Search for weak white-light flares by time-wise photographic cancellation     

Yutaka Uchida  Hugh Hudson 《Solar physics》1972,26(2):414-417

This study proposes as a working hypothesis that small white-light flares accompany all major (proton) flare events and suggests a new method for systematically finding these patches of white-light emission. The new technique consists of the time-wise application of the photographic cancellation method to detect small time-varying features around the time of the impulsive phase of a flare.  相似文献   

Equilibrium configuration of the magnetosphere of a star loaded with accreted magnetized mass     

Yutaka Uchida  B. C. Low 《Journal of Astrophysics and Astronomy》1981,2(4):405-419

Equilibrium configuration of the magnetosphere of a star loaded by the gravitationally accreted plasma having its own magnetic field is investigated. Axisymmetry around the star’s magnetic axis is assumed for simplicity. It is seen that two distinct configurations appear for the cases of parallel and antiparallel magnetic field of the accreted plasma with respect to the star’s magnetic moment. If the external field is antiparallel to the star’s magnetic moment, the stellar magnetosphere is confined within a spherical region surrounded by the external field with a separatric surface between them. This is an extension of the case of the spherical accretion of non-magnetic plasma dealt with thus far in connection with the mass accretion by the degenerate stars in X-ray binaries. It is noticed that the mass slides down along the field lines to the point closest to the star and is stratified hydrostatically in equilibrium to form a disk in the equatorial plane. The mass loading compresses the sphere as a whole in this case. If, on the other hand, the external field is parallel to the star’s magnetic moment, there appears a ring of magnetic neutral point in the equatorial plane. Polar field is open and extends to infinity while the low-latitude field is closed and faces the external field of opposite polarity across the neutral point. The increase of the loaded mass in this case causes a shrink of the closed field region, and the open polar flux is increased. Therefore, the transition between equilibria with small and large amount of the loaded mass requires the reconnection of magnetic lines of force, and the reconnection of the flux through the magnetic neutral ring is proposed as the mechanism of the steady or the intermittent mass leakage like the ones postulated for some X-ray bursters. Visiting Scientist supported by the Japan Society for the Promotion of Sciences.  相似文献   

N-body simulation of giant molecular clouds in a galaxy     

Tosa  Makoto  Fukunaga  Masataka 《Astrophysics and Space Science》1986,118(1-2):463-465

We madeN-body simulation of Giant Molecular Clouds in a model galaxy and confirmed that their random motion is generated and accelerated by purely gravitational interaction among them in some 10^7–8 yr. The results of the present simulation agree well with those of the previous theoretical calculation by Fukunaga (1984a, b).Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.  相似文献   

Time variation of the spectrum of Gyro-synchrotron emission from the Sun     

Tatsuo Takakura  Yutaka Uchida  Keizo Kai 《Solar physics》1968,4(1):45-57

The emission spectra and their time variations of gyro-synchrotron emission from an ensemble of energetic electrons are computed for some initial power-law distributions of the electron energies N()d= ^– with =2 or 4. The spectra and decay curves of the emission are compared with solar microwave bursts in order to separately estimate the magnetic field H and . From a limited number of observations, we have 3 and H 10³ gauss for the microwave impulsive bursts, and 2 and H (500–1000) gauss for the microwave type-IV bursts.  相似文献   

Line width observation of Heii 4686 Å and Hei 4713 Å in the chromosphere     

Tadashi Hirayama  Makoto Irie 《Solar physics》1984,90(2):291-302

Line profiles of He ii 4686 Å and He i 4713 Å from active regions in the chromosphere were observed during the total solar eclipse of February 16, 1980, with a grazing incidence objective grating spectrograph. The Doppler width of the He i triplet line of 4713 Å increases with height and the average width is compatible with width of metallic and hydrogen lines, suggesting that the kinetic temperature of He i triplet emitting region is T 8000 K. This can only be explained by recombination after photo-ionization due to coronal UV radiation. The Doppler width of the Paschen line of He ii 4686 is, without any correction for the separation of subcomponents of the line nor non-thermal velocity, 18.4 km s^-1. This line width also shows a tendency to increase with height. After comparison with Doppler widths of He i 4713 and the EUV lines, and a necessary subtraction of non-thermal velocity, it is shown that this line is emitted in a 2 × 10⁴ K temperature region, which again supports the view that this line is emitted through the recombination process after photoionization due to coronal XUV radiation below 228 Å.  相似文献   

