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2003


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Computational approaches to motor learning by imitation

Schaal, S., Ijspeert, A., Billard, A.

Philosophical Transaction of the Royal Society of London: Series B, Biological Sciences, 358(1431):537-547, 2003, clmc (article)

Abstract
Movement imitation requires a complex set of mechanisms that map an observed movement of a teacher onto one's own movement apparatus. Relevant problems include movement recognition, pose estimation, pose tracking, body correspondence, coordinate transformation from external to egocentric space, matching of observed against previously learned movement, resolution of redundant degrees-of-freedom that are unconstrained by the observation, suitable movement representations for imitation, modularization of motor control, etc. All of these topics by themselves are active research problems in computational and neurobiological sciences, such that their combination into a complete imitation system remains a daunting undertaking - indeed, one could argue that we need to understand the complete perception-action loop. As a strategy to untangle the complexity of imitation, this paper will examine imitation purely from a computational point of view, i.e. we will review statistical and mathematical approaches that have been suggested for tackling parts of the imitation problem, and discuss their merits, disadvantages and underlying principles. Given the focus on action recognition of other contributions in this special issue, this paper will primarily emphasize the motor side of imitation, assuming that a perceptual system has already identified important features of a demonstrated movement and created their corresponding spatial information. Based on the formalization of motor control in terms of control policies and their associated performance criteria, useful taxonomies of imitation learning can be generated that clarify different approaches and future research directions.

am

link (url) [BibTex]

2003


link (url) [BibTex]


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Efficient charge recovery method for driving piezoelectric actuators with quasi-square waves

Campolo, D., Sitti, M., Fearing, R. S.

IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 50(3):237-244, IEEE, 2003 (article)

pi

[BibTex]

[BibTex]


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Synthetic gecko foot-hair micro/nano-structures for future wall-climbing robots

Sitti, M., Fearing, R. S.

In Robotics and Automation, 2003. Proceedings. ICRA’03. IEEE International Conference on, 1, pages: 1164-1170, 2003 (inproceedings)

pi

[BibTex]

[BibTex]


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Magnetization reversal study of CoCrPt alloy thin films on a nanogranular-length scale using magnetic transmission soft x-ray microscopy

Im, M. Y., Fischer, P., Eimüller, T., Denbeaux, G., Shin, S. C.

{Applied Physics Letters}, 83(22):4589-4591, 2003 (article)

mms

[BibTex]

[BibTex]


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XANES und MEXAFS an magnetischen Übergangsmetalloxiden: Entwicklung eines digitalen Lock-In XMCD Experimentes mit Phasenschieber

Weigand, F.

Bayerische Julius-Maximilians-Universität Würzburg, Würzburg, 2003 (phdthesis)

mms

[BibTex]

[BibTex]


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Temperature-dependent pinning of vortices in low-angle grain boundaries in YBa2Cu3O7-δ

Albrecht, J.

{Physical Review B}, 68, 2003 (article)

mms

[BibTex]


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Magnetic soft X-ray transmission microscopy

Fischer, P.

{Current Opinion in Solid State \& Materials Science}, 7(2):173-179, 2003 (article)

mms

[BibTex]

[BibTex]


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The magnetic transmission X-ray microscopy project at BESSY II

Eimüller, T., Niemann, B., Guttmann, P., Fischer, P., Englisch, U., Vatter, R., Wolter, C., Seiffert, S., Schmahl, G., Schütz, G.

{Journal de Physique IV}, 104, pages: 91-94, 2003 (article)

mms

[BibTex]

[BibTex]


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Ab-initio statistical mechanics for ordered compounds: single-defect theory vs. cluster-expansion techniques

Drautz, R., Schultz, I., Lechermann, F., Fähnle, M.

{Physica Status Solidi B}, 240(1):37-44, 2003 (article)

mms

[BibTex]

[BibTex]


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Magnetic imaging with soft x-ray microscopies

Fischer, P., Denbeaux, G., Stoll, H., Puzic, A., Raabe, J., Nolting, F., Eimüller, T., Schütz, G.

