Multiwavelength focusing with the Sun as gravitational lens     

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   

Citation on the Award of the Leonard Medal of The Meteoritical Society     

Gerald J. Wasserburg  Ursula B. Marvin 《Meteoritics & planetary science》1976,11(3):239-241

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Role of Phase Transitions in a Dynamic Mantle     

Gerald Schubert  David A. Yuen  Donald L. Turcotte 《Geophysical Journal International》1975,42(2):705-735

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Book reviews     

George Kish  Wolf Tietze  C. Paddick  Dietrich Barsch  Keith Clayton  Michael F. Thomas  Thomas Peucker  Alexander Zaporozec  Georg Matthess  German Müller  K. Ernstson  Olusegun Areola  Gerald M. Friedman  Maurice K. -Seguin  C. Koeman  Risto Aario 《GeoJournal》1979,3(4):410-416

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Galaxy magnitudes     

Gerald E. Kron  C. D. Shane 《Astrophysics and Space Science》1974,27(1):233-240

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   

System dynamics modeling of transboundary systems: the bear river basin model   总被引：4，自引：0，他引：4  

Sehlke G  Jacobson J 《Ground water》2005,43(5):722-730

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   

Implosions and emplosions in supermassive objects     

Giora Shaviv  Gerald E. Tauber 《Astrophysics and Space Science》1971,14(2):396-398

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   

Footprints in Homogeneously and Heterogeneously Driven Boundary Layers Derived from a Lagrangian Stochastic Particle Model Embedded into Large-Eddy Simulation   总被引：1，自引：1，他引：0  

Gerald Steinfeld  Siegfried Raasch  Tiina Markkanen 《Boundary-Layer Meteorology》2008,129(2):225-248

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   

Decompression and H<Subscript>2</Subscript>O exsolution driven crystallization and fractionation: development of a new model for low-pressure fractional crystallization in calc-alkaline magmatic systems     

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   

La–SiO<Subscript>2</Subscript> and Yb–SiO<Subscript>2</Subscript> systematics in mid-ocean ridge magmas: implications for the origin of oceanic plagiogranite     

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