用计算机技术实现Mark Ⅳ解码

从硬件实现和软件实现的角度介绍了如何利用计算机技术实现Mark Ⅳ解码。利用它可对Mark Ⅳ记录设备输出的数据进行质量分析并提取相位校正信号，检测VLBI观测设备的工作状态，消除设备对Mark Ⅳ记录数据的影响。     

VLBI MK5B通道检测软件的设计与实现

针对国际上VLBI专用硬盘记录终端升级到MK5B后,数据记录格式发生了显著变化,设计了能够适应MK5B数据格式的通道检测软件。MK5B通道检测软件主要用于检查硬盘记录器记录数据的可读性以及确认接收机和VLBI终端等观测设备的参数设定。在软件设计过程中,考虑到软件的可维护性及可移植性,采用面向对象的设计方法。通过对两段观测数据的处理表明,MK5B通道检测软件工作稳定,处理结果正确,能够满足工作需要。     

中国古代天象记录数据库的设计与实现

中国古代天象记录是世界上独一无二的天文观测数据宝库,具有十分重要的科学价值。近年来,随着天文观测与理论的快速发展,对历史超新星、太阳活动周期等问题的研究有了许多新的进展。但古代天象记录的整理工作还停留在上世纪八十年代末的水平,在信息利用方面存在检索不便、文献不全、缺乏相应分析等问题,已难以满足天文研究工作的需求。基于面向文档数据库、全文检索、语法分析、Web等技术,设计开发了中国古代天象记录数据库,实现了对古代天象记录中各类科学和文史信息的数字化存储与检索。这一基础平台的建设和研发为中国古代天象记录更好地服务于全世界天文学家,促进对古代天象记录的校勘、证认、利用等多学科交叉研究打下了基础。     

多制式FX型VLBI相关处理机系统的研究

介绍了在上海天文台现有两台站VLBA型VLBI相关处理机的基础上同时处理多制式磁带的研究方案，为适应MarkIV薄磁带，并兼顾1Gbit/s的VLBA格式，需升级现有处理机的高速高密度磁带机，增加磁头组，更换精密薄带读取机构，扩充数据恢复系统和FFT流水张容量，系统采用实时操作系统与FPGA（Field Programmable Gate Array)相结合，完成多制式磁带高速度数据流的高精度同时控制与实时解码回放，多种实时计算，最终实现Mark4擞据的相关处理，并兼容MarkIIIA,VLBA格式。     

转发式测距设备时延中的温度效应

为实现高精度卫星测距,测定了转发式卫星测距地面设备时延与环境温度之间的关系.利用已知发射通道和接收通道时延的调制解调器测定了待测调制解调器的接收通道和发射通道时延,使用转发式卫星测距地面设备测定了地面站设备整体时延.由地面气象仪器获得环境温度参数.利用测定的时延和温度数据研究了设备时延与温度之间的变化关系.统计分析表明:在自然温度条件下,设备时延的变化与温度的变化之间基本呈线性关系.对于高精度卫星测距,温度对设备时延的影响不能忽略.     

基于GPS射频信号模拟的定时方法

针对采用GPS定时的设备提出了基于GPS射频信号模拟的定时方法,在不更改原有设备的情况下,可利用外部时间基准进行同步。首先建立卫星的轨道模型,模拟出卫星的导航电文;然后根据设备的位置模拟产生观测数据;再将导航电文调制到卫星的伪随机码上,根据观测数据计算出伪距,对调制的信号进行延迟;最后,通过正交射频调制得到GPS模拟信号。已建立的实验模型能实现以上模拟过程。测试表明,该方法可达到10ns级的定时精度。     

应用于射电天文的高效实时管道数据流传输与处理技术

针对超宽带及多波束接收系统海量天文信号实时高效传输与处理问题,对基于现场可编程门阵列(Field Programmable Gate Array, FPGA)+图形处理器(Graphics Processing Unit, GPU)的主流终端设备软件系统进行了测试分析。超宽带接收设备要求终端系统软件能够在更宽带宽、更高时间分辨率和频率分辨率的条件下,实现数据流实时传输与处理。结合大口径射电观测设备未来发展的方向,提出了利用高速并行环形缓冲区实现数据流缓存,基于图形处理器集群实现数据流实时处理,基于BeeGFS实现分布式并行数据存储,模块化构建射电天文信号传输管道软件的设计思路。     

