The Relationship Between Classroom Age Composition and Children’s Language and Social School Readiness Outcomes: Examining the Role of Peer Effects

Younger and older preschool-age children are commonly placed together in mixed age classrooms. However, both theory and empirical evidence conflict over whether mixed age classrooms are the best environment for developing children. A factor that may play a role in the is peer skill as children may benefit from being around more skilled peers. The present study uses a large sample of preschoolers from low income families to examine the influence of classroom age composition and peer skill on children’s social and language outcomes. Using hierarchical linear analyses, results suggested that being in a mixed age classroom did not relate to the outcomes of children categorized into younger and older age groups. However, being around peers with higher language skills and fewer behavior problems tended to relate to more positive child outcomes. These findings suggest a need to support peer-to-peer contact in preschool between more and less skilled children.Master of Art

Relating the chemical reactivity of supramolecular hydrogelators and the physical properties of their gels

This thesis reports a number of studies that examines low molecular weight hydrogelators forming through in situ chemical reactions and gel the water in which this reaction occurs. This in situ gelation process has allowed a number of chemical and physical reactions and assembly processes to be investigated. Pathway complexity, an exciting concept within chemical systems has been explored with a multi-reactive hydrazone based gelation system that allows different gels to be formed from a single starting point through navigation of the systems’ energy landscape. This work inspired the development of a large family of imine based gelators that would undergo an effectively irreversible tautomerisation. This allowed exploration and characterisation of the systems’ ability to self-sort and co-assemble, at both the molecular and macroscopic level. One particular imine inspired gelator featured a much slower in situ reaction. This allowed characterisation of its reaction kinetics and demonstrated its autocatalytic behaviour. This thesis highlights the link between the chemical reactions that form the individual gelator molecules and the supramolecular assembly process. By using one to control the other, an in-depth understanding of the presented systems has been developed, allowing for the accurate targeting of desired physical properties

A mathematical model for mechanically-induced deterioration of the binder in lithium-ion electrodes

This study is concerned with modeling detrimental deformations of the binder phase within lithium-ion batteries that occur during cell assembly and usage. A two-dimensional poroviscoelastic model for the mechanical behavior of porous electrodes is formulated and posed on a geometry corresponding to a thin rectangular electrode, with a regular square array of microscopic circular electrode particles, stuck to a rigid base formed by the current collector. Deformation is forced both by (i) electrolyte absorption driven binder swelling, and; (ii) cyclic growth and shrinkage of electrode particles as the battery is charged and discharged. The governing equations are upscaled in order to obtain macroscopic effective-medium equations. A solution to these equations is obtained, in the asymptotic limit that the height of the rectangular electrode is much smaller than its width, that shows the macroscopic deformation is one-dimensional. The confinement of macroscopic deformations to one dimension is used to obtain boundary conditions on the microscopic problem for the deformations in a 'unit cell' centered on a single electrode particle. The resulting microscale problem is solved using numerical (finite element) techniques. The two different forcing mechanisms are found to cause distinctly different patterns of deformation within the microstructure. Swelling of the binder induces stresses that tend to lead to binder delamination from the electrode particle surfaces in a direction parallel to the current collector, whilst cycling causes stresses that tend to lead to delamination orthogonal to that caused by swelling. The differences between the cycling-induced damage in both: (i) anodes and cathodes, and; (ii) fast and slow cycling are discussed. Finally, the model predictions are compared to microscopy images of nickel manganese cobalt oxide cathodes and a qualitative agreement is found.Comment: 25 pages, 11 figure

The intelligence quotient in justice

This project was designed to research information about intellectually disabled individuals in the criminal justice system. The beginning stages of this project focused on defining intellectual and developmental disabilities as well as the testing that is utilized to determine intellectual disabilities. Additional information that was searched for included characterizing crimes that are committed by individuals with intellectual or developmental disabilities and the questioning techniques that would be utilized during the first stages of the judicial process. The final aspect included rehabilitation programs that are being utilized for offenders with intellectual disabilities. The final stages of this project included risk factors, programs that have worked for adults with intellectual disabilities and reentry into the community. The recommendations incorporate issues from when an individual would come into contact with an officer, interrogation, the legal team, intake, habilitation and reentry

Peer Effects in the Preschool Classroom: Examining the Role of Child and Peer Characteristics

Having highly skilled classmates appears to positively influence preschool children’s academic and social development. Despite relatively consistent evidence to indicate that peers can promote positive child development, there are many issues regarding the role of peers in preschool that need to be understood in order to provide guidance to teachers and administrators who wish to capitalize on peer influence in the classroom. The goal of the present dissertation was to conduct three studies to expand current research on peer influence by reaching a more in-depth understanding of the child- and peer-level factors that contribute to the strength of peer influence in preschool. In Study One, I examined the role of child skill at entry to pre-kindergarten, in Study Two I considered child dual language learner status, and in Study Three I explored whether the relation between peer skill and child development depends on peer gender and age cohort. Study One and Two drew from a sample of 455 children who attended a state-funded prekindergarten program in rural areas of North Carolina. Study Three used data from 4,005 children attending a high-quality preschool program at 16 sites across the United States. Hierarchical linear models were used for all analyses to account for the nesting of children in classrooms. Overall, results indicated that child and peer characteristics can moderate the relation between peer skill and child development. However, the pattern of results was found to differ across the examined outcomes. Implications of these findings for the preschool classroom context are discussed.Doctor of Philosoph

