大比例尺区域土壤养分空间变异定量分析

应用地质统计学的方法对北京昌平县南邵乡２６４０ｈｍ＾２,土地上的土壤有机质,全氮,有效氮,有效磷及有效钾的空间分布特征,进行了定量分析,并绘出它们的等值线图,对于研究和评价大比例尺区域土壤养分空间变异规律和动态变化有一定的理论和实践意义。     

海南海花岛软基处理工程中真空预压法的改进与机理分析

疏浚淤泥这种超软土地基目前主要采用排水固结法进行加固,然而,工程实践发现,淤堵是一个重要的问题,新型防淤堵材料和施工工艺是研究的热点。依托恒大海南海花岛真空预压处理工程,引入一种应用于超软土地基处理的新型防淤堵真空预压法。该方法是直排式真空预压方法的进一步改进,将防淤堵排水板取代传统排水板,在连接方式上,将无孔钢丝软管取代了水平波纹管,也将传统的包扎捆绑改进成了三通密封接头,枪钉固定。结合施工动态监测和加固后检测,表明了该方法的加固效果和实用性。在此基础上,结合已有的室内模型试验研究,阐述其抽真空过程中在排水板附近防淤堵的原理和改善机制。     

拖拉机液压悬挂装置的建模及仿真分析

分析了拖拉机液压悬挂装置的组成及工作原理,建立了系统的数学模型;并应用MATLAB软件对系统进行了稳定性分析和仿真,效果良好.建模仿真技术是研究机组系统整体的最佳设计(匹配)、最佳使用和提高机组效益的有效途径,为解决拖拉机机组系统分析与综合有效途径提供了参考依据.     

基于UG平台的直齿圆锥齿轮的三维精确建模

直齿圆锥齿轮是现代机械中应用最为广泛的一种传动机构。它可以用来传递空间两轴之间的运动和动力，而且传动准确、平稳、机械效率高。为此，介绍了一个在UG平台上建立直齿圆锥齿轮三维模型的新方法，该方法符合《机械原理》一书对直齿圆锥齿轮齿廓线的定义．实现了精确建模的目的。最后通过一个简单的实例。进一步阐明了该方法的实现过程。     

奶牛饲喂装置中螺旋输送器的设计及三维造型

螺旋输送器用于物料输送过程的设计在设计资料中较为常见,但它应用于奶牛饲喂装置时,从设计角度讲有许多特殊性。螺旋输送器的主要尺寸及动力参数设计得是否合理,将直接影响到物料的计量精度。为此,对奶牛饲喂装置中螺旋输送器的设计做了较为详尽的论述,并对其三维造型过程进行了简要的论述。     

移动式绿篱修剪机设计

针对绿篱修剪机的发展现状,设计开发了一种小型自走式绿篱修剪机,包括动力系统设计和行走装置设计、修剪装置设计,并且利用三维建模软件建立了移动式绿篱修剪机的三维模型。所设计的移动式绿篱修剪机在所查阅的文献中尚未发现有相同机型的报道,属原创型产品。相比现在小型绿篱修剪机以手持式为主的状况,该绿篱修剪机能够有效降低绿篱修剪的劳动强度,提高修剪质量,有比较广阔的市场前景。     

The use of lysimeter data for the test of two soil–water balance models: A case study

