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2009


Full phase and amplitude control in computer-generated holography
Full phase and amplitude control in computer-generated holography

Fratz, M., Fischer, P., Giel, D. M.

OPTICS LETTERS, 34(23):3659-3661, 2009 (article)

Abstract
We report what we believe to be the first realization of a computer-generated complex-valued hologram recorded in a single film of photoactive polymer. Complex-valued holograms give rise to a diffracted optical field with control over its amplitude and phase. The holograms are generated by a one-step direct laser writing process in which a spatial light modulator (SLM) is imaged onto a polymer film. Temporal modulation of the SLM during exposure controls both the strength of the induced birefringence and the orientation of the fast axis. We demonstrate that complex holograms can be used to impart arbitrary amplitude and phase profiles onto a beam and thereby open new possibilities in the control of optical beams. (C) 2009 Optical Society of America

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[BibTex]

2009


[BibTex]


Digital polarization holograms with defined magnitude and orientation of each pixel's birefringence
Digital polarization holograms with defined magnitude and orientation of each pixel’s birefringence

Fratz, M., Giel, D. M., Fischer, P.

OPTICS LETTERS, 34(8):1270-1272, 2009 (article)

Abstract
A new form of digital polarization holography is demonstrated that permits both the amplitude and the phase of a diffracted beam to be independently controlled. This permits two independent intensity images to be stored in the same hologram. To fabricate the holograms, a birefringence with defined retardance and orientation of the fast axis is recorded into a photopolymer film. The holograms are selectively read out by choosing the polarization state of the read beam. Polarization holograms of this kind increase the data density in holographic data storage and allow higher quality diffractive optical elements to be written. (C) 2009 Optical Society of America

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[BibTex]


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Interplay of complete wetting, critical adsorption, and capillary condensation

Drzewinski, A., Maciolek, A., Barasinski, A., Dietrich, S.

Physical Review E, 79, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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The critical Casimir effect: universal fluctuation-induced forces at work

Gambassi, A., Hertlein, C., Helden, L., Dietrich, S., Bechinger, C.

Europhysics News, 40(01):18-22, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Effective interactions of colloids on nematic films

Oettel, M., Dominguez, A., Tasinkevych, M., Dietrich, S.

European Physical Journal E, 28(02):99-111, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Self-diffusion and cooperative diffusion in semidilute polymer solutions as measured by fluorescence correlation spectroscopy

Zettl, U., Hoffmann, S. T., Koberling, F., Krausch, G., Enderlein, J., Harnau, L., Ballauff, M.

Macromolecules, 42, pages: 9537-9547, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Free-energy function based on an all-atom model for proteins

Yoshidome, T., Oda, K., Harano, Y., Roth, R., Sugita, Y., Ikeguchi, M., Kinoshita, M.

Proteins: Structure, Function, and Bioinformatics, 77(4):950-961, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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On scale-free and poly-scale behaviors of random hierarchical networks

Avetisov, V. A., Chertovitch, A. V., Nechaev, S .K., Vasilyev, O. A.

Journal of Statistical Mechanics: Theory and Experiment, July 2009, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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3D Brownian diffusion of submicron-sized particle clusters

Hoffmann, M., Wagner, C. S., Harnau, L., Wittemann, A.

ACS Nano, 3(10):3326-3334, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


Controlled Propulsion of Artificial Magnetic Nanostructured Propellers
Controlled Propulsion of Artificial Magnetic Nanostructured Propellers

Ghosh, A., Fischer, P.

NANO LETTERS, 9(6):2243-2245, 2009, Featured highlight ‘Nanotechnology: The helix that delivers’ Nature 459, 13 (2009). (article)

Abstract
For biomedical applications, such as targeted drug delivery and microsurgery, it is essential to develop a system of swimmers that can be propelled wirelessly in fluidic environments with good control. Here, we report the construction and operation of chiral colloidal propellers that can be navigated in water with micrometer-level precision using homogeneous magnetic fields. The propellers are made via nanostructured surfaces and can be produced in large numbers. The nanopropellers can carry chemicals, push loads, and act as local probes in rheological measurements.

Featured highlight ‘Nanotechnology: The helix that delivers’ Nature 459, 13 (2009).

