This paper describes a practical method for finding the invariant orbits in Ja relative dynamics. Working with the Hamiltonian model of the relative motion including the J2 perturbation, the effective differential cor...This paper describes a practical method for finding the invariant orbits in Ja relative dynamics. Working with the Hamiltonian model of the relative motion including the J2 perturbation, the effective differential correction algorithm for finding periodic orbits in three-body problem is extended to formation flying of Earth＇s orbiters. Rather than using orbital elements, the analysis is done directly in physical space, which makes a direct connection with physical requirements. The asymptotic behavior of the invariant orbit is indicated by its stable and unstable manifolds. The period of the relative orbits is proved numerically to be slightly different from the ascending node period of the leader satellite, and a preliminary explanation for this phenomenon is presented. Then the compatibility between J2 invariant orbit and desired relative geometry is considered, and the design procedure for the initial values of the compatible configuration is proposed. The influences of measure errors on the invariant orbit are also investigated by the Monte-Carlo simulation.展开更多
This paper presents the interpolation method of generating the differential correction to coordinates and pseudorange.As a consequence,to improve the quality and stability of the generated correction of amendments,it ...This paper presents the interpolation method of generating the differential correction to coordinates and pseudorange.As a consequence,to improve the quality and stability of the generated correction of amendments,it is advisable to use a system of three reference points.Experiment demonstrates the advantages of the interpolation method in comparison with the standard method of differential correction.展开更多
The DGPS technique can provide considerably better relative positioning accuracy than the stand_alone GPS positioning,but the improvement depends on the distance between the user and the reference station (spatial cor...The DGPS technique can provide considerably better relative positioning accuracy than the stand_alone GPS positioning,but the improvement depends on the distance between the user and the reference station (spatial correlation),the latency of differential corrections (temporal correlation),and the quality of differential corrections.Therefore,how to correctly generate differential corrections as well as their pricision is very important to the DGPS positioning technique.This paper presents a new algorithm for generating differential GPS corrections.This algorithm directly uses code and carrier observations in the measurement model of a Kalman filter,so that it is possible to use a simple stochastic model and to use the standard algorithm of the Kalman filter.The algorithm accounts for biases like multipath errors and instrumental delays in code observations and it shows how differential corrections are differently affected by code biases when dual or single frequency data is used.In addition,the algorithm can be integrated with a real time quality control procedure.As a result,the quality of differential corrections can be guaranteed with a certain probability.展开更多
Correction to:Nuclear Science and Techniques(2024)35:61 https://doi.org/10.1007/s41365-024-01421-5 In this article,the figures were wrongly numbered.The Fig.7 and 8 should have been Fig.11 and 12.The Fig.9,10,11,and 1...Correction to:Nuclear Science and Techniques(2024)35:61 https://doi.org/10.1007/s41365-024-01421-5 In this article,the figures were wrongly numbered.The Fig.7 and 8 should have been Fig.11 and 12.The Fig.9,10,11,and 12 should have been 7,8,9 and 10.The original article has been corrected.展开更多
The Five-hundred-meter Aperture Spherical radio Telescope （FAST） adopts an active deformable main reflector which is composed of 4450 triangular panels. During an observation, the illuminated area of the reflector i...The Five-hundred-meter Aperture Spherical radio Telescope （FAST） adopts an active deformable main reflector which is composed of 4450 triangular panels. During an observation, the illuminated area of the reflector is deformed into a 300-m diameter paraboloid and directed toward a source. To achieve accurate control of the reflector shape, positions of 2226 nodes distributed around the entire reflector must be measured with sufficient precision within a limited time, which is a challenging task because of the large scale. Measurement of the FAST reflector makes use of stations and node targets. However, in this case the effect of the atmosphere on measurement accuracy is a significant issue. This paper investigates a differen- tial correction method for total stations measurement of the FAST reflector. A multi-benchmark differential correction method, including a scheme for benchmark selection and weight assignment, is proposed. On- site evaluation experiments show there is an improvement of 70%-80% in measurement accuracy compared with the uncorrected measurement, verifying the effectiveness of the proposed method.展开更多
