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2008


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Learning to control in operational space

Peters, J., Schaal, S.

International Journal of Robotics Research, 27, pages: 197-212, 2008, clmc (article)

Abstract
One of the most general frameworks for phrasing control problems for complex, redundant robots is operational space control. However, while this framework is of essential importance for robotics and well-understood from an analytical point of view, it can be prohibitively hard to achieve accurate control in face of modeling errors, which are inevitable in com- plex robots, e.g., humanoid robots. In this paper, we suggest a learning approach for opertional space control as a direct inverse model learning problem. A first important insight for this paper is that a physically cor- rect solution to the inverse problem with redundant degrees-of-freedom does exist when learning of the inverse map is performed in a suitable piecewise linear way. The second crucial component for our work is based on the insight that many operational space controllers can be understood in terms of a constrained optimal control problem. The cost function as- sociated with this optimal control problem allows us to formulate a learn- ing algorithm that automatically synthesizes a globally consistent desired resolution of redundancy while learning the operational space controller. From the machine learning point of view, this learning problem corre- sponds to a reinforcement learning problem that maximizes an immediate reward. We employ an expectation-maximization policy search algorithm in order to solve this problem. Evaluations on a three degrees of freedom robot arm are used to illustrate the suggested approach. The applica- tion to a physically realistic simulator of the anthropomorphic SARCOS Master arm demonstrates feasibility for complex high degree-of-freedom robots. We also show that the proposed method works in the setting of learning resolved motion rate control on real, physical Mitsubishi PA-10 medical robotics arm.

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link (url) DOI [BibTex]

2008


link (url) DOI [BibTex]


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Adaptation to a sub-optimal desired trajectory

M. Mistry, E. A. G. L. T. Y. S. S. M. K.

Advances in Computational Motor Control VII, Symposium at the Society for Neuroscience Meeting, Washington DC, 2008, 2008, clmc (article)

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PDF [BibTex]

PDF [BibTex]


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Texture, microstructure and mechanical properties of equiaxed ultrafine-grained Zr fabricated by accumulative roll bonding

Jiang, L., Perez-Prado, M. T., Gruber, P. A., Arzt, E., Ruano, O. A., Kassner, M. E.

{Acta Materialia}, 56(6):1228-1242, 2008 (article)

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[BibTex]

[BibTex]


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Theory of size mismatched alloy systems: many-body Kanzaki forces

Shchyglo, O., Diaz-Ortiz, A., Udyansky, A., Bugaev, V. N., Reichert, H., Dosch, H., Drautz, R.

{Journal of Physics: Condensed Matter}, 20, pages: 1-9, 2008 (article)

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[BibTex]

[BibTex]


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Pinning of domain walls in composite particles

Kronmüller, H., Goll, D.

{Physica B}, 403, pages: 237-241, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Chaotic vortex dynamics and low current phases in the remanent state of MgB2 thin films

Albrecht, J., Audehm, P., Djupmyr, M.

{Superconductor Science and Technology}, 21, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Continuous and discontinuous grain-boundary wetting in ZnxAl1-x

Straumal, B. B., Gornakova, A. S., Kogtenkova, O. A., Protasova, S. G., Sursaeva, V. G., Baretzky, B.

{Physical Review B}, 78, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetic circular dichroism in two-photon absorption and depth-resolved magnetic microscopy

Seib, J., Fähnle, M.

{Physical Review B}, 77, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Heat of adsorption for hydrogen in microporous high-surface-area materials

Schmitz, B., Müller, U., Trukhan, N., Schubert, M., Férey, G., Hirscher, M.

{ChemPhysChem}, 9, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Untersuchungen der Desorption von Wasserstoff in metall-organischen Gerüsten

Panella, B., Hönes, K., Müller, U., Trukhan, N., Schubert, M., Pütter, H., Hirscher, M.

{Angewandte Chemie}, 120, pages: 2169-2173, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Influence of domain wall pinning on the dynamic behavior of magnetic vortex structures: Time-resolved scanning x-ray transmission microscopy in NiFe thin film structures

Vansteenkiste, A., De Baerdemaeker, J., Chou, K. W., Stoll, H., Curcic, M., Tyliszczak, T., Woltersdorf, G., Back, C. H., Schütz, G., Van Waeyenberge, B.