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Video - Nanospropellers DOI [BibTex]

Video - Nanospropellers DOI [BibTex]


Absolute Asymmetric Reduction Based on the Relative Orientation of Achiral Reactants
Absolute Asymmetric Reduction Based on the Relative Orientation of Achiral Reactants

Kuhn, A., Fischer, P.

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 48(37):6857-6860, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Normal and lateral critical Casimir forces between colloids and patterned substrates

Tröndle, M., Kondrat, S., Gambassi, A., Harnau, L., Dietrich, S.

EPL, 88, 2009 (article)

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DOI [BibTex]


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Critical wetting transitions in two-dimensional systems subject to long-ranged boundary fields

Drzewinski, A., Maciolek, A., Barasinski, A., Dietrich, S.

Physical Review E, 79, 2009 (article)

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DOI [BibTex]


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Derivation of a non-local interfacial model for 3D wetting in an external field

Bernardino, N. R., Parry, A. O., Rascon, C., Romero-Enrique, J. M.

Journal of Physics: Condensed Matter, 21(46), 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Coupling of rotational motion with shape fluctuations of core-shell microgels having tunable softness

Bolisetty, S., Hoffmann, M., Lekkala, S., Hellweg, T., Ballauff, M., Harnau, L.

Macromolecules, 42, pages: 1264-1269, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Strong-disorder paramagnetic-ferromagnetic fixed point in the square-lattice +/-J Ising model

Parisen Toldin, F., Pelissetto, A., Vicari, E.

Journal of Statistical Physics, 135(5):1039-1061, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Structure and interaction of flexible dendrimers in concentrated solution

Rosenfeldt, S., Ballauff, M., Lindner, P., Harnau, L.

The Journal of Chemical Physics, 130, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Layering of (BMIM)+-based ionic liquids at a charged sapphire interface

Mezger, M., Schramm, S., Schröder, H., Reichert, H., Deutsch, M., de Souza, E. J., Okasinski, J. S., Ocko, B. M., Honkimäki, V., Dosch, H.

Journal of Chemical Physics, 131, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Nano-droplets on structured substrates

Rauscher, M. A., Dietrich, S.

Soft Matter, 5(16):2997-3001, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Self-assembly of Janus cylinders into hierarchical superstructures

Walther, A., Drechsler, M., Rosenfeldt, S., Harnau, L., Ballauff, M., Abetz, V., Müller, A. H. E.

Journal of the American Chemical Society, 131, pages: 4720-4728, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Solvent-mediated interactions between nanoparticles at fluid interfaces

Bresme, F., Lehle, H., Oettel, M.

Journal of Chemical Physics, 130(21), 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Diffusion of a sphere in a dilute solution of polymer coils

Krüger, M., Rauscher, M.

Journal of Chemical Physics, 131(9), 2009 (article)

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Dynamics of nanodroplets on topographically structured substrates

Moosavi, A., Rauscher, M., Dietrich, S.

Journal of Physics: Condensed Matter, 21(46), 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Critical Casimir effect in classical binary liquid mixtures

Gambassi, A., Maciolek, A., Hertlein, C., Nellen, U., Helden, L., Bechinger, C., Dietrich, S.

Physical Review E, 80, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Phase transitions and ordering of confined dipolar fluids

Szalai, I., Dietrich, S.

European Physical Journal E, 28(3):347-359, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Nonlinear dielectric effect of dipolar fluids

Szalai, I., Nagy, S., Dietrich, S.

Journal of Chemical Physics, 131(15), 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Some physical applications of random hierarchical matrices

Avetisov, V. A., Bikulov, A. K., Vasilyev, O. A., Nechaev, S. K., Chertovich, A. V.

Journal of Experimental and Theoretical Physics, 109(3):485-504, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Interaction of cylindrical polymer brushes in dilute and semi-dilute solution

Bolisetty, S., Rosenfeldt, S., Rochette, C. N., Harnau, L., Lindner, P., Xu, Y., Mueller, A. H. E., Ballauff, M.

Colloid and Polymer Science, 287, pages: 129-138, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Survival of an evasive prey

Oshanin, G., Vasilyev, O., Krapivsky, P. L., Klafter, J.

