Les réactions non-linéaires peuvent donner naissance à des phénomènes coopératifs nouveaux dans des systèmes microstructurés en fonction de la taille des éléments actifs et du couplage entre eux. Nous avons étudié la dynamique de l'électrooxydation de CO, une réaction bistable présentant une branche de résistance différentielle négative en forme de S, sur une microélectrode de platine et des réseaux. Au voisinage d'une instabilité spatiale, une amplification du bruit moléculaire a été observée à cause de l'interaction avec la bifurcation spatiale. Le comportement dynamique est fortement affecté par la concentration en acide sulfurique et par la présence d'une faible quantité de chlorures dans la solution. Quand plusieurs microélectrodes sont couplées globalement, des comportements coopératifs nouveaux ont été mis en évidence comme l'émergence d'oscillations cohérentes et la présence d'un régime d'échange dynamique complexe faisant intervenir des processus inter et intra électrodes. / Nonlinear reactions may give rise to new cooperative phenomena when they occur in microstructured systems depending on the size of the active elements and on the coupling between them. We have studied the dynamics of CO electrooxidation, a bistable electrochemical reaction With an S-shaped negative differential resistance on single Pt microelectrode and on their array. For microelectrodes, close to a spatial instability threshold, strong enhancement of the molecular noise was observed due to its interaction With the spatial bifurcation. The dynamic behaviour of the reaction was shown to be strongly affected by the sulfuric acid concentration and by the presence of a small amount of chlorides in solution. When several microelectrodes are globally coupled, the emergence of new cooperative behaviour could be evidenced such as the emergence of coherent oscillations and the presence of a complex dynamic switching regime involving the interplay of inter and intra electrode processes.

Bistable microrelays have many possible applications and have the potential to reduce the size, weight, power consumption, and cost of products in which they are used. This research outlines the current state of microrelays, presents three new compliant bistable micromechanisms, and characterizes their performance as microrelays. The characterization includes a treatment of a new force-tester, a preliminary contact resistance study, contact-force measurements, switching time measurements, insertion loss, AC isolation, breakdown voltage, and DC isolation. This document also includes recommendations for further research.

Passive vibration mitigation via multi-stable, mechanical means is relatively unexplored. In addition, achieving vibration suppression through avoiding resonance is at the forefront of up and coming research. This thesis investigates the application of a purely mechanical, bistable device as a passive method of vibration suppression. A purely mechanical device does not require power, multiple materials, or electrical circuits, and a passive device does not require external interaction or control. Therefore, a passive, mechanical device could be implemented with ease even in physically constrained environments with large dynamic loads, such as turbomachinery. The purely mechanical, bistable device presented herein replicates the two switches per resonance crossing evident in semi-active Resonance Frequency Detuning method. This work explores two different bistable, mass-spring models. The first is a single degree of freedom nonlinear mass spring model aiming to utilize asymmetry in the potential function to change the stiffness of the overall system. The second model is a coupled, two degree of freedom system that combines the nonlinear softening and hardening spring characteristics with the unique stiffnesses of two stable states. The performance is verified by targeting the first mode of a cantilever beam, with the device shifting the resonance away from the excitation frequency. Future research could apply these idealized models to complex, rotating structures and replicate the performance of the passive, mechanical devices in a physical geometry that could be manufactured as a part of a target structure.

