Objective:To reveal the neural network of active and passive hand movements. Method:Seven healthy aged people were checked, and acquired functional magnetic resonance imaging data on a 1.5T scanner. Active movement co...Objective:To reveal the neural network of active and passive hand movements. Method:Seven healthy aged people were checked, and acquired functional magnetic resonance imaging data on a 1.5T scanner. Active movement consisted of repetitive grasping and loosening of hand; passive movement involved the same movement performed by examiner. Both types of hand movements were assessed separately. These data were analysed by Statistical Parametric Mapping Microsoft. Result:The main activated brain areas were the contralateral supplemental motor area, primary motor area, primary sensory area and the ipsilateral cerebellum when subjects gripped right hands actively and passively. The supplemental area was less active in passive hand movement than active hand movement. The activated brain areas were mainly within Brodmann area 4 during active hand movement; in the contrast, the voxels triggered by passive movement were mainly within Brodmann areas 3,1,2 areas. Conclusion:The results suggest that the neural networks of passive and active tasks spared some common areas, and the passive movement could be as effective as active movement to facilitate the recovery of limbs motor function in patients with brain damage.展开更多
Recently, the code division multiple access （CDMA） waveform exists in the large area across the world. However, when using the CDMA system as the illuminator of opportunity for the passive bistatic radar （PBR）, th...Recently, the code division multiple access （CDMA） waveform exists in the large area across the world. However, when using the CDMA system as the illuminator of opportunity for the passive bistatic radar （PBR）, there exists interference not only from the base station used as the illuminator of opportunity but also from other base stations with the same frequency. And be cause in the CDMA system, the signal transmitted by each base station is different, using the direct signal of one base station can not cancel the interference from other base stations. A CDMA based PBR using an element linear array antenna as both the reference antenna and surveillance antenna is introduced. To deal with the interference in this PBR system, an adaptive temporal cancellation algorithm is used to remove the interference from the base station used as the illuminator of opportunity firstly. And then a robust adaptive beamformer is used to suppress the interference from other base stations. Finally, the preliminary experiment re sults demonstrate the feasibility of using CDMA signals as a radar waveform.展开更多
Wireless sensor network (WSN) of active sensors suffers from serious inter-sensor interference (ISI) and imposes new design and implementation challenges. In this paper, based on the ultrasonic sensor network, two tim...Wireless sensor network (WSN) of active sensors suffers from serious inter-sensor interference (ISI) and imposes new design and implementation challenges. In this paper, based on the ultrasonic sensor network, two time-division based distributed sensor scheduling schemes are proposed to deal with ISI by scheduling sensors periodically and adaptively respectively. Extended Kalman filter (EKF) is used as the tracking algorithm in distributed manner. Simulation results show that the adaptive sensor scheduling scheme can achieve superior tracking accuracy with faster tracking convergence speed.展开更多
Time delay and Doppler shift between the echo signal and the reference signal are two most commonly used measurements in target localization for the passive radar. Doppler rate, which can be obtained from the extended...Time delay and Doppler shift between the echo signal and the reference signal are two most commonly used measurements in target localization for the passive radar. Doppler rate, which can be obtained from the extended cross ambiguity function, offers an opportunity to further enhance the localization accuracy. This paper considers using the measurement Doppler rate in addition to measurements of time delay and Doppler shift to locate a moving target. A closed-form solution is developed to accurately and efficiently estimate the target position and velocity.The proposed solution establishes a pseudolinear set of equations by introducing some additional variables, imposes weighted least squares formulation to yield a rough estimate, and utilizes the function relation among the target location parameters and additional variables to improve the estimation accuracy. Theoretical covariance and Cramer-Rao lower bound(CRLB) are derived and compared, analytically indicating that the proposed solution attains the CRLB. Numerical simulations corroborate this analysis and demonstrate that the proposed solution outperforms existing methods.展开更多
