基于光能利用率模型的河南省冬小麦单产估算研究

[目的]快速、准确估算空间尺度上作物产量,对于评价农田生态系统对气候变化的响应、制定科学合理的粮食政策、对外粮食贸易等具有重要意义。河南省冬小麦产量占全国1/4,准确估算河南省冬小麦产量对维护国家粮食安全具有重要作用。单产估算作为农作物估产中的关键技术,也是作物估产的难点之一。[方法]文章首先利用VPM(Vegetation Photosynthesis Model)估算冬小麦NPP(Net Primary Product),结合收获指数、冬小麦收获部分的含水量、含碳量、NPP分配到地上或地下部分比例等一系列符合该研究区的经验指数,进行河南省冬小麦单产估算研究,并分析了引起模拟误差的原因。[结果]模拟单产较实测单产低估4.4%(实测单产为6 810kg/hm~2,模拟单产为6 519kg/hm~2),但两者之间存在显著相关关系,两者相关系数的平方R2=0.70(n=50,p0.01)。通过与MODIS-GPP产品获得的冬小麦单产数据比较,基于VPM模型的模拟结果优于MODIS-GPP产品。[结论]基于VPM可快速、准确估算河南省空间尺度冬小麦单产,该方法具有较好的适用性。     

Herding behavior in the Pakistan stock exchange: Some new insights

This study attempts to examine the presence of herding behavior in the Pakistan Stock Exchange (PSX). The novel contribution of this paper is that it investigates the herding phenomenon from a large number of facets such as herding of firms towards market, herding of firms towards industry portfolios, herding of industry portfolios towards market, herding in mostly traded stocks and in large and small stocks, and herding in the crisis period. For this purpose, we use the herding behavior model of Christie and Huang (1995) on the daily closing prices data of 609 firms listed on the PSX from January 2004 to December 2013. Results show that individual firms do not herd towards market index, except when the market experiences a negative return of 5%. However, when we sort firms into small and large groups based on median market capitalization, results indicate that large firms show herding behavior in extreme market movements. Further, we find that firms in several industries herd towards their industry portfolios. However, we find weak evidence of industry portfolios herding towards the market. We also segregate the impact of financial crisis of 2008 from normal times. These findings support results of our baseline estimation.     

Socio-economic and biophysical determinants of land degradation in Vietnam: An integrated causal analysis at the national level

Recognizing the socio-economic and biophysical causes of land degradation at the national level is important for cause-targeted strategies when designing policies for combating land degradation. This study aims to identify the biophysical and socio-economic factors that significantly affect land degradation across Vietnam and to interpret the causalities underlying the effects. The dependent variables considered in the study are spatial, the extent and intensity of degradation in three land-use zones (agriculture, forest and severely degraded abandonment). The hypothesized explanatory variables are common economic and demographic drivers and bio-physical factors such as soil, terrain constraints, and neighborhood land-use structures that are often neglected in many large-scale land degradation assessments. Instead of using a single inferential statistic technique, we used multi-linear regression and binary logistic regression in a complementary manner to increase the detectability and credibility of the degradation cause analyses. The results showed agricultural production growth had strong and consistent effects on land degradation extent and intensity. Population growth, especially in rural areas, had a strong effect on the extent of overall land degradation. The importance of a neighboring forest was revealed for its ability to reduce land degradation intensity in abandoned, unproductive lands. The concrete faceting of the causal analysis for each land-use zone as social–ecological stratum allowed us to combine the defined social–ecological contexts, contemporary theories, and hypotheses in the field to clarify the causal factors of a complex phenomenon like land degradation. The study demonstrates these contemporary inferential statistics can be complementarily used to sufficiently detect and understand land degradation causes at the national level. The results suggest implications for national land management policy: internalizing land degradation costs in the farming system evaluation for payment for ecosystem services policy, restricting forest conversion, and improving extension services and education in agrarian communities.     

四川省重点生态功能区有机农业生产效率研究——基于三阶段DEA模型的实证分析

[目的]有机农业为我国农业绿色发展起到良好的带动作用,但我国有机农业发展中,西部贫困地区较为滞后。针对西部贫困地区有机农业生产效率进行定量分析,揭示影响有机农业生产效率的主要因素,旨在提高该地区有机农业生产效率,丰富区域视角下的有机农业生产研究。[方法]采用三阶段DEA模型对2014年四川省重点生态功能区有机农业生产效率进行量化分析,识别环境变量对有机农业生产效率的影响。[结果]环境因素和随机误差对四川省重点生态功能区有机农业生产效率产生了显著的影响。环境因素中,农民人均纯收入的增加有利于促使农机、耕地等资源的有效利用,但同时也导致化肥投入冗余增加;城镇化率的提高会降低耕地、劳动力、化肥、农药等使用效率,从而对有机农业生产效率产生不利影响;财政支出占GDP比重的增加有利于提高农机使用效率,但同时也导致化肥和农药投入冗余增加;粮食播种面积占耕地面积比重对有机农业生产效率产生了不利影响。剔除环境因素和随机误差的影响后,四川省重点生态功能区各县平均技术效率和规模效率有所下降,纯技术效率则略有提升。基于纯技术效率和规模效率,四川省重点生态功能区各县有机农业生产效率可分为"双高型""高低型""低高型"和"双低型"等4种类型。[结论]三阶段DEA模型有效剔除了环境因素和随机误差对有机农业生产效率的影响,估计的效率值更真实地反映了四川省重点生态功能区有机农业生产效率水平。针对四川省重点生态功能区各县有机农业生产效率的不同特征,应结合地方实际,通过扩大要素投入规模或改进要素配置效率和使用效率,提高有机农业生产效率。     

