Dynamic compression of SiO_2: A new interpretation

In light of recent discoveries of post-stishovite phases of SiO_2, with the CaCl_2 and α-PbO_2 structures, we have reassigned the regimes along the Hugoniots for initial quartz, coesite, cristobalite, porous coesite, and fused silica. Calculated Hugoniots for fused silica, cristobalite and porous coesite indicate transition to stishovite, and then melt. Hugoniots for crystal quartz and coesite indicate that transition occurs to stishovite, then the CaCl2 structure and finally to melt

Shock-compressed MgSiO_3 glass, enstatite, olivine, and quartz: Optical emission, temperatures, and melting

Optical emission of MgSiO_3 glass, enstatite, olivine, and quartz under shock wave compression was investigated with optical pyrometry at discrete wavelengths ranging from visible to near infrared. We develop a new analysis of optical emission that does not require a gray body assumption. Instead, at each wavelength, the optical linear absorption coefficients (α) and blackbody spectral radiances (L_(λb)) of shocked and unshocked materials were obtained by nonlinear fitting to the time-resolved radiance from the target assembly. The absorption spectra of unshocked samples corresponding to the measured values of α reproduce those from independent static optical spectroscopic measurements. The measured values of α (ranging from 7 to 56 mm^(−1)) for shocked samples indicate that shock-induced high-pressure phases (including melt) can be regarded essentially as black bodies in the optical range investigated, although starting phases such as enstatite and olivine have band-like spectra at ambient conditions. The effect of emission from the air gap at the driver sample interface on the recorded radiance can be resolved, but α and L_(λb) cannot be separated for this component of the signal. The shock velocity-particle velocity relationships of these silicates derived from radiance history are in accord with previous investigations using independent techniques. Given the limited amount of shock wave data, possible high-pressure melting curves of Mg-perovskite and its assemblage with periclase are deduced; their melting temperatures near the core-mantle boundary (CMB) being 6000 ± 500 K and 4000 ± 300 K, respectively. It is proposed that Mg-perovskite melts with density increase at the CMB pressure

Shock-induced melting of MgSiO_3 perovskite and implications for melts in Earth's lowermost mantle

New shock wave equation of state (EOS) data for enstatite and MgSiO_3 glass constrain the density change upon melting of Mg-silicate perovskite up to 200 GPa. The melt becomes denser than perovskite near the base of Earth's lower mantle. This inference is confirmed by shock temperature data suggesting a negative pressure-temperature slope along the melting curve at high pressure. Although melting of Earth's mantle involves multiple phases and chemical components, this implies that the partial melts invoked to explain anomalous seismic velocities in the lowermost mantle may be dynamically stable

Microwave Observations of Venus with CLASS

We report on the disk-averaged absolute brightness temperatures of Venus measured at four microwave frequency bands with the Cosmology Large Angular Scale Surveyor (CLASS). We measure temperatures of 432.3 $\pm$ 2.8 K, 355.6 $\pm$ 1.3 K, 317.9 $\pm$ 1.7 K, and 294.7 $\pm$ 1.9 K for frequency bands centered at 38.8, 93.7, 147.9, and 217.5 GHz, respectively. We do not observe any dependence of the measured brightness temperatures on solar illumination for all four frequency bands. A joint analysis of our measurements with lower frequency Very Large Array (VLA) observations suggests relatively warmer ($\sim$ 7 K higher) mean atmospheric temperatures and lower abundances of microwave continuum absorbers than those inferred from prior radio occultation measurements.Comment: 10 pages, 3 figures, published in PS

TRANSFORM (Multicenter Experience With Rapid Deployment Edwards INTUITY Valve System for Aortic Valve Replacement) US clinical trial: Performance of a rapid deployment aortic valve

