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Mon, 22 Aug 2016 13:59:02 +0200Mon, 22 Aug 2016 13:59:02 +0200Worst-Case Performance Analysis of Feed-Forward Networks – An Efficient and Accurate Network Calculus
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4432
Distributed systems are omnipresent nowadays and networking them is fundamental for the continuous dissemination and thus availability of data. Provision of data in real-time is one of the most important non-functional aspects that safety-critical networks must guarantee. Formal verification of data communication against worst-case deadline requirements is key to certification of emerging x-by-wire systems. Verification allows aircraft to take off, cars to steer by wire, and safety-critical industrial facilities to operate. Therefore, different methodologies for worst-case modeling and analysis of real-time systems have been established. Among them is deterministic Network Calculus (NC), a versatile technique that is applicable across multiple domains such as packet switching, task scheduling, system on chip, software-defined networking, data center networking and network virtualization. NC is a methodology to derive deterministic bounds on two crucial performance metrics of communication systems:
(a) the end-to-end delay data flows experience and
(b) the buffer space required by a server to queue all incoming data.
NC has already seen application in the industry, for instance, basic results have been used to certify the backbone network of the Airbus A380 aircraft.
The NC methodology for worst-case performance analysis of distributed real-time systems consists of two branches. Both share the NC network model but diverge regarding their respective derivation of performance bounds, i.e., their analysis principle. NC was created as a deterministic system theory for queueing analysis and its operations were later cast in a (min,+)-algebraic framework. This branch is known as algebraic Network Calculus (algNC). While algNC can efficiently compute bounds on delay and backlog, the algebraic manipulations do not allow NC to attain the most accurate bounds achievable for the given network model. These tight performance bounds can only be attained with the other, newly established branch of NC, the optimization-based analysis (optNC). However, the only optNC analysis that can currently derive tight bounds was proven to be computationally infeasible even for the analysis of moderately sized networks other than simple sequences of servers.
This thesis makes various contributions in the area of algNC: accuracy within the existing framework is improved, distributivity of the sensor network calculus analysis is established, and most significantly the algNC is extended with optimization principles. They allow algNC to derive performance bounds that are competitive with optNC. Moreover, the computational efficiency of the new NC approach is improved such that this thesis presents the first NC analysis that is both accurate and computationally feasible at the same time. It allows NC to scale to larger, more complex systems that require formal verification of their real-time capabilities.Steffen Bondorfdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4432Mon, 22 Aug 2016 13:59:02 +0200Gröbner Bases over Extention Fields of \(\mathbb{Q}\)
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4428
Gröbner bases are one of the most powerful tools in computer algebra and commutative algebra, with applications in algebraic geometry and singularity theory. From the theoretical point of view, these bases can be computed over any field using Buchberger's algorithm. In practice, however, the computational efficiency depends on the arithmetic of the coefficient field.
In this thesis, we consider Gröbner bases computations over two types of coefficient fields. First, consider a simple extension \(K=\mathbb{Q}(\alpha)\) of \(\mathbb{Q}\), where \(\alpha\) is an algebraic number, and let \(f\in \mathbb{Q}[t]\) be the minimal polynomial of \(\alpha\). Second, let \(K'\) be the algebraic function field over \(\mathbb{Q}\) with transcendental parameters \(t_1,\ldots,t_m\), that is, \(K' = \mathbb{Q}(t_1,\ldots,t_m)\). In particular, we present efficient algorithms for computing Gröbner bases over \(K\) and \(K'\). Moreover, we present an efficient method for computing syzygy modules over \(K\).
To compute Gröbner bases over \(K\), starting from the ideas of Noro [35], we proceed by joining \(f\) to the ideal to be considered, adding \(t\) as an extra variable. But instead of avoiding superfluous S-pair reductions by inverting algebraic numbers, we achieve the same goal by applying modular methods as in [2,4,27], that is, by inferring information in characteristic zero from information in characteristic \(p > 0\). For suitable primes \(p\), the minimal polynomial \(f\) is reducible over \(\mathbb{F}_p\). This allows us to apply modular methods once again, on a second level, with respect to the
modular factors of \(f\). The algorithm thus resembles a divide and conquer strategy and
is in particular easily parallelizable. Moreover, using a similar approach, we present an algorithm for computing syzygy modules over \(K\).
On the other hand, to compute Gröbner bases over \(K'\), our new algorithm first specializes the parameters \(t_1,\ldots,t_m\) to reduce the problem from \(K'[x_1,\ldots,x_n]\) to \(\mathbb{Q}[x_1,\ldots,x_n]\). The algorithm then computes a set of Gröbner bases of specialized ideals. From this set of Gröbner bases with coefficients in \(\mathbb{Q}\), it obtains a Gröbner basis of the input ideal using sparse multivariate rational interpolation.
At current state, these algorithms are probabilistic in the sense that, as for other modular Gröbner basis computations, an effective final verification test is only known for homogeneous ideals or for local monomial orderings. The presented timings show that for most examples, our algorithms, which have been implemented in SINGULAR [17], are considerably faster than other known methods.Dereje Kifle Bokudoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4428Wed, 10 Aug 2016 15:34:30 +0200Regionalized Assortment Planning for Multiple Chain Stores: Complexity, Approximability, and Solution Methods
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4424
In retail, assortment planning refers to selecting a subset of products to offer that maximizes profit. Assortments can be planned for a single store or a retailer with multiple chain stores where demand varies between stores. In this paper, we assume that a retailer with a multitude of stores wants to specify her offered assortment. To suit all local preferences, regionalization and store-level assortment optimization are widely used in practice and lead to competitive advantages. When selecting regionalized assortments, a tradeoff between expensive, customized assortments in every store and inexpensive, identical assortments in all stores that neglect demand variation is preferable.