Este trabalho apresenta um estudo experimental a respeito do fenômeno da biestabilidade em cilindros finitos com média razão de aspecto. Na biestabilidade, há uma esteira estreita a jusante de um dos cilindros e uma esteira larga a jusante do outro. Pode estar presente em muitas situações práticas da engenharia dependendo da distância entre os cilindros. Em cilindros finitos ainda é pouco compreendida e explorada. Para compreender o mecanismo do desprendimento de vórtices, são estudados o escoamento em torno de um único cilindro finito, com cilindros de diâmetros entre 25 e 60 mm e razão de aspecto entre 1 e 4 e após, o escoamento em torno de dois cilindros finitos dispostos lado a lado, com cilindros de diâmetros entre 25 e 32 mm e razão de aspecto entre 3 e 4. A técnica experimental aplicada consiste na medição das flutuações de velocidade em canal aerodinâmico, utilizando a técnica de anemometria de fio quente e na visualização do escoamento no mesmo canal, mantendo os parâmetros, utilizando gelo seco e laser. Além disso, foi realizada a visualização do escoamento em canal hidráulico com as mesmas dimensões do canal aerodinâmico, utilizando injeção de tinta através de agulhas. Para o estudo foram utilizados Re=2,00×104 para um cilindro finito e 3,86×103 ≤ Re ≤ 4,81×104 para cilindros finitos dispostos lado a lado. Os dados medidos em canal aerodinâmico são tratados através de ferramentas estatísticas, espectrais e de ondaletas, e os resultados das visualizações do escoamento são apresentados por meio de imagens obtidas das filmagens realizadas com uma câmera digital. Além disso, os vídeos são tratados com softwares de edição de vídeo e com ferramentas estatísticas. Os resultados confirmam a existência do fenômeno da biestabilidade para dois cilindros finitos dispostos lado a lado, que é um dos objetivos do estudo, nas três posições estudadas. A técnica de visualização de escoamento reforça a interpretação dos resultados obtidos através da técnica de anemometria de fio quente. Neste trabalho é considerada a existência de três escoamentos concomitantes: o escoamento ascendente, caracterizado pela estrutura de vórtices na base; o escoamento descendente, caracterizado pela estrutura de vórtices no topo; e o aqui chamado escoamento principal, caracterizado pelo desprendimento de vórtices a meia altura dos cilindros. / This work presents an experimental study on the bistability phenomenon in finite cylinders with a mid-aspect ratio. In the bistability phenomenon the flow to form two wakes behind the cylinders, a large wake behind a cylinder and a narrow wake after another. It can be present in many practical engineering situations depending on the distance between the cylinders. In finite cylinders, it is still poorly understood and explored. To understand the vortex shedding mechanism are studied the flow in a single finite cylinder with diameters between 25 and 60 mm and aspect ratio between 1 and 4 is studied. After that, the flow of two finite cylinders placed side by side with cylinders of diameters between 25 and 32 mm and aspect ratio between 3 and 4 was studied. The experimental technique of hot wire anemometry in aerodynamic channel is applied in the measurement of velocity fluctuations of the flow. The flow visualization was performed on the same aerodynamic channel, keeping the parameters, through using dry ice and laser. In addition, flow visualization is performed on the hydraulic channel with the same dimensions of the aerodynamic channel using ink injection through needles. All images are captured with a camera digital. For the study, Re=2.00×104 for a finite cylinder and 3.86×103 ≤ Re ≤ 4.81×104 for finite cylinders arranged side by side were used. The data measured in aerodynamic channel are treated through statistics, spectral and wavelet tools and the videos are treated through video editing software and with statistical tools. The results show the existence of two different levels of mean velocity in time series, corresponding to two flow modes confirming the phenomenon of bistability for two finite cylinders placed side by side, which is one of the objectives of the study. The flow visualization technique strengthens the interpretation of the results obtained through the hot wire anemometer technique. In this work the existence of three concomitant flows is considered: the upwash flow, characterized by the vortex structure in the base; the downwash flow, characterized by the vortex structure at the top; and the so-called main flow, characterized by the vortex shedding at half height of the cylinders.

In this thesis, we study a class of multi-stable reaction-diffusion systems used to model competing species. Systems in this class possess uniform stable steady states representing semi-trivial solutions. We start by considering a bistable, interaction, where the interactions are of classic “Lotka-Volterra” type and we consider a particular problem with relevance to applications in population dynamics: essentially, we study under what conditions the interplay of relative motility (diffusion) and competitive strength can cause waves of invasion to be halted and reversed. By establishing rigorous results concerning related degenerate and near-degenerate systems,we build a picture of the dependence of the wave speed on system parameters. Our results lead us to conjecture that this class of competition model has three “zones of response” in which the wave direction is left-moving, reversible and right-moving, respectively and indeed that in all three zones, the wave speed is an increasing function of the relative motility. Moreover, we study the effects of domain size on planar and non-planar interfaces and show that curvature plays an important role in determining competitive outcomes. Finally, we study a 3-species Lotka-Volterra model, where the third species is treated as a bio-control agent or a bio-buffer and investigate under what conditions the third species can alter the existing competition interaction.

