Quantifizierung der Grundwassersströmung in einem alpinen Talkessel

Grundwasser - In dem alpinen Talkessel der Laubau südlich von Ruhpolding ist in glazialen Schottern ein Grundwassersystem ausgebildet, das durch eine ausgeprägte Dynamik gekennzeichnet...     

Atomic force microscopy study on structure and properties of irradiation grafted silica particles in polypropylene‐based nanocomposites

Nanosilica particles treated by irradiation grafting polymerization can effectively improve the strength and toughness of a thermoplastic polymer at a rather low filler content. A detailed investigation on the modified nanoparticles in the absence and presence of a polypropylene matrix is carried out by using atomic force microscopy. The results indicate that the loosen agglomerates of the untreated SiO₂ became more compact due to the linkage between the nanoparticles offered by the grafting polymer. In addition, the molecules of the polypropylene matrix are able to diffuse into the modified nanoparticle agglomerates during the melt processing. Entanglement between the molecules of the grafting polymer and the matrix is thus available, which in turn facilitates a strong particle–matrix interfacial interaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2218–2227, 2001     

Occurrence of methanogenesis during start-up of a full-scale synthesis gas-fed reactor treating sulfate and metal-rich wastewater

The start-up of a full-scale synthesis gas-fed gas-lift reactor treating metal and sulfate-rich wastewater was investigated. Sludge from a pilot-scale reactor was used to seed the full-scale reactor. The main difference in design between the pilot- and full-scale reactor was that metal precipitation and sulfate reduction occurred in the same reactor. After 7 weeks the full-scale reactor achieved the sulfate conversion design rate of 15 kg/m3day. Zinc sulfide precipitation inside the reactor did not interfere with obtaining a high rate of sulfate reduction. 16S rRNA gene analysis demonstrated that the bacterial communities in both reactors were dominated by the sulfate-reducing genus Desulfomicrobium. Archaeal communities of both reactors were dominated by the methanogenic genus Methanobacterium. Most Probable Number (MPN) counts confirmed that heterotrophic Sulfate-Reducing Bacteria (SRB) were dominant (10(11) -10(12) cells/g VSS) compared to homoacetogens (10(5) -10(6) cells/g VSS) and methanogens (10(8) -10(9) cells/g VSS). Methanogenesis was not suppressed during start-up of the full scale-reactor, despite the predominance of SRB, which have a lower hydrogen threshold. Due to the short sludge retention time (4-7 days) competition for hydrogen is determined by Monod kinetics, not hydrogen thresholds. As the kinetic parameters for SRB and methanogens are similar, methanogenesis may persist which results in a loss of hydrogen.     

Metathesis of 1‐Octene in Ionic Liquids and Other Solvents: Effects of Substrate Solubility,Solvent Polarity and Impurities

With the self‐metathesis of 1‐octene to 7‐tetradecene catalyzed by Grubbs 1^st generation [benzylidene‐bis(tricyclohexylphosphine)dichlororuthenium, ( 1 )] precursor at low concentrations (0.02 mol %) as basis, the effects of the solubility of the substrate in ionic liquids, the solvent polarity, as well as the influence of various impurities stemming from the preparation of ionic liquids have been investigated. The solubility of the substrate in the ionic liquid has little effect on the conversion, and the reaction is not mass‐transfer limited. While a higher polarity of an organic solvent increases the rate, it is independent of the polarity excerted by the cation of an ionic liquid. Of paramount importance for reproducible results is the purity of ionic liquids. An extensive study shows that catalyst deactivation by impurities increases in the order of water<halide<1‐methylimidazole. In the presence of water or 1‐methylimidazole impurities, the Grubbs‐Hoveyda precursor ( 3 ) is superior to both the 1^st ( 1 ) and 2^nd ( 2 ) generation Grubbs complexes. Under impurity‐free conditions or in the presence of chloride, the performance of 2 is equivalent to that of 3 .     

