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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
811

Active Learning with Semi-Supervised Support Vector Machines

Chinaei, Leila January 2007 (has links)
A significant problem in many machine learning tasks is that it is time consuming and costly to gather the necessary labeled data for training the learning algorithm to a reasonable level of performance. In reality, it is often the case that a small amount of labeled data is available and that more unlabeled data could be labeled on demand at a cost. If the labeled data is obtained by a process outside of the control of the learner, then the learner is passive. If the learner picks the data to be labeled, then this becomes active learning. This has the advantage that the learner can pick data to gain specific information that will speed up the learning process. Support Vector Machines (SVMs) have many properties that make them attractive to use as a learning algorithm for many real world applications including classification tasks. Some researchers have proposed algorithms for active learning with SVMs, i.e. algorithms for choosing the next unlabeled instance to get label for. Their approach is supervised in nature since they do not consider all unlabeled instances while looking for the next instance. In this thesis, we propose three new algorithms for applying active learning for SVMs in a semi-supervised setting which takes advantage of the presence of all unlabeled points. The suggested approaches might, by reducing the number of experiments needed, yield considerable savings in costly classification problems in the cases when finding the training data for a classifier is expensive.
812

Development of Hybrid Electromagnetic Dampers for Vehicle Suspension Systems

Ebrahimi, Babak 30 April 2009 (has links)
Vehicle suspension systems have been extensively explored in the past decades, contributing to ride comfort, handling and safety improvements. The new generation of powertrain and propulsion systems, as a new trend in modern vehicles, poses significant challenges to suspension system design. Consequently, novel suspension concepts are required, not only to improve the vehicle’s dynamic performance, but also to enhance the fuel economy by utilizing regeneration functions. However, the development of new-generation suspension systems necessitates advanced suspension components, such as springs and dampers. This Ph.D. thesis, on the development of hybrid electromagnetic dampers is an Ontario Centres of Excellence (OCE) collaborative project sponsored by Mechworks Systems Inc. The ultimate goal of this project is to conduct feasibility study of the development of electromagnetic dampers for automotive suspension system applications. With new improvements in power electronics and magnetic materials, electromagnetic dampers are forging the way as a new technology in vibration isolation systems such as vehicle suspension systems. The use of electromagnetic dampers in active vehicle suspension systems has drawn considerable attention in the recent years, attributed to the fact that active suspension systems have superior performance in terms of ride comfort and road-handling performances compared to their passive and semi-active counterparts in automotive applications. As a response to the expanding demand for superior vehicle suspension systems, this thesis describes the design and development of a new electromagnetic damper as a customized linear permanent magnet actuator to be used in active suspension systems. The proposed electromagnetic damper has energy harvesting capability. Unlike commercial passive/semi-active dampers that convert the vibration kinetic energy into heat, the dissipated energy in electromagnetic dampers can be regenerated as useful electrical energy. Electromagnetic dampers are used in active suspension systems, where the damping coefficient is controlled rapidly and reliably through electrical manipulations. Although demonstrating superb performance, active suspensions still have some issues that must be overcome. They have high energy consumption, weight, and cost, and are not fail-safe in case of a power break-down. Since the introduction of the electromagnetic dampers, the challenge was to address these drawbacks. Hybrid electromagnetic dampers, which are proposed in this Ph.D. thesis, are potential solutions to high weight, high cost, and fail-safety issues of an active suspension system. The hybrid electromagnetic damper utilizes the high performance of an active electromagnetic damper with the reliability of passive dampers in a single package, offering a fail-safe damper while decreasing weight and cost. Two hybrid damper designs are proposed in this thesis. The first one operates based on hydraulic damping as a source of passive damping, while the second design employs the eddy current damping effect to provide the passive damping part of the system. It is demonstrated that the introduction of the passive damping can reduce power consumption and weight in an active automotive suspension system. The ultimate objective of this thesis is to employ existing suspension system and damper design knowledge together with new ideas from electromagnetic theories to develop new electromagnetic dampers. At the same time, the development of eddy current dampers, as a potential source for passive damping element in the final hybrid design, is considered and thoroughly studied. For the very first time, the eddy current damping effect is introduced for the automotive suspension applications. The eddy current passive damper, as a stand-alone unit, is designed, modeled, fabricated and successfully tested. The feasibility of using passive eddy current dampers for automotive suspension applications is also studied. The structure of new passive eddy current dampers is straightforward, requiring no external power supply or any other electronic devices. Proposed novel eddy current dampers are oil-free and non-contact, offering high reliability and durability with their simplified design. To achieve the defined goals, analytical modeling, numerical simulations, and lab-based experiments are conducted. A number of experimental test-beds are prepared for various experimental analyses on the fabricated prototypes as well as off-the-shelf dampers. Various prototypes, such as eddy current and electromagnetic dampers, are manufactured, and tested in frequency/time domains for verification of the derived analytical and numerical models, and for proof of concept. In addition, fluid and heat transfer analyses are done during the process of the feasibility study to ensure the durability and practical viability of the proposed hybrid electromagnetic dampers. The presented study is only a small portion of the growing research in this area, and it is hoped that the results obtained here will lead to the realization of a safer and more superior automotive suspension system.
813

