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We study experimentally and theoretically the dynamics of permanent paramagnetic chains and mixed clusters formed by permanent paramagnetic chains and paramagnetic particles under the influence of a time-varying magnetic field. First, we examine the dynamics of permanent chains at high frequencies (∼50 to 1000 Hz). These permanent chains exhibit continuous rotational motion with a frequency several orders of magnitude lower than that of the magnetic field. We develop a theoretical model that accurately describes the dependence of the rotational dynamics of chains on their length, as well as the amplitude and frequency of the external magnetic field in this high frequency regime. Next, we examine how cluster dynamics are affected by the presence of permanent chains. We show that the rotation of clusters composed of a high proportion of permanent chains is slowed down but remains qualitatively well described by the theoretical model we developed for homogeneous clusters of isotropic particles. We propose that the decrease in angular velocity for mixed clusters is due to the hardening of the cluster's 2D elastic modulus caused by the increase of the steric interaction parameter stemming from the presence of chemical links between particles in the chains. [ABSTRACT FROM AUTHOR]

Magnetic skyrmion bags are composite topological spin textures with arbitrary topological charges. Here, we computationally study the transient rotational motion of skyrmion bags, which is characterized by a global rotation of inner skyrmions around the central point. Distinct from conventional rotational modes found in skyrmions, the observed rotation is a forced motion associated with the breathing mode induced solely by vertical microwave fields. The driving force behind this rotation originates from the interactions between outer and inner skyrmions, with the angular velocity determined by the phase difference resulting from their asynchronous breathing behaviors. It is also found that skyrmion bags with larger skyrmion numbers are more conducive to the occurrence of the rotation. Our results are useful for understanding the cluster dynamics of complex topological spin textures driven by dynamic fields. [ABSTRACT FROM AUTHOR]

In this study, laser Directed Energy Deposition technology is employed to fabricate internal structures within the hollow interiors of rotating parts such as tubes and cylinders. A three-dimensional transient multiphysics model for C276 material was developed, which anticipated the impact of angular velocity from tube rotation on various aspects. This model, validated by experiments, focused on the melt pool morphology, Marangoni convection, oriented crystal microevolution, and deposited material microhardness. It was found that at 150 ms deposition, the dimensions of the melt pool stabilized. With an increase in the Peclet number, heat transfer within the melt pool transitioned from conduction to convection. A rise in angular velocity reduced the melt pool deposition height, limited by the volume of the deposited material. Additionally, this angular velocity generated tangential forces, leading to an asymmetric melt distribution in the longitudinal section of the melt pool and a movement of the melt toward the melting front. At the bottom of the melt pool, the growth of C276 columnar crystals was notably inclined toward the center of Marangoni convection. The microhardness of the deposited material showed a stable distribution along the inclined crystal direction, whereas significant fluctuations were observed perpendicular to the cylinder substrate. These findings highlighted the considerable effect of Marangoni convection on microstructural evolution. [ABSTRACT FROM AUTHOR]

We present a derivation from the first principles of the coupled equations of motion of an active self-diffusiophoretic Janus motor and the hydrodynamic densities of its fluid environment that are nonlinearly displaced from equilibrium. The derivation makes use of time-dependent projection operator techniques defined in terms of slowly varying coarse-grained microscopic densities of the fluid species number, total momentum, and energy. The exact equations of motion are simplified using time scale arguments, resulting in Markovian equations for the Janus motor linear and angular velocities with average forces and torques that depend on the fluid densities. For a large colloid, the fluid equations are separated into bulk and interfacial contributions, and the conditions under which the dynamics of the fluid densities can be accurately represented by bulk hydrodynamic equations subject to boundary conditions on the colloid are determined. We show how the results for boundary conditions based on continuum theory can be obtained from the molecular description and provide Green–Kubo expressions for all transport coefficients, including the diffusiophoretic coupling and the slip coefficient. [ABSTRACT FROM AUTHOR]

• A fixed-time dynamic surface attitude controller for the tethered chained satellite system has been designed. • The proposed algorithm explicitly considers control input constraints. • An extended state observer is introduced to achieve output feedback and lumped disturbance estimation. • The filter error of dynamic surface control is eliminated by the compensation module. A fixed-time attitude stabilization scheme based on dynamic surface control (DSC) is proposed for the attitude of the three-body chained tethered system during tether deployment. Considering that the angular velocity of the satellite is difficult to measure, an extended state observer (ESO) is introduced to simultaneously compensate for the adverse effects of flexible panel vibrations and uncertain inertia tensors. On this basis, a fixed-time convergence attitude control scheme using DSC is designed, accounting for filtering error compensation. To offset the limitations of traditional fixed-time control strategies that ignore actuator saturation, an auxiliary system is introduced to incorporate control input constraints directly into controller design. The stability of the closed system is analyzed based on Lyapunov theory. Finally, the effectiveness and superiority of the proposed algorithm are verified by numerical simulation. [ABSTRACT FROM AUTHOR]

• A comparative assessment of the "surveying" vs. "tracking" strategy is discussed, to reach a better inventory of the orbiting population at a certain epoch. • Objective criteria are outlined for a best trade-off between telescope field of viev (FOV), CCD/CMOS platescale, telescope aperture and exposure time in order to maximize target(s) detection and astrometry. • Counter-intuitive aspects are discussed, compared with a more classical "astronomical" approach, delving the inherent link between time-tag accuracy and resolving power of optical imagery to track LEO objects. The main technical and strategic aspects related to Space Surveillance and Tracking (SST) with optical sensors are set in context in this study to lead to an efficient inventory of the active satellites and un-cooperant space debris population at Low-Earth orbital regimes (LEO). In particular, special emphasis is devoted to the combined interplay between timing of observations, target illumination conditions, instrumental fine tuning and data acquisition mode (surveying vs. active tracking). At LEO altitudes, satellites are seen to cross the sky at very high angular velocity, in excess to 0.5–1.5 deg/sec, always making their positional measurements (and the inferred dynamical properties) a challenging task for ground telescopes. To this aim, objective criteria have to be identified for a best trade-off between instrument field of viev (FOV), CCD/CMOS platescale, telescope aperture and exposure time in order to maximize target(s) detection and reference grid of stars valuable for astrometry. Many counter-intuitive aspects are discussed in this regard, compared for instance with a more classical "astronomical" approach, delving in particular the widely recognized inherent link between time-tag accuracy and resolving power of optical imagery to track LEO objects. A number of tables and graphical plots are provided for practical use to the reader. [ABSTRACT FROM AUTHOR]

Integral forms of Eringen's nonlocal theory are employed to model nanoscale constitutive relations without possible potential paradoxes. The Timoshenko beam theory as well as the element-free Galerkin method are accepted to model rotating nanobeams and develop numerical solutions of critical rotating angular velocities for nanobeams. Optional setting angles as natural defects are taken into account in buckling analyses. Important design parameters, including length-to-height ratios, ratios of hub radii to lengths, setting angles, and additional supports are carefully assessed between local and nonlocal beams. [ABSTRACT FROM AUTHOR]

The effects of viscous force on magnetohydrodynamic flow in coaxial cylinders are discussed in this article. The inner cylinder stretches linearly along the axis, while the outer cylinder rotates with some fixed angular velocity. The movement of the fluid between these concentric cylinders depends on the stretching of the inner cylinder and the outer cylinder's rotation. Understanding this type of flow is crucial for applications in engineering and industrial processes, such as magnetic materials processing and fluid transport in rotating machinery. The inner cylinder's surface is also considered slippery, that is, the first order slip condition is incorporated on the internal cylinder surface. The impact of viscous dissipation is also calculated in the current study. After using suitable transformations, we turn mass conservation, Navier‐stokes, and energy equations into dimensionless ordinary differential equations. Meanwhile, the numerical solutions of these equations are conducted via the shooting method. The numerical outcomes are graphically presented by varying the values of some certain parameters like the curvature parameter, the gap between the cylinders, the magnetic parameter, the slip parameter, and so forth. It is noted that the expanding gap size enhances the velocity of the fluid, accompanied by a rise in the fluid temperature. Additionally, the findings indicate that cylinders with a smaller gap exhibit a higher heat flux rate. The novelty of this work lies in the combined effects of viscous dissipation, slip conditions, and MHD on flow and heat transfer, offering insights beyond what has been previously explored in the literature. [ABSTRACT FROM AUTHOR]

