Clock synchronization has important applications in multi-agent collaboration(such as drone light shows,intelligent transportation systems,and game AI),group decision-making,and emergency rescue operations.Synchroniza...Clock synchronization has important applications in multi-agent collaboration(such as drone light shows,intelligent transportation systems,and game AI),group decision-making,and emergency rescue operations.Synchronization method based on pulse-coupled oscillators(PCOs)provides an effective solution for clock synchronization in wireless networks.However,the existing clock synchronization algorithms in multi-agent ad hoc networks are difficult to meet the requirements of high precision and high stability of synchronization clock in group cooperation.Hence,this paper constructs a network model,named DAUNet(unsupervised neural network based on dual attention),to enhance clock synchronization accuracy in multi-agent wireless ad hoc networks.Specifically,we design an unsupervised distributed neural network framework as the backbone,building upon classical PCO-based synchronization methods.This framework resolves issues such as prolonged time synchronization message exchange between nodes,difficulties in centralized node coordination,and challenges in distributed training.Furthermore,we introduce a dual-attention mechanism as the core module of DAUNet.By integrating a Multi-Head Attention module and a Gated Attention module,the model significantly improves information extraction capabilities while reducing computational complexity,effectively mitigating synchronization inaccuracies and instability in multi-agent ad hoc networks.To evaluate the effectiveness of the proposed model,comparative experiments and ablation studies were conducted against classical methods and existing deep learning models.The research results show that,compared with the deep learning networks based on DASA and LSTM,DAUNet can reduce the mean normalized phase difference(NPD)by 1 to 2 orders of magnitude.Compared with the attention models based on additive attention and self-attention mechanisms,the performance of DAUNet has improved by more than ten times.This study demonstrates DAUNet’s potential in advancing multi-agent ad hoc networking technologies.展开更多
A progressive decline in fertility is a well-documented aspect of female aging and is associated with a range of cellular and molecular alterations,including genomic instability and modifications in epigenetic regulat...A progressive decline in fertility is a well-documented aspect of female aging and is associated with a range of cellular and molecular alterations,including genomic instability and modifications in epigenetic regulation.Epigenetic clocks,which estimate biological age based on DNA methylation patterns,have been extensively utilized to evaluate general health status and the risk of various diseases.Despite their broad application,the utility of epigenetic clocks in assessing female reproductive health remains only partially characterized.This minireview consolidates recent advancements in the application of epigenetic clocks to evaluate the functional status of the female reproductive system.The objective is to investigate their potential for quantifying and predicting the biological age of reproductive tissues,thereby establishing a theoretical basis for clinical applications in reproductive medicine.To date,no comprehensive minireview has systematically examined multi-tissue epigenetic clock models in the context of female reproductive aging,positioning this minireview as a novel contribution to the field.展开更多
Owing to the presence of a low-energy,long-lived nuclear isomeric state,^(229)Th is an ideal candidate for developing the next generation clock—the nuclear clock—holding great promise for both applied and fundamenta...Owing to the presence of a low-energy,long-lived nuclear isomeric state,^(229)Th is an ideal candidate for developing the next generation clock—the nuclear clock—holding great promise for both applied and fundamental physics.The^(229)Th ionic nuclear optical clock has garnered considerable attention,attributed to its high precision with a relative uncertainty of≤1.5×10^(-19)and the potential for common-mode noise cancellation via self-comparison between the nuclear transition and the electronic transition of thorium ions.In this article,we focus on Th^(n+)ions(n=1,2,3)and present a comprehensive review of the current progress in the development of ionic nuclear clocks,covering essential steps such as ion generation,trapping,and cooling.Furthermore,we discuss the realization of a closed-loop clock cycle,addressing key aspects including stable isomer excitation and efficient isomer deexcitation.展开更多
The isomeric transition of thorium-229(^(229)Th),as the only known laser-accessible nuclear transition,offers the possibility for the development of a new generation of optical clocks.Solid-state nuclear optical clock...The isomeric transition of thorium-229(^(229)Th),as the only known laser-accessible nuclear transition,offers the possibility for the development of a new generation of optical clocks.Solid-state nuclear optical clock based on^(229)Th-doped crystals or thin films has attracted much attention due to its potential advantages in high stability,miniaturization,and robustness.This paper reviews the research progress of solid-state nuclear optical clock materials,analyzes the preparation,defects,and properties of the candidate solid material systems for^(229)Th,explores the influence of the local crystal environment on the nuclear transition,focuses on introducing the latest research results of crystal materials such as Th-doped CaF_(2)and LiSrAlF_(6),and looks forward to the future development direction of this field.It could provide a reference for the material selection and optimization of solid-state nuclear optical clocks.展开更多
