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Faculty / Organisational entity
- Kaiserslautern - Fachbereich Mathematik (15)
- Kaiserslautern - Fachbereich Informatik (14)
- Kaiserslautern - Fachbereich Chemie (12)
- Kaiserslautern - Fachbereich Maschinenbau und Verfahrenstechnik (12)
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- Kaiserslautern - Fachbereich Sozialwissenschaften (7)
- Kaiserslautern - Fachbereich Biologie (3)
- Kaiserslautern - Fachbereich Elektrotechnik und Informationstechnik (3)
- Kaiserslautern - Fachbereich ARUBI (2)
- Kaiserslautern - Fachbereich Wirtschaftswissenschaften (2)
Mechanical ventilation of patients with severe lung injury is an important clinical treatment to ensure proper lung oxygenation and to mitigate the extent of collapsed lung regions. While current imaging technologies such as Computed Tomography (CT) and chest X-ray allow for a thorough inspection of the thorax, they are limited to static pictures and exhibit several disadvantages, including exposure to ionizing radiation and high cost. Electrical Impedance Tomography (EIT) is a novel method to determine functional processes inside the thorax such as lung ventilation and cardiac activity. EIT reconstructs the internal electrical conductivity distribution within the thorax from voltage measurements on the body surface. Conductivity changes correlate with important clinical parameters such as lung volume and perfusion. Current EIT systems and algorithms use simplified or generalized thorax models to solve the reconstruction problem, which reduce image quality and anatomical significance. In this thesis, the development of a clinically relevant workflow to compute sophisticated three-dimensional thorax models from patient-specific CT data is described. The method allows medical experts to generate a multi-material segmentation in an interactive and fast way, while a volumetric mesh is computed automatically from the segmentation. The significantly improved image quality and anatomical precision of EIT images reconstructed with these 3D models is reported, and the impact on clinical applicability is discussed. In addition, three projects concerning quantitative CT (qCT) measurements and multi-modal 3D visualization are presented, which demonstrate the importance and productivity of interdisciplinary research groups including computer scientists and medical experts. The results presented in this thesis contribute significantly to clinical research efforts to pave the way towards improved patient-specific treatments of lung injury using EIT and qCT.
The work presented in this thesis discusses the thermal and power management of multi-core processors (MCPs) with both two dimensional (2D) package and there dimensional (3D) package chips. The power and thermal management/balancing is of increasing concern and is a technological challenge to the MCP development and will be a main performance bottleneck for the development of MCPs. This thesis develops optimal thermal and power management policies for MCPs. The system thermal behavior for both 2D package and 3D package chips is analyzed and mathematical models are developed. Thereafter, the optimal thermal and power management methods are introduced.
Nowadays, the chips are generally packed in 2D technique, which means that there is only one layer of dies in the chip. The chip thermal behavior can be described by a 3D heat conduction partial differential equation (PDE). As the target is to balance the thermal behavior and power consumption among the cores, a group of one dimensional (1D) PDEs, which is derived from the developed 3D PDE heat conduction equation, is proposed to describe the thermal behavior of each core. Therefore, the thermal behavior of the MCP is described by a group of 1D PDEs. An optimal controller is designed to manage the power consumption and balance the temperature among the cores based on the proposed 1D model.
3D package is an advanced package technology, which contains at least 2 layers of dies stacked in one chip. Different from 2D package, the cooling system should be installed among the layers to reduce the internal temperature of the chip. In this thesis, the micro-channel liquid cooling system is considered, and the heat transfer character of the micro-channel is analyzed and modeled as an ordinary differential equation (ODE). The dies are discretized to blocks based on the chip layout with each block modeled as a thermal resistance and capacitance (R-C) circuit. Thereafter, the micro-channels are discretized. The thermal behavior of the whole system is modeled as an ODE system. The micro-channel liquid velocity is set according to the workload and the temperature of the dies. Under each velocity, the system can be described as a linear ODE model system and the whole system is a switched linear system. An H-infinity observer is designed to estimate the states. The model predictive control (MPC) method is employed to design the thermal and power management/balancing controller for each submodel.
