TY - JOUR A1 - Krafft, B. A1 - Förster, Arnold A1 - Hart, A. van der A1 - Schäpers, T. T1 - Control of Aharonov-Bohm oscillations in a AlGaAs/GaAs ring by asymmetric and symmetric gate biasing JF - Physica E: Low-dimensional Systems and Nanostructures. 9 (2001), H. 4 Y1 - 2001 SN - 1386-9477 SP - 635 EP - 641 ER - TY - JOUR A1 - Kraff, Oliver A1 - Wrede, Karsten H. A1 - Schoemberg, Tobias A1 - Dammann, Philipp A1 - Noureddine, Yacine A1 - Orzada, Stephan A1 - Ladd, Mark E. A1 - Bitz, Andreas T1 - MR safety assessment of potential RF heating from cranial fixation plates at 7 T JF - Medical Physics Y1 - 2013 U6 - https://doi.org/10.1118/1.4795347 SN - 2473-4209 VL - 40 IS - 4 SP - 042302-1 EP - 042302-10 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Kraff, Oliver A1 - Bitz, Andreas A1 - Kruszona, Stefan A1 - Orzada, Stephan A1 - Schaefer, Lena C. A1 - Theysohn, Jens M. A1 - Maderwald, Stefan A1 - Ladd, Mark E. A1 - Quick, Harald H. T1 - An eight-channel phased array RF coil for spine MR imaging at 7 T JF - Investigative Radiology Y1 - 2009 U6 - https://doi.org/10.1097/RLI.0b013e3181b24ab7 SN - 1536-0210 VL - 44 IS - 11 SP - 734 EP - 740 PB - Lippincott Williams & Wilkins ER - TY - JOUR A1 - Kraff, Oliver A1 - Bitz, Andreas A1 - Dammann, Philipp A1 - Ladd, Susanne C. A1 - Ladd, Mark E. A1 - Quick, Harald H. T1 - An eight-channel transmit/receive multipurpose coil for musculoskeletal MR imaging at 7 T JF - Medical Physics N2 - Purpose: MRI plays a leading diagnostic role in assessing the musculoskeletal (MSK) system and is well established for most questions at clinically used field strengths (up to 3 T). However, there are still limitations in imaging early stages of cartilage degeneration, very fine tendons and ligaments, or in locating nerve lesions, for example. 7 T MRI of the knee has already received increasing attention in the current published literature, but there is a strong need to develop new radiofrequency (RF) coils to assess more regions of the MSK system. In this work, an eight-channel transmit/receive RF array was built as a multipurpose coil for imaging some of the thus far neglected regions. An extensive coil characterization protocol and first in vivo results of the human wrist, shoulder, elbow, knee, and ankle imaged at 7 T will be presented. Methods: Eight surface loop coils with a dimension ofurn:x-wiley:00942405:media:mp7176:mp7176-math-0001 were machined from FR4 circuit board material. To facilitate easy positioning, two coil clusters, each with four loop elements, were combined to one RF transmit/receive array. An overlapped and shifted arrangement of the coil elements was chosen to reduce the mutual inductance between neighboring coils. A phantom made of body-simulating liquid was used for tuning and matching on the bench. Afterward, the S-parameters were verified on a human wrist, elbow, and shoulder. For safety validation, a detailed compliance test was performed including full wave simulations of the RF field distribution and the corresponding specific absorption rate (SAR) for all joints. In vivo images of four volunteers were assessed with gradient echo and spin echo sequences modified to obtain optimal image contrast, full anatomic coverage, and the highest spatial resolution within a reasonable acquisition time. The performance of the RF coil was additionally evaluated by in vivo B1 mapping. Results: A comparison of B1 per unit power, flip angle distribution, and anatomic images showed a fairly homogeneous excitation for the smaller joints (elbow, wrist, and ankle), while for the larger joints, the shoulder and especially the knee, B1 inhomogeneities and limited penetration depth were more