ALBERT

Description:    We have measured the friction force acting on a rubber block slid on a concrete surface. We used both unfilled and filled (with carbon black) styrene butadiene (SB) rubber and have varied the temperature from −10 °C to 100 °C and the sliding velocity from 1 μ m/s to 1000 μ m/s. We find that the experimental data at different temperatures can be shifted into a smooth master-curve, using the temperature-frequency shifting factors obtained from measurements of the bulk viscoelastic modulus. The experimental data has been analyzed using a theory which takes into account the contributions to the friction from both the substrate asperity-induced viscoelastic deformations of the rubber, and from shearing the area of real contact. For filled SB rubber the frictional shear stress σ f in the area of real contact results mainly from the energy dissipation at the opening crack on the exit side of the rubber-asperity contact regions. For unfilled rubber we instead attribute σ f to shearing of a thin rubber smear film, which is deposited on the concrete surface during run in. We observe very different rubber wear processes for filled and unfilled SB rubber, which is consistent with the different frictional processes. Thus, the wear of filled SB rubber results in micrometer-sized rubber particles which accumulate as dry dust, which is easily removed by blowing air on the concrete surface. This wear process seams to occur at a steady rate. For unfilled rubber a smear film forms on the concrete surface, which cannot be removed even using a high-pressure air stream. In this case the wear rate appears to slow down after some run in time period. Content Type Journal Article Category Regular Article Pages 1-11 DOI 10.1140/epje/i2011-11129-1 Authors B. Lorenz, IFF, FZ-Jülich, D-52425 Jülich, Germany B. N. J. Persson, IFF, FZ-Jülich, D-52425 Jülich, Germany S. Dieluweit, ICS, FZ-Jülich, D-52425 Jülich, Germany T. Tada, Sumitomo rubber industries, 2-1-1, Tsutsui-cho, Chuo-ku, 651-0071 Kobe, Japan Journal The European Physical Journal E: Soft Matter and Biological Physics Online ISSN 1292-895X Print ISSN 1292-8941 Journal Volume Volume 34 Journal Issue Volume 34, Number 12

Description:    We report on the rotation of colloidal clusters of diamagnetic beads and of mixtures of paramagnetic and diamagnetic beads in a ferrofluid in a precessing external magnetic field. The precession angle of the external field is a control parameter determining the stability of the cluster. Clusters become locally unstable when the local precession angle reaches the magic angle. Cluster shape dependent depolarization fields lead to a deviation of the local from the external precession angle such that close to the external magic angle different cluster shapes might coexist. For this reason cluster transitions are weakly or strongly first-order transitions. If the transition is weakly first order a critical speeding up of the cluster rotation is observed. No speeding up occurs for strongly first-order cluster transitions with hysteresis. The strength of the first-order transition is controlled by the size of the core of the cluster. Content Type Journal Article Category Regular Article Pages 1-6 DOI 10.1140/epje/i2012-12017-x Authors A. Ray, Institut für Experimentalphysik, Universität Bayreuth, 95440 Bayreuth, Germany Th. M. Fischer, Institut für Experimentalphysik, Universität Bayreuth, 95440 Bayreuth, Germany Journal The European Physical Journal E: Soft Matter and Biological Physics Online ISSN 1292-895X Print ISSN 1292-8941 Journal Volume Volume 35 Journal Issue Volume 35, Number 3

Description: Erratum to: Permeability of aqueous foams Content Type Journal Article Category Erratum Pages 1-1 DOI 10.1140/epje/i2012-12016-y Authors E. Lorenceau, Laboratoire de Physique des Matériaux Divisés et des Interfaces, UMR 8108 du CNRS, Université Paris-Est, 5 Boulevard Descartes, 77 454 Marne-la-Vallée cedex 2, France N. Louvet, Laboratoire de Physique des Matériaux Divisés et des Interfaces, UMR 8108 du CNRS, Université Paris-Est, 5 Boulevard Descartes, 77 454 Marne-la-Vallée cedex 2, France F. Rouyer, Laboratoire de Physique des Matériaux Divisés et des Interfaces, UMR 8108 du CNRS, Université Paris-Est, 5 Boulevard Descartes, 77 454 Marne-la-Vallée cedex 2, France O. Pitois, Laboratoire de Physique des Matériaux Divisés et des Interfaces, UMR 8108 du CNRS, Université Paris-Est, 5 Boulevard Descartes, 77 454 Marne-la-Vallée cedex 2, France Journal The European Physical Journal E: Soft Matter and Biological Physics Online ISSN 1292-895X Print ISSN 1292-8941 Journal Volume Volume 35 Journal Issue Volume 35, Number 2

