车用汽油机活塞销座轴承润滑特性

利用活塞、连杆系统多体动力学分析结合弹性流体动力学润滑(EHL)模型,研究了活塞销座轴承的润滑特性.首先建立了活塞、活塞销和连杆的有限元模型,利用Craig-Bampton方法对其进行了自由度缩减以降低求解规模,然后在活塞销座轴承和连杆小头轴承引入EHL润滑模型,计算了活塞销座轴承的油膜厚度、油膜压力和干接触压力等轴承润滑特性参数.研究了是否考虑活塞和活塞销的结构弹性及油膜空穴对计算结果可能产生的影响,分析了活塞销孔间隙、活塞销刚度和活塞销孔几何形状等参数对其润滑特性的影响,用不同形状销孔的润滑特性计算结果解释了发动机热拉伤试验中出现的活塞销孔拉伤情况.结果表明:活塞和活塞销的结构弹性及油膜空穴是汽油机活塞销座轴承分析中不可忽略的影响因素;活塞销刚度和活塞销孔几何形状对活塞销座轴承润滑特性有重要的影响.     

壳聚糖改性竹粉/PVC复合材料的制备和性能

壳聚糖、竹粉和PVC等按一定比例混合,用挤出成型法制备了竹粉/PVC复合材料。考察了壳聚糖添加量对复合材料物理力学性能、热稳定性、防水性能和防腐性能的影响。结果表明,适量壳聚糖的添加,可以改善复合材料的综合性能。且当壳聚糖含量为3wt%时复合材料的性能最佳,与未添加壳聚糖的复合材料相比,其拉伸强度、冲击强度和弯曲强度分别提高了44.7%、58.2%和79.6%,腐蚀前8天的吸水率从2.2%降低为1.6%,被白腐菌和褐腐菌腐蚀后材料的质量损失率分别降低了94.1%和75.0%。     

一种提高小区干扰协调中用户公平性的载波调度算法

针对LTE-Advanced系统中小区干扰协调的用户公平性问题,提出一种基于用户优先级的比例公平调度算法。该算法通过引入用户优先级因子来调节小区边缘用户与小区中心用户的载波分配,进而在保障系统吞吐量的前提下改善频谱资源受限的小区边缘用户的公平性。仿真结果表明,该算法在以系统吞吐量下降了0.7%的代价下使小区边缘平均用户数据速率提高了90%以上。     

Children conceived by in vitro fertilisation after fresh embryo transfer

AIMS: To compare the outcome in in vitro fertilisation (IVF) children (after fresh embryo transfer) from multiple and singleton births with one another, and with normally conceived control children. METHODS: A cohort of 278 children (150 singletons, 100 twins, 24 triplets and four quadruplets), conceived by IVF after three fresh embryos had been transferred, born between October 1984 and December 1991, and 278 normally conceived control children (all singletons), were followed up for four years after birth. They were assessed for neonatal conditions, minor congenital anomalies, major congenital malformations, cerebral palsy and other disabilities. Control children, all born at term, were matched for age, sex and social class. RESULTS: The ratio of male:female births was 1.03. Forty six per cent of IVF children were from multiple births; 34.9% were from preterm deliveries; and 43.2% weighed less than 2500 g at birth. The IVF singletons were on average born one week earlier than the controls, weighed 400 g less, and had a threefold greater chance of being born by caesarean section. The higher percentage of preterm deliveries was largely due to multiple births and they contributed to neonatal conditions in 45.0% of all IVF children. The types of congenital abnormalities varied: 3.6% of IVF children and 2.5% of controls had minor congenital anomalies, and 2.5% of IVF children and none of the controls had major congenital malformations. The numbers of each specific type of congenital abnormality were small and were not significantly related to multiple births. IVF children (2.1%) and 0.4% of the controls had mild/moderate disabilities. They were all from multiple births, including two children with cerebral palsy who were triplets. CONCLUSIONS: The outcome of IVF treatment leading to multiple births is less satisfactory than that in singletons because of neonatal conditions associated with preterm delivery and disabilities in later childhood. A reduction of multiple pregnancies by limiting the transfer of embryos to two instead of three remains a high priority.     

胶体金免疫层析法快速检测烟草中吡虫啉残留

目的建立胶体金免疫层析法快速检测烟草中残留的吡虫啉。方法用柠檬酸三钠还原法制备胶体金,并用它标记吡虫啉单克隆抗体,建立并优化胶体金免疫层析法。结果本方法对烟草中吡虫啉的检测限为5μg/mL,重复性较高,有假阳性情况出现,但假阳性率较低,与烟草中其他常用药物没有交叉反应,特异性良好,且与气相色谱检测法所得的结果差异较小。结论该方法快速、高效、可靠,可满足现场快速检测烟草中吡虫啉残留的需要,实现生物技术在烟草流通、消费领域的方便、快速检测。     

Modeling and optimizing of steel and mushy Al-28Pb alloy bonding

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基于TINI平台的嵌入式互联网接入技术研究

随着网络技术的发展,将各种设备接人互联网,利用互联网实现数据传输与远程监控成为当今电子设备发展的必然趋势.文中介绍了DS80OC400芯片以及基于此芯片的TINI系统.提出了采用TINI系统来实现非网络设备接入互联网的方法,包括硬件结构、软件设计以及开发流程等,并以RS-232接口为例,给出了此方法的具体实现.与传统的通过PC机转接的方法相比,此方法具有开发成本低、效率高、运行稳定、低功耗、体积小等特点.     

丹江口水库汛期水位动态控制方案研究

丹江口水库加高完成后,为保障汉江中下游防洪安全和南水北调供水的顺利进行,防洪和蓄水的矛盾更加突出,根据目前的蓄水方案,蓄满率可能进一步降低。以62 a实测洪水资料为输入,对丹江口水库的运行方式进行了模拟调度和预泄能力分析,并根据汉江流域洪水特性,提出了不同时期丹江口水库的运行水位动态控制方案。根据提出的运行方案,丹江口水库在保证各项设计功能正常发挥的前提下,可进一步挖掘水库的防洪效益,并做到风险可控,供水保证率可提高10%左右,发电效益可增加5%左右。