In this paper,a novel train positioning method considering satellite raw observation data was proposed,which aims to promote train positioning performance from an innovative perspective of the train satellite-based po...In this paper,a novel train positioning method considering satellite raw observation data was proposed,which aims to promote train positioning performance from an innovative perspective of the train satellite-based positioning error sources.The method focused on overcoming the abnormal observations in satellite observation data caused by railway environment rather than the positioning results.Specifically,the relative positioning experimental platform was built and the zero-baseline method was firstly employed to evaluate the carrier phase data quality,and then,GNSS combined observation models were adopted to construct the detection values,which were applied to judge abnormal-data through the dual-frequency observations.Further,ambiguity fixing optimization was investigated based on observation data selection in partly-blocked environments.The results show that the proposed method can effectively detect and address abnormal observations and improve positioning stability.Cycle slips and gross errors can be detected and identified based on dual-frequency global navigation satellite system data.After adopting the data selection strategy,the ambiguity fixing percentage was improved by 29.2%,and the standard deviation in the East,North,and Up components was enhanced by 12.7%,7.4%,and 12.5%,respectively.The proposed method can provide references for train positioning performance optimization in railway environments from the perspective of positioning error sources.展开更多
The existing Low-Earth-Orbit(LEO)positioning performance cannot meet the requirements of Unmanned Aerial Vehicle(UAV)clusters for high-precision real-time positioning in the Global Navigation Satellite System(GNSS)den...The existing Low-Earth-Orbit(LEO)positioning performance cannot meet the requirements of Unmanned Aerial Vehicle(UAV)clusters for high-precision real-time positioning in the Global Navigation Satellite System(GNSS)denial conditions.Therefore,this paper proposes a UAV Clusters Information Geometry Fusion Positioning(UC-IGFP)method using pseudoranges from the LEO satellites.A novel graph model for linking and computing between the UAV clusters and LEO satellites was established.By utilizing probability to describe the positional states of UAVs and sensor errors,the distributed multivariate Probability Fusion Cooperative Positioning(PF-CP)algorithm is proposed to achieve high-precision cooperative positioning and integration of the cluster.Criteria to select the centroid of the cluster were set.A new Kalman filter algorithm that is suitable for UAV clusters was designed based on the global benchmark and Riemann information geometry theory,which overcomes the discontinuity problem caused by the change of cluster centroids.Finally,the UC-IGFP method achieves the LEO continuous highprecision positioning of UAV clusters.The proposed method effectively addresses the positioning challenges caused by the strong direction of signal beams from LEO satellites and the insufficient constraint quantity of information sources at the edge nodes of the cluster.It significantly improves the accuracy and reliability of LEO-UAV cluster positioning.The results of comprehensive simulation experiments show that the proposed method has a 30.5%improvement in performance over the mainstream positioning methods,with a positioning error of 14.267 m.展开更多
Global Navigation Satellite System(GNSS)-based continuous and accurate train positioning is one of the key technologies for advanced train operations such as train virtual coupling.However,GNSS-based train positioning...Global Navigation Satellite System(GNSS)-based continuous and accurate train positioning is one of the key technologies for advanced train operations such as train virtual coupling.However,GNSS-based train positioning faces significant challenges in real-world scenarios due to environmental complexities and signal interferences.Considering this issue,this paper presents an approach for modeling and performance analysis of GNSS-based train positioning systems using Colored Petri Nets(CPNs).By systematically modeling the GNSS signal reception and processing process,the performance of the positioning system under various environment scenarios is evaluated.The system model integrates three types of interference signals(i.e.,Amplitude Modulation(AM)signals,Frequency Modulation(FM)signals,and pulse signals)while incorporating environmental factors such as terrain obstructions and tunnel shielding.Additionally,the Extended Kalman Filter(EKF)algorithm is employed to process GNSS observation data,providing accurate train position estimations.The simulation results demonstrate that signal interferences and complex environmental conditions significantly affect the GNSS-based positioning accuracy.This study offers a comprehensive framework for evaluating the performance of GNSS-based train positioning systems in different scenarios,highlighting critical factors that influence positioning accuracy and stability.展开更多
In the context of security systems,adequate signal coverage is paramount for the communication between security personnel and the accurate positioning of personnel.Most studies focus on optimizing base station deploym...In the context of security systems,adequate signal coverage is paramount for the communication between security personnel and the accurate positioning of personnel.Most studies focus on optimizing base station deployment under the assumption of static obstacles,aiming to maximize the perception coverage of wireless RF(Radio Frequency)signals and reduce positioning blind spots.However,in practical security systems,obstacles are subject to change,necessitating the consideration of base station deployment in dynamic environments.Nevertheless,research in this area still needs to be conducted.This paper proposes a Dynamic Indoor Environment Beacon Deployment Algorithm(DIE-BDA)to address this problem.This algorithm considers the dynamic alterations in obstacle locations within the designated area.It determines the requisite number of base stations,the requisite time,and the area’s practical and overall signal coverage rates.The experimental results demonstrate that the algorithm can calculate the deployment strategy in 0.12 s following a change in obstacle positions.Experimental results show that the algorithm in this paper requires 0.12 s to compute the deployment strategy after the positions of obstacles change.With 13 base stations,it achieves an effective coverage rate of 93.5%and an overall coverage rate of 97.75%.The algorithm can rapidly compute a revised deployment strategy in response to changes in obstacle positions within security systems,thereby ensuring the efficacy of signal coverage.展开更多
Numerous arthropods evolve and optimize sensory systems, enabling them to effectively adapt complex and competitive habitats. Typically, scorpions can precisely perceive the prey location with the lowest metabolic rat...Numerous arthropods evolve and optimize sensory systems, enabling them to effectively adapt complex and competitive habitats. Typically, scorpions can precisely perceive the prey location with the lowest metabolic rate among invertebrates. This biological phenomenon contrasts sharply with engineered systems, which generally associates high accuracy with substantial energy consumption. Inspired by the Scorpion Compound Slit Sensilla (SCSS) with a stress field modulation strategy, a bionic positioning sensor with superior precision and minimal power consumption is developed for the first time, which utilizes the particular Minimum Positioning Units (MPUs) to efficiently locate vibration signals. The single MPU of the SCSS can recognize the direction of collinear loads by regulating the stress field distribution and further, the coupling action of three MPUs can realize all-angle vibration monitoring in plane. Experiments demonstrate that the bionic positioning sensor achieves 1.43 degrees of angle-error-free accuracy without additional energy supply. As a proof of concept, two bionic positioning sensors and machine learning algorithm are integrated to provide centimeter (cm)-accuracy target localization, ideally suited for the man-machine interaction. The novel design offers a new mechanism for the design of traditional positioning devices, improving precision and efficiency in both the meta-universe and real-world Internet-connected systems.展开更多
