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2006


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Chiral molecules split light: Reflection and refraction in a chiral liquid

Ghosh, A., Fischer, P.

PHYSICAL REVIEW LETTERS, 97(17), 2006, Featured highlight ‘Fundamental optical physics: Refraction’ Nature Photonics, Nov. 2006. (article)

Abstract
A light beam changes direction as it enters a liquid at an angle from another medium, such as air. Should the liquid contain molecules that lack mirror symmetry, then it has been predicted by Fresnel that the light beam will not only change direction, but will actually split into two separate beams with a small difference in the respective angles of refraction. Here we report the observation of this phenomenon. We also demonstrate that the angle of reflection does not equal the angle of incidence in a chiral medium. Unlike conventional optical rotation, which depends on the path-length through the sample, the reported reflection and refraction phenomena arise within a few wavelengths at the interface and thereby suggest a new approach to polarimetry that can be used in microfluidic volumes.

Featured highlight ‘Fundamental optical physics: Refraction’ Nature Photonics, Nov. 2006.

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DOI [BibTex]

2006


DOI [BibTex]


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Direct chiral discrimination in NMR spectroscopy

Buckingham, A., Fischer, P.

CHEMICAL PHYSICS, 324(1):111-116, 2006 (article)

Abstract
Conventional nuclear magnetic resonance spectroscopy is unable to distinguish between the two mirror-image forms (enantiomers) of a chiral molecule. This is because the NMR spectrum is determined by the chemical shifts and spin-spin coupling constants which - in the absence of a chiral solvent - are identical for the two enantiomers. We discuss how chirality may nevertheless be directly detected in liquid-state NMR spectroscopy: In a chiral molecule, the rotating nuclear magnetic moment induces an electric dipole moment in the direction perpendicular to itself and to the permanent magnetic field of the spectrometer. We present computations of the precessing electric polarization following a pi/2 pulse. Our estimates indicate that the electric polarization should be detectable in favourable cases. We also predict that application of an electrostatic field induces a chirally sensitive magnetization oscillating in the direction of the permanent magnetic field. We show that the electric-field-perturbed chemical shift tensor, the nuclear magnetic shielding polarizability, underlies these chiral NMR effects. (c) 2005 Elsevier B.V. All rights reserved.

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DOI [BibTex]

DOI [BibTex]


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An ultrasonic standing-wave-actuated nano-positioning walking robot: piezoelectric-metal composite beam modeling

Son, K. J., Kartik, V., Wickert, J. A., Sitti, M.

Journal of vibration and control, 12(12):1293-1309, Sage Publications, 2006 (article)

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[BibTex]

[BibTex]


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Ring-resonator-based frequency-domain optical activity measurements of a chiral liquid

Vollmer, F., Fischer, P.

OPTICS LETTERS, 31(4):453-455, 2006 (article)

Abstract
Chiral liquids rotate the plane of polarization of linearly polarized light and are therefore optically active. Here we show that optical rotation can be observed in the frequency domain. A chiral liquid introduced in a fiber-loop ring resonator that supports left and right circularly polarized modes gives rise to relative frequency shifts that are a direct measure of the liquid's circular birefringence and hence of its optical activity. The effect is in principle not diminished if the circumference of the ring is reduced. The technique is similarly applicable to refractive index and linear birefringence measurements. (c) 2006 Optical Society of America.

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DOI [BibTex]


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Sign of the refractive index in a gain medium with negative permittivity and permeability

Chen, Y., Fischer, P., Wise, F.

JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 23(1):45-50, 2006 (article)

Abstract
We show how the sign of the refractive index in any medium may be derived using a rigorous analysis based on Einstein causality. In particular, we consider left-handed materials, i.e., media that have negative permittivities and permeabilities at the frequency of interest. We find that the consideration of gain in such media can give rise to a positive refractive index. (c) 2006 Optical Society of America.

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DOI [BibTex]

DOI [BibTex]


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IEEE TRANSACTIONS ON ROBOTICS

VOLZ, RICHARD A, TARN, TJ, MACIEJEWSKI, ANTHONY A, LEE, SUKHAN, BICCHI, ANTONIO, DE LUCA, ALESSANDRO, LUH, PETER B, TAYLOR, RUSSELL H, BEKEY, GEORGE A, ARAI, HIROHIKO, others

2006 (article)

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[BibTex]

[BibTex]


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Design methodology for biomimetic propulsion of miniature swimming robots

Behkam, B., Sitti, M.

