汽车动力总成液压悬置建模与仿真研究

介绍功率键合图在动态系统特性分析中的特点和优势,以此为理论基础建立汽车动力总成液压悬置的数学模型,并结合MATLAB进行仿真,为液压悬置的研究提供了一种高效的建模仿真方法。应用这种方法,可以在液阻悬置的设计开发阶段较精确地预测产品的性能和进行优化设计,有利于提高产品设计质量、缩短开发周期。     

Milk let-down in goats can be influenced by the type of stimuli applied or to which goats are exposed during suckling and hand milking

The present experiments on goats were conducted with the aim of verifying (a) whether the identity of the goat kids can affect the characteristics of milk let-down during suckling (Study 1) and (b) whether the presence of the goat kids may improve the milk let-down during hand milking (Study 2). In Study 1, 16 lactating goats with twins and 12 with single kids were used. Dams with single goat kids ejected more milk when suckling their kids at Days 5 and 20 of lactation, than when suckling aliens. Dams with twins ejected more milk when suckling their own kids than aliens only at Day 5 of lactation. Taking into account all the dams, they ejected more milk with more fat, protein, and lactose during suckling their own litter than when suckling aliens. In Study 2, when dams (n = 13) were hand milked in the presence of their own litter or in its absence, they ejected more milk with more fat, protein, and lactose than when milked in the presence of alien kids. We conclude that milk let-down in goats can be influenced by the type of stimuli applied or to which they are exposed to during suckling and milking.     

流动复合树脂封闭法预防正畸治疗中牙釉质脱矿的疗效观察

目的观察光固化流动复合树脂封闭法预防正畸托槽周边牙釉质脱矿的疗效.方法实验组前牙托槽周边的牙釉质用光固化流动复合树脂封闭,而对照组不作封闭.治疗结束后比较两组牙釉质脱矿的差异.将26颗离体前磨牙随机均分为2组,即(1)single bond流动复合树脂组;(2)京津釉质粘接剂组,从每组中随机抽取10颗样本,检测各组材料的粘接抗剪强度;剩余6颗样本用以在扫描电镜下观察不同材料与牙釉质形成的粘接面.结果实验组牙釉质脱矿减少,有显著性差异.2组粘接抗剪强度为(1)组(13.64±11.06)MPa,(2)组(20.30±1.83)MPa[(1)vs(2)组P＜0.01].single bond流动复合树脂在牙釉质表面能形成树脂突.结论光固化流动复合树脂封闭正畸托槽周边的牙釉质,能有效预防在正畸治疗过程中牙釉质脱矿.     

高温脱脂处理对马尾松材质的影响

脱脂处理后的木材弦向干缩系数为0.244,比素材的0.301减少19.1%,径向和体积干缩系数也具有相同性。脱脂处理材弦向湿胀性为7.3,比素材的8.4减少13.1%。因此,脱脂处理能明显改善木材尺寸稳定性。实验结果还证实了脱脂处理能够提高木材胶合强度和油漆效果。但是脱脂处理后木材顺纹静曲强度为58.21 MPa、顺纹抗压强度为35.38 MPa,比马尾松木材的减少10%-11%。所以在选择脱脂处理工艺时要充分考虑到脱脂对木材力学强度的影响,让固态的树脂酸尽量地保留在木材内,这样做既可缩短处理时间,又可降低生产成本,同时也确保了木材力学性能不受大的影响。     

微纳纤丝改性豆胶制造染色杨木胶合板

将不同微纳纤丝添加量的三聚氰胺树脂涂饰在杨木单板表面,并以添加微纳纤丝的豆胶作为胶黏剂,制造杨木胶合板,检测微纳纤丝添加量对染色杨木单板表面色牢度、胶合板表面耐磨性能、胶合强度的影响。结果表明:微纳纤丝可明显改善单板表面色牢度及表面耐磨性能;在豆胶中加入微纳纤丝,可提高胶合板的胶合强度。     