We formulate a stylized model for the regionalized assortment planning problem (APP) with capacity constraints and given demand. In our approach, a 'common assortment' that is supplemented by regionalized products is selected. While products in the common assortment are offered in all stores, products in the local assortments are customized and vary from store to store.
Concerning the computational complexity, we show that the APP is strongly NP-complete. The core of this hardness result lies in the selection of the common assortment. We formulate the APP as an integer program and provide algorithms and methods for obtaining approximate solutions and solving large-scale instances.
Lastly, we perform computational experiments to analyze the benefits of regionalized assortment planning depending on the variation in customer demands between stores.Michael Hopf; Clemens Thielen; Benedikt Kasper; Hans Corstenworkingpaperhttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4424Tue, 09 Aug 2016 09:43:13 +0200Assuring Functional Safety in Open Systems of Systems
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4422
Interconnected, autonomously driving cars shall realize the vision of a zero-accident, low energy mobility in spite of a fast increasing traffic volume. Tightly interconnected medical devices and health care systems shall ensure the health of an aging society. And interconnected virtual power plants based on renewable energy sources shall ensure a clean energy supply in a society that consumes more energy than ever before. Such open systems of systems will play an essential role for economy and society.
Open systems of systems dynamically connect to each other in order to collectively provide a superordinate functionality, which could not be provided by a single system alone. The structure as well as the behavior of an open system of system dynamically emerge at runtime leading to very flexible solutions working under various different environmental conditions. This flexibility and adaptivity of systems of systems are a key for realizing the above mentioned scenarios.
On the other hand, however, this leads to uncertainties since the emerging structure and behavior of a system of system can hardly be anticipated at design time. This impedes the indispensable safety assessment of such systems in safety-critical application domains. Existing safety assurance approaches presume that a system is completely specified and configured prior to a safety assessment. Therefore, they cannot be applied to open systems of systems. In consequence, safety assurance of open systems of systems could easily become a bottleneck impeding or even preventing the success of this promising new generation of embedded systems.
For this reason, this thesis introduces an approach for the safety assurance of open systems of systems. To this end, we shift parts of the safety assurance lifecycle into runtime in order to dynamically assess the safety of the emerging system of system. We use so-called safety models at runtime for enabling systems to assess the safety of an emerging system of system themselves. This leads to a very flexible runtime safety assurance framework.
To this end, this thesis describes the fundamental knowledge on safety assurance and model-driven development, which are the indispensable prerequisites for defining safety models at runtime. Based on these fundamentals, we illustrate how we modularized and formalized conventional safety assurance techniques using model-based representations and analyses. Finally, we explain how we advanced these design time safety models to safety models that can be used by the systems themselves at runtime and how we use these safety models at runtime to create an efficient and flexible runtime safety assurance framework for open systems of systems.Mario Trapphabilitationhttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4422Fri, 05 Aug 2016 13:35:55 +0200Interest Rate Modeling - The Potential Approach and Multi-Curve Potential Models
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4420
This thesis is concerned with interest rate modeling by means of the potential approach. The contribution of this work is twofold. First, by making use of the potential approach and the theory of affine Markov processes, we develop a general class of rational models to the term structure of interest rates which we refer to as "the affine rational potential model". These models feature positive interest rates and analytical pricing formulae for zero-coupon bonds, caps, swaptions, and European currency options. We present some concrete models to illustrate the scope of the affine rational potential model and calibrate a model specification to real-world market data. Second, we develop a general family of "multi-curve potential models" for post-crisis interest rates. Our models feature positive stochastic basis spreads, positive term structures, and analytic pricing formulae for interest rate derivatives. This modeling framework is also flexible enough to accommodate negative interest rates and positive basis spreads.Anh-The Nguyendoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4420Fri, 05 Aug 2016 12:31:23 +0200Plants, herbivores, and their interactions in human-modified landscapes
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4417
Human forest modification is among the largest global drivers of terrestrial degradation
of biodiversity, species interactions, and ecosystem functioning. One of the most
pertinent components, forest fragmentation, has a long history in ecological research
across the globe, particularly in lower latitudes. However, we still know little how
fragmentation shapes temperate ecosystems, irrespective of the ancient status quo of
European deforestation. Furthermore, its interaction with another pivotal component
of European forests, silvicultural management, are practically unexplored. Hence,
answering the question how anthropogenic modification of temperate forests affects
fundamental components of forest ecosystems is essential basic research that has
been neglected thus far. Most basal ecosystem elements are plants and their insect
herbivores, as they form the energetic basis of the tropic pyramid. Furthermore, their
respective biodiversity, functional traits, and the networks of interactions they
establish are key for a multitude of ecosystem functions, not least ecosystem stability.
Hence, the thesis at hand aimed to disentangle this complex system of
interdependencies of human impacts, biodiversity, species traits and inter-species
interactions.
The first step lay in understanding how woody plant assemblages are shaped by
human forest modification. For this purpose, field investigations in 57 plots in the
hyperfragmented cultural landscape of the Northern Palatinate highlands (SW
Germany) were conducted, censusing > 4,000 tree/shrub individuals from 34 species.
Use of novel, integrative indices for different types of land-use allowed an accurate
quantification of biotic responses. Intriguingly, woody tree/shrub communities reacted
strikingly positive to forest fragmentation, with increases in alpha and beta diversity,
as well as proliferation of heat/drought/light adapted pioneer species. Contrarily,
managed interior forests were homogenized/constrained in biodiversity, with
dominance of shade/cold adapted commercial tree species. Comparisons with recently
unmanaged stands (> 40 a) revealed first indications for nascent conversion to oldgrowth
conditions, with larger variability in light conditions and subsequent
community composition. Reactions to microclimatic conditions, the relationship
between associated species traits and the corresponding species pool, as well as
facilitative/constraining effects by foresters were discussed as underlying mechanisms.
