The problem of navigation for the distributed satellites system using relative range mea- surements is investigated. Firstly, observability for every participating satellites is analyzed based on the nonlinear Kepleri...The problem of navigation for the distributed satellites system using relative range mea- surements is investigated. Firstly, observability for every participating satellites is analyzed based on the nonlinear Keplerian model containing J2 perturbation and the nonlinear measurements. It is proven that the minimum number of tracking satellites to assure the observability of the distributed satellites system is three. Additionally, the analysis shows that the J2 perturbation and the nonlinearity make little contribution to improve the observability for the navigation. Then, a quasi-consistent extended Kalman filter based navigation algorithm is proposed, which is quasi-consistent and can provide an on- line evaluation of the navigation precision. The simulation illustrates the feasibility and effectiveness of the proposed navigation algorithm for the distributed satellites system.展开更多
In the internet of battlefield things, ammunition is becoming networked and intelligent, which depends on location information. Therefore, this paper focuses on the self-organized network collaborative localization of...In the internet of battlefield things, ammunition is becoming networked and intelligent, which depends on location information. Therefore, this paper focuses on the self-organized network collaborative localization of munitions with an aerial three-dimensional(3D) highly-dynamic topographic structure under a satellite denied environment. As for aerial networked munitions, the measurement of munitions is objectively incomplete due to the degenerated and interrupted link of munitions. For this reason, a cluster-oriented collaborative localization method is put forward in this paper. Multidimensional scaling(MDS) was first integrated with a trilateration localization method(TLM) to construct a relative localization algorithm for determining the relative location of a mobile cluster network. The information related to relative velocity was then combined into a collaborative localization framework to devise a TLM-vMDS algorithm. Finally, an iterative refinement algorithm based on scaling by majorizing a complicated function(SMACOF) was employed to effectively eliminate the influence of incomplete link observation on localization accuracy. Compared with the currently available advanced algorithms, the proposed TLM-vMDS algorithm achieves higher localization accuracy and faster convergence for a cluster of extensively networked munitions, and also offers better numerical stability and robustness for highspeed motion models.展开更多
Magnetic exchange interactions(MEIs) define networks of coupled magnetic moments and lead to a surprisingly rich variety of their magnetic properties. Typically MEIs can be estimated by fitting experimental results.Un...Magnetic exchange interactions(MEIs) define networks of coupled magnetic moments and lead to a surprisingly rich variety of their magnetic properties. Typically MEIs can be estimated by fitting experimental results.Unfortunately, how many MEIs need to be included in the fitting process for a material is unclear a priori,which limits the results obtained by these conventional methods. Based on linear spin-wave theory but without performing matrix diagonalization, we show that for a general quadratic spin Hamiltonian, there is a simple relation between the Fourier transform of MEIs and the sum of square of magnon energies(SSME). We further show that according to the real-space distance range within which MEIs are considered relevant, one can obtain the corresponding relationships between SSME in momentum space. By directly utilizing these characteristics and the experimental magnon energies at only a few high-symmetry k points in the Brillouin zone, one can obtain strong constraints about the range of exchange path beyond which MEIs can be safely neglected. Our methodology is also generally applicable for other Hamiltonian with quadratic Fermi or Boson operators.展开更多
Objectives To analyses heart rate （HR） distribution of healthy adults in the south China community and evaluate relative risk of HR to total cause of death and cardiac cerebral vascular death. Methods Analytical dat...Objectives To analyses heart rate （HR） distribution of healthy adults in the south China community and evaluate relative risk of HR to total cause of death and cardiac cerebral vascular death. Methods Analytical data come from the baseline survey and follow-up visits in the PRC-USA Collaborative Study of Cardiovascular Epidemiology in urban and rural samples of Guangzhou. The baseline survey was initiated in 1983 and 1984, and rescanned in 1987 and 1988. Since 1991 Follow-up visits for endpoint events were carried once every two years. Average follow-up year was 16.2 from baseline to 2000. People excluded from cardiac cerebral vascular disease, diabetes and other various chronic diseases were regarded as ＂healthy adults＂. Heart rates of these subjects were measured on resting electrocardiogram. Endpoint evens include： total cause of death, first attack of coronary disease and cerebral vascular events. SAS software was used for analysis. Cox Proportional Hazards model was used to evaluate the impact of HR on total death and cardiac cerebral vascular disease. Results A total of 4570 men and women aged 35-55 years from urban and rural Guangzhou were investigated. 