等效电流极模型的脑电分析以及AD诊断中的应用

80年代以来，基于脑电图进行无创性病灶定位的研究，特别是基于等效电流极子定位法，得到了相当的发展并已经投入到正式的临床应用之中，因此等效电流极子模型在脑电图分析中逐步得到了广泛地应用。本文介绍并分析了等效电流极子模型在脑电分析以及阿尔滋海默病症（Alzheimer‘s Disease，简称AD）诊断中的应用状况。     

退耕还林还草工程对陕北地区生态系统服务价值时空演变的影响

基于陕北地区1990、2000、2015年土地利用数据，运用单位面积生态系统价值当量因子法、格网法、探索性空间数据法（ESDA），分析了退耕还林还草工程实施前后生态系统服务价值（ESV）的空间分布和演化规律，探讨了退耕还林还草工程对ESV的影响。结果表明：（1）陕北地区退耕还林还草工程实施效果显著，工程实施后共有297066.15 hm2耕地转化为林地和草地，林草覆盖率由57.33%增长至60.50%。（2）退耕还林还草工程使得陕北地区ESV得到了显著提升。25年间陕北地区ESV共增加了32.82亿元，ESV在工程实施后比工程实施前多增加了5.93亿元，增长主要源于退耕引起林地和草地面积的增加。（3）ESV空间分布上呈显著的“南高北低”分布格局，并表现出正向的集聚性和依存性，ESV热点区和冷点区集聚效果明显，热点区集聚与林地、草地的空间分布相吻合，冷点区集聚与未利用地、耕地和建设用地的空间分布相吻合。（4）受退耕还林还草工程影响，陕北地区中部中等等级和次高ESV分布区域逐渐增大、次热点区空间集聚性逐渐增强，北部次低等级和低等级ESV分布区域逐渐减少、冷点区空间集聚性逐渐减弱。整体而言，陕北地区土地利用类型转移和ESV的增减变化与推行退耕还林还草工程在时间上相呼应、在空间上相匹配，退耕还林还草工程实施使得陕北地区生态环境得到了有效改善，ESV得到了显著提升。     

Fractal root system of Melica przewalskyi along different aspect in degraded grassland

Aims Fractal root system is phenotypic plasticity result of plant root architecture to respond to environmental heterogeneity, may reflect the growth strategy of plants to adapt to environmental conditions. Our objective was to explore the relationship between root fractal dimension and fractal abundance of fractal root system of Melica przewalskyi population in response to aspect variation in the northwest of China. Methods The study site was located in a degraded alpine grassland on the northern slope in Qilian Mountains, Gansu Province, China. Survey and sampling were carried out at 40 plots which were set up along four slope aspects transects with 20 m distance between adjacent plots. Handheld GPS was used to determine the elevation, longitude and latitude of each plot. ArcGIS was used to set up digital elevation model (DEM). Community traits were investigated and six individuals roots of M. przewalskyi were collected randomly at each plot. The samples were cleaned and divided into different organs, then scanning the root with the Win-RHIZO for measurements of fractal dimension and fractal abundance in laboratory, and their biomass were then measured after being dried at 80 °C in an oven. Important findings With the slope aspect turned from north to east, west, and south, the density, height and soil moisture content of the plant community displayed a pattern of initial decline, the height, density, root fractal abundance of M. przewalskyi increased and the root fractal dimension decreased. The root fractal dimension was negatively associated with the fractal abundance in all aspects, but the relationship varied along the slope aspects gradient; there was a highly significant negative correlation (p < 0.01) between the root fractal dimension and fractal abundance at north slope and south slope aspect, whereas the correlation only reached a significant level (p < 0.05) at the east slope aspect and west slope aspect; indicating that there is a trade-off between the root fractal dimension and fractal abundance. In addition, when the slope aspect changed from north to east, west and south, the standardized major axis (SMA) slope of the regression equation in the scaling relationships between root fractal dimension and fractal abundance increased (p < 0.05), indicating that the roots of M. przewalskyi at the droughty southern slope have less branch and more sparse in the same soil volume of root exploitation and utilization. Consequently, the resource allocation pattern on reasonable trade-off between root fractal dimension and fractal abundance in different slope aspect of M. przewalskyi, reflects the relationship between the income and the cost of construction of plant root architecture.