Subchannel analysis of a fast reactor cooled by supercritical light water

The concept of a high temperature fast reactor cooled by supercritical water (SCFR-H) was developed for achieving high thermal efficiency and a compact reactor system. The core characteristics were obtained from single channel thermal-hydraulic analysis. Thus, it is necessary to carry out subchannel analysis to estimate the effect of local power peaking and cross flows. For this purpose, a subchannel analysis code is developed. It is verified by comparing the results with experimental data of High Conversion Pressurized Water Reactor (HCPWR). Sensitivities of the outlet coolant and cladding temperature to the subchannel flow area and local power peaking are high. One of the reasons is that the ratio of the coolant flow rate of SCFR-H to the power is smaller than that of LWR. Another reason is that, temperature of supercritical water is more sensitive to the enthalpy change above 450°C. The outlet coolant temperature distribution can be flattened by reducing the area of the peripheral subchannels and by enhancing the mixing between the subchannels.     

超声波探针水平位置变化对Al-1.0%Cu铸锭凝固组织的影响

本文通过使用Al-1.0%Cu合金进行了一系列试验,研究了超声波探针水平位置变化对铸锭凝固组织的影响,并且使用铝粉-水的混合物进行了模拟试验,观察了探针水平位置变化对透明容器内物质流动的影响,最后,探讨了超声波的晶粒细化机理。结果表明:(1)在探针固定于水平方向不同位置的条件下,当探针位于铸型中心线浸入熔体时,得到的细等轴晶区最大,且呈对称分布。(2)当探针的固定位置贴近铸型壁时,细等轴晶区向探针端面附近集中并缩减,柱状晶区进一步扩大。(3)根据克劳修斯-克拉柏龙方程,细等轴晶是由于超声波引起压力脉冲而导致金属的熔点上升,生成稳定的固相而形成的。(4)强声流起着分散金属熔体内刚形成的固相的作用。     

Roles of Macrophages in Advanced Liver Fibrosis,Identified Using a Newly Established Mouse Model of Diet-Induced Non-Alcoholic Steatohepatitis

Macrophages play critical roles in the pathogenesis of non-alcoholic steatohepatitis (NASH). However, it is unclear which macrophage subsets are critically involved in the development of inflammation and fibrosis in NASH. In TSNO mice fed a high-fat/cholesterol/cholate-based diet, which exhibit advanced liver fibrosis that mimics human NASH, we found that Kupffer cells (KCs) were less abundant and recruited macrophages were more abundant, forming hepatic crown-like structures (hCLS) in the liver. The recruited macrophages comprised two subsets: CD11c⁺/Ly6C⁻ and CD11c⁻/Ly6C⁺ cells. CD11c⁺ cells were present in a mesh-like pattern around the lipid droplets, constituting the hCLS. In addition, CD11c⁺ cells colocalized with collagen fibers, suggesting that this subset of recruited macrophages might promote advanced liver fibrosis. In contrast, Ly6C⁺ cells were present in doughnut-like inflammatory lesions, with a lipid droplet in the center. Finally, RNA sequence analysis indicates that CD11c⁺/Ly6C⁻ cells promote liver fibrosis and hepatic stellate cell (HSC) activation, whereas CD11c⁻/Ly6C⁺ cells are a macrophage subset that play an anti-inflammatory role and promote tissue repair in NASH. Taken together, our data revealed changes in liver macrophage subsets during the development of NASH and shed light on the roles of the recruited macrophages in the pathogenesis of advanced fibrosis in NASH.     

Motion and conversion energies of ad-atom, di-adatom and tri-adatoms on copper (0 0 1) surface

Beginning of epitaxial growth of vapor deposition on (0 0 1) surface has been studied by use of molecular dynamics. The activation energies of motion and conversion have been calculated using an embedded atom potential at all temperatures. The activation energy of the motion of an ad-atom on (0 0 1) of copper is calculated to be 0.48 eV. The activation energy of dissociation in the direction of a di-adatom is 0.83 eV, and 0.55 eV from the nearest neighbor to the next nearest neighbor. Tri-adatoms are classified by the angle between the two bonds in the ad-atoms and the lengths of the two bonds. The conversion energies of tri-adatoms have also been calculated. The activation energy for the motion of an ad-atom on (0 0 1) is much higher than those corresponding values of the motion on (1 1 1) planes.     

Matrix-free laser desorption/ionization-mass spectrometry using self-assembled germanium nanodots

A novel ionization platform for matrix-free laser desorption/ionization-mass spectrometry (LDI-MS) was developed using self-assembled germanium nanodots (GeNDs) of uniform size (approximately 150 - 200-nm width and approximately 50-nm height) grown on a silicon wafer produced by molecular beam epitaxy. The performance of LDI-MS using GeNDs (GeND-MS) was investigated through measurements of a broad range of analytes, including peptides, proteins, synthetic oligomers, and polymer additives. Mass spectra of tryptic digests were clearly observed even for the mass range lower than m/z 800 without obstructive peaks. A detection limit of subfemtomole level was achieved for angiotensin-I. The upper limit of detectable mass range was approximately 17 kDa (myoglobin). GeND-MS also has potential for application to the characterization of industrial compounds. Almost accurate molecular weight distribution was obtained for a nonionic surfactant (Triton X-100) and for poly(ethylene glycol) oligomer. Furthermore, a brominated flame retardant, tetrabromobisphenol-A bis(2,3-dibromopropyl ether), was successfully ionized with less fragmentation, a result not obtainable by matrix-assisted laser desorption/ionization-mass spectrometry or desorption/ionization on porous silicon-mass spectrometry.     

