AN ABSTRACT OF THE DISSERTATION OF PAYAM SHARIFI, for the Doctor of Philosophy degree in ENGINEERING SCIENCE, presented on April 2011, at Southern Illinois University Carbondale. TITLE: FUNDAMENTAL STUDIES ON THE EFFECT OF ELECTRIC FIELD ON INTERFACE INSTABILITY, FILM BOILING, AND FILM CONDENSATION MAJOR PROFESSOR: Dr. A. Esmaeeli This research focuses on investigation of uniform electric field on three inter-related interfacial phenomena including interface under electric field, film boiling under applied electric field, and film condensation under applied electric field. The idea of applying electric field to enhancement boiling and condensation heat transfer has been considered one of the active enhancement methods. However, understanding the details of interaction of electric field and phase change demands a strong tool to go beyond the limitations of experimental and theoretical approaches. We perform Direct Numerical Simulations (DNS) using front-tracking/finite-difference techniques to fully resolve the electric, flow, and heat transfer fields in continuum scales. In terms of electric field-induced interface instability problem, we studied the dynamics of interface under AC/DC uniform electric fields for a wide range of fluid physical properties and investigated the individual effect of their corresponding nondimensional numbers. We observed that application of DC electric field destabilizes the interface in such a way that it goes over several cycles of oscillations and then settles to its steady-state form and remains quiescent. However, for AC electric field, the interface oscillations follows the frequency of applied electric potential source. For the film boiling under applied electric field, we studied the effect of individual governing nondimensional numbers on the behavior of film boiling under DC/AC electric fields. Electric field makes the interface more unstable by elongating the bubbles, decreasing the most dangerous wavelength, and expediting the formation of bubbles. The impact of these effects on heat transfer can be observed from the evolution of Nu number in the course of film boiling. We realized that for the same conditions AC field alters the transient spatially averaged Nu number in a way that it follows the oscillations of applied electric potential source. However, the heat transfer enhancement does not get affected by applying either AC or DC electric fields. We extended our research to multimode film boiling to observe the interaction of bubbles growing next to each other. Also, we carried out a study on the effect of electric field on downward-facing film condensation over a horizontal flat plate. This problem is similar to film boiling over a horizontal flat plate which we already studied although the phase change occurs in opposite direction. Like the effect of electric field on film boiling, electric field made the interface of condensate more unstable by decreasing its most dangerous wave length. However, in this case, the enhancement becomes more effective due to cooperation of gravitational and electrical forces. Our studies show that phase change heat transfer coefficient can be enhanced in the presence of electric field by more that 70%. Condensation of vapors over the bank of horizontal tubes has always been the host of many engineering applications in power plants, chemical and petrochemical plants, etc. To take the first step toward the study of enhancement effect of electric field on complex geometries, we also carried out a study on the condensation over tube banks in the absence of electric field. This study mainly concentrates on the effect of tube distance on heat transfer coefficient in a vertically in-lined tube bank. Our study reveals that heat transfer coefficient can be highly dependent on tube diameter and spacing such that choosing an appropriate spacing can lead to a more than 50% enhancement.

