A Water‐Soluble Mechanochromic Luminescent Pyrene Derivative Exhibiting Recovery of the Initial Photoluminescence Color in a High‐Humidity Environment

Switching of the luminescence properties of molecular materials in response to mechanical stimulation is of fundamental interest and also has a range of potential applications. Herein, a water‐soluble mechanochromic luminescent pyrene derivative having two hydrophilic dendrons is reported. This pyrene derivative is the first example of a mechanochromic luminescent organic compound that responds to relative humidity. Mechanical stimulation (grinding) of this pyrene derivative in the solid state results in a change of the photoluminescence from yellow to green. Subsequent exposure to water vapor induces recovery of the initial yellow photoluminescence. The color change is reversible through at least ten cycles. It is also demonstrated that this compound can be applied as a mechano‐sensing material in frictional wear testing for grease, owing to its immiscibility in non‐polar solvents and its non‐crystalline behavior. Transmission electron microscope and atomic force microscope observations of samples prepared from dilute aqueous solutions of the pyrene derivative on suitable substrates, together with dynamic light scattering measurements for the compound in aqueous solution, indicate that this amphiphilic dumbbell‐shaped molecule forms micelles in water.     

A study on physical and mechanical properties for soft to firm clays in Yangon area – Properties of clays deposit at the sedimentary basins in Myanmar

Recently, a great deal of foreign investment has been entered into construction of the social infrastructure of Myanmar. Many construction projects are therefore on-going, and these are especially planned in the Yangon area. While these construction booms are increasing, existing studies on the geotechnical problems in the Yangon area such as problematic soils like soft clays are limited at present. Information on soil properties has also not been shared and has been confined to individual projects. In this paper, the boring and laboratory tests carried out in the Yangon area are selected and focused upon among the tests carried out in Myanmar. Laboratory test results for clay deposits in the Yangon area are analyzed and the differences in soil properties between different sedimentary basins and sub-areas divided by the Tertiary sediment ridge that runs from north to south at the center of Yangon are clarified together with a comparison to the clays found in other countries, which have been previously investigated.     

A TEM study on melt-crystallized poly(butylene terephthalate)

A study was made to investigate an optimum condition for ruthenium tetraoxide staining of poly(butylene terephthalate) (PBT) with glass transition temperature as low as ca. 23 degrees C for TEM observation of melt-grown PBT crystals. The morphological study of ultrathin sections prepared based on optimum staining at 25 degrees C for 8 h revealed formation of fringed-micellar crystal nuclei in the early stage and folded-chain fringed-micellar crystals in the later stage of isothermal crystallization at 40 degrees C from melt. The fraction of chain-folded crystals increased with increasing crystallization temperature from the quantitative analysis of crystal thickness in comparison with the reported morphology using the replica method.     

Pore structure of porous ceramics synthesized from water-based slurry by freeze-dry process

A unique porous ceramic with complex pore structure was synthesized by the freeze-dry process. A water-based ceramic slurry was frozen while controlling the growth direction of ice, and sublimation of the ice were generated by drying it at a reduced pressure. By sintering this green body, a porous ceramic with complex pore structure was obtained, where macroscopically aligned open pores exceeding 10 m in size contained minute pores of about 0.1 m in their internal walls. Wide control of the porosity was possible by changing the concentration of the starting slurry. The pore size distribution as well as the microstructure were substantially affected by the freezing and sintering temperatures. Optimization of the synthesis conditions was investigated in order to obtain the desired pore structure.     

