八轮四摆臂无人机动平台越障性能分析与试验

针对南方山区丘陵地带地形复杂、传统农田运输车辆通过性不足的问题,提出并设计了一种具有仿生液压驱动摆臂机构的八轮无人机动平台,其车体姿态可通过四摆臂协同动作进行调节,以适应不同形式地面障碍。越障性能是制约平台通过性的根本因素,建立了无人平台姿态规划模型和关键越障过程动力学模型,得到无人平台在典型垂直障碍的越障性能。为验证理论分析,在ADAMS建立了二次开发仿真平台,并进行了样机动力性试验。研究表明,八轮四摆臂无人机动平台可攀爬高度为轮胎直径1. 13倍的垂直障碍,具有良好的复杂地面环境通过能力,可满足丘陵地带农用运输车辆在复杂农田地形的行走需求。     

低山丘陵区景观类型与地形因子耦合关系研究——以伏牛山余脉区为例

选择伏牛山局部低山丘陵区为对象,运用ArcGIS的空间分析功能和数理统计分析方法探讨8种类型景观在高程、坡度、坡向带上的分布特征、分布指数与显著性。结果表明,高程因子与林地景观呈显著正相关,与工矿用地景观、自然保留地景观呈显著负相关;坡度因子与基本农田景观呈极显著负相关,与耕地景观、自然保留用地景观呈显著负相关;坡向因子与牧草地景观、林地景观呈显著负相关,与自然保留地景观呈显著正相关。建议根据地形因子进行景观布局,低海拔与平缓坡区宜发展生产、生活型景观,中高海拔与陡、急、陡峭坡区域宜丰富生态型景观。协调(半)阴坡、(半)阳坡的景观类型,宜增加阳坡区生态型景观。本研究为区域景观合理化建设提供了定量化依据,也为低山丘陵区景观建设提供参考。     

不同坡位植被生长状况与土壤养分空间分布特征

地形和土壤是影响植被群落的重要因素,植被生长状况与土壤养分含量随地形而变化。以吴起县枣庄沟小流域为研究区,采用样方法对不同坡位草地植被群落进行了植被调查,采集0—20cm的表层土壤测定土壤有机质、全氮、全磷含量,研究不同坡位上植被群落与土壤养分变化关系,以期了解黄土高原丘陵沟壑区地形对植被恢复的影响机制,为当地生态恢复提供科学依据与指导。结果表明:不同坡位上草地植被群落物种多样性、丰富度及地上生物量虽无显著差异,但各项指标均表现出坡下>坡中>坡上的趋势,这与土壤养分含量变化趋势相同。其中坡下位置各项土壤养分含量均为最大,植被生长状况最好;而沟坡位置土壤有机质含量、全氮含量、物种丰富度指数与地上生物量均为最低。植被生长状况与土壤养分在不同地形上变化趋势基本一致,具有一定相关性。     

基于DEM的马莲河流域数字地形分析

研究基于DEM的数字地形分析可以为各个领域提供地形分析的基础理论及实现手段。DEM水平分辨率作为重要的尺度参数,是确定地形参数和应用尺度的重要指标。选取陇东黄土高原地区的马莲河流域作为研究对象,应用美国ESRI公司开发的ArcGIS地理信息系统软件,基于数字高程模型进行流域地形特征的提取与分析。研究提取流域的基本地形特征如坡度和坡向,提取流域水系,划分了小流域。通过分析比较,得出DEM水平分辨率对提取的地形特征及水文特征的影响,为马莲河流域的数字地形分析提供了理论依据。     

Centimetre-scale digital representations of terrain and impacts on depression storage and runoff

The microscale topography of a 20 × 10 m hillslope in a burned portion of Kootenay National Park, British Columbia, Canada was determined through laser scanning at a sub-centimetre scale. Digital terrain models (DTM) were developed for this hillslope at the 0.75 cm, 10 cm, 25 cm, 50 cm, 75 cm and 1 m scales. Random Roughness, Tortuosity and Mean Upslope Depression were computed for bare and vegetated surfaces created at each resolution to determine mean depression storage as a function of resolution. Results for these various roughness parameters and associated depression storage values are not found to change appreciably between the vegetated and bare surface DTMs, and moreover do not change notably with increasing grid cell resolution. Depression storage was also computed using a GIS-based method, the values of which are considered to be, at the highest resolution of 0.75 cm, the most realistic for comparative purposes. Mean depression storage using this latter approach decreases significantly with an increase in grid cell size, in contrast to the values based on Random Roughness which remain stable with increasing grid cell size. The generation of Hortonian overland flow was modelled at different scales using the GIS-derived DTMs. The values of depression storage for the various scales of DTM are demonstrated to have significant influences on overland flow generation. The scale of the DTM affects the changes over time between the proportion of water going into depression storage and that contributing to overland flow, with more water being retained as depression storage at a particular value of rainfall excess after infiltration for the smaller DTM scalings. When overland flow develops from a rising groundwater table in a simulation exercise, water depths are initially lower than the primary roughness elements on the land surface and water is relatively disconnected. As water depths increase, more integrated connections form.     

