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DSpace at MIT (77,612 recursos)
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Electrical Engineering and Computer Sciences - Master's degree

Mostrando recursos 1 - 20 de 5,510

1. Neural network architectures for Prepositional Phrase attachment disambiguation - Belinkov, Yonatan
This thesis addresses the problem of Prepositional Phrase (PP) attachment disambiguation, a key challenge in syntactic parsing. In natural language sentences, a PP may often be attached to several possible candidates. While humans can usually identify the correct candidate successfully, syntactic parsers are known to have high error rated on this kind of construction. This work explores the use of compositional models of meaning in choosing the correct attachment location. The compositional model is defined using a recursive neural network. Word vector representations are obtained from large amounts of raw text and fed into the neural network. The vectors are...

2. A delay-constrained cross-layer model using network coding - Adams, David C. (David Christopher)
Traditionally, most packet-switched networks have only one wireless hop: the link between the end users and their access point. However, there is increasing interest in using wireless links to reach the edge of the network. Having more than one wireless link is a game changer. Network layer architecture is predicated on the assumption that the lower layers are reliable, but this comes at a high cost in terms of data rate on a band-limited, lossy wireless channel. This cost is tolerable over one underutilized link, but when the network demands high-capacity wireless links, it may be time to rethink the...

3. Better embeddings for Planar Earth-Mover Distance over sparse sets - Backurs, Arturs
We consider the problem of constructing low-distortion embeddings of the Planar Earth-Mover Distance (EMD) into lp spaces. EMD is a popular measure of dissimilarity between sets of points, e.g., bags of geometric features. We present a collection of embeddings with the property that their distortion and/or host-space dimension are parametrized by the size (or the sparsity) of the embedded sets s. Our specific results include: -- An O(log s)-distortion embedding of EMD over s-subsets into l1-e. This is the first embedding of EMD into a "tractable" lp, space whose distortion is a function of the sparsity, not the size of...

4. The structure of promises in quantum speedups - Ben David, Shalev
It has long been known that in the usual black-box model, one cannot get super-polynomial quantum speedups without some promise on the inputs. In this thesis, we examine certain types of symmetric promises, and show that they also cannot give rise to super-polynomial quantum speedups. We conclude that exponential quantum speedups only occur given "structured" promises on the input. Specifically, we show that there is a polynomial relationship of degree 12 between D(f) and Q(f) for any function f defined on permutations (elements of {0, 1, ... , M - 1}1 in which each alphabet element occurs exactly once). We...

5. (OR)² : operations research applied to operating room supply chain - Ben-Zvi, Noa
Massachusetts General Hospital (MGH) is ranked as the top hospital in New England and second nation-wide. It is also the largest hospital in New England; it uses an average of 58 operating rooms, where approximately 150 surgical procedures are performed daily. Management of surgical supplies is a critical component of the processes supporting this infrastructure. Specifically, ensuring the right equipment and supplies are available at the right time is critical for the efficiency and quality outcomes of each of the procedures. The materials management group handles over 10,000 unique items, purchased from more than 400 vendors. The majority (60-70%) of...

6. Energy-efficient SRAM design in 28nm FDSOI Technology - Biswas, Avishek, S.M. Massachusetts Institute of Technology
As CMOS scaling continues to sub-32nm regime, the effects of device variations become more prominent. This is very critical in SRAMs, which use very small transistor dimensions to achieve high memory density. The conventional 6T SRAM bit-cell, which provides the smallest cell-area, fails to operate at lower supply voltages (Vdd). This is due to the significant degradation of functional margins as the supply voltage is scaled down. However, Vdd scaling is crucial in reducing the energy consumption of SRAMs, which is a significant portion of the overall energy consumption in modern micro-processors. Energy savings in SRAM is particularly important for...

7. StreamJIT : a commensal compiler for high-performance stream programming - Bosboom, Jeffrey
There are domain-specific libraries for many domains, enabling rapid and cost-effective development of complex applications. On the other hand, domain-specific languages are rare despite the performance advantages of compilation. We believe the reason is the multiple orders-of-magnitude higher cost of building a compiler compared to building a library. We propose commensal compilation, a new strategy for compiling embedded domain-specific languages by reusing the massive investment in modern language virtual machine platforms. Commensal compilers use the host language's front-end, use an autotuner instead of optimization heuristics, and use host platform APIs that enable back-end optimizations by the host platform JIT. The...