In this study, we demonstrated a flexible cholesteric liquid crystal display using polymerization induced phase separation (PIPS) on a single substrate. Cholesteric liquid-crystal displays (ChLCDs) provide with color reflection owing to their periodic helical layer, without any optic device like polarizer or color filter. We discussed the influence of surface treatment and process conditions on PIPS, and improve the reflectivity of single substrate Ch-LC display from 9.05% to 19.27%.

Este trabalho apresenta um estudo experimental a respeito do fenômeno da biestabilidade em cilindros finitos com média razão de aspecto. Na biestabilidade, há uma esteira estreita a jusante de um dos cilindros e uma esteira larga a jusante do outro. Pode estar presente em muitas situações práticas da engenharia dependendo da distância entre os cilindros. Em cilindros finitos ainda é pouco compreendida e explorada. Para compreender o mecanismo do desprendimento de vórtices, são estudados o escoamento em torno de um único cilindro finito, com cilindros de diâmetros entre 25 e 60 mm e razão de aspecto entre 1 e 4 e após, o escoamento em torno de dois cilindros finitos dispostos lado a lado, com cilindros de diâmetros entre 25 e 32 mm e razão de aspecto entre 3 e 4. A técnica experimental aplicada consiste na medição das flutuações de velocidade em canal aerodinâmico, utilizando a técnica de anemometria de fio quente e na visualização do escoamento no mesmo canal, mantendo os parâmetros, utilizando gelo seco e laser. Além disso, foi realizada a visualização do escoamento em canal hidráulico com as mesmas dimensões do canal aerodinâmico, utilizando injeção de tinta através de agulhas. Para o estudo foram utilizados Re=2,00×104 para um cilindro finito e 3,86×103 ≤ Re ≤ 4,81×104 para cilindros finitos dispostos lado a lado. Os dados medidos em canal aerodinâmico são tratados através de ferramentas estatísticas, espectrais e de ondaletas, e os resultados das visualizações do escoamento são apresentados por meio de imagens obtidas das filmagens realizadas com uma câmera digital. Além disso, os vídeos são tratados com softwares de edição de vídeo e com ferramentas estatísticas. Os resultados confirmam a existência do fenômeno da biestabilidade para dois cilindros finitos dispostos lado a lado, que é um dos objetivos do estudo, nas três posições estudadas. A técnica de visualização de escoamento reforça a interpretação dos resultados obtidos através da técnica de anemometria de fio quente. Neste trabalho é considerada a existência de três escoamentos concomitantes: o escoamento ascendente, caracterizado pela estrutura de vórtices na base; o escoamento descendente, caracterizado pela estrutura de vórtices no topo; e o aqui chamado escoamento principal, caracterizado pelo desprendimento de vórtices a meia altura dos cilindros. / This work presents an experimental study on the bistability phenomenon in finite cylinders with a mid-aspect ratio. In the bistability phenomenon the flow to form two wakes behind the cylinders, a large wake behind a cylinder and a narrow wake after another. It can be present in many practical engineering situations depending on the distance between the cylinders. In finite cylinders, it is still poorly understood and explored. To understand the vortex shedding mechanism are studied the flow in a single finite cylinder with diameters between 25 and 60 mm and aspect ratio between 1 and 4 is studied. After that, the flow of two finite cylinders placed side by side with cylinders of diameters between 25 and 32 mm and aspect ratio between 3 and 4 was studied. The experimental technique of hot wire anemometry in aerodynamic channel is applied in the measurement of velocity fluctuations of the flow. The flow visualization was performed on the same aerodynamic channel, keeping the parameters, through using dry ice and laser. In addition, flow visualization is performed on the hydraulic channel with the same dimensions of the aerodynamic channel using ink injection through needles. All images are captured with a camera digital. For the study, Re=2.00×104 for a finite cylinder and 3.86×103 ≤ Re ≤ 4.81×104 for finite cylinders arranged side by side were used. The data measured in aerodynamic channel are treated through statistics, spectral and wavelet tools and the videos are treated through video editing software and with statistical tools. The results show the existence of two different levels of mean velocity in time series, corresponding to two flow modes confirming the phenomenon of bistability for two finite cylinders placed side by side, which is one of the objectives of the study. The flow visualization technique strengthens the interpretation of the results obtained through the hot wire anemometer technique. In this work the existence of three concomitant flows is considered: the upwash flow, characterized by the vortex structure in the base; the downwash flow, characterized by the vortex structure at the top; and the so-called main flow, characterized by the vortex shedding at half height of the cylinders.

