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Flexible vibration has a great impact on flexible spacecraft attitude control, which will reduce the pointing accuracy of the spacecraft platform and bring severe challenges to the design of a high-precision attitude control system for flexible spacecraft. Aiming at the problem of attitude and vibration coupling control of flexible spacecraft, an anti-unwinding attitude coupling controller using the positive position feedback (PPF) control is proposed in this paper. The model compensation control term is constructed based on the prior information to improve the tracking performance. The proposed attitude coupling control method can effectively suppress the flexible vibration while achieving more accurate attitude control. The obtained closed-loop system under the proposed control scheme is asymptotically stable, which is proved by the Lyapunov stability theory. The numerical simulation illustrates that the proposed method can effectively improve the attitude control accuracy of the flexible spacecraft and is capable of large-angle attitude maneuver control because of its prominent performance in attitude tracking and its unwinding-free performance. • Coupling control for flexible spacecraft. • Active vibration control using positive position feedback. • Model compensation control term is constructed to improve the dynamic performance. • The obtained closed-loop system achieves the asymptotic stability and anti-unwinding performance. [ABSTRACT FROM AUTHOR]

Generation of multi-quadrotor trajectories in real-time in complex three-dimensional environments remains a grand challenge. Trajectory planning becomes computationally prohibitive as the number of quadrotors and obstacles increases. This paper proposes the distributed receding architecture-based hierarchical trajectory planning method (drHTP) to tackle this issue. The distributed receding architecture is established to formulate and solve a series of single-quadrotor short-horizon planning problems for reducing the computation complexity. In distributed planning, the time-heuristic priority mechanism is devised to assign a reasonable planning sequence to enhance the convergence performance. The hierarchical planning, including front-end initial trajectory generation and back-end trajectory optimization, is introduced for the single-quadrotor in each short horizon to further reduce the computation time. The sparse A* search algorithm is modified to only consider adjacent obstacles for obtaining the initial trajectory rapidly. The convergence of drHTP is analyzed theoretically. Numerical simulations with moving and dense obstacle scenarios are carried out to verify the effectiveness of drHTP. The comparative simulation results demonstrate that drHTP outperforms the state-of-the-art distributed sequential convex programming and distributed model predictive control methods in terms of computational efficiency. drHTP is also validated by the physical experiment in an indoor testbed. • The distributed receding architecture is constructed to reduce the computation complexity of multi-quadrotor trajectory planning. • The SAS algorithm is modified to only consider the adjacent obstacles to improve the computation efficiency. • The trajectory tracking experiments using Crazyflie 2.1 are implemented to validate that the generated trajectory is executable. [ABSTRACT FROM AUTHOR]

This paper studies the distributed formation control problem of second-order multi-agent systems (MASs) with limited communication ranges and collision avoidance constraints. A novel connectivity preservation and collision-free distributed control algorithm is proposed by combining prescribed performance control (PPC) and exponential zeroing control barrier Lyapunov functions (EZCBFs). In particular, we impose the time-varying performance constraints on the relative position and velocity errors between the neighboring agents, and then a PPC-based formation control algorithm is developed such that the connectivity of the communication graph can be preserved at all times, and the prescribed transient and steady performance on the relative position and velocity error can be achieved. Subsequently, by introducing the EZCBFs method, an inequality constraint condition on the control input is derived to guarantee the collision-free formation motion. By regarding the PPC-based formation controller as a nominal input, an actual formation control input is given by solving the quadratic programming (QP) problem such that each agent achieves collision-free formation motion while guaranteeing the connectivity and prescribed performance as much as possible. Finally, numerical simulation is carried out to validate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we investigate the stability problem of switched homogeneous positive systems of degree one. We first show that the positiveness of the considered system is guaranteed when each switched subsystem is cooperative. Then, an integral excitation condition is formulated to ensure the exponential stability of the switched homogeneous positive system of degree one. In particular, the proposed condition allows that some or even all switched subsystems are only Lyapunov stable rather than asymptotically stable. In the second part of this paper, we further consider the cases of sub-homogeneous systems, time-varying delay systems and discrete-time systems. In the sub-homogeneous case, we first show that the previous integral excitation condition is also sufficient such that the exponential stability is achieved. We also derive an exponential stability result by relaxing the cooperative and integral excitation conditions. In the time-varying delay case, a delay-independent exponential stability result is shown under the extended integral excitation condition. Finally, in the discrete-time case, based on the fact that each switched subsystem is order-preserving instead of cooperative, the exponential stability of the considered system is shown under a weak excitation condition. [ABSTRACT FROM AUTHOR]

