Search Results (1,395)

The traction behavior in cryogenic solid-lubricated ball bearings (CSLBBs) used in liquid rocket engines (LREs) affects not only the dynamic response of the bearing but also the lubricity and wear characteristics of the solid lubrication coating. The traction coefficient between the ball and raceway depends on factors such as contact material, relative sliding velocity, and contact pressure. However, existing traction curve models for CSLBBs typically consider only one or two of these factors, limiting the accuracy and applicability of theoretical predictions. In this study, a novel traction model for CSLBBs is proposed, which incorporates the combined effects of contact material, relative sliding velocity, and contact pressure. Based on this model, a tribo-dynamic framework is developed to investigate the tribological and dynamic behavior of CSLBBs. The model is validated through both theoretical analysis and experimental data. Results show that the inclusion of solid lubricant effects significantly alters the relative sliding and frictional forces between the rolling elements and the raceway. These changes in turn influence the impact dynamics between the rolling elements and the cage, leading to notable variations in the bearing’s vibrational response. The findings may offer valuable insights for the wear resistance and vibration reduction design of CSLBBs. Full article

Granite formations provide suitable geological conditions for building gravity dams. However, the presence of intruding granite creates a fractured zone. The interaction of this fractured zone with structural planes and faults can create geological conditions that are unfavorable for the anti-sliding stability of gravity dams. This paper identifies the dominant structural planes that affect the anti-sliding stability of dams by studying the three-dimensional intersection relationships between groups of structural planes, faults, and fracture zones. The three-dimensional distribution and occurrence of the dominant structural planes directly impact the anti-sliding stability and sliding failure mode of gravity dams. Through comprehensive field investigations and systematic analysis of engineering geological data, the spatial distribution characteristics of structural planes and fracture zones were quantitatively characterized. Subsequently, the potential for deep-seated sliding failure of the gravity dam was rigorously evaluated and conclusively dismissed through application of the rigid body limit equilibrium method. It was established that the sliding mode of the foundation of the dam under this combination of structural planes is primarily shallow sliding. Additionally, based on the engineering geological data of the area around the dam, a three-dimensional finite element numerical model was developed to analyze stress–strain calculations under seepage stress coupling conditions and compared with calculations made without considering seepage stress coupling. The importance of seepage in the anti-sliding stability of the foundation of the dam was determined. The research findings provide engineering insights into enhancing the anti-sliding stability of gravity dams in granite distribution areas by (1) identifying critical structural planes and fracture zones that control sliding behavior, (2) demonstrating the necessity of seepage-stress coupling analysis in stability assessments, and (3) guiding targeted reinforcement measures to mitigate shallow sliding risks. Full article

The dynamics of the vibrational mode of motion of the driving member of a nonideal system, a mixing–whipping device based on a simple slide-crank mechanism, was studied. The highly nonlinear differential equations of motion were solved numerically by the Runge–Kutta method. The interaction of the mixing–whipping device with the nonideal excitation source causes the rotational speed of the engine shaft and the rotation angle of the driving member to fluctuate, accomplishing a damped process. The parameters of the device and the nonideal energy source have an effect on the kinematic, vibrational and energy characteristics of the system. An increase in the engine’s torque, crank length, number and radius of piston holes, and piston mass, as well as a decrease in the fluid’s density, leads to a reduction in the oscillation range of the crank angle, amplitude and period of angular velocity oscillations of the engine shaft and the mixing–whipping force power. The effects of a nonideal energy source may be used in designing a mixing–whipping device based on a slider-crank mechanism to select effective system parameters and an energy-saving motor in accordance with the requirements of technological processes and products. Full article

