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2014


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Finite-size scaling study of shear viscosity anomaly at liquid-liquid criticality

Roy, S., Das, S. K.

The Journal of Chemical Physics, 141(23), December 2014 (article)

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DOI [BibTex]

2014


DOI [BibTex]


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Ultracompact Three-Dimensional Tubular Conductivity Microsensors for Ionic and Biosensing Applications

Martinez-Cisneros, C. S., Sanchez, S., Schmidt, O. G., Xi, W.

Nano Letters, pages: 2219-2224, American Chemical Society, Washington, DC, 2014 (article)

Abstract
We present ultracompact three-dimensional tubular structures integrating Au-based electrodes as impedimetric microsensors for the in-flow determination of mono- and divalent ionic species and HeLa cells. The microsensors show an improved performance of 2 orders of magnitude (limit of detection \textequals 0.1 nM for KCl) compared to conventional planar conductivity detection systems integrated in microfluidic platforms and the capability to detect single HeLa cells in flowing phosphate buffered saline. These highly integrated conductivity tubular sensors thus open new possibilities for lab-in-a-tube devices for bioapplications such as biosensing and bioelectronics.

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DOI [BibTex]

DOI [BibTex]


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Catalytic nanomotors for environmental monitoring and water remediation

Soler, L., Sanchez, S.

Nanoscale, 6(13):7175-7182, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Proton-proton collisions at ultra-relativistic energies in quark-gluon string model

Bravina, L., Bleibel, J., Malinina, L., Nilsson, M. S., Zabrodin, E.

EPJ Web of Conferences, 70, EDP Sciences, Les Ulis, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Hydrodynamic interactions induce anomalous diffusion under partial confinement

Bleibel, J., Dominguez, A., Günther, F., Harting, J., Oettel, M.

Soft Matter, 10(17):2945-2948, Royal Society of Chemistry, Cambridge, UK, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Clay nanotube encapsulation for functional biocomposites

Lvov, Y., Aerov, Artem A., Aerov, A. A., Fakhrullin, R.

Advances in Colloid and Interface Science, 207, pages: 189-198, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Wetting phenomena in electrolyte solutions

Ibagon, I.

Universität Stuttgart, Stuttgart, 2014 (phdthesis)

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link (url) [BibTex]

link (url) [BibTex]


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Control of Self-Propelled Microjets Inside a Microchannel With Time-Varying Flow Rates

Magdanz, V., Sanchez, S., Schmidt, O. G., Khalil, I. S. M., Misra, S.

IEEE Transactions on Robotics and Automation, pages: 49-58, IEEE, New York, NY, 2014 (article)

Abstract
We demonstrate the closed-loop motion control of self-propelled microjets inside a fluidic microchannel. The motion control of the microjets is achieved in hydrogen peroxide solution with time-varying flow rates, under the influence of the controlled magnetic fields and the self-propulsion force. Magnetic dipole mo- ment of the microjets is characterized using the U-turn and the rotating field techniques. The characterized magnetic dipole mo- ment has an average of 1.4 $\times$ 10 \textminus 13 A.m 2 at magnetic field, linear velocity, and boundary frequency of 2 mT, 100 $\mu$ m/s, and 25 rad/s, respectively. We implement a closed-loop control system that is based on the characterized magnetic dipole moment of the mi- crojets. This closed-loop control system positions the microjets by directing the magnetic field lines toward the reference position. Experiments are done using a magnetic system and a fluidic mi- crochannel with a width of 500 $\mu$ m. In the absence of a fluid flow, our control system positions the microjets at an average velocity and within an average region-of-convergence (ROC) of 119 $\mu$ m/s and 390 $\mu$ m, respectively. As a representative case, we observe that our control system positions the microjets at an average velocity and within an average ROC of 90 $\mu$ m/s and 600 $\mu$ m and 120 $\mu$ m/s and 600 $\mu$ m when a flow rate of 2.5 $\mu$ l/min is applied against and along the direction of the microjets, respectively. Furthermore, the average velocity and ROC are determined throughout the flow range (0 to 7.5 $\mu$ l/min) to characterize the motion of the microjets inside the microchannel

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DOI [BibTex]

DOI [BibTex]


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Electrostatic interaction between colloidal particles trapped at an electrolyte interface

Majee, A., Bier, M., Dietrich, S.

