Página 13 dos resultados de 2566 itens digitais encontrados em 0.038 segundos

A scalable mixed-level approach to dynamic analysis of C and C++ programs

Guo, Philip Jia
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 112 p.
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This thesis addresses the difficult task of constructing robust and scalable dynamic program analysis tools for programs written in memory-unsafe languages such as C and C++, especially those that are interested in observing the contents of data structures at run time. In this thesis, I first introduce my novel mixed-level approach to dynamic analysis, which combines the advantages of both source- and binary-based approaches. Second, I present a tool framework that embodies the mixed-level approach. This framework provides memory safety guarantees, allows tools built upon it to access rich source- and binary-level information simultaneously at run time, and enables tools to scale to large, real-world C and C++ programs on the order of millions of lines of code. Third, I present two dynamic analysis tools built upon my framework - one for performing value profiling and the other for performing dynamic inference of abstract types - and describe how they far surpass previous analyses in terms of scalability, robustness, and applicability. Lastly, I present several case studies demonstrating how these tools aid both humans and automated tools in several program analysis tasks: improving human understanding of unfamiliar code, invariant detection...

Modeling trust in human conversation

Miller, Catherine (Catherine T.)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 43 leaves
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If we are ever to have intelligent systems, they will need memory. Memory is the core of learning; intelligence is about entering, extracting, and synthesizing its contents. What makes the memory problem difficult is that memory is not a simple collection of facts. The how and why of where those facts were acquired is a key part of how they are internalized and used later. As a step towards solving this large and difficult problem, I have focused on how people learn to trust each other when they have a conversation. The model I have created represents people as sets of self-organizing maps; each has a map to represent his own beliefs, and a map to represent what he thinks of another person. Beliefs are in this model restricted to likes and dislikes, across a wide range of topics. In this thesis I describe the program implemented in Java to test this model. The model has been tested on four different kinds of conversations. with the topics of animals and cars, to determine whether its behavior looks reasonable to a human observer. In this work I show how a simple, natural model can closely approximate human behavior. without need for tweaking parameters.; by Catherine Miller.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

MIT integrated microelectronics device experimentation and simulation iLab; Massachusetts Institute of Technology integrated microelectronics device experimentation and simulation iLab

Cukalovic, Boris
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 58 p.
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We developed the MIT Integrated Microelectronics Device Experimentation and Simulation iLab, a new online laboratory that combines and significantly upgrades the capabilities of two existing online microelectronics labs: WebLab, a device characterization lab, and WebLabSim, a device simulation lab. The new integrated tool allows users to simultaneously run experiments on actual devices and simulations on the virtual ones, as well as to compare the results of the two. In order to achieve this, we considerably extended the capabilities of the original clients. We added the ability to graph the results of multiple experiments and simulations simultaneously, on top of each other, which allows for much easier comparison. We also added the ability to load, view and graph the results of experiments and simulations that were ran at any point in the past, even when the corresponding lab configurations are no longer available. Our hope is that this new integrated iLab will enrich microelectronics teaching and learning by allowing students to compare real life device behavior with theoretical expectations.; by Boris Cukalovic.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.; Includes bibliographical references (p. 57-58).

Iterative algorithms for lossy source coding

Chandar, Venkat (Venkat Bala)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 68 p.
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This thesis explores the problems of lossy source coding and information embedding. For lossy source coding, we analyze low density parity check (LDPC) codes and low density generator matrix (LDGM) codes for quantization under a Hamming distortion. We prove that LDPC codes can achieve the rate-distortion function. We also show that the variable node degree of any LDGM code must become unbounded for these codes to come arbitrarily close to the rate-distortion bound. For information embedding, we introduce the double-erasure information embedding channel model. We develop capacity-achieving codes for the double-erasure channel model. Furthermore, we show that our codes can be efficiently encoded and decoded using belief propagation techniques. We also discuss a generalization of the double-erasure model which shows that the double-erasure model is closely related to other models considered in the literature.; by Venkat Chandar.; Thesis (M. Eng. and S.B.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.; Includes bibliographical references (p. 65-68).

