Showing papers by "University of Science and Technology Beijing published in 2021"

TransBTS: Multimodal Brain Tumor Segmentation Using Transformer.

Abstract: Transformer, which can benefit from global (long-range) information modeling using self-attention mechanisms, has been successful in natural language processing and 2D image classification recently. However, both local and global features are crucial for dense prediction tasks, especially for 3D medical image segmentation. In this paper, we for the first time exploit Transformer in 3D CNN for MRI Brain Tumor Segmentation and propose a novel network named TransBTS based on the encoder-decoder structure. To capture the local 3D context information, the encoder first utilizes 3D CNN to extract the volumetric spatial feature maps. Meanwhile, the feature maps are reformed elaborately for tokens that are fed into Transformer for global feature modeling. The decoder leverages the features embedded by Transformer and performs progressive upsampling to predict the detailed segmentation map. Extensive experimental results on both BraTS 2019 and 2020 datasets show that TransBTS achieves comparable or higher results than previous state-of-the-art 3D methods for brain tumor segmentation on 3D MRI scans. The source code is available at https://github.com/Wenxuan-1119/TransBTS.

ZnS-SnS@NC Heterostructure as Robust Lithiophilicity and Sulfiphilicity Mediator toward High-Rate and Long-Life Lithium-Sulfur Batteries.

Abstract: Lithium-sulfur (Li-S) batteries are severely hindered by the low sulfur utilization and short cycling life, especially at high rates. One of the effective solutions to address these problems is to improve the sulfiphilicity of lithium polysulfides (LiPSs) and the lithiophilicity of the lithium anode. However, it is a great challenge to simultaneously optimize both aspects. Herein, by incorporating the merits of strong absorbability and high conductivity of SnS with good catalytic capability of ZnS, a ZnS-SnS heterojunction coated with a polydopamine-derived N-doped carbon shell (denoted as ZnS-SnS@NC) with uniform cubic morphology was obtained and compared with the ZnS-SnS2@NC heterostructure and its single-component counterparts (SnS@NC and SnS2@NC). Theoretical calculations, ex situ XANES, and in situ Raman spectrum were utilized to elucidate rapid anchoring-diffusion-transformation of LiPSs, inhibition of the shuttling effect, and improvement of the sulfur electrochemistry of bimetal ZnS-SnS heterostructure at the molecular level. When applied as a modification layer coated on the separator, the ZnS-SnS@NC-based cell with optimized lithiophilicity and sulfiphilicity enables desirable sulfur electrochemistry, including high reversibility of 1149 mAh g-1 for 300 cycles at 0.2 C, high rate performance of 661 mAh g-1 at 10 C, and long cycle life with a low fading rate of 0.0126% each cycle after 2000 cycles at 4 C. Furthermore, a favorable areal capacity of 8.27 mAh cm-2 is maintained under high sulfur mass loading of 10.3 mg cm-2. This work furnishes a feasible scheme to the rational design of bimetal sulfides heterostructures and boosts the development of other electrochemical applications.

Recent progress of zero-dimensional luminescent metal halides

Abstract: Zero-dimensional (0D) all-inorganic/organic-inorganic metal halides, as emerging luminescent materials, have attracted unparalleled interest from versatile perspectives due to their unique crystallographic/electronic structures with isolated building units and fascinating optical characteristics. However, significant challenges still exist for 0D metal halides, including their chemical molecular design, photoluminescence (PL) mechanism, PL modification and applications. In this review, we summarize the 0D metal halides through the classification of all-inorganic and organic-inorganic hybrid metal halides, and further emphasize the unique role of B-site cations with different electronic configurations in the PL process. Furthermore, the PL mechanisms focusing on the self-trapped excitons (STEs) model and PL regulation engineering are examined to explore their extraordinary PL properties and further reveal new application prospects. This review aims to provide in-depth insight into the structure-luminescence-application relationship of 0D metal halides and pave the way for the realization of next-generation high-performance luminescent materials.

