狭义相对论同时性定义的任意性

一、同步钟的建立自然界并不存在同步钟,同步钟是由观察者依一定的方式建立的．人们使用同步钟的目的是为了描述不同地点的两个事件的因果关系．因果关系是客观存在的,它是不依人的意志为转移的．但是因果关系的描述形式可有选择的自由．同步钟的定义不同,则时间坐标也有差别．为了简单起见,我们规定时间坐标满足下述条件：在空间中任何一直线上的单程光速为常数（包括无限大）,但其模数不为负数．满足这个条件的时间坐标?...     

基于PTP的多节点微震数据同步采集技术研究

为了同步微震监测系统中各分布式采集节点时钟和提高其精度,提出一种基于PTP(precision time protocol)时钟协议的微震数据同步采集设计方案。该方案将计算机时钟作为系统主时钟,以STM32为处理器,IP178CH为网卡驱动设计时钟分配器,并在其中植入PTP时钟协议,然后通过时钟分配器向网络中各采集节点周期性发送同步信号,最后通过时间偏差和网络延迟时间对每个节点的RTC时钟进行校准,使其与主时钟保持一致,从而实现了节点数据同步采集,其时钟同步精度达到了μs级。     

光晶格钟为守时设立新标准

<正>这类钟的优势在于使用的原子数量;它不是按照单个原子的节奏嘀嗒走针,而是同时与几千个原子同步。从1955年原子钟出现至今,量子时间计量的准则一直没有改变:将原子与外场隔离,调谐相干辐射源频率到原子跃迁,并通过对辐射振荡周期的计数来测量时间。     

氢钟测量死时间导致的光频测量统计不确定度分析

利用87Sr光晶格钟与氢钟的频率比对测量了氢钟的频率稳定度。在89%的光晶格钟有效运行率下，经过约10 d的测量得出氢钟的频率稳定度，并由此推导出氢钟噪声模型的相关参数。根据氢钟噪声模型生成的随机噪声序列，对由测量死时间导致的频差进行了100次模拟，并以模拟结果的1倍标准差为测量不确定度。不同有效运行率下，氢钟测量不确定度的计算结果表明，由氢钟测量死时间导致的不确定度随有效运行率的增加而减小，且在有效运行率小于10%时，增加总的测量时间可以显著减小测量不确定。     

基于BP神经网络模型时钟同步误差补偿算法

误差补偿是保证水下传感器网络时钟同步精度的一个重要保障,现有研究方法主要采用线性拟合和最小二乘法对时钟同步参数进行误差补偿,但该类方法并未考虑受海流影响时节点移动所导致的时钟同步精度问题.针对此问题,本文提出一种基于BP神经网络模型的时钟同步误差补偿算法.首先采用深海拉格朗日洋流模型描述水下节点运动规律,模拟水下节点运动速度,进而建立时钟同步参数模型,最后构建符合水下环境的BP神经网络时钟同步误差补偿模型,通过定义激励函数,引入正则项因子和补偿性因子避免模型过拟合,建立误差反向传播的BP神经网络模型时钟同步误差补偿算法.仿真实验表明,本文提出的算法与TSHL算法、MU-sync算法、MM-sync算法相比,在时钟同步精度(即时钟同步时间与标准时间的误差)上分别提升了37.42%, 17.29%和21.86%,并且均方误差得到显著降低.     

光晶格钟为守时设立新标准

这类钟的优势在于使用的原子数量;它不是按照单个原子的节奏嘀嗒走针,而是同时与几千个原子同步。     

基于GPS/北斗共视技术的铷钟驯服方法

在分析了现有铷钟驯服方法的基础上,提出了一种基于GPS/北斗共视技术的铷钟驯服方法,将铷钟的输出频率驯服到时间频率的最高国家基准UTC(NIM)上。试验结果表明,本文提出的方法可以有效实现对铷钟的驯服,经驯服的铷钟频率信号指标良好,能够提供铯钟量级的高精度频率标准。     