Tetraploid cells, which typically arise from errors in mitosis, are genomically unstable and promote tumorigenesis. Recent evidence suggests that ~40% of tumors undergo a tetraploid intermediate during their evolution, with ~20% of all solid tumors maintaining a tetraploid karyotype. Consequently, tumor suppression mechanisms have evolved to limit the proliferation of tetraploid cells. However, it remains unclear how tetraploid cells are able to overcome these tumor suppression mechanisms to initiate tumorigenesis. To address this unresolved question, we developed and validated a genome-wide screening assay to comprehensively identify miRNAs whose overexpression promotes tetraploid cell proliferation. We then profiled those miRNAs to mechanistically define how each miRNA functions to overcome tetraploid induced arrest. Our results demonstrate that miRNAs can promote proliferation via multiple mechanisms, including inhibition of the p53 tumor suppressor pathway, hyperactivation of growth factor signaling, and inactivation of the Hippo tumor suppressor pathway. Additionally, we investigated mechanisms that facilitate tumorigenesis from proliferating tetraploid cells. It is well established that tetraploid cell proliferation promotes both numerical and structural chromosome abnormalities, although the precise mechanisms underlying these phenomena remain incompletely understood. Chromosome missegregation can lead to the formation of micronuclei separate from the primary nucleus, a result of either lagging or polar chromosomes. Micronuclei have been shown to rupture during interphase, leading to massive amounts of DNA damage and chromothripsis, resulting in extensive DNA breaks and rearrangements. We followed micronuclei formed from both lagging and polar chromosomes to determine whether all micronuclei are equally prone to nuclear envelope rupture. Our results show that polar micronuclei have nuclear envelopes that are significantly more stable than the nuclear envelopes of micronuclei formed from lagging chromosomes. Furthermore, micronuclei have been shown to be deficient at nuclear import of proteins. Kinetochore assembly, vital for proper chromosome segregation, is dependent upon the nuclear import of many proteins. We sought to establish whether micronuclei have defects in kinetochore assembly since without functional kinetochores, chromosomes cannot bind to the mitotic spindle. We found that chromosomes in micronuclei fail to assemble kinetochores efficiently, and thus promote additional chromosome missegregation. Overall, this dissertation identifies multiple mechanisms that facilitate tumorigenesis from tetraploid intermediates.

abstract: Recent literature indicates potential benefits in microchannel cooling if an inlet orifice is used to suppress pressure oscillations that develop under two-phase conditions. This study investigates the costs and benefits of using an adjustable microchannel inlet orifice. The focus is on orifice effect during steady-state boiling and critical heat flux (CHF) in the channels using R134a in a pumped refrigerant loop (PRL). To change orifice size, a dam controlled with a micrometer was placed in front of 31 parallel microchannels. Each channel had a hydraulic diameter of 0.235 mm and a length of 1.33 cm. For steady state two-phase conditions, mass fluxes of 300 kg m-2 s-1 and 600 kg m-2 s-1were investigated. For orifice sizes with a hydraulic diameter to unrestricted hydraulic diameter (Dh:Dh,ur) ratio less than 35 percent, oscillations were reduced and wall temperatures fell up to 1.5 °C. Critical heat flux data were obtained for 7 orifice sizes with mass fluxes from 186 kg m-2 s-1 to 847 kg m-2 s-1. For all mass fluxes and inlet conditions tested, CHF values for a Dh:Dh,ur ratio of 1.8 percent became increasingly lower (up to 37 W cm-2 less) than those obtained with larger orifices. An optimum orifice size with Dh:Dh,ur of 35 percent emerged, offering up to 5 W cm-2 increase in CHF over unrestricted conditions at the highest mass flux tested, 847 kg m-2 s-1. These improvements in cooling ability with inlet orifices in place under both steady-state and impending CHF conditions are modest, leading to the conclusion that inlet orifices are only mildly effective at improving heat transfer coefficients. Stability of the PRL used for experimentation was also studied and improved. A vapor compression cycle's (VCC) proportional, integral, and derivative controller was found to adversely affect stability within the PRL and cause premature CHF. Replacing the VCC with an ice water heat sink maintained steady pumped loop system pressures and mass flow rates. The ice water heat sink was shown to have energy cost savings over the use of a directly coupled VCC for removing heat from the PRL. / Dissertation/Thesis / Ph.D. Mechanical Engineering 2012

