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The seismic discontinuity around 520 km is believed to be caused by the phase transition from wadsleyite to ringwoodite, the dominant minerals in the mantle transition zone (MTZ). Both wadsleyite and ringwoodite can contain more than 1.0 wt% water at MTZ’s conditions, but it is not well known how water affects the wadsleyite-ringwoodite transition. Here we investigated water partitioning between wadsleyite and ringwoodite and the water effect on this phase boundary using first-principles calculations. Our results show that the presence of water will shift the phase boundary to higher pressures, and the width of the two-phase coexistence domain in the Mg2SiO4-H2O system is insignificant at mid-MTZ conditions. For the (Mg0.9Fe0.1)2SiO4 system, the incorporation of 1.0 wt% water can narrow the effective width of two-phase coexistence by two-thirds. Together with elastic data, we find that velocity and impedance contrasts are only mildly changed by the water partitioning. We suggest that compared to the anhydrous condition, the presence of 1.0 wt% water will increase velocity gradients across the wadsleyite-ringwoodite transition by threefold, enhancing the detectability of the 520 km discontinuity.

Phase D is a potential water carrier in the slab subducted to the uppermost lower mantle (ULM) and its velocity and density characteristics are important for seismological detection of water cycle in the deep Earth. Here we obtained the density and velocities of phase D under the conditions of the ULM using first-principles calculations based on the density functional theory. In contrast to previous results, both hydrogen bond symmetrization and the corresponding abrupt increase in bulk modulus are absent in the optimized structure up to 80 GPa. The velocities of phase D are higher than those of periclase and only slightly lower than those of bridgmanite by 0.5%–3.5% for VP and by 0%–2.0% for VS in the ULM (660–1000 km), thus the accumulation of phase D can hardly produce obvious low-velocity anomaly in the ULM observed by seismological studies, but it may contribute significantly to the seismic anisotropy because of its strong elastic anisotropy.Phase D will dehydrate into bridgmanite and stishovite at the depth of ~700–1200 km. The velocity jumps are 6.6% for VP and 5.1% for VS at the depth of 660 km but reduce to 2.3% and 0.3% at the depth of 1000 km, respectively. However, phase D is ~15% less dense than bridgmanite, so the dehydration of phase D could still produce large impedance jumps in the ULM, which may account for some discontinuities observed at the depth of ~1000–1200 km in subduction zones.

The originations of the Archean continents and sub continental lithospheric mantle (SCLM) were most important events in the early Earth and crucial for understanding how the early Earth worked. The mechanisms for the originations of the Archean continents and SCLM remain unclear. This study suggests that these events were controlled by a deep-water cycle (DWC) in the early Earth. With the solidification of the basal magma ocean (BMO), water in the BMO moved toward the core-mantle boundary and the BMO eventually became gravity unstable because of the enrichment of water. The gravity instability triggered the massive mantle overturns and transported a huge amount of water upward to the shallow part of the Earth. The massive overturn events resulted in the major pulses of the thick SCLM and continental crust generations in the Neoarchean. The DWC model in the early Earth can account for the episodic feature of continental growth and why TTG and thick SCLM basically occurred in the Archean. The DWC model also shows why only the Earth among inner solar system planets was covered with the continental crust. Our results suggest that the DWC played a first-order role in the evolution and dynamics of the early Earth just like the current DWC driven by the plate tectonics on the nowadays Earth.

How and when Earth’s volatile content was established is controversial with several mechanisms postulated, including planetesimal evaporation, core formation and the late delivery of undifferentiated chondrite-like materials. The isotopes of volatile elements such as sulfur can be fractionated during planetary accretion and differentiation and thus are potential tracers of these processes. Using first-principles calculations, we examine sulfur isotope fractionation during core formation and planetesimal evaporation. We find no measurable sulfur isotope fractionation between silicate and metallic melts at core-forming conditions, indicating that the observed light sulfur isotope composition of the bulk silicate Earth relative to chondrites cannot be explained by metal–silicate fractionation. Our thermodynamic calculations show that sulfur evaporates mostly as H2S during planetesimal evaporation when nebular H2 is present. The observed bulk Earth sulfur isotope signature and abundance can be reproduced by evaporative loss of about 90% sulfur mainly as H2S from molten planetesimals before nebular H2 is dissipated. The heavy sulfur isotope composition of the Moon relative to the Earth is consistent with evaporative sulfur loss under 94–98% saturation condition during the Moon-forming giant impact. In summary, volatile evaporation from molten planetesimals before Earth’s formation probably played a key role in establishing Earth’s volatile element content. Earth’s volatile element content was established largely by volatile evaporation from molten planetesimals before Earth’s formation, according to first-principles calculations and examination of sulfur isotope fractionation.

