Página 14 dos resultados de 100905 itens digitais encontrados em 0.107 segundos

‣ Electrostatic vibration-to-electric energy conversion

Mur Miranda, José Oscar, 1972-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 197 p.; 4672340 bytes; 2956536 bytes; application/pdf; application/pdf
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Ultra-Low-Power electronics can perform useful functions with power levels as low as 170 nW. This makes them amenable to powering from ambient sources such as vibration. In this case, they can become autonomous. Motivated by this application, this thesis provides the necessary tools to analyze, design and fabricate MEMS devices capable of electrostatic vibration-to-electric energy conversion at the microwatt level. The fundamental means of en- ergy conversion is a variable capacitor that is excited through a generating energy conversion cycle with every vibration cycle of the converter. This thesis presents a road map on how to design MEMS electrostatic vibration-to- electric energy converters. A proposed converter is designed to illustrate the design process, and is based on vibration levels typical of rotating machinery, which are around 2% of the acceleration of gravity from 1-5 kHz. The converter consists of a square centimeter with a 195 mg proof mass which travels ±200 pm. This mass and travel can couple to a sinusoidal acceleration source of 0.02g at 2.5 kHz, typical of rotating machinery, so as to capture 24 nJ per cycle. This moving proof mass is designed to provide a variable capacitor ranging from 1 pF to 80 pF. Adding a capacitor of 88 pF in parallel with this device will result in a capacitance change from 168 pF to 89 pF that is required to extract 24 nJ using a charge-constrained cycle.; (cont.) This device can be attached to power electronics that implement a charge-constrained cycle and deliver 0.5 nJ back to the reservoir for a total power output of 1.3 [mu]/W at 2.5 kHz. The efficiency of the electrical conversion is 2%. Including packaging...

‣ Robust decision-support tools for airport surface traffic

Carr, Francis R. (Francis Russell), 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 113 p.; 961043 bytes; 960804 bytes; application/pdf; application/pdf
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Forecasts of departure demand are one of the driving inputs to tactical decision-support tools (DSTs) for airport surface traffic. While there are well-known results on average- or worst-case forecast uncertainty, it is the forecast errors which occur under best-case minimum-uncertainty conditions which constrain robust DST design and the achievable traffic benefits. These best-case errors have never previously been characterized. Several quantitative models and techniques for computing pushback forecasts are developed. These are tested against a dataset of 17,344 real-world airline ground operations covering 3 months of Lufthansa flights transiting Frankfurt International Airport. The Lufthansa dataset includes detailed timing information on all of the turn processes, including deboarding, catering, cleaning, fueling and boarding. The dataset is carefully filtered to obtain a sample of 3820 minimum-uncertainty ground events. The forecast models and techniques are tested against this sample, and it is observed that current pushback forecast errors (on the order of ±15min) cannot be reduced by a factor of more than 2 or 3. Furthermore, for each ground event, only 3 observations are necessary to achieve this best-case performance: the available ground-time between actual onblock and scheduled offblock; the time until deboarding begins; and the time until boarding ends. Any DST used in real-world operations must be robust to this "noise floor". To support the development of robust DSTs...

‣ Predictive multiple sampling algorithm with overlapping integration intervals for linear wide dynamic range integrating image sensors

Acosta Serafini, Pablo M. (Pablo Manuel), 1971-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 173 p.; 2999717 bytes; 3042388 bytes; application/pdf; application/pdf
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Machine vision systems are used in a wide range of applications such as security, automated quality control and intelligent transportation systems. Several of these systems need to extract information from natural scenes in the section of the electromagnetic spectrum visible to humans. These scenes can easily have intra-frame illumination ratios in excess of 10⁶ : 1. Solid-state image sensors that can correctly process wide illumination dynamic range scenes are therefore required to ensure correct reliability and performance. This thesis describes a new algorithm to linearly increase the illumination dynamic range of integrating-type image sensors. A user-defined integration time is taken as a reference to create a potentially large set of integration intervals of different duration (the selected integration time being the longest) but with a common end. The light intensity received by each pixel in the sensing array is used to choose the optimal integration interval from the set, while a pixel saturation predictive decision is used to overlap the integration intervals within the given integration time such that only one frame using the optimal integration interval for each pixel is produced. The total integration time is never exceeded. Benefits from this approach are motion minimization...

