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Parabolic trough solar collector (PTC) is one of the most mature technologies in the medium and high temperature solar thermal utilization field, and PTC is the key component which transforms solar radiation into heat. PTC performance directly affects the performance of solar energy heat utilization system. In order to improve the thermal efficiency and provide the theoretical basis for PTC design, this paper analyzes the heat transfer characteristics of PTC. One-dimensional heat transfer mathematical model of PTC is established, and using this model, heat transfer characteristics for PTR70 2008 type PTC are analyzed. The result shows solar radiation heat absorbed by PTC is significantly affected by the solar incident angle. Heat absorbed by PTC is calculated by direct normal irradiance data in September 21st and October 25th, and the mean direct solar radiation data of October 25th is higher than the data in September 21st by 37.5894 W/m2, solar radiation heat absorbed by PTC in September 21st is higher than the data in October 25th by 196.644 W/m. The heat transferred from the outer absorber surface to the inner absorber surface increases with the increase of temperature difference of the outer and inner absorber surface, decreases with the increase of the ratio of outer absorber diameter to inner absorber diameter. When the ratio of outer absorber diameter to inner absorber diameter is greater than 1.05, the thermal resistance increases to 0.00046-0.00047 K/(Wom). Convection and radiation heat transfer occur between the absorber and the glass envelope. The heat transferred across the evacuated annulus from the outer absorber surface to the inner glass surface through radiation increases with the increase of the temperature of the outer absorber surface. The convection heat transfer between the absorber and glass envelope is very small and plays a negligible role. The heat is associated with annulus gas type, and heat transfer of annulus hydrogen is greater than annulus air and heat transfer of annulus air is greater than annulus argon. The heat transfers from the glass envelope to the atmosphere by convection and radiation. The convection will either be forced or natural, depending on whether there is wind. Radiation heat loss occurs due to the temperature difference between the glass envelope and the sky. Radiation heat loss increases by 105 W when ambient temperature drops by 10°C. The convection heat increases by 116 W when wind speed increases from 0.5 to 6 m/s under the glass envelope outer surface temperature of 50°C. The value reaches 340 W when the glass envelope outer surface temperature is 80°C. The transient thermal efficiency of PTC is significantly affected by heat transfer fluid (HTF) temperature. The transient thermal efficiency decreases with the increase of the temperature of HTF, and increases with the increase of the direct solar radiation. PTC thermal efficiency is calculated by using the mathematical model established in this paper, and compared with the experimental data of the national renewable energy laboratory (NREL) in America, and the results show that the maximum deviation is about 3%. It shows that the mathematical model can reflect the heat transfer law of PTC. The characteristics of heat transfer mathematical model can provide theoretical basis for PTC design and system operation. [ABSTRACT FROM AUTHOR]

This work presents a new method for numerical computation of the two-dimensional nearly singular integrals by using the eight-node second-order quadrilateral surface elements in 3D BEM. A new indirect regularized boundary element formulation excluding the CPV (Cauchy Principal Value) and HFP (Hadamard-Finite-Part) integrals is proposed. Based on this, a new approximation formula of the distance from the fixed calculation point to a generic point of the aforementioned surface geometry elements is developed firstly, and then the exponential transformation, which has been widely employed in 2D BEM, is extended to 3D BEM to remove the near singularities of integrands for considered integrals. Several numerical examples are given to verify the high efficiency and the stability of the proposed scheme. [ABSTRACT FROM AUTHOR]

Concentrating Solar Power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Heat transfer fluid is heated by sun rays through the solar concentrator, then used as a heat source for a conventional power plant. A wide range of concentrating technologies has existed; the most developed are parabolic trough collector (PTC), linear fresnel reflector system (LF), power tower, and dish/engine system (DE). Parabolic trough collector is considered as one of the most mature applications of solar energy in these four technologies, which makes it worth developing. Sun-tracking system plays an important role in the development of solar energy applications, especially for the high solar concentration systems that directly convert the solar energy into thermal or electrical energy. High accuracy of sun-tracking is required to ensure that the solar collector is capable of harnessing the maximum solar energy throughout the day. Compared to fixed systems, power output of single-axis and dual-axis tracking systems can increase by 25% and 41% respectively under the same condition. It is clear that an accurate sun-tracking control system can make solar collectors receive more solar radiation energy to improve the solar energy utilization. A good sun-tracking system must be reliable and able to track the sun at the right angle even in the periods of cloud cover. Although the tracking system is more complex and costs higher than the fixed system, increasing the annual output power can reduce cost effectively. As for photoelectric tracking mode, a sun position sensor is used to provide feedback signals to judge where the sun is, but they don't work on cloudy days because of the lower sensitivity. The stability of the solar tracking system is a key factor to obtain the maximum sunlight from parabolic trough collector. In order to improve tracking stability and accuracy of the parabolic trough collector sun-tracking control system, this paper chose the more reliable hydraulic drive mechanism to match the system and mainly focused on the design of sun-tracking control system and analysis of operational data from the parabolic trough collector sun-tracking system. Based on the existed working platform of parabolic trough collector system with a length of 50 meters, this paper developed a sun-tracking control system for parabolic trough solar collector. Based on programmable logic controller (PLC), active control mode on the trajectory of the sun was adopted, which could calculate the rotation angle of the parabolic trough solar collector and control commands to drive the hydraulic cylinder to achieve real-time tracking of the sun. The system's basic operating principle, design of sun-tracking, rotation angle algorithm of parabolic trough solar collector and PLC's programs have been analyzed. Experiments were conducted in the 4 typical dates (March 20, June 21, September 23, and December 22, in 2013). The analytical result showed that sun-tracking errors of parabolic trough solar collector were nearly 0.5°. Compared to more accurate SPA (solar position algorithm) algorithm, calculation error of algorithm to calculate the position of the sun was within 0.12°. The maximum error of intermittent operation tracking mode was within 0.398°. The maximum operating speed of parabolic trough collector in the year appeared at noon on the winter solstice, the maximum operating speed was 0.398°/min, and transmission error of an angle sensor was at 0.044° or less. This study may provide the theoretical basis for mechanical transmission design of parabolic trough collector. [ABSTRACT FROM AUTHOR]

