Dark energy as space-time curvature induced by quantum vacuum fluctuations

It is shown that quantum vacuum fluctuations give rise to a curvature of space-time equivalent to a cosmological constant, that is a homogeneous energy density ρ and pressure p fulfilling −p=ρ>0. The fact that the fluctuations produce curvature, even if the vacuum expectation of the energy vanishes, is a consequence of the non-linear character of the Einstein equation. A calculation is made, involving plausible hypotheses within quantized gravity, which establishes a relation between the two-point correlation of the vacuum fluctuations and the space-time curvature. Arguments are given which suggest that the density ρ might be of order the “dark energy” density currently assumed to explain the observed accelerated expansion of the universe.     

Heavy metal mobility assessment in sediments from the Odiel River (Iberian Pyritic Belt) using sequential extraction

The Tessier sequential extraction scheme (SES) was applied to sediments from the Odiel river catchment (Iberian Pyritic Belt, SW of Spain), one of the most acid rivers on Earth, to assess the chemical association (exchangeable, carbonatic, bound to manganese and iron oxides, bound to organic matter and residual mineral) of heavy metals (Zn, Cd, Pb, Cu, Cr, Mn, Ni, Fe, and Hg). Sediments are very heterogeneous in their textural characteristics, showing different grain size. Twenty-seven samples were studied from from areas along the Odiel River, from the source to the mouth, with special interest in the Odiel Marshes Natural Park due to its ecological significance. Samples were classified as sandy (especially at the river mouth with low iron oxide and organic matter content) and clay-silty (in the middle of the river catchment with high iron oxide content). The numerous sandy samples with low pH values explain the low levels of metals upstream, although potential metals contributions arise from mining and ore. However, the presence of sulfate in the mining area and carbonate at the mouth may explain the high presence of lead and iron in these sandy zones. Some percentage of mobile Ni, Cu, and Zn were detected in the mining area, but the elevated relative percentage of exchangeable Cd in the estuary is even more remarkable. The percentage of Zn bound to carbonate is considerable in the catchment but especially in the estuary. However, Cu is only detected in the carbonate phase downstream, in spite of the low concentration of carbonate, which represents a drawback in the application of the Tessier SES to these types of samples. Finally, relatively high percentages of residual, non-mobile, Hg and Pb were observed, in the estuarine and mining areas, respectively. Sand, lime, and clay fractions of representative samples from Areas I, II, and III were used in a metal speciation study. Mainly, the elements analyzed had accumulated in the non-residual fractions. In the mining area of the Pyrite Belt, the elements analyzed are mainly bound to Fe–Mn oxides (Fe + Mn + Cu + Cr + Pb + Mn ± Zn) and the organic matter/sulfide fraction (Ni + Zn + Hg ± Cd), independent of sediment grain size. In conclusion, we show that the results of the study of chemical speciation in sediments from acid rivers are independent of the sediment grain size considered.     

Experimental study of the generation, damping, and reflexion of a solitary wave

In a (36 m × 0.55 m × 1.30 m) channel we did numerous experiments to study the generation, propagation, damping and reflexion along a wall of a solitary wave. The data are compared with the available analytical or numerical results. From a given paddle movement, the Inverse Scattering Method is proved to provide with great accuracy the number and amplitude of the generated solitary waves. Then, studying the damping of the wave due to dispersion and viscosity, we find that the formula proposed by Keulegan describes the phenomenon well. This last result enables us to modify the KdV equation with the second term used by Kakutani and Matsuuchi, to compute the solitary wave and tail generated by a given intumescence or a given paddle movement. We notice that the computations fit well with the experimental measurements. Finally, we study the reflexion of a solitary wave from a plane vertical wall. To obtain good experimental data requires great care, but the results agree with the analytical prediction. The reflexion appears to be a rather complex phenomenon and needs further theoretical developments. We present here some experimetal data which confirm recent numerical observations (Mirie and Su, Fenton and Rienecker).     

New ICP‐MS Results for Trace Elements in Five Iron‐Formation Reference Materials

Iron formations (IFs) typically contain low mass fractions of most trace elements, including the rare earth elements (REE), and few publications describe analytical methods dedicated to this matrix. In this study, we used bomb and table‐top acid dissolution procedures and ICP‐MS to determine the mass fractions of trace elements in IF reference materials FER‐1, FER‐2, FER‐3, FER‐4 and IF‐G. The full digestion of the IF samples with the bomb procedure required the addition of a small amount of water together with the acids. The results obtained by this method mostly agreed statistically with published values. The most remarkable exception was the higher values obtained for the heavy REE in FER‐3. The recoveries of the REE obtained with the table‐top procedure were slightly higher than those of the bomb digestion, except for the values of the heavy REE in FER‐3 and FER‐4, which were up to 30% lower than published values. Sintering of the samples with sodium peroxide was performed to determine the REE, but the results tended to be lower than those derived following acid digestion. On the whole, the recoveries showed dependence on the conditions of digestion, but subtle differences in trace mineral composition between samples also exerted influence on the analytical results for trace elements.     

The mobility of rare-earth and other elements in the process of alteration of rhyolitic rocks to bentonite (Lebombo Volcanic Mountainous Chain, Mozambique)

Ca-type bentonite deposits of economic interest occur associated with rhyolitic rocks in the Lebombo volcanics. From previous geological studies on the deposits, besides the economic aspects, little is known about the main formation mechanism of beds of bentonite that can be more than 15 m thick, in some places. Chemical analyses of bentonite samples indicate that elements such as Ca, Mg, Sr, Zn, Cu and Sc are markedly enriched in bentonite in comparison to the parent rock. Other elements such as K, Na, Rb and Ba are depleted in bentonite. HREE (Yb, Lu) and Y are depleted in the bentonite samples, as well as Cs, Rb, Ta, U, Ba, Co, Cr and Pb. Concentrations of the LREE (La, Ce, Nd, Sm, Eu), Sc and Ga are slightly higher in the bentonites than in the parent rocks. The chondrite-normalized REE patterns show identical trends both in the rhyolites and bentonites samples. Alteration of the parent rocks to bentonite is associated with leaching and subsequent removal of, principally, K and Na in open-system conditions.     

Analyzing the spatial interactions between rainfall levels and flooding prediction in São Paulo

Rainfall is one of the primary triggers for many geological and hydrological natural disasters. While the geological events are related to mass movements in land collapse due to waterlogging, the hydrological ones are usually assigned to runoff or flooding. Studies in the literature propose predicting mass movement events as a function of accumulated rainfall levels recorded at distinct periods. According to these approaches, a two-dimensional rainfall levels feature space is segmented into the occurrence and non-occurrence decision regions by an empirical critical curve (CC). Although this scheme may easily be extended to other purposes and applications, studies in the literature need to discuss its use for flooding prediction. In light of this motivation, the present study is unfolded in (1) verifying that defining CCs in the rainfall levels feature space is a practical approach for flooding prediction and (2) analyzing how geospatial components interact with rainfall levels and flooding prediction. A database containing the rainfall levels recorded for flooding and non-flooding events in São Paulo city, Brazil, regarding the period 2015–2016, was considered in this study. The results indicate good accuracy for flooding prediction using only partial rain, which can be improved by adding physical characteristics of the flooding locations, demonstrating a direct correlation with spatial interactions, and rainfall levels.