EPJ B Colloquium - The strong disorder renormalization group (SDRG) method for random systems
- Published on 26 November 2018
The strong disorder renormalization group (SDRG) approach has been developed to study the low-energy excitations and spatial and temporal correlations of random systems. Since 2005 it has been extended in many new directions and beyond its initial scope. In this EPJ B Colloquium Ferenc Iglói and Cécile Monthus give an overview of the many recent developments.
EPJ B Highlight - Factors affecting turbulence scaling
- Published on 06 November 2018
Study focuses on hydrodynamic effects of external disturbances on fluids at critical points, including inconsistent turbulence in all directions, or anisotropy, and varying degrees of compressibility
Fluids exhibiting scaling behaviour can be found in diverse physical phenomena occurring both in the laboratory and in real-world conditions. For instance, they occur at the critical point when a liquid becomes a vapour, at the phase transition of superfluids, and at the phase separation of binary liquids whose components exhibit two different types of behaviour.
Until now, models have not fully taken the effect of external turbulences into account. In a recent study published in EPJ B, Michal Hnatič from Šafárik University in Košice, Slovakia and colleagues investigate the influence of ambient turbulent speed fluctuations in physical systems when they reach a critical point. These fluctuations are found to be the result of a lack of spatial regularity in these systems, or anisotropy, and of the compressibility of fluids. What is unique about this study is that the turbulence introduced in the model is novel and helps to elucidate the extent to which the speed of these fluctuations affects their scaling behaviour.
EPJ B Colloquium - A retrospective on Hardy Gross’ work
- Published on 09 October 2018
In this EPJ B Colloquium, Carlos Fiolhais offers a brief retrospective on the important scientific contributions of Hardy Gross during 25 productive years of his career, from 1976, when he published the first paper his doctoral years, until 2000, when he moved from Würzburg to Berlin. Fiolhais traces all of Gross’ publications and points out the most impressive scientific achievements, punctuating the physics with episodes from the life of Hardy Gross and other physicists in his circle, which adds extra colour to this piece.
EPJ B Highlight - Freeloaders beware: incentives to foster cooperation are just around the corner
- Published on 08 October 2018
Numerical simulations show that it is possible to coerce people to collaborate for the common good
In our society, there are always a certain percentage of people who adopt a freeloader attitude. They let other members of society do all the work and do not do their part. By not contributing their share of effort, to the detriment of the rest of society, freeloaders pose a serious social threat, and can even lead to social collapse. In a new study published in EPJ B, Chunpeng Du from Yunnan University of Finance and Economics, Kunming, China, and colleagues show that it is possible to incentivise members of society to cooperate by providing them fixed bonuses and, thus, prevent freeloader behaviour from becoming prevalent.
EPJ B Highlight - Precise electron spin control yields faster memory storage
- Published on 05 October 2018
New ultra-fast laser method aims to improve control over the electron’s degree of freedom, called spins, could enhance memory storage devices
Data storage devices are not improving as fast as scientists would like. Faster and more compact memory storage devices will become a reality when physicists gain precise control of the spins of electrons. They typically rely on ultra-short lasers to control spins. However, improvement of storage devices via spin control requires first to develop ways of controlling the forces acting on these electronic spins. In a recent study published in EPJ B, John Kay Dewhurst and colleagues, have developed a new theory to predict the complex dynamics of spin procession once a material is subjected to ultra-short laser pulses. The advantage of this approach, which takes into account the effect of internal spin rotation forces, is that it is predictive.
EPJ B Highlight - Clearer vision of the biochemical reaction that allows us to see
- Published on 31 July 2018
Physicists develop improved algorithms for simulating how complex molecules respond to excitation by photons, and explaining what happens when photons hit our eyes
What makes it possible for our eyes to see? It stems from a reaction that occurs when photons come into contact with a protein in our eyes, called rhodopsin, which adsorbs the photons making up light. In a paper published in EPJ B, Federica Agostini, University Paris-Sud, Orsay, France, and colleagues propose a refined approximation of the equation that describes the effect of this photo-excitation on the building blocks of molecules. Their findings also have implications for other molecules, such as azobenzene, a chemical used in dyes. The incoming photon triggers certain reactions, which can result, over time, in dramatic changes in the properties of the molecule itself. This study was included in a special anniversary issue of EPJB in honour of Hardy Gross.