The Co-based double perovskite oxides have been attracting great attention for their unique physical properties. Herein, we perform first-principles calculations on the structure, magnetic and electronic properties of fully ordered Sr 2 CoTeO 6. The tolerance factor (τ) of ∼0.99 approves the stability of the perovskite structure. Studying the magnetic and electronic structure demonstrates that Sr 2 CoTeO 6 is a semiconducting antiferromagnet. The effective magnetic interactions generate from B-site Co(↑)-Co(↓) antiferromagnetic spins and the chemical composition is Sr2+ 2 Co2+Te6+O2- 6. Detailed analysis of Co 3d orbitals indicates the B-site Co2+ with 3d7 (t 2g 5e g 2) electronic configuration is in the high-spin state. The spin-orbital coupling effects of the Co cations do not alter the semiconducting performance of Sr 2 CoTeO 6 but produce a large orbital magnetic moment of −1.07 μ B /atom. This work is a useful complement for understanding the inextricable effects of Co on the physical properties, paving a credible way for the investigation of Co-based double perovskite oxides. Sr 2 CoTeO 6 is an antiferromagnetic semiconductor with the antiparallel spins Co2+, and unraveling the inextricable effects of high-spin Co2+ on the physical properties is vital to understand the interesting characteristics of the compound. [Display omitted] • Sr 2 CoTeO 6 is a semiconducting antiferromagnet in low-temperature P 2 1 /n phase. • The effective magnetic coupling attributes to Co(↑)-Co(↓) spin arrangement. • The charge combination is confirmed to be Sr2+ 2 Co2+Te6+O2- 6. • B-site Co2+ with 3 ​d7 (t 2g 5e g 2) electronic configuration is in the high-spin state. • A large orbital magnetic moment of −1.07 μ B /atom is found on B-site Co. [ABSTRACT FROM AUTHOR]

A Eu-polymer complex containing Eu(BA)3phen (BA stands for benzoic acid and phen is 1,10-phenanthroline) and epoxy resin was synthesized in. It was found that the emission light color under 254 nm UV light could change reversibly between red and blue with addition and evaporation of acetone in the Eu-polymer complex. To explain the reversibility of the emission color, the chemical structure and fluorescence property of the complexes were investigated using FTIR, UV-vis, and photoluminescence (PL) spectra. It is proposed that the competitive coordination between Eu/epoxy and Eu/acetone was responsible for the reversible emission color change. [ABSTRACT FROM PUBLISHER]

Abstract: A simple route for fabricating highly ordered luminescent thin films based on hybrid material of diblock copolymer and europium complex, assisted with self-organization of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer upon solvent annealing, is presented. PS-b-PEO self-organized into hexagonal patterns and europium complex of Eu(BA)3Phen was selectively embedded in PS blocks after solvent annealing in benzene or benzene/water vapor. During benzene annealing, the orientation of the PEO cylindrical domains strongly depended on the Eu(BA)3Phen concentration. In contrast, when the hybrid thin films were annealed in mixture of benzene and water vapor, high degree of orientation of the PEO cylindrical domains is more easily obtained, which is independent of Eu(BA)3Phen concentration. Furthermore, preferential interaction of PEO domains with water induces a generation of nanopores in the hybrid thin film. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the long-range lateral order and phase composition of the hybrid thin films. The ordered nanohybrid thin films kept the fluorescence property of Eu(BA)3Phen and showed a strong red emission under the 254nm light''s irradiation. The fluorescence property was confirmed by photoluminescence (PL) spectra. [Copyright &y& Elsevier]