[Display omitted] • EEG can track modulation of cortical proprioceptive processing to joint rotations. • Volitional muscle activation intensifies the cortical proprioceptive processing. • Cortical inhibition is enhanced during passive joint-rotation stimulation. • Mechanisms likely at muscle, spinal, sub-cortical and cortical levels. Cortical proprioceptive processing of intermittent, passive movements can be assessed by extracting evoked and induced electroencephalographic (EEG) responses to somatosensory stimuli. Although the existent prior research on somatosensory stimulations, it remains unknown to what extent ongoing volitional muscle activation modulates the proprioceptive cortical processing of passive ankle-joint rotations. Twenty-five healthy volunteers (28.8 ± 7 yr, 14 males) underwent a total of 100 right ankle-joint passive rotations (4° dorsiflexions, 4 ± 0.25 s inter-stimulus interval, 30°/s peak angular velocity) evoked by a movement actuator during passive condition with relaxed ankle and active condition with a constant plantarflexion torque of 5 ± 2.5 Nm. Simultaneously, EEG, electromyographic (EMG) and kinematic signals were collected. Spatiotemporal features of evoked and induced EEG responses to the stimuli were extracted to estimate the modulation of the cortical proprioceptive processing between the active and passive conditions. Proprioceptive stimuli during the active condition elicited robustly ∼26 % larger evoked response and ∼38 % larger beta suppression amplitudes, but ∼42 % weaker beta rebound amplitude over the primary sensorimotor cortex than the passive condition, with no differences in terms of response latencies. These findings indicate that the active volitional motor task during naturalistic proprioceptive stimulation of the ankle joint enhances related cortical activation and reduces related cortical inhibition with respect to the passive condition. Possible factors explaining these results include mechanisms occurring at several levels of the proprioceptive processing from the peripheral muscle (i.e. mechanical, muscle spindle status, etc.) to the different central (i.e. spinal, sub-cortical and cortical) levels. [ABSTRACT FROM AUTHOR]

Golf is an international sport that has become increasingly more popular in recent times. Previous literature has shown that golf approach shots are crucial to the success of elite golfers. However, there is no known publication investigating distances less than 100 yards, known as the short game. The primary purpose of this study was to collect comprehensive data on 3D biomechanical variables of the short game at four target distances in college-aged, male golfers. Participants were instructed to hit five successful shots at each target distance: 30 yards, 50 yards, 70 yards and full swing (maximal distance) yardage. A motion capture system recorded kinematic and temporal parameters of golfer movement, additional to a golf simulator that collected ball carry distance of each shot. Distance did have a significant (p ≤ 0.05) effect on swing phase timing, angular velocities and motion sequencing. Movement sequencing within the short game displayed irregular patterns across all distances and phases, with a partial proximal-to-distal pattern (pelvis → shoulder girdle → arms → club) at best. The findings of this study show that the short game swing did present its own unique motion patterns that will require practice as its own skill. [ABSTRACT FROM AUTHOR]

Background: This research aims to compare the differences in kinematic parameters associated with cross and uppercut punches between Sanda athletes (SA) and Boxing athletes (BA) to analyze their impacts on peak punching speed. Methods: The punches of BA (n = 20) and SA (n = 20) were compared utilizing a three-dimensional (3D) framework and high-speed cameras in terms of 13 key parameters. An independent samples t -test (α = 0.05) was employed to analyze the differences in punching between BA and SA. Meanwhile, a stepwise multiple linear regression equation was developed to analyze the influence of selected parameters on peak punching speed. Results: The results reveal that, among the 13 kinematic parameters, the six cross-related parameters and four uppercut-related parameters are significantly different (both p ≤ 0.05). The results of multivariate regression analysis unveils that the peak punching speed for the cross are influenced by the anteroposterior position of the center of gravity (in BA) and the maximum angular velocity of the shoulder (in SA). In contrast, for both BA and SA, the maximum angular velocity of the shoulder plays a critical impact on uppercut. Conclusions: These findings indicate that trunk and upper limbs significantly influence the peak punching speed, which provides suggestions for daily training regimen of SA and BA as well as their coaches. [ABSTRACT FROM AUTHOR]

The purpose of this study was to compare the joint, racket, and ball kinematics between the different levels of male tennis players in tennis serve-return at slow and high serve speeds. Thirty male tennis players were divided into an advanced group (n = 15) and an intermediate group (n = 15) based on skill level. The advanced group and intermediate group matched shake hand-grip players performed serve-receive test at the different serve speeds. Kinematic data were collected on the trunk, upper limbs, racket and ball to compare the differences between the advanced and intermediate groups at different serve speeds. At both serve speeds, the AG has faster racket speed and ball speed, and is closer to the baseline placement (p<0.05). It is characterized by a faster trunk turn, greater speed with the shoulder joint forward and outward and greater angle of wrist flexion and extension during the stroke (p<0.05), and greater speed with the forearm inward and internal rotation during the follow-through swing, at the same time, there is a difference in the angle of the racket to the ground between the advanced group and an intermediate group(p<0.05). Elbow internal rotation and abduction angular velocity in the backswing phase, Timing of peak racket resultant velocity and Wrist extension in the stroke phase, and shoulder and elbow joint activities in the follow-through phase were significantly correlated with the ball speed of the return. With faster serve speeds, higher quality serve-receive can be achieved by shortening the duration of the backswing lifting the upper arm and rotating the forearm inward quickly, accelerating the speed of movement of wrist joints at the impact phase, adjusting the speed of shoulder adduction and elbow internal rotation to complete the follow-through swing. These findings help to improve elite players' serve-receive skills at faster serve speed. [ABSTRACT FROM AUTHOR]

Pipelines are critical components in various industrial applications, responsible for the safe and efficient transportation of fluids and gases. However, over time, these structures experience a reduction in wall thickness due to prolonged service, which can significantly compromise their structural integrity. To address this issue, a rapid and non-contact method for measuring pipe thickness is proposed. This method utilises the angular velocity invariance of circumferential SH1 (CSH1) guided waves, generated by a wholly stepped electromagnetic acoustic transducer (EMAT), which is specifically designed for effective in-line inspection. The novel EMAT improves the excitation efficiency of the CSH1 mode, allowing the dispersive CSH1 mode to effectively collect information from both circumferential directions of the pipeline. Finite element simulations and experimental validation on a defective aluminium pipe demonstrated the method’s accuracy, achieving a relative error of less than 0.5%. This technique offers a contactless, reliable baseline for pipeline condition assessment, unaffected by lift-off, and significantly improves defect detection and real-time condition monitoring, making it suitable for potential robotic inspection applications. [ABSTRACT FROM AUTHOR]

To solve the problems of difficulty in speed measurement and low accuracy of speed measurement of induction motor (IM) during fast starting, the electromagnetic field coupling circuit (EFCC) and open‐loop control of IM considering rapid speed change are proposed. First, the EFCC of IM is established through the stator circuit, air gap magnetic field circuit and rotor circuit, and the stator voltage and electromagnetic torque of the fast starting process are deduced from the air gap magnetic density on the basis of constant slip angular velocity, and then the open‐loop control method based on the EFCC is given. Finally, compared with the open‐loop control based on the TEC, the results of simulation and experiment show that the open‐loop control based on the EFCC can follow the acceleration starting more quickly and the starting current is smaller, which is conducive to reducing the cost of the drive. [ABSTRACT FROM AUTHOR]