A model for the operation of perovskite based hybrid solar cells:formation, analysis and comparison to experiment

This work is concerned with the modeling of perovskite based hybrid solar cells formed by sandwiching a slab of organic lead halide perovskite (CH3NH3PbI3?xClx) photo-absorber between (n-type) acceptor and (p-type) donor materials—typically titanium dioxide and spiro. A model for the electrical behavior of these cells is formulated based on drift-diffusion equations for the motion of the charge carriers and Poisson’s equation for the electric potential. It is closed by (i) internal interface conditions accounting for charge recombination/generation and jumps in charge carrier densities arising from differences in the electron affinity/ionization potential between the materials and (ii) ohmic boundary conditions on the contacts. The model is analyzed by using a combination of asymptotic and numerical techniques. This leads to an approximate—yet highly accurate—expression for the current-voltage relationship as a function of the solar induced photo- current. In addition, we show that this approximate current-voltage relation can be interpreted as an equivalent circuit model consisting of three diodes, a resistor, and a current source. For sufficiently small biases the device’s behavior is diodic and the current is limited by the recombination at the internal interfaces, whereas for sufficiently large biases the device acts like a resistor and the current is dictated by the ohmic dissipation in the acceptor and donor. The results of the model are also compared to experimental current-voltage curves, and good agreement is shown

Nutritive evaluation of two native north Texas legumes (Strophostyles) for goats

The objective of this study was to determine effects of supplementing coastal bermudagrass (Cynodon dactylon; CBG) hay with Strophostyles helvula (98 g kg-1 crude protein (CP), 476 g kg-1 neutral detergent fiber (NDF)), S. leiosperma (117 g kg-1 CP, 497 g kg-1 NDF), or cottonseed meal (506 g kg-1 CP, 352 g kg-1 NDF; CSM) upon intake of CBG hay (127 g kg-1 CP, 691 g kg-1 NDF) and apparent digestibility of dietary organic matter (OM), NDF, and true digestibility of CP. Six Boer-Spanish goats (46.22 +- 3.99 Kg) were fed CBG plus S. helvula, S. leiosperma, or CSM at 0.34 and 0.68% of BW in a 6*6 Latin square with 3*2 factorial arrangement of treatments. The CBG was fed ad libitum, and the legumes/CSM were fed in two equal daily feedings during a 7-d adjustment period and 7-d collection period in metabolism crates. Feces were collected every 24-h, and CBG, legumes/CSM, and fecal samples were analyzed for OM, NDF, and CP. There were no supplement type*amount interactions (P > 0.05). Supplement type did not affect OM digestibility (P = 0.21), but OM digestibility increased 6.4% (P = 0.05) at the 0.68% versus 0.34% level of supplementation with the legumes or CSM. Supplementation with CSM and S. leiosperma improved NDF digestibility 7% versus supplementation with S. helvula (P = 0.02); and as supplement amount increased NDF digestibility by 5.5% (P = 0.02). The diet supplemented with CSM had the greatest CP digestibility, and S. helvula CP was 6% less digestible than S. leiosperma (P = 0.02). As supplement amount increased, CP digestibility increased 7% (P = 0.01). Intake of DM, OM, and NDF of CBG was unaffected (P = 0.56) by supplementation with CSM, S. helvula, and S. leiosperma, but total diet NDF intake of diets supplemented with CSM and S. helvula was 10.5% less than diet supplemented with S. leiosperma (P = 0.01). Considering digestibility and intake, CSM and S. leiosperma were the best supplements fed in this experiment. Strophostyles leiosperma is recommended as use for diet supplementation for goats when CBG hay basal diet is fed

Binder migration during drying of lithium-ion battery electrodes: modelling and comparison to experiment

The drying process is a crucial step in electrode manufacture as it can affect the component distribution within the electrode. Phenomena such as binder migration can have negative effects in the form of poor cell performance (e.g. capacity fade) or mechanical failure (e.g. electrode delamination from the current collector). We present a mathematical model that tracks the evolution of the binder concentration in the electrode during drying. Solutions to the model predict that low drying rates lead to a favourable homogeneous binder profile across the electrode film, whereas high drying rates result in an unfavourable accumulation of binder near the evaporation surface. These results show strong qualitative agreement with experimental observations and provide a cogent explanation for why fast drying conditions result in poorly performing electrodes. Finally, we provide some guidelines on how the drying process could be optimised to offer relatively short drying times whilst simultaneously maintaining a roughly homogeneous binder distribution