Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001. / Includes bibliographical references (p. 74-75). / by Nin C. Loh. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004. / Includes bibliographical references (p. 161-167). / Atherosclerosis is an inflammatory disease characterized by an accumulation of lipid and fibrous tissue in the arterial wall. Postmortem studies have characterized rupture-prone atherosclerotic plaques by the presence of a large lipid-rich core covered by a thin fibrous cap. Studies employing finite element analysis (FEA) based on ex vivo plaque geometry have found that most plaques rupture at sites of high circumferential stress, thus diagnosis of plaque vulnerability may be enhanced by probing the mechanical behavior of individual plaques. Elastography is a method of strain imaging in which an image sequence of the artery undergoing deformation is acquired, pixel motion is estimated between each frame, and the resulting velocity field is used to calculate strain. In this thesis, optical coherence tomography (OCT), a high-resolution optical imaging modality, is investigated as a basis for FEA and elastography of atherosclerotic plaques. FEA was performed using plaque geometries derived from both histology and OCT images of the same plaque. Patterns of mechanical stress and strain distributions computed from OCT-based models were compared with those from histology-based models, the current gold standard for FEA. The results indicate that the vascular structure and composition determined by OCT provides an adequate basis for investigating the biomechanical factors relevant to atherosclerosis. A new variational algorithm was developed for OCT elastography that improves upon the conventional algorithm by incorporating strain smoothness and incompressibility constraints into the estimation algorithm. / (cont.) In simulated OCT images, the variational algorithm offers significant improvement in velocity and strain accuracy over the conventional algorithm, particularly in the presence of image noise. Polyvinyl alcohol (PVA) phantoms of homogeneous and heterogeneous elastic modulus distribution were developed for further testing of the variational algorithm. Testing with the phantoms indicated that motion- and strain-induced decorrelation between images presents a practical challenge to the implementation of OCT elastography. Analysis of the experimental results led to the identification of potential improvements to the elastography algorithm that may increase accuracy. These improvements may include relaxation of the strain smoothness constraint to incorporate strain discontinuities at boundaries of elastic modulus in heterogeneous regions, and enforcement of geometry compatibility to prevent the estimation of non-physical velocity fields. / by Alexandra H. Chau. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995. / Includes bibliographical references (leaves 111-117). / by Michael B. Binnard. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1964. / MICROFICHE COPY AVAILABLE IN ENGINEERING. / Appendix contains numerous pamphlets. / Includes bibliographical references (leaves 46-48). / by Thomas Dormer, Jr. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1993. / Includes bibliographical references (leaf 82). / by Aris G. Constantinides. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 50-52). / Multiphase flows in microchannels are encountered in a variety of microfluidic applications. Two-phase microchannel heat sinks leverage the latent heat of vaporization to offer an efficient method of dissipating large heat fluxes in a compact device. In microscale methanol-based fuel cells, the chemical reactions produce a two-phase flow of methanol solution and carbon dioxide gas. Differences in the underlying physics between microscale and macroscale systems, however, provide a new set of challenges for multiphase microscale devices. In thermal management devices, large pressure fluctuations caused by the rapid expansion of vapor are prevalent in the flow channels. In fuel cells, the gaseous carbon dioxide blocks reaction sites. In both of these cases, dry-out is a problem that limits device performance. We propose a design for a microscale breather that uses surface chemistry and microstructures to separate gas from a liquid flow to improve two-phase microchannel performance. To better understand the physics and governing parameters of the proposed breather, we have designed and fabricated test devices that allow cross-sectional visualization of the breathing events. We have conducted various experiments to examine the effects of device channel hydraulic diameters ranging from 72 [mu]m to 340 [mu]m and liquid inlet flow rates ranging from 0.5 cm/s to 4 cm/s on the maximum gas removal rate. We demonstrated a maximum breather removal rate of 48.1 [mu]l/min through breather ports with a hydraulic diameter of 4.6 [mu]m connected to a microchannel with a hydraulic diameter of 72 [mu]m, and a liquid inlet flow velocity of 0.5 cm/s. A model was developed that accurately predicts the exponential dependence of the maximum gas removal rate on a non-dimensional ratio of the pressure across the breather ports compared to the pressure drop in the main channel caused by the venting bubble. / (cont.) These results serve as design guidelines to aid in the development of more efficient and sophisticated breathing devices. The successful implementation of a microchannel with an efficient breather will allow for new technologies with higher heat removal capacities or chemical reaction rates that can be effectively used by industry. / by Brentan R. Alexander. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998. / Includes bibliographical references (leaves 63-66). / One to three percent of the Open Heart Surgery procedures have abnormal bleeding due to acquired platelet dysfunction. Standard clotting tests to determine the cause of bleeding usually take between 25 and 60 minutes to get results. This time frame is not useful for deciding what type of treatment to give to a patient. More importantly, the standard clotting tests is they cannot determine platelet function. The Thrombo-Visco Elastogram (TVE) is a new test that provides results in less than 15 minutes and has the potential to evaluate platelet function. In this study, we used the TVE test to assess viscoelasticity of clotting blood from patients before and after CPB. For each patient and condition, we tested the blood alone and after incubation with a saturation concentration of ReoProTM, a glycoprotein Ilb/Illa inhibitor. The major findings of this study are: 1) The TVE device is capable of determining with accuracy quantitative changes in blood viscoelasticity during clotting; 2) The TVE-derived coagulation parameters maximum elastic modulus (Emax), maximum rate of change of elastic modulus (E'max), maximum viscosity ([eta]max), and maximum rate of change of viscosity ([eta]'max) and the coagulation parameters prothrombin time (PT), platelet count, fibrinogen concentration and hematocrit are all affected by CPB; 3) The TVE-derived parameters were all substantially affected by incubation of the blood with the platelet GP inhibitor suggesting that these parameters are exquisitely sensitive to platelet function; and 4) In ReoProTM-free blood samples, values of E'max for all patients, before and after CPB, could be predicted as a function of platelet count, fibrinogen concentration and hematocrit. We concluded that the TVE/ReoProTM assay has the potential to assess the contribution of platelet function and soluble components to coagulation in a quantitative, reproducible and practical manner. / by Peta Gaye Sonya Whitbourne. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Growing concern over greenhouse gas emissions has driven research into clean coal power production alternatives. Novel coal power plant designs that lower CO2 emissions are imperative in the coming decades to mitigate global temperature rise. High-efficiency stationary power systems that integrate coal gasification with solid oxide fuel cells (SOFCs) have been championed by the Department of Energy for the past couple of decades. However, many fundamental questions about this system still need to be addressed by modeling the complex coupling between SOFC's and gasification. More specifically, work is needed to characterize SOFC performance with a range of syngas (H₂+CO) mixtures produced by coal gasification. This thesis used a multiscale modeling approach to analyze SOFC performance with coal syngas at both the systems level and at the surface reaction scale. The first investigation in this thesis couples an equilibrium gasifier model to a detailed ID SOFC model to study the theoretical performance of the coupled system run on steam or carbon dioxide. The results of this study indicate that the system performs substantially better with steam gasification than with CO₂ gasification as a result of the faster electro-oxidation kinetics of H₂ relative to CO. The coupled system is then shown to reach higher current densities and efficiencies when the heat released by the fuel cell is sent to the gasifier instead of a bottoming cycle. 55-60% efficiency is then predicted for the system with heat transfer and steam gasification, making this technology competitive with other advanced system designs and almost twice as efficient as conventional coal-fired power plants. The second study in this thesis investigates SOFC behavior with H₂ and CO (syngas) mixtures that come from coal gasification. SOFC models typically neglect CO electrochemistry in the presence of H₂ and H₂0, assuming that the water-gas-shift reaction proceeds faster than CO electrooxidation. The results of this study show, however, that CO electro-oxidation cannot be neglected in syngas mixtures, particularly at high current densities for high CO-content syigas. First the simulations demonstrate that incoming CO is not all shifted to form H₂ by reforming reactions before reaching the electrochemical reaction