Balance control, a complex sensorimotor skill, declines with age. Assessing balance is crucial for identifying fall risk and implementing interventions in the older population. This study aimed to measure age-dependent changes in static and dynamic balance using inertial measurement units in a clinical setting. This study included 82 healthy participants aged 20–85 years. For the dynamic balance test, participants stood on a horizontally swaying balance board. For the static balance test, they stood on one leg. Inertial measurement units attached to their bodies recorded kinematic data, with average absolute angular velocities assessing balance capabilities. In the dynamic test, the younger participants had smaller average absolute angular velocities in most body parts than those of the middle-aged and older groups, with no significant differences between the middle-aged and older groups. Conversely, in the single-leg stance tests, the young and middle-aged groups outperformed the older group, with no significant differences between the young and middle-aged groups. Thus, dynamic and static balance decline at different stages with age. These results highlight the complementary role of inertial measurement unit-based evaluation in understanding the effect of age on postural control mechanisms, offering valuable insights for tailoring rehabilitation protocols in clinical settings. [ABSTRACT FROM AUTHOR]

Traditional rehabilitation training for stroke patients with ankle joint issues typically relies on the expertise of physicians. However, when confronted with complex challenges, such as online decision-making or assessing rehabilitation progress, even seasoned experts may not anticipate all potential hurdles. A novel approach is necessary—one that effectively addresses these complexities without solely leaning on expert experience. Previous studies have introduced a rehabilitation assessment method based on fuzzy neural networks. This paper proposes a novel approach, which is a VR-aided ankle rehabilitation decision-making model based on a convolutional gated recurrent neural network. This model takes various inputs, including ankle dorsiflexion range of motion, angular velocity, jerk, and motion performance scores, gathered from wearable motion inertial sensors during virtual reality rehabilitation. To overcome the challenge of limited data, data augmentation techniques are employed. This allows for the simulation of five stages of rehabilitation based on the Brunnstrom staging scale, providing tailored control parameters for virtual training scenarios suited to patients at different stages of recovery. Experiments comparing the classification performance of convolutional neural networks and long short-term memory networks were conducted. The results were compelling: the optimized convolutional gated recurrent neural network outperformed both alternatives, boasting an average accuracy of 99.16% and a Macro-F1 score of 0.9786. Importantly, it demonstrated a strong correlation (correlation coefficient r > 0.9) with the assessments made by clinical rehabilitation experts, showing its effectiveness in real-world applications. [ABSTRACT FROM AUTHOR]

This study aimed to determine the characteristics of accelerations and angular velocities obtained by an inertial measurement unit (IMU) attached to a cane between older people with and without physical frailty. Community-dwelling older people walked at a comfortable speed using a cane with a built-in IMU. Physical frailty was assessed using exercise-related items extracted from the Kihon Check List. The efficacy of five machine learning models in distinguishing older people with physical frailty was investigated. This study included 48 older people, of which 24 were frail and 24 were not. Compared with the non-frail participants, the older people with physical frailty had a small root mean square value in the vertical and anteroposterior directions and angular velocity in the anteroposterior direction (p < 0.001, r = 0.36; p < 0.001, r = 0.29; p < 0.001, r = 0.30, respectively) and a large mean power frequency value in the vertical direction (p = 0.042, r = 0.18). The decision tree model could most effectively classify physical frailty, with an accuracy, F1 score, and area under the curve of 78.6%, 91.8%, and 0.81, respectively. The characteristics of IMU-attached cane usage by older adults with physical frailty can be utilized to effectively evaluate and determine physical frailty in their usual environments. [ABSTRACT FROM AUTHOR]

This article addresses critical challenges in the transition to clean energy sources by highlighting the importance of advanced mathematical modeling and computational techniques in turbine design and operation. Specifically, we extend and generalize the work of Camporeale to advance the modeling of hydrogen turbine systems. By utilizing conformable calculus, we develop dynamic equations that analyze key aspects of turbine performance, including temperature variations in turbine blades, angular velocities of rotating shafts, and mass–energy balances within the plenum and combustion chamber. Furthermore, we incorporate Kirchhoff's equation in its generalized conformable integral form, enhancing the precision of energy balance calculations and improving the representation of heat transfer processes in the combustion chamber. This methodology introduces novel perspectives in hydrogen turbine research, contributing to the advancement of sustainable and efficient technologies. Our comprehensive approach aims to provide more accurate and efficient predictions of turbine behavior, thereby impacting the design and optimization of hydrogen-based clean energy systems. [ABSTRACT FROM AUTHOR]

Purpose: Eccentric quasi-isometric (EQI) resistance training is emerging as a promising option in sports medicine and rehabilitation. Despite prior research on EQI contractions in quadriceps and biceps brachii, their use in hamstring injury contexts is underexplored. Therefore, our study examines and contrasts the biomechanics and fatigue effects of EQI training on knee extensors and flexors. Methods: Following familiarization, 16 healthy, active participants (9 men, 7 women; 23.5 ± 2.6 years, 72.1 ± 12.8 kg, 173.4 ± 10.7 cm) performed, in random order, four EQI contractions for knee extensions and flexions, respectively. EQI contractions were isotonically loaded to 70% of concentric (60°·s−1) maximal voluntary contraction. Rest between repetitions was set at three minutes, while four minutes separated each muscle group. Peak torque, mean torque, and optimal angle were evaluated pre- and post-bouts. Inter-repetition contraction time and angular velocity were also assessed. Results: Average torque was 160.9 ± 44.2 and 71.5 ± 23.2 Nm for the extensors and flexors. Peak and mean torque significantly decreased for both extensors (p < 0.001, d = 0.70–0.71) and flexors (p ≤ 0.022, d = 0.36) after EQI contractions, respectively. However, the optimal angle increased for extensors (p < 0.001, d = 1.00) but not flexors (p = 0.811, d = 0.06). During EQI contractions, knee flexors exhibited greater intra-repetition velocity than extensors (p = 0.002; η2 = 0.50). Decreases in inter-repetition time and range of motion were more consistent for the extensors. Conclusions: Distinct responses exist when comparing EQI contractions of the knee extensors and flexors, particularly their effect on peak torque angles. These findings suggest knee flexors may require lower relative intensities to align more closely with extensor EQI contractions. [ABSTRACT FROM AUTHOR]

The current investigation deals with the deformation of a non-homogeneous thermoelastic half space under hydrostatic initial stress for the Green–Naghdi model III. The medium is supposed to be rotating with a constant angular velocity. The non-homogeneous properties of the material are along the x-direction. At the first instance, the problem has been solved analytically to obtain stress and displacement components. Further, the numerical values of these expressions are evaluated using a computer program for a particular medium. The numerical values obtained are then presented graphically to show the effect of initial stress parameter and non-homogeneity parameter on the quantities. [ABSTRACT FROM AUTHOR]

