共查询到20条相似文献，搜索用时 171 毫秒
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《天文学进展》2016,(2)
高精度时间频率的产生和超高精度时频信号的传递是现代物理学、天文学和计量科学的基础。空间原子钟组计划(Atomic Clock Ensemble in Space,ACES)是由欧洲空间局实施的基于国际空间站(International Space Station,ISS)微重力环境下的新型空间微波原子钟实验验证项目。概要介绍ACES项目基本情况,重点介绍ACES项目的主要科学和技术目标,围绕科学目标而形成的ACES组成结构,并梳理涉及的关键技术,特别介绍了ACES将应用的超高精度时频传递技术,为我国自主研究并实现相关空间时间频率系统及其应用提供参考。最后简述了我国正在建设的空间站时频系统主要情况和实施计划。 相似文献
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该文根据NTSC 20多台原子钟的ADEV和HDEV的分析、BIPM发表的TAI系统中原子钟的速率公报和权重报告.讨论了在高精度守时系统中对原子钟频率稳定度的要求.建议用τ≈30 d铯钟的ADEV和氢钟的HDEV至少达到1E-14来作为一个钟能否用于高精度守时的判断标准. 相似文献
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1985年8月22日在美国国家标准局召开了一个题为“用地球上最好的原子钟测量毫秒脉冲星”的科学讨论会。会上提供了不少关于原子时、频方面的文章,诸如,改善原子时尺度的新算法,关于GPS定时和定位,新型原子频率标准以及利用Loran-c进行毫秒脉冲星的观测等。内容相当丰富,在原子时、频领域推出了某些新技术和新方法。 相似文献
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NTSC的双混频时差测量系统试运转结果分析 总被引：1，自引：1，他引：1
中国科学院国家授时中心(NTSC)新进口的由德国Timetech公司制造的双混频时差测量系统(dual mixer time difference system,DMTD)已经通过了试运行。介绍了DMTD的工作原理和设备结构。NTSC时频基准实验室的主钟(MC)信号作为DMTD的频率参考信号,5个氢钟和18个铯钟的频率信号作为被测信号与MC信号进行相位比对。用频率分配放大器输出的多路MC信号也作为被测信号用以监测DMTD本身的精度和稳定度。给出了DMTD和时间间隔计数器TIC实际测量结果的比较及误差分析。测量结果表明DMTD特别适用于频率短期稳定度非常高的氢原子钟这样的频标之间的频率和时间比对。该设备将用于NTSC的守时工作,不久的将来也将用于铯喷泉与氢钟的频率比对。 相似文献
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地方原子时算法研究 总被引：1，自引：0，他引：1
产生和保持一个稳定、准确、可靠的时间尺度是所有时间实验室追求的目标.传统的ALGOS算法主要考虑时间尺度的长期稳定度,而地方原子时尺度需兼顾长、短期的稳定度.通过对原子钟噪声模型的分析研究,在保证地方原子时尺度长期稳定度不降低的条件下,提出适合中国科学院国家授时中心(National Time Service Center,NTSC)守时钟类型单一、钟性能相近的时间实验室计算地方时间尺度TA(NTSC)的一套完整算法.应用NTSC 2008年全年所有参加国际原子时(International Atomic Time,TAI)计算的钟的数据进行新算法的验证计算,得到的TA(NTSC)的短期稳定度指标与长期稳定度指标均有提高.研究结果适用于与NTSC守时系统结构相似的时间实验室的原子时尺度计算. 相似文献
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描述了采用光学望远镜辅助天马13m射电望远镜进行指向测量以及建立指向误差修正模型的方法. 对于小口径望远镜, 指向校准目标源比较少, 用射电法建立指向模型难以覆盖全天区. 利用上海天文台天马13m射 电望远镜进行光学望远镜辅助射电望远镜指向测量研究, 在13m天线背架上安装一套光学指向系统, 获得了优 于3''的重复测量误差. 此外, 通过对影响天线指向因素的分析, 建立了包含8个误差项的指向误差修正模型以及 光轴和电轴偏差模型. 将指向模型代入天线伺服控制系统, 对校准目标射电源进行十字扫描, 得到指向样本残差约 为5''. 该研究可以为实现高精度指向建模提供一种参考方法. 相似文献
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The problems of using the spectral index of radio galaxies in various tests, in particular, in selecting distant radio sources
are considered. The history of the question of choosing a criterion of searching for distant radio galaxies based on the spectral
index is presented. For a new catalog of 2442 radio galaxies constructed from NED, SDSS, and CATS data, an analytical form
of the spectral index-redshift relation has been determined for the first time. The spectral index-angular size and spectral
index-flux density diagrams have also been constructed. Peculiarities of the distribution of sources on these diagrams are
discussed. 相似文献
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先进天基太阳天文台(Advanced Space-based Solar Observatory, ASO-S)卫星姿控分系统的主要任务是实现高精度、高稳定度对日指向控制. ASO-S卫星的科学载荷中,白光望远镜(White-light Solar Telescope, WST)前端配置了太阳导行镜(Guide Telescope, GT)稳像系统,利用正交分布光电二极管组成的边缘探测器测量导行镜光轴与太阳中心的偏差角.提出了一种将GT测量值引入姿态控制闭环的控制方法:利用星敏陀螺定姿算法获得卫星-太阳方向姿态偏差, GT测量值确定非卫星-太阳方向姿态偏差;以4斜装反作用轮组为执行机构,进行三轴零动量稳定姿态控制.通过数学仿真验证,基于GT测量值的姿态控制器在非卫星-太阳方向的绝对指向精度优于2′′、相对姿态稳定度优于1′′/60 s,满足ASO-S卫星高精度高稳定度的对日指向要求. 相似文献
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为解决常规射电望远镜归心测量工作耗时耗力的问题,引入GNSS (Global Navigation Satellite System)同步监测技术实现了一种针对射电望远镜参考点的无人值守监测方法.设计了针对GNSS靶标点观测数据的归算方法,包括数据匹配、数据检核以及后续精度评估等步骤,并对2018年佘山25-m射电VLBI (Very Long Baseline Interferometry)望远镜的GNSS靶标点实测数据开展了数据预处理、解析与归心解算等,证明了该方法的可行性.结果表明基于该方法,采用单日内部分(5%)数据(约7600个靶标点),所测定的VLBI望远镜参考点的点位形式精度可达3 mm.总结了针对射电望远镜采用GNSS开展无人值守归心测量先行试验中的一些经验教训,明确了利用该方法测量过程中应该注意的问题,为今后更高精度射电望远镜参考点无人值守归心监测提供重要参考. 相似文献
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Hardcastle Alexander Pooley & Riley 《Monthly notices of the Royal Astronomical Society》1998,296(2):445-462
