Search Results (138)

(1) Background: Military personnel are required to perform high-intensity actions and tactical tasks under external load, which increases system weight and alters movement mechanics. Understanding how these loaded conditions influence neuromuscular performance is essential for informing physical preparation and readiness monitoring. This study quantified the effects of tactical equipment on countermovement jump (CMJ) and countermovement rebound jump (CMRJ) force–time characteristics in active military personnel and evaluated the within-session reliability of these metrics under loaded and unloaded conditions; (2) Methods: Eighteen male soldiers performed CMJ and CMRJ assessments on dual force plates (1000 Hz) under unloaded and loaded conditions (standardized tactical equipment: 10.6 ± 1.18 kg). Force–time variables were categorized as strategy (phase durations, countermovement depth), driver (mean braking and propulsive force), and outcome (jump height, jump momentum, and modified reactive strength index; mRSI) metrics; (3) Results: CMJ outcome and driver metrics demonstrated good to excellent reliability under load (ICC ≥ 0.87; CV ≤ 8.4%), whereas CMRJ outcome variables showed reduced reliability and greater variability. Loaded conditions reduced jump height and mRSI in both CMJ and CMRJ (p < 0.05), while jump momentum and absolute mean force production increased, whereas force production relative to body mass decreased. During the CMJ (slow-SSC), participants exhibited longer braking and propulsive phase durations, indicating a temporal change in movement strategy under load, whereas CMRJ (fast-SSC) force–time characteristics showed increased contact time and reduced rebound metrics; (4) Conclusions: Overall, fast stretch–shortening cycle tasks appear more sensitive to loading conditions, whereas the CMJ provides a more robust and reliable assessment for monitoring neuromuscular performance in military personnel, particularly when considering both absolute and relative force responses. Full article

Airborne electromagnetic (AEM) surveys map subsurface electrical structures by deploying transmitter and receiver coils on an airborne platform. However, platform-induced vibrations are transmitted to the sensors, generating strong motion-induced noise that severely degrades signal quality. To mitigate such noise, this study proposed the use of granular materials as a cushioning medium. An impact model based on the Discrete Element Method (DEM) was developed and validated against drop-weight experiments. Both granular material properties and impactor characteristics were investigated. The study examined the cushioning effects on both the base plate and the impactor under impact loading, and the sensitivity of key parameters was evaluated. The results showed that granular properties had minimal influence on the impactor peak force. Increasing particle Young’s modulus, density, or friction coefficient led to higher peak forces on the base plate, with Young’s modulus and density having significantly stronger effects than friction coefficient. Additionally, both the impactor size and velocity correlate positively with the peak forces transmitted to the base plate and experienced by the impactor. Under thin layer conditions, the impactor force was more sensitive to impact parameters, while in thick layers it was mainly determined by particle rearrangement and energy dissipation mechanisms. These findings reveal the mechanisms governing granular cushioning and provide a theoretical basis for vibration isolation design in AEM systems to preserve high-fidelity signals. Full article

This study aims to advance the understanding of laminar magnetohydrodynamic (MHD) fluid flow between two parallel plates subjected to a uniform transverse magnetic field, motivated by its significant applications in engineering and industrial systems such as nuclear reactor cooling, MHD generators, and electromagnetic pumping devices. The governing equations are simplified using a one-parameter Lie group symmetry transformation, which exploits the inherent symmetry properties of the system to reduce the original unsteady partial differential equations to a system of ordinary differential equations. The reduced equations are solved exactly under appropriate boundary and initial conditions, ensuring mathematically consistent and physically realistic solutions. A comprehensive analysis is conducted to examine the influence of key physical parameters, along with the applied magnetic field, on the velocity, temperature, and concentration profiles. The selected parameter ranges encompass a broad spectrum of physically relevant cases, enabling a detailed assessment of their effects. The results indicate that the transverse magnetic field exerts a damping effect on the flow, reducing the velocity profile due to the Lorentz force. Moreover, an increase in the Schmidt number accelerates the achievement of a steady-state concentration, while higher Prandtl numbers reduce the temperature profile. In contrast, the radiation parameter enhances the temperature distribution. In addition, the skin-friction coefficient is presented graphically, and the Nusselt number is evaluated to characterize the heat transfer performance. Overall, the findings provide valuable insight into the effects of magnetic, thermal, and solutal parameters on laminar MHD flow between parallel plates. Full article

