RESUMO
We describe a method for the active control of terahertz (THz) waves using hybrid vanadium dioxide (VO2) periodic corrugated waveguide. Unlike liquid crystals, graphene and semiconductors and other active materials, VO2 exhibits a unique insulator-metal transition characteristic by the electric fields, optical, and thermal pumps, resulting in five orders of magnitude changes in its conductivity. Our waveguide consists of two gold coated plates with the VO2-embedded periodic grooves, which are placed in parallel with the grooves face to face. Simulations show that this waveguide can realize mode switching by changing the conductivity of the embedded VO2 pads, whose mechanism is attributed to the local resonance induced by defect mode. Such a VO2-embedded hybrid THz waveguide is favorable in practical applications such as THz modulators, sensors and optical switches, and provides an innovative technique for manipulating THz waves.
RESUMO
OBJECTIVE: To compare the quality of cultivated Chinese yam (Dioscorea polystachya Turcz.) from Yunnan (Kunming yam) and Henan (Tiegum yam) by determining the content of dry substance in fresh sample and the contents of water extracts, ethanol extracts, starch, protein, crude-fat and polysaccharide in dry sample. METHOD: The above-mentioned indexes were determined by methods of air desiccation, cold-immersing, hot-immersing, iodine-blue coloration, half Micro-Kjeldahl, Soxhlet extraction and spectrophotometric method respectively. RESULT: In fresh sample, the content of dry substance of Kunming yam is a little lower than Tiegun yam; in dry sample, all indexes of Kunming yam are higher than or approach to those of Tiegun yam except the content of crude-fat. Especially the content of polysaccharide in Kunming yam is 64% higher than that of Tiegun yam. CONCLUSION: Kunming yam, with high quality, high yield and good taste, deserves paying close attention as a good variety.
