Search Results (5,181)

Rotating stall and surge are complex, unsteady flow instability phenomena in aeroengine compressors that pose serious threats to the safety and reliability of both the compressor and the engine as a whole. As aeroengine performance continues to improve, the average stage total pressure ratio and stage loading have steadily increased, presenting significant challenges in designing compressors with sufficient stall margins. In this study, we review key advances in the understanding of axial compressor instability, organizing prior research into three representative historical periods. This chronological framework aims to clarify evolving theoretical insights into the relationship between flow instability and tip-region flow dynamics in modern axial compressors. We then summarize the development of casing treatments, including their discovery, major configurations, and applicability across different compressor types. Subsequently, we systematically examine research on slot-type casing treatments, covering early-stage performance investigations, structural optimization based on experimental and numerical methods, and the underlying mechanisms responsible for stability enhancement. Finally, we offer recommendations and outline future research directions to guide further advancements in this field. Full article

Blade pitch control is one of the most important control systems for a wind turbine: blade pitch controller malfunction can lead to increased vertical bending moment at the tower base, which may result in structural failure. This study investigated the collapse behavior mechanism at the tower root due to an extreme event of blade pitch malfunction for onshore and spar-floating wind turbines. An aero-hydro-elastoplastic coupled analysis tool previously developed and validated by one of the authors was utilized to capture the structural response at the tower root in elastic and plastic regions. Three strength models—(i) SM-01, (ii) SM-02, and (iii) SM-03—were selected to demonstrate the collapse behavior mechanism of onshore and spar-floating 5 MW wind turbines in a time-series simulation. The damage in the plastic region, termed the collapse extent, was evaluated at the collapsing section. Moment–rotational angle relationships are discussed under the same wind conditions. The tower vibrations were found to dominate the structural response of the onshore wind turbine, whereas the tower vibrations and floater response dominate the spar-floating wind turbine response during the failure event. The collapse extent of the spar-floating wind turbine was found to be 8 times larger than the onshore wind turbine under the same wind conditions. Furthermore, simulations were carried out for the spar-floating wind turbine to understand the effect of incoming waves on the collapse behavior: the collapse extent increases as the wave amplitude and period increase under the same wind conditions. Full article

Graphene, a 2D carbon allotrope with a hexagonal atomic structure, exhibits an exceptionally low friction coefficient of approximately 0.004, making it a superior alternative to traditional lubricants. This research investigates the performance of graphene as an additive in oil-based lubricants. Experimental trials will be conducted using a block-on-ring (B-o-R) setup involving a steel rod pressed against a rotating steel ring under a fixed load. By varying the sliding velocities, the study will map the Stribeck curve across the boundary (BL), mixed (ML), and hydrodynamic (HL) lubrication regimes. Furthermore, the lubricant’s durability under extreme pressure will be assessed via Timken testing. The study identified 0.08 wt.% as the optimal concentration for PAO8, achieving a 21.25% friction reduction in the boundary regime. Furthermore, graphene as an additive mitigated wear volume by up to 90% under extreme pressure conditions (1.3 GPa), whereas epoxidized soybean oil proved to be highly effective as a base lubricant without additional nano-additives. Full article

Strengthening cropping patterns and crop planting structure policies is significant for ensuring sustainable agriculture, with broader implications for food security and cultivated land quality conservation. In this context, enhancing the crop rotation project in China’s Black Soil region requires exploring the coupling relationship between the rotation ratio and crop planting structure. Selecting China’s Black Soil region as a case study, this paper presents an equation-based model to determine regional rotation probabilities for the years 2020 to 2021. The Tupu method of geo-information analysis is utilized to explore the characteristics of crop planting structures and rotations. Furthermore, the study explored the relationship between the rotation ratio and crop planting structure, with rotation probability serving as a mediator. The results revealed that corn had a significant impact on the crop planting structure due to its prevalence in continuous cropping. The area dedicated to corn and soybean rotation accounted for only 12.09%. Additionally, correlation analysis showed that a more balanced cropping ratio results in a higher rotation ratio. Therefore, this research suggests that increasing the subsidy standard for crops in relatively low areas and allocating rotation indicators from south to north may help improve the regional rotation ratio in the Black Soil region. These insights should guide policy formulation and implementation to promote sustainable agricultural practices and optimize the rotation policy in China’s Black Soil region. Full article

