Effect of corrosive solutions on C-S-H microstructure in portland cement paste with fly ash

By means of ²⁹Si and ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR) combined with deconvolution technique, X-ray diffraction (XRD), scanning electron microscopy (SEM) as well as energy dispersive X-ray system(EDX), the effect of 5 wt% corrosive solutions (viz. 5 wt% Na₂SO₄, MgSO₄, Na2SO4+NaCl and Na₂SO₄+NaCl+Na₂CO₃) on C-S-H microstructure in Portland cement containing 30 wt% fly ash was investigated.The results show that, in MgSO₄ solution, Mg²⁺ promotes the decalcification of C-S-H by SO ₄ ^2- ,increasing silicate tetrahedra polymerization and mean chain length (MCL) of C-S-H. However, the substituting degree of Al³⁺ for Si⁴⁺ (Al[4]/Si) in the paste does not change evidently. Effect of Na²SO⁴ solution on C-S-H is not significantly influenced by NaCl solution, while the MCL and Al[4]/Si of C-S-H in fly ashcement paste slightly change. However, the decalcification of C-S-H by SO ₄ ^2- and CO ₃ ^2- attack, as well as the activation of fly ash by SO ₄ ^2- attack will increase the MCL and Al[4]/Si, which are both higher than that under Na₂SO₄ corrosion, MgSO₄ or Na₂SO₄ +NaCl coordination corrosion.     

Corrosion mechanism and corrosion model of Mg-Y alloy in NaCl solution

Corrosion of Mg–Y alloy was studied using electrochemical evaluations, immersion tests and SEM observations. Corrosion mechanisms of Mg-(0.25 and 2.5) Y alloy and Mg-(5, 8, and 15) Y alloy were uniform corrosion and pitting corrosion respectively, and the content of Mg_(24)Y_5 phases determined its effect acting as cathode to accelerate the corrosion or corrosion barrier to inhibit the corrosion. Corrosion resistance of Mg-(0.25, 2.5, 5, 8, and 15) Y alloys was as follows: Rt(Mg-0.25Y) Rt(Mg-8Y) Rt(Mg-15Y) Rt(Mg-5Y) Rt(Mg-2.5Y). Y could significantly improve the corrosion resistance of the Mg-Y alloy, but the excess of Y deteriorated the corrosion resistance of the Mg-Y alloy. The optimum content of Y in the studied alloys was 2.5%.     

Effects of ultrasonic treatment on microstructure and mechanical properties of semisolid Sn-52Bi alloy

The effects of ultrasonic vibration temperature on the microstructure of semisolid Sn-52 Bi alloy and mechanical properties were investigated. The results show that the microstructure and mechanical properties are improved obviously after the ultrasonic treatment. Nearly round and uniformly distributed primary Sn phase particles were obtained under the cavitation and acoustic streaming caused by ultrasonic treatment. The best effects of ultrasonic treatment on microstructure and mechanical properties were obtained with the ultrasonic vibration for 120 s at 140 ℃. The elongation of semisolid Sn-52 Bi alloy treated by ultrasonic vibration for 120 s at 140 ℃ was 42% and increased by 156.09% compared to conventional liquid casting Sn-52 Bi alloy without ultrasonic vibration. It is a feasible and effective method to adopt the semisolid metal forming technology assisted with ultrasonic vibration to improve the ductility of Sn-Bi alloys.     

奎屯河流域健康评价

以新疆典型的干旱内陆河流域--奎屯河流域为研究对象,在确定流域健康评价时空尺度的基础上,提出涵盖流域水资源健康、涉水生态环境健康、社会经济健康的评价指标体系,构建基于组合赋权与协调发展度的流域健康评价模型。结果表明:现状年(2015年)处于亚健康状态的分区有:子区1、子区2、子区3、子区6,综合评价指数分别为:0.419、0.404、0.408、0.401,协调发展类型为临界协调发展;处于不健康状态的分区有:子区4和子区5,综合评价指数为0.358和0.343,协调发展类型属于中度不协调衰退型。     

Winglet geometry effects on tip leakage loss over the plane tip in a turbine cascade

The effects of winglet offset distance, winglet coverage, and winglet cross section on the over-tip leakage loss for the plane tip have been investigated experimentally in a turbine blade cascade for a tip gap height-to-span ratio of h/s = 1.36 %. The results show that the over-tip leakage loss for the full coverage winglet increases steeply with increasing the winglet offset distance. This loss generation is attributed to flow disturbances over the forward-facing and backward-facing steps within the tip gap. The winglet flush mounted to the tip surface provides the best result. With the leading edge winglet portion or without it, the both-side winglet always provides better aerodynamic performance than the corresponding pressure-side winglet or suction-side winglet. Longer coverage of the both-side winglet leads to lower loss. Therefore, the full coverage winglet performs best in the loss reduction for the plane tip. In general, thinner winglet leads to better aerodynamic result, and the winglet cross section having a slant bottom surface with the smallest thickness at its outer end is recommended.     

