Heavy metals in soil are naturally occurring but may be enhanced by anthropogenic activities such as mining. Bio-accumulation of heavy metals in the food chain, following their uptake to plants can ...increase the ecotoxicological risks associated with remediation of contaminated soils using plants. In the current experiment sugar cane straw-derived biochar (BC), produced at 700 °C, was applied to a heavy metal contaminated mine soil at 1.5%, 3.0% and 5.0% (w/w). Jack bean (Canavalia ensiformis) and Mucuna aterrima were grown in pots containing soil and biochar mixtures, and control pots without biochar. Pore water was sampled from each pot to confirm the effects of biochar on metal solubility, whilst soils were analyzed by DTPA extraction to confirm available metal concentrations. Leaves were sampled for SEM analysis to detect possible morphological and anatomical changes. The application of BC decreased the available concentrations of Cd, Pb and Zn in 56, 50 and 54% respectively, in the mine contaminated soil leading to a consistent reduction in the concentration of Zn in the pore water (1st collect: 99 to 39 μg L−1, 2nd: 97 to 57 μg L−1 and 3rd: 71 to 12 μg L−1). The application of BC reduced the uptake of Cd, Pb and Zn by plants with the jack bean translocating high proportions of metals (especially Cd) to shoots. Metals were also taken up by Mucuna aterrima but translocation to shoot was more limited than for jack bean. There were no differences in the internal structures of leaves observed by scanning electron microscopy. This study indicates that biochar application during mine soil remediation reduce plant concentrations of potential toxic metals.
•Biochar from sugarcane straw reduces Cd, Pb and Zn plant accumulation.•Biochar increases available P and K in soil.•Biochar decreases the Zn concentration in pore water.
Accumulation of heavy metals in unconsolidated soils can prove toxic to proximal environments, if measures are not taken to stabilize soils. One way to minimize the toxicity of metals in soils is the ...use of materials capable of immobilizing these contaminants by sorption. Biochar (BC) can retain large amounts of heavy metals due to, among other characteristics, its large surface area. In the current experiment, sugarcane-straw-derived biochar, produced at 700 °C, was applied to a heavy-metal-contaminated mine soil at 1.5, 3.0, and 5.0 % (w/w). Jack bean and Mucuna aterrima were grown in pots containing a mine contaminated soil and soil mixed with BC. Pore water was sampled to assess the effects of biochar on zinc solubility, while soils were analyzed by DTPA extraction to confirm available metal concentrations. The application of BC decreased the available concentrations of Cd, Pb, and Zn in the mine contaminated soil leading to a consistent reduction in the concentration of Zn in the pore water. Amendment with BC reduced plant uptake of Cd, Pb, and Zn with the jack bean uptaking higher amounts of Cd and Pb than M. aterrima. This study indicates that biochar application during mine soil remediation could reduce plant concentrations of heavy metals. Coupled with this, symptoms of heavy metal toxicity were absent only in plants growing in pots amended with biochar. The reduction in metal bioavailability and other modifications to the substrate induced by the application of biochar may be beneficial to the establishment of a green cover on top of mine soil to aid remediation and reduce risks.
Through the last years, it was demonstrated that quantum corrections of entropy, represented by logarithmic and power law corrections terms, constituted an association between semi-classical entropic ...areas and the curvature correction in Einstein–Hilbert’s Lagrangian and vice-versa. Loop quantum gravity approach provided the logarithmic corrections, which arises from quantum and thermal equilibrium fluctuations. On the other hand, Barrow’s entropy was introduced from the fact that the black hole surface can be modified due to quantum gravitational effects. The new exponent
Δ
that appears in Barrow’s entropy is a measure of this perturbation. In this letter we have analyzed the thermodynamical effects of the quantum fluctuations upon the geometry of a Barrow’s black hole. We demonstrated that new formulations of the equipartition law, which corresponds to the horizon energy, can be constructed from both entropic formalisms. Besides, we have calculated the heat capacity for both formulations and we discussed their thermal viability. We have also establish a condition on one of the constant pre-factors of the logarithmic correction.
Time series of environmental measurements are essential for detecting, measuring and understanding changes in the Earth system and its biological communities. Observational series have accumulated ...over the past 2–5 decades from measurements across the world's estuaries, bays, lagoons, inland seas and shelf waters influenced by runoff. We synthesize information contained in these time series to develop a global view of changes occurring in marine systems influenced by connectivity to land. Our review is organized around four themes: (i) human activities as drivers of change; (ii) variability of the climate system as a driver of change; (iii) successes, disappointments and challenges of managing change at the sea‐land interface; and (iv) discoveries made from observations over time. Multidecadal time series reveal that many of the world's estuarine–coastal ecosystems are in a continuing state of change, and the pace of change is faster than we could have imagined a decade ago. Some have been transformed into novel ecosystems with habitats, biogeochemistry and biological communities outside the natural range of variability. Change takes many forms including linear and nonlinear trends, abrupt state changes and oscillations. The challenge of managing change is daunting in the coastal zone where diverse human pressures are concentrated and intersect with different responses to climate variability over land and over ocean basins. The pace of change in estuarine–coastal ecosystems will likely accelerate as the human population and economies continue to grow and as global climate change accelerates. Wise stewardship of the resources upon which we depend is critically dependent upon a continuing flow of information from observations to measure, understand and anticipate future changes along the world's coastlines.
