Global ETD Search

1	Transforming GPS Points to Daily Activities Using Simultaneously Optimized DBSCAN-TE Parameters Riches, Gillian Michele 05 December 2022 (has links) With the recent upsurge in mental health concerns and ongoing isolation regulations brought about by the COVID-19 pandemic, it is important to understand how an individual's daily travel behavior can affect their mental health. Before finding any correlations to mental health, researchers must first have individual travel behavior information: an accurate number of activities and locations of those activities. One way to obtain daily travel behavior information is through the interpretation of cellular Global Positioning System (GPS) data. Previous methods that interpret GPS data into travel behavior information have limitations. Specifically, rule-based algorithms are structured around subjective rule-based tests, clustering algorithms include only spatial parameters that are chosen sequentially or require further exploration, and imputation algorithms are sensitive to provided context (input parameters) and/or require lots of training data to validate the results of the algorithm. Due to the lack of provided training data that would be required for an imputation algorithm, this thesis uses a previously adopted clustering method. The objective of this thesis is to determine which spatial, entropy, and time parameters cause the clustering algorithm to give the most accurate travel behavior results. This optimal set of parameters was determined using a comparison of two non-linear optimization methods: simulated annealing and a limited-memory Broyden-Fletcher-Goldfarb-Shanno Bound (L-BFGS-B) optimizer. Ultimately, simulated annealing optimization found the best set of clustering parameters leading to 91% clustering algorithm accuracy whereas L-BFGS-B optimization found parameters that were only able to produce a maximum of 79% accuracy. Using the most optimal set of parameters in the clustering algorithm, an entire set of GPS data can be interpreted to determine an individual's daily travel behavior. This resulting individual travel behavior sets the groundwork to answer the question of how individual travel behavior can affect mental health. travel behavior GPS data clustering algorithm simulated annealing L-BFGS-B Engineering
2	Theoretical investigation of size effects in multiferroic nanoparticles Allen, Marc Alexander 05 August 2020 (has links) Over the last two decades, great progress has been made in the understanding of multiferroic materials, ones where multiple long-range orders simultaneously exist. However, much of the research has focused on bulk systems. If these materials are to be incorporated into devices, they would not be in bulk form, but would be miniaturized, such as in nanoparticle form. Accordingly, a better understanding of multiferroic nanoparticles is necessary. This manuscript examines the multiferroic phase diagram of multiferroic nanoparticles related to system size and surface-induced magnetic anisotropy. There is a particular focus on bismuth ferrite, the room-temperature antiferromagnetic-ferroelectric multiferroic. Theoretical results will be presented which show that at certain sizes, a bistability develops in the cycloidal wavevector. This implies bistability in the ferroelectric and magnetic moments of the nanoparticles. This novel magnetoelectric bistability may be of use in the creation of an electrically-written, magnetically-read memory element. / Graduate bismuth ferrite bfo nanoparticle nanomagnetism multiferroics optimization magnetism ferroelectric bistability anisotropy surface anisotropy weak ferromagnetism antiferromagnetism Dzyaloshinskii-Moriya interaction cycloid numerical methods condensed matter solid state physics magnetoelectric effect room-temperature multiferroic superexchange magnetic memory spin canting g-type antiferromagnetism Heisenberg Hamiltonian Nelder-Mead L-BFGS-B mathematica python ferroelectricity perovskite antiferromagnet bifeo3 rhombohedral pseudocubic r3c trigonal physics magnetic memory electrically-written memory curie temperature néel temperature materials science

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Transforming GPS Points to Daily Activities Using Simultaneously Optimized DBSCAN-TE Parameters

Theoretical investigation of size effects in multiferroic nanoparticles