Στην παρούσα διπλωματική εργασία παρουσιάζονται και συζητούνται τα χαρακτηριστικά τυρβωδών φλογών μερικής προανάμιξης. Οι φλόγες που εξετάζονται προέρχονται από ένα επίπεδο καυστήρα-σταθεροποιητή ορθογωνικής διατομής, δύο επάλληλων κοιλοτήτων, που σχηματίζονται κατά μήκος τριών παραλλήλων επιπέδων. Οι φλόγες σταθεροποιούνται στην ανακυκλοφορία των καπναερίων που δημιουργείτε κατάντη του φλογοσταθεροποιητή. Στόχος της έρευνας ήταν να διερευνηθεί η συγκεκριμένη διάταξη ως προς το θερμοκρασιακό της πεδίο και την σταθεροποίηση της συγκεκριμένης φλόγας που προκαλεί η καύση της βαθμιαίας διαστρωμάτωσης προπανίου- αέρα. Για να επιτευχθεί ο στόχος αυτός πραγματοποιήθηκαν διαφορετικά είδη μετρήσεων σε διαφορετικές παροχές καυσίμου και καταγράφηκαν τα αποτελέσματα, τα οποία στη συνέχεια συγκρίθηκαν και με διερευνήσεις που πήραμε από ειδικευμένο υπολογιστικό πρόγραμμα υπό τις ίδιες οριακές συνθήκες. Τέλος, μετά τη σύγκριση των αποτελεσμάτων μεταξύ πειράματος και προσομοίωσης έγινε προσπάθεια να εξηγηθούν οι διαφορές που παρατηρήθηκαν και τα χαρακτηριστικά δομικά στοιχεία που συντέλεσαν στην περιγραφή της λειτουργικής συμπεριφοράς των χρησιμοποιηθέντων στρωματοποιημένων φλογών ώστε να δοθούν ιδέες για την περαιτέρω εξέλιξη της έρευνας. / In this study the characteristics of partially premixed turbulent flames are presented and discussed. The investigated flames come from a planar stabilization burner of two superimposed cavities formed along three parallel planes. The flames are stabilized within the downstream vortex region of the afterbody. The aim of this study was to investigate the specific experimental arrangement as for the temperature field and the stabilization of these stratified propane- air flames. To achieve this goal different types of measurements have been made at different fuel supplies and the results have been recorded and compared with computational investigations which have been carried out using a specialized commercial simulation package under the same boundary conditions. Finally, after comparing the experimental and computational results effort has been made to explain the differences observed and the characteristic structural elements that contributed to the description of the functional behavior of stratified flames in order to provide ideas for further investigation.

Στη συγκεκριμένη Διατριβή μελετήσαμε την ανάλυση ευστάθειας υβριδικών δυναμικών συστημάτων τα οποία έχουν μοντελοποιηθεί με Διαφορικά Δίκτυα Petri. Τα αποτελέσματα που προτείναμε για την ανάλυση ευστάθειας χρησιμοποιούν Γραμμικές Ανισότητες Πινάκων γεγονός που τις καθιστά υπολογιστικά επιλύσιμες. Προτείναμε επίσης μια μεθοδολογία σχεδίασης ευσταθών υβριδικών συστημάτων. Χρησιμοποιήσαμε το μοντέλο Διαφορικά Δίκτυα Petri για την μοντελοποίηση δικτυακών υβριδικών συστημάτων. Προτείναμε επίσης συνθήκες ευστάθειας για διακοπτικά χρονικά καθυστερούμενα συστήματα. / In this thesis we study stability for hybrid dynamical systems modelled by Differential Petri Nets.Our stability results are formulated as Linear Matrix Inequalities in order to be computational solvable. A methodology for stabilization of hybrid dynamical systems is also introduced. The notion of Networked Hybrid System is also introduced and the model of Differential Petri Net is proposed for modelling. Stability results for switched time-dealy systems are also proposed.