{Physical Review B}, 77, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Temperature dependence of mechanical properties in ultrathin Au films with and without passivation

Gruber, P. A., Olliges, S., Arzt, E., Spolenak, R.

{Journal of Materials Research}, 23(9):2406-2419, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Structure, phase composition, and microhardness of carbon steels after high-pressure torsion

Mazilkin, A. A., Straumal, B., Protasova, S. G., Dobatkin, S. V., Baretzky, B.

{Journal of Materials Science}, 43, pages: 3800-3805, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Operational space control: A theoretical and emprical comparison

Nakanishi, J., Cory, R., Mistry, M., Peters, J., Schaal, S.

International Journal of Robotics Research, 27(6):737-757, 2008, clmc (article)

Abstract
Dexterous manipulation with a highly redundant movement system is one of the hallmarks of hu- man motor skills. From numerous behavioral studies, there is strong evidence that humans employ compliant task space control, i.e., they focus control only on task variables while keeping redundant degrees-of-freedom as compliant as possible. This strategy is robust towards unknown disturbances and simultaneously safe for the operator and the environment. The theory of operational space con- trol in robotics aims to achieve similar performance properties. However, despite various compelling theoretical lines of research, advanced operational space control is hardly found in actual robotics imple- mentations, in particular new kinds of robots like humanoids and service robots, which would strongly profit from compliant dexterous manipulation. To analyze the pros and cons of different approaches to operational space control, this paper focuses on a theoretical and empirical evaluation of different methods that have been suggested in the literature, but also some new variants of operational space controllers. We address formulations at the velocity, acceleration and force levels. First, we formulate all controllers in a common notational framework, including quaternion-based orientation control, and discuss some of their theoretical properties. Second, we present experimental comparisons of these approaches on a seven-degree-of-freedom anthropomorphic robot arm with several benchmark tasks. As an aside, we also introduce a novel parameter estimation algorithm for rigid body dynamics, which ensures physical consistency, as this issue was crucial for our successful robot implementations. Our extensive empirical results demonstrate that one of the simplified acceleration-based approaches can be advantageous in terms of task performance, ease of parameter tuning, and general robustness and compliance in face of inevitable modeling errors.

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link (url) [BibTex]

link (url) [BibTex]


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Interfaces in driven Ising models: shear enhances confinement

Smith, T. H. R., Vasilyev, O., Abraham, D. B., Maciolek, A., Schmidt, M.

{Physical Review Letters}, 101(6), 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Planar high-Tc superconducting quantum interference device gradiometer for simultaneous measurements of two magnetic field gradients

Steppke, A., Becker, C., Grosse, V., Dörrer, L., Schmidl, F., Seidel, P., Djupmyr, M., Albrecht, J.

{Applied Physics Letters}, 92, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Terminal contact elements of insect attachment devices studied by transmission X-ray microscopy

Eimüller, T., Guttmann, P., Gorb, S. N.

{Journal of Experimental Biology}, 211, pages: 1958-1963, 2008 (article)

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[BibTex]

[BibTex]


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Increase of Co solubility with decreasing grain size in ZnO

Straumal, B. B., Mazilkin, A. A., Protasova, S. G., Myatiev, A. A., Straumal, P. B., Baretzky, B.

{Acta Materialia}, 56, pages: 6246-6256, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Uncompensated moments in the MnPd/Fe exchange bias system

Brück, S., Schütz, G., Goering, E., Ji, X., Krishnan, K. M.

{Physical Review Letters}, 101, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Aqueous deposition of ultraviolet luminescent columnar tin-doped indium hydroxide films

Qiu, Y., Bellina, P., Jeurgens, L. P. H., Leineweber, A., Welzel, U., Gerstel, P., Jiang, L., van Aken, P. A., Bill, J., Aldinger, F.

{Advanced Functional Materials}, 18, pages: 2572-2583, 2008 (article)

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[BibTex]

[BibTex]


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Unified theory of near-adiabatic magnetization dynamics for collinear and noncollinear magnetization

Steiauf, D., Seib, J., Fähnle, M.

