奶业产业链纵向价格传导的时滞效应与政策启示

奶业产业链纵向价格传导受阻,导致奶牛养殖长期处于价值链的低增值环节,甚至出现"行业萎缩"现象。本文对上游奶牛养殖成本向下游乳品加工环节价格传导机制进行理论分析,并基于2008年1-12月份奶牛饲养成本和原料奶价格的月度数据,运用有限分布滞后模型测度价格传导的滞后效应。结果表明:饲养成本向下游传导存在显著的滞后性,饲养成本变化1%,滞后5和6期,分别引起原料奶价格变动0.086%、0.111%。奶业价值链体系自身难以实现价格的无阻滞传导以及形成合理的利益分配机制,政府和行业必须推动原料奶生产提高组织化程度,构建价格预警平台,完善产业链各方利益关系。     

Fish functional diversity responses following flood pulses in the upper Paraná River floodplain

Flood pulses are the main force driving the dynamics of aquatic communities in floodplains. The responses of communities to environmental changes following flood pulses usually demand a time lag to appear and reach the climax. We assembled a data set of 16 years of fish samplings to assess the relationship between water level and four functional diversity measures, in the upper Paraná River floodplain. Specifically, we approached four aspects of each relationship between water level and functional diversity: nature (positive or negative), sensitivity (response intensity), responsiveness (response delay) and extent (response duration). The nature of the relationship between water level and functional diversity was positive in all cases. Functional richness (FRic) responded right after flood pulses, although with shorter extent. Abundance‐dependent functional measures (evenness—FEve; divergence—FDiv; and Rao's quadratic entropy—Rao's Q) presented delayed responses, reaching peaks more than 1.5 years after flood pulses. Significant effects of floods on fish functional diversity were observed for more than 3 years, although the highest functional diversity was observed with 1.8 years, on average. More importantly, flood pulses had no longer significant effects on functional diversity after 4 years. Regarding conservation strategies in regulated systems, flood events should occur every 2 or 3 years, with adequate timing (October‐November), intensity (up to 450 cm) and duration (at least 50 uninterrupted days). Intervals longer than 3 years or inadequate timing, intensity and duration could dramatically decrease functional diversity and compromise ecosystem services.     

基于纵向传导的蔬菜批零价格关系研究——以北京市果类蔬菜为例

从蔬菜产业的纵向看,批发和零售是两个重要环节,蔬菜批发价格和零售价格的走势以及它们之间的关系是各界关注的焦点。本文以北京市场为例,以番茄和黄瓜两种果类蔬菜的按日批零价格为对象,运用有限分布滞后模型和误差修正模型进行实证分析,研究蔬菜批零价格间的传导关系,并在此基础上揭示蔬菜批发价格在蔬菜价格形成中的作用。研究发现:蔬菜批零价格走势基本一致,相关系数很高;批零价格间存在批发价格向零售价格单向传导的因果关系;批零价格的传导是顺畅的,但不同种蔬菜传导的时间效应有所不同;批发价格在蔬菜价格形成中占据主导作用,当蔬菜价格受到冲击时,若零售价格过高则其会向着批发价格下调,若批发价格过高则零售价格会随之走高。     

Ratio control strategy for solving system response lag of continuously variable transmission system

Generally, there’s a system response lag in the continuously variable transmission system, and this leads to a deviation of the engine work point from the optimal operation line of the minimum fuel consumption. To reduce the influence of system response lag, a new CVT ratio control strategy with the system response lag parameter during computing target ratio is proposed. Simulation results indicate that the proposed control strategy can overcome the effect of system response lag, so as to keep the engine work point on the optimal operation line effectively. A comparison of fuel consumption is made between the proposed control strategy and the traditional one by simulation, and results indicate that the proposed control strategy reduces the fuel consumption of the system by 2.85％.     

THE INDUSTRIAL ORGANIZATIONS AND THE L-S-BUSINESS STRATEGIES

This papar presents an evolution model in business behaviors-the L-S Business Strategies,gives some examples and predictions which support these strategies,and analyzes the relationship between the industrial organizations in China and the L-S Business strategies.     