Position-sensitive detector(PSD)is widely used in precision measurement fields such as flatness detection,auto-collimator systems,and degrees of freedom testing.However,due to factors such as uneven surface resistance...Position-sensitive detector(PSD)is widely used in precision measurement fields such as flatness detection,auto-collimator systems,and degrees of freedom testing.However,due to factors such as uneven surface resistance and differences in electrode structures,the nonlinearity of PSD becomes increasingly severe as the photosensitive surface moves from the center toward the edges of the four electrodes.To address this issue,a PSD nonlinearity correction algorithm is proposed.The algorithm utilizes the particle swarm optimization(PSO)algorithm to determine the optimal weights and thresholds,providing better initial parameters for the back propagation(BP)neural network.The BP neural network then iterates continuously until the error conditions are met,completing the correction process.Furthermore,a PSD nonlinearity correction system was developed,and the influence of different spot sizes on PSD positioning accuracy was simulated based on the current equation under the Gaussian spot model.This validated the robustness of the correction algorithm under varying spot sizes.The results demonstrate that the overall optimized error is reduced by 84.51%,and for spot sizes smaller than 1 mm,the error reduction exceeds 93.89%.This method not only meets the measurement accuracy requirements but also extends the measurement range of PSD.展开更多
This study explores the use of the Global Navigation Satellite System(GNSS)precise point positioning(PPP)technology to determine the natural vibration periods of towering structures through simulations and field testi...This study explores the use of the Global Navigation Satellite System(GNSS)precise point positioning(PPP)technology to determine the natural vibration periods of towering structures through simulations and field testing.During the simulation phase,a GNSS receiver captured vi-bration waveforms generated by a single-axis motion simulator based on preset signal parameters,analyzing how different satellite system configurations affect the efficiency of extracting vibration parameters.Subsequently,field tests were conducted on a high-rise steel singletube tower.The results indicate that in the simulation environment,no matter the PPP positioning data under single GPS or multisystem combination,the vibration frequency of singleaxis motion simulator can be accurately extracted after frequency do-main analysis,with multisystem setups providing more precise amplitude parameters.In the field test,the natural vibration periods of the main vibration modes of high-rise steel single-tube tower measured by PPP technology closely match the results of the first two modes derived from finite element analysis.The first mode period calculated by the em-pirical formula is approximately 6%higher than those determined through finite element analysis and PPP.This study demonstrates the potential of PPP for structural vibration analysis,offering significant benefits for assessing dynamic responses and monitoring the health of towering structures.展开更多
BACKGROUND:Tracheal intubation(TI)is a fundamental procedure for securing the airway or assisting ventilation in emergency medicine.Tracheal intubation in the lateral position(TILP)has been utilized in clinical practi...BACKGROUND:Tracheal intubation(TI)is a fundamental procedure for securing the airway or assisting ventilation in emergency medicine.Tracheal intubation in the lateral position(TILP)has been utilized in clinical practice,demonstrating potential advantages in specific scenarios,including emergency settings.However,there is a lack of comprehensive reviews and practical protocols on TILP application.To address this gap,we performed a narrative review,and provided evidence-based recommendations to formulate a practice protocol,to assist clinicians to effectively apply TILP.METHODS:We conducted a narrative review of TILP applications and developed recommendations based on clinical research evidence and clinical experience.Delphi method was used among the TILP consortium to grade the strength of the recommendations and to help reach consensus.The practice protocols were formulated as warranted by advancements in medical knowledge,technology,and practice.RESULTS:This narrative review summarized the current evidence on TILP application,highlighting its safety,efficacy,challenges,and potential complications.In total,24 recommendations and a clinical protocol for TILP application in emergency patients were established.CONCLUSION:TILP is a valuable technique in emergency medicine.We reviewed its application in emergency settings and formulated recommendations along with a clinical practice protocol.Future studies are needed to evaluate the safety and efficacy of TILP,broaden its scope of application,and explore effective training protocols.展开更多
For multi-vehicle networks,Cooperative Positioning(CP)technique has become a promising way to enhance vehicle positioning accuracy.Especially,the CP performance could be further improved by introducing Sensor-Rich Veh...For multi-vehicle networks,Cooperative Positioning(CP)technique has become a promising way to enhance vehicle positioning accuracy.Especially,the CP performance could be further improved by introducing Sensor-Rich Vehicles(SRVs)into CP networks,which is called SRV-aided CP.However,the CP system may split into several sub-clusters that cannot be connected with each other in dense urban environments,in which the sub-clusters with few SRVs will suffer from degradation of CP performance.Since Unmanned Aerial Vehicles(UAVs)have been widely used to aid vehicular communications,we intend to utilize UAVs to assist sub-clusters in CP.In this paper,a UAV-aided CP network is constructed to fully utilize information from SRVs.First,the inter-node connection structure among the UAV and vehicles is designed to share available information from SRVs.After that,the clustering optimization strategy is proposed,in which the UAV cooperates with the high-precision sub-cluster to obtain available information from SRVs,and then broadcasts this positioning-related information to other low-precision sub-clusters.Finally,the Locally-Centralized Factor Graph Optimization(LC-FGO)algorithm is designed to fuse positioning information from cooperators.Simulation results indicate that the positioning accuracy of the CP system could be improved by fully utilizing positioning-related information from SRVs.展开更多
The accuracy of spot centroid positioning has a significant impact on the tracking accuracy of the system and the stability of the laser link construction.In satellite laser communication systems,the use of short-wave...The accuracy of spot centroid positioning has a significant impact on the tracking accuracy of the system and the stability of the laser link construction.In satellite laser communication systems,the use of short-wave infrared wavelengths as beacon light can reduce atmospheric absorption and signal attenuation.However,there are strong non-uniformity and blind pixels in the short-wave infrared image,which makes the image distorted and leads to the decrease of spot centroid positioning accuracy.Therefore,the high-precision localization of the spot centroid of the short-wave infrared images is of great research significance.A high-precision spot centroid positioning model for short-wave infrared is proposed to correct for non-uniformity and blind pixels in short-wave infrared images and quantify the localization errors caused by the two,further model-based localization error simulations are performed,and a novel spot centroid positioning payload for satellite laser communications has been designed using the latest 640×512 planar array InGaAs shortwave infrared detector.The experimental results show that the non-uniformity of the corrected image is reduced from 7%to 0.6%,the blind pixels rejection rate reaches 100%,the frame rate can be up to 2000 Hz,and the spot centroid localization accuracy is as high as 0.1 pixel point,which realizes high-precision spot centroid localization of high-frame-frequency short-wave infrared images.展开更多
Sunflower leaf photosynthesis strongly depends on the leaf position in the plant stem conditioning,which directly affects other physiological processes.Therefore,a study of the leaf’s physiological status regarding t...Sunflower leaf photosynthesis strongly depends on the leaf position in the plant stem conditioning,which directly affects other physiological processes.Therefore,a study of the leaf’s physiological status regarding the leaf position in the stem was performed on sunflowers in the flowering stage.Eight differently positioned leaves were investigated,starting with the youngest leaf on the top of the stem to the leaves of the stem bottom,assigned as the oldest senescent leaves.According to chlorophyll fluorescence(ChlF)parameters connected to photosystem II(PSII)processes,significant changes in PSII functioning occurred only in the senescent leaves,while photosystem I(PSI)describing parameters showed a linear decrease with leaf age,i.e.,position on the stem.The antioxidative status of the leaves was dynamic,as stress indicators(lipid peroxidation and hydrogen peroxide content)fluctuated regarding leaf position on the stem,but no link was found between the activities of antioxidative enzymes and oxidative stress indicators.Linear decrease trend of secondary metabolites(mainly phenolic compounds)correlated with antioxidant activity,except for some phenolic acids(caffeic and ferulic acid),which increased in senescent leaves.The most changes in the physiological status of the leaves were confirmed in senescent leaves,which stand out the importance of younger leaves in maintaining the plant’s vitality after flowering,which is the most important for sunflower yield.展开更多
