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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.
51

An Analysis Tool for Flight Dynamics Monte Carlo Simulations

Restrepo, Carolina 1982- 16 December 2013 (has links)
Spacecraft design is inherently difficult due to the nonlinearity of the systems involved as well as the expense of testing hardware in a realistic environment. The number and cost of flight tests can be reduced by performing extensive simulation and analysis work to understand vehicle operating limits and identify circumstances that lead to mission failure. A Monte Carlo simulation approach that varies a wide range of physical parameters is typically used to generate thousands of test cases. Currently, the data analysis process for a fully integrated spacecraft is mostly performed manually on a case-by-case basis, often requiring several analysts to write additional scripts in order to sort through the large data sets. There is no single method that can be used to identify these complex variable interactions in a reliable and timely manner as well as be applied to a wide range of flight dynamics problems. This dissertation investigates the feasibility of a unified, general approach to the process of analyzing flight dynamics Monte Carlo data. The main contribution of this work is the development of a systematic approach to finding and ranking the most influential variables and combinations of variables for a given system failure. Specifically, a practical and interactive analysis tool that uses tractable pattern recognition methods to automate the analysis process has been developed. The analysis tool has two main parts: the analysis of individual influential variables and the analysis of influential combinations of variables. This dissertation describes in detail the two main algorithms used: kernel density estimation and nearest neighbors. Both are non-parametric density estimation methods that are used to analyze hundreds of variables and combinations thereof to provide an analyst with insightful information about the potential cause for a specific system failure. Examples of dynamical systems analysis tasks using the tool are provided.
52

Resampling Evaluation of Signal Detection and Classification : With Special Reference to Breast Cancer, Computer-Aided Detection and the Free-Response Approach

Bornefalk Hermansson, Anna January 2007 (has links)
The first part of this thesis is concerned with trend modelling of breast cancer mortality rates. By using an age-period-cohort model, the relative contributions of period and cohort effects are evaluated once the unquestionable existence of the age effect is controlled for. The result of such a modelling gives indications in the search for explanatory factors. While this type of modelling is usually performed with 5-year period intervals, the use of 1-year period data, as in Paper I, may be more appropriate. The main theme of the thesis is the evaluation of the ability to detect signals in x-ray images of breasts. Early detection is the most important tool to achieve a reduction in breast cancer mortality rates, and computer-aided detection systems can be an aid for the radiologist in the diagnosing process. The evaluation of computer-aided detection systems includes the estimation of distributions. One way of obtaining estimates of distributions when no assumptions are at hand is kernel density estimation, or the adaptive version thereof that smoothes to a greater extent in the tails of the distribution, thereby reducing spurious effects caused by outliers. The technique is described in the context of econometrics in Paper II and then applied together with the bootstrap in the breast cancer research area in Papers III-V. Here, estimates of the sampling distributions of different parameters are used in a new model for free-response receiver operating characteristic (FROC) curve analysis. Compared to earlier work in the field, this model benefits from the advantage of not assuming independence of detections in the images, and in particular, from the incorporation of the sampling distribution of the system's operating point. Confidence intervals obtained from the proposed model with different approaches with respect to the estimation of the distributions and the confidence interval extraction methods are compared in terms of coverage and length of the intervals by simulations of lifelike data.
53

Noninvasive approaches to reduce human-cougar conflict in protected areas on the west coast of Vancouver Island

Thompson, Danielle M. 26 July 2010 (has links)
Cougars (Puma concolor) are a growing concern for managers of Pacific Rim National Park Reserve and Clayoquot Sound UNESCO Biosphere Reserve on the west coast of Vancouver Island, British Columbia. Since the mid-1990s, the frequency and intensity of human-cougar interactions have dramatically increased. Concurrently, these areas have become increasingly popular for human activities. The primary goal of my study was to recommend ways to reduce the potential risk of human-cougar interactions to ensure long-term conservation of cougars while minimizing risks to visitor safety. To achieve this goal, I examined the use of two noninvasive approaches. First, during 2005-2006, I compared the rate of detection, cost and time required for a detector dog, sign surveys, scented rub pads and remotely triggered cameras to detect cougars in coastal temperate rainforests. Sign surveys were the most effective method due to the availability of good tracking substrate throughout the study areas. Cameras were also practical because they could be used by less skilled personnel and had the capacity to detect several species of wildlife. Second, I demonstrated the utility of pre-existing data by analysing the spatiotemporal trends of human-cougar interactions on the West Coast Trail from 1993-2006. My results showed a moderate increase of reported human-cougar interactions (n = 157) despite a steady decline in hiker numbers across these years. I identified four areas where activities of people and cougars repeatedly overlapped (hotspots). In general, interaction locations were primarily associated with high human activity: near campsites and landscape characteristics that were associated with campsites (i.e., beaches and freshwater drainages >20 m wide). However, the distribution of hotspots suggests that the co-occurrence of human-use areas (e.g., campsites) and important travel routes (e.g., freshwater drainages and logging roads) used by cougars may increase the likelihood of interactions. These findings will allow protected area managers to proactively mitigate human-cougar conflict through visitor education and protocols that reduce people and cougars from intersecting in space and time.
54

