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Item Transparent and Crack-Free Silica Aerogels(North Dakota State University, 2012) Athmuri, Kalyan RamThe process of making silica aerogels has been studied in detail over the past two decades due to its usage in a wide range of low end applications such as thermal insulators, supercapacitors etc., as well as high end applications like particle physics, space explorations. These applications call for control over the properties of aerogels, such as their transparency, density, porosity, pore size, and integrity. However, despite all the past research, controlling properties of aerogels is still not a fully developed science, a lot more research needs to be done. The literature on silica aerogels does not cover the study of the relation between transparency and cracks in aerogels – which can be a key factor in making aerogels for many applications. Hence, optimization of the transparency and integrity of the aerogels in order to obtain high transparency and low cracks was attempted in this thesis.Item Applying Simulation and Genetic Algorithm for Patient Appointment Scheduling Optimization(North Dakota State University, 2013) Peng, YidongIn this study, we discuss the implementation of integrated simulation and genetic algorithm for patient scheduling optimization under two different settings, namely the "traditional" scheduling system and the "open access" scheduling system. Under the "traditional" setting, we propose a two-phase approach for designing a weekly scheduling template for outpatient clinics providing multiple types of services. Our results demonstrate that the two-phase approach can efficiently find the promising weekly appointment scheduling templates for outpatient clinics. Under the "open access" setting, we propose a discrete event simulation and genetic algorithm (DES-GA) approach to find the heuristic optimal scheduling template for the clinic allowing both open access and walk-in patients. The solution provides scheduling templates consisting of not only the optimal number of reservations for open access appointments and walk-ins, but also the optimized allocation of these reserved slots, by minimizing the average cost per admission of open access or walk-in patient.Item Evacuation Trees with Contraflow and Divergence Considerations(North Dakota State University, 2018) Achrekar, Omkar ShirishIn this thesis, we investigate how to evacuate people using the available road transportation network efficiently. To successfully do that, we need to design evacuation model that is fast, safe, and seamless. We enable the first two criteria by developing a macroscopic, time-dynamic evacuation model that aims to maximize the number of people in relatively safer areas of the network at each time point; the third criterion is optimized by constructing an evacuation tree, where the vehicles are evacuated using a single path to safety. Divergence and contraflow policies have been incorporated to enhance the network capacity. Divergence enables specific nodes to diverge their flows into two or more streets, while contraflow allows certain streets to reverse their flow, effectively increasing their capacity. We investigate the performance of these policies in the evacuation networks obtained, and present results on two benchmark networks of Sioux Falls and Chicago.Item Multiresponse Optimization Methodology Considering Related Quality Characteristics(North Dakota State University, 2011) Thambidorai, GaneshEngineering problems often involve many conflicting quality characteristics that must be optimized simultaneously. Engineers are required to select suitable design parameter values which provide better trade-off among all quality characteristics. Multiresponse optimization is one of the most essential tools for solving engineering problems involving multiple quality characteristics. Optimizing several quality characteristics when the quality characteristics are correlated makes the optimization process more complex. The aim of this research is to evaluate the performance of several existing multiresponse optimization methods and investigate their capabilities in dealing with correlated quality characteristics. This study also investigates the impact of uncertainty in terms of input parameter selection. A new multi-response optimization approach has been proposed for solving correlated quality characteristics. The proposed approach is compared with the existing methods and found more robust in terms dealing with uncertainty in target selection. The comparative study and application of the proposed approach is demonstrated by considering two examples from the literature having correlated quality characteristics.Item A New Reliability Assessment Model for Power Electronic Modules Considering Failure Mechanism Interaction(North Dakota State University, 2015) Zhuang, XingA reliability prediction method is proposed to determine the lifetime of IGBTs (Insulated Gate Bipolar Transistors) under power cycling test based on the performance of solder joint and wire bond. The failure characteristics of solder joint and wire bond are captured via selected PoF model respectively. To provide precise reliability prediction, PoF models are converted into probabilistic models. In addition, the failure interaction between wire bond and solder joint is studied. Wire bond lift-off is treated as the predominant failure mode based upon experiments from literature and solder joint degradation process is triggered by wire bond degradation process. Increased junction temperature is captured as it is affected by the degradation process of both components. In the end, the system reliability is computed in a series system configuration.Item