ヨウケツ ギョウカイガン ノ フウカ ニヨル ガンセキ ブッセイ ノ ヘンカ

Temporal changes in colour and physical properties due to weathering during 240 ka were examined using welded tuff gravel in fluvial terrace deposits with a known emergence time that were distributed in Miyazaki Plain, Japan. The time between the age of each terrace formation (8, 90, 120 and 240 ka) and the present was assumed to be the weathering period. The results of the measurements are as follows: (1) effective porosity increases as the weathering period increases; (2) the a*, b*-values of colour induces increase as the weathering period increases. These results suggest that (1) the increase in pores in gravel that occurs as the weathering period increases is caused by the dissolution of biotite; (2) iron concentration and the formation of goethite occur in older gravels. Dissolution of biotite and increasing pore volume play major roles in the weathering of welded tuff

Charged Vortices in High Temperature Superconductors Probed by NMR

We report a first experimental evidence that a vortex in the high temperature superconductors (HTSC) traps a finite electric charge from the high resolution measurements of the nuclear quadrupole frequencies. In slightly overdoped YBa_2Cu_3O_7 the vortex is negatively charged by trapping electrons, while in underdoped YBa_2Cu_4O_8 it is positively charged by expelling electrons. The sign of the trapped charge is opposite to the sign predicted by the conventional BCS theory. Moreover, in both materials, the deviation of the magnitude of the charge from the theory is also significant. These unexpected features can be attributed to the novel electronic structure of the vortex in HTSC.Comment: 6 pages, 7 figures, to be published in Phys Rev.

Development and application of a ray-tracing code integrating with 3D equilibrium mapping in LHD ECH experiments

The central electron temperature has successfully reached up to 7.5 keV in large helical device(LHD) plasmas with a central high-ion temperature of 5 keV and a central electron density of1.3×1019 m−3. This result was obtained by heating with a newly-installed 154 GHz gyrotronand also the optimisation of injection geometry in electron cyclotron heating (ECH). Theoptimisation was carried out by using the ray-tracing code ‘LHDGauss’, which was upgradedto include the rapid post-processing three-dimensional (3D) equilibrium mapping obtainedfrom experiments. For ray-tracing calculations, LHDGauss can automatically read the relevantdata registered in the LHD database after a discharge, such as ECH injection settings (e.g.Gaussian beam parameters, target positions, polarisation and ECH power) and Thomsonscattering diagnostic data along with the 3D equilibrium mapping data. The equilibrium mapof the electron density and temperature profiles are then extrapolated into the region outsidethe last closed flux surface. Mode purity, or the ratio between the ordinary mode and theextraordinary mode, is obtained by calculating the 1D full-wave equation along the directionof the rays from the antenna to the absorption target point. Using the virtual magnetic fluxsurfaces, the effects of the modelled density profiles and the magnetic shear at the peripheralregion with a given polarisation are taken into account. Power deposition profiles calculatedfor each Thomson scattering measurement timing are registered in the LHD database. Theadjustment of the injection settings for the desired deposition profile from the feedbackprovided on a shot-by-shot basis resulted in an effective experimental procedure

Carbon Deposition during Carbon Dioxide Reforming of Methane—Comparison between Pt/Al2O3 and Pt/ZrO2

The relation between coke formation and the deactivation of supported Pt catalysts during CO2 reforming of methane at temperatures above 1070 K such as used in the commercial process was studied. Temperature-programmed oxidation and temperature-programmed reaction with CO2 were applied to Pt catalysts (Pt/Al2O3 and Pt/ZrO2) which were exposed to CH4/CO2 (reforming reaction conditions) or CH4/He (facile coke formation) to identify the carbon species. The activity decrease for Pt/Al2O3 was rather slow and minor at high temperature (≥1070 K), while it was fast and almost complete during a comparative experiment at low temperature (875 K). Coke deposited on the supported Pt particles was oxidized by CO2, but coke on the Al2O3 support was not removed at 1070 K. At this temperature the decay in activity with time on stream corresponded solely to the amount of coke accumulated on Pt particles. This indicates the main reaction between CO2 and CH4 on all Pt atoms without significant participation of the support. The activity is concluded to decrease gradually due to coverage of Pt by coke induced by CH4 decomposition (initial phase of deactivation observed at high temperature). After a while only the perimeter of Pt particles remains as site of activity. There, the activity is speculated to be stable because of the higher reactivity of CO2 at the metal–support boundary. Gradually, the coke on the support (Al2O3) increases to an extent that it blocks the reaction also at that location. In contrast to the situation with Pt/Al2O3, coke was not observed on Pt/ZrO2 even after exposure to reforming gas (CH4/CO2) for 12 h. The combination of three factors is concluded to cause the high catalytic stability of Pt/ZrO2 in CO2/methane reforming: (i) coke on Pt (supported on ZrO2) is more reactive toward CO2 than coke on Pt (supported on Al2O3) under reforming reaction conditions/ (ii) methane decomposition is slower on Pt/ZrO2 than on Pt/Al2O3; and (iii) coke is hardly formed on the ZrO2 support

