Página 16 dos resultados de 2566 itens digitais encontrados em 0.031 segundos

Vector-thread architecture and implementation

Krashinsky, Ronny (Ronny Meir), 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 186 p.
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This thesis proposes vector-thread architectures as a performance-efficient solution for all-purpose computing. The VT architectural paradigm unifies the vector and multithreaded compute models. VT provides the programmer with a control processor and a vector of virtual processors. The control processor can use vector-fetch commands to broadcast instructions to all the VPs or each VP can use thread-fetches to direct its own control flow. A seamless intermixing of the vector and threaded control mechanisms allows a VT architecture to flexibly and compactly encode application parallelism and locality. VT architectures can efficiently exploit a wide variety of loop-level parallelism, including non-vectorizable loops with cross-iteration dependencies or internal control flow. The Scale VT architecture is an instantiation of the vector-thread paradigm designed for low-power and high-performance embedded systems. Scale includes a scalar RISC control processor and a four-lane vector-thread unit that can execute 16 operations per cycle and supports up to 128 simultaneously active virtual processor threads. Scale provides unit-stride and strided-segment vector loads and stores, and it implements cache refill/access decoupling. The Scale memory system includes a four-port...

Optimally controlling hybrid electric vehicles using path forecasting; Optimally controlling HEVs using path forecasting

Katsargyri, Georgia-Evangelina
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 65 p.
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Hybrid Electric Vehicles (HEVs) with path-forecasting belong to the class of fuel efficient vehicles, which use external sensory information and powertrains with multiple operating modes in order to increase fuel economy. Their main characteristic is that the decision to charge and discharge the battery is made in part by using a prediction of future road conditions. The increasing presence of GPS navigational systems in the standard feature sets of the modern vehicles suggests that path predictive methods applied to HEVs constitute one of the most promising directions towards the solution of serious problems of our era, such as the energy problem, the increasing cost of oil, and the greenhouse gas emissions. In the current project we are given a route and an HEV simulation model, and we aim to minimize the fuel consumption of the vehicle along the route. Towards this direction, we adopt a novel way of decomposing the route into a series of route segments connected to each other and linking the origin to the destination. For each route segment, the road grade, the segment length, and the nominal speed are available. Then, the main idea of our method is to prescribe those set-points of the state of charge of the battery for each road segment...

Robust and efficient robotic mapping

Olson, Edwin B. (Edwin Brock), 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 129 p.
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Mobile robots are dependent upon a model of the environment for many of their basic functions. Locally accurate maps are critical to collision avoidance, while large-scale maps (accurate both metrically and topologically) are necessary for efficient route planning. Solutions to these problems have immediate and important applications to autonomous vehicles, precision surveying, and domestic robots. Building accurate maps can be cast as an optimization problem: find the map that is most probable given the set of observations of the environment. However, the problem rapidly becomes difficult when dealing with large maps or large numbers of observations. Sensor noise and non-linearities make the problem even more difficult especially when using inexpensive (and therefore preferable) sensors. This thesis describes an optimization algorithm that can rapidly estimate the maximum likelihood map given a set of observations. The algorithm, which iteratively reduces map error by considering a single observation at a time, scales well to large environments with many observations. The approach is particularly robust to noise and non-linearities, quickly escaping local minima that trap current methods. Both batch and online versions of the algorithm are described. In order to build a map...

Analysis and implementation of distributed algorithms for multi-robot systems

McLurkin, James D. (James Dwight), 1972-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 166 p.
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Distributed algorithms for multi-robot systems rely on network communications to share information. However, the motion of the robots changes the network topology, which affects the information presented to the algorithm. For an algorithm to produce accurate output, robots need to communicate rapidly enough to keep the network topology correlated to their physical configuration. Infrequent communications will cause most multirobot distributed algorithms to produce less accurate results, and cause some algorithms to stop working altogether. The central theme of this work is that algorithm accuracy, communications bandwidth, and physical robot speed are related. This thesis has three main contributions: First, I develop a prototypical multi-robot application and computational model, propose a set of complexity metrics to evaluate distributed algorithm performance on multi-robot systems, and introduce the idea of the robot speed ratio, a dimensionless measure of robot speed relative to message speed in networks that rely on multi-hop communication. The robot speed ratio captures key relationships between communications bandwidth, mobility, and algorithm accuracy, and can be used at design time to trade off between them. I use this speed ratio to evaluate the performance of existing distributed algorithms for multi-hop communication and navigation. Second...