Systematic atomistic simulations of oblique collisions between spherical crystalline, 6H and 3C, and amorphous SiC nanoparticles (NPs) are performed in the bouncing and fragmentation regimes for the particles with diameters from 8 nm to 30 nm, impact velocities from 100 ms−1 to 5000 ms−1, and in the whole range of the geometric impact parameter. The critical sticking velocity of 6H-SiC NPs reduces from ∼490 ms−1 to ∼150 ms−1 when the NP diameter increases from 10 nm to 30 nm. Below the melting threshold, the collision of crystalline NPs induces the formation of localized zones of densified material, while the remaining parts of NPs are not affected by plastic deformations. The impact of amorphous NPs results in the plastic deformation of significant parts of the NP material and much larger irreversible losses of mechanical energy. The post-collision translational and rotational velocities of crystalline NPs as well as coefficients of restitution (CORs) demonstrate weak dependence on the NP size if the NP diameter is greater than 20 nm. At constant impact velocity, the normal COR only marginally varies for head-on and oblique collisions, when the collision angle is smaller than ∼53°. The tangential center-of-mass and point-of-contact CORs, as functions of the impact parameter, demonstrate extremal behavior with the minima at collision angles from ∼27° to ∼37°. The normal COR exhibits a linear decay as a function of the impact velocity where the slope coefficient is different below and above the melting threshold. The tangential CORs attain the minimum values at the impact velocity of ∼300 ms−1. The obtained results are summarized in the form of fitting equations for CORs as functions of the impact parameter and velocity, which can be readily used to predict the post-collision translational and angular velocities of NPs in large-scale simulations of granular gas flows. [ABSTRACT FROM AUTHOR]

With considerably small structure and ultrahigh sensitivity, the graphene resonant gyroscope has been widely used in aviation, aerospace and deep-sea exploration where sensing the extremely weak angular velocity changes is required. However, small difference in the size of graphene resonant gyroscope caused by inherent uncertainties in various processing and material parameters will lead to huge differences in the output results. This will reduce the reliability of graphene resonant gyroscope. Based on the above issues, the uncertainty analysis method is adopted to establish a numerical model on the direct output resonant frequency and sensitivity of the graphene resonant gyroscope, and a random model based on sampling is introduced. The influence of the uncertainty of six input parameters on the graphene resonant frequency and sensitivity output is clarified, and thus the effect degree of the main parameters, which play a key role in the performance of the graphene resonant gyroscope, is obtained. The results show that the length, width and thickness of the graphene resonant beam have greater impacts on the output parameters, which provides theoretical guidance for the graphene resonant gyroscope to adapt to different measurement ranges. [ABSTRACT FROM AUTHOR]

This paper proposes a saturation-optimized, quasi-sliding-mode model-free adaptive control (SM-MFAC) method to control the postcollision calming motion of an unstable free-flying space robot with saturated output torque. Initially, the dynamics model of the unstable free-flying space robot is transformed into a class of multiple-input, multiple-output (MIMO) discrete-time nonlinear systems. Here, the system characteristics can be estimated based on measured base attitude and joint angle data. The discrete sliding-mode control helps calculate the desired angular velocity at the current moment. Next, Hildreth's method is used to introduce constraints to the control input criterion function for real-time tracking of the desired angular velocity, which enables the completion of the calming motion control of the free-flying space robot. The proposed algorithm simplifies the traditional calming motion control process by avoiding complex and redundant modeling requirements, ensuring that the control torque remains within predefined limits to optimize possible saturation. It also proves the convergence of the system output theoretically, and good stability and dynamic characteristics of the control scheme are verified through numerical simulations. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of guiding a rocket-powered vehicle to land using aerodynamic and thrust controls. The vehicle initially glides towards the landing site, flying at an unprecedentedly high angle-of-attack to decelerate, thereby reducing the propellant needed for a later retro-thrust landing. The high angle-of-attack pure aerodynamic flight leads to highly nonlinear dynamics that have not been addressed by existing powered descent guidance methods. In particular, real-time optimization of the vehicle's landing trajectory has been very challenging. In this paper, a closed-loop guidance method is proposed that optimizes a restricted 6-degrees-of-freedom (6-DoF) trajectory in real-time. To remedy the difficulty caused by the highly nonlinear dynamics, the general propellant-optimal problem is regularized with two modifications. The first is to augment the angular velocity to the performance index, removing possible singularity arcs that cause numerical difficulties. The second is to parameterize the thrust magnitude with a piecewise-constant form, reducing the number of control variables to be optimized. The regularized problem is then solved with successive convexification to update the restricted 6-DoF landing trajectory in each guidance cycle. Monte Carlo experiments with aerodynamic and thrust dispersions are conducted to examine the proposed guidance method. • A new guidance method is proposed that uses both aerodynamic and thrust controls. • The guided vehicle can fly at unprecedentedly high angle-of-attack to decelerate. • The guidance method optimizes a restricted 6-degree-of-freedom trajectory in real-time. • The guidance problem is regularized twice to address the highly nonlinear dynamics. [ABSTRACT FROM AUTHOR]

(1) Background: This case study analyzed the successful performances of female gymnasts in the finals of the 39th and 40th World Cup in Maribor (SLO). The aim was to identify variations in their execution of the Clear Hip Circle to Handstand (CHCH) on uneven bars based on kinematic parameters. (2) Methods: This study involved elite female gymnasts from the 39th (n = 5, age: 17 ± 6 months) and 40th (n = 8, age: 17.5 ± 6 months) World Cups, totaling 13 gymnasts. Kinematic analysis was performed on 15 successful routines using the Ariel Performance Analysis System (Ariel Dynamics Inc., San Diego, CA). The analysis focused on 16 anthropometric reference points and 8 body segments, including the body mass center of gravity (CG). The main reference points analyzed were the hip joint, the shoulder joint, and the CG along the xy-axes. Trajectory, velocity, angle, and angular velocity of the hips and shoulders were calculated. Pearson correlation analysis was employed to assess the relationships between the kinematic variables. (3) Results: High intercorrelations between the reference points along the xy-axes (0.81–0.99) and optimal movement velocity were found. Dispersed results were observed for kinematic parameters of angle (0.10–0.16) and angular velocity of the hip joints (0.60–1.00), with similar dispersions for shoulder joints (0.51–1.00). Three distinct techniques were identified: (1) stretched body with minimal hip joint flexion throughout; (2) extended body with a short, quick hip joint extension during shoulder movement; and (3) hyperextension in the hip joint. (4) Conclusions: The kinematic analysis revealed three different performance styles of the CHCH among finalists. These variations in technique do not affect the success of the performance. This research contributes to a better understanding of the technique but does not prefer one style over another. [ABSTRACT FROM AUTHOR]

In this paper, an energy-saving scheme in rotor field-orientated vector control is developed for induction motor drives. The energy-saving scheme minimizes copper and core losses in induction motors, which are equally applicable to induction generators. In efficiency optimization, an optimal stator angular velocity is uniquely obtained, and consequently, a corresponding optimal slip at any given rotor speed is determined. The challenge of determining a reference for rotor flux linkage that guarantees the minimal copper and core loss regime is overcome by developing a load torque observer loop. The torque observer is developed alongside a rotor speed observer for a sensorless speed operation. The observed mechanical torque is further used to enhance the outer-loop rotor speed control that generates an electromagnetic torque command used in building the reference for the inner-loop stator current control. The results obtained justified the effective operation of the torque and rotor speed observer, which consequently verified the effective minimal electrical loss regime at the optimal stator angular velocity and optimal rotor flux linkage. The results are further compared to results obtained from the equivalent induction machine drive on a finite-set model predictive control (FS-MPC) scheme with the same values of the optimal stator angular velocity and optimal rotor flux linkage. The developed efficiency-optimized vector control scheme gave lower ripples in developed electromagnetic torque and dampened overshoot better during step change in load torque. [ABSTRACT FROM AUTHOR]

