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There is a great abundance of sedimentary dolomite in the Proterozoic and Lower Paleozoic, but examples of primary dolomite are scarce in the Cenozoic. This discrepancy suggests a poorly understood but dramatic shift in the geochemical system that inhibited dolomite formation. Previous research on microbial-mediated dolomite formation demonstrated that microbial activity could promote disordered dolomite precipitation through the catalytic role of polysaccharides. However, the microbial-mediated model cannot explain some of the Precambrian dolomite for which there is no evidence of microbial origin. Here, we present an abiotic mechanism with dissolved silica catalyzed dolomite precipitation that provides new insight into this long-lasting “dolomite problem.” In this study, we demonstrate that the presence of 1–2 mM of aqueous Si(OH)4 in high Mg:Ca ratio solutions at room temperature will promote disordered dolomite precipitation (with up to 48.7 mol% MgCO3) and inhibit aragonite formation. Dissolved silica in solution also promotes Mg incorporation into the Ca-Mg carbonates. Dissolved silica possesses low-dipole moment and dielectric constant similar to hydrogen sulfide, dioxane, polysaccharide, and exopolymeric substances (EPS), which are catalysts in previously established room-temperature dolomite synthesis. The molecules with low-dipole moment adsorbed on the dolomite surface can lower the dehydration energy barrier of a surface Mg2+-water complex and promote dolomite nucleation and growth. This study provides a new model for abiotic sedimentary dolomite formation, which is likely to be responsible for the significant amount of primary dolomite in Earth history.

Oxidative weathering of pyrite plays an important role in the biogeochemical cycling of Fe and S in terrestrial environments. While the mechanism and occurrence of biologically accelerated pyrite oxidation under acidic conditions are well established, much less is known about microbially mediated pyrite oxidation at circumneutral pH. Recent work (Percak-Dennett et al., 2017, Geobiology, 15, 690) has demonstrated the ability of aerobic chemolithotrophic microorganisms to accelerate pyrite oxidation at circumneutral pH and proposed two mechanistic models by which this phenomenon might occur. Here, we assess the potential relevance of aerobic microbially catalyzed circumneutral pH pyrite oxidation in relation to subsurface shale weathering at Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) in Pennsylvania, USA. Specimen pyrite mixed with native shale was incubated in groundwater for 3 months at the inferred depth of in situ pyrite oxidation. The colonized materials were used as an inoculum for pyrite-oxidizing enrichment cultures. Microbial activity accelerated the release of sulfate across all conditions. 16S rRNA gene sequencing and metagenomic analysis revealed the dominance of a putative chemolithoautotrophic sulfur-oxidizing bacterium from the genus Thiobacillus in the enrichment cultures. Previously proposed models for aerobic microbial pyrite oxidation were assessed in terms of physical constraints, enrichment culture geochemistry, and metagenomic analysis. Although we conclude that subsurface pyrite oxidation at SSCHZO is largely abiotic, this work nonetheless yields new insight into the potential pathways by which aerobic microorganisms may accelerate pyrite oxidation at circumneutral pH. We propose a new "direct sulfur oxidation" pathway, whereby sulfhydryl-bearing outer membrane proteins mediate oxidation of pyrite surfaces through a persulfide intermediate, analogous to previously proposed mechanisms for direct microbial oxidation of elemental sulfur. The action of this and other direct microbial pyrite oxidation pathways have major implications for controls on pyrite weathering rates in circumneutral pH sedimentary environments where pore throat sizes permit widespread access of microorganisms to pyrite surfaces.