基于键合图的电动汽车驱动系统建模与仿真

该文阐述了键合图理论的基本原理,并根据电动汽车纵向运动时传动系统各单元的动态特性及其相互作用的工作原理和结构特点,运用键合图理论构建出电动汽车电机驱动系统的键合图模型,并推导出该系统的状态方程,应用Matlab仿真软件对建立的数学模型进行仿真分析.仿真结果表明:键合图法是一种对系统进行动态数字仿真时有效的建模工具,应用该理论对系统进行仿真能较好地反映系统的动态特性和整车性能,并可以利用仿真结果来检验动力系统的参数选择是否合理,以此作为对参数进行修改的依据.     

基于键合图的全液压转向器鲁棒优化设计

为了实现全液压转向器的稳健设计,该文基于键合图方法建立了全液压转向器的动力学模型,并推导得出了转向器的状态方程,以转向器阀芯直径、等效转动惯量及转向器内部总压缩容积作为设计变量,以转向器流量动态响应超调量最小为设计目标,首先对转向器进行了传统优化设计,然后以传统优化设计结果作为设计初值,对全液压转向器进行了稳健优化设计。通过分别基于传统优化设计和稳健优化设计所得动态响应结果比较、分析得知,稳健优化后的转向器结构参数更加合理,动态响应峰值超调量降低了12.5%,稳健性有所提高。以传统优化设计结果为初值对转向器进行稳健设计是切实有效的。     

施硫对小麦籽粒形成过程中蛋白质与巯基、二硫键的含量及加工品质的影响

在土壤耕层有效硫含量为728 mg/kg的条件下,选用不同冬小麦品种济麦20、淄麦12、鲁麦21和山农1391为试验材料,研究了施用硫肥对小麦不同穗位和不同粒位子粒蛋白质与巯基、二硫键含量及加工品质的影响。结果表明,施用硫肥对上部穗位粒的蛋白质含量的提高作用大于其他穗位粒; 增加了高蛋白含量品种济麦20和淄麦12 的弱势粒子粒蛋白质含量,增加了上部小穗位子粒和中部穗位强势粒的巯基含量,提高了不同穗位子粒二硫键含量; 而对不同粒位子粒二硫键含量的影响则因品种而异。施用硫肥使小麦面粉湿面筋含量、面团形成时间、稳定时间和粉质评价值均有一定提高,但不同品质指标对施用硫肥的反应存在差异。与子粒形成过程中蛋白质含量的变化相反,巯基的含量变化呈先升后降的规律; 二硫键的含量变化趋势与蛋白质含量的变化相似,但最小值出现时间略有延迟。     

发达国家巨灾保险研究——基于英、美、日三国的经验

通过对英国、美国和日本三个国家的巨灾保险研究,并结合中国当前的具体国情,对中国巨灾保险模式提出了一些具体的建议。     

Determining the effect of tree size,bark-wood bond strength and tree form on the productivity of an excavator-based harvester in Acacia mearnsii in the KwaZulu-Natal forestry region of South Africa

The aim of this study was to determine the effect of tree size, bark-wood bond strength and tree form on the productivity of cut-to-length harvesting of Acacia mearnsii, using an excavator-based harvester with a SP Maskiner harvester head in the KwaZulu-Natal forestry region of South Africa. Tree diameter and height measurements were used to determine individual tree volumes, after which the trees were classified into different bark-wood bond strength and tree-form classes. Time studies were carried out to determine harvester productivity. The results showed that tree size plays a crucial role in the productivity of the harvester, but bark-wood bond strength and tree form also influence productivity. The harvester productivity varied from 5.5 m³ per productive machine hour (PMH) in 0.05 m³ trees to 16.9 m³ PMH^?1 in 0.25 m³ trees The bark-wood bond strength did not influence harvester productivity when handling small trees of less than 0.1 m³. In small trees, the productivity of the harvester was also not affected by different form classes, but as tree size increased, there was greater productivity variation between the different form classes.