Reactions of herbivore assemblages to forest fragmentation and the subsequent
changes in host plant communities were assessed by comprehensive sampling of >
1,000 live herbivores from 134 species in the forest understory. Diversity was –
similarly to plant communities - higher in fragmentation affected habitats, particularly
in edges of continuous control forests. Furthermore, average trophic specialization
showed an identical pattern. Mechanistically, benefits from microclimatic conditions,
host availability, as well as pronounced niche differentiation are deemed responsible.
While communities were heterogeneous, with no segregation across habitats, (smallforest fragments, edges, and interior of control forests), vegetation diversity, herbivore
diversity, as well as trophic specialization were identified to shape community
composition. This probably reflected a gradient from generalistic/species poor vs.
specialist/species rich herbivore assemblages.
Insect studies conducted in forest systems are doomed to incompleteness
without considering ‘the last biological frontier’, the tree canopies. To access their
biodiversity, relationship to edge effects, and their conservational value, the
arboricolous arthropod fauna of 24 beech (Fagus sylvatica) canopies was sampled via
insecticidal knockdown (‘fogging’). This resulted in an exhaustive collection of > 46,000
specimens from 24 major taxonomic/functional groups. Abundance distributions were
markedly negative exponential, indicating high abundance variability in tree crowns.
Individuals of six pertinent orders were identified to species level, returning > 3,100
individuals from 175 species and 52 families. This high diversity did marginally differ
across habitats, with slightly higher species richness in edge canopies. However,
communities in edge crowns were noticeably more heterogeneous than those in the
forest interior, possibly due to higher variability in environmental edge conditions. In
total, 49 species with protective value were identified, of which only one showed
habitat preferences (for near-natural interior forests). Among them, six species (all
beetles, Coleoptera) were classified as ‘priority species’ for conservation efforts. Hence,
beech canopies of the Northern Palatinate highlands can be considered strongholds of
insect biodiversity, incorporating many species of particular protective value.
The intricacy of plant-herbivore interaction networks and their relationship to
forest fragmentation is largely unexplored, particularly in Central Europe. Illumination
of this matter is all the more important, as ecological networks are highly relevant for
ecosystem stability, particularly in the face of additional anthropogenic disturbances,
such as climate change. Hence, plant-herbivore interaction networks (PHNs) were
constructed from woody plants and their associated herbivores, sampled alive in the
understory. Herbivory verification was achieved using no-choice-feeding assays, as well
as literature references. In total, networks across small forest fragments, edges, and
the forest interior consisted of 696 interactions. Network complexity and trophic niche
redundancy were compared across habitats using a rarefaction-like resampling
procedure. PHNs in fragmentation affected forest habitats were significantly more
complex, as well as more redundant in their realized niches, despite being composed of
relatively more specialist species. Furthermore, network robustness to climate change
was quantified utilizing four different scenarios for climate change susceptibility of
involved plants. In this procedure, remaining herbivores in the network were measured
upon successive loss of their host plant species. Consistently, PHNs in edges (and to a
smaller degree in small fragments) withstood primary extinction of plant species
longer, making them more robust. This was attributed to the high prevalence of
heat/drought-adapted species, as well as to beneficial effects of network topography
(complexity and redundancy). Consequently, strong correlative relationships were
found between realized niche redundancy and climate change robustness of PHNs.
This was both the first time that biologically realistic extinctions (instead of e.g.random extinctions) were used to measure network robustness, and that topographical
network parameters were identified as potential indicators for network robustness
against climate change.
In synthesis, in the light of global biotic degradation due to human forest
modification, the necessity to differentiate must be claimed. Ecosystems react
differently to anthropogenic disturbances, and it seems the particular features present
in Central European forests (ancient deforestation, extensive management, and, most
importantly, high richness in open-forest plant species) cause partly opposed patterns
to other biomes. Lenient microclimates and diverse plant communities facilitate
equally diverse herbivore assemblages, and hence complex and robust networks,
opposed to the forest interior. Therefore, in the reality of extensively used cultural
landscapes, fragmentation affected forest ecosystems, particularly forest edges, can be
perceived as reservoir for biodiversity, and ecosystem functionality. Nevertheless, as
practically all forest habitats considered in this thesis are under human cultivation,
recommendations for ecological enhancement of all forest habitats are discussed.Kevin Bähnerdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4417Wed, 27 Jul 2016 10:35:07 +0200Interactive Visualizations Supporting Minimal Cut Set Analysis II
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4412
The Context and Its Importance: In safety and reliability analysis, the information generated by Minimal Cut Set (MCS) analysis is large.
The Top Level event (TLE) that is the root of the fault tree (FT) represents a hazardous state of the system being analyzed.
MCS analysis helps in analyzing the fault tree (FT) qualitatively-and quantitatively when accompanied with quantitative measures.
The information shows the bottlenecks in the fault tree design leading to identifying weaknesses of the system being examined.
Safety analysis (containing the MCS analysis) is especially important for critical systems, where harm can be done to the environment or human causing injuries, or even death during the system usage.
Minimal Cut Set (MCS) analysis is performed using computers and generating a lot of information.
This phase is called MCS analysis I in this thesis.
The information is then analyzed by the analysts to determine possible issues and to improve the design of the system regarding its safety as early as possible.
This phase is called MCS analysis II in this thesis.
The goal of my thesis was developing interactive visualizations to support MCS analysis II of one fault tree (FT).
The Methodology: As safety visualization-in this thesis, Minimal Cut Set analysis II visualization-is an emerging field and no complete checklist regarding Minimal Cut Set analysis II requirements and gaps were available from the perspective of visualization and interaction capabilities,
I have conducted multiple studies using different methods with different data sources (i.e., triangulation of methods and data) for determining these requirements and gaps before developing and evaluating visualizations and interactions supporting Minimal Cut Set analysis II.
Thus, the following approach was taken in my thesis:
1- First, a triangulation of mixed methods and data sources was conducted.
2- Then, four novel interactive visualizations and one novel interaction widget were developed.
