高精度时间间隔测量技术与方法

时间间隔测量技术,尤其是高精度的时间间隔测量技术意义重大。不论是电信通讯、芯片设计等工程实践,还是原子物理、天文观测实验等理论研究,以及激光测距、卫星定位等航天军事技术,都离不开高精度的时间间隔测量技术。经过几十年的研究,目前已经有多种测量方法。在阐明插值原理之后,依次介绍了直接计数法、扩展法、时间幅度转换法、游标法、抽头延迟线法和差分延迟线法等主要方法。然后对影响测量的几个因素,包括非线性和不定态作了讨论。针对这些不良影响,还探讨了一些提高精度和稳定度的方法,比如非线性校正、PLL(Phase Lock Loop)和DLL (Delay Lock Loop)技术。最后,对时间间隔测量技术的前景作了展望。     

基于声表面波技术的高精度时间间隔测量方法系统误差研究

提出了一种新的高精度时间间隔测量方法,单次测量可以达到亚皮秒(rms1 ps)量级测量精度。简单介绍了这种基于声表面波技术的高精度时间间隔测量方法原理与系统组成,阐述了影响系统测量精度的主要因素,分为系统误差和随机误差。针对系统误差进行详细分析,给出其对测量精度的影响范围。通过理论分析,得到决定系统误差大小的重要参数,从而合理设计参数来降低系统误差对测量精度的影响。     

空间载钟的天体物理学实验

原子钟在空间天体物理测量中起着重要作用。最近研制的氢原子钟,对于超过1,000秒的平均时间间隔,其稳定度好到10~(-16)。这些装置对空间VLBI高精度的角度测量以及多普勒技术高精度测距和测速是非常适用的。本文主要概述几个通常感兴趣的空间载钟的天体物理实验.为了作这些测量,实验必须扩展到太阳系内进行。     

嵌入式时间间隔计数器的研制

介绍了一种新研制的嵌入式时间间隔计数器，它可作为一种功能模块用于用户的设备或时统中，实现高精度时间测量。从基本原理、硬、软件和功能等不同角度对计数器进行了较为详细的讨论。在该计数器的研制过程中还开发了用来调试计数器和供计数器用户使用的计算机应用软件，对此也作了简要介绍。最后，给出了计数器的设计指标和一些实测数据。     

一种高精度时间同步器的研制与性能测试

针对移动通信网络基站间需要建立高精度时间同步的需求,研制了一种具有高精度时间同步功能和高精度频率输出的时间同步器,并设计了相应的性能测试方法。测试结果表明,在同等条件下,不同时间同步器输出的1PPS平均同步精度优于5ns／d,24h内输出的频率准确度优于10^-12／s,其他各项指标基本合格,符合设计要求。     

基于CPLD的高精度可调脉冲信号发生器研制

为满足精密时间间隔测量设备的测试需要,研制了一种时间间隔可调的高精度脉冲信号发生器。利用计算机串口控制的方式,结合复杂可编程逻辑器件（CPLD）集成度高、可靠性好及工作速度快的优点,采用A1tera公司的设计软件QuartusII进行设计仿真及实现。仿真与实测实验表明,该脉冲信号发生器不仅可以产生单路可调脉冲信号,而且能产生多路可调脉冲信号,产生的单路秒脉冲信号的1s取样Allan方差为1．84×10^-11;产生的时间间隔为100ns的多路脉冲信号的1s取样Allan方差为2．36×10^-11,2路信号之间的时间间隔数据系列的峰一峰值为101ps,可以满足多通道时间间隔测量设备测试要求的稳定度与准确度。     

用于守时工作的时间间隔计数法与双混频时差测量比对法的比较

为了比较用于守时工作的时间间隔计数法和双混频时差测量法,分析了国家授时中心时频基准实验室的两种测量比对设备(SR620时间间隔计数器和PCOMP多通道相位比较仪)对同一组原子钟进行测量时所得到的结果(钟的速率、RMS、测量精度和稳定度)。分析所得的主要结论是:双混频时差测量法具有更高的比对精度,更适用于氢原子钟短期(τ≤5 d)稳定度的测量。     

