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2. Observation of gyromagnetic reversal

Author

Imai, Masaki, Ogata, Yudai, Chudo, Hiroyuki, Ono, Masao, Harii, Kazuya, Matsuo, Mamoru, Ohnuma, Yuichi, Maekawa, Sadamichi, and Saitoh, Eiji

Subjects
Condensed Matter - Materials Science
Abstract

We report direct observation of gyromagnetic reversal, which is the sign change of gyromagnetic ratio in a ferrimagnet Ho$_3$Fe$_5$O$_{12}$, by using the Barnett effect measurement technique at low temperatures. The Barnett effect is a phenomenon in which magnetization is induced by mechanical rotation through the coupling between rotation and total angular momentum $J$ of electrons. The magnetization of Ho$_3$Fe$_5$O$_{12}$ induced by mechanical rotation disappears at 135~K and 240~K. The temperatures correspond to the magnetization compensation temperature $T_{\rm M}$ and the angular momentum compensation temperature $T_{\rm A}$, respectively. Between $T_{\rm M}$ and $T_{\rm A}$, the magnetization flips over to be parallel against the angular momentum due to the sign change of gyromagnetic ratio. This study provides an unprecedented technique to explore the gyromagnetic properties., Comment: 4pages,4figures

Published
2018
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18. Solvent Dependence of Double Proton Transfer in the Formic Acid–Formamidine Complex: Path Integral Molecular Dynamics Investigation

Author

Kungwan, Nawee, Ngaojampa, Chanisorn, Ogata, Yudai, Kawatsu, Tsutomu, Oba, Yuki, Kawashima, Yukio, and Tachikawa, Masanori

Abstract

Solvent dependence of double proton transfer in the formic acid–formamidine (FA–FN) complex at room temperature was investigated by means of ab initiopath integral molecular dynamics (AIPIMD) simulation with taking nuclear quantum and thermal effects into account. The conductor-like screening model (COSMO) was applied for solvent effect. In comparison with gas phase, double proton delocalization between two heavy atoms (O and N) in FA–FN were observed with reduced proton transfer barrier height in low dielectric constant medium (<4.8). For dielectric constant medium at 4.8, the chance of finding these two protons are more pronounced due to the solvent effect which completely washes out the proton transfer barrier. In the case of higher dielectric constant medium (>4.8), the ionic species becomes more stable than the neutral ones and the formate anion and formamidium cation are thermodynamically stable. For ab initiomolecular dynamics simulation, in low dielectric constant medium (<4.8) a reduction of proton transfer barrier with solvent effect is found to be less pronounced than the AIPIMD due to the absence of nuclear quantum effect. Moreover, the motions of FA–FN complex are significantly different with increasing dielectric constant medium. Such a difference is revealed in detail by the principal component analysis.

Published
2024
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19. Observation of gyromagnetic reversal

Author

Imai, Masaki, primary, Ogata, Yudai, additional, Chudo, Hiroyuki, additional, Ono, Masao, additional, Harii, Kazuya, additional, Matsuo, Mamoru, additional, Ohnuma, Yuichi, additional, Maekawa, Sadamichi, additional, and Saitoh, Eiji, additional

Published
2018
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36. Theoretical vibrational spectra of OH−(H2O)2: the effect of quantum distribution and vibrational coupling.

Author

Ogata, Yudai, Kawashima, Yukio, Takahashi, Kaito, and Tachikawa, Masanori

Abstract

We performed ab initio path integral molecular dynamics simulations for the hydroxide–water cluster, OH−(H2O)2, at 50 K, 100 K, and 150 K to investigate its flexible structure. From our simulations, we found that nuclear quantum effects enhance hydroxide hydrogen atom inversion and the conformational change between isomers occurs by simultaneous rotation of the free hydrogen atom. We propose the importance of including the transition state conformer with C2 symmetry, for the description of this system at temperatures realized in predissociation experiments. Temperature dependence of relative populations of each conformer along with multidimensional vibrational calculations were used to simulate the vibrational spectra and compare with the experimental spectra of Johnson and coworkers. We assign the doublet peaks seen in the experiment at 2500 to 3000 cm−1, as the mixture of the ionic hydrogen bonded OH stretching overtone, ionic hydrogen bonded OH bending overtone, and the combination band of the ionic hydrogen bonded OH stretch and bend, which are modulated by the van der Waals OO vibrations. We concluded that for OH−(H2O)2, the vibrational couplings between the ionic hydrogen bonded motion and floppy modes contribute to the broadening of peaks observed in the 2500 to 3000 cm−1 region. [ABSTRACT FROM AUTHOR]