This paper studies the distributed resource allocation problem with nonsmooth local cost functions subject to the coupled equality and inequality constraints. In particular, each local cost function is expressed as the sum of a differentiable function and two nonsmooth functions. By using the operator splitting and primal–dual method, a continuous-time distributed proximal algorithm is developed, which can be applied to more general local cost functions that are convex but not necessarily smooth. In addition, the proposed algorithm is fully distributed in the sense that the gain parameter can be determined locally and does not require any global information of the network. By applying Lyapunov stability analysis and convex optimization theory, it is shown that the decision variables of all the agents converge to an optimal solution. Finally, a simulation example is carried out to demonstrate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates the coordinated trajectory tracking problem of multiple vertical take-off and landing (VTOL) unmanned aerial vehicles (UAVs). The case of unidirectional information flow is considered and the objective is to drive all the follower VTOL UAVs to accurately track a desired trajectory associated with a leader. Firstly, a novel distributed estimator is developed for each VTOL UAV to obtain the leader's desired information asymptotically. With the outputs of the estimators, the solution to the coordinated trajectory tracking problem of multiple VTOL UAVs is transformed to individually solving the tracking problem of each VTOL UAV. Due to the under-actuated nature of the VTOL UAV, a hierarchical framework is introduced for each VTOL UAV such that a command force and an applied torque are exploited in sequence, then the position tracking to the estimated desired position and the attitude tracking to the command attitude are achieved. Moreover, an auxiliary system with proper parameters is implemented to guarantee the singularity-free command attitude extraction and to obviate the use of the unavailable desired information. The stability analysis and simulations effectively validate the achievement of the coordinated trajectory tracking of multiple VTOL UAVs with the proposed control approach. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive collision-free formation control strategy for a team of under-actuated spacecraft subject to parametric uncertainties. The objective is to drive follower spacecraft to form a prescribed shape around a leader, while collision avoidance is achieved among different spacecraft. To explore the under-actuated nature of the studied spacecraft, a hierarchical inner-outer loop strategy is adopted. First, in the outer position loop, a virtual force is synthesized by introducing negative gradients of novel potential functions with respect to the distances between spacecraft such that the collision-free formation objective is completed. Based on the synthesized virtual force, an applied thrust and a command attitude are extracted. Then, in the inner attitude loop, an applied torque is designed for each individual spacecraft to track the command attitude. Moreover, during the virtual force and applied torque syntheses, adaptive laws are developed to estimate and compensate the uncertain inertial parameters. In terms of Lyapunov theory, it is shown that the spacecraft trajectories driven by the proposed controller ultimately converges to a neighborhood of the desired formation. Finally, illustrative simulations are performed to verify the proposed theoretical results. [ABSTRACT FROM AUTHOR]

This paper contributes to developing necessary convergence conditions for directed signed networks subject to cooperative and antagonistic interactions. A class of Laplacian-dependent convergence conditions is presented in the presence of switching topologies. It is shown that the switching signed networks converge monotonically to the intersection space of the null spaces of all Laplacian matrices. Furthermore, the uniform bipartite consensus (respectively, uniform asymptotic stability) of switching signed networks is tied closely to the simultaneous structural balance (respectively, unbalance) of the switching signed digraphs associated with them. [ABSTRACT FROM AUTHOR]

