Search Results (282)

The accurate prediction of resistance and running attitudes of high-speed planing crafts is of great significance for the improvement of ship hydrodynamics. In this study, the lab model tests and computational fluid dynamics (CFD) methods are employed to investigate the effects of volumetric Froude number and longitudinal center of gravity (LCG) position on the resistance performance, motion characteristics, and free-surface wave patterns for a planing craft. The capability of the CFD model was validated through towing tank resistance tests conducted under various LCG conditions. A systematic analysis of the influence mechanism of LCG variation on the hydrodynamic performance of the craft was conducted. The results indicate that an aftward LCG position can improve the resistance performance; however, it also leads to an increase in the pitch angle. These findings can provide a foundation for the optimization design of high-speed planing craft. Full article

Capillary imbibition is the process by which liquids are absorbed into porous materials as a result of capillary pressure differences at the pore scale. Accurate characterization of imbibition dynamics, particularly in the presence of gravitational potential, is essential for understanding fluid transport in diverse systems such as soil, fractured rocks, filtration media, and plant roots. This study presents systematic imbibition experiments using filter papers with pore sizes of 2.5 µm, 11 µm, and 20 µm, each inclined at 80° to quantify the influence of gravitational potential on imbibition behavior. For horizontally positioned samples, the imbibition front propagated radially and symmetrically, exhibiting a power law dependence on time. The measured temporal exponents ranged from 0.386 to 0.403, consistently lower than the theoretical value of 1/2 predicted by the Lucas–Washburn law. With increasing permeability, the temporal exponent approached the Washburn limit, indicating a marked dependence of imbibition dynamics on pore structure. For the inclined configuration at an 80° angle, the imbibition fronts remained nearly circular but exhibited a pronounced displacement of the front center toward gravity. This displacement increased with permeability, from approximately 0.497 cm for the 11 µm filter paper to 3545 cm for the 20 µm filter paper, highlighting the combined effects of permeability and gravitational potential on fluid movement. Furthermore, the advance of the imbibition front was significantly slower in the smallest pores (2.5 µm) compared to the larger ones. Experimental results were evaluated against a theoretical model proposed by Medina, demonstrating moderate quantitative agreement at early times, when gravitational potential effects are less significant. These findings confirm that both the temporal scaling exponent and the spatial evolution of the imbibition front are governed by the porous medium’s permeability and inclination angle, providing experimental evidence of deviations from ideal Washburn behavior in real porous systems. Full article

Mapping directed spillover pathways in urban housing prices is essential for monitoring the contagion of housing prices across cities. However, existing studies typically rely on either spatial gravity models or time-series models in isolation to analyze intercity connections, thus failing to simultaneously capture the spatiotemporal integration characteristics of housing price contagion. To address this, we embed a finite-length sequence correlation analysis (Correlation-Dependent Balanced Estimation of Diffusion Transfer Entropy, $CBEDTE$) into the gravity model, yielding the $CBEDTE$-GM integrated model. Using housing price data from 296 Chinese cities, we construct a spatiotemporal correlation matrix and employ the directed minimum spanning tree algorithm to extract core directed spillover pathways. Results reveal that China’s urban housing price spillover network exhibits a hierarchical architecture with pronounced ripple effects, where eastern coastal cities and the national core city serve as dominant radiation hubs. The East China sub-network occupies a distinctive net spillover position. We identify heterogeneous structural evolution patterns across regional sub-networks: (1) North China evolved from a dispersed multi-centered configuration to a Beijing-dominated single-core structure; (2) East China developed a robust multi-centered architecture anchored by Shanghai; and (3) South China transitioned from a Guangzhou-centered single-core pattern to a tri-polar configuration co-driven by Guangzhou, Shenzhen, and Nanning. Full article

