Distributed Event-Triggered Circle Formation Control for Multiagent Systems with Nonuniform Quantization

This article focuses on circle formation control problem of multiagent systems based on event-triggered strategy under limited communication bandwidth. In such system, each agent can only perceive the angular distance of its nearest neighbor in the counterclockwise direction, and the angular distance of the nearest neighbor in the clockwise direction needs to be obtained by communicating with each other. In order to address the aforementioned problem, a novel distributed algorithm based on the combination of nonuniform quantitative communication technology and event-triggered control is proposed. Sufficient conditions on circle formation control are derived under which the states of all agents can be confirmed to converge to some desired equilibrium point. Different from the traditional uniform quantization communication framework, nonuniform quantization can be beneficial for handling small signals and improving the performance of multiagent systems concerned. Furthermore, under the proposed policy, all the designed quantizers do not emerge saturated. Numerical simulation results are provided to verify the effectiveness of the proposed algorithm.

Mobile Robots with Uncertain Visibility Sensors: Possibility Results and Lower Bounds

We consider mobile robotic entities that have to cooperate to solve assigned tasks. In the literature, two models have been used to model their visibility sensors: the full visibility model, where all robots can see all other robots, and the limited visibility model, where there exists a limit [Formula: see text] such that all robots closer than [Formula: see text] are seen and all robots further than [Formula: see text] are not seen. We introduce the uncertain visibility model, which generalizes both models by considering that a subset of the robots further than [Formula: see text] cannot be seen. An empty subset corresponds to the full visibility model, and a subset containing every such robot corresponds to the limited visibility model. Then, we explore the impact of this new visibility model on the feasibility of benchmarking tasks in mobile robots computing: gathering, uniform circle formation, luminous rendezvous, and leader election. For each task, we determine the weakest visibility adversary that prevents task solvability, and the strongest adversary that allows task solvability. Our work sheds new light on the impact of visibility sensors in the context of mobile robot computing, and paves the way for more realistic algorithms that can cope with uncertain visibility sensors.

k-Circle Formation and k-epf by Asynchronous Robots

For a given positive integer k, the k-circle formation problem asks a set of autonomous, asynchronous robots to form disjoint circles having k robots each at distinct locations, centered at a set of fixed points in the Euclidean plane. The robots are identical, anonymous, oblivious, and they operate in Look–Compute–Move cycles. This paper studies the k-circle formation problem and its relationship with the k-epf problem, a generalized version of the embedded pattern formation problem, which asks exactly k robots to reach and remain at each fixed point. First, the k-circle formation problem is studied in a setting where the robots have an agreement on the common direction and orientation of one of the axes. We have characterized all the configurations and the values of k, for which the k-circle formation problem is deterministically unsolvable in this setting. For the remaining configurations and the values of k, a deterministic distributed algorithm has been proposed, in order to solve the problem. It has been proved that for the initial configurations with distinct robot positions, if the k-circle formation problem is deterministically solvable then the k-epf problem is also deterministically solvable. It has been shown that by modifying the proposed algorithm, the k-epf problem can be solved deterministically.

Circle formation by asynchronous opaque robots on infinite grid

This paper presents a distributed algorithm for circle formation problem under the infinite grid environment by asynchronous mobile opaque robots. Initially all the robots are acquiring distinct positions and they have to form a circle over the grid. Movements of the robots are restricted only along the grid lines. They do not share any global co-ordinate system. Robots are controlled by an asynchronous adversarial scheduler that operates in Look-Compute-Move cycles. The robots are indistinguishable by their nature, do not have any memory of their past configurations and previous actions. We consider the problem under luminous model, where robots communicate via lights, other than that they do not have any external communication system. Our protocol solves the circle formation problem using seven colors. A subroutine of our algorithm also solves the line formation problem using three colors.

Implicit coordination for 3D underwater collective behaviors in a fish-inspired robot swarm

Many fish species gather by the thousands and swim in harmony with seemingly no effort. Large schools display a range of impressive collective behaviors, from simple shoaling to collective migration and from basic predator evasion to dynamic maneuvers such as bait balls and flash expansion. A wealth of experimental and theoretical work has shown that these complex three-dimensional (3D) behaviors can arise from visual observations of nearby neighbors, without explicit communication. By contrast, most underwater robot collectives rely on centralized, above-water, explicit communication and, as a result, exhibit limited coordination complexity. Here, we demonstrate 3D collective behaviors with a swarm of fish-inspired miniature underwater robots that use only implicit communication mediated through the production and sensing of blue light. We show that complex and dynamic 3D collective behaviors—synchrony, dispersion/aggregation, dynamic circle formation, and search-capture—can be achieved by sensing minimal, noisy impressions of neighbors, without any centralized intervention. Our results provide insights into the power of implicit coordination and are of interest for future underwater robots that display collective capabilities on par with fish schools for applications such as environmental monitoring and search in coral reefs and coastal environments.

A Cooperative Guidance Law for UAVs Target Tracking

The problem of automatic tracking of ground targets is one of the important issues that UAVs need to face in task applications. The main concern of cooperative tracking is how to track a ground target and maintain the UAV formation simultaneously. In this paper, a new leader-follower formation is constructed to track a ground target. Firstly, a new leader UAV guidance law is proposed to track the ground target in the standoff mode, the stability is proved using a Lyapunov function. Secondly, new guidance laws for standoff tracking of the leader UAV and controlling of the inter-UAV angle of the circle formation are designed for follower UAVs, respectively, stabilities are also proved using two Lyapunov functions. Numerical simulation experiments show that the new leader-follower formation can track the static and moving targets well and its performance is better than the classic LVFG algorithm

Pathophysiological aspects of “vicious circle” formation in case of liver cells damage and cirrhosis development

This review highlights fundamental knowledge about the processes within a damaged liver cell, mechanisms of fi bro- and angiogenesis, as well as hypoxia and hypoxemia. Th e causes and consequences of endothelial dysfunction, the role of cytokines in vascular remodeling and the formation of hemodynamic disorders are described. Th ese changes lead to disorder of local and systemic hemodynamics in case of liver cirrhosis. Such complications as: hepatopulmonary syndrome and portopulmonary hypertension are also described.