Search Results (88)

This paper proposes a comprehensive framework, Theory–Simulation–Experimental Verification, for the elasto-aerodynamic analysis of elastic foil gas bearings (EFGBs). In contrast to many studies that approximate the foil structure using simplified two-dimensional models, the present work adopts a macro-element beam theory model that incorporates the actual 3D geometry, nonlinear elasticity, and frictional contact effects, and couples it directly with the Reynolds equation. To improve accuracy and robustness, the macro-beam results are validated against a fully coupled fluid–structure interaction (FSI) model developed in COMSOL Multiphysics. Emphasis is placed on quantifying the influence of foil thickness, clearance, and eccentricity, where the pressure distribution, foil deflection, and load capacity are obtained through the coupled solver. The results reveal that increasing foil thickness from 0.1 mm to 0.2 mm elevates the peak gas film pressure from 1.36 × 10⁵ Pa to 1.97 × 10⁵ Pa while simultaneously reducing displacement and pressure fluctuations, thereby enhancing bearing stability. Smaller clearances are shown to increase load capacity but also induce stronger oscillatory flow behavior, indicating a stiffness–stability trade-off. Additionally, prototype experiments with a 0.05 mm clearance confirm practical lift-off at 4300–7000 rpm under 10–30 N external loads, with measured torques of 0.18–0.30 N·m. By combining computational efficiency, 3D fidelity, and experimental validation, the proposed framework provides quantitative guidance for the design and optimization of EFGBs used in high-speed turbomachinery, such as aviation and compact energy systems, including turbine-based air-cycle refrigeration units and small gas-turbine rotors for unmanned aerial vehicles. Full article

This study aimed to compare the acute effects of three eccentric training strategies—constant resistance (CR), accentuated eccentric loading (AEL), and accelerated eccentrics (AE)—on the performance and biomechanical characteristics of the concentric phase of the squat, while maintaining a consistent squat depth. Twenty-four experienced resistance-trained male collegiate athletes (age: 21.92 ± 2.66 years; height: 175.88 ± 4.39 cm; body mass: 73.18 ± 8.08 kg) were recruited. A randomized crossover design was employed, where participants completed three squat protocols (eccentric load/concentric load/eccentric duration): AEL (90% 1RM/60% 1RM/2 s), CR (60% 1RM/60% 1RM/2 s), and AE (60% 1RM/60% 1RM/as fast as possible). Throughout the squats, kinematic and kinetic data were synchronously collected using an 8-camera 3D infrared motion capture system and two 3D force plates. The mean concentric barbell velocity in the AE condition was significantly higher than in both the AEL and CR conditions (p < 0.001). Furthermore, the AE condition demonstrated significant advantages in multiple biomechanical variables, including peak ground reaction force, as well as peak angular velocity and peak joint moments of the three lower limb joints (p < 0.05). With identical concentric loads and range of motion, increasing the velocity of the eccentric phase significantly enhances subsequent concentric performance and force output. In contrast, while the AEL strategy increases the mechanical load during the eccentric phase, its potentiating effect on concentric performance is relatively limited. These findings suggest that eccentric velocity may be a more critical variable than eccentric load in strength training. Full article

Optimization design is an effective strategy for reducing carbon emissions in building structures. Various exhaustive and metaheuristic methods have been proposed to optimize the carbon emissions of structural components, which has primarily focused on sustainable design during the construction phase. This study proposes a hybrid approach for the life cycle sustainable design of reinforced concrete components, encompassing the material production, construction, carbonization, and end-of-life phases. The resistance of structural components was evaluated through time-dependent reliability indices, and surrogate models were developed using machine learning techniques. The surrogate models were subsequently integrated into a dual-objective genetic algorithm for life cycle sustainable design. Based on the proposed approach, numerical examples including a singly reinforced beam and a biaxially eccentric compressed column were analyzed. The minimum carbon emissions were optimized to 486.2 kg CO_2e and 307.8 kg CO_2e, respectively, representing a reduction of more than 10% compared to the original design. Moreover, parametric and comparative analyses were conducted to identify the key factors influencing life cycle sustainable design. The findings underlined the impact of design methods, system boundaries, and specific design variables such as material strengths and concrete cover depth. Overall, this study enhances the efficiency and applicability of sustainable design for structural components while considering life cycle impacts. Full article

