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  • 1
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    Diatom frustules show increased mechanical strength and altered valve morphology under iron limitation (2011)
    Wiley
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    Publication Date: 2011-06-26
    Print ISSN: 0024-3590
    Electronic ISSN: 1939-5590
    Topics: Biology , Geosciences , Physics
    Published by Wiley on behalf of Association for the Sciences of Limnology and Oceanography.
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  • 2
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    Zn3 and Ga3 Triangles as Building Units in Sr2Au6Zn3 and Sr2Au6Ga3 (2013)
    Wiley
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    Publication Date: 2013-09-07
    Description: The intermetallic compounds Sr 2 Au 6.52 Zn 2.48 , Sr 2 Au 6 Zn 3 , and Sr 2 Au 6 Ga 3 were obtained by induction melting of the elements in sealed tantalum tubes. Their structures were studied by X-ray diffraction on powders and refined from single crystal diffraction data: R c , a = 844.5(2), c = 2187.7(5) pm, wR 2 = 0.0411, 936 F 2 values and 20 variables for Sr 2 Au 6.52 Zn 2.48 ; a = 841.6(2), c = 2191.5(7) pm, wR 2 = 0.0126, 587 F 2 values and 19 variables for Sr 2 Au 6 Zn 3 ; and a = 841.9(2), c = 2191.1(7) pm, wR 2 = 0.0199, 660 F 2 values and 19 variables for Sr 2 Au 6 Ga 3 . The gold substructures of Sr 2 Au 6 Zn 3 and Sr 2 Au 6 Ga 3 can be considered as diamond polytypes with 6R stacking sequences (287–304 pm Au–Au in Sr 2 Au 6 Zn 3 ). The cavities formed by this network are filled in an ordered manner by strontium atoms and Zn 3 (281 pm Zn–Zn), respectively Ga 3 (286 pm Ga–Ga) triangles in a 2:1 ratio. Consequently one can describe the Sr 2 Au 6 Zn 3 and Sr 2 Au 6 Ga 3 structures as ordered substitution variants of the Zintl phase CaIn 2 . This structural relationship is discussed on the basis of a group-subgroup Scheme. Sr 2 Au 6.52 Zn 2.48 shows Zn/Au mixing on the triangle.
    Print ISSN: 0044-2313
    Electronic ISSN: 1521-3749
    Topics: Chemistry and Pharmacology
    Published by Wiley
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  • 3
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    Dissection of Different Donor Abilities Within Bis(pyrazolyl)­pyridinylmethane Transition Metal Complexes (2013)
    Wiley
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    Publication Date: 2013-04-10
    Description: Using the bis(pyrazolyl)pyridinylmethane ligand α,α,α-bis(1-pyrazolyl)(2-pyridinyl)toluene {(ph)C(pz) 2 (py)} for bioinorganic inspired coordination chemistry studies, we synthesised and structurally characterised three monofacial complexes [{(ph)C(pz) 2 (py)}CoCl 2 ] ( C1 ), [{(ph)C(pz) 2 (py)}CuCl 2 ] ( C2 ), [{(ph)C(pz) 2 (py)}ZnCl 2 ] ( C3 ) and the binuclear halogenido-bridged complexes [{(ph)C(pz) 2 (py)} 2 (μ-Cl) 2 Fe 2 Cl 2 ] ( C4 ) and [{(ph)C(pz) 2 (py)} 2 (μ-Br) 2 Cu 2 Br 2 ] ( C5 ). In four of these complexes, severe disorders between pyrazolyl and pyridinyl donor groups are observed such that bis(pyrazolyl) and (pyrazolyl)(pyridinyl) coordination modes are concomitantly found. The donor competition is dissected by DFT calculation of the energy differences between the two coordination modes and NBO analysis of the donor situation. The pyrazolyl units provide with more donor strength although pyridine is considerably more basic.
