Shock conditions recorded in NWA 8159 martian augite basalt with implications for the impact cratering history on Mars

NWA 8159 is an augite-rich martian basalt, formed by cooling of a relatively evolved, Ca-rich, Ti-poor and LREE-depleted lava, under relatively oxidizing conditions, during the early Amazonian. In addition to its distinct igneous petrogenesis and high fO_2, NWA 8159 is also set apart from most martian shergottites with respect to the low degree of shock metamorphism required to preserve crystalline igneous plagioclase (An_(50–65)). In this study, mineral transformations within and adjacent to shock veins in NWA 8159 were investigated using scanning electron microscopy, Raman spectroscopy and transmission electron microscopy to better constrain the unusal shock history of this meteorite. The transformation of olivine to ahrensite (Fe-ringwoodite) along shock vein margins, and tissintite and coesiteformed from igneous mineral (labradorite and silica) grains entrained as clasts within shock veins has been documented in this study. We report on a previously unidentified mineral assemblage of Ca-Na-majoritic garnet, sodic-clinopyroxene and stishovite crystallized from shock melt. This mineral assemblage indicates a crystallization pressure of approximately 16 GPa, which is within the range of previous shock pressure estimates for this meteorite (15–23 GPa). The presence of a majoritic garnet-bearing assemblage throughout veins up to 0.6 mm wide indicates that the sample remained at high-pressure throughout the melt vein quench. Based on thermal models, the sample must have remained at high pressure for ∼100 ms. This shock duration is an order of magnitude longer than those experienced by more highly shocked shergottites such as Tissint or Zagami (>30 GPa; 10–20 ms) and would seem to imply a relatively large impact event. Recent numerical models demonstrate that a range of shock pressures and durations are realized by rocks within the ejected spall zone of a hypervelocity impact. The shock conditions experienced by NWA 8159 therefore do not require an impact event distinct from other shergottites. Rather, our findings suggest that this meteorite originated from near the martian surface at the edge of the impact site. The shock history of NWA 8159 provides a picture of Mars consistent with that derived from remote observation; that of a random cratering process that samples a geologically long-lived and complex planet

Shock conditions recorded in NWA 8159 martian augite basalt with implications for the impact cratering history on Mars

NWA 8159 is an augite-rich martian basalt, formed by cooling of a relatively evolved, Ca-rich, Ti-poor and LREE-depleted lava, under relatively oxidizing conditions, during the early Amazonian. In addition to its distinct igneous petrogenesis and high fO_2, NWA 8159 is also set apart from most martian shergottites with respect to the low degree of shock metamorphism required to preserve crystalline igneous plagioclase (An_(50–65)). In this study, mineral transformations within and adjacent to shock veins in NWA 8159 were investigated using scanning electron microscopy, Raman spectroscopy and transmission electron microscopy to better constrain the unusal shock history of this meteorite. The transformation of olivine to ahrensite (Fe-ringwoodite) along shock vein margins, and tissintite and coesiteformed from igneous mineral (labradorite and silica) grains entrained as clasts within shock veins has been documented in this study. We report on a previously unidentified mineral assemblage of Ca-Na-majoritic garnet, sodic-clinopyroxene and stishovite crystallized from shock melt. This mineral assemblage indicates a crystallization pressure of approximately 16 GPa, which is within the range of previous shock pressure estimates for this meteorite (15–23 GPa). The presence of a majoritic garnet-bearing assemblage throughout veins up to 0.6 mm wide indicates that the sample remained at high-pressure throughout the melt vein quench. Based on thermal models, the sample must have remained at high pressure for ∼100 ms. This shock duration is an order of magnitude longer than those experienced by more highly shocked shergottites such as Tissint or Zagami (>30 GPa; 10–20 ms) and would seem to imply a relatively large impact event. Recent numerical models demonstrate that a range of shock pressures and durations are realized by rocks within the ejected spall zone of a hypervelocity impact. The shock conditions experienced by NWA 8159 therefore do not require an impact event distinct from other shergottites. Rather, our findings suggest that this meteorite originated from near the martian surface at the edge of the impact site. The shock history of NWA 8159 provides a picture of Mars consistent with that derived from remote observation; that of a random cratering process that samples a geologically long-lived and complex planet

Sexually Transmitted Infection History among Adolescents Presenting to the Emergency Department

