关于农业工程中阶梯连续梁的刚度分析

为了便于计算机对于农业工程中阶梯梁（轴）进行分析计算,本文首先根据阶梯悬臂梁挠曲线的曲率,与假定直径为ｃ的等截面梁的挠曲线的曲率完全相同的条件,对阶梯悬臂梁进行等效变换,从而达到用等截面梁代替阶梯梁的目的。其次利用简支梁挠度,相对挠度及支座截面转角的关系,推导并建立阶梯连续梁的三弯矩等效方程及其挠曲线等效方程。利用上述方程,具有分析程序化、计算公式化的特点,方程可靠实用。     

Relationship between cultivar height and severity of Fusarium ear blight in wheat

A significant negative relationship between tiller height and resistance to Fusarium ear blight (FEB), following inoculation, was observed in 17 cultivars of winter wheat in the 1995/96 growing season. Tall cultivars such as Kraka and Spark showed fewer symptoms of FEB (6 and 4%) than the shorter cultivars Brigadier and Virtue (35 and 51%). To determine if this relationship was caused by a genetic association or an effect of the microclimate, height and disease were measured in segregating populations derived from tall × short cultivars and humidity was measured in near-isogenic lines with and without the Rht1 and Rht2 dwarfing genes. Among random F₃ populations there was a clear tendency for tall strawed lines to show less severe disease symptoms than shorter strawed lines following inoculation. The effect of the individual dwarfing genes Rht1 and Rht2 on the severity of FEB was also studied in an inoculation trial using a number of near-isogenic lines of Maris Huntsman and Maris Widgeon. Within isogenic lines of Maris Huntsman, there was a clear tendency for tall straw to be associated with fewer symptoms, but this was not apparent within lines of Maris Widgeon. Monitoring relative humidity at ear height in a short and tall isogenic line of Maris Huntsman revealed no significant differences between these genotypes from GS 65 to GS 85, suggesting that microclimate cannot explain differences in severity of FEB between these lines. It is suggested that there are independent genes affecting the severity of FEB that may allow plant breeders to select resistant cultivars of any height.     

黄土丘陵区白羊草群落冠层结构和多样性特征对氮磷添加的响应

为探究氮磷添加对黄土丘陵区典型草地群落冠层结构和多样性特征的影响,本研究以白羊草(Bothriochloa ischaemum)群落为研究对象,采用裂区试验设计,主区设4个氮(N)处理(0,25,50,100kg·hm^-2·a^-1),副区设4个磷(P₂O₅)处理(0,20,40,80kg·hm^-2·a^-1),测定了群落高度、叶面积指数、光合有效辐射百分比、光不对称性、地上生物量和Shannon-Wiener指数。结果表明：氮添加显著增加了群落高度和叶面积指数;氮磷添加显著增加了光合有效辐射百分比、光不对称性和地上生物量,降低了Shannon-Wiener指数。单施氮和磷分别增加了矮多年生禾本科草和多年生豆科草生物量贡献比;50和100kg·hm^-2·a^-1的氮添加水平与磷配施增加了高多年生杂类草生物量贡献比。结构方程模型表明,氮磷添加下光不对称性的增加对物种多样性的影响不显著。综上所述,黄土丘陵区在采取施肥措施促进退化草地恢复过程中,要权衡地上生物量提高和物种多样性下降的关系。     

多形林分生长模型研究

为了减少自变量,避免出现因子间相互预测,精确描述样本数据,有效减小系统误差,文章以一平浪林场为例,介绍了只选择年龄单因子为自变量构成建云南松多形树高生长模型的方法.该生长模型可用于云南松的生长预估及计算机仿真.     

基于能量法的B样条农机工作部件曲线光顺研究

在农机工作部件曲面设计中关键曲线的好坏直接影响整个曲面的质量，因此对关键曲线的光顺成为其曲面造型的重点。基于能量的曲线光顺以应变能最小为光顺准则对数据点进行光顺，而当数据点较多时，传统能量法的存储量较大，计算速度较慢。该文对基于B样条的农机工作部件曲面关键曲线的光顺处理的传统能量法进行了改进，利用B样条曲线的性质直接对目标函数的线性方程组进行求解，大大地减少了数据的存储量，提高了计算速度。其基本原理是：用光顺后的农机工作部件曲面的特殊曲线，对整张曲面进行反求，得到新的曲面控制顶点，并依据新的控制顶点得到新的曲面，以达到对农机工作部件曲面光顺的目的。文中以农机工作部件中的犁体曲面为对象进行了算例研究，研究结果表明，利用该文的方法可以使光顺前后犁体曲面的等高斯曲率线图的平滑状况明显好转，新曲面的光顺状况比旧曲面得到改善。     

长江支流嘉陵江水沙变化趋势及其驱动因素分析

近20年来,嘉陵江流域输沙量明显减少,其变化将对长江三峡库区水沙运动以及泥沙冲淤变化等产生重要影响。根据嘉陵江控制水文站实测水沙资料,采用定量分析的方法,分析了嘉陵江流域年降水量、河道径流量和输沙量的变化趋势及其发生显著变化的临界年份。结果表明:嘉陵江流域的径流量和输沙量都有显著的减少趋势;年降水量没有表现出明显的变化趋势。年径流量及输沙量发生显著趋势性减小的临界年份分别为1993年和1984年。同时,利用历时曲线和双累积曲线两种方法,量化了嘉陵江流域径流量与输沙量的减少量,定量分析了降水和人类活动对嘉陵江径流及输沙量的影响,进一步探讨了嘉陵江流域水沙变化的驱动因素。     