‣ Data selection in binary hypothesis testing

Sestok, Charles K. (Charles Kasimer)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 123 p.; 734239 bytes; 741965 bytes; application/pdf; application/pdf
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Traditionally, statistical signal processing algorithms are developed from probabilistic models for data. The design of the algorithms and their ultimate performance depend upon these assumed models. In certain situations, collecting or processing all available measurements may be inefficient or prohibitively costly. A potential technique to cope with such situations is data selection, where a subset of the measurements that can be collected and processed in a cost-effective manner is used as input to the signal processing algorithm. Careful evaluation of the selection procedure is important, since the probabilistic description of distinct data subsets can vary significantly. An algorithm designed for the probabilistic description of a poorly chosen data subset can lose much of the potential performance available to a well-chosen subset. This thesis considers algorithms for data selection combined with binary hypothesis testing. We develop models for data selection in several cases, considering both random and deterministic approaches. Our considerations are divided into two classes depending upon the amount of information available about the competing hypotheses. In the first class, the target signal is precisely known, and data selection is done deterministically. In the second class...

‣ Bipolar thermoelectric devices

Pipe, Kevin P. (Kevin Patrick), 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 133 p.; 1035057 bytes; 1080011 bytes; application/pdf; application/pdf
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The work presented here is a theoretical and experimental study of heat production and transport in bipolar electrical devices, with detailed treatment of thermoelectric effects. Both homojunction and heterojunction devices are considered, and particular attention is given to semiconductor laser diodes. The mechanisms that govern both internal heat exchange and heat transfer between a device and its environment are examined, leading to structures which are optimized for thermal management.; by Kevin Patrick Pipe.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.; Includes bibliographical references (p. 124-133).; This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.

‣ Dynamic power allocation and routing for satellite and wireless networks with time varying channels

Neely, Michael J. (Michael James), 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 295 p.; 1502113 bytes; 1500707 bytes; application/pdf; application/pdf
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Satellite and wireless networks operate over time varying channels that depend on attenuation conditions, power allocation decisions, and inter-channel interference. In order to reliably integrate these systems into a high speed data network and meet the increasing demand for high throughput and low delay, it is necessary to develop efficient network layer strategies that fully utilize the physical layer capabilities of each network element. In this thesis, we develop the notion of network layer capacity and describe capacity achieving power allocation and routing algorithms for general networks with wireless links and adaptive transmission rates. Fundamental issues of delay, throughput optimality, fairness, implementation complexity, and robustness to time varying channel conditions and changing user demands are discussed. Analysis is performed at the packet level and fully considers the queueing dynamics in systems with arbitrary, potentially bursty, arrival processes. Applications of this research are examined for the specific cases of satellite networks and ad-hoc wireless networks. Indeed, in Chapter 3 we consider a multi-beam satellite downlink and develop a dynamic power allocation algorithm that allocates power to each link in reaction to queue backlog and current channel conditions. The algorithm operates without knowledge of the arriving traffic or channel statistics...

‣ Model-based motion estimation and its application to restoration and interpolation of motion pictures

Martinez, Dennis Michael
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: [4], 160 leaves; 12882796 bytes; 12882551 bytes; application/pdf; application/pdf
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by Dennis Michael Martinez.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1986.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.; Supported, in part, by the National Science Foundation. Title as it appeared in M.I.T. Graduate List, September 1986: Model-based motion estimation and its applications.; Bibliography: leaves 157-160.

‣ Robust time and frequency domain estimation methods in adaptive control

LaMaire, Richard O
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 2 v. (337 leaves); 22412218 bytes; 22411977 bytes; application/pdf; application/pdf
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by Richard Orville LaMaire.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1987.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.; Supported, in part, by the NASA Ames & Langley Research Centers, the Office of Naval Research, and the National Science Foundation.; Bibliography: v. 2, leaves 334-337.