Trans.-ASME Journal of Dynamic Systems Measurement and Control, 128(1):36, ASME, 2006 (article)

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Project Page [BibTex]

Project Page [BibTex]


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Augmented reality user interface for an atomic force microscope-based nanorobotic system

Vogl, W., Ma, B. K., Sitti, M.

IEEE transactions on nanotechnology, 5(4):397-406, IEEE, 2006 (article)

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[BibTex]

[BibTex]


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Friction enhancement via micro-patterned wet elastomer adhesives on small intestinal surfaces

Kwon, J., Cheung, E., Park, S., Sitti, M.

Biomedical Materials, 1(4):216, IOP Publishing, 2006 (article)

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[BibTex]

[BibTex]


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Influence of the substrate on the magnetic anisotropy of monatomic wires

Komelj, M., Steiauf, D., Fähnle, M.

{Physical Review B}, 73, 2006 (article)

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[BibTex]


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Mechanical properties of single-walled carbon nanotubes based on higher order Cauchy-Born rule

Guo, X., Wang, J. B., Zhang, H. W.

{International Journal of Solids and Structures}, 43, pages: 1276-1290, 2006 (article)

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[BibTex]

[BibTex]


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Vanishing Fe 3d orbital moments in single-crystalline magnetite

Goering, E., Gold, S., Lafkioti, M., Schütz, G.

{Europhysics Letters}, 73(1):97-103, 2006 (article)

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[BibTex]

[BibTex]


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Enhancement of L10 phase formation in FePt nanoparticles by nitrogenization

Dmitrieva, O., Acet, M., Dumpich, G., Kästner, J., Antoniak, C., Farle, M., Fauth, K.

{Journal of Physics D}, 39, pages: 4741-4745, 2006 (article)

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[BibTex]


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Structure of historical brass tonques and shallots from baroque organs

Baretzky, B., Friesel, M., Petelin, A., Mazilkin, A., Straumal, B.

{Defect and Diffusion Forum}, 249, pages: 275-280, 2006 (article)

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[BibTex]


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Three-dimensional modeling of mechanical forces in the extra-cellular matrix during epithelial lumen formation

Zeng, D., Ferrari, A., Ulmer, J., Veligodskiy, A., Fischer, P., Spatz, J. P., Ventikos, Y., Poulikakos, D., Kroschewski, R.

{Biophysical Journal}, 90(12):4380-4391, 2006 (article)

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[BibTex]


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Dynamic Hebbian learning in adaptive frequency oscillators

Righetti, L., Buchli, J., Ijspeert, A.

Physica D: Nonlinear Phenomena, 216(2):269-281, 2006 (article)

Abstract
Nonlinear oscillators are widely used in biology, physics and engineering for modeling and control. They are interesting because of their synchronization properties when coupled to other dynamical systems. In this paper, we propose a learning rule for oscillators which adapts their frequency to the frequency of any periodic or pseudo-periodic input signal. Learning is done in a dynamic way: it is part of the dynamical system and not an offline process. An interesting property of our model is that it is easily generalizable to a large class of oscillators, from phase oscillators to relaxation oscillators and strange attractors with a generic learning rule. One major feature of our learning rule is that the oscillators constructed can adapt their frequency without any signal processing or the need to specify a time window or similar free parameters. All the processing is embedded in the dynamics of the adaptive oscillator. The convergence of the learning is proved for the Hopf oscillator, then numerical experiments are carried out to explore the learning capabilities of the system. Finally, we generalize the learning rule to non-harmonic oscillators like relaxation oscillators and strange attractors.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Bayesian population decoding of motor cortical activity using a Kalman filter

Wu, W., Gao, Y., Bienenstock, E., Donoghue, J. P., Black, M. J.

