Increase In Speed Research Articles

Modelling Method and Meshing Characteristics of a Novel Curve-Surface Conjugate Internal Gear Drive

Space exploration has become a major focus in the field of technology, with gear transmissions in aerospace equipment playing a crucial role. In the extreme environment of space, gear transmissions face challenges like large temperature differentials, deformation and maintenance difficulties, which will severely impact transmission accuracy and service life. To meet the growing demands for high-performance gear transmissions with high transmission efficiency and error adaptability in the aerospace field, this paper proposes a novel curve-surface conjugate internal gear drive consisting of an involute internal gear and a curve-surface gear. The fundamental theory of curve-surface conjugation is introduced, and the construction method for curve-surface gear based on a selected contact path and meshing tube is presented. The analysis models including induced curvature, sliding ratio and tooth contact analysis with errors (ETCA) are simulated to evaluate the meshing characteristics. Additionally, prototypes are manufactured and experimental setups are established to validate the transmission performance. These results indicate that as the rotational speed increases, the transmission efficiency of the curve-surface conjugate internal gear drive improves, which is contrary to the trend observed in involute gear drives. And the transmission efficiency of the curve-surface conjugate internal gear drive surpasses that of the involute gear drive at higher rotational speeds. Moreover, this novel gear drive exhibits excellent error adaptability, maintaining intact contact paths and high transmission efficiency even in the presence of assembly errors. This study provides new ideas for the design and manufacture of high-performance gear transmissions from the perspective of spatial geometric elements.

Pollutant Dispersion of Aircraft Exhaust Gas during the Landing and Takeoff Cycle with Improved Gaussian Diffusion Model

Evaluating aviation emissions and examining the dispersion properties of contaminants are crucial for understanding atmospheric pollution. To assess the pollutant emissions and dispersion of aircraft during the landing and takeoff (LTO) cycle, and address air pollution surrounding the airport resulting from flight operations, this study evaluated emissions throughout the LTO phase based on Quick Access Recorder (QAR) data in conjunction with the first-order approximation method. An improved Gaussian diffusion model for mobile point sources was employed to examine the diffusion characteristics of contaminants. Additionally, CFD calculation outcomes for various exhaust velocities and wind speeds were utilized to validate the trustworthiness of the improved Gaussian model. The discussion also encompasses the influence of diffusion time, wind direction, wind speed, temperature gradient, and particle deposition on the concentration distribution of contaminants. The findings indicated that the Gaussian diffusion model aligned with the results of the CFD calculations. The diffusion distribution of contaminants around airports varies over time and is significantly influenced by atmospheric environmental factors, including wind direction, wind speed, and atmospheric stability. Specifically, a change in wind direction from 0° to 45° caused a shift of approximately 1000 m in the contaminant’s center. An increase in wind speed from 3 m/s to 5 m/s led to a decrease in concentration by about 15%. Furthermore, a transition in atmospheric stability from category ‘a’ (very unstable) to ‘f’ (very stable) resulted in a two-order-of-magnitude increase in contaminant concentrations.

Assessing acute effects of two motor-cognitive training modalities on cognitive functions, postural control, and gait stability in older adults: a randomized crossover study.

The process of aging often accompanies a decline in cognitive function, postural control, and gait stability, consequently increasing the susceptibility to falls among older individuals. In response to these challenges, motor-cognitive training has emerged as a potential intervention to mitigate age-related declines. This study aims to assess the acute effects of two distinct motor-cognitive training modalities, treadmill dual-task training (TMDT) and interactive motor-cognitive training (IMCT), on cognitive function, postural control, walking ability, and dual-task performance in the elderly population. In this randomized crossover study, 35 healthy elderly individuals (aged 60-75) participated in three acute training sessions involving TMDT, IMCT, and a control reading condition. Assessments of executive function, postural control, gait performance, and cognitive accuracy were conducted both before and after each session. Both TMDT and IMCT improved executive functions. Notably, IMCT resulted in a significant enhancement in correct response rates and a reduction in reaction times in the Stroop task (p < 0.05) compared to TMDT and the control condition. IMCT also led to an increase in dual-task gait speed (p < 0.001) and showed a trend towards improved cognitive accuracy (p = 0.07). Conversely, TMDT increased postural sway with eyes open (p = 0.013), indicating a potential detriment to postural control. The findings suggest that IMCT holds greater immediate efficacy in enhancing cognitive function and gait stability among older adults compared to TMDT, with a lesser adverse impact on postural control. This underscores the potential of IMCT as a preferred approach for mitigating fall risk and enhancing both cognitive and physical functions in the elderly population.

