Are the light-harvesting I complexes from Rhodospirillum rubrum arranged around the reaction centre in a square geometry?

The basic photosynthetic unit containing the reaction centre and the light-harvesting I complex (RC-LHI) of the purple non-sulphur bacterium Rhodospirillum rubrum was purified and reconstituted into two-dimensional (2D) membrane crystals. Transmission electron microscopy using conventional techniques and cryoelectron microscopy of the purified single particles and of 2D crystals yielded a projection of the RC-LHI complex at a resolution of at least 1.6 nm. In this projection the LHI ring appears to have a square symmetry and packs in a square crystal lattice. The square geometry of the LHI ring was observed also in images of single isolated particles of the RC-LHI complex. However, although the LHI units are packed identically within the crystal lattice, a new rotational analysis developed here showed that the reaction centres take up one of four possible orientations within the ring. This fourfold disorder supports our interpretation of a square ring symmetry and suggests that a hitherto undetected component may be present within the photosynthetic unit.     

Low-dose aberration corrected cryo-electron microscopy of organic specimens

Spherical aberration (C(s)) correction in the transmission electron microscope has enabled sub-angstrom resolution imaging of inorganic materials. To achieve similar resolution for radiation-sensitive organic materials requires the microscope to be operated under hybrid conditions: low electron dose illumination of the specimen at liquid nitrogen temperature and low defocus values. Initial images from standard inorganic and organic test specimens have indicated that under these conditions C(s)-correction can provide a significant improvement in resolution (to less than 0.16nm) for direct imaging of organic samples.     

Designing for Young Visitors’ Co-composition of Doubts in Cultural Historical Exhibitions

This paper reports from a design experiment that investigated how social media may introduce new types of participation in museum exhibitions. We used the perspectives of assemblage and co-composition as frameworks to rethink participation in museums. The design experiment's aim was to give visitors an experience of the uncertainties and doubts of historical knowledge creation by inviting visitors to participate in solving dilemmas and filling gaps in the reconstruction of a Viking boat. We introduced three design concepts in our lab-based exhibition experiment—collecting, reflecting and sharing—to capture the social interactions and collaborative media production that enacts the exhibition assembly. We conclude that visitors’ reflections may evolve through participatory activities of collecting and sharing, and social media may open possibilities for new types of interpretation and learning activities in museum exhibitions.     

Methodische Untersuchungen zur metallkundlichen Analyse mittels elektrochemischer Phasenisolation

Untersuchung von Ausscheidungsvorgängen in hochtemperatur-thermomechanisch und konventionell wärmebehandelten Stählen. Zielgrößen bei der Phasenisolation. Kriterien zur Auswahl der Elektrolysebedingungen und Zusammenhang mit der Carbidphasenausbeute.     

Theoretical and experimental evaluation of phase-dispersion effects caused by brain motion in diffusion and perfusion MR imaging

We investigated intravoxel phase dispersion caused by pulsatile brain motion in diffusion spin-echo pulse sequences. Mathematical models were used to describe the spatial and temporal velocity distributions of human brain motion. The spatial distribution of brain-tissue velocity introduces a phase spread over one voxel, leading to signal loss. This signal loss was estimated theoretically, and effects on observed diffusion coefficient and perfused capillary fraction were assessed. When parameters from a diffusion pulse sequence without motion compensation were used, and ECG triggering with inappropriate delay times was assumed, the maximal signal loss caused by brain-motion-induced phase dispersion was predicted to be 21%. This corresponds to a 95% overestimation of the diffusion coefficient, and the perfusion-fraction error was small. Corresponding calculations for motion-compensated pulse sequences predicted a 1% to 1.5% signal loss due to undesired phase dispersion, whereas experimental results indicated a signal loss related to brain motion of 4%.     

Novel processing,testing and characterization of copper/carbon nanotube (Cu/CNT) yarn composite conductor

Sustainable electrified aircraft propulsion (EAP) is likely to lead to an increase in the electrical wiring contained within a single aircraft. Since the electrical resistance and mass of copper (Cu) conductors are associated with power losses, it is desirable to design high-conductivity lightweight conductor materials, thus reducing the mass of components like motor windings, low-voltage signal cables, and transmission cables for data and power to improve the overall energy efficiency. This paper describes a unique framework for manufacturing metalized carbon nanotube (CNT) composite conductors, measuring their electrical conductivity and strength, and modeling the overall conductivity and current sharing within such composites. Tensile testing was conducted on the processed composite conductor cables with the use of acoustic emission and electrical resistivity to determine stress-dependent-failure mechanisms while monitoring the electrical conductivity. The average of measured electrical conductivities of annealed Cu/CNT samples from batch 5 was greater than theoretical predictions by 9.8 percent and was also greater than the conductivity of pure annealed Cu by 4.8 percent and had comparable ultimate tensile strengths. Additionally, those Cu/CNT samples provide a 13.5% weight saving over current state of the art copper wires. Theories explaining improved intrinsic conductivity are discussed.