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In this article, a multilayered and distributed architecture for mission-oriented miniature fixed-wing UAV swarms is presented. Based on the concept of modularity, the proposed architecture divides the overall system into five layers: 1) low-level control layer; 2) high-level control layer; 3) coordination layer; 4) communication layer; and 5) human interaction layer, and many modules that can be viewed as black boxes with interfaces of inputs and outputs. In this way, not only the complexity of developing a large system can be reduced but also the versatility of supporting diversified missions can be ensured. Furthermore, the proposed architecture is fully distributed that each UAV performs the decision-making procedure autonomously so as to achieve better scalability. Moreover, different kinds of aerial platforms can be feasibly extended by using the control allocation matrices and the integrated hardware box. A prototype swarm system based on the proposed architecture is built and the proposed architecture is evaluated through field experiments with a scale of 21 fixed-wing UAVs. Particularly, to the best of our knowledge, this article is the first work which successfully demonstrates formation flight, target recognition, and tracking missions within an integrated architecture for fixed-wing UAV swarms through field experiments. [ABSTRACT FROM AUTHOR]

Summary: This paper considers the leader‐follower formation flight of fixed‐wing unmanned aerial vehicles (UAVs) subject to velocity constraints. A novel distributed sliding mode control law is proposed for each UAV, whose kinematics is described by a unicycle model with a saturated angular velocity and a bounded linear velocity within an interval. The designed control law of each follower UAV only uses its own information and the information of its leader UAV. Driven by the designed control law, the desired formation is achieved with rigorous proof, while the follower UAVs' constraints of both the linear and angular velocities are satisfied. Moreover, the follower's speed adjustment range is relaxed and not required to be strictly larger than their leaders'. Finally, numerical simulations are presented to verify the results. [ABSTRACT FROM AUTHOR]

In this paper, a curved path following scheme with the aid of the vector field (VF) and the notion of input-to-state stable (ISS) for a fixed-wing unmanned aerial vehicle (UAV) is developed. The VF strategy is a robust and valid guidance method and its stability is proved using ISS properties. Many existing path following algorithms for fixed-wing UAVs are only proposed for straight-lines and orbits. However, the path required to be followed is always in approximate curves rather than straight-lines and orbits in many high-level missions, such as obstacle avoidance, search, and surveillance. The nonlinear-theoretic notion of ISS is playing a central role in the control law design and stability analysis. The error kinematics are converted into two interconnected subsystems with proven ISS properties, which yield the overall system that is globally asymptotically stable, i.e., and the along-track error and the cross-track error asymptotically approach zeros from any initial position in the space. The followed path is defined in terms of the arc-length parameter, and it can be expanded according to the waypoint fitting without the need to obtain a global function representation. The singularity of multiple closest points on the path is eliminated by constructing a speed profile of a virtual point on the path. The scheme is validated with a semi-physical experiment combined by an actual autopilot, ground station and the X-Plane flight simulator. Flight tests using a small fixed-wing UAV show excellent tracking performance of the curved path following. [ABSTRACT FROM AUTHOR]

This paper is concerned with general coopetition networks with signed graphs, based on which both the bipartite consensus and tracking control problems for networked systems subject to nonidentical matching uncertainties are studied. For the case of undirected and connected communication graphs, we propose a distributed discontinuous nonlinear controller which can achieve the bipartite consensus. To cancel the chattering phenomenon of the discontinuous controller, a continuous one is designed by using the boundary layer technique, under which the bipartite consensus error is shown to be uniformly ultimately bounded and can exponentially converge to a small adjustable bounded set. Further, considering the case of a leader having a bounded control action, we present a continuous controller to guarantee the ultimate boundedness of the bipartite tracking error. [ABSTRACT FROM AUTHOR]

Summary: A liquid sphere‐inspired physicomimetics approach is presented for multiagent formation control. The agents are formulated as a liquid sphere, which is modeled by a virtual spring network. Then, a decentralized controller is obtained for each agent. The stability and convergence are proved. The scalability and flexibility are analyzed. Using the proposed approach, arbitrarily shaped formations can be obtained; and an extra agent can be added to a formation like mixing a drop of liquid into a liquid sphere. By designing extra virtual repulsive forces from obstacles, a formation avoids obstacles like a fluid flowing over obstacles or squeezing through narrow passages. The required number of communication links is N for N agents. The use of physicomimetics makes the approach computationally simple, and the physical meanings of the parameters definite. To illustrate the advantages of the proposed approach, a structural potential function‐based approach is selected as the comparative method. Simulation results demonstrate the effectiveness of the liquid sphere‐inspired formation control approach. [ABSTRACT FROM AUTHOR]

This paper presents a novel method—continuous-time Markov decision process (CTMDP)—to address the uncertainties in pursuit-evasion problem. The primary difference between the CTMDP and the Markov decision process (MDP) is that the former takes into account the influence of the transition time between the states. The policy iteration method-based potential performance for solving the CTMDP and its convergence are also presented. The results obtained by MDP-based method demonstrate that it is a special case of CTMDP-based method involving the identity transition rate matrix. To compare the methods, a well-known pursuit-evasion problem, involving two identical cars, is solved as a benchmark. The CTMDP-based method can provide a discretization solution that is close to the analytical solution obtained by the differential game method. Besides, it shows strong robustness against changes in the transition probability, as compared with the traditional MDP-based method. To the best of our knowledge, this is the first attempt to validate the influence of the transition time between the states in such a pursuit-evasion scenario, or in a similar application, solved by an MDP-related model. The CTMDP-based method offers a new approach to solving the pursuit-evasion problem and can be extended to similar optimization applications. [ABSTRACT FROM AUTHOR]

This work explores the edge agreement problem of second‐order non‐linear multi‐agent systems under quantised measurements. Under the edge agreement framework, the authors introduce an important concept about the essential edge Laplacian and also obtain a reduced model of the edge agreement dynamics based on the spanning tree subgraph. The quantised edge agreement problem of second‐order non‐linear multi‐agent systems is studied, in which both uniform and logarithmic quantisers are considered. The authors do not only guarantee the stability of the proposed quantised control law, but also reveal the explicit mathematical connection of the quantised interval and the convergence properties for both uniform and logarithmic quantisers, which has not been addressed before. Particularly, for uniform quantisers, they provide the upper bound of the radius of the agreement neighborhood and indicate that the radius increases with the quantisation interval. While for logarithmic quantisers, the agents converge exponentially to the desired agreement equilibrium. In addition, the authors figure out the relationship of the quantisation interval and the convergence speed and also provide the estimates of the convergence rate. Finally, simulation results are given to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this paper, the recent developments of distributed coordination control problems are summarized in a graph-theory-based framework. Distributed coordination has attracted tremendous attention in control and robot communities because of its potential applications in the past decade. The graph is used to describe the interconnections among agents, and different distributed coordination control problems, such as consensus, formation control, rendezvous, alignment, swarming, flocking, containment control and circumnavigation control, are adopted to this description by considering different cooperative objects. Therefore it is natural to study the distributed coordination control problems via graph theory, and the graph-theory-based results on consensus, formation control, and some closely related issues, i.e., rendezvous/alignment, swarming/flocking, containment control and circumnavigation control, are reviewed, and provide a cohesive overview in the coordination control problems, in system modeling, control law designs and analysis, and structure transformation. Finally, towards the practical applications, some potential directions possibly deserving investigation in distributed coordination control are discussed. [ABSTRACT FROM AUTHOR]

