遥测接收机基带信号处理的数字化实现方法

根据VLBI系统中接收的遥测信号基带信号的特点,介绍了利用虚拟无线电技术实现遥测接收机基带信号处理的基本原理,并分别概述了接收机的载波解调、副载波解调、数据转换环3个功能模块的数字化实现方法。仿真结果和实测数据表明,利用虚拟无线电技术能够很好地实现对遥测信号的解调和同步工作,又因该技术本身具有容易更新、方便添加接口、可并行化等优点,这种基于虚拟无线电技术的遥测接收机基带处理系统,将能够为遥测、导航、天线组阵等相关技术提供很好的实验和应用平台。     

用ASM／RXTE数据对Crab天区的直接解调成像

利用对象重建的直接解调技术,对ＡＳＭ／ＲＸＴＥ的模拟数据和Ｃｒａｂ天区观测数据进行了成像分析。结果表明,借助于对象重建的直接解调技术,可以利用正在运行的Ｘ射线天卫星ＲＸＴＥ上的全天监测器ＡＳＭ实现硬Ｘ射线天空的成像。     

一种新的射电源表综合方法

本文提出利用正交完备函数系拟合射电源表的局部系统差，并通过选择初始星表确定综合射电源表系统的轴方向，在综合计算时以射电源表包含的所有源坐标决定其轴方向．整个综合过程概念清晰，计算量较小．检验结果表明，用新方法得到的综合射电源表可靠性与稳定性都很好．     

ME／EXOSAT银道扫描数据的直接解调成像

利用对象重建的直接解调方法，我们对EXOSAT卫星ME探测器银道扫描观测数据进行了重新分析，研究了在以往的分析中难以分辨的几个天区中的分立X射线源．利用Bootstrap方法，我们对成像结果进行了统计误差分析，给出了点源位置和流强的误差．     

天文底片保存和我国天文底片数字化的建议

阐述了国际上天文照相底片数字化工作的进展:底片的保存、底片数字化的意义和相关技术。扼要地介绍了国际虚拟天文台的情况及其与底片数字化的关系。分析了我国天文底片资料的保存现状,并提出了底片数字化建议:成立由各天文台专家组成的全国底片数字化协调小组,建立各单位保存底片的信息库、改进底片的保存条件、有步骤地对有价值底片上的全部目标进行扫描,以便将其与现代高精度的观测资料相结合,开展有意义的课题研究。     

计算机打印口用作天文仪器接口

目前基本上所有天文仪器都是数字化的，几乎所有天文设备与计算机都有接口问题。我们在多套系统中采用计算机打印口来控制天文终端，认为这样做有不少好处。本文介绍了利用打印机接口天文仪器控制的技术，并给出两个例子。     

γ暴GRB910601的直接解调成像

利用直接解调方法分析了ＣＯＭＰＴＥＬ对γ暴ＧＲＢ９１０６０１的观测数据,发现该γ暴的直接解调成像定位较ＣＯＭＰＴＥＬ用最大似然法分析得到的结果更接近于Ｕｌｙｓｓｅｓ－ＢＡＴＳＥ系统联合定位的圆环．结果表明,采用直接解调方法对γ暴这类信噪比高、统计性差的瞬变源进行成像分析是完全可行的,而且,γ暴的成像定位精度可由此而获得提高．     

基于FPGA的IRIG-B（DC）码的解码方案的设计与实现

IRIG-B码是国际上通用的时间码格式,广泛应用于各种系统的时间同步。针对IRIG-B（DC）码的调制特性,介绍一种基于FPGA的B码解调方案。重点描述了如何在同步时序中准确提取秒同步信号并解调B码中包含的时间信息。整个方案中采用Verilog HDL语言进行设计,已成功实现,并给出了验证结果。     

γ暴GRB 910601的直接解调成像

利用直接解调方法分析了ＣＯＭＰＴＥＬ对γ暴ＧＲＢ９１０６０１的观测数据,发现该γ暴的直接解调成像定位较ＣＯＭＰＴＥＬ用最大似然法分析得到的结果更接近于ＵｌｙｓｅｓＢＡＴＳＥ系统联合定位的圆环．结果表明,采用直接解调方法对γ暴这类信噪比高、统计性差的瞬变源进行成像分析是完全可行的,而且,γ暴的成像定位精度可由此而获得提高．     

