Recursos de colección

DSpace at MIT (104.280 recursos)

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Electrical Engineering and Computer Sciences - Ph.D. / Sc.D.

Mostrando recursos 1 - 20 de 2.710

  1. Nanoscale engineering of spin-based quantum devices in diamond

    Trusheim, Matthew Edwin
    The development of quantum technologies from the bottom-up requires engineering and control at the level of single quanta. In this thesis, we explore the engineering of a particular quantum system: optically active defects in diamond, known as color centers. Color centers have a variety of advantageous characteristics, including long-lived quantum phase coherence in their electron spin degrees of freedom, available highfidelity control and readout at the single-spin level, and strong interactions with other quantum systems such as photons. In addition, color centers can be controllably created and their local environment shaped through semiconductor fabrication processes that form a toolkit for...

  2. Energy-efficient circuits and systems for computational imaging and vision on mobile devices

    Raina, Priyanka
    Eighty five percent of images today are taken by cell phones. These images are not merely projections of light from the scene onto the camera sensor but result from a deep calculation. This calculation involves a number of computational imaging algorithms such as high dynamic range (HDR) imaging, panorama stitching, image deblurring and low-light imaging that compensate for camera limitations, and a number of deep learning based vision algorithms such as face recognition, object recognition and scene understanding that make inference on these images for a variety of emerging applications. However, because of their high computational complexity, mobile CPU or...

  3. Development in utilizing singlet fission and triplet-triplet annihilation to improve solar cell efficiency

    Wu, Tony Chang-Chi
    Our main energy source are burning fossil fuels. Solar energy is a clean, sustainable energy source that does not emit greenhouse gas that causes global warming. In this thesis, singlet fission and triplet-triplet annihilation would be discussed and studied to increase solar cell power conversion efficiency. Singlet fission splits a singlet exciton into two lower energy triplet excitons. This energy down conversion is efficient and have shown near 200% triplet exciton yield. With energy down conversion, thermalization loss in solar cell could be reduced. We have shown singlet fission in tetracene, a suitable down conversion fission material to pair with...

  4. Latent variable models for understanding user behavior in software applications

    Saeedi, Ardavan
    Understanding user behavior in software applications is of significant interest to software developers and companies. By having a better understanding of the user needs and usage patterns, the developers can design a more efficient workflow, add new features, or even automate the user's workflow. In this thesis, I propose novel latent variable models to understand, predict and eventually automate the user interaction with a software application. I start by analyzing users' clicks using time series models; I introduce models and inference algorithms for time series segmentation which are scalable to large-scale user datasets. Next, using a conditional variational autoencoder and...

  5. Exploring valleytronics in 2D transition metal dichalcogenides

    Modtland, Brian Joseph
    Monolayer transition metal dichalcogenides (TMDs) exhibit distinct electrical and optical properties according to the relative occupation of each of two valleys in their dispersion relation. The resulting valley degree of freedom is robust, linked to a large spin-orbit splitting between valence bands, and shows promise in electro-optical devices or as an information token for logic applications. In order to explore applications of these properties, monolayer crystals are required that have reduced intervalley scattering. To date, the majority of valley-related studies have focused on exfoliated samples for their quality and ease of production. In this thesis, valley polarization is explored in...

  6. Logical leases : scalable hardware and software systems through time traveling

    Yu, Xiangyao
    Parallelism is the key to performance in modern computer systems. However, parallel systems are hard to design and to use. Challenges of parallelism exist across the whole system stack in both hardware and software. In this thesis, we improve the scalability and performance of shared-memory parallel systems in both hardware and software. We propose a simple technique, called logical leases, to achieve this goal. Logical leases allow a parallel system to dynamically reorder operations to minimize conflicts, leading to high performance and scalability. The power of logical leases comes from its novel way of combining physical and logical time. The...

  7. Automatic patch generation via learning from successful human patches

    Long, Fan, Ph. D. Massachusetts Institute of Technology
    Automatic patch generation holds out the promise of automatically correcting software defects without the need for developers to manually diagnose, understand, and correct these defects. This dissertation presents two novel patch generation systems, Prophet and Genesis, which learn from past successful human patches to enhance the patch generation process. The core of Prophet and Genesis is a novel learning technique that extracts universal properties of correct code and a novel inference technique that generalizes universal patching strategies across different applications. The results show that the learning and inference techniques enable Prophet and Genesis to operate with rich and tractable search...

