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When discrepancies between planned and actual movements arise due to environmental changes, humans adjust movement parameters to achieve task goals. While motor adaptation has been extensively studied, the mechanisms involved in redundant movement parameters remain unclear. Split-belt treadmill adaptation, where each belt moves at a different speed, is an example of this phenomenon. Such adaptation initially induces gait asymmetry, which diminishes over time. Previous studies have postulated step length asymmetry as the target function; however, recent evidence challenges this assumption, leaving the target function undefined. This study investigates the target function by analyzing step parameter asymmetry using the goal-equivalent manifold and generalization predictability. The goal-equivalent manifold assesses whether adaptation is close to optimal in minimizing step parameter asymmetry, while generalization predictability reflects adaptation effects across different contexts, indicating potential target functions. We propose that step velocity asymmetry, rather than step length asymmetry, serves as the target function in split-belt treadmill adaptation. This framework facilitates the prediction and interpretation of both the learning process and the transfer of learning effects from trained to untrained conditions. In addition, it explains the overadaptation of step length asymmetry and the achievement of energy-efficient gait after adaptation. Therefore, we propose that step velocity asymmetry is the primary target function in split-belt treadmill adaptation.

In this paper, a numerical simulation of jet impingement quenching is provided. The VOF method in the basic solver of the OpenFOAM CFD package is developed to simulate boiling and condensation phenomena. In simulations, surface tension and mass transfer between two phases were modeled with continuous surface force (CSF) model and Lee mass transfer model, respectively, and energy equation was solved in the solid region. Numerical simulation of jet impingement quenching process is validated by experimental data and a good agreement is observed. The effects of pulsating jet velocity and step jet velocity on quenching process are studied, and parameters such as temporal and spatial variation of solid part temperature and standard temperature uniformity index (STUI) are investigated. The effects of frequency and amplitude of sinusoidal single jet and also the period of two jets with step pulse are investigated. The results revealed that using two jets with step velocity profile leads to the best performance or least uniformity index (best temperature distribution) among the considered cases. Studying the maximum temperature difference inside the solid region indicated that for pulse flows this parameter is considerably lower than the continuous flows. Also, at a constant flow rate, 43% reduction in STUI is achieved by sinusoidal pulsating jet compared to the single continuous jet, while 66% STUI reduction was reached for two-jet cases. These substantial reductions in uniformity index present these methods as promising approaches for the quenching process in various industrial applications.

Industrial robot path planning faces mechanical stress accumulation and motion instability caused by velocity step in complex scenarios. In this study, an adaptive optimization model is proposed, integrating the improved differential evolutionary algorithm and asymmetric S-type velocity planning. This model achieves global-local cooperative optimization through dynamic parameter coupling and velocity field feedback mechanism. Moreover, this study constructed a 10m×6m dynamic simulation environment (including 12 static/dynamic obstacles) based on the Gazebo platform, and set parameters such as the maximum linear velocity of the robot as 2m/s and the safety distance as 0.3m. The performance of the model was also compared with traditional benchmark methods (ant colony optimization algorithm, etc.) and most advanced methods (improved dynamic window algorithm, etc.). Simulation experiments showed that the average path error of the model was reduced by 76.3%, the number of convergence iterations was reduced by 33.3%, and the AUC value was improved by 9.6%. The model's dynamic obstacle scenario planning efficiency in real-world environments was improved by 23.5%, the motion stability index was improved by 7.2%, and the trajectory tracking energy consumption was reduced by 34.7%. In summary, the adaptive population initialization strategy of IDE and the segmented plus acceleration constraints of IASCV achieve a smooth transition of the velocity profile through the dynamic replanning mechanism in the overspeed region, breaking the limitation of the decoupling of the existing trajectory optimization and dynamics constraints. In conclusion, the research model reaches the advanced level in terms of convergence speed, environmental adaptability and industrial energy efficiency, providing a highly robust solution for complex industrial scenarios.

