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2020


Interface-mediated spontaneous symmetry breaking and mutual communication between drops containing chemically active particles
Interface-mediated spontaneous symmetry breaking and mutual communication between drops containing chemically active particles

Singh, D., Domínguez, A., Choudhury, U., Kottapalli, S., Popescu, M., Dietrich, S., Fischer, P.

Nature Communications, 11(2210), May 2020 (article)

Abstract
Symmetry breaking and the emergence of self-organized patterns is the hallmark of com- plexity. Here, we demonstrate that a sessile drop, containing titania powder particles with negligible self-propulsion, exhibits a transition to collective motion leading to self-organized flow patterns. This phenomenology emerges through a novel mechanism involving the interplay between the chemical activity of the photocatalytic particles, which induces Mar- angoni stresses at the liquid–liquid interface, and the geometrical confinement provided by the drop. The response of the interface to the chemical activity of the particles is the source of a significantly amplified hydrodynamic flow within the drop, which moves the particles. Furthermore, in ensembles of such active drops long-ranged ordering of the flow patterns within the drops is observed. We show that the ordering is dictated by a chemical com- munication between drops, i.e., an alignment of the flow patterns is induced by the gradients of the chemicals emanating from the active particles, rather than by hydrodynamic interactions.

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link (url) DOI [BibTex]


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Wetting transitions on soft substrates

Napiorkowski, M., Schimmele, L., Dietrich, S.

{EPL}, 129(1), EDP Science, Les-Ulis, 2020 (article)

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DOI [BibTex]

DOI [BibTex]


Effective Viscous Damping Enables Morphological Computation in Legged Locomotion
Effective Viscous Damping Enables Morphological Computation in Legged Locomotion

Mo, A., Izzi, F., Haeufle, D. F. B., Badri-Spröwitz, A.

2020 (article) In revision

Abstract
Muscle models and animal observations suggest that physical damping is beneficial for stabilization. Still, only a few implementations of mechanical damping exist in compliant robotic legged locomotion. It remains unclear how physical damping can be exploited for locomotion tasks, while its advantages as sensor-free, adaptive force- and negative work-producing actuators are promising. In a simplified numerical leg model, we studied the energy dissipation from viscous and Coulomb damping during vertical drops with ground-level perturbations. A parallel spring-damper is engaged between touch-down and mid-stance, and its damper auto-disengages during mid-stance and takeoff. Our simulations indicate that an adjustable and viscous damper is desired. In hardware we explored effective viscous damping and adjustability and quantified the dissipated energy. We tested two mechanical, leg-mounted damping mechanisms; a commercial hydraulic damper, and a custom-made pneumatic damper. The pneumatic damper exploits a rolling diaphragm with an adjustable orifice, minimizing Coulomb damping effects while permitting adjustable resistance. Experimental results show that the leg-mounted, hydraulic damper exhibits the most effective viscous damping. Adjusting the orifice setting did not result in substantial changes of dissipated energy per drop, unlike adjusting damping parameters in the numerical model. Consequently, we also emphasize the importance of characterizing physical dampers during real legged impacts to evaluate their effectiveness for compliant legged locomotion.

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link (url) [BibTex]

link (url) [BibTex]


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Blessing and Curse: How a Supercapacitor Large Capacitance Causes its Slow Charging

Lian, C., Janssen, M., Liu, H., van Roij, R.

Physical Review Letters, 124(7), American Physical Society, Woodbury, N.Y., 2020 (article)

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DOI [BibTex]

DOI [BibTex]


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Fractal-seaweeds type functionalization of graphene

Amsharov, K., Sharapa, D. I., Vasilyev, O. A., Martin, O., Hauke, F., Görling, A., Soni, H., Hirsch, A.

Carbon, 158, pages: 435-448, Elsevier, Amsterdam, 2020 (article)

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DOI [BibTex]

DOI [BibTex]


Trunk pitch oscillations for energy trade-offs in bipedal running birds and robots
Trunk pitch oscillations for energy trade-offs in bipedal running birds and robots

Drama, Ö., Badri-Spröwitz, A.

