Modeling of time to corrosion-induced cover cracking in reinforced concrete structures

Service life of the concrete structures depends on the protective action provided by the cover concrete against the susceptibility of the reinforcement to the corrosive environment. Depending on the level of the oxidation of metallic iron, corrosion products may have much greater volume than the original iron that gets consumed by the process of corrosion. This volume expansion is mainly responsible for exerting the expansive radial pressure at the steel-concrete interface and development of hoop tensile stresses in the surrounding concrete resulting ultimately in the through cracking of the cover concrete. This cover cracking would indicate the loss of the service life for the corrosion-affected structures. In the present paper, an attempt has been made to develop analytical models for predicting the time to cover cracking by considering the residual strength of the cracked concrete and the stiffness provided by the combination of the reinforcement and expansive corrosion products. The problem is modeled as a boundary value problem wherein the governing equations are expressed in terms of the radial displacement and the analytical solutions are presented considering a simple 2-zone model for the cover concrete viz. cracked or uncracked. The analytical models are then evaluated through their ability to reproduce available experimental trends and subsequently a sensitivity analysis has also been carried out to show the influence of the various variable parameters of the proposed models with reference to the experimental trends.     

Inhibitions of cotton seedling growth by volatile ketones emitted by cover crop residues

Low-input, sustainable agriculture (LISA) systems can include soil incorporation of residues of weeds and legume cover crop species. However, both seed germination and seedling growth of crops, including cotton (Gossypium hirsutum L.), are inhibited by volatile organic compounds emitted by these residues during decomposition. A cotton seedling-growth assay was used to demonstrate that C₄ through C₉ ketones released by decomposing legume residues significantly inhibited root and shoot elongation, root and shoot fresh and dry weight gain, and cotyledon expansion. Seedling root and shoot water relationships were relatively insensitive to those components of plant residue volatile emissions. Concentration (0.0, 0.5, 1.0, 1.5, or 2.0M/cm³ sterile greenhouse soil mix) and root-zone temperature (20 or 30°C) altered the activity of the more inhibitory ketones. Molecular weight (carbon chain length), carbon chain branching, and position of the carbonyl group also influenced ketone inhibitory activity.Mention of a commercial or proprietary product does not constitute an endorsement by the U.S. Department of Agriculture.     

土工格栅加筋包边填砂路堤模型试验研究

为探究包边填砂路堤荷载作用下的极限承载力特性、破坏形态规律及加筋性状,设计了土工格栅加筋包边填砂路堤结构,改装美国GCTS公司的USTX-2000动静三轴加载装置进行加载,通过改变加筋层数、筋材布置长度及包边土厚度对土工格栅包边填砂路堤进行一系列试验。对不同工况下包边填砂路堤的极限承载力、封层及坡面法向累积变形、位移变化进行研究。试验结果表明:土工格栅加筋和增加包边土厚度可以显著提高包边填砂路堤的极限承载力,并能减小封层中、封层右及坡顶、坡中的法向累积变形;无筋路堤的滑动面在路堤内呈折线状且并未通过坡脚侵入地基,在坡顶的黏土和砂芯交界处产生最大位移;土工格栅加筋及增加包边土厚度可以使滑动面向路堤内部迁移但形态不变,且最大位移处向路堤内部迁移。     

长江源区浮游植物群落特征与水环境因子关系研究

为研究长江源头区域河流浮游植物群落结构与水环境因子的关系,于2017年5,8,9月份和2018年5,7,9月份在长江源区进行调查分析,并对浮游植物及水环境因子进行了Pearson相关性分析和典范排序分析。结果表明,共发现浮游植物6门79种,以硅藻门和蓝藻门为主。各采样点浮游植物平均密度71.66×10⁴ ind./L。典范分析表明,温度、化学需氧量、高锰酸盐指数、氨氮、总氮、溶解氧是影响长江源区河流浮游植物群落结构的主要因子。研究成果有助于了解长江源头地区浮游植物群落特征,为三江源生态保护提供数据支撑。     

Design of a new type of mine rescue relay cabin

This paper presents the design of an innovative mine emergency rescue relay cabin, and investigates a detailed comparison of existing shelter facilities, their function, service object, structures, size, and system components with the newly designed mine emergency rescue relay cabin. Air-tightness test indicated a test chamber relief rate of 26 Pa/min, which meets the design requirements. Furthermore,respirator replacement test showed an average time of 73.7 s to replace a respirator. The air cover air supply test indicated an air supply rate of 220 L/min, which is sufficient for the staff replacing the respirator in the emergency rescue relay cabin. The total air supply volume is 9680 L, which can be supplied via two compressed air cylinders of 40 L, pressurized to15 MPa.     

基于SWAT分布式流域水文模型的下垫面变化和水利工程对径流影响分析

近年来随着人类活动的加剧,兴建了许多中、小型水利和水土保持工程,迅速改变着流域的自然面貌,因而改变了径流的原有规律。选取1960以前水利工程较少的时期作为人类活动不明显期来率定SWAT模型参数,对于1990以后人类活动稳定期的径流分别设置3个情景:应用原SWAT模型、应用只考虑下垫面变化的SWAT模型和应用考虑下垫面变化和水利工程影响的SWAT模型分别进行模拟。对于五道沟以上流域和流域内东丰、磐石、样子哨3个子流域模拟结果显示:考虑下垫面变化和水利工程影响后的径流模拟相关系数R2和纳什效率系数NSE分别从0.82、0.56提高到0.91、0.79,分别提高了11.0%和41.1%。其中模拟精度的提高量中91.3%是由于考虑水利工程作用所引起的,剩余部分是由考虑下垫面变化引起的。相比下垫面变化,水利工程运行对该流域径流变化占据主导作用。     

经济语篇中多模态隐喻的构建——以《经济学人》封面漫画为例

作为认知语言学的研究新趋势,多模态隐喻不仅存在于语言中,还通过其他诸如图像、隐喻、声音和手势等沟通形式表现出来。以《经济学人》封面漫画为例,从认知语言学视角探讨多模态隐喻的构建,试图阐释不同的模态,例如图像,文字,排版,甚至颜色如何互相作用以及共同构建语篇,从而展现经济语篇中文字-图像的关系以及多模态隐喻的实现。     

基于ANSYS-Workbench的汽车水箱散热器护风罩模态分析

介绍了汽车水箱散热器的作用,并采用Pro/e对某型号水箱散热器护风罩造型。利用ANSYS-Workbench对其进行静力学及模态分析,求得了该型护风罩的六阶固有频率及相应的变形云图。     

移动硬盘盒精密热流道注塑模具设计

热流道注塑模具在模具行业中的应用越来越广泛,采用热流道系统不仅可以保证塑件质量、提高材料的利用率,还能显著提高塑件的生产效率。通过对移动硬盘塑料件的结构及成型工艺特点进行分析,设计了移动硬盘塑料件热流道注射模具,重点对热流道模具热平衡计算和热流道浇注系统进行了分析计算,模具采用单点热流道、一模两件潜伏式浇口、外滑块抽芯机构及斜推杆抽芯成型倒扣设计。实践证明,该移动硬盘塑料件模具设计结构合理,在提高塑料件成型质量的同时,提高了材料的利用率及生产效率,为同类结构特点的热流道注塑模设计提供了参考。     

车门外板覆盖件成形工艺研究

分析了车门外板覆盖件的成形方法及易产生的缺陷 ,制定了CA6471车门外板的冲压工艺 ,采用该工艺生产的车门外板零件表面质量及尺寸精度均满足要求。