Seismic recordings made during the InSight mission 1 suggested that Mars's liquid core would need to be approximately 27% lighter than pure liquid iron 2,3 , implying a considerable complement of light elements. Core compositions based on seismic and bulk geophysical constraints, however, require larger quantities of the volatile elements hydrogen, carbon and sulfur than those that were cosmochemically available in the likely building blocks of Mars 4 . Here we show that multiply diffracted P waves along a stratified core–mantle boundary region of Mars in combination with first-principles computations of the thermoelastic properties of liquid iron-rich alloys 3 require the presence of a fully molten silicate layer overlying a smaller, denser liquid core. Inverting differential body wave travel time data with particular sensitivity to the core–mantle boundary region suggests a decreased core radius of 1,675 ± 30 km associated with an increased density of 6.65 ± 0.1 g cm −3 , relative to previous models 2,4–8 , while the thickness and density of the molten silicate layer are 150 ± 15 km and 4.05 ± 0.05 g cm −3 , respectively. The core properties inferred here reconcile bulk geophysical and cosmochemical requirements, consistent with a core containing 85–91 wt% iron–nickel and 9–15 wt% light elements, chiefly sulfur, carbon, oxygen and hydrogen. The chemical characteristics of a molten silicate layer above the core may be revealed by products of Martian magmatism.
Abstract Aim Pollination is an essential stage of angiosperm reproduction, and the mode of pollination plays a major role in driving evolutionary and ecological responses of plants to environmental changes. However, the effects of climate, evolutionary history and floral traits (i.e. plant sexual systems) on pollination mode variation remain unclear. Here, we explored the biogeographic patterns in pollination mode frequency and tested the hypothesis that insect pollination prevails in warm humid regions with old floras due to high pollinator dependence, whereas wind pollination is more frequent in arid regions with younger floras and is more strongly associated with dioecy. Location China. Time period Since the Last Glacial Maximum. Major taxa studied Angiosperms. Methods Using data on pollination modes and geographic ranges of 29,719 angiosperm species in China, we mapped the biogeographic pattern of pollination mode frequency. Phylogenetic logistic regressions and generalized linear mixed models were employed to evaluate the relative importance of climate, evolutionary history (represented by phylogenetic conservatism and grid-level mean genus age) and sexual systems on variations in pollination modes across species and space. Results Evolutionary history was the strongest correlate of pollination mode variation across species and space. The proportion of insect-pollinated species was higher in humid regions with old floras, but lower in arid regions with young floras. Evolutionary history and temperature dominated variations in pollination mode frequency in humid areas, while precipitation dominated in arid areas. Climate influenced geographic pattern in pollination mode frequency both directly and indirectly via its effects on species richness and plant sexual systems. Main Conclusions Our results showed that geographic pattern in angiosperm pollination mode frequency is dominated by evolutionary history followed by climate, which extended previous findings of climate-driven mechanisms. Our findings demonstrate the importance to incorporate evolutionary history in understanding the mechanisms underlying the functional biogeography of plant traits.
Abstract Aim Climate has been regarded as an important explanation for large-scale species richness patterns. However, the mechanisms underlying the significant variations in species richness?climate relationships across different clades remain to be tested. We explored how niche conservatism, diversification rates and time for speciation influenced species richness?climate relationships between clades. Location The globe. Time Period Present day. Major Taxa Studied Angiosperms. Methods Based on a newly complied database of the global distributions of 288,735 angiosperm species, we used generalized linear models to assess the relationships between species richness of different angiosperm families and climatic factors. We also conducted phylogenetic comparative analysis to test whether niche conservatism, diversification rates and time for speciation affect the variations in species richness?climate relationships. Results We found that temperature seasonality dominated the global angiosperm diversity patterns. Closely related families had more similar species richness?climate relationships than distantly related ones. The discrepancy between the current and ancestral niches of different clades had much stronger effects on variations in species richness?climate relationships than diversification rates and time for speciation. With the increase in the discrepancy between current and ancestral niches, the explanatory power (i.e., R2) of contemporary temperature and precipitation in explaining species richness patterns increased. Main Conclusions Overall, our findings strongly support that niche conservatism dominates the variations in species richness?climate relationships across taxonomic groups. These findings allow better understanding on how large-scale species diversity patterns are formed.
Abstract Organic aerosol particles are oxidized by atmospheric oxidants. These particles are occasionally internally mixed with solid materials such as soot and inorganic crystals. However, potential impacts of the particles' mixing states on chemical reactivity have rarely been investigated. This study investigated the influence of the existence of crystalline ammonium sulfate on chemical reactivity of oleic acid particles with ozone for the temperature range of −20°C to +35°C using an aerosol flow tube reactor. The chemical compositions of the resulting particles were monitored using online instruments for deriving the reactive uptake coefficients (γ) of ozone by oleic acid. The values of γ were not significantly influenced by the existence of ammonium sulfate when the temperature of the reactor was higher than the melting point of oleic acid (∼13°C). The values of γ were unmeasurably small for the lower temperature range when oleic acid particles were internally mixed with crystalline ammonium sulfate. No significant change in γ was observed for the temperature range down to −13°C when the inorganic salt was absent, likely due to the formation of supercooled liquid. The difference in chemical reactivity can be explained by the occurrence of heterogeneous nucleation induced by inorganic seed.
