Evaluation of a New Particle Trap in a Laser Desorption Mass Spectrometer for Online Measurement of Aerosol Composition

We have developed a new analyzer for the online measurement of aerosol composition: a particle trap laser desorption mass spectrometer (PT-LDMS). The main components of the instrument include an aerodynamic lens, a particle trap enclosed by a quartz cell, a quadrupole mass spectrometer (QMS), a vacuum chamber incorporating the above components, and a carbon dioxide (CO₂) laser (wavelength 10.6 μm). The aerodynamic lens generates a beam of submicron particles, which is focused on a small area on the particle trap. The particle trap consists of custom-made mesh layers, the structure of which was newly designed using engineering techniques for micro electro mechanical systems (MEMS). A large number of mesh frames are well arranged in the trap, and particles can be efficiently captured after multiple impactions on the frames. The CO₂ laser is used to vaporize aerosol compounds captured on the particle trap. The evolved gas confined within the quartz cell is analyzed using an electron impact ionization (EI) QMS to quantify the chemical composition of the particles. The concept of the PT-LDMS and first evaluation of its performance are presented, specifically focusing on the structure and performance of the particle trap.     

薄板搭接接头固有变形逆解析方法

文中采用变形测试和数值模拟技术相结合的研究手段对低碳钢薄板搭接接头固有变形的求解方法进行了研究,提出了该接头的固有变形分布简化模型,并利用固有变形逆解析方法推定了3 mm低碳钢薄板的固有变形.使用该方法得到的固有变形值来预测焊接变形能较好的再现试验结果.结果表明,采用文中提出的固有变形分布简化模型能获得高精度的固有变形值,搭接接头固有变形的逆解析算法是正确有效的.     

Capillary Networks for Bio-Artificial Three-Dimensional Tissues Fabricated Using Cell Sheet Based Tissue Engineering

One of the most important challenges facing researchers in the field of regenerative medicine is to develop methods to introduce vascular networks into bioengineered tissues. Although cell scaffolds that slowly release angiogenic factors can promote post-transplantation angiogenesis, they cannot be used to construct thick tissues because of the time required for sufficient vascular network formation. Recently, the co-culture of graft tissue with vascular cells before transplantation has attracted attention as a way of promoting capillary angiogenesis. Although the co-cultured vascular cells can directly contribute to blood vessel formation within the tissue, a key objective that needs to be met is the construction of a continuous circulatory structure. Previously described strategies to reconstruct blood vessels include the culture of endothelial cells in a scaffold that contains microchannels or within the original vascular framework after decellularization of an entire organ. The technique, as developed by authors, involves the progressive stacking of three-layered cell sheets onto a vascular bed to induce the formation of a capillary network within the cell sheets. This approach enables the construction of thick, functional tissue of high cell density that can be transplanted by anastomosing its artery and vein (provided by the vascular bed) with host blood vessels.     

Preparation and properties of C/SiC/ZrO2 porous composites by hot isostatic pressing the pyrolyzed preforms

Three phase mixture of C/SiC/ZrO₂ porous composites were prepared from commercially available phenolic resin, Si and ZrO₂ powders. In the first step, mixed powders were pyrolyzed at 850 °C in vacuum to obtain a carbonized microporous material and then hot isostatically pressed at 1200, 1300 and 1350 °C for 10 min in an argon pressure of 50 MPa to prepare C/SiC/ZrO₂ porous composites, in second step. The hot isostatic pressing led to the increase in density from 3.28 to 3.48 g/cm³ and reduction in porosity (from 32 to 20%) of the composites. X-ray diffraction analyses revealed the existence of β-SiC and carbon might be amorphous in the composites. According to the results of scanning electron microscopy, the crystal growth of β-SiC with facets was observed at 1350 °C. In addition, the energy dispersive spectroscopy showed that carbon/silicon atomic ratio was 1:1 in the crystals. X-ray photoelectron spectroscopy of the composites suggested that evolved gaseous molecules, due to the decomposition of phenolic resin, reacted with molecules containing Si to form β-SiC. The formation and growth of β-SiC in addition to the densification of matrix by hot isostatic pressing led to the increase in hardness (max.: 13.99 GPa) at higher temperatures.     

Quantitative dynamic reliability evaluation of AP1000 passive safety systems by using FMEA and GO-FLOW methodology

The passive safety systems utilized in advanced pressurized water reactor (PWR) design such as AP1000 should be more reliable than that of active safety systems of conventional PWR by less possible opportunities of hardware failures and human errors (less human intervention). The objectives of present study are to evaluate the dynamic reliability of AP1000 plant in order to check the effectiveness of passive safety systems by comparing the reliability-related issues with that of active safety systems in the event of the big accidents. How should the dynamic reliability of passive safety systems properly evaluated? And then what will be the comparison of reliability results of AP1000 passive safety systems with the active safety systems of conventional PWR.

For this purpose, a single loop model of AP1000 passive core cooling system (PXS) and passive containment cooling system (PCCS) are assumed separately for quantitative reliability evaluation. The transient behaviors of these passive safety systems are taken under the large break loss-of-coolant accident in the cold leg. The analysis is made by utilizing the qualitative method failure mode and effect analysis in order to identify the potential failure mode and success-oriented reliability analysis tool called GO-FLOW for quantitative reliability evaluation. The GO-FLOW analysis has been conducted separately for PXS and PCCS systems under the same accident. The analysis results show that reliability of AP1000 passive safety systems (PXS and PCCS) is increased due to redundancies and diversity of passive safety subsystems and components, and four stages automatic depressurization system is the key subsystem for successful actuation of PXS and PCCS system. The reliability results of PCCS system of AP1000 are more reliable than that of the containment spray system of conventional PWR. And also GO-FLOW method can be utilized for reliability evaluation of passive safety systems.     

