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阻尼莱曼α吸收线系统研究进展(Ⅰ)--巡天观测和统计性质 被引量:3
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作者 侯金良 史习珩 傅承启 《天文学进展》 CSCD 北大核心 2010年第3期195-212,共18页
阻尼莱曼α吸收线系统(DLAs)是中性氢柱密度超过2×10^(20) cm^(-2)的类星体吸收线系统。按照现有的观点,DLAs是高红移环境中星系及恒星形成的中性气体库,它们很可能是现今星系的前身。近20年来随着DLAs巡天观测的迅猛发展,尤其是S... 阻尼莱曼α吸收线系统(DLAs)是中性氢柱密度超过2×10^(20) cm^(-2)的类星体吸收线系统。按照现有的观点,DLAs是高红移环境中星系及恒星形成的中性气体库,它们很可能是现今星系的前身。近20年来随着DLAs巡天观测的迅猛发展,尤其是SDSS巡天观测数据的释放,DLAs统计样本达到千计的量级,大大推动了DLAs的观测和研究。由于受到观测的某些限制,样本还有偏,尤其是缺少低红移DLAs,但是,通过大样本DLAs系统的研究,已经获得了有关宇宙中性气体演化的许多信息,如DLAs的数密度在高红移处(z>1.5)是有演化的,但在低红移处基本不演化,从而确认了今天的星系形成于较高红移处。研究也发现DLAs对宇宙质量密度的贡献随红移的演化减弱,DLAs的中性氢气体柱密度分布函数与本地星系的中性氢柱密度分布函数十分相似等一些有趣的结论。着重介绍DLAs的基本知识以及20年来巡天的有关进展,包括DLAs的观测证认、统计特性等,并指出目前DLAs样本不完备的主要原因。 展开更多
关键词 类星体 吸收线系统 星系际介质 星系演化
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Theoretical and Experimental Study of a Cylindro-Parabolic Solar Collector
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作者 Y. Boukhchana A. Fellah A. Ben Brahim 《Journal of Environmental Science and Engineering》 2011年第8期1026-1030,共5页
This article outlines the theoretical and experimental performance studies of a cylindro-parabolic solar collector. The theoretical study consists on the establishment, through mass and energy balances, of a mathemati... This article outlines the theoretical and experimental performance studies of a cylindro-parabolic solar collector. The theoretical study consists on the establishment, through mass and energy balances, of a mathematical model to control the exiting temperature of the heating fluid as well as the temperatures of the absorber and the glass. The experimental level investigates the influence of the solar absorber tube diameter on the performances of the driving device. Several experiments were made in order to know the possibility to reach temperatures being able to ensure for example the ammonia vaporization in the generator of a solar absorption refrigeration system. These experiments were carried out under various operating and climatic conditions. The results are presented and discussed. 展开更多
关键词 Solar energy EXPERIMENTATION absorption refrigeration solar collector.
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CO and CO_2 dual-gas detection based on mid-infrared wideband absorption spectroscopy 被引量:2
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作者 董明 钟国强 +2 位作者 苗澍茁 郑传涛 王一丁 《Optoelectronics Letters》 EI 2018年第2期119-123,共5页
A dual-gas sensor system is developed for CO and CO_2 detection using a single broadband light source, pyroelectric detectors and time-division multiplexing(TDM) technique. A stepper motor based rotating system and a ... A dual-gas sensor system is developed for CO and CO_2 detection using a single broadband light source, pyroelectric detectors and time-division multiplexing(TDM) technique. A stepper motor based rotating system and a single-reflection spherical optical mirror are designed and adopted for realizing and enhancing dual-gas detection. Detailed measurements under static detection mode(without rotation) and dynamic mode(with rotation) are performed to study the performance of the sensor system for the two gas samples. The detection period is 7.9 s in one round of detection by scanning the two detectors. Based on an Allan deviation analysis, the 1σ detection limits under static operation are 3.0 parts per million(ppm) in volume and 2.6 ppm for CO and CO_2, respectively, and those under dynamic operation are 9.4 ppm and 10.8 ppm for CO and CO_2, respectively. The reported sensor has potential applications in various fields requiring CO and CO_2 detection such as in the coal mine. 展开更多
关键词 CO and CO_2 dual-gas detection based on mid-infrared wideband absorption spectroscopy
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