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Phase transformation of hydrous ringwoodite to the lower-mantle phases and the formation of dense hydrous silica
In order to understand the effects of H 2 O on the mineral phases forming under the pressure-temperature conditions of the lower mantle, we have conducted laser-heated diamond-anvil cell experiments on hydrous ringwoodite (Mg 2 SiO 4 with 1.1wt% H 2 O) at pressures between 29 and 59 GPa and temperatures between 1200 and 2400 K. Our experimental results show that hydrous ringwoodite (hRw) converts to crystalline dense hydrous silica, stishovite (Stv) or CaCl 2 -type SiO 2 (mStv), containing 1 wt% H 2 O together with Brd and MgO at the pressure-temperature conditions expected for shallow lower-mantle depths between approximately 660 to 1600 km. Considering lack of sign for melting in our experiments, our preferred interpretation of the observation is that Brd partially breaks down to dense hydrous silica and periclase (Pc), forming Brd + Pc + Stv mineralogy. Our experiments may provide an explanation for the enigmatic coexistence of Stv and Fp inclusions in lower-mantle diamonds
Small Business Innovation Research GRC Phase I, Phase II, and Post-Phase II Opportunity Assessment for 2015
This report outlines the 2015 Small Business Innovation Research/Small Business Technology Transfer (SBIR/STTR) Phase I, Phase II, and Post-Phase II opportunity contract award results associated with NASA's Aeronautics Research Mission Directorate (ARMD), Human Exploration and Operations Mission Directorate (HEOMD), Science Mission Directorate (SMD), and Space Technology Mission Directorate (STMD) for NASA Glenn Research Center. The report also highlights the number of Phase I, Phase II, and Post-Phase II contracts awarded by mission directorate. The 2015 Phase I contract awards to companies in Ohio and their corresponding technologies are also discussed.
Phase relationship in three-phase composites which include a void phase
The paper shows the relationship among polymer, particles, and voids in a three-phase composite and how some of the properties of a composite may be changed by changing the proportions of the phases. The three-phase composite is an aggregate of microspheres bonded together with a small amount of polymer which may not form a continuous matrix. The void space (third phase) is obtained by limiting the amount of polymer which is mixed with the microspheres. A ternary phase diagram is used to show the proportional relationship among the three phases, with each apex representing a volume fraction of unity for a constituent while the side opposite the apex represents a volume fraction of zero for that constituent. The vertical dimension represents some composite property such as density or strength. The effect of composition on composite properties is shown by plotting them on a binary phase diagram which represents a perpendicular plane coincident with the 0.60 volume fraction microsphere line.
Emergent Low-Symmetry Phases and Large Property Enhancements in Ferroelectric KNbO 3 Bulk Crystals [Emergent Low-Symmetry Phases with Large Property Enhancement in Ferroelectric KNbO 3 Bulk Crystals]
The design of new or enhanced functionality in materials is traditionally viewed as requiring the discovery of new chemical compositions through synthesis. Large property enhancements may however also be hidden within already well-known materials, when their structural symmetry is deviated from equilibrium through a small local strain or field. Here, the discovery of enhanced material properties associated with a new metastable phase of monoclinic symmetry within bulk KNbO 3 is reported. This phase is found to coexist with the nominal orthorhombic phase at room temperature, and is both induced by and stabilized with local strains generated by a network of ferroelectric domain walls. While the local microstructural shear strain involved is only ≈0.017%, the concurrent symmetry reduction results in an optical second harmonic generation response that is over 550% higher at room temperature. Moreover, the meandering walls of the low-symmetry domains also exhibit enhanced electrical conductivity on the order of 1 S m -1 . In conclusion, this discovery reveals a potential new route to local engineering of significant property enhancements and conductivity through symmetry lowering in ferroelectric crystals.
Algebraic multigrid preconditioners for two-phase flow in porous media with phase transitions [Algebraic multigrid preconditioners for multiphase flow in porous media with phase transitions]
Multiphase flow is a critical process in a wide range of applications, including oil and gas recovery, carbon sequestration, and contaminant remediation. Numerical simulation of multiphase flow requires solving of a large, sparse linear system resulting from the discretization of the partial differential equations modeling the flow. In the case of multiphase multicomponent flow with miscible effect, this is a very challenging task. The problem becomes even more difficult if phase transitions are taken into account. A new approach to handle phase transitions is to formulate the system as a nonlinear complementarity problem (NCP). Unlike in the primary variable switching technique, the set of primary variables in this approach is fixed even when there is phase transition. Not only does this improve the robustness of the nonlinear solver, it opens up the possibility to use multigrid methods to solve the resulting linear system. The disadvantage of the complementarity approach, however, is that when a phase disappears, the linear system has the structure of a saddle point problem and becomes indefinite, and current algebraic multigrid (AMG) algorithms cannot be applied directly. In this study, we explore the effectiveness of a new multilevel strategy, based on the multigrid reduction technique, to deal with problems of this type. We demonstrate the effectiveness of the method through numerical results for the case of two-phase, two-component flow with phase appearance/disappearance. In conclusion, we also show that the strategy is efficient and scales optimally with problem size.