In this paper,we present a novel particle filter(PF)-based direct position tracking method utilizing multiple distributed observation stations.Traditional passive tracking methods are anchored on repetitive position e...In this paper,we present a novel particle filter(PF)-based direct position tracking method utilizing multiple distributed observation stations.Traditional passive tracking methods are anchored on repetitive position estimation,where the set of consecutive estimates provides the tracking trajectory,such as Two-step and direct position determination methods.However,duplicate estimates can be computationally expensive.In addition,these techniques suffer from data association problems.The PF algorithm is a tracking method that avoids these drawbacks,but the conventional PF algorithm is unable to construct a likelihood function from the received signals of multiple observatories to determine the weights of particles.Therefore,we developed an improved PF algorithm with the likelihood function modified by the projection approximation subspace tracking with deflation(PASTd)algorithm.The proposed algorithm uses the projection subspace and spectral function to replace the likelihood function of PF.Then,the weights of particles are calculated jointly by multiple likelihood functions.Finally,the tracking problem of multiple targets is solved by multiple sets of particles.Simulations demonstrate the effectiveness of the proposed method in terms of computational complexity and tracking accuracy.展开更多
Forest ecosystems can be characterized by a set of catenas arranged along the slope in mountainous areas as these affect microhabitat features,which in turn influence soil properties.Heretofore,few studies have examin...Forest ecosystems can be characterized by a set of catenas arranged along the slope in mountainous areas as these affect microhabitat features,which in turn influence soil properties.Heretofore,few studies have examined how topographic variables affect soil properties and quality in semiarid regions.This study aimed to provide important insights into how catena position and shape influence soil properties,soil quality,and their interrelationships in a semiarid protected oak forest in western Iran.Basic soil properties were measured in the laboratory.In addition,the soil quality index(SQI)was calculated at different topographic positions along both convex(Λ-shaped)and concave(V-shaped)catenas at two soil depths(0-15 and 15-30 cm).The findings indicated that soil organic carbon and total nitrogen declined in the lower depth in both V-andΛ-shaped catenas and at all catena positions.The lowest porosity was observed in the lower depth at toeslope positions(TS)of both catenas.Substrate-induced respiration(SIR),microbial biomass carbon(MBC),and basal respiration(BR)were higher in the upper depths at TS positions on V-shaped catenas than onΛ-shaped catenas.These biological indices were consistently higher in the upper depths than in the lower depths across all positions of both catenas.SQI had the highest values at TS positions on both catenas and in the upper depths across all positions.Pearson correlations between soil properties indicated that SQI was most strongly and positively correlated with biological properties in both catenas.The nutrient levels,microbial activity,and soil porosity in both catena shapes and at both soil depths displayed a relatively downward trend with increasing elevation from toeslope to summit positions.The results showed that catena topographic sequence shape and position affected most of the soil properties,providing evidence of the important role of topography in creating pedodiversity in oak forest ecosystems.展开更多
Four benzocoumarin-based two-photon fluorescent probes(BH1-BH4)are proposed for ra-tiometric detection of hypochlorous acid(HClO)and their two-photon sensing perfor-mance are evaluated by means of time-dependent densi...Four benzocoumarin-based two-photon fluorescent probes(BH1-BH4)are proposed for ra-tiometric detection of hypochlorous acid(HClO)and their two-photon sensing perfor-mance are evaluated by means of time-dependent density func-tional theory and quadratic re-sponse theory.The effects of benzene-fused position on Stokes shift,fluorescence quantum yield and two-photon absorption are discussed comprehensively.The results show that fusing a benzene ring in coumarin can enhance Stokes shift efficiently.The benzene-fused position has important effects on these photophysical properties.The benzo[g]coumarins(BH1)and benzo[f]coumarins(BH2)derivatives have larger Stokes shifts in comparison with benzo[h]coumarins(BH3)and dihydrophenazine(BH4)derivatives.The two-photon absorp-tion of benzo[f]coumarins(BH2)derivative is much smaller than those of other benzo-coumarins derivatives.The large Stokes shift and increased two-photon action cross section can be achieved simultaneously in the dihydrophenazine(BH4)derivative.Therefore,the de-signed BH4 is expected to have superior performance for the ratiometric detection of HClO.To explore the reasons behind these effects,the intramolecular charge transfer degrees are il-lustrated quantitatively by plotting the hole-electron isosurface map,and the relation be-tween charge transfer and Stokes shift is revealed.A two-state model analysis is employed to understand two-photon absorption ability.Moreover,the fluorescence near-quenching mecha-nism of the product molecules B1 and B3 is explained by analyzing reorganization energy and Huang-Rhys factor,as well as related normal mode.Our research could contribute to the effi-cient design of ratiometric two-photon fluorescent probes with large Stokes shift and signifi-cant two-photon action cross section.展开更多
Objectives A systematic review and network meta-analysis was conducted to evaluate the effectiveness of different childbirth positions in reducing the duration of the second stage of labor,providing evidence-based ins...Objectives A systematic review and network meta-analysis was conducted to evaluate the effectiveness of different childbirth positions in reducing the duration of the second stage of labor,providing evidence-based insights for obstetric institutions to guide interventions related to childbirth positions.Methods A comprehensive literature search was conducted in databases,including PubMed,Web of Science,the Cochrane Library,Embase,Wanfang Databases,China National Knowledge Infrastructure Databases(CNKI),China Science and Technology Journal Database(CSTJ),and China Biology Medicine disc(CBMdisc)to identify studies on the effectiveness of different childbirth positions in reducing the duration of the second stage of labor.The search included randomized controlled trials published from database inception to September 30,2024.The Cochrane risk-of-bias tool was used to assess the quality of the studies.Two independent reviewers screened the literature,extracted data,and evaluated study quality.Subsequently,a network meta-analysis was performed using STATA software.The study protocol has been registered in PROSPERO(CRD42023428217).Results This study analyzed data from 25 randomized controlled trials involving 9,844 women.The findings indicated that in comparison to lithotomy position,free position(MD=20.53,95%CI[11.38,29.68])and upright position(MD=−24.13,95%CI[−42.94,-5.32])were found to be superior in reducing the duration of the second stage of labor.Free position outperformed kneeling position(MD=21.48,95%CI[4.67,38.28])and squatting position(MD=23.43,95%CI[1.88,44.97]);upright position was superior to kneeling position(MD=−25.08,95%CI[−46.93,−3.22]);semirecumbent position surpassed squatting position(MD=19.71,95%CI[2.05,37.38]);and upright position was also superior to squatting position(MD=−27.03,95%CI[−51.48,−2.57]).According to the surface under the cumulative ranking curve(SUCRA),the upright position emerged as the most effective for reducing the duration of the second stage of labor(87.4%),followed by free position(81.1%),semirecumbent position(70.0%),and lateral position(62.3%).Conclusion These findings offer valuable insights for midwifery practice and help inform future research directions.Considering the limitations of this review,more larger-scale,multicenter randomized controlled trials are warranted to further evaluate the relative effectiveness of different childbirth positions in reducing the duration of the second stage of labor.展开更多
Granite residual soil slope is often destroyed,which poses great threats to Rong County in southeastern Guangxi,China.Heavy rainfall and fissures are the major triggering and internal factors.The fissure that controls...Granite residual soil slope is often destroyed,which poses great threats to Rong County in southeastern Guangxi,China.Heavy rainfall and fissures are the major triggering and internal factors.The fissure that controls the slope stability and the associated failure mechanisms remain unclear.The purpose of this study was to identify the controlling fissures through field investigation,elucidate the effect of its position,and analyze the failure process and hydrological response of residual soil slope through artificial flume model tests.The results comprised five aspects.(1)Surface weathering and unloading fissures could affect slope stability.(2)The failure processes with different fissure positions exhibited inconsistent characteristics.(3)The volume moisture content(VMC)had the most direct response at the fissure tip.The corresponding infiltration rate was the highest.The response time of pore water pressure(PWP)was longer than that of VMC.Fluctuations in PWP were associated with VMC and changes in the soil microstructure due to local deformation.(4)Slope failure was accompanied by serious soil erosion.This could be attributed to the infiltration direction and the interaction between soil and water.(5)Fissured soil slopes experienced five similar failure processes:sheet erosion and partial failure of the slope foot,occurrence of preferential flow and enlargement of the sliding area,creep deformation and tension fissure emergence,block sliding and gully erosion,and flow-slip.展开更多