Bioinspiration & Biomimetics, 2020 (article)

Abstract
Bipedal animals have diverse morphologies and advanced locomotion abilities. Terrestrial birds, in particular, display agile, efficient, and robust running motion, in which they exploit the interplay between the body segment masses and moment of inertias. On the other hand, most legged robots are not able to generate such versatile and energy-efficient motion and often disregard trunk movements as a means to enhance their locomotion capabilities. Recent research investigated how trunk motions affect the gait characteristics of humans, but there is a lack of analysis across different bipedal morphologies. To address this issue, we analyze avian running based on a spring-loaded inverted pendulum model with a pronograde (horizontal) trunk. We use a virtual point based control scheme and modify the alignment of the ground reaction forces to assess how our control strategy influences the trunk pitch oscillations and energetics of the locomotion. We derive three potential key strategies to leverage trunk pitch motions that minimize either the energy fluctuations of the center of mass or the work performed by the hip and leg. We suggest how these strategies could be used in legged robotics.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


Postural Stability in Human Running with Step-down Perturbations: An Experimental and Numerical Study
Postural Stability in Human Running with Step-down Perturbations: An Experimental and Numerical Study

Oezge Drama, , Johanna Vielemeyer, , Alexander Badri-Spröwitz, , Müller, R.

2020 (article) In revision

Abstract
Postural stability is one of the most crucial elements in bipedal locomotion. Bipeds are dynamically unstable and need to maintain their trunk upright against the rotations induced by the ground reaction forces (GRFs), especially when running. Gait studies report that the GRF vectors focus around a virtual point above the center of mass (VPA), while the trunk moves forward in pitch axis during the stance phase of human running. However, a recent simulation study suggests that a virtual point below the center of mass (VPB) might be present in human running, since a VPA yields backward trunk rotation during the stance phase. In this work, we perform a gait analysis to investigate the existence and location of the VP in human running at 5 m s−1, and support our findings numerically using the spring-loaded inverted pendulum model with a trunk (TSLIP). We extend our analysis to include perturbations in terrain height (visible and camouflaged), and investigate the response of the VP mechanism to step-down perturbations both experimentally and numerically. Our experimental results show that the human running gait displays a VPB of ≈ −30 cm and a forward trunk motion during the stance phase. The camouflaged step-down perturbations affect the location of the VPB. Our simulation results suggest that the VPB is able to encounter the step-down perturbations and bring the system back to its initial equilibrium state.

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link (url) [BibTex]

link (url) [BibTex]


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Energy storage in steady states under cyclic local energy input

Zhang, Y., Holyst, R., Maciolek, A.

Physical Review E, 101(1), American Physical Society, Melville, NY, 2020 (article)

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DOI [BibTex]

DOI [BibTex]

2019


Series Elastic Behavior of Biarticular Muscle-Tendon Structure in a Robotic Leg
Series Elastic Behavior of Biarticular Muscle-Tendon Structure in a Robotic Leg

Ruppert, F., Badri-Spröwitz, A.

Frontiers in Neurorobotics, 64, pages: 13, 13, August 2019 (article)

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Frontiers YouTube link (url) DOI [BibTex]

2019


Frontiers YouTube link (url) DOI [BibTex]


Beyond Basins of Attraction: Quantifying Robustness of Natural Dynamics
Beyond Basins of Attraction: Quantifying Robustness of Natural Dynamics

Steve Heim, , Spröwitz, A.

