Search Results (155)

The Ministry of Land, Infrastructure, and Transport conducted a demonstration project targeting pilot areas to commercialize drone delivery services in urban areas and to present a standard model. In this study, flight data on drone delivery routes in Ulju and drone hovering in Yeosu were collected and analyzed for flight safety. Since there are no domestic or international regulations on the stability of drone flight, we were given the task of analyzing whether drone path flight should be maintained within a 10 m error range from the planned path line by the Korea Transportation Safety Authority and whether hovering works while satisfying the left and right radius errors and altitude errors within 3 m. Accordingly, the drone flight path data analyzed in Ulju met the criteria of up to 1.07%, and the hovering data analyzed in Yeosu met the criteria of less than 3% for the entire section data. Therefore, the drone flight stability evaluation analyzed in this paper is considered to have been passed. Based on the results of this study, is the data are expected to serve as a cornerstone for establishing guidelines for drone delivery flight data analysis regulations. Full article

Sports stadiums significantly influence urban morphology; however, empirical quantification of these effects remains limited. This study quantitatively examines the spatiotemporal relationship between sports architecture and urban functional evolution using Jiangwan Stadium in Shanghai—China’s first Western-style sports facility—as a case study. Employing Point of Interest (POI) data, ArcGIS spatial analyses, chi-square tests, and linear regression-based predictive modeling, we illustrate how the stadium has catalyzed urban regeneration and functional diversification over nearly a century. Our findings demonstrate a transition from sparse distributions to concentrated commercial and service clusters within a 1000 m radius around the stadium, notably in food and beverage, shopping, finance, insurance, and transportation sectors, significantly boosting local economic vitality. The area achieved peak functional diversity in 2016, showcasing a balanced integration of residential, commercial, and service activities. This research provides actionable insights for urban planners and policymakers on leveraging sports facilities to foster sustainable urban regeneration. Full article

Symmetrical bearing raceway led to the axial sliding of rolling elements, which is a crucial factor in shortening the operational lifespan. This study addresses this limitation through three-step advancements: first, a parametric equation for logarithmic spiral raceways is developed by analyzing their asymmetric geometric features; second, based on the geometrical model, we systematically investigate the parameters of the logarithmic spiral that affects the bearing performance metrics; and finally, a novel fatigue life prediction framework that integrates static mechanical analysis with raceway parameters establishes the theoretical foundation for optimizing the raceway parameters. The results of the model analysis show that the error of the maximum contact stress verified by the finite element method is less than 8.3%, which verifies the model’s accuracy. Increasing the contact angle α of the outer ring from 82 to 85 can increase fatigue life by 15.6 times while increasing the initial polar radius O of the inner ring from 7.8 mm to 8.1 mm will cause fatigue life to drop by 86.9%. The orthogonal experiment shows that the contact angle α of the outer ring has the most significant influence on the service life, and the optimal parameter combination (clearance δ of 0.02 mm, inner race and outer race strike angles α of 85°, an inner race initial polar radius $r_o$ of 7.8 mm, and an outer race initial polar radius $r_o$ of 7.9 mm) achieves a 60.7% fatigue life increase. The findings provide theoretical support and parameter guidance for the optimal bearing design with logarithmic spiral raceways. Full article

With the increasing number of cislunar space missions, real-time and reliable navigation and communication services have become critical. It is necessary to develop the navigation constellations dedicated to cislunar space services. However, there are plenty of orbits in cislunar space providing alternative orbits, which makes constellation design a challenging task. To address this, this paper proposes a method for a cislunar navigation constellations configuration design via orbits with resonant periods. First, a periodic orbit catalog for the Earth–Moon system is constructed. Baseline orbits are selected from different orbital families, and all resonant orbits with periods proportional to the baseline orbits are compiled into a resonant orbit set. Second, a Dilution of Precision (DOP) model for navigation performance and a spatial zoning model are established. Then, resonant orbital combinations are screened based on orbital type composition, followed by resonance constellation generation according to predetermined constellation scales. All constellation configurations are categorized by orbital type to obtain a full resonant constellation set. Finally, the proposed method is applied to design optimal configurations providing navigation services for near-Earth and lunar regions. The simulation results shows that constellations combining L2 southern/northern Near-Rectilinear Halo Orbits (NRHOs) with vertical orbits at L4/L5 points deliver the optimal navigation performance in cislunar regions. The relationships between orbital radius and DOP values in target areas, as well as the DOP evolution patterns over constellation periods, are analyzed. The mean DOP values of the optimal constellation in both the near-Earth region and the lunar region increase as the spatial radius expands. Full article

