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This paper investigates the problem of cooperative localization (CL) for a multi-robot system (MRS) under dynamic measurement topology, which involves a group of robots collectively estimating their poses with respect to a common reference frame using ego-motion measurements and robot-to-robot relative measurements. The authors provide a theoretical analysis of the time-varying unobservable subspace and propose a consistent cooperative localization algorithm. First, the authors introduce the relative measurement graph (RMG) to represent the relative pose measurements obtained by the MRS at each instant. Then, the authors derive the local observability matrix over a time interval. An equivalent relationship is established between the local observability matrix and the spectral matrices of the RMG. Moreover, the authors present a method for constructing the unobservable subspace based on the RMG under different topology conditions. Based on this analysis, the authors design a consistent cooperative localization algorithm that satisfies the constraints of the time-varying unobservable subspace. An analytical optimal solution is derived for the constrained optimization problem. Monte Carlo numerical simulations are conducted to demonstrate the consistency and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive output feedback tracking control scheme is proposed for a class of uncertain nonlinear systems where unknown parameters appear in the form of nonlinear parameterisation. Specific filters are constructed with the output signal and parameter estimates to make state estimation. The nonlinearly parameterised uncertainties are approximated by the Taylor expansion technique and compensation for remainder terms is realised with a series of high-order derivable functions to play the role of sign functions. A smooth positive function and parameter adaption technique are combined to deal with the effect made by state estimation error in the process of stability analysis of the closed-loop system. It is proved that all the signals are guaranteed to be bounded and the tracking error will converge to a small bounded set which is adjustable by tuning certain design constants. Numerical simulation is conducted to verify the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Summary: In this article, considering actuator constraints and possible failures, an adaptive compensation control scheme is developed to realize tracking control for a class of uncertain nonlinear systems with quantized inputs. A new variable is generated to evaluate the effect of actuator saturation and is used in the process of controller design to compensate for the influence of actuator saturation constraint. Moreover, the controller is able to show certain accommodation capability to tolerate possible actuator failures and input quantization error via integrating parameter update process of unknown fault constants into adaption of parametric uncertainties under the backstepping procedure. Specifically, actuator saturation effect and possible actuator failures as well as input quantization error can be dealt with uniformly under the framework of the proposed scheme and the control system has certain robustness to external disturbances. It is proved that all the signals of the closed‐loop system are ensured to be bounded and the tracking error is enabled to converge toward a compact set, which is adjustable by tuning design parameters. Finally, experiments are carried out on an active suspension plant to illustrate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Objective: To assess and compare fetal loss rates before 28 weeks of singleton and twin pregnancies after mid-trimester amniocentesis.Method: This historic cohort study included 13 773 women with singletons and 426 women with twins undergoing mid-trimester amniocentesis from 1/2015 to 3/2017. Pregnancies resulting in termination or selective reduction before 28 weeks were excluded, as well as twin gestations undergoing single-puncture amniocentesis. Fetal loss rates were compared between singleton and twins taking into account maternal characteristics, amniocentesis procedure, and fetal chromosomal abnormalities.Results: The rates of fetal chromosomal abnormalities were similar in singleton and twin gestations (1.13% vs 0.70%, P = .253). No difference was found in maternal or fetal characteristics, or amniocentesis procedure between the two groups. The fetal loss rate was significantly higher in twin compared with singleton pregnancies (1.91% vs 0.24%, P < .001, RR = 8.25 [95% CI: 4.51 to 15.09]). The fetal loss rate between monochorionic twins and dichorionic twins was similar (1.80% vs 1.78%, P = 1.000).Conclusions: Twin pregnancies have higher risk of fetal loss after mid-trimester amniocentesis, which cannot be explained by differences in rates of fetal chromosomal abnormalities, maternal characteristic, or amniocentesis technique. [ABSTRACT FROM AUTHOR]

The study investigates the trajectory estimation problem of a noncooperative gliding flight vehicle with complex and atypical maneuvers. An active switching multiple model (ASMM) method is proposed. This method employs a motion behavior model set (MBMS), a motion behavior recognition algorithm, and an active switching estimation and fusion algorithm. First, a recognizable MBMS, which can capture all the motion behaviors of a gliding flight vehicle, is established. Then, a motion behavior recognition algorithm based on recurrent neural networks (RNNs) is developed to obtain the current probability of each motion behavior. Then, an active switching estimation and fusion algorithm is proposed, in which the adopted models are actively chosen at each time instant according to a model selection strategy. Last, the proposed ASMM method is applied to a noncooperative gliding flight vehicle. The simulation results show that the proposed method has higher estimation precision and better dynamic performance. [ABSTRACT FROM AUTHOR]

