Animal behaviour: coalition among male fiddler crabs

Until now, no compelling evidence has emerged from studies of animal territoriality to indicate that a resident will strategically help a neighbour to defend its territory against an intruder. We show here that territory-owning Australian fiddler crabs will judiciously assist other crabs in defending their neighbouring territories. This cooperation supports the prediction that it is sometimes less costly to assist a familiar neighbour than to renegotiate boundaries with a new, and possibly stronger, neighbour.     

Biomechanics: a pneumo-hydrostatic skeleton in land crabs

Like their aquatic counterparts, terrestrial crabs repeatedly shed their rigid exoskeleton during moulting. But in the case of land crabs, little water is available to provide a temporary hydrostatic skeleton before the new skeleton hardens, and air does not provide the buoyancy necessary to support the animal. Here we show that whenever its exoskeleton is shed, the blackback land crab Gecarcinus lateralis relies on an unconventional type of hydrostatic skeleton that uses both gas and liquid (a 'pneumo-hydrostat'). To our knowledge, this is the first experimental evidence for a locomotor skeleton that depends on a gas. It establishes a new category of hydrostatic skeletal support and possibly a critical adaptation to life on land for the Crustacea.     

大通湖水域河蟹体长、体重及头胸甲关系研究

为了了解养殖环境对河蟹生长特性的影响,对大通湖水域中湖泊和池塘养殖的河蟹体长、体重及头胸甲关系进行了研究。结果表明:2种环境下雌雄河蟹头胸甲长、宽、厚与体重均存在密切的线性相关性,且湖泊河蟹其相关性(0.821 4~0.903 3)比池塘河蟹(0.898 8~0.945 7)要稍高;同环境下,母蟹头胸甲宽、厚与体重相关性均比公蟹高,公蟹头胸甲长与体重相关性比同环境下母蟹高。因此,河蟹部分生长特性与养殖环境、性别与其环境相互作用明显。     

汽车空调变排量压缩机排量调节技术进展

在对国内外大量技术文献调研的基础上,以GM公司V5与日本电装公司7SB16两种类型变排量压缩机为例,对摇板式和斜板式变排量压缩机的结构组成及其排量调节原理进行了分析.针对斜盘式变排量压缩机控制阀电子控制技术研究现状,讨论了变排量压缩机控制阀直动电磁式与步进数字式控制技术原理及其特点,指出步进数字式控制技术在变排量压缩机中的应用更具有技术潜力.     

复合置换通风的非稳态流动

以两开口单区建筑为研究对象,采用理论分析方法,推导出风机与热压共同驱动的复合置换通风的非稳态数学模型。研究了机械风量、两开口面积比和无量纲特征时间对室内热分层高度和自然通风量的影响。研究结果表明:在复合置换通风中,增大机械风量使热分层高度增大而自然通风量减小。无量纲特征时间增大,使热压主导通风模式存在所对应的机械风量的上限值减小。对于机械送风,开口面积比增大引起热分层高度和自然通风量随机械风量的变化率增加,热压主导模式存在所对应的机械风量的上限值增大,而对于机械排风,情况相反。当两开口面积相等时,采用机械送风和机械排风的效果是一样的。     

介质阻挡放电中的位移电流

在低频介质阻挡放电系统中，引入位移电流的概念，解决了将安培环路定理应用于含有电容的交变电路中出现的矛盾．运用麦克斯韦电磁场理论讨论了介质阻挡放电中的微放电和位移电流，并指出介质阻挡放电中放电通道内fd和fc在时间上是有规律交替出现的，各个放电通道之间各自jd与jc的转换不一定在同时刻进行.     

位移法在静定结构的应用

通过算例说明,当熟悉了单跨超静定梁的形常数和载常数之后,通过对静定结构的适当改造,可以采用位移法很方便地进行静定结构的位移计算;同时,对于某些特定的结构可以不必求解支座反力,即能做出弯矩图。     

Evolution of king crabs from hermit crab ancestors.

King crabs (Family Lithodidae) are among the world's largest arthropods, having a crab-like morphology and a strongly calcified exoskeleton. The hermit crabs, by contrast, have depended on gastropod shells for protection for over 150 million years. Shell-living has constrained the morphological evolution of hermit crabs by requiring a decalcified asymmetrical abdomen capable of coiling into gastropod shells and by preventing crabs from growing past the size of the largest available shells. Whereas reduction in shell-living and acquisition of a crab-like morphology (carcinization) has taken place independently in several hermit crab lineages, and most dramatically in king crabs, the rate at which this process has occurred was entirely unknown. We present molecular evidence that king crabs are not only descended from hermit crabs, but are nested within the hermit crab genus Pagurus. We estimate that loss of the shell-living habit and the complete carcinization of king crabs has taken between 13 and 25 million years.     

