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Journal Articles

Efficiency improvement of contamination screening site layout for nuclear disaster using traffic simulation

Saito, Shota; Kimura, Masanori; Hiraoka, Hirokazu

Kotsu Kogaku Kenkyu Happyokai Koenshu, 45, p.844 - 849, 2025/00

no abstracts in English

Journal Articles

Phase-field mobility for crystal growth rates in undercooled silicates, SiO$$_2$$ and GeO$$_2$$ liquids

Kawaguchi, Munemichi; Uno, Masayoshi*

Journal of Crystal Growth, 585, p.126590_1 - 126590_7, 2022/05

Phase-field mobility, $$L$$, and crystal growth rates in crystallization of 11 oxides or mixed oxides in undercooled silicates, SiO$$_2$$ and GeO$$_2$$ liquids were calculated with a simple phase-field model (PFM), and material dependence of the $$L$$ was discussed. Ratios between experimental crystal growth rates and the PFM simulation with $$L=1$$ were confirmed to be proportional to a power of $$frac{TDelta T}{eta}$$ on the solid/liquid interface process during the crystal growth in a log-log plot. We determined that parameters, $$A$$ and $$B$$, of the $$L=A(frac{k_{B}TDelta T}{6pi^{2}lambda^{3}eta T_{m} })^{B}$$ were $$A=6.7times 10^{-6}$$ to $$2.6$$m$$^4$$J$$^{-1}$$s$$^{-1}$$ and $$B=0.65$$ to $$1.3$$, which were unique for the materials. It was confirmed that our PFM simulation with the determined $$L$$ reproduced quantitively the experimental crystal growth rates. The $$A$$ has a proportional relationship with the diffusion coefficient of a cation molar mass average per unit an oxygen molar mass at $$T_{m}$$ in a log-log graph. The $$B$$ depends on the sum of the cation molar mass per the oxygen molar mass, $$frac{Sigma_{i}M_{i}}{M_{O}}$$, in a compound. In $$frac{Sigma_{i}M_{i}}{M_{O}}leq 25$$, the $$B$$ decreases with the cation molar mass increasing. The assumed cause is that the B represents the degree of the temperature dependence of the $$L$$. Since the cation molar mass is proportional to an inertial resistance of the cation transfer, the $$B$$ decreases with inverse of the cation molar mass. In crystallization of the silicates of heavy cation in $$frac{Sigma_{i}M_{i}}{M_{O}}geq 25$$, the $$B$$ saturates at approximately 0.67, which leads to $$T_{p}approx 0.9T_{m}$$.

Journal Articles

Phase-field model for crystallization in alkali disilicate glasses; Li$$_2$$O-2SiO$$_2$$, Na$$_2$$O-2SiO$$_2$$ and K$$_2$$O-2SiO$$_2$$

Kawaguchi, Munemichi; Uno, Masayoshi*

Journal of the Ceramic Society of Japan, 128(10), p.832 - 838, 2020/10

 Times Cited Count:5 Percentile:18.31(Materials Science, Ceramics)

This study developed phase-field method (PFM) technique in oxide melt system by using a new mobility coefficient ($$L$$). The crystal growth rates ($$v_0$$) obtained by the PFM calculation with the constant $$L$$ were comparable to the thermodynamic driving force in normal growth model. The temperature dependence of the $$L$$ was determined from the experimental crystal growth rates and the $$v_0$$. Using the determined $$L$$, the crystal growth rates ($$v$$) in alkali disilicate glasses, Li$$_2$$O-2SiO$$_2$$, Na$$_2$$O-2SiO$$_2$$ and K$$_2$$O-2SiO$$_2$$ were simulated. The temperature dependence of the $$v$$ was qualitatively and quantitatively so similar that the PFM calculation results demonstrated the validity of the $$L$$. Especially, the $$v$$ obtained by the PFM calculation appeared the rapid increase just below the thermodynamic melting point ($$T_{rm m}$$) and the steep peak at around $$T_{rm m}$$-100 K. Additionally, as the temperature decreased, the $$v$$ apparently approached zero ms$$^-1$$, which is limited by the $$L$$ representing the interface jump process. Furthermore, we implemented the PFM calculation for the variation of the parameter $$B$$ in the $$L$$. As the $$B$$ increased from zero to two, the peak of the $$v$$ became steeper and the peak temperature of the $$v$$ shifted to the high temperature side. The parameters $$A$$ and $$B$$ in the $$L$$ increased exponentially and decreased linearly as the atomic number of the alkali metal increased due to the ionic potential, respectively. This calculation revealed that the $$A$$ and $$B$$ in the $$L$$ were close and reasonable for each other.

