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To make the sound absorber easy to fabricate and convenient for practical application, a modular composable acoustic metamaterial with multiple nonunique chambers (MCAM–MNCs) was proposed and investigated, which was divided into a front panel with the same perforated apertures and a rear chamber with a nonunique grouped cavity. Through the acoustic finite element simulation, the parametric studies of the diameter of aperture d, depth of chamber T0, and thickness of panel t0 were conducted, which could tune the sound absorption performances of MCAM–MNCs–1 and MCAM–MNCs–2 for the expected noise reduction effect. The effective sound absorption band of MCAM–MNCs–1 was 556 Hz (773–1329 Hz), 456 Hz (646–1102 Hz), and 387 Hz (564–951 Hz) for T = 30 mm, T = 40 mm, and T = 50 mm, respectively, and the corresponding average sound absorption coefficient was 0.8696, 0.8854, and 0.8916, accordingly, which exhibited excellent noise attenuation performance. The sound absorption mechanism of MCAM–MNCs was investigated by the distributions of the total sound energy density (TSED). The components used to assemble the MCAM–MNCs sample were fabricated by additive manufacturing, and its actual sound absorption coefficients were tested according to the transfer matrix method, which demonstrated its feasibility and promoted its actual application.

By using XRD diffraction patterns and SEM scanning electron microscopy, the study included exploring the effects of carbonation on the types of cations, namely Na+ and Mg2+, on the chloride concentration and mechanism, which is an important factor that has received little attention. The results show that carbonization has a greater negative impact on the binding capacity of chloride ions in cement mixed with NaCl, and CaCl2 can weaken the negative effect of carbonization on the binding capacity of chloride ions and improve the binding capacity of free chloride ion ;During the carbonization of cement mixed with NaCl, the chloride content corresponding to the maximum chloride ion binding rate was reduced from 0.9 % to 0.8 %, while the value was 0.8 % in cement mixed with CaCl2;Carbonization can improve the structure of the cement and reduce the porosity in the cement structure.

This was an experiment in which chloride was externally permeated into cement paste. The influence of Cl- on the content and distribution of free-form NO2- in the cement paste was researched using the chemical quantitative analysis method. The action mechanism was investigated by the micro-means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the physical competitive adsorption of Cl- with NO2- on C-S-H and the chemical substitution of Cl- to NO2-AFm caused more free-form NO2- in the cement paste. In the cement paste with chloride salt erosion, the NO2- concentration in the erosion surface was the lowest, and the NO2- concentration reached the highest value at 10mm from the erosion surface. The concentration decreased gradually with the depth from the erosion surface.

Chemical quantitative analysis of effective anticorrosion component and micro-analysis of hydration products of fly ash and slag on the influence of the nitrites corrosion inhibition was studied by the free nitrite ion concentration and X-ray diffraction pattern. The free nitrite ion concentration was used to describe the corrosion inhibition effect of nitrites. And the X-ray diffraction patterns were used to analyze the adsorption properties. The research results show that fly ash and slag were beneficial for improving the corrosion inhibition effect of nitrites. Cement-based materials with slag at low content presented high free nitrite ion concentration, but the addition of low content of fly ash harmed the corrosion inhibition effect of nitrites. The specimens incorporated with both fly ash and slag can reach the highest free nitrite ion concentration when the compounding proportion was 1:1. It was concluded that the extent of mineral admixtures of the corrosion inhibition effect of nitrites was affected by its type and content.

In this paper, we consider a two-dimensional linear nonlocal model involving a singular matrix kernel. For the initial value problem, we first give well-posedness results and energy conservation via Fourier transform. Meanwhile, we also discuss the corresponding Dirichlet-type nonlocal boundary value problems in the cases of both positive and semi-positive definite kernels, where the core is the coercivity of bilinear forms. In addition, in the limit of vanishing nonlocality, the solution of the nonlocal model is seen to converge to a solution of its classical elasticity local model provided that ct = 0. [ABSTRACT FROM AUTHOR]

The cultural self-confidence is the full affirmation to the cultural deposits and the cultural value and the foundation of national culture to maintain vitality. There is a subtle connection between art and culture, so art education is of great significance to cultivate students' own sentiment, keep the harmony between body and mind, and realize the learning and control of traditional culture. Taking public art education in colleges and universities as the research object, this paper makes a survey of the present situation and development strategies of public art education in colleges and universities, analyzes the unique value and significance of public art education to youth education in colleges and universities, and reveals the necessity of cultivating art education in colleges and universities to improve the cultural self-confidence of college students. The research shows that public art education is an important link in college education, which plays a positive role in improving college students' cultural self-confidence, and should be paid enough attention to in colleges and universities. [ABSTRACT FROM AUTHOR]