OH as an Alternate Tracer for Molecular Gas: A Study in the W5 Star-Forming Region

Tracing molecular H2 gas in the Galactic interstellar medium is complicated by the fact that diffuse, cold H2 is not detectable. The usual tracer for molecular gas is 12CO(1-0); however, questions have been posed about the universality of CO for this purpose, and evidence has suggested reservoirs of undetected “CO-dark” molecular gas. This dissertation contributes to research into the use of OH 18 cm lines as an alternate tracer for molecular gas. The focus of this dissertation is a survey of the W5 star-forming region using the Green Bank Telescope to determine the structure and quantity of molecular gas in W5, and to compare the properties of W5 to those of a quiescent region according to both tracers. Calculating column densities of OH requires knowledge of the excitation temperature of the observed molecular transi- tion. I have measured excitation temperatures of the OH 18 cm lines in W5 using two distinct methods: the traditional “expected profile” method, and a “continuum background method.” The latter yields more precise results, and demonstrates that the excitation temperature is different for the two 18 cm main lines. Results of the OH survey in W5 are then presented. In W5, the OH and CO trace a similar morphology of molecular gas, in contrast to quiescent regions which can contain CO-dark OH detections. The molecular gas mass traced by OH emission is slightly larger than that traced by CO, but the difference is not considered significant. I propose a volume density-based explanation for the presence or absence of CO-dark molecular gas, and estimate the average volume density for three regions using a diffuse cloud model. The CO-dark gas correlates with lower volume density portions of the qui- escent region, and the highest average volume density occurs in W5. These results suggest that CO-dark molecular gas primarily exists in interstellar space outside of star-forming regions, and that volume density is the primary distinction between the molecular gas in W5 and the quiescent region. I also discuss a novel method based on excitation temperatures for estimating physical conditions in molecular gas without relying on CO

Practising the Space Between: Embodying Belief as an Evangelical Anglican Student

This article explores the formation of British evangelical university students as believers. Drawing on ethnographic fieldwork conducted with a conservative evangelical Anglican congregation in London, I describe how students in this church come to embody a highly cognitive, word-based mode of belief through particular material practices. As they learn to identify themselves as believers, practices of reflexivity and accountability enable them to develop a sense of narrative coherence in their lives that allows them to negotiate tensions that arise from their participation in church and broader social structures. I demonstrate that propositional belief – in contexts where it becomes an identity marker – is bound up with relational practices of belief, such that distinctions between “belief in” and “belief that” are necessarily blurred in the lives of young evangelicals

Atomic Resonance and Scattering

Contains reports on eight research projects.National Science Foundation (Grant PHY79-09743)National Bureau of Standards (Grant NB-8-NAHA-3017)Joint Services Electronics Program (Contract DAAG29-80-C-0104)National Science Foundation (Grant PHY82-10486)U.S. Navy - Office of Naval Research (Contract N00014-79-C-0183)National Science Foundation (Grant CHE79-02967-A04)U.S. Air Force - Office of Scientific Research (Contract AFOSR-81-0067)Joint Services Electronics Program (Contract DAAG29-83-K-0003

A Novel Recombinant DNA System for High Efficiency Affinity Purification of Proteins in Saccharomyces cerevisiae

Isolation of endogenous proteins from Saccharomyces cerevisiae has been facilitated by inserting encoding polypeptide affinity tags at the C-termini of chromosomal open reading frames (ORFs) using homologous recombination of DNA fragments. Tagged protein isolation is limited by a number of factors, including high cost of affinity resins for bulk isolation and low concentration of ligands on the resin surface, leading to low isolation efficiencies and trapping of contaminants. To address this, we have created a recombinant “CelTag” DNA construct from which PCR fragments can be created to easily tag C-termini of S. cerevisiae ORFs using selection for a nat1 marker. The tag has a C-terminal cellulose binding module to be used in the first affinity step. Microgranular cellulose is very inexpensive and has an effectively continuous ligand on its surface, allowing rapid, highly efficient purification with minimal background. Cellulose-bound proteins are released by specific cleavage of an included site for TEV protease, giving nearly pure product. The tag can be lifted from the recombinant DNA construct either with or without a 13x myc epitope tag between the target ORF and the TEV protease site. Binding of CelTag protein fusions to cellulose is stable to high salt, nonionic detergents, and 1 M urea, allowing stringent washing conditions to remove loosely associated components, as needed, before specific elution. It is anticipated that this reagent could allow isolation of protein complexes from large quantities of yeast extract, including soluble, membrane-bound, or nucleic acid-associated assemblies

Point of View: The future of graduate and postdoctoral training in the biosciences

This article summarizes the outcomes of the second national conference on the Future of Bioscience Graduate and Postdoctoral Training. Five topics were addressed during the conference: diversity in leadership positions; mentoring; modernizing the curriculum; experiential learning; and the need for better data on trainees. The goal of the conference was to develop a consensus around these five topics and to recommend policies that can be implemented by academic and research institutions and federal funding agencies in the United States

The future of graduate and postdoctoral training in the biosciences

This article summarizes the outcomes of the second national conference on the Future of Bioscience Graduate and Postdoctoral Training. Five topics were addressed during the conference: diversity in leadership positions; mentoring; modernizing the curriculum; experiential learning; and the need for better data on trainees. The goal of the conference was to develop a consensus around these five topics and to recommend policies that can be implemented by academic and research institutions and federal funding agencies in the United States

Pro-Apoptotic and Immunostimulatory Tetrahydroxanthone Dimers from the Endophytic Fungus Phomopsis longicolla

Four tetrahydroxanthone dimers (<b>1</b>–<b>4</b>) and four biogenetically related monomers (<b>5</b>–<b>8</b>), including the new derivatives <b>4</b>–<b>6</b>, were isolated from the endophyte Phomopsis longicolla. The absolute configurations of <b>2</b>–<b>4</b> were established for the first time by TDDFT electronic circular dichroism calculations, and that of phomoxanthone A (<b>1</b>) was revised by X-ray crystallography. Phomoxanthone A (<b>1</b>) showed the strongest pro-apoptotic activity when tested against a panel of human cancer cell lines, including cisplatin-resistant cells, whereas it was up to 100-fold less active against healthy blood cells. It was also the most potent activator of murine T lymphocytes, NK cells, and macrophages, suggesting an activation of the immune system in parallel to its pro-apoptotic activity. This dual effect in combating cancer cells could help in fighting resistance during chemotherapy. Preliminary structure–activity studies of isolated compounds and derivatives obtained by semisynthesis (<b>9a</b>–<b>11</b>) hinted at the location of the biaryl axis and the presence of acetyl groups as important structural elements for the biological activity of the studied tetrahydroxanthones