Dielectric behavior pertains to the polarization of cement-based materials, in which the positive and negative charge centers are separated. Recent work on the dielectric behavior of common Portland cement-based materials in a low frequency regime were carried out, including the dependence of dielectric behavior on microstructures, hydration process, loadings, etc. This review represented the results of dielectric behavior of common Portland cement-based materials over the past decade and introduced the dielectric measurement method and the dependence of polarization on aggregates, water cement ratio, stress/strain, and temperature. It is indicated that some movable ions in pore solution dominate the dielectric behavior, in which the electric dipoles are in series. Aggregates and admixtures affect dielectric behavior due to relevant changes in microstructures. Heating and compression strengthen the dielectric behavior, while cooling and tension weaken the dielectric behavior. In addition, some related future research aspects were also prospected.

As a promising sustainable building material, alkali-activated concrete (AAC) is subjected to complex stresses. However, current investigations on the triaxial compression performance of AAC have restricted confinement ratios and do not account for specimen strength effects. In this work, conventional triaxial compression tests were conducted for AAC to investigate the damage mode, mechanical properties, constitutive model and failure criterion under confining pressure. The confinement ratio range is 0-1.4. The results show that the damage mode of AAC transforms from brittle to pseudo-ductile as the confining pressure increases. The triaxial compression strength increases significantly with AAC strength, attaining the deformation capacity with lower strength. A triaxial compression constitutive model available for Portland cement concrete (PCC) can substantially overestimate the axial strain of AAC at peak stress. Based on the experimental results, the triaxial compression constitutive model and failure criterion for AAC were proposed.

The conventional extension degree cannot fully reflect the construction performance of ultra-high performance concrete (UHPC), and it should be supplemented by the rheological properties. However, the proprietary equipment for the measurement of rheological properties is expensive, which is inconvenient to be directly used on the construction site. Therefore, 18 kinds of mix proportions of UHPC were prepared via changing the water-to-binder ratio and superplasticizer dosage. In this work, the flow and rheological parameters of various mix proportions of UHPC were obtained via testing the extension degree, characteristic time of extension degree (i.e., the time required for extension diameter of 0.7 and 0.8 times), rheological behavior, and mechanical properties after curing of the corresponding mix proportions. Finally, a relationship between fluidity and rheology of fresh UHPC (without steel fibers), which the mechanical properties belong to UHPC (with steel fibers), was established. The results show that the Bingham model can be used to describe the rheological behavior of fresh UHPC. The proposed characteristic time of extension degree index has a relatively high test accuracy. The rheological parameters of fresh UHPC can be obtained from the flowability-rheology relationship established. It is indicated that the calculated data by the proposed method agree well with the experimental results.

Nano-catalytic materials have broad application prospects in solving bacterial resistance caused by overuse of antibiotics. However, their catalytic efficiency usually depends on a lower pH value range (i.e., pH=2.0-5.0) rather than on a weakly acidic bacterial microenvironment (i.e., pH=6.0-7.0), leading to an limited catalytic efficiency and an insignificant bactericidal effect. In this paper, MnSiO₃ samples were prepared by a simple co-precipitation method. The morphology, structure and catalytic properties of the samples were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and ultraviolet-visible spectroscopy (UV-Vis). The antibacterial performance against E. coli and S. aureus were investigated. The results show that the morphology of amorphous MnSiO₃ samples transforms from nano-sized particles to micron-sized blobs in buffer solutions at pH 6.4 and 7.0. MnSiO₃ nano-sized particles had an intense catalytic ability at a higher pH value and an excellent antibacterial performance against E. coli and S. aureus. Therefore, the in-situ structure transformation of MnSiO₃ presents a promising treatment strategy for bacterial infection.

MoS₂ hollow microspheres with a high surface activity and superior piezoelectric properties were prepared by a one-step template-free hydrothermal method with MoO₃, KSCN and NaF as raw materials. The effects of hydrothermal reaction temperature, reaction time and NaF addition on the preparation of MoS₂ hollow microspheres were investigated. The results show that the samples prepared are 1T phase MoS₂ hollow microspheres with the sizes of 0.5-1.0 μm at the hydrothermal temperature of 220 ℃, the hydrothermal time of 16 h, and the amount of NaF added of 12 mmol. According to the results of N₂ adsorption-desorption experiments, the specific surface area of MoS₂ microspheres is 57.67 m²/g, the pore sizes are mainly distributed between 2-6 nm, and the average pore size is 4.25 nm. The catalytic performance of MoS₂ microspheres was evaluated via piezoelectric catalytic degradation of methylene blue solution. Under the action of ultrasound, the degradation rate of MB is 89.3%, and Rhodamine B is 98.9% at 60 s. In the degradation of antibiotics in water, the degradation rate of ciprofloxacin within 120 s is 94.7%.

