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2005


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Composite adaptive control with locally weighted statistical learning

Nakanishi, J., Farrell, J. A., Schaal, S.

Neural Networks, 18(1):71-90, January 2005, clmc (article)

Abstract
This paper introduces a provably stable learning adaptive control framework with statistical learning. The proposed algorithm employs nonlinear function approximation with automatic growth of the learning network according to the nonlinearities and the working domain of the control system. The unknown function in the dynamical system is approximated by piecewise linear models using a nonparametric regression technique. Local models are allocated as necessary and their parameters are optimized on-line. Inspired by composite adaptive control methods, the proposed learning adaptive control algorithm uses both the tracking error and the estimation error to update the parameters. We first discuss statistical learning of nonlinear functions, and motivate our choice of the locally weighted learning framework. Second, we begin with a class of first order SISO systems for theoretical development of our learning adaptive control framework, and present a stability proof including a parameter projection method that is needed to avoid potential singularities during adaptation. Then, we generalize our adaptive controller to higher order SISO systems, and discuss further extension to MIMO problems. Finally, we evaluate our theoretical control framework in numerical simulations to illustrate the effectiveness of the proposed learning adaptive controller for rapid convergence and high accuracy of control.

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link (url) [BibTex]

2005


link (url) [BibTex]


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Natural Actor-Critic

Peters, J., Vijayakumar, S., Schaal, S.

In Proceedings of the 16th European Conference on Machine Learning, 3720, pages: 280-291, (Editors: Gama, J.;Camacho, R.;Brazdil, P.;Jorge, A.;Torgo, L.), Springer, ECML, 2005, clmc (inproceedings)

Abstract
This paper investigates a novel model-free reinforcement learning architecture, the Natural Actor-Critic. The actor updates are based on stochastic policy gradients employing AmariÕs natural gradient approach, while the critic obtains both the natural policy gradient and additional parameters of a value function simultaneously by linear regres- sion. We show that actor improvements with natural policy gradients are particularly appealing as these are independent of coordinate frame of the chosen policy representation, and can be estimated more efficiently than regular policy gradients. The critic makes use of a special basis function parameterization motivated by the policy-gradient compatible function approximation. We show that several well-known reinforcement learning methods such as the original Actor-Critic and BradtkeÕs Linear Quadratic Q-Learning are in fact Natural Actor-Critic algorithms. Em- pirical evaluations illustrate the effectiveness of our techniques in com- parison to previous methods, and also demonstrate their applicability for learning control on an anthropomorphic robot arm.

am ei

link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Comparative experiments on task space control with redundancy resolution

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

In Proceedings of the 2005 IEEE/RSJ International Conference on Intelligent Robots and Systems, pages: 3901-3908, Edmonton, Alberta, Canada, Aug. 2-6, IROS, 2005, clmc (inproceedings)

Abstract
Understanding the principles of motor coordination with redundant degrees of freedom still remains a challenging problem, particularly for new research in highly redundant robots like humanoids. Even after more than a decade of research, task space control with redundacy resolution still remains an incompletely understood theoretical topic, and also lacks a larger body of thorough experimental investigation on complex robotic systems. This paper presents our first steps towards the development of a working redundancy resolution algorithm which is robust against modeling errors and unforeseen disturbances arising from contact forces. To gain a better understanding of the pros and cons of different approaches to redundancy resolution, we focus on a comparative empirical evaluation. First, we review several redundancy resolution schemes at the velocity, acceleration and torque levels presented in the literature in a common notational framework and also introduce some new variants of these previous approaches. Second, we present experimental comparisons of these approaches on a seven-degree-of-freedom anthropomorphic robot arm. Surprisingly, one of our simplest algorithms empirically demonstrates the best performance, despite, from a theoretical point, the algorithm does not share the same beauty as some of the other methods. Finally, we discuss practical properties of these control algorithms, particularly in light of inevitable modeling errors of the robot dynamics.

am ei

link (url) DOI [BibTex]

link (url) DOI [BibTex]


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A model of smooth pursuit based on learning of the target dynamics using only retinal signals

Shibata, T., Tabata, H., Schaal, S., Kawato, M.

