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2017


Active colloidal propulsion over a crystalline surface
Active colloidal propulsion over a crystalline surface

Choudhury, U., Straube, A., Fischer, P., Gibbs, J., Höfling, F.

New Journal of Physics, 19, pages: 125010, December 2017 (article)

Abstract
We study both experimentally and theoretically the dynamics of chemically self-propelled Janus colloids moving atop a two-dimensional crystalline surface. The surface is a hexagonally close-packed monolayer of colloidal particles of the same size as the mobile one. The dynamics of the self-propelled colloid reflects the competition between hindered diffusion due to the periodic surface and enhanced diffusion due to active motion. Which contribution dominates depends on the propulsion strength, which can be systematically tuned by changing the concentration of a chemical fuel. The mean-square displacements obtained from the experiment exhibit enhanced diffusion at long lag times. Our experimental data are consistent with a Langevin model for the effectively two-dimensional translational motion of an active Brownian particle in a periodic potential, combining the confining effects of gravity and the crystalline surface with the free rotational diffusion of the colloid. Approximate analytical predictions are made for the mean-square displacement describing the crossover from free Brownian motion at short times to active diffusion at long times. The results are in semi-quantitative agreement with numerical results of a refined Langevin model that treats translational and rotational degrees of freedom on the same footing.

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link (url) DOI [BibTex]

2017


link (url) DOI [BibTex]


Wireless Acoustic-Surface Actuators for Miniaturized Endoscopes
Wireless Acoustic-Surface Actuators for Miniaturized Endoscopes

Qiu, T., Adams, F., Palagi, S., Melde, K., Mark, A. G., Wetterauer, U., Miernik, A., Fischer, P.

ACS Applied Materials & Interfaces, 9(49):42536 - 42543, November 2017 (article)

Abstract
Endoscopy enables minimally invasive procedures in many medical fields, such as urology. However, current endoscopes are normally cable-driven, which limits their dexterity and makes them hard to miniaturize. Indeed current urological endoscopes have an outer diameter of about 3 mm and still only possess one bending degree of freedom. In this paper, we report a novel wireless actuation mechanism that increases the dexterity and that permits the miniaturization of a urological endoscope. The novel actuator consists of thin active surfaces that can be readily attached to any device and are wirelessly powered by ultrasound. The surfaces consist of two-dimensional arrays of micro-bubbles, which oscillate under ultrasound excitation and thereby generate an acoustic streaming force. Bubbles of different sizes are addressed by their unique resonance frequency, thus multiple degrees of freedom can readily be incorporated. Two active miniaturized devices (with a side length of around 1 mm) are demonstrated: a miniaturized mechanical arm that realizes two degrees of freedom, and a flexible endoscope prototype equipped with a camera at the tip. With the flexible endoscope, an active endoscopic examination is successfully performed in a rabbit bladder. This results show the potential medical applicability of surface actuators wirelessly powered by ultrasound penetrating through biological tissues.

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link (url) DOI Project Page [BibTex]

link (url) DOI Project Page [BibTex]


Active Acoustic Surfaces Enable the Propulsion of a Wireless Robot
Active Acoustic Surfaces Enable the Propulsion of a Wireless Robot

Qiu, T., Palagi, S., Mark, A. G., Melde, K., Adams, F., Fischer, P.

Advanced Materials Interfaces, 4(21):1700933, September 2017 (article)

Abstract
A major challenge that prevents the miniaturization of mechanically actuated systems is the lack of suitable methods that permit the efficient transfer of power to small scales. Acoustic energy holds great potential, as it is wireless, penetrates deep into biological tissues, and the mechanical vibrations can be directly converted into directional forces. Recently, active acoustic surfaces are developed that consist of 2D arrays of microcavities holding microbubbles that can be excited with an external acoustic field. At resonance, the surfaces give rise to acoustic streaming and thus provide a highly directional propulsive force. Here, this study advances these wireless surface actuators by studying their force output as the size of the bubble-array is increased. In particular, a general method is reported to dramatically improve the propulsive force, demonstrating that the surface actuators are actually able to propel centimeter-scale devices. To prove the flexibility of the functional surfaces as wireless ready-to-attach actuator, a mobile mini-robot capable of propulsion in water along multiple directions is presented. This work paves the way toward effectively exploiting acoustic surfaces as a novel wireless actuation scheme at small scales.

