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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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EPJ B Highlight - Potential new applications stem from controlling particles’ spin configurations

credit: Creativity103.

Physicists prove important constraints for fermion gases with spin population imbalance

Fermions are ubiquitous elementary particles. They span from electrons in metals, to protons and neutrons in nuclei and to quarks at the sub-nuclear level. Further, they possess an intrinsic degree of freedom called spin with only two possible configurations, either up or down. In a new study published in EPJ B, theoretical physicists explore the possibility of separately controlling the up and down spin populations of a group of interacting fermions. Their detailed theory describing the spin population imbalance could be relevant, for instance, to the field of spintronics, which exploits polarised spin populations.

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EPJ D Highlight - Reading between the lines of highly turbulent plasmas

A short sequence of solitons.

Study shows how to identify highly turbulent plasma signatures in the broadening of the shapes of lines emitted by ions and atoms within

Plasma, the ionised state of matter found in stars, is still not fully understood, largely due to its instability. Astrophysicists have long-since sought to develop models that can account for the turbulent motions inside plasma, based on observing line shapes emitted by atoms and ions in the plasma. Turbulences are typically detected through the observation of broadened lines due to the Doppler effect, similar to the principle behind radar. In a new study published in EPJ D, Roland Stamm from the CNRS and Aix-Marseille University, France, and colleagues develop an iterative simulation model that accurately predicts, for the first time, the changes to the line shape in the presence of strong plasma turbulence. Ultimately, the authors aim to provide a system for assessing plasma turbulence that is valid for both a stellar atmosphere and the ITER tokamak designed to generate fusion energy. Line shapes are extensively employed as a powerful diagnostic tool for detecting turbulences in stable gases and plasmas. For many years now, astrophysicists have developed and employed models that gauge the effect of turbulent motions in the broadening of line shapes due to the Doppler effect. Such models are now also being employed to understand the role of turbulences in plasmas created to harvest energy from fusion.

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EPJ Plus Highlight - Does the universe have a rest frame?

A simplified diagram showing the basic idea of the experimental design.

Experiment aims at resolving divergence between special relativity and standard model of cosmology

Physics is sometimes closer to philosophy when it comes to understanding the universe. Donald Chang from Hong Kong University of Science and Technology, China, attempts to elucidate whether the universe has a resting frame. The results have recently been published in EPJ Plus.

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EPJB Colloquium: The continuous-time random walk, fifty years on

This Colloquium paper published in EPJ B by R. Kutner and J. Masoliver revisits the most significant achievements and future possibilities for continuous-time random walk (CTRW), a versatile and widely applied formalism.

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EPJ E Highlight - Molecular scale transporter with a twist, powered by liquid crystal defects

Twisting effect, called chirogyral, dictated by the handedness of the fibre in a vertical magnetic field.

Delivery of biochemical substances is now possible using a novel application of liquid crystal defects, forming a loop enclosing the substance travelling alongside twisted fibres

Defects that break the symmetry of otherwise orderly material are called topological defects. In solid crystals, they are called dislocations because they interrupt the regularly structured atom lattice. In contrast, topological defects called disclinations take the form of loops in liquid crystal of the nematic variety, whose elongated molecules look like a shoal of fish. New experiments supported by a theoretical model show how defects forming loops around twisted plastic fibres dipped in liquid crystal could be used for the transport of biochemical substances, when controlled by electric and magnetic fields. Published in EPJ E, these findings - achieved by Mallory Dazza from the Ecole normale supérieure Cachan, France, and colleagues - have potential applications in electro-optical micromechanical and microfluidic systems.

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EPJ Data Science - View featured video: How teams and players stack up and why

“Winning is not a sometime thing; it’s an all the time thing. Winning is a habit,” said legendary American football coach Vince Lombardi.

Human sports and games, with their rules of competition and measures of performance, serve as an ideal test-bed to look for universal features of hierarchy formation. In a recent article published in EPJ Data Science, José A. Morales and colleagues study the behaviour of performance rankings over time of players and teams for several sports and games, and find statistical regularities in the dynamics of ranks. This finding dispels the commonly held notion that rank changes are due to the intrinsic strengths or qualities of teams and players. The same phenomenon may apply to more complex competition settings with further examinations.

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EPJ B Highlight - The secrets of vibration-enhanced conductivity in graphene

Graphene structure. The transverse short-wavelength vibrational mode is excited by applying initial displacements to the atoms of the red and blue sublattices in opposite directions along the Z axis.

Physicists define a smart way of inducing large-amplitude vibrations in graphene models, which could open the door for novel electronic applications

Graphene, the one-atom-thick material made of carbon atoms, still holds some unexplained qualities, which are important in connection with electronic applications where high-conductivity matters, ranging from smart materials that collectively respond to external stimuli in a coherent, tunable fashion, to light-induced, all-optical networks. Materials like graphene can exhibit a particular type of large-amplitude, stable vibrational modes that are localised, referred to as Discrete Breathers (DBs). The secret to enhancing conductivity by creating DBs lies in creating the external constraints to make atoms within the material oscillate perpendicular to the direction of the graphene sheet. Simulations-based models describing what happens at the atomic level are not straightforward, making it necessary to determine the initial conditions leading to the emergence of DBs. In a new paper published in EPJ B, Elham Barani from the Ferdowsi University of Mashhad, Iran, and colleagues from Russia, Iran and Singapore use a systematic approach to identify the initial conditions that lend themselves to exciting DBs in graphene, ultimately opening the door to understanding the keys to greater conductivity.

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EPJ D Highlight - Ionisation mechanisms of captive atoms struck by light matter

Ejected electron spectrum of the bare and caged hydrogen atom subjected to an external light pulse.

Physicists elucidate the effects of light rays falling onto hydrogen atoms trapped in a carbon atom cage

Light interacting with hydrogen atoms enclosed in hollow cages composed of carbon atoms - referred to as fullerene material - produces ionisation. This phenomenon, which has been the subject of intense theoretical scrutiny, is particularly interesting because the light rays can have dramatic effects in inducing small external energy potentials. Specifically, they alter the structural and dynamic properties of the atoms confined within the fullerene molecule. Ana Frapiccini from the CONICET research centre at the Universidad Nacional del Sur, in Bahía Blanca, Argentina, and colleagues have just published a study in EPJ D explaining the theory behind the ionisation. Applications of this process include drug delivery, quantum computation, photovoltaics and hydrogen storage.

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EPJ E Review - Water and ionic liquids. Two very different solvents, two intriguing behaviours when nanoconfined

Confinement of liquids at the nanoscale gives rise to intriguing new chemical and physical behaviours and structures. Scientists are studying the phenomenon also because of its relevance to molecular biology (permeability of ion channels and protein stability), chemical engineering (nano-fluidic devices and molecular sieves) and geology (transport through porous rocks).

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