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2019


Soft-magnetic coatings as possible sensors for magnetic imaging of superconductors
Soft-magnetic coatings as possible sensors for magnetic imaging of superconductors

Ionescu, A., Simmendinger, J., Bihler, M., Miksch, C., Fischer, P., Soltan, S., Schütz, G., Albrecht, J.

Supercond. Sci. and Tech., 33, pages: 015002, IOP, December 2019 (article)

Abstract
Magnetic imaging of superconductors typically requires a soft-magnetic material placed on top of the superconductor to probe local magnetic fields. For reasonable results the influence of the magnet onto the superconductor has to be small. Thin YBCO films with soft-magnetic coatings are investigated using SQUID magnetometry. Detailed measurements of the magnetic moment as a function of temperature, magnetic field and time have been performed for different heterostructures. It is found that the modification of the superconducting transport in these heterostructures strongly depends on the magnetic and structural properties of the soft-magnetic material. This effect is especially pronounced for an inhomogeneous coating consisting of ferromagnetic nanoparticles.

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link (url) DOI [BibTex]

2019


link (url) DOI [BibTex]


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Dynamics of beneficial epidemics

Berdahl, A., Brelsford, C., De Bacco, C., Dumas, M., Ferdinand, V., Grochow, J. A., nt Hébert-Dufresne, L., Kallus, Y., Kempes, C. P., Kolchinsky, A., Larremore, D. B., Libby, E., Power, E. A., A., S. C., Tracey, B. D.

Scientific Reports, 9, pages: 15093, October 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Convolutional neural networks: A magic bullet for gravitational-wave detection?

Gebhard, T., Kilbertus, N., Harry, I., Schölkopf, B.

Physical Review D, 100(6):063015, American Physical Society, September 2019 (article)

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Data scarcity, robustness and extreme multi-label classification

Babbar, R., Schölkopf, B.

Machine Learning, 108(8):1329-1351, September 2019, Special Issue of the ECML PKDD 2019 Journal Track (article)

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DOI [BibTex]

DOI [BibTex]


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Automatic Segmentation and Labelling for Robot Table Tennis Time Series

Lutz, P.

Technical University Darmstadt, Germany, August 2019 (thesis)

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[BibTex]

[BibTex]


Superior Magnetic Performance in FePt L1_0 Nanomaterials
Superior Magnetic Performance in FePt L1_0 Nanomaterials

Son, K., Ryu, G. H., Jeong, H., Fink, L., Merz, M., Nagel, P., Schuppler, S., Richter, G., Goering, E., Schütz, G.

Small, 15(1902353), July 2019 (article)

Abstract
The discovery of the high maximum energy product of 59 MGOe for NdFeB magnets is a breakthrough in the development of permanent magnets with a tremendous impact in many fields of technology. This value is still the world record, for 40 years. This work reports on a reliable and robust route to realize nearly perfectly ordered L1_0-phase FePt nanoparticles, leading to an unprecedented energy product of 80 MGOe at room temperature. Furthermore, with a 3 nm Au coverage, the magnetic polarization of these nanomagnets can be enhanced by 25% exceeding 1.8 T. This exceptional magnetization and anisotropy is confirmed by using multiple imaging and spectroscopic methods, which reveal highly consistent results. Due to the unprecedented huge energy product, this material can be envisaged as a new advanced basic magnetic component in modern micro and nanosized devices.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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SPINDLE: End-to-end learning from EEG/EMG to extrapolate animal sleep scoring across experimental settings, labs and species

Miladinovic, D., Muheim, C., Bauer, S., Spinnler, A., Noain, D., Bandarabadi, M., Gallusser, B., Krummenacher, G., Baumann, C., Adamantidis, A., Brown, S. A., Buhmann, J. M.

PLOS Computational Biology, 15(4):1-30, Public Library of Science, April 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Extracting the dynamic magnetic contrast in time-resolved X-ray transmission microscopy

Schaffers, T., Feggeler, T., Pile, S., Meckenstock, R., Buchner, M., Spoddig, D., Ney, V., Farle, M., Wende, H., Wintz, S., Weigand, M., Ohldag, H., Ollefs, K, Ney, A.