Nanosilica is widely used in various applications, with its market expected to grow over USD 5 billion by 2025. The fluidized bed technology, owing to its intimate contact and efficient mixing of phases, is ideally suited for the large scale processing of powders. However, the bulk processing and dispersion of ultrafine nanosilica using the fluidized bed technology are critically affected by the interparticle forces, such that the hydrophilic nanosilica shows agglomerate bubbling fluidization (ABF), while the hydrophobic nanosilica undergoes agglomerate particulate fluidization (APF). This study carried out a detailed investigation into the fluidization hydrodynamic of the hydrophobic nanosilica by monitoring the region-wise dynamics of the fluidized bed subjected to a regular step change of fixed duration in the gas velocity. The gas flow was controlled using a mass controller operated with an analog output signal from a data acquisition system. The analog input data were acquired at the sampling rate of 100 Hz and analyzed in both time and temporal frequency domains. The effect of velocity transients on the bed dynamics was quickly mitigated and appeared as lower frequency events, especially in regions away from the distributor. Despite the apparent particulate nature of the fluidization, strong hysteresis was observed in both pressure drop and bed expansion. Moreover, the fully fluidized bed’s pressure drop was less than 75% of the theoretical value even though the bed appeared to free from non-homogeneities. Key fluidization parameters, e.g., minimum fluidization velocity (Umf) and the agglomerate size, were evaluated, which can be readily used in the large scale processing of nanosilica powders using fluidized bed technology.

Introduction. The aim of this study was to examine the changes in selected kinematics in the long jump, triple jump, and pole vault to highlight the unique movement pattern characteristics in the approach runs utilised in these events. Material and methods. Data were collected during 1 international and 2 national competitions from 36 male athletes (12 in each event) using an Optojump Next system. Results. This study showed the long jumpers achieved the highest mean step velocity, with the pole vaulters showing the lowest velocity. The velocity of the last step before the take-off was greater (p < 0.05) than the velocity of the penultimate step in all groups of athletes. The length of the last step before the take-off was greater (p < 0.01) than the length of the penultimate step in long jump and pole vault athletes compared to the triple jumpers. The long jumpers demonstrated less contact time (p < 0.01) than the pole vaulters. The contact time of the take-off leg was shorter (p < 0.01) compared to that of the non-take-off leg in pole vaulters. The pole vaulters demonstrated less flight time (p < 0.05) compared to the triple jumpers. Lastly, the flight time during the last step before the take-off was shorter (p < 0.01) than the flight time during the penultimate step in all groups. Conclusions. These findings revealed that each of the track and field jumping events required a distinctive approach run. Therefore, training workouts need to be designed specifically to train the unique gait pattern of the long jump, triple jump, and pole vault.

The semi-solid casting process has a lot of advantages in controlling casting defects. High quality impellers have been produced successfully by the semi-solid process for several years. The semi-solid processed impellers have uniform microstructure and premier mechanical properties, and therefore excellent durability. Further improvement of performance of the impellers is demanded and achieved by increasing curvature and length of blades of impellers. These changes create potential trend of casting defects in blades of impellers, such as non-filling holes. In our recently work, castings were made in different conditions, including two-step plunger velocity and one-step plunger velocity. The experimental results show that the change of plunger velocity played a decisive role in the forming of non-filling holes. Entrapped gas is the direct reason of the non-filling holes. With the increasing of plunger velocity, the area of non-filling holes increased. The non-filling holes in blades could be avoided by eliminating the plunger velocity’s changing during filling blades.

The objective of this study was to investigate the effects of foam rolling of the hamstrings or quadriceps muscle groups on the step kinematics during a30-m sprint run.Moderately active physical education male students (n =23, 21.4 ± 0.7 years, 79.2 ± 8.3 kg, 1.80 ± 0.06 m) participated in this study. The Optojump Next with the Witty timing system were used to measure the kinematics of sprint running (contact time, step length, flight time, step velocity). Each subject completed two maximal 30-m sprints after the warm-upunder three conditions: foam rolling of quadriceps, foam rolling of hamstrings, and dynamic stretching. The main results of this study showed that the foam rolling of quadriceps decreased velocity of step, step length and flight time as well as increased contact time during sprint immediately after warm-up (2 min) compared to warm-up with foam rolling of hamstrings. There were not significant differences between the three warm-up conditions during the second run (after 8 min passive break). The results suggest that practitioners should avoid the foam rolling of quadriceps exclusively in terms of performance a 30-m maximal sprint. It should also pay more attention to apply the optimal volume of quadriceps to hamstrings foam rolling during the warm-up procedures.

