The meteorites of Alberta     

Caroline Smith 《Meteoritics & planetary science》2010,45(5):915-916

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Direct Sequential Co-simulation with Joint Probability Distributions   总被引：1，自引：1，他引：0  

Ana Horta  Amílcar Soares 《Mathematical Geosciences》2010,42(3):269-292

The practice of stochastic simulation for different environmental and earth sciences applications creates new theoretical problems that motivate the improvement of existing algorithms. In this context, we present the implementation of a new version of the direct sequential co-simulation (Co-DSS) algorithm. This new approach, titled Co-DSS with joint probability distributions, intends to solve the problem of mismatch between co-simulation results and experimental data, i.e. when the final biplot of simulated values does not respect the experimental relation known for the original data values. This situation occurs mostly in the beginning of the simulation process. To solve this issue, the new co-simulation algorithm, applied to a pair of covariates Z ₁(x) and Z ₂(x), proposes to resample Z ₂(x) from the joint distribution F(z ₁,z ₂) or, more precisely, from the conditional distribution of Z ₂(x ₀), at a location x ₀, given the previously simulated value z₁^(l)(x₀)z_{1}^{(l)}(x_{0}) (F(Z₂|Z₁=z₁^(l)(x₀)F(Z_{2}|Z_{1}=z_{1}^{(l)}(x_{0}) ). The work developed demonstrates that Co-DSS with joint probability distributions reproduces the experimental bivariate cdf and, consequently, the conditional distributions, even when the correlation coefficient between the covariates is low.  相似文献   

Element-Enrichment Factors in Lichens from Terceira, Santa Maria and Madeira Islands (Azores and Madeira Archipelagoes)     

B. J. Vieira  M. C. Freitas  A. F. Rodrigues  A. M. G. Pacheco  P. M. Soares  N. Correia 《Journal of Atmospheric Chemistry》2004,49(1-3):231-249

In this study, more than 20 minor and trace elements have been determined by INAA (instrumental neutron activation analysis), in different species of lichens in three Portuguese islands of the Central North Atlantic (Santa Maria, Terceira, and Madeira Islands). The foliose species Parmotrema bangii, Parmotrema robustum, Parmotrema crinitum, Flavoparmelia caperata, Platismatia glauca, and the fruiticose species Ramalina canariensis, Ramalina farinacea, Ramalina implectens, Ramalina pusilla, Cladonia furcata, Cladonia coniocraea, Usnea dasaea, Usnea esperantiana, were the collected species. Samples of superficial soils were also collected and the fraction below 64 m was analysed. The enrichment factors relative to this fraction using Al as the normalising element were calculated. Fruiticose and foliose lichens displayed different EF values concerning bromine and potassium. The first was more enriched in the foliose species while the latter was more enriched in the fruiticose species and was assigned to the physiological response. Enrichment was found for Mg, Cs, As, Hg, Na, Zn, and Cl, in all the species. Lichen-based concentration patterns were shown for Na, Al, Cl, Br, Sb, Ce, and Hg and compared to similar patterns in Portugal mainland. In general, the patterns compared well except for Cl, Na, and Br. Background levels of the epiphytic lichens collected in the islands were obtained.  相似文献   

A finite-volume ELLAM for three-dimensional solute-transport modeling     

Russell TF  Heberton CI  Konikow LF  Hornberger GZ 《Ground water》2003,41(2):258-272

A three-dimensional finite-volume ELLAM method has been developed, tested, and successfully implemented as part of the U.S. Geological Survey (USGS) MODFLOW-2000 ground water modeling package. It is included as a solver option for the Ground Water Transport process. The FVELLAM uses space-time finite volumes oriented along the streamlines of the flow field to solve an integral form of the solute-transport equation, thus combining local and global mass conservation with the advantages of Eulerian-Lagrangian characteristic methods. The USGS FVELLAM code simulates solute transport in flowing ground water for a single dissolved solute constituent and represents the processes of advective transport, hydrodynamic dispersion, mixing from fluid sources, retardation, and decay. Implicit time discretization of the dispersive and source/sink terms is combined with a Lagrangian treatment of advection, in which forward tracking moves mass to the new time level, distributing mass among destination cells using approximate indicator functions. This allows the use of large transport time increments (large Courant numbers) with accurate results, even for advection-dominated systems (large Peclet numbers). Four test cases, including comparisons with analytical solutions and benchmarking against other numerical codes, are presented that indicate that the FVELLAM can usually yield excellent results, even if relatively few transport time steps are used, although the quality of the results is problem-dependent.  相似文献   

Hypsometric Curves as a Tool for Paleosurface Mapping     

Paulo Cesar Soares  Silvana Bressan Riffel 《Mathematical Geology》2006,38(6):679-695

A procedural paleosurface mapping tool, using hypsometric curves and digital elevation models, was developed and applied to three hydrographic basins that erode common areas in the coastal ranges of Brazil, in southeastern South America. The method consists of identifying areas favorable for the occurrence of paleosurfaces and their corresponding surficial formations as correlated to specific erosion events. Attributes from hypsometric curves, and logarithmic functions fitted to proper curve segments, are combined with common morphometric properties of paleosurfaces given a set of criteria. Zones satisfying the criteria are mapped as pertaining to specific paleosurfaces. Field survey confirms the agreement between predicted and observed occurrence and absence of paleosurfaces.  相似文献   

River dissolved and solid loads in the Lesser Antilles: New insight into basalt weathering processes   总被引：1，自引：0，他引：1  

Stareh Rad  Pascale Louvat  Caroline Gorge  Jrme Gaillardet  Claude Jean Allgre 《Journal of Geochemical Exploration》2006,88(1-3):308