Wear is inevitable during the process of materials friction. Herein, inspired by organisms such as earthworms, we have developed a novel material that can repair itself after wear. The self-healing material was fabricated through injecting a phase-change material into the porous matrix to form a composite, which can spontaneously release the internal medium and form a stable lubricating layer. When the lubricating layer is worn, the internal medium can be continuously released to the surface under thermal stimulation, due to the solidifiable/liquid properties of the internal medium, which realize self-healing of the damaged lubricating layer. The as-prepared composite not only provides multiple self-healing and smart lubrication properties, but also maintain stable friction due to the presence of the lubricating layer. • A novel smart lubrication material with self-healing function was prepared. • The COF of the PPI-wax is reduced by 54.5% (PPI-PAO 10 = 0.121, PPI-Wax = 0.055), and the matrix has no obvious wear. • The self-repair process can last at least 353 times. • The outstanding lubricity and self-healing of PPI-wax is ascribed to dynamic responsiveness of the surface lubricant layer. [ABSTRACT FROM AUTHOR]

• A new elastomer structure with three elements（soft-hard-rigid）was synthesized. • The synergistic effects of three elements cause outstanding mechanical properties. • Outstanding toughness endows elastomer excellent tear and wear resistance. • New structure overcomes the difficulty of coexistence of strength and toughness. In materials science, achieving polymers that possess both high strength and high toughness—traditionally seen as contradictory properties—remains a significant challenge. In this study, a poly (urethane-imide-urea) (PUIU) was synthesized, featuring soft, hard, and rigid segment groups alternately distributed along the main chain. By integrating a polyurethane (PU) prepolymer, urea, and imide, with the PU prepolymer acting as the soft segment to confer malleability, urea-formed hydrogen bonds serving as the hard segment to provide toughness, and imide acting as the rigid segment to enhance material strength. The synergistic effects of these elements result in an elastomer with outstanding strength (70.1 ± 2.6 MPa), high elongation at break (1813.9 ± 76.0 %), and high toughness (420.4 ± 22.3 MJ/m3). Furthermore, it demonstrates superior fatigue, tear, and wear resistance. Through a blend of simulation and experimentation, we uncover the reasons behind its high performance. This study demonstrates the feasibility of preparing an elastomer that combines softness, hardness, and rigidity, meanwhile, achieving a balance between strength and toughness, thereby offering valuable theoretical guidance for the integration of high strength and high toughness. [ABSTRACT FROM AUTHOR]

Developing advanced engineering polymers that combine high strength and toughness represents not only a necessary path to excellence but also a major technical challenge. Here for the first time a rigid‐flexible interlocking polymer (RFIP) is reported featuring remarkable mechanical properties, consisting of flexible polyurethane (PU) and rigid polyimide (PI) chains cleverly woven together around the copper(I) ions center. By rationally weaving PI, PU chains, and copper(I) ions, RFIP exhibits ultra‐high strength (twice that of unwoven polymers, 91.4 ± 3.3 MPa), toughness (448.0 ± 14.2 MJ m−3), fatigue resistance (recoverable after 10 000 cyclic stretches), and shape memory properties. Simulation results and characterization analysis together support the correlation between microstructure and macroscopic features, confirming the greater cohesive energy of the interwoven network and providing insights into strengthening toughening mechanisms. The essence of weaving on the atomic and molecular levels is fused to obtain brilliant and valuable mechanical properties, opening new perspectives in designing robust and stable polymers. [ABSTRACT FROM AUTHOR]

Addressing the demand for integrating strength and durability reinforcement in shape memory polyurethane (SMPU) for diverse applications remains a significant challenge. Here a series of SMPUs with ultra‐high strength, self‐healing and recyclability, and excellent shape memory properties through introducing dynamic boron–urethane bonds are synthesized. The introducing of boric acid (BA) to polyurethane leading to the formation of dynamic covalent bonds (DCB) boron–urethane, that confer a robust cross‐linking structure on the SMPUs led to the formation of ordered stable hydrogen‐bonding network within the SMPUs. The flexible crosslinking with DCB represents a novel strategy for balancing the trade‐off between strength and durability, with their strengths reaching up to 82.2 MPa while also addressing the issue of durability in prolonged usage through the provision of self‐healing and recyclability. The self‐healing and recyclability of SMPU are demonstrated through rapid dynamic exchange reaction of boron–urethane bonds, systematically investigated by dynamic mechanical analysis (DMA). This study sheds light on the essential role of such PU with self‐healing and recyclability, contributing to the extension of the PU's service life. The findings of this work provide a general strategy for overcoming traditional trade‐offs in preparing SMPUs with both high strength and good durability. [ABSTRACT FROM AUTHOR]

Tribological behaviors of porous polyimide (PPI) impregnated with polyalphaolefin at different temperatures were investigated. As temperature increases, the coefficient of friction (COF) of PPI decreases at 0.15 m/s but no obviously changes at 0.01 m/s. In contrast, the COF of non-porous polyimide under external oil-supply increases regardless of speeds. This is due to the fact that COF is related to the oil-supply and viscosity determined by temperature. At 0.15 m/s, PPI is in mixed lubrication, self-healing of desorbed adsorption-film and reducing interlaminar shear-force lead to lower COF. However, at 0.01 m/s, PPI is in boundary lubrication, the stored oil can be slowly released and migrated to the interface to heal the adsorption-film, and prevent COF from further increasing. • Tribological mechanisms of oil-containing polyimides (OCPPIs) at different temperatures were studied. • Viscosity and amount of lubricating oil supply strongly depend on temperature. • The lubricating oil migrates to interface to realize the self-healing of desorbed boundary film. • OCPPIs are in mixed lubrication at higher speed, and OCPPIs are in boundary lubrication at lower speed. [ABSTRACT FROM AUTHOR]

