose the majority of the material deposited in amyloid plaques. In humans, the APP gene maps to the distal segment of the long arm of chromosome 21, but in mice the homolog gene locus is on chromosome 16. The naturally occuring Robertsonian translocations in feral mice (Mus musculus sp.) allow to breed trisomy 16 mice. The aim of this study was to establish an in vivo model to investigate the consequences of increased APP gene dosage on the generation of neuropathological abnormalities typical for DS and AD using trisomy 16 mice. Since trisomy 16 mice die at the end of prenatal development, basal forebrain tissue of diploid and trisomic fetuses was prepared and transplanted into lateral ventricles of adult euploid mice. Grafts were identified immunocytochemically using an antibody against thymocyte antigen-1.2, selectively labeling graftet tissue. Antibodies against the neuronal markerprotein PGP-9.5, choline acetyltransferase, parvalbumin and glutamate decarboxylase were used to characterize grafted neurons over a period of twelve months after implantation. The immunological tissue response in the brains of acceptor mice was monitored using antibodies against glial fibrillary acidic protein (GFAP), the macrophage antigen F4/80, CD3,CD45/B220 and using the Lycopersicon esculentum lectin. To detect APP and beta-amyloid-peptides,antibodies against a C-terminal APP fragment and the antibody 4G8 were used. Additionally, the APP mRNA expression in trisomy 16 mice was followed employing Northern-blot analysis and RT-PCR. The developmental state of basal forebrain tissue to be transplanted was characterized at the time of transplantation (gestation day 15) by means of histochemistry and immunohistochemistry.

Doctor of Philosophy(PhD) / This body of research uses numerical and experimental investigative techniques to further the understanding of autoignition. Hydrogen/nitrogen and methane/air fuel configurations of turbulent lifted flames in a vitiated coflow burner are used as model flames for this investigation. Characterisation was undertaken to understand the impact of controlling parameters and the overall behaviour of the flames, and to provide a body of data for modelling comparisons. Modelling of the flames was conducted using the PDF-RANS technique with detailed chemistry incorporated using In-situ Adaptive Tabulation (ISAT) within the commercial CFD package, FLUENT 6.2. From these investigations, two numerical indicators for autoignition were developed: convection-reaction balance in the species transport budget at the mean flame base; and the build-up of ignition precursors prior to key ignition species. These indicators were tested in well defined autoignition and premixed flame cases, and subsequently used with the calculated turbulent lifted flames to identify if these are stabilised through autoignition. Based on learnings from the modelling, a quantitative, high-resolution simultaneous imaging experiment was designed to investigate the correlations of an ignition precursor (formaldehyde: CH2O) with a key flame radical (OH) and temperature. Rayleigh scattering was used to measure temperature, while Laser Induced Fluorescence (LIF) was used to measure OH and CH2O concentrations. The high resolution in the Rayleigh imaging permitted the extraction of temperature gradient data, and the product of the OH and CH2O images was shown to be a valid and useful proxy for peak heat release rate in autoigniting and transient flames. The experimental data confirmed the presence of formaldehyde as a precursor for autoignition in methane flames and led to the identification of other indicators. Sequenced images of CH2O, OH and temperature show clearly that formaldehyde exists before OH and peaks when autoignition occurs, as confirmed by images of heat release. The CH2O peaks decrease later while those of OH remain almost unchanged in the reaction zone.

Thesis (Ph.D.)--University of Alabama at Birmingham, 2008. / Title from first page of PDF file (viewed on June 29, 2009). Includes bibliographical references.