In recent years, there has been a call for a shift to transportation with lower greenhouse gas (GHG) emissions in order to combat global warming. One of the ecofriendly transportation methods is an electric moped scooter (e-moped)-sharing service that does not emit GHG when it runs. It is necessary to plan the location of charging stations and the material procurement through the manufacturing of e-mopeds in order to reduce the cost and GHG emissions and to improve the accessibility of the service. In this study, a two-stage design on the e-moped-sharing services is proposed to allocate charging stations and select material suppliers for e-mopeds using integer programming. The analysis method to determine the suitable charging station locations and sizes and supplier selection are also presented. Numerical experiments are conducted to illustrate the proposed design and analysis method by assuming Kumpan’s 1954 i model installation in Bochum city, Germany. In the numerical experiments, set covering and maximal covering location problems with small coverage radius of charging stations would be better by evaluating accessibility, GHG emissions, and cost comprehensively. Moreover, 11 prioritized demand points were picked out by introducing new indexes such as geographical and demand importance. Full article

Facility agriculture is essential for diversifying food supply and advancing agricultural modernization. Guided by the concept of new quality productive forces, this study establishes a comprehensive framework to analyze the optimization of facility agricultural land allocation in Zhejiang Province. The findings indicate a relatively low overall allocation level, with higher intensity in the breeding industry compared to crop cultivation. Facility agricultural land is predominantly located in areas with lower elevations, gentler slopes, proximity to roads and rivers, and moderate distances from urban centers. Service areas vary significantly, with grain cultivation having the largest impact, followed by other crop cultivation, fruit and vegetable cultivation, aquaculture, other livestock breeding, and pig farming. As agriculture transitions from small-scale to large-scale and facility-based production, service areas exhibit an inverted U-shaped trend, initially increasing before declining. To optimize decision-making, this study proposes a classification system (shared, modern, safeguard), an entry list (encouraged, restricted, prohibited), and strategies for spatial layout, flexible control, and intensive land use. Guided by green and high-quality development goals, this research establishes a contemporary standard system and optimization strategies, offering scientific and practical guidance for sustainable facility agricultural land development and supporting land resource allocation and industry upgrading. Full article

This study aims to investigate the dynamic behavior of water-lubricated stern bearings during service. A transient rotor dynamics numerical model is developed to research the effects of operating conditions and critical structural parameters on the variation patterns of the dynamic characteristic coefficients and journal orbit of WLBs. The main stiffness and damping formulas for dimensionless bearings are fitted based on numerical results. Additionally, the accuracy of the model calculations is experimentally verified on a water-lubricated bearing test rig. The results demonstrate that the variation trends of the main stiffness and main damping coefficients in the horizontal and vertical directions of the bearings are proportional to the external load and inversely proportional to the rotational speed. Under eccentric excitation, the dynamic characteristic coefficients of the bearings change periodically with time as an approximately sinusoidal function. With the increase in the bearing length-to-diameter ratio or the decrease in the radial clearance-to-radius ratio, the main stiffness and the main damping coefficients in the horizontal direction increase, while the main stiffness coefficient in the vertical direction decreases. This study provides theoretical support for modeling the transient transverse vibration of a propulsion shaft system. Full article

With the increasing demand for various autonomous driving services in urban environments, low-speed autonomous vehicles, such as autonomous shuttles and purpose-built vehicles, equipped with enhanced driving characteristics suitable for urban roads featuring narrow streets, intersections, congested traffic, and small radii, are emerging. In particular, the 4WS (four-wheel steering) system, which is being integrated into these vehicles, is designed to steer both the front and rear wheels. This system improves steering responsiveness and stability, providing maneuverability under various driving conditions and making it highly suitable for urban environments. However, the 4WS system involves complex dynamic modeling and poses challenges in designing a path tracker, especially if factors such as the vehicle’s turning radius and road curvature are not properly considered. To address these challenges, this paper proposes a path tracker for a low-speed autonomous driving system based on a 4WS system, optimized for the characteristics of urban roads to minimize the vehicle’s turning radius and enhance driving performance. The proposed path tracker independently controls the front and rear wheels and incorporates road curvature and vehicle turning radius as feedforward terms to improve the response performance of the path tracker. The performance of the proposed path tracker was evaluated through simulations and real-car experiments. Full article

