ジキアラシキュウシブニカンレンシタユウゲンシンプクジキリュウタイハノヒイチヨウジキケンデノデンパ

京都大学0048新制・論文博士理学博士乙第1536号論理博第294号新制||理||116(附属図書館)2544UT51-45-U35(主査)教授 前田 坦, 教授 山元 龍三郎, 教授 国司 秀明学位規則第5条第2項該当Kyoto UniversityDA

Influence of density irregularities on high-frequency wave propagation:Computer experiments of stimulated emissions

We study the mechanism of stimulated electromagnetic emissions, called Broad Upshifted Maximum (BUM) feature observed in high-frequency ionospheric heating experiments with the aid of two-dimensional electromagnetic particle computer experiments. The pump is set up as an O-mode wave in the computer experiments propagating through the plasma with small-scale field aligned irregularity. A proposed theoretical study shows that the irregularity is important in the excitation mechanism. High-frequency electromagnetic emissions are observed, accompanied by electrostatic upper hybrid and lower hybrid waves in agreement with the theory

STRUCTURE OF THE HELIOMAGNETOSPHERE IN FEBRUARY-MARCH 1986

The time interval from January to March 1986 is remembered by many people for several reasons. Comet Halley approached the sun and the earth for the first time in 76 years, and a very large flares on the sun occurred in February 1986. Many kinds of instruments were aimed at these remarkable phenomena. Several spacecraft were also launched for exploring the comet and many interesting phenomena were observed. Japan's interplanetary spacecraft "Sakigake" observed the interaction region between the solar wind and the comet. In addition to this observation, "Sakigake" provided us with background parameters of the solar wind about the heliomagnetosphere during this time. The result shows that at least three corotating high-speed streams existed near the solar equatorial plane. Two of them caused recurrent geomagnetic activity in Feb. - March 1986.This special issue contains contributed papers presented at the symposium "Solar Terrestrial Events in February-March 1986" (January 19, 1989, Nagoya

Optimum mean ionospheric height in total electron content observations

In order to obtain an accurate TEC (Total Electron Content) from the differential Doppler frequency measurements of two coherent signals transmitted from NNSS (Navy Navigation Satellite System) satellites received at a pair of ground stations, it is necessary to solve an integral constant which depends greatly on the assumed mean ionospheric height h_s. We propose here a novel method which enables us to determine h_s in a reasonable way as follows. By examining the rms sum of the calculated difference of TEC_v\u27s ("composite difference" of the vertically corrected TEC) from six pairs of the four stations, Kokubunji, Sendai, Ebetsu, and Wakkanai, located in the northern part of Japan in the North-South direction, with various assumed h_s values, we select the combinations of neighboring nearest stations, Kokubunji-Sendai and Ebetsu-Wakkanai only, for which we obtain suitable h_s\u27s with which the composite difference takes a single minimum for each pair of the stations. Then, we determine the latitudinal dependence of h_s by least-squares fit to a straight line for these locally deduced values. The mean ionospheric height h_s as a function of latitude thus derived should be optimum. In practice, we examined the data set during the period from November 11 to 18,and from 21 to 25,1994,throughout which magnetic activity remained low with K_p index in the range of 0_+～3_+, and we found 13 events to apply the present method effectively.After showing a possible signature of medium-scale TID (Traveling Ionospheric Disturbance) observed at the time of K_p=4_ on May 4,1994,we give some comments on the observations of the medium-scale TID in the polar region

磁気圏物理学入門

This paper provides an introduction to basic concepts about magnetospheric physics for the beginning students, focusing on the interaction of solar wind with the Earth's magnetosphere for substorm as well as quiet conditions. The origin of the solar wind is also emphasized. Substorm research has not revealed all of the facts so far. However, this indicates that research on this complex phenomenon will be highly fruitful in near future

Contributions of Alveolar Bone Density and Habitual Chewing Side to the Unilateral Failure of Orthodontic Mini-Screws: A Cross-Sectional Study

This study aimed to analyze the relationship between bone density, habitual chewing side (HCS), and mini-screw stability to investigate the intra-individual factors contributing to mini-screw failure. This retrospective study included 86 sides in 43 adults, who underwent bilateral maxillary mini-screw placement with subsequent unilateral failure of the mini-screw. Pre-treatment cone-beam computed tomography was used to measure the buccal cortical bone thickness and bone density on the failed and successful sides. Pre-treatment mandibular kinesiographic records were used to determine the HCS. Paired t-tests, one-proportion z-tests, and multivariable multilevel Poisson regression were used to examine the statistical significance. The buccal cortical bone thicknesses were 0.93 ± 0.27 mm (unsuccessful side) and 1.01 ± 0.27 mm (successful side), with no significant difference. The bone density on the unsuccessful side (1059.64 ± 202.64 mg/cm3) was significantly lower than the success side (1317.89 ± 332.23 mg/cm3). Regarding HCS, 27.9% of failures occurred on the preferred side, and 62.8% occurred on the non-preferred side. After adjusting for all factors, the non-preferred side showed a 2.22 times higher prevalence ratio for mini-screw failure than the preferred side. HCS is significantly related to mini-screw stability, while the cortical bone thickness, bone density, and site of mini-screw implantation were not correlated