EtherCAT时钟同步技术研究

EtherCAT是一种实时工业以太网协议;基于EtherCAT实时性强的特点,重点研究了EtherCAT分布时钟机制,并提出了在嵌入式设备上基于实时操作系统μC/OS II完成主站设计的方案;通过分析传输延时补偿、初始偏移补偿、动态漂移补偿等时钟同步过程,完成了对主站系统时钟同步技术的设计;基于环形冗余结构搭建了一主三从的EtherCAT测试系统,并通过计算机、示波器等设备采集得到从站间产生SYNC0信号的时间差值数据;最后,根据SYNC0周期为1 ms的数据,分析得到系统时钟误差维持在55 ns以内的同步性能,为时钟同步技术的理论研究提供了数据支持。     

基于光纤环形网的多点高精度时频传递方法

研究了基于光纤环形网的多点高精度时频传递的方法,提出了终端站对钟差自感知的方案,将对钟差的感知测量以及补偿转移到终端站执行,实现网络中各个终端站与中心站的时频同步。搭建了长度为100 km的光纤环形网多点时频传递系统,实验研究了链路中色散带来的不对称性偏差的校消方法,验证了链路温度变化下的多点时频传递性能,测量的时频传递同步误差的峰峰值低于400 ps,均方根误差小于60 ps,表明终端站可以在光纤环形网的任意位置灵活接入。     

《广义相对论入门讲座》连载——时间与空间

1坐标钟与标准钟对于弯曲时空的任意坐标系x~μ(μ=0,1,2,3),如果视x0为时间坐标,则以速率t=x~0/c运行的钟,叫坐标钟.t称为坐标时间.c是平直时空中的真空光速.     

Why two clocks synchronize: energy balance of the synchronized clocks

We consider the synchronization of two clocks which are accurate (show the same time) but have pendulums with different masses. We show that such clocks hanging on the same beam beside the complete (in-phase) and antiphase synchronizations perform the third type of synchronization in which the difference of the pendulums' displacements is a periodic function of time. We identify this period to be a few times larger than the period of pendulums' oscillations in the case when the beam is at rest. Our approximate analytical analysis allows to derive the synchronizations conditions, explains the observed types of synchronizations, and gives the approximate formula for both the pendulums' amplitudes and the phase shift between them. We consider the energy balance in the system and show how the energy is transferred between pendulums via oscillating beam allowing pendulums' synchronization.     

Satellite virtual atomic clock with pseudorange difference function

Satellite atomic clocks are the basis of GPS for the control of time and frequency of navigation signals. In the Chinese Area Positioning System (CAPS), a satellite navigation system without the satellite atomic clocks onboard is successfully developed. Thus, the method of time synchronization based on satellite atomic clocks in GPS is not suitable. Satellite virtual atomic clocks are used to implement satellite navigation. With the satellite virtual atomic clocks, the time at which the signals are transmitted from the ground can be delayed into the time that the signals are transmitted from the satellites and the pseudorange measuring can be fulfilled as in GPS. Satellite virtual atomic clocks can implement the navigation, make a pseudorange difference, remove the ephemeris error, and improve the accuracy of navigation positioning. They not only provide a navigation system without satellite clocks, but also a navigation system with pseudorange difference. Supported by the National Basic Research Program of China (Grant No. 2007CB815502) and the National High Technology Research and Development Program of China (Grant No. 2007AA12Z300)     

Time synchronization and carrier frequency control of CAPS navigation signals generated on the ground

The Chinese Area Positioning System (CAPS) works without atomic clocks on the satellite, and the CAPS navigation signals transmitted on the ground may achieve the same effect as that with high-performance atomic clocks on the satellite. The primary means of achieving that effect is through the time synchronization and carrier frequency control of the CAPS navigation signals generated on the ground. In this paper the synchronization requirements of different time signals are analyzed by the formation of navigation signals, and the theories and methods of the time synchronization of the CAPS navigation signals generated on the ground are also introduced. According to the conditions of the high-precision satellite velocity-measurement signal source, the carrier frequency and its chains of the navigation signals are constructed. CAPS velocity measurement is realized by the expected deviation of real time control to the carrier frequency, and the precision degree of this method is also analyzed. The experimental results show that the time synchronization precision of CAPS generating signals is about 0.3 ns and the precision of the velocity measurement signal source is about 4 cm/s. This proves that the theories and methods of the generating time synchronization and carrier frequency control are workable. Supported by the Major Knowledge Innovation Programs of the Chinese Academy of Sciences (Grant No. KGCX1-21), the National High Technology Research and Development Program of China (Grant Nos. 2004AA105030 and 2006AA12Z314), the National Natural Science Foundation of China (Grant No. 10453001), and the Major State Basic Research Development Program of China (Grant No. 2007CB815502)     

