Microplastics(MPs)have recently emerged as a significant environmental problem with devastating consequences for organisms.Understanding MPs pollution in the Bay of Bengal is crucial for assessing its ecological impac...Microplastics(MPs)have recently emerged as a significant environmental problem with devastating consequences for organisms.Understanding MPs pollution in the Bay of Bengal is crucial for assessing its ecological impact on marine biodiversity and human health.This study examined the occurrence,spatial distribution,physical and chemical properties,ecological risks,and probable sources of MPs in estuarine and coastal marine environments in the northeastern Bay of Bengal.The average concentration of MPs in surface water of the Karnaphuli estuary,the Meghna estuary,and the southeastern coastal region were 916.7±462.6 items/m^(3),462.9±324.5 items/m^(3),and 350.0±190.5 items/m^(3),respectively,varying from 105.0±324.5 items/m^(3)to 1640.0±462.6 items/m^(3).In the sediments of the Karnaphuli estuary,the Meghna estuary,and the southeast coast of Bangladesh,the average amount of MPs were 94.3±33.1 items/kg,157.6±89.0 items/kg,and 134.3±38.7 items/kg,with a range of 60±33.1 items/kg to 334.3±89.0 items/kg.Most observed MPs were fibers(60.0%in the water;56.0%in the sediments),followed by fragments and lines.Detected MPs were dominated by polypropylene(20.7%)in the water,and acrylic(15.4%)in the sediment,black colored(76.2%in the water,72.7%in the sediments),and 200-500μm sized(48%in the water,37%in the sediments).Pollution Risk Index(PRI)indicated significant pollution levels(from medium to very high)in estuarine and coastal areas.Multi-statistical analysis indicated land-based inputs(tourists,local waste,agriculture,and industry)dominated the studied regions.The study emphasized the potential impact of MPs pollution on aquatic ecosystems,emphasizing the need for effective management,mitigation methods,continuous surveillance,and thorough evaluation.展开更多
So far, large uncertainties of the Indonesian throughflow(ITF) reside in the eastern Indonesian seas, such as the Maluku Sea and the Halmahera Sea. In this study, the water sources of the Maluku Sea and the Halmahera ...So far, large uncertainties of the Indonesian throughflow(ITF) reside in the eastern Indonesian seas, such as the Maluku Sea and the Halmahera Sea. In this study, the water sources of the Maluku Sea and the Halmahera Sea are diagnosed at seasonal and interannual timescales and at different vertical layers, using the state-of-the-art simulations of the Ocean General Circulation Model(OGCM) for Earth Simulator(OFES). Asian monsoon leaves clear seasonal footprints on the eastern Indonesian seas. Consequently, the subsurface waters(around 24.5σ_θ and at ～150 m) in both the Maluku Sea and the Halmahera Sea stem from the South Pacific(SP) during winter monsoon, but during summer monsoon the Maluku Sea is from the North Pacific(NP), and the Halmahera Sea is a mixture of waters originating from the NP and the SP. The monsoon impact decreases with depth, so that in the Maluku Sea, the intermediate water(around 26.8σ_θ and at ～480 m) is always from the northern Banda Sea and the Halmahera Sea water is mainly from the SP in winter and the Banda Sea in summer. The deep waters(around27.2σ_θ and at ～1 040 m) in both seas are from the SP, with weak seasonal variability. At the interannual timescale,the subsurface water in the Maluku Sea originates from the NP/SP during El Ni?o/La Ni?a, while the subsurface water in the Halmahera Sea always originates from the SP. Similar to the seasonal variability, the intermediate water in Maluku Sea mainly comes from the Banda Sea and the Halmahera Sea always originates from the SP. The deep waters in both seas are from the SP. Our findings are helpful for drawing a comprehensive picture of the water properties in the Indonesian seas and will contribute to a better understanding of the ocean-atmosphere interaction over the maritime continent.展开更多
For generating a uniform and steady magnetic field, Helmholtz coil is extensively used in nuclear magnetic resonance gyro(NMRG). Unfortunately, the volume of Helmholtz coil makes it inconvenient to miniaturize NMRG. T...For generating a uniform and steady magnetic field, Helmholtz coil is extensively used in nuclear magnetic resonance gyro(NMRG). Unfortunately, the volume of Helmholtz coil makes it inconvenient to miniaturize NMRG. This study introduces Braunbeck coil that can be used in magnetic field excitation system. Braunbeck coil can produce homogeneous magnetic field within a limit space, and occupy a small volume. In addition, this study presents mathematical expressions that can be used to calculate the area of uniform magnetic field. Experimental test verifies the effectiveness of the proposed design, and the results accord closely with the actual simulation.展开更多
