Impulsive control strategies in biological control of pesticide

By presenting and analyzing the pest-predator model under insecticides used impulsively, two impulsive strategies in biological control are put forward. The first strategy: the pulse period is fixed, but the proportional constant E(1) changes, which represents the fraction of pests killed by applying insecticide. For this scheme, two thresholds, E(1)(**) and E(1)(*) for E(1) are obtained. If E(1)>or=E(1)(*), both the pest and predator (natural enemies) populations go to extinction. If E(1)(**)相似文献   

Intermittent control: a computational theory of human control

The paradigm of continuous control using internal models has advanced understanding of human motor control. However, this paradigm ignores some aspects of human control, including intermittent feedback, serial ballistic control, triggered responses and refractory periods. It is shown that event-driven intermittent control provides a framework to explain the behaviour of the human operator under a wider range of conditions than continuous control. Continuous control is included as a special case, but sampling, system matched hold, an intermittent predictor and an event trigger allow serial open-loop trajectories using intermittent feedback. The implementation here may be described as ??continuous observation, intermittent action??. Beyond explaining unimodal regulation distributions in common with continuous control, these features naturally explain refractoriness and bimodal stabilisation distributions observed in double stimulus tracking experiments and quiet standing, respectively. Moreover, given that human control systems contain significant time delays, a biological-cybernetic rationale favours intermittent over continuous control: intermittent predictive control is computationally less demanding than continuous predictive control. A standard continuous-time predictive control model of the human operator is used as the underlying design method for an event-driven intermittent controller. It is shown that when event thresholds are small and sampling is regular, the intermittent controller can masquerade as the underlying continuous-time controller and thus, under these conditions, the continuous-time and intermittent controller cannot be distinguished. This explains why the intermittent control hypothesis is consistent with the continuous control hypothesis for certain experimental conditions.     

Brain hypoxia and control of breathing: neuromechanical control

The effects of graded brain hypoxia on respiratory cycle timing, the lung inflation reflex, and respiratory compensation for an inspiratory flow-resistive load were studied in unanesthetized goats. Two models, inhalation and CO and acute reduction of brain blood flow (BBF) were used to produce comparable levels of brain hypoxia. The lung inflation reflex was assessed as the ratio of inspiratory time of an occluded breath to that of the preceding spontaneous breath (TIoccl/TIspont). Compensation for flow-resistive loading was assessed as the effect of the load upon the airway occlusion pressure response to rebreathing CO2 (delta P 0.1/delta PCO2). Major findings were 1) severe brain hypoxia (HbCO of 60% or BBF of 42%) caused tachypnea due to a 50% or more reduction of expiratory time but only a 20% or less reduction of inspiratory time; 2) moderate carboxyhemoglobinemia (HbCO of 25-30%) enhanced TIoccl/TIspont from 1.5 +/- 0.1 at control to 2.1 +/- 0.1, while severe brain hypoxia (HbCO of 60% and BBF of 42%) reduced the ratio to 1.0 +/- 0.2; and 3) compensation for a flow-resistive load, manifested by increases of delta P 0.1/delta PCO2 of 75-300% in the control state, was abolished at HbCO of 45-50% and BBF of 60%. The data suggest that in unanesthetized animals brain hypoxia elicits tachypnea largely by an effect on the expiratory phase of the bulbopontine timing mechanism. The observed enhancement of the lung inflation reflex and abolition of flow-resistive load compensation are best explained by hypoxic depression of higher than brain stem neural function.     

Translational control by antisense RNA in control of plasmid replication

Control of replication of plasmids involves two processes: measurement of the copy number of the plasmid and adjustment of the replication frequency accordingly. For both these processes IncFII plasmids use an antisense RNA (CopA RNA) that forms a duplex with the upstream region (CopT) of the mRNA of the rate-limiting RepA protein. The kinetics of duplex formation was measured in vitro for the wild type and for a cop mutant plasmid; the mutant showed a reduction in the second-order rate constant for the formation of the RNA duplex and a similar increase in copy number. Hence, the kinetics of duplex formation and the concentration of CopA RNA determines the copy number of the plasmid.     

Metabolic control analysis. Sensitivity of control coefficients to elasticities

This paper illustrates a method to calculate the sensitivities of control coefficients to the elasticities which determine their values and it is shown that these sensitivities are systemic properties. We show, both theoretically and with a practical example, how they can be used to investigate: (a) the relative importance of a particular elasticity in the determination of the value of a control coefficient; (b) the effect of experimental error on the values of the control coefficients and (c) the construction of confidence limits around the values of the control coefficients.     

On control and optimal control in biodynamic systems

In any control system for which the number of independent controls is smaller than the number of degrees of freedom to be controlled, our choice of control in any state is restricted to a submanifold of smaller dimension than the tangent space. This simple fact has a number of important consequences for questions of biological import; we consider its implications for adaptation, for senescent phenomena and for the determination of tertiary structures of polypeptides through control of certain average properties. We also formulate the Pontryagin Maximum Principle of Optimal control theory in such a way as to inquire whether specific biodynamic systems can be regarded as optimal with respect to rate of accumulation of particular quantities of the system. We find that if this is possible, the quantity in question must play the role of a clock.     

Internet congestion control using nature population control tactics

In this paper we present a novel bio-inspired approach for congestion control in communication networks. This scheme is based on inspiration by natural population interactions: predator–prey and competition. We show that the relations of those Internet entities that are involved in congestion control mechanisms are similar to predator–prey and competition interactions. In order to apply these population control mechanisms to the Internet congestion control scheme, we combine the mathematical models of these interactions and obtain a hybrid mathematical model. The simulation results show that using appropriately defined parameters, this model leads to a scalable, stable, fair, and high-performance congestion control algorithm.     

Elusive control

The concept of a single rate-limiting step was proven to be too simplistic for understanding control and regulation of metabolism. Consequently, searches have identified relatively few steps with high control. Here we review a number of such searches and indicate what mechanisms may be responsible for this elusiveness of control. It turns out that this elusiveness of control has itself led to increased understanding of the roles played in metabolic control and regulation of such diverse factors as distributiveness of control, condition dependence, enzyme elasticity, homeostasis, control hierarchies, the input into a pathway, coenzyme sequestration, and redundancy and diversity of control function.     

林木白蚁的生物防治和生物源农药防治研究进展

林木白蚁在我国南方林区危害严重.目前,林木白蚁的防治仍以化学防治为主.但化学农药残毒严重,对环境和人类健康已构成极大威胁.利用生物防治以及生物源农药对林木白蚁进行防治具有高效、低毒,与环境兼容的特性,极具发展潜力.本文综述了生物防治以及生物源农药防治林木白蚁的研究现状与进展,并对其目前存在的问题和未来应用前景进行了分析...     

Trypanosomiasis control

In July 2000, Heads of State of the 36th Session of the Organisation for African Unity signed a potentially important declaration on African trypanosomiasis, urging member states "to act collectively to rise to the challenge of eliminating the problem through concerted efforts in mobilising the necessary human, financial and material resources required to render Africa tsetse-free within the shortest time possible". To many, such an ambitious dream is received with some scepticism, recalling the doubts that surrounded a similar declaration signed in Brasilia in 1991, which paved the way for the Southern Cone Initiative against American trypanosomiasis (Chagas disease). True, the two diseases are quite different. But the operational challenges are quite similar, and there are sufficient biological parallels to suggest that the Latin American experience in controlling Chagas disease may provide a useful model for the control of African trypanosomiasis.