Due to fast-growing urbanization,the traffic management system becomes a crucial problem owing to the rapid growth in the number of vehicles The research proposes an Intelligent public transportation system where info...Due to fast-growing urbanization,the traffic management system becomes a crucial problem owing to the rapid growth in the number of vehicles The research proposes an Intelligent public transportation system where informa-tion regarding all the buses connecting in a city will be gathered,processed and accurate bus arrival time prediction will be presented to the user.Various linear and time-varying parameters such as distance,waiting time at stops,red signal duration at a traffic signal,traffic density,turning density,rush hours,weather conditions,number of passengers on the bus,type of day,road type,average vehi-cle speed limit,current vehicle speed affecting traffic are used for the analysis.The proposed model exploits the feasibility and applicability of ELM in the travel time forecasting area.Multiple ELMs(MELM)for explicitly training dynamic,road and trajectory information are used in the proposed approach.A large-scale dataset(historical data)obtained from Kerala State Road Transport Corporation is used for training.Simulations are carried out by using MATLAB R2021a.The experiments revealed that the efficiency of MELM is independent of the time of day and day of the week.It can manage huge volumes of data with less human intervention at greater learning speeds.It is found MELM yields prediction with accuracy in the range of 96.7%to 99.08%.The MAE value is between 0.28 to 1.74 minutes with the proposed approach.The study revealed that there could be regularity in bus usage and daily bus rides are predictable with a better degree of accuracy.The research has proved that MELM is superior for arrival time pre-dictions in terms of accuracy and error,compared with other approaches.展开更多
Serious stretch appears in shallow long offsset signals after NMO correction. In this article we study the generation mechanism of NMO stretch, demonstrate that the conventional travel time equation cannot accurately ...Serious stretch appears in shallow long offsset signals after NMO correction. In this article we study the generation mechanism of NMO stretch, demonstrate that the conventional travel time equation cannot accurately describe the travel time of the samples within the same reflection wavelet. As a result, conventional NMO inversion based on the travel time of the wavelet's central point occurs with errors. In this article, a travel time equation for the samples within the same wavelet is reconstructed through our theoretical derivation (the shifted first arrival point travel time equation), a new NMO inversion method based on the wavelet's first arrival point is proposed. While dealing with synthetic data, the semblance coefficient algorithm equation is modified so that wavelet first arrival points can be extracted. After that, NMO inversion based on the new velocity analysis is adopted on shot offset records. The precision of the results is significantly improved compared with the traditional method. Finally, the block move NMO correction based on the first arrival points travel times is adopted on long offset records and non-stretched results are achieved, which verify the proposed new equation.展开更多
为了解决传统室内定位技术成本较高、稳定性差以及难于部署等问题,提出一种将到达时间(time of arrival,TOA)与到达角(angle of arrival,AOA)相结合的室内定位系统.该系统由定位基站与被控定位单元组成,其特征在于使用对射式布置的超声...为了解决传统室内定位技术成本较高、稳定性差以及难于部署等问题,提出一种将到达时间(time of arrival,TOA)与到达角(angle of arrival,AOA)相结合的室内定位系统.该系统由定位基站与被控定位单元组成,其特征在于使用对射式布置的超声波传感器获取定位基站与被控定位单元之间的距离特征,利用角度传感器获取被控定位单元相对于定位基站的角度特征,以单基站就实现了精确的室内定位过程.分析了该系统基本结构与原理,建立定位与控制模型,在一定范围内对其定点定位精度与跟随定位精度进行了实验验证.实验结果表明:该系统结构简单,易于安装布置,鲁棒性强,在测试范围内的最大定点定位误差不超过5 cm,跟随定位误差不超过15 cm.展开更多
Free electron lasers provide high-power and ultrashort pulses with extreme brightness. In order to improve a facility's capabilities and explore the possibility of performing high-resolution time-resolved experime...Free electron lasers provide high-power and ultrashort pulses with extreme brightness. In order to improve a facility's capabilities and explore the possibility of performing high-resolution time-resolved experiments, a beam arrival time resolution under 100 fs is required. In this article, a novel beam arrival time monitor(BAM)equipped with two cavities has been designed and a beam flight time measurement scheme based on the BAM prototype has been proposed to estimate phase jitter in the signal measurement system. The two BAM cavities work at different frequencies and the frequency difference is designed to be 35 MHz. Therefore, a self-mixing intermediate frequency signal can be generated using the two cavities. The measured beam flight time shows a temporal deviation of 37 fs(rms).展开更多
