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Modern Magnetic Systems Article Positron age-momentum correlation (AMOC) measurements on organic liquids Castellaz, P., Siegle, A., Stoll, H. {Journal of Nuclear and Radiochemical Sciences}, 3:R1-R7, 2002 BibTeX
Modern Magnetic Systems Conference Paper Pressure Isotherms of Hydrogen Adsorption in Carbon Nanostructures Chen, X., Dettlaff-Weglikowska, U., Haluska, M., Hulman, M., Roth, S., Hirscher, M., Becher, M. In Making Functional Materials with Nanotubes, Z9.11.1-Z9.11.6, Materials Research Society Symposium Proceedings, MRS, Boston [Mass.], 2002 BibTeX
Modern Magnetic Systems Article Pt magnetization profile in a Pt/Co bilayer studied by resonant magnetic x-ray reflectometry Geissler, J., Goering, E., Justen, M., Weigand, F., Schütz, G., Langer, J., Schmitz, D., Maletta, H., Mattheis, R. {Physical Review B}, 65, 2002 DOI BibTeX
Modern Magnetic Systems Miscellaneous Rumpfniveau-Photoemissions-Spektroskopie an Platinclustern auf HOPG Schneider, N. Würzburg, 2002 BibTeX
Modern Magnetic Systems Article Second-order magnetoelastic effects: From the Dirac equation to the magnetic properties of ultrathin epitaxial films for magnetic thin-film applications Fähnle, M., Komelj, M. {Zeitschrift f\"ur Metallkunde}, 93(10):970-973, 2002 BibTeX
Modern Magnetic Systems Article Shear-strain-related nonlinear magnetoelastic properties of epitaxial films Komelj, M., Fähnle, M. {Physical Review B}, 65(9), 2002 BibTeX
Modern Magnetic Systems Article Strong anisotropy of projected 3d moments in epitaxial CrO2 films Goering, E., Bayer, A., Gold, S., Schütz, G., Rabe, M., Rüdiger, U., Güntherodt, G. {Physical Review Letters}, 88(20), 2002 BibTeX
Modern Magnetic Systems Article Strong anisotropy of projected Cr3d moments of epitaxial grown CrO2-films Goering, E., Bayer, A., Gold, S., Schütz, G. {Bessy-Highlights}, 26-27, 2002 BibTeX
Modern Magnetic Systems Article Study of magnetic domains by magnetic soft x-ray transmission microscopy Fischer, P., Denbeaux, G., Ono, T., Okuno, T., Eimüller, T., Goll, D., Schütz, G. {Journal of Physics D-Applied Physics}, 35(19):2391-2397, 2002 BibTeX
Modern Magnetic Systems Article Surface magnetization reversal of sputtered CrO2 Goering, E., Gold, S., Will, J. {Zeitschrift f\"ur Metallkunde}, 93(5):372-376, 2002 BibTeX
Modern Magnetic Systems Article Switching behavior of single nanowires inside dense nickel nanowire arrays Nielsch, K., Hertel, R., Wehrspohn, R. B., Barthel, J., Kirschner, J., Gösele, U., Fischer, S. F., Kronmüller, H. {IEEE Transactions on Magnetics}, 38(5):2571-2573, 2002 BibTeX
Modern Magnetic Systems Article The Verwey transition - a topical review Walz, F. {Journal of Physics-Condensed Matter}, 14(12):R285-R340, 2002 BibTeX
Modern Magnetic Systems Article The Verwey transition in magnetite as studied by means of definite impurity doping Walz, F., Brabers, J. H. V. J., Brabers, V. A. M. {Zeitschrift f\"ur Metallkunde}, 93(10):1095-1102, 2002 BibTeX
Modern Magnetic Systems Article The existence of more than one jump process of hydrogen in palladium-silver alloys - an NMR study Züchner, H., Barlag, H., Majer, G. {Journal of Alloys and Compounds}, 330-332:448-453, 2002 BibTeX
Modern Magnetic Systems Article The initial stages of oxidation of γ-TiAl: an X-ray photoelectron study Schmiedgen, M., Graat, P. C. J., Baretzky, B., Mittemeijer, E. J. {Thin Solid Films}, 415(1-2):114-122, 2002 BibTeX
Modern Magnetic Systems Article Theory of crystal field states for heavy rare-earth impurities in MgB2 Welsch, F., Kremer, R., Fähnle, M. {Journal of Physics-Condensed Matter}, 14(43):10273-10279, 2002 BibTeX
Modern Magnetic Systems Article Theory of induced magnetic moments and x-ray magnetic circular dichroism in Co-Pt multilayers Ederer, C., Komelj, M., Fähnle, M., Schütz, G. {Physical Review B}, 66(9), 2002 BibTeX
Modern Magnetic Systems Article Undulation instabilities in laterally structured magnetic multilayers Eimüller, T., Scholz, M., Guttmann, P., Köhler, M., Bayreuther, G., Schmahl, G., Fischer, P., Schütz, G. {Journal of Applied Physics}, 91(10):7334-7336, 2002 BibTeX
Modern Magnetic Systems Master Thesis Untersuchungen zur Spindynamik in nanostrukturierten ferromagnetischen Schichtsystemen Puzic, A. Universität Stuttgart, Stuttgart, 2002 BibTeX
Modern Magnetic Systems Article Vacancies in thermal equilibrium and ferromagnetism near the Curie temperature Seeger, A., Fähnle, M. {Zeitschrift f\"ur Metallkunde}, 93(10):1030-1042, 2002 BibTeX
Empirical Inference Article Regularized principal manifolds Smola, A., Mika, S., Schölkopf, B., Williamson, R. Journal of Machine Learning Research, 1:179-209, June 2001