We present here the first available estimations of chemical weathering and associated atmospheric CO₂ consumption rates as well as mechanical erosion rate for the Lesser Antilles. The chemical weathering (100–120 t/km²/year) and CO₂ consumption (1.1–1.4 × 10⁶ mol/km²/year) rates are calculated after subtraction of the atmospheric and hydrothermal inputs in the chemical composition of the river dissolved loads. These rates thus reflect only the low-temperature basalt weathering. Mechanical erosion rates (approx. 800–4000 t/km²/year) are estimated by a geochemical mass balance between the dissolved and solid loads and mean unaltered rock. The calculated chemical weathering rates and associated atmospheric CO₂ consumption rates are among the highest values worldwide but are still lower than those of other tropical volcanic islands and do not fit with the HCO₃⁻ concentration vs. 1/T correlation proposed by Dessert et al. (2001). The thick soils and explosive volcanism context of the Lesser Antilles are the two possible keys to this different weathering behaviour; the development of thick soils limits the chemical weathering and the presence of very porous pyroclastic flows allows an important water infiltration and thus subsurface weathering mechanisms, which are less effective for atmospheric CO₂ consumption.  相似文献   

Bayesian and multivariate methods applied to favorability quantification in Recôncavo Basin and Ribeira Belt, Brazil     

Sidnei Pires Rostirolla  Paulo César Soares  Hung Kiang Chang 《Natural Resources Research》1998,7(1):7-24

A methology to define favorable areas in petroleum and mineral exploration is applied, which consists in weighting the exploratory variables, in order to characterize their importance as exploration guides. The exploration data are spatially integrated in the selected area to establish the association between variables and deposits, and the relationships among distribution, topology, and indicator pattern of all variables. Two methods of statistical analysis were compared. The first one is the Weights of Evidence Modeling, a conditional probability approach (Agterberg, 1989a), and the second one is the Principal Components Analysis (Pan, 1993). In the conditional method, the favorability estimation is based on the probability of deposit and variable joint occurrence, with the weights being defined as natural logarithms of likelihood ratios. In the multivariate analysis, the cells which contain deposits are selected as control cells and the weights are determined by eigendecomposition, being represented by the coefficients of the eigenvector related to the system’s largest eigenvalue. The two techniques of weighting and complementary procedures were tested on two case studies: 1. Recôncavo Basin, Northeast Brazil (for Petroleum) and 2. Itaiacoca Formation of Ribeira Belt, Southeast Brazil (for Pb-Zn Mississippi Valley Type deposits). The applied methdology proved to be easy to use and of great assistance to predict the favorability in large areas, particularly in the initial phase of exploration programs.  相似文献   

Decompression experiments as an insight into ascent rates of silicic magmas     

Caroline Martel  Burkhard C. Schmidt 《Contributions to Mineralogy and Petrology》2003,144(4):397-415

An experimental study of H₂O exsolution, bubble growth and microlite crystallisation during ascent (decompression) of silicic magmas in the volcanic conduit is presented. Isobaric and decompression experiments were performed on a rhyolitic melt at 860 °C, NNO+1, H₂O saturation, and pressures between 15 and 170 MPa. Two sets of decompression experiments were performed, with decompression rates varying between 0.001 and 960 MPa/min: (1) from 150 to 50 MPa (high-pressure decompression), and (2) from 50 to 15 MPa (low-pressure decompression). The experiments highlight incomplete H₂O exsolution for decompression rates>100 MPa/min, incomplete bubble growth for decompression rates>0.1 MPa/min, crystal nucleation time lags, and incomplete chemical re-equilibration to final pressures. The observed crystallisation process, i.e. growth versus nucleation, depends on the decompression range. Indeed, decompression-induced crystallisation during high-pressure decompressions is dominated by growth of existing crystals, whereas during low-pressure decompressions crystal nucleation is the dominating process. This study provides a means to infer magma ascent rates in eruptions of silicic magmas through a combined petrologic and experimental approach.  相似文献   

P and S tomography using normal-mode and surface waves data with a neighbourhood algorithm   总被引：1，自引：0，他引：1  

Caroline Beghein  Joseph S. Resovsky  Jeannot Trampert 《Geophysical Journal International》2002,149(3):646-658

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Meteorological inventory of rain-on-snow events in the Canadian Arctic Archipelago and satellite detection assessment using passive microwave data     

Caroline Dolant  A. Langlois  L. Brucker  A. Royer  A. Roy  B. Montpetit 《自然地理学》2018,39(5):428-444

The spatial and temporal distributions of rain-on-snow (ROS) events across the Canadian Arctic Archipelago (CAA) remain poorly understood owing to their sporadic nature in time and space. This situation motivated the development of remote sensing detection algorithms. This paper uses a large meteorological dataset across the CAA to adapt an existing ROS-detection algorithm developed in a previous study by our group. Results highlight the spatial distribution and evolution of ROS occurrences reported since 1985 at 14 weather stations across the CAA. Results show that >600 ROS events were inventoried since 1985, for which >70% were classified as pure rain (liquid form) and 30% as mixed precipitation (solid/liquid). Of the pure rain events, 75% occurred during spring, 14% during fall, 8% during summer and <1% during winter. Such events can have significant impacts on ungulate grazing conditions through the creation of ice layers, causing serious problems for caribou calf survival, especially during the migration period. This paper introduces an adaptation for larger scale Arctic application of a detection algorithm (sensitivity analysis on the detection threshold) with an error of ~5%. The validation, however, remains limited due to a short study period and limited number of sites.  相似文献