In the tracking problem for the maritime radiation source by a passive sensor,there are three main difficulties,i.e.,the poor observability of the radiation source,the detection uncertainty(false and missed detections...In the tracking problem for the maritime radiation source by a passive sensor,there are three main difficulties,i.e.,the poor observability of the radiation source,the detection uncertainty(false and missed detections)and the uncertainty of the target appearing/disappearing in the field of view.These difficulties can make the establishment or maintenance of the radiation source target track invalid.By incorporating the elevation information of the passive sensor into the automatic bearings-only tracking(BOT)and consolidating these uncertainties under the framework of random finite set(RFS),a novel approach for tracking maritime radiation source target with intermittent measurement was proposed.Under the RFS framework,the target state was represented as a set that can take on either an empty set or a singleton; meanwhile,the measurement uncertainty was modeled as a Bernoulli random finite set.Moreover,the elevation information of the sensor platform was introduced to ensure observability of passive measurements and obtain the unique target localization.Simulation experiments verify the validity of the proposed approach for tracking maritime radiation source and demonstrate the superiority of the proposed approach in comparison with the traditional integrated probabilistic data association(IPDA)method.The tracking performance under different conditions,particularly involving different existence probabilities and different appearance durations of the target,indicates that the method to solve our problem is robust and effective.展开更多
Owing to the advantages in detecting the low altitude and stealth target,passive bistatic radar(PBR)has received much attention in surveillance purposes.Due to the uncontrollable characteristic of the transmitted sign...Owing to the advantages in detecting the low altitude and stealth target,passive bistatic radar(PBR)has received much attention in surveillance purposes.Due to the uncontrollable characteristic of the transmitted signal,a high level range or Doppler sidelobes may exist in the ambiguity function which will degrade the target detection performance.Mismatched filtering is a common method to deal with the ambiguity sidelobe problem.However,when mismatched filtering is applied,sidelobes cannot be eliminated completely.The residual sidelobes will cause false-alarm when the constant false alarm ratio(CFAR)is applied.To deal with this problem,a new target detection method based on preprocessing is proposed.In this new method,the ambiguity range and Doppler sidelobes are recognized and eliminated by the preprocessing method according to the prior information.CFAR is also employed to obtain the information of the target echo.Simulation results and results on real data illustrate the effectiveness of the proposed method.展开更多
Radar cross section(RCS)is an important attribute of radar targets and has been widely used in automatic target recognition(ATR).In a passive radar,only the RCS multiplied by a coefficient is available due to the unkn...Radar cross section(RCS)is an important attribute of radar targets and has been widely used in automatic target recognition(ATR).In a passive radar,only the RCS multiplied by a coefficient is available due to the unknown transmitting parameters.For different transmitter-receiver(bistatic)pairs,the coefficients are different.Thus,the recovered RCS in different transmitter-receiver(bistatic)pairs cannot be fused for further use.In this paper,we propose a quantity named quasi-echo-power(QEP)as well as a method for eliminating differences of this quantity among different transmitter-receiver(bistatic)pairs.The QEP is defined as the target echo power after being compensated for distance and pattern propagation factor.The proposed method estimates the station difference coefficients(SDCs)of transmitter-receiver(bistatic)pairs relative to the reference transmitter-receiver(bistatic)pair first.Then,it compensates the QEP and gets the compensated QEP.The compensated QEP possesses a linear relationship with the target RCS.Statistical analyses on the simulated and real-life QEP data show that the proposed method can effectively estimate the SDC between different stations,and the compensated QEP from different receiving stations has the same distribution characteristics for the same target.展开更多
In this paper a new method of passive underwater TMA (target motion analysis) using data fusion is presented. The findings of this research are based on an understanding that there is a powerful sonar system that cons...In this paper a new method of passive underwater TMA (target motion analysis) using data fusion is presented. The findings of this research are based on an understanding that there is a powerful sonar system that consists of many types of sonar but with one own-ship, and that different target parameter measurements can be obtained simultaneously. For the analysis 3 data measurements, passive bearing, elevation and multipath time-delay, are used, which are divided into two groups: a group with estimates of two preliminary target parameter obtained by dealing with each group measurement independently, and a group where correlated estimates are sent to a fusion center where the correlation between two data groups are considered so that the passive underwater TMA is realized. Simulation results show that curves of parameter estimation errors obtained by using the data fusion have fast convergence and the estimation accuracy is noticeably improved. The TMA algorithm presented is verified and is of practical significance because it is easy to be realized in one ship.展开更多
