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Space non-cooperative target recognition is crucial for on-orbit servicing. Multi-satellite cooperation has great potential for broadening the observation scope and enhancing identification efficiency. However, there is currently a lack of research on recognition methods tailored for multi-satellite cooperative observation. In this paper, we propose a novel space non-cooperative target recognition method to identify satellites and debris in images from multi-satellite observations. Firstly, we design an image-stitching algorithm to generate space-wide-area images. Secondly, we propose a two-stage multi-target detection model, a lighter CNN model with distance merge threshold (LCNN-DMT). Specifically, in the first stage, we propose a novel foreground extraction model based on a minimum bounding rectangle with the threshold for distance merging (MBRT-D) to address redundant detection box extraction for satellite components. Then, in the second stage, we propose an improved SqueezeNet model by introducing separable convolution and attention mechanisms for target classification. Moreover, due to the absence of a public multi-target detection dataset containing satellites and debris, we construct two space datasets by introducing a randomized data augmentation strategy. Further experiments demonstrate that our method can achieve high-precision image stitching and superior recognition performance. Our LCNN-DMT model outperforms mainstream algorithms in target localization accuracy with only 0.928 M parameters and 0.464 GFLOPs, making it ideal for on-orbit deployment.

To improve the Solar Array Drive Assembly (SADA) system, a servo control method known as Linear Active Disturbance Rejection Control (LADRC) is introduced, utilizing a speed loop for a Permanent Magnet Synchronous Motor (PMSM). This method serves as an alternative to the conventional proportional–integral (PI) controller, which exhibits a limited stability margin. The use of the LADRC controller leads to decreased overshoot and enhances the system’s robustness against disturbances. First, the mathematical representation of the PMSM alongside the dynamic model of the solar wing is established. Following that, the application of the Lyapunov stability theory is employed to illustrate the stability of the drive system utilizing LADRC, thereby validating the stability of the SADA. Lastly, simulation experiments are performed using the MATLAB2021a/Simulink digital environment. The simulation results under various operational conditions indicate the significant improvement in stability compared to the PI controller, achieving the stability level of 9.603×10−5, demonstrates enhanced performance in terms of speed and resistance to disturbances.

Abstract The hydraulic turbine in turbine mode (TMHT) has significant advantages in residual energy recovery, but rapid optimization of its runner parameters has always been a challenge. To address this issue, the optimization algorithm ISMA‐BPNN is proposed based on the improved slime mold algorithm (ISMA) and back propagation neural network (BPNN). First, an efficiency characteristic neural network (ECNN) and a water head characteristic neural network (HCNN), which take the geometric parameters of the runner as input, and the efficiency and water head as outputs, respectively, are constructed by combining the orthogonal test‐based sample data, computational fluid dynamics (CFD), and BPNN. Then, the slime mold algorithm is improved and the optimal runner geometric parameters are obtained based on the ISMA, ECNN, and HCNN, to achieve rapid optimization of the TMHT runner. Finally, the CFD‐based numerical calculation accuracy is verified through real machine tests, and the feasibility of the ISMA‐BPNN‐based rapid optimization strategy for TMHT performance is further verified through CFD numerical simulation.

This paper addresses the problems of valve-turning operation in rescue environments where a wheeled mobile manipulator (WMM) is employed, including the possible occurrence of large internal forces. Rather than attempting to obtain the exact position of the valve, this paper presents a solution to two main problems in robotic valve-turning operations: the radial position deviation between the rotation axes of the tool and the valve handle, which may cause large radial forces, and the possible axial displacement of the valve handle as the valve turns, which may lead to large axial forces. For the former problem, we designed a compliant end-effector with a tolerance of approximately 3.5° (angle) and 9.7 mm (position), and provided a hybrid passive/active compliance method. For the latter problem, a passivity-based force tracking algorithm was employed. Combining the custom-built compliant end-effector and the passivity-based control method can significantly reduce both the radial and the axial forces. Additionally, for valves with different installation types and WMMs with different configurations, we analyzed the minimum required number of actuators for valve turning. Simulation and experimental results are presented to show the effectiveness of the proposed approach.

For the needs of manned landing, station construction, and material transfer in future lunar exploration missions, the paper proposes a landing–moving integrated gear (LMIG) for mobile lunar lander (MLL), establishes and optimizes the models of cushioning energy-absorbing and movement planning, respectively, and conducts the prototype tests. First, the design requirements of LMIG are given, and the system composition of LMIG and the configuration design of each subsystem are introduced. Second, the effective energy-absorbing model of the aluminum honeycomb is established and experimentally verified, a three-stage aluminum honeycomb buffer is designed and experimentally verified, and the buffer mechanism of LMIG is verified by simulations under various landing conditions. Furthermore, the kinematic and dynamic models of LMIG are established, the moving gait is designed by the center of gravity trajectory planning method, and the driving trajectory during the stepping process is optimized with the goal of minimal jerk of motion. Finally, a cushioning test prototype and a walking test scaled prototype of LMIG are developed, and single leg drop test and ground walking test are carried out. The results show that the established model of LMIG is reasonable, the designed buffer and gait of LMIG are effective, the developed prototypes of LMIG have good cushioning and movement performance, the LMIG’s maximum value of overload acceleration is 6.5g, and the moving speed is 108 m/h, which meets the design requirements.

Based on the variable gain extended state observer, a finite-time fault-tolerant control strategy is developed for the quadrotor unmanned aerial vehicle with actuator faults and external disturbances. Firstly, a novel variable gain extended state observer is designed to estimate the unknown external disturbances, which mitigates the initial peaking phenomenon existing in traditional extended state observer-based methods. Meanwhile, the neural networks are applied to accurately approximate unknown couplings online. Moreover, with the help of the projection operator technique, the unknown actuator faults are observed in real time. Combined with the backstepping framework, the finite-time robust fault-tolerant control scheme is constructed and the stability is strictly proved via Lyapunov’s theory. Finally, the validity of the developed control scheme is demonstrated through numerical simulations.

