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211.
ABSTRACT Quenching dynamics of excited quinone molecules are given much attention in photochemistry and biochemistry. In order to study the viscosity effect on the quenching of triplet excited state of duroquinone (3DQ?) by stable radical, 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO), this study measured chemically induced dynamic electron polarization (CIDEP) spectra and transient absorptive spectra in various solvents. The solvents used were ethylene glycol, 1,2-propanol and their mixtures with different ratio in volume. The Stern-Volmer plot was obtained form CIDEP spectra of photolysis of DQ with different TEMPO concentrations. Combining the slope of the Stern-Volmer plot with lifetime of 3DQ?, determined from the 3DQ? transient absorbance decay curve, the quenching rate constants of 3DQ? by TEMPO were calculated in each solvent. The results indicate that the quenching rate constant is viscosity-dependent, and that it decreases linearly with the increase in solvent viscosity in the range used in our experiment. 相似文献
212.
Based on the multifractal detrended fluctuation analysis (MF-DFA) and multifractal spectrum analysis, this paper empirically studies the multifractal properties of the Chinese stock index futures market. Using a total of 2942 ten-minute closing prices, we find that the Chinese stock index futures returns exhibit long-range correlations and multifractality, making the single-scale index insufficient to describe the futures price fluctuations. Further, by comparing the original time series with the transformed time series through shuffling procedure and phase randomization procedure, we show the existence of two different sources of the multifractality for the Chinese stock index futures market. Our results suggest that the multifractality is mainly due to long-range correlations, although the fat-tailed probability distributions also contribute to such multifractal behaviour. 相似文献
213.
A second-order smooth penalty function algorithm for constrained optimization problems 总被引:1,自引:0,他引:1
Xinsheng Xu Zhiqing Meng Jianwu Sun Liguo Huang Rui Shen 《Computational Optimization and Applications》2013,55(1):155-172
This paper introduces a second-order differentiability smoothing technique to the classical l 1 exact penalty function for constrained optimization problems(COP). Error estimations among the optimal objective values of the nonsmooth penalty problem, the smoothed penalty problem and the original optimization problem are obtained. Based on the smoothed problem, an algorithm for solving COP is proposed and some preliminary numerical results indicate that the algorithm is quite promising. 相似文献
214.
A chitosan/ionic liquid composite electrode was prepared and used to determine uric acid (UA) in the presence of a large excess of ascorbic acid (AA) and dopamine (DA) by linear sweep voltammetry (LSV). The modified electrode shows large peak separations between DA, AA, and UA. Due to the existence of chitosan and ionic liquid in the composite, the modified electrode exhibits strong electrochemical catalytic activity toward the oxidation of UA. Under optimal conditions, the peak current is linearly dependent on the UA concentration in the range of 5?×?10?7–2?×?10?4 M in the presence of 5?×?10?4 M AA and 5?×?10?5 M DA with a correlation coefficient of 0.9978, and the detection limit is 5?×?10?8 M at a signal-to-noise ratio of 3. With good sensitivity and stability, the constructed sensor was applied in the determination of UA in human serum samples and satisfactory results were obtained. 相似文献
215.
Hongwen Chen Bei-Er Jia Xinsheng Lu Dr. Yichuan Guo Rui Hu Dr. Rabia Khatoon Prof. Dr. Lei Jiao Prof. Dr. Jianxing Leng Prof. Dr. Liqiang Zhang Prof. Dr. Jianguo Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(42):9973-9983
Tin diselenide (SnSe2), as an anode material, has outstanding potential for use in advanced lithium-ion batteries. However, like other tin-based anodes, SnSe2 suffers from poor cycle life and low rate capability due to large volume expansion during the repeated Li+ insertion/de-insertion process. This work reports an effective and easy strategy to combine SnSe2 and carbon nanotubes (CNTs) to form a SnSe2/CNTs hybrid nanostructure. The synthesized SnSe2 has a regular hexagonal shape with a typical 2D nanostructure and the carbon nanotubes combine well with the SnSe2 nanosheets. The hybrid nanostructure can significantly reduce the serious damage to electrodes that occurs during electrochemical cycling processes. Remarkably, the SnSe2/CNTs electrode exhibits a high reversible specific capacity of 457.6 mA h g−1 at 0.1 C and 210.3 mA h g−1 after 100 cycles. At a cycling rate of 0.5 C, the SnSe2/CNTs electrode can still achieve a high value of 176.5 mA h g−1, whereas a value of 45.8 mA h g−1 is achieved for the pure SnSe2 electrode. The enhanced electrochemical performance of the SnSe2/CNTs electrode demonstrates its great potential for use in lithium-ion batteries. Thus, this work reports a facile approach to the synthesis of SnSe2/CNTs as a promising anode material for lithium-ion batteries. 相似文献
216.
