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Dataflow process networks (DPNs) are intrinsically data-driven, i.e., node actions are not synchronized among each other and may fire whenever sufficient input operands arrived at a node. While the general model of computation (MoC) of DPNs does not impose further restrictions, many different subclasses of DPNs representing different dataflow MoCs have been considered over time. These classes mainly differ in the kinds of behaviors of the processes. A DPN may be heterogeneous in that different processes in the network belong to different classes of DPNs. A heterogeneous DPN can therefore be effectively used to model and to implement different components of a system with different kinds of processes and, therefore, different dataflow MoCs. This paper presents a model-based design based on different dataflow MoCs including their heterogeneous combinations. In particular, it covers the automatic software synthesis of systems from DPN models. The main objective is to validate, evaluate and compare the artifacts exhibited by different dataflow MoCs at the implementation level of systems under the supervision of a common design tool. Moreover, this work also offers an efficient synthesis method that targets and exploits heterogeneity in DPNs by generating implementations based on the kinds of behaviors of the processes. The proposed synthesis method provides a tool chain including different specialized code generators for specific dataflow MoCs, and a runtime system that finally maps models using a combination of different dataflow MoCs on cross-vendor target hardware.
This paper presents an iterative finite element (FE)–based method to calculate the gravity-free shape of nonrigid parts from
an optical measurement performed on a non-over-constrained fixture. Measuring these kinds of parts in a stress-free state
is almost impossible because deflections caused by their weight occur. To solve this problem, a simulation model of the
measurement is created using available methods of reverse engineering. Then, an iterative algorithm calculates the gravityfree
shape. The approach does not require a CAD model of the measured part, implying the whole part can be fully scanned.
The application of this method mainly addresses thin, unstable sheet metal parts, like those commonly used in the automotive
or aerospace industry. To show the performance of the proposed method, validations with simulation and experimental
data are presented. The shown results meet the predefined quality goal to predict shapes within a tolerance of ±0.05 mm
measured in surface normal direction.
We propose a universal method for the evaluation of generalized standard materials that greatly simplifies the material law implementation process. By means of automatic differentiation and a numerical integration scheme, AutoMat reduces the implementation effort to two potential functions. By moving AutoMat to the GPU, we close the performance gap to conventional evaluation routines and demonstrate in detail that the expression level reverse mode of automatic differentiation as well as its extension to second order derivatives can be applied inside CUDA kernels. We underline the effectiveness and the applicability of AutoMat by integrating it into the FFT-based homogenization scheme of Moulinec and Suquet and discuss the benefits of using AutoMat with respect to runtime and solution accuracy for an elasto-viscoplastic example.
When considering complex systems, identifying the most important actors is often of relevance. When the system is modeled
as a network, centrality measures are used which assign each node a value due to its position in the network. It is often
disregarded that they implicitly assume a network process flowing through a network, and also make assumptions of how
the network process flows through the network. A node is then central with respect to this network process (Borgatti in Soc
Netw 27(1):55–71, 2005, https ://doi.org/10.1016/j.socne t.2004.11.008). It has been shown that real-world processes often
do not fulfill these assumptions (Bockholt and Zweig, in Complex networks and their applications VIII, Springer, Cham,
2019, https ://doi.org/10.1007/978-3-030-36683 -4_7). In this work, we systematically investigate the impact of the measures’
assumptions by using four datasets of real-world processes. In order to do so, we introduce several variants of the betweenness
and closeness centrality which, for each assumption, use either the assumed process model or the behavior of the real-world
process. The results are twofold: on the one hand, for all measure variants and almost all datasets, we find that, in general,
the standard centrality measures are quite robust against deviations in their process model. On the other hand, we observe a
large variation of ranking positions of single nodes, even among the nodes ranked high by the standard measures. This has
implications for the interpretability of results of those centrality measures. Since a mismatch of the behaviour of the real
network process and the assumed process model does even affect the highly-ranked nodes, resulting rankings need to be
interpreted with care.
Since the h-index has been invented, it is the most frequently discussed bibliometric value and one of the most commonly used metrics to quantify a researcher’s scientific output. The more it is increasingly gaining popularity to use the metric as an indication of the quality of a job applicant or an employee the more important it is to assure its correctitude. Many platforms offer the h-index of a scientist as a service, sometimes without the explicit knowledge of the respective person. In this article we show that looking up the h-index for a researcher on the five most commonly used platforms, namely AMiner, Google Scholar, ResearchGate, Scopus and Web of Science, results in a variance that is in many cases as large as the average value. This is due to the varying definitions of what a scientific article is, the underlying data basis, and different qualities of the entity recognition problem. To perform our study, we crawled the h-index of the worlds top researchers according to two different rankings, all the Nobel Prize laureates except Literature and Peace, and the teaching staff of the computer science department of the TU Kaiserslautern Germany with whom we additionally computed their h-index manually. Thus we showed that the individual h-indices differ to an alarming extent between the platforms. We observed that researchers with an extraordinary high h-index and researchers with an index appropriate to the scientific career path and the respective scientific field are affected alike by these problems.