Atomic force microscopy (AFM) was used to study the rates of migration of the (10¯1 4) plane of a single-crystal of calcite dissolving in 0.1 M NaCl aqueous solutions at room temperature. The solution pH and P^sub CO^^sub 2^ controlled in the ranges 4.4 < pH < 12.2 and 0 < P^sub CO^^sub 2^ < 10^sup -3.5^ atm (ambient), respectively. Measured step velocities were compared with the mineral dissolution rates determined from the calcium fluxes. The step velocity is defined as the average of the velocities of the obtuse and acute steps. Rates of step motion increased gradually from 1.4(±0.2) at pH 5.3 to 2.4(±0.3) nm s^sup -1^ at pH 8.2, whereas the rates inverted and decreased to the minimum value of 0.69(±0.18) nm s^sup -1^ at pH 10.8. For pH > 10.8, only the velocity of the obtuse steps increased as pH increased, whereas that of acute steps gradually decreased. The dissolution rate of the mineral can be calculated from the measured step velocities and average slope, which is proportional to the concentration of exposed monomolecular steps on the surface. The average slope of the dissolving mineral, measured at pH 5.6 and 9.7, was 0.026 (±0.015). Using this slope, we calculate bulk dissolution rates for 5.3 < pH < 12.2 of 4.9(±3.0) × 10^sup -11^ to 1.8(±1.0) × 10^sup -10^ mol cm^sup -2^ s^sup -1^. The obtained dissolution rate can be expressed by the following empirical equation: R^sub dss^ = 10^sup -4.66(±0.13)^[H^sup +^] + 10^sup -3.87(±0.06)^[HCO^sub 3^^sup -^] + 10^sup -7.99(plusmn; 0.08)^[OH^sup -^] We propose that calcite dissolution in these solutions is controlled by elementary reactions that are similar to those that control the dissolution of other amphoteric solids, such as oxides. The mechanisms include the proton-enhanced hydration and detachment of calcium-carbonate ion pairs. The detachments are enhanced by the presence of adsorbed nucleophiles, such as hydroxyl and bicarbonate ions, and by protons adsorbed to key oxygens. A molecular model is proposed that illustrates these processes.[PUBLICATION ABSTRACT]

This article aims to analyze the performance of a magnetic-fluid-based porous rough step bearing considering slip velocity. The Neuringer-Rosensweig model governs the fluid flow while the velocity slip is modeled by the method of Beavers and Joseph. The bearing surfaces are assumed transversely rough and the transverse surface roughness of the bearing surfaces is characterized by a stochastic random variable with non-zero mean, variance, and skewness. With the usual assumptions of hydrodynamic lubrication, the related stochastically averaged Reynolds’ equation for the fluid pressure is solved with appropriate boundary conditions, which is then used to calculate the loadcarrying capacity. It is found that although the bearing suffers owing to transverse surface roughness, the performance of the bearing system can be improved to some extent by the positive effect of magnetization, considering the slip parameter at the minimum; at least in the case of negatively skewed roughness. A comparison of this paper with some established investigations indicates that here, the reduction of loadcarrying capacity due to porosity and slip velocity is comparatively less, especially, when negative variance occurs. In augmenting the performance of the bearing system, the step ratio plays a central role, even if the slip parameter is at the minimum.

This paper studies the computation method of two-step inversion of interface and velocity in a region. The 3-D interface is described by a segmented incomplete polynomial; while the reconstruction of 3-D velocity is accomplished by the principle of least squares in functional space. The computation is carried out in two steps. The first step is to inverse the shape of 3-D interface; while the second step is to do 3-D velocity inversion by distributing the remaining residual errors of travel time in accordance with their weights. The data of seismic sounding in the Tangshan-Luanxian seismic region are processed, from which the 3-D structural form in depth of the Tangshan seismic region and the 3-D velocity distribution in the crust below the Tangshan-Luanxian seismic region are obtained. The result shows that the deep 3-D structure in the Tangshan seismic region trends NE on the whole and the structure sandwiched between the NE-trending Fengtai-Yejituo fault and the NE-trending Tangshan fault is an uplifted zone of the Moho. In the 3-D velocity structure of middle-lower crust below that region, there is an obvious belt of low-velocity anomaly to exist along the NE-trending Tangshan fault, the position of which tallies with that of the Tangshan seismicity belt. The larger block of low-velocity anomaly near Shaheyi corresponds to a denser earthquake distribution. In that region, there is an NW-trending belt of high-velocity anomaly, probably a buried fault zone. The lower crust below the epicentral region of the Tangshan M ^sub S^=7.8 earthquake is a place where the NE-trending belt of low-velocity anomaly meets the NW-trending belt of high-velocity anomaly. The two sets of structures had played an important role in controlling the preparation and occurrence of the M ^sub S^=7.8 Tangshan earthquake.[PUBLICATION ABSTRACT]