This study conducts a cyclostratigraphic analysis of the third member of the Eocene Shahejie Formation (Es3) in the Laizhou Bay Sag, Bohai Bay Basin, to investigate the influences of astronomically driven climate variations on sea-level changes, sedimentation rates, and depositional environments. We integrated high-resolution geophysical well logs, ostracod fossils, and palynological data from Well B-2 for cyclostratigraphic and paleoclimate analyses. Time series analysis identified orbital cyclicity in the natural gamma-ray (GR) log, with its significance confirmed by correlation coefficients and statistical significance tests. By tuning the GR log to the 405 kyr eccentricity cycle, we constructed a ~7.695 Myr floating astronomical timescale. Integrating the preliminary biostratigraphic framework (based on ostracods and palynology) with the La2010d astronomical solution yielded a high-resolution absolute astronomical timescale for the 1317–2594 m interval of Well B-2, spanning from 33.9 to 41.6 Ma. Sedimentary noise modeling reconstructed the Eocene sea-level curve in the study area, revealing that the 1.2 Myr obliquity modulation cycle was a key driver of sea-level fluctuations. The δ¹³C and δ¹⁸O records confirm the presence of the Middle Eocene Climatic Optimum (MECO), indicating that its stratigraphic signature constitutes a robust marker for regional stratigraphic subdivision in the southern Bohai Bay Basin. Our findings provide new insights into the climatic evolution of the Es3 member in the southern Bohai Bay Basin. Full article

This study investigated the effects of lightweight wearable resistance on the kinetics and kinematics of squat jumps (SJ) and countermovement jumps (CMJ) with 2%, 4%, and 6% body mass (BM). Twenty male athletes (age: 18.05 ± 0.6 years; weight: 76.4 ± 7.6 kg; height: 182.4 ± 5 cm) were assessed on a force plate. Key variables included jump height (JH), concentric (ConT) and eccentric (EccT) phase durations, concentric impulse (CI), mean force (CMF), mean velocity (CMV), mean power (CMP), and relative metrics. Elastic utilization ratios (EUR) were calculated to quantify stretch-shortening cycle enhancement. Load led to decrements in both jumps but with varying sensitivity. With 2% BM the CMJ significantly reduced JH (−8.6%), EccT (−7%), CMV (−4.1%), rCI (−4.1%), rPP (−4.4%), and velocity at PP (−4.8%), whereas variables in the SJ were non-significant until 4–6% BM. EURs observed the greatest differences with 2% BM with JH, CMV, rCMP, and VPP all significantly decreasing (p < 0.05). The varying sensitivity to load across variables observed in the two jumps supports the hypothesis that SJ and CMJ offer distinct diagnostic insights due to varying MTU contraction dynamics and neural factors. This has implications for WR use in training. Further, absolute metrics showed limited load sensitivity. However, when accounting for body mass, relative metrics revealed substantial declines. This indicates absolute values can misrepresent the effects of WR loading. Full article

Transient dynamic balancing of flexible rotors is of significant practical value in engineering. Traditional dynamic balancing requires repeated trial weights and start–stop cycles, resulting in inefficient balancing. This paper proposed a multi-layer LSTM (Long Short-Term Memory) network-based method for transient dynamic balancing of flexible rotors. Firstly, a dynamic model of the rotor bearing system is established using the finite element method. Secondly, leveraging the relationship between transient unbalance force and quantity, a formula using the force zero-crossing to identify unbalance magnitude and phase is derived, and a multi-layer LSTM architecture is established to predict the unbalance force from the rotor dynamic response. Finally, a complete transient dynamic balancing solution based on the multi-layer LSTM network is developed. Simulation verification is conducted on a three-disc rotor, and the identification errors of unbalance phase and eccentricity are both less than 5%. After balancing, the maximum amplitude of the rotor decreases by about 93%. Additional verification is carried out on the rotor test rig. The experimental results show that the multi-layer LSTM flexible rotor transient dynamic balancing method can significantly reduce unbalance vibration: the transient amplitude of the rotor decreases by 70.22%, and the steady-state amplitude decreases by 69.3% after balancing. Full article