一米新真空太阳望远镜光谱扫描观测系统设计

1 m新真空太阳望远镜(New Vacuum Solar Telescope,NVST)是国内用于对太阳进行观测和研究的大型科研设备,针对太阳活动区光谱观测的需求,在现有的大色散光谱仪及多波段光谱仪基础上,设计了光谱扫描设备,并基于C#设计了一套观测控制系统软件,实现扫描设备的运动控制和观测数据的采集。进行光谱扫描观测时,计算机控制扫描设备步进运动,并利用图像采集卡通过Camera Link总线采集CCD/CMOS相机的探测数据,基于多线程技术采集观测数据,将采集的图像数据存储成FITS(Flexible Image Transport System)文件,并将光谱图像数据处理成灰度图像用于软件界面监视。此套软件已用于1 m太阳望远镜光谱扫描观测,测试结果满足预期功能需求,为后续观测系统功能升级提供了良好的扩展性。     

NVST狭缝扫描及定标单元的电动控制实现

利用1 m红外太阳望远镜(New Vacuum Solar Telescope,NVST)对太阳进行观测和研究,需要控制狭缝扫描系统和磁分析系统中各设备的运动以配合观测系统采集数据。针对实际观测中对设备运动控制的需求,并利用控制器对相应设备的直接控制,提出基于TCP协议及UDP协议的Win Sock网络编程以及串口通信编程的设计方案,设计了一套基于Client/Server架构的控制系统软件,实现各仪器在局域网范围内的远程控制。通过对设备的运动控制测试,客户端发送控制命令给服务器端,服务器计算机解析命令并通过串口控制各仪器运行,同时采集设备的状态信息反馈给客户端,测试结果表明此系统能良好地控制各设备运行,结合网络通信及串口通信的设计为后续的观测系统功能升级打下了基础。     

太阳射电Ⅰ型爆发频谱观测和处理程序设计

本文主要介绍利用微型计算机和光电二极管阵连机系统作为实时观测数据记录、处理终端,对太阳射电Ⅰ型爆发频谱进行观测和处理的程序设计及其方法。     

A baseband recorder for radio pulsar observations

Digital signal recorders are becoming widely used in several subfields of centimetre-wavelength radio astronomy. We review the benefits and design considerations of such systems and describe the Princeton Mark IV instrument, an implementation designed for coherent-dedispersion pulsar observations. Features of this instrument include corrections for the distortions caused by coarse quantization of the incoming signal, as well as algorithms that effectively excise both narrow-band and broad-band radio frequency interference. Observations at 430 MHz, using the Mark IV system in parallel with a system using a 250-kHz filter bank and incoherent dedispersion, demonstrated timing precision improvement by a factor of 3 or better for typical millisecond pulsars.     

Radioheliograph observations of a pulsating structure associated with a moving type IV burst

Observations of a pulsating structure with the Mark II Nançay Radioheliograph are reported. These fluctuations are found to occur early in the development of a moving type IV burst. It is confirmed that the source of these fluctuations is of small extent and that it is embedded in the moving type IV continuum, plausibly at the top of an expanding arch.The observations suggest that the pulsating structure consists of recurrent enhanced pulses (mean recurrency time 1.7 s) followed by trains of periodic pulses (mean periodicity 0.37 s). The intensity of the enhanced pulses has a damping time of about 5 s. It is shown that previous interpretation of the pulsating structure by Rosenberg (1970) cannot account for the present observations.     

The VLBA GigaBit-per-second data recording system

The VLBA Data Recording System was designed to support a peak aggregate data rate of 512 Megabits per second initially, and be expandable to peak aggregate rates of 1024 Megabits per second (“1 Gbps”). Budgetary constraints prevented even the planned initial capability from being completed as part of the VLBA construction project, and it is only now nearing completion. In the meantime, while the VLBA was being completed, Haystack Observatory developed and partially implemented the design of the Mark 4 recording system, a further development beyond the Mark 3A system upon which the VLBA system design was based. Mark 4 can record at aggregate data rates up to 1 Gbps. To maintain the VLBA's competitiveness in terms of sensitivity, and in particular to be ready for the ARISE Space VLBI mission's wideband data downlink, it is time now to exercise the expansion option designed into the VLBA Data Recording System. This paper describes current plans within NRAO for such a development. Besides the Gbps implementation originally foreseen for the VLBA Data Recording System, development of the Mark 4 system has made possible as alternative implementation. The relative merits of these two implementations are discussed.     

