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.     

Argumentative Agent Deliberation, Roles and Context

This paper presents an argumentation based framework to support an agent's deliberation process for drawing conclusions under a given policy. The argumentative policy of the agent is able to take into account the roles agents can have within a context pertaining to an environment of interaction. The framework uses roles and context to define policy preferences at different levels of deliberation allowing a modular representation of the agent's knowledge that avoids the need for explicit qualification of the agent's decision rules. We also employ a simple form of abduction to deal with the incompleteness and evolving nature of the agent's knowledge of the external environment and illustrate how an agent's self deliberation can affect the mode of interaction between agents. The high degree of modularity of the framework gives it a simple computational model in which the agent's deliberation can be naturally implemented.     

Compatibility of poly(vinyl chloride) with epoxidized copolymers of butadiene-styrene

The compatibility of poly(vinyl chloride) (PVC) with epoxidized styrene-butadiene copolymers is examined at different levels of epoxidation. The copolymers modified were a random (SBR) containing 45 wt% styrene and a triblock (SBS) with 30 wt% bound styrene. Blends were examined in the complete composition range and the approximate levels of epoxidation to ensure blend miscibility were determined. Epoxidized SBS (ESBS) was more effective in miscibility compared with ESBR requiring a lesser degree of epoxidation (43 versus 46 mol%). Tensile properties of the ESBS/PVC blends showed the efficiency of ESBS as a polymeric plasticizer even at levels of epoxidation (ca. 35 mol%) where immiscibility sets in.     

Shape from interaction

We present “shape from interaction” (SfI), an approach to the problem of acquiring 3D representations of rigid objects through observing the activity of a human who handles a tool. SfI relies on the fact that two rigid objects cannot share the same physical space. The 3D reconstruction of the unknown object is achieved by tracking the known 3D tool and by carving out the space it occupies as a function of time. Due to this indirection, SfI reconstructs rigid objects regardless of their material and appearance properties and proves particularly useful for the cases of textureless, transparent, translucent, refractive and specular objects for which there exists no practical vision-based 3D reconstruction method. Additionally, object concavities that are not directly observable can also be reconstructed. The 3D tracking of the tool is formulated as an optimization problem that is solved based on visual input acquired by a multicamera system. Experimental results from a prototype implementation of SfI support qualitatively and quantitatively the effectiveness of the proposed approach.     

Information Foraging—A Model for Exploration Breadth and Depth

The optimal path choice theory from biology implies that foragers should evaluate all sites before selecting something feasible when site relocation costs are low and there are few sites to explore. In internet information foraging, although the cost of moving to another site is negligible, the number of relevant sites can be large and exploration costs vary. We examine human internet information foraging behaviors and propose a model relating them to established cognitive measures.     

Calibrating multibody ulno-humeral joint cartilage using a validated finite element model

Correct prediction of contact characteristic in multibody models is a challenging issue, which requires both employing an appropriate contact model and choosing its corresponding contact parameters. This study employed two subject specific multibody models of the ulno-humeral joint where the humerus cartilage was discretized and interacted with the ulna cartilage through a deformable contact. Parameters for the deformable contact were optimized by matching the maximum predicted contact pressure in the multibody models with contact pressures predicted in identical finite element models under axial 110 N compressive load. The performance of the optimized contact parameters and employed approach was evaluated under two other loading conditions of 80 and 140 N. Moreover, the effect of discretized element size on the contact prediction was also addressed. After optimization of the contact parameters, the difference between the multibody and FE models in terms of peak and average contact pressure, and contact area was significantly reduced (more than a factor of 10). Smaller discretization size of the humerus cartilage in the multibody models resulted in better predictions especially on highly curved regions. However, the optimized parameters of our study were different between the two elbows. This indicates that optimized contact parameters can be different not only among different joints, but also among different specimens and optimization conditions. Therefore, in order to improve contact predictions, separate contact optimization should be performed for each subject.     

Distributed High-End Audio-Visual Content Creation: An Experience Report

In the recent years the world has witnessed an unprecedented expansion in the global audio-visual industry and actions have been initiated to strengthen its actors, especially in filmmaking and video production. Companies seeking ways to improve their performance and productivity and become more competitive are investing in modern digital technologies. High-performance computingsystems are found today even in small production facilities. Yet, little effort has been used to implement activities other than production/post-production and even less tointegrate the whole cycle of contentdevelopment and creation within a networkedcollaborative environment. This paper reportsthe experience of the DAViD project aiming toestablish ways to interact and collaborate during pre-production phases. Several benefitshave been demonstrated, such as reduction ofthe overall production time and cost, increasedproductivity and increased ability to executecomplex, multi-company productions in shortertimes and lower budgets.     

Investigation of protozoa as indicators of wastewater treatment efficiency in constructed wetlands

Wetlands represent an efficient wastewater treatment technique, with several benefits over the conventional activated sludge system. Microfaunal community is of outmost importance in treatment processes as the microorganisms are able to achieve substantial decontamination through biodegradation. The objectives of this work were the monitoring of protozoan's abundance and diversity in the matrix of six bench scale Free Water Surface constructed wetlands and the investigation of their applicability as indicator organisms for treatment efficiency in these systems. A correlation between the phosphorous and Total Coliforms removal rates was observed in the presence of increased protozoan taxa, while removal of organic loading and inorganic nitrogen was increased in the case of increased protozoan diversity in the soil/water interface. Results revealed that protozoa may be used as bioindicators of treatment efficiency in constructed wetlands; in addition their presence was related to the effluent quality.     

Strategies for contextual reasoning with conflicts in ambient intelligence

Ambient Intelligence environments host various agents that collect, process, change and share the available context information. The imperfect nature of context, the open and dynamic nature of such environments and the special characteristics of ambient agents have introduced new research challenges in the study of Distributed Artificial Intelligence. This paper proposes a solution based on the Multi-Context Systems paradigm, according to which local knowledge of ambient agents is encoded in rule theories (contexts), and information flow between agents is achieved through mapping rules that associate concepts used by different contexts. To resolve potential inconsistencies that may arise from the interaction of contexts through their mappings (global conflicts), we use a preference ordering on the system contexts, which may express the confidence that an agent has in the knowledge imported by other agents. On top of this model, we have developed four alternative strategies for global conflicts resolution, which mainly differ in the type and extent of context and preference information that is used to resolve potential conflicts. The four strategies have been respectively implemented in four versions of a distributed algorithm for query evaluation and evaluated in a simulated P2P system.