EPJ E Highlight - Liquid foam: plastic, elastic and fluid


Snapshots of the foam at the exit of the convergent channel

What differentiates complex fluids from mere fluids? What makes them unique is that they are neither solid nor liquid. Among such complex fluids are foams. They are used as a model to understand the mechanisms underlying complex fluids flow. Now, a team of French physicists has gained new insights into predicting how complex fluids react under stretching conditions due to the interplay between elasticity, plasticity and flow. These findings were recently published in EPJ E by Benjamin Dollet and Claire Bocher from the Rennes Institute of Physics, in Brittany, France. Ultimately, potential applications include the design of new, optimised acoustic insulators based on liquid forms, or the mitigation of blast waves caused by explosions.


EPJ E Highlight - Zooplankton: not-so-passive motion in turbulence


Physicists show that despite their limited swimming abilities, zooplankton called calanoid copepods display active, energetic behaviour in turbulent flows

Imagine a species that is only one millimetre long and has only a limited swimming ability. Yet, its mobility is sufficient for moving, feeding and reproducing in freshwater and seawater. That’s exactly what a type of zooplankton of the crustaceans family - namely the calanoid copepods - does. In a study published in EPJ E, physicists shed new light on how these zooplankton steer large-scale collective motion under strong turbulence. To do so, the authors study the zooplankton’s small-scale motion mechanisms when subjected to background flow motion. These findings are the work of François-Gaël Michalec from the Institute of Environmental Engineering, ETH Zurich, Switzerland, and European colleagues. Ecological applications in the field of zooplankton behaviour ecology include, for example, modelling the feeding efficiency of their predator, fish larvae.


EPJ E Colloquium: Adhesion induced pattern formation in constrained soft films

Formation of an interfacial pattern between a thin film of soft gel and a rigid glass plate that also shows the motion of bubbles.
© Chaudhury et al.

A hydrostatically-stressed soft elastic film responds by developing a morphological instability, the wavelength of which is dictated by minimisation of the surface and elastic strain energies of the film. For a single film, the wavelength of this transition is entirely dependent on the film's thickness, however in the case of two contacting films a co-operative energy minimisation dictates that the wavelength depends on both the elastic moduli and the thicknesses of the two films.


EPJ E Highlight - Improving insulation materials, down to wetting crossed fibres

Evolution of the morphology of a drop of silicone oil on two touching crossed fibres

Scientists model the manner in which a liquid wets fibres, gaining useful insights for improving glass wool properties

Sandcastles are a prime example of how adding a small amount of liquid to a granular material changes its characteristics. But understanding the effect of a liquid wetting randomly oriented fibres in a fibrous medium remains a mystery. Relevant to the building industry, which uses glass wool, for instance, this phenomenon can be better understood by studying the behaviour of a liquid trapped between two parallel fibres. It can either remain in the shape of a drop or spread between the fibres into a long and thin column of liquid. Now, scientists have demonstrated that the spreading of the liquid is controlled by three key parameters: the amount of liquid on the fibres, the fibres’ orientation and the minimum distance between them. These findings, based on experimental and modelling work, were recently published in EPJ E. The authors are Alban Sauret, a scientist working at a laboratory jointly operated by the CNRS and Saint-Gobain, a building materials manufacturer in France, and international colleagues based at Princeton University and the NYU School of Engineering, USA.


EPJ E Colloquium - The role of acoustic streaming in vertically vibrated granular beds

Photo by Robert Hartley and co-workers at Duke University (Robert Behringer’s Group)

A recent EPJ E Colloquium by Jose Manuel Valverde looks at the fundamental physics that causes convection and fluidization in vibrated beds of particles with large inertia. The author examines the question of whether acoustic streaming arising from oscillatory viscous flows might play a role on the onset of convection and fluidization in vertically vibrated granular beds.

Acoustic streaming, first observed by Faraday in 1831, is an enigmatic phenomenon that has puzzled physicists for a long time. It occurs when a viscous fluid oscillates in the presence of a solid boundary. The dissipation of energy by viscous friction leads to a secondary steady circulation of fluid in a boundary layer near the surface of the solid, which enhances the gas-solid viscous interaction. Granular beds display, at sufficiently high vibrational intensities, surface patterns that bear a stunning resemblance to the surface ripples (Faraday waves) observed for low viscosity liquids. This suggests that the granular bed transits to a liquid-like regime, despite the large inertia of the particles.


