A sintered lunar regolith is expected to be used to construct buildings, roads, and landing pads for spacecrafts on the Moon. Here, we demonstrate that focused microwave heating is effective for the ...rapid solidification of the lunar regolith simulant to obtain regolith gravel without any microwave susceptor. The conventional multimode microwave oven cannot heat lunar regolith simulants and requires microwave susceptors such as silicon carbide (SiC) and thermal insulators because of its low dielectric loss. We achieved rapid microwave heating of a lunar regolith simulant without using a susceptor or thermal insulator by forming an intense microwave electric field using a cavity resonator and a semiconductor microwave oscillator. Focused microwaves at 2.45 GHz produced the gravel-shaped and solidified lunar regolith at 300 °C lower temperature than a conventional electrical furnace, where more than 1050 °C temperature was required to sinter the lunar regolith simulant. In addition, we produced larger gravel of the lunar regolith simulant using 915 MHz. The intense electric field generated by the single-mode resonator promoted the solidification of the lunar regolith simulant without any additional substances. This process enables the local production of structured lunar regoliths on the Moon without the transport of any materials from the Earth.
This study provides the health effects assessment of rice cultivated from plasma-irradiated seeds. The rice (Oryza sativa L.) cultivated from seeds with plasma irradiation showed a growth improvement ...(slope-ratios of with plasma to without plasma were 1.066, 1.042, and 1.255 for tiller, and earing, and ripening periods, respectively) and an 4% increase in yield. The cultivated rice was used for repeated oral administrations to mice for 4-week period. Distilled water and rice cultivated from seeds without plasma irradiation were also used as control. The weights of the lung, kidney, liver, and spleen, with corresponding average values of 0.22 g, 0.72 g, 2.1 g, and 0.17 g for w/ plasma group and 0.22 g, 0.68 g, 2.16 g, and 0.14 g for w/o plasma group, respectively, showing no effect due to the administration of rice cultivated from plasma-irradiated seeds. Nutritional status, liver function, kidney function, and lipid, neutral fat profiles, and glucose metabolism have no significant difference between with and without plasma groups. These results show no obvious subacute effects were observed on rice grains cultivated and harvested from the mother plant that experienced growth improvement by plasma irradiation. This study provides a new finding that there is no apparent adverse health effect on the grains harvested from the plasma-irradiated seeds.
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Oxygen-deficient tungsten oxide is one of the promising materials for broad applications due to its enhanced characteristics owing to the oxygen-deficiency. Development of a mass ...production process is crucial in consideration of the increasing demand of this material in industrial purposes. A continuous screw reactor was employed to the production of oxygen-deficient tungsten oxide. The effects of hydrogen concentration and the reduction time on the composition of products were investigated. The maximum WO2.72 mole fraction of 0.95 was achieved by optimum hydrogen concentration and reduction time. X-ray Photoelectron Spectroscopy (XPS) spectra of the products indicated the introduction of oxygen-deficiency. Anisotropic crystal growth in the (010) direction is found in the cross-section observation by Scanning Electron Microscope (SEM). The displacing value from High-Resolution Transmission Electron Microscope (HR-TEM) demonstrated the existence of WO2.72. The reaction kinetic was investigated by thermogravimetric analysis. Estimated activation energy supported the results from the continuous process. This work suggests the promising process for the large-scale production of functional materials.
Although there have been some studies on safety culture, studies on specific methods to foster safety culture have been limited. Moreover, it is deemed necessary to assess and foster safety cultures ...not only for individual organizations but also inter-organizationally. In this study, we developed a program to foster safety culture. Thereafter, we applied the program to multi-tiered industrial organizations. Hence, this paper focuses on interorganizational approaches. The program consisted of multiple questionnaire surveys, interview surveys, group works, and monitoring surveys. The subjects of the surveys were members of energy plants. As a result, in general, improvements in the safety culture evaluation were seen after the implementation of countermeasures. In the program consisting of multiple surveys and activities, a certain effect of fostering safety culture in multi-tiered organizations was recognized. Henceforth, more studies will be required on the means of assessing and fostering safety cultures in multi-tiered industrial organizations of various types.
A continuous screw reactor for hydrogen reduction of lunar soil simulant was assembled. The water production rates were measured with different reduction conditions. Reduced simulants were analyzed ...by XRD (X-ray Diffraction), SEM (Scanning Electron Microscope), and EDS (Energy dispersive X-ray spectroscopy). The effect of reduction temperatures in the range of 1173-1373 K in 3 vol% hydrogen was clarified. The highest water production rate at the steady-state is obtained at 1273 K. The water production rate becomes higher with the higher reduction temperature up to 1273 K. It becomes lower at the temperature above 1273 K because Na-rich components in lunar simulant melt and it inhibits the hydrogen diffusion. The impact of hydrogen concentrations between 3-10 vol% was revealed with the fixed reduction temperature of 1273 K. The reaction rate has linear relationship to the hydrogen concentration. The reduced lunar simulant contain α-Fe, and the amount increases with higher hydrogen concentrations. The reduced ilmenite has porous structures due to the vacancy of oxygen. This work suggests the continuous hydrogen reduction system as a promising process to acquire oxygen on the moon.