The Journal of Chemical Physics, 140(16), American Institute of Physics, Woodbury, N.Y., 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Capillary attraction induced collapse of colloidal monolayers at fluid interfaces

Bleibel, J., Dominguez, A., Oettel, M., Dietrich, S.

Soft Matter, 10(23):4091-4109, Royal Society of Chemistry, Cambridge, UK, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Trapping self-propelled micromotors with microfabricated chevron and heart-shaped chips

Restrepo-Pérez, L., Soler, L., Mart\’\inez-Cisneros, C. S., Sanchez, S., Schmidt, O. G.

Lab on a Chip, 14(9):1515-1518, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Order of wetting transitions in electrolyte solutions

Ibagon, I., Bier, M., Dietrich, S.

The Journal of Chemical Physics, 140(17), American Institute of Physics, Woodbury, N.Y., 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Specific salt effects on thermophoresis of charged colloids

Eslahian, K. A., Majee, A., Maskos, M., Würger, A.

Soft Matter, 10(12):1931-1936, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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H5MD: A structured, efficient, and portable file format for molecular data

De Buyl, P., Colberg, P. H., Höfling, F.

Computer Physics Communications, 185(6):1546-1553, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Emergent Long-Range Couplings in Arrays of Fluid Cells

Abraham, D. B., Maciolek, A., Vasilyev, O.

Physical Review Letters, 113(7), American Physical Society, Woodbury, N.Y., 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Effective interaction between a colloid and a soft interface near criticality

Law, A. D., Harnau, L., Tröndle, M., Dietrich, S.

The Journal of Chemical Physics, 141(13), 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Tubular micro- nanorobots: smart design for bio-related applications

Sanchez, S., Wang, X., Solovev, A. A., Soler, L., Magdanz, V., Schmidt, O. G.

In Small-Scale Robotics, 8336, pages: 16-27, Lecture Notes in Computer Science, Springer, Karlsruhe, 2014 (inproceedings)

Abstract
We designed microrobots in the form of autonomous and remotely guided microtubes. One of the challenges at small scales is the effective conversion of energy into mechanical force to overcome the high viscosity of the fluid at low Reynolds numbers. This can be achieved by integration of catalytic nano-materials and processes to decompose chemical fuels. However, up to now, mostly hydrogen peroxide has been employed as a fuel which renders the potential applications in biomedicine and in vivo experiments. Therefore, other sources of energy to achieve motion at the micro- nanoscale are highly sought-after. Here, we present different types of tubular micro- and nanorobots, alternative approaches to toxic fuels and also, steps towards the use of tubular microrobots as micro- and nanotools

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DOI [BibTex]

DOI [BibTex]


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Photoactive rolled-up TiO2 microtubes: fabrition, characterization and applications

Giuducatti, S., Marz, S. M., Soler, L., Madani, A., Jorgensen, M. R., Sanchez, S., Schmidt, O. G.

Journal of Materials Chemistry C: Materials for Optical and Electronic Devices, pages: 5892-5901, Royal Society of Chemistry, London, UK, 2014 (article)

Abstract
Because of its unique properties, titania (TiO2) represents a promising candidate in a wide variety of research fields. In this paper, some of the properties and potential applications of titania within rolled-up nanotechnology are explored. It is shown how the structural and optical properties of rolled titania microtubes can be controlled by properly tuning the microfabrication parameters. The rolling up of titania films on different sacrificial layers and containing different shapes, achieving a control on the diameter of the fabricated titania microtubes, is presented. In order to obtain the more photoactive crystalline form of titania, one during-fabrication and two post-fabrication methods are demonstrated. Interesting applications in the fields of photocatalysis and photonics are suggested: the use of titania rolled-up microtubes as micromotors and optical microresonators is presented.

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DOI [BibTex]

DOI [BibTex]


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How ions in solution can change the sign of the critical Casimir potential

Pousaneh, F., Ciach, A., Maciolek, A.

Soft Matter, 10(3):470-483, Royal Society of Chemistry, Cambridge, UK, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Critical Casimir interactions around the consolute point of a binary solvent

Mohry, T. F., Kondrat, S., Maciolek, A., Dietrich, S.