Background/Objectives: This study examined the effects of a six-week eccentric–reactive training program on neuromechanical markers of lateral explosiveness, asymmetry, and stretch-shortening cycle (SSC) efficiency in elite male youth table tennis players. Fourteen national-level athletes (mean age = 16.6 years) were assigned to either an experimental group (EG, n = 7) or a control group (CG, n = 7). EG performed flywheel squats and lateral depth jumps three times per week, while CG maintained regular training. Pre- and post-intervention testing included countermovement jumps, reactive strength index (RSI_DJ), force asymmetry, time-to-stabilization, SSC efficiency, and energy transfer ratio (ETR), measured via force plates, EMG, and inertial sensors. Methods: Multi-dimensional statistical analysis revealed coordinated improvements in explosive power and movement efficiency following eccentric training that were not visible when examining individual measures separately. Athletes in the training group showed enhanced neuromechanical control and developed more efficient movement patterns compared to controls. The analysis successfully identified distinct performance profiles and demonstrated that the training program improved explosive characteristics in elite table tennis players. Results: Univariate ANOVAs showed no significant Group × Time effects for RSI_DJ, ETR, or SSC_Eff, although RSI_DJ displayed a moderate effect size in EG (d = 0.47, 95% CI [0.12, 0.82], p = 0.043). In contrast, MANOVA confirmed a significant multivariate Group × Time interaction (p = 0.013), demonstrating integrated neuromechanical adaptations. Regression analysis indicated lower baseline CMJ and RSI_DJ predicted greater RSI improvements. Conclusions: In conclusion, eccentric–reactive training promoted multidimensional neuromechanical adaptations in elite racket sport athletes, supporting the use of integrated monitoring and targeted eccentric loading to enhance lateral explosiveness and efficiency. Full article

This study aimed to evaluate the impact of an 8-week reverse Nordic exercise training (RNET) program on physical fitness in male youth soccer players. A total of 35 players participated in the study and were divided into two groups: the RNET group (n = 19, age 16.39 ± 0.46 years) and the active control group (CG: n = 16, age 16.53 ± 0.48 years). To assess fitness changes, participants were tested on linear sprint speed (5, 10, and 20 m sprints), change-of-direction (CiD) speed (505-CiD), vertical jump (countermovement jump [CMJ]), horizontal jump (standing long jump [SLJ]), drop jump (20 cm drop jump [DJ-20]), and repeated sprint ability (RSA). Significant group-by-time interactions were observed (effect size, [ES] = 0.70 to 1.37), with substantial improvements in the RNET group across linear sprint, CiD, and jumping performances (ES = 0.61 to 1.47), while no significant changes were noted in the CG. However, no significant group-by-time interactions were observed for RSA parameters. Individual response analysis revealed that 63–89% of RNET group exhibited improvements exceeding the smallest worthwhile change (SWC_0.2) threshold. These results suggest that the RNET program is both effective and safe for enhancing physical fitness in male youth soccer players. Full article

The organic working fluid journal bearing is expected to enhance organic Rankine cycle system compactness significantly. In order to serve the practical application of organic working fluid bearings, this study analyzes the influence of key design parameters on the static characteristics under microscale effects. Uncertainty quantification is performed using three methods to address operational deviations. The results reveal the correlations for static characteristic indicators with design parameters in detail. Rarefied gas effects cause negligible pressure deviations (<0.21%), whereas surface roughness significantly improves load capacity. Sensitivity analyses (Morris and Sobol methods) identify eccentricity ratio and gas film thickness as the most influential parameters. KDE results indicate near-normal probability distributions for load and attitude angle. This study provides valuable insights for the design optimization and operational control of organic fluid bearings. Full article

In response to issues of long construction cycles, high pollution, and labor shortages in traditional cast in situ subway station construction, a refined 3D model of a large-segment prefabricated subway station was established using ABAQUS software 2024, with mechanical behavior throughout the construction process studied based on the Shenzhen Huaxia Station project case. The model incorporates a concrete inelastic damage constitutive model and a steel elastic–plastic model, accurately simulates key components, including dry joints of mortise–tenon grooves, prestressed reinforcement, and bolted connections, and implements a seven-phase construction sequence. Research findings indicate the following: (1) During component assembly, the roof vault settlement remains ≤3.8 mm, but backfilling significantly increases displacements (roof settlement reaches 45 mm, middle slab deflection measures 66.91 mm). (2) Longitudinal mortise–tenon joints develop stress concentrations due to stiffness disparities, with mid-column installation slots identified as vulnerable zones exhibiting maximum Von Mises stress of 32 MPa. (3) Mid-column eccentricity induces structural asymmetry, causing increased deflection in longer-span middle slabs, corbel contact stress differentials up to 6 MPa, and bolt tensile stresses exceeding 1.1 GPa. (4) The arched roof effectively transfers loads via three-hinged arch mechanisms, though spandrel horizontal displacement triggers 5 cm rebound in diaphragm wall displacement. Conclusions confirm overall the stability of the prefabricated structure while recommending the optimization of member stiffness matching, avoidance of asymmetric designs, and localized reinforcement for mortise–tenon edges and mid-column joints. Results provide valuable references for analogous projects. Full article