Many settings of unsupervised learning can be viewed as quantization problems - the minimization of the expected quantization error subject to some restrictions. This allows the use of tools such as regularization from the theory of (supervised) risk minimization for unsupervised learning. This setting turns out to be closely related to principal curves, the generative topographic map, and robust coding. We explore this connection in two ways: (1) we propose an algorithm for finding principal manifolds that can be regularized in a variety of ways; and (2) we derive uniform convergence bounds and hence bounds on the learning rates of the algorithm. In particular, we give bounds on the covering numbers which allows us to obtain nearly optimal learning rates for certain types of regularization operators. Experimental results demonstrate the feasibility of the approach.
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Empirical Inference Thesis Variationsverfahren zur Untersuchung von Grundzustandseigenschaften des Ein-Band Hubbard-Modells Eichhorn, J. Biologische Kybernetik, Technische Universität Dresden, Dresden/Germany, May 2001
Using different modifications of a new variational approach, statical groundstate properties of the one-band Hubbard model such as energy and staggered magnetisation are calculated. By taking into account additional fluctuations, the method ist gradually improved so that a very good description of the energy in one and two dimensions can be achieved. After a detailed discussion of the application in one dimension, extensions for two dimensions are introduced. By use of a modified version of the variational ansatz in particular a description of the quantum phase transition for the magnetisation should be possible.
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Theory of Inhomogeneous Condensed Matter Article Adsorption isotherms of hydrogen: The role of thermal fluctuations Vorberg, J., Herminghaus, S., Mecke, K. Physical Review Letters, 87(19), 2001 BibTeX
Autonomous Motion Article Biomimetic gaze stabilization based on feedback-error learning with nonparametric regression networks Shibata, T., Schaal, S. Neural Networks, 14(2):201-216, 2001, clmc
Oculomotor control in a humanoid robot faces similar problems as biological oculomotor systems, i.e. the stabilization of gaze in face of unknown perturbations of the body, selective attention, stereo vision, and dealing with large information processing delays. Given the nonlinearities of the geometry of binocular vision as well as the possible nonlinearities of the oculomotor plant, it is desirable to accomplish accurate control of these behaviors through learning approaches. This paper develops a learning control system for the phylogenetically oldest behaviors of oculomotor control, the stabilization reflexes of gaze. In a step-wise procedure, we demonstrate how control theoretic reasonable choices of control components result in an oculomotor control system that resembles the known functional anatomy of the primate oculomotor system. The core of the learning system is derived from the biologically inspired principle of feedback-error learning combined with a state-of-the-art non-parametric statistical learning network. With this circuitry, we demonstrate that our humanoid robot is able to acquire high performance visual stabilization reflexes after about 40 s of learning despite significant nonlinearities and processing delays in the system.
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Autonomous Motion Article Biomimetic oculomotor control Shibata, T., Vijayakumar, S., Conradt, J., Schaal, S. Adaptive Behavior, 9(3/4):189-207, 2001, clmc
Oculomotor control in a humanoid robot faces similar problems as biological oculomotor systems, i.e., capturing targets accurately on a very narrow fovea, dealing with large delays in the control system, the stabilization of gaze in face of unknown perturbations of the body, selective attention, and the complexity of stereo vision. In this paper, we suggest control circuits to realize three of the most basic oculomotor behaviors and their integration - the vestibulo-ocular and optokinetic reflex (VOR-OKR) for gaze stabilization, smooth pursuit for tracking moving objects, and saccades for overt visual attention. Each of these behaviors and the mechanism for their integration was derived with inspiration from computational theories as well as behavioral and physiological data in neuroscience. Our implementations on a humanoid robot demonstrate good performance of the oculomotor behaviors, which proves to be a viable strategy to explore novel control mechanisms for humanoid robotics. Conversely, insights gained from our models have been able to directly influence views and provide new directions for computational neuroscience research.
