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The process of repeating shape memory cycle of the shape memory foam whose initial structure is nonauxetic is more complex. In this cases, only one-shot deformation, which will greatly limit the application of this smart metamaterial. Thus, in this study, we report a feasible approach of fabricating the original structure of shape memory foams with auxetic property based on second curing method. The commercial soft polyurethane foam material and shape memory epoxy resin was used in fabricating the shape memory auxetic foam. Polyurethane component plays role in the similar function of “auxetic mold,” while shape memory polymer act as fixing auxetic structure of foam. The negative Poisson’s ratio was achieved around −0.22. Tunable foam mechanical property was demonstrated by structural control according to its shape memory property. The functional filler was employed to realize the wireless actuation of auxetic foam. The excellent shape memory properties have been achieved as well. The combination of smart materials and metamaterial structure makes it have excellent structural mechanical properties and intelligent properties of materials, which greatly expands their potential application prospects.

Linerless composite cryogenic tank is significant for weight reducing in launch vehicles, and a microscopic-to-macroscopic model is presented in this paper to capture the burst behaviors of the car...

The motivation of this work is to build a multimodal-based COVID-19 pandemic forecasting platform for a large-scale academic institution to minimize the impact of COVID-19 after resuming academic activities. The design of this multimodality work is steered by video, audio, and tweets. Before conducting COVID-19 prediction, we first trained diverse models including traditional machine learning models (e.g., Navie Bayes, SVM, and TF-IDF) and deep learning models (e.g., LSTM, MobileNetV2 and SSD) to extract meaningful information from video, audio, and tweets by i) detecting and counting face masks, ii) detecting and counting cough for potential infected cases, and iii) conducting sentiment analysis based on COVID-19 related tweets. Finally, we fed the multimodal analysis results together with daily confirmed cases data and social distancing metrics into the LSTM model to predict the daily increase rate of confirmed cases for the next seventh day. Finally, important observations with supporting evidence are presented.

As a novel type of additive manufacturing, three-dimensional (3D) printing can efficiently realize the manufacturing of ceramic devices with more sophisticated structures. In this study, the method combining digital light processing (DLP) 3D printing technology and modified ceramic precursor polysiloxane (PSO) was not only used to fabricate Al2O3 ceramic devices with a gradient impedance bilayer structure, which consist of a cross-twist/flat structure with a torsion angle of 60°, but also to prepare needle-like SiC nanowire absorbents grown in situ to further endow the ceramic functional characteristics. The microstructure was regulated by different times of impregnation, light-curing, and thermal treatment of ferrocene-modified PSO, and Al2O3/SiCnw/SiOC composites with different electromagnetic absorption properties were prepared. We found that the Al2O3/SiCnw/SiOC composite (sample 1400–2) exhibited the optimal microwave absorption performance when it was immersed and light-cured twice, which was ascribed to its comprehensive satisfaction of the impedance matching and attenuation characteristics. When the thickness of sample 1400–2 was as thin as 2.5 mm, the minimum reflection coefficient (RCmin) reached −44.35 dB, indicating that more than 99.9990% of the electromagnetic waves could be absorbed. As the thickness increased to 2.8 mm, the effective absorption bandwidth (EAB) in the X-band was 3.6 GHz, which indicated that the effective coverage rate was as high as 85.7%. The results indicate that the generation of the stacking fault, dipole and interfacial polarization of the Al2O3/SiCnw/SiOC composites, and increasing conductivity contribute to the promotion of dielectric loss. Thus, the Al2O3/SiCnw/SiOC composite with bilayer gradient impedance structures is a good candidate for stealth radar wave absorption.