IEEE Transactions on Robotics (T-RO) , 35(4), pages: 939-952, August 2019 (article)

Abstract
Properly designing a system to exhibit favorable natural dynamics can greatly simplify designing or learning the control policy. However, it is still unclear what constitutes favorable natural dynamics and how to quantify its effect. Most studies of simple walking and running models have focused on the basins of attraction of passive limit cycles and the notion of self-stability. We instead emphasize the importance of stepping beyond basins of attraction. In this paper, we show an approach based on viability theory to quantify robust sets in state-action space. These sets are valid for the family of all robust control policies, which allows us to quantify the robustness inherent to the natural dynamics before designing the control policy or specifying a control objective. We illustrate our formulation using spring-mass models, simple low-dimensional models of running systems. We then show an example application by optimizing robustness of a simulated planar monoped, using a gradient-free optimization scheme. Both case studies result in a nonlinear effective stiffness providing more robustness.

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arXiv preprint arXiv:1806.08081 T-RO link (url) DOI Project Page [BibTex]

arXiv preprint arXiv:1806.08081 T-RO link (url) DOI Project Page [BibTex]


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Response of active Brownian particles to shear flow

Asheichyk, K., Solon, A., Rohwer, C. M., Krüger, M.

The Journal of Chemical Physics, 150(14), American Institute of Physics, Woodbury, N.Y., 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Vortex Mass in the Three-Dimensional O(2) Scalar Theory

Delfino, G., Selke, W., Squarcini, A.

Physical Review Letters, 122(5), American Physical Society, Woodbury, N.Y., 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Dynamics near planar walls for various model self-phoretic particles

Bayati, P., Popescu, M. N., Uspal, W. E., Dietrich, S., Najafi, A.

Soft Matter, 15(28):5644-5672, Royal Society of Chemistry, Cambridge, UK, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Glucose Oxidase Micropumps: Multi-Faceted Effects of Chemical Activity on Tracer Particles Near the Solid-Liquid Interface

Munteanu, R. E., Popescu, M. N., Gáspár, S.

Condensed Matter, 4(3), MDPI, Basel, 2019 (article)

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DOI [BibTex]


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Criticality senses topology

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

EPL, 128(2), EDP Science, Les-Ulis, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Drag Force for Asymmetrically Grafted Colloids in Polymer Solutions

Werner, M., Malgaretti, P., Maciolek, A.

Frontiers in Physics, 7, Frontiers Media, Lausanne, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Feeling Your Neighbors across the Walls: How Interpore Ionic Interactions Affect Capacitive Energy Storage

Kondrat, S., Vasilyev, O., Kornyshev, A. A.

The Journal of Physical Chemistry Letters, 10(16):4523-4527, American Chemical Society, Washington, DC, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Active Janus colloids at chemically structured surfaces

Uspal, W. E., Popescu, M. N., Dietrich, S., Tasinkevych, M.

The Journal of Chemical Physics, 150(20), American Institute of Physics, Woodbury, N.Y., 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Illumination-induced motion of a Janus nanoparticle in binary solvents

Araki, T., Maciolek, A.

Soft Matter, 15(26):5243-5254, Royal Society of Chemistry, Cambridge, UK, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Transient response of an electrolyte to a thermal quench

Janssen, M., Bier, M.

Physical Review E, 99(4), American Physical Society, Melville, NY, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Aging phenomena during phase separation in fluids: decay of autocorrelation for vapor\textendashliquid transitions

Roy, Sutapa, Bera, Arabinda, Majumder, Suman, Das, Subir K.

Soft Matter, 15(23):4743-4750, Royal Society of Chemistry, Cambridge, UK, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Flux and storage of energy in nonequilibrium stationary states

Holyst, R., Maciolek, A., Zhang, Y., Litniewski, M., Knycha\la, P., Kasprzak, M., Banaszak, M.

Physical Review E, 99(4), American Physical Society, Melville, NY, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Correlations and forces in sheared fluids with or without quenching

Rohwer, C. M., Maciolek, A., Dietrich, S., Krüger, M.

New Journal of Physics, 21, IOP Publishing, Bristol, 2019 (article)

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DOI [BibTex]


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Ensemble dependence of critical Casimir forces in films with Dirichlet boundary conditions

Rohwer, C. M., Squarcini, A., Vasilyev, O., Dietrich, S., Gross, M.

