Publikationen an der Fakultät für Informatik und Automatisierung ab 2015

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Lasch, Robert; Legler, Thomas; May, Norman; Scheirle, Bernhard; Sattler, Kai-Uwe
Cooperative memory management for table and temporary data. - In: 1st Workshop on Simplicity in Management of Data, (2023), 2, insges. 5 S.

The traditional paradigm for managing memory in database management systems (DBMS) treats memory used for caching table data and memory for temporary data as separate entities. This leads to inefficient utilization of the available memory capacity for mixed workloads. With memory being a significant factor in the costs of operating a DBMS, utilizing memory as efficiently as possible is highly desirable. As an alternative to the traditional paradigm, we propose managing the entire available memory in a cooperative manner to achieve better memory utilization and consequently higher cost-effectiveness for DBMSs. Initial experimental evaluation of cooperative memory management using a prototype implementation shows promising results and leads to several interesting further research directions.
Korte, Jana; Voß, Samuel; Janiga, Gábor; Beuing, Oliver; Behme, Daniel; Saalfeld, Sylvia; Berg, Philipp
Is accurate lumen segmentation more important than outlet boundary condition in image-based blood flow simulations for intracranial aneurysms?. - In: Cardiovascular engineering and technology, ISSN 1869-4098, Bd. 0 (2023), 0, insges. 14 S.

Purpose: Image-based blood flow simulations are increasingly used to investigate the hemodynamics in intracranial aneurysms (IAs). However, a strong variability in segmentation approaches as well as the absence of individualized boundary conditions (BCs) influence the quality of these simulation results leading to imprecision and decreased reliability. This study aims to analyze these influences on relevant hemodynamic parameters within IAs. Methods: As a follow-up study of an international multiple aneurysms challenge, the segmentation results of five IAs differing in size and location were investigated. Specifically, five possible outlet BCs were considered in each of the IAs. These are comprised of the zero-pressure condition (BC1), a flow distribution based on Murray’s law with the exponents n = 2 (BC2) and n = 3 (BC3) as well as two advanced flow-splitting models considering the real vessels by including circular cross sections (BC4) or anatomical cross sections (BC5), respectively. In total, 120 time-dependent blood flow simulations were analyzed qualitatively and quantitatively, focusing on five representative intra-aneurysmal flow and five shear parameters such as vorticity and wall shear stress. Results: The outlet BC variation revealed substantial differences. Higher shear stresses (up to Δ9.69 Pa), intrasaccular velocities (up to Δ0.15 m/s) and vorticities (up to Δ629.22 1/s) were detected when advanced flow-splitting was applied compared to the widely used zero-pressure BC. The tendency of outlets BCs to over- or underestimate hemodynamic parameters is consistent across different segmentations of a single aneurysm model. Segmentation-induced variability reaches Δ19.58 Pa, Δ0.42 m/s and Δ957.27 1/s, respectively. Excluding low fidelity segmentations, however, (a) reduces the deviation drastically (>43%) and (b) leads to a lower impact of the outlet BC on hemodynamic predictions. Conclusion: With a more realistic lumen segmentation, the influence of the BC on the resulting hemodynamics is decreased. A realistic lumen segmentation can be ensured, e.g., by using high-resolved 2D images. Furthermore, the selection of an advanced outflow-splitting model is advised and the use of a zero-pressure BC and BC based on Murray’s law with exponent n = 3 should be avoided.
Berkholz, Christoph; Vinall-Smeeth, Harry
A dichotomy for succinct representations of homomorphisms. - In: 50th International Colloquium on Automata, Languages, and Programming, (2023), S. 113:1-113:19

The task of computing homomorphisms between two finite relational structures A and B is a well-studied question with numerous applications. Since the set Hom(A, B) of all homomorphisms may be very large having a method of representing it in a succinct way, especially one which enables us to perform efficient enumeration and counting, could be extremely useful. One simple yet powerful way of doing so is to decompose Hom(A, B) using union and Cartesian product. Such data structures, called d-representations, have been introduced by Olteanu and Závodný [Olteanu and Závodný, 2015] in the context of database theory. Their results also imply that if the treewidth of the left-hand side structure A is bounded, then a d-representation of polynomial size can be found in polynomial time. We show that for structures of bounded arity this is optimal: if the treewidth is unbounded then there are instances where the size of any d-representation is superpolynomial. Along the way we develop tools for proving lower bounds on the size of d-representations, in particular we define a notion of reduction suitable for this context and prove an almost tight lower bound on the size of d-representations of all k-cliques in a graph.
Jochmann, Thomas; Seibel, Marc S.; Jochmann, Elisabeth; Khan, Sheraz; Hämäläinen, Matti; Haueisen, Jens
Sex-related patterns in the electroencephalogram and their relevance in machine learning classifiers. - In: Human brain mapping, ISSN 1097-0193, Bd. 44 (2023), 14, S. 4848-4858

