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Bursts of X‐rays and γ‐rays are observed from lightning and laboratory sparks. They are bremsstrahlung from energetic electrons interacting with neutral air molecules, but it is still unclear how the electrons achieve the required energies. It has been proposed that the enhanced electric field of streamers, found in the corona of leader tips, may account for the acceleration; however, their efficiency is questioned because of the relatively low production rate found in simulations. Here we emphasize that streamers usually are simulated with the assumption of homogeneous gas, which may not be the case on the small temporal and spatial scales of discharges. Since the streamer properties strongly depend on the reduced electric field E/n, where n is the neutral number density, fluctuations may potentially have a significant effect. To explore what might be expected if the assumption of homogeneity is relaxed, we conducted simple numerical experiments based on simulations of streamers in a neutral gas with a radial gradient in the neutral density, assumed to be created, for instance, by a previous spark. We also studied the effects of background electron density from previous discharges. We find that X‐radiation and γ‐radiation are enhanced when the on‐axis air density is reduced by more than ∼25%. Pre‐ionization tends to reduce the streamer field and thereby the production rate of high‐energy electrons; however, the reduction is modest. The simulations suggest that fluctuations in the neutral densities, on the temporal and spacial scales of streamers, may be important for electron acceleration and bremsstrahlung radiation., Key Points Air perturbations significantly increase the velocity of streamer frontsAir perturbations facilitate the emission of X‐rays from streamer dischargesPre‐ionization moderately lowers the maximum energy of electrons and photons

Copper and cast iron are potential materials for the storage canisters of high-level radioactive waste. We designed slurry-experiments for analyzing the microbial influence on the corrosion process of these metals. These slurry experiments contain the Bavarian B25 bentonite, synthetic Opalinus Clay pore water or diluted cap rock solution as well as copper- or cast iron plates in various combinations. During an incubation time of 400 days under anaerobic conditions at 37 °C cast iron plates corrode very fast. The respective metal surfaces show the formation of iron oxides and –carbonates which could form a passivating film that protects the cast iron from further corrosion.

Every year 12,000 metric tonnes of high-level radioactive waste (HLW) are produced worldwide. For the long-term storage of this highly radiotoxic waste, a deep geological disposal by using multiple barriers is favored. Bentonite is proposed as a potential material for sealing the space between the canister containing the HLW and the surrounding host rock. In order to investigate the microbial diversity and metabolic activity of naturally occurring microorganisms as well as their time-dependent evolution, we conducted anaerobic microcosm experiments containing bentonite and a synthetic Opalinus Clay pore water solution. During the one-year incubation at 30 and 60 °C, lactate- or H2-stimulated microcosms at 30 °C showed the dominance and activity of strictly anaerobic, sulfate-reducing and spore-forming microorganisms. The subsequent generation of hydrogen sulfide gas in the respective set ups, led to the formation of fractures and iron-sulfur precipitations. In microcosms that incubated at 60 °C, thermophilic bacteria dominated, independent from the availability of substrates. In the respective microcosms, no significant metabolic activity was detected and there was no change in the analyzed bio-geochemical parameters. Our results show that indigenous microorganisms evolve in a temperature- and substrate-dependent manner. Potentially formed metabolites could affect the dissolution behavior of minerals and ions within the bentonite as well as the corrosion process of the canister material and require further investigations.

37th European Photovoltaic Solar Energy Conference and Exhibition; 482-486, Passivated contacts that use polysilicon on oxide (POLO) show outstanding electrical surface passivation of silicon. However, the parasitic absorption of photons within highly doped poly-Si layer confines its implementation to the rear side silicon solar cells or locally under the front metal contacts. Here, we demonstrate that by irradiating the poly-Si with UV ps-laser pulses, it becomes selectively etch resistant in a KOH solution, due to a laser-induced amorphization of the surface of the poly-Si layer. This poses a low-effort method to structure poly-Si layers with a resolution of the spot size of 25 μm and thus facilitates the implementation as local (front) contacts. We explore the impact of the laser fluence, the gas ambient and the surface morphology (planar and textured) on the surface passivation quality of the so obtained poly-Si layers. The laser-modified and structured poly-Si sample reaches implied open-circuit voltage values of iVoc = 722 mV (planar) and thus the same passivation quality as the non-lasered reference, and iVoc = 680 mV for textured surfaces. A hydrogenation step improves the iVoc of the textured surfaces to 726 mV, which corresponds to a recombination current density of 5 fA/cm2.