8. A time and frequency domain analysis of contrarian trading strategies/ - Chaudhuri, Shomesh E
This thesis applies time and frequency domain analyses to a high-frequency market making strategy to study the profitability of liquidity provision over multiple time horizons from 1964 to 2013. Using daily returns and inside quotes, we provide evidence that widening spreads on the NASDAQ National Market System in the late 1980s and early 1990s were facilitated by implicit pricing agreements amongst security dealers. In contrast, we show that regulatory changes, such as decimalization, and the development of liquidity providing algorithmic trading strategies acted to narrow spreads and reduce transaction costs. Increasing the focus of our analytical lens to the intraday...

9. Reducing pause times with clustered collection - Cutler, Cody
Clustered Collection reduces garbage collection pauses in programs with large amounts of live data. A full collection of millions of live objects can pause the program for multiple seconds. Much of this work, however, is repeated from one collection to the next, particularly for programs that modify only a small fraction of their object graphs between collections. Clustered Collection reduces redundant work by identifying regions of the object graph which, once traced, need not be traced by subsequent collections. Each of these regions, or "clusters," consists of objects reachable from a single head object. If the collector can reach a...

10. Improving clinical risk-stratification tools : instance-transfer for selecting relevant training data - Gong, Jen J. (Jen Jian)
One of the primary problems in constructing risk-stratification models for medical applications is that the data are often noisy, incomplete, and suffer from high class-imbalance. This problem becomes more severe when the total amount of data relevant to the task of interest is small. We address this problem in the context of risk-stratifying patients receiving isolated surgical aortic valve replacements (isolated AVR) for the adverse outcomes of operative mortality and stroke. We work with data from two hospitals (Hospital 1 and Hospital 2) in the Society of Thoracic Surgeons (STS) Adult Cardiac Surgery Database. Because the data available for our...

11. Wearable-assisted social interaction as assistive technology for the blind - Hayden, David S. (David Scott)
This work presents an end-to-end wearable system designed to learn and assist its (potentially blind) wearers with daily social interactions. In particular, it visually identifies nearby acquaintances and provides timely, discreet notifications of their presence to the wearer. Offline, the system learns the people with whom the wearer interacts by automatically detecting social interactions through egocentric audio, video and accelerometer data and querying the wearer for the identities of persons unknown to the system.

12. The assessment of battery-ultracapacitor hybrid energy storage systems - He, Yiou
Battery-ultracapacitors hybrid energy storage systems (ESS) could combine the high power density and high life cycle of ultracapacitors with the high energy density of batteries, which forms a promising energy storage system. In this thesis, an assessment of the benefits of the hybrid ESS relative to its battery-only counterpart in pulse-load applications is investigated for both Nickel-Metal Hydride (NiMH) batteries and Lithium-ion (Li-ion) batteries, and under different load profiles. Specifically, the hybrid ESS in this assessment is of the simplest type - paralleling the ultracapacitors across the batteries without any power electronics interface between them. To quantify this assessment, Discharge...

13. Algorithms, architectures and circuits for low power HEVC codecs - Juvekar, Chiraag
In order to satisfy the demand for high quality video streaming, aggressive compression is necessary. High Efficiency Video Coding (HEVC) is a new standard that has been designed with the goal of satisfying this need in the coming decade. For a given quality, of video HEVC offers 2x better compression than existing standards. However, this compression comes at the cost of a commensurate increase in complexity. Our work aims to control this complexity in the context of real-time hardware video codecs. Our work focused on two specific areas: Motion Compensation Bandwidth and Intra Estimation. HEVC uses larger filters for motion...

14. Fast long lived renaming - Kopinsky, Justin
The long-lived renaming problem appears in shared-memory systems where a set of threads need to register and deregister frequently from the computation, while concurrent operations scan the set of currently registered threads. Instances of this problem show up in concurrent implementations of transactional memory, flat combining, thread barriers, and memory reclamation schemes for lock-free data structures. In this thesis, we analyze a randomized solution for long-lived renaming. The algorithmic technique we consider, called the LevelArray, has previously been used for hashing and one-shot (single-use) renaming. Our main contribution is to prove that, in long-lived executions, where processes may register and...