pronounced. However, the greater part of the shoulder joint could be imaged.In vivo images rendered very fine anatomic details such as fascicles of the median nerve and the branching of the nerve bundles. High-resolution images of cartilage, labrum, and tendons could be acquired. Additionally, turbo spin echo (TSE) and inversion recovery sequences performed very well. Conclusions: This study demonstrates that the concept of two four-channel transmit/receive RF arrays can be used as a multipurpose coil for high-resolutionin vivo MR imaging of the musculoskeletal system at 7 T. Not only gradient echo but also typical clinical and SAR-intensive sequences such as STIR and TSE performed well. Imaging of small structures and peripheral nerves could in particular benefit from this technique. Y1 - 2010 U6 - https://doi.org/10.1118/1.3517176 SN - 2473-4209 VL - 37 IS - 12 SP - 6368 EP - 6376 PB - Wiley CY - Hoboken, NJ ER - TY - JOUR A1 - Kraff, Oliver A1 - Bitz, Andreas A1 - Breyer, Tobias A1 - Kruszona, Stefan A1 - Maderwald, Stefan A1 - Brote, Irina A1 - Gizewski, Elke R. A1 - Ladd, Mark E. A1 - Quick, Harald H. T1 - A transmit/receive radiofrequency array for imaging the carotid arteries at 7 Tesla: coil design and first in vivo results JF - Investigative Radiology N2 - Objective: To develop a transmit/receive radiofrequency (RF) array for magnetic resonance imaging (MRI) of the carotid arteries at 7 T. The prototype is characterized in numerical simulations and bench measurements, and the feasibility of plaque imaging at 7 T is demonstrated in first in vivo images. Materials and Methods: The RF phased array coil consists of 8 surface loop coils. To allow imaging of both sides of the neck, the RF array is divided into 2 coil clusters, each with 4 overlapping loop elements. For safety validation, numerical computations of the RF field distribution and the corresponding specific absorption rate were performed on the basis of a heterogeneous human body model. To validate the coil model, maps of the transmit B1+ field were compared between simulation and measurement. In vivo images of a healthy volunteer and a patient (ulcerating plaque and a 50% stenosis of the right internal carotid artery) were acquired using a 3-dimensional FLASH sequence with a high isotropic spatial resolution of 0.54 mm as well as using pulse-triggered proton density (PD)/T2-weighted turbo spin echo sequences. Results: Measurements of the S-parameters yielded a reflection and isolation of the coil elements of better than −18 and −13 dB, respectively. Measurements of the g-factor indicated good image quality for parallel imaging acceleration factors up to 2.4. A similar distribution and a very good match of the absolute values were found between the measured and simulated B1+ transmit RF field for the validation of the coil model. In vivo images revealed good signal excitation of both sides of the neck and a high vessel-to-background image contrast for the noncontrast-enhanced 3-dimensional FLASH sequence. Imaging at 7 T could depict the extent of stenosis, and revealed the disruption and ulcer of the plaque. Conclusions: This study demonstrates that 2 four-channel transmit/receive RF arrays for each side of the neck is a suitable concept for in vivo MRI of the carotid arteries at 7 Tesla. Further studies are needed to explore and exploit the full potential of 7 T high-field MRI for carotid atherosclerotic plaque imaging. Y1 - 2011 U6 - https://doi.org/10.1097/RLI.0b013e318206cee4 SN - 1536-0210 VL - 46 IS - 4 SP - 246 EP - 254 PB - Wolters Kluwer CY - Köln ER - TY - JOUR A1 - Kozhalakova, A. A. A1 - Zhubanova, Azhar A. A1 - Mansurov, Z. A. A1 - Digel, Ilya A1 - Tazhibayeva, S. M. A1 - Artmann, Gerhard A1 - Temiz Artmann, Aysegül T1 - Adsorption of bacterial lipopolysaccharides on carbonized rice shell JF - Science of Central Asia (2010) Y1 - 2010 SP - 50 EP - 54 ER - TY - JOUR A1 - Kowalski, Julia A1 - McElwaine, Jim N. T1 - Shallow two-component gravity-driven flows with vertical variation JF - Journal of Fluid Mechanics Y1 - 2013 SN - 0022-1120 VL - 714 SP - 434 EP - 462 PB - Cambridge Univ. Press CY - Cambridge ER - TY - CHAP A1 - Kowalski, Julia A1 - McElwaine, J. T1 - Two-phase debris flow modeling T2 - Geophysical Research Abstracts Y1 - 2008 N1 - A-01048 ER - TY - CHAP A1 - Kowalski, Julia A1 - McArdell, B. W. A1 - Bartelt, Perry T1 - A comparison of two approaches to modeling multiphase gravity currents T2 - Geophysical Research Abstracts Y1 - 2006 N1 - A-08738 VL - 8 ER - TY - JOUR A1 - Kowalski, Julia A1 - Linder, Peter A1 - Zierke, S. A1 - Wulfen, B. van A1 - Clemens, J. A1 - Konstantinidis, K. A1 - Ameres, G. A1 - Hoffmann, R. A1 - Mikucki, J. A1 - Tulaczyk, S. A1 - Funke, O. A1 - Blandfort, D. A1 - Espe, Clemens A1 - Feldmann, Marco A1 - Francke, Gero A1 - Hiecker, S. A1 - Plescher, Engelbert A1 - Schöngarth, Sarah A1 - Dachwald, Bernd A1 - Digel, Ilya A1 - Artmann, Gerhard A1 - Eliseev, D. A1 - Heinen, D. A1 - Scholz, F. A1 - Wiebusch, C. A1 - Macht, S. A1 - Bestmann, U. A1 - Reineking, T. A1 - Zetzsche, C. A1 - Schill, K. A1 - Förstner, R. A1 - Niedermeier, H. A1 - Szumski, A. A1 - Eissfeller, B. A1 - Naumann, U. A1 - Helbing, K. T1 - Navigation technology for exploration of glacier ice with maneuverable melting probes JF - Cold Regions Science and Technology N2 - The Saturnian moon Enceladus with its extensive water bodies underneath a thick ice sheet cover is a potential candidate for extraterrestrial life. Direct exploration of such extraterrestrial aquatic ecosystems requires advanced access and sampling technologies with a high level of autonomy. A new technological approach has been developed as part of the collaborative research project Enceladus Explorer (EnEx). The concept is based upon a minimally invasive melting probe called the IceMole. The force-regulated, heater-controlled IceMole is able to travel along a curved trajectory as well as upwards. Hence, it allows maneuvers which may be necessary for obstacle avoidance or target selection. Maneuverability, however, necessitates a sophisticated on-board navigation system capable of autonomous operations. The development of such a navigational system has been the focal part of the EnEx project. The original IceMole has been further developed to include relative positioning based on in-ice attitude determination, acoustic positioning, ultrasonic obstacle and target detection integrated through a high-level sensor fusion. This paper describes the EnEx technology and discusses implications for an actual extraterrestrial mission concept. Y1 - 2016 U6 - https://doi.org/10.1016/j.coldregions.2015.11.006 SN - 0165-232X IS - 123 SP - 53 EP - 70 PB - Elsevier CY - Amsterdam ER - TY - CHAP A1 - Kowalski, Julia A1 - Bartelt, Perry A1 - McElwaine, J. T1 - Two-phase debris flow modeling T2 - Geophysical Research Abstracts Y1 - 2007 N1 - A-08119 ER - TY - THES A1 - Kowalski, Julia T1 - Two-phase Modeling of Debris Flows Y1 - 2008 SN - 978-3-86664-524-0 N1 - Diss., Eidgenössische Technische Hochschule ETH Zürich, Nr. 17827, 2008 PB - Mensch und Buch CY - Berlin ER - TY - CHAP A1 - Kowalski, Julia T1 - Numerical Debris Flow Simulation T2 - Schweizer Numerik Kolloquium : Book of Abstracts 12. April 2006 Y1 - 2006 ER - TY - JOUR A1 - Kowalewski, Paul A1 - Bragard, Michael A1 - Hüning, Felix A1 - De Doncker, Rik W. T1 - An inexpensive