Polyorthoesters and analogues from a cyclic ketene acetal as surface-erodible materials in additive manufacturing and elastomer fabrication

Motivated by the advantageous rapid surface-erosion behaviour but problematic manufacturing of pure polyorthoesters (POE), in this thesis, the synthesis and manufacturing of poly(orthoester-thioether) (POETE) materials from stable orthoester (OE) monomers via thiol-ene Michael addition are described. Initially, a variety of novel OE compounds was synthesised and comprehensively characterised, followed by UV-initiated thiol-ene coupling with a selection of thiols. The full scope of OE-TE compounds ranged from small molecules over POETE polymer chains and networks, to the use of POETEs as soft segments in polyurethanes (PUs).Subsequently, chromatographic, spectroscopic and microscopic, as well as thermo-mechanical analyses were performed in order to facilitate conclusions on the structure/composition-function relationship, as well as to further investigate the degradation process. Chapter 1 provides an introduction into the importance, synthesis and degradation properties of polymers like POEs and elastomers such as polyurethanes (PUs), as well as principles of rapid additive manufacturing to process polymers for direct application, as used in the rest of the work. Chapter 2 details the synthesis of simple OEs, acetals (ATs) and the respective thioethers (TEs) in the form of small molecules and chain polymers, including their comprehensive spectroscopic and chromatographic analysis. The method is then used to produce a strong network material, on which subsequent surface erosion behaviour is documented and degradation products investigated. Chapter 3 offers an overview of a library of new OE monomers and their spectroscopic properties, as well as comprehensively displays the thermo-mechanical properties of a variety of network materials obtained by crosslinking the OEs with multifunctional thiols. In addition, the results of 3D printing, degradation and cytocompatibility studies are presented. Chapter 4 introduces a strategy to manufacture poly(thio-urethanes) from POETE oligomers and demonstrates that hydrolytically degradable, strong and elastic, glassy and semi-crystalline materials can be obtained. Chapter 5 summarises the work reported in Chapters 2 to 4 and advises on future perspectives, optimisations and potential applications

A novel inactivated virus system (InViS) for a fast and inexpensive assessment of viral disintegration.

The COVID-19 pandemic has caused considerable interest worldwide in antiviral surfaces, and there has been a dramatic increase in the research and development of innovative material systems to reduce virus transmission in the past few years. The International Organization for Standardization (ISO) norms 18,184 and 21,702 are two standard methods to characterize the antiviral properties of porous and non-porous surfaces. However, during the last years of the pandemic, a need for faster and inexpensive characterization of antiviral material was identified. Therefore, a complementary method based on an Inactivated Virus System (InViS) was developed to facilitate the early-stage development of antiviral technologies and quality surveillance of the production of antiviral materials safely and efficiently. The InViS is loaded with a self-quenched fluorescent dye that produces a measurable increase in fluorescence when the viral envelope disintegrates. In the present work, the sensitivity of InViS to viral disintegration by known antiviral agents is demonstrated and its potential to characterize novel materials and surfaces is explored. Finally, the InViS is used to determine the fate of viral particles within facemasks layers, rendering it an interesting tool to support the development of antiviral surface systems for technical and medical applications

Joint Analysis of near-infrared properties and surface brightness fluctuations of LMC star clusters

Surface brightness fluctuations have been proved to be a very powerful technique to determine the distance and characterize the stellar content in extragalactic systems. Nevertheless, before facing the problem of stellar content in distant galaxies, we need to calibrate the method onto nearby well-known systems. In this paper we analyze the properties at $J$ and $K_s$ bands of a sample of 19 star clusters in the Large Magellanic Cloud (LMC), for which accurate near-infrared (NIR) resolved star photometry, and integrated photometry are available. For the same sample, we derive the SBF measurements in $J$ and $K_s$-bands. We use the multi-purpose stellar population code \emph{SPoT (Stellar POpulations Tools)} to simulate the color-magnitude diagram, stellar counts, integrated magnitudes, colors, and surface brightness fluctuations of each cluster. The present procedure allows us to estimate the age and metallicity of the clusters in a consistent way, and provides a new calibration of the empirical $s$-parameter. We take advantage of the high sensitivity of NIR surface brightness fluctuations to thermally pulsing asymptotic (TP-AGB) stars to test different mass-loss rates affecting the evolution of such stars. We argue that NIR-SBFs can contribute to the disentangling of the observable properties of TP-AGB stars, especially in galaxies, where a large number of these stars are present.Comment: 25 pages, 12 figures, 4 tables, Accepted for publication in Ap

Radiative transfer in disc galaxies II - The influence of scattering and geometry on the attenuation curve

We investigate the influence of scattering and geometry on the attenuation curve in disc galaxies. We investigate both qualitatively and quantitatively which errors are made by either neglecting or approximating scattering, and which uncertainties are introduced due to a simplification of the star-dust geometry. We find that the magnitude of these errors depends on the inclination of the galaxy, and in particular that for face-on galaxies, the errors due to an improper treatment of scattering dominate those due to an imprecise star-dust geometry. Therefore we argue that in all methods which aim at determining the opacity of disc galaxies, scattering should be taken into account in a proper way.Comment: 13 pages, 8 figures, accepted for publication in MNRA

