News / Highlights / Colloquia

EPJ B Highlight - Predicting epilepsy from neural network models

Details: Published on 07 December 2020

Modelling complex branching in neural networks

Improved modelling techniques have enabled a group of researchers to better predict how damaging conditions in the brain can be triggered by complex dynamics in branching networks of neurons.

Within the staggeringly complex networks of neurons which make up our brains, electric currents display intricate dynamics in the electric currents they convey. To better understand how these networks behave, researchers in the past have developed models which aim to mimic their dynamics. In some rare circumstances, their results have indicated that ‘tipping points’ can occur, where the systems abruptly transition from one state to another: events now commonly thought to be associated with episodes of epilepsy. In a new study published in EPJ B, researchers led by Fahimeh Nazarimehr at the University of Technology, Tehran, Iran, show how these dangerous events can be better predicted by accounting for branches in networks of neurons.

EPJ B Colloquium - A colloquium on the variational method applied to excitons in 2D materials

Details: Published on 04 December 2020

An interlayer exciton in a van der Waals heterostructure of 2D materials. The two stacked materials are different from each other and the electron and the hole rest in different layers.

Two-dimensional (2D) materials are condensed matter systems whose thickness varies from a single atom, as in graphene, to few atoms, as in transition metal dichalcogenides (TMDs). These exceedingly thin materials present, nevertheless, strong light-matter interaction.

EPJ B Colloquium - Hierarchically nanostructured thermoelectric materials: challenges and opportunities for improved power factors

Details: Published on 26 November 2020

Schematic of a hierarchically nanostructured thermoelectric material consisting of a matrix material with embedded atomic defects, nanoinclusions (NIs), and grain boundaries. Phonons scatter of the defects. Such geometry also provides possibilities for power factor improvements.

The field of thermoelectric materials has undergone a revolutionary transformation over the last couple of decades as a result of the ability to nanostructure and synthesize myriads of materials and their alloys. The ZT figure of merit, which quantifies the performance of a thermoelectric material has more than doubled after decades of inactivity, reaching values larger than two, consistently across materials and temperatures. Central to this, is the drastic reduction in the materials’ thermal conductivity due to the hierarchical scattering of phonons on the purposely included numerous interfaces, boundaries, dislocations, point defects, phases, etc. However, as the thermal conductivity has reached amorphous values, these benefits are reaching their limits. Any further benefits would come from the power factor, namely the product of the electronic conductivity and Seebeck coefficient squared. These quantities need to be maximized, however, they are in general inversely related, which makes power factor improvement a significant challenge.

EPJ B Highlight - Investigating optical activity under an external magnetic field

Details: Published on 06 November 2020

A schematic of a monolayer of black phosphorus under the influence of an external magnetic field. (Liu. C., Wu. F., Jiang. Q., Chen. Y., Yin. C.)

New research reveals that applying a magnetic field to a chiral metamaterial can change the way it polarises light.

Optical activity in chiral molecules has become a hot topic in physics and optics, representing the ability to manipulate the polarized state of light. Understanding how molecules rotate the plane of plane-polarized light has widespread applications, from analytic chemistry to biology and medicine — where it can, for example, be used to detect the amount of sugar in a substance. A new study published in EPJ B by Chengping Yin of the Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China, aims to derive an analytical model of optical activity in black phosphorous under an external magnetic field.

EPJ B Highlight - Antiferromagnet lattice arrangements influence phase transitions

Details: Published on 25 September 2020

Antiferromagnets display orderly lattice formations. From https://en.wikipedia.org/wiki/ Antiferromagnetism#/media/ File:Antiferromagnetic_ordering.svg credit Michael Schmid

Calculations involving ‘imaginary’ magnetic fields show how the transitioning behaviours of antiferromagnets are subtly shaped by their lattice arrangements.

Antiferromagnets contain orderly lattices of atoms and molecules, whose magnetic moments are always pointed in exactly opposite directions to those of their neighbours. These materials are driven to transition to other, more disorderly quantum states of matter, or ‘phases,’ by the quantum fluctuations of their atoms and molecules – but so far, the precise nature of this process hasn’t been fully explored. Through new research published in EPJ B, Yoshihiro Nishiyama at Okayama University in Japan has found that the nature of the boundary at which this transition occurs depends on the geometry of an antiferromagnet’s lattice arrangement.