Bus networks are a crucial support for urban commuting. By studying the evolutionary characteristics of bus networks, we can uncover their development patterns, coverage efficiency, and changes in regional balance, providing a scientific basis for sustainable urban development and the optimization of transportation resources. This study systematically analyzes the spatiotemporal evolution characteristics of the bus network in Beijing from 2006 to 2024 using specific spatial analysis tools to analyze spatiotemporal evolution characteristics. By analyzing spatial coverage rates of transit stations using road network and administrative division data, the study reveals the convenience of bus networks in different regions. By combining the research methodology of the Sustainable Development Goals (SDGs) report, a 500-m service radius for bus stops was assessed. A complex network model was used to extract the nodes and edges of the bus network, and the betweenness centrality (BC) characteristics were analyzed. The findings indicate that Beijing’s bus network has gradually expanded from the central urban areas to peripheral regions, with notable expansion in Tongzhou and Yanqing, resulting in an improved balance in the distribution of stations and routes and the emergence of Tongzhou as a new bus hub. The diffusion characteristics of the bus network are significantly influenced by administrative boundaries and the layout of the ring roads. Bus routes and stops are highly concentrated in the central urban areas and within the Second Ring Road, while as the number of ring roads increases, various network indices gradually decrease. The distribution of bus stops shows notable clustering and an uneven directional development. Beijing’s bus stop distribution exhibits significant clustering characteristics, and the areas with a high Population Conveniently Served by Buses (PCSB) are predominantly concentrated in the central urban areas, with a large gap compared to the outer suburban districts. These conclusions expand on the exploration of isolated and static characteristics of the bus network structure, revealing the dynamic mechanisms and evolution patterns of Beijing’s bus network. They provide guidance and recommendations for improving the bus network and offer more comprehensive support for urban planning and resource allocation. Full article

The majority of freight trains are characterized by a braking system that does not guarantee synchronous braking between different wagons. This results in the generation of considerable in-train forces during emergency braking operations, which are sometimes imposed by the railway infrastructure due to certain running speeds being exceeded. The magnitude of in-train forces is contingent upon a number of factors, the most significant ones being the length, mass and load composition of the trainset, in addition to the specific braking imposed. The application of excessive compressive in-train forces has the potential to cause the wagon to derail, particularly if the wagon is lightweight and traversing a small radius curve. Similarly, excessive tensile in-train forces applied to the screw couplers can cause them to fail, typically through fatigue, resulting in train disruption and necessitating the recovery of both portions of the trainset. The objective of this study is to perform a preliminary analysis of the UIC (International Union of Railways) unified screw couplers fatigue phenomenon, employing load spectra computed by the UIC 1.4.6 software TrainDy. A possible future development is developing a maintenance model functional to predict the extent of damage in freight wagon screw couplers during their service life. Full article

This article presents the design and implementation of an API that delivers real-time promotional notifications to mobile devices based on their proximity to shopping centers, calculated using the Haversine formula. Developed in Laravel, the API determines whether a mobile device is within a 600 m radius of any registered shopping center, such as Soriana, GranD, and HEB, and sends the relevant promotional information. The system uses Petri nets to model asynchronous behavior, enabling efficient concurrency management between the mobile application and the API. This structure ensures optimized message delivery, preventing communication collisions and delays. The mobile application, developed in Kotlin, integrates geolocation services to capture and update the user’s location in real time. The results indicate an improvement in response time and proximity detection accuracy, highlighting the effectiveness of the Petri net model for systems requiring concurrent interaction. The combination of Laravel, Kotlin, and formal modeling with Petri nets proves to be an effective and scalable solution for proximity-based mobile applications. Full article

The Low Earth Orbit (LEO) small satellites are extensively used for global connectivity to enable services in underpopulated, remote or underdeveloped areas. Their inherent broadcast nature exposes LEO–terrestrial communication links to severe security threats, which always reveal new challenges. The secrecy performance of the satellite-to-ground user link in the presence of a ground eavesdropper is studied in this paper. We observe both scenarios of the eavesdropper’s channel state information (CSI) being known or unknown to the satellite. Throughout the analysis, we consider that locations of the intended and unauthorized user are both arbitrary in the satellite’s footprint. On the other hand, we analyze the case when the user is in the center of the satellite’s central beam. In order to achieve realistic physical layer security features of the system, the satellite channels are assumed to undergo Gamma-shadowed Ricean fading, where both line-of-site and scattering components are influenced by shadowing effect. In addition, some practical effects, such as satellite multi-beam pattern and free space loss, are considered in the analysis. Capitalizing on the aforementioned scenarios, we derive the novel analytical expressions for the average secrecy capacity, secrecy outage probability, probability of non-zero secrecy capacity, and probability of intercept events in the form of Meijer’s G functions. In addition, novel asymptotic expressions are derived from previously mentioned metrics. Numerical results are presented to illustrate the effects of beam radius, satellite altitude, receivers’ position, as well as the interplay of the fading or/and shadowing impacts over main and wiretap channels on the system security. Analytical results are confirmed by Monte Carlo simulations. Full article