Neural Networks, 18, pages: 213-225, 2005, clmc (article)

Abstract
While the predictive nature of the primate smooth pursuit system has been evident through several behavioural and neurophysiological experiments, few models have attempted to explain these results comprehensively. The model we propose in this paper in line with previous models employing optimal control theory; however, we hypothesize two new issues: (1) the medical superior temporal (MST) area in the cerebral cortex implements a recurrent neural network (RNN) in order to predict the current or future target velocity, and (2) a forward model of the target motion is acquired by on-line learning. We use stimulation studies to demonstrate how our new model supports these hypotheses.

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link (url) [BibTex]

link (url) [BibTex]


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Predicting EMG Data from M1 Neurons with Variational Bayesian Least Squares

Ting, J., D’Souza, A., Yamamoto, K., Yoshioka, T., Hoffman, D., Kakei, S., Sergio, L., Kalaska, J., Kawato, M., Strick, P., Schaal, S.

In Advances in Neural Information Processing Systems 18 (NIPS 2005), (Editors: Weiss, Y.;Schölkopf, B.;Platt, J.), Cambridge, MA: MIT Press, Vancouver, BC, Dec. 6-11, 2005, clmc (inproceedings)

Abstract
An increasing number of projects in neuroscience requires the statistical analysis of high dimensional data sets, as, for instance, in predicting behavior from neural firing, or in operating artificial devices from brain recordings in brain-machine interfaces. Linear analysis techniques remain prevalent in such cases, but classi-cal linear regression approaches are often numercially too fragile in high dimen-sions. In this paper, we address the question of whether EMG data collected from arm movements of monkeys can be faithfully reconstructed with linear ap-proaches from neural activity in primary motor cortex (M1). To achieve robust data analysis, we develop a full Bayesian approach to linear regression that automatically detects and excludes irrelevant features in the data, and regular-izes against overfitting. In comparison with ordinary least squares, stepwise re-gression, partial least squares, and a brute force combinatorial search for the most predictive input features in the data, we demonstrate that the new Bayesian method offers a superior mixture of characteristics in terms of regularization against overfitting, computational efficiency, and ease of use, demonstrating its potential as a drop-in replacement for other linear regression techniques. As neuroscientific results, our analyses demonstrate that EMG data can be well pre-dicted from M1 neurons, further opening the path for possible real-time inter-faces between brains and machines.

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link (url) [BibTex]

link (url) [BibTex]


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From colloidal Co/CoO core/shell nanoparticles to arrays of metallic nanomagnets: surface modification and magnetic properties

Wiedwald, U., Fauth, K., Hessler, M., Boyen, H. G., Weigl, F., Hilgendorff, M., Giersig, M., Schütz, G., Ziemann, P., Farle, M.

{ChemPhysChem}, 6(12):2522-2526, 2005 (article)

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[BibTex]

[BibTex]


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Competition between order and phase separation in Au-Ni

Reichert, H., Schöps, A., Ramsteiner, I. B., Bugaev, V. N., Shchyglo, O., Udyansky, A., Dosch, H., Asta, M., Drautz, R., Honkimäki, V.

{Physical Review Letters}, 95(23), 2005 (article)

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[BibTex]

[BibTex]


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Influence of faceting-roughening on triple-junction migration in zinc

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

{Zeitschrift f\"ur Metallkunde}, 96(10):1147-1151, 2005 (article)

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[BibTex]

[BibTex]


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Damping of spin dynamics in nanostructures: an ab initio study

Steiauf, D., Fähnle, M.

{Physical Review B}, 72, 2005 (article)

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[BibTex]

[BibTex]


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Test of the hypothesis of transient molten state diffusion for swift-heavy-ion induced mixing

Srivastava, S. K.., Avasthi, D. K., Assmann, W., Wang, Z. G., Kucal, H., Jaquet, E., Carstanjen, H. D., Toulemonde, M.

{Physical Review B}, 71, 2005 (article)

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[BibTex]

[BibTex]


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Hydrogen physisorption in metal-organic porous crystals

Panella, B., Hirscher, M.

