DSpace at MIT
This site is a university repository providing access to the publication output of the institution. Registered users can set up email alerts to notify them of newly added relevant content. A certain level of encryption and security is embedded in the site which may cause some users accessibility problems.
Electrical Engineering and Computer Sciences - Master's degree
Mostrando recursos 1 - 20 de 4.280
MobiTest : an evaluation infrastructure for mobile distributed applications - Sivaraman Kaushalram, Anirudh
Sophisticated applications that run on mobile devices have become commonplace. Within the wide realm of mobile software applications there exists a significant number that make use of networking in some form. Unfortunately, such distributed mobile applications are inherently difficult to evaluate. Conventional evaluations of such distributed applications are limited to small, real-world deployments consisting of, perhaps, a handful of phones. Such tests often do not have the requisite number of users to produce the desired performance. Also, these experiments do not scale and are not repeatable. To address all these issues, we sought to evaluate distributed applications in a virtual...
Flying between obstacles with an autonomous knife-edge maneuver - Barry, Andrew J. (Andrew James)
We develop an aircraft and control system that is capable of repeatedly performing a high speed (7m/s or 16 MPH) "knife-edge" maneuver through a gap that is smaller than the aircraft's wingspan. The maneuver consists of flying towards a gap, rolling to a significant angle, accurately navigating between the obstacles, and rolling back to horizontal. The speed and roll-rate required demand a control system capable of highly precise, repeatable maneuvers. We address the necessary control theory, path planning, and hardware requirements for such a maneuver, and give a proposal for a new system that may improve upon the existing techniques.
Surface functionalization of graphene devices - Zhang, Xu, S.M. Massachusetts Institute of Technology
Graphene, a zero-gap semiconductor with massless charge carriers, is emerging as an amazing material for future electronics, due to its outstanding electrical and mechanical performances. However, the lack of a bandgap results in a high off-state current leakage and a nonsaturating drive current, both of which severely limit graphene's practical applications in electronic devices. Chemical functionalization on its surface promises a powerful tool to manipulate its electronic properties and modify its atomic structures. Graphene is a true two-dimensional material; every carbon atom in single layer graphene is exposed to its environment. Therefore, the surface functionalization in graphene can significantly change...
Amplitude and phase modulation techniques for an asymmetric multi-level outphasing transmitter - Yahalom, Gilad
New techniques for improving outphasing transmitters show potential of breaking the traditional linearity-efficiency trade-off by using highly efficient non-linear switching Power Amplifiers (PAs). This work focuses on two of the main building blocks of modem outphasing systems, the power supply switching network and the phase modulator. Both are ubiquitous building blocks in modern RF transceivers, and both are especially critical in Asymmetric Multilevel Outphasing (AMO) systems. A design of the power supply network and control scheme is proposed for an implementation in mm-wave operating frequencies as part of a complete transmitter in 45nm SOI CMOS utilizing four discrete power supplies...
Matroid prophet inequalities and Bayesian mechanism design - Weinberg, S. Matthew (Seth Matthew)
Consider a gambler who observes a sequence of independent, non-negative random numbers and is allowed to stop the sequence at any time, claiming a reward equal to the most recent observation. The famous prophet inequality of Krengel, Sucheston, and Garling asserts that a gambler who knows the distribution of each random variable can achieve at least half as much reward, in expectation, as a "prophet" who knows the sampled values of each random variable and can choose the largest one. We generalize this result to the setting in which the gambler and the prophet are allowed to make more than...
Building compressed sensing systems : sensors and analog-to-information converters - Salehi-Abari, Omid
Compressed sensing (CS) is a promising method for recovering sparse signals from fewer measurements than ordinarily used in the Shannon's sampling theorem . Introducing the CS theory has sparked interest in designing new hardware architectures which can be potential substitutions for traditional architectures in communication systems. CS-based wireless sensors and analog-to-information converters (AIC) are two examples of CS-based systems. It has been claimed that such systems can potentially provide higher performance and lower power consumption compared to traditional systems. However, since there is no end-to-end hardware implementation of these systems, it is difficult to make a fair hardware-to-hardware comparison with...
