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Electrical Engineering and Computer Sciences - Master's degree
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Efficient THz lasers and broadband amplifiers based on quantum cascade gain media - Cai, Xiaowei, S.M. Massachusetts Institute of Technology
One of the most important applications for Terahertz (THz) quantum cascade (QC) lasers is to provide compact and powerful frequency-stabilized solid-state sources as local oscillators in heterodyne receivers for astronomical studies. The first part of the thesis is dedicated to the device cavity design, fabrication and characterization of the microstrip antenna coupled third-order distributed feedback QC lasers aimed for 2.060 THz atomic oxygen line. THz travelling-wave QC amplifiers are highly desired to achieve broadband amplification of THz radiation in free space. The second part of the thesis focuses on the development of 4.3 THz travelling-wave QC amplifier by monolithically integrating...
Vocal modulation features in the prediction of major depressive disorder severity - Horwitz, Rachelle (Rachelle Laura)
This thesis develops a model of vocal modulations up to 50 Hz in sustained vowels as a basis for biomarkers of neurological disease, particularly Major Depressive Disorder (MDD). Two model components contribute to amplitude modulation (AM): AM from respiratory muscles and from interaction between formants and frequency modulation in the fundamental frequency harmonics. Based on the modulation model, we test three methods to extract the envelope of the third formant from which features are extracted using sustained vowels from the 2013 AudioNisual Emotion Challenge. Using a Gaussian-Mixture-Model-based predictor, we evaluate performance of each feature in predicting subjects' Beck MDD severity...
A novel few-cycle optical source in the mid-infrared - Krogen, Peter Ra
In this thesis, I designed, simulated, and implemented a novel optical pulse generation system which is shown to be able to generate exceptionally short optical pulses in the mid-infrared, tunable from 2-4[mu]m with pulse widths as low as 1.5 optical cycles at 3.5[mu]m (18fs). Energies as high a 1[mu]J were achieved, representing a peak power of roughly 100MW, at a 1kHz repetition rate, with excellent beam quality. The system was based on adiabatic difference frequency generation in an aperiodically polled lithium niobate crystal of an amplified, mode-locked Ti:Sapphire laser system.
Fabrication of graphene-on-GaN vertical transistors - Zubair, Ahmad, S.M. Massachusetts Institute of Technology
The excellent transport properties of graphene make it an excellent option for very high frequency electronics. However, the poor output resistance and difficult lithography of lateral transistors significantly limit its performance. In this thesis, we propose a new kind of vertical graphene base transistor to take advantage of both wide bandgap GaN semiconductors and zero bandgap graphene for high frequency transistors. This majority-carrier device has a metal collector, a graphene base and an AlGaN/GaN emitter. The first device prototype exhibits very promising current density(~mA/cm 2 ) and current gain ([alpha] ~ 50 %). Simulations further support that with proper optimization...
Optical properties of two-dimensional transition metal dichalcogenides - Lin, Yuxuan, S.M. Massachusetts Institute of Technology
The re-discovery of the atomically thin transition metal dichalcogenides (TMDs), which are mostly semiconductors with a wide range of band gaps, has diversified the family of two-dimensional materials and boosted the research on their potential applications in the fields of logic nanoelectronics and high-performance nanophotonics. Many body effects are of great significance in 2-dimensional TMDs, especially when thinned down to a monolayer. As a result, the exciton-related phenomena are prominent in TMD monolayers, which distinguish the monolayers significantly from their bulk counterparts. This thesis systematically studies the optical properties in semiconducting, monolayer TMDs, including Raman spectroscopy, photoluminescence (PL), and optical...
High energy femtosecond fiber laser at 1018 nm and high power Cherenkov radiation generation - Yang, Hongyu, S.M. Massachusetts Institute of Technology
Two novel laser systems for ultrafast applications have been designed and built. For the seeding of a high energy cryogenically cooled Yb:YLF laser, a novel 1018 nm fiber laser system is demonstrated. It produces >35 nJ pulse energy and 5 nm spectral bandwidth. A double-cladd amplifier and an appropriate filter to optimize the system for the amplifier seeding application were employed. This is the highest pulse energy with narrow spectrum at 1018 nm. For a photonic analog-to-digital conversion system operating at 1250 nm, a fiber laser system generating 4 W of femtosecond Cherenkov radiation at that wavelength was built. The...
Design, implementation, and evaluation of a social learning network for Chess - Shen, Shen S.M. Massachusetts Institute of Technology
Abstract This thesis demonstrates how an active team environment, enabled by educational technology, enhances an individual's learning experience. With the inspiration and insight from international chess Grandmaster Maurice Ashley, who is also an experienced and successful chess coach, this thesis examines the question in the context of chess. Two of GM Ashley's acclaimed chess skill builders, Pawn Mower and Chess- Maze are digitally transformed, and then extended to create a social learning network. Three types of team interactions are designed, which we call EnLighten Me, Peers' Peek, and Heat Map respectively. EnLighten Me and Peers' Peek are implemented into browser-based...
Local computation algorithms for graphs of non-constant degrees - Yodpinyanee, Anak
In the model of local computation algorithms (LCAs), we aim to compute the queried part of the output by examining only a small (sublinear) portion of the input. Many recently developed LCAs on graph problems achieve time and space complexities with very low dependence on n, the number of vertices. Nonetheless, these complexities are generally at least exponential in d, the upper bound on the degree of the input graph. Instead, we consider the case where parameter d can be moderately dependent on n, and aim for complexities with quasi-polynomial dependence on d, while maintaining polylogarithmic dependence on n. In...