Organic aerosol particles are oxidized by atmospheric oxidants. These particles are occasionally internally mixed with solid materials such as soot and inorganic crystals. However, potential impacts of the particles' mixing states on chemical reactivity have rarely been investigated. This study investigated the influence of the existence of crystalline ammonium sulfate on chemical reactivity of oleic acid particles with ozone for the temperature range of −20°C to +35°C using an aerosol flow tube reactor. The chemical compositions of the resulting particles were monitored using online instruments for deriving the reactive uptake coefficients (γ) of ozone by oleic acid. The values of γ were not significantly influenced by the existence of ammonium sulfate when the temperature of the reactor was higher than the melting point of oleic acid (∼13°C). The values of γ were unmeasurably small for the lower temperature range when oleic acid particles were internally mixed with crystalline ammonium sulfate. No significant change in γ was observed for the temperature range down to −13°C when the inorganic salt was absent, likely due to the formation of supercooled liquid. The difference in chemical reactivity can be explained by the occurrence of heterogeneous nucleation induced by inorganic seed.
In the presence of the difficulties pertinent to the selective oxidation of cyanide and the high-efficient hydrolysis of cyanate, the mineralization of cyanide into nitrogen could not be realized during the traditional processes. Herein, a novel system of electrocatalysis coupled with ultraviolet-based advanced oxidation processes (UV/EC/PS, PS: persulfate) is developed, exhibiting astonishingly high activity and selectivity for cyanide mineralization. The achieved results reveal that adequate active-chlorine species (ClO•/Cl2•−) are generated due to the synergistic effects of electrocatalysis and advanced oxidation processes and these are high-selective for cyanide mineralization. Concurrently, induced by the interconversion between active species, the pH value in the UV/EC/PS system vigorously lessens from 11.5 to 3.3 at a rate of 1.1 × 10-2 min−1, hugely speeding up the hydrolysis of cyanate intermediates. The results display that PS plays a pivotal role in the formation of ClO•/Cl2•− and the self-reduction of pH value in the UV/EC/PS system. Under the action of ClO•/Cl2•− and self-decreased pH value, 0.25 mM of ferricyanide is thoroughly mineralized into nitrogen within 80 min and no HCN evolves. Additionally, the UV/EC/PS system exhibits exceptional feasibility for the practical purifications of cyanide-containing wastewater (CCWW). This study aims to give new insights into developing technologies associated with the mineralization treatment of CCWW.
A novel PbO2 electrode modified with rare earth elements (La, Ce, Gd and Er) doping (named as Re-PbO2) was prepared by electrodeposition in the present study. The micro-morphology and crystal structure of Re-PbO2 were characterized by scanning electronic microscopy (SEM), energy dispersive spectroscope (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Their electrochemical properties were determined by linear sweep voltammetry (LSV), cyclic voltammetry (CV), accelerated life test and hydroxyl radicals (•OH) formation analysis. Electrochemical oxidation of p-nitrophenol (p-NP) by Re-PbO2 compared with un-doped PbO2 has been investigated and the degradation rate followed the order of Er-PbO2 > Gd-PbO2 > La-PbO2 > Ce-PbO2 > PbO2. Especially for Er-PbO2, the pseudo-first order kinetic for p-NP (kp-NP) degradation was 0.41, which was only 0.19 for un-doped PbO2. Rare earths elements doping improved the oxidation ability of Re-PbO2 mainly through reducing grain size, increasing oxygen evolution potential, enlarging electrochemical active surface area and enhancing •OH formation ability. In addition, existing formation of oxygen species on PbO2 electrode surface was investigated by XPS. For Re-PbO2, percentage of lattice oxygen species (Oads) were higher than that on the un-doped one. These results demonstrated that rare earth elements can enhance the oxidation ability of PbO2 electrode significantly.
MnFe Prussian blue analogues (MnFe PBAs) were fabricated for acetamiprid degradation with peroxymonosulfate (PMS) as an oxidant. MnFe PBAs (200) are the most active facets for PMS activation due to the superior chemisorption affinity and electron-transfer ability. Density functional theory calculation verified that Mn(III) served as an electron donor and acceptor to adjust the electron density between Fe and Mn, which played a crucial role in the high activation performance of MnFe PBAs (200). PBA lattice (−C═N) did not exhibit direct PMS activation capability in this system, which differed from previously reported Fenton counterparts. Based on the electronic localization function calculation and probe experiments, the O–O of HSO5– was broken, and the bonds of PBA could be restored during the activation reaction, leading to the continuous generation of reactive oxygen species in the MnFe PBAs/PMS system. Transformation product studies indicated that the oxidized products were primarily the result of aromatic hydroxylation, N–C bond cleavage, azo reaction, and so forth, achieving the mineralization and ecotoxicity mitigation of acetamiprid efficiently. Findings in this study provided new insights into developing advanced facet-dependent catalysts to activate PMS for the efficient degradation of emerging contaminants in the aqueous environment.