Recursos de colección

CaltechTHESIS (9.863 recursos)

CALIFORNIA INST OF TECH (CIT) Thesis

Status = Unpublished

Mostrando recursos 1 - 20 de 1.157

  1. An Analysis of Linear Induction Motors for Propulsion and Suspension of Magnetically Levitated Vehicles

    Yang, Fang-Chou
    A four-layer single-sided LIM used for propulsion and suspension of magnetically levitated vehicles is studied . The track is assumed to be made of conductors with uniaxial μ and σ. A general analysis allows us to exclude unsuitable geometries. The machine performance is given for the promising geometries. A possible way of computing the effective μ and σ for a composite track is sketched. From the analysis of an extremely simplified geometry, the conditions for the validity of the effective μ and σ concept are given. Finally, a three-dimensional correction is introduced.

  2. Integrated Nonlinear Photonic Devices

    Oh, Dong Yoon
    Chip-scale nonlinear optics can provide important new functions in communications, frequency metrology and spectroscopy. Optical microcavities enhance nonlinear optical effects through resonant recirculation. This recirculation dramatically reduces the required power in applications and also lowers signal noise. A key figure-of-merit is the optical Q factor, which provides a dimensionless scale of optical storage time within the microcavity. In this thesis, a novel integrated ultra-high-Q microcavity with Q as high as 230 million is presented. The device is applied to demonstrate multiple functions including electronic-rate soliton microcomb generation and stimulated Brillouin laser operation. For soliton generation, the resonator must be engineered...

  3. Improving the Performance and Sensitivity of Gravitational Wave Detectors

    Quintero, Eric Antonio

    The field of observational gravitational wave astronomy has begun in earnest, starting with the detection of the strain signal from the binary black hole merger GW150914 by the Laser Interferometer Gravitational-wave Observatory (LIGO) in 2015. The current incarnation of the LIGO observatories, known as Advanced LIGO, has achieved strain sensitivities on the order of 10−23/√Hz in the hundreds of Hz region, which has enabled unambiguous detection of astrophysical gravitational wave signals. Nevertheless, the scientific output from the LIGO observatories is constrained by the instrumental performance and sensitivity, as there remain many more distant and exotic sources to be observed.

    This thesis...

  4. Ultrasound Speckle Image Velocimetry: Studies on System Performance and Application to Cardiovascular Fluid Dynamics

    Lin, Ben Albert
    Knowledge of detailed blood flow characteristics can be extremely valuable in a variety of settings. Examples range from studying disease processes such as atherosclerosis to aiding in the design of medical devices such as prosthetic cardiac valves. For in vivo and optically inaccessible in vitro flows, accurate measurements of velocity fields and shear stresses can be difficult to obtain. Doppler ultrasound and magnetic resonance imaging are the most commonly used techniques, but have important limitations. Recently, there has been increased interest in the application of particle image velocimetry principles towards tracking of ultrasound speckle patterns to determine multidimensional flow velocities with...

  5. Development of Ferromagnetic Metallic Glasses into Low Loss Power Transformer Cores

    Floyd, Michael

    Currently, 3% of energy losses in the U.S. electrical grid occur at power transformers. With a transition to Metglas, transformer efficiency could be increased, but is Metglas the best replacement material for power transformers?

    With this in mind we develop a Fe-based metallic glass for its glass forming ability and soft magnetic properties. During this development we identify a redox reaction of boron oxide by Si during melt fluxing of the Fe-based glass, which promotes an unexpected exchange of Si and B in the alloy. Taking this reaction into account, a unique optimization strategy is implemented, enabling oxide purification of the...

  6. Investigations on the Performances of Centrifugal Pumps with Various Alterations of the Impeller

    Murdock, Keith

    Several years ago the writer conferred in settling the problem of changing the operation of a pump delivering 5500 gal. per minute at 168 feet head to that of delivering 3000 gal. per minute at 146 feet head. The driving motor was a 2200 volt A.C. synchronous motor.

    The driving speed could not be altered, and the diameter of the impeller could be cut down only a certain amount before the delivery head would be below that required. At the lowest permissible head of operation the delivery was still excessive unless throttling was resorted to. The head delivery curve was so...

  7. The Hydrodynamics of Active Particles Inside of a Porous Container and the Galerkin Boundary Element Discretization of Stokes Flow

    Marshall, Kevin J.