Optimization of Ring‐Closing Metathesis: Inert Gas Sparging and Microwave Irradiation

A systematic study of a ring‐closing metathesis towards a tetrasubstituted double bond as part of a seven‐membered ring in a 5.7.5‐tricyclic guaianolide system is described. By combining two techniques, namely sparging an inert gas through the solution together with dielectric heating via microwave irradiation a high‐yielding ring‐closing metathesis reaction in this particularly challenging case was achieved. The results obtained compare favorably with conventional heating conditions or with microwave irradiation in a closed system. The key aspects seem to be that rapid microwave irradiation diminishes catalyst decay by allowing the required high reaction temperature to be reached quickly and homogeneously and thereby providing enough energy for a successful metathesis reaction, while inert gas sparging is purging off evolving ethylene to shift the equilibrium to the product.     

Designing of Copper Nanoparticle Size Formed via Aerosol Pyrolysis

In this article, the synthesis and structural design of spherical, nonagglomerated particles of copper powder, synthesized by ultrasonic atomization of copper sulfate solutions in hydrogen atmosphere at 1173?K (900?°C), was investigated. Well-controlled particle sizes of Cu powders were obtained from precursor solutions of various concentrations. The mean particle diameters and the ranges of particle size distribution were investigated by scanning electron microscopy (SEM). The diameter values of Cu particles obtained experimentally and estimated theoretically, using the most frequently applied atomization models, were compared. Special attention was paid to our break up capillary waves model, described elsewhere and significantly advanced by Jokanovi???s theoretical approach, which was applied for the first time to a copper metal system as described in this article. The best agreement between the calculated and the experimentally obtained values was found using this model.     

Missing Link

Abstract

This is not the place to describe in detail all the links that existed—particularly during the twenties—between the avant-garde art movements in Soviet Russia and those of Western Europe—even if we had all the details at our disposal. In any event, much remains to be discovered anew, as many of the main Soviet protagonists fell into disgrace when they were accused of ‘formalism’ in the Stalinist thirties. The years of international conflict and the Cold War mentality whicli followed did not further the recognition of the work of those artists.     

Direct Monitoring of Ultrafast Redox Commutation at the Nanosecond and Nanometer Scales by Ultrafast Voltammetry: From Molecular Wires to Cation Releasing Systems

This review documents that, contrary to the general impression that molecular electrochemistry is mostly devoted to the analysis of reaction mechanisms induced by electron transfer into homogeneous solutions of molecules, its concepts and methods are perfectly suited to the investigation of extremely fast molecular events occurring within nano- and sub-nanometric distances from a working electrode surface. Ultrafast cyclic voltammetry (i.e., up to the range of a few megavolts per second) coupled to online electronic compensation of ohmic drop is thus shown to provide direct measurements of extremely fast electron transfer between redox centers tethered to electrodes, by conducting molecular bridges, or of dendrimers adsorbed onto the electrode surface. This allows discussing in particular the role of counterions in the process of electronic commutation of self-assembled monolayers.     

A Novel Prodrug of a nNOS Inhibitor with Improved Pharmacokinetic Potential

Under different pathological conditions, aberrant induction of neuronal nitric oxide synthase (nNOS) generates overproduction of NO that can cause irreversible cell damage. The aim of this study was to develop an amidoxime prodrug of a potent nNOS inhibitor, the benzhydryl acetamidine. We synthesized the benzhydryl acetamidoxime, which was evaluated in vitro to ascertain the potential NOS inhibitory activity, as well as conducting bioconversion into the parent acetamidine. The prodrug was also profiled for in vitro physicochemical properties, by determining the lipophilicity, passive permeation through the human gastrointestinal tract and across the blood-brain barrier by PAMPA, and chemical, enzymatic, and plasma stability. The obtained data demonstrate that the amidoxime prodrug shows an improved pharmacokinetic profile with respect to the acetamidine nNOS inhibitor, thus suggesting that it could be a promising lead compound to treat all those pathological conditions in which nNOS activity is dysregulated.     

Continuous Neutralization of NaOH Solution with CO2 in an Internal‐Loop Airlift Reactor

The neutralization of NaOH with CO₂ in a continuously operated airlift reactor with gas flow rates up to 10 NL min^?1 and gas phase recycle was investigated. Neutralization experiments were performed at 25 °C and the amount of absorbed CO₂, as well as the NaOH feed rate, were recorded. The reaction rate was calculated based on the two‐film theory and empirical equations for several parameters. The calculations of the volumetric mass transfer coefficient, the liquid phase circulation velocity, and the gas holdup were experimentally validated. The reaction rate and the process efficiency were modeled with a deviation of 5 %.