Ti(C,N)-TiB2 cermets were fabricated from Ti(C,N), TiB2, Co and WC powder mixtures via a vacuum hot pressing process. The influence of TiB2 content on their microstructures and mechanical properties was investigated. As a result of the elevated TiB2 contents, two types of core-rim microstructures were present in the Ti(C,N)-TiB2 cermets, and remarkably improved mechanical properties were achieved. With the increase of TiB2 content, the flexural strength, fracture toughness and hardness of the Ti(C,N)-TiB2 cermets first increased, and then decreased, while their relative density consistently decreased. Attributed to an integration of the intergranular and intrangranular fracture behaviors, the Ti(C,N)-TiB2 cermets with 20 wt% TiB2 content exhibited the best overall properties with the relative density, hardness, fracture toughness and flexural strength at 99.3%, 1 995 H V, 7.92 MPa·m1/2 and 1 114 MPa, respectively. The underlying mechanism for their enhanced properties was studied in detail.

The aim of this study was to improve the mechanical properties of Al 2 O 3 ceramics by the addition of Y 2 O 3 -stabilized ZrO 2 whiskers (designated as Al 2 O 3 /YSZ W composite) through the flux method and hot-pressing technology. The effect of YSZ W content on their microstructure , phase composition and transformability, mechanical properties, and wear resistance was systematically investigated. The Al 2 O 3 /YSZ W composites containing 10 wt% YSZ W exhibited the best mechanical performance, including the highest content of YSZ W tetragonal phase and transformability as well as the largest values in their relative density (99.5%), hardness (1969 HV), fracture toughness (9.57 MPa m 1/2 ) and flexural strength (855 MPa). The strengthening and toughening of the Al 2 O 3 /YSZ W composites were attributed to the YSZ W tetragonal-monoclinic phase transformation as well as the whiskers reinforcing effect. Furthermore, the Al 2 O 3 /YSZ W composites also showed the highest friction and wearing properties.

Although calcareous anatomical structures have evolved in diverse animal groups, such structures have been unknown in insects. Here, we report the discovery of high-magnesium calcite [CaMg(CO3)2] armor overlaying the exoskeletons of major workers of the leaf-cutter ant Acromyrmex echinatior. Live-rearing and in vitro synthesis experiments indicate that the biomineral layer accumulates rapidly as ant workers mature, that the layer is continuously distributed, covering nearly the entire integument, and that the ant epicuticle catalyzes biomineral nucleation and growth. In situ nanoindentation demonstrates that the biomineral layer significantly hardens the exoskeleton. Increased survival of ant workers with biomineralized exoskeletons during aggressive encounters with other ants and reduced infection by entomopathogenic fungi demonstrate the protective role of the biomineral layer. The discovery of biosynthesized high-magnesium calcite in the relatively well-studied leaf-cutting ants suggests that calcareous biominerals enriched in magnesium may be more common in metazoans than previously recognized.

Si3N4 ceramics with excellent mechanical properties and microstructure were fabricated by microwave sintering. The effects of sintering additives on the densification, phase transformation and grain growth of Si3N4 ceramics were investigated. The results showed that Y2O3 can promote the phase transformation, MgO can decrease the sintering temperature, Al2O3 can increase the Vickers hardness of the samples and the combination of Y2O3 and MgO was more effective in enhancing the densification and phase transformation in the microwave sintering. The samples with 5 wt%Y2O3, 5 wt%MgO and 2 wt%Al2O3 sintering additives had the optimum mechanical properties when sintered at 1700 ℃ for 10 min. Its relative density, fracture toughness and Vickers hardness were 98.52±0.13%, 6.44±0.02 MPa m1/2 and 14.92±0.20 GPa, respectively. Compared to other microwave sintered Si3N4, the hardness and fracture toughness were enhanced by 6.6–24.3% and 5.6–11%, respectively, while the sintering holding time was reduced by 33.3–83.3%.

