Plant species richness (PSR) is known to affect soil organic carbon (SOC) storage. However, due to the complex origin and composition of SOC, mechanisms driving the PSR-SOC relationship are not yet fully revealed, hampering an accurate prediction of SOC dynamics under changing plant diversity. Here we investigate the effect of PSR on SOC accumulation along a natural PSR and stand age gradient in a subtropical forest with plot, litter and soil properties being considered. Biomarkers and soil fractionation are used to delineate plant and microbial components of SOC and their influences on the PSR-SOC relationship in the topsoil (0–10 cm) versus subsoil (30–40 cm). We show that PSR does positively affect SOC concentrations at both depths even after considering the effects of substrate, edaphic properties and stand age. However, the PSR-SOC relationship is driven by different pathways in the topsoil versus subsoil. In the topsoil, PSR exerts a strong additive effect on SOC accumulation after the positive influence of substrate, edaphic properties and stand age, mainly regulated by plant-derived components (represented by lignin phenols, light fraction and particulate organic matter), followed by microbial residues. By contrast, PSR has a positive effect on the accrual of microbial-derived components (represented by amino sugars and mineral-associated organic matter) but not plant residues likely via affecting dissolved organic matter (DOM) and nitrogen availability in the subsoil (i.e., DOM-microbial pathway). As a result, microbial-derived components dominate SOC variations in the subsoil, while plant-derived components play a more important role in the topsoil. These findings provide novel information on the mechanistic links between PSR and SOC accumulation at different depths and highlight the role of PSR on long-term carbon sink potentials of soils, which may aid in predicting soil carbon dynamics with plant diversity changes in Earth's system model.
Reverse osmosis (RO) membranes are prone to fouling, which increases the cost of operation and decreases water recovery. In this study, a commercial membrane (ESPA2) was coated with an antiscaling material, i.e. polyacrylic acid (PAA), and an antimicrobial material, i.e. graphene oxide (GO), to reduce biofouling and scaling. Bare and modified membranes with polydopamine (ESPA2-PD), as a control, GO (ESPA2-GO), GO and PAA (ESPA2-GO-PAA), and PAA (ESPA2-PAA) were tested for their antiscaling and antibiofouling properties. ESPA2-GO and ESPA2-GO-PAA had the best performance. The latter showed 15% and 10% increase in normalized water flux compared to ESPA2 in mineral scaling and biofouling tests, respectively. This improvement can be attributed to the decrease in surface charge and the increase in hydrophilicity of membrane surface by both GO and PAA coating. Moreover, the antimicrobial characteristic of GO played a crucial role in reducing biofouling and PAA slightly enhanced antiscaling property when coated on ESPA2 but it did not improve the antibiofouling property. These results highlight the importance of antimicrobial property of the coating for biofouling prevention and show antiscaling materials can be effective not only as an additive to the feed but also as a coating on the membrane to reduce scaling.
Carbon dioxide storage combined with enhanced oil recovery (CCS-EOR) is an important approach for reducing greenhouse gas emissions. We use pore-scale imaging to help understand CO2 storage and oil recovery during CCS-EOR at immiscible and near-miscible CO2 injection conditions. We study in situ immiscible CO2 flooding in an oil-wet reservoir rock at elevated temperature and pressure using X-ray micro-tomography. We observe the predicted, but hitherto unreported, three-phase wettability order in strongly oil-wet rocks, where water occupies the largest pores, oil the smallest, while CO2 occupies pores of intermediate size. We investigate the pore occupancy, existence of CO2 layers, recovery and CO2 trapping in the oil-wet rock at immiscible conditions and compare to the results obtained on the same rock type under slightly more weakly oil-wet near-miscible conditions, with the same wettability order. CO2 spreads in connected layers at near-miscible conditions, while it exists as disconnected ganglia in medium-sized pores at immiscible conditions. Hence, capillary trapping of CO2 by oil occurs at immiscible but not at near-miscible conditions. Moreover, capillary trapping of CO2 by water is not possible in both cases since CO2 is more wetting to the rock than water. The oil recovery by CO2 injection alone is reduced at immiscible conditions compared to near-miscible conditions, where low gas-oil capillary pressure improves microscopic displacement efficiency. Based on these results, to maximize the amount of oil recovered and CO2 stored at immiscible conditions, a water-alternating-gas injection strategy is suggested, while a strategy of continuous CO2 injection is recommended at near-miscible conditions.
Parallel-group thorough QT/QTc studies focus on the change of QT/QTc values at several time-matched points from a pre-treatment day (baseline) to a post-treatment day for different groups of treatment. The International Council for Harmonisation (ICH) E14 stresses that QTc prolongation beyond a threshold represents high cardiac risk and calls for a test on the largest time-matched treatment effect (QTc prolongation). QT/QTc analysis usually assumes a jointly multivariate normal (MVN) distribution of pre-treatment and post-treatment QT/QTc values, with a blocked compound symmetry covariance matrix. Existing methods use an analysis of covariance model including day-averaged baseline as a covariate to deal with the MVN model. However, the analysis of covariance model tends to underestimate the variation of the estimator for treatment effects, resulting in the inflation of empirical type I error rate when testing whether the largest QTc prolongation is beyond a threshold. In this paper, we propose two new methods to estimate the time-matched treatment effects under the MVN model, including maximum likelihood estimation and ordinary-least-square-based two-stage estimation. These two methods take advantage of the covariance structure and are asymptotically efficient. Based on these estimators, powerful tests for QT/QTc prolongation are constructed. Simulation shows that the proposed estimators have smaller mean square error, and the tests can control the type I error rate with high power. The proposed methods are applied on testing the carryover effect of diltiazem to inhibit dofetilide in a randomized phase 1 trial.
Oxidation of sulfapyridine (SPY) by typical oxidant, hydrogen peroxide (H2O2) and/or potassium peroxydisulfate (PDS), was used as a pre-treatment for antibiotic wastewater. The degradation dynamics showed that SPY was successfully removed, and the trend was fitted to the first-order reaction kinetics. H2O2 removed SPY more efficiently in acid condition than in basic condition, while PDS was the opposite. Better performance was achieved by using PDS than using H2O2, but combined using of PDS and H2O2 got the best performance. Although SPY was oxidized by those oxidants and biodegradability was improved, the intermediates still exhibited antibacterial activity. The degradation pathways and mechanism of SPY were deduced through density functional theory (DFT) and evidenced by intermediates product detection. Nucleophilic attack and radical attack were determined to be the major attack pathways in H2O2 and PDS systems, respectively. The SPY degradation pathways proposed in the two systems were based on the cleavage of bonds and hydroxyl substitution. Additionally, intermediate ΔG value showed that stubborn molecules remained in the wastewater even after pre-oxidation, which is harmful for further bio-treatment. This study provides a new insight for the improvement of biodegradability and the efficient degradation of SPY in antibiotic wastewater.
Two-dimensional (2D) materials have drawn much attention in recent years ascribing to their unique properties associated with atomic thickness. Besides graphene, which has aroused tremendous research interest, other 2D materials such as [Bi2O2]-based layered compounds, i.e., Bi2O2Se, BiOCl, and Bi2Sr2CaCu2Ox, have also been studied widely and show promising application prospects in electronics, optoelectronics, photocatalysis fields, and so on. In this Perspective, we systematically review the progress on preparation methods of 2D [Bi2O2]-based layered materials, discuss the strengths and drawbacks of different methods, and give an outlook toward future research directions.