A target localization algorithm,which uses the measurement information from onboard GPS and onboard laser detector to acquire the target position,is proposed to obtain the accurate position of ground target in real ti...A target localization algorithm,which uses the measurement information from onboard GPS and onboard laser detector to acquire the target position,is proposed to obtain the accurate position of ground target in real time in the trajectory correction process of semi-active laser terminal correction projectile.A target localization model is established according to projectile position,attitude and line-of-sight angle.The effects of measurement errors of projectile position,attitude and line-of-sight angle on localization accuracy at different quadrant elevation angles are analyzed through Monte-Carlo simulation.The simulation results show that the measurement error of line-of-sight angle has the largest influence on the localization accuracy.The localization accuracy decreases with the increase in quadrant elevation angle.However,the maximum localization accuracy is less than 7 m.The proposed algorithm meets the accuracy and real-time requirements of target localization.展开更多
In this paper, the problem of underwater passive target motion analysis (TMA) in three dimensions is discussed using the measurements of passive bearings and elevation and frequency on the condition that acoustic sour...In this paper, the problem of underwater passive target motion analysis (TMA) in three dimensions is discussed using the measurements of passive bearings and elevation and frequency on the condition that acoustic source and observer are in different horizontal planes. Simulation results with both of the PLE (pseudo-linear estimation) and MLE (Maximum likelihood estimation) show that the TMA method is effective in oceanic environment. Its error covariance curves tend to its Cramer-Rao lower bounds.展开更多
A marginalized particle filtering （MPF） approach is proposed for target tracking under the background of passive measurement. Essentially, the MPF is a combination of particle filtering technique and Kalman filter. ...A marginalized particle filtering （MPF） approach is proposed for target tracking under the background of passive measurement. Essentially, the MPF is a combination of particle filtering technique and Kalman filter. By making full use of marginalization, the distributions of the tractable linear part of the total state variables are updated analytically using Kalman filter, and only the lower-dimensional nonlinear state variable needs to be dealt with using particle filter. Simulation studies are performed on an illustrative example, and the results show that the MPF method leads to a significant reduction of the tracking errors when compared with the direct particle implementation. Real data test results also validate the effectiveness of the presented method.展开更多
Integrins are heterodimeric cell surface receptors that bind to ligands on another cell,e.g.intercellular adhesion molecule 1(ICAM-1),or the extracellular matrix.Integrins play an important role in immune system,and t...Integrins are heterodimeric cell surface receptors that bind to ligands on another cell,e.g.intercellular adhesion molecule 1(ICAM-1),or the extracellular matrix.Integrins play an important role in immune system,and they participate in inflammation,thrombosis,and proliferation,migration and apoptosis of tumor cells.They mediate adhesion and transduce signals across the membrane usually under the influence of forces.A recent study has shown that integrins bind and activate transforming growth factorβisoform(TGF-β)which is involved in tumor suppression and growth,and blocking the binding of TGF-βto integrin can inhibit tumor growth.RGD(arginine-glycine-aspartate)small peptide,which competitively inhibits ligand binding to integrins,has been approved as an injectable drug.However,when the RGD is used to block cancer-related extracellular signaling pathways,it will also cause activation of integrins for a period,and stimulate the transduction of intracellular signals constantly.Therefore,it is necessary to explore for new drugs that can selectively control conformational state of integrins without activating or blocking all of them.In this study,we selected two small peptides,KQAGDV and RTDLDSLRT,that combined with integrins and do not contain an RGD sequence.The non-RGD polypeptide RTDLDSLRT has been reported to have a binding site with integrins and the binding affinity is on nanomolar scale.For the motif of the fibrinogen y chain C-terminal KQAGDV,it can adhere to the head of the integrins.The micropipette aspiration technique and electron microscopy techniques were used to study the adhesion and activation of integrins by peptides,respectively.Micropipette aspiration technique was used to investigate the adhesion frequency of peptide and integrin on Jurkat cell.The pressure system was used to supply a controllable negative pression to the microtube,and two micropipettes were used to absorb red blood cells and Jurkat cells,respectively.The red blood cells were coated with small peptides and can serve as a force sensor after