‣ Toward single-cycle optical pulses

Kim, Jung-Won, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 151 p.; 6280040 bytes; 6288174 bytes; application/pdf; application/pdf
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Single-cycle optical pulses, the never-before-achieved regime, have a great potential for attosecond science and phase-sensitive nonlinear optics. To achieve single-cycle optical pulses by active synchronization, three major steps are required. Firstly, two very stable and broadband mode-locked lasers with overlapping spectra are necessary. Secondly, a tight timing synchronization with timing jitter under one-tenth of the synthesized pulsewidth has to be implemented. Finally, the carrier-envelope offset frequency lock between two lasers completes the coherent pulse synthesis process. In this thesis, the major ideas, techniques, and experimental results for single-cycle optical pulse synthesis are presented. A broadband Cr:forsterite laser mode-locked by a semiconductor saturable absorber is designed and implemented. The output spectrum spans from 1080 nm to 1500 nm range, and has a 3-dB bandwidth of 90 nm. This is the broadest spectrum from a prismless Cr:forsterite laser to our best knowledge, and corresponds to a sub-20 fs Fourier-transform limited pulsewidth. A new broadband output coupler is designed to optimize the output spectrum of an octavespanning Ti:sapphire laser. The resulting combined spectrum covers 1.5 octave from 600 nm to 1500 nm and has a strong overlap in 1100 to 1200 nm range...

‣ Optical studies of super-collimation in photonic crystals

Dahlem, Marcus
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 125 p.; 4608659 bytes; 4613886 bytes; application/pdf; application/pdf
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Recent developments in material science and engineering have made possible the fabrication of photonic crystals for optical wavelengths. These periodic structures of alternating high-to-low index of refraction materials allow the observation of peculiar effects, in particular, the propagation of optical beams without spatial spreading. This effect, called super-collimation (also known as self-collimation), allows diffraction-free propagation of micron-sized beams over centimeter-scale distances. This linear effect is a natural result of the unique dispersive properties of photonic crystals. In this thesis, these dispersive properties are studied in a two-dimensional photonic crystal slab. Both qualitative and quantitative descriptions are presented. The beam propagation method was used to simulate the evolution of a Gaussian beam inside such structures. The wavelength dependence of the super-collimation effect was studied, and it was observed that the optimum wavelength for this device was around 1500 nm. A precise contact-mode near-field optical microscopy technique was used to obtain high-resolution images of the beam profile at different positions along the photonic crystal, and showed that a 2 [micro]m beam width was conserved over 3 mm. In addition...

‣ Investigations on resource-limited quantum control through NMR pulses

Lee, Karen Ka Yan
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 61 p.
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Universal high fidelity coherent control over large Hilbert spaces is essential for quantum information processing to become a useful tool in science, engineering, communications and computation. The development of methods for coherent control are however still in their infancy. In particular, very little is known about the efficiency of quantum control subject to limitations in resources such as drive power, drive bandwidth and system decoherence. Here we report the results of numerical simulations to investigate the influence of limited resources. We introduce the curvature of fidelity as a measure of robustness. We apply these ideas to strongly modulating NMR pulse sequences and study the effects of increasing resources on the fidelity and curvature.; by Karen Ka Yan Lee.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.; Includes bibliographical references (p. 59-61).

‣ Real-time spatial-phase-locked electron-beam lithography; Real-time SPLEBL

Zhang, Feng, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 139 p.
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The ability of electron-beam lithography (EBL) to create sub-10-nm features with arbitrary geometry makes it a critical tool in many important applications in nanoscale science and technology. The conventional EBL system is limited by its poor absolute-placement accuracy, often worse than its resolution. Spatial-phase-locked electron-Beam lithography (SPLEBL) improves the placement accuracy of EBL tools to the nanometer level by directly referencing the beam position via a global-fiducial grid placed on the substrate, and providing feedback corrections to the beam position. SPLEBL has several different modes of operation, and it can be applied to both scanning electron-beam lithography (SEBL) and variable-shaped-beam lithography. This research focuses primarily on implementing real-time SPLEBL in SEBL systems. Real-time SPLEBL consists of three major components: a fiducial-reference grid, a beam-position detection algorithm and a partial-beam blanker. Several types of fiducial grids and their fabrication processes were developed and evaluated for their signal-to-noise ratio and ease of usage. An algorithm for detecting the beam position based on Fourier techniques was implemented, and -1 nm placement accuracy achieved. Finally, various approaches to partial-beam blanking were examined...

