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Epoxy resins have achieved acceptance as adhesives, coatings, and potting compounds,
but their main application is as matrix to produce reinforced composites.
However, their usefulness in this field still limited due to their brittle nature. Some
studies have been done to increase the toughness of epoxy composites, of which the
most successful one is the modification of the polymer matrix with a second toughening
phase.
Resin Transfer Molding (RTM) is one of the most important technologies to manufacture
fiber reinforced composites. In the last decade it has experimented new impulse,
due to its favorable application to produce large surface composites with good technical
properties and at relative low cost.
This research work focuses on the development of novel modified epoxy matrices,
with enhanced mechanical and thermal properties, suitable to be processed by resin
transfer molding technology, to manufacture Glass Fiber Reinforced Composites
(GFRC’s) with improved performance in comparison to the commercially available
ones.
In the first stage of the project, a neat epoxy resin (EP) was modified using two different
nano-sized ceramics: silicium dioxide (SiO2) and zirconium dioxide (ZrO2); and
micro-sized particles of silicone rubber (SR) as second filler. Series of nanocomposites
and hybrid modified epoxy resins were obtained by systematic variation of filler
contents. The rheology and curing process of the modified epoxy resins were determined
in order to define their aptness to be processed by RTM. The resulting matrices
were extensively characterized qualitatively and quantitatively to precise the effect
of each filler on the polymer properties.
It was shown that the nanoparticles confer better mechanical properties to the epoxy
resin, including modulus and toughness. It was possible to improve simultaneously
the tensile modulus and toughness of the epoxy matrix in more than 30 % and 50 %
respectively, only by using 8 vol.-% nano-SiO2 as filler. A similar performance was
obtained by nanocomposites containing zirconia. The epoxy matrix modified with 8 vol.-% ZrO2 recorded tensile modulus and toughness improved up to 36% and 45%
respectively regarding EP.
On the other hand, the addition of silicone rubber to EP and nanocomposites results
in a superior toughness but has a slightly negative effect on modulus and strength.
The addition of 3 vol.-% SR to the neat epoxy and nanocomposites increases their
toughness between 1.5 and 2.5 fold; but implies also a reduction in their tensile modulus
and strength in range 5-10%. Therefore, when the right proportion of nanoceramic
and rubber were added to the epoxy resin, hybrid epoxy matrices with fracture
toughness 3 fold higher than EP but also with up to 20% improved modulus were
obtained.
Widespread investigations were carried out to define the structural mechanisms responsible
for these improvements. It was stated, that each type of filler induces specific
energy dissipating mechanisms during the mechanical loading and fracture
processes, which are closely related to their nature, morphology and of course to
their bonding with the epoxy matrix. When both nanoceramic and silicone rubber are
involved in the epoxy formulation, a superposition of their corresponding energy release
mechanisms is generated, which provides the matrix with an unusual properties
balance.
From the modified matrices glass fiber reinforced RTM-plates were produced. The
structure of the obtained composites was microscopically analyzed to determine their
impregnation quality. In all cases composites with no structural defects (i.e. voids,
delaminations) and good superficial finish were reached. The composites were also
properly characterized. As expected the final performance of the GFRCs is strongly
determined by the matrix properties. Thus, the enhancement reached by epoxy matrices
is translated into better GFRC´s macroscopical properties. Composites with up
to 15% enhanced strength and toughness improved up to 50%, were obtained from
the modified epoxy matrices.
The dissertation describes a practically proven, particularly efficient approach for the verification of digital circuit designs. The approach outperforms simulation based verification wrt. final circuit quality as well as wrt. required verification effort. In the dissertation, the paradigm of transaction based verification is ported from simulation to formal verification. One consequence is a particular format of formal properties, called operation properties. Circuit descriptions are verified by proof of operation properties with Interval Property Checking (IPC), a particularly strong SAT based formal verification algorithm. Furtheron, a completeness checker is presented that identifies all verification gaps in sets of operation properties. This completeness checker can handle the large operation properties that arise, if this approach is applied to realistic circuits. The methodology of operation properties, Interval Property Checking, and the completeness checker form a symbiosis that is of particular benefit to the verification of digital circuit designs. On top of this symbiosis an approach to completely verify the interaction of completely verified modules has been developed by adaptation of the modelling theories of digital systems. The approach presented in the dissertation has proven in multiple commercial application projects that it indeed completely verifies modules. After reaching a termination criterion that is well defined by completeness checking, no further bugs were found in the verified modules. The approach is marketed by OneSpin Solutions GmbH, Munich, under the names "Operation Based Verification" and "Gap Free Verification".