EPJ E Highlight - How supercooled water is prevented from turning into ice

Representative configurations of ice in its Ic format, which is a simulation in a cube with 216 molecules, Ih format, which is in a rectangular cell with 432 molecules, and in liquid water

Calculating the energy barrier that keeps liquid water below zero from immediately turning into ice provides the key to understanding its ability to be compressed as temperature drops

Water behaves in mysterious ways. Especially below zero, where it is dubbed supercooled water, before it turns into ice. Physicists have recently observed the spontaneous first steps of the ice formation process, as tiny crystal clusters as small as 15 molecules start to exhibit the recognisable structural pattern of crystalline ice. This is part of a new study, which shows that liquid water does not become completely unstable as it becomes supercooled, prior to turning into ice crystals. The team reached this conclusion by proving that an energy barrier for crystal formation exists throughout the region in which supercooled water’s compressibility continues to rise. Previous work argued that this barrier vanished as the liquid gets colder. These findings have been published in EPJ E by Connor Buhariwalla from St. Francis Xavier University in Antigonish, Canada and colleagues.


EPJ E Colloquium – The importance of rheology in tissue development

Our understanding of biomechanics increasingly improves through the use of physics models. There are some intriguing biological questions regarding the interplay between the behaviour of cells and the mechanics at the level of tissues. For example, how does a collective behavior, not apparent at the cell scale, emerge at the tissue level? Or how can the mechanical state of a tissue affect the cell division rate or the orientation of cells undergoing division?

The authors of this new EPJ E Colloquium entitled “Mechanical Formalism for Tissue Dynamics” think that the interplay between genes and mechanics is key to understanding how the adult shape emerges from a developing tissue.


EPJ E Highlight - Space lab to elucidate how liquid cocktails mix

International Space Station salutes the Sun. © NASA/ESA

Zero-gravity experiments can tell us a great deal about the effects of temperature change on the concentrations of three different liquids that are mixed together

What does space experimentation have in common with liquid cocktails? Both help in understanding what happens when multiple fluids are mixed together and subjected to temperature change - a phenomenon ubiquitous in nature and industrial applications such as oil fluids contained in natural reservoirs. The latest experimental data performed in zero gravity on the International Space Station is now available in the newly published Topical Issue of EPJ E. The results constitute the first set of highly accurate and broadly validated data on the thermodiffusion effects that occur when three different liquids are mixed. Such experiments were made possible by a collaboration of space agencies including the ESA, NASA, CSA and ROSCOSMOS.


EPJ E Highlight - Rodeo in liquid crystal

Binding of a dipolar microsphere with a point monopole on a fiber.

Scientists have achieved an unprecedented level of control over defects in liquid crystals that can be engineered for applications in liquid matter photonics

Sitting with a joystick in the comfort of their chairs, scientists can play “rodeo” on a screen magnifying what is happening under their microscope. They rely on optical tweezers to manipulate an intangible ring created out of liquid crystal defects capable of attaching a microsphere to a long thin fibre. Maryam Nikkhou and colleagues from the Jožef Stefan Institute, in Ljubljana, Slovenia, recently published in EPJ E the results of work performed under the supervision of Igor Muševič. They believe that their findings could ultimately open the door to controlling the flow of light using light of a specific frequency in the Gigahertz range in liquid crystal photonic microdevices.


EPJ E Highlight - Building sound foundations: a matter of granular dynamics

The behaviour of the granular medium sand can be modelled using a hydrodynamics theory, a new study shows. © sergign / Fotolia

Applying the hydrodynamics approach to granular matter helps explain its wide range of behaviour, regardless of whether the material is solid- or fluid-like

Sand, rocks, grains, salt or sugar are what physicists call granular media. A better understanding of granular media is important - particularly when mixed with water and air, as it forms the foundations of houses and off-shore windmills. Until recently, there was no single theory that could account for granular media’s flows at different speeds. Now, a new theory dubbed GSH, which stands for granular solid hydrodynamics, is supplementing previous models of granular material that work only for narrow speed ranges. And Yimin Jiang from Central South University, Changsha, China and Mario Liu from the University of Tübingen, Germany have now applied GSH to different experimental circumstances, for a wide range of flow speeds, in a study published in EPJ E.


After having contacted few journals for the publication of the proceedings of our conference (...), I finally got in contact with EPJ WoC. They have been the first to give me straightforward answers to my questions, and overtime right away. Since then, all further interactions have been based on professionalism and efficiency

Michele Doro, INFN Padova, Italy
Editor, EPJ Web of Conferences vol. 89, 2015

ISSN: 2100-014X (Electronic Edition)

© EDP Sciences