Mechanism of the CO oxidation reaction on O-precovered Pt(111) surfaces studied with near-edge x-ray absorption fine structure spectroscopy.

The mechanism of CO oxidation reaction on oxygen-precovered Pt(111) surfaces has been studied by using time-resolved near-edge x-ray absorption fine structure spectroscopy. The whole reaction process is composed of two distinct paths: (1) a reaction of isolated oxygen atoms with adsorbed CO, and (2) a reaction of island-periphery oxygen atoms after the CO saturation. CO coadsorption plays a role to induce the dynamic change in spatial distribution of O atoms, which switches over the two reaction paths. These mechanisms were confirmed by kinetic Monte Carlo simulations. The effect of coadsorbed water in the reaction mechanism was also examined.

Reaction-path switching induced by spatial-distribution change of reactants: CO oxidation on Pt(111).

We studied the mechanism of CO oxidation on O-covered Pt(111) surfaces during CO exposure by means of time-resolved near edge x-ray absorption fine structure spectroscopy. Two distinct reaction processes were found to occur sequentially; isolated O atoms and island-periphery O atoms contribute to each process. Combination of in situ monitoring of the reaction kinetics and Monte Carlo simulations revealed that CO coadsorption plays a role of inducing the dynamic change in spatial distribution of O atoms, which switches over the two reaction paths.

Development of multipurpose laboratory XIEES spectrometer and its application to surface XAFS analysis of Al2O3 films.

A new laboratory spectrometer for X-ray Induced Electron Emission Spectroscopy (XIEES) has been developed. This spectrometer is suitable for measurements of X-ray Absorption Fine Structure (XAFS) spectrum in surface sensitive fluorescence and electron emission detection modes as well as in standard transmission mode. It is the advantage of this spectrometer that a wide range of x-ray energy scanning between 0.48 and 41 keV is available. At the Cu K-edge, a energy resolution of about 2 eV has been achieved. The spectrometer has been used to analyze the Al2O3 (40 A and 500 A)/Si(100) with total electron yield measurement.

XANES spectra of mechanical alloyed Y-Cu system.

We report changes in the structure and the electronic states of YCu2 during mechanical alloying. The x-ray diffraction shows that milling for about 60 h transforms mixture of elemental powders of Y and Cu into an amorphous alloy. We have measured the x-ray absorption near edge structure (XANES) spectra of mechanically alloyed YCu2 at Cu K and Y K edges at various milling time. The pre-edge peak near the Cu K threshold grows remarkably and its central energy decreases with increasing the milling time. The absorption near the Y K threshold, on the other hand, decreases with milling time. We discuss these features of XANES spectra in connection with the phase transformation from the crystalline to amorphous states.

XANES study in the solid state reaction of Zr-Ni system.

We have measured x-ray absorption near edge structure (XANES) spectra of mechanically alloyed ZrNi near Ni and Zr K edges as a function of milling time. The x-ray diffraction shows that the system is transformed into an amorphous phase by milling for about 60 h. With increasing the milling time, a small absorption near the Ni threshold rises and finally forms a peak in the amorphous phase, while an absorption near the Zr threshold shows a gradual decrease. The peak of the Ni K edge reflects 3d character strongly hybridized with 4p states, while the absorption of the Zr K edge comes from states having a 4d orbital character.

Use of highly energetic (116 keV) synchrotron radiation for X-ray fluorescence analysis of trace rare-earth and heavy elements.

This study has revealed the advantages of the use of 116 keV X-rays as an excitation source of X-ray fluorescence (XRF) analyses. This technique is suitable for nondestructive multielemental analyses of heavy elements such as rare-earth elements. The lowest MDL value evaluated for the bulk analysis of a JG-1 standard reference sample (granite rock) was 0.1 ppm for W for a 500 s measurement. The spectrum of standard glass samples of SRM612 demonstrated clearly resolved K-line peaks of more than 30 elements, including all the existing rare-earth elements, at 50 ppm levels. The calibration curve for the determination of a rare-earth element shows a linear relation between the XRF intensity and concentrations from 10 to 0.03 ng. This powerful technique should be useful for nondestructive analyses of rare-earth and heavy elements in geological, geochemical and archaeological samples as well as industrial materials.

Effect of troglitazone on blood insulin levels after pancreas transplantation with systemic venous drainage in rats.

BACKGROUND: Troglitazone is a new oral antidiabetic agent and has been reported to reduce insulin resistance and improve peripheral hyperinsulinemia in patients with noninsulin-dependent diabetes mellitus. To examine the effect of troglitazone on insulin regulation after pancreas transplantation with systemic venous drainage, we measured peripheral glucose and insulin levels and performed an intravenous glucose tolerance test. METHODS: We divided the rats into four groups: diabetic rats with a pancreas graft and administration of troglitazone at 40 mg/day orally (group P+T, n=4), rats with a pancreas graft only (group P, n=4), age-matched normal rats (group N, n=5), and diabetic rats (group DM, n=4). RESULTS: Fasting insulin levels in group P were relatively higher than those in group N, whereas the values in group P+T were normalized. In the intravenous glucose tolerance test, troglitazone clearly regulates sigma immunoreactive insulin levels of pancreas transplanted rats (P vs. P+T: 244+/-23 vs. 145+/-14 microU/ml, P<0.05). CONCLUSION: Hyperinsulinemia induced by systemic venous drainage, which may progress atherosclerosis, can be controlled with troglitazone treatment.

Long-term prognosis of renal transplant surviving for over 10 yr, and clinical, renal and rehabilitation features of 20-yr successes.

Long-term mortality and morbidity was evaluated in 267 patients with a minimum follow-up of 10 yr and the physical status, graft function and quality of life in 15 patients with a functioning graft surviving for over 20 yr were reviewed. Actual patient and graft survival rates were 80.2% and 51.1% at 10 yr (n = 267) and 56.4% and 32.7% at 20 yr (n = 55), respectively. Although the rate of graft failure due to rejection was 4 times higher than that of patient death within 10 yr, it decreased to the level of patient death in the second decade. Dominant causes of death in patients with graft surviving for over 10 yr were hepatic failure due to viral hepatitis and malignancies. In 15 patients with graft currently surviving beyond 20 yr, while all patients have excellent graft function, malignancy occurred in 5, viral hepatitis in 3, aseptic necrosis in 3, and diabetes mellitus in one patient. No patient has suffered cardiovascular complications. Despite a high rate of morbidity, they show a satisfying status of rehabilitation (full time working 11/ 15, 73.3%). In order to attain more improved QOL in patients with long-term surviving renal transplant, close follow-up aiming at diminution of complications is required throughout the period after transplantation.