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231.
Sean J. McKenna 《Astrophysics and Space Science》1985,108(1):31-66
A general treatment of the transfer of polarized radiation in spectral lines assuming a Rayleigh phase function and a general law of frequency redistribution is derived. It is shown how nine families of coupled integral equations for the moments of the radiation field arise which are necessary to fully describe the state of polarization of the emergent radiation from a plane-parallel, semi-infinite atmosphere. The special case of angle independent redistribution functions is derived from the general formalism, and it is shown how the nine families of integral equations reduce to the six linearly independent integral equations derived by Collins (1972). To serve as a test of the formulation, solutions for isothermal atmospheres are given. 相似文献
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234.
J.LR. Touret 《地学学报》1992,4(1):87-98
The CO2 atmospheric content has shown large variations over geological times. High contents (up to one order of magnitude more than present-day values) ultimately correspond to discrete episodes of mantle degassing, either juvenile, or subduction-related (carbon recycling). A number of arguments (e.g. the continuous volume increase of carbonate-bearing sediments with time) suggest that, throughout the Earth's history, juvenile CO2 has formed a major contribution to the global carbon budget of the Earth.
The absence of a direct relationship between major volcanic episodes and the average CO2 atmospheric content suggests that volcanoes might not be the only way by which mantle CO2 is transported to the surface. It is proposed that large quantities of juvenile CO2 could temporarily be stored in the lower continental crust during major episodes of granulite formation. These are primarily caused by magmatic underplating and they result in a vertical accretion of the crust by accumulation of CO2 -bearing, mantle-derived magmas. Most of the CO2 migrates through the crust during post-metamorphic evolution and isostatic restoration of the normal continental thickness. However, large quantities of CO2 can still be present in some areas, notably as high-density fluids enclosed in minerals. 相似文献
The absence of a direct relationship between major volcanic episodes and the average CO
235.
The Ivrea-Verbano Zone in northern Italy represents a section through the lower continental crust which has been tilted and emplaced into its present position during the Alpine orogeny. Recent and on-going structurally-oriented geological mapping in this region is providing new information about the geometry of the complex. The central part of the zone is dominated by a large basic complex (the 'mafic formation') which is intrusive into the surrounding gneisses. The foliation within the envelope of gneisses is deflected around the intrusive complex as if by ballooning, but in the region south-west of Monte Capio both units are folded together into a tight to isoclinal steeply plunging fold with an amplitude of c. 10 km. This fold locally inverts the stratigraphy of the layered basic group of the complex, and is thought to be the result of gravitational collapse following intrusion and inflation of a large magma body into the lower crust.
Several high-temperature shear zones have now been traced within the country rock for distances up to 20 km. The geometry of these, and their relationship to the basic complex suggests that at least some of the extensional collapse of the mafic body is related to uplift caused by intrusion of this body.
Close parallels can be drawn between the observed structure in the Ivrea-Verbano Zone (after removing the effects of late, low-temperature faulting and folding related to emplacement of the rocks into their present position), and those inferred from deep seismic reflection profiling in areas of current extension such as parts of the US Basin and Range province. 相似文献
Several high-temperature shear zones have now been traced within the country rock for distances up to 20 km. The geometry of these, and their relationship to the basic complex suggests that at least some of the extensional collapse of the mafic body is related to uplift caused by intrusion of this body.
Close parallels can be drawn between the observed structure in the Ivrea-Verbano Zone (after removing the effects of late, low-temperature faulting and folding related to emplacement of the rocks into their present position), and those inferred from deep seismic reflection profiling in areas of current extension such as parts of the US Basin and Range province. 相似文献
236.
J. D. Leatherdale 《The Photogrammetric Record》1994,14(83):759-769
Some of the economic and operational aspects of mapping are discussed, including the conditions that may offer air survey a competitive advantage over other methods. The financing of national mapping programmes around the world is increasingly market oriented, driven by the need to provide the end users with information that they can turn into sustainable economic growth and social progress. Despite these economic pressures, map makers seem to find their work more enjoyable and rewarding than most professionals. 相似文献
237.