Micro-cleaved ridge lasers for optoelectronic integration on silicon

Rumpler, Joseph John, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 245 p.
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This thesis addresses one of the last hurdles to optoelectronic integration on silicon, namely the incorporation of room-temperature, electrically-pumped edge-emitting laser diodes. To this end, thin (-6 pm) InP-based multiple quantum well (MQW) ridge laser platelets emitting at a wavelength of 1550 nm have been manufactured and integrated by metal-to-metal bonding onto silicon substrates. These laser platelets can be thought of as freestanding optoelectronic building blocks that can be integrated as desired on diverse substrates. These blocks are fully processed lasers, with both top side and bottom side electrical contacts. The thinness of these optoelectronic building blocks and the precision with which their dimensions are defined are conducive to assembling them in dielectric recesses on a substrate, such as silicon, as part of an end-fire coupled, coaxial alignment optoelectronic integration strategy. They are assembled by a micro-scale pick and place technique that allows the blocks to be picked up individually and placed as desired on any substrate. Integration is accomplished by metal-to-metal solder bonding. To enable the manufacture of these laser blocks, a novel micro-cleaving process technology has been developed. This novel micro-cleaving process is used to simultaneously obtain both smooth end laser facets and precisely defined laser cavity lengths. As a proof of concept...

Consonant landmark detection for speech recognition

Park, Chi-youn, 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 197 p.
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This thesis focuses on the detection of abrupt acoustic discontinuities in the speech signal, which constitute landmarks for consonant sounds. Because a large amount of phonetic information is concentrated near acoustic discontinuities, more focused speech analysis and recognition can be performed based on the landmarks. Three types of consonant landmarks are defined according to its characteristics -- glottal vibration, turbulence noise, and sonorant consonant -- so that the appropriate analysis method for each landmark point can be determined. A probabilistic knowledge-based algorithm is developed in three steps. First, landmark candidates are detected and their landmark types are classified based on changes in spectral amplitude. Next, a bigram model describing the physiologically-feasible sequences of consonant landmarks is proposed, so that the most likely landmark sequence among the candidates can be found. Finally, it has been observed that certain landmarks are ambiguous in certain sets of phonetic and prosodic contexts, while they can be reliably detected in other contexts. A method to represent the regions where the landmarks are reliably detected versus where they are ambiguous is presented. On TIMIT test set, 91% of all the consonant landmarks and 95% of obstruent landmarks are located as landmark candidates. The bigram-based process for determining the most likely landmark sequences yields 12% deletion and substitution rates and a 15% insertion rate. An alternative representation that distinguishes reliable and ambiguous regions can detect 92% of the landmarks and 40% of the landmarks are judged to be reliable. The deletion rate within reliable regions is as low as 5%.; (cont.) The resulting landmark sequences form a basis for a knowledge-based speech recognition system since the landmarks imply broad phonetic classes of the speech signal and indicate the points of focus for estimating detailed phonetic information. In addition...

Middle ear pressure gain and cochlear input impedance in the chinchilla

Slama, Michaël C. C. (Michaël Charles Chalom)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 67 p.
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Measurements of middle ear conducted sound pressure in the cochlear vestibule PV have been performed in only a few individuals from a few mammalian species. Simultaneous measurements of sound-induced stapes velocity VS are even more rare. We report simultaneous measurements of VS and PV in chinchillas. The VS measurements were performed using single-beam laser-Doppler vibrometry; PV was measured with fiber optic pressure sensors like those described by Olson [JASA 1998; 103: 3445-63]. Accurate in-vivo measurements of PV are limited by anatomical access to the vestibule, the relative sizes of the sensor and vestibule, and damage to the cochlea when inserting the measurement device. The small size (170 [mu]m diameter) of the fiber-optic pressure sensors helps overcome these three constraints. PV and VS were measured in six animals, and the middle ear pressure gain (ratio of PV to the sound pressure in the ear canal) and the cochlear input impedance (ratio of PV to the product of VS and area of the footplate) computed. Our measurements of middle ear pressure gain are similar to published data in the chinchilla at stimulus frequencies of 500 Hz to 3 kHz, but are different at other frequencies. Our measurements of cochlear input impedance differ somewhat from previous estimates in the chinchilla and show a resistive input impedance up to at least 10 kHz. To our knowledge...

