Animal communication: ground squirrel uses ultrasonic alarms

Apart from echolocation and the pursuit of prey by bats, the function of ultrasound in animal communication is poorly understood. This is mainly because of the broad range of responses that it can evoke and the widely varied contexts in which it is used (for example, in rodents of the Muridae family it may indicate distress in infants or a sexual or predatory encounter in adults). Here we find that a purely ultrasonic signal is produced in the wild by a rodent of the Sciuridae family, Richardson's ground squirrel, and show that its function is to warn conspecifics of impending danger. To our knowledge, ultrasonic alarm calls have not previously been detected in any animal group, despite their twin advantages of being highly directional and inaudible to key predators.     

调制式旋转导向系统导向力"等力合成模型"的建立与分析

导向力的形成机理是研制旋转导向工具的核心。在深入研究国外旋转导向工具的基础上,参考导弹制导原理,提出了调制式旋转导向工具新的导向方式,建立了导向力"等力合成模型",并对其影响规律进行了分析。结果表明,这种导向方式与PowerDriveSRD导向系统相比,有其独特的优点。控制面不稳定程度对合导向力的影响并不很大,在控制面摆动度达14°时,合导向力仅下降1%。这为调制式旋转导向工具稳定平台的研制提供了宽松的约束条件。     

Rocket UV flash spectra from the solar eclipse of March 7, 1970

Flash spectra of the total solar eclipse throughout all its phases have been obtained in the extreme ultraviolet for the first time.     

略论把流通业提升为先导产业(一)

流通业的兴起具有深刻的经济渊源。把流通业提升为先导产业是社会主义市场经济体制初步确立、“生产相对过剩”和加入WTO新形势的必然要求。将这一要求转化成政策并付诸实践,需要我们大胆创新,确立相应的软环境和硬环境。     

Endogenous cannabinoids mediate retrograde signalling at hippocampal synapses

Marijuana affects brain function primarily by activating the G-protein-coupled cannabinoid receptor-1 (CB1), which is expressed throughout the brain at high levels. Two endogenous lipids, anandamide and 2-arachidonylglycerol (2-AG), have been identified as CB1 ligands. Depolarized hippocampal neurons rapidly release both anandamide and 2-AG in a Ca2+-dependent manner. In the hippocampus, CB1 is expressed mainly by GABA (gamma-aminobutyric acid)-mediated inhibitory interneurons, where CB1 clusters on the axon terminal. A synthetic CB1 agonist depresses GABA release from hippocampal slices. These findings indicate that the function of endogenous cannabinoids released by depolarized hippocampal neurons might be to downregulate GABA release. Here we show that the transient suppression of GABA-mediated transmission that follows depolarization of hippocampal pyramidal neurons is mediated by retrograde signalling through release of endogenous cannabinoids. Signalling by the endocannabinoid system thus represents a mechanism by which neurons can communicate backwards across synapses to modulate their inputs.