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1.
Kentaro Terada Hitoshi Negoro Kiyoshi Hayashida Shunji Kitamoto Hiroshi Tsunemi Hiroshi Oya Takayuki Ono Akira Morioka Yuzuru Tawara Toshifumi Mukai Masahiro Hoshino Toshio Terasawa 《Earth, Moon, and Planets》1994,66(1):75-81
An ASCA observation of the Jovian impact of the comet Shoemaker-Levy 9 is reported. Four impacts of H, L, Q1 and R were observed and four impacts of B, C, G, and Q2 were observed within 60 minutes after their impacts. No significant flaring of X-ray emission was observed. Upper limit X-ray fluxes of 90 % confidence level, averaged 5 minutes just after the impacts, were 2.4 × 10–13 erg sec–1 cm–2, 3.5 × 10–13 erg sec–1 cm–2, 1.6 × 10–13 erg sec–1 cm–2 and 2.9 × 10–13 erg sec–1 cm–2 for the impacts of H, L, Q1 and R, respectively, in the 0.5(0.7 for H and Q1)–10 keV energy range. However, a hint of X-ray enhancement around Jupiter from July 17 to July 19 was detected with about 2 6 × 10–14 erg sec–1 cm–2 in the 0.5–10 keV energy range. 相似文献
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Diffusion coefficients of Co2+ and Ni2+ in synthetic single crystal forsterite along the c-axis were determined in the temperature ranges, 700–1200?°C and 800–1300?°C, respectively. The synthesized forsterite specimens were coated with thin evaporated films of CoO and NiO on the c-surface and annealed for diffusion experiments. The short penetration distance of diffusing ions in forsterite was measured by secondary ion mass spectrometry using the depth profile method. The diffusion coefficients of Co (700–1200?°C) and Ni (800–1300?°C) are given by: and The observed diffusion coefficient values show good linear relationships in Arrhenius plots and the activation energy values obtained agree well with the previous values, although the diffusion coefficient values observed at the high temperature end of the experimental range deviate from the previous values. These results indicate that Co and Ni diffuse in olivine with a single mechanism within the temperature range observed, possibly with an extrinsic in nature as in the case of Mg tracer diffusion observed by Chakraborty et?al. 1994 and of Fe-Mg interdiffusion by Chakraborty. 相似文献
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Concurrent variations of CNA fluctuations and geomagnetic fluctuations are classified into Type 1 (substorm-type), Type 2 (Pc5-type), and Type 3 which is the object of the present study. Type 3 apparently has peculiar characteristics in that CNA fluctuations at a certain auroral-zone station show a pronounced positive correlation with magnetic fluctuations at distant low-latitude stations. The magnetic fluctuations of this type are identified to generalized Si which tends to take place much more frequently than the so-called Si. The CNA fluctuations of this type are found to take place on the dayside auroral zone only when preceded by a magnetic substorm on the night side. Considering the change of the growth rate of electron cyclotron instability and enhancement of pitch angle diffusion due to the change of magnetic field intensity, the following model is proposed to explain the occurrence mechanism of Type 3 concurrent variations. The CNA fluctuations take place only when two conditions are satisfied; generation of the accelerated electrons in association with substorm onset and modulation of the precipitation of the electrons by compression and expansion of the magnetosphere, in other words, by generalized Si. 相似文献
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A new radio spectropolarimeter for solar radio observation has been developed at Tohoku University and installed on the Iitate Planetary Radio Telescope (IPRT) at the Iitate observatory in Fukushima prefecture, Japan. This system, named AMATERAS (the Assembly of Metric-band Aperture TElescope and Real-time Analysis System), enables us to observe solar radio bursts in the frequency range between 150 and 500 MHz. The minimum detectable flux in
the observation frequency range is less than 0.7 SFU with an integration time of 10 ms and a bandwidth of 61 kHz. Both left
and right polarization components are simultaneously observed in this system. These specifications are accomplished by combining
the large aperture of IPRT with a high-speed digital receiver. Observational data are calibrated and archived soon after the
daily observation. The database is available online. The high-sensitivity observational data with the high time and frequency
resolutions from AMATERAS will be used to analyze spectral fine structures of solar radio bursts. 相似文献
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Investigation of local time dependence of Mercury's sodium exosphere based on a numerical simulation
Mercury has a surface-bounded exosphere (SBE) similar to that of the Moon. One of the atmospheric species, sodium, was found by ground-based observations to be the most prominent component. Mercury's sodium SBE is known to be non-uniform with respect to local time (LT) in low-latitude regions: the sodium column density in the dawn-side region is larger than that in the dusk-side region, and the sodium abundance is the largest in the morning-noon region. To reveal the production processes for the exosphere near Mercury's surface, the LT dependence of the exosphere was investigated through a numerical simulation. Three data sets of sodium column densities observed for the dawn-side hemisphere, observed by Sprague et al. [1997. Distribution and abundance of sodium in Mercury's atmosphere, 1985-1988. Icarus 12, 506-527], were compared with results simulated by a 3D Monte Carlo method, and the source rates and density of sodium of the planetary surface were estimated. In the simulation, the photon-stimulated desorption (PSD) and thermal desorption (TD) processes were assumed as the release mechanisms. The sodium source rates for the three data sets, at respective heliocentric distances of about 0.33, 0.42, and 0.44 AU, were estimated as 1-4×108 Na/cm2/s with weak LT dependence. In contrast, the expected sodium surface density showed clear dependence on LT and the heliocentric distance. The sodium surface density decreases from early morning to noon by a few orders, and, particularly for large heliocentric distances, the surface is in a condition of sodium excess and depletion with respect to the surface sodium density assumed by Killen et al. [2004. Source rates and ion recycling rates for Na and K in Mercury's atmosphere. Icarus 171, 1-19] in the early morning and morning-noon regions, respectively. This study implies that the decrease in sodium surface density from the early morning to noon regions might produce the characteristic LT dependence in the low-latitude dawn-side region. 相似文献
