Exciting advancements have been made in the field of flexible electronic devices in the last two decades and will certainly lead to a revolution in peoples’ lives in the future. However, because of ...the poor sustainability of the active materials in complex stress environments, new requirements have been adopted for the construction of flexible devices. Thus, hierarchical architectures in natural materials, which have developed various environment-adapted structures and materials through natural selection, can serve as guides to solve the limitations of materials and engineering techniques. This review covers the smart designs of structural materials inspired by natural materials and their utility in the construction of flexible devices. First, we summarize structural materials that accommodate mechanical deformations, which is the fundamental requirement for flexible devices to work properly in complex environments. Second, we discuss the functionalities of flexible devices induced by nature-inspired structural materials, including mechanical sensing, energy harvesting, physically interacting, and so on. Finally, we provide a perspective on newly developed structural materials and their potential applications in future flexible devices, as well as frontier strategies for biomimetic functions. These analyses and summaries are valuable for a systematic understanding of structural materials in electronic devices and will serve as inspirations for smart designs in flexible electronics.
In the case of a smart home, the ability to recognize daily activities depends primarily on the strategy used for selecting the appropriate features related to these activities. To achieve the goal, ...this paper presents a daily activity feature selection strategy based on the Pearson Correlation Coefficient. Firstly, a daily activity feature is viewed as a vector in Pearson Correlation Coefficient formula. Secondly, the relation degree between daily activity features is obtained according to weighted Pearson Correlation Coefficient formula. At last, redundant features are removed by the relation degree between daily activity features. Two distinct datasets are adopted to mitigate the effects of the coupling of the dataset used and the sensor configuration. Three different machine learning techniques are employed to evaluate the performance of the proposed approach in activity recognition. The experiment results show that the proposed approach yields higher recognition rates and achieves average improvement F-measures of 1.56% and 2.7%, respectively.
This paper studies reverse space and/or time nonlocal Fokas–Lenells (FL) equation, which describes the propagation of nonlinear light pulses in monomode optical fibers when certain higher-order ...nonlinear effects are considered, by Hirota bilinear method. Firstly, we construct variable transformations from reverse space nonlocal FL equation to reverse time and reverse space-time nonlocal FL equations. Secondly, the multisoliton and quasi-periodic solutions of the reverse space nonlocal FL equation are derived through Hirota bilinear method, and the soliton solutions of reverse time and reverse space-time nonlocal FL equations are given through variable transformations. Also, dynamical behaviors of the multisoliton solutions are discussed in detail by analyzing their wave structures. Thirdly, asymptotic analysis of two- and three-soliton solutions of reverse space nonlocal FL equation is used to investigate the elastic interaction and inelastic interaction. Finally, the infinite conservation laws of three types of nonlocal FL equations are found by using their lax pairs. The results obtained in this paper possess new properties that different from the ones for FL equation, which are useful in exploring novel physical phenomena of nonlocal systems in nonlinear media.
Stretchable strain sensors play a pivotal role in wearable devices, soft robotics, and Internet‐of‐Things, yet these viable applications, which require subtle strain detection under various strain, ...are often limited by low sensitivity. This inadequate sensitivity stems from the Poisson effect in conventional strain sensors, where stretched elastomer substrates expand in the longitudinal direction but compress transversely. In stretchable strain sensors, expansion separates the active materials and contributes to the sensitivity, while Poisson compression squeezes active materials together, and thus intrinsically limits the sensitivity. Alternatively, auxetic mechanical metamaterials undergo 2D expansion in both directions, due to their negative structural Poisson's ratio. Herein, it is demonstrated that such auxetic metamaterials can be incorporated into stretchable strain sensors to significantly enhance the sensitivity. Compared to conventional sensors, the sensitivity is greatly elevated with a 24‐fold improvement. This sensitivity enhancement is due to the synergistic effect of reduced structural Poisson's ratio and strain concentration. Furthermore, microcracks are elongated as an underlying mechanism, verified by both experiments and numerical simulations. This strategy of employing auxetic metamaterials can be further applied to other stretchable strain sensors with different constituent materials. Moreover, it paves the way for utilizing mechanical metamaterials into a broader library of stretchable electronics.
Auxetic mechanical metamaterials are employed to significantly enhance the sensitivity of stretchable strain sensors, by regulating the transverse Poisson effect due to auxetic expansion. High sensitivity with almost 24‐fold improvement is achieved, together with high maximum stretchability and cyclic durability. Additionally, the underlying mechanism, elongated microcracks, is proven by both experiments and numerical simulations.
Infections caused by foodborne microorganisms are a great threat to the global environment and public healthcare today. Thus, rapid, portable and sensitive assays that can realize the identification ...of foodborne bacteria are highly desired. In this study, a smart fluorescent and colorimetric dual-readout sensing system has been established for simple and rapid
E. coli
determination by utilizing the Cu
2+
-triggered oxidation of
o
-phenylenediamine (OPD). Initially, Cu
2+
can oxidize OPD to OPDox, resulting in an orange-yellow fluorescence and visible pale-yellow color. However,
E. coli
can effectively reduce Cu
2+
into Cu
+
, inhibiting the Cu
2+
-triggered oxidation of OPD to OPDox. Consequently, the introduction of
E. coli
can turn off both the fluorescence and the UV-vis absorbance signals of the OPD-Cu
2+
system, illustrating an original mechanism for fluorescent and colorimetric dual-channel detection of
E. coli
. Moreover, a filter paper-based visual sensor was built and coupled with OPD-Cu
2+
solution under the assistance of a UV lamp. The as-prepared sensor can detect
E. coli
quantitatively with the help of a typical smartphone color-scanning application (APP). Thus, this study offers a valid dual-mode assay for sensitive and on-site visible detection of
E. coli
, guaranteeing the reliability of the results and is more attractive for practical use.
