Isotopic evolution of planetary crusts by hypervelocity impacts evidenced by Fe in microtektites.

Fractionation effects related to evaporation and condensation had a major impact on the current elemental and isotopic composition of the Solar System. Although isotopic fractionation of moderately volatile elements has been observed in tektites due to impact heating, the exact nature of the processes taking place during hypervelocity impacts remains poorly understood. By studying Fe in microtektites, here we show that impact events do not simply lead to melting, melt expulsion and evaporation, but involve a convoluted sequence of processes including condensation, variable degrees of mixing between isotopically distinct reservoirs and ablative evaporation during atmospheric re-entry. Hypervelocity impacts can as such not only generate isotopically heavy, but also isotopically light ejecta, with δ56/54Fe spanning over nearly 5‰ and likely even larger variations for more volatile elements. The mechanisms demonstrated here for terrestrial impact ejecta modify our understanding of the effects of impact processing on the isotopic evolution of planetary crusts.

A large meteoritic event over Antarctica ca. 430 ka ago inferred from chondritic spherules from the Sør Rondane Mountains.

Large airbursts, the most frequent hazardous impact events, are estimated to occur orders of magnitude more frequently than crater-forming impacts. However, finding traces of these events is impeded by the difficulty of identifying them in the recent geological record. Here, we describe condensation spherules found on top of Walnumfjellet in the Sør Rondane Mountains, Antarctica. Affinities with similar spherules found in EPICA Dome C and Dome Fuji ice cores suggest that these particles were produced during a single-asteroid impact ca. 430 thousand years (ka) ago. The lack of a confirmed crater on the Antarctic ice sheet and geochemical and 18O-poor oxygen isotope signatures allow us to hypothesize that the impact particles result from a touchdown event, in which a projectile vapor jet interacts with the Antarctic ice sheet. Numerical models support a touchdown scenario. This study has implications for the identification and inventory of large cosmic events on Earth.

[The effect of increased concentration of lipoprotein (a) on identification of sub-faction of lipoproteins using native electrophoresis technique].

The quantitative analysis of sub-fractions of lipoproteins acquires growing significance in diagnostic and prognosis of cardiovascular diseases. It is well known that presence of lipoprotein (a) in high concentrations significantly distorts results of biochemical analysis, in particular detection of level of cholesterol of low-density lipoproteins. The lipoprotein (a) is a heterogeneous particle and its mobility in the systems used for analysis of sub-fractions of lipoproteins can have significant variability that will bring inaccuracy into results. The data concerning relationship between lipoprotein (a) and sub-fractions of lipoproteins and also their differentiation in various systems of determination of lipid spectrum are quite numerous. The given study is considered as actual one because it analyses input of lipoprotein (a) into results of detection of sub-fractions using the technique with diagnostic significance. The study was carried out for evaluating possible input of lipoprotein (a) into results of quantitative estimation of sub-fractions of lipoproteins by technique of native electrophoresis in polyacrylamide gel used for diagnostic of cardio-vascular diseases. To detect concentration of lipoprotein (a) in blood serum the technique of enzyme-linked immunosorbent assay was applied. The qualitative valuation of content of sub-fractions of lipoproteins was implemented using system Lipoprint Quantimetrix (USA). The sub-fractions of lipoproteins were detected in samples of serum of healthy donor and normolipidic patients before and after removal of lipoprotein (a) using technique of affine chromatography in vitro. It turned out that after removal of lipoprotein (a) analysis of sub-fractions of lipoproteins in plasma of healthy donor detects significant decreasing of level of lipoproteins of medium density. The samples of serum of patients with atherosclerosis besides removal of sub-fractions of lipoproteins of medium density, decreasing of level of large sub-fractions of low density lipoproteins was observed. The analysis of samples obtained after procedures of therapeutic lipoprotein (a) apheresis using columns "Lp (a) Lipopak" (Russia) demonstrated that along with removal of lipoprotein (a), decreasing of concentration of sub-fraction C lipoproteins of medium density in all samples that substantiates in vitro data. In patients without affection and with multi-vessel lesion of coronary bloodstream reliable differences in concentration of lipoproteins of medium density were established. The received data testify that high level of lipoprotein (a) can contribute significant inaccuracies into results of detection of subfractions of lipoproteins. Therefore, application of system Lipoprint (Quantimetrix USA) provides no opportunity to unequivocally interpret data concerning input of sub-fractions of lipoproteins into risk of development of cardio-vascular diseases in patients with pathological lipid profile and higher concentration of lipoprotein (a).

