Triboelectric nanogenerators (TENGs), a promising energy harvesting technology, have been rapidly developed in past few years. However, the specific structure and complicated preparation method ...greatly limited their mechanical flexibility as well as their potential applications. In this work, a novel and effective strategy to fabricate all-in-one triboelectric nanogenerator(TENG) was reported. The as-mentioned TENG was based on rubber/carbon nano-fiber composites achieved by supercritical carbon dioxide foaming process, which is environmentally friendly and suitable for mass production. Under the optimal condition, 91 V of the open voltage, 2.87 μA of short current and 40 nC of transferred charge was obtained, while this structure contributed to about 10-fold enhancement to transferred charge compared with the single-layer structured TENG at the same area of 4 cm2. The flexible silicone rubber based TENG can collect complex mechanical energy, such as stretching, twisting, bending and compressing. Moreover, when being pasted on soles, it can harvest the mechanical energy from human motion and the outputs can also be regarded as sensing signals which can be used to analyze the gait and sense the motion. This work provides a feasible and effective way to prepare an all-in-one TENG with high outputs, which can bring potential for the industrialized production and widespread application.
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•Achieving an all-in-one and porous TENG based on rubber/carbon nano-fiber composites.•Fabricating flexible TENG by easily supercritical carbon dioxide foaming strategy.•Simple structure and excellent flexibility makes TENG collect complex mechanical energy, judge gait when pasting on soles.
The development of triboelectric nanogenerators (TENGs) can convert mechanical energy into electricity and bring new prospect for energy crisis. Improving tribo-charge surface density and contact ...area are two pivotal factors to enhance the output performance of TENG. However, improving the charge density and manipulating surface structure cannot be achieved simultaneously and complicated fabrication procedures may limit application of TENG. In this work, an environment friendly TENG based on bacteria cellulose film fabricated via facile vacuum filtration method was reported. In the presence of modifications, high dielectric particles BaTiO3 were introduced into BC nanofiber film to improve the dielectric constant as well as construct micro-nano structure at the same. With the combination of the enhancement of dielectric constant and surface structure of BC nanofibers layer, the open voltage of 181 V, the short current of 21 μA, and transfer charge of 76.6 nC was achieved at a frequency of 2 Hz and a peak force of 42 N with the optimized film consisting of 13.5 vol% BaTiO3 particles. Additionally, a peak power density of 4.8 W/m2 was achieved when connecting with the resistance in series. Moreover, the TENG showed excellent stability and can harvest the mechanical energy by human motion. This work gives a better understanding of the triboelectricity produced by the TENG from the point of materials and provides a feasible and effective way to enhance the output performance of TENG from the material itself as well as surface modification.
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•Improving the dielectric constant and surface roughness of triboelectric material simultaneously when introducing BaTiO3 particles.•Fabricating environmentally friendly TENG by easily vacuum filtration method.•Excellent flexibility greatly facilitates the application of TENG integrating with the clothes to harvest mechanical energy from human motion.•Achieving outstanding electric output performance by facile method.
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To address the problem that capacitor electrode being low in capacitance and reliant on binder to retain shape, a binder-free, self-supporting supercapacitor electrode is made via ...pyrolysis of porous polyacrylonitrile (PAN) formed by phase separation, supported by hydrothermally treated nickel foam backbone. The role of hydrothermal reaction time and PAN solution concentration on electrochemical properties was thoroughly studied, and the results indicate a generally peaked capacitance at 4 h of hydrothermal reaction time, but after a certain threshold, a supposed micro-domain buffering mechanism would take over and enhance the pseudocapacitance from NiO to reach a specific capacitance as high as 152 F/g at a high active material mass load of 14.98 mg/cm2, providing the area specific capacitance up to 1.98 F/cm2. The use of temperature-controlled phase separation and incorporation of nickel oxide together guarantees the electrode sufficient ion and electron transportation pathway while improving its capacitance by redox electrochemical reactions.
•A novel precast ultra-lightweight ECC-concrete composite slab is investigated.•The four-point bending tests were conducted on six full-scale composite slabs.•The proposed slabs exhibited excellent ...flexural behavior and cracking resistance.•The specific bearing capacity of slabs was increased significantly by using ULECC.
Precast concrete (PC) slab has extensive application in PC structure. The conventional PC slab is susceptible to cracking during transportation and hoisting, due to the low tensile performance of normal concrete. Besides, the large self-weight of normal concrete also impedes efficient PC slab construction. Unlike normal concrete, ultra-lightweight engineered cementitious composite (ULECC) with a combination of low density and high tensile performance is a promising material for PC slab construction. The objective of this research is to investigate the feasibility of using ULECC in novel PC composite slab to reduce its self-weight, while improve the flexural performance. The effects of precast ULECC thickness, lattice girders configuration, and overall slab thickness on the structural performance of ULECC composite slab were investigated. The introduction of ULECC for the precast plank improved load bearing capacity by 29% with the self-weight decreased by 24% than the control specimen. Multiple micro-cracks appeared in tensile zone due to high tensile performance with excellent crack width control capacity of ULECC. The structural performance of PC slab is further simulated by ABAQUS and demonstrates good consistent with the experimental results. This research lays the groundwork for the application of ULECC in PC slab for an efficient construction and high flexural performance.
