In recent decades, flexible and wearable devices have been extensively investigated due to their promising applications in portable mobile electronics and human motion monitoring. MXene, a novel ...growing family of 2D nanomaterials, demonstrates superiorities such as outstanding electrical conductivity, abundant terminal groups, unique layered‐structure, large surface area, and hydrophilicity, making it to be a potential candidate material for flexible and wearable devices. Numerous pioneering works are devoted to develop flexible MXene‐based composites with various functions and designed structures. Therefore, the latest progress of the flexible MXene‐based composites for wearable devices is summarized in this review, focusing on the preparation strategies, working mechanisms, performances, and applications in sensors, supercapacitors, and electromagnetic interference shielding materials. Moreover, the current challenges and future outlooks are also discussed.
This is a comprehensive review of flexible MXene‐based composites for various applications as wearable devices in sensors, supercapacitors, and electromagnetic interference shielding materials. The preparation strategies, working mechanisms, performances, and applications of flexible MXene‐based composites are highlighted. Additional work is suggested to be conducted to improve the performance of the flexible MXene‐based composites for wearable devices.
Although widely used in many applications, accurate and efficient human action recognition remains a challenging area of research in the field of computer vision. Most recent surveys have focused on ...narrow problems such as human action recognition methods using depth data, 3D-skeleton data, still image data, spatiotemporal interest point-based methods, and human walking motion recognition. However, there has been no systematic survey of human action recognition. To this end, we present a thorough review of human action recognition methods and provide a comprehensive overview of recent approaches in human action recognition research, including progress in hand-designed action features in RGB and depth data, current deep learning-based action feature representation methods, advances in human⁻object interaction recognition methods, and the current prominent research topic of action detection methods. Finally, we present several analysis recommendations for researchers. This survey paper provides an essential reference for those interested in further research on human action recognition.
Motivated by the concept of energy-optimized air/space vehicles, the design of more-electric and all-electric vehicles has become increasingly popular. With the advance of micro-electro-mechanical ...systems, on-board electronic/electrical devices become more integrated and miniaturized. It means that these highly-advanced devices should rely on a high heat-flux dissipation method to maintain an effective and safe operation. Spray cooling, universally recognized as the next-generation cooling scheme, has been extensively utilized in the thermal protection of the ground-based electric/electronic equipment. In contrast, the aerospace-oriented spray cooling (AOSC) application is extremely rare. It can be attributed to the fact that the research into the space/air-oriented spray cooling technologies is still in its infancy, which leads to a lack in the knowledge of alternations of flow patterns and heat transfer behaviors caused by the complicated space or high-altitude space. This paper presents a comprehensive review of the up-to-date published articles on AOSC and divides these published articles into four categories: 1) investigation into the effect of gravity on the cooling performance; 2) investigation into the effect of environmental pressure on the cooling performance; 3) study of the effect of acceleration and vibration on the cooling performance; 4) investigation of the aerospace spray cooling system. Additionally, comments, perspectives, and orientations are provided, in which several promising contributions are highlighted. This paper aims to promote the practical application of the AOSC system which could facilitate the development of the energy-optimized green air/space vehicle.
•A review of aerospace-oriented spray cooling technology is performed.•Gravity plays a significant role in the flow pattern and heat & mass transfer.•A heat transfer enhancement can be gained by flash Boiling/evaporation.•Gravity-immune spray cooling systems promote its practical aerospace application.•Affordable ground-based research method for aerospace application is imperative.
Plant-parasitic nematodes cause substantial economic losses to global agriculture yearly. The use of nematicides is an effective way of controlling plant-parasitic nematodes. However, the long-term ...use of traditional organophosphorus and carbamate chemical nematicides can lead to increased nematode resistance. With the increasing awareness of the necessity for the protection of the environment and human health, highly toxic nematicides no longer meet the developmental requirements of modern agriculture. Recently, many studies have been undertaken on the isolation and nematicidal activity of natural products against plant-parasitic nematodes and Caenorhabditis elegans. As an important model nematode, C. elegans plays a vital reference role in studying plant-parasitic nematodes regarding nematicidal activity, metabolic mechanism, and modes of action and target. We reviewed the latest research progress of natural nematicidal active compounds against plant-parasitic nematodes and C. elegans over the past ten years, discussed the structure-activity relationship and mechanism of action, and examined the development and application of natural nematicidal active compounds.
This paper presents a wind turbine (WT) control strategy to deliver frequency response (FR) that is similar to conventional synchronous generators, i.e., to deliver accurate and efficient FR. This is ...achieved by the coordination of WT's rotor speed control (RSC) and pitch angle control (PAC), wherein the RSC is the summation of the proposed deloading power point tracking curves and FR signal; the PAC is kept as adjusting its control law according to the WT rotor speed. Through the above coordination, the strategy pre-reserves a portion of wind power and releasing it during underfrequency events. Compared with existing methods, the strategy has two significant advantages: 1) it does not need the switching of WT controls according to the real-time wind speed (WS), nor the identification of the boundaries among high, medium and low WSs according to the required reserved power, ultimately reducing the complexity of applying the strategy to practice; 2) its active power response during FR period is independent of the deviated rotor speed and is equal to the FR signal, ultimately enabling the WT to provide accurate and efficient FR. The simulations focusing on the grid frequency side demonstrated the advantages of the strategy over existing methods.