Weak memory consistency models capture the outcomes of concurrent
programs that appear in practice and yet cannot be explained by thread
interleavings. Such outcomes pose two major challenges to formal
methods. First, establishing that a memory model satisfies its
intended properties (e.g., supports a certain compilation scheme) is
extremely error-prone: most proposed language models were initially
broken and required multiple iterations to achieve soundness. Second,
weak memory models make verification of concurrent programs much
harder, as a result of which there are no scalable verification
techniques beyond a few that target very simple models.
This thesis presents solutions to both of these problems.
First, it shows that the relevant metatheory of weak memory
models can be effectively decided (sparing years of manual proof
efforts), and presents Kater, a tool that can answer metatheoretic
queries in a matter of seconds. Second, it presents GenMC, the first
(and only) scalable stateless model checker that is parametric in the
choice of the memory model, often improving the prior state of the art
by orders of magnitude.
In one-dimensional (1-D) Ultrasound (US) measurements, signals are
acquired that form the basis of more sophisticated two-dimensional (2-D) or
three-dimensional (3-D) US imaging. These 1-D signals contain a lot of raw
information about the US wave propagation and interaction with the
medium that is only processed in parts during image generation. While
image representations are easy to interpret for humans, the analysis of US
wave signals is hard to perform without applying algorithms to extract
desired features.
This work investigates reliable and fast 1-D US signal classifications to
distinguish between different stages or states in biomedical US scenarios and
shows how the new field of Machine Learning (ML) on raw US wave data
provides advantages and different applications. To achieve good results, the
input signals are treated as time series, which requires the deployment of
comparatively complex Time Series Classification (TSC) algorithms.
The literature shows that a lot of research efforts have previously only
tackled the classification and segmentation of US Brightness mode (B-Mode)
images, while neglecting approaches to classify 1-D signals to a large extent.
This research contributes by developing, deploying and evaluating
classification approaches for three distinct biomedical US classification tasks
and finds that respective signal classifications for different scenarios are
possible with varying degrees of accuracies. It entails the comparison of
several combinations of data types (e.g. temporal, spectral and statistical
features or raw signals), ML models and pre-processing steps to provide a
strong foundation for robust, binary classifications of 1-D US signals for
scenarios based on low-cost wearable, mobile and stationary devices. This
research addresses scientific questions not answered before by informing on
detailed descriptions of beneficial domain specific knowledge (domain specific
knowledge (DSK)), achieved accuracies and times needed for training and
evaluation of the examined ML models.
The resulting ML pipelines includes solutions based on data acquired from
custom experimental setups or clinical trials. Possible real-world applications
might include muscle contraction trackers, muscle fatigue detectors,
epiphyseal radius bone closure detectors or devices providing information
about advanced liver disease stages.
Automated machine-assisted
classifications requiring as little DSK as possible from the end user enable
application scenarios ranging from fitness or rehabilitation trackers as
consumer devices to solutions providing diagnostic support without requiring
extensive knowledge from professional medical practitioners. For example,
decision support systems for bone age assessments in clinical use or liver
health assessment systems for gastroenterologists.
This work shows that reliable, robust and fast classifications based on 1-D
US signals are possible with high degrees of accuracies depending on the
examined scenario with achieved F 1 -scores ranging from ≈ 70% to ≈ 87%.
These results prove that real-life applications for recreational purposes are
already possible and that critical applications for clinical use are highly likely
to be achieved once the presented approaches are further optimized in the future.
The field of 3D reconstruction is one of the most important areas in computer
vision. It is not only of theoretical importance, but it is also increasingly
used in practical applications, be it in reverse engineering, quality control or
robotics. In practical applications, where high precision reconstructions are
required for a large variety of different objects, structured light reconstruction
is often the method of choice. It allows to achieve accurate and dense
point correspondences over the entire scene, regardless of object texture or
features. Techniques that project phase-shifted sinusoidals are widely used
because, based on the harmonic addition theorem, they theoretically allow
surface encoding in full camera resolution invariant to the object’s coloring.
In this thesis, a fully-automatic reconstruction pipeline based on the sinusoidal
structured light technique is presented. From the projection of the
fringe patterns for encoding the object’s surface, the robust matching of the
point correspondences in sub-pixel accuracy, the auto-calibration of the setup
including the active device, up to the fully-automatic alignment of the partial
reconstructions, all steps will be described and examined in detail. During
that, improvements will be achieved in the area of matching, obtaining highly
accurate and topologically consistent correspondences in sub-pixel precision
between all the devices used. Furthermore, the auto-calibration from point
correspondences, based on the epipolar geometry of the structured light system
is improved. Weaknesses of previous methods in the extraction of focal
lengths from the fundamental matrices are discovered and addressed. The partial
point clouds, reconstructed from the auto-calibrated devices, are finally
pre-aligned using a neural network approach, based on light-resistant optical
flow estimation and subsequently refined using a global approach.