A series of mono-substituted pyrene derivatives having a pyrene mesogenic core and aldehyde group peripherals were designed and synthesized, which had typical D--A structures. Photophysical properties of the compounds were characterized by UV/Vis spectroscopy and the third-order nonlinearities of the compounds were studied by 'open aperture' and 'closed aperture' -scan techniques. Both of the compounds showed typical nonlinear absorptions and refractions, and the third-order nonlinear susceptibilities have been found to be very high in all cases. The significant nonlinear optical response combined with the possibility to further modify it, by changing the electron acceptor and the electron-donor groups, suggests that these systems can prove to be important candidates for a variety of photonic/optoelectronic applications. [ABSTRACT FROM AUTHOR]

A novel series of D-π-A bi-alkyne liquid crystal derivatives were designed and synthesized, which had typical D-π-A structures. The third-order nonlinearities of the compounds were studied by “open aperture” and “closed aperture” Z-scan techniques. Both compounds showed typical nonlinear absorptions and refractions, and the third-order nonlinear susceptibilities have been found to be very high in all cases. The significant nonlinear optical response, combined with the possibility to further modify it, by changing the π-linking groups and the electron donors or acceptors, suggests that these systems can prove to be important candidates for a variety of photonic/optoelectronic applications. [ABSTRACT FROM AUTHOR]

This study develops an original and innovative matrix representation with respect to the information flow for networked multi-agent system. To begin with, the general concepts of the edge Laplacian of digraph are proposed with its algebraic properties. Benefit from this novel graph-theoretic tool, we can build a bridge between the consensus problem and the edge agreement problem, we also show that the edge Laplacian sheds a new light on solving the leaderless consensus problem. Based on the edge agreement framework, the technical challenges caused by unknown but bounded disturbances and inherently nonlinear dynamics can be well handled. In particular, we design an integrated procedure for a new robust consensus protocol that is based on a blend of algebraic graph theory and the newly developed cyclic-small-gain theorem. Besides, to highlight the intricate relationship between the original graph and cyclic-small-gain theorem, the concept of edge-interconnection graph is introduced for the first time. Finally, simulation results are provided to verify the theoretical analysis. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C 3 N 4 ) was synthesized from urea with a facile approach and was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transformed infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The as-synthesized g-C 3 N 4 was applied as sorbent to remove Pb(II) and aniline from aqueous solutions as a function of contact time, solid content, pH, ionic strength, temperature, and initial concentrations of Pb(II) and aniline. The results indicated that the sorption of Pb(II) was mainly dominated by outer-sphere surface complexation or ion exchange at pH < 7.0, but by inner-sphere surface complexation at pH > 7.0. The sorption of aniline was mainly attributed to electrostatic interaction at pH < 5.0, whereas the π–π electron donor–acceptor (EDA) interaction was the predominant sorption mechanism at pH > 5.0. The sorption isotherms of Pb(II) and aniline on g-C 3 N 4 were well described by the Langmuir model. The thermodynamic parameters calculated from the temperature-dependent sorption isotherms indicated that the sorption of Pb(II) and aniline on g-C 3 N 4 was endothermic and spontaneous processes. Moreover, g-C 3 N 4 could be regenerated through the desorption of Pb(II) and aniline by using 1.0 M HCl solution and alcohol, respectively, and no obvious decline of sorption capacity was found for the recycling results. All these results indicated that g-C 3 N 4 was a promising material for the preconcentration of Pb(II) and aniline from aqueous solutions in real pollution management. [ABSTRACT FROM AUTHOR]

In this paper, the model-free formation control problem is addressed for multiple satellites, whose dynamics involves rotation-translation coupling and nonlinearities. A two-step adaptive control strategy is proposed based on the reinforcement learning theory to iteratively solve the optimal formation control problem without knowledge of each satellite dynamics. The resulted controller is composed of an attitude controller to achieve the desired attitude, and a relative position controller to construct the satellite formation. The proposed global closed-loop control system is proven to be asymptotically stable. Simulation results on rotation-translation coupled satellite system confirm the effectiveness of the proposed adaptive optimal formation control strategy. • The model-free formation control problem is addressed for multiple satellites. • The dynamics of each satellite involves rotation-translation coupling and nonlinearities. • Optimal formation control for the real uncertain coupled multi-satellite system can be achieved. • A two-step learning scheme is proposed to address the rotation-translation coupled dynamics. • The accurate dynamical model parameters are not required to be known by the learning method. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) and graphene, and materials based on these, are largely used in multidisciplinary fields. Many techniques have been put forward to synthesize them. Among all kinds of approaches, the low-temperature plasma approach is widely used due to its numerous advantages, such as highly distributed active species, reduced energy requirements, enhanced catalyst activation, shortened operation time and decreased environmental pollution. This tutorial review focuses on the recent development of plasma synthesis of CNTs and graphene based materials and their electrochemical application in fuel cells. [ABSTRACT FROM AUTHOR]

In this article, a novel design scheme is introduced to solve the optimal control problem for nonlinear systems with unsymmetrical and state-dependent input constraints. By introducing an initial stabilizing control policy as the baseline of the constructed optimal control policy, we remove the assumption in the current study for the adaptive optimal control, that is, the internal dynamics should hold zero when the state of the system is in the origin. Particularly, nonlinear control systems with partially unknown dynamics are investigated and the procedure to acquire the corresponding optimal control policy is presented. The stability for the closed-loop dynamics and the optimality of the obtained control policy are both proved. Besides, we apply the proposed control design framework to solve the optimal circumnavigation problem based on the accumulative Fisher information for a fixed-wing unmanned aerial vehicle (UAV). The control performance of our algorithm is compared with that of the existing circumnavigation control policy in a numerical simulation. [ABSTRACT FROM AUTHOR]