3- Finally, these interactive visualizations were evaluated both objectively and subjectively (compared to multiple safety tools)
from the point of view of users and developers of the safety tools that perform MCS analysis I with respect to their degree in supporting MCS analysis II and from the point of non-domain people using empirical strategies.
The Spiral tool supports analysts with different visions, i.e., full vision, color deficiency protanopia, deuteranopia, and tritanopia. It supports 100 out of 103 (97%) requirements obtained from the triangulation and it fills 37 out of 39 (95%) gaps. Its usability was rated high (better than their best currently used tools) by the users of the safety and reliability tools (RiskSpectrum, ESSaRel, FaultTree+, and a self-developed tool) and at least similar to the best currently used tools from the point of view of the CAFTA tool developers. Its quality was higher regarding its degree of supporting MCS analysis II compared to the FaultTree+ tool. The time spent for discovering the critical MCSs from a problem size of 540 MCSs (with a worst case of all equal order) was less than a minute while achieving 99.5% accuracy. The scalability of the Spiral visualization was above 4000 MCSs for a comparison task. The Dynamic Slider reduces the interaction movements up to 85.71% of the previous sliders and solves the overlapping thumb issues by the sliders provides the 3D model view of the system being analyzed provides the ability to change the coloring of MCSs according to the color vision of the user provides selecting a BE (i.e., multi-selection of MCSs), thus, can observe the BEs' NoO and provides its quality provides two interaction speeds for panning and zooming in the MCS, BE, and model views provide a MCS, a BE, and a physical tab for supporting the analysis starting by the MCSs, the BEs, or the physical parts. It combines MCS analysis results and the model of an embedded system enabling the analysts to directly relate safety information with the corresponding parts of the system being analyzed and provides an interactive mapping between the textual information of the BEs and MCSs and the parts related to the BEs.
Verifications and Assessments: I have evaluated all visualizations and the interaction widget both objectively and subjectively, and finally evaluated the final Spiral visualization tool also both objectively and subjectively regarding its perceived quality and regarding its degree of supporting MCS analysis II.Yasmin Al-Zokaridoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4412Thu, 07 Jul 2016 10:11:41 +0200The Bootstrap for the Functional Autoregressive Model FAR(1)
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4410
Functional data analysis is a branch of statistics that deals with observations \(X_1,..., X_n\) which are curves. We are interested in particular in time series of dependent curves and, specifically, consider the functional autoregressive process of order one (FAR(1)), which is defined as \(X_{n+1}=\Psi(X_{n})+\epsilon_{n+1}\) with independent innovations \(\epsilon_t\). Estimates \(\hat{\Psi}\) for the autoregressive operator \(\Psi\) have been investigated a lot during the last two decades, and their asymptotic properties are well understood. Particularly difficult and different from scalar- or vector-valued autoregressions are the weak convergence properties which also form the basis of the bootstrap theory.
Although the asymptotics for \(\hat{\Psi}{(X_{n})}\) are still tractable, they are only useful for large enough samples. In applications, however, frequently only small samples of data are available such that an alternative method for approximating the distribution of \(\hat{\Psi}{(X_{n})}\) is welcome. As a motivation, we discuss a real-data example where we investigate a changepoint detection problem for a stimulus response dataset obtained from the animal physiology group at the Technical University of Kaiserslautern.
To get an alternative for asymptotic approximations, we employ the naive or residual-based bootstrap procedure. In this thesis, we prove theoretically and show via simulations that the bootstrap provides asymptotically valid and practically useful approximations of the distributions of certain functions of the data. Such results may be used to calculate approximate confidence bands or critical bounds for tests.
Euna Gesare Nyarigedoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4410Wed, 06 Jul 2016 12:30:55 +0200Integrality of representations of finite groups
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4408
Since the early days of representation theory of finite groups in the 19th century, it was known that complex linear representations of finite groups live over number fields, that is, over finite extensions of the field of rational numbers.
While the related question of integrality of representations was answered negatively by the work of Cliff, Ritter and Weiss as well as by Serre and Feit, it was not known how to decide integrality of a given representation.
In this thesis we show that there exists an algorithm that given a representation of a finite group over a number field decides whether this representation can be made integral.
Moreover, we provide theoretical and numerical evidence for a conjecture, which predicts the existence of splitting fields of irreducible characters with integrality properties.
In the first part, we describe two algorithms for the pseudo-Hermite normal form, which is crucial when handling modules over ring of integers.
Using a newly developed computational model for ideal and element arithmetic in number fields, we show that our pseudo-Hermite normal form algorithms have polynomial running time.
Furthermore, we address a range of algorithmic questions related to orders and lattices over Dedekind domains, including computation of genera, testing local isomorphism, computation of various homomorphism rings and computation of Solomon zeta functions.
In the second part we turn to the integrality of representations of finite groups and show that an important ingredient is a thorough understanding of the reduction of lattices at almost all prime ideals.
By employing class field theory and tools from representation theory we solve this problem and eventually describe an algorithm for testing integrality.
After running the algorithm on a large set of examples we are led to a conjecture on the existence of integral and nonintegral splitting fields of characters.
By extending techniques of Serre we prove the conjecture for characters with rational character field and Schur index two.Tommy Hofmanndoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4408Mon, 04 Jul 2016 16:07:15 +0200Development of nano/micro hybrid susceptor sheet for induction heating applications
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4405
Thermoplastic composite materials are being widely used in the automotive and aerospace industries. Due to the limitations of shape complexity, different components
need to be joined. They can be joined by mechanical fasteners, adhesive bonding or
both. However, these methods have several limitations. Components can be joined
by fusion bonding due to the property of thermoplastics. Thermoplastics can be melted on heating and regain their shape on cooling. This property makes them ideal for
joining through fusion bonding by induction heating. Joining of non-conducting or
non-magnetic thermoplastic composites needs an additional material that can generate heat by induction heating.
