2016 Impact factor 2.787

EPJ E Highlight - Resolving tension on the surface of polymer mixes

Polymers © iker-urteaga via Unsplash.

A new study finds a simple formula to explain what happens on the surface of melted mixes of short- and long-strand polymers

Better than playing with Legos, throwing polymer chains of different lengths into a mix can yield surprising results. In a new study published in EPJ E, physicists focus on how a mixture of chemically identical chains into a melt produces unique effects on their surface. That’s because of the way short and long polymer chains interact with each other. In these kinds of melts, polymer chain ends have, over time, a preference for the surface. Now, Pendar Mahmoudi and Mark Matsen from the University of Waterloo, Ontario, Canada, have studied the effects of enriching long-chain polymer melts with short-chain polymers. They performed numerical simulations to explain the decreased tension on the surface of the melt, due to short chains segregating at the surface over time as disorder grows in the melt. They found an elegant formula to calculate the surface tension of such melts, connected to the relative weight of their components.

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EPJ E Highlight - The secret to improving liquid crystal's mechanical performance

3D plot of the concentration of nanoparticles around a moving edge dislocation in a smectic A liquid crystal.

Better lubricating properties of lamellar liquid crystals could stem from changing the mobility of their structural dislocations by adding nanoparticles

By deliberately interrupting the order of materials - by introducing different atoms in metal or nanoparticles in liquid crystals - we can induce new qualities. For example, metallic alloys like duralumin, which is composed of 95% of aluminium and 5% copper, are usually harder than the pure metals. This is due to an elastic interaction between the defects of the crystal, called dislocations, and the solute atoms, which form what are referred to as Cottrell clouds around them. In such clouds, the concentration of solute atoms is higher than the mean concentration in the material. In a paper published in EPJ E, Patrick Oswald from the École Normale Supérieure of Lyon, France, and Lubor Lejček from the Czech Academy of Sciences have now theoretically calculated the static and dynamical properties of the Cottrell clouds, which form around edge dislocations in lamellar liquid crystals of the smectic A variety decorated with nanoparticles. This work could be important, for example, in the context of improving the lubricating performance of such liquid crystals.

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EPJ E Highlight - Like a game of 'spot the difference' for disease-prone versus healthy people

Dynamical behaviour of different low-density lipoproteins as a function of temperature and pressure.

The change in behaviour of natural nanoparticles, called lipoproteins, under pressure could provide new insights to better understand the genesis of high cholesterol and atherosclerosis

Understanding common diseases sometimes boils down to grasping some of their basic mechanisms. For instance, a specific kind of natural nanoparticles, called low-density lipoproteins (LDL), are fascinating scientists because their modification plays a key role in people affected by high cholesterol. They are also known for their role in the formation of atherosclerosis. Judith Peters from the University Grenoble Alpes and the Institute Laue Langevin, Grenoble, France and colleagues from the Medical University of Graz, Austria, mimicked variations of LDL found in people affected by such diseases. They then compared their responses to temperature variations and increased pressure with those of lipoproteins found in healthy people. Their findings, recently published in EPJ E, show that the LDL from healthy people behaved differently when subjected to high pressure compared to LDL affected by the common diseases studied.

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EPJ E Highlight - Granular media friction explained: Da Vinci would be proud

Heather Shevlin / Unsplash Caption: Physicists show how solid friction affects sand grains.

New study explains how solid friction forces affect granular materials in two or more dimensions

Leonardo Da Vinci had already noticed it. There is a very peculiar dynamics of granular matter, such as dry sand or grains of wheat. When these granular particles are left on a vibrating solid surface, they are not only subject to random vibrations, they are also under the spell of solid friction forces, like the force a dry floor would exert on a brick in contact with that floor. In a study published in EPJ E, Prasenjit Das from the Jawaharlal Nehru University, India, and colleagues extended our understanding of this problem from the well-known, one-dimensional case to multiple dimensions.

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EPJ E Highlight - Granular material conductivity increases in mysterious ways under pressure

Image of grains of copper powder through a microscope.

Scientists reveal how electrical resistance in metallic granular media decreases as the pressure on the micro-contact interface between the grains increases

What happens when you put pressure on bunch of metallic microbeads? According to physicists, the conductivity of this granular material increases in unusual ways. So what drives these changes? The large variations in the contact surface between two grains or the rearranging electrical paths within the granular structure? In a recent study published in EPJ E, a French team of physicists made systematic measurements of the electrical resistance - which is inversely related to conductivity - of metallic, oxidised granular materials in a single 1D layer and in 3D under compression. Mathieu Creyssels from the Ecole Centrale of Lyons, Ecully, France, and colleagues showed that the granular medium conducts electricity in a way that is dictated by the non-homogenous contacts between the grains. These finding have implications for industrial applications based on metallic granular material.