Neural Computation, 18(1):80-118, 2006 (article)

Abstract
Effective neural motor prostheses require a method for decoding neural activity representing desired movement. In particular, the accurate reconstruction of a continuous motion signal is necessary for the control of devices such as computer cursors, robots, or a patient's own paralyzed limbs. For such applications, we developed a real-time system that uses Bayesian inference techniques to estimate hand motion from the firing rates of multiple neurons. In this study, we used recordings that were previously made in the arm area of primary motor cortex in awake behaving monkeys using a chronically implanted multielectrode microarray. Bayesian inference involves computing the posterior probability of the hand motion conditioned on a sequence of observed firing rates; this is formulated in terms of the product of a likelihood and a prior. The likelihood term models the probability of firing rates given a particular hand motion. We found that a linear gaussian model could be used to approximate this likelihood and could be readily learned from a small amount of training data. The prior term defines a probabilistic model of hand kinematics and was also taken to be a linear gaussian model. Decoding was performed using a Kalman filter, which gives an efficient recursive method for Bayesian inference when the likelihood and prior are linear and gaussian. In off-line experiments, the Kalman filter reconstructions of hand trajectory were more accurate than previously reported results. The resulting decoding algorithm provides a principled probabilistic model of motor-cortical coding, decodes hand motion in real time, provides an estimate of uncertainty, and is straightforward to implement. Additionally the formulation unifies and extends previous models of neural coding while providing insights into the motor-cortical code.

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pdf preprint pdf from publisher abstract [BibTex]

pdf preprint pdf from publisher abstract [BibTex]


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Compliant and low-cost humidity nanosensors using nanoporous polymer membranes

Yang, B., Aksak, B., Lin, Q., Sitti, M.

Sensors and Actuators B: Chemical, 114(1):254-262, Elsevier, 2006 (article)

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[BibTex]

[BibTex]


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Task-based and stable telenanomanipulation in a nanoscale virtual environment

Kim, S., Sitti, M.

IEEE Transactions on automation science and engineering, 3(3):240-247, IEEE, 2006 (article)

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[BibTex]

[BibTex]


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Drawing suspended polymer micro-/nanofibers using glass micropipettes

Nain, A. S., Wong, J. C., Amon, C., Sitti, M.

Applied Physics Letters, 89(18):183105, AIP, 2006 (article)

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[BibTex]

[BibTex]


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Theoretical justification of ground-state moment analysis of magnetic dichroic x-ray absorption spectra for 3d transition metals

Dörfler, F., Fähnle, M.

{Physical Review B}, 74, 2006 (article)

Abstract
{(6 pages)}

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Vortex dynamics in coupled ferromagnetic multilayer structures

Chou, K., Puzic, A., Stoll, H., Schütz, G., Van Waeyenberge, B., Tyliszczak, T., Rott, K., Reiss, G., Brückl, H., Neudecker, I., Weiss, D., Back, C. H.

{Journal of Applied Physics}, 99, 2006 (article)

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[BibTex]

[BibTex]


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Electrical transport, magnetic and thermal properties of icosahedral Al-Pd-Mn quasicrystals

Poddar, A., Das, S., Plachke, D., Carstanjen, H.D.

{Journal of Magnetism and Magnetic Materials}, 300(2):263-272, 2006 (article)

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[BibTex]

[BibTex]


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Aqueous solution deposition of indium hydroxide and indium oxide columnar type thin films

Qiu, Y., Gerstel, P., Jiang, L., Lipowsky, P., Pitta Bauermann, L., Bill, J.

{International Journal of Materials Research}, 97(6):808-811, 2006 (article)

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[BibTex]

[BibTex]


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Enhanced orbital magnetism in Fe50Pt50 nanoparticles

Antoniak, C., Lindner, J., Spasova, M., Sudfeld, D., Acet, M., Farle, M., Fauth, K., Wiedwald, U., Boyen, H.-G., Ziemann, P., Wilhelm, F., Rogalev, A., Sun, S.

{Physical Review Letters}, 97, 2006 (article)

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[BibTex]

[BibTex]


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Biologically inspired polymer microfibers with spatulate tips as repeatable fibrillar adhesives

Kim, S., Sitti, M.

Applied Physics Letters, 89(26):261911-261911, AIP, 2006 (article)

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Project Page [BibTex]


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Converting polycrystals into single crystals - Selective grain growth by high-energy ion bombardment

Olliges, S., Gruber, P., Bardill, A., Ehrler, D., Carstanjen, H. D., Spolenak, R.

