This article investigates the approaching control for fixed-wing Unmanned Aerial Vehi-cle(UAV)aerial recovery in the presence of pre-specified performance requirements,complex air-flows,maneuvering flight of transport...This article investigates the approaching control for fixed-wing Unmanned Aerial Vehi-cle(UAV)aerial recovery in the presence of pre-specified performance requirements,complex air-flows,maneuvering flight of transport aircraft,and different initial deviations.First,a novelcontrol-oriented Six-Degree-Of-Freedom(6-DOF)UAV model considering airflow disturbancesis established for better consistency with the actual UAV system.Then,to achieve satisfactory per-formance in the approaching process,a Flexible Appointed-time Prescribed Performance Control(FAPPC)algorithm,with the features of user-specified time convergence,no overshoot,indepen-dence from the initial value,and singularity-free,is proposed.Specifically,to solve the singularityissue encountered by the existing PPC methods in dealing with sudden disturbances,an adaptiveadjustment signal is introduced in FAPPC to perceive the threat of increasing error and relax thepreset boundaries appropriately.Moreover,minimum learning parameter-based neural networkestimators are developed to approximate unknown lumped disturbances at a low computationalcost.Finally,the stability of the closed system is analyzed via Lyapunov synthesis,and the effective-ness and advantages of the proposed control scheme are demonstrated via simulation andHardware-In-the-Loop(HIL)experimental validation.展开更多
By establishing the concepts of fuzzy approaching set and fuzzy approaching functional mapping and making research on them, a new method for time series prediction is introduced.
We demonstrate a diode pumped Yb：LuVO4 laser that can be passively Q-switched by a Cr^（4＋）：YAG saturable absorber having an initial transmission as high as 99.3%.A maximum pulsed output power of 2.35 W is generat...We demonstrate a diode pumped Yb：LuVO4 laser that can be passively Q-switched by a Cr^（4＋）：YAG saturable absorber having an initial transmission as high as 99.3%.A maximum pulsed output power of 2.35 W is generated at a repetition rate of 285.7 kHz,approaching or very near the intrinsic upper limit imposed by the recovery time of the Cr^（4＋）：YAG saturable absorber,and the resulting pulse energy,duration and peak power are,respectively,8.2μJ,39.2ns and 0.209kW.展开更多
For most universities and colleges in China, literary theory is taught at the graduate level of literary studies. Most English teachers think literary theory is such a complex field with jargon-ridden disciplines and ...For most universities and colleges in China, literary theory is taught at the graduate level of literary studies. Most English teachers think literary theory is such a complex field with jargon-ridden disciplines and concepts that it is often considered as ＂a hot potato＂ in classroom teaching. Based on a case study from ＂Approaching Fiction＂ in China Youth University of Political Studies （CYUPS）, the present paper claims that application of literary theory in teaching literature not only greatly broadens students＇ horizon but also deepens their interpretation and understanding of literary works. With proper selection of teaching material and carefully designed teaching approaches, application of critical theory plays an increasingly important role in the undergraduate literature classroom.展开更多
The year 1993 was the fifteenth of China’s reform and opening to the outside. Its economy sustained double digit growth for two years running. Last year, domestic GNP was RMB3,138 billion, a 13.4 percent increase com...The year 1993 was the fifteenth of China’s reform and opening to the outside. Its economy sustained double digit growth for two years running. Last year, domestic GNP was RMB3,138 billion, a 13.4 percent increase compared with the previous year’s 13.2 percent.展开更多
The use of finite element method leads to replacing the initial domain by an approaching domain. Under some appropriate assumptions, we prove that there exists a W1,+∞-diffeomorphism from the original domain to the a...The use of finite element method leads to replacing the initial domain by an approaching domain. Under some appropriate assumptions, we prove that there exists a W1,+∞-diffeomorphism from the original domain to the approaching domain.展开更多
