关于碾压混凝土坝防渗结构的探讨

碾压混凝土坝具有水泥用量少、施工速度快、温控简单、工程造价低等一系列优点，因而在世界各国得到广泛发展，然而，碾压混凝土坝的抗渗性较差，目前采用的各种防渗措施也不甚理想。采用空心模板回填常态混凝土作防渗体方案，能有效提高其抗渗性。     

Plasma-assisted deposition of lithium phosphorus oxynitride films: Substrate bias effects

Lithium phosphorus oxynitride (Lipon) films have been synthesized by a plasma-assisted directed vapor deposition (PA-DVD) approach. In this approach, a hollow cathode technique was used to create an argon plasma through which was propagated an electron-beam generated Li₃PO₄ vapor entrained in a N₂-doped helium gas jet. Without plasma assistance, amorphous, mud cracked and highly porous Li₃PO₄ films were formed. When plasma-assistance was used, nitrogen was incorporated creating a Lipon film whose composition, morphology, structure, and deposition rate could be manipulated by modifying the substrate bias. Films with spiral or very smooth surfaces could be made in this way. Fully amorphous films or films with locally crystallized regions in an amorphous matrix could be synthesized by varying the bias voltage. The presence of these local regions of crystallinity within a Lipon film decreased the Li-ion conductivities from the 10⁻⁷ S cm⁻¹ to 10⁻¹⁰ S cm⁻¹ range.     

Phenol recovery with tributyl phosphate in a hollow fiber membrane contactor: Experimental and model analysis

The extraction and stripping of phenol using a solution of tributyl phosphate in kerosene in a hydrophobic polypropylene hollow fiber membrane contactor has been studied. The effect of the aqueous and the organic phase flow rates on the overall mass transfer coefficient for both extraction and stripping steps was investigated. Experimental values of the overall mass transfer coefficient were determined and compared with predicted values from the resistance in series model. Results showed that the overall mass transfer coefficients for extraction were about one order of magnitude greater than those measured during the stripping process. The experimental values were in good agreement with the predicted values for the extraction module. However, the predicted values were slightly overestimated for the stripping module. The individual mass transfer resistances were analyzed and the rate-controlling steps of mass transfer were also identified in both extraction and stripping modules. The major resistance in extraction and stripping was in the aqueous phase and in the membrane phase, respectively.     

Effect of principal stress direction during consolidation on the shear strength properties of natural granite residual soil

In numerous real-life civil engineering practices, including multi-stage embankment construction and foundation pit excavation, the direction of the major principal stress σ₁ becomes rotated. In these cases, the granite residual soil may be subjected to inclined consolidation (IC) with σ₁ being inclined, because of the relatively high permeability as a result of the fissures formed during weathering. While the effect of the σ₁ direction during the shear on the strength of granite residual soil (inherent strength anisotropy) has been primarily established, little is known about how the soil strength is affected by the direction of σ₁ during consolidation. This paper presents the effects of IC on the shear strength properties of natural granite residual soil through undrained hollow cylinder torsional shear tests. The effect of the soil structure is also considered by testing remolded soil specimens. The results reveal that while IC changes neither the shape of stress–strain curve nor the specimen features at failure, it leads to an increased ultimate shear strength in terms of both the undrained strength and stress ratio, with the remolded soil being more affected. The presented data provide new insights into the understanding of residual soil strength behaviors.     

空心/实心滚珠丝杠机床伺服进给系统热特性分析

机床正向着高速高精度的方向发展,解决机床伺服进给系统在高速运行下产生的大量摩擦热及热变形,成为推进机床发展的突破口。提出采用通入冷却介质的空心滚珠丝杠来抑制温升从而控制热变形。先对轴承副和螺母副摩擦生热、热边界条件及滚珠丝杠变形进行理论计算,运用ANSYS分别对不同载荷不同转速下实心/空心滚珠丝杠的传热进行分析,再对空心/实心滚珠丝杠机床伺服进给系统变形进行分析,通过完整的仿真得出:通入冷却介质的空心滚珠丝杠伺服进给系统可以有效地抑制温升和热变形,为机床伺服进给系统的设计和研究提供理论依据。     

Concrete filled steel tube stub columns under combined temperature and loading

A finite element analysis (FEA) model was developed to predict the load versus deformation relationships of concrete filled steel tube (CFST) stub columns subjected to a combination of temperature and axial compression. This model was used to simulate a set of CFST stub column experiments under various thermal and mechanical loading conditions, including tests at high temperature, tests on the residual strength of specimens subjected to uniform heating, and tests on specimens exposed to the ISO-834 standard fire without initial loads. Comparisons between the predicted results and the test results show that this model can predict the load versus deformation relationships with reasonable accuracy. The FEA model was then used to investigate the behaviour of CFST stub columns in a complete loading history including initial loading, heating and cooling by examing the cross-sectional stress distribution and confinement stress development at different loading phases. All specimens were loaded to ultimate strength after cooling and the residual stress index was studied with respect to a group of parameters. It can be found that the ultimate strength when considering the mutual actions of temperature and loading was slightly lower than that after exposure to fire without initial load, but the peak strain corresponding to the ultimate strength was increased significantly.     