{Advanced Materials}, 17(5):538-541, 2005 (article)

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[BibTex]

[BibTex]


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The influence of misorientation deviation on the faceting of \Sigma3 grain boundaries in aluminium

Kogtenkova, O., Straumal, B., Protasova, S., Tsurekawa, S., Watanabe, T.

{Zeitschrift f\"ur Metallkunde}, 96(2):216-219, 2005 (article)

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[BibTex]

[BibTex]


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Metal-oxide interfacial reactions: encapsulation of Pd on TiO2(110)

Fu, Q., Wagner, Th., Olliges, S., Carstanjen, H. D.

{Journal of Physical Chemistry B}, 109, pages: 944-951, 2005 (article)

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[BibTex]

[BibTex]


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Faceting of \Sigma3 and \Sigma9 grain boundaries in Cu-Bi alloys

Straumal, B. B., Polyakov, S. A., Bischoff, E., Gust, W., Baretzky, B.

{Acta Materialia}, 53(2):247-254, 2005 (article)

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[BibTex]

[BibTex]


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Dependence of damage efficiency of ions in diamond on electronic stopping

Friedland, E., Carstanjen, H. D., Myberg, G., Nasr, M. A.

{Nuclear Instruments and Methods in Physics Research B}, 230, pages: 129-132, 2005 (article)

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[BibTex]

[BibTex]


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Volumetric measurement of hydrogen storage in HCl-treated polyaniline and polypyrrole

Panella, B., Kossykh, L., Dettlaff-Weglikowska, U., Hirscher, M., Zerbi, G., Roth, S.

{Synthetic Metals}, 151, pages: 208-210, 2005 (article)

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[BibTex]

[BibTex]


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Permanent magnet alloys based on Sm2Co17; phase evolution in the quinary system Sm-Zr-FeCo-Cu

Stadelmaier, H. H., Goll, D., Kronmüller, H.

{Zeitschrift f\"ur Metallkunde}, 96(1):17-23, 2005 (article)

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[BibTex]

[BibTex]


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Rapbid synchronization and accurate phase-locking of rhythmic motor primitives

Pongas, D., Billard, A., Schaal, S.

In IEEE International Conference on Intelligent Robots and Systems (IROS 2005), pages: 2911-2916, Edmonton, Alberta, Canada, Aug. 2-6, 2005, clmc (inproceedings)

Abstract
Rhythmic movement is ubiquitous in human and animal behavior, e.g., as in locomotion, dancing, swimming, chewing, scratching, music playing, etc. A particular feature of rhythmic movement in biology is the rapid synchronization and phase locking with other rhythmic events in the environment, for instance music or visual stimuli as in ball juggling. In traditional oscillator theories to rhythmic movement generation, synchronization with another signal is relatively slow, and it is not easy to achieve accurate phase locking with a particular feature of the driving stimulus. Using a recently developed framework of dynamic motor primitives, we demonstrate a novel algorithm for very rapid synchronizaton of a rhythmic movement pattern, which can phase lock any feature of the movement to any particulur event in the driving stimulus. As an example application, we demonstrate how an anthropomorphic robot can use imitation learning to acquire a complex rumming pattern and keep it synchronized with an external rhythm generator that changes its frequency over time.

am

link (url) [BibTex]

link (url) [BibTex]


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Parametric and Non-Parametric approaches for nonlinear tracking of moving objects

Hidaka, Y, Theodorou, E.

Technical Report-2005-1, 2005, clmc (article)

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PDF [BibTex]

PDF [BibTex]


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Anisotropic temperature-dependent current densities in vicinal YBCO

Djupmyr, M., Cristiani, G., Habermeier, H.-U., Albrecht, J.

{Physical Review B}, 72, 2005 (article)

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[BibTex]

[BibTex]


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Effects of catalysts on the dehydriding of alanates monitored by proton NMR

Majer, G., Stanik, E., Valiente-Banuet, L. E., Grinberg, F., Kircher, O., Fichtner, M.

{Journal of Alloys and Compounds}, 404, pages: 738-742, 2005 (article)

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[BibTex]

[BibTex]


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Kinetics of carbon precipitation and re-solution in low Si-content silicon iron

Walz, F., Wakisaka, T., Kronmüller, H.