{Journal de Physique IV}, 104, pages: 471-476, 2003 (article)

mms

[BibTex]

[BibTex]


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Hydrogen storage in carbon nanotubes

Hirscher, M., Becher, M.

{Journal of Nanoscience and Nanotechnology}, 3(1/2):3-17, 2003 (article)

mms

[BibTex]

[BibTex]


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Grain boundary faceting phase transition and thermal grooving in Cu

Straumal, B. B., Polyakov, S. A., Bischoff, E., Mittemeijer, E. J., Gust, W.

In Proceedings of the International Conference on Diffusion, Segregation and Stresses in Materials, 216/217, pages: 93-100, Diffusion and Defect Data, Pt. A, Defect and Diffusion Forum, Scitec Publ., Moscow, 2003 (inproceedings)

mms

[BibTex]

[BibTex]


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AMOC in positron and positronium chemistry

Stoll, H., Castellaz, P., Siegle, A.

In Principles and Applications of Positron and Positronium Chemistry, pages: 344-366, World Scientific Publishers, Singapore, 2003 (incollection)

mms

[BibTex]

[BibTex]


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Strong influence on the electronic structure of Pt adatoms and clusters on graphite

Fauth, K., He\ssler, M., Batchelor, D., Schütz, G.

{Surface Science}, 529(3):397-402, 2003 (article)

mms

[BibTex]

[BibTex]


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NMR studies of hydrogen diffusion in the dihydrides of hafnium

Gottwald, J., Majer, G., Peterson, D. T., Barnes, R. G.

{Journal of Alloys and Compounds}, 356-357, pages: 274-278, 2003 (article)

mms

[BibTex]

[BibTex]


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The +/-45 degrees correlation interferometer as a means to measure phase noise of parametric origin

Rubiola, E., Giordano, V., Stoll, H.

{IEEE Transactions on Instrumentation and Measurement}, 52, pages: 182-188, 2003 (article)

mms

[BibTex]

[BibTex]


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Piezoelectrically actuated four-bar mechanism with two flexible links for micromechanical flying insect thorax

Sitti, M.

IEEE/ASME transactions on mechatronics, 8(1):26-36, IEEE, 2003 (article)

pi

[BibTex]


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Biomimetic propulsion for a swimming surgical micro-robot

Edd, J., Payen, S., Rubinsky, B., Stoller, M. L., Sitti, M.

In Intelligent Robots and Systems, 2003.(IROS 2003). Proceedings. 2003 IEEE/RSJ International Conference on, 3, pages: 2583-2588, 2003 (inproceedings)

pi

Project Page [BibTex]

Project Page [BibTex]


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Slow removal of vacancies in B2-Ni52Al48 upon long-term low-temperature annealing

Zhang, X. Y., Sprengel, W., Reichle, K. J., Blaurock, K., Henes, R., Schaefer, H. E.

{Physical Review B}, 68(22), 2003 (article)

mms

[BibTex]

[BibTex]


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Magnetic domain structure in SmCo 2 : 17 permanent magnets

Zhang, Y., Tang, W., Hadjipanayis, G. C., Chen, C. H., Goll, D., Kronmüller, H.

{IEEE Transactions on Magnetics}, 39(5):2905-2907, 2003 (article)

mms

[BibTex]

[BibTex]


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Energy loss and charge state dependency of swift Nq+ ions scattered off a Pt(110)(1 x 2) surface

Robin, A., Hatke, N., Jensen, J., Plachke, D., Carstanjen, H. D., Heiland, W.

{Nuclear Instruments \& Methods in Physics Research B-Beam Interactions with Materials and Atoms}, 209, pages: 259-264, 2003 (article)

mms

[BibTex]

[BibTex]


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Preparation and properties of [NdFeBx/Nbz]n multi-layer films

Tsai, J. L., Chin, T. S., Yao, Y. D., Melsheimer, A., Fischer, S. F., Dragon, T., Kelsch, M., Kronmüller, H.

