A miniature triaxial apparatus for investigating the micromechanics of granular soils with in situ X-ray micro-tomography scanning

The development of a miniature triaxial apparatus is presented. In conjunction with an X-ray micro-tomography (termed as X-ray μCT hereafter) facility and advanced image processing techniques, this apparatus can be used for in situ investigation of the micro-scale mechanical behavior of granular soils under shear. The apparatus allows for triaxial testing of a miniature dry sample with a size of \mathrm{8}\hspace{0.17em}\mathrm{mm}\times \mathrm{16}\hspace{0.17em}\mathrm{mm} (diameter \times height). In situ triaxial testing of a 0.4–0.8 mm Leighton Buzzard sand (LBS) under a constant confining pressure of 500 kPa is presented. The evolutions of local porosities (i.e., the porosities of regions associated with individual particles), particle kinematics (i.e., particle translation and particle rotation) of the sample during the shear are quantitatively studied using image processing and analysis techniques. Meanwhile, a novel method is presented to quantify the volumetric strain distribution of the sample based on the results of local porosities and particle tracking. It is found that the sample, with nearly homogenous initial local porosities, starts to exhibit obvious inhomogeneity of local porosities and localization of particle kinematics and volumetric strain around the peak of deviatoric stress. In the post-peak shear stage, large local porosities and volumetric dilation mainly occur in a localized band. The developed triaxial apparatus, in its combined use of X-ray μCT imaging techniques, is a powerful tool to investigate the micro-scale mechanical behavior of granular soils.     

Post‐polymerization modification of bio‐based polymers: maximizing the high functionality of polymers derived from biomass

The renaissance of the bio‐based chemical industry over the last 20 years has seen an ever growing interest in the synthesis of new bio‐based polymers. The building blocks of these new polymers, so called platform molecules, contain significantly more chemical functionality than their petrochemical counterparts (such as ethene, propene and para‐xylene). As a result bio‐based polymers often contain greater residual chemical functionality in their chains, with groups such as alkenes and hydroxyls commonly observed. These functional groups can act as sites for post‐polymerization modification (PPM), thus further extending the range of applications for bio‐based polymers by tailoring the polymers' final properties. This mini‐review highlights some of the most recent and compelling examples of how to make use of bio‐based polymers with residual functional groups for PPM. It also looks at how the emerging interdisciplinary field of enzymatic polymer synthesis allows for increased functionality in polymers by avoiding side‐reactions as a result of milder reaction conditions, and additionally offers an alternative means of polymer surface modification. © 2018 Society of Chemical Industry     

Fair‐Weather Friends: Evidence of Lipoxin Dysregulation in Neurodegeneration

Lipoxins (LXs) are autacoids, specialized proresolving lipid mediators (SPMs) acting locally in a paracrine or autocrine fashion. They belong to a complex superfamily of dietary small polyunsaturated fatty acid (PUFA)–metabolites, which direct potent cellular responses to resolve inflammation and restore tissue homeostasis. Together, these SPM activities have been intensely studied in systemic inflammation and acute injury or infection, but less is known about LX signaling and activities in the central nervous system. LXs are derived from arachidonic acid, an omega‐6 PUFA. In addition to well‐established roles in systemic inflammation resolution, they have increasingly become implicated in regulating neuroinflammatory and neurodegenerative processes. In particular, chronic inflammation plays a central role in Alzheimer's disease (AD) etiology, and dysregulated LX production and activities have been reported in a variety of AD rodent models and clinical tissue samples, yet with complex and sometimes conflicting results. In addition, reduced LX production following retinal injury has been reported recently by the authors, and an intriguing direct neuronal activity promoting survival and homeostasis in retinal and cortical neurons is demonstrated. Here, the authors review and clarify this growing literature and suggest new research directions to further elaborate the role of lipoxins in neurodegeneration.     

Stability assessment of 3D reinforced soil structures under steady unsaturated infiltration

Internal stability assessment of geosynthetic-reinforced soil structures (GRSSs) has been commonly carried out assuming plane-strain conditions and dry backfills. However, failures of GRSSs usually show three-dimensional (3D) features and occur under unsaturated conditions. A procedure based on the kinematic limit-analysis method is proposed herein to assess 3D effects and the role of steady unsaturated infiltration on the required geosynthetic strength for GRSSs. A suction stress-based framework is used to describe the soil stress behavior under steady unsaturated infiltration. Based on the principle of energy-work balance, the required geosynthetic strength is determined. A comparison analysis with the prior research is conducted to verify the developed method. Two kinds of backfills, i.e., high-quality backfill and marginal backfill, are considered for comparison in this work. It is shown that accounting for 3D effects and the role of unsaturated infiltration considerably reduces the required geosynthetic strength. The 3D effects are primarily affected by the width-to-height ratio of GRSSs, and the contribution of unsaturated infiltration is mainly influenced by the soil type, flow rate, GRSS's height, and location of the water table.     

A Generalized Relationship for Determination of Tensile Strength of Fine-Grained Soils from Shrinkage Characteristics

Tensile strength of fine-grained soils has been extensively investigated by earlier researchers and several methodologies have been evolved for its determination. However, either most of these methods are not valid/applicable for a wide range of moisture contents or they involve tedious sample/specimen preparation. In this context, the methodology of determining tensile strength by employing thin films, which is available in the literature, has been found to be quite handy and useful. It has been observed that a unique relationship exists among the tensile strength, moisture content, and shrinkage characteristics of fine-grained soils. This methodology is appreciable due to its applicability to a wide range of moisture contents, comparable ease of sample preparation and testing, and the obtained results lack generalization. Exhaustive tests were conducted on fine-grained soils of entirely different characteristics and generalized relationships have been proposed between the percentage linear shrinkage, tensile strength, and moisture content (defined as liquid to solid ratio). Based on a critical analysis of the results available in the literature, the efficiency of such relationships for determination of tensile strength of fine-grained soils has been demonstrated. In the authors’ opinion, such relationships would be quite useful for determining tensile strength of fine-grained soils from their linear shrinkage, which can easily be measured in a conventional geotechnical engineering laboratory.     

土壤汞污染生物修复法的研究现状及发展前景

近年来,利用生物修复法来治理受汞污染的土壤得到了迅速发展,并取得了很多的成果。文章对土壤汞污染生物修复技术的国内外研究现状进行综述,进而展望其发展前景,以对今后土壤修复进行指导。     

原子灰(不饱和聚酯)腻子的研制及涂刮技巧

研制了一种多用途原子灰(不饱和聚酯)腻子,该产品采用科学、先进的工艺制成。在机械行业包括汽车、军工、拖拉机、摩托车、钢结构、工程机械、家用电器、造船、铸造制造等行业应用潜力较大,它能改善整体结构的丰满度与外观,达到其理想的产品外观效果。而且对于平面、半圆、椭圆、特种结构件的形状通过巧妙的应用与包装,使产品在外观上达到理想的要求。     

不饱和聚酯树脂室温固化体系研究进展

概述了不饱和聚酯树脂室温固化用氧化还原引发体系中引发剂、促进剂的种类和特点,并介绍了近年来不饱和聚酯树脂室温固化体系及其反应动力学的研究进展,旨在使人们对室温固化体系及其应用有一定的认识和了解。