{Nanomaterials}, 9(7), MDPI, Basel, Schweiz, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Generation of switchable singular beams with dynamic metasurfaces

Yu, P., Li, J., Li, X., Schütz, G., Hirscher, M., Zhang, S., Liu, N.

{ACS Nano}, 13(6):7100-7106, American Chemical Society, Washington, DC, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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A 32-channel multi-coil setup optimized for human brain shimming at 9.4T

Aghaeifar, A., Zhou, J., Heule, R., Tabibian, B., Schölkopf, B., Jia, F., Zaitsev, M., Scheffler, K.

Magnetic Resonance in Medicine, 2019, (Early View) (article)

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DOI [BibTex]

DOI [BibTex]


Multidimensional Contrast Limited Adaptive Histogram Equalization
Multidimensional Contrast Limited Adaptive Histogram Equalization

Stimper, V., Bauer, S., Ernstorfer, R., Schölkopf, B., Xian, R. P.

IEEE Access, 7, pages: 165437-165447, 2019 (article)

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arXiv link (url) DOI [BibTex]

arXiv link (url) DOI [BibTex]


Tailored Magnetic Springs for Shape-Memory Alloy Actuated Mechanisms in Miniature Robots
Tailored Magnetic Springs for Shape-Memory Alloy Actuated Mechanisms in Miniature Robots

Woodward, M. A., Sitti, M.

IEEE Transactions on Robotics, 35, 2019 (article)

Abstract
Animals can incorporate large numbers of actuators because of the characteristics of muscles; whereas, robots cannot, as typical motors tend to be large, heavy, and inefficient. However, shape-memory alloys (SMA), materials that contract during heating because of change in their crystal structure, provide another option. SMA, though, is unidirectional and therefore requires an additional force to reset (extend) the actuator, which is typically provided by springs or antagonistic actuation. These strategies, however, tend to limit the actuator's work output and functionality as their force-displacement relationships typically produce increasing resistive force with limited variability. In contrast, magnetic springs-composed of permanent magnets, where the interaction force between magnets mimics a spring force-have much more variable force-displacement relationships and scale well with SMA. However, as of yet, no method for designing magnetic springs for SMA-actuators has been demonstrated. Therefore, in this paper, we present a new methodology to tailor magnetic springs to the characteristics of these actuators, with experimental results both for the device and robot-integrated SMA-actuators. We found magnetic building blocks, based on sets of permanent magnets, which are well-suited to SMAs and have the potential to incorporate features such as holding force, state transitioning, friction minimization, auto-alignment, and self-mounting. We show magnetic springs that vary by more than 3 N in 750 $\mu$m and two SMA-actuated devices that allow the MultiMo-Bat to reach heights of up to 4.5 m without, and 3.6 m with, integrated gliding airfoils. Our results demonstrate the potential of this methodology to add previously impossible functionality to smart material actuators. We anticipate this methodology will inspire broader consideration of the use of magnetic springs in miniature robots and further study of the potential of tailored magnetic springs throughout mechanical systems.

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DOI [BibTex]


Thrust and Hydrodynamic Efficiency of the Bundled Flagella
Thrust and Hydrodynamic Efficiency of the Bundled Flagella

Danis, U., Rasooli, R., Chen, C., Dur, O., Sitti, M., Pekkan, K.

Micromachines, 10, 2019 (article)

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[BibTex]

[BibTex]


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Piezo-electrical control of gyration dynamics of magnetic vortices

Filianina, M., Baldrati, L., Hajiri, T., Litzius, K., Foerster, M., Aballe, L., Kläui, M.