Land-use change substantially contributes to carbon emissions, yet systematic research on complex human–environment interactions in old industrial bases remains scarce. Here, we integrated multi-temporal land-use data and socio-economic statistics from 1990 to 2023 to analyze the spatiotemporal dynamics and drivers of land-use carbon emissions in Northeast China. The land-use transfer matrix, the carbon emission coefficient, exploratory spatiotemporal data analysis (ESTDA), standard deviational ellipses, and modified Kaya–LMDI models were applied. Construction land area expanded by 120%, with its share of total emissions increasing from 87% to 95%. Meanwhile, forest and grassland shrank, reducing their carbon sink capacity and increasing their net carbon emissions 1.9-fold. Spatially, emissions showed a weak global correlation but strong local lock-in (i.e., persistent stability of local spatial patterns over time), with the emission center of gravity shifting southwestward. Economic development was the dominant positive driver (provincial contribution rates: 275–529%), whereas energy intensity was the main mitigating factor (up to −409%). Population loss exerted a slight negative contribution, while energy structure showed only a weak inhibitory effect (−9.1%), reflecting the region’s path-dependent lock-in to fossil fuels. This study provides a scientific basis for differentiated carbon management strategies in Northeast China and analogous regions. Full article

As a crucial national ecological barrier, China’s Southern Collective Forest Region (SCFR) plays an essential role in maintaining regional ecological security and promoting sustainable development. Understanding the mechanisms driving the evolution of its ecosystem service value (ESV) is of great significance. Based on county-level data from 2000 to 2023, this study integrated the equivalent factor method, spatial autocorrelation analysis, the XGBoost-SHAP model, geographically and temporally weighted regression (GTWR), and partial least squares structural equation modeling (PLS-SEM) to examine the spatio-temporal evolution patterns and driving mechanisms of ESV in the SCFR. The results showed that ESV in the SCFR exhibited an overall downward trend, with a cumulative loss of 1973.77 × 10⁸ CNY. This was primarily due to marked reductions in hydrological and climate regulation services. The spatial distribution of ESV exhibited a significant heterogeneity—higher in the southwestern and southeastern mountainous regions, and lower in the northern plains and coastal zones, with the center of gravity shifting first to the northeast and then to the southwest. Local spatial autocorrelation revealed relatively stable “High–High” and “Low–Low” clustering characteristics, where high-value clusters were consistently distributed in core forest zones, while low-value clusters overlapped highly with urban agglomerations. Socio-economic factors exerted a significantly stronger influence on ESV than natural factors. Population density (POP), land use intensity (LUI), and gross domestic product (GDP) were identified as the dominant drivers, exhibiting distinct non-linear threshold effects and significant spatio-temporal heterogeneity. PLS-SEM analysis further quantified LUI as the dominant direct inhibitory pathway on ESV, highlighting urbanization’s indirect negative effect mediated through intensified LUI. Meanwhile, terrain effects were confirmed to positively influence ESV indirectly by constraining LUI and modulating local climate. The analytical framework of “threshold identification–spatio-temporal heterogeneity–causal pathway analysis” proposed in this study elucidated the complex driving mechanisms of ESV evolution, providing valuable guidance for ecological restoration evaluation and differentiated environmental governance. Full article

The flying car, academically known as electric vertical takeoff and landing (eVTOL) aircraft, is one of the core vehicles for low-altitude transportation. The split-type tilt-rotor cargo flying vehicle that is composed of tilt rotors, a fixed wing, and a detachable cargo pod exhibits characteristics of rotor–wing coupling and significant changes in weight and center of gravity (CG). Therefore, empirical design rules for conventional aircraft are not directly applicable. This paper presents the stability analysis of two configurations, i.e., the aerial vehicle module (AVM) and the aerial cargo configuration (ACC). The dynamic model of the proposed cargo flying vehicle is developed. Based on test data from the tilt-rotor experimental bench, the CFD models of the rotor subsystems and the full vehicle were validated and subsequently used to simulate the aerodynamic performance and stability of the flying vehicle under various operating conditions. The results indicate that vertical takeoff and landing (VTOL) stability is highly sensitive to the rotor–CG lever arm. Under cruise conditions, the CG positions were tested within a range of 1.4–1.7 $c_A$ (mean aerodynamic chord) from the wing leading edge with the most favorable static stability observed at 1.62 $c_A$. Among the three proposed tilt-rotor strategies, initiating the secondary tilt rotors first while keeping the main tilt rotors vertical results in the weakest rotor–surface aerodynamic coupling, the lowest pitching-moment peaks, and favorable longitudinal static stability. These findings inform CG management, aerodynamic layout, and tilt-schedule design for split-type tilt-rotor cargo vehicles in low-altitude transportation. Full article

