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High-performance computing (HPC) variability management is an important topic in computer science. Research topics include experimental designs for efficient data collection, surrogate models for predicting the performance variability, and system configuration optimization. Due to the complex architecture of HPC systems, a comprehensive study of HPC variability needs large-scale datasets, and experimental design techniques are useful for improved data collection. Surrogate models are essential to understand the variability as a function of system parameters, which can be obtained by mathematical and statistical models. After predicting the variability, optimization tools are needed for future system designs. This dissertation focuses on HPC input/output (I/O) variability through three main chapters. After the general introduction in Chapter 1, Chapter 2 focuses on the prediction models for the scalar description of I/O variability. A comprehensive comparison study is conducted, and major surrogate models for computer experiments are investigated. In addition, a tool is developed for system configuration optimization based on the chosen surrogate model. Chapter 3 conducts a detailed study for the multimodal phenomena in I/O throughput distribution and proposes an uncertainty estimation method for the optimal number of runs for future experiments. Mixture models are used to identify the number of modes for throughput distributions at different configurations. This chapter also addresses the uncertainty in parameter estimation and derives a formula for sample size calculation. The developed method is then applied to HPC variability data. Chapter 4 focuses on the prediction of functional outcomes with both qualitative and quantitative factors. Instead of a scalar description of I/O variability, the distribution of I/O throughput provides a comprehensive description of I/O variability. We develop a modified Gaussian process for functional prediction and apply the developed method to the large-scale HPC I/O variability data. Chapter 5 contains some general conclusions and areas for future work. / Doctor of Philosophy / This dissertation focuses on three projects that are all related to statistical methods in performance variability management in high-performance computing (HPC). HPC systems are computer systems that create high performance by aggregating a large number of computing units. The performance of HPC is measured by the throughput of a benchmark called the IOZone Filesystem Benchmark. The performance variability is the variation among throughputs when the system configuration is fixed. Variability management involves studying the relationship between performance variability and the system configuration. In Chapter 2, we use several existing prediction models to predict the standard deviation of throughputs given different system configurations and compare the accuracy of predictions. We also conduct HPC system optimization using the chosen prediction model as the objective function. In Chapter 3, we use the mixture model to determine the number of modes in the distribution of throughput under different system configurations. In addition, we develop a model to determine the number of additional runs for future benchmark experiments. In Chapter 4, we develop a statistical model that can predict the throughout distributions given the system configurations. We also compare the prediction of summary statistics of the throughput distributions with existing prediction models.

Environmental fluctuations in operating fuel cells impose significant biaxial stresses in the constrained proton exchange membranes (PEM). The PEM's ability to withstand cyclic environment-induced stresses plays an important role in membrane integrity and consequently, fuel cell durability. In this thesis, pressure loaded blister tests are used to study the mechanical durability of Gore-Select® series 57 over a range of times, temperatures, and loading histories. Ramped pressure tests are used with a linear viscoelastic analog to Hencky's classical solution for a pressurized circular membrane to estimate biaxial burst strength values. Biaxial strength master curves are constructed using traditional time-temperature superposition principle techniques and the associated temperature shift factors show good agreement when compared with shifts obtained from other modes of testing on the material. Investigating a more rigorous blister stress analysis becomes nontrivial due to the substantial deflections and thinning of the membrane. To further improve the analysis, the digital image correlation (DIC) technique is used to measure full-field displacements under ramped and constant pressure loading. The measured displacements are then used to validate the constitutive model and methods of the finite element analysis (FEA). With confidence in the FEA, stress histories of constant pressure tests are used to develop linear damage accumulation and residual strength based lifetime prediction models. Robust models, validated by successfully predicting fatigue failures, suggest the ability to predict failures under any given stress history whether mechanically or environmentally induced - a critical step in the effort to predict fuel cell failures caused by membrane mechanical failure. / Master of Science

Yes / This paper investigated the bond strength of eight nanoinclusions reinforced concrete with old concrete through a splitting tensile test. The reinforcing mechanisms of bond due to nanoinclusion was also explored by means of scanning electron microscope and energy dispersive spectrometer. A prediction model for the bond strength between nanoinclusion reinforced concrete with old concrete substrate was developed and calibrated against the experimental results obtained. The experimental results indicated that bond strength between nanoinclusions reinforced concrete and old concrete can reach 2.85 MPa, which is 0.8 MPa/39.0% higher than that between new concrete without nanoinclusions and old concrete. The reinforcing mechanisms can be attributed to the enrichment of nanoinclusions in the new-to-old concrete interface, compacting the interfacial microstructures and connecting hydration products in micropores of old concrete with that in bulk new concrete. In addition, the prediction model proposed on the basis of reinforcing mechanisms can accurately describe the relationship of the nanoinclusion content and the bond strength of nanoinclusions reinforced concrete with old concrete.

