ALMA as the ideal probe of the solar chromosphere     

Maria A. Loukitcheva  Sami K. Solanki  Stephen White 《Astrophysics and Space Science》2008,313(1-3):197-200

The very nature of the solar chromosphere, its structuring and dynamics, remains far from being properly understood, in spite of intensive research. Here we point out the potential of chromospheric observations at millimeter wavelengths to resolve this long-standing problem. Computations carried out with a sophisticated dynamic model of the solar chromosphere due to Carlsson and Stein demonstrate that millimeter emission is extremely sensitive to dynamic processes in the chromosphere and the appropriate wavelengths to look for dynamic signatures are in the range 0.8–5.0 mm. The model also suggests that high resolution observations at mm wavelengths, as will be provided by ALMA, will have the unique property of reacting to both the hot and the cool gas, and thus will have the potential of distinguishing between rival models of the solar atmosphere. Thus, initial results obtained from the observations of the quiet Sun at 3.5 mm with the BIMA array (resolution of 12″) reveal significant oscillations with amplitudes of 50–150 K and frequencies of 1.5–8 mHz with a tendency toward short-period oscillations in internetwork and longer periods in network regions. However higher spatial resolution, such as that provided by ALMA, is required for a clean separation between the features within the solar atmosphere and for an adequate comparison with the output of the comprehensive dynamic simulations.  相似文献   

Ichnology of prodeltaic hyperpycnite–turbidite channel complexes and lobes from the Upper Cretaceous Prairie Canyon Member of the Mancos Shale,Book Cliffs,Utah, USA     

Luis A. Buatois  Maria G. Mngano  Simon A. J. Pattison 《Sedimentology》2019,66(5):1825-1860

The Upper Cretaceous Prairie Canyon Member of the Mancos Shale, Book Cliffs, Utah, contain outstanding examples of prodeltaic turbidity and hyperpycnal flow deposits. Sandstone‐rich, heterolithic and mudstone‐rich channel fills occur near the north‐west entrance to Tusher Canyon, Gunnison Butte and Bootlegger Wash. Mudstone‐rich and heterolithic‐rich hyperpycnal channel deposits are mostly unbioturbated, locally displaying a few specimens of Phycosiphon incertum, Protovirgularia dichotoma, Rosselia socialis, Schaubcylindrichnus coronus and Palaeophycus tubularis. Sandstone‐rich channel deposits consist of wave‐reworked turbidites and hyperpycnites, containing Helminthoidichnites tenuis, Lockeia siliquaria, Phycodes isp., Phycosiphon incertum, Protovirgularia dichotoma, Rosselia socialis, Skolithos linearis and Fugichnia. Scolicia isp. and Chondrites isp. occur locally. Strata along the south‐west entrance of Tusher Canyon record deposition in a prodelta turbidite lobe, but far from its axis. With the exception of a few specimens of Ophiomorpha isp., bioturbation is restricted to the top of the succession, where Curvolithus simplex, Gyrochorte comosa, Lockeia siliquaria, Palaeophycus tubularis and Ptychoplasma excelsum occur. Strata at Hatch Mesa record deposition in a hyperpycnal lobe, near to its axis. Sandstone beds include Curvolithus simplex, Gyrochorte comosa, Ophiomorpha nodosa, Palaeophycus tubularis, Phycosiphon incertum, Protovirgularia dichotoma, Ptychoplasma excelsum, Schaubcylindrichnus freyi, Skolithos linearis, large specimens of Rosselia socialis and indeterminate crustacean burrows. Chondrites isp. is present in the mudstone. High rates of both episodic and sustained sedimentation, degree of substrate consolidation, freshwater discharge and water turbidity are the most important stress factors in both channels and lobes. Taxonomic composition, uneven distribution of bioturbation through the successions, and overall low ichnodiversity help to distinguish these prodeltaic deposits from bathymetrically equivalent offshore strata in the same basin. Hyperpycnal flow deposits are formed in a wide variety of environmental settings, therefore displaying high ichnological variability. Such variability is summarized by characterising ichnofaunas from four different depositional settings: (i) lakes; (ii) shelf deltas; (iii) shelf‐edge deltas; and (iv) deep‐marine systems.  相似文献   

A SOLAR α - ω DYNAMO STUDY AND ITS TRANSITION TO CHAOS     

Grassmugg  Maria  Hanslmeier  Arnold  Laback  Otto 《Solar physics》1997,174(1-2):437-441

