A new glycoluril derivative‐1H, 4H, 5H, 8H‐2, 3a, 4a, 6, 7a, 8a‐hexaazacyclopenta[def]fluorene‐4, 8‐dione, hexahydro‐2, 6‐bis(phenylmethyl) (3) is strategically designed and synthesized through the reaction between glycoluril, formaldehyde and benzylamine with the optimized molar ratio of 1:6:2. Compound 3 is fully characterized by 1H NMR, 13C NMR, IR, MS and X‐ray single crystal diffraction. Reduction of compound 3 delivers a potential precursor‐imidazo[4, 5‐d]imidazole, octahydro‐hexahydro‐2, 6‐bis(phenylmethyl) (4) for the synthesis of novel nitramine explosives (i.e. bicyclo‐HMX and bi‐RDX). The nitration and hydrolysis of compound 4 are investigated in detail and three ring‐opened molecules N, 2, 4‐trinitro‐benzenemethanamine (8a), N, 2‐dinitro‐benzenemethanamine (8b) and N‐methylene‐benzenemethanamine (9) are obtained.
The usage of PBL is one of the heated topics in the education area. The present paper reviews the application of PBL group learning mode for improving the oral competence of English-majored students in China. After reviewing previous literature, this paper found that speaking classes of English majors, in current Chinese higher education, have long been characterized by vague teaching content, poor classroom quality and weak student learning outcomes. Besides, the group learning model under the PBL teaching method has great importance for the efficient development of the speaking classroom. However, there are still scant studies in the analysis and construction of the group learning model for the speaking classes of the English major, which is a research gap. Through reviewing a large amount of literature, conducting in-depth analysis and summarizing, the paper explores the application of the PBL group learning model in the speaking classes. The study shows that this learning model can avoid the drawbacks of the traditional speaking classroom, substantially improve students' speaking ability, promote the quality of teaching and put forward higher teaching requirements for teachers. Therefore, the effective construction of the PBL group learning model is essential for speaking learning in current Chinese higher education.
Based on the face-centered cubic structure, several different types of cubic lattice structures are designed in this paper, the quasi-static compression behavior of the lattice structure is thoroughly investigated by finite element simulation and experimental testing, in which mechanical properties and energy absorption capacities are summarized. The experimental specimens made from thermoplastic polyurethane TPU are additively manufactured using the fused deposition technology. Effects of strut style, strut distance, arrangement form, curvature, and several honeycomb lattice structures are considered. The results show that: under the condition of the same relative density, the selection of sinusoidal struts with larger curvature, the arrangement of 45°/135°, and the inward gradient of the strut distance can all improve the energy absorption characteristics of the structure. Compared with the traditional face-centered cubic structure (specimen L-1), the SEA of the structure with the strut curvature of 0.25, the 45°/135° arrangement of the sinusoidal struts, and the inward gradient of the strut distance is improved by 64% , 190%, and 107%; the introduction of a honeycomb structure with a high relative density can effectively resist the buckling deformation of the structure, and the SEA of the triangular, re-entrant and hexagonal honeycomb structures are 354%, 603% and 548% higher than that of the basic structure, respectively. In addition, reducing the lattice height also resists destabilization.
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