投资激励视角下农产品供应链治理结构优化

本研究针对"公司+农户"型供应链面临的双边投资意愿不足的现实困境,论文尝试在不对称纳什谈判博弈和Stacklberg博弈的框架下,分析"公司+合作社+农户"型农产品供应链提升双边投资意愿的理论依据,从而为农产品供应链的治理结构优化提出政策建议。数理模型分析显示:1与"公司+农户"型供应链相比,"公司+合作社+农户"型供应链中的农户种植投资和公司销售投资的意愿均能得到提升。2"公司+合作社+农户"型供应链的农户利润水平与合作社谈判力正相关;当合作社具有相对较强的谈判力时,即使合作社规定的资本留存率较高,农户利润水平依然能够高于"公司+农户"型供应链。3当合作社谈判力在某一特定范围内时,公司与农户利润水平均能实现Pareto改进。4当考虑到公司和农户进行长期合作时,"公司+合作社+农户"型供应链中确保农户履约的保证金阈值显著低于"公司+农户"型供应链。最后,利用数值仿真分析了合作社谈判能力、资本留存率等因素对公司与农户利润水平的影响以及农户保证金阈值的变化。论文研究结果表明,由于农户和公司在"公司+合作社+农户"型供应链中的地位更为平等,合作社能够形成对于公司的制衡力量,这大大降低了农户进行种植投资后可能面临的"敲竹杠"风险,农户的种植投资意愿得到提升。当农户加大种植投资后,合格农产品产量将会提高,这反过来又会激励公司提升销售投资意愿来获得更多的利润。因此,我国未来农业产业化经营模式的制度创新必须以农民专业合作社的壮大为基础,大力发展"公司+合作社+农户"型供应链,这不仅有助于更好地保障农产品质量安全;也有助于让农户平等参与现代化进程,共同分享现代化成果。     

Thermodynamic prediction and experimental investigation of short-term dynamic membrane formation in dynamic membrane bioreactors: Effects of sludge properties

In dynamic membrane bioreactors(DMBRs), a dynamic membrane(DM) forms on a support material to act as the separation membrane for solids and liquids. In this study, batch filtration tests were carried out in a DMBR using nylon mesh(25 μm) as support material to filtrate sludge suspensions of variable properties from three different sources to evaluate the effects on the short-term DM formation process(within 240 min). Furthermore, the extended Derjaguin–Landau–Verwey–Overbeek(XDLVO) theory was applied to analyze the sludge adhesion and cohesion behaviors on the mesh surface to predict quantitative parameters of the short-term DM formation process(including initial formation and maturation stage). The filtration results showed that the order of the initial DM formation time(permeate turbidity 1 NTU as an indicator) was as follows: sludge with poor settleability and dewaterability normal sludge sludge with poor flocculability. Moreover, normal sludge(regarding settleability, dewaterability,flocculability, and extracellular polymeric substance) showed a more acceptable DM formation performance(short DM formation time, low permeate turbidity, and high permeate flux) than sludge with poor settleability, dewaterability and flocculability. The influence of sludge properties on the initial DM formation time corroborates the prediction of sludge adhesion behaviors by XDLVO theory. Additionally, the XDLVO calculation results showed that acid–based interaction, energy barrier, and secondary energy minimum were important determinants of the sludge adhesion and cohesion behaviors. Therefore, short-term DM formation process may be enhanced to achieve stable long-term DMBR operation through positive modification of the sludge properties.     

Dynamic membrane bioreactor performance enhancement by powdered activated carbon addition: Evaluation of sludge morphological, aggregative and microbial properties

