In response surface methodology, the central composite design is the most popular choice for fitting a second order model. The choice of the distance for the axial runs, alpha, in a central composite design is very crucial to the performance of the design. In the literature, there are plenty of discussions and recommendations for the choice of alpha, among which a rotatable alpha and an orthogonal blocking alpha receive the greatest attention. Box and Hunter (1957) discuss and calculate the values for alpha that achieve rotatability, which is a way to stabilize prediction variance of the design. They also give the values for alpha that make the design orthogonally blocked, where the estimates of the model coefficients remain the same even when the block effects are added to the model. In the last ten years, people have begun to realize the importance of a split-plot structure in industrial experiments. Constructing response surface designs with a split-plot structure is a hot research area now. In this dissertation, Box and Hunters' choice of alpha for rotatablity and orthogonal blocking is extended to central composite designs with a split-plot structure. By assigning different values to the axial run distances of the whole plot factors and the subplot factors, we propose two-strata rotatable splitplot central composite designs and orthogonally blocked split-plot central composite designs. Since the construction of the two-strata rotatable split-plot central composite design involves an unknown variance components ratio d, we further study the robustness of the two-strata rotatability on d through simulation. Our goal is to provide practical recommendations for the value of the design parameter alpha based on the philosophy of traditional response surface methodology. / Ph. D.

Complex mathematical models are often built to describe a physical process that would otherwise be extremely difficult, too costly or sometimes impossible to analyze. Generally, these models require solutions to many partial differential equations. As a result, the computer codes may take a considerable amount of time to complete a single evaluation. A time tested method of analysis for such models is Monte Carlo simulation. These simulations, however, often require many model evaluations, making this approach too computationally expensive. To limit the number of experimental runs, it is common practice to model the departure as a Gaussian stochastic process (GaSP) to develop an emulator of the computer model. One advantage for using an emulator is that once a GaSP is fit to realized outcomes, the computer model is easy to predict in unsampled regions of the input space. This is an attempt to 'characterize' the overall model of the computer code. Most of the historical work on design and analysis of computer experiments focus on the characterization of the computer model over a large region of interest. However, many practitioners seek other objectives, such as input screening (Welch et al., 1992), mapping a response surface, or optimization (Jones et al., 1998). Only recently have researchers begun to consider these topics in the design and analysis of computer experiments. In this dissertation, we explore a more traditional response surface approach (Myers, Montgomery and Anderson-Cook, 2009) in conjunction with traditional computer experiment methods to search for the optimum response of a process. For global optimization, Jones, Schonlau, and Welch's (1998) Efficient Global Optimization (EGO) algorithm remains a benchmark for subsequent research of computer experiments. We compare the proposed method in this paper to this leading benchmark. Our goal is to show that response surface methods can be effective means towards estimating an optimum response in the computer experiment framework. / Ph. D.

Within the realms of biological and medical research, toxicity studies which measure impaired reproduction are becoming more and more common, yet methods for efficiently designing experiments for these studies have received little attention. In this research, response surface design criteria are applied to four models for impaired reproduction data. The important role of control observations in impairment studies is discussed, and for one model, a normal error linear model, a design criterion is introduced for allocating a portion of the sample to the control. Special attention is focused on issues surrounding optimal design of experiments for two of the models, a Poisson exponential model and a Poisson linear model. As most of the optimal designs for these models are obtained via numerical methods rather than directly from criteria, equivalence theory is used to prove analytically that the numerically obtained designs are truly optimal. A further complication associated with designing experiments for Poisson regression is the need to know parameter values in order to implement the optimal designs. Thus, two stage design of experiments is investigated as one solution to this problem. Finally, since researchers frequently do not know the appropriate model for their data a priori, the optimal designs for these two different models are compared, and designs which are robust to model misspecification are highlighted. / Ph. D.

Yes / This paper investigates the coupled effect of functionalized multiwall carbon nanotubes (MWCNTs-COOH), nanomontmorillonite (NM), and sodium dodecyl benzene sulfonate (SDBS) anionic surfactant on compressive and flexural strengths of cement paste. The response surface methodology (RSM) was used to optimize the content of the two nanomaterials and surfactant, and to analyze the effect of their interactions on mechanical properties and microstructural characteristics of the paste. Test results indicate that the simultaneous use of NM and MWCNT can lead to 30% gain in compressive strength and 40% increase in flexural strength. Using analysis of variance, it was possible to predict the optimal weight percentage of nanomaterials. Atomic Force Microscope observations showed that the use of NM and MWCNT can reduce the surface roughness of cement paste and refine porosity, thus reducing the risk of cracking at the cement matrix and improving the homogeneity of the microstructure.

This dissertation explored how a change in the work/home boundary stemming from a mandatory switch to full-time telework influenced employee well-being. Organizational scholars have called for more investigations into how crisis events impact employees, and the COVID-19 pandemic presented an opportunity to examine a change in employees' work and home domains as it unfolded. Additionally, as full-time telework becomes a more common way of work, understanding how this once rare work arrangement affects employee well-being holistically is important. Using boundary theory, I hypothesized that a switch to full-time telework would increase the level of integration between employees' work and home domains, and that a greater change in integration level would associate with worse daily well-being outcomes. To explain this association, I turned to recovery theorizing and proposed daily work-related rumination and lack of psychological detachment as linking mechanisms. Additionally, I expected that teleworkers whose current level of integration was closer to their preferred level would experience better well-being. Using multilevel response surface analysis (MRSA), which enabled illustration of these complex associations in a more nuanced manner than is possible via either change scores or moderation analyses, I found that maintaining higher work/home integration both before and after telework co-varied with worse holistic well-being through work-related rumination and lack of psychological detachment. I also found that having higher integration than preferred and even high integration when preferred associated with worse well-being through work-related rumination and lack of psychological detachment. Based on these results, I point to boundary work and its facilitation of segmentation as a potential means of protecting employee well-being in the event of a future crisis that moves work into the home. / Doctor of Philosophy / This dissertation examined the influence of the COVID-19-induced abrupt and mandatory switch to telework on employees' well-being. More understanding is needed regarding how crisis events impact employees, according to organizational scholars, and the COVID-19 pandemic presented an opportunity to conduct an investigation of change in employees' work situations in real time. As employees experienced change in numerous ways due to the pandemic and stay-at-home orders, I expected that experiencing greater changes in the separation between one's work and home would correlate with well-being impairments. I expected that less separation (i.e., more integration) between work and home would associate with the tendency to ruminate about work during non-work time (work-related rumination) and an inability to detach from work (lack of psychological detachment), which would in turn relate to worse well-being. I also anticipated that employees whose preference in level of work/home integration more closely matched their current situation would enjoy better well-being, potentially due to less work-related rumination and better psychological detachment. Instead, I found that maintaining old habits in how closely integrated employees keep their work and home lives from before to during telework associated with worse well-being. Employees who had more work/home integration pre-telework and maintained more integration during telework showed worse well-being through more work-related rumination and less psychological detachment. Preferring more integration did not appear to protect one's well-being, as those teleworkers who both preferred and enacted more work/home integration had worse well-being through more work-related rumination and less psychological detachment, as did those who had more integration than preferred. Based on these findings, I recommend that in crisis situations and abrupt, mandatory transitions to full-time telework, teleworkers protect their ability to recover from the workday's often strenuous demands by creating separation between work and home. Employees, organizations, and managers can all facilitate boundary work, wherein the teleworker performs actions to create greater separation between work and home, even when fully working from home.

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