We report the SrII optical lattice clock at the National Time Service Center(NTSC).In this system,a blackbody radiation shield with movable lattice mitigates blackbody radiation shifts through active temperature contr...We report the SrII optical lattice clock at the National Time Service Center(NTSC).In this system,a blackbody radiation shield with movable lattice mitigates blackbody radiation shifts through active temperature control.A shallow optical lattice with minimal tunneling minimizes AC Stark shifts.Phase-locked counter-propagating lattice beams and conductive vacuum viewports further reduce systematic uncertainties and a novel initial-state preparation method simplifies the system.Clock transition spectra achieve a linewidth of 2.5 Hz with a 400 ms clock pulse,and self-comparison stability reaches 5.1×10^(-16)at 1 s.These advancements give this clock the potential to be a critical platform for realizing outstanding systematic uncertainties in the future.展开更多
Recent advances in atomic optical clocks based on electronic transitions have achieved frequency uncertainties at the10^(-19)level,enabling wide applications in testing variations of physical constants,exploring dark ...Recent advances in atomic optical clocks based on electronic transitions have achieved frequency uncertainties at the10^(-19)level,enabling wide applications in testing variations of physical constants,exploring dark matter signatures,and enhancing precision metrology for position,navigation,and timing systems.To pursue higher-precision optical clocks,the development of nuclear optical clocks has emerged,with the^(229)Th system distinguished by its unique low-lying isomeric state at~8.4 eV and a natural linewidth of approximately 100μHz,promising uncertainties below 10^(-19).The intrinsic insensitivity of nuclear transitions to external perturbations and their subatomic-scale spatial confinement provide significant advantages over electronic transitions in mitigating environmental shifts.Recent experimental breakthroughs include the excitation of the nuclear clock transition in solid-state^(229)Th-doped crystals with spectral resolution at the k Hz level.However,critical challenges persist,particularly in implementing effective laser excitation schemes(e.g.,via the electronic bridge mechanism)and closed-loop quantum control in trapped ion systems.Addressing these requires comprehensive understanding of complex many-body interactions in^(229)Th,encompassing electronic structure,nuclear deformation,hyperfine and field shift,and solid-state environmental coupling.This review synthesizes recent advancements in(i)the characterization of nuclear and atomic structures of the^(229)Th nuclear clock,and(ii)precise evaluation and mitigation of external perturbations affecting the clock transitions.The analysis provides a solid theoretical and experimental foundation for optimizing^(229)Th-based nuclear clock performance.展开更多
Power is the major challenge threatening the progress of very large scale integration （VLSI） technology development. In ultra-deep submicron VLSI designs, clock network size must be minimized to reduce power consump...Power is the major challenge threatening the progress of very large scale integration （VLSI） technology development. In ultra-deep submicron VLSI designs, clock network size must be minimized to reduce power consumption, power supply noise, and the number of clock buffers which are vulnerable to process variations. Traditional design methodologies usually let the clock router independently undertake the clock network minimization. Since clock routing is based on register locations, register placement actually strongly influences the clock network size. This paper describes a clock network design methodology that optimizes register placement. For a given cell placement result, incremental modifications are performed based on the clock skew specifications by moving registers toward preferred locations that may reduce the clock network size. At the same time, the side-effects to logic cell placement, such as signal net wirelength and critical path delay, are controlled. Test results on benchmark circuits show that the methodology can considerably reduce clock network size with limited impact on signal net wirelength and critical path delay.展开更多
This paper investigates the synchronization problem of clock oscillators in nonlinear dynamical network with arbitrary time-delays.First,a dynamic synchronization algorithm based on consensus control strategy,named fa...This paper investigates the synchronization problem of clock oscillators in nonlinear dynamical network with arbitrary time-delays.First,a dynamic synchronization algorithm based on consensus control strategy,named fast averaging syn-chronization algorithm(FASA),is presented to find a solution to the synchronization problem.This algorithm can compensate the clock skew and offset differences between clock nodes,achieving the synchronization of clock nodes in a shorter time as compared to previous synchronization methods.Second,because of the dynamical performance of FASA,it is characterized from the perspective of compartmental dynamical system with arbitrary time-delays.In this case,the algorithm guarantees the states of all clock nodes in dynamical network converge to Lyapunov stable equilibria.Finally,numerical simulations and experimental results demonstrate the correctness and effciency of the FASA,which means that the clock nodes can reach global consensus,and the synchronization error can reach nanosecond order of magnitude.展开更多