China’s most important traditional festival,the Spring Festival,is approaching.Unlike religious festivals in Western countries,the Spring Festival is closely related to nature.By celebrating the arrival of spring,it ...China’s most important traditional festival,the Spring Festival,is approaching.Unlike religious festivals in Western countries,the Spring Festival is closely related to nature.By celebrating the arrival of spring,it embodies the idea of the renewal of all manifestations and the unity of nature and humans.At the same time,it is also a festival about family reunion,fully showing how much Chinese people cherish kinship,friendship,and familial harmony.This harmony between humans and nature,humans and society,and among humans themselves is the essence of the tradition of the Spring Festival,and is also a core cultural value pursued and cherished by the Chinese nation for thousands of years.Today,China’s internal affairs and diplomatic thoughts are permeated with the values of harmonious coexistence,and the Doctrine of the Mean is still the quintessential wisdom embraced by Chinese people who seek to achieve harmonious interpersonal relations with it.展开更多
Desertification creeps across the landscape like a silent thief,stealing life and leaving behind a barren wasteland.This year's World Environment Day theme,‘Land Restoration,desertification and drought resilience...Desertification creeps across the landscape like a silent thief,stealing life and leaving behind a barren wasteland.This year's World Environment Day theme,‘Land Restoration,desertification and drought resilience’,is a stark reminder of the pressing need to heal the wounds we've inflicted on our planet.展开更多
There is no historical evidence of a connection between Chinese and African art, but today, artists from the two sides are making efforts to build just such a connection. On June 18, an art exhibition entitled Approac...There is no historical evidence of a connection between Chinese and African art, but today, artists from the two sides are making efforts to build just such a connection. On June 18, an art exhibition entitled Approaching Africa was held at Shenzhen University＇s art museum. The exhibition included more than 60 works by nine artists from Shenzhen＇s art institutes. The works were created by the artists during a tour of African countries including Benin, Kenya, Tanzania, Ethiopia and Zimbabwe.展开更多
A soil remediation method combining in situ reduction of Cr（VI） with approaching anodes electroki- netic （AAs-EK） remediation is proposed. EK experiments were conducted to compare the effect of approaching anodes ...A soil remediation method combining in situ reduction of Cr（VI） with approaching anodes electroki- netic （AAs-EK） remediation is proposed. EK experiments were conducted to compare the effect of approaching anodes （AAs） and fixed electrodes （FEs） with and without sodium bisulfite （NaHSO3） as a reducing agent. When NaHSO3 was added to the soil before EK treatment, 90.3% of the Cr（VI） was reduced to Cr（III）. EK experiments showed that the adverse effect of contrasting migration of Cr（III） and Cr（VI） species, which limits the practical application of this technique, was eliminated in the presence of the reducing agent. Furthermore, Tessier fractionation analysis indicated that the reducing agent changed the distribution of the chemical forms of Cr. The AAs-EK method was shown to acidize the soil as the anode moved toward the cathode and this acid front pushed the ＂focusing＂ region toward the cathode. After remedia- tion, the pH of the soil was between 1.8 and 5.0 in AAs-EK experiments. The total Cr removal efficiency was 64.4% （except in the ＂focusing＂ region） when the reduction reaction was combined with AAs-EK method. We conclude that AAs-EK remediation in the presence of NaHSO3 is an appropriate method for Cr-contaminated soil.展开更多
As a new technology used for the cleaning of chromium-contaminated soil, worldwide interest in ele- trokinetic （EK） remediation has grown considerably in recent times. However, owing to the fact that chromium exists...As a new technology used for the cleaning of chromium-contaminated soil, worldwide interest in ele- trokinetic （EK） remediation has grown considerably in recent times. However, owing to the fact that chromium exists as both cationic and anionic species in the soil, it is not an efficient method. This paper reports upon a study in which a process using approaching anodes （AAs） was used to enhance the removal efficiency of chromium by eletrokinetics. Two bench-scale experiments to remove chromium from contaminated soil were performed, one using a fixed anode （FA） and the other using AAs. In the AAs experiment, the anode moved toward the cathode by 7 cm every three days. After remediation, soil pH, total chromium, and fractionation of chromium in the soil were determined. The average removal efficiency of total chromium was 11.32% and 18.96% in the FA and AAs experiments, respectively. After remediation, acidic soil conditions throughout the soil were generated through the use of AAs, while 80% of the soil remained neutral or alkalic when using the FA approach. The acidic soil environment and high field intensity in the AAs experi- ment might have favored chromium desorption, dissolu- tion and dissociation from the soil, plus the mobility of chromium in the soil was also enhanced. The results demonstrate that AAs used in the process of EK remediation can enhance the efficiency of chromium removal from soil.展开更多