3493 healthy subjects were enrolled in the analysis, including 1694 men and 1799 women. Mean oftheHRis （67.9 ±10.6） beats/min （bpm） in the whole population, （66.3±10.7）bpm in men and （69.3± 10.4） in women. The 52 percentile of the HR was 51 in men and 54 in women. The 952 percentile of the HR was 85 in men and 88 in women. Single correlation analysis showed there was negative relationship between age and HR, but it was only statistical significant in female. Analysis with Cox Proportional Hazards model show that HR 〈 50 bpm tops the risk of total causes of death （1.725）and HR 50-59 bpm decreased the risk of total causes of death （0.843）. Relative risk of cardiac cerebral vascular events exceeds 1 when HR 〈 50 and 〉90 bpm （1.486 and 7.008 respectively）. It was less than 1 in other groups but there was no significant difference between each group. Conclusions Traditional normal range of HR in adult should be adjusted. In certain extent lower HR is advantageous to decrease cardiac cerebral vascular events, total causes of death and has better prognosis.展开更多
We report on the properties of strong pulses from PSR B0656＋14 by analyzing the data obtained using the Urumqi 25-m radio telescope at 1540 MHz from August 2007 to September 2010.In 44 h of observational data,a total...We report on the properties of strong pulses from PSR B0656＋14 by analyzing the data obtained using the Urumqi 25-m radio telescope at 1540 MHz from August 2007 to September 2010.In 44 h of observational data,a total of 67 pulses with signal-to-noise ratios above a 5σthreshold were detected.The peak flux densities of these pulses are 58 to 194 times that of the average profile,and their pulse energies are 3 to 68 times that of the average pulse.These pulses are clustered around phases about 5-ahead of the peak of the average profile.Compared with the width of the average profile,they are relatively narrow,with the full widths at half-maximum ranging from 0.28 ° to 1.78 °.The distribution of pulse-energies follows a lognormal distribution.These sporadic strong pulses detected from PSR B0656＋14 have different characteristics from both typical giant pulses and its regular pulses.展开更多
The problem of estimating quantization error in 2D images is an inherent problem in computer vision.The outcome of this problem is directly related to the error in reconstructed 3D position coordinates of an object.Th...The problem of estimating quantization error in 2D images is an inherent problem in computer vision.The outcome of this problem is directly related to the error in reconstructed 3D position coordinates of an object.Thus estimation of quantization error has its own importance in stereo vision.Although the quantization error cannot be controlled fully,still statistical error analysis helps us to measure the performance of stereo systems that relies on the imaging parameters.Generally,it is assumed that the quantization error in 2D images is distributed uniformly that need not to be true from a practical aspect.In this paper,we have incorporated noise distributions(Triangular and Trapezoidal)for the stochastic error analysis of the quantization error in stereo imaging systems.For the validation of the theoretical analysis,the detailed simulation study is carried out by considering different cases.展开更多
Currently beach morphodynamic classification is the most important foundation to conduct associated coastal geomorphological studies.This paper carried out beach morphodynamic classifications for 12 straight beaches o...Currently beach morphodynamic classification is the most important foundation to conduct associated coastal geomorphological studies.This paper carried out beach morphodynamic classifications for 12 straight beaches on headland-bay coasts based on field survey and evaluated the applicability of the most widely used dimensional fall velocity parameter(Ω)and relative tidal range parameter(RTR).One reflective,five intermediate and six non-barred dissipative beaches were visually classified and sand size seemed to be a key factor to differentiate these beaches.The studied beaches were in relatively low wave energy environments(Hs<1 m)and the absolute deep-water wave energy level of P0=3 KWm-1 was supposed to a critical threshold to characterize the applicability of theΩand RTR parameters.These two morphodynamic parameters were applicable for the beaches with P0>3 KWm-1 and MSR<2 m.It was found that the model of the traditional winter-and-summer profiles was not applicable in the study area in despite of distinct wave seasonality.The studied beaches were more possible to hover around a limited range due to relatively low background wave environments and variability without considering typhoon impacts,which needs further research on actual breaker wave conditions and beach morphodynamic type responses to typhoon events.展开更多
基金supported by the National Basic Research Program of China under Grant No.2014CB845303the National Center for Mathematics and Interdisciplinary Sciences,Chinese Academy of Sciences
文摘The problem of navigation for the distributed satellites system using relative range mea- surements is investigated. Firstly, observability for every participating satellites is analyzed based on the nonlinear Keplerian model containing J2 perturbation and the nonlinear measurements. It is proven that the minimum number of tracking satellites to assure the observability of the distributed satellites system is three. Additionally, the analysis shows that the J2 perturbation and the nonlinearity make little contribution to improve the observability for the navigation. Then, a quasi-consistent extended Kalman filter based navigation algorithm is proposed, which is quasi-consistent and can provide an on- line evaluation of the navigation precision. The simulation illustrates the feasibility and effectiveness of the proposed navigation algorithm for the distributed satellites system.