When the cold atom clock operates in microgravity around the near-earth orbit, its performance will be affected by the fluctuation of magnetic field. A strategy is proposed to suppress the fluctuation of magnetic fiel...When the cold atom clock operates in microgravity around the near-earth orbit, its performance will be affected by the fluctuation of magnetic field. A strategy is proposed to suppress the fluctuation of magnetic field by additional coils, whose current is changed accordingly to compensate the magnetic fluctuation by the linear and incremental compensation. The flight model of the cold atom clock is tested in a simulated orbital magnetic environment and the magnetic field fluctuation in the Ramsey cavity is reduced from 17 nT to 2 nT, which implied the uncertainty due to the second order Zeeman shift is reduced to be less than 2×10^（-16）. In addition, utilizing the compensation, the magnetic field in the trapping zone can be suppressed from 7.5 μT to less than 0.3 μT to meet the magnetic field requirement of polarization gradients cooling of atoms.展开更多
This paper presents a source localization algorithm based on the source signal's time-difference-of-arrival(TDOA) for asynchronous wireless sensor network.To obtain synchronization among anchors,all anchors broadc...This paper presents a source localization algorithm based on the source signal's time-difference-of-arrival(TDOA) for asynchronous wireless sensor network.To obtain synchronization among anchors,all anchors broadcast signals periodically,the clock offsets and skews of anchor pairs can be estimated using broadcasting signal's time-of-arrivals(TOA) at anchors.A kalman filter is adopted to improve the accuracy of clock offsets and track the clock drifts due to random fluctuations.Once the source transmits signal,the TOAs at anchors are stamped respectively and source's TDOA error due to clock offset and skew of anchor pair can be mitigated by a compensation operation.Based on a Gaussian noise model,maximum likelihood estimation(MLE) for the source position is obtained.Performance issues are addressed by evaluating the Cramer-Rao lower bound and the selection of broadcasting period.The proposed algorithm is simple and effective,which has close performance with synchronous TDOA algorithm.展开更多
We presented a clock synchronization method that contained a clock adjusting algorithm and a frequency compensated clock to achieve precise synchronization among distributed clocks based on IEEE 1588 protocol.Further,...We presented a clock synchronization method that contained a clock adjusting algorithm and a frequency compensated clock to achieve precise synchronization among distributed clocks based on IEEE 1588 protocol.Further,we presented its application on Ethernet and implementation of the frequency compensated clock in a field programmable gate array(FPGA) as experiments.The results indicate that this method can support sub-microsecond synchronization with inexpensive standard crystal oscillators.展开更多
New synchronization algorithm and analysis of its convergence rate for clock oscillators in dynamical network with time-delays are presented.A network of nodes equipped with hardware clock oscillators with bounded dri...New synchronization algorithm and analysis of its convergence rate for clock oscillators in dynamical network with time-delays are presented.A network of nodes equipped with hardware clock oscillators with bounded drift is considered.Firstly,a dynamic synchronization algorithm based on consensus control strategy,namely fast averaging synchronization algorithm （FASA）,is presented to find the solutions to the synchronization problem.By FASA,each node computes the logical clock value based on its value of hardware clock and message exchange.The goal is to synchronize all the nodes＇ logical clocks as closely as possible.Secondly,the convergence rate of FASA is analyzed that proves it is related to the bound by a nondecreasing function of the uncertainty in message delay and network parameters.Then,FASA＇s convergence rate is proven by means of the robust optimal design.Meanwhile,several practical applications for FASA,especially the application to inverse global positioning system （IGPS） base station network are discussed.Finally,numerical simulation results demonstrate the correctness and efficiency of the proposed FASA.Compared FASA with traditional clock synchronization algorithms （CSAs）,the convergence rate of the proposed algorithm converges faster than that of the CSAs evidently.展开更多
We report a longitudinal Zeeman slower based on ring-shaped permanent magnetic dipoles used for the strontium optical lattice clock. The Zeeman slower is composed of 40 permanent magnets with the same outer diameter b...We report a longitudinal Zeeman slower based on ring-shaped permanent magnetic dipoles used for the strontium optical lattice clock. The Zeeman slower is composed of 40 permanent magnets with the same outer diameter but different inner diameters. The maximum variation of the axial field from its target values is less than 2%. In most parts of the Zeeman slower, the intensity variations of the field in radial spatial distribution are less than 0.1 roT. With this Zeeman slower, the strontium atoms are slowed down to 95m/s, and approximately 2% of the total atoms are slowed down to less than 50m/s.展开更多
