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The optical transparency of silica glass significantly improves when subjected to compression at its melting temperature. Using a rare hydrostatic iso-pressure apparatus capable of reaching 0.98 GPa at 1800 °C with Ar gas as the pressure medium, we obtained centimeter-sized glass samples, allowing us to measure various properties. Both the density and refractive index increased with pressure, while the refractive index dispersion decreased monotonically. However, Rayleigh scattering intensity, and small ring structures show a minimum around 0.8 GPa. High-energy X-ray scattering analysis indicates that the short-range structure, around 4 Å, governs the monotonic trends in the averaged physical properties, such as density and refractive index. In contrast, non-monotonic changes are observed with the disappearance of intermediate-range order at around 8 Å. This simplification of structural ordering is crucial for achieving extreme transparency in silica glass. The effect of suppression of the 8 Å order is well explained by the predicted topological pruning phenomenon, where large voids and small unstable ring structures vanish, leading to the minimal light scattering under high pressure. Our experimental findings also reveal that the optimal pressure for achieving this transparency is much lower than previously predicted, which makes the process more feasible for mass-production applications. There is an urgent need to enhance silica glass transparency for optical fibers. This study achieves this by hot compression above the melting point. Measurements of density, refractive index, Rayleigh scattering, and ring structures reveal two pressure-dependent trends. High-energy X-ray scattering links these to structural changes at ~4 Å (short-range) and ~8 Å (intermediate-range). Notably, optimal enhancement occurs at pressures as low as 0.8 GPa, far below the 4 GPa predicted by molecular dynamics simulations, making the process practical for high-transparency silica glass fiber production. [ABSTRACT FROM AUTHOR]

An analytical technique to measure reactions in biological membranes was developed and applied to monitoring the hydrolysis reaction of phospholipids (dipalmitoylphosphatidylcholine, DPPC) by phospholipase [A.sub.2]. The technique uses the time-resolved quasi-elastic laser scattering (TR-QELS) method to measure an oil/phospholipid monolayer/water membrane system by monitoring the change of interfacial tension under a noncontact condition and in real time. When the TR-QELS method is used with the newly developed oil/phospholipid monolayer/water membrane system, measurement of the hydrolysis reaction of phospholipids with long alkyl chains (C [greater than or equal to] 16), which are the major components in biological membranes, becomes possible. The reaction progress is monitored by the increase of interfacial tension at the oil/water interface caused by the decrease of surface-active DPPC molecules due to the reaction. The characteristic phases, namely, lag, burst, and equilibrium, are observed. The relationship between the duration of the lag phase (the rate-limiting step of the reaction) and the concentration of calcium ion (an essential cofactor of the reaction) is also investigated. Increase of calcium ion concentration in the subphase is found to shorten the duration of the lag phase. In addition, the real-time measurement simplifies the estimation process for the reaction activation energy.

Research into the dynamic behaviour of the phase transfer catalyst, quaternary ammonium bromide R4N+Br- (R: n-C4H9, N-C3H7,C2H5), at a water/nitrobenzene interface is presented. The results reflected an interfacial specificity for a chemical reaction and mass transfer.

A levitation melting/thermoconductometric method for determination of nitrogen in steel has been developed, in which metal samples are melted in a state of floatation by magnetic pressure. The present method needs no crucible, so it is free from contamination from crucibles. Nitrogen extracted from a steel sample in a state of floatation was measured quantitatively with a thermal conductivity detector. About 5 min was required for nitrogen to be sufficiently extracted, versus only about 2 min for hydrogen. This difference was explained in terms of their diffusion velocities in molten iron. The calibration curve for nitrogen was linear to 156 [[micro]gram]/g, with a relative standard deviation of (6.5% at the 20 [[micro]gram]/g level. The present method was applied to determination of nitrogen in certified reference material JSS GS-5a, and the analytical result (17.5 [+ or -] 1.1 [[micro]gram]/g) was in good agreement with the certified value (17.0 [[micro]gram]/g).