  8. Design-space and scalable technology for GaN based power transistors

    Piedra, Daniel, Ph. D. Massachusetts Institute of Technology
    As silicon devices approach their intrinsic material and technological limit, there is an opportunity for alternative semiconductor materials to push the performance of electronics forward. Gallium nitride (GaN) has demonstrated very promising performance for advanced electronics, but there is still room for improvement. This thesis discusses several new transistor designs to improve the performance of GaN-based power devices as well as demonstrations of their scaling potential and integration capability with silicon. Specifically, we have developed a wide-periphery GaN fin-based high electron mobility transistor process for power switching. The process was developed with emphasis on the passivation, field plates, gate periphery...

  9. Uplift modeling for randomized experiments and observational studies

    Fang, Xiao, Ph. D. Massachusetts Institute of Technology
    Uplift modeling refers to the problem where we need to identify from a set of treatments the candidate that leads to the most desirable outcome based on subject characteristics. Most work in the last century focus on the average effect of a treatment across a population of interest, but ignores subject heterogeneity which is very common in real world. Recently there has been explosion of empirical settings which makes it possible to infer individualized treatment responses. We first consider the problem with data from randomized experiments. We put forward an unbiased estimate of the expected response, which makes it possible...

  10. Optical signal generation, stabilization, and manipulation in broadband silicon photonics

    Magden, Emir Salih
    Together with the increasing number of applications in vastly different parts of the electromagnetic spectrum, more versatile, stable, and capable light generation and manipulation techniques are required in integrated photonics. In this thesis, using CMOS fabrication capabilities, and a single layer back-end deposition process, CMOS-compatible lasers are developed using aluminum oxide as the host medium. First, a low temperature deposition process is detailed, and erbium-based lasers are demonstrated in the C-band. Then, thulium is studied and characterized as a dopant for applications at longer wavelengths. On-chip frequency stability issues are addressed by investigating the thermo-optic characteristics of various CMOS-compatible media....

  11. High-dimensional quantum communication over deployed fiber

    Lee, Catherine, Ph. D. Massachusetts Institute of Technology
    Quantum key distribution (QKD) exploits the inherent strangeness of quantum mechanics to improve secure communication, enabling two pre-authenticated participants to establish symmetric encryption keys over long distances, without making any assumptions about the computational abilities of an adversary. QKD commonly relies on the transmission and detection of single photons to distribute the secret keys, but the secret-key generation rates are often limited by hardware, namely the ability to produce or detect nonclassical states of light. We address this challenge by using high-dimensional encoding to increase the secure information yield per detected photon. In this thesis, we present security analysis for...

  12. Software-hardware systems for the Internet-of-Things

    Salehi-Abari, Omid
    Although interest in connected devices has surged in recent years, barriers still remain in realizing the dream of the Internet of Things (IoT). The main challenge in delivering IoT systems stems from a huge diversity in their demands and constraints. Some applications work with small sensors and operate using minimal energy and bandwidth. Others use high-data-rate multimedia and virtual reality systems, which require multiple-gigabits-per-second throughput and substantial computing power. While both extremes stress the computation, communications, and energy resources available to the underlying devices, each intrinsically requires different solutions to satisfy its needs. This thesis addresses both bandwidth and energy...

  13. Architectures for photon-mediated quantum information processing

    Pant, Mihir
    In this thesis, I present architectures for quantum information processing where photons are used as the quantum bit (qubit) or for mediating entanglement between other qubits. The emphasis of this research is to simplify the basic building blocks required in such processors. The all-photonic repeater and computing architectures do not require material nonlinearities, and their resource requirements are reduced by several orders of magnitude. The photon-mediated atomic memory architecture is designed to work with faulty memories and experimentally demonstrated values of coherence time and photonic coupling efficiency. In the quantum network architecture, the only operation at every node is probabilistic...

  14. Algorithms and algorithmic obstacles for probabilistic combinatorial structures

    Li, Quan, Ph. D. Massachusetts Institute of Technology
    We study efficient average-case (approximation) algorithms for combinatorial optimization problems, as well as explore the algorithmic obstacles for a variety of discrete optimization problems arising in the theory of random graphs, statistics and machine learning. In particular, we consider the average-case optimization for three NP-hard combinatorial optimization problems: Large Submatrix Selection, Maximum Cut (Max-Cut) of a graph and Matrix Completion. The Large Submatrix Selection problem is to find a k x k submatrix of an n x n matrix with i.i.d. standard Gaussian entries, which has the largest average entry. It was shown in [13] using non-constructive methods that the...