Lorentz Covariant Canonical Formalism for Free Massive, Massless and Tachyonic Particles

We construct a consistent Lorentz-covariant canonical formalism for a free massive, massless and tachyonic particle in the framework of the absolute synchronization scheme of clocks. In the case of a massive particle our approach is canonically equivalent to the standard formulation which is not manifestly covariant. The absolute synchronization scheme seems to be the only one we can apply in the case of massless and tachyonic particles.     

Adjustability as a requirement of ideal clocks

A coordinate frame is considered as an arrangement of clocks that meet certain criteria of synchronization. Einstein's ideal clock is compared with the behavior required for clocks to maintain synchrony in the group of coordinate frames that leaves Maxwell's equations invariant. The required clock rates differ from the rate of Einstein's clock. An ideal adjustable clock is defined as an Einstein clock augmented by variable “gearing” that can offset its rate. Ongoing adjustment of these clocks enables them to meet all synchronization criteria in the group of coordinate frames. The need for adjustment is due to the well known invariance of Maxwell's equations under a group of coordinate transformations larger than the Lorentz group, and has nothing to do with imperfections in clocks. It is shown that the adjustments needed by ideal adjustable clocks to maintain synchrony can be measurably separated from additional adjustments that may be needed to compensate for random imperfections. The necessity for adjustment brings with it the necessity for ongoing measurement of the light signals whose exchange defines synchronization. Implications are discussed, both for the interpretation of Maxwell's equations and for the role of measuring instruments.     

Satellite test for dragging of inertial frames

It is shown that it is possible by using the lack of synchronization of clocks by light signal synchronization in elliptical orbits to test for the dragging of inertial frames in Einstein's theory of general relativity. Possible experiments are discussed.     

On the use of clocks in satellites for the testing of dragging of inertial frames in Einstein's general relativity

It is shown that it is possible by using the lack of synchronization of clocks by light signal synchronization in circular orbits to test for the dragging of inertial frames in Einsteins's theory of general relativity. Possible experiments are discussed.     

How to Define the Equality of Durations in Measurement of Time

We develop the research on measurement of time worked by Poincarh, Einstein, Landau and other researchers. Based on the convention that the velocity of light is isotropic and is a constant in empty spacetime, we not only answer the question about the definition of the synchronization of rate of clocks located at different places, but also find the solution to the issue of how to define the equality of two durations in measurement of time.     

Multipartite Quantum Clock Synchronization under The Influence of Unruh Thermal Noise

A protocol for multipartite quantum clock synchronization is performed under the influence of Unruh thermal noise. The dynamics of multipartite quantum system consisting of Unruh–DeWitt detectors when one of the detectors is accelerated are obtained. To estimate the time difference between the clocks, the time probability is calculated and how the probability is influenced by the Unruh thermal noise and other factors is analyzed. It is shown that both relativistic motion and interaction between the atom and the external scalar field affect the choice of optimal number of excited atoms in the initial state, which leads to a higher clock adjustment accuracy. Time probabilities for different types of initial states approach the same value in the limit of infinite acceleration, while tend to different minimums with increasing number of atoms. In addition, the accuracy of clock synchronization using a pair of entangled clocks in two‐party system is always higher than in a multipartite system, while the optimal Z‐type multipartite initial state always performs better than the W‐type state.     

Consequential noise-induced synchronization of indirectly coupled self-sustained oscillators

We consider the dynamics of identical self-sustained oscillators coupled via a common linear system (beam), which is perturbed by noise. We demonstrate that increasing the noise intensity induces complete synchronization between the oscillators and, surprisingly, their in-phase synchronization with the beam. This new phenomenon of in-phase synchronization of both the oscillators and the oscillating beam arises when the noise intensity exceeds a threshold value, and can not appear in the deterministic case where the beam stably oscillates in anti-phase with the synchronized oscillators (as it is in the case of the Huygens clocks synchronization). Similar behavior persists for slightly non-identical oscillators.