55 research outputs found

    Modern pollen rain–vegetation relationships along a forest–steppe transect in the Golestan National Park, NE Iran

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    Pollen rain-vegetation relationships were studied over a forest-steppe transect in Golestan National Park, NE Iran. The surface pollen percentages were compared to the vegetation composition of the respective vegetation types in 18 sampling points using both descriptive and numerical approaches. Hyrcanian lowland forests are characterized by pollen assemblages dominated by Quercus, Carpinus betulus and low frequencies of Zelkova carpinifolia. Both Parrotia persica and Zelkova carpinifolia show a very low pollen representation in modern surface samples, an under-representation that should be taken into account in the interpretation of past vegetation records. Transitional communities between the forest and steppe including Acer monspessulanum subsp. turcomanicum, Crataegus and Paliurus scrubs, Juniperus excelsa woodlands and shrub-steppe patches are more difficult to distinguish in pollen assemblages, however, they are characterized by higher values of the dominant shrub species. The transitional vegetation communities at the immediate vicinity of the forest show also a substantial amount of grass pollen. Many insect-pollinated taxa are strongly under-represented in the pollen rain including most of the rosaceous trees and shrubs, Rhamnus, Paliurus, Acer and Berberis. Artemisia steppes are characterized by very high values of Artemisia pollen and the near absence of tree pollen

    SOME APPLICATIONS OF LOW ENERGY ACCELERATORS

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    Double 1s shell ionization of Si induced in collisions with protons and heavy ions

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    The double 1s ionization of Si induced in collisions with protons and heavier ions (C, Ne) was studied by measuring the K X-ray emission of a solid Si target. In order to resolve the hypersatellite contributions in the spectra, high-resolution crystal diffractometry was employed yielding subelectronvolt energy resolution. Experimentally obtained hypersatellite yields were used to determine the double to single K shell ionization cross-section ratios σKK/σK corresponding to the investigated collisions. The experimental ratios for collisions with heavy ions, where direct Coulomb ionization and electron capture need both to be considered, were compared to the theoretical values calculated within the independent electron approximation employing single electron ionization probabilities calculated by the three body classical trajectory Monte-Carlo (CTMC) method. For proton collisions where direct ionization solely contributes to 1s ionization the semiclassical approximation (SCA) was employed

    Double-K-shell ionization of Mg and Si induced in collisions with C and Ne ions

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    The satellite and hypersatellite K x-ray emission of a thin Mg foil and thick polycrystalline Si target bombarded by 34-MeV C and 50-MeV Ne ions was measured using high-resolution crystal diffractometry. The corresponding projectile reduced velocities v/vK were 1.09 and 0.92 for C ions and 1.02, 0.86 for Ne ions in case of Mg and Si targets, respectively. An energy resolution of approximately 0.5 eV enabled separation of contributions corresponding to states with different numbers of K- and L-shell vacancies. The relative intensities of satellite and hypersatellite lines were determined by fitting the measured spectra with line shapes calculated using the GRASP92 computer code. To determine the production yields of initial states from the measured x-ray yields, the total decay schemes of initial states were considered. The decay schemes were also used to determine the relative intensities of components contributing to the observed Kalpha satellites and hypersatellites and Kβ satellite intensities. Including theoretical predictions in the fitted model is crucial to analyze properly the Kα hypersatellite region which overlaps the Kβ satellites. The initial-state production yields were then used to determine the L-shell ionization probabilities and the double- to single-K-shell ionization ratio corresponding to the four investigated collisions. The experimental values were compared to the theoretical predictions obtained within the independent electron model using single-electron ionization probabilities calculated by the three-body classical trajectory Monte Carlo (CTMC) method. Since the targets used were thick enough, the equilibrium projectile charge-state distributions in the solid media were assumed. While for the double- to single-K-shell ionization ratios a satisfactory agreement was observed between the CTMC predictions and our experimental results, the L-shell ionization probabilities were found to be overestimated by the CTMC calculations by a factor of about 2

    Analysis of Slovenian historic materials

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    ABSTRACT Systematic investigations by PIXE are performed on medieval glass, metal objects, inks and papers, and metal pigments on paints and textiles

    Functional implications of O-GlcNAcylation-dependent phosphorylation at a proximal site on keratin 18

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    Keratins 8/18 (K8/18) are phosphoglycoproteins and form the major intermediate filament network of simple epithelia. The three O-GlcNAcylation (Ser , Ser , and Ser ) and two phosphorylation (Ser and Ser ) serine sites on K18 are well characterized. Both of these modifications have been reported to increase K18 solubility and regulate its filament organization. In this report, we investigated the site-specific interplay between these two modifications in regulating the functional properties of K18, like solubility, stability, and filament organization. An immortalized hepatocyte cell line (HHL-17) stably expressing site-specific single, double, and triple O-GlcNAc and phosphomutants of K18 were used to identify the site(s) critical for regulating these functions. Keratin 18 mutants where O-GlcNAcylation at Ser was abolished (K18-S30A) exhibited reduced phosphorylation induced solubility, increased stability, defective filament architecture, and slower migration. Interestingly, K18-S30A mutants also showed loss of phosphorylation at Ser , a modification known to regulate the solubility of K18. Further to this, the K18 phosphomutant (K18-S33A) mimicked K18-S30A in its stability, filament organization, and cell migration. These results indicate that O-GlcNAcylation at Ser promotes phosphorylation at Ser to regulate the functional properties of K18 and also impact cellular processes like migration. O-GlcNAcylation and phosphorylation on the same or adjacent sites on most proteins antagonize each other in regulating protein functions. Here we report a novel, positive interplay between O-GlcNAcylation and phosphorylation at adjacent sites on K18 to regulate its fundamental properties
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