Onset of phase separation in the double perovskite oxide La 2 MnNiO 6
Not Available
Dynamic evolution of liquid-liquid phase separation during continuous cooling
Solidification from a multiphase fluid involves many unknown quantities due to the difficulty of predicting the impact of fluid flow on chemical partitioning. Real-time x-ray radiography has been used to observe liquideliquid phase separation in Al90In10 prior to solidification. Quantitative image analysis has been used to measure the motion and population characteristics of the dispersed indium-rich liquid phase during cooling. Here we determine that the droplet growth characteristics resemble well known steady-state coarsening laws with likely enhancement by concurrent growth due to supersaturation. Simplistic views of droplet motion are found to be insufficient until late in the reaction due to a hydrodynamic instability caused by the large density difference between the dispersed and matrix liquid phases.
Mechanical behaviors and phase transition of Ho{sub 2}O{sub 3} nanocrystals under high pressure
Mechanical properties and phase transition often show quite large crystal size dependent behavior, especially at nanoscale under high pressure. Here, we have investigated Ho{sub 2}O{sub 3} nanocrystals with in-situ x-ray diffraction and Raman spectroscopy under high pressure up to 33.5 GPa. When compared to the structural transition routine cubic -> monoclinic -> hexagonal phase in bulk Ho{sub 2}O{sub 3} under high pressure, the nano-sized Ho{sub 2}O{sub 3} shows a much higher onset transition pressure from cubic to monoclinic structure and followed by a pressure-induced-amorphization under compression. The detailed analysis on the Q (Q = 2π/d) dependent bulk moduli reveals the nanosized Ho{sub 2}O{sub 3} particles consist of a clear higher compressible shell and a less compressible core. Insight into these phenomena shed lights on micro-mechanism studies of the mechanical behavior and phase evolution for nanomaterials under high pressure, in general.
Anomalous compression behavior of germanium during phase transformation
Abstract not provided
Correlated structural and electronic phase transformations in transition metal chalcogenide under high pressure
Here, we report comprehensive studies on the high-pressure structural and electrical transport properties of the layered transition metal chalcogenide (Cr{sub 2}S{sub 3}) up to 36.3 GPa. A structural phase transition was observed in the rhombohedral Cr{sub 2}S{sub 3} near 16.5 GPa by the synchrotron angle dispersive X-ray diffraction measurement using a diamond anvil cell. Through in situ resistance measurement, the electric resistance value was detected to decrease by an order of three over the pressure range of 7–15 GPa coincided with the structural phase transition. Measurements on the temperature dependence of resistivity indicate that it is a semiconductor-to-metal transition in nature. The results were also confirmed by the electronic energy band calculations. Above results may shed a light on optimizing the performance of Cr{sub 2}S{sub 3} based applications under extreme conditions.
The phase diagram of Ti-6Al-4V at high-pressures and high-temperatures
We report results from a series of diamond-anvil-cell synchrotron x-ray diffraction and large-volume-press experiments, and calculations, to investigate the phase diagram of commercial polycrystalline high-strength Ti-6Al-4V alloy in pressure–temperature space. Up to ~30 GPa and 886 K, Ti-6Al-4V is found to be stable in the hexagonal-close-packed, or α phase. The effect of temperature on the volume expansion and compressibility of α–Ti-6Al-4V is modest. The martensitic α → ω (hexagonal) transition occurs at ~30 GPa, with both phases coexisting until at ~38–40 GPa the transition to the ω phase is completed. Between 300 K and 844 K the α → ω transition appears to be independent of temperature. ω–Ti-6Al-4V is stable to ~91 GPa and 844 K, the highest combined pressure and temperature reached in these experiments. Pressure–volume–temperature equations-of-state for the α and ω phases of Ti-6Al-4V are generated and found to be similar to pure Ti. A pronounced hysteresis is observed in the ω–Ti-6Al-4V on decompression, with the hexagonal structure reverting back to the α phase at pressures below ~9 GPa at room temperature, and at a higher pressure at elevated temperatures. Based on our data, we estimate the Ti-6Al-4V α–β–ω triple point to occur at ~900 K and 30 GPa, in good agreement with our calculations.
Discovery of a metastable Al{sub 20}Sm{sub 4} phase
We present an efficient genetic algorithm, integrated with experimental diffraction data, to solve a nanoscale metastable Al{sub 20}Sm{sub 4} phase that evolves during crystallization of an amorphous magnetron sputtered Al{sub 90}Sm{sub 10} alloy. The excellent match between calculated and experimental X-ray diffraction patterns confirms an accurate description of this metastable phase. Molecular dynamic simulations of crystal growth from the liquid phase predict the formation of disordered defects in the devitrified crystal.
Pressure suppression of electron correlation in the collapsed tetragonal phase of CaFe2As2
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Comparison of three-phase modulation with two-phase and four-phase modulation
For a constant added noise density at high signal-to-noise ratios and for the same error rate, three-phase PSK requires about 0.75 dB less energy per bit than two-phase or four-phase PSK. However, at very low signal-to-noise ratios, three-phase PSK requires about 0.74 dB more energy per bit of channel capacity than two-phase or four-phase PSK.