    Print ISSN: 0044-2313
    Electronic ISSN: 1521-3749
    Topics: Chemistry and Pharmacology
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  • 4
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    Constraints on the major sources of dissolved organic carbon in Alpine ice cores from Radiocarbon analysis over the bomb peak period (2013)
    Wiley
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    Publication Date: 2013-03-30
    Description: [1]  Radiocarbon ( 14 C) has proven to be a powerful tool in distinguishing modern and fossil fuel sources contributing to organic aerosols. By applying this concept to ice core records of the dissolved organic carbon (DOC) fraction, we developed a setup dedicated to the extraction of DOC from Alpine ice core samples for 14 C micro-analysis. With respect to the difficulties and limitations of this analytical method, it is shown that a total process blank mass of (6 ± 3) μgC with a 14 C signature of (0.71 ± 0.17) can be obtained, corresponding to a minimum sample size between 200 g for industrial and 600 g for pre-industrial ice. Radiocarbon analyses of eight DOC ice core samples from the high accumulation glacier Col du Dôme (European Alps) were mainly performed over the bomb peak period. These data, being associated with snow deposition over the summer half-years, show an overall mean fossil contribution of (25 ± 9) %. Adaptation of the DO 14 C values to the atmospheric 14 CO 2 record revealed that the biogenic input to ice core DOC is associated with a fast recycling biospheric component, likely linked to a turnover time of less than three years.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Interaction of Modified (K,Na)NbO3 Ceramics with Ag-Containing Electrodes (2011)
    Wiley
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    Publication Date: 2011-05-25
    Description: Interaction between modified (K,Na)NbO 3 ceramics and metallic silver has been experimentally studied to simulate effects of using Ag-containing electrode pastes in multilayer actuators with alkali-based ferroelectric layers. The solubility limit of silver added as an excess component is found to vary in the range of 0.8–2.5 mol% depending on composition and stoichiometry of the ceramics. Inhomogeneous distribution of the residual undissolved silver across the thickness of a single ceramic layer between the co-fired Ag–Pd electrodes is evidenced by X-ray diffraction. The overall effect of Ag as excess component on temperature of the orthorhombic–tetragonal phase transition is found different from the known effect of Ag as alkali substituent.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 6
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    First three-dimensional observations of polar mesosphere winter echoes: Resolving space-time ambiguity (2011)
    Wiley
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    Publication Date: 2011-11-09
    Description: We present the first three-dimensionally resolved observations of polar mesosphere winter echoes obtained with a 25 beam-experiment covering a volume of about 50 km in diameter (horizontal distance) at altitudes between 65 and 85 km. This allows us to resolve the classical space time ambiguity of single beam observations and reveals that the echoing structure was tilted in the East–West direction but showed no considerable tilt in the North–South direction. The Doppler shifts derived from the 24 off-zenith beam directions are consistent with the mean background wind measured independently by a co-located MF-radar. The time development of the 3-D echo-pattern is consistent with scattering structures that follow the constant phase lines of a medium frequency gravity wave that is propagating against the mean flow. Wave parameters derived from these observations are independently confirmed by the analysis of co-located wind measurements with the aforementioned MF-radar. Overall, the observed echo morphology in time and space is reminiscent of gravity wave breaking which is known to lead to a maximum of turbulence activity that moves with the phase of the wave.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Inferring catchment precipitation by doing hydrology backward: A test in 24 small and mesoscale catchments in Luxembourg (2012)
    Wiley
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    Publication Date: 2012-10-10
    Description: The complexity of hydrological systems and the necessary simplification of models describing these systems remain major challenges in hydrological modeling. Kirchner's (2009) approach of inferring rainfall and evaporation from discharge fluctuations by “doing hydrology backward” is based on the assumption that catchment behavior can be conceptualized with a single storage-discharge relationship. Here we test Kirchner's approach using a densely instrumented hydrologic measurement network spanning 24 geologically diverse subbasins of the Alzette catchment in Luxembourg. We show that effective rainfall rates inferred from discharge fluctuations generally correlate well with catchment-averaged precipitation radar estimates in catchments ranging from less than 10 to more than 1000 km2 in size. The correlation between predicted and observed effective precipitation was 0.8 or better in 23 of our 24 catchments, and prediction skill did not vary systematically with catchment size or with the complexity of the underlying geology. Model performance improves systematically at higher soil moisture levels, indicating that our study catchments behave more like simple dynamical systems with unambiguous storage-discharge relationships during wet conditions. The overall mean correlation coefficient for all subbasins for the entire data set increases from 0.80 to 0.95, and the mean bias for all basins decreases from –0.61 to –0.35 mm d−1. We propose an extension of Kirchner's approach that uses in situ soil moisture measurements to distinguish wet and dry catchment conditions.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    The benefit of modeled ozone data for the reconstruction of a 99-year UV radiation time series (2012)