How to predict the bus arrival time accurately is a crucial problem to be solved in Internet of Vehicle. Existed methods cannot solve the problem effectively for ignoring the traffic delay jitter. In this paper,a thre...How to predict the bus arrival time accurately is a crucial problem to be solved in Internet of Vehicle. Existed methods cannot solve the problem effectively for ignoring the traffic delay jitter. In this paper,a three-stage mixed model is proposed for bus arrival time prediction. The first stage is pattern training. In this stage,the traffic delay jitter patterns(TDJP)are mined by K nearest neighbor and K-means in the historical traffic time data. The second stage is the single-step prediction,which is based on real-time adjusted Kalman filter with a modification of historical TDJP. In the third stage,as the influence of historical law is increasing in long distance prediction,we combine the single-step prediction dynamically with Markov historical transfer model to conduct the multi-step prediction. The experimental results show that the proposed single-step prediction model performs better in accuracy and efficiency than short-term traffic flow prediction and dynamic Kalman filter. The multi-step prediction provides a higher level veracity and reliability in travel time forecasting than short-term traffic flow and historical traffic pattern prediction models.展开更多
To improve the accuracy of real-time public transport information release system, a collaborative prediction model was proposed based on cyber-physical systems architecture. In the model, the total bus travel time was...To improve the accuracy of real-time public transport information release system, a collaborative prediction model was proposed based on cyber-physical systems architecture. In the model, the total bus travel time was divided into three parts: running time, dwell time and intersection delay time, and the data were divided into three categories of historical data, static data and real-time data. The bus arrival time was obtained by fusion computing the real-time data in perception layer together with historical data and static data in collaborative layer. The validity of the collaborative model was verified by the data of a typical urban bus line in Shanghai, and 1538 sets of data were collected and analyzed from three different perspectives. By comparing the experimental results with the actual results, it is shown that the experimental results are with higher prediction accuracy, and the collaborative prediction model adopted is able to meet the demand for bus arrival prediction.展开更多
Accurately detecting the arrival time of a channel wave in a coal seam is very important for in-seam seismic data processing. The arrival time greatly affects the accuracy of the channel wave inversion and the compute...Accurately detecting the arrival time of a channel wave in a coal seam is very important for in-seam seismic data processing. The arrival time greatly affects the accuracy of the channel wave inversion and the computed tomography (CT) result. However, because the signal-to-noise ratio of in-seam seismic data is reduced by the long wavelength and strong frequency dispersion, accurately timing the arrival of channel waves is extremely difficult. For this purpose, we propose a method that automatically picks up the arrival time of channel waves based on multi-channel constraints. We first estimate the Jaccard similarity coefficient of two ray paths, then apply it as a weight coefficient for stacking the multi- channel dispersion spectra. The reasonableness and effectiveness of the proposed method is verified in an actual data application. Most importantly, the method increases the degree of automation and the pickup precision of the channel-wave arrival time.展开更多
In order to improve the accuracy and engineering feasibility of four-Satellite localization system, the frequency difference measurement is introduced to the four-Satellite TDOA (Time Difference of Arrival) localizati...In order to improve the accuracy and engineering feasibility of four-Satellite localization system, the frequency difference measurement is introduced to the four-Satellite TDOA (Time Difference of Arrival) localization algorithm. The TDOA/FDOA (Frequency Difference of Arrival) localization algorithm is used to optimize the GDOP (geometric dilution of precision) of four-Satellite localization. The simulation results show that the absolute position measurement accuracy has little influence on TDOA/FDOA localization accuracy as compared with TDOA localization. Under the same conditions, TDOA/FDOA localization has better accuracy and its GDOP shows more uniform distribution in diamond configuration case. The localization accuracy of four-Satellite TDOA/FDOA is better than the localization accuracy of four-Satellite TDOA.展开更多
