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.     

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   

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.     

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.     

Epigenetic control

Epigenetics refers to mitotically and/or meiotically heritable variations in gene expression that are not caused by changes in DNA sequence. Epigenetic mechanisms regulate all biological processes from conception to death, including genome reprogramming during early embryogenesis and gametogenesis, cell differentiation and maintenance of a committed lineage. Key epigenetic players are DNA methylation and histone post‐translational modifications, which interplay with each other, with regulatory proteins and with non‐coding RNAs, to remodel chromatin into domains such as euchromatin, constitutive or facultative heterochromatin and to achieve nuclear compartmentalization. Besides epigenetic mechanisms such as imprinting, chromosome X inactivation or mitotic bookmarking which establish heritable states, other rapid and transient mechanisms, such as histone H3 phosphorylation, allow cells to respond and adapt to environmental stimuli. However, these epigenetic marks can also have long‐term effects, for example in learning and memory formation or in cancer. Erroneous epigenetic marks are responsible for a whole gamut of diseases including diseases evident at birth or infancy or diseases becoming symptomatic later in life. Moreover, although epigenetic marks are deposited early in development, adaptations occurring through life can lead to diseases and cancer. With epigenetic marks being reversible, research has started to focus on epigenetic therapy which has had encouraging success. As we witness an explosion of knowledge in the field of epigenetics, we are forced to revisit our dogma. For example, recent studies challenge the idea that DNA methylation is irreversible. Further, research on Rett syndrome has revealed an unforeseen role for methyl‐CpG‐binding protein 2 (MeCP2) in neurons. J. Cell. Physiol. 219: 243–250, 2009. © 2009 Wiley‐Liss, Inc.     

Perceived control

The present study tested the hypothesis that perceived control results in reduced depressive cognitions. Subjects were divided into two groups, high and low in depressive cognitions (HDC and LDC) based on their scores on a Depression Scale. Subjects (HDC and LDC) were assigned randomly to one of the following treatment conditions: contingent feedback (CF), noncontingent (yoked) feedback (YF), or no feedback (NF) in pulse-rate (PR) regulation. Half the subjects were instructed to decrease (D) and half were instructed to increase (I) PR. The study consisted of three sessions spaced one week apart. Each session was comprised of a three-minute baseline (nonfeedback) trial followed by a 15-minute experimental session. After each experimental session, subjects completed a questionnaire which assessed how well they felt they regulated PR, and the extent to which they attributed such regulation to their ability, effort, the difficulty or ease of the task, and luck. After three sessions, subjects were posttested on the Depression Scale. Results indicated that a significant, though small, reduction in depressive cognitions occurred for CF and YF subjects who were instructed to decrease PR, and this effect was mediated by subjects attributing PR regulation to ability and effort. Results are discussed in terms of the effect that perceived control may have on attributions and reported depression. Also, limitations regarding the generalizability of the findings to a clinical population are discussed.