Metallic iron limits silicate hydration in Earth's transition zone.

The Earth's mantle transition zone (MTZ) is often considered an internal reservoir for water because its major minerals wadsleyite and ringwoodite can store several oceans of structural water. Whether it is a hydrous layer or an empty reservoir is still under debate. Previous studies suggested the MTZ may be saturated with iron metal. Here we show that metallic iron reacts with hydrous wadsleyite under the pressure and temperature conditions of the MTZ to form iron hydride or molecular hydrogen and silicate with less than tens of parts per million (ppm) water, implying that water enrichment is incompatible with iron saturation in the MTZ. With the current estimate of water flux to the MTZ, the iron metal preserved from early Earth could transform a significant fraction of subducted water into reduced hydrogen species, thus limiting the hydration of silicates in the bulk MTZ. Meanwhile, the MTZ would become gradually oxidized and metal depleted. As a result, water-rich region can still exist near modern active slabs where iron metal was consumed by reaction with subducted water. Heterogeneous water distribution resolves the apparent contradiction between the extreme water enrichment indicated by the occurrence of hydrous ringwoodite and ice VII in superdeep diamonds and the relatively low water content in bulk MTZ silicates inferred from electrical conductivity studies.

Origins of ultralow velocity zones through slab-derived metallic melt.

Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron-carbon system crosses the current geotherm near Earth's core-mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce the seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich postbridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth's core-mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle.

Hidden carbon in Earth's inner core revealed by shear softening in dense Fe7C3.

Earth's inner core is known to consist of crystalline iron alloyed with a small amount of nickel and lighter elements, but the shear wave (S wave) travels through the inner core at about half the speed expected for most iron-rich alloys under relevant pressures. The anomalously low S-wave velocity (vS) has been attributed to the presence of liquid, hence questioning the solidity of the inner core. Here we report new experimental data up to core pressures on iron carbide Fe7C3, a candidate component of the inner core, showing that its sound velocities dropped significantly near the end of a pressure-induced spin-pairing transition, which took place gradually between 10 GPa and 53 GPa. Following the transition, the sound velocities increased with density at an exceptionally low rate. Extrapolating the data to the inner core pressure and accounting for the temperature effect, we found that low-spin Fe7C3 can reproduce the observed vS of the inner core, thus eliminating the need to invoke partial melting or a postulated large temperature effect. The model of a carbon-rich inner core may be consistent with existing constraints on the Earth's carbon budget and would imply that as much as two thirds of the planet's carbon is hidden in its center sphere.

Design and stability analysis of the gear-type mobile mechanism with a single actuator.

Gear mechanism transmits the motion and power of parallel axes, intersecting axes and staggered axes, which has been widely employed in production and life. Gear-type mobile mechanism is a type of robot that can achieve motion through gear transmission. Due to its unique motion mode, it can handle various tasks in certain unconventional environments, such as particularly steep surfaces. Cylindrical gear, bevel gear and non-cylindrical gear are taken as the main parts of the mechanism to form a novel research series, respectively. The models of gear-type mobile mechanism are established in this paper, and the degrees of freedom of the mechanism are briefly calculated based on the screw theory. Simultaneously, the influence of centroid trajectory on motion stability is discussed to solve the possible problem that opposite rotation occur during the movement. Furthermore, the trajectory model of zero moment point is calculated considering the motion of the gear-type mobile mechanism. After that, the simulation and experimental analysis of its motion capability show that the gear-type mobile mechanism has excellent characteristics in stability, flexibility and continuity.

Formation of large low shear velocity provinces through the decomposition of oxidized mantle.

Large Low Shear Velocity Provinces (LLSVPs) in the lowermost mantle are key to understanding the chemical composition and thermal structure of the deep Earth, but their origins have long been debated. Bridgmanite, the most abundant lower-mantle mineral, can incorporate extensive amounts of iron (Fe) with effects on various geophysical properties. Here our high-pressure experiments and ab initio calculations reveal that a ferric-iron-rich bridgmanite coexists with an Fe-poor bridgmanite in the 90 mol% MgSiO3-10 mol% Fe2O3 system, rather than forming a homogeneous single phase. The Fe3+-rich bridgmanite has substantially lower velocities and a higher VP/VS ratio than MgSiO3 bridgmanite under lowermost-mantle conditions. Our modeling shows that the enrichment of Fe3+-rich bridgmanite in a pyrolitic composition can explain the observed features of the LLSVPs. The presence of Fe3+-rich materials within LLSVPs may have profound effects on the deep reservoirs of redox-sensitive elements and their isotopes.

Valence and spin states of iron are invisible in Earth's lower mantle.

Heterogeneity in Earth's mantle is a record of chemical and dynamic processes over Earth's history. The geophysical signatures of heterogeneity can only be interpreted with quantitative constraints on effects of major elements such as iron on physical properties including density, compressibility, and electrical conductivity. However, deconvolution of the effects of multiple valence and spin states of iron in bridgmanite (Bdg), the most abundant mineral in the lower mantle, has been challenging. Here we show through a study of a ferric-iron-only (Mg0.46Fe3+0.53)(Si0.49Fe3+0.51)O3 Bdg that Fe3+ in the octahedral site undergoes a spin transition between 43 and 53 GPa at 300 K. The resolved effects of the spin transition on density, bulk sound velocity, and electrical conductivity are smaller than previous estimations, consistent with the smooth depth profiles from geophysical observations. For likely mantle compositions, the valence state of iron has minor effects on density and sound velocities relative to major cation composition.

Correlation between high density lipoprotein and monocyte subpopulations among stable coronary atherosclerotic heart disease patients.

High density lipoprotein (HDL) is a structurally and functionally heterogeneous molecular particle whose function is unclear in atherosclerosis at present. Studies show that small HDL functional imbalance may exist in Coronary Atherosclerotic Heart Disease (CAD) patients. Monocyte is considered to play an important role in atherosclerosis, in accordance with the expression of superficial CD14 and CD16, it can be divided into three subpopulations. The purpose of this study was to explore the relation between HDL and monocyte subpopulations among CAD patients. We report 90 cases of stable CAD patients and define the monocyte subpopulations as classical monocyte (CD14++CD16-; CM), intermediate monocyte (CD14+CD16+; IM), and non-classical monocyte (CD14+CD16++; NCM); HDL group is measured by polyacrylamide gel electrophoresis. The results indicated that the small HDL in blood serum has a correlation with proinflammatory NCM in circulation but a negative correction with CM and no relationship with diabetes, saccharify hemoglobin, hypertension, smoking history and taking dose of statins drugs and severity of disease. In conclusion, this study primarily confirms that micromolecule HDL level correlates with the increase of non-classical monocyte subpopulations and decrease of classical monocyte quantity. Thus demonstrates the proinflammatory correlation between micromolecule HDL and internal immunity in the development of stable atherosclerosis.