In this study, we focused on full-region cruise survey data, near-bottom continuous mooring observations and sea surface wind products from the western South Yellow Sea in winter; after ensuring the data reliability a...In this study, we focused on full-region cruise survey data, near-bottom continuous mooring observations and sea surface wind products from the western South Yellow Sea in winter; after ensuring the data reliability and accuracy, we processed and analyzed the data. Image resolution experiments were carried out to determine the lowest recognition resolutions for all image types, which represent the resolution characteristics of the data. The existence of a warm water tongue originating from the Yellow Sea Warm Current(YSWC) that approached waters offshore Qingdao was confirmed. For the first time, a high salinity water tongue, corresponding to the warm water tongue, was described and found to be more representative of the YSWC branch path. This warm tongue is a sign of the branch originating from the YSWC, which we defined as the Yellow Sea Warm Current Branch approaching waters offshore Qingdao(YSWC-QDB). The pattern of the warm and salty water tongues showed remarkable rear, branching middle, shrinking neck and expanding top regions. These patterns showed a temporal feature of the tongues, and were the result of multi-temporal branches in front of the YSWC main section as well as the YSWC-QDB crossing the southwestward path of the extension of the North Shandong Coastal Current flowing along the southeast coast of the Shandong Peninsula(NSCC-SESE). Analysis using mooring data at a sensitive and representative station also showed the existence of the YSWC-QDB. It is a probabilistic event that manifests as a northwestward flow that decreases gradually from the bottom to the surface in the early cold air transit stage and consistent in the whole water column profile in the later stage. It varies quasi-periodically with weather processes. It also transports some of the YSWC water stored in the entrance area of the Bohai and Yellow seas under winter wind conditions to the western South Yellow Sea as a compensatory current. This current, caused by northerly winds, especially northwest winds and obstruction of the NSCC-SESE, was present, and strong water reduction and compensation caused significant residual sea level oscillations. The compensatory current, if caused by strong northwest wind,began to appear when its direction was opposite to the wind direction. In addition, confirmation of the YSWC-QDB provides an oceanographic basis for the short cooling time and rapid warming in the Qingdao area in winter. This research provides a basis for further studies of the YSWC-QDB at high spatial and temporal resolutions using large sea surface datasets. For monsoon basin dynamics, this study can also be extended to the whole Bohai and Yellow seas and closed or semi-closed basins on the continental margin.展开更多
Noncoherent underwater acoustic communication channel in adverse conditions is modeled as a phase-random Rayleigh fading channel,and its capacity curve is derived.To approach the channel capacity curve,the concatenate...Noncoherent underwater acoustic communication channel in adverse conditions is modeled as a phase-random Rayleigh fading channel,and its capacity curve is derived.To approach the channel capacity curve,the concatenated code of the nonbinary LDPC code and the constant weight code is proposed for noncoherent communication which can late be iteratively decoded in the probability domain.Without information of channel amplitude or phase in the receiver,statistic parameters of the respective signal and noise bins were estimated based on the moment estimation method,the posterior probabilities of the constant weight code words were further calculated,and the nonbinary LDPC code was decoded with the nonbinary factor graph algorithm.It is verified by simulations that by utilizing the proposed concatenated code and its processing algorithm,gap to channel capacity curve is reduced by 3 dB when compared to the existing method.Underwater communication experiments were carried out in both deep ocean（vertical communication,5 km）and shallow lake（horizontal communication,near 3 km,delay spread larger than 50 ms）,in which the signal frequency band was 6 kHz to10 kHz,and the data transmission rate Was 357 bps.The proposed scheme can work properly in both experiments with a signal-to-noise ratio threshold of 2 dB.The performance of the proposed algorithm Was well verified by the experiments.展开更多
