Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004. / Includes bibliographical references (p. 75-77). / Actin filaments are a major constituent of the cytoskeleton in most eukaryotic cells. They function as a connection between the cell body to the focal adhesions in order to transmit forces into and out of the cell. During the force transduction process, many proteins bind to actin filaments in order to initiate a signaling cascade that reaches the cell nucleus. However, the effects of forces in the binding kinetics between actin filaments and actin binding proteins are unknown. This work proposes an experimental setup to study the force-dependent binding kinetics of such proteins at the single molecule level by using an instrument that combines optical trapping with single molecule fluorescence. The main focus of this work was the design and construction of the experimental equipment. The results show position detection capabilities with a resolution of 5 nm. Also, the trap stiffness recorded was in the order of 0.05 pN/nm. With the combination of position and trap stiffness, the force resolution of the instrument is about 0.25 pN. Also, a photobleaching event for a single dye molecule was recorded, proving the single molecule fluorescence capabilities. In addition, a complete experimental assay is described in order to perform studies on how force application affects the binding of actin and actin binding proteins. / by Jorge M. Ferrer. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 76-79). / Existing skin mechanical testing devices focus on measuring skin elasticity and are not tailored to assess the dynamic behavior of skin. The mathematical techniques used to analyze data collected using these devices are often not optimal. A new dynamic mechanical device that measures the linear dynamics of skin was developed and tested. The mechanical properties of skin were evaluated in experiments in which the stiffness and damping parameter were measured at different locations on the arm and hand, when stratum corneum hydration was varied by controlled changes in environmental humidity, and following the application of film-forming polymers. Parallel measurements were made with the Cutometer® so that the two devices could be compared. The findings revealed that reliable and valid measurements of skin mechanical properties can be obtained from the device. The stiffness of the skin was shown to vary significantly as a function of skin site, changes in stratum corneum hydration, and following the application of the polymer films. Changes in the damping parameter were less consistently associated with varying the condition of the skin. The high reliability and speed of measurement make this device and analytic procedure an attractive option for testing skin mechanics. / by Erika Sandford. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 125-129). / One of the most fundamental questions in developmental biology and tissue engineering is how cells organize to form complex structures characterized by tissues, organs and whole organisms. The coordination of cells to form complex structures is facilitated by their communication via the surrounding gel (or extracellular matrix) where they live. In addition to answering questions in development, studying how cells communicate and coordinate over distance via the extracellular matrix (ECM) can give insight into pathological situations such as cancer metastasis, and wound healing. Although the exchange of molecular and biochemical signals is a key mechanism in cell to cell communication, cells can also communicate biomechanically through the ECM. Modeling mechanical interactions between cells and the ECM can advance understanding of biomechanical signaling during tissue formation. Observation of the mechanisms for mechanical interaction between contractile cells within an extracellular matrix has resulted in detailed models that can describe single-cell migration and spreading on (and within) various of substrates. By incorporating sub-cellular behaviors (such as focal adhesion dynamics, cytoskeleton remodeling, actin motor activity and remodeling of the surrounding fibrous matrix), these models can integrate both the purely mechanical interaction within the surrounding matrix as well as the internal adaptive response to mechanical cues from the surrounding matrix. As a result, a vast amount of simulation data can be created from analyzing single-cell/matrix interactions numerically. In addition, numerous cell types and environmental conditions may be represented by varying multiple parameters within the model. However, complex and extensive mechanisms involved in emergent behavior of multiple interacting cells and surrounding matrix may become intractable due to mathematical and computational complexity. This thesis will address how we can exploit simulation data describing the nonlinear dynamics of single-cell/matrix behavior to create a reduced-order linear state equation in latent variable space. Furthermore, in order to predict multi-cell emergent behavior, the reduced-order linear models of single cells are used as components in a comprehensive framework based on linear superposition of mutually shared matrix dynamics. The linear latent state equation describing the nonlinear dynamics of a single-cell and surrounding matrix is created in three steps. First, using Bond Graph Theory, a set of independent state equations(derived from the bond graph) may be augmented by adding equations using auxiliary variables necessary to "sufficiently inform" the nonlinear dynamics. This creates an augmented state space where a linear description of the nonlinear system can be found. Second, the augmented (auxiliary and state) variables are simulated for various initial conditions. Using the resulting simulated data, we perform Principal Component Analysis in order to approximate a lower dimensional linear