Chiba Institute of Technology

About: Chiba Institute of Technology is a education organization based out in Narashino, Japan. It is known for research contribution in the topics: RNA & Magnet. The organization has 2663 authors who have published 4999 publications receiving 56870 citations. The organization is also known as: Chiba kōgyō daigaku & Kōa Institute of Technology.

Excited-state intramolecular proton transfer and charge transfer in 2-(2′-hydroxyphenyl)benzimidazole crystals studied by polymorphs-selected electronic spectroscopy

Abstract: Crystal structures of polymorphs of 2-(2′-hydroxyphenyl)benzimidazole (HPBI), Forms α and β, are analyzed by X-ray crystallography. The fluorescence excitation (FE) and fluorescence spectra of the polymorphs are separately observed at temperatures 77–298 K. It has been found that the electronic spectra of the two crystal forms are significantly different from each other. Photo-excitation of the enol forms in Forms α and β induces the excited-state intramolecular proton transfer (ESIPT) to produce the S1 state of the keto forms. In the FE spectra of Forms α and β, the S1 ← S0 (ππ*) transition of the keto form is observed in the 360–420 nm region in addition to that of the enol form in the 250–420 nm region. In the FE spectrum of Form β a new band peaking at 305 nm is observed, which is assigned to the S1 ← S0 transition of a non-planar enol form based on the observation of dual fluorescence in the UV and visible regions and quantum chemical calculation on the transition energy against the twisted angle between the benzimidazole and hydroxyphenyl rings. The fluorescence quantum yield (ϕT) for the keto form is remarkably dependent on polymorphs at room temperature; ϕT = 0.53 for Form α is much larger than ϕT ≤ 0.23 for Form β. At 77 K the ϕT values for Forms α and β increase to 0.67 and ≤0.57, respectively. The changes in the ϕT values are associated with the intramolecular charge transfer (ICT) state. The potential barrier height between the S1-keto and S1-ICT states is significantly lower for Form β than for Form α. At 77 K the S1-keto → S1-ICT process followed by S1-ICT → S0-keto internal conversion is significantly suppressed in Form β. We compare difference in the dynamics between Forms α and β in the electronic ground and excited states.

Harmonic Loss and Torque Analysis of High-Speed Induction Motors

Abstract: In this paper, we investigate the harmonic losses and torque of high-speed induction motors from both results of measurements and calculations. The calculation method of harmonic core losses and torque has been developed from the viewpoint of practical and useful application to rotating machines. This method is based on the combination of 2-D and 1-D finite-element methods with approximated core loss modeling, which requires only few material constants obtained by Epstein frame tests. The frequency and the flux density dependence of the core loss are modeled by the 1-D analysis along the thickness direction of electrical steel sheets. Furthermore, the proposed method can decompose the total loss and torque into harmonic components because of its simple modeling. This decomposition reveals the main loss factors and the decrease in the torque of the high-speed induction motors due to the harmonic core losses. The validity of the calculation is confirmed by measurements. In addition, useful information for the design of high-speed induction motors is obtained by using the proposed method.