Current Programmed Active Pixel Sensors for Large Area Diagnostic X-ray Imaging

Safavian, Nader 28 August 2009 (has links)
Rapid progress over the last decade on large area thin film transistor (TFT) arrays led to the emergence of high-performance, low-power, low-cost active matrix flat panel imagers. Despite the shortcomings associated with the instability and low mobility of TFTs, the amorphous silicon TFT technology still remains the primary solution for the backplane of flat panel imagers. The use of a-Si:H TFTs as the building block of the large area integrated circuit becomes challenging particularly when the role of the TFT is extended from traditional switching applications to on-pixel signal amplifier for large area digital imaging. This is the idea behind active pixel sensor (APS) architectures in which under each pixel an amplifier circuit consisting of one or two switching TFTs integrated with one amplifying TFT is fabricated. To take advantage of the full potential of these amplifiers, it is crucial to develop APS architectures to compensate for the limitations of the TFTs. In this thesis several APS architectures are designed, simulated, fabricated, and tested addressing these challenges using the mask sets presented in Appendix A. The proposed APS architectures can compensate for inherent stabilities of the comprising TFTs. Therefore, the sensitivity of their output data to the transistor variations is significantly suppressed. This is achieved by using a well defined external current source instead of the traditional voltage source to reset the APS architectures during the reset cycle of their periodic operation. The performance of these circuits is analyzed in terms of their stability, settling time, noise, and temperature-dependence. For appropriate readout of the current mode APS architectures, high gain transresistance amplifiers with correlated double sampling capability is designed, simulated and fabricated in CMOS technology. Measurement and measurement based calculation results reveal that the proposed APS architectures can meet even the stringent requirements of low noise, real-time digital fluoroscopy.
814

The Relationship between Within-Day Energy Balance and Menstruation in Active Females

Friel, Alexandra J 08 August 2010 (has links)
Background: Past studies suggest that inadequate energy intake (EI) is directly related to menstrual dysfunction (MD) in active females. Inadequate EI causes activation of the hypothalamic-pituitary-adrenal axis, disrupting the normal hormonal signaling of reproductive cycling and resulting in MD. However, studies have also demonstrated similar EI in athletes, but with different menstrual function. Traditionally, energy balance has been evaluated in 24-hour time periods. Recent research suggests there is benefit to analyzing energy balance at smaller intervals to better address physiologic response in real time. It is possible that women who meet their daily EI needs could still, therefore, experience MD if the majority of the day is spent in energy deficit. Objective: The purpose of this study is to determine whether within-day energy balance is a factor in menstrual status in active adult females. Methods: Twenty active females tracked hourly EI and energy expenditure over three days. A two-page survey was utilized to obtain information on training, health, and menstrual status. Participants were also asked to respond to several questions regarding eating habits and attitude towards food. Within-day energy balance was calculated and evaluated using NutriTimingTM software. Collected energy balance data were analyzed for associations with menstrual status. Results: Participants spent more hours in a catabolic state (energy balance less than zero) than in an anabolic state (20.5 hrs vs 3.5 hrs) and averaged a caloric deficit of -504 kcal over 24-hours. Nine subjects (45%) had experienced loss of menses for greater than 3 months (LoM>3mos), indicative of amenorrhea. Hours spent in energy surplus >400 kcal was inversely correlated with LoM>3mos (r = -0.463; P = 0.04). The impact of number of miles run per week and menstrual dysfunction, based on a quartile stratification of miles run, were analyzed using an ANOVA with Tamhane non-parametric post hoc test. Significant differences were found between the upper two quartiles of distance run per week and LoM>3mos (P = 0.048). There was no relationship between end-of-day energy balance and Lom>3mos. Conclusion: Researchers and healthcare professionals would do well to examine energy balance in an hour-by-hour manner as it is has implications for MD. This would help to clarify whether within-day energy balance is a factor in MD, and allow for the development of appropriate intervention strategies to improve health and athletic outcomes for active women.
815

