In recent years portable electronic devices, such as mobile phones and personal digital assistants, have increased the demand for high performance displays with low power consumption. An interesting candidate with the potential of fulfilling these demands is the reflective single-polarizer surface controlled bistable twisted nematic liquid crystal display. The main focus of this work involves the optical properties of displays based on these bistable structures. In the investigations, the display is considered as an integrated optical system, containing not only the liquid crystal cell, but also components such as polarizers and retardation films. The specific aim of the thesis was to derive new optical modes of the reflective single-polarizer bistable twisted nematic device using the Jones matrix method to study the interaction between the polarization of light and the optically anisotropic media. The electro-optical properties of the derived modes have been studied and evaluated both theoretically and experimentally. The modes possess excellent brightness and high contrast ratio. By introducing a quarter-wave retardation film into the optical configuration, the contrast ratio can be significantly increased by preventing spectral leakage of light in the dark state. To experimentally realize the derived optical modes, special layers for the alignment of the liquid crystal molecules on the cell substrate surface have been proved needed. Therefore, also the photo-alignment technology of nematic liquid crystals on novel alignment materials has been studied with the aim to control liquid crystal cell parameters such as pretilt angle and anchoring energy, both critical for the bistable switching. The results of this thesis will increase the understanding of the optical properties of the reflective single-polarizer bistable twisted nematic liquid crystal display and will be valuable when considering this type of device for practical applications.

The central concern of this thesis is the study of non-equilibrium behaviour in magnetic materials and its interpretation within the framework of the Preisach model of hysteresis. Comprehensive experimental characterizations of the field and temperature and time dependence of a suite of standard magnetic response functions have been performed on a variety of magnetic materials, including a naturally occurring mineral of nanodimensional titanomagnetite particles embedded in volcanic glass, a compressed powder of nanodimensional magnetite particles immobilized in an organic binder, a thin film of nanodimensional Fe particles embedded in alumina, and a series of sintered, bond-disordered CaxSr1-xRuO3 ferromagnets. The measurements were compared with numerical simulations based on a model Preisach ensemble of thermally activated two-level subsystems, characterized individually by a double well free energy profile in a two-dimensional configuration space, an elementary moment reversal, a dissipation field and a bias field, and characterized collectively by a distribution of these characteristic fields. Our efforts were concentrated on two principal spheres of investigation. (1) By performing detailed numerical simulations of the relaxation response of model Preisach collections of two-level subsystems under the same field and temperature protocols used to probe experimentally the relaxation dynamics of spin glasses, we have been able to show that aging, memory and rejuvenation effects are ubiquitous features of all materials which possess a broad distribution of free energy barriers which block the approach to thermal equilibrium. (2) We propose a general strategy for isolating and quantifying the two principal mechanisms, thermal fluctuations and barrier growth, which are jointly responsible for shaping the measured temperature dependence of the magnetic properties of all magnetic materials which exhibit a history dependent response to an external field excitation, and is based on the analysis of viscosity isotherms and, in particular, on a plot of T ln(tr/0) versus Ha , where tr is the time at which a viscosity isotherm measured in a field Ha at temperature T reverses sign. When thermal activation dominates barrier growth, this plot will yield a universal curve while, in the opposite limit the plot fractures into a family of isothermal curves. The strategy is applied to the analysis of each magnetic material listed above. / February 2009

<p>Cellular dynamics arise from intricate interactions among diverse components, such as metabolites, RNAs, and proteins. An in-depth understanding of these interactions requires an integrated approach to the investigation of biological systems. This task can benefit from a combination of mathematical modeling and experimental validations, which is becoming increasingly indispensable for basic and applied biological research. </p> <p>Utilizing a combination of modeling and experimentation, we investigate mammalian cell cycle entry. We begin our investigation by making predictions with a mathematical model, which is constructed based on the current knowledge of biology. To test these predictions, we develop experimental platforms for validations, which in turn can be used to further refine the model. Such iteration of model predictions and experimental validations has allowed us to gain an in-depth understanding of the cell cycle entry dynamics. </p> <p>In this dissertation, we have focused on the Myc-Rb-E2F signaling pathway and its associated pathways, dysregulation of which is associated with virtually all cancers. Our analyses of these signaling pathways provide insights into three questions in biology: 1) regulation of the restriction point (R-point) in cell cycle entry, 2) regulation of the temporal dynamics in cell cycle entry, and 3) post-translational regulation of Myc by its upstream signaling pathways. The well-studied pathways can serve as a foundation for perturbations and tight control of cell cycle entry dynamics, which may be useful in developing cancer therapeutics. </p> <p>We conclude by demonstrating how a combination of mathematical modeling and experimental validations provide mechanistic insights into the regulatory networks in cell cycle entry.</p> / Dissertation