Polymers are neither conductive nor electromagnetic so they don’t have inherent potential for inductive heating. A susceptor sheet having conductive materials (e.g. carbon fiber) or magnetic materials (e.g. nickel) can generate heat during induction. The
main issues related with induction heating are non-homogeneous and uncontrolled
heating.
In this work, it was observed that to generate heat with a susceptor sheet depends
on its filler, its concentration, and its dispersion. It also depends on the coil, magnetic
field strength and coupling distance. The combination of different fillers not only increased the heating rate but also changed the heating mechanism. Heating of 40ºC/
sec was achieved with 15wt.-% nickel coated short carbon fibers and 3wt.-% multiwalled carbon nanotubes. However, only nickel coated short carbon fibers (15wt-.%)
attained the heating rate of 24ºC/ sec. In this study, electrical conductivity, thermal
conductivity and magnetic properties testing were also performed. The results also
showed that electrical percolation was achieved around 15wt.-% in fibers and (13-
6)wt.-% with hybrid fillers. Induction heating tests were also performed by making
parallel and perpendicular susceptor sheet as fibers were uni-directionally aligned.
The susceptor sheet was also tested by making perforations.
The susceptor sheet showed homogeneous and fast heating, and can be used for
joining of non-conductive or non-magnetic thermoplastic composites.Muhammad Muddassirdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4405Thu, 30 Jun 2016 13:47:41 +0200Verification & Performance Measurement for Transport Protocol Parallel Routing of an AUTOSAR Gateway System
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4404
A wide range of methods and techniques have been developed over the years to manage the increasing
complexity of automotive Electrical/Electronic systems. Standardization is an example
of such complexity managing techniques that aims to minimize the costs, avoid compatibility
problems and improve the efficiency of development processes.
A well-known and -practiced standard in automotive industry is AUTOSAR (Automotive
Open System Architecture). AUTOSAR is a common standard among OEMs (Original Equipment
Manufacturer), suppliers and other involved companies. It was developed originally with
the goal of simplifying the overall development and integration process of Electrical/Electronic
artifacts from different functional domains, such as hardware, software, and vehicle communication.
However, the AUTOSAR standard, in its current status, is not able to manage the problems
in some areas of the system development. Validation and optimization process of system configuration
handled in this thesis are examples of such areas, in which the AUTOSAR standard
offers so far no mature solutions.
Generally, systems developed on the basis of AUTOSAR must be configured in a way that all
defined requirements are met. In most cases, the number of configuration parameters and their
possible settings in AUTOSAR systems are large, especially if the developed system is complex
with modules from various knowledge domains. The verification process here can consume a
lot of resources to test all possible combinations of configuration settings, and ideally find the
optimal configuration variant, since the number of test cases can be very high. This problem is
referred to in literature as the combinatorial explosion problem.
Combinatorial testing is an active and promising area of functional testing that offers ideas
to solve the combinatorial explosion problem. Thereby, the focus is to cover the interaction
errors by selecting a sample of system input parameters or configuration settings for test case
generation. However, the industrial acceptance of combinatorial testing is still weak because of
the deficiency of real industrial examples.
This thesis is tempted to fill this gap between the industry and the academy in the area
of combinatorial testing to emphasizes the effectiveness of combinatorial testing in verifying
complex configurable systems.
The particular intention of the thesis is to provide a new applicable approach to combinatorial
testing to fight the combinatorial explosion problem emerged during the verification and
performance measurement of transport protocol parallel routing of an AUTOSAR gateway. The
proposed approach has been validated and evaluated by means of two real industrial examples
of AUTOSAR gateways with multiple communication buses and two different degrees of complexity
to illustrate its applicability.Hassan Mohammaddoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4404Thu, 30 Jun 2016 08:31:11 +0200Centimeter-Level Accuracy Path Tracking Control of Tractors and Actively Steered Implements
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4401
Accurate path tracking control of tractors became a key technology for automation in agriculture. Increasingly sophisticated solutions, however, revealed that accurate path tracking control of implements is at least equally important. Therefore, this work focuses on accurate path tracking control of both tractors and implements. The latter, as a prerequisite for improved control, are equipped with steering actuators like steerable wheels or a steerable drawbar, i.e. the implements are actively steered. This work contributes both new plant models and new control approaches for those kinds of tractor-implement combinations. Plant models comprise dynamic vehicle models accounting for forces and moments causing the vehicle motion as well as simplified kinematic descriptions. All models have been derived in a systematic and automated manner to allow for variants of implements and actuator combinations. Path tracking controller design begins with a comprehensive overview and discussion of existing approaches in related domains. Two new approaches have been proposed combining the systematic setup and tuning of a Linear-Quadratic-Regulator with the simplicity of a static output feedback approximation. The first approach ensures accurate path tracking on slopes and curves by including integral control for a selection of controlled variables. The second approach, instead, ensures this by adding disturbance feedforward control based on side-slip estimation using a non-linear kinematic plant model and an Extended Kalman Filter. For both approaches a feedforward control approach for curved path tracking has been newly derived. In addition, a straightforward extension of control accounting for the implement orientation has been developed. All control approaches have been validated in simulations and experiments carried out with a mid-size tractor and a custom built demonstrator implement. Roland Wernerdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4401Wed, 22 Jun 2016 11:18:09 +0200Model-based Design of Embedded Systems by Desynchronization
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4399
In this thesis we developed a desynchronization design flow in the goal of easing the de- velopment effort of distributed embedded systems. The starting point of this design flow is a network of synchronous components. By transforming this synchronous network into a dataflow process network (DPN), we ensures important properties that are difficult or theoretically impossible to analyze directly on DPNs are preserved by construction. In particular, both deadlock-freeness and buffer boundedness can be preserved after desyn- chronization. For the correctness of desynchronization, we developed a criteria consisting of two properties: a global property that demands the correctness of the synchronous network, as well as a local property that requires the latency-insensitivity of each local synchronous component. As the global property is also a correctness requirement of synchronous systems in general, we take this property as an assumption of our desyn- chronization. However, the local property is in general not satisfied by all synchronous components, and therefore needs to be verified before desynchronization. In this thesis we developed a novel technique for the verification of the local property that can be carried out very efficiently. Finally we developed a model transformation method that translates a set of synchronous guarded actions – an intermediate format for synchronous systems – to an asynchronous actor description language (CAL). Our theorem ensures that one passed the correctness verification, the generated DPN of asynchronous pro- cesses (or actors) preserves the functional behavior of the original synchronous network. Moreover, by the correctness of the synchronous network, our theorem guarantees that the derived DPN is deadlock-free and can be implemented with only finitely bounded buffers.Yu Baidoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4399Mon, 20 Jun 2016 11:18:55 +0200Monoids as Storage Mechanisms
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4400
Automata theory has given rise to a variety of automata models that consist
of a finite-state control and an infinite-state storage mechanism. The aim
of this work is to provide insights into how the structure of the storage
mechanism influences the expressiveness and the analyzability of the
resulting model. To this end, it presents generalizations of results about
individual storage mechanisms to larger classes. These generalizations
characterize those storage mechanisms for which the given result remains
true and for which it fails.