COMPUTER MODELING OF TRANSIENT ELECTROMECHANICAL PROCESSES IN A WIND POWER PLANT WITH A MAGNETIC GEARBOX

In this work, a computer Simulink model of a wind power plant has been developed, which uses a magnetic gearbox instead of a mechanical gearbox and also contains a synchronous permanent magnet generator. A separate Simulink model of a magnetic gearbox built on the basis of a modulated magnetic field in the air gap was developed, which al-lows to study the stability of its operation both in steady-state and transient modes. Calculations of various dynamic modes of the wind power plant’s operation were carried out, based on the developed model, such as the starting mode, an instantaneous increase in the wind speed acting on the wind turbine, and an increase in the load of the electric gen-erator. According to the results of the calculations, it is shown that in transient modes, when short-term overloads oc-cur, both rotors of the magnetic gearbox can fall out of synchronous motion for a certain period of time and then, de-pending on the parameters of the gearbox (as well as its other elements), the electromechanical system either reaches a certain operating steady-state mode or loses the ability to transfer mechanical power from the wind turbine to the gen-erator. It has been shown that the use of a more powerful magnetic gearbox, with an increased value of the maximum magnetic torque, allows of a more overload-resistant operation of both: a gearbox and the wind plant as a whole. Ref-erences 9, figures 10.

Efficient Nonlinear Model Predictive Path Tracking Control for Autonomous Vehicle: Investigating the Effects of Vehicle Dynamics Stiffness

Motion control is one of the three core modules of autonomous driving, and nonlinear model predictive control (NMPC) has recently attracted widespread attention in the field of motion control. Vehicle dynamics equations, as a widely used model, have a significant impact on the solution efficiency of NMPC due to their stiffness. This paper first theoretically analyzes the limitations on the discretized time step caused by the stiffness of the vehicle dynamics model equations when using existing common numerical methods to solve NMPC, thereby revealing the reasons for the low computational efficiency of NMPC. Then, an A-stable controller based on the finite element orthogonal collocation method is proposed, which greatly expands the stable domain range of the numerical solution process of NMPC, thus achieving the purpose of relaxing the discretized time step restrictions and improving the real-time performance of NMPC. Finally, through CarSim 8.0/Simulink 2021a co-simulation, it is verified that the vehicle dynamics model equations are with great stiffness when the vehicle speed is low, and the proposed controller can enhance the real-time performance of NMPC. As the vehicle speed increases, the stiffness of the vehicle dynamics model equation decreases. In addition to the superior capability in addressing the integration stability issues arising from the stiffness nature of the vehicle dynamics equations, the proposed NMPC controller also demonstrates higher accuracy across a broad range of vehicle speeds.

Efficacy and Safety of Single Clip Traction Assisted Endoscopic Submucosal Dissection for Colonic Neoplasms: A Propensity Score Matching Analysis.

Endoscopic submucosal dissection (ESD) for colonic neoplasms is a technically intricate procedure. Internal traction using a single clip has emerged as a promising supportive technique for colonic ESD. Therefore, this study aimed to comprehensively evaluate and compare the efficacy and safety of ESD with and without the aid of single-clip traction. This retrospective study encompassed 36 patients who underwent single clip traction-assisted colonic ESD and 66 who underwent the traditional method of colonic ESD at Nanjing Drum Tower Hospital Clinical College of Nanjing Medical University. We employed the propensity score-matching method to mitigate disparities in resected specimen size and tumor location. Post-matching, we comprehensively assessed treatment outcomes and incidence of adverse events between the two treatment groups (single clip traction-assisted ESD (scESD) and conventional ESD (cESD)). After propensity score matching, we observed 34 matched pairs. There were no significant differences between the two treatment groups regarding the en bloc resection rate, complete resection rate, and curative rate. However, the procedure duration was significantly shorter in the single clip traction-assisted ESD group compared to the conventional ESD group (20.00 [Interquatile Range (IQR)] (16.00-32.50) minutes vs 31.50 [IQR] (17.00-54.00) minutes, p = 0.0474). Furthermore, there was a significant increase in dissection speed in the single clip traction-assisted ESD group compared to the conventional ESD group (0.29 [IQR] (0.20-0.45) mm2/min vs 0.19 [IQR] (0.11-0.35) mm2/min, p = 0.0015). All lesions were resected in a single piece. Among the propensity-score-matched patients, only those treated with single clip traction-assisted ESD exhibited faster dissection speeds (p = 0.015). Furthermore, there were no substantial differences in adverse events such as intraoperative perforation, delayed perforation, or delayed bleeding. Our findings suggest that single clip traction-assisted colonic ESD is preferable to traditional colonic ESD, owing to its shorter procedure duration and faster dissection speed.

