Microplastics' toxic effects and influencing factors on microorganisms in biological wastewater treatment units.

Prior to entering the water body, microplastics (MPs) are mostly collected at the sewage treatment plant and the biological treatment unit is the sewage treatment facility's central processing unit. This review aims to present a comprehensive analysis of the detrimental impacts of MPs on the biological treatment unit of a sewage treatment plant and it covers how MPs harm the effluent quality of biological treatment processes. The structure of microbial communities is altered by MPs presence and additive release, which reduces functional microbial activity. Extracellular polymers, oxidative stress, and enzyme activity are explored as micro views on the harmful mechanism of MPs on microorganisms, examining the toxicity of additives released by MPs and the harm caused to microorganisms by harmful compounds that have been adsorbed in the aqueous environment. This article offers a theoretical framework for a thorough understanding of the potential problems posed by MPs in sewage treatment plants and suggests countermeasures to mitigate those risks to the aquatic environment.

The formation mechanism of twin type shear bands in ß-HMX: molecular rotation and translation.

CONTEXT: Molecular dynamics simulations are performed to clarify the deformation mechanism of ß-HMX crystal in the [Formula: see text] space group setting under uniaxial compression. Nanoscale shear bands whose internal structure is regular enough to form twin with parent structure were found under high strain rate loading in the [010] direction. These deformation twins are formed by the change of lattice orientation due to atomic translation under shear stress, with [Formula: see text] (or [Formula: see text] twin planes and [Formula: see text] (or [Formula: see text] twin directions. Molecular rotation can significantly reduce the activation barrier of twin systems; meanwhile, the change of lattice direction is accomplished by a serial of fractional translation steps. Our results implicate that these factors, such as decreasing the activation energy barrier of twin systems via molecular rotation and new twin systems introducing shear bands, should be considered via applying the crystal plasticity model to investigate the hot spot formation in energetic explosive crystals. METHODS: All simulations were carried out with the MD code package LAMMPS. The non-reactive and flexible molecular force field proposed by Smith and Bharadwaj was adopted to simulate the uniaxial compression of the monoclinic ß-HMX molecular crystal in the [Formula: see text] space group setting on (010) plane along [010] direction. In addition, the Shake algorithm was used to constrain all C-H bonds to the equilibrium length. Two methods, i.e., the Von Mises strain and the relative displacements of molecules, were applied to analyze the structure of twin type shear bands of ß-HMX during compression. Visualization analysis for atomistic simulations was performed by using OVITO.

Individual cascade annealing in BCC tungsten: effects of size and spatial distributions of defects.

To investigate effects of size and spatial distributions of defects from primary damage to annealing of an individual cascade, molecular dynamics (MD) and object kinetic Monte Carlo (OKMC) are applied for simulating cascade generation and annealing. MD cascade simulations of tungsten are carried out with two typical embedded atom method potentials for cascade energies in the range from 0.1 to 100 keV at 300 K. The simulation results show that even though the number of survival defects varies slightly, these two potentials produce very different interstitial cluster (IC) size distribution and defect spatial distribution with cascade energies larger than 30 keV. Furthermore, OKMC is used to model individual cascade annealing. It demonstrates that larger-sized ICs and closely distributed SIAs in the cascade region will induce a much higher recombination fraction for individual cascade annealing. Therefore, special attention should be paid to the size and spatial distributions of defects for primary damage in the multi-scale simulation framework.

Investigation of iron spin crossover pressure in Fe-bearing MgO using hybrid functional.

Pressure-induced spin crossover behaviors of Fe-bearing MgO were widely investigated by using an LDA + U functional for describing the strongly correlated Fe-O bonding. Moreover, the simulated spin crossover pressures depend on the applied U values, which are sensitive to environments and parameters. In this work, the spin crossover pressures of (Mg1-x ,Fe x )O are investigated by using the hybrid functional with a uniform parameter. Our results indicate that the spin crossover pressures increase with increasing iron concentration. For example, the spin crossover pressure of (Mg0.03125,Fe0.96875)O and FeO was 56 GPa and 127 GPa, respectively. The calculated crossover pressures agreed well with the experimental observations. Therefore, the hybrid functional should be an effective method for describing the pressure-induced spin crossover behaviors in transition metal oxides.

Effects of vacancy defects on Fe properties incorporated in MgO.

Distributions of Fe in MgO containing Mg vacancy, O vacancy, and Schottky defect are investigated based on the density functional theory (DFT). Our results show that since Mg vacancy will remove electrons from MgO, Fe tends to get close to Mg vacancy but far from O vacancy. The Mg vacancy can decrease the magnetic moment of iron and change its valence state from 2+ to 3+, which leads to ~5% decrease of Fe-O bond length comparable to the effect of 30 GPa external pressure. Furthermore, iron incorporation can increase the Schottky defect concentration of MgO especially in the environment of the Earth's lower mantle, where ~20 mol% Fe-bearing MgO locates at extreme high temperature conditions.