The Satellite Research Centre at Nanyang Technological University is currently developing the Atmospheric Coupling and Dynamics Explorer (ARCADE) Mission, which is flying a hall effect thruster to progressively lower the altitude from an initial 500 km to 250 km. ARCADE is also the fourth satellite in the INSPIRE (International Satellite Program in Research and Education) satellite series with joint development from IIST, India and NCU, Taiwan. ARCADE is a 27U spacecraft carrying an ionospheric plasma payload which will make ion temperature, velocity, density and electron temperature measurements. The satellite will be launched along with six other Singaporean satellites on a Singapore dedicated PSLV in 2020 into a near equatorial orbit. Since the final altitude is expected to be 250 km, the ARCADE/INSPIRESat-4 mission provides an excellent opportunity to study the equatorial ionosphere at low altitudes where the ion and electron density are much higher. The mission is expected to provide new information on plasma irregularities along the magnetic equator. The mission is also a technology demonstration of a hall effect thruster developed by French Startup 'Thrust Me'. Another addition to the mission is a Spatial Heterodyne Interferometer Infra-Red Imager for imaging the Mesosphere and Lower thermosphere region between 60-120 km. The SHI instrument will provide temperature information and help for understanding the dynamics of the equatorial MLT region. The presentation will cover the teams approaches to dealing with Very Low Earth Orbit (VLEO) and the challenges it poses in terms of thermal and atomic oxygen effects.

The Atmosphere-Space Interactions Monitor (ASIM) was launched to the International Space Station (ISS) on April 2, 2018. The ASIM payload consists of two main instruments, the Modular X- and Gamma-ray Sensor (MXGS) for imaging and spectral analysis of Terrestrial Gamma-ray Flashes (TGFs) and the Modular Multi-spectral Imaging Array (MMIA) for detection, imaging and spectral analysis of Transient Luminous Events (TLEs) and lightning. ASIM is the first space mission designed for simultaneous observations of TLEs, TGFs and optical lightning. During the first ten months of operation (June 2, 2018 to April 1, 2019) the MXGS has observed 217 TGFs. In this paper we report several unprecedented measurements and new scientific results obtained by ASIM during this period: 1) simultaneous TGF observations by Fermi Gamma-ray Burst Monitor (GBM) and ASIM MXGS revealing the very good detection capability of ASIM MXGS and showing substructures in the TGF, 2) TGFs and Elves produced during the same lightning flash and even simultaneously have been observed, 3) first imaging of TGFs giving a unique source location, 4) strong statistical support for TGFs being produced during the upward propagation of a leader just before a large current pulse heats up the channel and emits a strong optical pulse, and 5) the t50 duration of TGFs observed from space is shorter than previously reported.

3‐D‐Druck kombiniert mit einer Atmosphärendruck‐Gasphasenabscheidungsquelle erlaubt, Beschichtungen mit funktionellen Gruppen auf Polymerbauteilen aufzutragen. Hierdurch lässt sich die Adhäsion steuern.

Nach einer Atmosphärendruck-Plasmabehandlung auf 3D-gedruckten Polymeroberflächen mit einem Plasmajet, können hierauf Beschichtungen mit funktionelle Gruppen erzeugt werden. Hierdurch ist es möglich, weitere Materialien (Polymere, Metalle, keramische Materialien) an die Polymeroberflächen haftfest anzukoppeln, wodurch neue Funktionen der 3D-gedruckten Bauteile erzeugt werden können. In dem internationalen EU-Projekt Fast wird diese Technik genutzt, um das Zellwachstum auf medizinischen Polymerimplantaten zu verbessern.

In dieser Arbeit wird die Herstellung optischer Interferenzfilter auf Polymerfolien zur spektralen Kanaltrennung in der 3D-Projektion vorgestellt. Hierzu wurde zunächst die Eignung verschiedener Polymersubstrate durch Messungen der Schichthaftung und der Lichtstreuung untersucht. Hierauf basierend ermöglichten Optimierungen des Energieeintrages bei der Schichtabscheidung und des optischen Schichtdesigns die Abscheidung von optischen Interferenzfiltern zur spektralen Kanaltrennung auf PET-Polymerfolien. Mit diesen Filtern konnten funktionsfähige 3D-Brillen hergestellt werden. Darüber hinaus wird auf die Verwendung von Gradientenfiltern zur Kompensation des spektralen Shifts durch verschiedene Blickwinkel durch den Filter sowie auf die Prozessierung der Filterfolien eingegangen.