The models and controllers developed in this thesis are verified by simulation experiments via MATLAB. The IBM cell 8 cores processor and water micro-channel cooling system developed by IBM Research in collaboration with EPFL and ETHZ are employed as the experiment objects.
According to the domain specific models of speech perception, speech is supposed to be processed distinctively compared to non-speech. This assumption is supported by many studies dealing with the processing of speech and non-speech stimuli. However, the complexity of both stimulus classes is not matched in most studies, which might be a confounding factor, according to the cue specific models of speech perception. One solution is spectrally rotated speech, which has already been used in a range of fMRI and PET studies. In order to be able to investigate the role of stimulus complexity, vowels, spectrally rotated vowels and a second non-speech condition with two bands of sinusoidal waves, representing the first two formants of the vowels, were used in the present thesis. A detailed description of the creation and the properties of the whole stimulus set are given in Chapter 2 (Experiment 1) of this work. These stimuli were used to investigate the auditory processing of speech and non-speech sounds in a group of dyslexic adults and age matched controls (Experiment 2). The results support the assumption of a general auditory deficit in dyslexia. In order to compare the sensory processing of speech and non-speech in healthy adults on the electrophysiological level, stimuli were also presented within a multifeature oddball paradigm (Experiment 3). Vowels evoked a larger mismatch negativity (MMN) compared to both non-speech stimulus types. The MMN evoked by tones and spectrally rotated tones were compared in Experiment 4, to investigate the role of harmony. No difference in the area of MMN was found, indicating that the results found in Experiment 3 were not moderated by the harmonic structure of the vowels. All results are discussed in the context of the domain and cue specific models of speech perception.
We consider two major topics in this thesis: spatial domain partitioning which serves as a framework to simulate creep flows in representative volume elements.
First, we introduce a novel multi-dimensional space partitioning method. A new type of tree combines the advantages of the Octree and the KD-tree without having their disadvantages. We present a new data structure allowing local refinement, parallelization and proper restriction of transition ratios between nodes. Our technique has no dimensional restrictions at all. The tree's data structure is defined by a topological algebra based on the symbols \( A = \{ L, I, R \} \) that encode the partitioning steps. The set of successors is restricted such that each node has the partition of unity property to partition domains without overlap. With our method it is possible to construct a wide choice of spline spaces to compress or reconstruct scientific data such as pressure and velocity fields and multidimensional images. We present a generator function to build a tree that represents a voxel geometry. The space partitioning system is used as a framework to allow numerical computations. This work is triggered by the problem of representing, in a numerically appropriate way, huge three-dimensional voxel geometries that could have up to billions of voxels. These large datasets occure in situations where it is needed to deal with large representative volume elements (REV).
Second, we introduce a novel approach of variable arrangement for pressure and velocity to solve the Stokes equations. The basic idea of our method is to arrange variables in a way such that each cell is able to satisfy a given physical law independently from its neighbor cells. This is done by splitting velocity values to a left and right converging component. For each cell we can set up a small linear system that describes the momentum and mass conservation equations. This formulation allows to use the Gauß-Seidel algorithm to solve the global linear system. Our tree structure is used for spatial partitioning of the geometry and provides a proper initial guess. In addition, we introduce a method that uses the actual velocity field to refine the tree and improve the numerical accuracy where it is needed. We developed a novel approach rather than using existing approaches such as the SIMPLE algorithm, Lattice-Boltzmann methods or Exlicit jump methods since they are suited for regular grid structures. Other standard CFD approaches extract surfaces and creates tetrahedral meshes to solve on unstructured grids thus can not be applied to our datastructure. The discretization converges to the analytical solution with respect to grid refinement. We conclude a high strength in computational time and memory for high porosity geometries and a high strength in memory requirement for low porosity geometries.
