Showing papers by "University of Science and Technology Beijing published in 2016"
TL;DR: In this paper, the authors demonstrate the possibility to precipitate a coherent reinforcing phase in a fcc-FeCoNiCr HEA matrix using minor additions of Ti and Al, and demonstrate that extraordinary balanced tensile properties at room temperature were achieved, which was due to a well combination of various hardening mechanisms, particularly precipitation hardening.
1,486 citations
TL;DR: Adaptive neural network control for the robotic system with full-state constraints is designed, and the adaptive NNs are adopted to handle system uncertainties and disturbances.
Abstract: This paper studies the tracking control problem for an uncertain ${n}$ -link robot with full-state constraints The rigid robotic manipulator is described as a multiinput and multioutput system Adaptive neural network (NN) control for the robotic system with full-state constraints is designed In the control design, the adaptive NNs are adopted to handle system uncertainties and disturbances The Moore–Penrose inverse term is employed in order to prevent the violation of the full-state constraints A barrier Lyapunov function is used to guarantee the uniform ultimate boundedness of the closed-loop system The control performance of the closed-loop system is guaranteed by appropriately choosing the design parameters Simulation studies are performed to illustrate the effectiveness of the proposed control
1,021 citations
TL;DR: In this paper, a review of the recent advances in the discovery and structural design of LED phosphors is presented, including the discovery of the novel phosphors from the existing structural models, discovery of new crystal materials by doping and structural modification of the known phosphors.
848 citations
TL;DR: In this article, the authors showed that the precipitation of hard σ and μ intermetallic compounds tremendously strengthened the CoCrFeNiMo 0.3 HEA but without causing a serious embrittlement.
597 citations
TL;DR: Wang et al. as discussed by the authors developed a p-n junction BiOI@Bi12O17Cl2 heterostructure via facilely in situ depositing biOI nanosheets on the surface of Bi 12O 17Cl2 plates.
Abstract: Synthesis of reactive exposing facets and p-n junction are of great importance for semiconductor photocatalysis. Herein, we develop a p-n junction BiOI@Bi12O17Cl2 heterostructure via facilely in situ depositing BiOI nanosheets on the surface of Bi12O17Cl2 plates. Owing to the charge inducement, the BiOI nanosheets are all vertically assembled onto the Bi12O17Cl2 large plates to form a unique front-lateral surfaces coupling heterostructure, which enables high exposure of {001} reactive exposing facets of BiOI. The photocatalytic properties are systematically evaluated by degrading multiform industrial contaminants and antibiotic, like 2,4-dichlorophenol (2,4-DCP), rhodamine B (RhB), phenol, bisphenol A (BPA), and tetracycline hydrochloride. It reveals that the BiOI@Bi12O17Cl2 heterostructure not only shows dramatically strengthened photocatalytic activity, but also unfold powerful and nonselective photooxidation ability under visible-light illumination. The photoelectrochemical characterizations demonstrated that the drastically promoted separation and transfer of charge carriers that derived from the benefits of BiOI {001} active facets and BiOI@Bi12O17Cl2 p-n junction are in charge of the high photo-activity. Detailed radicals detection and quantification experiments further corroborate our conclusions. The study may give us some new hints on designing novel heterostructured photoelectronic materials with integrating p-n junction and active exposing facets.
554 citations
TL;DR: Cooperative control laws are proposed and the integral-barrier Lyapunov functions are employed for stability analysis of the closed-loop system and Adaption laws are developed for handling parametric uncertainties.
496 citations
29 Feb 2016
TL;DR: This treatise discusses a range of critical issues related to the implementation, performance enhancement and optimization of FD systems, including important topics such as hybrid FD/HD scheme, optimal relay selection and optimal power allocation, etc.
