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294 results on '"Seiichiro IZAWA"'

210. 203 Numerical Simulation of the Behavior of a Vortex Generated between a Pair of Rotating Cylinders

Author

Shota Teramoto, Yu Fukunishi, Masaya Shigeta, Seiichiro Izawa, and Tetuya Kawamura

Subjects
Physics, Circulation (fluid dynamics), Computer simulation, Position (vector), Condensed Matter::Superconductivity, Bent molecular geometry, Flow (psychology), Oblique case, Mechanics, Freestream, Vortex
Abstract

The behavior of a vortex generated between a pair of rotating cylinders in a freestream is investigated using a three-dimensional numerical simulation. The cylinders are coaxially arranged with their axes normal to the flow. By changing the freestream velocity while keeping the rotating speed of the cylinders constant, it is found that the state of the vortex can be classified into three patterns. When the freestream velocity is small, the vortex is bent and stretched in the direction oblique to the freestream. The mechanism that allows the vortex between the two cylinders to stay at the same position without being washed away by the freestream is presented. It is also shown that with the increase in the freestream velocity, the circulation of the vortex decreases until the circulation becomes zero and the vortex is split into two.

Published
2008
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234. Enhancement ofVOCwithout Loss ofJSCin Organic Solar Cells by Modification of Donor/Acceptor Interfaces

Author

Yufei Zhong, Kazuhito Hashimoto, Keisuke Tajima, Seiichiro Izawa, and Akira Tada

Subjects
Materials science, Chemical substance, Organic solar cell, Renewable Energy, Sustainability and the Environment, Open-circuit voltage, business.industry, Bilayer, Doping, Energy conversion efficiency, Analytical chemistry, Acceptor, Optoelectronics, General Materials Science, business, Short circuit
Abstract

Organic solar cells (OSCs) are promising low-cost devices for generating electricity. In addition to fill factor, the short circuit current density (JSC) and the open circuit voltage (VOC) are two key factors that have critical influence on the device performance. The energy levels of the donor and acceptor materials are crucial for achieving a high JSC and VOC. However, the interfacial structures between the organic materials substantially affect the JSC and VOC through the energy of the charge transfer (CT) states and the charge separation and recombination reaction kinetics. Here, it is reported that separating the donor and acceptor layer in bilayer OSCs with a thin insulating layer increases the energy of the CT state by weakening the Coulomb interaction at the interface and this also suppresses photoinduced CT and recombination. Although these effects usually increase VOC and decrease JSC, the trade-off is avoided by doping the insulating layer with a dye to utilize the energy transfer process. The increase in VOC without the reduction in JSC enhances the conversion efficiency of the OSCs by 30%.

Published
2013
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