Abstract: The development cost-effective life support technologies is a highly relevant topic for space biology. Currently, food and water supply during space flights is currently restricted by technical and economic constraints: daily water consumption of an average crew of 6 members is about 72 L, with an estimated cost of 2,160,000 d-1. To reduce these costs and sustain long term space missions, the European Space Agency designed MELiSSA, an artificial ecosystem based on 5 compartments for the recycling gas, liquid and solid waste (Lasseur et al., 2011). In the CI stage, crew and inedible solid waste is fermented by thermophilic anaerobic bacteria, producing volatile fatty acids (VFAs), CO2 and ammonium (NH4+). In the CII compartment the VFAs are converted into edible biomass, using the photoheterotroph Rodospirillum rubrum. Afterwards, the nitrifying CIII unit converts toxic levels of ammonia/ammonium into nitrate, which enables the effluent to be fed to the photoautotrohopic CIV stage, that provides food and oxygen for the crew (Godia et al., 2002). The highest nitrogen flux in a Life Support System is human urine. As nitrate is the preferred form of nitrogen fertilizer for hydroponic plant cultivation, urine nitrification is an essential process in the MELiSSA loop. The development of the Additional Unit for Water Treatment or Urine NItrification ConsortiUM (UNICUM) requires the selection and characterization of the microorganisms that will be used. The key microorganisms in the biological treatment of urine are heterotrophs, for the hydrolysis of urea into ammonia and carbon dioxide, Ammonia Oxidizing Bacteria (AOB), for the ammonia oxidation into nitrite and Nitrite Oxidizing Bacteria (NOB), for the conversion of nitrite into nitrate. The strains were selected according to predefined safety (non sporogenic and BSL 1) and metabolic (Ks, μmax) criteria. To evaluate functional consortia for space applications, ureolysis, nitritation and nitratation of the selected microorganisms and synthetic communities were elucidated. Additionally, urine is a matrix with a high salt content. Unhydrolised urine's EC ranges from 1.1 to 33.9 mS/cm, the mean value being 21.5 mS/cm (Marickar, 2010), while hydrolysed urine can reach higher levels, up to 75 mS/cm. This conditions could inhibit microbial metabolism, therefore the effect of salinity on urine nitrification was also elucidated.

Abstract: The present PhD research investigated the possibility of catalytic detoxification of poplar wood based and steam exploded lignocellulosic hydrolyzate with different types of laccase enzymes, with special focus on ethanol and lactic acid products at industrially relevant parameters: high final product concentration, high initial substrate loading and integrated processes. The simultaneous saccharification and fermentation (SSF) process was taken as a base case and five types of laccases were thoroughly investigated on their utilization potential. Phenolic removal from the liquid xylose rich fraction (XRF) was higher with fungal laccases (65-90 %) compared to approximately 30 % removal with bacterial laccase. Moreover, the optimal pH of fungal laccases was close to pH 4.5, the optimum for cellulase, while the bacterial laccase worked at basic pH. Integrating laccase treatment and hydrolysis together showed that fungal laccases have negative impact on final sugar concentration, while bacterial laccase had a strong positive effect. Although bacterial laccase removed less phenol and although its optimal conditions are difficult to integrate with hydrolysis, its enhancing effect on cellulase activity makes it a better candidate for application. The presence of the solid fraction (SF) alters the phenolic concentration evolution significantly, thus screening experiments with the liquid fraction alone do not provide sufficient information for the combined process. Magnetic Cross-Linked Enzyme Aggregates (m-CLEAs) immobilization was assessed for bacterial laccase. m-CLEAs decreased phenolic concentration faster at every pH compared to free bacterial laccase; however, the removal was caused by adsorption rather than by enzyme activity. Although the size of m-CLEAs particles are in the µm range, around 90 % of the initial catalyst mass was recycled from a dense (15 % substrate loading) mixture via magnetic separation. The high recycling rate is promising; m-CLEAs immobilization method can have industrial utilization potential. Minimum sugar revenue (MSR) estimations show that currently hardwood based MSR is 70 % more expensive than corn grain based MSR. About 7-10 fold cellulase activity increase will be needed until MSR will be competitive with corn grain MSR. However, m-CLEAs cellulase can already be competitive if the corn prices are in the higher regime of last year’s prices.