Orientador: Amarildo Tabone Paschoalini / Resumo: Estruturas de parede fina são amplamente utilizadas na engenharia contemporânea devido à sua boa relação peso x resistência. Sua aplicação vai da construção civil, como cúpulas e pontes, até a aeronáutica e aeroespacial. Uma geometria de parede fina comum são os cilindros, observados em oleodutos, fuselagem e vasos de pressão. Para ser classificados como parede fina, a razão entre a espessura da parede e seu raio não deve ultrapassar 1:10. Eles ficam submetidos a esforços constantes e suscetíveis à instabilidade estrutural, em especial à flambagem, entrando em colapso repentinamente, muito abaixo da carga de projeto estipulada. Assim, compreender o comportamento desta instabilidade torna-se essencial para o avanço da engenharia. Para iniciar a compreensão da instabilidade, primeiro necessita-se conhecer as imperfeições geométricas da estrutura, ocasionadas, muitas vezes, pelo próprio processo de fabricação. A concepção destas imperfeições foi tratada por duas técnicas: CMM – Coordinates Mensuring Machine e CAI –Computer Aided Inspection. A primeira, tradicional, por contato, utilizando sensores LVDT – Linear Variable Differential Transformer, e, a segunda, vanguardista, sem contato, denominada "fotogrametria". Com isto, foi possível conceber uma estrutura tridimensional a ser analisada numericamente para obtenção das cargas críticas de flambagem, na qual estas duas técnicas apresentaram desvios condizentes com a literatura atual. Isto demonstrou, não somente, a acuracidade da... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Thin wall structures are widely used in contemporary engineering because of their good weight and strength ratio. Their application goes from civil construction such as domes and bridges, to aeronautics and aerospace. A common thin wall geometry are the cylinders, observed in oil pipelines, fuselage and pressure vessels. In order to be classified as thin wall, the ratio between the wall thickness and its radius must not exceed 1:10. They are subjected to constant efforts and susceptible to structural instability, especially buckling, suddenly collapsing, quite below the stipulated design load. Thus, understanding the behavior of this instability becomes essential for the advance of engineering. In order to begin the understanding of instability, it is firstly necessary to know the geometrical imperfections of the structure, often caused by the manufacturing process itself. The design of these imperfections was treated by two techniques, CMM – Coordinates Measuring Machine and CAI – Computer Aided Inspection. The first one, more conservative, by contact, using LVDT sensors, and, the second one, avant-garde, contactless, called “photogrammetry”. With this, it was possible to design a three-dimensional structure to be numerically analyzed to obtain the critical loads of buckling, in which these two techniques presented follow deviations from the current literature. This demonstrates not only the accuracy of the traditional contact technique to obtain geometry, but also how photo... (Complete abstract click electronic access below) / Mestre

Submitted by Bernardo Luis Pessutto (b_pessutto@hotmail.com) on 2018-08-22T02:28:26Z No. of bitstreams: 1 Trabalho Rev17.pdf: 4549693 bytes, checksum: 1dd1971769da127eccb0da40a664879e (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-08-22T17:32:16Z (GMT) No. of bitstreams: 1 pessutto_bl_me_ilha.pdf: 4549693 bytes, checksum: 1dd1971769da127eccb0da40a664879e (MD5) / Made available in DSpace on 2018-08-22T17:32:16Z (GMT). No. of bitstreams: 1 pessutto_bl_me_ilha.pdf: 4549693 bytes, checksum: 1dd1971769da127eccb0da40a664879e (MD5) Previous issue date: 2018-02-23 / Estruturas de parede fina são amplamente utilizadas na engenharia contemporânea devido à sua boa relação peso x resistência. Sua aplicação vai da construção civil, como cúpulas e pontes, até a aeronáutica e aeroespacial. Uma geometria de parede fina comum são os cilindros, observados em oleodutos, fuselagem e vasos de pressão. Para ser classificados como parede fina, a razão entre a espessura da parede e seu raio não deve ultrapassar 1:10. Eles ficam submetidos a esforços constantes e suscetíveis à instabilidade estrutural, em especial à flambagem, entrando em colapso repentinamente, muito abaixo da carga de projeto estipulada. Assim, compreender o comportamento desta instabilidade torna-se essencial para o avanço da engenharia. Para iniciar a compreensão da instabilidade, primeiro necessita-se conhecer as imperfeições geométricas da estrutura, ocasionadas, muitas vezes, pelo próprio processo de fabricação. A concepção destas imperfeições foi tratada por duas técnicas: CMM – Coordinates Mensuring Machine e CAI –Computer Aided Inspection. A primeira, tradicional, por contato, utilizando sensores LVDT – Linear Variable Differential Transformer, e, a segunda, vanguardista, sem contato, denominada "fotogrametria". Com isto, foi possível conceber uma estrutura tridimensional a ser analisada numericamente para obtenção das cargas críticas de flambagem, na qual estas duas técnicas apresentaram desvios