Surface dispersive energy determined with IGC-ID in anti-graffiti-coated building materials

Coating building materials with anti-graffiti treatments hinders or prevents spray paint adherence by generating low energy surfaces. This paper describes the effect of coating cement paste, lime mortar, granite, limestone and brick with two anti-graffiti agents (a water-base fluoroalkylsiloxane, “Protectosil Antigraffiti^®”, and a Zr ormosil) on the dispersive component of the surface energy of these five construction materials. The agents were rediluted in their respective solvents at concentrations of 5 and 75% and the values were determined with inverse gas chromatography at infinite dilution (IGC-ID).     

齿上开槽对滤波减速器力学性能的影响

本文使用有限元法研究滤波减速器轮齿上开槽对滤波减速器轮齿的动力学性能和传动性能的影响。通过对滤波减速器齿上不同开槽形状进行有限元对比分析,结果显示直槽对轮齿力学性能有很好的改善作用。在此基础上分析了直槽的槽深、槽宽、应力释放孔大小和应力释放孔与直槽的倒角大小对轮齿力学性能的影响以及不同载荷下轮齿应力分布情况。研究结果表明在滤波减速器齿上开直槽,当槽深大于轮齿模数的三倍,应力释放孔和倒角的半径大于槽宽的十倍,槽缝宽度不超过轮齿模数的十分之一时,其接触应力、弯曲应力和冲击振动较小。     

《第一次的亲密接触》变异修辞分析

蔡智恒的语言具有浓厚的变异修辞特点,而《第一次的亲密接触》更是用口语对话的形式将这种特点发挥到淋漓尽致。其变异修辞在语音层面上表现为谐音变异;词汇层面主要表现为词语分拆、抽换语素、曲解语义、语义偏离、语体变异、色彩变异、语域变异、超常组词、方言夹用、简单符号变异;语法层面上表现为超常搭配、词类活用。     

国外触发引信防雨装置研究和防雨性能现状

本文分析了国外触发引信的防雨性能现状,介绍了西方国家的一些新的触发引信防雨装置。对防雨装置的设计思想也作了初步探讨。     

硝酸钠晶体接触成核的形成和成长

作者采用显微摄影技术对NaNO_3-H_2O系统中的接触成核现象进行了研究,用一个NaNO_3母晶的(100)晶面靠滑动与玻片进行接触。当母晶在饱和溶液中进行接触时,没有接触核形成,但在过饱和溶液中进行接触时,却形成了接触核。这个研究结果说明,必须有一个生长的晶体表面才能形成晶核,母晶的破碎并非晶核的来源。通过连续摄影测出了晶核的成长速率。每粒单晶的成长速率均不随时间而变,但各晶体的成长速率却有所不同,并发现其成长速率受该晶核的初始尺寸及溶液过冷度(即过饱和度)所影响。用线性回归法处理实验数据,分别关联出了在相同过冷度条件下晶体成长速率与初始尺寸的关系。最后再用最小二乘法关联其在各个过冷度条件下所得的结果,得出了NaNO_3接触成核成长速率的数学模型。     

高重合度直齿渐开线圆柱齿轮传动承载能力与优化设计研究

本文系统地研究了高重合度齿轮齿副的变形与刚度、同时啮合齿对之间的载荷分配、胶合承载能力、弯曲强度、接触强度、参数优化设计.     

Investigation of nanofluid bubble characteristics under non-equilibrium conditions

We report experimental and theoretical investigations of the bubble characteristics during the oscillatory growth period for several nanofluids. The nanoparticles were found to affect liquid–gas and solid surface tensions, which modulated the bubble contact angle, radius of triple line, bubble volume and the dynamics of bubble growth. To increase the accuracy of the Young–Laplace equation predictions during the bubble growth in the oscillatory period, a new method multi-section bubble (MSB) approach was developed. In this method, the bubble was divided into n sections (i.e., n = 1:N) and the Young–Laplace equation was solved for each section individually. As N increases, within each section the effects of inertia force and viscosity become reduced comparing to that of the liquid-gas surface tension. Unlike the conventional Young–Laplace approach (i.e., N = 1), the new approach is able to predict the bubble characteristics reliably in the following cases: (a) the oscillatory period when bubble is fluctuating; (b) the departure period when bubble is stretched upward, right before departure; and (c) the high shear stress condition when gas velocity is relatively high.     