Wiegand-sensor-based rotary encoder without rotating magnets for use in electrical drives JF - IEEE Transactions on Instrumentation and Measurement N2 - This paper introduces an inexpensive Wiegand-sensor-based rotary encoder that avoids rotating magnets and is suitable for electrical-drive applications. So far, Wiegand-sensor-based encoders usually include a magnetic pole wheel with rotating permanent magnets. These encoders combine the disadvantages of an increased magnet demand and a limited maximal speed due to the centripetal force acting on the rotating magnets. The proposed approach reduces the total demand of permanent magnets drastically. Moreover, the rotating part is manufacturable from a single piece of steel, which makes it very robust and cheap. This work presents the theoretical operating principle of the proposed approach and validates its benefits on a hardware prototype. The presented proof-of-concept prototype achieves a mechanical resolution of 4.5 ° by using only 4 permanent magnets, 2Wiegand sensors and a rotating steel gear wheel with 20 teeth. KW - Rotary encoder KW - Wiegand sensor Y1 - 2023 U6 - https://doi.org/10.1109/TIM.2023.3326166 SN - 0018-9456 (Print) SN - 1557-9662 (Online) VL - 72 SP - 10 Seiten PB - IEEE CY - New York ER - TY - JOUR A1 - Kotter, Michael A1 - Riekert, Lothar A1 - Weyland, Friedrich T1 - The performance of base metal oxides on ceramic carriers as catalysts for air pollution control JF - International chemical engineering. 25 (1985), H. 3 Y1 - 1985 SN - 0020-6318 SP - 418 EP - 427 ER - TY - JOUR A1 - Kotter, Michael A1 - Riekert, L. A1 - Weyland, F. T1 - Deposition of ternary oxides as active components by impregnation of porous carriers JF - Preparation of Catalysts III : scientific bases for the preparation of heterogeneous catalysts ; proceedings of the Third International Symposium, Louvain-la-Neuve, September 6-9, 1982 / ed.: G. Poncelet ... - (Studies in surface science and catalysis ; 16) Y1 - 1983 SN - 0-444-42184-X N1 - International Symposium on the Scientific Bases for the Preparation of Heterogeneous Catalysts <3, 1982, Louvain-la-Neuve> SP - 521 EP - 530 PB - Elsevier CY - Amsterdam [u.a.] ER - TY - JOUR A1 - Kotter, Michael A1 - Riekert, L. T1 - Impregnation-type catalysts with nonuniform distribution of the active component JF - Chemical engineering fundamentals. 2 (1983) Y1 - 1983 SN - 0723-0966 SP - 19 EP - 38 ER - TY - JOUR A1 - Kotter, Michael A1 - Riekert, L. T1 - The influence of impregnation, drying and activation on the activity and distribution of CuO on α-Alumina JF - Preparation of Catalysts II : scientific bases for the preparation of heterogeneous catalysts ; Proceedings of the Second International Symposium, Louvain-la-Neuve, September 4-7, 1978 / Eds.: B. Delmon ... - (Studies in surface science and catalysis ; 3) Y1 - 1979 SN - 0-444-41733-8 N1 - International Symposium on the Scientific Bases for the Preparation of Heterogeneous Catalysts <2, 1978, Louvain-la-Neuve> SP - 51 EP - 63 PB - Elsevier CY - Amsterdam [u.a.] ER - TY - JOUR A1 - Kotter, Michael A1 - Lintz, Hans-Günther A1 - Turek, Thomas T1 - Selective catalytic reduction of nitrogen oxide by use of the Ljungstroem air heater as reactor : a case study JF - Chemical engineering science . 47 (1992), H. 9-11 Y1 - 1992 SN - 0009-2509 SP - 2763 EP - 2768 ER - TY - JOUR A1 - Kotter, Michael A1 - Lintz, Hans-Günther A1 - Riekert, Lothar A1 - Trimm, D. L. T1 - Structure and selectivity changes in vanadia-titania catalysts used to promote the reduction of nitric oxide with ammonia JF - Applied catalysis. 52 (1989), H. 1 Y1 - 1989 SN - 0166-9834 N1 - ISSN der E-Ausg.: 0166-9834 SP - 225 EP - 235 ER -