Tailoring inorganic–polymer composites for the mass production of solid-state batteries

Abstract: Solid-state batteries (SSBs) have recently been revived to increase the energy density and eliminate safety concerns associated with conventional Li-ion batteries with flammable liquid electrolytes. To achieve large-scale, low-cost production of SSBs as soon as possible, it would be advantageous to modify the mature manufacturing platform, involving slurry casting and roll-to-roll technologies, used for conventional Li-ion batteries for application to SSBs. However, the manufacturing of SSBs depends on the development of suitable solid electrolytes. Inorganic–polymer composite electrolytes combine the advantages of inorganic and polymer solid electrolytes, making them particularly suitable for the mass production of SSBs. In this Review, we discuss the properties of solid electrolytes comprising inorganic–polymer composites and outline the design of composite electrolytes for realizing high-performance devices. We also assess the challenges of integrating the composite electrolytes into batteries, which will enable the mass production of SSBs. Inorganic–polymer composites have emerged as viable solid electrolytes for the mass production of solid-state batteries. In this Review, we examine the properties and design of inorganic–polymer composite electrolytes, discuss the processing technologies for multilayer and multiphase composite structures, and outline the challenges of integrating composite electrolytes into solid-state batteries.

MIL-101-Derived Mesoporous Carbon Supporting Highly Exposed Fe Single-Atom Sites as Efficient Oxygen Reduction Reaction Catalysts.

Abstract: Fe single-atom catalysts (Fe SACs) with atomic FeNx active sites are very promising alternatives to platinum-based catalysts for the oxygen reduction reaction (ORR). The pyrolysis of metal-organic frameworks (MOFs) is a common approach for preparing Fe SACs, though most MOF-derived catalysts reported to date are microporous and thus suffer from poor mass transfer and a high proportion of catalytically inaccessible FeNx active sites. Herein, NH2 -MIL-101(Al), a MOF possessing a mesoporous cage architecture, is used as the precursor to prepare a series of N-doped carbon supports (denoted herein as NC-MIL101-T) with a well-defined mesoporous structure at different pyrolysis temperatures. The NC-MIL101-T supports are then impregnated with a Fe(II)-phenanthroline complex, and heated again to yield Fe SAC-MIL101-T catalysts rich in accessible FeNx single atom sites. The best performing Fe SAC-MIL101-1000 catalyst offers outstanding ORR activity in alkaline media, evidenced by an ORR half-wave potential of 0.94 V (vs RHE) in 0.1 m KOH, as well as excellent performance in both aqueous primary zinc-air batteries (a near maximum theoretical energy density of 984.2 Wh kgZn -1 ) and solid-state zinc-air batteries (a peak power density of 50.6 mW cm-2 and a specific capacity of 724.0 mAh kgZn -1 ).

Modeling and trajectory tracking control for flapping-wing micro aerial vehicles

Abstract: This paper studies the trajectory tracking problem of flapping-wing micro aerial vehicles ( FWMAVs ) in the longitudinal plane. First of all, the kinematics and dynamics of the FWMAV are established, wherein the aerodynamic force and torque generated by flapping wings and the tail wing are explicitly formulated with respect to the flapping frequency of the wings and the degree of tail wing inclination. To achieve autonomous tracking, an adaptive control scheme is proposed under the hierarchical framework. Specifically, a bounded position controller with hyperbolic tangent functions is designed to produce the desired aerodynamic force, and a pitch command is extracted from the designed position controller. Next, an adaptive attitude controller is designed to track the extracted pitch command, where a radial basis function neural network is introduced to approximate the unknown aerodynamic perturbation torque. Finally, the flapping frequency of the wings and the degree of tail wing inclination are calculated from the designed position and attitude controllers, respectively. In terms of Lyapunovʼ s direct method, it is shown that the tracking errors are bounded and ultimately converge to a small neighborhood around the origin. Simulations are carried out to verify the effectiveness of the proposed control scheme.

