Abstract Aim Understanding the evolution of the latitudinal diversity gradient (i.e. increase in species diversity towards the tropics) is a prominent issue in ecology and biogeography. Disentangling the relative contributions of environment and evolutionary history in shaping this gradient remains a major challenge because their relative importance has been found to vary across regions and taxa. Here, using the global distributions and a molecular phylogeny of Rhododendron, one of the largest genera of flowering plants, we aim to compare the relative contributions of contemporary environment, evolutionary time and diversification rates in generating extant species diversity patterns. Location Global. Time period Undefined. Major taxa studied Rhododendron. Methods We compiled the global distributions of all Rhododendron species, and constructed a dated molecular phylogeny using nine chloroplast genes and seven nuclear regions. By integrating these two datasets, we estimated the temporal trends of Rhododendron diversification, and explored the global patterns of its species diversity, net diversification rates, and species ages. Next, we reconstructed the geographical ancestral area of the clade. Finally, we compared the relative contribution of contemporary environment, time-for-speciation, and diversification rates on the species diversity pattern of Rhododendron. Results In contrast to the predictions of the time-for-speciation hypothesis, we found that although Rhododendron originated at a temperate latitude, its contemporary species diversity is highest in the tropics/subtropics, suggesting an into-the-tropics colonization for this genus. We found that the elevated diversification induced by heterogeneous environmental conditions in the tropics/subtropics shapes the global pattern of Rhododendron diversity. Main conclusions Our findings support tropical and subtropical mountains as not only biodiversity and endemism hotspots, but also as cradles for the diversification of Rhododendron. Our study emphasizes the need of unifying ecological and evolutionary approaches in order to gain comprehensive understanding of the mechanisms underlying the global patterns of plant diversity.
We study the effects of sons versus daughters on parental joint time allocation between the labor market and the household. Using data from the China Health and Nutrition Survey from 1989 to 2006, we apply a fixed-effects model to control for cross-household heterogeneity in son preference. We find that the birth of sons rather than daughters significantly reduces maternal time spent on household chores, which we argue represents an increase in maternal intra-household bargaining power. However, the effects of sex composition of children on paternal time allocation and maternal time on labor-market activities are weak or mixed. Results are robust to a series of sensitive analyses.
In recent years, ground-level ozone pollution in China has become an increasingly prominent problem. This study simulated and analyzed spatiotemporal distribution of ozone and exposure level by the Weather Research and Forecasting (WRF)-Community Multiscale Air Quality (CMAQ) models and monitoring data from 1516 national air quality monitoring stations in China during 2015. The simulation results show that the Sichuan Basin, Shandong, Shanxi, Henan, Anhui, Qinghai-Tibetan Plateau, Yangtze River Delta (YRD), Pearl River Delta (PRD) and Beijing-Tianjin-Hebei (BTH) region had relatively high average annual concentrations of ozone. The regions with more than 10% nonattainment days of 160 mu g/m(3) (daily maximum 8-h) are mainly concentrated in BTH, Shandong Peninsula and YRD, where large seasonal variations were also found. Exposure levels were calculated based on population data and simulated ozone concentrations. The cumulative population exposed to daily maximum 8-h concentration greater than or equal to 100 mu g/m(3) was 816.04 million, 61.17% of the total. Three methods were used to estimate the mortality of chronic obstructive pulmonary disease (COPD) attributable to ozone. A comparative study using different exposure concentrations and threshold concentrations found large variations among these methods, although they were all peer-reviewed methods. The estimated mortality of COPD caused by ozone in China in 2015 ranged from 55341 to 80280, which mainly distributed in Beijing, Shandong, Henan, Hubei and Sichuan Province, the YRD and PRD region.