Description:    We investigate the dynamics of clusters made of aggregating particles on a membrane which exchanges particles with a reservoir. Exchanges are driven by chemical reactions which supply energy to the system, leading to the establishment of a non-equilibrium steady state. We predict the distribution of cluster size at steady state. We show in particular that in a regime, that cannot exist at equilibrium, the distribution is bimodal: the membrane is mainly populated of single particles and finite-size clusters. This work is motivated by the observations that have revealed the existence of submicrometric clusters of proteins in biological membranes. Content Type Journal Article Category Regular Article Pages 1-13 DOI 10.1140/epje/i2012-12012-3 Authors L. Foret, Ecole Normale Supérieure, Université Pierre et Marie Curie Paris 6, CNRS, Laboratoire de Physique Statistique, 24 rue Lhomond, 75005 Paris, France Journal The European Physical Journal E: Soft Matter and Biological Physics Online ISSN 1292-895X Print ISSN 1292-8941 Journal Volume Volume 35 Journal Issue Volume 35, Number 2

Description:    Two key cellular processes, namely transcription and replication, require the opening of the DNA double helix and act differently on the two DNA strands, generating different mutational patterns (mutational asymmetry) that may result, after long evolutionary time, in different nucleotide compositions on the two DNA strands (compositional asymmetry). We elaborate on the simplest model of neutral substitution rates that takes into account the strand asymmetries generated by the transcription and replication processes. Using perturbation theory, we then solve the time evolution of the DNA composition under strand-asymmetric substitution rates. In our minimal model, the compositional and substitutional asymmetries are predicted to decompose into a transcription- and a replication-associated components. The transcription-associated asymmetry increases in magnitude with transcription rate and changes sign with gene orientation while the replication-associated asymmetry is proportional to the replication fork polarity. These results are confirmed experimentally in the human genome, using substitution rates obtained by aligning the human and chimpanzee genomes using macaca and orangutan as outgroups, and replication fork polarity determined in the HeLa cell line as estimated from the derivative of the mean replication timing. When further investigating the dynamics of compositional skew evolution, we show that it is not at equilibrium yet and that its evolution is an extremely slow process with characteristic time scales of several hundred Myrs. Graphical abstract   Content Type Journal Article Category Regular Article Pages 1-25 DOI 10.1140/epje/i2012-12092-y Authors A. Baker, Université de Lyon, F-69000 Lyon, France H. Julienne, Université de Lyon, F-69000 Lyon, France C. L. Chen, Centre de Génétique Moléculaire, CNRS, Allée de la Terrasse, 91198 Gif-sur-Yvette, France B. Audit, Université de Lyon, F-69000 Lyon, France Y. d’Aubenton-Carafa, Centre de Génétique Moléculaire, CNRS, Allée de la Terrasse, 91198 Gif-sur-Yvette, France C. Thermes, Centre de Génétique Moléculaire, CNRS, Allée de la Terrasse, 91198 Gif-sur-Yvette, France A. Arneodo, Université de Lyon, F-69000 Lyon, France Journal The European Physical Journal E: Soft Matter and Biological Physics Online ISSN 1292-895X Print ISSN 1292-8941 Journal Volume Volume 35 Journal Issue Volume 35, Number 9

Description:    We report experimental observations of polygon-shaped patterns formed in a vertically vibrated bed of circular cross-section. A phase map is determined, showing that the polygon pattern is established for Γ = A (2 πf ) 2 / g ≳ 10 . The sensitivity of the polygon structure to bed parameters was tested by studying beds of different particle sizes and fill levels. It was hypothesized that the polygon pattern observed in cylindrical beds is the corresponding pattern to the formation of arches in square-shaped beds. The close relationship between these two patterns was demonstrated by two observations: i) the radii of the arches of a corresponding square bed and the inner radius of the cylindrical bed were found to be very similar and ii) the boundary lengths of the two patterns were in good agreement. Content Type Journal Article Category Regular Article Pages 1-5 DOI 10.1140/epje/i2012-12090-1 Authors G. Lu, ETH Zürich, Leonhardstrasse 27, 8092 Zürich, Switzerland J. R. Third, ETH Zürich, Leonhardstrasse 27, 8092 Zürich, Switzerland M. H. Köhl, ETH Zürich, Leonhardstrasse 27, 8092 Zürich, Switzerland C. R. Müller, ETH Zürich, Leonhardstrasse 27, 8092 Zürich, Switzerland Journal The European Physical Journal E: Soft Matter and Biological Physics Online ISSN 1292-895X Print ISSN 1292-8941 Journal Volume Volume 35 Journal Issue Volume 35, Number 9