Objective To genetically correct a disease-causing point mutation in human induced pluripotent stem cells （iPSCs） derived from a hemophilia B patient. Methods First, the disease-causing mutation was detected by ...Objective To genetically correct a disease-causing point mutation in human induced pluripotent stem cells （iPSCs） derived from a hemophilia B patient. Methods First, the disease-causing mutation was detected by sequencing the encoding area of human coagulation factor IX （F IX） gene. Genomic DNA was extracted from the iPSCs, and the primers were designed to amplify the eight exons of F IX. Next, the point mutation in those iPSCs was genetically corrected using CRISPR/Cas9 technology in the presence of a 129-nucleotide homologous repair template that contained two synonymous mutations. Then, top 8 potential off-target sites were subsequently analyzed using Sanger sequencing. Finally, the corrected clones were differentiated into hepatocyte-like cells, and the secretion of F IX was validated by immunocytochemistry and ELISA assay.Results The cell line bore a missense mutation in the 6th coding exon （c.676 C〉T） of F IX gene. Correction of the point mutation was achieved via CRISPR/Cas9 technology in situ with a high efficacy at about 22% （10/45） and no off-target effects detected in the corrected iPSC clones. F IX secretion, which was further visualized by immunocytochemistry and quantified by ELISA in vitro, reached about 6 ng/ml on day 21 of differentiation procedure. Conclusions Mutations in human disease-specific iPSCs could be precisely corrected by CRISPR/Cas9 technology, and corrected cells still maintained hepatic differentiation capability. Our findings might throw a light on iPSC-based personalized therapies in the clinical application, especially for hemophilia B.展开更多
The pseudorange residual error of imperfect correction of the ionospheric time delay in pseudorange (PR) differential global positioning system (DGPS) is analyzed. The different vertical total electron content (TEC) a...The pseudorange residual error of imperfect correction of the ionospheric time delay in pseudorange (PR) differential global positioning system (DGPS) is analyzed. The different vertical total electron content (TEC) and slant factors at the pierce points of satellite signals are the reasons of the residual error. An improved pseudorange differential approach is proposed and the effect of this new PR differential operation verified by using the simulation.展开更多
DV-Hop localization algorithm has greater localization error which estimates distance from an unknown node to the different anchor nodes by using estimated average size of a hop to achieve the location of the unknown ...DV-Hop localization algorithm has greater localization error which estimates distance from an unknown node to the different anchor nodes by using estimated average size of a hop to achieve the location of the unknown node.So an improved DV-Hop localization algorithm based on correctional average size of a hop,HDCDV-Hop algorithm,is proposed.The improved algorithm corrects the estimated distance between the unknown node and different anchor nodes based on fractional hop count information and relatively accurate coordinates of the anchor nodes information,and it uses the improved Differential Evolution algorithm to get the estimate location of unknown nodes so as to further reduce the localization error.Simulation results show that our proposed algorithm have lower localization error and higher localization accuracy compared with the original DV-Hop algorithm and other classical improved algorithms.展开更多
Aiming to the reliable estimates of the ionosphere differential corrections for the satellite navigation system in the presence of the ionosphere anomaly, a fault-tolerance estimating method, which is based on the dis...Aiming to the reliable estimates of the ionosphere differential corrections for the satellite navigation system in the presence of the ionosphere anomaly, a fault-tolerance estimating method, which is based on the distributed Kalman filtering, is proposed. The method utilizes the parallel sub-filters for estimating the ionosphere differential corrections. Meanwhile, an infinite norm （IN） method is proposed for the detection of the ionosphere irregularity in the filter processing. Once the anomaly is detected, the sub-filter contaminated by the anomaly measurements will be excluded to ensure the reliability of the estimates. The simulation is conducted to validate the method and the results indicate that the anomaly can be found timely due to the novel fault detection method based on the infinite norm. Because of the parallel sub-filter architecture, the measurements are classified by the spatial distribution so that the ionosphere anomaly can be positioned and excluded more easily. Thus, the method can provide the robust and accurate ionosphere differential corrections.展开更多
