Information flow and cooperative control of vehicle formations

We consider the problem of cooperation among a collection of vehicles performing a shared task using intervehicle communication to coordinate their actions. Tools from algebraic graph theory prove useful in modeling the communication network and relating its topology to formation stability. We prove a Nyquist criterion that uses the eigenvalues of the graph Laplacian matrix to determine the effect of the communication topology on formation stability. We also propose a method for decentralized information exchange between vehicles. This approach realizes a dynamical system that supplies each vehicle with a common reference to be used for cooperative motion. We prove a separation principle that decomposes formation stability into two components: Stability of this is achieved information flow for the given graph and stability of an individual vehicle for the given controller. The information flow can thus be rendered highly robust to changes in the graph, enabling tight formation control despite limitations in intervehicle communication capability

Graph Laplacians and Stabilization of Vehicle Formations

Control of vehicle formations has emerged as a topic of significant interest to the controls community. In this paper, we merge tools from graph theory and control theory to derive stability criteria for formation stabilization. The interconnection between vehicles (i.e., which vehicles are sensed by other vehicles) is modeled as a graph, and the eigenvalues of the Laplacian matrix of the graph are used in stating a Nyquist-like stability criterion for vehicle formations. The location of the Laplacian eigenvalues can be correlated to the graph structure, and therefore used to identify desirable and undesirable formation interconnection topologies

Distributed LQR-based Suboptimal Control for Coupled Linear Systems

A well-established distributed LQR method for decoupled systems is extended to the dynamically coupled case where the open-loop systems are dynamically dependent. First, a fully centralized controller is designed which is subsequently substituted by a distributed state-feedback gain with sparse structure. The control scheme is obtained by optimizing an LQR performance index with a tuning parameter utilized to emphasize/de-emphasize relative state difference between interconnected systems. Overall stability is guaranteed via a simple test applied to a convex combination of Hurwitz matrices, the validity of which leads to stable global operation for a class of interconnection schemes. It is also shown that the suboptimality of the method can be assessed by measuring a certain distance between two positive definite matrices which can be obtained by solving two Lyapunov equations

Reply to “Comments on “Consensus and Cooperation in Networked Multi-Agent Systems””

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Tracking control for multi-agent consensus with an active leader and variable topology

In this paper, we consider the coordination control of a group of autonomous mobile agents with multiple leaders. Different interconnection topologies are investigated. At first, a necessary and sufficient condition is proved in the case of fixed interconnection topology. Then a sufficient condition is proposed when the interconnection topology is switched. With a simple first-order dynamics model by using the neighborhood rule, both results show that the group behavior of the agents will converge to the polytope formed by the leaders.Comment: 6 page

Investigating the synergistic antioxidant effects of some flavonoid and phenolic compounds

Abstract Phenolic and flavonoid compounds are secondary metabolites of plants which possess various activities such as anti-inflammatory, analgesic, anti-diabetes and anticancer effects. It has been established that these compounds can scavenge free radicals produced in the body. Because of this ability, not only the plants containing phenolic and flavonoid compounds but also, the pure compounds are used in medicinal products for prevention and treatment of many disorders. Considering that the golden aim of the pharmaceutical industries is using the most effective compounds with lower concentrations, determination of the best combination of the compounds with synergistic effects is important. In the present study, synergistic antioxidant effects of four phenolic compounds including caffeic acid, gallic acid, rosmarinic acid, chlorogenic acid and two flavonoids, rutin and quercetin, have been investigated by FRAP (Ferric Reducing Antioxidant Power) method. The synergistic effect was assessed by comparing the experimental antioxidant activity of the mixtures with calculated theoretical values and the interactions of the compounds were determined. The results showed that combination of gallic acid and caffeic acid demonstrated considerable synergistic effects (137.8%) while other combinations were less potent. Among examined substances, rutin was the only one which had no effect on the other compounds. The results of ternary combinations of compounds demonstrated antagonistic effects in some cases. This was more considerable in mixture of rutin, caffeic acid, rosmarinic acid (-21.8%), chlorogenic acid, caffeic acid, rosmarinic acid (-20%), rutin, rosmarinic acid, gallic acid (-18.5%) and rutin, chlorogenic acid, caffeic acid (-15.8%), while, combination of quercetin, gallic acid, caffeic acid (59.4%) and quercetin, gallic acid, rutin (55.2%) showed the most synergistic effects. It was concluded that binary and ternary combination of quercetin, rutin, caffeic acid, chlorogenic acid, gallic acid and rosmarinic acid could influence the antioxidant ability; therefore, to obtain the best antioxidant effects in products containing these materials, the interactions should be mentioned