Abstract: The family of conventional half-duplex (HD) wireless systems relied on transmitting and receiving in different time slots or frequency subbands. Hence, the wireless research community aspires to conceive full-duplex (FD) operation for supporting concurrent transmission and reception in a single time/frequency channel, which would improve the attainable spectral efficiency by a factor of two. The main challenge encountered in implementing an FD wireless device is the large power difference between the self-interference (SI) imposed by the device’s own transmissions and the signal of interest received from a remote source. In this survey, we present a comprehensive list of the potential FD techniques and highlight their pros and cons. We classify the SI cancellation techniques into three categories, namely passive suppression, analog cancellation and digital cancellation, with the advantages and disadvantages of each technique compared. Specifically, we analyze the main impairments (e.g., phase noise, power amplifier nonlinearity, as well as in-phase and quadrature-phase (I/Q) imbalance, etc.) that degrading the SI cancellation. We then discuss the FD-based media access control (MAC)-layer protocol design for the sake of addressing some of the critical issues, such as the problem of hidden terminals, the resultant end-to-end delay and the high packet loss ratio (PLR) due to network congestion. After elaborating on a variety of physical/MAC-layer techniques, we discuss potential solutions conceived for meeting the challenges imposed by the aforementioned techniques. Furthermore, we also discuss a range of critical issues related to the implementation, performance enhancement and optimization of FD systems, including important topics such as hybrid FD/HD scheme, optimal relay selection and optimal power allocation, etc. Finally, a variety of new directions and open problems associated with FD technology are pointed out. Our hope is that this treatise will stimulate future research efforts in the emerging field of FD communications.
493 citations
TL;DR: An overview of the recent developments of LED phosphor systems is presented and methodologies for the discovery of new LED phosphors by mineral-inspired prototype evolution and new phase construction, as well as combinatorial optimization screening, and the single-particle-diagnosis approach are analyzed and exemplified.
Abstract: Stable and efficient phosphor systems for white light-emitting diodes (LEDs) are highly important with respect to their application in solid-state lighting beyond the technical limitations of traditional lighting technologies. Therefore, inorganic solid-state conversion phosphors must be precisely selected and evaluated with regard to their special material properties and synergistic optical parameters. In this perspective, we present an overview of the recent developments of LED phosphors; firstly, general photoluminescence-controlling strategies for phosphors to match LED applications have been evaluated; secondly, state-of-the-art and emerging new LED phosphors have been demonstrated. Then, methodologies for the discovery of new LED phosphors by mineral-inspired prototype evolution and new phase construction, as well as combinatorial optimization screening, and the single-particle-diagnosis approach, have been analyzed and exemplified. Finally, future developments of LED phosphors have been proposed.
454 citations
TL;DR: Water pollution was negatively associated with health outcomes, and the common pollutants in industrial wastewater had differential impacts on health outcomes.
437 citations
TL;DR: In this paper, the authors report the fabrication of a self-assembled 3D films platform that combines a natural viscoelastic property material P(VDF-TrFe) with an electrically conductive material rGO for the first time.
434 citations
TL;DR: A review of the progress in TENGs for both high performance energy conversion and self-powered electrochemical systems in application such as water splitting, sea water desalination, air pollution cleaning, degradation of organic pollutant, collecting of heavy metal ions and many more can be found in this paper.
Abstract: Ever since the discovery of triboelectric nanogenerator (TENG) by Wang's group in January 2012, various breakthroughs have been achieved in the fundamental mechanisms of TENG as well as the demonstrated self-powered systems. TENG has shown many advantages in micro-scale energy harvesting for applications in sensors and portable devices. As a self-sufficient power source, TENG can be used in conjunction with electrochemical processes as self-powered electrochemistry without the use of external power source. This review mainly focuses on the updated progress in TENGs for both high performance energy conversion and self-powered electrochemical systems in application such as water splitting, sea water desalination, air pollution cleaning, degradation of organic pollutant, collecting of heavy metal ions and many more. The idea of performing electrochemistry without using an external power could be useful for large-scale application in environmental science.
TL;DR: In this article, the effect of MnO2 structure on ozone decomposition has been investigated, and three tunnel-structure polymorphs, i.e., α-, β- and γ-MnO2 were prepared and characterized by BET, TEM, XRD, H2-TPR, O2TPD, NH3-TPD and TGA-MS and XPS.
Abstract: Ozone is a ubiquitous pollutant and manganese dioxide (MnO2) has been widely used for ozone decomposition. However, the effect of MnO2 structure on ozone decomposition has never been investigated. Three tunnel-structure polymorphs, i.e., α-, β- and γ-MnO2 were prepared and characterized by BET, TEM, XRD, H2-TPR, O2-TPD, NH3-TPD, TGA-MS and XPS. The activity of three MnO2 polymorphs for ozone decomposition followed the order of α- > γ- > β-MnO2. The α-MnO2 owned the largest specific surface area and lowest average oxidation state of Mn. Furthermore, the adsorbed oxygen species on the surface of α-MnO2 were more easily reduced. In-situ Raman spectroscopy results showed that peroxide species formed during ozone decomposition, and over α-MnO2 they were more easily decomposed by increasing reaction temperature. It was found that the catalytic activity of MnO2 strongly depended on the density of oxygen vacancies. Accordingly, the ozone decomposition mechanism based on the involvement and recycling of oxygen vacancy (VO) is proposed. The decomposition of peroxide species is a rate-limiting step. These findings are helpful for designing more effective catalyst for ozone removal.
