Flux and source term discretization in two‐dimensional shallow water models with porosity on unstructured grids

Two‐dimensional shallow water models with porosity appear as an interesting path for the large‐scale modelling of floodplains with urbanized areas. The porosity accounts for the reduction in storage and in the exchange sections due to the presence of buildings and other structures in the floodplain. The introduction of a porosity into the two‐dimensional shallow water equations leads to modified expressions for the fluxes and source terms. An extra source term appears in the momentum equation. This paper presents a discretization of the modified fluxes using a modified HLL Riemann solver on unstructured grids. The source term arising from the gradients in the topography and in the porosity is treated in an upwind fashion so as to enhance the stability of the solution. The Riemann solver is tested against new analytical solutions with variable porosity. A new formulation is proposed for the macroscopic head loss in urban areas. An application example is presented, where the large scale model with porosity is compared to a refined flow model containing obstacles that represent a schematic urban area. The quality of the results illustrates the potential usefulness of porosity‐based shallow water models for large scale floodplain simulations. Copyright © 2005 John Wiley & Sons, Ltd.     

Porous structure and hydrophilic-hydrophobic properties of gas diffusion layers of the electrodes in proton-exchange membrane fuel cells

The porous structure and hydrophilic-hydrophobic properties of the gas diffusion layers (GDL) of electrodes on a substrate of carbon paper in proton-exchange membrane fuel cells have been investigated with the methods of standard porosimetry and of pycnometry. GDL containing various fluoroplast concentrations were impregnated with water, and this process has been investigated at 20 and 80°C. The impregnation rate is significantly higher for untreated carbon paper than for teflonated GDL and also increases significantly with increasing temperature. With teflonization of the carbon paper, hydrophilic porosity decreases, while hydrophobic porosity increases. This increase, however, ceases at high fluoroplast concentrations. The concept of hydrophobization effectiveness of the porous carbon substrate of GDL is introduced. It has been established that hydrophobization effectiveness decreases with increasing fluoroplast concentration and depends on the type of suspension. Curves of the angle of wetting of GDL by water versus the pore radius exhibit a minimum. Different values of the angle of wetting of GDL by water in different pores are explained by nonuniform distributions of both fluoroplast particles and hydrophilic surface groups in pores of different dimensions.     

Generalisations of disjunctive sequences

The present paper proposes a generalisation of the notion of disjunctive (or rich) sequence, that is, of an infinite sequence of letters having each finite sequence as a subword. Our aim is to give a reasonable notion of disjunctiveness relative to a given set of sequences F. We show that a definition like “every subword which occurs at infinitely many different positions in sequences in F has to occur infinitely often in the sequence” fulfils properties similar to the original unrelativised notion of disjunctiveness. Finally, we investigate our concept of generalised disjunctiveness in spaces of Cantor expansions of reals. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The influence of porosity on the Phillips Cr/silica catalyst 2. Polyethylene elasticity

The Phillips Cr/silica catalyst produces low levels of long chain branching (LCB) in polyethylene, which have a powerful influence on industrial molding behavior. Although many catalyst and reactor variables determine the degree of LCB, perhaps the most significant of these is the morphology of the silica support. In this study many different types of silicas were converted into Cr/silica catalysts, which were tested in ethylene polymerization, and the resultant polymer elasticity was then determined. In some experiments, the surface area of the catalyst seemed to correlate quite well with polymer elasticity. In other tests, however, no connection with surface area was evident but the pore volume was quite influential. Together, all these studies suggest that it is the degree of structural reinforcement of the silica matrix, rather than any one physical measurement of porosity, that influences elasticity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 845–865, 2009     

回归分析方法在大庆葡西地区地层压力预测上的应用

本根据数理统计分析,应用渗流力学理论,结合油田实际生产资料,得出大庆探区西部葡西地区各压力系统的地层压力预测公式,经实际资料验证,相对误差在0.27～4.89%之间,效果较好,有力地指导了油田钻井、固井、射孔和试油等项工作。     

