To date, areas contaminated by radionuclides discharged from the Fukushima Dai-ichi nuclear power plant accident have been mapped in detail. However, size of the radionuclides and their mixing state with other aerosol components, which are critical in their removal from the atmosphere, have not yet been revealed. We measured activity size distributions of (134)Cs and (137)Cs in aerosols collected 47 days after the accident at Tsukuba, Japan, and found that the activity median aerodynamic diameters of (134)Cs and (137)Cs in the first sample (April 28-May 12) were 0.54 and 0.53 μm, respectively, and those in the second sample (May 12-26) were both 0.63 μm. The activity size distributions of these radiocesium were within the accumulation mode size range and almost overlapped with the mass size distribution of non-sea-salt sulfate aerosol. From the analysis of other aerosol components, we found that sulfate was the potential transport medium for these radionuclides, and resuspended soil particles that attached radionuclides were not the major airborne radioactive substances at the time of measurement. This explains the relatively similar activity sizes of radiocesium measured at various sites during the Chernobyl accident. Our results can serve as basic data for modeling the transport/deposition of radionuclides.

For the purpose of simulating the surface alteration process called "space weathering", experiments of pulse laser irradiation, proton implantation, and laser irradiation to proton implanted samples were performed and reflectance spectra of altered materials were measured. To simulate the impact heating by micrometeorite bombardments, we made a new apparatus using a pulse laser whose pulse duration is 6-8 nanoseconds, comparable with a timescale of micrometeorite impacts. We find that the degree of space weathering, i.e., change of reflectance spectrum should depend on mineral composition. Laser irradiation onto olivine produces the largest reduction of albedo and the highest reddening of reflectance spectrum. In general, variation of olivine spectra is much larger than that of pyroxenes. Depths of absorption bands do not change in the scaled spectra. The olivine spectrum after the laser irradiation can match spectra of some olivine asteroids within a subtype of S-type asteroids. Comparison of Vesta spectrum with altered pyroxene spectra suggests that Vesta surface would be relatively older than olivine asteroids. We also investigate the influence of solar wind proton and pyroxene FeO content. The proton implantation causes small changes in olivine and enstatite spectra. Implanted protons do not influence spectral change by the laser irradiation: the laser irradiation and the proton implantation do not produce multiplicative but additive changes on the reflectance spectra. FeO content of pyroxenes does not relate to the degree of reflectance change.

A theoretical and experimental study has been made on the transient characteristics of a centrifugal pump during its rapid acceleration from standstill to final speed. Instantaneous rotatinal speed, flow-rate, and total pressure rise are measured for various start-up schemes. Theoretical calculations for the prediction of transient characteristics are developed and compared with the corresponding experimental results. As the results of this study, it becomes clear that the impulsive pressure and the lag in circulation formation around impeller vanes play predominant roles for the difference between dynamic and quasi-steady characteristics of turbopump during its starting period.

Thin film formation using the process of spin coating is investigated. The liquid film and surrounding gas phase two-dimensional (2-D) full governing equations with applicable boundary conditions are formulated. The heat and mass transfer that occurs in the gas and liquid phase and across the free surface, including the evaporation of solvent, are taken into account. The governing equations and boundary conditions are then reduced to a I-D case based on the variables radial dependency. The detailed film formation process that commences at the start of the spinning and ends with the dry-up of the coated film is numerically simulated by utilizing the I-D governing equations. The complex effects of various process parameters, e.g., spinning speed, initial solute concentration, and disk heating, are clarified by the present numerical analysis. It was found that the final film thickness is mainly determined at the time when the film thinning rate resulting from radial convection has the same order as the film thinning rate resulting from solvent evaporation.

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