Spectral goodness of fit for network models

We introduce a new statistic, ‘spectral goodness of fit’ (SGOF) to measure how well a network model explains the structure of the pattern of ties in an observed network. SGOF provides a measure of fit analogous to the standard R² in linear regression. Additionally, as it takes advantage of the properties of the spectrum of the graph Laplacian, it is suitable for comparing network models of diverse functional forms, including both fitted statistical models and algorithmic generative models of networks. After introducing, defining, and providing guidance for interpreting SGOF, we illustrate the properties of the statistic with a number of examples and comparisons to existing techniques. We show that such a spectral approach to assessing model fit fills gaps left by earlier methods and can be widely applied.     

基于知识图谱分析的国内外智慧教育研究热点

以“智慧教育”和“smart education”为关键词，时间跨度设为2009-2018，分别在中国知网和Web of Science数据库中进行检索，经过筛选后，将所得文献作为研究对象。利用CiteSpaceⅤ软件制作出国内外智慧教育研究高频关键词共现图表，并由此展开分析，总结出国内外智慧教育的研究热点。通过比较分析，获得以下启示：理论与实践并进，共建智慧教育生态系统；立体化与多样化并行，发展混合式动态教学模式；智能技术与深度学习并举，优化智慧教育学习场域；技术与育人并重，重视学习主体情感体验。     

Does biomass energy consumption reduce total energy CO2 emissions in the US?

This study investigates the causal relationship between total biomass energy consumption, total energy CO₂ emissions, and GDP in the United States for the period January 1973–December 2016 by employing a directed acyclic graph (DAG) techniques and the Autoregressive Distributed Lag (ARDL) model. Additionally, this paper examines the existence of the environmental Kuznets curve (EKC) hypothesis. The result of the DAG reveals that total biomass energy consumption and GDP have a unidirectional contemporaneous causal relationship with total energy CO₂ emissions. Based on the results of the ARDL, we find that a 1% increase in per capita total biomass energy consumption causes a 0.65% reduction in per capita total energy CO₂ emissions in the long-run. This finding implies that expanding the usage of biomass is one way to reduce and control greenhouse gases in the US. Moreover, we find that the inverted U-shaped EKC hypothesis is satisfied for the US case. Findings from this study suggest that energy policies should stimulate an increase of biomass production for reducing total energy CO₂.     

Facility Location with Dynamic Distance Functions

Facility location problems have always been studied with theassumption that the edge lengths in the network are static anddo not change over time. The underlying network could be used to model a city street networkfor emergency facility location/hospitals, or an electronic network for locating information centers. In any case, it is clear that due to trafficcongestion the traversal time on links changes with time. Very often, we have estimates as to how the edge lengths change over time, and our objective is to choose a set of locations (vertices) ascenters, such that at every time instant each vertex has a center close to it (clearly, the center close to a vertex may change over time). We also provide approximation algorithms as well as hardness results forthe K-center problem under this model. This is the first comprehensive study regarding approximation algorithmsfor facility location for good time-invariant solutions.     

Likelihood Factorizations for Mixed Discrete and Continuous Variables

Some general remarks are made about likelihood factorizations, distinguishing parameter-based factorizations and concentration-graph factorizations. Two parametric families of distributions for mixed discrete and continuous variables are discussed. Conditions on graphs are given for the circumstances under which their joint analysis can be split into separate analyses, each involving a reduced set of component variables and parameters. The result shows marked differences between the two families although both involve the same necessary condition on prime graphs. This condition is both necessary and sufficient for simplified estimation in Gaussian and for discrete log linear models.     

基于新型图论聚类法的物流系统多设施选址策略研究

提出了一类基于图论的新型聚类算法并将其应用于物流系统中的多设施选址问题。与其他聚类算法相比,该新型算法聚类效率更高且具有更小的聚类树,从而使得有意义的聚类结果更加清晰。比较算例验证了该算法应用于多设施选址问题的高效性和实用性。     

Motivations for self-assembling into project teams

This study investigates the self-assembly mechanisms of ad hoc project teams using a bipartite network perspective. Individuals and projects are modeled as two types of nodes and team membership as relations between them. This approach enables us to investigate factors that impact voluntary team assembly at the individual, dyadic, and team levels simultaneously. Using Exponential Random Graph Models (ERGM/p*), we study players’ combat teams in a Massively Multiplayer Online Role-Playing Game (MMORPG) as a case of self-assembled project teams. Empirical results show that individuals are motivated to join ad hoc teams to complete difficult projects but not projects with long durations. We also found that individuals tend to collaborate with specific teammates who have complementary skills, those who have similar age or skill level, and those who are affiliated with the same organizational entity.     

Implementation of new technology: towards greater manufacturing flexibility

Changes in market characteristics over the past several years are forcing firms to eliminate/minimize dependency on costly buffers of capacity, lead time, or inventory. One way to accomplish this is via appropriate adaptation and enhancement of existing technological infrastructure. Recent technological advances present firms with a wide array of alternative technologies. In this paper, we discuss the impact of new technology on the manufacturing environment and the problems associated with its implementation. We present an integrated framework for implementing such technology based on a consistent hierarchy of organizational objectives and a general foundation of constraint theory.     

澳大利亚上市公司年报图形手段评介

文本与图形相结合已是当前澳洲上市公司年报篇章一大特色。文章从传播学角度统计并分析了该国50家上市公司2005年英文年报中出现的图形手段,即图片、图解和表格等信息载体,探讨了年报图形的直观性、易读性和生动性等特征,并归纳了年报图形功能,认为图形丰富了年报页面内容、增强了文本信息表述功能并强化了公司重要财务信息等。     

Using intersection matrices to identify graphical structure

Intersection matrices help identify the common graphical structure of two or more objects. They arise naturally in a variety of settings. Several examples of their use in a computer algebra environment are given. These include: simplifying an expression involving array products, automating cumulant calculations, determining the behaviour of an expected value operator and identifying model hierarchy in a factorial experiment. The emphasis is placed on the graphical structure, and the symmetry of arrays help reduce the complexity of the graphical problem.