Both time-delays and anti-windup(AW)problems are conventional problems in system design,which are scarcely discussed in cellular neural networks(CNNs).This paper discusses stabilization for a class of distributed time...Both time-delays and anti-windup(AW)problems are conventional problems in system design,which are scarcely discussed in cellular neural networks(CNNs).This paper discusses stabilization for a class of distributed time-delayed CNNs with input saturation.Based on the Lyapunov theory and the Schur complement principle,a bilinear matrix inequality(BMI)criterion is designed to stabilize the system with input saturation.By matrix congruent transformation,the BMI control criterion can be changed into linear matrix inequality(LMI)criterion,then it can be easily solved by the computer.It is a one-step AW strategy that the feedback compensator and the AW compensator can be determined simultaneously.The attraction domain and its optimization are also discussed.The structure of CNNs with both constant timedelays and distribute time-delays is more general.This method is simple and systematic,allowing dealing with a large class of such systems whose excitation satisfies the Lipschitz condition.The simulation results verify the effectiveness and feasibility of the proposed method.展开更多
A systematic and comprehensive comparison of the five commonly used earth radii in geodesy and cartography is carried out,and the differences between the most common points of the earth radii,their corresponding maxim...A systematic and comprehensive comparison of the five commonly used earth radii in geodesy and cartography is carried out,and the differences between the most common points of the earth radii,their corresponding maximum values,and the latitudes of equal points between them are derived with the help of computer algebraic systems.The symbolic expressions are expressed as a power series of the first eccentricity.Taking the CGCS2000 ellipsoid as an example,the differences between the commonly used earth radii are clarified to numerical values.The results show that the difference between the commonly used earth radii has a maximum at 90 degrees and a minimum at 0 degree.The difference between the average radius of curvature and the rectifying sphere radius is the biggest,and the difference between the average radius of curvature and the average sphere radius is the smallest.These results can provide a theoretical basis for corresponding research in the geosciences,space science,navigation and positioning.展开更多
The existing methods of downward continuation of potential field cannot be used to continue the aeromagnetic data to the marine surface because of the limited continuation distance. An iteration method for the downwar...The existing methods of downward continuation of potential field cannot be used to continue the aeromagnetic data to the marine surface because of the limited continuation distance. An iteration method for the downward continuation of potential field with a much larger continuation distance has been developed, which can continue the aeromagnetic data to the marine surface and get the marine - magnetic chart with the same scale as the aeromagnetic data. This downward continuation method will greatly raise the ef- ficiency of marine - magnetic investigation. The principle of the iteration method is presented. The method is demonstrated on synthetic models and real aeromagnetic data. Also, the error brought by continuation is discussed. The efficiency of the iteration method for the downward continuation of potential field is compared with the fast fourier transform （FFT） method, the former is much better than the latter.展开更多
Due to variable symbol length of digital pulse interval modulation(DPIM),it is difficult to analyze the error performances of Turbo coded DPIM.To solve this problem,a fixed-length digital pulse interval modulation(FDP...Due to variable symbol length of digital pulse interval modulation(DPIM),it is difficult to analyze the error performances of Turbo coded DPIM.To solve this problem,a fixed-length digital pulse interval modulation(FDPIM) method is provided.The FDPIM modulation structure is introduced.The packet error rates of uncoded FDPIM are analyzed and compared with that of DPIM.Bit error rates of Turbo coded FDPIM are simulated based on three kinds of analytical models under weak turbulence channel.The results show that packet error rate of uncoded FDPIM is inferior to that of uncoded DPIM.However,FDPIM is easy to be implemented and easy to be combined.with Turbo code for soft-decision because of its fixed length.Besides,the introduction of Turbo code in this modulation can decrease the average power about 10 dBm,which means that it can improve the error performance of the system effectively.展开更多
To achieve accurate classification and recognition of ship target types,it is necessary to establish a sample library of ship targets to be identified.On the basis of exploring the principles of building a ship target...To achieve accurate classification and recognition of ship target types,it is necessary to establish a sample library of ship targets to be identified.On the basis of exploring the principles of building a ship target image library,the paper determines the sample set.Using 3DS MAX software as the platform,combined with the accurate 3D model of the ship in an offline state,the software fully utilizes its own rendering and animation functions to achieve the automatic generation of multi-view and multi-scale views of ship targets.To reduce the storage capacity of the image database,a construction method of the ship target image database based on the AP algorithm is presented.The algorithm can obtain the optimal cluster number,reduce the data storage capacity of the image database,and save the calculation amount for the subsequent matching calculation.展开更多
