哈尔滨市快递自提点空间布局与影响因素研究

快递自提点作为解决物流"最后一公里"服务瓶颈问题的关键,逐渐成为地理学研究新的关注点.本文基于2020年3月哈尔滨市菜鸟驿站和邮政站点的POI数据,综合运用文本分析、数理统计等方法,分析哈尔滨市快递自提点的空间布局特征和影响因素,研究发现:哈尔滨市快递自提点存在布局不平衡现象已初步显现,市辖区快递自提点布局存在冗余和空间浪费现象,而远郊县快递自提点存在建设较薄弱等问题,并有针对性地提出了哈尔滨市快递网点布局服务体系的优化对策.     

基于Python平台通过单因子指标法进行地下水质量评价

水质评价关系到水质质量,常见的评价方法有层次分析法、综合评价法等,这些方法评价过程非常复杂,单因子评价方法相比具有操作容易.实际中单因子进行评价时存在概念理解难、计算容易出错等问题.为解决单因子计算问题,本文提出采用Python编程语言进行单因子评价.本文详细分析了Python进行单因子评价流程,从数据采集、数据清洗、数据处理、系统实现进行分析.应用结果表明基于Python编程的单因子评价方法具有评价效率高、准确度高优点.     

内隔墙对小尺寸基坑围护结构变形特性影响研究

深基坑开挖对基坑变形及周围环境的影响一直是工程中关心的问题.而利用好基坑的空间效应则可以控制好变形.本文采用plaxis有限元分析对利用内隔墙产生的二次空间效应来控制基坑变形的影响,分析了内隔墙的刚度、埋入深度和基坑尺寸之间的相互影响.分析结果对城市中心复杂环境下施工过程中对基坑的监测和周围环境保护有较好的指导作用.     

Childhood adversity and the propensity for entrepreneurship: A quasi-experimental study of the Great Chinese Famine

Studies on the determinants of entrepreneurship emphasize that challenged adults tend to become entrepreneurs. However, research has not addressed the childhood origins surrounding the propensity for entrepreneurship. This article links childhood adversity to the propensity of individuals to become migrant entrepreneurs later in life. We test hypotheses derived from this theory in the context of whether, and when, children who survived the Great Chinese Famine of 1959–1961 became migrant entrepreneurs. Results strongly indicate that those who survived greater hardship during the Famine are more likely to become entrepreneurs, especially when they were younger during the famine years. We also find that being younger at the time of migration increased the likelihood of becoming entrepreneurs in their new locale. Overall, this study casts light on why, how and when childhood adversity shapes the propensity for entrepreneurship.     

EMPIRICAL PERFORMANCE OF GARCH MODELS WITH HEAVY‐TAILED INNOVATIONS

We introduce a new type of heavy‐tailed distribution, the normal reciprocal inverse Gaussian distribution (NRIG), to the GARCH and Glosten‐Jagannathan‐Runkle (1993) GARCH models, and compare its empirical performance with two other popular types of heavy‐tailed distribution, the Student's t distribution and the normal inverse Gaussian distribution (NIG), using a variety of asset return series. Our results illustrate that there is no overwhelmingly dominant distribution in fitting the data under the GARCH framework, although the NRIG distribution performs slightly better than the other two types of distribution. For market indexes series, it is important to introduce both GJR‐terms and the NRIG distribution to improve the models’ performance, but it is ambiguous for individual stock prices series. Our results also show the GJR‐GARCH NRIG model has practical advantages in quantitative risk management. Finally, the convergence of numerical solutions in maximum‐likelihood estimation of GARCH and GJR‐GARCH models with the three types of heavy‐tailed distribution is investigated.     

Social media affordances in entry‐level employees’ socialization: employee agency in the management of their professional impressions and vulnerability during early stages of socialization

This study examined how entry‐level employees interacted with social media during three stages of organizational socialization. They navigated between four different media affordances (persistence, editability, visibility, and association) while experiencing them as both enabling and constraining in different socialization stages. Qualitative interview data analysis revealed during anticipatory socialization, job applicants realized visibility and persistence in relation to institutional and individualized socialization. During encounter, new employees managed personal and professional life boundaries carefully against the association and visibility affordances. Although some participants used both public and enterprise social media for obtaining job‐related information and understanding coworkers and company culture, during metamorphosis, most interviewees adopted passive information seeking strategies and experienced a paradoxical tension between the enabling and constraining affordances of social media. Findings are discussed with regards to employees’ exertion of agency in managing their professional impressions and coping with high levels of uncertainty and vulnerability during early stages of socialization.     

南宋筑城防御风潮的兴起与实施

南宋时期的城市,迫于军事对峙形势,在强化其经济功能之外,防御性能也日渐加强,表现为军事性城寨普遍存在。南宋凭借强大的人力和财力支持,在南渡之初练兵与筑城之争后,形成了筑城防御之风。在城郭的结构和防御设计上,呈现出对唐城的因袭和创新,采取城砖包砌法,并设有专门的筑城队伍和人员。在中国古代城市发展史上,具有重要的意义。     

工业体系和民营企业兴起——基于252家中国最大民营制造业企业的经验研究

主流经济学家把改革开放后民营企业的大规模兴起，主要归因为市场经济条件下发挥企业家精神和遵循比较优势的必然结果。但是这无法解释为什么民营企业在兴起之初就广泛和快速地进入到各个工业，尤其是技术和资本密集型工业。基于中国工业史和252家中国最大民营制造业企业创业发展史的历史证据，文章找回"工业体系"这一被主流所忽略的重大历史现象和学术概念，从而首次提出一种理解中国民营企业发展独特性的结构性解释。文章发现：从计划经济时期继承而来的门类齐全和独立完整的工业体系，是解释民营企业创业和发展独特性的关键变量；已有的由国有企业和科研院所组成的工业体系，从市场机会、技术能力和组织资源等方面塑造了民营企业的创业选择和发展路径。所以，中国民营企业的快速发展不是仅凭自由市场就会自动出现的普遍现象，而是在市场条件下充分利用工业体系提供的技术和市场条件才得以出现的特殊现象。     

Estimating yield curves of the U.S. Treasury securities: An interpolation approach

Following the approach of interpolation, this paper proposes the multiple exponential decay model to fit yield curves for both the U.S. TIPS market and the conventional Treasury security market. Several estimation methods, including the unconstrained/constrained nonlinear minimization, quadratic programming, and the iterative linear least squares, are applied to estimate the unknown parameters according to different curve‐fitting purposes. Comparisons between the proposed model and the alternatives show that the multiple exponential decay successfully (1) adapts to a variety of shapes associated with yield curves, (2) (partially) keeps in line with the economic interpretations of Nelson–Siegel summarized by Diebold and Li ( 2006 ), and (3) dominates the competing models in curve‐fitting performance measured by mean fitted‐price errors over the sample period. In addition, the exact specification of a nonparametric interpolation model is pinned down by applying three statistical tools, which enable us to jointly take into account validity, optimality, and parsimoniousness of the proposed model.     

巢湖市实施长江禁渔期制度的调查与思考

本文通过总结分析巢湖市实施长江春季禁渔的做法与经验，探讨了实施长江禁渔的重要性，指出了存在的问题，提出了今后实施的具体措施。