The development of an automated system for electrical characterization of cells using a novel force balance method - Su, Hao-Wei
Dielectrophoresis (DEP), a cell separation technique based on the dielectric properties, has significantly advanced biomedical research in diverse applications ranging from blood stem cells purification to cancer cells isolation from heterogeneous populations. The ability to accurately measure the dielectric properties of individual cells is not only critical for effective sorting applications, but is also advantageous for enhancing the current knowledge of cell biology. This thesis proposes a novel method: the n-DEP spring, which applies an electrical field gradient upon continuously flowing cells to distinguish them based on their individual DEP properties. Specifically, the method uses the equilibrium position originating from...
Understanding sketch-and-speech descriptions of machines - Scott, Jeremy (Jeremy Kenneth)
In this thesis, we present PhysInk, a sketching application that provides a natural way to describe physical structure and behavior to a computer. The user describes structure by sketching physical objects and constraints on a canvas backed by a 2D physics engine. The user can then move the objects to explicitly demonstrate physical behavior and can utter simple speech commands to label objects and events. These interactions are captured in PhysInk's timeline - a causal graph of physical events - which is used to build a deeper understanding of behavior. The events capture the geometry of movement and contact between...
Chemical and physical methods of the templated direction of block copolymers - Nicaise, Samuel M. (Samuel Mospens)
This thesis discusses the investigation of various aspects of templated self-assembly of block copolymer (BCP) thin films for nanofeature fabrication. Two chapters outline the research of a combined physical and chemical templating method with two BCPs. The method was not effective in templating poly(styrene-block-methyl methacrylate) (PS-b-PMMA) BCP because of limited template wettability. The method effectively templated poly(octofluro pentamethacrylate-block-hydroxystyrene) (OFPMA-b-HSM) BCP to fabricate orthogonally-directed lamellar microdomains and nanohole-mesh arrays. Chapter 4 discusses the achievement of a mean overlay accuracy of 52 nm and 0' for two electron-beam-based lithographic features as a result of an investigated overlay process. Lastly, the thesis reports...
Digital pulse processing - McCormick, Martin (Martin Steven)
This thesis develops an exact approach for processing pulse signals from an integrate-and-fire system directly in the time-domain. Processing is deterministic and built from simple asynchronous finite-state machines that can perform general piecewise-linear operations. The pulses can then be converted back into an analog or fixed-point digital representation through a filter-based reconstruction. Integrate-and-fire is shown to be equivalent to the first-order sigma-delta modulation used in oversampled noise-shaping converters. The encoder circuits are well known and have simple construction using both current and next-generation technologies. Processing in the pulse-domain provides many benefits including: lower area and power consumption, error tolerance, signal...
Transfer learning by borrowing examples for multiclass object detection - Lim, Joseph J. (Joseph Jaewhan)
Despite the recent trend of increasingly large datasets for object detection, there still exist many classes with few training examples. To overcome this lack of training data for certain classes, we propose a novel way of augmenting the training data for each class by borrowing and transforming examples from other classes. Our model learns which training instances from other classes to borrow and how to transform the borrowed examples so that they become more similar to instances from the target class. Our experimental results demonstrate that our new object detector, with borrowed and transformed examples, improves upon the current state-of-the-art...
Adaptive mechanisms for self-aware multicore systems - Lau, Eric (Eric Chi Young)
As the push for extreme scale performance continues to make computer architectures increasingly complex, there has been a call for better programming models, and the systems to support them. Todays microprocessors now expose more system resources than ever to software, leaving it up to the application programmer to manage them. Studies have shown that the energy efficiency of future technologies may eventually affect the ultimate performance of multicore processors, and so programmers are forced to optimize systems for both performance and energy in the midst of countless configurable parameters - an extremely difficult task. Self-aware systems can configure themselves through...
Robust bipedal locomotion on unknown terrain - Dai, Hongkai, S.M. Massachusetts Institute of Technology
A wide variety of bipedal robots have been constructed with the goal of achieving natural and efficient walking in outdoor environments. Unfortunately, there is still a lack of general schemes enabling the robots to reject terrain disturbances. In this thesis, two approaches are presented to enhance the performance of bipedal robots walking on modest terrain. The first approach searches for a walking gait that is intrinsically easily stabilized. The second approach constructs a robust controller to steer the robot towards the designated walking gait. Mathematically, the problem is modeled as rejecting the uncertainty in the guard function of a hybrid...