This thesis presents a prediction model for e-bikes and e-scooters, aimed at enhancing traffic safety and efficiency by sharing their intentions of future possible positions among road users. The research addresses the current automated vehicle technologies which lack communication between road users. The prediction model is based on and tested with a mobility model, adapted for modelling e-bikes and e-scooters in a simulator program primarily used for pedestrians. This implementation has produced the ability to predict future positions and further the development of intention-sharing capabilities in urban traffic scenarios. The model is built upon physical parameters and mathematical models for a controlled and regulated model. Polynomial regression was applied to predict positions based on historical data and the results were evaluated with RMSE metrics, demonstrating the prediction accuracy in different scenarios. The thesis also includes the integration of the prediction model into a hardware setup, a Raspberry Pi. Demonstrating the practical application and retaining the effectiveness of the model in a real-time environment. Gathered from the results, the model can reserve a predicted area every second but also has the capability to work during faster or slower time intervals, depending on the hardware used to enable the model in the protocol. With this, the research highlights the possibility of implementing this in CCAM systems. The results show promising accuracy with a simple controlled model using as little necessary data as possible. The project work contributes to the field of intelligent transport systems by providing a scalable solution to enhance the interaction between VRUs and vehicles, creating a step closer to achieving the Vision-Zero goal of having zero traffic-related accidents or fatalities.

A bridge approach is usually built to provide a smooth and safe transition for vehicles from the roadway pavement to the bridge structure. However, differential settlement between the roadway pavement resting on embankment fill and the bridge abutment built on more rigid foundation often creates a bump in the roadway. Previous work examined this issue at a microscopic level and presented new methods for eliminating or minimizing the effects at specific locations. This research studies the problem at a macroscopic level by determining methods to predict settlement severity to assist designers in developing remediation plans during project development to minimize the lifecycle costs of bridge bump repairs. The study is based on historic data from a wide range of Kentucky roads and bridges relating to bridge approach inspection and maintenance history. A macro method considering a combination of maintenance times, maintenance measures, and observed settlement was used to classify the differential settlement scale as minimal, moderate, and severe, corresponding to the approach performance status good, fair, and poor. A series of project characteristics influencing differential settlement were identified and used as parameters to develop a model to accurately predict settlement severity during preliminary design. Eighty-seven bridges with different settlement severities were collected as the first sample by conducting a survey of local bridge engineers in 12 transportation districts. Sample two was created by randomly selecting 600 bridges in the inspection history of bridges in Kentucky. Ordinal and/or multinomial logistic regression analyses were implemented to identify the relationships between the levels of differential settlement and the input variables. Two predictive models were developed. Prediction of bridge approach settlement can play an important role in selecting proper design, construction, and maintenance techniques and measures. The users can select one or two models to predict the approach settlement level for a new bridge or an existing bridge with different purposes. The significance of this study lies in its identification of parameters that had the most influence on the settlement severity at bridge ends, and how those parameters interacted in developing of a prediction model. The important parameters include geographic regions, approach age, average daily traffic (ADT), the use of approach slabs, and the foundation soil depth. The regression results indicate that the use of approach slabs can improve the performance of approaches on mitigating the problem caused by differential settlement. In addition, current practices regarding differential settlement prediction and mitigation were summarized by surveying the bridge engineers in 5 transportation districts.