In order to speak of classes of storage mechanisms, we need an overarching
framework that accommodates each of the concrete storage mechanisms we wish
to address. Such a framework is provided by the model of valence automata,
in which the storage mechanism is represented by a monoid. Since the monoid
serves as a parameter to specifying the storage mechanism, our aim
translates into the question: For which monoids does the given
(automata-theoretic) result hold?
As a first result, we present an algebraic characterization of those monoids
over which valence automata accept only regular languages. In addition, it
turns out that for each monoid, this is the case if and only if valence
grammars, an analogous grammar model, can generate only context-free
languages.
Furthermore, we are concerned with closure properties: We study which
monoids result in a Boolean closed language class. For every language class
that is closed under rational transductions (in particular, those induced by
valence automata), we show: If the class is Boolean closed and contains any
non-regular language, then it already includes the whole arithmetical
hierarchy.
This work also introduces the class of graph monoids, which are defined by
finite graphs. By choosing appropriate graphs, one can realize a number of
prominent storage mechanisms, but also combinations and variants thereof.
Examples are pushdowns, counters, and Turing tapes. We can therefore relate
the structure of the graphs to computational properties of the resulting
storage mechanisms.
In the case of graph monoids, we study (i) the decidability of the emptiness
problem, (ii) which storage mechanisms guarantee semilinear Parikh images,
(iii) when silent transitions (i.e. those that read no input) can be
avoided, and (iv) which storage mechanisms permit the computation of
downward closures.
Georg Zetzschedoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4400Fri, 17 Jun 2016 10:05:27 +0200 Annual Report 2015
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4395
Burkard Hillebrandsperiodicalparthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4395Wed, 08 Jun 2016 15:27:11 +0200 Annual Report 2014
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4394
Burkard Hillebrandsperiodicalparthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4394Wed, 08 Jun 2016 15:21:02 +0200Hecke algebras of type A: Auslander--Reiten quivers and branching rules
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4386
The thesis consists of two parts. In the first part we consider the stable Auslander--Reiten quiver of a block \(B\) of a Hecke algebra of the symmetric group at a root of unity in characteristic zero. The main theorem states that if the ground field is algebraically closed and \(B\) is of wild representation type, then the tree class of every connected component of the stable Auslander--Reiten quiver \(\Gamma_{s}(B)\) of \(B\) is \(A_{\infty}\). The main ingredient of the proof is a skew group algebra construction over a quantum complete intersection. Also, for these algebras the stable Auslander--Reiten quiver is computed in the case where the defining parameters are roots of unity. As a result, the tree class of every connected component of the stable Auslander--Reiten quiver is \(A_{\infty}\).\[\]
In the second part of the thesis we are concerned with branching rules for Hecke algebras of the symmetric group at a root of unity. We give a detailed survey of the theory initiated by I. Grojnowski and A. Kleshchev, describing the Lie-theoretic structure that the Grothendieck group of finite-dimensional modules over a cyclotomic Hecke algebra carries. A decisive role in this approach is played by various functors that give branching rules for cyclotomic Hecke algebras that are independent of the underlying field. We give a thorough definition of divided power functors that will enable us to reformulate the Scopes equivalence of a Scopes pair of blocks of Hecke algebras of the symmetric group. As a consequence we prove that two indecomposable modules that correspond under this equivalence have a common vertex. In particular, we verify the Dipper--Du Conjecture in the case where the blocks under consideration have finite representation type.Simon Schmiderdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4386Wed, 01 Jun 2016 15:32:16 +0200Getting Ready to Read: Promoting Children´s Emergent Literacy Through Shared Book Reading in a German Context
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4382
The present study investigated the effects of two methods of shared book reading on children´s emergent literacy skills, such as language skills (expressive vocabulary and semantic skills) and grapheme awareness, i.e. before the alphabetic phase of reading acquisition (Lachmann & van Leeuwen, 2014) in home and in kindergarten contexts. The two following shared book reading methods were investigated: Method I - literacy enrichment: 200 extra children's books were distributed in kindergartens and children were encouraged every week to borrow a book to take home and read with their parents. Further, a written letter was sent to the parents encouraging them to frequently read the books with their children at home. Method II - teacher training: kindergarten teachers participated in structured training which included formal instruction on how to promote child language development through shared book reading. The training was an adaptation of the Heidelberger Interaktionstraining für pädagogisches Fachpersonal zur Förderung ein- und mehrsprachiger Kinder - HIT (Buschmann & Jooss, 2011). In addition, the effects of the two methods in combination were investigated. Three questions were addressed in the present study: (1) What effect does method I (literacy enrichment), method II (teacher training) and the combination of both methods have on children's expressive vocabulary? (2) What effect does method I (literacy enrichment), method II (teacher training) and the combination of both methods have on children's semantic skills? (3) What effect does method I (literacy enrichment), method II (teacher training) and the combination of both methods have on children's grapheme awareness? Accordingly, 69 children, ranged in age from 3;0 to 4;8 years, were recruited from four kindergartens in the city of Kaiserslautern, Germany. The kindergartens were divided into: kindergarten 1 – Method I (N = 13); kindergarten 2 - Method II (N = 18); kindergarten 3 - Combination of both methods (N = 17); kindergarten 4 - Control group (N = 21). Half of the participants (N = 35) reported having a migration background. All groups were similar in regards to socioeconomic status and literacy activities at home. In a pre- posttest design, children performed three tests: expressive vocabulary (AWSTR, 3-5; Kiese-Himmel, 2005), semantic skills (SETK, 3-5 subtests ESR; Grimm, 2001), and grapheme awareness which is a task