Página 3 dos resultados de 10730 itens digitais encontrados em 0.071 segundos

## Wireless power transmission utilizing a phased array of Tesla coils

Stark, Joseph C. (Joseph Charles), 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 247 p.; 12286117 bytes; 12318505 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
666.3548%
This thesis discusses the theory and design of coupled resonant systems and how they can be linked in a phased array for the wireless transmission of electrical power. A detailed derivation of their operational theory is presented with a strong emphasis on the current and voltage waveforms produced. Formulas are presented relating the features of the waveforms to specific parameters of the system. They provide a theoretical basis for the design of the TeslaE coil systems. Unloaded and loaded operating efficiency is considered from both a power and energy perspective with emphasis on maximizing the two quantities. With these design formulas, a working set of two distinct coupled resonant systems were locked in frequency and controllable in phase to produce a phased array capable of wireless power transmission. The operational details and practical design considerations are presented and explained. The measured output waveforms were found to closely agree with the predicted models.; by Joseph C. Stark, III.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.; Includes bibliographical references (p. 245-247).

## Queing analysis of a shared voice/data link

Friedman, Daniel Uri
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: [2], iv, 157 p.; 7886972 bytes; 7886732 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
666.3548%
by Daniel Uri Friedman.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engieering and Computer Science, 1982.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. Engineering copy is in leaves.; Bibliography: p. 156-157.

## Scanning standing-wave illumination microscopy : a path to nanometer resolution in X-ray microscopy

Hong, Stanley Seokjong, 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 88 leaves; 2148858 bytes; 2147772 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
666.3548%
X-ray microscopy can potentially combine the advantages of light microscopy with resolution approaching that of electron microscopy. In theory, x-ray microscopes can image unsectioned hydrated cells with nanometer resolution. In practice, however, the resolution of x-ray microscopes is limited to approximately 20 nm due to difficulties in the construction of high numerical-aperture (NA) x-ray focusing optics. This thesis represents a step on a new path to nanometer resolution in x-ray microscopy by proposing and demonstrating scanning standing-wave illumination (SWI) microscopy. In scanning SWI microscopy, lensless focusing is achieved with the interference of large numbers of phase-aligned planar wavefronts. Resolution is determined primarily by the NA synthesized by the planar wavefronts, circumventing the need for high-NA optical components. Both theoretical and experimental work conducted at visible wavelengths is presented. An electromagnetic theory of image formation in scanning SWI fluorescence microscopy is developed. The point spread function is remarkably well-suited to Fourier analysis and can be analyzed using graphical techniques. Phase alignment is accomplished by maximizing the intensity of light scattered or fluoresced by a point-like particle using an iterative algorithm that is guaranteed to converge monotonically. A prototype scanning SWI microscope with 15 phase-modulated linearly-polarized laser beams arranged in a 0.95-NA radially-polarized circular cone and a 0.25-NA objective lens is presented. Sub-wavelength resolution according to both classical resolution criteria (i.e....

## Measurement and device design of left-handed metamaterials

Thomas Zachary M. (Zachary Michael)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 128 p.; 5816207 bytes; 5821581 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
666.3548%
The properties of a variety of left-handed metamaterial (LHM) structures are analyzed and measured to verify consistent behavior between theory an measurements. The structures are simulated using a commercial software program and a retrieval algorithm is used to determine the effective constitutive parameters. The constitutive parameters are used to predict the behavior of the metamaterial under various configurations. Measurements are conducted to verify the presence of a negative index of refraction. Transmission through an LHM slab from several incidences is shown to be consistent with theory. A four-port device utilizing the dispersive nature of an LHM prism is designed and measured. The measurements show that the refraction angle of an incident signal is frequency dependent. Two ports are constructed to receive the positively refracted and negatively refracted power. In the frequency band where the incident signal cannot propagate in the LHM prism, the power is reflected from the interface towards a third measurement port. The three ports are shown to achieve unique mutually exclusive bandwidths. A general study is conducted on the design of such a device. Finally, the use of a left-handed metamaterial as a substrate for a microstrip line is investigated.; (cont.) An LHM substrate consisting of split-ring resonators is shown to enhance the performance of a stop band filter. The measurement results are in good agreement with simulation where the substrate is modelled by its effective medium parameters.; by Zachary M. Thomas.; Thesis (S.M.)--Massachusetts Institute of Technology...

