Shock compression of single-crystal forsterite

Dynamic compression results are reported for single-crystal forsterite loaded along the orthorhombic a and c axes to pressures from 130 to 165 GPa. Hugoniot states for the two axes are well described by a single curve offset to densities 0.15–0.20 g/cm^3 lower than earlier data for single-crystal forsterite shocked along the b axis above 100 GPa. Earlier data of Syono et al. [1981a] show marginal support for similar b-axis behavior in the mixed-phase region from 50 to 92 GPa. Thus shocked forsterite is most compressible in the b direction for the mixed-phase and high-pressure regimes (P > 50 GPa). These data represent the highest pressures for which shock properties have been observed to depend on crystal orientation. Theoretical Hugoniots for mixed-oxide and perovskite-structure high-pressure assemblages of forsterite calculated from recent experimental data are virtually identical and agree with the b-axis data. The a- and c-axis data are also consistent with both high-pressure assemblages because uncertainties in equation of state parameters produce a broad range of computed Hugoniots. Our calculated “average” Hugoniot is up to 0.13 g/cm^3 less dense than the preferred theoretical Hugoniots, in agreement with earlier measurements on dense polycrystalline forsterite. Interpolation between the single-crystal forsterite Hugoniots and Hugoniots for fayalite and Fo_(45) gives Fo_(88) Hugoniots bracketing Twin Sisters dunite data not previously well fit by systematics. Release paths are steep for the a and b axes but c-axis release paths are much shallower. Hugoniot elastic limits measured for the a and b axes are in good agreement with previous data of Syono et al.; however, the present data for the a axis reveal a triple wave structure: two deformational shock waves as well as the elastic shock, a feature not previously found. The second shock, with amplitude about 9 GPa and a shock temperature of about 350°K, could perhaps be explained by the forsterite α→β or γ phase transformation

Shock wave equations of state using mixed-phase regime data

A method is given that uses Hugoniot data in the mixed-phase regime to constrain further equation of state (EOS) parameters of low- and high-pressure phases of materials under-going phase transformations on shock loading. We compute the relative proportion of low- and high-pressure phases present in the mixed-phase region and apply additional tests to the EOS parameters of the separate low- and high-pressure phases by invoking two simple requirements: the fraction of high-pressure phase (1) must increase with increasing shock pressure, and (2) must approach one at the high-pressure end of the mixed-phase regime. We apply our analysis to previously published data for potassium thioferrite, KfeS_2, and pyrrhotite, Fe_(0.9)S. We find that including the mixed-phase regime data in the KfeS_2 analysis requires no change in the published high-pressure EOS parameters. For Fe_(0.9)S we must modify the high-pressure phase EOS parameters to account for both the mixed-phase and high-pressure phase Hugoniot data. Our values of zero-pressure density, bulk modulus and first pressure derivative of the bulk modulus of the high-pressure phase of Fe_(0.9)S are 5.3 Mg/m^3, 106 GPa, and 4.9, respectively

The role of iron partitioning in mantle composition, evolution, and scale of convection

The effect on composition and evolution of the mantle of the recently-observed strong concentration of iron in (Mg, Fe)O-magnesiowüstite (mw) at the expense of (Mg, Fe)SiO_3-perovskite (pv) structure is studied by calculating a temperature- and pressure-dependent iron partitioning coefficient for the lower mantle. The value of the standard entropy for MgSiO_3-perovskite is found to be 69.4±10.3 J/mole deg from the recently determined phase diagram of forsterite. Iron remains concentrated in (Mg, Fe)O throughout the entire lower mantle if account is taken of an FeO phase change, with the partitioning coefficient (x^(pv)_(Fe)/x^(pv)_(Mg))/(x^(mw)_(Fe)/x^(mw)_(Mg)) increasing from 0.04 to 0.8 between 670 Km a the core-mantle boundary. Partitioning has negligible effect on gross density and elastic properties Of the lower mantle. By using recent shock wave and static compression results for FeO and MgSiO_3-perovskite, we find that the lower mantle is more pyroxene-rich than the upper mantle and as iron-rich, or somewhat less so, than the upper mantle. Mg/(Mg + Fe) = 0.93–0.95 for the lower mantle compared with 0.85–0.90 for the uppermost mantle. The lower mantle Mg/Si ratio is closer to chondritic values (0.99± 0.03) (≈1.5 for a peridotite with px/ol = 0.4(molar)), thus supporting the idea of a chemically layered mantle with implications for the style of mantle convection. While partitioning of iron has no significant effect on gross lower mantle density, we find that the (Mg, Fe)O and perovskite components of the lower mantle have essentially the same densities. Mantles with higher bulk iron contents have (Mg, Fe)O denser than the perovskite component; for a bulk magnesium mole fraction of, 0.80, the density difference is 0.7–0.8 g/cm^3. We investigate the feasibility of the Mao, Bell, and Yagi gravitational separation hypothesis of mantle evolution in which a mantle more iron-rich than present loses iron through gravitational sinking of the denser (Mg, Fe) O, and we conclude that the process cannot successfully compete with solid state convection unless implausibly large grain sizes or unacceptably low viscosities are invoked. A likely explanation for removal of iron from an initially iron rich lower mantle is upward extraction of FeO-enriched basalts or picrites and concentration of iron in upper mantle garnets during accretion of the earth or subsequent convection with the entire mantle passing through the partial melt zone. Thus the lower mantle was depleted of iron relative to both the upper mantle and the mantles of the small terrestrial planets and satellites, which do not have mantle pressures sufficient to form perovskite-structure silicates, or which had lower accretional temperatures and less extensive melting. On this basis, Venus would be expected to have a mantle similarly depleted in iron

