Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 26). / Have cell phones and the Internet created a revolution in the way that protests are organized? Or are they merely a substitution for previous methods of communication? The literature on the topic is divided between the cyberphiles, who argue that information and communication technologies (ICTs) allow individuals to better organize and amplify social movements and the cyberskeptics, who reject the idea that ICT represents a different mechanism of communication and instead argue that protests stem from underlying structural issues. I analyze protests from the Arab Spring and the dissolution of the Soviet Union in order to answer the question of substitution versus revolution. Through my empirical analysis, I find that cell phone subscriptions correlate positively with protest size, meaning countries with more cell phone subscriptions experienced larger protests, ceteris paribus. I did not, however, find the same result with Internet usage. My findings support the "amplification model" - that ICT amplifies existing social movements - but with some added nuance. I argue that the Internet amplifies information about protests to the wrong individuals - namely Internet users abroad who cannot participate in protests - while cell phones are used for domestic communication and thus increase the size of protests. / by Joseph P. Schuman. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 51-54). / Our ability to move across various terrains depends heavily on the mechanical interactions between our feet and the external environment. Understanding how to best replicate mechanoreceptors in feet can lead to major improvements in plantar sensing for athletic performance analysis and medical devices. However, current plantar sensing technologies are unable to meet the associated demands for accuracy, sensitivity, and durability. In addition, current sensors are also unable to withstand the large impact forces and inertial noise associated with human locomotion. To address this issue, this thesis investigates alternative designs for a tactile force sensors that are largely inspired by mechanoreceptors found in human skin. Two different sensing methodologies will be analyzed: piezoresistive elastomer and Hall-effect integration. The piezoresistive elastomer method will involve testing mixtures of urethane or silicone rubbers with various conductive substances such as carbon black. Compressing the sensors at various forces will correspond to lower resistance measurements as more electrical connections are made by the conductive particulates. Though these designs have high sensitivity to changes in force, the resulting data is inconsistent and slow to stabilize due to material creep. The Hall-effect integrated method will involve a magnet and four Hall-effect sensors molded in an elastomer matrix. Compressing the sensors will register different readings in each of the four embedded Hall-effect sensors which will correspond to a certain shear and deflection measurement. This sensor design shows promise as a cost-effective plantar sensor, but additional analysis is needed. / by Ann (Annie) Chen. / S.B.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 73-78). / Autonomous driving on highways and freeways, as a feature, is already available in quite a few high-end commercial vehicles being sold today. Autonomous driving in urban environments, on the other hand, is still an active area of academic and industrial research [6], because of its relatively complex nature. Urban driving requires the self-driving vehicle to interact with not just other vehicles, but also other moving agents such as cyclists and pedestrians. Pedestrian trajectory prediction is challenging because of the relatively higher number of degrees of freedom in pedestrian movement and absence of uniform rules across different cities and different scenarios within a city. Furthermore, in scenarios such as intersections, context, such as pedestrian traffic lights, stop signs and sidewalk geometry, significantly influences pedestrian movement. The objective of this thesis is to present a general, context-aware, long term (order of few seconds) trajectory prediction model for pedestrians in urban intersections. To meet this objective, first, the Augmented Semi Nonnegative Sparse Coding (ASNSC) [13] framework, for trajectory prediction, is extended to embed context, and build the Context-aware Augmented Semi Nonnegative Sparse Coding (CASNSC) algorithm. For prediction in new, unseen intersections with different curbside geometries (orthogonal versus skewed), CASNSC is further extended to build the Transferable Augmented Semi Nonnegative Sparse Coding (TASNSC) algorithm. Urban intersections can at times vary significantly in the type of pedestrian behaviors encountered, even across intersections with similar geometries. For instance, faster, rule breaking students near a college campus versus slower pedestrians in a residential area. While TASNSC is capable of successfully transferring knowledge from one intersection to another, it lacks the ability to update its prediction model as, and when, new intersections are visited and novel behaviors are encountered. An online model, based on TASNSC, is also presented in this thesis to account for this particular limitation. / by Nikita Jaipuria. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 87-88). / Solar power plants with surface receivers have low overall energy conversion efficiencies due to large emissive losses at high temperatures. Alternatively, volumetric receivers promise increased performance because solar radiation can be transferred into a fluid medium, which subsequently reduces the concentrated heat at the surface. Nanofluid-based direct solar receivers, where nanoparticles in a liquid medium can scatter and absorb solar radiation, have recently received interest to efficiently distribute and store the thermal energy. In this thesis, a combined modeling and experimental study to investigate the efficiency of fluid-based solar receivers seeded with carbon-coated absorbing nanoparticles is presented. The ability to tune the absorption in a volumetric receiver using the volume fraction of nanoparticles was demonstrated using a semi-empirical method to model the radiative properties of the nanofluid. A volumetric receiver was designed and built to experimentally demonstrate the concept of nanofluid-based receivers and validate the modeling efforts. A one-dimensional combined radiative and heat transfer model was developed to compare idealized surface receivers to idealized volumetric receivers. The effect of particle characteristics such as distribution and selectivity, as well as collector parameters such as absorbing height and level of solar concentration was investigated. In the limit of idealized behavior, non-selective volumetric receivers were shown to be more efficient than selective-surfaces for high concentration levels (C> 100) and/or tall receiver designs (H > 10 cm). The numerical results indicate a major benefit of using volumetric receivers: they are more efficient at higher levels of concentration and can lead to ideal power generation efficiencies exceeding 55% in these regimes. The work offers design guidelines for the development of efficient volumetric receivers for future solar thermal energy conversion systems. / by Andrej Lenert. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001. / Includes bibliographical references (p. 205-209). / Two design methods are explored to reduce vibration, minimize unwanted acoustic noise, and increase stiffness in structures. The first design approach is to create nearly isotropic panels with increased stiffness using two-dimensional curvature. These quasi-isotropic designs can be used in lieu of typical panel reinforcements, and can provide an inexpensive alternative to honeycomb sandwich designs. The second approach is to design panels formed into the shape of a mode shape to reduce detrimental modal dynamics. The effects of combining the two-dimensionally curved designs with constrained layer damping is also investigated. Further, it is also the goal of this research that these panels can be inexpensively manufactured with current manufacturing methods (e.g. stamping, rolling, thermoforming, etc.), resulting in a more effective structural element that does not require significant extra cost or weight. Initial analysis was performed using geometric modeling and finite element analysis. Experimental analysis involved both static and dynamic system identification. The experimental results indicate that quasi-isotropic designs can be accomplished with two-dimensional curvature. / (cont.) These quasi-isotropic designs increase the stiffness of a panel and raise the natural frequency by a factor of 2 (compared to a flat panel of the same mass). Although the quasi-isotropic designs have no acoustic benefit, they were shown to be effective replacements as honeycomb cores. The mode-shaped designs demonstrated the unique quality of simultaneously reducing vibration and acoustic noise over a broad frequency range (50-10,000 Hz). The mode-shaped panels demonstrated a factor of 3 increase in the natural frequency, a ten-fold reduction in dynamic deflection displacements, and a 3 to 4 dB RMS reduction in the radiation index over a broad frequency range. / by Donald Quinn O'Sullivan. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 90-92). / Electrodes are necessary components for measuring changes in electrical properties in many microfluidic devices. Daktari CD4 Cell Counter system utilizes an interdigitated electrode foil in order to measure the concentration of the CD4 cells in an assay chamber by measuring the impedance drop. Thus the consistency in the dimensions of the interdigitated fingers in the electrode is critical to the repeatability of impedance measurements. This work involved a thorough variation analysis of the electrode dimensions to characterize the repeatability of the new manufacturing process developed by Daktari. For this purpose optical imaging was used to obtain high-resolution images of the electrodes and an algorithm was developed in order to estimate the critical dimensions of interdigitated fingers from the images. The results showed that the dimensional variation in the electrodes had insignificant effect on the performance of the electrodes and that the new manufacturing process is capable of producing satisfactory electrodes within the desired target. The relation between the electrode's dimensional variations was found and the effect of critical process parameters was determined in order to maintain the process statistically in control. / by Kasra Namvari. / M.Eng.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008. / Includes bibliographical references (p. 129-135). / A new technology is proposed for lightweight, high density energy storage. The objective of this thesis is to study the potential of storing energy in the elastic deformation of carbon nanotubes (CNTs). Prior experimental and modeling studies of the mechanical properties of CNTs have revealed nanoscale structures with a unique combination of high stiffness, strength and flexibility. With a Young's modulus of 1 TPa and the ability to sustain reversible tensile strains of 6% [1, 2] and potentially as high as 20% [3-5], mechanical springs based on these structures are likely to surpass the current energy storage capabilities of existing steel springs and provide a viable alternative to electrochemical batteries. Models were generated to estimate the strain energy of CNTs subject to axial tension, compression, bending and torsion. The obtainable energy density is predicted to be highest under tensile loading, with an energy density in the springs themselves about 2500 times greater than the maximum energy density that can be reached in steel springs, and ten times greater than the energy density of lithium-ion batteries. Practical systems will have lower overall stored energy density once the mass and volume of the spring's support structure and any additional extraction hardware are taken into account, with a maximum achievable stored energy density predicted to be comparable to lithium-ion batteries. Due to the poor load transfer between MWCNT shells and the radial deformation of larger SWCNTs, bundles of SWCNTs with diameters of 1 nm or smaller are identified as the best structure for high-performance springs. The conceptual design of a rechargeable portable power source is developed as a tool to study the performance and feasibility of building such a device. / (cont.) In this design, energy is stored in a grouping of denselypacked, aligned CNTs stretched in tension. The design includes an escapement mechanism to regulate the. energy release from the spring and a generator to convert the output work from the spring into the electrical domain. The results indicate that the performance of the power source scales well with size so there is flexibility in choosing the overall scale of the device. Achieving a high fraction of CNTs in the overall device proved to be challenging. Future work should concentrate on building and testing high-quality, densely-packed macroscale SWCNT assemblies that are expected to form the basis of super-springs for implementation into practical devices. / by Frances Ann Hill. / S.M.