访问控制策略一致性和完备性检测方法研究

为实现对复杂访问控制策略的统一管理,检测并排除冲突和不完备的访问控制策略,提出了利用访问控制策略集合中的偏序信息构造融合主体、客体层级结构的有向无环图模型。首先从理论上证明了构建有向无环图模型的可行性,并提出利用偏序关系构建有向无环图模型的实施算法,然后利用有向无环图模型的节点集合设计了访问控制策略一致性和完备性检测算法,最后对模型构建算法及访问控制策略一致性和完备性检测算法进行实验验证。实验结果表明,融合主体、客体层级结构的有向无环图模型可以有效管理复杂系统中访问控制策略中出现的冲突与策略不完备情况。相关算法可以有效地实现对复杂访问控制策略的统一管理。     

Drivers of food price in China: A heterogeneous panel SVAR approach

In this paper, we examine the effects of shocks in agricultural output, production material price and production price on China's food price using panel data of 26 provinces for the period 2004 Q1–2015 Q4. Employing a heterogeneous panel structural vector autoregressive (SVAR) model, we identify the causal flows between the endogenous variables via directed acyclic graphs method. The empirical results from impulse response functions and variance decompositions suggest sizeable cross‐province variations. The main driving force of food price is the price inertia shock, rather than the agricultural output or the vertical chain of price transmission shocks. The findings support the view that price expectation is the key shifter of food price. Moreover, the shocks in the vertical chain of price transmission are only weakly linked to food price. Our findings are robust to an alternative panel SVAR model identified via Cholesky decomposition.     

流动妇女收入影响的DAG图模型研究

基于江苏省流动妇女生存状况的实地调查,运用贝叶斯网络构造流动妇女收入影响因素的DAG图模型。与线性模型结果不同,流动妇女个体特征并不都直接影响月收入,其中年龄对教育程度和婚姻状况有直接影响,来源地对教育程度有直接影响,教育程度和婚姻状况对职业类型选择有直接影响,职业类型对月收入有直接影响,年龄、来源地、教育程度和婚姻状况对月收入有间接影响。     

后现代视野下中华传统图形的再设计

中华传统图像资源作为一种镌刻着深刻民族记忆痕迹的媒介符号,蕴含着中华民族深层的民族精神和独特审美价值。在后现代设计思潮的背景下,日益体现出巨大的视觉文化价值。本文分别从意蕴、造型、材料、色彩等方面展开阐述,说明后现代视野下中华传统图形的再设计应结合新的表现手法、新的审美观念以及新的科技手段等使其焕发新的生命力。     

Food environment in the United States as a complex economic system

The food environment in the United States is complex. Sixteen socio-economic-demographic variables from various public data sources are studied with a machine learning algorithm to ascertain the causality structure associated with the food environment in the United States. High levels of unemployment and poverty are direct causes of high levels of food insecurity, while low income causes high levels of food insecurity via increased levels of poverty. Unemployment is a common cause for both increased levels of food insecurity and poverty. We find that food insecurity and participation in Supplemental Nutrition Assistance Program (SNAP) are related, yet no direct causality is observed. Contrary to past studies which find that SNAP participation decreased the occurrences of poverty, in contemporaneous time, we find that poverty and SNAP participation are related through several back-door paths, via food insecurity, unemployment, race and food taxes. Obesity and SNAP participation are indirectly related via several back-door paths, namely, race income, poverty and food insecurity and unemployment. Also, food insecurity and obesity are related by several back-door paths. Low income, high food taxes, and race (being Black and non-Hispanic) are direct causes of obesity. The complex causality structure in the US food environment reveals that policy variables cannot be treated independently of their rich causal structure. Government agencies responsible for designing policies for food assistance, poverty alleviation, combating food insecurity and obesity need to consider the interrelationships among these variables.     

用图论法确定工艺尺寸链

本文介绍了应用图论的基本知识如何确定工艺过程中的尺寸链,并通过实例总结了确定工艺尺寸链的具体方法、步骤和注意事项。为确定复杂工艺尺寸链提供了一种新的方法。     

A gender perspective on the use of supplemental healthcare plans

Because employer‐provided health coverage represents the main source of health insurance for Americans and its costs for employees are rising, accurate knowledge about health coverage would seem to be crucial for making sound decisions on choosing the plans that best meet the specific needs of a family. However, previous research suggests that most employees have little understanding of the scope and monetary value, or even the existence of many components of their health benefit package. This paper re‐examines employees’ general financial learning efforts and knowledge level, and how they relate to participation in and importance attached to supplemental healthcare plans. We find that, while self‐directed financial learning and general financial knowledge significantly predicted plan participation and the importance attached to them, demographic factors, such as gender, age and job classification, dominated the supplemental healthcare decisions.     

Millsian causation

The Directed Acyclic Graph (DAG) theory of causation is based on the assumption that randomly sampling the variables of a causal system will yield a joint probability distribution that satisfies the Markovian condition. It is shown here that this condition can be split into two parts, one of which is named the Millsian condition. It is further shown that the Millsian condition alone implies that causally unrelated sets of variables are conditionally independent given their common causes, very likely a key requirement stated by John Stuart Mill 150 years ago. In Millsian causation, unlike Markovian causation, it is possible for an indirect cause to be associated with its effect even when controlling for the intermediate direct causes. This phenomenon is explained by taking into account the existence of potential causal modulation.     

一般图形Voronoi图的离散生成

由于一般图形形状和位置的任意性,一般图形Voronoi图往往比较复杂,难以将传统的构造法直接应用到一般图形Voronoi图的构造中。本文介绍了一般图形Voronoi图的离散构造法,并给出算法步骤及优势分析。     

Foreign GTAs Can Be Effective Teachers of Economics

The authors tested whether student performance in the principles of economics course is affected by the use of graphs as part of a lecture. They conducted two experiments at the University of South Carolina, one in spring 1995 and another in spring 1997. Students were randomly assigned to either a nographs lecture or a lecture with graphs. The main hypothesis was that students in the lectures with graphs would show higher gain scores than those in the nograph lectures (both lectures were videotaped). The authors found that students in the lecture with graphs in 1995 had significantly lower gain scores than those in the no-graphs lecture. For 1997, they found no significant differences in student performance between the two groups.