Potential impact of surface microstructure change on reduction of emission current in tungsten filament

ORCID　0000-0002-4453-953XWhen a helium beam is extracted, a significant decrease in arc current is observed in the filament arc ion source of the Neutral Beam Injector. Microstructural changes in the tungsten filament surface of the ion source are observed by electron microscopy to investigate the cause of the reduction of arc current. Helium bubbles with 100–800 nm diameters appear immediately beneath the surface within 1 μm, and the bubbles develop into surface hole structures with surface erosion by sputtering. The decrease in arc current with helium beam extraction can be explained by a reduced effective surface area, due to the increase in hole porosity. It has been shown that the reduction of the arc current can be recovered by removing the helium-irradiation-affected layer by sputtering with argon discharge

Promotional Effect of La in the Three-Way Catalysis of La-Loaded Al2O3-Supported Pd Catalysts (Pd/La/Al2O3)

La-loaded Al2O3 (La/Al2O3) is a practical support for three-way catalysis (TWC) reactions. Although it has been reported that the addition of La to Al2O3 results in improved thermal stability to retain high specific surface areas, its effect on the catalytic reduction of NOx (DeNO(x)) has not been studied systematically. Herein, we describe the role of La in La/Al2O3-supported Pd catalysts (Pd/La/Al2O3) for TWC reactions. For that purpose, we employed various in situ spectroscopic studies, including infrared (IR), X-ray absorption fine structure (XAFS), and near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) in combination with density functional theory (DFT) calculations. The obtained results revealed that Pd-0 species supported on La/Al2O3 are more electron-deficient compared to those on pristine Al2O3 without La(Pd/Al2O3). Kinetic studies using powdered catalysts revealed that the addition of La suppresses the poisoning effect by CO during the DeNO(x) reactions. In addition to the catalytic tests with powdered catalysts, monolithic honeycomb forms of the catalysts were prepared and employed for TWC reactions, which showed that Pd/La/Al2O3 exhibits higher DeNO(x) activity than Pd/Al2O3. In this study, we also reexamined the effective loading amount of La, which has traditionally been similar to 3-5 wt % of La for TWC processes in order to retain the high specific surface area of the La/Al2O3 supports. Our investigations showed that an increased La loading (15 wt %) is even more effective for the DeNO(x) reactions tested in this study due to the higher reactivity toward NO and the greater suppression of the poisoning effect of CO. The developed catalyst Pd/La(15)/Al2O3 has also been tested in a commercial vehicle and has been evaluated on a practical driving mode test cycle (LA-4; city cycle of U.S. Federal and California), where it showed a better catalytic performance than the conventionally used Pd/La(3-5)/Al2O3 catalysts. Our study suggests that the loading amount of La in Pd/La/Al2O3 catalysts needs to be adjusted depending on the application systems, considering not only the support stability (surface areas) but also the promotional effect in the TWC process

Roles of the basic metals La, Ba, and Sr as additives in Al2O3-supported Pd-based three-way catalysts

Three-way catalytic converters are widely used to regulate emissions from gasoline-powered vehicles. Although significant effort over the past 40 years has resulted in the discovery of several metal additives that improve the thermal stability of three-way catalysts (TWCs), their effects on the actual catalytic process have not been studied systematically. The present work examines the roles of the typical basic metal additives La, Ba, and Sr in Pd-based TWC systems, using various spectroscopic and kinetic studies. Metallic Pd-0 species on Sr/Al2O3 and Ba/Al2O3 supports were found to be more electron-rich than those on pristine Al2O3, whereas those on La/Al2O3 were more electron-deficient. Consequently, Pd/La/Al2O3 showed a lessened CO poisoning effect during NO reduction reactions. Evaluations were performed using powdered catalysts as well as monolithic honeycomb catalysts under conditions simulating actual use. Pd/La/Al2O3 was observed to promote the catalytic reduction of NO most efficiently, while Pd/Ba/Al2O3 exhibited the highest activity for the oxidations of CO and C3H6. The present data suggest that the optimal metal additive for a Pd-based TWC will be determined by the specific application. The selection of such metals should take into account not only the stability but also the promotional effect during the exhaust purification process. (C) 2021 Elsevier Inc. All rights reserved