We demonstrated a simple approach for constructing black phosphorus/covalent triazine frameworks metal-free hetero-photocatalysts, achieving one of the highest hydrogen evolution activities (17.1 mmol h−1 g−1). • We demonstrated a simple approach for constructing black phosphorus/covalent triazine frameworks metal-free photocatalysts. • The outstanding hydrogen evolution activities (17.1 mmol h-1 g-1) among all metal-free photocatalysts has been achieved. • The enhanced activity was attributed to the efficient interfacial bonding for efficient charge separation and transfer. • This work provides a new insight toward understanding the intrinsic mechanisms in metal-free photocatalysts. Herein, we employed a simple approach for incorporating covalent triazine frameworks (CTF) with ultrathin black phosphorus (BP) nanosheets, resulting in one of the highest hydrogen evolution activities (17.1 mmol h−1 g−1) among all reported metal-free photocatalysts. More importantly, a detailed mechanistic study on dynamic charge transfer and interfacial bonding was conducted by an in-situ irradiation X-ray photoelectron spectroscopy (SI-XPS). The related results clearly reveal that the interfacial P C bonding between ultrathin BP and CTFs is crucial for promoting both photocatalytic activity and stability. More specifically, under light irradiation, the interfacial P C bonds were remarkably enhanced, which efficiently accelerate the photo-generated electron transfer from CTF to BP surfaces for hydrogen evolution reactions. Moreover, owing to the electron enrichments on BP for effectively restraining surface oxidation, the photocatalytic stability of BP/CTF has also been significantly improved. This work not only reported an effective way for fabricating highly efficient metal-free photocatalysts, but also provided the unique insights into the fundamental understanding of the intrinsic mechanisms during photocatalytic reactions. [ABSTRACT FROM AUTHOR]

Solid tribofilm plays a vital role in lubricating and separating friction pairs during relative movement especially under mixed/boundary conditions. However, the present of the ultra-low sulfur diesel retrogrades the formation of the high-performance tribofilm on the counter steel. Two-dimensional (2D) transition metal carbides, carbonitrides or nitrides (MXene) with abundant surface functional groups are promising for forming robust tribofilm at the sliding interface when adding it into self-lubricating polymer. Herein, the design of MXene/epoxy (EP) nanocomposites with enhanced tribology performance is reported. Furthermore, we demonstrated an efficient approach for realizing superlubricity and extraordinary low wear rates (97% off) by incorporating 0D Al 2 O 3 and 2D MXenes. Here, we ascribed the splendid tribological properties to the hybrid tribofilm which can effectively avoid direct contact of the friction pairs. This study provides a basis for exploring the structure-properties relationship of tribofilms, also exploring the potentials of MXene for developing advanced functional materials. Image 1 • Tribological mechanisms of EP composites lubricated by ULSD were studied. • MXene is promising for forming robust tribofilm at the sliding interface. • Superlubricity was realized by incorporating MXene, Al 2 O 3 and EP resin. • MXene-Al 2 O 3 has a synergistic effect on reducing wear rate of EP by 97% off. • Hybrid nanostructure tribofilm is crucial on enhancing tribological performance. [ABSTRACT FROM AUTHOR]

The compound parabolic concentrator (CPC) is a highly interesting solar collector technology for different low-concentration applications due to no tracking requirement. The CPC with a tubular absorber is the most common type of CPC. Here, a comprehensive state-of-the-art review of this CPC type is presented, including design features, structure, applications, etc. Key design guidelines, structural improvements, and recent developments are also presented. [ABSTRACT FROM AUTHOR]

• Hyperbranched polyurethane was applied through grafting epoxy resin to obtain interpenetrating polymer networks. • Crosslinking network points help enhancing thermal and mechanical properties. • All interpenetrating polymer networks express excellent shape memory effect. In this article, a type of hyperbranched polyurethane (HBPU) with triazine structure was successfully synthesized. Afterwards, HBPU was applied through grafting epoxy resin (EP) to fabricate the interpenetrating polymer networks (IPNs) with different ratio of HBPU/EP. The structure of HBPU prepolymer and the formation of the HBPU/EP IPNs were characterized and confirmed by Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared (FTIR) spectroscopy, and the nanoscale phase separation in IPNs composite was analyzed by Atomic Force Microscope (AFM). Besides, the thermal and mechanical results indicated that the IPNs structure enables the material with high strength and thermal stability. Shape memory cycles test demonstrated that the HBPU/EP INPs possess an excellent shape memory performance, and the best shape fixity and recovery were presented by IPNs composite with 20 wt% HBPU. [ABSTRACT FROM AUTHOR]

