共查询到20条相似文献，搜索用时 62 毫秒
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氢原子钟具有较高的短期稳定度,将其作为主钟可在短期内产生高精度的本地时间信号.但氢钟存在频率漂移现象,导致其长期稳定度较差,从而影响本地时间的准确性.毫秒脉冲星自转高度稳定,借助于其长期稳定度高的特性,可定期实现对氢原子钟的频率驾驭,并对实时信号加以控制.首先分析了国际脉冲星计时阵(International Pulsar Timing Array,IPTA)第二批发布数据中四颗毫秒脉冲星的稳定度随时间的变化,同时采用哈达玛方差分析了中国科学院国家授时中心(National Time Service Center,NTSC)一台氢钟的频率稳定性能,最终给出了利用脉冲星驾驭氢原子钟频率的方法. 相似文献
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W. K. Yip 《Solar physics》1973,30(2):513-526
The radio emissions caused by electron streams in a non-isothermal plasma are studied quantitatively. It is proposed that conversion of the stream-excited plasma waves into electromagnetic waves by scattering on the thermal fluctuations at nonisothermal sonic oscillation frequency is the origin of the emission of the split-pair burst near the plasma frequency. The occurrence of the split-pair bursts near the second harmonic of the plasma frequency can be due to combination scattering of the stream-excited plasma waves by electron density fluctuations which are produced by the scattered plasma waves. With a streamer model in which the electron densities are two times those in Newkirk's model, both the observed frequency splitting and the rate of drift of the split pair can be explained as the result of plasma radiation caused by a stream of 10 keV electrons. A tentative model for the split-pair emission is suggested. 相似文献
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Chris Koen 《Monthly notices of the Royal Astronomical Society》2006,371(3):1390-1394
Eyer & Bartholdi showed that the Nyquist frequency of irregularly sampled time-series can be very high. In this paper, a calculation formula for the Nyquist frequency is presented. In practice there is an upper limit of 0.5/Δ on this frequency, where Δ is the best accuracy with which time is recorded. 相似文献
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《天文和天体物理学研究(英文版)》2021,(9)
In deep space exploration,many engineering and scientific requirements require the accuracy of the measured Doppler frequency to be as high as possible.In our paper,we analyze the possible frequency measurement points of the third-order phase-locked loop(PLL) and find a new Doppler measurement strategy.Based on this finding,a Doppler frequency measurement algorithm with significantly higher measurement accuracy is obtained.In the actual data processing,compared with the existing engineering software,the accuracy of frequency of 1 second integration is about 5.5 times higher when using the new algorithm.The improved algorithm is simple and easy to implement.This improvement can be easily combined with other improvement methods of PLL,so that the performance of PLL can be further improved. 相似文献
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CygX-1 X辐射的功率谱 总被引：1，自引：1，他引：0
运用自回归功率谱研究CygX－1X辐射的频谱特征,结果显示CygX－1转换态和高／软态时变频谱的连续成分,可以统一由有截断的幂律加噪声成分描述,转换态存在小于3Hz的宽峰结构及准周期振荡（QPO）成分（4－12Hz）,而高／软态完全可由截断幂律谱描述,不存在显著的QPO．截断频率在各态都相当稳定,在不同态的演化与平流为主的吸积流模型（ADAF）预期的情形一致．本文结果表明,自回归功率港分析是研究X射线双星光变特征的一个有效的方法． 相似文献
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由单脉冲星定义的脉冲星时受几种噪声源的影响,为削弱这些影响得到一种更稳定的时间尺度,采取将多颗脉冲星定义的单脉冲星时进行综合的分析方法得到综合脉冲星时．用两种方法:经典加权算法和小波分解算法,对PSRB1855 09和PSR B1937 21两颗脉冲星进行综合计算并做出比较,经典加权算法无法兼顾脉冲星不同频率上的稳定度,而用小波分析的方法对PSR B1855 09和PSR B1937 21两颗脉冲星进行综合,能够有效抑制不同频率上噪声的影响,达到更好的效果． 相似文献
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The possible variation of the flare frequency of flare stars in the Orion association is considered. It is shown that of the 23 chosen stars, each having exhibited four or more flares, a change in flare frequency at the 0.1 significance level can be suspected for 13. 相似文献
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I. W. Roxburgh S. V. Vorontsov 《Monthly notices of the Royal Astronomical Society》2006,369(3):1491-1496
The basic properties of acoustic wave propagation in stellar interiors can be analysed from the autocorrelation function (ACF) of intensity (or velocity) observations without measuring the resonant p-mode frequencies. We show how the strength of acoustic wave refraction in the stellar core, or forward acoustic amplitude, can be measured from a modulation in the ACF. This is the basic physical quantity which governs the so-called 'small frequency separations', and its measurement from the ACF can be used for determining the small frequency separations when the data is of insufficient quality for a reliable identification of the stellar p-mode frequencies. 相似文献