Deep seismic reflection profiling across the Ou Backbone range, northern Honshu Island, Japan     

Hiroshi Sato  Naoshi Hirata  Takaya Iwasaki  Makoto Matsubara  Takeshi Ikawa   《Tectonophysics》2002,355(1-4)

Knowledge of the crustal structure, especially the geometry of seismogenic faults, is key to understanding active tectonic processes and assessing the size and frequency of future earthquakes. To reveal the relationship between crustal structure and earthquake activity in northern Honshu Island, common midpoint (CMP) deep reflection profiling and earthquake observations by densely deployed seismic stations were carried out across the active reverse faults that bound the Ou Backbone range. The 40-km-long CMP profiles portray a relatively simple fault geometry within the seismogenic layer. The reverse faults merge at a midcrustal detachment just below the base of the seismogenic layer, producing a pop-up structure that forms the Ou Backbone range. The top of the reflective middle to lower crust (4.5 s in travel time (TWT)) nearly coincides with the bottom of seismogenic layer. The P-wave velocity structure and surface geology suggest that the bounding faults are Miocene normal faults that have been reactivated as reverse faults.  相似文献   

Runoff generation processes estimated from hydrological observations on a steep forested hillslope with a thin soil layer   总被引：4，自引：0，他引：4  

Makoto Tani 《Journal of Hydrology》1997,200(1-4):84-109

In order to understand runoff generation processes on a forested hillslope involving large heterogeneities, this study monitored runoff from a steep hillslope with a thin soil layer as well as matric potential within it and analyzed their responses to storm rainfall. A comparison of storm runoff responses from the study slope with those from two adjacent catchments, one of which includes it, showed that physical properties of the slope reflected the runoff characteristics: although no responses occurred in very dry conditions because of the absence of wet zones near the stream, the area contributing to storm runoff more rapidly extended to the whole slope due to its topographic properties. They also caused its steep hydrographs produced in the wettest condition where almost all the rainfall contributed to storm runoff. In this wettest condition, tensiometric responses near bedrock showed the vertical quick propagation of the rainfall pulse, and a good agreement of storm hydrograph simulated through a kinematic wave runoff model suggested that runoff from the slope was produced by a lateral flow on the bedrock receiving the quick propagation. In a transition process from dry to the wettest conditions, the development of the lateral flow producing smaller responses at the downslope end was estimated from decreasing of matric potential near bedrock from high negative to low values with increasing cumulative rainfall.  相似文献   

Dynamics of Lithosphere Convergence     

Makoto Yamano  Manik Tulwuni  Kensaku Turnuki 《Island Arc》1997,6(3):233-233

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Long-term temperature monitoring in a borehole drilled into the Nojima Fault, southwest Japan   总被引：2，自引：0，他引：2  

Makoto Yamano  Shusaku Goto 《Island Arc》2001,10(3-4):326-335

Abstract Long-term monitoring of temperature distribution in an active fault zone was carried out using the optical fiber temperature-sensing technique. An optical fiber cable was installed in a borehole drilled into the Nojima Fault in Awaji Island, south-west Japan, and the temperature profile to a depth of 1460 m had been measured for 2.5 years (July 1997–January 2000). Although the obtained temperature records showed small temporal variations due to drifts of the measurement system all along the cable, local temperature anomalies were detected at two depths. One at around 80 m seems to correspond to a fracture zone and may be attributed to groundwater flow in the fracture zone. This anomaly had been stable throughout the monitoring period, whereas the other anomaly at around 500 m was a transient one. The water level in the borehole could be estimated from the diurnal temperature variations in the uppermost part of the borehole and may provide information on the hydrological characteristics of the fault zone, which is connected to the borehole through perforations on the casing pipe. Except for these minor variations, the temperature profile had been very stable for 2.5 years. The conductive heat flow calculated from this profile and the thermal conductivity measured on core samples increases with depth, probably resulting from errors in thermal conductivity due to sampling problems and/or from advective heat transfer by regional groundwater flow. Assuming that the middle part of the borehole (less fractured granite layer) is least affected by these factors, heat flow at this site is estimated to be approximately 70 mW/m².  相似文献   

The Fourier transform of controlled-source time-domain electromagnetic data by smooth spectrum inversion   总被引：1，自引：0，他引：1  

Yuji Mitsuhata  Toshihiro Uchida  Yutaka Murakami  Hiroshi Amano 《Geophysical Journal International》2001,144(1):123-135

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