The intensified kernel position effect is a common phenomenon in maize production under higher plant density,which limits crop productivity.Subsoiling is an effective agronomic practice for improving crop productivity...The intensified kernel position effect is a common phenomenon in maize production under higher plant density,which limits crop productivity.Subsoiling is an effective agronomic practice for improving crop productivity.To clarify the effect of subsoiling before winter wheat on the kernel position effect of densely grown summer maize and its regulatory mechanism,field experiments were conducted during the 2020-2021 and 2021-2022 growing seasons using a split-plot design.The main plots included two tillage practices:conventional tillage practice(CT)and subsoiling before the sowing of winter wheat(SS);and the subplots consisted of three plant densities(D1-D3 at 6.0×10~4,7.5×10~4,and 9.0×10~4 plants ha-1).Compared with CT,SS alleviated the kernel position effect by increasing the weight ratio of inferior to superior kernels(WR)in the D2 and D3 treated plants.The higher WR of SS treated plants contributed largely to the improved flling of inferior kernels.Under the same plant density,SS signifcantly improved the root dry matter accumulation(DMA)and antioxidant enzyme activities(superoxide dismutase(SOD)and peroxidase(POD)),and it reduced the malondialdehyde(MDA)content,especially for the plants grown under higher plant densities.These results indicated that SS delayed the root senescence,which is associated with the reduced soil bulk density.In addition,compared with CT,SS increased the leaf chlorophyll content from 20 days after silking to physiological maturity and the post-silking leaf area duration,and it reduced the post-silking leaf chlorophyll reduction rate and leaf area reduction rate,indicating that the post-silking leaf senescence had been alleviated.Under the same plant density,the post-silking DMA of SS was obviously higher than that of CT,which was probably related to the improved leaf area duration and photosynthetic enzyme activities(phosphoenolpyruvate carboxylase(PEPC)and Rubisco).The correlation analysis revealed that the main mechanism of SS in alleviating the kernel position effect of densely grown summer maize is as follows:SS delays the post-silking root-shoot senescence by regulating soil physical properties,and further improves the post-silking DMA and flling of inferior kernels,which ultimately alleviates the kernel position effect and improves grain yield.The results of this study provide new theoretical support for the promotion of summer maize yield by subsoiling before winter wheat.展开更多
Tendon-driven robots have distinct advantages in high-dynamic performance motion and high-degree-of-freedom manipulation.However,these robots face challenges related to control complexity,intricate tendon drive paths,...Tendon-driven robots have distinct advantages in high-dynamic performance motion and high-degree-of-freedom manipulation.However,these robots face challenges related to control complexity,intricate tendon drive paths,and tendon slackness.In this study,the authors present a novel modular tendon-driven actuator design that integrates a series elastic element.The actuator incorporates a unique magnetic position sensing technology that enables observation of the length and tension of the tendon and features an exceptionally compact design.The modular architecture of the tendon-driven actuator addresses the complexity of tendon drive paths,while the tension observation functionality mitigates slackness issues.The design and modeling of the actuator are described in this paper,and a series of tests are conducted to validate the simulation model and to test the performance of the proposed actuator.The model can be used for training robot control neural networks based on simulation,thereby overcoming the challenges associated with controlling tendon-driven robots.展开更多
This study presents a novel analytical algorithm for solving the forward position problem of a triangular platform Stewart-type parallel robot(STPR).By introducing a virtual chain and leveraging tetrahedral geometric ...This study presents a novel analytical algorithm for solving the forward position problem of a triangular platform Stewart-type parallel robot(STPR).By introducing a virtual chain and leveraging tetrahedral geometric principles,the proposed method derives analytical solutions for the position and orientation of the moving platform.The algorithm systematically addresses the nonlinearity inherent in the kinematic equations of parallel mechanisms,providing explicit expressions for the coordinates of key moving attachment points.Furthermore,the methodology is extended to general triangular platform STPRs with non-coplanar fixed attachments.Numerical validation through virtual experiments confirms the accuracy of the solutions,demonstrating that the mechanism admits eight distinct configurations for a given set of limb lengths.The results align with established kinematic principles and offer a computationally efficient alternative to iterative analytical approaches,contributing to the advancement of precision control in parallel robotic systems.展开更多
Null compensation interferometry is the primary testing method for the manufacture of ultra-high-precision aspheric mirrors.The crosstalk fringes generated by stray light in interferometry can affect accuracy and pote...Null compensation interferometry is the primary testing method for the manufacture of ultra-high-precision aspheric mirrors.The crosstalk fringes generated by stray light in interferometry can affect accuracy and potentially prevent the testing from proceeding normally.Position errors include the decenter error,tilt error,and distance error.During the testing process,position errors will impact the testing accuracy and the crosstalk fringes generated by stray light.To determine the specific impact of position errors,we use the concept of Hindle shell testing of a convex aspheric mirror,and propose the simulation method of crosstalk fringes in null compensation interferometry.We also propose evaluation indices of crosstalk fringes in interferometry and simulate the influence of position errors on the crosstalk fringes.This work aims to help improve the design of compensation interferometry schemes,enhance the feasibility of the design,reduce engineering risks,and improve efficiency.展开更多
基金Project(52272339)supported by the National Natural Science Foundation of ChinaProject(2023YFB390730303)supported by the National Key Research and Development Program of China+2 种基金Project(L2023G004)supported by the Science and Technology Research and Development Program of China State Railway Group Co.,Ltd.Project(QZKFKT2023-005)supported by the State Key Laboratory of Heavy-duty and Express High-power Electric Locomotive,ChinaProject(2022JZZ05)supported by the Open Foundation of MOE Key Laboratory of Engineering Structures of Heavy Haul Railway(Central South University),China。
文摘In this paper,a novel train positioning method considering satellite raw observation data was proposed,which aims to promote train positioning performance from an innovative perspective of the train satellite-based positioning error sources.The method focused on overcoming the abnormal observations in satellite observation data caused by railway environment rather than the positioning results.Specifically,the relative positioning experimental platform was built and the zero-baseline method was firstly employed to evaluate the carrier phase data quality,and then,GNSS combined observation models were adopted to construct the detection values,which were applied to judge abnormal-data through the dual-frequency observations.Further,ambiguity fixing optimization was investigated based on observation data selection in partly-blocked environments.The results show that the proposed method can effectively detect and address abnormal observations and improve positioning stability.Cycle slips and gross errors can be detected and identified based on dual-frequency global navigation satellite system data.After adopting the data selection strategy,the ambiguity fixing percentage was improved by 29.2%,and the standard deviation in the East,North,and Up components was enhanced by 12.7%,7.4%,and 12.5%,respectively.The proposed method can provide references for train positioning performance optimization in railway environments from the perspective of positioning error sources.
