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Charge accumulation on the surface of insulation dielectric used in high voltage DC equipment is one of the important causes of surface flashover. Surface charge accumulation is closely related to surface trap characteristics. In this paper, the surface trap energy level distribution of polyimide (PI) was calculated and analyzed by the corona charging method and surface potential decay method. Besides, electron and hole trap characteristics were studied by changing the polarity and amplitude of the charging voltage. Furthermore, the influence of surface charge polarity and quantity on the flashover voltage was researched. Experimental results indicate that the energy level of traps corresponding to the maximum trapped charge density ranges around 0.94 eV. In addition, the energy level of the hole trap is slightly higher than that of the electron trap. The maximum charge density captured by the electron trap and hole trap is about 1.17 × 1021 and 1.03 × 1021 eV−1 m−3, respectively. The polarity of the surface charge can influence the conductivity characteristics of PI, the surface heterocharge reduces the volume conductivity by about 80% while the surface homocharge improves the volume conductivity of PI by about 6.4 times. Besides, both negative and positive surface charges can improve surface conductivity. The polarity of surface charge influences the flashover characteristics of PI, the flashover voltage increases by about 37.8% with the increase of homocharge density and decreases by about 23.8% with the increase of heterocharge density, which is related to the change of electric field near the cathode caused by surface charge accumulation. [ABSTRACT FROM AUTHOR]

Developing multicomponent composite materials with delicate morphology and tailored structure is of vital importance for designing advanced sodium‐ion batteries (SIBs). Herein, a confinement‐structured Fe2Mo3O8@C@MoS2 with local‐expanded interlayer spacing is designed via high‐temperature phase transition from FeMoO4 to Fe2Mo3O8 and the tactically introducing dopamine molecules into the interlayer of MoS2 nanosheets. By analysis of the in situ generated solid electrolyte interphase film in different electrolytes, the favorable compatibility of Fe2Mo3O8@C@MoS2 in ether‐based electrolytes is well illustrated. Importantly, the sodium storage mechanism and detailed structural evolution of Fe2Mo3O8 are established for the first time by in situ X‐ray diffraction. Furthermore, theoretical calculations indicate the unique structure facilitates internal charge transfer and enhances Na+ adsorption ability. Thanks to the unique confinement structure, local‐expanded interlayers and robust framework, the Fe2Mo3O8@C@MoS2 composite achieves a high reversible specific capacity of 636 mAh g‒1 at 0.1 A g‒1, excellent rate capability (301 mAh g‒1 at 5.0 A g‒1) and ultralong cycling stability (365 mAh g–1 after 6000 cycles at 2.0 A g–1). The study provides an essential understanding of the Na storage mechanism of Fe2Mo3O8 and a promising strategy for constructing high‐performance anodes for SIBs. [ABSTRACT FROM AUTHOR]

Transition metal sulfides and selenides are common electrode materials in supercapacitors. However, the slow redox kinetics and structural collapse during charge–discharge cycles of single-component materials have impeded their electrochemical performance. In this study, hollow Co9S8 nanotubes were synthesized through a rational morphology design approach. Subsequently, NiSe2 or Co0.85Se was electrodeposited onto the Co9S8 nanotubes, yielding two core–shell heterostructure arrays, namely, NiSe2@Co9S8 and Co0.85Se@Co9S8. By fully leveraging the advantages and synergistic effects of these dual-phase heterostructures, the NiSe2@Co9S8 and Co0.85Se@Co9S8 configurations demonstrated outstanding areal capacitances of 12.54 F cm−2 and 9.61 F cm−2, respectively, at 2 mA cm−2. When integrated with activated carbon in hybrid supercapacitors, the NiSe2@Co9S8//AC and Co0.85Se@Co9S8//AC devices exhibited excellent energy storage performance, with energy densities of 0.959 mW h at 1.681 mW and 0.745 mW h at 1.569 mW, respectively. Additionally, these hybrid supercapacitors demonstrated remarkable cycling stability, with capacitance retention of 87.5% and 89.5% after 5000 cycles for NiSe2@Co9S8//AC and Co0.85Se@Co9S8//AC, respectively. This study provides a novel approach to the synthesis of multiphase core–shell heterostructures based on metal sulfides and selenides, opening new avenues for future research. [ABSTRACT FROM AUTHOR]

Limited by sluggish reaction kinetics, insufficient electrode utilization and severe volume deformation, designing nickel‐based materials with high capacity and rate capability is still a challenge. Herein, a carbon nanotubes threaded NiSe2/Co3Se4 quantum dots embedded in carbon nanospheres with rich Se vacancies both in NiSe2 and Co3Se4 is elaborately designed via MOF template method. The formation mechanism of the Se vacancies is elucidated for the first time, which is ascribed to the release of gas during the decomposition of organic ligand inhibits the ordered arrangement of atoms. The CNT‐V‐NiCoSe possesses many significant superiorities, such as sufficiently exposed active sites, high electrode utilization, favorable charge‐carrier migration, and relaxed structure deformation. Consequently, the CNT‐V‐NiCoSe electrode shows top‐level specific capacity (384 mAh g−1 at 1 A g−1), ultrahigh rate capability (209 mAh g−1 at 150 A g−1) and remarkable cycling durability. The CNT‐V‐NiCoSe//Zn battery achieves maximum energy density of 615.6 Wh kg−1 and maximum power density of 81.7 kW kg−1. Density functional theory calculations elucidate the Se vacancies improve the density of states at Fermi level, facilitates internal charge transfer, and enhances OH− adsorption ability. This study provides guidance for the preparation of high‐performance electrode materials with rich vacancies by template method. [ABSTRACT FROM AUTHOR]

With the rapid development of offshore wind power, large‐capacity wind turbine generators have put forward higher electrical and mechanical performance requirements for the cable. In this paper, kaolin/ethylene propylene diene monomer (EPDM) composites are prepared to investigate the effect of kaolin content on the electrical properties, mechanical properties and thermal conductivity of EPDM composites. The results show that appropriate amount of kaolin could synergistically improve the electrical‐thermal‐mechanical properties of EPDM. The composite with 30 wt% kaolin content achieves the best performance. The breakdown strength of kaolin/EPDM composites increases by 13.47%–72.19 kV/mm compared with that before modification, and the volume resistivity increases from 1013 to 1015 Ω·cm after modification. In addition, with the doping of kaolin, the tensile strength of composites significantly improves by over 500%–6.97 MPa, and the thermal conductivity of the composite is slightly improved. This work has important guiding significance for the development of insulation materials for cables. Highlights: Kaolin in EPDM scattered more uniform after modification.The addition of kaolin improves the electrical‐thermal‐mechanical properties of the composite.Kaolin/EPDM composites have promising applications. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) have been extensively applied in supercapacitors. Unfortunately, metal active sites in MOFs are commonly blocked and saturated by organic ligands, leading to insufficient positions available for the electrochemical reaction. To address this issue, we develop a novel strategy to design and prepare a series of hollow metal sulfide/MOF heterostructures, which simultaneously alleviate the large volume expansion, avoid slow kinetics of metal sulfides and expose more electrochemically active sites of the MOF. Consequently, the optimized Co9S8/Co-BDC MOF heterostructure presents outstanding electrochemical performance with a high areal specific capacitance of 15.84 F cm−2 at 2 mA cm−2 and a capacitance retention rate of 87.5% after 5000 charge–discharge cycles. The asymmetric supercapacitors based on the heterostructure deliver a high energy density of 0.87 mW h cm−2 and a power density of 19.84 mW cm−2, as well as long cycling stability. This study provides a new strategy for the rational design and in situ synthesis of metal sulfide/MOF heterostructures for electrochemical applications. [ABSTRACT FROM AUTHOR]

