著者

菖蒲迫 健介 吉田 茂生 川田 佳史 中島 涼輔

雑誌

日本地球惑星科学連合2022年大会

巻号頁・発行日

2022-03-24

著者

吉田 茂生

出版者

日本放射線安全管理学会

雑誌

日本放射線安全管理学会誌 (ISSN:13471503)

巻号頁・発行日

vol.1, no.1, pp.56-60, 2002 (Released:2011-03-17)

参考文献数

6

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On the basis of many human tritium metabolic data accumulated in the Intense 14MeV Neutron Source Facility OKTAVIAN of Osaka University, Japan, until now, the characteristics of the measured data have been analyzed for bioassay samples of urine, exhaled water and water distilled from urine. It has been found that the tritium concentration of exhaled water is equal to that in water distilled from urine. A new method has been developed to follow up each metabolism of two chemical forms, that is, free water tritium (FWT) and organically bound tritium (OBT) in urine. In case of repeated tritium intake, it was found that the tritium concentration could be approximated by single exponential function corresponding to the fastest excretion component for about 50 days after each intake. In this approximate method, the biological half-life of second intake exceeded compared with that of first intake. The distribution ratio of FWT and OBT components changed at the next intake compared with the previous intake. Consequently, the ratio of the OBT component increased and brought the apparent increase of the biological half-life.

著者

中島 涼輔 吉田 茂生

雑誌

日本地球惑星科学連合2022年大会

巻号頁・発行日

2022-03-24

著者

中島 涼輔 吉田 茂生

雑誌

JpGU-AGU Joint Meeting 2020

巻号頁・発行日

2020-03-13

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Magnetohydrodynamic (MHD) shallow water linear waves are investigated over a rotating sphere with an imposed equatorially antisymmetric toroidal magnetic field: B0Φ=B0sinθcosθ, where B0 is a constant, θ is the colatitude and Φ is the azimuth. This system can imitatively represent the dynamics of a liquid metal within a stably stratified layer at the top of the Earth's core, which was detected through seismological surveys (e.g. Helffrich & Kaneshima, 2010[1]) and also has been deduced from geophysical and geochemical knowledge (e.g. Buffett & Seagle, 2010[2]; Pozzo et al., 2012[3]; Gubbins & Davies, 2013[4]; Brodholt & Badro, 2017[5]). Because slowly propagating waves in the liquid core can result in geomagnetic secular variations, comparison between exhaustive studies of MHD waves in a rotating stratified fluid and observations of geomagnetic fluctuations should provide constraints on the obscure stratified layer in the outermost core (e.g. Braginsky, 1993[6]; Buffett, 2014[7]).The adopted configuration of the background field complicates solving the eigenvalue problem of linear waves due to the emergence of an Alfvén continuum and critical latitudes unless dissipation effects are taken into account. These result from non-dissipative Alfvén resonance, which occurs only when B0Φ/sinθ depends on θ, that is, regular singular points appear in the differential equation of linear problems. The solutions of the continuum are required to express the transient evolution of an arbitrary initial disturbance (e.g. Case, 1960[8]; Goedbloed & Poedts, 2004[9]). We can confirm numerically and analytically that introducing magnetic diffusion eliminates these Alfvén continuous modes and their singular structures around critical latitudes (Nakashima, Ph.D. thesis, 2020[10]).For the Earth's core-like parameter (B0≃0.5—5mT and magnetic diffusivity η≃1m2/s), westward polar trapped modes are obtained as eigenmodes, which have a period of around from several to 1000 years. We may be able to observe these modes as geomagnetic secular variations in high latitude regions, if the strength of stratification in the stratified layer is close to the estimate of Buffett (2014)[7]. The analyses of recent geomagnetic models and paleomagnetic data in terms of such waves could confirm the robustness of previous estimates of the properties of the layer.[ Reference ][1] Helffrich, G., Kaneshima, S. (2010) Nature, 468, 807. doi: 10.1038/nature09636[2] Buffett, B. A., Seagle, C. T. (2010) J. Geophys. Res., 115, B04407. doi: 10.1029/2009JB006751[3] Pozzo, M., Davies, C., Gubbins, D., Alfè, D. (2012) Nature, 485, 355. doi: 10.1038/nature11031[4] Gubbins, D., Davies, C. J. (2013) Phys. Earth Planet. Inter., 215, 21. doi: 10.1016/j.pepi.2012.11.001[5] Brodholt, J., Badro, J. (2017) Geophys. Res. Lett., 44, 8303. doi: 10.1002/2017GL074261[6] Braginsky, S. I. (1993) J. Geomag. Geoelectr., 45, 1517. doi: 10.5636/jgg.45.1517[7] Buffett, B. (2014) Nature, 507, 484. doi: 10.1038/nature13122[8] Case, K. M. (1960) Phys. Fluids, 3, 143. doi: 10.1063/1.1706010[9] Goedbloed, J. P., Poedts, S. (2004) Principles of magnetohydrodynamics: with applications to laboratory and astrophysical plasmas, Cambridge Univ. Press, Cambridge.[10] Nakashima, R. (2020) Ph.D. thesis, Kyushu University. http://dyna.geo.kyushu-u.ac.jp/HomePage/nakashima/pdf/doctoral_thesis.pdf

