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Reaction kinetics of end-functionalized chains at polymer-polymer interfaces
Schulze, Jonathan Scott University of Minnesota 2001 해외박사(DDOD)
Polymer blending often relies on reactive compatibilization to create stable mixtures of two otherwise immiscible polymers. In reactive compatibilization, a small number of polymer chains in each phase is functionalized. During blending, these functionalized chains react at the interface to form block or graft copolymers that stabilize the mixture. Several factors may affect the rate of reaction during compatibilization: external convection that creates interfacial area between the polymer phases, diffusion of the reactive polymer chains through the bulk to the interface, and the chemical reaction that occurs between different functional groups. This thesis details model experiments that separate these factors to pinpoint the most important to reactive compatibilization. Forward recoil spectrometry (FRES) was used to monitor the diffusion and reaction of model end-functional polymers at a polystyrene/poly(methyl methacrylate) interface in the absence of external convection. FRES concentration profiles indicated the reaction kinetics as a function of reactant concentration, and reactant and matrix molecular weight. In all cases, the reaction required several hours to attain a steady state, and was <italic>much slower</italic> than expected from diffusion-controlled kinetics. Furthermore, a novel sample geometry directly revealed that the reactive chains diffused several hundred nanometers in minutes and sampled the interface many times before significant interfacial reaction occurred. Thus, <italic>in situ</italic> copolymer formation is limited by the movement of the reactive chains near the interface, rather than the diffusion of the chains through the bulk. The interface likely represents an enthalpic barrier to reaction, because the reactive chains must experience many unfavorable contacts with the other phase for reaction to occur. Additional model experiments subjected reactive multilayer samples to both pure shear and extensional flows using available rheometers, as well as intensive mixing in a small cup-and-rotor mixer. The results of these experiments indicate that external convection changes the reaction time scale from hours to minutes, and suggest that the barrier to reaction posed by the interface can be overcome by applying large deformations at a high rate.
Model-based Testing of Off-nominal Behaviors
Schulze, Christoph University of Maryland, College Park ProQuest Diss 2018 해외박사(DDOD)
Off-nominal behaviors (ONBs) are unexpected or unintended behaviors that may be exhibited by a system. They can be caused by implementation and documentation errors and are often triggered by unanticipated external stimuli, such as unforeseen se. This thesis describes the development and evaluation of model-based techniques for the identification and documentation of ONBs. Model-Based Testing (MBT) techniques have been used to provide automated support for thorough evaluation of software. The second part of the thesis presents a framework and associated tooling for the extraction and analysis of specifications for identifying and documenting ONBs. The framework infers behavioral specifications in the form of system invariants fro.
Calcium kinetics and bone health in girls with cystic fibrosis
Schulze, Kerry J The Johns Hopkins University 2003 해외박사(DDOD)
As the life span of individuals with cystic fibrosis (CF) increases, osteopenia and osteoporosis have emerged as important secondary consequences of the disorder. Peak bone mass is nearly entirely achieved by late puberty, making adolescence an important time of life for optimizing bone mineralization. Characterizing calcium metabolism will identify alterations in bone mineralization that may compromise bone mass in individuals with CF. Calcium absorption, losses and bone turnover were studied using calcium stable isotopes in 23 girls with CF (ages 7–18 years) who maintained regular treatment regimens (including pancreatic enzymes and ADEK vitamins). Oral (<super>44</super>Ca) and intravenous (<super>42</super>Ca) isotopes were administered with breakfast in the Pediatric Clinical Research Unit (PCRU) of The Johns Hopkins Hospital. A 24-h urine collection and blood samples (5, 15, 30, 60, 120, 240, 360, and 480 minutes post-dosing) were obtained. Spot urine samples and complete stool output were collected for 5 additional days. Dietary intake data was collected for 4 days, and bone mineral content was measured. Calcium absorption (%) (<super>44</super>Ca relative to <super>42</super>Ca in 24-h urine collection) was similar to values observed in healthy girls, and total calcium absorption (Va) was highest during early puberty (breast Tanner stage 2–3). Urinary calcium and sodium excretion were positively associated. Endogenous fecal calcium (Vendo; n = 13) (<super>42</super>Ca in stool) was elevated and compromised calcium balance. Increased intestinal permeability in patients with CF may contribute to both adequate Va and elevated Vendo. Bone calcium deposition (Vo+) (evaluated by fitting a 3 compartment model to the disappearance of <super> 42</super>Ca in serum and urine), and retention (n = 22) were comparable among early pubertal girls with CF to values observed in healthy girls, but were low in the prepubertal (Tanner stage 1) and late pubertal (Tanner stage 4–5) girls with CF. Bone calcium deposition was positively associated with serum leptin. Bone mineral content was positively associated with body mass index and insulin-like growth factor-1. Bone health is influenced by calcium balance, nutritional status, and pubertal development in girls with CF. Findings from this study will help clinicians identify individuals with CF who are at risk for osteoporosis and will help to determine beneficial interventions to preserve bone mass.