Five novel bis-tridentate Ir(III) complexes (Ir-1–Ir-5) incorporating versatile N^N^C ligands and a N^C^N ligand (1,3-di(2-pyridyl)-4,6-dimethylbenzene) were synthesized. With the combination of experimental and theoretical methods, their steady and transient state characteristics were researched scientifically. The UV-visible absorption spectra show that the broadband charge transfer absorbance of those bis-tridentate Ir(III) complexes can reach 550 nm, all of these complexes reveal the long-lasting phosphorescent emission. Because the excited-state absorption is more powerful than the ground-state absorption, a sturdy reverse saturable absorption (RSA) process can ensue in the visible and near-infrared regions when the complexes are exposed to a 532 nm laser. Therefore, the optical power limiting (OPL) effect follows the trend: Ir-5 > Ir-4 ≈ Ir-3 > Ir-2 > Ir-1. Generally speaking, the expansion of π-conjugation and the introduction of electron donating/withdrawing groups on the N^N^C ligand could effectively elevate the OPL effect. Therefore, these octahedral bis-tridentate Ir(III) complexes might be exploited as potential OPL materials. [ABSTRACT FROM AUTHOR]

High-strength concrete-filled steel tubular (HCFHST) square columns are commonly used as critical members in super high-rise and high-rise structures. These columns are susceptible to being impacted by vehicles in service, resulting in column damage and even structural collapse. Therefore, a lateral impact test of HSCFST columns is conducted using a rigid test truck. The failure mode, impact force, deformation and energy dissipation capacity are analyzed to reveal its dynamic response. Then, the refined finite element models are established, and the damage evolution law, energy dissipation mechanism, and dynamic distribution of internal load of HSCFST columns under different span-to-height ratios (H/L) are analyzed to reveal its working mechanism. The effects of H/L on column dynamic responses with varying impact mass, velocity, steel and concrete strength, steel ratio, and section size are investigated. The results indicate that HCFHST specimens display bending deformation and superior impact resistance. Based on internal force distribution laws, the failure section of HCFHST columns is close to the support. When H/L < 0.25, the column dynamic performance changes, and the failure mode gradually shifts from bending failure to shear failure. Therefore, it is suggested to locally reinforce the support to prevent the fixed-fixed supported HCFHST columns from a shear failure. Additionally, the section size and the steel tube thickness are the critical factors that influence the impact resistance and energy dissipation capability of the column under different H/L. A calculation formula for evaluating the energy dissipation capacity of HCFHST columns is proposed based on the data regression method. • Conduct impact tests on HCFHST specimens under impact with fixed-fixed support. • Analyze the failure mode and dynamic response of HCFHST column under impact loading. • Analyze the effect of span-to-height ratio on the dynamic response of HCFHST column. • Propose a calculation formula to evaluate the energy dissipation capacity of column. [ABSTRACT FROM AUTHOR]

To fully understand the distribution network cable accessories’ moisture fault, the variation in insulation parameters of the cable main insulation of cross-linked polyethylene (XLPE) and the cable accessory reinforced insulation of silicone rubber (SIR) under different moisture conditions are studied experimentally. Furthermore, the effects of typical moisture defect forms and moisture positions on electric field distributions are studied by establishing the interface defect model. The experimental results show that the insulation properties of XLPE after water immersion are more seriously reduced than SIR. The resistivity of XLPE and SIR specimens decreases significantly with the increase in moisture time, decreasing by 90.3% and 48.3% after 720 h, respectively. The relative dielectric constants of the two kinds of specimens increase with different degrees after moisture, increasing by 5.16% and 7.83%, respectively, and the breakdown strength decreases by 18.3% and 13.1% after 720 h, respectively. The simulated results show that the moisture form and position have a great influence on electric field distribution. The electric field distortion caused by water trees’ defect is the most serious, followed by water film defects and water droplet defects. Besides, for different types of moisture defects, the position of the maximum distortion electric field is different. [ABSTRACT FROM AUTHOR]

Using ultra-high-strength materials in the concrete-filled steel tubular columns has potential to optimize cross-sectional dimensions and improve the performance and sustainability of offshore structures under the complex marine conditions. This study investigated the behavior and performance of ultra-high-strength concrete-filled square steel tubular (UHSCFST) stub columns when subjected to eccentric compressive loads using experimental tests and finite element analysis. Six UHSCFST column specimens were tested considering variations in material strength and eccentricity. The column response to the eccentric loads was analyzed, taking into account the failure mode, load-lateral deflection response, and longitudinal and transverse strains obtained from the tests. Additionally, finite element models of the tested UHSCFST columns were developed and validated by comparing the numerical and experimental results. Baseline simulations were conducted to extensively analyze the stress distributions of each component and identify the load-transfer mechanism during the loading process. The column models were also used to examine the effects of key parameters on the eccentric compression behaviors of the UHSCFST stub columns and determine the dominant parameters for developing design suggestions. These findings provide valuable information on the utilization of ultra-high-strength materials in CFST members for performance improvement. Furthermore, the results serve as references for the further design and evaluation of UHSCFST columns under different loading conditions. • Using ultra-high-strength materials in CFST stub column for coastal structures. • Eccentric compression testing of UHSCFST stub column. • Examining capacity and load transfer mechanism of UHSCFST stub column. • Creating and validating numerical model of eccentrically loaded UHSCFST stub column. • Conducting parametric studies on column mechanical behaviors for design suggestions. [ABSTRACT FROM AUTHOR]

This study conducts experimental and numerical investigations into the response of ultra-high-strength (UHS) concrete-filled ultra-high-strength steel tubular (UHSCFST) columns under eccentric loading, varying the slenderness ratio, to develop effective design guidelines for engineering applications. A series of eccentric compression tests were conducted on twelve UHSCFST columns with varying slenderness ratios to identify failure mechanisms and load-bearing characteristics. In the experimental program, critical influencing factors, including load eccentricity ratio, slenderness ratio, and UHS steel strength, were considered. Finite element models of eccentrically loaded UHSCFST columns were developed using ABAQUS and validated through a comparison of tested and simulated results to analyze load-sharing ratios and stress distribution for each column component. The findings indicated that UHSCFST column failure modes were characterized by compression-controlled and flexure-dominated damage under the combined effects of slenderness ratio and load eccentricity ratio. UHS concrete played a dominant role in bearing the eccentric load, and a judicious selection of UHS steel yield strength can improve column capacity and resistance. Additionally, these validated models were employed to conduct parametric studies that evaluated the effects of design and load parameters on the eccentric load capacity of UHSCFST columns. Design equations were developed based on tested and simulated results to predict the ultimate load capacity of UHSCFST column with varying slenderness ratios under eccentric loading conditions. • Conducting eccentric compression tests and nonlinear numerical simulations on UHSCFST column • Evaluating effects of slenderness ratio and load eccentricity on column behaviors • Extensive studies of capacity, load transfer mechanism, and failure mode for columns • Identifying compression-controlled and flexure-dominated damage for UHSCFST column • Proposing design equations for estimating eccentric load capacity [ABSTRACT FROM AUTHOR]

The lateral impact resistance of cantilever concrete-filled steel tubular (CFST) members stiffened with encased I-shaped carbon fiber reinforced plastic (CFRP) profiles subjected to lateral impact is investigated in this paper. The impact tests are performed on four specimens to examine the dynamic response. Finite element analysis models are established and verified against tested results. Baseline simulations are also created using the validated models to further analyze the damage pattern and energy dissipation mechanism of each component in the impact events. It is found that compared with traditional CFST members, the new composite members have higher peak impact force, lower dynamic displacement, and larger energy dissipation capacity. Additionally, the effects of design parameters on the impact performance are evaluated by parametric analyses, and the results provide valuable suggestions for developing design guidance. • Lateral impact test of CFST member stiffened with encased I-shaped CFRP under cantilever boundary condition was conducted. • The cooperative working mechanism of steel tube, concrete and CFRP profile in composite member was revealed. • The energy dissipation capacity of each component in different impact stages was quantitatively evaluated. • The influencing rules of different parameters on the impact resistance of composite members were summarized. [ABSTRACT FROM AUTHOR]

