Assessment of hemodynamic conditions in the aorta following root replacement with composite valve-conduit graft

This paper presents the analysis of detailed hemodynamics in the aortas of four patients following replacement with a composite bio-prosthetic valve-conduit. Magnetic resonance image-based computational models were set up for each patient with boundary conditions comprising subject-specific three-dimensional inflow velocity profiles at the aortic root and central pressure waveform at the model outlet. Two normal subjects were also included for comparison. The purpose of the study was to investigate the effects of the valve-conduit on flow in the proximal and distal aorta. The results suggested that following the composite valve-conduit implantation, the vortical flow structure and hemodynamic parameters in the aorta were altered, with slightly reduced helical flow index, elevated wall shear stress and higher non-uniformity in wall shear compared to normal aortas. Inter-individual analysis revealed different hemodynamic conditions among the patients depending on the conduit configuration in the ascending aorta, which is a key factor in determining post-operative aortic flow. Introducing a natural curvature in the conduit to create a smooth transition between the conduit and native aorta may help prevent the occurrence of retrograde and recirculating flow in the aortic arch, which is particularly important when a large portion or the entire ascending aorta needs to be replaced

Phase diagram and thermal expansion of orthopyroxene-, clinopyroxene-, and ilmenite-structured MgGeO<inf>3</inf>

The MgGeO3 system is a low-pressure analog for the Earth-forming (Mg,Fe)SiO3 system and exhibits recoverable orthopyroxene, clinopyroxene, and ilmenite structures below 6 GPa. The pressure-temperature conditions of the clinopyroxene to ilmenite phase transition are reasonably consistent between studies, having a positive Clapeyron slope and occurring between 4 and 7 GPa in the temperature range 900-1600 K. There are, though, significant discrepancies in the Clapeyron slope of the orthopyroxene to clinopyroxene phase transition in existing works that also disagree on the stable phase at ambient conditions. The most significant factor in these differences is the method used; high-pressure experiments and thermophysical property measurements yield apparently contradicting results. Here, we perform both high pressure and temperature experiments as well as thermal expansion measurements to reconcile the measurements. High-pressure and -temperature experiments yield a Clapeyron slope of -1.0-+1.0-0.7 MPa/K for the MgGeO3 orthopyroxene-clinopyroxene phase transition, consistent with previous high-pressure and -temperature experiments. The MgGeO3 orthopyroxene-clinopyroxene-ilmenite triple point is determined to be at 0.98 GPa and 752 K, with the ilmenite phase stable at ambient conditions. The high-temperature (>600 K) thermal expansion of the clinopyroxene phase is greater than that of the other phases. Debye-Grüneisen relationships fitted to the volume-temperature data give Debye temperatures for the orthopyroxene, clinopyroxene, and ilmenite phases of 602(7), 693(10), and 758(13) K and V0 of 897.299(16), 433.192(10), and 289.156(6) Å3, respectively. The Clapeyron slopes calculated directly from the Debye-Grüneisen relationships are consistent with previous thermophysical property measurements. The presence of significant anharmonicity and/or formation of defects in the clinopyroxene phase at high-temperatures, which is not apparent in the other phases, accounts for the previous contradictions between studies. The inferred increased heat capacity of the clinopyroxene corresponds to an increase in entropy and an expanded phase field at high temperatures

The thermal expansion of (Fe1-y Ni y )Si

We have measured the thermal expansion of (Fe1-y Ni y )Si for y  =  0, 0.1 and 0.2, between 40 and 1273 K. Above ~700 K the unit-cell volumes of the samples decrease approximately linearly with increasing Ni content. Below ~200 K the unit-cell volume of FeSi falls to a value between that of (Fe0.9Ni0.1)Si and (Fe0.8Ni0.2)Si. We attribute this extra contraction of the FeSi, which is a narrow band-gap semiconductor, to the depopulation of the conduction band at low temperatures; in the two alloys the additional electrons introduced by the substitution of Ni lead to the conduction band always being populated. We have fit the unit-cell volume data with a Debye internal energy model of thermal expansion and an additional volume term, above 800 K, to take account of the volumetric changes associated with changes in the composition of the sample. Using the thermophysical parameters of the fit we have estimated the band gap in FeSi to be 21(1) meV and the unit-cell volume change in FeSi associated with the depopulation of the conduction band to be 0.066(35) Å(3)/unit-cell

The effect of rare variants on inflation of the test statistics in case-control analyses.

BACKGROUND: The detection of bias due to cryptic population structure is an important step in the evaluation of findings of genetic association studies. The standard method of measuring this bias in a genetic association study is to compare the observed median association test statistic to the expected median test statistic. This ratio is inflated in the presence of cryptic population structure. However, inflation may also be caused by the properties of the association test itself particularly in the analysis of rare variants. We compared the properties of the three most commonly used association tests: the likelihood ratio test, the Wald test and the score test when testing rare variants for association using simulated data. RESULTS: We found evidence of inflation in the median test statistics of the likelihood ratio and score tests for tests of variants with less than 20 heterozygotes across the sample, regardless of the total sample size. The test statistics for the Wald test were under-inflated at the median for variants below the same minor allele frequency. CONCLUSIONS: In a genetic association study, if a substantial proportion of the genetic variants tested have rare minor allele frequencies, the properties of the association test may mask the presence or absence of bias due to population structure. The use of either the likelihood ratio test or the score test is likely to lead to inflation in the median test statistic in the absence of population structure. In contrast, the use of the Wald test is likely to result in under-inflation of the median test statistic which may mask the presence of population structure.This work was supported by a grant from Cancer Research UK (C490/A16561). AP is funded by a Medical Research Council studentship.This is the final published version. It first appeared at http://dx.doi.org/10.1186%2Fs12859-015-0496-1