基于第二次全国R&D资源清查的农业科技资源配置效率分析

[目的]农业科技资源配置效率的高低在一定程度上决定着农业科技系统的运行效率,而农业科技系统的运行效率状况对提高农业科技资源的高效利用、增强农业科技创新能力、加快促进农业现代化进程有着重要的影响。文章基于2009年第二次全国RD资源清查数据,对政府部门属农业科研机构的配置效率进行测算,并分析其规模报酬以便为相关决策部门提供参考。[方法]通过构建农业科技资源配置效率评价的投入产出指标体系,选取包含科技人员、科技经费及科技成果在内的6个投入产出指标,运用数据包络分析方法 (DEA)中的超效率模型测算全国32个省份政府部门属自然科学和技术领域研究机构(含直辖市)的综合效率、纯技术效率、规模效率。[结果]全国农业科研机构科技资源技术效率平均值为0.581,科技运行效率还有较大的提升空间。按机构学科领域分,水产学学科的效率值最高(TE Score=2.867 9);按机构服务的国民经济行业分,渔业的效率值最高(TE Score=1.901 1)。各省(市、区)农、林、牧、渔业农业科研机构的综合运行效率值大于1的有天津、吉林、贵州、宁夏、北京、辽宁。规模效率的平均值是0.686,规模收益递减的省(市、区)占87%。[结论]DEA非效率地区所占比例较大,技术效率低于全国平均值的地区占56%,地区规模效率的提升可以依靠加大科研投入来实现。农业科技资源配置的结构需要进行调整,在合理调控种植业科研机构的发展规模的同时优化其科技人员结构。通过开展农业科技计划绩效评价、组建农业科技创新联盟来促进农业科技协同创新。同时应根据农业科研机构的不同类型提出相应的管理措施,以便实现分类指导和科学管理。     

对外直接投资对小微企业的就业效应分析——基于企业规模异质性视角的实证研究

从企业异质性视角出发，系统地考察了大中型企业对外直接投资对母国小微企业就业的影响，并在阐明大中型企业OFDI对小微企业就业的影响机制之上，利用我国2001-2013年省际面板数据对理论分析的结论进行验证。研究发现：从总体来看，我国大中型企业对外直接投资对母国小微企业的就业具有显著的影响；从分地区估计结果来看，大中型对外直接投资对小微企业就业的影响存在空间异质性，在东部地区，OFDI对小微企业的发展影响显著为正，对于中部地区影响虽然依然显著，但其影响系数明显降低，而西部地区的影响则显著为负；地区的金融发展水平在大中型企业OFDI对母国小微企业就业的影响中起到重要的调节作用。     

Efficiency,total factor productivity and returns to scale in a sustainable perspective: An analysis in the European Union at farm and regional level

For global sustainability it is imperative to find a balance across the three main components of sustainable development which are the economic, social and environmental aspects. However, it is not a simple task to make these contexts compatible, usually because of economic pressures which transform them into opposed objectives. This framework occurs across several dimensions within society and the economy, where the agricultural sector is not an exception. The objective of this study is to analyse the efficiency, total factor productivity and returns to scale in an economic, social and environmental perspective in farms of the European Union (EU) regions through Data Envelopment Analysis (DEA) approaches. The research concerning the returns to scale will be complemented by the Keynesian models. Data obtained from the European Union Farm Accountancy Data Network (FADN) was considered. The results show that in maintaining or improving the levels of production in farms, it is often possible to greatly reduce, in some cases, the consumption of fertilizers and crop protection products. On the other hand, from a social perspective, some European Union regions are more generous in the salaries paid to farming workers and absorb more labour, which in a European context of unemployment, may be an interesting way to realistically look at and be engaged in the agricultural planning in a sustainable way, founding a balanced trade-off among the economic, social and environmental dimensions.     

PRICING FOR LARGE POSITIONS IN CONTINGENT CLAIMS

Approximations to utility indifference prices are provided for a contingent claim in the large position size limit. Results are valid for general utility functions on the real line and semi‐martingale models. It is shown that as the position size approaches infinity, the utility function's decay rate for large negative wealths is the primary driver of prices. For utilities with exponential decay, one may price like an exponential investor. For utilities with a power decay, one may price like a power investor after a suitable adjustment to the rate at which the position size becomes large. In a sizable class of diffusion models, limiting indifference prices are explicitly computed for an exponential investor. Furthermore, the large claim limit arises endogenously as the hedging error for the claim vanishes.     

Endogenous ranking and equilibrium Lorenz curve across (ex-ante) identical countries: A generalization

This paper proposes a symmetry-breaking model of trade with a finite number of identical countries and a continuum of tradeable consumption goods, which differ in their dependence on nontradeable intermediate inputs, “producer services”. Productivity of each country is endogenous due to country-specific external economies of scale in its service sector. It is shown that, in any stable equilibrium, the countries sort themselves into specializing in different sets of tradeable goods and that a strict ranking of countries in per capita income, TFP, the service sector share, and the capital–labor ratio emerge endogenously. Furthermore, the distribution of country shares, the Lorenz curve, is unique and analytically solvable in the limit, as the number of countries grows unbounded. Using this limit as an approximation allows us to study what determines the shape of distribution, perform various comparative statics and to evaluate the welfare effects of trade. In doing so, this paper extends the analysis of Matsuyama (Econometrica, 81:5 (September 2013), 2009–2031) for more general and flexible forms of scale economies. It turns out that the technique introduced in Matsuyama (Econometrica, 81:5 (September 2013), 2009–2031) is useful for the equilibrium characterization in this general case as well. Although some results of comparative statics and on welfare inevitably need to be modified, they change in ways that illuminate the underlying mechanism of symmetry-breaking.     

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.