Background and Objectives: Dental restorations can be composed of various materials, including amalgams and methacrylate-based resins. The health risks associated with the components of the restorative materials have always been a concern, even more so with the ageing of the restorations. As the micronucleus (MN) test is a standard, accessible, and minimally invasive technique for studying the genotoxic effect of clastogenic chemicals on oral mucosal cells, the current study was conducted to determine the frequency and morphological properties of MN in the exfoliated oral mucosal cells. Materials and Methods: A total of 115 aged composite and amalgam restorations were included in this study. Epithelial cells were collected from the gingival tissue adjacent to the restorations of each patient and stained with a hematoxylin–eosin (HE) stain. After evaluation of the slides, the results were subjected to statistical analysis using Chi-square tests. The level of significance was set at 0.05. Results: The mean number of MN was significantly lower for composite restorations compared to amalgam restorations. There were no statistically significant differences between composite restorations aged 1–5 years, 5–10 years, over 10 years, and amalgam restorations aged over 10 years in the location (p = 0.11), staining (p = 0.11), or morphological characteristics (p = 0.18) of the MN. Conclusions: Despite the main limitation of this study, the lack of a control group, our results suggest that long-term exposure to restorative fillings and the ageing of these materials can cause DNA damage locally in the adjacent sites of oral cavity. Full article

Gantry cranes play a pivotal role in industrial production. Gantry cranes exhibit clear double-swing characteristics in actual working conditions, complicating anti-swing control. Most existing anti-swing control methods are based on a simplified single-pendulum model. The present paper puts forward a double-pendulum model for gantry cranes and proposes an adaptive hierarchical sliding mode control based on a neural network according to the actual working conditions. The use of a neural network and adaptive layered sliding mode control can effectively inhibit chattering, thus improving control performance and stability and achieving the goal of anti-shaking control, thus effectively inhibiting residual oscillation. This method has been demonstrated to be effective in achieving the objective of anti-shudder control, thereby effectively suppressing residual oscillation. Compared with hierarchical sliding mode control, the proposed method reduces the maximum residual oscillation angle of the hook and payload by approximately 80%. In comparison with the conventional sliding mode control, the maximum residual oscillation angle is reduced by approximately 84%. Furthermore, the control force amplitude is reduced to 5.23 N, representing decreases of 30.2% and 37.4%, respectively. These comparative results demonstrate the superior oscillation suppression. The system also shows a reliable performance against potential disturbances. Full article

In comparison to shallow coal seams, deep coal seams exhibit characteristics of high temperature, pressure, and in-situ stress, leading to significant differences in reservoir properties that constrain the effective development of deep coalbed methane (CBM). This study takes the Carboniferous deep 8# coal seam in the Yulin area of Ordos basin as the research subject. Based on the test results from core drilling wells, a comprehensive analysis of the characteristics and variation patterns of coal reservoir properties and a comparative analysis of the exploration and development potential of deep CBM are conducted, aiming to provide guidance for the development of deep CBM in the Ordos basin. The research results indicate that the coal seams are primarily composed of primary structure coal, with semi-bright to bright being the dominant macroscopic coal types. The maximum vitrinite reflectance (R_o,max) ranges between 1.99% and 2.24%, the organic is type III, and the high Vitrinite content provides a substantial material basis for the generation of CBM. Longitudinally, influenced by sedimentary environment and plant types, the lower part of the coal seam exhibits higher Vitrinite content and fixed carbon (FC_ad). The pore morphology is mainly characterized by wedge-shaped/parallel plate-shaped pores and open ventilation pores, with good connectivity, which is favorable for the storage and output of CBM. Micropores (<2 nm) have the highest volume proportion, showing an increasing trend with burial depth, and due to interlayer sliding and capillary condensation, the pore size (<2 nm) distribution follows an N shape. The full-scale pore heterogeneity (fractal dimension) gradually increases with increasing buried depth. Macroscopic fractures are mostly found in bright coal bands, while microscopic fractures are more developed in Vitrinite, showing a positive correlation between fracture density and Vitrinite content. The porosity and permeability conditions of reservoirs are comparable to the Daning–Jixian block, mostly constituting oversaturated gas reservoirs with a critical depth of 2400–2600 m and a high proportion of free gas, exhibiting promising development prospects, and the middle and upper coal seams are favorable intervals. In terms of resource conditions, preservation conditions, and reservoir alterability, the development potential of CBM from the Carboniferous deep 8# coal seam is comparable to the Linxing block but inferior to the Daning–Jixian block and Baijiahai uplift. Full article