Chao Lake is a Geoheritage site on the active Tan-Lu Fault between the Yangtze craton,the North China craton,and the Dabie orogenic belt in the southeast.This segment of the fault is not well constrained at depth part...Chao Lake is a Geoheritage site on the active Tan-Lu Fault between the Yangtze craton,the North China craton,and the Dabie orogenic belt in the southeast.This segment of the fault is not well constrained at depth partly due to the overprinting of the fault zone by intrusive materials and its relatively low seismic activity and sparse seismic station coverage.This study took advantage of a dense seismic array deployed around Chao Lake to delineate the P-wave velocity variations in the crust and uppermost mantle using teleseismic earthquake arrival time tomography.The station-pair double-difference with waveform crosscorrelation technique was employed.We used a multiscale resolution 3-D initial model derived from the combination of highresolution 3-D v S models within the region of interest to account for the lateral heterogeneity in the upper crust.The results revealed that the velocity of the upper crust is segmented with structures trending in the direction of the strike of the fault.Sedimentary basins are delineated on both sides of the fault with slow velocities,while the fault zone is characterized by high velocity in the crust and uppermost mantle.The high-velocity structure in the fault zone shows characteristics of magma intrusion that may be connected to the Mesozoic magmatism in and around the Middle and Lower Yangtze River Metallogenic Belt(MLYMB),implying that the Tan-Lu fault might have formed a channel for magma intrusion.Magmatic material in Chao Lake is likely connected to the partial melting,assimilation,storage,and homogenization of the uppermost mantle and the lower crustal rocks.The intrusions,however,seem to have suffered severe regional extension along the Tan-Lu fault driven by the eastward Paleo-Pacific plate subduction,thereby losing its deep trail due to extensional erosion.展开更多
Bus arrival time prediction contributes to the quality improvement of public transport services.Passengers can arrange departure time effectively if they know the accurate bus arrival time in advance.We proposed a mac...Bus arrival time prediction contributes to the quality improvement of public transport services.Passengers can arrange departure time effectively if they know the accurate bus arrival time in advance.We proposed a machine⁃learning approach,RTSI⁃ResNet,to forecast the bus arrival time at target stations.The residual neural network framework was employed to model the bus route temporal⁃spatial information.It was found that the bus travel time on a segment between two stations not only had correlation with the preceding buses,but also had common change trends with nearby downstream/upstream segments.Two features about bus travel time and headway were extracted from bus route including target section in both forward and reverse directions to constitute the route temporal⁃spatial information,which reflects the road traffic conditions comprehensively.Experiments on the bus trajectory data of route No.10 in Shenzhen public transport system demonstrated that the proposed RTSI⁃ResNet outperformed other well⁃known methods(e.g.,RNN/LSTM,SVM).Specifically,the advantage was more significant when the distance between bus and the target station was farther.展开更多
The effect of vibratory stress relief (VSR) is usually evaluated with the indirect method of observing the change of amplitude frequency response characteristics of structures. A new kind of evaluating method of VSR...The effect of vibratory stress relief (VSR) is usually evaluated with the indirect method of observing the change of amplitude frequency response characteristics of structures. A new kind of evaluating method of VSR based on the ultrasonic time-of-arrival method (UTM), which can obtain the residual stress directly through measuring the propagation time of ultrasonic wave in the material, is presented. At first, the principle of the measuring method of residual stress based on UTM is analyzed. Then the measuring system of the method is described, which is in virtue of ultrasonic flaw detector and high-sampling-rate digital oscillograph. And a set of calibration system that contains a piece of standard specimen is also introduced. Experimental results prove the relation between the residual stress and the propagation time of ultrasonic in workpieces. Finally, the measuring and calibration systems are applied in evaluating the effect of VSR. The final test results show that the method is effective.展开更多