Fluids with microstructures and microinertia play a vital role in microfluidics and nanfluidics system. One of such significant fluid is micropolar fluid. The characteristic behavior of micropolar fluid flow in conduit/pipe, etc. filled with porous medium helps us understand the flow behavior of biological fluids in porous media, groundwater flow in aquifiers, rotatory machines or viscometer. To understand such real-world problems, it is necessary to get into the mathematical model of such flow models. One such model with wide number of application is presented in this paper. This work investigated the flow of two micropolar fluids between the region formed by two concentric cylinders. Authors have considered inner cylinder to be at rest and outer cylinder rotating at a constant angular velocity. The region between two concentric cylinder is filled with an isotropic porous material. A slip condition at the outer wall and continuity conditions at interface of two fluids has been utilized to obtain an analytical solution for the proposed model. The numerical solution of the obtained solution for present problem is used to graphically analyze the motion of immisicble micropolar fluids rotating in an annulus filled with the porous medium. It is found that an outer cylinder has a notable influence on the flow behavior of immiscible micropolar fluids, contrary to the effect observed within the inner region. An analytical approach of this work not only helps us obtain precise results and analysis of the flow, but it also serves as a useful validation for future approximations within the scope of this work. [ABSTRACT FROM AUTHOR]

This paper presents an optimal design and simulation of a novel enhanced model reference adaptive proportional–integral–derivative controller (MRAPIDC) for underactuated nonlinear systems with parametric uncertainty. The controller is applied to a cart‐inverted pendulum mechanical system, a fourth‐order, nonminimum phase system with pronounced nonlinearity and unstable dynamics. This system includes a single input and multiple outputs, specifically the position and velocity of the cart, as well as the angle and angular velocity of the inverted pendulum arm. The main objective of the proposed controller is to maintain the pendulum in an upright position against gravity while moving the cart to a desired displacement regardless of parametric uncertainty, input variation, external disturbances, and random noise. The hybrid controller design is developed by combining the MRAPIDC design with controller gains applied to each output and incorporating the system adaptation error in a specific configuration. Optimal performance is achieved through parameter tuning via the social spider optimization (SSO) algorithm, and MIT (Massachusetts Institute of Technology) rule criteria are employed to ensure system stability. Performance improvements are demonstrated through several error indices, showing enhanced transient and steady‐state responses compared to both the reference model adaptive controller and the conventional proportional–integral–derivative (PID) controller. The proposed controller can effectively achieve system stability with a short settling time of 2.55 s and establishes a steady swinging balance within 2.9 s. [ABSTRACT FROM AUTHOR]

Mixing performance in reactors producing biogas through anaerobic digestion is one of the parameters that directly affect biogas yield. The most commonly used mixing model for bioreactors in biogas-production processes is mechanical mixing. In the present study, we focus on the geometry of the tank, where the mechanical mixing actually takes place. In this context, by using the six-blade standard Rushton impeller in two different types of tank, flow patterns involving velocity, dead zone volume, turbulent kinetic energy, and turbulent eddy dissipation rate in the angular velocity range of 25–100 rpm were observed, and the possible effects of the results on biogas production were interpreted. A new impeller design was proposed that maximizes the interface between the fluid inside the reactor tank and the impeller, which has the potential to reduce the dead zone volume to significantly lower levels. Our results showed that the lowest dead zone volume was achieved for a 60° slope reactor tank compared to the conventional 90° slope reactor tank at an angular velocity of 100 rpm. The dead zone volume decreased to 0.000094 m3 at 100 rpm in the 60° slope reactor tank with a total volume of 0.0305 m3, which by comparison was 0.000374 m3 in the 90° slope reactor tank. The magnitudes of both maximum turbulent kinetic energy and maximum turbulent eddy dissipation were higher in the 60° slope reactor tank at all angular velocities examined, which would be expected to enhance mixing performance. It is hoped that the reader will benefit from the results of this study; however, further studies should be conducted on the use of actual biowaste as the working fluid instead of water. [ABSTRACT FROM AUTHOR]

Simultaneous localization and mapping, a critical technology for enabling the autonomous driving of vehicles and mobile robots, increasingly incorporates multi-sensor configurations. Inertial measurement units (IMUs), known for their ability to measure acceleration and angular velocity, are widely utilized for motion estimation due to their cost efficiency. However, the inherent noise in IMU measurements necessitates the integration of additional sensors to facilitate spatial understanding for mapping. Visual–inertial odometry (VIO) is a prominent approach that combines cameras with IMUs, offering high spatial resolution while maintaining cost-effectiveness. In this paper, we introduce our uncertainty-aware depth network (UD-Net), which is designed to estimate both depth and uncertainty maps. We propose a novel loss function for the training of UD-Net, and unreliable depth values are filtered out to improve VIO performance based on the uncertainty maps. Experiments were conducted on the KITTI dataset and our custom dataset acquired from various driving scenarios. Experimental results demonstrated that the proposed VIO algorithm based on UD-Net outperforms previous methods with a significant margin. [ABSTRACT FROM AUTHOR]

Ankle–foot orthoses (AFOs) are commonly prescribed to children with cerebral palsy (CP). The conventional AFO successfully controls the first and second ankle rocker, but it fails to correct the third ankle rocker, which negatively effects push-off power. The current study evaluated a new powered AFO (PAFO) design, developed to address the shortcomings of the conventional AFO. Eight children with spastic CP (12.4 ± 3.4 years; GMFCS I-III; 4/4-♂/♀; 3/5-bi/unilateral) were included. Sagittal kinematic and kinetic data were collected from 20 steps during barefoot walking, with conventional AFOs and PAFOs. In the PAFO-condition, an actuation unit was attached to a hinged AFO and through push–pull cables to a backpack that was carried by the child and provided patient-specific assistance-as-needed. SnPM-analysis indicated gait cycle sections that differed significantly between conditions. For the total group, differences between the three conditions were found in ankle kinematics (49.6–66.1%, p = 0.006; 88.0–100%, p = 0.011) and angular velocity (0.0–6.0%, p = 0.001; 45.1–51.1%, p = 0.006; 62.2–73.0%, p = 0.001; 81.2–93.0%, p = 0.001). Individual SnPM-analysis revealed a greater number of significant gait cycle sections for kinematics and kinetics of the ankle, knee, and hip. These individual results were heterogeneous and specific per gait pattern. In conclusion, the new PAFO improved the ankle range-of-motion, angular velocity, and power during push-off in comparison to the conventional AFO. [ABSTRACT FROM AUTHOR]

A superhydrophobic cylinder is a circular cylinder with a boundary pattern of alternating shear-free menisci and solid portions. This article derives analytical solutions for the torque-driven Stokes flow around a superhydrophobic cylinder that is free to move, or 'swim', subject to the constraint that it is free of net force. The mathematical approach is a natural generalization of one used to solve for transverse shear flow over a superhydrophobic surface comprising a periodic array of no-shear slots (Crowdy 2011 Phys. Fluids23 (doi:10.1063/1.3605575)). First, the torque-driven Stokes flow around a superhydrophobic cylinder with two unequal no-shear menisci and two equal solid portions is solved in detail. It is then shown how that analysis generalizes, in a natural way, to a cylinder with M no-shear menisci between M solid portions with full exposition given of the case of M=3 equal solid portions. A further generalization to flow around a superhydrophobic cylinder with an N -fold rotationally symmetric patterning with M menisci in each 2π/N sector is made. Torque-driven superhydrophobic cylinders with a no-shear pattern devoid of any rotational symmetry are shown to swim on circular trajectories with formulas for the radius and cylinder angular velocity on these trajectories derived here as functions of the no-shear pattern geometry. The M=1 case of a 'Janus' superhydrophobic cylinder having one meniscus and one solid portion can be solved completely explicitly. [ABSTRACT FROM AUTHOR]

