Thorsten Ehlers

Thorsten Ehlers
German Aerospace Center (DLR) | DLR · Department of Air Transport Operations

PhD

About

29
Publications
3,577
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153
Citations
Citations since 2017
15 Research Items
117 Citations
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20172018201920202021202220230510152025
20172018201920202021202220230510152025

Publications

Publications (29)
Article
Full-text available
Zusammenfassung Die Europäische Union strebt mit den Maßnahmen des Fit-for-55-Pakets eine Verringerung der CO 2 -Emissionen bis 2030 um 55% an, verglichen mit dem Stand von 1990. Diese Reduktion soll durch verschiedene Maßnahmen erreicht werden, die auch die kommerzielle Luftfahrt betreffen. Dies sind unter anderem eine Verschärfung des Emissionsha...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-3546.vid Long range drones (either fixed wing or VTOL) represent a novel approach for monitoring and inspection of extensive longitudinal infrastructures such as power lines, pipelines and railway tracks including overhead lines. This paper proposes a method to find efficient system of systems...
Conference Paper
In this paper, we present a globally applicable approach for estimating the potential passenger demand for On- Demand Inter-City Air Mobility based on three different use cases. All of these cases are concerned with pas- sengers who nowadays travel with conventional airlines, and might choose On-Demand Air Mobility (ODAM) as an alternative mode of...
Article
How do changing jet fuel prices impact airline revenues? As expenses for jet fuel are one of the most relevant cost factors for airlines, their economic success largely depends on the ability to match changes on the cost side with an adaption on the revenue side. While previous studies primarily focused on the impact of fuel price changes to consum...
Conference Paper
Full-text available
Commercial airlines pay navigation charges for each flight in the European airspace. These charges differ between countries. Thus, flying detours may lead to reduced costs if the longer route uses the airspace of countries with cheaper charges. In this paper, we analyze this incentive for flying routes longer than the shortest ones. While previous...
Chapter
Full-text available
We present Woorpje, a string solver for bounded word equations (i.e., equations where the length of each variable is upper bounded by a given integer). Our algorithm works by reformulating the satisfiability of bounded word equations as a reachability problem for nondeterministic finite automata, and then carefully encoding this as a propositional...
Preprint
Full-text available
We present Woorpje, a string solver for bounded word equations (i.e., equations where the length of each variable is upper bounded by a given integer). Our algorithm works by reformulating the satisfiability of bounded word equations as a reachability problem for nondeterministic finite automata, and then carefully encoding this as a propositional...
Preprint
Solving avoidability problems in the area of string combinatorics often requires, in an initial step, the construction, via a computer program, of a very long word that does not contain any word that matches a given pattern. It is well known that this is a computationally hard task. Despite being rather straightforward that, ultimately, all such ta...
Conference Paper
We suggest some benchmarks based on a propositional encoding of tree decompositions of graphs.
Article
Full-text available
The computation of a cyber-physical system's reaction to a stimulus typically involves the execution of several tasks. The delay between stimulus and reaction thus depends on the interaction of these tasks and is subject to timing constraints. Such constraints exist for a number of reasons and range from possible impacts on customer experiences to...
Conference Paper
Full-text available
While the theoretical aspects concerning the computation of tree width - one of the most important graph parameters - are well understood, it is not clear how it can be computed practically.We present the open source Java library Jdrasil that implements several different state of the art algorithms for this task. By experimentally comparing these a...
Article
Full-text available
The Directed Layering Problem (DLP) solves a step of the widely used layer-based approach to automatically draw directed acyclic graphs. To cater for cyclic graphs, usually a preprocessing step is used that solves the Feedback Arc Set Problem (FASP) to make the graph acyclic before a layering is determined. Here we present the Generalized Layering...
Conference Paper
The Directed Layering Problem (DLP) solves a step of the widely used layer-based approach to automatically draw directed acyclic graphs. To cater for cyclic graphs, usually a preprocessing step is used that solves the Feedback Arc Set Problem (FASP) to make the graph acyclic before a layering is determined. Here we present the Generalized Layering...
Article
Full-text available
We present a new sorting network on 24 channels, which uses only 12 layers, improving the previously best known bound by one layer. By monotonicity, this also implies improved sorting networks for 23 channels. This result was obtained by combining techniques for generating prefixes of sorting networks with propositional encodings.
Article
Full-text available
The Directed Layering Problem (DLP) solves a step of the widely used layer-based approach to automatically draw directed acyclic graphs. To cater for cyclic graphs, usually a preprocessing step is used that solves the Feedback Arc Set Problem (FASP) to make the graph acyclic before a layering is determined. Here we present the Generalized Layering...
Conference Paper
Parallel Constraint Programming (CP) solvers typically split the search space in disjoint subspaces, and run solvers independently on these. This may induce significant overhead when solving optimization problems. Parallel Boolean Satisfiability (SAT) solvers typically run a portfolio of solvers, all solving the same problem but sharing some limite...
Article
This paper studies new properties of the front and back ends of a sorting network, and illustrates the utility of these in the search for new bounds on optimal sorting networks. Search focuses first on the "outsides" of the network and then on the inner part. All previous works focus only on properties of the front end of networks and on how to app...
Article
Two words are called k-abelian equivalent, if they share the same multiplicities for all factors of length at most k. We present an optimal linear time algorithm for identifying all occurrences of factors in a text that are k-abelian equivalent to some pattern P. Moreover, an optimal algorithm for finding the largest k for which two words are k-abe...
Conference Paper
Full-text available
We present new parallel sorting networks for $17$ to $20$ inputs. For $17, 19,$ and $20$ inputs these new networks are faster (i.e., they require less computation steps) than the previously known best networks. Therefore, we improve upon the known upper bounds for minimal depth sorting networks on $17, 19,$ and $20$ channels. Furthermore, we show t...
Conference Paper
The exchange of learnt clauses is a key feature in parallel SAT solving. We present an approach based on a communication graph. Each solver thread corresponds to a node in this graph. Communication between two solvers is allowed if the respective nodes are connected by an edge. This yields another dimension in controlling the amount of communicatio...
Article
Full-text available
We present new parallel sorting networks for $17$ to $20$ inputs. For $17, 19,$ and $20$ inputs these new networks are faster (i.e., they require less computation steps) than the previously known best networks. Therefore, we improve upon the known upper bounds for minimal depth sorting networks on $17, 19,$ and $20$ channels. The networks were obta...
Article
Full-text available
The introduction of multicore hardware to the field of embedded and safety-critical systems implies great safety challenges. An important issue in this context is the migration of legacy code to multicore systems. In this paper, we present approaches to support the migration process in the domain of safety-critical, embedded systems. Given a progra...
Article
Full-text available
The introduction of multicore hardware to the field of embedded and safety-critical systems implies great challenges. An important issue in this context is the migration of legacy code to multicore systems. Starting from the field of formal verification, we aim to improve the usability of our methods for software engineers. In this paper, we presen...
Conference Paper
We present a robust EPTAS for scheduling on identical machines. The running time for adding one job is bounded by 2O((1/ε2) log3(1/ε)). The migration factor required to gain a (1+ ε)-approximate schedule in each iteration is bounded by 2O((1/ε) log2(1/ε)).

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Project (1)
Project
While the theoretical aspects concerning the computation of tree width - one of the most important graph parameters - are well understood, it is not clear how it can be computed practically. As tree width has a wide range of applications, \eg in bioinformatics or artificial intelligence, this lack of understanding hinders the applicability of many important algorithms in the real world.