1,5-己二烯交联烯烃聚合物的合成及其抗剪切稳定性

以金属配合物为催化剂、1,5-己二烯为交联剂,采用本体聚合法合成了交联超高相对分子质量烯烃类聚合物(简称交联聚合物)。用傅里叶变换红外光谱、核磁共振、凝胶渗透色潜表征交联聚合物的结构和相对分子质量。用旋转黏度计和超声波仪研究了1,5-己二烯用量对交联聚合物溶液表观黏度的影响及交联聚合物的相对分子质量对交联聚合物溶液抗剪切稳定性的影响。实验结果表明,在最佳聚合条件(单体80mL、助催化剂0．4mL、CS-1催化剂0．090g、1,5-己二烯0．40mL、0℃、24 b)下所合成的交联聚合物的重均相对分子质量为7．7×106,数均相对分子质量3．6×106。加入少量1,5-己二烯能提高交联聚合物的抗剪切能力,同时也能提高交联聚合物的相对分子质量。交联聚合物的相对分子质量越大,抗剪切稳定性越好。1,5-己二烯用量约为0．1 mL时(单体40 mL),交联聚合物溶液的表观黏度达到最大值(16．8 mPa·s)。     

滦河上游植被指数NDVI及EVI对SPEI的响应差异

在全球气候变化和人类活动的双重影响下,干旱呈广发、频发态势,使植被生长受到限制,进而影响生态系统结构,威胁区域生态安全。以滦河上游为研究区,基于2000-2019年归一化植被指数NDVI和增强型植被指数EVI,并结合标准化降水蒸散指数SPEI,分析滦河上游气象干旱和植被生长状况的变化趋势及空间分布特征,探讨植被变化对多时间尺度SPEI指数的响应差异。结果表明：近20年滦河上游SPEI呈波动式增大趋势,年尺度SPEI增大速率为0.040 1/a;干旱面积总体减少,减少速率为-1.430 4％/a;NDVI和EVI空间分布特征和变化趋势大体一致,植被覆盖度呈东南高西北低的特征,NDVI和EVI增大速率分别达0.027/a和0.026/a;大部分区域SPEI与植被指数呈正相关,其中NDVI对SPEI-3的响应最强,EVI对SPEI-6的响应最强,总体上EVI与SPEI的相关性强于NDVI;草地对气象干旱最敏感,农田次之,林地最弱。     

Investigations on Structured Polyamide for Laser Sintered Body Armor

Stab resistance body armor (SRBA) is essential in protecting people from knife injuries. The protective parts of traditional SRBA are made of multi-layered ultra-high molecular weight polyethylene (UHMWPE), which causes heavy heat stress for people wearing it. The protective parts of SRBA manufactured using laser sintering (LS) 3D printing technology provide high manufacturing flexibility and low weight. Two different structures, plain plate and pyramid-structured plate, were investigated. The pyramid structure showed much higher stab resistance property then the plain plate, because of the angle and thickness effects. This is the first effort applying the LS technology and polyamide (PA) material (PA 3200) on SRBA. By applying the pyramid structure on the protective layer of the SRBA, the total weight could reduce 30%-40%.     

Vortices around Janus droplets under externally applied electrical field

In this study, the Janus droplet is an oil droplet covered with aluminum oxide nanoparticles on one side of the droplet surface under applied DC electrical field. The vortices around Janus droplets fixed on a horizontal surface were studied in this paper. A numerical model was set up to simulate the vortices around the Janus droplet in electric field. The simulation results illustrate that the electric field determines the strength of the vortices around a fixed Janus droplet, and the surface coverage of the positively charged nanoparticles on a Janus droplet affects the size and location of the vortices. The numerically predicted results were further validated experimentally by visualizing the vortices around Janus droplets in an externally applied DC electric field. Furthermore, as the Janus droplets are generated in electric field, the surface coverage by the nanoparticles depends on the strength of the electric field; therefore, the effect of the electric field on the nanoparticle covered surface area of a Janus droplet and the vortices was analyzed.     

异步电机低速电制动控制

阐述了异步电机电制动的控制策略;分析实际应用中低速电制动转矩出现偏差的原因,并通过MATLAB绘制出当定向角度出现偏差时给定转矩与实际转矩在三维空间中的比例关系。为解决低速电制动时由于转子磁场定向偏差引起电机转矩不准的问题,采用基于无功功率模型的转子时间常数自适应控制进行校正。试验结果表明该控制策略可以实现校正转子磁场定向偏差的功能,具有良好的动态性能,可以满足地铁列车的性能要求。     

铝铸轧机轧辊表面脱辊技术进展

铝制品在现代社会中的广泛使用使得铝铸轧工艺的要求越来越高,并推动铝铸轧机脱辊技术的发展和更新。综述了清辊器机械脱辊、水基石墨乳润滑脱辊、炭黑润滑脱辊的工作原理,阐述了脱辊技术对铝板表面质量、环境污染、原料利用率等方面影响,并对在线裂解制备炭黑润滑技术前景进行了展望。     

丽江西林瓦村纳西聚落美之要素研究

本文以云南丽江西林瓦村纳西聚落为研究对象。通过实地调研、案例分析、归纳总结等方法,分析其选址生聚、街道脉络、院落秩序、建筑造型、细部涵义诸方面对于生态之美、形式之美、生活之美的积极作用,提出院落组织的逻辑有序,因势相宜是纳西聚落之美的核心,是进一步研究和发扬的岀发点.     

A new strategy to reduce edge chipping using stress wave impedance matching

To restrain edge chipping and elucidate its mechanism during machining, the initiation of edge chipping was investigated in this study from the propagation properties of stress waves in the fractured media. Three technological principles of the support for chipping suppression were proposed to reduce the intensity of reflected extension waves, namely, the wave impedance matching, the smaller residual gap and the higher viscosity of the gap filler between the workpiece and the support. As demonstrated from the experimental results, using brass support with non-solid epoxy gap filler can significantly restrain the edge chipping of pressureless sintered silicon carbide during grinding.     

丙烯酸β-环糊精酯共聚物对染料的吸附性能

以丙烯酸β-环糊精酯共聚物为吸附剂,采用分光光度法测定该吸附剂对亚甲基蓝和碱性品红溶液的静态吸附效果,考察了吸附时间、体系pH值等对吸附量的影响。结果表明:常温下,亚甲基蓝的较佳吸附条件为静态吸附时间约7h、体系pH=8.0时,最大吸附量达到166.3mg/g;碱性品红的较佳吸附条件为静态吸附时间约7h、体系pH=10时,最大吸附量达到137.9mg/g。该共聚物对亚甲基蓝染料吸附性能更好。