Ceramics and Socio-Economic Statues of the Green Family, Windsor, Vermont

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Magnesium Coprecipitation with Calcite at Low Supersaturation: Implications for Mg-Enriched Water in Calcareous Soils

The concentrations of magnesium (Mg) and calcium (Ca) in natural aqueous environments are controlled by sorption and dissolution–precipitation reactions. Ca binding in calcareous soils depends on the degree of solution saturation with respect to CaCO$_{3}$. Mg may be bound in precipitating calcite. Here, we investigated Mg incorporation into calcite via the recrystallization of vaterite, which simulates a very low supersaturation in a wide range of Mg to Ca ratios and pH conditions. Increasing the Mg to Ca ratios (0.2 to 10) decreased the partition coefficient of Mg in calcite from 0.03 to 0.005. An approximate thermodynamic mixing parameter (Guggenheim a0 = 3.3 ± 0.2), that is valid for dilute systems was derived from the experiments at the lowest initial Mg to Ca ratio (i.e., 0.2). At elevated Mg to Ca ratios, aragonite was preferentially formed, indicating kinetic controls on Mg partitioning into Mg-calcite. Scanning electron microscopy (SEM-EDX) analyses indicated that Mg is not incorporated into aragonite. The thermodynamic mixing model suggests that at elevated Mg to Ca ratio (i.e., ≥1) Mg-calcite becomes unstable relative to pure aragonite. Finally, our results suggest that the abiotic incorporation of Mg into calcite is only effective for the removal of Mg from aqueous environments like calcareous soil solution, if the initial Mg to Ca ratio is already low

Electrolyte layering at the calcite(104)-water interface indicated by Rb⁺- and Se(VI) K-edge resonant interface diffraction

Calcite-water interface reactions are of major importance in various environmental settings as well as in industrial applications. Here we present resonant interface diffraction results on the calcite(104)-aqueous solution interface{,} measured in solutions containing either 10 mmol L-1 RbCl or 0.5 mmol L-1 Se(vi). Results indicate that Rb+ ions enter the surface adsorbed water layers and adsorb at the calcite(104)-water interface in an inner-sphere fashion. A detailed analysis based on specular and off-specular resonant interface diffraction data reveals three distinct Rb+ adsorption species: one 1.2 A above the surface{,} the second associated with surface adsorbed water molecules 3.2 A above the surface{,} and the third adsorbed in an outer-sphere fashion 5.6 A above the surface. A peak in resonant amplitude between L = 1.5 and L = 3.0 is interpreted as signal from a layered electrolyte structure. The presence of a layered electrolyte structure seems to be confirmed by data measured in the presence of Se(vi)

The influences of cement hydration and temperature on the thixotropy of cement paste

The rheological properties of fresh cement paste are highly influenced by a large number of parameters, among which the most important factors are the applied shear stress, and the shear history, the age of the sample and the temperature. The effects of these parameters on the yield stress (designated as structural limit stress in this work), the viscosity and the structural recovery rate (i.e., the change in dynamic viscosity with time at rest) were studied. In parallel, the changes in ion composition of the carrier liquid, mineral phase content and granulometry were investigated. The results reveal that all investigated rheological parameters exhibit an approximated bi-linear trend with respect to the degree of hydration, with a period of quasi-constant properties until a degree of hydration of approximately 0.07, followed by a non-linear increase. This increase could be attributed to the formation of calcium hydroxide (CH) and calcium-silicate-hydrate (C-S-H) via calorimetry results. With regard to the effect of the shear history of the sample on the rheological properties, the structural limit stress showed a minor dependency on the shear history immediately after the end of shearing, which, however, vanished within the first minute at rest. The same is true for the structural recovery rate. The presented results give detailed insights into the influences of hydration and shear on the rheological properties—especially the thixotropy—of fresh cement pastes

High-throughput detection and multiplex identification of cell contaminations

Unnoticed cell culture contamination by viruses, Mycoplasma, or other cell lines is not uncommon and a threat to laboratory safety and the quality of scientific results. We developed and validated a novel high-throughput Multiplex cell Contamination Test (McCT), which is currently able to detect 37 contamination markers in a single reaction. The assay is based on multiplex PCR with target-specific primers and subsequent hybridization of amplimers to specific oligonucleotide probes. McCT proved to be highly specific, sensitive and robust, and allows to analyze more than 1000 cell lysates per week. In conclusion, the novel McCT assay is a powerful high-throughput tool in assessing cell line purity

XAS signatures of Am(III) adsorbed onto magnetite and maghemite

Trivalent americium was adsorbed on magnetite and maghemite under similar chemical conditions and the local environment probed by EXAFS spectroscopy. In both samples, partially hydrated Am(III) binds the surface but slightly different surface complexes were identified. On Fe3O4, Am(III) forms monomeric tridentate surface complexes similar to that reported for Pu(III) at the (111) surface. In contrast, the lower number of detected Fe atoms may suggest that Am(III) forms monomeric bidentate surface complexes on γ-Fe2O3. Alternatively, the lower Fe coordination number can also be due to the presence of vacancies in maghemite. XPS data imply very similar binding environments for Am at both Fe oxide surfaces

Phase Measurement for Driven Spin Oscillations in a Storage Ring

This paper reports the first simultaneous measurement of the horizontal and vertical components of the polarization vector in a storage ring under the influence of a radio frequency (rf) solenoid. The experiments were performed at the Cooler Synchrotron COSY in J\"ulich using a vector polarized, bunched $0.97\,\textrm{GeV/c}$ deuteron beam. Using the new spin feedback system, we set the initial phase difference between the solenoid field and the precession of the polarization vector to a predefined value. The feedback system was then switched off, allowing the phase difference to change over time, and the solenoid was switched on to rotate the polarization vector. We observed an oscillation of the vertical polarization component and the phase difference. The oscillations can be described using an analytical model. The results of this experiment also apply to other rf devices with horizontal magnetic fields, such as Wien filters. The precise manipulation of particle spins in storage rings is a prerequisite for measuring the electric dipole moment (EDM) of charged particles