The impact of large boulders transported by debris flows is a primary cause of structural damage to mitigation works. However, quantitative modeling remains difficult because of the scarcity of field measurements and the complexity of the flow medium. In this study, a theoretical model for boulder impact force in debris flows is developed using dimensional analysis based on the Buckingham theorem, subsequently simplified to two dimensionless parameters, and then validated through a series of controlled laboratory experiments. Marble spheres were used as impactors and were released to strike a rigid steel plate under three types of media: clear water, bentonite slurry, and debris flows containing particles of different size classes. The experiments were designed to isolate and quantify the influence of the flow rheology and the suspended solid phase on impact forces. The results show that the impact coefficient c is strongly governed by the debris flow yield stress, bulk density, and the size of suspended particles, following the relationship c = 0.183[τ/(rgd₁)]^−0.1(d/d₀)^0.05. Based on this relationship, a generalized formula for calculating boulder impact forces in debris flows is proposed. The model is further evaluated using field monitoring data from Jiangjiagou, Yunnan Province. The back-calculated boulder diameters fall predominantly within the range of 0.1–0.3 m (76.3–86.8%), which is consistent with field observations. These results indicate that the proposed model captures the essential physical mechanisms governing boulder impacts and provides a rational basis for selecting design parameters in debris flow mitigation engineering. The array-type piezoelectric impact sensing system designed in this study achieves high-precision and high-stability measurement of the impact force of large boulders in debris flows, providing a new sensing technology for debris flow impact monitoring. Full article

The automotive sector is currently undergoing a rapid and complex transition from classic internal combustion engines to hybrid or fully electric propulsion systems, at the core of which is the battery pack. Currently, the battery packs of almost all electric vehicles on the road consist of lithium-ion cells. The thermal management of these cells represents a complex and fundamental challenge, essential not only to ensure optimal vehicle performance but also to guarantee passenger safety. Therefore, this paper examines and compares four main systems used for battery thermal management, highlighting their strengths, weaknesses, and overall effectiveness. First, a standard module comprising 21700 cylindrical cells, representative of automotive applications, is designed. Subsequently, computational fluid dynamics (CFD) thermal analyses of this module are performed to evaluate four different cooling methods: forced air cooling, bottom cold plate cooling, liquid tube cooling, and immersion cooling combined with tab cooling. Finally, an experimental validation is conducted by testing these systems on a physical module, which is subjected to the same electrical discharge profile simulated in the CFD analyses, to verify the effectiveness of the four considered methods. Full article

Background: CrossFit^® has gained widespread popularity as a high-intensity training modality, yet evidence describing neuromuscular performance characteristics in this population remains limited. This study aimed to evaluate isometric and ballistic strength profiles in trained CrossFit^® athletes and to identify sex-based differences in absolute and relative neuromuscular performance. Methods: Seventy-two athletes participated (41 males and 31 females) participated in the study, completing two maximal isometric mid-thigh pull (IMTP) tests and three countermovement jump (CMJ) tests within a single testing session. Assessments were conducted using a dual force plate system (Hawkin Dynamics, Westbrook, ME, USA). Results: In the IMTP, males exhibited substantially higher absolute isometric force outputs, including peak force (3059 ± 576 vs. 1899 ± 324 N; p < 0.001) and relative peak force (36.34 ± 6.74 vs. 30.99 ± 4.41 N/kg; p < 0.001). Rates of force development were also greater in males for both early (0–50 ms: 7665 ± 5420 vs. 4001 ± 3021 N/s; p < 0.001) and late phases (0–250 ms: 5350 ± 1832 vs. 3035 ± 886 N/s; p < 0.001). However, no significant sex differences were detected in time to peak force (2.31 ± 1.27 vs. 1.94 ± 1.04 s) or dynamic strength index (0.72 ± 0.12 vs. 0.73 ± 0.12 a.u.). In ballistic performance using CMJ, males achieved higher jump height (0.33 ± 0.07 vs. 0.23 ± 0.05 m; p < 0.001), jump momentum (215 ± 27.9 vs. 131 ± 19.1 kg·m/s; p < 0.001), and modified reactive strength index (0.46 ± 0.11 vs. 0.32 ± 0.08 a.u.; p < 0.001). Relative propulsive and braking forces were also moderately greater in males. Notably, sex differences were reduced when variables were normalized to body mass or peak force, indicating comparable relative neuromuscular function across sexes. Conclusions: These findings provide descriptive neuromuscular performance data for CrossFit^® athletes and show that sex-based differences primarily reflect disparities in absolute force-production capacity rather than intrinsic neuromuscular efficiency. Such insights may support more precise, evidence-informed, and sex-specific training prescriptions to optimize performance. Full article

