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Void defect is prevalent during the composite manufacturing process and may reduce the mechanical properties of composite structures, while limited information about three‐dimensional void distribution and evolution can be found due to the difficulties in void observation. In this work, void defects at different positions were detected and analyzed using x‐ray microtomography (XRM), and the random forest algorithm was implemented for segmenting components of CFRP samples. Results showed a trend of gradual rising porosity in the axial direction, with an increase of ~250% of porosity at the outlet of resin injection compared to the one at the inlet during the composite manufacturing process. The voids mainly featured with microscale between carbon fibers, with less distribution between fiber bundles and resin‐rich zones. Void defects achieved aggregation at the middle position of manufactured laminate, which is probably related to pressure interception. In the axial direction, the proportion of large‐diameter voids gradually increased, and a large volume of connected voids appeared near the outlet. Due to the shear deformation of resin and fiber and the pressure gradient effect, most of the voids showed stripe shape. The spatial orientation of voids was predominantly along the direction of resin flow and fluctuated due to fiber curl. Highlights: 3D void characteristics in CFRP were studied using the XRM technique.Void formation and the effects of fibers on void morphology were analyzed.Dynamic void transport mechanisms during CFRP manufacturing were studied.Location and morphology of voids are helpful for CFRP damage modeling.The effective partitioning of CFRP was achieved using a random forest algorithm. [ABSTRACT FROM AUTHOR]

The concept of superhydrophobicity has been widely used after years of theoretical and experimental exploration. Researchers have obtained materials with excellent surface superhydrophobicity for numerous areas (e.g. textiles, paints, and coatings industries), through different design and synthesis methods using low surface energy components (LSECs) and micro/nanohierarchy composite structures. However, the durability of superhydrophobic material surfaces has gradually become a prominent obstacle to restricting applications. In this paper, advances in improving the durability of superhydrophobic surfaces in the past decade are reviewed, covering different schemes for recovering fractal surfaces based on the LSECs and micro/nanocomposite structures. It also presents a balanced review on wet chemical methods, chemical vapor deposition (CVD), layer-by-layer (LbL), microarc oxidation (MAO), and self-healing of the fractal surfaces, with the aim at developing sustainable superhydrophobicity. In addition, it innovatively summarized the research on the synthesis of self-healing superhydrophobic materials by machine learning methods. By the end it discusses perspectives on future development in this emerging research area. [ABSTRACT FROM AUTHOR]

In this paper, a class of nonlinear ordinary differential equations with impulses at variable times is considered. The existence and uniqueness of the solution are given. At the same time, modifying the classical definitions of continuous dependence and Gâteaux differentiability, some results on the continuous dependence and Gâteaux differentiable of the solution relative to the initial value are also presented in a new topology sense. For the autonomous impulsive system, the periodicity of the solution is given. As an application, the properties of the solution for a type of controlled nonlinear ordinary differential equation with impulses at variable times is obtained. These results are a foundation to study optimal control problems of systems governed by differential equations with impulses at variable times. [ABSTRACT FROM AUTHOR]

In this paper, a novel state-dependent switching controller with delayed positive partial state feedback is proposed to stabilise a controlled system with insufficient state information. At first, the controlled system is converted to a single-degree-of-freedom vibrational system by using an invertible transform and a second-order Taylor approximation for the time delay term. Then, appropriate control gain parameters and a state-dependent switching rule are designed via the physical meaning of the resulting vibrational system. By combining the advantages of delayed positive position feedback with the state-dependent switching mechanism, we find that the time delay can considerably improve the asymptotic stability of the controlled system. Finally, three numerical examples show that the proposed controller is effective and that time delay indeed plays a prominent positive role in switched control systems. [ABSTRACT FROM AUTHOR]

In the present work, a state‐dependent switching controller design approach for controlled systems under control constraints is proposed. First, the controlled system with control gain parameters is converted into a single‐degree‐of‐freedom vibration system by using an invertible transform. Second, based on the physical significance of the single‐degree‐of‐freedom linear vibration systems, two pairs of gain parameters are properly chosen to obtain two subsystems with sufficiently small equivalent negative‐damping coefficients and sufficiently large equivalent stiffness coefficient difference. Third, by introducing an identical invertible transform, two subsystems are converted into the form of vibration systems simultaneously. As such, it is reasonable to compare the two corresponding energy functions directly. Fourth, two switching lines with maximum and minimum energy ratio between two subsystems are derived to construct a state‐dependent switching law. Combining the selected control gain parameters, a state‐dependent switching controller is then designed for stabilizing the original controlled system with control constraints. In the end, the effectiveness and robustness of the developed control approach are illustrated by three numerical examples. [ABSTRACT FROM AUTHOR]

