The flexible Li‐O2 battery is suitable to satisfy the requirements of a self‐powered energy system, thanks to environmental friendliness, low cost, and high theoretical energy density. Herein, a ...flexible porous bifunctional electrode with both electrocatalytic and photocatalytic activity was synthesized and introduced as a cathode to assemble a high‐performance Li‐O2 battery that achieved an overpotential of 0.19 V by charging with the aid of solar energy. As a proof‐of‐concept application, a flexible Li‐O2 battery was constructed and integrated with a solar cell via a scalable encapsulate method to fabricate a flexible self‐powered energy system with excellent flexibility and mechanical stability. Moreover, by exploring the evolution of the electrode morphology and discharge products (Li2O2), the charging process of the Li‐O2 battery powered by solar energy and solar cell was demonstrated.
A flexible self‐powered energy system was fabricated by combining a flexible Li‐O2 battery with a flexible solar cell. By exploring the evolution of the electrode morphology and discharge products (Li2O2), the charging process of the Li‐O2 battery powered by solar energy and solar cell is demonstrated.
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•A new WPD-FEEMD-Elman method is proposed for the wind speed predictions.•A new secondary algorithm is presented for the wind speed decomposition.•The FEEMD algorithm is adopted in ...the hybrid decomposition.•The Elman neural network is employed in the hybrid forecasting.
Wind speed forecasting technology is important in the field of wind power. However, the wind speed signals are always nonlinear and non-stationary so that it is difficult to predict them accurately. Aims at this challenge, a new hybrid approach has been proposed for the wind speed high-accuracy predictions based on the Secondary Decomposition Algorithm (SDA) and the Elman neural networks. The proposed SDA combines the Wavelet Packet Decomposition (WPD) and the Fast Ensemble Empirical Mode Decomposition (FEEMD), which includes twice decomposing processes as: (a) the WPD decomposes the original wind speed into the appropriate components and the detailed components; and (b) the FEEMD further decomposes the WPD generating detailed components into a number of wind speed Intrinsic Mode Functions (IMFs). The experimental results in five real forecasting cases show that: (a) the proposed hybrid WPD-FEEMD-Elman model has satisfactory performance in the multi-step wind speed predictions; and (b) the hybrid WPD-FEEMD-Elman model has improved the forecasting performance of the hybrid WPD-Elman model and the standard Elman neural networks considerably.
The confinement effect of external and internal steel tubes on sandwiched concrete in concrete-filled double-skin circular steel tubular (CFDST) short columns has a significant impact on the ...compressive strength and ductility of columns. Limited researches on CFDST columns have only considered the influences of a part of column parameters on the confinement effect, leading to the absence of appropriate compressive strength formulas in international standards. To comprehend the compressive behavior of circular CFDST short columns and suitably evaluate their compressive strength for practical engineering design, it is necessary to further launch the experiments on circular CFDST short columns and develop a suitable estimated formula for their compressive strength. The purpose of this paper is to develop a simple and accurate formula for predicting the compressive strength of axially loaded CFDST short circular columns with a wide range of parameters. A total of 24 specimens with outer and inner circular carbon steel tubes that withstand axial compression were tested. A new confinement coefficient reflecting the confinement effect of concrete strength in CFDST columns was proposed on the basis of the test data in the present paper and data collected from literature. Utilizing the proposed confinement coefficient, a novel strength design formula was developed to estimate the compressive strength of CFDST short circular columns. It shows that the proposed confinement coefficient can reasonably reflect the interaction effect between the sandwiched concrete and steel tubes, and the formula suggested in this paper offers better predictions of the compressive strength than current design formulas.
•Tests on 24 circular CFDST short columns were conducted.•Existing strength prediction formulas were evaluated using conducted and collected test data.•New confinement coefficient reflecting the confinement effect of concrete strength was proposed.•The influences of column parameters on the confinement effects were clarified.•Novel design formula was proposed to predict the strengths of circular CFDST short columns.
•Tests on 28 circular concrete axially loaded CFDST short columns are conducted.•The confinement effects of outer and inner to sandwiched concrete are briefly analyzed.•The tested CFDST columns show ...good ductility performance similar to that of circular STCC columns.•A enhancement coefficient reflecting the increase of concrete strength is developed using the test and numerical results.•A strength formula incorporating the enhancement coefficient is proposed and high prediction performance is achieved.
