Force-velocity correlations in a dense, collisional, granular flow

We report measurements in a 2-dimensional, gravity-driven, collisional, granular flow of the normal force delivered to the wall and of particle velocity at several points in the flow. The wall force and the flow velocity are negatively correlated. This correlation falls off only slowly with distance transverse to the flow, but dies away on the scale of a few particle diameters upstream or downstream. The data support a picture of short-lived chains of frequently colliding particles that extend transverse to the flow direction, making transient load-bearing bridges that cause bulk fluctuations in the flow velocity. The time-dependence of these spatial correlation functions indicate that while the force-bearing structures are local in space, their influence extends far upstream in the flow, albeit with a time-lag. This leads to correlated velocity fluctuations, whose spatial range increases as the jamming threshold is approached.Comment: to be submitted for publicatio

The development of thirty self-administering and self-scoring elaborative thinking exercises

Thesis (Ed.M.)--Boston Universit

The stigma turbine:A theoretical framework for conceptualizing and contextualizing marketplace stigma

Stigmas, or discredited personal attributes, emanate from social perceptions of physical characteristics, aspects of character, and “tribal” associations (e.g., race; Goffman 1963). Extant research emphasizes the perspective of the stigma target, with some scholars exploring how social institutions shape stigma. Yet the ways stakeholders within the socio-commercial sphere create, perpetuate, or resist stigma remain overlooked. We introduce and define marketplace stigma as the labeling, stereotyping, and devaluation by and of commercial stakeholders (consumers, companies and their employees, stockholders, institutions) and their offerings (products, services, experiences). We offer the Stigma Turbine (ST) as a unifying conceptual framework that locates marketplace stigma within the broader sociocultural context, and illuminates its relationship to forces that exacerbate or blunt stigma. In unpacking the ST, we reveal the critical role market stakeholders can play in (de)stigmatization, explore implications for marketing practice and public policy, and offer a research agenda to further our understanding of marketplace stigma and stakeholder welfare

Matrix - Mineral Interfaces In Biomineralization: Designing An In Vitro Assay For Nacre Formation

The formation of biogenic crystals in vivo (biomineralization) is controlled in part by the interface between organic and inorganic components. These interfaces can control the nucleation and growth of crystals, leading to the desired crystal polymorph, morphology, size, and orientation. By studying these interfaces, and developing increasingly complex synthetic systems, scientists can better understand biological systems and develop new materials with novel materials properties. Mollusk nacre (mother-of-pearl) is a composite material composed of aragonite (CaCO3) and various biopolymers. Synthetically, aragonite is difficult to nucleate. Mollusks utilize an organic matrix ([beta]-chitin, silk fibroin-like hydrogel, and proteins) to control shell formation. Here, I present an in vitro assay for calcium carbonate mineralization where the assay complexity is systematically increased to understand the role of each matrix component in controlling crystallization. First, functionalized organic surfaces with soluble peptides were combined to probe the role of surface-peptide interactions in polymorph selectivity. Specifically, n16N (a 30 amino acid peptide from the Japanese pearl oyster Pinctada fucata) and its sequence variants, n16Ns (randomly scrambled) and n16NN (global Asp [RIGHTWARDS ARROW] Asn, Glu [RIGHTWARDS ARROW] Gln substitution), were combined with different forms of chitin ([alpha] and [beta]) as well as synthetic Self-Assembled Monolayers (SAMs). Only the combination of n16N adsorbed onto [beta]-chitin leads to the formation of aragonite in vitro. The n16N peptide and its variants have different binding affinities for [beta]-chitin which correlate to their ability to nucleate aragonite. The complexity of the original in vitro assay was further increased to probe the role of another matrix component: silk fibroin hydrogels. With the addition of silk to synthetic, functionalized surfaces (SAMs), the ability of the SAM to affect crystal orientation and nucleation (as compared to controls) changed due to protein adsorption and denaturation on the functionalized surfaces. With the addition of silk fibroin to the chitin-n16N system, orientation and morphological control is gained (regardless of the n16N sequence). Flat vaterite crystals and amorphous calcium carbonate deposits are oriented with the [beta]-chitin fibers. The work in this thesis provides evidence for the possible roles of the chitin-protein interface on mineralization in nacre

Evaluating Color and Fading of Red-Shafted Flicker (Colaptes auratus cafer) Feathers: Technical and Cultural Considerations

Fading behavior of undyed feathers has not received much attention in conservation literature and as a result feathers are categorized with other natural materials as being fugitive to display lighting, based on anecdotal evidence. The authors investigated Red-shafted Flicker feathers, which have carotenoid-based colorant systems and significance in North American native regalia, to demonstrate how lighting guidelines could be informed by a multivariate approach that considers material sensitivity, properties of value, and use before entering a museum collection. Ornithological literature reviewed demonstrates that feathers are highly differentiated in their sources of coloration, which include chemistry, structure, diet, age and,gender, all resulting in varying responses to illumination. The authors explore the value placed on color by original fabricators, and how use and attitudes toward color contribute to the collections for which we assume stewardship. Red-shafted Flicker feathers were exposed to equivalent photometric doses in order to compare results from window-fading and microfading to Blue Wool Standards. Results indicate color changes more stable than Blue Wool 1 and 2, with ultraviolet radiation playing a significant role in fading. Microfading is beneficial for measuring color change because the variability within and between feathers is eliminated as the sample site remains unvaried

Effects of mixed-valent composition and bathing environment on solid-state electron self-exchanges in osmium bipyridine redox polymer films

Rate constants for the electrical gradient driven, bimolecular electron-self-exchange reaction between Os(II) and Os(III) sites in dry, mixed-valent films of the undiluted, polymeric metal complexes poly[Os(bpy)₂(vpy)₂](BF₄)(subscript m) and poly[Os(vbpy)₃](BF₄)(subscript m) in interdigitated array electrodes and in sandwich electrodes are measured as a function of m. Linear potential sweep and ac impedance measurements show that the reaction follows the expected, but in solid-state materials, seldom evaluated, bimolecular rate law from C[subscript (Osⁱⁱⁱ)]/C[subscript (Osⁱⁱ)] = 6 to 0.1. Comparison of rate constants for poly[Os(bpy)₂(vpy)₂](BF₄)(subscript m) and poly[Os(vbpy)₃](BF₄)(subscript m) self-exchanges driven by electrical and concentration gradients, measured in a variety of bathing environments, shows that electron hopping rates decrease in the order liquid solvent > solvent vapor > dry N₂ bathing environment, and in each environment, the rate constant for the former complex is larger. It appears that the electron hopping rate is affected by the rigidity of the polymeric matrix; matrices that are more rigid by virtue of the absence of solvent or through enhanced cross-linking (as in the vbpy complex) exhibit slower rates. The results imply that electron hopping involves (short range) nuclear displacement of the pendant osmium site from its equilibrium location in solvent-wetted polymers and is slowed when polymer rigidity inhibits such displacement