排序方式： 共有7条查询结果，搜索用时 78 毫秒
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Michael A. Dopita Lee Armus Lisa J. Kewley Jeff A. Rich Dave Sanders Phillip N. Appleton Ben H. P. Chan Vassilis Charmandaris Aaron S. Evans David T. Frayer Justin H. Howell Hanae Inami Joseph A. Mazzarella Andreea Petric Sabrina Stierwalt Jason Surace 《Astrophysics and Space Science》2011,333(1):225-239
This paper describes a pilot study into the spectral energy distribution (SED) fitting and the derivation of physical parameters for 19 galaxies observed as part of the Great Observatories All-sky LIRG Survey (GOALS) survey as observed with the Spitzer Space Telescope. For this we have used the pan-spectral fitting tools developed in a series of papers by Dopita and his co-workers. We show that the standard Lee and Draine ??astronomical silicate?? model cannot provide a good fit to the silicate absorption features as observed in the heavily dust-extinguished (A V??50 mag.) starbursts. We have derived an empirical fit to the ??starburst silicate?? absorption in these objects. This absorption curve is consistent with the silicate grains being systematically larger in starburst environments than in the local Galactic interstellar medium. We demonstrate the sensitivity of the SED fitting to each of the fitted parameters, and derive these parameters for those galaxies which do not have an embedded AGN. This technique is simple and provides reasonably robust and uniform parameters for the starburst, especially as far as the star formation rate, population of old stars, compactness of the starburst region and total foreground extinction are concerned. However, the chemical abundances and the optical extinction cannot be reliably determined by this analysis, and optical SEDs will also be required to provide a complete characterization of the starburst region and of the surrounding galaxy. 相似文献
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Geomagnetic (magnetic susceptibility), geoelectrical (resistivity and conductivity, self-potential/SP, induced polarization/IP), and radiometric measurements (gamma radiation of K, U, and Th) are well adapted to the needs and wants of geoscientists and exploration geologists, in particular, who widely use them in wireline tools and for ground surveys. Miniaturization of technical components resulted in the production of handheld devices which enable field geologists to an improving of the mineralogical and chemical database and the efficiency of the routine work in the field or at a drill site. The tools and devices used by a field geologist are categorized and presented in a tripartite set. The tools for routine field work with “hammer and laptop” belong to the A-level kit. The handheld devices under consideration constitute an intermediate level (B-level) to enhance the mineralogical and chemical database using physical methods. More advanced level applications make use of short-wave infra-red mineral analyzers or portable X-ray fluorescence devices (C-level). Handheld tools are designed for one-dimensional (cross-sectioning) and two-dimensional (mapping) surveys as well as drill core and cuttings examinations during terrain analysis. They can be operated in foot-borne surveys by one field geologist and the obtained data interpreted without an exuberant computing capacity. In the present overview, siliciclastic rocks and residual deposits have been singled out for their good response to the afore-mentioned methods. Their practical use is demonstrated by means of some case histories, each standing for a particular sedimentary lithology and discussed in combination with similar applications from literature: mixed-type (calcareous) siliciclastic rocks from Mesozoic–Cenozoic basins, SE Germany; residual argillaceous/kaolin deposits on top of granites of the Variscan basement, SE Germany; Neogene red-bed sediments from the promontory of the Tien Shan, East Uzbekistan; and Cretaceous gray-bed sediments with coal seams from the Baganuur basin, Central Mongolia. Cobweb diagrams, histograms, ternary diagrams, simple x-y plots and x-y plots in combination with spider diagrams have proved to be the most suitable ways when it comes to combine the data obtained from various methods and to illustrate these results for further interpretation on screen. The geophysical methods are discussed as to their strong and weak points to cater for a solution in three important subject matters of applied and genetic sedimentology: (1) constraining the redox regime, (2) determination of the lithology and mineralogy, (3) and provenance analysis and lithostratigraphy. Magnetic methods have proved to be useful for all objectives (1, 2, and 3), gamma spectrometry can successfully be applied for objectives 1 and 2, and micro-resistivity contributes significantly to solutions of objective 2. Magnetic and gamma spectrometric methods do not need any direct contact with the sedimentary rocks and therefore can be correlated with equivalent airborne surveys and are less depending on the wetability of the substrate and climate than the geoelectrical methods under study. The final goal of this review is to create a matrix of applicability of the methods and enable the field geologist to select the most suitable type of geophysical measurement or combination of tools for a solution to one of the three issues as a function of the sediment types under study. 相似文献
