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151.
A. Brahic J. Breton J. Caubel A. Cazenave P. Cruvellier Y. Dupuis B. Lago J.F. Minster A. Perret A. Scribot 《Icarus》1979,40(3):423-433
Specific information on the surface morphology, composition, mean density, and internal structure of asteroids, which is necessary to advance our understanding of asteroids, can be obtained only by a detailed investigation of individual bodies: this will require space missions to individual targets. Since an essential characteristic of the asteroids is their variety, several objects must be visited. The Ariane launcher developed presently in Europe makes a multiple flyby mission possible. The first results of our feasibility study are particularly encouraging: during one revolution, five to six preselected main belt asteroids may be approached to within 1000 km with relative velocities which lie between 3 and 14 km/sec using a total impulse correction on the order of 1 to 2 km/sec. The weight of the spacecraft, excluding the engine and the propellant, would be at least 250 kg. This allows a scientific payload of 50 to 60 kg, in which priority will be given to an imaging system and radar altimeter. 相似文献
152.
This paper reports the study concerning the latitudinal dispalacement of the auroral oval as a function of the northward orientation of the Bz-component IMF and the relation between southward Bz and the auroral dynamics in the night sector. 相似文献
153.
154.
155.
A one-dimensional model for thinning of the plasma sheet is developed on the basis of launching a fast mode MHD rarefaction wave propagating in the tailward direction along the plasma sheet. Behind the rarefaction wave the pressure is reduced, leading to thinning of the plasma sheet and also to an Earthward plasma flow with a speed on the order of the sound speed a0. The plasma sheet thickness is reduced by a factor of 2 if an Earthward plasma flow speed of 0.8a0 is induced. The predictions of the model are in reasonable agreement with observations. 相似文献
156.
The propagation and interference of Alfvén waves in magnetic regions is studied. A multilayer approximation of the standard models of the solar atmosphere is used. In each layer, there is a linear law of temperature variation and a power law of Alfvén velocity variation. The analytical solutions of a wave equation are stitched at the layer boundaries. The low-frequency Alfvén waves (P > 1 s) are able to transfer the energy from sunspots into the corona by tunneling only. The chromosphere is not a resonance filter for the Alfvén waves. The interference and resonance of Alfvén waves are found to be important to wave propagation through the magnetic coronal arches. The transmission coefficient of Alfvén waves into the corona increases sharply on the resonance frequences. To take into account the wave absorption in the corona, a method of equivalent schemes is developed. The heating of a coronal arch by Alfvén waves is discussed. 相似文献
157.
Sawant SB Khan YS 《Population geography : a journal of the Association of Population Geographers of India》1982,4(1-2):67-75
This paper analyzes the impact of various factors on variations in the rate of natural increase of population in Western Maharashtra, India. By using district level data, coefficients of correlation have been calculated between the rate of natural increase, the birth rate and the death rate on the 1 hand and different factors affecting them on the other. The analysis shows that in Western Maharashtra the birth rate is high in response to the high death rate and the high infant mortality rate. It is also revealed that the rate of natural increase of the population declines with an increase in the proportion of working females as well as the proportion of educated males. All this signifies that the region under study is in the 2nd stage of the "demographic transition." 相似文献
158.
Summary Beppu is a water-dominated active geothermal system in Kyushu (Japan). Gold mineralization exists in places within altered Pleistocene volcanites in the southernmost part of this field. A shallow 300 m well was drilled in an alluvial fan deposit made up of unsorted volcanic clasts of andesite and dacite. Water and core samples were collected and a temperature log was carried out. In the depth range of 150-230 m and at temperatures of 126-148° C the main authigenic minerals are quartz, calcite, K-feldspar, mixed layers illite/smectite, stilbite and pyrite. The chemical data of the waters indicate that mixing occurs between shallow bicarbonate waters and deep Na-Cl geothermal waters in the outflow zone. The authigenic mineral assemblages found in the well are analogous to those found in the epithermal gold deposits of southern Kyushu. Au concentration data for the hydrothermal springs of Beppu (0.53 g/kg) indicate that the fluids found in the borehole at 148° C could theoretically deposit gold. It is reasonable to hypothesise that a process of mixing between deep Na-Cl fluids and shallow Ca-HCO3-SO4 fluids were responsible for massive silicate deposition, accompanied in places by Au mineralizations.
Contribution No 4. Foreign Visiting Scientist Section, Beppu Geophysical Research Laboratory, Kyoto University.