Rational design of isostructural 2D porphyrin-based covalent organic frameworks for tunable photocatalytic hydrogen evolution

Abstract: Covalent organic frameworks have recently gained increasing attention in photocatalytic hydrogen generation from water. However, their structure-property-activity relationship, which should be beneficial for the structural design, is still far-away explored. Herein, we report the designed synthesis of four isostructural porphyrinic two-dimensional covalent organic frameworks (MPor-DETH-COF, M = H2, Co, Ni, Zn) and their photocatalytic activity in hydrogen generation. Our results clearly show that all four covalent organic frameworks adopt AA stacking structures, with high crystallinity and large surface area. Interestingly, the incorporation of different transition metals into the porphyrin rings can rationally tune the photocatalytic hydrogen evolution rate of corresponding covalent organic frameworks, with the order of CoPor-DETH-COF < H2Por-DETH-COF < NiPor-DETH-COF < ZnPor-DETH-COF. Based on the detailed experiments and calculations, this tunable performance can be mainly explained by their tailored charge-carrier dynamics via molecular engineering. This study not only represents a simple and effective way for efficient tuning of the photocatalytic hydrogen evolution activities of covalent organic frameworks at molecular level, but also provides valuable insight on the structure design of covalent organic frameworks for better photocatalysis. Covalent organic frameworks (COFs) present well-defined materials for constructing structure-property-activity relationships. Herein, authors explore isostructural porphyrinic two-dimensional COFs with tunable of photocatalytic H2 production rates arising from tailored charge-carrier dynamics.

Hierarchical crack buffering triples ductility in eutectic herringbone high-entropy alloys

Abstract: In human-made malleable materials, microdamage such as cracking usually limits material lifetime. Some biological composites, such as bone, have hierarchical microstructures that tolerate cracks but cannot withstand high elongation. We demonstrate a directionally solidified eutectic high-entropy alloy (EHEA) that successfully reconciles crack tolerance and high elongation. The solidified alloy has a hierarchically organized herringbone structure that enables bionic-inspired hierarchical crack buffering. This effect guides stable, persistent crystallographic nucleation and growth of multiple microcracks in abundant poor-deformability microstructures. Hierarchical buffering by adjacent dynamic strain-hardened features helps the cracks to avoid catastrophic growth and percolation. Our self-buffering herringbone material yields an ultrahigh uniform tensile elongation (~50%), three times that of conventional nonbuffering EHEAs, without sacrificing strength.

Distribution control enables efficient reduced-dimensional perovskite LEDs.

Abstract: Light-emitting diodes (LEDs) based on perovskite quantum dots have shown external quantum efficiencies (EQEs) of over 23% and narrowband emission, but suffer from limited operating stability1. Reduced-dimensional perovskites (RDPs) consisting of quantum wells (QWs) separated by organic intercalating cations show high exciton binding energies and have the potential to increase the stability and the photoluminescence quantum yield2,3. However, until now, RDP-based LEDs have exhibited lower EQEs and inferior colour purities4–6. We posit that the presence of variably confined QWs may contribute to non-radiative recombination losses and broadened emission. Here we report bright RDPs with a more monodispersed QW thickness distribution, achieved through the use of a bifunctional molecular additive that simultaneously controls the RDP polydispersity while passivating the perovskite QW surfaces. We synthesize a fluorinated triphenylphosphine oxide additive that hydrogen bonds with the organic cations, controlling their diffusion during RDP film deposition and suppressing the formation of low-thickness QWs. The phosphine oxide moiety passivates the perovskite grain boundaries via coordination bonding with unsaturated sites, which suppresses defect formation. This results in compact, smooth and uniform RDP thin films with narrowband emission and high photoluminescence quantum yield. This enables LEDs with an EQE of 25.6% with an average of 22.1 ±1.2% over 40 devices, and an operating half-life of two hours at an initial luminance of 7,200 candela per metre squared, indicating tenfold-enhanced operating stability relative to the best-known perovskite LEDs with an EQE exceeding 20%1,4–6. The efficiency and operating lifetimes of perovskite light-emitting diodes is improved by using a fluorinated triphenylphosphine oxide additive to control the cation diffusion during film deposition and passivate the surface.

