Search Results (14)

The paper studies finite and infinite periodic point-circle configurations in ordinary Euclidean 3-space associated with regular skeletal polyhedra or related structures. The configurations preserve all the symmetries of the underlying polyhedron and, in most cases, are point-circle transitive. Illustrations of many highly symmetric point-circle configurations are provided. Full article

The velocity obstacles (VO) method is widely employed in real-time obstacle avoidance research for UAVs due to its succinct mathematical foundation and rapid, dynamic planning abilities. Traditionally, VO assumes a circle protection domain with a fixed radius, leading to issues such as excessive conservatism of obstacle avoidance areas, longer detour paths, and unnecessary avoidance angles. To overcome these challenges, this paper firstly reviews the fundamentals and pre-existing defects of the VO methodology. Next, we explore a scenario involving UAVs in head-on conflicts and introduce an elliptic velocity obstacle method tailored to the UAV’s current flight state. This method connects the protection domain size directly to the UAV’s flight state, transitioning from the conventional circle domain to a more efficient elliptic domain. Additionally, to manage the computational demands of Minkowski sums and velocity obstacle cones, an approximation algorithm for discretizing elliptic boundary points is introduced. A strategy to mitigate unilateral velocity oscillation had is developed. Comparative validation simulations in MATLAB R2022a confirm that, based on the experimental results for the first 10 s, the apex angle of the velocity obstacle cone for the elliptical domain is, on average, reduced by 0.1733 radians compared to the circular domain per unit simulation time interval, saving an airspace area of 13,292 square meters and reducing the detour distance by 14.92 m throughout the obstacle avoidance process, facilitating navigation in crowded situations and improving airspace utilization. Full article

With the increasing pressure of resource decline and environmental pollution faced by the green transformation of marine fisheries, marine fishery carbon sinks are an increasingly close link to national strategic interests and economic lifelines. It is, therefore, necessary to explore paths for the enhancement and development of the carbon sink capacity of marine fisheries. Based on the economic data of marine fisheries from 2002 to 2021, this paper measures the capacity and characteristics of marine fishery carbon sinks in provincial areas, applies the kernel density estimation method to depict the dynamic evolution of the distribution of absolute differences in marine fishery carbon sinks, and at the same time, identifies the factors influencing the spatial imbalance in the development of marine fishery carbon sinks as well as the spatial spillover effects. The results show the following: (1) From the total amount, the fishery carbon sink capacity of China’s three marine economic circles has fluctuated and increased over the past 20 years, with obvious differences among different circles, and the marine fishery carbon sink capacity of the eastern, northern, and southern marine economic circles has risen sequentially. This trend corresponds to the economic disparities among the three circles, demonstrating a transition from economic to industrial driving effects. (2) From the spatial point of view, the fishery carbon sink capacity shows a trend of increasing year by year, concentrating in the circles, and overflowing between the circles. (3) The results of a partial derivative test further show that among the main influencing factors of marine fishery carbon sinks, capital, labor, and market openness have direct positive effects on marine fishery carbon sinks, and the direct effect of innovation is the strongest, and the significance of the indirect effect of the three circles is weaker compared to the direct effect and total effect. As a result, the carbon sink of China’s marine fisheries has a large room for improvement, and in order to promote the high-quality development of China’s marine fisheries, it is still necessary to accelerate the circulation of resources within the marine economic circle, accelerate the research of fishery technology, actively develop the carbon sink fishery, and enhance the specialization of aquatic product processing. Full article

This paper focuses on the level of urban–rural integration development and its spatio–temporal evolution patterns in the Chengdu-Chongqing Economic Circle. It constructs an evaluation indicator system encompassing five dimensions: population, economy, society, ecology, and space. By comprehensively using statistical data and multi-source spatio–temporal data and employing methods such as the entropy method, ESDA, obstacle degree model, and various statistical techniques, the study measures and analyzes the level of urban–rural integration development at three time points: 2010, 2015, and 2020. The findings are as follows: (1) The overall level of urban–rural integration is low, predominantly at low to lower-middle levels, with a clear core-periphery spatial pattern where central urban areas such as Chengdu’s central seven districts and Chongqing’s central urban districts are high-value cores, whereas peripheral and central regional areas are less integrated. (2) From 2010 to 2020, there was a steady increase in integration levels, transitioning from a single-core to a more dynamic point-axis structure with emerging regional growth poles. However, this transition was accompanied by reduced inequality of urban–rural integration within each city, while disparities among central urban areas within its cities gradually increased. (3) The analysis of obstacles across dimensions indicates that spatial integration faces the most significant barriers, mainly due to geographical conditions and development constraints in southwestern mountainous counties. In contrast, barriers to economic and social integration, though initially lower, have gradually increased, highlighting imbalances between economic growth and social service provision. Overall, this study not only provides a systematic measurement and analytical framework for the integration and development of urban and rural areas in the Chengdu-Chongqing Economic Circle but also offers theoretical and empirical support for global research and practice on urban–rural integration. Additionally, it proposes targeted policy recommendations. Full article