Slender masonry structures, in the absence of disintegration phenomena, can be idealized as rigid bodies subjected to seismic excitation. In this study, a closed-form expression for the behavior factor (q-factor) associated with overturning collapse under out-of-plane seismic loading is derived. The analysis considers five-step pulse seismic inputs. In the proposed approach, valid for slender masonry structures, sliding failure is neglected, and collapse is assumed to occur when, at the end of the seismic excitation, the rotation of the structure reaches a value equal to its slenderness. Based on this criterion, it is possible to derive a formulation for the q-factor as a function of a dimensionless parameter that combines the geometric characteristics of the slender structure and the period of the applied accelerogram. To validate the proposed formulation, a comparative analysis is conducted against the results obtained from a numerical integration of the motion equation using a set of 20 natural accelerograms recorded in Italy. The characteristic period of each accelerogram is evaluated through different methodologies, with the aim of identifying the most suitable approach for application in simplified seismic assessment procedures. Full article

Reconfigurable Intelligent Surface (RIS) has emerged as a promising enabling technology for wireless communications, which significantly enhances system performance through real-time manipulation of electromagnetic wave reflection characteristics. In RIS-assisted communication systems, existing deep learning-based channel state information (CSI) feedback methods often suffer from excessive parameter requirements and high computational complexity. To address this challenge, this paper proposes LwCSI-Net, a lightweight autoencoder network specifically designed for RIS-assisted multiple-input single-output (MISO) systems, aiming to achieve efficient and low-complexity CSI feedback. The core contribution of this work lies in an innovative lightweight feedback architecture that deeply integrates multi-layer convolutional neural networks (CNNs) with attention mechanisms. Specifically, the network employs 1D convolutional operations with unidirectional kernel sliding, which effectively reduces trainable parameters while maintaining robust feature-extraction capabilities. Furthermore, by incorporating an efficient channel attention (ECA) mechanism, the model dynamically allocates weights to different feature channels, thereby enhancing the capture of critical features. This approach not only improves network representational efficiency but also reduces redundant computations, leading to optimized computational complexity. Additionally, the proposed cross-channel residual block (CRBlock) establishes inter-channel information-exchange paths, strengthening feature fusion and ensuring outstanding stability and robustness under high compression ratio (CR) conditions. Our experimental results show that for CRs of 16, 32, and 64, LwCSI-Net significantly improves CSI reconstruction performance while maintaining fewer parameters and lower computational complexity, achieving an average complexity reduction of 35.63% compared to state-of-the-art (SOTA) CSI feedback autoencoder architectures. Full article

Federated learning (FL) enables multiple participants to collaboratively train models while efficiently mitigating the issue of data silos. However, large-scale heterogeneous data distributions result in inconsistent client objectives and catastrophic forgetting, leading to model bias and slow convergence. To address the challenges under non-independent and identically distributed (non-IID) data, we propose DPAO-PFL, a Dynamic Parameter-Aware Optimization framework that leverages continual learning principles to improve Personalized Federated Learning under non-IID conditions. We decomposed the parameters into two components: local personalized parameters tailored to client characteristics, and global shared parameters that capture the accumulated marginal effects of parameter updates over historical rounds. Specifically, we leverage the Fisher information matrix to estimate parameter importance online, integrate the path sensitivity scores within a time-series sliding window to construct a dynamic regularization term, and adaptively adjust the constraint strength to mitigate the conflict overall tasks. We evaluate the effectiveness of DPAO-PFL through extensive experiments on several benchmarks under IID and non-IID data distributions. Comprehensive experimental results indicate that DPAO-PFL outperforms baselines with improvements from $5.41\%$ to $30.42\%$ in average classification accuracy. By decoupling model parameters and incorporating an adaptive regularization mechanism, DPAO-PFL effectively balances generalization and personalization. Furthermore, DPAO-PFL exhibits superior performance in convergence and collaborative optimization compared to state-of-the-art FL methods. Full article