EPJ B Highlight - Caffeine offers clues to ultra-transient positive charges' migration
- Published on 04 July 2018
A new study investigates the extremely rapid changes in the density of electrons in specific sites of the caffeine molecules thanks to an ultra-fast laser pulse that persists long enough to be observed
Caffeine keeps physicists up at night. Particularly those concerned with the capacity of electrons to absorb energy. In a new study published in EPJ B, a Franco-Japanese team of physicists have used the caffeine molecule as a playground to test the effect of ionising radiation on its electrons as they approach excited states. Their model accounts for the ionisation phenomenon in electrons, which are in a site-specific, localised orbit in the caffeine molecule. The electron excitation leaves the door open to positive charge progression along a molecular backbone. Thomas Niehaus from Claude Bernard Lyon 1 University, France, and colleagues have now developed a method for quantifying this positive charge migration in line with the ultra-short laser impulse. The observed charge motion happens on an attosecond time scale charge rearrangements driven by nuclear motion.
EPJ B Highlight - Is the Bitcoin network an oligarchy?
- Published on 26 June 2018
New study of Bitcoin transactions reveals hidden owner communities and a high-concentration of wealth distributed between a few people
Cryptocurrencies like Bitcoin can be analysed because every transaction is traceable. This means that they are an attractive system for physicists to study. In a paper published in EPJ B, Leonardo Ermann from the National Commission for Atomic Energy in Buenos Aires, Argentina, and colleagues from the University of Toulouse, France, have examined the structure of the Bitcoin-owner community by looking at the transactions of this cryptocurrency between 2009 and 2013. The team’s findings reveal that Bitcoin owners are close to an oligarchy with hidden communities whose members are highly interconnected. This research has implications for our understanding of these emerging cryptocurrency communities in our society - as usual bank transactions are typically deeply hidden from the public eye. They could also be helpful to computer scientists, economists and politicians who could better understand handle them.
EPJ B Highlight - Futuristic data storage based on controlling the interactions between nanodots magnetic ‘mood’ twirls
- Published on 18 June 2018
Better understanding of the changing magnetic state of nanometric squares in an array could be the basis for future ultrahigh density data storage
The magnetisation of nanometric square material is not fixed. It moves around in a helical motion. This is caused by the electron whose degree of freedom, referred to as spin, which follows a precession motion centred on the middle of a square nano-magnet. To study the magnetisation of such material, physicists can rely on two-dimensional arrays of square nanomagnets. In a paper published in EPJ B, P. Kim from the Kirensky Institute of Physics, associated with the Russian Academy of Sciences, in Krasnoyarsk, Siberia, Russia, and colleagues have devised a new model taking into account the factors affecting the magnetic interaction between individual nanomagnets. Better controlling such nanomagnets arrays could have applications in ultrahigh density data storage,in an electronic application called spintronics exploiting electron spins and its magnetism, and in micro- and nanosurgery controlled by magnets.
EPJ B Colloquium - Laser and hot-electrons induced ultrafast magnetic phenomena in multilayers and nanostructures
- Published on 04 June 2018
Understanding and controlling the magnetization dynamics in magnetic multilayers and nanostructures on the femtosecond timescale is becoming indispensable, both at the fundamental level and to develop future technological applications. While direct laser excitation of a ferromagnetic layer was commonly used during the past twenty years, laser-induced hot-electrons femtosecond pulses and subsequent transport in magnetic multilayers have attracted a lot of attention. Indeed, replacing photons by hot-electrons offers complementary information to improve our understanding of ultrafast magnetization dynamics and to provide new possibilities for manipulating the magnetization in a thin layer on the femtosecond timescale.