Two soil–water balance models were tested by a comparison of simulated with measured daily rates of actual evapotranspiration, soil water storage, groundwater recharge, and capillary rise. These rates were obtained from twelve weighable lysimeters with three different soils and two different lower boundary conditions for the time period from January 1, 1996 to December 31, 1998. In that period, grass vegetation was grown on all lysimeters. These lysimeters are located in Berlin‐Dahlem, Germany. One model calculated the soil water balance using the Richards equation. The other one used a capacitance approach. Both models used the same modified Penman formula for the estimation of potential evapotranspiration and the same simple empirical vegetation model for the calculation of transpiration, interception, and evaporation. The comparisons of simulated with measured model outputs were analyzed using the modeling‐efficiency index IA and the root mean squared error RMSE. At some lysimeters, the uncalibrated application of both models led to an underestimation of cumulative and annual rates of groundwater recharge and capillary rise, despite a good simulation quality in terms of IA and RMSE. A calibration of soil‐hydraulic and vegetation parameters such as maximum rooting depth resulted in a better fit between simulated and observed cumulative and annual rates of groundwater recharge and capillary rise, but in some cases also decreased the simulation quality of both models in terms of IA and RMSE. The results of this calibration indicated that, in addition to a precise determination of the soil water‐retention functions, vegetation parameters such as rooting depth should also be observed. Without such information, the rooting depth is a calibration parameter. However, in some cases, the uncalibrated application of both models also led to an acceptable fit between measured and simulated model outputs.     

海南岛农用地土壤重金属含量的空间分布

利用地理信息系统(GIS)及地统计学方法,对海南岛农用地中的Hg、Cd、Cr、Pb和As 5种重金属的污染状况进行空间变异性分析.结果表明,5种重金属的平均含量均未超过国家环境质量2级标准(GB15618-1995);Hg、Cd、Cr和Pb含量的变异函数理论模型符合指数模型,Hg和Pb空间相关程度弱,显示出其含量受成土因素的影响较大;As含量的变异函数理论模型符合高斯模型;Cd、Cr和As空间相关程度中等,显示出其含量受外源污染的影响较大;运用Kriging插值方法得出海南岛该5种土壤重金属的插值梯度分布图,海南岛外源性重金属污染在工业区最为严重.     

Spatial pattern and heterogeneity of soil properties in sand dunes under grazing and restoration in Horqin Sandy Land, Northern China

Applying a combination of classical and geostatistical methods, we identified soil properties and their spatial variation in a 5-year grazed sand dune (GSD5) and a 20-year recovered sand dune (RSD20) in Horqin Sandy Land, northern China. The paper assesses the effect of grazing, topography and vegetation restoration on spatial heterogeneity of soil properties. The results showed that soil organic carbon, total nitrogen, very fine sand (0.1–0.05 mm) content and their coefficients of variation were lower in GSD5 than in RSD20, while soil water contents (0–20 cm and 20–40 cm depths) were higher in GSD5 than in RSD20. Geostatistical analysis revealed that the spatial structured variance accounted for the largest proportion of total sample variance in soil properties at the measured scale under grazing and restoration. The spatial autocorrelation ranges were 66.30 m for soil organic carbon and 50.80 m for total nitrogen in GSD5 less than those in RSD20 (70.00 m and 76.10 m, respectively), while the spatial autocorrelation ranges of soil particle size fractions and soil water contents in RSD20 were less than those in GSD5. Kriging-interpolated maps also showed that the heterogeneity of soil organic carbon and total nitrogen and their degree of patch fragmentation were higher in GSD5 than in RSD20. These results suggested that continuous grazing resulted in an increase in spatial variability of soil nutrient and a decrease in spatial variability of soil particle size fractions and soil water content. Soil organic carbon and total nitrogen of sand dunes are associated closely with soil particle size fractions, relative height of sampling site and vegetation cover. Spatial patterns of soil properties are most strongly related to grazing, topography and plant-induced heterogeneity in sand dune ecosystems prone to wind erosion.     

高等农林院校数学建模教育研究与实践

结合1994～1998年甘肃农业大学大学生数学协会数学建模讨论班的实践经验,提出了：高等农林院校数学素质教育内容应包括数学基础教育、数学建模教育、数学建模实践3方面;数学建模教育的形式是“讨论班”;数学建模能力巩固、提高的方式是数学建模竞赛;要培养真正合格的素质型建设人才必须在大学期间参加适当的数学建模实践。并指出只有更多的专家、教授、学者参与到数学素质教育中来,使专业与数学教育真正相结合,数学建模教育乃至数学素质教育的口的才能真正实现。