Unsteady stirring method used in suspension polymerization of styrene

An unsteady stirring method, that is, coreverse rotation with different periodic intervals, was adopted to the suspension polymerization of styrene. Experiments were carried out in a 0.5‐L flat‐bottom flask with a six‐blade Rushton turbine. Parameters affecting the final particle size and the particle size distribution under the unsteady stirring conditions, such as the agitation speed and the periodic interval, had been studied in detail, and the results were compared with those under a steady stirring one. The experimental results showed that the average particle size decreased and the uniformity final particle size distribution could be significantly improved when unsteady stirring approach is used. These were explained as the result of the decrease of the coalescence rate during the suspension polymerization when the unsteady stirring method was used. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1431–1438, 2000     

Evaluation of aseismic integrity in the HTTR core-bottom structure V. On the static and dynamic behavior of graphitic HTTR key-keyway structures

The graphite components in high temperature gas-cooled reactors are connected to each other through a key-keyway structure that has gaps between the key and the keyway to accomodate thermal expansion. Because a dynamic load concentrates on the key-keyway structure during earthquakes, it is considered to be a crucial element for assessing the integrity of the graphite components. A combination of experiments and analyses was employed to investigate the dynamic behavior of the key-keyway structure, i.e. the equivalent stiffness associated with vibrational characteristics of the graphite components and the stress distribution under dynamic loading. The experiments were performed using a graphite scale model and a dynamic photo-elastic method. The analysis was carried out using the finite element method (FEM) code Abaqus, taking account of the contact between the key and the keyway. The following conclusions were derived. (1) The equivalent stiffness of the key-keyway structure shows nonlinearity, owing to the contact deformation. (2) The equivalent stiffness evaluated by the FEM analysis, taking account of the non-inear contact deformation, is applicable for predicting the vibrational characteristics of ky-keyway structure. (3) The stress concentration under dynamic loading is lower than or nearly equal to that under static loading. The maximum stress concentration of the seismic load can be sufficiently evaluated under static loading conditions.     

Characteristics of Lean Premixed Flame in Various Oxygen Concentrations Measured by Laser Imaging Techniques

For heavy-duty gas-turbine engines, one of the promising approaches to reducing NO_X emissions is the adoption of lean premixed combustion. This technique could be combined with the conventional technique of exhaust gas recirculation (EGR). However, the reduction in the oxygen concentration will influence the burning velocity and reaction zone characteristics of the lean premixed flame. To elucidate this effect, in this study, we measured the lean premixed flame temperature and OH concentration distributions for various oxygen concentrations instantaneously and simultaneously using laser imaging techniques. Based on the results, we investigated the characteristics of a lean premixed flame under various oxygen concentrations and found that the OH laser-induced fluorescence (LIF) intensity in the reaction zone decreased with the oxygen concentration, as did the flame temperature at a given axial distance from the exit nozzle. The characteristics of the premixed flame changed from a small-scale convexo-concave surface to a smoother one, leading to a decrease in the ratio of turbulent to laminar burning velocity. In addition, local extinction of the premixed flame was observed under conditions with a high air ratio and low oxygen concentration.     

Residual impurities in GaN/Al2O3 grown by metalorganic vapor phase epitaxy

Residual impurities in GaN films on sapphire (A1₂O₃) substrates grown by two-step metalorganic vapor phase epitaxy (MOVPE) have been investigated. We have mainly investigated the incorporation of carbon into the GaN films with GaN buffer layers on A1₂O₃ during MOVPE growth, comparing trimethygallium (TMGa) and triethygallium (TEGa) as the typical gallium precursors. The films were characterized by secondary ion mass spectroscopy analysis, photolu-minescence, and Hall measurements. The carbon, hydrogen, and oxygen concentrations increase with decreasing growth temperature in using TMGa. Especially the carbon concentration increases with decreasing a V/III ratio, for both TMGa and TEGa. There is about two times more carbon in the GaN films grown using TEGa than those using TMGa. The carbon from TMGa mainly enhances the D-A pair emission (∼378 nm), which shows the carbon makes an acceptor level at nitrogen sites in GaN. On the other hand, the carbon from TEGa enhances a deep emission (∼550 nm), which shows the carbon makes not only an acceptor level but deep levels at interstitial sites in GaN. The carbon impurities originate from methyl radicals for TMGa, or ethyl radicals for TEGa. It is supposed that, in the case of TEGa, the carbon impurities are not always located at nitrogen sites, but are also located at interstitial sites because of the C-C bonding in ethyl radicals.     