Background: Bufalin, the main active ingredient of the traditional Chinese medicine huachansu, is used in the clinical treatment of colorectal cancer and has multiple effects, including the inhibition of migratory invasion, reversal of multi-drug resistance, induction of apoptosis and differentiation, and inhibition of angiogenesis. Methods: We collected relevant articles on bufalin from 2003 to 2022 using the Web Science platform, and analysed the information using VOSviewer, CiteSpace, and Microsoft Excel to categorise and summarise the publications over the past 20 years. Results: We collected 371 papers, with a steady increase in the number of articles published globally. China has the highest number of published articles, whereas Japan has the highest number of citations. Currently, there is considerable enthusiasm for investigating the anti-tumour mechanism of bufalin and optimising drug delivery systems for its administration. Conclusion: For the first time, we present a comprehensive overview of papers published worldwide on bufalin over the past two decades and the progress of its application in tumour therapy. We summarised the key authors, institutions, and countries that have contributed to the field and the potential of bufalin for the treatment of cancer. This will help other researchers obtain an overview of progress in the field, enhance collaboration and knowledge sharing, and promote future research on bufalin.

The sample carried back by the Mars Ascent Vehicle (MAV) is a potential flagship mission of deep space exploration in recent years. A low-gravity simulation experiment is an effective method and a necessary stage for verifying the performance of the MAV launch dynamic in Earth’s gravity. In this paper, the uniqueness of low-gravity simulation is illustrated by the classical pulley balance method for the high dynamic process of a test model of the MAV. Its movement direction is the same as the compensation force, which leads to the relaxation of the sling and the failure of the compensation force in traditional cable suspension. Here, three cable suspension schemes including an improved pulley balancing scheme based on a coordinate transformation scheme and based on a dynamic pulley group scheme are proposed. For the actual launch condition of the MAV, the motion state of the ascent under the schemes and the real Mars launch are compared, which proves the feasibility of the schemes. Among them, the improved pulley balancing scheme has the best gravity compensation effect, and the error between the average value and the required value is the smallest, only 1%.

In this paper, the development of a high-power continuous wave (CW) fiber laser near 980 nm is reviewed. This review is focused primary on the power evolution resulting from the designation of Yb-doped fibers, which is important in the suppression of the amplified spontaneous emission (ASE) around 1030 nm. Current studies on the in-band ASE as the power limitation of the Yb-doped fiber lasers near 980 nm are also summarized in this review.

For the formation and obstacle avoidance challenges of UAVs (unmanned aerial vehicles) in complex scenarios, this paper proposes an improved collaborative strategy based on APF (artificial potential field). This strategy combines graph theory, the Leader–Follower method, and APF. Firstly, we used graph theory to design formation topology and dynamically adjust the distances between UAVs in real time. Secondly, we introduced APF to avoid obstacles in complicated environments. This algorithm innovatively integrates the Leader–Follower formation method. The design of this attractive field is replaced by the leader’s attraction to the followers, overcoming the problem of unreachable targets in APF. Meanwhile, the introduced Leader–Follower mode reduces information exchange within the swarm, realizing a more efficient “few controlling many” paradigm. Afterwards, we incorporated rotational force to assist the swarm in breaking free from local minima. Ultimately, the stability of the integrated formation strategy was demonstrated using Lyapunov functions. The feasibility and effectiveness of the proposed strategy were validated across multiple platforms.

Fiber laser has been developed to the point where the average power scaling can reach several kilowatts readily for oscillators and more for amplifiers. In the meanwhile, the thermal effects inside the fiber laser also become prominent. Temperature rise of the fiber core caused by thermal effects has a conspicuous impact on laser performance. In this paper, the spectral properties of superfluorescent fiber sources at low temperature have been studied experimentally and theoretically. We observe a significant flattening of the arc top of the spectra and a broadening to the short-wave direction as the gain fiber temperature decreases from 25 °C to −95 °C. The corresponding 10 dB bandwidth and 20 dB bandwidth increased by 7.216 and 4.004 nm, respectively. The 10 dB center position and the 20 dB center position of the spectrum also move 6.1 nm and 4.2 nm towards short-wave direction, respectively. The absorption and emission cross-sections at different temperatures, calculated based on Lorenz fitting theory, are used to simulate the experimental phenomena, and the results are consistent with the experiment. Additionally, the small signal gain coefficient at low temperature is calculated to help explain the observed phenomena in the experiment.

Single-stage high-power narrow-linewidth fiber laser has been investigated intensively recently because of its simple and robust configuration and great potential in spectral/coherent beam combination. In this work, a 6 kW narrow-linewidth fiber amplifier was experimentally achieved based on a fiber oscillator seed. By employing a few-mode ytterbium-doped fiber, the spectral broadening and SRS effects are both significantly mitigated. Combined with a wavelength-stabilized 981 nm pump source, the threshold of transverse mode instability is improved, then, a maximum output power of 6020 W at the central wavelength 1080 nm was achieved with 3-dB bandwidth of ∼0.37 nm and optical-to-optical efficiency of ∼85.6%. The mode instability and nonlinear effects were balanced well. The measured beam quality and the signal to Raman ratio were M2∼2.7 and ∼27 dB, respectively. This work shows the great potential of such amplification structure for the power scaling of high-power narrow-linewidth fiber lasers.

The hydraulic turbine in turbine mode (TMHT) with ultra-low specific speed is a new type of energy recovery device for recovering energy stored in the high-pressure fluid. In order to solve the problem of insufficient consideration of runner geometric parameter optimization, this paper proposes an optimization strategy (OT-CFD), which is based on the orthogonal test method and computational fluid dynamics (CFD), to optimize the performance of the TMHT runner. Firstly, the orthogonal test schemes are established with 5 levels of runner inlet diameter, outlet diameter, inlet height, blade inlet angle, and blade number. Then 25 three-dimensional models of two-stage TMHT containing flow passage components such as Francis runner are built. Further, the internal flow characteristics and energy characteristics of TMHT are calculated and then verified by the real machine test. By comparing the numerical simulation results, the design schemes of runner geometry parameters corresponding to the highest head (H) and the highest efficiency (η) are determined, respectively. On this basis, the optimization effect of runner geometry parameters is analyzed by numerical simulation based on CFD. In conclusion, the inlet angle is the most important factor affecting the efficiency, and the runner inlet diameter is the most important factor affecting the water head. Compared with the comparison scheme, the optimal η scheme has a more stable flow pattern, which provides an efficiency increase of 10.9%, a water head increase of 26.75 m, and a power increase of 646.32kW, greatly reduces the energy loss in the process of residual pressure recovery; the optimal H scheme has an efficiency increase of 2.61%, but more stable and regular flow pattern. More importantly, the optimal water head scheme, which has a water head increase of 185.53 m and a power increase of 1518.3kW, greatly increases the capacity of recovering the water head.