{Physica Status Solidi A}, 202(14):2667-2678, 2005 (article)

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[BibTex]

[BibTex]


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Untersuchung über die Grenzflächenmagnetisierung an (FM) Kobalt- und (AFM) Eisen-Mangan-Schichten

Harlander, M.

Stuttgart, Universität Stuttgart, 2005 (mastersthesis)

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[BibTex]

[BibTex]


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Highly homogeneous MgB2 films prepared by a new post-annealing process

Matveev, A., Albrecht, J., Konuma, M., Stuhlhofer, B., Starke, U., Habermeier, H.-U.

{Superconductor Science and Technology}, 18, pages: 1313-1316, 2005 (article)

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[BibTex]

[BibTex]


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Spin-polarized quasiparticle injection effects in YBCO thin films

Soltan, S., Albrecht, J., Habermeier, H.-U.

{Solid State Communications}, 135, pages: 461-465, 2005 (article)

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[BibTex]

[BibTex]


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Thermodynamic properties from ab-initio calculations: New theoretical developments, and applications to various materials systems

Fähnle, M., Drautz, R., Lechermann, F., Singer, R., Diaz-Ortiz, A., Dosch, H.

{Physica Status Solidi (B)}, 242, pages: 1159-1173, 2005 (article)

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[BibTex]

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Magnetization reversal behavior of nanogranular CoCrPt alloy thin films studied with magnetic transmission X-ray microscopy

Fischer, P., Im, M., Eimüller, T., Schütz, G., Shin, S.

In 286, pages: 311-314, Boulder, CO, USA, 2005 (inproceedings)

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[BibTex]

[BibTex]


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Nuclear magnetic resonance measurements of the hydrogen dynamics in nanocrystalline graphite

Stanik, E., Majer, G., Orimo, S., Ichikawa, T., Fujii, H.

{Journal of Applied Physics}, 98, 2005 (article)

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[BibTex]

[BibTex]


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Oxygen K-edge shift at the Verwey transition of magnetite

Goering, E., Gold, S., Lafkioti, M., Schütz, G., Brabers, V. A. M.

{Physical Review B}, 72, 2005 (article)

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[BibTex]

[BibTex]


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First-principles investigation of the Ni-Fe-Al system

Lechermann, F., Fähnle, M., Sanchez, J. M.

{Intermetallics}, 13((10)):1096-1109, 2005 (article)

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[BibTex]

[BibTex]


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GdN thin films: Bulk and local electronic and magnetic properties

Leuenberger, F., Parge, A., Felsch, W., Fauth, K., He\ssler, M.

{Physical Review B}, 72(1), 2005 (article)

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[BibTex]

[BibTex]


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Hydrogen permeation through Pd/Fe and Pd/Ni multilayer systems

Yamakawa, K., Ege, M., Hirscher, M., Ludescher, B., Kronmüller, H.

{Journal of Alloys and Compounds}, 393(1-2):5-10, 2005 (article)

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[BibTex]

[BibTex]


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Parametrization of the magnetic energy at the atomic level

Drautz, R., Fähnle, M.

{Physical Review B}, 72, 2005 (article)

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[BibTex]

[BibTex]


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Time-scales of electronic processes in Fe3O4 - An attempt to resolve a recently accentuated controversy

Fähnle, M., Kronmüller, H., Walz, F.

{Physica B}, 369, pages: 177-180, 2005 (article)

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[BibTex]

[BibTex]


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Interlayer contraction in MgB2 upon replacement of Mg by Al: Effect of the covalent bond energy

Bester, G., Fähnle, M.

{Physical Review B}, 72, 2005 (article)

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[BibTex]

[BibTex]


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First-principles atomistic modeling of ordering phenomena and phase diagrams

Fähnle, M., Drautz, R., Lechermann, F., Singer, R., Diaz-Ortiz, A., Dosch, H.

{TMS Letters}, 2(1):7-8, 2005 (article)

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[BibTex]

[BibTex]


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Constrained spin-density functional theory for excited magnetic configurations in an adiabatic approximation

Singer, R., Fähnle, M., Bihlmayer, G.