In order to achieve a straight ballistic trajectory of missile and reduce the update frequency of the missile normal acceleration for the interception of maneuvering target,a backstepping-based parallel approaching gu...In order to achieve a straight ballistic trajectory of missile and reduce the update frequency of the missile normal acceleration for the interception of maneuvering target,a backstepping-based parallel approaching guidance method is designed with nonlinear disturbance observer(NDO)technique and event-triggered(ET)mechanism in this paper.In order to suppress the adverse e®ect of target maneuver,the NDO is designed to estimate the target maneuvering acceleration.Then,the NDO-based backstepping method is used to obtain the normal acceleration of missile and realize the parallel approaching guidance.In order to reduce the update frequency of missile normal acceleration,the ET mechanism is employed in the parallel approaching guidance method.If the missile trajectory is relatively straight,the normal acceleration of missile remains unchanged.On the contrary,if the missile trajectory is not straight,the normal acceleration of missile is updated to make the missile trajectory straight.In this way,the ET-based parallel approaching guidance can be obtained.Furthermore,a determined method for the initial missile°ight-path angle is proposed to keep the normal acceleration of missile at zero in the initial stage of interception.Besides,Lyapunov stability analysis method is used to prove that all signals in the closed-loop guidance system are uniformly ultimately bounded.Finally,simulation results show the e®ectiveness of the proposed guidance method.展开更多
In this paper, we use a qualitative method to study global and local bifurcations in a disturbedHamiltonian vector field approaching a Poincare map in the 3:1 resonant case. We give explicitcalculation formulas to det...In this paper, we use a qualitative method to study global and local bifurcations in a disturbedHamiltonian vector field approaching a Poincare map in the 3:1 resonant case. We give explicitcalculation formulas to determine bifurcation parameters and draw various bifurcations and phaseportraits in the phase plane.展开更多
Synchronous approaching is an important capability for autonomous cooperation of multiple unmanned aerial vehicles(UAVs).In this paper,a homotopy-based trajectory planning method is presented for the multi-UAV synchro...Synchronous approaching is an important capability for autonomous cooperation of multiple unmanned aerial vehicles(UAVs).In this paper,a homotopy-based trajectory planning method is presented for the multi-UAV synchronous approaching problem.A homotopic trajectory description is employed to construct the trajectory solution space of the UAVs.A novel onionlike homotopy structure is proposed to decouple the performance indexes of the trajectory planning problem.Local trajectory homotopy structures are designed based on the detouring model and the hovering model of UAV.The optimal trajectories for synchronous approaching are searched within the homotopy structures.Simulation results show how synchronous the UAVs are,by using the proposed homotopy-based trajectory planning method.展开更多
This paper presents a calculation method that evaluates the extent of disturbance based on structural safety limits.Additionally,it summarizes the assessment methods for construction disturbance zones in shield tunnel...This paper presents a calculation method that evaluates the extent of disturbance based on structural safety limits.Additionally,it summarizes the assessment methods for construction disturbance zones in shield tunneling near pile foundations,urban ground structures,and underground structures.Furthermore,taking the construction of the Chengdu Jinxiu Tunnel under bridges and urban pipelines as the engineering background,a study on the disturbance zoning of adjacent structures was conducted.The most intense disturbance occurs within one week of the tunnel underpass process,and it has a significant impact within a range of two times the tunnel diameter