Sector-zoned clinopyroxene is common in igneous rocks, but has been overlooked in the study of magmatic processes. Whilst concentric zoning is commonly used as a record of physicochemical changes in ...the melt feeding crystal growth, clinopyroxene is also highly sensitive to crystallisation kinetics. In sector-zoned crystals, the fidelity of compositional changes as recorders of magma history is dubious and the interplay between thermodynamic and kinetic controls remains poorly understood. Here we combine electron probe and laser ablation micro-chemical maps of titanaugite crystals from Mt. Etna (Sicily, Italy) to explore the origin of sector zoning at the major and trace element levels, and its implications for the interpretation of magmatic histories. Elemental maps afford the possibility to revisit sector zoning from a spatially controlled perspective. The most striking observation is a clear decoupling of elements into sectors vs. concentric zones within single crystals. Most notably, Al-Ti enrichments and Si-Mg depletions in the prism sectors {1 0 0}, {1 1 0} and {0 1 0} relative to the hourglass (or basal) sectors {−1 1 1} correlate with enrichments in rare earth elements and highly charged high field strength elements due to cation exchanges driven by kinetic effects. In contrast, transition metals (Cr, Ni, Sc) show little partitioning into sectors and strong enrichments in concentric zones following resorbed surfaces, interpreted as evidence of mafic recharge and magma mixing. Our results document that kinetic partitioning has minor effects on the compositional variations of cations with low charge relative to the ideal charge/radius of the structural site they occupy in the clinopyroxene lattice. We suggest that this may be due to a lower efficiency in charge balance mechanisms compared to highly charged cations. It follows that compatible metals such as Cr can be considered trustworthy recorders of mafic intrusions and eruption triggers even in sector-zoned crystals. We also observe that in alkaline systems where clinopyroxene crystallisation takes place at near-equilibrium conditions, sector zoning should have little effect on Na-Ca partitioning and in turn, on the application of experimentally calibrated thermobarometers. Our data show that whilst non-sector-zoned crystals form under relatively stagnant conditions, sector zoning develops in response to low degrees of undercooling, such as during slow magma ascent. Thus, we propose that the chemistry of sector-zoned crystals can provide information on magma history, eruption triggers, and possibly ascent rates.
Microbially mediated anaerobic oxidation of methane (AOM) is a key process in the regulation of methane emissions to the atmosphere. Iron can serve as an electron acceptor for AOM, and it has been ...suggested that Fe(III)-dependent AOM potentially comprises a major global methane sink. Although it has been proposed that anaerobic methanotrophic (ANME) archaea can facilitate this process, their active metabolic pathways have not been confirmed. Here we report the enrichment and characterisation of a novel archaeon in a laboratory-scale bioreactor fed with Fe(III) oxide (ferrihydrite) and methane. Long-term performance data, in conjunction with the
C- and
Fe-labelling batch experiments, demonstrated that AOM was coupled to Fe(III) reduction to Fe(II) in this bioreactor. Metagenomic analysis showed that this archaeon belongs to a novel genus within family Candidatus Methanoperedenaceae, and possesses genes encoding the "reverse methanogenesis" pathway, as well as multi-heme c-type cytochromes which are hypothesised to facilitate dissimilatory Fe(III) reduction. Metatranscriptomic analysis revealed upregulation of these genes, supporting that this archaeon can independently mediate AOM using Fe(III) as the terminal electron acceptor. We propose the name Candidatus "Methanoperedens ferrireducens" for this microorganism. The potential role of "M. ferrireducens" in linking the carbon and iron cycles in environments rich in methane and iron should be investigated in future research.
Thermocatalysis of CO2 into high valuable products is an efficient and green method for mitigating global warming and other environmental problems, of which Noble‐metal‐free metal–organic frameworks ...(MOFs) are one of the most promising heterogeneous catalysts for CO2 thermocatalysis, and many excellent researches have been published. Hence, this review focuses on the valuable products obtained from various CO2 conversion reactions catalyzed by noble‐metal‐free MOFs, such as cyclic carbonates, oxazolidinones, carboxylic acids, N‐phenylformamide, methanol, ethanol, and methane. We classified these published references according to the types of products, and analyzed the methods for improving the catalytic efficiency of MOFs in CO2 reaction. The advantages of using noble‐metal‐free MOF catalysts for CO2 conversion were also discussed along the text. This review concludes with future perspectives on the challenges to be addressed and potential research directions. We believe that this review will be helpful to readers and attract more scientists to join the topic of CO2 conversion.
Constructing efficient catalysts for thermocatalysis of CO2 to valuable products has attracted wide attention, and noble‐metal‐free metal–organic frameworks (MOFs) have become promising candidates owing to high efficiency and low cost. This review discusses CO2 conversion catalysed by noble‐metal‐free MOFs, such as conversion of CO2 to benzimidazoles, N‐formamides, carboxylic acids, carbonic esters, or oxazolidinones.
