Temporal and spatial evolution of global major grain trade patterns

The complex and volatile international landscape has significantly impacted global grain supply security. This study uses a complex network analysis model to examine the evolution and trends of the global major grain trade from 1990 to 2020, focusing on network topology, centrality ranking, and community structure. There are three major findings. First, the global major grain trade network has expanded in scale, with a growing emphasis on diversification and balance. During the study period, the United States, Canada, China, and Brazil were the core nodes of the network. Grain-exporting countries were mainly situated in Asia, the Americas, and Europe, and importing countries in Asia, Africa, and Europe. Second, a significant increase in the number of high centrality countries with high export capacity occurred, benefiting from natural advantages such as fertile land and favorable climates. Third, the main global grain trade network is divided into four communities, with the Americas-Europe community being the largest and most widespread. The formation of the community pattern was influenced by geographic proximity, driven by the core exporting countries. Therefore, the world needs to enhance the existing trade model, promote the multi-polarization of the grain trade network, and establish a global vision for the future community. Countries and regions should participate actively in global grain trade security governance and institutional reform, expand trade links with other countries, and optimize import and export policies to reduce trade risks.

Spatial Pattern Evolution and Influencing Factors of Cold Storage in China

Cold storage is the vital infrastructure of cold chain logistics. In this study, we analyzed the spatial pattern evolution characteristics, spatial autocorrelation and influencing factors of cold storage in China by using kernel density estimation(KDE), spatial autocorrelation analysis(SAA), and spatial error model(SEM). Results showed that: 1) the spatial distribution of cold storage in China is unbalanced, and has evolved from ‘one core’ to ‘one core and many spots’, that is, ‘one core’ refers to the Bohai Rim region mainly including Beijing, Tianjin, Hebei, Shandong and Liaoning regions, and ‘many spots’ mainly include the high-density areas such as Shanghai, Fuzhou, Guangzhou, Zhengzhou, Hefei, Wuhan, ürümqi. 2) The distribution of cold storage has significant global spatial autocorrelation and local spatial autocorrelation, and the ‘High-High’ cluster area is the most stable, mainly concentrated in the Bohai Rim;the ‘Low-Low’ cluster area is grouped in the southern China. 3) Economic development level, population density, traffic accessibility, temperature and land price, all affect the location choice of cold storage in varying degrees, while the impact of market demand on it is not explicit.

A Monte-Carlo Approach to Cellular Pattern Evolution for Binary Alloys during Directional Solidification

A Monte-Carlo approach of cellular pattern evolution during directional solidification of a binary alloy has been carried out by imposing a non-uniform probability distribution of particle emission from the particle source, as an approach to the contribution of solute redistribution to the interface evolution. Both the bulk and interface diffusion have been involved in the simulation,and coarsening of the cellular patterns with time has been clearly revealed. The remarkable influence of the interface relaxation and the solute redistribution on the profile of solidifying interface has been presented.

Quantum Adiabatic Evolution for Pattern Recognition Problem

Quantum pattern recognition algorithm for two-qubit systems has been implemented by quantum adiabatic evolution.We will estimate required running time for this algorithm by means of an analytical solution of timedependent Hamiltonian since the time complexity of adiabatic quantum evolution is a limitation on the quantum computing.These results can be useful for experimental implementation.

Evolution characteristics of hydrological connectivity pattern of marsh wetland in Naoli River Basin

As an important indicator of the structural and functional stability of wetland landscapes,hydrological connectivity plays an important role in maintaining the stability of wetland ecosystems.Large-scale human activities have led to significant changes in the hydrological connectivity pattern of wetlands in Naoli River Basin since 1950 s.Combined with the availability of wetland habitat and the spreading capacity of aquatic birds,hydrological connectivity indices of marsh wetlands were calculated in the studied area,and the temporal and spatial changes were analyzed from 1950 s to 2015.The results indicate that:(1)the hydrological connectivity index of the marsh wetlands shows a growth trend with increasing distance threshold.All patches of marsh wetlands linked together when the distance threshold reached 35--40 km;(2)the optimal distance of hydrological connectivity is about 10 km for marsh wetlands of whole Naoli River Basin;(3)the total hydrological connectivity of marsh wetlands decreased in the Naoli River Basin from 1950 s to 2015.Although the hydrological connectivity index increased after 2005,the fragmentation of the landscape has not been improved.The analysis of the wetland hydrological connectivity can provide a scientific basis for the ecological restoration and protection of the wetland in the Naoli River Basin.

