复杂地形城市SO2扩散特征的模拟研究

利用中尺度气象模式RAMS和大气扩散模式HYPACT,结合甘肃省-中科院科技合作项目"兰州市大气污染及对策研究"于2000年12月在兰州市城区进行的大气污染物监测资料,通过资料分析与模拟计算,研究了兰州市冬季SO2的扩散特点。研究结果表明:大气扩散模式较好地模拟出了SO2时空分布特征,与同期监测资料的分析结果比较一致,模式模拟的SO2浓度分布的日变化与环流场的日变化紧密相关;模拟的SO2浓度的空间分布与污染源的排放方式有关,污染源的排放高度不同,造成污染的高度也不同,高架源对地面的影响比较小,而中、低架源对地面的影响比较大。     

Influence of host migration between woodland and pasture on the population dynamics of the tick Ixodes ricinus: A modelling approach

Ticks act as vectors of pathogens that can be harmful to animals and/or humans. Epidemiological models can be useful tools to investigate the potential effects of control strategies on diseases such as tick-borne diseases. The modelling of tick population dynamics is a prerequisite to simulating tick-borne diseases and the corresponding spread of the pathogen. We have developed a dynamic model to simulate changes in tick density at different stages (egg, larva, nymph and adult) under the influence of temperature. We have focused on the tick Ixodes ricinus, which is widespread in Europe. The main processes governing the biological cycles of ticks were taken into account: egg laying, hatching, development, host (small, mainly rodents, or large, like deer and cattle, mammals) questing, feeding and mortality. This model was first applied to a homogeneous habitat, where simulations showed the ability of the model to reproduce the general patterns of tick population dynamics. We considered thereafter a multi-habitat model, where three different habitats (woodland, ecotone and meadow) were connected through host migration. Based on this second application, it appears that migration from woodland, via the ecotone, is necessary to sustain the presence of ticks in the meadow. Woodland can therefore be considered as a source of ticks for the meadow, which in turn can be regarded as a sink. The influence of woodland on surrounding tick densities increases in line with the area of this habitat before reaching a plateau. A sensitivity analysis to parameter values was carried out and demonstrated that demographic parameters (sex ratio, development, mortality during feeding and questing, host finding) played a crucial role in the determination of questing nymph densities. This type of modelling approach provides insight into the influence of spatial heterogeneity on tick population dynamics.