Surface characterization of selected LDEF tray clamps

The surface characterization of chromic acid anodized 6061-T6 aluminum alloy tray clamps has shown differences in surface chemistry depending upon the position on the Long Duration Exposure Facility (LDEF). Water contact angle results showed no changes in wettability of the tray clamps. The overall surface topography of the control, trailing edge(E3) and leading edge(D9) samples was similar. The thickness of the aluminum oxide layer for all samples determined by Auger depth profiling was less than one micron. X-ray photoelectron spectroscopy (XPS) analysis of the tray clamps showed significant differences in the surface composition. Carbon and silicon containing compounds were the primary contaminants detected

X-Ray Diffuse Scattering Study on Ionic-Pair Displacement Correlations in Relaxor Lead Magnesium Niobate

Ionic-pair equal-time displacement correlations in relaxor lead magnesium niobate, $Pb(Mg_{1/3}Nb_{2/3})O_{3}$, have been investigated at room temperature in terms of an x-ray diffuse scattering technique. Functions of the distinct correlations have been determined quantitatively. The results show the significantly strong rhombohedral-polar correlations regarding Pb-O, Mg/Nb-O, and O-O' pairs. Their spatial distribution forms an ellipse or a sphere with the radii of 30-80$\AA$. This observation of local structure in the system proves precursory presence of the polar microregions in the paraelectric state which leads to the dielectric dispersion.Comment: 11 pages, 3 figure

High-pressure behaviour of GeO2: a simulation study

In this work we study the high pressure behaviour of liquid and glassy GeO2 by means of molecular dynamics simulations. The interaction potential, which includes dipole polarization effects, was parameterized from first-principles calculations. Our simulations reproduce the most recent experimental data to a high degree of precision. The proportion of the various GeOn polyhedra is determined as a function of the pressure: a smooth transition from tetrahedral to octahedral network is observed. Finally, the study of high-pressure, liquid germania confirms that this material presents an anomalous behaviour of the diffusivity as observed in analog systems such as silica and water. The importance of penta-coordinated germanium ions for such behaviour is stressed.Comment: 16 pages, 4 figures, accepted as a Fast Track Communication on Journal of Physics: Condensed Matte

Application of relativistic scattering theory of x rays to diffraction anomalous fine structure in Cu

We apply our recent first-principles formalism of magnetic scattering of circularly polarized x rays to a single Cu crystal. We demonstrate the ability of our formalism to interpret the crystalline environment related near-edge fine structure features in the resonant x-ray scattering spectra at the Cu K absorption edge. We find good agreement between the computed and measured diffraction anomalous fine structure features of the x-ray scattering spectra

Structure of the Janus Protein Human CLIC2

Chloride intracellular channel (CLIC) proteins possess the remarkable property of being able to convert from a water-soluble state to a membrane channel state. We determined the three-dimensional structure of human CLIC2 in its water-soluble form by X-ray crystallography at 1.8-Å resolution from two crystal forms. In contrast to the previously characterized CLIC1 protein, which forms a possibly functionally important disulfide-induced dimer under oxidizing conditions, we show that CLIC2 possesses an intramolecular disulfide and that the protein remains monomeric irrespective of redox conditions. Site-directed mutagenesis studies show that removal of the intramolecular disulfide or introduction of cysteine residues in CLIC2, equivalent to those that form the intramolecular disulfide in CLIC1, does not cause dimer formation under oxidizing conditions.We also show that CLIC2 forms pH-dependent chloride channels in vitro with higher channel activity at low pH levels and that the channels are subject to redox regulation. In both crystal forms, we observed an extended loop region from the C-terminal domain, called the foot loop, inserting itself into an interdomain crevice of a neighboring molecule. The equivalent region in the structurally related glutathione transferase superfamily corresponds to the active site. This so-called foot-in-mouth interaction suggests that CLIC2 might recognize other proteins such as the ryanodine receptor through a similar interaction

Axon initial segment dysfunction in a mouse model of human genetic epilepsy with febrile seizures plus

