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101.
We present new high-pressure temperature experiments on melting phase relations of Fe-C-S systems with applications to metallic core formation in planetary interiors. Experiments were performed on Fe-5 wt% C-5 wt% S and Fe-5 wt% C-15 wt% S at 2-6 GPa and 1050-2000 °C in MgO capsules and on Fe-13 wt% S, Fe-5 wt% S, and Fe-1.4 wt% S at 2 GPa and 1600 °C in graphite capsules. Our experiments show that: (a) At a given P-T, the solubility of carbon in iron-rich metallic melt decreases modestly with increasing sulfur content and at sufficiently high concentration, the interaction between carbon and sulfur can cause formation of two immiscible melts, one rich in Fe-carbide and the other rich in Fe-sulfide. (b) The mutual solubility of carbon and sulfur increases with increasing pressure and no super-liquidus immiscibility in Fe-rich compositions is likely expected at pressures greater than 5-6 GPa even for bulk compositions that are volatile-rich. (c) The liquidus temperature in the Fe-C-S ternary is significantly different compared to the binary liquidus in the Fe-C and Fe-S systems. At 6 GPa, the liquidus of Fe-5 wt% C-5 wt% S is 150-200 °C lower than the Fe-5 wt% S. (d) For Fe-C-S bulk compositions with modest concentration of carbon, the sole liquidus phase is iron carbide, Fe3C at 2 GPa and Fe7C3 at 6 GPa and metallic iron crystallizes only with further cooling as sulfur is concentrated in the late crystallizing liquid. Our results suggest that for carbon and sulfur-rich core compositions, immiscibility induced core stratification can be expected for planets with core pressure less than ∼6 GPa. Thus planetary bodies in the outer solar system such as Ganymede, Europa, and Io with present day core-mantle boundary (CMB) pressures of ∼8, ∼5, and 7 GPa, respectively, if sufficiently volatile-rich, may either have a stratified core or may have experienced core stratification owing to liquid immiscibility at some stage of their accretion. A similar argument can be made for terrestrial planetary bodies such as Mercury and Earth’s Moon, but no such stratification is predicted for cores of terrestrial planets such as Earth, Venus, and Mars with the present day core pressure in the order ?136 GPa, ?100 GPa, and ?23 GPa. (e) Owing to different expected densities of Fe-rich (and carbon-bearing) and sulfur-rich metallic melts, their settling velocities are likely different; thus core formation in terrestrial planets may involve rain of more than one metallic melt through silicate magma ocean. (f) For small planetary bodies that have core pressures <6 GPa and have a molten core or outer core, settling of denser carbide-rich liquid or flotation of lighter, sulfide-rich melt may contribute to an early, short-lived geodynamo. 相似文献
102.
WORLD DELTAS AND THEIR EVOLUTION 总被引:1,自引:0,他引:1
H. Jesse Walker 《地理学报》1999,(1):30-41
In August 1998, an international symposium on the world deltas was held in New Orleans, Louisiana, USA. This symposium attracted discussion about more than 25 deltas from around the world with emphasis placed on those that are most densely populated and impacted by humans. Keynote papers printed details about the physical, biological, engineering and socioeconomic aspects of six deltas including the Mississippi, Nile, Ganges-Brahmaputra, Rhine-Meuse, Changjiang and Po. The main purpose of this symposium was to inform scientists, engineers and decision-makers about information that is currently available and to provide them a basis for working in such environments. 相似文献
103.
Ureilite smelting 总被引:2,自引:0,他引:2
Abstract— Ureilites containing homogeneous Fo76 olivine cores in intimate co-existence with graphite must have recrystallized at pressures of at least ~100 bars to suppress smelting of the fayalite component of the olivine to Fe metal. Smelting of olivine and pyroxene-saturated magmatic liquids produces orthopyroxene-without-olivine crystalline derivatives unlike those in ureilites. Thus the Mg# compositional variation within the ureilite suite, which is commonly attributed to partial smelting, cannot plausibly be produced by assemblages rich in liquid. In situ smelting of graphitic olivine + pigeonite crystal mushes can produce the correct crystal assemblage, but fails to provide a plausible account for the removal of metal from ureilites or for the correlation of Mg# with Δ17O. Even if Mg# and Δ17O variations are established in the nebula, ureilite recrystallization with graphite must have occurred at pressures greater than the minima we have experimentally established, corresponding to parent objects not less than ~100 km in radius. 相似文献
104.