The first part of the thesis investigates the enhancement of fly ash-based geopolymer with alkali pretreated sweet sorghum fiber. The unconfined compression, splitting tensile and flexural tests were conducted to investigate the mechanical properties of geopolymer composite. The results indicate that the inclusion of sweet sorghum fiber slightly decreases the unconfined compressive strength (UCS), however, the splitting tensile and flexural strengths as well as the post-peak toughness increase with the fiber content up to 2% and then decrease thereafter. A durability test program containing 10 wet/dry cycles was performed to evaluate the long-term performance of the geopolymer composite related to wet/dry cycling. The results indicate that both the UCS and the splitting tensile strength of the geopolymer composite progressively decrease with the number of wet/dry cycles. The second part of the thesis investigates the utilization of biopolymers to stabilize MT for dust control. First, a fall cone method was adopted to evaluate the Atterberg limits and undrained shear strength of MT stabilized with biopolymers. The results indicate that the inclusion of biopolymers increases both the liquid limit and the undriained shear strength of MT. Two new equations are proposed for predicting the undrained shear strength of MT based on liquid limit and water content, and liquidity index. Second, an experimental program including moisture retention, wind tunnel and surface strength tests was performed to evaluate the effectiveness of biopolymer stabilization for dust control. The results indicate that biopolymers are effective in enhancing the moisture retention capacity, improving the dust resistance, and increasing the surface strength of MT. Third, a durability test program containing 10 wet/dry cycles was applied to MT samples treated with biopolymer solutions of different concentrations. The results show that the dust resistance of MT samples progressively decreases with the number of wet/dry cycles. Finally, experimental and numerical studies on the unconfined compressive strength (UCS) of MT stabilized with biopolymer were carried out. It is found that inclusion of biopolymer into MT favors the increase of adhesion between MT particles and thus the increase of the UCS of MT.

This dissertation aims to investigate systems in which several optical and mechanical degrees of freedom are coupled through optomechanical interactions. Multimode optomechanics creates the prospect of integrated functional devices and it allows us to explore new types of optomechanical interactions which account for collective dynamics and optically mediated mechanical interactions. Owing to the development of fabrication techniques for micro- and nano-sized mechanical elements, macroscopic mechanical oscillators can be cooled to the deep quantum regime via optomechanical interaction. Based on the possibility to control the motion of mechanical oscillators at the quantum level, we design several schemes involving mechanical systems of macroscopic length and mass scales and we explore the nonlinear dynamics of mechanical oscillators. The first scheme includes a quantum cantilever coupled to a classical tuning fork via magnetic dipole-dipole interaction and also coupled to a single optical field mode via optomechanical interaction. We investigate the generation of nonclassical squeezed states in the quantum cantilever and their detection by transferring them to the optical field. The second scheme involves a quantum membrane coupled to two optical modes via optomechanical interaction. We explore dynamic stabilization of an unstable position of a quantum mechanical oscillator via modulation of the optical fields. We then develop a general formalism to fully describe cavity mediated mechanical interactions. We explore a rather general configuration in which multiple mechanical oscillators interact with a single cavity field mode. We specifically consider the situation in which the cavity dissipation is the dominant source of damping so that the cavity field follows the dynamics of the mechanical modes. In particular, we study two limiting regimes with specific applications: the weak-coupling regime and single-photon strong-coupling regime. In the weak-coupling regime, we build a protocol for quantum state transfer between mechanical modes. In the single-photon coupling regime, we investigate the nonlinear nature of the mechanical system which generates bistability and bifurcation in the classical analysis and we also explore how these features manifest themselves in interference, entanglement, and correlation in the quantum theory.

