Two 1H-imidazol-4-yl-containing ligands 1,3-di(1H-imidazol-4yl)benzene (L 1 ) and 4,4′-di(1H-imidazol-4-yl)biphenyl (L 2 ) were employed to react with corresponding metal salt together with varied carboxylate ligands under hydro-and solvothermal conditions, and six new metal−organic frameworks 6) [H 2 oba = 4,4′-oxybis-(benzoic acid), H 3 BPT = biphenyl-3,4′,5-tricarboxylic acid, H 4 BPTC = biphenyl-3,3′,5,5′-tetracarboxylic acid, DMF = N,N-dimethylformamide] were achieved and structurally characterized. MOFs 1, 3, 4, and 5 are different two-dimensional networks, which are further joined together by hydrogen bonds to generate three-dimensional (3D) supramolecular frameworks. 2 is a (4,4)-connected binodal 3D framework with a point symbol of {3•4•5•8 3 } 4 {3 2 •8 2 •9 2 }, while 6 is a diamond 3D framework. The results show that coordination geometry of the metal centers and coordination mode of the ligands play important roles in the formation of MOFs with diverse structures. Moreover, luminescent studies showed that 1 and 3 represent highly efficient quenching for detecting Fe 3+ ions and acetone molecules. In addition, 6 exhibits selectively adsorption of CO 2 over N 2 .
The behavior of a simple concrete beam driven by heated shape memory alloy (SMA) wires using electrical currents is studied in this paper. The test results indicate that recovery forces of the SMA wires can decrease the mid-span deflection of the simple concrete beam, decrease the absolute value of compressive strains and even compress the concrete in the tensile zone. Furthermore, the heated SMA wires can make cracks close and perform the task of emergency damage repair in civil structures. This study also attempts to conduct permanent damage repair using carbon fiber reinforced polymer (CFRP) plates after emergency damage repair using SMA wires. Moreover, the relationship between rate of change of resistance of the SMAs and mid-span deflection of the beam is obtained in this paper. It is devoted to damage detection for civil structures.
In this work, a new strategy for achieving efficient p-type doping in high bandgap nitride semiconductors to overcome the fundamental issue of high activation energy has been proposed and investigated theoretically, and demonstrated experimentally. Specifically, in an AlxGa1−xN/GaN superlattice structure, by modulation doping of Mg in the AlxGa1−xN barriers, high concentration of holes are generated throughout the material. A hole concentration as high as 1.1 × 1018 cm−3 has been achieved, which is about one order of magnitude higher than that typically achievable by direct doping GaN. Results from first-principle calculations indicate that the coupling and hybridization between Mg 2p impurity and the host N 2p orbitals are main reasons for the generation of resonant states in the GaN wells, which further results in the high hole concentration. We expect this approach to be equally applicable for other high bandgap materials where efficient p-type doing is difficult. Furthermore, a two-carrier-species Hall-effect model is proposed to delineate and discriminate the characteristics of the bulk and 2D hole, which usually coexist in superlattice-like doping systems. The model reported here can also be used to explain the abnormal freeze-in effect observed in many previous reports.
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