Abstract: This paper provides a unified solution for the attitude and position tracking problem of a rigid body in 3-dimensional space, using the concept of the unit dual quaternion. The error dynamics described by a unit dual quaternion are deduced after the dual-quaternion-based dynamics of a single rigid body are given. Then by utilizing the feedback linearization principle, a unit dual quaternion based tracker is proposed based on the error dynamics, which is proven to render the equilibrium point of the closed loop system asymptotically stable, and includes the attitude and position regulation problems as particular cases. Furthermore, to solve the two equilibria problem, a switching parameter is introduced to improve the tracker, which causes the system to converge to the ‘nearer’ equilibrium with a ‘shorter’ path. Both the trackers uniquely deal with the rotational and translational dynamics simultaneously with non-singularity and maintain the interconnection between rotation and translation. Finally, the proposed control schemes with applications to the regulation problem and the tracking problem are simulated to illustrate the theoretical results. [Copyright &y& Elsevier]

This paper focuses on finding a dual quaternion solution to attitude and position control for multiple rigid body coordination. Representing rigid bodies in 3-D space by unit dual quaternion kinematics, a distributed control strategy, together with a specified rooted-tree structure, are proposed to control the attitude and position of networked rigid bodies simultaneously with notion concision and nonsingularity. A property called pairwise asymptotic stability of the overall system is then analyzed and validated by an example of seven quad-rotor formation in the Urban Search And Rescue Simulation (USARSim) platform. As a separate but related issue, a maximum depth condition of the rooted tree is found with respect to error accumulation along each path using dual quaternion algebra, such that a given safety bound on attitude and position errors can be satisfied. [ABSTRACT FROM AUTHOR]

In this article, we address the problem of robust fixed-time attitude stabilization for tilt trirotor unmanned aerial vehicle subjects to parameter uncertainties and external disturbances. First, a novel fixed-time stable system with a faster convergence rate is proposed. Second, a nonsingular fixed-time sliding mode surface is developed, which has better convergence performance than existing methods. Third, a continuous fast fixed-time sliding mode control law is proposed by applying the developed sliding mode surface and adaptive technique. As a result, the convergence time of the closed-loop system is bounded and independent of the initial conditions. Simulation and experiments are presented to verify that the proposed scheme can effectively and rapidly achieve attitude stabilization while maintaining high control precision and robustness. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the geometric structure, especially the Lie-group related properties, of unit dual quaternion is investigated. The exponential form of unit dual quaternion and its approximate logarithmic mapping are derived. Correspondingly, Lie-group and Lie-algebra on unit dual quaternions and the approximate logarithms are explored, respectively. Afterwards, error and metric based on unit dual quaternion are given, which naturally result in a new kinematic control model with unit dual quaternion descriptors. Finally, as a case study, a generalized proportional control law using unit dual quaternion is developed. [Copyright &y& Elsevier]

The microstructure and physical properties of glass foams prepared by using waste glass and SiC podwers were greatly improved by introduction of a new foaming promoter which was KNO 3 . KNO 3 which can produce oxygen by thermal decomposition reaction was another free oxygen supplier except the atmospheric oxygen. The foaming ability of SiC was directly dependent on the content of the oxygen around, so the addition of KNO 3 could notably promote the foaming process of glass foam. In addition, K 2 O, another thermal decomposition product of KNO 3 , was a classic network modifier in silicate glass networks and would enable glass batches to melt at lower temperatures. The effect of the addition of KNO 3 on the bulk density, crystalline phase, and microstructure of glass foams was studied. The experimental results showed that good correlation between physical properties and microstructure was observed with appropriate KNO 3 addition due to the formation of microstructure with homogeneous distribution of pores. [ABSTRACT FROM AUTHOR]

Abstract: Photocatalytic reduction of Cr(VI) to Cr(III) in aqueous solution containing ZnO or ZSM-5 zeolite under ambient condition was studied by using oxalate as model organic compound in the natural environment. ZSM-5 zeolite was characterized by X-ray diffraction (XRD), and point of zero net proton charge (PZNPC) titration. The effect of illumination time, mass content of catalyst (m/V), Cr(VI) initial concentrations, pH, ionic strength, and oxalate concentrations on the photocatalytic reduction of Cr(VI) was determined. The results indicate that the PZNPC of ZSM-5 zeolite is at pH 3.6±0.1. At C[Cr(VI)(initial)]=2.00×10−4 mol/L, pH 7.5±0.1 and after illumination time of 24h, the reduction of Cr(VI) were 1.1×10−5 mol/L (no ZSM-5 zeolite, 4.0×10−3 mol/L oxalate) and 1.0×10−5 mol/L (0.4g/L ZSM-5 zeolite, no oxalate), respectively; whereas the reduction of Cr(VI) achieved 1.0×10−4 mol/L in the presence of 0.4g/L ZSM-5 zeolite and 4.0×10−3 mol/L oxalate. The removal of Cr(VI) from solution is dependent on pH value. The results are important for the application of zeolites in the treatment of Cr(VI) polluted solution in the natural environment. [Copyright &y& Elsevier]

Abstract: Humic substances (HSs) can be easily adsorbed on natural solid surface and thereby affect the physicochemical behavior of metal ions in the natural environment. The influence of HSs is mainly attributed to the macromolecular structures and shapes of solution soluble and surface adsorbed HSs. Herein, to our knowledge, we firstly use both AFM and SEM to image and to compare the macromolecular structures of humic acid on the basal-plane surface of mica and silicon. Under our experimental conditions, spherical colloids are formed at low pH and high salt concentrations, while network or linear structures are formed at high pH and low salt concentrations. The shapes of HA are heterogeneous under different natural environmental conditions. The knowledge of macromolecular structures and shapes of HA in the natural environment is significant for the evaluation of metal ions’ behavior in HA–metal ion–mineral ternary systems. [Copyright &y& Elsevier]

Abstract: Removal of Ni(II) from aqueous solutions by sorption onto Na-rectorite was investigated under ambient conditions. Experiments were carried out as a function of mass content, pH, ionic strength and temperature. The results indicated that the sorption of Ni(II) was strongly dependent on pH value and ionic strength. Sorption of Ni(II) increased with increasing pH and decreasing ionic strength. The sorption of Ni(II) on Na-rectorite was mainly dominated by cation exchange at acidic conditions, whereas surface complexation was the main sorption mechanism at neutral to alkaline pH values. The effect of temperature on Ni(II) sorption on Na-rectorite was negligible at low pH (∼pH<6), whereas the effect of temperature was obvious at pH>6. The thermodynamic parameters (ΔH, ΔS, and ΔG) for Ni(II) sorption onto Na-rectorite were calculated from the temperature dependence, and the results suggested that the sorption reaction was endothermic. [Copyright &y& Elsevier]