    Wiley
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    Publication Date: 2012-08-17
    Description: Solar erythemal UV radiation (UVER) is highly relevant for numerous biological processes that affect plants, animals, and human health. Nevertheless, long-term UVER records are scarce. As significant declines in the column ozone concentration were observed in the past and a recovery of the stratospheric ozone layer is anticipated by the middle of the 21st century, there is a strong interest in the temporal variation of UVER time series. Therefore, we combined ground-based measurements of different meteorological variables with modeled ozone data sets to reconstruct time series of daily totals of UVER at the Meteorological Observatory, Potsdam, Germany. Artificial neural networks were trained with measured UVER, sunshine duration, the day of year, measured and modeled total column ozone, as well as the minimum solar zenith angle. This allows for the reconstruction of daily totals of UVER for the period from 1901 to 1999. Additionally, analyses of the long-term variations from 1901 until 1999 of the reconstructed, new UVER data set are presented. The time series of monthly and annual totals of UVER provide a long-term meteorological basis for epidemiological investigations in human health and occupational medicine for the region of Potsdam and Berlin. A strong benefit of our ANN-approach is the fact that it can be easily adapted to different geographical locations, as successfully tested in the framework of the COSTAction 726.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Fatigue Crack Growth Behavior of Silicon Nitride: Roles of Grain Aspect Ratio and Intergranular Film Composition (2012)
    Wiley
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    Publication Date: 2012-10-17
    Description: The role of microstructure in affecting the fatigue crack growth resistance of grain bridging silicon nitride ceramics doped with rare earth ( RE  =  Y , La , Lu ) oxide sintering additives was investigated. Three silicon nitride ceramics were prepared using MgO - RE 2 O 3 and results were compared with a commercial Al 2 O 3 - Y 2 O 3 -doped material. Decreasing stress intensity range (Δ K ) fatigue tests were conducted using compact-tension specimens to measure steady-state fatigue crack growth rates. Specimens doped with MgO - RE 2 O 3 additives showed a significantly higher resistance to crack growth than those with Al 2 O 3 - Y 2 O 3 additives and this difference was attributed to the much higher grain aspect ratio for the MgO - RE 2 O 3 -doped ceramics. When the crack growth data were normalized with respect to the total contribution of toughening by bridging determined from the monotonically loaded R -curves, the differences in fatigue resistance were greatly reduced with the data overlapping considerably. Finally, all of the MgO - RE 2 O 3 -doped silicon nitrides displayed similar steady-state fatigue crack growth behavior suggesting that they are relatively insensitive to the intergranular film.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 10
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    The Role of Binder Adsorption for High Solid Loading Nano-Zirconia Extrusion Pastes (2012)
    Wiley
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    Publication Date: 2012-04-05
    Description: The viscosity behavior of extrusion pastes comprised of a PVB melt and varying amounts of nano-zirconia powder have been explored with special emphasis on the impact of a dispersant to reduce the viscosity. In contrast to suspensions with nanopowders, the maximum solid loading in the highly viscous extrusion pastes studied is not limited by attractive interparticle forces. However, at a solid loading 〉30 vol% the pastes had too high viscosity to be processed due to the high number of adsorbed polymer molecules. By adding a decoupling agent that reduced the work of adhesion of the polymer molecules on the zirconia particles, the viscosity of the pastes could be lowered significantly. The calculated work of adhesion is consistent with the viscosity behavior of the feedstock and is confirmed by wetting angles that have been experimentally determined. It is shown that the effect of the dispersant cannot be explained by electrostatic or steric stabilization of the particles in the melt. A unifying scheme is proposed where the limiting factors “agglomeration” and “adsorption” for a high solid loading combined with the necessary mode of function of the dispersant are illustrated as a function of the viscosity of the medium and the particle size. The viscosity-lowering decoupling effect of the dispersant was a prerequisite for reaching a solid loading of 50 vol% in the additional feedstock development. The feedstock with 50 vol% nano-zirconia could be extruded to a tape and sintered to a relative density of 97% at 1200°C.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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