Noncovalent Functionalized Graphene-Filled Polyimides with Improved Thermal,Mechanical, and Wear Resistance Properties

A facile method is proposed to prepare poly-o-phenylenediamine (PoPD) noncovalent functionalized graphene (G)-reinforced polyimide (PI) nanocomposites. PoPD-G exhibited excellent dispersibility in various organic solvents. The structures of PoPD-G were characterized by Raman and UV spectrum, which verified the π–π interactions between PoPD and G. The effective exfoliation of graphene nanosheets was investigated by observation of the morphology of PoPD-G with SEM, SPM, and TEM. Compared to PI/G composites, the interfacial adhesion between graphene nanosheets and PI matrices promoted efficient stress transfer from PI chains to PoPD-G nanofillers. Polyimide nanocomposites with different incorporations of PoPD-G exhibited outstanding thermal properties. It is interesting to note that only 0.5 wt% PoPD-G-reinforced PI composites increased by 20.8% in hardness, enhanced by 84.0% in storage modulus, and reduced by 72.8% in wear rate compared with neat PI. The eminent enhancement was attributed to the facile dispersion of graphene nanosheets and strong interface adhesion between PI and PoPD-G.     

基于特征频繁度的勒索软件检测方法研究*

勒索软件的变种及新的家族呈指数型增长,检测勒索软件及其未知家族的成员逐渐成为了研究热点。杀毒软件通常使用检测恶意代码的方法来检测勒索软件,存在构造的特征复杂、检测率低的问题。在对勒索软件的行为进行分析时,发现勒索软件有频繁读取、加密和删除文件等特点。根据其行为特点,提出一种基于行为频繁度的特征构造方法,该方法基于动态分析,计算勒索软件对特定后缀、路径以及API调用等行为的频繁度并结合内存行为构建特征,再使用优化参数后的随机森林算法构造勒索软件检测模型。测试数据集包括16类勒索软件家族的1412个软件和379个正常软件。通过与其他算法及多种杀毒软件进行比较,来检测算法的性能。实验结果表明该方法能很好的检测勒索软件以及未知类型的勒索样本。     

钢管混凝土拱抗冲击影响因素

为研究钢管混凝土拱的抗冲击力学性能,在试验结果验证的基础上,采用有限元分析方法,研究了集中冲击荷载作用下矢跨比、混凝土强度等级、钢材屈服强度和冲击质量4个因素对钢管混凝土拱抗冲击力学性能的影响.计算结果表明:相同冲击能量下,钢管混凝土拱存在着一个矢跨比阈值f,当试件矢跨比大于f时,试件的抗冲击性能基本相同;与钢管混凝土梁、柱类似,增大混凝土强度对提高试件的抗冲击性能影响不明显,而增大钢材屈服强度可以使试件的抗冲击性能明显改善;随着冲击质量增加,试件的冲击力峰值变化不大,挠度变大,冲击持续时间变长,冲击质量与跨中挠度成线性关系.     

基于特征矢量化的肺结节特征选择算法*

针对肺结节良恶性分类模型中特征选择过程无法避免特征多样性不受破坏的问题,提出一种将肺结节特征矢量化处理的特征选择方法。首先,假设每个肺结节特征都是由数据、类型构成的一个矢量。然后,按照特征类型添加特征到相应的特征子集,并分别利用Relief算法评价特征、特征子集的分类重要性。最后,通过动态阈值的方式筛选得到优化后的特征子集。在150个肺结节样本的分类实验中,采用本文算法所取得的敏感性为94.7%、特异性为93.7%、虚警率为5.2%、受试者工作特性曲线下面积为97.3%。分析表明,本文算法几乎不破坏肺结节特征的多样性,能够显著提高肺结节良恶性分类的准确性。     

An experimental investigation on acoustic emission characteristics of sandstone rockburst with different moisture contents

Rockburst occurred frequently during deep mining in China. The mechanism of rockburst is very complicated and related to many factors. In order to investigate the influence of moisture contents of rockmass on rockburst, we conducted a series of laboratory rockburst experiments of sandstone under three different moisture contents by the Modified True-Triaxial Apparatus (MTTA), in which the acoustic emission (AE) system was employed to monitor the internal damage of rock mass. A high-speed video camera was utilized to record the detail of rockburst. Based on the experimental results, the AE characteristics, such as AE count, AE energy, and AE frequency, were analyzed. The rockburst process, type, and indensity under different moisture contents were discussed. The research results show that with the increase of moisture contents, rock strength was soften, the elastic and the cumulative damage of the rock were reduced, resulting in a gradual decrease in AE cumulative counts and cumulative energy over the course of rockburst. This study provides an experimental basis and reference for better understanding to the rockburst mechanism and control.