基金supported in part by the National Natural Science Foundation of China(Nos.62171375,62271397,62001392,62101458,62173276,61803310 and 61801394)the Shenzhen Science and Technology Innovation ProgramChina(No.JCYJ20220530161615033)。
文摘The existing Low-Earth-Orbit(LEO)positioning performance cannot meet the requirements of Unmanned Aerial Vehicle(UAV)clusters for high-precision real-time positioning in the Global Navigation Satellite System(GNSS)denial conditions.Therefore,this paper proposes a UAV Clusters Information Geometry Fusion Positioning(UC-IGFP)method using pseudoranges from the LEO satellites.A novel graph model for linking and computing between the UAV clusters and LEO satellites was established.By utilizing probability to describe the positional states of UAVs and sensor errors,the distributed multivariate Probability Fusion Cooperative Positioning(PF-CP)algorithm is proposed to achieve high-precision cooperative positioning and integration of the cluster.Criteria to select the centroid of the cluster were set.A new Kalman filter algorithm that is suitable for UAV clusters was designed based on the global benchmark and Riemann information geometry theory,which overcomes the discontinuity problem caused by the change of cluster centroids.Finally,the UC-IGFP method achieves the LEO continuous highprecision positioning of UAV clusters.The proposed method effectively addresses the positioning challenges caused by the strong direction of signal beams from LEO satellites and the insufficient constraint quantity of information sources at the edge nodes of the cluster.It significantly improves the accuracy and reliability of LEO-UAV cluster positioning.The results of comprehensive simulation experiments show that the proposed method has a 30.5%improvement in performance over the mainstream positioning methods,with a positioning error of 14.267 m.
基金supported by the National Key Research and Development Program of China(2023YFB3907300)the Fundamental Research Funds for the Central Universities(2024JBMC002)the National Natural Science Foundation of China(T2222015,U2268206).
文摘Global Navigation Satellite System(GNSS)-based continuous and accurate train positioning is one of the key technologies for advanced train operations such as train virtual coupling.However,GNSS-based train positioning faces significant challenges in real-world scenarios due to environmental complexities and signal interferences.Considering this issue,this paper presents an approach for modeling and performance analysis of GNSS-based train positioning systems using Colored Petri Nets(CPNs).By systematically modeling the GNSS signal reception and processing process,the performance of the positioning system under various environment scenarios is evaluated.The system model integrates three types of interference signals(i.e.,Amplitude Modulation(AM)signals,Frequency Modulation(FM)signals,and pulse signals)while incorporating environmental factors such as terrain obstructions and tunnel shielding.Additionally,the Extended Kalman Filter(EKF)algorithm is employed to process GNSS observation data,providing accurate train position estimations.The simulation results demonstrate that signal interferences and complex environmental conditions significantly affect the GNSS-based positioning accuracy.This study offers a comprehensive framework for evaluating the performance of GNSS-based train positioning systems in different scenarios,highlighting critical factors that influence positioning accuracy and stability.
文摘In the context of security systems,adequate signal coverage is paramount for the communication between security personnel and the accurate positioning of personnel.Most studies focus on optimizing base station deployment under the assumption of static obstacles,aiming to maximize the perception coverage of wireless RF(Radio Frequency)signals and reduce positioning blind spots.However,in practical security systems,obstacles are subject to change,necessitating the consideration of base station deployment in dynamic environments.Nevertheless,research in this area still needs to be conducted.This paper proposes a Dynamic Indoor Environment Beacon Deployment Algorithm(DIE-BDA)to address this problem.This algorithm considers the dynamic alterations in obstacle locations within the designated area.It determines the requisite number of base stations,the requisite time,and the area’s practical and overall signal coverage rates.The experimental results demonstrate that the algorithm can calculate the deployment strategy in 0.12 s following a change in obstacle positions.Experimental results show that the algorithm in this paper requires 0.12 s to compute the deployment strategy after the positions of obstacles change.With 13 base stations,it achieves an effective coverage rate of 93.5%and an overall coverage rate of 97.75%.The algorithm can rapidly compute a revised deployment strategy in response to changes in obstacle positions within security systems,thereby ensuring the efficacy of signal coverage.
基金supported by the National Natural Science Foundation of China(No.52175269)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(No.52021003)+2 种基金Science and Technology Research Project of Education Department of Jilin Province(JJKH20231146KJ,JJKH20241262KJ)Project ZR2024ME104 supported by Shandong Provincial Natural Science FoundationChina Postdoctoral Science Foundation(No.2024M751086).
文摘Numerous arthropods evolve and optimize sensory systems, enabling them to effectively adapt complex and competitive habitats. Typically, scorpions can precisely perceive the prey location with the lowest metabolic rate among invertebrates. This biological phenomenon contrasts sharply with engineered systems, which generally associates high accuracy with substantial energy consumption. Inspired by the Scorpion Compound Slit Sensilla (SCSS) with a stress field modulation strategy, a bionic positioning sensor with superior precision and minimal power consumption is developed for the first time, which utilizes the particular Minimum Positioning Units (MPUs) to efficiently locate vibration signals. The single MPU of the SCSS can recognize the direction of collinear loads by regulating the stress field distribution and further, the coupling action of three MPUs can realize all-angle vibration monitoring in plane. Experiments demonstrate that the bionic positioning sensor achieves 1.43 degrees of angle-error-free accuracy without additional energy supply. As a proof of concept, two bionic positioning sensors and machine learning algorithm are integrated to provide centimeter (cm)-accuracy target localization, ideally suited for the man-machine interaction. The novel design offers a new mechanism for the design of traditional positioning devices, improving precision and efficiency in both the meta-universe and real-world Internet-connected systems.