{Applied Physics Letters}, 115(6), American Institute of Physics, Melville, NY, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Barely porous organic cages for hydrogen isotrope separation

Liu, M., Zhang, L., Little, M. A., Kapil, V., Ceriotti, M., Yang, S., Ding, L., Holden, D. L., Balderas-Xicohténcatl, R., He, D., Clowes, R., Chong, S. Y., Schütz, G., Chen, L., Hirscher, M., Cooper, A. I.

{Science}, 366(6465):613-620, American Association for the Advancement of Science, Washington, D.C., 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetically induced anisotropy of flux penetration into strong-pinning superconductor/ferromagnet bilayers

Simmendinger, J., Hänisch, J., Bihler, M., Ionescu, A. M., Weigand, M., Sieger, M., Hühne, R., Rijckaert, H., van Driessche, I., Schütz, G., Albrecht, J.

{New Journal of Physics}, 21, IOP Publishing, Bristol, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


Microrobotics and Microorganisms: Biohybrid Autonomous Cellular Robots
Microrobotics and Microorganisms: Biohybrid Autonomous Cellular Robots

Alapan, Y., Yasa, O., Yigit, B., Yasa, I. C., Erkoc, P., Sitti, M.

Annual Review of Control, Robotics, and Autonomous Systems, 2019 (article)

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[BibTex]

[BibTex]


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X-ray Optics Fabrication Using Unorthodox Approaches

Sanli, U., Baluktsian, M., Ceylan, H., Sitti, M., Weigand, M., Schütz, G., Keskinbora, K.

Bulletin of the American Physical Society, APS, 2019 (article)

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[BibTex]

[BibTex]


{Direct observation of coherent magnons with suboptical wavelengths in a single-crystalline ferrimagnetic insulator}
Direct observation of coherent magnons with suboptical wavelengths in a single-crystalline ferrimagnetic insulator

Förster, J., Gräfe, J., Bailey, J., Finizio, S., Träger, N., Groß, F., Mayr, S., Stoll, H., Dubs, C., Surzhenko, O., Liebing, N., Woltersdorf, G., Raabe, J., Weigand, M., Schütz, G., Wintz, S.

{Physical Review B}, 100(21), American Physical Society, Woodbury, NY, 2019 (article)

Abstract
Spin-wave dynamics were studied in an extended thin film of single-crystalline yttrium iron garnet using time-resolved scanning transmission x-ray microscopy. A combination of mechanical grinding and focused ion beam milling has been utilized to achieve a soft x-ray transparent thickness of the underlying bulk gadolinium gallium garnet substrate. Damon-Eshbach type spin waves down to about 100 nm wavelength have been directly imaged in real space for varying frequencies and external magnetic fields. The dispersion relation extracted from the experimental data agreed well with theoretical predictions. A significant influence of the ion milling process on the local magnetic properties was not detected.

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DOI [BibTex]

DOI [BibTex]


{Nanoscale detection of spin wave deflection angles in permalloy}
Nanoscale detection of spin wave deflection angles in permalloy

Gross, F., Träger, N., Förster, J., Weigand, M., Schütz, G., Gräfe, J.

{Applied Physics Letters}, 114(1), American Institute of Physics, Melville, NY, 2019 (article)

Abstract
Magnonics is a potential candidate for beyond CMOS and neuromorphic computing technologies with advanced phase encoded logic. However, nanoscale imaging of spin waves with full phase and magnetization amplitude information is a challenge. We show a generalized scanning transmission x-ray microscopy platform to get a complete understanding of spin waves, including the k-vector, phase, and absolute magnetization deflection angle. As an example, this is demonstrated using a 50 nm thin permalloy film where we find a maximum deflection angle of 1.5° and good agreement with the k-vector dispersion previously reported in the literature. With a spatial resolution approximately ten times better than any other methods for spin wave imaging, x-ray microscopy opens a vast range of possibilities for the observation of spin waves and various magnetic structures.

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DOI [BibTex]

DOI [BibTex]


{gFORC: A graphics processing unit accelerated first-order reversal-curve calculator}
gFORC: A graphics processing unit accelerated first-order reversal-curve calculator

Groß, F., Martínez-García, J. C., Ilse, S. E., Schütz, G., Goering, E., Rivas, M., Gräfe, J.