TL;DR: In this article, a rechargeable aluminum-ion battery based on Al3+ intercalation and deintercalation is fabricated with Ni3S2/graphene microflakes composite as cathode material and high-purity Al foil as anode.
Abstract: Due to an ever-increasing demand for electronic devices, rechargeable batteries are attractive for energy storage systems. A novel rechargeable aluminum-ion battery based on Al3+ intercalation and deintercalation is fabricated with Ni3S2/graphene microflakes composite as cathode material and high-purity Al foil as anode. This kind of aluminum-ion battery comprises of an electrolyte containing AlCl3 in an ionic liquid of 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl). Galvanostatic charge/discharge measurements have been performed in a voltage range of 0.1–2.0 V versus Al/AlCl4 −. An initial discharge specific capacity of 350 mA h g−1 at a current density of 100 mA g−1 is achieved, and the discharge capacity remains over 60 mA h g−1 and coulombic efficiency of 99% after 100 cycles. Typically, for the current density at 200 mA g−1, the initial charge and discharge capacities are 300 and 235 mA h g−1, respectively. More importantly, it should be emphasized that the battery has a high discharge voltage plateau (≈1.0 V vs Al/AlCl4 −). These meaningful results represent a significant step forward in the development of aluminum-ion batteries.
TL;DR: In this article, the authors report the development of multi-shelled vanadium oxide hollow microspheres and their related electrochemical properties, in contrast to the conventional cation-adsorption process, which the metal cations adsorb on negatively charged carbonaceous templates, their approach enables the adsorption of metal anions.
Abstract: One of the major problems in the development of lithium-ion batteries is the relatively low capacity of cathode materials compared to anode materials. Owing to its high theoretical capacity, vanadium oxide is widely considered as an attractive cathode candidate. However, the main hindrances for its application in batteries are its poor capacity retention and low rate capability. Here, we report the development of multi-shelled vanadium oxide hollow microspheres and their related electrochemical properties. In contrast to the conventional cation-adsorption process, in which the metal cations adsorb on negatively charged carbonaceous templates, our approach enables the adsorption of metal anions. We demonstrate controlled syntheses of several multi-shelled metal oxide hollow microspheres. In particular, the multi-shelled vanadium oxide hollow microspheres deliver a specific capacity of 447.9 and 402.4mAhg(-1) for the first and 100th cycle at 1,000mAg(-1), respectively. The significant performance improvement offers the potential to reduce the wide capacity gap often seen between the cathode and anode materials.
TL;DR: In this paper, for the first time, the admissibility properties of the iterative control laws are developed for value iteration algorithms and it is emphasized that new termination criteria are established to guarantee the effectiveness of the iteration control laws.
Abstract: In this paper, a value iteration adaptive dynamic programming (ADP) algorithm is developed to solve infinite horizon undiscounted optimal control problems for discrete-time nonlinear systems. The present value iteration ADP algorithm permits an arbitrary positive semi-definite function to initialize the algorithm. A novel convergence analysis is developed to guarantee that the iterative value function converges to the optimal performance index function. Initialized by different initial functions, it is proven that the iterative value function will be monotonically nonincreasing, monotonically nondecreasing, or nonmonotonic and will converge to the optimum. In this paper, for the first time, the admissibility properties of the iterative control laws are developed for value iteration algorithms. It is emphasized that new termination criteria are established to guarantee the effectiveness of the iterative control laws. Neural networks are used to approximate the iterative value function and compute the iterative control law, respectively, for facilitating the implementation of the iterative ADP algorithm. Finally, two simulation examples are given to illustrate the performance of the present method.
TL;DR: In this paper, a review of the recent advances with respect to five well-known PBDTTT polymers and their design considerations, basic properties, photovoltaic performance, as well as device application in conventional, inverted, tandem solar cells.