A novel neural network based on iterated unscented Kalman filter （IUKF） algorithm is established to model and com- pensate for the fiber optic gyro （FOG） bias drift caused by temperature. In the network, FOG tempe...A novel neural network based on iterated unscented Kalman filter （IUKF） algorithm is established to model and com- pensate for the fiber optic gyro （FOG） bias drift caused by temperature. In the network, FOG temperature and its gradient are set as input and the FOG bias drift is set as the expected output. A 2-5-1 network trained with IUKF algorithm is established. The IUKF algorithm is developed on the basis of the unscented Kalman filter （UKF）. The weight and bias vectors of the hidden layer are set as the state of the UKF and its process and measurement equations are deduced according to the network architecture. To solve the unavoidable estimation deviation of the mean and covariance of the states in the UKF algorithm, iterative computation is introduced into the UKF after the measurement update. While the measure- ment noise R is extended into the state vectors before iteration in order to meet the statistic orthogonality of estimate and mea- surement noise. The IUKF algorithm can provide the optimized estimation for the neural network because of its state expansion and iteration. Temperature rise （-20-20℃） and drop （70-20℃） tests for FOG are carried out in an attemperator. The temperature drift model is built with neural network, and it is trained respectively with BP, UKF and IUKF algorithms. The results prove that the proposed model has higher precision compared with the back- propagation （BP） and UKF network models.展开更多
Texture-based visualization method is a common method in the visualization of vector field data.Aiming at adding color mapping to the texture of ocean vector field and solving the ambiguity of vector direction in text...Texture-based visualization method is a common method in the visualization of vector field data.Aiming at adding color mapping to the texture of ocean vector field and solving the ambiguity of vector direction in texture image,a new color texture enhancement algorithm based on the Line Integral Convolution(LIC)for the vector field data is proposed,which combines the HSV color mapping and cumulative distribution function calculation of vector field data.This algorithm can be summarized as follows:firstly,the vector field data is convoluted twice by line integration to get the gray texture image.Secondly,the method of mapping vector data to each component of the HSV color space is established.And then,the vector field data is mapped into HSV color space and converted from HSV to RGB values to get the color image.Thirdly,the cumulative distribution function of the RGB color components of the gray texture image and the color image is constructed to enhance the gray texture and RGB color values.Finally,both the gray texture image and the color image are fused to get the color texture.The experimental results show that the proposed LIC color texture enhancement algorithm is capable of generating a better display of vector field data.Furthermore,the ambiguity of vector direction in the texture images is solved and the direction information of the vector field is expressed more accurately.展开更多
An algorithm using fixed-lag smooth filtering to improve the precision of EIS algorithm is presented in this paper. Ftrstly, gray projection algorithm (GPA) is used to calculate the interframe global motion vectors. S...An algorithm using fixed-lag smooth filtering to improve the precision of EIS algorithm is presented in this paper. Ftrstly, gray projection algorithm (GPA) is used to calculate the interframe global motion vectors. Secondly, the fixed-lag smooth filter is used to smoothen the motion track of the original video sequence, according to different motion models. At last, the original sequence is compensated by using the compensation vectors calculated from filtering. This algorithm has been proved superior in filtering precision by experiments of video sequences in different motion scenes. This algorithm also satisfies the real-time request.展开更多
In inertial navigation system(INS) and global positioning system(GPS) integrated system, GPS antennas are usually not located at the same location as the inertial measurement unit(IMU) of the INS, so the lever arm eff...In inertial navigation system(INS) and global positioning system(GPS) integrated system, GPS antennas are usually not located at the same location as the inertial measurement unit(IMU) of the INS, so the lever arm effect exists, which makes the observation equation highly nonlinear. The INS/GPS integration with constant lever arm effect is studied. The position relation of IMU and GPS's antenna is represented in the earth centered earth fixed frame, while the velocity relation of these two systems is represented in local horizontal frame. Due to the small integration time interval of INS, i.e. 0.1 s in this work, the nonlinearity in the INS error equation is trivial, so the linear INS error model is constructed and addressed by Kalman filter's prediction step. On the other hand, the high nonlinearity in the observation equation due to lever arm effect is addressed by unscented Kalman filter's update step to attain higher accuracy and better applicability. Simulation is designed and the performance of the hybrid filter is validated.展开更多
