2019 Impact factor 0.630
Applied Physics

EPJ E Highlight - Characterising complex flows in 2D bubble swarms

Bubble swarms introduce complex flows.

In 2D simulations, the flows surrounding rising swarms of bubbles display characteristically different behaviours to those observed in 3D models

When swarms of bubbles are driven upwards through a fluid by their buoyancy, they can generate complex flow patterns in their wake. Named ‘pseudo-turbulence,’ these patterns are characterised by a universal mathematical relationship between the energy of flows of different sizes, and the frequency of their occurrence. This relationship has now been widely observed through 3D simulations, but it is less clear whether it would still hold for 2D swarms of bubbles. Through research published in EPJ E, Rashmi Ramadugu and colleagues at the TIFR Centre for Interdisciplinary Sciences in Hyderabad, India, show that in 2D simulated fluids, this pattern changes within larger-scale flows in less viscous fluids.

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EPJ E Highlight - Building better diffusion models for active systems

Deviating from Brownian motion.

Modifications to existing theories have enabled researchers to better understand and model the dynamics of systems which don’t obey conventional laws of diffusion

In normal circumstances, particles will follow well-established random motions as they diffuse through liquids and gases. Yet in some types of system, this behaviour can be disrupted – meaning the diffusion motions of particles are no longer influenced by the outcomes of chains of previous events. Through research published in EPJ E, Bernhard Mitterwallner, a Ph.D. student in the team of Roland Netz at the Free University of Berlin, Germany, has developed new theories detailing how these unusual dynamics can be reproduced in generalised mathematical models.

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EPJ E Highlight - Modelling microswimmers for drug delivery

Streamlines of the fluid flow induced by a single point force (Stokeslet) representing a microswimmer inside a freely moving viscous drop.

Mathematical models of the motion of cells in viscous liquids that show how this motion is affected by the presence of a surfactant coating have applications in the design of artificial microswimmers for targeted drug delivery, micro-surgery and other applications.

Many types of motile cells, such as the bacteria in our guts and spermatozoa in the female reproductive tracts, need to propel themselves through confined spaces filled with viscous liquid. In recent years, the motion of these ‘microswimmers’ has been mimicked in the design of self-propelled micro- and nano-scale machines for applications including targeted drug delivery. Optimising the design of these machines requires a detailed, mathematical understanding of microswimmers in these environments. A large, international group of physicists led by Abdallah Daddi-Moussa-Ider of Heinrich-Heine-Universität Düsseldorf, Germany has now generated mathematical models of microswimmers in clean and surfactant-covered viscous drops, showing that the surfactant significantly alters the swimmers’ behaviour. They have published their work in EPJ E.

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EPJ E Celebrates 20th Anniversary

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In 2020 The European Physical Journal E - Soft Matter and Biological Physics marks twenty years since the publication of its first papers. To commemorate this milestone, the Editors-in-Chief have made a selection of articles published over these two decades, representing the breadth of coverage of the journal. These articles are now freely accessible until 15 October via this Q&A with Prof Holger Stark, Editor-in-Chief of EPJ E.

EPJ E Highlight - Polymers can fine-tune attractions between suspended nanocubes

Simulating motions of bottom-heavy squirmers.

Interactions between hollow silica nanocubes suspended in a solution can be adjusted by varying the concentration of polymer molecules added to the mixture.

Colloids are complex mixtures in which microscopic particles of one substance are suspended evenly throughout another. They can be prepared in many different ways, but to achieve desirable properties in the final mixture, researchers must maintain a delicate control over the interactions which take place between the particles. In new research published in EPJ E, a team led by Remco Tuinier at the Eindhoven University of Technology in the Netherlands demonstrate this level of control for a type of colloid in which the suspended particles take the form of hollow, nanoscale cubes – a case which has only previously been explored through theoretical calculations.

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EPJ E Highlight - ‘Bottom-heavy squirmers’ adopt characteristic group behaviours

Simulating motions of bottom-heavy squirmers.

Simulated particles which mimic the behaviours of self-propelling microorganisms have distinct collective properties which depend on their velocities and bottom-heaviness.

From starling aberrations to self-turbulent fluids, ‘active systems’ encompass a wide family of phenomena in which individual objects propel themselves forward, allowing them to display intriguing collective behaviours. On microscopic scales, they are found in groups of living organisms which move around by squirming, and are aligned with Earth’s gravitational fields due to their bottom-heavy mass distributions. Through research published in EPJ E, Felix Rühle and Holger Stark at the Technical University of Berlin find that depending on their properties, these objects collectively spend most of their time in one of two states, between which some intriguing behaviours can emerge.

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EPJ E Highlight - Modelling wrinkling and buckling in materials that form the basis of flexible electronics

A Side view of an elastomeric film placed under strain undergoing buckling and wrinkling.

As the demand for flexible electronics grows, researchers must develop robust models of how the materials that comprise them behave under stress.

Flexible circuits have become a highly desirable commodity in modern technology, with applications in biotechnology, electronics, monitors and screens, being of particular importance. A new paper authored by John F. Niven, Department of Physics & Astronomy, McMaster University, Hamilton, Ontario, published in EPJ E, aims to understand how materials used in flexible electronics behave under stress and strain, particularly, how they wrinkle and buckle.

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EPJ E Highlight - Distortion isn’t a drag on fluid-straddling particles

Straddling particles deform fluid interfaces.

The drag forces experienced by particles which straddle and distort the interfaces between un-mixable fluids are less influenced by the shape of the distortion than previously thought.

Some intriguing physics can be found at the interfaces between fluids, particularly if they are straddled by particles like proteins or dust grains. When placed between un-mixable fluids such as oil and water, a variety of processes, including inter-molecular interactions, will cause the particles to move around. These motions are characterised by the drag force experienced by the particles, which is itself thought to depend on the extent to which they distort fluid interfaces. So far, however, experiments investigating the intriguing effect haven’t yet fully confirmed the influence of this distortion. In new research published in EPJ E, a team led by Jean-Christophe Loudet at the University of Bordeaux, France, showed that the drag force experienced by fluid-straddling particles is less affected by interface distortion than previously believed.

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EPJE Topical review - Viscosity of nanofluids containing anisotropic particles: A critical review and a comprehensive model

When compared to nanofluids with spherical particles, nanofluids with anisotropic particles possess higher thermal conductivity and thus offer a better enhancement option in heat transfer applications. The viscosity variation of such nanofluids becomes of great importance in evaluating their pumping power in thermal systems.

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EPJE appoints new Editors-in-Chief

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EPJ is pleased to announce that January 2020 will see the appointment of two new Editors-in-Chief for EPJ E, Prof Fabrizio Croccolo (Université de Pau et des Pays de l'Adour, France) and Prof Dr Holger Stark (Technische Universität Berlin, Germany).

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Editors-in-Chief
S. Giorgio and D. Jacob
ISSN (Print Edition): 1286-0042
ISSN (Electronic Edition): 1286-0050

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