An output formation consensus control for leader–follower networked multi-agent systems under communication constraints and switching topologies

In this paper, the formation consensus problem for a class of leader–follower networked multi-agent systems under communication constraints and switching topologies is investigated. A networked predictive control scheme is proposed to achieve stability and output formation consensus with the switching topology, capable of compensating for data loss and time delays in the network. By equating the whole closed-loop networked multi-agent system with the proposed control scheme to the corresponding switched system, the sufficient and necessary condition of output formation consensus and stability for agents is given. Finally, using three-degree-of-freedom air-bearing spacecraft simulators as the control objects, the proposed scheme is demonstrated to be able to actively compensate for the communication constraints through numerical simulations, and it is also verified to have a good control performance by further realizing the formation task of the simulators through practical experiments.     

Encryption–decryption-based event-triggered consensus control for nonlinear MASs under DoS attacks

In this article, the consensus tracking problem is discussed for a class of discrete-time nonlinear multi-agent systems (MASs) subject to denial-of-service (DoS) attacks. The individual agents interact with each other via communication network whose topology is assumed to be time-varying and strongly connected. Two techniques are employed to deal with the network-induced complexities. On one hand, an event-triggering scheme is adopted to regulate the data transmission among agents with the purpose of making full utilization of the limited communication resources; and on the other hand, an encryption–decryption mechanism is designed with the aim to provide compensation, thereby mitigating the DoS attack effects. It is the objective of the addressed problem to develop a distributed model-free adaptive control law to enforce the MASs achieve desirable consensus performance. By using a specific projection algorithm in combination with a dynamic linearization method, the desired control protocol is formulated explicitly, whose effectiveness and applicability are demonstrated via an illustrative numerical example.     

Leader-following consensus of multiple uncertain Euler–Lagrange systems under switching network topology

In recent years, the leader-following consensus problem for multiple uncertain Euler–Lagrange systems has been studied under some restrictive assumptions on the network topology. In this paper, we further study the same problem under switching network topology. We propose a distributed adaptive control law that can solve the problem under a switching network satisfying jointly connected condition. Under this condition, our results do not require the network to be undirected and allow the network to be disconnected at any time instant. Moreover, by introducing an exosystem to generate various reference signals, our control law can handle a class of reference signals such as sinusoidal signals with arbitrary amplitudes and initial phases or ramp signals with arbitrary slopes.     

Min–max time consensus tracking on a multi-quadrotor testbed

In this work, min–max time consensus tracking is implemented on a multi-quadrotor testbed. The trajectory of a leader quadrotor is generated manually. The remaining quadrotors converge onto this reference trajectory in min–max time using a local feedback control strategy which is known to be globally optimal. Further, the effect of finite communication/measurement rate on consensus tracking is analysed. The bounds on the deviations of the trajectories due to finite communication/measurement rate are characterized. The theoretical claims made are verified through experiments.     

Bayesian revision of the individual pair-wise comparison matrices under consensus in AHP–GDM

Analytic hierarchy process (AHP) has been widely used in group decision making (GDM). There are two traditional aggregation methods for the synthesis of group priorities in AHP–GDM: aggregation of the individual judgments (AIJ) and aggregation of the individual priorities (AIP). However, AIJ and AIP may be less reliable because of inconsistency of the individual pair-wise comparison matrices (PCMs) and deviation among decision makers. Based on multiplicative AHP model with lognormal errors, we propose a Bayesian revision method for improving the individual PCMs under the assumption that the consensus exists among decision makers, which is considered an aid to AIJ and AIP. In order to effectively deal with decision making involving multiple actors when using AHP as the methodological support, we revise the individual PCMs using the Bayesian revision method before using AIJ and AIP for the synthesis of group priorities. The Bayesian revision method not only makes full use of the prior distribution for parameters and sample information while complying with the Pareto principal of social choice theory, but also provides the reliable individual Bayesian PCMs for AIJ and AIP. Finally two numerical examples are examined to illustrate the applications and advantages of the Bayesian revision method.     