This study presents experimental and numerical research on the dynamic behaviors and resistances of square concrete-filled steel tubular members internally strengthened by I-shaped CFRP profile (SCFST-CFRP) with fixed boundary conditions subjected to lateral impact loads. Dynamic impact tests were conducted on five SCFST-CFRP specimens and a traditional concrete-filled steel tubular (SCFST) specimen, examining their dynamic responses with respect to deformation modes, impact force, displacement, and strain distribution at different levels of impact energies and impact momentums. The test results indicated that the deformation of the specimens was concentrated in the impact region, approximately 0.38 L above the base, due to the transient localized characteristics of the lateral impact load. In terms of displacement and impact force, the SCFST-CFRP member exhibited better impact resistance compared to the SCFST member. Finite element models of the SCFST-CFRP members were created using LS-DYNA and validated against the impact tests. These validated models were then utilized to explore the damage patterns, dynamic bending moment, and load transfer mechanism of the SCFST-CFRP member under lateral impact loading. Additionally, a parametric study was conducted to evaluate the effects of load and structural parameters, including CFRP profile, impact energy, and impact momentum, on the impact resistance and dynamic flexural capacity of the SCFST-CFRP member. The results demonstrate that the enhancement in impact resistance caused by the inner CFRP profile was more significant under higher impact energy. Based on the parametric analysis results, empirical equations were proposed to predict the dynamic flexural capacity of lateral impact-loaded SCFST-CFRP members. • Impact tests of CFST member strengthened with CFRP profile under fixed boundaries. • Evolutions and distributions of deformation and internal force were summarized. • Impact load transfer mechanisms of the composite member were revealed. • Effects of load and structural parameters on the impact resistance were evaluated. • An equation for the dynamic flexural capacity of the composite member was proposed. [ABSTRACT FROM AUTHOR]

• Conduct impact tests on CFSTS-CFRP members to study the effect of velocity and CFRP. • In-depth analyze the working mechanism of CFSTS-CFRP members under impact loading. • Clarify the contribution of each part to the impact resistance of CFSTS-CFRP members. • Propose a simplified dynamic flexural capacity model of CFSTS-CFRP members. • Propose a maximum deflection prediction model of CFSTS-CFRP members. Concrete-filled steel tubular simply supported members stiffened with encased I-shaped CFRP (CFSTS-CFRP members) have been developed due to their excellent mechanical performance, promoting promising applications in bridge and building structures. However, these members are susceptible to collision impacts during service, leading to serious accidents. This paper aims to investigate the structural behavior of CFSTS-CFRP members subjected to transverse impact loading, utilizing experimental, numerical, and theoretical studies. Drop hammer impact tests were conducted on three CFSTS-CFRP specimens with varying impact velocities, while a CFST specimen was used as the benchmark. The experimental results demonstrate that all CFSTS-CFRP specimens experienced bending failure. The cooperation between the I-shaped CFRP and CFST members was observed, with the mechanical properties of CFSTS-CFRP specimens being fully utilized. The working mechanism of CFSTS-CFRP members is revealed by numerical simulation results obtained from the FE models of the tested CFSTS-CFRP members, which consist of the analyses of failure mode, inertia force, sectional moment, energy absorption, etc. Furthermore, by investigating the effects of different parameters on the structural response of CFSTS-CFRP members, predicted models for dynamic flexural capacity and maximum deflection are proposed for the purpose of impact design. Additionally, the contribution of the steel tube, concrete, and I-shaped CFRP to the transverse impact resistance of CFSTS-CFRP members is clarified. This clarification provides a scientific basis for determining the respective weight coefficients in subsequent damage assessment research. The findings from the experimental, numerical, and theoretical analyses contribute to the understanding of their mechanical performance and assist in the development of more efficient design approaches. [ABSTRACT FROM AUTHOR]

Four prestressed high-strength concrete pile- (PHC pile-) pile cap connections under low-cycle loading were tested to study the test phenomena, failure modes, hysteretic performance, ductility, and bearing capacity. The PHC piles were reinforced with steel fiber and deformed bars and CFRP. The tests results showed that the connections were damaged by bending. The concrete of the caps were squeezed to be crushed. The concrete of connection was crushed and formed a hinge joint that resulted in the connection rotating unrestricted, and the rotation capacity of connection increased. The PHC pile reinforced with steel fiber and deformed bars can improve the displacement ductility of the connections. The finite element software ABAQUS was used to simulate the nonlinear behavior of pile-cap connections. The prediction agreed relatively well with the experimental results. The stress and strain of specimens were studied. The connections should be designed with enough rotating capacity and make sure the cap will not be damaged by squeezing or prying due to the rotation of pile end. [ABSTRACT FROM AUTHOR]

[Display omitted] • Improve the space charge injection characteristics of insulating layer by modifying the semiconducting layer. • Change the charge migration path by the action of the Lorentz force in the semiconducting layer. • Semiconducting layer composites with various particle sizes (SrFe 12 O19, from 80 nm to 1000 nm). • Concern the matching characteristics of semiconducting layer. and insulating layer. The key problem limiting the development of high-voltage direct current (HVDC) cable is the space charge accumulation within the insulation layer. A method is proposed to reduce the accumulation of space charge of cable insulation by a semi-conductive layer modified by magnetic particles. The physical essence is to change the charge migration path by the action of the Lorentz force in the semi-conductive layer. SrFe 12 O 19 particles with different particle sizes from 80 nm to 1000 nm are prepared by the sol-gel self-combustion method. The magnetic properties and resistivity of the semi-conductive layer composites with various particle sizes are investigated. In addition, the effect of the semi-conductive layer electrode for charge accumulation in the insulation layer is studied. Finally, the relationship among SrFe 12 O 19 particle size, magnetization intensity of the semi-conductive layer, and charge inhibition effect of the insulation layer is analyzed. The results of the experiments demonstrate that residual magnetization of magnetic particles has a significant impact on the space charge suppression. When SrFe 12 O 19 particle size is 200 nm, the charge inhibition effect is the best. This work can provide a new view for the charge suppression of insulation layer. [ABSTRACT FROM AUTHOR]

Temperature and electric field are important factors affecting space charge accumulation in high voltage dc (HVDC) cable insulation. Charge conduction and accumulation in XLPE have been studied by correlating the polarization and depolarization processes. The experimental results indicate that the steady current of XLPE increases about 2 or 3 orders with the increasing temperature from 25 °C to 90 °C, and the stronger electric field, the less the increased amplitudes. The trap level in XLPE stressed by different electric fields and temperatures have a tiny change from 0.89 eV to 1.15 eV. Besides, there exists an inflection temperature of charge accumulation in XLPE, around 50 °C∼ 60 °C. At the room temperature, the trapped charges are difficult to release from the traps, and these homo-charges near the electrode can depress the further injection of charges. With the increase of temperature, part of trapped charges near the interface will gradually migrate towards the bulk of the material, and more charges are injected. When the temperature exceeds around 50 °C, the molecular movement is accelerated which can dramatically enhance the hopping probability of charges between the adjacent traps, and little accumulated charges are left. [ABSTRACT FROM AUTHOR]