Many water treatment technologies for arsenic removal that are used today produce arsenic-bearing solid residuals (ABSR), which are disposed in mixed solid waste landfills. It is now well established that many of these residuals will release arsenic into the environment to a much greater extent than predicted by standard regulatory leaching tests and, consequently, require stabilization to ensure benign behaviour after disposal. Conventional waste stabilization technologies, such as cement encapsulation and vitrification, are not suitable for ABSR applications due to their lack of effectiveness or high cost, thus creating a need for a more effective and low-cost treatment technology for ABSR. Arsenic Crystallization Technology (ACT) is a proposed arsenic stabilization method that involves in converting the ABSR into arsenic-bearing minerals that resemble natural materials and have high arsenic capacity, long term stability, and low solubility compared to untreated ABSR. Three arsenic minerals, scorodite, arsenate apatite and ferrous arsenate, have been investigated in this research for their potential application as ACT for ABSR stabilization. Among the three minerals, ferrous arsenate is demonstrated to be the most suitable arsenate mineral for safe arsenic disposal due to its low arsenic solubility and ease of synthesis. An innovative treatment procedure has been developed in this research for stabilization of ABSR to a stable phase of ferrous arsenate using zero-valent iron (ZVI) as the reducing agent. The procedure works at ambient temperature and pressure, and neutral pH. In addition, a modified four-step sequential extraction method has been developed as a means to determine the proportions of various arsenic phases in the stabilized as well as untreated ABSR matrices. This extraction method, as well as traditional leach and solubility tests, show that arsenic stability in the solid phase is dramatically increased after formation of crystalline ferrous arsenate.

TAR DNA binding protein of 43 kDa (TDP-43) has been implicated in the pathogenesis of amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Pathologically misfolded and aggregated forms of TDP-43 are found in cytoplasmic inclusion bodies of affected neurons in these diseases. The mechanism by which TDP-43 misfolding causes disease is not well understood. We postulate that the aggregation process plays a major role in pathogenesis, and we hypothesize that oligonucleotide ligands of TDP-43 can stabilize the native functional state of the protein and ameliorate aggregation of this aggregation-prone protein. Using recombinant TDP-43 we were able to examine the extent to which various oligonucleotide molecules affects its aggregation in vitro. We have found that certain natural sequence and de novo designed oligonucleotides bind TDP-43 and prevent its natural tendency to aggregate. The clinical and therapeutic implications of these findings are discussed.

TAR DNA binding protein of 43 kDa (TDP-43) has been implicated in the pathogenesis of amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Pathologically misfolded and aggregated forms of TDP-43 are found in cytoplasmic inclusion bodies of affected neurons in these diseases. The mechanism by which TDP-43 misfolding causes disease is not well understood. We postulate that the aggregation process plays a major role in pathogenesis, and we hypothesize that oligonucleotide ligands of TDP-43 can stabilize the native functional state of the protein and ameliorate aggregation of this aggregation-prone protein. Using recombinant TDP-43 we were able to examine the extent to which various oligonucleotide molecules affects its aggregation in vitro. We have found that certain natural sequence and de novo designed oligonucleotides bind TDP-43 and prevent its natural tendency to aggregate. The clinical and therapeutic implications of these findings are discussed.

To assess the long-term performance of soil-cement materials used in source-control remediation methods (i.e. cement-based solidification/stabilization), procedures to measure or estimate contaminant migration parameters are essential. Previous research indicates that diffusion may be an important mechanism in contaminant transport through soil-cement materials. However, there is a paucity of information regarding the diffusion of contaminants through these materials. The development of a single-reservoir diffusion apparatus and methodology to assess the effective diffusion coefficient (De) and effective porosity (ne) of dissolved, conservative, inorganic chemicals for saturated, cured, monolithic soil-cement specimens is discussed. This is the only study known to investigate these parameters for these materials. The results of tritiated water diffusion tests on 14 different soil-cement mixtures are presented and the influence of curing time and mixture properties such as water-to-cement ratio, cement content, and grain-size distribution are examined. Results suggest that, to determine reasonable assessments of the longer-term parameters, soil-cement samples should be cured for a minimum of 70 days before commencing diffusion testing. Values of ne (0.21 to 0.41) and De (2.50×10-10 m2/s to 7.0×10-10 m2/s) determined are similar to those previously determined for a number other low-hydraulic conductivity materials (i.e. saturated inactive clays). The water content of the initial mixture is shown to have a substantial effect on the diffusive properties as the results indicate that both the total porosity (n) and the effective porosity, ne, generally increase with increasing initial water content. For the range of soils used in this investigation, grain-size distribution did not have a substantial effect on the values of ne or De determined from diffusion testing. The adaptation of a double-reservoir diffusion testing apparatus and methodology to evaluate the distribution coefficient (Kd) and De of organic contaminants is also presented. This apparatus is used to evaluate Kd and De of benzene, ethylbenzene, naphthalene, and trichloroethylene for three soil-cement mixtures. Values of Kd (0 to 2.5 cm3/g depending on the compound and soil-cement mixture tested) determined from diffusion testing, batch testing, and theoretical estimates from the literature were in general agreement. Values of De for the organic compounds ranged from 1.50×10-10 to 3.0×10-10 m2/s.

