1,908 research outputs found

    Zur Mordtat des Täufers Schugger in St. Gallen

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    Zu den St. Galler Täufern

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    Electric field gradients and charge density in lithium nitride

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    Self-guided smartphone excursions in university teaching—experiences from exploring “Water in the City”

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    Like many other university teachers, we were faced with an unprecedented situation in spring 2020, when we had to cancel on-site teaching and excursions due to the Covid-19 pandemic. However, we were in the fortunate position that we had already started to develop a smartphone-based self-guided excursion on the topic of “Water in the City”. We accelerated this development and used it to replace the traditional group excursion in our Bachelor level introductory course in Hydrology and Climatology. The excursion of this course is visited by around 150 students each year. Because the student feedback was overall very positive, we used the self-guided excursion again in 2021 and plan to continue to use it in the coming years. In this paper, we describe the excursion, discuss the experiences of the students and ourselves, and present recommendations and ideas that could be useful for similar excursions at other universities

    Reductive Transformations of Anthropogenic Chemicals in Natural and Technical Systems

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    Reductive transformation reactions of chemical pollutants (e.g., polyhalogenated hydrocarbons, aromatic azo and nitro compounds, chromium(VI) species) in the environment are important both from an ecotoxicological and from an environmental technology point of view. Using well-defined model reactors as well as more complex 'real world' systems, several groups at EAWAG are trying to unravel compound- and system-specific factors that control the reduction of a variety of anthropogenic chemicals under different conditions in the environment. The examples presented in this article include the reduction of nitroaromatic compounds under iron- and sulfate-reducing conditions, the reductive dehalogenation of chlorinated ethenes by cob(I)alamin and by a bacterium that uses such compounds as terminal electron acceptors, and the reduction of chromium(VI) by various reduced iron species. The link between microbial and abiotic (chemical) processes involved in reductive transformations of pollutants is emphasized. The major goal of this article is to illustrate the approaches taken to elucidate the mechanisms and kinetics of environmentally relevant reduction reactions of pollutants, and to discuss how the results of such studies can be used 1) to gain insight into what is actually happening in the environment, and 2) to develop methods for the treatment of chemical wastes or contaminated sites

    Determination of liposome/water partition coefficients of organic acids and bases by solid-phase microextraction

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    The extraction of two methylated anilines and three chlorinated phenols by solid-phase microextraction (SPME) fibers coated with polyacrylate was investigated as a function of pH. Only the neutral species of the acids and bases partitioned into the polymer. Extraction kinetics were accelerated for the hydrophobic phenols at pH values around their acidity constant. This is presumably due to a reconstitution of the neutral species in the unstirred aqueous layer adjacent to the polymer surface by the charged species through the fast acid-base equilibrium. Although the charged species is not taken up into the polymer. liposome/water distribution ratios could be measured up to a pH value, where 99% of the compounds were present as charged species. The partition coefficients of the neutral and charged species were extrapolated from the pH profiles of the liposome/water distribution ratios. The resulting values were slightly lower than those measured with equilibrium dialysis. The discrepancies are discussed with respect to differences in the experimental conditions and the possibility of matrix effects during SPME measurements

    Rigid-link constraints and rigid-body molecules

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    Effect of water activity on rates of serpentinization of olivine

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    The hydrothermal alteration of mantle rocks (referred to as serpentinization) occurs in submarine environments extending from mid-ocean ridges to subduction zones. Serpentinization affects the physical and chemical properties of oceanic lithosphere, represents one of the major mechanisms driving mass exchange between the mantle and the Earth’s surface, and is central to current origin of life hypotheses as well as the search for microbial life on the icy moons of Jupiter and Saturn. In spite of increasing interest in the serpentinization process by researchers in diverse fields, the rates of serpentinization and the controlling factors are poorly understood. Here we use a novel in situ experimental method involving olivine micro-reactors and show that the rate of serpentinization is strongly controlled by the salinity (water activity) of the reacting fluid and demonstrate that the rate of serpentinization of olivine slows down as salinity increases and H2O activity decreases

    Sulphur and carbon cycling in the subduction zone mélange

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    Subduction zones impose an important control on the geochemical cycling between the surficial and internal reservoirs of the Earth. Sulphur and carbon are transferred into Earth’s mantle by subduction of pelagic sediments and altered oceanic lithosphere. Release of oxidizing sulphate- and carbonate-bearing fluids modifies the redox state of the mantle and the chemical budget of subduction zones. Yet, the mechanisms of sulphur and carbon cycling within subduction zones are still unclear, in part because data are typically derived from arc volcanoes where fluid compositions are modified during transport through the mantle wedge. We determined the bulk rock elemental, and sulphur and carbon isotope compositions of exhumed ultramafic and metabasic rocks from Syros, Greece. Comparison of isotopic data with major and trace element compositions indicates seawater alteration and chemical exchange with sediment-derived fluids within the subduction zone channel. We show that small bodies of detached slab material are subject to metasomatic processes during exhumation, in contrast to large sequences of obducted ophiolitic sections that retain their seafloor alteration signatures. In particular, fluids circulating along the plate interface can cause sulphur mobilization during several stages of exhumation within high-pressure rocks. This takes place more pervasively in serpentinites compared to mafic rocks
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