developed with the purpose of testing children’s familiarity with grapheme forms. The intervention period had duration of six months. The data analysis was performed using the software IBM SPSS Statistics version 22. Regarding language skills, Method I showed no significant effects on children expressive vocabulary and semantic skills. Method II showed significant effects for children expressive vocabulary. In addition, the children with migration background took more advantage of the method. Regarding semantic skills, no significant effects were found. No significant effects of the combination of both methods in children's language skills were found. For grapheme awareness, however, results showed positive effects for Method I, and Method II, as well as for the combination of both methods. The combination group, as reported by a large effect size, showed to be more effective than Method I and Method II alone. Moreover, the results indicated that in grapheme awareness, all children (in regards to age, gender, with and without migration background) took equal advantage in all three intervention groups. Overall, it can be concluded with the results of the present study, that by providing access to good books, Method I may help parents involve themselves in the active process of their child's literacy skills development. However, in order to improve language skills, access to books alone showed to be not enough. Therefore, it is suggested that access combined with additional support to parents in how to improve their language interactions with their children is highly recommended. In respect to Method II, the present study suggests that shared book reading through professional training is an important tool that supports children´s language development. For grapheme awareness it is concluded that with the combination of the two performed methods, high exposure to shared book reading helps children to informally learn about the surface characteristics of print, acquire some familiarity with the visual characteristics of the letters and learn to differentiate them from other visual patterns. Finally, it is suggested to organizations and institutions as well as to future research, the importance of having more programs that offer different possibilities to children to have more contact with adequate language interaction as well as more experiences with print through shared book reading as showed in the present study.Patricia de Brito Castilho Wesselingdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4382Tue, 31 May 2016 11:01:46 +0200Global existence for a degenerate haptotaxis model of tumor invasion under the go-or-grow dichotomy hypothesis
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4384
We propose and study a strongly coupled PDE-ODE-ODE system modeling cancer cell invasion through a tissue network
under the go-or-grow hypothesis asserting that cancer cells can either move or proliferate. Hence our setting features
two interacting cell populations with their mutual transitions and involves tissue-dependent degenerate diffusion and
haptotaxis for the moving subpopulation. The proliferating cells and the tissue evolution are characterized by way of ODEs
for the respective densities. We prove the global existence of weak solutions and illustrate the model behaviour by
numerical simulations in a two-dimensional setting.Anna Zhigun; Christina Surulescu; Alexander Huntpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4384Tue, 31 May 2016 08:55:45 +0200New Aspects of Inflation Modeling
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4381
Inflation modeling is a very important tool for conducting an efficient monetary policy. This doctoral thesis reviewed inflation models, in particular the Phillips curve models of inflation dynamics. We focused on a well known and widely used model, the so-called three equation new Keynesian model which is a system of equations consisting of a new Keynesian Phillips curve (NKPC), an investment and saving (IS) curve and an interest rate rule.
We gave a detailed derivation of these equations. The interest rate rule used in this model is normally determined by using a Lagrangian method to solve an optimal control problem constrained by a standard discrete time NKPC which describes the inflation dynamics and an IS curve that represents the output gaps dynamics. In contrast to the real world, this method assumes that the policy makers intervene continuously. This means that the costs resulting from the change in the interest rates are ignored. We showed also that there are approximation errors made, when one log-linearizes non linear equations, by doing the derivation of the standard discrete time NKPC.
We agreed with other researchers as mentioned in this thesis, that errors which result from ignoring such log-linear approximation errors and the costs of altering interest rates by determining interest rate rule, can lead to a suboptimal interest rate rule and hence to non-optimal paths of output gaps and inflation rate.
To overcome such a problem, we proposed a stochastic optimal impulse control method. We formulated the problem as a stochastic optimal impulse control problem by considering the costs of change in interest rates and the approximation error terms. In order to formulate this problem, we first transform the standard discrete time NKPC and the IS curve into their high-frequency versions and hence into their continuous time versions where error terms are described by a zero mean Gaussian white noise with a finite and constant variance. After formulating this problem, we use the quasi-variational inequality approach to solve analytically a special case of the central bank problem, where an inflation rate is supposed to be on target and a central bank has to optimally control output gap dynamics. This method gives an optimal control band in which output gap process has to be maintained and an optimal control strategy, which includes the optimal size of intervention and optimal intervention time, that can be used to keep the process into the optimal control band.
Finally, using a numerical example, we examined the impact of some model parameters on optimal control strategy. The results show that an increase in the output gap volatility as well as in the fixed and proportional costs of the change in interest rate lead to an increase in the width of the optimal control band. In this case, the optimal intervention requires the central bank to wait longer before undertaking another control action.François Sindamubaradoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4381Tue, 24 May 2016 15:03:18 +0200Recursive Utility and Stochastic Differential Utility: From Discrete to Continuous Time
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4380
In this thesis, mathematical research questions related to recursive utility and stochastic differential utility (SDU) are explored.