Sandwich-Like Heterostructures of MoS2/Graphene with Enlarged Interlayer Spacing and Enhanced Hydrophilicity as High-Performance Cathodes for Aqueous Zinc-Ion Batteries

Abstract: Layered materials have great potential as cathodes for aqueous zinc-ion batteries (AZIBs) because of their facile 2D Zn2+ transport channels; however, either low capacity or poor cycling stability limits their practical applications. Herein, two classical layered materials are innovatively combined by intercalating graphene into MoS2 gallery, which results in significantly enlarged MoS2 interlayers (from 0.62 to 1.16 nm) and enhanced hydrophilicity. The sandwich-structured MoS2 /graphene nanosheets self-assemble into a flower-like architecture that facilitates Zn-ion diffusion, promotes electrolyte infiltration, and ensures high structural stability. Therefore, this novel MoS2 /graphene nanocomposite exhibits exceptional high-rate capability (285.4 mA h g-1 at 0.05 A g-1 with 141.6 mA h g-1 at 5 A g-1 ) and long-term cycling stability (88.2% capacity retention after 1800 cycles). The superior Zn2+ migration kinetics and desirable pseudocapacitive behaviors are confirmed by electrochemical measurements and density functional theory computations. The energy storage mechanism regarding the highly reversible phase transition between 2H- and 1T-MoS2 upon Zn-ion insertion/extraction is elucidated through ex situ investigations. As a proof of concept, a flexible quasi-solid-state zinc-ion battery employing the MoS2 /graphene cathode demonstrates great stability under different bending conditions. This study paves a new direction for the design and on-going development of 2D materials as high-performance cathodes for AZIBs.

A review of modeling, acquisition, and application of lithium-ion battery impedance for onboard battery management

Abstract: Impedance is closely related to the internal physical and chemical processes of lithium-ion batteries. And the properties of the processes can be characterized and thus more detailed information be provided based on it. In the past decades, the impedance is frequently reported as a powerful tool used in the field of lithium-ion battery state estimation and diagnosis. This paper reviews more than 170 papers and organizes the related research according to three themes of impedance modeling, acquisition, and application under the premise of electric vehicle implementation. The strength and weaknesses of the research in each theme are discussed. Based on the research, the possibility and the value of impedance in onboard battery management are revealed. However, challenges are still faced due to the cost limitations, the complex vehicular conditions, and the time-varying battery states. The unsolved issues are summarized in the conclusion. To realize a more smart battery management system with the impedance, more significant work is still needed.

A Tandem Organic Photovoltaic Cell with 19.6% Efficiency Enabled by Light Distribution Control.

Abstract: Despite more potential in realizing higher photovoltaic performance, the highest power conversion efficiency (PCE) of tandem organic photovoltaic (OPV) cells still lags behind that of state-of-the-art single-junction cells. In this work, highly efficient double-junction tandem OPV cells are fabricated by optimizing the photoactive layers with low voltage losses and developing an effective method to tune optical field distribution. The tandem OPV cells studied are structured as indium tin oxide (ITO)/ZnO/bottom photoactive layer/interconnecting layer (ICL)/top photoactive layer/MoOx /Ag, where the bottom and top photoactive layers are based on blends of PBDB-TF:ITCC and PBDB-TF:BTP-eC11, respectively, and ICL refers to interconnecting layer structured as MoOx /Ag/ZnO:PFN-Br. As these results indicate that there is not much room for optimizing the bottom photoactive layer, more effort is put into fine-tuning the top photoactive layer. By rationally modulating the composition and thickness of PBDB-TF:BTP-eC11 blend films, the 300 nm-thick PBDB-TF:BTP-eC11 film with 1:2 D/A ratio is found to be an ideal photoactive layer for the top sub-cell in terms of photovoltaic characteristics and light distribution control. For the optimized tandem cell, a PCE of 19.64% is realized, which is the highest result in the OPV field and certified as 19.50% by the National Institute of Metrology.