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Numerical models of mantle convection that include the ‘basalt barrier’ mechanism are explored for Venus. The ‘basalt barrier’ mechanism is due to the positive buoyancy of subducted basaltic crust between the mantle depths of 660 and 750 km. The inclusion of this mechanism in models of Earth’s evolution has been shown to cause episodic mantle layering early in Earth history and we explore whether it can also operate on Venus. The models presented here include a moderately mobile lithosphere, which is not representative of the current state of Venus, but this allows us to exclude the effects of episodic lithosphere mobility and thus to isolate the effect of the basalt barrier. This is a step in a systematic approach to models with a mostly-static lithosphere. We find the basalt barrier does yield episodically layered mantle convection in some Venus models. The likelihood of episodic layering is increased by Venus high surface temperature and by its less mobile or immobile lithosphere. Surprisingly, secondary differences from Earth, including the lower gravity, density and mantle depth also promote episodic layering. The models suggest that mantle layering and overturns may still be likely to occur in Venus. The breakdown of mantle layering and consequent mantle overturns would lead to dramatic episodes of volcanism, formation of large amounts of crust, and tectonic activity on the planet’s surface, as has been inferred to have happened on Venus around 500 Ma ago from surface morphology and cratering. These results thus suggest that a transient layering of the mantle by the ‘basalt barrier’ mechanism and mantle overturns may be part of the explanation for Venus’s recent resurfacing. 相似文献
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We model the internal thermal evolution of planets with Earth-like composition and masses ranging from 0.1 to 10 Earth masses over a period of 10 billion years. We also characterize the internal activity of the planets by the velocity of putative tectonic plates, the rate at which mantle material is processed through melting zones, and the time taken to process one mantle mass. The more massive the planet the larger its processing rate (?), which scales approximately as ?∝M0.8-1.0. The processing times for all the planets increase with time as they cool and become less active. As would be expected, the surface heat flow scales with planet mass. All planets have similar declines in mantle temperature except for the largest, in which pressure effects cause a larger decline. The larger planets have higher mantle temperatures over all times. The less massive the planet, the larger the decrease in core temperature with time. The core heat flow is also found to decrease more rapidly for smaller planet masses. Finally, rough predictions are made for the time required to generate an atmosphere from estimates of the time to degas water and carbon dioxide in mantle melting zones. The degassing times depend strongly on the initial temperature of the planet, but for the temperatures used in our model all the planets degas within ∼32 Ma after their formation. 相似文献
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Andreea Cetateanu Bogdan-Alexandru Luca Andrei Alin Popescu Angie Page Ashley Cooper Andy Jones 《International journal of geographical information science》2016,30(10):1944-1960
Aim: While studies using global positioning systems (GPS) have the potential to refine measures of exposure to the neighbourhood environment in health research, one limitation is that they do not typically identify time spent undertaking journeys in motorised vehicles when contact with the environment is reduced. This paper presents and tests a novel methodology to explore the impact of this concern.
Methods: Using a case study of exposure assessment to food environments, an unsupervised computational algorithm is employed in order to infer two travel modes: motorised and non-motorised, on the basis of which trips were extracted. Additional criteria are imposed in order to improve robustness of the algorithm.
Results: After removing noise in the GPS data and motorised vehicle journeys, 82.43% of the initial GPS points remained. In addition, after comparing a sub-sample of trips classified visually of motorised, non-motorised and mixed mode trips with the algorithm classifications, it was found that there was an agreement of 88%. The measures of exposure to the food environment calculated before and after algorithm classification were strongly correlated.
Conclusion: Identifying non-motorised exposures to the food environment makes little difference to exposure estimates in urban children but might be important for adults or rural populations who spend more time in motorised vehicles. 相似文献
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A variety of human activities can negatively impact on sensitive karst environments, especially on karst water. To protect such water adequately it is necessary to obtain as much information as possible on the extent of the recharge zones and characteristics of the groundwater flow. The authors experience has shown tracer tests to be a very useful tool in acquiring such information. Three examples from Slovenia are presented in this paper. In the first, an estimate was made of the danger of water contamination resulting from a petrochemical storage depot. In the second, the possible impacts of an area used for military training were studied. In the third, the effects of the construction of a railway line on regionally important water resources were assessed. Besides basic information about the direction and velocity of groundwater flow, some methodological principles were also identified by the studies. In all three test areas sampling was carried out for a lengthy period and continued after the detection of the peak concentrations. The results show that only the use of such lengthy tracer tests enable the definition of those flow paths, which are activated in extreme hydrological conditions. 相似文献
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