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BACKGROUND Perfluorinated compounds (PFCs) have been extensively studied in recent years due to their persistence, bioaccumulation and toxicity. However, most of the studies are concentrated in surface water with high concentration of PFCs in rivers, sewage and lakes, while few studies explore the status of PFCs pollution in groundwater. OBJECTIVES To investigate the content, distribution and ecological risk of typical PFCs compounds in groundwater in the reclaimed water irrigation area of Beijing. METHODS 52 groundwater samples were collected from the reclaimed water irrigation area in May to June 2020 and were analyzed by solid phase extraction and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). RESULTS The results showed that 10 target PFCs including perfluorocarboxylic acid (PFCAs) and perfluorosulfonic acid (PFSAs) were detected in groundwater in Beijing, with a concentration of 1.07-24.19ng/L. Among them, the highest detected concentration of perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA), and perfluorobutane sulfonate (PFBS) averaged 2.94ng/L, 2.88ng/L and 1.15ng/L, respectively. The concentration of ∑PFCs in this study was relatively low compared to the groundwater from the fluorochemical industrial park, which was related to the mostly farmland location of the observation wells in the study area. After observing the performance of PFCs in shallow wells (< 50m) and deep wells (>50m), it was found that the concentration of PFCs decreased significantly with increasing well depth. In addition, in view of the spatial distribution of groundwater PFCs in the whole region, the concentration of groundwater PFCs around the landfill was significantly high and decreased with increasing distance from the landfill, indicating that the landfill had a certain contribution to the pollution of surrounding groundwater PFCs. CONCLUSIONS By calculating the risk quotient of PFOA, perfluorooctane sulfonate (PFOS) and PFBA, the landfill has not posed an ecological risk to the surrounding environment. However, in view of the concealment and persistence of groundwater PFCs, it is recommended to carry out continuous regular monitoring and evaluation.

Comprehensive Summary: Discovery of unprecedented donor‐acceptor patterns can essentially enrich the chemistry of donor‐acceptor cyclopropanes. We herein introduce a concept of vinylogous fluorine stabilizing effect, which guides rational design of a novel donor‐acceptor cyclopropane employing gem‐difluorovinyl group as the electron donor, namely dFVCP. Application of such dFVCPs in a [3+2] cycloaddition with aldehydes and a controlled ring‐opening polymerization by a Mg(OTf)2/DIPEA/C(sp3)‐H initiator system have been demonstrated, providing direct access to fluorine‐containing tetrahydrofurans and all‐carbon main‐chain polymers. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Discovery of unprecedented donor‐acceptor patterns can essentially enrich the chemistry of donor‐acceptor cyclopropanes. We herein introduce a concept of vinylogous fluorine stabilizing effect, which guides rational design of a novel donor‐acceptor cyclopropane employing gem‐difluorovinyl group as the electron donor, namely dFVCP. Application of such dFVCPs in a [3+2] cycloaddition with aldehydes and a controlled ring‐opening polymerization by a Mg(OTf)2/DIPEA/C(sp3)‐H initiator system have been demonstrated, providing direct access to fluorine‐containing tetrahydrofurans and all‐carbon main‐chain polymers. [ABSTRACT FROM AUTHOR]

Aging degradation of the geomembrane (GMB) significantly influences the dynamic shear characteristics of the composite liner interface, which comprises the GMB and the compacted clay liner (CCL), potentially jeopardizing the dynamic stability of landfills. In this study, cyclic shear tests were performed on two types of aging GMB/CCL interfaces, concurrently with shear tests on the nonaging GMB/CCL interface for comparison. The results suggest that the impact of aging on the dynamic shear characteristics of the GMB/CCL interface is essentially governed by the surface roughness and brittleness of the GMB, with the effect degree of brittleness influenced by the normal stress. Under low normal stress, aging increased the vertical displacement, dynamic shear strength, and shear stiffness of the GMB/CCL interface. However, under high normal stress, the dynamic shear strength and shear stiffness of the aging GMB/CCL interface were more likely to be lower than those of the nonaging interface. As the displacement amplitude increased, the influence of aging on the shear stiffness of the GMB/CCL interface gradually diminished. Aging also reduced the damping ratio of the GMB/CCL interface. The difference in vertical displacement between the exposed GMB/CCL interface and the in soil GMB/CCL interface caused by brittleness was not significant. In practical engineering, when the overlying load on the GMB/CCL composite liner is relatively small, aging makes the GMB more susceptible to tearing under seismic loads, whereas with larger overlying loads, aging is more likely to increase the shear displacement, thereby increasing the likelihood of instability in landfill. Finally, based on classic models of soil, fitting models for the normalized shear stiffness and damping ratio of the GMB/CCL interface were established and validated. This study can provide reference for analyzing the dynamic stability of landfills during long-term use. [ABSTRACT FROM AUTHOR]