A function from the domain (x-set) to the codomain (y-set) connects each x element to precisely one y element. Since each x-point originating from the domain corresponds to two y-points on the graph of a closed curve (i.e., circle, ellipse, superellipse, or ovoid) in a rectangular (Cartesian) diagram, it does not fulfil the function’s requirements. This non-function phenomenon obstructs the nonlinear regression application for fitting observed data resembling a closed curve; thus, it requires transforming the rectangular coordinate system into a polar coordinate system. This study discusses nonlinear regression to fit the circumference of a tree stem’s cross-section and its sapwood–heartwood transition by transforming rectangular coordinates (x, y) of the observed data points’ positions into polar coordinates (r, θ). Following a polar coordinate model, circular curve fitting fits a log’s cross-sectional shape and sapwood–heartwood transition. Ellipse models result in better goodness of fit than circular ones, while the rotated ellipse is the best-fit one. Deviation from the circular shape indicates environmental effects on vascular cambium differentiation. Foresters have good choices: (1) continuing using the circular model as the simplest one or (2) changing to the rotated ellipse model because it gives the best fit to estimate a tree stem’s cross-sectional shape; therefore, it is more reliable to determine basal area, tree volume, and tree trunk biomass. Computer modelling transforms the best-fit model’s formulas of the rotated ellipse using Python scripts provided by Wolfram engine libraries. Full article

This paper explores the typological attributes, practical characteristics, and policy connotations of Christian social service organizations in present China. This is achieved from the perspectives of religion, public administration, social work, and history. Data collection and analysis are based on the literature research and field research methods. The main points are as follows: (1) Christian social service organizations are simultaneously faith-based organizations, legal-person organizations, and professional organizations. These different types of characteristics put forward different requirements for their service functions and performance standards. It is necessary to understand their corresponding boundaries in theory and coordinate or optimize their corresponding functions in the system; (2) Christian social service organizations present the characteristics of pluralism and transition in the practice process, as well as form complex symbiosis and embedded relationships with non-religious professional service systems. Further, they have begun to reach a consensus on industry codes of practice, service concepts, and clinical models, especially in regard to the culturally sensitive service centered on the clients; and (3) the triple-type attributes of Christian social service organizations require government departments and professional circles to direct more attention to the “matrix” of policy tools—in other words, formulate more discerning and diverse policy measures in line with policy objectives, as well as strengthen the legalization of the policy implementation mechanism and the level of collaborative governance of religious social service organizations. Full article

Ideally, to carry out screening for eye diseases, it is expected to use specialized medical equipment to capture retinal fundus images. However, since this kind of equipment is generally expensive and has low portability, and with the development of technology and the emergence of smartphones, new portable and cheaper screening options have emerged, one of them being the D-Eye device. When compared to specialized equipment, this equipment and other similar devices associated with a smartphone present lower quality and less field-of-view in the retinal video captured, yet with sufficient quality to perform a medical pre-screening. Individuals can be referred for specialized screening to obtain a medical diagnosis if necessary. Two methods were proposed to extract the relevant regions from these lower-quality videos (the retinal zone). The first one is based on classical image processing approaches such as thresholds and Hough Circle transform. The other performs the extraction of the retinal location by applying a neural network, which is one of the methods reported in the literature with good performance for object detection, the YOLO v4, which was demonstrated to be the preferred method to apply. A mosaicing technique was implemented from the relevant retina regions to obtain a more informative single image with a higher field of view. It was divided into two stages: the GLAMpoints neural network was applied to extract relevant points in the first stage. Some homography transformations are carried out to have in the same referential the overlap of common regions of the images. In the second stage, a smoothing process was performed in the transition between images. Full article

