排序方式： 共有23条查询结果，搜索用时 15 毫秒
1.
德令哈13.7 m望远镜是中国最重要的射电望远镜之一.望远镜自安装超导成像频谱仪以及采用飞行观测模式以来,运行近10 yr.在此期间,望远镜开展并完成大量的天文观测,累积了巨量的天文数据,取得了一系列重要的科研成果.介绍了超导成像频谱仪在天文观测中的运行状态,运行中疑难问题、故障现象及解决方案.详述了超导成像频谱仪各方面性能测试及多年来的性能分析,包含接收机噪声温度及望远镜系统噪声温度、镜像抑制比、接收机稳定性、波束性能等方面.列举了超导成像频谱仪更新发展方面的工作,包含本振功率自动化调整、边带分离型超导混频器预放大电路的更新、控制程序的优化等.总结经验和规律,承前启后,将过去的超导成像频谱仪的维护运行经验应用到之后新一代大规模接收机系统中. 相似文献
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Surface waters of Alsea Bay, an unpolluted estuary on the Oregon coast, were analysed for nitrous oxide, nitrate and nitrite on a weekly or biweekly basis during the summer of 1979. The estuary was found to be a variable source of N2O to the atmosphere. Large and rapid increases in the concentrations of N2O, NO3?, and NO2? occurred at the beginning of the sampling period and are attributed to the influx of nutrient-rich upwelling water into the estuary with the tide. The subsequent decline in concentrations of nitrate, nitrite and nitrous oxide over the remainder of the summer is attributed to a decrease in upwelling intensity, a decline in nitrification rates and to assimilatory nitrate reduction. Measurements of nitrous oxide at six stations along the Alsea River were also made in September and October before and after the onset of the rainy season. Samples taken after flood conditions were established were systematically 50% higher than pre-flood samples. The data suggest that soil runoff results in elevated concentrations of N2O in rivers. 相似文献
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《地理学报(英文版)》1996,(3)
I.IntroductionTherearealotofstudiesdealingwithhydrodwiaAncsoflakes,numericalsimulationoflakecurrentsystemst5,7,lO,l31,andwiti1windsystemsoverlakesandnumericalsimulationontheland-lake/seaormountain-valleybreeze[4,6,8].Usually,ti1emodelsinti1eatmosphericboundarylayerandinlakewaterweresimulatedseParately.InfaCt,theprocessesintheatmosphericboundarylayeroverlakesandti1eprocessesinthelakewaterareinteraCtedstronglyeachoti1er.Collecteddatashow,thatalmoStalllargelakes,marginalseas,estuariesandlagoon… 相似文献
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水面的镜面反射是影响水环境遥感的关键因素之一。通过分析气-水界面反射光的偏振特性,从多角度偏振遥感的角度,提出一种剥离水面反射光的方法,并通过室内实验进行了验证。将ASD光谱仪与线偏振片结合扩展成高光谱偏振传感器,获取不同观测天顶角时水面反射光的偏振光谱。结果表明,当探测角不满足布儒斯特角时,在偏振片的主消光方向能剥离绝大部分的水面反射光;当入射角越接近布儒斯特角,其剥离效果越佳;以布儒斯特角观测时,可以达到完全剥离的效果。即该方法能显著削弱、甚至完全剥离水面的反射光,直接获取离水辐亮度,对于提高水色遥感的精度有着重要的应用价值。 相似文献
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水-气界面是一个重要的物质交换过程界面，对生态系统及生物地球化学循环过程有着重要影响。自然界的降雨可以改变水体表面平衡状态，提高气体在界面的通量交换速率，使得水体界面溶解氧和pH的水平、垂直方向浓度分布发生变化。本文利用平面传感膜具有高时空分辨率、可提供两维浓度分布信息的特点，开展了雨滴对水-气微界面层中的氧气扩散和pH值分布变化模拟实验，采用双参数平面光极同步测量获取低溶解气体在水-气界面的两维分布浓度变化。实验结果证明在受风速、温度影响较小区域，降雨过程对调节表层水体的溶解氧含量和pH值变化具有重要作用，雨滴可以打破水-气界面的微表层平衡机制，促进大气中氧气在表层水体的溶解，使得水面垂直方向23 mm内的溶解氧平均升高2.3 mg/L；降雨对水面12 mm之内表层水体pH值产生的影响较为明显，pH值平均降低了0.2~0.4个单位，表明降雨雨滴促进大气在水-气界面的迁移进程，溶解的CO2使得表层水体向酸性方向转化。本文提出的基于平面光极两维观测方法为评估低风速、高降雨或低降雨区域的海岸带溶解氧和pH值的变化提供高空间分辨率的水-气界面实时观测新的技术支撑。 相似文献