Proceedings of the National Academy of Sciences of the United States of America, 106(33):13696-13701, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Manipulating cylindrical polyelectrolyte brushes on the nanoscale by counterions: collapse transition to helical structures

Xu, Y., Bolisetty, S., Drechsler, M., Fang, B., Yuan, J., Harnau, L., Ballauff, M., Mueller, A. H. E.

Soft Matter, 5, pages: 379-384, 2009 (article)

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link (url) [BibTex]

link (url) [BibTex]


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Confinement effects on diffusiophoretic self-propellers

Popescu, M. N., Dietrich, S., Oshanin, G.

Journal of Chemical Physics, 130(19), 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Line tension and the shape of nanodroplets

Schimmele, L., Dietrich, S.

European Physical Journal E, 30(4):427-430, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Critical Casimir interaction of ellipsoidal colloids with a planar wall

Kondrat, S., Harnau, L., Dietrich, S.

The Journal of Chemical Physics, 131, 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Selectivity in binary fluid mixtures: static and dynamical properties

Roth, R., Rauscher, M., Archer, A. J.

Physical Review E, 80(2), 2009 (article)

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Depletion interactions of two spheres - Full density functional theory vs. morphometric results

Oettel, M., Hansen-Goos, H., Bryk, P., Roth, R.

EPL, 85(03), 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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Fundamental measure theory for inhomogeneous fluids of nonspherical particles

Hansen-Goos, H., Mecke, K.

Physical Review Letters, 102(1), 2009 (article)

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DOI [BibTex]

DOI [BibTex]


Valero-Cuevas, F., Hoffmann, H., Kurse, M. U., Kutch, J. J., Theodorou, E. A.

IEEE Reviews in Biomedical Engineering – (All authors have equally contributed), (2):110?135, 2009, clmc (article)

Abstract
Computational models of the neuromuscular system hold the potential to allow us to reach a deeper understanding of neuromuscular function and clinical rehabilitation by complementing experimentation. By serving as a means to distill and explore specific hypotheses, computational models emerge from prior experimental data and motivate future experimental work. Here we review computational tools used to understand neuromuscular function including musculoskeletal modeling, machine learning, control theory, and statistical model analysis. We conclude that these tools, when used in combination, have the potential to further our understanding of neuromuscular function by serving as a rigorous means to test scientific hypotheses in ways that complement and leverage experimental data.

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link (url) [BibTex]

link (url) [BibTex]


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Adaptive compliance control of a multi-legged stair-climbing robot based on proprioceptive data

Waldron, K. J., Eich, M., Grimminger, F., Kirchner, F.

Industrial Robot: An International Journal, 36, pages: 331-339, Emerald Group Publishing Limited, June 2009 (article)

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DOI [BibTex]

DOI [BibTex]


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On-line learning and modulation of periodic movements with nonlinear dynamical systems

Gams, A., Ijspeert, A., Schaal, S., Lenarčič, J.

Autonomous Robots, 27(1):3-23, 2009, clmc (article)

Abstract
Abstract  The paper presents a two-layered system for (1) learning and encoding a periodic signal without any knowledge on its frequency and waveform, and (2) modulating the learned periodic trajectory in response to external events. The system is used to learn periodic tasks on a humanoid HOAP-2 robot. The first layer of the system is a dynamical system responsible for extracting the fundamental frequency of the input signal, based on adaptive frequency oscillators. The second layer is a dynamical system responsible for learning of the waveform based on a built-in learning algorithm. By combining the two dynamical systems into one system we can rapidly teach new trajectories to robots without any knowledge of the frequency of the demonstration signal. The system extracts and learns only one period of the demonstration signal. Furthermore, the trajectories are robust to perturbations and can be modulated to cope with a dynamic environment. The system is computationally inexpensive, works on-line for any periodic signal, requires no additional signal processing to determine the frequency of the input signal and can be applied in parallel to multiple dimensions. Additionally, it can adapt to changes in frequency and shape, e.g. to non-stationary signals, such as hand-generated signals and human demonstrations.

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link (url) [BibTex]

link (url) [BibTex]


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Local dimensionality reduction for non-parametric regression

Hoffman, H., Schaal, S., Vijayakumar, S.