The aim of this study is to design a compliant lock mechanism for a dishwasher, using a systematic approach. Functionally binary pinned-pinned segment that exhibits bistable behavior is utilized. Pseudo-rigid-body model of the whole mechanism and the half segment is developed separately and the corresponding calculations are carried out. Among current solutions a different method namely &ldquo / arc fitting method&rdquo / is developed and it is utilized to construct the model. A software code is written to get the exact solutions, which require the evaluation of elliptic integrals. Results are compared with the analytical model and confirmed with physical prototype. Predefined tip forces are seen to provide the transition from one stable position to other. Durability, reliability and compactness characteristics are particularly considered.

This paper presents designs for Multistable Shape-Shifting Surfaces (MSSS) by introducing bistability into the Shape-Shifting Surface (SSS). SSSs are defined as surfaces that retain their effectiveness as a physical barrier while undergoing changes in shape. The addition of bistability to the SSS gives the surface multiple distinct positions in which it remains when shifted to, i.e. by designing bistability into a single SSS link, the SSS unit cell can change into multiple shapes, and stabilize within the resulting shape, while maintaining integrity against various forms of external assaults normal to its surface. Planar stable configurations of the unit cell include, expanded, compressed, sheared, half-compressed, and partially-compressed, resulting in the planar shapes of a large square, small square, rhombus, rectangle, and trapezoid respectively. Tiling methods were introduced which gave the ability to produce out-of-plane assemblies using planar MSSS unit cells. A five-walled rigid storage container prototype was produced that allowed for numerous stable positions and volumes. Applications for MSSSs can include size-changing vehicle beds, expandable laptop screens, deformable walls, and volume-changing rigid-storage containers. Analysis of the MSSS was done using pseudo-rigid-Body Models (PRBMs) and Finite Element Analysis (FEA) which ensured bistable characteristics before prototypes were fabricated.

Biochemical reactions make up most of the activity in a cell. There is inherent stochasticity in the kinetic behavior of biochemical reactions which in turn governs the fate of various cellular processes. In this work, the precision of a method for dimensionality reduction for stochastic modeling of biochemical reactions is evaluated. Further, a method of stochastic simulation of reaction kinetics is implemented in case of a specific biochemical network involved in maintenance of long-term potentiation (LTP), the basic substrate for learning and memory formation. The dimensionality reduction method diverges significantly from a full stochastic model in prediction the variance of the fluctuations. The application of the stochastic simulation method to LTP modeling was used to find qualitative dependence of stochastic fluctuations on reaction volume and model parameters. / text

The central concern of this thesis is the study of non-equilibrium behaviour in magnetic materials and its interpretation within the framework of the Preisach model of hysteresis. Comprehensive experimental characterizations of the field and temperature and time dependence of a suite of standard magnetic response functions have been performed on a variety of magnetic materials, including a naturally occurring mineral of nanodimensional titanomagnetite particles embedded in volcanic glass, a compressed powder of nanodimensional magnetite particles immobilized in an organic binder, a thin film of nanodimensional Fe particles embedded in alumina, and a series of sintered, bond-disordered CaxSr1-xRuO3 ferromagnets. The measurements were compared with numerical simulations based on a model Preisach ensemble of thermally activated two-level subsystems, characterized individually by a double well free energy profile in a two-dimensional configuration space, an elementary moment reversal, a dissipation field and a bias field, and characterized collectively by a distribution of these characteristic fields. Our efforts were concentrated on two principal spheres of investigation. (1) By performing detailed numerical simulations of the relaxation response of model Preisach collections of two-level subsystems under the same field and temperature protocols used to probe experimentally the relaxation dynamics of spin glasses, we have been able to show that aging, memory and rejuvenation effects are ubiquitous features of all materials which possess a broad distribution of free energy barriers which block the approach to thermal equilibrium. (2) We propose a general strategy for isolating and quantifying the two principal mechanisms, thermal fluctuations and barrier growth, which are jointly responsible for shaping the measured temperature dependence of the magnetic properties of all magnetic materials which exhibit a history dependent response to an external field excitation, and is based on the analysis of viscosity isotherms and, in particular, on a plot of T ln(tr/0) versus Ha , where tr is the time at which a viscosity isotherm measured in a field Ha at temperature T reverses sign. When thermal activation dominates barrier growth, this plot will yield a universal curve while, in the opposite limit the plot fractures into a family of isothermal curves. The strategy is applied to the analysis of each magnetic material listed above.

