具有Holling Ⅳ类功能反应的三维顺环捕食者-食饵模型

考虑具有Holling Ⅳ类功能反应三维顺环捕食者一食饵系统,利用常微分方程比较定理及Liapunov函数方法,得到了该系统持久性的充分条件,并且对于周期系统在一定条件下。系统存在唯一一个全局渐进稳定的周期正解,最后讨论了概周期解现象,得出了概周期正解的唯一存在性和全局渐进稳定性的充分条件。     

群体感应抑制剂的筛选及其在微生物病害防治中的应用

在绝大多数病原菌中都发现有群体感应机制存在,用于调控侵染过程中微生物致病基因的表达。群体感应抑制剂处理既能控制微生物致病毒性,又不影响细胞生长,因此不会导致抗性株的形成,是一种理想的抗病原性药物。本文重点探讨了群体感应抑制剂的筛选、种类以及在群体感应过程中的作用机理和潜在应用价值。     

具有反馈控制和功能性反应的两种群竞争系统的概周期解

研究了具有反馈控制和功能性反应的两种群竞争系统．通过构造适当的Lyapunov函数,得到了系统存在全局渐进稳定的概周期解的充分性条件。     

一类具有时滞的微生物连续培养数学模型研究

研究了具有强核函数时滞的微生物连续培养数学模型,利用泛函微分方程理论和数值解法得到系统在一定操作条件下存在Hopf分叉以及分叉值随操作参数变化的规律,并研究了Hopf分叉产生的方向及周期解的稳定性,绘制了周期解的图形和相图.该模型定性地描述了实验中的振荡和过渡现象.最后与弱核函数时滞模型、离散时滞模型进行比较,分析了它们对多态、振荡等动态行为的影响。     

具有变消耗率微生物连续培养模型的定性分析

研究了一类具有变消耗率的微生物连续培养系统,当消耗率是线性函数时得到了正平衡点全局渐近稳定的充要条件,当消耗率是二次函数时得到了系统存在极限环的充分条件,同时利用分支理论研究系统存在Hopf分支的条件,判定了极限环的稳定性．     

枯草杆菌中性蛋白酶天然抑制剂的筛选

用透明因法和福林──酚法筛选了２１种植物中的蛋白酶活性抑制剂,其中来自鼓皮、高粱、玉米和土豆的抑制剂的活性在本研究条件下达５０％以上。进一步研究了麸皮、玉米两种抑制剂在不同温度和ｐＨ值下的稳定性,结果表明,两者的稳定性相差甚远,是两类不同的抑制剂。玉米抑制剂比麸皮抑制剂更稳定。     

食饵染病的非自治生态-流行病模型的分析

研究了一类疾病仅在食饵中传播的非自治捕食者-食饵模型.文中假定捕食者受密度制约影响,在捕食时具有甄别能力而只捕食健康的食饵,且具有HollingⅢ类功效函数;对于食饵,将其分为食饵易感者和食饵染病者两类,模型假定疾病发生率为非线性的,且考虑到了环境对食饵种群的容纳量.文中运用Barbalat引理、比较原理等稳定性理论的相关方法,找到了系统的正向不变集,证明了模型解的最终有界性;通过理论分析,分别得到了两种群持续生存、周期解的存在性以及周期解全局渐进稳定的相关条件;最后,通过MATLAB数值模拟,验证了有关结论.     

一个新的多序列比对算法

多序列比对是生物信息学中基础而又重要的序列分析方法.本文提出一种新的多序列比对算法,该算法综合了渐进比对方法和迭代策略,采用加权函数以调整序列的有偏分布,用neighbor-joining方法构建指导树以确定渐进比对的顺序.通过对BAlibASE中142组蛋白质序列比对的测试,验证了本算法的有效性.与Multalin算法比较的结果表明,本算法能有效地提高分歧较大序列的比对准确率.     

