Yuko Motizuki - Academia.edu (original) (raw)

Papers by Yuko Motizuki

Our Astro-Glaciology Research Unit (AGU), established on July 1, 2011, is the only group worldwid... more Our Astro-Glaciology Research Unit (AGU), established on July 1, 2011, is the only group worldwide investigating the new cross-disciplinary research field of astro-glaciology, which combines astrophysics, climate science and solar-terrestrial physics, and glaciology, both experimentally and theoretically (Figs. 1 and 2). Gamma rays, X-rays, and UV radiation arising from solar activity and supernova explosions in our galaxy cause changes in the chemical composition of the stratosphere (from ∼10 − 50 km altitude). The effects of radiation on the stratosphere are then recorded in the chemical and isotopic composition of terrestrial ice. An ice core is therefore a time capsule. The cylindrical ice core drilled by the Japanese Antarctic Research Expedition (JARE) at the Dome Fuji station in Antarctica is 3,035 m long and corresponds to a time period from 720,000 years ago to the present (Fig. 3). We have been studying the uppermost ∼100 m of an

We have carried out 2-D simulations of core-collapse supernova explosions. The local neutrino rad... more We have carried out 2-D simulations of core-collapse supernova explosions. The local neutrino radiation field is assumed to have its maximum value either at the symmetry (polar) axis or on the equatorial plane. These lead to the prolate and oblate explosions, respectively. We find that the gain of the explosion energy in the prolate explosion evolves more predominately than that in the oblate one when the total neutrino luminosity is given. Namely, the prolate explosion is more energetic than the oblate one. One of the authors (Shimizu et al. 2001) showed for the first time that globally anisotropic neutrino radiation produces more powerful explosion than the spherical neutrino radiation does. In our previous study (Madokoro, Shimizu, & Motizuki 2003), we improved the numerical code of Shimizu et al. and demonstrated that the globally anisotropic neutrino radiation yields more energetic explosion than spatiallyfluctuated neutrino radiation does. Together with the result of this pape...

Japan Geoscience Union, 2016

arXiv: High Energy Astrophysical Phenomena, 2019

Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pre... more Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pressing puzzles in contemporary astrophysics. It encompasses a wide range of objects and phenomena: stars, supernovae, novae, neutron stars, stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays and relativistic-particle acceleration, and the evolution of galaxies. MeV gamma-rays provide a unique probe of nuclear processes in astronomy, directly measuring radioactive decay, nuclear de-excitation, and positron annihilation. The substantial information carried by gamma-ray photons allows us to see deeper into these objects, the bulk of the power is often emitted at gamma-ray energies, and radioactivity provides a natural physical clock that adds unique information. New science will be driven by time-domain population studies at gamma-ray energies. This science is enabled by next-generation gamma-ray instruments with one to two orders of magnitude better sensitivity,...

<p>Ice cores preserve past climatic changes and, in some cases, astronomical signals. Here ... more <p>Ice cores preserve past climatic changes and, in some cases, astronomical signals. Here we present a newly developed automated ice-core sampler that employs laser melting. A hole in an ice core approximately 3 mm in diameter is melted and heated well below the boiling point by laser irradiation, and the meltwater is simultaneously siphoned by a 2 mm diameter movable evacuation nozzle that also holds the laser fiber. The advantage of sampling by laser melting is that molecular ion concentrations and stable water isotope compositions in ice cores can be measured at high depth resolution, which is advantageous for ice cores with low accumulation rates. This device takes highly discrete samples from ice cores, attaining depth resolution as small as ~3 mm with negligible cross contamination; the resolution can also be set at longer lengths suitable for validating longer-term profiles of various ionic and water isotopic constituents in ice cores. This technique allows the detailed reconstruction of past climatic changes at annual resolution and the investigation of transient ionic and isotopic signals within single annual layers in low-accumulation cores, potentially by annual layer counting.</p>

