Influence of subsequent curing on water sorptivity and pore structure of steam-cured concrete

Steam-cured condition is found to cause larger porosity and worse properties of concrete compared with normal curing condition. For the sake of seeking effective measurements to eliminate this bad effect of steam-cured condition on concrete, the water sorptivity and pore structure of steam-cured concretes exposed to different subsequent curing conditions were investigated after steam-curing treatment. The capillary absorption coefficient and porosity of the corresponding concretes were analyzed, and their mechanisms were also discussed. The results indicate that water sorptivity and pore structure of steam-cured concrete are greatly influenced by the curing condition used in subsequent ages. Exposure steam-cured concrete to air condition has an obviously bad effect on its properties and microstructures. Adopting subsequent curing of immersing steam-cured concrete into about 20 °C water after steam curing period can significantly decrease its capillary absorption coefficient and porosity. Steam-cured concrete with 7 d water curing has minimum capillary absorption coefficient and total porosity. Its water sorptivity is decreased by 23% compared with standard curing concrete and the porosity is 9.6% lower. Moreover, the corresponding gradient of water sorptivity and porosity of steam-cured concrete both decrease, thus microstructure of concrete becomes more homogeneous.     

V的碳氮化合物析出对36Mn2V非调质钢组织性能的影响

在φ340机组上进行非调质36Mn2V和37Mn5油井管钢工艺试验,对比分析二者组织性能．研究36Mn2V钢中微合金元素V的碳氯化物析出对其组织性能的影响。结果表明。36Mn2V、37Mn5钢可分别用于高钢级N80-1和低钢级J55、K55油井管的生产,36Mn2V非调质钢在高温形变诱导下析出V（C、N）,促进了晶内细小铁素体和珠光体的析出,反之细晶铁素体析出促进了V（C、N）沿y／a界面弥散析出,故而显著改善了36Mn2V非调质钢组织性能。     

One-dimensional consolidation of double-layered soil with non-Darcian flow described by exponent and threshold gradient

Based on non-Darcian flow law described by exponent and threshold gradient within a double-layered soil, the classic theory of one-dimensional consolidation of double-layered soil was modified to consider the change of vertical total stress with depth and time together. Because of the complexity of governing equations, the numerical solutions were obtained in detail by finite difference method. Then, the numerical solutions were compared with the analytical solutions in condition that non-Darcian flow law was degenerated to Dary’s law, and the comparison results show that numerical solutions are reliable. Finally, consolidation behavior of double-layered soil with different parameters was analyzed, and the results show that the consolidation rate of double-layered soil decreases with increasing the value of exponent and threshold of non-Darcian flow, and the exponent and threshold gradient of the first soil layer greatly influence the consolidation rate of double-layered soil. The larger the ratio of the equivalent water head of external load to the total thickness of double-layered soil, the larger the rate of the consolidation, and the similitude relationship in classical consolidation theory of double-layered soil is not satisfied. The other consolidation behavior of double-layered soil with non-Darcian flow is the same as that with Darcy’s law.     

商品房预售中购房人的风险及其防范

随着我国经济体制改革的不断深入,近年来我国的房地产交易日趋活跃,为适应住房制度的改革,商品房预售应运而生.但由于商品房预售在我国尚处于起步阶段,而且这种交易行为涉及的法律关系比较复杂,相关法律不尽完善,导致预售中出现一些新的问题.为此,本文将对商品房预售中购房人的风险及其防范进行初步探析.     

三相光伏并网发电系统的建模与仿真

本文系统地介绍了三相光伏并网发电系统的建模与仿真。根据光伏阵列的等效电路,在Matlab/simulink中采用S函数的方式,建立了光伏阵列的数学模型。基于光伏阵列的V-I曲线,利用牛顿迭代求解方法,确定了光伏阵列并网运行的最大功率点。根据三相光伏并网发电系统的结构图,结合双闭环并网的控制策略,实现了光伏阵列的最大功率点跟踪控制、光伏并网电流的正弦化和单位功率因数。最后,将光伏并网接入到电力系统的配电网络中,结合算例,研究了日照强度、环境温度、控制策略等变化时,光伏阵列的仿真结果。通过仿真分析,证明了本文所建立的三相光伏并网的模型和控制策略的正确性。     

新生代农民工职业技能培训现状、问题和对策研究

新生代农民工逐渐成为农民工的主体,为我国经济增长和城市发展作出了重要的贡献。新生代农民工素质的高低对中国未来社会可持续发展、经济可持续增长有着重要的影响。新生代农民工受教育程度比传统农民工高,有较强烈的培训意愿,他们对培训所持的态度在一定程度上将决定他们是否参加培训。农民工职业技能培训是全面提高农民工自身素质,增强其就业能力和市场竞争地位的一项重要措施。为了适应形势上的变化,农民工技能培训内容、模式也必须随着职业、技术的发展新趋势及培训对象的变化而不断创新。     

适应动态安全需求的实时任务调度算法研究

现有的实时容错调度算法没有将实时任务的动态安全需求与其可调度性结合起来考虑.针对这一问题,文章展开以下研究工作:基于安全分级思想,构建了一个适应动态安全需求的实时调度模型,该模型详细地描述了实时任务、系统安全服务、任务容错等实时调度过程涉及的关键要素.以此模型为基础,提出了一种自适应实时容错调度算法(AFTS),该算法支持优先级抢占式调度策略,以牺牲普通任务的运行为代价来保证关键任务的可调度性,并采用主副本备份技术实现了关键任务的容错功能.当系统安全级别被动态调整时,该算法能够为实时任务选择满足当前安全需求的最优安全策略.仿真实验表明,文中提出的算法与同类算法相比,在系统动态安全需求的适应性,以及关键任务的可调度性和容错能力等方面有较好的表现.     

外腐蚀管道剩余寿命的有限元分析

预测油气管道的剩余寿命, 对避免管道泄漏事故的发生和节省维修费用具有重要意义。针对国内某成品油管道开挖点处的两个腐蚀缺陷, 基于有限元分析方法, 建立了管道椭球形缺陷的三维有限元结构模型。以管道实测缺陷尺寸为依据, 在已知腐蚀速率的情况下, 采用非线性分析技术对腐蚀管道进行了应力分析, 依据塑性极 限状态失效准则预测了管道的剩余寿命。结果表明, 两个腐蚀缺陷的剩余寿命分别为8a和1 3a, 预测结果可为管道的维护维修提供理论依据。     

Two-step anodization of maltilayer TiO2 nanotube and its photocatalytic activity under UV light

A double-layer TiO2 nanotube arrays were formed by two-step anodization of Ti foils in different electrolytes. First, Ti in 0.5 wt% HF was anodized to form thin nanotube layer. Afterwards a second anodization was conducted in a formamide based electrolyte, which allowed the second layer of nanotube growing directly underneath the first one. From FESEM investigation we found that the thickness of second layer corresponded to the anodization time, the increasing of which would lead to the excessive etching on the first layer. The first layer protected the lower one from fluoride corrosion during anodization process. The double layer TiO2 nanotube arrays showed no benefit to photodegradation effect in methyl orange degradation experiments.