Composition distribution of ethylene or propylene–norbornene copolymers obtained with zirconocene catalysts

Copolymerization of ethylene or propylene and norbornene (NB) was carried out with stereospecific zirconocene catalysts rac‐ethylenebis(indenyl)zirconium dichloride, rac‐dimethylsilylenebis(indenyl)zirconium dichloride ( 2 ), rac‐dimethylsilylenebis(2‐methylindenyl)zirconium dichloride, and diphenylmethylene(cyclopentadienyl)(9‐fluorenyl)zirconium dichloride combined with cocatalysts at 40 °C. Temperature‐rising elution fractionation of the copolymers was carried out with cross‐fractionation chromatography with o‐dichlorobenzene as a solvent, and a broad distribution of the copolymer composition was detected. The fraction eluted at lower temperature contained higher NB. The effect of the polymerization time was examined in the ethylene–NB copolymerization with catalyst 2 , and the higher‐temperature elution fraction increased with increasing polymerization time. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 441–448, 2003     

Integrated Micro Flow Synthesis Based on Sequential Br–Li Exchange Reactions of p‐, m‐, and o‐Dibromobenzenes

A micro flow system consisting of micromixers and microtube reactors provides an effective method for the introduction of two electrophiles onto p‐, m‐, and o‐dibromobenzenes. The Br–Li exchange reaction of p‐dibromobenzene with nBuLi can be conducted by using the micro flow system at 20 °C, although much lower temperatures (p‐bromophenyllithium was allowed to react with an electrophile in the micro flow system at 20 °C. The p‐substituted bromobenzene thus obtained was subjected to a second Br–Li exchange reaction followed by reaction with a second electrophile at 20 °C in one flow. A similar transformation can be carried out with m‐dibromobenzene by using the micro flow system. However, the Br–Li exchange reaction of o‐dibromobenzene followed by reaction with an electrophile should be conducted at ?78 °C to avoid benzyne formation. The second Br–Li exchange reaction followed by reaction with an electrophile can be carried out at 0 °C. By using the present method, a variety of p‐, m‐, and o‐disubstituted benzenes were synthesized in one flow at much higher temperatures than are required for conventional batch reactions.     

Parallel computing of radiative transfer in relativistic jets using Monte Carlo method

We present numerical attempts of radiative transfer in a relativistic scattering flow that can produce gamma rays using a three-dimensional Monte Carlo code. We prepared an initial background flowfield obtained from hydrodynamical simulation of a relativistic jet in which Thomson scattering dominates compared to absorption, and solved the radiative transfer equation for the background evolved by a simple expansion model. Since a large number of sample particles is required for an accurate computation, we have parallelized the Monte Carlo code in order to obtain solutions in a practical computational time even for a long-term simulation coupled with a time-dependent flowfield. Using this code, higher parallel efficiency is achieved with larger number of particles. The obtained light curve from the simple model shows a signal of the transition from the opaque post-shock flow to the transparent regime as the flow expands, and the high-energy photons are generated by not only the Doppler boosting but also the inverse Compton scattering.     

Determination of tritium activity and chemical forms in the exhaust gas from a large fusion test device

A water bubbler system that can distinguish chemical forms of tritium was proposed for long-term tritium monitoring of the exhaust gas of a large fusion test device. The characteristics and performance of the water bubbler system were evaluated under operational conditions and confirmed to be suitable for tritium monitoring. For the tritium measurements, the water bubbler system determined the tritium activity and distinguished the chemical forms of tritium. The tritium activity and chemical forms in the exhaust gas provided helpful information to understand the tritium behavior in the large fusion test device.     

Effects of discharge mode and gas composition for plasma-hydrophilized titanium surface on hydrophilic sustainability

Plasma hydrophilization under various conditions was carried out on Ti substrates to investigate the effect of the applied parameters on the hydrophilic sustainability. The plasma was discharged from gases comprising Ar and/or O₂ at various ratios using DC and RF modes. Notable differences in the surface morphology by the plasma conditions was hardly found, while the ratio of hydroxide on the surface was influenced by the discharge mode. The hydrophilicity was significantly improved regardless of the treatment conditions, that is, the gas composition and discharge mode. The deterioration of the hydrophilicity was occurred by storing in the ambient atmosphere or distilled water, wherein the deterioration in distilled water was suppressed when using DC as a discharge mode. The hydrophilicity was preserved when the specimens was stored in a physiological solution such as phosphate buffered saline solution due to the adsorption of Na⁺ and Cl⁻ in the solution; its effect was far superior to that contributed by the parameter settings. In conclusion, plasma discharge mode enabled to improve the deterioration of hydrophilicity only slightly.     

XPS study of a laser-nitrided iron surface using a focused pulsed Nd:YAG laser under various conditions

Laser nitridation of a pure iron (Fe) surface was conducted using a focused pulsed Nd:YAG laser under a nitrogen atmosphere, and the effects of nitrogen gas pressure, laser power, and repetition number of laser shots on the surface characteristics were analyzed using XPS. The laser-irradiated surface consisted of the topmost surface layer of Fe oxynitride (FeO_xN_y) and the underlayer beneath, which mainly comprised Fe nitride (Fe₄N). The topmost surface layer is a post-formed layer due to the oxidation of the nitride layer. The thickness of the underlayer corresponding to the original nitride layer drastically increased under nitrogen gas at atmospheric pressure. Increasing the repetition number of laser shots enhanced layer thickness up to 5 shots, after which no change was observed. Moreover, the layer thickness increased monotonically with increasing laser power. Nitridation through pulsed laser irradiation was likely predominated by the melting and resolidification of a specific surface area, as well as the convection of nitrogen therein. Thickness variation under various conditions can be explained appropriately using this assumption.