关于水力机械磨蚀的研究

用磁致伸缩振动仪与含砂射流设备所构成的新型试验装置对空蚀、磨蚀单独作用或联合作用下几种金属材料的表面损伤状况和失重量等进行了研究.研究发现,联合作用时失重量也随时间而增长,但没有通常情况下的潜伏期,且不是各自单独作用时失重量的叠加.还发现泥沙的存在,对空蚀可起到某种抑制作用.     

Synthesis and physical properties of poly(l‐lactic acid)‐poly(dimethyl siloxane) multiblock copolymers prepared by direct polycondensation

Multiblock copolymers consisting of poly(l ‐lactic acid) and poly(dimethyl siloxane) were prepared by the polycondensation of oligo(l ‐lactic acid) (OLLA) with dihydroxyl‐terminated oligo(dimethyl siloxane) and dicarboxyl‐terminated oligo(dimethyl siloxane). Copolymers with number‐average molecular weights of 18,000?33,000 Da and various content ratios of oligo(dimethyl siloxane) (ODMS) unit were obtained by changing the feed ratio of these oligomers. A film prepared from the copolymer with an ODMS content ratio of 0.37 exhibited two independent peaks at ?107°C and 37°C in the mechanical loss tangent for temperature dependence, suggesting the formation of microphase separation between the OLLA and ODMS segments. The film had a tensile strength of 3.2 MPa and a high elongation of 132%. The film also exhibited a high strain recovery even after repeated straining. The incorporation of dimethyl siloxane units as multiblock segments was confirmed to improve the flexibility of poly(l ‐lactic acid). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40211.     

Preparation of carboxylate group-containing rod-like polysilsesquioxane with hexagonally stacked structure by sol–gel reaction of 2-cyanoethyltriethoxysilane

Carboxylate group-containing rod-like polysilsesquioxane (PSQ-COO^?Na⁺) with a hexagonally stacked structure was successfully prepared by the sol–gel reaction (hydrolytic polycondensation) of 2-cyanoethyltriethoxysilane (CETEOS) monomer in sodium hydroxide aqueous solution. The X-ray diffraction pattern of the cast film of PSQ-COO^?Na⁺ showed three diffraction peaks with the d-value ratio of 1 : 1/√3 : 1/2, indicating the formation of hexagonal phase. In addition, the transmission electron microscopic image of PSQ-COO^?Na⁺ showed a stripe pattern, indicating that the rod-like PSQs were stacked parallel. Self-organization of an ion pair composed of a carboxylate anion and a sodium cation, which was converted from the cyano group of CETEOS by hydrolysis under alkaline conditions, was a driving force for the formation of such regular higher-ordered structures of PSQ-COO^?Na⁺.     

Three-dimensional observation of SiO2 hollow spheres with a double-shell structure using aberration-corrected scanning confocal electron microscopy

Optical sectioning using scanning confocal electron microscopy (SCEM) is a new three-dimensional (3D) imaging technique which promises improved depth resolution, particularly for laterally extended objects. Using a stage-scanning system to move the specimen in three dimensions, two-dimensional (2D) images sliced from any plane in XYZ space can be obtained in shorter acquisition times than those required for conventional electron tomography. In this paper, a double aberration-corrected SCEM used in annular dark-field mode was used to observe the 3D structure of SiO(2) hollow spheres fabricated by a carbon template method. The double-shell structure of the sample was clearly reflected in both XY- and XZ-sliced images. However, elongation along the optical axis was still evident in the XZ-sliced images even when double aberration correctors were used. Application of a deconvolution technique to the experimental XZ-sliced images reduced the elongated shell thicknesses of the SiO(2) sphere by 40-50% and the selectivity of information at a certain sample depth was also enhanced. Subsequently, 3D reconstruction by stacking the deconvoluted slice images restored the spherical surface of a SiO(2) sphere.     