{Physical Review B}, 78, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Hardmetals with nanograin reinforced binder: binder fine structure and hardness

Konyashin, I., Ries, B., Lachmann, F., Cooper, R., Mazilkin, A., Straumal, B., Aretz, A., Babaev, V.

{International Journal of Refractory Metals \& Hard Materials}, 26, pages: 583-588, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Interfaces in confined Ising models: Kawasaki, Glauber and sheared dynamics

Smith, T. H. R., Vasilyev, O., Abraham, D. B., Maciolek, A., Schmidt, M.

{Journal of Physics: Condensed Matter}, 20(49), 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Critical fields of an exchange coupled two-layer composite particle

Goll, D., Kronmüller, H.

{Physica B}, 403, pages: 1854-1859, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Coercivity and domain structure of nanograined Fe-C alloys after high-pressure torsion

Protasova, S. G., Straumal, B., Dobatkin, S. V., Goll, D., Schütz, G., Baretzky, B., Mazilkin, A. A., Nebrasov, A. N.

{Journal of Materials Science}, 43, pages: 3775-3781, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Epitaxial growth and properties of (001)-oriented TbBaCo2O6-αfilms

Kasper, N. V., Wochner, P., Vigliante, A., Dosch, H., Jakob, G., Carstanjen, H. D., Kremer, R. K.

{Journal of Applied Physics}, 103, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetic properties of exchange-coupled L10-FePt/Fe composite elements

Goll, D., Breitling, A., Macke, S.

{IEEE Transactions on Magnetics}, 44(11):3472-3475, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Colloidal cobalt-doped ZnO nanorods: synthesis, structural, and magnetic properties

Büsgen, T., Hilgendorff, M., Irsen, S., Wilhelm, F., Rogalev, A., Goll, D., Giersig, M.

{Journal of Physical Chemistry C}, 112(7):2412-2417, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Raman studies of hydrogen adsorbed on nanostructured porous materials

Panella, B., Hirscher, M.

{Physical Chemistry Chemical Physics}, 10, pages: 2910-2917, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Thermal evolution and grain boundary phase transformations in severely deformed nanograined Al-Zn alloys

Straumal, B., Valiev, R., Kogtenkova, O., Zieba, P., Czeppe, T., Bielanska, E., Faryna, M.

{Acta Materialia}, 56(20):6123-6131, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Hydrogen storage properties of Pd nanoparticle/carbon template composites

Campesi, R., Cuevas, F., Gadiou, R., Leroy, E., Hirscher, M., Vix-Guterl, C., Latroche, M.

{Carbon}, 46, pages: 206-214, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Reversible transformation of a grain-boundary facet into a rough-to-rough ridge in zinc

Straumal, B. B., Gornakova, A. S., Sursaeva, V. G.

{Philosophical Magazine Letters}, 88(1):27-36, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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A library for locally weighted projection regression

Klanke, S., Vijayakumar, S., Schaal, S.

Journal of Machine Learning Research, 9, pages: 623-626, 2008, clmc (article)

Abstract
In this paper we introduce an improved implementation of locally weighted projection regression (LWPR), a supervised learning algorithm that is capable of handling high-dimensional input data. As the key features, our code supports multi-threading, is available for multiple platforms, and provides wrappers for several programming languages.

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link (url) [BibTex]

link (url) [BibTex]


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The hole is important! The quest for ferromagnetism in doped ZnO

Tietze, T., Gacic, M., Schütz, G., Jakob, G., Brück, S., Goering, E.

{BESSY Highlights 2007}, pages: 14-15, 2008 (article)

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[BibTex]

[BibTex]


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Limitations of a simple quantum mechanical model: Magnetic dichroism in a relativistic one-electron atom

Rodr\’\iguez, J. C., Kostoglou, C., Singer, R., Seib, J., Fähnle, M.

{Physica Status Solidi (B)}, 245(4):735-739, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Impact of irradiation-induced point defects on electronically and ionically induced magnetic relaxation mechanisms in titano-magnetites

Walz, F., Brabers, V. A. M., Kronmüller, H.