抗炎药的新探索

许多科学家对炎症越是了解,就越是感到烦恼.尽管炎症的过程促进伤口的愈合,并便于捕获微生物,但它也带来很多伤害,如引起人的关节炎、哮喘以及大量的机体失调.遗憾的是,当今的抗炎药存在着其自身的问题,如抗炎药引起胃部不适,有些抗炎药则增加心脏病发作的危险率,故而寻找安全的抗炎药正在继续进行中.研究者现在报道了2种实验性药物,它们可以保护实验室小鼠免于罹患严重炎症.该发现发表于即将出版的ProceedingsoftheNationalAcademyofSciences.较早期的研究提示,有一种讨厌的酶,称为可溶性环氧化物酶,可降解天然的炎症抑制剂,该炎症抑制剂…     

抑制剂在氨氧化微生物研究中的应用

在氨氧化微生物的相关研究中经常使用各类抑制剂,包括针对硝化作用的抑制剂和针对微生物生长的抑制剂。自发现氨氧化古菌以来,人们在氨氧化细菌抑制剂的基础上重新筛选和使用不同的抑制剂来满足氨氧化微生物研究的需求。抑制剂既可以加速氨氧化古菌的富集,也可以帮助研究者区分古菌与细菌对硝化作用的贡献以及它们自身合成代谢能力的差别。本文综述了各类抑制剂的使用浓度和抑制效果,包括双氰胺(DCD)、3,4-二甲基吡啶磷酸盐(DMPP)、丙烯基硫脲(ATU)等传统抑制剂,乙炔和辛炔等炔烃类抑制剂,一氧化氮清除剂以及抗生素等对氨氧化微生物的活性和生长有特异性或通用抑制能力的抑制剂。通过对氨氧化微生物抑制剂的归纳总结,可为氨氧化微生物研究过程中抑制剂的选择提供参考。     

Competition between plasmid-bearing and plasmid-free organisms in a chemostat with nutrient recycling and an inhibitor

The asymptotic behavior of solutions of a model for competition between plasmid-bearing and plasmid-free organisms in the chemostat with two distributed delays and an external inhibitor is considered. The model presents a refinement of the one considered by Lu and Hadeler [Z. Lu, K.P. Hadeler, Model of plasmid-bearing plasmid-free competition in the chemostat with nutrient recycling and an inhibitor, Math. Biosci. 167 (2000) p. 177]. The delays model the fact that the nutrient is partially recycled after the death of the biomass by bacterial decomposition. Furthermore, it is assumed that there is inter-specific competition between the plasmid-bearing and plasmid-free organisms as well as intra-specific competition within each population. Conditions for boundedness of solutions and existence of non-negative equilibrium are given. Analysis of the extinction of the organisms, including plasmid-bearing and plasmid-free organisms, and the uniform persistence of the system are also carried out. By constructing appropriate Liapunov-like functionals, some sufficient conditions of global attractivity to the extinction equilibria are obtained and the combined effects of the delays and the inhibitor are studied.     

具有时滞再生养分竞争模型的全局稳定性

考虑具有再生养分的两个微生物种群竞争一个有限食物营养液的数学模型．利用构造李雅普诺夫函数得到模型内部平衡点全局稳定的充分条件．     

Nutrient flows between ecosystems can destabilize simple food chains

Dispersal of organisms has large effects on the dynamics and stability of populations and communities. However, current metacommunity theory largely ignores how the flows of limiting nutrients across ecosystems can influence communities. We studied a meta-ecosystem model where two autotroph-consumer communities are spatially coupled through the diffusion of the limiting nutrient. We analyzed regional and local stability, as well as spatial and temporal synchrony to elucidate the impacts of nutrient recycling and diffusion on trophic dynamics. We show that nutrient diffusion is capable of inducing asynchronous local destabilization of biotic compartments through a diffusion-induced spatiotemporal bifurcation. Nutrient recycling interacts with nutrient diffusion and influences the susceptibility of the meta-ecosystem to diffusion-induced instabilities. This interaction between nutrient recycling and transport is further shown to depend on ecosystem enrichment. It more generally emphasizes the importance of meta-ecosystem theory for predicting species persistence and distribution in managed ecosystems.     

Competition in the presence of a lethal external inhibitor

The study considers two organisms competing for a nutrient in an open system in the presence of an inhibitor (or toxicant). The inhibitor is input at a constant rate and is lethal to one competitor while being taken up by the other without harm. This is in contrast to previous studies, where the inhibitor decreases the reproductive rate of one of the organisms. The mathematical result of the lethal effect, modeled by a mass action term, is that the system cannot be reduced to a monotone dynamical system of one order lower as is common with chemostat-like problems. The model is described by four non-linear, ordinary differential equations and we seek to describe the asymptotic behavior as a function of the parameters of the system. Several global exclusion results are presented with mathematical proofs. However, in the case of coexistence, oscillatory behavior is possible and the study proceeds with numerical examples. The model is relevant to bioremediation problems in nature and to laboratory bio-reactors.     

单资源中带有化感作用的两种浮游植物的动力学行为（英文）

讨论了带有化感作用机制的两种浮游植物的营养竞争模型,获得系统平衡点的存在性和稳定性条件.     