manifold within the augmented space. Third, we transform the augmented state equation to latent space representation by orthogonal projection onto the basis defined within the lower dimensional linear manifold. While the resultant latent state equation is linear, complex nonlinearities are embedded in the compact model, leading to precise and global linearization of nonlinear dynamics. Using the linear representation of single-cell/matrix dynamics we may perform linear operations such as projection, to isolate matrix dynamics of individual cells, and superposition, to combine matrix dynamics of individual cells and approximate a multi-cell matrix environment. Using these linear operations, we can effectively link single-cell models to predict multi-cell emergent behaviors. The hypothesis to prove (drawn from experimental evidence) is that multiple cells can effectively interact by transmitting force to neighboring cells through the shared matrix environment. In this thesis, I consider two models describing the nonlinear dynamics of single-cell/ECM mechanics. The first model is a 1-D lumped parameter model created to explore the aspects of cell sensing over an elastic ECM. Although it is possible to reproduce bio-mechanical interactive behaviors, polarity is not considered within the 1-Dmodel. The second model is a highly detailed biophysical distributed parameter system describing cell/ECM mechanics based on previous works and can accurately reproduce experimental observations. / by Michaëlle Ntala Mayalu. / Ph. D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006. / Includes bibliographical references (leaves 23-26). / To expand on the understanding of effective leadership and management, this study provides new evidence on the relation between employee satisfaction, project success, and managerial characteristics for the optimization of both. During the twentieth century, many have tried to uncover what it really means to be a good leader and to determine if it is possible to identify or create such people. In the managerial context, researchers have looked at project success and employee satisfaction as potential measures of leadership effectiveness. This study evaluates a behavioral and a value-based leadership theory and provides evidence consistent with both. The findings do not point to a strong direct relation between employee satisfaction and project success. However, the results do offer two sets of unique leadership characteristics, one with a strong relation to employee satisfaction and one with a strong relation to project success. / by Valerie Kuo. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007. / Includes bibliographical references (p. 119-124). / In nature, one finds many examples of collective motion, from flocking birds to swarming bees. Any one organism makes its decisions based solely on local information; either it can sense what its close neighbors are doing, or in the case of a single-celled organism, it can sense some local property of its environment. Yet complex global behaviors arise from these local interactions, and these large-scale patterns have neither a leader nor any other centralized control system. In this thesis, two specific cases of collective motion are studied: fish schooling and bacteria swimming across a surface. When fish swim in schools, they swim in the same direction as each other at approximately the same speed. Previous studies of fish have discovered three primary behaviors that, together, lead to large-scale coordination and schooling in the animals. This thesis demonstrates that the same algorithms can be applied to a group of identical underwater robots. If the robots need to coordinate with each other, they can use biomimetic control laws and adopt the interaction algorithms used by fish. A series of simulations are run to see what possible group behaviors can come from these control laws. At a smaller scale, prior experiments have revealed that bacteria and other small organisms also show collective motion. / (cont.) Unlike fish, bacteria cannot see their neighbors; the individual can only sense the bulk contribution of its neighbors to the flow at its location. The single-celled organisms are small and swim slowly, so they have very small Reynolds numbers. They are modeled in this work in a Stokes flow regime; the model is built bottom-up starting from the hydrodynamic field created by one organism and then superimposing these fields on top of each other. Different possible control policies are tested where each organism has an instantaneous desired direction based on some local property of the flow. While simulations of the current model do not yield results that fully emulate real bacteria, they have some similarities and provide insight into the complex hydrodynamic interactions between low Reynolds number swimmers. / Joanna Cohen. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998. / Includes bibliographical references (leaves 72-77). / by Anthony Christopher Leier. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009. / Includes bibliographical references (leaves 53-54). / Thermal management is a critical challenge for a variety of applications including integrated circuits (ICs) and energy conversion devices. As the heat fluxes exceed 100 W/cm2, novel cooling solutions need to be developed. Thin film evaporation is a promising approach because the large latent heat associated with phase change can be utilized while the thermal resistance associated with the liquid film thickness can be minimized. However, traditional thin film evaporation schemes such as jet impingement and sprays suffer from several limitations, such as high power consumption, complex flow patterns, and localized cooling. In this thesis, micro- and nanostructured surfaces were investigated to enhance fluid and heat transport for thin film evaporation. This thesis includes studies of fluid