Study on Atomization Mechanism of Oil Injection Lubrication for Rolling Bearing Based on Stratified Method

The atomization mechanism of lubrication fluid in rolling bearings under high-speed airflow between the rings was investigated. A simulation model of gas–liquid two-phase flow in angular contact ball bearings was developed, and the jet lubrication process between the bearing rings was simulated using FLUENT computational fluid dynamics software (Ansys 19.2). The complex motion boundary conditions of the rolling elements were addressed through a layered approach. We can obtain more accurate boundary layer flow field changes and statistics of the diameter of oil particles in lubricating oil atomization, which lays the foundation for analyzing the law of influence on lubricating oil atomization. The results show that as the number of boundary layer layers increases, the influence of the boundary layer flow field on the lubricating oil is more obvious. The oil particle size is excessively flat, and the concentration of large particles of oil appears to decrease. As the speed increases, the amount of oil in the cavity decreases, but the oil droplets are also fragmented, which intensifies the atomization and reduces the particle diameter. This reduces the Sauter Mean Diameter (SMD), which is not conducive to the lubrication of the bearing. Under different injection pressures, when the injection pressure is large, it is beneficial to the lubrication of the bearing.

Effects of a 12-Week Mixed-Method Physical Exercise Program on Physical Fitness, Stress, Anxiety, and Quality of Life in Adolescents with Cerebral Palsy: A Case Series Study.

Although the health benefits related to physical exercise for adolescents with cerebral palsy (CP) have been recognized, studies indicate that individuals with CP at school age are less involved in physical activities than their typical peers and are twice as likely to engage in sedentary behaviors. Therefore, our study aims to investigate the effects of a physical exercise program on physical fitness, stress, anxiety, and quality-of-life variables. A total of 15 teenagers with ambulatory CP (n = 8 boys, n = 7 girls, between 12 and 18 years old; M = 14.35; SD = 1.76) completed a 12-week program based on a mixed-method approach with face-to-face and live online activities. The outcome measures were physical fitness, stress, anxiety, and quality of life. The 12-week exercise program resulted in gains in muscular strength, flexibility, and aerobic endurance tests, characterized by an increase in average walking speed and average VO2 max. There was also a significant change in the perception of emotional states of depression, anxiety, and stress reported by the participants. The program proved to be effective in physical fitness tests and perception of emotional states. Given the positive effects produced by the program, its design appears to meet the demands of adolescents with cerebral palsy.

Dynamic Modeling of Angular Contact Ball Bearing with Local Defects under EHL Considering Impact Force

In order to analyze the operating status of angular contact ball bearings(ACBBs) with local defects in more detail, a dynamic model of ACBB with local defects considering impact force under elastohydrodynamic lubrication conditions is proposed. Firstly, an elastohydrodynamic lubrication model for defective bearings considering spin is established, the film thickness and film stiffness of the defective bearings are calculated, and then time-varying displacement excitation model and time-varying stiffness model for local defects in angular contact ball bearings is presented. Based on this, an instantaneous impact force function related to defect size and bearing speed is established. Secondly, based on Hertz contact theory and impact force function, a dynamic calculation method for ACBBs with local defects on the outer ring is proposed. Finally, the vibration characteristics of ball bearings with faults are investigated, and the influence of different parameters on the dynamic response of the bearings is analyzed. The calculation results show that under lubrication conditions, the impact force on the vibration of the bearing is significantly weakened. With the increase of defect size and load, the frequency of bearing fault characteristics remain unchanged, but its amplitude increases. As the bearing speed increases, the characteristic frequency and amplitude of bearing faults increase.

