Expansion Mode Research Articles

¿Por qué los países latinoamericanos sufren un estancamiento económico de largo plazo? Un estudio a partir de los casos de Argentina, Brasil y México

El artículo trata de la situación de crisis latente que existe en América Latina desde hace varias décadas. Las tasas medias de crecimiento per cápita durante un largo periodo en la mayoría de los países de la región se sitúan entre 0 y 2%. Desde los años ochenta y noventa la tendencia al estancamiento no puede explicarse de la misma manera en los grandes países de América Latina. Si bien hay causas comunes, el peso de cada factor difiere. En este artículo se exponen las diversas teorías sobre la tendencia al estancamiento económico. Su originalidad radica en que no sólo pone en relieve el papel de las desigualdades en materia de ingresos y riqueza, o el papel de los procesos de desindustrialización, sino también las causas de la volatilidad económica y sus consecuencias para la baja tasa media de crecimiento per cápita, que es particularmente pronunciada en algunos países.
 Contrarias a una idea relativamente compartida, estas economías han sido poco o nada emergentes a partir de los años 1980-1990, a excepción, tal vez, de los años 2000 a 2012, más o menos. Por lo tanto, no han convergido, o sólo lo han hecho de manera limitada, hacia el nivel de ingresos per cápita de los países avanzados, a diferencia de muchos países asiáticos. Los países de América Latina están experimentando varias dificultades al mismo tiempo que se alimentan unas de otras. La crisis es profunda. Es estructural en el sentido de que pone en duda los propios modos de expansión del capitalismo en las últimas décadas. Por lo tanto, sólo respuestas a este nivel pueden hacer posible la superación de los obstáculos al desarrollo sostenible, y la inclusión de aquellos, la mayoría, que son rechazados.

Joule–Thomson expansion and quasinormal modes of regular non-minimal magnetic black hole

The Joule–Thomson effect and quasinormal modes (QNM) onto regular non-minimal magnetic charged black hole with a cosmological constant are being investigated. For this purpose, we extract some thermodynamical parameters such as pressure [Formula: see text] and mass [Formula: see text] in the presence of magnetic [Formula: see text] as well as electric [Formula: see text] charge. These parameters lead to inversion temperature [Formula: see text], pressure [Formula: see text] and corresponding isenthalpic curves. We introduce the tortoise coordinate and the Klein–Gordon wave equation which leads to the second-order ordinary Schrödinger equation. We find out the complex frequencies of QNMs through the massless scalar field perturbation which satisfy boundary conditions by using the first-order Wentzel–Kramers–Brillouin (WKB) technique.

Relationship between Three-Dimensional Magnetic Resonance Imaging Eyeball Shape and Optic Nerve Head Morphology

To determine if the 3-dimensional (3D) eyeball shape is associated with the positions of the central retinal vascular trunk (CRVT) and the externally oblique border (EOB) in the optic nerve head (ONH). Prospective, cross-sectional study. Fifty-six subjects (112 eyes) with a diagnosis of glaucoma or glaucoma suspect. The eyeball shape on 3D magnetic resonance imaging (MRI) scans was classified according to the dimension of the longest diameter: axial dimension (prolate sphere), group 1; horizontal dimension (horizontally oblate sphere), group 2; and vertical dimension (vertically oblate sphere), group 3. The deviation of the CRVT, as a surrogate of lamina cribrosa (LC) shift, was measured from the center of the Bruch's membrane opening (BMO) demarcated by OCT imaging, with the horizontal midline as 0° and the superior location as a positive value. The angular location of the longest EOB was also measured. Positions of CRVT and EOB according to the 3D eyeball shape. Among 112 eyes, 54 (48%) had a prolate shape (group 1), 23 (21%) had a horizontally oblate shape (group 2), and 35 (31%) had a vertically oblate shape (group 3). The angular deviation of the CRVT differed among the groups: to the nasal side in group 1, to the temporal side in group 2, and along the vertical meridian in group 3. In cases of asymmetric eyeball shape, the CRVT was deviated toward the undergrown side from the overgrown side, regardless of grouping. The angular location of the longest EOB was in the direction opposite to the CRVT position (P < 0.001). A generalized estimating equation analysis revealed that the temporal location of the CRVT was associated with older age (P= 0.001), nasal location of the longest EOB (P < 0.001), and oblate shape of the eyeball (P < 0.001, group 2; P= 0.007, group 3). The position of the CRVT and EOB were associated with the 3D eyeball shape. Considering that infant ONH morphology is highly uniform, various modes of eyeball expansion during growth can result in diverse directionalities of offset between the LC and the BMO in adults.

