A novel fully implicit finite volume method applied to the lid‐driven cavity problem—Part I: High Reynolds number flow calculations

A novel implicit cell‐vertex finite volume method is described for the solution of the Navier–Stokes equations at high Reynolds numbers. The key idea is the elimination of the pressure term from the momentum equation by multiplying the momentum equation with the unit normal vector to a control volume boundary and integrating thereafter around this boundary. The resulting equations are expressed solely in terms of the velocity components. Thus any difficulties with pressure or vorticity boundary conditions are circumvented and the number of primary variables that need to be determined equals the number of space dimensions. The method is applied to both the steady and unsteady two‐dimensional lid‐driven cavity problem at Reynolds numbers up to 10000. Results are compared with those in the literature and show excellent agreement. Copyright © 2003 John Wiley & Sons, Ltd.     

Kinetic analysis of thermal decomposition of some Co-complexes of three unsymmetrical <Emphasis Type="Italic">vic</Emphasis>-dioximes ligands

The thermal decomposition of three new reagent cyclohexylamine-p-tolylglyoxime (L₁H₂), tertiarybutyl amine-p-tolylglyoxime (L₂H₂) and secondary butylamine-p-tolylglyoxime (L₃H₂ and their Co-complexes were studied by both isothermal and nonisothermal methods. As expected, the complex structure of Co-complexes, different steps with different activation energies were realized in decomposition process. Model-fitting and model-free kinetic approaches were applied to nonisothermal and isothermal data. The kinetic triplet (f(α), A and E) related to nonisothermal model-fitting method can not be meaningfully compared with values obtained from isothermal method. The complex nature of the multi-step process of the studied compounds was more easily revealed using a wider temperature range in nonisothermal isoconversional method.     

Effect of Molecular Weight on Packing during Latex Film Formation

A UV-visible technique is used to study the evolution of transparency during film formation from latex particles. Latex particles with high and low molecular weight (HM and LM) polymethyl methacrylate (PMMA) are used to prepare films. Two sets of films with different latex content were prepared from HM and LM particles separately, by annealing PMMA particles above the glass transition temperature. Transmitted photon intensity, I(tr), from HM and LM films increased as the annealing temperature was increased. The increase in the transmitted photon intensity is attributed to the latex content (film thickness) for the annealed film samples. It is suggested that as the latex particles are packed (film thickness is increased) fewer voids or cracks are formed in the films. Positive and negative absorption coefficients are measured below and above 210 and 180 degrees C annealing temperatures for the HM and LM films. Packing coefficients are obtained for films in various latex contents. It is observed that LM particles are packed much easier than HM particles. Copyright 2001 Academic Press.     

Improvement of catalytic activity of lipase in the presence of wide rim substituted calix[4]arene carboxylic acid-grafted magnetic nanoparticles

Candida rugosa lipase immobilized on calix[4]arene carboxylic acid-grafted magnetic nanoparticles using a sol–gel encapsulation technique was tested for activity, which was assessed both in the enantioselective hydrolysis of racemic Naproxen methyl ester and that of p-nitrophenylpalmitate. It has also been noticed that, compared to the free enzyme (E = 137) with an ee value of >98 %, S-Naproxen calix[4]arene carboxylic acid-grafted magnetic nanoparticles based on encapsulated lipase (Calix-1-MN and Calix-2-MN) offer excellent enantioselectivity (E = 373 and E = 381). Moreover, the results indicated that after the fifth reuse in the enantioselective reaction, the encapsulated lipase (Calix-2-MN) still retained about 43 % of its conversion power.     

Microwave Assisted Synthesis of Chitosan Nanoparticles

Chitosan nanoparticles (CHN) were prepared based on ionotropic gelation between low moleculer weight chitosan and sodium tripolyphosphate (TPP) under microwave irradiation. Particle size, zeta potential, and FT-IR techniques were used for characterization of CHN. The influence of reaction time on the nanoparticle size distribution was investigated, and the results showed that the microwave irradiation method evidently decreases the reaction times and particle size over the conventional method. It was determined by the results of the zeta potential measurements that synthesized CHN under microwave irradiation clearly exhibits more homogeneous and stable dispersion.     

Effect of Linewidth Enhancement Factor on Doppler Beat Waveform Obtained from a Self-Mixing Laser Diode

The asymmetry and fringe inclination of the sawtooth-like waveform observed in the self-mixing signal obtained from a semiconductor laser with optical feedback enable the direction discrimination of line-of-sight motion of external target surfaces. We investigated the effects of linewidth enhancement factor and feedback strength on the asymmetry and the direction of fringe inclination of the signal by numerical simulations. For the first time, we show that direction of the fringe inclination is determined not only by the direction of the target motion but also by the value of the linewidth enhancement factor.     

Kinetics and modeling of (R,S)‐1‐phenylethanol acylation over lipase

The kinetics of the acylation of (R,S)‐1‐phenylethanol was investigated using lipase as a catalyst. The main parameters were temperature, reaction atmosphere, different acyl donors, and different amounts of acyl donor as well as the presence of some additives in the reaction mixture. The initial reaction rate increased with increasing temperature and with a decreasing amount of an acyl donor. The activated esters, such as isopropenyl‐ and vinyl acetate, exhibited very high acylation rates for R‐1‐phenylethanol, whereas low rates were obtained with ethyl acetate and 2‐methoxyethyl acetate. The addition of water and acetophenone decreased the acylation rate. A kinetic model was developed based on a sequential step mechanism, in which enzyme was reacting in the first step with an acyl donor followed by the reaction of a modified enzyme complex with the reactant, R‐1‐phenylethanol. Comparison with experimental data obtained at different temperatures allowed simplification of this model, leading to a kinetic equation with just one apparent parameter. The influence of the amount of acyl donor, ethyl acetate, could be quantitatively described by taking into account the competitive inhibition of the ethanol produced. The rate constants and apparent activation energy for experiments performed under different temperatures and the amounts of acylation agent were determined. The apparent activation energy was 24.5 kJ/mol. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 629–639, 2010     

Synthesis of Phenyl‐Substituted Conduritol B and Its Mechanism of Formation

The phenyl‐substituted conduritol B 8 was prepared in racemic form in a five‐step sequence starting from 2‐phenyl‐1,4‐benzoquinone ( 10 ) (Scheme 1). The reaction mechanism of the key step 12b → 13 is discussed (Scheme 2).