As the rapid development of electronic devices and wireless communication tools, it is urgent to design and fabricate low-cost, lightweight and effective electromagnetic absorption materials to solve ...electromagnetic interference of electromagnetic wave. Herein, a feasible and low-cost method has been developed to synthesize an effective carbon-based microwave absorber. The hierarchically porous structures derived from eggshell membrane (ESM) and the anchored CoFe2O4 nanoparticles (NPs) helped the C/CoFe2O4 nanocomposites perform a favor for strengthening electromagnetic absorption capability. The porous C@CoFe2O4 nanocomposites achieves the maximum reflection loss value of −49.6 dB at 9.2 GHz with 30% loading in the paraffin matrix. Detailed investigation reveals that the porous structure as well as strong synergetic effect between porous carbon matrix and magnetic nanoparticles can effectively improve the impedance matching condition and attenuation ability of the nanocomposites, leading to a high microwave absorption performance. In addition, the simulation results indicate that the radar cross section (RCS) of a strong metal scattering sources at different degrees can be significantly reduced after coating with C@CoFe2O4 nanocomposites. These achievements light the way to prepare low-cost and sustainable microwave absorbents with excellent electromagnetic wave absorbing performances, utilizing the wasted eggshell membrane biomasses as precursors.
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Nanocomposites, multiphase solid materials with at least one nanoscaled component, have been attracting ever‐increasing attention because of their unique properties. Graphene is an ideal filler for ...high‐performance multifunctional nanocomposites in light of its superior mechanical, electrical, thermal, and optical properties. However, the 2D nature of graphene usually gives rise to highly anisotropic features, which brings new opportunities to tailor nanocomposites by making full use of its excellent in‐plane properties. Here, recent progress on graphene/polymer nanocomposites is summarized with emphasis on strengthening/toughening, electrical conduction, thermal transportation, and photothermal energy conversion. The influence of the graphene configuration, including layer number, defects, and lateral size, on its intrinsic properties and the properties of graphene/polymer nanocomposites is systematically analyzed. Meanwhile, the role of the interfacial interaction between graphene and polymer in affecting the properties of nanocomposites is also explored. The correlation between the graphene distribution in the matrix and the properties of the nanocomposite is discussed in detail. The key challenges and possible solutions are also addressed. This review may provide a constructive guidance for preparing high‐performance graphene/polymer nanocomposite in the future.
Recent progress on graphene/polymer nanocomposites is reviewed, with emphasis on strengthening and toughening, electrical conduction, thermal transportation, and photothermal conversion. The roles of graphene configuration, interfacial interaction, and distribution of graphene in the polymer to determine the properties of the nanocomposites are systematically explored. This may provide constructive guidance to develop high‐performance nanocomposites in the future.
In smart city, all kinds of users' data are stored in electronic devices to make everything intelligent. A smartphone is the most widely used electronic device and it is the pivot of all smart ...systems. However, current smartphones are not competent to manage users' sensitive data, and they are facing the privacy leakage caused by data over-collection. Data over-collection, which means smartphones apps collect users' data more than its original function while within the permission scope, is rapidly becoming one of the most serious potential security hazards in smart city. In this paper, we study the current state of data over-collection and study some most frequent data over-collected cases. We present a mobile-cloud framework, which is an active approach to eradicate the data over-collection. By putting all users' data into a cloud, the security of users' data can be greatly improved. We have done extensive experiments and the experimental results have demonstrated the effectiveness of our approach.
The convolutional neural network (CNN) has been widely used in image recognition field due to its good performance. This paper proposes a facial expression recognition method based on the CNN model. ...Regarding the complexity of the hierarchic structure of the CNN model, the activation function is its core, because the nonlinear ability of the activation function really makes the deep neural network have authentic artificial intelligence. Among common activation functions, the ReLu function is one of the best of them, but it also has some shortcomings. Since the derivative of the ReLu function is always zero when the input value is negative, it is likely to appear as the phenomenon of neuronal necrosis. In order to solve the above problem, the influence of the activation function in the CNN model is studied in this paper. According to the design principle of the activation function in CNN model, a new piecewise activation function is proposed. Five common activation functions (i.e., sigmoid, tanh, ReLu, leaky ReLus and softplus–ReLu, plus the new activation function) have been analysed and compared in facial expression recognition tasks based on the Keras framework. The Experimental results on two public facial expression databases (i.e., JAFFE and FER2013) show that the convolutional neural network based on the improved activation function has a better performance than most-of-the-art activation functions.
Non‐fullerene acceptors with fused‐ring structures have rapidly improved the performance of organic solar cells over the past five years, but they still suffer from synthetic complexity and thus high ...material costs, one of the major obstacles of hindering their commercialization process. The construction of non‐fused ring acceptors (NFRAs) has recently been regarded as a feasible solution due to their facile synthesis and satisfactory device performances. Thus in this concept, we highlight the important progress of NFRAs in recent years, and discuss the key relationship between molecular design strategies and device performance. Finally, we provide some potential molecular insights for the future design of high‐performance NFRAs.
In this concept, the recently representative progress of non‐fused ring electron acceptors (NFRAs) for organic solar cells is highlighted by focusing on introducing the newly developed molecular design strategies and discussing the structure‐performance relationships. A perspective on the future design of high‐performance NFRAs is also discussed.
