关于含r对k间隔的组合数

ｆｒｋ记（ｎ，ｍ）为从排列在一直线上的ｎ个元素中选取ｍ个元素且恰含ｒ对ｋ间隔元素的选取方式数．ｇｒｋ（ｎ，ｍ）为从排列在圆周上的ｎ个元素中选取ｍ个元素且恰含ｒ对ｋ间隔元素的选取方式数，给出了ｆｒｋ（ｎ，ｍ）及ｇｒｋ（ｎ，ｍ）的递归关系式和卷积形式表达式，在ｋ＝０时得到ｆｒ０（ｎ，ｍ）与ｇｒ０（ｎ，ｍ）的显式．     

The impact of alternative development strategies: Simulations with a dynamic input-output model

This paper analyzes the implications of two different development strategies: outward-looking strategy led by manufacturing exports and inward-looking strategy focused on import substitution strategy. Our approach is to do counterfactual experiments with a dynamic input-output model in order to explore the impact of the different strategy on economic performance. We apply the model to two different countries (Turkey and Korea), which exemplify the two strategies, and explore the impact in each case of a switching strategy. We impose an export-led strategy on Turkey and inward-looking strategy on Korea. Our results confirm the view that export-led strategy leads to better economic performance. However, we also find that there are risks associated with this choice. An export-led strategy requires high level of foreign capital inflows in the early phase, to be paid back later as export levels rise. The strategy also requires a high level of factor productivity growth. If export growth is not maintained, the country will be left with a dangerous level of foreign debt. If high productivity growth is not achieved, the growth in factor inputs (particularly investment) required to achieve adequate growth of manufacturing is not sustainable. Finally, our results indicate that the dynamic input-output model provides a good framework for exploring the structural implications of a choice of development strategy.     

Affinity Paths and information diffusion in social networks

Widespread interest in the diffusion of information through social networks has produced a large number of Social Dynamics models. A majority of them use theoretical hypothesis to explain their diffusion mechanisms while the few empirically based ones average out their measures over many messages of different contents. Our empirical research tracking the step-by-step email propagation of an invariable viral marketing message delves into the content impact and has discovered new and striking features. The topology and dynamics of the propagation cascades display patterns not inherited from the email networks carrying the message. Their disconnected, low transitivity, tree-like cascades present positive correlation between their nodes probability to forward the message and the average number of neighbors they target and show increased participants’ involvement as the propagation paths length grows. Such patterns not described before, nor replicated by any of the existing models of information diffusion, can be explained if participants make their pass-along decisions based uniquely on local knowledge of their network neighbors affinity with the message content. We prove the plausibility of such mechanism through a stylized, agent-based model that replicates the Affinity Paths observed in real information diffusion cascades.     

户主外地生活经历与家庭风险金融资产投资

当前,我国居民家庭存在风险金融市场有限参与的问题,这也是造成我国直接融资占比较低的客观原因。然而,学术界少有文献从户主经历角度分析其对家庭风险金融资产投资决策的影响。基于此,利用CHFS2017年数据,研究了户主的外地生活经历对家庭风险金融资产投资的影响及其作用机制。研究发现,户主有外地生活经历、户主外地生活经历时长增加均显著提升了家庭风险金融市场参与和风险金融资产投资占比。影响机制方面,户主外地生活经历会通过拓宽户主获取经济金融相关信息的渠道、增强家庭的社会互动进而提升家庭风险金融资产投资。异质性分析显示,上述促进作用仅在户主有社会医疗保险、不存在借贷约束的家庭中显著。因此,要积极完善就业政策和人才引进政策,建立健全外来人员的权益保障机制,加快普及社会医疗保险；同时,要大力发展普惠金融,引导居民家庭合理利用信贷工具优化资产配置。