Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 39-40). / This thesis investigates the role of mass flux on flow boiling heat transfer in microchannels with surface micropillar arrays. The motivation for this investigation was to determine the general trends of the optimal micropillar array geometry in terms of its heat transfer capabilities. The experiment was conducted with three microchannels: a flat surface microchannel, a sample called the 5-15 (height h = 25 [mu]m, diameter d = 5 [mu]m, and pitch l = 15 [mu]m) and a sample called the 10-40 (height h = 25 [mu]m, diameter d = 10 [mu]m, and pitch l = 40 [mu]m). The structured surface microchannels, due to their capillary pressure-induced wicking capabilities, exhibited less temperature rise and pressure drop fluctuations at high heat fluxes. Furthermore, it was verified that the critical heat flux value of all microchannels increased with mass flux. In addition, it was concluded that at lower mass fluxes, the relative percentage heat transfer enhancement of the structured surface microchannels over the flat surface microchannel was greater. The trend observed suggests that denser samples are better at lower mass fluxes. However, if a sample is too dense, there may be too much viscous drag. Thus, an optimal balance between capillary force and viscous drag must be found in order to determine the optimum micropillar array geometry and density for maximizing the critical heat flux value. Finally, for a given mass flux, the pressure drop across every microchannel was approximately equal at all heat fluxes. This implies that no additional power consumption is required to pump a particular mass flux through a structured surface microchannel than a flat surface microchannel, though there is certainly additional power required to increase the mass flux. This work provides insights into the roles of both the micropillar array surface structures and the mass fluxes on the heat transfer performance of flow boiling in microchannels. The results and observations of this experiment may prove helpful in guiding future work in an attempt to optimize microchannels for heat transfer applications in electronics. / by David Bian. / S.B.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1993. / Includes bibliographical references (p. 83-84). / by Christopher Eric Kim. / M.S.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 24-25). / Japanese and English speech structures are different in terms of harmony, rhythm, and frequency of sound. Voice samples of 5 native speakers of English and Japanese were collected and analyzed through fast Fourier transform, autocorrelation, and statistical analysis. The harmony of language refers to the spatial frequency content of speech and is analyzed through two different measures, Harmonics-to-Noise-Ratio (HNR) developed by Boersma (1993) and a new parameter "harmonicity" which evaluates the consistency of the frequency content of a speech sample. Higher HNR values and lower harmonicity values mean that the speech is more harmonious. The HNR values are 9.6+0.6Hz and 8.9±0.4Hz and harmonicities are 27±13Hz and 41+26Hz, for Japanese and English, respectively; therefore, both parameters show that Japanese speech is more harmonious than English. A profound conclusion can be drawn from the harmonicity analysis that Japanese is a pitch-type language in which the exact pitch or tone of the voice is a critical parameter of speech, whereas in English the exact pitch is less important. The rhythm of the language is measured by "rhythmicity", which relates to the periodic structure of speech in time and identifies the overall periodicity in continuous speech. Lower rhythmicity values indicate that the speech for one language is more rhythmic than another. The rhythmicities are 0.84±0.02 and 1.35±0.02 for Japanese and English respectively, indicating that Japanese is more rhythmic than English. An additional parameter, the 80th percentile frequency, was also determined from the data to be 1407±242 and 2021±642Hz for the two languages. They are comparable to the known values from previous research. / by Aiko Nakano. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 38-40). / User innovation is steadily becoming an irreplaceable factor in product development. Thus it is necessary to find ways to measure these workarounds and ways to utilize these figures. I selected three (3) particular styles of workarounds to quantify and discuss. With makeshift window workarounds, I found that user workarounds in automobiles cost 84.9 times and households cost 67.9 less in magnitude compared to full repairs. Table adjustments workarounds were found to be many times greater than then replacing the table and the gap became greater with the increase in table price. Lastly examining medical instrument workarounds, I discovered that many these innovations can create profitable, niche markets. By using workarounds in general, producers can manufacture consumer desired products that generate revenue. In the future, I hypothesize that companies will lower their research and development funding in place of observing potentially, profitable workarounds. / by Wayne Jacob Mario Hollman. