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21.
阐述了用分形耦合贴体网格坐标和流体有限控制容积法,求解具有多分支、变曲率和变截面的复杂几何形状和边界条件的柴油机模件式脉冲转换系统中的非定常粘性可压三维流动计算问题,编制了计算程序进行计算.计算结果表明,这种计算方法对柴油机模件式脉冲转换系统的流动计算是相当有效的.其计算程序不仅可用于柴油机模件式脉冲转换系统,亦可用于脉冲系统和定压系统的流动计算,具有一定的通用性.  相似文献   
22.
Recent studies suggest that thermogenesis in brown adipose tissue has an important role in the regulation of energy balance. Thermogenesis is effected by noradrenaline released from sympathetic nerve endings; the noradrenaline stimulates beta-adrenoceptors, causing lipolysis, and the released fatty acids then promote the uncoupling of oxidative phosphorylation from electron transport. It has been widely accepted that mammalian beta-adrenoceptors exist as two subtypes, beta 1 and beta 2, and rat brown adipocyte beta-adrenoceptors have been classed as beta 1 or as a mixed beta 1/beta 2 population. The beta 1 subtype predominates in atria, whereas the beta 2 subtype predominates in trachea. However, we have now found a novel group of beta-adrenoceptor agonists that selectively stimulate lipolysis in brown adipocytes. In contrast, isoprenaline, fenoterol and salbutamol are less potent as stimulants of lipolysis than as stimulants of atrial rate or tracheal relaxation. Therefore, beta-adrenoceptors in rat brown adipocytes are of neither the beta 1 nor beta 2 subtypes. Compounds that selectively stimulate brown adipocyte beta-adrenoceptors should have potential as thermogenic anti-obesity agents and this has been demonstrated with BRL 26830A , BRL 33725A and BRL 35135A .  相似文献   
23.
分析了变通道涡流室式燃烧室和涡流室式燃烧室气体流动的差异,以及变通道涡流室式燃烧室通道结构参数对流动损失的影响;根据计算与试验结果,提出了变通道涡流室式燃烧室通道结构参数的最佳取值范围,研究表明,变通道涡流室式燃烧室的气体流动特性有利于加快油气混合与燃烧的进程,减少流动损失,从而获得比常规涡流室式燃烧室更高的热效率。  相似文献   
24.
针对赛艇运动图像序列的特点,提出了跟踪匹配的自动解析方法,即在模板匹配法中加入跟踪的概念,使得样本模板的中心随特征点的移动而变化,这种算法与一般的模板匹配法比较,可以进一步缩小搜索区域,减少计算量,降低失跟率。  相似文献   
25.
剖析了传统的船舶坐墩墩反力计算方法,并用有限元法进行了对比分析计算,指出了前者存在着适应范围的局限性和计算结果不完整及不直观等问题。认为采用有限元法进行船舶坐墩墩反力分析计算较适宜。最后讨论了墩木刚性对船体结构安全性的影响,提出了墩木设置的一般原则。  相似文献   
26.
Shen JX  Feng AS  Xu ZM  Yu ZL  Arch VS  Yu XJ  Narins PM 《Nature》2008,453(7197):914-916
Sound communication plays a vital role in frog reproduction, in which vocal advertisement is generally the domain of males. Females are typically silent, but in a few anuran species they can produce a feeble reciprocal call or rapping sounds during courtship. Males of concave-eared torrent frogs (Odorrana tormota) have demonstrated ultrasonic communication capacity. Although females of O. tormota have an unusually well-developed vocal production system, it is unclear whether or not they produce calls or are only passive partners in a communication system dominated by males. Here we show that before ovulation, gravid females of O. tormota emit calls that are distinct from males' advertisement calls, having higher fundamental frequencies and harmonics and shorter call duration. In the field and in a quiet, darkened indoor arena, these female calls evoke vocalizations and extraordinarily precise positive phonotaxis (a localization error of <1 degrees ), rivalling that of vertebrates with the highest localization acuity (barn owls, dolphins, elephants and humans). The localization accuracy of O. tormota is remarkable in light of their small head size (interaural distance of <1 cm), and suggests an additional selective advantage of high-frequency hearing beyond the ability to avoid masking by low-frequency background noise.  相似文献   
27.
土拨鼠肝炎病毒(WHV)是一种哺乳类动物的肝炎病毒.这种病毒在结构和抗原怕与人类乙型肝炎病毒(HBV)非常相似.以往的研究报告指出,在一种称为鸭乙型肝炎病毒(DHBV)的Pre-S包膜蛋白中,含有一个特定区域.这一区域由天冬氨酸-天冬氨酸-脯氨酸-亮氨酸-亮氨酸(DDPLL)5个氨基酸残基所组成.已发现,这一区域在像DHBV这一类禽类乙肝病毒的病毒装配和分泌时所必需的(LenhoffR,SummersJ.JVirol,1994,68:4565~4571).在WHV的Pre-S包胰蛋白中第201个氨基酸到第205个氨基酸所包含的顺序,甘氨酸-天冬氨酸-脯氨…  相似文献   
28.
考虑铺层的耦合效应和筋条的扭转效应,推导了复合材料加筋层合柱壳的稳定性计算公式,研究了加筋柱壳各项设计参数对屈曲性能的影响.由计算结果总结的规律可以指导复合材料铺层设计和选择结构形式,并为定量计算提供理论依据  相似文献   
29.
论述了程控机房远端集中监控系统的工作原理,给出了系统的硬件结构、外部I/O接口电路、V/F变换与隔离电路,分析了程序设计的任务及系统的特点.  相似文献   
30.
对于两端简支短圆柱壳在余弦脉冲载荷作用下的初始动力响应,着重考虑膜力对其影响.推导了关于周向应力及轴向应力的动力方程,采用双Fourier级数求解动力方程.计算结果表明,圆柱壳长度对膜力响应有着十分显著的影响,通常情况下,膜力随壳长的增加而增加  相似文献   
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