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2011


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Learning, planning, and control for quadruped locomotion over challenging terrain

Kalakrishnan, Mrinal, Buchli, Jonas, Pastor, Peter, Mistry, Michael, Schaal, S.

International Journal of Robotics Research, 30(2):236-258, February 2011 (article)

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[BibTex]

2011


[BibTex]


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Design and application of a wire-driven bidirectional telescopic mechanism for workspace expansion with a focus on shipbuilding tasks

Lee, D., Chang, D., Shin, Y., Son, D., Kim, T., Lee, K., Kim, J.

Advanced Robotics, 25, 2011 (article)

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[BibTex]

[BibTex]


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Bayesian robot system identification with input and output noise

Ting, J., D’Souza, A., Schaal, S.

Neural Networks, 24(1):99-108, 2011, clmc (article)

Abstract
For complex robots such as humanoids, model-based control is highly beneficial for accurate tracking while keeping negative feedback gains low for compliance. However, in such multi degree-of-freedom lightweight systems, conventional identification of rigid body dynamics models using CAD data and actuator models is inaccurate due to unknown nonlinear robot dynamic effects. An alternative method is data-driven parameter estimation, but significant noise in measured and inferred variables affects it adversely. Moreover, standard estimation procedures may give physically inconsistent results due to unmodeled nonlinearities or insufficiently rich data. This paper addresses these problems, proposing a Bayesian system identification technique for linear or piecewise linear systems. Inspired by Factor Analysis regression, we develop a computationally efficient variational Bayesian regression algorithm that is robust to ill-conditioned data, automatically detects relevant features, and identifies input and output noise. We evaluate our approach on rigid body parameter estimation for various robotic systems, achieving an error of up to three times lower than other state-of-the-art machine learning methods

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link (url) [BibTex]

link (url) [BibTex]


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The Oxidation of Fe(111)

Davies, R., Edwards, D., Gräfe, J., Gilbert, L., Davies, P., Hutchings, G., Bowker, M.

Surface Science, 605(17-18):1754-1762, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Learning variable impedance control

Buchli, J., Stulp, F., Theodorou, E., Schaal, S.

International Journal of Robotics Research, 2011, clmc (article)

Abstract
One of the hallmarks of the performance, versatility, and robustness of biological motor control is the ability to adapt the impedance of the overall biomechanical system to different task requirements and stochastic disturbances. A transfer of this principle to robotics is desirable, for instance to enable robots to work robustly and safely in everyday human environments. It is, however, not trivial to derive variable impedance controllers for practical high degree-of-freedom (DOF) robotic tasks. In this contribution, we accomplish such variable impedance control with the reinforcement learning (RL) algorithm PISq ({f P}olicy {f I}mprovement with {f P}ath {f I}ntegrals). PISq is a model-free, sampling based learning method derived from first principles of stochastic optimal control. The PISq algorithm requires no tuning of algorithmic parameters besides the exploration noise. The designer can thus fully focus on cost function design to specify the task. From the viewpoint of robotics, a particular useful property of PISq is that it can scale to problems of many DOFs, so that reinforcement learning on real robotic systems becomes feasible. We sketch the PISq algorithm and its theoretical properties, and how it is applied to gain scheduling for variable impedance control. We evaluate our approach by presenting results on several simulated and real robots. We consider tasks involving accurate tracking through via-points, and manipulation tasks requiring physical contact with the environment. In these tasks, the optimal strategy requires both tuning of a reference trajectory emph{and} the impedance of the end-effector. The results show that we can use path integral based reinforcement learning not only for planning but also to derive variable gain feedback controllers in realistic scenarios. Thus, the power of variable impedance control is made available to a wide variety of robotic systems and practical applications.

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link (url) [BibTex]

link (url) [BibTex]


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High-resolution x-ray absorption spectroscopy of BaTiO_3: Experiment and first-principles calculations

Chassé, A., Borek, S., Schindler, K., Trautmann, M., Huth, M., Steudel, F., Makhova, L., Gräfe, J., Denecke, R.