EPJ B Highlight - Impurities enhance polymer LED efficiencies

Details: Published on 23 September 2020

PLED polymers evolve characteristically during operation

Molecular dynamics simulations have shown that the mysteriously high efficiency of polymer LEDs arises from interactions between triplet excitons in their polymer chains, and unpaired electrons in their molecular impurities.

Polymer LEDs (PLEDs) are devices containing single layers of luminescent polymers, sandwiched between two metal electrodes. They produce light as the metal layers inject electrons and holes into the polymer, creating distortions which can combine to form two different types of electron-hole pair: either light-emitting ‘singlets,’ or a non-emitting ‘triplets.’ Previous theories have suggested that the ratio between these two types should be around 1:3, which would produce a light emission efficiency of 25%. However, subsequent experiments showed that the real value can be as high as 83%. In new research published in EPJ B, physicists in China, led by Yadong Wang at Hebei North University, found that this higher-than-expected efficiency can be reached through interactions between triplet excitons, and impurities embedded in the polymer.

EPJ B Colloquium - Understanding nonequilibrium scaling laws governing collapse of a polymer

Details: Published on 03 September 2020

Recent emerging interest in experiments of single-polymer dynamics have encouraged computational physicists to revive their understanding of these phenomena, particularly in the nonequilibrium context. In a Colloquium recently published in EPJB, authors from Institut für Theoretische Physik at the University of Leipzig discuss the currently evolving approaches of investigating the evolution dynamics of homopolymer collapse using computer simulations.

EPJ B Highlight - Updating Turing’s model of pattern formation

Details: Published on 03 August 2020

Turing instabilities driven by asymmetry

Through fresh analysis of a method first proposed by Alan Turing to explain the diversity of natural patterns, a team of researchers offer new explanations of how living systems can order themselves on large scales.

In 1952, Alan Turing published a study which described mathematically how systems composed of many living organisms can form rich and diverse arrays of orderly patterns. He proposed that this ‘self-organisation’ arises from instabilities in un-patterned systems, which can form as different species jostle for space and resources. So far, however, researchers have struggled to reproduce Turing patterns in laboratory conditions, raising serious doubts about its applicability. In a new study published in EPJ B, researchers led by Malbor Asllani at the University of Limerick, Ireland, have revisited Turing’s theory to prove mathematically how instabilities can occur through simple reactions, and in widely varied environmental conditions.

EPJ B Highlight - Skyrmion dynamics and traverse mobility

Details: Published on 19 June 2020

Skyrmion trajectory with red circles representing obstacles

Skyrmions could revolutionise computing exhibiting great potential in the electronic storage of information, and the key to such a breakthrough could be understanding their behaviour under applied currents.

As the demands on information technology increase, the need to improve the storage of data also grows. Many solid-state systems suggested for such a task are founded on the manipulation of skyrmions, perfect for such a role due to their size and stability. In a study published in EPJ B, authors N.P. Vizarim and C.J.O. Reichhardt from the Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, New Mexico, USA and their colleagues aim to understand how skyrmions behave in a substrate under dc and ac drives.

EPJ B Highlight - Simulating cooperation in local communities

Details: Published on 12 June 2020

Simulations reveal how the social benefits of supplies to goods and service providers in China could be improved through a payoff transfer system, which rewards individuals who cooperate the most with their local communities.

Many goods and service providers in China rely on supplies from local governments, but these are often limited by financial budgets – especially in rural villages. Members of the public must cooperate with their governments and each other in order for this system to run smoothly, but unfortunately, this balance is threatened by a small proportion of individuals who take in welfare without contributing fairly to their communities. In new research published in EPJ B, Ran Yang and colleagues at Tianjin University, China, introduce a new simulation-based approach which could help to solve this issue, through a cost-effective system which rewards individuals who use welfare systems responsibly.