The pressure medium as a solid-state oxygen buffer

We present a simple method to buffer oxygen fugacity at high pressures and high temperatures where the traditional 'double capsule' method is inappropriate. The pressure medium is doped with a metal which partially reacts with the free oxygen in the pore spaces of the, cell. The resultant finely intergrown metal-metal oxide assemblage buffers the oxygen fugacity in the sample as long as the capsule and furnace materials are oxygen permeable

The electrical conductivity and thermal profile of the Earth's mid-mantle

Electrical conductivity in the Earth's mantle is sensitive to temperature and chemical environment. Recent laboratory measurements of electrical conductivity are combined with candidate mantle geotherms to produce synthetic electrical conductivity profiles. These profiles are used to forward model the Earth's geomagnetic response function C, results of which are compared with the observed globally averaged response function at periods of 3.5 days to 4 months. Candidate lower mantle geotherms, representing whole-mantle and layered convection end-members, are compared using published electrical conductivity measurements on alumina-bearing and alumina-free perovskite in the conductivity models. Comparison of the predicted response functions with the observed geomagnetic response of the Earth shows that a) if lower mantle alumina is incorporated into perovskite, then the lower mantle must be cool, and b) if the alumina is not incorporated in perovskite then the results are only consistent with a hot lower mantle. In addition, the maximum alumina content of lower mantle MgSiO3 perovskite is constrained at 4%

Electronic spin transitions and the seismic properties of ferrous iron-bearing MgSiO3 post-perovskite

The elastic constants of post-perovskite of chemical composition Mg0.9375Fe0.0625SiO3 and Mg0.8750Fe0.1250SiO3 have been calculated at 0 K and 136 GPa using ab initio methods. For both compositions studied, iron remains in a high-spin state below 180 GPa at 0 K. The effect of spin state on elastic properties is small. Logarithmic derivations of isotropic wave velocities and density with respect to ferrous iron content are similar to those predicted from pure end-members. Citation: Stackhouse, S., J. P. Brodholt, D. P. Dobson, and G. D. Price ( 2006), Electronic spin transitions and the seismic properties of ferrous iron-bearing MgSiO3 post-perovskite

Ab initio study of the phase separation of argon in molten iron at high pressures

Using first-principles molecular dynamics (MD) simulations, we study the solubility of argon in molten iron at high pressures and temperatures. In particular we explore whether the low pressure immiscibility of liquid Fe and Ar persists to high pressure (130 GPa) and temperature (4500K), or whether they mix. Starting from a variety of Fe/Ar mixtures we find that they always separate rapidly into two liquids. We conclude that there is no evidence for a significant increase in the solubility of Ar in Fe at these conditions. We cannot, therefore, attribute the lower melting temperatures of Fe obtained from DAC experiments compared to those obtained from ab initio calculations and shock experiments, to eutectic melting between Fe and the Ar pressure medium

Determination of Clinical Outcome in Mitral Regurgitation With Cardiovascular Magnetic Resonance Quantification

Background—Surgery for severe mitral regurgitation is indicated if symptoms or left ventricular dilation or dysfunction occur. However, prognosis is already reduced by this stage, and earlier surgery on asymptomatic patients has been advocated if valve repair is likely, but identifying suitable patients for early surgery is difficult. Quantifying the regurgitation may help, but evidence for its link with outcome is limited. Cardiovascular magnetic resonance (CMR) can accurately quantify mitral regurgitation, and we examined whether this was associated with the future need for surgery. Methods and Results—One hundred nine asymptomatic patients with echocardiographic moderate or severe mitral regurgitation had baseline CMR scans and were followed up for up to 8 years (mean, 2.5±1.9 years). CMR quantification accurately identified patients who progressed to symptoms or other indications for surgery: 91% of subjects with regurgitant volume ≤55 mL survived to 5 years without surgery compared with only 21% with regurgitant volume >55 mL (P40%. CMR-derived end-diastolic volume index showed a weaker association with outcome (proportions surviving without surgery at 5 years, 90% for left ventricular end-diastolic volume index <100 mL/m2 versus 48% for ≥100 mL/m2) and added little to the discriminatory power of regurgitant fraction/volume alone. Conclusions—CMR quantification of mitral regurgitation was associated with the development of symptoms or other indications for surgery and showed better discriminatory ability than the reference-standard CMR-derived ventricular volumes. CMR may be able to identify appropriate patients for early surgery, with the potential to change clinical practice, although the clinical benefits of early surgery require confirmation in a clinical trial

Deformation of NaCoF3 perovskite and post-perovskite up to 30 GPa and 1013 K: implications for plastic deformation and transformation mechanism