Rest Frame Variability Characteristics of Blazars

McFarland, John Patrick 08 August 2005 (has links)
Blazars exhibit the most extreme variability of the class of objects known asactive galactic nuclei (AGN). They are characterized by a featureless continuum, high polarization, and variability at all wavelengths and timescales. The amplitude of optical variations can range from less than 0.1 magnitude on the timescale of minutes to hours, to greater than 5.0 magnitudes on timescales of months to years, and gamma-ray variability amplitudes can span a range of as much as three orders of magnitude in a time-scale as short as a few days. These characteristics are consistent with a supermassive black hole accreting matter at the heart of the host galaxy. However, the observed properties of these objects don't necessarily reflect the intrinsic properties because the emissions have been modified by cosmological distances. The variability of these blazars, which have very different redshifts, have been investigated using several different analytical approaches; i.e. structure function analysis, variability index analysis, and light curve analysis. By transforming observed measurements into the rest frame of the source, the intrinsic properties of the variability can be compared. These variability characteristics of blazars, as seen in their rest frame, and as a function of state, will be discussed in reference to their general characteristics and classification schemes.
816

The X-ray Variability of Seyfert Galaxies

Marshall, Kevin 04 December 2006 (has links)
Strong and variable X-ray emission has long been known to be a universal property of active galaxies. However, despite years of study, the exact nature of the variability remains relatively unknown. We present here results of a multi-year monitoring campaign of a sample of Seyfert galaxies (3C 120, Mkn 509, 3C 390.3, and Akn 120), carried out using the Rossi X-ray Timing Explorer (RXTE). For Mkn 509, we also present results of optical monitoring. Mkn 509 shows a strong correlation between X-ray and optical variations, with the optical leading the X-ray by 25 days. We also investigate the rms-flux relationship in our sample. The two radio loud objects in our sample (3C 120, 3C 390.3) show a clear correlation between flux and rms variability, while the two radio quiet objects (Mkn 509, Akn 120) show no such relationship. Monte Carlo simulations were used to estimate the shape of the underlying power spectrum, and we find that all of our objects have a break frequency below which the power spectrum flattens. The relationship between optical and X-ray variability is discussed, with lags occurring most likely as a result of instabilities or changes in accretion flow propagating inwards through the disk. We also discuss possible physical timescales that could be related to the break frequency, along with connections to galactic X-ray binaries.
817

Microvariability of the Blazar 3C279

Clemmons, Hannah M 01 December 2010 (has links)
Active Galactic Nuclei (AGN) are some of the most extreme objects in the universe. They output copious amounts of energy spanning the entire electromagnetic spectrum. There are many different subclasses of AGN depending on your viewing angle. Blazars, viewing down the relativistic jet, are the most variable class of AGN known. They exhibit extreme variability in all wavelengths on timescales as short as minutes. In this thesis I will consider the extreme faintness of 3C279 with respect to the long-term light curve as well as recent observations of microvariability. I am able to confirm small amplitude events using simultaneous observations from two telescopes and cross correlation analysis. Transitory quasi-periodic oscillations are observed during two of the nights with confirmed microvariability.
818

