Experimenting with concentrated sunlight using the DLR solar furnace

The high flux solar furnace that is operated by the Deutsche Forschungsanstalt für Luft- und Raumfahrt (DLR) at Cologne was inaugurated in June 1994 and we are now able to look back onto one year of successful operation. The solar furnace project was founded by the government of the State Northrhine Westfalia within the Study Group AG Solar. The optical design is a two-stage off-axis configuration which uses a flat 52 m² heliostat and a concentrator composed of 147 spherical mirror facets. The heliostat redirects the solar light onto the concentrator which focuses the beam out of the optical axis of the system into the laboratory building. At high insolation levels (>800 W/m²) it is possible to collect a total power of 20 kW with peak flux densities of 4 MW/m². Sixteen different experiment campaigns were carried out during this first year of operation. The main research fields for these experiments were material science, component development and solar chemistry. The furnace also has its own research program leading to develop sofisticated measurement techniques like remote infrared temperature sensing and flux mapping. Another future goal to be realized within the next five years is the improvement of the performance of the furnace itself.     

Spatial Input for Temporal Navigation in Scientific Visualizations

Scientific-visualization tools can make time-varying simulations easier to understand. The growing efficiency of today's high-performance computers enables simulation of physical phenomena with a high temporal resolution. Consequently, visualization systems require efficient navigation in the temporal dimension. This 3D user interface employs direct-manipulation metaphors for temporal navigation in scientific visualizations. By interacting with objects using their 3D trajectory, users can navigate in time by specifying spatial inputs. This article is part of a special issue on 3D user interfaces.     

Bildung von oxydischen Einschlüssen in halbberuhigtem Stahl

Untersuchung von 20-t-Blöcken mit unterschiedlichen Aluminiumzugaben für die Feindesoxydation während der Erstarrung in der Kokille. Oberflächenfehler von halbberuhigtem Stahl. Bildung von oxydischen Einschlüssen dicht unter der Blockoberfläche und im Blockinnern. Maßnahmen zur Beeinflussung der Einschlußausbildung.     

On a method for model structure selection in system identification

Bohlin has recently suggested an appealing method for model structure selection. It is shown that the method can be interpreted as a modified F-test. The minimal loss in a larger model structure is substituted by an estimate. The estimate is obtained by minimization of a quadratic approximation of the loss function.     

Polyplexes of polyethylenimine and per-N-methylated polyethylenimine-cytotoxicity and transfection efficiency

For non-viral gene delivery, the carriers for DNA transfer into cells must be vastly improved. The branched cationic polymer polyethylenimine has been described as an efficient gene carrier. However, polyethylenimine was demonstrated to mediate substantial cytotoxicity. Therefore, this study is aimed at investigating per-N-methylated polyethylenimine, which is thought to have a much lower cytotoxicity due to its lower charge density. Results from a gel retardation assay and laser light scattering indicated that per-N-methylated polyethylenimine condenses DNA into small and compact nanoparticles with a mean diameter <150 nm. Furthermore, polyplexes of polyethylenimine and per-N-methylated polyethylenimine with DNA had a positive zeta potential and the polymers protected DNA from nuclease-mediated digestion. The transfection efficiency of polyethylenimine and per-N-methylated polyethylenimine was tested in CHO-K1 cells. Using green fluorescent protein as reporter gene and flow cytometry analysis, we demonstrated that per-N-methylated polyethylenimine has a lower cytotoxicity, but also a significantly lower transfection efficiency. Using propidium iodide staining, we could additionally distinguish between viable and dead cells. At NP > or = 12, per-N-methylated polyethylenimine showed a much higher cell viability and the ratio of viable and transfected cells to dead and transfected cells was about 1.5 to 1.7 fold higher than for polyethylenimine. The results of cell viability from flow cytometry analysis were confirmed by the MTS assay. Using luciferase reporter gene for transfection experiments, the gene expression of per-N-methylated polyethylenimine was lower at NP 6, 12 and 18 as compared to polyethylenimine, but at NP 24 it yielded similar levels.     

High-power deuterium Raman laser at 632 nm

We demonstrate a continuous-wave deuterium Raman laser that generates more than 160 mW of Stokes output power despite severe thermal effects. This output power represents nearly an order-of-magnitude increase over any previously reported continuous-wave Raman laser and is the first such system to our knowledge that uses deuterium gas as the Raman medium. The high output power is achieved through careful consideration of the electronic feedback design, frequency actuators, and pump-laser intensity noise.