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This article, published in the journal Insect Science, examines the nesting behavior of paper wasps from a physics perspective. The study focuses on how paper wasps arrange their larvae within the nest to achieve mechanical stability. By analyzing various paper wasp nests in Central Java, Indonesia, the study finds that the closer the distance between the center of mass of the larval system and the center of mass of the nest, the more stable the nest becomes. The findings suggest that paper wasps strategically arrange their larvae to achieve equilibrium in their nests. [Extracted from the article]

To improve the handling stability of distributed drive electric vehicles, this paper introduces an electronic differential control strategy based on the stability criterion of the phase plane method. The strategy first plots the distributed electric vehicle's center of mass side angle and center of mass angular speed on the phase plane, and then it analyzes the vehicle's stability under various working conditions to determine the parameters that ensure the stability performance. Subsequently, an adaptive fuzzy control strategy is employed to achieve fast and accurate distribution of the torque to each wheel, thereby enhancing the vehicle's stability. A joint simulation platform is constructed using MATLAB/Simulink and CarSim. A comparison with the traditional electronic differential strategy demonstrates that the proposed distribution strategy based on phase plane stability exhibited excellent stability. [ABSTRACT FROM AUTHOR]

The paper industry is a traditional industry with extensive consumption of resources and energy and more pollutant discharge. This industry is closely related to production and life activities. Under the general requirement of "to step up conservation of the Yangtze River and stop its over development", the paper industry in the Yangtze River Economic Belt should urgently undergo green transformation and development. Based on the undesirable slack-based measure model, spatial gravity center, Kernel density function, Theil index, and panel model, this study examines the green development efficiency and its influencing factors of the paper industry in the Yangtze River Economic Belt from 2001 to 2016. Results showed the following: (1) from 2001 to 2016, the green development efficiency of the paper industry in the Yangtze River Economic Belt had been steadily improved, but the overall efficiency value is not high, which has a great potential for improvement. The green development efficiency of the paper industry in the Yangtze River Economic Belt presents the regional differentiation law of gradient increasing in the upper, middle, and lower reaches. (2) According to the gravity center trajectory, the efficiency center of the green development of the paper industry in the Yangtze River Economic Belt is located in the middle reaches of Hunan Province and Hubei Province and moves to the southwest. This case indicates that the green development efficiency of the paper industry in provinces and cities in the southwest has been improved. (3) The regional differences in the green development efficiency of the paper industry in the Yangtze River Economic Belt show the characteristics of narrowing fluctuations. The regional differences are the primary sources of the difference in the green development efficiency of the paper industry. (4) The enterprise scale, science and technology investment, and industrial structure have significant positive effects on the green development efficiency of the paper industry in the Yangtze River Economic Belt. On the contrary, environmental regulation and foreign investment intensity have significant negative effects. However, the above factors have different effects on the green development efficiency of the paper industry in the upper, middle, and lower reaches of the Yangtze River Economic Belt. [ABSTRACT FROM AUTHOR]

This paper describes a new, fast, Wave‐Length of Center‐of‐gravity (WLC) detection method, named "λ‐Capture". The paper presents and explains the principle of this new technology as a wavelength management technique for displays, utilizing a Linear Reflectance Gradient on the wavelength axis (LRG) dichroic mirror. It is then applied to a mini‐LED wafer: sample of actual display elements and demonstrated to have satisfactory performance. Furthermore, the possibility of new applications based on this principle is demonstrated. [ABSTRACT FROM AUTHOR]

Introduction: This study aimed to explore foot pronation deformity on the postural control of the body and the onset time of the electrical activity of ankle muscles during landing. Materials and Methods: In this cross-sectional study, 27 people with a pronated foot deformity and 27 normal people participated. The force plate was used to measure the postural control of the body. Surface electromyography signals were recorded in landing tests with electromyography, which synchronized with a force plate. To compare the performance of the two groups, we used multivariate analysis of variance. Results: The results indicated a statistically significant difference in the medial-lateral direction of differences between center of pressure and center of mass (COP-COM) between foot pronation (pronated) and normal group during landing (P<0.05). Regarding the variable of the onset time of the muscular electrical activity during landing, there was a statistically significant difference in medial gastrocnemius, soleus, tibialis anterior, and peroneus longus muscles between the two groups (P<0.001). Conclusion: Foot pronation can be regarded as a factor affecting the biomechanics of landing by changing postural control of the body in the medial-lateral direction and the onset time of the electrical activity of medial gastrocnemius, soleus, tibialis anterior, and peroneus longus muscles during landing movement. [ABSTRACT FROM AUTHOR]

In a recent paper, Idrisi, Ullah and Sikkandhar [[1]] considered some aspects of the Restricted Six-Body Problem. Besides, as is known from elemental Mechanics courses (see e.g. [[18], p. 55]), the Coriolis force (per unit mass) I C i with angular velocity vector I i perpendicular to the plane I O i I x i I y i is HT ht Graph and the centrifugal force I Z i is HT ht Graph Hence, if they put in the Coriolis term HT ht , the corresponding term in the centrifugal force would be HT ht , that is, in their paper there should be I i = I i SP 2 sp , which means that I i is determined by I i , and cannot be a different parameter. [Extracted from the article]