Agricultural practices (APs) comprehensively regulate crop growth; however, comprehensive studies evaluating the effects of APs on crop yield, water use efficiency (WUE), and nitrogen use efficiency (NUE) remain scarce, particularly regarding determining optimal APs for winter wheat in wheat–maize rotation systems. Here, this study conducted a meta-analysis based on 305 studies globally (4009 pairs of observations), focusing on five APs: irrigation, fertilization, tillage, residue utilization, and mulching. And the results indicated that APs significantly increased winter wheat yield (31.1%), NUE (14.7%), and WUE (27.6%), with fertilization showing the most pronounced effects at 43.7%, 16.9%, and 44.7%, respectively. Specifically, compared to no fertilization, combined organic and mineral fertilizer produced the highest yield increase (141.5%); among conventional fertilization, biochar addition showed the best yield increase (19.1%). Slow-controlled/-release fertilizer and inhibitor addition increased NUE by 17.7% and 26.6%, respectively, and residue utilization and mulching improved WUE (by 17.3% and 33.2%). Moreover, in cold and arid regions (mean annual temperature [MAT] < 13 °C and total annual precipitation [TAP] < 550 mm), APs showed stronger promotion of wheat yield and WUE, while in warm and humid regions, the increase in NUE was more significant (15.3–16.1%). When experiment duration was ≥5 years, APs resulted in the highest yield increase (47.9%), while NUE and WUE increased in short-term experiments. Although APs with high nitrogen application rates resulted in a greater yield increase (51.5%), fertilization significantly reduced NUE above 198 kg N ha⁻¹. Structural equation modeling revealed that, among APs, climatic conditions, soil properties, and management factors, APs were the primary driver of changes in yield and WUE, while NUE was mainly regulated by management factors. Overall, these findings provided an empirical basis for optimizing agricultural practices in wheat–maize systems and offer guidance for developing site-specific policy design. Full article

To address the lack of systematic comparison regarding rheological properties and the unclear structure–property relationships among three core fracturing fluid materials including synthetic polymers, vegetable gums, and microbial polysaccharides, this study selected acrylamide-based polymers, hydroxypropyl guar gum and xanthan gum as the representative systems. The steady-state viscosity, rheological curves, thixotropy, viscoelasticity, and temperature-shear resistance of the three samples were systematically characterized at concentrations ranging from 0.1 to 0.7 wt% using an MCR301 rotational rheometer. The outcomes indicate that the structural strength values of all three materials increase with rising concentration, but their rheological behaviors and stability differ significantly due to distinct molecular structures. The acrylamide-based copolymer forms a temporary network via weak hydrogen bonds (amide-carboxyl or amide-amide) and physical entanglements, exhibiting thixotropy and a stress pre-elastic response. The most significant effects occur at 0.7 wt%, with a thixotropic loop area of 2.874 Pa·s⁻¹ and a stress overshoot of 4.97 Pa.; hydroxypropyl guar gum has insufficient thermal stability and poor heat resistance. Its viscosity retention rate is as low as 31%, and it always exhibits a solution-type rheological property of G′ < G″; the xanthan gum exhibits elastic gel properties with tanδ < 1 due to its double-helix molecular structure. It has excellent temperature shear tolerance and the viscosity retention value can reach up to 98.6 mPa·s. Two mathematical models were established and demonstrated strong applicability: a modified Carreau model for flow curve fitting yielded a coefficient of determination (R²) greater than 0.95, enabling accurate description of fluid-type transitions; a four-parameter equation for temperature–shear resistance curves also achieved an R² above 0.95, effectively characterizing viscosity evolution with temperature. Full article

