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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 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]

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]

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]

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]

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]

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 considers four satellites connected to each other by electrodynamic tethers, which are assumed to be rigid in the mathematical model of the system's motion. In the Earth's magnetic field, current-carrying conductors are affected by Lorentz forces, which are used to control the motion of the system's center of mass and the angular motion. The paper presents an algorithm for calculating the magnitude of the current to stop the drift of the center of mass of a tetrahedral formation relative to the desired orbital reference frame in low Earth orbit and spin the system up to a constant angular velocity relative to the center of mass. A numerical study of the convergence time to achieve the required motion is carried out depending on the maximum possible current and initial conditions. [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]

Runaway accidents caused by vehicle braking have been extensively studied from the perspective of passenger safety. The traditional escape ramp alleviates such conditions to some extent, which places higher demands on human protection and more complex application scenarios (slope and long-distance site requirements). This paper proposes a new type of escape ramp arresting system (ERAS) and developed a novel type of variable cable force damper. The combination of the damper and the arresting net in the ERAS could more effectively restrict the speed of the runaway vehicle and ensure the safety of the occupants, while being able to adapt to more practical scenarios (flat slopes and short-distance site requirements). Six sets of real low- and high-speed intercept tests with different models were conducted to obtain some key data, such as the acceleration of the vehicle’s center of gravity, the impact velocity of occupants, and the sequence diagram of the vehicle during the impact. The vehicle impact force at low speed and the crash safety performance were effectively evaluated. The results indicated ERAS was applicable to runaway vehicles including sedans and large buses (60–120 km=h), but further optimization was needed for overweight trucks. In addition, the paper provides valuable experimental data for the future study of real vehicle crash tests and the calibration of the finite-element model. [ABSTRACT FROM AUTHOR]

The FCDET is considered as a promising and advanced agricultural machinery due to its convenience and controllability. To enhance the control performance of the FCDET unit dynamic system, understanding the accurate position of the center of gravity (CoG) of the tractor unit in longitudinal motion and the operating environment is essential. In this paper, we proposed a real-time estimation method of CoG position of longitudinal motion for FCDET plowing and transportation conditions. CoG height and longitudinal axis distance distribution coefficients are used as state estimation variables, and the data obtained from displacement and velocity sensors are used as state observation variables, establishing a discrete system state space model and proving the observability. The proposed Derived UKF algorithm introduces the Sage-Husa adaptive noise equation within the Square-Root UKF framework to address the non-positive definite matrix problem. The research shows that the precise CoG longitudinal position effectively reflects changes in operational pavement load. The Derived UKF algorithm exhibits high state estimation accuracy in plowing and transportation conditions, with mean absolute errors of 14.2% and 5.0% of the state amplitude, respectively. This study supports the practical application of real-time state parameter estimation algorithms in controlling advanced agricultural machinery distributed drive systems. [ABSTRACT FROM AUTHOR]

In the era of the internet, people are increasingly interested in highly personalized customization, which has been leading the global industry to transform from "Enterprise centered Mass Manufacturing" to "User centered Mass Customization". In recent decades, ontology-based semantic models have been used for semantic association description and syntax consistency alignment of product structures. However, the description of industrial terminology and general concepts has difficulty achieving accurate end-to-end matching of personalized user customization requirements and manufacturing capabilities. This requires detailed descriptions of process standards, component/assembly/part specifications, etc. Therefore, we propose the Abstraction-Instance-Capability (AIC) model based on a knowledge graph, which is a multigrained and multiview industrial knowledge model. By modeling industrial knowledge at a deeper level from various perspectives and by considering the expression of the relationships between knowledge, an industrial knowledge graph was constructed to support personalized customization. This graph can be used for personalized customization plan generation and other related operations, such as Design BOM (Bill of Materials) modification and verification. First, a meta-object facility (MOF)-based meta-model is defined for AIC model design. Second, the proposed model is used to define a multiview structure for modeling knowledge from various perspectives. Such a design realizes efficient industrial knowledge retrieval from various aspects, such as manufacturing resource retrieval, and production capacity analysis. Finally, in this paper we validate operability and introduce two case studies to demonstrate that the model has good performance in the recommendation of components (BOM modification) and the verification of personalized customization schemes (BOM verification). [ABSTRACT FROM AUTHOR]