Compton γ射线望远镜的直接解调成像

Ｃｏｍｐｔｏｎγ射线望远镜ＣＯＭＰＴＥＬ／ＣＧＲＯ工作于０．７５－３０ＭｅＶ能区，本文应用直接解调方法分析ＣＧＲＯ＃１观测的ＣＯＭＰＴＥＬ数据，准确定出Ｃｒａｂγ射线源的位置，在１０－３０ＭｅＶ能区，分辨开最大似然法所不能完全分辨的Ｃｒａｂγ射线源和类星体ＰＫＳ０５２８＋１３４，得出优于传统成像方法所得的成像结果．应用直接成像方法处理γ射线脉冲星Ｇｅｍｉｎｇａ分位相数据，发现Ｇｅｍｉｎｇａ在１０－３０ＭｅＶ能区仍存在辐射，辐射集中在Ｇｅｍｉｎｇａ第一个峰的位相区域．结果表明，应用直接解调方法对Ｃｏｍｐｔｏｎ望远镜数据作成像分析是完全可行的     

Detection and temporal coherence of p‐modes below 1.4 mHz

Data collected recently by the helioseismic experiments aboard the SOHO spacecraft have allowed the detection of low degree p‐modes with increasingly lower order n. In particular, the GOLF experiment is currently able to unambiguously identify low degree modes with frequencies as low as 1.3 mHz. The detection of p‐modes with very low frequency (i.e., low n), is difficult due to the low signal‐to‐noise ratio in this spectral region and its contamination by solar signals that are not of acoustic origin. To address this problem without using any theoretical a priory, we propose a methodology that relies only on the inversion of observed values to define a spectral window for the expected locations of these low frequency modes. The application of this method to 2920‐day‐long GOLF observations is presented and its results discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Digital Archive of the Photographic Images of the Córdoba Observatory Plates Collections

The astronomical events registered in photographic plates are unique. A remarkable interest in using old plates in many areas of the current astronomical research is widely recognized by the IAU. There are almost ten thousand plates in several collections at the Córdoba Observatory and most of them are nearly one century old. This photographic material is difficult to handle in order to get the information stored in it. The goal of this project is to make a digital archive of images of these collections. In this first survey plates are being scanned with a standard commercial transparency scanner. These low spatial resolution, low digital resolution and low signal-to-noise ratio images are intended for facilitating handling and visual inspection. However, one arc-second positions can be obtained. Photometric quality has not been yet determined. Otherwise high quality digital images can be acquired with a microdenstitometer based on a scientific grade CCD whose implementation is at its final stage. The possibility of using a better-performance scanner is being evaluated. It is planned to permit the access to low-resolution images via internet. High-resolution images of selected zones will be available upon request. At this first stage, collections totally digitized at low resolution are:Carte du Ciel and Small Magellanic Cloud Zones. Gaviola's Eta Carinae Spectra and Pulkovo Zones are still in process.     

Giant Low Surface Brightness Galaxies: Evolution in Isolation

Giant Low Surface Brightness (GLSB) galaxies are amongst the most massive spiral galaxies that we know of in our Universe. Although they fall in the class of late type spiral galaxies, their properties are far more extreme. They have very faint stellar disks that are extremely rich in neutral hydrogen gas but low in star formation and hence low in surface brightness. They often have bright bulges that are similar to those found in early type galaxies. The bulges can host low luminosity Active Galactic Nuclei (AGN) that have relatively low mass black holes. GLSB galaxies are usually isolated systems and are rarely found to be interacting with other galaxies. In fact many GLSB galaxies are found under dense regions close to the edges of voids. These galaxies have very massive dark matter halos that also contribute to their stability and lack of evolution. In this paper we briefly review the properties of this unique class of galaxies and conclude that both their isolation and their massive dark matter halos have led to the low star formation rates and the slower rate of evolution in these galaxies.     

低频时码信号场强计的研制

介绍了BPC低频时码信号场强计的设计方案和原理,并结合出仪器硬件设计和控制软件框图,该仪器体积小,重量轻,测量精度高,对低频时码系统工程应用和低频电波传播特征研究具有重要意义。     

电网频率的快速,高分辨率测量方法与技术

介绍了快速、高分辨率测量电网频率的方法与技术 ,并在电力生产与调度中得到实际应用。这一方法与技术对于一般低频频率的测量具有普遍意义。     

The Tempe volcanic province of Mars and comparisons with the Snake River Plains of Idaho