针对无线传感器网络中如何准确获取节点位置信息的问题,研究了多径传播条件下基于到达时间(Time-of-Arrival,TOA)并兼顾路径时延的目标定位问题。所提算法在高斯噪声假设基础上,首先根据时间-距离观测模型推导出包含目标位置坐标及时延...针对无线传感器网络中如何准确获取节点位置信息的问题,研究了多径传播条件下基于到达时间(Time-of-Arrival,TOA)并兼顾路径时延的目标定位问题。所提算法在高斯噪声假设基础上,首先根据时间-距离观测模型推导出包含目标位置坐标及时延的测量方程;然后基于加权最小二乘(Weighted Least Squares,WLS)准则,计算出在目标坐标估计性能上严密逼近Cramér-Rao下界(CRLB)的解;最后通过理论分析得出位置和时延的误差方差及算法开销。仿真测试了单节点及多节点场景下测距误差对定位和延时性能的影响,结果表明,所提出算法的估计性能非常接近CRLB的估计性能,明显优于两步加权最小二乘(Two Step Weighted Least Squares,TSWLS)方法。展开更多
The arrival times of first teleseismic phases are difficult to be measured precisely because of slowly and gradually changed onsets and weak amplitudes. The arrival times measured manually are usually behind the real ...The arrival times of first teleseismic phases are difficult to be measured precisely because of slowly and gradually changed onsets and weak amplitudes. The arrival times measured manually are usually behind the real ones. In this paper, using the ratio method of fixed scale wavelet transformations improved by us, the arrival times for the first arrival phases (such as P and PKIKP) at the teleseismic and far-teleseismic distances were measured. The results are reasonable and reliable based on the analysis and discussion of the reliabilities and errors.展开更多
Due to photoluminescence intermittency of single tional exponential fluorescence lifetime analysis is colloidal quantum dots (QDs), the tradinot perfect to characterize QDs' fluores- cent emission behavior. In this...Due to photoluminescence intermittency of single tional exponential fluorescence lifetime analysis is colloidal quantum dots (QDs), the tradinot perfect to characterize QDs' fluores- cent emission behavior. In this work we used the time-tagged time-resolved (TTTR) mode to record the fluorescent photons from single QDs. We showed that this method is compatible with the traditional lifetime analysis. In addition, by constructing the trajectory over time and the distribution of average arrival time (AAT) of the fluorescent photons, inore details about the emission behavior of QDs were revealed.展开更多
A bunch arrival-time monitor(BAM) system,based on electro-optical intensity modulation scheme, is under study at Shanghai Soft X-ray Free Electron Laser.The aim of the study is to achieve high-precision time measureme...A bunch arrival-time monitor(BAM) system,based on electro-optical intensity modulation scheme, is under study at Shanghai Soft X-ray Free Electron Laser.The aim of the study is to achieve high-precision time measurement for minimizing bunch fluctuations. A readout electronics is developed to fulfill the requirements of the BAM system. The readout electronics is mainly composed of a signal conditioning circuit, field-programmable gate array(FPGA), mezzanine card(FMC150), and powerful FPGA carrier board. The signal conditioning circuit converts the laser pulses into electrical pulse signals using a photodiode. Thereafter, it performs splitting and low-noise amplification to achieve the best voltage sampling performance of the dual-channel analog-to-digital converter(ADC) in FMC150. The FMC150 ADC daughter card includes a 14-bit 250 Msps dual-channel high-speed ADC,a clock configuration, and a management module. The powerful FPGA carrier board is a commercial high-performance Xilinx Kintex-7 FPGA evaluation board. To achieve clock and data alignment for ADC data capture at a high sampling rate, we used ISERDES, IDELAY, and dedicated carry-in resources in the Kintex-7 FPGA. This paper presents a detailed development of the readout electronics in the BAM system and its performance.展开更多
目标定位是指利用传感信息估计目标在特定坐标系中的空间位置。基于到达时间(Time of Arrival,TOA)或等价的,基于距离的定位方法凭借其高精度特点得到了广泛研究。现有TOA定位方法一般假设传感器位置是精确的,只考虑距离测量噪声。而考...目标定位是指利用传感信息估计目标在特定坐标系中的空间位置。基于到达时间(Time of Arrival,TOA)或等价的,基于距离的定位方法凭借其高精度特点得到了广泛研究。现有TOA定位方法一般假设传感器位置是精确的,只考虑距离测量噪声。而考虑了传感器位置不确定性的文献通常缺少统计学优化与分析,无法得到一致性估计。本文同时考虑距离测量噪声和传感器部署不确定性,将目标位置与传感器坐标均当成未知变量构建最大似然问题。本文首先给出关于观测噪声和传感器空间分布的假设,以保证一致性估计器的存在性。有趣的是,本文分析了最大似然估计性质,证明了其不一定具有一致性。本文进一步变换原始观测方程,构建可最优求解的优化问题。特别地,针对距离测量噪声方差已知情况,构建了含二次目标函数和一个二次等式约束的广义信赖域问题,并给出了其最优解求解算法;针对距离测量噪声方差未知情况,构建了普通线性最小二乘问题,实现目标位置和距离测量噪声方差的同时估计。本文针对两种情况分别提出了相应的偏差消除方法,实现了一致估计,即随着观测数量增加,估计值收敛至真实目标位置。一致性特性使所提算法在大样本观测场景可实现超高精度定位。此外,推导了高斯-牛顿迭代算法,可在观测样本和传感器位置不确定性较小时提高算法定位精度。仿真结果验证了所得理论结果的正确性和所提算法在大样本观测下的优越性。展开更多
A practical transportation problem for finding the “departure” time at “all source nodes” in order to arrive at “some destination nodes” at specified time for both FIFO (i.e., First In First Out) and Non-FIFO “...A practical transportation problem for finding the “departure” time at “all source nodes” in order to arrive at “some destination nodes” at specified time for both FIFO (i.e., First In First Out) and Non-FIFO “Dynamic ” Networks is considered in this study. Although shortest path (SP) for dynamic networks have been studied/documented by various researchers, contributions from this present work consists of a sparse matrix storage scheme for efficiently storing large scale sparse network’s connectivity, a concept of Time