Singularities in cascade models of the Euler equation

The formation of singularities in the three-dimensional Euler equation is investigated. This is done by restricting the number of Fourier modes to a set which allows only for local interactions in wave number space. Starting from an initial large-scale energy distribution, the energy rushes towards smaller scales, forming a universal front independent of initial conditions. The front results in a singularity of the vorticity in finite time, and has scaling form as function of the time difference from the singularity. Using a simplified model, we compute the values of the exponents and the shape of the front analytically. The results are in good agreement with numerical simulations.     

Der Einfluß von Grenzflächenerscheinungen auf den Stoffübergang und die Prozeßführung in Gegenstromkolonnen mit überkritischem CO2

Zusammenfassung Mittels des Einsatzes einer Hochdrucksichtzelle wurden Eigenschaften der Kontaktbereiche in Trennverfahren mit unterschiedlichen wäßrigen Lösungen und CO₂ unter hohen Drücken untersucht. Die Methode des hängenden Tropfens wurde zur Messung der Grenzflächenspannung bis zu Drücken von 280 bar angewandt. Der mit dem Druck abnehmende Verlauf weist nach der Gibbs'schen Theorie auf die Anreicherung von CO₂ in der Phasengrenze. Weiterhin wurde die für Packungskolonnen bedeutsame Feststoffbenetzung in Abhängigkeit von Druck und Oberflächenbeschaffenheit des Feststoffes untersucht. Der die Feststoffbenetzung charakterisierende Kontaktwinkel wurde mittels der Methode der gekippten Platte vermessen und ergab eine schlechtere Benetzung bei höheren Drücken und glatten Stahloberflächen.

---

The effect of interfacial phenomena on mass transport and performance of separations in countercurrent columns with supercritical CO₂

Interfacial phenomena affecting countercurrent separation processes have been studied in systems containing aqueous solutions and CO₂ at elevated pressures by means of a high pressure optical cell. The pendant drop method was applied in order to measure the interfacial tension up to 280 bar. The decreasing course as a function of the pressure is due to the adsorption of CO₂ at the interface according to Gibbs' law. Further, wetting characteristics have been investigated as they are of considerable importance to packed columns. Therefore, the contact angle was determined by the method of the tilting plate and came out to increase with pressure and smoothness of the solid surface, indicating the loss of wettability.

---

     

Membrane-immobilized haptoglobin as affinity matrix for a hemoglobin-A1c immunosensor

An amperometric immunosensor for hemoglobin-A1c (HbA1c) determination has been developed utilizing membrane-immobilized haptoglobin as affinity matrix fixed in front of a Pt-working electrode. The HbA1c assay was carried out in a two-step procedure including the selective hemoglobin enrichment on the sensor surface and the specific HbA1c detection by a glucose oxidase (GOx) labeled anti-HbA1c antibody. Hydrogen peroxide generated by the enzyme label was oxidized at +600 mV versus Ag/AgCl. A standard curve for HbA1c was obtained with a linear range between 0 and 25% HbA1c of total hemoglobin which correspond to 7.8–39 nM. ELISA studies confirmed the advantage of a sandwich-type format with haptoglobin as capture molecule for selective hemoglobin binding over the direct adsorption method. Results by the sandwich immunoassay showed a linear correlation within the clinically relevant range 5–20% (CV < 3). For sensor application the immobilization procedure of haptoglobin onto CDI-activated cellulose membranes was optimized.     

Luminescent organoboron quinolate polymers

The synthesis of well-defined luminescent organoboron polymers via a novel three-step procedure starting from silylated polystyrene is reported. Highly selective borylation of poly(4-trimethylsilylstyrene) (PS-Si), followed by replacement of the bromine substituents in poly(4-dibromoborylstyrene) (PS-BBr) with substituted thienyl groups (R = H, 3-hexyl, 5-hexyl), and final introduction of the 8-hydroxyquinolato moiety yields a series of new organoboron quinolate polymers in 67-83% isolated yield. The hexyl-substituted polymers are highly soluble and solution-processable yielding thin films that efficiently emit light at 513-514 nm upon excitation at 395 nm.     

Polarographic determination of α-amylase activity

The enzyme α-amylase splits blue starch in fragments bearing electroactive groups which exhibit two waves in the pulse polarograms. This behaviour is the basis of the polagraphic determination of bacterial and human serum α-amylase activity. The differential pulse mode is more sensitive by a factor of 25 as compared with normal pulse polarography. With serum α-amylase, protein adsorption disturbs the determination of low activities.     

Quantum chemical calculations for the determination of the molecular structure of conjugated compounds: Part XIII. On the conformational structure of rans-benzylideneaniline in the gas phase and in solution

Contrary to the results of other semi-empirical all-valence electron methods, the main features concerning the conformation of trans-benzylideneaniline are correctly accounted for using the NDDO method. Based on a modified continuum model the influence of solvents on the molecular structure was estimated.     

Laccase-catalyzed carbon-carbon bond formation: oxidative dimerization of salicylic esters by air in aqueous solution

The laccase catalyzed oxidative dimerization of salicylic esters, a rare example of a laccase-catalyzed carbon-carbon bond formation, was studied. This reaction allows the use of air as stoichiometric oxidant and proceeds in aqueous solution. The preparative scope and the mechanism of the method, which provides a new and convenient access to functionalized biaryls under mild conditions, were investigated.     

Determination of the turnover number of the restriction endonuclease EcoRI using evanescent wave technology

Binding and catalytic activity of the type II restriction endonuclease EcoRI on immobilized DNA has been observed in real time using three different evanescent wave biosensors and two different immobilization techniques. The method gives direct access to the turnover number (kcat) without the necessity for the determination of any concentration or activity. The combination of different evanescent wave techniques gives access to the catalytic mechanism and allows the determination of the rate limiting step.