Reexamination of the crystal structure of phosgenite,Pb2Cl2(CO3)     

Prof G. Giuseppetti  Prof Carla Tadini 《Mineralogy and Petrology》1974,21(2):101-109

  相似文献   

Soil-water behaviour of sandy soils under semi-arid conditions in the Duero Basin (Spain)     

Antonio Ceballos  Jos Mart&#x;&#x;nez-Fernndez  Fernando Santos  Pilar Alonso 《Journal of Arid Environments》2002,51(4):501

This paper examines the soil-water behaviour of sandy soils representative of a broad area in the Duero river basin (Spain), with semi-arid bioclimatic characteristics. Soil-moisture measurements of the first 25 cm of soil profile were taken using time domain reflectometry (TDR) methodology. The infiltration process was studied by means of field experiments combining rainfall simulations and TDR techniques. Finally, a set of hydrodynamic variables was calculated in the laboratory (i.e. available soil-water content, soil-water-retention curves and hydraulic conductivity).The average available soil-water content is 0·07 cm³ cm⁻³, in accordance with the predominance of the sandy textural fraction (85%). The rainfall simulation experiments show that infiltration prevails over overland flow, with a steady-state infiltration rate higher than rainfall application (40mmh⁻¹) in most cases; a low water-retention capacity was also observed. The evolution of soil-moisture over time indicates a close dependence on intra-annual rainfall variability due to the low water-retention capacity of sandy soils. With a maximum water-storage capacity of around 0·18 cm³ cm⁻³, the soils studied show high sensitivity to dry spells and may remain with <50% of the available soil-water content for several months during the year.  相似文献   

Major Ion Chemistry in a Freshwater Coastal Lagoon from Southern Brazil (Mangueira Lagoon): Influence of Groundwater Inputs   总被引：1，自引：0，他引：1  

Isaac R. Santos  Maria I. Machado  Luis F. Niencheski  William Burnett  Idel B. Milani  Carlos F. F. Andrade  Richard N. Peterson  Jeffrey Chanton  Paulo Baisch 《Aquatic Geochemistry》2008,14(2):133-146

This paper characterizes major ion distributions and investigates whether groundwater exerts a major control on the chemical functioning of Mangueira Lagoon, a large (90 km long), shallow (∼4–5 m deep), and fresh coastal lagoon in southern Brazil. Water volumes equivalent to ∼80% of the total annual input are used in the summer for irrigating nearby rice plantations, the most important regional economic activity. While Na⁺ and Cl⁻ are the major ions in local groundwater, Na⁺ and HCO₃⁻ are the most enriched ions in lagoon water. The ion concentrations measured in Mangueira Lagoon were homogeneous, except for a few samples affected by rainwater and groundwater inputs. A shore-normal transect starting at the pump house of a rice irrigation canal indicated strong groundwater input at this canal. In spite of the small volume contribution (∼2% of precipitation), groundwater discharge accounts for 50–70% of major ion inputs into the lagoon, with ∼70% of the groundwater inputs being anthropogenically derived (e.g., from the rice irrigation canals). This may have serious implications for the management of the coastal water resources from Mangueira Lagoon and other similar areas as groundwater associated with agricultural systems may be contaminated by fertilizers and pesticides. The results imply that groundwater should not be neglected in dissolved species’ budgets even when its volume contribution is small.  相似文献   

Seasonal Influence of the Needle Rush <Emphasis Type="Italic">Juncus roemarianus</Emphasis> on Saltmarsh Pore Water Geochemistry     

Carla M. Koretsky  Douglas Miller 《Estuaries and Coasts》2008,31(1):70-84

Previous studies have shown that saltmarsh macrophytes have a significant influence on sediment biogeochemistry, both through radial release of oxygen from roots and also via primary production and release of labile organic exudates from roots. To assess the seasonal influence of the needle rush, Juncus roemarianus, on saltmarsh sediment geochemistry, pore waters and sediments were collected from the upper 50 cm of two adjacent sites, one unvegetated and the other vegetated by Juncus roemarianus, in a Georgia saltmarsh during winter and summer. Pore waters collected at 1- to 2-cm intervals were analyzed for pH, alkalinity, dissolved phosphate, ammonium, Fe(II), Fe(III), Mn(II), sulfide, sulfate, and organic carbon. Sediments were collected at 5-cm intervals and analyzed for iron distribution in the solid phase using a two-step sequential extraction. The upper 50 cm of the sediment pore waters are mostly sulfidic during both winter and summer. The pore water and sediment geochemistry suggest organic matter degradation is coupled mostly to Fe(III) and sulfate reduction. In summer, there is greater accumulation of alkalinity, sulfide, ammonium, and phosphate in the pore waters and lower levels of ascorbate extractable Fe, which is presumed to be comprised primarily of readily reducible Fe(III) oxides, in the sediments, consistent with higher organic matter degradation rates in summer compared to winter. Lower pH, alkalinity, ammonium, and sulfide concentrations in sediments with Juncus, compared to nearby unvegetated sediments, is consistent with release of oxygen into the Juncus rhizosphere, especially during summer.  相似文献   