SERP-test: a taxonomy for supporting industry–academia communication

This paper presents the construction and evaluation of SERP-test, a taxonomy aimed to improve communication between researchers and practitioners in the area of software testing. SERP-test can be utilized for direct communication in industry academia collaborations. It may also facilitate indirect communication between practitioners adopting software engineering research and researchers who are striving for industry relevance. SERP-test was constructed through a systematic and goal-oriented approach which included literature reviews and interviews with practitioners and researchers. SERP-test was evaluated through an online survey and by utilizing it in an industry–academia collaboration project. SERP-test comprises four facets along which both research contributions and practical challenges may be classified: Intervention, Scope, Effect target and Context constraints. This paper explains the available categories for each of these facets (i.e., their definitions and rationales) and presents examples of categorized entities. Several tasks may benefit from SERP-test, such as formulating research goals from a problem perspective, describing practical challenges in a researchable fashion, analyzing primary studies in a literature review, or identifying relevant points of comparison and generalization of research.     

SDMSim: A manufacturing service supply–demand matching simulator under cloud environment

Nowadays, with the introduction and application of new information technologies in manufacturing, various advanced manufacturing modes and national strategies have been put forward and paid more and more attention, such as Industry 4.0, Industrial Internet, Cyber-Physical System or Cyber Manufacturing, Made in China 2025, Internet Plus Manufacturing, Cloud Manufacturing, etc. For these modes and strategies, how to realize the effective and intelligent supply–demand matching (SDM) of various manufacturing resources and capabilities (MR&C) in the form of service is one of the common issues and aims. In order to provide a uniformed research platform for related researchers both in academic and industry, the concept of manufacturing service SDM simulator (SDMSim) is proposed in this paper. A hypernetwork based architecture for the simulator is designed, as well as its seven key functions and subsystems, including manufacturing service management, manufacturing task management, manufacturing service SDM hypernetwork, manufacturing service SDM problem formulation and configuration, matching and scheduling algorithms/strategies selection and design, statistical analysis, and visualization. It illustrates that SDMSim has the potential to serve the users of manufacturing service provider, manufacturing service consumer, manufacturing service operator in the field of SoM, as well as the related researchers.     

A study on facility location–allocation problem in mixed environment of randomness and fuzziness

In logistics system, facility location–allocation problem, which can be used to determine the mode, the structure and the form of the whole logistics system, is a very important decision problem in the logistics network. It involves locating plants and distribution centers, and determining the best strategy for allocation the product from the plants to the distribution centers and from the distribution centers to the customers. Often uncertainty may be associated with demand, supply or various relevant costs. In many cases, randomness and fuzziness simultaneously appear in a system, in order to describe this phenomenon; we introduce the concept of hybrid variable and propose a mixed-integer programming model for random fuzzy facility location–allocation problem. By expected value and chance constraint programming technique, this model is reduced to a deterministic model. Furthermore, a priority-based genetic algorithm is designed for solving the proposed programming model and the efficacy and the efficiency of this method and algorithm are demonstrated by a numerical example. Till now, few has formulated or attacked the FLA problems in the above manner. Furthermore, the techniques illustrated in this paper can easily be applied to other SCN problems. Therefore, these techniques are the appropriate tools to tackle other supply chain network problems in realistic environments.     

Parlay-based service engineering in a converged Internet–PSTN environment

This paper examines current approaches to signalling and service interworking between Internet and public switched telephone network (PSTN). It notes that until now convergence between the two networks has for the most part taken place in the transport and signalling layers. Signalling interworking architectures cater for the specific class of telephony-like services and although they can accommodate the extension of the intelligent network's (IN) realm of control in the Internet, they do not provide a generic platform for service interworking. Through the adoption of the Parlay APIs, a way is foreseen for (a) consolidation of telephone service over both Internet and PSTN through the imposition of a uniform call control API while allowing the installed IN infrastructure to be used also for Internet telephony services and (b) for service interworking between telephony-like services and open distributed services in the Internet. The paper proposes a service architecture that can be used as a platform for Parlay-based service interworking while offsetting some drawbacks that the Parlay approach incurs.     

