医疗器械产业创新集群的现状及路径研究——以宁波市为例

产业集群能提高企业、区域和国家竞争力。当前以产业创新集群为代表的新一轮产业集群正在各地兴起。通过行业融合、知识外溢和集体行动，产业创新集群促进相关企业和支持性机构紧密互动而加速创新。医疗器械产业科技含量高，创新性强，是当前少数几个涉及学科最多的产业之一。以医疗器械产业为研究对象，从集群和区域创新发展的要义出发，挑选宁波地区的医疗器械行业，测算其行业集中度和产业集群效应，提出提升医疗器械行业集群度，激发产业创新集群活力的对策建议。     

Concentration behavior of the penalized least squares estimator

Consider the standard nonparametric regression model and take as estimator the penalized least squares function. In this article, we study the trade‐off between closeness to the true function and complexity penalization of the estimator, where complexity is described by a seminorm on a class of functions. First, we present an exponential concentration inequality revealing the concentration behavior of the trade‐off of the penalized least squares estimator around a nonrandom quantity, where such quantity depends on the problem under consideration. Then, under some conditions and for the proper choice of the tuning parameter, we obtain bounds for this nonrandom quantity. We illustrate our results with some examples that include the smoothing splines estimator.     

Customer concentration and loan contract terms

We study pricing and non-pricing features of loan contracts to gauge how the credit market evaluates a firm’s customer-base profile and supply-chain relations. Higher customer concentration increases interest rate spreads and the number of restrictive covenants featured in newly initiated as well as renegotiated bank loans. Customer concentration also abbreviates the maturity of those loans as well as the relationship between firms and their banks. These effects are intensified by customers’ financial distress, the level of relationship-specific investments, and the use of trade credit in customer–supplier relations. Our evidence shows that a deeper exposure to a small set of large customers bears negative consequences for a firm’s relations with its creditors, revealing limits to integration along the supply chain.     

湖州地区辐射影响因子分析

[目的]为了探究湖州地区太阳辐射情况,利用2009年1月至2017年12月湖州国家基本气象站的辐射观测资料、地面常规观测资料以及大气成分观测资料。[方法]文章分析了湖州地区太阳辐射的变化特征,并检验了太阳辐射与部分气象要素极值的相关性。[结果]太阳辐射日变化基本呈抛物线型。6月因湖州地区进入梅雨季节,阴雨寡照,并不是一年中辐射最大的月份,一年中辐射的最大值出现在7月,之后逐渐下降。按季节统计,夏季辐射最大,春季次之,秋季比冬季略高。除了2015年以外,近几年辐射总量平稳中稍有下降,考虑到可能存在的辐射年际变化,并不能就此认为该地区的辐射处于下降趋势中。辐射强度与总云量、低云量、最小相对湿度为负相关,与日最高温度、日最高地温呈正相关。晴天时,太阳辐射强度与颗粒物浓度PM10、PM2. 5、PM1三者相关性基本一致,均为春、秋和冬季呈负相关,夏季呈正相关,两者的关系应该按季节具体分析。[结论]影响湖州地区辐射的因子有很多,部分气象因子相关性较好,颗粒物浓度不能简单看成全年太阳辐射的影响因子。     

Does aid for trade diversify the export structure of recipient countries?

The importance of aid for trade as a tool for facilitating trade, economic growth and social development has received attention since the concept was introduced in 2005. While one of the main targets of aid for trade is export diversification, reflecting the fact that the exports of many developing countries are concentrated in a small range of items, there have not been many efforts to measure the effect of aid for trade on export structure. This study, therefore, attempts to trace the relationship between aid for trade and 133 aid recipients' export structure between 1996 and 2013. Using the Herfindahl–Hirschman Index to measure the degree of export concentration, the findings suggest that total aid for trade has reduced the concentration level in the short run. In the long run, on the other hand, aid for trade has had no significant effect on export structure of recipient countries. Only aid for building productive capacity, which is one of the three categories of aid for trade, contributes to lower concentration. Yet, this change is not caused by an increase in export diversity but by the redistribution of shares of existing products of a similar sophistication level.     