Organic carbon accumulation in oligotrophic coastal lakes in southern Brazil during the last century     

Bueno  Carolina  Sanders  Christian J.  Niencheski  Felipe Hax  Andrade  Carlos  Burnett  William  Santos  Isaac R. 《Journal of Paleolimnology》2021,66(1):71-82

Journal of Paleolimnology - We report organic carbon (OC) accumulation rates in three freshwater ecosystems in southern Brazil, along the largest shallow coastal lagoon ecosystem in the world, the...  相似文献   

A general relativistic effect in quasi-spherical objects as the possible origin of relativistic jets     

L. Herrera  N. O. Santos 《Astrophysics and Space Science》2007,310(3-4):251-254

Based on recently reported results, we present arguments indicating that sign changes in proper acceleration of test particles on the symmetry axis and close to the r=2M surface of quasi-spherical objects—related to the quadrupole moment of the source—might be at the origin of relativistic jets of quasars and micro-quasars.  相似文献   

The Rupture Process and Location of the 2003 Zemmouri–Boumerdes Earthquake (Mw 6.8) Inferred from Seismic and Geodetic Data     

Rúben Santos  Bento Caldeira  Mourad Bezzeghoud  José Fernando Borges 《Pure and Applied Geophysics》2015,172(9):2421-2434

  相似文献   

A test for directional-linear independence,with applications to wildfire orientation and size     

Eduardo García-Portugués  Ana M. G. Barros  Rosa M. Crujeiras  Wenceslao González-Manteiga  José Pereira 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(5):1261-1275

A nonparametric test for assessing the independence between a directional random variable (circular or spherical, as particular cases) and a linear one is proposed in this paper. The statistic is based on the squared distance between nonparametric kernel density estimates and its calibration is done by a permutation approach. The size and power characteristics of various variants of the test are investigated and compared with those for classical correlation-based tests of independence in an extensive simulation study. Finally, the best-performing variant of the new test is applied in the analysis of the relation between the orientation and size of Portuguese wildfires.  相似文献   

Associations between outdoor air quality and birth weight: a geostatistical sequential simulation approach in Coastal Alentejo,Portugal   总被引：3，自引：2，他引：1  

Manuel Castro Ribeiro  Pedro Pinho  Esteve Llop  Cristina Branquinho  Amílcar Soares  Maria João Pereira 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(3):527-540

Several environmental health studies suggest birth weight is associated with outdoor air pollution during gestation. In these studies, exposure assignments are usually based on measurements collected at air quality monitoring stations that do not coincide with health data locations. So, estimated exposures can be misleading if they do not take into account the uncertainty of exposure estimates. In this article we conducted a semi-ecological study to analyze associations between air quality during gestation and birth weight. Air quality during gestation was measured using a biomonitor, as an alternative to traditional air quality monitoring stations data, in order to increase spatial resolution of exposure measurements. To our knowledge this is the first time that the association between air quality and birth weight is studied using biomonitors. To address exposure uncertainty at health locations, we applied geostatistical simulation on biomonitoring data that provided multiple equally probable realizations of biomonitoring data, with reproduction of observed histogram and spatial covariance while matching for conditioning data. Each simulation represented a measure of exposure at each location. The set of simulations provided a measure of exposure uncertainty at each location. To incorporate uncertainty in our analysis we used generalized linear models, fitted simulation outputs and health data on birth weights and assessed statistical significance of exposure parameter using non-parametric bootstrap techniques. We found a positive association between air quality and birth weight. However, this association was not statistically significant. We also found a modest but significant association between air quality and birth weight among babies exposed to gestational tobacco smoke.  相似文献   

A Joint Inversion of Ground Deformation and Focal Mechanisms Data for Magmatic Source Modelling     

Flavio Cannavò  Danila Scandura  Mimmo Palano  Carla Musumeci 《Pure and Applied Geophysics》2014,171(8):1695-1704

The paucity of geodetic data acquired on active volcanoes can make the understanding of modelling magmatic systems quite difficult. In this study, we propose a novel approach, which allows improving the parameter estimation of analytical models of magmatic sources (e.g., shape, depth, dimensions, volume change, etc.) by means of a joint inversion of surface ground deformation data and P-axes of focal plane solutions. The methodology is first verified against a synthetic dataset of surface deformation and strain within the medium, and then applied to real data from an unrest episode occurred before the May 13 2008 eruption at Mt. Etna (Italy). The main results clearly indicate the joint inversion improves the accuracy of the estimated source parameters by about 70 %. The statistical tests indicate that the source depth is the parameter with the highest increment of accuracy. In addition, a sensitivity analysis confirms that displacements data are more useful to constrain the pressure and the horizontal location of the source than its depth, while the P-axes better constrain the depth estimation.  相似文献