Thermodynamic data for phases in the FeO-MgO-SiO2 system and phase relations in the mantle transition zone

Based on the available experimental data on phase equilibria in the FeO -MgO -SiO₂ system the mixing properties of the solid solutions (olivine, β- and γ-spinel, pyroxene, majorite, ilmenite and perovskite and magnesiowustite), the enthalpies of FeO and fictive FeSiO₃ phases with ilmenite and majorite structures have been assessed. The entropies, temperature dependance of heat capacities for fictive FeSiO₃ end-members were estimated from structural analogies. The calculated phase diagrams for Mg₂SiO₄-Fe₂SiO₄ and MgSiO₃ — FeSiO₃ systems at pressures up to 30 GPa and temperatures between 1000 and 2100 K are quite consistent with the available experimental determinations except for the fine features of the phase diagram at 2073 K.     

Arsenic Speciation in a Contaminated Gold Processing Tailings Dam

Gold recovery in ores containing arsenopyrite releases significant amounts of arsenic into the environment due to mineral processing and oxidation during storage. The extent of arsenic weathering in a tailings dam has been investigated. Speciation of As in surface and pore waters and pond sediments showed that for gold tailings in the dam, As enrichment took place in the pore water relative to the surface water. In pond sediments As was predominantly present as residual arsenopyrite and partly as a substance co-precipitated with iron hydroxide. The arsenic release from the sediment results from a reductive dissolution of the arsenopyrite and Fe oxides. In the surface water, arsenate and arsenite are the main arsenic species (arsenate is dominant), but in the pore waters methylation processes play a significant role. Arsenic transport is accompanied by the transformation of As into the less toxic compounds (methylated species) co-existing with the most toxic species (arsenite).     

Seasonal variations of water quality in a highly populated drainage basin,SE Brazil: water chemistry assessment and geochemical modeling approaches

The São João Drainage Basin is a very important and strategic waterbody located in the Lagos Region, Rio de Janeiro State, one of the most popular tourist regions of Brazil. However, the fast economic and subsequent population growth in that region has created untreated wastes from several anthropogenic activities, which include the trace metals disposal into the surface waterbody. This study aims to relate the major ions and trace metals behavior during a 1-year sampling campaign and to provide information about the sources of chemical constituents and the factors that control their concentrations in the three main fluvial compartments of the drainage basin, including the Juturnaíba Reservoir which has a crucial role for water supply in the Lagos Region. The chemical data reveal that rainfall is the main factor responsible for the physicochemical parameters and the water dissolved constituent’s variations. The geological and anthropogenic factors which are the main sources of water constituents were assessed by the Inorganic Chemical Index. Those data corroborate the great influence of rainfall and reveal the importance of anthropogenic sources of chemical constituents in some parts of the Juturnaíba Reservoir. The geochemical modeling suggests that hydrolysis reactions are primarily responsible for the trace metals availability in the three fluvial compartments in both dry and wet seasons, followed by carbonate and sulfate complexation.     

Modified Chaplygin gas and solvable F-essence cosmologies

The Modified Chaplygin Gas (MCG) model belongs to the class of a unified models of dark energy and dark matter. In this paper, we have modeled MCG in the framework of f-essence cosmology. By constructing an equation connecting the MCG and the f-essence, we solve it to obtain explicitly the pressure and energy density of MCG. As special cases, we obtain both positive and negative pressure solutions for suitable choices of free parameters. We also calculate the state parameter which describes the phantom crossing.     

Features of the Comacchio ecosystem transformed during persistent bloom of picocyanobacteria

The big Comacchio lagoons (NW Adriatic coast) have been experiencing a super-dense, long-term bloom of picocyanobacteria (PCB) since 1985. This bloom has caused profound transformations in their ecosystem and has resulted in the loss of valuable fish and clam resources. The composition, density and seasonal dynamics of this bloom and its impact on the ecosystem were studied between spring and autumn 1995 and in the summer of 2001. The density of the blooming phytoplankton assemblages varied from 8 to 35 × 10⁶ cells ml⁻¹, and biomass from 20 to 40 g m⁻³, thus demonstrating a quasi-stable status since 1993. The share of pico + nanocyanobacterial fraction of the total phytoplankton biomass was 98% in spring to early summer, and 92% in autumn. The remaining 0.2–5% comprised eukaryotic nano-algae. All components of the animal food web were found to be drastically depleted in the lagoons. Their biomass range in the open lagoons areas were: 2 to 20 mg m⁻³ of microzooplankton, 10 to 40 mg m⁻³ mesozooplankton, and 5 to 12 g m⁻² macrozoobenthos. The share of filtering fauna in the whole ecosystem metabolism was less than 2%. The malfunction of the deteriorated animal food web resulted in the hyper-accumulation of non-grazed microplankton biomass and detritus in the water column and in bottom sediments. The sequence brought the acceleration of sulfide production and the accumulation of acid soluble sulfides in the upper sediment layer of up to 700–800 mg S dm⁻³ of wet silt. The results of this study provide evidence that the state of ecological collapse continues in the lagoons since 1993.     

