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2013


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MR-based Attenuation Correction Methods for Improved PET Quantification in Lesions within Bone and Susceptibility Artifact Regions

Bezrukov, I., Schmidt, H., Mantlik, F., Schwenzer, N., Brendle, C., Schölkopf, B., Pichler, B.

Journal of Nuclear Medicine, 54(10):1768-1774, 2013 (article)

Abstract
Hybrid PET/MR systems have recently entered clinical practice. Thus, the accuracy of MR-based attenuation correction in simultaneously acquired data can now be investigated. We assessed the accuracy of 4 methods of MR-based attenuation correction in lesions within soft tissue, bone, and MR susceptibility artifacts: 2 segmentation-based methods (SEG1, provided by the manufacturer, and SEG2, a method with atlas-based susceptibility artifact correction); an atlas- and pattern recognition–based method (AT&PR), which also used artifact correction; and a new method combining AT&PR and SEG2 (SEG2wBONE). Methods: Attenuation maps were calculated for the PET/MR datasets of 10 patients acquired on a whole-body PET/MR system, allowing for simultaneous acquisition of PET and MR data. Eighty percent iso-contour volumes of interest were placed on lesions in soft tissue (n = 21), in bone (n = 20), near bone (n = 19), and within or near MR susceptibility artifacts (n = 9). Relative mean volume-of-interest differences were calculated with CT-based attenuation correction as a reference. Results: For soft-tissue lesions, none of the methods revealed a significant difference in PET standardized uptake value relative to CT-based attenuation correction (SEG1, −2.6% ± 5.8%; SEG2, −1.6% ± 4.9%; AT&PR, −4.7% ± 6.5%; SEG2wBONE, 0.2% ± 5.3%). For bone lesions, underestimation of PET standardized uptake values was found for all methods, with minimized error for the atlas-based approaches (SEG1, −16.1% ± 9.7%; SEG2, −11.0% ± 6.7%; AT&PR, −6.6% ± 5.0%; SEG2wBONE, −4.7% ± 4.4%). For lesions near bone, underestimations of lower magnitude were observed (SEG1, −12.0% ± 7.4%; SEG2, −9.2% ± 6.5%; AT&PR, −4.6% ± 7.8%; SEG2wBONE, −4.2% ± 6.2%). For lesions affected by MR susceptibility artifacts, quantification errors could be reduced using the atlas-based artifact correction (SEG1, −54.0% ± 38.4%; SEG2, −15.0% ± 12.2%; AT&PR, −4.1% ± 11.2%; SEG2wBONE, 0.6% ± 11.1%). Conclusion: For soft-tissue lesions, none of the evaluated methods showed statistically significant errors. For bone lesions, significant underestimations of −16% and −11% occurred for methods in which bone tissue was ignored (SEG1 and SEG2). In the present attenuation correction schemes, uncorrected MR susceptibility artifacts typically result in reduced attenuation values, potentially leading to highly reduced PET standardized uptake values, rendering lesions indistinguishable from background. While AT&PR and SEG2wBONE show accurate results in both soft tissue and bone, SEG2wBONE uses a two-step approach for tissue classification, which increases the robustness of prediction and can be applied retrospectively if more precision in bone areas is needed.

ei

Web DOI [BibTex]

2013


Web DOI [BibTex]


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Learning output kernels for multi-task problems

Dinuzzo, F.

Neurocomputing, 118, pages: 119-126, 2013 (article)

ei

DOI [BibTex]

DOI [BibTex]


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Analytical probabilistic modeling for radiation therapy treatment planning

Bangert, M., Hennig, P., Oelfke, U.

Physics in Medicine and Biology, 58(16):5401-5419, 2013 (article)

ei pn

PDF DOI [BibTex]

PDF DOI [BibTex]


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Imaging Findings and Therapy Response Monitoring in Chronic Sclerodermatous Graft-Versus-Host Disease: Preliminary Data of a Simultaneous PET/MRI Approach

Sauter, A., Schmidt, H., Mantlik, F., Kolb, A., Federmann, B., Pfannenberg, C., Reimold, M., Pichler, B., Bethge, W., Horger, M.

