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Quasilinear parabolic problems with nonlinear boundary conditions

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we have to show that there exist c > 0 and η ∈ (0, π/2) such that the inequality<br />

�<br />

� � �<br />

�<br />

�<br />

1 � �<br />

� + 2�<br />

� 1<br />

â(z)τ 2 � ≤ c � +<br />

�â(z)τ<br />

2<br />

�<br />

� 1<br />

â(z)τ 2 + 1<br />

4ˆb(z)+ 4<br />

3 â(z)<br />

ˆ 4<br />

b(z)+ 3 â(z)<br />

�<br />

1<br />

â(z)τ 2 + 1 + �<br />

1<br />

( ˆb(z)+ 4<br />

3<br />

�<br />

�<br />

�<br />

�<br />

�<br />

+ 1�<br />

â(z))τ 2 �<br />

, (z, τ) ∈ Σ π<br />

2 +η × Ση<br />

holds true; here Σθ = {λ ∈ C \ {0} : |arg λ| < θ}. This crucial estimate is obtained by a<br />

careful function theoretic analysis.<br />

Finally, in Chapter 6 we study the <strong>nonlinear</strong> problem (1.1) described at the beginning<br />

and prove the last main result of the present thesis, Theorem 6.1.2, by means of the<br />

contraction mapping principle employing the optimal regularity results obtained for the<br />

linear problem (1.19). Section 6.1 deals <strong>with</strong> the fixed point construction and the basic<br />

estimates. It also contains the list of all assumptions needed for our treatment of (1.1).<br />

The proof of the harder estimates concerning in particular the <strong>nonlinear</strong>ities on the<br />

<strong>boundary</strong> is deferred to Section 6.2.<br />

Acknowledgements. In the first place, I would like to express my gratitude to my<br />

supervisor, Prof. Dr. Jan Prüss. He is always open for discussing <strong>problems</strong> and an excellent<br />

teacher to me. I am also indebted to him for the participation in numerous national<br />

and international workshops and conferences. I am grateful to my colleagues, PD Dr.<br />

Roland Schnaubelt and Dipl.-Math. Matthias Kotschote, for many fruitful discussions<br />

and valuable suggestions. I would like to thank the Studienstiftung des deutschen Volkes,<br />

Bonn, for financial and non-material support. The thesis was also partially financially<br />

supported by a grant of the Graduiertenförderung des Landes Sachsen-Anhalt. I am<br />

grateful to Dr. Nina Grosser who critically and carefully read the manuscript of this<br />

work. I cannot forget all my friends who accompanied me during the last years. Finally,<br />

I would like to express my most sincere thanks to my parents for their constant support<br />

in every respect.<br />

10

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