著者

Y. Otsuka T. Ogawa A. Saito T. Tsugawa S. Fukao S. Miyazaki

出版者

The Seismological Society of Japan, Society of Geomagnetism and Earth, Planetary and Space Sciences, The Volcanological Society of Japan , The Geodetic Society of Japan , The Japanese Society for Planetary Sciences

雑誌

Earth, Planets and Space (ISSN:13438832)

巻号頁・発行日

vol.54, no.1, pp.63-70, 2002 (Released:2010-03-09)

参考文献数

24

被引用文献数

239

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The dual frequency radio signals of the Global Positioning System (GPS) allow measurements of the total number of electrons, called total electron content (TEC), along a ray path from GPS satellite to receiver. We have developed a new technique to construct two-dimensional maps of absolute TEC over Japan by using GPS data from more than 1000 GPS receivers. A least squares fitting procedure is used to remove instrumental biases inherent in the GPS satellite and receiver. Two-dimensional maps of absolute vertical TEC are derived with time resolution of 30 seconds and spatial resolution of 0.15° × 0.15° in latitude and longitude. Our method is validated in two ways. First, TECs along ray paths from the GPS satellites are simulated using a model for electron contents based on the IRI-95 model. It is found that TEC from our method is underestimated by less than 3 TECU. Then, estimated vertical GPS TEC is compared with ionospheric TEC that is calculated from simultaneous electron density profile obtained with the MU radar. Diurnal and day-to-day variation of the GPS TEC follows the TEC behavior derived from MU radar observation but the GPS TEC is 2 TECU larger than the MU radar TEC on average. This difference can be attributed to the plasmaspheric electron content along the GPS ray path. This method is also applied to GPS data during a magnetic storm of September 25, 1998. An intense TEC enhancement, probably caused by a northward expansion of the equatorial anomaly, was observed in the southern part of Japan in the evening during the main phase of the storm.

著者

M. Tobise T. Ogawa S. Saito

出版者

The Magnetics Society of Japan

雑誌

Journal of the Magnetics Society of Japan (ISSN:18822924)

巻号頁・発行日

vol.41, no.3, pp.58-62, 2017-05-01 (Released:2017-05-01)

参考文献数

15

被引用文献数

14

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Metastable α”-Fe16N2 have attracted much interest as a candidate for rare-earth-free hard magnetic materials. To realize high coercivity, it is necessary to utilize not only the magnetocrystalline anisotropy but also the shape anisotropy of α”-Fe16N2 nanoparticles assemblies. An increase in magnetostatic couplings and intergranular exchange couplings among particles typically reduces the coercivity. Therefore, it is very important to evaluate the anisotropy and magnetic interactions among α”-Fe16N2 nanoparticles. We have examined the changes in morphology, structure and magnetic properties through the synthesis of α”-Fe16N2 nanoparticles from various materials such as α-FeOOH, ɤ-Fe2O3, and Fe3O4. The magnetic interactions were also estimated based on experimental results obtained by analysis of the rotational hysteresis loss of randomly oriented nanoparticles. Hc and Hkptc for the α”-Fe16N2 nanoparticle assemblies for different starting materials ranged from 2.2 to 1.1 kOe, and from 11 to 12 kOe respectively. Experimental results of the normalized coercive force and normalized switching field suggests that the existence of large magnetic interactions among α”-Fe16N2 nanoparticles.