This paper presents a method to design a suspension controller with a human body model for ride comfort improvement and motion sickness mitigation. Generally, it has been known that the vertical acceleration of a sprung mass should be reduced for ride comfort. On the other hand, recent studies have shown that, combined, the vertical acceleration and pitch rate of a sprung mass are key factors that cause motion sickness. However, those variables have been considered with respect to the center of gravity of a sprung mass. For motion sickness mitigation, the vertical acceleration of a human head should be also considered. In this paper, the vertical accelerations and pitch rates of a sprung mass and a human head are controlled by a suspension controller for ride comfort improvement and motion sickness mitigation. For the controller design, a half-car and human body models are adopted. With those models, several types of static output feedback suspension controller are designed with linear quadratic optimal control methodology. To reduce the pitch rate of the sprung mass and the vertical acceleration of the head, a filtered-X LMS algorithm is adopted as an adaptive feedforward algorithm and combined with the static output feedback controllers. A frequency response analysis and simulation are performed with the designed controllers on vehicle simulation software, CarSim®. From the simulation results, it is shown that the proposed controllers can effectively reduce the vertical accelerations and the pitch rate of the sprung mass and the human head. [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue of the journal Applied Sciences titled "Biomechanics and Human Motion Analysis." The special issue includes twenty papers that cover a wide range of topics related to the analysis of human motion and biomechanics. The studies involve both healthy subjects and patients with joint diseases, and they utilize musculoskeletal modeling to support their investigations. The papers were contributed by researchers from different countries and continents, highlighting the global nature of this field of study. The special issue aims to promote the integration of biomechanical analysis and instruments into motion analysis and to demonstrate the potential of modern techniques in addressing complex biomechanical problems in human body dynamics. The contributions cover a range of topics related to biomechanics and motion analysis, including the assessment of patellofemoral pain, shoulder kinematics in overhead sporting motions, tibiofemoral kinematics, military crawl locomotion, instability during stepping, upper body posture recognition, optimal control strategies during obstacle crossing, scoring of human body-balance ability, center of mass motion during gait, kinematic analysis of basketball shots, hidden Markov models in movement pattern identification, smart phone-based motion capture, gait analysis in personalized high tibial osteotomy, walking without an anterior cruciate ligament, crouch gait analysis, spine, pelvis, and hip kinematics, hamstring torque measurements, modeling musculoskeletal dynamics during gait, comparison of joint axis estimation approaches, and balanced foot dorsiflex [Extracted from the article]

This paper presents a new control approach for a humanoid biped robot to perform highly dynamic locomotion and keep balance under large external disturbances. The proposed control approach mainly contains two parts: a simplified model-based task planner and an online whole-body controller. The periodic stability is achieved with a foot placement policy presented in this paper. The landing position is predicted and adjusted at every time step to adapt to uncertain disturbances. Then the desired task trajectories are tracked with a quadratic programming (QP) based task space whole-body controller, while satisfying some specific physical constraints. The whole-body controller outputs the optimized joint accelerations, which are then used to produce desired joint torques for the robot's actuators. The positions of the center of mass (CoM) along sagittal and lateral axes are not controlled in the whole-body controller. Meanwhile, the torques at the ankles are constrained to be small and the robot follows a passive-like behavior, which is energetically efficient and helps the feet of the robot to fit better in the environment. Simulations on several highly dynamic gaits have been conducted, two examples among which are presented in this paper. The first demonstrates a walking gait with an increasing sagittal speed and its capability to resist large external disturbances. In the second example, the robot is able to run stably on uneven terrain without knowing any information about it. [ABSTRACT FROM AUTHOR]

This paper describes a new method for ranking of z-numbers according to the radii of gyration in the circulating dynamics of objects. We improve the center of mass technique that was used for ranking of fuzzy data, and by using moments of inertia or second moments, we present the new method for ranking z-numbers by the Radii of Gyration (ROG). In this paper, seven principles are stated to make any ranking method of z-numbers well defined. Eventually, three different types of examples are given, first comparing two z-numbers with each other and also a comparison of the proposed approach with the existing methods is conducted. [ABSTRACT FROM AUTHOR]

In this paper, we use tracked vehicles as an example to study complex systems and surrogate model building method. Due to the high cost and long development cycle associated with the traditional development approach, involving static design and experimental verification, there is an urgent need to explore an effective dynamic optimization design method to enhance vibration reduction performance. This paper introduces a methodology for constructing a model of complex equipment surrogate, aimed at streamlining subsequent parameter optimization processes. The dynamics model of the tracked vehicle is utilized, and the root-mean-square value of plumb vertical acceleration at the center of mass is selected as the dynamic performance index. The impact of structure parameters on dynamic performance is analyzed, and a range of design parameters are determined. The optimal Latin hypercube experimental design method is employed to generate sample data. A radial basis function neural network, optimized by particle swarm optimization, is used to construct a dynamic surrogate model for the tracked vehicle. The surrogate model constructed in this paper greatly reduces the time cost in optimizing complex equipment parameters. In the past, parameter optimization required conducting numerous simulations to collect data, with each simulation taking about 700 s. However, the surrogate model introduced in this paper only requires ∼100 s for completion. This significant reduction in time not only saves costs but also maintains a high level of accuracy. [ABSTRACT FROM AUTHOR]

