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Mark Nelson William F. Dempster John P. Allen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Closed ecological systems are desirable for a number of purposes. In space life support systems, material closure allows precious life-supporting resources to be kept inside and recycled. Closure in small biospheric systems facilitates detailed measurement of global ecological processes and biogeochemical cycles. Closed testbeds facilitate research topics which require isolation from the outside (e.g. genetically modified organisms; radioisotopes) so their ecological interactions and fluxes can be studied separate from interactions with the outside environment. But to achieve and maintain closure entails solving complex ecological challenges. These challenges include being able to handle faster cycling rates and accentuated daily and seasonal fluxes of critical life elements such as carbon dioxide, oxygen, water, macro- and mico-nutrients. The problems of achieving sustainability in closed systems for life support include how to handle atmospheric dynamics including trace gases, producing a complete human diet, recycling nutrients and maintaining soil fertility, the maintenance of healthy air and water and preventing the loss of critical elements from active circulation. In biospheric facilities, the challenge is also to produce analogues to natural biomes and ecosystems, studying processes of self-organization and adaptation in systems that allow specification or determination of state variables and cycles which may be followed through all interactions from atmosphere to soils. Other challenges include the dynamics and genetics of small populations, the psychological challenges for small isolated human groups and backup technologies and strategic options which may be necessary to ensure long-term operation of closed ecological systems. 相似文献
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企业应用的各种信息技术通过信息集成组成企业的信息技术组合系统,各子系统相互配合而产生协同效应,使得系统总体功能可以大于各子系统功能之和,本文提出一种方法,首先根据企业的竞争重点确定待实施的各项信息技术,然后根据数据流表通过对协同效应的估计确定各项信息技术的实施顺序,最后对决策支持系统的实现进行了讨论。 相似文献
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R.M. Wheeler C.L. Mackowiak G.W. Stutte N.C. Yorio L.M. Ruffe J.C. Sager R.P. Prince W.M. Knott 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(5):706-713
NASA’s Biomass Production Chamber (BPC) at Kennedy Space Center was decommissioned in 1998, but several crop tests were conducted that have not been reported in the open literature. These include several monoculture studies with wheat, soybean, potato, lettuce, and tomato. For all of these studies, either 10 or 20 m2 of plants were grown in an atmospherically closed chamber (113 m3 vol.) using a hydroponic nutrient film technique along with elevated CO2 (1000 or 1200 μmol mol−1). Canopy light (PAR) levels ranged from 17 to 85 mol m−2 d−1 depending on the species and photoperiod. Total biomass (DM) productivities reached 39.6 g m−2 d−1 for wheat, 27.2 g m−2 d−1 for potato, 19.6 g m−2 d−1 for tomato, 15.7 g m−2 d−1 for soybean, and 7.7 g m−2 d−1 for lettuce. Edible biomass (DM) productivities reached 18.4 g m−2 d−1 for potato, 11.3 g m−2 d−1 for wheat, 9.8 g m−2 d−1 for tomato, 7.1 g m−2 d−1 for lettuce, and 6.0 g m−2 d−1 for soybean. The corresponding radiation (light) use efficiencies for total biomass were 0.64 g mol−1 PAR for potato, 0.59 g DM mol−1 for wheat, 0.51 g mol−1 for tomato, 0.46 g mol−1 for lettuce, and 0.43 g mol−1 for soybean. Radiation use efficiencies for edible biomass were 0.44 g mol−1 for potato, 0.42 g mol−1 for lettuce, 0.25 g mol−1 for tomato, 0.17 g DM mol−1 for wheat, and 0.16 g mol−1 for soybean. By initially growing seedlings at a dense spacing and then transplanting them to the final production area could have saved about 12 d in each production cycle, and hence improved edible biomass productivities and radiation use efficiencies by 66% for lettuce (to 11.8 g m−2 d−1 and 0.70 g mol−1), 16% for tomato (to 11.4 g m−2 d−1and 0.29 g mol−1), 13% for soybean (to 6.9 g m−2 d−1 and 0.19 g mol−1), and 13% for potato (to 20.8 g m−2 d−1 and 0.50 g mol−1). Since wheat was grown at higher densities, transplanting seedlings would not have improved yields. Tests with wheat resulted in a relatively low harvest index of 29%, which may have been caused by ethylene or other organic volatile compounds (VOCs) accumulating in the chamber. Assuming a higher harvest index of 40% could be achieved by scrubbing VOCs, productivity of wheat seed could have been improved nearly 40% to 15.8 g m−2 d−1 and edible biomass radiation use efficiency to 0.30 g mol−1. 相似文献