First, a class of backward equations under nonlinear expectations is investigated: Existence and uniqueness of solutions are established, and the issues of stability and discrete-time approximation are addressed. It is then shown that backward equations of this class naturally appear as a continuous-time limit in the context of recursive utility with nonlinear expectations.
Then, the Epstein-Zin parametrization of SDU is studied. The focus is on specifications with both relative risk aversion and elasitcity of intertemporal substitution greater that one. A concave utility functional is constructed and a utility gradient inequality is established.
Finally, consumption-portfolio problems with recursive preferences and unspanned risk are investigated. The investor's optimal strategies are characterized by a specific semilinear partial differential equation. The solution of this equation is constructed by a fixed point argument, and a corresponding efficient and accurate method to calculate optimal strategies numerically is given.Thomas Seiferlingdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4380Mon, 23 May 2016 10:55:22 +0200Utility-Based Risk Measures and Time Consistency of Dynamic Risk Measures
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4370
This thesis deals with risk measures based on utility functions and time consistency of dynamic risk measures. It is therefore aimed at readers interested in both, the theory of static and dynamic financial risk measures in the sense of Artzner, Delbaen, Eber and Heath [7], [8] and the theory of preferences in the tradition of von Neumann and Morgenstern [134].
A main contribution of this thesis is the introduction of optimal expected utility (OEU) risk measures as a new class of utility-based risk measures. We introduce OEU, investigate its main properties, and its applicability to risk measurement and put it in perspective to alternative risk measures and notions of certainty equivalents. To the best of our knowledge, OEU is the only existing utility-based risk measure that is (non-trivial and) coherent if the utility function u has constant relative risk aversion. We present several different risk measures that can be derived with special choices of u and illustrate that OEU reacts in a more sensitive way to slight changes of the probability of a financial loss than value at risk (V@R) and average value at risk.
Further, we propose implied risk aversion as a coherent rating methodology for retail structured products (RSPs). Implied risk aversion is based on optimal expected utility risk measures and, in contrast to standard V@R-based ratings, takes into account both the upside potential and the downside risks of such products. In addition, implied risk aversion is easily interpreted in terms of an individual investor's risk aversion: A product is attractive (unattractive) for an investor if its implied risk aversion is higher (lower) than his individual risk aversion. We illustrate this approach in a case study with more than 15,000 warrants on DAX ® and find that implied risk aversion is able to identify favorable products; in particular, implied risk aversion is not necessarily increasing with respect to the strikes of call warrants.
Another main focus of this thesis is on consistency of dynamic risk measures. To this end, we study risk measures on the space of distributions, discuss concavity on the level of distributions and slightly generalize Weber's [137] findings on the relation of time consistent dynamic risk measures to static risk measures to the case of dynamic risk measures with time-dependent parameters. Finally, this thesis investigates how recursively composed dynamic risk measures in discrete time, which are time consistent by construction, can be related to corresponding dynamic risk measures in continuous time. We present different approaches to establish this link and outline the theoretical basis and the practical benefits of this relation. The thesis concludes with a numerical implementation of this theory.Sebastian Geisseldoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4370Tue, 17 May 2016 10:22:33 +0200Towards A Non-tracking Web
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4358
Today, many publishers (e.g., websites, mobile application developers) commonly use third-party analytics services and social widgets. Unfortunately, this scheme allows these third parties to track individual users across the web, creating privacy concerns and leading to reactions to prevent tracking via blocking, legislation and standards. While improving user privacy, these efforts do not consider the functionality third-party tracking enables publishers to use: to obtain aggregate statistics about their users and increase their exposure to other users via online social networks. Simply preventing third-party tracking without replacing the functionality it provides cannot be a viable solution; leaving publishers without essential services will hurt the sustainability of the entire ecosystem.
In this thesis, we present alternative approaches to bridge this gap between privacy for users and functionality for publishers and other entities. We first propose a general and interaction-based third-party cookie policy that prevents third-party tracking via cookies, yet enables social networking features for users when wanted, and does not interfere with non-tracking services for analytics and advertisements. We then present a system that enables publishers to obtain rich web analytics information (e.g., user demographics, other sites visited) without tracking the users across the web. While this system requires no new organizational players and is practical to deploy, it necessitates the publishers to pre-define answer values for the queries, which may not be feasible for many analytics scenarios (e.g., search phrases used, free-text photo labels). Our second system complements the first system by enabling publishers to discover previously unknown string values to be used as potential answers in a privacy-preserving fashion and with low computation overhead for clients as well as servers. These systems suggest that it is possible to provide non-tracking services with (at least) the same functionality as today’s tracking services.Istemi Ekin Akkusdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4358Thu, 21 Apr 2016 15:20:47 +0200Qualitative and Quantitative Analysis of CFTs Taking Security Causes into Account
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4361
Component fault trees that contain safety basic events as well as security basic events cannot be analyzed like normal CFTs. Safety basic events are rated with probabilities in an interval [0,1], for security basic events simpler scales such as \{low, medium, high\} make more sense. In this paper an approach is described how to handle a quantitative safety analysis with different rating schemes for safety and security basic events. By doing so, it is possible to take security causes for safety failures into account and to rate their effect on system safety.Max Steiner; Peter Liggesmeyerconferenceobjecthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4361Wed, 20 Apr 2016 16:03:48 +0200Combination of Safety and Security Analysis - Finding Security Problems That Threaten the Safety of a System
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4360
In most cases in a safety analysis the influences of security problems are omitted or even forgotten. Because more and more systems are accessible from outside the system via maintenance interfaces, this missing security analysis is becoming a problem. This is why we propose an approach on how to extend the safety analysis by security aspects. Such a more comprehensive analysis should lead to systems that react in less catastrophic ways to attacks.Max Steiner; Peter Liggesmeyerconferenceobjecthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/4360Wed, 20 Apr 2016 16:00:46 +0200