Additives distribution and electrical properties in zinc oxide varistor prepared by a wet chemical method

Cobalt-, praseodymium-added zinc oxide varistor was prepared through a wet chemical method followed by sintering with or without calcination. Changes in grain size, compact density, additives distribution, and voltagecurrent/ capacitance-voltage relations were investigated for the characterization of the samples sintered at temperatures from 1473 to 1573 K without calcination or with calcination at 773 K for 2 h. The electrical properties were compared with nhose of samples prepared by two types of ball mill methods. The wet chemical method provided almost the same additives-distribution profile and less impurities in comparison with the ball grinding method carried out for 10–100 h. The donor concentration and the potential-barrier height for the samples were evaluated by Double Schottky Barrier Model. Addition of small amount of both cobalt and praseodymium in preparation by the wet chemical method was effective for a better nonlinearity relation between voltage and current, which has potential for a smaller sized varistor.     

水相酶促酯化法拆分dl－薄荷醇的连续操作

对影响脂肪酶活性、稳定性和对映选择性的因素，如有机溶剂和反应温度等首先进行了优化。其次，使用悬浮于环已烷的粉末状游离脂肪酶（ＣａｎｄｉｄａｃｙｌｉｎｄｒａｃｅａｌｉｐａｓｅＯＦ３６０）作生物催化剂，成功地构建了一个高效的非水相游离酶连续搅拌釜反应器。当使用高度反应性的丙酸酐作为薄荷醇的酰基给体，进行连续的酶促对映选择性酯化反应时，醇的转化率在两周内可保持４０％以上，所生成酯的光学纯度超过９５％ｅ．ｅ。但是，当使用相应的游离丙酸（而不是酸酐）作酰基给体时，薄荷醇的转化率在连续操作开始后迅速下降，表明使用酸酐时的生产力要比使用游离酸时高。最后，对底物溶液的浓度和流速进行了进一步优化；同时对反应器系统的含水量进行了监测，并通过对酸酐料液的浓度或流速进行微调的方法，有效地将有机溶液相的水分浓度控制在一定的范围（２～４ｍｍｏｌ／Ｌ）之内，结果，ｄｌ－薄荷醇对映选择性连续酯化反应非常稳定地运行了两个月之久（转化率４７～３５％，光学纯度９５～９８％ｅ．ｅ．），酶反应器的半衰期超过２００天。     

Formation of Bromate Ion Through a Radical Pathway in a Continuous Flow Reactor

The contribution of ozone and hydroxyl radical to the formation of bromate ion was investigated in a continuous flow reactor. Experiments were conducted under a wide range of ozone dose (0.7 ～ 3.8 mgL), pH (6.5 ～ 8.5), and t-butanol concentration (0 ～ 0.5 mM). The formation of bromate ion was found to depend on radical reaction pathway, because the amount of bromate ion formed increased with pH and decreased with t-butanol, a radical scavenger, even when dissolved ozone concentrations were almost the same. In fact, the amount of bromate ion formed was reduced by 90% in the presence of t-butanol. Furthermore, the formation of bromate ion occurred even when dissolved ozone was not significantly detected in the presence of organic matter (TOC of 1 mgCL). The second-order reaction rate constant of hydroxyl radical with bromide ion, k _HO,Br^? of 1.7 × 10⁹ (M^?1s^?1), was obtained on the assumption that the reactions of bromide ion and t-butanol with hydroxyl radical were competitive with each other in the presence of t-butanol and that the formation of bromate ion depended on the reaction of bromide ion with hydroxyl radical. Therefore, it is concluded that the reaction of bromide ion with hydroxyl radical dominated in the overall reaction from bromide ion to bromate ion in the continuous flow reactor.     

Combustion of Aluminum Particles near the Burning Surface in AP/AN Composite Propellants

Aluminum (Al) particles are commonly used in ammonium perchlorate (AP) composite propellants of solid rockets for increasing performance. When propellants including Al particles burn, Al particles easily agglomerate on the burning surface of the propellant. The diameters of agglomerated Al particles are greater than those of mixed particles. The combustion efficiency of the propellant decreases with increasing burning time of the agglomerated Al particles. Therefore, it is important to observe how the agglomerated Al particles burn on the burning surface of AP composite propellant. A lot of researchers have studied Al agglomerate characteristics. Previous studies clarified the relation between the agglomerated Al particle diameter and luminous flame diameter around Al particles near the burning surface. The shapes of luminous flames around agglomerated Al particles are spherical or elliptical. This study evaluates the shapes of the luminous flame around agglomerated Al particles at a constant diameter or a different diameter. When the proportion of the luminous flame diameter (D_f) to the diameter of agglomerated Al particles (D₀) is 1.54–1.71 at a constant D₀, the luminous flames are almost perfectly spherical. Otherwise, the luminous flames are elliptical at a constant D₀. Furthermore, when D_f/D₀ is close to the mean value, the luminous flame is more spherical than elliptical at different D₀. The evaporation rate and the burning rate of Al vapor are inversely proportional to D₀. The oxidation gas temperatures were changed and the activation energy of Al vapor was obtained as 39.2 kJ mol⁻¹.     