When testing an electrohydraulic proportional valve,it is necessary to test the high frequency dynamic flow with bias.Because of the limitation of the piston stroke,a no-load hydraulic cylinder is only suitable for a ...When testing an electrohydraulic proportional valve,it is necessary to test the high frequency dynamic flow with bias.Because of the limitation of the piston stroke,a no-load hydraulic cylinder is only suitable for a reciprocating symmetrical dynamic flow test.Since the traditional differential pressure flowmeter is affected by viscosity and inertia of the fluid,it is only suitable for measuring steady flow.Therefore,a new type of double pressure differential dynamic flowmeter is designed to improve the traditional differential pressure flowmeter.The influence of fluid viscosity and inertia in the flow process are negated by subtracting the differential pressure in section expansion from the differential pressure in section contraction.The double differential pressure flowmeter is modeled and a flow meter prototype is designed.Then,the flow coefficients are identified and corrected by a practical test.Finally,the dynamic performance and steady-state precision of the flowmeter are verified by comparing with the test results of the no-load hydraulic cylinder.The double differential pressure dynamic flowmeter is proven to measure dynamic flow accurately,especially at higher dynamic frequencies.展开更多
In order to solve the linear variable differential transformer （LVDT） displacement sensor nonlinearity of overall range and extend its working range, a novel line-element based adaptively seg- menting method for pie...In order to solve the linear variable differential transformer （LVDT） displacement sensor nonlinearity of overall range and extend its working range, a novel line-element based adaptively seg- menting method for piecewise compensating correction was proposed. According to the mechanical structure of LVDT, the output equation was calculated, and then the theoretic nonlinear source of output was analyzed. By the proposed line-element adaptive segmentation method, the nonlinear output of LVDT was divided into linear and nonlinear regions with a given threshold. Then the com- pensating correction function was designed for nonlinear parts employing polynomial regression tech- nique. The simulation of LVDT validates the feasibility of proposed scheme, and the results of cali- bration and testing experiments fully prove that the proposed method has higher accuracy than the state-of-art correction algorithms.展开更多
Differential electrochemical mass spectrometry(DEMS)is one of the most powerful techniques for both the mechanistic and kinetic study of complicated electrocatalytic reactions.It can provide information on the nature ...Differential electrochemical mass spectrometry(DEMS)is one of the most powerful techniques for both the mechanistic and kinetic study of complicated electrocatalytic reactions.It can provide information on the nature and yields of the products generated,their production rate,and the structure-activity relationship between the electrocatalysts and the target reactions.The precise calibration of the mass signal is a prerequisite for the accurate evaluation of reaction kinetics.In this work,we use the oxidation reactions of CO and HCOOH to demonstrate how certain conditions,such as the flow rate and solution composition,affect the collection efficiency and ionization probability of the species to be detected.These parameters can affect the determination of the mass calibration constant and the accuracy of the subsequent quantitative DEMS analysis.We show the relationship between the mass calibration constant and the flow rate,and provide strategies for eliminating this and the related problems.展开更多
In this paper, we study an efficient asymptotically correction of a-posteriori er- ror estimator for the numerical approximation of Volterra integro-differential equations by piecewise polynomial collocation method. T...In this paper, we study an efficient asymptotically correction of a-posteriori er- ror estimator for the numerical approximation of Volterra integro-differential equations by piecewise polynomial collocation method. The deviation of the error for Volterra integro- differential equations by using the defect correction principle is defined. Also, it is shown that for m degree piecewise polynomial collocation method, our method provides O（hm＋l） as the order of the deviation of the error. The theoretical behavior is tested on examples and it is shown that the numerical results confirm the theoretical part.展开更多