This paper aims to experimentally and numerically investigate the compressive behavior of circular concrete-filled double-skin steel tubular (CFDST) short columns, in which only the sandwiched concrete is under axial compression. In total, 28 CFDST columns were loaded axially, and their axial load-shortening curves, ultimate strength and failure modes were briefly discussed. Results suggest that the wall thickness and yield stress of outer steel tube have a significant effect on the failure modes, while the concrete strength shows an insignificant effect. The tested columns exhibited good ductility concerned by seismic resistant design. The ultimate strength of the columns using STK490 outer steel tubes was about 20–26% than that of ones with STK400 outer steel tubes. With an increase in the concrete strength and wall thickness of outer steel tube, the ultimate strength of the columns was improved by 32% and 43%, respectively. Moreover, finite element (FE) models were established and verified by comparing with the test results, and then an extensive parametric analysis was carried out to ascertain the effects of key variables on the compressive behaviour of the studied CFDST short columns. Finally, based on the numerical and test results, a novel formula was proposed to estimate the ultimate strength of CFDST columns, and high prediction performance was found in the proposed formula. The proposed formula is not only applicable for the strength prediction of CFDST columns, but also for that of steel tube confined concrete (STCC) columns.
Concrete-filled double-skin steel tubular (CFDST) columns possess lower self-weight, higher ductility and energy absorption than conventional concrete-filled steel tubular (CFST) ones. The use of ...high-strength concrete (HSC) can further enhance their advantages, such as greater mechanical and economical benefits. However, there is little information on the structural performance of CFDST columns with HSC, especially ones with ultrahigh-strength concrete (UHSC). In this paper, a comprehensive experimental program consisted of 24 specimens was carried out to investigate the compressive behaviour of circular CFDST short columns with HSC and UHSC. The test results show that CFDST columns with higher strength concrete generally achieve higher initial stiffness and axial strengths but lower ductility. Additionally, the axial strengths of CFDST columns are improved as the yield stress and wall thickness of the outer steel tubes increase and as the hollow ratio decreases. A finite element (FE) model was established and verified against the present test results, based on which the interaction of the steel tubes and concrete and the load distribution on components were analysed. A parametric study using the verified FE model was conducted to further ascertain the influences of column variables on the compressive behaviour of the studied CFDST columns. Finally, the applicability of the existing design codes and empirical models to design the CFDST columns was evaluated based on the test results in the present and previous studies. It is shown that European code EN 1994−1−1 (EC4) achieves better strength predictions than other design models.
•Tests on 24 circular CFDST short columns with HSC and UHSC are conducted.•The findings from experimental tests are discussed.•The FE models are established and verified against the present test results.•A summary of 150 experimental data in the present and previous studies is performed.•The applicability of the existing design codes and empirical models to design the CFDST columns is evaluated.
Previous investigations have shown that the confining stress paths (CSPs) of confined concrete significantly affected the compressive behaviour of confined concrete in fibre-reinforced polymer (FRP) ...confined concrete or concrete-filled steel tube (CFST) columns. Unlike the concrete in FRP-confined concrete or CFST columns, which is only confined by external materials, e.g., FRP sheet or steel tube, the concrete in concrete-filled double-skin steel tubular (CFDST) columns is confined by both the external and internal steel tubes. Due to different confinement mechanisms, the CSPs of confined concrete in CFDST columns may be different from those in FRP-confined concrete or CFST ones, but they have not been investigated so far. In this paper, the CSPs of confined concrete in circular CFDST stub columns were experimentally investigated, and their corresponding influences on the compressive strength were also discussed. It is shown that the CSPs of confined concrete induced by the external tube are considerably influenced by column variables, whereas those generated by the internal tube found no obvious trend. Moreover, the results suggest that the compressive strength of confined concrete in specimens with a confinement coefficient η less than 2.731 is CSP-dependent, based on which, a compressive strength model of confined concrete considering the CSP effect is developed for circular CFDST columns. Based on this model, a CSP-based compressive strength model for estimating the ultimate strength of CFDST columns is proposed, and comparison with existing models against the collected test data indicates a higher accuracy of the predictions for the proposed model.
