Effects of Cationic Micelles on the Rate of Intramolecular General Base-Catalyzed Reaction of Ionized Phenyl Salicylate with DL-Proline

Pseudo-first order rate constants (k_obs) obtained for the reaction of ionized phenyl salicylate (PS^-) with anionic DL-proline (Prl^-) at a constant [NaOH] and [CTABr] (where CTABr represents cetyltrimethylammonium bromide) and 35°C, show a linear increase with increasing total concentration of Prl^-; Nucleophilic second-order rate constants (k_n ^obs) for the reactions of Prl^- with PS^- reveal a nearly 5-fold decrease with the increase in [CTABr] from 0.0 to 0.01 M.     

下部有常热通量加热作用时非均匀温度梯度和磁场对Marangoni对流作用的影响

在一个水平流体层中,下部加热和上部致冷,热通量为常数时,研究磁场和非均匀温度梯度对Marangoni对流作用的影响.对线性稳定分析进行了详细的研究.分析了各种参数对对流作用的影响.考虑了6种基本的温度分布曲线,给出了造成失稳影响的一些普遍结论.     

Effect of nitrile butadiene rubber/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/YSZ fillers for PMMA denture base on the thermal and mechanical properties

This study is to investigate the effect of nitrile butadiene rubber (NBR as impact modifier) together with Al₂O₃/YSZ (toughening) as filler loading in PMMA denture base on the thermal and mechanical properties. PMMA matrix without fillers was mixed between PMMA powder and 0.5 mass% of BPO, and it is used as the control group. The liquid components consist of 90% of methyl methacrylate (MMA) and 10% as the cross-linking agent of ethylene glycol dimethacrylate. The denture base composites were fabricated by incorporating PMMA powder and BPO and fixed at 7.5 mass% NBR particles and filler loading (1, 3, 5, 7 and 10 mass%) of Al₂O₃/YSZ mixture filler by (1:1 ratio) as the powder components. The ceramic fillers were treated with silane (γ-MPS) and the powder/liquid ratio (P/L) according to dental laboratory practice. The TGA data obtained show that the PMMA composites have better thermal stability compared to unreinforced PMMA, while DSC curves show slightly similar Tg values. DSC results also indicated the presence of unreacted monomer content for both reinforced and unreinforced PMMA composites. The fracture toughness, Vickers hardness and flexural modulus values were statistically increased compared to the unreinforced PMMA matrix (P?<?0.05).     

Thermal property determination of hybridized kenaf/PALF reinforced HDPE composite by thermogravimetric analysis

This article presents the thermal degradation behavior of hybridized kenaf (bast)/pineapple leaf fiber (PALF) reinforced high density polyethylene (HDPE) composites by thermogravimetric and derivative thermogravimetric analyses (TG/DTG) with respect to the proportions of fiber in the composite, variation in fiber loading and fiber length. It was observed that the thermal decomposition of all the samples had taken place within the scheduled temperature range of 35?C615?°C. For hybrid composites prepared at 40% fiber loading, the initial peak between 236.9 and 331?°C corresponds to a mass loss of between 23 and 26%, and expectedly, PALF composite and 1:1 hybrid composite have the highest mass lost at this point. Main decomposition temperature as revealed from DTG curves occurred around 467?°C for all except composite prepared with 0.75 and 2?mm fiber length. The mass loss at this temperature was between 64.4 and 73.7%. However, at 464.87?°C, around 98% of neat HDPE had already degraded. Decomposition temperature of other composites was a little higher than the temperature at which HDPE concluded decomposition. Kenaf composite on its own showed initial thermal resistance, but above 240?°C, a sharp increase in decomposition occurred with temperature. Interestingly, hybridization took care of this. Kenaf and PALF composite have shown weaker thermal stability compared to neat HDPE at lower temperatures. The introduction of more fiber into the matrix at onset caused the thermal stability of the hybridized composite to decrease. This reduction in thermal stability of the hybrid with increase in fiber loading became obvious after the dehydration process. Decomposition of hybrid composite is directly proportional to increase in fiber loading. However, at 385?°C, where neat HDPE started decomposing, the percentage degradation of the hybrid showed inverse proportionality with increase in fiber loading. As observed, the size of the lignin and hemicelluloses shoulders in DTG curves deepen with increase in fiber loading, an indication of increased presence with increase in fiber loading.     

