莲花山主要森林群落空间格局的分形特征

应用信息维数对莲花山主要森林群落的空间格局进行了研究.结果表明:森林群落的格局强度尺度变化程度由高至低的次序为:岷江冷杉一糙皮桦一白桦群落(Q4)1.84＞云杉-紫果云杉-糙皮桦群落(Q2)1.53＞岷江冷杉群落(Q3)1.14＞紫果云杉-云杉-岷江冷杉群落(Q7)1.10＞华山松群落(Q5)0.99＞岷江冷杉人工林(Q1)0.82＞辽东栎群落(Q6)0.45;群落格局信息维数的差异反映了更新状况的差异,揭示出群落个体分布的非均匀性状况.综合3种分形维数,确定各亚高山寒温性森林群落生长与更新状况的次序为Q4＞Q2＞Q3＞Q7＞Q5＞Q1＞Q6.各群落总体平均记盒维数为1.76,关联维数为1.71,信息维数为1.12;各森林群落生长状况较好,个体聚集程度较低,更新状况一般.分形维数谱将不同森林群落的空间结构特征明确区分开来.     

基于分形理论的乡村聚落景观空间特征及演变——以厦门市为例

空间结构和空间形态共同构成乡村聚落景观空间特征,对二者的科学分析是乡村土地利用格局优化的基础.本研究采用分形理论,从全市与分乡镇两个尺度上对厦门市乡村聚落景观空间结构的特征和演变进行定量分析,并提出空间格局优化的相应对策.结果表明: 厦门市乡村聚落景观空间结构与形态的分形特征明显.在全市尺度上,聚集维数、交通网络直通度和空间形态维数随时间变化而增大,而空间关联维数持续减少;乡村聚落景观空间结构呈多中心聚集态分布,交通网络通达性变好,空间结构自组织不断优化,而乡村聚落景观空间形态日趋复杂,空间呈扩展的趋势.在分乡镇尺度上,乡村聚落景观空间特征差异显著,空间结构松散、通达性较弱等问题存在于部分乡镇.未来需加强交通等基础设施投入和中心村建设,提高乡村聚落内部各要素的关联度,促使其空间结构优化.本研究结果为优化乡村聚落空间布局、科学编制乡村土地利用规划提供了有力的技术手段和理论支撑.     

Nitrogen‐mediated effects of elevated CO2 on intra‐aggregate soil pore structure

Soil pore structure has a strong influence on water retention, and is itself influenced by plant and microbial dynamics such as root proliferation and microbial exudation. Although increased nitrogen (N) availability and elevated atmospheric CO₂ concentrations (eCO₂) often have interacting effects on root and microbial dynamics, it is unclear whether these biotic effects can translate into altered soil pore structure and water retention. This study was based on a long‐term experiment (7 yr at the time of sampling) in which a C₄ pasture grass (Paspalum notatum) was grown on a sandy loam soil while provided factorial additions of N and CO₂. Through an analysis of soil aggregate fractal properties supported by 3D microtomographic imagery, we found that N fertilization induced an increase in intra‐aggregate porosity and a simultaneous shift toward greater accumulation of pore space in larger aggregates. These effects were enhanced by eCO₂ and yielded an increase in water retention at pressure potentials near the wilting point of plants. However, eCO₂ alone induced changes in the opposite direction, with larger aggregates containing less pore space than under control conditions, and water retention decreasing accordingly. Results on biotic factors further suggested that organic matter gains or losses induced the observed structural changes. Based on our results, we postulate that the pore structure of many mineral soils could undergo N‐dependent changes as atmospheric CO₂ concentrations rise, having global‐scale implications for water balance, carbon storage, and related rhizosphere functions.     

希拉穆仁草原近自然恢复状态下植被-土壤响应特征

通过对内蒙古阴山北麓围封区域草原近自然状态下植被群落特征及其土壤颗粒物理特性的研究,探讨草地群落与土壤颗粒物理特性在自然风蚀条件下的特征。结果表明:(1)草地全覆盖时以羊草、赖草为优势种,当草地盖度下降为40%以下时以指示草地退化的冷蒿为优势种;且随着植被盖度的降低,草地植物群落生物量呈降低趋势,Shannon-Wiener指数、Simpson指数均呈现出先升高后降低的趋势;(2)草地植被覆盖度对地表土壤颗粒分形维数有显著影响(P0.05),随着盖度的降低,其地表土壤颗粒分形维数呈显著降低趋势,地表土壤颗粒粗化明显;(3)在近自然状态下,草地植被覆盖较低时,地表0—1 cm土壤颗粒粗粒化现象尤为显著,粒度累计差异达到1 mm,垂直结构上表现为由3—5 cm、1—3 cm土层至0—1 cm土层,土壤颗粒粗粒化程度加重,粗颗粒粒度累积差异分别出现在0.1、0.25、1 mm;(4)在近自然状态下,随着草地植被盖度增加,表层土壤受植物遮蔽,得到有效保护,土壤颗粒逐渐细化,容重也缓慢下降。在近自然状态下,草地及土壤环境发生有层次且多样性的变化,草地植被的斑块状变化使得希拉穆仁围封区草原在近原始状态下出现自然风蚀现象成为可能。     

