PMA件的过去、现在与未来

<正>通过对PMA件市场的起步、发展和现状的简述,以及对市场背后本质因素的分析,预测了PMA件市场的未来发展趋势。在竞争激烈的飞机部件制造市场中,PMA件正在逐渐打破以往由OEM件垄断的局面,并占有一定的市场份额。在欧洲、亚洲、拉丁美洲和中东地区,PMA     

关于复合材料修理标准化

随着波音787飞机和空客A350XWB等复合材料飞机的投入运营,许多运营商呼吁要实现复合材料培训认证的标准化。由OEM、运营商和管理当局组成的美国汽车工程师学会(SAE)民用飞机复合材料修理委员会(CACRC)自1991年以来     

三维技术在维修领域的应用

航空维修业很早以前就了解三维技术,如用于计算机辅助设计与制造（CAD／CAM）的CATIA等软件创造了很多的奇迹。这些可视化软件过去多为设计师或工程师所使用,但近期将在维修工程的日常工作中得以应用。     

支线飞机的维修策略转变

支线飞机的维修模式正在发生改变,OEM的全面维修协议广受运营商青睐。     

Life at the wedge: the activity and diversity of arctic ice wedge microbial communities

The discovery of polygonal terrain on Mars underlain by ice heightens interest in the possibility that this water-bearing habitat may be, or may have been, a suitable habitat for extant life. The possibility is supported by the recurring detection of terrestrial microorganisms in subsurface ice environments, such as ice wedges found beneath tundra polygon features. A characterization of the microbial community of ice wedges from the high Arctic was performed to determine whether this ice environment can sustain actively respiring microorganisms and to assess the ecology of this extreme niche. We found that ice wedge samples contained a relatively abundant number of culturable cells compared to other ice habitats (～10(5) CFU·mL(-1)). Respiration assays in which radio-labeled acetate and in situ measurement of CO(2) flux were used suggested low levels of microbial activity, though more sensitive techniques are required to confirm these findings. Based on 16S rRNA gene pyrosequencing, bacterial and archaeal ice wedge communities appeared to reflect surrounding soil communities. Two Pseudomonas sp. were the most abundant taxa in the ice wedge bacterial library (～50%), while taxa related to ammonia-oxidizing Thaumarchaeota occupied 90% of the archaeal library. The tolerance of a variety of isolates to salinity and temperature revealed characteristics of a psychrotolerant, halotolerant community. Our findings support the hypothesis that ice wedges are capable of sustaining a diverse, plausibly active microbial community. As such, ice wedges, compared to other forms of less habitable ground ice, could serve as a reservoir for life on permanently cold, water-scarce, ice-rich extraterrestrial bodies and are therefore of interest to astrobiologists and ecologists alike. .     

Fe XVII X-ray lines in solar coronal plasmas

Calculated intensities of the Fe X-ray lines due to transitions 2p⁶ − 2p⁵3d lines (near 15 Å) and 2p⁶ − 2p⁵3s lines (near 17 Å) are compared with measured line intensities in solar and tokamak spectra. For the solar spectra, temperature T_e is obtained from the ratio of the Fe 16.776 Å line to a nearby Fe line. We find excellent agreement for all the major Fe line features in the 15–17 Å region except the Fe 15.015 Å line, the observed flux of which is less than the theoretical by a factor f. We find that f strongly depends on the heliocentric angle θ of the emitting region, being smallest (0.2) when the region is nearest Sun centre, but nearly 1 near the limb. Attributing this to resonance scattering, we are able to deduce the path length and electron density from the observations. Possible application to stellar active regions is given.