Comparative experimental study of hot-rolled and cold-formed rectangular hollow sections

Square and rectangular hollow sections are generally produced either by hot-rolling or cold-forming. Cross-sections of nominally similar geometries, but from the two different production routes may vary significantly in terms of their general material properties, geometric imperfections, residual stresses, corner geometry and material response and general structural behaviour and load-carrying capacity. In this paper, an experimental programme comprising tensile coupon tests on flat and corner material, measurements of geometric imperfections and residual stresses, stub column tests and simple and continuous beam tests is described. The results of the tests have been combined with other available test data on square and rectangular hollow sections and analysed. Enhancements in yield and ultimate strengths, beyond those quoted in the respective mill certificates, were observed in the corner regions of the cold-formed sections—these are caused by cold-working of the material during production, and predictive models have been proposed. Initial geometric imperfections were generally low in both the hot-rolled and cold-formed sections, with larger imperfections emerging towards the ends of the cold-formed members—these were attributed largely to the release of through thickness residual stresses, which were themselves quantified. The results of the stub column and simple bending tests were used to assess the current slenderness limits given in Eurocode 3, including the possible dependency on production route, whilst the results of the continuous beam tests were evaluated with reference to the assumptions typically made in plastic analysis and design. Current slenderness limits, assessed on the basis of bending tests, appear appropriate, though the Class 3 slenderness limit, assessed on the basis of compression tests, seems optimistic. Of the features investigated, strain hardening characteristics of the material were identified as being primarily responsible for the differences in structural behaviour between hot-rolled and cold-formed sections.     

Polymer hollow particles: Encapsulation of phosphoric acid partial esters and morphology manipulation

The present work demonstrates the possible use of emulsion polymerization for fabricating structured-polymer particles which can store active materials. The hollow polymer particles were synthesized by multi-stage emulsion polymerization consisting of four main stages, (1) the preparation of alkali-swellable core latexes containing active materials, (2) first core-shell polymerization of a monomer mixture of methyl methacrylate (MMA), butyl acrylate (BA) and methacrylic acid (MAA), (3) second core-shell polymerization of styrene and (4) a neutralization stage. The morphology of synthesized capsules was observed by transmission electron microscopy (TEM). The size of the capsule prepared by standard recipe was around 300 nm and the polydispersity index was 0.024 representing that size distribution was highly monodisperse. The specific target material of encapsulation was the phosphoric acid partial ester. The amount of phosphoric acid partial ester encapsulated was determined by thermogravimetric analysis (TGA). From studies of encapsulation behaviors, it was found that the encapsulation efficiency and location of phosphoric acid partial ester in the interior of the particles were mainly dependant on its partition coefficient. In addition, the morphology of polymer capsule was manipulated by varying process parameters. The morphology changes, such as those of pore size and roughness of polymer shell, were characterized by scanning electron microscopy (SEM) and analysis of nitrogen adsorption and desorption isotherm. When neutralized with N,N′-dimethylethanolamine simultaneously during the styrene polymerization, the surface area of polymer capsule was increased drastically by about 5 times due to the formation of mesopores and the roughening of the surface on the hollow polymer shell.     

Preparation of Pt/CeO2/HCSs anode electrocatalysts for direct methanol fuel cells

Hollow carbon spheres (HCSs) were prepared through a simple hydrothermal method using silica particles and glucose as the template and carbon precursor, respectively. HCSs used as supports for platinum catalysts deposited with cerium oxide (CeO₂) were prepared for application as anode catalysts in direct methanol fuel cells. The composition and structure of the samples were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The electrocatalytic properties of the as-prepared catalysts for methanol oxidation were investigated by cyclic voltammetry (CV). The Pt/CeO₂/HCSs catalyst heated at 550 °C for 1 h exhibited the best catalytic activity for methanol oxidation.     

Hollow Nanostructured Anode Materials for Li-Ion Batteries

Hollow nanostructured anode materials lie at the heart of research relating to Li-ion batteries, which require high capacity, high rate capability, and high safety. The higher capacity and higher rate capability for hollow nanostructured anode materials than that for the bulk counterparts can be attributed to their higher surface area, shorter path length for Li⁺ transport, and more freedom for volume change, which can reduce the overpotential and allow better reaction kinetics at the electrode surface. In this article, we review recent research activities on hollow nanostructured anode materials for Li-ion batteries, including carbon materials, metals, metal oxides, and their hybrid materials. The major goal of this review is to highlight some recent progresses in using these hollow nanomaterials as anode materials to develop Li-ion batteries with high capacity, high rate capability, and excellent cycling stability.