## Physical modeling of electrical conduction in printed circuit board insulation

Sarathy, Vasanth
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 301 p.; 14003469 bytes; 14024327 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
666.3548%
This thesis is concerned with understanding the degradation of electrical and electronic components in automobiles due to environmental effects. A special emphasis is placed on understanding the physical processes underlying the degradation, so that accelerated reliability tests can be specified with increased confidence of their validity. As a first case,printed circuit board (PCB) insulation was selected as a target for investigation. With an increase in the electronics and circuit miniaturization coupled with an increase in voltage in 42 volt as well as hybrid vehicles, PCB reliability has become an important issue. We first provide a broad presentation of insulation degradation theory as well as electrical conduction theory according to existing literature and then narrow our focus towards printed circuit board insulation. We develop a novel first-order mathematical model to describe electrical currents in printed circuit board insulation as a function of temperature, relative humidity, absorbed moisture content, voltage and geometrical characteristics. This model was developed from a series of experiments that were carefully performed under controlled laboratory conditions. In addition to describing the experimental procedure and results...

## Exploring predistortion training algorithms in a Cartesian feedback-trained digital predistortion system for RF power amplifier linearization

Huang, Jeffrey B
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 118 p.
Português
Relevância na Pesquisa
666.3548%
A Cartesian feedback-trained digital predistortion system for RF power amplifier linearization offers many advantages with its combination of two different linearization techniques. This thesis describes such a system, focusing on the important issue of predistorter training. It examines and analyzes in great detail the promising loop filter pre-charging optimization and the tradeoffs associated with such training, developing a model that provides many valuable system design insights. In order establish a means to experimentally verify the theory and explore predistortion training algorithms, this thesis presents the design, development, and characterization of a mock-up prototype that models the essential features of the actual Cartesian feedback-trained digital predistortion system. The mock-up serves as a standalone proof-of-concept system that demonstrates the benefits and tradeoffs of loop filter pre-charging in predistorter training. It confirms the theory while also revealing practical issues pertaining to the limits on performance.; by Jeffrey B. Huang.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.; Includes bibliographical references (p. 117-118).

## Risk and robust optimization

Brown, David Benjamin, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 213 p.
Português
Relevância na Pesquisa
666.3548%
This thesis develops and explores the connections between risk theory and robust optimization. Specifically, we show that there is a one-to-one correspondence between a class of risk measures known as coherent risk measures and uncertainty sets in robust optimization. An important consequence of this is that one may construct uncertainty sets, which are the critical primitives of robust optimization, using decision-maker risk preferences. In addition, we show some results on the geometry of such uncertainty sets. We also consider a more general class of risk measures known as convex risk measures, and show that these risk measures lead to a more flexible approach to robust optimization. In particular, these models allow one to specify not only the values of the uncertain parameters for which feasibility should be ensured, but also the degree of feasibility. We show that traditional, robust optimization models are a special case of this framework. As a result, this framework implies a family of probability guarantees on infeasibility at different levels, as opposed to standard, robust approaches which generally imply a single guarantee.; (cont.) Furthermore, we illustrate the performance of these risk measures on a real-world portfolio optimization application and show promising results that our methodology can...

## Discriminating noise from chaos in heart rate variability : application to prognosis in heart failure

Arzeno, Natalia M. (Natalia María Arzeno Soltero)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 109 p.
Português
Relevância na Pesquisa
666.3548%
This thesis examines two challenging problems in chaos analysis: distinguishing deterministic chaos and stochastic (noise-induced) chaos, and applying chaotic heart rate variability (HRV) analysis to the prognosis of mortality in congestive heart failure (CHF). Distinguishing noise from chaos poses a major challenge in nonlinear dynamics theory since the addition of dynamic noise can make a non-chaotic nonlinear system exhibit stochastic chaos, a concept which is not well-defined and is the center of heated debate in chaos theory. A novel method for detecting dynamic noise in chaotic series is proposed in Part I of this thesis. In Part II, we show that linear and nonlinear analyses of HRV yield independent predictors of mortality. Specifically, sudden death is best predicted by frequency analysis whereas nonlinear and chaos indices are more selective for progressive pump failure death. These findings suggest a novel noninvasive probe for the clinical management of CHF patients.; by Natalia M. Arzeno.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.; Includes bibliographical references (p. 103-109).