condizentes com a literatura atual. Isto demonstrou, não somente, a acuracidade da técnica tradicional de contato para obtenção da geometria, mas, também, como a fotogrametria pode ser uma alternativa viável para inspeções rápidas de geometria. / Thin wall structures are widely used in contemporary engineering because of their good weight and strength ratio. Their application goes from civil construction such as domes and bridges, to aeronautics and aerospace. A common thin wall geometry are the cylinders, observed in oil pipelines, fuselage and pressure vessels. In order to be classified as thin wall, the ratio between the wall thickness and its radius must not exceed 1:10. They are subjected to constant efforts and susceptible to structural instability, especially buckling, suddenly collapsing, quite below the stipulated design load. Thus, understanding the behavior of this instability becomes essential for the advance of engineering. In order to begin the understanding of instability, it is firstly necessary to know the geometrical imperfections of the structure, often caused by the manufacturing process itself. The design of these imperfections was treated by two techniques, CMM – Coordinates Measuring Machine and CAI – Computer Aided Inspection. The first one, more conservative, by contact, using LVDT sensors, and, the second one, avant-garde, contactless, called “photogrammetry”. With this, it was possible to design a three-dimensional structure to be numerically analyzed to obtain the critical loads of buckling, in which these two techniques presented follow deviations from the current literature. This demonstrates not only the accuracy of the traditional contact technique to obtain geometry, but also how photogrammetry can be a viable alternative for rapid geometry inspections.

Du fait de ses propriétés intéressantes, le domaine de fréquence térahertz (THz) du spectre électromagnétique peut avoir de nombreuses applications technologiques, de l'imagerie à la spectroscopie en passant par les télécommunications. Toutefois, les contraintes technologiques empêchant l'émission et la détection efficaces de ces ondes par des systèmes conventionnels ont valu à cette partie du spectre électromagnétique le nom de gap THz. Au cours des deux dernières décennies, plusieurs solutions novatrices sont apparues. Parmi elles, l'utilisation de transistors à effet de champ s'est imposée comme une solution originale, bon marché, avec un fort potentiel d'intégration. Le mécanisme identifié fait intervenir l'interaction entre les ondes THz et des ondes de courant (dites ondes plasma) dans le canal du transistor. Le canal du transistor agit tel une cavité pour ces ondes plasma. Le dispositif peut alors se comporter de manière résonante ou non-résonante en fonction de divers paramètres. Dans ce manuscrit, nous étudions numériquement ces différents régimes à l'aide de modèles hydrodynamiques. Les modèles utilisés élargissent les phénomènes pris en compte dans de précédentes études théoriques. Les résultats portent sur la détection d'ondes THz par des transistors et dans une moindre mesure sur leur émission. Dans le régime non-résonant, nous étudions dans quelle mesure la plage de linéarité de détection peut être étendue. Dans le régime résonant, nous montrons l'existence de nouvelles fréquences de résonance, permettant d'élargir le spectre d'intérêt de ces détecteurs. / Due to its interesting properties, the electromagnetic THz frequency range may lead to numerous technological applications, ranging from imaging to spectroscopy or even communications. However, technological constraints prevented the efficient emission and detection of such waves with conventional electronics, leading to the idea of the terahertz gap. In the last decades, multiple novel solutions to resolve this gap have been proposed. Amongst these, one may find the use of simple field effect transistors as the most promising one. Their production benefits from currently available CMOS technology thus drastically decreasing the fabrication cost of such a device while allowing it to be easily integrated within electronic circuits. The mechanism behind the emission and detection is the interaction between THz electromagnetic radiations and current oscillations, that is plasma waves, in the transistor's channel. This channel forms a cavity for plasma oscillations, hence, the device may act either resonantly or non-resonantly, depending on various parameters. This thesis deals with the numerical simulation of the transistor in different regimes using hydrodynamical models. These models account for multiple phenomena that have been considered in previous theoretical studies. Some theoretical results on both the emission and detection of THz radiation are presented. In the non-resonant case, we study how one can increase the linear regime of detection. In the resonant case, we show the existence of unexpected resonance frequencies, enlarging the detection spectrum of such detectors.