Clinical Nuclear Medicine, 38(8):e309-e317, 2013 (article)

Abstract
PURPOSE: Our objective was a multifunctional imaging approach of chronic sclerodermatous graft-versus-host disease (ScGVHD) and its course during therapy using PET/MRI. METHODS: We performed partial-body PET/CT and PET/MRI of the calf in 6 consecutively recruited patients presenting with severe ScGVHD. The patients were treated with different immunosuppressive regimens and supportive therapies. PET/CT scanning started 60.5 +/- 3.3 minutes, PET/MRI imaging 139.5 +/- 16.7 minutes after F-FDG application. MRI acquisition included T1- (precontrast and postcontrast) and T2-weighted sequences. SUVmean, T1 contrast enhancement, and T2 signal intensity from region-of-interest analysis were calculated for different fascial and muscular compartments. In addition, musculoskeletal MRI findings and the modified Rodnan skin score were assessed. All patients underwent imaging follow-up. RESULTS: At baseline PET/MRI, ScGVHD-related musculoskeletal abnormalities consisted of increased signal and/or thickening of involved anatomical structures on T2-weighted and T1 postcontrast images as well as an increased FDG uptake. At follow-up, ScGVHD-related imaging findings decreased (SUVmean n = 4, mean T1 contrast enhancement n = 5, mean T2 signal intensity n = 3) or progressed (SUVmean n = 3, mean T1 contrast enhancement n = 2, mean T2 signal intensity n = 4). Clinically modified Rodnan skin score improved for 5 follow-ups and progressed for 2. SUVmean values correlated between PET/CT and PET/MRI acquisition (r = 0.660, P = 0.014), T1 contrast enhancement, and T2 signal (r = 0.668, P = 0.012), but not between the SUVmean values and the MRI parameters. CONCLUSIONS: PET/MRI as a combined morphological and functional technique seems to assess the inflammatory processes from different points of view and provides therefore in part complementary information

ei

Web [BibTex]

Web [BibTex]


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A Survey on Policy Search for Robotics, Foundations and Trends in Robotics

Deisenroth, M., Neumann, G., Peters, J.

Foundations and Trends in Robotics, 2(1-2):1-142, 2013 (article)

ei

DOI [BibTex]

DOI [BibTex]


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Reinforcement Learning in Robotics: A Review

Kober, J., Bagnell, D., Peters, J.

International Journal of Robotics Research, 32(11):1238–1274, 2013 (article)

ei

PDF DOI [BibTex]

PDF DOI [BibTex]


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Multimodal information improves the rapid detection of mental fatigue

Laurent, F., Valderrama, M., Besserve, M., Guillard, M., Lachaux, J., Martinerie, J., Florence, G.

Biomedical Signal Processing and Control, 8(4):400 - 408, 2013 (article)

ei

Web DOI [BibTex]

Web DOI [BibTex]


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Interactive Domain Adaptation for the Classification of Remote Sensing Images using Active Learning

Persello, C.

IEEE Geoscience and Remote Sensing Letters, 10(4):736-740, 2013 (article)

ei

DOI [BibTex]

DOI [BibTex]


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Learning to Select and Generalize Striking Movements in Robot Table Tennis

Mülling, K., Kober, J., Kroemer, O., Peters, J.

International Journal of Robotics Research, 32(3):263-279, 2013 (article)

ei

PDF DOI [BibTex]

PDF DOI [BibTex]


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HiFiVE: A Hilbert Space Embedding of Fiber Variability Estimates for Uncertainty Modeling and Visualization

Schultz, T., Schlaffke, L., Schölkopf, B., Schmidt-Wilcke, T.

Computer Graphics Forum, 32(3):121-130, (Editors: B Preim, P Rheingans, and H Theisel), Blackwell Publishing, Oxford, UK, Eurographics Conference on Visualization (EuroVis), 2013 (article)

ei

DOI [BibTex]

DOI [BibTex]


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Detection and attribution of large spatiotemporal extreme events in Earth observation data

Zscheischler, J., Mahecha, M., Harmeling, S., Reichstein, M.