Soft Matter, 10(30):5510-5522, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Collapse and reversibility of the superhydrophobic state on nanotextured surfaces

Checco, A., Ocko, B. M., Rahman, A., Black, C. T., Tasinkevych, M., Giacomello, A., Dietrich, S.

Physical Review Letters, 112(21), American Physical Society., Woodbury, N.Y., etc., 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Density functional theory of electrowetting

Bier, M., Ibagon, I.

Physical Review E, 89(4), American Physical Society, Melville, NY, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Alignment of cylindrical colloids near chemically patterned substrates induced by critical Casimir torques

Labbe-Laurent, M., Tröndle, M., Harnau, L., Dietrich, S.

Soft Matter, 10(13):2270-2291, Royal Society of Chemistry, Cambridge, UK, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Heat transfer between anisotropic nanoparticles: Enhancement and switching

Incardone, R., Emig, T., Krüger, M.

Europhysics Letters, 106(4), 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Rolled-up Functionalized Nanomembranes as Three-Dimensional Cavities for Single Cell Studies

Xi, W., Schmidt, C., Sanchez, S., Gracias, D., Carazo-Salas, R., Jackson, S., Schmidt, O. G.

Nano Letters, 14(8):4197-4204, American Chemical Society, Washington, DC, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Cosmology in a petri dish? Simulation of collective dynamics of colloids at fluid interfaces

Bleibel, J.

In EPJ Web of Conferences, 70, EDP Sciences, 2014 (inproceedings)

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DOI [BibTex]


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Dispersions of ellipsoidal particles in a nematic liquid crystal

Tasinkevych, M., Mondiot, F., Mondain-Monval, O., Loudet, J. C.

Soft Matter, 10(12):2047-2058, Royal Society of Chemistry, Cambridge, UK, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Critical Casimir interactions between spherical particles in the presence of bulk ordering fields

Vasilyev, O.

Physical Review E, 90, American Physical Society, Melville, NY, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Towards Template-Assisted Assembly of Nematic Colloids

Silvestre, N. M., Liu, Q., Senyuk, B., Smalyukh, I. I., Tasinkevych, M.

Physical Review Letters, 112(22), American Physical Society, Woodbury, N.Y., 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Biocompatible, accurate, and fully autonomous: a sperm-driven micro-bio-robot

Khalil, I. S. M., Magdanz, V., Sanchez, S., Schmidt, O. G., Misra, S.

Journal of Micro-Bio Robotics, 9(3-4):79-86, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Stimuli-Responsive Microjets with Reconfigurable Shape

Magdanz, V., Stoychev, G., Ionov, L., Sanchez, S., Schmidt, O. G.

Angewandte Chemie International Edition : a journal of the Gesellschaft Deutscher Chemiker, 53, pages: 2673-2677, Wiley-VCH, Weinheim, 2014 (article)

Abstract
Flexible thermoresponsive polymeric microjets are formed by the self-folding of polymeric layers containing a thin Pt film used as catalyst for self-propulsion in solutions containing hydrogen peroxide. The flexible microjets can reversibly fold and unfold in an accurate manner by applying changes in temperature to the solution in which they are immersed. This effect allows microjets to rapidly start and stop multiple times by controlling the radius of curvature of the microjet. This work opens many possibilities in the field of artificial nanodevices, for fundamental studies on self-propulsion at the microscale, and also for bio related applications.

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DOI [BibTex]

DOI [BibTex]


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Effect of surfactants on the performance of tubular and spherical micromotors –a comparative study

Simmchen, J., Magdanz, V., Sanchez, S., Chokmaviroj, S., Ruiz-Molina, D., Baeza, A., Schmidt, O. G.

RSC Advances, 4(39):20334-20340, Royal Society of Chemistry, Cambridge, UK, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Rolled-up Functionalized Nanomembranes as Three-Dimensional Cavities for Single Cell Studies

Xi, W., Schmidt, C. K., Sanchez, S., Gracias, D. H., Carazo-Salas, R. E., Jackson, S. P., Schmidt, O. G.

Nano Letters, 14(2):4197-4204, American Chemical Society, Washington, DC, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Wireless Magnetic-Based Closed-Loop Control of Self-Propelled Microjets

Khalil, I. S. M., Magdanz, V., Sanchez, S., Schmidt, O. G., Misra, S.