聚乳酸与聚乳酸-羟基乙酸多孔细胞支架的制备及孔隙的表征

应用溶液烧铸致孔剂浸出技术制备了不同致孔剂用量与不同致孔剂颗粒尺寸条件下的一系列聚乳酸及不同组成的聚乳酸－羟基乙酸多孔细胞支架;用一种改进的方法－重量法测定其孔隙率;在聚乳酸－羟基乙酸多孔支架上进行了软骨细胞培养。研究结果表明,随着制备过程中致孔剂用量的增加,多孔支架的孔隙逐渐增加,而与致孔剂的颗粒大小基本无关;致孔剂的颗粒大小只影响多孔支架的孔径;在致孔剂用量及致孔剂颗粒尺寸都相同的情况下,随着共聚物中乙交酯含量的增加,孔隙率逐渐下降;软骨细胞在支架上繁殖情况良好,三周后已开始分泌细胞外基质。     

Demixing Time and Temperature Influence on Porosity and Interconnection of PLLA Scaffolds Prepared via TIPS

Scaffolds suitable for tissue engineering applications were prepared by Thermally Induced Phase Separation (TIPS) starting from a ternary solution PLLA/dioxane/water. The experimental protocol consisted of three consecutive steps, a first quench from the homogeneous solution to an appropriate demixing temperature (within the binodal region), a liquid-liquid demixing stage for a given time and a final quench from the demixing temperature to a low temperature (within the spinodal region). A large variety of morphologies, in terms of average pore size and interconnection were obtained upon modifying the demixing time and temperature, owing to the interplay of nucleation and growth processes during the residence in the metastable state. An interesting combination of micro and macro-porosity was observed for longer demixing times (above 30 min at 35 °C).     

Evaluation of Efficiency of Polymerization,Surface Roughness,Porosity and Adaptation of Flowable and Sculptable Bulk Fill Composite Resins

A new category of commercial bulk fill composite resins (CRs) enables the placement of 4-mm-thick layers as an alternative to the traditional time-consuming incremental technique. The purpose of the present study was to compare the efficiency of the polymerization, adaptation and porosity of two high-viscosity ‘sculptable’ bulk fill CRs (Filtek™ Bulk Fill (3M™ ESPE, St. Paul, MN, USA) and Tetric EvoCeram^® Bulk Fill (Ivoclar Vivadent AG, Schwan, Liechtenstein)) and two low-viscosity ‘flowable’ bulk fill CRs (SureFil^® SDR™ flow (Dentsply Sirona, Charlotte, NC, USA) and Tetric EvoFlow^® Bulk Fill (Ivoclar Vivadent AG, Schaan, Liechtenstein)). Cylindrical samples of the bulk fill CRs (4 mm height × 10 mm diameter) were analyzed by Fourier-transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Additionally, occlusal cavities were prepared in twelve extracted human molars and restored with the bulk fill CRs (n = 3 for each CR). The adaptation and porosity of the bulk fill CRs were evaluated by X-ray microcomputed tomography (µCT) with a 3D morphometric analysis, and the adaptation was also analyzed by scanning electron microscopy (SEM) on longitudinal vestibulo-oral sections of the restored teeth. The AFM analysis demonstrated that the surface roughness of the SureFil^® SDR™ flow was higher than that of the Tetric EvoFlow^® Bulk Fill and that the surface roughness of Filtek™ Bulk Fill was higher than that of Tetric EvoCeram^® Bulk Fill. µCT and SEM confirmed that the flowable bulk fill CRs had excellent adaptation to the cavity walls. The 3D morphometric analysis showed the highest and lowest degrees of porosity in Filtek™ Bulk Fill and Tetric EvoFlow^® Bulk Fill, respectively. In general, the flowable bulk fill CRs exhibited better adaptation, a higher efficiency of polymerization and lower porosity than the sculptable materials.     

孔隙度数值反演计算

由渗流微分方程定解问题和Peaceman方程给出了网格压力、井底压力对网格孔隙度的导数,利用三维渗流方程压强数值解计算井底压力对网格孔隙度的导数;采用共轭梯度法实现孔隙度均匀(或分块均匀)分布油藏模型的反演计算.算例表明,经过8~10次迭代后反演结果与真值的最大相对误差在0.03%以内,反演收敛于真值.     

Simulation of coupled flowing-reaction-deformation with mass transfer in heap leaching processes

Governing equations for a fully coupled flowing-reaction-deformation behavior with mass transfer in heap leaching are developed. The model equations are solved using an explicit finite difference method under the conditions of invariable application rate and constant hydraulic head. The distribution of the degree of the saturation, as well as the distributions of the concentration of the reagent and the solute is given. A cubic relationship between the mineral recovery and the leaching duration is obtained based on the numerical results. The relationship can be used to predict the recovery percentage of the valuable metal.