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Autonomous Motion Conference Paper Biomimetic smooth pursuit based on fast learning of the target dynamics Shibata, T., Schaal, S. In IEEE International Conference on Intelligent Robots and Systems (IROS 2001), 2001, clmc
Following a moving target with a narrow-view foveal vision system is one of the essential oculomotor behaviors of humans and humanoids. This oculomotor behavior, called ``Smooth Pursuit'', requires accurate tracking control which cannot be achieved by a simple visual negative feedback controller due to the significant delays in visual information processing. In this paper, we present a biologically inspired and control theoretically sound smooth pursuit controller consisting of two cascaded subsystems. One is an inverse model controller for the oculomotor system, and the other is a learning controller for the dynamics of the visual target. The latter controller learns how to predict the target's motion in head coordinates such that tracking performance can be improved. We investigate our smooth pursuit system in simulations and experiments on a humanoid robot. By using a fast on-line statistical learning network, our humanoid oculomotor system is able to acquire high performance smooth pursuit after about 5 seconds of learning despite significant processing delays in the syste
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Autonomous Motion Article Bouncing a ball: Tuning into dynamic stability Sternad, D., Duarte, M., Katsumata, H., Schaal, S. Journal of Experimental Psychology: Human Perception and Performance, 27(5):1163-1184, 2001, clmc
Rhythmically bouncing a ball with a racket was investigated and modeled with a nonlinear map. Model analyses provided a variable defining a dynamically stable solution that obviates computationally expensive corrections. Three experiments evaluated whether dynamic stability is optimized and what perceptual support is necessary for stable behavior. Two hypotheses were tested: (a) Performance is stable if racket acceleration is negative at impact, and (b) variability is lowest at an impact acceleration between -4 and -1 m/s2. In Experiment 1 participants performed the task, eyes open or closed, bouncing a ball confined to a 1-dimensional trajectory. Experiment 2 eliminated constraints on racket and ball trajectory. Experiment 3 excluded visual or haptic information. Movements were performed with negative racket accelerations in the range of highest stability. Performance with eyes closed was more variable, leaving acceleration unaffected. With haptic information, performance was more stable than with visual information alone.
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Theory of Inhomogeneous Condensed Matter Article Crystal structures and freezing of dipolar fluids Groh, B., Dietrich, S. Physical Review E, 63(2):021203, 2001 DOI BibTeX
Physical Intelligence Conference Paper Development of PZT and PZN-PT based unimorph actuators for micromechanical flapping mechanisms Sitti, M., Campolo, D., Yan, J., Fearing, R. S. In Robotics and Automation, 2001. Proceedings 2001 ICRA. IEEE International Conference on, 4:3839-3846, 2001 BibTeX
Physical Intelligence Conference Paper Development of a scaled teleoperation system for nano scale interaction and manipulation Sitti, M., Aruk, B., Shintani, H., Hashimoto, H. In Robotics and Automation, 2001. Proceedings 2001 ICRA. IEEE International Conference on, 1:860-867, 2001 BibTeX
Theory of Inhomogeneous Condensed Matter Ph.D. Thesis Diffusion im unterkühlten flüssigen und amorphen Zustand von Zr65Cu175,Ni10Al17,5 Schaaff, P. Universität Stuttgart, Stuttgart, 2001 BibTeX
Theory of Inhomogeneous Condensed Matter Article Diffusion of 195Au in amorphous Si3N4 and Si4N3 Voss, T., Matics, S., Strohm, A., Frank, W., Bilger, G. Physica B, 308:431-433, 2001 BibTeX
Theory of Inhomogeneous Condensed Matter Conference Paper Diffusion of gold in germanium Strohm, A., Matics, S., Frank, W. In Proceedings of DIMAT 2000, the Fifth International Conference on Diffusion in Materials, 194/199:629-634, Defect and Diffusion Forum, Scitech Publ. Ltd., Paris, France, 2001 BibTeX
Theory of Inhomogeneous Condensed Matter Conference Paper Diffusion of gold in the amorphous ceramic Si28C36N36 Matics, S., Frank, W. In Proceedings of DIMAT 2000, the Fifth International Conference on Diffusion in Materials, 194/199:947-952, Diffusion and Defect Forum, Scitec Publications Ltd., Paris, France, 2001 BibTeX
Theory of Inhomogeneous Condensed Matter Conference Paper Diffusion of implanted 195Au radiotracer atoms in amorphous silicon under irradiation with 1 MeV-N+ ions Voss, T., Scharwaechter, P., Frank, W. In Proceedings of DIMAT 2000, the Fifth International Conference on Diffusion in Materials, 194/199:659-665, Defect and Diffusion Forum, Scitec Publications Ltd., Paris, France, 2001 BibTeX