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《Chinese Astronomy and Astrophysics》2021,45(4):559-586
Delingha 13.7 m telescope is one of the most important radio telescopes in China. Since installing the superconducting spectroscopic array receiver (SSAR) and adopting the On The Fly (OTF) observation mode, the telescope has operated for nearly 10 years. During this period, a large number of astronomical observation projects have been carried out and completed, a large amount of astronomical data have been accumulated, and a series of important scientific results have been achieved. This paper introduces the operating status of SSAR in astronomical observations, the problems in operations, as well as the fault phenomena and solutions. The performance test and performance analysis of SSAR are described in detail, including the receiver noise temperature and telescope system noise temperature, image rejection ratio (IRR), receiver stability, beam performance and so on. The updating and development of SSAR are listed, including the automatic adjustment of LO (Local Oscillator) power, the updating of pre-amplification circuits of the sideband separation superconducting mixer, and the optimization of control program, etc. This paper summarizes the experiences and rules, and connects the past with the future, for applying the experiences of the maintenance and operation of SSAR to the next-generation large-scale receiver system. 相似文献
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为研究明渠水流自掺气发展区内水气结构特征,采用针式掺气流速仪对自掺气发展区内气泡尺寸与数量进行了试验研究,比较了气泡尺寸与数量随自掺气发展的变化规律,结果显示,同一水流断面上,随着掺气浓度的减小,气泡弦长尺寸分布范围与弦长平均值逐渐减小,掺气区内小尺寸气泡在数量上占有较大的比例,而大尺寸气泡则在含气量上占有较大的比例,分析认为从水面附近高掺气浓度区至自掺气区域底缘低掺气浓度区,明渠自掺气水流水气结构发展过程为“水面变形为主—水面变形与个体空气泡共存—个体空气泡”,为进一步研究明渠自掺气形成机理提供了一定的参考。 相似文献
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在VLBI(VeryLongBaselineInterferometry)数据采集终端中,用数字滤波代替模拟滤波有其显著的优势。本文首先介绍了国外在VLBI数据采集终端中采用数字滤波的进展情况,然后阐述了数字滤波在系统中的实现方案。实现数字滤波的关键是信号处理的速度,降低运算量是实现快速处理的关键,本文给出了实现FIR数字滤波器的3种结构,并在运算量方面进行了分析和比较。在这基础上,还对数字滤波的2种系统实现方案进行了具体分析。高性能的FPGA(FieldProgrammablegateArray)芯片是实现数字滤波器的较好选择,文章最后给出了基于FPGA芯片、用查表(LUT:LookUpTable)的方式实现的数字滤波系统框图。 相似文献
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Carbon dioxide partial pressure and carbon fluxes of air-water interface in Taihu Lake, China 总被引：2，自引：0，他引：2
1 INTRODUCTION Carbon dioxide (CO2) is principal greenhouse gas. Its air-water exchange is important in terrestrial ecosystems for climate change (Frankignoulle et al., 1998; Schimel et al., 2001). The direction of CO2 gas movement depends on the CO2 concentration gradient between air and surface water. The amount of CO2 exchange is related to the gas exchange coefficient, k. All lakes, with their small area but large atmospheric CO2 flux are important to under-stand the CO2 fluxes … 相似文献