Recent advances in high-precision potassium (K) isotopic analysis have found considerable isotopic variation in rock samples of the Earth’s continental and oceanic crusts; however, it is still uncertain whether there is any resolvable inter-mineral and mineral-melt K isotopic fractionation during igneous and metamorphic processes. Here, we report K isotope compositions of mineral separates from three extremely well preserved igneous rocks (intrusive/extrusive and mafic/intermediate/felsic) in order to investigate possible inter-mineral and mineral-melt K isotopic fractionation at magmatic temperatures. For the first time, we found large inter-mineral fractionation of K isotopes in natural samples (up to 1.072‰), where plagioclase displays a significant enrichment of heavier K isotopes compared to potassium feldspar and biotite in a granite. In addition, we also observed smaller but measurable K isotope fractionation (0.280‰±0.030‰) between ternary feldspar phenocrysts and matrix in a trachyandesite, as well as a comparable isotope fractionation (0.331‰±0.010‰) between plagioclase and the bulk in a gabbroic intrusive rock. We also evaluated such results by comparing the theoretically calculated equilibrium K isotope fractionation factors between relevant igneous minerals in literature and this study. In general, the measured inter-mineral fractionations are consistent with the theoretical calculations (i.e., plagioclase is enriched in heavier isotopes compared to potassium feldspar). Specifically, the measured K isotope fractionation between phenocryst rim and matrix in the trachyandesite agrees well with the calculated equilibrium isotope fractionation. However, the measured K isotope fractionations between phenocryst core and matrix as well as between plagioclase and K-feldspar are significantly larger (by a factor of ~2-3) than the calculated isotope fractionations, which suggest isotopic disequilibrium due to kinetic processes. Using a range of plagioclase-melt isotope fractionation factors inferred from the theoretical calculations in this study, we modeled the K isotopic fractionation during the formation of lunar anorthositic crust, and the result shows a negligible effect on the K isotopic compositions in both lunar crust and mantle. The K isotopic difference between Earth and Moon, therefore, cannot be the result of Lunar Magma Ocean differentiation. Finally, we evaluate the effect of observed inter-mineral fractionations on K-Ar and (40)Ar-(39)Ar dating. This study indicates the variation of (40)K/K ratio would contribute a maximum 0.08% error to the K-Ar and (40)Ar-(39)Ar age uncertainties. We propose a refined (40)K/total K ratio as 0.00011664±0.00000011 (116.64±0.11ppm) instead of the conventional value, 0.0001167(2) for the present Earth. Because some minerals fractionate K isotopes, ultrahigh precision age dating with the K-Ca-Ar dating systems must measure the K isotope fractionation in the same mineral fractions used for age dating.

The simultaneous therapy of tumor recurrence and bone defects resulting from surgical resection of osteosarcoma is still a challenge in the clinic. Combination therapy based on a localized drug-delivery system shows great promise in the treatment of osteosarcoma. Herein, bifunctional polydopamine (PDA)-modified curcumin (CM)-loaded silk fibroin (SF) composite (SF/CM-PDA) nanofibrous scaffolds, which combined photothermal therapy with chemotherapy to synergistically enhance osteosarcoma therapy, were prepared by PDA coating of the SF/CM nanofibrous scaffolds fabricated by supercritical carbon dioxide (SC-CO2) technology. The PDA coating improved hydrophilicity and mechanical strength of the SF/CM scaffolds. The SF/CM-PDA scaffolds present good photothermal conversion capacity and excellent photostability. The low pH and near-infrared (NIR) irradiation could effectively accelerate release of CM in the SF/CM-PDA scaffolds. The in vitro anticancer results indicated that the biocompatible SF/CM-PDA scaffolds had a long-term, stable, and superior anticancer effect compared to pure CM. Furthermore, the SF/CM-PDA scaffolds significantly increased the growth inhibition of osteosarcoma MG-63 cells under NIR irradiation (808 nm and 1.3 W/cm2). Besides, the SF/CM-PDA scaffolds could enhance osteoblast MC3T3-E1 cell proliferation in vitro when the mass ratio of CM was 0.05–0.5%. This work has therefore demonstrated that the bifunctional SF/CM-PDA scaffolds provide a competitive strategy for local osteosarcoma therapy and bone regeneration.