Electron transmission through semiconductor superlattices is studied with transfer matrix method and resonance theory. The formation of electron band-pass transmission is ascribed to the coupling of different modes in those semiconductor superlattices with the symmetric unit cell. Upon Fabry-Pérot resonance condition, Bloch modes and two other resonant modes are identified to be related to the nature of the superlattice and its unit cell, respectively. The bands related to the unit cell and the superlattice overlap spontaneously in the tunneling region due to the shared wells, and the coupling of perfect resonances results in the band-pass tunneling. Our findings provide a promising way to study electronic systems with more complicated superlattices or even optical systems with photonic crystals. [ABSTRACT FROM AUTHOR]

Material extrusion additive manufacturing provides an effective solution for fabrication of highly customized polyether ether ketone (PEEK) composite parts with any complex shape. Nevertheless, compared with conventional methods, the mechanical strength of 3D printed carbon fiber reinforced PEEK (CF/PEEK) composites is unsatisfactory due to the weak interface bonding strength and high voids content induced by the temperature difference. To overcome this challenge, a temperature‐control 3D printer was used to investigate the effects of ambient temperature and annealing temperature on the microstructure, crystallization behavior and mechanical properties of 3D printed parts. Moreover, the tribological properties of parts printed at different ambient temperature were also studied under various contact pressure. Experimental results showed that the ambient temperature and annealing treatment directly affected the interfacial bonding (fiber/matrix, filament/filament, layer/layer), crystallinity of printed samples, thus affecting their mechanical and tribological properties. The CF/PEEK parts printed at high ambient temperature of 200°C exhibited outstanding mechanical and tribological properties. This study has positive significance for promoting the application of 3D printed PEEK composites in the field of structural load‐bearing and friction materials. Highlights: Structure–property relationships for 3D printed CF/PEEK composites.The ambient temperature strongly affects the thermal and microstructural propertiesInteraction between crystallization and molecular interface diffusion.Interfacial bonding and crystallinity determine the mechanical properties.Tribological properties are highly dependent on applied pressures. [ABSTRACT FROM AUTHOR]

The evolution of particle morphology occurring during polymerization‐induced self‐assembly (PISA) of a block copolymer poly(oligo(ethylene glycol) methacrylate)‐b‐poly(benzyl methacrylate) (POEGMA‐b‐PBzMA) is studied. A well‐controlled reversible addition–fragmentation chain transfer (RAFT) polymerization yields nano‐objects with various morphologies: spheres, aggregates, worm‐like structures, and vesicles. A comparison of the morphology of the nano‐objects formed from two different chain‐length stabilizers established that the unreacted monomer played an important role during the morphology transitions, which is contrary to previous observations. In addition, morphology evolution to higher‐order structures could be attained simply by extending the reaction time, after reaching full monomer conversion. The evolution of morphology of POEGMA‐b‐PBzMA during polymerization‐induced self‐assembly (PISA) was studied. Various morphologies including spheres, worm‐like structures, and vesicles were obtained by PISA. The morphology evolution to higher‐order structures could be attained by extending the reaction time, after reaching full monomer conversion. [ABSTRACT FROM AUTHOR]

Epoxy resins (EPs) are known for their remarkable shape memory capabilities, attributed to their robust covalent cross-linked networks. The research we conducted elaborates on a flexible epoxy composite exhibiting both shape memory and dual photothermal response characteristics. Creation of the composite involved a combination of soft-hard strengthening methods, incorporating polyetheramine (T3000) with pliable chain parts and rigid reduced graphene oxide (rGO) into the epoxy. In terms of tensile properties, a joint strengthening impact is observed between the rigidity of rGO and the pliable agent T3000. At elevated temperatures (T g + 10 °C), the strengthening between rGO and chain segments amplifies the material's final distortion. Regarding thermomechanical properties, T3000 enhances both the crosslink density and the storage modulus, with the T g value being modifiable by altering the T3000 content. Regarding the properties of shape memory, a concentration of 0.25 wt% rGO enhances the film's R f , augments the T3000 content to adjust the system for optimal crosslink density, resulting in composites with an R f exceeding 99% and an R r of 100%. rGO improves the network's thermal conductivity, significantly reduces the duration of thermal activation, and allows for distant alteration of shape memory through a reaction in the NIR. The tailored features, coupled with its exceptional performance, render it apt for real-world uses in fields like smart molding. [Display omitted] • rGO enhances the ultimate deformation of SMEPs at high temperatures (T g + 10 °C). • The T3000 can adjust the system's toughness, E' g , T g , and cross-linking density. • rGO/epoxy composites have R f of over 99% and R r of 100%. • rGO enhances the system's recovery stress. • Composites exhibit shape memory responsive to heat and near-infrared light. [ABSTRACT FROM AUTHOR]

[Display omitted] • The magnetic couplings of SrCaCoTeO 6 are significantly influenced by the A-site disorder. • The effect of A-site disorder can be negligible on the electronic structure. • All structures with different cationic arrangements show semiconducting nature. • The chemical combination is confirmed to be Sr2+Ca2+Co2+Te6+O2− 6. Herein, the effect of A-site disorder on the electronic structures and magnetic properties in double perovskite SrCaCoTeO 6 was systemically investigated using the first-principles calculations. Our results indicate that its magnetic coupling is significantly influenced by the A-site disorder, i.e., the ground magnetic properties vary with different cationic arrangement. However, this effect can be negligible on the electronic structure. Its semiconducting nature does not alter despite of different structures. Further analysis confirms that the B-site Co2+ is magnetic cation in the high-spin state with 3d7 (t 2g 5e g 2) electronic configuration, while Te at B′-site is nonmagnetic with no contribution to the magnetism. [ABSTRACT FROM AUTHOR]

