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.     

一种基于自适应相似矩阵的谱聚类算法

为了消除在构建谱聚类算法的相似矩阵时,高斯核函数中尺度参数的波动影响,构建了一种自适应相似矩阵,并应用到谱聚类算法中。自适应相似矩阵中数据点间的距离度量采用测地距离算法,相距较近的两点间的距离近似于欧氏距离,相距较远的两点则先根据欧氏距离得到每个数据点的k个近邻点,然后累加近邻点的测地距离,由此得到每对数据点间的最短距离。两点间的局部密度用共享近邻的定义来表示,更好地刻画了数据集的本征结构。在5个人工数据集和国际通用UCI数据库中的5个真实数据集上进行实验。实验结果表明,所提算法的聚类准确率高于对比算法的准确率,对复杂分布数据有很强的自适应能力。研究成果为数据挖掘及机器学习提供了思路和方法。     

基于耕地保护的中国城镇化发展战略研究

研究目的：研究中国城市位序 — 规模规律的演化和城市建成区人口密度同城市规模关系的变化,预测未来城镇化发展占用耕地情况,提出基于耕地保护的中国城镇化发展对策建议。研究方法：文献资料法、回归分析法和函数模型预测法。研究结果：中国城市建成区人口密度随城市人口规模的增加而增加,但正在快速下降,中国城镇化同耕地保护之间的矛盾日益突出。研究结论：为更加有效地保护耕地,中国应加快制定以发展大城市为主导,各级城市城镇全面发展的城镇化战略,推行高人口密度的城镇化发展政策措施,走紧凑型城镇化道路。     

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。     

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。     

中国省际城镇职工工资收入分布演进的时空特征

运用Kernel密度估计方法和空间马尔科夫链分析方法,并将空间因素纳入分析框架中,对1978—2009年期间中国省际城镇职工工资收入分布演进的时空特征进行了分析。研究结果表明:从时间动态性看,中国省际城镇职工工资收入的差距正逐步固化和深化,多俱乐部收敛特征明显、贫困陷阱问题日益突出;从空间动态性看,近邻效应对省际城镇职工工资收入分布演进存在一定影响,多数省份的工资收入水平向邻区的平均工资收入水平演进。     

浅析上市公司消耗性林木资产的会计信息披露

消耗性林木资产是林业经营主体的重要资产,消耗性林木资产的会计信息披露对于提高会计信息的质量以及促进资本市场的持续健康发展具有重要的意义。文章在阐述了会计信息披露相关理论的基础上,重点分析了2010年中国上市公司消耗性林木资产信息披露中存在的主要问题,即缺乏对经营风险的必要提示、有关郁闭度方面的信息披露不充分、成本结转方法披露过于随意、公允价值的披露主观性强等,并有针对性地提出了相应的完善建议,即应在完善消耗性林木资产表内信息披露的同时,强化会计报表附注和财务情况说明书的披露。     

呼伦贝尔贝加尔针茅草甸草原 光能利用率变化规律分析

光能利用率（LUE）是植被光合作用的重要概念,也是研究草地生态系统不同尺度的总第一性生 产力（GPP）、净第一性生产力（NPP）估算模型的重要参数之一。该文通过地面遥感测量、暗箱—气相色 谱法（DC-GC）和涡度相关技术（EC）的方法,在2011年8月初至9月初,获取呼伦贝尔地区以贝加尔 针茅为主要优势种的草甸草原光能利用率,并动态分析光能利用率的日变化和季节变化。研究表明,光能 利用率日变化呈先降低后增加的单峰趋势,即在早晚出现较高值,中午出现较低值;光能利用率的季节变 化总体呈下降趋势。日变化研究中光合有效辐射PAR和温度都与光能利用率呈显著负相关;季节变化研究 中,温度与光能利用率呈弱正相关,叶面积指数与光能利用率呈显著正相关。     

Shifting cultivation and forest pressure in Cameroon

Shifting cultivation is often blamed as a principal cause of deforestation in tropical Africa. It is claimed that the practice is unsustainable because shortened fallow lengths result in soils too degraded to support forest vegetation. The decline in fallow lengths is often attributed to increases in population density and greater market participation. The conventional wisdom makes several claims that are as yet unsubstantiated. This article investigates whether there is evidence to support two of these claims in southern Cameroon. First, using both cross‐sectional and panel data, I find that there is indeed a robust negative association between fallow lengths and population density in the study area and weaker evidence for a negative relationship between fallow lengths and market participation. Second, a stochastic frontier production function approach is used to investigate the marginal contribution of fallow to output. Results indicate that fallow lengths are not low enough to be affecting yields and therefore do not appear to be resulting in declines in soil fertility. Thus overall, while some of the assumptions of the conventional wisdom appear to be true, there is little evidence to support its dramatic conclusion that shifting cultivators are causing deforestation in the forested region of Cameroon.     

Spatial welfare economics versus ecological footprint: modeling agglomeration,externalities and trade

A welfare framework for the analysis of the spatial dimensions of sustainability is developed. It covers agglomeration effects, interregional trade, negative environmental externalities, and various land use categories. The model is used to compare rankings of spatial configurations according to evaluations based on social welfare and ecological footprint indicators. Five spatial configurations are considered for this purpose. The exercise is operationalized with the help of a two-region model of the economy, that is, in line with the ‘new economic geography.’ By generating a number of numerical ‘counter-examples,’ it is shown that the footprint method is inconsistent with an approach aimed at maximum social welfare. Unless environmental externalities are such a large problem that they overwhelm all other components of economic well-being, a ‘spatial welfare economic’ approach delivers totally different rankings of alternative land use configurations than the ecological footprint.