Spatial and seasonal variations in the stable C isotope composition of dissolved inorganic carbon and in physico-chemical water parameters in the Plitvice Lakes system

Plitvice Lakes waters were collected at 14 sampling points, including springs, tributaries and lakes, for the period 2002-2007. The results of the physical and chemical conditions of calcite precipitation as well as the δ(13)C values of dissolved inorganic carbon (DIC) were used to study the processes influencing calcite precipitation. Significant differences between spring, lake and stream waters as well as changes in the downstream direction were observed. The correlation between δ(13)C(DIC) values and physico-chemical conditions for calcite precipitation showed that calcite precipitates in lake waters which are oversaturated with respect to CaCO(3) (I (sat) values 4-10) and with δ(13)C(DIC) values between-11.5 and-8.5 ‰. In spring waters, the δ(13)C(DIC) values were more negative, from-14 to-12 ‰, and I (sat) values of 1-2 indicated that equilibrium conditions for calcite precipitation were not attained. The downstream increase in δ(13)C(DIC) correlated with the increase in the δ(13)C values of calcite in the lake sediments, suggesting that the freshwater calcite was mainly of autochthonous origin and precipitated within the water column in isotopic equilibrium with DIC.     

Spatial and seasonal variations in the stable C isotope composition of dissolved inorganic carbon and in physico-chemical water parameters in the Plitvice Lakes system

Plitvice Lakes waters were collected at 14 sampling points, including springs, tributaries and lakes, for the period 2002–2007. The results of the physical and chemical conditions of calcite precipitation as well as the δ¹³C values of dissolved inorganic carbon (DIC) were used to study the processes influencing calcite precipitation. Significant differences between spring, lake and stream waters as well as changes in the downstream direction were observed. The correlation between δ¹³C_DIC values and physico-chemical conditions for calcite precipitation showed that calcite precipitates in lake waters which are oversaturated with respect to CaCO₃ (I _sat values 4–10) and with δ¹³C_DIC values between?11.5 and?8.5 ‰. In spring waters, the δ¹³C_DIC values were more negative, from?14 to?12 ‰, and I _sat values of 1–2 indicated that equilibrium conditions for calcite precipitation were not attained. The downstream increase in δ¹³C_DIC correlated with the increase in the δ¹³C values of calcite in the lake sediments, suggesting that the freshwater calcite was mainly of autochthonous origin and precipitated within the water column in isotopic equilibrium with DIC.     

Engineering of Ruthenium–Iron Oxide Colloidal Heterostructures: Improved Yields in CO2 Hydrogenation to Hydrocarbons

Catalytic CO₂ reduction to fuels and chemicals is a major pursuit in reducing greenhouse gas emissions. One approach utilizes the reverse water‐gas shift reaction, followed by Fischer–Tropsch synthesis, and iron is a well‐known candidate for this process. Some attempts have been made to modify and improve its reactivity, but resulted in limited success. Now, using ruthenium–iron oxide colloidal heterodimers, close contact between the two phases promotes the reduction of iron oxide via a proximal hydrogen spillover effect, leading to the formation of ruthenium–iron core–shell structures active for the reaction at significantly lower temperatures than in bare iron catalysts. Furthermore, by engineering the iron oxide shell thickness, a fourfold increase in hydrocarbon yield is achieved compared to the heterodimers. This work shows how rational design of colloidal heterostructures can result in materials with significantly improved catalytic performance in CO₂ conversion processes.     

Dielectric dispersion of oriented polymers

Summary Expressions have been derived for the tensor of the complex dielectric permitivity of an oriented polymer containing polar groups in the main chain. The relevant intramolecular and intermolecular interactions have been assumed to be independent of the degree of orientation; the anisotropy of dielectric permitivity is expected to be given only by the orientation of local equilibrium positions of the dipoles. For the low-temperature dispersion of a polymer oriented by cold-drawing, both the spectra of relaxation times and the magnitudes of the components of the dielelectric permitivity tensor have been calculated. Relation between the calculated values and the dipole-dipole interaction parameters, diffusion coefficients and average dipole-chain angle are given.

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Zusammenfassung Es wurden Ausdrücke für den komplexen Tensor der Dielektrizitätskonstantante an orientierten Polymeren, die polare Gruppen in der Hauptkette enthalten, abgeleitet. Die maßgebenden intra- und intermolekularen Wechselwirkungen wurden als unabhängig vom Orientierungsgrad angenommen; die Anisotropie der Dielektrizitätskonstante dürfte nur durch die Orientierung lokaler Gleichgewichtspositionen der Dipole gegeben sein. Für die Tieftemperaturdispersion eines kalt verstreckten Polymeren wurden das Spektrum der Relaxationszeiten und die Relaxationsstärken des Tensors berechnet. Beziehungen zwischen berechneten Werten und den Dipol-Dipol-Wechselwirkungsparametern, Diffusionskoeffizienten und den mittleren Winkel zwischen Dipol und Kette sind angegeben.

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With 5 figures     

Synthesis of a water-soluble triazole-linked cavitand-guanosine conjugate

A convergent synthesis of a water-soluble cavitand bearing four triazole-linked guanosines was achieved. The critical coupling reaction entailed a copper-catalysed azide-alkyne cycloaddition between 5′-azido-5′-deoxyguanosine and a cavitand template functionalized with propargyl ether rim groups and water-solubilizing phosphate pendant groups.     

Asymptotics for thin elastic fibers in unilateral contact

What is the contact condition in a 1D beam-model and is it possible to obtain the frictional moments and forces from the 3D traction? If it is possible does the cross-section of the beams influence these values? These questions motivate to study the dimension reduction of a 3D contact problem for beams. This paper is a continuation of [1]. In [1] the asymptotic dimension reduction of a Robin-type elasticity boundary value problem was presented. In this work the explicit relation between a 3D contact problem and a 3D Robin-type elasticity boundary value problem are established and the 1D equations derived in [1] are interpreted as 1D contact conditions, further some numerical examples are shown. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Reactivity of di-n-butyl-dicyclopentadienylzirconium towards amido stabilized stannylenes

Reaction of Sn[(N(C₆H₃iPr₂-2,6)(SiMe₃)]₂ and [{Sn(N(C₆H₃iPr₂-2,6)(SiMe₃)(μ-Cl)₂] with di-n-butyl-dicyclopentadienylzirconium yielded the trimetallic a carbene-like complex {[(N(C₆H₃iPr₂-2,6)(SiMe₃)](n-Bu)Sn}₂Cp₂Zr. The oxidation of {[(N(C₆H₃iPr₂-2,6)(SiMe₃)](n-Bu)Sn}₂Cp₂Zr by oxygen gives the five-membered dioxadistannazirconacyclic complex {[(N(C₆H₃iPr₂-2,6)(SiMe₃)](n-Bu)Sn}₂O₂Cp₂Zr.