Many fishes routinely exploit resources in high-energy marine habitats of interest to ocean engineers, including rocky coasts and coral reefs. How fishes modulate fin motions to correct perturbations to the preferred heading or to maneuver in complex structure should interest both biologists and ocean engineers. These fin motions are reviewed in order to generate simple models of causal relationships between fin design, motion, and maneuvering performance. The available data on maneuvering performance in fishes is reviewed to compare to the simple models, to identify gaps in our knowledge, and to outline a research program to address these gaps more effectively. 相似文献
105.
Westneat M.W. Thorsen D.H. Walker J.A. Hale M.E. 《Oceanic Engineering, IEEE Journal of》2004,29(3):674-683
Fin-based propulsion systems perform well for both high-speed cruising and high maneuverability in fishes, making them good models for propulsors of autonomous underwater vehicles. Labriform locomotion in fishes is actuated by oscillation of the paired pectoral fins. Here, we present recent research on fin structure, fin motion, and neural control in fishes to outline important future directions for this field and to assist engineers in attempting biomimicry of maneuverable fin-based locomotion in shallow surge zones. Three areas of structure and function are discussed in this review: 1) the anatomical structure of the fin blade, skeleton, and muscles that drive fin motion; 2) the rowing and flapping motions that fins undergo for propulsion in fishes; and 3) the neuroanatomy, neural circuitry, and electrical muscle activity that are characteristic of pectoral fins. Research on fin biomechanics, muscle physiology and neural control is important to the comparative biology of locomotion in fishes and application of fin function for aid in aquatic vehicle design. Recommendations are made regarding fin propulsor designs based on the fin shape, activation pattern, and motion. Research on neural control of fins is a key piece in the puzzle for a complete understanding of comparative fin function and may provide important principles for engineers designing control systems for fin-like propulsors. 相似文献
106.
Ian W. Walker 《Celestial Mechanics and Dynamical Astronomy》1983,29(3):215-228
The Hill-type stability (cf. closure of the zero-velocity curves in the circular restricted three-body problem) of general hierarchical three-body systems is examined analytically in the case where the total mass of the binary is small in comparison to the mass of the external body (e.g. systems of the type Planet-Satellite-Sun, Planet-Planet-Star, etc.). This is compared with results derived by Szebehely, Markellos and Roy in the Planet-Satellite-Sun case of the circular restricted three-body problem. It is demonstrated how the Hill-type stability is affected by the sense of revolution of the binary, i.e. corotational or contrarotational, and the mass ratio within the binary. The effect of the difference in longitudes of the bodies in their orbits is also examined. 相似文献
107.
108.
When a satellite orbit decaying slowly under the action of air drag experiences 15th-order resonance with the Earth's gravitational field, so that the ground track repeats after 15 rev, the orbital inclination suffers appreciable changes due to the perturbations from the harmonics in the geopotential of order 15 and odd degree (15,17,19 …). In this paper the changes in inclination at resonance of 11 satellites at inclinations between 30° and 90° have been analysed to determine values of the geopotential coefficients of order 15 and degree and in the usual notation. The recommended solution, going up to l = 31, is:
l | 109C?l,15 | 109S?l,15 |
15 | ?21.5 ± 0.9 | ?8.4 ± 0.9 |
17 | 4.4 ± 1.6 | 9.0 ± 1.5 |
19 | ?15.6 ± 2.6 | ?14.1 ± 2.7 |
21 | 10.4 ± 3.0 | 7.3 ± 3.5 |
23 | 22.5 ± 2.8 | 1.2 ± 4.4 |
25 | ?0.9 ± 4.7 | ?3.8 ± 5.3 |
27 | ?11.2 ±3.3 | 9.1 ± 3.2 |
29 | ?20.5 ± 5.4 | ?1.2 ± 6.1 |
31 | 17.7 ± 6.6 | ?1.0 ± 7.1 |