Physical Review E, 99(6), American Physical Society, Melville, NY, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Controlling the dynamics of colloidal particles by critical Casimir forces

Magazzù, A., Callegari, A., Staforelli, J. P., Gambassi, A., Dietrich, S., Volpe, G.

Soft Matter, 15(10):2152-2162, Royal Society of Chemistry, Cambridge, UK, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Charge regulation radically modifies electrostatics in membrane stacks

Majee, A., Bier, M., Blossey, R., Podgornik, R.

Physical Review E, 100(5), American Physical Society, Melville, NY, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Comment on "Which interactions dominate in active colloids?" [J. Chem. Phys. 150, 061102 (2019)]

Popescu, M. N., Dominguez, A., Uspal, W. E., Tasinkevych, M., Dietrich, S.

The Journal of Chemical Physics, 151(6), American Institute of Physics, Woodbury, N.Y., 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Current-mediated synchronization of a pair of beating non-identical flagella

Dotsenko, V., Maciolek, A., Oshanin, G., Vasilyev, O., Dietrich, S.

New Journal of Physics, 21, IOP Publishing, Bristol, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Driving an electrolyte through a corrugated nanopore

Malgaretti, P., Janssen, M., Pagonabarraga, I., Rubi, J. M.

The Journal of Chemical Physics, 151(8), American Institute of Physics, Woodbury, N.Y., 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Spectral Content of a Single Non-Brownian Trajectory

Krapf, D., Lukat, N., Marinari, E., Metzler, R., Oshanin, G., Selhuber-Unkel, C., Squarcini, A., Stadler, L., Weiss, M., Xu, X.

Physical Review X, 9(1), American Physical Society, New York, NY, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Curvature affects electrolyte relaxation: Studies of spherical and cylindrical electrodes

Janssen, M.

Physical Review E, 100(4), American Physical Society, Melville, NY, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Dynamics of the critical Casimir force for a conserved order parameter after a critical quench

Gross, M., Rohwer, C. M., Dietrich, S.

Physical Review E, 100(1), American Physical Society, Melville, NY, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Interface structures in ionic liquid crystals

Bartsch, H., Bier, M., Dietrich, S.

Soft Matter, 15(20):4109-4126, Royal Society of Chemistry, Cambridge, UK, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Interfacial premelting of ice in nano composite materials

Li, H., Bier, M., Mars, J., Weiss, H., Dippel, A., Gutowski, O., Honkimäki, V., Mezger, M.

Physical Chemistry Chemical Physics, 21(7):3734-3741, Royal Society of Chemistry, Cambridge, England, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Connections Matter: On the Importance of Pore Percolation for Nanoporous Supercapacitors

Vasilyev, O., Kornyshev, A. A., Kondrat, S.

ACS Applied Energy Materials, 2(8):5386-5390, American Chemical Society, Washington, DC, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Theory of light-activated catalytic Janus particles

Uspal, W. E.

The Journal of Chemical Physics, 150(11), American Institute of Physics, Woodbury, N.Y., 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Recovering superhydrophobicity in nanoscale and macroscale surface textures

Giacomello, A., Schimmele, L., Dietrich, S., Tasinkevych, M.

Soft Matter, 15(37):7462-7471, Royal Society of Chemistry, Cambridge, UK, 2019 (article)

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DOI [BibTex]

DOI [BibTex]


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Brownian dynamics assessment of enhanced diffusion exhibited by "fluctuating-dumbbell enzymes".

Kondrat, S., Popescu, M. N.

Physical Chemistry Chemical Physics, 21(35):18811-18815, Royal Society of Chemistry, Cambridge, England, 2019 (article)

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DOI [BibTex]

DOI [BibTex]

2018


Oncilla robot: a versatile open-source quadruped research robot with compliant pantograph legs
Oncilla robot: a versatile open-source quadruped research robot with compliant pantograph legs

Sproewitz, A., Tuleu, A., Ajallooeian, M., Vespignani, M., Moeckel, R., Eckert, P., D’Haene, M., Degrave, J., Nordmann, A., Schrauwen, B., Steil, J., Ijspeert, A. J.