sites. Furthermore, the results of this 'study confirm that direct electro-oxidation of CO contributes non-negligible current relative to H₂ at high anode overpotentials. Together these results show that CO electro-oxidation plays an important role in SOFC performance not only via water-gas-shift reforming, but also via direct electro-oxidation when H₂ is also present. This work suggests that accurate models for both surface reforming and direct electro-oxidation of CO in SOFC anodes must be included in order to capture performance when using coal syngas mixtures. Finally, a multi-step mechanism for the simultaneous electro-oxidation of H₂ and CO in SOFCs is implemented and studied. This mechanism combines a couple of reaction pathways: hydrogen (H) spillover to the electrolyte, and oxygen (O) spillover to hydrogen and CO on the anode. This mechanism is successfully verified in the model against a wide range of experimental data for mixtures of CO/CO₂, H₂/N₂, H₂/H₂0, H₂/CO, and H₂/CO₂ . The simulations show that H spillover is the dominant source of current at low anode activation overpotentials, but also demonstrate that the currents produced by 0 spillover are non-negligible at high overpotentials. Furthermore, it is shown that the current produced by 0 spillover to CO is not limited by the rate of CO adsorption on nickel, which leads CO to contribute more to cell performance at high currents. Together these three modeling studies demonstrate how coal can be efficiently converted to electricity via gasification and the simultaneous electro-oxidation of H₂ and CO in a solid oxide fuel cell. / by Katherine M. Ong. / Ph. D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006. / Includes bibliographical references (leaf 34). / This paper investigates computer simulations of deterministic and exponential models of a production line with full-batch processing and a finite buffer in order to validate the theoretical models already developed, and to gain more insight to the production line behavior through the simulations. The steady-state overall production rate is the performance measure that is used to compare systems. The effects of buffer size, repair rate, and machine size on the production rate; the conditions of ergodicity; and the differences between the deterministic model and the exponential model are discussed. / by Ying Zheng. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007. / Includes bibliographical references (p. 131-137). / Electromechanical probing applications continuously require smaller pitches, faster manufacturing and lower electrical resistance. Conventional techniques, such as MEMS based cantilever probes have their shortcomings in terms of the lowest pitch that can be achieved, cost and yield. Given their promising mechanical and electrical properties, carbon nanotubes (CNTs) are strong candidates for future probing applications. A new class of metal-CNT hybrid electromechanical probes is presented where vertically aligned carbon nanotube structures, grown with a chemical vapor deposition (CVD) technique, act as elastic springs, and a metal coating on the probes is used for increased electrical conduction. This design and architecture presents a scalable approach where thousands of probes can be fabricated in very short production times. 1.5 Ohm resistance and reliable performance for 6000 cycles at 50 [mu]m over-travel was achieved for a column of 200 [mu]m x 200[mu]m cross-section and 1plm of Au deposition. In-situ scanning electron microscope mechanical compression tests revealed a unique deformation mechanism of the CNT structures where continued compression results in successive buckle formation which later can serve as micro-bellows and elastic springs. / (cont.) A novel stiffness tuning method is presented to control the elastic properties of a given CNT probe by controlling the initial compressing amount. Further stiffness tuning is achieved by changing gas composition during CVD growth where CNT diameter and density is modified. Lateral compression and densification tests show that these CNT structures are highly anisotropic and have very different deformation mechanisms in vertical and lateral directions. Mechanical properties resulting from two main CVD growth techniques, namely fixed catalyst where a thin film of catalyst layer is deposited onto the growth substrate, and floating catalyst where the catalyst particles are introduced in the gas phase, are compared. It is found that floating catalyst CVD growth yields much stiffer structures due to the relatively larger CNT diameters. As the adhesion of CNT structures to the growth substrate is very weak and the support layer is typically an insulator, a versatile transfer printing technique is developed which enables simultaneous placement and reinforcement of the probes on a wide range of substrates, including metals and printed circuit boards. Electromechanical performance and failure mechanisms of fully functional metal-CNT hybrid probes are presented. / by Onnik Yaglioglu. / Ph.D.