2023 Impact factor 2.6
Special Topics

EPJ E Highlight - α-SAS: Improving measurements of complex molecular structures

α-SAS for Janus particles. Credit: E M Anitas.

Integrating small-angle neutron scattering with machine learning algorithms could enable more accurate measurements of complex molecular structures.

Small-angle scattering (SAS) is a powerful technique for studying nanoscale samples. So far, however, its use in research has been held back by its inability to operate without some prior knowledge of a sample’s chemical composition. Through new research published in EPJ E, Eugen Anitas at the Bogoliubov Laboratory of Theoretical Physics in Dubna, Russia, presents a more advanced approach, which integrates SAS with machine learning algorithms.

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EPJ E Topical Issue: Festschrift in honor of Philip (Fyl) Pincus

Guest Editors: David Andelman,
Jean-Marc Di Meglio, and Cyrus R. Safinya

This topical issue comprises 49 contributions covering a broad range of topics, which advance the understanding of soft and biological matter systems from physical and chemical aspects. More than 200 scientists globally contributed to this noteworthy Festschrift, which is divided into thematic categories.

The first theme is focused on equilibrium and non-equilibrium soft matter systems, including topics associated with polymers and colloidal systems, in uncharged and charged systems, where Pincus has made lasting contributions. In addition, other contributions are concerned with liquids, flowing and active matter, and granular systems. The second theme groups together many contributions that are focused on biological physics, including properties of the cell cytoskeleton and associated proteins, intrinsically disordered proteins, lipid membranes, membrane-associated proteins, and assembly and interactions of viral capsids with lipids and polymers. A third group of contributions is in the nascent field of biomolecular and biomimetic materials at the crossroads between physics, chemistry, bioengineering, and materials science. Finally, systems dealing with far-from-equilibrium states of matter in biology are addressed by a few contributions focusing on the physical properties of living cells.

All articles of this collection are available here and are freely accessible until 20 August 2024. For further information read the Editorial.

EPJ E Highlight - Tuning the movement of a self-propelled robot to the physics of living matter

The team’s dynamic robot model. Credit: S. Paramanick., EPJ E (2024)

The two-wheeled robot employs a range of complex active dynamics that can be implemented with precise control.

Robots are becoming an increasingly important part of our lives, performing jobs that are too dangerous for humans. This can often involve navigating complex environments, something rigid-bodied autonomous robots find difficult. Such robots faced similar challenges when miniaturised and used to model physics of living matter.

These challenges could be countered by a robot that can move with the mobility of living things and can respond to environmental signals just like a cellular organism. To model such systems experimentally, it is necessary to develop a tunable system that can replicate life-like dynamics.

In a new paper in the EPJ E, the authors, including Nitin Kumar from the Indian Institute of Technology Bombay and his co-authors, describe the development of a scheme for generating tunable active dynamics in a self-propelled robotic device. The result is a two-wheeled robot that utilizes a simple differential-drive mechanism, enabling a range of complex active dynamics to be implemented with precise control.

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EPJ E Highlight - Investigating collective motions in schools of zebrafish

Zebrafish display interesting collective dynamics. By Azul - Own work, Copyrighted free use, https://commons.wikimedia.org/w/ index.php?curid=260841

Observations reveal new insights into the evolution of collective motions within schools of zebrafish, and how their complexity and structure vary with density.

Active systems display a wide range of complex and fascinating behaviours, many of which are not yet fully understood. Found on scales ranging from microbes and self-propelling particles to large groups of fish, birds, and mammals, they are made up of many individual parts, which each convert energy from their surroundings into motion.

Through new analysis published in EPJ E, Antonio Romaguera and collaborators at the Rural Federal University of Pernambuco, Brazil, have gained deeper insights into the collective motions of schools of zebrafish: active systems in which multiple fish can collectively move in the same direction. The team’s discoveries could help researchers to better understand the unique properties of active matter, and how complex behaviours emerge and evolve on different scales.

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EPJ E Highlight - Modelling vibration patterns in granular materials

Building statistical models of grain behaviours

The ‘Laguerre ensemble’ statistical model can better describe the vibrational patterns of granular materials at a critical point of transition in their behaviour.

Granular materials are collections of solid particles which can behave in similar ways to both solids and liquids via interactions between grains. Previously, researchers have explored how the behaviours of these materials can be described in the language of statistical mechanics.

Through new research published in EPJ E , Onuttom Narayan at the University of California, together with Harsh Mathur at Case Western Reserve University, show how the characteristic vibrational patterns associated with granular materials at the point where they transition to more solid-like states can be reproduced more accurately. The work could help researchers to gain a deeper understanding of how granular materials behave.