Description:    Active processes in biological systems often exhibit chiral asymmetries. Examples are the chirality of cytoskeletal filaments which interact with motor proteins, the chirality of the beat of cilia and flagella as well as the helical trajectories of many biological microswimmers. Here, we derive constitutive material equations for active fluids which account for the effects of active chiral processes. We identify active contributions to the antisymmetric part of the stress as well as active angular momentum fluxes. We discuss four types of elementary chiral motors and their effects on a surrounding fluid. We show that large-scale chiral flows can result from the collective behavior of such motors even in cases where isolated motors do not create a hydrodynamic far field. Content Type Journal Article Category Regular Article Pages 1-13 DOI 10.1140/epje/i2012-12089-6 Authors S. Fürthauer, Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany M. Strempel, Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany S. W. Grill, Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany F. Jülicher, Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany Journal The European Physical Journal E: Soft Matter and Biological Physics Online ISSN 1292-895X Print ISSN 1292-8941 Journal Volume Volume 35 Journal Issue Volume 35, Number 9

Description:    Shear-banding is ubiquitous in complex fluids. It is related to the organization of the flow into macroscopic bands bearing different viscosities and local shear rates and stacked along the velocity gradient direction. This flow-induced transition towards a heterogeneous flow state has been reported in a variety of systems, including wormlike micellar solutions, telechelic polymers, emulsions, clay suspensions, colloidal gels, star polymers, granular materials, or foams. In the past twenty years, shear-banding flows have been probed by various techniques, such as rheometry, velocimetry and flow birefringence. In wormlike micelle solutions, many of the data collected exhibit unexplained spatio-temporal fluctuations. Different candidates have been identified, the main ones being wall slip, interfacial instability between bands or bulk instability of one of the bands. In this review, we present experimental evidence for a purely elastic instability of the high shear rate band as the main origin for fluctuating shear-banding flows. Content Type Journal Article Category Colloquium Pages 1-29 DOI 10.1140/epje/i2012-12091-0 Authors M. -A. Fardin, Laboratoire Matière et Systèmes Complexes, CNRS UMR 7057-Université Paris Diderot, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cédex 13, France S. Lerouge, Laboratoire Matière et Systèmes Complexes, CNRS UMR 7057-Université Paris Diderot, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cédex 13, France Journal The European Physical Journal E: Soft Matter and Biological Physics Online ISSN 1292-895X Print ISSN 1292-8941 Journal Volume Volume 35 Journal Issue Volume 35, Number 9

Description:    A theoretical model is developed for predicting dynamic polymer depletion under the influence of fluid flow. The results are established by combining the two-fluid model and the self-consistent field theory. We consider a uniform fluid flow across a slit containing a solution with polymer chains. The two parallel and infinitely long walls are permeable to solvent only and the polymers do not adsorb to these walls. For a weak flow and a narrow slit, an analytic expression is derived to describe the steady-state polymer concentration profiles in a -solvent. In both - and good-solvents, we compute the time evolution of the concentration profiles for various flow rates characterized by the Peclet number. The model reveals the interplay of depletion, solvent condition, slit width, and the relative strength of the fluid flow. Graphical abstract   Content Type Journal Article Category Regular Article Pages 1-12 DOI 10.1140/epje/i2012-12088-7 Authors T. Taniguchi, Graduate School of Engineering, Kyoto University Katsura Campus, 615-8510 Nishikyo-ku, Kyoto, Japan Y. Arai, Graduate School of Engineering, Kyoto University Katsura Campus, 615-8510 Nishikyo-ku, Kyoto, Japan R. Tuinier, DSM ChemTech, ACES, P.O. Box 18, 6160 MD Geleen, The Netherlands T. -H. Fan, Department of Mechanical Engineering, University of Connecticut, Massachusetts, 06269 CT, USA Journal The European Physical Journal E: Soft Matter and Biological Physics Online ISSN 1292-895X Print ISSN 1292-8941

Description:    Using molecular-dynamics simulation, we investigate the consequences of ultrafast laser-induced heating of a water droplet containing a solvated polymer, using the example of a 1 ps laser irradiation. We study the isolation process and the properties of the isolated polymer as a function of the polymer size, the droplet size, and the temperature to which the droplet is heated. We find that the isolation process occurs on a time scale of a few ten ps. The final polymer temperature increases linearly with the heating. Polymers embedded in larger droplets acquire higher temperatures, while larger polymers are less heated. In spite of the ultrafast heating, the isolated polymer remains in its coiled conformation. Graphical abstract   Content Type Journal Article Category Regular Article Pages 1-6 DOI 10.1140/epje/i2012-12099-4 Authors S. N. Sun, Physics Department and Research Center OPTIMAS, University Kaiserslautern, Erwin-Schrödinger-Straße, D-67663 Kaiserslautern, Germany H. M. Urbassek, Physics Department and Research Center OPTIMAS, University Kaiserslautern, Erwin-Schrödinger-Straße, D-67663 Kaiserslautern, Germany Journal The European Physical Journal E: Soft Matter and Biological Physics Online ISSN 1292-895X Print ISSN 1292-8941 Journal Volume Volume 35 Journal Issue Volume 35, Number 10