Resource availability: Ancient homes for hard-up hermit crabs

Mollusc shells are a vital but sometimes scarce resource for hermit crabs, protecting them from mechanical damage and desiccation, but they require continual replacement as the crab grows. I have discovered that Coenobita rugosus, a large, tropical, semi-terrestrial hermit crab, will resort to using fossil shells when no other suitable casing is available. These unlikely mobile homes fall out of coastal limestone as it is eroded by the sea in southwestern Madagascar, placing the occupants alongside Homo sapiens as resourceful exploiters of prehistoric animal remains.     

微位移测量技术的分析

针对通常微位移测量方法的昂贵、不能连续自动观测的缺点,提出了一种基于角反射器和微波相干比相的微位移测量系统;当微位移方向与电波传播方向平行时,采用基本测量系统.当微位移方向与电波传播方向不平行时,采用弯管测量系统.详细介绍了微位移测量系统的工作过程,还给出了信道计算方法和传输测量结果的通信电路.该通信电路可通过移动电话把测量结果传到指定电话号码的终端,并给出了实测结果.     

化学置换镀铜

本文介绍了置换镀铜的原理和方法,并探讨了除锈工艺、镀液浓度、温度、添加剂等诸多因素对镀层质量的影响。     

也论电位移矢量''''非汉字符号''''

本文阐明电位移矢量D与哪些物理量有关,并指出极化电荷分布与介质分布两个物理概念的区别和联系,其次论证了。与极化电荷分布无关和D只与自由电荷分布有关的条件以及两者的区别与联系。     

Feeding behaviour: hydrothermal vent crabs feast on sea 'snow'

The crab Xenograpsus testudinatus lives at enormously high densities around the sulphur-rich hydrothermal vents found in shallow waters off Taiwan, even though this acidic environment is low in nutrients. Here we show that these crabs swarm out of their crevices at slack water and feed on the vast numbers of zooplankton that are killed by the vents' sulphurous plumes, and that rain down like marine 'snow'. This opportunistic feeding behaviour explains how the crabs are able to survive in the adverse toxic environment of these shallow hydrothermal vents.     

结构拟动力试验的位移控制

拟动力结构试验的过程,是试验加载与时程反应分析逐步交替进行的过程,计算机时程分析的位移反应,作为下一步试验加载量的控制指令,而相应于此位移加载量的试验恢复力,又是时程分析的参数。文章对采用中央差分法进行的拟动力试验过程控制,分析了x-1、x1等几种起步试验位移控制方法。     

影剧院建筑内置换通风方式的优化设计

为了更好地研究置换通风方式在影剧院建筑内的应用,采用CFD方法,对影剧院内采用地面附近侧送风形式的置换通风进行了数值模拟．计算结果显示,CFD技术能够较好地应用在影剧院建筑内置换通风方式的优化设计方面,并能够得出比较合理的设计参数．在原有设计的基础上,通过合理地调整风口位置及送风参数获得了较好的通风效果．把CFD技术引入到对影剧院建筑内空调系统气流组织方案的设计中,有利于地面附近侧送风方式的应用,也有助于节能措施的推广与实施．     

随机多孔介质中的不混溶驱替

对随机多孔介质中粘滞指进的分形性质进行研究,建立正方网格来模拟多孔介质中润湿流体的侵入和流动,运用决定论模型进行研究。结果表明,多孔介质的几何拓扑强烈地影响了粘滞指进的结构和驱替过程。粘滞指进图像扫及面积随着迭代次数n的增加而增大。增加迭代次数n和网格尺寸,会导致驱扫效率E的增大。     

高等级公路路面沥青层剪应力分布研究

采用实测轮胎接地有效面积和接地压力,通过编写Fortran程序将交通荷载转化为移动均布荷载,对三维多层的沥青路面进行有限元动态分析,得到路面沥青结构层剪应力沿深度方向的分布规律.结果表明,不同荷载条件下路面沥青层剪应力的差异明显,水平力对剪应力亦有较大影响;路面面层回弹模量、泊松比及基层回弹模量对剪应力的影响均比较显著.