{Journal of Applied Physics}, 126(16), AIP Publishing, New York, NY, 2019 (article)

Abstract
First-order reversal-curves have proven to be an indispensable characterization tool for physics as well as for geology. However, the conventional evaluation algorithm requires a lot of computational effort for a comparable easy task to overcome measurement noise. In this work, we present a new evaluation approach, which exploits the diversity of Fourier space to not only speed up the calculation by a factor of 1000 but also move away from the conventional smoothing factor toward real field resolution. By comparing the baseline resolution of the new and the old algorithm, we are able to deduce an analytical equation that converts the smoothing factor into field resolution, making the old and new algorithm comparable. We find excellent agreement not only for various systems of increasing complexity but also over a large range of smoothing factors. The achieved speedup enables us to calculate a large number of first-order reversal-curve diagrams with increasing smoothing factor allowing for an autocorrelation approach to find a hard criterion for the optimum smoothing factor. This previously computational prohibitive evaluation of first-order reversal-curves solves the problem of over- and undersmoothing by increasing general readability and preventing information destruction.

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DOI [BibTex]

DOI [BibTex]


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TD-regularized actor-critic methods

Parisi, S., Tangkaratt, V., Peters, J., Khan, M. E.

Machine Learning, 108(8):1467-1501, (Editors: Karsten Borgwardt, Po-Ling Loh, Evimaria Terzi, and Antti Ukkonen), 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Statistical Coverage Control of Mobile Sensor Networks

Arslan, Ö.

IEEE Transactions on Robotics, 35(4):889-908, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Probabilistic solutions to ordinary differential equations as nonlinear Bayesian filtering: a new perspective

Tronarp, F., Kersting, H., Särkkä, S. H. P.

Statistics and Computing, 29(6):1297-1315, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


Nitrogen doped carbon quantum dots demonstrate no toxicity under in vitro conditions in a cervical cell line and in vivo in Swiss albino mice
Nitrogen doped carbon quantum dots demonstrate no toxicity under in vitro conditions in a cervical cell line and in vivo in Swiss albino mice

Singh, V., Kashyap, S., Yadav, U., Srivastava, A., Singh, A. V., Singh, R. K., Singh, S. K., Saxena, P. S.

Toxicology research, 8, Oxford University Press, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


Learning to Control Highly Accelerated Ballistic Movements on Muscular Robots
Learning to Control Highly Accelerated Ballistic Movements on Muscular Robots

Büchler, D., Calandra, R., Peters, J.

2019 (article) Submitted

Abstract
High-speed and high-acceleration movements are inherently hard to control. Applying learning to the control of such motions on anthropomorphic robot arms can improve the accuracy of the control but might damage the system. The inherent exploration of learning approaches can lead to instabilities and the robot reaching joint limits at high speeds. Having hardware that enables safe exploration of high-speed and high-acceleration movements is therefore desirable. To address this issue, we propose to use robots actuated by Pneumatic Artificial Muscles (PAMs). In this paper, we present a four degrees of freedom (DoFs) robot arm that reaches high joint angle accelerations of up to 28000 °/s^2 while avoiding dangerous joint limits thanks to the antagonistic actuation and limits on the air pressure ranges. With this robot arm, we are able to tune control parameters using Bayesian optimization directly on the hardware without additional safety considerations. The achieved tracking performance on a fast trajectory exceeds previous results on comparable PAM-driven robots. We also show that our system can be controlled well on slow trajectories with PID controllers due to careful construction considerations such as minimal bending of cables, lightweight kinematics and minimal contact between PAMs and PAMs with the links. Finally, we propose a novel technique to control the the co-contraction of antagonistic muscle pairs. Experimental results illustrate that choosing the optimal co-contraction level is vital to reach better tracking performance. Through the use of PAM-driven robots and learning, we do a small step towards the future development of robots capable of more human-like motions.