Double-leg circles on pommel horse exercises require a high degree of dynamic balance. However, theoretical conditions for maintaining dynamic balance are unclear. The purpose of this paper is to propose a simple theoretical model of the dynamic balance of the circles, and to illustrate its qualitative properties. To this end, the body of a gymnast is simply modeled as one rigid body with one support point, and symmetric and constant-velocity circles are assumed in most analyses. The condition that the torques of wrist and shoulder joints are zero is assumed as a dynamic balance condition with minimum strength. A control law is proposed to demonstrate the motion. Various properties of the dynamic balance condition are analyzed as follows. In the symmetric circles, (1) as the period of a circle decrease, the heights and the radius of the toes increase, and (2) the rotation of the body around its longitudinal axis in the double-leg circle has the effect of lifting the toes. (3) The shoulder and wrist torques can change the pose around the dynamic balance condition. In asymmetric circles, (4) the radius of the center of mass (CoM) increases as the angular velocity of the CoM around the support point decreases, and (5) the body angle with respect to the horizontal plane increases as the upward acceleration of the CoM increases. Moreover, mechanical principles of the circles are discussed as follows. (6) The CoM motion during the symmetric circles of the simple model can be related to the conical pendulum. In the simple model, (7) the pommel reaction force should be parallel to the arm segment when the wrist torque and the shoulder torque are equal or zero, and (8) to change the vertical component of the angular momentum of the body around the support point, the wrist torque around the vertical axis is needed. These results provide theoretical and qualitative insights into understanding and improving pommel horse exercise. [ABSTRACT FROM AUTHOR]

In this paper, the bending, dynamic responses and multi-objective optimization of the pyramidal lattice sandwich plate are studied. Initially, the paper calculates the equivalent elasticity moduli and equivalent shearing moduli of pyramid lattice core. Then, the kinematic relations between the plate and the pyramid grid core are established by using the improved FSDT. The governing differential equations and the conditions for boundaries are deduced from the Hamilton principle, and solved by using Navier’s method. To validate that the theoretical model is accurate, the paper compares the center deflection and natural frequency derived from theoretical calculations with the experimental and finite element results. In detail, this paper studies the influence of the number of single cells, thickness ratio, and lattice rod radius on the bending and free vibration behavior. Then, the key elements are chosen as design parameters. Next, the space of design variables is explored using the hybrid PSO-GWO algorithm to find Pareto optimal solutions. The optimum number of single cells, thickness ratio and radius of the pyramid lattice sandwich plates are finally derived to satisfy the conflicting desired objectives of maximizing natural frequency and minimizing center displacement and mass. The results show that the proposed equivalent model can predict the static bending and dynamic responses of pyramidal lattice sandwich plate well. In order to satisfy maximizing natural frequency and minimizing center displacement and mass, different Pareto optimal solutions are given for different design options by using the hybrid PSO-GWO algorithm. [ABSTRACT FROM AUTHOR]

We explore the stability of floating objects at a two-fluid interface through mathematical modeling and experimentation. Our models are based on standard ideas of center of gravity, center of buoyancy, and Archimedes' Principle extended to the two-fluid scenario. We investigate floating shapes with uniform, two-dimensional cross sections and identify analytically and/or computationally a potential energy landscape that helps identify stable and unstable floating orientations. We compare our analyses and computations to experiments on floating objects designed and created through 3D printing. Additionally, the paper includes open problems for further study. [ABSTRACT FROM AUTHOR]