Published
2015
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39. Strong-Gravity Experiments on Perovskite-Type Oxides

Author

Tokuda, Makoto, Isram, Khandaker Jahirul, Ogata, Yudai, Mine, Yoji, Nishiyama, Tadao, Hayami, Shinya, Yoshiasa, Akira, and Mashimo, Tsutomu

Abstract

Strong gravitational field causes the displacement or/and sedimentation of atoms in solids, by which we can changes the crystalline state or/and composition in multicomponent condensed matter. Perovskite-type doped manganite, La1-xSrxMnO3 (LSMO) has unique magnetoresistance effect which is called “colossal magnetoresistance (CMR)”. In this study, the strong gravity experiment (0.40x106G, 400°C, 20h) was performed on the LSMO oriented crystal to examine the change in composition or structure. The LSMO crystal whose growing crystal direction is normal to (214) plane was prepared by the floating zone method. The EPMA and XRD results of the gravity sample revealed that the La compositions decrease in the crystal grain, while the structure did not change much. The SQUID analysis showed that the magnetic property of the gravity sample had changed.

Published
2006
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40. [Ulcerative colitis diagnosed with facial pyoderma gangrenosum: a case report].

Author

Ogata Y, Soeda A, Saura I, Nemoto E, Tange Y, Enami C, Ochi D, Dai Y, Akiyama S, and Ikezawa K

Subjects
Humans, Male, Adolescent, Facial Dermatoses etiology, Facial Dermatoses drug therapy, Facial Dermatoses diagnosis, Antibodies, Monoclonal therapeutic use, Antibodies, Monoclonal administration & dosage, Pyoderma Gangrenosum diagnosis, Pyoderma Gangrenosum drug therapy, Colitis, Ulcerative complications
Abstract

Pyoderma gangrenosum (PG) is a sterile inflammatory skin condition that is frequently associated with immune-related diseases, including inflammatory bowel disease (IBD). PG causes noninfectious ulcers. Facial PG is uncommon while PG usually occurs on the trunk and lower limbs. Herein, we report a case of a male teenager with fever, pustules, ulcers, and necrosis on both cheeks. He was initially diagnosed with complicated acne with bacterial infection, but the condition progressed to subcutaneous ulcers despite treatment. Biopsy revealed inflammatory lesions in dermal and subcutaneous tissue with neutrophil infiltration, consistent with PG. Although lacking typical IBD symptoms, blood tests revealed anemia and positive fecal occult blood. Sigmoidoscopy revealed inflammation, ulcers, and pseudopolyps in the colon and rectum, thereby diagnosing ulcerative colitis (UC). After treating PG and UC with prednisolone and skin grafts, golimumab was prescribed. The patient is now in remission. Necrotic tissue buildup can complicate closure in PG cases;this emphasizes the need for effective IBD treatment to facilitate procedures such as skin grafts.

Published
2024
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41. Theoretical vibrational spectra of OH(-)(H2O)2: the effect of quantum distribution and vibrational coupling.

Author

Ogata Y, Kawashima Y, Takahashi K, and Tachikawa M

Subjects
Hydrogen chemistry, Hydrogen Bonding, Molecular Dynamics Simulation, Quantum Theory, Spectrophotometry, Infrared, Hydroxides chemistry, Water chemistry
Abstract

We performed ab initio path integral molecular dynamics simulations for the hydroxide-water cluster, OH(-)(H2O)2, at 50 K, 100 K, and 150 K to investigate its flexible structure. From our simulations, we found that nuclear quantum effects enhance hydroxide hydrogen atom inversion and the conformational change between isomers occurs by simultaneous rotation of the free hydrogen atom. We propose the importance of including the transition state conformer with C2 symmetry, for the description of this system at temperatures realized in predissociation experiments. Temperature dependence of relative populations of each conformer along with multidimensional vibrational calculations were used to simulate the vibrational spectra and compare with the experimental spectra of Johnson and coworkers. We assign the doublet peaks seen in the experiment at 2500 to 3000 cm(-1), as the mixture of the ionic hydrogen bonded OH stretching overtone, ionic hydrogen bonded OH bending overtone, and the combination band of the ionic hydrogen bonded OH stretch and bend, which are modulated by the van der Waals OO vibrations. We concluded that for OH(-)(H2O)2, the vibrational couplings between the ionic hydrogen bonded motion and floppy modes contribute to the broadening of peaks observed in the 2500 to 3000 cm(-1) region.

Published
2015
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