Abstract: Thorium is considered as a chemical analog of other tetravalent actinides. Herein, the sorption of Th(IV) on TiO2 in the presence or absence of soil fulvic acid (FA)/humic acid (HA) as a function of pH, ionic strength and FA/HA concentration has been studied by a batch method. The morphology was characterized by scanning electron microscopy (SEM). The results indicate that sorption of Th(IV) on TiO2 increases from 0% to ∼94% at pH 1∼4, and then maintains level with increasing pH values. Both FA and HA have a positive effect on Th(IV) sorption at low pH values and the contribution of FA on Th(IV) sorption is rather higher than that of HA at pH<4. The sorption is weakly dependent on the concentration of KNO3 in solution, but the cations K+, Na+ and Li+ influence Th(IV) sorption more obviously. The batch results indicate that the inner sphere complex formation is formed at bare surfaces or FA/HA-bound TiO2 particle surfaces. Results of SEM analysis show that the particle sizes of TiO2, Th–TiO2 and Th–HA–TiO2 colloids are quite different. Surface complexation may be considered as the main sorption mechanism. [Copyright &y& Elsevier]

Abstract: The removal of Th(IV) from aqueous solution by using nanoparticles of anatase is studied under ambient conditions. The sorption of Th(IV) on TiO2 increases markedly at pH 1.5–4 and then maintains level with increasing pH values. The presence of HA/FA enhances the sorption of Th(IV) on TiO2 at low pH values. The Langmuir, Freundlich, Redlich-Peterson and Dubini-Radushkevich models are used to simulate the sorption isotherms, respectively. The results suggest that the sorption of Th(IV) on TiO2 occurs mainly by surface complexation. The adsorbed Th(IV) is very difficult to be desorbed from the solid surface. The results of XRD and Raman analysis indicate that the matrix of TiO2 does not undergo any structural change after the sorption of Th(IV) ions. The Ti-O-H stretching occurred in the IR spectral region of 1000–1300cm−1 for the hydrated TiO2 samples is responsible for sorption of metal binding, and provides indirect evidence for the surface complexation mechanism. [Copyright &y& Elsevier]

Abstract: The removal behavior of thorium (Th(IV)) has been investigated in multicomponent systems containing silica (SiO2) as the model of inorganic particles because of its widespread presence in the earth''s crust and soil humic acid (HA)/fulvic acid (FA) by batch experiments. The influence of pH from 2 to 12, ionic strength from 0.02 to 0.2M KNO3, soil HA/FA concentration from 8.3 to 22.5mg/L, and foreign cations (Li+, Na+, K+) and anions (NO3 −, Cl−) on the sorption of Th(IV) onto SiO2 was also tested. The sorption isotherms of Th(IV) at approximately constant pH (3.50±0.02) were determined and analyzed regressively with three kinds of sorption isotherm models, i.e., linear, Langmuir, and Freundlich models. The results demonstrated that the sorption of Th(IV) onto SiO2 increased steeply with increasing pH from 2 to 4. Generally, humic substances (HSs) were shown to enhance Th(IV) sorption at low pH, but to reduce Th(IV) sorption at intermediate and high pH. It was a hypothesis that the significantly positive influence of HA/FA at pH from 2 to 4 on the sorption of Th(IV) onto SiO2 was attributed to strong surface binding of HA/FA on SiO2 and subsequently the formation of ternary surface complexes such as ;O–HA–Th or ;O–FA–Th. The results also demonstrated that the sorption was strongly dependent on the concentration of HA/FA, and independent of ionic strength and foreign ions under our experimental conditions. [Copyright &y& Elsevier]

Abstract: The association of organic–inorganic colloid-borne trace elements was investigated. Radionuclide 152+154Eu(III) was chosen as a representative and chemical homologue for trivalent lanthanide and actinide ions present in radioactive nuclear waste. Effect of pH and contact time of organic–inorganic/Eu(III) on the kinetic dissociation of Eu(III) from HA–Al2O3 colloids was studied. The kinetic desorption behavior of sorbed 152+154Eu(III) from humic acid–γ-Al2O3 colloids was studied at pH values of 4.5±0.2, 5.3±0.2 and 6.5±0.2, respectively, by the addition of the chelating resin. The experimental results suggest that the fractions of irreversible sorption of radionuclide 152+154Eu(III) to HA–Al2O3 colloids increase with increasing pH values, and are independent of aging time. At least two different species, “weak” and “strong” dissociation fractions, are required to simulate the kinetic desorption of 152+154Eu(III) from HA–Al2O3 colloids. The species of Eu(III) sorbed on HA–Al2O3 colloids move from “weak” sites to “strong” sites with increasing aging time, whereas the fractions of irreversible sorption are independent of aging time. The results are important for the evaluation of radionuclides’ behavior in the environment. [Copyright &y& Elsevier]

Abstract: The ‘in-diffusion’ method was used to study the diffusion behavior of radionuclide 137Cs in compacted bentonite using a capillary. The results (distribution coefficient, K d, apparent and effective diffusion coefficients, D a and D e) derived from the capillary method are in good agreement with the literature data, and fit the Fick’s second law very well. The experiments were carried out at 3.3×10−3 and 3.3×10−5mol/l cesium, pH 3–12, ionic strength 0.1M NaClO4, and at room temperature. The results suggest that the diffusion of cesium in compacted bentonite is dependent on solution concentrations and pH values. In agreement with the literatures, the K d values derived from the capillary experiments are in most cases lower than those derived from batch experiments: the K d values are about one-half to one-third the values of those from batch experiments. The interlaminary space plays a very important role to the sorption, diffusion and transport of Cs+ in compacted bentonite. The effective diffusion coefficient is higher than that of other nuclides in compacted bentonite, and the diffusion of cesium in compacted bentonite may be dominated by the surface diffusion. [Copyright &y& Elsevier]

Abstract: The distribution coefficients of radionuclides derived from batch experiments are used to evaluate the migration behavior of radionuclides 99Tc and 243Am in compacted bentonite after different times. The effects of times, dispersion coefficient, distribution coefficient and pore water velocity on the concentration distribution of 99Tc and 243Am in the environment are also calculated from the theoretical migration equation. 99Tc is poorly sorbed to bentonite and moves quickly into the environment. Migration of radionuclide increases with increasing dispersion coefficient and decreasing distribution coefficient. The effects of water velocity on the migration of Tc and Am are obvious. Most 243Am is retained in the first several meters, and 20m of the backfill-compacted bentonites are sufficient to prevent the migration of radionuclide Am from the repository to the environment. [Copyright &y& Elsevier]

