Effects of nitrate on the treatment of lead contaminated groundwater by nanoscale zerovalent iron

Nanoscale zerovalent iron (nZVI) is efficient for removing Pb(2+) and nitrate from water. However, the influence of nitrate, a common groundwater anion, on Pb(2+) removal by nZVI is not well understood. In this study, we showed that under excess Fe(0) conditions (molar ratio of Fe(0)/nitrate>4), Pb(2+) ions were immobilized more quickly (<5 min) than in nitrate-free systems (∼ 15 min) due to increasing pH. With nitrate in excess (molar ratio of Fe(0)/nitrate<4), nitrate stimulated the formation of crystal PbxFe3-xO4 (ferrite), which provided additional Pb(2+) removal. However, ∼ 7% of immobilized Pb(2+) ions were released into aqueous phase within 2h due to ferrite deformation. Oxidation-reduction potential (ORP) values below -600 mV correlated with excess Fe(0) conditions (complete Pb(2+) immobilization), while ORP values ≥-475 mV characterized excess nitrate conditions (ferrite process and Pb(2+) release occurrence). This study indicates that ORP monitoring is important for proper management of nZVI-based remediation in the subsurface to avoid lead remobilization in the presence of nitrate

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Exploring fundamental laws of classical mechanics via predicting the orbits of planets based on neural networks

Neural networks have provided powerful approaches to solve various scientific problems. Many of them are even difficult for human experts who are good at accessing the physical laws from experimental data. We investigate whether neural networks can assist us in exploring the fundamental laws of classical mechanics from data of planetary motion. Firstly, we predict the orbits of planets in the geocentric system using the gate recurrent unit, one of the common neural networks. We find that the precision of the prediction is obviously improved when the information of the Sun is included in the training set. This result implies that the Sun is particularly important in the geocentric system without any prior knowledge, which inspires us to gain Copernicus' heliocentric theory. Secondly, we turn to the heliocentric system and make successfully mutual predictions between the position and velocity of planets. We hold that the successful prediction is due to the existence of enough conserved quantities (such as conservations of mechanical energy and angular momentum) in the system. Our research provides a new way to explore the existence of conserved quantities in mechanics system based on neural networks.Comment: 6 pages, 5 figure

Effect of aging cycle on T800 carbon fiber/epoxy resin composites in seawater environment

The hygrothermal aging of T800 carbon fiber/epoxy resin composites in seawater environment were studied. The prepared specimens were immersed in artificial seawater 70 ℃, 3.5% NaCl solution for 30, 60 and 90 days for corrosion. The mechanical properties of the materials were analyzed by mass change, surface morphology before and after aging, infrared spectroscopy, dynamic mechanical properties, compression test and interlayer shear test. The results show that the moisture absorption rate of T800 carbon fiber/epoxy resin matrix composites in 3.5% NaCl solution is 0.39%, 0.47%, 0.53%. Good adhesion between unaging sample fiber and matrix, and the damage of the interface between the fiber and the matrix become more serious with the increase of time after aging in 3.5% NaCl solution. The glass transition temperature(Tg) is decreased from 189.16 ℃ to 177.54, 171.88 ℃ and 168.06 ℃ after 30, 60 and 90 days aging. After aging with 3.5%NaCl solution, the maximum compressive failure load of specimens for 30, 60 and 90 days is decreased by 3.2%, 8.4% and 15.3%, respectively, and the compressive strength is decreased by 3.0%, 8.2% and 15.9%, respectively. The maximum interlaminar shear failure load is reduced by 3.0%, 9.2% and 14.9%, and the shear strength is reduced by 3.0%, 9.7% and 16.4%, respectively