An efficient mathematical model to virtually generate woven metal wire meshes is
presented. The accuracy of this model is verified by the comparison of virtual structures with three-dimensional
images of real meshes, which are produced via computer tomography. Virtual structures
are generated for three types of metal wire meshes using only easy to measure parameters. For these
geometries the velocity-dependent pressure drop is simulated and compared with measurements
performed by the GKD - Gebr. Kufferath AG. The simulation results lie within the tolerances of
the measurements. The generation of the structures and the numerical simulations were done at
GKD using the Fraunhofer GeoDict software.
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly toxic and persistent organic pollutant, which is ubiquitously found in the environment. The prototype dioxin compound was classified as a human carcinogen by the International Agency for Research on Cancer. TCDD acts as a potent liver tumor promoter in rats, which is one of the major concerns related to TCDD exposure. There is extensive evidence, that TCDD exerts anti-estrogenic effects via arylhydrocarbon receptor (AhR)-mediated induction of cytochromes P450 and interferes with the estrogen receptor alpha (ERalpha)-mediated signaling pathway. The present work was conducted to shed light on the hypothesis that enhanced activation of estradiol metabolism by TCDD-induced enzymes, mainly CYP1A1 and CYP1B1, leads to oxidative DNA damage in liver cells. Furthermore, the possible modulation by 17beta-estradiol (E2) was investigated. The effects were examined using four different AhR-responsive species- and sex-specific liver cell models, rat H4II2 and human HepG2 hepatoma cell lines as well as rat primary hepatocytes from male and female Wistar rats. The effective induction of CYP1A1 and CYP1B1 by TCDD was demonstrated in all liver cell models. Basal and TCDD-induced expression of CYP1B1, which is a key enzyme in stimulating E2 metabolism via the more reactive formation of the genotoxic 4-hydroxyestradiol, was most pronounced in rat primary hepatocytes. CYP-dependent induction of reactive oxygen species (ROS) was only observed in rodent cells. E2 induced ROS only in primary rat hepatocytes, which was associated with a weak CYP1B1 mRNA induction. Thus, E2 itself was suggested to induce its own metabolism in primary rat hepatocytes, resulting in the redox cycling of catechol estradiol metabolites leading to ROS formation. In this study the role of TCDD and E2 on oxidative DNA damage was investigated for the first time in vitro in the comet assay using liver cells. Both TCDD and E2 were shown to induce oxidative DNA base modifications only in rat hepatocytes. Additionally, direct oxidative DNA-damaging effects of the two main E2 metabolites, 4-hydroxyestradiol and 2-hydroxyestradiol, were only observed in rat hepatocytes and revealed that E2 damaged the DNA to the same extent. However, the induction of oxidative DNA damage by E2 could not completely be explained by the metabolic conversion of E2 via CYP1A1 and CYP1B1 and has to be further investigated. The expression of low levels of endogenous ERalpha mRNA in primary rat hepatocytes and the lack of ERalpha in hepatoma cell lines were identified as crucial. Therefore, the effects of interference of ERalpha with AhR were examined in HepG2 cells, which were transiently transfected with ERalpha. The over-expression of ERalpha led to enhanced AhR-mediated transcriptional activity by E2, suggesting a possible regulation of E2 levels. In turn, TCDD reduced E2-mediated ERalpha signaling, confirming the anti-estrogenic action of TCDD. Such a modulation of the combined effects of TCDD with E2 was not observed in any of the other experiments. Thus, the role of low endogenous ERalpha levels has to be further investigated in transfection experiments using rat primary hepatocytes. Overall, rat primary hepatocyte culture turned out to be the more adaptive cell model to investigate metabolism in the liver, reflecting a more realistic situation of the liver tissue. Nevertheless, during this work a crosstalk between ERalpha and AhR was shown for the first time using human hepatoma cell line HepG2 by transiently transfecting ERalpha.
Nowadays, vehicle control systems such as anti-lock braking systems, electronic stability control, and cruise control systems yield many advantages. The electronic control units that are deployed in this specific application domain are embedded systems that are integrated in larger systems to achieve predefined applications. Embedded systems consist of embedded hardware and a large software part. Model-based development for embedded systems offers significant software-development benefits that are pointed out in this thesis. The vehicle control system Adaptive Cruise Control is developed in this thesis using a model-based software development process for embedded systems. As a modern industrial design tool that is prevalent in this domain, simulink,is used for modeling the environment, the system behavior, for determining controller parameters, and for simulation purposes. Using an appropriate toolchain, the embedded code is automatically generated. The adaptive cruise control system could be successfully implemented and tested within this short timespan using a waterfall model without increments. The vehicle plant and important filters are fully deduced in detail. Therefore, the design of further vehicle control systems needs less effort for development and precise simulation.