Although stimuli‐responsive gels have received significant attention due to their flexible structure and high tolerance to various stimuli, the high solvent content leads to relatively low mechanical properties and instability in performance due to water evaporation. This limits their application to some extent. Here, catkins enhanced ionogel is crafted that prevents solvent vaporization‐induced properties from abating yet remains humidity responsiveness. By using direct ink writing (DIW) 3D printing, the catkins can be aligned within the ionogel, resulting in a significant increase in ionic conductivity (0.17 S·cm−1) and mechanical properties (4.75 times). Moreover, the environment stability (−50–150 °C) and hygroscopicity of the ionic liquid (IL) allow the 3D‐printed composite to perform a controllable lubrication behavior in response to changes in humidity and temperature. This work demonstrates the significant enhancement of responsive ionogels through DIW 3D printing with aligned catkins and presents a new strategy for achieving the lubricating regulation. [ABSTRACT FROM AUTHOR]

In this work, diamondoid metal-organic frameworks (MOFs) were efficiently prepared by sonochemical synthesis and grown on polyimide (PI), aiming to improve the anti-wear performance of the PI matrix. By introducing MOFs into the PI matrix, the free movement of PI molecular chains were restricted, and its hardness and elastic modulus were improved. It was found that the wear rate of the 3 wt.% MOFs/PI composites was reduced by 72.6% compared to pure PI at a load of 4 N after tribological testing by using a ball-on-disk tribometer. This can be attributed to the excellent load-bearing and shear resistance of the fourfold-interpenetrated diamondoid networks, in which the transition metal elements can favor the formation of transfer films. It is worth noting that the 3 wt.% MOFs/PI composites still exhibited great tribological properties under high loads or high speeds. The findings of the present study indicate that diamondoid metal-organic frameworks can be used as efficient modifiers to enhance the tribological properties of PI. [ABSTRACT FROM AUTHOR]

The orientation of fibers in polymer matrix plays a crucial role in governing the performance of composites including friction and wear. In the present work, the effect of fiber orientation on tribological behavior of 3D printed short carbon fiber reinforced PEEK composites (CF/PEEK) was studied by two series of tribo‐tests, namely macro‐scale continuous sliding and micro‐scale multiple scratching. Fiber orientations studied included parallel, tilted and anti‐parallel relative to the sliding direction in both macro sliding and micro scratching. It was revealed that the effect of fiber orientation showed strong dependence on applied loads. In most cases, lower wear were obtained when the fiber orientation was tilted rather than parallel or anti‐parallel in macro continuous sliding. With tilted orientation, the composite also exhibited the best scratching behavior except for that at the lowest normal load. To reveal the mechanisms behind this orientation effects, the composite's worn surface, as well as those of the counter rings, were characterized. Findings of the present work indicates that scratching tests can help understand the macro sliding mechanisms and appropriate fiber orientation is beneficial in improving the tribological properties of polymer composites, which can be realized through 3D printing. Highlights: PEEK composites filled with highly oriented carbon fibers were manufactured by fused deposition modeling (FDM).Tribological anisotropy was studied through macro sliding and micro scratching measurements with respect to carbon fiber orientation.The coupling mechanism of load and fiber orientation was discussed in influencing the composites' friction and wear properties. [ABSTRACT FROM AUTHOR]

Rock collapse with large volumes can attain high speeds during their freefall motion. The impact of such a falling mass on the ground surface can initiate a powerful air blast with far-field destructive impact. To investigate the formation, disaster-causing mechanism and dynamic characteristics of rock collapse-induced air blasts, an existing coupled discrete-element method (DEM)–computational fluid dynamics (CFD) approach is employed on a rock collapse-generated air blast in Zengziyan, China (ZRC). The generated air blast shows a maximum velocity of over 50 m/s and subsequently dissipated rapidly. The high consistency between the simulated air blast dynamics and the video verified the DEM–CFD coupled method in the air blast modeling. Combined with the ZRC-induced air blast analysis, a simplified generalized model was designed to observe the potential effect of geomorphology. Results highlight the great contribution of geomorphology, to both air blast initiation and propagation. Collapsed rock mass with a free fall motion is prone to generate significant air blasts when colliding with the slope surface. Tremendous energy was transferred to the surrounding air at the moment. Compared with falling straight down, air blasts resulting from an airborne trajectory case show a longer propagation because the collapsed materials impart air a higher initial momentum parallel to the slope surface. In addition, air blast propagation in wide distribution areas in comparison to narrow valleys shows greater attenuation. This study will aid in understanding the mechanism of a rock collapse-induced air blast as well as the forward simulation of similar events for risk assessment. Highlights: DEM-CFD coupled method provides good performance in simulating the air blast dynamics. Large rock collapse with a free fall motion is prone to generate powerful air blasts when colliding with the slope surface. Geomorphology is greatly influential in both air blast initiation and propagation. [ABSTRACT FROM AUTHOR]

