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Electrical Engineering and Computer Sciences - Master's degree
Mostrando recursos 1 - 20 de 5,635
Magnetostatic interaction in nanowires - Siddiqui, Saima Afroz
Nonvolatile memory and logic devices rely on the manipulation of domain walls in magnetic nanowires, and scaling of these devices requires an understanding of domain wall behavior as a function of the wire width. Due to the increased importance of edge roughness and microstructure in narrow lines, domain wall pinning increases dramatically as the wire dimensions decrease and stochastic behavior is expected depending on the distribution of pinning sites. This work reports on the field driven domain wall statistics in sub-100 nm wide nanowires made from Co films of 8 nm thickness made by an electron beam lithography and etching...
Theory of terahertz generation by optical rectification - Ravi, Koustuban
Intense pulses of light with wavelengths approximately ten times smaller than microwave sources and a hundred times larger than optical/near infra-red sources may be categorized as high-field Terahertz (THz) sources. By virtue of their large electromagnetic field amplitudes and relatively long wavelengths, they are uniquely amenable for electron acceleration, coherent X-ray generation and non-linear spectroscopy. Intra-pulse difference frequency generation or optical rectification of ultrafast optical pump pulses in nonlinear crystals has emerged as the most efficient approach for high-field THz generation. Earlier theoretical treatment of these systems had predicted conversion efficiencies as high as 10%, which opened up the possibility...
Integrative analysis of heterogeneous genomic datasets to discover genetic etiology of autism spectrum disorders - Nazeen, Sumaiya
Understanding the genetic background of complex diseases is crucial to medical research, with implications to diagnosis, treatment and drug development. As molecular approaches to this challenge are time consuming and costly, computational approaches offer an efficient alternative. Such approaches aim at predicting and prioritizing genes for a particular disease of interest. State-of-the-art gene prediction and prioritization methods rely on the observation that disease-causing genes have some sort of functional similarity based on either sequence, phenotype, protein-protein interaction (PPI) network, or functional annotation. Another increasingly accepted view is that human diseases result from perturbations of molecular networks, and genes causing the...
Design, fabrication, and characterization of a compact deep reactive ion etching system for MEMS processing - Gould, Parker Andrew; Hsing, Mitchell David
A general rule of thumb for new semiconductor fabrication facilities (Fabs) is that revenues from the first year of production must match the capital cost of building the fab itself. With modem Fabs routinely exceeding $1 billion to build, this rule serves as a significant barrier to entry for groups seeking to commercialize new semiconductor devices aimed at smaller market segments which require a dedicated process. To eliminate this cost barrier we are working to create a small-scale production suite of tools that will processes small (~1") substrates and cost less than $1 million. By shrinking the size of the...
ScaleFS : a multicore-scalable file system - Rasha Eqbal
It is difficult to achieve durability and crash consistency in file systems along with multicore scalability. Commutative file system operations, which should scale according to the Scalable Commutativity Property, conflict on shared resources like coarse-grained locks and pages present in the page cache or buffer cache. Furthermore, data structures that are on separate cache lines in memory (e.g., directory entries) are grouped together when the file system writes them to disk for durability. This grouping results in additional conflicts. This thesis introduces a new design approach that decouples the in-memory file system from the on-disk file system, using per core...
Unified RAW Path Oblivious RAM - Ren, Ling, S.M. Massachusetts Institute of Technology
Oblivious RAM (ORAM) is a cryptographic primitive that conceals memory access patterns to untrusted storage. Its applications include oblivious cloud storage, trusted processors, software protection, secure multi-party computation, and so on. This thesis improves the state-of-the-art Path ORAM in several aspects. On the theoretical side, we improve Path ORAM's memory bandwidth overhead by a factor of O(log logN) when the block size is small. With this improvement, Path ORAM is asymptotically the most ecient ORAM construction with constant or polylogarithmic client storage under any block size. Our technique to achieve this improvement involves using pseudorandom functions to compress the position...
Towards integrated QPSK transceiver on zero-change CMOS foundry process - Meng, Huaiyu
In recent years, the demand for Internet bandwidth increases while the unit price of bandwidth decreases. To keep up with the trend, more cost-eective optical telecommunication links are required. Due to the limited amount of optical fibers and wave- length range, increasing spectral eciency is a desirable approach. Advance modulation scheme, such as quadrature phase-shift keying (QPSK), is a possible solution. Another limitation is energy consumption. Power density within telecommunication data centers are regulated by law in consideration of ambient temperature and noise level. Therefore, optical transceivers with higher energy eciency is desired. Traditional transceivers use III-V chips for photonic...
Three-dimensional nanofabrication by electron-beam lithography and directed self-assembly - Do, Hyung Wan
In this thesis, we investigated three-dimensional (3D) nanofabrication using electron-beam lithography (EBL), block copolymer (BCP) self-assembly, and capillary force-induced self-assembly. We first developed new processes for fabricating 3D nanostructures using a hydrogen silsesquioxane (HSQ) and poly(methylmeth-acrylate) (PMMA) bilayer resist stack. We demonstrated self-aligned mushroom-shaped posts and freestanding supported structures. Next, we used the 3D nanostructures as topographical templates guiding the self-assembly of polystyrene-b-polydimethylsiloxane (PS-b-PDMS) block copolymer thin films. We observed parallel cylinders, mesh-shaped structures, and bar-shaped structures in PDMS. Finally, we studied capillary force-induced self-assembly of linear nanostructures using a spin drying process. We developed a computation schema based on...
Finite blocklength analysis of the MISO Coherent Block Fading Channel - Collins, Austin Daniel
The Coherent MISO Block Fading Channel is a wireless communication channel model in which the transmitter has access to multiple antennas while the receiver has access to one. This model is becoming increasingly important in communication networks because a base station is often able to use many antennas whereas smaller receivers, such as mobile devices, have a strict size limitation. The capacity of this channel is known, but the finite blocklength limits of codes over this channel is still unknown. In this thesis, we analyze these finite blocklength fundamental limits. Specifically, we give the coding theorem showing the achievable dispersion...
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...