along the tunnel axis.The bridge pile and bridge deck experience less disturbance from tunnel approaching construction,with a maximum disturbance zone characterized as medium disturbance.On the other hand,underground pipelines are subjected to more significant disturbances from tunnel construction,with a maximum disturbance zone classified as strong disturbance.The implementation of“bridge pile sleeve valve pipe grouting&underground pipeline ground grouting&tunnel advance grouting”in the field effectively limits the vertical settlement of bridges and pipelines,resulting in a decrease of approximately 0.1 in disturbance level for the structures.The disturbance zoning method can assess tunnel disturbance with structures,identify high-risk interference locations,and facilitate targeted design reinforcement solutions.展开更多
基金funded by the National Natural Science Foundation of China(Nos.62173022,61673042)the Academic Excellence Foundation of Beihang University for Ph.D.Studentsthe Outstanding Research Project of Shen Yuan Honors College,Beihang University,China(No.230123104)。
文摘This article investigates the approaching control for fixed-wing Unmanned Aerial Vehi-cle(UAV)aerial recovery in the presence of pre-specified performance requirements,complex air-flows,maneuvering flight of transport aircraft,and different initial deviations.First,a novelcontrol-oriented Six-Degree-Of-Freedom(6-DOF)UAV model considering airflow disturbancesis established for better consistency with the actual UAV system.Then,to achieve satisfactory per-formance in the approaching process,a Flexible Appointed-time Prescribed Performance Control(FAPPC)algorithm,with the features of user-specified time convergence,no overshoot,indepen-dence from the initial value,and singularity-free,is proposed.Specifically,to solve the singularityissue encountered by the existing PPC methods in dealing with sudden disturbances,an adaptiveadjustment signal is introduced in FAPPC to perceive the threat of increasing error and relax thepreset boundaries appropriately.Moreover,minimum learning parameter-based neural networkestimators are developed to approximate unknown lumped disturbances at a low computationalcost.Finally,the stability of the closed system is analyzed via Lyapunov synthesis,and the effective-ness and advantages of the proposed control scheme are demonstrated via simulation andHardware-In-the-Loop(HIL)experimental validation.
文摘By establishing the concepts of fuzzy approaching set and fuzzy approaching functional mapping and making research on them, a new method for time series prediction is introduced.
基金Supported by the National Natural Science Foundation of China under Grant No 11574170
文摘We demonstrate a diode pumped Yb：LuVO4 laser that can be passively Q-switched by a Cr^（4＋）：YAG saturable absorber having an initial transmission as high as 99.3%.A maximum pulsed output power of 2.35 W is generated at a repetition rate of 285.7 kHz,approaching or very near the intrinsic upper limit imposed by the recovery time of the Cr^（4＋）：YAG saturable absorber,and the resulting pulse energy,duration and peak power are,respectively,8.2μJ,39.2ns and 0.209kW.
文摘For most universities and colleges in China, literary theory is taught at the graduate level of literary studies. Most English teachers think literary theory is such a complex field with jargon-ridden disciplines and concepts that it is often considered as ＂a hot potato＂ in classroom teaching. Based on a case study from ＂Approaching Fiction＂ in China Youth University of Political Studies （CYUPS）, the present paper claims that application of literary theory in teaching literature not only greatly broadens students＇ horizon but also deepens their interpretation and understanding of literary works. With proper selection of teaching material and carefully designed teaching approaches, application of critical theory plays an increasingly important role in the undergraduate literature classroom.
文摘The year 1993 was the fifteenth of China’s reform and opening to the outside. Its economy sustained double digit growth for two years running. Last year, domestic GNP was RMB3,138 billion, a 13.4 percent increase compared with the previous year’s 13.2 percent.
基金Partially supported by Professor Xu Yuesheng and his program "One hundred distinguished Young Scientists" Partially supported by "Programme Sino-Francais de Recherches Advancees(PRA).
文摘The use of finite element method leads to replacing the initial domain by an approaching domain. Under some appropriate assumptions, we prove that there exists a W1,+∞-diffeomorphism from the original domain to the approaching domain.