Peculiarities of adaptive phase correction of optical wave distortions under conditions of ‘strong’ intensity fluctuations

The reason for the loss of efficiency of adaptive phase correction in the propagation of optical waves in a turbulent atmosphere under conditions of ‘strong’ intensity fluctuations is experimentally explained for the first time. Based on the data from experiments conducted on both horizontal and vertical atmospheric paths, we have found that intensity fluctuations begin to significantly affect phase measurements when the coherence radius of the optical wave becomes less than the radius of the first Fresnel zone. Under these conditions, the main meter of adaptive optics systems, i. e. the Hartmann sensor, no longer provides correct measurements of the phase distribution in the presence of deep amplitude modulation. Based on the study of the behaviour of the mode components of the phase fluctuations reconstructed from the results of measurements in various operating regimes, we have found that, first of all, the amplitudes of the lowest modes of phase fluctuation expansion (tilts, defocusing, and astigmatism) are distorted, which, as the analysis shows, is very different from the regime of weak fluctuations.

A RISC-V Based Coprocessor Accelerator Technology Research for Convolution Neural Networks

The advancements of neural networks have significantly improved the accuracy of a variety of intelligent applications, such as image processing, voice recognition and so on. However, one of the challenges is to accelerate the speed of inference with the networks designed to be deeper. In this paper, we first realize the algorithm involved in software. Then, combined with the expanded characteristic of RISC-V architecture, the acceleration of convolution operation taking up the largest proportion of computation in CNN is realized by coprocessor expansion mode on open-source Hummingbird E203 processor. Through tests, convolution coprocessor improves the performance of CNN while ensuring the accuracy in function. Finally, the Cifar-10 image classification, a common benchmark in machine learning, is used to verify the feasibility in functions and comparatively analysis the pure software-based and coprocessor-based implementations.

Urban-rural spatial transformation process and influences from the perspective of land use: A case study of the Pearl River Delta Region

The process of rapid urbanization results in the flow and agglomeration of regional production factors, which leads to the transformation of the urban-rural territorial system and changes the spatial patterns of urban and rural areas. On the basis of the dynamic changes about urban and rural construction land, this research focuses on the processes, influencing factors, and driving mechanisms motivating the urban-rural transformation in the Pearl River Delta Region. Vector data of urban construction land use in 1990, 2000, 2005, and 2017, natural elements, socioeconomic data, geostatistical analysis method, and logistic regression model were all utilized to identify the characteristics of the processes and influencing factors. The driving mechanisms of spatial evolution in urban-rural transformation from regional growth, market development, and government controls were also explained according to analytics. The results reveal the following: (1) The spatial agglomeration of urban-rural transformation was highlighted, and a stable “A” regional spatial structure was formed around Guangzhou, Foshan, Zhuhai, Shenzhen, and Dongguan. (2) The urban-rural transformation changed from a high-intensity expansion mode in the core region to a low-intensity expansion mode in the core periphery region. (3) The urban-rural transformation in the east coast of the Pearl River Delta was better than that in the west coast, and the transformation pace of the Pearl River estuary was faster than that of the periphery region. (4) The urban-rural transformation was affected by natural conditions and socioeconomic development, of which traffic location was the most significant factor. (5) The urban-rural spatial variation originated from the combined effects of regional growth forces, market driving forces, and government control forces.