In this paper, we study the targeted agreement problem for a group of Lagrangian systems. Each system observes a convex set as its local target and the objective of the group is to reach a generalized coordinate agreement towards these target sets. Typically, the generalized coordinate represents position or angle. We first consider the case when the communication graphs are fixed. A control law is proposed based on each system’s own target sensing and information exchange with neighbors. With necessary connectivity, the generalized coordinates of multiple Lagrangian systems are shown to achieve agreement in the intersection of all the local target sets while generalized coordinate derivatives are driven to zero. We also discuss the case when the intersection of the local target sets is empty. Exact targeted agreement cannot be achieved in this case. Instead, we show that approximate targeted agreement can be guaranteed if the control gains are properly chosen. In addition, when communication graphs are allowed to be switching, we propose a model-dependent control algorithm and show that global targeted agreement is achieved when joint connectivity is guaranteed and the intersection of local target sets is nonempty. Simulations are given to validate the theoretical results. [ABSTRACT FROM AUTHOR]

We consider a distributed consensus problem over a network, where at each time instant every node receives two pieces of information from disjoint neighboring sets: a weighted average of current states of neighbors from a primary network, and a weighted average of one-hop delayed states of neighbors from a secondary network. The proposed algorithm makes each node update its state to a weighted average of these individual averages. We show that convergence to consensus is guaranteed with non-trivial weights. We also present an explicit formula for the weights allocated to each piece of the information for the optimal rate of convergence, when the secondary network is the complement of the primary network. Finally numerical examples are given to explore the case when the neighbor sets of the agents do not cover the whole network. [ABSTRACT FROM AUTHOR]

In this paper, we study the discrete-time consensus problem over networks with antagonistic and cooperative interactions. A cooperative interaction between two nodes takes place when one node receives the true state of the other while an antagonistic interaction happens when the former receives the opposite of the true state of the latter. We adopt a quite general model where the node communications can be either unidirectional or bidirectional, the network topology graph may vary over time, and the cooperative or antagonistic relations can be time-varying. It is proven that, the limits of all the node states exist, and the absolute values of the node states reach consensus if the switching interaction graph is uniformly jointly strongly connected for unidirectional topologies, or infinitely jointly connected for bidirectional topologies. These results are independent of the switching of the interaction relations. We construct a counterexample to indicate a rather surprising fact that quasi-strong connectivity of the interaction graph, i.e., the graph contains a directed spanning tree, is not sufficient to guarantee the consensus in absolute values even under fixed topologies. Based on these results, we also propose sufficient conditions for bipartite consensus to be achieved over the network with joint connectivity. Finally, simulation results using a discrete-time Kuramoto model are given to illustrate the convergence results showing that the proposed framework is applicable to a class of networks with general nonlinear dynamics. [ABSTRACT FROM AUTHOR]

This paper studies the consensus problem for multi-agent systems. A distributed consensus algorithm is developed by constructing homogeneous pulse width modulators for agents in the network. In particular, a certain percentage of the sampling period named duty cycle is modulated according to some state difference with respect to the neighbors at each sampling instant. During each duty cycle, the amplitude of the pulse is fixed. The proposed pulse width modulation scheme enables all agents to sample asynchronously with arbitrarily large sampling periods. It provides an alternative digital implementation strategy for multi-agent systems. We show that consensus is achieved asymptotically under the proposed scheme. The results are compared with the self-triggered ternary controller. [ABSTRACT FROM AUTHOR]

This article addresses the formation control problem with mismatched compasses. Depending on the sensing and communication technology, compass mismatches may arise due to biases in measurement, drift in inertial sensing despite initial alignment, and even spatial variations in the earth’s magnetic field. To illustrate the key concepts underlying what happens, we first consider the two agent case and show that the agents converge to a fixed, but distorted formation exponentially fast. In contrast to the matched compass case, the formation is not asymptotically stationary. The distance error and the angular error between the actual final formation and the desired formation are explicitly given, as is the steady state velocity of the formation. The case of time-varying mismatched compasses is also studied. Based on the results, we then propose estimators to obtain the mismatched angle, which allow a compensation algorithm to be proposed such that the desired formation shape is achieved. Finally, the extensions to the n agent case are also considered and similar phenomena are encountered. Simulations are provided to validate the theoretical results. [ABSTRACT FROM AUTHOR]

