Multiple Dynamic Processes Contribute to the Complex Steady Shear Behavior of Cross-Linked Supramolecular Networks of Semidilute Entangled Polymer Solutions.

Molecular theories of shear thickening and shear thinning in associative polymer networks are typically united in that they involve a single kinetic parameter that describes the network -- a relaxation time that is related to the lifetime of the associative bonds. Here we report the steady-shear behavior of two structurally identical metallo-supramolecular polymer networks, for which single-relaxation parameter models break down in dramatic fashion. The networks are formed by the addition of reversible cross-linkers to semidilute entangled solutions of PVP in DMSO, and they differ only in the lifetime of the reversible cross-links. Shear thickening is observed for cross-linkers that have a slower dissociation rate (17 s(-1)), while shear thinning is observed for samples that have a faster dissociation rate (ca. 1400 s(-1)). The difference in the steady shear behavior of the unentangled vs. entangled regime reveals an unexpected, additional competing relaxation, ascribed to topological disentanglement in the semidilute entangled regime that contributes to the rheological properties.

Magnetic resonance water proton relaxation in protein solutions and tissue: T(1rho) dispersion characterization.

BACKGROUND: Image contrast in clinical MRI is often determined by differences in tissue water proton relaxation behavior. However, many aspects of water proton relaxation in complex biological media, such as protein solutions and tissue are not well understood, perhaps due to the limited empirical data. PRINCIPAL FINDINGS: Water proton T(1), T(2), and T(1rho) of protein solutions and tissue were measured systematically under multiple conditions. Crosslinking or aggregation of protein decreased T(2) and T(1rho), but did not change high-field T(1). T(1rho) dispersion profiles were similar for crosslinked protein solutions, myocardial tissue, and cartilage, and exhibited power law behavior with T(1rho)(0) values that closely approximated T(2). The T(1rho) dispersion of mobile protein solutions was flat above 5 kHz, but showed a steep curve below 5 kHz that was sensitive to changes in pH. The T(1rho) dispersion of crosslinked BSA and cartilage in DMSO solvent closely resembled that of water solvent above 5 kHz but showed decreased dispersion below 5 kHz. CONCLUSIONS: Proton exchange is a minor pathway for tissue T(1) and T(1rho) relaxation above 5 kHz. Potential models for relaxation are discussed, however the same molecular mechanism appears to be responsible across 5 decades of frequencies from T(1rho) to T(1).

A Multiple Goal Perspective on Eating Behavior

Although people frequently pursue multiple goals simultaneously, these goals often conflict with each other. For instance, consumers may have both a healthy eating goal and a goal to have an enjoyable eating experience. In this dissertation, I focus on two sources of enjoyment in eating experiences that may conflict with healthy eating: consuming tasty food (Essay 1) and affiliating with indulging dining companions (Essay 2). In both essays, I examine solutions and strategies that decrease the conflict between healthy eating and these aspects of enjoyment in the eating experience, thereby enabling consumers to resolve such goal conflicts.

Essay 1 focuses on the well-established conflict between having healthy food and having tasty food and introduces a novel product offering (“vice-virtue bundles”) that can help consumers simultaneously address both health and taste goals. Through several experiments, I demonstrate that consumers often choose vice-virtue bundles with small proportions (¼) of vice and that they view such bundles as healthier than but equally tasty as bundles with larger vice proportions, indicating that “healthier” does not always have to equal “less tasty.”

Essay 2 focuses on a conflict between healthy eating and affiliation with indulging dining companions. The first set of experiments provides evidence of this conflict and examine why it arises (Studies 1 to 3). Based on this conflict’s origins, the second set of experiments tests strategies that consumers can use to decrease the conflict between healthy eating and affiliation with an indulging dining companion (Studies 4 and 5), such that they can make healthy food choices while still being liked by an indulging dining companion. Thus, Essay 2 broadens the existing picture of goals that conflict with the healthy eating goal and, together with Essay 1, identifies solutions to such goal conflicts.