Maggi, C.F.
Delabie, E.
Biewer, T.M.
Groth, M.
Hawkes, N.C.
Lehnen, M.
de la Luna, E.
McCormick, K.
Reux, C.
Rimini, F.
Solano, E.R.
Andrew, Y.
Bourdelle, C.
Bobkov, V.
Brix, M.
Calabro, G.
Czarnecka, A.
Flanagan, J.
Lerche, E.
Marsen, S.
Nunes, I.
Van Eester, D.
Stamp, M.F.
A comparison of the L-H power threshold ( Pthr) in JET with all carbon, JET-C, and beryllium/tungsten wall (the ITER-like choice), JET-ILW, has been carried out in experiments with slow input power ramps and matched plasma shapes, divertor configuration and IP/ BT pairs. The low density dependence of the L-H power threshold, namely an increase below a minimum density ne,min, which was first observed in JET with the MkII-GB divertor and C wall and subsequently not observed with the current MkII-HD geometry, is observed again with JET-ILW. At plasma densities above ne,min, Pthr is reduced by ~30%, and by ~40% when the radiation from the bulk plasma is subtracted ( Psep), with JET-ILW compared to JET-C. At the L-H transition the electron temperature at the edge, where the pedestal later develops, is also lower with JET-ILW, for a given edge density. With JET-ILW the minimum density is found to increase roughly linearly with magnetic field, , while the power threshold at the minimum density scales as . The H-mode power threshold in JET-ILW is found to be sensitive both to variations in main plasma shape ( Psep decreases with increasing lower triangularity and increases with upper triangularity) and in divertor configuration. When the data are recast in terms of Psep and Zeff or subdivertor neutral pressure a linear correlation is found, pointing to a possible role of Zeff and/or subdivertor neutral pressure in the L-H transition physics. Depending on the chosen divertor configuration, Pthr can be up to a factor of two lower than the ITPA scaling law for densities above ne,min. A shallow edge radial electric field well is observed at the L-H transition. The edge impurity ion poloidal velocity remains low, close to its L-mode values, les5 km s -1 +or- 2-3 km s -1, at the L-H transition and throughout the H-mode phase, with no measureable increase within the experimental uncertainties. The edge toroidal rotation profile does not contribute to the depth of the negative Er well and thus may not be correlated with the formation of the edge transport barrier in JET.
Let a be an infinite ordinal and gamma the unique ordinal satisfying omega(omega gamma) <= alpha < omega(omega gamma+1). We show that the Banach space C([0, alpha]) of all continuous scalar-valued functions on the compact ordinal interval [0, alpha] has Szlenk index equal to omega(gamma+1) and w*-dentability index equal to omega(1+gamma+1). (C) 2012 Elsevier Inc. All rights reserved.
This paper is aimed on a perspective low-friction coatings, the W-S-C system deposited by magnetron sputtering, which exhibits extremely low-friction coefficient together with high-load-bearing capacity. Special attention has been paid to the analysis of the frictional and wear mechanisms under different operating conditions, such as the contact pressure, the air humidity, and the temperature. The formation of a thin self-lubricating WS 2 tribolayer, which was observed regardless on the sliding conditions, is the driving force for the promising frictional properties of the coatings. copy2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Bayram, C.
Shiu, K. T.
Zhu, Y.
Cheng, C. W.
Sadana, D. K.
Teherani, F. H.
Rogers, D. J.
Sandana, V. E.
Bove, P.
Zhang, Y.
Gautier, S.
Cho, C. -Y.
Cicek, E.
Vashaei, Z.
McClintock, R.
Razeghi, M.
Indium Gallium Nitride (InGaN) based PV have the best fit to the solar spectrum of any alloy system and emerging LED lighting based on InGaN technology and has the potential to reduce energy consumption by nearly one half while enabling significant carbon emission reduction. However, getting the maximum benefit from GaN diode -based PV and LEDs will require wide-scale adoption. A key bottleneck for this is the device cost, which is currently dominated by the substrate (i.e. sapphire) and the epitaxy (i.e. GaN). This work investigates two schemes for reducing such costs. First, we investigated the integration of Zinc Oxide (ZnO) in InGaN-based diodes. (Successful growth of GaN on ZnO template layers (on sapphire) was illustrated. These templates can then be used as sacrificial release layers for chemical lift-off. Such an approach provides an alternative to laser lift-off for the transfer of GaN to substrates with a superior cost-performance profile, plus an added advantage of reclaiming the expensive single-crystal sapphire. It was also illustrated that substitution of low temperature n-type ZnO for n-GaN layers can combat indium leakage from InGaN quantum well active layers in inverted p-n junction structures. The ZnO overlayers can also double as transparent contacts with a nanostructured surface which enhances light in/out coupling. Thus ZnO was confirmed to be an effective GaN substitute which offers added flexibility in device design and can be used in order to simultaneously reduce the epitaxial cost and boost the device performance. Second, we investigated the use of GaN templates on patterned Silicon (100) substrates for reduced substrate cost LED applications. Controlled local metal organic chemical vapor deposition epitaxy of cubic phase GaN with on-axis Si(100) substrates was illustrated. Scanning electron microscopy and transmission electron microscopy techniques were used to investigate uniformity and examine the defect structure in the GaN. Our results suggest that groove structures are very promising for controlled local epitaxy of cubic phase GaN. Overall, it is concluded that there are significant opportunities for cost reduction in novel hybrid diodes based on ZnO-InGaN-Si hybridization.