This paper proposes scalable distributed least square algorithms for solving large-scale linear algebraic equations via multi-agent network. We consider two kinds of different decomposition structures of A x = b , in which each agent only knows a sub-block of linear equation instead of the complete row or column information in the existing results. By introducing one extra variable, the least square problem of linear equation can be transformed into a distributed constrained optimization problem. Based on the augmented Lagrange method, two continuous-time scalable distributed primal–dual algorithms are developed, in which all the states of agents have fewer dimension and can be even scalars. Subsequently, the discrete-time distributed algorithms with constant step-sizes are proposed by using the Euler discretization method, and the explicit bounds of constant step-sizes are provided. Based on the KKT condition and Lyapunov stability, we show that the proposed continuous-time and discrete-time distributed algorithms collaboratively obtain a least square solution with a linear convergence speed, and also own an additional property that verifies whether the obtained solution is an exact solution. Finally, some simulation examples are carried out to verify the effectiveness of the proposed algorithms. [ABSTRACT FROM AUTHOR]

In this paper, we construct a framework to describe and study the coordinated output regulation problem for multiple heterogeneous linear systems. Each agent is modeled as a general linear multiple-input multiple-output system with an autonomous exosystem which represents the individual offset from the group reference for the agent. The multi-agent system as a whole has a group exogenous state which represents the tracking reference for the whole group. Under the constraints that the group exogenous output is only locally available to each agent and that the agents have only access to their neighbors’ information, we propose observer-based feedback controllers to solve the coordinated output regulation problem using output feedback information. A high-gain approach is used and the information interactions are allowed to be switching over a finite set of networks containing both graphs that have a directed spanning tree and graphs that do not. Simulations are shown to validate the theoretical results. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we consider the global consensus problem for discrete-time multi-agent systems with input saturation constraints under fixed undirected topologies. We first give necessary conditions for achieving global consensus via a distributed protocol based on relative state measurements of the agent itself and its neighboring agents. We then focus on two special cases, where the agent model is either neutrally stable or a double integrator. For the neutrally stable case, any linear protocol of a particular form, which solves the consensus problem for the case without input saturation constraints, also solves the global consensus problem for the case with input saturation constraints. For the double integrator case, we show that a subset of linear protocols, which solve the consensus problem for the case without saturation constraints, also solve the global consensus problem for the case with input saturation constraints. The results are illustrated by numerical simulations. [Copyright &y& Elsevier]

Instead of using the conventional discrete-time or continuous-time protocols with arbitrary values, this paper studies a cooperative–antagonistic multi-agent network with three-option decision mechanism. In particular, each agent over the network periodically makes decisions just from three available options (i.e., "1", "0" and " − 1 ") at decision instants for the promotion of agreement with its cooperative neighbors or disagreement with its antagonistic neighbors. The asynchronous decisions of distinct agents are allowed herein. A digraph with signs is implemented to characterize the information delivery. Next, the consensus behaviors of the concerned cooperative–antagonistic multi-agent network are analyzed. In particular, on the basis of an intermediate modulus consensus result in terms of a strongly connected topology condition, it is first shown that structural balance is a sufficient and necessary condition for the bipartite consensus result. Besides this, a stabilizing result that all the agents reach an agreement at the origin is shown under the structurally unbalanced condition. On the other hand, for a relaxed signed digraph that contains a spanning tree, if only the root subgraph is strongly connected and structurally balanced, it is shown that only the root agents reach the bipartite consensus while the states of the non-root agents converge between the polarized values of the root agents. In addition, if the structural balance condition associated with the root subgraph cannot be guaranteed, the considered cooperative–antagonistic multi-agent network is shown stabilizing. Finally, simulations are carried out to verify the proposed theoretical results. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a distributed cooperative tracking problem is studied for a group of non-identical second-order nonlinear systems with bounded external disturbances. The control goal is to drive the states of the followers to converge to those of a time-varying leader in the presence of only local information interactions from the leader to the followers and between the followers. We first propose a simple distributed control algorithm for the case when both the relative position and relative velocity measurements are available for feedback. It is shown that distributed cooperative tracking can be achieved if in the sensing topology the leader has directed paths to all followers. Then, the extension to the case when the velocity measurements are not available is studied. We consider two different scenarios, i.e., when the absolute position measurements and local communication between neighbors are available and only the relative position measurements are available. Distributed observers and distributed control inputs are designed to address these two scenarios. Numerical studies are carried out to illustrate the theoretical results. [Copyright &y& Elsevier]

