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Multi-parameter detection for supporting monitoring and control of biogas processes in agriculture
(2014)
High-intensity discharge lamps can be driven by radio-frequency signals in the ISM frequency band at 2.45 GHz, using a matching network to transform the impedance of the plasma to the source impedance. To achieve an optimal operating condition, a good characterization of the lamp in terms of radio frequency equivalent circuits under operating conditions is necessary, enabling the design of an efficient matching network. This paper presents the characterization technique for such lamps and presents the design of the required matching network. For the characterization, a high-intensity discharge lamp was driven by a monofrequent large signal at 2.45 GHz, whereas a frequency sweep over 300 MHz was performed across this signal to measure so-called small-signal hot S-parameters using a vector network analyzer. These parameters are then used as an equivalent load in a circuit simulator to design an appropriate matching network. Using the measured data as a black-box model in the simulation results in a quick and efficient method to simulate and design efficient matching networks in spite of the complex plasma behavior. Furthermore, photometric analysis of high-intensity discharge lamps are carried out, comparing microwave operation to conventional operation.
Access to promising radiometals as isotopes for novel molecular imaging agents requires that they are routinely available and inexpensive to obtain. Proximity to a cyclotron center outfitted with solid target hardware, or to an isotope generator for the metal of interest is necessary, both of which can introduce significant hurdles in development of less common isotopes. Herein, we describe the production of ⁴⁴Sc (t₁⸝₂ = 3.97 h, Eavg,β⁺ = 1.47 MeV, branching ratio = 94.27%) in a solution target and an automated loading system which allows a quick turn-around between different radiometallic isotopes and therefore greatly improves their availability for tracer development. Experimental yields are compared to theoretical calculations.
Mikrowellentechnik
(2014)
Aktiver und passiver antimikrobieller Oberflächenschutz durch funktionalisierte Mikropartikel
(2014)
Mikrobielle Verunreinigungen von Oberflächen in technischen und medizinischen Systemen sind allgegenwärtig. Sie basieren üblicherweise auf adsorptiven Oberflächenbindungen organischer Komponenten (Proteine und Fette) oder Membrankomponenten aerogener sowie wassergebundener Mikroorganismen. In laufenden Forschungsarbeiten wird eine aktive sowie passive Biomodifikation von Oberflächen zu deren Schutz vor Adsorption von Proteinen und Mikroorganismen verfolgt. Der antimikrobielle Schutz soll dabei sowohl durch die Mikrostrukturierung bzw. Rauheitsanpassung der Oberflächen durch deren Beschichtung mit Mikro-und Nanopartikeln erfolgen. Ferner werden antimikrobielle Enzyme und funktionelle Gruppen auf den Mikropartikeln gebunden, um den Oberflächenschutz zu verstärken. In ersten Versuchen wurden quartäre Ammoniumverbindungen auf eigens synthetisierten superparamagnetischen Eisenoxid-Nanopartikeln (Durchmesser 10 – 30 nm) immobilisiert und die wachstumshemmende Wirkung untersucht. Erste Ergebnisse zeigten, dass eine Konzentration von 10 mg mL⁻¹ der Ammoniumverbindung in einer Wachstumshemmung des verwendeten Gram-negativen Modell-Mikroorganismus E. coli GFPmut2 resultiert. Zurzeit werden synergistisch wirkende Kombinationen von Partikeln mit Proteasen, quartären Ammoniumverbindungen, hydrophoben Oberflächen und mikrostrukturierten Oberflächen als antimikrobieller Schutz untersucht.