In this contribution we present a nonlinear dynamo model, described by an infinite dimensional system of differential equations, whose solutions depend on the essential parameter D, the dynamo number. The solutions and the bifurcation points of the system are determined with the help of a new developed computer code. We show that, depending on D, stationary, oscillatory and chaotic solutions, which are characterized by Lyapunov exponents, result. We find that the solar dynamo may operate either in the chaotic or in the stable limit cycle domain, depending on the characteristic value of the dynamo number or the motion of the convection zone.  相似文献   

Strukturuntersuchung an einer Hornblende aus dem eklogitischen Gestein von Stramez,südliche Koralpe     

Felix Trojer  Eva Maria Walitzi 《Mineralogy and Petrology》1965,10(1-4):233-240

Zusammenfassung Eine Strukturuntersuchung auf Grund zweidimensionaler Fouriermethoden bestätigt für die Hornblende aus dem eklogitischen Gestein von Stramez die vermutete kristallchemische Formel, wobei sich die Position A in 10-Koordination als besetzt erweist. Außerdem ist für die 6-koordinierten Kationen eine nichtstatistische Besetzung der Atomlagen wahrscheinlich.

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Summary An investigation by two-dimensional Fourier methods of a hornblende, occurring in eclogitic rocks at Stramez, Saualpe, confirms an atomic arrangement, which shows the 10-coordinated position A being occupied. For the cations in 6-coordination a nonstatistical distribution may be assumed.

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Herrn Professor Dr.F. Machatschki zum 70. Geburtstag gewidmet  相似文献   

Arsenic pollution in Patos Lagoon estuarine sediments, Brazil     

Mirlean N  Andrus VE  Baisch P  Griep G  Casartelli MR 《Marine pollution bulletin》2003,46(11):1480-1484

Arsenic distribution in sediments of the Mirim-Patos lagoonal system is investigated. Deposits of fresh water Mirim Lagoon and those of the fresh water part of the Patos Lagoon contain 2.5 and 7.7 mg kg(-1), respectively, on average of total arsenic. In contrast, estuarine sediments of the Patos Lagoon are evidently contaminated by arsenic in high concentrations (up to 50 mg kg(-1)), and about 80% of the arsenic there is found in a bioavailable form. Analytical data coupled with direct, visual observations of estuarine water contamination by raw phosphorites and fertilizers suggest that the major source of arsenic in the estuarine sediments originated from the fertilizer industry.  相似文献   

Carbonate systems along nutrient and temperature gradients: some sedimentological and geochemical constraints   总被引：3，自引：0，他引：3  

Maria Mutti  Pamela Hallock 《International Journal of Earth Sciences》2003,92(4):465-475

Research over the past several decades has clearly demonstrated that changes in the ocean environment have had major impacts on carbonate systems. Changes in climate, ocean circulation and seafloor spreading rates have influenced temperature and seawater chemistry, including carbonate saturation state and nutrient availability, and thereby have determined boundary conditions for the biota that form carbonate platforms. In turn, the biota determine accumulation rates and facies zonations, thus controlling platform geometry and facies dynamics. In the first section of this paper, we examine how nutrient availability influences carbonate facies associations. We first discuss the role of temperature and nutrient gradients in the modern ocean and their influence on biotic associations. Then we discuss how carbonate sedimentation can be characterized along nutrient gradients. In the second section, we review proxies currently used to reconstruct paleoproductivity in open ocean environments and discuss their applicability to neritic carbonate systems. We highlight the variety of existing proxies and their limitations, and suggest that multiple lines of evidence are needed for valid interpretations. Our short review discusses sedimentological, biogenic, and geochemical proxies that can be used to reconstruct past nutrient fluxes and to constrain paleoceanographic controls over the distribution of carbonate associations. However, it also reveals that more data and case studies are needed that integrate shallow and deep water carbonate sequences and elucidate the links between temperature vs. nutrient supplies changes and facies in ancient carbonate sequences.