This study introduces a new method for modeling the nonlinear behavior of adhesively bonded composite steel–concrete T-beam systems. The model characterizes the interfacial behavior between the steel beam and the concrete slab using a strain compatibility approach within the framework of linear elasticity. It captures the nonlinear distribution of shear stresses over the entire depth of the composite section, making it applicable to various material combinations. The approach accounts for both continuous and discontinuous bonding conditions at the bonded steel–concrete interface. The analysis focuses on the top flange of the steel section, using a T-beam configuration commonly employed in bridge construction. This configuration stabilizes slab sliding, making the composite beam rigid, strong, and resistant to deformation. The numerical results demonstrate the advantages of the proposed solution over existing steel beam models and highlight key characteristics at the steel–concrete interface. The theoretical predictions are validated through comparison with existing analytical and experimental results, as well as finite element models, confirming the model’s accuracy and offering a deeper understanding of critical design parameters. The comparison shows excellent agreement between analytical predictions and finite element simulations, with discrepancies ranging from 1.7% to 4%. This research contributes to a better understanding of the mechanical behavior at the interface and supports the design of hybrid steel–concrete structures. Full article

The diagnosis of open-circuit (OC) faults in power switches is the premise for implementing fault-tolerant control, a critical aspect in ensuring the reliable operation of three-level hybrid active neutral-point-clamped (HANPC) converters in flexible distribution networks. However, existing fault diagnosis methods do not clearly reveal the relationship between the switching-state sequence state and the modulation voltage before and after the fault, which limits their applicability in grid-tied HANPC converters. In this article, a generalized voltage residuals model, taken as the primary diagnostic variable, is proposed for switch OC fault diagnosis in HANPC converters, and the physical meaning is established by introducing the metric of “the variation of the pulse equivalent area”. To distinguish between faulty switches with similar fault characteristics, the neutral current path is reconfigured with a set of rearranged gate sequences. Meanwhile, the auxiliary diagnostic variable, named the current polarity state variable, is developed by means of a sliding window counting algorithm. Additionally, as a case study, a diagnostic criterion for the single-switch fault of HANPC converters is designed by using proposed diagnostic variables. Experimental results are presented to verify the effectiveness of the proposed fault diagnosis method, which achieves accurate faulty switch identification in all tested scenarios within 25 ms. Full article

Stones in farmland soil affect the efficiency of agricultural mechanization and the efficient growth of crops. In order to solve the problems of traditional stone pickers, such as large soil disturbance, high soil content and low picking rate, this paper introduces the Archimedean curve with constant radial expansion characteristics into the design of the core working parts of the drum picker and designs a new type of drum stone picker. The key components such as spiral blades, rollers, and scrapers were theoretically analyzed, the structural parameters of the main components were determined, and the reliability of the spiral blades was checked using ANSYS Workbench software. Through the preliminary stone-picking performance test, the forward speed of the stone picker, the rotation speed of the drum, and the starting sliding angle of the spiral blade were determined as the test influencing factors. The picking rate and soil content of the stone picker were determined as the test indicators. The response surface test was carried out in the Design-Expert13.0 software. The results show that, when the forward speed of the stone picker is 0.726 m/s, the drum speed is 30 rpm, and the initial sliding angle of the spiral blade is 26.214°, the picking rate is 91.458% and the soil content is 3.513%. Field tests were carried out with the same parameters, and the picking rate was 91.42% and the soil content was 3.567%, with errors of 0.038% and 0.054% compared with the predicted values, indicating that the stone picker meets the field operation requirements. These research results can provide new ideas and technical paths for improving the performance of pickers and are of great value in promoting the development of advanced harvesting equipment and the efficient use of agricultural resources. Full article

Hydraulic actuated legged robots display bright prospects and significant research value in areas such as unmanned area surveying, disaster rescue, military fields, and other scenarios owing to their excellent bionic characteristics, particularly their heavy payload capabilities and high power density. To realize the all-terrain adaptation locomotion of the hydraulic hexapod robot (HHR) with a heavy payload, one alternative control framework is position–posture control based on joint position control. As the foundation for the steady locomotion of HHRs, it is imperative to realize high-precision joint position control to improve the robustness under external disturbances during the walking process and to complete the attitude control task. To address the above issues, this paper proposes a sliding mode repetitive control based on the unknown dynamics estimator (SMRC + UDE) for the knee and hip joints of the HHR with a two-stage supply pressure hydraulic system (TSS). The effectiveness of the SMRC + UDE method is verified using a simulation environment and the ZJUHEX01 prototype experimental platform, and it is compared with the results for PID and adaptive robust sliding mode control (ARSMC). The results show that SMRC + UDE may be more suitable for our HHR, considering both the control performance and efficiency factors. Full article