The ICoN integrated communication and navigation protocol for underwater acoustic networks

Kanthan, Rupesh R
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 82 p.
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The deployment of autonomous underwater devices has increased dramatically in the last several years, presenting a strong and growing need for a network protocol to mediate acoustic communications between devices. This network protocol must also provide an infrastructure for acoustic navigation, while ensuring that provisions for communication and navigation do not interfere with each other. To approach this difficult problem, we begin with a discussion of the limitations of traditional networking protocols when subjected to the complexities introduced by the underwater acoustic environment. We then present ICoN, a proposed network protocol, designed to integrate acoustic communication and navigation and optimized to operate in the low-bandwidth, high-loss underwater environment. A working description of ICoN and a discussion of its features are followed by analysis of the protocol through simulation, indicating its potential for improved performance over traditional networking protocols. The simulation results are reinforced through real-world experimental validation of ICoN, which, though limited, appears to confirm the effectiveness of the new protocol. We conclude with possible future extensions to ICoN, discussing various methods that might increase its potency in dealing with more demanding underwater acoustic applications.; by Rupesh R. Kanthan.; Thesis (M. Eng. and S.B.)--Massachusetts Institute of Technology...

Topologies for ad-hoc networks utilizing directional antennas with restricted fields of view

Anderson, Brian C. (Brian Curtis)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 64 p.
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ORCLE (Optical/RF Combined Link Experiment), is an airborne network in which aircraft have multiple directional antennas that are restricted in their pointing direction. A pair of aircraft in ORCLE can be linked if they both have an antenna pointing at each other. Four topology algorithms, which coordinate the pointing of the antennas and attempt to maximize a connectedness metric, are presented and analyzed using a custom 2D simulation platform. Three of the algorithms are based on the Relative Neighbor Graph (RNG): the first constrains the RNG to requirements of the ORCLE network, the second augments the constrained RNG with edges from the Delaunay Triangulation, and the third algorithm tries to improve on the second by adding edges to reduce the diameter. The final algorithm uses a novel concept of overlapping sets of nested convex hulls to select the links of the network. All algorithms are stateless and interface with a Target Transition Layer, which gradually migrates topologies to prevent a large number of edges from being lost simultaneously. Scenes with varying node density, number of terminals per node, fields of view, and re-targeting delays are used to test the algorithms against a wide range of possible situations.; by Brian C. Anderson.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

Assisted auscultation : creation and visualization of high dimensional feature spaces for the detection of mitral regurgitation

Leeds, Daniel Demeny
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 83 p.
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Cardiac auscultation, listening to the heart using a stethoscope, often constitutes the first step in detection of common heart problems. Unfortunately, primary care physicians, who perform this initial screening, often lack the experience to correctly evaluate what they hear. False referrals are frequent, costing hundreds of dollars and hours of time for many patients. We report on a system we have built to aid medical practitioners in diagnosing Mitral Regurgitation (MR) based on heart sounds. Our work builds on the "prototypical beat" introduced by Syed in [17] to extract two different feature sets characterizing systolic acoustic activity. One feature set is derived from current medical knowledge. The other is based on unsupervised learning of systolic shapes, using component Analysis. Our system employs self-organizing maps (SOMs) to depict the distribution of patients in each feature space as labels within a two-dimensional colored grid. A user screens new patients by viewing their projections onto the SOM, and determining whether they are closer in space, and thus more similar, to patients with or without MR. We evaluated our system on 46 patients. Using a combination of the two feature sets, SOM-based diagnosis classified patients with accuracy similar to that of a cardiologist.; by Daniel Demeny Leeds.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

Techniques for identifying long-range residue correlations in the fifth binding module of LDLR

Lin, Jennifer W
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 90 p.
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The study of correlations between residues in distal regions of a protein structure may provide insights into the mechanism of protein folding. Such long-range correlations may exist between distant residues that are conserved by evolution or physically related by motion. Two computational approaches, one involving hidden Markov models (HMMs) and the other applying molecular dynamics (MD), were implemented to identify a comprehensive set of residue couplings, as well as provide possible explanations for the correlations. HMMs were employed to model the secondary structural elements of proteins in order to discover residues correlated by coevolution. MD simulations and cross-correlation analyses were performed to determine residues coupled by motion. The protein system that was chosen for the study of long-range correlated residues was the fifth binding module (LR5) of the low-density lipoprotein receptor (LDLR) which regulates the cholesterol level in the bloodstream.; (cont.) The LR5 repeat is crucial to the binding of LDLR to lipoprotein particles that carry cholesterol. The HMM and MD approach identified correlations between residues that have been postulated to bind to a particular type of lipoprotein and residues involved in calcium ion coordination which maintains the folding of the LDLR structure. Energetic pathways of the LR5 module were constructed to provide insights into structural stability and functional importance of the residue couplings.; by Jennifer W. Lin.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