To address a problem of autonomous attitude determination algorithm using gravitational field and geomagnetic field observation, a new recursive optimization autonomous attitude estimation algorithm is proposed. The a...To address a problem of autonomous attitude determination algorithm using gravitational field and geomagnetic field observation, a new recursive optimization autonomous attitude estimation algorithm is proposed. The algorithm is based on unscented Kalman filter(UKF), and can synchronously provide the attitude rate information. The simulated results show that the measurement precision of the method could be increased by 2 times compared to that of the common methods.展开更多
In this paper the relations between two spreads, between two group delays, and between one spread and one group delay in fractional Fourier transform （FRFT） domains, are presented and three theorems on the uncertain...In this paper the relations between two spreads, between two group delays, and between one spread and one group delay in fractional Fourier transform （FRFT） domains, are presented and three theorems on the uncertainty principle in FRFT domains are also developed. Theorem 1 gives the bounds of two spreads in two FRFT domains. Theorem 2 shows the uncertainty relation between two group delays in two FRFT domains. Theorem 3 presents the crossed uncertainty relation between one group delay and one spread in two FRFT domains. The novelty of their results lies in connecting the products of different physical measures and giving their physical interpretations. The existing uncertainty principle in the FRFT domain is only a special ease of theorem 1, and the conventional uncertainty principle in time-frequency domains is a special case of their results. Therefore, three theorems develop the relations of two spreads in time-frequency domains into the relations between two spreads, between two group delays, and between one spread and one group delay in FRFT domains.展开更多
The general structure of ship-borne helicopter landing forecast system is presented, and a novel ship motion prediction model based on minor component analysis (MCA) is built up to improve the forecast effectiveness. ...The general structure of ship-borne helicopter landing forecast system is presented, and a novel ship motion prediction model based on minor component analysis (MCA) is built up to improve the forecast effectiveness. To validate the feasibility of this landing forecast system, time series for the roll, pitch and heave are generated by simulation and then forecasted based on MCA. Simulation results show that ship-borne helicopters can land safely in higher sea condition while carrying on rescue or replenishment tasks at sea in terms of the landing forecast system.展开更多
With the revision work of the IMO Model Course 6.09, the trainee-centered methodology is greatly highlighted, together with the newly merging technology for education, especially for language learning. This paper will...With the revision work of the IMO Model Course 6.09, the trainee-centered methodology is greatly highlighted, together with the newly merging technology for education, especially for language learning. This paper will consider blended learning, for instance. Blended learning is adorable for many educators in recent years, which demonstrates the principle of student-centered as well as alternates the role of the teachers from the traditional way. MOOC （Massive Online Open Course） is initiated in most schools as well, for the purpose of mutual share of the best education in the world. Within the framework of blended learning, the MOOC can also be the essential section in a whole circle. With some successful examples for the application of blended learning in elementary and middle schools, the author is suddenly inspired to make assumptions for better MET （maritime education and training）： the blended learning is applicable in MET to stimulate the students＇ initiatives.展开更多
Underwater inertial navigation is particularly difficult for the long-durance operations as many navigation systems such global satellite navigation systems are unavailable.The acoustic signal is a marvelous choice fo...Underwater inertial navigation is particularly difficult for the long-durance operations as many navigation systems such global satellite navigation systems are unavailable.The acoustic signal is a marvelous choice for underwater inertial error rectification due to its underwater penetration capability.However,the traditional Acoustic Positioning Systems(APS)are expensive and incapable of positioning with limited acoustic observations.Two novel underwater inertial error rectification algorithms with limited acoustic observations are proposed.The first one is the single acoustic-beacon Range-only Matching Aided Navigation(RMAN)method,which is inspired by