Journal of Geophysical Research: Space Physics, 2021

Cosmogenic nuclides in tree rings and polar ice cores record the information of past cosmic ray i... more Cosmogenic nuclides in tree rings and polar ice cores record the information of past cosmic ray intensities and solar activities. A large 14C increase over 10 years has been discovered around 5480 BCE. The 14C variations in this event differ from those of other short‐term cosmic ray events and typical grand solar minima. To elucidate the cause of the 14C increase around 5480 BCE, we measured the 10Be and 36Cl concentrations in the Antarctic Dome Fuji ice core at quasi‐annual and 4–5 years resolutions, respectively. Based on the combined 14C, 10Be, and 36Cl data, the 5480 BCE event was probably not caused by a solar proton event (SPE) or a gamma‐ray event, because the 36Cl concentration did not significantly increase as expected in these events. The incremented 10Be data were enhanced similarly to those of recent grand solar minima, but more rapidly increased (over ∼10 years). These results suggest that an unusual grand solar minimum occurred around 5480 BCE, characterized by a rapidly decreasing solar activity.

• Combined O and N densities at altitudes 70-200 km are measured from Earth occultations of the C... more • Combined O and N densities at altitudes 70-200 km are measured from Earth occultations of the Crab Nebula using X-ray astronomy satellites, Suzaku and Hitomi. • The vertical density profile is in general agreement with a predicted profile from the NRLMSISE-00 model, except for altitudes 70-110 km in which the density is significantly smaller than the prediction by the NRL model. • This density deficit could be due to either long-term radiative cooling of the upper atmosphere or imperfect modeling.

Proceedings of The Golden Age of Cataclysmic Variables and Related Objects IV — PoS(GOLDEN 2017), 2018

Journal of Archaeological Science: Reports, 2019

Abstract Vermilion is a red pigment found in burials or decorating artifact surfaces at many arch... more Abstract Vermilion is a red pigment found in burials or decorating artifact surfaces at many archaeological sites worldwide. The source of such vermilion is important information for clarifying ancient socioeconomic structures such as goods distribution networks. The sulfur isotopic ratio (δ34S) of vermilion can be used to estimate possible sources of vermilion found at an archaeological site. Here, we describe a method that uses sulfur-free polyester adhesive tape to sample trace amounts of vermilion from the surfaces of artifacts for δ34S analysis. We also present an example of the application of the method to artifacts from the Kyoden site (Jomon period), western Japan. The δ34S results indicated that the vermilion used at Kyoden probably originated in Hokkaido. These results suggest that a goods distribution network covered much of Japan during the Jomon period. This minimally destructive method for sampling trace amounts of vermilion for δ34S analysis can be used to sample vermilion from various surfaces, including many kinds of artifacts and wall paintings.

… New science will be driven by time-domain population studies at MeV γ-ray energies. This scienc... more … New science will be driven by time-domain population studies at MeV γ-ray energies. This science is enabled by next-generation γ-ray instruments with one to two orders of magnitude better sensitivity, larger sky coverage, and faster cadence than all previous γ-ray instruments. This transformative capability …

Rapid Communications in Mass Spectrometry, 2018

Sulfur is widely distributed in nature, and sulfur isotopic measurements have been applied to elu... more Sulfur is widely distributed in nature, and sulfur isotopic measurements have been applied to elucidate the origin and transport of sulfuric compounds in the lithosphere, biosphere, and atmosphere. Analyses of samples containing small amounts of sulfur, such as the Antarctic ice core samples analyzed herein, require a high-sensitivity analytical method. Methods: We developed a high-sensitivity sulfur isotopic ratio (δ 34 S value) analytical system equipped with an elemental analyzer, a cryo-flow device, and an isotope ratio mass spectrometer, and established a measurement and calibration procedure. Results: Using this system, we precisely measured the δ 34 S values of samples containing 5-40 nmol sulfate. Test runs were performed on samples from the Antarctic shallow ice core DF01, and the data obtained were consistent with those obtained by previous studies that reported δ 34 S values for Antarctic snow and ice samples of more than 200 g (containing more than 150 nmol sulfate). Among the analyzed samples, one showed a peak sulfate concentration in its depth profile that is considered to have resulted from a large volcanic eruption. The δ 34 S value obtained at that depth in the sample was distinct from values at other depths and consistent with reported values for volcanic sulfates. Conclusions: The analytical system developed herein is a powerful tool for trace sulfur isotopic analyses. The results obtained from the DF01 ice core samples are the first step towards elucidating high-time-resolution (less than 1 year) paleo-environmental changes by sulfur isotopic analyses.