Single‐crystalline nanotubes of spinel LiMn2O4 with a diameter of about 600 nm, a wall thickness of about 200 nm and a length of 1–4 μm have been synthesized via a template‐engaged reaction using ...β‐MnO2 nanotubes as a self‐sacrifice template. In this fabrication, a minimal structural reorganization can be responsible for the chemical transformation from 001‐oriented β‐MnO2 template to 110‐oriented LiMn2O4. Galvanostatic charge/discharge measurements indicate that the nanotubes exhibit superior high‐rate capabilities and good cycling stability. About 70% of its initial capacity can be retained after 1500 cycles at 5 C rate. Importantly, the tubular nanostructures and the single‐crystalline nature of the most LiMn2O4 nanotubes are also well preserved after prolonged charge/discharge cycling at a relatively high current density, indicating good structural stability of the single‐crystalline nanotubes during lithium intercalation/deintercalation process. As is confirmed from Raman spectra analyses, no evident microstructural changes occur upon long‐term cycling. These results reveal that single‐crystalline nanotubes of LiMn2O4 will be one of the most promising cathode materials for high‐power lithium ion batteries.
1D single‐crystalline nanotubes of spinel LiMn2O4 targeted for high‐power lithium ion batteries are fabricated based on a template‐engaged reaction. This product delivers superior high‐rate capabilities and good cycling stability. Even after prolonged cycling at high‐current densities, the tubular morphology and high‐crystallinity characteristics of LiMn2O4 can be retained, indicating their potential application in high‐power lithium ion batteries, especially for electric vehicles.
Mesoscale Auroral Curls in Antarctica Li, Xing‐Yu; Zong, Qiu‐Gang; Hu, Ze‐Jun ...
Geophysical research letters,
16 May 2024, Letnik:
51, Številka:
9
Journal Article
Recenzirano
Odprti dostop
The morphology and motion of auroras have been widely studied due to their indications on magnetospheric processes. Here, we report a new kind of “auroral curls,” which have wavelengths in the ...mesoscale (∼100 km) and propagate azimuthally. Utilizing data from the Chinese Antarctic Zhongshan Station (the all‐sky imager and the high‐frequency radar), the Active Magnetosphere and Planetary Electrodynamics Response Experiment and the Defense Meteorological Satellite Program, we analyze an event occurred on 23 April 2019. We find these curls are fine structures in the poleward boundary of multiple arcs. Corresponding field‐aligned currents manifest as a series of longitudinally arranged pairs, while ionospheric flow velocities nearby oscillate with periods in the Pc 5 band. Observational evidence suggests these curls are connected with ultra‐low frequency (ULF) waves, which opens the possibility of using auroras to globally image ULF waves.
Plain Language Summary
Auroras caused by precipitation of magnetospheric particles contain information about physical processes happened in the magnetosphere. In this letter, we report a new kind of auroral dynamic forms observed in Antarctica. These structures present both spatial and temporal periodic characteristics, which have similar scales with those of magnetospheric ultra‐low frequency (ULF) waves. We propose these auroral forms are connected with ULF waves, which provides a potential method to globally image ULF waves by analyzing properties of these auroras.
Key Points
Azimuthally propagating “auroral curls” with mesoscale wavelengths were observed in Antarctica
These curls are fine structures in the poleward boundary of multiple arcs formed by longitudinal‐arranged field‐aligned current pairs
Ionospheric flow velocities nearby oscillate with periods in the Pc 5 band, indicating connections with ultra‐low frequency waves
The cell microenvironment has emerged as a key determinant of cell behavior and function in development, physiology, and pathophysiology. The extracellular matrix (ECM) within the cell ...microenvironment serves not only as a structural foundation for cells but also as a source of three-dimensional (3D) biochemical and biophysical cues that trigger and regulate cell behaviors. Increasing evidence suggests that the 3D character of the microenvironment is required for development of many critical cell responses observed in vivo, fueling a surge in the development of functional and biomimetic materials for engineering the 3D cell microenvironment. Progress in the design of such materials has improved control of cell behaviors in 3D and advanced the fields of tissue regeneration, in vitro tissue models, large-scale cell differentiation, immunotherapy, and gene therapy. However, the field is still in its infancy, and discoveries about the nature of cell–microenvironment interactions continue to overturn much early progress in the field. Key challenges continue to be dissecting the roles of chemistry, structure, mechanics, and electrophysiology in the cell microenvironment, and understanding and harnessing the roles of periodicity and drift in these factors. This review encapsulates where recent advances appear to leave the ever-shifting state of the art, and it highlights areas in which substantial potential and uncertainty remain.