As big data continues to evolve, cluster analysis still has a place. Among them, the K-means algorithm is the most widely used method in the field of clustering, which can cause unstable clustering results due to the random selection of the initial clustering center of mass. In this paper, an improved honey badger optimization algorithm is proposed: (1) The population is initialized using sin chaos to make the population uniformly distributed. (2) The density factor is improved to enhance the optimization accuracy of the population. (3) A nonlinear inertia weight factor is introduced to prevent honey badger individuals from relying on the behavior of past individuals during position updating. (4) To improve the diversity of solutions, random opposition learning is performed on the optimal individuals. The improved algorithm outperforms the comparison algorithm in terms of performance through experiments on 23 benchmark test functions. Finally, in this paper, the improved algorithm is applied to K-means clustering and experiments are conducted on three data sets from the UCI data set. The results show that the improved honey badger optimized K-means algorithm improves the clustering effect over the traditional K-means algorithm. [ABSTRACT FROM AUTHOR]

Background: China is one of the top countries with the most significant number or proportion of retracted publications, which has garnered significant attention. Methods: Using the Retraction Watch Database, we collected retracted articles written by Chinese authors from 31 provinces in mainland China, spanning the period between January 1, 2012, and December 31, 2023. We used Geographical Information Science to analyze spatial distribution characteristics of retracted articles by Chinese authors and identify high-risk clusters of retracted areas. Results: A total of 14,445 retracted articles authored by researchers from 31 provinces in China between 2012 and 2023 were analyzed. The Spatial trend surface analysis and Gravity center movement indicated a gradual increase in the number of retracted articles from the west to the east. The spatial autocorrelation analysis showed that revealed significant spatial clustering in the distribution of retracted articles across the 31 provinces. The results of the spatial-temporal clustering analysis showed that the hotspots were primarily concentrated in Shandong, Jiangsu, Shanghai, Henan, and Anhui. Conclusion: There is a discernible spatial clustering among these retractions, with a gradual increase in the number of retracted articles from west to east. Shandong, Jiangsu, Shanghai, Henan, and Anhui are the hotspots for retractions. [ABSTRACT FROM AUTHOR]

The five-bar linkage, used in the form of a planar manipulator, benefits from easy controllability and relatively simple kinematic structures, which mean that it can be used in several applications in robotics, rehabilitation, and haptic devices, etc. This paper proposes an optimal synthesis method for a symmetrical five-bar linkage of type 5-RRRRR, with a singularity-free dexterous workspace, based on workspaces with predefined shapes, like squares, rectangles, triangles, circles, and ellipses. The synthesis conditions, to avoid singularities, are given as inequations, which can be further substituted with a system of equations, by introducing the supraunitary coefficient, k. The analytical solutions of the resulting system of equations enable the computation of the link lengths of the five-bar linkage. The optimization method provides the optimal value of the supraunitary coefficient, in order to obtain a maximum value for the minimum input transmission angle and a minimum value for the manipulator size. In this paper, the authors present an analytical approach to the optimal synthesis of a symmetrical five-bar linkage for different shapes of workspace, with the same surface and coordinates in terms of the mass center, as well as the resulting link lengths. In regard to the numerical examples, the authors considered and compared performance indices, such as manipulability, the condition number, and stiffness. The considered examples showed that an equilateral triangle-shaped workspace achieved higher global manipulability, a square-shaped workspace achieved higher global dexterity and the minimum input transmission angle, and circular workspaces achieved the highest mean stiffness and total surface size. It was observed that the synthesis method generates structures that are well-suited to singularity-free dexterous workspaces, with nonzero stiffness values. [ABSTRACT FROM AUTHOR]

In a previous work, we showed that Newton's third law does not strictly hold in a system with remote elements due the finite speed of signal propagation, and thus force imbalance occurs at the system's center of mass. As the said system is affected by a total force for a finite time interval, mechanical energy and momentum are gained by the system. In early works, we assumed that the bodies were macroscopically charge-neutral. Later, we removed this restriction, thus analyzing the consequences of a possible electrically charged relativistic motor. In the first published paper on this subject, we studied this phenomenon in general but gave only an example of a system reaching a stationary state. In this paper, we shall analyze a charged retarded electromagnetic motor in a more general time-dependent setting, giving specific examples in which the system never reaches a stationary state yet produces steady linear momentum nonetheless. We show that the device is more efficient in the microwave (or higher) frequencies. [ABSTRACT FROM AUTHOR]

Objective. 3D-localization of gamma sources has the potential to improve the outcome of radio-guided surgery. The goal of this paper is to analyze the localization accuracy for point-like sources with a single coded aperture camera. Approach. We both simulated and measured a point-like 241 Am source at 17 positions distributed within the field of view of an experimental gamma camera. The setup includes a 0.11 mm thick Tungsten sheet with a MURA mask of rank 31 and pinholes of 0.08 mm in diameter and a detector based on the photon counting readout circuit Timepix3. Two methods, namely an iterative search including either a symmetric Gaussian fitting or an exponentially modified Gaussian fitting (EMG) and a center of mass method were compared to estimate the 3D source position. Main results. Considering the decreasing axial resolution with source-to-mask distance, the EMG improved the results by a factor of 4 compared to the Gaussian fitting based on the simulated data. Overall, we obtained a mean localization error of 0.77 mm on the simulated and 2.64 mm on the experimental data in the imaging range of 20 − 100 mm . Significance. This paper shows that despite the low axial resolution, point-like sources in the nearfield can be localized as well as with more sophisticated imaging devices such as stereo cameras. The influence of the source size and the photon count on the imaging and localization accuracy remains an important issue for further research. [ABSTRACT FROM AUTHOR]