We develop a permanent-magnet Zeeman slower with adjustable magnets along the longitudinal and radial directions.Produced by four arrays of cylindrical magnets, the longitudinal magnetic field in the slower is tunable...We develop a permanent-magnet Zeeman slower with adjustable magnets along the longitudinal and radial directions.Produced by four arrays of cylindrical magnets, the longitudinal magnetic field in the slower is tunable if relevant parameters vary, for example, laser detuning or intensity. The proposed Zeeman slower can be reconfigured for Sr atoms. Additionally,we demonstrate that the residual magnetic field produced by the permanent magnets in the magneto-optical trap region can be as small as 0.5 Gs.展开更多
As an extension of the＂teleparallel＂equivalent of general relativity,f（T）gravity is proposed to explain some puzzling cosmological behaviors,such as accelerating expansion of the Universe.Given the fact that modif...As an extension of the＂teleparallel＂equivalent of general relativity,f（T）gravity is proposed to explain some puzzling cosmological behaviors,such as accelerating expansion of the Universe.Given the fact that modified gravity also has impacts on the Solar System,we might test it during future interplanetary missions with ultrastable clocks.In this work,we investigate the effects of f（T）gravity on the dynamics of the clock and its time transfer link.Under these influences,theΛ-term and theα-term of f（T）gravity play important roles.Here,Λis the cosmological constant andαrepresents a model parameter in f（T）gravity that determines the divergence from teleparallel gravity at the first order approximation.We find that the signal of f（T）gravity in the time transfer is much more difficult to detect with the current state of development for clocks than those effects on dynamics of an interplanetary spacecraft with a bounded orbit with parameters 0.5 au≤a≤5.5 au and 0≤e≤0.1.展开更多
As technology scales down, clock distribution networks(CDNs) in integrated circuits(ICs) are becoming increasingly sensitive to single-event transients(SETs).The SET occurring in the CDN can even lead to failure of th...As technology scales down, clock distribution networks(CDNs) in integrated circuits(ICs) are becoming increasingly sensitive to single-event transients(SETs).The SET occurring in the CDN can even lead to failure of the entire circuit system. Understanding the factors that influence the SET sensitivity of the CDN is crucial to achieving radiation hardening of the CDN and realizing the design of highly reliable ICs. In this paper, the influences of different sequential elements(D-flip-flops and D-latches, the two most commonly used sequential elements in modern synchronous digital systems) on the SET susceptibility of the CDN were quantitatively studied. Electrical simulation and heavy ion experiment results reveal that the CDN-SET-induced incorrect latching is much more likely to occur in DFF and DFF-based designs. This can supply guidelines for the design of IC with high reliability.展开更多
By use of the global PPMLR Magnetohydrodynamics(MHD) model,a serial of quasisteady-state numerical simulations were conducted to examine the modulation property of the interplanetary magnetic field clock angle θ on t...By use of the global PPMLR Magnetohydrodynamics(MHD) model,a serial of quasisteady-state numerical simulations were conducted to examine the modulation property of the interplanetary magnetic field clock angle θ on the solar wind energy input into the magnetosphere.All the simulations can be divided into seven groups according to different criteria of solar wind conditions.For each group,37 numerical examples are analyzed,with the clock angle varying from 0° to 360° with an interval of 10°,keeping the other solar wind parameters(such as the solar wind number density,velocity,and the magnetic field magnitude) unchanged.As expected,the solar wind energy input into the magnetosphere is modulated by the IMF clock angle.The axisymmetrical bell-shaped curve peaks at the clock angle of 180°.However,the modulation effect remains invariant with varying other solar wind conditions.The function form of such an invariant modulation is found to be sin(0/2)^(2.70) + 0.25.展开更多
We present a precise measurement of171Yb magnetic constants for 1S_(0)-3P_(0) clock transition. The background magnetic field is firstly compensated to < 1 m Gs(1 Gs = 10^(-4)T) through measuring the splitting of t...We present a precise measurement of171Yb magnetic constants for 1S_(0)-3P_(0) clock transition. The background magnetic field is firstly compensated to < 1 m Gs(1 Gs = 10^(-4)T) through measuring the splitting of two π transitins of171Yb clock transition at different compensation coils currents. Then, the splitting ratios of the π and σ components of171Yb clock transition at different bias magnetic fields are measured, and the first-order Zeeman coefficient is determined to beα = 199.49(5) Hz/Gs. The second-order Zeeman shifts at various bias magnetic fields are also measured through interleaved self-comparison in which the bias magnetic fields are modulated between high and low values. The second-order Zeeman coefficient is fitted to be β =-6.09(3) Hz/m T^(2), which is consistent with the result of NIST group.展开更多