Experimental investigation on wind loads and wind-induced responses of large-span flexible photovoltaic support structure

Flexible photovoltaic (PV) support structure offers benefits such as low construction costs, large span length, high clearance, and high adaptability to complex terrains. However, due to the high flexibility and low damping of the cable system, wind load becomes the primary control factor for structural safety and the key consideration in the design. In this study, a 45 m span flexible PV support structure with 3 spans and 12 rows was designed. The wind loads on PV panels were obtained by wind tunnel tests on a rigid model and the wind-induced responses were investigated by wind tunnel tests on an aeroelastic model. The shielding effects and tilt angle of PV modules on the wind load and wind-induced vibration of the flexible PV support were studied. The experimental results show that in the rigid model wind tunnel test, the wind pressure on the surface of PV modules exhibits a gradient distribution along the direction of wind flow, with symmetric distribution along the mid span. With the increase in the tilt angle of the PV module, the shielding effect becomes significant and the most pronounced shielding effect on the mean wind pressure coefficient occurs in the second row of the windward zone. In aeroelastic model wind tunnel tests, the mean vertical displacement of the flexible PV support structure increases with the increase of wind speed and tilt angle of PV modules. Due to the wind-resistant anchor cables set in both the windward and leeward zones, the vibration amplitude near the edge rows is significantly smaller than that of the middle rows when the structure is subjected to wind suction. When the flexible PV support structure is subjected to wind pressure, the maximum mean vertical displacement occurs in the first rows at high wind speeds. The shielding effect has a noticeable impact on the wind-induced response of the leeward zone at α = 20° under wind pressure, resulting in the decrease of amplitude vibration by approximately 53 %. The wind vibration coefficients in different zones under the wind pressure or wind suction are mostly between 2.0 and 2.15. Compared with the experimental results, the current Chinese national standards are relatively conservative in the equivalent static wind loads of flexible PV support structure.

Overnight changes in performance fatigability and their relationship to modulated deep sleep oscillations via auditory stimulation.

Deep sleep oscillations are proposed to be central in restoring brain function and to affect different aspects of motor performance such as facilitating the consolidation of motor sequences resulting in faster and more accurate sequence tapping. Yet, whether deep sleep modulates performance fatigability during fatiguing tasks remains unexplored. We investigated overnight changes in tapping speed and resistance against performance fatigability via a finger tapping task. During fast tapping, fatigability manifests as a reduction in speed (or "motor slowing") which affects all tapping tasks, including motor sequences used to study motor memory formation. We further tested whether overnight changes in performance fatigability are influenced by enhancing deep sleep oscillations using auditory stimulation. We found an overnight increase in tapping speed alongside a reduction in performance fatigability and perceived workload. Auditory stimulation led to a global enhancement of slow waves and both slow and fast spindles during the stimulation window and a local increase in slow spindles in motor areas across the night. However, overnight performance improvements were not significantly modulated by auditory stimulation and changes in tapping speed or performance fatigability were not predicted by individual changes in deep sleep oscillations. Our findings demonstrate overnight changes in fatigability but revealed no evidence suggesting that this effect is causally linked to temporary augmentation of slow waves or sleep spindles. Our results are important for future studies using tapping tasks to test the relationship between sleep and motor memory consolidation, as overnight changes in objectively measured and subjectively perceived fatigue likely impact behavioural outcomes.

Analysis of mixed traffic flow characteristics based on cellular automata model under lane management measures

