Diametral strain of fast reactor MOX fuel pins with austenitic stainless steel cladding irradiated to high burnup

The C3M irradiation test, which was conducted in the experimental fast reactor, “Joyo”, demonstrated that mixed oxide (MOX) fuel pins with austenitic steel cladding could attain a peak pellet burnup of about 130 GWd/t safely. The test fuel assembly consisted of 61 fuel pins, whose design specifications were similar to those of driver fuel pins of a prototype fast breeder reactor, “Monju”. The irradiated fuel pins exhibited diametral strain due to cladding void swelling and irradiation creep. The cladding irradiation creep strain were due to the pellet-cladding mechanical interaction (PCMI) as well as the internal gas pressure. From the fuel pin ceramographs and ¹³⁷Cs gamma scanning, it was found that the PCMI was associated with the pellet swelling which was enhanced by the rim structure formation or by cesium uranate formation. The PCMI due to cesium uranate, which occurred near the top of the MOX fuel column, significantly affected cladding hoop stress and thermal creep, and the latter effect tended to increase the cumulative damage fraction (CDF) of the cladding though the CDF indicated that the cladding still had some margin to failure due to the creep damage.     

Rice sodium-insensitive potassium transporter, OsHAK5, confers increased salt tolerance in tobacco BY2 cells

Potassium ion (K(+)) plays vital roles in many aspects of cellular homeostasis including competing with sodium ion (Na(+)) during potassium starvation and salt stress. Therefore, one way to engineer plant cells with improved salt tolerance is to enhance K(+) uptake activity of the cells, while keeping Na(+) out during salt stress. Here, in search for Na(+)-insensitive K(+) transporter for this purpose, bacterial expression system was used to characterize two K(+) transporters, OsHAK2 and OsHAK5, isolated from rice (Oryza sativa cv. Nipponbare). The two OsHAK transporters are members of a KT/HAK/KUP transporter family, which is one of the major K(+) transporter families in bacteria, fungi and plants. When expressed in an Escherichia coli K(+) transport mutant strain LB2003, both OsHAK transporters rescued the growth defect in K(+)-limiting conditions by significantly increasing the K(+) content of the cells. Under the condition with a large amount of extracellular Na(+), we found that OsHAK5 functions as a Na(+)-insensitive K(+) transporter, while OsHAK2 is sensitive to extracellular Na(+) and exhibits higher Na(+) over K(+) transport activities. Moreover, constitutive expression of OsHAK5 in cultured-tobacco BY2 (Nicotiana tabacum cv. Bright Yellow 2) cells enhanced the accumulation of K(+) but not Na(+) in the cells during salt stress and conferred increased salt tolerance to the cells. Transient expression experiment indicated that OsHAK5 is localized to the plant plasma membrane. These results suggest that the plasma-membrane localized Na(+) insensitive K(+) transporters, similar to OsHAK5 identified here, could be used as a tool to enhance salt tolerance in plant cells.     

Molecular Stacking Induced by Intermolecular C–H···N Hydrogen Bonds Leading to High Carrier Mobility in Vacuum‐Deposited Organic Films

Simple bottom‐up fabrication processes for molecular self‐assembly have been developed for the construction of higher‐order structures using organic materials, and have contributed to maximization of the potential of organic materials in chemical and bioengineering. However, their application to organic thin‐film devices such as organic light‐emitting diodes have not been widely considered because simple fabrication of a solid film containing an internal self‐assembly structure has been regarded as difficult. Here it is shown that the intermolecular C–H···N hydrogen bonds can be simply formed even in vacuum‐deposited organic films having flat interfaces. By designing the molecules containing pyridine rings properly for the intermolecular interaction, one can control the molecular stacking induced by the intermolecular hydrogen bonds. It is also demonstrated that the molecular stacking contributes to the high carrier mobility of the film. These findings provide new guidelines to improve the performance of organic optoelectronic devices and open up the possibilities for further development of organic devices with higher‐order structures.     

Synthesis of esters by immobilized-lipase-catalyzed condensation reaction of sugars and fatty acids in water-miscible organic solvent

A lipase-catalyzed condensation reaction in an organic solvent is a promising means of synthesizing esters. Reaction equilibrium constant, which is usually defined on the basis of reactant concentration, is an important parameter for estimating equilibrium yield. It is shown that the constant is markedly, affected by some factors, such as the hydration of a sugar substrate and the interaction of a reactant with a solvent. To reasonably design the reaction system or determine the reaction conditions, attention should be paid to these factors. From the viewpoint of kinetics, substrate selectivity for carboxylic acids also numerically correlates to the electrical and steric properties of these acids. Reactor systems for continuously producing esters through an immobilized-lipase-catalyzed condensation reaction are developed.     