Neural Processing Letters, 2009, clmc (article)

Abstract
Locally-weighted regression is a computationally-efficient technique for non-linear regression. However, for high-dimensional data, this technique becomes numerically brittle and computationally too expensive if many local models need to be maintained simultaneously. Thus, local linear dimensionality reduction combined with locally-weighted regression seems to be a promising solution. In this context, we review linear dimensionality-reduction methods, compare their performance on nonparametric locally-linear regression, and discuss their ability to extend to incremental learning. The considered methods belong to the following three groups: (1) reducing dimensionality only on the input data, (2) modeling the joint input-output data distribution, and (3) optimizing the correlation between projection directions and output data. Group 1 contains principal component regression (PCR); group 2 contains principal component analysis (PCA) in joint input and output space, factor analysis, and probabilistic PCA; and group 3 contains reduced rank regression (RRR) and partial least squares (PLS) regression. Among the tested methods, only group 3 managed to achieve robust performance even for a non-optimal number of components (factors or projection directions). In contrast, group 1 and 2 failed for fewer components since these methods rely on the correct estimate of the true intrinsic dimensionality. In group 3, PLS is the only method for which a computationally-efficient incremental implementation exists. Thus, PLS appears to be ideally suited as a building block for a locally-weighted regressor in which projection directions are incrementally added on the fly.

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link (url) [BibTex]

link (url) [BibTex]


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A Sensor-Based Learning Algorithm for the Self-Organization of Robot Behavior

Hesse, F., Martius, G., Der, R., Herrmann, J. M.

Algorithms, 2(1):398-409, 2009 (article)

Abstract
Ideally, sensory information forms the only source of information to a robot. We consider an algorithm for the self-organization of a controller. At short timescales the controller is merely reactive but the parameter dynamics and the acquisition of knowledge by an internal model lead to seemingly purposeful behavior on longer timescales. As a paradigmatic example, we study the simulation of an underactuated snake-like robot. By interacting with the real physical system formed by the robotic hardware and the environment, the controller achieves a sensitive and body-specific actuation of the robot.

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link (url) [BibTex]

link (url) [BibTex]


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Incorporating Muscle Activation-Contraction dynamics to an optimal control framework for finger movements

Theodorou, Evangelos A., Valero-Cuevas, Francisco J.

Abstracts of Neural Control of Movement Conference (NCM 2009), 2009, clmc (article)

Abstract
Recent experimental and theoretical work [1] investigated the neural control of contact transition between motion and force during tapping with the index finger as a nonlinear optimization problem. Such transitions from motion to well-directed contact force are a fundamental part of dexterous manipulation. There are 3 alternative hypotheses of how this transition could be accomplished by the nervous system as a function of changes in direction and magnitude of the torque vector controlling the finger. These hypotheses are 1) an initial change in direction with a subsequent change in magnitude of the torque vector; 2) an initial change in magnitude with a subsequent directional change of the torque vector; and 3) a simultaneous and proportionally equal change of both direction and magnitude of the torque vector. Experimental work in [2] shows that the nervous system selects the first strategy, and in [1] we suggest that this may in fact be the optimal strategy. In [4] the framework of Iterative Linear Quadratic Optimal Regulator (ILQR) was extended to incorporate motion and force control. However, our prior simulation work assumed direct and instantaneous control of joint torques, which ignores the known delays and filtering properties of skeletal muscle. In this study, we implement an ILQR controller for a more biologically plausible biomechanical model of the index finger than [4], and add activation-contraction dynamics to the system to simulate muscle function. The planar biomechanical model includes the kinematics of the 3 joints while the applied torques are driven by activation?contraction dynamics with biologically plausible time constants [3]. In agreement with our experimental work [2], the task is to, within 500 ms, move the finger from a given resting configuration to target configuration with a desired terminal velocity. ILQR does not only stabilize the finger dynamics according to the objective function, but it also generates smooth joint space trajectories with minimal tuning and without an a-priori initial control policy (which is difficult to find for highly dimensional biomechanical systems). Furthemore, the use of this optimal control framework and the addition of activation-contraction dynamics considers the full nonlinear dynamics of the index finger and produces a sequence of postures which are compatible with experimental motion data [2]. These simulations combined with prior experimental results suggest that optimal control is a strong candidate for the generation of finger movements prior to abrupt motion-to-force transitions. This work is funded in part by grants NIH R01 0505520 and NSF EFRI-0836042 to Dr. Francisco J. Valero- Cuevas 1 Venkadesan M, Valero-Cuevas FJ. 
Effects of neuromuscular lags on controlling contact transitions. 
Philosophical Transactions of the Royal Society A: 2008. 2 Venkadesan M, Valero-Cuevas FJ. 
Neural Control of Motion-to-Force Transitions with the Fingertip. 
J. Neurosci., Feb 2008; 28: 1366 - 1373; 3 Zajac. Muscle and tendon: properties, models, scaling, and application to biomechanics and motor control. Crit Rev Biomed Eng, 17 4. Weiwei Li., Francisco Valero Cuevas: ?Linear Quadratic Optimal Control of Contact Transition with Fingertip ? ACC 2009

