由微分方程所描述的微生物连续培养动力系统(Ⅰ)

陆续介绍微生物连续培养(Chemostat)的基本原理,以单种微生物连续培养模型为基础,较详细地介绍几类由微分方程所描述的微生物连续培养动力系统模型,涉及的问题有解的稳定性,系统的持久性,周期解和Hopf分支等．     

由微分方程所描述的微生物连续培养动力系统(I)*

陆续介绍微生物连续培养 (Chemostat)的基本原理 ,以单种微生物连续培养模型为基础 ,较详细地介绍几类由微分方程所描述的微生物连续培养动力系统模型 ,涉及的问题有解的稳定性 ,系统的持久性 ,周期解和Hopf分支等。     

时变环境下Chemostat中微生物连续培养食物链模型的分歧分析

研究均匀搅拌的Chemostat中微生物连续培养的单食物链模型．模型的特点是在营养输入项中引入时变环境,以便更逼真地模拟自然现象．用单特征值分歧定理得到了周期解存在的条件,用Crandall-Rabinowitz定理证明了单种群分歧解的稳定性．     

单纯形法在微生物生长动力学和能学参数估算中的应用

本文基于作者所导出的用于描述微生物分批和连续培养的数学模型^［6,7］,就单纯形法在微生物生长动力学和能学参数估算中的应用进行研究。根据模型的特点,提出确定目标函数及单纯形初始值的方法,并以大肠杆菌单罐连续培养为例介绍了估算的全过程。     

由微分方程所描述的微生物连续培养动力系统(II)

该文为论文 [1 ]的继续 ,主要介绍具有时间滞后的微生物连续培养模型     

由微分方程所描述的微生物连续培养动力系统(II)*

该文为论文 [1 ]的继续 ,主要介绍具有时间滞后的微生物连续培养模型。     

由微分方程所描述的微生物连续培养动力系统(Ⅱ)

该为论[1]的继续,主要介绍具有时间滞后的微生物连续培养模型。     

一类微生物连续培养竞争模型的定性分析

研究一类微生物连续培养竞争模型的解的结构,分析了平衡点的稳定性及平衡点附近极限环存在唯一性,证明系统存在正向不变集。     

螺旋藻批式与连续培养及其生长动力学

在内循环气升式光生物反应器中,分别研究了螺旋藻细胞在批式和连续培养条件下的生长特性,结果表明：Richards模型和指数衰减模型可较好地描述批式培养时细胞和碳源底物浓度与培养时间的关系;批式培养时最大细胞生长速率为0371g/d/L,细胞对碳的得率系数为3.439g/gC;连续培养时随着稀释率的增大,细胞和底物浓度分别呈下降和上升趋势;连续培养时最大细胞产率为0.362g/L/d,最佳稀释率为0.45/d,细胞对碳的得率系数为2.050g/gC;所提出的连续培养动力学模型可较好地拟合实验数据。     

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．     

Preparation of bioindicators for controlling the efficacy of sterilization processes

A test microbe for the control of the efficacy of vacuum steam sterilization was selected. Conditions for the spore cultivation were developed. The optimal bioindicator composition, test microbe loading, nutrient medium, pH indicator, carbohydrates and a carrier were defined.     

Natural variation in the contribution of microbial density to inducible immune dynamics

Immune responses evolve to balance the benefits of microbial killing against the costs of autoimmunity and energetic resource use. Models that explore the evolution of optimal immune responses generally include a term for constitutive immunity, or the level of immunological investment prior to microbial exposure, and for inducible immunity, or investment in immune function after microbial challenge. However, studies rarely consider the functional form of inducible immune responses with respect to microbial density, despite the theoretical dependence of immune system evolution on microbe‐ versus immune‐mediated damage to the host. In this study, we analyse antimicrobial peptide (AMP) gene expression from seven wild‐caught flour beetle populations (Tribolium spp.) during acute infection with the virulent bacteria Bacillus thuringiensis (Bt) and Photorhabdus luminescens (P.lum) to demonstrate that inducible immune responses mediated by the humoral IMD pathway exhibit natural variation in both microbe density‐dependent and independent temporal dynamics. Beetle populations that exhibited greater AMP expression sensitivity to Bt density were also more likely to die from infection, while populations that exhibited higher microbe density‐independent AMP expression were more likely to survive P. luminescens infection. Reduction in pathway signalling efficiency through RNAi‐mediated knockdown of the imd gene reduced the magnitude of both microbe‐independent and dependent responses and reduced host resistance to Bt growth, but had no net effect on host survival. This study provides a framework for understanding natural variation in the flexibility of investment in inducible immune responses and should inform theory on the contribution of nonequilibrium host‐microbe dynamics to immune system evolution.     

Biofilm formation and chemostat dynamics: Pure and mixed culture considerations

Time-dependent biofilm formation effects on continuous fermenter operation are modelled here in general for a mixed culture of N different microorganisms growing on a single substrate. Dynamic computer solutions are detailed for two versions of the general model: a pure culture and a simple two-cell mixed culture. Pure culture model predictions compare favorably with two pure culture experiments in the literature where significant biofilm formation was noted. A mixed culture of one microbe (C(1)) having a higher growth rate than a second microbe (C(2)) is simulated for two hypothetical scenarios of microbe C(2) having different magnitudes of cell deposition rate. Biofilm effects on the estimation of kinetic and stoichiometric parameters in both model versions, plus the impact of biofilms on mixed culture dynamics, are discussed.     