{Physical Review B}, 71, 2005 (article)

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[BibTex]

[BibTex]


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The influence of magnetism on atomic defects and diffusion: model calculations and ab initio electron theory

Fähnle, M., Schimmele, L.

{Defect and Diffusion Forum}, 237-240, pages: 19-29, 2005 (article)

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[BibTex]

[BibTex]


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X-ray magnetic circular dichroism sum rule correction for the light transition metals

Goering, E.

{Philosophical Magazine}, 85, pages: 2895-2911, 2005 (article)

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[BibTex]

[BibTex]


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Temperature dependence of the magnetocrystalline anisotropy energy and projected microscopic magnetic moments in epitaxial CrO2 films

Gold, S., Goering, E., König, C., Rüdiger, U., Güntherodt, G., Schütz, G.

{Physical Review B}, 71(22), 2005 (article)

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On the imaging of the flux-line lattice of a type-II superconductor by soft X-ray absorption spectroscopy

Fähnle, M., Albrecht, J., Eimüller, T., Fisher, P., Goering, E., Steiauf, D., Schütz, G.

{Journal of Synchrotron Radiation}, 12, pages: 251-253, 2005 (article)

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[BibTex]

[BibTex]


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Grain-boundary melting phase transition in the Cu-Bi system

Divinski, S., Lohmann, M., Herzig, C., Straumal, B., Baretzky, B., Gust, W.

{Physical Review B}, 71, 2005 (article)

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[BibTex]

[BibTex]


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A fast ab initio approach to the simulation of spin dynamics

Fähnle, M., Drautz, R., Singer, R., Steiauf, D., Berkov, D. V.

{Computational Materials Science}, 32, pages: 118-122, 2005 (article)

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[BibTex]

[BibTex]


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Hydrogen adsorption in different carbon nanostructures

Panella, B., Hirscher, M., Roth, S.

{Carbon}, 43, pages: 2209-2214, 2005 (article)

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[BibTex]

[BibTex]


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A new methodology for robot control design

Peters, J., Mistry, M., Udwadia, F. E., Schaal, S.

In The 5th ASME International Conference on Multibody Systems, Nonlinear Dynamics, and Control (MSNDC 2005), Long Beach, CA, Sept. 24-28, 2005, clmc (inproceedings)

Abstract
Gauss principle of least constraint and its generalizations have provided a useful insights for the development of tracking controllers for mechanical systems (Udwadia,2003). Using this concept, we present a novel methodology for the design of a specific class of robot controllers. With our new framework, we demonstrate that well-known and also several novel nonlinear robot control laws can be derived from this generic framework, and show experimental verifications on a Sarcos Master Arm robot for some of these controllers. We believe that the suggested approach unifies and simplifies the design of optimal nonlinear control laws for robots obeying rigid body dynamics equations, both with or without external constraints, holonomic or nonholonomic constraints, with over-actuation or underactuation, as well as open-chain and closed-chain kinematics.

am

link (url) [BibTex]

link (url) [BibTex]


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Synthesis of the nanocrystalline MgS and its interaction with hydrogen

Goo, N. H., Hirscher, M.

{Journal of Alloys and Compounds}, 404, pages: 503-506, 2005 (article)

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[BibTex]

[BibTex]


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Time-scales of electronic processes in Fe3O4 - An attempt to resolve a recently accentuated controversy

Fähnle, M., Kronmüller, H., Walz, F.

{Physica B}, 369, pages: 177-180, 2005 (article)

mms

[BibTex]

[BibTex]


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Bending of magnetic avalanches in MgB2 thin films

Albrecht, J., Matveev, A., Djupmyr, M., Schütz, G., Stuhlhofer, B., Habermeier, H.

{Applied Physics Letters}, 87, 2005 (article)

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[BibTex]

[BibTex]


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Magnetic pinning of flux lines in heterostructures of cuprates and manganites

Albrecht, J., Soltan, S., Habermeier, H.-U.

{Physical Review B}, 72, 2005 (article)

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[BibTex]


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On the pair-potential modelling of alloy surfaces

Drautz, R., Fähnle, M.

{Surface Science}, 585, pages: 108-112, 2005 (article)

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[BibTex]

[BibTex]