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151.
A. Gelencsér A. Hoffer G. Kiss E. Tombácz R. Kurdi L. Bencze 《Journal of Atmospheric Chemistry》2003,45(1):25-33
Current climate models seem to underestimate the flux of solar energy absorbed by the global troposphere. All of these models are constrained with the assumption that cloud droplets consist of pure water. Here we demonstrate in a simple laboratory experiment that aromatic hydroxy-acids which are found in continental fine aerosol can react with hydroxyl radicals under typical conditions prevalent in cloud water influenced by biomass burning. The reactions yield colored organic species which do absorb solar radiation. We also suggest that the products of such reactions may be humic-like substances whose presence in continental aerosol has been confirmed but their source mechanisms are still much sought after. We also attempt to give a first order estimate of the enhancement of water absorption at a visible wavelength under atmospheric conditions. 相似文献
152.
Synoptic and mesoscale study of a severe convective outbreak with the nonhydrostatic Global Environmental Multiscale (GEM) model 总被引:1,自引:0,他引:1
A. Erfani A. Méthot R. Goodson S. Bélair K.-S. Yeh J. Côté R. Moffet 《Meteorology and Atmospheric Physics》2003,82(1-4):31-53
Summary ?A nonhydrostatic 4-km version of the Global Environmental Multiscale (GEM) model, with detailed microphysics included, was
used to forecast the initiation, development, and structure of a tornado-producing supercell storm that occurred near Pine
Lake (Alberta, Canada) on 15 July 2000. Examination of observations and comparison with conceptual models indicate that this
storm is a good example of supercell storms that regularly produce summertime severe weather over Alberta.
It was found that the high-resolution model was able to reproduce the early initiation of convective activity along the Rocky
Mountains foothills, as well as the rapid northeastward propagation towards the Pine Lake area and the subsequent intensification
into a supercell storm. The general structures of the forecasted convective system correspond well with conceptual representations
of such events. Overall, this high-resolution forecast of the Pine Lake supercell storm was a significant improvement over
the current operational version of the GEM model (24 km), which was not able to intensify the foothills’ convection into a
supercell storm. Finally, it was found that the nonhydrostatic version of the model produces better trajectory and propagation
speed of the convective system, as compared with the hydrostatic one.
Received March 20, 2001; revised August 24, 2001 相似文献
153.
Frédérick Delay Hélène Housset-Resche Gilles Porel Ghislain de Marsily 《Mathematical Geology》1996,28(1):45-71
A new method for solving the transport equation based on the management of a large numbe of particles in a discretized 2-D domain is presented. The method uses numerical variables to represent the number of particles in a given mesh and is more complex than the 1-D problem. The first part of the paper focuses on the specific management of particles in a 2-D problem. The method also would be valid for three dimensions as long as the medium can be modeled similar to a layered system. As the particles are no longer tracked individually, the algorithm is fast and does not depend on the number of particles present. The numerical tests show that the method is nearly numerical dispersion free and permits accurate calculations even for simulations of low-concentration transport. Because each mesh is considered as a closed system between two successive time steps, it is easy to add adsorption phenomenon without any problem of numerical stability. The model is tested under conditions that are extremely demanding for its operating mode and gives a good fit to analytical solutions. The conditions in which it can be used to best advantage are discussed. 相似文献
154.
The age and thermal history of Cerro Rico de Potosi, Bolivia 总被引:1,自引:0,他引:1
C. G. Cunningham R. E. Zartman E. H. McKee R. O. Rye C. W. Naeser O. Sanjinés V G. E. Ericksen F. Tavera V 《Mineralium Deposita》1996,31(5):374-385
Cerro Rico de Potosi, Bolivia, is the world’s largest silver deposit and has been mined since the sixteenth century for silver,
and for tin and zinc during the twentieth century, together with by-product copper and lead. The deposit consists primarily
of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and
explosion breccia. The deposit is compositionally and thermally zoned, having a core of cassiterite, wolframite, bismuthinite,
and arsenopyrite surrounded by a peripheral, lower-temperature mineral assemblage consisting principally of sphalerite, galena,
lead sulfosalt, and silver minerals. The low-temperature assemblage also was superimposed on the high-temperature assemblage
in response to cooling of the main hydrothermal system. Both the dacite dome and the ore fluids were derived from a larger
magmatic/hydrothermal source at depth. The dome was repeatedly fractured by recurrent movement on the fault system that guided
its initial emplacement. The dome was extruded at 13.8±0.2 Ma (2σ), based on U-Th-Pb dating of zircon. Mineralization and
alteration occurred within about 0.3 my of dome emplacement, as indicated by a 40Ar/39Ar date of 13.76±0.10 Ma (1σ) for sericite from the pervasive quartz-sericite-pyrite alteration associated with the main-stage,
high-temperature, mineralization. The last thermal event able to reset zircon fission tracks occurred no later than 12.5±1.1 Ma
(1σ), as indicated by fission-tract dating. Minor sericite, and magmatic-steam alunite veins, were episodically formed around
11 Ma and between 8.3 and 5.7 Ma; the younger episodes occurring at the time of extensional fracturing at Cerro Rico and widespread
volcanism in the adjacent Los Frailes volcanic field. None of these younger events appear to be significant thermal/mineralizing
events; the exceptionally flat thermal release pattern of 39Ar from sericite and the results of the fission-tract dating of zircon show that none of the younger events was hot enough,
and lasted long enough, to cause significant loss of Ar or annealing of zircon fission tracks. U-Th-Pb dating of zircon cores
indicates a Precambrian progenitor for some zircons, and REE analyses of dated samples of hydrothermally altered dacite show
the presence of a prominent positive Eu anomaly, which constrains interpretations of the origin and evolution of the magmatic/hydrothermal
system.
