Interaction between U/UO2 bilayers and hydrogen studied by in-situ X-ray diffraction

This paper reports experiments investigating the reaction of H$_{2}$ with uranium metal-oxide bilayers. The bilayers consist of $\leq$ 100 nm of epitaxial $\alpha$-U (grown on a Nb buffer deposited on sapphire) with a UO$_{2}$ overlayer of thicknesses of between 20 and 80 nm. The oxides were made either by depositing via reactive magnetron sputtering, or allowing the uranium metal to oxidise in air at room temperature. The bilayers were exposed to hydrogen, with sample temperatures between 80 and 200 C, and monitored via in-situ x-ray diffraction and complimentary experiments conducted using Scanning Transmission Electron Microscopy - Electron Energy Loss Spectroscopy (STEM-EELS). Small partial pressures of H$_{2}$ caused rapid consumption of the U metal and lead to changes in the intensity and position of the diffraction peaks from both the UO$_{2}$ overlayers and the U metal. There is an orientational dependence in the rate of U consumption. From changes in the lattice parameter we deduce that hydrogen enters both the oxide and metal layers, contracting the oxide and expanding the metal. The air-grown oxide overlayers appear to hinder the H$_{2}$-reaction up to a threshold dose, but then on heating from 80 to 140 C the consumption is more rapid than for the as-deposited overlayers. STEM-EELS establishes that the U-hydride layer lies at the oxide-metal interface, and that the initial formation is at defects or grain boundaries, and involves the formation of amorphous and/or nanocrystalline UH$_{3}$. This explains why no diffraction peaks from UH$_{3}$ are observed. {\textcopyright British Crown Owned Copyright 2017/AWE}Comment: Submitted for peer revie

GRAIN PROPERTIES OF COMET C/1995 O1 (HALE-BOPP)

We present the analysis of 7.6-13.2 μm infrared (IR) spectrophotometry (R 250) of comet C/1995 O1 (Hale-Bopp), in conjunction with concurrent observations that extend the wavelength coverage of the spectral energy distribution from near- to far-infrared wavelengths. The observations include temporal epochs preperihelion (1996 October and 1997 February UT), near perihelion (1997 April UT), and postperihelion (1997 June UT). Through the modeling of the thermal emission from small, amorphous carbon grains and crystalline and amorphous silicate grains in Hale-Bopp's coma, we find that as the comet approached perihelion, the grain size distribution (the Hanner modified power law) steepened (from N = 3.4 preperihelion to N = 3.7 near and postperihelion), along with an increase in the fractal porosity of larger (greater than 1 μm) grains. The peak of the grain size distribution remained constant (ap = 0.2 μm) at each epoch. We attribute the emergence of the 9.3 μm peak near perihelion to crystalline orthopyroxene grains released during epochs of high jet activity. Crystalline silicates (olivine and orthopyroxene) make up about 30% (by mass) of the submicron-sized (≤1 μm) dust grains in Hale-Bopp's coma during each epoch

Radius Dependent Luminosity Evolution of Blue Galaxies in GOODS-N

We examine the radius-luminosity (R-L) relation for blue galaxies in the Team Keck Redshift Survey (TKRS) of GOODS-N. We compare with a volume-limited, Sloan Digital Sky Survey sample and find that the R-L relation has evolved to lower surface brightness since z=1. Based on the detection limits of GOODS this can not be explained by incompleteness in low surface-brightness galaxies. Number density arguments rule out a pure radius evolution. It can be explained by a radius dependent decline in B-band luminosity with time. Assuming a linear shift in M_B with z, we use a maximum likelihood method to quantify the evolution. Under these assumptions, large (R_{1/2} > 5 kpc), and intermediate sized (3 < R_{1/2} < 5 kpc) galaxies, have experienced Delta M_B =1.53 (-0.10,+0.13) and 1.65 (-0.18, +0.08) magnitudes of dimming since z=1. A simple exponential decline in star formation with an e-folding time of 3 Gyr can result in this amount of dimming. Meanwhile, small galaxies, or some subset thereof, have experienced more evolution, 2.55 (+/- 0.38) magnitudes. This factor of ten decline in luminosity can be explained by sub-samples of starbursting dwarf systems that fade rapidly, coupled with a decline in burst strength or frequency. Samples of bursting, luminous, blue, compact galaxies at intermediate redshifts have been identified by various previous studies. If there has been some growth in galaxy size with time, these measurements are upper limits on luminosity fading.Comment: 34 Total pages, 15 Written pages, 19 pages of Data Table, 13 Figures, accepted for publication in Ap