Physical Review B, 84, pages: 195135, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Waalbot II: Adhesion recovery and improved performance of a climbing robot using fibrillar adhesives

Murphy, M. P., Kute, C., Mengüç, Y., Sitti, M.

The International Journal of Robotics Research, 30(1):118-133, SAGE Publications Sage UK: London, England, 2011 (article)

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Project Page [BibTex]

Project Page [BibTex]


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Automated 2-D nanoparticle manipulation using atomic force microscopy

Onal, C. D., Ozcan, O., Sitti, M.

IEEE Transactions on Nanotechnology, 10(3):472-481, IEEE, 2011 (article)

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[BibTex]

[BibTex]


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Biaxial mechanical modeling of the small intestine

Bellini, C., Glass, P., Sitti, M., Di Martino, E. S.

Journal of the mechanical behavior of biomedical materials, 4(8):1727-1740, Elsevier, 2011 (article)

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Project Page [BibTex]

Project Page [BibTex]


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Electron theory of fast and ultrafast dissipative magnetization dynamics

Fähnle, M., Illg, C.

{Journal of Physics: Condensed Matter}, 23, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Large-area hard magnetic L10-FePt nanopatterns by nanoimprint lithography

Bublat, T., Goll, D.

{Nanotechnology}, 22(31), 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Hydrogen storage by cryoadsorption in ultrahigh-porosity metal-organic frameworks

Hirscher, M.

{Angewandte Chemie International Edition}, 50(3):581-582, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Multilayer Fresnel zone plate for soft X-ray microscopy resolves sub-39 nm structures

Mayer, M., Grévent, C., Szeghalmi, A., Knez, M., Weigand, M., Rehbein, S., Schneider, G., Baretzky, B., Schütz, G.

{Ultramicroscopy}, 111, pages: 1706-1711, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Generalized Gilbert equation including inertial damping: derivation from an extended breathing Fermi surface model

Fähnle, M., Steiauf, D., Illg, C.

{Physical Review B}, 84, 2011 (article)

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DOI [BibTex]


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Hydrogen physisorption in high SSA microporous materials - A comparison between AX-21\textunderscore33 and MOF-177 at cryogenic conditions

Schlichtenmayer, M., Streppel, B., Hirscher, M.

{International Journal of Hydrogen Energy}, 36, pages: 586-591, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetic vortex core reversal by excitation of spin waves

Kammerer, M., Weigand, M., Curcic, M., Noske, M., Sproll, M., Vansteenkiste, A., Van Waeyenberge, B., Stoll, H., Woltersdorf, G., Back, C. H., Schütz, G.

{Nature Communications}, 2, pages: 279-284, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Understanding haptics by evolving mechatronic systems

Loeb, G. E., Tsianos, G.A., Fishel, J.A., Wettels, N., Schaal, S.

Progress in Brain Research, 192, pages: 129, 2011 (article)

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[BibTex]

[BibTex]


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Assembly and disassembly of magnetic mobile micro-robots towards deterministic 2-D reconfigurable micro-systems

Diller, E., Pawashe, C., Floyd, S., Sitti, M.

The International Journal of Robotics Research, 30(14):1667-1680, SAGE Publications Sage UK: London, England, 2011 (article)

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[BibTex]

[BibTex]


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Magnetism studied with circularly polarized X-rays

Schütz, G., Goering, E., Stoll, H.

{International Journal of Materials Research}, 102(7):773-783, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Coupled vortex oscillations in spatially separated permalloy squares

Vogel, A., Kamionka, T., Martens, M., Drews, A., Chou, K., Tyliszczak, T., Stoll, H., Van Waeyenberge, B., Meier, G.

{Physical Review Letters}, 106, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Contruction of basis functions with crystal symmetry for the spin-cluster expansion of the magnetic energy on the atomic scale

Dietermann, F., Singer, R., Fähnle, M.

