Evaluation of Spaceborne SiC Mirror Materials Using Samples Cut from the Periphery of a Mirror Body

The Japan Aerospace Exploration Agency has studied large-scale, lightweight mirrors constructed of SiC-based materials as a key technology for future earth observations and astronomical missions. One of the most important technical issues for large-scale ceramic components is their quality stability (viz., differences in material properties depending on the part and the processing), which might influence the structural and/or thermal reliability through unforeseen deformation and breakage. In this study, the authors used a simple, low-cost method for evaluating the properties of SiC mirror materials. Using mechanical testing, thermodilatometry, and microstructural analysis on samples cut from the periphery of a prototype 800-mm-diameter mirror body, the overall quality of the mirror body material was determined.     

A magnetic MEMS actuator using a permanent magnet and magnetic fluid enclosed in a cavity sandwiched by polymer diaphragms

A magnetic microelectromechanical systems (MEMS) actuator using a small permanent neodymium-magnet surrounded by magnetic fluid (MF) was developed and characterized. The magnet is enclosed in a cavity sandwiched by two identical thin PET-sheet diaphragms and is able to move smoothly due to the MF. The diaphragms deflect when an external magnetic force is applied to the magnet. This structure was adopted to prevent the diaphragms from being stiffened by attaching or fabricating a magnetic layer on the diaphragm surface and to secure the necessary volume of magnetic material. The magnets are 2–4 mm in diameter and the cavity is 5 mm in diameter and 1 mm in depth. The diaphragms are 20 μm in thickness. Experiments showed the displacement amplitude generated at the diaphragm center was in the range of 10–50 μm for attractive and repulsive magnetic force when magnetic flux density of 4–30 mT was applied. The response was within about 1 s. The deflection profile of the diaphragms can also be varied by changing the magnet position.     

Subcriticality measurement using time-domain decomposition-based integral method for simultaneous reactivity and source changes

ABSTRACT

To estimate the subcriticality in dollar units for an arbitrary state-change, the time-domain decomposition-based integral method (TDDI) is proposed using the point kinetics theory based on the fundamental mode approximation. In a general transient subcritical system, reactivity, neutron source intensity, and point kinetics parameters can vary simultaneously. Furthermore, the state-change may not necessarily be a stepwise change. For such a transient, the TDDI method can estimate the subcriticality after the transient using only the time variation of the neutron count rate. Therefore, the proposed method is useful to approximately estimate the subcriticality in a system where a detailed core configuration is unknown. To investigate the applicability of the TDDI method, transient experiments with simultaneous reactivity and source changes or to two successive safety rods dropping were performed at the Kindai University Training and Research Reactor (UTR-KINKI). By comparing with reference values using excess reactivity and control rod worth, it was validated that the subcriticality values obtained by the TDDI method better agree with the reference values than the previous integral method.     

Biohydrogen production from sago starch in wastewater using an enriched thermophilic mixed culture from hot spring

We investigated the feasibility of producing biohydrogen from sago starch in wastewater using a thermophilic mixed culture enriched from a hot spring in southern Thailand (PGK). The effects of repeated batch cultivations, the dependence of the initial pH values ranging from 5.0 to 8.0 and the initial sago starch concentrations ranging from 2.5 to 60 g/l as well as the utilization of 4 different starch types (gelatinized dry starch, non-gelatinized dry starch, gelatinized wet starch, and non-gelatinized wet starch) were examined in batch experiments at 60 °C. Microbial community structures were also investigated. The methane-free biogas evolved contained up to 55% hydrogen, with the remainder comprising carbon dioxide. Repeated batch cultivation under identical conditions improved the hydrogen yield. Gelatinized dry starch at an initial pH of 6.5 and an initial starch concentration of 2.5 g/l gave the maximum hydrogen yield of 422 ml-H₂/g-starchadded (80% of the theoretical limit). PCR-DGGE profiles of 16S rRNA gene fragments from the cultures showed that the predominant hydrogen producers were closely related to thermophilic anaerobic bacteria, including Thermoanaerobacterium saccharolyticum, Thermoanaerobacterium thermosulfurigenes, and uncultured Thermoanaerobacterium sp., all of which probably produced hydrogen with simultaneous generation of ethanol. The thermophilic bacilli capable of utilizing starch, including Bacillus sp., Anoxybacillus sp., Bacillus lentus, and Geobacillus sp., were also found in the starch cultures, but mainly in the non-gelatinized wet starch culture.     