matching navigation without reference maps and presented for the first time.The second is the improved single acoustic-beacon Virtual Long Baseline(VLBL)method,which considers the impact of indicated relative position increments on virtual beacon reconstruction.Both RMAN and improved VLBL are further developed when multi acoustic-beacons are available,named mAB-RMAN and mAB-VLBL.The comprehensive simulations and field investigations were conducted.The results demonstrated that the proposed methods achieved excellent accuracy and stability compared to the baseline,specifically,the mAB-RMAN and mAB-VLBL can reduce the inertial error by more than 90%and 98%when using single and double acoustic-beacons,respectively.These proposed techniques will provide new perspectives for underwater positioning,navigation,and timing.展开更多
基金Supported by the National Natural Science Foundation of China(NSFC)Shared Voyage Project(Nos.41776088,41976018,42049911,U20A20103,U2005207)the Natural Science Key Foundation of Fujian Province,China(No.2020J01412103)+5 种基金the Hainan Province Science and Technology Special Fund(No.ZDYF2022SHFZ317)the Guangxi Talent and Innovation Base Project(No.2018AD19280)the Guangxi Funding Project(No.04024XM20N0006)the Beihai Science&Technology Project(Nos.201995037,202082031,202082022)the Natural Science Foundation of Xiamen City of China(No.502Z20227322)the China Scholarship Council(CSC Marine Scholarship)。
文摘Microplastics(MPs)have recently emerged as a significant environmental problem with devastating consequences for organisms.Understanding MPs pollution in the Bay of Bengal is crucial for assessing its ecological impact on marine biodiversity and human health.This study examined the occurrence,spatial distribution,physical and chemical properties,ecological risks,and probable sources of MPs in estuarine and coastal marine environments in the northeastern Bay of Bengal.The average concentration of MPs in surface water of the Karnaphuli estuary,the Meghna estuary,and the southeastern coastal region were 916.7±462.6 items/m^(3),462.9±324.5 items/m^(3),and 350.0±190.5 items/m^(3),respectively,varying from 105.0±324.5 items/m^(3)to 1640.0±462.6 items/m^(3).In the sediments of the Karnaphuli estuary,the Meghna estuary,and the southeast coast of Bangladesh,the average amount of MPs were 94.3±33.1 items/kg,157.6±89.0 items/kg,and 134.3±38.7 items/kg,with a range of 60±33.1 items/kg to 334.3±89.0 items/kg.Most observed MPs were fibers(60.0%in the water;56.0%in the sediments),followed by fragments and lines.Detected MPs were dominated by polypropylene(20.7%)in the water,and acrylic(15.4%)in the sediment,black colored(76.2%in the water,72.7%in the sediments),and 200-500μm sized(48%in the water,37%in the sediments).Pollution Risk Index(PRI)indicated significant pollution levels(from medium to very high)in estuarine and coastal areas.Multi-statistical analysis indicated land-based inputs(tourists,local waste,agriculture,and industry)dominated the studied regions.The study emphasized the potential impact of MPs pollution on aquatic ecosystems,emphasizing the need for effective management,mitigation methods,continuous surveillance,and thorough evaluation.
基金The GASI Project under contract Nos GASI-IPOVAI-01-02 and GASI-02-SCS-YGST2-02the National Natural Science Foundation of China under contract Nos 41776034 and 41706025the Foundation of Guangdong Province for Outstanding Young Teachers in University under contract No.YQ201588
文摘So far, large uncertainties of the Indonesian throughflow(ITF) reside in the eastern Indonesian seas, such as the Maluku Sea and the Halmahera Sea. In this study, the water sources of the Maluku Sea and the Halmahera Sea are diagnosed at seasonal and interannual timescales and at different vertical layers, using the state-of-the-art simulations of the Ocean General Circulation Model(OGCM) for Earth Simulator(OFES). Asian monsoon leaves clear seasonal footprints on the eastern Indonesian seas. Consequently, the subsurface waters(around 24.5σ_θ and at ～150 m) in both the Maluku Sea and the Halmahera Sea stem from the South Pacific(SP) during winter monsoon, but during summer monsoon the Maluku Sea is from the North Pacific(NP), and the Halmahera Sea is a mixture of waters originating from the NP and the SP. The monsoon impact decreases with depth, so that in the Maluku Sea, the intermediate water(around 26.8σ_θ and at ～480 m) is always from the northern Banda Sea and the Halmahera Sea water is mainly from the SP in winter and the Banda Sea in summer. The deep waters(around27.2σ_θ and at ～1 040 m) in both seas are from the SP, with weak seasonal variability. At the interannual timescale,the subsurface water in the Maluku Sea originates from the NP/SP during El Ni?o/La Ni?a, while the subsurface water in the Halmahera Sea always originates from the SP. Similar to the seasonal variability, the intermediate water in Maluku Sea mainly comes from the Banda Sea and the Halmahera Sea always originates from the SP. The deep waters in both seas are from the SP. Our findings are helpful for drawing a comprehensive picture of the water properties in the Indonesian seas and will contribute to a better understanding of the ocean-atmosphere interaction over the maritime continent.