About metastable cellular structure in additively manufactured austenitic stainless steels

Abstract: The quick-emerging paradigm of additive manufacturing technology has revealed salient advantages in enabling the tailored-design of structural components with more exceptional performances over ordinary subtractive processing routines. As a peculiar feature, sub-micro cellular structures widely exist in additively manufactured (AM) metallic materials. This phenomenon primarily appears with high-density dislocations and segregated elements or precipitates at the cellular boundaries. The discovery of novel metastable substructures in various alloys through numerous investigations has proven their substantial effects on the engineering properties of AM components. This paper reviews the most recent research momentum regarding the formation mechanisms (elemental segregation, dislocation cell and oxide inclusion), the kinetics of the size and morphology, the growth orientation and the thermodynamic stability of these cellular structures by taking AM austenitic stainless steel as an exemplary material. Another topic of concern here is the inherent correlation between the unique cellular microstructure and the corresponding mechanical properties (strength, ductility, fatigue, etc.) and corrosion responses (passivity, irradiation damage, hydrogen embrittlement, etc.) for this category of AM materials. The design, control, and optimization of cellular structures for additive manufacturing techniques are expected to inspire new strategies for advancing high-performance structural alloy development.

Adaptive Fuzzy Full-State and Output-Feedback Control for Uncertain Robots With Output Constraint

Abstract: This article focuses on the tracking control issue of robotic systems with dynamic uncertainties. To enhance tracking accuracy in a robotic manipulator with uncertainties, an adaptive fuzzy full-state feedback control is proposed. In view of output-feedback control with unknown states, a high-gain observer is employed to estimate unknown states. Considering the particular requirement that output of systems should be constrained in some practical working fields, we further design adaptive fuzzy full-state and output-feedback control schemes with output constraint to ensure that output maintains in constrained regions. By applying the Lyapunov theory, it is guaranteed that closed-loop systems are semiglobally uniformly ultimately bounded (SGUUB). Tangent-type barrier Lyapunov function is used for the controller design with output constraint and ensure stability. Finally, the effectiveness of our proposed methods is shown through both simulation examples and experimental results, comparative experiments in Baxter robot are proposed for evaluating the practicability of our proposed methods in actual applications.

Boundary Disturbance Observer-Based Control of a Vibrating Single-Link Flexible Manipulator

Abstract: This paper examines the boundary disturbance observer-based control for a vibrating single-link flexible manipulator system possessing external disturbances. Two new boundary anti-disturbance control strategies are presented to eliminate vibration, track disturbance, and determine angle position for the flexible manipulator system. Achieving rigorous analysis with no model reduction, the derived control can ensure the angle positioning and bounded stability in the controlled system. By appropriately designing parameters, the resulting simulation results can demonstrate the control performance.

Multifunctional conductive hydrogel-based flexible wearable sensors

Abstract: Flexible sensors have shown great potential in remote health monitoring, body movements track, electronic skin, human-machine interfaces, and soft robotics. Hydrogels possess exceptional stretchability, flexibility and biocompatibility that render them appealing candidates for wearable flexible sensors. Among them, considerable efforts have been devoted to developing conductive hydrogels to achieve multifunctional wearable sensing through using functional groups/additives/nanofillers to modify the hydrogel network in recent years. This review summarizes recent advances of applications of hydrogels in flexible wearable sensors, such as sweat sampling and flexible electrodes, strain/pressure sensors and touch panels, focuses on the multifunctional conductive hydrogels-based flexible wearable sensors with self-healing, self-adhesion, or anti-freezing capabilities. A brief introduction to representative synthesis methods and strategies of conductive hydrogels is also presented. In the end, we also provide a personal perspective on the future development, and address the remaining challenges in the commercialization of conductive hydrogels-based multifunctional flexible wearable sensors.