文摘In the internet of battlefield things, ammunition is becoming networked and intelligent, which depends on location information. Therefore, this paper focuses on the self-organized network collaborative localization of munitions with an aerial three-dimensional(3D) highly-dynamic topographic structure under a satellite denied environment. As for aerial networked munitions, the measurement of munitions is objectively incomplete due to the degenerated and interrupted link of munitions. For this reason, a cluster-oriented collaborative localization method is put forward in this paper. Multidimensional scaling(MDS) was first integrated with a trilateration localization method(TLM) to construct a relative localization algorithm for determining the relative location of a mobile cluster network. The information related to relative velocity was then combined into a collaborative localization framework to devise a TLM-vMDS algorithm. Finally, an iterative refinement algorithm based on scaling by majorizing a complicated function(SMACOF) was employed to effectively eliminate the influence of incomplete link observation on localization accuracy. Compared with the currently available advanced algorithms, the proposed TLM-vMDS algorithm achieves higher localization accuracy and faster convergence for a cluster of extensively networked munitions, and also offers better numerical stability and robustness for highspeed motion models.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 11834006, 12004170, and 12104215)the Natural Science Foundation of Jiangsu Province,China (Grant No. BK20200326)+1 种基金the Excellent Programme in Nanjing Universitythe support from the Tencent Foundation through the XPLORER PRIZE。
文摘Magnetic exchange interactions(MEIs) define networks of coupled magnetic moments and lead to a surprisingly rich variety of their magnetic properties. Typically MEIs can be estimated by fitting experimental results.Unfortunately, how many MEIs need to be included in the fitting process for a material is unclear a priori,which limits the results obtained by these conventional methods. Based on linear spin-wave theory but without performing matrix diagonalization, we show that for a general quadratic spin Hamiltonian, there is a simple relation between the Fourier transform of MEIs and the sum of square of magnon energies(SSME). We further show that according to the real-space distance range within which MEIs are considered relevant, one can obtain the corresponding relationships between SSME in momentum space. By directly utilizing these characteristics and the experimental magnon energies at only a few high-symmetry k points in the Brillouin zone, one can obtain strong constraints about the range of exchange path beyond which MEIs can be safely neglected. Our methodology is also generally applicable for other Hamiltonian with quadratic Fermi or Boson operators.
