Gb3 Glycosphingolipids with Fluorescent Oligoene Fatty Acids: Synthesis and Phase Behavior in Model Membranes

Glycosphingolipids are involved in a number of physiological and pathophysiological processes, and they serve as receptors for a variety of bacterial toxins and viruses. To investigate their function in lipid membranes, fluorescently labeled glycosphingolipids are highly desirable. Herein, a synthetic route to access Gb₃ glycosphingolipids with fluorescently labeled fatty acids, consisting of pentaene and hexaene moieties either at the terminus or in the middle of the acyl chain, has been developed. The fluorescent properties of the Gb₃ derivatives were investigated in small unilamellar vesicles composed of a raft-like mixture. Phase-separated giant unilamellar vesicles (GUVs) allowed the quantification of the apparent partitioning coefficients of the Gb₃ compounds by means of confocal fluorescence laser scanning microscopy. The determined partition coefficients demonstrate that the Gb₃ derivatives are preferentially localized in the liquid-disordered (l_d) phase. To analyze whether the compounds behave like their physiological counterparts, Cy3-labeled (Cy: cyanine) Shiga toxin B subunits (STxB) were specifically bound to Gb₃-doped GUVs. However, the protein was favorably localized in the l_d phase, in contrast to results reported for STxB bound to naturally occurring Gb₃, which is discussed in terms of the packing density of the lipids in the liquid-ordered (l_o) phase.     

Studying Organizational Creativity as Process: Fluidity or Duality?

This paper contributes to process studies on organizational creativity by developing two competing research agendas. The first perspective, the ‘becoming’ view, depicts creativity as a constant flow of activity that crystallizes every once in a while in unpredictable moments of creativity. The second perspective, the ‘practice’ view, understands creativity as a practised social process, in which structures play the important role of both enabling and constraining individual agents in pursuing creativity as a collective phenomenon. We compare and contrast these two theoretical perspectives, which are based on different process ontologies, and discuss their methodological implications. We argue that the practice perspective offers particular promise, because it allows us to address the important yet paradoxical question of how creativity may be organized and managed.     

Development of a Comprehensive Oxide Scale Failure Diagram

This paper describes a new approach towards the development of a comprehensive oxide scale failure diagram (OSFD) that delineates the mechanical limits of scales for the different types of failure mechanisms. While former diagrams of a similar type were based on relating the critical strain to scale failure to oxide scale thickness, the new approach replaces scale thickness with a comprehensive operational parameter ω_o that summarizes in a multi-level treatment all contributing factors, e.g. physical defect size, interface roughness, scale thickness, Young’s modulus, fracture toughness, etc., that influence failure strain. While this approach should ideally be based on a comprehensive treatment of ω_o using fully implemented coding, further considerations based on the identification of “low-impact” and “high-impact” parameters lead to a simplified OSFD where only the physical defect size is needed. This simplified approach can be used to assess the strain tolerance of oxide scales in industrial operation once the particular diagram has been established from laboratory data.     

Experimental Investigation of the Epsilon Phase in Pb–Bi System

The Pb–Bi (Lead–Bismuth) binary system has gained some prominence in recent years due to the possible use of eutectic alloys as primary-circuit coolant in generation IV nuclear reactors. Apart from the terminal solid solutions A1-Pb and A7-Bi, the system presents also one intermetallic phase with the hexagonal close-packed structure (A3), usually denoted ε phase. Due to the low temperatures involved in this system, attainment of equilibrium is difficult, and in addition, the proximity of x-ray scattering factors for both elements raises questions about a possible polymorphic transition. In the present work, three samples with compositions Pb–29 wt.%Bi, Pb–31 wt.%Bi and Pb–33 wt.%Bi were prepared and characterized by x-ray diffraction. The lattice parameters of ε are consistent with those reported in the literature, and their dependence on Bi content was determined as well. Only the hexagonal phase was identified in the 29 wt.%Bi sample, although the currently assessed Pb–Bi phase diagram predicts the presence of the Pb-rich A1 terminal solid solution in this composition. A 2-year annealing at room temperature was performed and the XRD characterization results for these samples are compared with the original data.     

A single step process to form in-situ an alumina foam/aluminide TBC system for alloys in extreme environments at high temperatures

A new approach to manufacture a complete thermal barrier coating system in a single step is studied in the frame of the European FP7 project PARTICOAT. Spherical μm-Al particles are deposited on different substrate alloys. During the sintering process in air, the μm-Al particles are oxidized and converted into hollow alumina spheres forming a ceramic “foam” (top coat), and simultaneously an Al rich diffusion layer (bond coat) is formed in the subsurface zone of the substrate.The “green” coatings deposited by air brush on IN738, René80 and CM247 nickel based alloys were cured at 300 °C and then isothermally exposed at 800 and 1000 °C in air for up to 1000 h. The oxide formation and the microstructure of the coatings were studied by thermo gravimetrical analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX).The coatings were adherent for all the substrates and temperatures tested. René80 shows the lowest mass gain whereas IN738 and CM247 show higher mass gains at the temperatures studied. Additionally, the use of reactive element oxides in the coating was investigated, demonstrating the flexibility and viability of this low cost coating concept.