Friction Properties of Medical Metallic Alloys on Soft Tissue–Mimicking Poly(Vinyl Alcohol) Hydrogel Biomodel

In order to investigate the tribological behavior of medical devices in contact with tissue, friction tests for four kinds of medical metallic alloys (316L stainless steel, CoCr, NiTi and TiMoSn) on soft tissue–mimicking poly(vinyl alcohol) hydrogel (PVA-H) biomodel were carried out at low normal load. XPS analysis and wettability tests for them were prepared to understand the difference in friction. According to the surface oxide compositions, these alloys can be divided into two groups: “Fe/Cr-oxide-surface alloys” for 316L and CoCr, and “Ti-oxide-surface alloys” for NiTi and TiMoSn. From the wettability test, Fe/Cr-oxide-surface alloys show lower polar components of surface free energy than Ti-oxide-surface alloys. Fe/Cr-oxide-surface alloys show higher friction coefficients in the elastic friction domain than those of Ti-oxide-surface alloys, while there was no significant difference in the hydrodynamic lubrication. Since elastic friction is governed by the adsorption of hydrogel polymer on counterbody, the surface characteristic of alloys plays an important role in friction. A tentative explanation for this tendency is expressed by linking two different theories describing the adsorption force of hydrogel and wettability of countermaterial.     

Fate of perfluorooctanesulfonate and perfluorooctanoate in drinking water treatment processes

Perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) have been recognized as global environmental pollutants. Although PFOS and PFOA have been detected in tap water from Japan and several other countries, very few studies have examined the fate, especially removal, of perfluorinated compounds (PFCs) in drinking water treatment processes. In this study, we analyzed PFOS and PFOA at every stages of drinking water treatment processes in several water purification plants that employ advanced water treatment technologies. PFOS and PFOA concentrations did not vary considerably in raw water, sand filtered water, settled water, and ozonated water. Sand filtration and ozonation did not have an effect on the removal of PFOS and PFOA in drinking water. PFOS and PFOA were removed effectively by activated carbon that had been used for less than one year. However, activated carbon that had been used for a longer period of time (>1 year) was not effective in removing PFOS and PFOA from water. Variations in the removal ratios of PFOS and PFOA by activated carbon were found between summer and winter months.     

Exposure to polycyclic aromatic hydrocarbons, arsenic and environmental tobacco smoke, nutrient intake, and oxidative stress in Japanese preschool children

The association between oxidative stress and exposure to environmental chemicals was assessed in a group of Japanese preschool children. The concentrations of 8-hydroxy-2′-deoxyguanosine (8-OHdG), 1-hydroxypyrene (1-OHP), inorganic arsenic (iAs) and monomethylarsonic acid (MMA), and cotinine in spot urine samples, collected from 134 children (3-6 yrs) from a kindergarten in Kanagawa, Japan, were measured as biomarkers of oxidative stress or exposure to environmental chemicals. For 76 subjects of the 134, intakes of anti-oxidant nutrients (vitamins A, C, and E, manganese, copper, zinc and selenium (Se)) were estimated from a food consumption survey carried out 2-4 weeks after urine sampling and by urine analysis (Se). The median (min-max) creatinine-corrected concentrations of urinary biomarkers were 4.45 (1.98-12.3), 0.127 (0.04-2.41), 4.78 (1.18-12.7), and 0.62 (< 0.6-19.0) μg/g cre for 8-OHdG, 1-OHP, iAs + MMA, and cotinine, respectively. Multiple regression analysis was carried out using 8-OHdG concentration as a dependent variable and urinary biomarkers of exposure and Se intake, intakes of vitamins and biological attributes of the subjects as independent variables. To explain 8-OHdG concentrations, intake of vitamin A and age were significant variables with negative coefficients, while 1-OHP concentration had a positive coefficient. These results indicated that oxidative stress of children is affected by chemical exposure at environmental levels, by nutrient intake and by physiological factors in a complex manner. On the other hand, unstable statistical results due to sub-grouping of subject, based on the availability of food consumption data, were found: the present results should further be validated by future studies with suitable research design.     

Dispersion of multi-walled carbon nanotube using soluble polysilsesquioxane containing alkylammonium side chains and triiodide counterions

In this study, we found that 1-pentanol dispersion of multi-walled carbon nanotube (MWCNT) was obtained when ultrasonication of MWCNT was performed in 1-pentanol solution of ammonium group-containing polysilsesquioxane with triiodide anions (PSQ-I₃). Dispersibility of MWCNT in 1-pentanol was first investigated by the presence of absorption at 750 nm in UV–Vis measurements. In addition, the number-average particle size estimated by dynamic light scattering measurement of 1-pentanol dispersion of MWCNT/PSQ-I₃ was assessed to be 120.3 ± 34.8 nm. The dispersion passed through a membrane filter with ca. 7 μm pores, indicating that large MWCNT aggregates in micrometer scale did not exist in 1-pentanol. Furthermore, the transmission electron microscopy image of the sample obtained by drying 1-pentanol dispersion of MWCNT/PSQ-I₃ showed many lines with ca. 10 nm diameter derived from MWCNT, indicating that MWCNTs were individually dispersed in PSQ matrix.