Compressively strained Ge trigate p-MOSFETs - Chern, Winston
State of the art MOSFET performance is limited by the electronic properties of the material that is being used, silicon (Si). In order to continue performance enhancements, different materials are being studied for the extension of Si CMOS. One of the materials of interest, particularly for p-MOSFETs, is Ge because it has very high intrinsic hole mobility. Further improvements in hole mobility can be achieved by straining the material. At the same time it is important to study strained Ge transport in device architectures such as trigate MOSFETs. These devices offer the potential for better scalability than planar MOSFETs via...
A medication extraction framework for electronic health records - Bodnari, Andreea
This thesis addresses the problem of concept and relation extraction in medical documents. We present a medical concept and relation extraction system (medNERR) that incorporates hand-built rules and constrained conditional models. We focus on two concept types (i.e., medications and medical conditions) and the pairwise administered-for relation between these two concepts. For medication extraction, we design a rule-based baseline medNERRgreedy med that identifies medications using the UMLS dictionary. We enhance medNERRgreedy med with information from topic models and additional corpus-derived heuristics, and show that the final medication extraction system outperforms the baseline and improves on state-of-the-art systems. For medical conditions...
Extending and characterizing quantum magic games - Arkhipov, Alex (Aleksandr)
The Mermin-Peres magic square game is a cooperative two-player nonlocal game in which shared quantum entanglement allows the players to win with certainty, while players limited to classical operations cannot do so, a phenomenon dubbed "quantum pseudo-telepathy". The game has a referee separately ask each player to color a subset of a 3x3 grid. The referee checks that their colorings satisfy certain parity constraints that can't all be simultaneously realized. We define a generalization of these games to be played on an arbitrary arrangement of intersecting sets of elements. We characterize exactly which of these games exhibit quantum pseudo-telepathy, and...
Stability effects of frequency controllers and transmission line configurations on power systems with integration of wind power - Abdelhalim, Hussein Mohamed
This thesis investigates the stability effects of the integration of wind power on multi-machine power systems. First, the small-signal stability effects of turbine governors connected to synchronous generators in the presence of large-scale penetration of wind and load power disturbances are analyzed. Results suggest that tuning the turbine governors when wind power generation is present can improve the small-signal stability of an interconnected system. Then, the transient stability effects of integrating doubly-fed induction wind turbine generators through different transmission line configurations and at different buses are analyzed. Results show that connecting the wind through transmission lines and to different buses...
Nano-scale metal contacts for future III-V CMOS - Guo, Alex
As modem transistors continue to scale down in size, conventional Si CMOS is reaching its physical limits and alternative technologies are needed to extend Moore's law. Among different candidates, MOSFETs with a III-V compound semiconductor channel are of great interest. Specifically, designs with an InGaAs channel have shown promising results for N type MOSFETs. In a new generation of III-V MOSFETs, one of the key challenges is to shrink device footprint while improving transistor's electrical performance. For future technology nodes, the gate length of MOSFETs needs to shrink below 10 nm, and the source and drain contacts must also decrease...
Non-Rayleigh scattering by a randomly oriented elongated scatterer - Bhatia, Saurav
The echo statistics of a randomly rough, randomly oriented prolate spheroid that is randomly located in a beampattern are investigated from physics-based principles both analytically and by Monte Carlo methods. This is a direct-path geometry in which reflections from neighboring boundaries are not a factor. The center of the prolate spheroid is assumed to be confined to the plane containing the MRA (maximum response axis). Additionally, the rotation of the prolate spheroid is assumed to always be in this plane. The statistics and, in particular, the tails of the probability density function (PDF) and probability of false alarm (PFA) are...
Resonant photonic crystal photodetectors for the infrared in silicon - Mehta, Karan K. (Karan Kartik)
The challenge of overcoming energy efficiency and bandwidth limitations in interconnects between components in computer systems (e.g. between memory and processors) has motivated the development of short-range optical interconnects, which in many approaches require optical devices and waveguides fabricated within the same CMOS environments as the electronics. This thesis centers on developing photodetectors for infrared light within the silicon of commercial CMOS processes; silicon's lack of strong absorption at the wavelengths of interest makes this challenging. The approach uses defect-state mediated linear absorption and two-photon absorption (TPA) in small mode-volume resonators to generate photocarriers. Such resonators allow efficient linear absorption...