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link (url) DOI Project Page [BibTex]


Corrosion-Protected Hybrid Nanoparticles
Corrosion-Protected Hybrid Nanoparticles

Jeong, H. H., Alarcon-Correa, M., Mark, A. G., Son, K., Lee, T., Fischer, P.

Advanced Science, 4(12):1700234, September 2017 (article)

Abstract
Nanoparticles composed of functional materials hold great promise for applications due to their unique electronic, optical, magnetic, and catalytic properties. However, a number of functional materials are not only difficult to fabricate at the nanoscale, but are also chemically unstable in solution. Hence, protecting nanoparticles from corrosion is a major challenge for those applications that require stability in aqueous solutions and biological fluids. Here, this study presents a generic scheme to grow hybrid 3D nanoparticles that are completely encapsulated by a nm thick protective shell. The method consists of vacuum-based growth and protection, and combines oblique physical vapor deposition with atomic layer deposition. It provides wide flexibility in the shape and composition of the nanoparticles, and the environments against which particles are protected. The work demonstrates the approach with multifunctional nanoparticles possessing ferromagnetic, plasmonic, and chiral properties. The present scheme allows nanocolloids, which immediately corrode without protection, to remain functional, at least for a week, in acidic solutions.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


Non-Equilibrium Assembly of Light-Activated Colloidal Mixtures
Non-Equilibrium Assembly of Light-Activated Colloidal Mixtures

Singh, D. P., Choudhury, U., Fischer, P., Mark, A. G.

Advanced Materials, 29, pages: 1701328, June 2017, 32 (article)

Abstract
The collective phenomena exhibited by artificial active matter systems present novel routes to fabricating out-of-equilibrium microscale assemblies. Here, the crystallization of passive silica colloids into well-controlled 2D assemblies is shown, which is directed by a small number of self-propelled active colloids. The active colloids are titania–silica Janus particles that are propelled when illuminated by UV light. The strength of the attractive interaction and thus the extent of the assembled clusters can be regulated by the light intensity. A remarkably small number of the active colloids is sufficient to induce the assembly of the dynamic crystals. The approach produces rationally designed colloidal clusters and crystals with controllable sizes, shapes, and symmetries. This multicomponent active matter system offers the possibility of obtaining structures and assemblies that cannot be found in equilibrium systems.

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link (url) DOI [BibTex]


Nanodiamonds That Swim
Nanodiamonds That Swim

Kim, J. T., Choudhury, U., Hyeon-Ho, J., Fischer, P.

Advanced Materials, 29(30):1701024, June 2017, Back Cover (article)

Abstract
Nanodiamonds are emerging as nanoscale quantum probes for bio-sensing and imaging. This necessitates the development of new methods to accurately manipulate their position and orientation in aqueous solutions. The realization of an “active” nanodiamond (ND) swimmer in fluids, composed of a ND crystal containing nitrogen vacancy centers and a light-driven self-thermophoretic micromotor, is reported. The swimmer is propelled by a local temperature gradient created by laser illumination on its metal-coated side. Its locomotion—from translational to rotational motion—is successfully controlled by shape-dependent hydrodynamic interactions. The precise engineering of the swimmer's geometry is achieved by self-assembly combined with physical vapor shadow growth. The optical addressability of the suspended ND swimmers is demonstrated by observing the electron spin resonance in the presence of magnetic fields. Active motion at the nanoscale enables new sensing capabilities combined with active transport including, potentially, in living organisms.

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link (url) DOI [BibTex]

link (url) DOI [BibTex]


Soft 3D-Printed Phantom of the Human Kidney with Collecting System
Soft 3D-Printed Phantom of the Human Kidney with Collecting System

Adams, F., Qiu, T., Mark, A., Fritz, B., Kramer, L., Schlager, D., Wetterauer, U., Miernik, A., Fischer, P.

