Maturation of the lantibiotic subtilin: matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to monitor precursors and their proteolytic processing in crude bacterial cultures.

Bacillus subtilis synthesizes the lanthionine containing 32-amino-acid peptide antibiotic (lanti-biotic) subtilin from a ribosomally generated 56-amino-acid precursor pre-propeptide by extensive posttranslational modifications. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used to monitor the production of matured subtilin within crude samples taken from B. subtilis culture media without prior fractionation. The processing reaction of subtilin was blocked with the serine protease inhibitor phenylmethylsulfonyl fluoride and different subtilin precursor peptides in the molecular mass range up to 6220 were observed. Two of these species were isolated by reversed-phase high-performance liquid chromatography (HPLC) and structurally analyzed by post-source decay MALDI-TOFMS. We provide evidence that the precursor species comprise the posttranslational modified C-terminal part of subtilin to which leader peptide moieties with different chain lengths are attached. These antimicrobial-inactive species could be processed to antibiotic-active subtilin by incubation with culture media of different subtilin-nonproducing B. subtilis strains as indicated by a combination of antimicrobial growth assays and MALDI-TOFMS analyses. These achievements are strong evidence for the sensitivity of MALDI-TOFMS methodology that allows straightforward investigations of analytes even in complex mixtures without time-consuming sample preparations.     

Toward an understanding of white-light generation in cubic media - polarization properties across the entire spectral range

We present an extensive investigation of the polarization properties of a femtosecond-laser-induced white-light (WL) continuum generated in a cubic crystal (CaF(2)). The WL spectrum and threshold energies have been examined for input polarizations with various degrees of ellipticity. For linear input polarization, the WL spectrum shows strong depolarization around the input wavelength, while the preservation of the input polarization is pronounced toward the blue spectral region. The observed depolarization effect has been elucidated in the framework of current models for WL generation.     

Investigation of Alternative Length Scale Substitutions in Detached-Eddy Simulation

The objective of this work is the comparison of three different DES-style hybrid RANS/LES implementations based on the Wilcox k– model. The three variants are designed to investigate alternative methods of substitution of the DES length scale within the background Reynolds Averaged Navier-Stokes (RANS) model. Basis for comparison is provided by both the idealised case of the decay of isotropic turbulence (DIT) as well as the practical case of the massively separated, turbulent flow around an airfoil at high angle of attack. The results of the investigations are discussed in detail, the outcome of which is an emphasis of the importance of DIT as a method for calibration, as well as of the relative freedom with which alternative DES-inspired approaches can be implemented for flows of practical relevance.     

On the Realizability of Nonlinear Stress–Strain Relationships for Reynolds Stress Closures

A class of recently developed explicit algebraic stress models based on tensorially quadratic stress--strain relations [7] is subjected to a systematical realizability analysis. It is found that these models, which are of particular interest for their rigorous derivation from linear second-moment closure models, tend to produce inappropriate unrealizable results like negative turbulence energy components, even in simple shear flows. The cause of the defect is identified in conjunction with a set of realizability-furnishing constraints on the model coefficients. With the exception of the silent normal stress component in accelerated flow, the nature and rationale of the explicit algebraic stress model suggested by Gatski and Speziale [7] can be extended to maintain the realizability principle. Results obtained from the corresponding quasi-realizable quadratic eddy-viscosity model are reported in comparison with other nonlinear modelling practices.     

Viskositätsmessungen an Gußeisenschmelzen

Zusammenfassung Es wird ein Viskosimeter zur Messung von Gußeisenschmelzen bis zu 1400°C aus dem Rotationsviskosimeter Bauart MPA und der dazu erforderliche keramische Drehkörper bezüglich Form und Material entwickelt.Dieses Viskosimeter kann für Kontrollmessungen im Gießereibetrieb eingesetzt werden, da es durch die elektrische Fernanzeige möglich ist, die feinen Meßinstrumente in größerer Entfernung von der eigentlichen Meßstelle aufzubauen und sie vor den Einflüssen des rauhen Betriebes zu schützen.Es wird für diese Temperaturbereiche eine völlig neue Methode beschrieben, die sich von den bisherigen Messungen vonP. Oberhoffer undA. Wimmer (4) nach der Torsionsmethode und Messungen vonH. Thielmann undA. Wimmer (5) nach der Schwingtiegelmethode an weißem Gußeisen dadurch unterscheidet, daß während der Messung keine Temperaturkonstanz angestrebt zu werden braucht, da die einzelne Messung kein Zeitintervall erfordert und die dazugehörige Temperatur exakt bestimmt werden kann.Leider können die hier erhaltenen Ergebnisse nicht mit den Messungen vonOberhoffer undWimmer verglichen werden, da die Verfasser keine absoluten Werte angeben. Bei den Messungen vonThielmann undWimmer handelt es sich um weißes Gußeisen, das auf Grund unterschiedlicher Siliziumgehalte gegenüber Grauguß nicht vergleichbar mit den gefundenen Ergebnissen ist.     

Extending N-heterocyclic carbene ligands into the third dimension: a new type of hybrid phosphazane/NHC system

A simple, “click” synthetic approach to a new type of hybrid phosph(III)azane/NHC system is described. The presence of the phosphazane P₂N₂ ring unit, with P atoms flanking the NCN fragment and with this ring perpendicular to the binding site of the NHC, provides unique opportunities for modifying the electronic and steric character of these carbenes.