坡面薄层水流流动型态与侵蚀搬运方式的研究

采用人工模拟降雨方法,首次对发生在坡面上部及细沟之间的薄层水流流动型态与侵蚀搬运方式进行试验研究。结果表明,薄层水流仍属层流范畴,雨滴打击未能增加其紊动,该文定义它为搅动层流,其流态为超临界流,它是通过推移运动完成其侵蚀搬运的。同时,坡面产生的泥沙是接触质,只要水流的拖曳力大于泥沙颗粒与坡面之间摩擦力,它就会沿坡向前滑动,进而输出坡面。

Wear behavior of high strength and high conductivity Cu alloys under dry sliding

In order to study the wear behavior of different kinds of contact wires,the dry sliding wear behaviors of Cu-Sn,Cu-Ag and Cu-Mg alloys prepared by up-drawn continuous casting and followed continuous extrusion were studied.The research was tested on a block-on-ring wear tester.The results indicate that the friction coefficient is remarkably influenced by the formation of a continuous tribofilm,which consists of oxidation film.The abrasion,adhesion,oxidation and plastic deformation are observed.Oxidation and abrasion wear mechanisms dominate at the lower sliding velocity and load.The combination of oxidation and adhesion play leading roles with the increasing load and velocity.Plastic deformation is detected under higher applied load and sliding velocities.

附带词汇习得中接触的量与质的比较——一项基于投入量假设的实证研究

本研究以合肥某高校非英语专业大二学生为实验对象,旨在检验具有不同投入量的阅读任务对中国中等水平英语学习者附带词汇习得的影响,主要探讨阅读任务投入量高低与词汇附带习得效果的相关性,以及附带词汇习得中对目标词的接触量和接触的质的比较。通过对实验对象的调查研究和统计分析后发现,研究结果支持投入量假设的合理性,同时发现接触量少但诱导高投入量的阅读任务和接触量多但诱导低投入量的阅读任务对词汇附带习得的效果没有统计学上的显著差异。

Treatment of chitin-producing wastewater by micro-electrolysis-contact oxidization

The technique of micro-electrolysis-contact oxidization was exploited to treat chitin-producing wastewater. Results showed that Fe-C micro-electrolysis can remove about 30% CODcr, raise pH from 0.7 to 5.5. The CODcr removal efficiency by biochemical process can be more than 80%. During a half year抯 operation, the whole system worked very stably and had good results, as proved by the fact that every quality indicator of effluent met the expected discharge stan-dards; which means that chitin wastewater can be treated by the technique of micro-electrolysis, contact oxidization.

Investigation on the factors influencing the thickness distribution of superplastic-formed components

In the superplastic sheet forming process, the uniformity of the sheet's final thickness distribution is vital for ensuring the good mechanical quality of the formed components. The influences of the component shape and the contact friction on the final thickness distribution were investigated in this work by using finite element method on a series of axisymmetric models. It was concluded that shape optimization and friction elimination are required to get uniform thickness distribution, and eventually to improve the mechanical quality of the formed components. The constitutive equation of the Ti-6A1-4V superplastic material was also determined on the basis of experimental data.

Mechanical behavior and deformation mechanism of ballast bed with various fouling materials

In order to study the interaction between various fouling particles and ballast,a multi-layer and multi-scale discrete element model(DEM)including the sleeper,ballast bed and the surface layer of subgrade was developed.Two typical fouling particles,the hard particles(sand)and soft ones(coal fines),are considered.A support stiffness test of the ballast bed under various fouling conditions was conducted to calibrate the microscopic parameters of the contact model.With the model,the influence of fouling particles on the mechanical behavior and deformation of the ballast bed was analyzed from macro and micro perspectives.The results show that the increase in the strength of the fouling particles enlarges the stiffness of the ballast bed.Hard particles increase the uniformity coefficient of the contact force bondγof ballast by 50.4%.Fouling particles increase the average stress in the subgrade,soft particles by 2 kPa and hard particles by 1 kPa.Hard particles can reduce the elasticity,plastic deformation and energy dissipation in the track structure.As the fouling particle changes from hard to soft,the proportion of the settlement in ballast bed increases to 40.5%and surface layer of swbgrade settlement decreases to 59.5%.Thus,the influence of fouling particles should be considered carefully in railway design and maintenance.

Effect of surfactant type on interfacial area and liquid mass transfer for CO_2 absorption in a bubble column

The effect of different surfactants(n-octyltrimethylammonium bromide(OTABr),sodium dodecyl benzene sulfonate(SDBS) and Tween 80) with different critical micelle concentrations(CMC) on the CO_2 absorption into aqueous solutions in a bubble column is analyzed in the present work.The presence of these surfactants increased the gas-liquid interfacial area,and decreased the liquid phase mass transfer coefficient,but with significant different extent.The results indicated that the CMC can be a key parameter affecting the mass transfer of CO_2 absorption into a dilute aqueous solution of a surfactant.Sardeing's model was used to fit the experimental data successfully by re-correlating the parameters.

THE INVESTIGATION OF CONTACT RESISTANCE CHARACTERISTICS ON ELECTRICAL CONTACTS USED IN COAL MINES

Based on the electrical contact and arc theory, the experiments on contact resistance characteristics of electrical contacts are carried out, by analyzing the experimental results, some conclusions of contact resistance characteristics have been obtained in this paper.