文摘Clock synchronization has important applications in multi-agent collaboration(such as drone light shows,intelligent transportation systems,and game AI),group decision-making,and emergency rescue operations.Synchronization method based on pulse-coupled oscillators(PCOs)provides an effective solution for clock synchronization in wireless networks.However,the existing clock synchronization algorithms in multi-agent ad hoc networks are difficult to meet the requirements of high precision and high stability of synchronization clock in group cooperation.Hence,this paper constructs a network model,named DAUNet(unsupervised neural network based on dual attention),to enhance clock synchronization accuracy in multi-agent wireless ad hoc networks.Specifically,we design an unsupervised distributed neural network framework as the backbone,building upon classical PCO-based synchronization methods.This framework resolves issues such as prolonged time synchronization message exchange between nodes,difficulties in centralized node coordination,and challenges in distributed training.Furthermore,we introduce a dual-attention mechanism as the core module of DAUNet.By integrating a Multi-Head Attention module and a Gated Attention module,the model significantly improves information extraction capabilities while reducing computational complexity,effectively mitigating synchronization inaccuracies and instability in multi-agent ad hoc networks.To evaluate the effectiveness of the proposed model,comparative experiments and ablation studies were conducted against classical methods and existing deep learning models.The research results show that,compared with the deep learning networks based on DASA and LSTM,DAUNet can reduce the mean normalized phase difference(NPD)by 1 to 2 orders of magnitude.Compared with the attention models based on additive attention and self-attention mechanisms,the performance of DAUNet has improved by more than ten times.This study demonstrates DAUNet’s potential in advancing multi-agent ad hoc networking technologies.
文摘A progressive decline in fertility is a well-documented aspect of female aging and is associated with a range of cellular and molecular alterations,including genomic instability and modifications in epigenetic regulation.Epigenetic clocks,which estimate biological age based on DNA methylation patterns,have been extensively utilized to evaluate general health status and the risk of various diseases.Despite their broad application,the utility of epigenetic clocks in assessing female reproductive health remains only partially characterized.This minireview consolidates recent advancements in the application of epigenetic clocks to evaluate the functional status of the female reproductive system.The objective is to investigate their potential for quantifying and predicting the biological age of reproductive tissues,thereby establishing a theoretical basis for clinical applications in reproductive medicine.To date,no comprehensive minireview has systematically examined multi-tissue epigenetic clock models in the context of female reproductive aging,positioning this minireview as a novel contribution to the field.
基金Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0920000)the National Natural Science Foundation of China(Grant No.12341401)。
文摘Owing to the presence of a low-energy,long-lived nuclear isomeric state,^(229)Th is an ideal candidate for developing the next generation clock—the nuclear clock—holding great promise for both applied and fundamental physics.The^(229)Th ionic nuclear optical clock has garnered considerable attention,attributed to its high precision with a relative uncertainty of≤1.5×10^(-19)and the potential for common-mode noise cancellation via self-comparison between the nuclear transition and the electronic transition of thorium ions.In this article,we focus on Th^(n+)ions(n=1,2,3)and present a comprehensive review of the current progress in the development of ionic nuclear clocks,covering essential steps such as ion generation,trapping,and cooling.Furthermore,we discuss the realization of a closed-loop clock cycle,addressing key aspects including stable isomer excitation and efficient isomer deexcitation.
基金supported by Zhangjiang Laboratory(Grant No.ZJSP21A001D)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0920000)the National Natural Science Foundation of China(Grant Nos.12341402 and 12341403)。
文摘The isomeric transition of thorium-229(^(229)Th),as the only known laser-accessible nuclear transition,offers the possibility for the development of a new generation of optical clocks.Solid-state nuclear optical clock based on^(229)Th-doped crystals or thin films has attracted much attention due to its potential advantages in high stability,miniaturization,and robustness.This paper reviews the research progress of solid-state nuclear optical clock materials,analyzes the preparation,defects,and properties of the candidate solid material systems for^(229)Th,explores the influence of the local crystal environment on the nuclear transition,focuses on introducing the latest research results of crystal materials such as Th-doped CaF_(2)and LiSrAlF_(6),and looks forward to the future development direction of this field.It could provide a reference for the material selection and optimization of solid-state nuclear optical clocks.
