Imaging and Understanding Atomic-Scale Adhesion and Wear: Quantitative investigations Using in situ TEM

The underlying physics governing tribological interactions - adhesion, friction, lubrication, and wear - are poorly understood. Significant progress has been enabled by nanoscale studies using the atomic force microscope (AFM). However, AFM lacks direct access to the contact geometry and structure. In this thesis, nanoscale adhesion and wear tests were performed inside of a transmission electron microscope (TEM), enabling real-time in situ interrogation of the contact in vacuum. Quantitative data was extracted using custom analysis routines to resolve tip shape, volume changes, and adhesive forces with unprecedented resolution. From in situ adhesion tests, a novel method was developed to extract the work of adhesion (0.66±0.14 J/m^2) and range of adhesion (0.25±0.06 nm) between silicon and diamond. The latter quantity has not previously been measured experimentally. TEM adhesion tests and complementary atomistic simulations reveal an order-of-magnitude reduction in apparent work of adhesion as tip roughness increased from atomic-scale to a root-mean-square value of 1 nm. Using an existing analytical model, an empirically derived roughness-independent adhesion parameter was extracted. In situ wear tests of silicon on diamond at low load revealed the mechanism of wear to be consistent with atom-by-atom processes. The rate of atomic removal varied exponentially with average normal stress, consistent with stress-mediated chemical reaction kinetics. This yields a physically reasonable activation energy (0.85±0.06 eV), and activation volume (6.7±0.3 �). This framework can be generalized to understand and potentially predict wear in many materials undergoing atom-by-atom removal. Together, these investigations advance the scientific understanding of nanoscale adhesion and wear and help bridge the gap between experiments and atomistic simulations. Three examples are demonstrated where nanometer-scale trends can be predicted using continuum approaches: nanoscale adhesive forces can be calculated using an interaction potential; apparent work of adhesion depends on nanoscale root-mean-square roughness; and the rate of atomic-scale wear reactions is determined by the average normal contact stress. These examples, while only demonstrated in the specific systems studied, suggest strategies and future research directions for understanding, predicting, and controlling tribological phenomena

Developmental Functioning of Infants and Toddlers with Autism and Down Syndrome

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social communication, as well as restricted interests and repetitive behaviors. Approximately 10% of individuals with ASD also have comorbid genetic or chromosomal conditions, like Down Syndrome (DS). While it was once believed that DS and ASD rarely co-occurred, it has been demonstrated that it is not uncommon for children with DS to also meet criteria for ASD. Due to the difficulties in differentiating between impairments associated with intellectual disability (ID) and ASD symptomology, DS often leads to delayed or misdiagnoses of ASD. This can interfere with early intervention services and appropriate educational placements. While prior research has compared developmental functioning in children with ASD and DS, no studies have examined the impact of ASD risk and DS on developmental functioning in infants and toddlers under the age of 3. Utilizing the Baby and Infant Screen for Children with aUtIsm Traits-Part 1 (BISCUIT-Part 1) and the Battelle Developmental Inventory, Second Edition (BDI-2), the current study aimed to expand the existing literature by investigating the effects of ASD risk and DS on developmental functioning in infants and toddlers. The current study compared three groups consisting of 46 toddlers each: ASD screen positive only without co-occurring DS (ASD+), DS screen negative (DS-), and DS screen positive (DS+). The results of the current study revealed significant group differences in the overall developmental functioning, as well as each developmental subdomain of the BDI-2. These findings support the need for early screening and identification of ASD among those with genetic conditions

Long-Term Behavioral Health Care Unbundled: The Impact of Comorbidity and Aggression on Caregiver Strain and Service Costs for Individuals with Intellectual Disabilities