On the dynamics of active documents for distributed data management

Bourhis, Pierre 11 February 2011 (has links) (PDF)
One of the major issues faced by Web applications is the management of evolving of data. In this thesis, we consider this problem and in particular the evolution of active documents. Active documents is a formalism describing the evolution of XML documents by activating Web services calls included in the document. It has already been used in the context of the management of distributed data \cite{axml}. The main contributions of this thesis are theoretical studies motivated by two systems for managing respectively stream applications and workflow applications. In a first contribution, we study the problem of view maintenance over active documents. The results served as the basis for an implementation of stream processors based on active documents called Axlog widgets. In a second one, we see active documents as the core of data centric workflows and consider various ways of expressing constraints on the evolution of documents. The implementation, called Axart, validated the approach of a data centric workflow system based on active documents. The hidden Web (also known as deep or invisible Web), that is, the partof the Web not directly accessible through hyperlinks, but through HTMLforms or Web services, is of great value, but difficult to exploit. Wediscuss a process for the fully automatic discovery, syntacticand semantic analysis, and querying of hidden-Web services. We proposefirst a general architecture that relies on a semi-structured warehouseof imprecise (probabilistic) content. We provide a detailed complexityanalysis of the underlying probabilistic tree model. We describe how wecan use a combination of heuristics and probing to understand thestructure of an HTML form. We present an original use of a supervisedmachine-learning method, namely conditional random fields,in an unsupervised manner, on an automatic, imperfect, andimprecise, annotation based on domain knowledge, in order to extractrelevant information from HTML result pages. So as to obtainsemantic relations between inputs and outputs of a hidden-Web service, weinvestigate the complexity of deriving a schema mapping between databaseinstances, solely relying on the presence of constants in the twoinstances. We finally describe a model for the semantic representationand intensional indexing of hidden-Web sources, and discuss how toprocess a user's high-level query using such descriptions.
819

Physical Modelling and Automatic Configuration of CES Valve

Gällsjö, Anders, Johansson, Mattias January 2012 (has links)
This thesis has been performed at Öhlins Racing AB which is known world-wide for its high quality racing shock absorbers. Öhlins have been developing shock absorbers for more than 30 years and in addition to this they also develop a technology for semi-active suspension. Semi-active suspension technology makes it possible to achieve an intelligent and dynamic vehicle chassis control. Compared to standard passive suspensions, semiactive dampers allow improving vehicle cornering performance while still providing good comfort when cruising. This is achieved by a real time adjustment of the suspensions damping characteristics. Öhlins system for semi-active suspension is called CES (Continuously controlled Electronic Suspension). The systems consist of electronically controlled hydraulic valves for uniflow dampers. These valves are mounted on all four dampers of the vehicle and are controlled individually to provide the desired ride quality. The valves are configurable to suit many types of vehicles by changing internal parts. The first goal of this thesis project was to study the behaviour of the CES valve and uniflow damper. In order to achieve this a simulation model was created using Hopsan which is a 1-dimensional multi-domain modelling tool developed at the division of Fluid and Mechatronic Systems at Linköping University. The model considers mechanical forces from for example springs together with hydraulic forces. It was validated against static and dynamic measurements made in a flow bench and a dynamometer. The second goal was to use the simulation model as part of a tool that configures the CES valve according to a requirements specification. To achieve this goal a method of estimating the characteristics of the internal damper valves was developed. This estimation method, together with the simulation model, was used to choose the best valve configuration by using weighted least-squares. The result is presented in a Matlab-based graphical user interface.
820

Development of a wearable sensor system for real-time control of knee prostheses

Almeida, Eduardo Carlos Venancio de January 2012 (has links)
It was demonstrated in recent studies that Complementary Limb Motion Estimation (CLME) is robust approach for controlling active knee prostheses. A wearable sensor system is then needed to provide inputs to the controller in a real-time platform. In the present work, a wearable sensor system based on magnetic and inertial measurement units (MIMU) together with a simple calibration procedure were proposed. This sensor system was intended to substitute and extend the capabilities of a previous device based on potentiometers and gyroscopes. The proposed sensor system and calibration were validated with an Optical Tracking System (OTS) in a standard gait lab and first results showed that the proposed solution had a performance comparable to similar studies in the literature.

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