@article{UffmannAbichtGroteetal.2002, author = {Uffmann, Kai and Abicht, Claus and Grote, Wolfgang and Quick, Harald H. and Ladd, Mark E.}, title = {Design of an MR-compatible piezoelectric actuator for MR elastography}, series = {Concepts in Magnetic Resonance Part A: Bridging Education and Research}, volume = {15}, journal = {Concepts in Magnetic Resonance Part A: Bridging Education and Research}, number = {4}, publisher = {Wiley}, doi = {https://doi.org/10.1002/cmr.10045}, pages = {239 -- 254}, year = {2002}, abstract = {Magnetic Resonance (MR) elastography is a method for measuring tissue elasticity via phase images acquired with an MR scanner. The propagation of periodic mechanical waves through the tissue can be captured by means of a modified phase contrast sequence. These waves are generated with a mechanical oscillator (actuator) and coupled into the tissue through the skin. The actuator must be capable of generating a sinusoidal excitation with excellent phase and amplitude stability, while not disturbing the MR imaging process. In this work, an actuator based on a piezoelectric principle was developed. Based on the imaging evaluation of several material samples, the housing for the piezoelectric ceramic was constructed of aluminum. Smaller parts of the housing were manufactured from brass and titanium to fulfill the mechanical constraints. A lever was used to transfer the oscillation generated by the piezoelectric ceramic to the point of excitation. The lever amplifies the piezoelectric motion, allowing for a more compact design. Three different lever designs were characterized by an acceleration sensor both outside and inside the magnet. It was shown that the rigidity of the lever, as determined by its material and form, was decisive in determining the resonant frequency of the system and therefore the maximum practical frequency of operation. It was also shown that the motion of the oscillator is unaffected by the electromagnetic fields of the MR imager. The final design can be placed directly in the magnet bore within a few centimeters of the tissue volume to be imaged without generating significant artifacts. An amplitude range of 0-1 mm in the frequency range from 0 to over 300 Hz was achieved, sufficient for performing most MR elastography applications. © 2002 Wiley Periodicals, Inc. Concepts in Magnetic Resonance (Magn Reson Engineering) 15: 239-254, 2002}, language = {en} } @article{GalbanMaderwaldHerrmannetal.2005, author = {Galban, Craig and Maderwald, Stefan and Herrmann, Burkhard and Brauck, K. and Grote, Wolfgang and de Greiff, A. and Uffmann, K. and Ladd, M.}, title = {Measuring Skeletal Muscle Elasticity in Patients with Hypogonadism by MR Elastography}, series = {Proc. Intl. Soc. Mag. Reson. Med.}, volume = {13}, journal = {Proc. Intl. Soc. Mag. Reson. Med.}, pages = {2016}, year = {2005}, abstract = {Men afflicted with hypogonadism have reduced fat-free mass and in some cases a loss in muscle strength. We hypothesize that muscle elasticity of the lower extremities differs between patients with hypogonadism and healthy controls. The shear modulus of the soleus muscle was measured non-invasively using MR elastography (MRE) at 0\%, 5\%, 10\%, 15\%, and 20\% of the subject's maximum applied force. The results from this study showed statistical differences between the patients and controls, even though there were no statistical differences in applied force.}, language = {en} } @article{GalbanMaderwaldEggebrechtetal.2005, author = {Galban, Craig and Maderwald, Stefan and Eggebrecht, Holger and Grote, Wolfgang and de Greiff, A. and Uffmann, K. and Ladd, M. E.}, title = {Monitoring the Effects of Chronic Obstructive Pulmonary Disease on Muscle Elasticity by MR Elastography}, series = {Proc. Intl. Soc. Mag. Reson. Med.}, volume = {13}, journal = {Proc. Intl. Soc. Mag. Reson. Med.}, pages = {2015}, year = {2005}, abstract = {Men afflicted with chronic obstructive pulmonary disease (COPD) show signs of muscle dysfunction, such as increased muscle fatigue and acidosis during exercise. We hypothesize that muscle elasticity of the lower extremities differs between patients with COPD and age-related controls. The shear modulus of the soleus muscle was measured non-invasively using MR elastography (MRE) at 0\%, 5\%, 10\%, 15\%, and 20\% of the subject's maximum applied force. The results from this study showed statistical differences between the patients and controls, even though there were no statistical differences in the maximum applied force.