Zero mode of the Fourier series of some modular graphs from Poincaré series

We consider specific linear combinations of two loop modular graph functions on the toroidal worldsheet with 2s links for s=2,3 and 4. In each case, it satisfies an eigenvalue equation with source terms involving E2s and Es2 only. On removing certain combinations of E2s and Es2 from it, we express the resulting expression as an absolutely convergent Poincaré series. This is used to calculate the power behaved terms in the asymptotic expansion of the zero mode of the Fourier expansion of these graphs in a simple manner.

Perfect Conversion of a TM Surface Wave Into a TM Leaky Wave by an Isotropic Periodic Metasurface Printed on a Grounded Dielectric Slab

This article presents an exact solution for a perfect conversion of a TM-polarized surface wave (SW) into a TM-polarized leaky wave (LW) using a reciprocal and lossless penetrable metasurface (MTS) characterized by a scalar sheet impedance, located on a grounded slab. On contrary to the known realizations of LW antennas, the optimal surface reactance modulation which is found here ensures the absence of evanescent higher-order modes of the field Floquet-wave expansion near the radiating surface. Thus, all the energy carried by the SW is used for launching the single inhomogeneous plane wave into space without accumulation of reactive energy in the higher-order modes. It is shown that the resulting penetrable MTS exhibits variation from an inductive to a capacitive reactance passing through a resonance. The present formulation complements a previous article of the authors, in which a perfect conversion from TM-polarized SW to TE-polarized LW was found for impenetrable boundary conditions. Here, the solution takes into account the grounded slab dispersion, and it is convenient for practical implementation.

Numerical simulation of fracture initiation, propagation and fracture complexity in the presence of multiple perforations

Perforation is the key to the successful implementation of hydraulic fracturing. The research on perforation mechanism is of great significance to perforation planning, completion design, hydraulic fracturing design, and proppant migration analysis. In this paper, a finite element model for simulating crack initiation and propagation in the presence of multiple perforations is established based on the global embedded cohesive zone model (CZM). The reservoir is considered as a dense, low-permeability porous elastic medium, and the coupling between fluid flow and geomechanics, as well as the back-stress effect, are considered. The Blanton's (1982) criteria were used to verify the accuracy of the global embedded CZM. Then five cases are used to discuss the effects of perforation density, horizontal stress difference (HSD) on fracture initiation, propagation, and fracture complexity. The results show: There are four competitive fracture initiation modes for multiple perforations: First, fracture initiation at an early stage and keeping on; Second, hole deformed but not cracked; Third, fracture initiation first and then close; Fourth, at the beginning, there is no fracture initiation, initiation later. With the increase of perforation density, affected by the decrease of flow distribution, increase of friction and stress interference, the initiation rate of perforations gradually decreases, and the fracture pressure shows a tendency of decreasing first and then increasing. When multiple perforations exist, the crack propagation changes from complex to simple, and the number of cracks changes from more to less. Finally, the expansion mode is formed with 2–3 main cracks as the main and micro cracks as the auxiliary. The increase of perforation density can increase the complexity of fractures around the wellbore, and is beneficial to the diversion of fractures and the expansion of the impact range of fractures. However, it can also cause distortion and deformation of the fracture wall and decrease of fracture opening near the wellbore, which can lead to difficulty in proppant migration. Under low HSD, under the influence of stress inversion, connected horizontal cracks are easy to form between holes, and the fractures are easier to turn and more complicated. Under high HSD, disconnected horizontal micro-cracks can be formed between holes, and the main fractures tend to develop into simple straight fractures. The results of our research have important practical guiding significance for the development of perforation plan, hydraulic fracturing design and proppant migration analysis.