Abstract: Distributed finite-time attitude containment control for multiple rigid bodies is addressed in this paper. When there exist multiple stationary leaders, we propose a model-independent control law to guarantee that the attitudes of the followers converge to the stationary convex hull formed by those of the leaders in finite time by using both the one-hop and two-hop neighbors’ information. We also discuss the special case of a single stationary leader and propose a control law using only the one-hop neighbors’ information to guarantee cooperative attitude regulation in finite time. When there exist multiple dynamic leaders, a distributed sliding-mode estimator and a non-singular sliding surface were given to guarantee that the attitudes and angular velocities of the followers converge, respectively, to the dynamic convex hull formed by those of the leaders in finite time. We also explicitly show the finite settling time. [Copyright &y& Elsevier]

This paper considers the global finite-time attitude synchronization and coordinated tracking problems of multiple rigid bodies without angular velocity measurements. First, for the attitude synchronization problem, by combining the hybrid technique and homogeneous theory, a new velocity-free attitude synchronization algorithm is constructed to prevent the unwinding problem and achieve finite-time convergence. In the second place, for the leader-following tracking problem, we firstly propose a nonlinear distributed hybrid observer for each follower such that the leader's information can be estimated accurately. Then, based on the outputs of the distributed observer, we propose a velocity-free distributed attitude tracking algorithm such that the global finite-time attitude tracking objective is achieved. Finally, simulation results are provided to demonstrate the effectiveness of the proposed algorithms. [ABSTRACT FROM AUTHOR]

The controllable α/β ratio of Si 3 N 4 powder was synthesized using tetraethyl orthosilicate (TEOS), glucose, MgCl 2 and YCl 3 ·6H 2 O by sol-gel assisted carbothermal reduction and nitridation (CRN). This study aimed to investigate the impact of various parameters, including a H 2 O/TEOS mol ratio of the sol, a C/Si mol ratio, sintering aids, and the temperature of CRN on the phase transformation of α-Si 3 N 4. The results demonstrated that the H 2 O/TEOS ratio significantly influenced the relative content of α and β phase in Si 3 N 4 by changing the morphological characteristics of SiO 2. When the H 2 O/TEOS ratio was 100, β-Si 3 N 4 powder with an approximate β content over 88 wt% was synthesized at 1500 °C. This remarkable phase transformation was likely facilitated by the eutectic liquid phase consisting of MgSiO 3 /Mg 2 SiO 4. The SEM image revealed rod-like whiskers with a length around 1.4 μm for the β-Si 3 N 4 grains. Due to the presence of liquid phase, the synthesis of spherical-like α-Si 3 N 4 nano-powder with an α-phase content of 91 wt% was achieved at a lower temperature of 1450 °C, with an H 2 O/TEOS ratio of 15 and a C/Si ratio of 4. The size of the particles was about 70 nm due to the reduced reaction temperature. Furthermore, without the addition of any sintering aids or Si 3 N 4 seeds, high purity α-Si 3 N 4 with an α phase content approaching 96 wt% could be synthesized at 1500 °C, using an H 2 O/TEOS ratio of 15 and a C/Si ratio of 4. The resulting α-Si 3 N 4 powder exhibited an extremely regular hexagonal prism shape with a length of approximately 2 μm. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper focuses on designing distributed algorithms for solving the linear matrix equation in the form of A X B = F via a double-layered multi-agent network. Firstly, we equivalently transform the least squares (LS) problem of A X B = F into two subproblems. We introduce a double-layered multi-agent network, in which each agent only has access to partial information of matrices A , B and F , to solve these two subproblems in a distributed structure. Subsequently, we develop continuous-time and discrete-time distributed algorithms to obtain an LS solution of A X B = F. In particular, the sufficient and necessary conditions about the step-sizes are established, under which the discrete-time algorithm can linearly converge to an LS solution. Compared with the previous results in which each agent needs to communicate multiple matrix variables with the neighbors, the proposed algorithms effectively reduce communication burden for each agent since only one matrix variable is communicated in the upper-layer network and the communication variables in the lower-layered network are vectors with lower dimensions than matrices. Finally, an application example is provided to demonstrate the effectiveness of the proposed algorithms. [ABSTRACT FROM AUTHOR]