Este trabalho apresenta um estudo experimental a respeito do fenômeno da biestabilidade em cilindros finitos com média razão de aspecto. Na biestabilidade, há uma esteira estreita a jusante de um dos cilindros e uma esteira larga a jusante do outro. Pode estar presente em muitas situações práticas da engenharia dependendo da distância entre os cilindros. Em cilindros finitos ainda é pouco compreendida e explorada. Para compreender o mecanismo do desprendimento de vórtices, são estudados o escoamento em torno de um único cilindro finito, com cilindros de diâmetros entre 25 e 60 mm e razão de aspecto entre 1 e 4 e após, o escoamento em torno de dois cilindros finitos dispostos lado a lado, com cilindros de diâmetros entre 25 e 32 mm e razão de aspecto entre 3 e 4. A técnica experimental aplicada consiste na medição das flutuações de velocidade em canal aerodinâmico, utilizando a técnica de anemometria de fio quente e na visualização do escoamento no mesmo canal, mantendo os parâmetros, utilizando gelo seco e laser. Além disso, foi realizada a visualização do escoamento em canal hidráulico com as mesmas dimensões do canal aerodinâmico, utilizando injeção de tinta através de agulhas. Para o estudo foram utilizados Re=2,00×104 para um cilindro finito e 3,86×103 ≤ Re ≤ 4,81×104 para cilindros finitos dispostos lado a lado. Os dados medidos em canal aerodinâmico são tratados através de ferramentas estatísticas, espectrais e de ondaletas, e os resultados das visualizações do escoamento são apresentados por meio de imagens obtidas das filmagens realizadas com uma câmera digital. Além disso, os vídeos são tratados com softwares de edição de vídeo e com ferramentas estatísticas. Os resultados confirmam a existência do fenômeno da biestabilidade para dois cilindros finitos dispostos lado a lado, que é um dos objetivos do estudo, nas três posições estudadas. A técnica de visualização de escoamento reforça a interpretação dos resultados obtidos através da técnica de anemometria de fio quente. Neste trabalho é considerada a existência de três escoamentos concomitantes: o escoamento ascendente, caracterizado pela estrutura de vórtices na base; o escoamento descendente, caracterizado pela estrutura de vórtices no topo; e o aqui chamado escoamento principal, caracterizado pelo desprendimento de vórtices a meia altura dos cilindros. / This work presents an experimental study on the bistability phenomenon in finite cylinders with a mid-aspect ratio. In the bistability phenomenon the flow to form two wakes behind the cylinders, a large wake behind a cylinder and a narrow wake after another. It can be present in many practical engineering situations depending on the distance between the cylinders. In finite cylinders, it is still poorly understood and explored. To understand the vortex shedding mechanism are studied the flow in a single finite cylinder with diameters between 25 and 60 mm and aspect ratio between 1 and 4 is studied. After that, the flow of two finite cylinders placed side by side with cylinders of diameters between 25 and 32 mm and aspect ratio between 3 and 4 was studied. The experimental technique of hot wire anemometry in aerodynamic channel is applied in the measurement of velocity fluctuations of the flow. The flow visualization was performed on the same aerodynamic channel, keeping the parameters, through using dry ice and laser. In addition, flow visualization is performed on the hydraulic channel with the same dimensions of the aerodynamic channel using ink injection through needles. All images are captured with a camera digital. For the study, Re=2.00×104 for a finite cylinder and 3.86×103 ≤ Re ≤ 4.81×104 for finite cylinders arranged side by side were used. The data measured in aerodynamic channel are treated through statistics, spectral and wavelet tools and the videos are treated through video editing software and with statistical tools. The results show the existence of two different levels of mean velocity in time series, corresponding to two flow modes confirming the phenomenon of bistability for two finite cylinders placed side by side, which is one of the objectives of the study. The flow visualization technique strengthens the interpretation of the results obtained through the hot wire anemometer technique. In this work the existence of three concomitant flows is considered: the upwash flow, characterized by the vortex structure in the base; the downwash flow, characterized by the vortex structure at the top; and the so-called main flow, characterized by the vortex shedding at half height of the cylinders.