Ecological Informatics, 15, pages: 66-73, 2013 (article)

Abstract
Latest climate projections suggest that both frequency and intensity of climate extremes will be substantially modified over the course of the coming decades. As a consequence, we need to understand to what extent and via which pathways climate extremes affect the state and functionality of terrestrial ecosystems and the associated biogeochemical cycles on a global scale. So far the impacts of climate extremes on the terrestrial biosphere were mainly investigated on the basis of case studies, while global assessments are widely lacking. In order to facilitate global analysis of this kind, we present a methodological framework that firstly detects spatiotemporally contiguous extremes in Earth observations, and secondly infers the likely pathway of the preceding climate anomaly. The approach does not require long time series, is computationally fast, and easily applicable to a variety of data sets with different spatial and temporal resolutions. The key element of our analysis strategy is to directly search in the relevant observations for spatiotemporally connected components exceeding a certain percentile threshold. We also put an emphasis on characterization of extreme event distribution, and scrutinize the attribution issue. We exemplify the analysis strategy by exploring the fraction of absorbed photosynthetically active radiation (fAPAR) from 1982 to 2011. Our results suggest that the hot spots of extremes in fAPAR lie in Northeastern Brazil, Southeastern Australia, Kenya and Tanzania. Moreover, we demonstrate that the size distribution of extremes follow a distinct power law. The attribution framework reveals that extremes in fAPAR are primarily driven by phases of water scarcity.

ei

Web DOI [BibTex]

Web DOI [BibTex]


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Simultaneous PET/MR reveals Brain Function in Activated and Resting State on Metabolic, Hemodynamic and Multiple Temporal Scales

Wehrl, H., Hossain, M., Lankes, K., Liu, C., Bezrukov, I., Martirosian, P., Schick, F., Reischl, G., Pichler, B.

Nature Medicine, 19, pages: 1184–1189, 2013 (article)

Abstract
Combined positron emission tomography (PET) and magnetic resonance imaging (MRI) is a new tool to study functional processes in the brain. Here we study brain function in response to a barrel-field stimulus simultaneously using PET, which traces changes in glucose metabolism on a slow time scale, and functional MRI (fMRI), which assesses fast vascular and oxygenation changes during activation. We found spatial and quantitative discrepancies between the PET and the fMRI activation data. The functional connectivity of the rat brain was assessed by both modalities: the fMRI approach determined a total of nine known neural networks, whereas the PET method identified seven glucose metabolism–related networks. These results demonstrate the feasibility of combined PET-MRI for the simultaneous study of the brain at activation and rest, revealing comprehensive and complementary information to further decode brain function and brain networks.

ei

Web DOI [BibTex]

Web DOI [BibTex]


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Finding Potential Support Vectors in Separable Classification Problems

Varagnolo, D., Del Favero, S., Dinuzzo, F., Schenato, L., Pillonetto, G.

IEEE Transactions on Neural Networks and Learning Systems, 24(11):1799-1813, 2013 (article)

ei

DOI [BibTex]

DOI [BibTex]


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Open-Box Spectral Clustering: Applications to Medical Image Analysis

Schultz, T., Kindlmann, G.

IEEE Transactions on Visualization and Computer Graphics, 19(12):2100-2108, 2013 (article)

ei

DOI [BibTex]

DOI [BibTex]


Hybrid nanocolloids with programmed three-dimensional shape and material composition
Hybrid nanocolloids with programmed three-dimensional shape and material composition

Mark, A. G., Gibbs, J. G., Lee, T., Fischer, P.

NATURE MATERIALS, 12(9):802-807, 2013, Max Planck Press Release. (article)

Abstract
Tuning the optical(1,2), electromagnetic(3,4) and mechanical properties of a material requires simultaneous control over its composition and shape(5). This is particularly challenging for complex structures at the nanoscale because surface-energy minimization generally causes small structures to be highly symmetric(5). Here we combine low-temperature shadow deposition with nanoscale patterning to realize nanocolloids with anisotropic three-dimensional shapes, feature sizes down to 20 nm and a wide choice of materials. We demonstrate the versatility of the fabrication scheme by growing three-dimensional hybrid nanostructures that contain several functional materials with the lowest possible symmetry, and by fabricating hundreds of billions of plasmonic nanohelices, which we use as chiral metafluids with record circular dichroism and tunable chiroptical properties.

Max Planck Press Release.

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Video - Fabrication of Designer Nanostructures DOI [BibTex]


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Optimal control of reaching includes kinematic constraints

Mistry, M., Theodorou, E., Schaal, S., Kawato, M.