Shock wave equation of state of enstatite

Shock compression data are reported for hot-pressed Bamble bronzite (En_(86)) loaded to pressures between 104 and 161 GPa. When compared to earlier shock wave data on En_(90) at lower pressures and to static compression data, our data require the presence of a phase change. In P-ρ space the data yield two distinct trajectories, which cannot be explained by experimental error. The higher-density data, corrected for porosity and a small amount of metallic iron impurity, agree with a theoretical En_(86) high-pressure phase Hugoniot calculated from static compression equation of state data for perovskite (pv) structure silicates when experimental errors and uncertainties in the equation of state parameters are considered. All the En86 data can be described by a calculated Hugoniot if the first pressure derivative of the MgSiO_3 (pv) bulk modulus is taken as 4.5 ± 1.0. Combining the present preferred data with recent shock wave data for single-crystal forsterite, we find that En_(86) is slightly more dense than Fo86 at pressures above 110 GPa. Comparison of the forsterite and enstatite data with the Preliminary Reference Earth Model (PREM) lower mantle densities, with corrections applied for the higher shock temperatures relative to lower mantle temperatures, shows that PREM densities are satisfied by olivine or pyroxene stoichiometries with Mg mole fractions from 0.82 to 0.90. These values are lower than estimates of 0.90 to 0.95 developed from extrapolating static compression data to lower mantle conditions

Depth from HDR: Depth Induction or Increased Realism?

Many people who first see a high dynamic range (HDR) display get the impression that it is a 3D display, even though it does not produce any binocular depth cues. Possible explanations of this effect include contrast-based depth induction and the increased re-alism due to the high brightness and contrast that makes an HDR display “like looking through a window”. In this paper we test both of these hypotheses by comparing the HDR depth illusion to real binocular depth cues using a carefully calibrated HDR stereo-scope. We confirm that contrast-based depth induction exists, but it is a vanishingly weak depth cue compared to binocular depth cues. We also demonstrate that for some observers, the increased con-trast of HDR displays indeed increases the realism. However, it is highly observer-dependent whether reduced, physically correct, or exaggerated contrast is perceived as most realistic, even in the pres-ence of the real-world reference scene. Similarly, observers differ in whether reduced, physically correct, or exaggerated stereo 3D is perceived as more realistic. To accommodate the binocular depth perception and realism concept of most observers, display technolo-gies must offer both HDR contrast and stereo personalization

A Novel Combination of Serum Markers in a Multivariate Model to Help Triage Patients Into “Low-” and “High-Risk” Categories for Prostate Cancer

BACKGROUND: Almost 50,000 men in the United Kingdom (UK) are diagnosed each year with prostate cancer (PCa). Secondary referrals for investigations rely on serum prostate-specific antigen (PSA) levels and digital rectal examination. However, both tests lack sensitivity and specificity, resulting in unnecessary referrals to secondary care for costly and invasive biopsies. MATERIALS AND METHODS: Serum samples and clinical information were collected from N = 125 age-matched patients (n = 61 non-PCa and n = 64 PCa) and analyzed using Biochip Array Technology on high-sensitivity cytokine array I (IL-2, IL-4, IL-6, IL-8, IL-10, IL-1α, IL-1β, TNFα, MCP-1, INFγ, EGF, and VEGF), cerebral array II (CRP, D-dimer, neuron-specific enolase, and sTNFR1), and tumor PSA oncology array (fPSA, tPSA, and CEA). RESULTS: The data showed that 11/19 (68.8%) markers were significantly different between the non-PCa and the PCa patients. A combination of EGF, log(10) IL-8, log(10) MCP-1, and log(10) tPSA significantly improved the predictive potential of tPSA alone to identify patients with PCa (DeLong, p < 0.001). This marker combination had an increased area under the receiver operator characteristic (0.860 vs. 0.700), sensitivity (78.7 vs. 68.9%), specificity (76.5 vs. 67.2%), PPV (76.2 vs. 66.7%), and NPV (79.0 vs. 69.4%) compared with tPSA. CONCLUSIONS: The novel combination of serum markers identified in this study could be employed to help triage patients into “low-” and “high-risk” categories, allowing general practitioners to improve the management of patients in primary care settings and potentially reducing the number of referrals for unnecessary, invasive, and costly treatments

Shock wave apparatus for studying minerals at high pressure and impact phenomena on planetary surfaces

Shock wave and experimental impact phenomena research on geological and planetary materials is being carried out using two propellant (18 and 40 mm) guns (up to 2.5 km/sec) and a two‐stage light gas gun (up to 7 km/sec). Equation of state measurements on samples initially at room temperature and at low and high temperatures are being conducted using the 40 mm propellant apparatus in conjunction with Helmholtz coils, and radiative detectors and, in the case of the light gas gun, with streak cameras. The 18 mm propellant gun is used for recovery experiments on minerals, impact on cryogenic targets, and radiative post‐shock temperature measurements