This paper proposes an innovative research algorithm “measurement—pattern—driving force—synergy” that determines the eco-efficiency of 83 Russian federal subjects (2000–2019) using the Slacks-Based Measure (SBM) model with non-desired outputs (incorporating comprehensive input indicators such as water resources and electricity input, and dual non-desired outputs of waste gas and wastewater). Combined with hot spot analysis, a gravity center model, and panel Tobit regression, we reveal the temporal-spatial evolution and driving mechanisms of eco-efficiency in resource-based economies. The research finds that the overall eco-efficiency of Russia is at a medium level and shows a dynamic correlation with the economic development stage. In the early stage of the period under review, there was a high degree of synergy, but the efficiency declined during the period of rapid economic growth. Later, it rebounded somewhat in tie with technological progress. Spatially, it presents a special pattern of low efficiency in the western European industrialized regions and high efficiency in the Arctic and Far East peripheral regions, reflecting the spatial heterogeneity of resource-dependent economies and the survival-constrained efficiency feature. The analysis of influencing factors indicates that per capita GDP has a significant positive driving effect on eco-efficiency, but the expansion of residents’ consumption, the improvement of education level and the dependence on foreign trade all have inhibitory effects, highlighting the path dependence of the current growth model on the structure of resource consumption. The research suggests that Russia should implement differentiated spatial governance in the future, promote the green transformation of consumption and trade structures, and strengthen the ecological orientation of the education and scientific research system to achieve a fundamental transformation of regional sustainable development from survival constraints to innovation-driven. Full article

This study constructs a global transportation carbon emission spatial correlation network via a modified gravity model and explores its evolutionary characteristics and dynamic mechanisms by integrating three-dimensional evolutionary analysis (node, overall, structural) and temporal exponential random graph model (TERGM). The main findings are as follows: (1) Global transportation carbon emission spatial correlation intensity keeps rising, with improved connectivity and integration, forming three regionally agglomerated correlation poles centered on the United States (America), China (Asia) and major European countries (Europe). (2) Network centrality distributes asymmetrically: Switzerland, Norway and the United States remain core nodes, while China, Japan and other Asian economies with strong direct correlation radiation are not in the core tier. (3) Third, evolutionary dynamics stem from the synergistic interaction of multidimensional attributes. ① Economic level positively drives bidirectional connection emission and attraction; economic scale and openness curb emission but boost attraction, while tertiary industry structure inhibits both. ② Only economic level and government efficiency exert significant positive effects on absdiff, fostering network heterophilic attraction. ③ Spatial and institutional proximity in edgecov effectively facilitate connection formation. ④ Endogenous network variables present a collaborative mechanism of reciprocity and transmission, constrained by network density. ⑤ Temporal effects show early connection structure forms path dependence, resulting in low dynamic variability and overall network stability. Full article

The rapid shrinkage of the climate-regulating cryosphere, driven by global warming and anthropogenic activities, underscores the urgency of understanding its impact on regional ecological vulnerability. This study develops a Sensitivity–Resilience–Pressure (SRP) model-based framework comprising 21 natural and socio-economic indicators, employs spatial autocorrelation and center of gravity migration to characterize spatiotemporal patterns in the Qilian Mountains region, and integrates Random Forests (RF) with Shapley Additive Explanations (SHAP) to identify key drivers. Results reveal a downward trend in the Ecological Vulnerability Index (EVI) from 2000 to 2020, with areas of very heavy vulnerability declining from 21.05% to 14.73%, indicating gradual ecological recovery. The study area exhibits moderate vulnerability, with the western region dominated by heavy and very heavy vulnerability, whereas the eastern region is characterized by potential and light vulnerability, indicating a high-west, low-east spatial pattern. A significant positive spatial autocorrelation is observed, revealing that areas with high vulnerability are highly clustered and primarily overlap with regions of high elevation and sparse vegetation. The RF–SHAP analysis demonstrates that natural factors dominate the EVI, with fractional vegetation cover, biological abundance, glacial meltwater volume, annual precipitation, and the landscape diversity index emerging as the main drivers, and the EVI changing sequentially as each indicator approaches its threshold: 0.16, 56.57, 2.23 mm, 400.73 mm, and 0.39. In conclusion, although ecological vulnerability in the Qilian Mountains has declined, future management strategies should leverage these threshold effects to implement precise, indicator-based monitoring and regulation. Full article