The Tempe volcanic province of Mars is a broad region adjacent to and superimposed upon the western Tempe Mareotis plateau. The volcanic region is a relatively low plain of probable basaltic flood lava affinity. Superimposed upon this plain are a variety of small constructional and nonconstructional volcanic features, all of which appear structurally controlled, along an orientation of approximately N60°E. Constructional features included low shields, composite (?) cones, and low irregular hills which may be silicic domes. The nonconstructional features include linear depressions which may be rift zones, fissure flows, and pit craters. The Tempe volcanic province appears comparable in many aspects to features of the Snake River Plains of Idaho. While the Tempe region may cover a significantly larger area than the Snake River Plains the same type and scale of features are observed on both areas. The tempe region includes three styles of volcanism: flood basalts, a capping of fissure- and vent-fed flows with scattered low shields, and areas where low shields have coalesced into plains-type volcanism. The Snake River Plains are represented by one style, plains volcanism. This represents one of the few examples where direct comparison can be made between Martian and terrestial geologic-geomorphic features and where a scale problem is not encountered.     

Geometric characterization of the Arjuna orbital domain

Arjuna‐type orbits are characterized by being Earth‐like, having both low‐eccentricity and low‐inclination. Objects following these trajectories experience repeated trappings in the 1:1 commensurability with the Earth and can become temporary Trojans, horseshoe librators, quasi‐satellites, and even transient natural satellites. Here, we review what we know about this peculiar dynamical group and use a Monte Carlo simulation to characterize geometrically the Arjuna orbital domain, studying its visibility both from the ground and with the European Space Agency Gaia spacecraft. The visibility analysis from the ground together with the discovery circumstances of known objects are used as proxies to estimate the current size of this population. The impact cross‐section of the Earth for minor bodies in this resonant group is also investigated. We find that, for ground‐based observations, the solar elongation at perigee of nearly half of these objects is less than 90°. They are best observed by space‐borne telescopes, but Gaia is not going to improve significantly the current discovery rate for members of this class. Our results suggest that the size of this population may have been underestimated by current models. On the other hand, their intrinsically low encounter velocities with the Earth induce a 10–1000‐fold increase in the impact cross‐section with respect to what is typical for objects in the Apollo or Aten asteroid populations. We estimate that their probability of capture as transient natural satellites of our planet is about 8 %. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photometry of rough planetary surfaces: The role of multiple scattering

Topographic features affect the scattering properties of planetary surfaces by casting shadows and altering the local incidence and emission angles. Measurements of this phenomenon were obtained on the Cornell goniometer for both high and low albedo surfaces. For the low albedo surface, the decrease in reflected radiation due to topography increases sharply with increasing phase angle, whereas for the high albedo sample the effects are approximately constant between phase angles of 30 and 70°. The observations are in good agreement with a theoretical model in the case of the dark surface. However, for the high albedo surface the model overestimates the effects by about a factor of 2, since it does not include the partial illumination of shadows by multiple scattering. For both high and low albedo surfaces, the effects of topography do not become significant until a phase angle of 30–40°.     

Enhanced runout and erosion by overland flow at low pressure and sub-freezing conditions: Experiments and application to Mars

We present the results of laboratory experiments to study the sediment transport and erosional capacity of water at current martian temperature and pressure. We have performed laboratory simulation experiments in which a stream of water flowed over test beds at low temperature (∼−20 °C) and low pressure (∼7 mbar). The slope angle was 14° and three sediment types were tested. We compared the erosive ability, runout and resulting morphologies to experiments performed at ambient terrestrial temperature (∼20 °C) and pressure (∼1000 mbar), and also to experiments performed under low pressure only. We observed that, as expected, water is unstable in the liquid phase at low temperature and low pressure, with boiling and freezing in competition. Despite this, our results show that water at low temperature and low pressure has an equivalent and sometimes greater erosion rate than at terrestrial temperature and pressure. Water flows faster over the sediment body under low temperature and low pressure conditions because the formation of ice below the liquid-sediment contact inhibits infiltration. Flow speed and therefore runout distance are increased. Experiments at low pressure but Earth-ambient temperature suggest that flow speeds are faster under these conditions than under Earth-ambient pressure and temperature. We hypothesise that this is due to gas bubbles, created by the boiling of the water under low atmospheric pressure, impeding liquid infiltration. We have found that both basal freezing and low pressure increase the flow propagation speed - effects not included in current models of fluvial activity on Mars. Any future modelling of water flows on Mars should consider this extra mobility and incorporate the large reduction in fluid loss through infiltration into the substrate.