In this paper, a fs-laser phase mask inscription system based on a galvanometer scanning strategy is designed and set up for the fabrication of large-core fiber Bragg gratings (FBGs). Based on this setup, a homogeneous cross-sectional refractive index modulation can be achieved in the core of a large-mode-area fiber, and a pair of FBGs are fabricated in fibers with a core diameter of 30 µm. To investigate the performance of the fabricated FBGs, a high power all-fiber oscillator is built using a pure backward pumping structure. The FBGs work well, and the maximum output power of 7920 W is achieved with an optical–optical conversion efficiency of 77.3%. To the best of our knowledge, this is the highest power of all-fiber oscillators based on fs-written FBGs. This work provides a flexible, stable, and economic scanning strategy for large-core FBG inscription and exhibits excellent performance for high power fiber lasers.

Abstract Compared with the traditional reverse multistage pump as hydraulic turbine, hydraulic turbine in turbine mode (T‐type turbine) with low specific speed has higher single‐stage energy head, which can effectively reduce stages and increase the stability when it is used to recycle high residual pressure liquid. Blade number of runner is an important design parameter, which has great influence on the performance of T‐type hydraulic turbine and need to be further studied. Therefore, two‐stage T‐type turbine models with different blade numbers are established through numerical simulation. Then, the accuracy of numerical simulation is verified by test. Finally, the performance and pressure fluctuating characteristics of turbine with different blade numbers are obtained. The results show that: (a) Taking same blade numbers in both stages (traditional design method), the turbine efficiency can be higher with the blade number of primary runner and secondary runner are 14, but resulting the superposition of pulsation in secondary runner; (b) Taking different blade numbers in both stages, respectively, the superposition of pulsation can be effectively avoided, which also leads to the increase in efficiency, and up to 81.169%; (c) The method of using different number of blades in different stages can replace the traditional design method and effectively improve the hydraulic performance of T‐type hydraulic turbine.

Speed governing control is significant in ensuring the stable operation of pumped storage units. In this study, a state-space equation mathematical model of the pumped storage governing system considering the complex hydraulic pipeline structure of the pumped storage plant is proposed to describe the system’s dynamic behaviors under small disturbance conditions. Considering the frequent operating condition transitions and the complicated nonlinear dynamic characteristics of the pumped storage units, the fractional-order PID (FOPID) scheme that possesses a higher degree of control freedom than the traditional PID scheme is discussed in detail. To optimize the control parameters of the unit governor, an improved gravitational search algorithm (IGSA) that combines the basic searching mechanisms of the gravitational search algorithm and chaotic search, elastic sphere boundary treatment, and elite guidance strategy is developed. Comparative studies have been carried out under frequency and load disturbance conditions. Simulation results indicate that the control performance of FOPID is better than that of PID under diverse operating conditions and the proposed IGSA has satisfactory parameter optimization capability.

Distributed time-varying formation technology for multi-agent systems is recently become a research hotspot in formation control field. However, the formation reconfiguration control technology for agents that randomly appeared to fail during maneuvers is rarely studied. In this paper, the topological relations between intelligence are designed by graph theory to simplify the cooperative interaction between multi-agent systems. Moreover, this paper constructs the time-varying configuration of the target formation based on the rigidity graph theory and leader–follower strategy. Drawing on the establishment of the expert experience database in a collaborative process, we innovatively propose the establishment of a graphic library to help the multi-agent system quickly form an affine transformation as soon as it is disabled. Secondly, the improved Hungarian algorithm is adopted to allocate the target point when the first failure occurs. This algorithm incorporates a gradient weighting factor from the auction algorithm to improve the speed of system reconfiguration with minimum path cost. On this basis, a distributed multi-agent control law based on consistency theory is established, and the system’s stability can be guaranteed via Lyapunov functions. Finally, the simulation results demonstrate the feasibility and effectiveness of the proposed formation reconfiguration control algorithm in a collaborative environment.

The hydraulic turbine in turbine mode (HTTM) with an ultra-low specific speed (HTTM-ULSS) has the advantages of a simplified structure, high efficiency, and good stability and has great application value in the industry. However, the influence of the runner inlet diameter (D1) on the performance of HTTM-ULSS has not yet been fully studied. Therefore, the three-dimensional models of Francis runners were established in the ultra-low specific speed range by examining D1 = 0.49 m, 0.5 m, and 0.51 m, and the two-stage hydraulic turbine models were constructed with flow passage components. Then, internal flow and energy characteristics were calculated using Fluent 16.0 software. Further, the influence of D1 on HTTM performance was studied by comparing numerical simulation results. The results show that the water head of the HTTM-ULSS can reach 540.87 m when D1 = 0.51 m, showing its powerful ability to recover the pressure energy in high-pressure water. Moreover, the head and efficiency are closely related to D1; when D1 increases, the circulation at the runner inlet increases, resulting in an enhancement in the ability to recover the water head and decreases in efficiency and in the operating range of the high-efficiency zone; with D1 increasing, the flow pattern inside the runner becomes better, but the high-pressure area of the blade increases. When selecting the D1, attention should not only be paid to the ability to recover the water head but also to the pressure of the runner blades and the internal water flow pattern.

In this paper, a novel 3D (three-dimensional) soft-landing dynamic theoretical model of a legged lander is developed in detail as well as its numerical solution process. The six degrees of freedom motion (6-DOF) of the base model of the lander with mass center offset setting is considered in the model as well as the spatial motion (3-DOF) of each landing gear. The characteristics of the buffering force, the footpad–ground contact, and the inter-structure friction are also taken into account during the motion of each landing gear. The direct constraint violation correction is used to control the constraint stabilization of the nonlinear dynamic equation. Comparative studies between the results from the proposed model and the simulated model (built in MSC Adams) under four classical load cases show the validity of the model. Additionally, the influences of different types of contact force models, friction force models, and a friction correction model used in the soft-landing dynamic model are further investigated as a step toward understanding the soft-landing dynamic performance and the feasibility of the dynamic model method of a legged lander. The results indicate that a precise lateral force model of the footpad–ground contact is necessary to obtain the soft-landing performance of one lander during soft landing.