Denitrification potential of intermittently saturated floodplain soils from a subtropical perennial stream and an ephemeral tributary

Denitrification has the potential to remove excess nitrogen from groundwater passing through riparian buffers, thus improving water quality downstream. In regions with markedly seasonal precipitation, transient stream flow events may be important in saturating adjacent floodplain soils and intermittently providing the anaerobic conditions necessary for denitrification to occur. In two experiments we characterised the denitrification potential of soils from two contrasting floodplains that experience intermittent saturation. We quantified under controlled laboratory conditions: 1) potential rates of denitrification in these soils with depth and over time, for a typical period of saturation; and 2) the influences on rates of nitrate and organic carbon. Treatments differed between experiments, but in each case soil-water slurries were incubated anaerobically with differing amendments of organic carbon and nitrate; denitrification rates were measured at selected time intervals by the acetylene-block technique; and slurry filtrates were analysed for various chemical constituents. In the first experiment (ephemeral tributary), denitrification was evident in soils from both depths (0-0.3 m; 0.3-1.1 m) within hours of saturation. Before Day 2, mean denitrification rates at each depth were generally comparable, irrespective of added substrates; mean rates (Days 0 and 1) were 5.2 ± 0.3 mg N kg dry soil⁻¹ day⁻¹ (0-0.3 m) and 1.6 ± 0.2 mg N kg dry soil⁻¹ day⁻¹ (0.3-1.1 m). Rates generally peaked on Days 2 or 3. The availability of labile organic carbon was a major constraint on denitrification in these soils. Acetate addition greatly increased rates, reaching a maximum in ephemeral floodplain soils of 17.4 ± 1.8 mg N kg dry soil⁻¹ day⁻¹ on Day 2: in one deep-soil treatment (low nitrate) this overcame differences in rates observed with depth when acetate was not added, although the rate increase in the other deep-soil treatment (high nitrate) was significantly less (P ≤ 0.01). Without acetate, peak denitrification rates in this experiment were 6.9 ± 0.4 and 2.8 ± 0.2 mg N kg dry soil⁻¹ day⁻¹ in surface and deep soils, respectively. Differences in rates were observed with depth on all occasions, despite similar initial concentrations of dissolved organic carbon (DOC) at both depths. Levels of substrate addition in the second experiment (perennial stream) more closely reflected natural conditions at the site. Mean denitrification rates were consistently much higher in surface soil (P ≤ 0.001), while the source of water used in the slurries (surface water or groundwater from the site) had little effect on rates at any depth. Mean rates when all treatments retained nitrate were: 4.5 ± 0.3 mg N kg dry soil⁻¹ day⁻¹ (0-0.3 m depth); 0.8 ± 0.3 mg N kg dry soil⁻¹ day⁻¹ (0.3-1.0 m); and 0.6 ± 0.1 mg N kg dry soil⁻¹ day⁻¹ (1.8-3.5 m). For comparable treatments and soil depths, denitrification potentials at both sites were similar, apart from higher initial rates in the ephemeral floodplain soils, probably associated with their higher DOC content and possibly also their history of more frequent saturation. The rapid onset of denitrification and the rates measured in these soils suggest there may be considerable potential for nitrate removal from groundwater in these floodplain environments during relatively short periods of saturation.     

试论我国农业资源的配置机制及其优化

从农业资源的涵义和特征入手，分析了我国农业资源配置存在的问题和原因，论述了建立农业资源配置机制的重要性。     

变量喷雾装置响应性能的试验研究

采用GPS定位和雷达测速技术,构建了一套变量喷雾装置,并开发设计出其相应的软件控制系统。在试验研究过程中,通过实时监测喷雾参数来描述喷雾过程的动态特性,以此测定该变量喷雾控制系统的响应能力,并为喷雾处方图与变量喷雾装置的精度匹配提供可靠依据。试验结果表明,变量喷雾装置的定量喷雾误差控制在4.65%以内前提之下,响应延时会影响到变量喷雾作业的均匀性,选择合适的行进速度以及设置一定的预留时间能在一定程度上减少这种影响。     

单跨简支渡槽剪力滞效应分析

应用ANSYS程序建立了几种不同渡槽槽体结构的有限元模型,数值结果表明,采用板壳单元能很好地模拟槽体的剪力滞效应,计算精度满足工程要求。对单跨简支单箱、多箱槽体的剪力滞效应进行了较详细的数值研究,得到了槽体底板与上部翼缘的纵向正应力分布规律,研究了渡槽的截面形式、宽跨比等参数对渡槽剪力滞效应的影响。研究结果对渡槽结构设计具有参考价值。