Drought, as a natural disaster with wide-ranging impacts and long duration, has an adverse effect on the global economy and ecosystems. In this paper, four remote sensing drought indices, namely the Crop Water Stress Index (CWSI), Vegetation Supply Water Index (VSWI), Temperature Vegetation Dryness Index (TVDI), and Normalized Difference Water Index (NDWI), are selected for drought analysis. The correlation analysis is carried out with the self-calibrated Palmer Drought Severity Index (sc-PDSI), and based on the optimal index (CWSI), the spatiotemporal characteristics of drought in Shaanxi Province from 2001 to 2021 were studied by SEN trend analysis, Mann–Kendall test, and a center of gravity migration model. The results show that (1) the CWSI performs best in drought monitoring in Shaanxi Province and is suitable for drought studies in this region. (2) Drought in Shaanxi Province shows a decreasing trend from 2001 to 2021; the main manifestation of this phenomenon is the decrease in the occurrence of severe drought, with severe drought covering less than 10% of the area in 2010 and subsequent years. The most severely affected regions in the province are the northern Loess Plateau region and Guanzhong Plain region. In terms of the overall trend, only 0.21% of the area shows an increase in drought, primarily concentrated in the Guanzhong Plain region and the outskirts of the Qinling–Bashan mountainous region. (3) Drought conditions are generally improving, with the droughts' center of gravity moving northeastward at a rate of 3.31 km per year. The results of this paper can provide a theoretical basis and a practical reference for drought control and decision-making in Shaanxi Province. [ABSTRACT FROM AUTHOR]

This paper explores the design and control of a center-rotor type pentacopter that can move in contact with a wall to accurately measure cracks in a concrete outer wall. A center rotor pentacopter is a type of pentacopter that uses an electric ducted fan (EDF) motor and two axis servomotors at the center of gravity of the quadcopter. Center-rotor pentacopters are characterized by the ability to generate thrust in the desired direction using two servomotors and an EDF motor to maintain a stable attitude without tilting or leaning during flight. In this paper, the mathematical modeling of a center-rotor pentacopter was verified through simulation and compared with a regular quadcopter. We also simulated the thrust of the center rotor to see how much it could withstand when a sudden gust of wind occurred. Then, we built a pentacopter and measured the cracks and calculated the width of the cracks through the actual pentacopter in addition to flight experiments. The results showed the advantages and applicability of the pentacopter. [ABSTRACT FROM AUTHOR]

When humanoid robots work in human environments, they are prone to falling. However, when there are objects around that can be utilized, humanoid robots can leverage them to achieve balance. To address this issue, this paper established the state equation of a robot using a variable height-inverted pendulum model and implemented online trajectory optimization using model predictive control. For the arms' optimal joint angles during movement, this paper took the distributed polygon method to calculate the arm postures. To ensure that the robot reached the target position smoothly and rapidly during its motion, this paper adopts a whole-body motion control approach, establishing a cost function for multi-objective constraints on the robot's movement. These constraints include whole-body dynamics, center of mass constraints, arm's end effector constraints, friction constraints, and center of pressure constraints. In the simulation, four sets of methods were compared, and the experimental results indicate that compared to free fall motion, adopting the method proposed in this paper reduces the maximum acceleration of the robot when it touches the wall to 69.1 m/s2, effectively reducing the impact force upon landing. Finally, in the actual experiment, we positioned the robot 0.85 m away from the wall and applied a forward pushing force. We observed that the robot could stably land on the wall, and the impact force was within the range acceptable to the robot, confirming the practical effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Nations worldwide are mobilizing to harness the power of Artificial Intelligence (AI) given its massive potential to shape global competitiveness over the coming decades. Using a dataset of 2.2 million AI papers, we study inter-city citations, collaborations, and talent migrations to uncover dependencies between Eastern and Western cities worldwide. Beijing emerges as a clear outlier, as it has been the most impactful city since 2007, the most productive since 2002, and the one housing the largest number of AI scientists since 1995. Our analysis also reveals that Western cities cite each other far more frequently than expected by chance, East–East collaborations are far more common than East–West or West–West collaborations, and migration of AI scientists mostly takes place from one Eastern city to another. We then propose a measure that quantifies each city's role in bridging East and West. Beijing's role surpasses that of all other cities combined, making it the central gateway through which knowledge and talent flow from one side to the other. We also track the center of mass of AI research by weighing each city's geographic location by its impact, productivity, and AI workforce. The center of mass has moved thousands of kilometers eastward over the past three decades, with Beijing's pull increasing each year. These findings highlight the eastward shift in the tides of global AI research, and the growing role of the Chinese capital as a hub connecting researchers across the globe. [ABSTRACT FROM AUTHOR]

High-speed small crafts are extensively used in various environments. However, these planing vessels are prone to motion instabilities, particularly during turning and course-changing maneuvers. Understanding their behavior under a fixed yaw angle is crucial in the early design stages. This paper presents a numerical study to evaluate the influence of yaw angle on the hydrodynamic performance of high-speed planing hulls. The results indicate that the yaw angle has a significant influence on the hull's running attitudes, as well as hydrodynamic forces and moments. At large yaw angles, air is drawn into the roll-down side, resulting in a small dynamic wetted surface area in high-speed cases. A negative pressure region is observed under high-speed conditions, with asymmetric conditions accentuating (mitigating) this negative pressure region on the roll-down (roll-up) sides. The peaks of sectional lift and resistance are typically observed near the stagnation line in most cases. The sectional sway force is more pronounced behind the center of gravity when the planing speed is slightly above the critical velocity of the trim angle, resulting in a positive yaw moment and suggesting a trend toward a reduction in the yaw angle. It is evident that the aerodynamic resistance on the transom surface is considerable in high-speed cases. The understanding of these phenomena is crucial for the effectiveness of high-speed small craft designs. [ABSTRACT FROM AUTHOR]