The effect of seed power on the inter-modal four-wave mixing (IM-FWM) effect in a distributed side-pumped fiber amplifier is investigated for the first time, to the best of our knowledge. By using a seed source smaller than 70 W, the effect of seed power on the IM-FWM is studied experimentally. Surprisingly, it is found that the IM-FWM effect becomes stronger with the weaker seed. To analyze the physics behind this result, a numerical model is introduced, and the numerical results are in good agreement with the experimental observations. It is revealed that the IM-FWM enhancement is induced by the gain competition between the signal light and the anti-Stokes light of the IM-FWM. It is also found that there is an optimized seed power for suppressing the IM-FWM effect. The experimental and numerical results which are presented in this work can provide significant guidance for understanding the IM-FWM in fiber lasers and amplifiers.

Abstract Nonlinear modeling of the hydroturbine is one of the current research hot spots. The existing nonlinear hydroturbine model lacks “memory capability,” which means that the output of the model is not related to the historical input and output; that is, the model is a description of the static characteristics of the hydroturbine. To address this issue, based on actual operation data, this paper proposes long short‐term memory artificial neural network (LSTMNN) with output feedback to realize real‐time dynamic modeling of hydroturbine. Firstly, the torque characteristic sample data are calculated from the actual operation data, and the operation data of the hydropower unit are converted into the discharge characteristic sample data through hydroturbine test data. Then, by training LSTM neural networks with different feedback orders, the optimal order is got, and at the same time, the superiority of replacing time lag with the output feedback is verified. On this basis, a feedback‐based hydroturbine LSTMNN model is obtained. Finally, the proposed modeling method is compared with standard back‐propagation neural network with output feedback (F‐BPNN), through which the effectiveness and applicability are verified. The results show that: (a) By introducing output feedback, the accuracy of nonlinear hydroturbine model can be increased and the proposed modeling method is better than F‐BPNN; (b) the hydroturbine LSTMNN model can not only describe the static characteristics, but also reflect the real‐time dynamic characteristics; (c) taking the actual operation data of hydroturbine as the sample data source, the proposed modeling method can replace the traditional modeling method and effectively improve the numerical simulation accuracy.

Abstract Purpose Growing evidence has demonstrated an indispensable role for N6‐methyladenosine (m6A) in human diseases, but the copy number variations (CNVs) of m6A regulatory genes in bladder cancer (BLCA) remains largely unknown. Methods We investigated the CNVs on all known m6A regulatory genes using the Cancer Genome Atlas (TCGA) database. The association between CNV events and clinicopathological as well as molecular characteristics of BLCA patients were explored. Gene set enrichment analysis (GSEA) was implemented to reveal relative cellular processes. Association between m6A regulatory genes and immune infiltrates was analyzed by The Tumor Immune Estimation Resource (TIMER) database. Results CNV events of m6A regulatory genes were frequently observed in BLCA. CNVs of METTL3, METTL14, and METTL16 correlated with molecular characteristics of BLCA patients including TP53 mutation. CNVs of METTL3 associated with the overall survival (OS) of BLCA patients. METTL3 was also associated with several cancer‐related cellular processes, including mitotic spindle assembly, G2/M checkpoint, and E2F targets signaling pathway. Besides, the CNVs of m6A regulatory genes were correlated with specific kinds of immune infiltrates. Conclusions There are significant correlations between m6A regulatory genes with CNVs and clinicopathological characteristics. METTL3 with CNVs were associated with the immune infiltrates and performed as a prognostic marker in BLCA.

Bidirectional output fiber laser oscillators can realize two high-power laser outputs employing only a single-laser resonant cavity and hold the advantages of being low cost and of compact size. However, like other fiber lasers, their power improvement is limited by transverse mode instability (TMI). To achieve higher power output, in this paper, the characteristics and corresponding suppression method of the TMI in bidirectional output fiber laser oscillators were investigated for the first time. Firstly, the TMI threshold was obtained when the fiber laser oscillator was pumped by 976 nm LDs and 981 nm LDs, separately, and the difference between the two pumping conditions was researched in detail. After that, a comparison study between the bidirectional and unidirectional output fiber laser oscillators pumped by 981 nm LDs was carried out. In the experiment, the effect of pump distribution on the TMI threshold was also considered. The results show that the TMI threshold of the bidirectional-output laser pumped by 981 nm LDs is much higher than that pump by 976 nm LDs, which means that the effective TMI suppression methods in the unidirectional output laser are also applicable in the bidirectional output laser. In addition, it is found that the TMI threshold of a bidirectional output fiber laser is much lower than that of a unidirectional output fiber laser.

During task execution, the autonomous robots would likely pass through many narrow corridors along with mobile obstacles in dynamically complex environments. In this case, the off-line path planning algorithm is rather difficult to be directly implemented to acquire the available path in real-time. Hence, this article proposes a probabilistic roadmap algorithm based on the obstacle potential field sampling strategy to tackle the online path planning, called Obstacle Potential field-Probabilistic Roadmap Method (OP-PRM). The obstacle potential field is introduced to determine the obstacle area so as to construct the potential linked roadmap. Then the specific range around the obstacle boundary is justified as the target sampling area. Based on this obstacle localization, the effectiveness of the sampling points falling into the narrow corridors can be increased greatly for feasible roadmap construction. Furthermore, an incremental heuristic D* Lite algorithm is applied to search the shortest paths between the starting point and the target point on the roadmap. Simulation experiments demonstrate that the OP-PRM path planning algorithm can enable robots to search the optimal path fast from the starting point to the destination and effectively cross narrow corridors in complex dynamic environments.

To solve integrals in the absolute nodal coordinate method and address the difficulty in applying it to an arbitrary-section beam, this paper focuses on two methods involving single integrals:the invariant matrix method and the Gerstmayr method, with cross-section characteristics by applying the interpolation of a discrete function. Such single integrals demonstrate that the nodal coordinate method can be applied to an arbitrary-section beam. The Euler–Bernoulli beam used in engineering structures is characterised by a symmetrical cross-section, small section size, zero odd integrals and negligible high-order even integrals, which simplifies the single integrals of the two methods. Finally, the Gaussian integration is adopted to improve the solving efficiency of elastic force and force Jacobian.