Abstract: With the advances in organic photovoltaics (OPVs), the invention of model polymers with superior properties and wide applicability is of vital importance to both the academic and industrial communities. The recent inspiring advances in OPV research have included the emergence of poly(benzodithiophene-co-thieno[3,4-b]thiophene) (PBDTTT)-based materials. Through the combined efforts on PBDTTT polymers, over 10% efficiencies have been realized recently in various types of OPV devices. This review attempts to critically summarize the recent advances with respect to five well-known PBDTTT polymers and their design considerations, basic properties, photovoltaic performance, as well as device application in conventional, inverted, tandem solar cells. These PBDTTT polymers also make great contributions to the rapid advances in the field of emerging ternary blends and fullerene-free OPVs with top performances. Addtionally, new challenges in developing novel photovoltaic polymers with more superior properties are prospected. More importantly, the research of highly efficient PBDTTT-based polymers provides useful insights and builds fundamentals for new types of OPV applications with various architectures.
01 Jun 2016
TL;DR: In this paper, adaptive neural network tracking control of a robotic manipulator with input deadzone and output constraint is presented, where adaptive neural networks are used to approximate the deadzone function and the unknown model of the robotic manipulators.
Abstract: In this paper, we present adaptive neural network tracking control of a robotic manipulator with input deadzone and output constraint A barrier Lyapunov function is employed to deal with the output constraints Adaptive neural networks are used to approximate the deadzone function and the unknown model of the robotic manipulator Both full state feedback control and output feedback control are considered in this paper For the output feedback control, the high gain observer is used to estimate unmeasurable states With the proposed control, the output constraints are not violated, and all the signals of the closed loop system are semi-globally uniformly bounded The performance of the proposed control is illustrated through simulations
TL;DR: By suppressing intrinsic excitation in p-type Bi2Te3-based materials, this paper reported maximum and average zT values of up to 1.4 and 1.2 between 100 and 300 °C, respectively.
Abstract: By suppressing intrinsic excitation in p-type Bi2Te3-based materials, we report maximum and average zT values of up to 1.4 and 1.2 between 100 and 300 °C, respectively. Thermoelectric modules based on these high performance materials show energy conversion efficiencies of up to 6.0% under a temperature gradient of 217 K, and are greatly superior to current Bi2Te3-based modules.
TL;DR: In this paper, Nitrogen-doped graphene (NG) has been used as a carbon matrix for sulfur impregnation to construct cathodes for lithium-sulfur (Li-S) batteries.
Abstract: Nitrogen-doped graphene (NG) has been fabricated and used as a carbon matrix for sulfur impregnation to construct cathodes for lithium–sulfur (Li–S) batteries. Atomic layers of TiO2 were further deposited on the electrode and the thickness was controlled by adjusting the number of deposition cycles to 0, 5, 20 and 40. The results showed that all the surface modified electrodes demonstrate high capacity, good rate capability, and enhanced cyclability compared to the bare electrode. Specifically, the electrode contained 59% (by weight, wt%) sulfur and with the addition of 20 cycle-TiO2 it demonstrated a superior boost in the active sulfur utilization (discharge capacity: 1374 mA h g−1 at 0.1C). It also delivered initial discharge capacity up to 1069.5 mA h g−1 and 918.3 mA h g−1 after 500 cycles at 1C with an average coulombic efficiency of about 99.7%. Moreover, the capacity retention increased from 42% to 61% from 0.1C to 4C with the addition of 20 cycle-TiO2. The improved electrochemical performance could be attributed to the on-site TiO2 absorption for polysulfide retention as well as the charge transfer enhancement. Theoretical calculations revealed that TiO2 exhibits a strong binding energy for lithium polysulfide species. These results suggest that the TiO2 modified NG has potential to be used as a cathode for high-performance Li–S batteries.
TL;DR: Electrochemical measurements manifest that the Co2P nanostructures exhibit excellent morphology-dependent supercapacitor properties, which paves the way to explore a new class of cobalt phosphide-based materials for super capacitor applications.
Abstract: Co2P nanostructures with rod-like and flower-like morphologies have been synthesized by controlling the decomposition process of Co(acac)3 in oleylamine system with triphenylphosphine as phosphorus source. Investigations indicate that the final morphologies of the products are determined by their peculiar phosphating processes. Electrochemical measurements manifest that the Co2P nanostructures exhibit excellent morphology-dependent supercapacitor properties. Compared with that of 284 F g–1 at a current density of 1 A g–1 for Co2P nanorods, the capacitance for Co2P nanoflowers reaches 416 F g–1 at the same current density. Furthermore, an optimized asymmetric supercapacitor by using Co2P nanoflowers as anode and graphene as cathode is fabricated. It can deliver a high energy density of 8.8 Wh kg–1 (at a high power density of 6 kW kg–1) and good cycling stability with over 97% specific capacitance remained after 6000 cycles, which makes the Co2P nanostructures potential applications in energy storage/conver...
