Fumier sequences play a primary role in the study of livestock management and the use of space in prehistoric pastoralist societies. These sequences are formed when dung accumulated in sheepfold... Show moreFumier sequences play a primary role in the study of livestock management and the use of space in prehistoric pastoralist societies. These sequences are formed when dung accumulated in sheepfold caves and rock shelters is burnt, resulting in an overlapping of burnt and unburnt sedimentary layers. Thus, fire is a key taphonomic agent in the formation and alteration of fumier sequences.The characteristics, functions, and management of burning events influence the preservation of the macro- and micro-remains potentially biasing the interpretation of the archeological record. Therefore, it is important to understand the taphonomic effects of fire in fumier sequences.In this chapter, we use a multi-scalar and interdisciplinary approach to the study of burning events at El Mirador cave. We analyzed the phytolith, fecal spherulites, pollen, non-pollen palynomorphs (NPP), and parasite remains in the fumier sequence, together with the mineral (FTIR) and magnetic properties of the sediments. In addition, we studied the effects of fire on the macrofaunal assemblages. The results obtained here provide the basis for a tapho-diagenetic framework that illustrates robustly the formation dynamics of the El Mirador fumier sequences. Show less
Astronomical observations of cold regions in the universe show a rich inventory of ices. Part of these ices may end up on planets like our own, but in that journey they will be exposed to... Show moreAstronomical observations of cold regions in the universe show a rich inventory of ices. Part of these ices may end up on planets like our own, but in that journey they will be exposed to considerable amounts of radiation. As water is the main component of these ices, the optical and photochemical properties of water ice largely determine how the radiation affects the molecules embedded in the ice. In this thesis, water ice is investigated as a host for photochemical reactions. A new laboratory setup is constructed, and two types of molecules are studied: glycine, an amino acid, and triphenylene, a polycyclic aromatic hydrocarbon. The photochemistry upon exposure to ultraviolet radiation is studied using UVvis and infrared spectroscopy. In addition, the optical properties of water ice are constrained in the UV-vis range, resulting in high-resolution optical constants, relevant for all ice-rich environments - from far away in space to our atmosphere. Water itself does not absorb light in this range, but as most organic molecules do, and are destroyed by radiation in this range, this is of high importance for molecules within the ice. Show less
In this thesis we have discussed several parameters that affect the electrochemical conversion of enviromentaly harmful molecules such as nitrates and carbon dioxide to more valuable and less... Show moreIn this thesis we have discussed several parameters that affect the electrochemical conversion of enviromentaly harmful molecules such as nitrates and carbon dioxide to more valuable and less deleterious compounds, in order to cast light onto the mechanism of the reaction to achieve an efficient and selective system.The thesis is divided in two main parts, the reduction of nitrates(chapter 2) and the mechanistic study of CO2 conversion to different products such as ethanol(chapter 3), ethylene(chapters 4 and 5) and propylene carbonate (chapter 6). Show less
Reidsma, F.H.; Hoesel, A. van; Os, B.J.H. van; Megens, L.; Braadbaart, F. 2016
The stratum corneum (SC), the thin uppermost layer of the skin, consists of dead flattened skin cells (corneocytes) embedded in a lipid matrix. The lipid matrix is considered to play a crucial role... Show moreThe stratum corneum (SC), the thin uppermost layer of the skin, consists of dead flattened skin cells (corneocytes) embedded in a lipid matrix. The lipid matrix is considered to play a crucial role in the skin barrier function. It consists of ceramides (CER), cholesterol (CHOL) and free fatty acids (FFA) forming crystalline lipid lamellae. From studies with native SC and SC lipid models much information has been gained on the phase behavior of the SC lipid matrix. However, little is known about the correlation between SC lipid organization and the permeability of the SC. This is difficult to investigate using native SC, due to its complex structure. Therefore SC lipids were casted on a porous membrane, resulting in a lipid organization and lamellar orientation similar to that in SC. This lipid membrane is referred to as the stratum corneum substitute (SCS). The SCS can be used to perform diffusion studies. Therefore, when modifying the lipid composition and thus the lipid organization in the SCS, it is possible to study the relationship between lipid organization and permeability. The main objectives of this thesis are 1) to investigate the influence of lipid organization on the barrier function in the SCS and 2) to obtain insights in the molecular organization within the unit cell of the lamellar phases in SC. Show less
The G protein coupled receptor rhodopsin was characterised by physical chemical methods like solid-state NMR, FTIR and UV/Vis spectroscopy. Goal of the research was to determine the impact of... Show moreThe G protein coupled receptor rhodopsin was characterised by physical chemical methods like solid-state NMR, FTIR and UV/Vis spectroscopy. Goal of the research was to determine the impact of steric and electronic properties of the retinal ligand on the rate and efficiency of the photochemical reaction of this light activated receptor. First the required 13C labelled and chemically modified retinal derivatives were obtained by chemical synthesis. Subsequently, solid-state 13C NMR was used as a tool to characterise the electronic structure of the native ligand bound to rhodopsin, while FTIR difference spectroscopy was applied to determine the effect retinal ligands that were modified in the isomerisation region. It transpires that the combined approach of synthesis and spectroscopic techniques can reveal fundamental aspects of the interplay of the electronic properties and the spatial arrangement of the ligand that may ultimately allow a more profound understanding of the activation of GPCRs, in addition to knowledge about the ultrafast and efficient isomerisation of the retinylidene chromophore in rhodopsin Show less
