2000年我国粮食战略目标预测及可行性分析与对策

本文针对我国社会主义市场经济的新形势及农业生产中的新问题,用系统工程的方法对我国在本世纪末粮食发展的战略目标进行了互验性预测,同时作了一定的可行性分析,提出了相应的对策。     

Modelling optimal crop sequences using network flows

In recent years there has been an increased focus on sustainable farming systems. This has led to an increase in the use of farm models built to assess the environmental impact from farming. In whole-farm models including crop production it is important to consider the rotation of crops, since this has a major impact on the consequences of the crop production.     

Ammonia abatement strategies in livestock production: A case study of a poultry installation

This study uses a linear programming approach to compare the potential effectiveness of uniform rules (under the Integrated Pollution Prevention and Control Directive) and a landscape-scale (a scale that includes different land-uses) based policy for reducing ammonia (NH₃) emissions and their related impacts from an operating case-study poultry installation. The model incorporates a variety of potential NH₃ abatement techniques. It also incorporates the first application of a spatial model of the diffusion of environmental impacts from NH₃ emissions. This models N deposition at a nearby nature reserve.     

假眼小绿叶蝉种群活动高峰始盛期预测模型的研究

通过建立线性回归-时间序刊AR(p)组分预测模型,提出利用前一年气象因子资料,预测翌年茶园主要害虫假眼小绿叶蝉(Empoasca vitis)活动高峰始盛期的方法,从而提前了虫灾预测的发布时间。并将该方法应用于福建省福安茶区,对防治害虫、减少农药用量、优化茶园生态有较好效果。     

水平不固定的试验结果的统计分析Ⅰ.一个因素的水平不固定时的分析

农业试验中某些数量因素的水平，常常难以控制到完全一致，而表现非固定变异。在结果分析时，如果忽略这种变异，对试验结果作方差分析，不仅使参数估计的方差增大，而且无法正确测验估计值的显著性。如果应用回归方法，可将因素的效应和互作定义相应的回归系数，参数的估计和假设测验均可得到保证。计算机模拟结果表明，当一     

用波形对线性分组码编码和译码的研究

为了在通讯时能安全和可靠地进行数据的发送和接收，应该对数据进行编码和译码，论文用Verylog HDL硬件描述语言对线性分组码的编码和译码进行了波形仿真研究，并且得到了几点结论。     

切梗丝厚度对梗丝质量影响的研究

[目的]研究切梗丝厚度对梗丝质量的影响.[方法]通过设计不同的切梗丝厚度,采用回归分析的方法研究切梗丝厚度对梗丝填充值、梗丝结构和烟梗损耗量的影响.[结果]试验表明,切梗丝厚度与梗丝填充值、整丝率、碎丝率、膨化后烟沫量、梗签量呈明显的线性关系;当切梗丝厚度为0.17 rmm时,梗丝加工质量较好.[结论]研究可为卷烟工业企业在降耗、降焦、提质和增效方面提供参考依据.     

贵州乌蒙烟区烤烟生育期气候因子变化特点分析

利用贵州乌蒙烟区1961~2000年的气温、日照时数、降雨量等主要气候因子数据,分析了烤烟生育期气候指标的变化特点,结果表明:乌蒙烟区光照充足、降雨丰富、气温相对偏低,但气温年际间相对稳定,光照和降雨量在不同年份间存在较大波动。线性趋势分析表明:旺长期(6月)气温呈现较显著的上升趋势,成熟初期(7月)气温显著下降;烤烟生育期每月日照时数呈减少趋势,其中成熟初期(7月)的日照时数减少趋势显著;降雨量在5月、6月呈减少趋势,7月、8月呈增加趋势,生育期每月降雨量的线性变化趋势未达到显著水平。突变检验表明:40年来该烟区烤烟生育期气温在1998年发生了明显突变,日照时数在1985年发生了明显突变,降雨量未发生明显突变。     

Generating crop sequences in land-use models using maximum entropy and Markov chains

Farm management models often produce average crop shares over a number of years, whereas models from the natural sciences often require inputs of sequences of crops grown on a specific field over several years. In interdisciplinary modelling, this difference can be a relevant obstacle. To bridge this gap, an approach is presented that allows disaggregating results from farm management models to the level required by many natural science models. The approach presented includes two methodological innovations: first, minimum cross entropy is used to ensure a unique solution when modelling a linear programming model at the field level, even when objective and constraint coefficients are identical for different fields. Second, the use of a calibrated Markov chain approach allows the creation of land-use sequences that are closer to the linear programming model’s results than an unconditional stochastic simulation would be. The calibrated Markov chain makes use of a prior matrix of transition probabilities that can be empirically derived. Both simulations and analytical calculations with case study data show that the variances of the Markov chain approach are systematically lower than those yielded by a simple stochastic simulation approach. The approach introduced in this paper can improve the coupling of farm-level economic models with natural science models at the field level.     

Decoupling of air flow above and in plant canopies and gravity waves affect micrometeorological estimates of net scalar exchange

Turbulence within open canopies is shown to undergo a dramatic change in character during the transition from convective to stable conditions. In convective conditions the flow within the canopy is coupled through turbulent exchange to the flow aloft. As the transition proceeds, the within- and above-canopy flows decouple and vertically coherent waves form within the canopy. The intensity of above-canopy turbulence is not a good indicator of flow decoupling. Within-canopy waves can lead to large random error in the measurement of the change of storage and the advection terms in the mass balance equation. More importantly, errors associated with sampling over incomplete wave cycles will inevitably be combined with true advective flux divergences at non-ideal sites. Quantitative estimates of likely errors on storage of heat and CO₂ within the canopy are presented.