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61.
Laurent Koechlin Denis Serre Gerald K. Skinner Peter Von Ballmoos Thomas Crouzil 《Experimental Astronomy》2005,20(1-3):307-315
The light deviation caused by the gravitational potential in the vicinity of the sun could be used as a means of focussing radiation that cannot be focussed easily otherwise. The gravitational lens formed by the sun is not stigmatic, but does have the advantage of being achromatic and acts identically on all types of mass-less radiations. For a source at infinity, its geometrical characteristics present a “caustic” line starting at 550 astronomical units (UA) downstream from the sun. In a plane perpendicular to that caustic line, images of distant objects are formed.The perturbations by the solar corona plasma will significantly blur electromagnetic radiation for wavelengths longer than those of the IR domain. At shorter wavelengths, for example the γ domain, the focussing process could lead to 108 amplification factors. In order to reach the regions where images are formed, long distance space missions are necessary. Once launched, missions of this type would be dedicated to a single field. Some possible targets are considered, such as Sagitarius A observed in X and γ rays.In this paper we study the point spread function (PSF) of the sun as a gravitational lens. Taking into account perturbations by the planets, the non sphericity of the sun and coronal plasma index, we derive limits within which such observations could be possible. 相似文献
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65.
In this, the first of a short series of papers on the magnitudes of galaxies, the dependence of magnitude on the aperture used in photoelectric measures is discussed. mean results from an empirical study are presented. 相似文献
66.
System dynamics is a computer-aided approach to evaluating the interrelationships of different components and activities within complex systems. Recently, system dynamics models have been developed in areas such as policy design, biological and medical modeling, energy and the environmental analysis, and in various other areas in the natural and social sciences. The Idaho National Engineering and Environmental Laboratory, a multipurpose national laboratory managed by the Department of Energy, has developed a system dynamics model in order to evaluate its utility for modeling large complex hydrological systems. We modeled the Bear River basin, a transboundary basin that includes portions of Idaho, Utah, and Wyoming. We found that system dynamics modeling is very useful for integrating surface water and ground water data and for simulating the interactions between these sources within a given basin. In addition, we also found that system dynamics modeling is useful for integrating complex hydrologic data with other information (e.g., policy, regulatory, and management criteria) to produce a decision support system. Such decision support systems can allow managers and stakeholders to better visualize the key hydrologic elements and management constraints in the basin, which enables them to better understand the system via the simulation of multiple "what-if" scenarios. Although system dynamics models can be developed to conduct traditional hydraulic/hydrologic surface water or ground water modeling, we believe that their strength lies in their ability to quickly evaluate trends and cause-effect relationships in large-scale hydrological systems, for integrating disparate data, for incorporating output from traditional hydraulic/hydrologic models, and for integration of interdisciplinary data, information, and criteria to support better management decisions. 相似文献
67.
It is shown that for small velocities the time dependent evolution of massive stars may be described by a series of static models. Those are linked to each other by one continuous time dependent parameter-the relativity effect. The fate of the dynamic system is analyzed by the behaviour of the static models. The method is illustrated for general relativistic polytropes. 相似文献
68.
A Lagrangian stochastic (LS) model, which is embedded into a parallelised large-eddy simulation (LES) model, is used for dispersion
and footprint evaluations. For the first time an online coupling between LES and LS models is applied. The new model reproduces
concentration patterns, which were obtained in prior studies, provided that subgrid-scale turbulence is included in the LS
model. Comparisons with prior studies show that the model evaluates footprints successfully. Streamwise dispersion leads to
footprint maxima that are situated less far upstream than previously reported. Negative flux footprints are detected in the
convective boundary layer (CBL). The wide range of applicability of the model is shown by applying it under neutral and stable
stratification. It is pointed out that the turning of the wind direction with height leads to a considerable dependency of
source areas on height. First results of an application to a heterogeneously heated CBL are presented, which emphasize that
footprints are severely affected by the inhomogeneity. 相似文献
69.
James Gerald Brophy 《Contributions to Mineralogy and Petrology》2009,157(6):797-811
Magma ascent, decompression-induced H2O exsolution and crystallization is now recognized as an important process in hydrous subduction zone magmas. During the course
of such a process calculations suggest that the ascent rate of a degassing and crystallizing mafic magma will be greater than
crystal settling velocities. Thus, any crystals formed as a consequence of volatile exsolution will remain suspended in the
magma. If the magma erupts before the percentage of suspended crystals reaches the critical crystallinity value for mafic
magma (~55 vol.%) it will produce the commonly observed crystal rich island arc basalt lava. If the magma reaches its critical
crystallinity before it erupts then it will stall within the crust. Extension of compaction experiments on a 55 vol.% sand-Karo
syrup suspension at different temperatures (and liquid viscosities) to the likely viscosities of interstitial andesitic to
dacitic liquid within such a stalled magma suggest that small amounts (up to ~10%) can be expelled on a time scale of 1–10 years.
The expelled liquid can create a new intermediate to silicic body of magma that is related to the original mafic magma via
fractional crystallization. The short time scale for liquid expulsion indicate that decompression-induced H2O exsolution and crystallization can be an important mechanism for fractional crystallization. Based on this assumption a
general model of decompression-induced crystallization and fractionation is proposed that explains many of the compositional,
mineralogical and textural features of Aleutian (and other andesites). 相似文献
70.
James Gerald Brophy 《Contributions to Mineralogy and Petrology》2009,158(1):99-111
Analytical expressions for the variation in D
La and D
Yb with increasing liquid SiO2 for olivine, plagioclase, augite, hornblende, orthopyroxene, magnetite and ilmenite (Brophy in Contrib Mineral Petrol 2008, online first) have been combined with numerical models of hydrous partial melting, of mid-ocean ridge (MOR) cumulate gabbro
melting, and fractional crystallization of slightly hydrous mid-ocean ridge basalt (MORB) magma to assess a melting versus
fractionation origin for oceanic plagiogranite. For felsic magmas (>63 wt.% SiO2) the modeling predicts the following. MOR cumulate gabbro melting should yield constant or decreasing La and constant Yb
abundances with increasing liquid SiO2. The overall abundances should be similar to those in associated mafic magmas. MORB fractional crystallization should yield
steadily increasing La and Yb abundances with increasing SiO2 with overall abundances significantly higher than those in associated mafic magmas. Application to natural occurrences of
oceanic plagiogranite indicate that both MOR cumulate gabbro melting and MORB fractionation are responsible. Application of
the model results to Icelandic rhyolites strongly support a fractional crystallization rather than a crustal melting origin. 相似文献