Experimental Studies of the Flow of Ferrofluid in Porous Media

This paper presents laboratory-scale experimental results of the behavior of ferrofluids in porous media consisting of sands and sediments. Ferrofluids are colloidal suspensions of magnetic particles stabilized in various carrier liquids. In the presence of an external magnetic field, a ferrofluid becomes magnetized as the particles align with the magnetic field. We investigate the potential for controlling fluid emplacement in porous media using magnetic fields. These experiments show that in laboratory-scale porous media experiments (up to 0.25m), with both vertical gravitational forces and lateral magnetic forces acting simultaneously, the magnetic field produces strong attractive forces on the ferrofluid, particularly in the vicinity of the magnet. These holding forces result in a predictable configuration of the fluid in the porous medium which is dependent on the magnetic field and independent of flow pathway or heterogeneity of the porous medium. No significant retention effects due to flow through variably saturated sands are observed. While the proposed field engineering applications of ferrofluids are promising, the observations to date are particularly relevant at the laboratory scale where the decrease in magnetic field strength with distance from a magnet is less of a limitation than in larger scale applications. Ferrofluids may find immediate application in any situation where it is desirable to control the motion or final configuration of fluid in an experimental flow apparatus without direct physical contact.     

防护林带：湍流的数学模型与计算机模拟

虽然防护林用于减小风速、控制热量和水汽传递及污染物扩散、 改善气候与环境、增加作物产量等已经有几百年了, 但直到近几十年, 人们才开始系统地研究防护林空气动力学的遮蔽机制.在本综述中,我 们考察了绕防护林带的流动与湍流控制机制,最新的模型与数值模拟 研究情况;通过数值模拟与实验数据的比较,来了解防护林带结构与防 风效果之间的关系;讨论数值分析如何及为什么能够得到所需要的结果. 本文将从多孔隙防护林带流动基本方程组的推导开始,讨论数值模型及 模拟过程,对附体与分离流动进行预测;分析了遮蔽机制与动量交换;对 风向、防护林密度、宽度和三维性对流动与湍流的影响作了系统的论 述.还对热流和土壤水分蒸发的新模型及数值模拟作了简述.最后,我们 对网络工作站、群和高性能分布式并行计算机及其对防护林带模型预 报能力的提高作了讨论.     

黄土构造节理研究及其应用

作者发现大量不同力学性质的黄土构造节理后，识别了它们的区域性、系统性特征；认定其两组扭裂面代表新构造应力场最大剪切应力方向，利用黄土构造节理系及由其控制的土层沟槽网络恢复了相应地区Q3-4构造应力场；提出构造节理是黄土区地下水运移的主要通道和赋存的场所；发现构造节理是黄土区地裂缝、滑坡、崩塌和水土流失等地质灾害的构造基础之一，证实构造节理是黄土地层的软弱面，风化和继之而来的应力侵蚀就由此开始，进而逐步塑造黄土碟、穴、井、桥、柱、墙、沟等潜蚀地貌和部分侵蚀地貌。研究黄土构造节理对恢复新构造应力场、帮助预测地裂乃至地震活动、控制水土流失和滑塌灾害、进行工程乃至区域稳定性评价、重新认识黄土潜蚀地貌发育规律、指导干旱半干旱黄土区找水，既有理论意义又有实际意义。     

共价有机框架(COFs)材料的结构控制及其在环境化学中的应用

近年来,共价有机框架(COFs)材料因其稳定的结构、高比表面积、大孔隙率、可修饰结构和易于功能化而受到了科学家们的广泛关注。通过控制COFs材料的孔径、形状和链接方式以及后合成修饰,功能性COFs材料在气体储存分离、传感器和药物传输等领域发挥了越来越重要的作用。尤其在环境化学领域,COFs材料的研究和应用已成为一热门课题。本文综述了COFs材料的结构控制、分类以及在环境污染物检测和去除中的应用,包括对重金属离子、放射性核素、有机污染物和气体污染物的吸附和催化等。通过改变构筑单体的大小和形状、引入特殊官能团和活性位点等方法,可以增强污染物与COFs材料的相互作用(氢键相互作用、π-π相互作用和范德华力等),使COFs材料在环境领域应用中有优异的表现。本文最后展望了COFs材料在环境领域的应用前景和今后的研究方向,希望能为该领域的研究提供参考。     

Environmentally Stable Polymer Gels with Super Deformability and High Recoverability Enhanced by Sub‐5 nm Particles in the Nonvolatile Solvent

It remains challenging to satisfy the combined performances for hydrogels with excellent mechanical behavior, high deformability, and super recoverability under harsh environmental conditions. In this study, we first established a strong polymer network via the crosslinking of polymer chains on the surfaces of sub‐5‐nm calcium hydroxide nanospherulites in ethylene glycol solvent. The organic gel expressed excellent mechanical properties such as a recoverable compressive engineering stress of 249 MPa and an elongation stress of 402 KPa, which was attributed to the uniform nanosized crosslinking structure as characterized by SEM. Moreover, the nonvolatile solvent remained in the gel, meaning that the sample can resist a wide temperature range of ?56 to 100 °C without losing the elastic properties. This novel organic gel could provide promising routes to develop the ideal elastic carriers for wearable devices, smart skin sensors, and damping materials. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 713–721     

The use of relative residues in fitting experimental data: an example from fluid mechanics

A curve fitting model is presented which minimizes the sum of squares of relative residues and expressions for the fit coefficients and their respective errors are derived. The new model is compared to the normal least squares model, using as an example the Reynolds number-drag coefficient data for a sphere. The results show that the best fit was obtained with the new model, indicating it may provide a useful tool for data analysis.     

Separation of Hydrocarbon Mixtures in the Microgram Range by Inclusion in a Urea-packed Mini Column

Abstract

The use of classical urea inclusion techniques for the separation of straight chain hydrocarbons from branched and cyclic compounds is satisfactory when applied to mixtures in the milligram to gram ranges, but leads to low separation efficiencies when quantities in the microgram to milligram range are involved. In this study, a modified inclusion technique using an urea-packed milli-bore column and a catalytic eluent is described. Examples of its use for the separation of mixtures of linear and cyclic hydrocarbons from 30μg up to a few milligrams are given. The versatility of this technique for the analyses of low amounts of environmental samples is described, and an application to the hydrocarbon fraction of surface sediment from lake Leman (Switzerland) is presented.     

Photocatalytic Activity of Supported Metal Nanoparticles and Single Atoms

Photocatalysis has been known as one of the promising technologies due to its eco-friendly nature. However, the potential application of many photocatalysts is limited owing to their large bandgaps and inefficient use of the solar spectrum. One strategy to overcome this problem is to combine the advantages of heteroatom-containing supports with active metal centers to accurately adjust the structural parameters. Metal nanoparticles (MNPs) and single atom catalysts (SACs) are excellent candidates due to their distinctive coordination environment which enhances photocatalytic activity. Metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and carbon nitride (g-C₃N₄) have shown great potential as catalyst support for SACs and MNPs. The numerous combinations of organic linkers with various heteroatoms and metal ions provide unique structural characteristics to achieve advanced materials. This review describes the recent advancement of the modified MOFs, COFs and g-C₃N₄ with SACs and NPs for enhanced photocatalytic applications with emphasis on environmental remediation.