In automotive testrigs we apply load time series to components such that the outcome is as close as possible to some reference data. The testing procedure should in general be less expensive and at the same time take less time for testing. In my thesis, I propose a testrig damage optimization problem (WSDP). This approach improves upon the testrig stress optimization problem (TSOP) used as a state of the art by industry experts.
In both (TSOP) and (WSDP), we optimize the load time series for a given testrig configuration. As the name suggests, in (TSOP) the reference data is the stress time series. The detailed behaviour of the stresses as functions of time are sometimes not the most important topic. Instead the damage potential of the stress signals are considered. Since damage is not part of the objectives in the (TSOP) the total damage computed from the optimized load time series is not optimal with respect to the reference damage. Additionally, the load time series obtained is as long as the reference stress time series and the total damage computation needs cycle counting algorithms and Goodmann corrections. The use of cycle counting algorithms makes the computation of damage from load time series non-differentiable.
To overcome the issues discussed in the previous paragraph this thesis uses block loads for the load time series. Using of block loads makes the damage differentiable with respect to the load time series. Additionally, in some special cases it is shown that damage is convex when block loads are used and no cycle counting algorithms are required. Using load time series with block loads enables us to use damage in the objective function of the (WSDP).
During every iteration of the (WSDP), we have to find the maximum total damage over all plane angles. The first attempt at solving the (WSDP) uses discretization of the interval for plane angle to find the maximum total damage at each iteration. This is shown to give unreliable results and makes maximum total damage function non-differentiable with respect to the plane angle. To overcome this, damage function for a given surface stress tensor due to a block load is remodelled by Gaussian functions. The parameters for the new model are derived.
When we model the damage by Gaussian function, the total damage is computed as a sum of Gaussian functions. The plane with the maximum damage is similar to the modes of the Gaussian Mixture Models (GMM), the difference being that the Gaussian functions used in GMM are probability density functions which is not the case in the damage approximation presented in this work. We derive conditions for a single maximum for Gaussian functions, similar to the ones given for the unimodality of GMM by Aprausheva et al. in [1].
By using the conditions for a single maximum we give a clustering algorithm that merges the Gaussian functions in the sum as clusters. Each cluster obtained through clustering is such that it has a single maximum in the absence of other Gaussian functions of the sum. The approximate point of the maximum of each cluster is used as the starting point for a fixed point equation on the original damage function to get the actual maximum total damage at each iteration.
We implement the method for the (TSOP) and the two methods (with discretization and with clustering) for (WSDP) on two example problems. The results obtained from the (WSDP) using discretization is shown to be better than the results obtained from the (TSOP). Furthermore we show that, (WSDP) using clustering approach to finding the maximum total damage, takes less number of iterations and is more reliable than using discretization.
Test rig optimization
(2014)
Designing good test rigs for fatigue life tests is a common task in the auto-
motive industry. The problem to find an optimal test rig configuration and
actuator load signals can be formulated as a mathematical program. We in-
troduce a new optimization model that includes multi-criteria, discrete and
continuous aspects. At the same time we manage to avoid the necessity to
deal with the rainflow-counting (RFC) method. RFC is an algorithm, which
extracts load cycles from an irregular time signal. As a mathematical func-
tion it is non-convex and non-differentiable and, hence, makes optimization
of the test rig intractable.
The block structure of the load signals is assumed from the beginning.
It highly reduces complexity of the problem without decreasing the feasible
set. Also, we optimize with respect to the actuators’ positions, which makes
it possible to take torques into account and thus extend the feasible set. As
a result, the new model gives significantly better results, compared with the
other approaches in the test rig optimization.
Under certain conditions, the non-convex test rig problem is a union of
convex problems on cones. Numerical methods for optimization usually need
constraints and a starting point. We describe an algorithm that detects each
cone and its interior point in a polynomial time.
The test rig problem belongs to the class of bilevel programs. For every
instance of the state vector, the sum of functions has to be maximized. We
propose a new branch and bound technique that uses local maxima of every
summand.