Bei der Verarbeitung nachwachsender Rohstoffe entsteht aus Cellulose oder Stärke u. a. das wichtige Produkt Glucose. Diese niedermolekulare Kohlenhydratquelle wird üblicherweise als Substrat für biotechnologische und chemische Synthesen verwendet. Ein wirtschaftlich interessantes Oxidationsprodukt der Glucose ist Gluconsäure, die beispielsweise als Lebensmittelzusatzstoff (E 574), in der Medizin und Metallindustrie Verwendung findet. Die Umsetzung des Monosaccharids zu Gluconsäure erfolgt entweder durch mikrobielle Fermentation oder der Oxidation an heterogenen Katalysatoren. Die Zielsetzung der Studie ist die Untersuchung der Glucoseoxidation an magnetisierbaren Gold-Nanopartikeln unter nachfolgender Bypass-Separation des Katalysators mittels einer neuen Mini-HGMS-Einheit (Hochgradient-Magnetseparation). Dieser Filtertyp ermöglicht die selektive Trennung magnetischer Partikel aus Suspensionen mit hohem Feststoffgehalt oder Viskosität. Erste Ergebnisse zeigen eine Beladungskapazität des selbstkonstruierten Mini-HGMS von 550 mg goldbeschichteter magnetisierbarer Nanopartikel. Die Oxidation erfolgt bei einem pH-Wertvon 9, bei 40 °C und mit 100 mM Glucose in einem begasten Rührkesselreaktor. Das System soll zukünftig zum Katalysatorrecycling von hochviskosen und Feststoffbelasteten Produktströmen aus Bioraffinerien eingesetzt werden.
Molecular Modeling Approach to the Prediction of Mechanical Properties of Silica-Reinforced Rubbers
(2014)
Recently, we have suggested a nanomechanical model for dissipative loss in filled elastomer networks in the context of the Payne effect. The mechanism is based on a total interfiller particle force exhibiting an intermittent loop, due to the combination of short-range repulsion and dispersion forces with a long-range elastic attraction. The sum of these forces leads, under external strain, to a spontaneous instability of “bonds” between the aggregates in a filler network and attendant energy dissipation. Here, we use molecular dynamics simulations to obtain chemically realistic forces between surface modified silica particles. The latter are combined with the above model to estimate the loss modulus and the low strain storage modulus in elastomers containing the aforementioned filler-compatibilizer systems. The model is compared to experimental dynamic moduli of silica filled rubbers. We find good agreement between the model predictions and the experiments as function of the compatibilizer's molecular structure and its bulk concentration.
Poly(vinyl acetate), PVAc, with a degree of polymerization Xn = 10 was prepared by chain-transfer radical polymerization using carbon tetrachloride and used as oligomeric plasticizer for commercial PVAc. However, the chlorinated chain ends cause a low thermal stability requiring mild Cl/H substitution. The product exhibits high thermal stability and excellent melt-compounding properties. Blends of oligomeric and commercial PVAc show single glass transition temperatures which decrease with higher oligomer content and exhibit small negative deviations from Fox' linear additivity rule. This indicates plasticization and miscibility being mainly due to entropic effects. Injection-moulded thick specimens show ductile behaviour at oligomer contents >10 wt %, while sheets with a thickness of 0.2–0.5 mm appear flexible already at 7.5 wt %. The oxygen permeability coefficients are an order of magnitude lower than those of low-density polyethylene. Due to the sum of their properties, the plasticized sheets present a promising alternative in the preparation of barrier materials.
Clostridium propionicum is the only organism known to ferment β-alanine, a constituent of coenzyme A (CoA) and the phosphopantetheinyl prosthetic group of holo-acyl carrier protein. The first step in the fermentation is a CoA-transfer to β-alanine. Subsequently, the resulting β-alanyl-CoA is deaminated by the enzyme β-alanyl-CoA:ammonia lyase (Acl) to reversibly form ammonia and acrylyl-CoA. We have determined the crystal structure of Acl in its apo-form at a resolution of 0.97 Å as well as in complex with CoA at a resolution of 1.59 Å. The structures reveal that the enyzme belongs to a superfamily of proteins exhibiting a so called “hot dog fold” which is characterized by a five-stranded antiparallel β-sheet with a long α-helix packed against it. The functional unit of all “hot dog fold” proteins is a homodimer containing two equivalent substrate binding sites which are established by the dimer interface. In the case of Acl, three functional dimers combine to a homohexamer strongly resembling the homohexamer formed by YciA-like acyl-CoA thioesterases. Here, we propose an enzymatic mechanism based on the crystal structure of the Acl·CoA complex and molecular docking. Proteins 2014; 82:2041–2053. © 2014 Wiley Periodicals, Inc.
Mehrwert
(2014)