Jádrové metody v částicových filtrech / Kernel Methods in Particle Filtering

Coufal, David January 2018 (has links)
Kernel Methods in Particle Filtering David Coufal Doctoral thesis - abstract The thesis deals with the use of kernel density estimates in particle filtering. In particular, it examines the convergence of the kernel density estimates to the filtering densities. The estimates are constructed on the basis of an out- put from particle filtering. It is proved theoretically that using the standard kernel density estimation methodology is effective in the context of particle filtering, although particle filtering does not produce random samples from the filtering densities. The main theoretical results are: 1) specification of the upper bounds on the MISE error of the estimates of the filtering densities and their partial derivatives; 2) specification of the related lower bounds and 3) providing a suitable tool for checking persistence of the Sobolev character of the filtering densities over time. In addition, the thesis also focuses on designing kernels suitable for practical use. 1
55

Measure of Dependence for Length-Biased Survival Data

Bentoumi, Rachid January 2017 (has links)
In epidemiological studies, subjects with disease (prevalent cases) differ from newly diseased (incident cases). They tend to survive longer due to sampling bias, and related covariates will also be biased. Methods for regression analyses have recently been proposed to measure the potential effects of covariates on survival. The goal is to extend the dependence measure of Kent (1983), based on the information gain, in the context of length-biased sampling. In this regard, to estimate information gain and dependence measure for length-biased data, we propose two different methods namely kernel density estimation with a regression procedure and parametric copulas. We will assess the consistency for all proposed estimators. Algorithms detailing how to generate length-biased data, using kernel density estimation with regression procedure and parametric copulas approaches, are given. Finally, the performances of the estimated information gain and dependence measure, under length-biased sampling, are demonstrated through simulation studies.
56

American Black Bears (Ursus americanus) of the Paunsaugunt Plateau: Movements and Habitat Use

Dungan, Rebekah Adriana Castro 02 December 2019 (has links)
Concerns over human-bear conflict and questions about the ecology of Paunsaugunt Plateau's population of black bears (Ursus americanus) arose due to their visitation to popular recreation sites. Greater insight about bears and their habitat use provides a foundation for conflict mitigation and effective management decisions. Between 2014 and 2017, seventeen black bears (11 female, 6 male) were fitted with global positioning system (GPS) radio-collars so that we could track their locations, daily activity patterns, and ambient temperatures. By analyzing bear locations, we calculated annual and seasonal home ranges for 16 bears, including 25 den sites. Home ranges typically consisted of three dominant vegetation types, Utah juniper, ponderosa pine and Douglas fir. I used mixed effects models to better understand den site selection and found that slope (27.87 ± 2.03) was the most significant factor (p < 0.001). I also used mixed effects models to understand black bear selection of annual and seasonal home ranges. Predictor variables with the greatest effect (p < 0.001) were elevation (2419.99 ± 1.35) and aspect (138.44 ± 0.64), with coefficients of 1.128 and -1.483 respectively. Male annual home ranges (327.20 km2 ± 133.58 km2) were significantly larger (p = 0.035) than female home ranges (175.10 km2 ± 55.37 km2). However, annual home ranges for both sexes were larger than those during hyperphagia (p = 0.003) or mating (p = 0.004) seasonal home ranges, between which there was no difference (p = 0.451). Individual home ranges overlapped for most bears, consistent with their non-territorial nature. I found that bears avoided roads and lower elevations, while showing a preference for sloping terrain throughout the non-denning period. Paunsaugunt black bear home ranges are larger than any other black bear home ranges reported in literature. We determined weekly average distances and directions for all bears. For two bears, one male and one female, we determined daily averages and directions. Nine bears provided daily averages for 12 seasonal units across all four years. Activity patterns indicate the typical crepuscular pattern noted in normal bear populations that lack human habituation. Identifying areas core use areas and potential den sites is helpful to understanding black bear ecology and useful when making decisions about how to plan infrastructure and educate the public. This research indicates that Paunsaugunt black bears avoid human activity; however, we need continued research to help determine specific interactions between bears and anthropomorphic influences.
57

Identifying Untapped Potential: A Geospatial Analysis of Florida and California’s 2009 Recycled Water Production