Combining phrase-based and tree-to-tree translation

Lieberman, Michael (Michael R.)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 40 p.
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We present a novel approach to multi-engine machine translation, using a feature-based classification algorithm. Instead of just using language models, translation models, or internal confidence scores, we sought out other features that could be used to determine which of two translations to select. We combined the outputs from a phrase-based system, Moses [Koehn et al., 2007] and a tree-to-tree system [Cowan et al., 2006]. Our main result is a 0.3 to 0.4 improvement in BLEU score over the best single system used, while also improving fluency and adequacy judgments. In addition, we used the same setup to directly predict which sentences would be judged by humans to be more fluent and more adequate. In those domains, we predicted the better sentence 6% to 7% more often than a baseline of always choosing the single best system.; by Michael Lieberman.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.; This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.; Includes bibliographical references (p. 39-40).

Microchemical systems for singlet oxygen generation

Hill, Tyrone F. (Tyrone Frank), 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 158 p.
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Chemical Oxygen-Iodine Lasers (COIL) are a technology of interest for industrial and military audiences. COILs are flowing gas lasers where the gain medium of iodine atoms is collisionally pumped by singlet delta oxygen molecules, which are created through the catalyzed multiphase reaction of hydrogen peroxide and chlorine. Currently the use of COIL technology is limited by size and efficiency issues. This thesis seeks to use MEMS technology towards the development of more compact and efficient COIL systems, with a focus on the singlet oxygen generator (SOG) stage. Based on success in other applications, MEMS technology offers opportunities for improved reactant mixing, product separation, and heat transfer in SOGs. A MEMS singlet oxygen generator (or microSOG) is built and demonstrated. The chip features 32 multiplexed packed bed reaction channels and utilizes capillarity effects to separate the gas and liquid products. Cooling channels are arranged on the chip such that they form a cross-flow heat exchanger with the reaction channels. Spontaneous optical emission measurements and mass spectroscopy are used to confirm singlet oxygen production in the chip. A singlet delta oxygen molar flow rate corresponding to a power of 1.37 W was measured in the chip. The singlet oxygen molar flow rate per unit of hardware volume is 6.7x10-2 mol/L/sec...

Spectral analysis for stochastic models of large-scale complex dynamical networks

Preciado, Víctor Manuel
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 196 p.
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Research on large-scale complex networks has important applications in diverse systems of current interest, including the Internet, the World-Wide Web, social, biological, and chemical networks. The growing availability of massive databases, computing facilities, and reliable data analysis tools has provided a powerful framework to explore structural properties of such real-world networks. However, one cannot efficiently retrieve and store the exact or full topology for many large-scale networks. As an alternative, several stochastic network models have been proposed that attempt to capture essential characteristics of such complex topologies. Network researchers then use these stochastic models to generate topologies similar to the complex network of interest and use these topologies to test, for example, the behavior of dynamical processes in the network. In general, the topological properties of a network are not directly evident in the behavior of dynamical processes running on it. On the other hand, the eigenvalue spectra of certain matricial representations of the network topology do relate quite directly to the behavior of many dynamical processes of interest, such as random walks, Markov processes, virus/rumor spreading, or synchronization of oscillators in a network. This thesis studies spectral properties of popular stochastic network models proposed in recent years. In particular...

Estimation and calibration algorithms for distributed sampling systems

Divi, Vijay, 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 157 p.
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Traditionally, the sampling of a signal is performed using a single component such as an analog-to-digital converter. However, many new technologies are motivating the use of multiple sampling components to capture a signal. In some cases such as sensor networks, multiple components are naturally found in the physical layout; while in other cases like time-interleaved analog-to-digital converters, additional components are added to increase the sampling rate. Although distributing the sampling load across multiple channels can provide large benefits in terms of speed, power, and resolution, a variety mismatch errors arise that require calibration in order to prevent a. degradation in system performance.In this thesis, we develop low-complexity, blind algorithms for the calibration of distributed sampling systems. In particular, we focus on recovery from timing skews that cause deviations from uniform timing. Methods for bandlimited input reconstruction from nonuniform recurrent samples are presented for both the small-mismatch and the low-SNR domains. Alternate iterative reconstruction methods are developed to give insight into the geometry of the problem.From these reconstruction methods, we develop time-skew estimation algorithms that have high performance and low complexity even for large numbers of components. We also extend these algorithms to compensate for gain mismatch between sampling components. To understand the feasibility of implementation...