Motivated by recent work on rotating black hole shadow (Chang and Zhu in Phys Rev D 101:084029, 2020), we investigate the shadow behaviours of rotating Hayward–de Sitter black hole for static ...observers at a finite distance in terms of astronomical observables. This paper uses the newly introduced distortion parameter (Chang and Zhu in Phys Rev D 102:044012, 2020) to describe the shadow’s shape quantitatively. We show that the spin parameter would distort shadows and the magnetic monopole charge would increase the degree of deformation. The distortion will increase as the distance between the observer and the black hole increases, and distortion reduces as the cosmological constant increases. Besides, the increase of the spin parameter, magnetic monopole charge and cosmological constant will cause the shadows shrunken.
Our previous work has shown that the coefficient symmetry can be efficiently exploited in designing variable finite-impulse-response (FIR) filters with simultaneously tunable magnitude and ...fractional-delay responses. This paper presents the optimal solutions for the weighted-least-squares (WLS) design of variable fractional-delay (VFD) FIR filters with same-order and different-order subfilters through utilizing the coefficient symmetry along with an imposed coefficient constraint. In deriving the closed-form error functions, since the Taylor series expansions of sin(omegap) and cos(omegap) are used, the numerical integrals using conventional quadrature rules can be completely removed, which speeds up the WLS design and guarantees the optimality of the final solution. Two design examples are given to illustrate that the proposed WLS methods can achieve better design with significantly reduced VFD filter complexity and computational cost than the existing ones including the WLS-SVD approach. Consequently, the proposed WLS design is the best among all the existing WLS methods so far
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•Hierarchical combination of mixed graphene oxide builds ideal ion transfer routes.•One-pot hydrothermal reaction constructs compact and flexible backbone.•Ice-template method helps ...to obtain orientated filled graphene oxide aerogel.•Novel recapture mechanism let the device activate on charging or deformation cycle.
This work demonstrates a hierarchical structure design with mixed holey graphene oxide (HGO) and Ni(OH)2 active material layer made by one-pot hydrothermal reaction clinging to Nickel foam as backbone and ice-template oriented graphene oxide (GO) aerogel as filling, aiming to create an asymmetric solid supercapacitor (ASC) device with compliable flexibility and high electrochemical performance. The effects of hydrothermal treatment and ice-template freezing parameters on electrochemical stability under repeated exterior deformation are discussed, the optimal parameters result in a high areal capacitance of 479.8 mF/cm2 in asymmetric supercapacitor device setup. The use of porous HGO and oriented GO aerogel synergistically contribute to the high energy and power density up to 1.69 Wh/m2 and 9 W/m2 as well as excellent electrochemical performance retention under repeated curving deformation which reaches 102% thanks to a novel activation process. The electrode assembly including metal foam and the buffering GO aerogel should be instructive for future supercapacitor design.
In this paper we describe an empirical forecasting method for epidemic outbreaks. It is an iterative process to find possible parameter values for epidemic models to best fit real data. As a ...demonstration of principle, we used the logistic model, the simplest model in epidemiology, for an experiment of live forecasting. Short-term forecasts can last to 5 or more days with relative errors consistently kept blow 5%. The method should improve with more realistic models.
This paper reveals a stability-constrained approach for designing an odd-order recursive digital filter whose frequency bandwidths are freely tunable. The tunable filter has a cascade structure, and ...it also has definitely ensured stability. The odd-order tunable-bandwidth (OO-TBW) filter consists of a single first-order (1st-order) recursive section and a few second-order (2nd-order) recursive sections. Those sections are cascaded together to form the overall OO-TBW filter. To ensure that the cascade-form OO-TBW filter is definitely stable, a strategic technique is adopted, which expresses the coefficients of both the single 1st-order and multiple 2nd-order sections as a kind of specifically-defined composite functions. With such specific parameterizations, the resulting cascade-form OO-TBW filter is able to meet the stability requirement definitely. As a result, the resulting OO-TBW filter not only has an odd-order cascade structure, but its stability issue is resolved. To demonstrate the ensured stability and also the significantly high accuracy of the resultant OO-TBW filter, a lowpass OO-TBW filter (tunable-bandwidth lowpass filter) is designed, and the simulation results are detailed and analyzed.
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