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PDF [BibTex]

PDF [BibTex]


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On-line learning and modulation of periodic movements with nonlinear dynamical systems

Gams, A., Ijspeert, A., Schaal, S., Lenarčič, J.

Autonomous Robots, 27(1):3-23, 2009, clmc (article)

Abstract
Abstract  The paper presents a two-layered system for (1) learning and encoding a periodic signal without any knowledge on its frequency and waveform, and (2) modulating the learned periodic trajectory in response to external events. The system is used to learn periodic tasks on a humanoid HOAP-2 robot. The first layer of the system is a dynamical system responsible for extracting the fundamental frequency of the input signal, based on adaptive frequency oscillators. The second layer is a dynamical system responsible for learning of the waveform based on a built-in learning algorithm. By combining the two dynamical systems into one system we can rapidly teach new trajectories to robots without any knowledge of the frequency of the demonstration signal. The system extracts and learns only one period of the demonstration signal. Furthermore, the trajectories are robust to perturbations and can be modulated to cope with a dynamic environment. The system is computationally inexpensive, works on-line for any periodic signal, requires no additional signal processing to determine the frequency of the input signal and can be applied in parallel to multiple dimensions. Additionally, it can adapt to changes in frequency and shape, e.g. to non-stationary signals, such as hand-generated signals and human demonstrations.

am

link (url) [BibTex]

link (url) [BibTex]

2007


Frequency-domain displacement sensing with a fiber ring-resonator containing a variable gap
Frequency-domain displacement sensing with a fiber ring-resonator containing a variable gap

Vollmer, F., Fischer, P.

SENSORS AND ACTUATORS A-PHYSICAL, 134(2):410-413, 2007 (article)

Abstract
Ring-resonators are in general not amenable to strain-free (non-contact) displacement measurements. We show that this limitation may be overcome if the ring-resonator, here a fiber-loop, is designed to contain a gap, such that the light traverses a free-space part between two aligned waveguide ends. Displacements are determined with nanometer sensitivity by measuring the associated changes in the resonance frequencies. Miniaturization should increase the sensitivity of the ring-resonator interferometer. Ring geometries that contain an optical circulator can be used to profile reflective samples. (c) 2006 Elsevier B.V. All rights reserved.

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DOI [BibTex]

2007


DOI [BibTex]


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Monte Carlo simulation results for critical Casimir forces

Vasilyev, O., Gambassi, A., Maciolek, A., Dietrich, S.

EPL, 80, 2007 (article)

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DOI [BibTex]

DOI [BibTex]


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Critical Casimir effect in superfluid wetting films

Maciolek, A., Gambassi, A., Dietrich, S.

Physical Review E, 76, 2007 (article)

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DOI [BibTex]

DOI [BibTex]


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Complete wetting of pits and grooves

Tasinkevych, M., Dietrich, S.

European Physical Journal e: Soft Matter, 23(1):117-128, 2007 (article)

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[BibTex]

[BibTex]


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Experimental observation of structural crossover in binary mixtures of colloidal hard spheres

Baumgartl, J., Dullens, R. P. A., Dijkstra, M., Roth, R., Bechinger, C.

Physical Review Letters, 98, 2007 (article)

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DOI [BibTex]

DOI [BibTex]