Measurements of thermal-neutron capture cross-section of Cesium-135 by applying mass spectrometry

ABSTRACT

The thermal-neutron capture cross-section (σ₀) and resonance integral (I₀) were measured for the ¹³⁵Cs(n,γ)¹³⁶Cs reaction by an activation method and mass spectrometry. Because of difficulty in the preparation of pure ¹³⁵Cs samples, we used ¹³⁵Cs contained as an impurity in a normally available ¹³⁷Cs standard solution. An isotope ratio of ¹³⁵Cs and ¹³⁷Cs in a standard ¹³⁷Cs solution was measured by mass spectrometry to quantify ¹³⁵Cs. Cesium-135 impurity along with the ¹³⁷Cs standard solution was irradiated at the hydraulic conveyer of the research reactor in the Institute for Integral Radiation and Nuclear Science, Kyoto University. Wires of Co/Al and Au/Al alloys were used as neutron monitors to measure thermal-neutron fluxes and epi-thermal Westcott’s indices at an irradiation position. A gadolinium filter was used to measure the σ₀, and a value of 0.133 eV was taken as the cut-off energy. Gamma-ray spectroscopy was used to measure induced activities of ¹³⁷Cs, ¹³⁶Cs and monitor wires. On the basis of Westcott’s convention, the σ₀ and I₀ values were derived as 8.57 ± 0.25 barn, and 45.3 ± 3.2 barn, respectively. The value of σ₀ obtained in the present study agreed within the limits of uncertainties with the past-reported value of 8.3 ± 0.3 barn.     

Molecular structures of traction fluids in relation to traction properties

In order to develop excellent traction fluids, guidelines for molecular design were studied through analyzing correlation between molecular structures and traction properties of traction fluids quantitatively. Some results among various simple compounds as model compounds of traction fluids and among various traction fluids were described in this article. This revised version was published online in June 2006 with corrections to the Cover Date.     

Electron cyclotron resonance plasma production by using pulse mode microwaves and dependences of ion beam current and plasma parameters on the pulse condition

We measure the ion beam current and the plasma parameters by using the pulse mode microwave operation in the first stage of a tandem type ECRIS. The time averaged extracted ion beam current in the pulse mode operation is larger than that of the cw mode operation with the same averaged microwave power. The electron density n(e) in the pulse mode is higher and the electron temperature T(e) is lower than those of the cw mode operation. These plasma parameters are considered to cause in the increase of the ion beam current and are suitable to produce molecular or cluster ions.     

Enhancement of methane production by Methanosarcina barkeri using Fe3O4 nanoparticles as iron sustained release agent

Anaerobic digestion has attracted attention because it does not require power for aeration, it reduces excess sludge and it generates methane gas. However, the growth rate of anaerobic microorganisms is slow, resulting in low treatment efficiency. In this study, the impact of Fe₃O₄ nanoparticles (NPs) on the growth of methanogens, which is the rate-determining step in anaerobic digestion, was investigated using a pure culture of Methanosarcina barkeri as the model methanogen. M. barkeri were cultivated in iron free medium, as well as in media amended with various concentrations of Fe₃O₄ NPs with a mean diameter of 8.1?±?2.4?nm. The production of methane gas was greatly increased when organisms were cultured in media containing NPs. After the methane production was saturated, methanol was newly added to the culture, which resulted in additional methane generation at a higher production rate than occurred during the initial round of cultivation in media containing 20?ppm Fe₃O₄ NPs. In addition, no evidence of negative impacts of Fe₃O₄ NPs on the growth of M. barkeri was observed. Taken together, these results strongly suggest that adding Fe₃O₄ NPs into the fermenter as an agent of sustained iron release can enable sustainable methane fermentation.     

Control of colloidal behavior of polystyrene latex nanoparticles and their cytotoxicity toward yeast cells using water-soluble polymers

Positively charged polystyrene latex (PSL) nanoparticles (NPs) dispersed in physiological saline (154?mM NaCl solution) are taken up by yeast cells. However, in low ionic strength solutions, the yeast cells are covered with the NPs, leading to cell death. The environmental conditions under which NPs are taken up are therefore limited. In this study, we attempted to control the uptake of positively charged PSL NPs by Saccharomyces cerevisiae in 5?mM NaCl solution using a water-soluble polymer. Addition of a small amount of anionic sodium carboxymethylcellulose (CMC), which has a carboxyl group, to 5?mM NaCl solution allowed the uptake of PSL NPs by living yeast cells. In contrast, non-ionic methylcellulose did not affect the NP behavior. This is because the negatively charged CMC adhered to the positively charged PSL NP surfaces and the surface charge changed from positive to negative. Atomic force microscopy using a single-NP probe consisting of one NP immobilized on the flattened end of the silicon nitride tip showed that CMC significantly reduced the interaction force between a negatively charged living yeast cell and a positively charged PSL NP.     

