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UCLA Ph.D. Thesis

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A. Stomakhin. Part I: Reconstruction of Missing Data in Social Networks Based on Temporal Patterns of Interactions, Part II: Constitutive Modeling in Solid Mechanics for Graphics Applications. UCLA Digital Library 2013.

Dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Mathematics. University of California, Los Angeles 2013. Copyright by Alexey Dmitrievich Stomakhin 2013.

Comittee Members:
Professor Joseph Teran, Co-chair
Professor Andrea Bertozzi, Co-chair
Professor Stanley Osher
Professor Jeffrey Eldredge

In Part I the author presents a mathematical framework based on a self-exciting point process aimed at analyzing temporal patterns in the series of interaction events between agents in a social network. We develop a reconstruction model formulated as a constraint optimization problem that allows one to predict the unknown participants in a portion of those events. The results are used to predict the perpetrators of the unsolved crimes in the Los Angeles gang network.

Part II discusses the work undertaken by the author in deformable solid body simulation. We first focus on purely elastic solids and develop a method for extending an arbitrary isotropic hyperelastic energy density function to inverted configurations. This energy based extension is designed to improve robustness of elasticity simulations with extremely large deformations typical in graphics applications and demonstrates significant improvements over similar stress based techniques presented in. Moreover, it yields continuous stress and unambiguous stress derivatives in all inverted configurations. We also introduce a novel concept of a hyper-elastic modelís primary contour which can be used to predict its robustness and stability. We demonstrate that our invertible energy-density-based approach outperforms the popular hyperelastic corotated model and show how to use the primary contour methodology to improve the robustness of this model to large deformations. We further develop a novel snow simulation method utilizing a user-controllable constitutive model defined by an elasto-plastic energy density function integrated with a hybrid Eulerian/Lagrangian Material Point Method (MPM). The method is continuum based and its hybrid nature allows us to use a regular Cartesian grid to automate treatment of self-collision and fracture. It also naturally allows us to derive a grid-based implicit integration scheme that has conditioning independent of the number of Lagrangian particles. We demonstrate the power of our method with a variety of snow phenomena.