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Short dipoles are a key element in new low frequency array antennas as proposed for LOFAR and other astronomical applications. Unfortunately standard texts on short dipole antennas are based on the effective area and do not lead to an astronomically useful sensitivity formulation in a straightforward manner. The concept of maximum effective area is applied to arrays of short dipoles and allows expressing the sensitivity as the ratio of this area over the effective sky brightness temperature as long as the output noise power is dominated by the antenna input radiation. For both quantities we only need to know the array directivity pattern that includes the mutual coupling effects when the actual loading conditions of the array elements are taken into account. Short dipole elements have a constant directivity pattern for frequencies below resonance, but they exhibit strong complex impedance variations that provide only narrow band performance when power matching is applied as required in transmit applications. However, in receive applications voltage or current sensing can be realized, for example with an active balun. Assisted by the steep increase of the sky brightness with wavelength for frequencies below 300 MHz, this can provide sky noise dominated performance over at least a three to one frequency range. Still the low frequency limit is determined by the amplifier noise contribution and the losses in the antenna and in the dielectric ground surrounding the elements. We show that for a sparse array with the elements non-uniformly distributed according to an exponential shell model, a constant sensitivity can be obtained over a frequency range of at least two octaves. In addition, such a configuration has a factor of six greater sensitivity than a rectangular array for a large part of the frequency band. 相似文献
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A. A. Akopian 《Astrophysics》2003,46(1):58-66
A new method is proposed for determining the frequency distribution of bursts from randomly flashing objects based on fitting Pearson distributions by the method of moments. This method is applied to flare stars in the Pleiades cluster and the Orion association. The desired frequency distribution of the bursts from flare stars can be approximated by a gamma distribution. The burst frequency distribution describes the observed statistical picture fairly well. The result is compared with other methods. 相似文献
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针对被动型铷原子频标电路模块中由三极管等数量众多的分立元件搭建的9倍选频放大模拟电路和种类繁多的集成电路搭建的5.3125 MHz综合器电路,给出了数字化电路解决方案。在此新方案中,通过使用一种复杂可编程逻辑器件对锁相环进行编程控制,可以实现对10 MHz参考信号18倍频的精确控制;同时,利用该复杂可编程逻辑器件内部"虚拟"的集成电路对10MHz参考信号进行分频变换可以得到5.3125MHz信号。实际使用证明,这种设计方案具备易于集成、调试简单的优点,在替换原有模拟倍频、综合器功能电路后,成功实现整机锁定,各项性能指标均达到或优于原有水平,使整机向数字化、小型化迈出重要的一步。 相似文献
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M. S. Pshirkov 《Monthly notices of the Royal Astronomical Society》2009,398(4):1932-1935
A method is suggested with which to explore the gravitational wave background (GWB) in the frequency range 10−12 –10−8 Hz. This method is based on the precise measurements of pulsar rotational parameters: the influence of gravitational waves (GWs) in this frequency range will affect these parameters and therefore some conclusions about the energy density of the GWB can be made using analysis of the derivatives of pulsar rotational frequency. The calculated values of the second derivative from a number of pulsars limit the density of the GWB, Ωgw , as follows: Ωgw < 2 × 10−6 . Also, the time series of the frequency ν of different pulsars in a pulsar array can be cross-correlated pairwise in the same manner as in anomalous residuals analysis, thus providing the possibility of GWB detection in the ultra-low-frequency range. 相似文献
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汪景琇 《中国天文和天体物理学报》1986,(3)
本文对充满垂直均匀磁场的等温大气内的磁声重力波做了严格的解析分析,并将其通解表述成广义超几何函数的形式。该解可用于对磁大气内振荡现象的进一步数值模拟研究。对解的分析澄清了若干磁声重力波的传播性质。 相似文献
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太阳射电尖峰辐射(spike)的窄频带是一个具有特征性的参数,不但可从它计算出Spike辐射源区的小尺度结构,而且观测结果与Spike辐射理论可相互验证.我们利用云南天文台0.5 MHz频率分辨率的射电频谱观测资料,作出了230—300MHz频段上单个Spike带宽分布,并由此给出一群Spike源区的最可几尺度为151km,最大源区尺度为830km. 相似文献
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The intensity and frequency spectrum of gyro-synchrotron emission from energetic solar electrons radiating in coronal magnetic fields are calculated. These calculations, based on a recent study of the generation of gyro-synchrotron emission in a magnetoactive plasma, are applied to a Type IV radio burst originating at a high altitude in the solar corona. It is shown that the observed frequency spectrum of the burst, which exhibits very sharp low and high frequency cutoffs, can be best understood in terms of gyro-synchrotron emission in an ionized medium and that from the observed frequency spectrum and the ambient coronal density it is possible to deduce both the magnetic field at the site of the emission and the range of electron energies responsible for the burst.NAS-NASA Post-Doctoral Resident Research Associate.Research supported by the National Research Foundation under grant GP-849. 相似文献