In many traditional soft-landing missions, researchers design the lander and the rover as two separate individuals, which has its limitations. At present, research on landers mainly focuses on the performance analysis of those who cannot move, and the motion of legged mobile lander has not yet been studied. In this paper, a novel Mobile Landing Mechanism (MLM) is proposed. Firstly, the monte-Carlo method is used to solve the workspace, and the motion feasibility of the mechanism is verified. Secondly, combining with the constraints of velocity, acceleration and secondary acceleration of each driving joint of the MLM, the trajectory of its joint space is planned by using cubic spline curve. And based on the weighted coefficient method, an optimal time-jerk pedestal trajectory planning model is established. Finally, by comparing the genetic algorithm (GA) with the adaptive genetic algorithm (AGA), an optimization algorithm is proposed to solve the joint trajectory optimization problem of the MLM, which can obtain better trajectory under constraints. Simulation shows that the motion performance of the mechanism is continuous and stable, which proves the rationality and effectiveness of the foot trajectory planning method.

Abstract Background The peak inspiratory pressure (PIP) is crucial in mechanical ventilation with supraglottic airway device (SAD). Pressure-controlled ventilation volume-guaranteed (PCV-VG), delivering a preset tidal volume with the lowest required airway pressure, is being increasingly used during general anesthesia. In this study, we compared respiratory mechanics and circulatory parameters between volume-controlled ventilation (VCV) and PCV-VG in elderly patients undergoing laparoscopic surgery using the laryngeal mask airway supreme (LMA). Methods Eighty participants scheduled for laparoscopic surgery were enrolled in this prospective, randomized clinical trial. The participants were randomly assigned to receive VCV or PCV-VG. PIP, dynamic compliance (Cdyn) and mean inspiratory pressure (Pmean) were recorded at 5 min after induction of anesthesia (T1), 5 min after pneumoperitoneum(T2), 30 and 60 min after pneumoperitoneum (T3 and T4). Data including other respiratory variables, hemodynamic variables, and arterial blood gases were also collected. The difference in PIP between VCV and PCV-VG was assessed as the primary outcome. Results PIP was significantly lower at T2, T3, and T4 in both groups compared with T1 (all P

This paper investigates a rapid modeling method and robust analysis of hypersonic vehicles using multidisciplinary integrated techniques. First, the geometrical configuration is described using parametric methods based on the class–shape technique. Aerodynamic forces and moments are estimated for the specific configuration using engineering methods. Moreover, the nonlinear model is simplified by the polynomial fitting expressions, and the linear variable parameter model is obtained for the tracking control design and dynamic characteristic analysis with the aid of the sensitivity analysis and gap metric methods. A velocity-driven trajectory design method is deduced for hypersonic ascent, and the tracking control law is developed to realize the flight process from the initial point to the cruise point. Furthermore, a robust analysis process based on gap margin is proposed for climb trajectory tracking. Simulation results are provided to verify the feasibility of the proposed modeling method and show that the flight control of a hypersonic vehicle is more sensitive to altitude variation.

To study the influence of rotational speed on the performance of hydraulic turbine in turbine mode (T-type turbine), the performance of turbine at different rotational speed was predicted through theoretical analysis, based on the Navier-Stokes equation and standard k-ε turbulence model, numerical simulation was used to study the performance of turbine at different rotational speed. The head loss, pressure distribution, turbulence kinetic energy, and unsteady pressure pulsation were also clarified. The results shows that with the increase of rotational speed, the high efficiency area of turbine gradually becomes wider, and there is little difference of the maximum efficiency at different rotational speeds. Under the optimal working condition, the pressure difference between inlet and outlet increase gradually, and turbulent kinetic energy of runner also increase. The inlet circulation increases with the increase of rotational speed, the outlet circulation increases with the increase of speed under small flow conditions, and decreases with the increase of rotational speed under large flow conditions. The study of pressure pulsation shows that the increase of rotating speed can effectively reduce the pressure pulsation in the runner. When the rotating speed is 2100 r/min, the amplitude of pressure pulsation at P7 is 10.39% lower than that at 900 r/min. Considering the hydraulic characteristics and the pulsation characteristics, it is recommended that the hydraulic turbine operates at or above the rated speed as far as possible.

The inter-modal four-wave mixing (IM-FWM) and transversal mode instabilities (TMI) are experimentally studied in high-power distributed side-pumped fiber amplifiers. To the best of our knowledge, we have made the first demonstration of TMI and IM-FWM which can be suppressed simultaneously by increasing the bending diameter. Besides, the experimental results show that the counter-pumping scheme is beneficial to suppress both of IM-FWM and TMI, when comparing with co-pumping scheme. Furthermore, these two effects cannot be observed when the M2 factor is lower than 1.3, which can give a condition to estimate whether these two effects should be considered or not. The pertinent study can provide some guidance for understanding TMI and IM-FWM in the high-power fiber laser and amplifier.

In the field of nondestructive testing (NDT) of wire rope, magnetic flux leakage (MFL) detection is the most widely used method. The traditional single-dimensional MFL detection system has the disadvantages of large volume, heavy weight, low sensitivity and low recognition rate. In order to overcome these problems, this paper designed the three-dimensional MFL acquisition system based on unsaturated magnetic excitation using the tunnel magnetoresistive (TMR) elements and proposed the three-dimensional MFL detection method. We mapped the three-dimensional MFL signals after noise reduction to Red-Green-Blue (RGB) space for color imaging. Then, the localization and segmentation algorithms were used to crop color images of broken wire defects. Finally, the color moment eigenvalues of color images of six types broken wire defects were extracted as the input of the back propagation (BP) neural network to quantitatively identify the broken wires. From the experimental results of the quantitative identification of broken wire defects, it can be seen that it is feasible to use the color images of the three-dimensional MFL signals to quantitatively identify the broken wire defects. Moreover, the three-dimensional MFL color imaging can effectively improve the recognition rate of broken wires.

