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81.
Herein, an efficient Lewis acid catalyzed protocol for the homo-Nazarov cyclizations of alkenyl cyclopropyl ketones is reported. Alkenes bearing β-hydrogens (or silyl groups) provide 1.5:1 mixtures of methylene cyclohexenols and cyclohexenones. When no β-hydrogens (or silyl groups) are present, only cyclohexenones are observed. Products are rapidly formed in good to high yields (up to 93%) under mild conditions and could be readily derivatized. 相似文献
82.
Ting‐Hao Yang Chun‐Yen Liao Jen‐Lin Chang Chien‐Hung Lien Jyh‐Myng Zen 《Electroanalysis》2009,21(21):2390-2394
A simple electrochemical approach to evaluate oxygen reduction catalysts using an inexpensive screen‐printed ring disk carbon electrode system, consisting of a ring electrode deposited with MnO2 and a disk electrode modified with the catalysts for study, is developed in this study. The as‐prepared MnO2 is selective and sensitive for H2O2 oxidation in the presence of O2 and is crucial to the proposed approach. By coupling with a wall‐jet electrochemical cell, the product generated from the reduction reaction at the disk electrode can effectively be monitored at the MnO2‐deposited ring electrode. Model catalysts of nano‐Au and nano‐Pd representing 2e? reduction of O2 to H2O2 and 4e? reduction to H2O, respectively, were evaluated as electrode materials in oxygen reduction reaction to demonstrate the applicability of the proposed method. 相似文献
83.
The interaction of a water-soluble ABA type of dumbbell-shaped polyethyleniminated copolymers (D400(EI)8) with H2PtCl6 in aqueous medium is studied by means of UV-visible absorption spectra, dynamic light scattering (DLS) measurements, and transmission electron microscopy (TEM). From TEM images of the stained polymer, it is evident that the spherical and well-structured polymer micelles are formed by the introduction of H2PtCl6, and totally nonstructured micelles are formed from D400(EI)8 itself. These findings coincide with the results obtained from DLS measurements, where the narrowly distributed polymer aggregates are remarkably observed. Moreover, it is directly evidenced from TEM that the reduced Pt(0) nanoparticles are embedded in the polyethylenimine (PEI) block at the exterior of micelles, whereas the polyoxypropylene (PPO) block is surrounded by the PEI block. Additionally, the resulting Pt(0) colloids are very stable for at least 4 months. 相似文献
84.
General probabilistic approach to the filtration process 总被引:1,自引:0,他引:1
We show experimentally that clogging is basically a matter of the probability of the presence of particles. We describe this process as a function of the main variables of the process, namely, the ratio of particle to mesh hole size, the solid fraction, and the number of grains arriving at each mesh hole during one test, with the help of a simple model, the predictions of which are in very good agreement with our experimental data. 相似文献
85.
Email: chlien{at}mail.nkmu.edu.tw
Received on August 10, 2006; Accepted on September 6, 2006 In this paper, delay-dependent guaranteed cost observer-basedcontrol for neutral systems with time-varying delays is considered.Control and observer gains will be given from the linear matrixinequality feasible solutions. Optimal guaranteed cost observer-basedcontrol which will minimize the guaranteed cost of the systemis provided. 相似文献
86.
Due to the special structure of a nanotube (NT), the different potential from piezoelectricity can be naturally divided by the hollow of the tube when the NT is bent or deformed. Furthermore, both the bent/deformed inner and outer wall can form a steady voltage/current, which might enhance the output voltage/current. We demonstrate a direct‐current nanogenerator (NG) based on zinc oxide (ZnO) NT arrays driven by an ultrasonic wave. The average output voltage is ca. 0.10 mV and the current density is ca. 0.069 μA/mm2. Our study shows that the maximum power output of the ZnO NT array NG is 0.112 nW and the power density is 1.4 nW/cm2. The success of energy harvesting from ZnO NTs reveals the potential of using nanogenerators for tubular piezoelectric materials. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
87.
Global asymptotic stability for Cohen-Grossberg neural networks (CGNNs) with time-varying delays is investigated. Criteria are proposed to guarantee the stability and uniqueness of equilibrium point of CGNNs via LMI approach. A numerical example is illustrated to show the effectiveness of our results. 相似文献
88.
The nature of some well known 2π + 2π cycloaddition reactions was studied by explicit construction of the quasiadiabatic potential-energy surfaces for the cycloaddition of ethene and various monosubstituted allylic cations. Such surfaces determined by ab initio MO computations are particularly suitable for analysis of symmetry selection rules. By examining the characteristics of such surfaces, we have studied the substituent effect and the role played by the positive charge in such systems. Qualitative discussion based on simplified MO, involving fewer electrons, is also given. 相似文献
89.
Determination of fatty acids in vegetable oil by reversed-phase liquid chromatography with fluorescence detection. 总被引:5,自引:0,他引:5
The effect of temperature and organic solvent composition (acetonitrile and methanol) on the reversed-phase separation of coumarin-derivatized fatty acids according to their carbon number (C14 to C22), the degree of unsaturation, as well as cis/trans (C18:1 c/t, C18:2 cc/tt, C18:3 ccc/ttt) configuration was investigated to find out the effective separation condition. Based on the linear plots of the logarithm of the capacity factor of saturated fatty acids versus their carbon number, the equivalent chain length (ECL) of unsaturated fatty acids was calculated. The ECL values were found to be significantly altered and the differentiation between cis and trans fatty acids was increased when either the temperature or organic solvent composition was decreased. These results generally led to a better resolution at the expense of separation time. A ternary gradient composed of water, acetonitrile, and methanol was then developed to elute the solutes at 55 degrees C within a separation time of 40 min with a minimum resolution of 1.0 for the worst pair. This method was demonstrated to resolve the fatty acids in a vegetable shortening. 相似文献
90.
Tran Ngoc Lien 《Journal of Mathematical Analysis and Applications》2008,337(2):1302-1314
We consider the problem of finding a function defined on (0,∞) from a countable set of values of its Laplace transform. The problem is severely ill-posed. We shall use the expansion of the function in a series of Laguerre polynomials to convert the problem in an analytic interpolation problem. Then, using the coefficients of Lagrange polynomials we shall construct a stable approximation solution. Error estimate is given. Numerical results are produced. 相似文献