TY - JOUR A1 - Uffmann, Kai A1 - Abicht, Claus A1 - Grote, Wolfgang A1 - Quick, Harald H. A1 - Ladd, Mark E. T1 - Design of an MR-compatible piezoelectric actuator for MR elastography JF - Concepts in Magnetic Resonance Part A: Bridging Education and Research N2 - 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 KW - Elasticity KW - Elastography KW - Actuator KW - MRI KW - Piezoelectric Y1 - 2002 UR - 1552-5023 U6 - https://doi.org/https://doi.org/10.1002/cmr.10045 VL - 15 IS - 4 SP - 239 EP - 254 PB - Wiley ER - TY - JOUR A1 - Galban, Craig A1 - Maderwald, Stefan A1 - Herrmann, Burkhard A1 - Brauck, K. A1 - Grote, Wolfgang A1 - de Greiff, A. A1 - Uffmann, K. A1 - Ladd, M. T1 - Measuring Skeletal Muscle Elasticity in Patients with Hypogonadism by MR Elastography JF - Proc. Intl. Soc. Mag. Reson. Med. N2 - 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. Y1 - 2005 UR - https://cds.ismrm.org/protected/05MProceedings/PDFfiles/02016.pdf VL - 13 SP - 2016 ER - TY - JOUR A1 - Galban, Craig A1 - Maderwald, Stefan A1 - Eggebrecht, Holger A1 - Grote, Wolfgang A1 - de Greiff, A. A1 - Uffmann, K. A1 - Ladd, M. E. T1 - Monitoring the Effects of Chronic Obstructive Pulmonary Disease on Muscle Elasticity by MR Elastography JF - Proc. Intl. Soc. Mag. Reson. Med. N2 - 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. Y1 - 2005 UR - https://cds.ismrm.org/protected/05MProceedings/PDFfiles/02015.pdf VL - 13 SP - 2015 ER - TY - JOUR A1 - Beyer, Marc-André A1 - Grote, Wolfgang A1 - Reinig, Gunter T1 - Adaptive exact linearization control of batch polymerization reactors using a Sigma-Point Kalman Filter JF - Journal of Process Control N2 - 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. KW - Batch process operation KW - Exact I/O-Linearization control KW - Online parameter estimation KW - Sigma-Point Kalman Filter Y1 - 2008 UR - 1873-2771 U6 - https://doi.org/10.1016/j.jprocont.2007.12.002 VL - 18 IS - 7-8 SP - 663 EP - 675 PB - Elsevier ER - TY - CHAP A1 - Grote, Wolfgang A1 - Kastsian, Darya A1 - Mönnigmann, Martin T1 - Optimal power system unit commitment with guaranteed local stability T2 - Proceedings of the 2011 American Control Conference N2 - This article deals with the cost optimal commitment of power systems. System stability is often only considered after solving the commitment problem. We show by example that a cost optimization may result in a mode of operation that, while economically optimal, is unstable or has otherwise unacceptable dynamics. As a remedy, we propose to use the so-called normal vector method, which has been developed for the optimization of nonlinear dynamical systems with stability boundaries and uncertain parameters. We apply the method to a small sample power grid, where the optimization goal is to minimize the energy production costs for a given power consumption. KW - Optimization KW - Power system stability KW - Robustness Y1 - 2011 U6 - https://doi.org/10.1109/ACC.2011.5991058 SN - 2378-5861 SP - 4526 EP - 4531 PB - IEEE ER - TY - JOUR A1 - Grote, Wolfgang A1 - Kastsian, Darya A1 - Mönnigmann, Martin T1 - Guaranteed stability in optimal power generation dispatching under uncertainty JF - IEEE Transactions on Power Systems N2 - 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. KW - Normal vector method KW - Power dispatch KW - Robust optimization KW - Stability KW - Unit commitment Y1 - 2013 U6 - https://doi.org/10.1109/TPWRS.2012.2207970 SN - 1558-0679 VL - 28 IS - 2 SP - 1103 EP - 1112 PB - IEEE ER - TY - JOUR A1 - Jost, Michael A1 - Grote, Wolfgang A1 - Möllenbruck, Florian A1 - Mönnigmann, Martin T1 - Plant-wide control of a parabolic trough power plant with thermal energy storage JF - IFAC Proceedings Volumes N2 - 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. KW - Control of power plants KW - Solar power plants KW - Thermal energy storage KW - Decoupling control Y1 - 2014 U6 - https://doi.org/10.3182/20140824-6-ZA-1003.00879 SN - 2589-3653 VL - 47 IS - 3 SP - 419 EP - 425 PB - Elsevier ER - TY - JOUR A1 - Mier, Dominik A1 - Möllenbruck, Florian A1 - Jost, Michael A1 - Grote, Wolfgang A1 - Mönnigmann, Martin T1 - Model predictive control of the steam cycle in a solar power plant JF - IFAC-PapersOnLine N2 - 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. KW - Power plant control KW - solar power KW - model predictive control Y1 - 2015 U6 - https://doi.org/10.1016/j.ifacol.2015.09.052 SN - 2405-8963 VL - 48 IS - 8 SP - 710 EP - 715 PB - Elsevier ER - TY - JOUR A1 - Sieberichs, Christian A1 - Geerkens, Simon A1 - Braun, Alexander A1 - Waschulzik, Thomas T1 - ECS: an interactive tool for data quality assurance JF - AI and Ethics N2 - With the increasing capabilities of machine learning systems and their potential use in safety-critical systems, ensuring high-quality data is becoming increasingly important. In this paper, we present a novel approach for the assurance of data quality. For this purpose, the mathematical basics are first discussed and the approach is presented using multiple examples. This results in the detection of data points with potentially harmful properties for the use in safety-critical systems. KW - DEAL KW - HSD Publikationsfonds KW - Data visulization KW - Distance based KW - Data quality assurance KW - Equivalence class sets KW - DFG Publikationskosten Y1 - 2024 U6 - https://doi.org/10.1007/s43681-023-00393-3 SN - 2730-5961 N1 - Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - 532148125 and supported by the central publication fund of Hochschule Düsseldorf University of Applied Sciences Data availability declaration: All data that support the findings of this scientific publication are available within this paper and/or its supplementary information files/materials. Otherwise: The data that support the findings of this scientific publication are available from the corresponding author upon reasonable request. PB - Springer Nature ER - TY - PAT A1 - Lessmann, Stephanie A1 - Meuter, Mirko A1 - Mueller, Dennis T1 - Method to determine distance of an object from an automated vehicle with a monocular device N2 - A method of determining the distance of an object from an automated vehicle based on images taken by a monocular image acquiring device. The object is recognized with an object-class by means of an image processing system. Respective position data are determined from the images using a pinhole camera model based on the object-class. Position data indicating in world coordinates the position of a reference point of the object with respect to the plane of the road is used with a scaling factor of the pinhole camera model estimated by means of a Bayes estimator using the position data as observations and under the assumption that the reference point of the object is located on the plane of the road with a predefined probability. The distance of the object from the automated vehicle is calculated from the estimated scaling factor using the pinhole camera model. Y1 - 2018 UR - https://depatisnet.dpma.de/DepatisNet/depatisnet?action=pdf&docid=US000009862318B2&xxxfull=1 ER -