基金Supported by the National Natural Science Foundation of China(U1831133)Open Fund of Key Laboratory of Space Active Optoelectronics Technology,Chinese Academy of Sciences(2021ZDKF4)。
文摘Position-sensitive detector(PSD)is widely used in precision measurement fields such as flatness detection,auto-collimator systems,and degrees of freedom testing.However,due to factors such as uneven surface resistance and differences in electrode structures,the nonlinearity of PSD becomes increasingly severe as the photosensitive surface moves from the center toward the edges of the four electrodes.To address this issue,a PSD nonlinearity correction algorithm is proposed.The algorithm utilizes the particle swarm optimization(PSO)algorithm to determine the optimal weights and thresholds,providing better initial parameters for the back propagation(BP)neural network.The BP neural network then iterates continuously until the error conditions are met,completing the correction process.Furthermore,a PSD nonlinearity correction system was developed,and the influence of different spot sizes on PSD positioning accuracy was simulated based on the current equation under the Gaussian spot model.This validated the robustness of the correction algorithm under varying spot sizes.The results demonstrate that the overall optimized error is reduced by 84.51%,and for spot sizes smaller than 1 mm,the error reduction exceeds 93.89%.This method not only meets the measurement accuracy requirements but also extends the measurement range of PSD.
基金The National Natural Science Foundation of China(No.41974214).
文摘This study explores the use of the Global Navigation Satellite System(GNSS)precise point positioning(PPP)technology to determine the natural vibration periods of towering structures through simulations and field testing.During the simulation phase,a GNSS receiver captured vi-bration waveforms generated by a single-axis motion simulator based on preset signal parameters,analyzing how different satellite system configurations affect the efficiency of extracting vibration parameters.Subsequently,field tests were conducted on a high-rise steel singletube tower.The results indicate that in the simulation environment,no matter the PPP positioning data under single GPS or multisystem combination,the vibration frequency of singleaxis motion simulator can be accurately extracted after frequency do-main analysis,with multisystem setups providing more precise amplitude parameters.In the field test,the natural vibration periods of the main vibration modes of high-rise steel single-tube tower measured by PPP technology closely match the results of the first two modes derived from finite element analysis.The first mode period calculated by the em-pirical formula is approximately 6%higher than those determined through finite element analysis and PPP.This study demonstrates the potential of PPP for structural vibration analysis,offering significant benefits for assessing dynamic responses and monitoring the health of towering structures.
基金National Natural Science Foundation of China(U24A20714 to XMF and 82102238 to PC)。
文摘BACKGROUND:Tracheal intubation(TI)is a fundamental procedure for securing the airway or assisting ventilation in emergency medicine.Tracheal intubation in the lateral position(TILP)has been utilized in clinical practice,demonstrating potential advantages in specific scenarios,including emergency settings.However,there is a lack of comprehensive reviews and practical protocols on TILP application.To address this gap,we performed a narrative review,and provided evidence-based recommendations to formulate a practice protocol,to assist clinicians to effectively apply TILP.METHODS:We conducted a narrative review of TILP applications and developed recommendations based on clinical research evidence and clinical experience.Delphi method was used among the TILP consortium to grade the strength of the recommendations and to help reach consensus.The practice protocols were formulated as warranted by advancements in medical knowledge,technology,and practice.RESULTS:This narrative review summarized the current evidence on TILP application,highlighting its safety,efficacy,challenges,and potential complications.In total,24 recommendations and a clinical protocol for TILP application in emergency patients were established.CONCLUSION:TILP is a valuable technique in emergency medicine.We reviewed its application in emergency settings and formulated recommendations along with a clinical practice protocol.Future studies are needed to evaluate the safety and efficacy of TILP,broaden its scope of application,and explore effective training protocols.
基金supported by the National Natural Science Foundation of China(No.62271399)the National Key Research and Development Program of China(No.2022YFB1807102)。
文摘For multi-vehicle networks,Cooperative Positioning(CP)technique has become a promising way to enhance vehicle positioning accuracy.Especially,the CP performance could be further improved by introducing Sensor-Rich Vehicles(SRVs)into CP networks,which is called SRV-aided CP.However,the CP system may split into several sub-clusters that cannot be connected with each other in dense urban environments,in which the sub-clusters with few SRVs will suffer from degradation of CP performance.Since Unmanned Aerial Vehicles(UAVs)have been widely used to aid vehicular communications,we intend to utilize UAVs to assist sub-clusters in CP.In this paper,a UAV-aided CP network is constructed to fully utilize information from SRVs.First,the inter-node connection structure among the UAV and vehicles is designed to share available information from SRVs.After that,the clustering optimization strategy is proposed,in which the UAV cooperates with the high-precision sub-cluster to obtain available information from SRVs,and then broadcasts this positioning-related information to other low-precision sub-clusters.Finally,the Locally-Centralized Factor Graph Optimization(LC-FGO)algorithm is designed to fuse positioning information from cooperators.Simulation results indicate that the positioning accuracy of the CP system could be improved by fully utilizing positioning-related information from SRVs.
基金Supported by the Short-wave Infrared Camera Systems(B025F40622024)。
文摘The accuracy of spot centroid positioning has a significant impact on the tracking accuracy of the system and the stability of the laser link construction.In satellite laser communication systems,the use of short-wave infrared wavelengths as beacon light can reduce atmospheric absorption and signal attenuation.However,there are strong non-uniformity and blind pixels in the short-wave infrared image,which makes the image distorted and leads to the decrease of spot centroid positioning accuracy.Therefore,the high-precision localization of the spot centroid of the short-wave infrared images is of great research significance.A high-precision spot centroid positioning model for short-wave infrared is proposed to correct for non-uniformity and blind pixels in short-wave infrared images and quantify the localization errors caused by the two,further model-based localization error simulations are performed,and a novel spot centroid positioning payload for satellite laser communications has been designed using the latest 640×512 planar array InGaAs shortwave infrared detector.The experimental results show that the non-uniformity of the corrected image is reduced from 7%to 0.6%,the blind pixels rejection rate reaches 100%,the frame rate can be up to 2000 Hz,and the spot centroid localization accuracy is as high as 0.1 pixel point,which realizes high-precision spot centroid localization of high-frame-frequency short-wave infrared images.
文摘Sunflower leaf photosynthesis strongly depends on the leaf position in the plant stem conditioning,which directly affects other physiological processes.Therefore,a study of the leaf’s physiological status regarding the leaf position in the stem was performed on sunflowers in the flowering stage.Eight differently positioned leaves were investigated,starting with the youngest leaf on the top of the stem to the leaves of the stem bottom,assigned as the oldest senescent leaves.According to chlorophyll fluorescence(ChlF)parameters connected to photosystem II(PSII)processes,significant changes in PSII functioning occurred only in the senescent leaves,while photosystem I(PSI)describing parameters showed a linear decrease with leaf age,i.e.,position on the stem.The antioxidative status of the leaves was dynamic,as stress indicators(lipid peroxidation and hydrogen peroxide content)fluctuated regarding leaf position on the stem,but no link was found between the activities of antioxidative enzymes and oxidative stress indicators.Linear decrease trend of secondary metabolites(mainly phenolic compounds)correlated with antioxidant activity,except for some phenolic acids(caffeic and ferulic acid),which increased in senescent leaves.The most changes in the physiological status of the leaves were confirmed in senescent leaves,which stand out the importance of younger leaves in maintaining the plant’s vitality after flowering,which is the most important for sunflower yield.