Theory of Inhomogeneous Condensed Matter Ph.D. Thesis Einfluß von Teilchenbestrahlung auf die Selbst- und Interdiffusion in amorphen Fe-Zr-Legierungen Schuler, T. Universität Stuttgart, Stuttgart, 2001 BibTeX
Materials Article Epitaxial growth of metals on (100) SrTiO3: The influence of lattice mismatch and reactivity Wagner, T., Polli, A. D., Richter, G., Stanzick, H. Zeitschrift Fur Metallkunde, 92(7):701-706, 2001 BibTeX
Materials Article Epitaxy of Pd thin films on (100) SrTiO3: A three-step growth process Wagner, T., Richter, G., Ruhle, M. Journal of Applied Physics, 89(5):2606-2612, 2001 DOI BibTeX
Autonomous Motion Article Fast learning of biomimetic oculomotor control with nonparametric regression networks (in Japanese) Shibata, T., Schaal, S. Journal of the Robotics Society of Japan, 19(4):468-479, 2001, clmc BibTeX
Autonomous Motion Article Graph-matching vs. entropy-based methods for object detection Neural Networks, 14(3):345-354, 2001, clmc
Labeled Graph Matching (LGM) has been shown successful in numerous ob-ject vision tasks. This method is the basis for arguably the best face recognition system in the world. We present an algorithm for visual pattern recognition that is an extension of LGM ("LGM+"). We compare the performance of LGM and LGM+ algorithms with a state of the art statistical method based on Mutual Information Maximization (MIM). We present an adaptation of the MIM method for multi-dimensional Gabor wavelet features. The three pattern recognition methods were evaluated on an object detection task, using a set of stimuli on which none of the methods had been tested previously. The results indicate that while the performance of the MIM method operating upon Gabor wavelets is superior to the same method operating on pixels and to LGM, it is surpassed by LGM+. LGM+ offers a significant improvement in performance over LGM without losing LGMâ??s virtues of simplicity, biological plausibility, and a computational cost that is 2-3 orders of magnitude lower than that of the MIM algorithm. 
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Autonomous Motion Conference Paper Humanoid oculomotor control based on concepts of computational neuroscience Shibata, T., Vijayakumar, S., Conradt, J., Schaal, S. In Humanoids2001, Second IEEE-RAS International Conference on Humanoid Robots, 2001, clmc
Oculomotor control in a humanoid robot faces similar problems as biological oculomotor systems, i.e., the stabilization of gaze in face of unknown perturbations of the body, selective attention, the complexity of stereo vision and dealing with large information processing delays. In this paper, we suggest control circuits to realize three of the most basic oculomotor behaviors - the vestibulo-ocular and optokinetic reflex (VOR-OKR) for gaze stabilization, smooth pursuit for tracking moving objects, and saccades for overt visual attention. Each of these behaviors was derived from inspirations from computational neuroscience, which proves to be a viable strategy to explore novel control mechanisms for humanoid robotics. Our implementations on a humanoid robot demonstrate good performance of the oculomotor behaviors that appears natural and human-like.
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Empirical Inference Technical Report Inference Principles and Model Selection Buhmann, J., Schölkopf, B. (01301), Dagstuhl Seminar, 2001 Web BibTeX
Micro, Nano, and Molecular Systems Article Isotropic second-order nonlinear optical susceptibilities Fischer, P., Buckingham, A., Albrecht, A. PHYSICAL REVIEW A, 64(5), 2001
The second-order nonlinear optical susceptibility, in the electric dipole approximation, is only nonvanishing for materials that are noncentrosymmetric. Should the medium be isotropic, then only a chiral system. such as an optically active liquid, satisfies this symmetry requirement. We derive the quantum-mechanical form of the isotropic component of the sum- and difference-frequency susceptibility and discuss its unusual spectral properties. We show that any coherent second-order nonlinear optical process in a system of randomly oriented molecules requires the medium to be chiral. and the incident frequencies to be different and nonzero. Furthermore, a minimum of two nondegenerate excited molecular states are needed for the isotropic part of the susceptibility to be nonvanishing. The rotationally invariant susceptibility is zero in the static field limit and shows exceptionally sensitive resonance and dephasing effects that are particular to chiral centers.