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Maria MuttiEmail:

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Knowledge Recovery for Continental-Scale Mineral Exploration by Neural Networks     

Bougrain  Laurent  Gonzalez  Maria  Bouchot  Vincent  Cassard  Daniel  Lips  Andor L. W.  Alexandre  Frédéric  Stein  Gilbert 《Natural Resources Research》2003,12(3):173-181

This study is concerned with understanding of the formation of ore deposits (precious and base metals) and contributes to the exploration and discovery of new occurrences using artificial neural networks. From the different digital data sets available in BRGM's GIS Andes (a comprehensive metallogenic continental-scale Geographic Information System) 25 attributes are identified as known factors or potential factors controlling the formation of gold deposits in the Andes Cordillera. Various multilayer perceptrons were applied to discriminate possible ore deposits from barren sites. Subsequently, because artificial neural networks can be used to construct a revised model for knowledge extraction, the optimal brain damage algorithm by LeCun was applied to order the 25 attributes by their relevance to the classification. The approach demonstrates how neural networks can be used efficiently in a practical problem of mineral exploration, where general domain knowledge alone is insufficient to satisfactorily model the potential controls on deposit formation using the available information in continent-scale information systems.  相似文献   

Multiple Collector ICP-MS: Introduction to Instrumentation, Measurement Techniques and Analytical Capabilities   总被引：3，自引：0，他引：3  

Mark Rehkämper  Maria Schönbächler  Claudine H. Stirling 《Geostandards and Geoanalytical Research》2001,25(1):23-40

The technique of multiple collector ICP-MS (MC-ICP-MS) has recently attracted much attention, because it permits the precise measurement of isotope compositions for a wide range of elements. This review article discusses the particular advantages of this mass spectrometric technique and provides an overview of the instrumentation. The performance characteristics of MC-ICP-MS instruments and procedures for the correction of instrumental mass discrimination are covered. The strategies that are employed to avoid analytical artefacts from spectral interferences and matrix effects are also considered. A range of applications are then discussed, to provide an overview of the versatility of this mass spectrometric technique. The diversity of applications, which include the measurement of radiogenic and stable isotope ratios, the determination of trace element concentrations by isotope dilution and in situ isotopic measurements using a laser ablation system, highlight the great relevance of MC-ICP-MS to present and future research in various Earth science disciplines.  相似文献   

Gas Chromatography-Mass Spectrometry in Geochemical Investigation of Organic Matter of the Grodziec Beds (Upper Carboniferous), Upper Silesian Coal Basin, Poland     

Monika J. Fabianńska  Gra?yna Bzowska  Aniela Matuszewska  Maria Racka  Urszula Skr?t 《Chemie der Erde / Geochemistry》2003,63(1):63-91

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Model biomimetic studies of templated growth and assembly of nanocrystalline FeOOH   总被引：1，自引：0，他引：1  

Maria Nesterova  John Moreau  Jillian F Banfield 《Geochimica et cosmochimica acta》2003,67(6):1185-1195

We studied biomimetic mineralization of self-assembling polymer matrices in order to develop a model for biomineralization of iron oxides in nature. High-resolution transmission electron microscopy (HRTEM), rheology, and fluorescence probe analyses show self-assembly of acidic polysaccharide alginic acid (Alg) to form fibrils in dilute solutions. The resulting Alg fibrils are subsequently mineralized by FeOOH in a biomimetically controlled process. Experiments were conducted in pH 9.2 solutions containing millimolar concentrations of iron at 38°C. The unperturbed state of the hybrid mineral-organic structures was studied by characterization of samples of interfacial films collected from an inorganic-organic interface. Progress of mineralization over a 4-week period was followed by HRTEM, energy-dispersive X-ray analysis, and selected area electron diffraction. Morphologies of hybrid structures determined by HRTEM, X-ray powder diffraction, Fourier transform infrared spectroscopy, energy-dispersive X-ray analysis, and selected area electron diffraction suggest formation of iron (III) oxyhydroxide phases and their assembly through a variety of mechanisms, possibly occurring simultaneously. An initial step involves precipitation of nanometer-scale amorphous particles and two-line ferrihydrite in bulk solution. Some nanoparticles assemble into chains that recrystallize to form akaganeite (β-FeOOH), presumably via a solid-state transformation pathway. Small organic molecules may mediate this process by stabilizing the akaganeite structure and controlling particle assembly. Ferrihydrite particles also bind to acidic polysaccharide fibrils and are transformed to ordered arrays of akaganeite. The parallel orientation of adjacent akaganeite nanocrystals may be inherited from the orientation of precursor ferrihydrite, possibly conferred during attachment of ferrihydrite to the polyacid fibrils. Alternatively, particle-particle interactions may induce orientation, leading to recrystallization. Subsequently, akaganeite is transformed to goethite that is characterized by nanoscale porosity and fine-scale twinning on {021}. Dislocation, twin, and nanopore microstructures are consistent with coarsening by nanoparticle assembly, possibly templated by the substrate. Nanoparticle assembly to generate biomimetic hybrid materials may be relevant to formation of complex natural biominerals in natural systems where mineral nanoparticles, small organic molecules, and more complex polymers coexist.  相似文献