The effect of solar zenith angle on MODIS cloud optical and microphysical retrievals within marine liquid water clouds

In this paper we use a novel observational approach to investigate MODIS satellite retrieval biases of τ and re (using three different MODIS bands: 1.6, 2.1 and 3.7 μm, denoted as re1.6, re2.1 and re3.7, respectively) that occur at high solar zenith angles (θ0) and how they affect retrievals of cloud droplet concentration (Nd). Utilizing the large number of overpasses for polar regions and the diurnal variation of θ0 we estimate biases in the above quantities for an open ocean region that is dominated by low level stratiform clouds. We find that the mean τ is fairly constant between θ0 = 50° and ∼65-707deg;, but then increases rapidly with an increase of over 70%between the lowest and highest θ0. The re2.1 and re3.7 decrease with θ0, with effects also starting at around θ0 =65-70°. At low θ0, the re values from the three different MODIS bands agree to within around 0.2 μm, whereas at high θ0 the spread is closer to 1 μm. The percentage changes of re with θ0 are considerably lower than those for τ , being around 5% and 7% for re2.1 and re3.7. For re1.6 there was very little change with θ0. Evidence is provided that these changes are unlikely to be due to any physical diurnal cycle. The increase in τ and decrease in re both contribute to an overall increase in Nd of 40-70% between low and high θ0. Whilst the overall re changes are quite small, they are not insignificant for the calculation of Nd; we find that the contributions to Nd biases from the τ and re biases were roughly comparable for re3.7, although for the other re bands the τ changes were considerably more important. Also, when considering only the clouds with the more heterogeneous tops, the importance of the re biases was considerably enhanced for both re2.1 and re3.7. When using the variability of 1 km resolution τ data (γτ) as a heterogeneity parameter we obtained the expected result of increasing differences in τ between high and low θ0 as heterogeneity increased, which was not the case when using the variability of 5 km resolution cloud top temperature (σCTT), suggesting that γτ is a better predictor of τ biases at high θ0 than σCTT. For a given θ0, large decreases in re were observed as the cloud top heterogeneity changed from low to high values, although it is possible that physical changes to the clouds associated with cloud heterogeneity variation may account for some of this. However, for a given cloud top heterogeneity we find that the value of θ0 affects the sign and magnitude of the relative differences between re1.6, re2.1 and re3.7, which has implications for attempts to retrieve vertical cloud information using the different MODIS bands. The relatively larger decrease in re3.7 and the lack of change of re1.6 with both θ0 and cloud top heterogeneity suggest that re3.7 is more prone to retrieval biases due to high θ0 than the other bands. We discuss some possible reasons for this. Our results have important implications for individual MODIS swaths at high θ0, which may be used for case studies for example. θ0 values> 65° can occur at latitudes as low as 28° in mid-winter and for higher latitudes the problem will be more acute. Also, Level-3 daily averaged MODIS cloud property data consist of the averages of several overpasses for the high latitudes, which will occur at a range of θ0 values. Thus, some biased data are likely to be included. It is also likely that some of the θ0 effects described here would apply to τ and re retrievals from satellite instruments that use visible light at similar wavelengths along with forward retrieval models that assume plane parallel clouds, such as the GOES imagers, SEVIRI, etc

The top-down crystallisation of Mercury's core

The regime governing the growth of Mercury's core is unknown, but the dynamics of core growth are vital to understanding the origin and properties of the planet's weak magnetic field. Here, we use advanced first-principles methods, which include a magnetic entropy contribution, to investigate the magnetic and thermo-elastic properties of liquid Fe-S-Si and of pure liquid iron at the conditions of Mercury's core. Our results support a ‘top-down’ evolution of the core, whereby solid iron-rich material crystallises at shallow depths and sinks. This process would likely result in a compositionally driven dynamo within a stably stratified uppermost liquid layer, providing an explanation for the observed properties of the weak magnetic field of Mercury

The global aerosol-cloud first indirect effect estimated using MODIS, MERRA, and AeroCom

Aerosol-cloud interactions (ACI) represent a significant source of forcing uncertainty in global climate models (GCMs). Estimates of radiative forcing due to ACI in Fifth Assessment Report range from −0.5 to −2.5 W m−2. A portion of this uncertainty is related to the first indirect, or Twomey, effect whereby aerosols act as nuclei for cloud droplets to condense upon. At constant liquid water content this increases the number of cloud droplets (Nd) and thus increases the cloud albedo. In this study we use remote-sensing estimates of Nd within stratocumulus regions in combination with state-of-the-art aerosol reanalysis from Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA2) to diagnose how aerosols affect Nd. As in previous studies, Nd is related to sulfate mass through a power law relationship. The slope of the log-log relationship between Nd and SO4 in maritime stratocumulus is found to be 0.31, which is similar to the range of 0.2–0.8 from previous in situ studies and remote-sensing studies in the pristine Southern Ocean. Using preindustrial emissions models, the change in Nd between preindustrial and present day is estimated. Nd is inferred to have more than tripled in some regions. Cloud properties from Moderate Resolution Imaging Spectroradiometer (MODIS) are used to estimate the radiative forcing due to this change in Nd. The Twomey effect operating in isolation is estimated to create a radiative forcing of −0.97 ± 0.23 W m−2 relative to the preindustrial era