文摘Objectives To analyses heart rate （HR） distribution of healthy adults in the south China community and evaluate relative risk of HR to total cause of death and cardiac cerebral vascular death. Methods Analytical data come from the baseline survey and follow-up visits in the PRC-USA Collaborative Study of Cardiovascular Epidemiology in urban and rural samples of Guangzhou. The baseline survey was initiated in 1983 and 1984, and rescanned in 1987 and 1988. Since 1991 Follow-up visits for endpoint events were carried once every two years. Average follow-up year was 16.2 from baseline to 2000. People excluded from cardiac cerebral vascular disease, diabetes and other various chronic diseases were regarded as ＂healthy adults＂. Heart rates of these subjects were measured on resting electrocardiogram. Endpoint evens include： total cause of death, first attack of coronary disease and cerebral vascular events. SAS software was used for analysis. Cox Proportional Hazards model was used to evaluate the impact of HR on total death and cardiac cerebral vascular disease. Results A total of 4570 men and women aged 35-55 years from urban and rural Guangzhou were investigated. 3493 healthy subjects were enrolled in the analysis, including 1694 men and 1799 women. Mean oftheHRis （67.9 ±10.6） beats/min （bpm） in the whole population, （66.3±10.7）bpm in men and （69.3± 10.4） in women. The 52 percentile of the HR was 51 in men and 54 in women. The 952 percentile of the HR was 85 in men and 88 in women. Single correlation analysis showed there was negative relationship between age and HR, but it was only statistical significant in female. Analysis with Cox Proportional Hazards model show that HR 〈 50 bpm tops the risk of total causes of death （1.725）and HR 50-59 bpm decreased the risk of total causes of death （0.843）. Relative risk of cardiac cerebral vascular events exceeds 1 when HR 〈 50 and 〉90 bpm （1.486 and 7.008 respectively）. It was less than 1 in other groups but there was no significant difference between each group. Conclusions Traditional normal range of HR in adult should be adjusted. In certain extent lower HR is advantageous to decrease cardiac cerebral vascular events, total causes of death and has better prognosis.
基金funded by the National Natural Science Foundation of China(Grant No.10973026)
文摘We report on the properties of strong pulses from PSR B0656＋14 by analyzing the data obtained using the Urumqi 25-m radio telescope at 1540 MHz from August 2007 to September 2010.In 44 h of observational data,a total of 67 pulses with signal-to-noise ratios above a 5σthreshold were detected.The peak flux densities of these pulses are 58 to 194 times that of the average profile,and their pulse energies are 3 to 68 times that of the average pulse.These pulses are clustered around phases about 5-ahead of the peak of the average profile.Compared with the width of the average profile,they are relatively narrow,with the full widths at half-maximum ranging from 0.28 ° to 1.78 °.The distribution of pulse-energies follows a lognormal distribution.These sporadic strong pulses detected from PSR B0656＋14 have different characteristics from both typical giant pulses and its regular pulses.
文摘The problem of estimating quantization error in 2D images is an inherent problem in computer vision.The outcome of this problem is directly related to the error in reconstructed 3D position coordinates of an object.Thus estimation of quantization error has its own importance in stereo vision.Although the quantization error cannot be controlled fully,still statistical error analysis helps us to measure the performance of stereo systems that relies on the imaging parameters.Generally,it is assumed that the quantization error in 2D images is distributed uniformly that need not to be true from a practical aspect.In this paper,we have incorporated noise distributions(Triangular and Trapezoidal)for the stochastic error analysis of the quantization error in stereo imaging systems.For the validation of the theoretical analysis,the detailed simulation study is carried out by considering different cases.
基金National Science Foundation of China,No.41301005,No.41701011Postdoctoral Science Foundation of China,No.2014M552118China Scholarship Council,No.201608410419。
文摘Currently beach morphodynamic classification is the most important foundation to conduct associated coastal geomorphological studies.This paper carried out beach morphodynamic classifications for 12 straight beaches on headland-bay coasts based on field survey and evaluated the applicability of the most widely used dimensional fall velocity parameter(Ω)and relative tidal range parameter(RTR).One reflective,five intermediate and six non-barred dissipative beaches were visually classified and sand size seemed to be a key factor to differentiate these beaches.The studied beaches were in relatively low wave energy environments(Hs<1 m)and the absolute deep-water wave energy level of P0=3 KWm-1 was supposed to a critical threshold to characterize the applicability of theΩand RTR parameters.These two morphodynamic parameters were applicable for the beaches with P0>3 KWm-1 and MSR<2 m.It was found that the model of the traditional winter-and-summer profiles was not applicable in the study area in despite of distinct wave seasonality.The studied beaches were more possible to hover around a limited range due to relatively low background wave environments and variability without considering typhoon impacts,which needs further research on actual breaker wave conditions and beach morphodynamic type responses to typhoon events.