This paper proposes a 4–5R rolling mechanism based on the spatial extension design of a planar 6R single-loop chain. By analyzing the locomotion of the planar equivalent form, a modular gait theory integrating different modes of gait with high efficiency, low energy consumption, and high speed is established. A unified kinematic strategy expression, encapsulated in the form of the gait period table, is tailored for the kinematic chain's gait on the flat terrain. A contrast gait is conducted to ascertain its velocity parameters and volatility of the center of mass (CM). By optimizing the corresponding indicators, two distinct gait patterns are achieved: a faster speed gait that prioritizes increased speed and a steady gait that emphasizes stability with reduced CM volatility. Drawing from the mobility analysis and simulation outcomes of the planar 6R single-loop kinematic chain, a theory of locomotion for a closed-chain linkage mechanism in space is proposed. A locomotion strategy on the flat ground is derived, and a unified evaluation index is proposed. Finally, the feasibility of the two working modes is verified using a physical prototype. The theoretical work in this paper simplifies the design process of closed-chain linkage robots and improves the mobility performance of closed-chain linkage robots. It lays the foundation for researching new types of closed-chain linkage robots. [ABSTRACT FROM AUTHOR]

Because the wheeled rolling robot has the characteristics of fast movement, high work efficiency and strong bearing capacity, it can be applied to industrial production and detection. Aiming at the problems of low motion efficiency and a large number of drivers of rolling robots based on the parallel mechanism, a new type of wheeled rolling robot composed of a planar 3-RRR parallel mechanism and a spoke-type variable-diameter wheel is proposed in this paper. By adjusting the output of the 3-RRR parallel center of gravity adjustment device, the robot can deform and roll. In this paper, the spoke-type variable-diameter wheel is designed and the eccentric torque workspace of the 3-RRR parallel center-of-gravity adjustment device is optimized. On the basis of clarifying the relationship between wheel diameter scaling and input angle, the kinematic and dynamic models of the wheeled rolling robot are established and simulated by Adams. Finally, the prototype was built and the experiments were carried out. The results show that the wheeled rolling robot has the ability to linearly roll, turn and climb at small angles. [ABSTRACT FROM AUTHOR]

This paper investigates the application of contusion stability yaw control of a lightweight solar-electric vehicle. The vehicle's customized design envelope makes it more sensitive to variations in load due to its low weight and relatively large size. To address this issue, control strategies were developed using differential motor torques to generate direct yaw moments using the vehicle's rear in-wheel motors. This paper introduces the working conditions of solar vehicles and demonstrates the necessity of stability control. Vehicle parameters such as mass and center of gravity position are obtained to apply control to the real vehicle. The paper then describes two stability control strategies, using (i) sliding-mode control (SMC) and (ii) model predictive control (MPC). To account for the road bank angle of the test area and the impact of additional weight from a driver and passenger, a Kinematic-Based Observer is designed to estimate the vehicle's side-slip based on measured values. To collect real-time data, a dSPACE MicroAutobox was installed on the solar vehicle. The results show the effect of the observer and controllers under different vehicle speeds and load conditions. Finally, closed-loop simulation results are presented to support the findings from the open-loop testing. [ABSTRACT FROM AUTHOR]

This paper describes control methods to improve electric vehicle performance in terms of handling, stability and cornering by adjusting the weight distribution and implementing control systems (e.g., wheel slip control, and yaw rate control). The vehicle is first simulated using the bicycle model to capture the dynamics. Then, a study on the effect of weight distribution on the driving behavior is conducted. The study is performed for three different weight configurations. Moreover, a yaw rate controller and a wheel slip controller are designed and implemented to improve the vehicle's performance for cornering and longitudinal motion under the different loading conditions. The simulation through the bicycle model is compared to the experiments conducted on a rear-wheel driven radio-controlled (RC) electric vehicle. The paper shows how the wheel slip controller contributes to the stabilization of the vehicle, how the yaw rate controller reduces understeering, and how the location of the center of gravity (CoG) affects steering behavior. Lastly, an analysis of the combination of control systems for each weight transfer is conducted to determine the configuration with the highest performance regarding acceleration time, braking distance, and steering behavior. [ABSTRACT FROM AUTHOR]

This paper investigates the application of reflectivity control devices in spacecraft attitude control. In reflectivity control devices, in particular, the polymer-dispersed liquid–crystal type, the light transmission properties of the film can be altered from transparent to opaque by adjusting the amount of applied voltage. This technology has previously been applied to residential and commercial buildings and, recently, it has been widely adopted in the automotive industry for purposes such as electrochromic glass roofs. Since spacecraft in orbit receive a continuous flow of photons emitted from the Sun (when in the sunlit portion of their orbits), the momentum transferred from these photons to the spacecraft can be utilized for attitude and orbit control. The focus of this paper is on attitude control through strategically adjusting the transparency of reflectivity-control panels attached to the spacecraft away from its center of mass. In this paper, a conceptual design for a spacecraft equipped with reflectivity-control device panels is presented, and the equations of attitude motion coupled with control torques produced by these devices are derived. Furthermore, a control strategy for detumbling a small satellite, such as a CubeSat, is investigated. To assess the viability of reflectivity-control technology in spacecraft attitude control, a number of case studies are presented. The performance of these devices is discussed in light of the results obtained from the numerical simulations. [ABSTRACT FROM AUTHOR]

