湖南栎类天然林自稀疏边界线及影响因素研究

为确定湖南栎类天然林自稀疏边界线的最优统计方法以及影响栎类自稀疏的主要因素,以湖南省225块栎类天然林长期监测样地为研究对象,运用最小二乘法、分位数回归法和随机前沿方法拟合栎类天然林自稀疏边界线,采用现实林分死亡率对3种统计方法进行比较与验证,依据自稀疏边界线对现实林分的自稀疏状态进行判别,并对未稀疏和已稀疏样地的立地因素和森林结构因素进行方差分析。结果表明,基于分位数回归方法(分位数值等于0.95)拟合的自稀疏边界线更加接近于栎类天然林的最大密度临界值,其拟合效果优于最小二乘法和随机前沿方法;栎类自稀疏边界线的斜率为-1.063,截距为10.232;海拔、坡度、Pielous指数和高径比是影响栎类天然林自稀疏速率和起始时间的显著因素。构建的自稀疏边界线可以准确反映栎类天然林最大密度与林分平均直径的异速生长关系,可以为湖南栎类天然林生长演替和森林抚育研究提供参考。

邻域平衡密度聚类算法

聚类是数据挖掘领域的一项重要分析手段.在分析核心对象与其邻域对象的分布特征后,引入对象的投影点,对象的邻域平衡、平衡核心对象、边界稀疏对象等概念.提出一种新的基于密度的聚类算法bDBSCAN(balance-DBSCAN).算法将核心对象邻域中的对象投影,进行向量单位化,考察核心对象的邻域平衡性,将与平衡核心对象平衡密度可达的对象聚成一个簇.理论分析和实验结果表明,算法可以处理任意形状的簇,有效地排除边界稀疏对象这类噪声,并且可以解决高维数据聚类边界区分不明显、噪声对象多等问题,提高了聚类精度.算法的时间复杂度与DBSCAN近似.

融合高低层多特征的显著性检测算法

针对单一显著性特征无法全面表达图像显著性致使显著性检测精度不高等问题,本文提出了一种多特征融合的显著性检测算法。算法在高层先验知识基础上,对靠近中心的超像素设置高显著值,利用高斯分布求解中心先验;在底层特征上融合图像的边界稀疏、全局对比度、颜色空间分布和超级像素差异等4种显著特征,利用类间差异最大阈值对高低层特征进行线性和非线性融合,最终得到高质量的显著图。在MSRA-1000、SED、SOD 3个公开的数据集上进行实验,结果表明:本文算法融合得到的显著图边缘清晰、显著区域突出均匀,在有效抑制背景信息的同时所得显著图像视觉感知更好,与其他显著性算法相比查全率和查准率上至少提高3.4%。

Mapping Detailed Soil Property Using Small Scale Soil Type Maps and Sparse Typical Samples

Soil type maps at the scale of I Z 1 000 000 are used extensively to provide soil spatial distribution information for soil erosion assessment and watershed management models in China. However, the soil property maps produced through conventional direct linking method usually suffer low accuracy as well as the lack of spatial details within a soil type polygon. This paper presents an effective method to produce detailed soil property map based on representative samples which were extracted from each polygon on the 1 ： 1 000 000 soil type map. The representative sample of each polygon is defined as the location that can represent the largest area within the polygon. The representativeness of a candidate sample is determined by calculating the soil-forming environment condition similarities between the sample and other locations. Once the representative sample of each polygon has been chosen, the property values of the existing typical samples are assigned to the corresponding representative samples with the same soil type. Finally, based on these representative samples, the detailed soil property map could be produced by using existing digital soil mapping methods. The case study in XuanCheng City, Anhui Province of China, demonstrated the proposed method could produce soil property map at a higher level of spatial details and accuracy： 1） The soil organic matter （SOM） map produced based on the representative samples can not only depict the detailed spatial distribution of SOM within a soil type polygon but also largely reduce the abrupt change of soil property at the boundaries of two adjacent polygons. 2） The Root Mean Squared Error （RMSE） of the SOM map based on the representative samples is 1.61, and it is 1.37 for the SOM map produced by using conventional direct linking method. Therefore, the proposed method is an effective approach to produce spatial detailed soil property map with higher accuracy for environment simulation models.

Effects of Periodic Boundary Condition on Traffic Waves

In this paper, we use the speed-gradient model proposed by Jiang et al. [Transp. Res. B 36 （2002） 405] to study the effect of boundary condition on shock and rarefaction wave. Our numerical results show that this model can reproduce the evolution of the two traffic waves, which further proves that this model can be used to perfectly explore the consequences caused by various boundary conditions.

Study of interaction between shock wave and unsteady boundary layer

This paper reports theoretical and experimental study of a new type of interaction of a moving shock wave with an unsteady boundary layer. This type of shock wave-boundary layer interaction describes a moving shock wave interaction with an unsteady boundary layer induced by another shock wave and a rarefaction wave. So it is different from the interaction of a stationary shock wave with steady boundary layer, also different from the interaction of a reflected moving shock wave at the end of a shock tube with unsteady boundary layer induced by an incident shock. Geometrical shock dynamics is used for the theoretical analysis of the shock wave-unsteady boundary layer interaction, and a double-driver shock tube with a rarefaction wave bursting diaphragm is used for the experimental investigation in this work.

Effects of rarefaction on the characteristics of micro gas journal bearings

Given the definition of the reference Knudsen number for micro gas journal bearings,the range in the number is related to the viscosity of air at different temperatures. A modified Reynolds equation for micro gas journal bearings based on Burgdorfer's first-order slip boundary condition is proposed that takes into account the gas rarefaction effect. The finite difference method (FDM) is adopted to solve the modified Reynolds equation to obtain the pressure profiles,load capacities and attitude angles for micro gas journal bearings at different reference Knudsen numbers,bearing numbers and journal eccentricity ratios. Numerical analysis shows that pressure profiles and non-dimensional load capacities decrease markedly as gas rarefaction in-creases. Attitude angles change conversely,and when the eccentricity ratio is less than 0.6,the attitude angles rise slightly and the influence of the reference Knudsen number is not marked. In addition,the effect of gas rarefaction on the non-dimensional load capacity and attitude angle decreases with smaller bearing numbers.