Different from conventional unidirectional outward-inward forming methods, this study employs a multidirectional internal expansion shaping approach to fabricate lightweight sandwich composite tubes. Integrating carbon fiber reinforced polymer (CFRP), thermal expansion foam and polymethacrylimide (PMI) foam, the sandwich composite tubes demonstrate adaptability in terms of material properties as validated through several experimental trials. The one-step molding process eliminates the requirements for subsequent structural assembly and bonding, while ensuring adhesion between diverse material components. The sandwich composite tubes exhibit superior impact resistance, showcasing a stable progressive crushing failure. The energy absorption mechanism shifts from single CFRP damage to a multi-material composite energy absorption mode. The specific energy absorption (SEA) value of designed sandwich composite tube is up to 102 J/g. The sandwich composite tubes fabricated in this study hold promising applications in advanced vehicle/aerospace lightweighting and crashworthiness safety. [Display omitted] [ABSTRACT FROM AUTHOR]

This study introduces an ultrasonic vibration assisted resin transfer molding (RTM) technique as an innovative approach to address the inherent challenges associated with traditional methods for producing CFRP laminates. It investigates the mechanism of void formation in CFRP composites under ultrasonic vibration using 3D X-ray microscopy. Numerical calculations and simulation analyses are also employed to validate the impact of ultrasonic vibration on mechanical properties of CFRP. The findings indicate that ultrasonic vibration results in CFRP laminates with more uniform thickness, leading to a substantial increase in fiber volume fraction up to ∼16 %. Concurrently, there are significant improvements in flexural strength (∼20 %) and fracture energy (∼90 %). Ultrasonic vibration also effectively reduces CFRP porosity by at least 25 %, resulting in a more consistent distribution of voids, primarily consisting of small circular voids. This porosity reduction is attributed to the cavitation effect and enhancing wettability, consequently improving the mechanical properties of CFRP. Moreover, simulations and numerical calculations demonstrate the significant occurrence of cavitation effect within the resin under specific process conditions. The intensity of cavitation is influenced by factors such as the initial bubble radius, acoustic pressure amplitude, and static pressure of the resin. The ultrasonic-assisted RTM process is proved as a promising method for producing CFRP laminates with superior properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Products from a million-ton DCL plant were comprehensively characterized in molecular level. • GC–MS and high-resolution MS were used for the composition analysis. • Pyrene and perhydropyrene are the most abundant compounds in the liquefaction oil. • Hydrocarbons with 1–4 and 4–8 aromatic rings were detected in the oil and the residue, respectively. • Partially hydrogenated PAHs show better hydrogen donation activity than tetrahydronaphthalene. The China Shenhua company has built and operated the only large industrial direct coal liquefaction (DCL) plant in the world for 15 years, with an oil product capacity of one million tons per year. However, there is insufficient information on the chemical composition of its products. In this study, the liquefaction product, including the distillate oil and the vacuum residue, as well as the circulating solvent were characterized by gas chromatography – mass spectrometry (GC–MS) and high-resolution mass spectrometry. The liquefaction oil has lower H/C ratio and higher oxygen and nitrogen contents compared to hydrogenation products derived from petroleum. The major component of the liquefaction oil is middle-temperature distillate, which is approximately 70 wt% concentrated in the range of 200–350 °C. Pyrene and perhydropyrene are the most abundant compounds in the liquefaction oil. Hydrocarbons with 1–4 aromatic rings were detected in the liquefaction oil, with skeletons of benzene, biphenyl, naphthalene, fluorene, phenanthrene, pyrene, etc.. Various partially hydrogenated and perhydrogenated aromatic compounds were identified in the oils and they even constitute the major component of the circulating solvent. 2,3-Dihydro-1H-phenalene was also found in high-relative abundance in the oils and has potential to be used as a marker for coal liquefaction produced through hydrogenation processes. Partially hydrogenated polycyclic aromatics exhibit higher dehydrogenation activity compared to tetralin. The organic component in the vacuum residue account for around 60 wt%, with toluene insoluble matter accounting for more than one third. The toluene soluble fraction has an H/C ratio of 0.82 and is mainly composed of aromatic with 4–8 rings. The molecular size and condensation degree of the residue are much higher than those of other fossil fuel-derived aromatic-rich substances. Further studies are necessary to evaluate whether aromatic hydrocarbons with such a high condensation degree are suitable for producing high-performance carbon materials. [ABSTRACT FROM AUTHOR]