Degradation characteristics of polylactide in thermophilic anaerobic digestion with hyperthermophilic solubilization condition

To test whether hyperthermophilic treatment promotes polylactide (PLA) dissolution and methane conversion under anaerobic digestion conditions, a single thermophilic control reactor (55 °C) and a two-phase system consisting of a hyperthermophilic reactor (80 °C) and a thermophilic reactor (55 °C) were continuously fed with a mixture of PLA and artificial kitchen garbage. In Runs 1 and 2, the PLA dissolution ratios in the two-phase system were 79.2 ± 6.5% and 85.2 ± 7.0%, respectively, higher than those of the control. Batch experimental results indicated that hyperthermophilic treatment could promote PLA dissolution to a greater degree as compared with single thermophilic treatment and that ammonia addition also had a promotional effect on PLA dissolution. In the two-phase system, after hyperthermophilic treatment, dissolved PLA was converted to methane gas under the subsequent thermophilic condition.     

BEM simulation of Wien filters

The boundary element method can provide accurate solutions to the electromagnetic problem in numerical simulations of electron optics devices. In this paper, we describe our approach, which applies a subsectional-bases method to generate a boundary division, representing the shape and behaviour of the Wien filter precisely. We investigate by direct ray tracing the origin of the second-order geometrical aberrations of this filter and propose new designs to reduce them.     

Production of functional substances from black rice bran by its treatment in subcritical water

Black rice bran was treated by water and subcritical water at temperatures ranging from 20 to 260 °C for 5 min and at 200 and 260 °C for 5-120 min. The bran extracts were analyzed for their radical scavenging activity, protein and carbohydrate contents, molecular-mass distribution, antioxidation activity, emulsifying activity, and emulsion-stabilizing activity. The radical scavenging activity and the protein content of the extract were higher at higher treatment temperature. The carbohydrate content also increased with increasing temperature up to 200 °C, then steeply decreased at the temperatures higher than 200 °C. The bran extracts treated at 260 °C for 5 min exhibited a suppressive activity toward autoxidation of linoleic acid with the increasing the weight ratio of the bran extract to linoleic acid. The bran extracts prepared at 40-200 °C for 5 min showed the emulsifying- and emulsion-stabilizing activities, while the extracts prepared at 220-260 °C were low in the activities.     

Enhancement of thermostability of kojibiose phosphorylase from Thermoanaerobacter brockii ATCC35047 by random mutagenesis

Random mutation by error-prone PCR was introduced into kojibiose phosphorylase from Thermoanaerobacter brockii ATCC35047. One thermostable mutant enzyme, D513N, was isolated. The D513N mutant enzyme showed an optimum temperature of 67.5-70 degrees C (the wild type, 65 degrees C), and thermostability up to 67.5 degrees C (the wild type, up to 60 degrees C). The half-lives of D513N were estimated to be 135 h at 60 degrees C, 110 min at 70 degrees C and 6 min at 75 degrees C, respectively. They were about 1.6-fold, 7-fold and 6-fold longer than those of the wild-type enzyme, respectively.     

Micro-/nanostructural investigation of laser-cut surfaces of single- and polycrystalline diamonds

Micrometer- to nanometer-scale structures of the cut surfaces of single- and polycrystalline diamonds by a pulsed ultraviolet laser have been thoroughly investigated by scanning and transmission electron microscopy. Within the laser-cut grooves, the processed diamond surfaces are extensively covered with laser-modified debris which consists of complex layered units of graphite with various crystallinities. The units consist of 1) highly oriented graphite, 2) corrugated graphite, and 3) nanocrystalline graphite, which are sequentially located from the surface of the underlying diamond substrate to the center of the grooves. Detailed textural examinations revealed that the highly oriented graphite unit is a product of the initial graphitization of diamond by a solid-state diffusion process, whereas the latter two units are deposition products from the liquid and/or vapor phases of carbon in the later stage. The present study demonstrates that the laser-cutting of diamonds proceeds in a two-step process: 1) extensive graphitization of laser-scanning path and 2) subsequent sublimation of the pre-formed graphite. These processes are basically identical among the three different types of diamonds (single crystal type Ib, single crystal type IIa and nano-polycrystalline aggregate) tested in this study.