being sucked when two cells were connected.The binding kinetics of integrin and peptides interactions was determined by fitting the curves constructed using adhesion probability between two cells as a function of time.The curves were fitted using a small system probabilistic kinetic model to estimate a pair of kinetic parameters,including the zero force reverse rate kr0,and the cellular binding affinity Acmrm1Ka0.The adhesion frequency yielded P(t)=75%and 57%for RGD and KQAG DV peptides,respectively.We obtained Acmrm1Ka0=1.40 and kr0=0.32 s-1,for RGD,and Acmrm1Ka0=0.85 and kr0=0.54 s-1 for KQAGDV.The RGD peptide has a higher adhesion frequency and lower dissociation rate than the KQAGDV peptide.Electron microscopy techniques was used to observe the activation of integrins by peptides.Jurkat cell expressing integrins was bound to a magnetic bead and bottom plate which were coated with different integrin-binding peptides.Then,we manipulated the beads in a controlled direction by changing the magnetic field nearby,and the forces were applied to the cell.The target cells were fixed and then observed by scanning electron microscope or transmission electron microscope.Jurkat cells contain abundant flexible microvilli of which there are many parallel bundles of actin filaments inside.By electron microscopy analysis,the cell connected with magnetic bead coated with RGD were found to be protruded and the size of microvilli increased up to#-fold of the length of the KQAGDV sample.The microvilli exhibited a curved agglomerate structure under a force-free condition.Moreover,a higher proportion of cells were activated in the presence of RGD than KQAGDV.In conclusion,the binding affinity of KQAGDV to integrin is weaker than RGD,and KQAGDV can bind with integrins effectively with a lower activated proportion.Our results indicate the peptides may selectively bind to integrins without activating them.展开更多
Global Navigation Satellite System(GNSS)-based passive radar(GBPR)has been widely used in remote sensing applications.However,for moving target detection(MTD),the quadratic phase error(QPE)introduced by the non-cooper...Global Navigation Satellite System(GNSS)-based passive radar(GBPR)has been widely used in remote sensing applications.However,for moving target detection(MTD),the quadratic phase error(QPE)introduced by the non-cooperative target motion is usually difficult to be compensated,as the low power level of the GBPR echo signal renders the estimation of the Doppler rate less effective.Consequently,the moving target in GBPR image is usually defocused,which aggravates the difficulty of target detection even further.In this paper,a spawning particle filter(SPF)is proposed for defocused MTD.Firstly,the measurement model and the likelihood ratio function(LRF)of the defocused point-like target image are deduced.Then,a spawning particle set is generated for subsequent target detection,with reference to traditional particles in particle filter(PF)as their parent.After that,based on the PF estimator,the SPF algorithm and its sequential Monte Carlo(SMC)implementation are proposed with a novel amplitude estimation method to decrease the target state dimension.Finally,the effectiveness of the proposed SPF is demonstrated by numerical simulations and pre-liminary experimental results,showing that the target range and Doppler can be estimated accurately.展开更多
We propose a target tracking method based on particle filtering(PF) to solve the nonlinear non-Gaussian target-tracking problem in the bistatic radar systems using external radiation sources. Traditional nonlinear sta...We propose a target tracking method based on particle filtering(PF) to solve the nonlinear non-Gaussian target-tracking problem in the bistatic radar systems using external radiation sources. Traditional nonlinear state estimation method is extended Kalman filtering (EKF), which is to do the first level Taylor series extension. It will cause an inaccuracy or even a scatter estimation result on condition that there is either a highly nonlinear target or a large noise square-error. Besides, Kalman filtering is the optimal resolution under a Gaussian noise assumption, and is not suitable to the non-Gaussian condition. PF is a sort of statistic filtering based on Monte Carlo simulation that is using some random samples (particles) to simulate the posterior probability density of system random variables. This method can be used in any nonlinear random system. It can be concluded through simulation that PF can achieve higher accuracy than the traditional EKF.展开更多
Focusing on the three-dimensional guidance problem in case of target maneuvers and response delay of the autopilot, the missile guidance law utilizing active disturbance rejection control （ADRC） is proposed. Based o...Focusing on the three-dimensional guidance problem in case of target maneuvers and response delay of the autopilot, the missile guidance law utilizing active disturbance rejection control （ADRC） is proposed. Based on the nonlinear three-dimensional missile target engagement kinematics, the guidance model is es- tablished, The target acceleration is treated as a disturbance and the dynamics of the autopilot is considered by using a first-order model. A nonlinear continuous robust guidance law is designed by using a cascaded structure ADRC controller. In this method the disturbance is estimated by using the extended state observer （ESO） and compensated during each sampling period. Simulation results show that the proposed cascaded loop structure is a viable solution to the guidance law design and has strong robustness with respect to target maneuvers and response delay of the autopilot.展开更多
