Consensus reaching in multi-agent packet-switched networks with non-linear coupling

An important task for multi-agent systems (MAS) is to reach a consensus, e.g. to align their velocity vectors. Recent results propose appropriate consensus protocols to achieve such tasks, but most of them do not consider the effect of communication constraints such as the presence of time-delays in the exchange of information between the agents. In this article, we provide conditions for a non-linear, locally passive MAS of arbitrary size to reach a consensus, when the agents communicate over a packet-switched network that is characterised by a given topology. Both the cases of constant and switching topologies are considered. The nature of the communication channel imposes constraints that are modelled using stochastic delays of arbitrary distribution. We first embed this model in another, distributed but deterministic delay model and provide conditions for the error introduced by this simplification. In our main result, we provide conditions for the locally passive MAS with distributed delays to reach a consensus. In the case of a fixed topology, the underlying directed graph has to contain a spanning tree. In the case of a switching topology, only the union graph of all graphs that persist over time is required to contain a spanning tree. These conditions are independent of the distribution and the size of the packet delays. To show attractivity of the consensus set, we use an invariance principle for systems described by functional differential equations based on an appropriate Lyapunov–Razumikhin function. This methodological approach is the main contribution of this work and can also be applied to other consensus problems with delays. We illustrate our results by numerical simulations showing synchronisation of non-linear Kuramoto oscillators over a digital network.     

Social networking and the risk to companies and institutions

Social networks open up new business opportunities for customer acquisition and retention, facilitate knowledge transfer within the company, and can positively influence work climate. However, they can also quickly destroy a company image that took years to build, while the use of social networks at work not only risks a loss in productivity but may also undermine legal obligations. Eager networkers might also divulge company internals to competitors or the public at large. And last but not least, “friendships” open up completely new attack vectors for professional hackers, thus significantly increasing company exposure to online break-ins. This article briefly summarizes the opportunities and dangers that this development poses for business. This contribution is based on an earlier article by the same authors (in German) (Langheinrich and Karjoth, 2010).     

Corrosion behaviour of cast and forced implant materials for artificial joints,particularly with respect to compound designs

Implants can fulfil their duty in the human body for decades only if the materials used are resistant to pitting corrosion, crevice corrosion, stress corrosion cracking and corrosion fatigue in chloride-containing body fluids. This applies especially to the new generation of compound endoprostheses. Though these combine the advantages of cast moving parts with those of forged anchorage shafts, there may be a possibility of galvanic cell formation. The susceptibility of various implant alloys to these different types of corrosion is determined, with special emphasis on the compound design of joint endoprostheses.     

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Kettenförderer in der Spanplattenindustrie,Einsatzmöglichkeiten und Berechnung

Zusammenfassung Die Frage des Sp?netransportes bei der Herstellung von Holzspanplatten geh?rt zu den wichtigen technischen und wirtschaftlichen Fragen in der Spanplattenindustrie. Unter den verschiedenen F?rdersystemen gilt der Kettenf?rderer als raumsparendes und leistungsstarkes Transportmittel. In der vorliegenden Arbeit werden die Einsatzm?glichkeiten des Kettenf?rderers innerhalb der Spanplattenproduktion dargestellt. Für die Bemessung von Kettenf?rderern werden Angaben über den Platzbedarf in Abh?ngigkeit von F?rdervolumen gemacht. Es werden ferner die rechnerischen M?glichkeiten zur Bestimmung der Antriebsleistung dargestellt und in vier Nomogrammen werden Mittel an die Hand gegeben, um die Antriebsleistung von Kettenf?rderern auf graphischem Wege rasch bestimmen zu k?nnen.

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Chain conveyors in particle board manufacture, their use and construction

Summary In the particle board industry, chip feeding represents one of the most important technical and economic problems during the production of particle board. Among the various conveying systems the chain conveyor is considered as a space-saving and efficient means of transportation. The operational possibilities of chain conveyors in particle board industry are discussed in this paper. For the dimensioning of chain conveyors, data on the required space in relation to the bulk to be conveyed are given. Mathematical methods for the determination of the feeding power are further depicted; by means of four nomographs it is demonstrated how the feeding power of chain conveyors may be determined graphically.

     

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