{Journal of Mathematical Physics}, 52, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetic patterning perpendicular anisotropy FePd alloy films by masked ion irradiation

Merkel, D. G., Bottyán, L., Tanczikó, F., Zolnai, Z., Nagy, N., Vértesy, G., Waizinger, J., Bommer, L.

{Journal of Applied Physics}, 109(12), 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Characterization of hydrogen/deuterium adsorption sites in nanoporous Cu-BTC by low-temperature thermal-desorption mass spectroscopy

Krkljus, I., Hirscher, M.

{Microporous and Mesoporous Materials}, 142, pages: 725-729, 2011 (article)

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DOI [BibTex]


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Stability of the current-carrying state in nonhomogeneous MgB2 films

Treiber, S., Stahl, C., Schütz, G., Albrecht, J.

{Physical Review B}, 84, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Orbital reflectometry of oxide heterostructures

Benckiser, E., Haverkort, M. W., Brück, S., Goering, E., Macke, S., Fraño, A., Yang, X., Andersen, O. K., Cristiani, G., Habermeier, H., Boris, A. V., Zegkinoglou, I., Wochner, P., Kim, H., Hinkov, V., Keimer, B.

{Nature Materials}, 10(3):189-193, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Potential explanation of charge response of magnetization in nanoporous systems

Subkow, S., Fähnle, M.

{Physical Review B}, 84, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Modeling of stochastic motion of bacteria propelled spherical microbeads

Arabagi, V., Behkam, B., Cheung, E., Sitti, M.

Journal of Applied Physics, 109(11):114702, AIP, 2011 (article)

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Project Page [BibTex]

Project Page [BibTex]


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The effect of aspect ratio on adhesion and stiffness for soft elastic fibres

Aksak, B., Hui, C., Sitti, M.

Journal of The Royal Society Interface, 8(61):1166-1175, The Royal Society, 2011 (article)

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Project Page [BibTex]

Project Page [BibTex]


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Large hidden orbital moments in magnetite

Goering, E.

{Physica Status Solidi B}, 248(10):2345-2351, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Cr magnetization reversal at the CrO2/RuO2 interface: Origin of the reduced GMR effect

Zafar, K., Audehm, P., Schütz, G., Goering, E., Pathak, M., Chetry, K. B., LeClair, P. R., Gupta, A.

{Physical Review B}, 84, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetocaloric effect, magnetic domain structure and spin-reorientation transitios in HoCo5 single crystals

Skokov, K. P., Pastushenkov, Y. G., Koshkid\textquotesingleko, Y. S., Schütz, G., Goll, D., Ivanova, T. I., Nikitin, S. A., Semenova, E. M., Petrenko, A. V.

{Journal of Magnetism and Magnetic Materials}, 323(5):447-450, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Elucidating gating effects for hydrogen sorption in MFU-4-type triazolate-based metal-organic frameworks featuring different pore sizes

Denysenko, D., Grzywa, M., Tonigold, M., Streppel, B., Krkljus, I., Hirscher, M., Mugnaioli, E., Kolb, U., Hanss, J., Volkmer, D.

{Chemistry - A European Journal}, 17(6):1837-1848, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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BET specific surface area and pore structure of MOFs determined by hydrogen adsorption at 20 K

Streppel, B., Hirscher, M.

{Physical Chemistry Chemical Physics}, 13(8):3220-3222, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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High contrast magnetic and nonmagnetic sample current microscopy for bulk and transparent samples using soft X-rays

Nolle, D., Weigand, M., Schütz, G., Goering, E.

{Microscopy and Microanalysis}, 17, pages: 834-842, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetic vortex core reversal by rotating magnetic fields generated on micrometer length scales

Curcic, M., Stoll, H., Weigand, M., Sackmann, V., Jüllig, P., Kammerer, M., Noske, M., Sproll, M., Van Waeyenberge, B., Vansteenkiste, A., Woltersdorf, G., Tyliszczak, T., Schütz, G.