Integrated optical isolators

Zaman, Tauhid R
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 129 p.
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Introduction: Optical isolators are important components in lasers. Their main function is to eliminate noise caused by back-reflections into these lasers. The need for integrated isolators comes from the continuing growth of telecommunication networks. Monolithic integration of isolators with other optical components such as lasers would reduce costs and increase functionality. This thesis presents the design and test of a monolithically integrated optical isolator for telecommunication networks. This chapter will begin with an explanation of how isolators actually eliminate noise in lasers and then it will then show how commercial bulk isolators function. Next, greater detail will be provided on the need for monolithically integrated isolators. Because isolators are non-reciprocal devices, they must use a non-reciprocal effect in order to function. A brief description of this phenomenon, known as Faraday rotation, will be given in this chapter. Then previous work on integrated isolators will be presented. Finally, an overview of this thesis will be given.; by Tauhid R. Zaman.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.; Includes bibliographical references (p. 127-129).

Pulsed field separation of biomolecules in a nanofluidic filter array

Reyes González, Noel I. (Noel Iván)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 42 leaves
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In this work, pulsed electric fields are introduced as a means to enhance separation efficiency of biomolecules in a nanofluidic filter array channel. Separation under pulsed fields was tested using PBR322 DNA, Lambda Hind III DNA, and a sample containing three SDS denatured proteins. Pulsed fields are divided into long pulse and short pulse regimes, depending on how long the duration of the higher electric field pulse is compared to the average trapping time of a molecule in a single nanofluidic filter. It was found that under long pulse fields, the separation selectivity cannot be enhanced since the difference in velocity between two different molecules will always be a weighted average of the velocity at the high and low field levels of the pulsed field. On the other hand, application of pulsed fields in the short pulse regime yielded more promising results. After the pulse duration became comparable to the average trapping time of migrating molecules, the average velocity of molecules decreased with a reduction in the pulse duration. Certain bands within a sample were slowed down more than others by appropriately choosing the pulse duration, therefore resulting in increased selectivity and higher separation efficiency.; (cont.) For PBR322 DNA...

Design of micropower operational amplifiers

Rayanakorn, Surapap
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 151 p.
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The operational amplifier is a fundamental building block for electronic devices and systems. The advancement of modern electronic technology has been setting more performance demand on the underlying integrated circuits including the operational amplifier. Reduction in power consumption and improvement in speed are some of the most important requirements. To address these concerns, this thesis presents a design of micropower Class AB operational amplifiers which has the ratio of gain bandwidth product to supply current higher than that of an existing IC. The design is in a 0.6pxm CMOS process. The input stage of the design has the folded-cascode architecture that allows the input common-mode range down to negative supply voltage. The Class AB output stage swings rail-to-rail and has the ratio of maximum current to quiescent current greater than 100. The bias cell of the operational amplifier is designed to consume only 6% of the total supply current. The thesis concludes the operational amplifier design with two frequency compensation options.; (cont.) The one with simple Miller compensation has a unity gain frequency of 360kHz with 61.5 degrees of phase margin at 100pF load while consuming 20[mu]A supply current. The other with the hybrid of simple Miller compensation and cascode compensation offers an improved unity gain frequency of 590kHz at the same loading and power condition.; by Surapap Rayanakorn.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

Design and implementation of a sector-based airspace model for the MIT Extensible Air Network Simulation

Whittaker, Colin J
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 84 p.
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The MIT Extensible Air Network Simulation (MEANS) is a tool that has been designed to assist airline schedulers and air traffic managers in predicting flight delays for given air traffic scenarios. One aspect of the simulation, the determination of flight times, has received criticism from the MEANS users as being too simplistic for their needs. Currently, MEANS predicts flight times based on a historical distribution of observed flight times between city pairs. This system ignores the effects of flight level winds and airspace congestion, two major determiners of flight time. The replacement flight time model presented divides the airspace into discrete sectors based on existing divisions in air traffic control. Each sector has its own wind conditions and capacity limitations which affect passing flights. Results show that, after some calibration, the new flight time model produces accurate flight times when the airspace is divided into ARTCC domains and does not introduce additional errors into other parts of the simulation. Additionally, test scenarios show that the new system is capable of modeling airspace capacity events, such as a radar failure. Comparative results reveal that the old, distribution model produces surprisingly accurate flight times for typical wind conditions and airspace utilization.; by Colin J. Whittaker.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