•28 specimens are tested to investigate the confining stress paths of confined concrete in CFDST columns.•A CSP-based compressive strength model for estimating the ultimate strength of CFDST columns is proposed.•A summary of 154 experimental data in the current and previous studies is performed.•Compared with existing models, the proposed model is more consistent with the test results.
High symmetric porous Co3O4 hollow dodecahedra constructed by nanometer‐sized building blocks are rationally synthesized by templating against Co‐containing zeolitic imidazolate framework‐67. The ...well‐defined hollow structure and highly porous framework render these hollow dodecahedra exhibit high specific capacity, excellent cycling stability and superior rate capability when evaluated as an anode material for lithium‐ion batteries.
•The compressive strengths of HCCFST columns are significantly affected by the column parameters.•A new confinement coefficient reflecting the confinement effect of concrete strength is proposed.•A ...novel formula is proposed to predict the compressive strengths of circular HCCFST stub columns.•The proposed formula can also be used to predict the compressive strength of circular CFST stub columns.•Han’s FE model can be used to reasonably predict the axial behavior of circular HCCFST stub columns.
Circular hollow centrifugal concrete-filled steel tubes (HCCFSTs) are employed widely as structural components, such as power station structures and building foundations, in virtue of their exceedingly good structural performance features. It is essential to comprehend the compressive behavior of circular HCCFST columns and suitably evaluate their compressive strength for practical engineering design. However, limited researches on HCCFST columns have almost not resulted in the development of appropriate design formulae in current international standards. This paper aims to propose a practical formula for estimating the compressive strength of circular HCCFST stub columns that have a wide range of parameters. A new confinement coefficient reflecting the confinement effect of concrete strength in circular HCCFST short columns is proposed, and using the proposed confinement coefficient, a novel strength design formula is developed to estimate the compressive strength of circular HCCFST short columns. The proposed formula is investigated using collected experimental data from literature and finite element analysis results. It is shown that the proposed confinement coefficient can reflect the interaction effect between the steel tube and infilled concrete, and the developed axial capacity formula in this paper offers better predictions of compressive strength than current design formulae.
In this study, Huperzia serrata polysaccharide (HSP) fraction was isolated using response surface methodology (RSM) and Box-Behnken design (BBD). The extraction time, temperature and ratio of water ...to raw material were employed effects. And properties of four polysaccharide (60%-HSP, 70%-HSP, 80%-HSP and 90%-HSP) were evaluated. The results indicated that the optimal extraction conditions were the following: 3.07 h, 49.46 °C and a liquid material ratio of 20.73:1. The four HSP presented irregular aggregation of shape. And all HSP exhibited antioxidant and anticancer activities.
•On the basis of virtual internal bond concept, a tension–shear–chain network model of nacre is proposed.•We investigate whether and how nacre suppresses the effect of microstructural randomness.•The ...ensemble strength of nacre is less dependent on the RVE size and obeys the classical type-I scaling law.
Biological materials have evolved various degrees of robustness against microscopic defects and structural randomness. Of particular interest here is whether and how nacre's brick–mortar structure suppresses the adverse effect of microstructural randomness. To this end, a tension–shear–chain (TSC) network model, combined with the virtual internal bond concept, is adopted to investigate the effects of microstructural randomness of nacre, where we show that the ensemble strength and failure behaviors of a larger TSC model exhibit substantially lower randomness. Our results indicate that the staggered brick–mortar structure renders nacre insensitive to microstructural randomness, resulting in enhanced resistance to strain localization and crack initiation at weaker interfaces. The influence of microstructural randomness on the size effect of the ensemble mechanical properties of nacre is also revealed. This study provides further insights and guidelines for designing strong and robust nacre-mimic composites.
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A tension-shear-chain (TSC) network model is proposed to reveal whether and how nacre suppresses the effects of microstructural randomness. The insensitiveness of the ensemble mechanical properties of nacre to microstructural randomness originates from the shear-stress transfer mechanism of its brick-mortar structure, and weakens the macroscopic size effect.