{Physica B-Condensed Matter}, 327(2-4):283-286, 2003 (article)

mms

[BibTex]

[BibTex]


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Multilayered magnetic nanostrips studied by transmission X-ray microscopy

Eimüller, T., Fischer, P., Guttmann, P., Denbeaux, G., Scholz, M., Köhler, M., Schmahl, G., Bayreuther, G., Schütz, G.

{Journal de Physique IV}, 104, pages: 483-486, 2003 (article)

mms

[BibTex]

[BibTex]


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Imaging magnetic domain structures with soft X-ray microscopy

Fischer, P., Eimüller, T., Schütz, G., Denbeaux, G.

{Structural Chemistry}, 14(1):39-47, 2003 (article)

mms

[BibTex]

[BibTex]


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Hydrogen solubility and diffusivity in amorphous La14Ni86 films

Cuevas, F., Hirscher, M.

{Acta Materialia}, 51, pages: 701-712, 2003 (article)

mms

[BibTex]

[BibTex]


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Coercivity mechanism in nanocrystalline and bonded magnets

Goll, D., Kronmüller, H.

In Bonded Magnets. Proceedings of the NATO Advanced Research Workshop on Science and Technology of Bonded Magnets, 118, pages: 115-127, NATO Science Series: Series 2, Mathematics, Physics and Chemistry, Kluwer Acad. Publ., Newark, USA, 2003 (inproceedings)

mms

[BibTex]

[BibTex]


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Hydrogen interaction with carbon nanostructures - current situation and future prospects

Orimo, S., Züttel, A., Schlapbach, L., Majer, G., Fukunaga, T., Fujii, H.

{Journal of Alloys and Compounds}, 356-357, pages: 716-719, 2003 (article)

mms

[BibTex]

[BibTex]


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Desorption of hydrogen from blowing agents used for foaming metals

von Zeppelin, F., Hirscher, M., Stanzick, H., Banhart, J.

{Composites Science and Technology}, 63, pages: 2293-2300, 2003 (article)

mms

[BibTex]

[BibTex]


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Investigation of Electromigration in Copper Interconnects by Noise Measurements

Emelianov, V., Ganesan, G., Puzic, A., Schulz, S., Eizenberg, M., Habermeier, H., Stoll, H.

In Noise as a Tool for Studying Materials, pages: 271-281, Proceedings of SPIE, Santa Fe, New Mexico, 2003 (inproceedings)

mms

[BibTex]

[BibTex]


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Entropic wetting of a colloidal rod-sphere mixture

Roth, R., Brader, J. M., Schmidt, M.

{Europhysics Letters}, 63(4):549-555, 2003 (article)

mms

[BibTex]

[BibTex]

2000


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Reciprocal excitation between biological and robotic research

Schaal, S., Sternad, D., Dean, W., Kotoska, S., Osu, R., Kawato, M.

In Sensor Fusion and Decentralized Control in Robotic Systems III, Proceedings of SPIE, 4196, pages: 30-40, Boston, MA, Nov.5-8, 2000, November 2000, clmc (inproceedings)

Abstract
While biological principles have inspired researchers in computational and engineering research for a long time, there is still rather limited knowledge flow back from computational to biological domains. This paper presents examples of our work where research on anthropomorphic robots lead us to new insights into explaining biological movement phenomena, starting from behavioral studies up to brain imaging studies. Our research over the past years has focused on principles of trajectory formation with nonlinear dynamical systems, on learning internal models for nonlinear control, and on advanced topics like imitation learning. The formal and empirical analyses of the kinematics and dynamics of movements systems and the tasks that they need to perform lead us to suggest principles of motor control that later on we found surprisingly related to human behavior and even brain activity.

am

link (url) [BibTex]

2000


link (url) [BibTex]