Development, tissue renewal and longevity of multi-cellular organisms require the ability to switch between a proliferative state and quiescence, a reversible arrest from the cell cycle. The balance of quiescence and proliferation underlies the fundamental feature of generating and maintaining the appropriate number of cells, which is essential for tissue architecture, regeneration, and function. Disruption of quiescence and proliferation balance leads to hypo- or hyper-proliferative diseases. To date, the regulatory mechanism of proliferation has been well established, while cellular quiescence has remained a phenotypic description without a clearly defined molecular control mechanism. Simply, quiescence has long been considered a passive counterpart to proliferation. However, recent findings have revealed that quiescence is an actively maintained state exhibiting a unique gene expression pattern. While quiescence has been traditionally considered as a state (namely G0) outside of the cell cycle, it is in fact a collection of heterogeneous states. In studies conducted in the 70's and 80's using fibroblasts and lymphocytes, it has been observed that the longer the cells were kept under quiescence inducing conditions such as contact inhibition, the deeper the cells moved into quiescence. Deep quiescent cells are still able to reenter the cell cycle upon growth stimulation but they exhibit a longer pre-DNA synthesis phase [1-4]. Shallow quiescent state has also been recently reported in muscle and neural stem cells termed GAlert and "prime" quiescent state, respectively. Heterogeneous quiescent depth entails that cells vary in their sensitivity to growth signals, representing an important yet underappreciated layer of complexity in cell growth control. The cellular mechanisms that control the depth of quiescence remains elusive. In my thesis work, I first investigate the strengths of serum stimulation required for cells to exit deep and shallow quiescence as a determinant of quiescence depth. Through model simulations and experimental measurements, I further demonstrate that various components of the Rb-E2F pathway control quiescence depth with varying efficacy. The Rb-E2F pathway interacts with diverse cellular pathways that respond to environmental signals to jointly modulate quiescence depth. Given that certain circadian clock genes (e.g., Cry) affect key components in the Rb-E2F pathway, I tested the effect of Cry activity on quiescence depth. I found that increased Cry activity resulted in deeper quiescence, contrary to our anticipation based on the literature. Next, we constructed a library of mathematical models that represent possible interactions between Cry and the Rb-E2F pathway. We computationally searched this model library for links that could explain the experimental observations. The modeling search suggested that Cry upregulation may lead to increased expression of cyclin dependent kinase inhibitor (e.g., p21), which in turn drives cells into deeper quiescence. This model prediction was confirmed by my follow-up experiments. Collectively, my thesis work establishes an integrated modeling and experimental framework that will help us to further investigate diverse cellular mechanisms controlling the heterogeneous quiescence depth.

Two compliant bistable micro-mechanisms have been developed which can be switched in either direction using on-chip thermal actuation. The energy storage and bistable behavior of the mechanisms are achieved through the elastic deflection of compliant segments. The pseudo-rigid-body model was used for the compliant mechanism design, and for analysis of the large-deflection flexible segments. To achieve on-chip actuation, the mechanism designs were optimized to reduce their required rotation, allow them to be switched using linear-motion thermal actuators. The modeling theory and analysis are presented for several design iterations. Each iteration was successfully fabricated and tested using either the MUMPs or SUMMiT surface micromachining technology.