基金supported by the Innovation Pro-gram for Quantum Science and Technology(Grant Nos.2021ZD0300900 and 2021ZD0300902)the Strate-gic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB35010202)the Operation and Maintenance of Major Scientific and Technological In-frastructure of the Chinese Academy of Sciences(Grant No.2024000014).
文摘We report the SrII optical lattice clock at the National Time Service Center(NTSC).In this system,a blackbody radiation shield with movable lattice mitigates blackbody radiation shifts through active temperature control.A shallow optical lattice with minimal tunneling minimizes AC Stark shifts.Phase-locked counter-propagating lattice beams and conductive vacuum viewports further reduce systematic uncertainties and a novel initial-state preparation method simplifies the system.Clock transition spectra achieve a linewidth of 2.5 Hz with a 400 ms clock pulse,and self-comparison stability reaches 5.1×10^(-16)at 1 s.These advancements give this clock the potential to be a critical platform for realizing outstanding systematic uncertainties in the future.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDB0920100 and XDB0920101)the National Natural Science Foundation of China(Grant Nos.12174402,12393821,12274417)the Chinese Academy of Sciences Project for Young Scientists in Basic Research(Grant No.YSBR-055)。
文摘Recent advances in atomic optical clocks based on electronic transitions have achieved frequency uncertainties at the10^(-19)level,enabling wide applications in testing variations of physical constants,exploring dark matter signatures,and enhancing precision metrology for position,navigation,and timing systems.To pursue higher-precision optical clocks,the development of nuclear optical clocks has emerged,with the^(229)Th system distinguished by its unique low-lying isomeric state at~8.4 eV and a natural linewidth of approximately 100μHz,promising uncertainties below 10^(-19).The intrinsic insensitivity of nuclear transitions to external perturbations and their subatomic-scale spatial confinement provide significant advantages over electronic transitions in mitigating environmental shifts.Recent experimental breakthroughs include the excitation of the nuclear clock transition in solid-state^(229)Th-doped crystals with spectral resolution at the k Hz level.However,critical challenges persist,particularly in implementing effective laser excitation schemes(e.g.,via the electronic bridge mechanism)and closed-loop quantum control in trapped ion systems.Addressing these requires comprehensive understanding of complex many-body interactions in^(229)Th,encompassing electronic structure,nuclear deformation,hyperfine and field shift,and solid-state environmental coupling.This review synthesizes recent advancements in(i)the characterization of nuclear and atomic structures of the^(229)Th nuclear clock,and(ii)precise evaluation and mitigation of external perturbations affecting the clock transitions.The analysis provides a solid theoretical and experimental foundation for optimizing^(229)Th-based nuclear clock performance.
基金the National Natural Science Foundation of China (No. 60776026)
文摘Power is the major challenge threatening the progress of very large scale integration （VLSI） technology development. In ultra-deep submicron VLSI designs, clock network size must be minimized to reduce power consumption, power supply noise, and the number of clock buffers which are vulnerable to process variations. Traditional design methodologies usually let the clock router independently undertake the clock network minimization. Since clock routing is based on register locations, register placement actually strongly influences the clock network size. This paper describes a clock network design methodology that optimizes register placement. For a given cell placement result, incremental modifications are performed based on the clock skew specifications by moving registers toward preferred locations that may reduce the clock network size. At the same time, the side-effects to logic cell placement, such as signal net wirelength and critical path delay, are controlled. Test results on benchmark circuits show that the methodology can considerably reduce clock network size with limited impact on signal net wirelength and critical path delay.
基金Supported by National Science Fund for Distinguished YoungScholars(60925011)
文摘This paper investigates the synchronization problem of clock oscillators in nonlinear dynamical network with arbitrary time-delays.First,a dynamic synchronization algorithm based on consensus control strategy,named fast averaging syn-chronization algorithm(FASA),is presented to find a solution to the synchronization problem.This algorithm can compensate the clock skew and offset differences between clock nodes,achieving the synchronization of clock nodes in a shorter time as compared to previous synchronization methods.Second,because of the dynamical performance of FASA,it is characterized from the perspective of compartmental dynamical system with arbitrary time-delays.In this case,the algorithm guarantees the states of all clock nodes in dynamical network converge to Lyapunov stable equilibria.Finally,numerical simulations and experimental results demonstrate the correctness and effciency of the FASA,which means that the clock nodes can reach global consensus,and the synchronization error can reach nanosecond order of magnitude.