The impact behavior of building and bridge structures is already a growing concern due to the frequent occurrence of vehicle collision accidents. Concrete-filled square steel tube stiffened with encased I-shaped carbon fiber reinforced plastic profile (CFST-CFRP) is suitable for building and bridge structures due to its high bearing capacity and small section size. Thus, this study experimentally and numerically presents the dynamic responses for CFST-CFRP columns under lateral impact to evaluate their impact resistance. Firstly, three CFST-CFRP columns and one CFST column were tested in a rigid vehicle impact device, with variations in impact velocity, impact type, impact impulse of the rigid vehicle, and CFRP profile. The impact force-displacement curve and failure mode of CFST-CFRP columns were obtained. Additionally, finite element analysis (FEA) models were built by ABAQUS and verified against tested results. Then, the working mechanisms of CSFT-CFRP columns under impact load were further revealed in-depth by analyzing displacement, impact force, inertia force, bending moment, shear force, and dissipated energy. Based on the working mechanisms, the effect of the CFRP profile on the dynamic response of CFST-CFRP member subject to different parameters was discussed. The results indicated that all the specimens fail at the support. With the additional CFRP profile in the CFST column, the failure pattern of the steel tube was transformed from fracture to local buckling. CFRP profiles enhance the impact resistance of CFST columns (incremented by 17%), and the increasing ratio rises with the decreasing steel ratio and steel strength of members. Steel tubes can share 72% and 78% of energy absorption and bending moment, which is the main impact-resistant component. For this study, valuable experimental data can be supplied for CFST-CFRP columns subjected to vehicle collision. Meanwhile, a theoretical reference for impact resistance design in the future is also provided. [ABSTRACT FROM AUTHOR]

Using high strength materials in concrete filled steel tube (CFST) columns is expected to achieve better structural performance and fulfil the requirements of sustainable construction. To study the mechanical behaviour of eccentrically loaded high strength concrete filled high strength square steel tube (HCFHSST) stub columns, this paper describes 12 tests with different eccentricity ratios and steel ratios. The cubic strength of high strength concrete under investigation was 110.5 MPa, and the yield strength of the high strength steel was about 434 MPa. Curves of load-lateral deformation were presented, along with values of ductility index, and the minimum ductility index based on the steel ratio of columns was suggested. Finite element analysis (FEA) software ABAQUS was applied to simulate HCFHSSTs. The analytical results were in good agreement with the experimental ones. The load-lateral deformation curve was divided into four stages: elastic, elastic-plastic, plastic hardening and descending. The confinement effect of steel tube at various stages was analysed. The parametric studies were carried out to evaluate the influences of the eccentricity ratio, concrete compressive strength, steel yield strength and steel ratio on the strength reduction factor (SRF), concrete contribution ratio (CCR), P-M and P/P u - M/M u interaction curves of the HCFHSST members. The bending moments at balanced points of P/P u - M/M u curves calculated by the plastic stress distribution models (PSDM) and FEA models were compared. The ultimate bearing capacities obtained from the tests and the values calculated from the AISC 360, GB 50936 and CECS 28: 90 design codes were compared. Finally, the formulas were proposed to predict the P/P u - M/M u curves for the HCFHSST stub columns subjected to eccentric load. The proposed formulas’ predictions agreed well with the test results. [ABSTRACT FROM AUTHOR]

We present the use of silica-polydopamine (SiO2@PDA) core–shell nanoparticles (NPs) as self-confined templates for the fabrication of ultra-stable hollow Pt anchored N-doped carbon nanospheres (Pt/HN-C). SiO2@PDA nanospheres were fabricated by a facile one-pot process, followed by the deposition of Pt NPs onto the outer shell layer. The confinement and adhesion of the PDA framework ensured the distribution and stability of Pt NPs after carbonization at the carbon shell layer. The converted Pt/HN-C exhibited excellent catalytic performance and durability for the oxygen reduction reaction (ORR). [ABSTRACT FROM AUTHOR]

To study the mechanical behavior of high-strength concrete filled high-strength square steel tube (HCFHST) under pure bending load, six specimens with different steel ratio were tested. The corresponding nonlinear finite-element models were established to analyze the mechanical properties. The load-displacement curves obtained from the numerical analyses are consistent with the experimental results. In addition, the influences of different materials are analyzed in this paper. The moment-curvature relationship can be divided into three stages: elastic stage, yield stage and hardening stage. And the ultimate bearing capacity increased with the steel ratio, steel yield strength and concrete compressive strength. Moreover, the ultimate bearing capacity of the experiment and finite-element analysis (FEA) model is compared with the requirements of codes: AISC-LRFD (1999), AIJ (1997), EC4 (1994) and GB50936-2014 (2014). The test and FEA result were the most compatible to the calculated result of EC4 (1994). And find the results in this paper is the most compatible to the code EC4 (1994). [ABSTRACT FROM AUTHOR]

Charge transport behaviors of dielectric under electron radiation have an important influence on surface flashover performance. In this paper, charging process and model of dielectric during electron radiation are investigated based on the synergistic effect of electron movement on dielectric surface and charge transport properties in dielectric surface layer. For one thing, electrons accumulated in dielectric surface layer will form a reverse electric field acting against kinetic electrons flowing to dielectric surface, which affects the energy and density of electrons reaching the surface. For another, the changes of electron energy and density will further affect the dynamic processes of electron deposition, transport and accumulation in the surface layer. A dielectric charging model is proposed, and charge transport characteristics in dielectric surface and surface layer are obtained, including the temporal behavior of the incident kinetic electrons flowing to dielectric surface, the temporal behavior of secondary electrons and surface conduction charge, as well as the spatial and temporal behavior of the interior potential and electric field. Based on surface potential decay curves of polyimide under different electron energy levels (3-11 keV), the surface potential decay process and model are investigated. The surface trap distribution of polyimide shows different properties under different energy levels. The shallow trap level increases slightly with the increase of electron energy, ranging from 0.81 eV-0.85 eV, while the deep trap level remains unchanged about 0.94 eV. Besides, the amount of trap charge density gradually increases with the increase of electron energy. [ABSTRACT FROM AUTHOR]

• Development of SCFST stub column internally reinforced by CFRP profile. • Axial compression tests on 10 SCFST-CFRP columns and 2 SCFST columns. • Study of mechanical properties of SCFST-CFRP column with varying parameters. • Evaluation of existing design codes of AIJ, EC4, AISC-LRFD, and GB50936. • Development of empirical equations for column axial load capacity. This paper presents experimental and numerical investigations of an innovative composite column, which is formed using a square concrete filled steel tubular (SCFST) column internally reinforced by a carbon fiber reinforced polymer (CFRP) profile (referred to as SCFST-CFRP column), under axial compression. Full-scale axial compression tests were conducted on ten SCFST-CFRP columns with different steel ratios and steel grades and two traditional SCFST columns. The test results, including failure mode, axial load–displacement response, and strain development, were analyzed to examine the column behavior under axial compression. Numerical models of SCFST-CFRP columns were developed and validated to further investigate the stress distribution and load-bearing contribution of each column component. The validated models were then used for parametric studies that evaluated the effects of material and structural parameters on column behavior and axial load capacity. Besides, design rules, as suggested in the codes of AIJ, EC4, AISC-LRFD, and GB50936, were evaluated using experimental and numerical data for axially loaded SCFST-CFRP columns. In addition, empirical equations were developed through unified criteria to predict the SCFST-CFRP column capacity under axial compression. [ABSTRACT FROM AUTHOR]

The vacuum surface flashover voltage of dielectric material irradiated by electron-beam is very low, which is the key scientific issue for developing high-voltage and high-power spacecraft technology. This paper proposes a novel research way of considering the combined impact of incident kinetic electrons flowing to dielectric surface and deposited electrons in dielectric surface layer on dc surface flashover performance in vacuum. The experiments on dc surface flashover of polyimide in vacuum after electron irradiation and during electron irradiation were investigated. The experimental results indicated flashover voltage showed a distinctly different variation tendency under the two cases. The dc surface flashover voltage of polyimide after electron irradiation became higher than that without electron irradiation, because of the effect of deposited electrons in dielectric surface layer. During electron irradiation, the dc surface flashover voltage exhibited a dramatic drop from 26.9 kV (energy: 5 keV) to 10.5 kV (energy: 30 keV). Furthermore, the surface flashover characteristics exerts different changes for incident electrons of different energies levels. It has been experimentally indicated that the energy and incident trajectory of incident kinetic electrons flowing to polyimide surface are altered by the combined action of the reverse electric field created by deposited electrons and the applied electric field. As a result, the surface flashover characteristics were changed. This work provides a new insight into the vacuum surface flashover of dielectric material under electron irradiation, and can be used as the research basis of surface flashover mitigation methods in space environment. [ABSTRACT FROM PUBLISHER]