In previous papers we have discussed high-resolution observations of a large sample of powerful radio galaxies with z < 0.3. Jets are detected in up to 80 per cent of the sample, and radio cores in nearly all the objects; in addition, we are able to resolve the hotspots in most sources. In this paper we present measurements of the radio properties of these components. The prominences of the jets detected do not appear to be a function of radio luminosity, providing the clearest evidence yet that the reported low detection rate of jets in radio galaxies has been an artefact of low-sensitivity observations. We find a positive correlation between the total source length and core prominence in the narrow-line radio galaxies. We have found evidence for a relationship between hotspot size and total source size, but few other significant relationships between hotspot properties and those of the jets or lobes. We compare our measurements with those of Bridle et al., based on observations of a sample of quasars, and argue that the results are consistent with a modification of the unified model in which the broad-line radio galaxies are the low-luminosity counterparts of quasars, although the situation is complicated by contamination with low-excitation radio galaxies which appear to have radio properties different from the high-excitation objects. We discuss the classes of empirical model that can be fitted to the data set. 相似文献
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《Chinese Astronomy and Astrophysics》1982,6(1):63-67
We compare the Earth's rotation parameters claculated from various input sets and conclude 1) A reference system comparable to the BIH sustem can be set up using just a few high-precision, evenly-distributed instruments. 2) Chinese instruments for time and latitude determination play an important role in the setting up and maintenance of a global reference system. 3) There seem to be no systematic differences, of an annual or a semi-annual character between the observations by the classical methods and the newer techniques. The difference BIH (1979) – BIH (1968) is probably what has remained of the station errors when the BIH (1968) system was set up. 4) It is possible that some unknown common source of error may exist over a large geographical region, hence, to set up a good reference system, the observing insrtuments should be distributed as evenly as possible over the globe. 相似文献
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Particle reacceleration in the Coma cluster: radio properties and hard X-ray emission 总被引：1，自引：0，他引：1
G. Brunetti G. Setti L. Feretti G. Giovannini 《Monthly notices of the Royal Astronomical Society》2001,320(3):365-378
The radio spectral index map of the Coma halo shows a progressive steepening of the spectral index with increasing radius. Such a steepening cannot be simply justified by models involving continuous injection of fresh particles in the Coma halo or by models involving diffusion of fresh electrons from the central regions.
We propose a two-phase model in which the relativistic electrons injected in the Coma cluster by some processes (starbursts, AGNs, shocks, turbulence) during a first phase in the past are systematically reaccelerated during a second phase for a relatively long time (∼1 Gyr) up to the present time. We show that for reacceleration time-scales of ∼0.1 Gyr this hypothesis can well account for the radio properties of Coma C. For the same range of parameters which explain Coma C we have calculated the expected fluxes from the inverse Compton scattering of the Cosmic Microwave Background (CMB) photons, finding that the hard X-ray tail discovered by BeppoSAX may be accounted for by the stronger reacceleration allowed by the model.