Characterization of process variability and robust optimization of analog circuits

Lim, Daihyun, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 174 p.
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Continuous scaling of CMOS technology has enabled dramatic performance enhancement of CMOS devices and has provided speed, power, and density improvement in both digital and analog circuits. CMOS millimeter-wave applications operating at more than 50GHz frequencies has become viable in sub-100nm CMOS technologies, providing advantages in cost and high density integration compared to other heterogeneous technologies such as SiGe and III-V compound semiconductors. However, as the operating frequency of CMOS circuits increases, it becomes more difficult to obtain sufficiently wide operating ranges for robust operation in essential analog building blocks such as voltage-controlled oscillators (VCOs) and frequency dividers. The fluctuations of circuit parameters caused by the random and systematic variations in key manufacturing steps become more significant in nano-scale technologies. The process variation of circuit performance is quickly becoming one of the main concerns in high performance analog design. In this thesis, we show design and analysis of a VCO and frequency divider operating beyond 70GHz in a 65nm SOI CMOS technology. The VCO and frequency divider employ design techniques enlarging frequency operating ranges to improve the robustness of circuit operation. Circuit performance is measured from a number of die samples to identify the statistical properties of performance variation. A back-propagation of variation (BPV) scheme based on sensitivity analysis of circuit performance is proposed to extract critical circuit parameter variation using statistical measurement results of the frequency divider. We analyze functional failure caused by performance variability...

The paradigm of partial erasures

Lim, Dah-Yoh, 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 145 p.
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This thesis is a study of erasures in cryptographic protocols. Erasing old data and keys is an important capability of honest parties in cryptographic protocols. It is useful in many settings, including proactive security in the presence of a mobile adversary, adaptive security in the presence of an adaptive adversary, forward security, and intrusion resilience. Some of these settings, such as achieving proactive security, is provably impossible without some form of erasures. Other settings, such as designing protocols that are secure against adaptive adversaries, are much simpler to achieve when erasures are allowed. Protocols for all these contexts typically assume the ability to perfectly erase information. Unfortunately, as amply demonstrated in the systems literature, perfect erasures are hard to implement in practice. We propose a model of imperfect or partial erasures where erasure instructions are only partially effective and leave almost all the data intact, thus giving the honest parties only a limited capability to dispose old data. Nonetheless, we show how to design protocols for all of the above settings (including proactive security, adaptive security, forward security, and intrusion resilience) for which this weak form of erasures suffices. We do not have to invent entirely new protocols...

Agent problem solving by inductive and deductive program synthesis

Fox, Harold, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 206 p.
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How do people learn abstract concepts unsupervised? Psychologists broadly recognize two types of concepts, declarative knowledge and procedural knowledge: know-what and know-how. While much work has focused on unsupervised learning of declarative concepts as clusters of features, there is much less clarity on the representation for procedural concepts and the methods for learning them. In this thesis, I claim that programs are a good representation for procedural knowledge, and that program synthesis is a promising mechanism for procedural learning. Prior attempts at AI program synthesis have taken a purely deductive approach to building provably corrent programs. This approach requires many axioms and non-trivial interaction with a human programmer. In contrast, this thesis introduces a new approach called SSGP (Sample Solve Generalize Prove), which combines inductive and deductive synthesis to autonomously synthesize programs with no extra knowledge outside of the program specification. The approach is to generate examples, solve the examples, generalize from the solutions, and then prove the generalization correct.This thesis presents two systems, Spec2Action and HELPS. Given a logical specification, Spec2Action determines the relations to change to perform simple operations on data structures. The main part of its task is to uncover the recursive structure of the domain from the purely logical input spec. HELPS generates sequential programs with loops and branches using STRIPS actions as the primitive statements. It solves generalizations of classic AI tasks like BlocksWorld. The two systems use SAT solving and other grounded reasoning techniques to solve the examples and generalize the solutions. To prove the abstracted hypotheses...

BlendDB : blending table layouts to support efficient browsing of relational databases

Marcus, Adam, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 65 p.
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The physical implementation of most relational databases follows their logical description, where each relation is stored in its own file or collection of files on disk. Such an implementation is good for queries that filter or aggregate large portions of a single table, and provides reasonable performance for queries that join many records from one table to another. It is much less ideal, however, for join queries that follow paths from a small number of tuples in one table to small collections of tuples in other tables to accumulate facts about a related collection of objects (e.g., co-authors of a particular author in a publications database), since answering such queries involves one or more random I/Os per table involved in the path. If the primary workload of a database consists of many such path queries, as is likely to be the case when supporting browsing-oriented applications, performance will be quite poor. This thesis focuses on optimizing the performance of these kinds of path queries in a system called BlendDB, a relational database that supports on-disk co-location of tuples from different relations. To make BlendDB efficient, the thesis will propose a clustering algorithm that, given knowledge of the database workload...