Journal of Neurophysiology, 2013, clmc (article)

Abstract
We investigate adaptation under a reaching task with an acceleration-based force field perturbation designed to alter the nominal straight hand trajectory in a potentially benign manner:pushing the hand of course in one direction before subsequently restoring towards the target. In this particular task, an explicit strategy to reduce motor effort requires a distinct deviation from the nominal rectilinear hand trajectory. Rather, our results display a clear directional preference during learning, as subjects adapted perturbed curved trajectories towards their initial baselines. We model this behavior using the framework of stochastic optimal control theory and an objective function that trades-of the discordant requirements of 1) target accuracy, 2) motor effort, and 3) desired trajectory. Our work addresses the underlying objective of a reaching movement, and we suggest that robustness, particularly against internal model uncertainly, is as essential to the reaching task as terminal accuracy and energy effciency.

am

PDF [BibTex]

PDF [BibTex]


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im3shape: a maximum likelihood galaxy shear measurement code for cosmic gravitational lensing

Zuntz, J., Kacprzak, T., Voigt, L., Hirsch, M., Rowe, B., Bridle, S.

Monthly Notices of the Royal Astronomical Society, 434(2):1604-1618, Oxford University Press, 2013 (article)

ei

DOI [BibTex]

DOI [BibTex]


Magnetoelastic coupling in epitaxial cobalt ferrite/barium titanate heterostructures
Magnetoelastic coupling in epitaxial cobalt ferrite/barium titanate heterostructures

Gräfe, J., Welke, M., Bern, F., Ziese, M., Denecke, R.

Journal of Magnetism and Magnetic Materials, 339, pages: 84-88, 2013 (article)

Abstract
Ultra-thin cobalt ferrite films have been synthesised on ferroelectric barium titanate crystals. The cobalt ferrite films exhibit a magnetic response to strain induced by structural changes in the barium titanate substrate, suggesting a pathway to multiferroic coupling. These structural changes are achieved by heating through the phase transition temperatures of barium titanate. In addition the ferromagnetic signal of the substrate itself is taken into account, addressing the influence of impurities or defects in the substrate. The cobalt ferrite/barium titanate heterostructure is a suitable oxidic platform for future magnetoelectric applications with an established ferroelectric substrate and widely tuneable magnetic properties by changing the transition metal in the ferrite film.

mms

DOI [BibTex]

DOI [BibTex]


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Self-Propelled Micromotors for Cleaning Polluted Watter

Soler, L., Magdanz, V., Fomin, V. M., Sanchez, S., Schmidt, O. G.

ACS Nano, 11, pages: 9611-9620, American Chemical Society, Washington, DC, 2013 (article)

Abstract
We describe the use of catalytically self-propelled microjets (dubbed micromotors) for degrading organic pollutants in water via the Fenton oxidation process. The tubular micromotors are composed of rolled-up functional nanomembranes consisting of Fe/Pt bilayers. The micromotors contain double functionality within their architecture, i.e., the inner Pt for the self-propulsion and the outer Fe for the in situ generation of ferrous ions boosting the remediation of contaminated water.The degradation of organic pollutants takes place in the presence of hydrogen peroxide, which acts as a reagent for the Fenton reaction and as main fuel to propel the micromotors. Factors influencing the efficiency of the Fenton oxidation process, including thickness of the Fe layer, pH, and concentration of hydrogen peroxide, are investigated. The ability of these catalytically self-propelled micromotors to improve intermixing in liquids results in the removal of organic pollutants ca. 12 times faster than when the Fenton oxidation process is carried out without catalytically active micromotors. The enhanced reaction\textendashdiffusion provided by micromotors has been theoretically modeled. The synergy between the internal and external functionalities of the micromotors, without the need of further functionalization, results into an enhanced degradation of nonbiodegradable and dangerous organic pollutants at small-scale environments and holds considerable promise for the remediation of contaminated water.

icm

DOI [BibTex]

DOI [BibTex]


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Stability of thin liquid films and sessile droplets under confinement

Dörfler, F., Rauscher, M., Dietrich, S.

Physical Review E, 88(1), American Physical Society, Melville, NY, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Nonequilibrium interfaces in colloidal fluids

Bier, M., Arnold, D.