PLoS One, 9(2), Public Library of Science, San Francisco, CA, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Trajectory to trajectory fluctuations in first-passage phenomena in bounded domains

Mattos, Thiago G., Mejia-Monasterio, Carlos, Metzler, Ralf, Oshanin, Gleb, Schehr, G.

In First-passage phenomena and their applications, pages: 203-225, World Scientific Publishing, Singapore, 2014 (incollection)

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DOI [BibTex]

DOI [BibTex]


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Topological Polymer Dispersed Liquid Crystals with Bulk Nematic Defect Lines Pinned to Handlebody Surfaces

Campbell, M. G., Tasinkevych, M., Smalyukh, I. I.

Physical Review Letters, 112(19), American Physical Society, Woodbury, N.Y., 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Periodic dynamics, localization metastability, and elastic interaction of colloidal particles with confining surfaces and helicoidal structure of cholesteric liquid crystals

Varney, M. C. M., Zhang, QX, Tasinkevych, M., Silvestre, N. M., Bertness, K. A., Smalyukh, I. I.

Physical Review E, 90(6), American Physical Society, Melville, NY, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Dynamik einer fast-kritischen binären Flüssigkeit in zwei Dimensionen

Maisch, J.

Universität Stuttgart, Stuttgart, 2014 (mastersthesis)

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[BibTex]

[BibTex]


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Brownsche Bewegung schraubenförmiger Nanoteilchen

Gehrmann, C.

Universität Stuttgart, Stuttgart, 2014 (mastersthesis)

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[BibTex]

[BibTex]


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Dual Execution of Optimized Contact Interaction Trajectories

Toussaint, M., Ratliff, N., Bohg, J., Righetti, L., Englert, P., Schaal, S.

In 2014 IEEE/RSJ Conference on Intelligent Robots and Systems, pages: 47-54, IEEE, Chicago, USA, 2014 (inproceedings)

Abstract
Efficient manipulation requires contact to reduce uncertainty. The manipulation literature refers to this as funneling: a methodology for increasing reliability and robustness by leveraging haptic feedback and control of environmental interaction. However, there is a fundamental gap between traditional approaches to trajectory optimization and this concept of robustness by funneling: traditional trajectory optimizers do not discover force feedback strategies. From a POMDP perspective, these behaviors could be regarded as explicit observation actions planned to sufficiently reduce uncertainty thereby enabling a task. While we are sympathetic to the full POMDP view, solving full continuous-space POMDPs in high-dimensions is hard. In this paper, we propose an alternative approach in which trajectory optimization objectives are augmented with new terms that reward uncertainty reduction through contacts, explicitly promoting funneling. This augmentation shifts the responsibility of robustness toward the actual execution of the optimized trajectories. Directly tracing trajectories through configuration space would lose all robustness-dual execution achieves robustness by devising force controllers to reproduce the temporal interaction profile encoded in the dual solution of the optimization problem. This work introduces dual execution in depth and analyze its performance through robustness experiments in both simulation and on a real-world robotic platform.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Splitting, linking, knotting, and solitonic escape of topological defects in nematic drops with handles

Tasinkevych, M., Campbell, M. G., Smalyukh, I. I.

Proceedings of the National Academy of Sciences of the United States of America, 111(46):16268-16273, National Academy of Sciences, 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Electromagnetic self-propulsion for small objects in the near field

Müller, Boris

Universität Stuttgart, Stuttgart, 2014 (mastersthesis)

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[BibTex]

[BibTex]


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An autonomous manipulation system based on force control and optimization

Righetti, L., Kalakrishnan, M., Pastor, P., Binney, J., Kelly, J., Voorhies, R. C., Sukhatme, G. S., Schaal, S.

Autonomous Robots, 36(1-2):11-30, January 2014 (article)

Abstract
In this paper we present an architecture for autonomous manipulation. Our approach is based on the belief that contact interactions during manipulation should be exploited to improve dexterity and that optimizing motion plans is useful to create more robust and repeatable manipulation behaviors. We therefore propose an architecture where state of the art force/torque control and optimization-based motion planning are the core components of the system. We give a detailed description of the modules that constitute the complete system and discuss the challenges inherent to creating such a system. We present experimental results for several grasping and manipulation tasks to demonstrate the performance and robustness of our approach.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Thermal and structural properties of dense ionic liquids

Bartsch, Hendrik

Universität Stuttgart, Stuttgart, 2014 (mastersthesis)

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[BibTex]

[BibTex]


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Lateral critical Casimir force in 2D Ising strip with inhomogeneous walls

Nowakowski, Piotr, Napiorkowski, Marek

The Journal of Chemical Physics, 141(6), 2014 (article)

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DOI [BibTex]

DOI [BibTex]


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Learning of grasp selection based on shape-templates

Herzog, A., Pastor, P., Kalakrishnan, M., Righetti, L., Bohg, J., Asfour, T., Schaal, S.

