The Influence of Redox Conditions on the Seismic Properties of Polycrystalline Olivine

Eight olivine specimens were fabricated by use of a solgel method and hot-pressing at 1200 degrees Centigrade and 300 megapascals (MPa) inside of welded Pt capsules. Each hot-pressed specimen was then recovered, precision ground, and wrapped in Pt, Ni or NiFe foil to vary oxygen fugacity (fO2) during the subsequent forced torsional oscillation measurements. Mechanical testing was conducted at 10 oscillation periods between 1 and 1000 seconds, at a confining pressure of 200 MPa, during a slow staged-cooling from a maximum temperature of 1200 degrees Centigrade down to room temperature. After mechanical testing, each specimen was axially sectioned and EBSD (Electron BackScatter Diffraction) was used for the determination of the representative grain size, and grain size distribution of each sample. In addition, each longitudinal section was mapped via FTIR (Fourier Transform Infrared Spectroscopy) to determine the spatial distribution and concentrations of chemically bound and molecular water. Amongst these eight specimens, chemically bound water contents were observed to vary between 0 and 1150 atom parts per million (ppm) H/Si, and molecular water concentrations varied between 0 and 245 atom ppm H/Si. Our forced-oscillation results demonstrate that the measured magnitude of anelastic relaxation within the experimental window of oscillation periods is unrelated to the water content. Rather, a relationship was observed between the magnitude of anelastic relaxation and the prevailing redox conditions, which is influenced by the choice of metal sleeving used during the mechanical test. Further, regardless of water content or metal sleeving, each specimen exhibits coupled variations in shear modulus and dissipation within the observational window, indicative of high-temperature background behavior, that can be described by a Burgers-type model. During initial fitting of the Burgers models, the unrelaxed shear modulus at a reference temperature of 900C (elastic unloading/reloading shear modulus G (sub UR)) and the temperature derivative of the unrelaxed shear modulus (dGU/dT), were treated as adjustable parameters. For all Fe-bearing olivine samples we observe deficits of G (sub UR) and increased values of dGU/dT, relative to the expected elastic (anharmonic) behavior for Fo (Forsterite content percentage) (sub 90) olivine. This behavior is indicative of anelastic relaxation occurring at shorter periods than observable within the window of oscillation periods used in the mechanical test. Moving towards a comprehensive and seismologically applicable Burgers model, which includes this newly observed effect of redox conditions on anelastic relaxation, we will present our progress on reconciling truly anharmonic and elastic behavior of Fo (sub 90) olivine with our observed forced-oscillation data

The Effect of Redox Conditions on Seismic Waves in Iron-Bearing Olivine: Implications for Understanding Planetary Interiros Through Seismilogy

Seismic data, inclusive of velocities and attenuation, can be utilized to elucidate the physical state of planetary interiors]. However, numerous micromechanical factors have been either experimentally demonstrated, or theoretically considered, to affect the propagation and dissipation of seismic energy within crystalline solids - including, but not limited to, changes in grain size, temperature, melt fraction, pressure and dislocation density. Thus, observed variations in seismic wave speeds and attenuation may be used to ultimately map variations in physical properties, such as those listed above, within planetary bodies. But, in order to complete a successful inversion of seismic data into representations of physical properties, a first requirement is to obtain a fundamental laboratory based understanding of how each of these possible factors individually influences seismic waves. Here we conduct an experimental study with the initial objective to further understand one of the most commonly invoked, yet least studied, mechanisms that could alter intrinsic seismic wave attenuation: water content (occurring as chemically-bound hydroxyl). The historical basis for determining the effect of water on seismic properties was established predominantly through analogy with large-strain creep experiments conducted on olivine under water-saturated conditions. While these deformation experiments routinely demonstrate a weakening of olivine in the presence of water, they represent a fundamentally different deformation regime in comparison to the microstrains experienced due to a passing seismic wave. Thus, in order to directly assess the effects of water on seismic properties, small-strain experiments are required. Substantially modified seismic properties in the presence of water have been observed previously at low strains and low frequencies, but only in a single exploratory study conducted under water-saturated conditions. Thus, to properly test the theoretical predictions we conducted a systematic study of the seismic properties of olivine using low-frequency torsional oscillation on aggregates containing varying concentrations of bound hydroxyl, for the first time at under saturated conditions

Promotion of importin α–mediated nuclear import by the phosphorylation-dependent binding of cargo protein to 14-3-3