A secure wireless communication system integrating RSA,Diffie–Hellman PKDS,intelligent protection-key chains and a Data Connection Core in a 4G environment

In broadband wireless technology, due to having many salient advantages, such as high data rates, quality of service, scalability, security, mobility, etc., LTE-A currently has been one of the trends of wireless system development. This system provides several sophisticated authentication and encryption techniques to enhance its system security. However, LTE-A still suffers from various attacks, like eavesdropping and replay attacks. Therefore, in this paper, we propose a novel security scheme, called the security system for a 4G environment (Se4GE for short), which as an LTE-A-based system integrates the RSA and Diffie–Hellman algorithms to solve some of LTE-A’s security drawbacks where LTE-A stands for LTE-Advance which is a 4G system. The Se4GE is an end-to-end ciphertext transfer mechanism which dynamically changes encryption keys to enforce the security of data transmission in an LTE-A system. The Se4GE also produces several logically connected random keys, called the intelligent protection-key chain, which invokes two encryption/decryption techniques to provide users with broader demands for security services. The analytical results show that the Se4GE has higher security level than that of an LTE-A system.     

“Solving” ambiguity in the virtual space: communication strategies in a collaborative virtual environment

Collaborative virtual environments (CVE) face the challenge of succeeding in incorporating critical dimensions of cooperation and communication in everyday working situations. One of these dimensions, situation ambiguity, is scarcely considered in studies on CVE although it can prove a key factor in future use of CVE in real work situations. Many computer-supported cooperative environments and telecommunication systems, like those currently used in telemedicine, would benefit from the incorporation of some degree of situation ambiguity allowing users to deploy their diagnostic and interpretive abilities. In the perspective adopted in this study, ambiguity is the contingent outcome of the ongoing interaction taking place between the environment and the interests of social actors. The research focuses on the cooperation within couples of participants facing situation ambiguity in a virtual environment: a simulated city named Babylon. Participants moved in the city through an avatar and could communicate in one of the following conditions: face-to-face, phone or chat. Their goal was that of meeting somewhere in the city, in a place that they did not know previously. Babylon contained elements designed to allow both production and detection of ambiguity. Ambiguity emerged when participants realized the presence of inconsistencies in the way they perceived the situations they had to face. The moments in which ambiguity was perceived—called “critical events” (CE)—were measured and described through qualitative (ethnographically oriented) methods. The different strategies that participants used to “solve” ambiguity were characterized as: looking for environmental cues, narrowing the focus of attention and investing on cooperation. Both CEs and strategies were analyzed with respect to the three communication conditions: face-to-face, phone and chat. All the communication conditions allowed the emergence of ambiguity and the negotiation of strategies to solve ambiguity between partners: according to literature, chat is very costly in terms of time spent on writing but this disadvantage did not block completely the emergence of ambiguity and the development of adequate strategies of solution. All navigations but three (on a total of 18 couples) succeeded: the partners did meet in a short time (less than 15 min) relying on their pragmatic resources in a new virtual place. Further research is required to clarify the possible factors influencing the choice of one strategy over the others, the order in which strategies follow each other and the role of leadership in ambiguity detection and solution.     

Fix-and-Relax-Coordination for a multi-period location–allocation problem under uncertainty

A multi-period discrete facility location problem is introduced for a risk neutral strategy with uncertainty in the costs and some of the requirements along the planning horizon. A compact 0–1 formulation for the Deterministic Equivalent Model of the problem under two alternative strategies for the location decisions is presented. Furthermore, a new algorithmic matheuristic, Fix-and-Relax-Coordination, is introduced. This solution scheme is based on a specialization of the Branch-and-Fix Coordination methodology, which exploits the Nonanticipativity Constraints and uses the Twin Node Family concept. The results of an extensive computational experience allow to compare the alternative modeling strategies and assess the effectiveness of the proposed approach versus the plain use of a state-of-the-art MIP solver.     

Understanding children’s behavior in an asynchronous video-mediated communication environment

Video-mediated communication (VMC) has become a feasible way to connect people in remote places for work and play. Nevertheless, little research has been done with regard to children and VMC. In this paper, we explore the behavior of a group of children, who exchanged video messages in an informal context. In particular, this paper presents the results of 11-week VMC study of 30 children from the USA and Greece, exploring children’s behavior with the asynchronous video-based messaging tool we developed called VideoPal. In the study, children’s interactions, perceptions, content exchanged and emotions were collected. The results from the analyses highlight that the emotion of happiness dominated in the communication. Moreover, the content included useful personal information and is connected with children’s interactions (e.g., number of views and of recipients). In addition, children generally preferred VideoPal to email because they felt that it was easier and has more fun.     