Graphene oxide (GO) coatings on membranes can improve antifouling performance against a variety of microorganisms and organics. However, the effects of GO coatings on mineral scaling were not investigated. Here gypsum scaling on bare (ESPA2) and GO-modified thin-film polyamide membranes (ESPA2-GO) followed by cleaning with deionized (DI) water were investigated with a bench-scale reverse osmosis setup. The flux decline caused by gypsum scaling on ESPA2-GO was slightly reduced than on ESPA2. This is because the ESPA2-GO membrane is more hydrophilic than ESPA2, indicating a higher energy barrier for heterogeneous nucleation and/or the deposition of gypsum on it. Moreover, the more negatively charged ESPA2-GO membrane lead to stronger electrostatic repulsive forces between the membrane and the negatively charged gypsum particles and thus further inhibiting gypsum deposition onto membranes. Interestingly, during the cleaning process, smaller flux recovery was observed for ESPA2-GO. This is because ESPA2-GO surfaces have higher densities of carboxyl (–COOH) groups, which form complexes with Ca2+, building strong bonds between GO coatings and gypsum. This study provided unique insights on the physicochemical interactions among membrane, the scaling mineral, and aqueous species, which can help the rational design of coatings for better simultaneous anti-scaling and anti-fouling performances.
Yang T, Gong J, Zhang H, Zou L, Shi L, Li X. HeavyGuardian: Separate and Guard Hot Items in Data Streams, in Proceedings of the 24th ACM SIGKDD International Conference on Knowledge Discovery & Data Mining, KDD 2018, London, UK, August 19-23, 2018.; 2018:2584–2593. link
Phosphate is added to Pb-contaminated soils to induce lead immobilization through lead phosphate precipitation. Organic coatings on soils, which may affect heterogeneous lead phosphate nucleation, can impact the effectiveness of lead immobilization. Here, SiO2 surfaces were coated with silanol self-assembled thin films terminated with −COOH and −OH functional groups to act as model organic coatings on soil particles. Using grazing incidence small-angle X-ray scattering (GISAXS), heterogeneous lead phosphate nucleation on coatings was measured from mixed Pb(NO3)2 and Na2HPO4/NaH2PO4 solutions at pH 7 with varied ionic strengths (IS = 0.58, 4, and 11 mM). Raman spectroscopy identified the homogeneous precipitates in solution as hydroxylpyromorphite (Pb5(PO4)3OH). The smallest lead phosphate nuclei (4.5 ± 0.5 nm) were observed on −COOH coatings, which resulted from the highest level of lead and phosphate ion adsorption on −COOH coatings. The IS of the solution also affected the sizes of the heterogeneous precipitates on −COOH coating, with smaller nuclei (1.3 ± 0.4 nm) forming under higher IS (4 and 11 mM). This study provided new findings that can improve our understanding of lead immobilization in contaminated soil environments.
Ultraviolet (UV) photodetectors with high responsivity and fast response are crucial for practical applications. Double perovskite Cs2AgBiBr6 has emerged as a promising optoelectronic material due to its excellent physics and photoelectric properties. However, no work is reported based on its film for photodetector applications. Herein, an ITO/SnO2/Cs2AgBiBr6/Au hole-transport layer free planar heterojunction device is fabricated for photodetector application. The device is self-powered with two responsivity peaks at 350 and 435 nm, which is suitable for ultraviolet-A (320-400 nm) and deep-blue light detecting. A high responsivity of 0.11 A W-1 at 350 nm and a quick response time of less than 3 ms are obtained, which is significantly higher than other semiconductor oxide heterojunction-based UV detectors. More importantly, the stability is significantly better than most of the hybrid perovskite photodetectors reported so far. Its photocurrent shows no obvious degradation after more than 6 months storage in ambient conditions without any encapsulation. Consequently, the utilization of Cs2AgBiBr6 film is a practical approach for high performance, large-area lead-free perovskite photodetector applications. For the mechanism, it is found that photogenerated carriers in Cs2AgBiBr6 film are separated at the Cs2AgBiBr6/SnO2 heterojunction interface by its built-in field. The low toxicity and high stability of this double perovskite active layer make it very promising for practical applications.