The composite time scale(CTS) provides an accurate and stable time-frequency reference for modern science and technology. Conventional CTS always features a centralized network topology, which means that the CTS is ac...The composite time scale(CTS) provides an accurate and stable time-frequency reference for modern science and technology. Conventional CTS always features a centralized network topology, which means that the CTS is accompanied by a local master clock. This largely restricts the stability and reliability of the CTS. We simulate the restriction and analyze the influence of the master clock on the CTS. It proves that the CTS's long-term stability is also positively related to that of the master clock, until the region dominated by the frequency drift of the H-maser(averaging time longer than ~10~5s).Aiming at this restriction, a real-time clock network is utilized. Based on the network, a real-time CTS referenced by a stable remote master clock is achieved. The experiment comparing two real-time CTSs referenced by a local and a remote master clock respectively reveals that under open-loop steering, the stability of the CTS is improved by referencing to a remote and more stable master clock instead of a local and less stable master clock. In this way, with the help of the proposed scheme, the CTS can be referenced to the most stable master clock within the network in real time, no matter whether it is local or remote, making democratic polycentric timekeeping possible.展开更多
Africa misappropriates time as it does to other resources, such as minerals. With this tradition, everything on the continent is always running behind schedule.
The relationship and the mutual benefits of timekeeping and Global Navigation Satellite Systems(GNSS)are reviewed,showing how each field has been enriched and will continue to progress,based on the progress of the oth...The relationship and the mutual benefits of timekeeping and Global Navigation Satellite Systems(GNSS)are reviewed,showing how each field has been enriched and will continue to progress,based on the progress of the other field.The role of GNSSs in the calculation of Coordinated Universal Time(UTC),as well as the capacity of GNSSs to provide UTC time dissemination services are described,leading now to a time transfer accuracy of the order of 1-2 ns.In addition,the fundamental role of atomic clocks in the GNSS positioning is illustrated.The paper presents a review of the current use of GNSS in the international timekeeping system,as well as illustrating the role of GNSS in disseminating time,and use the time and frequency metrology as fundamentals in the navigation service.展开更多
The timescales incorporated into the Primary Frequency Standard(PFS)exhibit excellent stability and accuracy.However,during the dead time of PFS,the reliability of the timescale can be compromised.To address this issu...The timescales incorporated into the Primary Frequency Standard(PFS)exhibit excellent stability and accuracy.However,during the dead time of PFS,the reliability of the timescale can be compromised.To address this issue,a resilient timekeeping algorithm with a Multi-observation Fusion Kalman Filter(MFKF)is proposed.This algorithm fuses the frequency measurements from hydrogen masers with various reference frequency standards,including PFS and commercial cesium beam atomic clocks.The simulation results show that the time deviation and instability of the timescale generated by MFKF are improved compared to those with Kalman filtering.The experimental results demonstrate that even within 70 days of PFS dead time the resilient timescale generated by MFKF can operate reliably.Furthermore,it is theoretically proven that MFKF produces a smaller post-covariance than that with singleobservation Kalman filtering.展开更多
In mathematics, space encompasses various structured sets such as Euclidean, metric, or vector space. This article introduces temporal space—a novel concept independent of traditional spatial dimensions and frames of...In mathematics, space encompasses various structured sets such as Euclidean, metric, or vector space. This article introduces temporal space—a novel concept independent of traditional spatial dimensions and frames of reference, accommodating multiple object-oriented durations in a dynamical system. The novelty of building temporal space using finite geometry is rooted in recent advancements in the theory of relationalism which utilizes Euclidean geometry, set theory, dimensional analysis, and a causal signal system. Multiple independent and co-existing cyclic durations are measurable as a network of finite one-dimensional timelines. The work aligns with Leibniz’s comments on relational measures of duration with the addition of using discrete cyclic relational events that define these finite temporal spaces, applicable to quantum and classical physics. Ancient formulas have symmetry along with divisional and subdivisional orders of operations that create discrete and ordered temporal geometric elements. Elements have cyclically conserved symmetry but unique cyclic dimensional quantities applicable for anchoring temporal equivalence relations in linear time. We present both fixed equivalences and expanded periods of temporal space offering a non-Greek calendar methodology consistent with ancient global timekeeping descriptions. Novel applications of Euclid’s division algorithm and Cantor’s pairing function introduce a novel paired function equation. The mathematical description of finite temporal space within relationalism theory offers an alternative discrete geometric methodology for examining ancient timekeeping with new hypotheses for Egyptian calendars.展开更多
