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21.
用从头算研究了d空穴位置不同对Ni—CO成键机制的影响。结果表明,Ni—CO键中σ/π接受作用的相对强弱,取决于Ni—CO簇所处的能态。σ空间电子云较π空间电子云弥散,因而Ni—CO簇的稳定性与σ空间电子云的排斥密切相关。随着Ni4pσ轨道上电子占据数的增加,Ni—CO稳定性减弱。比较了分子簇Ni—CO与NiCO分子及CO/Ni化学吸附体系之间的性质。 相似文献
22.
John A. Rogers Zhenan Bao 《Journal of polymer science. Part A, Polymer chemistry》2002,40(20):3327-3334
Plastic electronic materials and high‐resolution printing methods may be important technologies for new classes of consumer electronic devices that are lightweight, mechanically flexible and bendable, and that can cover large areas at low cost. This article summarizes some of our recent work in this area. It focuses on the materials and patterning techniques that we used to produce plastic active‐matrix backplane circuits for a type of paperlike display. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3327–3334, 2002 相似文献
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M. Asmann A. Wank H. Kim J. Heberlein E. Pfender 《Plasma Chemistry and Plasma Processing》2001,21(1):37-63
Enthalpy probe measurements were taken of the converging plasma plume in a triple torch plasma reactor and related to substrate heat flux measurements. Results show excellent entrainment of process gases injected into the converging plasma plume by way of the central injection probe. At lower pressures (40 kPa), the plasma volume is equivalent to at least a 3 cm diameter, 4 cm long cylinder, with relatively uniform temperature, velocity, and substrate heat flux profiles when compared to a typical dc arc jet. Converging plasma plume size, substrate heat flux, and enthalpy profiles are also shown to be a strong function of applied system power. Substrate heat flux measurements show smaller radial gradients than enthalpy probe measurements, because of the high radial velocity component of gases above the substrate boundary layer. Enthalpy probe measurements were also conducted for diamond deposition conditions and approximate temperature and velocity profiles obtained. Problems with the uniform gas mixture assumption prohibited more accurate measurements. Reproducibility of enthalpy measurement results was shown with an average standard deviation of 11.8% for the velocity and 7.6% for the temperature measurements. 相似文献
25.
Jiaming L Wenqi L Xuelin L Hailing C Qiaomei L Longdi L Zhimin L Guohui Z Cuilian C 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(13-14):3077-3081
Luminescent particles of lead carboxymethyl cellulose (Pb(CMC)2) containing salicyl fluorones (THBF), Pb(CMC)2-THBF were synthesized by the sol-gel method, using sodium carboxymethyl cellulose (NaCMC) as precursor and Pb2+ as precipitant. Pb(CMC)2-THBF can emit the intense and stable solid substrate room temperature phosphorescence (SS-RTP) on filter paper. And EDTA can chelate Pb2+ in Pb(CMC)2-THBF, causing it to decompose into aqueous soluble components PbY2-, CMC- and THBF, which can react with Ag+ to form Ag(CMC)2-THBF, causing the decrease of phosphorescence intensity. Based on the facts above, a new method for the determination of trace silver by SS-RTP quenching method was established. The linear range of this method is 8.0-40.0 fg spot(-1) (20.0-100.0 pg ml(-1)), with a detection limit (LD) of 2.2 fg spot(-1) (corresponding to a concentration range of 5.5 x 10(-13) g ml(-1)), and the regression equation of working curve is DeltaI(p) = 12.56 + 0.5527C(Ag+) (fg spot(-1), 0.4 microl spot(-1)), n = 8, r = 0.9992. This method has been applied to the determination of trace silver in human hair and tea sample with satisfactory results. The mechanism of SS-RTP emission is also discussed. 相似文献
26.