In this paper we give a complete analysis of the convergence acceleration method for collocation solutions of Volterra nonlinear integro-differential equations with smooth kernels. It will be shown that when continuou...In this paper we give a complete analysis of the convergence acceleration method for collocation solutions of Volterra nonlinear integro-differential equations with smooth kernels. It will be shown that when continuous piecewise polynomials of degree m are used and collocation is based on the Lobatto points, the first derivative of this collocation approximation admits, at the knots, an error expansion in even powers of the step-size h, beginning with a term in h2m. On the basis of this expansion we show that when a correction procedure is applied to this collocation approximation for k times, the global accurary of the corresponding corrected approximation will be increased to O(h2m(k+1)).展开更多
基金The project supported by the Innovation Foundation of Beihang University for Ph.D.Graduatesthe National Natural Science Foundation of China(60535010)
文摘This paper describes a practical method for finding the invariant orbits in Ja relative dynamics. Working with the Hamiltonian model of the relative motion including the J2 perturbation, the effective differential correction algorithm for finding periodic orbits in three-body problem is extended to formation flying of Earth＇s orbiters. Rather than using orbital elements, the analysis is done directly in physical space, which makes a direct connection with physical requirements. The asymptotic behavior of the invariant orbit is indicated by its stable and unstable manifolds. The period of the relative orbits is proved numerically to be slightly different from the ascending node period of the leader satellite, and a preliminary explanation for this phenomenon is presented. Then the compatibility between J2 invariant orbit and desired relative geometry is considered, and the design procedure for the initial values of the compatible configuration is proposed. The influences of measure errors on the invariant orbit are also investigated by the Monte-Carlo simulation.
基金Task Complex Program NAS of Ukraine on Space Research for 2012-2016
文摘This paper presents the interpolation method of generating the differential correction to coordinates and pseudorange.As a consequence,to improve the quality and stability of the generated correction of amendments,it is advisable to use a system of three reference points.Experiment demonstrates the advantages of the interpolation method in comparison with the standard method of differential correction.
文摘The DGPS technique can provide considerably better relative positioning accuracy than the stand_alone GPS positioning,but the improvement depends on the distance between the user and the reference station (spatial correlation),the latency of differential corrections (temporal correlation),and the quality of differential corrections.Therefore,how to correctly generate differential corrections as well as their pricision is very important to the DGPS positioning technique.This paper presents a new algorithm for generating differential GPS corrections.This algorithm directly uses code and carrier observations in the measurement model of a Kalman filter,so that it is possible to use a simple stochastic model and to use the standard algorithm of the Kalman filter.The algorithm accounts for biases like multipath errors and instrumental delays in code observations and it shows how differential corrections are differently affected by code biases when dual or single frequency data is used.In addition,the algorithm can be integrated with a real time quality control procedure.As a result,the quality of differential corrections can be guaranteed with a certain probability.
文摘Correction to:Nuclear Science and Techniques(2024)35:61 https://doi.org/10.1007/s41365-024-01421-5 In this article,the figures were wrongly numbered.The Fig.7 and 8 should have been Fig.11 and 12.The Fig.9,10,11,and 12 should have been 7,8,9 and 10.The original article has been corrected.
基金supported by the Project Research of Adaptive Modeling and Control Strategy in the FAST Active Reflector of the National Natural Science Foundation of China(Grant No.11273001)the Key Laboratory of Radio Astronomy,Chinese Academy of Sciences
文摘The Five-hundred-meter Aperture Spherical radio Telescope （FAST） adopts an active deformable main reflector which is composed of 4450 triangular panels. During an observation, the illuminated area of the reflector is deformed into a 300-m diameter paraboloid and directed toward a source. To achieve accurate control of the reflector shape, positions of 2226 nodes distributed around the entire reflector must be measured with sufficient precision within a limited time, which is a challenging task because of the large scale. Measurement of the FAST reflector makes use of stations and node targets. However, in this case the effect of the atmosphere on measurement accuracy is a significant issue. This paper investigates a differen- tial correction method for total stations measurement of the FAST reflector. A multi-benchmark differential correction method, including a scheme for benchmark selection and weight assignment, is proposed. On- site evaluation experiments show there is an improvement of 70%-80% in measurement accuracy compared with the uncorrected measurement, verifying the effectiveness of the proposed method.