For several years now, an experimental simulation of Titan's atmosphere has been on going at LISA. A cold plasma is established in a gas mixture representative of the atmosphere of the satellite. In these experiments, more than 70 organic compounds have been identified, including the first identification in this type of experimental simulation of C4N2 already detected in its solid form on Titan, which suggests that the setup correctly mimics the chemistry of Titan's atmosphere.We have carried out the first experimental simulation including O-containing compounds in order to study the influence of the presence of CO on the chemical behavior of Titan's atmosphere. With the help of gas chromatography–mass spectrometry (GC–MS) and infrared spectroscopy (IRS) we can thus determine which minor species still undetected in Titan's atmosphere are likely to be present and understand the complex chemistry of the atmosphere of this satellite. Surprisingly we have identified unpredicted O-containing gaseous compounds, mainly ethylene oxide (also named oxirane, C2H4O). This molecule has been observed in the interstellar medium by observation in the millimeter region (Astrophys. J. 489 (1997) 553; Astron. Astrophys. 337 (1998) 275). On the contrary, the predicted O-compounds (formaldehyde and methanol) have not been identified in this experiment. Furthermore, we have identified NH3 in the gaseous products with an initial mixture of N2 (98%) and CH4 (2%).The paper describes the experimental device used in this work, in particular the IRS and GC–MS techniques. We also comment the results related to the detection of the O-containing compounds and NH3 and their implications on our knowledge of the chemistry of Titan's atmosphere and on the retrieval of the future Titan data expected from Cassini-Huygens. 相似文献
238.
Natural and agricultural wetlands are considered to be the major sources of global atmospheric methane (CH4). A one‐dimensional model was developed to simulate methane emission and used to examine the influence of various physical processes on the rate of methane emission. Three processes involved in the methane emission are implemented in the model: production, reoxidation and transport. Three transport pathways were considered: diffusion across water–air or soil–air interfaces, ebullition and diffusion through plants. These pathways are influenced by soil properties, plant growth, water‐table conditions, temperature and external inputs (e.g. fertilizer). The model was used to examine the seasonal variation of the methane emission at a rice field in Hunan, China, which was observed during a field experiment for consecutive (early and late) rice seasons in 1992. The observed seasonal variations of methane emission, and role of plants in transporting methane to the atmosphere, are captured by the model simulation. Further model applications were conducted to simulate effects of fertilizer and water‐level condition on the methane emission. The results indicate that unfermented organic fertilizer produces a higher methane emission rate than mineral fertilizer. The simulations with treatments of a deep‐water covering and constant moisture reduced the methane emission. The rice field study provides a framework for further development of the model towards simulations based on spatially distributed variables (e.g. water table, soil temperature and vegetation) at a regional scale. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
239.
240.
The paper presents a simple approximate analytical solution of the remote stresses that cause the collapse of a borehole or other circular cylindrical cavity in an infinite elastic space. Regions of parallel equidistant splitting cracks are assumed to form on the sides of the cavity. Their boundary is assumed to be an ellipse of a growing horizontal axis, the other axis remaining equal to the borehole diameter. The slabs of rock between the splitting cracks are assumed to buckle as slender columns, and their post-critical stress is considered as the residual stress in the cracked rock. The buckling of these slab columns is assumed to be resisted not only by their elastic bending stiffness but also shear stresses produced on rough crack faces by relative shear displacements. The energy release from the infinite medium caused by the growth of the elliptical cracking region is evaluated according to Eschelby's theorem. This release is set equal to the energy dissipated by the formation of all the splitting cracks, which is calculated under the assumption of constant fracture energy. This yields the collapse stress as a function of the elastic moduli, fracture energy, ratio of the remote principal stresses, crack shear resistance characteristic and borehole diameter. The collapse stress as a function of crack spacing is found to have a minimum, and the correct crack spacing is determined from this minimum. For small enough diameters, the crack spacing increases as the (4/5)-power of the borehole diameter, while for large enough diameters a constant spacing is approached. In contrast to plastic solutions, the breakout stress exhibits a size effect, such that for small enough diameters the breakout stress decreases as the (? 2/5)-power of the borehole diameter, while for large enough diameters a constant limiting value is approached. Finally, some numerical estimates are given and the validity of various simplifying assumptions made is discussed. 相似文献