The deviation of the center of mass of a gravitational wave detection satellite from its calibrated position can severely impact the accuracy of gravitational wave detection. Therefore, there is an urgent need to develop effective identification methods to achieve precise center of mass identification while ensuring the alignment of the laser link. To address this issue, this paper proposes a method for the center of mass identification of gravitational wave detection spacecraft that ensures the pointing accuracy of the laser link. A study on the relative attitude dynamics modeling of gravitational wave detection spacecraft is conducted, and the conditions for small, periodic spacecraft maneuvers that maintain laser link alignment are analyzed. A high-precision, high-stability center of mass identification method based on dual-model data fusion is proposed and simulated. The results show that this method can maintain the alignment precision of the laser interferometer arms within 10 nrad, while achieving a center of mass identification accuracy of 25 μ m. Compared to existing methods, this method improves the identification accuracy by an order of magnitude, demonstrating its feasibility for application in gravitational wave detection constellations. It provides theoretical support for the center of mass identification of gravitational wave detection spacecraft. [ABSTRACT FROM AUTHOR]

This paper proposes a combination of movable masses and reaction wheels for the attitude control of ultra-low-orbit satellites. During the attitude control of ultra-low-orbit satellites, the satellite's attitude is significantly influenced by the aerodynamic torque. Therefore, this paper proposes a combined control method using movable masses and reaction wheels. By adjusting the position of the movable masses to modify the relative distance between the center of mass (CM) and the center of pressure (CP), the aerodynamic torque is effectively reduced. Additionally, a finite-time terminal sliding mode extended state observer (TSMESO) is incorporated to estimate the reduced aerodynamic torque. Then, a finite-time non-singular terminal sliding mode control (NTSMC) method is introduced to achieve rapid attitude stabilization. Simulations demonstrate that under the proposed control system, the aerodynamic torque acting on the ultra-low-orbit spacecraft can be significantly reduced in a short time, and the response and high precision attitude stability can be effectively achieved. [ABSTRACT FROM AUTHOR]

The relative motion of a spacecraft under the influence of gravitational forces and light pressure is considered. By spacecraft we mean a celestial body capable of reflecting light from the Sun. The orbital motion of the spacecraft is considered known. The spacecraft makes plane movements in a horizontal plane relative to its center of mass. The reflecting mirror can be placed perpendicular to the orbital plane. The main problem solved in this paper is the study of the stability of eccentric oscillations. This technology is being rolled out gradually. First, the existence of oscillations of a given type is established. To do this, the implicit function theorem is applied in a standard way. The subsequent stability analysis is based on linear theory and is reduced to the consideration of systems in variations. The paper is concluded with consideration of the nonlinear case. [ABSTRACT FROM AUTHOR]

Triple stellar systems allow us to study stellar processes that cannot be attained in binary stars. The evolutionary phases in which the stellar members undergo mass exchanges can alter the hierarchical layout of these systems. Yet, the lack of a self-consistent treatment of common-envelope (CE) in triple-star systems hinders the comprehensive understanding of their long-term fate. This paper examines the conditions predicted around binaries embedded within CEs using local 3D hydrodynamical simulations. We explore varying the initial binary separation, the flow Mach number, and the background stellar density gradients as informed by a wide array of CE conditions, including those invoked to explain the formation of the triple system hosting PSR J0337+1715. We find that the stellar density gradient governs the gaseous drag force, which determines the final configuration of the embedded binary. We observe a comparable net drag force on the center of mass but an overall reduction in the accretion rate of the binary compared to the single-object case. We find that, for most CE conditions, and in contrast to the uniform background density case, the binary orbital separation increases with time, softening the binary and preventing it from subsequently merging. We conclude that binaries spiraling within CEs become more vulnerable to disruption by tidal interactions. This can have profound implications on the final outcomes of triple-star systems. [ABSTRACT FROM AUTHOR]

Control decoupling is the basic control step for precision MIMO (Multi-Input-Multi-Output) motion systems. After decoupling, the MIMO logical controlled plant can be diagonal dominant so that the control design for each DOF (Degree of Freedom) can be separately treated. However, due to the manufacturing tolerances and the assembling errors, the actual CoG (Center of Gravity) and actuator positions are inconsistent with the designed values. The nominal static control decoupling matrix is inaccurate, which significantly deteriorates the decoupling performance. To address the problem, this paper develops a matrix update based iterative control decoupling tuning method. Tuning with feedback control signals to achieve accurate tuning is its first distinct feature. By employing rigid-body model information to construct more accurate basis functions, fast tuning can also be achieved, especially for relatively low control bandwidth occasions. Differing from the feedforward compensation based iterative control decoupling tuning method, the matrix update method improves the dynamics of the logical controlled plant, does not increase the control complexity and is more robust to the inaccuracy of the model information. Experimental results on the short-stroke module of a precision motion stage which is the key subsystem of the lithographic projection lens testing system present significant control decoupling performance improvement (for example the peak value of the Rx-DOF servo error caused by the Z-DOF movement is reduced from 1.29 ×10−5 m to 3.19 ×10−6 m) after just two trials. • This paper reveals the coupling mechanism of the multi-DOF motion stage in presence of the CoG and actuator position errors. • This paper analyzes the tuning principle by using feedback control signals to achieve accurate control decoupling tuning. • This paper proposes the matrix update based iterative control decoupling tuning method for the first time. [ABSTRACT FROM AUTHOR]