Febrile seizures are a common childhood seizure disorder and a defining feature of genetic epilepsy with febrile seizures plus (GEFS+), a syndrome frequently associated with Na+ channel mutations. Here, we describe the creation of a knockin mouse heterozygous for the C121W mutation of the ß1 Na+ channel accessory subunit seen in patients with GEFS+. Heterozygous mice with increased core temperature displayed behavioral arrest and were more susceptible to thermal challenge than wild-type mice. Wild-type ß1 was most concentrated in the membrane of axon initial segments (AIS) of pyramidal neurons, while the ß1(C121W) mutant subunit was excluded from AIS membranes. In addition, AIS function, an indicator of neuronal excitability, was substantially enhanced in hippocampal pyramidal neurons of the heterozygous mouse specifically at higher temperatures. Computational modeling predicted that this enhanced excitability was caused by hyperpolarized voltage activation of AIS Na+ channels. This heat-sensitive increased neuronal excitability presumably contributed to the heightened thermal seizure susceptibility and epileptiform discharges seen in patients and mice with ß1(C121W) subunits. We therefore conclude that Na+ channel ß1 subunits modulate AIS excitability and that epilepsy can arise if this modulation is impaired

A Close Companion Search Around L Dwarfs Using Aperture Masking Interferometry and Palomar Laser Guide Star Adaptive Optics

We present a close companion search around 16 known early L dwarfs using aperture masking interferometry with Palomar laser guide star adaptive optics (LGS AO). The use of aperture masking allows the detection of close binaries, corresponding to projected physical separations of 0.6-10.0 AU for the targets of our survey. This survey achieved median contrast limits of ΔK ~ 2.3 for separations between 1.2λ/D-4λ/D and ΔK ~ 1.4 at 2/3λ/D. We present four candidate binaries detected with moderate-to-high confidence (90%-98%). Two have projected physical separations less than 1.5 AU. This may indicate that tight-separation binaries contribute more significantly to the binary fraction than currently assumed, consistent with spectroscopic and photometric overluminosity studies. Ten targets of this survey have previously been observed with the Hubble Space Telescope as part of companion searches. We use the increased resolution of aperture masking to search for close or dim companions that would be obscured by full aperture imaging, finding two candidate binaries. This survey is the first application of aperture masking with LGS AO at Palomar. Several new techniques for the analysis of aperture masking data in the low signal-to-noise regime are explored

Similarly Efficacious Anti-Malarial Drugs SJ733 and Pyronaridine Differ in Their Ability to Remove Circulating Parasites in Mice

BACKGROUND: Artemisinin-based combination therapy (ACT) has been a mainstay for malaria prevention and treatment. However, emergence of drug resistance has incentivised development of new drugs. Defining the kinetics with which circulating parasitized red blood cells (pRBC) are lost after drug treatment, referred to as the parasite clearance curve , has been critical for assessing drug efficacy; yet underlying mechanisms remain partly unresolved. The clearance curve may be shaped both by the rate at which drugs kill parasites, and the rate at which drug-affected parasites are removed from circulation. METHODS: In this context, two anti-malarials, SJ733, and an ACT partner drug, pyronaridine were compared against sodium artesunate in mice infected with Plasmodium berghei (strain ANKA). To measure each compound\u27s capacity for pRBC removal in vivo, flow cytometric monitoring of a single cohort of fluorescently-labelled pRBC was employed, and combined with ex vivo parasite culture to assess parasite maturation and replication. RESULTS: These three compounds were found to be similarly efficacious in controlling established infection by reducing overall parasitaemia. While sodium artesunate acted relatively consistently across the life-stages, single-dose SJ733 elicited a biphasic effect, triggering rapid, partly phagocyte-dependent removal of trophozoites and schizonts, followed by arrest of residual ring-stages. In contrast, pyronaridine abrogated maturation of younger parasites, with less pronounced effects on mature parasites, while modestly increasing pRBC removal. CONCLUSIONS: Anti-malarials SJ733 and pyronaridine, though similarly efficacious in reducing overall parasitaemia in mice, differed markedly in their capacity to arrest replication and remove pRBC from circulation. Thus, similar parasite clearance curves can result for anti-malarials with distinct capacities to inhibit, kill and clear parasites

Power tests of a string of magnets comprising a full cell of the Superconducting Super Collider

In this paper we describe the operation and testing of a string of magnets comprising a full cell of the Superconducting Super Collider (SSC). The full cell configuration composed of ten dipoles, two quadrupoles, and three spool pieces is the longest SSC magnet string ever tested. Although the tests of the full cell were undertaken after the SSC project was marked for termination, their completion was deemed necessary and useful to future efforts at other accelerator laboratories utilizing Superconducting magnets. The focus of this work is on the electrical and cryogenic performance of the string components and the quench protection system with an emphasis on solving some of the questions concerning electrical performance raised during the previous two experimental runs involving a half cell configuration