TL;DR: In this paper, the formation of disordered solid solution in the hexagonal close-packed (hcp) structure in the GdHoLaTbY alloy and its mechanical properties were investigated.
TL;DR: In this article, the authors introduce the fundamental theories behind superhydrophobicity followed by a comprehensive review of the recent progresses of this rapidly growing field over the past 5 years.
Abstract: Due to their superior water-repelling effects, superhydrophobic surfaces have received increasing attention as a promising solution to corrosion of metallic materials. The present article introduces the fundamental theories behind superhydrophobicity followed by a comprehensive review of the recent progresses of this rapidly growing field over the past 5 years. A critical discussion over anticorrosion mechanisms of superhydrophobic surfaces is also provided. For many realistic applications, future efforts are pressingly demanded to prolong the corrosion resistance of these superhydrophobic surfaces. To this end, several important strategies and examples in designing stable, self-healable, or inhibitor-loaded superhydrophobic surfaces are discussed.
TL;DR: A highly efficient fullerene-free polymer solar cell (PSC) based on PDCBT, a polythiophene derivative substituted with alkoxycarbonyl, achieves an impressive power conversion efficiency of 10.16%, which is the best result in PSCs based on polythyphene derivatives to date.
Abstract: A highly efficient fullerene-free polymer solar cell (PSC) based on PDCBT, a polythiophene derivative substituted with alkoxycarbonyl, achieves an impressive power conversion efficiency of 10.16%, which is the best result in PSCs based on polythiophene derivatives to date. In comparison with a poly(3-hexylthiophene):ITIC-based device, the photovoltaic and morphological properties of the PDCBT:ITIC-based device are carefully investigated and interpreted.
TL;DR: This approach provides a new prospect for deformable and stretchable power sources, as well as self-powered sensors, and has potential applications in various areas such as robotics, biomechanics, physiology, kinesiology, and entertainment.
Abstract: The rapid growth of deformable and stretchable electronics calls for a deformable and stretchable power source. We report a scalable approach for energy harvesters and self-powered sensors that can be highly deformable and stretchable. With conductive liquid contained in a polymer cover, a shape-adaptive triboelectric nanogenerator (saTENG) unit can effectively harvest energy in various working modes. The saTENG can maintain its performance under a strain of as large as 300%. The saTENG is so flexible that it can be conformed to any three-dimensional and curvilinear surface. We demonstrate applications of the saTENG as a wearable power source and self-powered sensor to monitor biomechanical motion. A bracelet-like saTENG worn on the wrist can light up more than 80 light-emitting diodes. Owing to the highly scalable manufacturing process, the saTENG can be easily applied for large-area energy harvesting. In addition, the saTENG can be extended to extract energy from mechanical motion using flowing water as the electrode. This approach provides a new prospect for deformable and stretchable power sources, as well as self-powered sensors, and has potential applications in various areas such as robotics, biomechanics, physiology, kinesiology, and entertainment.
TL;DR: The prepared SFMNi material is a promising high-performance anode for solid oxide fuel cells and shows excellent structural stability and good coking resistance in wet CH4.
Abstract: A metallic nanoparticle-decorated ceramic anode was prepared by in situ reduction of the perovskite Sr2FeMo0.65Ni0.35O6−δ (SFMNi) in H2 at 850 °C. The reduction converts the pure perovksite phase into mixed phases containing the Ruddlesden–Popper structure Sr3FeMoO7−δ, perovskite Sr(FeMo)O3−δ, and the FeNi3 bimetallic alloy nanoparticle catalyst. The electrochemical performance of the SFMNi ceramic anode is greatly enhanced by the in situ exsolved Fe–Ni alloy nanoparticle catalysts that are homogeneously distributed on the ceramic backbone surface. The maximum power densities of the La0.8Sr0.2Ga0.8Mg0.2O3−δ electrolyte supported a single cell with SFMNi as the anode reached 590, 793, and 960 mW cm–2 in wet H2 at 750, 800, and 850 °C, respectively. The Sr2FeMo0.65Ni0.35O6−δ anode also shows excellent structural stability and good coking resistance in wet CH4. The prepared SFMNi material is a promising high-performance anode for solid oxide fuel cells.
TL;DR: A novel technique to fabricate high-quality perovskite thin films by introduction of weak coordination additives (e.g., acetonitrile) in the precursors is demonstrated.
