Gelling of cryogenic oxidizers Final report, 5 May 1965 - 4 Sep. 1966

Freeze dry methods for preparation of ultrafine, particle size lithium fluoride for cryogenic oxidizer

Statics and Dynamics of the Wormlike Bundle Model

Bundles of filamentous polymers are primary structural components of a broad range of cytoskeletal structures, and their mechanical properties play key roles in cellular functions ranging from locomotion to mechanotransduction and fertilization. We give a detailed derivation of a wormlike bundle model as a generic description for the statics and dynamics of polymer bundles consisting of semiflexible polymers interconnected by crosslinking agents. The elastic degrees of freedom include bending as well as twist deformations of the filaments and shear deformation of the crosslinks. We show that a competition between the elastic properties of the filaments and those of the crosslinks leads to renormalized effective bend and twist rigidities that become mode-number dependent. The strength and character of this dependence is found to vary with bundle architecture, such as the arrangement of filaments in the cross section and pretwist. We discuss two paradigmatic cases of bundle architecture, a uniform arrangement of filaments as found in F-actin bundles and a shell-like architecture as characteristic for microtubules. Each architecture is found to have its own universal ratio of maximal to minimal bending rigidity, independent of the specific type of crosslink induced filament coupling; our predictions are in reasonable agreement with available experimental data for microtubules. Moreover, we analyze the predictions of the wormlike bundle model for experimental observables such as the tangent-tangent correlation function and dynamic response and correlation functions. Finally, we analyze the effect of pretwist (helicity) on the mechanical properties of bundles. We predict that microtubules with different number of protofilaments should have distinct variations in their effective bending rigidity

A Portrait of MWrite as a Research Program: A Review of Research on Writing-to-Learn in STEM through the MWrite Program

The writing-to-learn (WTL) literature is varied in how assignments are structured and implemented in the classroom, making it difficult for instructors to identify how to incorporate writing effectively. Drawing on the WTL literature, the MWrite program was established to work with STEM faculty to design, implement, and assess evidence- based WTL assignments. Herein we present a review of the WTL research generated through the MWrite program, situating our findings in a four-dimensional framework of engagement to identify how the MWrite WTL assignment design and implementation has supported students’ learning. Our analysis indicates that the multi-faceted design of MWrite WTL assignments supports students’ development of conceptual knowledge and disciplinary thinking. The assignments’ rhetorical features (i.e., context, audience, and genre) guide how students write about content, and peer review and revision stages encourage a collaborative, knowledge building process between students and their peers

AMP!: A Cross-site Analysis of the Effects of a Theater-based Intervention on Adolescent Awareness, Attitudes, and Knowledge about HIV

AMP! (Arts-based, Multiple component, Peer-education) is an HIV intervention developed for high school adolescents. AMP! uses interactive theater-based scenarios developed by trained college undergraduates to deliver messages addressing HIV/STI prevention strategies, healthy relationships, and stigma reduction towards people living with HIV/AIDS. We used a pre-test/post-test, control group study design to simultaneously assess intervention effect on ninth grade students in an urban county in California (N = 159) and a suburban county in North Carolina (N = 317). In each location, the control group received standard health education curricula delivered by teachers; the intervention group received AMP! in addition to standard health education curricula. Structural equation modeling was used to determine intervention effects. The post-test sample was 46% male, 90% self-identified as heterosexual, 32% reported receiving free or reduced lunch, and 49% White. Structural models indicated that participation in AMP! predicted higher scores on HIV knowledge (p = .05), HIV awareness (p = .01), and HIV attitudes (p = .05) at the post-test. Latent means comparison analyses revealed post-test scores were significantly higher than pre-test scores on HIV knowledge (p = .001), HIV awareness (p = .001), and HIV attitudes (p = .001). Further analyses indicated that scores rose for both groups, but the post-test scores of intervention participants were significantly higher than controls (HIV knowledge (p = .01), HIV awareness (p = .01), and HIV attitudes (p = .05)). Thus, AMP!’s theater-based approach shows promise for addressing multiple adolescent risk factors and attitudes concerning HIV in school settings

