3D in vitro-based alternative approaches to ecotoxicity assessment

Given bioethics and the 3Rs (replacement, reduction, and refinement) principle, reliable test platforms are required due to the increased presence of endocrine-disrupting chemicals (EDCs) in the ecosystem. However, typical fish cell cultures show numerous limitations compared to primary cells. Therefore, there is a demand to develop novel systems for reproductive toxicity assessments as alternatives to animal testing. In this thesis, a zebrafish liver (ZFL) cell line was applied to three-dimensional (3D) cell culture techniques including in silico systems. The 3D structure of the zebrafish estrogen receptor was generated to evaluate modes of action upon estrogenic chemical exposure. The integration of the in silico model and in vitro platforms provided valuable tools for screening EDCs. Besides, 3D ZFL spheroids exhibited increased gene expressions in liver functions and vitellogenin levels compared to monolayer cells. The use of hydrogels and nanofibers regulated intercellular organization and physiological function and compensated for the shortcomings in the spheroid culture. These findings suggest the engineering of novel 3D platforms shows promise as alternative tools that are useful for further eco-environmental assessment. Therefore, the current studies have yielded robust alternative platforms to animal and primary cells for identifying potential EDCs. These approaches can contribute to reducing the experimental use of animals under the 3Rs principle.Angesichts der Bioethik, dem 3R-Prinzip (Replacement, Reduction, und Refinement) und des Bestehens endokrin aktive Substanzen (EASs) im Ökosystem sind Testplattformen notwendig. Typische Fischzellkulturen weisen im Vergleich zu Primärzellen Limitierungen auf. Daher besteht Bedarf an der Entwicklung neuartiger Systeme für Reproduktionstoxizitätsbewertungen als Alternative zu Tierversuchen. In dieser Doktorarbeit wurde eine Zebrafischleber-Zelllinie auf 3D-Zellkulturtechniken, samt in-silico Systeme eingesetzt. Die 3D-Struktur des Zebrafisch-Östrogenrezeptors wurde generiert, um Wirkungsweisen unter dem Einfluß von östrogenen Chemikalien auszuwerten. Die Integration des in silico Modells und in vitro Plattformen ergaben wertvolle Werkzeuge für das Screening von EASs. 3D Sphäroide zeigten im Vergleich zu Monoschichtzellen eine erhöhte leberspezifische Genexpression und Vtg Konzentrationen. Die Nutzung von Hydrogelen und Nanofasern regulierte die interzelluläre Organisation und physiologische Funktion und kompensierte die Mängel in der Sphäroidkultur. Diese Resultate deuten darauf hin, dass die Entwicklung neuartiger 3D-Plattformen ein vielversprechender Ansatz ist und für weitere Öko-Umweltbewertungen lohnend sind. Die vorgelegte Arbeit zeigt, dass die erzeugte, robuste, alternative Plattformen zu tierischen und primären Zellen es ermöglicht EASs zu identifizieren. Diese Ansätze können dazu beitragen die experimentelle Nutzung von Tieren nach dem 3R-Prinzip zu reduzieren

Learning-by-exporting in Korean Manufacturing: A Plant-level Analysis

The paper analyzes whether firms that start exporting become more productive utilizing recently developed sample matching procedures to control the problems from self-selection into the export market. We use plant level panel data on Korean manufacturing sector from 1990 to 1998. We find clear and robust empirical evidence in favor of the learning-by-exporting effect; total factor productivity differentials between exporters and their domestic counterparts arises and widens during several years after export market entry. We also find that the effect is more pronounced for firms that have higher skill-intensity, higher share of exports in production, and are small in size. Overall, the evidence suggests that exporting is one important channel through which domestic firms acquire accesses to advanced knowledge and better technology. Also, the stronger learning-by-doing effect for firms with higher skill-intensity seems to support the view that gabsorptive capacityh matters to receive knowledge spillovers from exporting activity.Learning-by-exporting, Productivity, Propensity score matching

Learning-by-exporting in Korean Manufacturing: A Plant-level Analysis

The paper analyzes whether firms that start exporting become more productive utilizing recently developed sample matching procedures to control the problems from self-selection into the export market. We use plant level panel data on Korean manufacturing sector from 1990 to 1998. We find clear and robust empirical evidence in favor of the learning-by-exporting effect; total factor productivity differentials between exporters and their domestic counterparts arises and widens during several years after export market entry. We also find that the effect is more pronounced for firms that have higher skill-intensity, higher share of exports in production, and are small in size. Overall, the evidence suggests that exporting is one important channel through which domestic firms acquire accesses to advanced knowledge and better technology. Also, the stronger learning-by-doing effect for firms with higher skill-intensity seems to support the view that "absorptive capacity" matters to receive knowledge spillovers from exporting activity.Learning-by-exporting, Productivity, Propensity score matching.

Evaluation of Frequency Dependent Equivalent Linear analysis

One dimensional equivalent linear site response analysis is widely used in practice due to the simplicity and ease of use. In the method, the dynamic soil properties are assumed to be independent of the loading frequency. To better simulate the nonlinear behavior, equivalent analysis methods that models the loading frequency dependence of the shear modulus and damping were developed. The backbone of the methods is the frequency-dependent shear strain curves. Various forms of the frequency-dependent shear strain curves were developed. However, the effect of the frequency - shear strain curves are not well known and documented. In this study, a series of frequency – strain curves were used to evaluate the accuracy of the frequency dependent equivalent linear analysis. Results show that the effect of the curves is significant and that the frequency dependent analysis does not always provide an improved estimate and can highly overestimate the amplification of the high frequency components of the ground motion. The degree of overestimation is dependent on the characteristics of the input ground motion and the soil profile. It is therefore concluded that the frequency dependent equivalent linear analysis should be used with caution and that standard equivalent linear analysis can be a more reliable option