Efficient out-of-plane microphotonic fiber-to-chip coupler designs

Fan, Mingyan
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 59 p.
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Due to the tremendous increase of data rates in optical communication, and as a result the forthcoming reliance on photonic circuits for all-optical switching, routing and signal processing, efficient coupling of light between a nanophotonic waveguide and a fiber has become a critical and interesting issue to investigate. The objective of this thesis is to explore new strategies for efficient fiber-to-chip coupler design and to come up with design rules based on these strategies and a competent device design. Some of the previous research in the area of coupler design is reviewed, and a novel out-of-plane fiber-to-chip coupler design that is based on phase-canceling gratings is proposed. The principle of operation of this grating is explained and may be applied to other grating designs.; by Mingyan Fan.; Thesis (M. Eng. and S.B.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.; Includes bibliographical references (p. 59).

New foundations for efficient authentication, commutative cryptography, and private disjointness testing

Weis, Stephen August, 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 115 p.
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This dissertation presents new constructions and security definitions related to three areas: authentication, cascadable and commutative crytpography, and private set operations. Existing works relevant to each of these areas fall into one of two categories: efficient solutions lacking formal proofs of security or provably-secure, but highly inefficient solutions. This work will bridge this gap by presenting new constructions and definitions that are both practical and provably-secure. The first contribution in the area of efficient authentication is a provably-secure authentication protocol named HB+. The HB+ protocol is efficient enough to be implemented on extremely low-cost devices, or even by a patient human with a coin to flip. The security of HB+ is based on the hardness of a long-standing learning problem that is closely related to coding theory. HB+ is the first authentication protocol that is both practical for low-cost devices, like radio frequency identification (RFID) tags, and provably secure against active adversaries. The second contribution of this work is a new framework for defining and proving the security of cascadable cryptosystems, specifically commutative cryptosystems.; (cont.) This new framework addresses a gap in existing security definitions that fail to handle cryptosystems where ciphertexts produced by cascadable encryption and decryption perations may contain some message-independent history. Several cryptosystems...

Optimal information storage : nonsequential sources and neural channels

Varshney, Lav R. (Lav Raj)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 163 p.
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Information storage and retrieval systems are communication systems from the present to the future and fall naturally into the framework of information theory. The goal of information storage is to preserve as much signal fidelity under resource constraints as possible. The information storage theorem delineates average fidelity and average resource values that are achievable and those that are not. Moreover, observable properties of optimal information storage systems and the robustness of optimal systems to parameter mismatch may be determined. In this thesis, we study the physical properties of a neural information storage channel and also the fundamental bounds on the storage of sources that have nonsequential semantics. Experimental investigations have revealed that synapses in the mammalian brain possess unexpected properties. Adopting the optimization approach to biology, we cast the brain as an optimal information storage system and propose a theoretical framework that accounts for many of these physical properties. Based on previous experimental and theoretical work, we use volume as a limited resource and utilize the empirical relationship between volume anrid synaptic weight.; (cont.) Our scientific hypotheses are based on maximizing information storage capacity per unit cost. We use properties of the capacity-cost function...

Multi-layer three-dimensional silicon electronics enabled by wafer bonding; Multi-layer 3D silicon electronics enabled by wafer bonding

Tan, Chuan Seng, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 179 p.
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Three-dimensional integrated circuits (3-D ICs), in the form of a vertical stack of several interconnected device layers, have many performance, form factor, and integration advantages. The main objective of this work is to develop reliable process technology to enable the fabrication of a vertically interconnected silicon multi-layer stack. Low temperature wafer bonding processes, both copper thermo-compression bonding and silicon dioxide fusion bonding, are studied extensively as key enabling technology. Cu thermo-compression bonding is studied for its feasibility as a permanent bond between active layers in a multi-layer stack. It is found that pre-bonding anneal in forming gas can remove surface oxide on Cu wafers and reduce the oxygen content in the bonded layer. The quality of bonded Cu layer is adversely degraded by the formation of interfacial voids. Void nucleation and growth are studied and counter-measures for void suppression are proposed and implemented. Silicon dioxide wafer bonding, on the other hand, is used as a temporary bond to attach a donor wafer to a handle wafer during donor wafer thinning and subsequent layer transfer. Sufficiently high bond strength is obtained with careful surface preparation and activation prior to bonding.; (cont.) Silicon layer can be stacked either in a "face down" or "face up" orientation. Using a combination of wafer bonding and thinning...

