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  • 1
    Language: English
    In: Analytical chemistry, 19 August 2014, Vol.86(16), pp.8376-82
    Description: Fourier Transform Ion Cyclotron Resonance mass spectra (FT-ICR-MS) of natural organic matter are complex and consist of several thousands of peaks. The corresponding mass to charge ratios (m/z) and signal intensities result from analytes and noise. The most commonly applied way of distinguishing between analyte and noise is a fixed signal-to-noise ratio below which a detected peak is considered noise. However, this procedure is problematic and can yield ambiguous results. For example, random noise peaks can occur slightly above the signal-to-noise threshold (false positives), while peaks of low abundance analytes may occasionally fall below the fixed threshold (false negatives). Thus, cumulative results from repeated measurements of the same sample contain more peaks than a single measurement. False positive and false negative signals are difficult to distinguish, which affects the reproducibility between replicates of a sample. To target this issue, we tested the feasibility of a method detection limit (MDL) for the analysis of natural organic matter to identify peaks that can reliably be distinguished from noise by estimating the uncertainty of the noise. We performed 556 replicate analyses of a dissolved organic matter sample from the deep North Pacific on a 15 T FT-ICR-MS; each of these replicate runs consisted of 500 cumulated broadband scans. To unambiguously identify analyte peaks in the mass spectra, the sample was also run at time-consuming high-sensitivity settings. The resulting data set was used to establish and thoroughly test a MDL. The new method is easy to establish with software help, does only require the additional analysis of replicate blanks (low time increase), and can implement all steps of sample preparation. Especially when analysis time does not allow for replicate runs, major merits of the MDL are reliable removal of false positive (noise) peaks and better reproducibility, while the risk of losing analytes with low signal intensities (false negative) is comparatively low. When replicate analyses are feasible, the removal of all singly detected peaks is further recommended, as these have the highest probability of being noise peaks. We suggest that the here proposed detection limit should become routine in FT-ICR-MS data processing.
    Keywords: Mass Spectrometry -- Methods ; Organic Chemicals -- Analysis ; Seawater -- Analysis
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 2
    Language: English
    In: Water Research, 01 February 2018, Vol.129, pp.29-38
    Description: Most of the knowledge on the occurrence of Uranium (U) in groundwater comes from in-situ manipulation experiments in the field, computational modelling studies or from laboratory analyses where individual processes of U mobilization were studied in isolation. Because of Uranium's vital redox chemistry it interacts, often simultaneously, with many other element cycles (e.g., sulfur, carbon, iron, and manganese) making it difficult to predict U concentrations in natural environments. For the present study a large data set was analyzed to predict the occurrence of U in groundwater from basic hydrochemistry. The data set consists of more than 8000 chemical groundwater analyses (including Uranium concentrations) from more than 2000 sampling locations. A strong relation between U concentrations and electric conductivity as well as alkalinity was observed, suggesting that weathering of geogenic source material and desorption from mineral surfaces is the principle mechanism of U release. Except for aquifers with strongly reducing conditions this process leads to a slow but continuous accumulation of U in groundwater in most cases. Importantly, the occurrence of U is modulated by the prevailing redox conditions in an aquifer. Uranium concentrations were moderate under oxic conditions and highest under manganese and nitrate-reducing conditions (heterotrophic as wells as autotrophic nitrate reduction). Only in iron- and sulfate-reducing groundwater the probability of U concentrations above 1 μg l was virtually zero, as these ground waters act as U sinks. The combination of mineral weathering (especially carbonates) with mobilization of U under manganese and nitrate reducing conditions results in the highest risk of detecting U. In contrast, a low risk is associated with low pH (〈7) and low mineralization of groundwater, which is the case in granitic catchments, for example. Our results further provide evidence, that agricultural practices such as liming, use of fertilizers and irrigation influence the occurrence of U in groundwater in multiple ways. Accurate management of aquifers underlying farmland will therefore become more and more important in the future. In summary, we find that the vulnerability of an aquifer to elevated U concentrations cannot be explained by a single factor. This complicates efforts to target elevated U concentrations in groundwaters that are abstracted for drinking water production.