文摘China’s most important traditional festival,the Spring Festival,is approaching.Unlike religious festivals in Western countries,the Spring Festival is closely related to nature.By celebrating the arrival of spring,it embodies the idea of the renewal of all manifestations and the unity of nature and humans.At the same time,it is also a festival about family reunion,fully showing how much Chinese people cherish kinship,friendship,and familial harmony.This harmony between humans and nature,humans and society,and among humans themselves is the essence of the tradition of the Spring Festival,and is also a core cultural value pursued and cherished by the Chinese nation for thousands of years.Today,China’s internal affairs and diplomatic thoughts are permeated with the values of harmonious coexistence,and the Doctrine of the Mean is still the quintessential wisdom embraced by Chinese people who seek to achieve harmonious interpersonal relations with it.
文摘Desertification creeps across the landscape like a silent thief,stealing life and leaving behind a barren wasteland.This year's World Environment Day theme,‘Land Restoration,desertification and drought resilience’,is a stark reminder of the pressing need to heal the wounds we've inflicted on our planet.
文摘There is no historical evidence of a connection between Chinese and African art, but today, artists from the two sides are making efforts to build just such a connection. On June 18, an art exhibition entitled Approaching Africa was held at Shenzhen University＇s art museum. The exhibition included more than 60 works by nine artists from Shenzhen＇s art institutes. The works were created by the artists during a tour of African countries including Benin, Kenya, Tanzania, Ethiopia and Zimbabwe.
文摘A soil remediation method combining in situ reduction of Cr（VI） with approaching anodes electroki- netic （AAs-EK） remediation is proposed. EK experiments were conducted to compare the effect of approaching anodes （AAs） and fixed electrodes （FEs） with and without sodium bisulfite （NaHSO3） as a reducing agent. When NaHSO3 was added to the soil before EK treatment, 90.3% of the Cr（VI） was reduced to Cr（III）. EK experiments showed that the adverse effect of contrasting migration of Cr（III） and Cr（VI） species, which limits the practical application of this technique, was eliminated in the presence of the reducing agent. Furthermore, Tessier fractionation analysis indicated that the reducing agent changed the distribution of the chemical forms of Cr. The AAs-EK method was shown to acidize the soil as the anode moved toward the cathode and this acid front pushed the ＂focusing＂ region toward the cathode. After remedia- tion, the pH of the soil was between 1.8 and 5.0 in AAs-EK experiments. The total Cr removal efficiency was 64.4% （except in the ＂focusing＂ region） when the reduction reaction was combined with AAs-EK method. We conclude that AAs-EK remediation in the presence of NaHSO3 is an appropriate method for Cr-contaminated soil.
文摘As a new technology used for the cleaning of chromium-contaminated soil, worldwide interest in ele- trokinetic （EK） remediation has grown considerably in recent times. However, owing to the fact that chromium exists as both cationic and anionic species in the soil, it is not an efficient method. This paper reports upon a study in which a process using approaching anodes （AAs） was used to enhance the removal efficiency of chromium by eletrokinetics. Two bench-scale experiments to remove chromium from contaminated soil were performed, one using a fixed anode （FA） and the other using AAs. In the AAs experiment, the anode moved toward the cathode by 7 cm every three days. After remediation, soil pH, total chromium, and fractionation of chromium in the soil were determined. The average removal efficiency of total chromium was 11.32% and 18.96% in the FA and AAs experiments, respectively. After remediation, acidic soil conditions throughout the soil were generated through the use of AAs, while 80% of the soil remained neutral or alkalic when using the FA approach. The acidic soil environment and high field intensity in the AAs experi- ment might have favored chromium desorption, dissolu- tion and dissociation from the soil, plus the mobility of chromium in the soil was also enhanced. The results demonstrate that AAs used in the process of EK remediation can enhance the efficiency of chromium removal from soil.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41376038, 40406009 & 41806123)the National Science and Technology Major Project of the Ministry of Science and Technology of China (Grant No. 2016ZX05057015)+1 种基金the NSFC-Shandong Joint Fund for Marine Science Research Centers of China (Grant No. U1606405)the National Program on Global Change and Air-Sea Interaction of China (Grant Nos. GASI-IPOVAI-01-05 & GASI02-IND-STSsum)