In this paper, a cooperative region reconnaissance problem is investigated where a group of agents are required to fly across and detect events occur in an environment with static obstacles until an effective coverage is achieved. First, the region reconnaissance is formulated as a non-convex optimization problem. A coverage performance index with additional collision and obstacle avoidance constraints is given. Since the optimization index is an implicit function of state variables and cannot be used to compute gradients on state variables directly, an approximate optimization index is selected. Then, a non-convex optimization-based coverage algorithm is proposed to find the optimal reconnaissance location for each agent and guarantee no collisions trajectories among agents and obstacles. Finally, simulation experiments are performed to verify the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

To investigate the topological structure of finite games, various decomposions of finite games have been proposed. The inner product of vectors plays a key role in the decomposition of finite games. This paper considers the effect of different inner products on the orthogonal decomposition of finite games. We found that only when the compatible condition is satisfied, a common decomposition can be induced by the standard inner product and the weighted inner product simultaneously. To explain the result, we studied the existing decompositions, including potential based decomposition, zero‐sum based decomposition, and normalization based decomposition. For zero‐sum based decomposition and normalization based decomposition, we redefine their subspaces in a linear algebraic framework, which shows their physical meanings clearly. Bases of subspaces in these two decompositions are constructed. [ABSTRACT FROM AUTHOR]

Suspension operation reliability is one of the most significant performance indexes that concerns maneuvering stability and drive safety. In this paper, in order to guarantee good suspension reliability, an adaptive fault detection and isolation scheme is proposed for quarter-car active suspension systems with parametric and nonlinear uncertainties. To realize fault diagnosis for active suspensions, an adaptive fault detection estimator and several fault isolation estimators are designed to generate state residuals. Corresponding adaptive thresholds are developed to help judge the occurrence and type of possible faults. In the process of constructing state estimators, the uncertain parameter is updated online so that good sensitivity of fault detection can be achieved. Illustrative simulation is carried out to validate the effectiveness of the fault diagnosis scheme, and results indicate that the proposed method is sensible to sudden faults and maintain robustness to model uncertainties appearing in suspension systems. [ABSTRACT FROM AUTHOR]

This paper proposes a coverage problem of multi-agent systems, in which a group of agents enter a given region at different times and are required to cover the given region cooperatively. The focus of this paper is to solve the coverage problem of multi-agent systems with a non-convex optimization approach. By introducing appropriate assumptions, a gradient-based control law is designed based on the information of the previous stage agents. However, the performance index of each stage is nonlinear and generally non-convex and may have multiple local optima to which a gradient may converge. Thus, an effective boosting function, which is used to prevent the non-convex optimization problem getting into local optimum, is shown. It is proved in the sense of Lyapunov that the global coverage for the multi-agent systems with different entry time for coming into the given region can be achieved. Numerical simulations with cooperative control of industries subsystems show the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Considering an aircraft threatened by an interceptor, one of the effective penetration strategies is to release a Defender from the aircraft to confront the interceptor. In this case, the aircraft, the Defender, and the interceptor constitute the three-body guidance relationship, and the cooperation of the aircraft and its Defender to achieve the best tactical effects turns into a concerned problem. This paper studies the triangle interception guidance problem via the finite-time theory. The paper presents linear system Input-Output Finite-Time Stabilization (IO-FTS) method. The sufficient conditions of the linear system, being IO-FTS, under Finite-Time Boundedness (FTB) constraint are proposed, by which the state feedback controllers design method is obtained, via Linear Matrix Inequalities (LMIs). The triangle interception guidance problems are studied in three different cases, where the proposed methods are applied to the guidance design. The simulation results illustrate the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

Combined with the current situation of test wells injection string, YHH high swelling particles of profile control construction process was designed based on studying the geological characteristics of profile control test block, and then its profile control mechanism was described in detail. Profile control pilot test results obtained from 4 injection wells of Block West 24-9 Fuyu oilfield confirmed that: the oil increment and water control effect is significant for the corresponding benefit well group, and the YHH high-swelling particles can applied to multi-stage separate injection pipe column in profile control construction process. Compared to the construction with cross-linked polymer, clay, fly ash and lime, the YHH high-swelling particles profile construction has the advantage of short cycle period, lower risk and quick returns, which broadens the way of carrying out the profile control process in the future. [ABSTRACT FROM AUTHOR]

In this study, we consider an acyclic rigid formation with a group of mobile autonomous agents moving in a two‐dimensional space. The formation is generated via a Henneberg sequence construction in which there is one global leader that does not follow any other agents, one first‐follower that only follows the global leader, and each of other agents has two leaders, which is added by a vertex addition or an edge splitting operation. The entire formation moves with the leadership of the global leader. Every follower agent tries to maintain distances towards its leaders. Under the constraint of the acceleration for the global leader, the distributed formation control laws are proposed for the followers that only use the locally relative distance measurement. The control law of the first‐follower is proposed, which needs to know the velocity of the global leader and the relative distance between the global leader and itself. The global asymptotic stability of the expected formation is proved via a Lyapunov‐based technique for the considered multi‐agent system. Moreover, the stable rigidity problem of a formation is investigated for the proposed distributed relative position‐only formation control law. Necessary and sufficient conditions are provided that must be satisfied by the architecture of the underlying graph. Simulation results illustrate the effectiveness of the proposed formation control approach. [ABSTRACT FROM AUTHOR]