广义延拓法在GPS精密星历内插和外推中的应用

利用精密星历解算卫星坐标是实现全球定位系统高精度差分定位的首要基础,受限于全球定位系统精密星历的采样时间间隔,为了得到任意时刻的卫星坐标,需要对全球定位系统精密星历数据做内插和外推处理。分析卫星位置随时间变化的规律后,采用广义延拓法对卫星的一段轨道构造以时间为坐标的内插和外推模型,在不引入较大位置误差的同时简化了卫星坐标的计算过程,并与拉格朗日插值法进行对比实验。研究结果表明,利用广义延拓法内插时误差小于5 cm,且在外推30 min内仍然能维持精度,明显优于拉格朗日插值法。     

卫星双向非连续时间比对的结果分析1

双向卫星时间比对是一种高精度的远程时间比对手段,其比对经常不是连续进行的。为分析非连续双向卫星时间比对的水平,使用中国科学院国家授时中心的C波段双向卫星时间比对网的数据进行试验。采用的方法是对非连续双向卫星时间比对的结果进行内插,将内插结果与连续双向卫星时间比对的结果进行比较。结果表明本文试验条件下观测间隔时间在2.5 d以内时,非连续与连续观测结果之差的RMS值小于1 ns;观测间隔时间为0.5 d时,非连续与连续观测结果之差的RMS值小于0.5 ns。     

毫秒脉冲星计时观测的研究进展

对毫秒脉冲星时间测量的理论、方法和技术研究的进展进行了阐述。根据近年来取得的观测研究结果,毫秒脉冲星计时测量误差～2×10－7秒,毫秒脉冲星自转周期稳定性足以和现代原子钟相媲美：其相对频率不稳定度达到1×10－14（1年≤γ≤5．2年）,并可望更高。近年来,脉冲星计时观测系统的接收灵敏度获得很大改进,计时观测的数据采集、处理技术、脉冲到达时间分析模型研究等都有长足发展。通过综合脉冲星时间算法得到的脉冲星时间尺度将比现代原子时具有更高的长期稳定度。叙述了脉冲星的物理特性及有关计时观测系统的技术成果,如观测频率和带宽的选择,消色散和接收系统灵敏度等问题。最后对毫秒脉冲星时间测量的误差源进行了讨论,并对脉冲星时间尺度的应用前景做了展望。     

Comments on the comment on Jordan-Brans-Dicke universes

The principal objections to our paper on Jordan-Brans-Dicke Bianchi-type universes are misleading. The intended solutions assume a power-law form, only in the limit of very large times. Although this is the only one for which we wrote down explicit solutions. The physical point of view behind our paper was to extend the re-scaling method, developed by one of us, to anisotropic universes in general and not to make a detailed study of each of the possible solutions that could be obtained through this process.     

Note on the solar wind-induced drag on comets

The solar wind-induced drag on magnetically large comets is estimated as follows. As the comet approaches the sun, solar radiation striking the comet surface generates a surrounding neutral atmosphere which is subsequently ionized. The resulting plasma cloud interacts with the solar wind to produce a comet magnetosphere and associated collision-free shock wave. An approximation to the accompanying drag is obtained using the similarity between the comet magnetosphere and that of the earth, and is shown to be much less than the mechanical mass loss force.     

基于EfficientNet的星系形态分类研究

星系的结构和形态能够反映星系自身的物理性质,其形态的分类是后续分析研究的一个重要环节.EfficientNet模型使用复合系数对深度网络模型的深度、宽度、输入图像分辨率进行更加结构化的统一缩放,是一种新的深度网络优化扩展方法.将该模型应用于星系数据形态的分类研究中,结果表明基于EfficientNetB5模型的平均准确率、精确率、召回率以及F1分数(精确率与召回率的调和平均数)都在96.6%以上,与残差网络(Residual network, ResNet)中ResNet-26模型的分类结果相比有较大的提升.实验结果证明EfficientNet的深度网络优化扩展方法可行且有效,可应用于星系的形态分类.     

Bandwidth effects on interstellar reddening and on theR-ratio

The energy distributions of 85 stars were combined with the transmittance ofB andV tilters and with an interstellar reddening law in order to investigate the effects of the bandwidth on the colour excess and on the ratioR=A _v/E(B-V). Since these depend both on the stellar spectral type and on the quantity of absorbing matter, corrective formulae are proposed to allow for these effects.     