文摘In this study, we focused on full-region cruise survey data, near-bottom continuous mooring observations and sea surface wind products from the western South Yellow Sea in winter; after ensuring the data reliability and accuracy, we processed and analyzed the data. Image resolution experiments were carried out to determine the lowest recognition resolutions for all image types, which represent the resolution characteristics of the data. The existence of a warm water tongue originating from the Yellow Sea Warm Current(YSWC) that approached waters offshore Qingdao was confirmed. For the first time, a high salinity water tongue, corresponding to the warm water tongue, was described and found to be more representative of the YSWC branch path. This warm tongue is a sign of the branch originating from the YSWC, which we defined as the Yellow Sea Warm Current Branch approaching waters offshore Qingdao(YSWC-QDB). The pattern of the warm and salty water tongues showed remarkable rear, branching middle, shrinking neck and expanding top regions. These patterns showed a temporal feature of the tongues, and were the result of multi-temporal branches in front of the YSWC main section as well as the YSWC-QDB crossing the southwestward path of the extension of the North Shandong Coastal Current flowing along the southeast coast of the Shandong Peninsula(NSCC-SESE). Analysis using mooring data at a sensitive and representative station also showed the existence of the YSWC-QDB. It is a probabilistic event that manifests as a northwestward flow that decreases gradually from the bottom to the surface in the early cold air transit stage and consistent in the whole water column profile in the later stage. It varies quasi-periodically with weather processes. It also transports some of the YSWC water stored in the entrance area of the Bohai and Yellow seas under winter wind conditions to the western South Yellow Sea as a compensatory current. This current, caused by northerly winds, especially northwest winds and obstruction of the NSCC-SESE, was present, and strong water reduction and compensation caused significant residual sea level oscillations. The compensatory current, if caused by strong northwest wind,began to appear when its direction was opposite to the wind direction. In addition, confirmation of the YSWC-QDB provides an oceanographic basis for the short cooling time and rapid warming in the Qingdao area in winter. This research provides a basis for further studies of the YSWC-QDB at high spatial and temporal resolutions using large sea surface datasets. For monsoon basin dynamics, this study can also be extended to the whole Bohai and Yellow seas and closed or semi-closed basins on the continental margin.
基金supported by the Chinese National 863 Projects(2002AA401004,2009AA093301,2009AA093601)
文摘Noncoherent underwater acoustic communication channel in adverse conditions is modeled as a phase-random Rayleigh fading channel,and its capacity curve is derived.To approach the channel capacity curve,the concatenated code of the nonbinary LDPC code and the constant weight code is proposed for noncoherent communication which can late be iteratively decoded in the probability domain.Without information of channel amplitude or phase in the receiver,statistic parameters of the respective signal and noise bins were estimated based on the moment estimation method,the posterior probabilities of the constant weight code words were further calculated,and the nonbinary LDPC code was decoded with the nonbinary factor graph algorithm.It is verified by simulations that by utilizing the proposed concatenated code and its processing algorithm,gap to channel capacity curve is reduced by 3 dB when compared to the existing method.Underwater communication experiments were carried out in both deep ocean（vertical communication,5 km）and shallow lake（horizontal communication,near 3 km,delay spread larger than 50 ms）,in which the signal frequency band was 6 kHz to10 kHz,and the data transmission rate Was 357 bps.The proposed scheme can work properly in both experiments with a signal-to-noise ratio threshold of 2 dB.The performance of the proposed algorithm Was well verified by the experiments.
基金supported in part by the National Natural Science Foundation of China under Grants No.62003269Foundation of Science and Technology on Aerospace Flight Dynamics Laboratory(6142210200308).
