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- 저자 : Takahiro Kojima (검색결과 5 건)
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Radio-photoluminescence observed in non-doped Mg2SiO4 single crystal
Go Okada,Takahiro Kojima,Jisaburo Ushizawa,Noriaki Kawaguchi,Takayuki Yanagida 한국물리학회 2017 Current Applied Physics Vol.17 No.3
The aim of this research is to investigate radiation-induced luminescence of non-doped Mg2SiO4 single crystal. The Mg2SiO4 single crystals were synthesized by the Czochralski process. The obtained crystal samples were studied to characterize the radio-photoluminescence (RPL), radio-luminescence (RL), and thermally-stimulated luminescence (TSL) properties. A non-irradiated (or as-prepared) sample shows no particular PL features whereas X-ray treated sample shows a broad PL emission around 630 nm under excitation at 270 nm. The latter observation indicates that RPL centre has been generated by X-ray irradiation. The X-ray induced RL can be observed due to the RPL centre around 630 nm, and the intensity monotonically increases with accumulating the incident radiation dose. TSL glow curve consists of three peaks at 160, 260, and 390 C, and the initial rise method derived the activation energies of 1.33, 1.47, and 1.85 eV, respectively. The first two TSL are associated with some shallow trapping centres, and annealing at this temperature range builds up the RPL response. On the other hand, annealing at higher temperatures supresses the RPL response; thus, the RPL centre is located at deeper site.
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Haruki Takayama,Tomohiko Shibata,Takahiro Ishii,Seiji Kojima 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.7
Ternary mixtures of water, sugar, and ionic liquid have been studied as new candidates for bioprotectants. To clarify the elastic properties and relaxation dynamics of the supercooled liquid and glassy states at low temperatures, the liquid-glass transitions were investigated by using a micro-Brillouin-scattering technique. The refractive index was measured accurately as a function of content and temperature to determine the sound velocity and the attenuation from Brillouin frequency shift and peak width. The relaxation times of structural relaxations related to liquidglass transitions were determined as functions of temperature. The Meyer-Neldel rule was found to hold for the activation energy and the prefactor of the Arrhenius law for the relaxation time.
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Kim, Yumi,Kim, Sehee,Kim, Chanyang,Sato, Takahiro,Kojima, Masayasu,Park, Seungjoon Japan Endocrine Society 2015 Endocrine journal Vol.62 No.3
<P>Neurogenesis occurs in the adult hippocampus and is enhanced by dietary restriction (DR), and neurogenesis enhancement is paralleled by circulating ghrelin level enhancement. We have previously reported that ghrelin modulates adult neurogenesis in the hippocampus. In order to investigate the possible role of ghrelin in DR-induced hippocampal neurogenesis in adult mice, ghrelin knockout (GKO) mice and wild-type (WT) mice were maintained for 3 months on DR or ad libitum (AL) diets. Protein levels of ghrelin in the stomach and the hippocampus were increased by DR in WT mice. One day after BrdU administration, the number of BrdU-labeled cells in the hippocampal dentate gyrus was decreased in GKO mice maintained on the AL diet. DR failed to alter the proliferation of progenitor cells in both WT and GKO mice. Four weeks after BrdU injection, the number of surviving cells in the dentate gyrus was decreased in AL-fed GKO mice. DR increased survival of newborn cells in WT mice, but not in GKO mice. Levels of brain-derived neurotrophic factor protein in the hippocampus were similar between WT and GKO mice, and were increased by DR both in WT and GKO mice. These results suggest that elevated levels of ghrelin during DR may have an important role in the enhancement of neurogenesis induced by DR.</P>
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Inui, Yuji,Shiro, Motoo,Kusukawa, Takahiro,Fukuzumi, Shunichi,Kojima, Takahiko The Royal Society of Chemistry 2013 Dalton transactions Vol.42 No.8
<P>[Ir<SUB>6</SUB>(μ-alloCl<SUB>2</SUB><SUP>2−</SUP>)<SUB>3</SUB>(Cp*)<SUB>6</SUB>(OH)<SUB>3</SUB>](PF<SUB>6</SUB>)<SUB>3</SUB> (<B>1</B>) having 7,8-dichloroalloxazine dianion (alloCl<SUB>2</SUB><SUP>2−</SUP>) as bridging ligands was synthesized and characterized by X-ray crystallography, spectroscopic and electrochemical measurements. The alloxazine ligands showed unprecedented coordination modes to link the six Ir(<SMALL>III</SMALL>) centres. The complex exhibited remarkable stability and reversible six-electron redox processes at the bridging alloxazine ligands in organic solvents. The first reversible reduction process occurred on each of three alloxazine ligands in <B>1</B> to produce a three-electron-reduced species, [Ir<SUP>III</SUP><SUB>6</SUB>Cp*<SUB>6</SUB>(μ-alloCl<SUB>2</SUB>&z.rad;<SUP>3−</SUP>)<SUB>3</SUB>(OH)<SUB>3</SUB>], and was observed as an apparent one-step reduction process at −0.65 V (<I>vs</I>. Fc<SUP>0/+</SUP>). The second reversible reduction process on each of the three alloxazine ligands in <B>1</B> was recorded at almost the same potential, −0.78 V (<I>vs</I>. Fc<SUP>0/+</SUP>), to afford the six-electron-reduced form, [Ir<SUP>III</SUP><SUB>6</SUB>Cp*<SUB>6</SUB>(μ-alloCl<SUB>2</SUB><SUP>4−</SUP>)<SUB>3</SUB>(OH)<SUB>3</SUB>]<SUP>3−</SUP>. The radical anion of the alloxazine derivative was detected by EPR measurements at room temperature. After the six-electron reduction of <B>1</B> with cobaltocene, the backward oxidation processes of reduced forms with <I>p</I>-chloranil were traced by UV-Vis spectroscopy to confirm the recovery of the original spectrum of <B>1</B>.</P> <P>Graphic Abstract</P><P>An alloxazine-bridged hexanuclear Ir(<SMALL>III</SMALL>) complex was synthesized and characterized. The complex exhibited two-step reversible reduction processes in CH<SUB>3</SUB>CN solution. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2dt32535g'> </P>
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