Exploitation of room temperature (RT) photochromism and photomagnetism to induce single-molecule magnet (SMM) behavior has potential applications toward optical switches and magnetic memories, and ...remains a tremendous challenge in the development of new bulk magnets. Herein, a series of chain complexes Ln3(H–HEDP)3(H2–HEDP)3·2H3–TPT·H4–HEDP·10H2O (QDU-1; Ln = Dy (QDU-1(Dy)), Gd (QDU-1(Gd)), and Y (QDU-1(Y)); HEDP = hydroxyethylidene diphosphonate; TPT = 2,4,6-tri(4-pyridyl)-1,3,5-triazine) were synthesized by solvothermal reactions. All the compounds exhibited reversible photochromic and photomagnetic behaviors via UV light irradiation at RT, induced by the photogenerated radicals via a photoinduced electron transfer (PET) mechanism. More importantly, the PET process induced significant variations in magnetic interactions for the Dy(III) congener. Strong ferromagnetic coupling with remarkably slow magnetic relaxation without applied dc fields was observed between DyIII ions and photogenerated O• radicals, showing SMM behavior after RT illumination. For the first time, we observed the reversible RT photochromism and photomagnetism in the lanthanide-based materials. This work realized the radicals-actuated on/off SMM behavior via RT light irradiation, providing a new strategy for constructing the light-induced SMMs.
As promising photoresponsive materials and potential smart materials, hybrid photochromic materials (HPMs), especially for crystalline HPMs (CHPMs), have been broadly explored for their potential in ...inheriting the merits of each constituents, and intriguing photomodulated functionality. Hitherto, the photoresponsive functionality in explored CHPMs mainly concentrate on dyad combination. By contrast, triple or quadruple photoresponsive properties are very rare because of the limited compatibility of multiple photoresponsive functionality in a single system. In this work, the electron‐transfer (ET) and crystal engineering strategies were utilized to predesign CHPMs with multiple photoresponsive properties via the collaboration of paramagnetic metal ion (Dy3+), electron‐donor (ED) ligand (benzene‐1,2,3‐tricarboxylic acid, H3BTA) and electron‐acceptor (EA) ligand (1,10‐phenanthroline, phen). The resulting complex Dy(BTA)(phen)2⋅2H2O (1) shows hybrid chain with the intrachain Dy3+ ions bridged and chelated by tricarboxylate and phen ligands, respectively. After photostimuli, the ET between tricarboxylate and phen results in photogenerated radicals and the resultant quadruple photoresponsive properties. Considering the abundant resources of paramagnetic metal ions, ED‐ and EA‐ligands, this work provides a general method to construct CHPMs with multiple photoresponsive performances via the collaboration of each unit under the guidance of ET and crystal engineering strategies.
A crystalline hybrid material is reported with quadruple photoresponsive functionality, which shows photochromism, photomodulated fluorescence, magnetism, and second‐order nonlinear optical properties. This work provides a general method to construct hybrid photochromic materials with multiple photoresponsive performances.
The realization of luminescent materials with narrowband and circularly polarized luminescence (CPL) is of great significance for the development of future optical and photonic devices. Herein, ...through a steric‐hindrance‐assisted dual‐core strategy, two pairs of chiral dual‐core multiple resonance thermally activated delayed fluorescence (MR‐TADF) materials (R/S‐DOBN and R/S‐DOBNT) are directly constructed by the bonding of two organoboron MR‐TADF monocores (SOBN and SOBNT) with carbazole/3,6‐di‐tert‐butyl‐9H‐carbazole and phenol derivative as donors, realizing obvious CPL and narrowband emissions. Furthermore, the dual‐core effect in the prepared R/S‐DOBN and R/S‐DOBNT increases the transition oscillator strength two times more than that of a monocore structure, while maintaining the ultrapure blue emissions peaking at 453 and 459 nm with a narrower full‐width at half‐maximum of 21 nm through reorganization energy reduction. The circularly polarized organic light‐emitting diodes based on the enantiomers exhibit ultrapure blue emission with Commission Internationale de L'Eclairage (CIE) coordinates of (0.14, 0.10) and (0.13, 0.12), high maximum external quantum efficiencies of 23.9% and 25.6%, and obvious circularly polarized electroluminescence with dissymmetry factors (|gEL|) ≈ 10−3.
Through a steric‐hindrance‐assisted dual‐core strategy, chiral organoboron structures are prepared by direct bonding of two multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) monocores, realizing superior chiroptical property and dual‐channel enhanced ultrapure blue emission. Furthermore, highly efficient circularly polarized organic light‐emitting diodes (CP‐OLEDs) with maximum external quantum efficiencies of 23.9% and 25.6% are achieved.
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