Reversible multiple timescale (MTS) integration algorithms have long been recognized as a straightforward way to increase efficiency and extend accessible timescales in molecular dynamics simulations ...without altering the ensemble distribution sampled. MTS methods are based on the idea that interatomic forces in a system drive motion on numerous timescales, and by decomposing force components according to these timescales and assigning an individual time step to each one, fast, computationally cheaper forces are evaluated more frequently than the slow, expensive forces. As it happens, the largest time step that can be employed in standard MTS methods is fundamentally limited by so-called resonance artifacts that originate in the fastest timescales. Thus, while it should be possible to assign the slowest timescales very large time steps approaching 100 fs in, for example, fully atomistic simulations, resonances impose a practical limit on this step size to around 5–10 fs, which allows for useful but only modest savings in computational overhead. This article will review the basic MTS approach and the origin of resonances and then will provide a perspective on how to solve the resonance problem for molecular dynamics simulations in different ensembles, showing how both statistical and dynamical properties can be generated with very large time steps.
The Alcubierre metric is a spacetime geometry where a massive particle inside a spacetime distortion, called warp bubble, is able to travel at velocities arbitrarily higher than the velocity of ...light, a feature known as the warp drive. This is a consequence of general relativity, which allows for global superluminal velocities but restricts local speeds to subluminal ones as required by special relativity. In this work we solved the Einstein equations for the Alcubierre warp drive spacetime geometry considering the dust matter distribution as source, since the Alcubierre metric was not originally advanced as a solution of the Einstein equations, but as a spacetime geometry proposed without a source gravity field. We found that all Einstein equations solutions of this geometry containing pressureless dust lead to vacuum solutions. We also concluded that these solutions connect the Alcubierre metric to the Burgers equation, which describes shock waves moving through an inviscid fluid. Our results also indicated that these shock waves behave as plane waves.
Fluid dynamics in the warp drive spacetime geometry Santos-Pereira, Osvaldo L.; Abreu, Everton M. C.; Ribeiro, Marcelo B.
The European physical journal. C, Particles and fields,
02/2021, Volume:
81, Issue:
2
Journal Article
Peer reviewed
Open access
The Alcubierre warp drive metric is a spacetime geometry featuring a spacetime distortion, called a warp bubble, where a massive particle inside it acquires global superluminal velocities, or warp ...speeds. This work presents solutions of the Einstein equations for the Alcubierre metric having fluid matter as gravity source. The energy–momentum tensor considered has two fluid contents, the perfect fluid and the parametrized perfect fluid (PPF), a tentative more flexible model whose aim is to explore the possibilities of warp drive solutions with positive matter density content. Santos-Pereira et al. (Eur Phys J C 80:786, 2020) already showed that the Alcubierre metric having dust as source connects this geometry to the Burgers equation, which describes shock waves moving through an inviscid fluid, but led the solutions back to vacuum. The same happened for two out of four solutions subcases for the perfect fluid. Other solutions for the perfect fluid indicate the possibility of warp drive with positive matter density, but at the cost of a complex solution for the warp drive regulating function. Regarding the PPF, solutions were also obtained indicating that warp speeds could be created with positive matter density. Weak, dominant, strong and null energy conditions were calculated for all studied subcases, being satisfied for the perfect fluid and creating constraints in the PPF quantities such that a positive matter density is also possible for creating a warp bubble. Summing up all results, energy–momentum tensors describing more complex forms of matter or field distributions generate solutions for the Einstein equations with the warp drive metric where a negative matter density might not be a strict precondition for attaining warp speeds.
Abstract
We consider a cosmological lepton asymmetry in the form of neutrinos and impose new expected sensitivities on such asymmetry through the degeneracy parameter (ξν) by using some future CMB ...experiment configurations, such as CORE and CMB-S4. Taking the default scenario with three neutrino states, we find $\xi _{\mu } = 0.05 \pm 0.10 \, (\pm \, 0.04)$, from CORE (CMB-S4) at 95 per cent CL, respectively. Also, within this scenario, we evaluate the neutrino mass scale, obtaining that the normal hierarchy mass scheme is privileged. Our results are an update concerning on the cosmological lepton asymmetry and the neutrino mass scale within this context, from which can bring a perspective on the null hypothesis for ξν (and its effects on ΔNeff), where perhaps, ξν may take a non-null value up to 95 per cent CL from future experiments such as CMB-S4. Sensitivity results for CMB-S4 obtained here not including all expected systematic errors.
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