Engineering topics
Publications and source records attributed to Takahashi, K..
To monitor solar neutron events, a new recording system will be installed at Mt. Norikura Cosmic Ray Observatory. The recording system is composed of a pulse counter with clock and a microcomputer with minifloppy disk. The counter and the microcomputer are connected through the General Purpose Interface Bus line. The one minute total count of the neutron monitor is recorded on the minifloppy disk.
The mechanisms for generating Alfven waves in the magnetosphere are determined, on the basis of a comprehensive survey of satellite magnetometer data. The mechanisms are classified in terms of the physical properties of standing Alfven waves such as the direction of the major axis of polarization, harmonic mode, and the azimuthal wave number. In an analysis of the statistical organization of the pulsations, it is shown that the most common transverse waves seem to be azimuthally polarized waves involving the fundamental and several harmonics, with radially polarized waves excited at the second harmonic. The former are probably driven externally, while the latter are likely to be excited internally through particle-wave interactions.
Harmonically related Pc 3-4 pulsations (7-100 mHz) are observed simultaneously by the three geosynchronous satellites ATS 6, SMS 1, and SMS 2, which are separated 20 deg from one another. At a given instant the frequency of the same harmonic is different from one spacecraft to another and each spacecraft observes a decrease in the fundamental frequency as it moves from morning (15 mHz) to afternoon (10 mHz). This frequency behavior is explained in terms of standing Alfven waves, for which the frequency is determined by the local magnetic field and plasma density. Occurrence of harmonic Pc 3-4 waves only during daytime hours (0400-2000 LT) and their frequency characteristics suggest a broadband energy source located on the dayside. Possible azimuthal wave number m and azimuthal phase velocity V(phi) of the second through fourth harmonics are determined from an unusual interval during which identical harmonic frequencies were observed at SMS 1 and ATS 6. Under the assumption of tailward propagation of constant-phase fronts at the same velocity for all these harmonics, V(phi) of about 1700 km/s is obtained.
Dependence of the power spectrum of Pc 3-4 magnetic pulsations observed at the ATS 6 geosynchronous satellite on the interplanetary magnetic field (IMF) has been studied. Pulsation events that were observed near noon and exhibited harmonic structure are chosen for analysis. Further selected are pulsation events with identical fundamental frequency to study dependence of the power of pulsations at different harmonic bands on the IMF. A weak negative correlation is observed between the IMF cone angle theta-XB and the power of pulsations in the frequency range 20-70 mHz. Also, a positive correlation between the intensity of the IMF B(IMF) and the power of pulsations at 50-70 mHz is found. This B(IMF) control is present at all ranges of the cone angle. A comparison is conducted of this observation with the frequency of bow shock associated upstream waves predicted from a model of wave generation by a cyclotron resonance of ions reflected at the bow shock. The predicted frequency depends on the IMF as B(IMF) (cos theta-XB)-squared. Although this relation gives a proportionality between the frequency and B(IMF) qualitatively consistent with the observation, it does not explain the most obvious IMF control of the spectrum of the pulsations.
The polarization of Pc 3 (22-100 MHz) magnetic pulsations measured by the ATS 6 fluxgate magnetometer at synchronous orbit has been examined by using dynamic autospectral analysis. In contrast to the result obtained by Arthur et al. (1977) using the same data set, very few cases of radially polarized Pc 3 pulsations are found. It is suggested that satellite noise in the radial component, which depends on frequency f as 0.015/f (nT-squared/Hz), is responsible for this disagreement. In the presence of this type of noise, diagonalization of the spectral matrix can produce an erroneous major axis of polarization. Most Pc 3 pulsations classified as radially polarized by Arthur et al. appear to be a consequence of small amplitude azimuthal pulsations contaminated by satellite noise.
Power spectra of magnetic pulsations observed at synchronous orbit by the ATS 6 satellite often show several spectral peaks simultaneously. Such pulsations, called harmonic events because of the nearly constant separation between successive peaks, are continuously observed in the dayside in the Pc 3-4 frequency range (6.6-100 mHz). The harmonic events are seen clearly only in the east-west magnetic field component. The spectral peaks are regularly spaced with a typical minimum separation of 14 mHz in the morning gradually decreasing to 10 mHz in the afternoon. In the dynamic spectra of harmonic events, the fundamental mode is usually absent. In addition, the relative amplitudes of the higher harmonics depend on the magnetic latitude. These observed features can be explained by a standing Alfven wave consisting of many discrete harmonic frequencies. A statistical analysis of power spectra demonstrates that at least 10-30% of Pc 3 pulsations can be classified as harmonic events. For a selected event on August 7, 1975, the plasma mass density at the synchronous orbit is estimated to be 3-8 hydrogen mass/cu cm.
The reported investigation has the purpose to extend the study of Pc 3 pulsations at synchronous orbit conducted by Arthur and McPherron (1977). A large data set is used with the goal of finding the factors related to the occurrence of Pc 3 pulsations at synchronous orbit. The results are compared with ground-based observations. The study demonstrates that the diurnal occurrence pattern has a maximum at a prenoon local time and shows a seasonal shift. Among the solar wind parameters, solar wind velocity and the direction of the IMF are found to be dominant factors. Attention is given to the analysis procedure, examples of 2-hour spectra, diurnal occurrence pattern, the correlation between solar wind parameters, and the solar wind stream structure and Pc 3 occurrence.
Fabrication and electrical properties of p-ZnTe/n-InAs heterojunctions obtained by interface alloying, suggesting p-i-n structure from characteristics and capacitance behavior
Solar radio emission spectroheliograms at different millimeter wave frequencies