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排序方式: 共有126条查询结果,搜索用时 15 毫秒
121.
122.
Microbial populations in Antarctic permafrost: biodiversity, state, age, and implication for astrobiology 总被引:1,自引:0,他引:1
Gilichinsky DA Wilson GS Friedmann EI McKay CP Sletten RS Rivkina EM Vishnivetskaya TA Erokhina LG Ivanushkina NE Kochkina GA Shcherbakova VA Soina VS Spirina EV Vorobyova EA Fyodorov-Davydov DG Hallet B Ozerskaya SM Sorokovikov VA Laurinavichyus KS Shatilovich AV Chanton JP Ostroumov VE Tiedje JM 《Astrobiology》2007,7(2):275-311
Antarctic permafrost soils have not received as much geocryological and biological study as has been devoted to the ice sheet, though the permafrost is more stable and older and inhabited by more microbes. This makes these soils potentially more informative and a more significant microbial repository than ice sheets. Due to the stability of the subsurface physicochemical regime, Antarctic permafrost is not an extreme environment but a balanced natural one. Up to 10(4) viable cells/g, whose age presumably corresponds to the longevity of the permanently frozen state of the sediments, have been isolated from Antarctic permafrost. Along with the microbes, metabolic by-products are preserved. This presumed natural cryopreservation makes it possible to observe what may be the oldest microbial communities on Earth. Here, we describe the Antarctic permafrost habitat and biodiversity and provide a model for martian ecosystems. 相似文献
123.
Wilson JR 《Aerospace America》2003,41(2):34-38
The application of microelectromechanical systems (MEMS) to space flight is reviewed. The applications include use as microthrusters on mini-size and smaller satellites, in missile defense systems, and as propulsion systems for miniature unmanned aerial vehicles. 相似文献
124.
An analysis technique is presented which permits the designer to explore the start-up transient of a dc-to-dc converter when it is powered by a current-limited source. The current versus voltage characteristics of the source are superimposed upon those of the dc-to-dc converter. By noting the nature of the intersection of these curves in the voltage-current plane, we are able to predict whether or not the converter is able to start up while powering a specified load. 相似文献
125.
Wilson T.G. Lee F.C.Y. Burns W.W. Owen H.A. 《IEEE transactions on aerospace and electronic systems》1975,(2):238-244
It recently has been shown in the literature that many dc-to-squarewave parallel inverters which are widely used in power-conditioning applications can be grouped into one of two families. Each family is characterized by an equivalent RLC network. Based on this approach, a classification procedure is presented for self-oscillating parallel inverters which makes evident natural relationships which exist between various inverter configurations. By utilizing concepts from the basic theory of negative resistance oscillators and the principle of duality as applied to nonlinear networks, a chain of relationships is established which enables a methodical transfer of knowledge gained about one family of inverters to any of the other families in the classification array. 相似文献
126.
Wilson T.G. Whelan E.W. Rodriguez R. Dishman J.M. 《IEEE transactions on aerospace and electronic systems》1983,(3):413-427
A new way is given to describe the independent and dependent design variables of the power train of a dc-to-dc converter in terms of a multidimensional design-parameter space. These concepts provide a framework for examining the problem of design optimization of the power train, with particular emphasis on the maximization of converter efficiency. Numerous examples of important parameterspace surfaces illustrate some of the major relationships between core volume, switching frequency, and output power and between efficiency, ripple, and temperature rise of the energy-storage reactor. Also, the difference in performance between the continuous and discontinuous magnetomotive (MMF) force modes of operation is explored. 相似文献