Technik ist in der heutigen Zeit allgegenwärtig. Bei all ihrer Omnipräsenz wird jedoch leicht übersehen, dass die Frage nach der Technik selber, d.h. die Frage danach, was genau unter „Technik“ überhaupt zu verstehen ist, bisher weitestgehend undeutlich geblieben ist.
Für die Philosophie erwächst daraus die Aufgabe, an dieser Stelle begriffsklärend einzugreifen.
Die vorliegende Arbeit hat zum Ziel, einen Beitrag zu einem besseren Verständnis von Technik und technischen Artefakten zu leisten. Die Argumentation gliedert sich dabei in zwei Schritte: Zuerst wird gezeigt, dass sich Technik nur in ihren Abgrenzungsverhältnissen zur Natur und zum Leben verstehen lässt und eine dem entsprechende Definition des Technikbegriffs vorgeschlagen. Anschließend wird daraus ein Verständnis technischer Artefakte im Sinne einer artefaktischen Technik abgeleitet.
Die Gliederung der Arbeit besteht dann im wesentlichen aus drei Teilen:
1. Das erste Kapitel dient der Einführung in die Problematik des Technikbegriffs:
Dabei wird in einem ersten Abschnitt auf die historische Dimension des Technikbegriffs verwiesen (1.1), anschließend die gegenwärtige Diskussion um den Technikbegriff zusammengefasst und kritisch bewertet (1.2) sowie Klassifikationen bzw. Kriterien hinsichtlich einer möglichen Definition des Technikbegriffs vorgeschlagen (1.3).
2. Das zweite Kapitel dient der Etablierung eines Technikbegriffs, der sich als semantisch abhängig von den Begriffen „Leben“ und „Natur“ erweist:
Dabei wird in einem ersten Abschnitt ein solches semantisches Verhältnis der Begriffe zueinander von anderen Möglichkeiten wechselseitiger Abgrenzung unterschieden (2.1). Sodann wird diese Abgrenzung mittels sogenannter Konstitutionsformen inhaltlich aufgefüllt (2.2). Nach der ausführlichen Erläuterung dieser Konstitutionsformen in ihrem paarweisen Zusammenhang, wird eine auf ihnen beruhende Definition von „Technik“ vorgeschlagen. In einem dritten Abschnitt wird das Modell der Konstitutionsformen um sogenannte Erschließungsformen erweitert, als diejenigen Fragehorizonte, mittels denen eine Binnendifferenzierung in verschieden Arten von Technik gelingt (2.3). In der Folge davon, wird eine Definition für eine jeweils „spezifische Technik“ vorgeschlagen.
3. Das dritte Kapitel dient der Untersuchung des ontologischen Status' technischer Artefakte:
Dabei werden technische Artefakte im Sinne einer „spezifischen Technik“ konkretisiert und damit als eine artefaktische Technik interpretiert (3.1). Anschließend wird überprüft, inwiefern sich eine solche Interpretation bezüglich a) der Frage, ob technische Artefakte natürliche Arten darstellen, bzw. b) des Problems der Koinzidenz von Objekten bewährt. Die aus diesen Überlegungen heraus gewonnenen Erkenntnisse werden abschließend in ihrer Anwendung auf Grenzfälle technischer Artefakte fruchtbar gemacht (3.2).
When stimulus and response overlap in a choice-reaction task, enhanced performance can be observed. This effect, the so-called Stimulus-Response Compatibility (SRC) has been shown to appear for a variety of different stimulus features such as numerical or physical size, luminance, or pitch height. While many of these SRC effects have been investigated in an isolated manner, only fewer studies focus on possible interferences when more than one stimulus dimension is varied. The present thesis investigated how the SRC effect of pitch heights, the so-called SPARC effect (Spatial Pitch Associations of Response Codes), is influenced by additionally varied stimulus information. In Study 1, the pitch heights of presented tones were varied along with timbre categories under two different task and pitch range conditions and with two different response alignments. Similarly, in Study 2, pitch heights as well as numerical values were varied within sung numbers under two different task conditions. The results showed simultaneous SRC effects appearing independently of each other in both studies: In Study 1, an expected SRC effect of pitch heights with horizontal responses (i.e., a horizontal SPARC effect) was observed. More interestingly, an additional and unexpected SRC effect of timbre with response sides presented itself independently of this SPARC effect. Similar results were obtained in Study 2: Here, an SRC effect for pitch heights (SPARC) and an SRC effect for numbers (i.e., SNARC or Spatial Numerical Associations of Response Codes, respectively) were observed and again the effects did not interfere with each other. Thus, results indicate that SPARC with horizontal responses does not interfere with SRC effects of other, simultaneously varied stimulus dimensions. These findings are discussed within the principle of polarity correspondence and the dimensional overlap model as theoretical accounts for SRC effects. In sum, it appears that the different types of information according to varied stimulus dimensions enter the decision stage of stimulus processing from separate channels.