著者

中島 涼輔 吉田 茂生

雑誌

JpGU-AGU Joint Meeting 2020

巻号頁・発行日

2020-03-13

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Magnetohydrodynamic (MHD) shallow water linear waves are examined on a rotating sphere with a background toroidal magnetic field expressed as B0Φ=B0sinθ, where B0 is constant, θ is the colatitude and Φ is the azimuth. The MHD shallow water equations are often used in studying the dynamics of the solar tachocline (e.g. Gilman & Dikpati, 2002[1]; Márquez-Artavia et al., 2017[2]) and sometimes the outermost Earth's core (Márquez-Artavia et al., 2017[2]; Nakashima, Ph.D. thesis, 2020[3]) and exoplanetary atmosphere (e.g. Heng & Workman, 2014[4]). In this poster, we especially focus on the propagation mechanisms and the force balances of polar trapped waves and unstable modes (Márquez-Artavia et al., 2017[2]; Nakashima, Ph.D. thesis, 2020[3]).Comprehensive searches for eigenmodes yield two polar trapped modes when the main magnetic field is weak (the Lehnert number α=VA/2ΩR2<0.5, where VA is the Alfvén wave velocity, Ω is the rotation rate and R is the sphere radius). One is the slow magnetic Rossby waves, which propagate eastward for zonal wave number m≧2 (Márquez-Artavia et al., 2017[2]). As the Lamb's parameter ε=4Ω2R2/gh→0 (where g is the gravity acceleration and h is the equivalent depth), these branches asymptotically approach the eigenvalues of two-dimensional slow magnetic Rossby waves. Another is newly discovered westward polar trapped modes (Nakashima, Ph.D. thesis, 2020[3]).In the case when α>0.5 (the background field is strong), these novel westward modes merge with the westward-propagating fast magnetic Rossby waves. In addition, only when m=1, polar trapped unstable modes appear due to the interaction between these fast magnetic Rossby waves and westward-propagating slow magnetic Rossby waves. These growth modes are believed to be the polar kink (Tayler) instability (Márquez-Artavia et al., 2017[2]).In order to easily understand the propagation mechanisms and the force balances of polar trapped modes, we investigate a cylindrical model around a pole with an artificial boundary condition. This model provides the approximate dispersion relations and eigenfunctions of polar trapped modes, and indicates that stable polar trapped modes are governed by magnetostrophic balance and that the metric magnetic tension force causes the difference between the slow magnetic Rossby waves and the novel westward modes. For m=1 and α>0.5, the balance between Coriolis and Lorentz forces is disrupted and the part of magnetic tension with which Coriolis force can not compete induces kink instability.[ Reference ][1] Gilman, P. A., Dikpati, M. (2002) Astrophys. J., 576, 1031. doi: 10.1086/341799[2] Márquez-Artavia, X., Jones, C. A., Tobias, S. M. (2017) Geophys. Astrophys. Fluid Dyn., 111, 282. doi: 10.1080/03091929.2017.1301937[3] Nakashima, R. (2020) Ph.D. thesis, Kyushu University. http://dyna.geo.kyushu-u.ac.jp/HomePage/nakashima/pdf/doctoral_thesis.pdf[4] Heng, K., Workman, J. (2014) Astrophys. J. Sup., 213, 27. doi: 10.1088/0067-0049/213/2/27

