Browsing by Subject "aggregation"

Now showing 1 - 4 of 4
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    Algorithms and Data Structures for Geometric Intersection Query Problems
    (2017-09) Saladi, Rahul
    The focus of this thesis is the topic of geometric intersection queries (GIQ) which has been very well studied by the computational geometry community and the database community. In a GIQ problem, the user is not interested in the entire input geometric dataset, but only in a small subset of it and requests an informative summary of that small subset of data. Formally, the goal is to preprocess a set A of n geometric objects into a data structure so that given a query geometric object q, a certain aggregation function can be applied efficiently on the objects of A intersecting q. The classical aggregation functions studied in the literature are reporting or counting the objects of A intersecting q. In many applications, the same set A is queried several times, in which case one would like to answer a query faster by preprocessing A into a data structure. The goal is to organize the data into a data structure which occupies a small amount of space and yet responds to any user query in real-time. In this thesis the study of the GIQ problems was conducted from the point-of-view of a computational geometry researcher. Given a model of computation and a GIQ problem, what are the best possible upper bounds (resp., lower bounds) on the space and the query time that can be achieved by a data structure? Also, what is the relative hardness of various GIQ problems and aggregate functions. Here relative hardness means that given two GIQ problems A and B (or, two aggregate functions f(A, q) and g(A, q)), which of them can be answered faster by a computer (assuming data structures for both of them occupy asymptotically the same amount of space)? This thesis presents results which increase our understanding of the above questions. For many GIQ problems, data structures with optimal (or near-optimal) space and query time bounds have been achieved. The geometric settings studied are primarily orthogonal range searching where the input is points and the query is an axes-aligned rectangle, and the dual setting of rectangle stabbing where the input is a set of axes-aligned rectangles and the query is a point. The aggregation functions studied are primarily reporting, top-k, and approximate counting. Most of the data structures are built for the internal memory model (word-RAM or pointer machine model), but in some settings they are generic enough to be efficient in the I/O-model as well.
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    Gawker, BuzzFeed, and Journalism: Case Studies in Boundaries, News Aggregation, and Journalistic Authority
    (2016-05) Toropin, Konstantin
    The study of boundary work in journalism generally has involved examining legacy news organizations and their efforts to expel deviant actors and otherwise patrol the boundaries around appropriate professional practice. This thesis extends this body of research by analyzing the interrelationships among newer, digitally centric actors: namely, Gawker and BuzzFeed. Using textual analysis, this research examines two case studies: a feud between BuzzFeed and Gawker over journalistic norms, and Gawker’s outing of a Condé Nast executive. By blending the existing frameworks of boundary work with concepts such as authority, as well as findings from research on blogging and news aggregation, this study offers a comprehensive examination of these emerging journalistic actors. In the first case, Gawker engaged BuzzFeed over what it believed to be failures of journalistic norms in deleting articles at the behest of advertisers. In the second, Gawker wrestled with the consequences of its own failure to exercise acceptable editorial judgment in the outing of a gay magazine executive. The resulting findings suggest that, as these cases unfolded, BuzzFeed and Gawker both readily adopted some of the traditional values of journalism in an effort to be accepted by the professional community. However, in other ways, these actors continued to distance themselves from legacy news media and refused to conform to certain journalistic norms, instead remaining more closely aligned with the values they brought from their own histories as digital upstarts. These findings suggest a need for further research into the boundary behaviors of born-digital actors and a deeper examination of the discourse between new and old media entities.
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    Nanoparticle Dynamics in the Non-Equilibrium to Equilibrium Transition Region of Plasma Reactors
    (2019-11) Chen, Xiaoshuang
    Nanocrystals are often assumed to be spherical and largely monodisperse during nonthermal plasma synthesis because of unipolar particle charging and selective particle heating originate from the non-equilibrium nature of nonthermal plasma synthesis environment. However, in sampling nanocrystals from nonthermal plasma reactor and utilizing inertial deposition to collect them, nanocrystals move from a non-equilibrium environment in the plasma to equilibrium environment beyond the plasma boundary. Nanocrystal charging and growth dynamics are altered inevitably during this transition; hence the state of aggregation needs to be addressed. However, lacking in non-thermal plasma nanocrystal synthesis and sampling has been (1) the development of online diagnostic techniques for monitoring nanocrystal growth in and beyond plasma reactors, and (2) fundamental investigations of the nanocrystal dynamics in spatial plasma afterglow environments. Therefore, this dissertation focuses on the development of cutting-edge nanometrologies for nonthermal plasma, as well as theoretical and numerical study of particle dynamics in nonthermal plasma spatial afterglow. First, a uniquely designed low pressure differential mobility analyzer (LPDMA) is applied to characterize particle size distribution from nonthermal plasma reactor for the first time. The LPDMA transfer function and complete data inversion routine to calculate particle size distribution is developed from tandem IMS-IMS calibration and Twomey-Markowski inversion algorithm. Second, the LPDMA measurement system is utilized to study Si nanocrystal charging and aggregation in the spatial afterglow of a flow through nonthermal plasma reactor. The bipolar charge state and aggregation of nanocrystals are revealed in measurements. Collectively, a specifically developed constant number Monte Carlo simulation model is implemented and compared with experimental results. The importance of transition diffusion of energetic species, electron desorption and collision model in spatial afterglow is noted through experiment-model comparison. Finally, ion mobility-mass spectrometry measurement yielding a 2-D size-mass distribution is utilized to analyze the morphology of aggregates from an atmospheric pressure DC microplasma. The fractal dimension of the aggregates is quantitatively analyzed by automated TEM image analysis. Both IM-MS and TEM image analysis illustrate the formation of highly polydispersity, branch-like structure aggregates exiting the microplasma. Comparison with Langevin dynamics simulation demonstrates that Coulomb interaction plays minimum role in particle aggregation out of plasma.
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    Selling Minnesota: Local Food Fact Sheet Series
    (Minnesota Institute for Sustainable Agriculture, 2017) Jewett, Jane G
    The Selling Minnesota series of fact sheets are intended to provide farmers and farm-based food business owners with detailed information about Minnesota state regulations and best practices for selling meat and poultry products, produce, and shell eggs. Additional fact sheets in the series cover aggregation of produce for sale, and approved sources of water for rural food businesses.