京津冀城市群土地经济密度时空格局演变与驱动因素分析

[目的]研究2006—2016年京津冀城市群土地经济密度的时空格局演变特征及其驱动机制。[方法]以京津冀城市群153个县区为例,运用空间自相关分析、热点分析、地理探测器等研究方法,对土地经济密度的时空演变规律及其驱动因素进行探讨。[结果](1)2006—2016年京津冀城市群县区和地市的土地经济密度及其发展速度在空间上均呈"东高西低,南高北低"格局,但随时间变化区域差异逐渐缩小;(2)Moran′s I指数由0.013 9上升至0.065 3,表明在空间上存在空间集聚状态,且随时间不断优化,区域一体化趋势逐渐增强;(3)空间集聚特征明显,热点显著区集中于北京、天津等经济优势区,并向四周梯度扩散;(4)人均GDP、当年实际使用外资额、固定资产投资额等经济类因子对土地经济密度的解释力较大,且任意两因子交互后作用力优于单项因子作用力。[结论]可为京津冀城市群土地资源的合理利用和差别化调控提供参考。     

企业规模对专利产出影响的实证分析——基于1998—2010年上市公司经验证据

使用1998—2010年中国A股上市公司的年度数据,研究了企业规模对专利产出和专利密度的影响。结果表明:发明专利和实用新型专利与企业规模之间存在U型关系,外观设计专利与公司规模呈倒U型关系;三类专利的专利密度都与企业规模之间存在U型关系;企业的知识存量、成立时间、财务杠杆、所有制类型等企业内部因素以及市场集中度、企业所处区域等外部环境因素都对企业的专利产出有显著影响。据此提出企业创新发展路径假说。     

MODELING SOVEREIGN RISKS: FROM A HYBRID MODEL TO THE GENERALIZED DENSITY APPROACH

Motivated by the European sovereign debt crisis, we propose a hybrid sovereign default model that combines an accessible part taking into account the evolution of the sovereign solvency and the impact of critical political events, and a totally inaccessible part for the idiosyncratic credit risk. We obtain closed‐form formulas for the probability that the default occurs at critical political dates in a Markovian setting. Moreover, we introduce a generalized density framework for the hybrid default time and deduce the compensator process of default. Finally, we apply the hybrid model and the generalized density to the valuation of sovereign bonds and explain the significant jumps in long‐term government bond yields during the sovereign crisis.     

Land pressures,the evolution of farming systems,and development strategies in Africa: A synthesis

Evidence assembled in this special issue of Food Policy shows that rising rural population densities in parts of Africa are profoundly affecting farming systems and the region’s economies in ways that are underappreciated in current discourse on African development issues. This study synthesizes how people, markets and governments are responding to rising land pressures in Africa, drawing on key findings from the various contributions in this special issue. The papers herein revisit the issue of Boserupian agricultural intensification as an important response to land constraints, but they also go further than Boserup and her followers to explore broader responses to land constraints, including non-farm diversification, migration, and reduced fertility rates. Agricultural and rural development strategies in the region will need to more fully anticipate the implications of Africa’s rapidly changing land and demographic situation, and the immense challenges that mounting land pressures pose in the context of current evidence of unsustainable agricultural intensification, a rapidly rising labor force associated with the region’s current demographic conditions, and limited nonfarm job creation. These challenges are manageable but will require explicit policy actions to address the unique development challenges in densely populated rural areas.     

环渤海地区区域经济空间网络关联结构研究

采用网络分析方法，对1995—2014年环渤海地区区域经济空间网络关联结构进行分析，研究发现：环渤海地区区域经济空间网络关联特征显著，分为“辽宁”和“京津冀鲁”两个子网络；网络密度稳步上升，但仍然较低；核心区域的经济比重有所降低，但份额始终较大；网络效率在波动中趋降，空间溢出效应趋于显著。其中，北京、天津、济南等9地属于“主受益”板块，石家庄、保定、潍坊等19地属于“经纪人”板块，沈阳、大连、鞍山等4地属于“双向溢出”板块，而秦皇岛、承德、葫芦岛等12地属于“净溢出”板块。产业结构转型升级、控制FDI区域差异以及投资多元化等有利于环渤海地区增强区域经济空间关联。应多途径构建区域经济关联通道，打造“环型”网状关联经济，并通过产业转型升级和经济多元化发展增进区域经济空间关联。     

我国农作物秸秆综合利用现状及焚烧碳排放估算

[目的]为加快推进秸秆资源化利用工作,有效缓解因秸秆焚烧带来的环境问题。[方法]将全国划分为黄淮海区、西北区、东北区、东南区、西南区五大区域,对各类农作物秸秆进行了统计分析,研究了秸秆产生量、秸秆资源密度、秸秆利用结构、秸秆焚烧碳排放量。[结果]全国秸秆理论资源量达到10.4亿t,可收集量达到9.0亿t,玉米、水稻和小麦3类农作物秸秆占总量的79.19%,黄淮海区秸秆产量最高,占总量的33.41%。秸秆已利用量为7.21亿t,综合利用率达到80.11%,其中肥料化、饲料化、基料化、燃料化、原料化利用量占已利用量的比例分别为53.93%、23.42%、4.98%、14.27%、3.40%,形成了农用为主的利用格局,但不同秸秆种类综合利用率和利用结构存在显著差异。全国秸秆资源密度和人均占有量分别为523.57kg/667m~2和1.75 t,东北区显著高于全国平均水平,西南区和东南区则显著低于全国平均水平。根据环保部卫星遥感监测的露天焚烧火点数比例估算,2015年我国秸秆露天焚烧量约为8 110万t,总碳排放量约为3 450万t,其中东北地区约占74.1%。[结论]我国秸秆综合利用的重点和难点在东北地区,进一步推动区域秸秆实现全量利用,对于促进低碳农业发展,应对气候变化有着十分重要的意义。     

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.     

基于GIS的铁路密度空间分异研究——以新疆铁路交通网络为例

城市对外交通中,铁路是发展较早的交通运输方式。本文以新疆的铁路交通网络为依据,以道路密度为指标,利用Arc GIS的叠加分析和空间分析功能,研究新疆铁路交通网络的空间分异,并分析新疆各区域人口、生产总值差异与铁路密度差异之间的相互关系。结果表明:(1)新疆铁路密度差异显著,大体呈现"南北低中部高"的趋势;(2)新疆各地区铁路密度与人口分布、生产总值高度正相关。     

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.     

Economies of traffic density and scale in the integrated air cargo industry: The cost structures of FedEx Express and UPS Airlines

This paper examines the cost structures of the leading integrated air cargo carriers, FedEx Express and UPS Airlines. A total cost model is estimated for the two carriers using quarterly data on domestic operations and costs over a nine-year period (2003–2011). The estimated model indicates that the integrated industry exhibits increasing returns to traffic density and constant returns to scale. Accounting for carrier-specific differences in cost structure and network size, FedEx Express is found to be more cost-efficient than UPS Airlines. Looking at the carriers individually, UPS Airlines exhibits substantial economies of traffic density and constant returns to scale while FedEx Express' cost structure is characterized by weak economies of density and constant returns to scale. The combined effect of returns to density and returns to scale on the cost structures of integrated carriers is captured by economies of size. Both FedEx Express and UPS Airlines exhibit economies of size, indicating that carriers in the integrated industry can be more cost efficient by making appropriate adjustments to their network size as their output grows. Moreover, the relative cost-efficiencies of the carriers are reversed when their network-size differences are not controlled.