Perovskite Quantum Dots with Ultralow Trap Density by Acid Etching-Driven Ligand Exchange for High Luminance and Stable Pure-Blue Light-Emitting Diodes

Abstract: The research on metal halide perovskite light-emitting diodes (PeLEDs) with green and infrared emission has demonstrated significant progress in achieving higher functional performance. However, the realization of stable pure-blue (≈470 nm wavelength) PeLEDs with increased brightness and efficiency still constitutes a considerable challenge. Here, a novel acid etching-driven ligand exchange strategy is devised for achieving pure-blue emitting small-sized (≈4 nm) CsPbBr3 perovskite quantum dots (QDs) with ultralow trap density and excellent stability. The acid, hydrogen bromide (HBr), is employed to etch imperfect [PbBr6 ]4- octahedrons, thereby removing surface defects and excessive carboxylate ligands. Subsequently, didodecylamine and phenethylamine are successively introduced to bond the residual uncoordinated sites of the QDs and attain in situ exchange with the original long-chain organic ligands, resulting in near-unity quantum yield (97%) and remarkable stability. The QD-based PeLEDs exhibit pure-blue electroluminescence at 470 nm (corresponding to the Commission Internationale del'Eclairage (CIE) (0.13, 0.11) coordinates), an external quantum efficiency of 4.7%, and a remarkable luminance of 3850 cd m-2 , which is the highest brightness reported so far for pure-blue PeLEDs. Furthermore, the PeLEDs exhibit robust durability, with a half-lifetime exceeding 12 h under continuous operation, representing a record performance value for blue PeLEDs.

Reinforcement Learning Control of a Flexible Two-Link Manipulator: An Experimental Investigation

Abstract: This article discusses the control design and experiment validation of a flexible two-link manipulator (FTLM) system represented by ordinary differential equations (ODEs). A reinforcement learning (RL) control strategy is developed that is based on actor–critic structure to enable vibration suppression while retaining trajectory tracking. Subsequently, the closed-loop system with the proposed RL control algorithm is proved to be semi-global uniform ultimate bounded (SGUUB) by Lyapunov’s direct method. In the simulations, the control approach presented has been tested on the discretized ODE dynamic model and the analytical claims have been justified under the existence of uncertainty. Eventually, a series of experiments in a Quanser laboratory platform are investigated to demonstrate the effectiveness of the presented control and its application effect is compared with PD control.

Carbon-Based Composite Phase Change Materials for Thermal Energy Storage, Transfer, and Conversion.

Abstract: Phase change materials (PCMs) can alleviate concerns over energy to some extent by reversibly storing a tremendous amount of renewable and sustainable thermal energy. However, the low thermal conductivity, low electrical conductivity, and weak photoabsorption of pure PCMs hinder their wider applicability and development. To overcome these deficiencies and improve the utilization efficiency of thermal energy, versatile carbon materials have been increasingly considered as supporting materials to construct shape-stabilized composite PCMs. Despite some carbon-based composite PCMs reviews regarding thermal conductivity enhancement, a comprehensive review of carbon-based composite PCMs does not exist. Herein, a systematic overview of recent carbon-based composite PCMs for thermal storage, transfer, conversion (solar-to-thermal, electro-to-thermal and magnetic-to-thermal), and advanced multifunctional applications, including novel metal organic framework (MOF)-derived carbon materials are provided. The current challenges and future opportunities are also highlighted. The authors hope this review can provide in-depth insights and serve as a useful guide for the targeted design of high-performance carbon-based composite PCMs.