Evidence in a glassy cosmic spherule from Antarctica for grazing incidence encounters with the Earth's atmosphere

Abstract— Cosmic dust accreted by the Earth can be extensively reprocessed during atmospheric encounters. The textures and compositions of reprocessed material provide important constraints by which the processes affecting extraterrestrial matter in the Earth's atmosphere can be better understood. Here we report results on an unusual Antarctic glassy cosmic spherule that demonstrates strong textural evidence for at least two grazing incidence encounters with the Earth's atmosphere prior to final reentry. The particle consists of a central glassy core with four peripheral glass lobes that transect a silicate particle rim. The texture of the particle confirms previous theoretical speculations that some high velocity, low incidence angle interplanetary particles experience numerous encounters with the Earth's atmosphere and also indicates that micrometeorites demonstrating multiple melting episodes should be interpreted with caution.     

Automated analysis of eclipsing binary light curves – II. Statistical analysis of OGLE LMC eclipsing binaries

In the first paper of this series, we presented EBAS – Eclipsing Binary Automated Solver, a new fully automated algorithm to analyse the light curves of eclipsing binaries, based on the ebop code. Here, we apply the new algorithm to the whole sample of 2580 binaries found in the Optical Gravitational Lensing Experiment (OGLE) Large Magellanic Cloud (LMC) photometric survey and derive the orbital elements for 1931 systems. To obtain the statistical properties of the short-period binaries of the LMC, we construct a well-defined subsample of 938 eclipsing binaries with main-sequence B-type primaries. Correcting for observational selection effects, we derive the distributions of the fractional radii of the two components and their sum, the brightness ratios and the periods of the short-period binaries. Somewhat surprisingly, the results are consistent with a flat distribution in log P between 2 and 10 d. We also estimate the total number of binaries in the LMC with the same characteristics, and not only the eclipsing binaries, to be about 5000. This figure leads us to suggest that  (0.7 ± 0.4)  per cent of the main-sequence B-type stars in the LMC are found in binaries with periods shorter than 10 d. This frequency is substantially smaller than the fraction of binaries found by small Galactic radial-velocity surveys of B stars. On the other hand, the binary frequency found by Hubble Space Telescope ( HST ) photometric searches within the late main-sequence stars of 47 Tuc is only slightly higher and still consistent with the frequency we deduced for the B stars in the LMC.     

Deglaciation of the younger dryas or Loch Lomond Stadial ice-field in the northern Highlands,Scotland

When viewed from the air, Scottish ‘hummocky moraine’ can be resolved into a series of linear ridges that resemble those found at the margins of actively retreating glaciers today. Recent work has supported the interpretation of these linear ridges as ice-marginal landforms and the authors believe that the majority of ‘hummocky moraine’ deposits can be interpreted in this way. Consequently the pattern of deglaciation can be established fairly precisely from the pattern of linear ridges. This approach is applied to the landforms of the northern part of the Loch Lomond Stadial ice-field in order to reconstruct the regional pattern of deglaciation. This leads to important inferences about the significance of topographic control during deglaciation and more importantly it provides fresh insight into the environment of the British Isles during the Loch Lomond Stadial.     

Urban effects of Chennai on sea breeze induced convection and precipitation

Doppler radar derived wind speed and direction profiles showed a well developed sea breeze circulation over the Chennai, India region on 28 June, 2003. Rainfall totals in excess of 100 mm resulted from convection along the sea breeze front. Inland propagation of the sea breeze front was observed in radar reflectivity imagery. High-resolution MM5 simulations were used to investigate the influence of Chennai urban land use on sea breeze initiated convection and precipitation. A comparison of observed and simulated 10m wind speed and direction over Chennai showed that the model was able to simulate the timing and strength of the sea breeze. Urban effects are shown to increase the near surface air temperature over Chennai by 3.0K during the early morning hours. The larger surface temperature gradient along the coast due to urban effects increased onshore flow by 4.0m s⁻¹. Model sensitivity study revealed that precipitation totals were enhanced by 25mm over a large region 150 km west of Chennai due to urban effects. Deficiency in model physics related to night-time forecasts are addressed.     

Late Quaternary Bison diminution on the Great Plains of North America: evaluating the role of human hunting versus climate change

Body size changes of Bison and mortality age structure data document the effects of climate-driven environmental change and human hunting pressure on large mammals in North America. Morphometric and mortality data are drawn from 58 archaeological and 9 paleontological localities dating between 37,000 and 250 calBP. Proxy information on body size is based on measurements recorded on 901 adult calcanei (os calcis) and 1026 humeri. In addition, published mortality profiles from 24 archaeological faunal assemblages spanning the last 14,000 years were used to approximate the age structure of bison populations. These results suggest that dramatic diminution in bison body size occurred in several short bursts, rather than a continuous gradual decline. These periods of rapid size reduction correlate with times of ecological reorganization, when aridity-driven changes in grasslands decreased forage quality and availability. Mortality age data indicate that the decrease in body size occurred in a context where there was no evidence for a progressively severe juvenile bias in bison populations. Overall, it appears that the changes in body size were a reaction to environmental conditions rather than the result of human predation pressure.     

Formation of Zn–Ca phyllomanganate nanoparticles in grass roots

It is now well established that a number of terrestrial and aquatic microorganisms have the capacity to oxidize and precipitate Mn as phyllomanganate. However, this biomineralization has never been shown to occur in plant tissues, nor has the structure of a natural Mn(IV) biooxide been characterized in detail. We show that the graminaceous plant Festuca rubra (red fescue) produces a Zn-rich phyllomanganate with constant Zn:Mn and Ca:Mn atomic ratios (0.46 and 0.38, respectively) when grown on a contaminated sediment. This new phase is so far the Zn-richest manganate known to form in nature (chalcophanite has a Zn:Mn ratio of 0.33) and has no synthetic equivalent. Visual examination of root fragments under a microscope shows black precipitates about ten to several tens of microns in size, and their imaging with backscattered and secondary electrons demonstrates that they are located in the root epidermis. In situ measurements by Mn and Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) with a micro-focused beam can be quantitatively described by a single-phase model consisting of Mn(IV) octahedral layers with 22% vacant sites capped with tetrahedral and octahedral Zn in proportions of 3:1. The layer charge deficit is also partly balanced by interlayer Mn and Ca. Diffracting crystallites have a domain radius of 33 Å in the ab plane and contain only 1.2 layers (8.6 Å) on average. Since this biogenic Mn oxide consists mostly of isolated layers, basal 00l reflections are essentially absent despite its lamellar structure. Individual Mn layers are probably held together in the Mn–Zn precipitates by stabilizing organic molecules. Zinc biomineralization by plants likely is a defense mechanism against toxicity induced by excess concentrations of this metal in the rhizosphere.