Electron Microscope Studies of Solids Produced by alpha-Radiolysis of Carbon Monoxide

A study has been made of the solids produced by radiolysis of carbon monoxide gas at room temperature using principally 5 MeV alpha-particles from plutonium-240. The solids were produced in situ within a Siemens Elmiskop I electron microscope and were examined directly The morphological nature of the solid particles has been studied and the effect of subsequent exposure of the particles to the atmosphere has been investigated using transmission electron microscopy and electron diffraction techniques. It has been established that the particles grow in the gas phase and are of an amorphous nature. The effect on the radiolysis of varying the gas composition has been investigated. Metallic carbonyl impurities in the carbon monoxide have been found to influence the nature and composition of the solids produced, Two distinct types of solid particles can be obtained. Initially these have a similar appearance but they behave differently on subsequent exposure to water vapour. Solids from carbon monoxide containing nickel tetracarbonyl impurity are hygroscopic and they become fluid on absorption of water vapour. Electron diffraction and electron probe microanalysis studies reveal the presence of several per cent of nickel in these solids. The presence of iron pentacarbonyl impurity in the carbon monoxide yields solids which are inert towards water vapour; these solids contain several per cent of iron. Higher yields of solid are obtained with the iron pentacarbonyl impurity. When both iron and nickel carbonyls are present in the carbon monoxide the influence exerted by the iron carbonyl predominates and the solids produced have all the characteristics of the material formed when iron carbonyl alone is present. A possible explanation to account for this phenomenon is proposed. Infrared spectroscopy studies of the alpha-radiolytic solids and of the solid from complementary proton radiolysis experiments provide evidence which suggests that the solids are composed of linear polymeric carbon suboxide units. The nature of the bonding between the basic polymer units and the iron and nickel is discussed. The alpha-radiolysis of carbon monoxide in the presence of graphite has been studied. It has been found that in addition to the gas-phase deposits which are produced there is a solid which grows on the surface of the graphite. This solid has similar characteristics to the nickel-containing gas-phase material

Novel targets of eiF2 kinases determine cell fate during the integrated stress response

Indiana University-Purdue University Indianapolis (IUPUI)Eukaryotic cells rapidly modulate protein synthesis in response to environmental cues through the reversible phosphorylation of eukaryotic initiation factor 2 (eIF2α~P) by a family of eIF2α kinases. The eIF2 delivers initiator Met-tRNAiMet to the translational apparatus, and eIF2α~P transforms its function from a translation initiation factor into a competitive inhibitor of the guanine nucleotide exchange factor (GEF) eIF2B, which is responsible for the recycling of eIF2-GDP to the translationally-competent eIF2-GTP state. Reduced eIF2-GTP levels lower general protein synthesis, which allows for the conservation of energy and nutrients, and a restructuring of gene expression. Coincident with global translational control, eIF2α~P directs the preferential translation of mRNA encoding ATF4, a transcriptional activator of genes important for stress remediation. The term Integrated Stress Response (ISR) describes this pathway in which multiple stresses converge to phosphorylate eIF2α and enhance synthesis of ATF4 and its downstream effectors. In this study, we used sucrose gradient ultracentrifugation and a genome-wide microarray approach to measure changes in mRNA translation during ER stress. Our analysis suggests that translational efficiencies vary across a broad range during ER stress, with the majority of transcripts being either repressed or resistant to eIF2α~P, while a notable cohort of key regulators are subject to preferential translation. From this latter group, we identify IBTKα as being subject to both translational and transcriptional induction during eIF2α~P in both cell lines and a mouse model of ER stress. Translational regulation of IBTKα mRNA involves the stress-induced relief of two inhibitory uORFs in the 5’-leader of the transcript. Also identified as being subject to preferential translation is mRNA encoding the bifunctional aminoacyl tRNA synthetase EPRS. During eIF2α~P, translational regulation of EPRS is suggested to occur through the bypass of a non-canonical upstream ORF encoded by a CUG start codon, highlighting the diversity by which upstream translation initiation events can regulate expression of a downstream coding sequence. This body of work provides for a better understanding of how translational control during stress is modulated genome-wide and for the processes by which this mode of gene regulation in the ISR contributes to cell fate

The moduli space of flat SU(2)-bundles over a nonorientable surface

We study the topology of the moduli space of flat SU(2)-bundles over a nonorientable surface X. This moduli space may be identified with the space of homomorphisms Hom(\pi_1(X),SU(2)) modulo conjugation by SU(2). In particular, we compute the (rational) equivariant cohomology ring of Hom(\pi_1(X),SU(2)) and use this to compute the ordinary cohomology groups of the quotient Hom(\pi_1(X),SU(2))/SU(2). A key property is that the conjugation action is equivariantly formal.Comment: 23 pages - some reviewer recommended edits, a "proof" is upgraded to a proo

Program for Generating Tables of SU(3) Coupling Coefficients

A C-Language program which tabulates the isoscalar factors and Clebsch-Gordan coefficients for products of representations in SU(3) is presented. These are efficiently computed using recursion relations, and the results are presented in exact precision as square roots of rational numbers. Output is in LaTeX format.Comment: LaTeX, 29 pages, no figure