Graphical Abstract
Schematic illustration of the smartphone-integrated sensing system for fluorescent and colorimetric dual-channel detection of
E. coli
based on the Cu
2+
-OPD system.
High‐adhesion stretchable electrodes are fabricated by utilizing a novel nanopile interlocking strategy. Nanopiles significantly enhance adhesion and redistribute the strain in the film, achieving ...high stretchability. The nanopile electrodes enable simultaneous monitoring of electromyography signals and mechanical deformations. This study opens up a new perspective of achieving stretchability and high adhesion for stretchable electronics.
Based on the panel data of Changjiang Economic Corridor (CEC), this paper includes agricultural carbon emissions as an unwanted output into the evaluation index system for agricultural carbon ...emissions performance (ACEP), and measured the ACEP of the 11 provinces in the CEC of 2005–2018, using the minimum distance to weak efficient frontier (MinDW) model. In addition, a Tobit model was constructed for empirical analysis on the impactors of CEC ACEP. The results show that: In general, the CEC achieved an excellent ACEP, with certain differences between the provinces; the ACEP trends varied between the upper, middle, and lower reaches of the CEC, and the lower reaches had a much higher ACEP than the upper and middle reaches; the results of Tobit model demonstrate that industrial upgrading and rural power consumption have significant positive correlations with CEC ACEP, while human capital, planting structure, and agricultural disaster have significantly negative correlations with CEC ACEP.
Owing to its remarkable electrical, mechanical and thermal properties, graphene has been considered the most promising reinforcing filler for the development of rubber nanocomposites. In this work, a ...novel interfacial structure consisting of reduced graphene oxide (rGO)/N-tert-butyl-2-benzothiazole sulfonamide (NS)/natural rubber (NR) (NR/NS-rGO) with covalent bond connections was fabricated using one-step modification and coprecipitation methods. When the filler loading of NS-rGO is 0.42 vol.%, not only the thermal conductivity of the rubber composite increases to 0.237 Wm
−1
K
−1
, which is 21.5% higher than that of pure NR; meanwhile, the internal heat generation decreases to 2.6 °C, which is 45.8% lower than that of reduced graphene oxide (rGO)/ascorbic acid (VC)/natural rubber (NR) (NR/VC-rGO), and the mechanical properties have been greatly improved. The results demonstrated that the covalent bond connections greatly reduced interfacial thermal resistance at the filler/matrix interface. Furthermore, the enhanced interfacial interaction reduced frictional heat generation at the filler/matrix interface. More importantly, this strategy provided creative insights into the high application potential of graphene in the rubber industry.
ZrO
2
nanoparticles were electrostatic self-assembled on the surface of graphene oxide (GO) for enhancing the mechanical and tribological properties of phenolic resin. Zeta potential analysis and ...structural characterization confirmed that ZrO
2
nanoparticles had been successfully adhered onto the surface of GO, and the as-prepared ZrO
2
@GO nanohybrid possessed good dispersity. The results showed that filling 1.5 wt% ZrO
2
@GO nanohybrid could improve the flexural strength, flexural modulus and impact strength of phenolic resin (PF) by 38.6%, 10.7% and 8.3%, respectively. When 0.5 wt% ZrO
2
@GO was added, the initial decomposition temperature and the residual content at 800 °C of PF increased by 20.0% and 16.9%, respectively. The ZrO
2
@GO nanohybrid also exhibited synergistic effect for improving the tribological performance of PF effectively, that when adding 0.5 wt% ZrO
2
@GO nanohybrid, the average friction coefficient and wear rate of the composites reduced by 21.8% and 30.6%, respectively. SEM observation and 3D non-contact surface topography analysis showed the wear surface of ZrO
2
@GO nanohybrid filling PF composite was smooth, low spalling and shallowly grooved with the typical characteristic of abrasive wear. It was explained that the ZrO
2
@GO nanohybrid could play the role of rolling bearings, form stable and smooth friction transfer film and enhance the interfacial interaction, thus indicated the synergistic wear-resisting performance for PF matrix. It provides a green, convenient and fast method for preparing ZrO
2
nanoparticles-attached GO nanohybrid that can enhance the mechanical and tribological performance of resin-based materials effectively.
Paramagnetic complexes containing gadolinium ions have been widely used for magnetic resonance imaging (MRI) in clinic. However, these paramagnetic complexes pose some safety concerns. There is still ...a demand for the development of stable MRI contrast agents that exhibit higher sensitivity and superior functionality to existing contrast agents. Here, we develop carbonized paramagnetic complexes of manganese (II) (Mn@CCs) to encapsulate Mn
in sealed carbonized shells with superhigh r
relaxivity. Compared to the most common clinical contrast agent Magnevist, investigations in vivo demonstrate that the Mn@CCs cross the intact blood-brain barrier of normal health mice with minor metal deposition; preferentially target the glioma tissues distribute homogeneously with high penetration in an intracranial mouse model; delineate clear tumor margins in MRIs of ultrasmall single-nodule brain tumors, and multi-nodular liver tumors. The sensitivity, accuracy and low toxicity offer by Mn@CCs provides new opportunities for early molecular diagnostics and imaging-guided biomedical applications.
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