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Electroreduction and Acid–Base Properties of Dipyrrolylquinoxalines
Fu, Zhen,Zhang, Min,Zhu, Weihua,Karnas, Elizabeth,Mase, Kentaro,Ohkubo, Kei,Sessler, Jonathan L.,Fukuzumi, Shunichi,Kadish, Karl M. American Chemical Society 2012 The journal of physical chemistry. A, Molecules, s Vol.116 No.41
<P>The electroreduction and acid–base properties of dipyrrolylquinoxalines of the form H<SUB>2</SUB>DPQ, H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>), and H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB>2</SUB> were investigated in benzonitrile (PhCN) containing 0.1 M tetra-<I>n</I>-butylammonium perchlorate (TBAP). This study focuses on elucidating the complete electrochemistry, spectroelectrochemistry, and acid–base properties of H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB><I>n</I></SUB> (<I>n</I> = 0, 1, or 2) in PhCN before and after the addition of trifluoroacetic acid (TFA), tetra-<I>n</I>-butylammonium hydroxide (TBAOH), tetra-<I>n</I>-butylammonium fluoride (TBAF), or tetra-<I>n</I>-butylammonium acetate (TBAOAc) to solution. Electrochemical and spectroelectrochemical data provide support for the formation of a monodeprotonated anion after disproportionation of a dipyrrolylquinoxaline radical anion produced initially. The generated monoanion is then further reduced in two reversible one-electron-transfer steps at more negative potentials in the case of H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>) and H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB>2</SUB>. Electrochemically monitored titrations of H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB><I>n</I></SUB> with OH<SUP>–</SUP>, F<SUP>–</SUP>, or OAc<SUP>–</SUP> (in the form of TBA<SUP>+</SUP>X<SUP>–</SUP> salts) give rise to the same monodeprotonated H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB><I>n</I></SUB> produced during electroreduction in PhCN. This latter anion can then be reduced in two additional one-electron-transfer steps in the case of H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>) and H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB>2</SUB>. Spectroscopically monitored titrations of H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB><I>n</I></SUB> with X<SUP>–</SUP> show a 1:2 stoichiometry and provide evidence for the production of both [H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB><I>n</I></SUB>]<SUP>−</SUP> and XHX<SUP>–</SUP>. The spectroscopically measured equilibrium constants range from log β<SUB>2</SUB> = 5.3 for the reaction of H<SUB>2</SUB>DPQ with TBAOAc to log β<SUB>2</SUB> = 8.8 for the reaction of H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB>2</SUB> with TBAOH. These results are consistent with a combined deprotonation and anion binding process. Equilibrium constants for the addition of one H<SUP>+</SUP> to each quinoxaline nitrogen of H<SUB>2</SUB>DPQ, H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>), and H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB>2</SUB> in PhCN containing 0.1 M TBAP were also determined via electrochemical and spectroscopic means; this gave rise to log β<SUB>2</SUB> values ranging from 0.7 to 4.6, depending upon the number of nitro substituents present on the H<SUB>2</SUB>DPQ core. The redox behavior of the H<SUB>2</SUB>DPQ(NO<SUB>2</SUB>)<SUB><I>n</I></SUB> compounds of the present study were further analyzed through comparisons with simple quinoxalines that lack the two linked pyrrole groups, i.e., Q(NO<SUB>2</SUB>)<SUB><I>n</I></SUB> where <I>n</I> = 0, 1, or 2. It is concluded that the pyrrolic substituents play a critical role in regulating the electrochemical and spectroscopic features of DPQs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcafh/2012/jpcafh.2012.116.issue-41/jp3074706/production/images/medium/jp-2012-074706_0017.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp3074706'>ACS Electronic Supporting Info</A></P>
Fuzhen Chen,Hanqiao Jiang,Xiaohu Bai,Wei Zheng 한국공업화학회 2013 Journal of Industrial and Engineering Chemistry Vol.19 No.2
Sodium metaborate, a novel alkali, is introduced into alkali/surfactant/polymer (ASP) flooding to solve the negative effects caused by conventional alkalis. Sodium metaborate can reduce the adsorption loss of the surfactant as well as the interfacial tension (IFT). Weak alkali sodium metaborate causes less viscosity reduction compared with strong alkalis. Scale precipitation study shows that sodium metaborate can be effective to avoid the scale precipitation damage. Study results indicate that sodium metaborate result in the highest oil recovery of 56% compared with sodium carbonate and sodium hydroxide, and at the same time avoid the problems caused by conventional alkalis.
Yingbo Liu,Jiujun Cheng,Chendan Yan,Xiao Wu,Fuzhen Chen 보안공학연구지원센터 2015 International Journal of Hybrid Information Techno Vol.8 No.1
The personalized recommendation systems could better improve the personalized service for network user and alleviate the problem of information overload in the Internet. As we all know, the key point of being a successful recommendation system is the performance of recommendation algorithm. When scholars put forward some new recommendation algorithms, they claim that the new algorithms have been improved in some respects, better than previous algorithm. So we need some evaluation metrics to evaluate the algorithm performance. Due to the scholar didn’t fully understand the evaluation mechanism of recommendation algorithms. They mainly emphasized some specific evaluation metrics like Accuracy, Diversity. What’s more, the academia did not establish a complete and unified assessment of recommendation algorithms evaluation system which is credibility to do the work of recommendation evaluation. So how to do this work objective and reasonable is still a challengeable task. In this article, we discussed the present evaluation metrics with its respective advantages and disadvantages. Then, we put forward to use the Matthews Correlation Coefficient to evaluate the recommendation algorithm’s performance. All this based on an open source projects called mahout which provides a rich set of components to construct the classic recommendation algorithm. The results of the experiments show that the applicability of Matthews correlation coefficient in the relative evaluation work of recommendation algorithm.
Free vibration analysis of uniform and stepped functionally graded circular cylindrical shells
Haichao Li,Fuzhen Pang,Yuan Du,Cong Gao 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.33 No.2
A semi analytical method is employed to analyze free vibration characteristics of uniform and stepped functionally graded circular cylindrical shells under complex boundary conditions. The analytical model is established based on multi-segment partitioning strategy and first-order shear deformation theory. The displacement functions are handled by unified Jacobi polynomials and Fourier series. In order to obtain continuous conditions and satisfy complex boundary conditions, the penalty method about spring technique is adopted. The solutions about free vibration behavior of functionally graded circular cylindrical shells were obtained by approach of Rayleigh-Ritz. To confirm the dependability and validity of present approach, numerical verifications and convergence studies are conducted on functionally graded cylindrical shells under various influencing factors such as boundaries, spring parameters <i>et al</i>. The present method apparently has rapid convergence ability and excellent stability, and the results of the paper are closely agreed with those obtained by FEM and published literatures.