Plasma cleaning of ITER first mirrors in magnetic field

To avoid reflectivity losses in ITER optical diagnostic systems, plasma sputtering of metallic First Mirrors is foreseen in order to remove deposits coming from the main wall (mainly beryllium and tungsten). Therefore plasma cleaning has to work on large mirrors (up to a size of 200*300 mm) and under the influence of strong magnetic fields (several Tesla). This work presents the results of plasma cleaning of aluminium and aluminium oxide (used as beryllium proxy) deposited on molybdenum mirrors. Using radio frequency (13.56 MHz) argon plasma, the removal of a 260 nm mixed aluminium/aluminium oxide film deposited by magnetron sputtering on a mirror (98 mm diameter) was demonstrated. 50 nm of pure aluminium oxide were removed from test mirrors (25 mm diameter) in a magnetic field of 0.35 T for various angles between the field lines and the mirrors surfaces. The cleaning efficiency was evaluated by performing reflectivity measurements, Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy.Comment: 5 pages, 6 figures and 1 table. Results presented on the 21st Plasma Surface Interaction conference held in Kanazawa Japan, May 201

Improvement in HSS grade for early stands of hot strip mills - Metallurgical features and mechanical properties assessment

peer reviewedAurora and Kosmos grades are HSS alloys belonging to the complex Fe-Cr-C-X system, where X is a strong carbide former element of the V, Mo or W type. Both alloys were metallurgically characterised prior to their comparison. Metallurgical analyses involved phases identification and carbides quantification by using Scanning Electron Microscopy and Energy Dispersive X rays. Differential Thermal Analysis was performed to allow a better understanding of the solidification sequence of studied alloys while mechanical tests performed were compressive at room temperature and bulk hardness at usual service temperatures. An attempt was made in order to connect experimental results to the good behaviour in operation of Aurora grade. In fact Aurora grade appeared to exhibit strong metallurgical differences when compared to Kosmos grade, especially as concern in nature and amount of carbides

Oligosaccharyltransferase is highly specific for the hydroxy amino acid in Asn-Xaa-Thr/Ser

AbstractPig liver oligosaccharyltransferase (OST), which is involved in the en bloc transfer of the Dol-PP-linked GlcNAc2-Man9-Glc3 precursor on to asparagine residues in the Asn-Xaa-Thr/Ser sequence, is highly stereospecific for the conformation of the 3-carbon atom in the hydroxy amino acid. Moreover, substitution of the hydroxy group by either SH as in cysteine, or NH2 as in β,γ-diamino-butanoic acid as reported previously [Bause, E. et al., Biochem. J. 312 (1995) 979–985], followed by the determination of the pH optimum for enzymatic activity, indicates that neither a negative nor a positive charge in the hydroxy amino acid position is tolerated by the enzyme. Binding of the threonine β-methyl group by OST is also specific, with serine, L-threo-β-hydroxynorvaline and L-β-hydroxynorleucine containing tripeptides all bound much less efficiently than the threonine peptide itself. The data are interpreted in terms of a highly stereospecific hydrophobic binding pocket for the threonine CH3-CH(OH) group

Mechanistic insights into allosteric regulation of the A2A adenosine G protein-coupled receptor by physiological cations.

Cations play key roles in regulating G-protein-coupled receptors (GPCRs), although their mechanisms are poorly understood. Here, 19F NMR is used to delineate the effects of cations on functional states of the adenosine A2A GPCR. While Na+ reinforces an inactive ensemble and a partial-agonist stabilized state, Ca2+ and Mg2+ shift the equilibrium toward active states. Positive allosteric effects of divalent cations are more pronounced with agonist and a G-protein-derived peptide. In cell membranes, divalent cations enhance both the affinity and fraction of the high affinity agonist-bound state. Molecular dynamics simulations suggest high concentrations of divalent cations bridge specific extracellular acidic residues, bringing TM5 and TM6 together at the extracellular surface and allosterically driving open the G-protein-binding cleft as shown by rigidity-transmission allostery theory. An understanding of cation allostery should enable the design of allosteric agents and enhance our understanding of GPCR regulation in the cellular milieu