基金the National Natural Science Foundation of China(Nos.30800235 and 31271069)the Shanghai Aerospace Science and Technology Innovation Fund(No.SAST2016084)+1 种基金the Medical Engineering and Science Interdisciplinary Fund of Shanghai Jiao Tong University(No.YG2013MS24)the Shanghai Sailing Program(No.17YF1408200)
文摘For generating a uniform and steady magnetic field, Helmholtz coil is extensively used in nuclear magnetic resonance gyro(NMRG). Unfortunately, the volume of Helmholtz coil makes it inconvenient to miniaturize NMRG. This study introduces Braunbeck coil that can be used in magnetic field excitation system. Braunbeck coil can produce homogeneous magnetic field within a limit space, and occupy a small volume. In addition, this study presents mathematical expressions that can be used to calculate the area of uniform magnetic field. Experimental test verifies the effectiveness of the proposed design, and the results accord closely with the actual simulation.
基金supported by the National Natural Science Foundation of China(61374003 41631072)the Academic Foundation of Naval University of Engineering(20161475)
文摘Both time-delays and anti-windup(AW)problems are conventional problems in system design,which are scarcely discussed in cellular neural networks(CNNs).This paper discusses stabilization for a class of distributed time-delayed CNNs with input saturation.Based on the Lyapunov theory and the Schur complement principle,a bilinear matrix inequality(BMI)criterion is designed to stabilize the system with input saturation.By matrix congruent transformation,the BMI control criterion can be changed into linear matrix inequality(LMI)criterion,then it can be easily solved by the computer.It is a one-step AW strategy that the feedback compensator and the AW compensator can be determined simultaneously.The attraction domain and its optimization are also discussed.The structure of CNNs with both constant timedelays and distribute time-delays is more general.This method is simple and systematic,allowing dealing with a large class of such systems whose excitation satisfies the Lipschitz condition.The simulation results verify the effectiveness and feasibility of the proposed method.
基金National Natural Science Foundation of China(Nos.41771487,41971416,41871376)Natural Science Foundation for Distinguished Young Scholars of Hubei Province of China(No.2019CFA086)。
文摘A systematic and comprehensive comparison of the five commonly used earth radii in geodesy and cartography is carried out,and the differences between the most common points of the earth radii,their corresponding maximum values,and the latitudes of equal points between them are derived with the help of computer algebraic systems.The symbolic expressions are expressed as a power series of the first eccentricity.Taking the CGCS2000 ellipsoid as an example,the differences between the commonly used earth radii are clarified to numerical values.The results show that the difference between the commonly used earth radii has a maximum at 90 degrees and a minimum at 0 degree.The difference between the average radius of curvature and the rectifying sphere radius is the biggest,and the difference between the average radius of curvature and the average sphere radius is the smallest.These results can provide a theoretical basis for corresponding research in the geosciences,space science,navigation and positioning.
基金The National Natural Science Foundation of China under contract No.40644022the China Post-doctor Science Foundation under contract No.20050335090.
文摘The existing methods of downward continuation of potential field cannot be used to continue the aeromagnetic data to the marine surface because of the limited continuation distance. An iteration method for the downward continuation of potential field with a much larger continuation distance has been developed, which can continue the aeromagnetic data to the marine surface and get the marine - magnetic chart with the same scale as the aeromagnetic data. This downward continuation method will greatly raise the ef- ficiency of marine - magnetic investigation. The principle of the iteration method is presented. The method is demonstrated on synthetic models and real aeromagnetic data. Also, the error brought by continuation is discussed. The efficiency of the iteration method for the downward continuation of potential field is compared with the fast fourier transform （FFT） method, the former is much better than the latter.
文摘Due to variable symbol length of digital pulse interval modulation(DPIM),it is difficult to analyze the error performances of Turbo coded DPIM.To solve this problem,a fixed-length digital pulse interval modulation(FDPIM) method is provided.The FDPIM modulation structure is introduced.The packet error rates of uncoded FDPIM are analyzed and compared with that of DPIM.Bit error rates of Turbo coded FDPIM are simulated based on three kinds of analytical models under weak turbulence channel.The results show that packet error rate of uncoded FDPIM is inferior to that of uncoded DPIM.However,FDPIM is easy to be implemented and easy to be combined.with Turbo code for soft-decision because of its fixed length.Besides,the introduction of Turbo code in this modulation can decrease the average power about 10 dBm,which means that it can improve the error performance of the system effectively.