## DNA binding economies; Deoxyribonucleic acid binding economies

Pérez-Breva, Luis
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 204 p.
Português
Relevância na Pesquisa
666.3548%
This thesis develops a new scalable modeling framework at the interface of game theory and machine learning to recover economic structures from limited slices of data. Inference using economic models has broad applicability in machine learning. Economic structures underlie a surprisingly broad array of problems including signaling and molecular control in biology, drug development, neural structures, distributed control, recommender problems, social networking, as well as market dynamics. We demonstrate the framework with an application to genetic regulation. Genetic regulation determines how DNA is read and interpreted, is responsible for cell specialization, reaction to drugs, metabolism, etc. Improved understanding of regulation has potential to impact research on genetic diseases including cancer. Genetic regulation relies on coordinate binding of regulators along DNA. Understanding how binding arrangements are achieved and their effect on regulation is challenging since it is not always possible to study regulatory processes in isolation. Indeed, observing the action of regulators is an experimental and computational challenge. We need causal genome-wide models that can work with existing high-throughput observations. We abstract DNA binding as an economy and develop fast algorithms to predict average binding arrangements as competitive equilibria. The framework supports viewing regulation as a succession of regulatory states. We complete the framework with algorithms to infer causal structure from high-throughput observations. Learning here deviates from work in learning in games...

## Charge-carrier transport in amorphous organic semiconductors

Limketkai, Benjie, 1982-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 106 p.
Português
Relevância na Pesquisa
666.3548%
Since the first reports of efficient luminescence and absorption in organic semiconductors, organic light-emitting devices (OLEDs) and photovoltaics (OPVs) have attracted increasing interest. Organic semiconductors have proven to be a promising material set for novel optical and/or electrical devices. Not only do they have the advantage of tunable properties using chemistry, but organic semiconductors hold the potential of being fabricated cheaply with low temperature deposition on flexible plastic substrates, ink jet printing, or roll-to-roll manufacturing. These fabrication techniques are possible because organic semiconductors are composed of molecules weakly held together by van der Waals forces rather than covalent bonds. Van der Waals bonding eliminates the danger of dangling bond traps in amorphous or polycrystalline inorganic films, but results in narrower electronic bandwidths. Combined with spatial and energetic disorder due to weak intermolecular interactions, the small bandwidth leads to localization of charge carriers and electron-hole pairs, called excitons. Thus, the charge-carrier mobility in organic semiconductors is generally much smaller than in their covalently-bonded, highly-ordered crystalline semiconductor counterparts. Indeed...

## Dynamic rate-control and scheduling algorithms for quality-of-service in wireless networks

Zafer, Murtaza Abbasali, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 202 p.
Português
Relevância na Pesquisa
666.3548%
Rapid growth of the Internet and multimedia applications, combined with an increasingly ubiquitous deployment of wireless systems, has created a huge demand for providing enhanced data services over wireless networks. Invariably, meeting the quality-of-service requirements for such services translates into stricter packet-delay and throughput constraints on communication. In addition, wireless systems have stringent limitations on resources which necessitates that these must be utilized in the most efficient manner. In this thesis, we develop dynamic rate-control and scheduling algorithms to meet quality-of-service requirements on data while making efficient utilization of resources. Ideas from Network Calculus theory, Continuous-time Stochastic Optimal Control and Convex Optimization are utilized to obtain a theoretical understanding of the problems considered, and to develop various insights from the analysis. We, first, address energy-efficient transmission of deadline-constrained data over wire-less fading channels. In this setup, a transmitter with controllable transmission rate is considered, and the objective is to obtain a rate-control policy for transmitting deadline- constrained data with minimum total energy expenditure. Towards this end...

