{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/105628"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/105628","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Avalanches in stars and at finite temperature","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.","abstract_html":"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.","abstract_has_math":false,"creators":["Sheikh, Mohammed Azeem"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Physics","degree_department":null,"school":null,"contributors":["Dahmen, Karin A","Weaver, Richard L","Weissman, Michael B","Cooper, Stephen L"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2019,"date_issued":"2019-11-26T20:33:46Z","date_published":"2019-11-26T20:33:46Z","updated_at":"2026-07-22T22:24:44Z","subjects":["Avalanches, Finite Temperature, Stars, Creep, Tabby's Star, Kepler"],"languages":["en"],"rights":["Copyright 2019 by Mohammed Azeem Sheikh. All rights reserved."],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/105628","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Dahmen, Karin A","Weaver, Richard L","Weissman, Michael B","Cooper, Stephen L"]},{"key":"dc:creator","label":"Author","values":["Sheikh, Mohammed Azeem"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2019-11-26T20:33:46Z","2019-07-11","2019-08"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Physics"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Avalanches, Finite Temperature, Stars, Creep, Tabby's Star, Kepler"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2019 by Mohammed Azeem Sheikh. All rights reserved."]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/105628"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["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.","Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2019-11-26 without embargo terms","The student, Mohammed Sheikh, accepted the attached license on 2019-07-01 at 00:03.","The student, Mohammed Sheikh, submitted this Dissertation for approval on 2019-07-01 at 00:11.","This Dissertation was approved for publication on 2019-07-11 at 07:58.","DSpace SAF Submission Ingestion Package generated from Vireo submission #14113 on 2019-11-26 at 12:50:18","Made available in DSpace on 2019-11-26T20:33:46Z (GMT). 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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.","Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2019-11-26 without embargo terms","The student, Mohammed Sheikh, accepted the attached license on 2019-07-01 at 00:03.","The student, Mohammed Sheikh, submitted this Dissertation for approval on 2019-07-01 at 00:11.","This Dissertation was approved for publication on 2019-07-11 at 07:58.","DSpace SAF Submission Ingestion Package generated from Vireo submission #14113 on 2019-11-26 at 12:50:18","Made available in DSpace on 2019-11-26T20:33:46Z (GMT). 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All rights reserved."],"dc:subject":["Avalanches, Finite Temperature, Stars, Creep, Tabby's Star, Kepler"],"dc:title":["Avalanches in stars and at finite temperature"],"dc:type":["text"],"thesis:degree_discipline":["Physics"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:24:44Z"}