On the interface error analysis for finite difference wave simulation

A common way to construct a finite difference scheme is to satisfy a desired order of approximation, typically as high as possible. For linear wave propagation problem approximation together with stability delivers convergence of the same order as approximation. If a wave propagation proses is considered convergence to a plane wave solution can be derived analytically by means of the dispersion analysis. However, mentioned techniques are applicable only to homogeneous media and provide no knowledge of reflection/transmission coefficients. In this paper we prove that the only way to get second order accuracy of the solution for media with discontinuous parameters is to use a conservative finite difference scheme of the second order, and the only way to do this is to use the arithmetic mean for the density and the harmonic mean for the bulk modulus in the vicinity of the interface.     

Magnitude and frequency relations: are there geological constraints to the rockfall size?

There exists a transition between rockfalls, large rock mass failures, and rock avalanches. The magnitude and frequency relations (M/F) of the slope failure are increasingly used to assess the hazard level. The management of the rockfall risk requires the knowledge of the frequency of the events but also defining the worst case scenario, which is the one associated to the maximum expected (credible) rockfall event. The analysis of the volume distribution of the historical rockfall events in the slopes of the Solà d’Andorra during the last 50 years shows that they can be fitted to a power law. We argue that the extrapolation of the F-M relations far beyond the historical data is not appropriate in this case. Neither geomorphological evidences of past events nor the size of the potentially unstable rock masses identified in the slope support the occurrence of the large rockfall/rock avalanche volumes predicted by the power law. We have observed that the stability of the slope at the Solà is controlled by the presence of two sets of unfavorably dipping joints (F3, F5) that act as basal sliding planes of the detachable rock masses. The area of the basal sliding planes outcropping at the rockfall scars was measured with a terrestrial laser scanner. The distribution of the areas of the basal planes may be also fitted to a power law that shows a truncation for values bigger than 50 m² and a maximum exposed surface of 200 m². The analysis of the geological structure of the rock mass at the Solà d’Andorra makes us conclude that the size of the failures is controlled by the fracture pattern and that the maximum size of the failure is constrained. Two sets of steeply dipping faults (F1 and F7) interrupt the other joint sets and prevent the formation of continuous failure surfaces (F3 and F5). We conclude that due to the structural control, large slope failures in Andorra are not randomly distributed thus confirming the findings in other mountain ranges.     

Geomorphic Effects of the Extreme Rainfall Event of 20–21 July, 2004 in the Latnjavagge Catchment, Northern Swedish Lapland

Mass transfers triggered by a rare rainfall event on 20–21 July, 2004, with 58.4 mm of rain within 24 h and 71.7 mm of rain within 48 h in the Latnjavagge catchment (9 km² , 950–1440 m a.s.l.; 68°20'N, 18°30'E) in the higher Abisko mountain region (Swedish Lapland), are quantified and analysed in direct comparison with mean annual mass transfers in this drainage basin. In years without rare rainfall events the Latnjavagge catchment is characterized by restricted sediment availability resulting in low mechanical denudation and mass transfers. During the rare rainfall event of 20–21 July, 2004, major stability thresholds on the slope systems (triggering debris flows and slides) and in the channel systems (break‐up of channel debris pavements and step–pool systems) in the Latnjavagge catchment were passed and mass transfers by debris flows, slides and fluvial debris transport in creeks and channels were several times higher than the mean annual mass transfers in Latnjavagge. In the calculation of longer‐term mass transfers and sediment budgets, rare events like the 20–21 July, 2004 rainfall event have to be considered as essential components. A reliable estimation of the recurrence intervals of such rare events is especially problematic. The general problem of defining an adequate length of process monitoring programmes is pointed out.     

Identifying factors of influence in the spatial distribution of domestic fires

Domestic fires at the city level, being causes for casualties and causing significant material damages, are stored as a point pattern in a GIS. In this paper we apply a statistical point pattern analysis to derive major causes from related layers of information. We fit a G-function to analyse neighbourhood relations and a Strauss process for inferring causal relations. Using open-source software we find significant differences in patterns and explaining factors between the different parts of the day, in particular for different building types and income groups. We conclude that a quantitative spatial model can be fitted and that this provides a useful opportunity for fire brigades to improve planning their efforts.     

Physical mechanisms of submesoscale eddies generation: evidences from laboratory modeling and satellite data in the Black Sea

Ocean Dynamics - The observed evidence of the implementation of three different mechanisms of the submesoscale eddies generation in the Black Sea previously studied by the field research and...