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MXene materials with efficient electromagnetic (EM) microwave absorber applications are in high demand. Herein, the EM wave absorption properties of two-dimensional MXene Ti 3 C 2 T x , fabricated by etching the Ti 3 AlC 2 phase with an enchant of HCl and LiF, was thoroughly investigated over a frequency range of 2–18 GHz. In addition, the impact of three critical factors (reactant concentration, reaction time, and reaction temperature) on the morphology control and dielectric properties was discussed. With increasing degree of exfoliation, the multilayer structure of Ti 3 C 2 T x changed gradually, thereby further influencing the microwave absorption properties. Among the etched samples, Ti 3 C 2 T x prepared with 9 M HCl at 35 °C for 24 h exhibited an excellent reflection loss of −40.8 dB at 13.9 GHz with a thickness of 1.45 mm, while also possessed the broadest effective bandwidth, reaching 3.66 GHz at 1.68 mm. The demonstrated EM wave response mechanism, indicated that the conduction loss and polarization loss contribute significantly to the EM wave absorption performance. These findings endow the Ti 3 C 2 T x material with an effective foundation for the construction of novel EM wave absorbers. [ABSTRACT FROM AUTHOR]

This study formulates a methodology to design an eight-bar linkage for four specified positions of an open 4R chain, by adding three RR (double revolute joint) constraints to the chain. The methodology is based on the solution region theory. An infinite number of mechanism solutions can be expressed in the solution region. Since defective solutions do not have the capacity to move continuously through four positions, these defective solutions need to be eliminated from the solution region by using a defect analysis method. After additional design requirements were considered and imposed, the useful solution region is established. Consequently, designers can directly select useful linkages from the useful solution region. An example is provided to illustrate that the synthesis method is simple, highly accessible, and convenient to design an eight-bar linkage for four specified positions. [ABSTRACT FROM AUTHOR]

Multiple lithium-ion battery cells and multi-contact connection methods increase the chances of connection failures in power battery packs, posing a significant threat to the operational safety of electric vehicles. To this end, the study proposes an intelligent diagnosis method for battery pack connection faults based on multiple correlation analysis and adaptive fusion decision-making. The method uses Pearson correlation coefficients (PCC), Spearman correlation coefficients (SCC), and Kendall correlation coefficients (KCC) to simultaneously quantify the voltage synchronization between different cells in the battery pack, which is used to shield against the voltage measurement noise. The images of the correlation series transformed by the Gramian angular field are used as the input values of the convolutional neural network to classify the fault states by combining the adaptive weights of the three correlation series images on the fault levels. The experimental data shows that the accuracy of the method is 97.75 %, which is an improvement of 4.56 %, 5.98 %, and 2.39 % over the fault diagnosis accuracy using only PCC, SCC, and KCC, respectively, and effectively avoids misdiagnosis and omission due to the limitation of a single measurement. The proposed battery pack connection fault diagnosis method is robust and reliable, and has great practical application value. • Establishment of a fault diagnosis framework based on multiple correlation analysis and adaptive fusion decision-making. • Conversion of one-dimensional electrical signals into synchronized two-dimensional images. • Feature self-learning using convolutional neural networks. • A new adaptive fusion decision-making mechanism is proposed. [ABSTRACT FROM AUTHOR]

Unary and binary M 2+ (M=Mn, Co, Ni, Zn) substituted hollow Fe 3 O 4 were prepared by one-step solvothermal method. The crystallographic structure, morphology, element components and microwave absorbing properties of as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), Energy-dispersive X-ray (EDX) and vector network analyzer (VNA). The unary and binary Co 2+ substitution of hollow Fe 3 O 4 could result in a significant improvement of microwave absorption performance, including the expanding of effective absorption bandwidth, the thinner thickness and the increment of absorbing intensity. The sample of CoFe 2 O 4 could reach an optimal reflection loss of − 28.78 dB at 15.52 GHz under the thickness of 1.5 mm, moreover, the efficient absorption bandwidth (less than −10 dB) is expanded to 5.56 GHz which is most outstanding among these samples. The minimum reflection loss of Co 0.75 Zn 0.25 Fe 2 O 4 could reach − 49.60 dB at 9.88 GHz under the thickness of 2 mm. The as-prepared products could be used as microwave absorber with the advantages of strong absorption, broad bandwidth and thin thickness. The favorable performance could be attributed to the strong magnetic loss, dielectric loss and good impedance matching properties. [ABSTRACT FROM AUTHOR]

• A novel test method coupling NMR + RSM data is proposed. • Pore-throats are mainly in size of 0.1 μm, taking a maximum of 48.39% of the space. • The relations of grouting effect with the permeability and pressure are discussed. • The optimal grouting pressure and the critical value of injectable permeability are found. Mudstone, a common sedimentary rock in coal measure strata, sees the softening and disintegration of its clay minerals such as kaolinite owing to groundwater, water accumulation in goaf, and high in-situ stress, resulting in serious deformation and shrinkage of roadway space. However, it can hardly be reinforced by grouting because of other factors such as dense occurrence and poor permeability. In view of this, the silica sol, a nano-sized grouting material featured with controllable solidification and colloidal compactness, may be able to grout the low-permeability mudstone. In this paper, using the response surface methodology (RSM) and low-field nuclear magnetic resonance (NMR), we designed a two-factor orthogonal experiment and proposed a new data coupling test method integrating the processes of design, monitoring, and analysis, thus illustrating the pore throat distribution characteristics and grouting feasibility of low-permeability mudstone and revealing the diffusion law of nano silica sol in this kind of rock under the dual influences of pressure and permeability. On this basis, the optimal grouting parameters as well as the critical value of injectability were eventually determined. Experimental results proved that low-permeability rocks primarily contained pore throats in the size of 0.1 μm; and as these rocks became less permeable, a larger proportion of throats narrower than this size were developed, accounting for 48.39% in 1 mD samples. The low-permeability mudstone, which was highly matched with the silica sol solution in the particle size of 6.23 nm, could be modified and reinforced. Based on a calculation model for response values, the experimental data were successively classified by permeability and grouting pressure, from which the following pore-sealing rates were obtained: A (60 ∼ 100 mD): 33.74%, B (30 ∼ 60 mD): 24.61%, C (0 ∼ 30 mD): 0.41%, D (2 ∼ 3 MPa): 0.75%, E (1 ∼ 2 MPa): 38.92%, and F (0 ∼ 1 MPa): 28.02%. This indicated that the grouting effect was proportional to permeability; and it first increased and then decreased under rising pressure. According to the response to these rates, the low-permeability mudstone had better be grouted with nano silica sol under the pressure of 0.804 MPa, with the critical value of injectable permeability being about 40.42 mD. [ABSTRACT FROM AUTHOR]