著者

中島 涼輔 吉田 茂生

出版者

日本地球惑星科学連合

雑誌

日本地球惑星科学連合2019年大会

巻号頁・発行日

2019-03-14

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Magnetohydrodynamic (MHD) waves in a thin layer on a rotating sphere with an imposed toroidal magnetic field are investigated. The system is often considered as a model of the stably stratified outermost Earth's outer core or the tachocline of the Sun. The stratification of the outermost core is suggested on the basis of seismological evidence (e.g. Helffrich and Kaneshima, 2010; Kaneshima, 2018) and interpretations of the geomagnetic variations with MHD waves (e.g. Braginsky, 1993; Buffett, 2014; Chulliat et al., 2015). In order to provide constraints on the obscure stratified layer by comparing with wavy variations in the geomagnetic field, we studied the linear waves of the two-dimensional MHD and the MHD shallow water system over a rotating sphere.We adopt an azimuthal equatorially antisymmetric field (BΦ(θ) = B0 sinθcosθ, where θ is colatitude, Φ is azimuth) as a background magnetic field. On the other hand, an equatorially symmetric field (BΦ(θ) = B0 sinθ) was assumed in Márquez-Artavia et al.(2017), whose results we replicated and reported in JpGU 2018.Compared with previous results, the dispersion diagrams obtained with the toroidal equatorially antisymmetric field show that some fast magnetic Rossby branches remain, while slow magnetic Rossby waves disappear. Besides, a continuous spectrum is found in the range where an azimuthal phase velocity is coincident with a local Alfvén velocity divided by sinθ. Similar continuous spectra are also seen in various physical situations, including inviscid shear flow (e.g. Case, 1960; Balmforth and Morrison, 1995; Iga, 2013) and plasma oscillations (e.g. Van Kampen, 1955; Case, 1959; Barston, 1964; Sedláček, 1971). The continuous spectra are accompanied by a singular eigenfunction, which is physically meaningful only when they are integrated over the continuous spectra. Its integrated solutions generally decay with time, which is referred to as phase mixing. Unlike exponentially damped discrete modes, this decaying is proportional to negative powers of time.In the case of the shallow water system with the antisymmetric field, discrete eigenvalues buried in the continuous spectrum is found, which include unstable modes. For the Earth-like parameters, polar trapped modes with decadal period and equatorial trapped Rossby waves with a few years period are found when the stratification is weak.

著者

吉田 茂生

出版者

名古屋大学人間情報学研究科情報創造論講座

雑誌

Nagoya journal of philosophy (ISSN:18821634)

巻号頁・発行日

vol.10, pp.126-145, 2013

著者

中島 涼輔 吉田 茂生

出版者

日本地球惑星科学連合

雑誌

日本地球惑星科学連合2018年大会

巻号頁・発行日

2018-03-14

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We investigated waves in a stably stratified thin layer in a rotating sphere with an imposed magnetic field. This represents the stably stratified outermost Earth's core or the tachocline of the Sun. Recently, many geophysicists focus on the stratification of the outermost outer core evidenced through seismological studies (e.g. Helffrich and Kaneshima, 2010) and an interpretation of the 60-year geomagnetic secular variations with Magnetic-Archimedes-Coriolis (MAC) waves (Buffett, 2014).Márquez-Artavia et al.(2017) studied the effect of a toroidal magnetic field on shallow water waves over a rotating sphere as the model of this stratified layer. On the other hand, MAC waves are strongly affected by a radial field (e.g. Knezek and Buffett, 2018). We added a non-zero radial magnetic perturbation and magnetic diffusion to Márquez-Artavia et al.(2017)'s equations. Unlike their paper's formulation, we applied velocity potential and stream function for both fluid motion and magnetic perturbation, which is similar to the first method of Longuet-Higgins(1968).In the non-diffusive case, the dispersion relation obtained with the azimuthal equatorially symmetric field (Bφ(θ) ∝ sinθ, where θ is colatitude) is almost the same as Márquez-Artavia et al.(2017)'s result, which includes magneto-inertia gravity (MIG) waves, fast magnetic Rossby waves, slow MC Rossby waves and an unexpected instability. In particular, we replicate the transition of the propagation direcition of zonal wavenumber m=1 slow MC Rossby waves from eastward to westward with increasing Lamb parameter (ε=4Ω2a2/gh, where Ω, a, g and h is the rotation rate, the sphere radius, the acceleration of gravity and a equivalent depth, respectively) and Lehnert number (α=vA/2Ωa, where vA is Alfvén wave speed). As a consequence, fast magnetic Rossby waves and slow MC Rossby waves interact, and the non-diffusive instability occur.Next, we are examining the case with an equatorially antisymmetric background field, which is more realistic in the Earth's core. In this case, if the magnetic diffusion is ignored, the continuous spectrums appear owing to Alfvén waves resonance (similar to the continuous spectrums in inviscid shear flow, e.g. Balmforth and Morrison, 1995). To solve this difficulty, our numerical model includes the magnetic diffusion term.

著者

青木 滋之 吉田 茂生 伊勢田 哲治 戸田山 和久 熊澤 峰夫 渡邊 誠一郎 矢島 道子

出版者

会津大学

雑誌

基盤研究(B)

巻号頁・発行日

2011-04-01

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これまでの科学哲学ではあまり中心的に扱われてこなかった、地球惑星科学の歴史・哲学に関する基盤研究を行った。第一班:地球惑星科学の方法論、第二班:地球惑星科学の科学史、第三班:科学の科学、という3つの班による研究成果は、Nagoya Journal of Philosophyの10号,11号に論文集として公刊された。

著者

西谷 健夫 落合 謙太郎 吉田 茂生 田中 良平 高橋 亮人 金子 純一 澤村 晃子

出版者

社団法人プラズマ・核融合学会

雑誌

プラズマ・核融合学会年会予稿集

巻号頁・発行日

no.19, 2002-11-20