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1.
CuBr/FeCl3 Catalysis as a novel and efficient method has been developed for the preparation of new aryl propargyl imine ether derivatives via C? H activation of aryl propargyl ethers, followed by reaction with imines generated from aldehydes and amines.  相似文献   
2.
The electrochemical detection of the hazardous pollutant 4‐nitrophenol (4‐NP) at low potentials, in order to avoid matrix interferences, is an important research challenge. This study describes the development, electrochemical characterization and utilization of a multiwall carbon nanotube (MWCNT) film electrode for the quantitative determination of 4‐NP in natural water. Electrochemical impedance spectroscopy measurements showed that the modified surface exhibits a decrease of ca. 13 times in the charge transfer resistance when compared with a bare glassy carbon (GC) surface. Voltammetric experiments showed the possibility to oxidize a hydroxylamine layer (produced by the electrochemical reduction of 4‐NP on the GC/MWNCT surface) in a potential region which is approximately 700 mV less positive than that needed to oxidize 4‐NP, thus minimizing the interference of matrix components. The limit of detection for 4‐NP obtained using square‐wave voltammetry (0.12 μmol L?1) was lower than the value advised by EPA. A natural water sample from a dam located in São Carlos (Brazil) was spiked with 4‐NP and analyzed by the standard addition method using the GC/MWCNT electrode, without any further purification step. The recovery procedure yielded a value of 96.5% for such sample, thus confirming the suitability of the developed method to determine 4‐NP in natural water samples. The electrochemical determination was compared with that obtained by HPLC with UV‐vis detection.  相似文献   
3.
A relaxation system based on a Lattice-Boltzmann type discrete velocity model is considered in the low Mach number limit. A third order relaxation scheme is developed working uniformly for all ranges of the mean free path and Mach number. In the incompressible Navier-Stokes limit the scheme reduces to an explicit high order finite difference scheme for the incompressible Navier-Stokes equations based on nonoscillatory upwind discretization. Numerical results and comparisons with other approaches are presented for several test cases in one and two space dimensions.

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We consider a multiscale network of natural gas pipelines. Different arcs of the network are to be modeled by possibly different models depending on the requisite qualitative detail required: an isothermal Euler system of equations; linearized model derived from the isothermal Euler system or a steady-state model of gas flow also referred to as an algebraic model. At the vertices (or joints) of the network coupling conditions are defined. An analysis of the well posedness of the hierarchial coupling conditions is presented. The analytical results are tested numerically on different network configurations including a real-world network based on the Canadian mainline gas network. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
6.
We apply the lattice Boltzmann (LB) method for solving the shallow water equations with source terms such as the bed slope and bed friction. Our aim is to use a simple and accurate representation of the source terms in order to simulate practical shallow water flows without relying on upwind discretization or Riemann problem solvers. We validate the algorithm on problems where analytical solutions are available. The numerical results are in good agreement with analytical solutions. Furthermore, we test the method on a practical problem by simulating mean flow in the Strait of Gibraltar. The main focus is to examine the performance of the LB method for complex geometries with irregular bathymetry. The results demonstrate its ability to capture the main flow features. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
7.
The first example of a Heck reaction with 9-vinylpurines and aryl halides is described. It gives exclusively E-9-(arenethenyl)purines in high yields. Subsequent hydrogenation furnishes 9-(arenethyl)purines quantitatively.  相似文献   
8.
In this paper, we present a finite difference method for the implementation of the rotation of a circular cylinder in the incompressible flow field by solving the two-dimensional unsteady Navier-Stokes equations. The approach is to use staggered grid method so that the accuracy and order of convergence of the associated algorithms can be maintained. The proposed method is easy to be implemented and is effective. A set of simulations for the flow dynamics is provided to show the computational results.  相似文献   
9.
The electrochemical methods cyclic and square‐wave voltammetry were applied to develop an electroanalytical procedure for the determination of N‐nitrosamines (N‐nitrosopyrrolidine, N‐nitrosopiperidine and N‐nitrosodiethylamine) in aqueous solutions. Cyclic voltammetry was used to evaluate the electrochemical behaviors of N‐nitrosamines on boron‐doped diamond electrodes. It was observed an irreversible electrooxidation peak located in approximately 1.8 V (vs. Ag/AgCl) for both N‐nitrosamines. The optimal electrochemical response was obtained using the following square‐wave voltammetry parameters: f=250 Hz, Esw=50 mV and Es=2 mV using a Britton–Robinson buffer solution as electrolyte (pH 2). The detection and quantification limits determined for total N‐nitrosamines were 6.0×10?8 and 2.0×10?7 mol L?1, respectively.  相似文献   
10.
This paper treats the question of feedback linearizing control oftwo-dimensional incompressible, unsteady wake flow. For definiteness,flow past a circular cylinder is considered, but the design approachpresented here is applicable to other flow control problems. Twofinite-dimensional lower-order models based on Proper OrthogonalDecomposition (POD) of dimension N with N actuators are considered.Models I and II are obtained using control function and penalty functionmethods, respectively. Control action can be achieved by a combinationof suction, injection, and synthetic jets. For the design ofcontrollers, it is assumed that the system matrices of the POD modelsare unknown. Nonlinear adaptive control systems for the two models arederived. For model I, nontrivial zero-error dynamics exists, which playa key role in the stability of the closed-loop system. But for model II,global adaptive trajectory control is achieved. In the closed-loopsystem, the mode amplitudes asymptotically follow the referencetrajectories. Simulation results for a 4-mode POD model obtained usingthe penalty function method are presented. These results show that inthe closed-loop system, unsteadiness in the mode amplitudes can besuppressed in spite of large uncertainties in the flow model.  相似文献   
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