{Physica Status Solidi B}, 248(10):2317-2322, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Enhancing adhesion of biologically inspired polymer microfibers with a viscous oil coating

Cheung, E., Sitti, M.

The Journal of Adhesion, 87(6):547-557, Taylor & Francis Group, 2011 (article)

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Project Page [BibTex]

Project Page [BibTex]


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Formation of two amorphous phases in the Ni60Nb18Y22 alloy after high pressure torsion

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

{Kovove Materialy-Metallic Materials}, 49(1):17-22, 2011 (article)

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link (url) [BibTex]

link (url) [BibTex]


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Structure and properties of nanograined Fe-C alloys after severe plastic deformation

Straumal, B. B., Dobatkin, S. V., Rodin, A. O., Protasova, S. G., Mazilkin, A. A., Goll, D., Baretzky, B.

{Advanced Engineering Materials}, 13(6):463-469, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Increased flux pinning in YBa2Cu3O7-δthin-film devices through embedding of Au nano crystals

Katzer, C., Schmidt, M., Michalowski, P., Kuhwald, D., Schmidl, F., Grosse, V., Treiber, S., Stahl, C., Albrecht, J., Hübner, U., Undisz, A., Rettenmayr, M., Schütz, G., Seidel, P.

{Europhysics Letters}, 95(6), 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Signal transfer in a chain of stray-field coupled ferromagnetic squares

Vogel, A., Martens, M., Weigand, M., Meier, G.

{Applied Physics Letters}, 99, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Electron theory of magnetoelectric effects in metallic ferromagnetic nanostructures

Subkow, S., Fähnle, M.

{Physical Review B}, 84, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetic antivortex-core reversal by rotating magnetic fields

Kamionka, T., Martens, M., Chou, K., Drews, A., Tyliszczak, T., Stoll, H., Van Waeyenberge, B., Meier, G.

{Physical Review B}, 83, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetic properties of exchange-spring composite films

Kronmüller, H., Goll, D.

{Physica Status Solidi B}, 248(10):2361-2367, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Wetting transition of grain boundaries in the Sn-rich part of the Sn-Bi phase diagram

Yeh, C.-H., Chang, L.-S., Straumal, B. B.

{Journal of Materials Science}, 46(5):1557-1562, 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Piezoelectric polymer fiber arrays for tactile sensing applications

Sümer, B., Aksak, B., Şsahin, K., Chuengsatiansup, K., Sitti, M.

Sensor Letters, 9(2):457-463, American Scientific Publishers, 2011 (article)

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Project Page [BibTex]

Project Page [BibTex]


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Control methodologies for a heterogeneous group of untethered magnetic micro-robots

Floyd, S., Diller, E., Pawashe, C., Sitti, M.

The International Journal of Robotics Research, 30(13):1553-1565, SAGE Publications, 2011 (article)

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[BibTex]

[BibTex]


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Influence of dot size and annealing on the magnetic properties of large-area L10-FePt nanopatterns

Bublat, T., Goll, D.

{Journal of Applied Physics}, 110(7), 2011 (article)

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DOI [BibTex]


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The temperature-dependent magnetization profile across an epitaxial bilayer of ferromagnetic La2/3Ca1/3MnO3 and superconducting YBa2Cu3O7-δ

Brück, S., Treiber, S., Macke, S., Audehm, P., Christiani, G., Soltan, S., Habermeier, H., Goering, E., Albrecht, J.

{New Journal of Physics}, 13(3), 2011 (article)

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DOI [BibTex]

DOI [BibTex]


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Spin interactions in bcc and fcc Fe beyond the Heisenberg model

Singer, R., Dietermann, F., Fähnle, M.

{Physical Review Letters}, 107, 2011 (article)

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DOI [BibTex]

DOI [BibTex]