In the future, mixed traffic flow comprising Human-Driven Vehicles (HDVs), Connected and Autonomous Vehicles (CAVs), and CAV platoons will coexist for an extended period. Exploring the operational characteristics of mixed traffic flow under different lane management measures is essential for effective management and control. Initially, we analyze the motion characteristics of HDVs, CAVs, and CAV platoons and identify the car-following types within mixed traffic. Based on vehicle motion characteristics and the variance in maximum desired speeds among HDV drivers, we establish longitudinal motion rules for HDVs using a safety distance model. For CAVs and their platoons, we develop longitudinal motion rules by considering platoon merging and splitting behaviors, as well as speed and spacing error requirements for platoon driving. Subsequently, we formulate lateral lane-change rules based on the Symmetric Two-lane Cellular Automata (STCA) model, considering differences in reaction times and following distances between HDVs and CAVs. Finally, we conducted simulation experiments on a unidirectional three-lane highway using the multi-lane mixed traffic flow cellular automata model, analyzing the characteristics of mixed traffic under various lane management measures, such as mixed lane, CAV-dedicated lane, and CAV-priority lane. The results show that as the proportion of CAV (denoted as p) increases, the traffic flow capacity, optimal density, and jam density also increase. When p≤0.6, the k−q diagram exhibits a triangular shape, whereas for p>0.6, it assumes a trapezoidal shape. Implementing CAV-dedicated lane can reduce Cooperative Adaptive Cruise Control (CACC) degradation rates but only enhances traffic flow capacity when the CAV proportion reaches a certain threshold. Compared to the mixed lane scheme, when p≤0.3 and k≤0.3, the CAV-priority lane schemes not only meet traffic demands but also reduce CACC degradation rates. The vehicle speed in CAV-priority lane surpasses that in HDV lanes, facilitating improved traffic efficiency for CAVs. The distribution of maximum speeds among HDV drivers affects the fundamental diagram of mixed traffic flow and the performance of CAV-priority lane, with greater impacts observed as the standard deviation of the HDVs' maximum speed increases.

Study on corrosion behavior and first-principle analysis of M50 steel in lubricating oil contaminated by salt water

The corrosive wear of M50 steel in lubricating oil contaminated with saline is a form of wear that often occurs within the main shaft bearings of aviation engines carried by aircraft working at sea. In the present paper, the corrosion behavior of M50 steel in lubricating oil contaminated with saline was studied. The open-circuit potential, polarization curve and impedance spectrum were analyzed by rotating electrochemical corrosion wear test. A three-layer interface microscopic molecular model was established with Materials Studio to simulate the dynamic corrosion evolution process of M50 steel self-matching pairs and the adsorption energy was calculated. The results show that the corrosion type is pitting corrosion. With the increase of saline concentration, the corrosion area becomes wider and shallower, and the size of the pitting core gradually decreases. The weight loss of M50 steel increases over time, but the trend slows down, which is also shown in the MS simulation results. Electrochemical tests show that the tribocorrosion of M50 steel is related to load, speed. As the load increases, the corrosion rate decreases. And, as the speed increases, the corrosion rate increases. This has practical significance for extending the understanding of tribocorrosion of M50 steel in marine atmospheric environments.

Study on combustion and emission characteristics of hydrogen/air mixtures in a constant volume combustion bomb

Hydrogen is an environmentally-friendly fuel with the characteristics of low carbon, high calorific value, and extensive combustible range, making it an optimal alternative fuel for internal combustion engines. In this study, an experiment using a spherical constant volume combustion bomb (CVCB) was conducted to investigate the combustion and emission characteristics of hydrogen/air mixtures. The results shows that the flame propagation velocity of hydrogen laminar flow initially increases and then decreases with the excess air coefficient (λ), reaching peak at λ = 0.6, and the flame becomes unstable on the side of lean burning (λ > 1.0). Both the NOx emissions and the average temperature in the CVCB initially rise before eventually declining with the λ, the peak values for both NOx emission and mean temperature are reached at λ = 1.0. The dilution of N2 inhibits the laminar combustion and emission of hydrogen. As the dilution rate of N2 increases, little change occurs in the Markstein length, while flame propagation velocity, NOx emission, and average temperature all decrease. An increase in initial pressure hinders the development of the initial flame, while promoting the formation of cellular structure within the flame. Consequently, unstable combustion leads to a rapid increase in flame propagation speed during later stages. The average temperature inside the CVCB and the NOx emission increase by 6.6 % and 25.9 %, respectively, with the initial pressure increasing from 0.1 MPa to 0.5 MPa. On the other hand, an increase in initial temperature can facilitate flame development and results in an increased flame propagation speed. Especially, Markstein length is less sensitive to changes in initial temperature than to changes in initial pressure. The average temperature and NOx emission present a pattern of increasing first and decreasing then with the increase in initial temperature. These results have provided empirical evidence for optimizing the combustion and emission control of hydrogen engines.

