空间溢出视角下的生产性服务业集聚与长三角城市群经济增长效率

本文利用空间杜宾模型实证研究了生产性服务业集聚对长三角城市群经济增长效率的影响及空间溢出效应。结果表明,生产性服务业集聚不仅能够显著提升本地区的经济增长效率,还对邻近城市具有正向的空间溢出效应,但这种影响在生产性服务业的细分行业之间存在一定异质性。进一步分析发现,生产性服务业集聚的MAR外部性和Jacobs外部性都有利于长三角城市群经济增长效率的提升,而Porter 外部性对经济增长效率具有负面影响。在空间溢出效应方面,Jacobs外部性对经济发展水平相近的城市具有负向溢出效应,Porter外部性对人力资本水平相近的城市具有正向溢出效应。此外,生产性服务业与制造业协同集聚对本地区和人力资本水平相近城市的经济增长效率具有显著促进作用,但对邻近城市和经济发展水平相近城市的经济增长效率因“虹吸效应”而产生一定的抑制作用。这些研究,对如何更有针对性地加快提升长三角城市群经济增长效率,提供了有价值的理论依据。     

中国若干重要领域政府决策能力论析

作为一个在社会剧变中建立新政权,并且在其后较长时期内经济社会发展各方面仍处于较落后状态之大国政府,60余年来中国政府亟需回应之内外事务繁难急重,是对政府决策能力的持续压力与严峻挑战。钩深致远,鉴往知来。审视并反思在若干重要领域中政府决策能力的表现及其影响,探赜索隐,论其得失与因由,不惟有助于激浊扬清,汲取经验教训,探寻优化政府决策能力之路径与对策,促进政府决策能力的提升,亦利于学理之辨析与深化。     

A discrete probability problem in card shuffling

Abstract

There are n cards serially numbered from 1 to n. The cards are shuffled and placed in a line one after the other on top of a table with faces up. The numbers on the faces are read from left to right. If there are consecutive numbers in increasing order of magnitude the corresponding cards are merged into one. After the merger, the cards are numbered serially from one to whatever the number of cards we now have. The cards are shuffled and placed in a line one after another on top of the table with faces up. The process continues until we have only one card left. In this paper, we develop a probabilistic recurrence relation approach to obtain the mean, variance, and distribution of the number of shuffles needed. A Markov chain formulation and its properties are discussed in the paper as well.     

Estimation of Seemingly Unrelated Tobit Regressions via the EM Algorithm

An expectation-maximum (EM) likelihood algorithm is used to estimate two seemingly unrelated Tobit regressions in which the dependent variables are truncated normal. An illustrative example on the determination of the life-health insurance and pension benefits is also given.     

Parenting stress and behavior among single mothers of preschoolers: The mediating role of self‐efficacy

Abstract

This study examines the role of perceived self‐efficacy in mediating relations between mothers’ parenting behavior and variables such as maternal employment status, depressive symptoms, parenting stress, and child behavior problems. Subjects were 93 employed and 95 nonemployed, single, black mothers of a 3–5‐year‐old child who were current and former welfare recipients. Using linear structural relations modeling (LISREL), the findings support a model whereby (a) the more behavior problems the child is perceived to have, the more depressive symptoms the mother feels; (b) the more depressive symptoms the mother feels, the more likely she is to rate herself high in parenting stress; (c) the more depressive symptoms and parenting stress the mother experiences, the lower is the mother's estimate of her self‐efficacy; and (d) the lower the mother's self‐efficacy, the less competent is her parenting. The findings for employment status are similar; i.e., maternal employment predicted a trajectory leading to somewhat better parenting. In addition, child behavior problems were associated with less competent parenting both directly and indirectly through their effect on parenting stress and self‐efficacy. These results suggest that self‐efficacy has import as a mediator of the relations between maternal parenting and other psychosocial variables. There is no evidence, based on these findings, that employment in the low‐wage market is harmful either for single black mothers or their preschool children. However, job availability and an increase in the minimum wage are important policy considerations.     

西部大学生网络创业及其相关影响因素

近十年来,我国创业成功的大学生中,有四成以上选择了与IT密切相关的行业。为了解我国西部地区大学生网络创业软硬件环境及相关状况,课题组专门设计制作问卷,历时半年,主要针对西部六个代表性城市的31所大学中各种学历层次的大学生,共计发出了21683份纸质问卷,用充分的数据详细展示了目前我国西部地区大学生的网络使用状况,对于网络创业的认知态度和相关创业知识获取的渠道,现实难题和困境等问题,并在数据的基础上做出客观剖析评价,为相关网络创业教育和经济支持政策的制定提供了现实依据。     

从人才大市迈向人才强市

高层次人才是稀缺资源,一个袁隆平带来了中国杂交稻产业的兴盛,一个比尔·盖茨创建了微软"帝国".人才重在使用,人才用起来是金子,不用变沙子.每个单位都应该认真检查和反省是否有压制和浪费人才的现象.     

国家治理结构转型视域下的大部制改革

改革开放以来,我国政府改革先后经历了"泛政治化"和"去政治化"两个阶段,前者罔顾国情,以西方国家治理体系为典范,后者回避矛盾,追求纯行政范畴的改革,其共同特点都是脱离了政治-行政统一体这一制度情境。目前中国政府改革目前再次走到了需要在政治改革上有所作为的时间节点上,但不是简单回归上世纪80年代的政治改革,而是要以大部制改革为契机,并基于政治-行政统一体这一制度情境去探索国家治理结构的重新建构。     

Time-Varying Risk Measurement for Ship Collision Prevention

We propose an innovative time-varying collision risk (TCR) measurement for ship collision prevention in this article. The proposed measurement considers the level of danger of the approaching ships and the capability of a ship to prevent collisions. We define the TCR as the probability of the overlap of ships’ positions in the future, given the uncertainty of maneuvers. Two sets are identified: (1) the velocity obstacle set as the maneuvers of the own ship that lead to collisions with target ships, and (2) the reachable velocity set as the maneuvers that the own ship can reach regarding its maneuverability. We then measure the TCR as the time-dependent percentage of overlap between these two sets. Several scenarios are presented to illustrate how the proposed measurement identifies the time-varying risk levels, and how the approach can be used as an intuitively understandable tool for collision avoidance.     

Integrating Entropy‐Based Naïve Bayes and GIS for Spatial Evaluation of Flood Hazard

Regional flood risk caused by intensive rainfall under extreme climate conditions has increasingly attracted global attention. Mapping and evaluation of flood hazard are vital parts in flood risk assessment. This study develops an integrated framework for estimating spatial likelihood of flood hazard by coupling weighted naïve Bayes (WNB), geographic information system, and remote sensing. The north part of Fitzroy River Basin in Queensland, Australia, was selected as a case study site. The environmental indices, including extreme rainfall, evapotranspiration, net‐water index, soil water retention, elevation, slope, drainage proximity, and density, were generated from spatial data representing climate, soil, vegetation, hydrology, and topography. These indices were weighted using the statistics‐based entropy method. The weighted indices were input into the WNB‐based model to delineate a regional flood risk map that indicates the likelihood of flood occurrence. The resultant map was validated by the maximum inundation extent extracted from moderate resolution imaging spectroradiometer (MODIS) imagery. The evaluation results, including mapping and evaluation of the distribution of flood hazard, are helpful in guiding flood inundation disaster responses for the region. The novel approach presented consists of weighted grid data, image‐based sampling and validation, cell‐by‐cell probability inferring and spatial mapping. It is superior to an existing spatial naive Bayes (NB) method for regional flood hazard assessment. It can also be extended to other likelihood‐related environmental hazard studies.