Experimental study of switching in a p-i(MQW)-n vertical coupler

Electrically controlled switching in a vertically arranged p-i(MQW)-n directional coupler with GaAs/GaAlAs multiple-quantum-well (MQW) waveguides is discussed. Coupling lengths and extinction parameters are determined by using a sample processed in such a way that injection conditions are well defined and that the coupler length can be varied continuously     

Very low power nonlinear directional coupling in a p-i (MQW)-nvertical coupler using an electrooptic feedback

An optically controlled 1×2 optical switch based on a vertically arranged directional coupler in which the guiding regions are GaAs/GaAlAs multiple quantum wells is discussed. The device can be switched electrically in a very efficient way (5-V driving voltage for a 330-μm-long sample) as well as optically. When connected to a constant-current source, the system shows high optical nonlinearities and can be all-optically switched with very low incident optical power on the order of 0.1 mW     

Different pools of esterified arachidonic acid in rabbit kidney medulla: Relationship to Ca2+-stimulated prostaglandin biosynthesis

We investigated the effect of Ca²⁺ ions on renal medulla metabolism of endogenous esterified arachidonic acid in contrast to that of radioactive arachidonate incorporated into medullary lipids. Some striking differences between the release of unlabeled prostaglandin E₂ and of¹⁴C-labeled prostaglandin E₂ and arachidonic acid were seen in incubations in absence or presence of Ca²⁺ ions. These differences indicated that exogenous [¹⁴C] arachidonate incubated with medulla slices is incorporated into both Ca²⁺-sensitive and Ca²⁺-insensitive lipid pools of esterified arachidonate and furthermore, the Ca²⁺-sensitive pool is itself heterogeneous and consists of at least 2 functionally different lipid pools of esterified arachidonate. The first Ca²⁺-sensitive pool is characterized by a higher arachidonate turnover rate and incorporates more rapidly added radioactive arachidonate. The acylhydrolase activity which releases arachidonate from this pool is not efficiently coupled to prostaglandin endoperoxide synthase. In contrast, the second Ca²⁺-sensitive lipid pool has a slower arachidonate turnover rate and, consequently, a slower incorporation of added¹⁴C-acid. The acylhydrolase activity associated with this pool is more tightly coupled to prostaglandin endoperoxide synthase, so that a higher portion of released arachidonate is converted to prostaglandin E₂. Studies on arachidonic acid metabolic transformations using exogenously radioactive free acid added to tissues should therefore be inerpreted with caution because the results obtained may not reflect accurately the metabolic fate of endogenous, lipid-esterified arachidonate which is released and metabolized under physiological conditions in vivo.     

Thermally Sprayed Coatings as Effective Tool Surfaces in Sheet Metal Forming Applications

Two approaches to produce wear-resistant effective surfaces for deep drawing tools by thermal arc wire spraying of hard materials are presented. Arc wire spraying is a very economic coating technique due to a high deposition rate. The coated surface is very rough compared to that of conventional sheet metal forming tools. In the first approach, the coated surface is smoothed in a subsequent CNC-based incremental roller burnishing process. In this process, the surface asperities on the surface are flattened, and the roughness is significantly reduced. In the second approach, the hard material coatings are not sprayed directly on the tool but on a negative mould. Afterward, the rough “as-sprayed” side of the coating is backfilled with a polymer. The bonded hard metal shell is removed from the negative mould and acts as the surface of the hybrid sheet metal forming tool. Sheet metal forming experiments using tools based on these two approaches demonstrate that they are suitable to form high-strength steels. Owing to a conventional body of steel or cast iron, the first approach is suitable for large batch sizes. The application of the second approach lies within the range of small up to medium batch size productions.     

Biofilm formation by Staphylococcus aureus strains and their control by selected phytochemicals

Biofilm formation by 30 Staphylococcus aureus dairy isolates and their control by phytochemicals were investigated. The majority of strains were biofilm positive by phenotypic analysis. The nuc and icaA genes were present in 30 and 27 strains, respectively. In addition, 13 strains were positive for all nuc, clfA, fnbA and icaA genes. The antimicrobial and antibiofilm activities of citral, cinnamaldehyde, eugenol, farnesol, limonene and terpinen‐4‐ol were also evaluated for seven strains. It was shown that the use of farnesol, cinnamaldehyde or terpinen‐4‐ol at a concentration of 2 mg/mL could be at least 80% effective on S. aureus strains and their biofilms.     

Effect of the wall thickness on the forming behavior and welding result during magnetic pulse welding

Magnetic pulse welding is a promising technology for the joining of dissimilar metals. Since the input of thermal energy is significantly reduced compared to conventional fusion welding technologies, critical intermetallic phases can largely be avoided. Therefore, proper collision conditions are necessary. Those require a careful adjustment of the energetic and geometric parameters at the impact welding setup. The thickness of the accelerated joining partner (flyer) determines the necessary energy input for a successful weld. However, at the same time, it has an effect on the weld formation. This study utilizes a novel optical measurement system to explain these findings and to gain insights into the forming behavior of the flyer parts. It is shown that the collision angle depends on the flyer tube thickness and, thus, directly has an effect on the welding result.     

Integrated simulation of the process chain composite extrusion–milling–welding for lightweight frame structures

Generally, the manufacturing of lightweight frame structures involves various processes that yield the final product. Simulation methods can be used to optimise the different process steps. When chaining these process steps together in the simulation, software interfaces become necessary to realise an integrated virtual process chain. In this paper two approaches are presented that solve this issue and demonstrate it for an exemplary part. Different software tools with appropriate interfaces and the use of only one software tool for the simulation of the whole process chain are investigated respectively. The results of both approaches are analysed and relevant conclusions are deduced.     

Imidazole binding to horse metmyoglobin: dependence upon pH and ionic strength

A series of substituted chalcone oxides (1,3-diphenyl-2-oxiranyl propanones) and structural analogs was synthesized to investigate the mechanism by which they inhibit soluble epoxide hydrolases (sEH). The inhibitor potency and inhibition kinetics were evaluated using both murine and human recombinant sEH. Inhibition kinetics were well described by the kinetic models of A. R. Main (1982, in Introduction to Biochemical Toxicology, pp. 193-223, Elsevier, New York) supporting the formation of a covalent enzyme-inhibitor intermediate with a half-life inversely proportional to inhibitor potency. Structure-activity relationships describe active-site steric constraints and support a mechanism of inhibition consistent with the electronic stabilization of the covalent enzyme-inhibitor intermediate. The electronic effects induced by altering the ketone functionality and the para-substitution of the phenyl attached to the epoxy C1 (i.e., the alpha-carbon) had the greatest influence on inhibitor potency. The direction of the observed influence was reversed for the inhibitory potency of glycidol (1-phenyl-2-oxiranylpropanol) derivatives. Recent insights into the mechanism of epoxide hydrolase activity are combined with these experimental results to support a proposed mechanism of sEH inhibition by chalcone oxides.