Delay Factor (TDF) combining with a “general piece- wise linear function” to describe the link cost as a function of time for Non-FIFO links’ costs, and Backward Dijkstra SP Algorithm with simple heuristic rules for rejecting unwanted solutions during the backward search algorithm. Both small-scale (academic) networks as well as large- scale (real-life) networks are investigated in this work to explain and validate the proposed dynamic algorithms. Numerical results obtained from this research work have indicated that the newly proposed dynamic algorithm is reliable, and efficient. Based on the numerical results, the calculated departure time at the source node(s), for a given/specified arrival time at the destination node(s), can be non-unique, for some Non-FIFO networks’ connectivity.展开更多
A model of an angle-spread source, termed the “Gaussian Channel Model” is considered. The cumulative distribution function of the Time-of-Arrival of the multipath components is derived for an arbitrary angle spread....A model of an angle-spread source, termed the “Gaussian Channel Model” is considered. The cumulative distribution function of the Time-of-Arrival of the multipath components is derived for an arbitrary angle spread. The simple approximate expressions for the Time-of-Arrival cumulative distribution function and probability density function are proposed. Numerical results obtained with the help of the derived expressions show the good coincidence with the experimental data and other known results.展开更多
文摘Due to fast-growing urbanization,the traffic management system becomes a crucial problem owing to the rapid growth in the number of vehicles The research proposes an Intelligent public transportation system where informa-tion regarding all the buses connecting in a city will be gathered,processed and accurate bus arrival time prediction will be presented to the user.Various linear and time-varying parameters such as distance,waiting time at stops,red signal duration at a traffic signal,traffic density,turning density,rush hours,weather conditions,number of passengers on the bus,type of day,road type,average vehi-cle speed limit,current vehicle speed affecting traffic are used for the analysis.The proposed model exploits the feasibility and applicability of ELM in the travel time forecasting area.Multiple ELMs(MELM)for explicitly training dynamic,road and trajectory information are used in the proposed approach.A large-scale dataset(historical data)obtained from Kerala State Road Transport Corporation is used for training.Simulations are carried out by using MATLAB R2021a.The experiments revealed that the efficiency of MELM is independent of the time of day and day of the week.It can manage huge volumes of data with less human intervention at greater learning speeds.It is found MELM yields prediction with accuracy in the range of 96.7%to 99.08%.The MAE value is between 0.28 to 1.74 minutes with the proposed approach.The study revealed that there could be regularity in bus usage and daily bus rides are predictable with a better degree of accuracy.The research has proved that MELM is superior for arrival time pre-dictions in terms of accuracy and error,compared with other approaches.
基金sponsored by the National Natural Science Foundation of China (No. 41074075)
文摘Serious stretch appears in shallow long offsset signals after NMO correction. In this article we study the generation mechanism of NMO stretch, demonstrate that the conventional travel time equation cannot accurately describe the travel time of the samples within the same reflection wavelet. As a result, conventional NMO inversion based on the travel time of the wavelet's central point occurs with errors. In this article, a travel time equation for the samples within the same wavelet is reconstructed through our theoretical derivation (the shifted first arrival point travel time equation), a new NMO inversion method based on the wavelet's first arrival point is proposed. While dealing with synthetic data, the semblance coefficient algorithm equation is modified so that wavelet first arrival points can be extracted. After that, NMO inversion based on the new velocity analysis is adopted on shot offset records. The precision of the results is significantly improved compared with the traditional method. Finally, the block move NMO correction based on the first arrival points travel times is adopted on long offset records and non-stretched results are achieved, which verify the proposed new equation.
文摘为了解决传统室内定位技术成本较高、稳定性差以及难于部署等问题,提出一种将到达时间(time of arrival,TOA)与到达角(angle of arrival,AOA)相结合的室内定位系统.该系统由定位基站与被控定位单元组成,其特征在于使用对射式布置的超声波传感器获取定位基站与被控定位单元之间的距离特征,利用角度传感器获取被控定位单元相对于定位基站的角度特征,以单基站就实现了精确的室内定位过程.分析了该系统基本结构与原理,建立定位与控制模型,在一定范围内对其定点定位精度与跟随定位精度进行了实验验证.实验结果表明:该系统结构简单,易于安装布置,鲁棒性强,在测试范围内的最大定点定位误差不超过5 cm,跟随定位误差不超过15 cm.
