液滴机械手的数值仿真与试验研究

为分析液滴机械手的控制机理, 建立液滴机械手的流体动力学仿真模型,仿真分析液滴机械手的控制机理,研究机械手端面形成液滴的形态跟随机械手端面形状的变化关系,讨论影响液滴机械手性能的因素,并通过试验验证仿真模型的正确性和提出方法的可行性．数值仿真和试验结果表明:通过控制各钨丝棒的上下移动量,可以改变液体和各钨丝棒的接触壁面,使机械手端面形成液滴的形态随之改变;基于表面张力吸附在液滴上的微小部件的姿态将随着液滴形态的改变而变化,从而可以实现对于微小部件姿态的控制．适当调整机械手的参数,如钨丝棒的数目、尺寸、各钨丝棒的移动量,以及改变液滴的性质等,可以满足微装配过程中各种操作目标的要求．     

Influence of electron donors on the initial stage of cyclopolymerization of 1,5‐hexadiene with MgCl2‐supported Ziegler catalysts analyzed by temperature rising elution fractionation

Additive effects of donors on the initial polymerization of 1,5‐hexadiene with the MgCl₂‐supported Ziegler catalysts were investigated by using the stopped‐flow method, temperature rising elution fractionation (TREF) analysis, and kinetic study. The cyclopolymerization of 1,5‐hexadiene proceeded within an extremely short period (≤ 0.2 s) and yielded a unique poly(methylene‐1,3‐cyclopentane). cis ring content and cis–cis unit in meso dyad of the resulting polymer were increased by the addition of electron donors. The influence of internal and external donors was examined by the estimation of kinetic parameters and TREF analysis. Because the addition of the internal donor caused an obvious change in one of the kinetic parameters and the microstructure, an isospecific active site was considered to be formed by the addition of the internal donor. In the case of the external donor, the additive effects on the stereospecificity were weaker than those of the internal donor. It was expected from TREF measurements that the external donor modified an aspecific active site into a lower isospecific active site. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2976–2983, 2002; DOI 10.1002/app.2326     

A Crystalline Si3N4/Amorphous Si3N4 Composite

A composite consisting of elongated α-Si₃N₄ crystallites (5–50 (Am in diameter) embedded in an amorphous Si₃N₄ matrix was synthesized by chemical vapor deposition. The hardness and indentation fracture toughness of the amorphous matrix and of the composite have been evaluated at temperatures from ambient to 1200°C. It was found that the crystallites have relatively little influence on the hardness and indentation fracture toughness when the surrounding matrix is amorphous. However, a 1400°C heat treatment of the material results in a matrix consisting of small crystals (100 nm in diameter) surrounded by carbon-containing regions which appear to be amorphous in the TEM; TEM and EELS in nearby triple points revealed the presence of amorphous carbon. After heat treatment, the indentation fracture toughness at ambient and at 1200°C is increased due to extensive microcracking. The Vickers hardness at 1200°C also increased significantly as a result of the heat treatment. The relationship between the mechanical properties and the microstructure is discussed.     

Factors influencing species diversity of ferns and fern allies in fragmented forest patches in the Kyoto city area

We investigated the relationship between species diversity of pteridophytes and the environmental factors of 39 fragmented forest patches in the Kyoto city area. There was a significant correlation between the number of species and the micro-landform diversity, artificial habitat diversity, and logarithm of the area of the forest patch. When we performed a multiple regression analysis to identify the best-fit model so as to optimize the amount of variation in species diversity explained by using stepwise selection, three species diversity indices (species richness or Shannon’s diversity index, logarithm of inverse Simpson index) had significant positive partial correlations with the logarithm of area of the forest patch, and negative correlations with the logarithm of isolation distance from mountain forest. Therefore, we conclude that pteridophyte species diversity depends on patch size and isolation distance from mountain forests. Comparison of the woody plant species–area curve with the pteridophyte species–area curve showed that the rate of increase of species number (inclination) with area was the same, but the Y-intercept of the pteridophyte species–area curve was lower than that of the woody plant curve. Therefore, the minimum conservation area required for ferns and fern allies is greater than that for woody plant species.     

