Towards better predicting the settling velocity of film-shaped microplastics based on experiment and simulation data.

The properties of microplastics determine their settling velocities and affect the fates and migration pathways of microplastics. This paper has simulated the settling velocities of film-shaped microplastics, which are present in natural aquatic environments. The numerical results provided more data to fit the terminal settling velocities of film-shaped microplastics. Comparison between the particle definition and the equivalent spherical diameter confirmed that the particle definition is more suitable for film-shaped microplastics. In the transitional flow regime, CD decreases linearly with Re. As Re further increases, CD gradually converges at approximately 1.20. By integrating the experimental and simulated data, a new explicit formula for predicting the settling velocity of film-shaped microplastics has been presented with the optimal shape parameter f. The presented formula achieves better performance (MAPE = 6.6 %, RMSE = 16.8 %, and R2 = 0.99) than the existing formulas for settling velocity for film-shaped microplastics, closely rivaling that of the ensemble learning algorithm.

Settling processes of cylindrical microplastics in quiescent water: A fully resolved numerical simulation study.

The settling process of marine microplastics (MPs) is crucial research concerning the transport and movement of MPs. The settling processes of MP fibers that possess a cylindrical geometry are affected by environmental factors and properties. In this study, a three-dimensional numerical model for the still water settling of MPs with complex shapes was constructed using the lattice Boltzmann method (LBM) and the immersed boundary method (IBM). The fully resolved settling simulation of cylindrical MPs was achieved, and the model results demonstrated good agreement with the semi-empirical settling velocity formulas. Based on the simulation results, the critical aspect ratio of the cylindrical MP was found to be between 0.93 and 0.94. Near this critical aspect ratio, there is a decline in the drag force. Additionally, it was found that the angular displacement and aspect ratio influence horizontal movement but not the vertical settling velocity, while the density only affects vertical movement.

Complete genomic sequence of Dracaena mottle virus, a distinct badnavirus.

The genome of Dracaena mottle virus (DrMV) was cloned from infected Dracaena sanderiana plants, and its complete nucleotide sequence was determined and analyzed. The circular DNA genome consists of 7531 base pairs (bp) and possesses seven putative open reading frames (ORFs) on the plus-strand that potentially encode proteins of 17.6, 14.9, 215.0, 11.9, 11.3, 16.1, and 11.0 kDa, respectively. ORF 3, the largest ORF, encodes a putative polyprotein that contains sequences for viral aspartyl proteinase, reverse transcriptase (RT) and ribonuclease H (RNase H), characteristic of pararetroviruses. Phylogenetic analysis based on the amino acid sequence of ORF 3 showed that DrMV is related to other badnaviruses. However, the nucleotide sequence coding for the RT and RNase H domain of DrMV shares less than 68% homology with that of any known badnaviruses. The seventh ORF of DrMV is not found in other badnaviruses described before. Our results strongly support that DrMV is a distinct species of the genus Badnavirus, family Caulimoviridae. Evidence that the DrMV sequence is integrated in the D. sanderiana genome is presented and discussed.