Microelectrode-based hydrogen peroxide detection during oxygen reduction at Pt disk electrode

We investigated the diffusion process of H₂O₂ generated during O₂ reduction at a Pt microdisk electrode used as a generator for scanning electrochemical microscopy (SECM). First, the amount of O₂ consumption and generated H₂O₂ at the Pt generator electrode are estimated using a detector electrode installed in the SECM. Based on the results, a large amount of O₂ consumption and generated H₂O₂ are detected at the center of each generator electrode. According to the measurement, the O₂ starvation and H₂O₂ detection currents can be defined. Subsequently, the O₂ starvation and H₂O₂ detection currents are measured by varying the generator size. As a result, these currents decrease with a decrease in the generator electrode size, however, the H₂O₂ diffusion process is changed for the generator diameter of less than 50 μm. Finally, the O₂ starvation and H₂O₂ detection measurements were conducted using a Nafion-coated Pt microdisk electrode. The amount of O₂ consumption is not suppressed, while the amount of generated H₂O₂ decreases with the Nafion layer prepared on the Pt electrode. This result indicates that the thickness of the H₂O₂ diffusion layer in the H₂SO₄ solution is dramatically diminished by coating the Nafion layer on the Pt generator.     

Estimation of concentrations of antifungal agents allowed as food additives in foods and their daily intake based on official inspection results in Japan in fiscal year 1998

The mean concentrations and daily intake of four antifungal agents were estimated based on the results of an analysis of 7,005 samples of food obtained in official inspections by Japanese local governments in fiscal year 1998. The mean concentration of diphenyl was 0.0004% of the allowable limit, and those of imazalil, o-phenylphenol, and thiabendazole were 14.0%, 3.5%, and 5.7%, respectively. The daily intakes of these antifungal agents per person, estimated from their concentrations and the daily consumption of the foods, were 0.000326, 1.89, 11.5, and 23.3 micrograms, respectively, and assuming a body weight of 50 kg, the amounts of these antifungal agents consumed were 0.000013%, 0.15%, 0.12%, and 0.47% of the acceptable daily intake, respectively. These values are similar to the values obtained on the basis of the results of the official inspection in fiscal years 1994 and 1996, except that the amount of diphenyl is much lower (1/100).     

A new concept for the nuclear fuel recycle system: Application of the fluoride volatility reprocessing

Hybrid Recycle System (HRS) is proposed as an advanced recycle system. The HRS consists of improved fluoride volatility reprocessing and vibration packing MOX fuel fabrication processing. For the former, a part of U is volatilized as hexafluoride with diluted F₂ gas, and then residual U and Pu are volatilized with concentrated F₂ gas. Plutonium content of the mixed fluoride gas can be adjusted as desired by controlling the U fluorination reaction in the first step. The U is highly decontaminated and the mixture gas of UF₆ and PuF₆ is not purified. The fluoride mixture is reacted with H₂O and H₂ and directly converted to the mixed oxide grain for the vibration packing. The HRS can reduce the costs of reprocessing and fuel fabrication, the amounts of radioactive wastes and the probability of Pu proliferation.     

Effects of Polymer Decomposition Behavior on Thermal Debinding Process in Metal Injection Molding

The thermal degradation mechanism of several polymers was studied for the metal injection molding (MIM) process. The depolymerization type polymers (polybutyl-methacrylate (PBMA) and polyacetal (POM)) had fast thermal degradation speed. On the other hand, the thermal degradation of the random type polymers (polypropylene (PP) and ethylene-vinyl acetate (EVA)) was influenced by the type of debinding atmosphere (air and nitrogen). In the thermal debinding process, it was clear that the thermal degradation speed of the feedstocks that contained more than 35.3 vol.% of depolymerization type polymers was faster than that of the feedstocks which contained more than 8.5 vol.% of random type polymers. For the feedstocks that contained more than 35.3 vol.% of POM and PBMA, the sintered test pieces had less than 30 ppm of carbon and the sintering relative density of the sintered parts was in the range of 95.5 to 96.5%. The debinding ratio of the test pieces decreased with an increase in the PP content. However, the thermal degradation gases of POM and PBMA (without any PP) caused some cracks and holes when a heating rate greater than 30°C hr^-1 was used to heat the specimen to the 270-300°C temperature range.