Autonomous Robots, 36(1-2):51-65, January 2014 (article)

Abstract
The ability to grasp unknown objects still remains an unsolved problem in the robotics community. One of the challenges is to choose an appropriate grasp configuration, i.e., the 6D pose of the hand relative to the object and its finger configuration. In this paper, we introduce an algorithm that is based on the assumption that similarly shaped objects can be grasped in a similar way. It is able to synthesize good grasp poses for unknown objects by finding the best matching object shape templates associated with previously demonstrated grasps. The grasp selection algorithm is able to improve over time by using the information of previous grasp attempts to adapt the ranking of the templates to new situations. We tested our approach on two different platforms, the Willow Garage PR2 and the Barrett WAM robot, which have very different hand kinematics. Furthermore, we compared our algorithm with other grasp planners and demonstrated its superior performance. The results presented in this paper show that the algorithm is able to find good grasp configurations for a large set of unknown objects from a relatively small set of demonstrations, and does improve its performance over time.

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link (url) DOI [BibTex]


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Balancing experiments on a torque-controlled humanoid with hierarchical inverse dynamics

Herzog, A., Righetti, L., Grimminger, F., Pastor, P., Schaal, S.

In 2014 IEEE/RSJ Conference on Intelligent Robots and Systems, pages: 981-988, IEEE, Chicago, USA, 2014 (inproceedings)

Abstract
Recently several hierarchical inverse dynamics controllers based on cascades of quadratic programs have been proposed for application on torque controlled robots. They have important theoretical benefits but have never been implemented on a torque controlled robot where model inaccuracies and real-time computation requirements can be problematic. In this contribution we present an experimental evaluation of these algorithms in the context of balance control for a humanoid robot. The presented experiments demonstrate the applicability of the approach under real robot conditions (i.e. model uncertainty, estimation errors, etc). We propose a simplification of the optimization problem that allows us to decrease computation time enough to implement it in a fast torque control loop. We implement a momentum-based balance controller which shows robust performance in face of unknown disturbances, even when the robot is standing on only one foot. In a second experiment, a tracking task is evaluated to demonstrate the performance of the controller with more complicated hierarchies. Our results show that hierarchical inverse dynamics controllers can be used for feedback control of humanoid robots and that momentum-based balance control can be efficiently implemented on a real robot.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


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Full Dynamics LQR Control of a Humanoid Robot: An Experimental Study on Balancing and Squatting

Mason, S., Righetti, L., Schaal, S.

In 2014 IEEE-RAS International Conference on Humanoid Robots, pages: 374-379, IEEE, Madrid, Spain, 2014 (inproceedings)

Abstract
Humanoid robots operating in human environments require whole-body controllers that can offer precise tracking and well-defined disturbance rejection behavior. In this contribution, we propose an experimental evaluation of a linear quadratic regulator (LQR) using a linearization of the full robot dynamics together with the contact constraints. The advantage of the controller is that it explicitly takes into account the coupling between the different joints to create optimal feedback controllers for whole-body control. We also propose a method to explicitly regulate other tasks of interest, such as the regulation of the center of mass of the robot or its angular momentum. In order to evaluate the performance of linear optimal control designs in a real-world scenario (model uncertainty, sensor noise, imperfect state estimation, etc), we test the controllers in a variety of tracking and balancing experiments on a torque controlled humanoid (e.g. balancing, split plane balancing, squatting, pushes while squatting, and balancing on a wheeled platform). The proposed control framework shows a reliable push recovery behavior competitive with more sophisticated balance controllers, rejecting impulses up to 11.7 Ns with peak forces of 650 N, with the added advantage of great computational simplicity. Furthermore, the controller is able to track squatting trajectories up to 1 Hz without relinearization, suggesting that the linearized dynamics is sufficient for significant ranges of motion.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]