规模化养殖罗曼粉商品蛋鸡产蛋率和累计产蛋数曲线拟合分析

[目的]探索规模化养殖罗曼粉商品蛋鸡的产蛋特点和规律。[方法]选择9万羽罗曼粉蛋鸡,统计18~85周龄的产蛋率和累计产蛋数,采用分室模型、杨宁模型、伍德模型对产蛋率进行拟合分析,采用Bertalanffy、Gompertz、Logistic模型对累计产蛋数进行拟合分析,并与实际观测值进行比较。[结果]分室模型、杨宁模型和伍德模型的产蛋率曲线拟合度分别为0.935、0.997和0.450,杨宁模型的预测值与实测值最接近;Gompertz模型拟合累计产蛋数曲线效果最好,拟合度为0.996,预测拐点周龄为47.38周,拐点产蛋数为166.36枚,极限产蛋数为365.12枚,比实际低11.64枚。[结论]杨宁模型和Gompertz模型分别对规模化养殖罗曼粉商品蛋鸡产蛋率和累计产蛋数的拟合效果最佳,适用于评估和预测规模化养殖条件下罗曼粉商品蛋鸡的产蛋性能。     

日光温室骨架合理曲线的一种数值化表达方法

日光温室骨架曲线形式直接影响前屋面采光和力学承载性能,为研究设计出合理骨架曲线形式,基于现有骨架的设计特点、应用情况等,对日光温室骨架合理曲线的数值化构建和表达方法进行研究。当屋脊点位置、最低作业高度、前屋面屋脊处的坡度以及底脚部位的坡度确定时,该方法可直接给出骨架曲线的数值化表达式,通过规范要求可筛选出合格的骨架曲线形式。提出了双抛物线骨架曲线,选取北京、沈阳、银川3个城市,对抛物线、椭圆面、双抛物线、幂函数、双圆5种骨架曲线形式的日光温室进行采光性能模拟。结果表明：1）5种骨架曲线形式下冬至日日累计太阳辐射量之间的最大差值为6.31%,双抛物线作为骨架曲线形式在采光性能上是可靠的;2）当前屋面水平投影为6~14 m、最低作业高度为1~1.8 m时,均可构造出既符合规范要求又符合工程实际的双抛物线曲线。     

基于无人机影像的冬小麦株高提取与LAI估测模型构建

株高和叶面积指数（Leaf Area Index, LAI）反映着作物的生长发育状况。为了探究基于无人机可见光遥感提取冬小麦株高的可靠性,以及利用株高和可见光植被指数估算LAI的精度,本文获取了拔节期、抽穗期、灌浆期的无人机影像,提取了冬小麦株高与可见光植被指数,使用逐步回归、偏最小二乘、随机森林、人工神经网络四种方法建立LAI估测模型,并对株高提取及LAI估测情况进行精度评价。结果显示：（1）株高提取值Hc与实测值Hd高度拟合（R = 0.894,RMSE = 6.695,NRMSE = 9.63%）,株高提取效果好;（2）与仅用可见光植被指数相比,基于株高与可见光植被指数构建的LAI估测模型精度更高,且随机森林为最优建模方法,当其决策树个数为50时模型估测效果最好（R=0.809,RMSE = 0.497,NRMSE = 13.85% ,RPD = 2.336）。利用无人机可见光遥感方法,高效、准确、无损地实现冬小麦株高及LAI提取估测可行性较高,该研究结果可为农情遥感监测提供参考。     

Spatial heterogeneity of plant species on the windward slope of active sand dunes in a semi-arid region of China

Species richness and abundance are two important species diversity variables that have attracted particular attention because of their significance in determining present and future species composition conditions.This paper aims to explain the qualitative and quantitative relationships between species diversity pattern and grain size(i.e.size of the sampling unit),and species diversity pattern and sampling area,and to analyze species diversity variability on active sand dunes in the Horqin Sandy Land,northeastern Inner Mongolia,China.A 50 m×50 m sampling plot was selected on the windward slope,where the dominant species was annual herb Agriophyllum squarrosum.Species composition and abundance at five grain sizes were recorded,and the species-area curves were produced for thirteen grain sizes.The range of values for species abundance tended to increase with increasing grain size in the study area,whereas,generally,species richness did not follow this rule because of poor species richness on the windward slope of active sand dunes.However,the homogeneity of species richness increased significantly.With the increase in sampling area,species abundance increased linearly,but richness increased logarithmically.Furthermore,variograms showed that species diversity on the windward slope of active sand dunes was weakly anisotropic and the distribution pattern was random,according to the Moran Coefficient.The results also showed that species richness was low,with a random distribution pattern.This conflicts with the results of previous studies that showed spatial aggregation in lower richness in a sampling area within a community and inferred that the physical processes play a more important role in species diversity than distribution pattern on active sand dunes.Further research into different diversity patterns and mechanisms between active sand dunes and interdune lowlands should be conducted to better understand biodiversity conservation in sand dune fields.