ABSTRACT
"Spin and orbital contribution to the magnetic moment of transition metal clusters and complexes"
The spin and orbital contributions to the magnetic moments of isolated iron \(Fe_n^+\) \((7 ≤ n ≤ 18)\), cobalt \(Co_n^+\) \((8 ≤ n ≤ 22)\) and nickel \(Ni_n^+\) \((7 ≤ n ≤ 17)\) clusters were investigated. An experimental access to both contributions is possible by the application of x-ray magnetic circular dichroism (XMCD) spectroscopy. XMCD spectroscopy is based on x-ray absorption spectroscopy (XAS). It exploits the fact that for a magnetic sample the resonant absorption cross sections for negative and positive circular polarized x-rays differ for the transition from a spin orbit split ground state to the valence level. The resulting dichroic effects contain the information about the magnetism of the investigated sample. It can be extracted from the experimental spectrum via application of the so called sum rules. However, only the projections of the magnetic moments onto the quantization axis are experimentally accessible which corresponds to the magnetization of the sample.
We developed a method to apply XMCD spectroscopy to isolated clusters in the gas phase. A modified Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometer was used to record the XA spectra in Total Ion Yield (TIY) mode, i.e. by recording the fragmentation intensity of the clusters in dependence of x-ray energy. The clusters can be considered to be a superparamagnetic ensemble. Thus, the magnetization follows a Langevin curve. The intrinsic magnetic moments can be calculated by Langevin correction of the experimental magnetic moments because the cluster temperature and the magnetic field are known.
The spin and the orbital magnetic moments are enhanced compared to the respective bulk values for all three investigated elements. The enhancement of the orbital contribution is more pronounced, by about a factor 3 - 4 compared to the bulk, than for the spin magnetic moment. However, if compared to the atomic value, both contributions are quenched. The orbital magnetic moment only amounts to about 10 - 15 % of the atomic value while the spin retains about 80 % of its atomic value. If the magnetic moments found for the clusters are put into perspective with respect to the atomic and bulk values by means of scaling laws, it becomes evident that both contributions follow different interpolations between the atomic and bulk value. The spin follows the well-known trend
\(n^{-1/3} = 1/(cluster radius)\) (n = number of atoms per cluster, assumption of a spherical particle). This trend relates to the ratio of surface to inner atoms in spherical particle. Hence, our interpretation is that the spin magnetic moment seems to follow the surface area of the cluster. On the other hand, the orbital magnetic moment follows \(1/n = 1/(cluster volume)\).
First XA spectra recorded with circularly polarized x-rays of a Single Molecule Magnet (SMM) \([Fe_4Ln_2(N_3)_4(Htea)_4(piv_6)]\) (Ln = Gd, Tb; \(H_3tea\) = triethanolamine, Hpiv = pivalic acid) are presented.
In the present work, the phase transitions in different Fe/FeC systems were studied by using the molecular dynamics simulation and the Meyer-Entel interaction potential (also the Johnson potential for Fe-C interaction). Fe-bicrystal, thin film, Fe-C bulk and Fe-C nanowire systems were investigated to study the behaviour of the phase transition, where the energetics, dynamics and transformations pathways were analysed.