The Expansion of the Dense Plasma of a Mixture of Deuterium and Tritium into the Empty Space in which There is a Magnetic Field

The work is aimed at determining parameters of a deuterium-tritium mixture expanding into a vacuum with an external magnetic field, the output of thermonuclear energy from which compensates or exceeds the initial thermal energy of the plasma. This type of assessment is usually based on the Lawson criterion. In the paper the parameters are determined on the basis of the model of adiabatic expansion into the surrounding homogeneous magnetic field of the plasma ball in the magnetohydrodynamic approximation for some special modes of expansion, providing a self-similar distribution of gas-dynamic quantities. The obtained minimum values of the energy expended for the initial heating of the plasma, providing its equality to the resulting integrated fusion energy, are compared with the known estimates within the framework of inertial confinement fusion.

Rapid urbanization in a mountainous landscape: patterns, drivers, and planning implications

Understanding patterns and drivers of urbanization is essential for urban sustainability, but such understanding is lacking for mountainous regions. This study had three objectives: (1) to quantify the spatiotemporal patterns of urban expansion in Chongqing, the largest mountainous metropolitan area in China, during 1990–2015; (2) to explore major drivers for the observed urbanization patterns; and (3) to identify the spatial signatures of Chongqing’s urbanization which differ from those of topographically flat urban regions for sustainable urban planning in mountainous regions. We used multiple metrics to characterize urbanization patterns and expansion modes. Pearson correlation analysis and Classification and Regression Trees (CART) were used to identify potential drivers. The built-up area of Chongqing increased five times during 1990–2015 with regional variations. Three growth modes—leapfrog, edge-expansion, and infilling, took place concurrently, but their relative dominance varied in time and space with leapfrog as the dominant mode in recent years. The major drivers of built-up area expansion changed from demography to economy, with topographic constraints attenuating over time. Compared to flat urban regions in China, the spatial signatures of Chongqing’s urbanization were characterized by greater dominance of leapfrog expansion mode with smaller and more regularly-shaped patches. The unique patterns and drivers of urban expansion in Chongqing provide new insights of urbanization in mountainous regions for sustainable urban planning. We have proposed a conceptual urban planning framework for mountainous cities based on landscape sustainability science, GeoDesign, and regional landscape characteristics.

Learning and meta-learning of stochastic advection–diffusion–reaction systems from sparse measurements

Physics-informed neural networks (PINNs) were recently proposed in [18] as an alternative way to solve partial differential equations (PDEs). A neural network (NN) represents the solution, while a PDE-induced NN is coupled to the solution NN, and all differential operators are treated using automatic differentiation. Here, we first employ the standard PINN and a stochastic version, sPINN, to solve forward and inverse problems governed by a non-linear advection–diffusion–reaction (ADR) equation, assuming we have some sparse measurements of the concentration field at random or pre-selected locations. Subsequently, we attempt to optimise the hyper-parameters of sPINN by using the Bayesian optimisation method (meta-learning) and compare the results with the empirically selected hyper-parameters of sPINN. In particular, for the first part in solving the inverse deterministic ADR, we assume that we only have a few high-fidelity measurements, whereas the rest of the data is of lower fidelity. Hence, the PINN is trained using a composite multi-fidelity network, first introduced in [12], that learns the correlations between the multi-fidelity data and predicts the unknown values of diffusivity, transport velocity and two reaction constants as well as the concentration field. For the stochastic ADR, we employ a Karhunen–Loève (KL) expansion to represent the stochastic diffusivity, and arbitrary polynomial chaos (aPC) to represent the stochastic solution. Correspondingly, we design multiple NNs to represent the mean of the solution and learn each aPC mode separately, whereas we employ a separate NN to represent the mean of diffusivity and another NN to learn all modes of the KL expansion. For the inverse problem, in addition to stochastic diffusivity and concentration fields, we also aim to obtain the (unknown) deterministic values of transport velocity and reaction constants. The available data correspond to 7spatial points for the diffusivity and 20 space–time points for the solution, both sampled 2000 times. We obtain good accuracy for the deterministic parameters of the order of 1–2% and excellent accuracy for the mean and variance of the stochastic fields, better than three digits of accuracy. In the second part, we consider the previous stochastic inverse problem, and we use Bayesian optimisation to find five hyper-parameters of sPINN, namely the width, depth and learning rate of two NNs for learning the modes. We obtain much deeper and wider optimal NNs compared to the manual tuning, leading to even better accuracy, i.e., errors less than 1% for the deterministic values, and about an order of magnitude less for the stochastic fields.