}, language = {en} } @article{BeyerGroteReinig2008, author = {Beyer, Marc-Andr{\´e} and Grote, Wolfgang and Reinig, Gunter}, title = {Adaptive exact linearization control of batch polymerization reactors using a Sigma-Point Kalman Filter}, series = {Journal of Process Control}, volume = {18}, journal = {Journal of Process Control}, number = {7-8}, publisher = {Elsevier}, doi = {10.1016/j.jprocont.2007.12.002}, pages = {663 -- 675}, year = {2008}, abstract = {The Chylla-Haase polymerization reactor is widely accepted as a benchmark process for the evaluation of control strategies for batch reactors. In this contribution a control concept based on Exact I/O-Linearization is proposed and compared to a conventional cascade control structure. In order to adapt the exact linearization control strategy to various polymerization products and batch conditions, an advanced probabilistic inference algorithm (Sigma-Point Kalman Filter) is applied and investigated. Sigma-Point Kalman Filters have the major improvement of simplified implementation compared to local linearization methods (i.e. Extended Kalman Filter) because no analytical Jacobians are required. Stochastic simulation studies are introduced and show the effectiveness, accuracy and benefit of the control concept. Within several scenarios a satisfying robustness against structural errors in the underlying model equations for the nonlinear control law and the inference algorithm is demonstrated. Furthermore it is pointed out, that with little effort in reassembling the plant design, control performance can be improved significantly.}, language = {en} } @article{GroteKastsianMoennigmann2013, author = {Grote, Wolfgang and Kastsian, Darya and M{\"o}nnigmann, Martin}, title = {Guaranteed stability in optimal power generation dispatching under uncertainty}, series = {IEEE Transactions on Power Systems}, volume = {28}, journal = {IEEE Transactions on Power Systems}, number = {2}, publisher = {IEEE}, issn = {1558-0679}, doi = {10.1109/TPWRS.2012.2207970}, pages = {1103 -- 1112}, year = {2013}, abstract = {Stability and cost optimality of power generation and supply systems must not be considered independently from one another. Simple examples show that optimizing cost without considering stability may result in modes of operation that, while economically optimal, are unstable. We demonstrate that stability, robustness, and optimality can be considered systematically and simultaneously by combining bifurcation theory and nonlinear optimization. Essentially, the proposed method enforces a backoff distance between the optimal point of operation and operational or stability boundaries in the space of the optimization variables, where bifurcation theory is used to describe nonlinear stability boundaries.}, language = {en} } @article{JostGroteMoellenbrucketal.2014, author = {Jost, Michael and Grote, Wolfgang and M{\"o}llenbruck, Florian and M{\"o}nnigmann, Martin}, title = {Plant-wide control of a parabolic trough power plant with thermal energy storage}, series = {IFAC Proceedings Volumes}, volume = {47}, journal = {IFAC Proceedings Volumes}, number = {3}, publisher = {Elsevier}, issn = {2589-3653}, doi = {10.3182/20140824-6-ZA-1003.00879}, pages = {419 -- 425}, year = {2014}, abstract = {We present a control scheme for a parabolic trough power plant that is equipped with a molten salt thermal energy storage system. We show that the multivariable control problem for the solar field can be decoupled by controlling the three way valve that splits the heat transfer fluid between the storage system and the steam generator. The steam generation cycle is regulated with inlet pressure control. The subsystems of the plant are modeled based on first principles, where we focus on the steam generation cycle. A multi-group extraction turbine with pre- and reheater is considered, which is suitable for solar power plants. We demonstrate the benefits of the proposed control scheme with a day-to-day simulation.}, language = {en} } @article{MierMoellenbruckJostetal.2015, author = {Mier, Dominik and M{\"o}llenbruck, Florian and Jost, Michael and Grote, Wolfgang and M{\"o}nnigmann, Martin}, title = {Model predictive control of the steam cycle in a solar power plant}, series = {IFAC-PapersOnLine}, volume = {48}, journal = {IFAC-PapersOnLine}, number = {8}, publisher = {Elsevier}, issn = {2405-8963}, doi = {10.1016/j.ifacol.2015.09.052}, pages = {710 -- 715}, year = {2015}, abstract = {We derive a nonlinear model of the steam cycle of a solar power plant, estimate its unknown parameters with measured data, and design a linear model predictive controller based on the resulting model. Simulations show that the linear model predictive controller is able to regulate the electrical power of the nonlinear steam process of the plant to a given reference trajectory very well. Moreover, it results in very good disturbance rejection.