Plankton-toxin interaction with a variable input nutrient

A simple model of phytoplankton–zooplankton interaction with a periodic input nutrient is presented. The model is then used to study a nutrient–plankton interaction with a toxic substance that inhibits the growth rate of plankton populations. The effects of the toxin upon the existence, magnitude, and stability of the periodic solutions are discussed. Numerical simulations are also provided to illustrate analytical results and to compare more complicated dynamical behaviour.     

Serpins in prokaryotes

Members of the serpin (serine proteinase inhibitor) superfamily have been identified in higher multicellular eukaryotes (plants and animals) and viruses but not in bacteria, archaea, or fungi. Thus, the ancestral serpin and the origin of the serpin inhibitory mechanism remain obscure. In this study we characterize 12 serpin-like sequences in the genomes of prokaryotic organisms, extending this protein family to all major branches of life. Notably, these organisms live in dramatically different environments and some are evolutionarily distantly related. A sequence-based analysis suggests that all 12 serpins are inhibitory. Despite considerable sequence divergence between the proteins, in four of the 12 sequences the region of the serpin that determines proteinase specificity is highly conserved, indicating that these inhibitors are likely to share a common target. Inhibitory serpins are typically prone to polymerization upon heating; thus, the existence of serpins in the moderate thermophilic bacterium Thermobifida fusca, the thermophilic bacterium Thermoanaerobacter tengcongensis, and the hyperthermophilic archaeon Pyrobaculum aerophilum is of particular interest. Using molecular modeling, we predict the means by which heat stability in the latter protein may be achieved without compromising inhibitory activity.     

Turing-Hopf instability in biochemical reaction networks arising from pairs of subnetworks

A three dimensional nutrient-plant-herbivore model was proposed and conditions for boundedness, positive invariance, existence and stability of different equilibrium points, Hopf-bifurcation and global stability were obtained. We performed numerical simulations to observe the simultaneous effect of the top-down and the bottom-up mechanism on the system. It was found that nutrient enrichment destroyed the coexistence steady state of the system. This nutrient enrichment could be due to high nutrient input rate or high nutrient recycling rate. In both cases the system showed instability. Moreover, these results were independent of the grazing pressure and the predation functional form.     

Persistence and coexistence in zooplankton-phytoplankton-nutrient models with instantaneous nutrient recycling

We consider plankton-nutrient interaction models consisting of phytoplankton, herbivorous zooplankton and dissolved limiting nutrient with general nutrient uptake functions and instantaneous nutrient recycling. For the model with constant nutrient input and different constant washout rates, conditions for boundedness of the solutions, existence and stability of non-negative equilibria, as well as persistence are given. We also consider the zooplankton-phytoplankton-nutrient interaction models with a fluctuating nutrient input and with a periodic washout rate, respectively. It is shown that coexistence of the zooplankton and phytoplankton may arise due to positive bifurcating periodic solutions.Research has been supported in part by a University of Alberta Ph.D. Scholarship and is in part based on the author's Ph.D. thesis under the supervision of Professor H. 1. Freedman, to whom the author owes a debt of appreciation and gratitude for his kind advice, helpful comments and continuous encouragement     

Enrichment of denitrifying glycogen-accumulating organisms in anaerobic/anoxic activated sludge system

Denitrifying glycogen-accumulating organisms (DGAO) were successfully enriched in a lab-scale sequencing batch reactor (SBR) running with anaerobic/anoxic cycles and acetate feeding during the anaerobic period. Acetate was completely taken up anaerobically, which was accompanied by the consumption of glycogen and the production of poly-beta-hydroxy-alkanoates (PHA). In the subsequent anoxic stage, nitrate or nitrite was utilized as electron acceptor for the oxidation of PHA, resulting in glycogen replenishment and cell growth. The above phenotype showed by the enrichment culture demonstrates the existence of DGAO. Further, it was found that the anaerobic behavior of DGAO could be predicted well by the anaerobic GAO model of Filipe et al. (2001) and Zeng et al. (2002a). The final product of denitrification during anoxic stage was mainly nitrous oxide (N(2)O) rather than N(2). The data strongly suggests that N(2)O production may be caused by the inhibition of nitrous oxide reductase by an elevated level of nitrite accumulated during denitrification. The existence of these organisms is a concern in biological nutrient removal systems that typically have an anaerobic/anoxic/aerobic reactor sequence since they are potential competitors to the polyphosphate-accumulating organisms.