Physical Review E, 88(6), American Physical Society, Melville, NY, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Colloidal particles at fluid interfaces: Effective interactions, dynamics and a gravitation\textendashlike instability

Bleibel, J., Dom\’\inguez, A., Oettel, M.

The European Physical Journal Special Topics, 222(11):3071-3087, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Anomalous transport in the crowded world of biological cells

Höfling, Felix, Franosch, Thomas

Reports on Progress in Physics, 76(4), IOP Pub., London, 2013, author: Höfling, Felix (article)

icm

link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Flow pattern in the vicinity of self-propelling hot Janus particles

Bickel, T., Majee, A., Würger, A.

Physical Review E, 88(1), American Physical Society, Melville, NY, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


Chiral Colloidal Molecules And Observation of The Propeller Effect
Chiral Colloidal Molecules And Observation of The Propeller Effect

Schamel, D., Pfeifer, M., Gibbs, J. G., Miksch, B., Mark, A. G., Fischer, P.

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 135(33):12353-12359, 2013 (article)

Abstract
Chiral molecules play an important role in biological and chemical processes, but physical effects due to their symmetry-breaking are generally weak. Several physical chiral separation schemes which could potentially be useful, including the propeller effect, have therefore not yet been demonstrated at the molecular scale. However, it has been proposed that complex nonspherical colloidal particles could act as ``colloidal molecules{''} in mesoscopic model systems to permit the visualization of molecular phenomena that are otherwise difficult to observe. Unfortunately, it is difficult to synthesize such colloids because surface minimization generally favors the growth of symmetric particles. Here we demonstrate the production of large numbers of complex colloids with glancing angle physical vapor deposition. We use chiral colloids to demonstrate the Baranova and Zel'dovich (Baranova, N. B.; Zel'dovich, B. Y. Chem. Phys. Lett. 1978, 57, 435) propeller effect: the separation of a racemic mixture by application of a rotating field that couples to the dipole moment of the enantiomers and screw propels them in opposite directions. The handedness of the colloidal suspensions is monitored with circular differential light scattering. An exact solution for the colloid's propulsion is derived, and comparisons between the colloidal system and the corresponding effect at the molecular scale are made.

pf

Video - Nanospropellers DOI [BibTex]

Video - Nanospropellers DOI [BibTex]


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Accurate detection of differential RNA processing

Drewe, P., Stegle, O., Hartmann, L., Kahles, A., Bohnert, R., Wachter, A., Borgwardt, K. M., Rätsch, G.

Nucleic Acids Research, 41(10):5189-5198, 2013 (article)

ei

DOI [BibTex]

DOI [BibTex]


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Nonequilibrium Critical Casimir Effect in Binary Fluids

Furukawa, A., Gambassi, A., Dietrich, S., Tanaka, H.

Physical Review Letters, 111(5), American Physical Society, Woodbury, N.Y., 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Many-body effects for critical Casimir forces

Gomes de Mattos, T., Harnau, L., Dietrich, S.

The Journal of Chemical Physics, 138(7), 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Propulsion Mechanism of Catalytic Microjet Engines

Magdanz, V., Fomin, V. M., Soler, L., Sanchez, S., Schmidt, O. G., Hippler, M.

IEEE Transactions on Robotics and Automation, pages: 40-48, IEEE, New York, NY, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Impedance spectroscopy of ions at liquid-liquid interfaces

Bier, M., Reindl, A.

Physical Review E, 88(5), American Physical Society, Melville, NY, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Precursors of order in aggregates of patchy particles

Vasilyev, O., Klumov, B. A., Tkachenko, A. V.

Physical Review E, 88(1), American Physical Society, Melville, NY, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Two-temperature Langevin dynamics in a parabolic potential

Dotsenko, V., Maciolek, Anna, Vasilyev, O., Oshanin, G.

Physical Review E, 87(6), American Physical Society, Melville, NY, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


Indirect absorption spectroscopy using quantum cascade lasers: mid-infrared refractometry and photothermal spectroscopy
Indirect absorption spectroscopy using quantum cascade lasers: mid-infrared refractometry and photothermal spectroscopy

Pfeifer, M., Ruf, A., Fischer, P.

