The ability of cells to probe their mechanical environment and react to external stimuli is critical for maintenance of their normal structure and function. Through connections to the extracellular matrix, cells can sense mechanical cues such as substrate rigidity and stretch, and through force transmission across their contractile cytoskeleton can react accordingly to those signals by applying contractile traction forces to their surrounding environment. Healthy cells can react to these mechanical cues to maintain their cytoskeletal prestress (tension) at a set or homeostatic level over time, a phenomenon known as tensional homeostasis. Progression of certain diseases such as asthma, atherosclerosis, and cancer have been linked to a loss of tensional homeostasis. As such, tools for quantifying the traction forces that adhered cells apply to their substrate are crucial for gaining a better understanding of not just how healthy cells interact mechanically with their environment, but also how changes to the extracellular matrix or mutations within the cell can impact their ability to maintain tensional homeostasis and therefore remain both functional and viable. Our group has previously developed a method of quantifying cellular traction forces using indirectly pattered, soft hydrogel substrates known as micropattern traction microscopy. This method was initially developed to create discrete grid micropatterns, which while useful for measuring cellular traction forces does not offer any ability for the user to control cell growth area shape or size. This technique was further improved on through the creation of a protocol for changing discrete grid patterns into isolated island micropatterns, but this two-step process was challenging and generated islands of inconsistent shape and size. Here, we propose a new method for generating isolated island micropatterns of essentially any desired shape and size in a single step, as well as a corresponding image analysis algorithm for calculating cellular traction forces from these island micropatterns. Additionally, this dissertation also includes an investigation into the impact of distinct Epithelial-cadherin mutations on the ability of gastric adenocarcinoma (AGS) cells to achieve tensional homeostasis. Disruption of tensional homeostasis in the epithelium is a hallmark of certain cancers, and mutations in E-cadherin proteins have been identified in malignant epithelial cells. Here, through analysis of AGS cell traction force data collected previously by Dr. Han Xu during her dissertation work, we have found that two distinct mutations in the intracellular domain of E-cadherins have an impact on the ability of AGS cells to achieve tensional homeostasis.

Many processes involving rotating machinery could benefit from the continuous feedback of force applied to the bearings that support the machinery. Such a system could be used to provide diagnostics for process monitoring in a manufacturing application or to provide information for machine health monitoring. Active Magnetic Bearings (AMBs) have the capability to act concurrently as a shaft force sensor and support bearing. This capability stems from the AMB's control system, which is designed to maintain a specific rotor position, regardless of forces acting on the rotor. Researchers have demonstrated the force sensing ability of AMBs; current state of the art methods typically rely on a direct measurement of magnetic flux density as provided by a Hall probe inserted in the magnetic field. In this work, a system identification approach to force measurement is proposed; the proposed approach is applicable to all active magnetic bearings and does not require Hall probes. Recent developments in system identification of bearing forces (Kasarda et al., 2000) indicate that a different approach is feasible. In the work of Marshall (Marshall et al., 2001), a variety of perturbations are applied to an AMB while the AMB controller signals are interrogated, no outside instrumentation such as force transducers or Hall probes are required. The work of Kasarda and Marshall is the starting point for the work presented here. The initial work was expanded to include a general characterization of air gap for any rotor position. Although this characterization relies on static testing to identify system parameters, the identified parameters can then be used in the measurement of dynamic forces. The identification procedure provides a measurement of effective air gap length. Effective gap length is used to infer the effective position of the rotor with respect to the stator. This measurement is made for several specific rotor locations. The relationship between the effective rotor positions provided by the identification and the rotor positions reported by the AMB system sensors establishes a coordinate transformation. The procedure is also applied at different shaft rotation angles. In this way rotor runout can be identified. / Ph. D.

