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Maximization of the smallest eigenfrequency of the linearized elasticity system with area constraint is investigated. The elasticity system is extended into a large background domain, but the void is vacuum and not filled with ersatz material. The piecewise constant level set (PCLS) method is applied to present two regions, the original material region and the void region. A quadratic PCLS function is proposed to represent the characteristic function. Consequently, the functional derivative of the smallest eigenfrequency with respect to PCLS function takes nonzero value in the original material region and zero in the void region. A penalty gradient algorithm is proposed, which initializes the whole background domain with the original material and decreases the area of original material region till the area constraint is satisfied. 2 D and 3 D numerical examples are presented, illustrating the validity of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Soils co-contaminated with polycyclic aromatic hydrocarbons (PAHs) and cadmium (Cd) have serious environmental impacts and are highly toxic to humans and ecosystems. Phytoremediation is an effective biotechnology for the remediation and restoration of PAH- and Cd-polluted soils. Pot experiments were conducted to investigate the individual and combined effects of PAHs (1238.62 mg kg−1) and Cd (23.1 mg kg−1) on the phytoremediation potential of Bermuda grass grown in contaminated soils. Bermuda grass exhibited a significant decrease in plant growth rate, leaf pigment content, root activity, plant height and biomass and a remarkable increase in malondialdehyde content and electrolyte leakage when grown in PAH- and Cd-contaminated soils compared with grass grown in uncontaminated soils. The activity of soil enzymes, including urease, alkaline phosphatase, sucrose, and fluorescein diacetate hydrolysis, were reduced in soil with PAH and Cd stress. Furthermore, the toxicity of combined PAHs and Cd on Bermuda grass growth and soil enzyme activity was much higher than that of PAH or Cd stress alone, suggesting a synergistic effect of PAHs and Cd on cytotoxicity. To scavenge redundant reactive oxygen species and avoid oxidative damage, Bermuda grass increased plant catalase, superoxide dismutase, and peroxidase activity and soluble sugar and proline content. The bioconcentration factor of Cd in Bermuda grass grown under Cd alone and combined PAH and Cd exposure was greater than 1 for both, suggesting that Bermuda grass has a high Cd accumulation ability. Under PAH alone and combined PAH and Cd exposure conditions, a higher PAH removal rate (41.5–56.8%) was observed in soils planted with Bermuda grass than in unplanted soils (24.8–29.8%), indicating that Bermuda grass has a great ability to degrade PAHs. Bermuda grass showed great phytoremediation potential for the degradation of PAHs and phytoextraction of Cd in co-contaminated soils. [Display omitted] • Soil PAHs and Cd stress negatively affected overall growth of Bermuda grass and soil enzyme activities. • Co-presence of PAHs exerted a synergistic effect synergistic effect on cytotoxicity. • Enzymatic and non-enzymatic antioxidant processes were developed for PAHs and Cd tolerance. • Bermuda grass showed great phytoremediation potential for the degradation of PAHs and phytoextraction of Cd. [ABSTRACT FROM AUTHOR]

With the broadly application of antibiotics to treat infectious diseases in humans and animals, antibiotic contaminants such as tetracycline (TC) and ciprofloxacin (CIP) have been detected in soil environments, where iron oxide minerals and phosphate are ubiquitous. To date, the influence of phosphate on the adsorption behaviors of TC/CIP onto iron oxides is still poorly understood. In this study, the effects of phosphate on the adsorptions of TC and CIP onto iron oxide minerals were investigated. Adsorption isotherms showed that the adsorption affinities of TC and CIP onto the three iron oxide minerals were in the order of goethite > hematite > magnetite with or without phosphate, the trend was dominated by different surface area and amount of surface hydroxyl groups of iron oxide minerals. Meanwhile, TC contains more functional groups than CIP for bonding, which resulted in greater adsorption affinity of three iron oxides to TC than that to CIP. Interestingly, phosphate weakened TC adsorption, while enhanced CIP adsorption, on the three iron oxides. This observation was ascribed to that phosphate anion enhanced the surface negative charge of iron oxides, which reinforced the electrostatic repulsion between iron oxides and negatively charged TC, also reinforced the electrostatic attraction between iron oxides and positively charged CIP. Furthermore, the inhibitory effect of phosphate on TC adsorption was dramatically enhanced at high pH, while the promoting effect of phosphate on CIP adsorption was slightly changed with various pH. Our results highlight the importance of phosphate in exploring the environmental fate of antibiotics in natural environment. Image 1 • The affinity to adsorb TC/CIP followed the order: goethite > hematite > magnetite. •Phosphate inhibited TC adsorption, while promoted CIP adsorption. •Phosphate affected TC/CIP adsorption mainly by changing electrostatic interactions. •The effect of phosphate on TC adsorption was more pH dependent as compared with CIP. [ABSTRACT FROM AUTHOR]