Introdução: Instabilidades adquiridas do ombro são uma afecção comum do membro superior na prática esportiva, ocasionadas particularmente pela posição de abdução e rotação lateral da articulação glenoumeral durante movimentos explosivos. O manguito rotador proporciona grande parte da estabilidade dinâmica do ombro, sendo que nos movimentos esportivos, a estabilização necessita ser rápida para evitar a movimentação excessiva da cabeça umeral. O tempo entre a ativação do músculo e a produção de tensão é conhecida como Retardo Eletromecânico (REM), podendo este estar associado à velocidade a qual um músculo transmite sua tensão à articulação. Objetivo: avaliar o REM do músculo infraespinhal durante a rotação lateral (RL), o REM do músculo Peitoral Maior durante a rotação medial (RM) e o atraso entre a ativação do Peitoral Maior e Infraespinhal durante uma RM e relacionar estes eventos com a presença ou não da instabilidade glenoumeral adquirida. O comportamento mecânico do infraespinhal foi avaliado também por meio de mecanomiografia, possibilitando subdividir o REM em relação aos eventos elétricos e mecânicos. Métodos: Os músculos Peitoral Maior e Infraespinhal foram monitorados por eletromiografia (EMG) de superfície (2 kHz); o sinal mecanomiográfico (MMG) (2 kHz) foi coletado do Infraespinhal e os torques (2 kHz) explosivos isométricos de RM e RL do ombro foram coletados na posição do ombro de abdução e rotação lateral a 90° em um dinamômetro. Após uma avaliação funcional do membro superior, 18 indivíduos do sexo masculino, praticantes de atividade esportiva overhead, participaram do estudo, sendo nove com ombros saudáveis e nove com instabilidade glenoumeral anterior. Após a coleta e armazenamento dos sinais, esses foram filtrados e analisados. Os sinais EMG do peitoral maior e EMG e MMG do infraespinhal foram filtrados (EMG 5-500 Hz e MMG 4-400 Hz) e um envoltório linear foi calculado. O início dos sinais foi identificado usando-se o limiar de repouso + 3 desvios padrão para EMG e MMG e 2% do pico de torque para o limiar de força. Os limiares de ativação foram usados para calcular o início de cada sinal (EMG, MMG e Torque). Os intervalos de tempo entre os eventos foram mensurados e comparados entre os grupos (ombro instável, ombro contra-lateral e ombro saudável). Os picos de torque e taxa de produção do torque de RM e RL foram calculados para todos os grupos. Resultados: O REM do infraespinhal em ombros com instabilidade e nos ombros contralaterais ao instável foi menor do que nos ombros saudáveis. Pico de Torque, Taxa de Produção de Torque, atraso entre EMG do peitoral maior e EMG do infraespinhal e REM do peitoral maior não apresentaram diferenças significativas entre os grupos. Conclusão: Ombros instáveis e contralaterais aos instáveis apresentam adaptação crônica do manguito rotador com diminuição do REM. O REM está possivelmente associado ao aumento da rigidez dos elementos elásticos em série. O aumento da demanda pelos estabilizadores dinâmicos em decorrência da falência dos mecanismos estáticos de estabilização do ombro poderia explicar tal adaptação do infraespinhal. / Introduction: Acquired shoulder instabilities are a common upper limb injury in sports, mostly related to abduction and external rotation of glenohumeral joint during explosive contractions. Most of the dynamic stabilization of the shoulder joint is provided by the rotator cuff. In sports movements the stabilization must be quick to avoid humeral head excessive motion. The time between muscle activation and force production is named Electromechanical Delay (EMD), and is related to the speed of transmited tension to the joint/bone. Objetive: Evaluate the EMD in the infraspinatus muscle during External Rotation (ER), the EMD of Pectoralis Major during an Internal Rotation (IR) and the delay between Pectoralis Major and Infraspinatus activation during an IR and relate those mesurements to the shoulder stability/instability. The mechanical behaviour of the infraspinatus muscle was also assessed by mechanomyography, enabling to subdivide the EMD with respect to the electrical and mechanical events. Methods: Pectoralis Major and Infraspinatus muscles were monitored by surface Electromyography (EMG) (2kHz); the mechanomyographic (MMG) signal was collected from infraspinatus muscle (2kHz) and the isometric explosive IR and ER of shoulder were collected