Ein Modell zur Untersuchung der Modulation des cAMP/PKA-abhängigen Signaltransduktionswegs durch das Ad12 E1A 12S -Onkoprotein

Die Regulation der E2-Region durch den E2-Promotor ist im lytischen Entwicklungszyklus der Adenoviren von entscheidender Bedeutung. Die Proteine dieser Region werden für die Replikation des Virusgenoms benötigt und sind somit für die erfolgreiche Vermehrung von Adenoviren essentiell. Die Aktivität vieler adenoviraler Promotoren, wie auch der in dieser Arbeit charakterisierte E2-Promotor des Adenovirus-Serotyp 12, wird durch cAMP-Response-Elemente (CRE) reguliert. Daher besteht für Adenoviren die Möglichkeit, den ubiquitären cAMP/PKA-abhängigen Signaltransduktionsweg für die Aktivierung der viralen Promotoren und somit die Expression viraler Gene in unterschiedlichen Zellsystemen zu gewährleisten. Jedoch ist die intrazelluläre Konzentration von cAMP in den Zellen niedrig und wird im Verlauf der adenoviralen Infektion nicht verändert. Für die Expression cAMP-abhängiger Zielgene ist aber die Erhöhung der intrazellulären cAMP-Konzentration und damit einhergehend die Aktivierung des PKA-Holoenzyms der entscheidende Schritt in der Expression dieser Zielgene. Bisher unverstanden ist, wie Adenoviren durch die E1A-Proteine die Fähigkeit besitzen, den für die Aktivierung der adenoviralen Promotoren notwendigen zellulären cAMP/PKA-abhängigen Signaltransduktionsweg, unabhängig von einer cAMP-Neusynthese, zu aktivieren. In den Untersuchungen zur Klärung der Regulationsmechanismen konnte ein völlig neuartiger Mechanismus der Transkriptionaktivierung CRE-abhängiger Gene durch die Translokation cytoplasmatischer Untereinheiten des PKA-Holoenzyms beschrieben werden

Chemical composition and antioxidant activity of Origanum vulgare subsp. vulgare essential oil from Iran

Abstract Background and Objectives: Essential oils are very complex mixture of components and their composition may vary in different species or varieties or even within the same variety. Origanum vulgare L. subsp. vulgare is one of the most distributed subspecies within the genus Origanum and has been found to be a poor-oil, categorized in cymyl, bornane or sabinyl chemotypes with higher proportion of sesquiterpenes. In this experiment, the Iranian sample was studied for the chemical composition of the oil and evaluation of its antioxidant activity. Methods: Essential oil was obtained by hydro-distillation and analyzed by GC/MS for determination of components. Antioxidant activity was evaluated by radical scavenging ability (DPPH method) and reducing power (FRAP assay). Results: The sample belonged to "thymol" chemotype with the main components as thymol (37.13%), gama-terpinene (9.67%), carvacrol (9.57%), carvacrol methyl ether (6.88), cis-alphabisabolene (6.80%), eucalyptol (3.82%), p-cymene (3.58%) and elemol (2.04%). The oil of plant showed very strong antioxidant activity (IC 50 =2.5 µg/mL in DPPH method), which was stronger than the standard antioxidants (Vit E and BHA, p<0.05) and it demonstrated good reducing power (467.25 μmole Eq FeSO 4 .7H 2 O/mg of the oil in FRAP assay). Conclusion: The data suggests the plant as a good potential natural antioxidant preservative