The dimension ordering of parallel coordinate plots has been widely studied, aiming at the insightful exploration of multi-dimensional data. However, few works focus on the category distributions across dimensions and construct an effective dimension ordering to enable the visual exploration of clusters. Therefore, we propose a cluster-aware arrangement method of the parallel coordinate plots and design a visualization framework for the multi-dimensional data exploration. Firstly, a hierarchical clustering scheme is employed to identify the categories of interest across different dimensions. Then we design a group of icicle views to present the hierarchies of dimensions, the colors of which also indicate the relationships between different categories. A cluster-aware correlation is defined to measure the relationships between different attribute axes, based on the distributions of categories. Furthermore, a matrix map is designed to present the relationships between dimensions, and the MDS method is employed to transform the dimensions into 2D coordinates, in which the correlations among the dimensions are conserved. At last, we solve the Traveling Salesman Problem (TSP) and achieve an automated dimension ordering of the parallel coordinate plots, which largely highlights the relations of categories across dimensions. A set of convenient interactions are also integrated in the visualization system, allowing users to get insights into the multi-dimensional data from various perspectives. A large number of experimental results and the credible user studies further demonstrate the usefulness of the cluster-aware arrangement of the parallel coordinate plots. [ABSTRACT FROM AUTHOR]

Inorganic ligands, ubiquitous in the natural environment, can interact with iron oxide minerals. To date, our knowledge regarding the effects of inorganic ligands on the adsorption properties of antibiotics onto iron oxides is still limited. In this work, the influences of different inorganic ligands (chosen iodate, silicate, and phosphate as the model ligands) on the adsorption of tetracycline (TC) onto hematite were examined. Adsorption isotherms indicated that inorganic ligands inhibited TC adsorption. The observations were attributed to the increase of electrostatic repulsion between anionic species (i.e., TC–) and negatively charged hematite particles as well as the competition between TC– species and inorganic ligand anions for the adsorption sites on hematite surfaces. Interestingly, the inhibitory effects of the three inorganic ligands were in the order of phosphate > silicate > iodate; the trend was stemmed from their differences in the binding affinities to hematite and the molecular size. When the background solutions contained divalent cations (e.g., Ca2+), surface precipitation of Ca-inorganic ligand compounds on hematite was another important mechanism for the inhibitory effects. Furthermore, adsorption of TC onto hematite with or without inorganic ligands was strongly affected by solution pH, which was due to the combination of the amphoteric behavior of TC and highly pH-dependent surface charges of the hematite mineral. Current results highlight the critical roles of ubiquitous inorganic ligands in revealing the fate of tetracycline antibiotics in natural systems. [Display omitted] • Inorganic ligands inhibited TC adsorption onto hematite. • The inhibitory effects followed the order phosphate > silicate > iodate. • Surface precipitation was another important mechanism in the presence of Ca2+. • Adsorption of TC with or without inorganic ligands was strongly dependent on pH. [ABSTRACT FROM AUTHOR]

Given the ubiquitous mineral (e.g., clays and iron oxides) playing critical roles in impacting the fate of antibiotics in the subsurface environment, the effects of two mineral colloids (i.e., ferrihydrite and montmorillonite) on tetracycline (TC, a representative of antibiotic) transport in sand columns were investigated in this study. Interestingly, the results clearly showed that ferrihydrite colloids inhibited TC transport, while montmorillonite colloids enhanced TC mobility under neutral conditions (pH 7.0). This phenomenon resulted from the positively charged ferrihydrite colloids with weak mobility, which assisted TC deposition; besides, providing additional deposition sites for TC by the deposited ferrihydrite colloids was another important mechanism. In contrast, the transport-enhancement effect of montmorillonite on TC was attributed to the strong binding affinity of TC to clay particles as well as the competition between colloids and TC for deposition sites on sand surfaces. Moreover, the transport-inhibition effect of ferrihydrite at pH 7.0 was greater than that at pH 5.0, mainly due to more colloid-associated TC under neutral conditions. Surprisingly, ferrihydrite colloids could act as carriers of antibiotics and enhanced TC transport at pH 9.0. Because the surface charge of colloids was altered to negative and could break through the column. Meanwhile, the transport-enhancement effect of montmorillonite decreased with increasing pH from 5.0 to 9.0, resulting from the decrease of colloid-adsorbed TC. Furthermore, colloid-mediated transport of TC was influenced by ionic strength, which affected the aggregation characteristics of colloids and the binding affinities of TC to minerals. These findings provide critical information for assessing the risks of antibiotics in aquatic ecosystems where abundant natural minerals are present. [Display omitted] • A comparison regarding the effect of iron oxide and clay on TC mobility was studied. • Ferrihydrite inhibited TC transport mainly due to colloid-associated TC deposition. • Providing additional sites by ferrihydrite was another deposition mechanism for TC. • Highly mobile montmorillonite acted as a carrier of TC and enhanced TC transport. • Colloid-mediated transport of TC considerably depended on solution chemistry. [ABSTRACT FROM AUTHOR]

Abstract: RS21-C6, which is highly expressed in all vertebrate genomes and green plants, is proposed to have nucleoside triphosphate pyrophosphohydrolase activity. Here, we report the crystal structures of the core fragment of RS21-C6, named RSCUT, and the complex with the substrate 5-methyl dCTP. The refined structure of RSCUT consists mainly of α-helices and shows formation of a tightly associated tetramer. On the basis of the structure of the RSCUT–m5dCTP complex and the results of pyrophosphatase activity assays, several key residues involved in the substrate binding of RS21-C6 have been identified. Tetramer formation is shown to be required for substrate binding. [Copyright &y& Elsevier]