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Advances in Large Margin Classifiers

Smola, A., Bartlett, P., Schölkopf, B., Schuurmans, D.

pages: 422, Neural Information Processing, MIT Press, Cambridge, MA, USA, October 2000 (book)

Abstract
The concept of large margins is a unifying principle for the analysis of many different approaches to the classification of data from examples, including boosting, mathematical programming, neural networks, and support vector machines. The fact that it is the margin, or confidence level, of a classification--that is, a scale parameter--rather than a raw training error that matters has become a key tool for dealing with classifiers. This book shows how this idea applies to both the theoretical analysis and the design of algorithms. The book provides an overview of recent developments in large margin classifiers, examines connections with other methods (e.g., Bayesian inference), and identifies strengths and weaknesses of the method, as well as directions for future research. Among the contributors are Manfred Opper, Vladimir Vapnik, and Grace Wahba.

ei

Web [BibTex]

Web [BibTex]


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Nonlinear dynamical systems as movement primitives

Schaal, S., Kotosaka, S., Sternad, D.

In Humanoids2000, First IEEE-RAS International Conference on Humanoid Robots, CD-Proceedings, Cambridge, MA, September 2000, clmc (inproceedings)

Abstract
This paper explores the idea to create complex human-like movements from movement primitives based on nonlinear attractor dynamics. Each degree-of-freedom of a limb is assumed to have two independent abilities to create movement, one through a discrete dynamic system, and one through a rhythmic system. The discrete system creates point-to-point movements based on internal or external target specifications. The rhythmic system can add an additional oscillatory movement relative to the current position of the discrete system. In the present study, we develop appropriate dynamic systems that can realize the above model, motivate the particular choice of the systems from a biological and engineering point of view, and present simulation results of the performance of such movement primitives. The model was implemented for a drumming task on a humanoid robot

am

link (url) [BibTex]

link (url) [BibTex]


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Real Time Learning in Humanoids: A challenge for scalability of Online Algorithms

Vijayakumar, S., Schaal, S.

In Humanoids2000, First IEEE-RAS International Conference on Humanoid Robots, CD-Proceedings, Cambridge, MA, September 2000, clmc (inproceedings)

Abstract
While recent research in neural networks and statistical learning has focused mostly on learning from finite data sets without stringent constraints on computational efficiency, there is an increasing number of learning problems that require real-time performance from an essentially infinite stream of incrementally arriving data. This paper demonstrates how even high-dimensional learning problems of this kind can successfully be dealt with by techniques from nonparametric regression and locally weighted learning. As an example, we describe the application of one of the most advanced of such algorithms, Locally Weighted Projection Regression (LWPR), to the on-line learning of the inverse dynamics model of an actual seven degree-of-freedom anthropomorphic robot arm. LWPR's linear computational complexity in the number of input dimensions, its inherent mechanisms of local dimensionality reduction, and its sound learning rule based on incremental stochastic leave-one-out cross validation allows -- to our knowledge for the first time -- implementing inverse dynamics learning for such a complex robot with real-time performance. In our sample task, the robot acquires the local inverse dynamics model needed to trace a figure-8 in only 60 seconds of training.

am

link (url) [BibTex]

link (url) [BibTex]


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Synchronized robot drumming by neural oscillator

Kotosaka, S., Schaal, S.

In The International Symposium on Adaptive Motion of Animals and Machines, Montreal, Canada, August 2000, clmc (inproceedings)

Abstract
Sensory-motor integration is one of the key issues in robotics. In this paper, we propose an approach to rhythmic arm movement control that is synchronized with an external signal based on exploiting a simple neural oscillator network. Trajectory generation by the neural oscillator is a biologically inspired method that can allow us to generate a smooth and continuous trajectory. The parameter tuning of the oscillators is used to generate a synchronized movement with wide intervals. We adopted the method for the drumming task as an example task. By using this method, the robot can realize synchronized drumming with wide drumming intervals in real time. The paper also shows the experimental results of drumming by a humanoid robot.

am

link (url) [BibTex]

link (url) [BibTex]


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An Introduction to Kernel-Based Learning Algorithms

Müller, K., Mika, S., Rätsch, G., Tsuda, K., Schölkopf, B.