Ann. of Biomed. Eng., 45(4):963-972, April 2017 (article)

Abstract
Organ models are used for planning and simulation of operations, developing new surgical instruments, and training purposes. There is a substantial demand for in vitro organ phantoms, especially in urological surgery. Animal models and existing simulator systems poorly mimic the detailed morphology and the physical properties of human organs. In this paper, we report a novel fabrication process to make a human kidney phantom with realistic anatomical structures and physical properties. The detailed anatomical structure was directly acquired from high resolution CT data sets of human cadaveric kidneys. The soft phantoms were constructed using a novel technique that combines 3D wax printing and polymer molding. Anatomical details and material properties of the phantoms were validated in detail by CT scan, ultrasound, and endoscopy. CT reconstruction, ultrasound examination, and endoscopy showed that the designed phantom mimics a real kidney's detailed anatomy and correctly corresponds to the targeted human cadaver's upper urinary tract. Soft materials with a tensile modulus of 0.8-1.5 MPa as well as biocompatible hydrogels were used to mimic human kidney tissues. We developed a method of constructing 3D organ models from medical imaging data using a 3D wax printing and molding process. This method is cost-effective means for obtaining a reproducible and robust model suitable for surgical simulation and training purposes.

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DOI Project Page [BibTex]

DOI Project Page [BibTex]


Pattern formation and collective effects in populations of magnetic microswimmers
Pattern formation and collective effects in populations of magnetic microswimmers

Vach, P. J., (Walker) Schamel, D., Fischer, P., Fratzl, P., Faivre, D.

J. of Phys. D: Appl. Phys., 50(11):11LT03, Febuary 2017 (article)

Abstract
Self-propelled particles are one prototype of synthetic active matter used to understand complex biological processes, such as the coordination of movement in bacterial colonies or schools of fishes. Collective patterns such as clusters were observed for such systems, reproducing features of biological organization. However, one limitation of this model is that the synthetic assemblies are made of identical individuals. Here we introduce an active system based on magnetic particles at colloidal scales. We use identical but also randomly-shaped magnetic micropropellers and show that they exhibit dynamic and reversible pattern formation.

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DOI [BibTex]

DOI [BibTex]


On-chip enzymatic microbiofuel cell-powered integrated circuits
On-chip enzymatic microbiofuel cell-powered integrated circuits

Mark, A. G., Suraniti, E., Roche, J., Richter, H., Kuhn, A., Mano, N., Fischer, P.

Lab on a Chip, 17(10):1761-1768, Febuary 2017, Recent HOT Article (article)

Abstract
A variety of diagnostic and therapeutic medical technologies rely on long term implantation of an electronic device to monitor or regulate a patient's condition. One proposed approach to powering these devices is to use a biofuel cell to convert the chemical energy from blood nutrients into electrical current to supply the electronics. We present here an enzymatic microbiofuel cell whose electrodes are directly integrated into a digital electronic circuit. Glucose oxidizing and oxygen reducing enzymes are immobilized on microelectrodes of an application specific integrated circuit (ASIC) using redox hydrogels to produce an enzymatic biofuel cell, capable of harvesting electrical power from just a single droplet of 5 mM glucose solution. Optimisation of the fuel cell voltage and power to match the requirements of the electronics allow self-powered operation of the on-board digital circuitry. This study represents a step towards implantable self-powered electronic devices that gather their energy from physiological fluids.

Recent HOT Article.

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DOI [BibTex]

DOI [BibTex]


Strong Rotational Anisotropies Affect Nonlinear Chiral Metamaterials
Strong Rotational Anisotropies Affect Nonlinear Chiral Metamaterials

Hooper, D. C., Mark, A. G., Kuppe, C., Collins, J. T., Fischer, P., Valev, V. K.

Advanced Materials, 29(13):1605110, January 2017 (article)

Abstract
Masked by rotational anisotropies, the nonlinear chiroptical response of a metamaterial is initially completely inaccessible. Upon rotating the sample the chiral information emerges. These results highlight the need for a general method to extract the true chiral contributions to the nonlinear optical signal, which would be hugely valuable in the present context of increasingly complex chiral meta/nanomaterials.

