Vibration assisted drilling of CFRP/metal stacks at low frequencies and high amplitudes

In many applications of automotive and aircraft industries the use of material combinations such as compound materials made from carbon fiber reinforced plastics (CFRP) and metal materials like steel, titanium or aluminum alloys is significantly increasing. For these industries, the lightweight and mechanical properties of the reinforced plastic materials gain more and more importance. When machining material combinations, a number of distinctive material related effects occur and hamper the straight-forward implementation of machining processes. These effects mainly derive from the distinctive chipping behavior of the material combination caused by the different material characteristics. Thus, the drilling process of CFRP/metal stacks is to be regarded as a challenging task due to the requirements of machining efficiency and quality aspects. In this regard, vibration assisted drilling at low frequencies but high amplitudes opens up significant opportunities for improvements of the machining processes. The feed rate is superimposed by a controlled harmonic motion in order to create an intermittent cutting state. The potential of vibration assisted drilling lies in the reduction of cutting forces and tool wear.     

Enzyme IIIlac of the staphylococcal phosphoenolpyruvate-dependent phosphotransferase system: site-specific mutagenesis of histidine residues, biochemical characterization and 1H-NMR studies

The lactose-specific pbosphocarrier protein enzyme III of thebacterial phosphoenol-pyruvate-dependent phosphotransferasesystem of Staphylococcus aureus was modified by sitespecificmutagenesis on the corresponding lacF gene in order to replacethe histidine residues 78 and 82 of the amino acid sequencewith a serine residue. Wild-type and both mutant genes wereoverexpressed in Escherichia coli and the gene products werepurified to homogeneity. The conformation of wild-type and mutantproteins were monitored by ¹H-NMR spectroscopy. In vitro phosphorylationstudies on mutant lactose-specific enzyme III, as well as evidencefrom NMR spectroscopy, lead to the conclusion that His78 isthe activesite for phosphorylation of lactose-specific enzymeIII by phospho-HPr (histidine-containing protein). The roleof His82 probably is the enhancement of velocity and efficiencyof the phosphotransfer from lactose-specific enzyme in to lactosespecifkenzyme II. This result refutes the conclusion of former workbased on data by protelytk cleavage and sequencing of the ³²P-labeledpeptide of lactose-specific enzyme DTI that His82 is the active-sitefor phosphorylation.     

Designing environment-friendly chromium-free Spinel-Periclase-Zirconia refractories for Ruhrstahl Heraeus degasser

Ruhrstahl Heraeus (RH) degassers are globally used to manufacture vacuum-treated steel for automotive and railroad applications. The state-of-the-art environment-friendly chromium-free alternatives for direct-bonded magnesia-chrome refractories used in RH degassers are expensive, and the scientific literature lacks direct correlation between materials chemistry, processing, and functional properties. We have designed a novel spinel-periclase-15 wt% ZrO₂ composition containing 14 wt% in situ spinel which exhibited 7.2 MPa hot modulus of rupture (1500℃), exceeding all reported Cr-free refractories for RH degasser applications. Investigation with scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) attributed this improvement to a reduction in interparticle Ca and Si content which forms low-melting phases, as supported by FactSage thermodynamic simulations. The spinel-periclase composition SP exhibited superior thermal shock resistance because thermal shock-induced cracks were stopped by fracture porosity around MgO particles, formed due to thermal expansion mismatch. SEM-EDS analysis of the SP composition corroded by RH slag at 1650°C revealed that Fe is the most corrosive element followed by Ca and Si. Contradicting the consensus, it was observed that corrosion resistance of fused MgO was better than that of ZrO₂. The cubic ZrO₂ phase reduced FeO_x penetration locally by incorporating CaO from the RH slag into a solid solution and forming a CaZrO₃ phase creating a “slag barrier”. Lastly, pore size was found to greatly exacerbate slag penetration following the Washburn percolation model.     

Staphylococcal lactose phosphoenolpyruvate-dependent phosphotransferase system: site-specific mutagenesis on the lacE gene gives evidence that a cysteine residue is responsible for phosphorylation

The lactose-specific phosphocarrier protein enzyme II of thebacterial phosphoenol-pymvate-dependent phosphotransferase systemof Staphylococcus aureus was modified by sitespecific mutagenesison the corresponding lacE gene in order to replace the histidineresidues 245, 274 and 510 and the cysteine residue 476 of theamino acid sequence with a serine residue. The wild-type andmutant genes were expressed in Escherichia coli and the geneproducts were characterized in different in vitro test systems.In vitro phosphorylation studies on mutant derivatives of thelactose-specific enzyme II led to the conclusion that cysteinersidue 476 is the active-site for phosphorylation of this enzymeII by a phospho-enzyme III of the same sugar specificity. Acysteine residue phosphor) lated intermediate was first postulatedfor the mannitol-specific enzyme II of E.coli and studies performedindependently concerning the lactose-specific enzyme II of Lactobacilluscasei are in agreement with the above results.