基金Supported by the National Science and Technology Major Project(2011ZX09102-010-04)
文摘Objective To genetically correct a disease-causing point mutation in human induced pluripotent stem cells （iPSCs） derived from a hemophilia B patient. Methods First, the disease-causing mutation was detected by sequencing the encoding area of human coagulation factor IX （F IX） gene. Genomic DNA was extracted from the iPSCs, and the primers were designed to amplify the eight exons of F IX. Next, the point mutation in those iPSCs was genetically corrected using CRISPR/Cas9 technology in the presence of a 129-nucleotide homologous repair template that contained two synonymous mutations. Then, top 8 potential off-target sites were subsequently analyzed using Sanger sequencing. Finally, the corrected clones were differentiated into hepatocyte-like cells, and the secretion of F IX was validated by immunocytochemistry and ELISA assay.Results The cell line bore a missense mutation in the 6th coding exon （c.676 C〉T） of F IX gene. Correction of the point mutation was achieved via CRISPR/Cas9 technology in situ with a high efficacy at about 22% （10/45） and no off-target effects detected in the corrected iPSC clones. F IX secretion, which was further visualized by immunocytochemistry and quantified by ELISA in vitro, reached about 6 ng/ml on day 21 of differentiation procedure. Conclusions Mutations in human disease-specific iPSCs could be precisely corrected by CRISPR/Cas9 technology, and corrected cells still maintained hepatic differentiation capability. Our findings might throw a light on iPSC-based personalized therapies in the clinical application, especially for hemophilia B.
文摘The pseudorange residual error of imperfect correction of the ionospheric time delay in pseudorange (PR) differential global positioning system (DGPS) is analyzed. The different vertical total electron content (TEC) and slant factors at the pierce points of satellite signals are the reasons of the residual error. An improved pseudorange differential approach is proposed and the effect of this new PR differential operation verified by using the simulation.
基金supported by Fundamental Research Funds of Jilin University(No.SXGJQY2017-9,No.2017TD-19)the National Natural Science Foundation of China(No.61771219)
文摘DV-Hop localization algorithm has greater localization error which estimates distance from an unknown node to the different anchor nodes by using estimated average size of a hop to achieve the location of the unknown node.So an improved DV-Hop localization algorithm based on correctional average size of a hop,HDCDV-Hop algorithm,is proposed.The improved algorithm corrects the estimated distance between the unknown node and different anchor nodes based on fractional hop count information and relatively accurate coordinates of the anchor nodes information,and it uses the improved Differential Evolution algorithm to get the estimate location of unknown nodes so as to further reduce the localization error.Simulation results show that our proposed algorithm have lower localization error and higher localization accuracy compared with the original DV-Hop algorithm and other classical improved algorithms.
基金National Basic Research Program of China (2010CB731800)
文摘Aiming to the reliable estimates of the ionosphere differential corrections for the satellite navigation system in the presence of the ionosphere anomaly, a fault-tolerance estimating method, which is based on the distributed Kalman filtering, is proposed. The method utilizes the parallel sub-filters for estimating the ionosphere differential corrections. Meanwhile, an infinite norm （IN） method is proposed for the detection of the ionosphere irregularity in the filter processing. Once the anomaly is detected, the sub-filter contaminated by the anomaly measurements will be excluded to ensure the reliability of the estimates. The simulation is conducted to validate the method and the results indicate that the anomaly can be found timely due to the novel fault detection method based on the infinite norm. Because of the parallel sub-filter architecture, the measurements are classified by the spatial distribution so that the ionosphere anomaly can be positioned and excluded more easily. Thus, the method can provide the robust and accurate ionosphere differential corrections.