To elucidate the key material parameters governing the tribological performance of ceramic composites under dry sliding against steel, this study presents a comprehensive comparative assessment of the microstructural characteristics, mechanical performance, and tribological behavior of two alumina–zirconia (Al₂O₃–ZrO₂) ceramic composites, each reinforced with a 42 vol.% carbide phase: zirconium carbide (ZrC) and tungsten carbide (WC). Specifically, tungsten carbide (WC) was selected for its exceptional bulk mechanical properties, while zirconium carbide (ZrC) was chosen to contrast its potentially different interfacial reactivity against a steel counterface. ZrC and WC were selected as reinforcing phases due to their high hardness and distinct chemical and interfacial properties, which were expected to critically affect the wear and friction behavior of the composites under demanding conditions. Specimens were consolidated via spark plasma sintering (SPS). The investigation encompassed macro- and nanoscale hardness measurements (Vickers hardness HV₁, HV₁₀; nanoindentation hardness H), elastic modulus (E), fracture toughness (K_IC), coefficient of friction (COF), and specific wear rate (W_s) under unlubricated reciprocating sliding against 100Cr6 steel at normal loads of 10 N and 25 N. The Al₂O₃–ZrO₂–WC composite exhibited an ultrafine-grained microstructure and markedly enhanced mechanical properties (HV₁₀ ≈ 20.9 GPa; H ≈ 33.6 GPa; K_IC ≈ 4.7 MPa·m^½) relative to the coarse-grained Al₂O₃–ZrO₂–ZrC counterpart (HV₁₀ ≈ 16.6 GPa; H ≈ 27.0 GPa; K_IC ≈ 3.2 MPa·m^½). Paradoxically, the ZrC-reinforced composite demonstrated superior tribological performance, with a low and load-independent specific wear rate (W_s ≈ 1.2 × 10⁻⁹ mm³/Nm) and a stable steady-state COF of approximately 0.46. Conversely, the WC-reinforced system exhibited significantly elevated wear volumes—particularly under the 25 N regime—and a higher, more fluctuating COF. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX) of the wear tracks revealed the formation of a continuous, iron-enriched tribofilm on the ZrC composite, derived from counterface material transfer, whereas the WC composite surface displayed only sparse tribofilm development. These findings underscore that, in steel-paired tribological applications of Al₂O₃–ZrO₂–based composites, the efficacy of interfacial tribolayer generation can supersede intrinsic bulk mechanical attributes as the dominant factor governing wear resistance. Full article

The strength parameters of fault gouge are critical factors that influence sealing capacity and fault reactivation in underground gas storage reservoirs. This study investigates the shear characteristics of remolded fault gouge under varying hydro-mechanical conditions, focusing on the coupled influence of water content and cementation. Sixty fault gouge samples are prepared using a mineral mixture of quartz, montmorillonite, and kaolinite, with five levels of water content (10–30%) and three cementation degrees (0%, 1%, 3%). Direct shear tests are conducted under four normal stress levels (100–400 kPa), and microstructural characteristics are examined using SEM. The results show that shear strength and cohesion exhibit a non-monotonic trend with water content, increasing initially and then decreasing, while the internal friction angle decreases continuously. Higher cementation degrees not only enhance shear strength and reduce the softening effect caused by water but also shift the failure mode from ductile sliding to brittle, cliff-type rupture. Moreover, clay content is found to modulate the degree—but not the trend—of strength parameter responses to water and cementation variations. Based on the observed mechanical behavior, a semi-empirical shear strength prediction model is developed by extending the classical Mohr–Coulomb criterion with water–cementation coupling terms. The model accurately predicts cohesion and internal friction angle as functions of water content and cementation degree, achieving strong agreement with experimental results (R² = 0.8309 for training and R² = 0.8172 for testing). These findings provide a practical and interpretable framework for predicting the mechanical response of fault gouge under complex geological conditions. Full article