Tribological characteristics of bonded MoS2 films evaluated in rolling-sliding contact in a vacuum

Tribological characteristics of bonded MoS₂ films have been evaluated in air, nitrogen and vacuum using a two-roller type rolling-sliding friction apparatus. Two conventional space-proven films, polyamideimide-bonded and sodium silicate-bonded, designated as film A and film B respectively, were tested at a speed of 998 rev min^-1 under a load of 100 N at slip ratios of 1–100%, the slip ratio being defined as (V₁ - V₂)/ V₁ × 100%, in which V₁ and V₂ was rotational speed of each roller.

The wear life of the film A was more slip ratio dependent than that of the film B. The wear life of the film A tested in a vacuum was the longest at 10% slip ratio but it reduced significantly at 1%. On the contrary, the best durability of the film B was obtained at 100% slip ratio (pure sliding). The wear life of the film A shortened considerably in air and nitrogen.

In general, a solid lubricant film applied to spur gears is subjected to rolling-sliding friction of 0-10% slip ratios. To improve the endurance life of the film A at 1% slip ratio, films prepared by changing content of pigments (MoS₂ and Sb₂0₃) were evaluated. The films with a pigment content of 5-15% showed a marked improvement in wear life at a slip ratio of 1%, while maintaining excellent durability at 10%.

The wear process of an improved film was monitored using a gap sensor. It appears to be dominated by fatigue.     

A pseudo-mastication sound presentation device to improve the texture of nursing care foods

The texture of foods is affected by concurrent auditory sensations. To improve the texture of nursing care foods, we developed a pseudo-mastication sound presentation device based on electromyogram (EMG) signals from the muscles of mastication. EMG signals have enabled us to promptly present care recipients with pseudo-mastication sounds. However, actual mastication sounds vary in intensity and duration more than EMG signals. Here, we investigated changes in EMG signals and actual mastication sounds during the mastication of two food types (rice crackers and Japanese pickles) to improve our device. We found that the intensity and duration of mastication sounds decreased as the number of mastication strokes increased. Furthermore, the intensity and duration of mastication sounds and the latency between the onset of EMG signals and the onset of mastication sounds also varied by food type. For EMG signals, only the intensity varied by food type. Based on our findings, we modified our pseudo-mastication sound presentation device to enable control of the intensity and duration of pseudo-mastication sounds based on the number of mastication strokes and food type. Reproducing more natural pseudo-mastication sounds can improve care recipients’ motivation for ingesting nursing care foods, thus preventing malnutrition and frailty.     

Effect of static magnetic field on thermal conductivity measurement of a molten Si droplet by an EML technique: Comparison between numerical and experimental results

In order to investigate quantitatively the effect of melt convection in an electromagnetically levitated molten droplet on the thermal conductivity of liquid silicon measured by the electromagnetic levitation (EML) technique superimposed with a static magnetic field, the numerical simulations for melt convection in the droplet and additionally, for the measurement of thermal conductivity were carried out. In addition, the thermal conductivity of molten silicon was measured by the EML technique, and then compared with those obtained numerically. In the numerical simulations of melt convection, the buoyancy force, thermocapillary force due to the temperature dependence of the surface tension on the melt surface, and electromagnetic force in the droplet were considered as the driving forces of convection. As a result, the numerical simulations could sufficiently explain the measurement of thermal conductivity by the EML technique under a static magnetic field. Also, it was suggested that a magnetic field of more than 4 T should be applied to measure the real thermal conductivity of molten silicon by the EML technique.     

Rapid control of hydrogen permeation in Pd membrane reactor by magnetic-field-induced heating under microwave irradiation

A microwave (MW) heating system induced by a magnetic field was designed and applied for uniform heating of a Pd membrane selectively through hydrogen. This system aimed to control the temperature of the membrane and the hydrogen permeation rate. Although the conventional dielectric heating by MWs is not suitable for metal membranes because of the reflection of MWs, a magnetic field can excite the surface current (eddy current) and causes Joule heating. First, this was successfully achieved for thin metal films in a frequency-variable single-mode MW reactor system with a cylindrical cavity. The temperature of the surface was controlled precisely by a resonance frequency autotracking function. Then, for the control of the hydrogen permeation rate through the Pd membrane, this system was applied to a pore-filling-type Pd membrane where the Pd nanoparticles were filled in the nanospace void of the Al₂O₃ support tube, suggesting high durability. The temperature of Pd membrane could be quickly and precisely controlled due to direct heating by this MW system. Hydrogen permeation rate was well controlled associated with the temperature of the membrane.     

Electrochemical detection of nonlabeled oligonucleotide DNA using biotin-modified DNA(ss) on a streptavidin-modified gold electrode

In the electrochemical detection of nonlabeled DNA, it is important to control the bonding at the interface between the DNA and the electrode. Atomic force microscope (AFM) was taken for the commonly used thiol-modified DNA on a gold surface. It was found that the coverage of the DNA was very low. On the other hand, a streptavidin-modified gold electrode provided a much better alternative where DNA hybridization resulted in large changes in the electrochemical reaction responses. This work demonstrates that streptavidin-modified gold electrodes could be used in the development of a new electrochemical protocol for the detection of nonlabeled DNA.