Statistical Mechanics of Semiflexible Bundles of Wormlike Polymer Chains

We demonstrate that a semiflexible bundle of wormlike chains exhibits a state-dependent bending stiffness that alters fundamentally its scaling behavior with respect to the standard wormlike chain. We explore the equilibrium conformational and mechanical behavior of wormlike bundles in isolation, in crosslinked networks, and in solution.Comment: 4 pages, 3 figures, final version as publishe

Nanomechanics of microtubules

We have determined the mechanical anisotropy of a single microtubule by simultaneously measuring the Young's and the shear moduli in vitro. This was achieved by elastically deforming the microtubule deposited on a substrate tailored by electron-beam lithography with a tip of an atomic force microscope. The shear modulus is 2 orders of magnitude lower than the Young's, giving rise to a length-dependent flexural rigidity of microtubules. The temperature dependence of the microtubule's bending stiffness in the (5-40) degreesC range shows a strong variation upon cooling coming from the increasing interaction between the protofilaments

Clubbing masculinities: Gender shifts in gay men's dance floor choreographies

This is an Author's Accepted Manuscript of an article published in Journal of Homosexuality, 58(5), 608-625, 2011 [copyright Taylor & Francis], available online at: http://www.tandfonline.com/10.1080/00918369.2011.563660This article adopts an interdisciplinary approach to understanding the intersections of gender, sexuality, and dance. It examines the expressions of sexuality among gay males through culturally popular forms of club dancing. Drawing on political and musical history, I outline an account of how gay men's gendered choreographies changed throughout the 1970s, 80s, and 90s. Through a notion of “technologies of the body,” I situate these developments in relation to cultural levels of homophobia, exploring how masculine expressions are entangled with and regulated by musical structures. My driving hypothesis is that as perceptions of cultural homophobia decrease, popular choreographies of gay men's dance have become more feminine in expression. Exploring this idea in the context of the first decade of the new millennium, I present a case study of TigerHeat, one of the largest weekly gay dance club events in the United States

Hydrostatic and uniaxial pressure tuning of iron-based superconductors: Insights into superconductivity, magnetism, nematicity and collapsed tetragonal transitions

Iron-based superconductors are well-known for their intriguing phase diagrams, which manifest a complex interplay of electronic, magnetic and structural degrees of freedom. Among the phase transitions observed are superconducting, magnetic, and several types of structural transitions, including a tetragonal-to-orthorhombic and a collapsed-tetragonal transition. In particular, the widely-observed tetragonal-to-orthorhombic transition is believed to be a result of an electronic order that is coupled to the crystalline lattice and is, thus, referred to as nematic transition. Nematicity is therefore a prominent feature of these materials, which signals the importance of the coupling of electronic and lattice properties. Correspondingly, these systems are particularly susceptible to tuning via pressure (hydrostatic, uniaxial, or some combination). We review efforts to probe the phase diagrams of pressure-tuned iron-based superconductors, with a strong focus on our own recent insights into the phase diagrams of several members of this material class under hydrostatic pressure. These studies on FeSe, Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, Ca(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and CaK(Fe$_{1-x}$Ni$_x$)$_4$As$_4$ were, to a significant extent, made possible by advances of what measurements can be adapted to the use under differing pressure environments. We point out the potential impact of these tools for the study of the wider class of strongly correlated electron systems.Comment: 31 pages, 17 figures, submitted to Annalen der Physi

Make a choice! Visual attention and choice behaviour in multialternative food choice situations

This study investigates the relationship between gazing behaviour and choice decision in multialternative forced choice tasks, focusing on the consistency across different food product groups including apple, beer, bread, chocolate, instant soup, salad, sausage, and soft drink. Each choice task consisted of pictures of four alternatives, similar in familiarity and liking ratings, of the corresponding product group. A Tobii T60 eye-tracker was used to present the stimuli and to analyse the gazing behaviour of 59 participants during decision-making. The results showed strong correlations between choice and gazing behaviour, in forms of more fixation counts, longer total dwell duration, and more dwell counts on the chosen alternative. No correlations for first fixation, time to first fixation, and first fixation duration were observed. These results were consistent across the eight tested product groups