Observing the Earth as an exoplanet with LOUPE, the Lunar Observatory for Unresolved Polarimetry of Earth

The detections of small, rocky exoplanets have surged in recent years and will likely continue to do so. To know whether a rocky exoplanet is habitable, we have to characterise its atmosphere and surface. A promising characterisation method for rocky exoplanets is direct detection using spectropolarimetry. This method will be based on single pixel signals, because spatially resolving exoplanets is impossible with current and near-future instruments. Well-tested retrieval algorithms are essential to interpret these single pixel signals in terms of atmospheric composition, cloud and surface coverage. Observations of Earth itself provide the obvious benchmark data for testing such algorithms. The observations should provide signals that are integrated over the Earth's disk, that capture day and night variations, and all phase angles. The Moon is a unique platform from where the Earth can be observed as an exoplanet, undisturbed, all of the time. Here, we present LOUPE, the Lunar Observatory for Unresolved Polarimetry of Earth, a small and robust spectropolarimeter to observe our Earth as an exoplanet.Comment: 14 pages, 3 figures, submitted in special Issue of Planetary and Space Science on Scientific Preparations for Lunar Exploratio

Filament rigidity and connectivity tune the deformation modes of active biopolymer networks

Molecular motors embedded within collections of actin and microtubule filaments underlie the dynamics of cytoskeletal assemblies. Understanding the physics of such motor-filament materials is critical to developing a physical model of the cytoskeleton and designing biomimetic active materials. Here, we demonstrate through experiments and simulations that the rigidity and connectivity of filaments in active biopolymer networks regulates the anisotropy and the length scale of the underlying deformations, yielding materials with variable contractility. We find that semiflexible filaments can be compressed and bent by motor stresses, yielding materials that undergo predominantly biaxial deformations. By contrast, rigid filament bundles slide without bending under motor stress, yielding materials that undergo predominantly uniaxial deformations. Networks dominated by biaxial deformations are robustly contractile over a wide range of connectivities, while networks dominated by uniaxial deformations can be tuned from extensile to contractile through cross-linking. These results identify physical parameters that control the forces generated within motor-filament arrays and provide insight into the self-organization and mechanics of cytoskeletal assemblies

Compound-specific stable isotope analysis of nitrogen-containing intact polar lipids

RATIONALE: Compound-specific isotope analysis (CSIA) of nitrogen in amino acids has proven a valuable tool in manyfields (e.g. ecology). Several intact polar lipids (IPLs) also contain nitrogen, and their nitrogen isotope ratios have thepotential to elucidate food-web interactions or metabolic pathways. Here we have developed novel methodology forthe determination of d15N values of nitrogen-containing headgroups of IPLs using gas chromatography coupled withisotope-ratio mass spectrometry. METHODS: Intact polar lipids with nitrogen-containing headgroups were hydrolyzed and the resulting compoundswere derivatized by (1) acetylation with pivaloyl chloride for compounds with amine and hydroxyl groups or(2) esterification using acidified 2-propanol followed by acetylation with pivaloyl chloride for compounds withboth carboxyl and amine groups. The d15N values of the derivatives were subsequently determined using gaschromatography/combustion/isotope-ratio mass spectrometry. RESULTS: Intact polar lipids with ethanolamine and amino acid headgroups, such as phosphatidylethanolamine andphosphatidylserine, were successfully released from the IPLs and derivatized. Using commercially available purecompounds it was established that d15N values of ethanolamine and glycine were not statistically different from theoffline-determined values. Application of the technique to microbial cultures and a microbial mat showed that themethod works well for the release and derivatization of the headgroup of phosphatidylethanolamine, a common IPLin bacteria. CONCLUSIONS: A method to enable CSIA of nitrogen of selected IPLs has been developed. The method is suitable formeasuring natural stable nitrogen isotope ratios in microbial lipids, in particular phosphatidylethanolamine, and will beespecially useful for tracing the fate of nitrogen in deliberate tracer experiments. Copyright © 2015 JohnWiley & Sons, Ltd

Advancing Qualitative Entrepreneurship Research: Leveraging Methodological Plurality for Achieving Scholarly Impact

This editorial aims to advance the use of qualitative research methods when studying entrepreneurship. First, it outlines four characteristics of the domain of entrepreneurship that qualitative research is uniquely placed to address. In studying these characteristics, we urge researchers to leverage the plurality of different qualitative approaches, including less conventional methods. Second, to help researchers develop high-level theoretical contributions, we point to multiple possible contributions, and highlight how such contributions can be developed through qualitative methods. Thus, we aim to broaden the types of contributions and forms that qualitative entrepreneurship research takes, in ways that move beyond prototypical inductive theory-building