The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018. We present Hayabusa2 observations of Ryugu's shape, mass, and geomorphology. Ryugu has an oblate ..."spinning top" shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu's shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge.
The μ10 gridded ion thruster, designed and developed at the Institute of Space and Astronautical Science, Japan, is used in the asteroid explorer Hayabusa2. In this propulsion system, the cathode is ...negatively biased with a power supply. The potential difference between the cathode and the system ground is regarded as an essential indicator of the cathode condition. In the operation of μ10 during the Hayabusa2 mission, it was found that the potential difference increased faster than that measured in a durability test on the ground. In this study, we performed a fault tree analysis of the on-orbit increase in the potential difference between the cathode and the system ground considering the total current balance (including electrons that flow back to the spacecraft). In addition, to understand the effect of the conductive surface around the thruster on the potential difference, we experimentally simulated the change in conductive area. It was found that the potential difference increased under a certain conductive surface condition. The results suggest that the on-orbit increase in the potential difference between the cathode and the system ground is caused by a loss of surface conductivity.
•Analysis on the cause of the increase in cathode voltage observed in the orbit.•A floating potential experiment simulating the loss conductivity around the thruster.•The voltage increases as the conductive surface area around the thruster decrease.•Conductive surface has position-dependent electron collection profile.•Control by the cathode bias power supply lowers the coupling voltage.
The angular and energy dependence of the sputtering yield of a carbon-carbon composite due to xenon ion bombardment was investigated. Instead of assuming surfaces to be flat, a simple carbon fiber ...distribution model was introduced to account for the carbon-carbon composite surface structure observed using a scanning electron microscope. Yamamura's semi-empirical sputtering formula, which accounted for 14% xenon adsorption, was used to calculate the sputtering yield of the carbon fiber surface. The proposed model provided fairly good estimates of the angular and energy dependence of the sputtering yield for the carbon-carbon composite. A comparative analysis of sputtering yield models demonstrated that the proposed model most accurately predicted both the accelerator and decelerator grid mass changes in the μ10 PM ion engine endurance test. In this paper, we present sputtering yield data over a range of xenon incidence energies from 0 to 2 keV and angles of incidence from 0 (normal incidence) to 90°.
In order to improve the thrust force of the μ 10 microwave discharge ion thruster, its ion source which is biased at a screen voltage is separated into three parts; 1.waveguide, magnet, and a grid ...holder, 2.magnet spacers, and 3.a screen grid by ceramic rings. Connection of a high voltage power supply is selectable among each component independently, and maximum beam currents are measured in all six cases in addition to the nominal setup. Except for one case, the maximum thrust force is increased from the HAYABUSA's 8mN and HAYABUSA2's 10mN. The highest thrust force 11.2mN is recorded at Isp 3150sec when the magnet spacers are not connected to the power supply. At this time, the potential of the isolated magnet spacers is increased from 1500V to 1525V. The increase of the potential of the spacers regulates collisions of ions, resulting in increase of the ion currents. This study firstly demonstrates the effect of the segmentation of the discharge chamber of microwave ion thrusters and achieves the improvement of 4% of the total efficiency and of 40% of the thrust force since the HAYABUSA's flight model.
Presented here are the observations and interpretations from a comprehensive analysis of 16 representative particles returned from the C-type asteroid Ryugu by the Hayabusa2 mission. On average Ryugu ...particles consist of 50% phyllosilicate matrix, 41% porosity and 9% minor phases, including organic matter. The abundances of 70 elements from the particles are in close agreement with those of CI chondrites. Bulk Ryugu particles show higher δ18O, Δ17O, and ε54Cr values than CI chondrites. As such, Ryugu sampled the most primitive and least-thermally processed protosolar nebula reservoirs. Such a finding is consistent with multi-scale H-C-N isotopic compositions that are compatible with an origin for Ryugu organic matter within both the protosolar nebula and the interstellar medium. The analytical data obtained here, suggests that complex soluble organic matter formed during aqueous alteration on the Ryugu progenitor planetesimal (several 10’s of km), <2.6 Myr after CAI formation. Subsequently, the Ryugu progenitor planetesimal was fragmented and evolved into the current asteroid Ryugu through sublimation.
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