The effect of different calcareous soil solid components on the sorption and desorption of radioselenium was investigated by using a selective extraction method. The distribution coefficients, the breakthrough curves and the displacement curves were experimentally determined by batch and column experiments. The experiments were carried out at pH 7.8±0.2, T=20±1°C and in the presence of 0.001 M CaCl2. It is found that all sorption isotherms are linear, the sorption–desorption hysteresis for untreated and treated soils to remove organic matter, CaCO3 and organic matter plus CaCO3 is obvious; and the retention of radioselenium can probably be attributed to clay and oxides. The contributions of organic matter and CaCO3 to the sorption of radioselenium are significant, and the interaction effects among organic matter, CaCO3 and other components play an important role in the sorption of radioselenium in calcareous soil. The content of interlaminary space of compacted soil plays an important role in the sorption of radioselenium in compacted soil. The presence of CaCO3 retards the transport of radioselenium in soils, CaCO3 is an important trap of radioselenium. It is very difficult for the effluent concentration to reach the influent concentration, although radioselenium is very quickly detected in the effluent solution. The breakthrough curves (BTCs) can be simulated by a one-dimensional convection–dispersion transport model. [Copyright &y& Elsevier]

Abstract: The tetrad effect in the variation with atomic number Z of partitioning between organic phase and water phase and of coprecipitation from aqueous solution for the lanthanides (III, Lns3+) was found and confirmed in 1960s and 1990s, respectively [D.F. Peppard, G.W. Masom, S. Lewey, J. Inorg. Nucl. Chem. 31 (1969) 2271; D.F. Peppard, G.W. Mason, S. Lewey, J. Inorg. Nucl. Chem. 27 (1965) 2065; D.F. Peppard, A.A. Bloomquist, E.P. Horwitz, S. Lewey, G.F. Mason, J. Inorg. Nucl. Chem. 32 (1979) 339; I. Fidelis, S. Siekierski, J. Inorg. Nucl. Chem. 28 (1966) 185; L.J. Nugent, J. Inorg. Nucl. Chem. 32 (1970) 3485; C.K. Jørgensen, in: K.A. Gschneider Jr., L. Eyring (Eds.), Handbook of the Physics and Chemistry of Rare Earth, vol. 3, North-Holland, Amsterdam, 1991, Chapter 23; I. Kawabe, Geochem. J. 26 (1992) 369; R.D. Shannon, Acta Crystallogr. A 32 (1976) 751; I. Kawabe, A. Ohta, S. Ishii, M. Tokumura, K. Miyaushi, Geochem. J. 33 (1999) 167; I. Kawabe, A. Ohta, N. Miura, Geochem. J. 33 (1999) 181; I. Kawabe, Geochem. J. 33 (1999) 267; A. Ohta, I. Kawabe, Geochem. J. 34 (2000) 439; A. Ohta, I. Kawabe, Geochem. J. 34 (2000) 455; I. Kawabe, Geochem. J. 33 (1999) 349; I. Kawabe, T. Toriumi, A. Ohta, N. Miura, Geochem. J. 32 (1998) 213]. In 2002, the tetrad effect in the adsorption of Lns3+ at solid–water interface was reported [A. Ohta, I. Kawabe, Geochem. J. 34 (2000) 455; I. Kawabe, Geochem. J. 33 (1999) 349]. Is this effect more likely to occur in liquid–liquid and precipitate–liquid systems? Is this effect is an intrinsic property of the 4f electron elements in adsorption systems from aqueous solutions? Based on the available experimental data of adsorption systems from aqueous solutions from our laboratory and other laboratories [I. Kawabe, T. Toriumi, A. Ohta, N. Miura, Geochem. J. 32 (1998) 213; F. Coppin, G. Nerger, A. Bauer, S. Castet, M. Loubet, Chem. Geol. 182 (2002) 57; M. Majdan, S. Pikus, A. Gladyysz-Plaska, L. Fuks, E. Zieba, Colloids Surf. A 209 (2002) 27; Z.Y. Tao, X.K. Wang, X.X. Dai, J.Z. Du, Appl. Radiat. Isot. 52 (2000) 821; J.Z. Du, X.X. Dai, X.K. Wang, Z.Y. Tao, J. Radioanal. Nucl. Chem. 230 (1998) 129; X.K. Wang, W.M. Dong, H.X. Zhang, Z.Y. Tao, J. Radioanal. Nucl. Chem. 250 (2001) 491; J.Z. Du, X.M. Yin, X.K. Wang, X.X. Dai, X. Zhang, T.Y. Sun, Z.Y. Tao, Adsorp. Sci. Technol. 15 (1997) 341; X.K. Wang, W.M. Dong, Z.Y. Tao, Colloids Surf. A 223 (2003) 135; D. Koeppenkastrop, E.H. Decarlo, Chem. Geol. 95 (1992) 251; D. Koeppenkastrop, E.H. Decarlo, M. Roth, J. Radioanal. Nucl. Chem. 152 (1991) 337] and the theoretical analyses of coulombic interaction, hydration energy and chemical energy, it may be concluded that this effect may be more likely to occur in liquid–liquid and precipitate–liquid systems than in adsorption systems from aqueous solutions and that though refined spin-paring energy theory (RSPET) [I. Kawabe, Geochem. J. 26 (1992) 369; I. Kawabe, A. Masuda, Geochem. J. 35 (2001) 215] provides a theoretical basis of the tetrad effect, the occurrence of this effect in the adsorption systems from aqueous solutions depends mainly on many external factors, because the adsorption mechanisms of Lns3+ from aqueous solution are obviously more complex than those in the liquid–liquid and precipitate–liquid systems. The tetrad effect in the adsorption of lanthanides (III) from aqueous solution awaits further theoretical and experimental developments. [Copyright &y& Elsevier]

The effects of pH and Sr2+ solution concentration on diffusion and sorption of Sr2+ in compacted bentonite (ρb=1000±30 kg/m3) were studied using an “in-diffusion” method at an ionic strength of 0.1 M NaClO4. The results (distribution coefficients, Kd, apparent and effective diffusion coefficients, Da and De) derived from the capillary method are in good agreement with the literature data obtained for similar bentonite dry densities and fit Fick''s second law very well. The results suggest that the diffusion of Sr2+ in compacted bentonite decreases slightly with increasing pH values and also increases slightly with increasing Sr2+ solution concentration. The distribution coefficients are weakly dependent on the solution concentrations and show a slight increase with increasing pH values. The average effective diffusion coefficient of Sr2+ in compacted bentonite is (1.2±0.2)×10-9 m2/s, surface diffusion effects are found for the diffusion of Sr2+ in compacted bentonite. [Copyright &y& Elsevier]