基金supported by China NSF Grants(62371225,62371227)Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX250590).
文摘In this paper,we present a novel particle filter(PF)-based direct position tracking method utilizing multiple distributed observation stations.Traditional passive tracking methods are anchored on repetitive position estimation,where the set of consecutive estimates provides the tracking trajectory,such as Two-step and direct position determination methods.However,duplicate estimates can be computationally expensive.In addition,these techniques suffer from data association problems.The PF algorithm is a tracking method that avoids these drawbacks,but the conventional PF algorithm is unable to construct a likelihood function from the received signals of multiple observatories to determine the weights of particles.Therefore,we developed an improved PF algorithm with the likelihood function modified by the projection approximation subspace tracking with deflation(PASTd)algorithm.The proposed algorithm uses the projection subspace and spectral function to replace the likelihood function of PF.Then,the weights of particles are calculated jointly by multiple likelihood functions.Finally,the tracking problem of multiple targets is solved by multiple sets of particles.Simulations demonstrate the effectiveness of the proposed method in terms of computational complexity and tracking accuracy.
文摘Forest ecosystems can be characterized by a set of catenas arranged along the slope in mountainous areas as these affect microhabitat features,which in turn influence soil properties.Heretofore,few studies have examined how topographic variables affect soil properties and quality in semiarid regions.This study aimed to provide important insights into how catena position and shape influence soil properties,soil quality,and their interrelationships in a semiarid protected oak forest in western Iran.Basic soil properties were measured in the laboratory.In addition,the soil quality index(SQI)was calculated at different topographic positions along both convex(Λ-shaped)and concave(V-shaped)catenas at two soil depths(0-15 and 15-30 cm).The findings indicated that soil organic carbon and total nitrogen declined in the lower depth in both V-andΛ-shaped catenas and at all catena positions.The lowest porosity was observed in the lower depth at toeslope positions(TS)of both catenas.Substrate-induced respiration(SIR),microbial biomass carbon(MBC),and basal respiration(BR)were higher in the upper depths at TS positions on V-shaped catenas than onΛ-shaped catenas.These biological indices were consistently higher in the upper depths than in the lower depths across all positions of both catenas.SQI had the highest values at TS positions on both catenas and in the upper depths across all positions.Pearson correlations between soil properties indicated that SQI was most strongly and positively correlated with biological properties in both catenas.The nutrient levels,microbial activity,and soil porosity in both catena shapes and at both soil depths displayed a relatively downward trend with increasing elevation from toeslope to summit positions.The results showed that catena topographic sequence shape and position affected most of the soil properties,providing evidence of the important role of topography in creating pedodiversity in oak forest ecosystems.
基金supported by the Shandong Provincial Natural Science Foundation,China(No.ZR2020MA078)。
文摘Four benzocoumarin-based two-photon fluorescent probes(BH1-BH4)are proposed for ra-tiometric detection of hypochlorous acid(HClO)and their two-photon sensing perfor-mance are evaluated by means of time-dependent density func-tional theory and quadratic re-sponse theory.The effects of benzene-fused position on Stokes shift,fluorescence quantum yield and two-photon absorption are discussed comprehensively.The results show that fusing a benzene ring in coumarin can enhance Stokes shift efficiently.The benzene-fused position has important effects on these photophysical properties.The benzo[g]coumarins(BH1)and benzo[f]coumarins(BH2)derivatives have larger Stokes shifts in comparison with benzo[h]coumarins(BH3)and dihydrophenazine(BH4)derivatives.The two-photon absorp-tion of benzo[f]coumarins(BH2)derivative is much smaller than those of other benzo-coumarins derivatives.The large Stokes shift and increased two-photon action cross section can be achieved simultaneously in the dihydrophenazine(BH4)derivative.Therefore,the de-signed BH4 is expected to have superior performance for the ratiometric detection of HClO.To explore the reasons behind these effects,the intramolecular charge transfer degrees are il-lustrated quantitatively by plotting the hole-electron isosurface map,and the relation be-tween charge transfer and Stokes shift is revealed.A two-state model analysis is employed to understand two-photon absorption ability.Moreover,the fluorescence near-quenching mecha-nism of the product molecules B1 and B3 is explained by analyzing reorganization energy and Huang-Rhys factor,as well as related normal mode.Our research could contribute to the effi-cient design of ratiometric two-photon fluorescent probes with large Stokes shift and signifi-cant two-photon action cross section.
基金the Obstetrics and Gynecology Hospital of Fudan University for supporting this project。
文摘Objectives A systematic review and network meta-analysis was conducted to evaluate the effectiveness of different childbirth positions in reducing the duration of the second stage of labor,providing evidence-based insights for obstetric institutions to guide interventions related to childbirth positions.Methods A comprehensive literature search was conducted in databases,including PubMed,Web of Science,the Cochrane Library,Embase,Wanfang Databases,China National Knowledge Infrastructure Databases(CNKI),China Science and Technology Journal Database(CSTJ),and China Biology Medicine disc(CBMdisc)to identify studies on the effectiveness of different childbirth positions in reducing the duration of the second stage of labor.The search included randomized controlled trials published from database inception to September 30,2024.The Cochrane risk-of-bias tool was used to assess the quality of the studies.Two independent reviewers screened the literature,extracted data,and evaluated study quality.Subsequently,a network meta-analysis was performed using STATA software.The study protocol has been registered in PROSPERO(CRD42023428217).Results This study analyzed data from 25 randomized controlled trials involving 9,844 women.The findings indicated that in comparison to lithotomy position,free position(MD=20.53,95%CI[11.38,29.68])and upright position(MD=−24.13,95%CI[−42.94,-5.32])were found to be superior in reducing the duration of the second stage of labor.Free position outperformed kneeling position(MD=21.48,95%CI[4.67,38.28])and squatting position(MD=23.43,95%CI[1.88,44.97]);upright position was superior to kneeling position(MD=−25.08,95%CI[−46.93,−3.22]);semirecumbent position surpassed squatting position(MD=19.71,95%CI[2.05,37.38]);and upright position was also superior to squatting position(MD=−27.03,95%CI[−51.48,−2.57]).According to the surface under the cumulative ranking curve(SUCRA),the upright position emerged as the most effective for reducing the duration of the second stage of labor(87.4%),followed by free position(81.1%),semirecumbent position(70.0%),and lateral position(62.3%).Conclusion These findings offer valuable insights for midwifery practice and help inform future research directions.Considering the limitations of this review,more larger-scale,multicenter randomized controlled trials are warranted to further evaluate the relative effectiveness of different childbirth positions in reducing the duration of the second stage of labor.