{Acta Materialia}, 54(20):5393-5399, 2006 (article)

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[BibTex]

[BibTex]


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Topological k-space refinement of the configurational energy of alloys

Shchyglo, O., Bugaev, V.N., Drautz, R., Udyanskyy, A., Reichert, H., Dosch, H.

{Physical Review B}, 72, 2006 (article)

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[BibTex]

[BibTex]


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Synthesis of MgB2 films in Mg vapour flow and their characterization

Matveev, A. T., Albrecht, J., Konuma, M., Christiani, G., Krockenberger, Y., Starke, U., Schütz, G., Habermeier, H.

{Superconductor Science and Technology}, 19, pages: 299-305, 2006 (article)

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[BibTex]

[BibTex]


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Analysis of switching times of inhomogeneous magnetization processes in thin platelets

Goll, D., Schütz, G., Kronmüller, H.

{Physica B: Condensed Matter}, 372(1-2):273-276, 2006 (article)

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[BibTex]

[BibTex]


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The initial oxidation of magnesium: an in situ study with XPS, HERDA and ellipsometry.

Kurth, M., Graat, P. C. J., Carstanjen, H. D., Mittemeijer, E. J.

{Surface and Interface Analysis}, 38, pages: 931-940, 2006 (article)

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[BibTex]

[BibTex]


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Temperature influence of the faceting of \sum3 and \sum9 grain boundaries in Cu

Straumal, B. B., Polyakov, S. A., Mittemeijer, E. J.

{Acta Materialia}, 54, pages: 167-172, 2006 (article)

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[BibTex]

[BibTex]


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Coercivity of 2 : 17 based permanent magnets

Kronmüller, H., Goll, D.

{Journal of the Iron and Steel Research International}, 13(Suppl. 1):39-47, 2006 (article)

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[BibTex]

[BibTex]


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Hydrogen adsorption in a nickel based coordination polymer with open metal sites in the cylindrical cavities of the desolvated framework

Dietzel, P. D. C., Panella, B., Hirscher, M., Blom, R., Fjellvag, H.

{Chemical Communications}, [2006], pages: 959-961, 2006 (article)

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DOI [BibTex]

DOI [BibTex]


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Magnetic ground states and the role of vortices in ferromagnetic hollow nanospheres

Goll, D., Macke, S., Berkowitz, A., Bertram, H. N.

{Physica B: Condensed Matter}, 372(1-2):282-285, 2006 (article)

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[BibTex]

[BibTex]


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Die Effektivität von schriftlichen und graphischen Warnhinweisen auf Zigarettenschachteln

Petersen, L., Lieder, F.

Zeitschrift f{\"u}r Sozialpsychologie, 37(4):245-258, Verlag Hans Huber, 2006 (article)

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[BibTex]

[BibTex]


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Engineering Entrainment and Adaptation in Limit Cycle Systems – From biological inspiration to applications in robotics

Buchli, J., Righetti, L., Ijspeert, A.

Biological Cybernetics, 95(6):645-664, December 2006 (article)

Abstract
Periodic behavior is key to life and is observed in multiple instances and at multiple time scales in our metabolism, our natural environment, and our engineered environment. A natural way of modeling or generating periodic behavior is done by using oscillators, i.e., dynamical systems that exhibit limit cycle behavior. While there is extensive literature on methods to analyze such dynamical systems, much less work has been done on methods to synthesize an oscillator to exhibit some specific desired characteristics. The goal of this article is twofold: (1) to provide a framework for characterizing and designing oscillators and (2) to review how classes of well-known oscillators can be understood and related to this framework. The basis of the framework is to characterize oscillators in terms of their fundamental temporal and spatial behavior and in terms of properties that these two behaviors can be designed to exhibit. This focus on fundamental properties is important because it allows us to systematically compare a large variety of oscillators that might at first sight appear very different from each other. We identify several specifications that are useful for design, such as frequency-locking behavior, phase-locking behavior, and specific output signal shape. We also identify two classes of design methods by which these specifications can be met, namely offline methods and online methods. By relating these specifications to our framework and by presenting several examples of how oscillators have been designed in the literature, this article provides a useful methodology and toolbox for designing oscillators for a wide range of purposes. In particular, the focus on synthesis of limit cycle dynamical systems should be useful both for engineering and for computational modeling of physical or biological phenomena.