Le développement récent en micro- et nanotechnologies (dans des domaines tels que l'horlogerie,l'électronique, l'optique, le biomédical, . . .) a créé un fort besoin concernant des systèmes capables de manipuler et d'assembler des objets de plus en plus petits. La conception de stations robotisées, capables de manipuler des micro-objets, s'est multipliée à travers le monde, faisant intervenir des actionneurs de haute résolution adaptés au micro monde, ainsi que de nombreux capteurs.Ce mémoire ouvre une nouvelle voie pour le développement de robots de micromanipulation. Il présente la conception, la modélisation, la fabrication et la commande d'un nouveau concept de micro robot, le DiMiBot (Digital MicroroBot). Il s'agit du premier micro robot numérique - inspiré 'e de l' 'électronique numérique - qui fait intervenir des actionneurs binaires pour générer un déplacement discret d'une grande précision sans nécessiter de capteur (en boucle ouverte). Ces actionneurs binaires extrêmement répétables et robustes (les modules bistables), assurent chacun un déplacement précis de 25 μm. Ils sont associés de manière monolithique à une architecture robotique parallèle flexible, assurant la génération d'un espace de travail discret, dont les 2N (N est le nombre de modules bistables utilisés au sein du DiMiBot) positions distincts atteignables sont parfaitement stables, répétables et robustes mécaniquement. Elles sont réparties de manière homogène dans un carré de 10,5 μm de côté La micro fabrication du premier prototype de micro robot numérique en silicium - faisant suite 'a un dimensionnement minutieux en élément finis - a été réalisé au sein de la salle blanche MIMENTO de l'institut FEMTO-ST. Ce DiMiBot possédant 4 modules bistables assure une résolution de 3,5 μm pour une répétable de chacune des 16 positions atteignables de 90 nm.

The central concern of this thesis is the study of non-equilibrium behaviour in magnetic materials and its interpretation within the framework of the Preisach model of hysteresis. Comprehensive experimental characterizations of the field and temperature and time dependence of a suite of standard magnetic response functions have been performed on a variety of magnetic materials, including a naturally occurring mineral of nanodimensional titanomagnetite particles embedded in volcanic glass, a compressed powder of nanodimensional magnetite particles immobilized in an organic binder, a thin film of nanodimensional Fe particles embedded in alumina, and a series of sintered, bond-disordered CaxSr1-xRuO3 ferromagnets. The measurements were compared with numerical simulations based on a model Preisach ensemble of thermally activated two-level subsystems, characterized individually by a double well free energy profile in a two-dimensional configuration space, an elementary moment reversal, a dissipation field and a bias field, and characterized collectively by a distribution of these characteristic fields. Our efforts were concentrated on two principal spheres of investigation. (1) By performing detailed numerical simulations of the relaxation response of model Preisach collections of two-level subsystems under the same field and temperature protocols used to probe experimentally the relaxation dynamics of spin glasses, we have been able to show that aging, memory and rejuvenation effects are ubiquitous features of all materials which possess a broad distribution of free energy barriers which block the approach to thermal equilibrium. (2) We propose a general strategy for isolating and quantifying the two principal mechanisms, thermal fluctuations and barrier growth, which are jointly responsible for shaping the measured temperature dependence of the magnetic properties of all magnetic materials which exhibit a history dependent response to an external field excitation, and is based on the analysis of viscosity isotherms and, in particular, on a plot of T ln(tr/0) versus Ha , where tr is the time at which a viscosity isotherm measured in a field Ha at temperature T reverses sign. When thermal activation dominates barrier growth, this plot will yield a universal curve while, in the opposite limit the plot fractures into a family of isothermal curves. The strategy is applied to the analysis of each magnetic material listed above.

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