磁放大器式硅弧焊整流器控制特性分析

本文详细分析了三相内反馈磁放大器式硅弧焊整流器的控制特性,给出了各铁心的磁通密度变化规律及输出电压 U_o 与控制电流 I_K 之间的数学表达式。对确定内反馈磁放大器式硅弧焊整流器一些参数有一定的指导意义。     

A logistic regression point of view toward loss given default distribution estimation

We propose a new procedure to estimate the loss given default (LGD) distribution. Owing to the complicated shape of the LGD distribution, using a smooth density function as a driver to estimate it may result in a decline in model fit. To overcome this problem, we first apply the logistic regression to estimate the LGD cumulative distribution function. Then, we convert the result into the LGD distribution estimate. To implement the newly proposed estimation procedure, we collect a sample of 5269 defaulted debts from Moody’s Default and Recovery Database. A performance study is performed using 2000 pairs of in-sample and out-of-sample data-sets with different sizes that are randomly selected from the entire sample. Our results show that the newly proposed procedure has better and more robust performance than its alternatives, in the sense of yielding more accurate in-sample and out-of-sample LGD distribution estimates. Thus, it is useful for studying the LGD distribution.     

Is the protection of beach and dune vegetation compatible with tourism?

The paradox of development vs. protection and conservation of the coasts highlights the need to determine if tourism and conservation can be compatible rather than opposite activities. We analyzed the spatial and temporal changes in vegetation cover, composition and diversity in three beaches located in the state of Veracruz (Mexico) with different levels of tourism activity (Natural, Trailer Park and Hotels). We calculated tourist density and evaluated vegetation cover, species richness and diversity and analyzed the changes before and after three holiday seasons (winter, spring and summer). The Natural site had the highest vegetation cover (42.8 m²), species richness (14) and diversity (1.50), and Trailer Park the lowest (4.9 m², 8 species, and 0.897 respectively). The BACI (Before-After-Control-Design) analysis showed no significant differences before and after the holiday seasons. Our results show how low and medium density tourism can be compatible with the protection of beach and coastal dune vegetation.     

Patterns of growth in Chinese cities: Implications of the land lease

A special feature of China’s housing market is land use rights in the form of land leasehold contracts granted by the government. We consider an equilibrium model in which a representative developer may choose to redevelop existing centrally located housing or to develop new housing at the periphery of the city. We show that as the city grows, the land leasehold system results in the city center being developed less intensely and more land being used on the outskirts of the city when compared to a fee simple environment. Thus, cities in China are likely to be relatively more spread out, with city centers relatively older than would be the case with “fee simple” ownership. Our model suggests that excess residential land use is about 6 percent. In addition, compared with the ownership case, housing supply will grow more quickly in the near future, but more slowly later on during the transition of the Chinese economy. Parallel to the supply growth pattern, equilibrium price grows relative slowly in the near future, but more quickly later on. While we focus on residential uses, we believe our model can be applied to other land uses.     

Do housing prices promote total factor productivity? Evidence from spatial panel data models in explaining the mediating role of population density

The issue of what to promote in total factor productivity (TFP) in urban areas has been widely discussed in academia and housing prices and population density are confirmed to be two of the most essential driving factors. However, research into the interaction of housing prices and population density with TFP has been neglected, with no previous studies taking spatial factors into consideration, which may bias the results. From this perspective, using spatial panel data models and employing instrumental variables to solve the endogenous problem, this study examines the impact of housing prices on TFP through the mediating effect of population density for 283 Chinese cities during the period 2000–2013, and confirms that the mediating effect accounts for 18.70 % of the total effect. The results show the positive and significant association of housing prices with TFP and the inverted U-shape of population density. The underlying logic is that housing prices change population density by attracting people with high purchasing power and discouraging those unable to afford housing, whereas increased density helps to promote productivity since the settled inhabitants always have highly developed work skills and are well educated. The influencing mechanism of housing prices on TFP through population density is analyzed, namely the spillover effect. We find that the spillover effect exists in the eastern and central regions, as well as first, second, and third tier cities, while for western regions and fifth tier cities, population mobility and increased in housing prices slows their economic development. There is no evidence of any spillover effect in fourth tier cities. A discussion and suggested policy implications are also provided.     