基金funded by the National Natural Science Foundation of China[grant number 42105063]the Youth Training Project of the Key Laboratory for Meteorological Disaster Monitoring and Early Warning and Risk Management of Characteristic Agriculture in Arid Regions[project number CAMT-202302]a funded project of Hengyang Normal University[project number 2022QD11].
文摘To achieve accurate classification and recognition of ship target types,it is necessary to establish a sample library of ship targets to be identified.On the basis of exploring the principles of building a ship target image library,the paper determines the sample set.Using 3DS MAX software as the platform,combined with the accurate 3D model of the ship in an offline state,the software fully utilizes its own rendering and animation functions to achieve the automatic generation of multi-view and multi-scale views of ship targets.To reduce the storage capacity of the image database,a construction method of the ship target image database based on the AP algorithm is presented.The algorithm can obtain the optimal cluster number,reduce the data storage capacity of the image database,and save the calculation amount for the subsequent matching calculation.
基金supported by the National Natural Science Foundation of China(6110418440904018)+3 种基金the National Key Scientific Instrument and Equipment Development Project(2011YQ12004502)the Research Foundation of General Armament Department(201300000008)the Doctor Innovation Fund of Naval University of Engineering(HGBSCXJJ2011008)the Youth Natural Science Foundation of Naval University of Engineering(HGDQNJJ12028)
文摘A novel neural network based on iterated unscented Kalman filter （IUKF） algorithm is established to model and com- pensate for the fiber optic gyro （FOG） bias drift caused by temperature. In the network, FOG temperature and its gradient are set as input and the FOG bias drift is set as the expected output. A 2-5-1 network trained with IUKF algorithm is established. The IUKF algorithm is developed on the basis of the unscented Kalman filter （UKF）. The weight and bias vectors of the hidden layer are set as the state of the UKF and its process and measurement equations are deduced according to the network architecture. To solve the unavoidable estimation deviation of the mean and covariance of the states in the UKF algorithm, iterative computation is introduced into the UKF after the measurement update. While the measure- ment noise R is extended into the state vectors before iteration in order to meet the statistic orthogonality of estimate and mea- surement noise. The IUKF algorithm can provide the optimized estimation for the neural network because of its state expansion and iteration. Temperature rise （-20-20℃） and drop （70-20℃） tests for FOG are carried out in an attemperator. The temperature drift model is built with neural network, and it is trained respectively with BP, UKF and IUKF algorithms. The results prove that the proposed model has higher precision compared with the back- propagation （BP） and UKF network models.
基金The National Natural Science Foundation of China under contract Nos 61702455,61672462 and 61902350the Natural Science Foundation of Zhejiang Province,China under contract No.LY20F020025。
文摘Texture-based visualization method is a common method in the visualization of vector field data.Aiming at adding color mapping to the texture of ocean vector field and solving the ambiguity of vector direction in texture image,a new color texture enhancement algorithm based on the Line Integral Convolution(LIC)for the vector field data is proposed,which combines the HSV color mapping and cumulative distribution function calculation of vector field data.This algorithm can be summarized as follows:firstly,the vector field data is convoluted twice by line integration to get the gray texture image.Secondly,the method of mapping vector data to each component of the HSV color space is established.And then,the vector field data is mapped into HSV color space and converted from HSV to RGB values to get the color image.Thirdly,the cumulative distribution function of the RGB color components of the gray texture image and the color image is constructed to enhance the gray texture and RGB color values.Finally,both the gray texture image and the color image are fused to get the color texture.The experimental results show that the proposed LIC color texture enhancement algorithm is capable of generating a better display of vector field data.Furthermore,the ambiguity of vector direction in the texture images is solved and the direction information of the vector field is expressed more accurately.
文摘An algorithm using fixed-lag smooth filtering to improve the precision of EIS algorithm is presented in this paper. Ftrstly, gray projection algorithm (GPA) is used to calculate the interframe global motion vectors. Secondly, the fixed-lag smooth filter is used to smoothen the motion track of the original video sequence, according to different motion models. At last, the original sequence is compensated by using the compensation vectors calculated from filtering. This algorithm has been proved superior in filtering precision by experiments of video sequences in different motion scenes. This algorithm also satisfies the real-time request.
