变形矩形和V形微屏蔽线传输特性的矢量有限元计算

微屏蔽线在使用过程中难免会产生变形。本文利用矢量有限元法讨论了矩形微屏蔽线和V形微屏蔽线的变形对其传输特性的影响，其中传输特性包括主模截止波长、单模带宽和主模电场结构。计算结果显示，两种微屏蔽线的变形对三种传输特性均有较大影响，这些数值计算结果对两种微屏蔽线在使用过程中出现变形时对整体器件的影响有较强的指导意义。     

Authenticity green coffee bean species and geographical origin using near-infrared spectroscopy combined with chemometrics

To prevent the adulteration of agricultural resources and provide a solution to enhance the green coffee bean supply chain, authentication using the near-infrared spectroscopy (NIRS) technique was investigated. Partial least square with discrimination analysis (PLS-DA) models combined with various preprocessing methods were built from NIR spectra of 153 Vietnamese green coffee samples. The model combined with the standard normal variate and the first order of derivative yielded excellent performance in predicting coffee species with the error cross-validation of 0.0261. PLS-DA model of mean centre and first-order derivative spectra also yielded good performance in verifying geographical indication of green coffee with the error of 0.0656. By contrast, the predicting abilities of post-harvest methods were poor. The overall results showed a high potential of the NIRS in online authentication practices.     

Development of ensemble machine learning approaches for designing fiber-reinforced polymer composite strain prediction model

Engineering with Computers - Over the past few decades, it has been observed a remarkable progression in the development of computer aid models in the field of civil engineering. Machine learning...     

Improving Properties of Poly(vinylidene fluoride) by Adding Expanded Graphite without Surface Modification via Water‐Assisted Mixing Extrusion

Expanded graphite (EG) is introduced into poly(vinylidene fluoride) (PVDF) by melt mixing extrusion with water injection. The results demonstrate that the unfunctionalized EG in composite prepared with water injection exbibits better dispersion than that in the one prepared without water injection due to the promoting role of water during extrusion. Thus, the PVDF/EG composite with loading of 4 wt% prepared by water‐assisted mixing extrusion (WAME) exhibits electrical conductivity of about three orders of magnitude higher than the neat PVDF and one order of magnitude higher than the one prepared without water injection. Comparing to the neat PVDF, the thermal conductivity of the composites prepared with and without water injection is increased by 101.5% and 75.0%, respectively. The introduced EG leads to increased Young’s modulus and tensile strength especially for the composite prepared by WAME. The present work indicates that WAME can promote the dispersion of EG in PVDF matrix without any extra functionalization.     

基于.NET技术的高校后勤报修系统设计与实现

随着高校办学规模的不断扩大,原基于师生服务中心的现场人工报修方式,已无法满足日益增长的后勤报修维修的需求。根据学校的实际情况,对学校后勤管理系统进行分析,得出高职院后勤管理系统应满足在线报修、在线查看、维修反馈、在线评价等功能的需求;同时对高校后勤报修系统进行系统架构设计、网络架构设计、UML类图设计、数据库设计等。通过C#完成系统的编写,最终实现后勤报修系统的开发。     

金属多孔材料喷墨制备法的研究与进展

喷墨三维打印作为金属增材制造技术的一种重要方法,已广泛应用于金属多孔材料的制备,具有成本低、操作简单、成型材料范围广、孔结构设计灵活性大,较好的制件精度和结构精细度等优点.系统地总结了钛及钛合金、不锈钢、镍基合金、铝合金等多孔材料喷墨三维打印技术制备工艺与组织结构的国内外最新研究进展、目前存在的问题,以及应用前景.     

来流马赫数影响高负荷扇形扩压叶栅气动性能的研究

为研究亚音速高负荷扇形扩压叶栅NACA0065-K48的变工况性能,采用数值方法研究了来流马赫数对叶栅气动性能和流场结构的影响,来流马赫数的取值范围为0.3～0.8。计算结果表明:随着来流马赫数的增大,叶栅静压比不断提高,但总压损失先减后增,马赫数在0.5～0.7范围内叶栅具有较好的综合气动性能。扇形叶栅下角区分离程度大于上角区的不平衡流动现象会随着马赫数的增大而加剧,通道涡则是这一发展趋势的主导,且马赫数达到0.7之后,下角区通道涡与集中脱落涡趋于融合。此外,下端壁分离螺旋点的形成与发展是控制下角区分离程度和损失大小的关键。     

Research on heat dissipation performance and flow characteristics of air‐cooled battery pack

With the depletion of fossil fuels and the aggravation of environmental pollution, the research and development speed of electric vehicles has been accelerating, and the thermal management of battery pack has become increasingly important. This paper selects the electric vehicle battery pack with natural air cooling as the study subject, conducts simulation analysis of the heat dissipation performance of battery packs with and without vents. Then this paper researches on the influence of internal flow field and external flow field. Field synergy principle is used to analyze the effect of velocity field and temperature field amplitude. The results show the following: it is found that the maximum temperature rise and the internal maximum temperature difference of the battery pack with vents are reduced by about 23.1% and 19.9%, raising speed value can improve the heat dissipation performance, and raising temperature value can decrease the heat dissipation performance. Reasonable design of the vents can make the inner and outer flow field work synergistically to achieve the best cooling effect. Then the reference basis for the air cooling heat dissipation performance analysis of electric vehicle, battery pack structure arrangement, and air‐inlet and air‐outlet pattern choosing are offered.     

配煤掺烧最小煤质偏差模型及煤场存放优化

定义了混煤和锅炉目标煤的煤质偏差,给出以煤质偏差作为目标函数的掺配优化模型,通过调整某个成分的期望误差,可单独调节该成分与目标煤的接近程度;通过对模型约束条件设定,可限制低灰熔点煤的掺配份额,控制炉膛结焦,或提高采购量大的单煤的掺配比例。基于最小煤质偏差模型,针对某670 MW超临界压力直流锅炉进行掺配优化模拟,提出煤场存放的优化概念和方法。结果表明:该模型能够从复杂的单煤煤源中找到最接近目标煤质的掺配方案,优化后入炉煤质稳定,且接近目标煤质。