A caged progesterone analog alters intracellular Ca2+ and flagellar bending in human sperm

Progesterone is a physiological agonist for mammalian sperm, modulating its flagellar movement and facilitating the acrosome reaction. To study the initial action of progesterone, we developed a caged analog with a photosensitive group: nitrophenylethanediol, at position 20. Using this compound combined with stroboscopic illumination, we performed Ca(2)(+) imaging of human spermatozoa and analyzed the effects of progesterone on the intracellular Ca(2)(+) concentration ([Ca(2)(+)](i)) of beating flagella for the first time. We observed a transient [Ca(2)(+)](i) increase in the head and the flagellum upon photolysis of the caged progesterone and an increase in flagellar curvature. Detailed kinetic analysis revealed that progesterone elicits an increase in the [Ca(2)(+)](i) immediately in the flagellum (mid-piece and principal piece), thereafter in the head with a short time lag. This observation is different from the progesterone-induced Ca(2)(+) mobilization in mouse spermatozoa, where the Ca(2)(+) rise initiates at the base of the sperm head. Our finding is mostly consistent with the recent discovery that progesterone activates CatSper channels in human spermatozoa, but not in mouse spermatozoa.     

Cloning and nucleotide sequence of carbaryl hydrolase gene (cahA) from Arthrobacter sp. RC100

A carbaryl hydrolase gene (cahA) encoded on the plasmid pRC1 in Arthrobacter sp. RC100 was cloned and sequenced. The entire region of the deduced amino acid sequence was found to be homologous to that of an amidase family. Parts of the consensus sequences of the amidase gene have been identified in CahA from strain RC100. CahA was overexpressed in Escherichia coli JM109, and the enzyme was purified to homogeneity by protamine sulfate treatment, ammonium sulfate precipitation, and hydrophobic and anion-exchange chromatographies. The purified enzyme showed hydrolase activity toward 1-naphthylacetamide and isobutyramide but showed no activity toward 1-naphthylacetate. This is the first report of an amidase that is able to hydrolyze N-methylcarbamate pesticides.     

Extractive solubilization, structural change, and functional conversion of cytochrome c in ionic liquids via crown ether complexation

This article reports on the extraction behavior of heme proteins from an aqueous phase into ionic liquids (ILs) with dicyclohexano-18-crown-6 (DCH18C6), and the structure-function relationship of cytochrome c (Cyt-c) dissolved in ILs. We have found that DCH18C6 enables transfer of Lys-rich proteins into ILs via supramolecular complexation. The hydrophobicity and functional groups of ILs have a great influence on protein partitioning, and a hydroxyl group-containing IL with DCH18C6 is capable of the quantitative partitioning of Cyt-c. On the other hand, protein transfer using conventional organic solvents is negligibly small. UV-visible, CD, and resonance Raman spectroscopic characterizations indicate that the sixth ligand Met 80 in the heme group of the Cyt-c-DCH18C6 complex in IL is replaced by other amino acid residues of the peptide chain and that a non-natural, six-coordinate, low-spin ferric heme structure is induced in IL. Solubilization of Cyt-c in IL causes the environmental change of the heme vicinity of Cyt-c, which triggers the functional conversion of Cyt-c from an electron-transfer protein to peroxidase. The Cyt-c-DCH18C6 complex in IL provides remarkably high peroxidase activity compared with native Cyt-c, because of enhancement of the affinity for H2O2.     

GaAs solar cells grown on Si substrates for space use

GaAs single‐junction and InGaP/GaAs multi‐junction thin‐film solar cells fabricated on Si substrates have great potential for high‐efficiency, low‐cost, lightweight and large‐area space solar cells. Heteroepitaxy of GaAs thin films on Si substrates has been examined and high‐efficiency GaAs thin‐film solar cells with total‐area efficiencies of 18·3% at AM0 and 20·0% at AM 1·5 on Si substrates (GaAs‐on‐Si solar cells) have been fabricated. In addition, 1‐MeV electron irradiation damage to GaAs‐on‐Si cells has been studied. The GaAs‐on‐Si cells are found to show higher end‐of‐life efficiency than the conventional GaAs cells fabricated on GaAs substrates (GaAs‐ on‐GaAs cells) under high‐fluence 1‐MeV electron irradiation of more than 1 × 10¹⁵ cm⁻². The first space flight to make use of them has been carried out. Forty‐eight 2 × 2 cm GaAs‐on‐Si cells with an average AM0 total‐area efficiency of 16·9% have been evaluated in the Engineering Test Satellite No.6 (ETS‐VI). The GaAs‐on‐Si cells have been demonstrated to be more radiation‐resistant in space than GaAs‐on‐GaAs cells and 50, 100 and 200‐μm‐thick Si cells. These results show that the GaAs‐on‐Si single‐junction and InGaP/GaAs‐on‐Si multi‐junction cells have great potential for space applications. Copyright © 2001 John Wiley & Sons, Ltd.