中央开槽钢箱梁悬索桥涡激共振及风振危险性的思考

介绍中央开槽钢箱梁悬索桥受低风速风作用发生的涡激共振实况。根据史料评述悬索桥风振危险性。     

平巷掘进的悬拱法

本文在总结先拱后墙平巷掘进经验的基础上，根据岩石力学理论和平巷掘进原理，提出了平巷掘进的悬拱法。实践证明，悬拱法是不稳定岩层中掘进大断面平巷或硐定行之有效的施工方法。     

水解聚丙烯腈铵对MMH／粘土体系胶体性能的影响

研究了水解聚丙烯腈铵盐（ＮＰＡＮ）对粘土颗粒、ＭＭＨ胶体粒子和ＭＭＨ／粘土复合体粒子电泳淌度的影响，发现ＮＰＡＮ能极大地增加粘土颗粒的负电性，说明ＮＰＡＮ在粘土颗粒表面发生了吸附作用；ＮＰＡＮ不仅能够削弱ＭＭＨ胶粒的正电性能，浓度足够大时甚至使ＭＭＨ胶粒由荷正电变为荷负电；ＭＭＨ／粘土复合体粒子电泳淌度的变化则是由于ＮＰＡＮ在粘土颗粒和ＭＭＨ胶粒上的共同吸附引起的。本文还研究了ＮＰＡＮ对ＭＭＨ／粘土体系流变性能的影响，认为ＮＰＡＮ在ＭＭＨ胶粒和粘土颗粒上的强吸附作用拆散了ＭＭＨ／粘土体系的网架结构，导致体系ＡＶ和ＹＰ降低。ＮＰＡＮ虽然能增加粘土颗粒的负电性，但是ＭＭＨ对含ＮＰＡＮ的粘土体系的增稠作用随ＮＰＡＮ加量的增加而削弱，说明ＭＭＨ胶粒与粘土颗粒的相互作用不宜简单地看作静电相互作用。     

Electrochemically instantaneous reduction of conducting polyaniline-coated latex particles dispersed in acidic solution

A cathodic voltammetric wave was observed in an aqueous suspension of mono-dispersed, spherical polyaniline-coated polystyrene particles, whereas no anodic wave was detected. This irreversibility was common to particles with eight different diameters ranging from 0.2 to 7.5 μm. Such irreversibility cannot be found at polyaniline-coated electrodes, and thus is a property of the dispersion of polyaniline latex. The reduction current was controlled by diffusion of dispersed particles. The reduction, being the conversion from the electrical conducting state to the resistive one, should begin at a point of contact between the conducting particle and the electrode in order to be propagated to the whole particle rapidly. In contrast, the oxidation proceeds slowly with the propagation of conducting zone, during which Brownian motion lets the particle detach from the electrode. The number of loaded aniline units per particle, determined by weight analysis, ranged from 6 × 10⁶ (Ø 0.2 μm) to 3 × 10¹¹ (Ø 7.5 μm) and was proportional to 2.9 powers of the particle diameter. The diffusion-controlled current of the cathodic wave was proportional to 2.4 powers of the diameter. The difference in these powers, 0.5, agreed with a theoretical estimation of the diffusion-controlled current, the diffusion coefficient for which was given by the Stokes-Einstein equation.     

The effects of some polyelectrolyte chemical compositions on the rheological behaviour of kaolin suspensions

Many ceramic materials are factory-made via ceramic suspensions. The rheology of these suspensions must be appropriate and their solid content must be as high as possible in order to minimize the drying cost. Currently, the addition of minor quantities of polyelectrolyte in the classical deflocculating mixture of sodium silicate and sodium tripolyphosphate has become useful to this effect. The present paper discusses a rheological test established to put the rheological behaviour of these suspensions in parametric form. These parameters cover different rheological aspects: equilibrium, kinetics (thixotropy) and structural elasticity. Different polyelectrolytes in different percentages were tested for their power to deflocculate different kaolin suspensions. The deflocculating power of these polyelectrolytes was then correlated with their chemical composition.     

Impedance spectroscopy of suspension plasma sprayed titania coatings

Two TiO₂ coatings were plasma sprayed, using an aqueous suspension as a feedstock onto initially prepared alumina substrates. Their thickness was about 7 and 15 μm. The coatings were tested using impedance spectroscopy (IS) in the frequency range from 100 Hz to 2 MHz at temperatures ranging from 320 to 1020 K. The measurements allowed to find the Nyquist plots and equivalent circuits of the tested samples. The IS results were interpreted by the microstructural features of the deposits such as chemical composition, atomic structural and phase analysis. The mechanism of electric current conduction in tested coatings was proposed.     

System reliability of suspension bridges

Provisions for the design of existing suspension bridges often rely on a deterministic basis. Consequently, the reliability of these bridges cannot be assessed if current provisions are applied. In order to develop cost-effective design and maintenance strategies for suspension bridges a system reliability-based approach has to be used. This is accomplished by a probabilistic finite element geometrically nonlinear analysis approach. This study forms part of an investigation into the system reliability evaluation of geometrically nonlinear large span bridges recently undertaken at the University of Colorado. A brief review of reliability analysis of geometrically nonlinear elastic structures allows for the determination of its relevance to the assessment of suspension bridges. A probabilistic finite element geometrically nonlinear elastic code is used for system reliability evaluation of suspension structures. The allowable stress design procedures used by the Honshu Shikoku Bridge Authority for the design of suspension bridges are presented along with their application to the design of an existing bridge. This bridge is studied from a system reliability viewpoint to evaluate its reliability under different loading and damage scenarios. Such information calls attention to the fact that the reliability of cables, hanger ropes and girders are very different. Therefore, optimal maintenance decisions for suspension bridges designed according to allowable stress method are not consistent with those based on equal component reliability values.     

蒙脱土颗粒表面带电性质的研究

研究了常用无机盐(NaCl、KCl、CaCl_2)、pH值以及CMC对蒙脱土颗粒表面电性质的影响。用501型激光电泳电动仪测定蒙脱土颗粒的电泳速度,并用Smoluchowski方程式计算出ζ电位。实验结果表明,无论是否有无机盐存在时,蒙脱土颗粒的ζ电位都不受pH值和离子活度变化的影响,均显负电性。阴离子聚合物CMC加入后,显示的ζ电位是蒙脱土颗粒与CMC负电性的综合效果或CMC的负电性。由此可以肯定就蒙脱土自身来说永远显负电性。     

Convective mass exchange between flows in a valve-pulsatory apparatus with permeable partition

A mathematical model of convective mass exchange between flows in a valve-pulsatory apparatus with permeable partition is proposed. The mass exchange between flows of aqueous Na₂CO₃ solution and distilled water, or pearlite suspension in water and aqueous solution of NaCl was studied on a pilot apparatus.