基金Project(41374018)supported by the National Natural Science Foundation of ChinaProject(J13LN74)supported by the Shandong Province Higher Educational Science and Technology Program,China
文摘In inertial navigation system(INS) and global positioning system(GPS) integrated system, GPS antennas are usually not located at the same location as the inertial measurement unit(IMU) of the INS, so the lever arm effect exists, which makes the observation equation highly nonlinear. The INS/GPS integration with constant lever arm effect is studied. The position relation of IMU and GPS's antenna is represented in the earth centered earth fixed frame, while the velocity relation of these two systems is represented in local horizontal frame. Due to the small integration time interval of INS, i.e. 0.1 s in this work, the nonlinearity in the INS error equation is trivial, so the linear INS error model is constructed and addressed by Kalman filter's prediction step. On the other hand, the high nonlinearity in the observation equation due to lever arm effect is addressed by unscented Kalman filter's update step to attain higher accuracy and better applicability. Simulation is designed and the performance of the hybrid filter is validated.
文摘To address a problem of autonomous attitude determination algorithm using gravitational field and geomagnetic field observation, a new recursive optimization autonomous attitude estimation algorithm is proposed. The algorithm is based on unscented Kalman filter(UKF), and can synchronously provide the attitude rate information. The simulated results show that the measurement precision of the method could be increased by 2 times compared to that of the common methods.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60473141)the Natural Science Foundation of Liaoning Province of China (Grant No. 20062191)
文摘In this paper the relations between two spreads, between two group delays, and between one spread and one group delay in fractional Fourier transform （FRFT） domains, are presented and three theorems on the uncertainty principle in FRFT domains are also developed. Theorem 1 gives the bounds of two spreads in two FRFT domains. Theorem 2 shows the uncertainty relation between two group delays in two FRFT domains. Theorem 3 presents the crossed uncertainty relation between one group delay and one spread in two FRFT domains. The novelty of their results lies in connecting the products of different physical measures and giving their physical interpretations. The existing uncertainty principle in the FRFT domain is only a special ease of theorem 1, and the conventional uncertainty principle in time-frequency domains is a special case of their results. Therefore, three theorems develop the relations of two spreads in time-frequency domains into the relations between two spreads, between two group delays, and between one spread and one group delay in FRFT domains.
文摘The general structure of ship-borne helicopter landing forecast system is presented, and a novel ship motion prediction model based on minor component analysis (MCA) is built up to improve the forecast effectiveness. To validate the feasibility of this landing forecast system, time series for the roll, pitch and heave are generated by simulation and then forecasted based on MCA. Simulation results show that ship-borne helicopters can land safely in higher sea condition while carrying on rescue or replenishment tasks at sea in terms of the landing forecast system.
文摘With the revision work of the IMO Model Course 6.09, the trainee-centered methodology is greatly highlighted, together with the newly merging technology for education, especially for language learning. This paper will consider blended learning, for instance. Blended learning is adorable for many educators in recent years, which demonstrates the principle of student-centered as well as alternates the role of the teachers from the traditional way. MOOC （Massive Online Open Course） is initiated in most schools as well, for the purpose of mutual share of the best education in the world. Within the framework of blended learning, the MOOC can also be the essential section in a whole circle. With some successful examples for the application of blended learning in elementary and middle schools, the author is suddenly inspired to make assumptions for better MET （maritime education and training）： the blended learning is applicable in MET to stimulate the students＇ initiatives.
基金funding was provided by Natural Science Foundation of China(Grant numbers 42004067,62373367,42176195)。
文摘Underwater inertial navigation is particularly difficult for the long-durance operations as many navigation systems such global satellite navigation systems are unavailable.The acoustic signal is a marvelous choice for underwater inertial error rectification due to its underwater penetration capability.However,the traditional Acoustic Positioning Systems(APS)are expensive and incapable of positioning with limited acoustic observations.Two novel underwater inertial error rectification algorithms with limited acoustic observations are proposed.The first one is the single acoustic-beacon Range-only Matching Aided Navigation(RMAN)method,which is inspired by matching navigation without reference maps and presented for the first time.The second is the improved single acoustic-beacon Virtual Long Baseline(VLBL)method,which considers the impact of indicated relative position increments on virtual beacon reconstruction.Both RMAN and improved VLBL are further developed when multi acoustic-beacons are available,named mAB-RMAN and mAB-VLBL.The comprehensive simulations and field investigations were conducted.The results demonstrated that the proposed methods achieved excellent accuracy and stability compared to the baseline,specifically,the mAB-RMAN and mAB-VLBL can reduce the inertial error by more than 90%and 98%when using single and double acoustic-beacons,respectively.These proposed techniques will provide new perspectives for underwater positioning,navigation,and timing.