This study investigates the impact of variable permeability as well as chemical reactions on the oscillatory free convective flow that passes parallel porous flat plates with fluctuating temperature and concentration in the presence of a magnetic field. A vertical channel is assumed to be rotating at an angular velocity Ω. Periodic free stream velocity causes oscillations in one plate, while periodic suction velocity causes oscillations in the other plate. Complex variable notations are used to solve the governing equations. The perturbation technique is used to derive analytical expressions for the temperature, concentration, and velocity fields. In this study, various parameters were investigated in relation to mean velocity, mean temperature, mean concentration, amplitude, and phase difference. The study also examines the impact on secondary velocity, primary velocity, temperature, concentration, and heat transfer rate during transients. The outcomes are presented graphically for the physical parameters of the problem. The findings contribute to optimizing systems and improving efficiency in heat transfer, fluid dynamics, and environmental remediation. [ABSTRACT FROM AUTHOR]

The Wide Angle Search for Planets (WASP) survey used transit photometry to discover nearly 200 gas-giant exoplanets and derive their planetary and stellar parameters. Reliable determination of the planetary density depends on accurate measurement of the planet's radius, obtained from the transit depth and photodynamical determination of the stellar radius. The stellar density and hence the stellar radius are typically determined in a model-independent way from the star's reflex orbital acceleration and the transit profile. Additional flux coming from the system due to a bright, undetected stellar binary companion can, however, potentially dilute the transit curve and radial velocity signal, leading to underestimation of the planet's mass and radius, and to overestimation of the planet's density. In this study, we cross-check the published radii of all the WASP planet-host stars, determined from their transit profiles and radial velocity curves, against radiometric measurements of stellar radii derived from their angular diameters (via the infrared flux method) and trigonometric parallaxes. We identify eight systems showing radiometric stellar radii significantly greater than their published photodynamical values: WASPs 20, 85, 86, 103, 105, 129, 144, and 171. We investigate these systems in more detail to establish plausible ranges of angular and radial velocity separations within which such 'stealth binaries' could evade detection, and deduce their likely orbital periods, mass ratios, and flux ratios. After accounting for the dilution of transit depth and radial velocity amplitude, we find that, on average, the planetary densities for the identified stealth binary systems should be reduced by a factor of 1.3. [ABSTRACT FROM AUTHOR]

Background: This research aims to compare the differences in kinematic parameters associated with cross and uppercut punches between Sanda athletes (SA) and Boxing athletes (BA) to analyze their impacts on peak punching speed. Methods: The punches of BA (n = 20) and SA (n = 20) were compared utilizing a three-dimensional (3D) framework and high-speed cameras in terms of 13 key parameters. An independent samples t-test (α = 0.05) was employed to analyze the differences in punching between BA and SA. Meanwhile, a stepwise multiple linear regression equation was developed to analyze the influence of selected parameters on peak punching speed. Results: The results reveal that, among the 13 kinematic parameters, the six cross-related parameters and four uppercut-related parameters are significantly different (both p ≤ 0.05). The results of multivariate regression analysis unveils that the peak punching speed for the cross are influenced by the anteroposterior position of the center of gravity (in BA) and the maximum angular velocity of the shoulder (in SA). In contrast, for both BA and SA, the maximum angular velocity of the shoulder plays a critical impact on uppercut. Conclusions: These findings indicate that trunk and upper limbs significantly influence the peak punching speed, which provides suggestions for daily training regimen of SA and BA as well as their coaches. [ABSTRACT FROM AUTHOR]

This paper presents an experimental methodology for tracking trajectories of rockfall-saltation and extracting kinematic parameters from collisions between rockfalls and a slope surface. We conducted a series of experiments, each featuring different initial impact angles. Rockfall trajectories and their three-dimensional angular velocities were measured by a high-speed camera and built-in Inertial Measurement Unit (IMU), respectively. Our experiments demonstrate that rockfall dissipates its total energy as it progresses along the slope, and the dissipation rates are largely determined by the initial impact angle. Following the classification of rockfall-bed collisions into two modes—Mode-1: saltation dominant and Mode-2: rolling and sliding dominant, we examined the correlations between impact angles and the probability density functions of kinetic, linear, and rotational kinetic energy, as well as the coefficients of kinetic friction and restitution in both modes. Our findings highlight the crucial role of three-dimensional angular velocities in rockfall kinematics, displaying a notable divergence of up to 60% when compared with their two-dimensional counterparts. This is particularly evident in Mode-2, where the increase in rotational energy following collisions exceeds that of Mode-1 × 25%. The experimental investigation contributes to a deeper understanding of the fundamental physical processes inherent in successive rockfall-slope collisions, thereby benefitting predictive capabilities for rockfall disasters in mountainous regions. [ABSTRACT FROM AUTHOR]

Generation, statistically steady state, and temporal decay of axially rotating thermal counterflow of superfluid 4He (He II) in a square channel is probed using the second sound attenuation technique, measuring the density of quantized vortex lines. The array of rectilinear quantized vortices created by rotation strongly affects the development of quantum turbulence (i.e., turbulence strongly affected by the presence of quantized vortices). At relatively slow angular velocities, the type of instability responsible for the destruction of the laminar counterflow qualitatively changes: the growth of seed vortex loops pinned on the channel wall becomes gradually replaced by the growth due to Donnelly–Glaberson instability, which leads to rapid growth of helical Kelvin waves on vortices parallel with applied counterflow. The initial transient growth of vortex line density that follows the sudden start of the counterflow appears self-similar, linear in dimensionless time, Ω t. We show numerically that Kelvin waves of sufficiently strong amplitude reorient the vortices into more flattened shapes, which grow similarly to a free vortex ring. The observed steady state vortex line density at sufficiently high counterflow velocity and its early temporal decay after the counterflow is switched off are not appreciably affected by rotation. It is striking, however, that although the steady state of rotating counterflow is very different from rotating classical grid-generated turbulence, the late temporal decay of both displays similar features: the decay exponent decreases with the rotation rate Ω from −3/2 toward approximately −0.7, typical for two-dimensional turbulence, consistent with the transition to bidirectional cascade. [ABSTRACT FROM AUTHOR]

This paper presents a robust numerical model to simulate the electro-hydrodynamic flows of a neutrally buoyant liquid droplet suspending in another liquid for varying electrical conductivities ranging from near-dielectric to highly conductive fluids. The effect of such conductivity on the interfacial charge transport in the droplets has been investigated. The model is first validated with the theory of electro-rotation corresponding to the strong electric field. The results are compared with the theoretical predictions from the Quincke theory. The angular velocities at different electric field ratios agree well with theoretical predictions. Furthermore, droplet investigations are performed in distinct conductivity regimes with the electric Reynolds number ranging from 10 − 2 to 104. The findings reveal that conductivity influences the evolution of diverse droplet shapes in the corresponding regimes through surface charge convection. We observe prolate shapes at very low electric conductivities, while larger conductivities of droplets and suspending media lead to oblate drop shapes. With increasing electrical conductivity of the droplet and the medium, we observe the onset of distinct droplet shapes similar to the existing literature. The mechanism for the onset of different regimes is adequately explained by quantifying surface properties like tangential stress and velocity. [ABSTRACT FROM AUTHOR]

The study of nanodroplets coalescence is crucial for the development of nanofluid technology and crude oil dehydration. The coalescence behavior of multiple nanodroplets in single electric field, single swirl centrifugal field, and the coupling of electric field and swirl centrifugal field (E&SC coupling fields) was investigated using the molecular dynamics (MD) method. The validation work verified the feasibility of the present MD models. The effects of electric field frequency (f) and strength (E), angular velocity (ω), water content (wt), and component types on the coalescence behavior of multiple nanodroplets were comprehensively investigated. The results show that direct current (DC) field was more suitable for dealing with low wt emulsions, while alternating current (AC) field was more suitable for dealing with high wt emulsions. The swirl centrifugal field with low (high) ω was correspondingly suitable for dealing with low (high) wt emulsions. The coalescence efficiency increased with increasing Re (20–160) and f (0–40 GHz). In addition, not only the large-sized droplets were easy to be formed, but also the small-sized droplets were easy to be removed in the E&SC coupling fields, which can enhance the coalescence efficiency between multiple nanodroplets. The critical CaE of AC&SC coupling fields was improved 18% than DC&SC coupling fields. Finally, the presence of Span-80 (SPAN) molecules increased the coalescence efficiency of multiple nanodroplets and raised the critical CaE to 0.11. The results of this paper can be potentially helpful for the development of high-efficiency electric dehydration technology at microscale. [ABSTRACT FROM AUTHOR]

