黄土低山丘陵及坨甸草原区风蚀规律的研究

本文通过对黄土低山丘陵及坨甸草原区248个风蚀图斑资料的分析,运用线性模型理论,对此地区的风蚀规律进行了研究。获得了下垫面各因素与风蚀量关系的数学模型。找出了影响风蚀的主导因素,并系统阐述了植被覆盖度和土地利用类型对风蚀量大小的影响,且与水蚀规律进行了比较分析。     

Spatio-temporal modelling of broad scale heterogeneity in soil moisture content: a basis for an ecologically meaningful classification of soil landscapes

We describe the classification of landscapes characterised bymineral soil using a model that calculates soil moisture availability on amonthly basis. Scotland is used as a case study area. The model uses potentialsoil moisture deficit, estimated using broad scale (40 × 40 km)climate patterns, in conjunction with meteorological station measurements toobtain finer scale values of climatic soil moisture deficit. Point estimates ofsoil available water are obtained for soil characteristics using appropriatepedotransfer functions, and geostatistical techniques are used to upscale theresults and interpolate to a 1-km grid. Known heterogeneityin soil physical characteristics is used to provide local corrections to thepotential soil moisture deficit, estimated using the climatic variables above.Temporal profiles of monthly water content are modelled for each1-km location and classified into six classes usingunsupervised cluster analysis. The spatial distribution of these classesreflects regional variations in the availability of moisture and energy, onwhich finer-grained topographic patterns are superimposed. In the case study,the broad scale spatial heterogeneity of heathlands and grasslands on mineralsoils in Scotland is shown to be strongly related to the soil moistureclassification. The results can be used in studies investigating the patternsofdistribution of communities at the landscape and regional scale.This revised version was published online in May 2005 with corrections to the Cover Date.     

基于MapGIS和植被数量指标的啮齿动物群落模拟专家系统的设计与实现

选择鼠害频发的阿拉善荒漠区分布面积较大的红砂+泡泡刺生境、红砂+杂类草生境和白刺生境,以夹日法记录三种生境中啮齿动物种群相对数量,利用啮齿动物种群相对数量与荒漠区灌木和草本植物之间的依存关系建立专家模拟系统,分析三种生境的主要害鼠子午沙鼠、三趾跳鼠和小毛足鼠种群相对数量与植物群落因子间的动态关系,并以MapGIS为地理信息平台,借助VB程序语言设计工具,设计阿拉善荒漠区啮齿动物群落模拟专家系统,探索植物群落与啮齿动物群落的反馈动态变化,实现利用植物群落指标预测啮齿动物群落组分及其相对数量变化的目标,为鼠害防控提供依据。     

大型复杂机械节点导入建模及有限元分析

针对一般有限元软件在大型复杂机构建模和划分网格方面的局限性,提出了节点导入有限元建模法。采用三维建模软件建立节点布局图,并提取源坐标数据,结合有限元分析软件建立有限元模型,同时完成网格划分,并成功地将此建模方法应用于大型振动筛的建模与分析。结果表明,这种建模方法使计算和存储大为简便,可为设计人员提供设计参考。     

模糊加权马尔可夫链模型及其应用

在传统的用马尔可夫链模型预测的方法基础上,建立了模糊加权马尔可夫链模型。以某地区梅雨期长度的预测作为实例,介绍了使用这种模型的方法与步骤,提出了具有模糊状态的马尔可夫链的转移概率计算公式,并采取以规范化的各阶自相关系数为权重,用加权的马尔可夫模型预测的结果与实际梅雨期长度相吻合。     

基于时空变异的旱地土壤有机碳高效采样策略研究

土壤有机碳(SOC)空间分布具有时序差异性,明确样点数量对不同时期SOC预测精度影响是制定高效采样策略的基础.选取3.93×104 km2江苏北部旱地作为案例区,运用普通克里金插值方法,分析样点数量对不同时期SOC空间预测精度的影响.结果表明:不同数量样点数据集下1980年苏北旱地SOC预测值与实测值的相关系数r和均方...     

描述农村劳动力转移状况的分室模型

为了分析农业化发展速度与农村劳动力转移速度之间的关系，本文肖试性地把史密斯提出的生态系统分室模型用于描述第一，第二，第三产业劳动力数量相互转移物动态变化中，提出了劳动力结构分室模型，为探讨农业机械化客观发展规律提供了构模思路。     

延边地区乡镇企业集群发展模式的探讨

在我国农村,要贯彻科学发展观,全面建设小康社会,进一步解决农民的就业和增收问题,解决农业的发展和农村稳定的问题,推进农村工业化、城镇化和现代化,都离不开乡镇企业的发展.本文从企业集群发展模式的角度,分析和阐述了乡镇企业发展规律,进而探讨了延边地区乡镇企业发展模式.这对于加快延边地区经济建设,解决延边地区“三农“问题,全面建设新延边,将起到积极的推进作用.     

春小麦高产叶龄模式的研究

本研究根据春小麦的叶龄进程，对水、肥、密等影响产量的主要因素进行优化组合，提出了旨在提高春小麦的产量及获得最佳效益的高产模式，为指导我国北方春小麦的生产提供了科学依据。     

Performance of CERES-Rice and CERES-Wheat models in rice–wheat systems: A review

Rice–wheat (RW) systems are critical to food security and livelihoods of rural and urban poor in south Asia and China, and to regional economies in southeast Australia. The sustainability of RW systems in south Asia is, however, threatened by yield stagnation or decline, and declining partial factor productivity, soil organic C and water availability. Crop models potentially offer a means to readily explore management options to increase yield, and to determine trade-off between yield, resource-use efficiency and environmental outcomes. This paper reviews the performance of CERES-Rice and CERES-Wheat in Asia and Australia in relation to their potential application towards increasing resource use efficiency and yield of RW systems.

The performance of the models was evaluated using simulated and observed data on anthesis and maturity dates, in-season LAI and growth, final grain yield and its components, and soil water and N balances from published studies across Asia and Australia, and then by computing the statistical parameters for the major characters. Over the four data sets examined for anthesis and six for maturity dates, CERES-Rice predicted those dates fairly well (normalised RMSE = 4–5%; D-index = 0.94–0.95), but over the 11 sets for grain and 4 for biomass yield, the predictions were more variable (normalised RMSE = 23% for both; D-index 0.90 and 0.76, for grain and biomass, respectively). Model performance was poorer under conditions of low N, water deficit, and low temperatures during the reproductive stages. Over the three data sets examined, CERES-Wheat predicted the anthesis and maturity dates quite well (normalised RMSE = 4–5%; D-index = 0.94–0.99), and over eight sets for grain and two sets for biomass yield the model predicted them also reasonably well (RMSE = 13–16%; D-index = 0.86–0.97). Only one study evaluated the DSSAT RW sequence model with fairly satisfactory predictions of rice and wheat yields over 20 years with adequate N, but not the long-term change in soil organic C and N. Predictions of in-season LAI and crop growth, and soil and water processes were quite limited to investigate the robustness of model processes.

Application of models to evaluate options to increase water and N use efficiency requires the ability to perform well at the margin where deficit stress begins. While both models generally perform satisfactorily under water and N non-limiting conditions, the little evidence available suggests that they do not perform well under resource-limiting situations. We recommend that the models’ key processes under the water and N limiting conditions be further evaluated urgently. The DSSAT sequence model also needs to be further evaluated against observations for a range of locations and management using data from long-term experiments in RW systems.