14-3-3 proteins are phosphoserine/threonine-binding proteins that play important roles in many regulatory processes, including intracellular protein targeting. 14-3-3 proteins can anchor target proteins in the cytoplasm and in the nucleus or can mediate their nuclear export. So far, no role for 14-3-3 in mediating nuclear import has been described. There is also mounting evidence that nuclear import is regulated by the phosphorylation of cargo proteins, but the underlying mechanism remains elusive. Myopodin is a dual-compartment, actin-bundling protein that functions as a tumor suppressor in human bladder cancer. In muscle cells, myopodin redistributes between the nucleus and the cytoplasm in a differentiation-dependent and stress-induced fashion. We show that importin α binding and the subsequent nuclear import of myopodin are regulated by the serine/threonine phosphorylation-dependent binding of myopodin to 14-3-3. These results establish a novel paradigm for the promotion of nuclear import by 14-3-3 binding. They provide a molecular explanation for the phosphorylation-dependent nuclear import of nuclear localization signal-containing cargo proteins

Dislocation recovery in fine-grained polycrystalline olivine

The rate of static dislocation recovery in Fo90 olivine has been studied under conditions of high temperature and controlled atmosphere in compressively deformed polycrystals hot-pressed from synthetic (sol-gel) and natural (San Carlos) precursor powders. The sol-gel olivine, containing a small fraction of orthopyroxene, was deformed to a final strain of 19% with a maximum differential stress of 266 MPa whereas the San Carlos specimen was deformed to 15% strain and 260 MPa differential stress. Small samples cut from these deformed materials were annealed under high-temperature, controlled atmosphere conditions, for different durations to allow partial recovery of the dislocation sub-structures. Oxidative-decoration of the microstructural features, followed by backscattered electron imaging at 5 kV and image analysis, was used to determine dislocation density. The variation of dislocation density ρ with time t at absolute temperature T was fitted to a second-order rate equation, in integral form, 1/ρ(t) - 1/ρ(0) = kt with k = k0 exp(-Ea/RT). The activation energy Ea of the recovery process is 240 ± 43 and 355 ± 81 kJ mol-1 for sol-gel and San Carlos olivine polycrystals, respectively. The measured rates are one to two orders of magnitude lower than those reported in previous studies on natural single crystal olivine. The difference may be explained by several factors such as high dislocation densities measurable from large areas at high magnification for the SEM and the technique used to estimate dislocation densities. Comparison between fine-grained sol-gel olivine and the coarser-grained San Carlos olivine aggregate did not indicate that grain boundaries play an important role in dislocation recovery, but the absence of grain boundaries might also have contributed to the high dislocation recovery rates previously measured for single crystals

Three-Nucleon Photodisintegration of 3He

The three-nucleon photodisintegration of 3He has been calculated in the whole phase space using consistent Faddeev equations for the three-nucleon bound and scattering states. Modern nucleon-nucleon and 3N forces have been applied as well as different approaches to nuclear currents. Phase space regions are localized where 3N force effects are especially large. In addition semi-exclusive cross sections for 3He(gamma,N) have been predicted which carry interesting peak structures. Finally some data for the exclusive 3N breakup process of 3He and its total breakup cross section have been compared to theory.Comment: 28 pages, 6 png figures, 11 ps figures, modified version with changed figures, conclusions unchanged, to appear in Phys.Rev.

Site 1222

Site 1222 (13°48.98´N, 143°53.35´W; 4989 meters below sea level [mbsl]; Fig. F1) forms a south-central component of the 56-Ma transect drilled during Leg 199 and is situated ~2° south of the Clarion Fracture Zone in typical abyssal hill topography. On the basis of regional magnetic anomalies, we anticipated basement age at Site 1222 to be equivalent to Chron C25r or Chron C25n (~56-57 Ma) (Cande et al., 1989), which is slightly older than at Site 1219. At the outset of drilling at Site 1222, our estimate for total sediment thickness was ~115 m (Fig. F2). Based upon a fixed hotspot model (Gripp and Gordon, 1990, for 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles) Site 1222 should have been located ~1° north of the equator at 56 Ma and ~4°N at 40 Ma. A nearby gravity core (EW9709-17GC), taken during the site survey cruise, recovered >5 m of red clay with a late-middle Miocene age on the basis of radiolarian biostratigraphy (Lyle, 2000). Deep Sea Drilling Project (DSDP) Site 42 located ~4° east of Site 1222, was not drilled to basement but contains a thin sedimentary section (~100 m thick) of upper Oligocene nannofossil ooze through middle Eocene radiolarian nannofossil ooze. In turn, DSDP Site 162 lies ~1° north of DSDP Site 42 and is situated on young crust (49 Ma) that contains ~150 m of clayey radiolarian and nannofossil oozes of early Oligocene-middle Eocene age. Site 1222 will be used to study the position of the Intertropical Convergence Zone in the late Eocene and Oligocene, to sample late Paleocene and early Eocene sediments in the central tropical Pacific Ocean, and to help determine whether or not there has been significant southward movement of the hotspots with respect to the spin axis prior to 40 Ma