The zinc (Zn) stable isotope system has great potential for tracing planetary formation and differentiation processes due to its chalcophile, lithophile and moderately volatile character. As an ...initial approach, the terrestrial mantle, and by inference, the bulk silicate Earth (BSE), have previously been suggested to have an average δ66Zn value of ∼+0.28‰ (relative to JMC 3-0749L) primarily based on oceanic basalts. Nevertheless, data for mantle peridotites are relatively scarce and it remains unclear whether Zn isotopes are fractionated during mantle melting. To address this issue, we report high-precision (±0.04‰; 2SD) Zn isotope data for well-characterized peridotites (n=47) from cratonic and orogenic settings, as well as their mineral separates. Basalts including mid-ocean ridge basalts (MORB) and ocean island basalts (OIB) were also measured to avoid inter-laboratory bias. The MORB analyzed have homogeneous δ66Zn values of +0.28±0.03‰ (here and throughout the text, errors are given as 2SD), similar to those of OIB obtained in this study and in the literature (+0.31±0.09‰). Excluding the metasomatized peridotites that exhibit a wide δ66Zn range of −0.44‰ to +0.42‰, the non-metasomatized peridotites have relatively uniform δ66Zn value of +0.18±0.06‰, which is lighter than both MORB and OIB. This difference suggests a small but detectable Zn isotope fractionation (∼0.1‰) during mantle partial melting. The magnitude of inter-mineral fractionation between olivine and pyroxene is, on average, close to zero, but spinels are always isotopically heavier than coexisting olivines (Δ66ZnSpl-Ol=+0.12±0.07‰) due to the stiffer Zn-O bonds in spinel than silicate minerals (Ol, Opx and Cpx). Zinc concentrations in spinels are 11–88 times higher than those in silicate minerals, and our modelling suggests that spinel consumption during mantle melting plays a key role in generating high Zn concentrations and heavy Zn isotopic compositions of MORB. Therefore, preferential melting of spinel in the peridotites may account for the Zn isotopic difference between spinel peridotites and basalts. By contrast, the absence of Zn isotope fractionation between silicate minerals suggests that Zn isotopes are not significantly fractionated during partial melting of spinel-free garnet-facies mantle. If the studied non-metasomatized peridotites represent the refractory upper mantle, mass balance calculation shows that the depleted MORB mantle (DMM) has a δ66Zn value of +0.20±0.05‰ (2SD), which is lighter than the primitive upper mantle (PUM) estimated in previous studies (+0.28±0.05‰, 2SD, Chen et al., 2013b; +0.30±0.07‰, 2SD, Doucet et al., 2016). This indicates that the Earth’s upper mantle has a heterogeneous Zn isotopic composition vertically, which is probably due to shallow mantle melting processes.
•The viability of using DCLs in partially encased composite columns is examined.•PEC columns’ stiffness and ultimate strength are less influenced by the incorporation of DCLs.•Post-peak behavior is ...negatively affected by DCLs, thus closer link spacing is needed.•A uniaxial constitutive model is proposed for the concrete core of PEC columns.
Steel-concrete composite members incorporating demolished concrete lumps (DCLs) have been devised to provide an innovative alternative means of recycling old concrete. Field applications have demonstrated those members’ potential. In this study the aforementioned recycling method is applied to steel-concrete partially encased composite (PEC) columns. To evaluate the viability of this new solution, a comparative experimental campaign was implemented to investigate the behavior of eleven large-scale PEC columns containing different content of DCLs under axial compression. The key parameters considered were replacement ratio of DCLs, steel flange thickness, spacing of transverse links, the source of DCLs.
Overall, the initial stiffness and axial load-carrying capacity of the PEC columns containing up to 33% DCLs were found to be comparable to those of the columns cast with new concrete alone. Nevertheless, a more rapid load drop right after the peak was observed for the columns containing DCLs when the link spacing equaled or exceeded half the column section depth. To remedy this, a maximum link spacing limit of 0.3d (d = the column section depth) is recommended for the columns containing DCLs. An analytical model is then developed to reproduce the full-range axial response of the PEC columns. The model accounts for the gain in strength due to concrete encasement and the loss due to flange buckling. It also attempts to capture the columns’ descending branch with recourse to the concept of compression fracture energy. Applicable to both types of PEC columns (i.e. containing DCLs or not), the proposed model exhibits a good accuracy, evidenced by comparing the prediction results against a set of test data compiled in this study.
Covering: up to the end of 2023
Cephalotane diterpenoids are a unique class of natural products exclusive to the genus
Cephalotaxus
, featuring a rigid 7,6,5,6-fused tetracyclic architecture. The ...study of cephalotanes dates back to the 1970s, when harringtonolide (
1
), a
Cephalotaxus
troponoid with a peculiar norditerpenoid carbon skeleton, was first discovered. In recent years, prototype C
20
diterpenoids proposed as cephalotane were disclosed, which triggered intense studies on this diterpenoid family. To date, a cumulative total of 105 cephalotane diterpenoids with great structural diversity and biological importance have been isolated. In addition, significant advances have been made in the field of total synthesis and biosynthesis of cephalotanes in recent years. This review provides a complete overview of the chemical structures, bioactivities, biosynthetic aspects, and completed total synthesis of all the isolated cephalotane diterpenoids, which will help guide future research on this class of compounds.
This review summarizes a total of 105 cephalotane diterpenoids, covering their isolation, structural features, biological activities, biosynthetic proposals, and completed total synthesis.
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