The effect of pH, Eu(III) solution concentration and humic acid on the diffusion of Eu(III) in compacted bentonite (ρb=1000±30 kg/m3) was studied with “in-diffusion” method at an ionic strength of 0.1 M NaClO4. The results (Kd values from the first slice and theoretical calculation, apparent and effective diffusion coefficients) derived from the new capillary method are in good agreement with the literature data under similar conditions, and fit the Fick''s second law very well. The results suggest that the diffusion of Eu(III) is dependent on pH values and independent on solution concentration in our experimental conditions. Humic acid forms precipitation/complexation with Eu(III) at the surface of compacted bentonite and thus deduces the diffusion/transport of Eu(III) in compacted bentonite. The Kd values in compacted bentonite are in most cases lower than those in powdered bentonite obtained from batch experiments. The difference between the Kd values from powdered and compacted bentonite is a strong function of the bulk density of the bentonite. The results suggest that the content of interlaminary space plays a very important role to the diffusion, sorption and migration of Eu(III) in compacted bentonite. [Copyright &y& Elsevier]

In order to assess radionuclide diffusion and transport properties in compacted bentonite, the “in-diffusion' method based on bentonite filled capillaries is used. The effect of 99TcO4- concentration and pH value of the solution, the contact time and the dry density of compacted bentonite on the apparent diffusion coefficient (Da) and on the distribution coefficient (Kd) values obtained from the capillary test was studied. The Da and Kd values decrease with increasing of the bulk dry density of compacted bentonite. Ion exclusion influences the diffusion of 99TcO4- in the same substance. As compared to literature data, the Kd values obtained from capillary tests are in most cases lower than those from batch tests, the difference between the two Kd values is a strong function of dry density of the compacted bentonite. [ABSTRACT FROM AUTHOR]

The sorption of cesium onto g-Al2O3 was studied by using batch technique and ultra-filtration method at room temperature, at pH 4.0, 6.0 and 8.0 and ionic strength ranged from 0.001M to 0.1M NaClO4. The pore size of the filter 1000K was used to separate the liquid from the solid phase. UV vis spectrophotometer was used to determine the concentration of humic acid in the solution at wavelength of 254 nm. The sorption of humic acid and Cs on the g-Al2O3 was studied in the pH range from 2 to 12. The sorption of humic acid on the g-Al2O3 was strong (»98% HA was sorbed on the surface of g-Al2O3 below pH 9) and strongly depended on the pH values (above pHzpc the sorption of HA decreased markedly with the increasing of pH), humic acid has a little negative effect on the sorption of cesium. This may be attributed to the formation of HA-Cs complexation in the solution. The sorption of Cs onto g-Al2O3 was weak depending on the pH and independent on the ionic strength. The sorption of Cs onto g-Al2O3 may be contributed to cation exchange and surface complexation mechanism. [ABSTRACT FROM AUTHOR]

The distribution coefficients (Kd) of 32 elements from Na to Bi on a natural hematite (α-Fe2O3) were determined at pH 4, 7, 9 and in the presence and absence of fulvic acid (FA) by using a multitracer technique and the batch method. The multitracer solution was prepared by irradiation of Th(NO3)4 with 40Ar ion beam. The effects of pH and FA on the Kd values of 32 elements on the natural hematite were studied. It was found that both the sequences of alkali elements and alkaline earth elements can be roughly explained in terms of chemical bond formation and ion hydration enthalpies. Though the various effects of pH and the positive and negative effects of FA on the Kd values of 32 elements were found, the prevailing tendencies were the increase in Kd value with increasing pH and the negative effect of FA on the adsorption of elements from Na to Bi at very low concentration and pH 7. The adsorption of lanthanides on the hematite against the atomic number exhibited approximately as a “W” figure, the peak was around the element Tb and the valley was around the elements Eu and Yb. [Copyright &y& Elsevier]

Green and clean photocatalytic technology has been extensively applied to degrade environmental pollutants and produce renewable energy, which is an important mean to solve environmental and energy problems. However, limited to the cost and efficiency of photocatalysts, it is difficult to realize large-scale application. In recent years, the single-atom photocatalysts (SAPCs) have added new vitality into this field. SAPCs have the active homogeneous centers, heterogeneous structures, stability, high catalytic activity and selectivity properties. The related researches on its synthesis, characterization and application have become a hot spot in many fields. In this review, the photocatalytic H2 production, CO2 reduction, nitrogen fixation, NOx removal, volatile organic compounds removal, pollutant degradation, reduction of radionuclides and heavy metal ions using SAPCs are reviewed. The advantages and disadvantages of the six kinds of SAPCs substrates are analyzed, and design strategies are carefully summarized. The mechanisms of photocatalysis, isolated-site reactions, photogenerated e−-h+ transfer and the construction of efficient photoactivation cycles are discussed. Finally, the future development trend of SAPCs is prospected. This review will provide a reference for the design of high efficiency SAPCs. The structures, characteristics and synthesis of SAPCs with different substrates are reviewed. The applications of SAPCs and their photocatalytic removal for different pollutants are introduced. The photocatalytic reaction processes and mechanisms for different pollutants are discussed. The development direction and challenges of SAPCs in the field of environmental energy are prospected. [ABSTRACT FROM AUTHOR]

It is necessary to develop methods for rapid degradation of untreated waterborne contaminants due to their serious impact on the environment and human health. Here, we proposed a rapid and efficient microplasma electrochemistry (MIPEC) method for organic dye and antibiotic degradation. The atmospheric-pressure plasma acted as the anode and it could generate reactive radicals for rapid and complete degradation of rhodamine B (RhB) in about 6 min, which is one of the fastest methods to our knowledge. Similarly, the degradation of ciprofloxacin (CIP) has also been achieved. This method with mild and convenient operation conditions could be applied in a wide pH range due to the unique properties of the plasma anode, unrestricted by the pH of wastewater. The mechanism study revealed that more reactive species could be generated at the plasma anode than at the cathode, leading to a faster reaction rate at the anode side and the presence of oxygen could also accelerate the generation of reactive species. Besides, the MIPEC method can be used to treat a variety of dyes separately and together in minutes in different water bodies, making it a universal method suitable for treating different dyes in wastewater. This work provides a rapid and efficient method for waterborne contaminant degradation without any secondary pollution and need for post treatment, and also broadens the application field of the MIPEC method. [ABSTRACT FROM AUTHOR]