微域环境因子对落基山圆柏插穗生根的影响

以8年生落基山圆柏(Juniperus scopulorum)的嫩枝为试验材料, 采用不同扦插密度和基质等处理措施, 研究了微域环境因子对插穗生根的影响。结果表明, 两种不同扦插密度的生根部位、愈伤率、生根率、炼存率、生根效果指数(root effect index, REI)、离散度指数(rooting dispersion index, RDI)和分形特征均存在显著差异。综合分析生根率、炼存率、REI和RDI等发现, 密插处理的效果好于稀插, 稀插处理的插穗生根能力较差, 生根性状离散度较大。密插处理的插穗的根系平均分形维数是稀插处理的1.24倍, 两者差异极显著(p < 0.01)。不同扦插密度下插穗的生根部位和生根机制不同: 插穗在密插处理下形成诱生根, 在稀插处理下形成原基根。不同的扦插密度造成了落基山圆柏微域环境的显著差异, 但同一密度下不同基质种类对微域环境因子的调控作用有限。密插处理下插穗的微域环境相对湿度较高(最高可达83.5%), 温度较低, 光合有效辐射较小。这些环境因子的差异导致密插处理下插穗的净光合速率(P_n)较高, 蒸腾速率(T_r)较低。在0-60天内, 密插和稀插处理的插穗的P_n均呈上升趋势, 并且二者相差的幅度随着试验时间的延长而迅速增大; 在60天以后, 二者均呈下降趋势, 相差幅度基本保持不变。密插处理下的T_r值在0-30天内基本保持不变, 而此时稀插处理下的T_r迅速增加。在30-60天内密插处理下的T_r快速增加, 60天时达到最大值, 但仍低于稀插处理。这些结果表明, 外部微域环境因子对插穗生根的影响是通过影响其内在生理指标来实现的, 插穗营养状况的差异是造成生根机制不同的主要原因。     

红树植物木榄幼树斑块形状的分形分析

应用分形理论分析了山口国家级红树林自然保护区木榄幼树斑块形状的分形特征。木榄幼树斑块在整体水平上的分形维数为 1 .1 2 ,而单个斑块的分形维数介于 1 .1 7～ 1 .3 7之间。分形维数的大小与斑块形状的复杂程度密切相关。频谱法和周长 -面积法都适用于分析幼树斑块形状的分形特征。     

Determinants of slowed diffusion in the complex space of the cerebellar glomerulus

Using analytical solutions for two- and three-dimensional (2D and 3D, respectively) and fractal 2D/3D geometry with an absorbing boundary, we modeled glutamate diffusion in a glomerulus, the structure situated around the mossy fiber (MF) terminal in the cerebellum and surrounded by a glial sheath. The model with fractal geometry gave the best fit of experimental AMPA and NMDA receptor-mediated evoked postsynaptic currents (EPSC) at the MF-granule cell synapse. A comparison of the numerically integrated glutamate concentration in an idealized model of glomerulus morphology with analytical solutions reveals that the peculiarities of glomerulus geometry can explain the better fit by the solution with fractal dimension only of experimental EPSC arising from local release, but not from spillover of glutamate. An asynchronous vesicle release only slightly influences the shape of the spillover waveform. Anomalously slow diffusion of glutamate can be an explanation of the observed discrepancy between experimental results and simulations with the 3D model. A good fit of spillover-induced EPSC obtained in the simulations that use a solution for fractional Brownian motion and a match of experimental estimations and theoretical parameters of the diffusion model confirms this assumption.Neirofiziologiya/Neurophysiology, Vol. 36, Nos. 5/6, pp. 418–431, September–December, 2004.This revised version was published online in April 2005 with a corrected cover date and copyright year.     

川西丘陵区景观空间格局分析

采用分形维数、平均斑块面积、形状指数和伸张度分析了川西不同丘陵地貌区灌溉水田、一般旱地、果园、有林地和农村居民点斑块的空间格局特征,并用分形维数、平均斑块面积和Shannon-Weiner指数3种方法研究了浅丘、中丘和高丘的综合景观特征。结果表明,不同景观斑块在同一丘陵区内的格局特征不同,同一景观斑块在3种丘陵区的格局也有差异。浅丘、中丘和高丘的综合景观格局特点是随着地势起伏的增加、人类活动和土地利用强度的减弱,分形维数增加,从1.1865到1.3123;斑块平均面积则依次变小,从2.2204hm^2减少到1.2403hm^2。3种丘陵区的景观多样性指数分别为1.7199、1.9802和2.0898。     

Genome analysis: A new approach for visualization of sequence organization in genomes

In this article we describe and demonstrate the versatility of a computer program, GENOME MAPPING, that uses interactive graphics and runs on an IRIS workstation. The program helps to visualize as well as analyse global and local patterns of genomic DNA sequences. It was developed keeping in mind the requirements of the human genome sequencing programme, which requires rapid analysis of the data. Using GENOME MAPPING one can discern signature patterns of different kinds of sequences and analyse such patterns for repetitive as well as rare sequence strings. Further, one can visualize the extent of global homology between different genomic sequences. An application of our method to the published yeast mitochondrial genome data shows similar sequence organizations in the entire sequence and in smaller subsequences     

肝炎和伤寒流行过程的混沌分维研究

以辽宁省本溪市１９５５－１９９６年的肝炎、伤寒逐月发病的数据为根据，利用混沌动力学中“相空间技术”，对流行病过程进行能量谱分析及混沌分析。发现伤寒的流行过程是混沌的，混沌迭代模型是Ｘｔ＋１＝ｒＸｔｅｘｐ｛－０．０００９２８７（Ｘｔ－３３．２５３３２）＾２｝；肝炎的流行过程是非混沌的。在模型参数变化范围内，经历了周期状态、混沌状态之间的转换，这表明伤寒的流行过程是复杂的，给出了流行病的“阈值”，以控制它们的流行涨落，求出伤寒的关联分维是３．０８７。