The bionic pectoral fin serves as the primary propulsion component of ray-inspired robots. In our previous research, a motion equation was proposed for the real pectoral fin, which can be modeled as a series of NACA airfoil-shaped cross-sections distributed along the spanwise direction. Each cross-section undergoes two coupled rotational motions about its chord line and spanwise rotational axis. To achieve this type of motion, this article introduces a novel bionic pectoral fin mechanism driven by a series of differential gear units. The differential unit generates two coupled rotational motions corresponding to the cross-section of the pectoral fin in motion. A series of interconnected differential units provides a unique topology for the bionic mechanism and can generate a diverse range of motions. Through kinematic analysis, the motion equation was mapped onto the rotational angles of motors in the differential units. The proposed bionic mechanism was then fabricated and subjected to experimental test, demonstrating its effectiveness with a maximum thrust of 0.71 N. The distinctive structure of this bionic mechanism differentiates it from conventional designs and is expected to provide some inspiration for bionic pectoral fins and ray-inspired robots. Full article

Rotary tillage blades are critical soil-engaging components in conservation tillage systems but are prone to adhesion of soil particles under cohesive soil conditions, which increases tillage resistance, degrades tillage quality, and lowers operational efficiency. To address these issues, this study proposed a collaborative strategy that combines parameter optimization of rotary tillage blades with a bionic microtexture design to reduce adhesion and resistance and improve operation performance. A coupled soil–wheat straw–rotary tillage blade model based on the Discrete Element Method (DEM) and Multibody Dynamics (MBD) was established in loessial soil environment. The structure and working parameters of the rotary tillage blade were optimized using a Box–Behnken experimental design. On this basis, a bionic microtexture design was introduced on regions prone to adhesion of the rotary tillage blade, inspired by the non-smooth convex hull microstructure on the head surface of the dung beetle. The results indicated that the optimal parameter combination (rotational speed 244 r·min⁻¹, tillage depth 110 mm, and bending angle 122°) reduced soil adhesion mass and tillage resistance by 74.47% and 23.44%, respectively. After applying the bionic microtexture, the corresponding reductions further increased to 82.93% and 28.35%. Moreover, the bionic-optimized rotary tillage blade outperformed the original design in disturbance depth and range and exhibited improved energy consumption performance. Overall, the results demonstrated that coupling parameter optimization with bionic microtexture design substantially enhanced adhesion and resistance reduction and improved soil-disturbance performance, thereby providing theoretical support for the development of high-performance rotary tillage blades. Full article

Crop rotation plays a critical role in enhancing cropping intensity and ensuring food security. To evaluate its long-term effects on soil quality, a fixed-site field experiment established in 2014 including four cropping systems—winter fallow–rice (Oryza sativa L.) (FR), potato (Solanum tuberosum L.) –maize (Zea mays L.) (PM), potato–rice (PR), and potato–rice → rapeseed (Brassica napus L.) –rice (RRPR)—was conducted. A minimum data set (MDS) was screened from 21 soil indicators via principal component analysis (PCA), and the soil quality index (SQI) was calculated by integrating membership functions and indicator weights to comprehensively evaluate the impact of different patterns on soil quality. Results showed that paddy–upland rotations (PR and RRPR) significantly improved soil physical properties, increasing soil moisture content, porosity, and macro-aggregate proportion by 2.27–10.17%, while reducing bulk density by 10.32–13.38%, compared to FR and PM. PR and RRPR rotations also increased total nitrogen (TN), available phosphorus (AP), and available potassium contents (AK) by 5.19–114.00% (p < 0.01). PM rotation notably enhanced available nutrients, with NH₄⁺-N, AP, and AK rising by 3.65–243.50% (p < 0.05), compared to FR. The MDS-based SQI, comprising NH₄⁺-N, AP, mean weight diameter, and soil porosity, showed a highly significant positive correlation with the total data set-based SQI (p < 0.0001). PM exhibited the highest and most stable SQI, exceeding other systems by 8.15–19.30%, while PR and RRPR increased SQI by 9.04–10.30%, compared to FR. In conclusion, potato-based cropping systems enhance soil quality by improving soil structure and increasing nutrient content and availability. The results of this study provide a theoretical basis for nutrient management and sustainable production in cropping systems. Full article