Electrospun Polyvinyl Borate/Poly(Methyl Methacrylate) (PVB/PMMA) Blend Nanofibers

The aim of this study was to prepare polyvinyl borate (PVB)/poly(methyl methacrylate) (PMMA) blend nanofibers by electrospinning process. Polyvinyl borate was synthesized by the condensation reaction of polyvinyl alcohol and boric acid. FTIR analyses showed that boron atoms were found to be integrated into the polymer network. Blending PMMA with PVB decreased the fiber diameter and enhanced the surface roughness of PVB/PMMA blend nanofiber mats. The water wetting property of the nanofiber mats was influenced by the surface roughness. The blend composition with the highest polyvinyl borate content was found to be suitable for thermally stable nanofiber formation.     

Surface wettability and flow properties of non-metallic pipes in laminar flow

In this paper, three liquids flowing in five pipes with the same inner diameter of 14 mm were studied to determine the relationship between the surface wettability and flow properties in laminar flow(Re b 2000). This was motivated by oilfield observations of increased pressure drops in non-metallic pipes compared to those in metal pipes,which was contrary to expectations. A new expression for the frictional coefficient that considers the Reynolds number and contact angle θ in laminar flow for non-metallic pipes was proposed based on the experimental results of single-phase flow using dimension and regression analyses. The solutions of the anomalous phenomenon were proposed from the perspectives of the pipe diameter, contact-angle difference, and the compatibility between flexible composite pipe and JLHW105 oil according to the new formula. The surprising finding was that the surface wettability could control the frictional resistance by the critical contact angle(39.9°) obtained at the same Reynolds number. If 0° b θ≤ 39.9°, the frictional coefficient increased as the contact angle increased. In contrast, if 39.9° b θ b 180°,the frictional coefficient decreased with increasing contact angle. The influences of the pipe diameter and contactangle difference on the pressure drop difference of JLHW105 oil showed an inversely proportional relation. A series of materials and liquids were tested. The selection of pipe material for transporting a given fluid can be based on the contact angle, surface tension, and critical limit of the contact angle obtained. The research results are expected to provide some guidelines for the selection of the appropriate pipe material for a given set of fluids.     

Wettability between Fe-Al alloy and sintered MgO

In the current study, the wettability between Fe-Al alloy and sintered MgO substrate was investigated. The stable contact angle between the sintered MgO substrate and the liquid iron was approximately 134° at 1550 °C, hardly influenced by Al concentrations of 18 ppm and 370 ppm in the liquid iron. By changing hydrogen partial pressure from 0 vol% to 1 vol%, the oxygen partial pressure decreased. Meanwhile, the contact angle between the MgO substrate and the liquid iron with 370 ppm Al increased with the decrease of oxygen partial pressure. The oxygen partial pressure and contact angle were scarcely affected by increasing hydrogen partial pressure from 1 vol% to 5 vol%. In all cases with 370 ppm Al in the liquid iron, oxide layers were detected on the surface of iron samples. The oxidation of iron could be effectively prevented by increasing the hydrogen partial pressure. The MgO substrate was reduced to Mg vapor in the reducing atmosphere at a high temperature. Then the Mg vapor was dissolved into the iron even before iron melting. Under thermodynamic equilibrium condition, an oxide layer containing two components, i.e. MgO·Al₂O₃ phase and CaO-SiO₂-MgO-Al₂O₃ phase, was generated on the surface of the iron sample. Due to the different wettability between the iron and the two phases, MgO·Al₂O₃ phase was repelled, while the CaO-SiO₂-MgO-Al₂O₃ phase adhered to the inside area.