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PublicationInformed Machine Learning - A Taxonomy and Survey of Integrating Prior Knowledge into Learning Systems( 2023)Despite its great success, machine learning can have its limits when dealing with insufficient training data. A potential solution is the additional integration of prior knowledge into the training process which leads to the notion of informed machine learning. In this paper, we present a structured overview of various approaches in this field. We provide a definition and propose a concept for informed machine learning which illustrates its building blocks and distinguishes it from conventional machine learning. We introduce a taxonomy that serves as a classification framework for informed machine learning approaches. It considers the source of knowledge, its representation, and its integration into the machine learning pipeline. Based on this taxonomy, we survey related research and describe how different knowledge representations such as algebraic equations, logic rules, or simulation results can be used in learning systems. This evaluation of numerous papers on the basis of our taxonomy uncovers key methods in the field of informed machine learning.
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PublicationFormation of spiraling infrared emission patterns by controlled interaction of optical filaments( 2021)We analyzed the formation of mid-infrared conical emission patterns possessing spiral and half-ring shaped wavelength contours from a beam of a few optical filaments. The complex patterns were generated and modified experimentally by adaptive wavefront shaping of the femtosecond laser pulse. Mutual interactions between co-propagating filaments can induce curvature in their paths, and the spiral and half-ring emissions were shown to be a direct consequence of this angular deflection. Based on our experimental and computational results, the spirals form in the far-field due to self-interference of conical emission from a helically moving filament. The presented findings will advance the tailoring of spatial conical emission patterns potentially beneficial for spectroscopic applications and terahertz generation.
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PublicationMicrogrid Systems: Towards a Technical Performance Assessment Frame( 2021)
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PublicationQuantum ghost imaging using asynchronous detection( 2021)We present first results of a novel type of setup for quantum ghost imaging based on asynchronous single photon timing using single photon avalanche diode (SPAD) detectors. This scheme enables photon pairing with arbitrary path length difference and does, therefore, obviate the dependence on optical delay lines of current quantum ghost imaging setups [Nat. Commun. 6, 5913 (2015) [CrossRef]]. It is also, to our knowledge, the first quantum ghost imaging setup to allow three-dimensional imaging.
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PublicationAlignment of safety and security risk assessments for modular production systems( 2021)In order to ensure the safety and security of industrial systems with regard to all life cycle phases from development through operation to disposal, specific regulatory and normative requirements are imposed. Due to the digitalization, interconnection, and constantly increasing complexity of manufacturing systems in the context of Industrie 4.0, the manual effort necessary to achieve the required safety and security is becoming ever greater and almost impossible to manage, especially for small and medium-sized enterprises. Therefore, this paper examines the existing challenges in this area in more detail and gives an outlook on the possible solutions to ensure safety and security much quicker and with less manual effort. The overall vision is a (partially) automated risk assessment of modular systems with respect to safety and security, including the alignment of the corresponding processes from both domains and the formalization of the information models needed.
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PublicationOptimal, blind-search modal wavefront correction in atmospheric turbulence. Part I: Simulations( 2021)Modal control is an established tool in adaptive optics. It allows not only for the reduction in the controllable degrees of freedom, but also for filtering out unseen modes and optimizing gain on a mode-by-mode basis. When Zernike polynomials are employed as the modal basis for correcting atmospheric turbulence, their cross-correlations translate to correction errors. We propose optimal modal decomposition for gradient-descent-based wavefront sensorless adaptive optics, which is free of this problem. We adopt statistically independent Karhunen-Loève functions for iterative blind correction and analyze performance of the algorithm in static as well as in dynamic simulated turbulence conditions.
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PublicationSmartSpectrometer - Embedded Optical Spectroscopy for Applications in Agriculture and Industry( 2021)The ongoing digitization of industry and agriculture can benefit significantly from optical spectroscopy. In many cases, optical spectroscopy enables the estimation of properties such as substance concentrations and compositions. Spectral data can be acquired and evaluated in real time, and the results can be integrated directly into process and automation units, saving resources and costs. Multivariate data analysis is needed to integrate optical spectrometers as sensors. Therefore, a spectrometer with integrated artificial intelligence (AI) called SmartSpectrometer and its interface is presented. The advantages of the SmartSpectrometer are exemplified by its integration into a harvesting vehicle, where quality is determined by predicting sugar and acid in grapes in the field.
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PublicationExperimental Evaluation of a Novel Sensor-Based Sorting Approach Featuring Predictive Real-Time Multiobject Tracking( 2021)Sensor-based sorting is a machine vision application that has found industrial application in various fields. An accept-or-reject task is executed by separating a material stream into two fractions. Current systems use line-scanning sensors, which is convenient as the material is perceived during transportation. However, line-scanning sensors yield a single observation of each object and no information about their movement. Due to a delay between localization and separation, assumptions regarding the location and point in time for separation need to be made based on the prior localization. Hence, it is necessary to ensure that all objects are transported at uniform velocities. This is often a complex and costly solution. In this paper, we propose a new method for reliably separating particles at non-uniform velocities. The problem is transferred from a mechanical to an algorithmic level. Our novel advanced image processing approach includes equipping the sorter with an area-scan camera in combination with a real-time multiobject tracking system, which enables predictions of the location of individual objects for separation. For the experimental validation of our approach, we present a modular sorting system, which allows comparing sorting results using a line-scan and area-scan camera. Results show that our approach performs reliable separation and hence increases sorting efficiency.
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PublicationTesting Automated Operation and Control Algorithms for Distribution Grids Using a Co-Simulation Environment( 2021)This publication presents a co-simulation framework that enables the coupling of various simulation components of energy systems that are not only modeled at three geographically distributed Fraunhofer Institutes, but are also vastly different in terms of their functionality, control algorithms, time resolution, speeds and used tools. This framework facilitates their joint usage despite these differences especially with regard to their time resolutions (real-time combined with non-real-time systems) and is applied in the DistributedGridLab of the Fraunhofer Cluster of Excellence Integrated Energy Systems (CINES) [1]. The DistributedGridLab thus allows users - e.g. grid operators, manufacturers and research institutes - to test their solutions before field deployment with special consideration of their interaction with other solutions at different remote testing facilities, and without the need to use the same software and hardware setups. A demonstrator of the DistributedGridLab is introduced where an electric energy system is modeled, which contains a medium voltage grid with three connected low voltage grids. The different control approaches interact to stabilize the entire system without a centrally controlled simulation of the systems.
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PublicationCleaning strategies and cost modelling of experimental membrane-based desalination plants( 2021)In Project WASTEC, an experimental Reverse Osmosis (RO) desalination system was developed. It serves as a platform for testing new technologies. For this system, we solved two problems, which are described in this paper. Firstly, we developed and investigated strategies for scheduling chemical enhanced backwashing and chemical cleaning and secondly, due to the experimental nature of the project, several new technological developments with respect to materials and methods were integrated into the system and requires tools for evaluating the economic viability of the new technologies. In this task, the economics of membrane-based desalination will be investigated. Baseline systems of reverse osmosis and pretreatment systems (microfiltration and ultrafiltration) will be economically examined and compared for their investments and operational costs. Sensitivity of the different plant and membrane parameters to the cost will be studied. Results show that with respect to costs, for a 200m3/hr design capacity plant, a volume of water is produced by a MF process at a cost of $0.494 and at a cost of $0.486 by an ultrafiltration process microfiltration. The reverse osmosis process cannot be compared directly, but it required $ 0.49 / m3 for a plant with 56 m3/hour design capacity. The values are in line with the costs reported in literature for membrane-based filtration.