Vector function optimization problems, in which one or more variables are multidimensional vectors or infinite-dimensional vectors, have been extensively studied and demonstrated in existing schemes. In various real life applications, a cost function to be optimized usually involves matrix variables subjected to certain constraints. Locating its minimum can be modeled as an optimization problem on matrix manifold which is investigated in this paper. We first present an index-notation-arrangement based chain rule ( I-Chain rule ) to obtain the gradient information of the cost function. Two iterative algorithms, namely, trace-constraint-based projected gradient method (TPGM) and orthonormal-constraint-based projected gradient method (OPGM) are proposed and their convergence properties are established. We find that the network control problems can be effectively solved by both TPGM and OPGM. Two important phenomena are observed. For controlling directed networks with selectable inputs, both TPGM and OPGM tend to locate the nodes that divides the elementary stem/circle/dilation equally for consuming less energy, with OPGM having a slightly higher chance than TPGM. For controlling directed networks by only evolving the connection strengths on a fixed network structure, we find that after a network adaptively changes its topology in such a way that many similar sub-networks are gradually evolved, the control cost attains its minimum. Our work takes a further step from understanding optimization problems on matrix manifold to extending their applications in science and engineering. [ABSTRACT FROM AUTHOR]

This paper develops a distributed primal–dual algorithm via an event-triggered mechanism to solve a class of convex optimization problems subject to local set constraints, coupled equality and inequality constraints. Different from some existing distributed algorithms with the diminishing step-sizes, our algorithm uses the constant step-sizes, and is shown to achieve an exact convergence to an optimal solution with an ergodic convergence rate of O (1 / k) for general convex objective functions, where k > 0 is the iteration number. Based on the event-triggered communication mechanism, the proposed algorithm can effectively reduce the communication cost without sacrificing the convergence rate. Finally, a numerical example is presented to verify the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

