一类多物种生物趋化模型解的整体有界性

本文主要研究一类多物种生物趋化模型在齐次Neumann初边值条件下证得方程组的解整体存在且一致有界。即在光滑且有界边界Ω■Rn(n≥1),非负初值满足(u10(x),…,uN0(x))∈(C0(Ω))N,w0∈W1,r(Ω),参数趋化敏感函数χi(w)及增长系数μi满足一定条件时,首先利用一个依赖趋化物质浓度的加权函数估计方程组的解在Lp(Ω)空间上的有界性,再由算子半群理论得到解在L∞(Ω)空间上的有界性。

一类多物种生物趋化模型解的局部性质

本文主要研究一类多物种生物趋化模型在齐次Neumann初边值条件下,证得方程组的解的局部存在性及唯一性。即在光滑且有界边界Ω?n(n≥1),当初值(u10(x),…,uN0(x))∈(C0(Ω))N,w0∈W1,r(Ω)非负,利用Banach空间不动点定理证明解的局部存在性,再利用Gronwall不等式和能量方法证得解的唯一性。

Evaluation and Performance of the APSIM Crop Growth Model for German Winter Wheat, Maize and Fieldpea Varieties in Monocropping and Intercropping Systems

Competition for solar radiation between plants grown in multi-species cropping systems can severely limit crop production of individual species within that system. There are various approaches for modeling light interception within mixed-cropping and row or strip intercropping systems. To extend the knowledge about model behavior and different model approaches under interspecific competition conditions, the Agricultural Production Systems Simulator （APSIM） was evaluated and calibrated for field experiments previously described and simulated by the Decision Support System for Agrotechnology Transfer （DSSAT）. Initially the APSIM plant model was successfully modified to simulate wheat, maize and fieldpea monocultures in the European agro-ecological zone. Once calibrated, the APSIM model was then used to simulate a strip relay intercropping maize/wheat and maize/fieldpea system. In DSSAT, a shading algorithm was introduced to modify the daily weather input in order to take competition for solar radiation into account. In contrast, APSIM simulates interspecific competition using a modified Beer＇s law for multi-component canopy conditions. After a re-evaluation of the model regarding a minimum change of crop coefficients and variables, APSIM was able to simulate dry matter and grain yield of German maize, wheat and fieldpea varieties adequately. However, APSIM is a point-based model, and many of the processes that influence strip cropping cannot be accommodated by adjusting Beer＇s Law alone. So far none of the tested frameworks successfully modeled strip or relay intercropping. The processes governing growth in the numerous and very diversifying intercropping systems are complex and at this point in time have not been captured in sufficient detail.

口腔静态生物膜模型研究进展

口腔静态生物膜模型是体外模拟口腔微生态环境的重要手段,因其成本低、通量高、可靠性好、操作容易等优点,已成为研究各种口腔疾病的发病机制,测试各种药物、口腔护理用品、食品的重要工具。建立口腔静态生物膜模型,可根据研究目的,选择不同的装置、接种源、培养基、基质和培养条件,并通过测定生物量、代谢活性、群落结构以及进行可视化分析等多种方法评价生物膜的生长情况。本文汇总了近年来报道的口腔静态生物膜模型建立和评价的方法学要素,并分析讨论了各种方法的适用范围,希望有助于相关领域研究和生产实践的开展。

A generalized model of island biogeography

MacArthur and Wilson's equilibrium theory is one of the most influential theories in ecology.Although evolution on islands is to be important to island biodiversity,speciation has not been well integrated into island biogeography models.By incorporating speciation and factors influencing it into the MacArthur-Wilson model,we propose a generalized model unifying ecological and evolutionary processes and island features.Intra-island speciation may play an important role in both island species richness and endemism,and the contribution of speciation to local species diversity may eventually be greater than that of immigration under certain conditions.Those conditions are related to the per species speciation rate,per species extinction rate,and island features,and they are independent of immigration rate.The model predicts that large islands will have a high,though not the highest,proportional endemism when other parameters are fixed.Based on the generalized model,changes in species richness and endemism on an oceanic island over time were predicted to be similar to empirical observations.Our model provides an ideal starting point for re-evaluating the role of speciation and re-analyzing available data on island species diversity,especially those biased by the MacArthur-Wilson model.

Small-time sampling behavior of a Fleming-Viot process

The Fleming-Viot process with parent-independent mutation process is one particular neutral pop- ulation genetic model. As time goes by, some initial species are replaced by mutated ones gradually. Once the population mutation rate is high, mutated species will elbow out all the initial species very quickly. Small-time behavior in thls case seems to be the key to understand this fast transition. The small-time asymptotic results related to time scale t and a（O）t, where lim0→∞θ θa（θ） = O, are obtained by Dawson and Shni （1998, 2001）, Shui and Xiong （2002）, and Xiang and Zhang （2005）, respectively. Only the behavior under the scale t（θ）, where limθ→∞θt（θ） = 0 and limθ→∞（O） =∞ was left untouched. In this paper, the weak limits under various small-time scales are obtained. Of particular interest is the large deviations for the small-time transient sam- pling distributions, which reveal interesting phase transition. Interestingly, such a phase transition is uniquely determined by some species diversity indices.

An island biogeography model for beta diversity and endemism： The roles of speciation, extinction and dispersal

A community composition island biogeography model was developed to explain and predict two community patterns （beta diversity and endemism） with the consideration of speciation, extinction and dispersal processes. Results showed that rate of speciation is positively and linearly associated with beta diversity and endemism, that is, increasing species rates typically could increase the percentage of both endemism and beta diversity. The influences of immigration and extinction rates on beta diversity and endemism are nonlinear, but with numerical simulation, I could observe that increasing extinction rates would lead to decreasing percentage of endemism and beta diversity. The role of immigration rate is very similar to that of speciation rate, having a positive relationship with beta diversity and endemism. Finally, I found that beta diversity is closely related to the percentage of endemism. The slope of this positive relationship is determined jointly by different combinations of speciation, extinction and immigration rates.