This study proposes a model for simulating the dynamics of electric bicycle flow in isolated non-motorized lanes. The model is an extension of the conventional social force model with an additional rotational degree of freedom that describes the steering angle of electric bicycles. In this model, two corrective relaxation terms are included in the driving force for the rotational degree of freedom: one on the steering angle and another on the angular velocity. Stability analysis shows that an appropriate amount of correction on the angular velocity helps to avoid oscillation and overshoots of the turning angle. The proposed model is validated both macroscopically and microscopically, and the agreement of the simulated fundamental diagram with that in the literature demonstrates the rationality of the model in characterizing the collective motions of electric bicycles. Comparison of simulated and observed trajectories confirms that the proposed model could reproduce electric bicycle motions with a certain accuracy at the microscopic level. Finally, predictions based on the validated model are provided. According to the simulation results, congestion starts to occur when the inlet flow rate of the lane reaches 1500–1750 ebike/h/m. For a mixed configuration, the maximum allowed flow rate in the lane is 2350–2400 ebike/h/m, and this value depends on the proportion of fast electric bicycles and the riding style in the flow. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) and three-dimensional (3D) numerical models are commonly employed to investigate the kinematic and hydrodynamic characteristics of fish maneuvers. In this study, we captured the posture characteristics of zebrafish during C-type maneuvers using high-speed photography and constructed a midline curvature model via the tandem principal characteristics method, which exhibited a "double peak and single valley" structure. Based on this curvature model, self-propelled simulations were conducted using the immersed boundary method with adaptive mesh refinement. The results showed that, under identical deformation conditions, the 2D simulation exhibited a 16.8% higher centroid velocity, 6.1% greater overall angular velocity, and an 11.9% larger turning angle compared to the 3D simulation. This discrepancy is primarily due to the 2D model's inability to accurately represent the fish body's mass distribution and force characteristics, resulting in artificially elevated performance. Nevertheless, 2D simulations remain applicable for studying the propulsion performance of fish with elongated cross-sections and large fin areas. Comparison between the simulated and real motion performance reveals that, under the self-propelled computational model, both 2D and 3D numerical simulations consistently capture the qualitative motion patterns. The quantitative results also reflect the actual swimming performance of the fish within an acceptable margin of error. [ABSTRACT FROM AUTHOR]

Amphibious robots have broad prospects in the fields of industry, defense, and transportation. To improve the propulsion performance and reduce operation complexity, a novel bionic amphibious robot, namely AmphiFinbot-II, is presented in this paper. The swimming and walking components adopt a compound drive mechanism, enabling simultaneous control for the rotation of the track and the wave-like motion of the undulating fin. The robot employs different propulsion methods but utilizes the same operation strategy, eliminating the need for mode switching. The structure and the locomotion principle are introduced. The performance of the robot in different motion patterns was analyzed via computational fluid dynamics simulation. The simulation results verified the feasibility of the wave-like swimming mechanism. Physical experiments were conducted for both land and underwater motion, and the results were consistent with the simulation regulation. Both the underwater linear and angular velocity were proportional to the undulating frequency. The robot's maximum linear speed and steering speed on land were 2.26 m/s (2.79 BL/s) and 442°/s, respectively, while the maximum speeds underwater were 0.54 m/s (0.67 BL/s) and 84°/s, respectively. The research findings indicate that the robot possesses outstanding amphibious motion capabilities and a simplistic yet unified control approach, thereby validating the feasibility of the robot's design scheme, and offering a novel concept for the development of high-performance and self-contained amphibious robots. [ABSTRACT FROM AUTHOR]

An inertial measurement system, using a combination of accelerometers, gyroscopes and magnetometers, is of great interest to capture tennis movements. We have assessed the key biomechanical moments of the serve phases and events, as well as the kinematic metrics during the serve, to analyze their influence on serve speed. Eighteen male competitive tennis players, equipped with the inertial measurement units, performed a prolonged serve game consisting of 12 simulated points. Participants were divided into groups A and B in accordance with their positioning above or below the sample average serve speed. Group A (compared with their counterparts) presented with lower back hip adduction and knee flexion, and a higher leftward thoracic tilt during the impact event (−14.9 ± 6.9 vs. 13.8 ± 6.4, 2.8 ± 5.9 vs. 14.3 ± 13.0 and −28.9 ± 6.3 vs. 28.0 ± 7.3°). In addition, group A exhibited higher maximal angular velocities in the wrist and thorax, as well as a lower maximal angular velocity in the back hip than group B (427.0 ± 99.8 vs. 205.4 ± 9.7, 162.4 ± 81.7 vs. 193.5 ± 43.8, 205.4 ± 9.7 vs. 308.3 ± 111.7, 193.5 ± 43.8 vs. 81.1 ± 49.7°/s). The relevant biomechanical differences during the serve were identified, highlighting the changes in joint angles and angular velocities between the groups, providing meaningful information for coaches and players to improve their serve proficiency. [ABSTRACT FROM AUTHOR]

This article addresses the design of angular velocity observer for rigid bodies using vector measurements directly. The main contributions of our observer compared with the classical estimation algorithms lie in that it does not need to reconstruct the attitude information from the measurements nor be implemented with velocity sensors. Meanwhile, it provides three‐degrees‐of‐freedom (3DOF) full state estimates. To avoid the unstable critical points for the attitude estimation errors on SO(3), the synergistic potential functions based hybrid method is adopted. Afterwards, an output feedback attitude tracking controller with a proportional‐derivative (PD) plus feedforward form is built based on the estimates from the observer, which can also be implemented using vector measurements directly. Rigorous analysis of the stability of the observer and the combined observer‐controller are presented in detail, with a separation property shown between the observer and the controller. Simulations are conducted to illustrate the effectiveness of the proposed observer and the combined attitude tracking law. [ABSTRACT FROM AUTHOR]