An animal's locomotor rate is an important indicator of its motility. In studies of the nematode Caenorhabditis elegans (C. elegans), assays of the frequency of body bending waves have often been used to discern the effects of mutations, drugs, or aging. Traditional manual methods for measuring locomotor frequency are low in throughput and subject to human error. Most current automated methods depend on image segmentation, which requires high image quality and is prone to errors. Here, we describe an algorithm for automated estimation of C. elegans locomotor frequency using image invariants, i.e. shape-based parameters that are independent of object translation, rotation, and scaling. For each video frame, the method calculates a combination of 8 Hu's moment invariants and a set of maximally stable extremal regions (MSER) invariants. The algorithm then calculates the locomotor frequency by computing the autocorrelation of the time sequence of the invariant ensemble. Results of our method show excellent agreement with manual or segmentation-based results over a wide range of frequencies. We show that compared to a segmentation-based method that analyzes a worm's shape and a method based on video covariance, our technique is more robust to low image quality and background noise. We demonstrate the system's capabilities by testing the effects of serotonin and serotonin pathway mutations on C. elegans locomotor frequency. [ABSTRACT FROM AUTHOR]

Biochar, an eco-friendly, porous carbon-rich material, is widely studied for immobilizing heavy metals in contaminated environments. This study prepared tobacco stalks, a typical agricultural waste, into biochar (TSB) modified by hydroxyapatite (HAP) at co-pyrolysis temperatures of 350 °C and 550 °C to explore its Cd(II) adsorption behavior and relevant mechanisms. XRD, SEM–EDS, FTIR, and BET analyses revealed that HAP successfully incorporated onto TSB, enriching the surface oxygen-containing functional groups (P–O and carboxyl), and contributing to the enhancement of the specific surface area from 2.52 (TSB350) and 3.63 m2/g (TSB550) to 14.07 (HAP–TSB350) and 18.36 m2/g (HAP–TSB550). The kinetics of Cd(II) adsorption onto TSB and HAP–TSB is well described by the pseudo-second-order model. Isotherm results revealed that the maximum adsorption capacities of Cd(II) on HAP–TSB350 and HAP–TSB550 were approximately 13.17 and 14.50 mg/g, 2.67 and 9.24 times those of TSB350 and TSB550, respectively. The Cd(II) adsorption amounts on TSBs and HAP–TSBs increased significantly with increasing pH, especially in HAP–TSB550. Ionic strength effects and XPS analysis showed that Cd(II) adsorption onto HAP–TSBs occurred mainly via electrostatic interaction, cation exchange with Ca2+, complexation with P–O and –COOH, and surface precipitation. These findings will provide a modification strategy for the reutilization of tobacco agricultural waste in the remediation of heavy metal contaminated areas. [ABSTRACT FROM AUTHOR]

In the present work, we investigate the productions of X 0 (2900) and its spin partners in the B + decay processes, where X 0 (2900) is regarded as a D ¯ ∗ K ∗ molecular state. We infer that the initial B + meson and the final D + X 0 (2900) are connected through the D s 1 ′ + (2460) D ¯ ∗ 0 mesons by exchanging a K ∗ 0 meson. The contributions of such a meson loop to the process B + → D + X 0 (2900) are evaluated and our estimations indicate that the measured branching fraction of B + → D + X 0 (2900) could be well reproduced in a reasonable range of model parameters, indicating that X 0 (2900) could be interpreted as a D ¯ ∗ K ∗ molecular state. In addition, the production processes B + → D + X ~ 1 , 2 , B + → D ∗ + X 0 (2900) , and B + → D ∗ + X ~ 1 , 2 are investigated, and we find that the fit fraction of X ~ 1 in the process B + → D ∗ + D ∗ - K + is about 6%, which should be accessible by the LHCb and Belle II Collaborations. [ABSTRACT FROM AUTHOR]