A starter culture ofTrichoderma reesei (Rut-C30) prepared in a liquid fluidized bed reactor (LFBR) gave better growth and greater cellulase production in submerged
fermentation than a conventional shake flask inoculum. The LFBR starter was prepared by first coatingT. reesei spores to 0.25 mm size corncob (1.0x108g-1) in a medium containing 1.0% corncob, 0.5 gL-1 xylose and 0.1 gL-1 lactose in a balanced salt solution, then fluidizing the particles in the LFBR for 36 h to allow germination of the spores,
and covering the particles with an approx 30 μm thick biofilm. This biofilm that developed in constant adherence to the lignocellulosic
carrier, apparently became well adapted to grow rapidly on insoluble cellulose substrates (Solca Floc), and had the enzymes
of the cellulase complex induced for increased cellulase production.
The LFBR starter used in a stirred tank reactor (STR) gave 15 gL-1 biomass production and 6.5 IU mL-1 overall cellulase activity with a volumetric productivity of 64 IU L-1h-1 in a 5 d fermentation, compared with a 7 d shake flask inoculum that gave 11 gL-1 biomass and 3.2 IU mL-1 cellulase activity, with a volumetric productivity of 31IU L-1h-1. The LFBR starter culture retained its viability in dry storage for 6–9 mo. 相似文献
27.
A novel, sensitive method for detecting protease inhibitors by using fluorescent protease substrates in gels is described. The protease inhibitors were separated on sodium dodecyl sulfate (SDS)-polyacrylamide gels containing a copolymerized peptide substrate, namely 4-methyl-coumaryl-7-amide (MCA). As the incorporated substrates in the gel, Boc-Phe Ser-Arg-MCA was used for trypsin, Suc-Ala-Ala-Pro-Phe-MCA for alpha-chymotrypsin, and Z-Phe-Arg-MCA for papain. After electrophoresis, washing and incubating the gel with the target protease solutions allowed the substrate to be cleaved by the protease, and the release of the fluorescent 7 amino-4 methyl-coumarin (AMC), which was detected under a UV transilluminator. The uncleaved peptide-MCA substrate remained where the inhibitors were present, and was visualized as dark blue bands on the light-green fluorescent background gel. This new method offers several advantages over other previous methods including: (i) greatly increased sensitivity can be achieved in a shorter period of time, which may be useful for discovering new protease inhibitors in small amounts of crude material; (ii) the procedure is quite simple and quick since the incubation period is very short and no time is needed for staining and destaining steps; (iii) since these probes using substrate specificity/target proteases, they are excellent tools for detection and discrimination of unknown protease inhibitors for various target proteases. 相似文献
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Fractal dimension of a carious tooth surface was determined using an electrochemical method. The method was based on time-dependent diffusion towards electrode surfaces, which is one of the most useful and reliable methods for the determination of fractal dimension of electrode surfaces. For this purpose, the tooth was covered with a gold layer, which acted as an electrode in electrochemical experiments. It is suggested that the fractal dimension can be used as a quantitative measure of the state of dental surfaces. The method presented demonstrates the power of electrochemical techniques for the determination of fractal dimension of surface of non-conducting objects. 相似文献
30.
Gottfried J. Palm Maren Thomsen Leona Berndt Winfried Hinrichs 《Molecules (Basel, Switzerland)》2022,27(22)
The bacterial chalcone isomerase (CHI) from Eubacterium ramulus catalyses the first step in a flavanone-degradation pathway by a reverse Michael addition. The overall fold and the constitution of the active site of the enzyme completely differ from the well-characterised chalcone isomerase of plants. For (+)-taxifolin, CHI catalyses the intramolecular ring contraction to alphitonin. In this study, Fwe perform crystal structure analyses of CHI and its active site mutant His33Ala in the presence of the substrate taxifolin at 2.15 and 2.8 Å resolution, respectively. The inactive enzyme binds the substrate (+)-taxifolin as well defined, whereas the electron density maps of the native CHI show a superposition of substrate, product alphitonin, and most probably also the reaction intermediate taxifolin chalcone. Evidently, His33 mediates the stereospecific acid-base reaction by abstracting a proton from the flavonoid scaffold. The stereospecificity of the product is discussed. 相似文献