217.
Yinghui Duan Yi Dai Liuyuan Chen Mingli Liu Yaolan Li Xinsheng Yao 《Magnetic resonance in chemistry : MRC》2012,50(9):642-645
Four new xanthones, 1‐methoxy‐3,7,8‐trihydroxyxanthone (1), 1‐methoxy‐4,7,8‐trihydroxyxanthone (2), 1‐methoxy‐4,7‐dihydroxyxanthone (3), and 1,4‐dimethoxy‐2,7‐dihydroxyxanthone (4) were isolated from the stems of Cratoxylum cochinchinense along with four known xanthones (5–8). The structures of new compounds were determined by extensive spectroscopic analyses, mainly 1D and 2D NMR and HRESIMS data. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
218.
3D 刚体摆是研究地球静止轨道航天器的一个力学简化模型, 它绕一个固定、无摩擦的支点旋转, 具有3 个转动自由度. 文章给出基于修正型罗德里格斯(Rodrigues) 参数描述的3D 刚体摆的姿态动力学方程, 针对3D 刚体摆姿态和角速度稳定的非线性控制设计问题, 基于无源性控制理论利用能量法设计了3D 刚体摆的系统控制器, 并证明了系统满足无源性. 构造了系统的李雅普诺夫(Lyapunov) 函数, 利用能量法设计出3D 刚体摆的姿态控制律, 并由拉萨尔(LaSalle) 不变集原理证明了该控制律的渐近稳定性. 仿真实验给出了3D 刚体摆在倒立平衡位置的姿态和角速度的渐近稳定性, 仿真实验结果表明基于能量方法的3D 刚体摆姿态控制是有效的. 相似文献
219.
针对目前电子信息类工程技术人才培养现状及社会需求,分析了目前我国工程教育存在的问题,提出了解决这些问题的方法和措施,并结合这些措施,介绍了具体的做法,即以项目为依托将工程设计与工程实践融入到教学中,基于校内实习平台强化实习环节,将"大学生创新、创业训练计划"常态化、多元化.经过实践,该措施初见成效,以待进一步推广. 相似文献
220.
Numerical Simulation of a Multi-Frequency Resistivity Logging-While-Drilling Tool Using a Highly Accurate and Adaptive Higher-Order Finite Element Method
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Zhonghua Ma Dejun Liu Hui Li & Xinsheng Gao 《advances in applied mathematics and mechanics.》2012,4(4):439-453
A novel, highly efficient and accurate adaptive higher-order finite element
method ($hp$-FEM) is used to simulate a multi-frequency resistivity logging-while-drilling (LWD)
tool response in a borehole environment. Presented in this study are the vector expression
of Maxwell's equations, three kinds of boundary conditions, stability weak formulation of
Maxwell's equations, and automatic $hp$-adaptivity strategy. The new $hp$-FEM can select
optimal refinement and calculation strategies based on the practical formation model and
error estimation. Numerical experiments show that the new $hp$-FEM has an exponential
convergence rate in terms of relative error in a user-prescribed quantity of interest
against the degrees of freedom, which provides more accurate results than those obtained
using the adaptive $h$-FEM. The numerical results illustrate the high efficiency and
accuracy of the method at a given LWD tool structure and parameters in different physical
models, which further confirm the accuracy of the results using the Hermes
library (http://hpfem.org/hermes) with a multi-frequency resistivity LWD tool
response in a borehole environment. 相似文献