Background: Eccentric cycling exercise (ECC) offers a low-metabolic-demand approach to exercise, potentially making it valuable for patients with pulmonary vascular disease (PVD). The aim of this study was to investigate how quadriceps and frontal cortex oxygenation, assessed by near-infrared spectroscopy (NIRS), differs during ECC compared to concentric cycling exercise (CON) in patients with PVD and in healthy individuals. Methods: This randomized controlled crossover trial involved patients with PVD, defined as either pulmonary arterial hypertension (PAH) or chronic thromboembolic pulmonary hypertension (CTEPH), and healthy volunteers. Participants performed both CON and ECC at identical submaximal work rates, following a stepwise incremental protocol. NIRS was used to continuously monitor tissue oxygenation and surrogates for blood volume changes in the quadriceps and frontal cortex. Results: A total of 57 participants were included, 33 PVD patients (19 with PAH and 14 with CTEPH; 13 women; mean age: 50 ± 15 years) and 24 healthy volunteers (14 women; 50 ± 14 years). In PVD patients, at end-exercise, cerebral tissue oxygenation (CTO) was significantly higher during ECC compared to CON (6.10%; 95% CI: 1.85 to 10.42; p < 0.01), whereas muscle tissue oxygenation (MTO) was similar. In healthy individuals, at end-exercise, CTO was similar during ECC and CON, whereas MTO was significantly higher (2.60%; 95% CI: 0.03 to 5.17; p = 0.047). There were no significant differences in CTO and MTO between patients with PVD and healthy individuals. Discussion: In this randomized controlled crossover trial, patients with PVD exhibited higher CTO during ECC compared to CON, which may indicate altered cerebral oxygen extraction and hemodynamic responses potentially related to impaired vascular function. In contrast, healthy individuals demonstrated higher MTO during ECC, likely reflecting improved muscular oxygen utilization and efficiency due to the mechanical and metabolic characteristics of eccentric exercise. Full article

The Lower–Middle Jurassic of the Kuqa Depression consists of terrestrial clastic deposits containing coal seams and thick lacustrine mudstones, and is of great significance for oil and gas exploration. Based on the comprehensive analysis of core, well-logging, outcrop, and seismic data, the sequence stratigraphy, depositional systems, and the controlling factors of the basin filling in the depression are systematically documented. Four primary depositional systems, including braided river delta, meandering river delta, lacustrine, and swamp deposits, are identified within the Ahe, Yangxia, and Kezilenuer Formations of the Lower–Middle Jurassic. The basin fills can be classified into two second-order and nine third-order sequences (SQ1–SQ9) confined by regional or local unconformities and their correlative conformities. This study shows that the sedimentary evolution has undergone the following three stages: Stage I (SQ1–SQ2) primarily developed braided river, braided river delta, and shallow lacustrine deposits; Stage II (SQ3–SQ5) primarily developed meandering river, meandering river delta, and extensive deep and semi-deep lacustrine deposits; Stage III (SQ6–SQ9) primarily developed swamp (SQ6–SQ7), meandering river delta, and shore–shallow lacustrine deposits (SQ8–SQ9). The uplift of the Tianshan Orogenic Belt in the Early Jurassic (Stage I) may have facilitated the development of braided fluvial–deltaic deposits. The subsequential expansion of the sedimentary area and the weakened sediment supply can be attributed to the planation of the source area and widespread basin subsidence, with the transition of the depositional environments from braided river delta deposits to meandering river delta and swamp deposits. The regional expansion or rise of the lake during Stage II was likely triggered by the hot and humid climate conditions, possibly associated with the Early Jurassic Toarcian Oceanic Anoxic Event. The thick swamp deposits formed during Stage III may be controlled by the interplay of rational accommodation, warm and humid climatic conditions, and limited sediment supply. Milankovitch cycles identified in Stage III further reveal that coal accumulation was primarily modulated by long-period eccentricity forcing. Full article