The effects of powdered activated carbon(PAC) addition on sludge morphological, aggregative and microbial properties in a dynamic membrane bioreactor(DMBR) were investigated to explore the enhancement mechanism of pollutants removal and filtration performance. Sludge properties were analyzed through various analytical measurements. The results showed that the improved sludge aggregation ability and the evolution of microbial communities affected sludge morphology in PAC-DMBR, as evidenced by the formation of large, regularly shaped and strengthened sludge flocs. The modifications of sludge characteristics promoted the formation process and filtration flux of the dynamic membrane(DM) layer. Additionally, PAC addition did not exert very significant influence on the propagation of eukaryotes(protists and metazoans)and microbial metabolic activity. High-throughput pyrosequencing results indicated that adding PAC improved the bacterial diversity in activated sludge, as PAC addition brought about additional microenvironment in the form of biological PAC(BPAC), which promoted the enrichment of Acinetobacter(13.9%), Comamonas(2.9%), Flavobacterium(0.31%) and Pseudomonas(0.62%), all contributing to sludge flocs formation and several(such as Acinetobacter) capable of biodegrading relatively complex organics. Therefore, PAC addition could favorably modify sludge properties from various aspects and thus enhance the DMBR performance.     

Learning and adaptation in the management of waterfowl harvests

A formal framework for the adaptive management of waterfowl harvests was adopted by the U.S. Fish and Wildlife Service in 1995. The process admits competing models of waterfowl population dynamics and harvest impacts, and relies on model averaging to compute optimal strategies for regulating harvest. Model weights, reflecting the relative ability of the alternative models to predict changes in population size, are used in the model averaging and are updated each year based on a comparison of model predictions and observations of population size. Since its inception the adaptive harvest program has focused principally on mallards (Anas platyrhynchos), which constitute a large portion of the U.S. waterfowl harvest. Four competing models, derived from a combination of two survival and two reproductive hypotheses, were originally assigned equal weights. In the last year of available information (2007), model weights favored the weakly density-dependent reproductive hypothesis over the strongly density-dependent one, and the additive mortality hypothesis over the compensatory one. The change in model weights led to a more conservative harvesting policy than what was in effect in the early years of the program. Adaptive harvest management has been successful in many ways, but nonetheless has exposed the difficulties in defining management objectives, in predicting and regulating harvests, and in coping with the tradeoffs inherent in managing multiple waterfowl stocks exposed to a common harvest. The key challenge now facing managers is whether adaptive harvest management as an institution can be sufficiently adaptive, and whether the knowledge and experience gained from the process can be reflected in higher-level policy decisions.     

Scale-dependent relations in land cover biophysical dynamics

The exploration of the relationships between plant biotic dynamics and scale can reveal important information on ecosystem spatial organization by addressing preservation of information integrity in upscaling/downscaling procedures of land-surface parameterization for environmental modeling applications. Scale-dependent relations of vegetation dynamics are investigated in this study by using emergent biophysical characteristics obtained through a predictive multidimensional model of vegetation anomalies derived from remote-sensing observations. In particular, the analysis is focused on the spatial organization of some phenological parameters including deterministic variations (seasonal range, interannual variability, jump discontinuities) and stochastic components (plant memory, spatial correlations). The analysis is performed using MODIS-based Normalized Difference Vegetation Index (NDVI) 16-day composites for the period from March 2000 to December 2006 over Italy at different levels of spatial aggregation (1-8 km). Scale-dependences of the statistical moments of the phenological parameters are quantified through simple power laws for five distinct vegetated land covers. Results suggest that some biophysical characteristics, especially deterministic components, show no preferential spatial scale for important coverage. In particular, broad-leaved forests and natural grasslands are characterized by deterministic and low-distance spatial components well explained by scale relationships, which are modulated by possible spatiotemporal dynamics of climatic drivers. Agricultural lands show high scale-dependent relations on short-term biophysical memory sources and low-distance spatial components of phenology likely related to hierarchical interactions of anthropogenic and ecological processes; whereas mixed patterns of croplands and natural areas generally present no consistent scaling relations.     

How temperature and habitat quality affect parasitoid lifetime reproductive success—A simulation study

