Thermal alteration of hydrated minerals during hypervelocity capture to silica aerogel at the flyby speed of Stardust

Abstract— Outside the Earth's atmosphere, silica aerogel is one of the best materials to capture finegrained extraterrestrial particles in impacts at hypervelocities. Because silica aerogel is a superior insulator, captured grains are inevitably influenced by frictional heat. Therefore, we performed laboratory simulations of hypervelocity capture by using light‐gas guns to impact into aerogels finegrained powders of serpentine, cronstedtite, and Murchison CM2 meteorite. The samples were shot at >6 km s^?1 similar to the flyby speed at comet P/Wild‐2 in the Stardust mission. We investigated mineralogical changes of each captured particle by using synchrotron radiation X‐ray diffraction (SR‐XRD), transmission electron microscope (TEM), and field emission scanning electron microscope (FE‐SEM). SR‐XRD of each grain showed that the majority of the bulk grains keep their original mineralogy. In particular, SR‐XRD and TEM investigations clearly exemplified the presence of tochilinite whose decomposition temperature is about 300 °C in the interior of the captured Murchison powder. However, TEM study of these grains also revealed that all the samples experienced melting and vesiculation on the surface. The cronstedtite and the Murchison meteorite powder show remarkable fracturing, disaggregation, melting, and vesiculation. Steep thermal gradients, about 2500 °C/μm were estimated near the surface of the grains (<2 μm thick) by TEM observation. Our data suggests that the interior of >4 μm across residual grains containing abundant materials that inhibit temperature rise would have not experienced >300 °C at the center.     

Structure Function Analysis of Two-Scale Scalar Ramps. Part II: Ramp Characteristics and Surface Renewal Flux Estimation

Ramp features in the turbulent scalar field are associated with turbulent coherent structures, which dominate energy and mass fluxes in the atmospheric surface layer. Although finer scale ramp-like shapes embedded within larger scale ramp-like shapes can readily be perceived in turbulent scalar traces, their presence has largely been overlooked in the literature. We demonstrate the signature of more than one ramp scale in structure functions of the turbulent scalar field measured from above bare ground and two types of short plant canopies, using structure-function time lags ranging in scale from isotropic to larger than the characteristic coherent structures. Spectral analysis of structure functions was used to characterize different scales of turbulent structures. By expanding structure function analysis to include two ramp scales, we characterized the intermittency, duration, and surface renewal flux contribution of the smallest (i.e., Scale One) and the dominant (i.e., Scale Two) coherent structure scales. The frequencies of the coherent structure scales increase with mean wind shear, implying that both Scale One and Scale Two are shear-driven. The embedded Scale One turbulent structure scale is ineffectual in the surface-layer energy and mass transport process. The new method reported here for obtaining surface renewal-based scalar exchange works well over bare ground and short canopies under unstable conditions, effectively eliminating the α calibration for these conditions and forming the foundation for analysis over taller and more complex surfaces.     

桶形基础沉贯室内模型试验研究

桶形基础采用负压沉贯法施工,其贯入阻力与压桩,打桩等施工方法显著不同。本文介绍了在粉土和粉质粘土地层中的一组模型试验情况,认为负压法施工可显著降低粉土的抗贯阻力,但在粉质粘土中减阻效果不明显。     

Simultaneous Sv and TS measurements on Young-of-the-Year (YOY) freshwater fish using three frequencies

When this article was originally published     

Tellurides from Sunrise Dam gold deposit, Yilgarn Craton, Western Australia: a new occurrence of nagyágite

Summary The Cu–Fe–Au–Mo (W) deposits in southeastern Hubei are an important component of the Middle–Lower Yangtze River metallogenic belt. Molybdenite from the Fengshandong Cu- (Mo), Ruanjiawan W–Cu- (Mo), Qianjiawan Cu–Au, Tongshankou Cu–Mo and Tonglüshan Cu- (Fe) deposits yielded Re–Os ages of 144.0 ± 2.1 Ma, 143.6 ± 1.7 Ma, 137.7 ± 1.7 Ma, 142.3 ± 1.8–143.7 ± 1.8 Ma and 137.8 ± 1.7–138.1 ± 1.8 Ma, respectively. Phlogopite from the Tieshan Fe- (Cu) deposit yielded an Ar–Ar age of 140.9 ± 1.2 Ma. These data and other published isotopic ages (Re–Os molybdenite and Ar–Ar mica ages) for the Cu–Fe–Au–Mo (W) deposits in the Middle–Lower Yangtze River metallogenic belt show that Cu–Fe–Au–Mo (W) mineralisation in the Tongling, Anqing, Jiurui and Edong ore districts developed in a narrow time span between 135.5 and 144.9 Ma, reflecting an important regional metallogenic event. An integrated study of available petrological and geochronological data, together with relationships to magmatism and the regional geodynamic framework, indicate that the Cu–Fe–Au–Mo (W) mineralisation in the Middle–Lower Yangtze River belt occurred during a regime of lithospheric extension. This extension is probably related to Late Mesozoic processes of lower crustal delamination and lithospheric thinning in East China.     

