气泡与弹性边界的相互作用研究

从气泡与弹性边界相互作用基本现象入手, 基于势流理论, 建立气泡与弹性边界相互作用的数值模型, 计及浮力与表面张力, 模拟弹性介质附近单个气泡的动态特性, 通过气泡周围压力场的分布来讨论蘑菇状气泡的成因, 数值结果与已有实验结果吻合良好. 讨论两个气泡与弹性边界的相互作用, 并通过与Robinson 和Blake的实验结果对比, 验证数值模型的正确性. 数值模拟发现, 浮力、弹性系数和密度比是影响气泡动态特性的重要特征参数.      

Mixed convection boundary layer flow near stagnation-point on vertical surface with slip

This paper considers the steady mixed convection boundary layer flow of a viscous and incompressible fluid near the stagnation-point on a vertical surface with the slip effect at the boundary. The temperature of the sheet and the velocity of the external flow are assumed to vary linearly with the distance from the stagnation-point. The governing partial differential equations are first transformed into a system of ordinary differential equations, which are then solved numerically by a shooting method. The features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed. Both assisting and opposing flows are considered. The results indicate that for the opposing flow, the dual solutions exist in a certain range of the buoyancy parameter, while for the assisting flow, the solution is unique. In general, the velocity slip increases the heat transfer rate at the surface, while the thermal slip decreases it.     

Nypa fruticans Frond Waste for Pure Cellulose Utilizing Sulphur-Free and Totally Chlorine-Free Processes

The search for alternative methods for the production of new materials or fuel from renewable and sustainable biomass feedstocks has gained increasing attention. In this study, Nypa fruticans (nipa palm) fronds from agricultural residues were evaluated to produce pure cellulose by combining prehydrolysis for 1–3 h at 150 °C, sulfur-free soda cooking for 1–1.5 h at 160 °C with 13–25% active alkali (AA), 0.1% soluble anthraquinone (SAQ) catalyst, and three-stage totally chlorine-free (TCF) bleaching, namely oxygen, peroxymonosulfuric acid, and alkaline hydrogen peroxide stages. The optimal conditions were 3 h prehydrolysis and 1.5 h cooking with 20% AA. Soda cooking with SAQ was better than the kraft and soda process without SAQ. The method decreased the kappa number as a residual lignin content index of pulp from 13.4 to 9.9–10.2 and improved the yields by approximately 6%. The TCF bleaching application produced pure cellulose with a brightness of 92.2% ISO, 94.8% α-cellulose, viscosity of 7.9 cP, and 0.2% ash content. These findings show that nipa palm fronds can be used to produce pure cellulose, serving as a dissolving pulp grade for viscose rayon and cellulose derivatives.     

Fluorescence studies of interactions of ionic surfactants with poly(amidoamine) dendrimers

The pyrene fluorescence measurements have been carried out for the micelle formation of sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and dimethylene bis(dodecyldimethylammonium bromide) (12-2-12) in the presence of fixed different amounts of various generations of poly(amidoamine) (PAMAM). The critical micelle concentration (cmc) of SDS decreases with an increase in the fixed amount of PAMAM, suggesting the facilitation of micellization due to the participation of SDS-PAMAM complex in the micelle formation. This behavior has not been observed for DTAB/12-2-12 in the presence of various generations of PAMAM. The results indicate that SDS always has stronger interactions with all the generations of PAMAM in comparison to those of DTAB and 12-2-12.     

Genotyping by dynamic heating of monolayered beads on a microheated surface

A miniaturized bead-based dynamic allele-specific hybridization (DASH) approach for single-nucleotide polymorphism analysis is presented. Chips with integrated heater and temperature sensors for open-surface DNA analysis were microfabricated. Microcontact printing using a poly(dimethylsiloxane) (PDMS) stamp was employed to create monolayers of immobilized beads on the surface of the chip. This chip allows fast, well-controllable temperature ramping. The temperature distribution was homogeneous over the entire heater area. All three possible variants of an SNP site of a synthesized oligonucleotide were accurately scored using the bead-based DASH approach. Our assay has a nonoptimized temperature ramping rate of 4 degrees C-6 degrees C/min compared to earlier reported values of 2 degrees C-3 degrees C/min, thereby reducing the total analysis time by a factor of 2. Reliable DASH measurement data from areas as small as 12 x 13 microm was achieved. Our bead-based DASH approach has enabled a dramatic volume reduction and is a step towards developing a cost-effective high-throughput DASH method on arrays of single beads.     

Potato peels as solid waste for the removal of heavy metal copper(II) from waste water/industrial effluent

A new sorbent potato peels, which are normally discarded as solid waste for removing toxic metal ion Cu(II) from water/industrial waste water have been studied. Potato peels charcoal (PPC) was investigated as an adsorbent of Cu(II) from aqueous solutions. Kinetic and isotherm studies were carried out by studying the effects of various parameters such as temperature, pH and solid liquid ratios. The optimum pH value for Cu(II) adsorption onto potato peels charcoal (PPC) was found to be 6.0. The thermodynamic parameters such as standard Gibb's free energy (Delta G degrees ), standard enthalpy (Delta H degrees ) and standard entropy (DeltaS degrees ) were evaluated by applying the Van't Hoff equation. The thermodynamics of Cu(II) adsorption onto PPC indicates its spontaneous and exothermic nature. The equilibrium data at different temperatures were analyzed by Langmuir and Freundlich isotherms.     

单个三维气泡的动力学特性研究

模拟了单个气泡在重力场作用下动态特性,假设流场为无粘、无旋且不可压的理想流体,采用三角形单元离散流场边界,并用边界积分法求解流场,用Mixed-Eulerian-Lagrangian方法模拟气泡的演化,并在必要的时候采用三维光顺方法对气泡表面及其速度势分布进行光顺,使计算程序更准确,更稳定.在分析过程中,将本文三维模型的计算结果与Rayleigh-Plesset气泡模型及试验数据进行对比分析,三维模型的计算值与精确解及实验数据吻合很好,表明本文方法及计算模型具有较高的精度,并通过对比改变不同物理参数时对气泡运动周期及射流速度的影响,得出一些规律性的曲线,旨在为相关的水下气泡动力学分析提供参考.