Angle profiles belong to the most common steel profiles used in several types of civil engineering structures, such as in lattice towers. Although, in such towers, they are usually considered as axially loaded (truss) members, an additional bending moment develops due to the eccentricity between the point of load application and the gravity center of the profile. Therefore, this paper focuses on the buckling resistance of single-angle members subjected to combined compression and bending. The investigations have been performed through numerical parametrical studies and have been compared to different normative documents where interaction equations are provided. [ABSTRACT FROM AUTHOR]

In the N-body problem, it is classical that there are conserved quantities of center of mass, linear momentum, angular momentum and energy. The level sets M (c , h) of these conserved quantities are parameterized by the angular momentum c and the energy h, and are known as the integral manifolds. A long-standing goal has been to identify the bifurcation values, especially the bifurcation values of energy for fixed non-zero angular momentum, and to describe the integral manifolds at the regular values. Alain Albouy identified two categories of singular values of energy: those corresponding to bifurcations at relative equilibria; and those corresponding to "bifurcations at infinity", and demonstrated that these are the only possible bifurcation values. This work examines the bifurcations for the four body problem with equal masses. There are four singular values corresponding to bifurcations at infinity. To establish that the topology of the integral manifolds changes at each of these values, and to describe the manifolds at the regular values of energy, the homology groups of the integral manifolds are computed for the five energy regions on either side of the singular values. The homology group calculations establish that all four energy levels are indeed bifurcation values, and allows some of the global properties of the integral manifolds to be explored. A companion paper will provide the corresponding analysis of the bifurcations at relative equilibria for the four-body problem with equal masses. [ABSTRACT FROM AUTHOR]

In this paper, for the first time, experimental tests of complete offline walking gaits generated by the essential model are performed. This model does not make simplifications in the dynamics of the robot, and its main advantage is the definition of desired Zero Moment Point trajectories. The designed gaits are implemented in the NAO robot, where starting and stopping stages are also included. Simulations in MATLAB and Webots, and experiments with the real robot are shown. Also, important remarks about the implementation of walking trajectories in the NAO robot are included, such as dealing with the hip joint shared by both legs. A comparison between the linear inverted pendulum (LIP) model and the essential model is also addressed in the experiments. As expected, the robot fails following the offline gait generated by the LIP model, but it does not with the essential model. Moreover, in order to push the boundaries of the essential model, a complex gait is designed with a vertical motion of the center of mass and an abrupt movement of the arms. As shown in experiments, no external balance controller is required to perform this complex gait. Thus, the efficiency of the essential model to design stable open-loop complex gaits is verified. [ABSTRACT FROM AUTHOR]

Considering that the existing path planning algorithms for mobile robots under rugged terrain do not consider the ground flatness and the lack of optimality, which leads to the instability of the center of mass of the mobile robot, this paper proposes an improved A* algorithm for mobile robots under rugged terrain based on the ground accessibility model and the ground ruggedness model. Firstly, the ground accessibility and ruggedness models are established based on the elevation map, expressing the ground flatness. Secondly, the elevation cost function that can obtain the optimal path is designed based on the two types of models combined with the characteristics of the A* algorithm, and the continuous cost function is established by connecting with the original distance cost function, which avoids the center-of-mass instability caused by the non-optimal path. Finally, the effectiveness of the improved algorithm is verified by simulation and experiment. The results show that compared with the existing commonly used path planning algorithms under rugged terrain, the enhanced algorithm improves the smoothness of paths and the optimization degree of paths in the path planning process under rough terrain. [ABSTRACT FROM AUTHOR]

