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Title:Avalanches in stars and at finite temperature
Author(s):Sheikh, Mohammed Azeem
Director of Research:Dahmen, Karin A
Doctoral Committee Chair(s):Weaver, Richard L
Doctoral Committee Member(s):Weissman, Michael B; Cooper, Stephen L
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Avalanches, Finite Temperature, Stars, Creep, Tabby's Star, Kepler
Abstract:We study two related but distinct aspects of avalanches in physical systems. The first is the study of avalanches that we have observed in stars. We apply results from the mean field avalanche model to observations made by the \emph{Kepler} spacecraft and the VIRGO instrument, looking at several stars including our own Sun and Tabby's star. In this examination, we use the stars' light curve, their integrated flux as a function of time, to extract avalanche information. Dimming events on the Sun are fairly well understood, and we find that there is scaling even in the Sun's data, likely caused by sunspots or combinations of such spots. We also look at Tabby's star, where the anomalous dimming has not been explained, and show that there is also avalanche scaling seen in this extraordinary star. We then look at avalanches at finite but low temperature in plastic deformation. The slow plastic deformation of materials under stress, known as creep motion, has long been studied in material's science. We hypothesize that at low temperatures, this deformation is the result of temperature activated avalanches. In order to explore this idea, we develop an extension of the mean field model to incorporate temperature. This model poses a problem since it requires exponentially many evaluations of rate constants when simulated using a kinetic monte carlo algorithm. We solve this problem by using a recursive strategy to pair down the number of evaluations and effectively choose the appropriate rate constants. Finally, we evaluate theoretically the interevent time distribution between these thermally activated avalanches. We identify high and low temperature regimes, at which the character of the distributions changes dramatically. We use simulations to verify our results, and connect them to experimental efforts currently underway to determine these distributions.
Issue Date:2019-07-11
Rights Information:Copyright 2019 by Mohammed Azeem Sheikh. All rights reserved.
Date Available in IDEALS:2019-11-26
Date Deposited:2019-08

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