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169 results on '"Matsuda, S."'

1. Longitudinal Structure of Oxygen Torus in the Inner Magnetosphere: Simultaneous Observations by Arase and Van Allen Probe A

Author

Nosé, M., Matsuoka, A., Kumamoto, A., Kasahara, Y., Goldstein, J., Teramoto, M., Tsuchiya, F., Matsuda, S., Shoji, M., Imajo, S., Oimatsu, S., Yamamoto, K., Obana, Y., Nomura, R., Fujimoto, A., Shinohara, I., Miyoshi, Y., Kurth, W. S., Kletzing, C. A., Smith, C. W., and MacDowall, R. J.

Subjects
Arase satellite, geomagnetic storm, inner magnetosphere, oxygen torus, simultaneous observation, Van Allen Probes satellite
Abstract

Simultaneous observations of the magnetic field and plasma waves made by the Arase and Van Allen Probe A satellites at different magnetic local time (MLT) enable us to deduce the longitudinal structure of an oxygen torus for the first time. During 04:00–07:10 UT on 24 April 2017, Arase flew from L = 6.2 to 2.0 in the morning sector and detected an enhancement of the average plasma mass up to ~3.5 amu around L = 4.9–5.2 and MLT = 5.0 hr, implying that the plasma consists of approximately 15% O^+ ions. Probe A moved outbound from L = 2.0 to 6.2 in the afternoon sector during 04:10–07:30 UT and observed no clear enhancements in the average plasma mass. For this event, the O^+ density enhancement in the inner magnetosphere (i.e., oxygen torus) does not extend over all MLT but is skewed toward the dawn, being described more precisely as a crescent‐shaped torus or a pinched torus., ファイル公開：2019-04-16

Published
2018

3. Study of an Equatorward Detachment of Auroral Arc From the Oval Using Ground‐Space Observations and the BATS‐R‐US–CIMI Model

Author

Yadav, Sneha, Shiokawa, K., Oyama, S., Inaba, Y., Takahashi, N., Seki, K., Keika, K., Chang, Tzu‐Fang, Tam, S. W. Y., Wang, B.‐J., Kazama, Y., Wang, S.‐Y., Asamura, K., Kasahara, S., Yokota, S., Hori, T., Kasaba, Y., Tsuchiya, F., Kumamoto, A., Shoji, M., Kasahara, Y., Matsuoka, A., Matsuda, S., Jun, C.‐W., Imajo, S., Miyoshi, Y., and Shinohara, I.

Subjects
Physics::Space Physics
Abstract

We present observations of an equatorward detachment of the auroral arc from the main oval and magnetically conjugate measurements made by the Arase satellite in the inner magnetosphere. The all-sky imager at Gakona (magnetic latitude = 63.6°N), Alaska, shows the detachment of the auroral arc in both red and green lines at local midnight (∼0130–0230 MLT) on 30 March 2017. The electron density derived from the Arase in-situ observations shows that this arc occurred outside the plasmapause. At the arc crossing, the electron flux of energies ∼0.1–2 keV is found to be locally enhanced at L∼4.3–4.5. We estimated auroral intensities for both red and green lines by using the Arase low-energy (0.1–19 keV) electron flux data. The peak latitude of the estimated intensity shows reasonably good correspondence with the observed intensity mapped at the ionospheric footprints of the Arase satellite. These findings indicate that the observed arc detachment at Gakona was associated with the localized enhancement of low-energy electrons (∼0.1–2 keV) at the inner edge of the electron plasma sheet. Further, we employ the simulation results of the Community Coordinated Modeling Center (CCMC), the BATS-R-US–CIMI 3-D MHD code to understand the conditions in the inner magnetosphere around the time of detachment. Although the simulation could not reproduce the lower-energy component responsible for the arc detachment, it successfully reproduced two earthward convection events at the lower radial distance (R) (R ≤ ∼4) around the time of arc detachment and the features of enhanced convection in similarity with the observations.

Published
2021

4. Spatial Extent of Quasiperiodic Emissions Simultaneously Observed by Arase and Van Allen Probes on 29 November 2018

Author

Martinez‐Calderon, C., Němec, F., Katoh, Y., Shiokawa, K., Kletzing, C., Hospodarsky, G., Santolik, O., Kasahara, Y., Matsuda, S., Kumamoto, A., Tsuchiya, F., Matsuoka, A., Shoji, M., Teramoto, M., Kurita, S., Miyoshi, Y., Ozaki, M., Nishitani, N., Oinats, A. V., and Kurkin, V. I.

Abstract

Recent availability of a considerable amount of satellite and ground-based data has allowed us to analyze rare conjugated events where extremely low and very low frequency waves from the same source region are observed in different locations. Here, we report a quasiperiodic (QP) emission, showing one-to-one correspondence, observed by three satellites in space (Arase and the Van Allen Probes) and a ground station. The main event was on 29 November 2018 from 12:06 to 13:08 UT during geomagnetically quiet times. Using the position of the satellites we estimated the spatial extent of the area where the one-to-one correspondence is observed. We found this to be up to 1.21 Earth's radii by 2.26 hr MLT, in radial and longitudinal directions, respectively. Using simple ray tracing calculations, we discuss the probable source location of these waves. At ∼12:20 UT, changes in the frequency sweep rate of the QP elements are observed at all locations associated with magnetic disturbances. We also discuss temporal changes of the spectral shape of QP observed simultaneously in space and on the ground, suggesting the changes are related to properties of the source mechanisms of the waves. This could be linked to two separate sources or a larger source region with different source intensities (i.e., electron flux). At frequencies below the low hybrid resonance, waves can experience attenuation and/or reflection in the magnetosphere. This could explain the sudden end of the observations at the spacecraft, which are moving away from the area where waves can propagate.

Published
2021

8. Characteristics of IgA Antibodies Against HIV-1 in Sera and Saliva from HIV-Seropositive Individuals in Different Clinical Stages

Author

Oka S, Mitsuo Honda, Takebe Y, Takemori T, and Matsuda S

Subjects
Saliva, Blotting, Western, Immunology, HIV Core Protein p24, HIV Antibodies, Biology, Asymptomatic, Virus, HIV Envelope Protein gp160, Serology, Immune system, AIDS-Related Complex, Immunopathology, HIV Seropositivity, medicine, Humans, Protein Precursors, Acquired Immunodeficiency Syndrome, Gene Products, env, General Medicine, Immunoglobulin A, Immunoglobulin M, Immunoglobulin G, HIV-1, biology.protein, Viral disease, medicine.symptom, Antibody
Abstract

IgA antibodies were analysed in sera and saliva from 40 HIV-1 seropositive individuals. The level of total IgA in serum was elevated according to the progress of the disease. IgA antibodies against p24 and gp160 were detected in the asymptomatic phase of infection. However, they declined in the symptomatic phases in contrast with IgG antibodies. Interestingly, three patients in the symptomatic phase who showed high levels of lgA antibodies were all in relatively good clinical condition. The IgG and IgA antibodies in saliva declined in the symptomatic phase. The level of IgG anti-p24 antibodies in saliva correlated with that in serum, suggesting that IgG anti-p24 antibodies in saliva originated from those in the serum. These results indicate that IgA antibodies are regulated independently from IgG antibodies and that the mucosal immune system is impaired early in the symptomatic phase of HIV infection, which starts with mucosal impairment. Detection of IgA antibodies may be useful for prognosis of the disease in HIV-infected individuals. The results indicate also that treatment for the impaired IgA mucosal immune system should be taken into consideration.

Published
1993

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