近20年藏北草地地表参数动态变化研究

草地的覆盖度、地表反照率和地表温度是评价、监测牧草生长状况和草地退化的重要参数.利用1982～2000年NOAA/AVHRR 1、2、4、5通道的10天合成资料以及常用的遥感反演和统计方法,分析了近20年藏北那曲地区3个参数的时空变化规律.主要结果:植被区内牧草覆盖度0.1～0.95,年变率-0.012～0.012 a-1,24%的草地在退化,变异系数0.05～0.6,植被覆盖度与变异系数成反比;6～9月平均地表反照率0.152～0.300,年变率-0.009～0.007 a-1,51%的草地在退化,变异系数0.02～0.23;7～8月平均地表温度20～44℃.结论:植被生长越好,植被覆盖度越高,地表反照率越小,地表温度越低.每个参数均可单独评价和监测草地退化,但综合考虑各个参数将更客观、更合理.     

DEM内插算法对坡度坡向的影响

虽然DEM的应用越来越广泛,但是在实际研究运用中获取DEM的方式主要是利用各种矢量高程信息通过插值而来,不同的插值算法必然会影响DEM分析的结果;以南方丘陵地区为研究区域,利用样区的1∶10000的矢量地形图为数据源,通过对不同算法生成不同分辨率的DEM坡度、坡向的对比研究发现:在坡度小于30°时,不同的算法对坡度具有显著的影响,而大于30°时分辨率和算法均不会对坡度产生显著影响;研究表明:在具有大量平坦区域的地区,尽管ANUDEM算法生成的DEM总体上的精度最高,但是不会产生平坦区域,所以并不适合于这类地区的地形分析。     

光谱特征变量和BP神经网络构建油用牡丹种子含水率估算模型

为了进一步提高种子含水率的高光谱估算精度，该研究测定了156份油用牡丹种子的近红外吸收光谱及其对应的含水率值，分析了近红外吸收光谱、一阶微分光谱、水分吸收特征参数与含水率的相关关系，构建了基于特征波长吸收光谱、特征波长一阶微分光谱、水分特征吸收参数和BP神经网络的油用牡丹种子含水率估算模型，并对模型进行了验证；再结合一元线性回归（SLR，Single Linear Regression）、逐步多元线性回归（SMLR，Stepwise MultipleLinear Regression）、偏最小二乘回归（PLSR，Partial Least Squares Regression）模型与BP神经网络（BPNN，BP Neural Network）模型进行比较。结果表明：1）油用牡丹种子含水率的吸收光谱特征波长位于1 410、1 900、1990 nm，一阶微分光谱特征波长位于1 150、1 950、2 080 nm；2）以DF2080和AD2140为自变量建立的一元线性回归模型预测效果较优，在能够满足水分估算精度的情况下，是最优的选择方法。3）将优选的特征参数作为输入，实测含水率值作为输出，构建BP神经网络模型，其建模与验模R2分别为0.978和0.973，RMSE分别为0.22%和0.242%，而RPD值分别为6.478和5.889，与其他模型相比，BP神经网络模型的建模及预测精度均最高，是估算油用牡丹种子含水率的最优模型，其次为逐步多元线性回归模型。研究结果表明BP神经网络模型对种子含水率具有更好的预测能力，是估算油用牡丹种子含水率的有效方法。     

The use of epidemiology to enhance production animal research

The approach to understanding the impact of management and disease in production animal systems has evolved with the advent of both routine on-farm data collection and new analytic epidemiology techniques. Epidemiology provides a tool to describe the host-agent-environment triad and the impact of multiple variables on productivity and health recognized by production animal veterinarians in their day-to-day work. Field trials enable veterinarians to systematically test whether or not a new treatment improves the health of the animal populations in their geographic region and under their production systems. Hypothesis-specific coding techniques, such as hierarchical variables, are used in a systematic manner to understand well-defined biological phenomenon. Clustering at multiple levels has provided the challenges of measuring management changes in each level. Using random effects models allow us to determine the relative importance of each level on the dependent variable. As epidemiologists, we have taken advantage of analytic techniques used in other fields of science. Geo-spatial statistics has been used to understand the clustering and spread of diseases and more recently, to interpret the laboratory findings related to the introduction of an exotic strain of the influenza virus. Dr. Martin, through his work as a veterinary epidemiologist and that of people he has influenced, has been an international leader in promoting the optimal health and productivity of animal populations and of ensuring the safety of foods of animal origin and preventing animal-related disease in humans.