Individuals with intellectual disabilities represent a unique population with an array of needs. High rates of comorbid mental and physical health conditions as well as the presence of disruptive behaviors pose significant challenges to service providers and funding entities. Existing cost models may underestimate these specialized needs and limit access to required services. Through secondary analysis of archival health data from individuals with intellectual disabilities at one agency in Nebraska (N=73), the current study examines how individual characteristics and aggression influence cost and caregiver strain from a systems theory perspective. Bivariate comparisons revealed that more severe aggression and more frequent aggressive behaviors (including verbal aggression, aggression against others, aggression against self, and aggression against property) relate to higher levels of caregiver strain and higher costs. Correlation and regression analyses revealed that existing rate models used to set service rates overlook significant factors when predicting actual costs. Individuals with comorbid physical and mental health conditions, especially those with serious and persistent mental illnesses, who also exhibit aggressive behaviors (measured by frequency and severity), significantly predict higher direct costs better than models that only account for levels of functioning. Despite consistent acuity based on similar behavioral severity ratings, IQ, and adaptive functioning scores, individuals served in extended family home settings displayed fewer aggressive behaviors and induced less strain on their caregivers, while receiving services at over $10,000 per month cost savings compared to their counterparts served in group home settings. Examination of emerging setting effects offers a progressive interpretation of the results with practical implications for developing rate-setting methodologies and public policy considerations. Advisors: Mario Scalora and Sarah Gervai

The experiences of undergraduate Black gay men who use hookup and dating apps while attending a predominantly White institution

The purpose of this study was to explore the experiences of undergraduate Black gay men who use hook up and dating apps while attending predominantly White colleges and universities. In using intersectionality as my theoretical framework, I was able to discover the essence of the experiences that Black gay men face while using these platforms. Intersectionality assisted the study in identifying the systems of privilege and oppression that are present for Black gay men, specifically when attempting to date within the LGBTQ+ community (Cho et al., 2013; Collins, 2015; Garcia & Ortiz, 2013). Through this framework I additionally began to understand that the multiple identities that Black gay men have are not viewed separately, but more so as intersecting (Collins, 2015; Harris & Patton, 2019). This study contributed to current research by revealing commonalities that Black gay students face when attempting to date at PWIs. The findings of this study indicated that through the use of hook up and dating apps undergraduate Black gay men experience racism and fetishism frequently. Other themes emerged in the study as prominent such as making friends with benefits and colorism, but every theme was associated with discrimination on the basis of race or fetishism in some form. This study shows the importance of creating an inclusive social environment for marginalized students that extends beyond the academic setting

Boundary element solution of Poisson\u27s equations in axisymmetric laminar flows

The primitive variable Navier-Stokes equations may be replaced by two equations using the derived variable of vorticity. These equations model separately the kinematic and kinetic parts of the problem. Two boundary element solutions for the kinematic equations were developed for axisymmetric flow geometries. The first was based on the fluid mechanics analogy of the Biot and Savart formula for the magnetic effects of a current. The second was the solution of the vector Poisson\u27s velocity equation using the direct boundary element equation. Numerical integration algorithms were developed which were used for all integrals;Integral solutions for Poisson\u27s pressure equation and Poisson\u27s vector potential equation were derived using the direct boundary element equation. The equations were integrated using the algorithms developed for the velocity solutions;The axisymmetric laminar Navier-Stokes solution was completed by solving the kinetic vorticity transport equation with finite difference methods. Two finite difference methods developed for the complete 2 dimensional non-linear Burger\u27s equation were modified for use on the axisymmetric form of the vorticity transport equation;This complete Navier-Stokes solution was then used to verify the form of the six boundary element equations and the accuracy of the integration algorithm developed. This was done by solving three steady state flow problems and one time dependent flow problem which were designed to simulate flow in power hydraulic components;Flow problems were encountered which produced ill-conditioned kinematic systems with attendant unstable solutions and large errors. Solution algorithms were developed which stabilized the associated matrix operator and improved solution performance. The method is based on the theory and numerical methods of Tikhonov regularization as it applies to linear algebraic systems of equations

Role of Spatial Ability in Musical Instrument Choice: Implications for Music Education

The intent of this thesis is to explore the relationship between spatial ability and the wide range of musical instruments musicians play. Existing literature has established a link between musicianship and improved spatial ability, but researchers have yet to look at how the spatial makeup of different musical instruments may, in turn, reveal unique levels of spatial proficiency from one instrumentalist to the next. This study was formatted as an online survey that included a music experience scale, a demographics scale, and two measures of spatial ability: the Card Rotations Test (CRT) and the Paper Folding Test (PFT). Participants who played larger instruments were hypothesized to score higher on the spatial ability tests. Results show that specific musical instruments score differently on spatial ability measures, and large instruments like the piano and marimba consistently outperform smaller instruments. This largely exploratory study attempts to show that the psychological discipline as a whole should reevaluate how it categorizes and studies musicians. Furthermore, these preliminary findings will encourage better practice for how music educators handle the musical instrument selection process, hopefully leading to a more long-term, student-centered approach