EPJ B Highlight - Impurities enhance polymer LED efficiencies
- Details
- Published on 23 September 2020
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
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
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.
EPJ B Colloquium - Origin of optical bandgap fluctuations in graphene oxide
- Details
- Published on 11 June 2020
Graphene Oxide (GO) is a carbon-based nanomaterial prepared through the chemical oxidation of natural graphite in the presence of strong oxidants. It was identified long before pristine graphene, first reported in the 17th century by Brodie et al. Among many potential applications, GO can be used to produce reduced GO (rGO) for transparent conducting electrodes (TCEs), which has been, for instance, employed in the preparation of organic-light emitting diodes and organic photovoltaic devices. Other works also report the successful use of GO for the preparation of membranes for desalination and water purification, as well as active layers in biosensors, among many other applications. To address the needs of theses versatile applications several modifications in the synthesis of GO have been developed.
EPJ B Highlight - Exploring mass dependence in electron-hole clusters
- Details
- Published on 09 June 2020
New calculations reveal that the behaviours of electron-hole clusters depend strongly on the masses of their particles.
In solid materials, when an electron changes position without another to fill its place, a positively charged ‘hole’ can appear which is attracted to the original electron. In more complex situations, the process can even result in stable clusters of multiple electrons and holes, whose behaviours all depend on each other. Strangely, the masses of each particle inside a cluster can be different to their masses when they are on their own. However, physicists aren’t yet entirely clear how these mass variations can affect the overall properties of clusters in real solids. Through a study published in EPJ B, Alexei Frolov at the University of Western Ontario, Canada, reveals that the behaviour of one type of three-particle cluster displays a distinct relationship with the ratio between the masses of its particles.
EPJ B Colloquium - Ergodicity and large deviations in physical systems with stochastic dynamics
- Details
- Published on 22 April 2020
In ergodic physical systems, time-averaged quantities converge (for large times) to their ensemble-averaged values. Large deviation theory describes rare events where these time averages differ significantly from the corresponding ensemble averages. It allows estimation of the probabilities of these events, and their mechanisms, and has been applied to a wide range of physical systems, including exclusion processes, glassy materials, models of heat transport, proteins, climate models, and non-equilibrium quantum systems.
EPJ B Highlight - What protects minority languages from extinction?
- Details
- Published on 21 April 2020
Mathematical modelling of competing languages in a geographical area suggests two scenarios in which one or more minority languages will be more likely to survive.
Over 6,000 languages are currently spoken worldwide, but a substantial minority - well over 5% - are in danger of dying out. It is perhaps surprising that this fraction is no higher, as most models have so far predicted that a minority language will be doomed to extinction once contacts with speakers of the majority language reach a certain level. Statistical physicists Jean-Marc Luck from Université Paris-Saclay, Paris, France and Anita Mehta from the University of Oxford, UK have described, using mathematical modelling, two mechanisms through which this doomsday scenario does not occur, i.e. several languages come to coexist in the same area. This work is now published in EPJ B.
EPJ B Highlight - Separations between earthquakes reveal clear patterns
- Details
- Published on 12 March 2020
A new analysis of real earthquake data shows that the similarity between inter-earthquake times and distances displays a distinct relationship with their separation from an initial earthquake.
When large earthquakes occur, seismologists are well aware that subsequent, smaller tremors are likely to take place afterwards in the surrounding geographical region. So far, however, few studies have explored how the similarity between these inter-earthquake times and distances is related to their separation from initial events. In a new study published in EPJ B, researchers led by Min Lin at the Ocean University of China in Qingdao show for the first time that the two values become increasingly correlated the closer they are in time and space to previous, larger earthquakes.