基于涡流成像的碳纤维增强树脂基复合材料细观结构可视化

对碳纤维增强树脂基复合材料（CFRP）的细观结构成像方法进行了研究,利用涡流成像技术实现了CFRP层合板中纤维方向及纤维缺失、褶皱和空隙过大等缺陷的可视化。首先通过有限元仿真和电路理论分析了CFRP板中涡流的生成机制和分布特性,阐述了基于涡流法的CFRP细观结构成像机制。然后介绍了用于扫描成像的高频涡流检测（HF-ECT）实验系统并确定了涡流探头的形式及其参数。最后利用涡流成像技术分别对单层板、正交层合板和四方向斜交层合板进行了检测,绘制了涡流检测（ECT）信号的三维伪彩图并得到了清晰的纤维纹路分布。通过引入滤波去噪技术和二维快速傅里叶变换（2D-FFT）对图像进行进一步处理,提高了图像分辨率并完成了不同方向上纤维纹路的分离,从而实现对层合板每单向层中缺陷的精确定位。     

Liquid Quinones for Solvent‐Free Redox Flow Batteries

Liquid benzoquinone and naphthoquinone having diethylene glycol monomethyl ether groups are designed and synthesized as redox active materials that dissolve supporting electrolytes. The Li‐ion batteries based on the liquid quinones using LiBF₄/PC show good performance in terms of voltage, capacity, energy efficiency, and cyclability in both static and flow modes. A battery is constructed without using intentionally added organic solvent, and its high energy density (264 W h L^?1) demonstrates the potential of solvent‐free organic redox flow batteries using liquid active materials.     

Evolving autonomous specialization in congested path formation task of robotic swarms

Redundancy in the number of robots is a fundamental feature of robotic swarms to confer robustness, flexibility, and scalability. However, robots tend to interfere with each other in a case, where multiple robots gather in a spatially limited environment. The aim of this paper is to understand how a robotic swarm develops an effective strategy to manage congestion. The controllers of the robots are obtained by an evolutionary robotics approach. The strategy of managing congestion is observed in the process of generating a collective path of robots visiting two landmarks alternately. The robotic swarm exhibits autonomous specialization that the robots traveling inside the path activate the LEDs, while the robots in the outer side deactivate them. We found that the congestion is regulated in an emergent way of autonomous specialization by the result of an artificial evolution.     

Synthesis and Sintering of Cerium(II) Monosulfide

Cerium monosulfide (CeS) powder was synthesized by the reduction of Ce₂S₃ powder with metallic Ce, which was obtained from ceria (CeO₂) powder using carbon disulfide (CS₂) gas. To obtain the maximum amount of CeS from a mixture of Ce₂S₃ and Ce, an excess amount of metallic Ce, a stoichiometric composition, was necessary in the synthesis at 1273 K for 10.8 ks. The preliminary sintering experiments also were performed using a synthetic CeS powder containing a small amount of Ce, Ce₂O₂S, and β-Ce₂S₃ as impurities. It was found that the oxygen content in the sintered compact decreases gradually as the sintering temperature increases, because of the removal of the impurities due to the evaporation of the volatile CeO. Single-phase CeS was formed by sintering at 2173 K. To evaluate the activation energy for densification of single-phase CeS, a CeS powder was prepared by milling an initial sintered compact and was used as an ingredient for hot-press experiments. Densification data during hot-press sintering were analyzed using a kinetic equation, showing that boundary diffusion is a rate-limiting process. The results suggest that this boundary diffusion model can explain well the densification data, with an apparent activation energy of 479 kJ·mol^-1.     

Tensile Behavior of Cement-Based Composites with Random Discontinuous Steel Fibers

In this paper, the tensile properties of cement-based composites containing random discontinuous steel fibers are reported. Direct tensile tests were performed to study the effects of fiber length (hence fiber aspect ratio), interfacial bonding, and processing conditions on composite properties. Composite tensile strength and ductility are highlighted and discussed.