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Arxiv Video [BibTex]


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Coordinated molecule-modulated magnetic phase with metamagnetism in metal-organic frameworks

Son, K., Kim, J. Y., Schütz, G., Kang, S. G., Moon, H. R., Oh, H.

{Inorganic Chemistry}, 58(14):8895-8899, American Chemical Society, Washington, DC, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


Multifarious Transit Gates for Programmable Delivery of Bio‐functionalized Matters
Multifarious Transit Gates for Programmable Delivery of Bio‐functionalized Matters

Hu, X., Torati, S. R., Kim, H., Yoon, J., Lim, B., Kim, K., Sitti, M., Kim, C.

Small, Wiley Online Library, 2019 (article)

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[BibTex]

[BibTex]


Multi-functional soft-bodied jellyfish-like swimming
Multi-functional soft-bodied jellyfish-like swimming

Ren, Z., Hu, W., Dong, X., Sitti, M.

Nature communications, 10, 2019 (article)

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[BibTex]


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Welcome to Progress in Biomedical Engineering

Sitti, M.

Progress in Biomedical Engineering, 1, IOP Publishing, 2019 (article)

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[BibTex]

[BibTex]


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Scaling of intrinsic domain wall magnetoresistance with confinement in electromigrated nanocontacts

Reeve, R. M., Loescher, A., Kazemi, H., Dupé, B., Mawass, M., Winkler, T., Schönke, D., Miao, J., Litzius, K., Sedlmayr, N., Schneider, I., Sinova, J., Eggert, S., Kläui, M.

{Physical Review B}, 99(21), American Physical Society, Woodbury, NY, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


{Coherent excitation of heterosymmetric spin waves with ultrashort wavelengths}
Coherent excitation of heterosymmetric spin waves with ultrashort wavelengths

Dieterle, G., Förster, J., Stoll, H., Semisalova, A. S., Finizio, S., Gangwar, A., Weigand, M., Noske, M., Fähnle, M., Bykova, I., Gräfe, J., Bozhko, D. A., Musiienko-Shmarova, H. Y., Tiberkevich, V., Slavin, A. N., Back, C. H., Raabe, J., Schütz, G., Wintz, S.

{Physical Review Letters}, 122(11), American Physical Society, Woodbury, N.Y., 2019 (article)

Abstract
In the emerging field of magnonics, spin waves are foreseen as signal carriers for future spintronic information processing and communication devices, owing to both the very low power losses and a high device miniaturization potential predicted for short-wavelength spin waves. Yet, the efficient excitation and controlled propagation of nanoscale spin waves remains a severe challenge. Here, we report the observation of high-amplitude, ultrashort dipole-exchange spin waves (down to 80 nm wavelength at 10 GHz frequency) in a ferromagnetic single layer system, coherently excited by the driven dynamics of a spin vortex core. We used time-resolved x-ray microscopy to directly image such propagating spin waves and their excitation over a wide range of frequencies. By further analysis, we found that these waves exhibit a heterosymmetric mode profile, involving regions with anti-Larmor precession sense and purely linear magnetic oscillation. In particular, this mode profile consists of dynamic vortices with laterally alternating helicity, leading to a partial magnetic flux closure over the film thickness, which is explained by a strong and unexpected mode hybridization. This spin-wave phenomenon observed is a general effect inherent to the dynamics of sufficiently thick ferromagnetic single layer films, independent of the specific excitation method employed.

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DOI [BibTex]

DOI [BibTex]


Reprogrammability and Scalability of Magnonic Fibonacci Quasicrystals
Reprogrammability and Scalability of Magnonic Fibonacci Quasicrystals

Lisiecki, F., Rychły, J., Kuświk, P., Głowiński, H., Kłos, J. W., Groß, F., Bykova, I., Weigand, M., Zelent, M., Goering, E. J., Schütz, G., Gubbiotti, G., Krawczyk, M., Stobiecki, F., Dubowik, J., Gräfe, J.