OPTICS EXPRESS, 21(22):25643-25654, 2013 (article)

Abstract
We record vibrational spectra with two indirect schemes that depend on the real part of the index of refraction: mid-infrared refractometry and photothermal spectroscopy. In the former, a quantum cascade laser (QCL) spot is imaged to determine the angles of total internal reflection, which yields the absorption line via a beam profile analysis. In the photothermal measurements, a tunable QCL excites vibrational resonances of a molecular monolayer, which heats the surrounding medium and changes its refractive index. This is observed with a probe laser in the visible. Sub-monolayer sensitivities are demonstrated. (C) 2013 Optical Society of America

pf

DOI [BibTex]


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Detecting regulatory gene–environment interactions with unmeasured environmental factors

Fusi, N., Lippert, C., Borgwardt, K. M., Lawrence, N. D., Stegle, O.

Bioinformatics, 29(11):1382-1389, 2013 (article)

ei

DOI [BibTex]

DOI [BibTex]


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Critical Casimir forces between homogeneous and chemically striped surfaces

Parisen Toldin, F., Tröndle, M., Dietrich, S.

Physical Review E, 88, American Physical Society, Melville, NY, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Comparison between theory and simulations for the magnetization and the susceptibility of polydisperse ferrofluids

Szalai, I., Nagy, S., Dietrich, S.

Journal of Physics: Condensed Matter, 25(46), IOP Pub., Bristol, UK, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Thermal activation of catalytic microjets in blood samples using microfluidic chips.

Soler, L., Mart\’\inez-Cisneros, C., Swiersy, A., Sanchez, S., Schmidt, O. G.

Lab on a Chip, 13, pages: 4299-4303, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Nematic liquid crystal boojums with handles on colloidal handlebodies

Liu, Q. K., Senyuk, B., Tasinkevych, M., Smalyukh, I. I.

Proceedings of the National Academy of Sciences of the United States of America, 110(23):9231-9236, National Academy of Sciences, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Critical Casimir torques and forces acting on needles in two spatial dimensions

Vasilyev, Oleg, Eisenriegler, E., Dietrich, Siegfried

Physical Review E, 88(1), American Physical Society, Melville, NY, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


Plasmonic nanohelix metamaterials with tailorable giant circular dichroism
Plasmonic nanohelix metamaterials with tailorable giant circular dichroism

Gibbs, J. G., Mark, A. G., Eslami, S., Fischer, P.

APPLIED PHYSICS LETTERS, 103(21), 2013, Featured cover article. (article)

Abstract
Plasmonic nanohelix arrays are shown to interact with electromagnetic fields in ways not typically seen with ordinary matter. Chiral metamaterials (CMMs) with feature sizes small with respect to the wavelength of visible light are a promising route to experimentally achieve such phenomena as negative refraction without the need for simultaneously negative e and mu. Here we not only show that giant circular dichroism in the visible is achievable with hexagonally arranged plasmonic nanohelix arrays, but that we can precisely tune the optical activity via morphology and lattice spacing. The discrete dipole approximation is implemented to support experimental data. (C) 2013 AIP Publishing LLC.

Featured cover article.

pf

DOI [BibTex]

DOI [BibTex]


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Dynamical Movement Primitives: Learning Attractor Models for Motor Behaviors

Ijspeert, A., Nakanishi, J., Pastor, P., Hoffmann, H., Schaal, S.

Neural Computation, (25):328-373, 2013, clmc (article)

Abstract
Nonlinear dynamical systems have been used in many disciplines to model complex behaviors, including biological motor control, robotics, perception, economics, traffic prediction, and neuroscience. While often the unexpected emergent behavior of nonlinear systems is the focus of investigations, it is of equal importance to create goal-directed behavior (e.g., stable locomotion from a system of coupled oscillators under perceptual guidance). Modeling goal-directed behavior with nonlinear systems is, however, rather difficult due to the parameter sensitivity of these systems, their complex phase transitions in response to subtle parameter changes, and the difficulty of analyzing and predicting their long-term behavior; intuition and time-consuming parameter tuning play a major role. This letter presents and reviews dynamical movement primitives, a line of research for modeling attractor behaviors of autonomous nonlinear dynamical systems with the help of statistical learning techniques. The essence of our approach is to start with a simple dynamical system, such as a set of linear differential equations, and transform those into a weakly nonlinear system with prescribed attractor dynamics by meansof a learnable autonomous forcing term. Both point attractors and limit cycle attractors of almost arbitrary complexity can be generated. We explain the design principle of our approach and evaluate its properties in several example applications in motor control and robotics.

am

link (url) [BibTex]

link (url) [BibTex]


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Fragmentation of Slow Wave Sleep after Onset of Complete Locked-In State

Soekadar, S. R., Born, J., Birbaumer, N., Bensch, M., Halder, S., Murguialday, A. R., Gharabaghi, A., Nijboer, F., Schölkopf, B., Martens, S.

