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.     

Kinetic theory for aquatic animal distribution simulation

Identifying the underlying mechanisms that influence the spatial patterns in populations improves the forecasts of the alternative management strategies on the spatial dynamics of the populations, which are critical for assessing and managing the fisheries and improving the water resource management. This paper described a new approach of the numerical model for the prediction of the aquatic animal distribution in the flows. The model was developed based on the kinetic theory of gases, the mechanism of the aquatic animal movement and the flow hydrodynamic patterns. The model was validated using the available experimental data and an acceptable agreement was obtained. A comprehensive parameter study was then conducted to help understand the impact and the sensitivity of each parameter to the aquatic animal distribution. The promising results of the model reveal the prospect of applying this model to the reliable prediction of the aquatic animal distribution within a relatively large water area.     

An efficient equivariant adaptive separation via independence algorithm for acoustical source separation and identification

To balance the convergence rate and steady-state error of blind source separation (BSS) algorithms, an efficient equivariant adaptive separation via independence (Efficient EASI) algorithm is proposed based on separating indicator, which was derived from the convergence condition of EASI, and can be used to evaluate the separation degree of separated signals. Furthermore, a nonlinear monotone increasing function between suitable step sizes and separating indicator is constructed to adaptively adjust step sizes, and forgetting factor is employed to weaken effects of data at the initial stage. Numerical case studies and experimental studies on a test bed with shell structures are provided to validate the efficiency improvement of the proposed method. This study can benefit for vibration & acoustic monitoring and control, and machinery condition monitoring and fault diagnosis.     

薄荷不同部位挥发油成分比较研究

研究武汉地区野生薄荷根茎叶挥发油的成分及含量。用水蒸气蒸馏法(SD)分别提取薄荷不同部位的挥发油,然后用气相色谱-质谱法分析薄荷不同部位挥发油的化学成分。结果表明:叶片挥发油出油率是0.45%,茎挥发油出油率是0.2%,根挥发油出油率是0.02%。用气相色谱-质谱法分析三种不同部位挥发油,共鉴定出43种化合物,叶和茎挥发油主要成分是薄荷醇,根挥发油的主要成分是二十四烷。用薄荷不同部位提取的挥发油含量和成分有较大差别。为获得较高产率的薄荷醇成分,以薄荷叶获取挥发油为最佳原料。     

臭氧活性炭联用工艺处理甲基橙废水试验研究

在印染废水处理中,废液浓度不同,臭氧、活性炭、臭氧—活性炭三种工艺对甲基橙的脱色效果不同。相同臭氧浓度条件下,不同浓度的甲基橙脱色率—时间曲线近似重合;活性炭在吸附饱和的情况下,能够催化空气降解甲基橙;溶液的浓度对臭氧—活性炭脱色效果有一定影响,甲基橙浓度越大,pH越高,脱色速率越大。     

Dynamic observation of bainite transformation in a Fe-C-Mn-Si superbainite steel

The dynamic observations of bainitic transformation in a Fe-C-Mn-Si superbainite steel were conducted on a high temperature laser scanning confocal microscope. It is indicated that the mutual intersection of bainite sheaves often occurs during growth of bainite ferrite, resulting in an interlocked bainite microstructure. Moreover, bainite transformation is promoted by higher austenization temperature and the longer and finer bainite platelets are obtained. Further, The average growth rate of bainite after austenization at 1 100 ° is calculated as 5.8 µm·s^?1. In situ observation investigation makes it possible to identify bainite transformation in real time during isothermal holding.