Background: Voluntary activation testing quantifies the ability of the motor nervous system to produce maximal force. Laboratory assessment of ankle plantar flexor voluntary activation is common, but field testing in practical settings is limited by equipment portability. We aimed to compare plantar flexor voluntary activation and maximal voluntary contraction (MVC) using a portable device with a standardised laboratory method and evaluate the test–retest reliability of the portable protocol. Methods: We performed a pseudo-randomised, crossover design. Participants completed two protocols: (1) portable force plate testing and (2) a laboratory-based isokinetic dynamometer. Voluntary activation was assessed using twitch interpolation via tibial nerve stimulation. Differences between protocols were analysed using generalised estimating equations. Reliability was assessed with the intraclass correlation coefficient (ICC), standard error of measurement (SEM), and coefficient of variation (CV). Results: Twenty healthy participants (8 females, 12 males; median age 28.5 years) were included. No difference between protocols was detected for voluntary activation (β = 0.6, p = 0.68). The portable protocol demonstrated good reliability (ICC = 0.85) and low measurement error (SEM = 2.56%, CV = 2.79%). Conclusions: We demonstrated that the portable protocol is a valid and reliable method for assessing plantar flexor voluntary activation. It is suitable for assessing within-subject changes over time and can reduce participant attendance burden for neurophysiological muscle testing. Full article

Air-cooled heat sinks remain a practical and cost-effective solution for thermal management in high power-density electronic systems. This study investigates the thermal–hydraulic performance of a plate pin-fin heat sink operating under forced convection, with emphasis on the coupled interaction between heat-transfer enhancement and pressure-drop penalty. The proposed hybrid configuration combines the low flow resistance of plate fins with the wake-induced mixing characteristics of pin-fin elements, thereby modifying boundary-layer development and flow structures within the fin channels. This review comprehensively analyzes existing experimental measurements across a range of Reynolds numbers to evaluate the average Nusselt number, thermal resistance, and friction factor. The results demonstrate that the inclusion of pin elements significantly enhances convective heat transfer through increased flow disruption and vortex formation, while incurring a moderate increase in pressure loss relative to conventional plate-fin designs. In addition, flow visualization and temperature mapping reveal improved heat transfer uniformity along the streamwise direction, particularly at intermediate Reynolds numbers where transition effects become pronounced. Empirical correlations were developed to relate the Nusselt number and friction factor to Reynolds number and key geometric ratios, providing predictive capability for thermo-hydraulic performance assessment. The findings indicate that fin-scale geometric optimization plays a dominant role in achieving improved overall performance and that the plate pin-fin configuration offers a favorable trade-off between heat-transfer augmentation and hydraulic efficiency for forced-convection electronic cooling applications. Full article

Ground reaction force (GRF) is essential for maintaining dynamic stability and generating power during the golf swing. Traditional GRF assessment relies on force plates, limiting measurement to laboratory environments and restricting evaluation of natural, field-based performance. Recent work has explored wearable inertial measurement units (IMUs) and data-driven models to estimate GRF during simple locomotor tasks, yet no study has examined whether coupled lower-limb kinematics can predict three-dimensional GRF during complex, high-speed movements such as the golf swing. This study collected bilateral hip, knee, and ankle joint angles from IMUs, along with 3D GRF data, to evaluate five biomimetic deep learning (DL) architectures across seven sensor configurations. The TCN-BiGRU model achieved the highest accuracy (R² = 0.94 ± 0.02, MRE = 0.044 ± 0.01, NRMSE = 0.064 ± 0.01) among the architectures evaluated in this study, effectively capturing both local and long-range temporal dependencies in human movement. The full bilateral lower-limb configuration yielded the best overall performance, whereas using only the lead leg provided a cost-efficient alternative with minimal loss of accuracy. Among the GRF components, the vertical direction showed the greatest predictive reliability. These findings demonstrate the feasibility and potential of kinematic–force modeling and support the development of wearable, field-ready systems for GRF estimation in dynamic sports environments. Full article

Heat creep is a critical failure mechanism in fused filament fabrication (FFF) extrusion systems, arising from insufficient thermal isolation between the hot end and cold end. It causes premature polymer softening, extrusion instability, and nozzle clogging, especially when active cooling is reduced or lost. This study experimentally evaluates passive cooling strategies for mitigating heat creep in consumer-class printers by exploiting ambient thermal stratification within the build volume. Vertical air-temperature gradients above heated build plates were measured for enclosed, semi-enclosed, and open-frame architectures, revealing pronounced stratification. Cold-end temperatures were then quantified for a stock extruder under forced and natural convection while printing polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS). Finally, a modified cold-end using a heat pipe to relocate heat rejection to an elevated heat sink was tested under identical conditions, assuming fan failure. Elevated heat-rejection locations experienced lower ambient temperatures and improved natural-convection heat transfer. Relative to the stock configuration, the augmented design reduced cold-end temperatures and improved thermal stability during representative printing cycles without continuous active cooling—the improvement percent is ~8%. The results demonstrate that coupling heat-pipe conduction with environmental thermal gradients can mitigate heat creep and improve extruder reliability with lower energy demand. Full article