    Keywords: Uranium ; Groundwater ; Drinking Water ; Geochemistry ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 3
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 18 June 2013, Vol.110(25), pp.10101-5
    Description: Reactive iron and organic carbon are intimately associated in soils and sediments. However, to date, the organic compounds involved are uncharacterized on the molecular level. At redox interfaces in peatlands, where the biogeochemical cycles of iron and dissolved organic matter (DOM) are coupled, this issue can readily be studied. We found that precipitation of iron hydroxides at the oxic surface layer of two rewetted fens removed a large fraction of DOM via coagulation. On aeration of anoxic fen pore waters, 〉90% of dissolved iron and 27 ± 7% (mean ± SD) of dissolved organic carbon were rapidly (within 24 h) removed. Using ultra-high-resolution MS, we show that vascular plant-derived aromatic and pyrogenic compounds were preferentially retained, whereas the majority of carboxyl-rich aliphatic acids remained in solution. We propose that redox interfaces, which are ubiquitous in marine and terrestrial settings, are selective yet intermediate barriers that limit the flux of land-derived DOM to oceanic waters.
    Keywords: Carbon Cycle ; Carbon Sequestration ; Phenolics ; Wetland Restoration ; Wetlands ; Carbon Cycle -- Physiology ; Carbon Sequestration -- Physiology ; Hydrocarbons, Aromatic -- Chemistry ; Hydroxybenzoates -- Chemistry ; Iron -- Chemistry
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 4
    Language: English
    In: European Journal of Applied Physiology, 2013, Vol.113(3), pp.591-598
    Description: Our understanding of regional filling of the lung and regional ventilation distribution is based on studies using stepwise inhalation of radiolabelled tracer gases, magnetic resonance imaging and positron emission tomography. We aimed to investigate whether these differences in ventilation distribution at different end-expiratory levels (EELs) and tidal volumes ( V T s) held also true during tidal breathing. Electrical impedance tomography (EIT) measurements were performed in ten healthy adults in the right lateral position. Five different EELs with four different V T s at each EEL were tested in random order, resulting in 19 combinations. There were no measurements for the combination of the highest EEL/highest V T . EEL and V T were controlled by visual feedback based on airflow. The fraction of ventilation directed to different slices of the lung (VENT RL1 −VENT RL8 ) and the rate of the regional filling of each slice versus the total lung were analysed. With increasing EEL but normal tidal volume, ventilation was preferentially distributed to the dependent lung and the filling of the right and left lung was more homogeneous. With increasing V T and maintained normal EEL (FRC), ventilation was preferentially distributed to the dependent lung and regional filling became more inhomogeneous ( p  〈 0.05). We could demonstrate that regional and temporal ventilation distribution during tidal breathing was highly influenced by EEL and V T .
    Keywords: Lung mechanics ; Electrical impedance tomography ; Regional filling ; Breathing pattern
    ISSN: 1439-6319
    E-ISSN: 1439-6327
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  • 5
    In: PLoS ONE, 2017, Vol.12(11)
    Description: Background Electrical impedance tomography (EIT) is used on the thorax to measure impedance changes due to the presence of air and blood in the lung. This experimental study was performed to investigate the effect of posture on cardiac and respiratory related impedance changes. Methods EIT measurements were performed on 14 healthy subjects in left-, right lateral, prone, supine and upright positions. Simultaneously, tidal volume was recorded with an ultrasonic flowmeter. For image reconstruction, the classic Sheffield back-projection and three variants of the modern GREIT algorithm were applied with two different reference frames. Amplitudes of cardiac- and respiratory impedance changes were extracted and compared between the positions. Results We found significant differences in both cardiac and respiratory amplitudes between postures. Especially, supine and upright positions showed dramatic changes in amplitude. These differences between postures were unaffected by the change of reference frames in all reconstruction methods except of the classic Sheffield back projection. Possible sources that explain the observed posture dependency are discussed. Conclusion Researchers and clinicians need to be aware of this phenomenon when comparing EIT amplitudes in different body positions.