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link (url) DOI [BibTex]


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Two-dimensional vision-based autonomous microparticle manipulation using a nanoprobe

Pawashe, C., Sitti, M.

Journal of Micromechatronics, 3(3):285-306, Brill, 2006 (article)

pi

[BibTex]

[BibTex]


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Pulsed-field-gradient NMR study of hydrogen diffusivity in random b.c.c. alloys VyTa1-y

Grinberg, F., Majer, G., Skripov, A. N.

{Journal of Alloys and Compounds}, 425(1-2):24-27, 2006 (article)

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[BibTex]

[BibTex]


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Breathing Fermi surface model for noncollinear magnetization: a generalization of the Gilbert equation

Fähnle, M., Steiauf, D.

{Physical Review B}, 73, 2006 (article)

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[BibTex]


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Reconstruction of brass for tongues and shallots from baroque organs

Baretzky, B., Friesel, M., Petelin, A., Shotanov, A., Straumal, B.

{Defect and Diffusion Forum}, 258-260, pages: 397-402, 2006 (article)

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DOI [BibTex]

DOI [BibTex]


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Softening of nanostructured Al-Zn and Al-Mg alloys after severe plastic deformation

Mazilkin, A.A., Straumal, B.B., Rabkin, E., Baretzky, B., Enders, S., Protasova, S.G., Kogtenkova, O.A., Valiev, R.Z.

{Acta Materialia}, 54, pages: 3933-3939, 2006 (article)

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[BibTex]

[BibTex]


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Comment on "Spin and orbital magnetic moments of Fe3O4

Goering, E., Lafkioti, M., Gold, S.

{Physical Review Letters}, 96(3), 2006 (article)

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[BibTex]

[BibTex]


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Effect of magnetic interaction on thermally activated reversal in a magnet with a distribution of energy barriers

Zhang, H. W., Zhang, S., Sun, J. R., Shen, B. G., Goll, D., Kronmüller, H.

{Journal of the Iron and Steel Research International}, 13(Suppl. 1):60-66, 2006 (article)

mms

[BibTex]

[BibTex]


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A biomimetic climbing robot based on the gecko

Menon, C., Sitti, M.

Journal of Bionic Engineering, 3(3):115-125, 2006 (article)

pi

[BibTex]

[BibTex]


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Proximal probes based nanorobotic drawing of polymer micro/nanofibers

Nain, A. S., Amon, C., Sitti, M.

IEEE transactions on nanotechnology, 5(5):499-510, IEEE, 2006 (article)

pi

[BibTex]

[BibTex]


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Rocking Stamper and Jumping Snake from a Dynamical System Approach to Artificial Life

Der, R., Hesse, F., Martius, G.

Adaptive Behavior, 14(2):105-115, 2006 (article)

Abstract
Dynamical systems offer intriguing possibilities as a substrate for the generation of behavior because of their rich behavioral complexity. However this complexity together with the largely covert relation between the parameters and the behavior of the agent is also the main hindrance in the goal-oriented design of a behavior system. This paper presents a general approach to the self-regulation of dynamical systems so that the design problem is circumvented. We consider the controller (a neural net work) as the mediator for changes in the sensor values over time and define a dynamics for the parameters of the controller by maximizing the dynamical complexity of the sensorimotor loop under the condition that the consequences of the actions taken are still predictable. This very general principle is given a concrete mathematical formulation and is implemented in an extremely robust and versatile algorithm for the parameter dynamics of the controller. We consider two different applications, a mechanical device called the rocking stamper and the ODE simulations of a "snake" with five degrees of freedom. In these and many other examples studied we observed various behavior modes of high dynamical complexity.

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DOI [BibTex]

DOI [BibTex]


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Magnetic vortex core reversal by excitation with short bursts of an alternating field

Van Waeyenberge, B., Puzic, A., Stoll, H., Chou, K. W., Tyliszczak, T., Hertel, R., Fähnle, M., Bruckl, H., Rott, K., Reiss, G., Neudecker, I., Weiss, D., Back, C. H., Schütz, G.

{Nature}, 444(7118):461-464, 2006 (article)

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[BibTex]

[BibTex]