GEOCHEMICAL JOURNAL, 2017

cal composition and ion balance of surface snow there are distinct from those of sea salt. At Dom... more cal composition and ion balance of surface snow there are distinct from those of sea salt. At Dome Fuji, a shallow ice core (112.6 m) was obtained in 1993, and the concentrations of anions and cations were analysed in approximately 100 samples collected at 50-cm intervals from the ice core by Watanabe et al. (2003). In 1995 and 1996, an ice core was recovered to a depth of 2503 m, and chemical analyses were performed by Iizuka et al. (2008) on samples from eight sections to estimate past environments during the Holocene and last glacial maximum. The SO 4 2profile to a depth of 40 m in a shallow core, the DF01 core, drilled at Dome Fuji in November 2001, was examined by Igarashi et al. (2011) and the SO 4 2peaks were compared with recorded volcanic eruptions to develop an age model for the core. Subsequently, Motizuki et al. (2014) extended the age model of the DF01 core to a depth of 85 m through non-sea-salt SO 4 2syn

Journal of Glaciology, 2016

ABSTRACTIn order to better understand the densification of polar firn, firn cores from the three ... more ABSTRACTIn order to better understand the densification of polar firn, firn cores from the three sites within ~10 km of Dome Fuji, Antarctica, were investigated using surrogates of density: dielectric permittivities εv and εh at microwave frequencies with electrical fields in the vertical and horizontal planes respectively. Dielectric anisotropy Δε (=εv − εh) was then examined as a surrogate of the anisotropic geometry of firn. We find that layered densification is explained as a result of complex effects of two phenomena that commonly occur at the three sites. Basically, layers with initially smaller density and smaller geometrical anisotropy deform preferentially throughout the densification process due to textural effects. Second, layers having a higher concentration of Cl− ions deform preferentially during a limited period from the near surface depths until smoothing out of layered Cl− ions by diffusion. We hypothesize that Cl− ions dissociated from sea salts soften firn due to ...

An evidence of possible nova eruption of the symbiotic star R Aquarii, which was recorded in the ... more An evidence of possible nova eruption of the symbiotic star R Aquarii, which was recorded in the historical books by ancient Korean astronomers, is discovered in an antarctic ice core as a nitrate ion concentration (spikes) .These spikes , separated by only one year,are as prominent as other spikes of the recorded supernovae in 11th century .These set of two spikes do not coincide with any supernova remnants but successfully coincide with the nova eruption of R Aquarii in the year of A.D. 1073 and A.D.1074 in the Korean historical records.

EAS Publications Series, 2004

We demonstrate the important role of anisotropic neutrino radiation on the mechanism of core-coll... more We demonstrate the important role of anisotropic neutrino radiation on the mechanism of core-collapse supernova explosions. Through a new parameter study with a fixed radiation field of neutrinos, we show that prolate explosions caused by globally anisotropic neutrino radiation is the most effective mechanism of increasing the explosion energy when the total neutrino luminosity is given. This is suggestive of the fact that the expanding materials of SN 1987A has a prolate geometry.

Proceedings of the International Astronomical Union, 2007

The second Women in Astronomy Lunchtime Meeting was held on Monday 21 August 2006, with more than... more The second Women in Astronomy Lunchtime Meeting was held on Monday 21 August 2006, with more than 250 participants. The meeting was hosted by the EC Working Group for Women in Astronomy, established at the 2003 IAU General Assembly, and was attended by the current President, the Presidents-Elect for this and the next General Assembly, the General Secretary and Vice-Presidents, many senior astronomers, as well as students and young astronomers. It was a particular pleasure to welcome and congratulate the incoming President, Dr Catherine Cesarsky, the first woman to hold the position.

第3回極域科学シンポジウム横断セッション「海・陸・氷床から探る後期新生代の南極寒冷圏環境変動」11月27日（火）国立国語研究所２階講