Large-scale non-Gaussianities in the 21-cm background anisotropies from the era of reionization     

Asantha Cooray 《Monthly notices of the Royal Astronomical Society》2005,363(3):1049-1056

The brightness temperature fluctuations in the 21-cm background related to the neutral hydrogen distribution provide a probe of the physics related to the era of reionization, when the intergalactic medium changed from being completely neutral to partially ionized. We formulate statistics of 21-cm brightness temperature anisotropies in terms of the angular power spectrum, the bispectrum, and the trispectrum. Using the trispectrum, we estimate the covariance related to the power spectrum measurements and show that correlations resulting from non-Gaussianities are below a per cent, at most. While all-sky observations of the 21-cm background at arcminute-scale resolution can be used to measure the bispectrum with a cumulative signal-to-noise ratio of the order of a few tens, in the presence of foregrounds and instrumental noise related to first-generation interferometers, the measurement is unlikely to be feasible. For most purposes, non-Gaussianities in 21-cm fluctuations can be ignored and the distribution can be described with Gaussian statistics. Because 21-cm fluctuations are significantly contaminated by foregrounds, such as galactic synchrotron or low-frequency radio point sources, the lack of significant non-Gaussianity in the signal suggests that any significant detection of non-Gaussianity could be the result of foregrounds. Similarly, in addition to the frequency information that is now proposed to separate 21-cm fluctuations from foregrounds, if the non-Gaussian structure of foregrounds is known a priori, this additional information could potentially be used to reduce the confusion further.  相似文献   

Clustering evolution between z=1 and today     

Stefanie Phleps  Klaus Meisenheimer 《Astrophysics and Space Science》2003,284(2):377-380

We present results of an investigation of clustering evolution of field galaxies between a redshift of z ∼ 1 and the present epoch. The current analysis relies on a sample of ∼ 14000 galaxies in two fields of the COMBO 17 survey. The redshift distribution extends to z ∼ 1. The amplitude of the three-dimensional correlation function can be estimated by means of the projected correlation function w(r _p ). The validity of the deprojection was tested on the Las Campanas Redshift Survey (LCRS). In a flat cosmology with non-zero cosmological constant for bright galaxies (M _B ≤-18) the clustering growth is proportional to (1+z) ^-2. However, the measured clustering evolution clearly depends on Hubble type. While locally the clustering strength of early type galaxies is equal to that of the bright galaxies, at high redshifts they are much stronger clustered, and thus the clustering has to evolve much more slowly. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

光学综合孔径干涉成像的关键技术及多光束干涉仿真     

王海涛  周必方 《紫金山天文台台刊》2003,(1)

闭合相位技术、U -V覆盖技术和像重构技术是光学综合孔径干涉成像的三个关键技术。文中简要介绍了光学综合孔径技术的发展历史、这三种关键技术和光学综合孔径望远镜阵的构成 ,对之进行了多光束干涉的计算机仿真和实验仿真 ,两者结果一致说明了光学综合孔径干涉成像技术中有关干涉的理论的正确性 ,指出了下一步的研究方向。  相似文献   

一个巨型望远镜方案   总被引：4，自引：0，他引：4  

苏定强  王亚男  崔向群 《天文学报》2004,45(1):105-114

提出一个有特色的巨型望远镜(FGT)方案．其主镜口径为30米，主焦比为1．2，由1095块圆环形子镜构成．采用地平式装置．光学系统包括Nasmyth系统、折轴(Coude)系统和一个大视场系统．提出一个由4个镜面组成的新的Nasmyth系统，在约10′的视场范围内像斑小于爱里斑，达到衍射极限．比传统的Nasmyth系统的衍射极限视场大得多．可在这样的大视场内同时作好几个小区域的衍射极限的观测．当由Nasmyth系统转换到折轴系统和大视场系统时，采用主动光学技术改变子镜的面形、倾斜和平移，产生一个新的主镜面形，使折轴系统和大视场系统都能得到很好的像质．大视场系统的视场直径25′，场曲轻微，并有可能校正大气色散．给出了子镜面形和位置的公差，并讨论了望远镜的装置和结构,方案中的特色和创新对未来大望远镜的研制有普遍意义．  相似文献   