Technical efficiency estimation of China's environmental protection enterprises and its heterogeneity.

The status of technical efficiency (TE) of environmental protection enterprises is crucial to the sustainable economic development. Based on the micro-survey data of China's environmental protection enterprises from 2003 to 2013, through a systematic calculation and comparison about TE level under stochastic frontier analysis, this article investigated the distribution characteristics and heterogeneous sources of them comprehensively and found that first, there are wide-ranging technical efficiency differences among sub-sectors, ownership, and regions within China's environmental protection industry, and this type of heterogeneity was significantly interfered by the institution and policy environment. Second, there is obvious scale economy effect and no scope economy effect in the TE distribution of China's environmental protection enterprises, and their TE level has a positive response to management improvement and competition enhancement, but has a negative feedback on heavy asset expansion and debt-driven growth mode. Third, the overall TE levels of non-state-owned enterprises are higher than that of state-owned enterprises; the overall TE levels of enterprises located in the eastern provinces are higher than those of enterprises located in the central and western provinces. Fourth, reducing tax burdens of environmental protection enterprises is more effective to promote their TE level than providing governmental subsidies directly. Therefore, to promote the quality of the development for China's environmental protection industry, it is necessary to emphasize the market mechanism. Based on the market power, we should accelerate the industry integration, cultivate the market demand, and promote market competition. Furthermore, the government should also need to design a targeted support system and differentiated policy arrangements for the development of environmental protection enterprises.

National urban land-use/cover change since the beginning of the 21st century and its policy implications in China

China has experienced rapid urban expansion since the beginning of the 21st century. Although many previous studies have explored the forces driving urbanization, how policies drive these changes at the national scale has not been fully examined. This research aims to delineate the regional differentiations of urban expansion and related impervious surface area (ISA) density and reveal the socioeconomic and macropolicy factors causing these changes. The result shows that national urban land expanded from 4.26 × 104 km² in 2000 to 6.90 × 104 km² in 2015 at an unprecedented rate, with an average increasing rate of 1760 km²/yr since 2000. The spatial metrics of ISA density diverted from a low-density sprawl mode during 2000–2010 to a dense expansion mode during 2010–2015, with the highest ISA density of 70.70% in 2015. Regionally, the rate of urban expansion and ISA growth reduced in the coastal zone in 2010–2015. In contrast, urban expansion accelerated in the western and central zones, due to the China Western Development Plan and the Rise of Central China Plan initiated in 1999 and 2006, respectively. Although the concept of “Sponge city” (an urban water management system) was proposed in 2013, the national ISA density still increased due to urban infilling. The overarching issue that must be seriously considered is the tradeoff between the magnitude of urban expansion and ISA density and building sustainable and livable cities in an era of urban transformation.