Le préconditionnement ischémique (IPC) consiste à induire des épisodes ischémiques brefs et répétés, entrecoupés d’épisodes de reperfusion. Cette technique initialement testée pour ses effets protecteurs sur le myocarde rendrait différents tissus du corps plus résistants à une réduction d’oxygénation, comme retrouvée durant l’exercice maximal. Très peu d’études ont étudié les effets de l’IPC sur l’oxygénation musculaire. À l’aide de la spectroscopie proche infrarouge, nous avons examiné les effets du préconditionnement sur l’hémodynamique et l’extraction d’oxygène pendant un protocole de contractions volontaires maximales répétées. Nos résultats démontrent que ce préconditionnement entraîne une augmentation du volume sanguin local au repos et pendant la récupération après les contractions, ainsi qu’une plus grande extraction d’oxygène en début d’effort. Ces améliorations s’accompagnent d’une augmentation de la force musculaire tout au long du protocole. L’utilisation de l’IPC comme aide ergogénique pourrait s’avérer utile pour optimiser l’oxygénation et la force musculaire avant une compétition ou un entraînement. / Repeated episodes of ischemia and reperfusion, commonly known as ischemic preconditioning (IPC), initially tested for its protective effects on the myocardium, renders different tissues more resistant to a subsequent reduction in oxygenation (i.e., tissue O2 saturation), as found during maximal exercise. Despite its likely effects on the oxidative function, studies examining the effects of IPC on tissue oxygenation are very scarce. We used near-infrared spectroscopy to study the effects of IPC on muscle haemodynamics and peripheral O2 extraction during repeated maximal efforts in resistance-trained participants. Our results demonstrate that IPC increased muscle blood volume at rest and during recovery between contractions, as well as muscle oxygen uptake during exercise. These acute physiological adaptations were associated with increased muscle strength throughout the protocol. The use of IPC as an ergogenic aid could be useful to optimize oxygenation and muscle strength during competition and training.

This thesis reflects two advances in atomic force microscopy. The first half is a new lateral force calibration procedure, which, in contrast to existing procedures, is independent of sample and cantilever shape, simple, direct, and quick. The second half is a high-throughput method for processing, fitting, and analyzing force curves taken on Pseudomonas aeruginosa bacteria in an effort to inspire better care for statistics and increase measurement precision.

Examining a countermovement jump (CMJ) force-time curve related to net impulse might be useful in monitoring athletes' performance. This study aimed to investigate the reliability of alternative net impulse calculation and net impulse characteristics (height, width, rate of force development, shape factor, and proportion) and validate against the traditional calculation in the CMJ. Twelve participants performed the CMJ in two sessions (48 hours apart) for test–retest reliability. Twenty participants were involved for the validity assessment. Results indicated intra-class correlation coefficient (ICC) of ≥ 0.89 and coefficient of variation (CV) of ≤ 5.1% for all of the variables except for rate of force development (ICC = 0.78 and CV = 22.3%). The relationship between the criterion and alternative calculations was r = 1.00. While the difference between them was statistically significant (245.96 ± 63.83 vs. 247.14 ± 64.08 N s, p < 0.0001), the effect size was trivial and deemed practically minimal (d = 0.02). In conclusion, variability of rate of force development will pose a greater challenge in detecting performance changes. Also, the alternative calculation can be used practically in place of the traditional calculation to identify net impulse characteristics and monitor and study athletes' performance in greater depth.

Examining a countermovement jump (CMJ) force-time curve related to net impulse might be useful in monitoring athletes' performance. This study aimed to investigate the reliability of alternative net impulse calculation and net impulse characteristics (height, width, rate of force development, shape factor, and proportion) and validate against the traditional calculation in the CMJ. Twelve participants performed the CMJ in two sessions (48 hours apart) for test–retest reliability. Twenty participants were involved for the validity assessment. Results indicated intra-class correlation coefficient (ICC) of ≥ 0.89 and coefficient of variation (CV) of ≤ 5.1% for all of the variables except for rate of force development (ICC = 0.78 and CV = 22.3%). The relationship between the criterion and alternative calculations was r = 1.00. While the difference between them was statistically significant (245.96 ± 63.83 vs. 247.14 ± 64.08 N s, p < 0.0001), the effect size was trivial and deemed practically minimal (d = 0.02). In conclusion, variability of rate of force development will pose a greater challenge in detecting performance changes. Also, the alternative calculation can be used practically in place of the traditional calculation to identify net impulse characteristics and monitor and study athletes' performance in greater depth.