Balance is referred to as a state of equilibrium where forces of agonist and antagonistic muscles are equal. This is particularly relevant in the practice of Goju-Ryu Karate-Do, a martial art style with combinations of hard and soft techniques. Particularly, karate stances not only depend on technical aspects but also on the ability to achieve a centered posture. In this narrative review, we aim to integrate the existing knowledge about alignment parameters of the spine to various stances in Goju-Ryu Karate-Do to improve biomechanical understanding, allow technical modifications, and consequently enhance positive training experience. Balance is constantly challenged during the interplay of accelerated movements and subsequent controlled postures (Japanese: “Kamae”). This requires continuous neuromuscular coordination to maintain the body’s equilibrium. In particular, the body’s center of gravity, which is located around the second sacral vertebra in a standing position, needs to be kept within Dubousset’s “efficiency cone” for low energy consumption and minimal fatigue. This state is primarily maintained by aligning the spine, the pelvis, and the lower extremities, which is a result of complex biomechanical interactions of various spinopelvic parameters. Applying these concepts of Dubousset to stances in Goju-Ryu Karate-Do helps to explain why during the aging process or natural degeneration, technical modifications are needed to guarantee an optimal training experience in senior or disabled practitioners of Karate-Do. Biomechanical parameters of the spinopelvic axis are crucial in mastering the art of Goju-Ryu Karate-Do. Only with a balanced stance and an optimally situated center of gravity, a block or attack may be successful and movement strategies effective. However, technical modifications of stances must be considered in aged or disabled karateka to allow a sustained training experience. Full article

Stalk lodging is one of the major constraints limiting global maize yield. Chemical regulation and fertilization are essential agronomic practices that play critical roles in improving maize yield and lodging resistance. This study aimed to investigate the effects of different fertilization methods on maize plant morphology, stem mechanical properties and chemical composition, and yield under spraying chemical regulator (EDAH, consist of 27% ethephon and 3% DA-6). The experiment was conducted from 2023 to 2025, using Jiangyu668 (JY668) and Jiangyu877 (JY877) with different plant heights. Three fertilization methods (no fertilization, N0; conventional fertilization, N15; and slow-release fertilization, SN15) were set up. Chemical regulation and fertilization methods had significant effects on plant morphology, stem mechanical properties and chemical composition, lodging rate, and grain yield. The combination of spraying EDAH and slow-release fertilization optimized ear position coefficient and gravity center, decreased stem–leaf angle, and increased leaf orientation value, which was beneficial for improving leaf photosynthetic capacity. EDAH and slow-release fertilization also increased the stem internode diameter and aerial root layers; enhanced bending resistance and puncture strength; and increased cellulose, hemicellulose, and lignin contents and the lodging resistance index. These changes synergistically increased grain number and weight, ultimately increased maize yield, and decreased the lodging rate. CSN15 had highest yield and lowest lodging rate in different years and varieties. SN15 increased yield by 10.58% compared with N15, and CSN15 increased yield by 10.53% compared with CN15. JY877, as a medium- to high-stem maize variety, had better performance in plant morphology and yield than JY668 (dwarf maize variety) under EDAH and slow-release fertilization. These findings demonstrate that the strategy of combining chemical regulation and slow-release fertilization represents an optimal management approach for enhancing grain yield by optimizing plant morphology and improving stem mechanical properties and stem chemical composition in maize production. This strategy can increase agricultural productivity by enhancing yield and lodging resistance and provide significant environmental benefits and a scientific basis for agronomic practice recommendations. Full article

Land use intensification profoundly impacts ecological quality, with this dynamic relationship being particularly pronounced in China’s Central Yunnan Plateau Lake Basin (CYP-LBs), an ecologically fragile area of significant socioeconomic value. Despite the critical importance of their interaction, existing research has largely overlooked their dynamic interplay—especially within plateau lake basins. To address this gap, this study employs the Remote Sensing Ecological Index (RSEI) to assess the ecological quality dynamics of CYP-LBs from 2005 to 2025 and its association with land use intensity (LUI), revealing spatiotemporal patterns of ecological quality evolution and its linkage to land use. Results indicate that CYP-LBs maintained overall moderate ecological quality (average RSEI ~0.50), exhibiting an initial increase followed by decline, peaking at 0.5519 in 2015. The center of gravity for ecological quality shifted eastward in most watersheds, with Moran’s I index consistently above 0.50 indicating significant spatial autocorrelation. The LUI showed an overall upward trend, with high-intensity areas primarily concentrated in lakeshore zones (e.g., eastern Dianchi Lake, Xingyun Lake) and exhibiting regional expansion over time. RSEI and LUI generally showed a negative correlation, but positive correlations emerged in localized areas of eastern and northern Dianchi Lake due to concurrent urbanization and ecological restoration efforts. Among land types, grasslands and forests were identified as the primary drivers influencing ecological quality changes in CYP-LBs. These findings provide crucial scientific basis for integrated conservation, land use optimization, and sustainable development in ecologically fragile plateau lake basins. Full article