Simultaneous stabilization is an important problem in the design of robust controllers. It is the problem of designing a single feedback controller which will simultaneously stabilize every member of a finite collection of liner time-invariant systems. This provides simplicity and reliability which is desirable in aerospace applications. It can be used as a back-up control system in sophisticated airplanes, or an inexpensive primary one for small aircraft. In this work the robustness of the simultaneous stabilization problem, known as the Robust Simultaneous Stabilization (RSS) problem, is addressed. First, an optimization methodology for finding a solution to the Simultaneous Stabilization (SS) problem is proposed. Next, in order to provide simultaneous stability while maximizing the stability robustness bounds, a multiple-robustness optimization design methodology for the RSS problem is presented. The two proposed design methodologies are then compared in terms of robustness of the designed controller.

In this thesis we investigate the problem of designing a control system for a modern bicycle so that the bicycle is stable and follows a path. We propose a multi-loop control architecture, where each loop is systematically designed using linear control techniques. The proposed strategy guarantees that the bicycle asymptotically converges to paths of constant curvature. A key advantage of our approach is that by using linear techniques analysis and controller design are relatively simple. We base our control design on the nonlinear (corrected) Whipple model, which has been previously verified for correctness and experimentally validated. The equations of motion for the nonlinear model are very complicated, and would take many pages to explicitly state. They also have no known closed form solution. To enable analysis of the model we linearize it about a trajectory such that the bicycle is upright and travelling straight ahead. This linearization allows us to arrive at a parameterized linear time-invariant state-space representation of the bicycle dynamics, suitable for analysis and control design. The inner-loop control consists of a forward-speed controller as well as a lean and steer controller. To keep the bicycle at a constant forward speed, we develop a high-bandwidth proportional controller that uses a torque along the axis of the rear wheel of the bicycle to keep the angular velocity of the rear wheel at a constant setpoint. To stabilize the bicycle at this forward speed, lean torque and steer torque are treated as the control signals. We design a state-feedback controller and augment integrators to the output feedback of the lean angle and steer angle to provide perfect steady-state tracking. To arrive at the gains for state feedback, linear-quadratic regulator methods are used. When following a constant-curvature path, a vehicle has a constant yaw rate. Using this knowledge, we begin designing the outer-loop path-following control by finding a map that converts a yaw rate into appropriate lean angle and steer angle references for the inner loop. After the map is completed, system identification is performed by applying a yaw-rate reference to the map and analyzing the response of the bicycle. Using the linear approximation obtained, a classical feedback controller for yaw-rate tracking is designed. In addition to yaw-rate control, to track a path the yaw angle of the bicycle must match that of the path and the bicycle must physically be on the path. To analyze these conditions a linear approximation for the distance between the bicycle to the path is found, enabling construction of a linear approximation of the entire system. We then find that by passing the signal for the difference in yaw rate and the distance through separate controllers, summing their output, and subtracting from the reference yaw rate of the path, the bicycle converges to the path. After developing the general design procedure, the final part of the thesis shows a step by step design example and demonstrates the results of applying the proposed control architecture to the nonlinear bicycle model. We highlight some problems that can arise when the bicycle is started far from the path. To overcome these problems we develop the concept of a virtual path, which is a path that when followed returns the bicycle to the actual path. We also recognize that, in practice, typical paths do not have constant curvature, so we construct more practical paths by joining straight line segments and circular arc segments, representing a practical path similar to a path that would be encountered when biking through a series of rural roads. Finally, we finish the design example by demonstrating the performance of the control architecture on such a path. From these simulations we show that using the suggested controller design that the bicycle will converge to a constant curvature path. Additionally with using the controllers we develop that in the absence of disturbance the bicycle will stay within the intended traffic lane when travelling on a typical rural road.