A novel fabrication method of dense ceria-based barrier layer was proposed to fulfil the low-cost fabrication and long-term operation of solid oxide fuel cell (SOFC). A Y₂O₃ stabilized ZrO₂ (YSZ) electrolyte of anode supported half-cell was immersed in a solution of gadolinium nitrate and cerium nitrate, and treated at 180 ℃ for 36 h, then yielding a dense Gd₂O₃ doped CeO₂ (GDC) thin film. The GDC thin film was co-sintered with screen printed La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ cathode at 1075 ℃, thus obtaining an anode supported single cell. The results show that the hydrothermal grown GDC barrier layer is continuous and dense, with a chemical composition of Gd_0.044Ce_0.956O_2-δ and a thickness of 0.23 μm. The Ohmic resistance of anode supported a single cell at 750 ℃ is 0.101 Ω·cm², which is 38% lower than that of the cell with a conventional screen printed GDC barrier layer. The maximum power density using a wet hydrogen fuel reaches 1.038 W/cm² with a decent long-term operation durability. This hydrothermal in-situ growth method can satisfy the low-cost and large-scale fabrication of dense and thin-film barrier layers for SOFC with multi-configurations and dimensions, showing a promising application prospect.

This paper was to construct ensemble feature selection and random forest for the identification of ancient glass products via integrating the machine learning algorithm into the identification and analysis of ancient glass products and taking accuracy rate and AUC as the measurement indexes of classification performance. The results of different feature selection methods were analyzed, and the important chemical components were selected. The selected important features with random forest, k-nearest neighbor learning and naive Bayesian were investigated. The results show that lead oxide, barium oxide, and potassium oxide have an impact on the weathering of the glass surface by using ensemble feature selection. In high potassium glass, three components are closely related, the accuracy of classification by the random forest based on the k-fold cross validation for selected important features is great, and the model is stable. This method can provide a theoretical reference for the composition analysis and category identification of ancient glass products, and other glasses.

Terahertz (THz) technology has attracted much attention due to its application potentials in high speed wireless communication, non-destructive imaging, spectroscopy and others. However, the development of the materials for THz modulation is still a challenge. Metamaterials composed of periodic subwavelength structures can precisely modulate the amplitude, phase and polarization of electromagnetic waves, providing some opportunities for designing ultra-compact and high-performance THz devices. THz metamaterials modulate THz based on its resonant behavior. However, the modulation efficiency of Mie resonance and other common resonances is not evident due to the low resonant strength. Fano resonance possesses a more intense resonant strength and is sensitive to external dielectric environment, thus greatly improving the efficiency and sensitivity of THz wave modulation. The optically-modulated all-dielectric THz Fano metamaterial with a high efficiency was proposed based on the mechanism of photogenerated non-equilibrium carriers in a high purity silicon. The results show that the optical pump of near infrared laser effectively modulates the Fano resonant strength via controlling the conductivity of high resistance silicon, and the modulation depth reaches 87%, which is 70% greater than that of Mie electric dipole resonance in the same structure, realizing the efficient modulation of terahertz wave. The preparation method is simple and the modulation effect is obvious. The resonant frequency of Fano metamaterial can be conveniently designed by varying the geometric size of the metamaterial, which provides a possible approach for the high-performance modulation devices in the THz regime.

To meet the requirements of low-latency communication technology in the 6G terahertz band, porous alumina ceramics with ultra-low dielectric constant and directional pore channels were prepared by a freeze-drying method. A relationship between the structure and the properties of samples from different locations was investigated. The effect of solid content on the microstructure, mechanical properties, terahertz optical and dielectric properties was analyzed. Porous alumina ceramics with high porosity (i.e., 68.9%-81.0%) and compressive strength (i.e., 17.6-87.8 MPa) can be obtained, having ultra-low refractive index (i.e., 1.38-1.63), absorption coefficient (i.e., ~2.5 cm^-1), dielectric constant (i.e., 1.90-2.67), and z dielectric loss (i.e., ~0.008) at 1 THz. The directional pore channels exhibit high compressive strength in the direction parallel to the pores, and the special structure has potential applications for terahertz waveguides and antenna substrates.