    In this thesis I formulate and present a novel and new framework for simulating the dynamics of arbitrarily shaped active or passive particles immersed in a Stokesian fluid and evolving under confinement by a porous container or in free space. I use a completed double layer boundary integral equation to model the particle's dynamics and combine this with a new formulation that uses a second kind integral equation for describing the motion of the porous container. This newly formulated porous container model permits fluid to pass through the container's surface at a velocity in proportion to a discontinuous jump in...

  8. Egospace Motion Planning Representations for Micro Air Vehicles

    Fragoso, Anthony T.
    Navigation of micro air vehicles (MAVs) in unknown environments is a complex sensing and trajectory generation task, particularly at high velocities. In this work, we introduce an efficient sense-and-avoid pipeline that compactly represents range measurements from multiple sensors, trajectory generation, and motion planning in a 2.5–dimensional projective data structure called an egospace representation. Egospace coordinates generalize depth image obstacle representations and are a particularly convenient choice for configuration flat mobile robots, which are differentially flat in their configuration variables and include a number of commonly used MAV plant models. After characterizing egospace obstacle avoidance for robots with trivial dynamics and...

  9. Egospace Motion Planning Representations for Micro Air Vehicles

    Fragoso, Anthony T.
    Navigation of micro air vehicles (MAVs) in unknown environments is a complex sensing and trajectory generation task, particularly at high velocities. In this work, we introduce an efficient sense-and-avoid pipeline that compactly represents range measurements from multiple sensors, trajectory generation, and motion planning in a 2.5–dimensional projective data structure called an egospace representation. Egospace coordinates generalize depth image obstacle representations and are a particularly convenient choice for configuration flat mobile robots, which are differentially flat in their configuration variables and include a number of commonly used MAV plant models. After characterizing egospace obstacle avoidance for robots with trivial dynamics and...

  10. Frequency Noise Control of Heterogeneous Si/III-V Lasers

    Kim, Dongwan

    Narrow-linewidth lasers have many applications including optical telecommunication, laser spectroscopy, atomic clocks, and light detection and ranging. Conventionally, narrow linewidth lasers have been realized in the form of fiber-based or solid-state lasers. These lasers are bulky and relatively expensive, limiting their usage as bench-top systems in laboratory environments. Historically, semiconductor lasers, also known as laser diodes, have served applications where size and cost are important factors, including fiber optic communications. The linewidth of the semiconductor lasers, however, has been limited to the MHz-level, due to high loss in laser cavities and small size.

    Recently, reduction of the frequency fluctuations in the...

  11. Glacial Ocean Dynamics: Insight from Deep-Sea Coral Reconstructions and A Time-Dependent Dynamical Box Model

    Hines, Sophia K.V.

    Glacial-interglacial cycles, occurring at a period of approximately 100,000 years, have dominated Earth's climate over the past 800,000 years. These cycles involve major changes in land ice, global sea level, ocean circulation, and the carbon cycle. While it is generally agreed that the ultimate driver of global climate is changes in insolation, glacial cycles do not look like insolation forcing. Notably, there is a highly non-linear warming response at 100,000 years to a relatively small forcing, implicating a more complicated system of biogeochemical and physical drivers. The ocean plays a pivotal role in glacial-interglacial climate through direct equator-to-pole transport of...

  12. The Coherence Collapse Regime of High-Coherence Si/III-V Lasers and the Use of Swept Frequency Semiconductor Lasers for Full Field 3D Imaging

    Harfouche, Mark

    The semiconductor laser is the linchpin of optical communication and is now also penetrating a wide spectrum of new applications such as biomedical sensing, coherent communication, metrology, and time keeping. These require a higher degree of temporal coherence than is available from the present generation. Recently, it has been proposed and shown that heterogeneously integrated lasers on silicon and InGaAsP can be used to design high coherence single mode lasers with a much narrower linewidth than their all InGaAsP counterparts. Unfortunately, these lasers suffer from large thermal impedances and their optical feedback characteristics have not yet been explored. In the...

  13. I. The Reduction of Nickelous and Ferric Oxides by Hydrogen. II. The Catalytic Synthesis of Water Vapor on the Presence of Metallic Nickel

    Emmett, Paul Hugh

    A study has been made by a flow method of the combination of hydrogen and oxygen in contact with reduced nickel, using oxygen concentrations up to 5%.

    1. At all temperatures at which any water formation could be detected it was found that superficial oxidation of the nickel readily took place. At the lower temperatures this oxidation eventually covered the whole surface, with the result that the rate of catalysis suddenly decreased to a small value.