The possibility of extending the main model assumptions and findings to the case of the other radio haloes is also discussed, the basic predictions being consistent with the observations. 相似文献
We propose a two-phase model in which the relativistic electrons injected in the Coma cluster by some processes (starbursts, AGNs, shocks, turbulence) during a first phase in the past are systematically reaccelerated during a second phase for a relatively long time (∼1 Gyr) up to the present time. We show that for reacceleration time-scales of ∼0.1 Gyr this hypothesis can well account for the radio properties of Coma C. For the same range of parameters which explain Coma C we have calculated the expected fluxes from the inverse Compton scattering of the Cosmic Microwave Background (CMB) photons, finding that the hard X-ray tail discovered by BeppoSAX may be accounted for by the stronger reacceleration allowed by the model.
The possibility of extending the main model assumptions and findings to the case of the other radio haloes is also discussed, the basic predictions being consistent with the observations. 相似文献
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收集了AO 0235+164天体射电4.8 GHz和14.5 GHz波段的光变测量数据,并获得了长期的光变曲线,从光变曲线可以看出其活动是非常剧烈的。利用Jurkevich方法和自相关函数方法分别对AO 0235+164射电波段宽带谱指数进行周期性分析,并对流量和谱指数进行相关性分析,研究结果表明:(1)AO 0235+164天体射电波段4.8 GHz～14.5 GHz对应的宽带谱指数,可能存在5.30年的光变周期,与Liu等人用功率谱法在射电波段发现其流量密度可能存在5.59±0.47年的光变周期基本吻合;(2)宽带谱指数与流量密度之间存在相关性。 相似文献
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G. M. Richter 《Astronomische Nachrichten》1970,292(2):59-63
An empirical relation between the observable properties radio surface brightness and radio index on the one hand, and the intrinsic properties linear diameter of the radio source, radio luminosity, and optical luminosity on the other hand is found and shown in a diagram. The relation is strong enough to yield useful distance estimates. In this manner, distances of 8 quasars and 17 unidentified radio sources are obtained. 相似文献
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B. Christophe P. H. Andersen J. D. Anderson S. Asmar Ph. Bério O. Bertolami R. Bingham F. Bondu Ph. Bouyer S. Bremer J.-M. Courty H. Dittus B. Foulon P. Gil U. Johann J. F. Jordan B. Kent C. Lämmerzahl A. Lévy G. Métris O. Olsen J. Pàramos J. D. Prestage S. V. Progrebenko E. Rasel A. Rathke S. Reynaud B. Rievers E. Samain T. J. Sumner S. Theil P. Touboul S. Turyshev P. Vrancken P. Wolf N. Yu 《Experimental Astronomy》2009,23(2):529-547
The Solar System Odyssey mission uses modern-day high-precision experimental techniques to test the laws of fundamental physics
which determine dynamics in the solar system. It could lead to major discoveries by using demonstrated technologies and could
be flown within the Cosmic Vision time frame. The mission proposes to perform a set of precision gravitation experiments from
the vicinity of Earth to the outer Solar System. Its scientific objectives can be summarized as follows: (1) test of the gravity
force law in the Solar System up to and beyond the orbit of Saturn; (2) precise investigation of navigation anomalies at the
fly-bys; (3) measurement of Eddington’s parameter at occultations; (4) mapping of gravity field in the outer solar system
and study of the Kuiper belt. To this aim, the Odyssey mission is built up on a main spacecraft, designed to fly up to 13
AU, with the following components: (a) a high-precision accelerometer, with bias-rejection system, measuring the deviation
of the trajectory from the geodesics, that is also giving gravitational forces; (b) Ka-band transponders, as for Cassini,
for a precise range and Doppler measurement up to 13 AU, with additional VLBI equipment; (c) optional laser equipment, which
would allow one to improve the range and Doppler measurement, resulting in particular in an improved measurement (with respect
to Cassini) of the Eddington’s parameter. In this baseline concept, the main spacecraft is designed to operate beyond the
Saturn orbit, up to 13 AU. It experiences multiple planetary fly-bys at Earth, Mars or Venus, and Jupiter. The cruise and
fly-by phases allow the mission to achieve its baseline scientific objectives [(1) to (3) in the above list]. In addition
to this baseline concept, the Odyssey mission proposes the release of the Enigma radio-beacon at Saturn, allowing one to extend
the deep space gravity test up to at least 50 AU, while achieving the scientific objective of a mapping of gravity field in
the outer Solar System [(4) in the above list].
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