‣ Three-dimensional nanofabrication of photonic crystals and polarization splitters and rotators; 3D nanofabrication of photonic crystals and polarization splitters and rotators

Qi, Minghao, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 133 leaves
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One of the most critical challenges in nanoscale science and engineering is to make functional 3D nanodevices with high-accuracy. While considerable progress has been made in the "bottom-up" approach, the lithographic "top-down" approach remains the only way to encode human engineering effort, and to meet the optimal theoretical designs. Probably the most prominent example of lithographic fabrication is semiconductor manufacturing. However such manufacturing, aside from being extremely expensive, is highly inflexible, virtually excluding any work other than silicon microelectronic devices. Meanwhile, the miniaturization and integration of optical devices can potentially revolutionize the field of optics, with an impact that may prove comparable to the transition of electronics from vacuum tubes to transistors. To achieve high-level functionalities and to meet the stringent tolerance in optical information processing, multilayered structures with both minimum feature sizes and layer-to-layer overlay accuracy down to a few of nanometers are required, thus posing significant challenges in fabrication. Some requirements, such as nanometer-level spatial coherence, are beyond the capability of current semiconductor manufacturing.; (cont.) As part of an effort to develop a low-cost...

‣ Convex optimization methods for model reduction

Sou, Kin Cheong, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 161 p.
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Model reduction and convex optimization are prevalent in science and engineering applications. In this thesis, convex optimization solution techniques to three different model reduction problems are studied.Parameterized reduced order modeling is important for rapid design and optimization of systems containing parameter dependent reducible sub-circuits such as interconnects and RF inductors. The first part of the thesis presents a quasi-convex optimization approach to solve the parameterized model order reduction problem for linear time-invariant systems. Formulation of the model reduction problem as a quasi-convex program allows the flexibility to enforce constraints such as stability and passivity in both non-parameterized and parameterized cases. Numerical results including the parameterized reduced modeling of a large RF inductor are given to demonstrate the practical value of the proposed algorithm.A majority of nonlinear model reduction techniques can be regarded as a two step procedure as follows. First the state dimension is reduced through a projection, and then the vector field of the reduced state is approximated for improved computation efficiency. Neither of the above steps has been thoroughly studied. The second part of this thesis presents a solution to a particular problem in the second step above...

‣ Statistical Saliency Model incorporating motion saliency and an application to driving

Raj, Alvin Andrew
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 53 p.
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This thesis extends the Statistical Saliency Model to include motion as a feature, enabling it to compute the saliency of video sequences more effectively. The motion feature is represented as optical flow and incorporated into the model. The model is validated by testing its capability in predicting reaction time performance in a driving simulator. We find that the model does help predict reaction time and some eye-movements in some simulated driving tasks.; by Alvin Raj.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.; At head of title on title-page: Master of Science thesis.; Includes bibliographical references (p. 43-44).

‣ DesignEye : a tool for design teams to analyze and address visual clutter; Design Eye : a tool for design teams to analyze and address visual clutter

Dorai, Amal Kumar
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 44 p.
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User interface design is critical for the success of any information technology, from software packages to automobile dashboards. Colleagues from many different job functions often need to collaborate to produce these designs, in work environments which can often be strained. Collaborative design software can alleviate some of the problems of these teams, but current software is rarely tailored to the needs of a cross-functional group and does not actively guide users to create better designs. In this thesis, I describe DesignEye, a tool that I have developed with the Perceptual Science Group at MIT. Our tool computes the clutter of images and identifies the most salient visual elements, and allows designers to work with the softare in a tight iterative feedback loop to ensure that the most important design elements garner the most end-user attention. DesignEye is tailored to the use cases we have observed in our studies of design teams, and facilitates side-by-side comparisons of multiple design candidates as interface designers test various ideas. I conclude by demonstrating the extensibility of DesignEye, and its role not only as a tool but as a generalized platform to assist interface designers. Any vision model which quantifies some aspect of human cognitive response to a stimulus can be incorporated into DesignEye...