Power monitoring in integrated circuits - Al Bastami, Anas Ibrahim
Power monitoring is needed in most electrical systems, and is crucial for ensuring reliability in everything from industrial and telecom applications, to automotive and consumer electronics. Power monitoring of integrated circuits (ICs) is also essential, as today ICs exist in most electrical and electronic systems, in a vast range of applications. Many ICs, including power ICs, have functional blocks across the chip that are used for different purposes. Measuring circuit block currents in both analog and digital ICs is important in a wide range of applications, including power management as well as IC testing and fault detection and analysis. For...
Exploiting chordal structure in systems of polynomial equations - Cifuentes Pardo, Diego Fernando
Chordal structure and bounded treewidth allow for efficient computation in linear algebra, graphical models, constraint satisfaction and many other areas. Nevertheless, it has not been studied whether chordality might also help solve systems of polynomials. We propose a new technique, which we refer to as chordal elimination, that relies in elimination theory and Gröbner bases. Chordal elimination can be seen as a generalization of sparse linear algebra. Unlike the linear case, the elimination process may not be exact. Nonetheless, we show that our methods are well-behaved for a large family of problems. We also use chordal elimination to obtain a...
convex segmentation and mixed-integer footstep planning for a walking robot - Deits, Robin L. H. (Robin Lloyd Henderson)
This work presents a novel formulation of the footstep planning problem as a mixed-integer convex optimization. The footstep planning problem involves choosing a set of footstep locations which a walking robot can follow to safely reach a goal through an environment with obstacles. Rather than attempting to avoid the obstacles, which would require nonconvex constraints, we use integer variables to assign each footstep to a convex region of obstacle-free terrain, while simultaneously optimizing its pose within that safe region. Since existing methods for generating convex obstacle-free regions were ill-suited to this task, we also present IRIS (Iterative Regional In Inflation...
On Learning and Covering Structured Distributions - Kamath, Gautam (Gautam Chetan)
We explore a number of problems related to learning and covering structured distributions: Hypothesis Selection: We provide an improved and generalized algorithm for selecting a good candidate distribution from among competing hypotheses. Namely, given a collection of ... hypotheses containing at least one candidate that is ...-close to an unknown distribution, our algorithm outputs a candidate which is ...-close to the distribution. The algorithm requires ... samples from the unknown distribution and ... time, which improves previous such results (such as the Scheffé estimator) from a quadratic dependence of the running time on ... to quasilinear. Given the wide use...
BlueFlash : a reconfigurable flash controller for BlueDBM - Liu, Ming Gang
NAND flash has risen to become a popular storage medium in recent years due to its significant bandwidth, access latency and power advantages over traditional hard disks. However, in modern Big Data systems, simply replacing disks with flash does not yield proportional performance gains. This is because of bottlenecks in various levels of the system stack: I/O interface, network, file system and processor. Introduced in 2012, BlueDBM is a novel Big Data flash storage platform that includes a dedicated low latency sideband storage network between flash controllers, reconfigurable fabric for implementing in-store hardware accelerators and a flash-aware file system. While...
Design of tool for the optimization of deck area assignments with integration into existing naval ship design programs - Oslebo, Damian G
Many tasks in the early stages of ship design are manual and repetitive processes. One such task is in the realm of deck area arrangements. The allocation and assignment of areas in early stage ship design involves tracking the difference of total ship area envelope and all required areas to be placed for habitability, mission support, and propulsion capability among many. The problem becomes more complex with the addition of constraints involving required separation zones between other areas, affinities for certain areas or deck levels, and compartment subdivision. The Leading Edge Architecture for Prototyping Systems (LEAPS) database structure output from...
Design of an Autonomous Underwater Vehicle (AUV) charging system for underway, underwater recharging - Ewachiw, Mark Alexander, Jr
Modern robotics have enabled the rapid proliferation of Autonomous Underwater Vehicles (AUVs) throughout the marine environment. As autonomy algorithms increase in robustness, complexity, and reliability, so too does the ability of AUVs to perform an even-increasing array of complex missions. Maritime tasks that once required a fleet of ships, months to complete, and numerous mariners are now being performed by AUVs with little to no logistical support elements. Despite the many AUV technology advances that have been made, power remains a limiting factor. Most AUVs use onboard stored electric energy and electric drive to perform their various missions. The current...
Development of MIT geospatial data to CityGML workflows - Wu, Bradley
BlindAid is a virtual environment system that helps blind people learn in advance about places they plan to visit. A core component of the BlindAid system is the actual set of virtual models that represent physical locations. In order for BlindAid to be useful, there must be a means to generate new virtual environments. The research in this thesis explores the process of translating geospatial data received from MIT into the CityGML data format, which will then be used to generate virtual environments for BlindAid. We discuss the main challenge of preserving both geometry and semantic information with respect to...
CyberVisual : designing user environments for large scale networks and simulations - Workie, Nahom Hailemariam
The growth of data collection within the technology sector has been increasing at an astounding rate over the last decade. This growth has given rise to techniques and statistical tools for computation that enable us to see trends and answer queries; however, most of this information has been in the form of numbers in a data set resulting from these computations. As this trend towards data collection and analysis continues, it becomes increasingly important to show and present this information to users and non-data scientists with quantifiable and concise methods. With respect to large data in the field of networks...
Design and implementation of a fiber optic doppler optical coherence microscopy system for cochlear imaging - Williams, Logan P
In this thesis, the design and implementation of a fiber optic Doppler optical coherence microscopy (FO-DOCM) system for cochlear imaging applications is presented. The use of a fiber optic design significantly reduces system size and complexity and the construction of a novel alignment and micropositioning apparatus increases ease of use for the researcher performing the imaging. To enable precise measurements of tissue motion, a time domain DOCM approach is used, utilizing an acousto-optic modulator (AOM) based optical heterodyne system to generate a stationary interference carrier frequency. By referencing this interference signal against the AOM drive signals, measurements of motions with...