Adult parasitoid females lay their eggs in or on host insects. Most species are incapable of de novo lipogenesis as adults, and lipids accumulated during the larval stage are allocated either to egg production or to adult survival. Lipid consumption increases with distance covered by the parasitoids and thus with the distance between available hosts within a habitat. Temperature should affect parasitoid fitness because it changes the constraint imposed by a limited reserve of lipids and because it influences behaviour. Climate change involves both an increase in average temperature and an increased frequency of extreme weather such as heat waves. We investigated how the predicted increase of temperature will affect parasitoid fitness and how this depends on habitat parameters (spatial distribution of hosts and lipid cost of habitat exploitation). We studied optimal behaviour and calculated fitness at different temperatures and in different habitats using a stochastic dynamic programming model for pro-ovigenic parasitoids (which mature all their eggs before becoming adult). We show that an increase in temperature decreases fitness of parasitoids adapted to lower temperatures. This decrease in fitness depends on habitat quality. In field conditions (assuming small costs of intra-patch foraging), the loss of fitness should be larger in habitats with high inter-patch distance and in habitats with a more aggregated distribution of hosts. The foraging behaviour of parasitoids is also affected; at higher temperature we show that intra-patch foraging becomes less efficient, and patch residence times are longer.     

LNG accident dynamic simulation: Application for hazardous consequence reduction

The evaluation of exclusion (hazard) zones around the LNG stations is essential for risk assessment in LNG industry. In this study, computational fluid dynamics (CFD) simulations have been conducted for the two potential hazards, LNG flammable vapor dispersion and LNG pool fire radiation, respectively, to evaluate the exclusion zones. The spatial and temporal distribution of hazard in complex spill scenario has been taken into account in the CFD model. Experimental data from Falcon and Montoir field tests have been used to validate the simulation results. With the valid CFD model, the mitigation of the vapor dispersion with spray water curtains and the pool fire with high expansion foam were investigated. The spray water curtains were studied as a shield to prevent LNG vapor dispersing, and two types of water spray curtain, flat and cone, were analyzed to show their performance for reduction and minimization of the hazard influencing distance and area. The high expansion foam firefighting process was studied with dynamic simulation of the foam action, and the characteristics of the foam action on the reduction of LNG vaporization rate, vapor cloud and flame size as well as the thermal radiation hazard were analyzed and discussed.     

Assessment of nitrogen leaching from arable land in large river basins: Part II: regionalisation using fuzzy rule based modelling

This study deals with fuzzy rule based modelling of nitrogen (N)-leaching from arable land. Main purpose is the elaboration of a method, which allows dynamical regionalisation of results from process-based models for large regions and can be efficiently included in metamodels or decision support systems for rapid integrated assessment of water resources. The paper is the second part of a two-part paper. In the first paper the distributed ecohydrological model SWIM had been applied to calculate and analyse nitrogen dynamics in arable soils for a set of representative natural and management conditions in the Saale River basin (Ecol. Model. (in press)). Here, in the second paper the results from those simulation experiments are used to define, train and validate fuzzy rule systems for the estimation of N-leaching. Nine fuzzy rule systems, specific for nine soil classes, were created from the simulation experiments, representing the conditions for the whole Saale River basin. The fuzzy rule systems operate on monthly time steps and consist of 15 rules and seven input variables each, which are compiled from time series of precipitation, percolation and evapotranspiration as well as from information about fertilizer and crop specific nitrogen uptake. Simulated annealing as a non-linear discrete optimisation method is used for automatic rule assessment. Validation of the fuzzy rule systems, carried out by split sampling of 30-year simulation period, shows satisfactory performance on an annual basis and good performance on the long-term basis with average correlation between SWIM-simulated and fuzzy rule-estimated N-leaching values of 0.78 and 0.94, respectively.     

浅谈动态工业源填报易出现的问题

按照国家环保部统一部署,2009年度全面开展了污染源普查数据更新调查工作。作为污染源调查的指导员,全面参加了动态更新调查工作,发现在填报过程中易出现问题的项目不少,文章总结、归纳了工业源填报易出现问题的项目,可供今后普查工作参考。     

大庆石油炼化厂废水深加工回用工程研究

为实现十一五大庆炼化石油节能减排,扩大再生产需要的高质量循环水和锅炉用水需要,用二次生化后排放污水经碟式过滤器——超滤—高级氧化——动态活性炭——动态生物膜沙滤+反渗透组合工艺处理废水回用生产。该工程规模600t/h,设计循环补充水量280t/h,锅炉用水补充量250t/h,是典型污水工厂管道化处理工程。工艺先进,设备板块简单,适应石油炼化、煤化工、钢铁、铜业电厂和城市污水深加工项目。