Opinion consensus of modified Hegselmann–Krause models

We consider the opinion consensus problem using a multi-agent setting based on the Hegselmann–Krause (H–K) Model. Firstly, we give a sufficient condition on the initial opinion distribution so that the system will converge to only one cluster. Then, modified models are proposed to guarantee convergence for more general initial conditions. The overall connectivity is maintained with these models, while the loss of certain edges can occur. Furthermore, a smooth control protocol is provided to avoid the difficulties that may arise due to the discontinuous right-hand side in the H–K model.     

Leader–follower consensus over numerosity-constrained random networks

In this work, we study a discrete-time consensus protocol for a group of agents which communicate over a class of stochastically switching networks inspired by fish schooling. The network model incorporates the phenomenon of numerosity, that plays a prominent role in the collective behavior of animal groups, by defining the individuals’ perception of numbers. The agents comprise leaders, which share a common state, and followers, which update their states based on information exchange among neighboring agents. We establish a closed form expression for the asymptotic convergence factor of the protocol, that measures the decay rate of disagreement among the followers’ and the leaders’ states. Handleable forms of this expression are derived for the physically relevant cases of large networks whose agents are composed of primarily leaders or followers. Numerical simulations are conducted to validate analytical results and illustrate the consensus dynamics as a function of the number of leaders in the group, the agents’ persuasibility, and the agents’ numerosity. We find that the maximum speed of convergence for a given population can be enhanced by increasing the proportion of leaders in the group or the agents’ numerosity. On the other hand, we find that increasing the numerosity has also a negative effect as it reduces the range of agents’ persuasibility for which consensus is possible. Finally, we compare the main features of this leader–follower consensus protocol with its leaderless counterpart to elucidate the benefits and drawbacks of leadership in numerosity-constrained random networks.     

State estimation over a communication network： measurement or estimate communication？

In this paper we consider the problem of state estimation over a communication network. Using estimation quality as a metric, two communication schemes are studied and compared. In scheme one, each sensor node communicates its measurement data to the remote estimator, while in scheme two, each sensor node communicates its local state estimate to the remote estimator. We show that with perfect communication link, if the sensor has unlimited computation capability, the two schemes produce the same estimate at the estimator, and if the sensor has limited computation capability, scheme one is always better than scheme two. On the other hand, when data packet drops occur over the communication link, we show that if the sensor has unlimited computation capability, scheme two always outperforms scheme one, and if the sensor has limited computation capability, we show that in general there exists a critical packet arrival rate, above which scheme one outperforms scheme two. Simulations are provided to demonstrate the two schemes under various circumstances.     

Towards a parallel component in a GPU–CUDA environment: a case study with the L-BFGS Harwell routine

Modern graphics processing units (GPUs) have been at the leading edge of increasing parallelism over the last 10 years. This fact has encouraged the use of GPUs in a broader range of applications, where developers are required to lever age this technology with new programming models which ease the task of writing programs to run efficiently on GPUs. In this paper, we discuss the main guidelines to assist the developer when porting sequential scientific code on modern GPUs. These guidelines were carried out by porting the L-BFGS, the (Limited memory-) BFGS algorithm for large scale optimization, available as Harwell routine VA15. The specific interest in the L-BFGS algorithm arises from the fact that this is the computational module with the longest running time of a Oceanographic Data Assimilation application software, on which some of the authors are working.     

Efficient numerical integration of an elastic–plastic damage law within a mixed velocity–pressure formulation

This study focuses on numerical integration of constitutive laws in numerical modeling of cold materials processing that involves large plastic strain together with ductile damage. A mixed velocity–pressure formulation is used to handle the incompressibility of plastic deformation. A Lemaitre damage model where dissipative phenomena are coupled is considered. Numerical aspects of the constitutive equations are addressed in detail. Three integration algorithms with different levels of coupling of damage with elastic–plastic behavior are presented and discussed in terms of accuracy and computational cost. The implicit gradient formulation with a non-local damage variable is used to regularize the localization phenomenon and thus to ensure the objectivity of numerical results for damage prediction problems. A tensile test on a plane plate specimen, where damage and plastic strain tend to localize in well-known shear bands, successfully shows both the objectivity and effectiveness of the developed approach.