Moisture Sensitivity of PLA/PBS Blends During Ultrasonic Welding and Fused Deposition Modeling(North Dakota State University, 2021) Quader, RaihanMoisture absorption into hygroscopic/hydrophilic materials used in fused deposition modeling (FDM) and ultrasonic welding (USW) can diminish desired mechanical properties. Sensitivity to moisture is dependent on material properties and environmental factors and needs characterization. In this thesis, moisture sensitivity of PLA filaments and PLA/PBS blended filaments was characterized in FDM printed ASTM test samples post-conditioning the filaments at different relative humidity levels. Tensile strength decreased with increase in moisture content. Parts made with PLA 4043D, PLA/PBS 75/25 filaments were most sensitive to moisture. Investigation of tensile properties of parts made with PLA filaments exposed to room temperature and humidity conditions for three months showed a more significant decrease. Moisture sensitivity of PLA, PBS, and PLA/PBS 25/75 blend characterized for USW using injection-molded industrial standard test parts (ISTeP) showed a downward trend in weld strength for 100% PLA and PLA/PBS 25/75 while 100% PBS was significantly affected at high moisture conditions.Item ISO 9001: 2015 Quality System Manual Development and Implementation for Business and Commerce with Expanded Emphasis on Risk Management(North Dakota State University, 2019) Mostafa, Mahmoud Hesham Ahmad ShawkyISO 9001: 2015 is the latest edition of the Quality Management System from the International Standard Organization. One of the most noticeable changes about the new edition is the emphasis on risk-based thinking. This study introduces a template for developing a Quality Manual and a systematic approach to Risk Assessment using a risk-based decision-making framework embedded in the Quality Management System. An extensive discussion on decision-making, risk and opportunity analysis is provided with the aim of developing a seamless integration between QMS, risk analysis, and decision-making. This study proposes a decision-making framework that aligns ISO 9001 requirements with the decision-making process. The proposed decision-making methodology is aimed specifically at product and service selection. A case study is used to demonstrate the methodology.Item A Study on the Impact of Patient Centered Medical Home (PCMH) Implementation on Nursing Work Practice(North Dakota State University, 2012) Shinde, Nikhil VijayPrimary care and nursing are important components of the U.S. healthcare system and are facing challenges of quality, access, cost, time spent and inefficiencies of clinical activities. Patient Centered Medical Home (PCMH) is a newly developed care model which has the potential to overcome these challenges. The present study uses a questionnaire approach to find the impact PCMH implementation may have on nursing practice and subsequently primary care. Analysis of the data collected from the questionnaire revealed some surprising results about the nursing practice. For example nurses spend less time on direct care and more time on indirect care and documentation. The nursing demand in terms of Full Time Equivalent (FTE) for nurses decreases. The future demand for nurses (not in FTE) shows an increase after PCMH implementation. The satisfaction level and overall health of patients, patient readmission, job satisfaction of nurses and department productivity shows improvement after PCMH implementation.Item Vulnerability Assessment of Interdependent Power and Communications Networks under Varying Level of Interdependency(North Dakota State University, 2017) Banothu, RahulMaintaining a continuous and robust supply of power could be challenging task, because power networks depend on proper communication to coordinate and schedule supply, as well as recognize and mitigate failures; communication networks depend on power to function. This interdependency is a cause for greater failure risks due to the rapid cascading of failures from one network to the other. The objective of this work is to investigate the vulnerability of interdependent networks under various scenarios and coupling assumptions. To do so, we employ heuristic techniques to detect critical nodes in either network which lead to the maximum number of failed nodes in the interdependent networks. We put to the test a series of topographical importance metrics to heuristically identify said important nodes and compare our results with the literature. Furthermore, we test different coupling methods for how interdependency works and compare the results under different failure assumptions.Item Resilience Assessment for Complex Networks Based on Recovery Strategies(North Dakota State University, 2019) Afrin, TanzinaThe vulnerability of complex networks to unexpected disruptive events could be reduced by increasing network resilience through the efficient recovery of the damaged network. To find the most efficient recovery strategy among the existing variety of strategies, a resilience-based framework was proposed and implemented for both localized attacks and cascading failures. For localized attacks, preferential recovery based on nodal weights (PRNW), periphery recovery (PR) and localized recovery (LR) were assessed. Additionally, probability-based recovery (RS1) and recovery of neighboring or boundary nodes (RS2) methods were evaluated for cascading failures. Considering the advantages and disadvantages of these strategies, a hybrid recovery strategy was proposed to achieve high network resilience in a timely manner with a manageable amount of cost. Overall, this study aids in the assessment and the development of a cost-effective resilience-based recovery strategy.