Deep dielectric charging in ring structure irradiated by energetic electrons is one of the major factors causing spacecraft anomalies. In this paper, based on the physical processes of charge deposition, transport and accumulation, we establish a 2-D deep dielectric charging physical model of a ring structure consisting of insulating materials, electrodes and aluminum shield. Deep dielectric charging properties of insulating materials irradiated by electron energy spectra are simulated and analyzed under typical space environment and extreme space environment. Furthermore, the influences of aluminum shield, insulating material properties and thickness on deep dielectric charging are investigated. When the thickness of aluminum shield is larger than 3 mm, the maximum electron-beam density reduces to 10-10 A/m2, which is so low that it can not induce high electric field within materials. Selected polyimide (PI), polytetrafluoroethylene (PTFE) and composite epoxy resin (FR4) as electrical insulating materials, space charge transport, accumulation and electric field in insulating material of the ring structure are analyzed. It is indicated that the maximum electric field obeys the sequence as follows: PTFE> FR4> PI. Finally, it is found that the electric field is obviously enhanced with the increasing thickness of insulating material. This work paves the way towards the mitigation of deep dielectric charging. [ABSTRACT FROM PUBLISHER]

• Conducted eccentric compression tests on 18 CFSST-CFRP long column. • Investigated eccentrically loaded behavior and resistance of CFSST-CFRP column. • Evaluated effects of slenderness ratios and load eccentricity ratio. • Analyzed load bearing capacity and load-transferring mechanism. • Performed parametric studies on column bearing capacity. • Developed design equations to predict ultimate eccentric load capacity. This study investigated behavior of concrete filled square steel tubular (CFSST) columns encased with I-shaped CFPR under eccentric compression. Full-scale eccentric compression tests were conducted on eighteen column specimens consisting of square steel tube, concrete, and an I-shaped CFRP profile. The test program considered effects of load eccentricity ratio and column slenderness ratio. The eccentrically loaded column behavior was investigated with respect to the mid-height deflection, load, and failure modes. The development and distribution of longitudinal strain and neural axis for the column were also studied. Finite element models were developed and validated against tested results to further analyze the load-transferring mechanism of the composite column and perform detailed parametric studies. The results indicated that the CFSST column encased with I-shaped CFRP behaved in a ductile manner with the improved capacity and increased stability. Finally, design equations were developed using tested and simulated data to estimate ultimate bearing capacity of the CFSST column encased with I-shaped CFRP when subjected to eccentric compression. The predicted column capacities using the design equations matched well with the tested and simulated capacities. [ABSTRACT FROM AUTHOR]

• High-strength CFSST stub column with an encased I-shaped CFRP profile was proposed. • Axial compression test was performed on HCFHSST-CFRP stub column. • Investigated effects of material strengths and steel ratio on column behavior. • The combinations of high-strength materials and CFRP improved column resistance. • Formulas were proposed to predict ultimate axial load capacity. A new composite column that consists of high-strength square steel tube, high-strength concrete, and carbon fiber reinforced polymer (CFRP) profile with a I-shaped cross section was developed and investigated in this study. This paper experimentally and numerically investigated axially loaded behavior of high-strength concrete filled high-strength steel tubular (HCFHSST) stub column with an encased I-shaped CFRP profile. In the experimental study, axial compression tests were completed on eight specimens to examine the axial load response of the composite column, including the load–displacement curves, failure mode, and strain distribution. Finite element models of the composite column were developed using ABAQUS and validated by comparing numerical results with experimental data. The validated models were used to further investigate the load sharing and transferring mechanism for each component of the composite column. Results showed that the composite column comprehensively used the advantageous merits of concrete, steel tube, and CFRP as a unit to share the applied load at different loading stages: linearly elastic, elastic–plastic, hardening, post-peak descending, and residual plateau stage. Parametric studies were performed that assessed influences of critical design parameters on the axially loaded behavior of the stub column. The examined parameters included the compressive strength of high-strength concrete, yield strength of high-strength steel, and steel ratio. Finally, empirical equations were proposed to determine the ultimate vertical strain and the ultimate axial load capacity of the HCFHSST stub column encased with a I-shaped CFRP profile. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to explore the seismic damage mechanism of the Dayemaling Bridge during the Maduo earthquake and discuss the seismic damage characteristics of the high-pier curved girder bridge. Design/methodology/approach: In this study, the numerical simulation method is used to analyze the seismic response using synthetic near-field ground motion records. Findings: The near-field ground motion of the Maduo earthquake has an obvious directional effect, it is more likely to cause bridge seismic damage. Considering the longitudinal slope of the bridge and adopting the continuous girder bridge form, the beam end displacement of the curved bridge can be effectively reduced, and the collision force of the block and the bending moment of the pier bottom are reduced, so the curved bridge with longitudinal slope is adopted. Originality/value: Combined with the seismic damage phenomenon of bridges in real earthquakes, the seismic damage mechanism and vulnerability characteristics of high-pier curved girder bridges are discussed by the numerical simulation method, which provides technical support for the application of such bridges in high seismic intensity areas. [ABSTRACT FROM AUTHOR]

Abstract: Colloidal hydroxyapatite (HA) with long-term stability was essential for its potential applications in the biomedical field. Polymer/surfactant pair of poly(ethylene oxide) and sodium oleate were used for surface modification of spherical HA particles with nanoscale sizes. Suspensions with different solid loadings were prepared and observed through sedimentation studies with purpose of investigating the effect of surface modification on the colloidal stability. It was found that after decorated with polymer/surfactant pair, colloidal HA particles were obtained with satisfied dispersion stability and less conglomeration due to the existence of both electrostatic repulsion and steric hindrance effects. Based on the investigation of surface chemistry of modified HA powders, a schematic illustration about multilayered surface structures with polymer/surfactant pair was put forward and might favor to prepare a wide range of dispersible particles in aqueous solutions. [Copyright &y& Elsevier]

Influence mechanism of side group types on the macroscopic electrical properties of silicone rubber (SiR) are analyzed based on the experimental comparison and the molecular simulation. The insulation properties of SiR with different side group types (vinyl, phenyl, and trifluoropropyl), as well as binary compound SiR (vinyl/phenyl and vinyl/trifluoropropyl) are compared and studied experimentally. Further, the effect of side groups on the movement of the molecular chain is analyzed by calculating the free volume, the mean square displacement (MSD), and the end distances. Then the mechanism of its influence on the macroscopic properties of SiR was studied. The experimental results indicated that the resistance and breakdown performance of the phenyl SiR surpasses both vinyl SiR and fluorosilicone rubber owing to the conjugated structure of benzene ring, which has a high electron affinity and reduces free charges and carrier migration rate. Besides, when 10wt% phenyl SiR was mixed into vinyl SiR, the resistivity increased by one order of magnitude, and the breakdown field strength increased by about 8%. In the aspect of dielectric properties, the fluorosilicone rubber is more qualified than the vinyl SiR and the phenyl SiR due to the addition of trifluoropropyl as a polar group to the non-polar dielectric SiR to boost its dielectric constant and dielectric loss. The molecular simulation results indicated that the SiR containing phenyl has a tiny free volume and weak molecular chain movement, the fluorosilicone rubber has the strongest molecular chain movement. The work has important guiding significance for improving and modifying SiR in power equipment. [ABSTRACT FROM AUTHOR]