Received: 14 October 1995/Accepted: 29 January 1996 相似文献
155.
Bernard Henry Grobéty 《Contributions to Mineralogy and Petrology》1997,127(3):237-247
Anthophyllite crystals found in ultramafic lenses of the Lepontine Alps (Switzerland) contain coherent, submicroscopic intergrowths
of ordered and disordered biopyribole polysomes. The chain width distributions of disordered polysomes were analyzed using
high resolution transmission electron microscopy (HRTEM). Chains wider than triple were interpreted as intermediate products
in the transformation of anthophyllite to the triple chain silicate jimthompsonite. The concentration of individual chain
types is strongly correlated with the reaction progress. Based on observed zipper terminations and the transformation rules
given by Veblen and Buseck (1980) a scheme of possible reaction paths leading from anthophyllite to jimthomp sonite is proposed.
The reaction scheme and a simple kinetic model for elementary reactions allow modeling of the observed chain width distributions.
The model suggests that the complex reaction paths involving steps with increasing and decreasing chain width are more important
in the formation of jimthompsonite than the direct transformation from anthophyllite. The wide chains (>triple) occurring
as intermediate products of the multi-step paths are structurally closer to talc than jimthompsonite. The back-transformation
of these wide chains to triple chains is, therefore, a strong argument that jimthompsonite is a stable phase and not only
a metastable intermediate product in the transformation of anthophyllite to talc.
Received: 8 July 1996 / Accepted: 13 December 1996 相似文献
156.
Thierry Rolland Stéphanie Fayolle Arlette Cazaubon Stéphane Pagnetti 《Aquatic Sciences - Research Across Boundaries》1997,59(1):57-73
In a sub-alpine river, the Asse, with an unpredictable discharge regime, chlorophyll, density and taxonomic diversity of both
drifting and periphytic communities were studied from a methodical approach. The investigations based on stamping two close
cross-sections to know their spatial distributions in a heterogeneous bed substrate showed a heterogeneous pattern of colonization
mainly influenced by hydrological variables as the current velocity, the size of the substrata (gravel-pebble-boulder). For
the drifting algae, mainly composed with benthic species temporarily unhooked to the substrata, the heterogeneity of the distribution
was reduced in fast flow which induced a mixing of the whole mass of water.
For the periphyton, some results indicated that the greatest diversity and the highest chlorophyll concentration were found
on pebble substratum where the current velocity was moderate. These results have also shown that the classical methods used
to day for investigations were inadequate for most Mediterranean rivers.
It was really difficult to estimate the water quality from classical index created for use in regular large plain rivers. 相似文献
157.
158.
Eric Barthélemy 《Surveys in Geophysics》2004,25(3-4):315-337
Ocean waves entering the near-shore zone undergo nonlinear and dispersive processes. This paper reviews nonlinear models, focusing on the so-called Serre equations. Techniques to overcome their limitations with respect to the phase speed are presented. Nonlinear behaviours are compared with theoretical results concerning the properties of Stokes waves. In addition, the models are tested against experiments concerning periodic wave transformation over a bar topography and of the shoaling of solitary waves on a beach. 相似文献
159.
Mountain Protection Forests against Natural Hazards and Risks: New French Developments by Integrating Forests in Risk Zoning 总被引:4,自引:0,他引:4
Forests can play a very significant role in protection against natural hazards and risks in mountain lands, especially against erosion and rockfalls. This paper first assesses knowledge concerning the capacity of forests to control natural hazards, with emphasis placed on forest location in catchments or slopes. Zoning aspects are then presented; based on the use of GIS, they allow determining priorities for forestry operations (cuts and biological engineering), in view to setting up an 'optimal management' of mountain forest ecosystems. Finally, an explanation is given of how the results of research are used for the management and planning of mountain ecosystems, illustrated by an example of researcher-practitioner transfer in France. Zoning, prevention, display and regular aspects are developed. On the basis of the experience and knowledge presented here, recommendations are proposed to better take into account the role of mountain forests in the control of natural hazards and risks. It is necessary to have an adapted legislative and economic framework, define priority forest intervention zones and determine an adapted sylviculture. 相似文献
160.
We give some results obtained for the Couplex test cases proposed by the ANDRA. In this paper our aim is twofold. Firstly, to compute the release of nuclides out of the repository by concentrating on the 3D near field (Couplex 2). The simulation of the transport phenomena takes into account the dissolution of the glass containers and congruent emissions of the radio-nuclides including filiation chains and some simplified chemistry. Secondly, it is to use the near field computations in order to simulate the nuclide migrations in a 2D far field (Couplex 3). Coupling in between the two simulations takes into consideration the periodicity of the disposal modules and the geometry of the repository described in Couplex 1. The mixed finite element and discontinuous Galerkin methods are used to solve the convection–diffusion equations. In order to handle the nonlinear precipitation/dissolution term, we developed a new iterative technique that combines Picard and Newton–Raphson methods. 相似文献