Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997. / Includes bibliographical references (p. 86-89). / by Sangmyeong Han. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008. / Includes bibliographical references (p. 73-74). / The photoplethysmogram (PPG) is an extremely useful wearable sensing medical diagnostic tool. However, the PPG signal becomes highly corrupted when the wearer is in motion, rendering the measured signal useless. This thesis develops an adaptive motion artifact reduction scheme to recover the underlying physiologic information from the corrupted signal using a collocated accelerometer as a motion reference and adaptively estimating the motion-to-artifact system dynamics. It has previously been shown that this artifact reduction scheme can be utilized, but many tunable parameters were required to model the system dynamics and performance was poor. This work quantifies algorithm performance based on confidence in the estimated system dynamics, which shows low confidence using the previous parameterization when the wearer is jogging. To improve confidence, the form of the system dynamics is established and a Laguerre series is implimented to compactly represent the system dynamics using just a few parameters that can be confidently estimated. Using the new model, heart rate and amplitude can be estimated from typical jogger data with variance similar to separate PPG sensors located on contralateral motionless hands. The standard artifact reduction scheme does not work when the physiologic signal is correlated with wearer motion. Since the signals may become correlated, this work develops a method of recovering the physiological signal even when it is correlated with wearer motion by adapting blind source seperation techniques. However, the success of this new method is limited. / by Levi Benjamin Wood. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1993. / Includes bibliographical references (leaves 68-70). / by Jeffrey Paul Hebb. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 69-71). / Incidence of surgical site infection is two to five times higher in developing nations as compared to developed nations. Autoclaves kill all dangerous pathogens, including heat-resistant endospores, and are an essential tool to achieving and maintaining a sterile environment, which decreases risk of infection. A low-cost, easy to use autoclave was designed to address the unique technical, behavioral, and market challenges present in rural health posts of the developing world. A thorough stakeholder analysis was performed very early in the design process to address needs for sustained user adoption as well as manufacturability and scalability. Twelve partnering clinics in Nepal trialed these autoclaves from July until December 2012. Usage statistics from this period and follow-up observations highlight important factors for successful adoption. These findings were used to improve the autoclave design in a second iteration. / by Gregory Tao. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2000. / Includes bibliographical references (p. 83-84). / by Caroline Combescot. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Nanostructured surfaces have given rise to many unique optical properties, such as broadband anti-reflectivity, structural coloring effects, and enhanced light extraction from high refractive index materials due to their potential to modulate optical behavior on their surfaces. This thesis focuses on design, analysis, and fabrication of functional nanostructured surfaces for efficient light transport, seeking optimized optical performance, high mechanical robustness, and manufacturability, with the aim of increasing the practicality of the photonic nanostructures. First, for the case when light propagates from a low-index material to a high-index material, I designed and fabricated an array of inverted nanocones that realizes anti-reflectivity with robust mechanical strength. The surface exhibits broadband, omnidirectional anti-reflectivity due to the axially varying effective refractive index of the inverted nanocone arrays. The surface also maintains its optical performance after being externally loaded, thanks to low stress concentration and small deflection of the inverted nanocone structure. In addition, for multi-optical interfacial surfaces, double-gradient- index nanostructures are proposed and demonstrated in order to achieve ultimate anti-reflectivity. The top surface, textured with inverted nanocones, maintains high mechanical robustness. Second, for the case where light has to be extracted from high-index materials, a conical photonic crystal is proposed and demonstrated. The tapered conical geometry suppresses Fresnel reflections at the optical interfaces due to adiabatic impedance matching. Periodicity of the arrays of cones diffracts light into higher-order modes with different propagating angles, enabling certain photons to overcome total internal reflection (TIR). After optimizing the structural geometries to balance Fresnel reflection and TIR, light yield efficiency is characterized experimentally on scintillator surfaces. In order to enhance the adaptability to industrial manufacturing, the fabrication methods are based on replicating the photonic nanostructures into a UV-curable polymer, with the help of laser interference lithography as a method of fabricating a master mold. Advanced techniques such as vacuum assisted-filling and a selective delaminating method are also developed to produce nanostructures more effectively. The novel nanostructured surfaces designed in the thesis, and the ability to imprint these topographies through several generations, are promising for large-scale commercial applications where efficient light transport is important. / by Jeong-Gil Kim. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 187-195). / Vibration energy harvesters work effectively only when the operating conditions match with the available vibration source. Typical resonating MEMS structures cannot be used with low-frequency, low-amplitude and unpredictable nature of ambient vibrations. Bi-stable nonlinear oscillator based energy harvesters are developed for lowering the operating frequency while widening the bandwidth, and are realized at MEMS scale for the first time. This design concept does not rely on the resonance of the MEMS structure but operates with the large snapping motion of the beam at very low frequencies when proper conditions are provided to overcome the energy barrier between the two energy wells of the structure. A fully functional piezoelectric MEMS energy harvester is designed, monolithically fabricated and tested. An electromechanical lumped parameter model is developed to analyze the nonlinear dynamics and to guide the design of the multi-layer buckled beam structure. Residual stress induced buckling is achieved through the progressive control of the deposition along the fabrication steps. Static surface profile of the released device shows bi-stable buckling of 200 [mu]m which matches very well with the design. Dynamic testing demonstrates the energy harvester operates with 35% bandwidth under 70Hz at 0.5g, operating conditions that have not been met before by MEMS vibration energy harvesters. / by Ruize Xu. / Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 107-122). / Protein-surfactant mixtures appear in many industrial and biological applications. Indeed, a fluid as vital as blood contains a mixture of serum albumin proteins with various other smaller surface-active components. Proteins and other surface active molecules are often adsorbed at an air-liquid or liquid-liquid interface due to favorable thermodynamics, and these interfaces play a role in such diverse fields as stabilizing foams and emulsions, controlling high speed coatings, the blood clotting process, designing synthetic replacements of biological fluids, etc. It is thus important to understand the interfacial behavior of protein-surfactant mixtures, especially the role it can play in bulk measurements of material properties. A complete description of the dynamics of these multi-component systems is still elusive. In this thesis, a comprehensive study of the rheology of a model globular protein solution is described. In conventional bulk rheological studies of globular protein solutions a yield-like behavior and shear thinning in the viscosity at low shear rates is observed, even for concentrations as low as 0.03% by weight. Typical explanations for this yield stress involve the introduction of long range colloidal forces that are stronger than electrostatic forces, and which stabilize a colloidal structure formed by the protein molecules. However, evidence for this structure from small angle X-ray scattering and small angle neutron scattering is lacking. In the first part of this thesis, it will be shown using interfacial steady and oscillatory shear experiments how the yield-like behavior observed in bulk rheology in fact arises out of a purely interfacial effect. We show that the yield-like behavior and shear-thinning observed in bulk rheology can be modeled by treating the interfacial layer of the adsorbed protein as a pure plastic material that yields at a critical strain. This model also accounts for the geometric dependence seen in bulk rheology experiments. The second part of this thesis investigates the rheological consequences of adding low molecular weight surfactants to globular protein solutions. Because non-ionic surfactants compete for the interface with the protein molecules, the resulting dynamics at the fluid interface can be complex. In addition to steady and oscillatory interfacial shear rheology, a new phenomenon called interfacial creep ringing-a term used to denote the periodic oscillations arising from the coupling between instrument inertia and interface elasticity-arises. It is demonstrated how these damped inertioelastic oscillations can be used to rapidly estimate interfacial viscoelastic moduli and also study the effect of the addition of non-ionic surfactants to globular protein solutions. We show that exploiting the interfacial creep ringing technique is useful as a way to rapidly determine the effects of interfacial viscoelasticity. It is also observed that increasing the concentration of the competing surfactant leads to progressively decreasing ringing frequencies and amplitudes, until visible ringing completely disappears beyond a certain concentration. Finally, we indicate future avenues of work including surface particle tracking to study these complex dynamics of protein surfactant mixtures. / by Aditya Jaishankar. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1990. / Includes bibliographical references (leaf 75). / by Woojin Lee. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007. / Includes bibliographical references (p. 105-116). / The reduction of oxygen from an organic phase dispersed in a concentrated electrolyte is investigated. Dispersed organic phases are used to enhance oxygen transport in fermenters and artificial blood substitutes. This work evaluates the feasibility of using a dispersed organic phase to transport oxygen in a fuel cell. An emulsion of perfluorohexane in a 20 wt% potassium hydroxide solution was formed with a lecithin surfactant. Oxygen was reduced from the emulsion on a rotating disk electrode. The dispersed phase did not contribute to the oxygen transport to the surface of a rotating disk electrode. An explanation is given based on the hydrodynamics of an emulsion under a rotating disk electrode. To eliminate the effect of hydrodynamics, the results of a hydrostatic transient diffusion experiment (Cottrell Experiment) are reported. Again, no significant enhancement of the oxygen transport rate was observed. The dispersed phase is shown to contain oxygen by NMR spectroscopy. It is argued that the expectation of an enhancement from the use of a dispersed phase may be based on inapplicable transport models. The presence of the lecithin surfactant may also impede transport. An oscillating electrode is used to reduce oxygen from a continuous perfluorohexane phase. In this case, the rate of reduction of oxygen is limited by diffusion across an aqueous layer trapped at the surface of the electrode by its relative affinity for aqueous solution over perfluorohexane. The implications for the use of a dispersed organic phase in fuel cells are discussed. The use of a rotating disk electrode in heterogeneous media and the need for a mass transport model in liquid-liquid dispersions are also discussed. / by Omar H. Roushdy. / Ph.D.