This study considers the dynamic stability of a three-layered annular plate, whose facings are made of functionally graded material in the radial direction. The plate is subjected to linearly increasing in-plane forces applied at either the inner or outer edge. The effect of the heterogeneity of the plate-facing material on the dynamic response is analyzed in detail. The main parameters defining the stability state—such as critical dynamic load, critical time, maximum deflection, and buckling mode—are specifically evaluated. The problem is analyzed using two approximation methods: the finite difference method and the finite element method. Numerical calculations were carried out using two approaches: the author’s program following analytical calculations, and the ABAQUS system. The results show the importance of modeling the plate with an appropriate material function describing the radial gradation, which significantly affects the plate’s dynamic stability response and critical parameters. Full article

The center of pressure (CoP) is a key biomechanical indicator for assessing balance and fall risk; however, force plates, the gold standard for CoP measurement, are costly and impractical for widespread use. Low-cost alternatives such as inertial units or pressure sensors are limited by drift, sparse sensor coverage, and directional performance imbalances, with previous supervised learning approaches reporting ML-AP NRMSE differences of 3.2–4.7% using 1D time-series models on sparse sensor arrays. Therefore, we propose a tactile sensor-based CoP estimation system using deep learning models that can extract 2D spatial features from each pressure distribution image with CNN/ResNet encoders followed by a Bi-LSTM for temporal patterns. Using data from 23 healthy adults performing four balance protocols, we compared ResNet-Bi-LSTM and CNN-Bi-LSTM with baseline CNN-LSTM and Bi-LSTM models used in previous studies. Model performance was validated using leave-one-out cross-validation (LOOCV) and evaluated with RMSE, NRMSE, and R². The ResNet-Bi-LSTM with angular features achieved the best performance, with RMSE values of 18.63 ± 4.57 mm in the mediolateral (ML) direction and 17.65 ± 3.48 mm in the anteroposterior (AP) direction, while reducing the ML/AP NRMSE difference to 1.3% compared to 3.2–4.7% in previous studies. Under dynamic protocols, ResNet-Bi-LSTM maintained the lowest RMSE across models. These findings suggest that tactile sensor-based systems may provide a cost-effective alternative to force plates and hold potential for applications in gait analysis and real-time balance monitoring. Future work will validate clinical applicability in patient populations and explore real-time implementation. Full article

Post-stroke gait dysfunction is biomechanically heterogeneous, yet biomechanically informed classifications of functional walking remain underdeveloped. In particular, there is a lack of clinically accessible methods for classifying gait deficits that account for propulsion impairments—a historically laboratory-dependent gait parameter requiring measurement with force plate systems. This study examined whether propulsion impairment can be classified by combining a global measure of walking function (i.e., the 10 m walk test speed) with specific measures of dynamic walking ability derived from the Functional Gait Assessment (FGA). Forty participants >6 months post-stroke completed biomechanical evaluations quantifying propulsion during walking and clinical assessments including the FGA. Multivariable stepwise regression identified the FGA items most strongly associated with paretic propulsion. Models augmented with these FGA items explained 15% greater variance in the paretic propulsion peak and 7% greater variance in paretic propulsion impulse compared with models using Comfortable Walking Speed (CWS) alone. Incorporating FGA items also yielded the highest overall accuracy (72.5% vs. 60% with CWS alone) and best per-class performance in propulsion severity classification. These findings establish the co-assessment of walking speed and targeted FGA items as a clinically feasible approach to biomechanically informed classification of post-stroke gait dysfunction. Full article

This study proposes an electromagnetic balance-based structural design and shim plate application to improve the response characteristics of an electromagnetic brake. Electromagnetic brakes typically experience response delay due to inductive effects and residual magnetic flux after power-off. To address this issue, the inner and outer thicknesses of the stator were parameterized to achieve balanced magnetic flux distribution, and a non-magnetic shim plate (SUS 304) was applied to reduce residual flux within the electromagnet. Finite element analysis (FEA) was conducted to evaluate the influence of structural parameters on the magnetic flux balance and attractive force. The optimized stator geometry provided a stable electromagnetic balance, and the shim plate effectively reduced the response delay and improved the overall response performance compared with the conventional design. These findings demonstrate that the proposed electromagnetic balance design combined with shim plate application is an effective approach to enhance the reliability and control responsiveness of electromagnetic brakes, with potential applicability to robotic and industrial actuator systems. Full article