Frontiers in Robotics and AI, 5(67), June 2018, arXiv: 1803.06259 (article)

Abstract
We present Oncilla robot, a novel mobile, quadruped legged locomotion machine. This large-cat sized, 5.1 robot is one of a kind of a recent, bioinspired legged robot class designed with the capability of model-free locomotion control. Animal legged locomotion in rough terrain is clearly shaped by sensor feedback systems. Results with Oncilla robot show that agile and versatile locomotion is possible without sensory signals to some extend, and tracking becomes robust when feedback control is added (Ajaoolleian 2015). By incorporating mechanical and control blueprints inspired from animals, and by observing the resulting robot locomotion characteristics, we aim to understand the contribution of individual components. Legged robots have a wide mechanical and control design parameter space, and a unique potential as research tools to investigate principles of biomechanics and legged locomotion control. But the hardware and controller design can be a steep initial hurdle for academic research. To facilitate the easy start and development of legged robots, Oncilla-robot's blueprints are available through open-source. [...]

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link (url) DOI Project Page [BibTex]

2018


link (url) DOI Project Page [BibTex]


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Active microrheology in corrugated channels

Puertas, A. M., Malgaretti, P., Pagonabarraga, I.

The Journal of Chemical Physics, 149(17), American Institute of Physics, Woodbury, N.Y., 2018 (article)

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DOI [BibTex]

DOI [BibTex]


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First-passage dynamics of linear stochastic interface models: weak-noise theory and influence of boundary conditions

Gross, M.

Journal of Statistical Mechanics: Theory and Experiment, 2018, Institute of Physics Publishing, Bristol, England, 2018 (article)

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DOI [BibTex]

DOI [BibTex]


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Cu@TiO2 Janus microswimmers with a versatile motion mechanism

Wang, L. L., Popescu, M. N., Stavale, F., Ali, A., Gemming, T., Simmchen, J.

Soft Matter, 14(34):6969-6973, Royal Society of Chemistry, Cambridge, UK, 2018 (article)

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DOI [BibTex]

DOI [BibTex]


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Probing interface localization-delocalization transitions by colloids

Kondrat, S., Vasilyev, O., Dietrich, S.

Journal of Physics: Condensed Matter, 30(41), IOP Publishing, Bristol, 2018 (article)

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DOI [BibTex]

DOI [BibTex]


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Medical imaging for the tracking of micromotors

Vilela, D., Coss\’\io, U., Parmar, J., Mart\’\inez-Villacorta, A. M., Gómez-Vallejo, V., Llop, J., Sánchez, S.

ACS Nano, 12(2):1220-1227, American Chemical Society, Washington, DC, 2018 (article)

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DOI [BibTex]

DOI [BibTex]


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Noncontinuous Super-Diffusive Dynamics of a Light-Activated Nanobottle Motor

Xuan, M., Mestre, R., Gao, C., Zhou, C., He, Q., Sánchez, S.

Angewandte Chemie International Edition, 57(23):6838-6842, Wiley-VCH, Weinheim, 2018 (article)

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DOI [BibTex]

DOI [BibTex]


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On the origin of forward-backward multiplicity correlations in pp collisions at ultrarelativistic energies

Bravina, L., Bleibel, J., Zabrodin, E.

Physics Letters B, 787, pages: 146-152, North-Holland, 2018 (article)

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DOI [BibTex]

DOI [BibTex]


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Autophoretic motion in three dimensions

Lisicki, M., Reigh, S., Lauga, E.

Soft Matter, 14(17):3304-3314, Royal Society of Chemistry, Cambridge, UK, 2018 (article)

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DOI [BibTex]

DOI [BibTex]