This paper was presented at the IGCP 291 Project Symposium Metamorphic Fluids and Mineral Deposits, ETH Zurich, March 21–23, 1991. 相似文献
Wasser-Gesteins-Wechselwirkung in einer Zone lateraler Fließbewegung: ein natürliches Beispiel aus der aktiven Geothermal-Golderz-Zone von Beppu (Kyushu, Japan)
Zusammenfassung Beppu ist ein geothermales System auf der Insel Kyushu, Japan, in der Wasser die dominante Rolle spielt. Goldvererzungen treten stellenweise in umgewandelten pleistozänen Vulkaniten im südlichsten Teil des Gebietes auf. Ein 300 m tiefes Bohrloch wurde in einem alluvialen Sedimentations-Fächer, der aus unsortierten vulkanischen Klasten, aus Andesit und Dazit besteht, niedergebracht. Wasserproben und Kernproben wurden genommen und die Temperaturen im Bohrloch systematisch gemessen. In Tiefen von 150–230 m und bei Temperaturen von 126–148°C sind die wichtigsten autigen gebildeten Minerale Quarz, Calcit, K-Feldspat, Illit/Smectit, Stilbit und Pyrit. Der Chemismus der Wässer zeigt, daß eine Mischung zwischen seichten Bikarbonat-Wässern und aus der Tiefe stammenden Na-Cl geothermalen Wässern erfolgt. Die autigenen Mineralassoziationen in diesem. Bohrloch sind vergleichbar mit denen in epithermalen Goldlagerstätten des südlichen Kyushu. Auf der Basis von existierenden Goldkonzentrationsdaten für die hydrothermalen Quellen auf Beppu (0.53 g/kg) läßt sich zeigen, daß die Fluide, die in dem Bohrloch bei 148 angetroffen wurden, theoretisch Gold absetzen könnten. Daher läßt sich die Theorie vertreten, daß Mischungsvorgänge zwischen einem aus der Tiefe stammenden Na-Cl Fluid und einem oberflächennahen Ca-HCO3-SO4 Wasser für die massive Silikatausscheidung verantwortlich waren, die stellenweise von Goldmineralisation begleitet wurden.
Contribution No 4. Foreign Visiting Scientist Section, Beppu Geophysical Research Laboratory, Kyoto University.
This paper was presented at the IGCP 291 Project Symposium Metamorphic Fluids and Mineral Deposits, ETH Zurich, March 21–23, 1991. 相似文献
159.
Avanesov G Zhukov B Ziman YA Kostenko V Kuzmin A Murav'ev V Fedotov V Bonev B Mishev D Petkov D Krumov A Simeonov S Boycheva V Uzunov YU Weide GG Halmann D Pössel W Head J Murchie S Schkuratov YuG Berghänel R Danz M Mangoldt T Pihan U Smith B 《Planetary and Space Science》1991,39(1-2):281-295
From February to March 1989 the Phobos 2 spacecraft took 37 TV images of Phobos at a distance of 190-1100 km. These images complement Mariner-9 and Viking data by providing higher-resolution coverage of a large region West of the crater Stickney (40-160 degrees W) and by providing disk-resolved measurements of surface brightness at a greater range of wavelengths and additional phase angles. These images have supported updated mapping and characterization of large craters and grooves, and have provided additional observations of craters' and grooves' bright rims. Variations in surface visible/near-infrared color ratio of almost a factor of 2 have been recognized; these variations appear to be associated with the ejecta of specific large impact craters. Updated determinations of satellite mass and volume allow calculation of a more accurate value of bulk density, 1.90 +/- 0.1 g cm-3. This is significantly lower than the density of meteoritic analogs to Phobos' surface, suggesting a porous interior perhaps containing interstitial ice. 相似文献
160.
This paper presents the case histories of two catastrophic landslips in hard rock terrains with varied climatic and geological environments. The first slip is associated with a power project in very close proximity (200 m) of the Porthimund Dam (11°22N, 76°3430E), in a charnockitic terrain in the Nilgiri hills (Tamil Nadu), and the second is associated with a railroad structure (19°525N, 78°1720E), in Adilabad district (Andhra Pradesh), in a basaltic terrain.The landslip in the charnockites is attributable to: (1) a high degree of saprolitization in the charnockites, with maximum intensity in the crest portion; (2) the coincidence of a major joint pattern in a NE-SW direction, with the strike of the foliation; and (3) the poor-to-fair physical rock quality in the crest and scarp portions.The slips in the basaltic terrain are due to: (1) the partially altered, highly jointed nature of the regional trap rocks with boulder sizes varying from 20 cm to 250 cm in diameter and the debris accumulating in a precarious condition on the northeast side of the rail track, with unfavorable alignment direction; and (2) the instability created in the weak rock mass by the vibrational forces of heavily loaded running trains.The weathered state of the rock masses in both the cases, showing good agreement with their physical state, accounts for the landslips. The remedial measures suggested are also discussed. 相似文献