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Autonomous Motion Conference Paper Learning inverse kinematics D’Souza, A., Vijayakumar, S., Schaal, S. In IEEE International Conference on Intelligent Robots and Systems (IROS 2001), Piscataway, NJ: IEEE, Maui, Hawaii, Oct.29-Nov.3, 2001, clmc
Real-time control of the endeffector of a humanoid robot in external coordinates requires computationally efficient solutions of the inverse kinematics problem. In this context, this paper investigates learning of inverse kinematics for resolved motion rate control (RMRC) employing an optimization criterion to resolve kinematic redundancies. Our learning approach is based on the key observations that learning an inverse of a non uniquely invertible function can be accomplished by augmenting the input representation to the inverse model and by using a spatially localized learning approach. We apply this strategy to inverse kinematics learning and demonstrate how a recently developed statistical learning algorithm, Locally Weighted Projection Regression, allows efficient learning of inverse kinematic mappings in an incremental fashion even when input spaces become rather high dimensional. The resulting performance of the inverse kinematics is comparable to Liegeois ([1]) analytical pseudo inverse with optimization. Our results are illustrated with a 30 degree-of-freedom humanoid robot.
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Physical Intelligence Conference Paper Man-machine interface for micro/nano manipulation with an afm probe Aruk, B., Hashimoto, H., Sitti, M. In Nanotechnology, 2001. IEEE-NANO 2001. Proceedings of the 2001 1st IEEE Conference on, 151-156, 2001 BibTeX
Empirical Inference Article Markovian domain fingerprinting: statistical segmentation of protein sequences Bejerano, G., Seldin, Y., Margalit, H., Tishby, N. Bioinformatics, 17(10):927-934, 2001 PDF Web BibTeX
Theory of Inhomogeneous Condensed Matter Article Morphological fluctuations of large-scale structure: The PSCz survey Kerscher, M., Mecke, K., Schmalzing, J., Beisbart, C., Buchert, T., Wagner, H. Astronomy \& Astrophysics, 373(1):1-11, 2001 BibTeX
Physical Intelligence Conference Paper Nanotribological characterization system by AFM based controlled pushing Sitti, M. In Nanotechnology, 2001. IEEE-NANO 2001. Proceedings of the 2001 1st IEEE Conference on, 99-104, 2001 BibTeX
Theory of Inhomogeneous Condensed Matter Article Non-Gaussian morphology on large scales: Minkowski functionals of the REFLEX cluster catalogue Kerscher, M., Mecke, K., Schuecker, P., Böhringer, H., Guzzo, L., Collins, C. A., Schindler, S., De Grandi, S., Cruddace, R. Astronomy & Astrophysics, 377(1):1-16, 2001 BibTeX
Autonomous Motion Article Origins and violations of the 2/3 power law in rhythmic 3D movements Schaal, S., Sternad, D. Experimental Brain Research, 136:60-72, 2001, clmc
The 2/3 power law, the nonlinear relationship between tangential velocity and radius of curvature of the endeffector trajectory, has been suggested as a fundamental constraint of the central nervous system in the formation of rhythmic endpoint trajectories. However, studies on the 2/3 power law have largely been confined to planar drawing patterns of relatively small size. With the hypothesis that this strategy overlooks nonlinear effects that are constitutive in movement generation, the present experiments tested the validity of the power law in elliptical patterns which were not confined to a planar surface and which were performed by the unconstrained 7-DOF arm with significant variations in pattern size and workspace orientation. Data were recorded from five human subjects where the seven joint angles and the endpoint trajectories were analyzed. Additionally, an anthropomorphic 7-DOF robot arm served as a "control subject" whose endpoint trajectories were generated on the basis of the human joint angle data, modeled as simple harmonic oscillations. Analyses of the endpoint trajectories demonstrate that the power law is systematically violated with increasing pattern size, in both exponent and the goodness of fit. The origins of these violations can be explained analytically based on smooth rhythmic trajectory formation and the kinematic structure of the human arm. We conclude that in unconstrained rhythmic movements, the power law seems to be a by-product of a movement system that favors smooth trajectories, and that it is unlikely to serve as a primary movement generating principle. Our data rather suggests that subjects employed smooth oscillatory pattern generators in joint space to realize the required movement patterns.
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