In this paper, an alignment-free bioinformatics technique, termed the 20D-Dynamic Representation of Protein Sequences, is utilized to investigate the similarity/dissimilarity between Baculovirus and Echinococcus multilocularis genome sequences. In this method, amino acid sequences are depicted as 20D-dynamic graphs, comprising sets of "material points" in a 20-dimensional space. The spatial distribution of these material points is indicative of the sequence characteristics and is quantitatively described by sequence descriptors akin to those employed in dynamics, such as coordinates of the center of mass of the 20D-dynamic graph and the tensor of the moment of inertia of the graph (defined as a symmetric matrix). Each descriptor unveils distinct features of similarity and is employed to establish similarity relations among the examined sequences, manifested either as a symmetric distance matrix ("similarity matrix"), a classification map, or a phylogenetic tree. The classification maps are introduced as a new way of visualizing the similarity relations obtained using the 20D-Dynamic Representation of Protein Sequences. Some classification maps are obtained using the Principal Component Analysis (PCA) for the center of mass coordinates and normalized moments of inertia of 20D-dynamic graphs as input data. Although the method operates in a multidimensional space, we also apply some visualization techniques, including the projection of 20D-dynamic graphs onto a 2D plane. Studies on model sequences indicate that the method is of high quality, both graphically and numerically. Despite the high similarity observed among the sequences of E. multilocularis, subtle discrepancies can be discerned on the 2D graphs. Employing this approach has led to the discovery of numerous new similarity relations compared to our prior study conducted at the DNA level, using the 4D-Dynamic Representation of DNA/RNA Sequences, another alignment-free bioinformatics method also introduced by us. [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 paper deals with a general problem of convex stochastic optimization in a space of small dimension (for example, 100 variables). It is known that for deterministic problems of convex optimization in small dimensions, the methods of centers of gravity type (for example, Vaidya's method) provide the best convergence. For stochastic optimization problems, the question of the possibility of applying Vaidya's method can be reduced to the question of how it accumulates inaccuracies in the subgradient. A recent result of the authors stating that there is no accumulation of inaccuracies at the iterations of Vaidya's method allows the authors to propose its analog for solving stochastic optimization problems. The main technique is to replace the subgradient in Vaidya's method by its batched analogue (the arithmetic mean of stochastic subgradients). In the present paper, this plan is implemented, which results in an efficient method (under conditions of the possibility of parallel calculations with batching) for solving problems of convex stochastic optimization in spaces of small dimensions. The work of the algorithm is illustrated by a numerical experiment. [ABSTRACT FROM AUTHOR]

Currently, the body balance control algorithm of a quadruped robot executing trot gait motion is more complex and computationally intensive, which is not conducive to improving the real-time control performance of the robot. This paper proposes a six-dimensional spatial mechanics decoupling algorithm to enhance the balance control accuracy during trot gait while optimizing the computational effort. A 6 × 6 matrix is established to describe the relationship between six ground reaction forces of the diagonal supporting leg and six spatial forces and torques controlling robot degrees of freedom, which is optimized to reach the full rank. Decoupling calculation is adopted to obtain required ground reaction forces by matrix inverse operation, and forces are converted to joint motor torques utilizing the Jacobian matrix. The trajectory of the swing leg foot is generated based on cubic interpolation, and the robot motion speed is adjusted by selecting the landing point. This paper also proposes a region intervention control method based on center of mass projection to regulate the moving speed while ensuring the balance of the robot. Finally, the algorithm is verified by simulation using open source software Webots. The results show that when the robot moves at an average speed of 0.5 m/s, the lateral displacement change of the robot is less than 0.009 m, the height change is less than 0.003 m, and the rotating angles around the x, y, and z axes are less than 0.0036 rad, 0.0013 rad, and 0.001 rad, respectively. [ABSTRACT FROM AUTHOR]

In order to improve the wavefront reconstruction accuracy of a large-aperture laser, this paper proposed an adaptive window preprocessing algorithm based on the threshold center of gravity method (AW-TCoG). The effects of median filtering and mean filtering on spot image processing and wavefront reconstruction accuracy are simulated and analyzed. The results show that the mean filtering method has a better effect on noise elimination and can further improve the accuracy of wavefront reconstruction. In addition, the centroid detection errors of large-aperture laser wavefront reconstruction through the center of gravity (CoG), the threshold center of gravity (T-CoG), and the Windowing method were studied. The analysis shows that, due to the influence of noise, the wavefront reconstruction accuracy is poor when the CoG and Windowing methods are used to calculate centroid parameters, while the wavefront reconstruction accuracy of the threshold centroid method is better and can reach 0.2λ. When using the AW-TCoG proposed in this paper, the wavefront reconstruction accuracy can be maintained within 0.1λ for different incident wavefront RMS values and spot images with different signal-to-noise ratio (SNR) levels. Compared with the traditional threshold centroid method, the wavefront reconstruction accuracy of this method is significantly improved. [ABSTRACT FROM AUTHOR]