Soluble amyloid precursor protein 770 is a novel biomarker candidate for acute coronary syndrome

Most Alzheimer disease patients show deposition of amyloid β (Aβ) peptide in blood vessels as well as the brain parenchyma. We previously found that vascular endothelial cells express amyloid β precursor protein (APP) 770, a different APP isoform from neuronal APP695, and that they produce amyloid β peptide. We analyzed the glycosylation of APP770 and found that O-glycosylated sAPP770 is preferentially processed by proteases for Aβ production. Because the soluble APP cleavage product sAPP is considered to be a possible marker for Alzheimer disease diagnosis, sAPP, consisting of a mixture of these variants, has been widely measured. We hypothesized that measurement of the endothelial APP770 cleavage product in patients separately from that of neuronal APP695 would enable us to discriminate between endothelial and neurological dysfunctions. Our recent findings, showing that the level of plasma sAPP770 is significantly higher in patients with acute coronary syndrome, raise the possibility that sAPP770 could be an indicator of endothelial dysfunction. In this review, we first describe the expression, glycosylation, and processing of APP770, and then discuss sAPP770 as a novel biomarker candidate of acute coronary syndrome.     

Tritium release from bulk of carbon-based tiles used in JT-60U

Tritium thermal release behavior from the isotropic graphite tile and the CFC tile used as the plasma facing material of JT-60U was experimentally examined. Whole tritium retained in the bulk of tile could not be released by dry gas purge at high temperature in such a period as one day. Utilization of the isotope exchange reaction using purge gas with hydrogen or humid gas was more effective to release the retained tritium. However, approximately 1% of retained tritium was not recovered by the isotope exchange reaction with dry hydrogen even though such high temperature as 1200 °C was applied. Combustion method with oxygen was required to recover all tritium left in the deeper site of the tile. It was observed that combustion of isotropic graphite tile and CFC tile became vigorous at higher temperature than 700 °C though the combustion rate was rather slow at 650 °C.     

Effect of hydrophobic paints coating for tritium reduction in concrete materials

The effects of hydrophobic paint coating on a concrete material of cement paste on the tritium transport are investigated. The cement paste is coated with two kinds of paints, acrylic-silicon resin paint and epoxy resin paint. We investigated the amount of tritium trapped in the samples exposed to tritiated water vapor by means of sorption and release. It was found that both the hydrophobic paints could reduce effectively tritium permeation during 50 days exposure of tritiated water vapor. The effect of tritium reduction of the epoxy paint was higher than that of silicon while the amount of tritium trapped in the epoxy paint was larger than that of silicon due to difference of the structure. Based on an analysis of a diffusion model, the rate-determining step of tritium migration through cement paste coated with the paints is diffusion through the paints respectively. It was found that tritium was easy to penetrate through silicon because there were many pores or voids in the silicon comparatively. In the case of tritium released from the epoxy paint, it is considered that tritium diffusion in epoxy is slow due to retardation by isotope exchange reaction to water included in epoxy paint.     

Optical and electroluminescent properties of samarium complex-based organic light-emitting diodes

The optical and electroluminescent (EL) properties of newly synthesized tris(hexafluoroacethylacetonato)(phenanthroline)samarium(III)mono-methanol [Sm(hfa)₃(phen)₂MeOH]-based organic light-emitting diodes (OLEDs) were investigated. The as-prepared photoluminescence (PL) spectrum of Sm(hfa)₃(phen)₂MeOH-doped PMMA film exhibits the peaks at the wavelength around 564, 598, 645 and 710 nm which correspond to the ⁴G_5/2 → ⁷H5_/2, ⁴G_7/2 → ⁷H_7/2, ⁴G_5/2 → ⁷H_9/2 and ⁴G_5/2 → ⁷H_11/2 transitions of the Sm³⁺ ion, respectively. The best organic light-emitting device performance is obtained for a device using 8 wt.% Sm(hfa)₃(phen)₂MeOH and 40 wt.% 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4,-oxadiazole doped in poly(N-vinylcarbazole) as a emitting layer. The optimal device exhibits maximum luminance of 135 candela (cd)/m² at the current density of 0.16 A/cm², with current efficiency of 0.1 cd/A at the current density of 0.08 A/cm². The EL spectrum from optimal device has the Commission Internationale De L'Eclairage (CIE) coordinate of (0.60, 0.36).