interactions on surfaces with micro- and nanopillar arrays with diameters and spacings ranging from 500 nm to 10 [mu]m. First, liquid transport studies were performed where a propagating liquid on an array of pillars with scalloped features can separate into multiple layers of liquid films. The scallops were found to act as energy barriers that favored liquid separation into several layers. An analytical model based on surface energy was developed to explain the phenomenon and was validated by experiments on additional tailored pillar geometries. Subsequently, a semi-analytical model was developed to predict the propagation velocity based on Modified Washburn's Model to optimize propagation of the liquid. The results were validated by measurements of liquid propagation velocity on micropillar arrays with various geometries. / (cont.) Finally, the heat transfer performance was investigated on microstructure pillar arrays with integrated heaters and temperature sensors. These test devices were fabricated and the behavior of the thin liquid film under varying heat fluxes was investigated, where a two-step "dry-out" behavior was observed. The thermal resistance of the thin film including the effect of the micropillars was also analyzed. This work demonstrates the potential of micro- and nanostructures to achieve high heat fluxes via thin film evaporation. / by Rong Xiao. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 25). / Energy generated from offshore resources is not reliable over short periods of time. Although wind and wave energy is fairly consistent in the long run, their short term capacity fluctuations prohibit these resources from replacing dependable fossil-fuel based energy systems. This limitation could be overcome if the energy harvested from these resources could be stored temporarily and then released when needed. The large hydrostatic head at the ocean floor provides a unique opportunity for storing energy offshore. Similar to hydroelectric dams storing water at a high potential, energy could be stored offshore by displacing water from a subsea chamber. This chamber could be incorporated into the mooring system of present offshore harvesting devices to yield more favorable economics. This report establishes the baseline assumptions for designing this energy storage device and proposes a methodology for constructing a beta level prototype. In addition to discerning the tradeoffs between different design options with respect to the marine environment, this study analyzes the cost of this structure per unit energy stored. The contents of this report comprise of the following. First, the hazards inherent to the marine environment are explored qualitatively, and methods to address these issues are proposed. Second, the chamber shape, mooring type, and amount of material are determined based on their respective costs. Finally, this report concludes with the final dimensions of a proposed beta prototype and a list of recommendations for future work. / by Alison S. Greenlee. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 62). / This thesis addresses control-oriented modeling of urea-selective catalytic reduction (SCR) after-treatment systems used for reducing NO, emission in diesel vehicles. Starting from first-principles, appropriate simplifications are made in the underlying energy and species equations to yield simple governing equations of the Urea-SCR. The resulting nonlinear partial differential equations are discretized and linearized to yield a family of linear finite-dimensional state-space models of the SCR at different operating points. It is shown that this family of models can be reduced to three operating regions that are classified based on the relative NO, and NH3 concentrations. Within each region, parametric dependencies of the system on physical mechanisms are derived. A further model reduction is shown to be possible in each of the three regions resulting in a second-order linear model with sufficient accuracy. These models together with structured parametric dependencies on operating conditions set the stage for a systematic advanced control design that can lead to a high NO, conversion efficiency with minimal peak-slip in NH3. All model properties are validated using simulation studies of a high fidelity nonlinear model of the Urea-SCR, and compared with experimental data from a flow-reactor. / by Hanbee Na. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 63-65). / In this thesis, the author introduces the first fully unreleased Micro-Electro-Mechanical (MEM) resonator, and the design of acoustic Bragg reflectors (ABRs) for energy localization and quality factor (Q)- enhancement for unreleased resonators. Two of the greatest challenges in MEMS are those of packaging and integration with CMOS technology. Development of unreleased MEMS resonators at the transistor level of the CMOS stack will enable direct integration into front-end-of-line (FEOL) processing, making these devices an attractive choice for onchip signal generation and signal processing. The demonstrated first fully unreleased resonator exhibits a resonance at 39 GHz with a Q of 129, corresponding to the 1st harmonic longitudinal resonance of the unreleased resonator, a silicon Resonant Body Transistor (RBT) fully clad in Si0 2. A spurious mode occurs at 41 GHz, which is in good correspondence with simulation results. The Q of 129 at 39 GHz is about 4 times lower than that of its released counterpart. Enhanced with the ABRs, the unreleased resonator is able to maintain high Q, and suppress spurious modes. Analysis on the ABR design for unreleased resonators covers design principles, fabrication variations, and comparison to released devices. In the end, it is demonstrated that the ABR is more favorable than the phononic crystal for acoustic energy localization for unreleased resonators, providing a 9 times higher Q. / by Wentao Wang. / S.M.