Abstract: Low-temperature plasma has received extensive attention due to its promising application prospects in the field of air pollutants degradation and energy conversion. To fulfill the need for particular applications, constructing stable plasma sources and investigating the interaction mechanisms between plasma and substances have been hot research topics. This thesis reports the diagnosis and improvement of plasma sources, diagnosis of the active species in plasma and a modeling study of chemical kinetics processes. The main research contents are as follows: In Chapter 3, a diffuse sine AC dielectric barrier discharge (DBD) is successfully obtained by optimizing the electrode structure. It is found that using double-layer dielectric plates can limit the discharge current intensity and significantly improve the discharge uniformity. The electrical characteristics and gas temperature with different operating time show that the discharge stability is also improved by using double-layer dielectric plates. In Chapter 4, nanosecond pulses are employed to generate diffuse DBD plasmas. Three main discharge stages are distinguished by ICCD images, i.e., the streamer breakdown from the needle tip to the plate electrode, the regime transition from streamer to diffuse plasma, and the propagation of surface discharge on the plate electrode surface. The chapter reveales that in nanosecond pulsed discharges the vibrational temperature of N2 increases with the discharge duration, while the rotational temperature mainly stays constant, which means electron energy is transferred into the vibrational levels, but gas heating is not obvious during the discharge pulse. In Chapter 5, both sine AC DBD and nanosecond pulsed DBD, studied in Chapter 2 and 3, are used for formaldehyde degradation. It is found that nanosecond pulsed DBD has more homogenous characteristics, better stability, and lower plasma gas temperature. Moreover, the energy consumption of nanosecond pulsed DBD is much lower than that of AC DBD. In Chapter 6, a 0D chemical kinetics model is developed to investigate the underlying plasma chemistry of methane dry reforming in a nanosecond pulsed discharge. An overview of the dominant reaction pathways of CO2 and CH4 conversion into the major products is given. Furthermore, most of the CO2 molecules are populated into vibrational states during the pulse. Hence, the vibrational states of CO2 play an important role in its dissociation process. In general, this PhD thesis contributes to a better insight in the mechanisms of sinusoidal AC DBD and nanosecond pulsed DBD plasmas and their applications, i.e., decomposition of formaldehyde and dry reforming of methane.

Abstract: Al-Zn-Mg-based high strength alloys are widely used in aerospace applications due to their low density and excellent mechanical properties. A systematic study of the structural evolution of the nano-precipitation phase and its growth mechanism is an important guide for the design of new high-strength alloys. In this work, the Laves structure precipitates in Al-Zn-Mg(-Cu/Y) alloy was systematically characterized. Based on the structure evolution, the structure of submicron Laves particles and quasicrystalline particles in the alloy at microscale, as well as the regulation of the precipitation behavior after adding Y at nanoscale were further investigated. The main innovative results are summarized as follows: (1) Investigation on coexistence of defect structures in Laves structural nanoprecipitates. Three types of Laves structures can coexist within the η-MgZn2 precipitates: C14, C15 and C36, and the Laves structure transition sequence of C14→C36→C15 in this system was determined. Meanwhile, it was found that there are diverse defect structures in the MgZn2 phase, including stacking faults, planar defects and five-fold domain structures, which have significant effects on relieving the internal stress/strain of the precipitates. (2) Investigation on multiple phase transition of Laves structural nanoprecipitates from C14 to C36 and from C14 to quasicrystal clusters. It is found that C14 precipitates can be completely transformed into the C36 precipitates. And it is also found that the C14 Laves phase structure can also transform into quasicrystalline clusters. These investigations on various phase transition mechanisms among Laves phases provide theoretical support for the microstructural characterization of materials containing multi-scale Laves phases. (3) Characterization of Laves and quasicrystal structural particles in submicron scale. Submicron-scale quasicrystal particles were obtained in conventional casting Al-Zn-Mg-Cu alloys for the first time. Industrial impurity elements Fe and Ni can induce the formation of quasicrystalline particles. When there is no Fe/Ni enriched in particles, the structure is characterized as C15-Laves phase. When Fe/Ni is as quasicrystalline core, a stable core-shell quasicrystalline structure with Al-Fe-Ni nucleus and Mg-Cu-Zn shell can be formed. (4) Investigation on the regulation of nanoscale Laves precipitates’ growth. To regulate the defect structure of the precipitates, rare earth element Y was added in Al-Zn-Mg alloys and its influence on the precipitation behavior was investigated. The addition of Y element can dynamically combine with different alloying elements during aging process, which can refine the size of precipitate and further improve the nucleation rate and precipitation rate of the precipitates.

Abstract: Laser microprobe mass analysis was applied to study the chemical composition of spheroliths in the Bowman's membrane of patients suffering from primary atypical bandkeratopathy. The inclusions appear to consist mainly of calcium phosphate.

Abstract: This chapter provides a description of colour changes in the Amsterdam Sunflowers due to chemical alteration of pigments, with a focus on geranium lakes and chrome yellows. The brilliant and forceful colours of these and other late nineteenth-century synthetic materials offered artists such as Vincent van Gogh new means of artistic expression that exploited a range of contrasting hues and tints. However, geranium lakes have a strong tendency to fade and chrome yellows to darken under the influence of light. Van Gogh, like other artists of his day, was aware of this drawback, yet he continued to favour the use of both pigments up until his death in July 1890 due to the unparalleled effects they gave. In April 1888, Vincent wrote to his brother Theo: Van Gogh's use of unstable colours opens a series of questions regarding the extent to which colour change affects the way his paintings look today, as discussed here in relation to the Amsterdam Sunflowers. Furthermore, given the frequency with which geranium lakes and chrome yellows occur in Van Gogh's paintings of the period 1888–90 and the predominance of chrome yellows in Sunflowers, it becomes important to understand the factors that can drive these processes of deterioration in order to develop appropriate strategies for conserving the artist's works.