基于冠层光谱和BP神经网络的水稻叶片氮素浓度估算模型

[目的]快速、准确地诊断水稻叶片氮素营养状况,为水稻氮肥精准管理提供依据。[方法]以江西省农科院8种不同施肥处理的晚稻为研究对象,于主要生育期同步测定了水稻冠层光谱反射率及叶片全氮浓度(Leaf Nitrogen Concentration,LNC),系统分析了原始光谱反射率、一阶微分光谱、"三边"参数以及由350～1 350nm两两波段组合的差值(SD (Rλ1,Rλ2))、比值(SR (Rλ1,Rλ2))及归一化(ND(Rλ1,Rλ2))光谱指数与水稻LNC的相关关系,筛选出敏感参数,并以之为自变量构建了水稻LNC的传统预测模型,另外构建不同指标个数的多元线性与BP神经网络模型,并对模型进行验证。[结果](1)水稻LNC与一阶微分光谱在751nm处的相关性最高(r=0. 822);(2)"三边"参数中的红边面积SDr与LNC的相关性较高(r=0. 687);(3) 750nm附近的红边波段与近红外波段差值组合、550nm附近的绿光波段与近红外波段的比值及归一化差值组合与水稻LNC的相关性较高,以SD (R752,R751)、SR (R534,R1 350)和ND (R534,R1 349)表现最好,相关系数分别为0. 827、-0. 790和0. 788;(4)传统回归模型中以SD(R752,R751)构建的一元线性模型最佳(RC2=0. 665、RV2=0. 750、RMSEV=0. 4%、RPD=2. 034);(5)利用5个指标((R'751、SDr、SD (R752,R751)、SR (R534,R1 350)、ND (R534,R1 349))经逐步回归筛选出的2个指标SD ((R752,R751)和SR (R534,R1 350))构建预测水稻氮素的BP神经网络模型,预测效果最佳,其验证参数值分别为R2=0. 859、RMSEV=0. 302%和RPD=2. 669。[结论]基于单指标构建的传统线性模型计算过程简单但精度略低,而基于2个指标(SD (R752,R751)、SR (R534,R1 350))构建的BP神经网络模型预测精度高于该2指标构建的多元线性模型,表明在指标适合的情况下,BP神经网络对氮素具有较好的预测能力,是一种快速准确估算水稻叶片全氮浓度的方法。     

City Size,Population Concentration and Productivity: Evidence from China

This paper investigates the impact of China's city size and urban population concentration on city productivity by developing a distinctive index based on global nighttime light data. Using the panel data of 280 prefecture cities from 2004 to 2013 and employing dynamic system generalized method of moments and panel threshold model regression techniques, our results show that city size has a positive impact on city productivity; therefore, cities in China still have the potential to expand. While moderate urban population concentration can benefit city productivity, excessively concentrated urban population distribution may impede the growth of city productivity. We also find that the level of labor income significantly affects the impacts of urban agglomeration on labor productivity. Therefore, our results imply that city development policies should focus more on how to appropriately allocate economic activities and adjust population distribution in urban areas according to different stages of economic development.     

Political hazards and firms' geographic concentration

Research summary : We examine the relationship between the geographic concentration of a firm's sales and the firm's vulnerability to expropriation hazards. Although expanding outside the home location can initially increase a firm's exposure to government expropriation, we find that this effect reverses when a firm's sales outside its home location have reached a point at which it has sufficient resources to better influence government actions and to pose a credible threat to exit the market in which it is being targeted. We supplement this main result by identifying two moderating factors: the firm's level of political capital and the effectiveness of institutional constraints on government behavior. We find support for these hypotheses from survey data on privately owned enterprises in China. Managerial summary : This research advises firm managers that certain market activities might knock their firms' economic interests out of alignment with the government's political interests, and thus, influence the political hazards they face, particularly in emerging markets such as China, which has attracted strong interest of many firms with respect to entering the market. Here, all else being equal, the firms' geographic concentration exposes them to different levels of state expropriation—but not in a simple linear fashion as suggested by the conventional wisdom of local protectionism or that of the bargaining advantage generated by the threat of relocation: Those who are “stuck in the middle” ended up paying twice or even three times as much unauthorized levies as the purely local or the most expansive firms. Copyright © 2015 John Wiley & Sons, Ltd.     

我国出租车牌照拍卖机制研究

论文以有效分配、促进竞争、实现经济价值为目标，建立了公开升价拍卖+密封拍卖的两阶段牌照拍卖模型，证明了其有效性和最优性。并以北京市为例讨论了牌照数量的确定、进入密封拍卖阶段的时机和牌照的流通等实际问题。这些讨论将有利于拍卖机制在现实中的操作实施。     

Network concentration and airport congestion in a post de-regulation context: A case study of Brazil 2000–2010

This paper empirically investigates the main drivers of airline network concentration in an air transport market subject to rapid growth. We consider the Brazilian air transport industry of the 2000s, in which network concentration rapidly increased and was followed by a period of massive flight delays and cancelations, which resulted in the “big blackout” of 2006–2007. We develop an econometric model of network concentration, accounting for demand, cost and competition variables that may affect the propensity of carriers to concentrate flights and passenger connections on a few airports of a network. The main focus of the paper is on the relation between networks leading to the problems of the blackout episode. We investigate the dynamic pattern of the evolution of concentration before and after the abnormal period of operations and find that concentration began to rise at least six quarters before, and persisted at a high level until two quarters after the blackout – and then plunged steeply toward the end of the decade. We believe that our analysis contributes to an improved understanding of the behavior of air transport systems subject to network concentration and congestion. With respect to methodology, we suggest and employ the use of alternative measures of network concentration to check the robustness and validity of our results.