Study of Wall Re-Deposition on DC-grounded ITER-relevant Mirrors with RF Plasma in a First Mirror Unit

In ITER, several first mirrors (FMs) are expected to be DC-grounded with the water cooling lines being implemented as a quarter wavelength ($lambda$/4) RF-filter. DC-grounding of the FMs can significantly increase the plasma potential V p, which could trigger an increased wall sputtering and associated re-deposition on the FMs during plasma cleaning. To understand the scope of this impact, helium discharges were excited with DC-grounded FMs in an ITER-sized mock-up of a first mirror unit (FMU) using wall materials with different sputtering energy thresholds (E th). Additionally, a part of the FM was electrically isolated from the RF to study its impact on the erosion/re-deposition properties on the surface. The E th of the wall materials, as well as its native oxide layers, had a significant influence on the re-deposition observed on the FMs. With high E th where walls were unsputtered, both the DC-grounded and electrically isolated parts of the FM were free of deposits. However, with low E th where the walls were sputtered, there was a net wall re-deposition on the DC-grounded parts of the FM, while electrically isolated parts were still relatively clean. Further, to study the impact of floating wall components, Cu walls in the FMU were isolated from the ground. Here the walls developed a floating potential V f and the ion energy at the walls was lowered to e(V p - V f). The floating walls, in this case, were relatively unsputtered and the FMs experienced a net cleaning with total reflectivity of the mirror preserved at pristine mirror levels. This work shows that electrically isolating the FM as well as the wall surface minimizes wall re-deposition in presence of $lambda$/4 filter and therefore are promising techniques for effective FM cleaning in ITER

Time Optimal Control in Spin Systems

In this paper, we study the design of pulse sequences for NMR spectroscopy as a problem of time optimal control of the unitary propagator. Radio frequency pulses are used in coherent spectroscopy to implement a unitary transfer of state. Pulse sequences that accomplish a desired transfer should be as short as possible in order to minimize the effects of relaxation and to optimize the sensitivity of the experiments. Here, we give an analytical characterization of such time optimal pulse sequences applicable to coherence transfer experiments in multiple-spin systems. We have adopted a general mathematical formulation, and present many of our results in this setting, mindful of the fact that new structures in optimal pulse design are constantly arising. Moreover, the general proofs are no more difficult than the specific problems of current interest. From a general control theory perspective, the problems we want to study have the following character. Suppose we are given a controllable right invariant system on a compact Lie group, what is the minimum time required to steer the system from some initial point to a specified final point? In NMR spectroscopy and quantum computing, this translates to, what is the minimum time required to produce a unitary propagator? We also give an analytical characterization of maximum achievable transfer in a given time for the two spin system.Comment: 20 Pages, 3 figure

The Grizzly, February 14, 2008

Writer\u27s Strike May See a Silver Lining • Ellison Unveils Art Exhibit in Berman • Relief for Students? College Endowments Skyrocket • Ursinus Designs New Certificate for International Studies • Is Everybody Really Doing It? The Indictment of the Greek Community at Ursinus College Surprises Many • Ursinus Community Shares its Dirty Little Secrets • Focus the Nation and Environmentalism: No Longer Just for Hippies • UC Study Abroad Helpful Hints • Opinions: Lessons from Super Tuesday; Does The Times Need Bill Kristol?; Lessons from the Hormuz Strait • Ursinus Wrestlers Clinch Dual Meet • UC Indoor Track Teams Make Big Moves, Heat Up Competitionhttps://digitalcommons.ursinus.edu/grizzlynews/1755/thumbnail.jp

A botanical demonstration of the potential of linking data using unique identifiers for people

Natural history collection data available digitally on the web have so far only made limited use of the potential of semantic links among themselves and with cross-disciplinary resources. In a pilot study, botanical collections of the Consortium of European Taxonomic Facilities (CETAF) have therefore begun to semantically annotate their collection data, starting with data on people, and to link them via a central index system. As a result, it is now possible to query data on collectors across different collections and automatically link them to a variety of external resources. The system is being continuously developed and is already in production use in an international collection portal