For the robot control problems, the input constraint is an issue that must be carefully considered. Considering the control inputs of the robots in the multi‐robot system are constrained by different saturations in reality, we address the cooperative circumnavigation control problem of multiple unicycle‐type robots with non‐identical and unknown input constraints in this paper. A distributed control law is designed to drive the robots constrained by different and unknown input saturations to achieve the cooperative circumnavigation around a moving target. The algorithm proposed in this paper largely reduces the requirement for the maneuverability of the robots to achieve the cooperative circumnavigation. As long as the robots owns the basic maneuverability of circumnavigating around the target, it is proved rigorously that the proposed control algorithm can achieve the desired cooperation circumnavigation of the multi‐robot system. The effectiveness of the proposed method is validated by a numerical simulation. [ABSTRACT FROM AUTHOR]

This article investigates the problem of coordinated path following for fixed-wing unmanned aerial vehicles (UAVs) with speed constraints in the two-dimensional plane. The objective is to steer a fleet of UAVs along the path(s) while achieving the desired sequenced inter-UAV arc distance. In contrast to the previous coordinated path-following studies, we are able through our proposed hybrid control law to deal with the forward speed and the angular speed constraints of fixed-wing UAVs. More specifically, the hybrid control law makes all the UAVs work at two different levels: 1) those UAVs whose path-following errors are within an invariant set (i.e., the designed coordination set) work at the coordination level and 2) the other UAVs work at the single-agent level. At the coordination level, we prove that even with speed constraints, the proposed control law can make sure the path-following errors reduce to zero, while the inter-UAV arc distances converge to the desired value. At the single-agent level, analysis for the path-following error entering the coordination set is provided. We develop a hardware-in-the-loop simulation testbed of the multi-UAV system by using actual autopilots and the X-Plane simulator. The effectiveness of the proposed approach is corroborated with both numerical simulation and the testbed. [ABSTRACT FROM AUTHOR]

• Different fabrication methods and their advantages and disadvantages of COF membranes are reviewed. • The application potential COF membrane in different liquid separations is introduced. • The mechanisms of COF membrane during liquid separation processes are summarized. • The challenges and prospects of the application of COF membrane are presented. Covalent organic frameworks (COFs) are a new kind of crystalline porous materials composed of organic molecules connected by covalent bonds, processes the characteristics of low density, large specific surface area, adjustable pore size and structure, and easy to functionalize, which have been widely used in the field of membrane separation technology. Recently, there are more and more researches focusing on the preparation methods, separation application, and mechanism of COF membranes, which need to be further summarized and compared. In this review, we primarily summarized several conventional preparation methods, such as two-phase interfacial polymerization, in-situ growth on substrate, unidirectional diffusion method, layer-by-layer assembly method, mixed matrix membranes, and so on. The advantages and disadvantages of each method are briefly summarized. The application potential of COF membrane in liquid separation are introduced from four aspects: dyeing wastewater treatment, heavy metal removal, seawater desalination and oil-water separation. Then, the mechanisms including pore structure, hydrophilic/hydrophobic, electrostatic repulsion/attraction and Donnan effect are introduced. For the efficient removal of different kind of pollutions, researchers can select different ligands to construct membranes with specific pore size, hydrophily, salt or organic rejection ability and functional group. The ideas for the design and preparation of COF membranes are introduced. Finally, the future direction and challenges of the next generation of COF membranes in the field of separation are prospected. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper investigates the formation of fixed-wing UAVs in 3D, which communicate via a directed acyclic graph. Different from common formation problems, we consider the roto-translation invariant (RTI) formation, where the "roto-translation" refers to a rigid-body motion obtained by composing rotation and translation. Besides, the fixed-wing UAV is modeled by a 3-D nonholonomic constrained rigid body instead of a particle agent. The main results of this paper include proposing the formation feasibility conditions and designing the formation controller. Firstly, we define the RTI formation and propose the conditions to guarantee that the formations are feasible for the fixed-wing UAVs under the nonholonomic and input saturation constraints. Secondly, given feasible formations, we design a formation controller by introducing a virtual leader and employing the compensation of rotation, followed by proving the stability of the closed-loop system. Finally, simulation examples are presented to verify the theoretical results. [ABSTRACT FROM AUTHOR]

Fault detection and localization are vital for ensuring the stability of data center networks (DCNs). Specifically, adaptive fault diagnosis is deemed a fundamental technology in achieving the fault tolerance of systems. The highly scalable data center network (HSDC) is a promising structure of server-centric DCNs, as it exhibits the capacity for incremental scalability, coupled with the assurance of low cost and energy consumption, low diameter, and high bisection width. In this paper, we first determine that both the connectivity and diagnosability of the m-dimensional complete HSDC, denoted by H S D C m (m) , are m. Further, we propose an efficient adaptive fault diagnosis algorithm to diagnose an H S D C m (m) within three test rounds, and at most N + 4 m (m − 2) tests with m ≥ 3 (resp. at most nine tests with m = 2 ), where N = m · 2 m is the total number of nodes in H S D C m (m) . Our experimental outcomes demonstrate that this diagnosis scheme of HSDC can achieve complete diagnosis and significantly reduce the number of required tests. [ABSTRACT FROM AUTHOR]

The use of machine learning (ML) in the field of predicting heavy metals interaction with biochar is a promising field of research, mainly because of the growing understanding of how removal efficiency is affected by characteristic variables, reaction conditions and biochar properties. The practical application in biochar still faces large challenges, such as difficulties in data collection, inadequate algorithm development, and insufficient information. However, the quantity, quality, and representation of data have a large impact on the accuracy, efficiency, and generalizability of machine learning tasks. From this perspective, the present data descriptors, the efficiency of machine learning-aided property and performance prediction, the interpretation of underlying mechanisms and complicated relationships, and some potential ways to augment the data are discussed regarding the interactions of heavy metals with biochar. Finally, future perspectives and challenges are discussed, and an enhanced model performance is proposed to reinforce the feasibility of a particular perspective. Highlights: A high growth rate of studies on the application of machine learning (ML) in biochar in recent years. ML interpretability of heavy metals (HMs) interaction mechanisms with biochar is explicated emphatically. Challenges and perspectives of ML application in the removal of HMs by biochar. Combining an advanced machine learning technique to achieve better predicted performance. [ABSTRACT FROM AUTHOR]