With the increase of the height of the filled slope, the application of multiple combination retaining structures (MCRS) is becoming more and more popular. However, the traditional design methods seldom consider the coupling effects between the substructures. To investigate the interaction of MCRS, this paper takes the filled slope project of a middle school in Quanzhou City, Fujian Province, China as an example. The filled slope was supported by MCRS, including reinforced soil, doublerow piles, anchors and counterfort retaining walls. The simulate procedure mainly included the following process: first, the MCRS model was established, then the mechanical response of the MCRS when replacing the fill materials and increasing the length of the rear row piles were obtained, and a comparative analysis was carried out. The following conclusions could be drawn: (1) The properties of backfill material have a significant impact on the displacement of backfill slope, and when the backfill is gravel soil, the displacement of slope can be controlled to a satisfactory degree. When the back-fill soil is replaced by silty clay, the shear strength and internal friction angle of soil become smaller, thus the displacement of slope increases significantly, which may lead to slope failure. (2) When the anchorage length is satisfied, increasing the length of the rear row pile has no significant effect on reducing the displacement of MCRS slope, but it can effectively reduce the axial force of anchor rod. (3) In MCRS, each substructure has complex interaction, and numerical simulation provides an effective means for accurate evaluation of MCRS.

Ediacaran phosphorites capture the dynamics of the ultimate biolimiting nutrient, phosphorus, during perhaps the most critical transition of Earth's climatic and ecological history. Concomitant with the Neoproterozoic Oxygenation Event was the deposition of the first extensive phosphorites across marine shelves, typically interpreted as a basinward shift in the locus of phosphogenesis facilitated by deep-ocean oxygenation. Petrographic and spectroscopic analyses of proximal phosphorites from the Ediacaran Doushantuo Formation near the Yangtze Gorges area of South China reveal the presence of interlaminated pristine, muddy, and granular phosphorites that were cemented by early diagenetic iron phosphate, an additional, previously undocumented seafloor P sink. Transmitted- and reflected-light microscopy, cathodoluminescence microscopy, and back-scattered electron scanning electron microscopy were used to reconstruct the paragenesis of phosphorites at the Wanjiagou section near Zhangcunping (Hubei Province) and demonstrate that pristine phosphorite precipitated authigenically as francolite via microbially-mediated phosphogenesis as evidenced by preserved microbial laminations along with filamentous and coccoidal microfossils. Subsequent tidal reworking of pristine hardgrounds and phosphatic mudstones produced minimally-coated intraclasts and peloidal phosphatic grains that were cemented by iron phosphate soon after deposition but before compaction. Raman spectroscopy, bulk-sample and micro-X-ray diffractometry indicate the iron phosphate cement is composed of phosphosiderite/strengite (Fe+3PO4•2H2O). The presence of phosphosiderite can be attributed to either syndepositional oxidation of phosphorites or thermal stabilization of vivianite (Fe2+3(PO4)2•8H2O). In both cases, the occurrence of phosphosiderite represents the first direct evidence for iron phosphate minerals as a P sink during the Ediacaran and suggests phosphogenesis may have partially proceeded in ferruginous porewaters in contrast to the redox-independent process of francolite precipitation. Integration of petrographic and geochemical techniques, such as those employed in this study, offers the ability to corroborate P speciation analyses and provides an independent determination of P phase partitioning. Ultimately, this approach is paramount in testing hypotheses that suggest ferrous iron phosphate minerals played a regulatory role in global Proterozoic oxygenation.

Naturally occurring porous minerals as adsorbents for the remediation of environmental pollution has been one of the hot topics in environmental science and material science. In this study, the adsorption of iodate (IO3−) on two nanosized tubular halloysite samples (HBHal and SCHal, from Hubei and Sichuan Province, China, respectively) were investigated for the first time. To evaluate the impact of nanopore of halloysite on the adsorption of IO3−, chemically similar platy kaolinite was used for comparative studies in the batch experiments. The adsorption of IO3− on HBHal reached equilibrium within 36 h, and the adsorption kinetics and isotherm fitted the pseudo-second-order and Langmuir equation well, respectively. Both HBHal and SCHal exhibited high adsorption capability to IO3−, with distribution coefficients (Kd's) of 131.6 ± 14.6 and 126.6 ± 3.1 mL/g, respectively, which were >30 times higher than that for kaolinite (4.2 ± 2.3 mL/g). The specific surface area normalized Kd values on halloysite samples were >13.5-fold higher than that on kaolinite. In addition, halloysite had high selectivity to IO3−, and the adsorption capacities on the two halloysite samples were slightly affected by the concurrent anions, such as SO42−, NO3−, or ClO3−. It was proposed that the curved octahedral sheet caused geometry match between three oxygen atoms in the iodate and three OH above the vacant site of the octahedral sheet. This work also gave insight into the potential application of halloysite on the adsorption of radioactive iodate in natural and engineering environments.

