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1.
Quantitative analysis of polyhexamethylene guanidine (PHMG) oligomers via matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry with an ionic‐liquid matrix 下载免费PDF全文
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Burn‐in is a widely used method to improve the quality of products or systems after they have been produced. In this paper, we consider the problem of determining the optimal burn‐in time and optimal work size maximizing the long‐run average amount of work saved per time unit in the computer applications. Assuming that the underlying lifetime distribution of the computer has an initially decreasing or/and eventually increasing failure rate function, an upper bound for the optimal burn‐in time is derived for each fixed work size and a uniform (with respect to the burn‐in time) upper bound for the optimal work size is also obtained. Furthermore, it is shown that a non‐trivial lower bound for the optimal burn‐in time can be derived if the underlying lifetime distribution has a large initial failure rate. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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H2CCF自由基与HNCO反应机理的理论研究 总被引:4,自引:0,他引:4
采用密度泛函理论的B3LYP方法, 在6-311++G(d,p)基组水平上研究了H2CCF自由基与HNCO的微观反应机理, 优化了反应过程中的反应物、中间体、过渡态和产物, 为了获得更精确的能量信息, 还在QCISD(T)/6-311++G(d,p)基组水平上计算了各物质的能量.振动分析结果和IRC分析结果证实了中间体和过渡态的真实性, 计算所得的成键临界点电荷密度的变化也确认了反应过程.对于H2CCF自由基与HNCO反应, 我们找到了六条可行的反应通道, 结果分析表明通道H2CCF+HNCO→IM3→TS5→H2CCFH+NCO控制步骤活化能最低, 是该反应的主要通道, 在此反应过程中有稳定的氢键复合物IM3生成, 还表现出氢原子迁移的反应特征. 相似文献
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[reaction: see text] A new iterative strategy for the synthesis of unsymmetrically substituted polyynes has been developed. The starting bromoalkyne is homologated by one acetylene unit through palladium-catalyzed cross-coupling with a TIPS-protected terminal acetylene and a subsequent in situ one-pot AgF-mediated desilylative bromination. The utility of this new synthetic method is demonstrated by its application to the total synthesis of (S)-(E)-15,16-dihydrominquartynoic acid. 相似文献
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K.B. Eisenthal N.J. Turro E.V. Sitzmann I.R. Gould G. Hefferon J. Langan Y. Cha 《Tetrahedron》1985,41(8):1543-1554
A combination of picosecond and nanosecond laser spectroscopy measurements, chemical quenching experiments and triplet sensitization experiments has allowed the determination of the rapid singlet to triplet and slower triplet to singlet intersystem crossing rates for diphenylmethylene in fluid solution at room temperature. It is shown that under the conditions of the kinetic measurements, singlet and triplet diphenylmethylene (1DPM and 3DPM, respectively) are in rapid equilibrium relative to reactions, so that knowledge of the values of kST and kTS allows determination of the equilibrium constant and change in free energy for the 1DPM 〈 3DPM process. The absolute reactivity of 1DPM toward a series of alcohols has been determined and is discussed in terms of other current investigations of carbene reactivity. 相似文献
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Uranium(VI) complexed with aluminon (3-[bis(3-carboxy-4-hydroxy-phenyl)methylene]-6-oxo-1,4-cyclohexadiene-1-carboxylic acid triammonium salt) was determined by adsorptive cathodic stripping voltammetry (ACSV) using a hanging mercury drop electrode. Trace uranium(VI) and zinc(II) can be simultaneously determined in a single scan in the presence of aluminon and urea. Optimal conditions were found to be: accumulation time; 180–200 s, accumulation potential; 50 mV versus Ag/AgCl, scan rate; 40 mV s−1, supporting electrolyte; 0.1 M sodium acetate buffer at pH 6.5–7.0, and concentration of aluminon; 1×10−6 M. The linear range of uranium(VI) and zinc(II) were observed over the concentration range 2–33 and 30–120 ng ml−1, respectively. The detection limit (S/N=3) are 0.2 ng ml−1 (uranium) and 30 ng ml−1 (zinc). A good reproducibility shows RSDs of 2.5–4.0% (n=10). The procedure offers high selectivity, with the presence of urea masking some metal ions. 相似文献
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制备了不同摩尔比的甲基丙烯酸-磷脂酰乙醇甲基丙烯酰胺共聚物,研究了这种共聚物在水面的表面压力(π)-分子面积(A)曲线、共聚物制成的MOS LB膜的电容(C)-电压(V)特性及此LB膜的相变温度。 相似文献
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Birck C Cha JY Cross J Schulze-Briese C Meroueh SO Schlegel HB Mobashery S Samama JP 《Journal of the American Chemical Society》2004,126(43):13945-13947