On August 10, 2019, typhoon "Lekima" and the associated heavy rainfall triggered a large landslide in Yongjia County, Zhejiang, China. The sliding mass blocked the river, resulted in an air blast and barrier lake disaster chain, and caused 32 deaths. A thorough survey was performed to investigate the characteristics and possible failure mechanisms of the event. The landslide initiation is caused by the combination of rock mass characteristics, wind load, heavy rainfall, and human activities. The presence of roots and cracks in the strongly weathered tuff provides preferential infiltration channels for the rainwater penetration, causing the rapid destabilization of the slope. Furthermore, we used the dynamic model RAMMS and empirical equations to analyze the disaster-causing process of the landslide. Results indicated that the landslide movement lasted for about 30 s with a maximum velocity of 21 m/s. The generated air blast shows a maximum pressure of 1.7 kPa and caused tree breakage on the opposite side of the river. Subsequently, the sliding mass blocked the river and generated a landslide dam with a maximum thickness of about 14 m. Its combination with heavy rainfall led to the rise of the upstream water level and the submersion of houses in the Shanzao village within 20 min. Our work is expected to improve the understanding of typhoon-induced large landslides and promote the risk assessment of this type of geohazard in coastal regions. [ABSTRACT FROM AUTHOR]

The present paper provides a new definition of the dual interpolation curve in a geometric-intuitive way based on adaptive curve refinement techniques. The dual interpolation curve is an implementation of the interpolatory subdivision scheme for curve modeling, which comprises polynomial segments of different degrees. Dual interpolation curves maintain various desirable properties of conventional curve modeling methods, such as local adaptive subdivision, high interpolation accuracy and convergence, and continuous and discontinuous boundary representation. In addition, the dual interpolation curve is mainly applied to solve the difficult geometry defeaturing problems for curve modeling in existing computer-aided technology. By adding fictitious and intrinsic nodes inside or at the vertices of interpolation elements, the dual interpolation curve is flexible and convenient for characterizing a set of ordered points or discrete segments. Combined with the Lagrange interpolation polynomial and meshless method, the proposed approach is capable of characterizing the non-smooth boundary for geometry defeaturing. Experimental results are given to verify the validity, robustness, and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

In the present study, novel polyether ether ketone (PEEK) based composites were fabricated by multi-material fused deposition modeling (FDM), which were composed of alternating short carbon fiber reinforced PEEK and silicon dioxide filled PEEK layers. And the composites' tribological properties were evaluated in order to guide their application in industrial parts where friction and wear are of special importance. It is revealed that the tribological properties of the composite were highly dependent on the contact pressure. The low friction and wear occurred at high contact pressure was found to be associated with the combined contribution of rolling of nanoparticles and graphitized self-lubricating transfer films. This work provides a simple strategy for manufacturing highly customized tribo-components with required functions to replace conventional hybrid materials. [ABSTRACT FROM AUTHOR]

Seabed data acquired from the Dongsha Region in the northern South China Sea (SCS) revealed the detailed morphology of sand dune fields on the upper continental slope, at depths between 230 and 1240 m. High-resolution multibeam echosounder bathymetry and multichannel seismic reflection data were used to describe and interpret the distribution, characteristics, and migration of these sand dunes. The sand dunes were distributed as patches on a generally gentle continental slope (gradients≤0.58°), on a seafloor mainly covered by silty and coarse sand. The dunes exhibited distinctly different distribution patterns, geometries, and migration behavior. The trough-to-trough wavelength ranged from 47 to 555 m, the height was 0.1 to 19.8 m, the crest length was 100 m to 10s of km, and the dominant orientation was NE-SW. Based on their distribution and characteristics, the sand dunes were further categorized into (i) sinuous, (ii) barchan, (iii) reticular, (iv) restricted, and (v) superimposed types. Most sand dunes migrated to both NW and SE directions. We infer that, in the Dongsha Region, northern SCS, sand dunes formed and migrated due the world's largest observed internal solitary waves (ISWs). Wave-wave and wave-topography interactions occur as ISWs propagate and undergo polarity conversion during shoaling process, reflection, refraction, diffraction at the Dongsha Atoll. These processes bring about variable and complex local hydrodynamic conditions in the Dongsha Region, dissipate vast amounts of energy, erode the seafloor, and supply the sediment and energy required to sustain the formation and migration of very large sand dunes. Our findings not only enhance our understanding of the intricate relationships between topographic and geomorphologic evolution, sedimentary dynamics and mesoscale motions, but also hold significant importance for various hydrographic applications, such as navigation and submarine pipeline installation. • Sand dunes occur at depths of 230–1240 m on the South China Sea continental slope. • These dunes vary in distribution, geometry, and migration. • Dune formation and migration is due to very large internal solitary waves (ISWs). • ISWs induce variable hydrodynamic conditions as they interact with the Dongsha Atoll. • Our findings have important implications for submarine engineering. [ABSTRACT FROM AUTHOR]