Microbubbles can enhance the detection in noninvasive ultrasound imaging.Recently,targeted microbubbles have been developed to selectively adhere to specific and overexpressed p molecules in endothelial cells in some ...Microbubbles can enhance the detection in noninvasive ultrasound imaging.Recently,targeted microbubbles have been developed to selectively adhere to specific and overexpressed p molecules in endothelial cells in some pathologic conditions.However,the law of展开更多
基金supported by the Key Projects of Shanghai Science and Technology on Biomedicine(NO.10DZ1950800)the Major Project of Shanghai Zhabei District Health Bureau (No. 2011ZD01)
文摘Objective:To reveal the neural network of active and passive hand movements. Method:Seven healthy aged people were checked, and acquired functional magnetic resonance imaging data on a 1.5T scanner. Active movement consisted of repetitive grasping and loosening of hand; passive movement involved the same movement performed by examiner. Both types of hand movements were assessed separately. These data were analysed by Statistical Parametric Mapping Microsoft. Result:The main activated brain areas were the contralateral supplemental motor area, primary motor area, primary sensory area and the ipsilateral cerebellum when subjects gripped right hands actively and passively. The supplemental area was less active in passive hand movement than active hand movement. The activated brain areas were mainly within Brodmann area 4 during active hand movement; in the contrast, the voxels triggered by passive movement were mainly within Brodmann areas 3,1,2 areas. Conclusion:The results suggest that the neural networks of passive and active tasks spared some common areas, and the passive movement could be as effective as active movement to facilitate the recovery of limbs motor function in patients with brain damage.
基金supported by the National Advanced Research Foundation of China (2010AAJ144)
文摘Recently, the code division multiple access （CDMA） waveform exists in the large area across the world. However, when using the CDMA system as the illuminator of opportunity for the passive bistatic radar （PBR）, there exists interference not only from the base station used as the illuminator of opportunity but also from other base stations with the same frequency. And be cause in the CDMA system, the signal transmitted by each base station is different, using the direct signal of one base station can not cancel the interference from other base stations. A CDMA based PBR using an element linear array antenna as both the reference antenna and surveillance antenna is introduced. To deal with the interference in this PBR system, an adaptive temporal cancellation algorithm is used to remove the interference from the base station used as the illuminator of opportunity firstly. And then a robust adaptive beamformer is used to suppress the interference from other base stations. Finally, the preliminary experiment re sults demonstrate the feasibility of using CDMA signals as a radar waveform.
基金Supported by Science & Engineering Research Council of Singnpore (0521010037)
文摘Wireless sensor network (WSN) of active sensors suffers from serious inter-sensor interference (ISI) and imposes new design and implementation challenges. In this paper, based on the ultrasonic sensor network, two time-division based distributed sensor scheduling schemes are proposed to deal with ISI by scheduling sensors periodically and adaptively respectively. Extended Kalman filter (EKF) is used as the tracking algorithm in distributed manner. Simulation results show that the adaptive sensor scheduling scheme can achieve superior tracking accuracy with faster tracking convergence speed.
基金supported by the National Natural Science Foundation of China (61703433)。
文摘Time delay and Doppler shift between the echo signal and the reference signal are two most commonly used measurements in target localization for the passive radar. Doppler rate, which can be obtained from the extended cross ambiguity function, offers an opportunity to further enhance the localization accuracy. This paper considers using the measurement Doppler rate in addition to measurements of time delay and Doppler shift to locate a moving target. A closed-form solution is developed to accurately and efficiently estimate the target position and velocity.The proposed solution establishes a pseudolinear set of equations by introducing some additional variables, imposes weighted least squares formulation to yield a rough estimate, and utilizes the function relation among the target location parameters and additional variables to improve the estimation accuracy. Theoretical covariance and Cramer-Rao lower bound(CRLB) are derived and compared, analytically indicating that the proposed solution attains the CRLB. Numerical simulations corroborate this analysis and demonstrate that the proposed solution outperforms existing methods.