Novel modification of polybut‐1‐ene using auto‐oxidation controlled by addition of limonene monomer

Free radical graft polymerization has been used as a modification method to incorporate functional groups into polyolefins using a melt‐mixing process. The presence of oxygen simultaneously brings about auto‐oxidation during the polymerization. Although functional groups such as ketones are easily incorporated into polyolefin chains by auto‐oxidation, the method is rarely employed because of the difficulty of handling. In the study reported here, a novel modification of polybut‐1‐ene (PB) was performed using auto‐oxidation controlled by the addition of limonene monomer. The modified PB samples were prepared using 2,2′‐azobis(2‐methylpropionitrile), benzyl peroxide, tert‐butyl peroxide (TBPO) and Nd₂O₃/dicumyl peroxide (DCP) radical initiators in air. It was found that excessive auto‐oxidation was suppressed by the presence of the limonene, and that the greatest numbers of grafted groups were contained in the modified PB samples prepared using TBPO and Nd₂O₃/DCP. The samples obtained showed slower crystallization behavior and slower crystal–crystal transformation rates, respectively. In addition, the modified PB sample prepared using Nd₂O₃/DCP showed less ductile behavior than that prepared using TBPO because of a much slower transformation rate. Copyright © 2009 Society of Chemical Industry     

Multi-Organ Protective Effects of Sodium Glucose Cotransporter 2 Inhibitors

Sodium glucose cotransporter 2 inhibitors (SGLT2i) block the reabsorption of glucose by inhibiting SGLT2, thus improving glucose control by promoting the renal excretion of glucose, without requiring insulin secretion. This pharmacological property of SGLT2i reduces body weight and improves insulin resistance in diabetic patients. Such beneficial metabolic changes caused by SGLT2i are expected to be useful not only for glucose metabolism, but also for the protection for various organs. Recent randomized controlled trials (RCTs) on cardiovascular diseases (EMPA-REG OUTCOME trial and CANVAS program) showed that SGLT2i prevented cardiovascular death and the development of heart failure. RCTs on renal events (EMPA-REG OUTCOME trial, CANVAS program, and CREDENCE trial) showed that SGLT2i suppressed the progression of kidney disease. Furthermore, SGLT2i effectively lowered the liver fat content, and our study demonstrated that SGLT2i reduced the degree of hepatic fibrosis in patients at high-risk of hepatic fibrosis. Such promising properties of SGLT2i for cardiovascular, renal, and hepatic protection provide us the chance to think about the underlying mechanisms for SGLT2i-induced improvement of multiple organs. SGLT2i have various mechanisms for organ protection beyond glucose-lowering effects, such as an increase in fatty acids utilization for hepatic protection, osmotic diuresis for cardiac protection, an improvement of insulin resistance for anti-atherogenesis, and an improvement of tubuloglomerular feedback for renal protection.     

How does heme axial ligand deletion affect the structure and the function of cytochrome b562?

We have recently generated a new mutant of cytochrome b₅₆₂ (cytb₅₆₂)in which Met7, one of the axial heme ligands, is replaced byAla (M7A cytb₅₆₂). The M7A cytb₅₆₂ can bind heme and the UV-visibleabsorption spectrum is of a typical high-spin ferric heme. Toinvestigate the effect of the lack of Met7 ligation on the structuralintegrity of cytb₅₆₂, thermal transition analyses of M7A cytb₅₆₂were conducted. From the thermodynamic parameters obtained,it is concluded that the folding of M7A cytb₅₆₂ is comparableto the apoprotein despite the presence of heme. On the otherhand, exogenous ligands such as cyanide and azide ions are readilybound to the heme iron, indicating that the axial coordinationsite is available for substrate binding. The peroxidase activityof this mutant is thus examined to evaluate new enzymatic functionat this site and M7A cytb₅₆₂ was found to catalyze an oxidationreaction of aromatic substrates with hydrogen peroxide. Theseobservations demonstrate that the Met7/His102 bis-ligation tothe heme iron is crucial for the stable folding of cytb₅₆₂,whereas the functional conversion of cytb₅₆₂ is successfullyachieved by the loose folding together with the open coordinationsite.     

Basic characterization of polypropene‐block‐poly(methylene‐1,3‐cyclopentane‐co‐propene) synthesized from propene and 1,5‐hexadiene with modified stopped‐flow method

Block copolymerization of propene and 1,5‐hexadiene was carried out by a modified stopped‐flow polymerization method with an MgCl₂‐supported Ziegler catalyst. The resulting polymer, polypropene‐block‐poly(methylene‐1,3‐cyclopentane‐co‐propene) (PP‐b‐(PMCP‐co‐PP)), in which the crystallizable PP part was linked with the non‐crystallizable PMCP‐co‐PP part, was characterized by optical microscopy, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile testing. The block copolymer having a chemical linkage between PP and PMCP‐co‐PP showed properties different from those of homopolymer, random copolymer and blend polymer. © 2001 Society of Chemical Industry