- Published on Wednesday, 14 June 2017 16:12
In high-temperature field theory applied to nuclear physics, in particular to relativistic heavy-ion collisions, it is a longstanding question how hadrons precisely transform into a quark-gluon matter and back. The change in the effective number of degrees of freedom is rather gradual than sudden, despite the identification of a single deconfinement temperature. In order to gain an insight into this issue while considering the structure of the QGP we review the spectral function approach and its main consequences for the medium properties, including the shear viscosity. The figure plots a sample spectral density on the left and the effective number of degrees of freedom (energy density relative to the free Boltzmann gas) to the right. Two thin spectral lines result in a doubled Stefan-Boltzmann limit (SB), while any finite width reduces the result down to a single SB. When spectral lines become wide, their individual contributions to energy density and pressure drops. Continuum parts have negligible contribution. This causes the melting of hadrons like butter melts in the Sun, with no latent heat in this process.
- Published on Wednesday, 14 June 2017 14:36
In the general framework of transient coupled calculations, new developments of an accurate neutron kinetics model able to characterize spatial decoupling are described, together with an application to sodium fast reactors.
- Published on Tuesday, 13 June 2017 10:03
The publishers of The European Physical Journal C – Particles and Fields are pleased to announce the appointment of Professor Dieter Zeppenfeld as new Editor-in-Chief for Theoretical Physics I: Phenomenology of the Standard Model and Beyond, replacing Professor Gino Isidori. Dieter Zeppenfeld is Head of the Institute for Theoretical Physics at the Karlsruher Institut für Technologie (KIT) and leads a research group on Collider Physics at KIT.
- Published on Thursday, 08 June 2017 12:44
Scientists reveal how electrical resistance in metallic granular media decreases as the pressure on the micro-contact interface between the grains increases
What happens when you put pressure on bunch of metallic microbeads? According to physicists, the conductivity of this granular material increases in unusual ways. So what drives these changes? The large variations in the contact surface between two grains or the rearranging electrical paths within the granular structure? In a recent study published in EPJ E, a French team of physicists made systematic measurements of the electrical resistance - which is inversely related to conductivity - of metallic, oxidised granular materials in a single 1D layer and in 3D under compression. Mathieu Creyssels from the Ecole Centrale of Lyons, Ecully, France, and colleagues showed that the granular medium conducts electricity in a way that is dictated by the non-homogenous contacts between the grains. These finding have implications for industrial applications based on metallic granular material.
- Published on Tuesday, 06 June 2017 15:29
In an era of fleeting but constant contact with extended online communities, it is common to find yourself wondering: are your friends happier/more popular than you? To put these feelings to the test, scientists have sifted through the timelines of thousands of Twitter users, to understand the ways in which social networks affect how we feel and relate to one another.
Guest post by Johan Bollen
Social media platforms have garnered billions of users, possibly because they satisfy a strong human need for feeling connected. However, do they actually contribute to our social happiness?
In EPJ Data Science we attempt to shed some light on this issue from the perspective of network science.
- Published on Monday, 05 June 2017 21:12
Combining neutron and X-ray imaging gives clues to how ancient weapons were manufactured
Since the 19th century, collectors have become increasingly interested in weapons from ancient Asia and the Middle East. In an attempt to fight forged copies, physicists are now adding their imaging power to better authenticate these weapons; the fakes can't resist the investigative power of X-rays combined with neutron imaging. In a study published in EPJ Plus, an Italian team, working in close collaboration with the Wallace Collection in London and the Neutron Imaging team at the Helmholtz Zentrum Berlin, has demonstrated the usefulness of such a combined imaging approach to help museum curators in their quest to ensure authenticity. Filament Salvemini, currently affiliated with the Australian Centre for Neutron Scattering ACNS at ANSTO in Lucas Heights near Sydney, and colleagues can now reliably tell first-class modern copies of early daggers and swords from authentic ones.
- Published on Friday, 02 June 2017 16:56
Social networks capture data about most aspects of the daily lives of millions of people around the world. The analysis of this rich and ready-available source of information can help us better understand the complex dynamics of society.
In a recent article published in EPJ Data Science the authors propose the use of location-based social networks to study the activity patterns of different gender groups, which they summarise in a guest post on the SpringerOpen blog.
Gender differences have a subjective nature and may vary greatly across cultures, making them challenging to explain. Indeed, over the past decades, this topic has received a lot of attention by researchers, but there is still a long way to reach a consensus on the subject.
- Published on Friday, 02 June 2017 16:33
The Editors of EPJE are delighted to announce the winner of the EPJE Pierre Gilles De Gennes Lecture Prize. This year the prestigious prize has been awarded to Iranian physicist Ramin Golestanian, for his outstanding theoretical contributions to the physics of microswimmers and their hydrodynamic interactions which have led to a series of exciting new discoveries and stimulated the development of the field of active matter.
The EPJE Pierre-Gilles de Gennes lecture will be delivered by Golestanian on Thursday 20th July at the 10th Liquid Matter Conference in Ljubljana, Slovenia.
- Published on Tuesday, 30 May 2017 13:30
Jan Kohlrus investigates relativitic effects to consider when setting up quantum communication systems.
The interplay and overlap between relativity and quantum theory are among the most complex and challenging open problems of modern theoretical physics. This grey area has been extensively studied on the theoretical side, sometimes following very speculative and exotic directions, while very few experiments have been proposed in a way that rigorously incorporates relativity and quantum features.
The purpose of our work is to propose feasible experiments that involve quantum fields in a relativistic framework. In our recent article in EPJ Quantum Technology, we study how observers that undergo different motion, and experience different strengths of the gravitational field, measure pulses of light that propagate from one user to another. In particular, we look at quantum communication schemes between Earth and satellite links, as well as between two satellites.
Continue reading Jan’s post here.
- Published on Tuesday, 23 May 2017 22:47
Physicists have found a way to better control high-energy particle emissions in an undulator device that could potentially be used as a source of radiation for cancer treatment or nuclear waste processing
There’s no substitute for using the right tool for the job at hand. Using low-energy radiation sources simply isn’t suitable for certain tasks: equipment used in cancer treatment requires a strong, monochromatic source of radiation to produce hard X-rays. Other similar radiation sources find applications in nuclear waste processing. To design devices that steadily emit a specific type of radiation, physicists use a special kind of crystal, referred to as a crystalline undulator. In a recent study published in EPJ D, a team has demonstrated the ability to control radiation emissions from a particle travelling through such a device. Tobias Wistisen from Aarhus University, Denmark, and colleagues have shown how to manipulate the emitted radiation by selecting a combination of incoming particle charge and energy, oscillation amplitude and period of the undulator’s crystalline lattice.