An inexact l2-norm penalty method for cardinality constrained portfolio optimization

Abstract

We analyze and solve a single-period portfolio optimization problem with non-convex constraints, which address practical concerns of investment such as the active share weights of sectors and the number of stocks held in a portfolio. We reformulate the problem to simplify the computation and propose an inexact l₂-norm penalty method to solve the problem.     

数字经济对区域经济高质量发展的影响研究

推动数字经济发展,是我国在当下推动经济转型,促进高质量发展的重要战略。本文基于2012~2019年省级面板数据,构建双向固定效应模型,运用基准回归、异质性检验和分位数回归的方法进行实证研究发现,数字经济助推经济高质量发展的同时还存在地区差异,对西部影响最大,中部影响最小,而数字经济的发展水平又受到产业结构、技术创新等因素影响。因此,本文针对不同地区差异分别提出建议,从而促进持续更新发展理念,以创新驱动发展,优化产业结构为数字经济提供良好环境,以期推动数字经济建设发展。     

Political hazards and entry modes of Chinese investments in Africa

Africa has achieved the fastest growth rate of inward foreign direct investment (FDI) recently. Yet heightened political hazards present substantial challenges to foreign firms in Africa. This study examines the entry strategies that firms may take to mitigate such hazards by exploring the relationship between political hazards and entry mode choices in Africa. We further consider how an investing firm’s host country experience and foreign aid provided by its home country government to host countries in Africa can influence this relationship. In a sample of listed Chinese firms’ investments in Africa from 2000 to 2014, we find that Chinese firms tend to use the joint venture mode when political hazards are high in an African country. This relationship is weakened when they accumulate host country experience and when the Chinese government’s foreign aid to an African country increases. Our findings point to firm-level strategies to mitigate political hazards as well as instruments available to home country governments to help their multinational firms operating in host countries characterized by unstable political environments.     

Diffusion of mobile telephony: An empirical study in Taiwan

Mobile telephony penetration is a major indicator of mobile telephony diffusion. Taiwan had a mobile telephony penetration of 108% in 2002, ranking first in the world. This study analyzes this accelerated diffusion in terms of growth model and determinants of the diffusion rate. To eliminate the inherent uncertainty associated with choosing the optimal growth model, this study compares the performance of three conventional models, namely Gompertz, Logistic and Bass, to identify the most appropriate model, and to distinguish the forces driving the diffusion rate. Empirical results indicate that the most appropriate model is the Logistic model. Network externalities, which this study shows to be the same as the imitation effect in the Bass model, explain the superiority of the Logistic model. Moreover, market competition, which markedly reduces service prices, is identified as a primary driver of the diffusion rate of mobile telephony in Taiwan. Economic conditions, technological innovation and number of operators are insignificant factors. Finally, mobile telephony is a substitute for fixed-line telephony in Taiwan.     

山东地区城市天然需求负荷与气温关系研究

作为清洁能源的天然气,近年来在山东的销售量持续增长.天然气的负荷需求主要受地区气象条件、工业企业生产情况、居民生活习惯、价格水平、节假日等多种因素的影响,其中气温是造成城市天然气短期负荷波动的主要原因之一.本文研究山东省天然气市场需求量与气温之间的关系,对天然气日均负荷进行周期分析,找出天然气日均负荷变化与日均气温之间的相关关系,为天然气公司进行地区性天然气计划平衡决策提供基础信息参考.     

大鼠脑缺血后缺血区VEGF表达变化及通心络的影响

目的观察大鼠脑缺血后缺血区VEGF mRNA及蛋白水平随时间表达的变化及通心络对其的影响。方法制备大鼠大脑中动脉梗塞局灶性脑缺血模型,采用RT—PCR法及免疫组化法检测脑缺血后每组实验动物不同时间缺血区VEGFmRNA及蛋白表达的变化以及通心络的作用。结果1、正常大鼠脑缺血后脑组织中VEGFmRNA表达很少,大鼠局灶性脑缺血后VEGF mRNA表达逐渐增强,3d达高峰,缺血7d后叉降至约正常水平。VEGF主要在神经元阳性表达,表达趋势与mRNA基本吻合。2、通心络高剂组VEGF mRNA表达显著增强（p〈0.01,p〈0.05）;通心络各组vEGF阳性神经元数量增加：结论局灶性脑缺血可促进缺血区内源性神经保护因子VEGF高表达;通心络可增强和延长缺血区VEGF高表达,发挥对脑缺血的保护作用.     

发展结果导向的公共项目绩效管理理念

在公共项目的绩效管理中引入“发展结果导向管理”理论和方法,改变了以往以投入产出理论为基础,注重项目的经济评价的的传统方法。发展结果导向的公共项目绩效管理要求关注项目的长期发展目标,在项目各个阶段致力于与结果相关的对话。运用结果链——投入、活动、产出、产效和影响,以及这些关键要素之间的因果关系进行绩效管理,同时运用绩效管理逻辑框架对项目的绩效进行监测评估。     

地方政府公信力：影响区域经济发展的重要因素

作为一种区域软实力,地方政府公信力是影响区域经济发展的一个重要因素。良好的政府公信力能够为区域经济发展营造公平的市场竞争秩序、促进区域内社会稳定发展以及塑造良好的区域形象。而目前我国一些地方政府公信力存在下降的趋势,在严重影响社会信用环境及地方投资环境的同时,也妨碍了政府与公众之间良好的互动关系的建构,增加了政府管理成本,制约着地方经济的发展。因此,有必要提高政府公信力,为区域经济发展营造一个良好的诚信环境