基金Project(61101186)supported by the National Natural Science Foundation of China
文摘In the tracking problem for the maritime radiation source by a passive sensor,there are three main difficulties,i.e.,the poor observability of the radiation source,the detection uncertainty(false and missed detections)and the uncertainty of the target appearing/disappearing in the field of view.These difficulties can make the establishment or maintenance of the radiation source target track invalid.By incorporating the elevation information of the passive sensor into the automatic bearings-only tracking(BOT)and consolidating these uncertainties under the framework of random finite set(RFS),a novel approach for tracking maritime radiation source target with intermittent measurement was proposed.Under the RFS framework,the target state was represented as a set that can take on either an empty set or a singleton; meanwhile,the measurement uncertainty was modeled as a Bernoulli random finite set.Moreover,the elevation information of the sensor platform was introduced to ensure observability of passive measurements and obtain the unique target localization.Simulation experiments verify the validity of the proposed approach for tracking maritime radiation source and demonstrate the superiority of the proposed approach in comparison with the traditional integrated probabilistic data association(IPDA)method.The tracking performance under different conditions,particularly involving different existence probabilities and different appearance durations of the target,indicates that the method to solve our problem is robust and effective.
基金the National Natural Science Foundation of China(61401526).
文摘Owing to the advantages in detecting the low altitude and stealth target,passive bistatic radar(PBR)has received much attention in surveillance purposes.Due to the uncontrollable characteristic of the transmitted signal,a high level range or Doppler sidelobes may exist in the ambiguity function which will degrade the target detection performance.Mismatched filtering is a common method to deal with the ambiguity sidelobe problem.However,when mismatched filtering is applied,sidelobes cannot be eliminated completely.The residual sidelobes will cause false-alarm when the constant false alarm ratio(CFAR)is applied.To deal with this problem,a new target detection method based on preprocessing is proposed.In this new method,the ambiguity range and Doppler sidelobes are recognized and eliminated by the preprocessing method according to the prior information.CFAR is also employed to obtain the information of the target echo.Simulation results and results on real data illustrate the effectiveness of the proposed method.
基金supported by the National Natural Science Foundation of China(61931015,62071335)the Science and Technology Program of Shenzhen(JCYJ20170818112037398)the Technological Innovation Project of Hubei Province of China(2019AAA061).
文摘Radar cross section(RCS)is an important attribute of radar targets and has been widely used in automatic target recognition(ATR).In a passive radar,only the RCS multiplied by a coefficient is available due to the unknown transmitting parameters.For different transmitter-receiver(bistatic)pairs,the coefficients are different.Thus,the recovered RCS in different transmitter-receiver(bistatic)pairs cannot be fused for further use.In this paper,we propose a quantity named quasi-echo-power(QEP)as well as a method for eliminating differences of this quantity among different transmitter-receiver(bistatic)pairs.The QEP is defined as the target echo power after being compensated for distance and pattern propagation factor.The proposed method estimates the station difference coefficients(SDCs)of transmitter-receiver(bistatic)pairs relative to the reference transmitter-receiver(bistatic)pair first.Then,it compensates the QEP and gets the compensated QEP.The compensated QEP possesses a linear relationship with the target RCS.Statistical analyses on the simulated and real-life QEP data show that the proposed method can effectively estimate the SDC between different stations,and the compensated QEP from different receiving stations has the same distribution characteristics for the same target.
文摘In this paper a new method of passive underwater TMA (target motion analysis) using data fusion is presented. The findings of this research are based on an understanding that there is a powerful sonar system that consists of many types of sonar but with one own-ship, and that different target parameter measurements can be obtained simultaneously. For the analysis 3 data measurements, passive bearing, elevation and multipath time-delay, are used, which are divided into two groups: a group with estimates of two preliminary target parameter obtained by dealing with each group measurement independently, and a group where correlated estimates are sent to a fusion center where the correlation between two data groups are considered so that the passive underwater TMA is realized. Simulation results show that curves of parameter estimation errors obtained by using the data fusion have fast convergence and the estimation accuracy is noticeably improved. The TMA algorithm presented is verified and is of practical significance because it is easy to be realized in one ship.