at 90° of abduction and external rotation on a dynamometer. After a functional evaluation of the shoulder, 18 male subjects, overhead sports participate in the study, nine with stable shoulders and nine with anterior shoulders instability. After data collection and storage, the signals were filtered and analysed. The EMG signals from Pectoralis Major and EMG and MMG from infraspinatus were filtered (EMG 5-500 Hz and MMG 4-400 Hz) and a linear envelope was calculated. The signal onset was identified using the threshold of resting signal plus 3 standart deviations for EMG and MMG and 2% of peak torque to torque threshold. The thresholds were used to calculate the beginning of each signal (EMG, MMG and Torque). The time delays between events were measured and compared between the groups (stable, unstable and contralateral to the unstable). Peak Torque and Rate of Torque Production of IR and ER were calculated to all groups. Results: The infraspinatus EMD in the unstable and contralateral to unstable shoulders were smaller than the healthy shoulders. Peak Torque, Rate of Torque Production, delay between pectoralis major EMG and infraspinatus EMG and pectoralis EMD were not different between the groups. Conclusions: Unstable and contralateral to unstable shoulders showed a chronic adaptation of rotator cuff with decrease in EMD. The EMD could be related to increase in stiffness of series elastic components. The increased demand for the dynamic stabilization caused by the loss of static stabilization mechanism could lead to the infraspinatus adaptation.

This thesis studies the prediction and reduction of installed jet noise, combining both analytical and experimental techniques. In the prediction part, it starts with formulating a low-order but robust isolated jet noise prediction model, based on which a remarkably fast code with pre-informed data is developed. A semi-empirical low-order model is then developed to predict installed jet noise. The model consists of two parts, the first of which is based on the Lighthill's acoustic analogy theory. The second part embraces Amiet's approach to model the sound due to the scattering of jet instability waves. It is shown that the significant low-frequency noise enhancement observed in installed jet experiments is due to the scattering of near-field instability waves. The trailing edge scattering model can successfully predict noise spectra at all distinct angles. The quadrupole-induced high-frequency sound is either efficiently shielded at $90^\circ$ to the jet axis on the shielded side or enhanced by around $3$ dB at $90^\circ$ on the reflected side. But these effects gradually diminish as the observer angle decreases. The high-frequency spectra can be robustly predicted at large observer angles while deviation occurs at low observer angles due to jet refraction effects. An experimental study on installed jet noise is then conducted. The effects of plate positions and Mach numbers are studied. Excellent agreement between the experimental results and model predictions is achieved at low frequencies for all plate positions and Mach numbers tested. At high frequencies, the noise spectra at $90^\circ$ on the reflected side can also be correctly predicted. At lower observer angles, deviations occur due to jet refraction effects. In the noise reduction part, an experimental study is firstly carried out to study the effects of lobed nozzles on installed jet noise at constant flow rates. It is found that lobed nozzles do not noticeably change the installed jet noise spectra at low frequencies. However, they do result in a slight noise reduction at high frequencies. To understand why lobed nozzles hardly change low-frequency installed jet noise, an analytical stability analysis for lobed vortex sheets is performed. The results show that lobed jets change both the convection velocity and the temporal growth rate of instability waves. The changes become more pronounced as the number of lobes $N$ and the penetration ratio $\epsilon$ increase. A second set of experiments is carried out to explore the possibility of reducing installed jet noise by using two pylons. The results show that even in the most conservative case installed jet noise is reduced by around $2\sim3$ dB at low frequencies. It is concluded that using two pylons to reduce installed jet noise has significant practical potential.