Background: The TRANSFORM (Multicenter Experience With Rapid Deployment Edwards INTUITY Valve System for Aortic Valve Replacement) trial (NCT01700439) evaluated the performance of the INTUITY rapid deployment aortic valve replacement (RDAVR) system in patients with severe aortic stenosis. Methods: TRANSFORM was a prospective, nonrandomized, multicenter (n 1�4 29), single-arm trial. INTUITY is comprised of a cloth-covered balloon- expandable frame attached to a Carpentier-Edwards PERIMOUNT Magna Ease aortic valve. Primary and effectiveness endpoints were evaluated at 1 year. Results: Between 2012 and 2015, 839 patients underwent RDAVR. Mean age was 73.5 8.3 years. Full sternotomy (FS) was used in 59% and minimally invasive surgical incisions in 41%. Technical success rate was 95%. For isolated RDAVR, mean crossclamp and cardiopulmonary bypass times for FS were 49.3 26.9 minutes and 69.2 34.7 minutes, respectively, and for minimally invasive surgical 63.1 25.4 minutes and 84.6 33.5 minutes, respectively. These times were favorable compared with Society of Thoracic Surgeons data- base comparators for FS: 76.3 minutes and 104.2 minutes, respectively, and for minimally invasive surgical, 82.9 minutes and 111.4 minutes, respectively (P<.001). At 30 days, all-cause mortality was 0.8%; valve explant, 0.1%; throm- boembolism, 3.5%; and major bleeding, 1.3%. In patients with isolated aortic valve replacement, the rate of permanent pacemaker implantation was 11.9%. At 1 year, mean effective orifice area was 1.7 cm2; mean gradient, 10.3 mm Hg; and moderate and severe paravalvular leak, 1.2% and 0.4%, respectively

Cyclic di-GMP is Essential for the Survival of the Lyme Disease Spirochete in Ticks

Cyclic dimeric GMP (c-di-GMP) is a bacterial second messenger that modulates many biological processes. Although its role in bacterial pathogenesis during mammalian infection has been documented, the role of c-di-GMP in a pathogen's life cycle within a vector host is less understood. The enzootic cycle of the Lyme disease pathogen Borrelia burgdorferi involves both a mammalian host and an Ixodes tick vector. The B. burgdorferi genome encodes a single copy of the diguanylate cyclase gene (rrp1), which is responsible for c-di-GMP synthesis. To determine the role of c-di-GMP in the life cycle of B. burgdorferi, an Rrp1-deficient B. burgdorferi strain was generated. The rrp1 mutant remains infectious in the mammalian host but cannot survive in the tick vector. Microarray analyses revealed that expression of a four-gene operon involved in glycerol transport and metabolism, bb0240-bb0243, was significantly downregulated by abrogation of Rrp1. In vitro, the rrp1 mutant is impaired in growth in the media containing glycerol as the carbon source (BSK-glycerol). To determine the contribution of the glycerol metabolic pathway to the rrp1 mutant phenotype, a glp mutant, in which the entire bb0240-bb0243 operon is not expressed, was generated. Similar to the rrp1 mutant, the glp mutant has a growth defect in BSK-glycerol medium. In vivo, the glp mutant is also infectious in mice but has reduced survival in ticks. Constitutive expression of the bb0240-bb0243 operon in the rrp1 mutant fully rescues the growth defect in BSK-glycerol medium and partially restores survival of the rrp1 mutant in ticks. Thus, c-di-GMP appears to govern a catabolic switch in B. burgdorferi and plays a vital role in the tick part of the spirochetal enzootic cycle. This work provides the first evidence that c-di-GMP is essential for a pathogen's survival in its vector host

Long-term retention and density-dependent herbivory from Diadema antillarum following translocation onto a reef restoration site

Most reported Diadema antillarum restocking has resulted in low survival and retention. These outcomes challenge conservation and restoration goals. A manipulative study was conducted to evaluate site retention, tandem coral-urchin restoration, and herbivory from 200 adult D. antillarum translocated to five experimental plots off Key Biscayne, Florida. Two additional plots were monitored as controls. Surveys revealed homogeneous dispersal over time, with overall retention of 94.5%, 79.5%, 56.0% and 22.5% at 1-, 7-, 84- and 267-days post-release, respectively. Rugosity significantly predicted urchin retention and plots with higher relief exhibited reduced emigration rates. Benthic image analysis revealed a significant decline in macroalgae relative to controls when urchin densities were above 0.15 m(-2) but not at 0.04 m(-2). Urchin plots experienced a 27% reduction in macroalgae from days 7 to 84. Results indicated higher long-term retention, especially within plots with greater relief, and evidence for ecologically significant herbivory following a single translocation event