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The reaction between enstatite (En95.3Fs4.7) and CaCO3 has been studied at pressures between 23 and 77 kbars and at temperatures between 800° and 1400°C. At 1000°C enstatite and CaCO3 react to form dolomite and diopside solid solutions at pressures below approximately 45 kbars and magnesite and diopside solid solutions at higher pressures. The curve for the reaction dolomitess + enstatitess ? magnesitess + diopsidess lies between 40 to 45 kbars at 1000°C and between 45 and 50 kbars at 1200°C. It is very close to the graphite-diamond transition curve. These experimental results indicate that calcite (or aragonite) is unstable in the presence of enstatite, and that dolomite and magnesite are the stable carbonates at high pressures. The forsterite + aragonite assemblage is, however, stable to at least 80 kbars at 800°C. It is suggested that in the upper mantle where enstatite is present, dolomite is stable to depths of about 150 km and magnesite is stable at greater depths in the continental regions, assuming that the partial pressure of CO2 is equal or close to the total pressure. It is also suggested that carbonate inclusions in pyroxene can be used as an indicator of the depth of their equilibration; dolomite inclusions in enstatite would be formed at depths shallower than 150 km and magnesite inclusions in diopside at greater depths. Eclogite and peridotite inclusions in kimberlite may be classified on this basis. 相似文献
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Aníbal Ojeda Kuvvet Atakan Eullia Masana Pere Santanach María-Jos Jimnez Mariano García-Fernndez 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):911-916
In this study, the influence of paleoseismic and geologic data in the seismic hazard estimation for the Catalan coastal ranges is analysed. We computed the probabilistic seismic hazard using area seismic sources with a Poissonian assumption for the earthquake occurrence. For the computations, a previously published attenuation relationship based on European strong motion data was applied. The resulting hazard estimates show similarities to the previous assessments in the region. These results were then used as a reference for comparison with other new models. In order to analyse the influence of the paleoseismic data three different models were tested. Since the number of faults that are investigated in detail are few, the same area sources that were used in the Poissonian assumption were kept in all three new models. In addition, the new paleoseismic data with faults expressed as line sources were used. In this case, a cyclic earthquake occurrence was assumed. The three models were based on the paleoseismic data with different assumptions on the time elapsed since last event. The time elapsed was set to 0, 10 and 85% of the recurrence interval in each model. The results are presented as maps showing the difference between the three models and the reference model with the Poissonian assumption. The results are given in horizontal peak ground acceleration contour maps for different return periods, also taking into account large return periods as high as 25,000 years. This is done to demonstrate the effect of large recurrence intervals found for some of the active faults. In general, we observe that for short return periods (<1000 years), the Poissonian assumption of earthquake occurrence is probably sufficient and provides a robust estimate of the hazard. However, for longer return periods (>5000 years) the effects of the paleoseismic data become increasingly significant. In order to estimate the true seismic hazard potential of this apparently low seismicity area, long-term behaviour of the possible active faults in the region needs to be investigated systematically. 相似文献
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We report on two-dimensional imaging observations of D-line emissions from the extended distribution of iogenic sodium atoms with two fields of view (±20 RJ (narrow FOV) and ±400 RJ (wide FOV)) simultaneously by using a portable small telescope or camera lens. We derived dynamic feature of the band-shaped and spray-shaped distributions near Io's orbit by means of continuous observation. The observations confirm the phenomenological behavior of the sodium cloud on two spatial scales, as previously observed by Pilcher et al. [Pilcher, C.B., Smyth, W.H., Combi, M.R., Fertel, J.H., 1984. Astrophys. J. 287, 427-444], Schneider et al. [Schneider, N.M., Trauger, J.T., Wilson, J.K., Brown, D.I., Evans, R.W., Shemansky, D.E., 1991. Science 253, 1394-1397], and Mendillo et al. [Mendillo, M., Baumgartner, J., Flynn, B., Hughes, W.S., 1990. Nature 348, 312-314]. We also confirm an elongated oval emission distribution of the sodium nebula and derivation of its detailed east-west asymmetry depending on Io's phase angle, which was first noted by Flynn et al. [Flynn, B., Mendillo, M., Baumgartner, J., 1994. J. Geophys. Res. 99, 8403-8409]. We then did model analyses to investigate the source process for sodium atoms and the dynamics behind their distribution. We conclude that the essential of molecular ion mechanisms to the band-shaped distribution is in agreement with Wilson and Schneider [Wilson, J.K., Schneider, N.M., 1999. J. Geophys. Res. 104, 16567-16583]. We differ from Wilson et al. [Wilson, J.K., Mendillo, M., Baumgartner, J., Schneider, N.M., Trauger, J.T., Flynn, B., 2002. Icarus 157, 476-489] in finding that charge exchange process contributes more to the spray-shaped distribution and sodium nebula than sputtering does. These results derived the double-peaked velocity distribution of released sodium atoms, and re-confirmed the source rates in agreement with past studies. 相似文献
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Beraki Asmerom F. Morioka Yushi Engelbrecht Francois A. Nonaka Masami Thatcher Marcus Kobo Nomkwezane Behera Swadhin 《Climate Dynamics》2020,54(11):4775-4792
Climate Dynamics - The study examines the influence of external climate forcings, and atmosphere–ocean–sea–ice coupled interaction on the Southern Hemisphere (SH) atmospheric... 相似文献