Degradation due to Quantization Noise in Radio Astronomy Phased Arrays     

A. B. J. Kokkeler  P. Fridman  A. van Ardenne 《Experimental Astronomy》2001,11(1):33-56

In this article, a model is developed for determining the probability distribution of the output of a digital adder in case of 2-, 3- and 4-level quantization before summation. This probability distribution is then used to determine the efficiency of a system which determines the total power of the signal at the output of the digital adder.The sum-signal is also used in a VLBI correlation mode where the sum-signal is correlated with the signal from a VLBI partner. The efficiency, expressed in so-called Degradation Factors, is determined for 1- and 2-bit correlation and 2-, 3- and 4-level quantization before summation.Furthermore, the application of the calculated values (Total Power Detector Efficiencies and Degradation Factors) is illustrated.  相似文献   

全球大尺度信息在3 km GRAPES-RAFS系统中的应用   总被引：3，自引：0，他引：3  

庄照荣  王瑞春  李兴良 《气象学报》2020,78(1):33-47

为了缓解快速分析预报循环过程中固定边界条件造成的预报锁定,缩短动力、热力调整时间,提高模式预报能力,全球模式产品的大尺度部分的信息被引入GRAPES-RAFS系统中,通过二维离散余弦变换方法对全球模式产品和区域分析进行谱分解,获得综合全球大尺度和区域中小尺度信息的混合尺度分析。通过2018年5月9日—6月9日1个月间歇分析预报循环,比较对照试验和混合尺度分析试验的冷启动和暖启动预报结果表明,在快速分析预报循环中,全球大尺度信息的加入不仅增加分析的大尺度部分信息和降低地面气压倾向,缩短模式预报的动力、热力调整时间,且地面要素场、分析场和降水的暖启动预报质量有显著提高;台风艾云尼路径预报也更加接近观测。另外,GRAPES-RAFS循环的暖启动与冷启动预报相比,初始场更加协调,但地面2 m气温和10 m风场的预报质量比冷启动预报差,且其ETS降水评分也明显低于冷启动预报。混合尺度方案在RAFS系统中的应用能有效提高初始场的协调性,地面、高空要素和降水预报质量得到提升。   相似文献   

电离层时空变化效应对星载及月基SAR成像影响:现状与展望     

陈锟山  许镇 《南京气象学院学报》2020,12(2):135-149

合成孔径雷达（SAR）作为一种主动传感器,具备全天时、全天候的观测能力,已广泛应用于对地观测中.然而,无线电信号在空间传播过程中会不可避免地受到电离层效应的影响,导致信号的相位、幅度发生变化,使得工作在电离层之上的SAR系统的成像性能受到干扰.本文分别从法拉第旋转、背景电离层和电离层不规则体三个方面介绍了电离层效应对不同轨道SAR系统成像性能的影响,并总结了电离层效应的补偿修正方案.最后,给出了电离层效应对星载和月基SAR成像影响的一些亟待解决的问题,以促进星载和月基SAR成像的发展及应用.  相似文献   

区域化探样点布置图大格编码自动生成   总被引：1，自引：1，他引：0  

张得恩  解庆锋  何镇  宁勇 《物探与化探》2011,35(3):406-408,430

区域化探样点布置工作中,大格编码是一项必不可少的内容,人工编制起来较繁琐,易出错。笔者根据多年区域化探工作经验,利用计算机程序编制语言,编制大格编码自动生成软件包,根据实际需要生成大格编码图层,提高了野外工作效率和室内制图质量。  相似文献   

高精度航空磁测在西藏一江两河地区找矿效果     

刘振军  王德发  范子梁  刘英才 《物探与化探》2011,35(1):47-51

为了提高航磁在西藏一江两河地区的找矿效果,深入研究了2000～2004年间中国国土资源航空物探遥感中心在该区开展的1:20万-1:25万高精度航磁调查资料,对一批具有找矿意义的航磁异常,经地面踏勘,总结了航磁局部异常与矿产的对应关系,阐述了利用航磁资料直接找矿的效果,为该地区的地质找矿工作提供了帮助.  相似文献   

Paterson高温高压流变仪及其在岩石流变学的应用   总被引：4，自引：1，他引：3  

邵同宾  嵇少丞  李建峰  王茜  宋茂双 《大地构造与成矿学》2011,35(3):457-476

地球作为一个动态体系,其内部岩石在各种物理化学条件下变形,形成各种地质构造.在过去的几十年里,得益于相关测试分析手段的不断发展,地球材料的流变学研究取得了许多实验突破,加深了人类对地壳和上地幔岩石变形行为的理解.本文对实验岩石变形装置的技术发展做了扼要的回顾,重点介绍了Paterson高温高压流变仪(HPT).HPT是...  相似文献