Tests and applications of an approach to absorbing reflected waves towards incident boundary

If the upstream boundary conditions are prescribed based on the incident wave only, the time-dependent numerical models cannot effectively simulate the wave field when the physical or spurious reflected waves become significant. This paper describes carefully an approach to specifying the incident wave boundary conditions combined with a set sponge layer to absorb the reflected waves towards the incident boundary. Incorporated into a time-dependent numerical model, whose governing equations are the Boussinesq-type ones, the effectiveness of the approach is studied in detail. The general boundary conditions, describing the down-wave boundary conditions are also generalized to the case of random waves. The numerical model is in detail examined. The test cases include both the normal one-dimensional incident regular or random waves and the two-dimensional oblique incident regular waves. The calculated results show that the present approach is effective on damping the reflected waves towards the incident wave boundary.     

Eignung mikrobieller Biotests für gebundene Schadstoffe Suitability of Microbial Bioassays for Bound Contaminants

Toxicity of soil spiked with water soluble and insoluble contaminants was assessed with bacteria. Three bioassays were used with common soil bacteria. Water soluble fractions from the soils were estimated in microtiterplates via dehydrogenase activity of B. cereus and growth of P. putida. A new method was developed using B. cereus to include effects of soil particles with bound contaminants. As contaminants p-nitrophenol and 2-naphthol were tested in these systems. Results indicated that the concentration of the contaminants in the soil solution is determined by soil properties. Toxicity of water soluble fractions was not only a result of the toxicant's concentration but further modified by soluble components of the soils. It is not possible to assess soil pollution from toxicity of the water soluble fraction in general, because unknown factors of the soluble soil fraction can influence toxicity greatly. The newly developed contact bioassay with B. cereus showed clearly higher toxicity of 2-naphthol estimated in soil suspension than did the comparable test system with the same bacteria using water soluble fractions only. The results stress the importance of including soil particles into bioassay procedures. It was shown that also water insoluble, bound contaminants can act as toxicants. For an estimation of toxicity under conditions more relevant for the environment, the suggested test system can provide useful information to bioavailability of bound contaminants.     

Anaerobic Metabolism in Tidal Freshwater Wetlands: I. Plant Removal Effects on Iron Reduction and Methanogenesis

For energetic reasons, iron reduction suppresses methanogenesis in tidal freshwater wetlands; however, when iron reduction is limited by iron oxide availability, methanogenesis dominates anaerobic carbon mineralization. Plants can mediate this microbial competition by releasing oxygen into the rhizosphere and supplying oxidized iron for iron reducers. We utilized a plant removal experiment in two wetland sites to test the hypothesis that, in the absence of plants, rates of iron reduction would be diminished, allowing methanogenesis to dominate anaerobic metabolism. In both sites, methanogenesis was the primary anaerobic mineralization pathway, with iron reduction dominating only early and late in the growing season in the site with a less organic soil. These patterns were not influenced by the presence of plants, demonstrating that plants were not a key control of microbial metabolism. Instead, we suggest that site conditions, including soil chemistry, and temperature are important controls of the pathways of anaerobic metabolism.     

PM2.5 co-benefits of climate change legislation part 2: California governor’s executive order S-3-05 applied to the transportation sector

California Governor’s Executive Order (CGEO) S-3-05 requires that California greenhouse gas (GHG) emissions be reduced to 80 % below 1990 levels by the year 2050. Meeting this target will require drastic changes in transportation technology, fuel, and behavior which will reduce criteria pollutant emissions as well as GHG emissions. The improvement to local air quality caused by the reduced criteria pollutant emissions must be calculated to fully evaluate the overall benefits and costs of CGEO S-3-05. In the present study, seven different transportation scenarios that move towards the goals of CGEO S-3-05 in the transportation sector were examined to determine how they would affect future airborne particulate matter (PM_2.5) concentrations in California: (1) hydrogen fuel cells, (2) electric vehicles, (3) high efficiency vehicles, (4) public mass transit, (5) biofuels, (6) biofuels + hybrid electric vehicles, and (7) hydrogen fuel cells + electric vehicles. The air quality implications of each scenario were evaluated using a chemical transport model applied during a wintertime stagnation episode representing future climate in California. Scenarios (6) and (7) reduced population-weighted PM_2.5 mass concentrations by ~9 % and PM_2.5 elemental carbon (EC) concentrations by ~30 % relative to base-case predictions.