NTP is nowadays the most widely used distributed network time protocol, which aims at synchronizing the clocks of computers in a network and keeping the accuracy and validation of the time information which is transmi...NTP is nowadays the most widely used distributed network time protocol, which aims at synchronizing the clocks of computers in a network and keeping the accuracy and validation of the time information which is transmitted in the network. Without automatic configuration mechanism, the stability and flexibility of the synchronization network built upon NTP protocol are not satisfying. P2P’s resource discovery mechanism is used to look for time sources in a synchronization network, and according to the network environment and node’s quality, the synchronization network is constructed dynamically.展开更多
One sunny morning,students are in a classroom Jake shows his smart watch,"It tells time,the heart rate,and the weather!""It's easy to know the time now,"Ms.Lee walks in,with a smile on her face...One sunny morning,students are in a classroom Jake shows his smart watch,"It tells time,the heart rate,and the weather!""It's easy to know the time now,"Ms.Lee walks in,with a smile on her face."But how did people know the time in ancient times?"展开更多
Circadian rhythm is a self-sustaining endogenous oscillation that serves as an internal timekeeping mechanism adapted to the Earth’s 24-h rotational schedule.It exists ubiquitously in nearly all organisms,from prokar...Circadian rhythm is a self-sustaining endogenous oscillation that serves as an internal timekeeping mechanism adapted to the Earth’s 24-h rotational schedule.It exists ubiquitously in nearly all organisms,from prokaryotes to mammals,and regulates diverse physiological and behavioral processes by synchronizing them with environmental fluctuations[1].Previous reports indicated that circadian rhythms exist in biological individuals and cells cultured in vitro[2].The mammalian circadian rhythm system consists of a central pacemaker located in the suprachiasmatic nucleus(SCN)of the hypothalamus,which coordinates peripheral rhythms through the sympathetic and parasympathetic nervous systems[3].This hierarchical mechanism uses neural populations as optimal models for circadian rhythm research.展开更多
The system time of the four major navigation satellite systems is mainly maintained by multiple high-performance atomic clocks at ground stations.This operational mode relies heavily on the support of ground stations....The system time of the four major navigation satellite systems is mainly maintained by multiple high-performance atomic clocks at ground stations.This operational mode relies heavily on the support of ground stations.To enhance the high-precision autonomous timing capability of next-generation navigation satellites,it is necessary to autonomously generate a comprehensive space-based time scale on orbit and make long-term,high-precision predictions for the clock error of this time scale.In order to solve these two problems,this paper proposed a two-level satellite timing system,and used multiple time-keeping node satellites to generate a more stable space-based time scale.Then this paper used the sparse sampling Long Short-Term Memory(LSTM)algorithm to improve the accuracy of clock error long-term prediction on space-based time scale.After simulation,at sampling times of 300 s,8.64×10^(4) s,and 1×10^(6) s,the frequency stabilities of the spaceborne timescale reach 1.35×10^(-15),3.37×10^(-16),and 2.81×10^(-16),respectively.When applying the improved clock error prediction algorithm,the ten-day prediction error is 3.16×10^(-10) s.Compared with those of the continuous sampling LSTM,Kalman filter,polynomial and quadratic polynomial models,the corresponding prediction accuracies are 1.72,1.56,1.83 and 1.36 times greater,respectively.展开更多
基金supported in part by the National Natural Science Foundation of China (Grant No.61971259)the National Key R&D Program of China (Grant No.2021YFA1402102)Tsinghua University Initiative Scientific Research Program。
文摘The composite time scale(CTS) provides an accurate and stable time-frequency reference for modern science and technology. Conventional CTS always features a centralized network topology, which means that the CTS is accompanied by a local master clock. This largely restricts the stability and reliability of the CTS. We simulate the restriction and analyze the influence of the master clock on the CTS. It proves that the CTS's long-term stability is also positively related to that of the master clock, until the region dominated by the frequency drift of the H-maser(averaging time longer than ~10~5s).Aiming at this restriction, a real-time clock network is utilized. Based on the network, a real-time CTS referenced by a stable remote master clock is achieved. The experiment comparing two real-time CTSs referenced by a local and a remote master clock respectively reveals that under open-loop steering, the stability of the CTS is improved by referencing to a remote and more stable master clock instead of a local and less stable master clock. In this way, with the help of the proposed scheme, the CTS can be referenced to the most stable master clock within the network in real time, no matter whether it is local or remote, making democratic polycentric timekeeping possible.
文摘Africa misappropriates time as it does to other resources, such as minerals. With this tradition, everything on the continent is always running behind schedule.
文摘The relationship and the mutual benefits of timekeeping and Global Navigation Satellite Systems(GNSS)are reviewed,showing how each field has been enriched and will continue to progress,based on the progress of the other field.The role of GNSSs in the calculation of Coordinated Universal Time(UTC),as well as the capacity of GNSSs to provide UTC time dissemination services are described,leading now to a time transfer accuracy of the order of 1-2 ns.In addition,the fundamental role of atomic clocks in the GNSS positioning is illustrated.The paper presents a review of the current use of GNSS in the international timekeeping system,as well as illustrating the role of GNSS in disseminating time,and use the time and frequency metrology as fundamentals in the navigation service.
基金This work was supported by the National Natural Science Foundation of China(Grant No.41931076)the National Key Research and Development Program of China(grant number 2020YFB0505801).