BACKGROUND: Adolescents and young adults account for about half of the annual diagnoses of sexually transmitted infections (STI) in the United States. Screening and treatment for STIs, as well as prevention, are needed in health-care settings to help offset the costs of untreated STIs. OBJECTIVE: Our aim was to evaluate the prevalence and correlates of self-reported STI history among adolescents presenting to an emergency department (ED). METHODS: Over two and a half years, 4389 youth (aged 14-20 years) presenting to the ED completed screening measures for a randomized controlled trial. About half (56%) reported lifetime sexual intercourse and were included in analyses examining sexual risk behaviors (e.g., inconsistent condom use), and relationships of STI history with demographics (sex, age, race, school enrollment), reason for ED presentation (i.e., medical or injury), and substance use. RESULTS: Among sexually active youth, 10% reported that a medical professional had ever told them they had an STI (212 females, 35 males). Using logistic regression, female sex, older age, non-Caucasian race, not being enrolled in school, medically related ED chief complaint, and inconsistent condom use were associated with increased odds of self-reported STI history. CONCLUSIONS: One in 10 sexually active youth in the ED reported a prior diagnosed STI. Previous STI was significantly higher among females than males. ED providers inquiring about inconsistent condom use and previous STI among male and female adolescents may be one strategy to focus biological testing resources and improve screening for current STI

Lean body mass associated with upper body strength in healthy older adults while higher body fat limits lower extremity performance and endurance

Impaired strength adversely influences an older person\u27s ability to perform activities of daily living. A cross-sectional study of 117 independently living men and women (age = 73.4 9.4 year; body mass index (BMI) = 27.6 4.8 kg/m2) aimed to assess the association between body composition and: (1) upper body strength (handgrip strength, HGS); (2) lower extremity performance (timed up and go (TUG) and sit to stand test (STS)); and (3) endurance (6-minute walk (SMWT). Body composition (% fat; lean body mass (LBM)) was assessed using bioelectrical impedance. Habitual physical activity was measured using the Minnesota Leisure Time Physical Activity Questionnaire (MLTPA) and dietary macronutrient intake, assessed using 24 h recalls and 3-day food records. Regression analyses included the covariates, protein intake (g/kg), MLTPA, age and sex. For natural logarithm (Ln) of right HGS, LBM (p \u3c 0.001) and % body fat (p \u3c 0.005) were significant (r2 = 46.5%; p \u3c 0.000). For left LnHGS, LBM (p \u3c 0.000), age (p = 0.036), protein intake (p = 0.015) and LnMLTPA (p = 0.015) were significant (r2 = 0.535; p \u3c 0.000). For SMW, % body fat, age and LnMLTPA were significant (r2 = 0.346; p \u3c 0.000). For STS, % body fat and age were significant (r2 = 0.251; p \u3c 0.000). LBM is a strong predictor of upper body strength while higher % body fat and lower physical activity are associated with poorer outcomes on tests of lower extremity performance

Shocks in supersonic sand

We measure time-averaged velocity, density, and temperature fields for steady granular flow past a wedge and calculate a speed of granular pressure disturbances (sound speed) equal to 10% of the flow speed. The flow is supersonic, forming shocks nearly identical to those in a supersonic gas. Molecular dynamics simulations of Newton's laws and Monte Carlo simulations of the Boltzmann equation yield fields in quantitative agreement with experiment. A numerical solution of Navier-Stokes-like equations agrees with a molecular dynamics simulation for experimental conditions excluding wall friction.Comment: 4 pages, 5 figure

High Density Reflection Spectroscopy – II. The density of the inner black hole accretion disc in AGN

We present a high density disc reflection spectral analysis of a sample of 17 Seyfert 1 galaxies to study the inner disc densities at different black hole mass scales and accretion rates. All the available XMM–Newton observations in the archive are used. OM observations in the optical/UV band are used to estimate their accretion rates. We find that 65 per cent of sources in our sample show a disc density significantly higher than n_e = 10^(15) cm^(−3), which was assumed in previous reflection-based spectral analyses. The best-fitting disc densities show an anticorrelation with black hole mass and mass accretion rate. High density disc reflection model can successfully explain the soft excess emission and significantly reduce inferred iron abundances. We also compare our black hole spin and disc inclination angle measurements with previous analyses