Development trend of marine shale gas reservoir evaluation and a suitable comprehensive evaluation system

At present, shale gas exploration and development in China is faced with some problems, such as the imperfect evaluation system of reservoir effectiveness and the limitations of reservoir evaluation system on efficient development of shale gas. In order to improve the content and the standard of reservoir evaluation, this paper analyzed the shortcomings and challenges in the static evaluation of shale gas reservoirs on the basis of existing reservoir evaluation, and established a method for evaluating shale gas reservoir effectiveness and a scheme for classifying pore systems. Then, the dynamic evaluation parameters after shale fracturing and their effects on drainage and production measures were discussed. In addition, the potential evaluation parameters of “automatic mitigating water blocking” were studied, and a comprehensive reservoir evaluation system of “static–dynamic” combination was established. And the following research results were obtained. First, new challenges to the shale gas reservoir evaluation are emerged as the lack of in-depth study on “reservoir effectiveness, dynamic evaluation parameter system after fracturing and drainage and production measures after fracturing”, which leads to the serious lag of existing shale gas reservoir evaluation system behind production. Second, the evaluation of reservoir effectiveness is mainly presented as the evaluation on the lower limit of effective porosity, and is embodied in the influence of clay bound water and unconnected pores on the development of shale gas. Third, the development of shale gas reservoir evaluation follows the trend of refining the static reservoir evaluation parameters, defining the potential evaluation indexes of “automatic mitigating water blocking” and establishing the reservoir comprehensive evaluation system of “static–dynamic” combination. Fourth, a post-frac dynamic evaluation system is determined for the potential evaluation indexes of “automatic mitigating water blocking” (e.g., wettability, water imbibition retention capacity, water imbibition expansion mode, expansion rate, and water imbibition cracking capacity). Fifth, a reservoir evaluation idea is put forward that “static evaluation of shale gas reservoir is the foundation and postfrac dynamic evaluation is the complement”, and a comprehensive reservoir evaluation system is established of “static–dynamic” combination suitable for the evaluation of marine shale gas reservoirs in China.

Experimental study on the change of reservoir characteristics of different lithotypes of lignite after dehydration and improvement of seepage capacity

Find out the changes in lignite properties accompanying dehydration will not only benefit the development of lignite coalbed methane (CBM), but also play a guiding role in the underground gasification, combustion, thermal fragmentation, coal cleaning, and carbon dioxide sequestration. Dehydration can significantly improve the gas flow capacity in the lignite reservoir with originally low permeability. Through nuclear magnetic resonance (NMR) tests, imaging experiments, and permeability tests, the changes in reservoir properties of different lithotypes of lignite during dehydration were comprehensively summarized. In general, the effect of dehydration on lignite reservoir structure is shown in two aspects: the rapid expansion of large fractures, and the shrinkage of relatively small pores. On this basis, different types of lignite exhibit different modes of fracture expansion. Imaging results show that the matrix lignite sample can quickly generate evenly distributed fractures with drying, but these fractures are short in length and poor in orientation. The xylite lignite sample has a lower dehydration efficiency, but can eventually form an extended and well-oriented fracture network. Fractures caused by matrix shrinkage significantly increase reservoir permeability. The results of permeability tests show that dehydration significantly improves the permeability of lignite reservoirs. Since coal permeability is highly stress-sensitive, the effect of stress on the permeability of these samples before and after dehydration was further analyzed. Although the effect of stress on permeability after drying has increased, the effective permeability after drying is always orders of magnitude higher than before drying. In sum, dehydration is an effective measure to improve the seepage capacity of lignite reservoirs.

Tourism land use simulation for regional tourism planning using POIs and cellular automata

AbstractPrevious studies on tourism land use primarily focus on the spatial distribution, and its related impacts on the environment. Here, we propose a future tourism land use simulation model for mountain vacations based on the cellular automata and Markov chain methods, having verified and simulated tourism land use in Emeishan city at a spatial resolution of 30 × 30 m using remote sensing and GIS. In addition, we introduced a tourism land use intensity index to study the spatial expansion mode of tourism land use. The results have confirmed the validity of the model and demonstrated its ability to simulate future tourism land use. The average growth rate of tourism land use from 2010 to 2015 is 33.36%, and tourism land use will rise from 1.26% of Emeishan city’s land area in 2015 to 2.95% in 2030. Tourism land use shows a spatial expansion pattern along channels from scenic spots to the urban area. The growth of tourism land use in the protected area has an increasing trend when there is no restriction on development, especially in the Eshan region. The simulation results can provide useful implications and guides for regional tourism planning and management.