Layered double hydroxides (LDH) can be transformed from alkaline supercapacitor material into metal-cation storage cathode working in neutral electrolytes through electrochemical activation. However, the rate performance for storing large cations is restricted by the small interlayer distance of LDH. Herein, the interlayer distance of NiCo-LDH is expanded by replacing the interlayer nitrate ions with 1,4-benzenedicarboxylic anions (BDC), leading to the enhanced rate performance for storing large cations (Na+, Mg2+, and Zn2+), whereas almost the unchanged one for storing small-radius Li+ ions. The improved rate performance of the BDC-pillared LDH (LDH-BDC) stems from the reduced charge-transfer and Warburg resistances during charge/discharge due to the increased interlayer distance, as revealed by in situ electrochemical impedance spectra. The asymmetric zinc-ion supercapacitor assembled with LDH-BDC and activated carbon presents high energy density and cycling stability. This study demonstrates an effective strategy to improve the large cation storage performance of LDH electrodes by increasing the interlayer distance. [ABSTRACT FROM AUTHOR]

Concrete-filled square steel tubular (CFSST) stub column stiffened with an encased I-section carbon fiber-reinforced polymer (CFRP) is a new composite member that consists of a square steel tube, concrete infill, and an encased CFRP profile. This paper conducted investigations that experimentally and numerically examined the behavior of CFSST stub column with an inner I-section CFRP profile under biaxial bending. Seven column specimens were tested using biaxially eccentric compression tests in the experimental study. The parameters considered in the test were the load eccentricity, steel yield strength, and steel tube thickness. Numerical models were developed to investigate the column load-carrying mechanism using ABAQUS and validated against experimental results. Results indicated that the CFSST column stiffened with an encased CFRP profile has favorable capacity and ductility when subjected to biaxial bending. Furthermore, parametric analyses were performed to assess the effects of steel yield strength, concrete compressive strength, and steel ratio (steel thickness) on the load bearing capacity and P / P u - M / M u curve of stub column under biaxial bending. Finally, formulas to predict the P / P u - M / M u curves of the composite column under bi-axial bending were proposed in this study. • Concrete-filled square steel tubular stub column stiffened with an encased I-section CFRP profile was proposed. • Biaxially eccentric compression test was performed on CFSST stub column stiffened with an encased I-section CFRP profile. • Effects of concrete compressive strength, steel yield strength, and steel ratio were investigated. • Parametric studies were conducted to study the mechanical behavior of the new composite stub column. • Formulas were proposed to predict the P / P u - M / M u curves. [ABSTRACT FROM AUTHOR]

Transition metal sulfides are promising electrode materials for supercapacitors due to their excellent electrochemical performance and high conductivity. Unfortunately, the low rate performance and poor cycling stability limited their progress towards commercial applications. Herein, the core–shell structure of MoO42−-intercalated LDHs coated on Co9S8 nanotubes was rationally designed and prepared to improve their electrochemical performance and cycling stability by adjusting the composition of LDHs. Compared to NiMo-LDH@Co9S8 and CoMo-LDH@Co9S8, the optimized NiCoMo-LDH@Co9S8 electrode exhibits excellent areal specific capacitance (11 F cm−2 at 3 mA cm−2) and excellent cycling stability (94.4% after 5000 cycles). In addition, asymmetric supercapacitor devices were assembled with NiCoMo-LDH@Co9S8 and activated carbon (AC), which delivered a high energy density of 0.94 mWh cm−2, at a power density of 1.70 mW cm−2, and good cycling stability (89.4% after 5000 cycles). These results indicate that the introduction of MoO42− can enhance the synergistic effect of multiple metals and the synthesized NiCoMo-LDH@Co9S8 core–shell composite has great potential in the development of high-performance electrode materials for supercapacitors. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) receives significant interests because of environmental friendship and excellent insulation. The development of PP cables depends heavily on the semi-conductive shielding layers that match the PP insulation layers. In this paper, propylene–ethylene copolymer (POP) is used to toughen the PP-based shielding layer. The effects of POP content (40 parts, 50 parts and 60 parts) on the electrical and mechanical characteristics are investigated. Further, the interface matching characteristics and toughening mechanism of the shielding layer are explored. According to the experimental findings, owing to the growth in POP content, the distribution of carbon black (CB) particles becomes more uniform, and the surface roughness decreases from 52.7 nm to 14.7 nm. When the POP content is 60 parts, the charge injected into the insulation layer is the least, which is 0.643 × 10−7 C, and the maximum electric field distortion decreases to 11.4 kV/mm. All three POP content shielding layers maintain a low resistivity at high temperatures (110 ℃, 80 Ω·cm). Besides, as the POP content increases, the toughness of PP-based shielding layer is improved and the elongation at break of POP-60 semi-conductive shielding layer reaches 420%. This research paves a new way for the development of semi-conductive shielding layer of PP cables. [ABSTRACT FROM AUTHOR]

Moisture in the insulation of distribution cable accessories is one of the important causes of insulation degradation and discharge failure of the accessories. The changes in the insulation properties of ethylene-propylene-diene monomer (EPDM) and silicone rubber (SIR) with the time of dampness are studied, and the mechanism of dampness is revealed by combining the surface water absorption characteristics and functional group analysis. The results show that the hydrophobicity of EPDM specimens is lower than that of SIR, resulting in the electrical properties of EPDM being significantly lower than those of SIR after water immersion. The resistivity and the flashover voltage of both specimens decrease significantly with the increase of moisture exposure time, and the decrease of EPDM is more obvious than that of SIR. The breakdown voltage of EPDM decreases by 26.6% and that of SIR decreased by 13.06%. Besides, the flashover voltage along the surface of both EPDM and SIR decreases with the increase of water immersion time, and the decreasing trend of both of them is basically the same. This work has guiding significance for the material selection of the cable accessories and the analysis of damp failure. [ABSTRACT FROM AUTHOR]

Temperature is one of the key factors affecting space charge accumulation in high voltage direct current (HVDC) cable insulation material. The influence of temperature on charge accumulation in low density polyethylene (LDPE) has been investigated with a combined thermally stimulated depolarization current (TSDC) method and pulsed electro-acoustic (PEA) method. The experimental results indicate that there exists a transition temperature region of charge accumulation around 50 °C. The total accumulated charges all firstly increase and then decrease with the increasing polarization temperature under three typical polarization electric fields, and they have more accumulated charges in LDPE around 50 °C. The phenomenon has a close link with the dynamic processes of charge trapping and de-trapping, which were verified by TSDC results. At room temperature, the trapped charges are difficult to release from the traps, and these homocharges near the cathode can depress the further injection of the charges. More charges can be injected from the electrodes with the increase of temperature, while the charge migration is relatively lower before 50 °C, leading to more accumulated charges. When the temperature exceeds around 50 °C, the molecular movement is accelerated which can enhance the hopping probability of charges between the adjacent traps, resulting in few accumulated charges. [ABSTRACT FROM AUTHOR]

Offshore wind power is clean energy with rapid growth in recent years. As a key part of wind turbines, improving the combination performance of wind turbine cable insulation has a crucial impact on the development of wind power systems. In this paper, kaolin is selected to improve the tensile strength of Ethylene-Propylene-Diene Monomer (EPDM) rubber, and Boron Nitride Nanosheeets (BNNSs) with good electrical insulation and thermal conductivity are co-doped into kaolin/EPDM to improve the breakdown strength and thermal conductivity of the composite. The results show that the properties of the composites are improved when the powders are doped into EPDM. When the kaolin doping amount is 30wt%, the dielectric properties and the mechanical properties are improved, but the breakdown strength has deteriorated. Based on 30wt% kaolin content, BNNSs are added to EPDM. The breakdown strength is improved. The breakdown strength of the 30wt% Kaolin/5wt%BNNSs co-doped EPDM is 83.33 kV/mm. In addition, due to the synergistic effect between the two powders, the tensile strength of the composite is increased to 8.06 MPa. Meanwhile, with the increase of BNNSs, the thermal conductivity of composite is improved. It increases to 1.247 W/(m⋅K) This work has important guiding significance for improving the combination performance of the wind turbine cable insulation. [ABSTRACT FROM AUTHOR]