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DOI [BibTex]

DOI [BibTex]


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Chemically active colloids near osmotic-responsive walls with surface-chemistry gradients

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

Journal of Physics: Condensed Matter, 29, IOP Publishing, Bristol, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Active colloids in the context of chemical kinetics

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

Journal of Physics A, 50, IOP Pub., Bristol, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Microbots Decorated with Silver Nanoparticles Kill Bacteria in Aqueous Media

Vilela, D., Stanton, M. M., Parmar, J., Sánchez, S.

ACS Applied Materials and Interfaces, 9(27):22093-22100, American Chemical Society, Washington, DC, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Measurement of second-order response without perturbation

Helden, L., Basu, U., Krüger, M., Bechinger, C.

EPL, 116(6), IOP Publishing, Bristol, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Swimming with a cage: low-Reynolds-number locomotion inside a droplet

Reigh, S., Zhu, L. L., Gallaire, F., Lauga, E.

Soft Matter, 13(17):3161-3173, Royal Society of Chemistry, Cambridge, UK, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Active Particle Accumulation at Boundaries: A Strategy to Measure Contact Angles

Simmchen, J., Malgaretti, P.

ChemNanoMat, 3(11):790-793, Wiley, Weinheim, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Two-fluid model for locomotion under self-confinement

Reigh, S., Lauga, E.

Physical Review Fluids, 2(9), American Physical Society, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Bubble gating in biological ion channels: A density functional theory study

Gu\ssmann, Florian, Roth, R.

Physical Review E, 95(6), American Physical Society, Melville, NY, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Nematic films at chemically structured surfaces

Silvestre, N. M., Telo da Gama, M. M., Tasinkevych, M.

Journal of Physics: Condensed Matter, 29(7), IOP Publishing, Bristol, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Nonadditive interactions and phase transitions in strongly confined colloidal systems

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

Soft Matter, 14(4):586-596, Royal Society of Chemistry, Cambridge, UK, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Platinum-free cobalt ferrite based micromotors for antibiotic removal

Parmar, J., Villa, K., Vilela, D., Sánchez, S.

Applied Materials Today, 9, pages: 605-611, Elsevier, Amsterdam, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Perils of ad hoc approximations for the activity function of chemically powered colloids

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

The European Physical Journal E, 40, EDP Sciences; Società Italiana di Fisica; Springer, Les Ulis; Bologna; Heidelberg, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Transient Casimir Forces from Quenches in Thermal and Active Matter

Rohwer, C. M., Kardar, M., Krüger, M.

Physical Review Letters, 118(1), American Physical Society, Woodbury, N.Y., 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Rotational motion of dimers of Janus particles

Majee, A.

European Physical Journal E, 40(3), Springer, Berlin, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Designing Micro- and Nanoswimmers for Specific Applications

Katuri, J., Ma, X., Stanton, M. M., Sanchez, S.

Accounts of Chemical Research, 50(1):2-11, American Chemical Society, Easton, Pa., 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Wedge wetting by electrolyte solutions

Mußotter, M., Bier, M.

Physical Review E, 96(3), American Physical Society, Melville, NY, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Effect of boundaries on vacuum field fluctuations and radiation-mediated interactions between atoms

Armata, F., Butera, S., Fiscelli, G., Incardone, R., Notararigo, V., Palacino, R., Passante, R., Rizzuto, L., Spagnolo, S.

Journal of Physics: Conference Series, 880, IOP Publishing, Bristol, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Smectic phases in ionic liquid crystals

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

Journal of Physics: Condensed Matter, 29(46), IOP Publishing, Bristol, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Pushing Bacterial Biohybrids to In Vivo Applications

Stanton, M. M., Sánchez, S.

Trends in Biotechnology, 35(10):910-913, Elsevier Current Trends, Amsterdam, Netherlands, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Particles with nonlinear electric response: Suppressing van der Waals forces by an external field

Soo, H., Dean, D. S., Krüger, M.

