Correlation length scalings in fusion edge plasma turbulence computations

The effect of changes in plasma parameters, that are characteristic near or at an L-H transition in fusion edge plasmas, on fluctuation correlation lengths are analysed by means of drift-Alfven turbulence computations. Scalings by density gradient length, collisionality, plasma beta, and by an imposed shear flow are considered. It is found that strongly sheared flows lead to the appearence of long-range correlations in electrostatic potential fluctuations parallel and perpendicular to the magnetic field.Comment: Submitted to "Plasma Physics and Controlled Fusion

Origin of different deactivation of Pd/SnO₂ and Pd/GeO₂ catalysts in methanol dehydrogenation and reforming: A comparative study

Pd particles supported on SnO2 and GeO2 have been structurally investigated by X-ray diffraction, (High-Resolution) transmission and scanning electron microscopy after different reductive treatments to monitor the eventual formation of bimetallic phases and catalytically tested in methanol dehydrogenation/reforming. For both oxides this included a thin film sample with well-defined Pd particles and a powder catalyst prepared by incipient wetness impregnation. The hexagonal and the tetragonal polymorph were studied for powder GeO2. Pd2Ge formation was observed on all GeO2-supported catalysts, strongly depending on the specific sample used. Reduction of the thin film at 573 K resulted in full transformation into the bimetallic state. The partial solubility of hexagonal GeO2 in water and its thermal structural instability yielded Pd2Ge formation at 473 K, at the cost of a structurally inhomogeneous support and Ge metal formation at higher reduction temperatures. Pd on tetragonal GeO2 entered a state of strong metal–support interaction after reduction at 573–673 K, resulting in coalescing Pd2Ge particles on a sintered and re-crystallized support, apparently partially covering the bimetallic particles and decreasing the catalytic activity. Pd2Ge on amorphous thin film and hexagonal GeO2 converted methanol primarily via dehydrogenation to CO and H2. At 573 K, formation of Pd2Sn and also PdSn occurred on the Pd/SnO2 thin film. Pd3Sn2 (and to some extent Pd2Sn) were predominantly obtained on the respective powder catalyst. Strong deactivation with increasing reduction temperature was observed, likely not based on the classical strong metal–support interaction effect, but rather on a combination of missing active structural ensembles on Sn-enriched bimetallic phases and the formation of metallic β-Sn. Correlations to Pd and its bimetallics supported on ZnO, Ga2O3 and In2O3 were also discussed

AN EXPERIMENTAL STUDY OF TRACE ELEMENT FLUXES FROM SUBDUCTED OCEANIC CRUST

ISSN:0022-3530ISSN:1460-241

The Physiology of Vasodilatation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68237/2/10.1177_000331976101200602.pd

Heat capacity and phase equilibria of hollandite polymorph of KAlSi 3 O 8

The low-temperature heat capacity ( C p ) of KAlSi 3 O 8 with a hollandite structure was measured over the range of 5–303 K with a physical properties measurement system. The standard entropy of KAlSi 3 O 8 hollandite is 166.2±0.2 J mol −1  K −1 , including an 18.7 J mol −1  K −1 contribution from the configurational entropy due to disorder of Al and Si in the octahedral sites. The entropy of K 2 Si 4 O 9 with a wadeite structure (Si-wadeite) was also estimated to facilitate calculation of phase equilibria in the system K 2 O–Al 2 O 3 –SiO 2 . The calculated phase equilibria obtained using Perple_x are in general agreement with experimental studies. Calculated phase relations in the system K 2 O–Al 2 O 3 –SiO 2 confirm a substantial stability field for kyanite–stishovite/coesite–Si-wadeite intervening between KAlSi 3 O 8 hollandite and sanidine. The upper stability of kyanite is bounded by the reaction kyanite (Al 2 SiO 5 ) = corundum (Al 2 O 3 )  + stishovite (SiO 2 ), which is located at 13–14 GPa for 1,100–1,400 K. The entropy and enthalpy of formation for K-cymrite (KAlSi 3 O 8 ·H 2 O) were modified to better fit global best-fit compilations of thermodynamic data and experimental studies. Thermodynamic calculations were undertaken on the reaction of K-cymrite to KAlSi 3 O 8 hollandite +  H 2 O, which is located at 8.3–10.0 GPa for the temperature range 800–1,600 K, well inside the stability field of stishovite. The reaction of muscovite to KAlSi 3 O 8 hollandite + corundum + H 2 O is placed at 10.0–10.6 GPa for the temperature range 900–1,500 K, in reasonable agreement with some but not all experiments on this reaction.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46910/1/269_2006_Article_63.pd

The Stability of Hydrous Potassic Phases in Lherzolitic Mantle—an Experimental Study to 9.5 GPa in Simplified and Natural Bulk Compositions

To investigate the pressure stability limit of phlogopite and the pressure-temperature stability field of its breakdown product K-richterite, experiments were conducted from 4.0 to 9.5 GPa and between 800°C and 1400°C in a subalkaline system K2o-Na2O-CaO-MgO-Al2O3-SiO2-H2O (KNCMASH) and in natural phlogopite and K-richterite-doped lherzolite systems. In KNCMASH, phlogopite breaks down between 6.0 and 6.5 GPa at 800°C and between 6.5 and 7.0 GPa at 1100°C to form potassic amphibole by the reaction phlogopite + clinopyroxene + orthopyroxene = K-richterite + garnet + olivine + H2O. In the natural system, the stability field of amphibole is shifted towards lower pressures by ∼0.5 GPa. The high-temperature stability limit of K-richterite in KNCMASH was located between 1300 and 1400°C at 8.0 GPa and at <1300°C at 7.0 GPa. Thus, K-richterite can be stable in the mantle wedge above subduction zones below a depth of ∼180-200 km. Because of the small difference in K/OH ratios between phlogopite and K-richterite, only a small amount of aqueous fluid is likely to be produced during phlogopite breakdown in an average mantle lherzolite bulk composition. This fluid might be trapped by nominally anhydrous minerals before it can migrate to hotter portions of the mantle wedge. Phlogopite breakdowntherefore is unlikely to be a factor in inducing significant melting of the wedge leading to arc magmatis

The Stability of Hydrous Potassic Phases in Lherzolitic Mantle—an Experimental Study to 9.5 GPa in Simplified and Natural Bulk Compositions

ISSN:0022-3530ISSN:1460-241