A general framework for genome interpretation using evolutionary signatures

Fujiwara, Guilherme Issao Camarinha
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 57 p.
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In the post-genomic era, characterized by the availability of the genome sequence data for many species, one of the biggest challenges to be solved is to identify the functional elements in our genome: the small subsequences containing units of biological function. Work has been done to computationally identify specific functional elements such as protein coding genes [11], RNA genes [17], microRNA genes [16], regulatory motifs and individual binding sites for transcription factors and microRNAs [10]. This work has benefited from the use of evolutionary signatures obtained by observing the genomics changes across the sequence data of related species. We propose in this work a general framework to perform functional element identification using evolutionary signatures. We first design several metrics of evolutionary signatures that are meant to capture different patterns of evolution expected from elements that have different biological function as well as novel patterns capturing diverse properties of evolutionary changes. We then compute these metrics for each of the elements in the human genome that are conserved across mammals and other vertebrate species in order to identify classes of functional elements. Based on these metrics...

A preliminary design of an integrated non-invasive brain recording and stimulation device

Hsu, Byron B
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 115 p.
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The purpose of this project is to create a device which can perform closed-loop brain recording and stimulation. Part of this is to create a device to amplify and digitize high frequency EEG signals up to 1 KHz. The other portion is to create a device to apply controlled and arbitrary current stimulation. This project has the potential to enhance human memory formation, an essential ability for people in everyday life. Along the way, I will create a device which has the potential to change how researchers record brain activity, enabling new insights into higher-frequency brain function and disorders.; by Byron B. Hsu.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.; Includes bibliographical references (p. 111-113).

Broadening the education of software engineers – some lessons and pointers.

Griffin, Joe; Ryan, Kevin
Fonte: IEEE Computer Society Publicador: IEEE Computer Society
Tipo: Conference item; all_ul_research; ul_published_reviewed; none
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non-peer-reviewed; Professional Issues in Software Engineering (PISE) has been taught as part of the computer systems undergraduate degree programme at the University of Limerick using a multiinstitutional collaborative pedagogy. PISE considers the ethical, legal and social consequences of the design, implementation and use of computer and information systems. Students from UL collaborated with students from other universities in USA, England and Malta, working together in geographically distributed virtual learning groups to consider ethical issues in software engineering. This paper reflects the longitudinal evaluation of teaching and assessment methods that have been developed over 20 years.

Herramienta de Apoyo para el Aprendizaje a Distancia de la Lógica en la Ingeniería Informática; Support Tool for E-learning in Logic in Computer Science Engineering

Huertas, Maria Antonia; Mor Pera, Enric; Guerrero Roldán, Ana Elena
Fonte: Universidade de Múrcia Publicador: Universidade de Múrcia
Tipo: Artigo de Revista Científica Formato: application/pdf
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Logic as a subject in computer engineering has characteristics and difficulties similar to those of other mathematics related subjects: very low academic achievement and high dropout. In instrumental disciplines such as logic, an interactive teaching-learning process is fundamental, and the immediate feedback is a key element of academic success. In a traditional face to face logic course the necessary feedback and support is usually provided by the classroom interaction between students and teacher. In contrast, in an e-learning paradigm based on the web, this feature can be provided through an intelligent tutor type tool. This article presents the design, development and implementation of a learning support tool for a non-face to face course of logic in the computer engineering program. This tool follows the perspective of student-centered design to provide the elements necessary for a successful learning experience. It also presents an pilot test with the evaluation of its results and a general discussion on the implementation of such tools for distance learning and self-learning; Las asignaturas de lógica en ingeniería informática presentan características y dificultades similares a las de otras materias de carácter matemático: un rendimiento académico muy bajo y un alto de abandono. En disciplinas instrumentales como es el caso de lógica...

Simultaneous sensor calibration and path estimation

Rudoy, Melanie Beth
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 75 leaves
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This thesis presents two topics related to the simultaneous calibration of a network of imaging sensors, i.e. cameras, and the recovery of the trajectory of an object moving among those sensors. The non-overlapping fields of view for the cameras do not cover the entire scene, and therefore there are time steps for which no measurements are available. A Bayesian framework is imposed on the problem in order to compute the MAP (maximum a posteriori) estimate, the solution that maximizes the probability of the sensor network configuration and target trajectory given the measurement set. The first topic discussed is model order reduction to decrease the number of unknown parameters in the motion and measurement models, thereby reducing the computational requirements of the optimization algorithm. It is possible to reduce the dimension of the search space, with no loss in accuracy, by treating the estimation of target's trajectory while it is outside the field of view of the network as an independent sub-problem that can be solved at a later time. Additionally, one can further reduce the dimension of the search space by taking advantage of the fact that the measurement noise is negligible compared to other sources of error in the problem...