Dissertation Defense Announcements

Customer churn leads to higher customer acquisition cost, lower volume of service consumption and reduced product purchase. Reducing the outflow of the customers by 5% can double the profit of a typical company. Therefore, it is of significant value for companies to reduce customer outflow. In this dissertation research, we mainly focus on identifying the customers with high chance of attrition and providing valid and trustworthy recommendations to reduce customer churn.

We designed and developed a customer attrition management system that can predict customer churn and yield actionable and measurable recommendations for the decision makers to reduce customer churn. Moreover, reviews from leaving customers reflect their unfulfilled needs, while reviews of active customers show their satisfactory experience. In order to extract the action knowledge from the unstructured customer review data, we thoroughly applied aspect-based sentiment analysis to transform the unstructured review text data into a structured table. Then, we utilized rough set theory, action rule mining and meta-action triggering mechanism on the structured table to generate effective recommendations for reducing customer churn. Lastly, in practical applications, an action rule is regarded as interesting only if its support and confidence exceed the predefined threshold values. If an action rule has a large support and high confidence, it indicates that this action can be applied to a large portion of customers with a high chance. However, there is little research focused on improving the confidence and coverage of action rules. Therefore, we proposed a guided semantic-aided agglomerative clustering algorithm to improve the discovered action rules.

Studies assessing health disparities in the United States primarily compare White and Black individuals without accounting for the heterogeneity within racial groups. The present study utilizes the racial context of origin framework to identify potential mechanisms that can explain differences in health between foreign-born Black (FBB) and US-born Black (USB) individuals. Using self-report questionnaires, this study examined the interactive effects of internalized racism, perceived discrimination, and racial context of origin on physical health and perceived discrimination reactivity. Further, motivation to succeed, belief in meritocracy, shared racial fate, and connection and belonging to the Black race were assessed to discern factors contributing to differential interactions by racial context of origin. Results indicate that internalized racism is negatively associated with physical health for FBB, but not USB. The 3-way interactions of internalized racism, perceived discrimination, and racial context of origin on physical health and perceived discrimination reactivity were not significant. Motivation to succeed, belief in meritocracy, shared racial fate, and connection and belonging to the Black race did not provide insight to differences in the role of racial context of origin in the association between internalized racism and physical health. Exploratory analyses revealed that racial centrality is a promising factor in understanding health differences by racial context of origin. Notable preliminary analyses and group differences are also discussed. These findings contribute to the understanding of racial context of origin and provide insight to race-related variables that may aid in understanding of differences in health by racial context of origin.

Fertility preservation would benefit young males who must undergo treatments that can result in sterilization, such as radiation treatments for cancer. This can be achieved by removing some testicular tissue before treatment and putting it into frozen storage for later use, a process known as cryopreservation. Cryopreservation requires the use of cryoprotective agents (CPAs), such as dimethyl sulfoxide (DMSO), to reduce injury from ice crystal formation. Because DMSO can be toxic at high exposure levels, it is important to determine the exposure time that is necessary to achieve adequate concentrations for freeze protection, without over-exposing the tissue. Mass diffusion models can be used to predict this loading time, but these models depend on property parameters that are often unknown, such as the mass diffusion coefficient for a given CPA in a specific tissue.
To facilitate the development of cryopreservation protocols for testicular tissue, we determined the mass diffusion coefficient for DMSO in thin (~1 mm) tissue sections that were precision cut from feline testes that were discarded from veterinary sterilization procedures. Samples were placed in a custom tube that was mounted on the surface of an Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) and then exposed to DMSO on the opposite side. Spectra were recorded for 60 minutes, and the area of peak centered at 950 cm-1 was determined as a function of time. This time course absorbance data was then fit to an equation developed by Barbari and Fieldson (1993) that considers both mass diffusion and tissue absorption properties. By minimizing the sum of squares, estimates for the DMSO diffusion coefficient were obtained from each time sequence. Samples were analyzed at 22°C and 4°C.
Because of the inherent variability in biological tissues, alginate-gelatin and agarose were also evaluated for their potential as reference standard materials, to facilitate methodology development and training. Alginate compacted to thicknesses of 1.7 ± 0.2 mm resulting in an effective DMSO diffusion coefficient of 4.3 ± 0.3 x 10-6 cm2/s (n=4). Agarose compacted to thicknesses of 1.1 ± 0.1 mm. The effective diffusion coefficient of DMSO in agarose was 9.2 ± 0.2 x 10-6 cm2/s at 22°C (n=9) and 5.6 ± 0.2 x 10-6 cm2/s (n=9) at 4°C. Although alginate and agarose had similar variability in their thicknesses, agarose had much lower within batch and between batch variability than alginate-gelatin for the effective diffusion coefficients and thus is the preferred reference material for ATR-FTIR diffusion studies. Testicular tissue samples compacted to 2.1 ± 0.7 mm. The effective diffusion coefficient was 10.3 ± 4 x 10-6 cm2/s at 22°C and 7.1 ± 5 x 10-6 cm2/s at 4°C. The high variability is likely due to native variability in the testicular tissue samples. However, these nominal values can be used to inform preservation procedure planning.

Diversity initiatives are often ineffective because they characterize differences at the group-level, and therefore, do not adequately address individuals’ specific identity-related challenges. The purpose of this study is to use a network-based approach to studying identity to provide a comprehensive examination of the wide range of identities that are salient and important for individuals who are members of diverse race and gender groups, namely White and Black men and women at work. Additionally, I apply intersectionality theory to understand how multiple identities are constructed into overall self-concepts at work and more specifically, how individuals perceive intersections between their multiple identities. According to intersectionality theory, I expect that multiple identities will co-exist and subordinate (i.e., historically marginalized) social identities will be more central for women and racial minorities employees as opposed to dominant (i.e., historically non-marginalized) identities. I also integrate job-demands resources theory to develop and test hypotheses concerning the structural relationships between identities (i.e., conflict, compatibility, centrality) and authenticity at work. Specifically, I propose that identity conflict, compatibility, and centrality are identity structures that serve as resources that can enable or constrain authentic self-expression at work. I test these hypotheses across two studies. In summary, this work sheds theoretical and empirical light on the complex nature of multiple identities at work and how diversity initiatives can more effectively address identity dimensions that intersect and affect personal work experiences.