H. P. Li and A. Sun performed the calculations and wrote the paper. Z. Y. Zhang and B. C. Guo carried out the draft preparation, H. B. Ji discussed the results. Y. Tian directed the entire study. All authors read and commented on the paper. [Display omitted] • CeCu 3 Co 4 O 12 is an antiferromagnetic semiconductor. • The chemical combination is confirmed to be Ce4+Cu2.67+ 3 Co3+ 4 O2- 12. • The magnetic interaction generates from the A-type antiferromagnetic coupling of A′-site Cu. • The B-site Co3+ with 3d6 (t 2g 6e g 0) electronic configuration is nonmagnetic in the low-spin state. We used the first-principles calculations to investigate the magnetic structure and electronic properties of quadruple perovskite CeCu 3 Co 4 O 12. Our calculations demonstrate that CeCu 3 Co 4 O 12 is an antiferromagnetic semiconductor, in which the A′-site Cu plays a decisive role in magnetic properties. The chemical combination is proved to be Ce4+Cu2.67+ 3 Co3+ 4 O2- 12. The mixed-valence Cu2.67+ at A′-site shows A-type antiferromagnetic coupling, whereas the B-site Co3+ with 3d6 (t 2g 6e g 0) electronic configuration is nonmagnetic in the low-spin state. Moreover, the spin-orbital coupling (SOC) effect does not alter the semiconducting performance of CeCu 3 Co 4 O 12 , although the bandgap is sharply reduced when SOC effect was taken into consideration. [ABSTRACT FROM AUTHOR]

The tribological properties of neat polyimide (PI) are incompatible with service conditions, necessitating the urgent modification of its tribological properties. Carbon fibers (CFs) were surface modified with in-situ grown metal-organic frameworks (MOFs) incorporated into PI coating towards the goal of improving its mechanical and tribological properties in combination with graphite (Gr). It is successfully demonstrated that the enhanced interfacial adhesion between the CFs and PI, due to the mechanical interlocking effect of the MOFs, improved the load-carrying capacity and anti-wear properties of the coatings. Additionally, the friction-reduction effect of Gr further contributed to the improvement of tribological properties of MCFs/5Gr/PI coating. Overall, findings of the present study promote the development of engineering plastics with enhanced tribological properties. [ABSTRACT FROM AUTHOR]

Nitrile butadiene rubber (NBR) composites possess remarkable wear-resistance and prominent damping properties enhanced by surface modified Ti 3 C 2 -MXene with polydopamine and amino silane, which are prepared through solution blending and hot pressing method. The characterization results show that surface modification of Ti 3 C 2 -MXene improves the hardness, damping and tribological properties of unfilled NBR. In the meantime, the result also reviews that there are a lot of amino and hydroxyl groups on the surface of MXene after grafting polydopamine and amino silane. This surface modification is of benefit to muscle interfacial strength of MXene with NBR and further boosts the tribological and damping properties of NBR composites. This work explores the potentials of MXene in the friction and damping field and provides guidance for preparing highly wear-resistant and damped NBR composites. • Surface modified Ti 3 C 2 -MXene with polydopamine and amino silane was prepared. • Nitrile Butadiene Rubber (NBR) composites with remarkable wear-resistance and prominent damping properties were obtained. • The max tanδ value of modified NBR composite is about 1.0 and it's the effect damping temperature range achieves to approximately 40 °C. • The wear rate of modified NBR composites has a biggest decline of 76% compared to unfilled NBR. [ABSTRACT FROM AUTHOR]

Thermoset shape memory polyimides (TPIs) are widely used in the fields of high-temperature smart devices. However, the recent molding of polyimides limits most of potentials in the form of two-dimensional film. In this work, we synthesized a novel shape memory polyimide (SMPI) ink that could be used for both Digital Light Process and extrusion molding 3D printing. Through UV-induced free radical polymerization, 3D custom polyimides ink can be cured rapidly. Remarkably, the 3D printed PI exhibits excellent shape memory performance, with R f of 99.8%, R r of 98.3%, therefore the 4D printing PI was successfully prepared. The 3D printed airplane, ultrasonic motor and pagoda can actively recover the film folding, expanding combined compressing, and vertical distorting to their permanent shape, which presents the outstanding 4D printing properties. Moreover, SMPI can be used in extrusion molding to print films, the residual stress induced the self-folding and then a vector model was applied to characterize transformation of extruded plates. In order to develop the application diversity of extruded 4D polyimide, self-folding box and stimuli-response gripper are designed, the gripper is able to pull up steel ball 15 times heavier than itself. Thus, SMPI will be benefit to expand the applied scope of SMPI. Unlabelled Image • A new shape memory polyimide ink for DLP 3D printing and extrusion molding has been developed. • The SMPI have high mechanical strength, excellent shape memory property (R f of 99.8%, R r of 98.3%) and low contraction. • Printed or extruded 4D products can actively recover to their permanent shape in a few minutes. • The SMPI-based self-folding box and stimuli-response gripper have been designed. [ABSTRACT FROM AUTHOR]