Fluid transport on Earth and aeolian transport on Mars

Experimental data on cohesion-free particle transport in fluid beds are applied, via a universal scaling relation, to atmospheric transport of fine grains on Mars. It may be that cohesion due to impact vitrification, vacuum sintering, and adsorbed thin films of water are absent on Mars—in which case the curve of threshold velocity versus grain size may show no turnup to small particle size, and one micron diameter grains may be injected directly by saltation into the Martian atmosphere more readily than 100 micron diameter grains. Curves for threshold and terminal velocities are presented for the full range of Martian pressures and temperatures. Suspension of fine grains is significantly easier at low temperatures and high pressures; late afternoon brightenings of many areas of Mars, and the generation of dust storms in such deep basins as Hellas, may be due to this effect.     

Research on Ensemble Pulsar Time Based on Observed Data

The applications of pulsar timing to several important aspects are introduced and a skeletal definition of the pulsar time scale is given. By taking advantage of the observational timing data of millisecond pulsars obtained at the Parkes Astronomical Observatory, Australia, the ensemble pulsar time based on 4 millisecond pulsars is built up, the comparison of its stability σz, with that of the atomic time is made, and finally a few of important factors which affect the ensemble pulsar time, as well as their influences on the pulsar timing accuracy and application are analyzed.     

在BPL信道上增加数据广播内容的探讨

分析了现有罗兰C（包括BPL）在授时方面存在的不足，提出了在BPL信道上实现数据广播的主要目的。详细讨论了各种可能的数据信息的结构，并给出了有关参数和数据的计算方式和公式。认为发播内容的选择是由期望的系统功能决定的，广播内容的编排则与具体实现技术相关。最后给出了在不同调制方法下的传输速率，这是合理编排广播内容的基础。     

Comment on Varshni's recent paper on quasar red shifts

A recent paper (Varshni, 1976) analyses the distribution of quasar red shifts for randomness, in an incorrect manner. A correct analysis shows that this distribution is in agreement with random expectation. Were the distribution highly non-random, the original conclusion was that, for the red shifts to be cosmological, the Earth would have a strongly privileged position in the Universe. A simple alternative model, in which this would not be so, is pointed out.     

A note on vacuum solutions based on Lyra's manifold

In a recent Letter to the Editor, Beesham (1986) has claimed that the models based on the Lyra manifold allow a wider class of solutions of the vacuum field equations than models based on a Riemannian manifold. It was also argued that the cosmological term is introduced in an arbitraryad hoc fashion in general relativity.In this note I will show that all the vacuum solutions found by Beesham, can equally well be solutions of the Friedmann equations of vacuum with a cosmological term. All these solutions are well known.     

Thermodynamic constraints on fayalite formation on parent bodies of chondrites

Abstract— Thermochemical equilibria are calculated in the multicomponent gas‐solution‐rock system in order to evaluate the formation conditions of fayalite, (Fe_0.88–1.0Mg_0.12–0)₂SiO₄, Fa_88–100, in unequilibrated chondrites. Effects of temperature, pressure, water/rock ratio, rock composition, and progress of alteration are evaluated. The modeling shows that fayalite can form as a minor secondary and transient phase with and without aqueous solution. Fayalite can form at temperatures below ?350 °C, but only in a narrow range of water/rock ratios that designates a transition between aqueous and metamorphic conditions. Pure fayalite forms at lower temperatures, higher water/rock ratios, and elevated pressures that correspond to higher H₂/H₂O ratios. Lower pressure and water/rock ratios and higher temperatures favor higher Mg content in olivine. In equilibrium assemblages, fayalite usually coexists with troilite, kamacite, magnetite, chromite, Ca‐Fe pyroxene, and phyllosilicates. Formation of fayalite can be driven by changes in temperature, pressure, H₂/H₂O, and water/rock ratios. However, in fayalite‐bearing ordinary and CV3 carbonaceous chondrites, the mineral could have formed during the aqueous‐to‐metamorphic transition. Dissolution of amorphous silicates in matrices and/or silica grains, as well as low activities of Mg solutes, favored aqueous precipitation of fayalite. During subsequent metamorphism, fayalite could have formed through the reduction of magnetite and/or dehydration of ferrous serpentine. Further metamorphism should have caused reductive transformation of fayalite to Ca‐Fe pyroxene and secondary metal, which is consistent with observations in metamorphosed chondrites. Although bulk compositions of matrices/chondrites have only a minor effect on fayalite stability, specific alteration paths led to different occurrences, quantities, and compositions of fayalite in chondrites.