文摘In order to achieve a straight ballistic trajectory of missile and reduce the update frequency of the missile normal acceleration for the interception of maneuvering target,a backstepping-based parallel approaching guidance method is designed with nonlinear disturbance observer(NDO)technique and event-triggered(ET)mechanism in this paper.In order to suppress the adverse e®ect of target maneuver,the NDO is designed to estimate the target maneuvering acceleration.Then,the NDO-based backstepping method is used to obtain the normal acceleration of missile and realize the parallel approaching guidance.In order to reduce the update frequency of missile normal acceleration,the ET mechanism is employed in the parallel approaching guidance method.If the missile trajectory is relatively straight,the normal acceleration of missile remains unchanged.On the contrary,if the missile trajectory is not straight,the normal acceleration of missile is updated to make the missile trajectory straight.In this way,the ET-based parallel approaching guidance can be obtained.Furthermore,a determined method for the initial missile°ight-path angle is proposed to keep the normal acceleration of missile at zero in the initial stage of interception.Besides,Lyapunov stability analysis method is used to prove that all signals in the closed-loop guidance system are uniformly ultimately bounded.Finally,simulation results show the e®ectiveness of the proposed guidance method.
基金The project supported by the National Natural Science Foundation of China
文摘In this paper, we use a qualitative method to study global and local bifurcations in a disturbedHamiltonian vector field approaching a Poincare map in the 3:1 resonant case. We give explicitcalculation formulas to determine bifurcation parameters and draw various bifurcations and phaseportraits in the phase plane.
基金supported in part by the National Key R&D Program of China under Grant 2019YFB1312000in part by the National Natural Science Foundation of China under Grants 62106062,62033005,and 62173107+2 种基金in part by the Heilongjiang Provincial Natural Science Foundation of China under Grant YQ2021F010in part by the Young Elite Scientist Sponsorship Program by the China Association for Science and Technology under Grant YESS20210382and in part by the Sichuan Province Science and Technology Support Program under Grant 2021YFSY0026.
文摘Synchronous approaching is an important capability for autonomous cooperation of multiple unmanned aerial vehicles(UAVs).In this paper,a homotopy-based trajectory planning method is presented for the multi-UAV synchronous approaching problem.A homotopic trajectory description is employed to construct the trajectory solution space of the UAVs.A novel onionlike homotopy structure is proposed to decouple the performance indexes of the trajectory planning problem.Local trajectory homotopy structures are designed based on the detouring model and the hovering model of UAV.The optimal trajectories for synchronous approaching are searched within the homotopy structures.Simulation results show how synchronous the UAVs are,by using the proposed homotopy-based trajectory planning method.
基金National Key R&D Program of China(No.2021YFB2600900)National Natural Science Foundation of China(Grant No.52078430).
文摘This paper presents a calculation method that evaluates the extent of disturbance based on structural safety limits.Additionally,it summarizes the assessment methods for construction disturbance zones in shield tunneling near pile foundations,urban ground structures,and underground structures.Furthermore,taking the construction of the Chengdu Jinxiu Tunnel under bridges and urban pipelines as the engineering background,a study on the disturbance zoning of adjacent structures was conducted.The most intense disturbance occurs within one week of the tunnel underpass process,and it has a significant impact within a range of two times the tunnel diameter along the tunnel axis.The bridge pile and bridge deck experience less disturbance from tunnel approaching construction,with a maximum disturbance zone characterized as medium disturbance.On the other hand,underground pipelines are subjected to more significant disturbances from tunnel construction,with a maximum disturbance zone classified as strong disturbance.The implementation of“bridge pile sleeve valve pipe grouting&underground pipeline ground grouting&tunnel advance grouting”in the field effectively limits the vertical settlement of bridges and pipelines,resulting in a decrease of approximately 0.1 in disturbance level for the structures.The disturbance zoning method can assess tunnel disturbance with structures,identify high-risk interference locations,and facilitate targeted design reinforcement solutions.