Post-AGB stars in the SMC as tracers of stellar evolution: the extreme s-process enrichment of the 21 micrometer star J004441.04-732136.4

By virtue of their spectral types, favourable bolometric corrections as well as their constrained distances, post-AGB stars in external galaxies offer unprecedented tests to AGB nucleosynthesis and dredge-up predictions. We focus here on one object J004441.04-732136.4, which is the only known 21 micrometer source of the SMC. Spectral abundance results reveal J004441.04-732136.4 to be one of the most s-process enriched objects found up to date, while the photospheric C/O ratio of 1.9 +- 0.7, shows the star is only modestly C-rich. J004441.04-732136.4 also displays a low [Fe/H] = -1.34 +- 0.32, which is significantly lower than the mean metallicity of the SMC. From the SED, a luminosity of 7600 +- 200 solar luminosities is found, together with E(B-V) = 0.64 +- 0.02. According to evolutionary post-AGB tracks, the initial mass should be approximately 1.3 solar masses. The photometric variability shows a clear period of 97.6 +- 0.3 days. The detected C/O as well as the high s-process overabundances (e.g. [Y/Fe] = 2.15, [La/Fe] = 2.84) are hard to reconcile with the predictions. The chemical models also predict a high Pb abundance, which is not compatible with the detected spectrum, and a very high 12C/13C, which is not yet constrained by observations. The predictions are only marginally dependent on the evolution codes used. We show that our theoretical predictions match the s-process distribution, but fail in reproducing the detected high overabundances and predict a high Pb abundance which is not detected. Additionally, there remain serious problems in explaining the observed pulsational properties of this source.Comment: 15 pages, 18 figures, accepted for publication in A&A Main Journa

Action planning with two-handed tools

In tool use, the intended external goals have to be transformed into bodily movements by taking into account the target-to-movement mapping implemented by the tool. In bimanual tool use, this mapping may depend on the part of the tool that is operated and the effector used (e.g. the left and right hand at the handle bar moving in opposite directions in order to generate the same bicycle movement). In our study, we investigated whether participants represent the behaviour of the tool or only the effector-specific mapping when using two-handed tools. In three experiments, participants touched target locations with a two-jointed lever, using either the left or the right hand. In one condition, the joint of the lever was constant and switching between hands was associated with switching the target-to-movement-mapping, whereas in another condition, switching between hands was associated with switching the joint, but the target-to-movement-mapping remained constant. Results indicate pronounced costs of switching hands in the condition with constant joint, whereas they were smaller with constant target-to-movement mapping. These results suggest that participants have tool-independent representations of the effector-specific mappings

Kinematics of elliptical galaxies with a diffuse dust component - III. A Monte Carlo approach to include the effects of scattering

This paper is the third one in a series, intended to investigate how the observed kinematics of elliptical galaxies are affected by dust attenuation. In Paper I and Paper II, we investigated the effects of dust absorption; here we extend our modelling in order to include the effects of scattering. We describe how kinematical information can be combined with the radiative transfer equation, and present a Monte Carlo code that can handle kinematical information in an elegant way. Compared to the case where only absorption is taken into account, we find that dust attenuation considerably affects the observed kinematics when scattering is included. For the central lines of sight, dust can either decrease or increase the central observed velocity dispersion. The most important effect of dust attenuation, however, is found at large projected radii. The kinematics at these lines of sight are strongly affected by photons scattered into these lines of sight, which were emitted by high-velocity stars in the central regions of the galaxy. These photons bias the LOSVDs towards high line-of-sight velocities, and significantly increase the observed velocity dispersion and LOSVD shape parameters. These effects are similar to the expected kinematical signature of a dark matter halo, such that dust attenuation may form an alternative explanation for the usual stellar kinematical evidence for dark matter halos around elliptical galaxies. We apply our results to discuss several other topics in galactic dynamics, where we feel dust attenuation should be taken into account. In particular, we argue that the kinematics observed at various wavelengths can help to constrain the spatial distribution of dust in elliptical galaxies.Comment: 21 pages, 10 figures, accepted for publication in MNRA

Dust Formation In Early Galaxies

We investigate the sources and amount of dust in early galaxies. We discuss dust nucleation in stellar atmospheres using published extended atmosphere models, stellar evolution tracks and nucleation conditions and conclude that the (TPAGB) phase of intermediate mass stars is likely to be the most promising site for dust formation in stellar winds. The implications of chemical evolution models for high redshift galaxies are investigated and we show there is no difficulty in producing dusty galaxies at redshifts above 5 if supernovae are a dominant source of interstellar dust. If dust does not condense efficiently in SNe then significant dust masses can only be generated at by galaxies with a high star formation efficiency. We find the visual optical depth for individual star forming clouds can reach values greater than 1 at very low metallicity (1/100 solar) provided that the mass-radius exponent of molecular clouds is less than two. Most of the radiation from star formation will emerge at IR wavelengths in the early universe provided that dust is present. The (patchy) visual optical depth through a typical early galaxy will however, remain less than 1 on average until a metallicity of 1/10 solar is reached.Comment: in press MNRAS, 17 pages with 19 figs, corrected typo