In Handbook of Neural Network Signal Processing, 4, (Editors: Yu Hen Hu and Jang-Neng Hwang), CRC Press, 2000 (inbook)

ei

[BibTex]

[BibTex]


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Choosing nu in support vector regression with different noise models — theory and experiments

Chalimourda, A., Schölkopf, B., Smola, A.

In Proceedings of the IEEE-INNS-ENNS International Joint Conference on Neural Networks, IJCNN 2000, Neural Computing: New Challenges and Perspectives for the New Millennium, IEEE, International Joint Conference on Neural Networks, 2000 (inproceedings)

ei

[BibTex]

[BibTex]


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Phenomenological damping in optical response tensors

Buckingham, A., Fischer, P.

PHYSICAL REVIEW A, 61(3), 2000 (article)

Abstract
Although perturbation theory applied to the optical response of a molecule or material system is only strictly valid far from resonances, it is often applied to ``near-resonance{''} conditions by means of complex energies incorporating damping. Inconsistent signs of the damping in optical response tensors have appeared in the recent literature, as have errors in the treatment of the perturbation by a static held. The ``equal-sign{''} convention used in a recent publication yields an unphysical material response, and Koroteev's intimation that linear electro-optical circular dichroism may exist in an optically active liquid under resonance conditions is also flawed. We show that the isotropic part of the Pockels tensor vanishes.

pf

DOI [BibTex]

DOI [BibTex]


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Ab initio investigation of the sum-frequency hyperpolarizability of small chiral molecules

Champagne, B., Fischer, P., Buckingham, A.

CHEMICAL PHYSICS LETTERS, 331(1):83-88, 2000 (article)

Abstract
Using a sum-over-states procedure based on configuration interaction singles /6-311++G{*}{*}, we have computed the sum-frequency hyperpolarizability beta (ijk)(-3 omega; 2 omega, omega) Of two small chiral molecules, R-monofluoro-oxirane and R-(+)-propylene oxide. Excitation energies were scaled to fit experimental UV-absorption data and checked with ab initio values from time-dependent density functional theory. The isotropic part of the computed hyperpolarizabilities, beta(-3 omega; 2 omega, omega), is much smaller than that reported previously from sum-frequency generation experiments on aqueous solutions of arabinose. Comparison is made with a single-centre chiral model. (C) 2000 Elsevier Science B.V. All rights reserved.

pf

DOI [BibTex]

DOI [BibTex]


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Three-wave mixing in chiral liquids

Fischer, P., Wiersma, D., Righini, R., Champagne, B., Buckingham, A.

PHYSICAL REVIEW LETTERS, 85(20):4253-4256, 2000 (article)

Abstract
Second-order nonlinear optical frequency conversion in isotropic systems is only dipole allowed for sum- and difference-frequency generation in chiral media. We develop a single-center chiral model of the three-wave mixing (sum:frequency generation) nonlinearity and estimate its magnitude. We also report results from ab initio calculations and from three- and four-wave mixing experiments in support of the theoretical estimates. We show that the second-order susceptibility in chiral liquids is much smaller than previously thought.

pf

DOI [BibTex]

DOI [BibTex]


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Two-dimensional fine particle positioning under an optical microscope using a piezoresistive cantilever as a manipulator

Sitti, M., Hashimoto, H.

journal of Micromechatronics, 1(1):25-48, Brill, 2000 (article)

pi

[BibTex]


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A brachiating robot controller

Nakanishi, J., Fukuda, T., Koditschek, D. E.

