Although a suction vortex is the one of the most common vortices appearing in our everyday life, its internal structure has not been fully understood yet. One of the few things that we understand is that the radius of the core results from the competition between the diffusion of the vorticity due to the kinematic viscosity and the transportation of the vorticity due to the inward flow. To understand the structure of the suction vortex, we investigated a suction vortex produced in liquid helium. In the normal fluid phase, liquid helium behaves as a viscous fluid. In contrast, in the superfluid phase, a quantum vortex line carries all the microscopic circulation, and the suction vortex can be understood as a complex of quantized vortex lines. We generated a superfluid suction vortex with a cryogenic turbine and measured its circulation with a pulsed first sound circulation meter, and also measured the vorticity by the second sound attenuation technique. The experimental results indicate that the quantized vortex lines accumulated in the narrow region around the axis of symmetry due to an inward flow, the core structure of which cannot be described by a simple bundle of fully polarized quantized vortex lines.

No abstract

It is necessary to control the internal stress of optical thin films in order to address problems such as peeling and cracking. Internal stress differs among films prepared by different deposition methods. We investigated the internal stress of films prepared by sputtering, electron beam (EB) evaporation, and a combination deposition method that we developed. The internal stress was successfully controlled, showing a value between that of EB evaporation and sputtering.

No abstract

We have performed time-resolved operando measurements based on continuous wave photo-induced absorption (cw-PIA) spectroscopy to investigate the behaviors of carriers in operating dye-sensitized solar cells (DSSCs). We demonstrate that PIA signals are obtained from the electron carriers of the fluorine-doped tin oxide (FTO) electrode and these signals can be utilized to study the operation dynamics of DSSCs. The time-resolved operando experiments observe the PIA signals of electron carriers individually from the FTO electrode and a TiO 2 layer together with photocurrent measured simultaneously. We reveal that the transfer of electron carriers in DSSCs after photoexcitation is very slow and occurs in the order of TiO 2 , FTO, and photocurrent. These PIA signals and photocurrents reach equilibrium at approximately the same response rate determined by the transfer rate of iodine ions, which corresponds to the rate for the entire operating cycle. These operando measurements from multiple perspectives are effective for elucidating the operational mechanism in real solar cells and are widely applicable to a variety of solar cells.