To accurately describe the killing effect of missiles especially dealing with the small or fast target, a new method for calculating the killing effect of missiles is proposed in this paper. The missile and the target are divided into several basic geometries based on their shapes, and then the equations of these geometries are established in their local frame. The mass center motion equations of the target and the missile are determined in the light of their initial positions and velocities, respectively, and every geometry moves with its center of mass according to its attitude. The equations of the fuze view field and the target can confirm whether the fuze detects the target, and whether the fragment hit the target can be certified by the same approach. This paper also writes a MATLAB simulation program for this calculation method and designs a new algorithm to determine the position relationship of space geometry using existing functions, and the simulation verifies the effectiveness of this method. [ABSTRACT FROM AUTHOR]

Ball-shell rotors with non-standard shapes, non-uniform conductive coatings, and eccentric masses machined by conventional processes constrain the improvement of levitation and torque accuracy of magnetically levitated momentum balls. This paper focuses on the machining method of multilayer ball-shell rotors to develop a ball-shell rotor with a standard shape and uniform conductive coating, which can improve the levitation and torque accuracy of magnetically levitated momentum balls. In this paper, a machining method for multi-coated ball-shell rotors is proposed. The machining process combining hemispherical surface and workpiece is adopted, and the whole sphere is assembled by threading, which effectively reduces the machining error. The influence of the cutting depth and feed rate of the tool on the cutting force of the ball shell was analyzed through the cutting force model. The effect of cutting force on the deformation of the ball shell was analyzed by the finite element method. The superiority of the machining method was verified by measuring the dimensions of the ball shell with a coordinate measuring machine. Compared with the traditional machining process and assembly method, the proposed ball-shell rotor machining method effectively improves the dimensional accuracy, reduces the center of mass to center of mass deviation, and ensures the levitation accuracy and output torque accuracy of the magnetically levitated momentum ball. Measurement results show that the diameter values of the pure iron ball shell are between 98.694 and 98.707 mm with a machining error of ±0.007 mm, and the diameter values of the spray-painted ball shell are between 99.490 and 99.510 mm with a machining error of ±0.01 mm. The machining static equilibrium of the pure iron ball shell and the spray-painted ball shell is good by the static equilibrium test method. [ABSTRACT FROM AUTHOR]

Flight maneuver recognition (FMR) is a critical tool for capturing essential information about the state of an aircraft, which is necessary to improve pilot training, flight safety, and autonomous air combat. However, due to the alignment of multidimensional, multimodal time series and insufficient data, challenges exist that limit the accuracy of FMR. In this paper, two FMR methods, including an improved dynamic time-warping distance-based algorithm (D-DTW) and a perceptually important point-based method, are proposed based on time series mining techniques. The differential dynamics equations of the aircraft's center of gravity in the trajectory coordinate system are established. Subsequently, based on the obtained flight data, the engine thrust is derived by employing criteria based on flight mechanics and coordinate system transformation methods. Finally, the flight profile is clustered and divided based on the preprocessed data. The engine load factor is obtained through centroid transformation and coordinate system translation based on flight dynamics calculations. The results indicate that the two methods exhibit varying applicability with respect to FMR. However, the second method is more suitable regarding the recognition or prediction of engine thrust and load factor. [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]