Effective electromagnetic interference (EMI) shielding requires materials with high permittivity. The current study reports 3D printed polymer-derived SiOC ceramics (PDC) modified with SiC nanowires (SiCnw) exhibiting both high real and imaginary parts of permittivity within X-band. SEM results indicated that a large number of pores and cracks exist in the SiOC, and twinned SiCnw were uniformly grown among them along with the existence of graphite microcrystals when the sintering temperature was 1500 ℃. The real part of permittivity ranged from 16.6 to 28.9 while the imaginary part from 31.7 to 34.2 in X-band. The EMI total shielding effectiveness (SET) of the ceramics could reach 34.7 dB with absorption loss (SEA) of 29.3 dB and reflection loss (SER) of 5.4 dB. Meanwhile, the 3D printed PDC-SiOC ceramics at 900 ℃ sintering temperature possess certain mechanical properties with the magnitude of compressive strength being 12.57 MPa.

The numerical method for predicting the permeability of a laminated composite based on matrix cracks is improved to meet the application at a cryogenic temperature. The number of the parameters tha...

The proliferation of edge computing technologies has boosted the development of new applications for a plethora of edge devices. However, many applications face privacy issues and bandwidth limitations. To solve these limitations, we propose a collaborative learning framework on the edges, named CLONE, which is steered by the real-world data sets collected from a large electric vehicle (EV) company and a grocery store of a shopping mall, respectively. We categorize two application scenarios for CLONE, i.e., CLONE in the training stage (CLONE_ training ) and CLONE in the inference stage (CLONE_ inference ). As to CLONE_ training , we choose the failure prediction of EV battery and associated components as the first use case. While as for CLONE_ inference , customer tracking in a grocery store is selected as another case study. In this work, the goal of the CLONE is to support real-time training and inference for connected vehicles and marketing intelligence services. Our experimental results on the EV data show that CLONE is able to reduce model training time without sacrificing algorithm performance. Furthermore, the experimental results on the video data from the grocery store reveal that CLONE is a useful approach to solve the multitarget multicamera tracking problem in a collaborative fashion.

The recent proliferation of computing technologies (e.g., sensors, computer vision, machine learning, and hardware acceleration) and the broad deployment of communication mechanisms (e.g., dedicated short-range communication, cellular vehicle-to-everything, 5G) have pushed the horizon of autonomous driving, which automates the decision and control of vehicles by leveraging the perception results based on multiple sensors. The key to the success of these autonomous systems is making a reliable decision in real-time fashion. However, accidents and fatalities caused by early deployed autonomous vehicles arise from time to time. The real traffic environment is too complicated for current autonomous driving computing systems to understand and handle. In this article, we present state-of-the-art computing systems for autonomous driving, including seven performance metrics and nine key technologies, followed by 12 challenges to realize autonomous driving. We hope this article will gain attention from both the computing and automotive communities and inspire more research in this direction.

Three types of representative unit cell (RUC) of [±θ/904]S composite laminates and cracked plies were created to obtain the constitutive model of the cracked plies and to compare their accuracy of ...

As a novel and attractive advanced manufacturing technology, three-dimensional (3D) printing can realize the manufacturing of devices with more sophisticated structures. Metamaterials (MMs) are a novel material design idea based on the variation of physical structural designs, in order to break through apparent and intrinsic natural laws of matter, and eventually obtain extraordinary material functions. With the development of stealth technology, it has become a hot topic to seek and design radar absorbing materials to realize the high-performance requirements of “thin, light weight, wide and strong”. At this time, 3D-printed MMs with various sophisticated structures exhibit great application potential. Recent studies report the development of a wide variety of 3D-printed electromagnetic MMs (EMMs), which are attracting increasing scientific attention. To better advance the design of 3D-printed MMs, it is necessary to fully comprehend the advantages and disadvantages of various printing technologies, and fully understand the latest progress in printed EMMs. Four-dimensional (4D) printing is a combination of 3D printing and smart materials, which unfolds new opportunities for intelligent and customized development in aerospace and electronic devices. The present work reviews the research progress in electrical MMs printed using various 3D/4D printers. Emphasis is placed on the structural design of EMMs, selection of absorbing bases, category of absorbing materials, 3D printing types and EM absorption performance. As the demand for data grows rapidly, 5G wireless mode is developed. Technology from 100 GHz to 1.0 THz frequency bands has great potential in wireless communications for the upcoming 6G. 3D-printed electronic antennas and 5G/6G antennas fabricated by other processes are also briefly summarized. Meanwhile, the article discusses and looks forward to the potential future design and development of 3D/4D printed electrical AMMs for stealth and antenna applications.