This paper aims to investigate the effects of the co-pyrolytic product produced from the co-pyrolysis of waste cooking oil (WCO) and polypropylene (PP) on pure bitumen by using some physical and rheological tests. To reach this goal, the product was obtained by producing from the co-pyrolysis of WCO and PP at distinct conditions. Different pyrolytic products with different structural properties can be obtained from the co-pyrolysis of various materials at different pyrolysis conditions. It was not found any study in which bitumen was modified with the co-pyrolytic product produced from the co-pyrolysis of WCO and PP materials at specified blending ratios and conditions, as described in this paper. For this reason, this paper investigates the effects of this co-pyrolytic product as an additive on bitumen in order to improve some of the rheological and physical properties of bitumen and to overcome some problems for the first time. The mixture ratio was determined as 1:2 (WCO:PP). PG 64-22 neat bitumen was modified with this co-pyrolytic product, and some features of the bituminous binders were detected by using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), penetration, softening point, dynamic shear rheometer (DSR), rotational viscometer (RV), a rolling thin film oven test (RTFOT), a pressurized aging vessel (PAV), a bending beam rheometer (BBR), storage stability, and scanning electron microscopy (SEM) tests. From the FTIR results of the modified binders, it was found that the intensity of the peak around 2357.69 cm⁻¹ increased with the addition of this pyrolytic product. This pyrolytic additive hardened the pure bitumen’s consistency, increased its viscosity, improved its resistance against rutting deformations, and enhanced its high-temperature performance. It can be said that PG 64-22 pure bitumen can easily be modified with this pyrolytic product at the conditions described in this study. Additionally, this co-pyrolytic product improved the high-temperature performance grade (PG) of pure bitumen from PG 64 to PG 76 when it was used at 5% of the weight of neat bitumen. The findings demonstrated that the modified bituminous binders containing 3% and 5% co-pyrolytic product had suitable storage stabilities. Full article

The high rate of bike commuting around the globe has greatly transformed the mode of transportation in cities, but the high speeds of motorized cycling have contributed to a high rate of serious road trauma. Although conventional helmets offer necessary passive structural protection, they do not consider the most important aspect of the emergency response, which is the Golden Hour the time frame during which medical intervention can have the most significant impact. This paper is a development and validation of an autonomous, low-cost smart helmet architecture that is programmed to operate in real-time to detect accidents and autonomously inform the operator of accidents. The system is built up of an ESP32 microcontroller with a multi-modal sensor package, which comprises an inertial measurement unit (IMU), force-impact sensors, and MQ-3 alcohol sensors to conduct proactive safety screening. To overcome the single threshold limitation of unreliable systems, a time-windowed sensor-fusion algorithm was applied in order to distinguish between normal riding dynamics and bona fide collisions. This reasoning involves concurrent cues of high-G inertial rotations and physical impacting features over a time window of 500 ms to reduce spurious activations. The architecture of the system is completely self-sufficient and employs an in-built GPS-GSM module to send the geographical location through SMS without the need to have a smartphone connection. The prototype was also put through 150 experimental tests, with some conducted in laboratories, and real-world running tests in diverse terrains. The findings reveal an accuracy in detection of 93.7, a false positive rate (FPR) of 2.6 and a mean emergency alert latency of 2.8 s. In addition, it was found that structural integrity was confirmed at ECE 22.05 impact conditions using Finite Element Analysis (FEA), with a safety factor of 1.38. These quantitative results mean that the proposed system is an effective way to address a cultural shift between passive structural protection and active rescue intervention as a statistical and computationally efficient safety measure of modern micro-mobility. Full article