Estimating Black Hole Masses of AGNs using Ultraviolet Emission Line Properties

Based on measured broad line region sizes in the reverberation-mapping AGN sample, two new empirical relations are introduced to estimate the central black hole masses of radio-loud high-redshift (z > 0.5) AGNs. First, using the archival IUE/HST spectroscopy data at UV band for the reverberation-mapping objects, we obtained two new empirical relations between the BLR size and Mg II/C IV emission line luminosity. Secondly, using the newly determined black hole masses of the reverberation-mapping sample as calibration, we found two new relationships for determining the black hole mass with the full width at half maximum and the luminosity of Mg II/C IV line. We then apply the relations to estimate the black hole masses of the AGNs in the Large Bright Quasar Survey and a sample of radio-loud quasars. For the objects with small radio-loudness, the black hole mass estimated using the RBLR-LMgII/C IV relation is consistent with that from the RBLR-L3000 (?)/1350(?) relation. For radio-loud AGNs, however, the mass estimated from the RBLR-LMgII/CIV relation is sys- tematically lower than that from the continuum luminosity L3000(?)/1350(?). Because jets could have significant contributions to the UV/optical continuum luminosity of radio-loud AGNs, we emphasize once again that for radio-loud AGNs, the emission line luminosity may be a better tracer of the ionizing luminosity than the continuum luminosity, so that the relations between the BLR size and UV emission line luminosities should be used to estimate the black hole masses of high redshift radio-loud AGNs.     

Mark4格式器升级为Mark5B采样器的方法及步骤

近年来世界VLBI（Very Large Baseline Interferometry）终端技术发展迅速,主流的记录终端已发展到Mark5B记录系统,Mark5C也正在研制和测试阶段。为了适应未来高速率、海量数据以及数字基带转换器观测的要求,需要将现有的Mark5A升级到Mark5B或Mark5B＋,相应地需要将Mark4格式器升级为MarkB采样器。主要描述了相关设备的原理以及Mark4格式器升级的步骤。     

Book and Multimedia Reviews

Book reviewed in this article: Geochronology and Thermochronology by the ⁴⁰Ar/³⁹Ar Method: Second Edition by Ian McDougall and T. Mark Harrison. Protostars and Planets IV edited by V. Mannings, A. P. Boss, and S. S. Russell. The Star Formation Newsletter edited by Bo Reipurth. Astronomical Origins of Life: Steps Towards Panspermia by F. Hoyle and N. C. Wickramasinghe. Here Be Dragons: The Scientific Quest for Extraterrestrial Life by David Koerner and Simon LeVay.     

UWB中Viterbi译码器的FPGA设计与实现

由于差错控制在超宽带室内导航系统中占据着十分重要的位置,并考虑到IEEE802．15．3a标准采用卷积编码和Viterbi译码来进行差错控制,因此利用现场可编程门阵列（FPGA）设计实现了一种约束长度为7,译码深度为64的全并行Viterbi译码器。本设计在xilinx ISE9．2环境下进行了综合,并采用Modelsim6．0对整个设计进行了仿真。仿真结果表明,该设计能够满足超宽带系统的要求。     

乌鲁木齐天文站Mark 5系统实施及其研究

分析了VLBIMark5磁盘记录系统的硬件结构和软件结构。对其软件实现做了设计层面上的分析。给出了乌鲁木齐天文站Mark5系统实施后的操作流程图。分析了Haystack天文台e VLBI软件的结构。     

乌鲁木齐天文站建立脉冲星相干消色散观测系统

脉冲星发射的辐射信号经过星际介质到达观测天线的过程中,存在色散效应。该效应导致有一定带宽脉冲信号的不同频率成份到达天线时间有延迟,影响对脉冲星的观测。消色散技术是脉冲星观测的关键技术,它对脉冲星观测系统的灵敏度和观测精度至关重要。脉冲星相干消色散过程是:通过对观测信号进行Nyquist采样,对采样数据做傅立叶变换,变换后的频域信号与星际介质Chirp函数乘积,然后再做逆傅立叶变换回时域,得到消色散后的时域信号。乌鲁木齐天文站依托现有的南山25m射电望远镜和VLBI记录终端MK5A系统,自行开发的相干消色散处理软件(Linux操作系统下C语言调用MPI库)和4节点机群系统,建立了脉冲星相干消色散观测系统。     

基于DBBC+Mark 5B记录系统的脉冲星观测

2009年11月,云南天文台射电天文研究团组采用40 m射电望远镜以及基于DBBC(Digital Base Band Conveter)和Mark 5B的VLBI记录系统对PSR J0835-4510和PSRJ0332+5434进行了观测。观测选用S波段右旋圆极化信号,起始频率为2 206.99 MHz,总带宽为32 MHz。对数据进行相干消色散和平均后,得到PSR J0332+5434的单脉冲图像和两颗脉冲星的平均脉冲轮廓。由平均轮廓的展宽随时间的变化关系,对脉冲星的视周期作了一定修正后,得到信噪比更高的平均轮廓图。最后对轮廓的信噪比随时间的变化作了初步分析,由此可了解整个系统在观测时的稳定性。