Impacts of land use change on landscape patterns in mountain human settlement:The case study of Hantai District(Shaanxi,China)

Mountain area is an important geographical unit of land,and its ecology is sensitive and fragile.Over the past few decades,human activities have caused dramatic changes in land use in mountainous areas,which caused changes in landscape patterns and impacts on the ecological environment.It is unknown how the mechanism of land use affects the landscape pattern at different scales.The Hantai District,a typical human settlement in the mountain area in Shaanxi,China,was chosen as the study area.Based on the remote sensing images,the mathematical models and landscape indexes were adopted to evaluate the impact of land use change from 1998 to 2017 on the landscape pattern at different scales,and its main driving forces were analyzed.The results showed that the urbanized land expanded largest from 15.39%to 24.30%,and cultivated land experienced the largest decline from 43.54%to 35.35%.Changes in land use have made the patch morphology of most land types developed from a natural random to a sawtooth shape,and its spatial pattern evolved from a ruleset to a fragmented expansion.This reflects the continuous strengthening of human intervention in the process of regional development.Under the jurisdiction of Hantai District,the biggest change in landscape pattern is in Hanzhong City and Qili Town.The improved economy and increasing population and urbanization rate were the main factors that cause these changes.This research could provide necessary information for understanding the evolution mechanism of land resources in mountainous human settlements for mountainous areas with significant geomorphic differentiation.

Evolution of 3D tectonic stress field and fault movement in North China

Based on data of fault movement surveying, we simulate the evolution process of three dimensional stress field in North China by three dimensional finite element method. Evolutional patterns in one-year time scale from 1986 to 1997 have been illustrated and the evolution characteristics of stress field have been analyzed. In comparison with the seismic activity among that time interval in North China, we have primarily discussed the relationship between the evolution of stress field and seismic activity.

Temporal and Spatial Evolution of Lakes in the Bashang Plateau for Nearly Recent 30 Years

Lakes are important ecological water sources in the Bashang Plateau. Its expansion or shrinkage directly affects the ecological security of the plateau and its surrounding areas. In this study, Landsat images from 1984 to 2015 were selected to monitor the area of lakes in the Bashang Plateau and to analyze the spatiotemporal evolution and driving forces of lakes in the Bashang Plateau. The results showed that there were 47 lakes in the Bashang Plateau in 2015, with a total area of 37.63 km2, mainly distributed in the central and western regions of the region. From 1984 to 2015, the lakes in Bashang Plateau showed a shrinking trend. At the same time, there are obvious stage differences in lake changes. During 1984-1996, the number of lakes increased by 99 and the total area increased by 124.43 km2. From 1996 to 2015, the number of lakes decreased by 142, and the total area decreased by 183.96 km2. Before 1996, climate change was the dominant factor. However, the shrinkage of lakes after 1996 is the result of climate change and human activities. Among them, the large-scale planting of water consuming crops such as vegetables is the main human activity mode leading to lake shrinkage. This study will help to understand the expansion and contraction factors of the Bashang Plateau lakes in Hebei province and provide a reference for the future protection and management of the lakes.

东方经济学,经济拓扑学,经济进化论和循环经济

在经济拓扑学中,经济均衡状态是静态经济学的平衡稳定态区域,经济过程分析是动态经济学,由定性分析理论讨论了经济学中的稳定性及经济变化曲线.基于东方经济学的生克原理的数学,类比于生态系统进化论数学,探讨了商业和经济的进化论与动力学,定性分析了动态微观经济学中的各种关系和变化模式.最后讨论了中国传统农业和农村中完全的循环经济及公共选择理论.

基于OSGi的自适应可进化软件框架

为解决复杂多变环境中软件开发跟不上需求变化的问题,需要设计一套具有自适应能力的软件框架.在深入研究OSGi规范的基础上,将进化论引入软件开发中,采用软件架构支持增量式开发和软件类对象能够自变化的方法,来满足需求的不断变化,最终形成了基于OSGi的自适应、可进化的软件框架.

文学进化观与中国近代文学转型的内在机制

近代文学转型是一个重新确立中国文学体系架构的复杂过程,由进化论主导构成的文化语境成为影响这一进程的决定性因素。应对危机和对先进文学观的积极继承促使国人接受了改写进化论的策略,使之成为改良和革命的理论支撑,并在文学内在价值系统及内容和形式诸方面引发深刻变革。文学进化论的逻辑是不成立的,文学工具主义的策略失控,革命意识和全盘西化的思维模式等弊端也日益引起学者的警觉。

大规模演化知识网络中的关联推理

网络大数据时代的到来使得知识网络中时空信息越来越丰富.现有的知识网络描述模型对知识的时空信息刻画不足.研究证明,利用网络中知识的时空信息以及相关性,能够提高网络中知识间的关联推理的准确率.针对以上问题,首先提出了一种包含时空信息的演化知识网络表示模型,然后研究在该网络模型上的关联推理问题,提出了一种基于背包问题的知识间关联推理方法.在多个数据集上的实验证明了所提出的关联推理方法的有效性以及对大规模知识网络的适应性.

Does the Belt and Road Initiative Promote Value Chain Connection Between China and the Silk Road Countries?