Abstract: The coordination effects of additives during perovskite crystal growth are investigated, and a novel technique to fabricate high-quality perovskite thin films by introduction of weak coordination additives (e.g., acetonitrile) in the precursors is demonstrated.
TL;DR: In this article, small size molybdenum disulfide (MoS2) quantum dots with desired optical properties were controllably synthesized by using tetrabutylammonium-assisted ultrasonication of multilayered MoS2 powder via OH-mediated chain-like MoS bond cleavage mode.
Abstract: Small size molybdenum disulfide (MoS2) quantum dots (QDs) with desired optical properties were controllably synthesized by using tetrabutylammonium-assisted ultrasonication of multilayered MoS2 powder via OH-mediated chain-like Mo–S bond cleavage mode. The tunable up-bottom approach of precise fabrication of MoS2 QDs finally enables detailed experimental investigations of their optical properties. The synthesized MoS2 QDs present good down-conversion photoluminescence behaviors and exhibit remarkable up-conversion photoluminescence for bioimaging. The mechanism of the emerging photoluminescence was investigated. Furthermore, superior 1O2 production ability of MoS2 QDs to commercial photosensitizer PpIX was demonstrated, which has great potential application for photodynamic therapy. These early affording results of tunable synthesis of MoS2 QDs with desired photo properties can lead to application in fields of biomedical and optoelectronics.
TL;DR: In this paper, the authors reported the development of new phosphors using the chemical unit cosubstituting solid solution design strategy, starting from Lu3Al5O12, the Al3+−Al3+ couple in respective octahedral and tetrahedral coordination was simultaneously substituted by a Mg2+−Si4+ pair forming the Lu3(Al2−xMgx)(Al3−xSix)O12:Ce3+ (x = 0.97Ce0.03Mg0.5Al4Si0
Abstract: This paper reports the development of new phosphors using the chemical unit cosubstituting solid solution design strategy. Starting from Lu3Al5O12, the Al3+–Al3+ couple in respective octahedral and tetrahedral coordination was simultaneously substituted by a Mg2+–Si4+ pair forming the Lu3(Al2−xMgx)(Al3−xSix)O12:Ce3+ (x = 0.5–2.0) series; as a result, the CeO8 polyhedrons were compressed and the emission got red-shifted from green to yellow together with the broadening. The evolution of, the unit cell, the local structural geometry as well as the optical properties of Ce3+ in these garnet creations, in response to the gradual Mg–Si substitution for Al–Al, were studied by combined techniques of structural refinement and luminescence measurements. The new composition Lu2.97Ce0.03Mg0.5Al4Si0.5O12 was comprehensively evaluated regarding its potential application in blue LED-driven solid state white lighting: the maximum emission is at 550 nm under λex = 450 nm; the internal and external quantum efficiencies can reach 85% and 49%, respectively; a 1-phosphor-converted wLED lamp fabricated using the as-prepared phosphor exhibits the luminous efficacy of 105 lm W−1, the correlated color temperature of 6164 K and the color rendering index (Ra) of 75.6. The new solid solution composition series is open for further optimization to enhance the competence for commercial consideration.
TL;DR: This paper aims to solve the model-free optimal tracking control problem of nonaffine nonlinear discrete-time systems with a critic-only Q-learning (CoQL) method, which avoids solving the tracking Hamilton-Jacobi-Bellman equation.
Abstract: Model-free control is an important and promising topic in control fields, which has attracted extensive attention in the past few years. In this paper, we aim to solve the model-free optimal tracking control problem of nonaffine nonlinear discrete-time systems. A critic-only Q-learning (CoQL) method is developed, which learns the optimal tracking control from real system data, and thus avoids solving the tracking Hamilton–Jacobi–Bellman equation. First, the Q-learning algorithm is proposed based on the augmented system, and its convergence is established. Using only one neural network for approximating the Q-function, the CoQL method is developed to implement the Q-learning algorithm. Furthermore, the convergence of the CoQL method is proved with the consideration of neural network approximation error. With the convergent Q-function obtained from the CoQL method, the adaptive optimal tracking control is designed based on the gradient descent scheme. Finally, the effectiveness of the developed CoQL method is demonstrated through simulation studies. The developed CoQL method learns with off-policy data and implements with a critic-only structure, thus it is easy to realize and overcome the inadequate exploration problem.
TL;DR: In this article, a review summarizes recent developments and progress in the research of binary metal sulfides, particularly for Bi2S3, Cu2−xS and PbS, and promising strategies are suggested to further enhance the thermoelectric figure of merit of these materials.