基金supported by the National Natural Science Foundation of China(No.11575282)
文摘Free electron lasers provide high-power and ultrashort pulses with extreme brightness. In order to improve a facility's capabilities and explore the possibility of performing high-resolution time-resolved experiments, a beam arrival time resolution under 100 fs is required. In this article, a novel beam arrival time monitor(BAM)equipped with two cavities has been designed and a beam flight time measurement scheme based on the BAM prototype has been proposed to estimate phase jitter in the signal measurement system. The two BAM cavities work at different frequencies and the frequency difference is designed to be 35 MHz. Therefore, a self-mixing intermediate frequency signal can be generated using the two cavities. The measured beam flight time shows a temporal deviation of 37 fs(rms).
基金National Science and Technology Major Project(2016ZX03001025-003)Special Found for Beijing Common Construction Project
文摘How to predict the bus arrival time accurately is a crucial problem to be solved in Internet of Vehicle. Existed methods cannot solve the problem effectively for ignoring the traffic delay jitter. In this paper,a three-stage mixed model is proposed for bus arrival time prediction. The first stage is pattern training. In this stage,the traffic delay jitter patterns(TDJP)are mined by K nearest neighbor and K-means in the historical traffic time data. The second stage is the single-step prediction,which is based on real-time adjusted Kalman filter with a modification of historical TDJP. In the third stage,as the influence of historical law is increasing in long distance prediction,we combine the single-step prediction dynamically with Markov historical transfer model to conduct the multi-step prediction. The experimental results show that the proposed single-step prediction model performs better in accuracy and efficiency than short-term traffic flow prediction and dynamic Kalman filter. The multi-step prediction provides a higher level veracity and reliability in travel time forecasting than short-term traffic flow and historical traffic pattern prediction models.
基金Project(2011AA010101) supported by the National High Technology Research and Development Program of China
文摘To improve the accuracy of real-time public transport information release system, a collaborative prediction model was proposed based on cyber-physical systems architecture. In the model, the total bus travel time was divided into three parts: running time, dwell time and intersection delay time, and the data were divided into three categories of historical data, static data and real-time data. The bus arrival time was obtained by fusion computing the real-time data in perception layer together with historical data and static data in collaborative layer. The validity of the collaborative model was verified by the data of a typical urban bus line in Shanghai, and 1538 sets of data were collected and analyzed from three different perspectives. By comparing the experimental results with the actual results, it is shown that the experimental results are with higher prediction accuracy, and the collaborative prediction model adopted is able to meet the demand for bus arrival prediction.
基金supported by the National Major Scientific and Technological Special Project during the 13th Five-year Plan Period(No.2016ZX05045003-005)
文摘Accurately detecting the arrival time of a channel wave in a coal seam is very important for in-seam seismic data processing. The arrival time greatly affects the accuracy of the channel wave inversion and the computed tomography (CT) result. However, because the signal-to-noise ratio of in-seam seismic data is reduced by the long wavelength and strong frequency dispersion, accurately timing the arrival of channel waves is extremely difficult. For this purpose, we propose a method that automatically picks up the arrival time of channel waves based on multi-channel constraints. We first estimate the Jaccard similarity coefficient of two ray paths, then apply it as a weight coefficient for stacking the multi- channel dispersion spectra. The reasonableness and effectiveness of the proposed method is verified in an actual data application. Most importantly, the method increases the degree of automation and the pickup precision of the channel-wave arrival time.
文摘In order to improve the accuracy and engineering feasibility of four-Satellite localization system, the frequency difference measurement is introduced to the four-Satellite TDOA (Time Difference of Arrival) localization algorithm. The TDOA/FDOA (Frequency Difference of Arrival) localization algorithm is used to optimize the GDOP (geometric dilution of precision) of four-Satellite localization. The simulation results show that the absolute position measurement accuracy has little influence on TDOA/FDOA localization accuracy as compared with TDOA localization. Under the same conditions, TDOA/FDOA localization has better accuracy and its GDOP shows more uniform distribution in diamond configuration case. The localization accuracy of four-Satellite TDOA/FDOA is better than the localization accuracy of four-Satellite TDOA.