    2. When hydrogen was passed over a catalyst superficially oxidized in this way, the rate of reduction accelerated auto-catalytically, in conformity with the previous observation that the reduction of ordinary nickel oxide...

  14. Semi-Active Control of Dynamically Excited Structures Using Active Interaction Control

    Zhang, Yunfeng

    This thesis presents a family of semi-active control algorithms termed Active Interaction Control (AIC) used for response control of dynamically excited structures. The AIC approach has been developed as a semi﷓active means of protecting building structures against large earthquakes. The AIC algorithms include the Active Interface Damping (AID), Optimal Connection Strategy (OCS), and newly developed Tuned Interaction Damping (TID) algorithms. All of the AIC algorithms are founded upon the same basic instantaneous optimal control strategy that involves minimization of an energy﷓based performance index at every time instant.

    A typical AIC system consists of a primary structure targeted for vibration control, a...

  15. A Study of the Selection of Flight Paths in Air Transport Operations

    Rockefeller, William Curtis

    1. GENERAL:

    With the introduction of the modern high perfor­mance airplane into the air transportation systems of the country it has become increasingly necessary to make some study of the variables which influence the proper selection of flight paths for the efficient operation of the aircraft.

    In the past it has been the practice in the air transport industry to make a very rough estimate of the ef­fect of the winds and thus determine the best altitude at which to fly on the course. There has been a complete neg­lect of the possibilities which are presented by a considera­tion of the airplane performance.

    It...

  16. More Fun Than Anything

    Harris, Daniel Charles

    An exhaustive study of piddling cyclopropenium salts is described. This includes synthesis, characterization and the study of ligand

    (See PDF)

    substitution reactions of the M2Cl62- anions. The electronic absorption spectra and vibrational spectra are interpreted. A normal coordinate analysis of the M2Cl62- anions are reported. Startling counterion effects in ligand substitution reactions in CH2Cl2 solvent were observed.

    The transformation M-M → M-H-M+, in which a metal-metal bond is protonated by strong acid, has been studied in several organomettalic systems. Electronic spectra are tentatively interpreted in terms of three-center two-electron M-H-M bonding. The stretching vibrations associated with a W-H-W bridge are assigned. Infrared spectra indicate the presence of isomeric protonated species for several...

  17. Online Algorithms: From Prediction to Decision

    Chen, Niangjun

    Making use of predictions is a crucial, but under-explored, area of sequential decision problems with limited information. While in practice most online algorithms rely on predictions to make real time decisions, in theory their performance is only analyzed in simplified models of prediction noise, either adversarial or i.i.d. The goal of this thesis is to bridge this divide between theory and practice: to study online algorithm under more practical predictions models, gain better understanding about the value of prediction, and design online algorithms that make the best use of predictions.

    This thesis makes three main contributions. First, we propose a stochastic...

  18. Online Algorithms: From Prediction to Decision

    Chen, Niangjun

    Making use of predictions is a crucial, but under-explored, area of sequential decision problems with limited information. While in practice most online algorithms rely on predictions to make real time decisions, in theory their performance is only analyzed in simplified models of prediction noise, either adversarial or i.i.d. The goal of this thesis is to bridge this divide between theory and practice: to study online algorithm under more practical predictions models, gain better understanding about the value of prediction, and design online algorithms that make the best use of predictions.

    This thesis makes three main contributions. First, we propose a stochastic...

  19. Optimal filtering for systems governed by coupled ordinary and partial differential equations

    Yu, Thomas King Lin

    The recursive estimation of states or parameters of stochastic dynamical systems with partial and imperfect measurements is generally referred to as filtering. The estimator itself is called the filter. In this dissertation optimal filters are derived for three important classes of nonlinear stochastic dynamical systems.

    The first class of systems, considered in Chapter II, is that governed by stochastic nonlinear hyperbolic and parabolic partial differential equations in which the dynamical disturbances in the system and in the boundary conditions can be both additive and nonadditive. This class of systems is important for it encompasses a large group of systems of practical...

  20. Modal Coupling and Earthquake Response of Tall Buildings

    Hoerner, John Brent

    The major dynamic features of tall buildings are within the scope of a shear beam model. Herein the usual one-dimensional model is extended to three dimensions to include modes with translational and rotational components. The analysis is restricted to the continuous model with linear response.

    A class of models for tall buildings is presented which possesses three sets of mutually orthogonal coupled modes. The amount of modal coupling is related to the eccentricities divided by the translational-torsional frequency differences. Strong modal coupling can occur if the eccentricities and frequency differences are small, as in a rectangular building with a smooth distribution...

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