The variable-sweep wing, as an important morphing wing technology, has received widespread attention because it can change the sweep angle according to different flight conditions. It has the advantage of simultaneously utilizing a large sweep angle to reduce shock wave drag at high speeds and improving lift characteristics at small sweep angles. However, it has always been the case that the variable-sweep wing will bring about a rearward shift of the center of gravity when the sweep angle increases, leading to a decrease in aircraft stability. This paper focuses on a structural design of a variable-sweep wing based on a four-bar planar linkage. The novel variable-sweep wing structure containing a four-bar planar linkage and an outer wing section is proposed, and key parameters are extracted to establish a mathematical model of the mechanism. Through parametric analysis, main parameters have been identified, and the structure is optimized: the longitudinal position (direction of the fuselage) of the wing's center of gravity is designed to maintain minimal change during the morphing process, but remain the same at both the beginning and ending states of the transformation. The structural design of the variable-sweep wing is carried out based on this. Then, the finite-element model is established to validate the load-bearing capacity of the variable-sweep wing and derive the driving force. Finally, as one of the main novelties, a full-size prototype is successfully manufactured for load testing. The results of finite-element simulation and load testing show that this variable-sweep wing structure can achieve movement from 30° to 70° under an aerodynamic load that is up to 460 kg/m2. The present study demonstrates the effectiveness and potential of the proposed morphing trailing edge concept for real application on aircraft. [ABSTRACT FROM AUTHOR]

To solve the problem that the robot often collides with the obstacles such as branches around the fruit during picking due to its inability to adapt to the fruit growing environment, this paper proposes an apple-picking robot picking path planning algorithm based on the improved PSO. The main contents of the algorithm are: firstly, the fruit and its surrounding branches are extracted from the 3D point cloud data, and the picking direction of the fruit is calculated; then the point cloud on the surface of the fruit and branches is used to establish the spatial model of obstacles; finally, an improved particle swarm optimization (PSO) algorithm is proposed to plan the obstacle avoidance trajectory of the end-effector in space, which can dynamically adjust the velocity weights according to the trend of the particle fitness value and the position of the particle swarm center of mass. The experimental results show that the improved PSO has faster convergence speed than the standard PSO, and the path planning method proposed in this paper improves the fruit-picking success rate to 85.93% and reduces the picking cycle to 12 s. This algorithm can effectively reduce the collision between the manipulator and branches during apple picking and improve the picking success rate and picking efficiency. [ABSTRACT FROM AUTHOR]

In this paper, the author proposes a novel solution to evaluate the dependence between the maximum roll angle and the minimum vertical force at the wheel on the vehicle's height and speed. 4D graphs that fully and clearly describe the dependence between parameters are used to replace conventional 2D and 3D graphs. A complex dynamic model is established to describe the vehicle's oscillations when steering. Calculations and simulations are performed using Simulink® software with many specific cases. In all cases, the input values such as steering angle, speed, and distance from RA (roll axis) to CG (the center of gravity), all change flexibly. According to the paper's findings, the roll angle will rise once speed or height increases. In addition, the maximum roll angle increases significantly once both the velocity and the height increase. This causes the vertical force at the wheel to drop suddenly, and rollover may occur if this value reduces to zero. 4D graphs provide a more specific and intuitive assessment of vehicle rollovers. [ABSTRACT FROM AUTHOR]

The efficient design of the aerodynamic surfaces in the aircraft allows the optimal performance of the vehicle and the reduction of the fuel consumption. Among these surfaces, the wing is the main contributor to the force which lifts the aircraft enabling the flight. However, the application of this force out of the center of gravity generates a moment that must be balanced through a force applied in the Horizontal-Tail-Plane (HTP) reaching the longitudinal trim of the aircraft. Traditionally, the design of the wing and HTP have been performed iteratively attaining suboptimal or time ineffective results. In this paper, we solve this problem through the application of a Genetic Algorithm for the combined optimization of the wing and the HTP by adjusting the aspect ratio, the taper ratio, the twist angle and the incidence angle of both surfaces to produce the optimal balance of lift adjusting its distribution to an elliptical configuration and enabling the longitudinal trim. Results show the automatic adjustment of the parameters of the aerodynamic surfaces thus fulfilling the objectives of this paper. [ABSTRACT FROM AUTHOR]