Over the last decade, the circular economy (CE) has attracted attention due to the current unsustainable model of production and consumption, which involves an increased resource use and depletion. Agri-food is one of the key sectors where action must be taken to ensure the transition to a more sustainable development model in line with circular economy principles. This study aims to evaluate the potential of implementing the circular economy in the pitahaya agri-food chain in Ecuador. The research was conducted from 2019 to 2021, during which a checklist was applied that included 91 items grouped into nine dimensions: source or supply of materials, design, manufacturing, economic circle, distribution and sales, consumption/use, 4R, remanufacturing, and sustainability. The level of the circular economy evaluated in the study was low (2.14 points out of 5). Therefore, improvements are required in the agri-food management of fruit cultivation and processing. Critical points were identified and strategies were proposed to increase competitiveness, improve environmental performance, and promote the implementation of the circular economy in this production chain. A final recommendation is to explore research on the concept of CE in the sector, mainly focused on the valorization of biomass as a contribution to the bioeconomy in order to contribute to the country’s growth within the context of sustainability. Full article

With its proposal of the “double carbon” (peak carbon dioxide emissions and carbon neutralization) goal, China has entered a new stage in creating an ecological civilization and achieving sustainable development. Based on the formation and evolution mechanism of the carbon emission efficiency network, in this study, a trilateral evolutionary game model—including efficiency groups (high- and low-efficiency groups) and local governments—was constructed, in an attempt to discuss the conditions needed for different players and trilateral interconnected systems to implement balanced and stable strategies. Furthermore, the sensitivity of the participants’ evolutionary trajectories toward factors such as the initial strategy ratio, transition cost, and network capital were tested via a system simulation. The main conclusions were as follows: (1) Efficiency groups form a virtuous circle when the initial proportion of the participants’ strategies reaches a certain threshold, and converge into a stable “win–win” state. Under these circumstances, high-efficiency groups tend to give full play to their efficiency advantages in terms of carbon emission reduction and green development, while low-efficiency groups tend to choose green transformation and accept the spillover effect from high-efficiency groups. (2) When efficiency groups achieve a “win–win” state or form good self-management, local governments move from active supervision to a passive supervision strategy in order to reduce supervision costs. (3) While different initial strategy proportions do not affect the stable convergence point of the evolutionary system, they have a differentiated impact on the convergence speed of the players. Under the condition of a low initial strategy ratio, transformation costs can reduce the green transformation enthusiasm of inefficient groups, while network capital can enhance the green transformation willingness of inefficient groups. Full article

The determination of a ship’s safe trajectory in collision situations at sea is one of the basic functions in autonomous navigation of ships. While planning a collision avoiding manoeuvre in open waters, the navigator has to take into account the ships manoeuvrability and hydrometeorological conditions. To this end, the ship’s state vector is predicted—position coordinates, speed, heading, and other movement parameters—at fixed time intervals for different steering scenarios. One possible way to solve this problem is a method using the interpolation of the ship’s state vector based on the data from measurements conducted during the sea trials of the ship. This article presents the interpolating function within any convex quadrilateral with the nodes being its vertices. The proposed function interpolates the parameters of the ship’s state vector for the specified point of a plane, where the values in the interpolation nodes are data obtained from measurements performed during a series of turning circle tests, conducted for different starting conditions and various rudder settings. The proposed method of interpolation was used in the process of determining the anti-collision manoeuvre trajectory. The mechanism is based on the principles of a modified Dijkstra algorithm, in which the graph takes the form of a regular network of points. The transition between the graph vertices depends on the safe passing level of other objects and the degree of departure from the planned route. The determined shortest path between the starting vertex and the target vertex is the optimal solution for the discrete space of solutions. The algorithm for determining the trajectory of the anti-collision manoeuvre was implemented in autonomous sea-going vessel technology. This article presents the results of laboratory tests and tests conducted under quasi-real conditions using physical ship models. The experiments confirmed the effective operation of the developed algorithm of the determination of the anti-collision manoeuvre trajectory in the technological framework of autonomous ship navigation. Full article

Both juvenile and adult criminal careers show regularities in the origins of delinquency, the dynamics of the criminal pathway, and the turning points that lead to desistance/persistence in crime. Research shows that family, education, and friendship environments contribute significantly to the individual choices that create criminal biographies. Our aim was to apply core aspects of life course theory (LCT): trajectory, the aged-graded process, transitions, institutions, and ultimately how desistance/persistence factor into explaining the criminal careers of Polish offenders. The research is based on in-depth interviews (130) carried out with both offenders (90) and experts (40). The offenders were divided into two groups: 30 were juveniles, and 60 were adults of whom half were sentenced for the first time (30) and half were recidivists (30) located in correctional institutions or released. The experts group (40) includes psychologists, educators, social rehabilitators, and prison and juvenile detention personnel working with offenders. We used triangulation of researcher, data, and methodology. Our data revealed that similar biographical experiences characterized by an early socialization, family and friends-based circles laid the groundwork for their entry and continued participation in criminal activity. Juvenile and adult first-time sentenced offenders led criminal careers significantly different from those of recidivists, who faced problems with social adaptation caused by lack of family and institutional support. Full article

