Applied Metamaterials


EPJ B Highlight - Predicting epilepsy from neural network models

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

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 D Highlight - Optimising laser-driven electron acceleration

The net energy gain of electrons as a function of time with corresponding electron momentum (centre). E. Molnár, D. Stutman, C. Ticos (2020)

A new paper examines how tuning aspects of a powerful laser beam can affect the acceleration of electrons, attempting to find the recipe for maximum net energy gain.

The interaction between lasers and matter is at the forefront of new investigations into fundamental physics as well as forming a potential bedrock for new technological innovations. One of the initiatives spearheading this investigation is the Extreme Light Infrastructure Nuclear Physics (ELI-NP) project. Here the project’s High-Power Laser System (HPLS) — the world’s most powerful laser—is just one of the tools driving electron acceleration with lasers, Direct Laser Acceleration (DLA). In a new paper published in EPJ D, Etele Molnár, ELI-NP, Bucharest, and co-authors study and review the characteristics of electron acceleration in a vacuum caused by the highest-power laser pulses achievable today looking for the key to maximum net energy gain.


EPJ C Highlight - Detecting solar neutrinos with the Borexino experiment

Distribution of best-fit results of 210Bi and CNO neutrinos interaction rates obtained fitting thousands of simulated datasets under different assumptions of 210Bi backgrounds.

Neutrinos produced by the CNO cycle within the core of the Sun are being hunted by the Borexino experiment so that we may learn more about this important nuclear process.

Neutrinos are chargeless particles with about a mass about a millionth that of an electron that are created by the nuclear processes that occur in the Sun and other stars. These particles are often colourfully described as the ‘ghosts’ of the particle zoo because they interact so weakly with matter. A paper published in EPJ C by the Borexino collaboration – including XueFeng Ding, Postdoc Associate of Physics at Princeton University, United States – documents the attempts of the Borexino experiment to measure low-energy neutrinos from the Sun’s carbon-nitrogen-oxygen (CNO) cycle for the first time.


EPJ Web of Conferences Highlight - CHEP2019: Computing in High Energy and Nuclear Physics

A snapshot of quantum field fluctuations present in the space-time vacuum that are experienced by quarks, the fundamental particles that constitute nuclear matter (here the gluonic topological charge density).

The CHEP conferences address the computing, networking and software issues for the world’s leading data‐intensive science experiments that currently analyse hundreds of petabytes of data using worldwide computing resources.

The 24th International Conference on Computing in High Energy and Nuclear Physics (CHEP 2019), took place at the Adelaide Convention Centre in Adelaide, South Australia from 4–8 November 2019.


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.


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

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 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.


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.


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

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.


Yang Hao
ISSN (Electronic Edition): 2272-2394

© EDP Sciences