Impact of Wind Speed on Vibration Levels in Water Cooling Systems

This study explores the intricate relationship between wind speed and structural vibrations, with a particular focus on water cooling systems in oil plants. Water cooling is a vital process in the oil and gas industry, used to dissipate excess heat generated during operations such as refining and petrochemical production. The efficient functioning of these systems is crucial to prevent overheating, which can lead to equipment failure and operational inefficiencies. The research utilizes a comprehensive dataset collected over six months, comprising 8688 observations, to perform a regression analysis that quantifies the impact of wind speed on vibration levels. The findings indicate a significant positive correlation, suggesting that as wind speed increases, so does the vibration within the system. This correlation highlights the influence of wind-induced forces on structural dynamics, potentially exacerbating mechanical wear and risking structural integrity. By understanding these dynamics, engineers can design more robust and resilient cooling systems capable of withstanding external environmental factors like wind. The results of this study provide essential insights for improving the design and maintenance strategies of water cooling systems, ensuring their efficiency and reliability in oil plants, especially in wind-prone regions. To evaluate the system's condition, vibration levels are continuously monitored and analyzed using key criteria such as mechanical stability, vibration intensity, and the system’s ability to maintain operational efficiency under varying wind conditions. These insights help identify critical points where vibrations could compromise the cooling system's performance. This methodology ensures a comprehensive assessment of how wind-induced forces affect system stability

Study of transient pressure and fluctuation characteristics in a centrifugal pump using the delayed detached-eddy simulation method

This study employed OpenFOAM, the delayed detached-eddy simulation (DDES) turbulence model, and structured grids to develop numerical models for three centrifugal pumps with twisted blades. The internal pressure field, velocity field, forces, and fluctuation characteristics of the centrifugal pumps are comprehensively analyzed under various operating conditions. The findings indicate that the pressure is relatively higher in the flow passages near the volute tongue and the outlet within the impeller. Regions of high relative velocity (slip velocity) are mainly found on the suction side of the blades, indicating that the design of the blade suction side affects the fluid outward slip performance. As the flow rate increases, the forces and force fluctuation amplitudes of each pump component also rise. Conversely, as the rotational speed increases, the force on the blades or impeller gradually increases while the fluctuation amplitude decreases. In the stationary domain, the force on the volute gradually decreases while the fluctuation amplitude of this force increases. The shape of the volute tongue influences the rate at which pressure inside the volute is converted to outlet pressure. The power spectral density (PSD) of pressure fluctuations is smallest at the nominal flow rate, displaying a clear and distinct axial frequency pattern without complex low-frequency fluctuations. Under low flow and high-speed conditions, the PSD at the axial frequency is relatively small, whereas the pressure PSD at other low frequencies is relatively large. This indicates instability in the flow under these conditions.

Application of synchronous music reinforcement to increase walking speed: A novel approach for training intensity.

Walking is a common and preferred form of exercise. Although there are current recommendations for walking volume (e.g., steps per day), recent research has begun to distinguish volume from intensity (e.g., "brisk" walking) as an important dimension of exercise. Increasing intensity may confer health advantages beyond volume measures because it shifts cardiovascular performance to more vigorous training zones. Reinforcement-based approaches have been valuable in increasing volume measures of exercise, and the present study sought to develop a corresponding reinforcement approach to training walking intensity. For this study, we used a continuous reinforcement paradigm where music played only while walking met specified criteria; otherwise, music playback stopped. As a result, music was synchronized with walking performance. Seventeen participants walked on a nonmotorized treadmill at a self-selected pace. Across the session, different conditions arranged for music to play independent of walking speed or contingent on speed increases or decreases. An extinction component assessed performance when music was withdrawn completely. Walking speed was selectively increased and decreased by adjusting the contingencies that were arranged for music, and variability in speed increased during extinction, with both findings indicating that music was a reinforcer. Heart rate was also increased to moderate-vigorous intensities during reinforcement. The findings provide a compelling case that walking intensity can be modified by music reinforcement. We suggest that synchronous schedules may be an important foundation for future exercise technologies that are based on reinforcement.

Acute ergogenic effects of repetitive maximal breath-holding maneuvers on hematological and physiological responses: a graded exercise test investigation.