Archer, Jana E., Luffman, Ingrid, Joyner, T. Andrew, Nandi, A. 01 June 2019 (has links)
Increased water demand attributed to population expansion and reduced freshwater availability caused by saltwater intrusion and drought, may lead to water shortages. These may be addressed, in part, by use of recycled water. Spatial patterns of recycled water use in Florida and California during 2009 were analyzed to detect gaps in distribution and identify potential areas for expansion. Databases of recycled water products and distribution centers for both states were developed by combining the 2008 Clean Water Needs Survey database with Florida’s 2009 Reuse Inventory and California’s 2009 Recycling Survey, respectively. Florida had over twice the number of distribution centers (n 1/4 426) than California (n 1/4 228) and produced a larger volume of recycled water (674.85 vs. 597.48 mgd (3.78 mL/d1/4 1 mgd), respectively). Kernel Density Estimation shows the majority of distribution in central Florida (Orlando and Tampa), California’s Central Valley region (Fresno and Bakersfield), and around major cities in California. Areas for growth were identified in the panhandle and southern regions of Florida, and northern, southwestern, and coastal California. Recycled water is an essential component of integrated water management and broader adoption of recycled water will increase water conservation in water-stressed coastal communities by allocating the recycled water for purposes that once used potable freshwater.
58

Persistent Places in the Late Archaic Landscape / A GIS-based Case Study of CRM Sites in the Lower Grand River Area, Ontario

Tincombe, Eric January 2020 (has links)
My aim in this study is to identify Late Archaic persistent places—places of continued importance throughout the long-term occupation of a region—within the lower Grand River Area of what is now southern Ontario. I accomplish this through the use of kernel density estimation applied to datasets containing the locations of Late Archaic (4000-2800 RCYBP) sites within this study area which were discovered through cultural resource management (CRM) survey and excavation. Areas identified as persistent places were investigated with regard to landscape features and environmental affordances that could have structured their consistent re-use throughout the Late Archaic, with particular attention paid to the hypothesis that persistent places may have developed around the riverine spawning grounds of spring-spawning fish. Two places with particularly intense concentrations of diagnostic materials dating to successive periods of the Late Archaic were identified: one surrounding Seneca Creek near Caledonia, and one near D’Aubigny Creek south of Brantford. The results show that the persistent use of these places would likely have been structured by the presence of landscape features which would have made these areas particularly rich in many different seasonal resources during the Late Archaic. Perhaps most significantly, both areas are located in close proximity to areas identified as walleye spawning grounds. The contributions of this thesis include the synthesis of the results of many years of CRM survey of the Grand River Area, evidence for the existence of Late Archaic riverine fishing sites related to the spawning runs of walleye, and an improved understanding of Late Archaic subsistence-settlement systems. / Thesis / Master of Arts (MA) / Lay Abstract: My aim in this study is to identify persistent places—places of continued importance throughout the long-term occupation of a region—within the lower Grand River Area of what is now southern Ontario during a period known as the Late Archaic (ca. 2500 B.C.- ca. 1000 B.C). This was accomplished using GIS spatial analysis of data produced through commercial archaeological assessments. As a result of this analysis, I identified two persistent places within the study area: one near D’Aubigny Creek south of Brantford, and one surrounding Seneca Creek near Caledonia. I also investigated the environments surrounding these places to determine what may have made them continuously appealing for over a millennium. Both areas were found to contain environmental features that would have likely made them particularly resource-rich and appealing to hunter-gatherers. One of the most important findings was that both areas are in close proximity to walleye spawning grounds.
59

Trajectory Similarity Based Prediction for Remaining Useful Life Estimation

Wang, Tianyi 06 December 2010 (has links)
No description available.
60

Stochastic distribution tracking control for stochastic non-linear systems via probability density function vectorisation

Liu, Y., Zhang, Qichun, Yue, H. 08 February 2022 (has links)
Yes / This paper presents a new control strategy for stochastic distribution shape tracking regarding non-Gaussian stochastic non-linear systems. The objective can be summarised as adjusting the probability density function (PDF) of the system output to any given desired distribution. In order to achieve this objective, the system output PDF has first been formulated analytically, which is time-variant. Then, the PDF vectorisation has been implemented to simplify the model description. Using the vector-based representation, the system identification and control design have been performed to achieve the PDF tracking. In practice, the PDF evolution is difficult to implement in real-time, thus a data-driven extension has also been discussed in this paper, where the vector-based model can be obtained using kernel density estimation (KDE) with the real-time data. Furthermore, the stability of the presented control design has been analysed, which is validated by a numerical example. As an extension, the multi-output stochastic systems have also been discussed for joint PDF tracking using the proposed algorithm, and the perspectives of advanced controller have been discussed. The main contribution of this paper is to propose: (1) a new sampling-based PDF transformation to reduce the modelling complexity, (2) a data-driven approach for online implementation without model pre-training, and (3) a feasible framework to integrate the existing control methods. / This paper is partly supported by National Science Foundation of China under Grants (61603262 and 62073226), Liaoning Province Natural Science Joint Foundation in Key Areas (2019- KF-03-08), Natural Science Foundation of Liaoning Province (20180550418), Liaoning BaiQianWan Talents Program, i5 Intelligent Manufacturing Institute Fund of Shenyang Institute of Technology (i5201701), Central Government Guides Local Science and Technology Development Funds of Liaoning Province (2021JH6/10500137).

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