Surface segregation of calcium oxide in wustite and its effects on the reduction

The segregation of calcium oxide to the surface of wustite was investigatedin situ by Auger electron spectroscopy at temperatures in the range of 973 to 1223 K. Calcium oxide indicated a strong tendency to segregate, with the molar fractions at the surface being 10 to 1000 times the molar fractions in the bulk (X _CaO ^bulk ). The segregation isotherms showed maxima at intermediate molar fractions in the bulk (X _CaO ^bulk = 0.003 or 0.005). The enthalpy change for the segregation increased from −43.3 to −5.20 kJ/mol with increasing X _CaO ^bulk . The main driving force of the segregation may be the relaxation of the strain energy generated around calcium ions. Calcium oxide also segregates at the surface of iron in contact with the wustite. By the segregation of calcium oxide, the surface energies of wustite and iron may decrease whereas the wustite/iron interfacial energy may increase. The enhancement of the reduction of wustite by calcium oxide is concluded to essentially occur by the good and continuous direct contact of wustite surface with reducing gases owing to the suppression of new iron nucleus and owing to the contraction of the wustite/iron-nuclei interfacial area compared with the free-surface area of wustite in order to decrease the total energy.     

Development of small-sized friction stirs welding equipment for hand-operated welding

Much attention has been paid to FSW as a useful joining process that provides superior characteristics compared with conventional fusion welding. However, the FSW equipment must have a high stiffness due to the applied load and the tool torque, which increases the size of the equipment. Therefore, it is difficult to use the FSW technique on-site for repairs and/or hand-operated welding. In this study, the relationship between the FSW parameters and the process loads was investigated for the FSW with a counterbalanced tool and preheating to evaluate the possible miniaturization of the equipment. The results revealed that the counterbalanced tool concept with preheating was effective for the miniaturization of the equipment because it reduces the applied l and the tool torque during the FSW. Welding direction force Fx and transverse direction force Fy can be reduced below 70 N and 50 N respectively.     

Synthesis and evaluation of positive-acting photosensitive polyimides with phenol moiety

Novel positive-acting photosensitive polyimide resists ( 1 ) developable with an alkaline aqueous solution were prepared. The resists consisted of a naphthoquinone diazide (NQ) and a polyamic acid bearing hydroxyphenyl groups (PA). The hydroxyphenyl moieties are newly incorporated by adding 2-N,N-dimethylaminoethyl-3-hydroxybenzoate (m-PEA) or 2-N,N-dimethylaminoethyl-4-hydroxybenzoate (p-PEA) to the polyamic acid, through ionic interaction between the carboxylic acid and the amine. The NQ acts as a solution inhibitor for the PA by the interaction with the hydroxyphenyl moiety. This system is similar to that of phenol-novolac resin/NQ resists currently conducted in the fabrication of the Large Scale Integrated circuit (LSI). The resist ( 1 ) is exposed to a G-line and is developed with tetramethylammonium hydroxide aqueous solution to provide fine patterns, proving that the ( 1 ) is compatible with LSI-production lines currently applied. A novel polyamic acid-curing mechanism found in the course of this study is also reported. © 1995 John Wiley & Sons, Inc.     

Preparation of Grain-Oriented Sr0.5Ba0.5Nb2O6 Ferroelectric Ceramics by Magnetic Alignment

The properties of polycrystalline ceramics are strongly influenced by their crystallographic texture. In this study, highly grain-oriented tungsten bronze structure ferroelectric ceramics, Sr_0.5Ba_0.5Nb₂O₆, were successfully fabricated by magnetic alignment and gelcasting techniques using only the conventional solid-state-synthesized starting powder. Spherical Sr_0.5Ba_0.5Nb₂O₆ particles were aligned according to their anisotropic magnetic property in 40 vol% slurry in a 10 T magnetic field, and then in situ locked by polymerization via a gelcasting technique for 30 min. A 〈00 l 〉-axis orientation perpendicular to the magnetic field direction ( B ) was obviously observed in the green compact and sintered sample. The sintered Sr_0.5Ba_0.5Nb₂O₆ sample contained equiaxial grains and reached 98% theoretical density. Compared with the sample with randomly oriented grains, the magnetically aligned sample showed an enhanced with dielectric constant in the ⊥ B direction (1100 versus 750 at room temperature and 4300 versus 2800 at Curie temperature). This new method is readily applicable to other ceramics with tungsten bronze structure, and is expected to facilitate mass preparation of large and dense grain-oriented ceramic materials.