基于粒子系统的土壤胶粒快速凝聚的三维可视化仿真

土壤胶体凝聚三维可视化有助于更好地理解土壤凝聚动力学过程和土壤团聚体形成.该文构建了土壤胶粒粒子系统算法,实现了土壤胶粒建模及其胶体快速凝聚动态演化可视化.首先将土壤整体当作土壤立方体,土壤胶体颗粒看作球形,实现所有胶粒的建模.然后胶粒在布朗运动作用下以扩散系数随机移动,移动后发生碰撞而快速凝聚.该文分别实现了有固定中...     

基于类二叉树的虚拟植物分枝结构三维重构

为了有效的提取自然界分枝植物的生长规则,该文在深入研究L系统的基础上,提出了一种基于类二叉树结构的虚拟植物生长三维重构方法。该方法用类二叉树结构来简化分枝植株的生长规则,以L系统描述植株的拓扑结构;对实际树木的仿真结果表明,该方法能够有效地描述植物的生长规则,为植物生长规则的提取提供了一条新的途径。     

Fractal characterisation of plant canopies and application in spray retention modelling for arable crops and weeds

Fractal analysis can provide a unique mathematical tool to quantify the geometry of irregular and complex plant canopies. This study demonstrated that a single numerical fractal dimension (FD) value derived from an image taken from above the plant canopy could differentiate between and rank the canopies of a range of plant species. We also investigated the influence of canopy architecture and surface characteristics on spray retention. Multiple regressions were used to derive mathematical relationships and develop a spray retention model. It was discovered that the FD value can successfully be used to replace the statistically generated plant morphological factor (M_p4) used in a previous retention model, with the major advantage being that the retention model now only involves variables that can be readily measured. There is an excellent relationship ( R ² = 0.99) between actual spray retention per plant (μL) and that predicted by the model incorporating the FD. The spray retentiveness of the plant species studied was ranked using a numerical index based on plant canopy architecture and surface characteristics.     

基于多重分形理论的油菜缺素叶片特征提取

为描述油菜缺素叶片图像的特征,该文提出了一种基于多重分形去趋势波动分析方法,即局部多重分形去趋势波动分析。该方法确定的hij(q)指数能有效刻画叶片图像每个像素点的多重分形特征,并以所有像素点hij(q)的平均值Lhq表征每幅图像的多重分形特征。选取4种油菜缺素叶片图像进行试验,结果表明所提取局部多重分形去趋势波动平均指数Lhq能很好地区分叶片,并通过方差分析指出当q={-10, -9, -8, -7, -6}时的Lhq区分效果最好。最后基于每个像素点的hij(q)指数利用模糊C均值聚类对缺镁油菜叶片图像进行模糊分割,并与传统的灰度值分割及经典的基于容量测度的指数分割进行了对比试验,结果表明以上述hij(q)为特征具有最佳的分割效果。     

The Geometric precision and Performance Analysis for machining Surface based on Fractals

A new analysis method for machining surface profile error is presented in this paper.The linear regression and nonlinear regression are first applied respectively,and then the Weierstrass Mandebrot fractal function is used to obtain the fractal parameters of machining profiles.A minimal parameter set which depicts the machining surface geometric precision is set up,and the surface profile can be reconstructed using these parameters,and an analysis method for part performance and its tolerance structure is proposed.Examples are provided to illustrate the method is feasible and effective.     

基于多重分形理论的再生水灌溉下土壤粒度分析

再生水灌溉是缓解水资源矛盾的有效途径,为表征再生水灌溉后土壤粒度分布(Soil particle size distribution, PSD)特性,通过室内土柱模拟试验,设置生活污水(W1)、再生水1(W2)和再生水2(W3)共计3种灌溉水质,并以自来水(W4)作为对照,采用马尔文激光粒度仪测定灌溉1 a后各处理土壤颗粒百分比,运用分形理论分析了4种水质处理下土壤PSD的分形特征。结果表明：(1)4种水质处理下土壤PSD呈单峰分布;与W4处理相比,W1、W2、W3处理下土壤黏粒含量增加0.40%～6.38%,砂粒含量降低1.58%～13.80%,土壤非均匀性增强,但各处理间差异不显著。(2)再生水灌溉下土壤颗粒呈细粒化趋势,土壤PSD多重分形参数增大,土壤PSD趋于不均匀。在0～10 cm土层,W3处理下土壤PSD多重分形参数容量维数D(0)、信息维数D(1)、相关维数D(2)和多重分形奇异谱宽Δα(q)最大,分别为0.943、0.837、0.823和1.035;在10～20 cm土层,W2处理下D(0)、D(1)、D(2)和Δα(q)最大,分别为0.943、0.851、0.852和...     