Fabrication of high-quality all-graphene devices with low contact resistances

All-graphene devices are new class of graphene devices with simple layouts and low contact resistances. Here we report a clean fabrication strategy for all-graphene devices via a defect-assisted anisotropic etching. The as-fabricated graphene is free of contamination and retains the quality of pristine graphene. The contact resistance at room temperature （RT） between a bilayer graphene channel and a multilayer graphene electrode can be as low as -5 Ω.·μm, the lowest ever achieved experimentally. Our results suggest the feasibility of employing such all-graphene devices in high performance carbon-based integrated circuits.

Relationship between Quality and Attributes of Elliptical Spot Welds of High Strength Steel

More high strength steel （HSS） sheets are being applied in the automobile industry to improve safety and fuel efficiency. When HSS is spot welded, the strength of the welded-joint is usually determined by the attributes of the weld nugget. However, it is difficult to obtain the circular nugget and to establish the relationship between the weld attributes and welding quality because of a large number of variables and experimental uncertainty. In the paper, the numerical analysis model of tensile-shear strength test for HSS spot welds was established. And the critical ellipticity of the elliptical spot weld was determined through finite element analysis. Quantitative relationship between elliptical weld attributes and weld strength was investigated statistically using the Latin hypercube and regression analysis method. The sheet thickness, nugget eUipticity, hardness radio and yield strength have the most influential attributes in affecting welding quality. The research results can be used as a guideline for HSS resistance spot welding design.

Characteristic investigation of permanent magnet actuator for vacuum contactors operating with an intrinsically safe low voltage

This paper reports a new application of permanent magnet actuator for vacuum contactors.A novel permanent magnet(PM) actuator to drive a vacuum contactor with intrinsically safe and low supply voltage is proposed.PM is mounted on the static iron of the contactor to enhance its holding force and reliability.While only one coil is used to break the vacuum contactor,two series coils are deployed to yield a high magnetomotive force to realize the making operation.The electrical circuit equation,mechanical equation and magnetic field are all coupled in the simulation.A prototype is manufactured and tested to validate and showcase the performance of the contactor which is equipped with the proposed PM actuator.

CuI-Si Heterojunction Solar Cells with Carbon Nanotube Films as Flexible Top-Contact Electrodes

We report the fabrication of CuI-Si heterojunction solar cells with carbon nanotubes （CNTs） as a transparent electrode. A flexible CNT network was transferred onto tile top of a polycrystalline CuI layer, making a conformal coating with good contact with the underlying CuI. The solar cells showed power conversion efficiencies in the range of 6% to 10.5%, while the efficiency degradation was less than 10% after the device was stored in air for 8 days. Compared with conventional rigid electrodes such as indium tin oxide （ITO） glass, the flexibility of the CNT films ensures better contact with the active layers and removes the need for press-contact electrodes. Degraded cells can recover their original performance by acid doping of the CNT electrode. Our results suggest that CNT films are suitable electrical contacts for rough materials and structures with an uneven surface.

Measurement of the association constants through micro-Raman spectra of supersaturated lithium perchlorate droplets

High quality micro-Raman spectra of the LiClO4 droplet with mass of nanogram scale were obtained at various concentrations from dilute to supersaturated state. From component band analysis of the v1-ClO4^- band, four peaks at 933.3, 936.8, 942.1 and 950.7 cm^-1 were identified and assigned to free solvated perchlorate anion, solvent-shared ion pair, contact ion pair and com- plex ion aggregates, respectively. As expected, the signature of free solvated CIO4 ion was observed to decrease in intensity with the increase in concentration. The intensity of the signature from solvent-shared ion pair was observed to rise with in- crease in concentration from 1.8 mol/kg to 5.0 mol/kg before decreasing as the concentration was further increased to 5.6 mol/kg. Signatures of contact ion pair and of complex ion aggregates were shown to increase as the concentration was enhanced. Based upon the Eigen mechanism, we show that three association equilibria can be used to describe the transfor- mations between free solvated perchlorate anion, solvent-shared ion pair, contact ion pair and complex ion aggregates. The overall association constant, K, and the stepwise association constants Ki （i = 1 to 3） in the Eigen mechanism were determined separately with values of 0.025 ± 0.003, 0.023 ± 0.002, 0.068 ± 0.033 and 0.686 ± 0.174. Based on these constants, the electronic performance can be reasonably predicted by the optimum choice of electrolyte concentrations.

Piezotronic transistors in nonlinear circuit:Model and simulation

For the materials that simultaneously exhibit piezoelectric and semiconductor properties,such as wurtzite Zn O,Ga N and In N,as well as two-dimensional single Mo S2,piezoelectric charges induced by externally applied strain can tune/control carrier transport at a metal-semiconductor contact or semiconductor junction,which is named piezotronic effect.Metal-semiconductor-metal piezotronic transistors are key piezotronic nanodevices for electromechanical applications,and they are typical nonlinear elements.In this paper,a simplified current-voltage analysis solution of piezotronic transistors is developed,which can be used for circuit design and simulation.Furthermore,the typical nonlinear circuit:Chua's circuit based on piezotronic transistors is simulated.We find that the output signal of the piezotronic transistor circuit can be switched and changed asymmetrically by externally applied strain.This study provides insight into the nonlinear properties of the piezotronic transistor,as well as guidance for piezotronic transistor nonlinear circuit application.