As a new type of molding technology, three dimensional (3D) printing can realize the manufacturing of devices with complex shapes. In the current study, 3D printed polymer-derived ceramics (PDCs), whose molecules are customizable and designable, were fabricated to achieve high-intensity broadband absorption performance of electromagnetic (EM) wave radiation. Based on improving the surface impedance matching characteristics, with the aim of optimizing the attenuation characteristics, cross convex/flat bilayer structures and cross concave/flat bilayer structures were fabricated, respectively. Remarkably, the former exhibited a minimum reflection coefficient (RCmin) of −58.97 dB at a thickness of 3 mm, and a broadband absorption of 4.0 GHz in X-band (8.2–12.4 GHz) at 3.4 mm. More significantly, we successfully combine the cross-convex structure with the cross-concave structure of PDCs–SiOC in the same as well as in different layers to obtain parallel and series structures respectively. It was found that the EM absorption performance of parallel structures was better than that of series structures, which is attributed to the stronger resonance between the parallel structures than between the series structures. The generation of dipole and interfacial polarization of PDCs–SiOC and the advancement of conductivity contribute to the increase of dielectric loss. Consequently, the PDCs–SiOC with multifarious structures are promising radar stealth absorbing materials in aerospace field.

This paper design two kinds of damping interleaves, traditional thermoplastic polyurethane (TPU) and novel carbon nanotube (CNT) modified TPU porous membranes are designed and respectively interleaved into the interfaces of a carbon fiber-reinforced plastic (CFRP). How the interleaves affect the damping behaviors and quasi-static mechanical properties of the CFRP is comparatively investigated. Results show that both TPU and CNT/TPU interleaved CFRPs possess good damping behaviors within a wide temperature range of 50∼150°C as well as a wide frequency band from 0.1 to 30 Hz, where, the former is a little better. But, storage modulus of the CNT/TPU interleaved CFRP is always higher than that of the TPU interleaved CFRP at different temperatures and frequencies. Moreover, the flexural strength and interlaminar shear strength are both decreased by 36.0% and 24.0% for the TPU interleaved CFRP, and 20.0% and 17.8% for the CNT/TPU interleaved CFRP, respectively, when compared to the baseline CFRP, suggesting the CNT/TPU interleaf brings less negative effect on the mechanical properties of CFRP. Comparatively, CNT/TPU interleaved CFRP is more multifunctional, possessing good damping feature and reasonable mechanical properties, which is maybe more potential in the structural-functional field, especially where needs shock absorption and noise reduction.

The porous carbon/Fe3O4 composites have been used to adsorb the dyes recently, however, most carbon sources are not preferable for the environment protection. In this paper, the porous carbon/Fe3O4 composites were synthesized by a simple step carbonization method using the waste cigarette butts and the ferric nitrate as carbon source and oxidizer, respectively. Notably, the obtained products can be reused. The results show that the crystallite size of as-prepared Fe3O4 will increase at high treating temperature. In addition, the sample of C-Fe3O4-1000 possesses the highest saturation magnetization of 92.2 emu g−1, and the sample of C-Fe3O4-600 has the highest specific surface area of 90.23 m2 g−1 and the maximum adsorption of 102.04 mg g−1 for methyl orange. Furthermore, the adsorbent can maintain an excellent adsorption capacity for the dye after 4 cycles. Therefore, as-prepared porous carbon/Fe3O4 composite is an excellent candidate for recyclable dye adsorbent, and the waste can be converted into products for reducing the environment pollution.