## A novel wideband 140 GHz gyrotron amplifier

Joye, Colin D., 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 156 p.
Português
Relevância na Pesquisa
668.9949%
The theory, design and experimental results of a wideband 140 GHz, 1 kW pulsed gyro-traveling wave amplifier are presented. The gyro- TWA operates in the HE(0,6) mode of a novel cylindrical confocal waveguide using a gyrating electron beam. The electromagnetic theory, interaction theory, design processes and experimental procedures have been described in detail. The experiment has produced over 820 W peak power, 34 dB linear gain, and a -3 dB bandwidth of over 1.5 GHz (1.1%) from a 37 kV, 2.7 A electron beam having a beam pitch factor of 0.6, radius of 1.9 mm and calculated perpendicular momentum spread of approximately 9%. The gyro-amplifier was nominally operated at a pulse length of 2 microseconds, but was tested to amplify pulses as short as 4 nanoseconds with no noticeable pulse broadening. Internal reflections in the amplifier were identified using these short pulses by time-domain reflectometry. A novel internal mode converter was designed for this device that transforms the confocal HE(0,6) fields into a fundamental Gaussian beam for ultra-low loss transmission of the millimeter wave output power through a corrugated transmission line. The demonstrated performance of this amplifier shows that it can be applied to Dynamic Nuclear Polarization (DNP) and Electron Paramagnetic Resonance (EPR) spectroscopy.; by Colin D. Joye.; Thesis (Ph. D.)--Massachusetts Institute of Technology...

## Mode conversation losses in overmolded millimeter wave transmission lines

Tax, David S. (David Samuel)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 109 p.
Português
Relevância na Pesquisa
668.9949%
Millimeter wave transmission lines are integral components for many important applications like nuclear fusion and NMR spectroscopy. In low loss corrugated transmission lines propagating the HE,1 mode with a high waveguide radius to wavelength ratio (a/X), the transmission line loss is predominantly a result of mode conversion in components such as miter bends. The theory for determining losses in miter bends though is only approximate, and is based instead on the problem of the loss across a diameter-length gap between two waveguide sections. Through simulation, we verified that the existing analytic theory of this gap loss is correct; however, our simulations could not verify the assumption that the miter bend loss is half the loss in the gap. We also considered the problem of higher order modes (HOMs) mixed with an HE11 input entering the miter bend. Using a numerical technique, we found that the loss through the miter bend is dependent on both the amplitude of the HOM content as well as its phase relative to the phase of the HE11 mode. While the overall loss averaged across all phases remains the same with increasing HOM content, the power that fails to traverse the gap tends to increase, and it is this power that appears as very high order modes that will cause heating around the miter bend. For the ITER transmission line...

## Research in Computer Science and Computer Engineering

Feldman, J. A. ; Merriam, C. W.
Fonte: University of Rochester. Computer Science Department. Publicador: University of Rochester. Computer Science Department.
Tipo: Relatório
Português
Relevância na Pesquisa
666.7428%
This report describes many of the computer related research efforts at the University of Rochester. The Department of Computer Science is involved in research in automatic programming, including very high level languages and data structures; machine perception; and in problem solving using combinations of traditional heuristic methods, artificial intelligence, and utility theory. The research of the Department of Electrical Engineering includes basic computer engineering research in the construction of computer systems and operating systems, research in image processing and in numerical methods, and research in production automation which is concerned with mechanical manufacturing and assembly, and is currently developing mathematical models of parts, raw materials and tools. In conjunction with other departments, Electrical Engineering is also using computers for biomedical applications including ultrasound diagnostic techniques for heart disease, and pattern recognition techniques for detection of cancer from PAP smears.

## Research in Computer Science and Computer Engineering

Feldman, J. A. ; Merriam, C. W.
Fonte: University of Rochester. Computer Science Department. Publicador: University of Rochester. Computer Science Department.
Tipo: Relatório
Português
Relevância na Pesquisa
666.7428%
This report describes many of the computer related research efforts at the University of Rochester. The Department of Computer Science is involved in research in automatic programming, including very high level languages and data structures; machine perception; and in problem solving using combinations of traditional heuristic methods, artificial intelligence, and utility theory. The research of the Department of Electrical Engineering includes basic computer engineering research in the construction of computer systems and operating systems, research in image processing and in numerical methods, and research in production automation which is concerned with mechanical manufacturing and assembly, and is currently developing mathematical models of parts, raw materials and tools. In conjunction with other departments, Electrical Engineering is also using computers for biomedical applications including ultrasound diagnostic techniques for heart disease, and pattern recognition techniques for detection of cancer from PAP smears.