‣ Defending the semantic conception of computation in cognitive science

O'Brien, G.
Fonte: International Association for Cognitive Science Publicador: International Association for Cognitive Science
Tipo: Artigo de Revista Científica
Publicado em //2011 Português
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Cognitive science is founded on the conjecture that natural intelligence can be explained in terms of computation. Yet, notoriously, there is no consensus among philosophers of cognitive science as to how computation should be characterised. While there are subtle differences between the various accounts of computation found in the literature, the largest fracture exists between those that unpack computation in semantic terms (and hence view computation as the processing of representations) and those, such as that defended by Chalmers (2011), that cleave towards a purely syntactic formulation (and hence view computation in terms of abstract functional organisation). It will be the main contention of this paper that this dispute arises because contemporary computer science is an amalgam of two different historical traditions, each of which has developed its own proprietary conception of computation. Once these historical trajectories have been properly delineated, and the motivations behind the associated conceptions of computation revealed, it becomes a little clearer which should form the foundation for cognitive science.; http://j-cs.org/issues/__vol012i4/3.html; Gerard O’Brien

‣ Automated de-identification of free-text medical records

Neamatullah, Ishna
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 73 p.
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This paper presents a de-identification study at the Harvard-MIT Division of Health Science and Technology (HST) to automatically de-identify confidential patient information from text medical records used in intensive care units (ICUs). Patient records are a vital resource in medical research. Before such records can be made available for research studies, protected health information (PHI) must be thoroughly scrubbed according to HIPAA specifications to preserve patient confidentiality. Manual de-identification on large databases tends to be prohibitively expensive, time-consuming and prone to error, making a computerized algorithm an urgent need for large-scale de-identification purposes. We have developed an automated pattern-matching deidentification algorithm that uses medical and hospital-specific information. The current version of the algorithm has an overall sensitivity of around 0.87 and an approximate positive predictive value of 0.63. In terms of sensitivity, it performs significantly better than 1 person (0.81) but not quite as well as a consensus of 2 human de-identifiers (0.94). The algorithm will be published as open-source software, and the de-identified medical records will be incorporated into HST's Multi-Parameter Intelligent Monitoring for Intensive Care (MIMIC II) physiologic database.; by Ishna Neamatullah.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

‣ Supporting finding and re-finding through personalization

Teevan, Jaime B. (Jaime Brooks), 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 176 p.
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Although one of the most common uses for the Internet to search for information, Web search tools often fail to connect people with what they are looking for. This is because search tools are designed to satisfy people in general, not the searcher in particular. Different individuals with different information needs often type the same search terms into a search box and expect different results. For example, the query "breast cancer" may be used by a student to find information on the disease for a fifth grade science report, and by a cancer patient to find treatment options. This thesis explores how Web search personalization can help individuals take advantage of their unique past information interactions when searching. Several studies of search behavior are presented and used to inform the design of a personalized search system that significantly improves result quality. Without requiring any extra effort from the user, the system is able to return simple breast cancer tutorials for the fifth grader's "breast cancer" query, and lists of treatment options for the patient's. While personalization can help identify relevant new information, new information can create problems re-finding when presented in a way that does not account for previous information interactions.; (cont.) Consider the cancer patient who repeats a search for breast cancer treatments: she may want to learn about new treatments while reviewing the information she found earlier about her current treatment. To not interfere with refinding...

‣ Brownian Functionals in Physics and Computer Science

Majumdar, Satya N.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/10/2005 Português
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This is a brief review on Brownian functionals in one dimension and their various applications, a contribution to the special issue ``The Legacy of Albert Einstein" of Current Science. After a brief description of Einstein's original derivation of the diffusion equation, this article provides a pedagogical introduction to the path integral methods leading to the derivation of the celebrated Feynman-Kac formula. The usefulness of this technique in calculating the statistical properties of Brownian functionals is illustrated with several examples in physics and probability theory, with particular emphasis on applications in computer science. The statistical properties of "first-passage Brownian functionals" and their applications are also discussed.; Comment: 21 pages, 5 .eps figures included