The weaknesses of the structured light method itself will also be addressed
and partially fixed during the course of this work. Since it is an active reconstruction method, certain surface properties can affect the quality of the
reconstruction. It will be shown how these problems can be eliminated or at
least be reduced using an iterative approach that combines fringe patterns with
an inverse texture. Another weakness of the method is its time-consuming acquisition procedure. Typically, a large number of horizontal and vertical fringe
patterns are projected onto the scene to achieve high-precision encoding despite
the limited dynamic range and resolution of the projector. Therefore, a
method will be presented which allows to combine the horizontal and vertical
patterns for a simultaneous two dimensional surface encoding.
During our daily lives, we are confronted with vast amounts of data, the processing of which can dramatically influence our lives, both positively and negatively. The enormous amount of data (images, texts, tables, and time series), its variety and possible applications are not always obvious. Due to advancements in the internet of things (IoT), there exist billions of sensors that produce time series which can be found everywhere, whether in medicine, the financial sector or the agricultural economy. This incredible amount of time series data has many hidden features which are useful for industry as well as for daily use, e.g. improving the cancer prediction can save real human lives. Recently, several deep learning methods have been proposed for analyzing this time series data. However, due to their black box nature, their applicability is limited in critical sectors like medicine, finance, and communication. In addition, it is now a compulsion as per artificial intelligence (AI) Act and per General Data Protection Regulation (GDPR) to protect any sensitive data and provide explanations in safety-critical domains. To enable use of DNNs in a broader domain scope, this thesis presents a framework for privacy-preserved and interpretable time series analysis. TimeFrame consists of four main components, namely, post-hoc interpretability, intrinsic interpretability, direct privacy, and indirect privacy. Interpretability is indispensable to avoid damaging people or the infrastructure. In the past years, the development mostly focused on image data, which prevented the full potential of DNNs in time series processing from being exploited. To overcome this limitation, TimeFrame introduces five (Time to Focus, TSViz, TimeREISE, TSInsight, Data Lens) novel post-hoc and two (PatchX, P2ExNet) novel intrinsic interpretability components. TimeFrame addresses multiple perspectives such as attribution, compression, visualization, influence, prototyping, and hierarchical splitting. Compared to existing methods, the components show better explanations, robustness, and scalability. Another crucial factor is the privacy when dealing with sensitive data and deep learning. In this context, TimeFrame introduces two (PPML, PPML x XAI) components for direct and one (From Private to Public) component for indirect privacy. These components benchmark privacy approaches, their effect on interpretability, and the synthetic generation of data to overcome privacy concerns. TimeFrame offers a large set of interpretability and privacy components that can be combined and consider numerous different aspects. Furthermore, the novel approaches have shown to consistently outperform twenty existing state-of-the-art methods across up to 20 different datasets. To guarantee the fairness, various metrics were used including performance change, Sensitivity, Infidelity, Continuity, runtime, model dependency, compression rate, and others. This broad set of metrics makes it possible to provide guidelines for a more appropriate use of existing state-of-the-art approaches as well as the novel components included in TimeFrame.
Highly Automated Driving (HAD) vehicles represent complex and safety critical systems. They are deployed in an open context i.e., an intricate environment which undergoes continual changes. The complexity of these systems and insufficiencies in sensing and understanding the open context may result in unsafe and uncertain behaviour. The safety critical nature of the HAD vehicles requires modelling of root causes for unsafe behaviour and their mitigation to argue sufficient reduction of residual risk.
Standardization activities such as ISO 21448 provide guidelines on the Safety Of The Intended Functionality (SOTIF) and focus on the analysis of performance limitations under the influence of triggering conditions that can lead to hazardous behaviour. SOTIF references traditional safety analyses methods e.g., Failure Mode and Effect Analysis (FMEA) and Fault Tree Analysis (FTA) to perform safety analysis. These analyses methods are based on certain assumptions e.g., single point failure in FMEA and independence of basic events in FTA. Moreover, these analyses are generally based on expert knowledge i.e., data-based models or hybrid approaches (expert and data) are seldom practised. The resulting safety model is fixed i.e., it is generally seen as a one-time artefact. Open context environment may contain triggering conditions which may not be evident to the expert. Open context also evolves over time and new phenomena may emerge.
This thesis explores the applicability of the traditional safety analyses techniques to provide safety models for HAD vehicles operating in the open context, under the light of modelling assumptions taken by traditional safety analyses techniques. Moreover, incorporating uncertainties into safety analyses models is also explored. An explicit distinction between the inherent uncertainty of a probabilistic event (aleatory) and uncertainty due to lack of knowledge (epistemic) is made to formalize models to perform SOTIF analysis. A further distinction is made for conditions of complete ignorance and termed as ontological uncertainty. The distinction is important as for HAD vehicles operating in open context the ontological uncertainty can never be completely disregarded.
This thesis proposes a novel framework of SOTIF to model, estimate and dis cover triggering conditions relevant to performance limitations. The framework provides the ability to model uncertainties while also providing a hybrid approach i.e., supporting inclusion of expert knowledge as well as data driven engineering processes. Two representative algorithms are provided to support the framework. Bayesian Network (BN) and p-value hypothesis testing are utilised in this regard. The framework is implemented on a real-world case study in which LIDARs based perception systems are used as vehicle detection system.