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An adaptive learning strategy for surrogate modeling of high-dimensional functions - Application to unsteady hypersonic flows in chemical nonequilibrium
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UnitCellSAED − An ImageJ-Based Tool for Determining Unit Cell Parameters from Selected Area Electron Diffraction Patterns
No full textCrosslinked (poly)vinylamine copolymers
No full textThis thesis deals mainly with the polymerization of N-Vinylamides and their subsequent gelation. Therefore, free amines are generated by hydrolysis of the pre-polymers, which are subsequently crosslinked by carbonate-based crosslinkers. Moreover, a method is presented to decorate inert surfaces with primary amin groups by nitren insertion. While Gels based on acrylamide, a constitution isomer of N-vinylformamide (NVF), is subject of manifold literature, examples of gel systems based on NVF are scarce. Nevertheless, gel systems based on NVF have the advantage of a (tailored) number of free primary amine groups via simple hydrolysis. Primary amine groups can be further functionalized by numerous reactions to gain specific properties, e.g. cell binding sequences. Thus, PVAm based gels can find entrance in medical applications. In general, the attractiveness of PVAm based systems is caused by the tailorable number of primary amine groups which in turn influence properties such as charge density/pH responsiveness, crosslinking density, hydrophilicity, etc. However, a direct polymerization to poly(Nvinylamine) (PVAm) is not possible, since the respective monomer, vinyl amine, is not stable. Therefore at least two step synthesis is necessary including a hydrolysis step. In Chapter 2, the latest methods are summarized to synthesize PVAm, especially with focus to defined molecular weights and a low polydispersity index. Moreover, methods are introduced to obtain thermoresponsive copolymers of polyvinlamide/PVAm. It is demonstrated how the lower critical solution temperature (LCST) can be tailored by the molar fraction of VAm or NVF with different co-monomers. The second part of Chapter 2 deals with the different gelation methods of PVAm. The synthesis of the gels is on the one hand discussed via an insitu gelation in the presence of a crosslinker during the polymerization with subsequent hydrolysis and on the other hand via the formation of prepolymers which are hydrolyzed and subsequently crosslinked via the free amine groups. Furthermore, thermoresponsive gels are presented. In Chapter 3 the copolymerization of NVF with N-vinylacetamide (NVA) is shown. The copolymerization parameters of both monomers reveals a statistical distribution. Further show the kinetics and the selectitivity of the hydrolysis with respect to NVF and NVA that NVF is hydrolyzed completely under defined conditions. The amin-functional prepolymers are crosslinked by phenylcarbonate telechelic poly(ethylene glycol) (PEG-PC) in presence of a base. The formed hydrogels are characterized by their swelling ratio and rheological ixproperties in dependence on the concentration of primary amines, the concentration of the base, and the concentration of the crosslinker. It is shown that with this gel system very high swelling ratios can be realized. In absence of a base leads the electrostatic interaction between the urethane groups to physical crosslinking. These are discussed in Chapter 4. The critical gelation concentration is determined via rheology. The physical interactions were examined by NMR and UV-Vis spectroscopy. Furthermore, it is shown, that the fast gelation leads to inhomogenities, which could be cured by subsequent heating/cooling cycles as revealed by a significant increase of the storage modulus. A possible chemical crosslinking-reaction is ruled out by NMR. In chapter 5 thermoresponsive copolymers and hydrogels are prepared. Therefore, NVF is copolymerized with N-isopropylacrylamide (NIPAm) und subsequently hydrolyzed. The copolymerization parameters reveal a slightly faster polymerization of NVF, which means within a polymer chain there is a gradient from a NVF rich to a NVF poor regime. NMR shows, that NVF can be selectively hydrolyzed under defined conditions. The LCST can be tailored via the ratio of NVF to NIPAm, what is shown in rheology and UV-Vis spectroscopy. The gelation via 1,2-bis(phenylcarbonate)-ethylene glycol yields in thermoresponsive hydrogels. These are characterized by NMR, UV-Vis spectroscopy, and rheology. A two-state model is applied to describe the phase transition. In Chapter 6 the surface of chemically inert foils, that means polymethyl-1-penten (TPX), poly(vinylidene fluorid) (PVDF), and poly(tetrafluoro ethylene) (PTFE) are functionalized with a thin hydrogel layer. Therefore a copolymer based on PVAm is functionalized with Nsuccinimidyl-4-azidotetrafluoro benzoate. The azide reacts to a highly reactive nitrene under UV light. These nitrenes can insert in e.g. a C-H bond leading to a stable covalent binding to the aliphatic and surprisingly also PTFE surfaces. Thorough investigations of the wetting behavior of the treated surfaces show, that the surfaces are hydrophilized. Dynamic contact angle measurements with the Wilhelmy balance suggest that the polymerchains can reorientate, which means that the hydrophobic polymer backbone is directed to the outside while in contact with air turning to the inside while in contact with water. This process is reversible. Consequently, the treated surfaces are amphiphile. This work might be the base to functionalize chemically inert surfaces to combine e.g. the mechanical properties of PTFE with cell recognition sequences, growth factors, drugs, and so on and so forth
Untersuchungen zum thermochemischen Zersetzungsverhalten von Carbonfasern in Kohlenstoffdioxidatmosphäre
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Experimental Dataset: Experimental investigation of 40 kWth methane-assisted and self-sustained pulverized biomass flames
No full textThis data publication contains the quantitative values of the narrow-band imaging and laser Doppler velocimetry measurements published in the journal article ”Experimental investigation of 40kWth methane-assisted and self-sustained pulverized biomass flames”. Experiments are carried out using a pilot-scale down-fired cylindrical combustion chamber equipped with a swirl burner. Studied operating conditions of the flames of biomass/methane fuel mixtures have an identical thermal output of 40kWth, with the thermal output share of methane gradually decreasing from 50 vol.% to 0 vol.% while the biomass share (walnut shells) increased from 50 vol.% to 100 vol.% (self-sustained condition). To visualize flame structure and to identify reaction zones, narrow-band imaging is employed. Narrowband flame imaging is conducted at two different wavelengths (OH* and CH* radical band heads). A detailed flow field characterization of the respective flames is conductedby two-dimensional laser Doppler velocimetry measurements. Radial profiles of axial and tangential velocities have been determined using an optical long-range laser Doppler velocimetry (LDV) system operated in backscatter mode and mounted to a traverse. Solid fuel particles are used as flow tracers. Results and the experimental conditions from the present dataset are in depth described in the journal article
