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71.
N. Ibriş J. Mirza-Rosca A. Santana T. Vişan 《Journal of Solid State Electrochemistry》2002,6(2):119-125
The corrosion and passivation of Zn powder particles dispersed in a paste electrode immersed in 0.5 M Na2SO4 and 5×10–3 M Na2HPO4 solutions were studied mainly by electrochemical impedance spectroscopy. The role played by diffusion in the mechanism of
anodic oxidation of zinc powder particles has been shown. It was demonstrated that the anodic reactionof Zn powder in neutral
or near neutral media involves at least two adsorbed intermediates. By simulating the porous structure of the electrode, some
information about porous nature of zinc electrode could be extracted.
Electronic Publication 相似文献
72.
用稀土化合物改性的钛系载体催化剂(SN催化剂)进行苯乙烯和丙烯顺序嵌段共聚合(Sequentialblockcopolymerization)的研究.考察了苯乙烯预聚时间、单体比、外加给电子体(EB)、烷基铝浓度、催化剂浓度和聚合温度等条件对共聚合的影响.发现外加酯(EB)降低了共聚合反应催化活性,在EB/Ti摩尔比为5范围内,外酯有助于提高嵌段共聚物(iPS—b—iPP)中PS段和PP段的等规度及增加苯乙烯链节含量.SN型催化剂对苯乙烯一丙烯嵌段共聚合有较高的催化活性,催化效率在100g聚合物/g-Ti以上.共聚物通过溶剂革取分级除去均聚物后,所得嵌段共聚物中苯乙烯链节含量可在15~85mol%之间调节.其结构表征续见第II报. 相似文献
73.
Mei Y Wu T Xu C Langenbach KJ Elliott JT Vogt BD Beers KL Amis EJ Washburn NR 《Langmuir : the ACS journal of surfaces and colloids》2005,21(26):12309-12314
A simple yet versatile method was developed to prepare a low-density polymerization initiator gradient, which was combined with surface-initiated atom transfer radical polymerization (ATRP) to produce a well-defined poly(2-hydroxyethyl methacrylate) (HEMA) gradient substrate. A smooth variation in film thickness was measured across the gradient, ranging from 20 A to over 80 A, but we observed a nonmonotonic variation in water contact angle. Fits of X-ray reflectivity profiles suggested that at the low graft density end, the polymer chain structure was in a "mushroom" regime, while the polymer chains at high graft density were in a "brush" regime. It was found that the "mushroom" region of the gradient could be made adhesive to cells by adsorbing adhesion proteins, and cell adhesion could be tuned by controlling the density of the polymer grafts. Fibroblasts were seeded on gradients precoated with fibronectin to test cellular responses to this novel substrate, but it was found that cell adhesion did not follow the expected trend; instead, saturated cell adhesion and spreading was found at the low grafting density region. 相似文献
74.
Hidalgo ME Bascuñan L Quilhot W Fernández E Rubio C 《Photochemistry and photobiology》2005,81(6):1447-1449
Lichens synthesize and accumulate photoprotective compounds against possible damage induced by UV radiation in the photobiont. A biological model has been recently formulated that allows the use of lichens to evaluate changes at different UV radiation levels. The thermodynamics, photophysical and photochemical properties of lobaric acid were studied in acetonitrile, ethanol and Brij 35(3%) micelles at different pH values. Also the sun protector factor (SPF) was determined by in vitro methods. Lobaric acid was extracted from Stereoculon alpinum Laur. and characterized by means of standard procedures. Solutions were irradiated in oxygen and under nitrogen conditions with a UV medium pressure lamp. Lobaric acid absorbs at 287, 303 nm, and no fluorescence emission was observed. The maximum value of the molar extinction coefficient (5479.6 M(-1) cm(-1)) was obtained in Brij 35 at pH 12. Solubility is pH dependant and is highest in Brij 35 at pH 12 (4.45 x 10(-4) M). Photoconsumption quantum yields ranged between 10(-4) and 10(-5) in aerobic and anaerobic experimental conditions. Lobaric acid SPF was very low (0.5) compared with homosalate (4.0), (reference solar filter). Two pKa values, 5.05 (carboxylic acid group deprotonation) and 9.75 (phenolic OH deprotonation), were determined. 相似文献
75.
Measurements of dipole strengths of chlorophylls in solution are reviewed and correlated. The refractive index dependence is found to be expressible in a simple empirical fashion that does not rely on the concept of vacuum dipole strength. The index dependence in some respects contradicts the dependence expected on the basis of effective field theories. 相似文献
76.
Quantitative comparisons of the product ratios of the mechanistically similar diazomethane and Tiffeneau-Demjanov homologations of 17β-hydroxy-5α-androstan-3-one and 5α-cholestan-3-one have shown that equatorial approach of diazomethane to the C-3 CO group predominates to the extent of 70–79%. The data for both the C-17β-OH and -C8H17 substituted steroids are in close agreement thereby confirming that the C-17 substituents do not exert any significant long range effect on the reactions studied. 相似文献
77.
78.
Jim Coykendall 《Proceedings of the American Mathematical Society》1996,124(6):1727-1732
The image of the norm map from to (two rings of algebraic integers) is a multiplicative monoid . We present conditions under which is a UFD if and only if has unique factorization into irreducible elements. From this we derive a bound for checking if is a UFD.
79.
80.
A -symmetric spaceM is a complete connected regular Sasakian manifold, that fibers over an Hermitian symmetric spaceN, so that the geodesic involutions ofN lift to define global (involutive) automorphisms of the Sasakian structure onM. In the present paper the complete classification of -symmetric spaces is obtained. The groups of automorphisms of the Sasakian structures and the groups of isometries of the underlying Riemannian metrics are determined. As a corollary, the Sasakian space forms are also determined. 相似文献