The WC-Co/(Ti, W)C graded cemented carbide was prepared by spark plasma sintering. The substrate is WC-8Co, and the hard layer is (Ti, W)C solid-solution. The effects of sintering temperature and holding time on the microstructure and properties of graded cemented carbide were analyzed. The hard layer is mainly formed by dissolving WC in the Co-phase and then by solid-solution reaction with TiC. As the sintering temperature increases, the migration rate of WC increases. When the holding time is 5 min, the thickness and the W content of the (Ti, W)C solid-solution hard layer increases with the increasing of sintering temperature. The thickness of the (Ti, W)C solid-solution can reach 51 +/- 2 mu m at the sintering temperature of 1700 degrees C for the holding time of 5 min. The hardness of hard layer surface increases first and then decreases with the increasing of sintering temperature. The Vickers hardness is the highest at 1600 degrees C, which can reach HV(0.2)21.53GPa. As the holding time increases, the thickness of the solid-solution hard layer increases, but the rate of growth decreases. As the thickness increases, the difference in the W element concentration between the solid-solutions of the same pitch decreases along the layer depth direction, and W element concentration in the entire hard layer increases. The oxidation behavior of graded cemented carbide at 400 degrees C and 600 degrees C was investigated. The (Ti, W)C hard layer has superior oxidation resistance relative to the WC-Co substrate.
A single crystal surface of ditungsten carbide, W(2)C(0001) was investigated using low-energy (LEED) and high-energy electron diffraction, Auger electron spectroscopy, x-ray photoelectron spectroscopy (XPS), and high-resolution electron energy loss spectroscopy (HREELS). A new reconstruction, root 13 x root 13R +/- 13.9 degrees, was found as a clean surface structure after annealing the W2C at > 1900 K. The surface carbon content is shown as larger than that in the bulk. Our preliminary results showed that the same structure is realized also on WC(0001). The same surface periodicity is described for an Mo(2)C(0001) LEED pattern in the literature. This reconstruction phase is presumably common on the (0001) surface of hexagonal group-6 transition-metal carbides. In the off-specular HREELS, an atomic vibration of 44.8 meV (361 cm(-1)) appeared within the gap energy region of the bulk phonon bands, which was assigned to a surface carbon vibration perpendicular to the surface. One possible explanation of the low vibrational frequency is very low adsorption height of the surface carbon atoms.
Nobom Gretta Hashe, Susanne M. Norgren, Hans-Olof André
n, Johannes H. Neethling
Large (W,V)C cubic carbides in WC–VC–Co cemented carbides are undesirable as their presence is one of the causes for poor properties in the material. Earlier attempts to reduce the (W,V)C cubic carbide grain sizes in the WC–VC–Co cemented carbide have been published before. The present investigation strives to reduce the cubic carbide grain size by using a pre-alloyed (W,V)C powder in the place of VC, to reduce the driving force for the formation of (W,V)C during sintering. This should in turn reduce the possibility of forming large (W,V)C grains. WC–VC–Co was prepared using WC, (W,V)C, and Co powders. The compositions were 8.1 wt%V and 12 wt%Co, with the balance comprising W and C. XRD diffraction patterns confirmed that the bulk of WC–(W,V)C–Co contains WC grains, cubic (W,V)C grains, and a Co-rich binder phase. SEM–EDS measurements yielded an average composition of (W0.31V0.69)Cx. TEM–EDS of the cubic carbide was in good agreement with the SEM–EDS measurement, yielding the average composition of (W0.30V0.70)Cx. The average grain size of the cubic carbide of WC–(W,V)C–Co material after sintering had grown to only the same size as that of the starting powder, 1.4 μm.
New relations and transformation formulas for the Appell function F-3 (a,a',b,b';v';w;z) and the confluent Appell functions (Humbert functions) Phi(2),Phi(3), Xi(1), Xi(2) are obtained. These relations include limit formulas, integral representations, differentiation formulas. Various finite and infinite summation formulas are also derived.
Satterfield, Benjamin A.
Cross, Robert W.
Fenton, Karla A.
Borisevich, Viktoriya
Agans, Krystle N.
Deer, Daniel J.
Graber, Jessica
Basler, Christopher F.
Geisbert, Thomas W.
Mire, Chad E.
Airila, M.I.
Bj?rkas, C.
Lasa, A.
Meinander, A.
Nordlund, K.
V?rtler, K.
We have implemented molecular dynamics (MD) generated sputtering data in the Monte Carlo impurity transport code ERO. The data set covers D bombardment of BeC, Be2C, Be2W, W2C and WC that are potentially formed on divertor targets in machines operating with an ITER-like wall. We see that intermediate compounds can have a sputtering yield different from that estimated from a homogeneous mixture, especially in the case of carbide formation with its characteristic strong bonding. At other stoichiometries, grain formation affect the yields. We also observe preferential sputtering of the lighter elements and molecular release. A linear interpolation method is proposed for the evaluation of the sputtering behaviour of any ternary Be/C/W composition. (C) 2013 Elsevier B.V. All rights reserved.
A t-hyperwheel (t a parts per thousand yen 3) of length l (or W (l) ((t)) for brevity) is a t-uniform hypergraph (V,E), where E = {e (1), e (2), aEuro broken vertical bar, e (l) } and v (1), v (2), aEuro broken vertical bar, v (l) are distinct vertices of such that for i = 1, aEuro broken vertical bar, l, v (i) , v (i) +1 a e (i) and e (i) a (c) e (j) = P, j a < {i - 1, i, i + 1}, where the operation on the subscripts is modulo l and P is a vertex of V which is different from v (i) , 1 a parts per thousand currency sign i a parts per thousand currency sign l. In this paper, the minimum covering problem of MC (lambda) (3,W (4) ((3)) , v) is investigated. Direct and recursive constructions on MC (lambda) (3,W (4) ((3)) , v) are presented. The covering number c (lambda) (3,W (4) ((3)) , v) is finally determined for any positive integers v a parts per thousand yen 5 and lambda.
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