Designing highly-efficient, cost-effective, and stable electrocatalysts for water splitting is essential to producing green hydrogen. In this work, a nanoflower quaternary heterostructured Ni(NO3)2(OH)4/Ni(OH)2/Ni3S2/NiFe-LDH electrocatalyst is successfully synthesized by two-step hydrothermal reactions. The sulfur in the electrocatalyst induces higher valence state metal atoms as active sites to accelerate the formation of O2. As expected, benefiting from the unique structural features and solid electronic interactions, Ni(NO3)2(OH)4/Ni(OH)2/Ni3S2/NiFe-LDH exhibits remarkable oxygen evolution reaction performance with a low overpotential of 223 mV at a current density of 100 mA cm−2, a slight Tafel slope of 65.4 mV dec−1, and outstanding stability in alkaline media. Attractively, using Ni(NO3)2(OH)4/Ni(OH)2/Ni3S2/NiFe-LDH as both a cathode and an anode, the alkaline electrolyzer delivers a current density of 10 mA cm−2 only at a cell voltage of 1.67 V, accompanied by superior durability. This work provides a facile method for the rational design of high-performance quaternary electrocatalysts. [ABSTRACT FROM AUTHOR]

Binary transition metal sulfides are considered to be a promising material for supercapacitors, possessing richer electrochemically active sites and superior electrochemical performance. Metal–organic frameworks (MOFs) are often used as self-sacrificing templates in the preparation of metal sulfides. Usually, direct sulfidation of MOFs tends to cause collapse of the morphological structure and blockage of the ion transport channels, so that the morphology of the original MOF template can be well preserved by using pyrolysis followed by S2− ion exchange. In this paper, we first prepared NiCo–MOF-74 on nickel foam by an in situ transformation method from layered double hydroxides (LDHs) through a ligand exchange reaction. Then, CoNi2S4 was synthesized in two steps involving the pyrolysis of NiCo–MOF-74 and a subsequent S2− ion exchange reaction. Compared with direct sulfidation, this synthetic strategy can well maintain the rod-like morphology of MOF-74 arrays and prevent structural collapse. The surface of CoNi2S4 has a fine nanosheet structure, which exposes more active sites and shows a high specific capacitance of 7.50 F cm−2 at 2 mA cm−2 and an excellent Coulomb efficiency (96.32%). In addition, the hybrid supercapacitor assembled with activated carbon shows a high energy density of 0.64 mW h cm−2 at a power density of 1.64 mW cm−2 and a high capacitance retention of 88.39% after 5000 cycles. These results indicate that rod-shaped CoNi2S4 can be controllably prepared from MOF-74 involving an exchange reaction and has promising application in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

Silicone rubber has been widely used in electric power equipment for its excellent insulation performance and weather resistance. However, the weak breakdown characteristic of silicone rubber limits its application in high-voltage grade power equipment. In this paper, the nano-modification system of silicone rubber based on a binary composite matrix of "phenyl-vinyl" was constructed. On the one hand, the benzene ring structure is introduced to improve the breakdown strength of the matrix. On the other hand, barium strontium titanate (BST) is used to improve the permittivity of composite, reducing the electric field shared by silicone rubber. The experimental results show using binary composite silicone rubber as the matrix, the appropriate amount of BST filling can greatly improve the permittivity of the composite. When the BST content is 30 wt%, the permittivity of the binary composite reaches the maximum value of 3.98, which is about 49.06% higher than that of vinyl silicone rubber. Accordingly, the electric field strength shared by silicone rubber insulation will decrease significantly. Meanwhile, the moderate amount of BST in the matrix can improve the breakdown strength. This work is an important guideline for the performance improvement of silicone rubber for high-voltage power equipment. [ABSTRACT FROM AUTHOR]

Developing highly efficient electrocatalysts is crucially significant for the application of advanced energy conversion. The Fe–N–C single-atom catalyst is promising for CO2 electroreduction reaction (CO2RR) but suffers from insufficient intrinsic activity and inferior conductivity, which could be addressed by redistributing the electron density via heteroatom doping. Herein, we synthesized S-doped Fe–N–C (Fe–SN–C) as an advanced electrocatalyst for CO2RR using a simple trapping–pyrolysis strategy. Density functional theory calculations and experimental results indicate that S doping increases the d-band electrons and conductivity of Fe–SN–C by electron donating, and thus boosts *CO desorption during the CO2RR process and suppresses the competing hydrogen evolution reaction. Consequently, Fe–SN–C exhibits the maximum CO faradaic efficiency of 93% at −0.5 V and the highest partial current density of 10.1 mA cm−2 at −0.8 V for 2e− CO2RR. This finding provides a feasible and controllable method to achieve advanced electrocatalysts for efficient energy conversion. [ABSTRACT FROM AUTHOR]

A satellite operates in a harsh environment including high vacuum and radiations. The vacuum-dielectric interface is the most vulnerable area to flashover discharge. Moreover, the presence of electron radiation will further decrease the flashover voltage. However, the influence of electron radiation on surface flashover remains unclear. We have performed a study on vacuum DC surface flashover during electron beam irradiation as a function of electron kinetic energy and incident direction on polyimide representative of spacecraft dielectrics. The electron radiation was accompanied by electron deposition and bombardment effects on the polyimide surface. The surface flashover voltage was experimentally found to significantly depend on the kinetic energy and incident angle of the electron beam. By calculating the trajectories of incident electron beam, we further found that the surface flashover voltages are closely connected to the irradiated area. During low energy electron beam irradiation, kinetic electrons are repelled away from the dielectric surface by the applied electric field, and deposited electrons will be dominant in the flashover process, promoting the surface flashover voltage. However, when the electron beam energy is high, kinetic electrons can overcome the applied electric field and strike the dielectric surface to generate secondary electrons, which will replace the field-emission electrons to serve as seed electrons, and initiate the flashover at a much lower applied voltage. These observations and analyses are expected to benefit the research into mitigating spacecraft discharge, and promote the knowledge of surface flashover. [ABSTRACT FROM PUBLISHER]

Near-surface mounted (NSM) fiber reinforced polymer (FRP) has been established as an effective technique for strengthening concrete member. In preview literatures, bond failure was observed usually in the strengthened beam test for increasing flexural capacity. Bond behavior is of primary importance for the transfer of stress between the concrete and the FRP reinforcement to develop composite action. In this paper, a total of 22 tests were conducted to study the bond failure performance between NSM FRP bars and concrete besides only one test as a comparison. Failure modes, load–deflection curves, strain distribution of FRP bars, and local bond stresses at the FRP-epoxy adhesive interface from the tests were analyzed in detail. Some of the factors expected to affect bond performance were presented, namely: diameter of FRP bars, type to FRP material, concrete compressive strength and bonded length. The test results reported in this paper should be useful for further establishing local bond–slip constitute relationship and further verification of numerical simulation models, in addition to gaining a better understanding of bond failures for flexural strengthening concrete structures with NSM FRP bars. [ABSTRACT FROM AUTHOR]