基金Supported by the National Natural Science Foundation of China(No.51875498)Hebei Provincial Natural Science Fund Key Project(No.E2018203339)Hebei Provincial Natural Science Foundation Steel Joint Research Fund(No.E2017203079)
文摘When testing an electrohydraulic proportional valve,it is necessary to test the high frequency dynamic flow with bias.Because of the limitation of the piston stroke,a no-load hydraulic cylinder is only suitable for a reciprocating symmetrical dynamic flow test.Since the traditional differential pressure flowmeter is affected by viscosity and inertia of the fluid,it is only suitable for measuring steady flow.Therefore,a new type of double pressure differential dynamic flowmeter is designed to improve the traditional differential pressure flowmeter.The influence of fluid viscosity and inertia in the flow process are negated by subtracting the differential pressure in section expansion from the differential pressure in section contraction.The double differential pressure flowmeter is modeled and a flow meter prototype is designed.Then,the flow coefficients are identified and corrected by a practical test.Finally,the dynamic performance and steady-state precision of the flowmeter are verified by comparing with the test results of the no-load hydraulic cylinder.The double differential pressure dynamic flowmeter is proven to measure dynamic flow accurately,especially at higher dynamic frequencies.
基金Supported by National High Technology Research and Development Program of China("863" Program)(2011AA041002)
文摘In order to solve the linear variable differential transformer （LVDT） displacement sensor nonlinearity of overall range and extend its working range, a novel line-element based adaptively seg- menting method for piecewise compensating correction was proposed. According to the mechanical structure of LVDT, the output equation was calculated, and then the theoretic nonlinear source of output was analyzed. By the proposed line-element adaptive segmentation method, the nonlinear output of LVDT was divided into linear and nonlinear regions with a given threshold. Then the com- pensating correction function was designed for nonlinear parts employing polynomial regression tech- nique. The simulation of LVDT validates the feasibility of proposed scheme, and the results of cali- bration and testing experiments fully prove that the proposed method has higher accuracy than the state-of-art correction algorithms.
基金supported by the National Natural Science Foundation of China(no.21872132,21832004,91545124)the 973 Program from the Ministry of Science and Technology of China(no.2015CB932301)。
文摘Differential electrochemical mass spectrometry(DEMS)is one of the most powerful techniques for both the mechanistic and kinetic study of complicated electrocatalytic reactions.It can provide information on the nature and yields of the products generated,their production rate,and the structure-activity relationship between the electrocatalysts and the target reactions.The precise calibration of the mass signal is a prerequisite for the accurate evaluation of reaction kinetics.In this work,we use the oxidation reactions of CO and HCOOH to demonstrate how certain conditions,such as the flow rate and solution composition,affect the collection efficiency and ionization probability of the species to be detected.These parameters can affect the determination of the mass calibration constant and the accuracy of the subsequent quantitative DEMS analysis.We show the relationship between the mass calibration constant and the flow rate,and provide strategies for eliminating this and the related problems.
文摘In this paper, we study an efficient asymptotically correction of a-posteriori er- ror estimator for the numerical approximation of Volterra integro-differential equations by piecewise polynomial collocation method. The deviation of the error for Volterra integro- differential equations by using the defect correction principle is defined. Also, it is shown that for m degree piecewise polynomial collocation method, our method provides O（hm＋l） as the order of the deviation of the error. The theoretical behavior is tested on examples and it is shown that the numerical results confirm the theoretical part.
基金This research is supported by the National Natural Science Foundation of China!19801030
文摘In this paper we give a complete analysis of the convergence acceleration method for collocation solutions of Volterra nonlinear integro-differential equations with smooth kernels. It will be shown that when continuous piecewise polynomials of degree m are used and collocation is based on the Lobatto points, the first derivative of this collocation approximation admits, at the knots, an error expansion in even powers of the step-size h, beginning with a term in h2m. On the basis of this expansion we show that when a correction procedure is applied to this collocation approximation for k times, the global accurary of the corresponding corrected approximation will be increased to O(h2m(k+1)).
