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In this study, polarity dependent and multilevel resistive switching characteristics of the Ta/TaO x /Pt device are investigated. The resistive switching polarity is decisively associated with the location of the Ta/ TaO x interface while at a specific switching polarity, and multiple (four) resistance states in the Ta/TaO x /Pt device are achieved by controlling the stop voltage during the reset process and are stable for more than 10 4 s under continuous readout testing. X-ray photoelectron spectroscopy reveals that the Ta/TaO x interface is rich in oxygen vacancies. A schematic on the configurations of oxygen-vacancy aggregated conducting paths is proposed, where the Ta/TaO x interface acts as an oxygen vacancy reservoir, and the migration of vacancies can be driven by the applied electric field as well as the vacancy concentration gradient emanated from the Ta/TaO x interface. The polarity-dependent and multilevel resistive switching behaviors are then discussed in terms of filament configuration variation, and their interrelationship is visibly unveiled.

This paper presents a sandwiched buckling-restrained brace (BRB) and a dual-core self-centering brace (SCB) for seismic resistance. The sandwiched BRB has two components: (1) a steel core plate that carries axial forces and (2) two restraining members that sandwich the core plate with A490 bolts. The proposed BRB can be disassembled easily in the field, which not only means that the core plate can be replaced independently of the restraining members but also provides an opportunity for inspection of the core after a large earthquake. Cyclic tests of five sandwiched BRBs and five BRB frames were conducted to verify their good cyclic performances up to a drift of 2.5%. To minimize residual deformations of structural systems under earthquakes, a new steel dual-core self-centering brace (SCB) with flag-shaped hysteretic responses is developed. The axial deformation capacity of the SCB is doubled by serial deformations of two sets of tensioning elements arranged in parallel. The mechanics and cyclic behavior of the brace are first explained; three 5350-mm long dual-core SCBs are tested and modeled to evaluate their cyclic performances. SCBs exhibit excellent performance up to a drift of 2.5% with a maximum axial load of 1300 kN. Test results showed that the application of dual cores in SCBs reduces significant strain demands on tensioning elements and enables self-centering responses to large deformation. Nonlinear time history analyses were conducted on three BRB and SCB frames to obtain seismic demands under both design and maximum considerable levels of earthquake motions. SCB frames generally exhibit smaller peak interstory drifts and residual drifts than BRB frames.