Faculty Profiles - TOKUNAGA, Tomoharu

Papers - TOKUNAGA, Tomoharu

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Cross-sectional Area Dependency of Shrinkages and Grain Sizes of Flash-sintered 3 mol%Y<inf>2</inf>O<inf>3</inf>–ZrO<inf>2</inf> Polycrystals with a Circular Truncated Cone-shape at High Frequency Alternating Electric Current Fields

Kurachi T., Kobayashi K., Tokunaga T., Yamamoto T.

Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy Vol. 68 ( 11 ) page： 487 - 493 2021

Publisher：Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy

The uniformity of shrinkages and the distribution of grain sizes were investigated for flash-sintered 3 mol%Y2O3-ZrO2 compacts in direct current and alternating current (AC) electric fields using rectangular-shaped and circular truncated cone-shaped green compacts. The use of a high-frequency AC electric field enough to suppress electrode overvoltage was confirmed to be advantageous for uniform shrinkages, regardless of the shapes of the green compacts. However, the grain size distribution became larger in cone-shaped green compacts, the cross-sectional areas of which varied along the compact. The grain sizes in flashed cone-shaped green compacts were found to exhibit a near linear relation to current density, which provides a means for determining the grain size distribution upon the flash sintering of green compacts with different cross-sectional areas along an electric field.

DOI： 10.2497/jjspm.68.487

Scopus

EBV status has prognostic implication among young patients with angioimmunoblastic T-cell lymphoma

Eladl Ahmed E., Shimada Kazuyuki, Suzuki Yuka, Takahara Taishi, Kato Seiichi, Kohno Kei, Elsayed Ahmed Ali, Wu Chun-Chieh, Tokunaga Takashi, Kinoshita Tomohiro, Sakata-Yanagimoto Mamiko, Nakamura Shigeo, Satou Akira

CANCER MEDICINE Vol. 9 ( 2 ) page： 678 - 688 2020.1

Language：Japanese Publisher：Cancer Medicine

Epstein-Barr virus (EBV)-positive B cells have been detected in 66%-86% of patients with angioimmunoblastic T-cell lymphoma (AITL). However, it remains controversial whether EBV status has an impact on the survival of patients with AITL. In this study, we aimed to reevaluate the impact of EBV on the clinicopathological characteristics of AITL. In particular, we focused on the impact of EBV in younger patients with AITL. In total, 270 cases of AITL were studied. Epstein-Barr virus-positive B cells were detected in 191 (71%) cases (EBER+ group). Among the patients who received anthracycline-based therapy, the EBER status did not affect the overall survival (OS) or progression-free survival (PFS). In the younger group of AITL (≤60 years), PFS was significantly worse in the EBER− group compared to the EBER+ group (P =.0013). Furthermore, the multivariate analysis identified EBER-negative status, thrombocytopenia, and elevated serum IgA level as significant adverse prognostic factors for PFS (P <.001, P <.001, and P =.002). Based on these findings, we constructed new prognostic model for the younger group, based on three adverse factors. We classified the patients into two risk groups: low risk (no or 1 adverse factor) and high risk (2 or 3 adverse factors). This new model for younger patients with AITL showed that both OS and PFS were significantly related to the level of risk (P <.0001). In summary, this study showed that, among younger patients with AITL, an EBER+ status significantly improved prognosis compared to an EBER− status. Our new prognostic model should be applicable to younger patients with AITL.

DOI： 10.1002/cam4.2742

Web of Science

Scopus

Characterisation of bovine embryos following prolonged culture in embryonic stem cell medium containing leukaemia inhibitory factor

Hosoe Misa, Furusawa Tadashi, Hayashi Ken-Go, Takahashi Toru, Hashiyada Yutaka, Kizaki Keiichiro, Hashizume Kazuyoshi, Tokunaga Tomoyuki, Matsuyama Shuichi, Sakumoto Ryosuke