    Keywords: Research Article ; Engineering And Technology ; Engineering And Technology ; Biology And Life Sciences ; Medicine And Health Sciences ; Biology And Life Sciences ; Medicine And Health Sciences ; Medicine And Health Sciences ; Biology And Life Sciences ; Medicine And Health Sciences ; Medicine And Health Sciences ; Medicine And Health Sciences ; Research And Analysis Methods ; Medicine And Health Sciences
    E-ISSN: 1932-6203
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  • 6
    In: PLoS ONE, 2014, Vol.9(9)
    Description: Background and objectives We investigated the effect of different breathing aids on ventilation distribution in healthy adults and subjects with cystic fibrosis (CF). Methods In 11 healthy adults and 9 adults with CF electrical impedance tomography measurements were performed during spontaneous breathing, continuous positive airway pressure (CPAP) and positive expiratory pressure (PEP) therapy randomly applied in upright and lateral position. Spatial and temporal ventilation distribution was assessed. Results The proportion of ventilation directed to the dependent lung significantly increased in lateral position compared to upright in healthy and CF. This effect was enhanced with CPAP but neutralised with PEP, whereas the effect of PEP was larger in the healthy group. Temporal ventilation distribution showed exactly the opposite with homogenisation during CPAP and increased inhomogeneity with PEP. Conclusions PEP shows distinct differences to CPAP with respect to its impact on ventilation distribution in healthy adults and CF subjects EIT might be used to individualise respiratory physiotherapy.
    Keywords: Research Article ; Biology And Life Sciences ; Medicine And Health Sciences ; Physical Sciences
    E-ISSN: 1932-6203
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  • 7
    Language: English
    In: Inorganic chemistry, 07 October 2013, Vol.52(19), pp.11593-9
    Description: Reaction of the donor-stabilized silylene 1 with [Cr(CO)6], [Mo(CO)6], [W(CO)6], or [Fe(CO)5] leads to the formation of the transition-metal silylene complexes 2-5, which contain five-coordinate silicon(II) moieties with Si-M bonds (M = Cr, Mo, W, Fe). These compounds were characterized by NMR spectroscopic studies in the solid state and in solution and by crystal structure analyses. These experimental investigations were complemented by computational studies to gain insight into the bonding situation of 2-5. The nature of the Si-M bonds is best described as a single bond.
    Keywords: Chemistry;
    ISSN: 00201669
    E-ISSN: 1520-510X
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  • 8
    Language: German
    In: Stahlbau, December 2013, Vol.82(12), pp.924-926
    Description: Byline: Thomas Riedel(1), Rudiger Schwarz(1), Gerhard Bretzke(2) Keywords: Bruckenlager; Stahlguss; Nachhaltigkeit; Linienkipplager ***** No abstract is available for this article. ***** Author Affiliation: (1)DB Netz AG, Regionalbereich Sudost, Brandenburger Stra[sz]e 1, 04103 Leipzig (2)Schachtbau Nordhausen GmbH, Industrieweg 2a, 99734 Nordhausen
    Keywords: Brückenlager ; Stahlguss ; Nachhaltigkeit ; Linienkipplager ; Bridge Bearing ; Cast Steel ; Substainability ; Line Rocker Bearing ; Stahlbrückenbau ‐ Steel Bridges ; Bestandssicherung Und Erhaltung ‐ Conservation And Maintenance ; Korrosionsschutz ‐ Corrosion Protection ; Sonderkonstruktionen ‐ Special Structures
    ISSN: 0038-9145
    E-ISSN: 1437-1049
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  • 9
    Language: German
    In: NeuroTransmitter, 12/2012, Vol.23(12), pp.58-58
    ISSN: 1436-123X
    Source: Springer (via CrossRef)
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  • 10
    Language: German
    In: NeuroTransmitter, 6/2012, Vol.23(6), pp.82-83
    ISSN: 1436-123X
    Source: Springer (via CrossRef)
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