Physical Review E, 95(1), American Physical Society, Melville, NY, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Electrolyte solutions at curved electrodes. I. Mesoscopic approach

Reindl, A., Bier, M., Dietrich, S.

The Journal of Chemical Physics, 146(15), American Institute of Physics, Woodbury, N.Y., 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Self-propelling micro-nanorobots: challenges and fututre perspectives in nanomedicine

Ma, X., Sánchez, S.

Nanomedicine, 12(12):1363-1367, Future Medicine Ltd, London, UK, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Salt-induced microheterogeneities in binary liquid mixtures

Bier, M., Mars, J., Li, H., Mezger, M.

Physical Review E, 96(2), American Physical Society, Melville, NY, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Forward-backward multiplicity correlations in proton-proton collisions from several GeV to LHC energies

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

EPJ Web of Conferences, 164, EDP Sciences, Les Ulis, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Key-lock colloids in a nematic liquid crystal

Silvestre, N. M., Tasinkevych, M.

Physical Review E, 95(1), American Physical Society, Melville, NY, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Fluctuation induced forces in critical films with disorder at their surfaces

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

Journal of Statistical Mechanics: Theory and Experiment, Institute of Physics Publishing, Bristol, England, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Action at a distance in classical uniaxial ferromagnetic arrays

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

Physical Review E, 96(4), American Physical Society, Melville, NY, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Cooperative behavior of biased probes in crowded interacting systems

Vasilyev, O., Bénichou, O., Mej\’\ia-Monasterio, C., Weeks, E. R., Oshanin, G.

Soft Matter, 13(41):7617-7624, Royal Society of Chemistry, Cambridge, UK, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Nonequilibrium Fluctuational Quantum Electrodynamics: Heat Radiation, Heat Transfer, and Force

Bimonte, G., Emig, T., Kardar, M., Krüger, M.

Annual Review of Condensed Matter Physics, 8, pages: 119-143, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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A Gaussian theory for fluctuations in simple liquids

Krüger, M., Dean, D. S.

The Journal of Chemical Physics, 146(13), American Institute of Physics, Woodbury, N.Y., 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Critical Casimir interactions between colloids around the critical point of binary solvents

Stuij, S. G., Labbe-Laurent, M., Kodger, T. E., Maciolek, A., Schall, P.

Soft Matter, 13(31):5233-5249, Royal Society of Chemistry, Cambridge, UK, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Bio-catalytic mesoporous Janus nano-motors powered by catalase enzyme

Ma, X., Sánchez, S.

Tetrahedron, 73(33):4883-4886, Elsevier Science, Kidlington, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Basic features of proton-proton interactions at ultra-relativistic energies and RFT-based quark-gluon string model

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

EPJ Web of Conferences, 164, EDP Sciences, Les Ulis, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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The modified Langevin description for probes in a nonlinear medium

Krüger, M., Maes, C.

Journal of Physics: Condensed Matter, 29(6), IOP Publishing, Bristol, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Smoluchowski rate for diffusion-controlled reactions of molecules with antenna

Vasilyev, O., Lizana, L., Oshanin, G.

Journal of Physics A, 50(26), IOP Pub., Bristol, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Model microswimmers in channels with varying cross section

Malgaretti, P., Stark, H.

The Journal of Chemical Physics, 146(17), American Institute of Physics, Woodbury, N.Y., 2017 (article)

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DOI [BibTex]


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Heat radiation and transfer for point particles in arbitrary geometries

Asheichyk, K., Müller, B., Krüger, M.

Physical Review B, 96(15), American Physical Society, Woodbury, NY, 2017 (article)

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DOI [BibTex]

DOI [BibTex]


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Surface induced smectic order in ionic liquids - an X-ray reflectivity study of [C(22)C(1)im](+)[NTf2](-)

Mars, J., Hou, B., Weiss, H., Li, H., Konovalov, O., Festersen, S., Murphy, B. M., Rütt, U., Bier, M., Mezger, M.

Physical Chemistry Chemical Physics, 19(39):26651-26661, Royal Society of Chemistry, Cambridge, England, 2017 (article)

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DOI [BibTex]