DSpace at MIT
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Electrical Engineering and Computer Sciences - Master's degree
Spectral sparsification and spectrally thin trees - Oliveira, Rafael (Rafael Mendes de Oliveira)
We provide results of intensive experimental data in order to investigate the existence of spectrally thin trees and unweighted spectral sparsifiers for graphs with small expansion. In addition, we also survey and prove some partial results on the existence of spectrally thin trees on dense graphs with high enough expansion.
W-SPSA : an Efficient Stochastic Approximation Algorithm for the off-line calibration of Dynamic Traffic Assignment models - Lu, Lu, S.M. Massachusetts Institute of Technology
The off-line calibration is a crucial step for the successful application of Dynamic Traffic Assignment (DTA) models in transportation planning and real time traffic management. While traditional approaches focus on the separate or sequential estimation of demand and supply in a DTA system, a recently proposed framework calibrates the demand and supply models simultaneously by formulating the off-line calibration as a constrained optimization problem. Simultaneous Perturbation Stochastic Approximation (SPSA) has been reported in the literature to be the most suitable solution algorithm for this problem due to its highly efficient gradient estimation approach. However, it turns out that the performance...
SNARKs for C : verifying program executions succinctly and in zero knowledge - Virza, Madars
We present a proof system that allows efficient verification of NP statements, given proofs produced by an untrusted yet computationally-bounded prover. Our system is publicly verifiable: after a trusted third-party has generated a proving key and a verification key, anyone can use the proving key to generate non-interactive proofs for adaptively-chosen NP statements, and the proofs can be verified by anyone using the verification key. Moreover, our system is statistically zero-knowledge and the generated public parameters are reusable. The NP-complete language we choose is the correct execution of programs on TinyRAM, a minimalistic (nondeterministic) random-access machine that we design. Together...
A doubly-fed machine for propulsion applications - Tomovich, Michael S. (Michael Stephen)
A doubly fed machine for propulsion applications is proposed, which, given the presence of AC and DC power sources, can be utilized in order to improve efficiency, weight, volume, and sizing of the rotor power electronics. In this case, a shipboard application is examined. A hardware demonstration of a control architecture is implemented, along with a benchtop demonstration of the replacement of standard slip rings in the machine with a contactless solution (i.e. a transformer). Along with the benchtop demonstration of the transformer for accessing the rotor terminals, an analysis of the power handling capability of different converters for rectifying...
Thermally-actuated piezoresistively-sensed mechanical silicon oscillator - Sundaram, Subramanian, S.M. Massachusetts Institute of Technology
In the past two decades, Microelectromechanical (MEMS) resonators have emerged as front runners for RF front-ends, high frequency filters, and frequency sources in various applications. The prospect of seamless integration with CMOS has provided a significant boost to displace Quartz, which for long has been the go-to option for timing sources. To construct an oscillator, a MEMS resonator is operated with an active feedback amplifier, the design of which can be a major challenge at high frequencies. In this work we implement a self sustaining mechanical Si oscillator that has an internal feedback mechanism. The oscillator is based on a...
Analysis and visualization of equilibrium in masonry structures - Shin, Hijung Valentina
This thesis presents novel analysis and visualization methods to explore the equilibrium of masonry structures. Following a previous approach, we model the stability problem as a quadratic program. When a structure is unstable the quadratic program returns a measure of infeasibility. We extend this model to include tensile structures such as cables. Then, we derive a closed-form gradient of stability with respect to geometry modifications, and apply it to the design of structurally sound buildings. In addition, we analyze various properties related to the equilibrium state of structures and visualize the result. We study the sensitivity of equilibrium with respect...
Smart IP of QR decomposition for rapid prototyping on FPGAs - Saqib, Sunila
The Digital Signal Processing (DSP) systems used in mobile wireless communication, such as MIMO detection, beam formation in smart antennas, and compressed sensing, all rely on quickly solving linear systems of equations. These applications of DSP have vastly different throughput, latency and area requirements, necessitating substantially different hardware solutions. The QR decomposition (QRD) method is an efficient way of solving linear equation systems using specialized hardware, and is known to be numerically stable . We present the design and FPGA implementation of smart IP (intellectual property) for QRD based on Givens-Rotation (GR) and Modified-Gram- Schmidt (MGS) algorithms. Our configurable designs...
Forward viewing OCT endomicroscopy - Liang, Kaicheng
A forward viewing fiber optic-based imaging probe device was designed and constructed for use with ultrahigh speed optical coherence tomography in the human gastrointestinal tract. The light source was a MEMS-VCSEL at 1300 nm wavelength running at 300 kHz sweep rate, giving an effective A-line rate of 600 kHz. Data was acquired with a 1.8 GS/s A/D card optically clocked by a maximum fringe frequency of 1 GHz. The optical beam from the probe was scanned by a freely deflecting optical fiber that was mounted proximally on a piezoelectric tubular actuator, which was electrically driven in two perpendicular dimensions to...
Scalable multi-access flash store for Big Data analytics - Jun, Sang-Woo
For many "Big Data" applications, the limiting factor in performance is often the transportation of large amount of data from hard disks to where it can be processed, i.e. DRAM. In this work we examine an architecture for a scalable distributed flash store which aims to overcome this limitation in two ways. First, the architecture provides a high-performance, high-capacity, scalable random-access storage. It achieves high-throughput by sharing large numbers of flash chips across a low-latency, chip-to-chip backplane network managed by the flash controllers. The additional latency for remote data access via this network is negligible as compared to flash access...
High field, high efficiency terahertz pulse generation by optical rectification - Huang, Wenqian Ronny
The great difficulty of producing high intensity radiation in the terahertz (THz) spectral region by conventional electronics has stimulated interest in development of sources based on photonics. Optical rectification in lithium niobate is an attractive approach, because it supports high generation efficiencies, uses low cost, bulk LN crystals, and is powered by common Yb-doped lasers at wavelengths of around 1 Pm. In this work, a theoretical framework for THz generation by optical rectification is developed. Several novel methods for optimizing the generation efficiency are shown, including pump beam imaging, pump pulse optimization, cryogenic cooling, and THz antirefiection coating. Finally, experimental...
Computation identification of transcription factor binding using DNase-seq - Hashimoto, Tatsunori B. (Tatsunori Benjamin)
Here we describe Protein Interaction Quantitation (PIQ), a computational method that models the magnitude and shape of genome-wide DNase profiles to facilitate the identification of transcription factor (TF) binding sites. Through the use of machine learning techniques, PIQ identified binding sites for >700 TFs from one DNase-seq experiment with accuracy comparable to ChIP-seq for motif-associated TFs (median AUC=0.93 across 303 TFs). We applied PIQ to analyze DNase-seq data from mouse embryonic stem cells differentiating into pre-pancreatic and intestinal endoderm. We identified (n=120) and experimentally validated eight 'pioneer' TF families that dynamically open chromatin, enabling other TFs to bind to adjacent...