基金financially supported by the National Natural Science Foundation of China(No.41901132)the Natural Scientific Project of Guangxi Zhuang Autonomous Region(Nos.2019GXNSFAA185015,2021GXNSFBA220025)+1 种基金the Interdisciplinary Scientific Research Foundation of Guangxi University(No.2022JCC026)the Project of Key Laboratory of Early Rapid Identification,Prevention and Control of Geological Diseases in Traffic Corridor of High Intensity Earthquake Mountainous Area of Yunnan Province(No.KLGDTC-2021-01)。
文摘Granite residual soil slope is often destroyed,which poses great threats to Rong County in southeastern Guangxi,China.Heavy rainfall and fissures are the major triggering and internal factors.The fissure that controls the slope stability and the associated failure mechanisms remain unclear.The purpose of this study was to identify the controlling fissures through field investigation,elucidate the effect of its position,and analyze the failure process and hydrological response of residual soil slope through artificial flume model tests.The results comprised five aspects.(1)Surface weathering and unloading fissures could affect slope stability.(2)The failure processes with different fissure positions exhibited inconsistent characteristics.(3)The volume moisture content(VMC)had the most direct response at the fissure tip.The corresponding infiltration rate was the highest.The response time of pore water pressure(PWP)was longer than that of VMC.Fluctuations in PWP were associated with VMC and changes in the soil microstructure due to local deformation.(4)Slope failure was accompanied by serious soil erosion.This could be attributed to the infiltration direction and the interaction between soil and water.(5)Fissured soil slopes experienced five similar failure processes:sheet erosion and partial failure of the slope foot,occurrence of preferential flow and enlargement of the sliding area,creep deformation and tension fissure emergence,block sliding and gully erosion,and flow-slip.
基金fnancially supported by the Natural Science Foundation of Hebei Province,China(C2021301004)the State Key Laboratory of North China Crop Improvement and Regulation,China(NCCIR2023KF-10)the HAAFS Science and Technology Innovation Special Project,China(2022KJCXZX-LYS-9)。
文摘The intensified kernel position effect is a common phenomenon in maize production under higher plant density,which limits crop productivity.Subsoiling is an effective agronomic practice for improving crop productivity.To clarify the effect of subsoiling before winter wheat on the kernel position effect of densely grown summer maize and its regulatory mechanism,field experiments were conducted during the 2020-2021 and 2021-2022 growing seasons using a split-plot design.The main plots included two tillage practices:conventional tillage practice(CT)and subsoiling before the sowing of winter wheat(SS);and the subplots consisted of three plant densities(D1-D3 at 6.0×10~4,7.5×10~4,and 9.0×10~4 plants ha-1).Compared with CT,SS alleviated the kernel position effect by increasing the weight ratio of inferior to superior kernels(WR)in the D2 and D3 treated plants.The higher WR of SS treated plants contributed largely to the improved flling of inferior kernels.Under the same plant density,SS signifcantly improved the root dry matter accumulation(DMA)and antioxidant enzyme activities(superoxide dismutase(SOD)and peroxidase(POD)),and it reduced the malondialdehyde(MDA)content,especially for the plants grown under higher plant densities.These results indicated that SS delayed the root senescence,which is associated with the reduced soil bulk density.In addition,compared with CT,SS increased the leaf chlorophyll content from 20 days after silking to physiological maturity and the post-silking leaf area duration,and it reduced the post-silking leaf chlorophyll reduction rate and leaf area reduction rate,indicating that the post-silking leaf senescence had been alleviated.Under the same plant density,the post-silking DMA of SS was obviously higher than that of CT,which was probably related to the improved leaf area duration and photosynthetic enzyme activities(phosphoenolpyruvate carboxylase(PEPC)and Rubisco).The correlation analysis revealed that the main mechanism of SS in alleviating the kernel position effect of densely grown summer maize is as follows:SS delays the post-silking root-shoot senescence by regulating soil physical properties,and further improves the post-silking DMA and flling of inferior kernels,which ultimately alleviates the kernel position effect and improves grain yield.The results of this study provide new theoretical support for the promotion of summer maize yield by subsoiling before winter wheat.
基金supported in part by the National Key R&D Program of China under Grant 2024YFB4707900the National Natural Science Foundation of China under Grant 91948302 and Grant 52021003.
文摘Tendon-driven robots have distinct advantages in high-dynamic performance motion and high-degree-of-freedom manipulation.However,these robots face challenges related to control complexity,intricate tendon drive paths,and tendon slackness.In this study,the authors present a novel modular tendon-driven actuator design that integrates a series elastic element.The actuator incorporates a unique magnetic position sensing technology that enables observation of the length and tension of the tendon and features an exceptionally compact design.The modular architecture of the tendon-driven actuator addresses the complexity of tendon drive paths,while the tension observation functionality mitigates slackness issues.The design and modeling of the actuator are described in this paper,and a series of tests are conducted to validate the simulation model and to test the performance of the proposed actuator.The model can be used for training robot control neural networks based on simulation,thereby overcoming the challenges associated with controlling tendon-driven robots.
基金supported by the Opening Project of State Key Laboratory of Mechanical Transmission for Advanced Equipment(No.SKLMT-MSKFKT202330)the National Natural Science Foundation of China(No.52575022)the Jiangsu Province Postgraduate Research&Practice Innovation Program(No.KYCX25_1403)。
文摘This study presents a novel analytical algorithm for solving the forward position problem of a triangular platform Stewart-type parallel robot(STPR).By introducing a virtual chain and leveraging tetrahedral geometric principles,the proposed method derives analytical solutions for the position and orientation of the moving platform.The algorithm systematically addresses the nonlinearity inherent in the kinematic equations of parallel mechanisms,providing explicit expressions for the coordinates of key moving attachment points.Furthermore,the methodology is extended to general triangular platform STPRs with non-coplanar fixed attachments.Numerical validation through virtual experiments confirms the accuracy of the solutions,demonstrating that the mechanism admits eight distinct configurations for a given set of limb lengths.The results align with established kinematic principles and offer a computationally efficient alternative to iterative analytical approaches,contributing to the advancement of precision control in parallel robotic systems.
基金the National Key Research and Development Program of China(2022YFB3403404)the Youth Innovation Promotion Association,CAS(2022213)the National Natural Science Foundation of China(62127901 and 62305334).
文摘Null compensation interferometry is the primary testing method for the manufacture of ultra-high-precision aspheric mirrors.The crosstalk fringes generated by stray light in interferometry can affect accuracy and potentially prevent the testing from proceeding normally.Position errors include the decenter error,tilt error,and distance error.During the testing process,position errors will impact the testing accuracy and the crosstalk fringes generated by stray light.To determine the specific impact of position errors,we use the concept of Hindle shell testing of a convex aspheric mirror,and propose the simulation method of crosstalk fringes in null compensation interferometry.We also propose evaluation indices of crosstalk fringes in interferometry and simulate the influence of position errors on the crosstalk fringes.This work aims to help improve the design of compensation interferometry schemes,enhance the feasibility of the design,reduce engineering risks,and improve efficiency.