As a focal point in contemporary land system science research, land use transitions significantly impact the ecological environment. Zhaosu County, a typical ecological county in the arid region of Northwest China, offers significant insights into the processes of land use transition and their effects on the ecological environment. Studying these dynamics is crucial for the county's rational spatial allocation and sustainable development. Based on the remote sensing monitoring data of land use in Zhaosu County in 2000, 2010, and 2018, this article classified land use according to three primary functions: "production, living, and ecological". By comprehensively applying the research methods of land use transfer matrix model, land use center of gravity shift model, eco-environmental quality index, and regional ecosystem contributions, this paper quantitatively analyzed the process of land use functional transition and spatial transition in Zhaosu County from 2000 to 2018 and scientifically investigated the spatiotemporal distribution characteristics of land use transitions as well as their varying impacts on the ecological environment. This research indicates that: (1) From 2000 to 2018, the ecological land in Zhaosu County initially experienced an increase followed by a decrease; in contrast, production land underwent a decline before rebounding, while living land has shown a continuous upward trajectory. (2) The spatial distribution of the three primary functional land uses in Zhaosu is unbalanced, and the center of gravity of all land uses has shifted during the study period. Among them, the center of gravity of water area and other ecological land underwent the most pronounced displacements, and the spatial migration intensified initially before gradually diminishing, while the degree of deviation of urban living land was the least pronounced. (3) The comprehensive eco-environmental quality index of Zhaosu County continued to decline from 0.584 in 2000 to 0.549 in 2018, indicating a persistent degradation trend of the ecological environment quality. (4) The negative effects of the ecological environment in Zhaosu County outweighed the positive effects, and the main factors contributing to the decline in ecological environment quality were grassland degradation and the decline of the snowline. [ABSTRACT FROM AUTHOR]

Investigating the experience and improvement measures for China's distinctive land supply participation in macro-control processes holds significance for full utilization of land policy. However, the spatial heterogeneity and its theoretical and comprehensive analysis of drivers are still poorly revealed. This paper uses spatial analysis methods and micro-scale big data on land transactions to depict the spatiotemporal heterogeneity of land supply, and analyses its driving mechanisms via an endogenous–exogenous factor framework and regression models. Land supply experienced fluctuating "growth–decline–growth" trends in 2001–2021, spatially showed a large cluster in the east, a small cluster in the center and scattering in the west, with the gravity center relocating southwest, and formed a multi-core, hierarchical, circular structure of high density in core cities, density in peripheral cities and sparseness in districts. Endogenously, total land resources and road accessibility facilitated land supply, while topographic relief and urban proximity showed inhibitory effects; land supply positively correlated with land finance dependence, officials' appraisal pressure, local government competition and officials' corruption but negatively related with fiscal tax revenues and fiscal transparency; construction land indicators directly determined land supply, while the intensity of use control restricted the conversion of arable land and weakened land supply. Exogenously, urbanization, industrialization, capital investment, technological innovation and marketization level promoted land supply, while the substitution of human capital reduced the demand for land; economic fluctuations showed non-significant relationships with land supply. Differentiated impacts of multiple factors on land supply pattern are emphasized and should be integrated into formulating land policy and optimizing land allocation. [ABSTRACT FROM AUTHOR]

This paper focuses on a comprehensive study of a four-axle vehicle, including dynamics analysis, equivalent modeling methods, and their comparison. Firstly, a linear two-degree lateral dynamic model is established, which has four drive axles and two steer axles. Secondly, the mathematical transfer function expressions for the yaw rate and the centroid sideslip angle were derived on the basis of the model. The steady-state parameters, such as yaw rate gain Gγss, centroid sideslip angle gain Gβss, stability factor Kn, equivalent axial distance ln, and equivalent centroid sideslip angle coefficient Kn' were obtained by using the transfer functions. Then, the steady-state and transient characteristics are roundly discussed, including steady-state parameters, system root trajectory, frequency domain, and time domain. Some recommendations for the four-axle vehicle's parameter design are also given. Finally, for a more simple and efficient analysis of response characteristics of four-axle vehicles and even n (n > 4) axle vehicles, the equivalent model is developed for the four-axle vehicle, and comprehensive analyses are presented with four equalization methods, which are based on the inner heart of the approximation triangle, the outer heart of the approximation triangle, the center of gravity of the approximation triangle and the compensation point. Following a thorough analysis of the four, it is determined that the inner approximation triangle solution approach is most suited for four-axle vehicles. [ABSTRACT FROM AUTHOR]