Deep learning is increasingly being proposed for detecting neurological and psychiatric diseases from electroencephalogram (EEG) data but the method is prone to inadvertently incorporate biases from training data and exploit illegitimate patterns. The recent demonstration that deep learning can detect the sex from EEG implies potential sex-related biases in deep learning-based disease detectors for the many diseases with unequal prevalence between males and females. In this work, we present the male- and female-typical patterns used by a convolutional neural network that detects the sex from clinical EEG (81% accuracy in a separate test set with 142 patients). We considered neural sources, anatomical differences, and non-neural artifacts as sources of differences in the EEG curves. Using EEGs from 1140 patients, we found electrocardiac artifacts to be leaking into the supposedly brain activity-based classifiers. Nevertheless, the sex remained detectable after rejecting heart-related and other artifacts. In the cleaned data, EEG topographies were critical to detect the sex, but waveforms and frequencies were not. None of the traditional frequency bands was particularly important for sex detection. We were able to determine the sex even from EEGs with shuffled time points and therewith completely destroyed waveforms. Researchers should consider neural and non-neural sources as potential origins of sex differences in their data, they should maintain best practices of artifact rejection, even when datasets are large, and they should test their classifiers for sex biases.
Honecker, Maria Christine; Gernandt, Hannes; Wulff, Kai; Trunk, Carsten; Reger, Johann
Feedback rectifiable pairs and stabilization of switched linear systems. - Ilmenau : Technische Universität Ilmenau, Institut für Mathematik, 2023. - 1 Online-Ressource (12 Seiten). - (Preprint ; M23,07)

We address the feedback design problem for switched linear systems. In particular we aim to design a switched state-feedback such that the resulting closed-loop switched system is in upper triangular form. To this effect we formulate and analyse the feedback rectification problem for pairs of matrices. We present necessary and sufficient conditions for the feedback rectifiability of pairs for two subsystems and give a constructive procedure to design stabilizing state-feedback for a class of switched systems. Several examples illustrate the characteristics of the problem considered and the application of the proposed constructive procedure.
Winkler, Alexander; Grabmair, Gernot; Reger, Johann
On implementing the implicit discrete-time super-twisting observer on mechanical systems. - In: International journal of robust and nonlinear control, ISSN 1099-1239, Bd. 33 (2023), 13, S. 7532-7562

In this paper, an extension of an algorithm for the implicit discretization of a super-twisting sliding mode observer is presented. Implicit and explicit discretization algorithms for homogeneous differentiators, where no physical model information is considered, are investigated in literature. This article studies the behavior when considering models of a rather general class of nonlinear systems. The discrete equations of the super-twisting observer are reformulated as generalized equation and an algorithm for the step-by-step solution is given. The uniqueness of the derived algorithm is investigated with an equivalent variational inequality formulation which is derived for a class of nonlinear systems. Furthermore, a semi-implicit predictor-corrector discretization is presented which is an approximation method for the presented algorithms and allows an explicit implementation in practical applications. Accuracy properties under noise and sampling are given. The algorithm is applied on two mechanical example systems taken from practice.
Lei, Xiong-Xin; Hu, Juan-Juan; Zou, Chen-Yu; Jiang, Yan-Lin; Zhao, Long-Mei; Zhang, Xiu-Zhen; Li, Ya-Xing; Peng, An-Ni; Song, Yu-Ting; Huang, Li-Ping; Li-Ling, Jesse; Xie, Hui-Qi
Multifunctional two-component in-situ hydrogel for esophageal submucosal dissection for mucosa uplift, postoperative wound closure and rapid healing. - In: Bioactive materials, ISSN 2452-199X, Bd. 27 (2023), S. 461-473