To accurately analyze the dynamic response and driving mechanism of forest carbon sequestration in the core area of the Loess Plateau’s Returning Farmland to Forestry Project, this study takes the Beiluo River Basin as the research area. Using spatial autocorrelation, gravity model, a geodetector, and spatiotemporal geographically weighted regression models, it analyzes the spatiotemporal evolution of forest carbon sequestration and the spatial heterogeneity of its influencing factors based on 2000–2023 data. The results show the following: (1) Forest carbon sequestration in the basin increased by 13.55% from 2000 to 2023; its spatial pattern shifted from “middle reaches concentration” to “stable middle reaches core plus significant upper reaches growth”, with the gravity center moving “southeast then northwest”. (2) Forest carbon sequestration had significant positive spatial correlation, with hotspots in soil–rock mountain forest areas and cold spots in ecologically fragile or high-human-activity areas. (3) Natural ecological factors dominated forest carbon sequestration evolution, socioeconomic factors enhanced synergy, and evapotranspiration and NDVI had significant impacts. (4) Factor impacts had spatiotemporal heterogeneity, such as the decaying positive effect of precipitation and the “positive-negative-equilibrium” change in forestry value-added. This study provides scientific guidance for basin and Loess Plateau ecological restoration and “double carbon” goal achievement. Full article

Road accidents cause 1.3 million deaths annually, motivating the United Nations (UN) to develop a strategy seeking to halve this number by 2030. Portugal, with 60 deaths per million inhabitants in 2022, ranks sixth in European Union (EU) road fatalities, although these numbers have been decreasing since 2010. Rollover accidents account for 33% of traffic fatalities in the U.S.; yet, only 3% of crashes involve rollover accidents. These are particularly dangerous and mainly involve medium-to-large-sized vehicles having high centers of gravity (CoG), such as SUVs and heavy vehicles. On the other hand, bus accidents make up only 2% of EU road deaths, often involving vulnerable road users. Road forensic investigations rely on CoG positioning data for accurate accident reconstructions, using key equations for calculating skid and overturning speed limits. To complement the already existing equations, and by using a rigid body system, an equation for the evaluation of the overturning velocity in a curved trajectory is developed and proposed, considering the suspension stiffness properties of a vehicle. Finally, a real-world accident investigation involving a bus overturning is presented, and the method that was developed is applied. The developed formulation showed good results compared to the ones that were obtained during the forensic investigation and reduced the error from 5% to 2% compared to the existing equations. Full article

Operation of vehicle–trailer combinations is currently popular throughout many countries. Connecting a trailer to a passenger car increases the car’s utility value because it is possible to transport more goods over shorter or longer distances. Trailers are also popular as caravans, which provide a home on wheels during holiday periods. As a trailer is connected to a towing vehicle by means of a spherical joint from the mechanics’ point of view, a vehicle–trailer combination has significantly different driving properties in comparison with a sole vehicle. These differences are manifested mainly while driving in a curve as lower stability of the vehicle. In this case, the lower stability is considered an uncontrolled sway motion. This study is focused on researching the driving stability of a vehicle–trailer combination regarding the sway motion problem. The research is fully performed by means of simulation computations in a commercial multibody simulation software. The investigated vehicle–trailer combination consists of an SUV passenger car and a single-axle goods trailer. Two model driving maneuvers are investigated, namely bypassing an obstacle in a lane and changing lanes on a road. Simulation computations are performed for chosen loads of the trailer and for a different position of the center of gravity of the load in the single-axle trailer. The performed research has proven that the applied simulation computations represent a robust tool to investigate real tasks related to vehicle safety without performing expensive and dangerous tests. Very important findings include identifying the proper position of the center of gravity of the load on the trailer to ensure safe driving properties for driving maneuvers that could pose potential danger during real operation. Full article