In this study, transparent Li–N co-doped ZnSnO (ZTO: (Li, N)) thin film transistors (TFTs) with a staggered bottom-gate structure were fabricated by radio frequency magnetron sputtering at room temperature. Emphasis was placed on investigating the effects of post-annealing temperature on their physical and electrical properties. An appropriate post-annealing temperature contributes not only to achieving good quality thin films, but also to improving the electrical performance of the ZTO: (Li, N) TFTs. The ZTO: (Li, N) TFTs annealed at 675 °C showed the best electrical characteristics with a high saturation mobility of 26.8 cm 2 V −1 s −1 , a threshold voltage of 6.0 V and a large on/off current ratio of 4.5×10 7 . [ABSTRACT FROM AUTHOR]

The preparation and electrical properties of ZnO: (Li,N) thin film transistors were studied in this work. The Li–N dual doped ZnO films, as the active layers with thickness varied from 20 to 60 nm, were deposited on SiO 2 /n-type Si substrates by radio frequency magnetron sputtering. The transistor with 30-nm-thick ZnO: (Li,N) film shows the best performance with a field effect mobility of 33.6 cm 2 /V.s, a threshold voltage of −6 V and an on/off current ratio of 1.08 × 10 8 . And the time-dependent instability of the device was studied. The mobility increases to 41.5 cm 2 /V after 120 days, and then decreases to 31.2 cm 2 /V after 180 days, accompanied by a negative shift of threshold voltage and a decrease of on/off ratio as day increases. The main cause of the instability may be the adsorption of humidity from ambient air. [ABSTRACT FROM AUTHOR]

InZnLiO thin film transistors with the bottom gate structure were fabricated by radio frequency magnetron sputtering. The structure of InZnLiO channel layers were studied by SEM and XRD. The electrical properties on the effect of the annealing temperature were investigated. As the annealing temperature increased, the field effect mobility and the on/off current ratio increased observably, and the threshold voltage was shifted to the negative direction. But when the temperature was too high, the electrical properties of InZnLiO TFTs deteriorated significantly. In all, the transistor annealed at 950 °C exhibited the best performance, with a field effect mobility of 63.1 cm 2 /V s, an on/off current ratio of 6.9 × 10 6 , and a threshold voltage of 0.2 V. [ABSTRACT FROM AUTHOR]

We have fabricated transparent thin-film transistors with ZnSnLiO as active layers deposited by radio frequency magnetron sputtering at room temperature. The TFTs structure used in this study was a staggered bottom-gate, which consists of SiO as a gate insulator and heavily doped p-type Si(1 1 1) as a gate electrode. In order to optimize the performance of the ZnSnLiO thin-film transistors, the thermal annealing is investigated. We find that appropriate annealing temperature is very beneficial for the ZnSnLiO TFTs, and when the annealing temperature is 500 °C, the transistor exhibited the high field-effect mobility of 45.1 cm/V s and a large I ratio of 6.0 × 10. [ABSTRACT FROM AUTHOR]

High-quality ZnO thin film was grown on (0001) sapphire substrate with a ZnO buffer layer by hydrothermal method under atmospheric pressure. The flat surface of the ZnO film was observed by SEM, and the wurtzite crystalline structure and preferred (0001) orientation of the ZnO film was observed by X-ray diffraction. Raman scattering and photoluminescence verified low density of impurities and defects. Test results overall demonstrate the proposed method simply and effectively synthesizes high-quality ZnO film. [ABSTRACT FROM AUTHOR]

Indium–zinc–lithium–oxygen (IZLO) thin film was produced by radio frequency magnetron sputtering, and the electronic properties of the TFT were investigated. The X-ray diffraction spectroscopy showed that IZLO film contains different Zn k In 2 O k +3 phases. Using this film as the channel layer, we fabricated a bottom gate thin film transistor (TFT), which exhibited n -channel enhancement mode behavior, and showed good performance with a field effect mobility of 80.4 cm 2 /V s, an on/off ratio of 4.0×10 6 , and a threshold voltage of 4.1 V. We also investigated the environmental stability of the IZLO TFT after exposure to air, and the device exhibited a relatively stable electrical performance. [ABSTRACT FROM AUTHOR]