REPRODUCTION FERTILITY AND DEVELOPMENT Vol. 31 ( 6 ) page： 1157 - 1165 2019.5

Language：Japanese Publisher：Reproduction, Fertility and Development

In order to help elucidate the process of epiblast and trophoblast cell differentiation in bovine embryos in vitro, we attempted to develop a suitable culture medium to allow extended embryo culture. Day 7 bovine blastocysts developed in conventional medium were cultured further in embryonic stem cell medium with or without leukaemia inhibitory factor (LIF) until Day 23. At Day 14, the expression of octamer-binding transcription factor 3/4 (OCT3/4) and VIMENTIN was significantly higher in embryos cultured with than without LIF, but embryonic disc formation was not observed. Although expression of SRY (sex determining region Y)-box 17 (SOX17) mRNA was significantly lower in Day 14 embryos cultured with and without LIF than in in vivo embryos, hypoblast cells formed just inside the trophoblast cells of the in vitro-cultured embryos. On Day 23, expression of placental lactogen (PL) and prolactin-related protein 1 (PRP1) was not affected by LIF in in vitro-cultured embryos, levels of both genes were significantly lower in the in vitro than in vivo embryos. Similar to in vivo embryos, binucleate cell clusters seen in Day 23 in vitro-cultured embryos were composed of PL-negative and -positive cells. These results suggest that our culture system partially reproduced the differentiation process of trophoblast cells in vivo.

DOI： 10.1071/RD18343

Web of Science

Scopus

Removal of carbon contamination in ETEM by introducing Ar during electron beam irradiation

Tokunaga T., Saito K., Kuno K., Higuchi K., Yamamoto Y., Yamamoto T.

JOURNAL OF MICROSCOPY Vol. 273 ( 1 ) page： 46 - 52 2019.1

Intentionally encapsulated metal alloys within vertically aligned multi-walled carbon nanotube array via chemical vapor deposition technique

Inoue H., Nishikawa T., Hayashi Y., Hada M., Tokunaga T., Amaratunga G., Amaratunga G.

Conference Program Digest - 7th International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale, IEEE 3M-NANO 2017 Vol. 2018-January page： 357 - 361 2018.2

Language：Japanese Publisher：Conference Program Digest - 7th International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale, IEEE 3M-NANO 2017

This paper presents a growth and characterization of vertically aligned PdxCoi-x alloy encapsulated inside Multi-Walled Carbon Nanotube (MWCNT) arrays on Pd/Co thin layers coated on Si substrate by a dc bias-enhanced plasma chemical vapor deposition (CVD) method. The Metal Alloy Encapsulated within MWCNTs (MAE-MWCNTs) were characterized by a scanning electron microscope (SEM) and a transmission electron microscopy (TEM). The SEM images show the teardrop-shape particles encapsulated within the tube top of MWCNTs. A vibrating sample magnetometer was used to study the magnetism of a large number of MAE-MWCNTs on Si substrate at room temperature. The hysteresis loop of the ME-MWCNTs shows clear ferromagnetic behavior and the easy axis of magnetization is parallel to the MEA-MWCNT tube axis, as can be elucidated from the large coercive fields and remanence values. Moreover, TEM off-axis electron holograms were used to study the magnetism of the individual MAE-MWCNT or the two pair of MAE-MWCNTs. Based on electron holography, we have successfully obtained the saturation magnetization of 0.7 T and 1.12 T for the individual MAE-MWCNT with diameters of 41 nm and 83 nm, respectively.

DOI： 10.1109/3M-NANO.2017.8286262

Scopus

Microstructure analysis for zirconium oxynitrides formed in 8 mol% yttria-doped zirconia by a flash event under a direct current electric field in an ambient atmosphere Reviewed

Vol. 45 ( 7 ) 2025.7

Ultrasonically Activated Liquid Metal Catalysts in Water for Enhanced Hydrogenation Efficiency

Nichayanan Manyuan, Naoya Tanimoto, Kousuke Ueda, Ken Yamamoto, Tomoharu Tokunaga, Masaki Nishio, Tetsu Yonezawa, Hideya Kawasaki

ACS Applied Materials & Interfaces Vol. 17 ( 4 ) page： 6414 - 6427 2025.1

Variation of (001) surface structures of strontium titanate single crystals caused by flash event under direct/alternative current electric fields

Yutaro Katsuyama, Shunske Kayukawa, Tomoharu Tokunaga, Shunsuke Kobayashi, Shigekazu Hidaka, Atsutomo Nakamura, Takahisa Yamamoto

Ceramics International Vol. 50 ( 19 ) page： 37366 - 37372 2024.10

Topographical and morphological changes of the single‐crystal (La0.3Sr0.7)(Al0.65Ta0.35)O3 (001) surface treated with high‐purity deionized water

Yoshinori Tokuda, Naoki Nishikawa, Takeshi Irimoto, Yutaro Katsuyama, Shunsuke Kobayashi, Tomoharu Tokunaga, Takahisa Yamamoto