Energetic evaluation of possible insertion sites of Cu into BaSi2 using first principle calculations

Electronic energy calculations of Cu-doped BaSi₂, an expected solar-energy material, have been performed by a density-functional theory assuming several possible insertion sites of Cu into the BaSi₂ lattice. The 4c sites, which are surrounded by three Si atoms, one of which is at a peak of one Si-tetrahedron and other two of which are composing an edge of the other Si-tetrahedron, will be the most favorably inserted by Cu atoms. This insertion reaction is energetically more favorable than the substitution reactions of Ba or Si by Cu. Insertion of Cu into BaSi₂ will cause the n-type behavior of semiconducting BaSi₂. This prediction is consistent with the observed facts.     

Highly Thermally Stable Microstructure in Mg Fabricated Via Powder Rolling

The purpose of this article is to demonstrate a fascinating microstructure that ensures Mg has a high thermal stability. This is achieved by fabricating the Mg sample via powder rolling followed by powder metallurgy method. It is found that after Mg powders are pretreated for 15 rolling passes at room temperature and then consolidated by using spark plasma sintering, the Mg specimen exhibits a much finer grain structure. Such a grain structure then shows a super high thermal stability. Worthy of note is that many fractions of tensile twins were presented in the Mg specimen and survived a heat treatment at 500°C. After the heat treatment, the microhardness of the sample remained almost unchanged. The finding then gives rise to the possibility of using Mg as structural material at elevated temperatures.     

In vivo evaluation of Zr-based bulk metallic glass alloy intramedullary nails in rat femora

Zr-based bulk metallic glasses (BMG) show high corrosion resistance in vitro and higher strength and lower Young’s modulus than crystalline alloys with the similar composition. This study aimed to perform an in vivo evaluation of Zr₆₅Al_7.5Ni₁₀Cu_17.5 BMG. Osteotomy of the femur was done in rats and stabilized with intramedullary nails made of Zr₆₅Al_7.5Ni₁₀Cu_17.5 BMG, Ti–6Al–4V alloy, or 316L stainless steel. Systemic and local effects of each type of nail were evaluated by measuring the levels of Cu and Ni in the blood and the surrounding soft tissue. Changes of the surface of each nail were examined by scanning electron microscopy (SEM). Healing of the osteotomy was evaluated by peripheral quantitative computed tomography and mechanical testing. No increase of Cu and Ni levels was recognized. Surface of the BMG showed no noticeable change, while Ti–6Al–4V alloy showed Ca and P deposition and 316L stainless steel showed surface irregularities and pitting by SEM observation. The stress strain index, maximum torque, torsional stiffness, and energy absorption values were larger for the BMG than those for Ti–6Al–4V alloy, although there was no significant difference. The Zr-based BMG can promote osteotomy healing as fast as Ti–6Al–4V alloy, with the possible advantage of the Zr-based BMG that bone bonding is less likely, allowing easier nail removal compared with Ti–6Al–4V alloy. The Zr-based BMG is promising for the use in osteosynthetic devices that are eventually removed.     

Urinary alpha1-microglobulin, beta2-microglobulin, and retinol-binding protein levels in general populations in Japan with references to cadmium in urine, blood, and 24-hour food duplicates

Possible cadmium (Cd) exposure-associated changes in urinary levels of low-molecular-weight proteins were studied in nonsmoking and non-drinking female members of the general Japanese population (378 subjects with no known occupational heavy metal exposure) who lived at 19 study sites (all without any known environmental heavy metal pollution) in 13 prefectures throughout Japan. The external Cd dose was evaluated in terms of daily Cd intake via food (Cd-F), whereas Cd levels in blood (Cd-B) and urine (Cd-U) were taken as internal dose indicators. When the subjects were classified according to Cd-F into three groups with "low" (20.4 micrograms/day as a geometric mean of 97 women), "middle" (35.0 micrograms/day, 120 women) and "high" (67.0 micrograms/day, 66 women) exposure, both Cd-B and Cd-U increased in parallel with the changes in Cd-F. However, there were no dose-dependent changes in beta2-microglobulin or retinol-binding protein levels in urine, alpha1-microglobulin levels appeared to increase, but the distribution of the cases above the two cutoff levels of 9.6 and 15.8 micrograms/mg creatinine among the three Cd-F groups did not show any bias. Overall, it was concluded that there was no apparent Cd exposure-associated elevation in urinary low-molecular-weight protein levels in the study population.