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Full-Text Articles in Physics

High Pressure Phase Transformations Revisited, Valery I. Levitas Jan 2018

High Pressure Phase Transformations Revisited, Valery I. Levitas

Aerospace Engineering Publications

High pressure phase transformations play an important role in the search for new materials and material synthesis, as well as in geophysics. However, they are poorly characterized, and phase transformation pressure and pressure hysteresis vary drastically in experiments of different researchers, with different pressure transmitting media, and with different material suppliers. Here we review the current state, challenges in studying phase transformations under high pressure, and the possible ways in overcoming the challenges. This field is critically compared with fields of phase transformations under normal pressure in steels and shape memory alloys, as well as plastic deformation of materials. The ...


Phase Transitions In Mgsio3 Post-Perovskite In Super-Earth Mantles, Koichiro Umemoto, Renata M. Wentzcovitch, Shunqing Wu, Min Ji, Cai-Zhuang Wang, Kai-Ming Ho Nov 2017

Phase Transitions In Mgsio3 Post-Perovskite In Super-Earth Mantles, Koichiro Umemoto, Renata M. Wentzcovitch, Shunqing Wu, Min Ji, Cai-Zhuang Wang, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

The highest pressure form of the major Earth-forming mantle silicate is MgSiO3 post-perovskite (PPv). Understanding the fate of PPv at TPa pressures is the first step for understanding the mineralogy of super-Earths-type exoplanets, arguably the most interesting for their similarities with Earth. Modeling their internal structure requires knowledge of stable mineral phases, their properties under compression, and major element abundances. Several studies of PPv under extreme pressures support the notion that a sequence of pressure induced dissociation transitions produce the elementary oxides SiO2 and MgO as the ultimate aggregation form at ∼3 TPa. However, none of these studies have addressed ...


Strain-Induced Disorder, Phase Transformations, And Transformation-Induced Plasticity In Hexagonal Boron Nitride Under Compression And Shear In A Rotational Diamond Anvil Cell: In Situ X-Ray Diffraction Study And Modeling, Valery I. Levitas, Yanzhang Ma, Javad Hashemi, Mark Holtz, Necip Guven Jan 2006

Strain-Induced Disorder, Phase Transformations, And Transformation-Induced Plasticity In Hexagonal Boron Nitride Under Compression And Shear In A Rotational Diamond Anvil Cell: In Situ X-Ray Diffraction Study And Modeling, Valery I. Levitas, Yanzhang Ma, Javad Hashemi, Mark Holtz, Necip Guven

Valery I. Levitas

Plastic shear significantly reduces the phase transformation (PT) pressure when compared to hydrostatic conditions. Here, a paradoxical result was obtained: PT of graphitelike hexagonal boron nitride (hBN) to superhard wurtzitic boron nitride under pressure and shear started at about the same pressure(∼10GPa) as under hydrostatic conditions. In situ x-ray diffraction measurement and modeling of the turbostratic stacking fault concentration (degree of disorder) and PT in hBN were performed. Under hydrostaticpressure, changes in the disorder were negligible. Under a complex compression and shear loading program, a strain-induced disorder was observed and quantitatively characterized. It is found that the strain-induced disorder ...


Role Of Stratospheric Air In A Severe Weather Event: Analysis Of Potential Vorticity And Total Ozone, Melissa A. Goering, William A. Gallus Jr., Mark A. Olsen, John L. Stanford Jun 2001

Role Of Stratospheric Air In A Severe Weather Event: Analysis Of Potential Vorticity And Total Ozone, Melissa A. Goering, William A. Gallus Jr., Mark A. Olsen, John L. Stanford

Geological and Atmospheric Sciences Publications

The role of dry stratospheric air descending to low and middle tropospheric levels in a severe weather outbreak in the midwestern United States is examined using NCEP Eta model output, Rapid Update Cycle (RUC) analyses, and Earth probe Total Ozone Mapping Spectrometer (EP/TOMS) total ozone data. While stratospheric air was not found to play a direct role in the convection, backward trajectories show stratospheric air descended to 800 hPa just west of the convection. Damaging surface winds not associated with thunderstorms also occurred in the region of greatest stratospheric descent. Small-scale features in the high-resolution total ozone data compare ...


Fine-Scale Comparison Of Toms Total Ozone Data With Model Analysis Of An Intense Midwestern Cyclone, Mark A. Olsen, William A. Gallus Jr., John L. Stanford, John M. Brown Aug 2000

Fine-Scale Comparison Of Toms Total Ozone Data With Model Analysis Of An Intense Midwestern Cyclone, Mark A. Olsen, William A. Gallus Jr., John L. Stanford, John M. Brown

Geological and Atmospheric Sciences Publications

High-resolution (∼40 km) along-track total column ozone data from the Total Ozone Mapping Spectrometer (TOMS) instrument are compared with a high-resolution mesoscale numerical model analysis of an intense cyclone in the Midwestern United States. Total ozone increased by ∼100 DU (nearly 38%) as the TOMS instrument passed over the associated tropopause fold region. Complex structure is seen in the meteorological fields and compares well with the total ozone observations. Ozone data support the meteorological analysis showing that stratospheric descent was confined to levels above ∼600 hPa; significant positive potential vorticity at lower levels is attributable to diabatic processes. Likewise, meteorological ...


Radiation- And Lag-Errors In The Measurement Of Turbulent Temperature Fluctuations, James E. Mcdonald Jan 1951

Radiation- And Lag-Errors In The Measurement Of Turbulent Temperature Fluctuations, James E. Mcdonald

Retrospective Theses and Dissertations

No abstract provided.