The global value chains have become the core skeleton of the global economy.As a large-scale international cooperation initiative,the Belt and Road Initiative(BRI hereafter)may have a significant impact on the global economic landscape.In this context,the spatiotemporal pattern and evolution of the value chain connection of the Silk Road countries and whether the BRI will promote the value chain connections between China and these countries are important research questions for understanding the changing global economic landscape.This paper employs input-output analysis,network analysis and difference-in-differences based on Propensity Score Matching(PSM-DID)to conduct an in-depth quantitative study of these questions.The results show that,first,the overall value chain connection between China and the Silk Road countries has been rising since 2001.From the perspective of geographical distribution,Southeast Asia is the highest value chain connection region with China,and the growth in the central and eastern Europe is the most significant,whereas the central Asia is the lowest value connection region.From the perspective of complex network analysis,China’s position in the network of value flow among the Silk Road countries has been increasing continuously,and it has been in the lead position since 2008.Besides,the implementation of the BRI has had a significant positive influence on the overall value chain connection between China and the Silk Road countries,but this positive influence is limited to the central and eastern Europe region,whereas it is not significant in other regions.Finally,this paper suggests that to promote the development of value chain connection,the Silk Road countries need to develop more specific policies related to value chains.Policymakers need to be able to correctly identify the comparative advantages of the region and the types of value chains that are compatible with them and then find suitable partners and formulate targeted promotion policies.

Prediction and Regulation of Delamination at Flexible Film/Finite-Thickness-Substrate Structure Interfaces

Regulating the surface instability of thin film/substrate structures has been successfully applied to prepare new ductile electronic devices.However,such electronic devices need to be subjected to external loads during operation,which can easily induce delamination of the thin-film electronic device from the substrate.This study aims to investigate the instability characteristics of hard films on flexible substrate surfaces from theoretical analysis and numerical simulation perspectives.Considering finite-thickness substrates,this paper establishes theoretical models for pure bending,bent wrinkle,partial delamination,and total delamination buckling of film/substrate structures based on the nonlinear Euler–Bernoulli beam theory and the principle of minimum energy;then the effects of material and geometric parameters of the structure,interfacial adhesion strength,and pre-strain on the evolutionary path of the four patterns are discussed.The study results show that:the greater Young’s modulus of the substrate is,the larger the parameter region where partial delamination of the film/substrate structure occurs,and the smaller the parameter region where bent wrinkle occurs.By varying Young’s modulus,thickness of the film and substrate,interfacial adhesion coefficient,and pre-strain,the buckling pattern of the structure can be predicted and regulated.The parametric design intervals for each pattern are summarized in the phase diagram.The results of this paper provide theoretical support for the design and reliability evaluation of flexible electronic devices.

High-amplitude pressure fluctuations of a pump-turbine with large head variable ratio during the turbine load rejection process

Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable-amplitude PTs, the load rejection process(LRP) was investigated using a one-and three-dimensional coupled flow simulation approach. The temporal,spatial, and frequency characteristics of the fluctuating pressures were analyzed for four monitoring points using a combined time-frequency analysis approach. The results indicated that PFs during the LRP of large-head variable-amplitude PTs had a new fluctuation frequency component related to Dean vortices(DVs) in the volute, in addition to the common fluctuation frequency components related to rotor-stator interaction phenomena and local backflow vortices near the impeller inlet. The PF frequency component existed throughout the LRP and had a significant influence on the transient maximum pressure at the volute end. This study provides a useful theoretical guide for the design and optimization of large-head variable-amplitude PTs.

基于投入产出技术的全球生产网络时空格局演变及驱动因素分析

Global production networks have become the most important organizational platforms for coordinating international production activities,and their evolution patterns profoundly affect value distribution across the world.In this study,we shall firstly carry out an in-depth quantitative research to analyze the patterns and evolution of global production networks,using a long time-sequenced multi-region input-output table and the network analysis approach.Then based on the method of value-added decomposition,we will develop an index system to measure the degree of participation of regions in global production networks.Finally,we will try to identify the factors affecting the degree of participation of countries in global production networks by constructing a regression model.The results show that from 1995 to 2015,the evolution of global production networks measured by input-output linkages experienced four stages:expansion,contraction,re-expansion,and re-contraction.In addition,the core communities of global production networks evolved from two major production communities(Europe and the Americas)to three pillars(Europe,Americas,and Asia)while more segmented communities are mainly affected by geographical proximity.The latter consists of European,North American,South American,African and Asian communities.The evolution of the global production network pattern primarily manifests as a process of cooperation strengthening or weakening among communities,based on changes in the external environment and the need for individual development strategies.Meanwhile,the United States,Germany,and the United Kingdom have consistently ranked among the top entities in global production networks,whereas China,Russia,and Southeast Asia have the fastest rises in ranking.In addition,government efficiency,resources endowment,infrastructure conditions and technology levels play important roles in the participation in global production networks.