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Time-dependent vorticity fields of elliptic vortex rings of aspect ratios 2, 3 and 4 were measured hy means of hot-wire anemornetry. The time evolution of their vorticity fields was analyzed and the processes of vortex ring formation, advection, interaction and decay, and the mechanism of vortex bifurcation arc studied. The following crosslinking model is proposed: A thick vortical region composed of many equivalent vortex filaments with distributed cores is initially formed at the orifice and they behave as inviscid filaments. The elliptic ring deforms and the end parts of its major axis get closer. Then. the vortex filaments interact at the touching point and the ring partially bifurcates. Almost simultaneously. turbulent spot appears at this point. and propagates around the ring cross section. thus preventing further bifurcation. And it becomes a turbulent blob, This model is also supported hy numerical simulation hy a high-order vortex method and the Navicr-i Stokes solution.

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Organic thin-film transistors (OTFTs) are studied intensively for realizing practical applications of flexible or large-area circuits, but rapid degradation of OTFTs due to stress voltage or reaction with water vapor or oxygen in the air limits their lifetime. In order to analyze the cause of rapid bias-stress degradation, we propose a method that separates the cause of threshold voltage (V th) shift into insulator carrier trapping (ICT) and semiconductor carrier trapping components. The experimental results show that the ICT components account for nearly 50% of the total V th shift in n-type OTFTs, while the ICT-induced V th shifts is about 20% of the total V th shift in p-type OTFTs regardless of the insulator materials: SAM or parylene. The experimental results suggest that the short lifetime of the n-type OTFTs with SAM-based insulator is caused by the instability of the SAM-based insulator due to ICT. In addition, the instability of the p-type OTFTs with SAM-based insulator is discussed based on measurement, and as a result, capacitance shift due to ICT may also affect the degradation of highly biased p-type OTFTs.