During the design and manufacturing process of the truss antenna, the surface accuracy of the truss antenna is inherently affected by tolerance. An appropriate optimal design of the truss antenna structure is important to improve surface accuracy. In order to receive the optimal design of the truss structure, this paper adopts the multiobjective optimization algorithm based on an approximate model to optimize the tolerance model with random error. Firstly, considering the influence of the processing and assembly errors of the members on the surface accuracy of the structure, the equilibrium state equation of the truss is established by the principle of minimum potential energy. Then, the relationship between the tolerance and the surface accuracy is obtained by the Monte Carlo method. For improving the computing efficiency of the Monte Carlo method, an approximate model of the truss antenna unit is established, where the rod length tolerance is set as the design variable, and the truss surface accuracy and processing cost are set as the objective functions. Finally, tolerance optimization is carried out by using the multiobjective genetic algorithm. The results indicate that the Pareto solution is obtained with an error less than 10%. Moreover, a set of solutions of the tolerance are obtained which can meet different antenna design requirements. And the results show that the influence of the web rod is significantly greater than that of the bottom rod on the surface accuracy of the structure.

In this paper, a 500-W-level all-fiber amplifier operating near 980 nm is demonstrated firstly, to the best of our knowledge. The amplifier is fabricated with a 105/250-μm core/cladding-diameter double-cladding Yb-doped fiber (DCYF). By optimizing the length of DCYF, the record 556-W output power and 50.5% slope efficiency are obtained with a 1.85-W seed light, and about 30.9 dB peak-to-peak suppression of 1030-nm amplified spontaneous emission (ASE) is realized. Furthermore, the strong in-band ASE is also observed in experiment, which limits the power up-scaling of the fiber amplifier. By analyzing the origin of the in-band ASE, it is revealed that optimizing the seed light should be beneficial to the suppression of in-band ASE. Besides, the beam quality is measured at the maximum output power and the M2 factor is about 23.6. The experimental study should be able to provide significant guidance for understanding and designing the high-power three-level fiber lasers and amplifiers.

Fiber lasers around 2 µm band have attractive applications, such as coherent detecting, material processing, pump source for mid-IR lasers based on nonlinear frequency shift, etc. Fiber gas Raman lasers (FGRLs) based on the stimulated Raman scattering of the gas molecules filled in the hollow-core fibers (HCFs) have been proved an efficient method to enrich the wavelengths of fiber lasers. In this paper, we demonstrated a deuterium-filled fiber gas Raman laser working at 2147 nm. The pump laser is directly coupled into the HCF through the fusion splice between the HCF and the solid-core fiber. By adjusting the pressure, fiber length as well as the repetition frequency of the 1971 nm pump laser, a maximum average Raman power of ~2.57 W was obtained, with corresponding efficiency of ~40%. This work provides a simple and compact configuration for 2.1 µm fiber lasers, which is significant for their application.

In this paper, the fabrication method of a pump/signal (6 + 1) × 1 combiner based on a large-core (48 μm) multimode signal fiber is introduced. Since the signal fiber is not tapered in the production, and an effective feedback alignment method is adopted during the splice process, the degradation ratio of the M2 value of the signal light is only about 5% after passing through the beam combiner. In addition, with the help of a home-made beam combiner, a counter-directional tandem-pumping amplifier is built. The maximum output power of the amplifier is 15.31 kW with the slope efficiency of 83.2%. The temperature rise coefficient of the home-made combiner is 3.2 °C/kW and the backward isolation degree is more than 36 dB from each pump pigtail. Both test results prove the outstanding potential of the pump-signal combiner in high-power laser applications.

Objective: The protective effects of exercise against glucose dysmetabolism have been generally reported. However, the mechanism by which exercise improves glucose homeostasis remains poorly understood. The FGF21–adiponectin axis participates in the regulation of glucose metabolism. Elevated levels of FGF21 and decreased levels of adiponectin in obesity indicate FGF21–adiponectin axis dysfunction. Hence, we investigated whether exercise could improve the FGF21–adiponectin axis impairment and ameliorate disturbed glucose metabolism in diet-induced obese mice. Methods: Eight-week-old C57BL/6J mice were randomly assigned to three groups: low-fat diet control group, high-fat diet group and high-fat diet plus exercise group. Glucose metabolic parameters, the ability of FGF21 to induce adiponectin, FGF21 receptors and co-receptor levels and adipose tissue inflammation were evaluated after 12 weeks of intervention. Results: Exercise training led to reduced levels of fasting blood glucose and insulin, improved glucose tolerance and better insulin sensitivity in high-fat diet-induced obese mice. Although serum FGF21 levels were not significantly changed, both total and high-molecular-weight adiponectin concentrations were markedly enhanced by exercise. Importantly, exercise protected against high-fat diet-induced impaired ability of FGF21 to stimulate adiponectin secretion. FGF21 co-receptor, β-klotho, as well as receptors, FGFR1 and FGFR2, were upregulated by exercise. We also found that exercise inhibited adipose tissue inflammation, which may contribute to the improvement in the FGF21–adiponectin axis impairment. Conclusions: Our data indicate exercise protects against high-fat diet-induced FGF21–adiponectin axis impairment, and may thereby exert beneficial effects on glucose metabolism.

As a non-metallic organic semiconductor photocatalyst, graphitic carbon nitride (g–C3N4, CN) has become a research hotspot due to its excellent performance in organic degradation, CO2 reduction and water splitting to produce hydrogen. However, the high recombination rate of electron-hole pairs, low specific surface area and weak light absorption of bulk CN synthesized by the traditional one-step thermal polymerization method seriously restrict its photocatalytic performance and practical application. To enhance the photocatalytic performance of CN, doping and surface modification strategies are usually employed to tune the band gap of carbon nitride and improve the separation of carriers. In this paper, the research progress of different methods to modify CN in recent years is introduced, and the mechanisms of improving the photocatalytic performance are mainly analyzed. Typical modification methods are mainly divided into metal doping, non-metal doping, co-doping and surface-functionalized modification. Some characterization methods that can analyze the doping state and surface modification are also discussed as examples. Finally, the difficulties that need to be addressed through modified CN photocatalysts and the directions for future research are pointed out.