文摘A target localization algorithm,which uses the measurement information from onboard GPS and onboard laser detector to acquire the target position,is proposed to obtain the accurate position of ground target in real time in the trajectory correction process of semi-active laser terminal correction projectile.A target localization model is established according to projectile position,attitude and line-of-sight angle.The effects of measurement errors of projectile position,attitude and line-of-sight angle on localization accuracy at different quadrant elevation angles are analyzed through Monte-Carlo simulation.The simulation results show that the measurement error of line-of-sight angle has the largest influence on the localization accuracy.The localization accuracy decreases with the increase in quadrant elevation angle.However,the maximum localization accuracy is less than 7 m.The proposed algorithm meets the accuracy and real-time requirements of target localization.
文摘In this paper, the problem of underwater passive target motion analysis (TMA) in three dimensions is discussed using the measurements of passive bearings and elevation and frequency on the condition that acoustic source and observer are in different horizontal planes. Simulation results with both of the PLE (pseudo-linear estimation) and MLE (Maximum likelihood estimation) show that the TMA method is effective in oceanic environment. Its error covariance curves tend to its Cramer-Rao lower bounds.
文摘A marginalized particle filtering （MPF） approach is proposed for target tracking under the background of passive measurement. Essentially, the MPF is a combination of particle filtering technique and Kalman filter. By making full use of marginalization, the distributions of the tractable linear part of the total state variables are updated analytically using Kalman filter, and only the lower-dimensional nonlinear state variable needs to be dealt with using particle filter. Simulation studies are performed on an illustrative example, and the results show that the MPF method leads to a significant reduction of the tracking errors when compared with the direct particle implementation. Real data test results also validate the effectiveness of the presented method.
基金supported by the National Science Foundation of China ( 11772133, 11372116)
文摘Integrins are heterodimeric cell surface receptors that bind to ligands on another cell,e.g.intercellular adhesion molecule 1(ICAM-1),or the extracellular matrix.Integrins play an important role in immune system,and they participate in inflammation,thrombosis,and proliferation,migration and apoptosis of tumor cells.They mediate adhesion and transduce signals across the membrane usually under the influence of forces.A recent study has shown that integrins bind and activate transforming growth factorβisoform(TGF-β)which is involved in tumor suppression and growth,and blocking the binding of TGF-βto integrin can inhibit tumor growth.RGD(arginine-glycine-aspartate)small peptide,which competitively inhibits ligand binding to integrins,has been approved as an injectable drug.However,when the RGD is used to block cancer-related extracellular signaling pathways,it will also cause activation of integrins for a period,and stimulate the transduction of intracellular signals constantly.Therefore,it is necessary to explore for new drugs that can selectively control conformational state of integrins without activating or blocking all of them.In this study,we selected two small peptides,KQAGDV and RTDLDSLRT,that combined with integrins and do not contain an RGD sequence.The non-RGD polypeptide RTDLDSLRT has been reported to have a binding site with integrins and the binding affinity is on nanomolar scale.For the motif of the fibrinogen y chain C-terminal KQAGDV,it can adhere to the head of the integrins.The micropipette aspiration technique and electron microscopy techniques were used to study the adhesion and activation of integrins by peptides,respectively.Micropipette aspiration technique was used to investigate the adhesion frequency of peptide and integrin on Jurkat cell.The pressure system was used to supply a controllable negative pression to the microtube,and two micropipettes were used to absorb red blood cells and Jurkat cells,respectively.The red blood cells were coated with small peptides and can serve as a force sensor after being sucked when two cells were connected.The binding kinetics of integrin and peptides interactions was determined by fitting the curves constructed using adhesion probability between two cells as a function of time.The curves were fitted using a small system probabilistic kinetic model to estimate a pair of kinetic parameters,including the zero force reverse rate kr0,and the cellular binding affinity Acmrm1Ka0.The adhesion frequency yielded P(t)=75%and 57%for RGD and KQAG DV peptides,respectively.We obtained Acmrm1Ka0=1.40 and kr0=0.32 s-1,for RGD,and Acmrm1Ka0=0.85 and kr0=0.54 s-1 for KQAGDV.The RGD peptide has a higher adhesion frequency and lower dissociation rate than the KQAGDV peptide.Electron microscopy techniques was used to observe the activation of integrins by peptides.Jurkat cell expressing integrins was bound to a magnetic bead and bottom plate which were coated with different integrin-binding peptides.Then,we manipulated the beads in a controlled direction by changing the magnetic field nearby,and the forces were applied to the cell.The target cells were fixed and then observed by scanning electron microscope or transmission electron microscope.Jurkat cells contain abundant flexible microvilli of which there are many parallel bundles of actin filaments inside.By electron microscopy analysis,the cell connected with magnetic bead coated with RGD were found to be protruded and the size of microvilli increased up to#-fold of the length of the KQAGDV sample.The microvilli exhibited a curved agglomerate structure under a force-free condition.Moreover,a higher proportion of cells were activated in the presence of RGD than KQAGDV.In conclusion,the binding affinity of KQAGDV to integrin is weaker than RGD,and KQAGDV can bind with integrins effectively with a lower activated proportion.Our results indicate the peptides may selectively bind to integrins without activating them.