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EPJ E Highlight - Breaking an electrolyte’s charge neutrality

Electrical charge (red) builds up on a varied cross-section channel. Credit: Malgaretti et al. (2024).

Excess charge builds up in salt solutions due to interactions between electrostatic forces and a channel’s varying cross section

Plant vascular circulation, ion channels, our own lymphatic network, and many energy harvesting systems rely on the transport of dissolved salt solutions through tortuous conduits. These solutions, or electrolytes, maintain a positive or negative charge that’s vital to how the system functions. However, this charge balance depends on the properties of the channel that contains the fluid. In a study published in EPJ E, Paolo Malgaretti, of the Helmholtz Institute Erlangen-Nürnberg for Renewable Energy/Forschungszentrum Jülich, Germany, and his colleagues, now derive equations that describe how local electrical charge in electrolytes changes in channels with varying cross sections, at equilibrium. The result could help to predict pathways for charged particles in biological and technological systems.

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EPJ E Colloquium - Convective mixing in porous media: A review of Darcy, pore-scale and Hele-Shaw studies

Solute concentration field of a convective flow in a porous medium

When a porous medium is filled with two fluid layers of different density, with the heavier fluid sitting on top of the lighter one, the system may become unstable. Due to the vertical density contrast, convective finger-like structures can form and accelerate fluid mixing. This configuration is representative of a variety of systems of practical interest, particularly in geophysical processes.

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EPJ E Topical review - Lift at low Reynolds number

In hydrodynamics, a lift phenomenon arises when a force acts on an object perpendicularly to its initial motion. In everyday life, we are familiar with this effect allowing for instance planes to take off or soccer balls to follow bent trajectories. For such big and fast objects, inertia combines with symmetry breaking (wing shape profile or ball rotation) to give rise to lift. However, lift forces are also at play at low Reynolds numbers, i.e. for small objects or slow flows where fluid viscosity dominates over inertia.

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EPJ E Topical Issue: Novel Molecular Materials and Devices from Functional Soft Matter

Guest Editors: Jean-Marc Di Meglio, Aritra Ghosh, Orlando Guzmán, P. Lakshmi Praveen.

This Topical issue focusses on soft matter materials and devices. Soft matter can be defined by a large response to weak external perturbations, with physical properties governed by local internal dynamics. It may contain ordered structures at mesoscopic scales, but appear disordered at molecular scales. Because of this, the ordered and disordered aspects of soft matter can be combined to manufacture innovative and original functional materials and devices. The most ambitious course of action is then to develop multi-functional materials and devices that exploit two or more rheological, electrical, electronic, photo-physical, quantum chemical or opto-electronic responses of soft matter. Solving grand challenges for new generations of functional materials demands. The aim of this Topical Issue is to provide an inspiring platform for the dissemination of the latest developments and discoveries in the design, simulation, modeling, synthesis, construction and characterization of soft matter structures for functional materials and devices. The emphasis of this Topical issue is on physical methodologies and characterizations to resolve multi-disciplinary issues.

All articles of this collection are available here and are freely accessible until 31 December 2023. For further information read the Editorial.

EPJ E Topical Issue: Quantitative AI in Complex Fluids and Complex Flows: Challenges and Benchmarks

Guest Editors: Luca Biferale, Michele Buzzicotti and Massimo Cencini.

The collection addresses open problems, challenges, and benchmarks for data-driven and equation-informed tools for data assimilation, prediction, (subgrid-scale) modeling, inpainting, classification, and (optimal) control of Eulerian and Lagrangian problems in complex flows.

The goal is to move from proof-of-concept to quantitative benchmarks and grand challenges, including scaling of algorithms and complexity of datasets.

The original research papers, presented in a colloquium format, focus on the latest experimental, theoretical, or computational advances and address the interpretability, superiority, and usability of data-driven tools when applied to realistic fluid dynamics problems in engineering, geophysics, biophysics, and other fields. Key topics covered include: (i) Modeling and controlling complex flows with data-driven methods. (ii) Prediction and data-assimilation of multiscale flows. (iii) Reconstruction, super-resolution of fluid flows with data-driven and physics-informed tools. (iv) Optimization of navigation and other tasks in complex flows. (v) Animal behavior in flows.

All articles of this collection are available here and are freely accessible until 27 December 2023. For further information read the Editorial.

Managing Editors
Sandrine Karpe and Vijala Kiruvanayagam (EDP Sciences) and Sabine Lehr (Springer-Verlag)
The collaboration for this special issue has been a pleasent experience.

Yong Zhou, Xiangtan University, China,
Editor EPJ Special Topics 222/8, 2013

ISSN: 1951-6355 (Print Edition)
ISSN: 1951-6401 (Electronic Edition)

© EDP Sciences and Springer-Verlag