Texture, plastic deformation, and phase transformation mechanisms in perovskite and post-perovskite are of general interest for our understanding of the Earth's mantle. Here, the perovskite analogue NaCoF3 is deformed in a resistive-heated diamond anvil cell (DAC) up to 30 GPa and 1013 K. The in situ state of the sample, including crystal structure, stress, and texture, is monitored using X-ray diffraction. A phase transformation from a perovskite to a post-perovskite structure is observed between 20.1 and 26.1 GPa. Normalized stress drops by a factor of 3 during transformation as a result of transient weakening during the transformation. The perovskite phase initially develops a texture with a maximum at 100 and a strong 010 minimum in the inverse pole figure of the compression direction. Additionally, a secondary weaker 001 maximum is observed later during compression. Texture simulations indicate that the initial deformation of perovskite requires slip along (100) planes with significant contributions of {110} twins. Following the phase transition to post-perovskite, we observe a 010 maximum, which later evolves with compression. The transformation follows orientation relationships previously suggested where the c axis is preserved between phases and hh0 vectors in reciprocal space of post-perovskite are parallel to [010] in perovskite, which indicates a martensitic-like transition mechanism. A comparison between past experiments on bridgmanite and current results indicates that NaCoF3 is a good analogue to understand the development of microstructures within the Earth's mantle

The phase diagrams of KCaF3 and NaMgF3 by ab initio simulations

ABF3 compounds have been found to make valuable low-pressure analogues for high-pressure silicate phases that are present in the Earth’s deep interior and that may also occur in the interiors of exoplanets. The phase diagrams of two of these materials, KCaF3 and NaMgF3, have been investigated in detail by static ab initio computer simulations based on density functional theory. Six ABF3 polymorphs were considered, as follows: the orthorhombic perovskite structure (GdFeO3-type; space group Pbnm); the orthorhombic CaIrO3 structure (Cmcm; commonly referred to as the “post-perovskite” structure); the orthorhombic Sb2S3 and La2S3 structures (both Pmcn); the hexagonal structure previously suggested in computer simulations of NaMgF3 (P63/mmc); the monoclinic structure found to be intermediate between the perovskite and CaIrO3 structures in CaRhO3 (P21/m). Volumetric and axial equations of state of all phases considered are presented. For KCaF3, as expected, the perovskite phase is shown to be the most thermodynamically stable at atmospheric pressure. With increasing pressure, the relative stability of the KCaF3 phases then follows the sequence: perovskite → La2S3 structure → Sb2S3 structure → P63/mmc structure; the CaIrO3 structure is never the most stable form. Above about 2.6 GPa, however, none of the KCaF3 polymorphs are stable with respect to dissociation into KF and CaF2. The possibility that high-pressure KCaF3 polymorphs might exist metastably at 300 K, or might be stabilised by chemical substitution so as to occur within the standard operating range of a multi-anvil press, is briefly discussed. For NaMgF3, the transitions to the high-pressure phases occur at pressures outside the normal range of a multi-anvil press. Two different sequences of transitions had previously been suggested from computer simulations. With increasing pressure, we find that the relative stability of the NaMgF3 phases follows the sequence: perovskite → CaIrO3 structure → Sb2S3 structure → P63/mmc structure. However, only the perovskite and CaIrO3 structures are stable with respect to dissociation into NaF and MgF2

A Comparison of the Wholesale Model and the Agency Model in Differentiated Markets

We compare the wholesale model and the agency model that characterise a vertical relation in a bilateral duopoly framework. Results suggest that the agency model may be regarded as an example of retailer power resale price maintenance and provide an economic view of why restraints of this kind should be evaluated under the rule of reason. While competition is more likely to be undercut under the agency model, relative to the wholesale model, the agency model benefits consumers by offering relatively lower retail prices and greater demand

Ventricular longitudinal function is associated with microvascular obstruction and intramyocardial haemorrhage.

Microvascular obstruction (MVO) and intramyocardial haemorrhage (IMH) are associated with adverse prognosis, independently of infarct size after reperfused ST-elevation myocardial infarction (STEMI). Mitral annular plane systolic excursion (MAPSE) is a well-established parameter of longitudinal function on echocardiography.We aimed to investigate how acute MAPSE, assessed by a four-chamber cine-cardiovascular MR (CMR), is associated with MVO, IMH and convalescent left ventricular (LV) remodelling.54 consecutive patients underwent CMR at 3T (Intera CV, Philips Healthcare, Best, The Netherlands) within 3 days of reperfused STEMI. Cine, T2-weighted, T2* and late gadolinium enhancement (LGE) imaging were performed. Infarct and MVO extent were measured from LGE images. The presence of IMH was investigated by combined analysis of T2w and T2* images. Averaged-MAPSE (medial-MAPSE+lateral-MAPSE/2) was calculated from 4-chamber cine imaging.44 patients completed the baseline scan and 38 patients completed 3-month scans. 26 (59%) patients had MVO and 25 (57%) patients had IMH. Presence of MVO and IMH were associated with lower averaged-MAPSE (11.7±0.4 mm vs 9.3±0.3 mm; p<0.001 and 11.8±0.4 mm vs 9.2±0.3 mm; p<0.001, respectively). IMH (β=-0.655, p<0.001) and MVO (β=-0.567, p<0.001) demonstrated a stronger correlation to MAPSE than other demographic and infarct characteristics. MAPSE ≤10.6 mm demonstrated 89% sensitivity and 72% specificity for the detection of MVO and 92% sensitivity and 74% specificity for IMH. LV remodelling in convalescence was not associated with MAPSE (AUC 0.62, 95% CI 0.44 to 0.77, p=0.22).Postreperfused STEMI, LV longitudinal function assessed by MAPSE can independently predict the presence of MVO and IMH