In this paper, the scalability of slope efficiency of a Yb-doped fiber amplifier operating near 980 nm is studied with the core-pumping scheme. By means of numerical prediction, it is found that the theoretical limit of slope efficiency should be about 92.2%. Then, the experiment study is carried out. An 85.3% slope efficiency of emission around 980 nm is achieved with the seed light around 976.5 nm, and the strong in-band amplified spontaneous emission (ASE) is supposed to be a factor limiting the upscaling of slope efficiency. In order to suppress the in-band ASE, the double-wavelength fiber oscillator near 980 nm is fabricated and used as the seed source, with which the slope efficiency is elevated to 90.7%. Such slope efficiency is very close to the theoretical limit and sets a new record of slope efficiency for the Yb-doped fiber amplifier operating near 980 nm, to the best of our knowledge. It is also revealed that the suppression of in-band ASE should be of great importance to elevate the slope efficiency of a Yb-doped fiber amplifier operating near 980 nm.

Deterioration trend prediction of hydropower units helps to detect abnormal conditions of hydropower units and can prevent early failures. The reliability and accuracy of the prediction results are crucial to ensure the safe operation of the units and promote the stable operation of the power system. In this paper, the long short-term neural network (LSTM) is introduced, a comprehensive deterioration index (CDI) trend prediction model based on the time–frequency domain is proposed, and the prediction accuracy of the situation trend of hydropower units is improved. Firstly, the time–domain health model (THM) is constructed with back-propagation neural network (BPNN) and condition parameters of active power, guide vane opening and blade opening and the time–domain indicators. Subsequently, a frequency-domain health model (FHM) is established based on ensemble empirical mode decomposition (EEMD), approximate entropy (ApEn), and k-means clustering algorithm. Later, the time–domain degradation index (TDI) is developed according to THM, the frequency-domain degradation index (FDI) is constructed according to FHM, and the CDI is calculated as a weighted sum by TDI and FDI. Finally, the prediction model of LSTM is proposed based on the CDI to achieve degradation trend prediction. In order to validate the effectiveness of the CDI and the accuracy of the prediction model, the vibration waveform dataset of a hydropower plant in China is taken as a case study and compared with four different prediction models. The results demonstrate that the proposed model outperforms other comparison models in terms of predicting accuracy and stability.

In this paper, the in-band amplified spontaneous emission (ASE) in the Yb-doped continuous-wave (CW) fiber amplifier operating near 980 nm is experimentally studied for the first time, to the best of our knowledge. A core-pumped single-mode Yb-doped fiber amplifier is fabricated and the effects of pump power, seed power, and active fiber length on the in-band ASE are investigated in the experiment. It is found that a strong in-band ASE around 980 nm can be observed even with no obvious ASE around 1030 nm present. It is also found that with the increment of pump power, the in-band ASE can be enhanced faster than the signal light. By studying the effects of seed power and active fiber length, it is found that, although increasing the seed power and shortening the active fiber can both suppress the in-band ASE, the latter method is less effective than the former one. The theoretical study is also carried out in order to understand the difference between the in-band ASE and 1030-nm ASE. The experimental observations are also discussed qualitatively with the theoretical results. We believe that the pertinent results and discussions can provide significant guidance for understanding the in-band ASE in the Yb-doped fiber amplifier operating near 980 nm.

In this study, a hybrid iteration force density method (HIFDM) was proposed to ensure both tension uniformity and accuracy of an antenna mesh reflector. Based on a genetic algorithm (GA), the boundary cable tension of the antenna reflector net was optimized, which further improved the precision of the antenna mesh reflector. The static model of the large deployable structure was established using the finite element method (FEM), and thus, an iterative strategy for form-finding of the antenna reflector net was proposed, which considered the influence of the elastic deformation of the deployable structure. The results showed that the HIFDM was effective for the form-finding of the antenna mesh reflector, and the shape precision was improved by further optimization using the GA. Finally, it was noted that the elastic deformation of the deployable structure will reduce the uniformity of cable tension and affect the precision of antenna reflectors. Due to the large-scale and soft stiffness, the large deployable structure had a high sensitivity to cable pretension, and it is important to design a reasonable cable pretension to ensure the accurate shape of antenna mesh reflectors.

Background and Purpose: The lifetime prevalence of benign paroxysmal positional vertigo (BPPV) is high, especially in the elderly. Patients with BPPV are more susceptible to ischemic stroke, dementia, and fractures, severely reducing quality of life of patients. Many studies have analyzed risk factors for the occurrence of BPPV. However, the results of these studies are not identical. We performed this meta-analysis to determine potential risk factors associated with the occurrence of BPPV.Methods: PubMed, EMBASE, and the Cochrane Library (January 2000 through March 2020) were systematically searched for eligible studies analyzing risk factors for the occurrence of BPPV. Reference lists of eligible studies were also reviewed. We selected observational studies in English with a control group and sufficient data. Pooled odds ratios (ORs) or the mean differences (MDs) and 95% confidence intervals (CIs) were calculated to measure the impacts of all potential risk factors. Heterogeneity among studies was evaluated using the Q-test and I2 statistics. We used the random-effect model or the fixed-effect model according to the heterogeneity among the included studies.Results: We eventually included 19 studies published between 2006 and 2019, including 2,618 patients with BPPV and 11,668 participants without BPPV in total. In this meta-analysis, the occurrence of BPPV was significantly associated with female gender (OR = 1.18; 95% CI, 1.05–1.32; P = 0.004), serum vitamin D level (MD = −2.12; 95% CI, −3.85 to −0.38; P = 0.02), osteoporosis (OR = 2.49; 95% CI, 1.39–4.46; P = 0.002), migraine (OR = 4.40; 95% CI, 2.67–7.25; P < 0.00001), head trauma (OR = 3.42; 95% CI, 1.21–9.70; P = 0.02), and total cholesterol level (MD = 0.32; 95% CI, 0.02–0.62; P = 0.03).Conclusion: Female gender, vitamin D deficiency, osteoporosis, migraine, head trauma, and high TC level were risk factors for the occurrence of BPPV. However, the effects of other risk factors on BPPV occurrence need further investigations.