Journal Articles

${it In-situ}$ investigation of radioactive Cs mobility around litter zone in contaminated forest using spent mushroom substrata

Onuki, Toshihiko*; Sakamoto, Fuminori; Kozai, Naofumi; Yamasaki, Shinya*; Sasaki, Yoshito; Niizato, Tadafumi

Journal of Nuclear Science and Technology, 56(9-10), p.814 - 821, 2019/09

 Times Cited Count:3 Percentile:22.68(Nuclear Science & Technology)

We used the spent mushroom substrata (SMSs) which are a kind of by-product after growing edible mushrooms for the ${it in-situ}$ investigation of radioactive Cs mobility in litter zone in a forest of Fukushima prefecture, Japan. The powder SMS was filled in a plastic net bag of 0.35$$times$$0.55 m, then was placed in a forest for $$sim$$6 months under three kinds of different conditions without treatment (No treatment), covered with wooden box (With box), and with zeolite placed on upper position of ground surface (With zeolite). We determined the ratio of radioactivity (TF) in the SMS to that of the soil and litter beneath the SMS bags. TFs of "No treatment" and of "With zeolite" were determined between $$sim$$0.01 and $$sim$$0.05 for 6 months. On the other hand, TFs of "With box" were lower by one order at 2 and 4 months than those of "No treatment" and of "With zeolite", and nearly the same values as TFs of "No treatment" and "With zeolite" at 6 months. These results clearly indicate that radioactive Cs accumulates in SMS mainly by throughfall. In addition, for a period of several months, fungi contribute to the accumulation of radioactive Cs in the litter zone, even though radioactive Cs was tightly associated with the soil.

Journal Articles

Design of play specific to the saddle type interface and its implementation

Yokota, Sho*; Chugo, Daisuke*; Hashimoto, Hiroshi*; Kawabata, Kuniaki

Proceedings of 25th IEEE International Symposium on Robot and Human Interactive Communication, p.910 - 911, 2016/08

The purpose of this paper is to experimentally investigate specific ranges of play (software backlash, deadzone) on the saddle type interface for the personal mobility (PM), and to implement them into the control scheme.

Journal Articles

Performance of $$gamma$$ lrradiated p-channel 6H-SiC MOSFETs; High total dose

Lee, K. K.; Oshima, Takeshi; Ito, Hisayoshi

IEEE Transactions on Nuclear Science, 50(1), p.194 - 200, 2003/02

 Times Cited Count:33 Percentile:86.99(Engineering, Electrical & Electronic)

p-channel SiC MOSFETs were fabricated on n-type 6H-SiC epitaxial layer. The effects of $$gamma$$-ray irradiation on the charecteristics of the MOSFETs were studied. Threshold voltage shifts to negative voltage side and the channel mobility reduces due to irradiation. Although the degradation of the channel mobility of the p-channel SiC MOSFETs is 10 times faster than n-channel SiC MOSFETs, p-channel SiC MOSFETs show 100 times stronger radiation resistance than Si MOSFETs. The values of interface traps and oxide-trapped-charge generated sue to irradiation were estimated from the subthreshold characteristics. As the result,it is concluded that the decrease in channel mobility can be explained by the generation of interface traps.

Journal Articles

Conversion of hydrophilic surface of poly(ethylene terephthalate) film surface to hydrophobic one under hydrophilic condition

Suzuki, Yasuyuki*; Li, J.; Maekawa, Yasunari; Yoshida, Masaru; Maeyama, Katsuya*; Yonezawa, Noriyuki*

Nihon Kagakkai-Shi, 2002(2), p.255 - 259, 2002/02

The hydrophilic surface of poly(ethylene terephthalate) (PET) film, obtained by partial hydrolysis, was converted to hydrophobic one under dry air, saturated water vapor atmosphere, nitrogen, and vacuum at temperatures ranging from 0 to 80$$^{circ}$$C. The hydrophilicity of the surface increased significantly faster under the saturated water vapor although it was the most hydrophilic in the examined conditions. From the dependence of the absolute temperature on the rate of hydrophilicity change for each storage condition, a discontinuous point at ca. 50$$^{circ}$$C was observable only under the water vapor condition. This relation indicates that the appreciable acceleration of the hydrophilicity change on the surface under the hydrophilic condition might be resulted from the increase of the surface mobility due to the water adsorption on the PET surface.

Journal Articles

A Model of ions interacting with neutrals in high electric field and the application to presheath formations

Senda, Ikuo*

Physics of Plasmas, 4(5), p.1308 - 1315, 1997/05

 Times Cited Count:1 Percentile:4.08(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Effect of molecular mobility on the reaction of free radicals with oxygen in irradiated polytetrafluoroethylene as studied by ESR

Seguchi, Tadao; Hayakawa, Naohiro;

Reports on Progress in Polymer Physics in Japan, 18, p.493 - 496, 1975/00

no abstracts in English

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