  15. Advanced functional and intraoperative ophthalmic optical coherence tomography imaging

    Lu, Chen David
    Optical coherence tomography (OCT) is a non-contact, non-invasive imaging technique that uses optical interferometry to generate high-resolution, depth-resolved images of tissue in vivo. Ophthalmologists now use commercial OCT systems as a standard diagnostic instrument for imaging the retina to detect or monitor pathologies. However, prototype OCT research instruments exceed commercial systems in terms of faster imaging speeds and higher resolutions. Finding applications for these improvements will improve clinical utility for future OCT systems. This thesis describes the design and use of an ultrahigh resolution spectral domain OCT system for detecting the photoreceptor changes during flash stimulus and an ultrahigh resolution...

  16. Deep learning and structured data

    Zhang, Chiyuan, Ph. D. Massachusetts Institute of Technology
    In the recent years deep learning has witnessed successful applications in many different domains such as visual object recognition, detection and segmentation, automatic speech recognition, natural language processing, and reinforcement learning. In this thesis, we will investigate deep learning from a spectrum of different perspectives. First of all, we will study the question of generalization, which is one of the most fundamental notion in machine learning theory. We will show how, in the regime of deep learning, the characterization of generalization becomes different from the conventional way, and propose alternative ways to approach it. Moving from theory to more practical...

  17. Fully Integrated CMOS-compatible mode-locked lasers

    Shtyrkova, Katia
    The field of integrated photonics has already revolutionized optical communications and is making rapid advances in signal processing, light detection and ranging, optical sensing, bio-medical diagnostics and imaging, and military-related applications. Large and complex radio-frequency and optical systems could be potentially replaced with compact, power-ecient, alignment-free, cost-effectively mass-produced integrated photonics components. An on-chip high repetition-rate mode-locked laser is a key enabler of many integrated photonics applications, such as all-optical sampling, on-chip frequency combs, low phase noise microwave oscillators, photonic ADCs and others. First-ever fully-integrated on-chip mode-locked lasers are demonstrated in this work, fabricated using a CMOS-compatible process. The lasers have...

  18. Theory and modeling of field electron emission from low-dimensional electron systems

    Patterson. Alex A. (Alex Andrew)
    While experimentalists have succeeded in fabricating nanoscale field electron emitters in a variety of geometries and materials for use as electron sources in vacuum nanoelectronic devices, theory and modeling of field electron emission have not kept pace. Treatments of field emission which address individual deviations of real emitter properties from conventional Fowler-Nordheim (FN) theory, such as emission from semiconductors, highly-curved surfaces, or low-dimensional systems, have been developed, but none have sought to treat these properties coherently within a single framework. As a result, the work in this thesis develops a multidimensional, semiclassical framework for field emission, from which models for...

  19. Computational aspects of communication amid uncertainty

    Ghazi, Badih
    This thesis focuses on the role of uncertainty in communication and effective (computational) methods to overcome uncertainty. A classical form of uncertainty arises from errors introduced by the communication channel but uncertainty can arise in many other ways if the communicating players do not completely know (or understand) each other. For example, it can occur as mismatches in the shared randomness used by the distributed agents, or as ambiguity in the shared context or goal of the communication. We study many modern models of uncertainty, some of which have been considered in the literature but are not well-understood, while others...

  20. Discovery and characterization of Cas13b, a differentially regulated RNA-targeting CRISPR system

    Smargon, Aaron Andrew
    RNA plays a significant role in human biology and disease, not only as messenger RNA encoding proteins but also as noncoding RNA regulating DNA, proteins, and other RNA species. Until recently, it has been challenging to target RNA in a simple, efficient manner. CRISPR-Cas (clustered regularly interspaced short palindromic repeats and CRISPR-associated proteins) systems, which confer adaptive immunity to prokaryotes, have revolutionized DNA targeting through the engineering of RNA-programmable Cas9-based tools. Effective RNA-programmable RNA-targeting tools would likewise transform RNA biology and biotechnology. Class 2 CRISPR-Cas systems, which rely only on a single effector protein and programmable CRISPR RNA (crRNA) to...

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