During Nov.2008 to Apr. 2009, firms in Taiwan encountered dramatic financial crisis, and this impact made unemployment rate still climbing and economic depression. In order to reduce the impact from financial tsunami, every firm takes some strategies to resist it. The objective of our study is to find out the influence from financial tsunami on the listed companies. More importantly, we base on the three mechanisms (mimetic force, normative force and coercive force) of institutional theory and the perspectives of population theory to analyze why firms choose those strategies. We collect and analyze 201 returned questionnaires. We find when firms face both high market force, mimetic force and coercive, they tend to choose manipulation strategies. When firms face both low market force, mimetic force and coercive force, they tend to choose compromise strategies. When firms face high market force and low mimetic force and coercive force, they tend to use defiance strategies. When firms face low market force and high mimetic force and coercive force, they tend to use acquiescence strategies.

In 2008-2009, firms in Taiwan encountered dramatic financial tsunami, and this crisis made unemployment rate still climbing and economic depression. In order to reduce the impact from financial tsunami, every firm chooses some strategies to resist it. The purpose of our study is to find out the influence from financial tsunami on the listed companies. More importantly, we base on the three mechanisms (mimetic force, normative force and coercive force) of institutional theory to analyze the real reason for choosing strategies. We collect and analyze 201 returned questionnaires. The finding of this study is that the main factor of choosing strategies is from the mimetic force and normative force. In fact, the enterprise is affected by mimetic pressure deeply, and then it would tend to use the passive strategies. The enterprise is affected by normative pressure deeply, and then it would tend to use the active strategy. Interestingly, whether the enterprise is affected by coercive pressure or not, it doesn¡¦t affect the strategies choosing.

Microfluidics and its applications to Lab-on-a-Chip have attracted a lot of attention. Because of the small length scale, the flow is characterized by a low Re number. The governing equations become linear. Boundary element method (BEM) is a very good option for simulating the fluid flow with high accuracy. In this thesis, we present a 2D numerical simulation of the electrothermal flow using BEM. In electrothermal flow the volumetric force is caused by electric field and temperature gradient. The physics is mathematically modeled by (i) Laplace equation for the electrical potential, (ii) Poisson equation for the heat conduction caused by Joule heating, (iii) continuity and Stokes equation for the low Reynolds number flow. We begin by solving the electrical potential and electrical field. The heat conduction is caused by the Joule heating as the heat generation term. Superposition principle is used to solve for the temperature field. The Coulomb and dielectric forces are generated by the electrical field and temperature gradient of the system. The buoyancy force is caused by the non-uniform temperature distribution inside the system. We analyze the Stokes flow problem by superposition of fundamental solution for free-space velocity caused by body force and BEM for the corresponding homogeneous Stokes equation. It is well known that a singularity integral arises when the source point approaches the field point. To overcome this problem, we solve the free-space velocity analytically. For the BEM part, we also calculate all the integrals analytically. With this effort, our solution is more accurate. In addition, we improve the robustness of the matrix system by combining the velocity integral equation with the traction integral equation when we simulate the electrothermal pump. One of our purpose is to design a pump for the microfluidics system. Since the system is a long channel, the flow is fully developed in the area far away from the electrodes. With this assumption, the velocity profile is parabolic at the inlet and outlet of the channel. So we can get appropriate boundary conditions for the BEM part of Stokes equation. Consequently, we can simulate the electrothermal flow in an open channel. In this thesis, we will present the formulation and implementation of BEM to model electrothermal flow. Results of electrical potential, temperature field, Joule heating, electrothermal force, buoyancy force and velocity field will be presented.

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