Endoscopic submucosal dissection (ESD) for gastrointestinal tumors and premalignant lesions needs submucosal fluid cushion (SFC) for mucosal uplift before dissection, and wound care including wound closure and rapid healing postoperatively. Current SFC materials as well as materials and/or methods for post-ESD wound care have single treatment effect and hold corresponding drawbacks, such as easy dispersion, short duration, weak hemostasis and insufficient repair function. Thus, designing materials that can serve as both SFC materials and wound care is highly desired, and remains a challenge. Herein, we report a two-component in-situ hydrogel prepared from maleimide-based oxidized sodium alginate and sulfhydryl carboxymethyl-chitosan, which gelated mainly based on "click" chemistry and Schiff base reaction. The hydrogels showed short gelation time, outstanding tissue adhesion, favorable hemostatic properties, and good biocompatibility. A rat subcutaneous ultrasound model confirmed the ability of suitable mucosal uplift height and durable maintenance time of AM solution. The in vivo/in vitro rabbit liver hemorrhage model demonstrated the effects of hydrogel in rapid hemostasis and prevention of delayed bleeding. The canine esophageal ESD model corroborated that the in-situ hydrogel provided good mucosal uplift and wound closure effects, and significantly accelerated wound healing with accelerating re-epithelization and ECM remodeling post-ESD. The two-component in-situ hydrogels exhibited great potential in gastrointestinal tract ESD.
Habermehl, Peter; Kuske, Dietrich
On Presburger arithmetic extended with non-unary counting quantifiers. - In: Logical methods in computer science, ISSN 1860-5974, Bd. 19 (2023), 3, S. 4:1-4:32

We consider a first-order logic for the integers with addition. This logic extends classical first-order logic by modulo-counting, threshold-counting and exact-counting quantifiers, all applied to tuples of variables (here, residues are given as terms while moduli and thresholds are given explicitly). Our main result shows that satisfaction for this logic is decidable in two-fold exponential space. If only threshold- and exact-counting quantifiers are allowed, we prove an upper bound of alternating two-fold exponential time with linearly many alternations. This latter result almost matches Berman's exact complexity of first-order logic without counting quantifiers. To obtain these results, we first translate threshold- and exact-counting quantifiers into classical first-order logic in polynomial time (which already proves the second result). To handle the remaining modulo-counting quantifiers for tuples, we first reduce them in doubly exponential time to modulo-counting quantifiers for single elements. For these quantifiers, we provide a quantifier elimination procedure similar to Reddy and Loveland's procedure for first-order logic and analyse the growth of coefficients, constants, and moduli appearing in this process. The bounds obtained this way allow to restrict quantification in the original formula to integers of bounded size which then implies the first result mentioned above. Our logic is incomparable with the logic considered by Chistikov et al. in 2022. They allow more general counting operations in quantifiers, but only unary quantifiers. The move from unary to non-unary quantifiers is non-trivial, since, e.g., the non-unary version of the Härtig quantifier results in an undecidable theory.
Schlegel, Marius; Sattler, Kai-Uwe
MLflow2PROV: extracting provenance from machine learning experiments. - In: Proceedings of the Seventh Workshop on Data Management for End-to-End Machine Learning (DEEM), (2023), 9, insges. 4 S.

Supporting iterative and explorative workflows for developing machine learning (ML) models, ML experiment management systems (ML EMSs), such as MLflow, are increasingly used to simplify the structured collection and management of ML artifacts, such as ML models, metadata, and code. However, EMSs typically suffer from limited provenance capabilities. As a consequence, it is hard to analyze provenance information and gain knowledge that can be used to improve both ML models and their development workflows. We propose a W3C-PROV-compliant provenance model capturing ML experiment activities that originate from Git and MLflow usage. Moreover, we present the tool MLflow2PROV that extracts provenance graphs according to our model, enabling querying, analyzing, and further processing of collected provenance information.
Baumstark, Alexander; Jibril, Muhammad Attahir; Sattler, Kai-Uwe
Processing-in-Memory for databases: query processing and data transfer. - In: 19th International Workshop on Data Management on New Hardware, (DaMoN 2023), June 19th 2023, (2023), S. 107-111

The Processing-in-Memory (PIM) paradigm promises to accelerate data processing by pushing down computation to memory, reducing the amount of data transfer between memory and CPU, and - in this way - relieving the CPU from processing. Particularly, in in-memory databases memory access becomes a performance bottleneck. Thus, PIM seems to offer an interesting solution for database processing. In this work, we investigate how commercially available PIM technology can be leveraged to accelerate query processing by offloading (parts of) query operators to memory. Furthermore, we show how to address the problem of limited PIM storage capacity by interleaving transfer and computation and present a cost model for the data placement problem.