The power conversion efficiency of organic solar cells (OSCs) has made exceptionally rapid progress in the past five years owing to the emergence of fused‐ring electron acceptors (FREAs). To achieve ...the commercialization, it is urgent to resolve the stability issues of OCSs from materials to devices. In particular, the state‐of‐the‐art FREAs, often synthesized by Knoevenagel condensation, generally contain two exocyclic vinyl groups (CC bond) as the conjugated bridges, which inevitably exhibit an obvious electron‐deficient characteristic due to the strong push‐pull electronic effect. As a result, these vinyl bridges are vulnerable to nucleophile attacking and/or photooxidation, leading to poor chemical and photochemical stabilities of FREAs that easily cause the degradation of device performance. In this perspective, an in‐depth understanding of the degradation mechanism of FREAs is provided, and then effective strategies reported recently are reviewed for improving the chemical and photochemical stabilities of FREAs from interfacial engineering to molecular engineering to additive engineering. Finally, a conclusion and outlook for the future design of highly efficient and stable FREAs are also presented.
Research on the stability of organic solar cells based on fused‐ring electron acceptors (FREAs) is now becoming more urgent. This perspective focuses on discussing the possible degradation mechanisms of FREAs and effective strategies of enhancing their stability reported recently. Also, a conclusion and outlook for the future design of highly efficient and stable FREAs are presented.
The creation of superelastic, flexible three-dimensional (3D) graphene-based architectures is still a great challenge due to structure collapse or significant plastic deformation. Herein, we report a ...facile approach of transforming the mechanically fragile reduced graphene oxide (rGO) aerogel into superflexible 3D architectures by introducing water-soluble polyimide (PI). The rGO/PI nanocomposites are fabricated using strategies of freeze casting and thermal annealing. The resulting monoliths exhibit low density, excellent flexibility, superelasticity with high recovery rate, and extraordinary reversible compressibility. The synergistic effect between rGO and PI endows the elastomer with desirable electrical conductivity, remarkable compression sensitivity, and excellent durable stability. The rGO/PI nanocomposites show potential applications in multifunctional strain sensors under the deformations of compression, bending, stretching, and torsion.
In the pattern recognition domain, deep architectures are currently widely used and they have achieved fine results. However, these deep architectures make particular demands, especially in terms of ...their requirement for big datasets and GPU. Aiming to gain better results without deep networks, we propose a simplified algorithm framework using fusion features extracted from the salient areas of faces. Furthermore, the proposed algorithm has achieved a better result than some deep architectures. For extracting more effective features, this paper firstly defines the salient areas on the faces. This paper normalizes the salient areas of the same location in the faces to the same size; therefore, it can extracts more similar features from different subjects. LBP and HOG features are extracted from the salient areas, fusion features' dimensions are reduced by Principal Component Analysis (PCA) and we apply several classifiers to classify the six basic expressions at once. This paper proposes a salient areas definitude method which uses peak expressions frames compared with neutral faces. This paper also proposes and applies the idea of normalizing the salient areas to align the specific areas which express the different expressions. As a result, the salient areas found from different subjects are the same size. In addition, the gamma correction method is firstly applied on LBP features in our algorithm framework which improves our recognition rates significantly. By applying this algorithm framework, our research has gained state-of-the-art performances on CK+ database and JAFFE database.
With the noticeable growing rate of electronics, materials with good flexibility and high conductivity that can provide electromagnetic interference (EMI) shielding with minimal thickness are ...urgently needed. Here, for the first time, we demonstrate the potential of a non-woven composite film with unique core-shell and sandwich combined microstructure for EMI shielding. A 0.27-mm-thick reduced graphene oxide coated Fe3O4@SiO2@polypyrrole (FSPG) composite film exhibited an average EMI shielding effectiveness of 32 dB (specific EMI shielding effectiveness can be ∼ 12,608.4 dB cm2 g−1). This performance originates from the relative high electrical conductivity of FSPG films (0.71 S/cm) and multiple internal reflections from the interconnected core-shell and sandwich microstructure in the free-standing films. The mechanical flexibility offered by the FSPG films enable them to be considered as a new alternative material with efficient EMI shielding.
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Wearable enzymatic biofuel cells would be the most prospective fuel cells for wearable devices because of their low cost, compactness and flexibility. As the high specificity and catalytic properties ...of enzymes, enzymatic biofuel cells (EBFCs) catalyze the fuel associated with the redox reaction and get electrical energy. Available biofuels such as glucose, lactate and pyruvate can be harvested from biofluids of sweat, tears and blood, which afford cells a favorable use in implantable and wearable devices. However, the development of wearable enzymatic biofuel cells requires significant improvements on the power density and enzymes lifetime. In this paper, some new advances in improving the performance of wearable enzymatic biofuel cells are reviewed based on the bioanode and biocathode by classifying single-enzyme and multi-enzyme catalysis system. Thereinto, the bioanode usually contains oxidases and dehydrogenases as catalyst, and the biocathode utilizes the catalysis of multi-copper oxidases (MCOs) in the single system. For further enhancing the power density, efforts to develop multi-enzyme catalysis strategies are discussed in bioanode and biocathode respectively. Moreover, some potential technologies in recent years, such as carbon nanodots, CNT sponges and mixed operational/storage electrode are summarized owing to notable efficiency and the capability of enhancing electron transfer on the electrode. Finally, major challenges and future prospects are discussed for the high power output, stable and practical wearable enzymatic biofuel cells.
•Progress for high power outputs and long lifetimes of wearable biofuel cells is reviewed from bioanode and biocathode.•Single-enzyme, multi-enzyme and other emerging materials are summarized for improving the wearable biofuel cell.•Major challenges and future prospects are discussed for the practical wearable enzymatic biofuel cells.
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