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EPJ E News - Ramin Golestanian awarded the Pierre-Gilles de Gennes Lecture Prize

Ramin Golestanian awarded the 2017 EPJE Pierre-Gilles de Gennes Lecture Prize.
Ramin Golestanian

The Editors of EPJE are delighted to announce the winner of the EPJE Pierre Gilles De Gennes Lecture Prize. This year the prestigious prize has been awarded to Iranian physicist Ramin Golestanian, for his outstanding theoretical contributions to the physics of microswimmers and their hydrodynamic interactions which have led to a series of exciting new discoveries and stimulated the development of the field of active matter.

The EPJE Pierre-Gilles de Gennes lecture will be delivered by Golestanian on Thursday 20th July at the 10th Liquid Matter Conference in Ljubljana, Slovenia.

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EPJ E Colloquium - Quantum effects are hot in supercooled water

The importance of nuclear quantum effects is well known for in solid systems at very low temperatures (T<10K). At higher temperature (above ~20-50K) usually the contribution of these quantum effects to structural relaxation is considered minor. Traditionally, researchers who study the structural relaxation in liquids and the glass transition neglect to consider quantum effects. However, it is becoming increasingly evident when studying light molecules (such as water) at temperature of 100-200K that quantum effects might play an important role in structural dynamics, and provide non-negligible contributions at temperatures as high as ambient.

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EPJE News - Welcome to the new Editor-in-Chief for Biological Physics

© François Graner

We are pleased to announce that François Graner joins Francesco Sciortino as co-Editor-in-Chief of EPJ E. He will lead and oversee the journal activities and editors in biological physics, with the aim to expand and strengthen the connections with the biological physics research community.

This is how Graner describes the benefits offered by the journal and its role in the community: “EPJ E is characterized by the outstanding quality of its editorial process and its panel of reviewers, something I already appreciated as an author. The journal plays an important role in maintaining high standards, as well as reinforcing the interface between soft condensed matter and biophysics. It is the perfect journal where to discuss the physical questions raised by current discoveries in biology and biophysics, and to report the related new physics methods and modeling.”

François Graner is Directeur de recherche at CNRS and Université Paris 7 "Denis Diderot". He is an accomplished expert on soft matter, statistical physics and biophysics.

We take this opportunity also to thank his predecessor Andreas Bausch for his excellent editorial service and dedication through the recent year.

EPJ E News - One year of Tips & Tricks

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It is the tricks that often form the commonality between researchers working in different fields. A little over a year ago the European Physical Journal E published the first papers in a new section called Tips and Tricks (T&T). The goal of this new section was simple: to provide a venue to publish a novel numerical recipe, sample preparation method, or experimental design.

Such details are often only briefly described in the scientific literature, passed only from student to student, or simply shared as a ‘personal communication’ between research groups. Sometimes such enabling techniques are not passed on at all. In all such cases, the scientific community as a whole is not able to use this knowledge to move forward. Moreover, while the research of some team may not be directly relevant to another, a computational method, experimental procedure, or sample cell design has the potential to be broadly transformative. We have found during our careers that various sample cell configurations, experimental designs, or sample preparation techniques were shared amongst our colleagues. In some cases the science became secondary to a particular technique, and more emails were shared describing a trick than citations earned on a paper where only a brief description was provided. The first year of EPJE's T&T has been exciting, with 13 papers that span many different tools and methods, from vesicles-on-a-chip to a three-body potential for molecular dynamics. You will find them all listed below with their respective links.

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EPJ E Highlight - Speed-dependent attraction governs what goes on at the heart of midge swarms

Trajectories of individual midges within a swarm recorded using high-speed cameras.

New study reveals swarm cohesion stems from an adaptive behaviour, where the faster individual midges fly, the stronger the gravitational-like force they experience

Ever wondered what makes the collective behaviour in insect swarms possible? Andy Reynolds from Rothamsted Research, UK, and colleagues at Stanford University, California, USA, modelled the effect of the attraction force, which resembles Newton’s gravity force, acting towards the centre of a midge swarm to give cohesion to their group movement. In a recent study published in EPJ E, their model reveals that the gravity-like attraction towards the heart of the swarm increases with an individual’s flight speed. The authors confirmed the existence of such an attractive force with experimental data.

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Editors-in-Chief
Frank Schweitzer and Alessandro Vespignani

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