Though the relevance of the concept of neighbourhood in both research and policy oriented circles is unquestionable, the concept remains contested and fluid, making its operationalisation a daunting task, particularly in practice. This study explores how the concept of neighbourhood has been operationalised in Kigali city and how the neighbourhood boundaries and typologies are defined. The paper dwells on the review of relevant literature, interviews with 25 practitioners and field observations. It is argued that neighbourhood conceptualisation in Kigali is both theory—it bears the common aspects of neighbourhood definitions—and practice driven, reflecting modernity and context. On the one hand, modernity suggests the desire of planning authorities to follow contemporary planning practices. Context, on the other hand, reflects the desire to tailor local policies to country specific challenges. While boundaries follow subjective, administrative and physical models, typologies tend to be overly physical, focusing mainly on housing structures. The study identified three conventional neighbourhood typologies—planned, informal and mixed types. Given the predominance of informal and mixed neighbourhoods, this study further argues that such areas form the ‘bedroom’ and ‘transit point’ for most lower- and middle-class workers, in addition to serving as a ‘laboratory’ for testing various social interventions. The study recommends a well-serviced mixed classification typology to foster a strong sense of belongingness. Full article

The expansion of urban space makes citizens more dependent on cars, resulting in various urban environmental and traffic problems. Advocating low-carbon travel and building a sustainable low-carbon city are the major trends of urban development. Many scholars have pointed out that the urban spatial environment will lead residents to change their travel modes, but the residents’ travel patterns will also have an impact on the urban spatial layout. Based on the interaction between the two, most of the studies have been evaluated and studied from the level of rail transit and normal bus transit. The traffic volume level of trams lies between the rail transit and the normal public transit. However, the research and discussion on the relationship between the surrounding land use and residents’ travel behaviors are not yet perfect domestically. This paper takes Nanjing Chilin Tram Line 1 in China as the research object, combines the research of the the social attributes of the passengers who live along the tram line and the psychological accessing threshold of different travel purposes, provides analysis and evaluations of the coupling degree between the present situation of land use around its various stations and the residents’ actual travel demand with the measure of accessibility. The traffic volume level of trams lies between the rail transit and the normal public transit. However, the research and discussion on the relationship between the surrounding land use and residents’ travel behaviors are not yet perfect domestically. Taking Nanjing Chilin Tram Line 1 in China as the research object, this paper combines the research of the the social attributes of the passengers who live along the tram line and the psychological accessing threshold of different travel purposes. Furthermore, based on the measure of accessibility, it provides the analysis and evaluations of the coupling degree between the present situation of land use around its various stations and the residents’ actual travel demand. The research method of this paper is divided into three parts. Firstly, based on the questionnaire and OD survey, the coupling degree between the type of the station along the tram line and the distribution of passenger flow and the purpose of passenger travel is analyzed. Secondly, the KLP model is used to calculate and determine the effective influence range of the tram through the critical accessing distance for pedestrians psychologically. Based on different psychological thresholds for different purposes, the land use index within the influence range of the station is evaluated and analyzed, and the controlled circle of land use around each type of station is defined. Finally, the coupling degree between the actual land use status in each circle and residents’ psychological threshold with different purposes is analyzed, and the optimization strategy is proposed from the coupling degree between the overall station type & passenger flow along the line and the land use layout around the station & the residents’ psychological threshold. Full article

Unmanned Aerial Vehicles (UAVs) play an important role in applications such as data collection and target reconnaissance. An accurate and optimal path can effectively increase the mission success rate in the case of small UAVs. Although path planning for UAVs is similar to that for traditional mobile robots, the special kinematic characteristics of UAVs (such as their minimum turning radius) have not been taken into account in previous studies. In this paper, we propose a locally-adjustable, continuous-curvature, bounded path-planning algorithm for fixed-wing UAVs. To deal with the curvature discontinuity problem, an optimal interpolation algorithm and a key-point shift algorithm are proposed based on the derivation of a curvature continuity condition. To meet the upper bound for curvature and to render the curvature extrema controllable, a local replanning scheme is designed by combining arcs and Bezier curves with monotonic curvature. In particular, a path transition mechanism is built for the replanning phase using minimum curvature circles for a planning philosophy. Numerical results demonstrate that the analytical planning algorithm can effectively generate continuous-curvature paths, while satisfying the curvature upper bound constraint and allowing UAVs to pass through all predefined waypoints in the desired mission region. Full article