No abstract

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.

The aim of the present investigation is to clarify the role and evaluate the importance of air entrainment in the swash zone by carrying out a set of detailed laboratory experiments. Experiments involved generating a single, highly repeatable, large-scale, bore-driven swash event on a sand-rough impermeable beach with slope 1:10. Measurements that yield the characteristics of the entrained air, including the void fractions, bubble size and bed-parallel bubble velocity, and the hydrodynamics are obtained at five crossshore locations in the swash zone using an optical probe and a combined PIV/LIF system. The results show that two distinct bubble clouds enter the swash zone, the first is the result of local entrainment at the wave tip and the second are the remaining bubbles of the air that is entrained at the second plunge point of wave breaking before the wave starts climbing the beach. The void fractions are up to 0.20 and bubble size up to 20mm which are similar to air entrainment after wave breaking in the surf zone and deep water. Local entrainment of air continues in the swash zone, but void fractions decrease rapidly with distance up the slope and no air is present after flow reversal. Energy dissipation in the swash zone attributable to entrained air is at least of order 1% of the total energy dissipation. This is smaller than in the surf zone or deep water because of the smaller volume of entrained air and the greater total energy dissipation in the swash zone.