Comprehensive land improvement causes strong disturbances of land use patterns in the short term, resulting in changes in landscape structure and function. This study adopts the moving window method and semi-variation function to explore the spatial scale effect of landscape pattern metrics in the comprehensive land consolidation project area of Baimahu Farm, and the spatial variability and homologous ecological processes. The results showed that: (1) patch density, largest patch index, area-weighted average shape index, contagion, and division index all showed obvious scale effects, and the suitable first and second scale domains in the study area are 5–7 m and 35–40 m, respectively, and 5 m is the most suitable grain size for the study of landscape pattern change. (2) The block basis ratio of the semi-variogram of the six landscape level indices begins to stabilize at the window radius of 210 m. This scale can reflect the spatial variability of the landscape pattern in the study area and is the most suitable analysis range. (3) The fragmentation degree of paddy fields as landscape matrix decreased and the landscape dominance degree increased in the comprehensive land improvement; the degree of fragmentation of irrigated land and agricultural land for facilities increased, the aggregation of land for construction increased, the dominance degree of the pond surface decreased, and the overall landscape diversity of each mosaic decreased; the landscape heterogeneity of ditches, rural roads, forest and grassland corridors was weakened, and the ecosystem service function was weakened. (4) The trend of increased fragmentation, simplification of landscape types, and decreased diversity presented by the landscape pattern clearly indicates that the landscape pattern of the study area has been seriously damaged to some extent under the influence of human activities. This damage not only has a direct negative impact on the local ecological environment, but also poses a potential threat to the sustainable development of the region. Full article

Land management strategies play a pivotal role in the sustainable development of a region. Integrating space syntax into the ecological–social perspective to assess habitat services and optimize multi-scenario simulations and evaluations is crucial for developing resilient strategies for the future. This study takes Lanzhou, a semi-arid region, as a case study, combining multi-model analysis to explore the relationship between habitat quality and spatial accessibility and to conduct habitat service zoning. The findings indicate that under four development scenarios, the ecological network generally shows a three-segment distribution. The factors that have the most significant impacts on cultivated land, forests, shrubs, construction land, and bare land are GDP, precipitation, temperature, population density, and NDVI, respectively. The ecological priority scenario features the most corridors, while the cultivated land protection scenario incurs the lowest construction costs. Across various analysis radii of space syntax, except for MED at a 6000 m radius, the ecological priority scenario exhibits excellent network accessibility. The coupling coordination degree of the four scenarios generally lies within a mild imbalance level, with a spatial distribution pattern characterized by “high in the west and low in the east”. Based on 10 types of habitat services, a priority management sequence for land and key governance towns was established, leading to the proposal of a “dual coordination” multi-center compact network layout model. This research not only enriches the theory of land ecology but also overcomes the shortcomings in land spatial planning, addresses the practical problems of land development transformation in Lanzhou, and offers new data support and ideas for the construction of ecological cities in semi-arid regions. Full article

The unclear time-distance decay law between supply and demand, which makes it difficult to coordinate their fairness, is a key factor in the disordered spatiotemporal development of supply and demand. In order to advance the standardized renewal of living circles with a people-oriented approach, this paper clarifies the time-distance decay law between supply and demand embedded in residents’ walking time-distance distributions and explores the spatiotemporal organizational order of supply and demand in living circle units aligned with this law. First, 24 sets of walking time-distance distribution data, each showing significant distribution differences, were standardized using a mean-based transformation relative to their own time-distance means, resulting in an observable law of relative time-distance distribution. Subsequently, an explanatory mechanism for the relative time-distance distribution was constructed based on the generation and decay effects of the relative time-distance between standard supply and demand. A functional model was fitted and verified, indicating that the decay law of the relative time-distance follows a negative exponential function with a parameter value of 2.08, and the time-distance threshold has a stable twofold relationship with the time-distance mean. Finally, by drawing an analogy between living circle units and the relative time-distance distribution and taking their standards as the mean time-distance, the study explored the layout relationships among living circle units. The spatiotemporal organizational order for same-level units was characterized by “one form where the time-distance mean and threshold serve as the service radius and influence radius, and another where supply and demand are placed at 0.5 times the time-distance mean inside and outside, respectively”. For different-level units, the order featured “one form where the center of the upper-level spatiotemporal unit is located at the four corners of the lower-level units, with a service radius twice that of the lower-level unit. Another form ensures coordination of service radius differences between upper and lower units through a twofold speed relationship in travel modes, guaranteeing relative fairness in travel time consumption for the same type of supply across different levels”. Additionally, an ideal layout pattern for living circle units was proposed, featuring a “snowflake-shaped” facility layout and a “twice-speed” transfer method. The findings suggest that the 15, 10, and 5 min living circle planning is not merely about the availability of services within their time-distance standards, but about ensuring multifaceted accessibility fairness for residents within these standards. Full article