15. Degradation of GaN High Electron Mobility Transistors under high-power and high-temperature stress - Wu, Yufei, S.M. Massachusetts Institute of Technology
GaN HEMTs (High Electron Mobility Transistors) are promising candidates for high power and high frequency applications but their reliability needs to be established before their wide deployment can be realized. In this thesis, degradation mechanisms of GaN HEMTs under high-power and high-temperature stress have been studied. A novel technique to extract activation energy of degradation rate from measurements on a single device has been proposed. High-power and high-temperature stress has revealed two sequential degradation mechanisms where the gate current degrades first and saturates only after which the drain current shows significant degradation. A study of the semiconductor surface of delaminated...

16. Sparkle vision : seeing the world through random specular microfacets - Zhang, Zhengdong, S.M. Massachusetts Institute of Technology
This thesis studies the problem of reproducing the world lighting from a single image of an object covered with random specular microfacets on the surface. Such a reflector can be interpreted as a randomized mapping from the lighting to the image. This intrinsic randomness makes it challenging for humans to interpret the image of a specular surface. We propose a system to solve it algorithmically and demonstrate how a simple yet reliable method can calibrate the proposed system and do the inference. The success of such system relies on accurate exposure of the specular surfaces. However, such objects have very...

17. Design considerations for Ge-on-Si waveguide photodetector - Živanović, Goran
In integrated photonic circuits photodetector is one of key components, modern applications require that photodetector has a high 3 dB bandwidth. The ultimate limit for the response time for conventional photodetectors (like vertically illuminated photodiode, Schotky photodiode, MSM photodetector etc.) is given by the transit time of the photogenerated electron-hole pairs, it can not be minimised by decreasing the thickness of the depletion region without reducing quantum efficiency (i.e. the fraction of the incident light that is absorbed). Waveguide photodetectors have been developed to overcome this trade-off. In the waveguide photodetector light propagates in a direction that is parallel to...

18. Learning a strategy for whole-arm grasping - Anders, Ariel (Ariel Sharone)
Traditionally, robot grasping has been approached in two separate phases: first, finding contact positions that yield optimal grasps and, then, moving the robot hand to these positions. This approach works well when the object's location is known exactly and the robot's control is perfect. However, in the presence of uncertainty, this approach often leads to failure, usually because the robot's gripper contacts the object and causes the object to move away from the grasp. To obtain reliable grasping in the presence of uncertainty, the robot needs to anticipate the possible motions of the object during grasping. Our approach is to...

19. An information-theoretic analysis of resampling in Sequential Monte Carlo - Huggins, Jonathan H. (Jonathan Hunter)
Sequential Monte Carlo (SMC) methods form a popular class of Bayesian inference algorithms. While originally applied primarily to state-space models, SMC is increasingly being used as a general-purpose Bayesian inference tool. Traditional analyses of SMC algorithms focus on their usage for approximating expectations with respect to the posterior of a Bayesian model. However, these algorithms can also be used to obtain approximate samples from the posterior distribution of interest. We investigate the asymptotic and non-asymptotic properties of SMC from this sampling viewpoint. Let P be a distribution of interest, such as a Bayesian posterior, and let P be a random...

20. Scaling address-space operations on Linux with TSX - Johnson, Christopher Ryan, S.M. Massachusetts Institute of Technology
Concurrent programming is important due to increasing core counts, but scalable concurrency control is difficult and error-prone to implement. Hardware Transactional Memory (HTM) addresses this problem by providing hardware support for concurrently executing arbitrary read-modify-write memory transactions. Intel released Transactional Synchronization eXtensions (TSX), a HTM implementation, in select processors to support scalable concurrency control. This thesis contributes a case study in applying TSX to the Linux virtual memory system, which currently serializes address-space operations with a lock. TSX should provide scalability by supporting concurrent address-space operations. Achieving scalability with TSX, however, turned out to be difficult due to transactional aborts....

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