Surface and Interface Analysis Vol. 56 ( 8 ) page： 564 - 572 2024.8

Publishing type：Research paper (scientific journal) Publisher：Wiley

The topological and morphological changes of the (001) surface of single‐crystal (La0.3Sr0.7)(Al0.65Ta0.35)O3 during treatment with high‐purity deionized water (DI) have been investigated by atomic force microscopy and scanning transmission electron microscopy (STEM). Etching by DI treatment at room temperature proceeded mainly in anisotropic etching mode, resulting in rectangular etch pits with {001} inner surfaces forming in the surface. The dominant etching mode changed from anisotropic to isotropic with increasing DI‐treatment temperature, and the lowest surface roughness occurred for DI treatment at 50°C for 60 min. Direct observation of the atomic structure of the surface by STEM showed that the etched surface was the B‐site‐terminated (001) surface after anisotropic etching at 50°C for 60 min, in which the B‐site‐terminated atomic layer was found to maintain the B‐site ordered structure existing in the crystal. This is because DI treatment, which does not require high‐temperature heat treatment of the substrate, suppresses element diffusion, sublimation, and formation of point defects on and in the vicinity of the surface.

DOI： 10.1002/sia.7313

Web of Science

Scopus

Optical and mechanical properties of rutile TiO2 subjected to AC flash processing

Hiroshi Masuda, Tomoharu Tokunaga, Takahisa Yamamoto, Hidehiro Yoshida

Scripta Materialia Vol. 246 page： 116088 - 116088 2024.6

Photoinduced dynamics during electronic transfer from narrow to wide bandgap layers in one-dimensional heterostructured materials Reviewed Open Access

Yuri Saida, Thomas Gauthier, Hiroo Suzuki, Satoshi Ohmura, Ryo Shikata, Yui Iwasaki, Godai Noyama, Misaki Kishibuchi, Yuichiro Tanaka, Wataru Yajima, Nicolas Godin, Gaël Privaul, Tomoharu Tokunaga, Shota Ono, Shin-ya Koshihara, Kenji Tsuruta, Yasuhiko Hayashi, Roman Bertoni, Masaki Hada

Nature Communications Vol. 15 ( 1 ) page： 4600 2024.5

The use of He buffer gas for moderating the plume kinetic energy during Nd:YAG-PLD growth of EuxY2−xO3 phosphor films Open Access

Shizuka Suzuki, Takuro Dazai, Tomoharu Tokunaga, Takahisa Yamamoto, Ryuzi Katoh, Mikk Lippmaa, Ryota Takahashi

Journal of Applied Physics Vol. 135 ( 19 ) 2024.5

Publishing type：Research paper (scientific journal) Publisher：AIP Publishing

We have investigated the He buffer gas process of moderating the kinetic energy of the pulsed laser deposition (PLD) plume during EuxY2−xO3 phosphor film growth. When using a neodymium yttrium aluminum garnet laser for PLD thin film growth, the kinetic energy of the ablation plumes can be high enough to cause the formation of point defects in the film. The buffer gas pressure is an important process parameter in PLD film growth. We find that the presence of the He buffer gas reduces the kinetic energy of the laser deposition plume through many low-angle collisions in the gas phase by a factor of 7 without reducing the deposition rate. This is because He is much lighter than any of the elements in the plume and it does not affect the composition of the oxide films. Consequently, the resputtering of the Y2O3 film surface by the plume was significantly suppressed in the presence of the He gas moderator, leading to a decrease of the defect density in the Y2O3 films. The improvement of the film quality was verified by a systematic analysis of time-resolved photoluminescence (PL) data for EuxY2−xO3 composition–gradient films. The PL lifetime and intensity of Eu0.2Y1.8O3, which shows the highest PL intensity, increased by 13.3% and 36.4%, respectively, when the He gas moderation process was used. The He buffer gas process is applicable to the PLD growth of the other oxide materials as well, where the reduction of the kinetic energy of the plume would bring the PLD process closer to the molecular beam epitaxy growth condition.