Optimal allocation of building blocks between nutrient uptake systems in a microbe

 A bacterial cell must distribute its molecular building blocks among various types of nutrient uptake systems. If the microbe is to maximize its average growth rate, this allocation of building blocks must be adjusted to the environmental availabilities of the various nutrients. The adjustments can be found from growth balancing considerations. We give a full proof of optimality and uniqueness of the optimal allocation regime for a simple model of microbial growth and internal stores kinetics. This proof suggests likely candidates for optimal control regimes in the case of a more realistic model. These candidate regimes differ with respect to the information that the cells control system must have access to. We pay particular attention to one of the three candidates, a feedback regime based on a cellular control system that monitors only internal reserve densities. We show that allocation converges rapidly to balanced growth under this control regime. Received: 20 November 2000 / Revised version: 7 August 2001 / Published online: 21 February 2002     

Determination of the biological parameters of bacterium-phage complexes.

The authors present a method of measurement and evaluation for continuous cultures of bacteria infected by virulent phages. By the comparison of the model describing the phage-bacterium interaction and their own experimental data they determined the following biological parameter values characterizing the interaction: the adsorption rate (mu), the expectation of the latency period (T) and its standard deviation ((sigma), the time required for lysis (d), the infection efficiency (eta) and the average burst size (C). The parameters were used for the determination of optimal cultivating conditions (maximum phage yield).     

Optimal foraging in nonpatchy habitats. I. Bounded one-dimensional resource

We present a model of optimal foraging in habitats where the food has an arbitrary density distribution (continuous or not). The classical models of foraging strategies assume that the food is distributed in patches and that the animal divides its time between the two distinct behaviors of patch exploitation and interpatch travel. This assumption is hard to accept in instances where the food distribution is continuous in space, and where travel and feeding cannot be sharply distinguished. In this paper, the habitat is assumed to be one-dimensional and bounded, and the animal is assumed to have a limited foraging time available. The problem is treated mathematically in the context of the calculus of variations. The optimal solution is to divide the habitat in two subsets according to the food density. In the richer subset, the animal equalizes the density distribution; in the poorer subset, it travels as fast as possible.     

Modeling and optimal control of insect pest populations

A distributed-parameter population dynamics model is developed specifically for use with variational optimization techniques. The objective is to develop a modeling/ optimization technique that will permit the development of optimal control policies which minimize combined costs of pest control and economic-yield loss. The model results and optimal control policies are continuous and distributed in time and in insect age. The technique is applied to a study of control by pesticide of the southern green stink bug, Nezara viridula (Linnaeus), a major pest of soybeans in the South. In this case study, the model results agree well with field-survey results, while the optimal control trajectories are reasonable and suggest several avenues for further study.     

Stabilizing feedback of a nonlinear process involving uncertain data

A nonlinear control system describing the process of continuous methane fermentation is considered. Assuming that the parameters of the model are not exactly known but bounded within intervals, the set of optimal static points according to a practical criterion is computed. A continuous feedback control is proposed, which asymptotically stabilizes the dynamic system towards this set. Numerical results are also reported.     

On boundary stimulation and optimal boundary control of the bidomain equations

The bidomain equations with Neumann boundary stimulation and optimal control of these stimuli are investigated. First an analytical framework for boundary control is provided. Then a parallel finite element based algorithm is devised and its efficiency is demonstrated not only for the direct problem but also for the optimal control problem. The computations realize a model configuration corresponding to optimal boundary defibrillation of a reentry phenomenon by applying current density stimuli.     

On optimal predator search

Search tactics are explored for animals hunting randomly distributed prey in two-dimensional habitats. The predator chooses between two modes of search: continuous travel and alternating pause-travel. A model based on renewal processes is derived for the predator's net rate of energy intake. The model is used to explore the optimal mode of search, search height, pause duration (“giving-up time”) and move length. Energy expenditure for search is assumed to increase from perchtravel over continuous travel to hover-travel. Prey detectability is assumed to be higher for the pausing than for the travelling predator. The following predictions emerge: The relative merits of the different search modes are mainly determined by the relative magnitudes of energy consumption rates and prey detection efficiencies at pausing and travelling. The energetically cheaper among two search modes reaches its highest relative merit at low prey density and detectability. As either increases, a more expensive search tactic may become superior. If the rate of energy expenditure increases considerably at locomotion, pause-travel tactics may be superior to continuous travel. This requires that the search can be performed from sufficient height, because net energy gain decreases rapidly below the optimum search height. It is greater for pause-travel than for continuous travel, and it increases slightly with decreasing prey density, and markedly with increasing prey detectability. With perch-travel or hover-travel tactics, the optimal giving-up time decreases with increasing prey density and detectability. The optimal move length increases with detectability. Empirical evidence coincides qualitatively with several predictions. Possibilities for further tests of the model are discussed, as are observed behavioural and morphological features on which the search model may shed light.