Electrical resistivity of nickel, iron and iron-silicon alloy melts at high pressure with implications for the thermal conductivity of the Earth’s core

The Earth’s liquid outer core (OC) is composed of Fe alloyed with up to 10% Ni and a small fraction of light elements. However, the effect of light elements such as Si on the transport properties of liquid Fe-alloy in Earth’s OC is not clear. Thermal conductivity (κ) and related electrical resistivity (ρ) are the least constrained parameters in OC. Therefore, the characterization of transport properties of Ni, Fe and Fe-Si at high pressure has important geophysical implications for the Earth’s core. The ρ of solid and liquid Ni, Fe and Fe 4%Si was measured at pressure and temperature up to 12 GPa and 2100 K, respectively. All experiments were conducted in a large volume multi-anvil press and the measurements were carried out using the new adaptation of the 4-wire method. A standard COnsortium on Materials Properties Research in Earth Sciences (COMPRES) octahedron cell was used as the pressure medium, while the internal components were redesigned to permit the preservation of the liquid sample geometry, to contain the melt and minimize the effect of diffusive contamination. In the solid state, the ρ of solid Fe and Ni exhibits the familiar pressure-dependent decrease after the Curie temperature (Tc). The anomalous ρ of Fe-4.5wt%Si above Tc is strongly modulated by temperature and pressure, and it is attributed to the phase transitions and structural ordering in the alloy. The ρ of liquid Ni remains constant at the onset of melting at all pressures. While ρ of liquid Fe decreases up to 5 GPa, it remains invariant along the melting boundary after the δ-γ-liquid triple point. The ρ of liquid Fe-4.5wt%Si remains constant along the melting boundary and matches 120 μΩcm for pure liquid Fe within the experimental uncertainties. The results are interpreted in the context of pressure dependent icosahedral short range ordering (ISRO) in liquid 3d metals and alloys. Based on this, it is postulated that ρ of Fe-alloys along the melting boundary remains invariant up to Earth’s inner core boundary. The κ at the core-mantle boundary and inner core boundary were calculated using the Weidemann-Franz law

Viscosity of Sulfur at 4.5 GPa in the L and L’ Liquid Regions

Sulfur is an element with the most complex phase diagram, both in solid and liquid form, of any element. Unique to liquid sulfur is the ^-transition, characterized by a sharp jump in specific heat and almost four orders of magnitude increase in viscosity in the narrow temperature range from 159°C to 187°C at room pressure. As a likely constituent of the Earth’s outer core, the behavior of sulfur under high pressure is important as it can elucidate the potential effect of sulfur on the dynamics and the viscosity of the Earth’s outer core. The viscosity of liquid sulfur was measured at 4.5 GPa and at 726°C and 1100°C, which corresponds to the L and L’ liquid regions of the phase diagram, respectively. The falling sphere and quench and recover method using a 1000 ton cubic anvil press was utilized to evaluate viscosity under indicated pressure and temperatures. The results show that the viscosity of liquid sulfur decreases with temperature and is in line with the results from Terasaki et al. (2004) at lower temperatures. The presence of polymer was established at 4.5 GPa and 726°C and subsequently measured to be 17.8% using CS2 solution method. Evidence from Raman spectroscopy on recovered samples, and experiments at isothermal temperature (800°C) and pressures ranging from 3.5 GPa to 4.5 GPa indicate that polymerization increases with temperature. Additionally, a density driven phase transition was observed at 726°C along with three distinct and time dependent phases coexisting at 1100°C. The existence of the second order liquid-liquid phase transition in liquid sulfur at reported pressure and below 726°C is discussed in the light of recent publications. Moreover, evidence supporting the proposed k-transition, suppressed by the high pressures and shifted significantly upward in the temperature range above the melting curve is presented

Potential for Measurement of Mesospheric Ozone Density from Overdense Meteor Trains with a Monostatic Meteor Radar

Thermally ablating meteoroids, colliding with the Earth’s atmosphere, leave a high temperature trail containing extremely energetic metallic ions and electrons. A well recognized, but unresolved, anomaly associated with ambipolar diffusion of meteor trains, which is more dominant in overdense meteors, takes place in the initial post-adiabatic train expansion. In this work, a newly proposed mechanism explaining this anomaly involves hyperthermal chemical reactions is presented. Data from the SKiYMET meteor radar system, deployed at latitudinally dispersed locations, were used to determine ozone density in the upper atmosphere by analyzing diffusion of overdense meteor trains. The results obtained in this study are in line with satellite measurements of ozone density. Moreover, it was demonstrated that backscatter can detect a direct signature of the newly discovered hyperthermal chemical reactions in overdense meteor trains. The hypothesis proposed in this thesis, suggesting the possibility of measuring the upper atmosphere ozone density using backscatter radar, has been validated

The nexus of vitamin homeostasis and DNA synthesis and modification in mammalian brain

The purpose of this review is to discuss the implications of the 2009 discovery of the sixth deoxyribonucleoside (dN) [5-hydroxymethyldeoxycytidine (hmdC)] in DNA which is the most abundant in neurons. The concurrent discovery of the three ten-eleven translocation enzymes (TET) which not only synthesize but also oxidize hmdC in DNA, prior to glycosylase removal and base excision repair, helps explain many heretofore unexplained phenomena in brain including: 1) the high concentration of ascorbic acid (AA) in neurons since AA is a cofactor for the TET enzymes, 2) the requirement for reduced folates and the dN synthetic enzymes in brain, 3) continued DNA synthesis in non-dividing neurons to repair the dynamic formation/removal of hmdC, and 4) the heretofore unexplained mechanism to remove 5-methyldeoxycytidine, the fifth nucleoside, from DNA. In these processes, we also describe the important role of choroid plexus and CSF in supporting vitamin homeostasis in brain: especially for AA and folates, for hmdC synthesis and removal, and methylated deoxycytidine (mdC) removal from DNA in brain. The nexus linking AA and folates to methylation, hydroxymethylation, and demethylation of DNA is pivotal to understanding not only brain development but also the subsequent function

GraphX: Unifying Data-Parallel and Graph-Parallel Analytics

From social networks to language modeling, the growing scale and importance of graph data has driven the development of numerous new graph-parallel systems (e.g., Pregel, GraphLab). By restricting the computation that can be expressed and introducing new techniques to partition and distribute the graph, these systems can efficiently execute iterative graph algorithms orders of magnitude faster than more general data-parallel systems. However, the same restrictions that enable the performance gains also make it difficult to express many of the important stages in a typical graph-analytics pipeline: constructing the graph, modifying its structure, or expressing computation that spans multiple graphs. As a consequence, existing graph analytics pipelines compose graph-parallel and data-parallel systems using external storage systems, leading to extensive data movement and complicated programming model. To address these challenges we introduce GraphX, a distributed graph computation framework that unifies graph-parallel and data-parallel computation. GraphX provides a small, core set of graph-parallel operators expressive enough to implement the Pregel and PowerGraph abstractions, yet simple enough to be cast in relational algebra. GraphX uses a collection of query optimization techniques such as automatic join rewrites to efficiently implement these graph-parallel operators. We evaluate GraphX on real-world graphs and workloads and demonstrate that GraphX achieves comparable performance as specialized graph computation systems, while outperforming them in end-to-end graph pipelines. Moreover, GraphX achieves a balance between expressiveness, performance, and ease of use