Nitrogen isotopes are a robust tool to study geological nitrogen cycle between Earth’s reservoirs. However, the application of nitrogen isotope system to understanding geological processes has been limited by the lack of constraints on equilibrium isotope fractionation factors between mineral and fluid and between mineral pairs. Here, we use first-principles methods to calculate the nitrogen isotope fractionations among aqueous ammonium, ammonium- and/or nitrate-bearing salts, and ammonium-bearing silicate minerals that commonly occur in Earth’s lithosphere. Our results show a first-order, large nitrogen isotope fractionations between the nitrate group and the ammonium group, with 15N being more enriched in the nitrate group. In detail, the nitrogen isotope fractionations among nitrate group minerals (NaNO3, KNO3, Ba(NO3)2, NH4NO3) are very small. The nitrogen isotope fractionations are also small among the ammonium group (e.g., aqueous ammonium, ammonium salts, phyllosilicate, and tectosilicate minerals) except inosilicate minerals (e.g., diopside and jadeite), which are however significantly more enriched in 15N than the other ammonium-bearing minerals. These results suggest that nitrogen isotopes may serve as a robust geothermometer only when the rock contains coexisting ammonium and nitrate minerals, or contain diopside and/or jadeite together with other ammonium-bearing silicate minerals. Given that common silicate minerals in crustal rocks (clays, micas, feldspars) do not significantly discriminate nitrogen isotopes, nitrogen isotopes can thus be used as a sensitive tool to trace material source and infer geochemical processes that may cause isotope disequilibrium, such as metamorphic devolatilization, hydrothermal alteration, crust-mantle interaction. Our results also demonstrate that authigenic clay minerals can inherit the nitrogen isotopic signature of organic matter and aqueous ammonium and thus can serve as an environmental proxy. However, it is crucial to distinguish detrital minerals from authigenic minerals in sediments when reconstruct marine and lacustrine environments in the deep time (Archean and Proterozoic).

The isotopic compositions of iron in major mantle minerals may record chemical exchange between deep-Earth reservoirs as a result of early differentiation and ongoing plate tectonics processes. Bridgmanite (Bdg), the most abundant mineral in the Earth’s lower mantle, can incorporate not only Al but also Fe with different oxidation states and spin states, which in turn can influence the distribution of Fe isotopes between Bdg and ferropericlase (Fp) and between the lower mantle and the core. In this study, we combined first-principles calculations with high-pressure nuclear resonant inelastic X-ray scattering measurements to evaluate the effects of Fe site occupancy, valence, and spin states at lower-mantle conditions on the reduced Fe partition function ratio (β-factor) of Bdg. Our results show that the spin transition of octahedral-site (B-site) Fe3+ in Bdg under mid-lower-mantle conditions generates a +0.09‰ increase in its β-factor, which is the most significant effect compared to Fe site occupancy and valence. Fe2+-bearing Bdg varieties have smaller β-factors relative to Fe3+-bearing varieties, especially those containing B-site Fe3+. Our models suggest that Fe isotopic fractionation between Bdg and Fp is only significant in the lowermost mantle due to the occurrence of low-spin Fe2+ in Fp. Assuming early segregation of an iron core from a deep magma ocean, we find that neither core formation nor magma ocean crystallization would have resulted in resolvable Fe isotope fractionation. In contrast, Fe isotopic fractionation between low-spin Fe3+-bearing Bdg/Fe2+-bearing Fp and metallic iron at the core-mantle boundary may have enriched the lowermost mantle in heavy Fe isotopes by up to +0.20‰.

Barium isotopes could be a novel tracer in low-temperature geochemical processes such as the Ba cycle in rivers and oceans. Equilibrium Ba isotope fractionation between Ba-hosting minerals and aqueous solution is of great importance for the applications of Ba isotopes in geochemistry, but it remains poorly constrained. In this study, we performed first-principles calculations based on the density functional theory (DFT) to determine the equilibrium Ba isotope fractionation between minerals and aqueous solution (103lnαmineral-Ba_aq of 137Ba/134Ba). The structural properties of aqueous Ba2+ are well predicted by the first-principles molecular dynamics (FPMD) simulation and 121 snapshots are extracted from FPMD trajectories to estimate the reduced partition function ratio (β factor or 103lnβ of 137Ba/134Ba) of aqueous Ba2+. The 103lnβ decreases in the sequence of aragonite > calcite > aqueous Ba2+ ∼ witherite > barite. The β factor is dominantly determined by the force constant, which is affected by both the average Ba O bond length and the coordination number. Our results show that 103lnαaragonite-Ba_aq and 103lnαwitherite-Ba_aq are 0.36‰ and −0.02‰ at 300 K, respectively, consistent with results of experimental studies at equilibrium. The depletion of heavy Ba isotopes observed in natural corals relative to seawater suggests that kinetic effects play an important role in Ba isotope fractionation during coral growth. The 103lnαbarite-Ba_aq is only −0.17‰ at 300 K, indicating limited Ba isotope fractionation caused by the Ba removal stemmed from inorganic barite precipitation. Overall, the equilibrium Ba isotope fractionation factors between minerals and aqueous Ba2+ calculated in this study provide a guideline for the applications of Ba isotopes in low-temperature geochemistry.