基金supported by the National Natural Science Foundation of China(62101014)the National Key Laboratory of Science and Technology on Space Microwave(6142411203307).
文摘Global Navigation Satellite System(GNSS)-based passive radar(GBPR)has been widely used in remote sensing applications.However,for moving target detection(MTD),the quadratic phase error(QPE)introduced by the non-cooperative target motion is usually difficult to be compensated,as the low power level of the GBPR echo signal renders the estimation of the Doppler rate less effective.Consequently,the moving target in GBPR image is usually defocused,which aggravates the difficulty of target detection even further.In this paper,a spawning particle filter(SPF)is proposed for defocused MTD.Firstly,the measurement model and the likelihood ratio function(LRF)of the defocused point-like target image are deduced.Then,a spawning particle set is generated for subsequent target detection,with reference to traditional particles in particle filter(PF)as their parent.After that,based on the PF estimator,the SPF algorithm and its sequential Monte Carlo(SMC)implementation are proposed with a novel amplitude estimation method to decrease the target state dimension.Finally,the effectiveness of the proposed SPF is demonstrated by numerical simulations and pre-liminary experimental results,showing that the target range and Doppler can be estimated accurately.
文摘We propose a target tracking method based on particle filtering(PF) to solve the nonlinear non-Gaussian target-tracking problem in the bistatic radar systems using external radiation sources. Traditional nonlinear state estimation method is extended Kalman filtering (EKF), which is to do the first level Taylor series extension. It will cause an inaccuracy or even a scatter estimation result on condition that there is either a highly nonlinear target or a large noise square-error. Besides, Kalman filtering is the optimal resolution under a Gaussian noise assumption, and is not suitable to the non-Gaussian condition. PF is a sort of statistic filtering based on Monte Carlo simulation that is using some random samples (particles) to simulate the posterior probability density of system random variables. This method can be used in any nonlinear random system. It can be concluded through simulation that PF can achieve higher accuracy than the traditional EKF.
基金supported by the Aviation Science Foundation(2013ZC12004)
文摘Focusing on the three-dimensional guidance problem in case of target maneuvers and response delay of the autopilot, the missile guidance law utilizing active disturbance rejection control （ADRC） is proposed. Based on the nonlinear three-dimensional missile target engagement kinematics, the guidance model is es- tablished, The target acceleration is treated as a disturbance and the dynamics of the autopilot is considered by using a first-order model. A nonlinear continuous robust guidance law is designed by using a cascaded structure ADRC controller. In this method the disturbance is estimated by using the extended state observer （ESO） and compensated during each sampling period. Simulation results show that the proposed cascaded loop structure is a viable solution to the guidance law design and has strong robustness with respect to target maneuvers and response delay of the autopilot.
基金supported by National Natural Science Foundation of China,No.30700151
文摘Microbubbles can enhance the detection in noninvasive ultrasound imaging.Recently,targeted microbubbles have been developed to selectively adhere to specific and overexpressed p molecules in endothelial cells in some pathologic conditions.However,the law of