Aiming at the problems of the difficulty to deal with the waste of banana stems after harvest and the high labor intensity and low efficiency of banana farmers, a banana stem roller squeeze dehydrator was designed, which aimed to realize the squeeze dehydration of the whole stem of banana stems in order to obtain the juice and fiber of banana stems. The banana stem roller squeeze dehydrator was mainly composed of juice storage tank, dehydration frame, upper pressure roll group, lower pressure roll group, transmission mechanism, feeding mechanism and so on. First of all, according to the characteristics of banana stems, such as easy winding and not easy to crush or slice, a four-stage roller squeeze mechanism with gradually reduced opening was designed. The four-stage roller squeeze mechanism was a classification squeeze, the first three stages of the roller were responsible for conveying and preliminary squeezing, and the fourth stage of the roller was mainly dehydrated. The upper and lower stages of the roller gap can be adjusted to adapt to different specifications of banana stems. The adjustment of the gap of the first stage of the roller was for the convenience of feeding, and the adjustment of the gap of the fourth stage of the roller was for the remarkable dehydration rate. The pattern design of the roller surface increased the friction between the roller and the banana stem, ensuring the smooth juice discharge of the squeeze mechanism and preventing the banana stem fiber from winding the roller. The transmission mechanism was designed, which made the angular velocity of the four-stage roller remain the same through the gear transmission, and drove the feeding mechanism and the slag discharge mechanism through the chain transmission. The first pair of rollers were analyzed by force, and the approximate diameter range of bananas that can enter the squeeze mechanism was obtained. Combined with the design of the roller pattern, the feeding was smooth. The mechanical analysis of the roller squeeze mechanism was carried out, and the theoretical formula of the pressure of the roller on the banana stem was obtained. It was concluded that under the condition of the characteristics of the raw material of the banana stem, the equipment parameters and the feeding meshing angle, the smaller the gap of the roller, the greater the pressure, which provided a reference for the adjustment of the gap of the roller in the squeeze dehydration test. The ANSYS/LS-DYNA module was used to analyze the squeeze dehydration of the banana stem. The banana stem was deformed by passing through each level of the roller to verify the feasibility of the squeeze dehydration of the squeeze mechanism. The simulation value and the theoretical value of the pressure of the roller on the banana were compared to verify the reliability of the squeeze dehydration of the squeeze mechanism. The relationship between the pressure and the gap of the roller was verified by the response surface design. Finally, the squeeze dehydration test was carried out on the banana stem roller squeeze dehydrator. The test results show that the squeeze dehydration rate of the banana stem is about 28%-47%, and in the case of feeding and no blockage, the larger the diameter of the banana stem, the smaller the gap of the fourth level of the roller, the higher the dehydration rate of the banana stem. The designed squeeze dehydrator greatly reduced the volume and weight of banana stems, reduced the labor intensity and transportation costs of banana farmers, and facilitated the subsequent high-value utilization of banana stem waste. The research can provide theoretical reference and practical reference for the design and development of whole stem press dewatering equipment of banana. [ABSTRACT FROM AUTHOR]

Residual film recovery machines has have been commonly used in cotton fields in Xinjiang Province in autumn. The plastic film can tear into strips and entangles with impurities on the film during picking. The film with impurities mixture cannot be effectively layered in the conveying process, resulting in low separation of the film with impurities, high impurity content of mulch film, and difficult recycling. This study aims to design the a two-order pin-tooth chain-plate type device for residual film recovery. The multiple tooth collaborative operation was achieved in the continuous picking for the whole residual film in the autumn season. The whole residual film was transported upward to spread on the pin-tooth chain plate. A better separation environment was obtained for the impurity to maintain the effective stratification of membrane impurity in the recovery process. The structure of film film-collecting mechanism was longitudinally arranged with 23 pin-tooth chain plates. The structural parameters of the pin-tooth chain plate were determined to analyze the force in the whole continuous picking of plastic film. The spacing range between the adjacent pin-tooth chain plates was 84mm before the pin-tooth broke the plastic film; The structural parameters were determined for the main, passive rollers, and the stripping ring in the film collecting mechanism; Meanwhile, the angle of the recovery device were also determined, where the angles of the first- and second-order pin-tooth chain plate film collecting mechanism were 125° and 105°, respectively. The kinematics and dynamics analysis showed that the film film-collecting mechanism was used to lift the residual film with impurity. The optimal conditions were clarified to realize the continuous picking, step-by-step spreading, and conveying of the whole residual film. A prototype was trial-produced to conduct the field performance tests. The main influencing factors on the residual film recovery rate of the recovery device were determined as the angular velocity of the picking-passive roller and the operating speed of machinery, according to the principle of picking up film recovery. As the two-order pin-tooth chain-plate type recovery device of the experimental prototype was driven by the front depth limiting roller, the angular velocity of the picking-passive roller was linearly related to the operating speed of the machinery; The first-order film collecting mechanism shared the little range of variation in the ratio of the linear velocity of the tooth end during picking. The operating speed of 0.97 was achieved in by the continuously picking the whole residual film. A single-factor experiment was conducted with the recovery rate of residual film and the rate of containing poles content inside the recycled plastic film as experimental indicators, while the operating speed of the machinery was the influencing factor. The field test showed that the two-order pin-tooth chain-plate type residual film recycling machine was realized for the continuous picking and step-by-step spreading and conveying of the whole film, when the operation speed was within 5.5-7.5 km/h. The average rate of residual film recovery was 89.4%, and the average rate of containing poles was 8.6% in the recovered film. The second-stage nail-tooth chain-plate type device of residual film recovery was enhanced the recovery rate of residual film, whereas, there was the a significant decrease in the rate of containing poles in the recovered film, compared with the commonly- used one. The findings can provide a strong reference for the design of residual film recovery machines. [ABSTRACT FROM AUTHOR]

The rotational speed vectors of the bearing balls affect their service life and running performance. Observing the actual rotational speed of the ball is a prerequisite for revealing its true motion law and conducting sliding behavior simulation analysis. To address the need for accuracy and real-time measurement of spin angular velocity, which is also under high-frequency and high-speed ball motion conditions, a new measurement method of ball rotation vectors based on a binocular vision system is proposed. Firstly, marker points are laid on the balls, and their three-dimensional (3D) coordinates in the camera coordinate system are calculated in real time using the triangulation principle. Secondly, based on the 3D coordinates before and after the movement of the marker point and the trajectory of the ball, the mathematical model of the spin motion of the ball was established. Finally, based on the ball spin motion model, the three-dimensional vision measurement technology was first applied to the measurement of the bearing ball rotation vector through formula derivation, achieving the analysis of bearing ball rolling and sliding characteristics. Experimental results demonstrate that the visual measurement system with the frame rate of 100 FPS (frames per second) yields a measurement error within ±0.2% over a speed range from 5 to 50 RPM (revolutions per minute), and the maximum measurement errors of spin angular velocity and linear velocity are 0.25 °/s and 0.028 mm/s, respectively. The experimental results show that this method has good accuracy and stability in measuring the rotation vector of the ball, providing a reference for bearing balls' rotational speed monitoring and the analysis of the sliding behavior of bearing balls. [ABSTRACT FROM AUTHOR]

AbstractPerformance of sport-related ballistic motor skills, like ball hitting in golf and baseball, requires wide movements to produce highly fast and spatially accurate movements. In this study, we assessed the effect of movement amplitude on directional accuracy in a ballistic hitting task. Participants performed the task of moving a manual handle over a flat surface to hit with high speed a moveable disc, aiming to propel it towards a frontal target. Five movement amplitudes were compared, ranging from 11.5 cm to 27.5 cm in steps of 4 cm. Kinematic analysis evaluated motions of the handle, disc, and arm joints. Results showed that greater movement amplitudes led to longer acceleration phases, with delayed peak velocities at the handle, shoulder and elbow, leading to higher contact and peak linear velocities of the handle, and higher angular velocities at the shoulder and elbow. Manipulation of movement amplitude led to no evidence for effects on either disc directional accuracy or variability. Results also revealed no evidence for differences in variability of contact velocity, peak velocity and time of peak velocity across movement amplitudes in the shoulder, elbow, and wrist. Our results indicated that greater movement amplitudes in hitting a spatial target lead to increased contact velocity while not affecting directional accuracy or movement variability. [ABSTRACT FROM AUTHOR]

We discuss a model describing the spin orbit resonance cascade. We assume that the body has a two-layer (core–shell) structure; it is composed of a thin external shell and an inner and heavier solid core that are interacting due to the presence of a viscous friction. We assume two sources of dissipation: a viscous one, depending on the relative angular velocity between core and shell and a tidal one, smaller than the first, due to the viscoelastic structure of the core. We show how these two sources of dissipation are needed for the capture in spin–orbit resonance. The shell and the core fall in resonance with different time scales if the viscous coupling between them is big enough. Finally, the tidal dissipation of the viscoelastic core, decreasing the eccentricity, brings the system out of the resonance in a third very long time scale. This mechanism of entry and exit from resonance ends in the 1 : 1 stable state. [ABSTRACT FROM AUTHOR]