RESUMEN
Electron backscatter diffraction (EBSD) on ice is a decade old. We have built upon previous work to select and develop methods of sample preparation and analysis that give >90% success rate in obtaining high-quality EBSD maps, for the whole surface area (potentially) of low porosity (<15%) water ice samples, including very fine-grained (<10 µm) and very large (up to 70 mm by 30 mm) samples. We present and explain two new methods of removing frost and providing a damage-free surface for EBSD: pressure cycle sublimation and 'ironing'. In general, the pressure cycle sublimation method is preferred as it is easier, faster and does not generate significant artefacts. We measure the thermal effects of sample preparation, transfer and storage procedures and model the likelihood of these modifying sample microstructures. We show results from laboratory ice samples, with a wide range of microstructures, to illustrate effectiveness and limitations of EBSD on ice and its potential applications. The methods we present can be implemented, with a modest investment, on any scanning electron microscope system with EBSD, a cryostage and a variable pressure capability.
RESUMEN
Lower Eocene flowers with Pistillipollenites macgregorii pollen represent the earliest megafossil evidence of the Gentianaceae. The Paleocene occurrence of P. macgregorii, the fossil's modern floral structure, and suggested trends in the evolution of pollen in the Gentianaceae indicate a considerably earlier origin for the family. Floral morphology typical of bee-pollinated flowers provides the earliest, albeit indirect, fossil evidence of bees.
RESUMEN
The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.
RESUMEN
Granulocytopenic patients with an intravascular catheter are at increased risk for infection with Staphylococcus epidermidis. During the intervals when the catheters are not being used for infusions, it is customary to maintain patency of the catheter lumen with a solution containing heparin. We show that heparin does not inhibit the growth of S. epidermidis isolated from the catheter of an infected patient. A 20-mg/ml solution of disodium EDTA, a chelating agent which effectively anticoagulates blood at this concentration, was shown to be bactericidal for an initial inoculum of 10(3) CFU of staphylococci per ml in 24 h. Vancomycin, an antibiotic which is often employed to treat Staphylococcus infections, was also bactericidal for initial inocula of 10(3) CFU/ml at doses of 6.7 micrograms/ml, a drug concentration in the therapeutic range. When 10(3) staphylococci per ml were cultured in the presence of catheter segments and disodium EDTA or vancomycin, subcultures of the catheters showed minimal or no growth, respectively. In contrast, when cultured with heparin alone, subcultures showed abundant growth. In view of its low cost, effectiveness as an anticoagulant, and bactericidal activity, EDTA should be studied as a replacement for heparin solutions for the maintenance of intravenous catheters in granulocytopenic patients.