Microfluidic Chamber Design for Controlled Droplet Expansion and Coalescence.

The defined formation and expansion of droplets are essential operations for droplet-based screening assays. The volumetric expansion of droplets causes a dilution of the ingredients. Dilution is required for the generation of concentration graduation which is mandatory for many different assay protocols. Here, we describe the design of a microfluidic operation unit based on a bypassed chamber and its operation modes. The different operation modes enable the defined formation of sub-µL droplets on the one hand and the expansion of low nL to sub-µL droplets by controlled coalescence on the other. In this way the chamber acts as fluidic interface between two fluidic network parts dimensioned for different droplet volumes. Hence, channel confined droplets of about 30–40 nL from the first network part were expanded to cannel confined droplets of about 500 to about 2500 nL in the second network part. Four different operation modes were realized: (a) flow rate independent droplet formation in a self-controlled way caused by the bypassed chamber design, (b) single droplet expansion mode, (c) multiple droplet expansion mode, and (d) multiple droplet coalescence mode. The last mode was used for the automated coalescence of 12 droplets of about 40 nL volume to produce a highly ordered output sequence with individual droplet volumes of about 500 nL volume. The experimental investigation confirmed a high tolerance of the developed chamber against the variation of key parameters of the dispersed-phase like salt content, pH value and fluid viscosity. The presented fluidic chamber provides a solution for the problem of bridging different droplet volumes in a fluidic network.

Laws and Trends of the Evolution of Traditional Villages in Plane Pattern

This study collected and analyzed dynamic spatial data of eight traditional villages scattered in different regions of China. A multi-temporal analysis of morphological metrics of spatial patterns and a regression analysis of the morphological evolution were used to analyze and contrast the historical spatial processes of different villages. These were then compared using patch texture and rural macro-morphology perspectives. This led to an assessment of the general laws and trends associated with rural spatial processes. (1) There has been a significant shift in the stability of rural spatial development since the founding of the People’s Republic of China (PRC). (2) Most small and medium-sized villages have maintained a relatively stable spatial texture, while large villages have changed significantly. (3) The mean and variance of the patch area, and the Euclidean nearest-neighbor distance, are correlated in some cases. (4) The mode of rural expansion may be relevant to limitations in the total area of growth. (5) The fractal dimension of the rural macro-morphology may follow a morphological order of oscillation around the equilibrium level. (6) The common mean value of the projected area of rural building patches is expected to be 100 m2.

Assessing 40 years of spatial dynamics and patterns in megacities along the Belt and Road region using satellite imagery

ABSTRACT The Belt and Road (B&R) region, a vital area with historical, economic, cultural and political significance, has undergone rapid urbanization in the past several decades, especially in the form of urban expansion. In this study, 20 megacities in the B&R region were selected to explore different spatiotemporal patterns of urban expansion. Object-oriented support vector machines (SVM), annual growth rate (AGR) models, and landscape metrics were employed to delineate the urban areas and characterize spatiotemporal characteristics and landscape patterns of these megacities during 1975–2015. All urban maps presented high overall accuracies (80.70%–95.90%) and overall Kappa coefficients (0.76–0.95). The study revealed that megacities in the B&R region have undergone different types of urban sprawl, mainly adopting a ‘concentric circle’ pattern in inland areas and a ‘sector’ pattern in coastal areas. Besides, six expansion modes were summarized according to the AGRs of individual megacities. Differences existed in megacities of the developing and developed countries and among five sub-regions. Moreover, ‘dispersion, gathering, and re-dispersion’ and ‘coalescence’ were two major landscape patterns of megacities in developing and developed countries. Results of this study can provide a scientific reference for urban planning and aid in sustainable development of local areas.