## Research in Computer Science and Computer Engineering

Feldman, J. A. ; Merriam, C. W.
Fonte: University of Rochester. Computer Science Department. Publicador: University of Rochester. Computer Science Department.
Tipo: Relatório
Português
Relevância na Pesquisa
666.7428%
This report describes many of the computer related research efforts at the University of Rochester. The Department of Computer Science is involved in research in automatic programming, including very high level languages and data structures; machine perception; and in problem solving using combinations of traditional heuristic methods, artificial intelligence, and utility theory. The research of the Department of Electrical Engineering includes basic computer engineering research in the construction of computer systems and operating systems, research in image processing and in numerical methods, and research in production automation which is concerned with mechanical manufacturing and assembly, and is currently developing mathematical models of parts, raw materials and tools. In conjunction with other departments, Electrical Engineering is also using computers for biomedical applications including ultrasound diagnostic techniques for heart disease, and pattern recognition techniques for detection of cancer from PAP smears.

## Control primitives for fast helicopter maneuvers

Perk Barıṣ Eren
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 82 leaves
Português
Relevância na Pesquisa
666.3548%
In this paper, we introduce a framework for learning aggressive maneuvers using dynamic movement primitives (DMP) for helicopters. Our ultimate goal is to combine these DMPs to generate new primitives and demonstrate them on a 3-DOF (3 Degrees of Freedom) helicopter. An observed movement is approximated and regenerated using DMP methods. After learning the movement primitives, the partial contraction theory is used to combine them. We imitate the aggressive maneuvers that are performed by a human and use these primitives to achieve new maneuvers that can fly over an obstacle. Experiments on the Quanser 3-DOF Helicopter demonstrate the effectiveness of our proposed method. In addition, we linearly combine DMPs and propose a new type of DMP. We also analyze Matsuoka's oscillator and Hopf oscillator using contraction theory.; by Barıṣ Eren Perk.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.; Includes bibliographical references (leaves 77-82).

## Ferrohydrodynamic flows in uniform and non-uniform rotating magnetic fields

He, Xiaowei, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 241, A1-A26 p.
Português
Relevância na Pesquisa
666.3548%
Ferrofluids are conventionally used in such DC magnetic field applications as rotary and exclusion seals, stepper motor dampers, and heat transfer fluids. Recent research demonstrates ferrofluid use in alternating and rotating magnetic fields for MEMS/NEMS application of microfluidic devices and bio-applications such as targeted drug delivery, enhanced Magnetic Resonance Imaging, and hypothermia. This thesis studies ferrofluid ferrohydrodynamics in uniform and non-uniform rotating magnetic fields through modeling and measurements of ferrofluid torque and spin-up flow profiles. To characterize the water-based and oil-based ferrofluids used in the experiments, measurements were made of the mass density, surface tension, viscosity, magnetization curve, nanoparticle size, and the speed of sound. Initial analysis for planar Couette and Poiseuille flows exploit DC magnetic field effects on flow and spin velocities with zero spin viscosity. Above critical values of magnetic field strength and flow velocity, multiple values of magnetic field, spin velocity, and effective magnetoviscosity result, indicating that zero spin viscosity may be non-physical. Torque and spin-up flow profile measurements show the effect of volume torque density and body force density in uniform and non-uniform rotating magnetic fields.; (cont.) Ferrofluid "negative viscosity" measurements in uniform and non-uniform rotating magnetic fields occur when magnetic field induced flow creates torque that exceeds the torque necessary to drive a viscometer spindle. Numerical simulations of torque and spin-up flow in uniform and non-uniform rotating magnetic fields...

## Homotopy invariants of higher dimensional categories and concurrency in computer science

Gaucher, Philippe
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
667.4917%
The strict globular $\omega$-categories formalize the execution paths of a parallel automaton and the homotopies between them. One associates to such (and any) $\omega$-category $\C$ three homology theories. The first one is called the globular homology. It contains the oriented loops of $\C$. The two other ones are called the negative (resp. positive) corner homology. They contain in a certain manner the branching areas of execution paths or negative corners (resp. the merging areas of execution paths or positive corners) of $\C$. Two natural linear maps called the negative (resp. the positive) Hurewicz morphism from the globular homology to the negative (resp. positive) corner homology are constructed. We explain the reason why these constructions allow to reinterprete some geometric problems coming from computer science.; Comment: 54 pages, 1 eps figure, LaTeX2e ; v2 construction of negative and positive Hurewicz morphisms added, corrected reference ; v3 reorganized paper for a better understanding ; v4 final version to appear in Mathematical Structure in Computer Science ; v5 last minute correction (very minor changes)

## The Baire partial quasi-metric space: A mathematical tool for asymptotic complexity analysis in Computer Science

Cerdà-Uguet, M. A.; Schellekens, M. P.; Valero, O.