Equilibrium Ti isotope fractionation factors among major Ti-bearing minerals are critical for understanding Ti isotope fractionation during magmatic processes. We use the first-principles calculations based on the density functional theory (DFT) to obtain Ti isotope reduced partition function ratios (103lnβ of 49Ti/47Ti) in a series of important Ti-bearing minerals, including Ti-doped clinopyroxene, orthopyroxene, olivine, and pyrope, geikielite-ilmenite solid solutions, and rutile. There is a large variation in our calculated 103lnβ, which are linearly correlated to their Ti force constants, a parameter related to the average Ti O bond length and the Ti valence state. Among all studied minerals, silicates with Ti4+ occupying the tetrahedral Si site have the highest 103lnβ, and rutile has the lowest 103lnβ. The valence state also significantly controls the 103lnβ. Typically, Ti3+-doped silicates have lower 103lnβ than those of Ti4+-doped silicates. At the natural abundance levels, the 103lnβ of Ti4+Si-doped and Ti3+Mg-doped (Ti3+ occupying the Mg site) silicate minerals show no concentration effect. That is, their 103lnβ do not vary with their Ti4+ and Ti3+ contents, respectively. In contrast, the 103lnβ of geikielite-ilmenite solutions significantly decrease with increasing Fe/(Fe + Mg) ratio. Our calculations predict no significant Ti isotope fractionation among Ti4+Si-doped clinopyroxene, orthopyroxene, olivine, and pyrope ( Ti oxides are important fractionating Ti isotopes during magma differentiation. Finally, the large equilibrium Ti isotope fractionation between geikielite-ilmenite solutions and clinopyroxene suggests that Ti isotopes can be used as a thermometer with precision comparable to that of elemental geothermometer.

Whether and where recycled oceanic crusts melt in the deep mantle are fundamentally important questions for understanding the evolution and dynamics of the Earth’s mantle, and they currently remain...

The 41K/39K reduced partition function ratios, 103lnβ, of 17 major K-bearing minerals have been calculated using the density functional theory (DFT) method. Their 103lnβ decrease in the order of alunite (KAl3(SO4)2(OH)6) ∼ K-hollandite I (KAlSi3O8) > niter (KNO3) > potassium carbonate (K2CO3) ∼ potassium bicarbonate (KHCO3) > muscovite (KAl2(AlSi3O10)(OH)2) > potassium hydroxide monohydrate (KOH·H2O) ∼ hydrated potassium carbonate (K2CO3·1.5H2O) > nepheline (Na3KAl4Si4O16) > potassium hydroxide dihydrate (KOH·2H2O) > kalsilite (KAlSiO4) > microcline (KAlSi3O8) ∼ phlogopite (KMg3AlSi3O10(OH)2) > lepidolite (KLi2AlSi4O10(OH)2) > sylvite (KCl) > leucite (KAlSi2O6) > djerfisherite (K6CuFe24S26Cl). The calculated 103lnβ varies from 6.80‰ in alunite to 2.08‰ in djerfisherite at 300 K, and from 0.63‰ to 0.19‰ at 1000 K. At 1000 K, there is only small variation (

Velocity and density jumps across the 410-km seismic discontinuity generally indicate olivine contents of ∼30 to 50 vol.% on the basis of the elastic properties of anhydrous olivine and wadsleyite, which is considerably less than the ∼60% olivine in the widely accepted pyrolite model for the upper mantle. A possible explanation for this discrepancy is that water dissolved in olivine and wadsleyite affects their elastic properties in ways that can reconcile the pyrolitic model with seismic observations. In order to more fully constrain the olivine content of the upper mantle near the 410-km discontinuity, and to place constraints on the mantle water content at this depth, we determined the full elasticity of hydrous wadsleyite at the P-T conditions of the discontinuity based on density functional theory calculations. Together with previous determinations for the effect of water on olivine elasticity, we simultaneously modeled the density and seismic velocity jumps (Δρ, Δ V P , Δ V S ) across the olivine-wadsleyite transition. Our models allow for several scenarios that can well reproduce the density and seismic velocity jumps across the 410-km discontinuity when compared to globally averaged seismic models. When the water content of olivine and wadsleyite is assumed to be equal as in a simple binary system, our modeling indicates a best fit for low water contents (