Site 1220

Site 1220 (10°10.600´N, 142°45.503´W; 5218 meters below sea level (mbsl); Fig. F1) forms a southerly component of the 56-Ma transect drilled during Leg 199. It is situated about midway between the Clipperton and Clarion Fracture Zones in typical abyssal hill topography. On the basis of regional magnetic anomalies, we anticipated basement age at Site 1220 to be equivalent to Chron C25n (~56 Ma; Cande et al., 1989), slightly older than at Site 1219. At the outset of drilling at Site 1220, our estimate for total sediment depth was ~225 meters below seafloor (mbsf) (Fig. F2). Based upon a fixed hotspot model (Gripp and Gordon, 1990, for 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles), Site 1220 should have been located ~3° south of the equator at 56 Ma and in an equatorial position at 40 Ma. Thus, Site 1220 should have been situated underneath the South Equatorial Current in the early Eocene. A nearby piston core (EW9709-13PC) taken during the site survey cruise recovered >16 m of red clay, with the base of the core dated as middle-early Miocene on the basis of radiolarian biostratigraphy (Lyle, 2000). Site 1220 will be used to study equatorial ocean circulation from the late Paleocene through the late Eocene during the early Cenozoic thermal maximum. Sediment records from this site will help to define the calcite compensation depth (CCD) and lysocline during the Paleocene-Eocene and Eocene-Oligocene transitions. In this and other respects, Site 1220 will act as an interesting analog to Site 1218. Both sites are thought to have been located on the equator at ~40 Ma, but the older crustal age anticipated at Site 1220 dictates a greater paleowater depth than for contemporaneous sediments accumulating at Site 1218

Site 1216

Site 1216 (21°27.16´N, 139°28.79´W; 5152 meters below sea level [mbsl]; Fig. F1) is situated in abyssal hill topography south of the Molokai Fracture Zone and two small associated unnamed parasitic fracture zones (Fig. F2). Based on magnetic lineations, Site 1216 appears to be situated on normal ocean crust formed during the C25r magnetic anomaly (~57 Ma; Atwater and Severinghaus, 1989). Site 1216 was chosen for drilling because it is near the thickest section of lower Eocene sediments along the 56-Ma transect, which was based upon the seismic stratigraphy of seismic reflection data acquired on site survey cruise EW9709 during transits between the proposed drill sites (Lyle et al., this volume; Moore et al., 2002). The Cenozoic history of sedimentation in this region was poorly constrained prior to Leg 199, being largely based on two Deep Sea Drilling Project (DSDP) drill sites (40 and 41) and piston core data (EW9709-3PC) from ~1.5° in latitude to the south. Based on data from these drill sites, we expected the sedimentary sequence at Site 1216 to comprise red clays (a mixture of wind-blown dust and authigenic precipitates) overlying a biogenic sediment section composed of an upper middle Eocene radiolarian ooze and lower carbonate ooze deposited when the site was near the ridge crest in the late Paleocene and early Eocene. The broad paleoceanographic objectives of drilling the sedimentary sequence anticipated at Site 1216 are as follows: (1) to help define the shift in the Intertropical Convergence Zone through the Paleogene by following the change in eolian-dust composition and flux through time (red clays) and (2) to help define the latitudinal extent, composition, and mass accumulation of plankton communities in the north equatorial Pacific region thereby constraining ocean circulation patterns and the extent of the equatorial high-productivity belt in the Eocene ocean. Results from Site 1216 will also provide important information to test whether there was significant motion of the Hawaiian hotspot with respect to the Earth's spin axis during the early Cenozoic. At 56 Ma, the backtracked location of Site 1216 based upon a hotspot reference frame (Gripp and Gordon, 1990, for 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles) is about 9°N, 108°W. If significant hotspot motion or true polar wander occurred since 57 Ma (Petronotis et al., 1994), this drill site could have been much nearer to the equator