基金funded by China’s National Natural Science Foundation (Nos. 42125401 and 42004031)the Hefei Key Technology Research and Development Project (No. J2020J06)
文摘Chao Lake is a Geoheritage site on the active Tan-Lu Fault between the Yangtze craton,the North China craton,and the Dabie orogenic belt in the southeast.This segment of the fault is not well constrained at depth partly due to the overprinting of the fault zone by intrusive materials and its relatively low seismic activity and sparse seismic station coverage.This study took advantage of a dense seismic array deployed around Chao Lake to delineate the P-wave velocity variations in the crust and uppermost mantle using teleseismic earthquake arrival time tomography.The station-pair double-difference with waveform crosscorrelation technique was employed.We used a multiscale resolution 3-D initial model derived from the combination of highresolution 3-D v S models within the region of interest to account for the lateral heterogeneity in the upper crust.The results revealed that the velocity of the upper crust is segmented with structures trending in the direction of the strike of the fault.Sedimentary basins are delineated on both sides of the fault with slow velocities,while the fault zone is characterized by high velocity in the crust and uppermost mantle.The high-velocity structure in the fault zone shows characteristics of magma intrusion that may be connected to the Mesozoic magmatism in and around the Middle and Lower Yangtze River Metallogenic Belt(MLYMB),implying that the Tan-Lu fault might have formed a channel for magma intrusion.Magmatic material in Chao Lake is likely connected to the partial melting,assimilation,storage,and homogenization of the uppermost mantle and the lower crustal rocks.The intrusions,however,seem to have suffered severe regional extension along the Tan-Lu fault driven by the eastward Paleo-Pacific plate subduction,thereby losing its deep trail due to extensional erosion.
基金Sponsored by the Transportation Science and Technology Planning Project of Henan Province,China(Grant No.2019G-2-2).
文摘Bus arrival time prediction contributes to the quality improvement of public transport services.Passengers can arrange departure time effectively if they know the accurate bus arrival time in advance.We proposed a machine⁃learning approach,RTSI⁃ResNet,to forecast the bus arrival time at target stations.The residual neural network framework was employed to model the bus route temporal⁃spatial information.It was found that the bus travel time on a segment between two stations not only had correlation with the preceding buses,but also had common change trends with nearby downstream/upstream segments.Two features about bus travel time and headway were extracted from bus route including target section in both forward and reverse directions to constitute the route temporal⁃spatial information,which reflects the road traffic conditions comprehensively.Experiments on the bus trajectory data of route No.10 in Shenzhen public transport system demonstrated that the proposed RTSI⁃ResNet outperformed other well⁃known methods(e.g.,RNN/LSTM,SVM).Specifically,the advantage was more significant when the distance between bus and the target station was farther.
基金This project is supported by National Natural Science Foundation of China(No.50305036).
文摘The effect of vibratory stress relief (VSR) is usually evaluated with the indirect method of observing the change of amplitude frequency response characteristics of structures. A new kind of evaluating method of VSR based on the ultrasonic time-of-arrival method (UTM), which can obtain the residual stress directly through measuring the propagation time of ultrasonic wave in the material, is presented. At first, the principle of the measuring method of residual stress based on UTM is analyzed. Then the measuring system of the method is described, which is in virtue of ultrasonic flaw detector and high-sampling-rate digital oscillograph. And a set of calibration system that contains a piece of standard specimen is also introduced. Experimental results prove the relation between the residual stress and the propagation time of ultrasonic in workpieces. Finally, the measuring and calibration systems are applied in evaluating the effect of VSR. The final test results show that the method is effective.
文摘针对无线传感器网络中如何准确获取节点位置信息的问题,研究了多径传播条件下基于到达时间(Time-of-Arrival,TOA)并兼顾路径时延的目标定位问题。所提算法在高斯噪声假设基础上,首先根据时间-距离观测模型推导出包含目标位置坐标及时延的测量方程;然后基于加权最小二乘(Weighted Least Squares,WLS)准则,计算出在目标坐标估计性能上严密逼近Cramér-Rao下界(CRLB)的解;最后通过理论分析得出位置和时延的误差方差及算法开销。仿真测试了单节点及多节点场景下测距误差对定位和延时性能的影响,结果表明,所提出算法的估计性能非常接近CRLB的估计性能,明显优于两步加权最小二乘(Two Step Weighted Least Squares,TSWLS)方法。
基金National Natural Science Foundation of China (40074007).
文摘The arrival times of first teleseismic phases are difficult to be measured precisely because of slowly and gradually changed onsets and weak amplitudes. The arrival times measured manually are usually behind the real ones. In this paper, using the ratio method of fixed scale wavelet transformations improved by us, the arrival times for the first arrival phases (such as P and PKIKP) at the teleseismic and far-teleseismic distances were measured. The results are reasonable and reliable based on the analysis and discussion of the reliabilities and errors.
