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排序方式: 共有446条查询结果,搜索用时 703 毫秒
41.
42.
Jin Bai Kin 《数学研究及应用》1991,11(2):203-206
We construct real valued functions from infinite sequences. We also consider some properties of such functions and null sequences. 相似文献
43.
Quantitative characterization of hydroxyl radicals produced by various photocatalysts 总被引:2,自引:0,他引:2
Hydroxyl radicals ((·)OH) have been deemed to be the major active species during the photocatalytic oxidation reaction. In this study, (·)OH produced on various semiconductor photocatalysts in aqueous solution under Xenon lamp irradiation was quantitatively investigated by the photoluminescence (PL) technique using coumarin (COU) as a probe molecule. The results indicated that the formation rate of (·)OH on the surface of irradiated commercial Degussa P25 (P25) was much higher than that of other semiconductor. The pH values of the solution and phase structure of TiO(2) significantly influenced the production rate of (·)OH. The acidic pH environment of the solutions and bi-phase structure (anatase and rutile) of TiO(2) were beneficial to enhancing the formation rate of (·)OH. In addition, the formation rate of (·)OH on anatase TiO(2) and P25 was much faster than that of (·)OH on the other semiconductors (such as rutile TiO(2), ZnO, WO(3), CdS, Bi(2)WO(4) and BiOCl, etc.). A new concept "OH-index" was first proposed to compare photocatalytic activity of photocatalysts, which would provide new insight into the investigation of semiconductor photocatalysts. 相似文献
44.
Li Z Rosenbaum MA Venkataraman A Tam TK Katz E Angenent LT 《Chemical communications (Cambridge, England)》2011,47(11):3060-3062
We developed a bacteria-based AND logic gate using a Pseudomonas aeruginosa lasI/rhlI double mutant with two quorum-sensing signaling molecules as the input signals. We showed a distinct electrical output signal, despite the complexity and continuous regulation of metabolic reactions of living cells. 相似文献
45.
A versatile palladium catalyst system for Suzuki-Miyaura coupling of alkenyl tosylates and mesylates
Wong PY Chow WK Chung KH So CM Lau CP Kwong FY 《Chemical communications (Cambridge, England)》2011,47(29):8328-8330
A general and effective palladium system for Suzuki-Miyaura coupling of alkenyl electrophiles under mild reaction conditions is reported. With the Pd(OAc)(2)/CM-phos system, a variety of alkenyl tosylates are coupled well with ArB(OH)(2). Moreover, the first successful examples of using alkenyl mesylates in alkenylation are also described. 相似文献
46.
Ming‐Zhong Wang Dr. Cong‐Ying Zhou Dr. Zhen Guo Dr. Ella Lai‐Ming Wong Dr. Man‐Kin Wong Prof. Chi‐Ming Che 《化学:亚洲杂志》2011,6(3):812-824
Chiral binuclear gold(I) phosphine complexes catalyze enantioselective intermolecular hydroarylation of allenes with indoles in high product yields (up to 90 %) and with moderate enantioselectivities (up to 63 % ee). Among the gold(I) complexes examined, better ee values were obtained with binuclear gold(I) complexes, which displayed intramolecular AuI AuI interactions. The binuclear gold(I) complex 4c [(AuCl)2( L3 )] with chiral biaryl phosphine ligand (S)‐(−)‐MeO‐biphep ( L3 ) is the most efficient catalyst and gives the best ee value of up to 63 %. Substituents on the allene reactants have a slight effect on the enantioselectivity of the reaction. Electron‐withdrawing groups on the indole substrates decrease the enantioselectivity of the reaction. The relative reaction rates of the hydroarylation of 4‐X‐substituted 1,3‐diarylallenes with N‐methylindole in the presence of catalyst 4c [(AuCl)2( L3 )] / AgOTf [ L3 =(S)‐(−)‐MeO‐biphep], determined through competition experiments, correlate (r2=0.996) with the substituent constants σ. The slope value is −2.30, revealing both the build‐up of positive charge at the allene and electrophilic nature of the reactive AuI species. Two plausible reaction pathways were investigated by density functional theory calculations, one pathway involving intermolecular nucleophilic addition of free indole to aurated allene intermediate and another pathway involving intramolecular nucleophilic addition of aurated indole to allene via diaurated intermediate E2 . Calculated results revealed that the reaction likely proceeds via the first pathway with a lower activation energy. The role of AuI AuI interactions in affecting the enantioselectivity is discussed. 相似文献
47.
48.
49.
Kin Seng Chiang 《光学学报》2003,23(Z1)
Our progress in the study of long-period gratings (LPGs) in planar optical waveguides is reviewed. In particular,experimental LPGs in glass and polymer waveguides are presented to demonstrate the potential of LPG-based waveguide devices. 相似文献
50.
关于3连通图的容错直径和宽直径 总被引:5,自引:0,他引:5
容错直径和宽直径是度量网络可靠性和有效性的重要参数.对任意k连通图,它的容错直径Dk不超过宽直径dk,本证明:当D2=2时,d3≤max{D, l,2D3-2};当D2≥3时,d3≤(D2-1)[2(D2-1)(D3-1)-D2-2] 1. 相似文献