Background: Athletes commonly use innovative strategies that aim to enhance their cycling performance. Among them, the effectiveness of non-circular chainrings has been a frequent topic of discussion. This systematic review aims to analyze the physiological and performance effects of using non-circular chainrings in cyclists. Methods: A literature search was conducted on populations ranging from recreational to elite-level athletes, following the PRISMA guidelines. The electronic databases searched were PubMed, Web of Science, Academic Search Complete, Scopus, and SportDiscus, using the search terms (“oval chainring*” OR “non-circular chainring*” OR “elliptical chainring*” OR “asymmetric chainring*” OR “Q-Ring*” OR “eccentric chainring*” OR “chainring*”) AND (cycl*), on 11 May 2025. The risk of bias was assessed using the Cochrane Risk of Bias tool with an extension for crossover studies, indicating some concerns regarding the included studies. Results: The initial search identified 291 research articles, which, after applying the screening criteria, resulted in the inclusion of 18 manuscripts. The results suggest that non-circular chainrings do not appear to improve cycling performance metrics or physiological variables during prolonged efforts; however, it is possible that they enhance the sprinting capacity. Conclusions: While the research remains inconclusive, future studies should further explore the effects of non-circular chainrings on sprinting performance. Full article

The purpose of this study was to determine the power produced by knee muscles in normal adults when performing self-selected walking. The power of a single knee muscle is not directly measurable without invasive methods. An EMG-to-force processing (EFP) model was developed, which scaled muscle–tendon unit (MTU) power output to gait EMG. Positive power by each muscle occurred when force was developed during concentric contractions, and negative power occurred with lengthening contractions. The sum of EFP power produced by knee muscles was compared with the kinematics plus kinetics (KIN) knee power at percent gait cycle intervals. Closeness-of-fit of the EFP and KIN power curves (during active muscle forces) was used to validate the model. Key findings were that most knee muscles have a characteristic eccentric-then-concentric contraction pattern, and greatest power was produced by the Semimembranosis, with peak magnitude nearly matched by two vastus muscles (VL, VMO). The EMG-to-force processing approach provides reasonable estimates of active individual knee muscle power in self-selected speed walking in neurologically intact adults. Further, a prolonged period of the gait cycle showed substantial knee flexion or extension in the absence of power produced by muscles acting at the knee. Full article

The theory of orbital forcing as formulated by Milankovitch involves the mediation by the advance (retreat) of ice sheets and the resulting variations in terrestrial albedo. This approach poses a major problem: that of the period of glacial cycles, which varies over time, as happened during the Mid-Pleistocene Transition (MPT). Here, we show that various hypotheses are called into question because of the finding of a second transition, the Early Quaternary Transition (EQT), resulting from the million-year period eccentricity parameter. We propose to complement the orbital forcing theory to explain both the MPT and the EQT by invoking the mediation of western boundary currents (WBCs) and the resulting variations in heat transfer from the low to the high latitudes. From observational and theoretical considerations, it appears that very long-period Rossby waves winding around subtropical gyres, the so-called “gyral” Rossby waves (GRWs), are resonantly forced in subharmonic modes from variations in solar irradiance resulting from the solar and orbital cycles. Two mutually reinforcing positive feedbacks of the climate response to orbital forcing have been evidenced: namely the change in the albedo resulting from the cyclic growth and retreat of ice sheets in accordance with the standard Milankovitch theory, and the modulation of the velocity of the WBCs of subtropical gyres. Due to the inherited resonance properties of GRWs, the response of the climate system to orbital forcing is sensitive to small changes in the forcing periods. For both the MPT and the EQT, the transition occurred when the forcing period merged with one of the natural periods of the climate system. The MPT occurred 1.25 Ma ago, when the dominant period shifted from 41 ka to 98 ka, with both periods corresponding to changes in the Earth’s obliquity and eccentricity. The EQT occurred 2.38 Ma ago, when the dominant period shifted from 408 ka to 786 ka, with both periods corresponding to changes in the Earth’s eccentricity. Through this paradigm shift, the objective of this self-consistent approach is essentially to spark new debates around a problem that has been pending since the discovery of glacial–interglacial cycles, where many hypotheses have been put forward without, however, fully answering all our questions. Full article