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002. / Includes bibliographical references. / A piezoelectrically-driven hydraulic amplification microvalve for use in high specific power hydraulic pumping applications was designed, fabricated, and experimentally characterized. High frequency, high force actuation capabilities were enabled through the incorporation of one or more bulk piezoelectric material elements beneath a micromachined annular tethered-piston structure. An hydraulic amplification mechanism was employed to amplify the limited stroke of this piezoelectrically-driven piston structure to a significantly larger motion (40-50x) of a micromachined valve membrane with attached valve cap. This valve cap was actuated through its stroke to open and close against a fluid orifice. These design features enabled the valve device to simultaneously meet a set of high frequency (1-10kHz), high pressure(0.1-IMPa), and large stroke (15-40,um) requirements that had not previously been satisfied by other microvalves presented in the literature. This research was carried out through a series of modeling, design, fabrication, assembly, and experimental testing tasks. Linear and non-linear modeling tools characterizing the structural deformations of the active valve sub-systems were developed. These tools enabled accurate prediction of real-time stresses along the micromachined valve membrane structure during deflection into its non-linear large-deflection regime. A systematic design procedure was developed to generate an active valve geometry to satisfy membrane stress limitations and valve power consumption requirements set forth by external hydraulic system performance goals. / (cont.) Fabrication challenges, such as deep-reactive ion etching (DRIE) of the drive element and valve membrane structures, wafer-level silicon-to-silicon fusion bonding and silicon-to-glass anodic bonding operations, preparation and integration of piezoelectric material elements within the micromachined tethered piston structure, die-level assembly and bonding of silicon and glass dies, and filling of degassed fluid within the hydraulic amplification chamber were overcome. The active valve structural behavior and flow regulation capabilities were evaluated over a range of applied piezoelectric voltages, actuation frequencies, and differential pressures across the valve. For applied piezoelectric voltages up to 500Vpp at lkHz, the valve devices demonstrated amplification ratios of drive element deflection to valve cap deflection of 40-50x. These amplification ratios correlated within 5 - 10% of the model expectations. Flow regulation experiments proved that a peak average flow rate through the device of 0.21mL/s under a lkHz sinusoidal drive voltage of 500Vpp, with valve opening of 17pm, against a differential pressure of 260kPa could be obtained. Tests revealed that fluid-structural interactions between the valve cap and membrane components and flow instabilities (due to transition between the laminar and turbulent flow regimes through the valve orifice) limited the valve performance capabilities. / by David C. Roberts. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 213-232). / Immunochromatography assays are ideal candidates for diagnosis of disease in remote areas, due to their low cost and rapid readout. Moreover, they can be stored at relatively high temperatures, and do not require electric power, specialized personnel, equipment or reagents. We use those devices to diagnose viral mosquito-borne tropical diseases that have caused major epidemics and hospitalization in the last years. By allowing mobile phone readability of the diagnosis results, we enable real-time epidemiologic data on the spread of the disease. lmmunochromatography assays use capillary flow and the accumulation of ligand-coated nanoparticles to detect the presence of target proteins. We build multiplexed diagnostics that allow the detection of the four serotypes of Dengue and Zika, and validate the performance of these diagnostics by using patient samples from endemic areas from the Americas and India. Moreover, we build a multiplexed diagnostic that can detect Dengue, Zika and Chikungunya by using a low volume of patient sample. In order to provide a rapid response to epidemics, lateral flow immunoassays need to be rapidly tested and manufactured. However, years of research are necessary to identify, screen and test disease-specific antibody pairs. To provide a faster response to outbreaks, we explore cross-reactive antibodies developed against a related pathogen. To avoid nonspecific signal from the related pathogens, gold nanoparticles of different colors are combined with cross-reactive antibodies of different affinities and used in order to distinguish between the two infections as well as co-infections. In this context, I present an Ebola and Marburg diagnostic and a Dengue and Zika diagnostic. Limit of detection, as well as sensitivity/specificity are critical issues in the development of rapid diagnostics; these parameters are dependent on the nature of the ligand-target pair and binding thermodynamics when attached on a surface. In this thesis, I explore strategies to increase the sensitivity and specificity of the lateral flow devices. These new, effective, fast, reliable and inexpensive lateral flow devices represent significant improvements to field detection of disease and real-time epidemiology in situations where the lack of specialized personnel, reagents or materials challenge the suitability of the standard diagnosis methods. / by Helena de Puig Guixe. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995. / by Hugo M. Ayala. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003. / Includes bibliographical references (leaves 65-68). / The estimation of terrain characteristics is an important missions of Martian exploration rovers. Since only limited resources and human supervision are available, efficient and autonomous method of estimation are required. In this thesis, an on-line estimation method of two important terrain parameters, cohesion and internal friction angle, is developed. The method uses onboard rover sensors and is computationally efficient. Terrain parameter estimation is of scientific interest, and can also be useful in predicting rover mobility on rough-terrain. A method to estimate traversability of a rover on deformable terrain using on-board sensors is presented. Simulation and experimental results show that the proposed methods can accurately and efficiently estimate traversability of deformable terrain. / by Shinwoo Kang. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 197-206). / Organic matter respiration in natural ecosystems is controlled by a network of biologically, physically, and chemically driven processes. Often it is important to estimate total carbon flux from a degradation system or the decay of mass in the system as a function of time. Historically, mass dynamics are predicted by a compartmental model consisting of various degradation processes. This approach provides a complete picture of mass in the model system, but includes extra information unnecessary for modeling overall mass dynamics. Furthermore, these models quickly become highly parameterized and are kept tangible by reducing the number of processes and system states. This thesis suggests a different approach. I allow the degradation system to be inherently complex, but only consider a simple projection of the system necessary to characterize mass dynamics. Because decomposing organic matter is often described as a heterogeneous continuum which transforms and degrades over a wide range of rates, I model degradation as a network consisting of a large, quasi-continuum of states. The retention of carbon in the network is then estimated by using an eigenvalue projection to calculate the impulse response of the degradation system. For a continuous network, the impulse response can be expressed as a Laplace transform of an "exit rate function." I then pose and solve an inverse problem in order to identify the rates of exit of carbon from decomposing plant matter from across North America. Analysis of the calculated exit rate functions and their associated decay data suggest that plant matter decomposition can often be mathematically approximated by a continuum of parallel processes. Within this approximation, the solution of the inverse problem yields the discovery that exit rate functions are on average lognormal. This result suggests that the overall mass dynamics of complex decay networks often collapse to just two parameters: the mean and the variance of the order of magnitude of exit rates from the network. These parameters are then used to assess the effects of climate and litter chemistry on organic carbon turnover and on rate heterogeneity. I also use observed patterns to explain the effect of natural selection in microbial communities on degradation network kinetics. / by David C. Forney, III. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 26). / This thesis documents my personal contribution to the development of a hydraulic-based actuation system for a solar trough collector. The goal of this project was to design the actuation system using hydraulic actuators for a four meter solar collector prototype in Pittsfield, New Hampshire. After considering several hydraulic system architectures and conducting in-depth analysis into two of them, the idler pulley scheme was chosen. This mechanism uses a double rod end hydraulic actuator connected to wire rope wrapped around a capstan drum and an idler pulley. The model was optimized for mechanical performance, and it is expected to be a more cost effective option than the existing actuation system in New Hampshire once the controls equipment required to actuate the hydraulic cylinders for the new design is specified. / by Juan Felipe Carrillo. / S.B.