Physical Review Applied, 11, pages: 054003, 2019 (article)

Abstract
Magnonic crystals are systems that can be used to design and tune the dynamic properties of magnetization. Here, we focus on one-dimensional Fibonacci magnonic quasicrystals. We confirm the existence of collective spin waves propagating through the structure as well as dispersionless modes; the reprogammability of the resonance frequencies, dependent on the magnetization order; and dynamic spin-wave interactions. With the fundamental understanding of these properties, we lay a foundation for the scalable and advanced design of spin-wave band structures for spintronic, microwave, and magnonic applications.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Robustifying Independent Component Analysis by Adjusting for Group-Wise Stationary Noise

Pfister*, N., Weichwald*, S., Bühlmann, P., Schölkopf, B.

Journal of Machine Learning Research, 20(147):1-50, 2019, *equal contribution (article)

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ArXiv Code Project page PDF link (url) Project Page Project Page [BibTex]

ArXiv Code Project page PDF link (url) Project Page Project Page [BibTex]


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Enhancing Human Learning via Spaced Repetition Optimization

Tabibian, B., Upadhyay, U., De, A., Zarezade, A., Schölkopf, B., Gomez Rodriguez, M.

Proceedings of the National Academy of Sciences, 116(10):3988-3993, National Academy of Sciences, 2019 (article)

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link (url) DOI Project Page Project Page [BibTex]

link (url) DOI Project Page Project Page [BibTex]


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Entropic Regularization of Markov Decision Processes

Belousov, B., Peters, J.

Entropy, 21(7):674, 2019 (article)

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


The near and far of a pair of magnetic capillary disks
The near and far of a pair of magnetic capillary disks

Koens, L., Wang, W., Sitti, M., Lauga, E.

Soft Matter, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Searchers adjust their eye-movement dynamics to target characteristics in natural scenes

Rothkegel, L., Schütt, H., Trukenbrod, H., Wichmann, F. A., Engbert, R.

Scientific Reports, 9(1635), 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Spatial statistics for gaze patterns in scene viewing: Effects of repeated viewing

Trukenbrod, H. A., Barthelmé, S., Wichmann, F. A., Engbert, R.

Journal of Vision, 19(6):19, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


Aerial robot control in close proximity to ceiling: A force estimation-based nonlinear mpc
Aerial robot control in close proximity to ceiling: A force estimation-based nonlinear mpc

Kocer, B. B., Tiryaki, M. E., Pratama, M., Tjahjowidodo, T., Seet, G. G. L.

arXiv preprint arXiv:1907.13594, 2019 (article)

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[BibTex]

[BibTex]


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Magnetic field dependence of magnetotransport properties of MgB2/CrO2 bilayer thin films

Alzayed, N. S., Shahabuddin, M., Ramey, S. M., Soltan, S.

{Journal of Superconductivity and Novel Magnetism}, 32(8):2447-2455, Springer Science + Business Media B.V., New York, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Structural and magnetic properties of FePt-Tb alloy thin films

Schmidt, N. Y., Laureti, S., Radu, F., Ryll, H., Luo, C., d\textquotesingleAcapito, F., Tripathi, S., Goering, E., Weller, D., Albrecht, M.

{Physical Review B}, 100(6), American Physical Society, Woodbury, NY, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


Mechanics of a pressure-controlled adhesive membrane for soft robotic gripping on curved surfaces
Mechanics of a pressure-controlled adhesive membrane for soft robotic gripping on curved surfaces

Song, S., Drotlef, D., Paik, J., Majidi, C., Sitti, M.

Extreme Mechanics Letters, Elsevier, 2019 (article)

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[BibTex]


Multifunctional and biodegradable self-propelled protein motors
Multifunctional and biodegradable self-propelled protein motors

Pena-Francesch, A., Giltinan, J., Sitti, M.

Nature communications, 10, Nature Publishing Group, 2019 (article)

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[BibTex]

[BibTex]