{Physica Status Solidi (A)}, 205(12):2934-2942, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Polarization selective magnetic vortex dynamics and core reversal in rotating magnetic fields

Curcic, M., van Waeyenberge, B., Vansteenkiste, A., Weigand, M., Sackmann, V., Stoll, H., Fähnle, M., Tyliszczak, T., Woltersdorf, G., Back, C. H., Schütz, G.

{Physical Review Letters}, 101, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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X-ray spectroscopic investigations of Zn0.94Co0.06O thin films

Mayer, G., Fonin, M., Voss, S., Rüdiger, U., Goering, E.

{IEEE Transactions on Magnetics}, 44(11):2700-2703, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Experimental realization of graded L10-FePt/Fe composite media with perpendicular magnetization

Goll, D., Breitling, A., Gu, L., van Aken, P. A., Sigle, W.

{Journal of Applied Physics}, 104, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Hard magnetic L10 FePt thin films and nanopatterns

Breitling, A., Goll, D.

{Journal of Magnetism and Magnetic Materials}, 320, pages: 1449-1456, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Spin-reorientation transition in Co/Pt multilayers on nanospheres

Eimüller, T., Ulbrich, T. C., Amaladass, E., Guhr, I. L., Tyliszczak, T., Albrecht, M.

{Physical Review B}, 77, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Non-destructive compositional analysis of historic organ reed pipes

Manescu, A., Fiori, F., Giuliani, A., Kardjilov, N., Kasztovszky, Z., Rustichelli, F., Straumal, B.

{Journal of Physics: Condensed Matter}, 20, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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An advanced magnetic reflectometer

Brück, S., Bauknecht, S., Ludescher, B., Goering, E., Schütz, G.

{Review of Scientific Instruments}, 79, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Optimization strategies in human reinforcement learning

Hoffmann, H., Theodorou, E., Schaal, S.

Advances in Computational Motor Control VII, Symposium at the Society for Neuroscience Meeting, Washington DC, 2008, 2008, clmc (article)

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PDF [BibTex]

PDF [BibTex]


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Frequency analysis with coupled nonlinear oscillators

Buchli, J., Righetti, L., Ijspeert, A.

Physica D: Nonlinear Phenomena, 237(13):1705-1718, August 2008 (article)

Abstract
We present a method to obtain the frequency spectrum of a signal with a nonlinear dynamical system. The dynamical system is composed of a pool of adaptive frequency oscillators with negative mean-field coupling. For the frequency analysis, the synchronization and adaptation properties of the component oscillators are exploited. The frequency spectrum of the signal is reflected in the statistics of the intrinsic frequencies of the oscillators. The frequency analysis is completely embedded in the dynamics of the system. Thus, no pre-processing or additional parameters, such as time windows, are needed. Representative results of the numerical integration of the system are presented. It is shown, that the oscillators tune to the correct frequencies for both discrete and continuous spectra. Due to its dynamic nature the system is also capable to track non-stationary spectra. Further, we show that the system can be modeled in a probabilistic manner by means of a nonlinear Fokker–Planck equation. The probabilistic treatment is in good agreement with the numerical results, and provides a useful tool to understand the underlying mechanisms leading to convergence.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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In situ observation of cracks in gold nano-interconnects on flexible substrates

Olliges, S., Gruber, P. A., Orso, S., Auzelyte, V., Ekinci, Y., Solak, H. H., Spolenak, R.

{Scripta Materialia}, 58(3):175-178, 2008 (article)

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[BibTex]

[BibTex]


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Transmission electron microscopy study of the intermixing of Fe-Pt multilayers

Kaiser, T., Sigle, W., Goll, D., Goo, N. H., Srot, V., van Aken, P. A., Detemple, E., Jäger, W.

{Journal of Applied Physics}, 103, 2008 (article)

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DOI [BibTex]

DOI [BibTex]


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Spin state and orbita moments across the metal-insulator-transition of REBaCo2O5.5 investigated by XMCD

Lafkioti, M., Goering, E., Gold, S., Schütz, G., Barilo, S. N., Shiryaev, S. V., Bychkov, G. L., Lemmens, P., Hinkov, V., Deisenhofer, J., Loidl, A.

{New Journal of Physics}, 10, 2008 (article)

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DOI [BibTex]

DOI [BibTex]