• The thermal-mechanical behavior of the CHS T-joints with a welded collar plate under load, including the evolution laws of temperature field, strain, and displacement, is elucidated. • The welding residual effects on the CHS T-joints reinforced with a collar plate under load are revealed, where the thermal expansion and contraction deformation induced by high temperature dominates. • The applicability of existing specifications' strength reduction factors for the CHS T-joints reinforced with collar plate under load is discussed. • Size recommendations for the compressive strength of the CHS T-joints reinforced with collar plate under the chord preload are presented. The paper presents a comprehensive test program on collar plate reinforced CHS T-joints under different preload conditions, in order to investigate the effect of preload and welding thermal on reinforced joints. A total of four specimens, including specimens with and without preload when the collar plates were welded, were tested under brace axial loading. The test results, including welding temperature field, development of strain as well as welding residual deformation during the welding process are measured and presented in this paper. Furthermore, the failure model and compressive strength of the collar plate reinforced T-joints were determined. The test results demonstrated that the localized high temperature and rapid attenuation are the characteristics of the welding temperature field, which instantaneous peak temperature rose to 1808 °C at the local area and attenuated to 600 °C in an elliptic range of about 3.1 cm × 1.7 cm. The failure modes of collar plate reinforced CHS T-joints do not change with preload on the chord and welding thermal. Furthermore, preload on the chord reduces the compressive strength of reinforced joints. The strain distribution and residual deformation are affected by the thermal expansion and cold shrinkage, while the development of the welding temperature field is not affected by the preload. Finally, for compressive strength of CHS T-joints reinforced with collar plate by welding, the applicability of the reduction coefficient due to preload calculated by existing codes was assessed by comparing design values with experimental results. A finite element model by ANSYS, considering the welding heat, was established. Key parameters affecting the strength of the T-joint at the reinforced collar plate under load were identified through parametric study with finite element models. Construction recommendations of welded CHS T-joints are proposed. [ABSTRACT FROM AUTHOR]

Co-based metallic glasses with ultrahigh strength and high microhardness are regarded as ideal surface-coating materials to significantly improve hardness and wear resistance of substrate materials. In this paper, a Co-based amorphous powder with high glass-forming ability was prepared by gas-atomization technique. Then a large-area Co-based amorphous coating was fabricated from the powder by laser cladding technology. The effects of different laser parameters (i.e., laser scanning speed and operating voltage) on glass formation of the amorphous coating were investigated. Furthermore, the thermal properties, microhardness and wear resistance of the amorphous coating produced with an optimal laser parameter were evaluated. The results indicate that the Co-based amorphous cladding layer exhibits extremely high microhardness of ~14.9 GPa, which can significantly improve the wear resistance of the substrate. A complex wear-failure mechanism of the Co-based coating is clarified as a mixture role of abrasive- & fatigue-wear, oxidation wear and adhesive wear proofed by microstructural and element-distribution analysis of various worn surface. • Co-based amorphous coatings were fabricated with optimal laser-cladding parameters. • The coating shows high microhardness of ~15 GPa, 10 times higher than steel matrix. • The coating exhibits excellent wear resistance, ~20 times higher than the matrix. [ABSTRACT FROM AUTHOR]

This paper studies the Nash equilibrium seeking problem for non-cooperative games subject to set and nonlinear inequality constraints. The cost function for each player and the constrained function are determined by all the players' decision variables. Each player is assigned a constrained set while all the players are subject to a coupling nonlinear inequality constraint. A continuous-time distributed seeking algorithm using local information interaction is proposed, where the players deliver/receive information unidirectionally over a directed network. In particular, a distributed observer is first introduced for each player to estimate all the others' decision variables. Then, by using these estimates, a seeking algorithm is synthesized with a projection operator. Based on the time-scale separation approach, it is shown that the proposed continuous-time distributed seeking algorithm guarantees the convergence of the strategy profile to an arbitrarily small neighborhood of the generalized Nash equilibrium satisfying a KKT condition. An illustrative example is finally presented to validate the theoretical results. [ABSTRACT FROM AUTHOR]

In distributed optimization of multi-agent systems, agents cooperate to minimize a global function which is a sum of local objective functions. Motivated by applications including power systems, sensor networks, smart buildings, and smart manufacturing, various distributed optimization algorithms have been developed. In these algorithms, each agent performs local computation based on its own information and information received from its neighboring agents through the underlying communication network, so that the optimization problem can be solved in a distributed manner. This survey paper aims to offer a detailed overview of existing distributed optimization algorithms and their applications in power systems. More specifically, we first review discrete-time and continuous-time distributed optimization algorithms for undirected graphs. We then discuss how to extend these algorithms in various directions to handle more realistic scenarios. Finally, we focus on the application of distributed optimization in the optimal coordination of distributed energy resources. [ABSTRACT FROM AUTHOR]