In this study, the authors consider a coordinated target assignment problem where a group of unmanned flight vehicles cooperate with each other to combat with a set of target vehicles which may perform various manoeuvres. Each flight vehicle is expected to be optimally assigned to a manoeuvring target vehicle such that the maximal possibility of successful interception can be guaranteed. Considering the course of the engagement, the target assignment should be achieved in terms of the performance over a limited time interval. The authors establish a linear time‐varying system in a finite‐time horizon to study the target assignment problem. A cost function is proposed based on the finite‐time generalised H2 gain measurement and the finite‐time final value performance measurement which can be viewed as the metric of the maximal required acceleration and the zero miss distance. For computation, the properties and performance criterion of the finite‐time generalised H2 gain are proved. The computation of the finite‐time final value performance measurement is also treated. The targets are assigned by minimising the value of the overall assignment evaluation function. Finally, the authors give some simulation results to illustrate the effectiveness of the proposed target assignment method. [ABSTRACT FROM AUTHOR]

This paper investigates a dynamic target-assignment problem. A close-loop integrated frame for target-assignment is proposed novelly which incorporates the kinematics between flight vehicles and targets. Based on an integral performance index which represents the energy cost, the optimal switching assignmentplan is obtained. Considering the configuration variation introduced by a switching assignment-plan, an H guidance law with switching-target is proposed which underlays a dynamic assignment process in cooperative tracking. Simulation results are given to show the effectiveness of the proposed guidance-law and the switchingplan for target assignment. [ABSTRACT FROM AUTHOR]

Recovering membrane backwash water (MBW) can improve productivity and reduce the costs of membrane treatment systems. To verify a recovery scheme in which MBW is pre-treated and recycled into an equalization tank, two lab-scale flocculation-microfiltration (MF) membrane systems were constructed. One membrane system used water from the Luan River (the Luan River system), and the other used a blend of pre-treated membrane backwash water plus water from the Luan River in a 1:9 ratio (the mixed water system). The operating parameters and coagulant dosages were the same for both systems. Ferric chloride was used as a coagulant in the pre-treatment of membrane backwash water, and powdered activated carbon (PAC) was added to improve water quality. Organic compounds, as represented by UV254 measurements, in the membrane backwash water were predominantly low molecular weight species (MW < 1 kDa), whereas the DOC fraction consisted primarily of compounds with an MW greater than 30 kDa and substances with an MW less than 1 kDa. These two fractions of organics were effectively reduced by flocculation and adsorption. No differences in the quality of treated water from the two membrane systems were observed. The results indicated that the scheme of recovering membrane backwash water was feasible. [ABSTRACT FROM AUTHOR]

pilot-scale ultrafiltration membrane plant was set up for treating Luanhe River water with flocculating and precipitation process of waterworks. The aim is to investigate the variation and characteristics of natural organic matter and disinfection byproducts formation potential in the whole process in winter. The results show that dissolved organic matter (DOM), UV, trihalomethanes formation potential (THMsFP) and haloacetic acids formation potential (HAAsFP) of Luanhe River water were mainly distributed in the range of molecular weight (MW) <1 kDa, so were the membrane feed water and treated water by membrane. Specific UV absorbance, specific THMsFP and specific HAAsFP have the maximal value in the MW fraction of 1-3 kDa, except that specific UV absorbance of membrane feed water is in the range of 3-10 kDa; DOM of membrane backwash water is mainly distributed in the range of MW>30 kDa and MW<1 kDa. It is the DOM in water backwashing in up way that made significant contribution to the higher dissolved organic carbon content in membrane backwash water. However, UV, THMsFP and HAAsFP were mainly distributed in the range of MW<1 kDa. The highest concentrations of specific THMsFP and specific HAAsFP appeared in the MW fraction of 3-10 kDa. CHCl was the major THMs species during MBW chlorination and occupied more than 60% of the total THMsFP. Dichloroacetic acid and trichloroacetic acid were the main components in HAAsFP. The concentration of THMsFP and HAAsFP in MBW was influenced by operation period. [ABSTRACT FROM AUTHOR]

In this paper, we present an interval model of networked control systems with time-varying sampling periods and time-varying network-induced delays and discuss the problem of stability of networked control systems using Lyapunov stability theory. A sufficient stability condition is obtained by solving a set of linear matrix inequalities. In the end, the illustrative example demonstrates the correctness and effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]