We experimentally demonstrate a monolithic single polarization nonlinear chirped pulse amplification (CPA) system producing high-average-power femtosecond pulses operating at 1.06 μm. Thanks to the fiber-based components and standard fiber splicing techniques, the system is nearly fully fiberized, except for the bulk grating pulse compressor. The main fiber amplifier delivers chirped picosecond pulses with average power of 193 W, repetition rate of 80 MHz, and duration of 209 ps. The pulse compressor is designed using high line density transmission gratings to keep small grating separation for the consideration of compactness and simplicity. After pulse compression, femtosecond pulses with average power of 119 W, duration of 352 fs, and peak power of 4.2 MW are obtained. The compression efficiency is 61.5%, limited by the diffraction efficiency of transmission gratings. Even so, to our knowledge, this is the highest average power ever reported in fiber CPA systems with a fiber-based stretcher. The mismatched third-order dispersion between fiber stretcher and bulk optical grating compressor is successfully compensated via optimization of the total nonlinear phase shift in the fiber amplifier chain.

Reusable launch vehicles (RLVs) are a solution for effective and economic transportation in future aerospace exploration. However, RLVs are limited to being used under simple landing conditions (small landing velocity and angle) due to their poor adaptability and the high rocket acceleration of current landing systems. In this paper, an adaptive RLV landing system with semi-active control is proposed. The proposed landing system can adjust the damping forces of primary strut dampers through semi-actively controlled currents in accordance with practical landing conditions. A landing dynamic model of the proposed landing system is built. According to the dynamic model, an light and effective RLV landing system is parametrically designed based on the response surface methodology. Dynamic simulations validate the proposed landing system under landing conditions including the highest rocket acceleration and the greatest damper compressions. The simulation results show that the proposed landing system with semi-active control has better landing performance than current landing systems that use passive liquid or liquid–honeycomb dampers. Additionally, the flexibility and friction of the structure are discussed in the simulations. Compared to rigid models, flexible models decrease rocket acceleration by 51% and 54% at the touch down moments under these two landing conditions, respectively. The friction increases rocket acceleration by less than 1%. However, both flexibility and friction have little influence on the distance between the rocket and ground, or the compression strokes of the dampers.

To improve the soft-landing crash performance of the movable lander (ML), this study presents an investigation of a newly designed gradual energy-absorbing structure subjected to impact loads using an ML for theoretical calculation and numerical simulations. In this work, we present a novel computational approach to optimizing the energy absorption (EA) of the ML. Our framework takes as inputting the geometrical parameter (GP) as well as EA. The finite element model of the HB1, HB2, and HB3 was established and effectively verified using numerical simulation and experimental data. The relationship between the GP of the buffer material and the EA was obtained through static experiment and impact experiment, and the cushioning performance of the lander was optimized according to the ML load mass, contact speed, and EA function. According to the optimization results, we chose an outer diameter of 240 mm, an inner diameter of 50 mm, heights of HB1 = 140 mm, HB2 = 110 mm, and HB3 = 225 as the collocation, and completed the numerical simulation of three different cases. By comparing the results of theoretical calculation and numerical simulation experiments, it can be found that the overload response rates of the main body in 4 type landing, 2-2 type landing, and 1-2-1 type landing are 4.72 G, 2.61 G, and 2.33 G, respectively. It also laid the foundation for the theoretical and methodological research of the ML and manned lander in the future.

Planning path rapidly and optimally is one of the key technologies for industrial manipulators. A novel method based on Memory-Goal-Biasing–Rapidly-exploring Random Tree is proposed to solve high-dimensional manipulation planning more rapidly and optimally. The tree extension of Memory-Goal-Biasing–Rapidly-exploring Random Tree can be divided into random extension and goal extension. In the goal extension, the nodes extended to the goal are recorded in a memory, and then the node closest to the goal is selected in the search tree excepting the nodes in the memory for overcoming the local minimum. In order to check collisions efficiently, the manipulator is simplified into several key points, and the obstacle area is appropriately enlarged for safety. Taking the redundant manipulator of Baxter robot as an example, the proposed algorithm is verified through MoveIt! software. The results show that Memory-Goal-Biasing–Rapidly-exploring Random Tree only takes a few seconds for the path planning of the redundant manipulator in some complex environments, and within an acceptable time, its optimization performance is better than that of traditional optimal method in terms of the obtained path costs and the corresponding standard deviation.

Since human hands have complex anatomical structure and are hard to be duplicated, lots of researches have been done to simplify it by gesture analysis, functional workspace evaluation and many other approaches. In this article, a novel light-duty four-finger hand driven by tendons is presented. The design is based on principal components analysis theory in order to reduce the minor degrees of freedom and lower the mechanism complexity. Meanwhile, optimization of the structure parameters is carried out with respect to the analyses of grasp ability and the single finger’s dexterity. A few simple and explicit indices are defined to evaluate the hand properties. In addition, this article also discusses the tendon routing method to realize the accuracy control of the tendon-driven hand’s joints. The approach presented in this article can be easily implemented on other mechanical hand platforms and assist the grasp planning in further works.

In this paper, an impedance control algorithm based on velocity for capturing two low impact docking mechanisms (LIDMs) is presented. The main idea of this algorithm is to track desired forces when the position errors of two LIDMs are random by designing the relationship between the velocity and contact forces measured by a load sensing ring to achieve low impact docking. In this paper, the governing equation of an impedance controller between the deviation of forces and velocity is derived, and simulations are designed to verify how impedance parameters affect the control characteristics. The performance of the presented control algorithm is validated by using the MATLAB and ADAMS software for capturing simulations. The results of capturing simulations demonstrate that the impedance control algorithm can respond fast and has excellent robustness when the environmental errors are random, and the contact forces and torques satisfy the low impact requirements.

An adaptive impedance control algorithm for tendon-driven dexterous hands is presented. The main idea of this algorithm is to compensate the output of the classical impedance control by an offset that is a proportion-integration-differentiation (PID) expression of force error. The adaptive impedance control can adjust the impedance parameters indirectly when the environment position and stiffness are uncertain. In addition, the position controller and inverse kinematics solver are specially designed for the tendon-driven hand. The performance of the proposed control algorithm is validated by using MATLAB and ADAMS software for joint simulation. ADAMS is a great software for virtual prototype analysis. A tendon-driven hand model is built and a control module is generated in ADAMS. Then the control system is built in MATLAB using the control module. The joint simulation results demonstrate fast response and robustness of the algorithm when the environment is not exactly known, so the algorithm is suitable for the control of tendon-driven dexterous hands.