基金Project supported by the Ministry of Science and Technology of China(Grant No.2013YQ09094304)the Youth Innovation Promotion Association,Chinese Academy of Sciencesthe National Natural Science Foundation of China(Grant Nos.11034008 and 11274324)
文摘When the cold atom clock operates in microgravity around the near-earth orbit, its performance will be affected by the fluctuation of magnetic field. A strategy is proposed to suppress the fluctuation of magnetic field by additional coils, whose current is changed accordingly to compensate the magnetic fluctuation by the linear and incremental compensation. The flight model of the cold atom clock is tested in a simulated orbital magnetic environment and the magnetic field fluctuation in the Ramsey cavity is reduced from 17 nT to 2 nT, which implied the uncertainty due to the second order Zeeman shift is reduced to be less than 2×10^（-16）. In addition, utilizing the compensation, the magnetic field in the trapping zone can be suppressed from 7.5 μT to less than 0.3 μT to meet the magnetic field requirement of polarization gradients cooling of atoms.
基金supported by the National Natural Science Foundation of China under Grant No.61571452 and No.61201331
文摘This paper presents a source localization algorithm based on the source signal's time-difference-of-arrival(TDOA) for asynchronous wireless sensor network.To obtain synchronization among anchors,all anchors broadcast signals periodically,the clock offsets and skews of anchor pairs can be estimated using broadcasting signal's time-of-arrivals(TOA) at anchors.A kalman filter is adopted to improve the accuracy of clock offsets and track the clock drifts due to random fluctuations.Once the source transmits signal,the TOAs at anchors are stamped respectively and source's TDOA error due to clock offset and skew of anchor pair can be mitigated by a compensation operation.Based on a Gaussian noise model,maximum likelihood estimation(MLE) for the source position is obtained.Performance issues are addressed by evaluating the Cramer-Rao lower bound and the selection of broadcasting period.The proposed algorithm is simple and effective,which has close performance with synchronous TDOA algorithm.
基金the Natural Science Foundation of Hubei (No.2006ABA065)
文摘We presented a clock synchronization method that contained a clock adjusting algorithm and a frequency compensated clock to achieve precise synchronization among distributed clocks based on IEEE 1588 protocol.Further,we presented its application on Ethernet and implementation of the frequency compensated clock in a field programmable gate array(FPGA) as experiments.The results indicate that this method can support sub-microsecond synchronization with inexpensive standard crystal oscillators.
基金Sponsored by the Cooperation Building Foundation Project of Beijing Education Committee (100070
文摘New synchronization algorithm and analysis of its convergence rate for clock oscillators in dynamical network with time-delays are presented.A network of nodes equipped with hardware clock oscillators with bounded drift is considered.Firstly,a dynamic synchronization algorithm based on consensus control strategy,namely fast averaging synchronization algorithm （FASA）,is presented to find the solutions to the synchronization problem.By FASA,each node computes the logical clock value based on its value of hardware clock and message exchange.The goal is to synchronize all the nodes＇ logical clocks as closely as possible.Secondly,the convergence rate of FASA is analyzed that proves it is related to the bound by a nondecreasing function of the uncertainty in message delay and network parameters.Then,FASA＇s convergence rate is proven by means of the robust optimal design.Meanwhile,several practical applications for FASA,especially the application to inverse global positioning system （IGPS） base station network are discussed.Finally,numerical simulation results demonstrate the correctness and efficiency of the proposed FASA.Compared FASA with traditional clock synchronization algorithms （CSAs）,the convergence rate of the proposed algorithm converges faster than that of the CSAs evidently.
基金Supported by the National Natural Science Foundation of China under Grant No 91336212
文摘We report a longitudinal Zeeman slower based on ring-shaped permanent magnetic dipoles used for the strontium optical lattice clock. The Zeeman slower is composed of 40 permanent magnets with the same outer diameter but different inner diameters. The maximum variation of the axial field from its target values is less than 2%. In most parts of the Zeeman slower, the intensity variations of the field in radial spatial distribution are less than 0.1 roT. With this Zeeman slower, the strontium atoms are slowed down to 95m/s, and approximately 2% of the total atoms are slowed down to less than 50m/s.