We study the extension of techniques from Inductive Logic Programming (ILP) to temporal logic programming languages. Therefore we present two temporal logic programming languages and analyse the learnability of programs from these languages from finite sets of examples. In first order temporal logic the following topics are analysed: - How can we characterize the denotational semantics of programs? - Which proof techniques are best suited? - How complex is the learning task? In propositional temporal logic we analyse the following topics: - How can we use well known techniques from model checking in order to refine programs? - How complex is the learning task? In both cases we present estimations for the VC-dimension of selected classes of programs.
Classical geometrically exact Kirchhoff and Cosserat models are used to study the nonlinear deformation of rods. Extension, bending and torsion of the rod may be represented by the Kirchhoff model. The Cosserat model additionally takes into account shearing effects. Second order finite differences on a staggered grid define discrete viscoelastic versions of these classical models. Since the rotations are parametrised by unit quaternions, the space discretisation results in differential-algebraic equations that are solved numerically by standard techniques like index reduction and projection methods. Using absolute coordinates, the mass and constraint matrices are sparse and this sparsity may be exploited to speed-up time integration. Further improvements are possible in the Cosserat model, because the constraints are just the normalisation conditions for unit quaternions such that the null space of the constraint matrix can be given analytically. The results of the theoretical investigations are illustrated by numerical tests.
This work is concerned with dynamic flow problems, especially maximal dynamic flows and earliest arrival flows - also called universally maximal flows. First of all, a survey of known results about existence, computation and approximation of earliest arrival flows is given. For the special case of series-parallel graphs a polynomial algorithm for computing maximal dynamic flows is presented and this maximal dynamic flow is proven to be an earliest arrival flow.
Proteins of the intermembrane space of mitochondria are generally encoded by nuclear genes that are synthesized in the cytosol. A group of small intermembrane space proteins lack classical mitochondrial targeting sequences, but these proteins are imported in an oxidation-driven reaction that relies on the activity of two components, Mia40 and Erv1. Both proteins constitute the mitochondrial disulfide relay system. Mia40 functions as an import receptor that interacts with incoming polypeptides via transient, intermolecular disulfide bonds. Erv1 is an FAD-binding sulfhydryl oxidase that activates Mia40 by re-oxidation, but the process how Erv1 itself is re-oxidized has been poorly understood. Here, I show that Erv1 interacts with cytochrome c which provides a functional link between the mitochondrial disulfide relay system and the respiratory chain. This mechanism not only increases the efficiency of mitochondrial inport by the re-oxidation of Erv1 and Mia40 but also prevents the formation of deleterious hydrogen peroxide within the intermembrane space. Thus, the miochondrial disulfide relay system is, analogous to that of the bacterial periplasm, connected to the electron transport chain of the inner membrane, which possibly allows an oxygen-dependend regulation of mitochondrial import rates. In addition, I modeled the structure of Erv1 on the basis of the Saccharomyces cerevisiae Erv2 crystal structure in order to gain insight into the molecular mechanism of Erv1. According to the high degree of sequence homologies, various characteristics found for Erv2 are also valid for Erv1. Finally, I propose a regulatory function of the disulfide relay system on the respiratory chain. The disulfide relay system senses the molecular oxygen levels in mitochondria and, thus, is able to adapt respiratory chain activity in order to prevent wastage of NADH and production of ROS.
This dissertation is intended to give a systematic treatment of hypersurface singularities in arbitrary characteristic which provides the necessary tools, theoretically and computationally, for the purpose of classification. This thesis consists of five chapters: In chapter 1, we introduce the background on isolated hypersurface singularities needed for our work. In chapter 2, we formalize the notions of piecewise-homogeneous grading and we discuss thoroughly non-degeneracy in arbitrary characteristic. Chapter 3 is devoted to determinacy and normal forms of isolated hypersurface singularities. In the first part, we give finite determinacy theorems in arbitrary characteristic with respect to right respectively contact equivalence. Furthermore, we show that "isolated" and finite determinacy properties are equivalent. In the second part, we formalize Arnol'd's key ideas for the computation of normal forms an define the conditions (AA) and (AAC). The last part of Chapter 3 is devoted to the study of normal forms in the general setting of hypersurface singularities imposing neither condition (A) nor Newton-Nondegeneracy. In Chapter 4, we present algorithms which we implement in Singular for the purpose of explicit computation of regular bases and normal forms. In chapter 5, we transfer some classical results on invariants over the field C of complex numbers to algebraically closed fields of characteristic zero known as Lefschetz principle.