Laminar Pipe Flow with Mixed Convection under the Influence of Magnetic Field

Magnetic influence on ferronanofluid flow is gaining increasing interest from not only the scientific community but also industry. The aim of this study is the examination of the potentials of magnetic forces to control heat transfer. Experiments are conducted to investigate the interaction between four different configurations of permanent magnets and laminar pipe flow with mixed convection. For that purpose a pipe flow test rig is operated with a water-magnetite ferronanofluid. The Reynolds number is varied over one order of magnitude (120–1200). To characterise this suspension, density, solid content, viscosity, thermal conductivity, and specific heat capacity are measured. It is found that, depending on the positioning of the magnet(s) and the Reynolds number, heat transfer is either increased or decreased. The experiments indicate that this is a local effect. After relaxation lengths ranging between 2 and 3.5 lengths of a magnet, all changes disappeared. The conclusion from these findings is that magnetic forces are rather a tool to control heat transfer locally than to enhance the overall heat transfer of heat exchangers or the like. Magnetically caused disturbances decay due to viscous dissipation and the flow approaches the basic state again

The Mechanism behind Bacterial Lipoprotein Release: Phenol-Soluble Modulins Mediate Toll-Like Receptor 2 Activation via Extracellular Vesicle Release from Staphylococcus aureus

Our study highlights the roles of surfactant-like molecules in bacterial inflammation with important implications for the prevention and therapy of inflammatory disorders. It describes a potential pathway for the transfer of hydrophobic bacterial lipoproteins, the major TLR2 agonists, from the cytoplasmic membrane of Gram-positive bacteria to the TLR2 receptor at the surface of host cells. Moreover, our study reveals a molecular mechanism that explains how cytoplasmic and membrane-embedded bacterial proteins can be released by bacterial cells without using any of the typical protein secretion routes, thereby contributing to our understanding of the processes used by bacteria to communicate with host organisms and the environment.The innate immune system uses Toll-like receptor (TLR) 2 to detect conserved bacterial lipoproteins of invading pathogens. The lipid anchor attaches lipoproteins to the cytoplasmic membrane and prevents their release from the bacterial cell envelope. How bacteria release lipoproteins and how these molecules reach TLR2 remain unknown. Staphylococcus aureus has been described to liberate membrane vesicles. The composition, mode of release, and relevance for microbe-host interaction of such membrane vesicles have remained ambiguous. We recently reported that S. aureus can release lipoproteins only when surfactant-like small peptides, the phenol-soluble modulins (PSMs), are expressed. Here we demonstrate that PSM peptides promote the release of membrane vesicles from the cytoplasmic membrane of S. aureus via an increase in membrane fluidity, and we provide evidence that the bacterial turgor is the driving force for vesicle budding under hypotonic osmotic conditions. Intriguingly, the majority of lipoproteins are released by S. aureus as components of membrane vesicles, and this process depends on surfactant-like molecules such as PSMs. Vesicle disruption at high detergent concentrations promotes the capacity of lipoproteins to activate TLR2. These results reveal that vesicle release by bacterium-derived surfactants is required for TLR2-mediated inflammation

Adsorption of Poly(vinylformamide-<i>co</i>-vinylamine) Polymers (PVFA-<i>co</i>-PVAm) on Copper

The adsorption of poly­(vinylformamide) (PVFA) and its derivative statistical copolymer poly­(vinyl-formamide-<i>co</i>-vinylamine) (PVFA-<i>co</i>-PVAm) on metallic copper and copper oxide particles as well as planar copper surfaces was studied as a function of the degree of hydrolysis of PVFA, the pH, and the polymer concentration in solution. The chemical composition and molecular structure of the PVFA-<i>co</i>-PVAm layers were investigated by surface-sensitive spectroscopic methods such as XPS, DRIFT spectroscopy, and ellipsometry. The findings allowed us to explain the adsorption mechanisms and the forces driving the PVFA-<i>co</i>-PVAm adsorption. It was shown that PVFA-<i>co</i>-PVAm layers thicker than 30 nm are able to protect the planar copper surface against corrosive attack

Tunable Hydrophilic or Amphiphilic Coatings: A “Reactive Layer Stack” Approach

Thin films with tunable properties are very interesting for potential applications as functional coatings with, for example, anti-icing or improved easy-to-clean properties. A novel “reactive layer stack” approach was developed to create covalently grafted mono- and multilayers of poly­(glycidyl methacrylate)/poly­(<i>tert</i>-butyl acrylate) diblock copolymers. Because these copolymers contain poly­(glycidyl methacrylate) blocks they behave as self-cross-linking materials after creation of acrylic acid functionalities by splitting off the <i>tert</i>-butyl units. The ellipsometrically determined coating thickness of the resulting hydrophilic multilayers depended linearly on the number of applied layers. Amphiphilic films with tunable wettability were prepared using triblock terpolymers with an additional poly­(methyl methacrylate) block. The mechanism of the formation of the (multi)­layers was investigated in detail by studying the acidolysis of the surface-linked <i>tert</i>-butyl acrylate blocks by infrared reflection absorbance spectroscopy, accompanied by surface analysis using atomic force microscopy and contact angle measurements. In the case of the amphiphilic and switchable terpolymer layers this reaction was very sensitive to the used acidic reagent

Neue funktionale und biomimetische Oberflächen zur Verhinderung/Verminderung von Eiswachstum : Schlussbericht - Verbundprojekt = New functional and biomimetical surfaces to reduce ice formation

[no abstract available