基金Project supported by the National Key Basic Research and Development Program of China(Grant Nos.2012CB821302 and 2016YFA0302103)the National Natural Science Foundation of China(Grant No.11134003)+1 种基金the National High Technology Research and Development Program of China(Grant No.2014AA123401)the Shanghai Excellent Academic Leaders Program of China(Grant No.12XD1402400)
文摘We develop a permanent-magnet Zeeman slower with adjustable magnets along the longitudinal and radial directions.Produced by four arrays of cylindrical magnets, the longitudinal magnetic field in the slower is tunable if relevant parameters vary, for example, laser detuning or intensity. The proposed Zeeman slower can be reconfigured for Sr atoms. Additionally,we demonstrate that the residual magnetic field produced by the permanent magnets in the magneto-optical trap region can be as small as 0.5 Gs.
基金Supported by the National Natural Science Foundation of China (Grant No. 11103010)funded by the Natural Science Foundation of China (Grant No. 11103085)+3 种基金the Fundamental Research Program of Jiangsu Province of China (Grant No. BK20131461Grant No. BK2011553)the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20110091120003)the Fundamental Research Funds for the Central Universities (No. 1107020116)
文摘As an extension of the＂teleparallel＂equivalent of general relativity,f（T）gravity is proposed to explain some puzzling cosmological behaviors,such as accelerating expansion of the Universe.Given the fact that modified gravity also has impacts on the Solar System,we might test it during future interplanetary missions with ultrastable clocks.In this work,we investigate the effects of f（T）gravity on the dynamics of the clock and its time transfer link.Under these influences,theΛ-term and theα-term of f（T）gravity play important roles.Here,Λis the cosmological constant andαrepresents a model parameter in f（T）gravity that determines the divergence from teleparallel gravity at the first order approximation.We find that the signal of f（T）gravity in the time transfer is much more difficult to detect with the current state of development for clocks than those effects on dynamics of an interplanetary spacecraft with a bounded orbit with parameters 0.5 au≤a≤5.5 au and 0≤e≤0.1.
基金supported by the National Natural Science Foundation of China(No.61434007)the National Natural Science Foundation of China(No.61704192)
文摘As technology scales down, clock distribution networks(CDNs) in integrated circuits(ICs) are becoming increasingly sensitive to single-event transients(SETs).The SET occurring in the CDN can even lead to failure of the entire circuit system. Understanding the factors that influence the SET sensitivity of the CDN is crucial to achieving radiation hardening of the CDN and realizing the design of highly reliable ICs. In this paper, the influences of different sequential elements(D-flip-flops and D-latches, the two most commonly used sequential elements in modern synchronous digital systems) on the SET susceptibility of the CDN were quantitatively studied. Electrical simulation and heavy ion experiment results reveal that the CDN-SET-induced incorrect latching is much more likely to occur in DFF and DFF-based designs. This can supply guidelines for the design of IC with high reliability.
基金Supported by the National Basic Research Program(2012CB825602)National Natural Science Foundation of China(NNSFC,41204118,41231067)in part by the Specialized Research Fund for State Key Laboratories of China
文摘By use of the global PPMLR Magnetohydrodynamics(MHD) model,a serial of quasisteady-state numerical simulations were conducted to examine the modulation property of the interplanetary magnetic field clock angle θ on the solar wind energy input into the magnetosphere.All the simulations can be divided into seven groups according to different criteria of solar wind conditions.For each group,37 numerical examples are analyzed,with the clock angle varying from 0° to 360° with an interval of 10°,keeping the other solar wind parameters(such as the solar wind number density,velocity,and the magnetic field magnitude) unchanged.As expected,the solar wind energy input into the magnetosphere is modulated by the IMF clock angle.The axisymmetrical bell-shaped curve peaks at the clock angle of 180°.However,the modulation effect remains invariant with varying other solar wind conditions.The function form of such an invariant modulation is found to be sin(0/2)^(2.70) + 0.25.
基金supported by the National Key Research and Development Program of China (Grant No. 2017YFA0304402)the National Natural Science Foundation of China (Grant Nos. U20A2075 and 11803072)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB21030100)。
文摘We present a precise measurement of171Yb magnetic constants for 1S_(0)-3P_(0) clock transition. The background magnetic field is firstly compensated to < 1 m Gs(1 Gs = 10^(-4)T) through measuring the splitting of two π transitins of171Yb clock transition at different compensation coils currents. Then, the splitting ratios of the π and σ components of171Yb clock transition at different bias magnetic fields are measured, and the first-order Zeeman coefficient is determined to beα = 199.49(5) Hz/Gs. The second-order Zeeman shifts at various bias magnetic fields are also measured through interleaved self-comparison in which the bias magnetic fields are modulated between high and low values. The second-order Zeeman coefficient is fitted to be β =-6.09(3) Hz/m T^(2), which is consistent with the result of NIST group.