Al0.3CoCrFeNi high-entropy alloy (HEA) prepared by mechanical alloying was used as a metal binder for the Ti(C,N)-based cermets by hot-pressing sintering. Room-temperature microstructure and high-temperature oxidation resistance, mechanical and wear resistance properties of the Ti(C,N)-based cermets with HEA metal binder (cermets TA) were comprehensively investigated and compared with the Ti(C,N)-based cermets containing the conventional Ni–Co metal binder (cermets TN). Different from the Ni–Co binder, the HEA metal binder not only largely enhanced the hardness and fracture toughness of Ti(C,N)-based cermets at room temperature, but also retained notably higher hardness (Vickers hardness 1137 HV), fracture toughness (6.46 MPa m1/2) and flexural strength (761 MPa) at 1000 °C. The mechanism for such an excellent retention of mechanical properties at high-temperature by the cermets TA is attributed to the hindrance of their slip systems and the higher oxidation resistance of HEA metal binder. Furthermore, the hardened cermets TA exhibited better friction and wearing properties at high-temperature.

Molecular biology shows that phenotype of the crop is the ultimate concern in the research of crop yield, and to evaluate quality of results of the selective breeding, and it's also needed to acquire ideal plants by measuring each key parameter of phenotype of the crop, so as to popularize them. This article takes general rapeseed plant as researching example. Through adopting the new automatic measurement method-LSD (Line Segment Detector), it extracts line segments of image of the rapeseed plant rapidly; Then we joint and combine the extracted line segments that belong to the same stem, and adopt reasonable threshold value restriction respectively at different stages to remove the line segments having few contributions; finally, on the basis of the endpoint information of the whole jointed line segment and proportional scale relationship of the reference substance, we calculate the overall plant height, height of the first effective branch and length of the branch. At the end of the experiment, the measuring result of this article is compared with the parameter value acquired by measurement of high precision laser scanner. The result shows that: measuring error of plant height is within 3.9% and that of other parameters is less than 1.3%. Thus it proves that the method proposed in this article is effective, it can automatically extract and measure parameters of rapeseed plant phenotype and lay the foundation of researching relationship between phenotype parameters and yield and mechanized production, so as to better guide field work; Moreover, due to the high speed, low price and large quantity of memory space of measurement based on two-dimensional space, it has more benefits in the practical application.

The substrate effect of mica and hematite on the nucleation and crystallization of calcite was investigated using scanning electron microscope (SEM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) methods. On mica, we found, in the absence of Mg2+, the substrates’ (001) surfaces with hexagonal and pseudo-hexagonal two-dimensional (2-D) structure can affect the orientation of calcite nucleation with calcite (001) ~// mica (001) and calcite (010) ~// mica (010) to be the major interfacial relationship. On hematite, we did not observe frequent twinning relationship between adjacent calcite gains, but often saw preferentially nucleation of calcite at surface steps on hematite substrate. We suggest that calcite crystals initially nucleate from the Ca2+ layers adsorbed on the surfaces. The pseudo-hexagonal symmetry on mica (001) surface also leads to the observed calcite (001) twinning. A second and less common orientation between calcite {104} and mica (001) was detected but could be due to local structure damage of the mica surface. Results in the presence of Mg2+ show that the substrate surfaces can weaken Mg toxicity to calcite nucleation and lead to a higher level of Mg incorporation into calcite lattice.