Machine-to-machine communication can realise considerably better information cognition of fixed and mobile equipment during rail transit. To assess the network access performance of the machine-type communication (MTC) of railway signal equipment for next-generation intelligent transportation system, the forecasting model of the machine communication traffic of railway signal equipment was divided into station indoor model, station outdoor model, and section movement model on the basis of cell units, and the traffic quantity and signaling overhead of the three models were calculated respectively. Based on Poisson's distribution and the Markov update process, an improved Markov-modulated Poisson Process (IMMPP) of the source traffic model was designed. Compared with the 3GPP traffic model, the IMMPP model maintains a good balance between the complexity and the relatively high accuracy of the signal equipment in the station outdoor and section scenarios. The simulation experiments showed that the IMMPP consumed 0.44 s more than 3GPP model 2 in the section scenario and 1.99 s in the station outdoor scenario, and the simulation equipment was in accordance with the actual railway signal equipment. The research result can provide a reference for the description of MTC traffic of other specialised equipment in the railway environment.

Previous theoretical studies have found that the concentration variations within a certain range have a prominent effect on inter-mineral equilibrium isotope fractionation (103lnα). Based on the density functional theory, we investigated how the average Ca–O bond length and the reduced partition function ratios (103lnβ) and 103lnα of 44Ca/40Ca in forsterite (Fo) are affected by its Ca concentration. Our results show that Ca–O bond length in forsterite ranges from 2.327 to 2.267 A with the Ca/(Ca + Mg) varying between a narrow range limited by an upper limit of 1/8 and a lower limit of 1/64. However, outside this narrow range, i.e., Ca/(Ca + Mg) is lower than 1/64 or higher than 1/8, Ca–O bond length becomes insensitive to Ca concentration and maintains to be a constant. Because the 103lnβ is negatively correlated with Ca–O bond length, the 103lnβ significantly increases with decreasing Ca/(Ca + Mg) when 1/64 orthopyroxene > clinopyroxene > calcite ≈ diopside > dolomite > aragonite. Olivine and pyroxenes are enriched in heavier Ca isotope compared to carbonates. The 103lnα between forsterite with a Ca/(Ca + Mg) of 1/64 and clinopyroxene (Ca/Mg = 1/1, i.e., diopside) is up to ~ 0.64‰ at 1200 K. The large 103lnαFo-diopside relative to the current analytical precision for Ca isotope measurements suggests that the dependence of 103lnαFo-diopside on temperature can be used as a thermometer, similar to the one based on the 103lnα of 44Ca/40Ca between orthopyroxene and diopside. These two Ca isotope thermometers both have a precision approximate to that of elemental thermometers and provide independent constraints on temperature.

Equilibrium Mg isotope fractionation properties between aqueous Mg2+ and minerals are the key for the applications of Mg isotopes in geochemistry. This study conducts first-principles molecular dynamics (FPMD) simulations for aqueous Mg2+ based on the density functional theory (DFT). Thirty-five snapshots are extracted from the FPMD trajectories after equilibration for the calculations of the reduced partition function ratio (β factor or 103lnβ). Combining with the β factors of minerals, we found that the β factor decreases in the sequence of lizardite > brucite > aqueous Mg2+ > dolomite > magnesite > calcite > aragonite. Our calculations also confirm the effect of Mg concentration on the β factor of calcite, and further show that the concentration effect is negligible when Mg/(Mg + Ca) (atomic ratio hereafter) is lower than 1/32. Our results depict significant equilibrium Mg isotope fractionations between minerals and aqueous Mg2+ (103lnαminerals-Mg_aq), which are dominantly controlled by the average force constant of Mg in these phases. Compared to aqueous Mg2+, carbonates are enriched in light Mg isotopes but brucite and lizardite show enrichment in heavy Mg isotopes. Among all minerals, 103lnαaragonite-Mg_aq is the largest, which is up to −14‰ at 300 K. Notably, 103lnαcalcite-Mg_aq is not only controlled by temperature, but also significantly affected by Mg content in calcite. 103lnαcalcite-Mg_aq is negatively correlated with Mg content in calcite. The experimentally measured Mg isotope fractionations between minerals (dolomite, magnesite, brucite) and solution at equilibrium are consistent with our predicted results, showing the accurate description of FPMD simulations for aqueous Mg2+ and the reliability of our calculations. Overall, the calculated equilibrium Mg isotope fractionations between minerals and aqueous Mg2+ provide a guideline for applications of Mg isotopes in aqueous geochemical processes.