DOI： 10.1063/5.0196987

Open Access

Web of Science

Scopus

Applying an alternating current to strontium titanate minimizes the change in oxidation state caused by flash sintering

Mikito Seko, Shunta Inagaki, Tomoharu Tokunaga, Shunsuke Kobayashi, Atsutomo Nakamura, Takahisa Yamamoto

Journal of the European Ceramic Society Vol. 44 ( 5 ) page： 2965 - 2971 2024.5

Flash healing of Vickers microcracks formed on the (001) surface of cubic zirconia single crystals

Shunsuke Kayukawa, Yutaro Katsuyama, Ayu Kodaira, Tomoharu Tokunaga, Koji Morita, Atsutomo Nakamura, Takahisa Yamamoto

Journal of the European Ceramic Society Vol. 43 ( 14 ) page： 6272 - 6278 2023.11

Near-full compaction within only 30min of total sintering time by shrinkage-rate-controlled flash sintering in 3mol% Y<inf>2</inf>O<inf>3</inf>-doped ZrO<inf>2</inf> polycrystal

Yuki Ishino, Masao Koike, Ayu Kodaira, Tomoharu Tokunaga, Takahisa Yamamoto

Journal of the Ceramic Society of Japan Vol. 131 ( 10 ) page： 600 - 607 2023.10

Publishing type：Research paper (scientific journal)

The development of a high-speed sintering method that can shorten the entire sintering time while guaranteeing the mechanical properties is very attractive as a sintering process for structural ceramic polycrystals. For this purpose, a sintering protocol that combines shrinkage-rate-controlled flash sintering, which controls the shrinkage rate to be constant with the use of an alternative current electric field, and a rapid furnace ramp were applied to 3-mol % Y2O3-doped ZrO2 (3YSZ). As a result, a 3YSZ sintered polycrystal with about the relative density of 99.5 % (6.06 g/cm3) could be successfully fabricated within 30 min as the entire sintering time, which includes the furnace-heating regime. The sintered 3YSZ polycrystal is confirmed to exhibit a Vickers hardness of approximately 1290 HV and a fracture toughness (KIC) of approximately 5.2 MPa m1/2, which are similar values to those obtained from a typical thermally sintered 3YSZ polycrystal.

DOI： 10.2109/jcersj2.23041

Web of Science

Scopus

Structural Defect Effect on the Concentration Quenching of TbxY2–xO3 Phosphor Thin Films

Shizuka Suzuki, Takuro Dazai, Tomoharu Tokunaga, Takahisa Yamamoto, Ryuzi Katoh, Ryota Takahashi

The Journal of Physical Chemistry C Vol. 127 ( 19 ) page： 9380 - 9387 2023.5

Mechanistic consideration of ZnTe microspheres formation in a PVP-contained polyol system via hot injection method

Yuen-ting Rachel Chau, Mai Thanh Nguyen, Tomoharu Tokunaga, Tetsu Yonezawa

Advanced Powder Technology Vol. 34 ( 4 ) page： 103970 - 103970 2023.4

Microcrack healing in single-crystal cubic zirconia by thermal annealing Reviewed

Shunsuke Kayukawa, Yutaro Katsuyama, Ayu Kodaira, Tomoharu Tokunaga, Koji Morita, Atsutomo Nakamura, Kimitaka Higuchi, Takahisa Yamamoto

Journal of the European Ceramic Society Vol. 43 ( 3 ) page： 1078 - 1086 2023.3

Flash self-joining of Y-TZP ceramics assisted with an AC electric field Reviewed

Kohta Nambu, Taisuke Kitaoka, Koji Morita, Kohei Soga, Tomoharu Tokunaga, Takahisa Yamamoto, Hiroshi Masuda, Hidehiro Yoshida

Journal of the American Ceramic Society Vol. 106 ( 3 ) page： 2073 - 2082 2023.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Wiley

In this study, flash joining experiments were conducted using an AC field on 3 mol% Y2O3‐stabilized tetragonal ZrO2 polycrystal (Y‐TZP) bodies. Furthermore, the necessary conditions to obtain an almost complete self‐joining of Y‐TZP bodies were clarified. The specimens were successfully joined by applying an AC field at 60 mA·mm−2 for 80 s at a furnace temperature of 1000°C, thus resulting in a successfully joined specimen with 92% of the flexural strength of the as‐sintered Y‐TZP body. Almost complete self‐joining of Y‐TZP was achieved at current densities above 30 mA·mm−2, and input energy densities of >24 J·mm−3. Both the input energy density and electric current were critical factors for producing the reliable joining of ceramics.

DOI： 10.1111/jace.18889

Web of Science

Scopus

A technique to modify the photoluminescence intensity of β-Ga2O3 polycrystals using an electric field during sintering Reviewed

Ryonosuke Ono, Ayu Kodaira, Tomoharu Tokunaga, Hidehiro Yoshida, Takahisa Yamamoto

Journal of Luminescence Vol. 254 page： 119508 - 119508 2023.2

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Papers - TOKUNAGA, Tomoharu