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Title: The evolution of division of labor in digital organisms
Creator: Goldsby, Heather J.
Date: 2011
Collection: Electronic Theses & Dissertations
Description: Division of labor is a hallmark strategy employed by a wide variety of groups ranging in complexity from bacteria to human economies. Within these groups, some individuals, such as worker ants, sacrifice their ability to reproduce and instead dedicate their lives to the maintenance of the colony and success of their kin. A worker ant may spend its entire life performing a single task, such as defending the colony or tending to the brood. The complexity of the strategies employed by these...
Show moreDivision of labor is a hallmark strategy employed by a wide variety of groups ranging in complexity from bacteria to human economies. Within these groups, some individuals, such as worker ants, sacrifice their ability to reproduce and instead dedicate their lives to the maintenance of the colony and success of their kin. A worker ant may spend its entire life performing a single task, such as defending the colony or tending to the brood. The complexity of the strategies employed by these groups, combined with their rampant success, gives rise to questions regarding why division of labor exists. While extensive research has been done to better understand the patterns and mechanisms of division of labor, exploring this topic in an evolutionary context remains challenging to study due to the slow pace of evolution and imperfect historical data. Understanding how and why division of labor arises is pertinent not just for understanding biological phenomena, but also as a means to enable evolutionary computation techniques to address complex problems using problem decomposition. The objective of problem-decomposition approaches is to have a group of individuals cooperatively solve a complex task by breaking it into pieces, having specialist individuals solve the pieces, and reassembling the solution. Essentially, problem-decomposition approaches use division of labor to enable groups to solve more challenging problems than any individual could alone. Unfortunately, human engineers have struggled with creating effective, automated problem-decomposition approaches.In this dissertation, I use digital evolution (i.e., populations of self-replicating computer programs that undergo open-ended evolution) to investigate questions related to the evolution of division of labor and to apply these insights to problem decomposition techniques. This dissertation has three primary components: First, we provide experimental evidence that evolutionary computation techniques can evolve groups of individuals that exhibit division of labor. Second, we explore two hypotheses for the evolution of division of labor. Specifically, we find support for the hypothesis that temporal polyethism (i.e., where a worker's age is related to the task it performs within the colony) may result from the evolutionary pressures of aging and risks associated with tasks. Additionally, we find support for a hypothesis initially proposed by Adam Smith, the premier economist, that the presence of task-switching costs results in an increase in the amount of division of labor exhibited by groups. Third, we describe how our analyses revealed that groups of organisms evolved as part of our task-switching work exhibit complex problem decomposition strategies that can potentially be applied to other evolutionary computation challenges. This work both informs biological studies of division of labor and also provides insights that can enable the development of new mechanisms for using evolutionary computation to solve increasingly complex engineering problems.
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Title: Computational modeling of cardiac mechanics : microstructual modeling & pulmonary arterial hypertension
Creator: Xi, Ce
Date: 2019
Collection: Electronic Theses & Dissertations
Description: Heart diseases, which approximately account for 31% of all human mortality every year, are the leading cause of death worldwide. Computational cardiac models have gained increasing popularity and become an indispensable and powerful tool in elucidating the pathological process of different heart diseases. They can be used to estimate important physiological and clinically relevant quantities that are difficult to directly measure in experiments. The broad goals of this thesis were to develop...
Show moreHeart diseases, which approximately account for 31% of all human mortality every year, are the leading cause of death worldwide. Computational cardiac models have gained increasing popularity and become an indispensable and powerful tool in elucidating the pathological process of different heart diseases. They can be used to estimate important physiological and clinically relevant quantities that are difficult to directly measure in experiments. The broad goals of this thesis were to develop 1) a microstructure-based constitutive model of the heart and 2) patient-specific computational models that would ultimately help medical scientists to diagnose and treat heart diseases.Heart diseases such as heart failure with preserved ejection fraction (HFpEF) are characterized by abnormalities of ventricular function that can be attributed to, changes in geometry, impaired myocyte (LV) relaxation, cardiac fibrosis and myocyte passive stiffening. Understanding how LV filling is affected by each of the many microstructural pathological features in heart diseases is very important and may help in the development of appropriate treatments. To address this need, we have developed and validated a microstructure-based computational model of the myocardium to investigate the role of tissue constituents and their ultrastructure in affecting the heart function. The model predicted that the LV filling function is sensitive to the collagen ultrastructure and the load taken up by the tissue constituents varies depending on the LV transmural location. This finding may have implications in the development of new pharmaceutical treatments targeting individual cardiac tissue constituents to normalize LV filling function in HFpEF.Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by elevated pulmonary artery pressure (PAP) and pulmonary artery vascular resistance, with limited survival rate and can affect patients of all ages. The increased pressure or afterload in the right ventricle (RV) can result in pathological changes in RV mechanics, which are currently not well-understood. To FB01ll this void, we have developed patient-specific computational models to investigate effects of PAH on ventricular mechanics. SpeciFB01cally, we have quantified regional ventricular myoFB01ber stress, myoFB01ber strain, contractility, and passive tissue stiffness in PAH patients, and compare them to those found in age- and gender-matched normal controls. Our results showed that RV longitudinal, circumferential and radial strain were depressed in PAH patients compared with controls; RV passive stiffness increased progressively with the degree of remodeling as indexed by the RV and LV end-diastolic volume ratio (RVEDV/LVEDV); Peak contractility of the RV was found to be strongly correlated, and had an inverse relationship with RVEDV/LVEDV. These results provide the mechanical basis of using RVEDV/LVEDV as a clinical index for delineating disease severity and estimating RVFW contractility in PAH patients.
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