Laser measurement technology is widely used for deformation or pose monitoring of the dual-reflector antenna systems. However, conventional models of surface temperature variation with altitude fail to accurately characterise the temperature gradients between the main reflector and the subreflector of the large-aperture antennas, due to the complex near-ground environment, the antenna’s dual-reflector structural properties, and the antenna’s own rotation changes. This temperature modelling discrepancy significantly influences the laser atmospheric propagation deflection characteristics, ultimately leading to a decrease in the accuracy of antenna attitude measurements. To address these issues, this paper proposes a theory of air stratification within large-aperture antennas and utilizes this theory to optimize the temperature gradient between the antenna’s dual reflectors. Secondly, a coupled heat-fluid dynamics model for the dual-reflector surfaces is established using Computational Fluid Dynamics to simulate the atmospheric stratification under different rotational positions of the antenna. Finally, the effectiveness and feasibility of the proposed theory were verified through experiments in the antenna model and the China Nanshan 25 m non-rotatable antenna. This research provides an original theoretical and practical basis for precision environmental modelling in antenna measurements, offering prior assurance for improving the accuracy of laser-based antenna attitude measurement. Full article

Under extreme fault conditions or during maintenance restarts, DC collection wind farms may experience a total blackout due to protective isolation. Addressing the black-start challenges arising from the unidirectional power flow structure and weak damping characteristics inherent to DC step-up collection wind farms, this paper proposes a sequential black-start control scheme predicated on grid-source coordination. A representative topology and an equivalent black-start model of the DC collection system are established to analyze the start-up mechanism and to design an active voltage build-up strategy with virtual impedance for the grid-side Modular Multilevel Converter (MMC). Meanwhile, generator-side permanent-magnet direct-drive wind turbines exploit their self-excitation capability and optimized pitch control to realize islanded self-bootstrapping and stable rotational speed. In addition, we develop a two-stage soft cut-in strategy that combines open-loop voltage scanning for pre-synchronization with closed-loop constant-current ramping of DC/DC converters, together with control logic for sequentially connecting multiple units to the DC grid. Simulation results show that the proposed approach smoothly restores the system from a zero-energy state to the rated operating point without external power sources, confirming the feasibility of full-farm start-up using the grid-side converter station and unit self-bootstrapping. Full article

This narrative review provides a contemporary synthesis of lateral cephalometric radiography (LCR), addressing both its foundational principles and the impact of technological integration, with a focus on enhancing diagnostic reliability. A structured literature search (PubMed, up to September 2025) was conducted around five domains: LCR’s diagnostic role, acquisition methods, positioning errors, comparisons with cone-beam computed tomography (CBCT), and Artificial Intelligence (AI)-driven quality control. Precise patient positioning—maintaining symmetry and a horizontal Frankfort plane—is paramount, as common errors (tilting, rotation, nodding) introduce quantifiable inaccuracies in key measurements. While digital innovation, particularly deep learning models for automated landmark detection and error flagging, improves the consistency of workflow, current AI tools require validation and human oversight to manage limitations in generalizability. When contextualized against three-dimensional imaging, LCR maintains a favorable balance of diagnostic utility and lower radiation dose, supporting its selective, indication-based use in contemporary practice. Ultimately, this review suggests that adherence to a meticulous acquisition technique remains the cornerstone of reliable LCR analysis, even as AI and digital tools evolve to augment the clinician’s role. Full article

Loop closure detection remains a critical challenge in LiDAR-based SLAM, particularly for achieving robust place recognition in environments with rotational and translational variations. To extract more concise environmental representations from point clouds and improve extraction efficiency, this paper proposes a novel composite descriptor—the vertical feature and circle combined (VCC) descriptor, a novel 3D local descriptor designed for efficient and rotation-invariant place recognition. The VCC descriptor captures environmental structure by extracting vertical features from voxelized point clouds and encoding them into circular arc-based histograms, ensuring robustness to viewpoint changes. Under the same hardware, experiments conducted on different datasets demonstrate that the proposed algorithm significantly improves both feature representation efficiency and loop closure recognition performance when compared with the other descriptors, completing loop closure retrieval within 30 ms, which satisfies real-time operation requirements. The results confirm that VCC provides a compact, efficient, and rotation-invariant representation suitable for LiDAR-based SLAM systems. Full article