Yoga is an exercise preferable for various users at different ages to enhance physical and mental health. To help beginner yoga self-practitioners avoid getting injured by selecting difficult yoga poses, the information of the difficulty level of yoga poses is very important to provide an objective metric to assist yoga self-practitioners in selecting appropriate exercises on the basis of their skill level by using the yoga self-practice system. To enhance the developed yoga self-practice system, the yoga difficulty level estimation function will enable users to clearly understand whether the selected yoga poses are suitable for them. In this paper, the newest difficulty level estimation method of yoga poses is proposed by using and analyzing OpenPose two-dimensional (2D) human body keypoints. The proposed method effectively uses the selected six keypoints areas of the upper and lower body, body support types, center of gravity calculations, and body tilt angles and slopes to produce estimations. Firstly, the method calculates the weighted centers of the upper and lower human body for each pose by using keypoints. Secondly, it refers the slope of the centroid line between the two centers and infers the body's balance state. Lastly, the system estimates the difficulty level by additionally considering the keypoints of the body to contact the ground. For evaluations of the proposal, more than one hundred yoga poses are collected from the Internet and applied to classify them into five difficulty levels. Through comparisons with subjective levels from one instructor and 10 users, the validity of the estimation results is confirmed, a comparison is performed with existing designs, and it is implemented in embedded systems. [ABSTRACT FROM AUTHOR]

In this paper we study the evolution of a small rigid body in a viscous incompressible fluid, in particular we show that a small particle is not accelerated by the fluid in the limit when its size converges to zero under a lower bound on its mass. This result is based on a new a priori estimate on the velocities of the centers of mass of rigid bodies that holds in the case when their masses are also allowed to decrease to zero. [ABSTRACT FROM AUTHOR]

Robots are becoming an integral part of space facilities construction and maintenance, and may need to move to and from different work locations. Robotic arms that are widely employed, which are mounted on fixed bases, have difficulty coping with increasingly complex missions. The challenge discussed in this paper is the problem of the efficient locomotion of robotic systems. Inspired by the gliding motion of a flying snake launched from a tree and combined with the weightlessness of the space environment, we design similar motions for the robot, including the following three steps. First, the robot folds its body like a snake and initiates flight by accelerating the global center of mass (CM), focusing on the movement direction and generating suitable momentum. Then, during the flight (free-floating) phase, the joint motions are planned using a nonlinear optimization technique, considering the nonholonomic constraints introduced by the momentum conservation and the system states at the initial and final states of the floating. Meanwhile, the difficulties caused by long-distance flights are addressed to reduce the motion computational cost and energy consumption by introducing the phase plane analysis method. Finally, the landing motion is designed to avoid rigid collisions and rollover on the radial plane. The numerical simulations illustrate that the three phases of maneuvers are smooth and continuous, which can help the space robots efficiently traverse the environment. [ABSTRACT FROM AUTHOR]

Image super-resolution is getting popularity these days in diverse fields, such as medical applications and industrial applications. The accuracy is imperative on image super-resolution. The traditional approaches for local edge feature point extraction algorithms are merely based on edge points for super-resolution images. The traditional algorithms are used to calculate the geometric center of gravity of the edge line when it is near, resulting in a low feature recall rate and unreliable results. In order to overcome these problems of lower accuracy in the existing system, an attempt is made in this research work to propose a new fast extraction algorithm for local edge features of super-resolution images. This paper primarily focuses on the super-resolution image reconstruction model, which is utilized to extract the super-resolution image. The edge contour of the super-resolution image feature is extracted based on the Chamfer distance function. Then, the geometric center of gravity of the closed edge line and the nonclosed edge line are calculated. The algorithm emphasizes on polarizing the edge points with the center of gravity to determine the local extreme points of the upper edge of the amplitude-diameter curve and to determine the feature points of the edges of the super-resolution image. The experimental results show that the proposed algorithm consumes 0.02 seconds to extract the local edge features of super-resolution images with an accuracy of up to 96.3%. The experimental results show that our proposed algorithm is an efficient method for the extraction of local edge features from the super-resolution images. [ABSTRACT FROM AUTHOR]

The dynamic model of cavitation bubbles serves as the foundation for the study of all cavitation phenomena. Solving the cavitation bubble dynamics equation can better elucidate the physical principles of bubble dynamics, assisting with the design of hydraulic machinery and fluid control. This paper employs a fourth-order explicit Runge–Kutta numerical method to solve the translational Keller–Miksis model for cavitation bubbles. It analyzes the collapse time, velocity, as well as the motion and force characteristics of bubbles under different wall distances γ values. The results indicate that as the distance between the cavitation bubble and the wall decreases, the cavitation bubble collapse time increases, the displacement of the center of mass and the amplitude of translational velocity of the cavitation bubble increase, and the minimum radius of the cavitation bubble gradually decreases linearly. During the stage when the cavitation bubble collapses to its minimum radius, the Bjerknes force and resistance experienced by the bubble also increase as the distance to the wall decreases. Especially in the cases where γ = 1.3 and 1.5, during the rebound stage of the bubble, the Bjerknes force and resistance increase, causing the bubble to move away from the wall. Meanwhile, this study proposes a radiation pressure coefficient to characterize the radial vibration behavior of cavitation bubbles when analyzing the radiation sound pressure. It is found that the wall distance has a relatively minor effect on the radiation pressure coefficient, providing an important basis for future research on the effects of different scale bubbles and multiple bubbles. The overall idea of this paper is to numerically solve the bubble dynamics equation, explore the characteristics of bubble dynamics, and elucidate the specific manifestations of physical quantities that affect bubble motion. This provides theoretical references for further engineering applications and flow analysis. [ABSTRACT FROM AUTHOR]