[Elevated Lipoprotein(a) Cncentration and Presence of Subfractions of Small Dense Low Density Lipoproteins as Independent Factors of Risk of Ischemic Heart Disease].

AIM: To study relation of lipoproteina - Lp(a) and subfractional composition of apoB containing lipoproteins to the presence of ischemic heart disease (IHD). Manerial and methods. Parameters of lipid spectrum, Lp(a), and subfractions of apoB containing lipoproteins were determined in blood serum of 187 patients with known data of instrumental examination. RESULTS: Lp(a) concentration was not linked to any of risk factors, levels total cholesterol (TC), low and high density lipoprotein CH, and subfractions of lipoproteins. In total group triglyceride (TGG) level correlated with content of small dense LDL (sdLDL) (r=0.445, <0.0001) and mean dimension of LDL particles (r=-0.424, p<0.0001). This correlation was absent in the subgroup with Lp(a) more or equal 30 mg/dl and was strengthered among patients with normal Lp(a) level. In total group presence of IHD was associated with sex (r=0.325, p<0.0001), Lp(a) concentration (r=0.271, p=0.0001), and level of triglycerides (r=0.159, p=0.030). In multiple regression analysis levels of TG, Lp(a) and sdLDL were selected as factors independently associated with presence of IHD. Detection of subfractions sdLDL>2 mg/dl in blood plasma (atherogenic profile B), as well as lowering of concentration of large LDL subfractions significantly increased probability of IHD presence in patients with elevated Lp(a) concentration Lp(a) concentration. CONCLUSION: Lp(a) is an independent factor of risk of coronary atherosclerosis more significant than shifts in subfractional composition of apoB containing lipoproteins. In patients with Lp(a) concentration less or equal 30 mg/dl subfractions of sdLDL were directly related to TG. Level of sdLDL and large lipoproteins of intermediate density are directly related to the presence of IHD. Large LDL correlates with concentration of HDL DL C and probably is cardioprotective. sdLDL content>2 mg/l or hypertriglyceridemia (TG>1.7 mmol/l) significantly increase chances of detection of confirmed IHD in patients with elevated Lp(a).

Efficient disruption of small asteroids by Earth's atmosphere.

Accurate modelling of the interaction between the atmosphere and an incoming bolide is a complex task, but crucial to determining the fraction of small asteroids that actually hit the Earth's surface. Most semi-analytical approaches have simplified the problem by considering the impactor as a strengthless liquid-like object ('pancake' models), but recently a more realistic model has been developed that calculates motion, aerodynamic loading and ablation for each separate particle or fragment in a disrupted impactor. Here we report the results of a large number of simulations in which we use both models to develop a statistical picture of atmosphere-bolide interaction for iron and stony objects with initial diameters up to approximately 1 km. We show that the separated-fragments model predicts the total atmospheric disruption of much larger stony bodies than previously thought. In addition, our data set of >1,000 simulated impacts, combined with the known pre-atmospheric flux of asteroids with diameters less than 1 km, elucidates the flux of small bolides at the Earth's surface. We estimate that bodies >220 m in diameter will impact every 170,000 years.

A possible tektite strewn field in the Argentinian Pampa.

Impact glass associated with 11 elongate depressions in the Pampean Plain of Argentina, north of the city of Rio Cuarto, was suggested to be proximal ejecta related to a highly oblique impact event. We have identified about 400 additional elongate features in the area that indicate an aeolian, rather than an impact, origin. We have also dated fragments of glass found at the Rio Cuarto depressions; the age is similar to that of glass recovered 800 kilometers to the southeast. This material may be tektite glass from an impact event around 0.48 million years ago, representing a new tektite strewn field.