Site 1217

Site 1217 (16°52.02´N, 138°06.00´W; 5342 meters below sea level [mbsl]; Fig. F1) is one of seven sites drilled to target upper Paleocene crust along a latitudinal transect during Leg 199 and will be used to investigate paleoceanographic processes in the northern tropical early Eocene Pacific Ocean. Site 1217 is situated ~1° north of the Clarion Fracture Zone on abyssal hill topography typical of the central Pacific. Based on magnetic lineations, basement age at Site 1217 should be in magnetic Anomaly C25r or ~57 Ma (Cande et al., 1989; timescale of Cande and Kent, 1995). The Cenozoic history of sedimentation in this region was poorly constrained prior to Leg 199 drilling because the nearest drill site (Deep Sea Drilling Project [DSDP] Site 162) is situated ~300 km south and west on 48-Ma crust. Based on data from this early rotary-cored hole, magnetic anomaly maps, a shallow-penetration piston core near Site 1217 (EW9709-4PC), and seismic profiling (Fig. F2), we expected the sedimentary sequence at Site 1217 to comprise a relatively thick (25 to 35 m thick) section of red clays overlying a radiolarian ooze and a basal carbonate section with possible chert near basement (estimated total depth ~125-150 meters below seafloor [mbsf]) deposited when the site was near the ridge crest in the late Paleocene and early Eocene. Site 1217 was chosen because it is anticipated to have been located just outside of the equatorial region at 56 Ma, ~5°N, 106°W based upon a fixed hotspot model (Gripp and Gordon, 1990, for 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles). On the same basis at 40 Ma, the site was located at ~8°N, 111°W. Thus, Site 1217 should help define the paleoceanography of the northern tropical Pacific, in particular locating the ancient North Equatorial Countercurrent (NECC) region. General circulation-model experiments for the early Eocene (see Huber, this volume) suggest that the NECC was a well-developed current during this time period. Other paleoceanographic and paleoclimatic objectives of drilling the sedimentary sequence anticipated at Site 1217 are as follows: (1) to help define the shift in the Intertropical Convergence Zone through the Paleogene by following the change in eolian dust composition and flux through time (red clays); (2) to help constrain the middle-late Eocene calcite compensation depth (CCD); and (3) to sample the Paleocene/Eocene (P/E) boundary, one of the most climatologically critical intervals of Cenozoic time. Recovery of deep-sea sediments from this time interval during Leg 199 is a high priority because the P/E boundary has never before been sampled in the central tropical Pacific Ocean. Results from Site 1217 will also provide important information to test whether there was significant motion of the Hawaiian hotspot, with respect to the Earth's spin axis during the early Cenozoic. At 56 Ma, the backtracked location based upon a hotspot reference frame is ~5°N, 106°W, and at 40 Ma is ~8°N, 106°W. If significant hotspot motion or true polar wander occurred since 57 Ma (Petronotis et al., 1994), this drill site could have been much nearer to the equator

Lung perfusion assessed by SPECT/CT after a minimum of three months anticoagulation therapy in patients with SARS-CoV-2-associated acute pulmonary embolism: a retrospective observational study

Background Anticoagulant treatment is recommended for at least three months after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-related acute pulmonary embolism (PE), but the persistent pulmonary clot burden after that time is unknown. Methods Lung perfusion was assessed by ventilation-perfusion (V/Q) SPECT/CT in 20 consecutive patients with SARS-CoV-2-associated acute PE after a minimum of three months anticoagulation therapy in a retrospective observational study. Results Remaining perfusion defects after a median treatment period of six months were observed in only two patients. All patients (13 men, seven women, mean age 55.6 ± 14.5 years) were on non-vitamin K direct oral anticoagulants (DOACs). No recurrent venous thromboembolism or anticoagulant-related bleeding complications were observed. Among patients with partial clinical recovery, high-risk PE and persistent pulmonary infiltrates were significantly more frequent (p < 0.001, respectively). Interpretation Temporary DOAC treatment seems to be safe and efficacious for resolving pulmonary clot burden in SARS-CoV-2-associated acute PE. Partial clinical recovery is more likely caused by prolonged SARS-CoV-2-related parenchymal lung damage rather than by persistent pulmonary perfusion defects