Unsteady flow and heat transfer past an axisymmetric permeable shrinking sheet with radiation effect

In this paper, the problem of unsteady axisymmetric boundary layer flow and heat transfer induced by a permeable shrinking sheet in the presence of radiation effect is studied. The transformed boundary layer equations are solved numerically by an implicit finite‐difference scheme known as the Keller‐box method. The influence of radiation, unsteadiness and mass suction parameters on the reduced skin friction coefficient f′′(0) and the heat transfer coefficient ?θ′(0), as well as the velocity and temperature profiles are presented and discussed in detail. It is found that dual solutions exist and suction parameter delays the separation of boundary layer. Copyright © 2010 John Wiley & Sons, Ltd.     

Radiation effects on Marangoni convection boundary layer over a permeable surface

The problem of Marangoni convection boundary layer flow that can be formed along the interface of two immiscible fluids when the wall is permeable, where there is suction or injection effect, is considered. Similarity equations are obtained through the application of similarity transformation techniques. The effects of suction/injection and radiation parameters on the heat transfer characteristics are numerically studied using the shooting method for a fixed value of the Prandtl number (Pr=0.7). Numerical results are obtained for the surface temperature gradient or the heat transfer rate as well as the temperature profiles for some values of the governing parameters. Comparisons with known results from the open literature show very good agreements. The results indicate that the heat transfer rate at the surface decreases as the radiation parameter increases. Further, results show that multiple (dual) solutions exist for a certain range of the governing parameters.     

Crystal structure of trans-C2SnO5 pentagonal bipyramidal dibutylbis(phenylacetato)tin(IV) hydrate

The Lewis acidity of tin in a diorganotin dicarboxylate is demonstrated in this first example of a 1/1 adduct of the ester with a neutral ligand. The structure of dibutyltin bisphenylacetate hydrate [(C₄H₉)₂Sn(O₂CCH₂C₆H₅)₂·H₂O] has been determined from 1211 F ₀6F _c MoK reflections and refined to anR _F of 0.061 [space groupP2/a witha=8.416(2),b=10.391(5),c=14.28(1) Å,=98.42(4)° andZ=2]. TheC atoms [Sn-C 2.101(8) Å; C-Sn-C 169.9(5)°] make up the apices and the O_carboxylate [Sn-O 2.234(5), 2.439(7) Å; O-Sn-O 55.7(2)°] and O_water [Sn-O 2.342(8) Å] atoms the equatorial points of thetrans-C₂SnO₅ pentagonal bipyramid around the Sn atom. The molecular symmetry isC ₂, and the Sn and O_water atoms lie along a crystallographic twofold axis. The aqua ligand forms donor H-bonds with neighboring carboxylato groups to link the molecules into a double zigzag chain running parallel toa.     

Mixed convection stagnation-point flow on vertical stretching sheet with external magnetic field

The problem of steady laminar magnetohydrodynamic （MHD） mixed con- vection stagnation-point flow of an incompressible viscous fluid over a vertical stretch- ing sheet is studied. The effect of an externally magnetic field is taken into account. The transformed boundary layer equations are solved numerically by using an implicit finite-difference scheme. Numerical results are obtained for various values of the mixed convection parameter, Hartmann number, and Prandtl number. The effects of an exter- nally magnetic field on the skin friction coefficient, local Nusselt number, velocity, and temperature profiles for both A 〉 1 and A ~ 1, where A is the velocity ratio parameter, are presented graphically and discussed in detail. Both assisting and opposing flows are considered, and it is found that dual solutions exist for the opposing flow.     

考虑感应磁场影响时,伸展表面上的MHD驻点流动及其热传递

考虑感应磁场的影响,研究不可压缩粘性流体在伸展表面上,作稳定磁流体动力学(MHD)的驻点流动.通过相似变换,将非线性的偏微分方程,变换成为常微分方程.用打靶法数值地求解变换后的边界层方程,得到不同的磁场参数和Prandtl数Pr时的数值解.对a/c>1和a/c<1两种情况(其中a和c均为正值),讨论感应磁场参数对表面摩擦因数、局部Nusselt数、速度和温度的影响,绘出变化曲线并给予讨论.