Purpose The purpose of this paper is to developing a kind of acoustic metamaterial with wide frequency band especially in low frequency region. At the same time, its the tunability of sound insulation frequency is achieved. Design/methodology/approach A three-dimensional (3D) acoustic metamaterial consisting of rigid frame, spherical attachment and thin film is proposed. The material parameters and the effect of the attachment hole on the forbidden band are investigated by finite element simulation. The sound insulation effect of the structure is validated by the combination of simulation and experiment. Findings The results show that the elastic modulus of the structural material determines the initial frequency of the forbidden band of the proposed 3D acoustic metamaterials. The lower the elastic modulus of the structural material, the lower the initial frequency of the forbidden band. The material parameters of the frame mainly affect the initial frequency of the first forbidden band, and the material parameters of the attachment will affect both the initial and termination frequency of the first forbidden band. Holes in the attachments reduce the band gap width. The characteristic curve moves down with the increase of subtracted mass. Research limitations/implications The findings may greatly benefit the application of the acoustic metamaterials in the fields of sound insulation and noise reduction. Originality/value This acoustic metamaterial structure has excellent sound insulation performance. At the same time, the single cell structure can be assembled into any shape. The structure can achieve sound selective filtering and combination control.

The tribological properties of hybrid polytetrafluoroethylene (PTFE)/aramid fibers 1414 (Kevlar) fabric self-lubricating composite under different conditions was studied. To improve tribological properties and the bonding performance of PTFE, the hybrid Kevlar/PTFE fabrics were treated by sodium-naphthalene complex liquid. PTFE/Kevlar fabric composite was prepared by phenolic-epoxy (6:4) resin. Tribological properties of the composite, friction coefficient and wear amount, were analyzed using varying loads and speeds on a friction and wear testing machine. Worn surface morphology and transfer film were observed by Scanning electron microscopy (SEM). The results showed that the coefficient of friction decreased with the decrease of load and the increase of rotating speed. In addition, the composites with higher PTFE content showed better lubricating behavior. The friction coefficient of the composites reinforced by modified fabrics were more stable and the PTFE transfer film remains more complete.

Mesoporous carbon/graphene composites (MCG) have exhibited good electrochemical performances; however, the fixed mesoporous carbon, the low specific surface area, and porosity are the main obstacles in their application in supercapacitors. In this paper, mesoporous carbon microspheres/graphene composites (MCMG) were synthesized in situ via a soft template method and subsequent thermal reduction by using cetyltrimethylammonium bromide (CTAB) as the structure-directing agent, and aqueous mesophase pitch (AMP) and graphene oxide (GO) as the carbon sources. The strong electrostatic interaction between GO/CTAB and AMP promoted the self-assembly of CTAB and AMP to form the MCMG precursor. The results showed that the CTAB concentration and aging temperature have an important effect on the morphology and pore structure of the synthesized MCMG. The high aging temperature promoted the formation of mesoporous carbon spheres and its diameter increased with the increase in the concentration of CTAB. The as-prepared MCMG at the aging temperature of 140 °C had obvious spherical and layered carbon materials after carbonization at 900 °C. When the concentration of CTAB was 10.6 g L−1, the formed mesoporous carbon spheres with the diameter of 30–40 nm were uniformly dispersed among the layered graphenes in MCMG-140-0.2 (the aging temperature of 140 °C and the CTAB content of 0.2 g). In addition, its specific surface area was 1150.5 m2 g−1 and the mesopore size was centered at 4.3 nm, 7.9 nm, and 17.1 nm. Compared with the MCMG precursor, the ordered degree of the mesopores for MCMG was reduced due to the high temperature carbonization. Importantly, the specific capacitance of MCMG-140-0.2 at the current density of 0.1 A g−1 was as high as 356.3 F g−1. Moreover, the specific capacitance of MCMG-140-0.2 at 1 A g−1 remained at 278.5 F g−1, the capacitance retention was 92.1% after 6000 cycles, and the coulombic efficiency was over 98% at a high current density of 2 A g−1. Therefore, the as-prepared MCMG can be an excellent candidate for electrode materials in supercapacitors.