基金supported by the National Science Foundation CAREER award(CHE-1554800)
文摘Due to photoluminescence intermittency of single tional exponential fluorescence lifetime analysis is colloidal quantum dots (QDs), the tradinot perfect to characterize QDs' fluores- cent emission behavior. In this work we used the time-tagged time-resolved (TTTR) mode to record the fluorescent photons from single QDs. We showed that this method is compatible with the traditional lifetime analysis. In addition, by constructing the trajectory over time and the distribution of average arrival time (AAT) of the fluorescent photons, inore details about the emission behavior of QDs were revealed.
基金supported by the National Key R&D Plan(No.2016YFA0401900)
文摘A bunch arrival-time monitor(BAM) system,based on electro-optical intensity modulation scheme, is under study at Shanghai Soft X-ray Free Electron Laser.The aim of the study is to achieve high-precision time measurement for minimizing bunch fluctuations. A readout electronics is developed to fulfill the requirements of the BAM system. The readout electronics is mainly composed of a signal conditioning circuit, field-programmable gate array(FPGA), mezzanine card(FMC150), and powerful FPGA carrier board. The signal conditioning circuit converts the laser pulses into electrical pulse signals using a photodiode. Thereafter, it performs splitting and low-noise amplification to achieve the best voltage sampling performance of the dual-channel analog-to-digital converter(ADC) in FMC150. The FMC150 ADC daughter card includes a 14-bit 250 Msps dual-channel high-speed ADC,a clock configuration, and a management module. The powerful FPGA carrier board is a commercial high-performance Xilinx Kintex-7 FPGA evaluation board. To achieve clock and data alignment for ADC data capture at a high sampling rate, we used ISERDES, IDELAY, and dedicated carry-in resources in the Kintex-7 FPGA. This paper presents a detailed development of the readout electronics in the BAM system and its performance.
文摘目标定位是指利用传感信息估计目标在特定坐标系中的空间位置。基于到达时间(Time of Arrival,TOA)或等价的,基于距离的定位方法凭借其高精度特点得到了广泛研究。现有TOA定位方法一般假设传感器位置是精确的,只考虑距离测量噪声。而考虑了传感器位置不确定性的文献通常缺少统计学优化与分析,无法得到一致性估计。本文同时考虑距离测量噪声和传感器部署不确定性,将目标位置与传感器坐标均当成未知变量构建最大似然问题。本文首先给出关于观测噪声和传感器空间分布的假设,以保证一致性估计器的存在性。有趣的是,本文分析了最大似然估计性质,证明了其不一定具有一致性。本文进一步变换原始观测方程,构建可最优求解的优化问题。特别地,针对距离测量噪声方差已知情况,构建了含二次目标函数和一个二次等式约束的广义信赖域问题,并给出了其最优解求解算法;针对距离测量噪声方差未知情况,构建了普通线性最小二乘问题,实现目标位置和距离测量噪声方差的同时估计。本文针对两种情况分别提出了相应的偏差消除方法,实现了一致估计,即随着观测数量增加,估计值收敛至真实目标位置。一致性特性使所提算法在大样本观测场景可实现超高精度定位。此外,推导了高斯-牛顿迭代算法,可在观测样本和传感器位置不确定性较小时提高算法定位精度。仿真结果验证了所得理论结果的正确性和所提算法在大样本观测下的优越性。
文摘A practical transportation problem for finding the “departure” time at “all source nodes” in order to arrive at “some destination nodes” at specified time for both FIFO (i.e., First In First Out) and Non-FIFO “Dynamic ” Networks is considered in this study. Although shortest path (SP) for dynamic networks have been studied/documented by various researchers, contributions from this present work consists of a sparse matrix storage scheme for efficiently storing large scale sparse network’s connectivity, a concept of Time Delay Factor (TDF) combining with a “general piece- wise linear function” to describe the link cost as a function of time for Non-FIFO links’ costs, and Backward Dijkstra SP Algorithm with simple heuristic rules for rejecting unwanted solutions during the backward search algorithm. Both small-scale (academic) networks as well as large- scale (real-life) networks are investigated in this work to explain and validate the proposed dynamic algorithms. Numerical results obtained from this research work have indicated that the newly proposed dynamic algorithm is reliable, and efficient. Based on the numerical results, the calculated departure time at the source node(s), for a given/specified arrival time at the destination node(s), can be non-unique, for some Non-FIFO networks’ connectivity.
文摘A model of an angle-spread source, termed the “Gaussian Channel Model” is considered. The cumulative distribution function of the Time-of-Arrival of the multipath components is derived for an arbitrary angle spread. The simple approximate expressions for the Time-of-Arrival cumulative distribution function and probability density function are proposed. Numerical results obtained with the help of the derived expressions show the good coincidence with the experimental data and other known results.