文摘The timescales incorporated into the Primary Frequency Standard(PFS)exhibit excellent stability and accuracy.However,during the dead time of PFS,the reliability of the timescale can be compromised.To address this issue,a resilient timekeeping algorithm with a Multi-observation Fusion Kalman Filter(MFKF)is proposed.This algorithm fuses the frequency measurements from hydrogen masers with various reference frequency standards,including PFS and commercial cesium beam atomic clocks.The simulation results show that the time deviation and instability of the timescale generated by MFKF are improved compared to those with Kalman filtering.The experimental results demonstrate that even within 70 days of PFS dead time the resilient timescale generated by MFKF can operate reliably.Furthermore,it is theoretically proven that MFKF produces a smaller post-covariance than that with singleobservation Kalman filtering.
文摘In mathematics, space encompasses various structured sets such as Euclidean, metric, or vector space. This article introduces temporal space—a novel concept independent of traditional spatial dimensions and frames of reference, accommodating multiple object-oriented durations in a dynamical system. The novelty of building temporal space using finite geometry is rooted in recent advancements in the theory of relationalism which utilizes Euclidean geometry, set theory, dimensional analysis, and a causal signal system. Multiple independent and co-existing cyclic durations are measurable as a network of finite one-dimensional timelines. The work aligns with Leibniz’s comments on relational measures of duration with the addition of using discrete cyclic relational events that define these finite temporal spaces, applicable to quantum and classical physics. Ancient formulas have symmetry along with divisional and subdivisional orders of operations that create discrete and ordered temporal geometric elements. Elements have cyclically conserved symmetry but unique cyclic dimensional quantities applicable for anchoring temporal equivalence relations in linear time. We present both fixed equivalences and expanded periods of temporal space offering a non-Greek calendar methodology consistent with ancient global timekeeping descriptions. Novel applications of Euclid’s division algorithm and Cantor’s pairing function introduce a novel paired function equation. The mathematical description of finite temporal space within relationalism theory offers an alternative discrete geometric methodology for examining ancient timekeeping with new hypotheses for Egyptian calendars.
文摘NTP is nowadays the most widely used distributed network time protocol, which aims at synchronizing the clocks of computers in a network and keeping the accuracy and validation of the time information which is transmitted in the network. Without automatic configuration mechanism, the stability and flexibility of the synchronization network built upon NTP protocol are not satisfying. P2P’s resource discovery mechanism is used to look for time sources in a synchronization network, and according to the network environment and node’s quality, the synchronization network is constructed dynamically.
文摘One sunny morning,students are in a classroom Jake shows his smart watch,"It tells time,the heart rate,and the weather!""It's easy to know the time now,"Ms.Lee walks in,with a smile on her face."But how did people know the time in ancient times?"
基金funded by the National Natural Science Foundation of China(no.12275329,Nan Ding,and no.12175289,Jufang Wang)the West Light Foundation of The Chinese Academy of Sciences(xbzglzb2022003,Nan Ding)+2 种基金the Science and Technology Research Project of Gansu Province(no.145RTSA012,Jufang Wang,and no.21JR7RA108,Nan Ding)the Gansu Provincial Science Fund for Distinguished Young Scholars(no.22JR5RA942,Wei Wang)the CuiYing Science and Technology Innovation Program of the Second Hospital of Lanzhou University(CY2023-MS-A03,Wei Wang).
文摘Circadian rhythm is a self-sustaining endogenous oscillation that serves as an internal timekeeping mechanism adapted to the Earth’s 24-h rotational schedule.It exists ubiquitously in nearly all organisms,from prokaryotes to mammals,and regulates diverse physiological and behavioral processes by synchronizing them with environmental fluctuations[1].Previous reports indicated that circadian rhythms exist in biological individuals and cells cultured in vitro[2].The mammalian circadian rhythm system consists of a central pacemaker located in the suprachiasmatic nucleus(SCN)of the hypothalamus,which coordinates peripheral rhythms through the sympathetic and parasympathetic nervous systems[3].This hierarchical mechanism uses neural populations as optimal models for circadian rhythm research.
基金funded by the National Natural Science Foundation of China Youth Project (Grant No.12104485)funding support from the basic research project of Microsatellite Innovation Institute,Chinese Academy of Sciences with grant number JCZX2022B-03.
文摘The system time of the four major navigation satellite systems is mainly maintained by multiple high-performance atomic clocks at ground stations.This operational mode relies heavily on the support of ground stations.To enhance the high-precision autonomous timing capability of next-generation navigation satellites,it is necessary to autonomously generate a comprehensive space-based time scale on orbit and make long-term,high-precision predictions for the clock error of this time scale.In order to solve these two problems,this paper proposed a two-level satellite timing system,and used multiple time-keeping node satellites to generate a more stable space-based time scale.Then this paper used the sparse sampling Long Short-Term Memory(LSTM)algorithm to improve the accuracy of clock error long-term prediction on space-based time scale.After simulation,at sampling times of 300 s,8.64×10^(4) s,and 1×10^(6) s,the frequency stabilities of the spaceborne timescale reach 1.35×10^(-15),3.37×10^(-16),and 2.81×10^(-16),respectively.When applying the improved clock error prediction algorithm,the ten-day prediction error is 3.16×10^(-10) s.Compared with those of the continuous sampling LSTM,Kalman filter,polynomial and quadratic polynomial models,the corresponding prediction accuracies are 1.72,1.56,1.83 and 1.36 times greater,respectively.