Thermoacoustic instability is one of the most significant problems faced in the design of some combustion systems. Thermoacoustic oscillations arise due to feedback between acoustic waves and unsteady heat release rate when the fluctuating heat release rate is sufficiently in phase with the unsteady pressure. The primary aim of designers is to design linearly stable thermoacoustic systems in which these dangerous oscillations do not arise. In thermoacoustics, adjoint-based sensitivity analysis has shown promise at predicting the parameters which have the most influence on the linear growth and decay rates as well as oscillation frequency observed during periods of linear growth and decay. Therefore, adjoint-based methods could prove to be a valuable tool for developing optimal passive control solutions. This thesis aims to develop novel experimental sensitivity analysis techniques and provide a first comparison with the predictions of adjoint-based sensitivity analysis. In this thesis experimental sensitivity analysis is performed on (i) a vertical electrically-driven Rijke tube, and (ii) a vertical flame-driven Rijke tube. On the electrically-driven Rijke tube, the feedback sensitivity is studied by investigating the shift in linear growth and decay rates and oscillation frequency observed during periods of linear growth and decay due to the introduction of a variety of passive control devices. On the flame-driven Rijke tube, the base-state sensitivity is studied by investigating how the linear growth and decay rates as well as oscillation frequency during periods of linear growth and decay change as the convective time delay of the flame is modified. Adjoint-based sensitivity analysis gives the shift in linear growth and decay rate and the oscillation frequency when parameters are changed. This thesis provides experimental measurements of the same quantities, for comparison with the numerical sensitivity analysis, opening up new avenues for the development, implementation and validation of optimal passive control strategies for more complex thermoacoustic systems.

abstract: Characterization and modeling of deformation and failure in metallic materials under extreme conditions, such as the high loads and strain rates found under shock loading due to explosive detonation and high velocity-impacts, are extremely important for a wide variety of military and industrial applications. When a shock wave causes stress in a material that exceeds the elastic limit, plasticity and eventually spallation occur in the material. The process of spall fracture, which in ductile materials stems from strain localization, void nucleation, growth and coalescence, can be caused by microstructural heterogeneity. The analysis of void nucleation performed from a microstructurally explicit simulation of a spall damage evolution in a multicrystalline copper indicated triple junctions as the preferred sites for incipient damage nucleation revealing 75% of them with at least two grain boundaries with misorientation angle between 20-55°. The analysis suggested the nature of the boundaries connecting at a triple junction is an indicator of their tendency to localize spall damage. The results also showed that damage propagated preferentially into one of the high angle boundaries after voids nucleate at triple junctions. Recently the Rayleigh-Taylor Instability (RTI) and the Richtmyer-Meshkov Instability (RMI) have been used to deduce dynamic material strength at very high pressures and strain rates. The RMI is used in this work since it allows using precise diagnostics such as Transient Imaging Displacement Interferometry (TIDI) due to its slower linear growth rate. The Preston-Tonks-Wallace (PTW) model is used to study the effects of dynamic strength on the behavior of samples with a fed-thru RMI, induced via direct laser drive on a perturbed surface, on stability of the shock front and the dynamic evolution of the amplitudes and velocities of the perturbation imprinted on the back (flat) surface by the perturbed shock front. Simulation results clearly showed that the amplitude of the hydrodynamic instability increases with a decrease in strength and vice versa and that the amplitude of the perturbed shock front produced by the fed-thru RMI is also affected by strength in the same way, which provides an alternative to amplitude measurements to study strength effects under dynamic conditions. Simulation results also indicate the presence of second harmonics in the surface perturbation after a certain time, which were also affected by the material strength. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2016