Repetitive maximal breath-holds (BHs or apneas) have been noted to induce advantageous hematological and blood buffering changes. Building on this, the hypothesis was formulated that the execution of repeated maximal BH efforts might lead to subsequent enhancements in performance during a time-to-exhaustion test. This study investigated the acute effects of five static maximal breath-holding maneuvers conducted with face immersion in cold water (10°C) on subsequent graded exercise test (GET) performance. Seventeen well-trained participants completed a GET on a motorized treadmill under two randomized cross-over conditions: baseline measurement (CON) and after five repeated maximal breath-holding efforts (EXP). The GET protocol consists of incremental increases in speed until exhaustion. After the fifth breath-hold, participants in the EXP condition exhibited significant (P < 0.05) increases in hematocrit, hemoglobin concentration, red blood cell count, and muscle deoxygenation, accompanied by a reduction in blood lactate concentration (4.09 ± 2.21%, 3.9 ± 1.76%, 3.96 ± 2.1%, 81.48 ± 23.83%, and 15.22 ± 17.64%, respectively), compared to CON. During GET, the EXP condition showed a significantly (P < 0.05) delayed onset time of the second ventilatory threshold (3.14 ± 5.85%) and (P < 0.05) increased time to exhaustion (0.75 ± 1.02%). This evidence suggests that repeated maximal static breath-holding maneuvers enhance the oxygen delivery system by increasing the circulation of reserve red blood cells, heightened muscle oxygen deoxygenation, enhanced aerobic metabolism utilization, and postponing the transition from aerobic to anaerobic metabolism, implying a potential ergogenic effect. While pre-exercise breath-holding shows promise for improving time-to-exhaustion and optimizing subsequent distance running performance, further in-depth investigation is essential to fully elucidate the underlying mechanistic factors.

Optimizing Cutting Parameters for Effective Turning of EN-31 Steel by Utilizing Vegetable-Based Cutting Fluids as a Coolant

&lt;div&gt;The primary objective of this article is to study the improvement of machining efficiency of EN-31 steel by optimizing turning parameters using newly developed cutting fluids with different proportions of aloe vera gel and coconut oil, utilizing the Taguchi technique. Furthermore, performance metrics including material removal rate (MRR), surface roughness, and tool wear rate (TWR) were assessed. Analysis of variance (ANOVA) suggested that as cutting speed and feed increase, the MRR is positively influenced, but likewise tool wear is intensified. The surface roughness exhibited a positive correlation with cutting speed, and a negative correlation with increasing both cutting speed and feed. It was found that the maximum MRR value was attained at a cutting speed of 275 m/min, a feed rate of 1.00 mm/rev, and a cutting fluid composition of 30% aloe vera and 70% coconut oil. For the best surface smoothness, it is advisable to adjust the cutting speed to 350 m/min and the feed rate to 0.075 mm/rev. A cutting speed of 275 m/min and a feed rate of 1.00 mm/rev led to a lower TWR. The results suggest that the combined use of coconut oil and aloe vera as cutting fluids improves the turning quality of EN-31 steel, particularly when employing a combination of 30% aloe vera and 70% coconut oil. As a possible solution for performance problems in achieving desired results during the turning of EN-31 steels, these recommendations may be used in industries to enhance turning performance.&lt;/div&gt;

Influence of Connecting Cables on Stator Winding Overvoltage Distribution under High-Frequency Pulse Width Modulation

In the variable frequency motor drive system, because the cable impedance does not match the motor impedance, the reflection wave of the voltage wave will be generated. The superposition of reflected voltage waves can lead to overvoltage at the motor ends, which can damage the insulation structure. In this paper, the equivalent circuit models of cable and stator winding are established, respectively. The overvoltage distribution under different power supply frequencies and cable lengths is simulated and analyzed. The influence mechanism of power supply frequency and cable length on the overvoltage distribution of stator winding are studied. The simulation results show that the overvoltage of the first pulse falling edge will be superimposed on the overvoltage of the second pulse rising edge under high-frequency conditions, resulting in a further increase in the overvoltage. The voltage appears in all coils after the middle of the winding. The ground voltage is up to 1.32 times the input voltage, and the inter-turn voltage is up to 9.2 times the average voltage. The increase in cable length will lead to an increase in ground voltage, but the increase in speed will slow down after exceeding the critical length of 300 m. The maximum ground voltage can reach 1.93 times of the input voltage, which is 3.6% different from the calculation result under ideal conditions. The inter-turn voltage changes with the cable length in an N-shaped manner, up to 185 V. The results of this paper are of great significance to further study the insulation design of generator end input.