Browsing by Author "Minami, M"

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    Clustering of charged colloidal particles in the microgravity environment of space
    (Springer Nature, 2023-04-29) Miki,.H.; Ishigami, T; Yamanaka, J; Okuzono, T; Toyotama, A; Mata, JP; Komazawa, H; Takeda, Y; Minami, M; Fujita, M; Doi, M; Higuchi, T; Takase, H; Adachi, S; Sakashita, T; Shimaoka, T; Nagai, M; Watanabe, Y; Fukuyama, S
    We conducted a charge–charge clustering experiment of positively and negatively charged colloidal particles in aqueous media under a microgravity environment at the International Space Station. A special setup was used to mix the colloid particles in microgravity and then these structures were immobilized in gel cured using ultraviolet (UV) light. The samples returned to the ground were observed by optical microscopy. The space sample of polystyrene particles with a specific gravity ρ (=1.05) close to the medium had an average association number of ~50% larger than the ground control and better structural symmetry. The effect of electrostatic interactions on the clustering was also confirmed for titania particles (ρ ~ 3), whose association structures were only possible in the microgravity environment without any sedimentation they generally suffer on the ground. This study suggests that even slight sedimentation and convection on the ground significantly affect the structure formation of colloids. Knowledge from this study will help us to develop a model which will be used to design photonic materials and better drugs. © 2023 The Authors, Open Access under a Creative Commons Attribution 4.0 International License. Published in cooperation with the Biodesign Institute at Arizona State University, with the support of NASA.
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    A first step toward small-mass AMS radiocarbon analysis at Nagoya University
    (GNS Science, 2010-03-22) Minami, M; Miyata, Y; Nakamura, T; Hua, Q
    We have started to establish a small-mass sample preparation system at Nagoya University. In the first step, NIST Ox-II standard samples <0.5 mgC, graphitized using our regular sample preparation protocol, were measured for 14C. The 14C/12C ratios of these small-mass samples were affected by the decrease in beam current intensity and incomplete graphitization especially for samples <0.3 mgC. In the second step, we have designed a compact graphitization system suitable for small-mass samples and compared its performance to that of our regular graphitization system. During the graphitization reaction following our regular protocol, by-product water vapor was incompletely trapped, which resulted in low graphite yield or no graphitization for samples of <0.5 mgC. Meanwhile graphite was successfully produced for samples of 0.2mgC using the new reactor. The SEM images of small-samples using the new reactor show spotted graphite covering the spherical iron particles. No or very little graphite was observed for the samples graphitized using our regular graphitization system. During the graphitization reaction using the sealed tube method, water vapor was incompletely trapped, which resulted in low graphite yield especially for samples of <0.5 mgC. Meanwhile graphite was successfully produced for samples of 0.2mgC using the new reactor. The cold trap at −80°C employed in the new graphitization system was effective in trapping water for small-mass samples. The combination of lower temperature for trapping water and a reduction in reactor volume delivered higher graphitization efficiency for small samples. We are now ready for 14C analysis of samples of around 0.2mgC. We also report an example of stepwise combustion of samples containing sulfur in a closed tube to produce graphite successfully. Copyright (c) 2010 AMS12
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    Small-mass AMS radiocarbon analysis at Nagoya University
    (Elsevier Science BV, 2013-01-01) Minami, M; Kato, T; Miyata, Y; Nakamura, T; Hua, Q
    As part of the ongoing development at the AMS facility of the Center for Chronological Research at Nagoya University to radiocarbon (C-14) analyze samples smaller than 0.5 mg carbon (mgC), a compact graphitization manifold has been built. Tests with various reference materials show it performs well for samples as small as 0.1 mgC. Preparation with this new system is compared with the performance of the older protocol for regular-sized samples. Furthermore, it is shown that the addition of Cu and Ag before and stepwise heating during sealed-tube combustion of samples with high S content improve the degree of conversion to CO2 without having to resort to special purification measures such as the use of Co3O4 + Ag reagent and an n-pentane/LN2 trap before graphitization. © 2013, Elsevier Ltd.