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Item type:Publication, Access status: with files , Finding subdigraphs in digraphs of bounded directed treewidthIt is well known that directed treewidth does not enjoy the nice algorithmic properties of its undirected counterpart. There exist, however, some positive results that, essentially, present XP algorithms for the problem of finding, in a given digraph D, a subdigraph isomorphic to a digraph H that can be formed by the union of k directed paths (with some extra properties), parameterized by k and the directed treewidth of D. Our motivation is to tackle the following question: Are there subdigraphs, other than the directed paths, that can be found efficiently in digraphs of bounded directed treewidth? In a nutshell, the main message of this article is that, other than the directed paths, the only digraphs that seem to behave well with respect to directed treewidth are the stars. For this, we present a number of positive and negative results, generalizing several results in the literature, as well as some directions for further research.Publicationtype: Conference Paper19 18 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A multi-perspective framework to address manufacturing and transportation challenges in green hydrogen supply chainsThe strategic changeover towards green hydrogen supply chains entails a large number of challenges in determining strategic manufacturing, transportation, and supply chain decisions such as the locations for the generation and storage or the transport mode for the transfer of green hydrogen. Such decisions face three dedicated obstacles interesting for research analysis. First, such decisions in a greenfield setting have in many cases never been made before, reducing the access to historical information about manufacturing and transportation volumes, aggravated by new levels of uncertainty in many global manufacturing and transportation contexts. Second, at the same time, new data sources and computation capabilities become available in a digital Industry 4.0 setting, creating big data and data lake settings where traditional decision support methodologies have limited access and use in this regard. Third, an integrated evaluation of economic, environmental, and social sustainability aspects together with a resilience perspective is required as trade-offs between these different performance dimensions have to be incorporated. This paper outlines and addresses the three specific challenges by deriving a concept of how to integrate the three standard sustainability perspectives with the added resilience perspective and how to tailor this towards decision-making in a strategic, data-driven and digital setting of emerging green hydrogen supply chains.Publicationtype: Conference Paper22 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Synthetic data generation procedures for domain-specific environments in manufacturingSynthetic data is being used lately for training deep neural networks in computer vision applications such as object detection, object segmentation and 6D object pose estimation. Domain randomization hereby plays an important role in reducing the simulation to reality gap. However, this generalization might not always be effective in specialized domains like manufacturing that involve complex assemblies. Individual parts are integrated in much larger assemblies making them indistinguishable from their counterparts. Moreover, individual parts are often partially occluded in the scene. These situations give rise to wrong detections. Target domain knowledge is vital in these cases and if conceived effectively while generating synthetic data, can show a considerable improvement in bridging the simulation to reality gap. This paper validates synthetic data generation procedures through practical experimentation ensuring that experiments are both comprehensive and reproducible. After combining domain randomization and domain adaptation procedures for parts and assemblies used in manufacturing the model performance improves by up to 15% than the state-of-the-art domain randomization techniques. Reducing the simulation to reality gap in this way can unlock the true potential of robot-assisted production using artificial intelligence.Publicationtype: Conference Paper37 17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Use of augmented reality for iterative robot program optimisation in robot-automated series production processesThe inspection, analysis, and modification of robot programs in series production processes is a challenging recurring task in the automotive industry. Especially the holistic analysis of detected defects and the subsequent derivation and application of corrective measures to the underlying robot program is a complex task requiring extensive knowledge in multiple fields. Existing scientific literature has demonstrated that the utilisation of Augmented Reality (AR) assisted robot programming systems (ARRPS) improves programming efficiency as well as intuitiveness when compared to traditional programming methods. However, the accuracy especially of mobile AR devices limits the applicability of AR in industrial applications. We propose to leverage the iterative nature of the optimisation process common in series production and utilise the visual capabilities of the human worker to define corrective measures based on the inspected real process result. This mitigates the impact of limited tracking accuracy as the optimisation is based on the visual perception of the user and thus decoupled from the accuracy of the employed AR device. We implemented our system based on the requirements of a sealing workstation of the Mercedes-Benz Group in Germany. A conducted experiment validates the functionality and indicates that the presented strategy of iterative AR assisted robot programming enables optimisations with a similar accuracy as the Teach-In programming as well as a significantly reduced programming time. This suggests that utilising an ARRPS can be highly beneficial in the inspection, analysis, and modification of sealing applications common in automotive series production processes. As the presented iterative AR assisted robot programming is neither limited to sealing nor to the automotive sector it can be adapted for various robot-automated applications like path-welding, gluing, or painting and can extend its utility to related sectors such as aviation or the marine industry.Publicationtype: Conference Paper27 88 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Simulation of database interactions for early validation of digitized enterprise processesDigitized enterprise processes often encompass interaction with relational databases. Describing and simulating large-scale and complex processes on different abstraction levels lead to the use of tools and methods of Model-based Systems Engineering. In practice, current entity-relationship modeling approaches solely enable modeling relational database structure without simulation of database interactions at an early development stage. However, in general, it is known that early validation improves common understanding and communication in the development team and reduces the risk of design flaws. This paper presents an approach for model-based enterprise process digitization and a previously developed and now enhanced broker-based SysML Toolbox for integrating real relational databases into SysML simulations. The approach comprises status quo documentation concerning enterprise processes, development of digitized processes and required relational database structures as well as validation of digitized processes using the SysML Toolbox.Publicationtype: Journal ArticleScopus© Citations 1 97 188 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Maximum size of r-cross t-intersecting families(2021-05); ; ; Given r families of subsets of a fixed n-set, we say that they are r-cross t-intersecting if for every choice of representatives, exactly one from each family, the common intersection of these representatives is of size at least t. We obtain a generalisation of a result by Hilton and Milner on cross intersecting families. In particular, we determine the maximum possible sum of the sizes of non-empty r-cross t-intersecting families in the case when all families are k-uniform and in the case when they are arbitrary subfamilies of the power set. Only some special cases of these results had been proved before. The method we use also yields more general results concerning measures of families instead of their sizes.Publicationtype: Conference Paper152 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Building-linked location-based Instantaneous services systemFor services which are meant to be used mainly inside buildings, a distribution using global app stores is inappropriate. Instead this work presents a provisioning system (BLISS) for building-linked location-based services. The multi-purpose application MultiApp implements the client-side of the BLISS specification. When a user enters a building, MultiApp instantaneously detects available services and allows to install and execute them. The client part of services is executed within the MultiApp environment and can provide functionalities similar to those offered by native applications. BLISS facilitates developing indoor location-based services by providing bi-directional communication between service providers and clients.Publicationtype: Journal ArticleScopus© Citations 1 253 268