Algorithms and lower bounds in finite automata size complexity

Kapoutsis, Christos, 1974-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 99 p.
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In this thesis we investigate the relative succinctness of several types of finite automata, focusing mainly on the following four basic models: one-way deterministic (1)FAs), one-way nondeterministic (1NFAs), two-way deterministic (2DFAS), and two-way nondeterministic (2NFAS). First, we establish the exact values of the trade-offs for all conversions from two-way to one-way automata. Specifically, we prove that the functions ... return the exact values of the trade-offs from 2DFAS to 1DFAS, from 2NFAS to 1DFAs, and from 2DFAs or 2NFAS to 1NFAs, respectively. Second, we examine the question whether the trade-offs from NFAs or 2NFAS to 2DiFAs are polynomial or not. We prove two theorems for liveness, the complete problem for the conversion from 1NFAS to 2DFAS. We first focus on moles, a restricted class of 2NFAs that includes the polynomially large 1NFAS which solve liveness. We prove that, in contrast, 2DFA moles cannot solve liveness, irrespective of size.; (cont.) We then focus on sweeping 2NFAS, which can change the direction of their input head only on the end-markers. We prove that all sweeping 2NFAs solving the complement of liveness are of exponential size. A simple modification of this argument also proves that the trade-off from 2DFAS to sweeping 2NFAS is exponential. Finally...

Integrated microbioreactor arrays for high-throughput experimentation

Lee, Harry, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 226 p.
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Bioprocesses with microbial cells play an important role in producing biopharmaceuticals such as human insulin and human growth hormone, and other products such as amino acids and biopolymers. Because bioprocesses involve the complicated interaction between the genetics of the microorganisms and their chemical and environmental conditions, hundreds or thousands of microbial growth experiments are necessary for to develop and optimize them. In addition, efforts to develop models for bioprocesses also require numerous growth experiments to study microorganism phenotypes. This work describes the design and development of integrated arrays of microbioreactors that can provide the oxygen transfer and control capabilities of a stirred tank bioreactor in a high-throughput format. The devices comprise a novel peristaltic oxygenating mixer and microfluidic injectors, which are fabricated using a process that allows combining multiple scale (100/,m-lcm) and multiple depth (100/im-2mm) structures in a single mold.; (cont.) The microbioreactors have a 100/L working volume, a high oxygen transfer rate (kLa ; 0.1s-1), and closed loop control over dissolved oxygen and pH ( 0.1). Overall, the system supports eight simultaneous batch cultures, in two parallel arrays...

Probabilistic framework for genome-wide phylogeny and ortholog determination

Rasmussen, Matthew D. (Matthew David)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 65 leaves
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Comparative genomics of multiple related species has emerged as a powerful tool for genome signal discovery. To that end, dozens of mammalian, fly, and fungal genomes have been fully sequenced. Making use of these genomes requires rigorous computational methods for determining the evolutionary history of every gene and region. In particular, comparative analysis requires the ability to distinguish between orthologous and paralogous regions. Current approaches to ortholog identification work adequately for pairs of species but are ineffective for multiple complete genomes. This thesis presents a new phylogenetic reconstruction method, SINDIR, that is designed specifically for genome-wide orthology determination. Unlike any other method, SINDIR exploits the known evolutionary history of a set of species to infer the history of their genes. This is done by learning a probabilistic model of evolution from a trusted set of unambiguous orthologs. Given this model, SINDIR can find the maximum likelihood phylogenetic tree for any set of the genes. In a novel technique, synteny maps are used to train and evaluate the evolutionary model on both simulated and real sequence data. SINDIR avoids errors commonly committed by current methods and achieves a significantly improved accuracy of orthology determination.; by Matthew D. Rasmussen.; Thesis (S.M.)--Massachusetts Institute of Technology...

Convergence speed in distributed consensus and averaging

Olshevsky, Alexander
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 75 leaves
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We propose three new algorithms for the distributed averaging and consensus problems: two for the fixed-graph case, and one for the dynamic-topology case. The convergence times of our fixed-graph algorithms compare favorably with other known methods, while our algorithm for the dynamic-topology case is the first to be accompanied by a polynomial-time bound on the worst-case convergence time.; by Alexander Olshevsky.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.; Includes bibliographical references (leaves 71-75).