一种新的快速视频图像边缘检测算法

一般常用的边缘检测算法计算量较大，对细小边缘检测效果较差，不适合实时边缘检测系统。针对这一问题，本文提出一种连续分割的快速边缘检测算法：从相互垂直两方向分割梯度图像，提取截面曲线极大值获得图像边缘，使用形态学梯度，检测出细小的图像边缘。实验结果表明此算法较Canny等经典算法减少了计算量，提高了边缘检测精度。     

THE ESTIMATED EFFECT OF CATHOLIC SCHOOLING ON EDUCATIONAL OUTCOMES USING PROPENSITY SCORE MATCHING

This paper examines the effect of attending a Catholic high school on educational outcomes. The statistical analysis is based on data obtained from the US National Educational Longitudinal Study. Using propensity score matching methods to control for selection bias, we find that Catholic schooling improves maths test scores, with stronger effects for males than for females, but appears to have little effect (if any) on reading scores. Catholic schooling also raises high school graduation rates and substantially increases the likelihood of enrolment in a 4‐year college. Use of the difference‐in‐difference method suggests that the effect of Catholic schooling on changes in maths scores is more muted, though still statistically significant.     

Markov equilibria in dynamic matching and bargaining games

Rubinstein and Wolinsky [Rev. Econ. Stud. 57 (1990) 63] show that a simple homogeneous market with exogenous matching has a continuum of (non-competitive) perfect equilibria; however, the unique Markov-perfect equilibrium of this model is competitive. By contrast, in the more general case of heterogeneous markets, even the Markov property is not enough to guarantee the perfectly competitive outcome. We define a market game that allows for heterogeneous values on both sides of the market and exhibit a number of examples of (non-competitive) Markov-perfect equilibria, with and without discounting. Unlike the homogeneous case, these equilibria allow for inefficient trades and for trade at non-uniform prices. The non-competitive equilibrium may be unique.     

Is performance driven by industry‐or firm‐specific factors? A new look at the evidence

In this study we revisit the question of whether firms' performance is driven primarily by industry or firm factors, extending past studies in two major ways. Firstly, in a departure from past research, we use value‐based measures of performance (economic profit or residual income and market‐to‐book value) instead of accounting ratios (such as return on assets). We also use a new data set and a different statistical approach for testing the significance of the independent effects. Secondly, we examine whether the findings of past research can be generalized across all firms in an industry or whether they apply to a particular class of firms within the same industry. We find that a significant proportion of the absolute estimates of the variance of firm factors is due to the presence of a few exceptional firms in any given industry. In other words, only for a few dominant value creators (leaders) and destroyers (losers) do firm‐specific assets seem to matter significantly more than industry factors. For most other firms, i.e., for those that are not notable leaders or losers in their industry, however, the industry effect turns out to be more important for performance than firm‐specific factors. Copyright © 2002 John Wiley & Sons, Ltd.     

Construction of D-optimal s 1 × s 2 × s 3 factorial designs using graph theory

In this paper, the maximum determinant of the associated 0-1 matrix in D-Optimal saturated main effect plans for 3× s_2 × s_3 factorials, is derived by the use of Graph theory and Combinatorics. The present work is related to a problem suggested by Chatterjee and Narasimhan (2002). Using the theoretical results, we also give the designs for s₃≥s₂ + 1. This research was supported by the State Scholarships Foundation of Greece.     

Safeguarding Jobs? Acquisition FDI and Employment Dynamics in U.K. Manufacturing

This paper applies a difference-in-differences methodology based on matched firms to isolate the direct employment effect of recent acquisition FDI in U.K. manufacturing. Our analysis indicates that acquisition FDI has led to a reduction in the inefficiency with which labour had been used, but this was not associated, on average, with any significant downsizing. However, by allowing for heterogeneity in the causal effect of foreign take-overs, we uncover detrimental employment effects amongst larger take-over targets, and beneficial impacts amongst smaller ones. JEL no. F23, J23     

现金持有量决策具有战略效应吗?——基于现金持有量的平均效应与区间效应的研究

文章根据掠夺理论来考察现金持有量是否具有增加产品市场业绩的战略效应。研究结果表明,就平均效应而言,现金持有量能够增加企业的产品市场业绩;就区间效应而言,现金持有量的战略效应呈现出随着现金持有水平的提高而逐渐增加的趋势。进一步地检验结果表明大量持有现金引起的投资是造成现金持有量的区间效应呈增加趋势的主要原因,且最终也增加了企业价值。文章还发现行业的竞争强度以及整体财务状态也会影响现金持有量的战略效应。     

基于多尺度多方向Gabor模板的光学/SAR景象匹配

合成孔径雷达（SAR）成像制导通常采用光学基准图和SAR实时图 进行特征提取和景象匹配。提出了一种光学/SAR异类影像匹配方法,利用多尺度多方向Gabo r模板提取图像的Gabor特征后进行特征匹配,首先对SAR图像进行方向Frost滤波预处理,然 后分别计算光学图像和SAR图像的高斯梯度图像,再利用多尺度多方向二维Gabor滤波器模板 分别对两幅高斯梯度图像进行特征提取,最后对两组特征矩阵进行归一化互相关匹配。该方 法直接利用光学图像和SAR实时图进行景象匹配,实验表明,该异类影像匹配方法较其他传 统方法具有较高的鲁棒性和准确性。     

文化资本、体制转轨与经济增长——兼及文化产业发展路径

本文回顾了关于经济增长的理论假说,发现围绕文化资本来解释体制转轨和经济增长以及讨论它们三者之间关系的文献较少。在此基础上提出制度是经济增长的重要但非决定性因素,适应文化资本的制度转轨才是经济绩效提高的关键,因此,文化资本中的市场观念在改革开放后被重新激发,构成中国经济增长的内在动力。最后基于结论从文化资本理论出发,兼述地域文化产业发展路径。     

Rural-urban gradient analysis of ecosystem services supply and demand dynamics

Urban regions are important places of ecosystem service demands and, at the same time, are the primary source of global environmental impacts. Although there is broad agreement on the importance of incorporating the concept of ecosystem services into policy strategies and decision-making, the lack of a standardized approach to quantifying ecosystem services at the landscape scale has hindered progress in this direction. Moreover, tradeoffs between ecosystem services and the supply/demand ratio of ecosystem services in urban landscapes have rarely been investigated. In our paper, we present a method to quantify and map the supply and demand of three essential provisioning services - energy, food, and water - along the rural-urban gradient of the eastern German region Leipzig-Halle. This urban region has experienced significant socio-economic dynamics and land use changes since the German reunification in 1990. The results show that both the demand and the supply of ecosystem services changed considerably during the time span under consideration (1990-2007). We identified an increasing supply/demand ratio of food and water but a decreasing supply/demand ratio of energy. In addition, the pattern of ecosystem demands shows a levelling of rural-urban gradients, reflecting profound modifications of traditional rural-urban relationships. The changes of ecosystem service supply gradients are determined more by land use intensity, such as the intensification of agricultural production, than by land cover changes such as urban sprawl. The comparison of supply/demand ratios and rural-urban patterns of ecosystem services can help decision-makers in landscape management in striving for a sustainable balance between resource supply and demand.