Polypropylene (PP) becomes a superior candidate material for new environmental-friendly cable insulation layer with its excellent heat resistance, electrical properties and degradability. At present, most of studies focus on the insulation layer of PP cable. However, there are few studies on semi-conductive shielding layer of PP cable which match its insulation layer. In this paper, polypropylene (PP)/styrene ethylene butylene styrene (SEBS) is adopted as matrix of PP cable semi-conductive layer to matching its insulation layer. Meanwhile, Maleic anhydride grafted polypropylene (MAH- g -PP) is used to cooperatively improve the compatibility between PP and SEBS. The physicochemical properties, space charge injection properties and compatibility of semi-conductive composites with different CB and MAH-g-PP contents is studied by combining experiment and simulation methods. The experimental results show that the surface roughness of the semi-conductive layer and the space charge inside the insulation layer decrease first and then increase with the increase of CB addition. Among them, the two parameters of 25 phr CB semi-conductive layer is the lowest, respectively 13.98 nm and 2.25 × 10−8C. These two parameters are significantly reduced after the addition of compatibilizer MAH-g-PP, which decreased by 29.47 % and 62.22 %, respectively. The simulation results show that the Flory-Huggins interaction parameters (χ) of MAH-g-PP with PP and SEBS are −73.3 and −45.2, respectively, which are 236.24 % and 107.34 % lower than those of PP/SEBS. The χ value of MAH-g-PP/CB is 8.20, which is 33.27 % and 9.59 % lower than CB/PP and CB/SEBS, respectively. It shows that MAH-g-PP can effectively improve the compatibility of matrix and filler. This work has important guiding significance for the research of semi-conductive layer formulation of PP cable. [ABSTRACT FROM AUTHOR]

Lithium‐metal anodes suffer from inadequate rate and cycling performances for practical application mainly due to the harmful dendrite growth, especially at high currents. Herein a facile construction of the porous and robust network with thermally conductive AlN nanowires onto the commercial polypropylene separator by convenient vacuum filtration is reported. The so‐constructed AlN‐network shield provides a uniform thermal distribution to realize homogeneous Li deposition, super electrolyte‐philic channels to enhance Li‐ion transport, and also a physical barrier to resist dendrite piercing as the last fence. Consequently, the symmetric Li|Li cell presents an ultralong lifetime over 8000 h (20 mA cm−2, 3 mAh cm−2) and over 1000 h even at an unprecedented high rate (80 mA cm−2, 80 mAh cm−2), which is far surpassing the corresponding performances reported to date. The corresponding Li|LiFePO4 cell delivers a high specific capacity of 84.3 mAh g−1 at 10 C. This study demonstrates an efficient approach with great application potential toward durable and high‐power Li–metal batteries and even beyond. [ABSTRACT FROM AUTHOR]

Space charge accumulation in polypropylene (PP) affect the dielectric properties and breakdown strength of the material. The pre-injected charge in PP under the action of different polarity voltage is quantitatively characterized, and the effects of the pre-injected charge inside the dielectric on the dielectric properties and breakdown strength are measured and analyzed. Based on the molecular simulations, the influence mechanism of the temperature on dielectric properties and breakdown are discussed. The experimental results show that the injected charges in PP under the negative polarity voltage is significantly larger than that of the positive polarity. These charges have a great influence on the dielectric constant and breakdown performance of PP, and the effect is different for different charge polarity. The effect of negative polarity pre-voltage conditions on the dielectric constant is much greater than that of positive polarity, and the dielectric constant of PP decreases from 2.2 to 1.3, decreasing about 41% under the negative polarity pre-voltage. By contrast, the dielectric constant slightly increases under the effect of the homopolar preload. Furthermore, the breakdown strength of the dielectric after the heteropolar preload is 249 kV/mm, which is 36% lower than that of PP without pre-voltage, and it slightly increases after the positive polarity pre-voltage. As the temperature increases, the increase in free volume favors the development of electron collision ionization and electron collapse processes, leading to a decrease in breakdown voltage at high temperatures. This work has a good guiding significance for the comprehensive evaluation of energy storage parameters. [ABSTRACT FROM AUTHOR]

An in situ hydrothermal crystallization method with presence of glutamic acid, urea and yttrium ions was employed to fabricate hexagonal hydroxyapatite (HAp, Ca 5 (PO 4 ) 3 (OH)) tubes with length of 200 nm–1 μm. Firstly, yttrium ion-doped HAp (Y-HAp, Ca 5 − x Y x (PO 4 ) 3 (OH)) was synthesized after hydrolysis of urea and HPO 4 2 − ions at 100 °C with a dwell time of 24 h. The shift of X-ray diffraction peaks of HAp to high angle was caused the substitution of Ca 2 + ions by small-sized Y 3 + ions. At 160 °C, further hydrolysis reactions of urea and HPO 4 2 − ions resulted in the generation of ample OH − and PO 4 3 − ions, which provided a high chemical potential for the dissolution of Y-HAp and recrystallization of HAp and YPO 4 . Finally, HAp tubes were formed in situ on Y-HAp according to the Kirkendall effect as a result of the difference of diffusion rate of cations (Ca 2 + ions, outward and slow) and anions (OH − and PO 4 3 − ions, inward and fast). The formation process of HAp tube was simulated by the encapsulation of fluorescein molecules in precipitates. Photoluminescence properties were enhanced for HAp tubes with thick and dense walls. This novel tubular material could find wide applications as carriers of drugs, dyes and catalysts. [ABSTRACT FROM AUTHOR]

A facile hydrothermal method was employed to synthesize submillimeter-long octacalcium phosphate (OCP) and hydroxyapatite (HAp) crystals as drug carriers. After hydrolysis reaction of urea, calcium phosphate fibers grew preferentially along c-axis due to modulation of crystallization by glutamic acid. With increasing addition of urea, OCP and HAp precipitated with decreased values of crystallite size and aspect ratio. It was found that the conversion of OCP to HAp was completed after hydrothermal treatment at 160 °C for 6 h. The formation of fibrous crystals and adsorption of water-insoluble drugs were accomplished in one-step synthesis process with presence of ibuprofen molecules. The sustained-release behavior of ibuprofen could be described by a Higuchi model. HAp and OCP fibers might be simultaneously used for high-performance reinforcements to improve mechanical properties of composite materials and sustained-release drug carriers to cure postoperative infection of bone replacement. [ABSTRACT FROM AUTHOR]

Abstract: The formations of non-metabolic stones, bones and teeth were seriously related to the morphology, size and surface reactivity of dicalcium phosphate dihydrate (DCPD). Herein, a facile biomimetic mineralization method with presence of glutamic acid and arginine was employed to fabricate DCPD with well-defined morphology and adjustable crystallite size. In reaction solution containing more arginine, crystallization of DCPD occurred with faster rate of nucleation and higher density of stacked layers due to the generation of more OH− ions after hydrolysis of arginine at 37°C. With addition of fluorescein or acetone, the consumption of OH− ions or desolvation reaction of Ca2+ ions was modulated, which resulted in the fabrication of DCPD with adjustable crystallite sizes and densities of stacked layers. In comparison with fluorescein-loading DCPD, dicalcium phosphate anhydrate was prepared with enhanced photoluminescence properties due to the reduction of self-quenching effect and regular arrangement of encapsulated fluorescein molecules. With addition of more acetone, DCPD was prepared with smaller crystallite size via antisolvent crystallization. The simulated process with addition of amino acids under 37°C would shed light on the dynamic process of biomineralization for calcium phosphate compounds. [Copyright &y& Elsevier]

A method of space charge suppression for high-voltage direct current (HVDC) cable is proposed by the modification of the semiconductive layer. In this work, the magnetic particle of SrFe12O19 is used to modify the semiconductive shielding layer, and the effect of SrFe12O19 orientation on the charge accumulation of the insulation layer has been studied. First, the semiconductive composite with different SrFe12O19 contents is prepared and their physicochemical properties are characterized. Second, the effect of the SrFe12O19 orientation in the semiconductive layer and the doping contents on the charge accumulation in the insulation layer is analyzed by measuring the resistivity and space charge. The experimental results show that a certain amount of SrFe12O19 (≤10 wt%) can effectively reduce the positive temperature coefficient (PTC) effect, and the orientation can more effectively reduce the space charge injection from the metal wire core to the insulation layer, thus inhibiting the charge accumulation in the insulation layer. While when the content of magnetic particles is high, it will promote the second injection of the charges, leading to an increase of the charge accumulation. The work provides a new idea for space charge suppression of HVDC cable insulation layer. [ABSTRACT FROM AUTHOR]