Transfer Learning (TL) has received a great deal of attention because of its ability to speed up Reinforcement Learning (RL) by reusing learned knowledge from other tasks. This paper proposes a new transfer learning framework, referred to as Transfer Learning via Artificial Neural Network Approximator (TL-ANNA). It builds an Artificial Neural Network (ANN) transfer approximator to transfer the related knowledge from the source task into the target task and reuses the transferred knowledge with a Probabilistic Policy Reuse (PPR) scheme. Specifically, the transfer approximator maps the state of the target task symmetrically to states of the source task with a certain mapping rule, and activates the related knowledge (components of the action-value function) of the source task as the input of the ANNs; it then predicts the quality of the actions in the target task with the ANNs. The target learner uses the PPR scheme to bias the RL with the suggested action from the transfer approximator. In this way, the transfer approximator builds a symmetric knowledge path between the target task and the source task. In addition, two mapping rules for the transfer approximator are designed, namely, Full Mapping Rule and Group Mapping Rule. Experiments performed on the RoboCup soccer Keepaway task verified that the proposed transfer learning methods outperform two other transfer learning methods in both jumpstart and time to threshold metrics and are more robust to the quality of source knowledge. In addition, the TL-ANNA with the group mapping rule exhibits slightly worse performance than the one with the full mapping rule, but with less computation and space cost when appropriate grouping method is used. [ABSTRACT FROM AUTHOR]

Abstract Green and clean photocatalytic technology has been extensively applied to degrade environmental pollutants and produce renewable energy, which is an important mean to solve environmental and energy problems. However, limited to the cost and efficiency of photocatalysts, it is difficult to realize large-scale application. In recent years, the single-atom photocatalysts (SAPCs) have added new vitality into this field. SAPCs have the active homogeneous centers, heterogeneous structures, stability, high catalytic activity and selectivity properties. The related researches on its synthesis, characterization and application have become a hot spot in many fields. In this review, the photocatalytic H2 production, CO2 reduction, nitrogen fixation, NOx removal, volatile organic compounds removal, pollutant degradation, reduction of radionuclides and heavy metal ions using SAPCs are reviewed. The advantages and disadvantages of the six kinds of SAPCs substrates are analyzed, and design strategies are carefully summarized. The mechanisms of photocatalysis, isolated-site reactions, photogenerated e−-h+ transfer and the construction of efficient photoactivation cycles are discussed. Finally, the future development trend of SAPCs is prospected. This review will provide a reference for the design of high efficiency SAPCs. HIGHLIGHTS The structures, characteristics and synthesis of SAPCs with different substrates are reviewed. The applications of SAPCs and their photocatalytic removal for different pollutants are introduced. The photocatalytic reaction processes and mechanisms for different pollutants are discussed. The development direction and challenges of SAPCs in the field of environmental energy are prospected. The structures, characteristics and synthesis of SAPCs with different substrates are reviewed.The applications of SAPCs and their photocatalytic removal for different pollutants are introduced.The photocatalytic reaction processes and mechanisms for different pollutants are discussed.The development direction and challenges of SAPCs in the field of environmental energy are prospected. [ABSTRACT FROM AUTHOR]

The selective removal of the β‐emitting pertechnetate ion (99TcO4−) from nuclear waste streams is technically challenging. Herein, a practical approach is proposed for the selective removal of 99TcO4− (or its surrogate ReO4−) under extreme conditions of high acidity, alkalinity, ionic strength, and radiation field. Hollow porous N‐doped carbon capsules loaded with ruthenium clusters (Ru@HNCC) are first prepared, then modified with a cationic polymeric network (R) containing imidazolium‐N+ units (Ru@HNCC‐R) for selective 99TcO4− and ReO4− binding. The Ru@HNCC‐R capsules offer high binding affinities for 99TcO4−/ReO4− under wide‐ranging conditions. An electrochemical redox process then transforms adsorbed ReO4− to bulk ReO3, delivering record‐high removal capacities, fast kinetics, and excellent long‐term durability for removing ReO4− (as a proxy for 99TcO4−) in a 3 m HNO3, simulated nuclear waste‐Hanford melter recycle stream and an alkaline high‐level waste stream (HLW) at the U.S. Savannah River Site (SRS). In situ Raman and X‐ray absorption spectroscopy (XAS) analyses showed that adsorbed Re(VII) is electrocatalytically reduced on Ru sites to a Re(IV)O2 intermediate, which can then be re‐oxidized to insoluble Re(VI)O3 for facile collection. This approach overcomes many of the challenges associated with the selective separation and removal of 99TcO4−/ReO4− under extreme conditions, offering new vistas for nuclear waste management and environmental remediation. [ABSTRACT FROM AUTHOR]

Abstract \nHighlights Green and clean photocatalytic technology has been extensively applied to degrade environmental pollutants and produce renewable energy, which is an important mean to solve environmental and energy problems. However, limited to the cost and efficiency of photocatalysts, it is difficult to realize large-scale application. In recent years, the SAPCs have added new vitality into this field. SAPCs have the active homogeneous centers, heterogeneous structures, stability, high catalytic activity and selectivity properties. The related researches on its synthesis, characterization and application have become a hot spot in many fields. In this review, the photocatalytic H2 production, CO2 reduction, nitrogen fixation, NOx removal, VOCs removal, pollutant degradation, reduction of radionuclides and heavy metal ions using SAPCs are reviewed. The advantages and disadvantages of the six kinds of SAPCs substrates are analyzed, and design strategies are carefully summarized. The mechanisms of photocatalysis, isolated-site reactions, photogenerated e−-h+ transfer and the construction of efficient photoactivation cycles are discussed. Finally, the future development trend of SAPCs is prospected. This review will provide a reference for the design of high efficiency SAPCs.The structures, characteristics and synthesis of SAPCs with different substrates are reviewed.The applications of SAPCs and their photocatalytic removal for different pollutants are introduced.The photocatalytic reaction processes and mechanisms for different pollutants are discussed.The development direction and challenges of SAPCs in the field of environmental energy are prospected. [ABSTRACT FROM AUTHOR]

The bearing‐based coordinated circumnavigation control for networked multi‐agent systems with only bearing measurements in the presence of moving target is studied. First, a distributed algorithm is proposed to estimate the target's velocity and the distances between the agents and the target, based on the velocity and the bearing information of the local network. Then, a distributed circumnavigation algorithm is designed to drive the agents to circumnavigate around a moving target at a desired distance. The stability of the proposed control algorithm is proven by employing the newly developed bearing rigidity theory. Finally, the simulation experiment is performed based on the Gazebo simulator to illustrate the effectiveness of the proposed circumnavigation control law. [ABSTRACT FROM AUTHOR]