IEEE Transactions on Robotics and Automation, 16(2):109-123, 2000, clmc (article)

Abstract
We report on our empirical studies of a new controller for a two-link brachiating robot. Motivated by the pendulum-like motion of an apeâ??s brachiation, we encode this task as the output of a â??target dynamical system.â? Numerical simulations indicate that the resulting controller solves a number of brachiation problems that we term the â??ladder,â? â??swing-up,â? and â??ropeâ? problems. Preliminary analysis provides some explanation for this success. The proposed controller is implemented on a physical system in our laboratory. The robot achieves behaviors including â??swing locomotionâ? and â??swing upâ? and is capable of continuous locomotion over several rungs of a ladder. We discuss a number of formal questions whose answers will be required to gain a full understanding of the strengths and weaknesses of this approach.

am

link (url) [BibTex]

link (url) [BibTex]


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Real-time robot learning with locally weighted statistical learning

Schaal, S., Atkeson, C. G., Vijayakumar, S.

In International Conference on Robotics and Automation (ICRA2000), San Francisco, April 2000, 2000, clmc (inproceedings)

Abstract
Locally weighted learning (LWL) is a class of statistical learning techniques that provides useful representations and training algorithms for learning about complex phenomena during autonomous adaptive control of robotic systems. This paper introduces several LWL algorithms that have been tested successfully in real-time learning of complex robot tasks. We discuss two major classes of LWL, memory-based LWL and purely incremental LWL that does not need to remember any data explicitly. In contrast to the traditional beliefs that LWL methods cannot work well in high-dimensional spaces, we provide new algorithms that have been tested in up to 50 dimensional learning problems. The applicability of our LWL algorithms is demonstrated in various robot learning examples, including the learning of devil-sticking, pole-balancing of a humanoid robot arm, and inverse-dynamics learning for a seven degree-of-freedom robot.

am

link (url) [BibTex]

link (url) [BibTex]


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Biomimetic gaze stabilization

Shibata, T., Schaal, S.

In Robot learning: an Interdisciplinary approach, pages: 31-52, (Editors: Demiris, J.;Birk, A.), World Scientific, 2000, clmc (inbook)

Abstract
Accurate oculomotor control is one of the essential pre-requisites for successful visuomotor coordination. In this paper, we suggest a biologically inspired control system for learning gaze stabilization with a biomimetic robotic oculomotor system. In a stepwise fashion, we develop a control circuit for the vestibulo-ocular reflex (VOR) and the opto-kinetic response (OKR), and add a nonlinear learning network to allow adaptivity. We discuss the parallels and differences of our system with biological oculomotor control and suggest solutions how to deal with nonlinearities and time delays in the control system. In simulation and actual robot studies, we demonstrate that our system can learn gaze stabilization in real time in only a few seconds with high final accuracy.

am

link (url) [BibTex]

link (url) [BibTex]


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Diffusion von Wasserstoff in Lavesphasen / Diffusion von Wasserstoff in heterogenen Systemen.

Herrmann, A.

Universität Stuttgart, Stuttgart, 2000 (phdthesis)

mms

[BibTex]

[BibTex]


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Anisotropic flux pinning in thin YBCO-films by substrate modifications

Leonhardt, S., Warthmann, R., Albrecht, J., Jooss, C., Kronmüller, H., Haage, T., Zegenhagen, J., Habermeier, H.-U.

{Physica C}, 332, pages: 214-218, 2000 (article)

mms

[BibTex]

[BibTex]


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A review of the magnetic relaxation and its application to the study of atomic defects in α-iron and its diuluted alloys

Blythe, H. J., Kronmüller, H., Seeger, A., Walz, F.

{Physica Status Solidi (A)}, 181, pages: 233-345, 2000 (article)

mms

[BibTex]

[BibTex]


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Magnetic properties of Sm2Co17-xGax (x \textequals 0-7) compounds

Liang, B., Kleinschroth, I., Shen, B. G., Kronmüller, H.

{Journal of Applied Physics}, 87, pages: 5314-5316, 2000 (article)

mms

[BibTex]

[BibTex]