Journal of Clinical Sleep Medicine, 9(9):951-953, 2013 (article)

ei

DOI [BibTex]

DOI [BibTex]


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Quantum cryo-sieving for hydrogen isotope separation in microporous frameworks: an experimental study on the correlation between effective quantum sieving and pore size

Oh, H., Park, K. S., Kalidindi, S. B., Fischer, R. A., Hirscher, M.

{Journal of Materials Chemistry A}, 1, pages: 3244-3248, Royal Society of Chemistry, Cambridge, UK, 2013 (article)

mms

DOI [BibTex]

DOI [BibTex]


{Switching modes in easy and hard axis magnetic reversal in a self-assembled antidot array}
Switching modes in easy and hard axis magnetic reversal in a self-assembled antidot array

Haering, F., Wiedwald, U., Nothelfer, S., Koslowski, B., Ziemann, P., Lechner, L., Wallucks, A., Lebecki, K., Nowak, U., Gräfe, J., Goering, E., Schütz, G.

{Nanotechnology}, 24, IOP Pub., Bristol, UK, 2013 (article)

Abstract
We study the reversal mechanisms in a self-assembled, hexagonally ordered Fe antidot array with a period of 200 nm and an antidot diameter of 100 nm which was prepared by polystyrene nanosphere lithography. Direction-dependent information in such a self-assembled sample is obtained by measuring the anisotropic magnetoresistance (AMR) through constrictions processed by focused ion beam milling in nearest neighbor and next nearest neighbor directions. We show that such an originally integral method can be used to investigate the strong in-plane anisotropy introduced by the antidot lattice. The easy and hard axis reversal mechanisms and corresponding AMR signals are modeled by micromagnetic simulations. Additional in-field magnetic force microscopy studies allow the correlation of microscopic switching to features in the integral AMR. We find that the easy axis of magnetization is connected to a distinct periodic magnetic domain pattern, which can be observed during the whole magnetization reversal. While this process is driven by nucleation and propagation of reversed domains, the hard axis reversal is characterized by a (stepwise) rotation of the magnetization via the antidot lattice' easy axes.

mms

DOI Project Page [BibTex]

DOI Project Page [BibTex]


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Critical Casimir forces along the isofields

Zubaszewska, M., Maciolek, A., Drzewinski, A.

Physical Review E, 88(5), American Physical Society, Melville, NY, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Surface states and the Casimir interaction in the Ising model

Abraham, D. B., Maciolek, A.

Europhysics letters, 101(2), Editrice Compositori., Bologna, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Crystallization, structural diversity, and anisotropy effects in 2D arrays of icosahedral viruses

Fukuto, M., Nguyen, Q. L., Vasilyev, O., Mank, N., Washington-Huges, C. L., Kuzmenko, I., Checco, A., Mao, Y., Wang, Q., Yang, L.

Soft Matter, 9(40):9633-9642, Royal Society of Chemistry, Cambridge, UK, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Dynamic arrest in model porous media-intermediate scattering functions

Spanner, Markus, Schnyder, Simon K., Höfling, Felix, Voigtmann, Thomas, Franosch, Thomas

Soft Matter, 9(5):1604-1611, Royal Society of Chemistry, Cambridge, UK, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Linear response relations in fluctuational electrodynamics

Golyk, V. A., Krüger, Matthias, Kardar, M.

Physical Review B, 88(15), American Physical Society, Woodbury, NY, 2013 (article)

icm

DOI [BibTex]

DOI [BibTex]


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Ideal Polyethylene Nanocrystals

Osichov, A., Rabe, C., Vogtt, K., Narayanan, T., Harnau, Ludger, Drechsler, M., Ballauff, M.

Journal of the American Chemical Society, 135(31):11645-11650, American Chemical Society, 2013 (article)

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DOI [BibTex]

DOI [BibTex]