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31.
Diamond-like carbon (DLC) films are deposited by the Hall ion source assisted by the mid-frequency unbalanced magnetron sput-tering technique. The effects of the substrate voltage bias, the substrate temperature, the Hall discharging current and the argon/nitrogen ratio on the DLC film’s performance were studied. The experimental results show that the film’s surface roughness, the hardness and the Young’s modulus increase firstly and then decrease with the bias voltage incrementally increases. Also when the substrate temperature rises, the surface roughness of the film varies slightly, but its hardness and Young’s modulus firstly increase followed by a sharp decrease when the temperature surpassing 120 ℃. With the Hall discharging current incrementally rising, the hardness and Young’s modulus of the film decrease and the surface roughness of the film on 316L stainless steel firstly decreased and then remains constant. 相似文献
32.
C. M. S. Cohen R. A. Mewaldt R. A. Leske A. C. Cummings E. C. Stone M. E. Wiedenbeck T. T. von Rosenvinge G. M. Mason 《Space Science Reviews》2007,130(1-4):183-194
Solar abundances can be derived from the composition of the solar wind and solar energetic particles (SEPs) as well as obtained
through spectroscopic means. Past comparisons have suggested that all three samples agree well, when rigidity-related fractionation
effects on the SEPs were accounted for. It has been known that such effects vary from one event to the next and should be
addressed on an event-by-event basis. This paper examines event variability more closely, particularly in terms of energy-dependent
SEP abundances. This is now possible using detailed SEP measurements spanning several decades in energy from the Ultra Low
Energy Isotope Spectrometer (ULEIS) and the Solar Isotope Spectrometer (SIS) on the ACE spacecraft. We present examples of
the variability of the elemental composition with energy and suggest they can be understood in terms of diffusion from the
acceleration region near the interplanetary shock. By means of a spectral scaling procedure, we obtain energy-independent
abundance ratios for 14 large SEP events and compare them to reported solar wind and coronal abundances as well as to previous
surveys of SEP events. 相似文献
33.
Segura A Kasting JF Meadows V Cohen M Scalo J Crisp D Butler RA Tinetti G 《Astrobiology》2005,5(6):706-725
Coupled one-dimensional photochemical-climate calculations have been performed for hypothetical Earth-like planets around M dwarfs. Visible/near-infrared and thermal-infrared synthetic spectra of these planets were generated to determine which biosignature gases might be observed by a future, space-based telescope. Our star sample included two observed active M dwarfs-AD Leo and GJ 643-and three quiescent model stars. The spectral distribution of these stars in the ultraviolet generates a different photochemistry on these planets. As a result, the biogenic gases CH4, N2O, and CH3Cl have substantially longer lifetimes and higher mixing ratios than on Earth, making them potentially observable by space-based telescopes. On the active M-star planets, an ozone layer similar to Earth's was developed that resulted in a spectroscopic signature comparable to the terrestrial one. The simultaneous detection of O2 (or O3) and a reduced gas in a planet's atmosphere has been suggested as strong evidence for life. Planets circling M stars may be good locations to search for such evidence. 相似文献
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对于武装型直升机,在设计上通常都会兼顾考虑其隐身性,如选择雷达隐身、红外隐身、激光隐身、可见光隐身或集多种隐身功能于一身。为了验证直升机的隐身性能,就雷达隐身、红外隐身、激光隐身、可见光隐身在试验时所设置的飞行科目和方法作几点阐述,供飞行试验技术人员和飞行人员参考,为改进设计和使用提供依据。 相似文献
37.
Bilik I. Tabrikian J. Cohen A. 《IEEE transactions on aerospace and electronic systems》2006,42(1):267-278
An automatic target recognition (ATR) algorithm, based on greedy learning of Gaussian mixture model (GMM) is developed. The GMMs were obtained for a wide range of ground surveillance radar targets such as walking person(s), tracked or wheeled vehicles, animals, and clutter. Maximum-likelihood (ML) and majority-voting decision schemes were applied to these models for target classification. The corresponding classifiers were trained and tested using distinct databases of target echoes, recorded by ground surveillance radar. ML and majority-voting classifiers obtained classification rates of 88% and 96%, correspondingly. Both classifiers outperform trained human operators. 相似文献
38.
Andrew S. Rivkin Jian-Yang Li Ralph E. Milliken Lucy F. Lim Amy J. Lovell Britney E. Schmidt Lucy A. McFadden Barbara A. Cohen 《Space Science Reviews》2011,163(1-4):95-116
Our understanding of the composition of Ceres is driven by remote sensing of its surface. We review spectral observations of Ceres over wavelengths from the ultraviolet to the radio, as well as non-spectral data such as thermal inertia, photometric properties, radar experiments, and surface variability. We also discuss the closest likely meteorite analogs to Ceres and consider the likelihood that material from Ceres could be delivered to Earth. 相似文献
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40.
R. A. Mewaldt C. M. S. Cohen G. M. Mason A. C. Cummings M. I. Desai R. A. Leske J. Raines E. C. Stone M. E. Wiedenbeck T. T. von Rosenvinge T. H. Zurbuchen 《Space Science Reviews》2007,130(1-4):207-219
Although the average composition of solar energetic particles (SEPs) and the bulk solar wind are similar in a number of ways,
there are key differences which imply that solar wind is not the principal seed population for SEPs accelerated by coronal
mass ejection (CME) driven shocks. This paper reviews these composition differences and considers the composition of other
possible seed populations, including coronal material, impulsive flare material, and interplanetary CME material. 相似文献