The structure and innervation of sheep extraocular muscles

The structure and innervation of the extrafusal muscle fibres and the muscle spindles in sheep superior rectus, levator palpebrae superioris, and peroneus brevis muscles are compared. Superior rectus is organized into three layers: A central core of mainly large-diameter fibres contains three plate-innervated types of 'twitch' fibre, with 7% large-diameter grape-innervated fibres; an orbital rim of small-diameter fibres contains mainly plate-innervated ‘twitch’ fibres, together with a third of small diameter grape-innervated fibres; and a thin peripheral patch at either end of the muscle is composed mainly of intermediate- diameter grape-innervated fibres. Levator palpebrae and peroneus brevis are not layered and they are composed of three plate-innervated types of 'twitch' fibre, the 'slowest' of which are not represented in superior rectus. The functional significance of the histochemical and ultrastructural characteristics of the fibre types is discussed. In superior rectus, about 180 spindles are peripherally distributed in the orbital rim and peripheral patch layers, throughout the length of the muscle. The ultrastructure, histochemical profile, and innervation of the nuclear-bag and nuclear-chain fibres are the same as the extrafusal peripheral grape-innervated (G) and plate- innervated (G) fibre types, respectively. Motor innervation is collateral and segregated with grape innervation distributed to the bag fibres, and plate innervation to the chains. Levator palpebrae has about 60 evenly-distributed spindles. The bag fibres correspond histochemically and ultrastructurally to the bag fibres of superior rectus, and receive a purely fusimotor grape innervation. The chain fibres correspond to those of superior rectus, and receive a similar plate innervation. Sheep extraocular spindles receive both a primary and secondary sensory innervation. In peroneus brevis the spindles are composed of typical bag, intermediate bag and nuclear-chain fibres, and these receive an innervation typical of mammalian hindlimb muscle spindles

An assessment of the 'road-to-health' card based on perceptions of clinic staff and mothers

Objectives. To describe the opinions of health personnel and parents at child health clinics in Cape Town; to determine the accuracy and completeness of data recorded on the present 'Road-to-Health' (RTB) card; and to ascertain the views of clinic staff and mothers regarding what information they would like to record.Design. Descriptive prospective study.Setting and subjects. Qualitative interviews of 35 health personnel and 150 mothers/caregivers were conducted at 17 child health clinics. The clinic practices of 32 health personnel were monitored and details of 150 RTH cards were examined.Main outcome measures. Responses of health personnel at public and private child health clinics and of mothers were analysed. Data recorded on the card were extracted under the headings: neonatal data, immunisation schedules, measurements, and weight-for-age chart.Results. Most nurses supported the concept of an RTH card but a large majority recommended that it be replaced with a notebook retained by the mother. A significant proportion of health personnel did not know how to use the weight-for-age chart. Most mothers attending clinics carried the card, but this number dropped for hospital visits and consultations with private doctors. Mothers' understanding of the card was limited. For mothers the weight-for-age chart, immunisation schedule and milestone section are obscure.Conclusion. Health personnel and mothers would like to replace the RTH card with a notebook in the parents' home language. It should contain more information on health matters, adequate space to record weight and infectious diseases, an illustrated milestone chart and an improved schedule for immunisations. Mothers perceived the RTH card as belonging to the clinic and wanted a 'baby's own' document

Bistable collective behavior of polymers tethered in a nanopore.

Polymer-coated pores play a crucial role in nucleo-cytoplasmic transport and in a number of biomimetic and nanotechnological applications. Here we present Monte Carlo and Density Functional Theory approaches to identify different collective phases of end-grafted polymers in a nanopore and to study their relative stability as a function of intermolecular interactions. Over a range of system parameters that is relevant for nuclear pore complexes, we observe two distinct phases: one with the bulk of the polymers condensed at the wall of the pore, and the other with the polymers condensed along its central axis. The relative stability of these two phases depends on the interpolymer interactions. The existence the two phases suggests a mechanism in which marginal changes in these interactions, possibly induced by nuclear transport receptors, cause the pore to transform between open and closed configurations, which will influence transport through the pore