}, language = {en} } @article{GroteRammLanuschnyLorenzenetal.2023, author = {Grote-Ramm, Wolfgang and Lanuschny, David and Lorenzen, Finn and Oliveira Brito, Marcel and Sch{\"o}nig, Felix}, title = {Continual learning for neural regression networks to cope with concept drift in industrial processes using convex optimisation}, series = {Engineering Applications of Artificial Intelligence}, volume = {120}, journal = {Engineering Applications of Artificial Intelligence}, publisher = {Elsevier}, address = {New York}, issn = {1873-6769}, doi = {10.1016/j.engappai.2023.105927}, pages = {10}, year = {2023}, abstract = {Process models in industrial applications, e.g. predictive maintenance or automation, are subject to both divergence from the underlying system due to their time-variant nature and to high complexity resulting from a wide operational range being covered. Hence, regression models require high accuracy for the present system state and at the same time need to be valid across the whole system operating space. While accuracy for the current system state can be gained by updating the model on the current data, the overall validity must often be retrieved from historical or design data. We propose a method to find an appropriate compromise for these two demands. A pre-trained artificial neural network (ANN) is continually updated on the current sensor data stream using convex optimisation. Thus, a unique and optimal solution is generated in each update step, while robust regression accuracy on the domain that is not covered by the arriving data subset is maintained. This is achieved by introducing a data management system to provide some historical data, constraining the optimisation problem and manipulating the architecture of the ANN. Models updated with this method show reasonable stability but display plastic behaviour at the current operating point.}, language = {en} } @article{MolloyMuellerDeeganetal.2024, author = {Molloy, Dara and M{\"u}ller, Patrick and Deegan, Brian and Mullins, Darragh and Horgan, Jonathan and Ward, Enda and Jones, Edward and Braun, Alexander and Glavin, Martin}, title = {Analysis of the Impact of Lens Blur on Safety-Critical Automotive Object Detection}, series = {IEEE Access}, volume = {12}, journal = {IEEE Access}, publisher = {IEEE}, issn = {2169-3536}, doi = {10.1109/ACCESS.2023.3348663}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:due62-opus-42999}, pages = {3554 -- 3569}, year = {2024}, abstract = {Camera-based object detection is widely used in safety-critical applications such as advanced driver assistance systems (ADAS) and autonomous vehicle research. Road infrastructure has been designed for human vision, so computer vision, with RGB cameras, is a vital source of semantic information from the environment. Sensors, such as LIDAR and RADAR, are also often utilized for these applications; however, cameras provide a higher spatial resolution and color information. The spatial frequency response (SFR), or sharpness of a camera, utilized in object detection systems must be sufficient to allow a detection algorithm to localize objects in the environment over its lifetime reliably. This study explores the relationship between object detection performance and SFR. Six state-of-the-art object detection models are evaluated with varying levels of lens defocus. A novel raw image dataset is created and utilized, containing pedestrians and cars over a range of distances up to 100-m from the sensor. Object detection performance for each defocused dataset is analyzed over a range of distances to determine the minimum SFR necessary in each case. Results show that the relationship between object detection performance and lens blur is much more complex than previous studies have found due to lens field curvature, chromatic aberration, and astigmatisms. We have found that smaller objects are disproportionately impacted by lens blur, and different object detection models have differing levels of robustness to lens blur}, language = {en} } @article{EnggruberLauber2024, author = {Enggruber, Ruth and Lauber, Dominique M.}, title = {Problembew{\"a}ltigung oder Erwerbsarbeit first?: W{\"u}nsche von B{\"u}rgergeldbezieher:innen mit Suchtverhalten an Unterst{\"u}tzungsangebote - empirische Einblicke}, series = {Soziale Passagen}, journal = {Soziale Passagen}, publisher = {Springer Nature}, issn = {1867-0199}, doi = {10.1007/s12592-023-00474-4}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:due62-opus-42953}, year = {2024}, abstract = {Menschen mit Suchtverhalten, die B{\"u}rgergeld nach dem Sozialgesetzbuch II beziehen, zu ihren W{\"u}nschen an f{\"u}r sie hilfreiche Unterst{\"u}tzungsangebote zu befragen und aus ihren Schilderungen herauszuarbeiten, welche Bedeutung f{\"u}r sie Erwerbarbeit hat, fordert die Forschenden zu kritischen Selbstvergewisserungen heraus.Denn die qualitative Studie, die im Rahmen eines Modellprojekts, gef{\"o}rdert vom Bundesarbeitsministerium, durchgef{\"u}hrt wurde, ber{\"u}hrt vier kritische Fachdebatten in der Sozialen Arbeit. Neben der (1) sozialpolitischen Aktivierungsprogrammatik sind hier v. a. die (2) Bezeichnung von Menschen mit Suchtverhalten sowie (3) methodologische Einw{\"a}nde gegen subjektorientierte Forschungsperspektiven und (4) Case Management bedeutsam. Nach der Positionierung in diesen Fachdebatten werden empirische Einblicke dazu gew{\"a}hrt, dass die Frage „Problembew{\"a}ltigung oder Erwerbsarbeit first?" differenziert beantwortet wird.Ferner {\"a}ußern die B{\"u}rgergeldbezieher:innen mit Suchtverhalten diverse W{\"u}nsche an die Unterst{\"u}tzung im Jobcenter und andere Hilfsangebote. Vor allem w{\"u}nschen sie sich vom Jobcenter, dass es dort nicht nur um die Vermittlung in Erwerbsarbeit gehen sollte, sondern weitere und damit hybride Zielsetzungen verfolgt werden sollten.}, language = {de} }