全球价值链下中国增加值贸易的核算及网络特征研究

基于投入产出模型和社会网络分析，利用世界投入产出表相关数据，对2000—2014年中国的增加值贸易进行核算，并分析全球增加值贸易的网络特征。研究结果显示：（1）从出口目的地来看，中国向美国、日本、德国等国家的增加值出口较大；（2）从行业来看，中国的纺织业、除汽车和摩托车之外的其他产品批发业、采矿业等行业的增加值出口较大；（3）根据网络密度的计算结果，世界范围的各国（地区）贸易联系程度在增强；（4）中国的相对点度数和点强度有上升的趋势，而日本和美国有下降的趋势，说明中国在世界增加值贸易格局中的地位在提升，不过美国仍在世界增加值贸易格局中占据主导地位；（5）核心边缘分析结果表明核心国家（地区）的数目经历了先增加后减少的过程，边缘国家（地区）数目则先减少后增加。其中，中国的核心度一直在增加，日本和美国的核心度呈现下降的趋势。因此，为了扩大增加值贸易，增强国际贸易的话语权，中国政府有必要采取调整进出口税率等政策，并重视与美国等国家的双边贸易合作，以实现双赢的结果。     

Arrow–Debreu equilibria for rank‐dependent utilities with heterogeneous probability weighting

We study Arrow–Debreu equilibria for a one‐period‐two‐date pure exchange economy with rank‐dependent utility agents having heterogeneous probability weighting and outcome utility functions. In particular, we allow the economy to have a mix of expected utility agents and rank‐dependent utility ones, with nonconvex probability weighting functions. The standard approach for convex economy equilibria fails due to the incompatibility with second‐order stochastic dominance. The representative agent approach devised in Xia and Zhou (2016) does not work either due to the heterogeneity of the weighting functions. We overcome these difficulties by considering the comonotone allocations, on which the rank‐dependent utilities become concave. Accordingly, we introduce the notion of comonotone Pareto optima, and derive their characterizing conditions. With the aid of the auxiliary problem of price equilibria with transfers, we provide a sufficient condition in terms of the model primitives under which an Arrow–Debreu equilibrium exists, along with the explicit expression of the state‐price density in equilibrium. This new, general sufficient condition distinguishes the paper from previous related studies with homogeneous and/or convex probability weightings.     

初探历史性与现代性在路易斯·康作品中的交汇

路易斯·康作为20世纪下半叶世界最具影响力的建筑师之一,因其作品风格与创作思想的独特而受到众多建筑师的喜爱和追捧,特别在第三世界,其名声完全可以和柯布相媲美。通过深入的研究,不难发现康的作品正是通过对历史性和现代性的交汇而产生的,康通过其不平凡的建筑生涯形成了自己对建筑历史性的独特观点以及表达方式。     

商业周期与区际经济一体化——自然壁垒、经济结构与政策

文章着重从商业周期角度来对我国区际一体化状况进行实证研究,即主要从"市场自然分割"与"政策与经济结构"两方面因素来探索商业周期的区域差异.总体来看,我国所有地区在两个时间样本期间(1992～1997年与1998～2004年)的就业和产出周期同步性均有所增加,说明商业周期的演进与我国经济体制改革基本同步;文章还分析了影响商业周期的不同解释变量,结果显示:控制变量的距离、规模与周期存在显著的相关性,而体现"东西边界"的外生变量则在绝大部分回归中则显著为负,说明在我国东西部之间可能存在一道明显的"区域分界线",阻碍了大区域间的经济联系;此外,樊刚指数对区域周期的解释具有两面性,经济结构差异越合理,商业周期越走向同步性,而财政政策差异和贸易密度差异是我国商业周期的波动因素.     

中国对拉美国家出口贸易影响因素实证分析——基于总量与技术结构视角

本文首先通过计算中国对拉美七国四类制成品出口密集度等,分析中国对拉美地区制成品出口结构;通过考察中国和拉美七国生产要素结构变化情况对中拉要素禀赋差异作深入分析,以期探究中国对拉美制成品出口结构背后深层次原因。然后构建扩展引力模型分别从总量视角和技术结构视角探析中国对拉美货物出口主要影响因素,结果显示拉美国家国内生产总值、中拉要素禀赋差异、中国货币自由度、中国对拉美直接投资水平对中国向拉美出口总量均产生显著促进作用,各影响因素对不同技术类别制成品出口的作用效果存在差异性。为实现中国对拉美出口贸易结构优化升级,推动中国产业结构调整升级,促进拉美地区经济更快发展,研究有针对性地提出了对策建议。