Methodological implications of critical realism for mixed-methods research

Building on recent developments in mixed methods, we discuss the methodological implications of critical realism and explore how these can guide dynamic mixed-methods research design in information systems. Specifically, we examine the core ontological assumptions of CR in order to gain some perspective on key epistemological issues such as causation and validity, and illustrate how these shape our logic of inference in the research process through what is known as retroduction. We demonstrate the value of a CR-led mixed-methods research approach by drawing on a study that examines the impact of ICT adoption in the financial services sector. In doing so, we provide insight into the interplay between qualitative and quantitative methods and the particular value of applying mixed methods guided by CR methodological principles. Our positioning of demi-regularities within the process of retroduction contributes a distinctive development in this regard. We argue that such a research design enables us to better address issues of validity and the development of more robust meta-inferences.

Biofunctionalization of PET/SiO2 surfaces for single molecule experiments and medical applications

PET/SiO2 layers were chemically modified to maintain immobilization of functional single molecules. GFP molecules provide an ideal system due to their stability and intrinsic fluorescence. GFP in vivo biotinylated within its NH2-terminal region and attached on the substrate via the biotinstreptavidin bond was further investigated with confocal microscopy, atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). AFM revealed monolayered donut-like structures representing assemblies of biotinstreptavidinbiotinGFP immobilized onto PET/SiO2 surfaces via mPEG. In particular, regions with an approximate height of 12 nm, which approaches the molecular dimensions of the above complex given by molecular modeling, could be detected. The dimensions of the donut-like structures suggest a close-to-each-other positioning of the GFP molecules - which, however, retain their functionality, as evidenced by confocal microscopy. © 2011 World Scientific Publishing Company.

Micro-ramp control for oblique shock wave / boundary layer interactions

Supersonic engine intakes operating supercritically feature shock wave / boundary layer interactions (SBLIs), which are conventionally controlled using boundary layer bleed. The momentum loss of bleed flow causes high drag, compromising intake performance. Micro-ramp sub-boundary layer vortex generators (SBVGs) have been proposed as an alternative form of flow control for oblique SBLIs in order to reduce the bleed requirement. Experiments have been conducted at Mach 2.5 to characterise the flow details on such devices and investigate their ability to control the interaction between an oblique shock wave and the naturally grown turbulent boundary layer on the tunnel floor. Micro-ramps of four sizes with heights ranging from 25% to 75% of the uncontrolled boundary layer thickness were tested. The flow over all sizes of microramp was found to be similar, featuring streamwise counter-rotating vortices which entrain high momentum fluid, locally reducing the boundary layer displacement thickness. When installed ahead of the shock interaction it was found that the positioning of the micro-ramps is of limited importance. Micro-ramps did not eliminate flow separation. However, the previously two-dimensional separation was broken up into periodic three-dimensional separation zones. The interaction length was reduced and the pressure gradient across the interaction was increased.