Dispersal success on fractal landscapes: a consequence of lacunarity thresholds

Habitat fragmentation is expected to disrupt dispersal, and thus we explored how patch metrics of landscape structure, such as percolation thresholds used to define landscape connectivity, corresponded with dispersal success on neutral landscapes. We simulated dispersal as either a purely random process (random direction and random step lengths) or as an area-limited random walk (random direction, but movement limited to an adjacent cell at each dispersal step) and quantified dispersal success for 1000 individuals on random and fractal landscape maps across a range of habitat abundance and fragmentation. Dispersal success increased with the number of cells a disperser could search (m), but poor dispersers (m<5) searching via area-limited dispersal on fractal landscapes were more successful at locating suitable habitat than random dispersers on either random or fractal landscapes. Dispersal success was enhanced on fractal landscapes relative to random ones because of the greater spatial contagion of habitat. Dispersal success decreased proportionate to habitat loss for poor dispersers (m=1) on random landscapes, but exhibited an abrupt threshold at low levels of habitat abundance (p<0.1) for area-limited dispersers (m<10) on fractal landscapes. Conventional metrics of patch structure, including percolation, did not exhibit threshold behavior in the region of the dispersal threshold. A lacunarity analysis of the gap structure of landscape patterns, however, revealed a strong threshold in the variability of gap sizes at low levels of habitat abundance (p<0.1) in fractal landscapes, the same region in which abrupt declines in dispersal success were observed. The interpatch distances or gaps across which dispersers must move in search of suitable habitat should influence dispersal success, and our results suggest that there is a critical gap-size structure to fractal landscapes that interferes with the ability of dispersers to locate suitable habitat when habitat is rare. We suggest that the gap structure of landscapes is a more important determinant of dispersal than patch structure, although both are ultimately required to predict the ecological consequences of habitat fragmentation.     

Foraging behavior of browsing ruminants in a heterogeneous landscape

Movement patterns of white-tailed deer (Odocoileus virginianus) and Spanish goats (Carpa hircus) were mapped and analyzed to test the hypothesis that foraging movements and behaviors within an Acacia shrub community are significantly related to environmental heterogeneity. Animal response to plant community heterogeneity was characterized using foraging velocity and the animals' foraging path fractal dimension (D_d). Environmental heterogeneity was characterized using the perimeter:area fractal dimension, which represents the shape of shrubs, and the grid count fractal dimension, which represents shrub spatial distribution. The foraging paths of deer were straighter and more directed (D_d = 1.27) than those of goats (D_d = 1.53), and deer responded to the shape of shrub patches, more so than to shrub distribution. The tortuosity of goat foraging paths was apparently affected by distribution of blackbrush (Acacia rigidula) and shrubby bluesage (Salvia ballotiflora). Foraging velocity of deer was affected by the distribution and shape complexity of guajillo (A. berlandieri), which was a major dietary component. In contrast, foraging velocity of goats was affected by the shape complexity of the entire shrub community and by the distribution of ceniza (Leucophylum frutescens), a non-dietary, but prevalent component of the plant community. Results indicate that these two browsing herbivores perceive the same landscape differently.     

四川盆地丘陵山区局地水系分形分维研究

通过应用ArcGIS9.3软件,选取了重庆市拔山镇的五一水系和石门水系作为研究对象,探讨分形分维理论在四川盆地丘陵山区局地水系的应用.结果表明:(1)五一水系的分支比、长度比、面积比和比降比分别为2.88,1.86,2.29和1.72;相应石门水系的Horton比分别为3.32,1.89,2.15和2.48;两水系的分维值分别为1.05和1.00,均属于初级发育水系.(2)四川盆地丘陵山区局地水系的分形分维特征不完全同于大流域水系,分支比能较精确地反映相邻级别间的水道发育程度.两水系相比较,复杂程度相对较高的五一水系的分形分维值和现有大范围、大流域分形分维研究成果间的差异更大.(3)局地水系的分形分维研究有助于深入认识局地水系,从而服务于农业小流域的水资源平衡分析,促进小流域灌排工程的合理布局,最终达到农业水资源的优化配置.