As vias pavimentadas se deterioram com o passar do tempo, por ação das cargas do tráfego e das intempéries. Por isso necessitam de intervenções (atividades de Manutenção e Reabilitação - M&R). No Brasil é mais comum que sejam realizadas apenas operações tapa-buracos e recapeamentos. São soluções sem eficiência técnica ou econômica. Uma alternativa mais racional e já em uso em países desenvolvidos é um Sistema de Gerência de Pavimentos Urbanos - SGPU. Os objetivos desta tese são apresentar uma propostas para avaliação da condição de vias urbanas com base na identificação dos defeitos da superfície do revestimento, um modelo de previsão de desempenho de vias urbanas com base em séries históricas obtidas no Município de São Carlos e uma análise econômica com a simulação de diferentes cenários para diferentes opções de M&R. Ainda como objetivos desta tese estão a apresentação das vantagens de utilizar um Sistema de Informações Geográficas - SIG, em uso no SGPU do Distrito Federal. Com base nos resultados encontrados, pode-se inferir que a avaliação de campo pode ser mais eficiente se forem considerados menos defeitos e os critérios de severidade e extensão forem fixados, com menos critérios subjetivos do avaliador. Considerando-se as estratégias de M&R adotadas pela Prefeitura Municipal de São Carlos e, ainda, de acordo com as avaliações de campo, pôde-se verificar que os pavimentos necessitam de Reforço Estrutural após 6 anos da sua construção. Os custos de manutenção, ao longo do tempo, são influenciados pela escolha da M&R a ser aplicada na preservação das vias e, também, pela época em que são realizadas, sendo as manutenções preventivas menos onerosas. Nos Estados Unidos, por exemplo, particularmente na cidade de San Antonio, Texas, são realizadas manutenções preventivas e, nas corretivas, há rigoroso controle de qualidade, o que não se verifica nas cidades brasileiras. Um SGPU possui critérios de análise de dados que, aliados ao Sistema de Informações Geográficas - SIG, garantem clareza na apresentação dos resultados, tanto em mapas temáticos quanto em gráficos e planilhas. Os relatórios no padrão SGPU possibilitam solicitar recursos federais e internacionais para manutenção viária, como o Programa Asfalto Novo do DF, que obteve, no ano de 2013, R$565 milhões para a pavimentação urbana. Em simulação de diferentes cenários de M&R, pôde-se concluir que a opção por tapa-buracos e recapeamentos é mais de duas vezes mais onerosa e mantém o pavimento em condição inferior ao que é possível com base nas técnicas de SGPU. Portanto, um SGPU proporciona benefícios socioeconômicos para toda a sociedade, com vantagens no médio e longo prazo e, ainda, mantém as vias em melhor condição. / The paved roads deteriorate over time, due to traffic loads and bad weather. Therefore, they need interventions (Maintenance and Rehabilitation activities - M & R). In Brazil, it is more common to carry out only hole-hole operations and resurfacing. They are solutions without technical or economic efficiency. A more rational alternative already in use in developed countries is an Urban Pavement Management System - UPMS. In this thesis proposals are presented for the evaluation of urban road conditions based on defects of the surface of the coating, a performance prediction model and an economic analysis with the simulation of different scenarios for different M & R options. Data were analyzed from the Municipality of São Carlos, in the State of São Paulo and the Distrito Federal - DF. Based on the results, it can be inferred that the field evaluation can be more efficient if less defects are considered and the criteria of severity and extension are fixed, with less subjectivity on the part of the evaluator. Considering the M & R strategies adopted by the municipal government of São Carlos and also, according to the field evaluations, it was possible to verify that the pavements have a useful life of 6 years. The maintenance costs, over time, are strongly influenced by the choice of M & R to be applied in the preservation of roads and also by the time in which they are carried out. In the United States, for example, preventive maintenance is carried out and, in the correctives, there is strict quality control, which is not the case in Brazilian cities. An UPMS has data analysis criteria that, together with the Geographic Information System - GIS, guarantee clarity in the presentation of results, both in thematic maps and in charts and spreadsheets. The reports in the UPMS standard make it possible to request federal and international resources for road maintenance, such as the DF Asphalt New Program, which obtained R$ 565 million for urban paving. In the simulation of different M & R scenarios, it was concluded that the option to cover holes and resurfacing is more than twice as expensive and keeps the pavement in a lower condition than is possible based on SGPU techniques. Therefore, an SGPU confers socio-economic benefits for the whole society, with advantages in the medium and long term, and also keeps the roads in better condition.