Nuclear Sciences & Technologies


EPJ B Highlight - Between extinction and survival of endangered populations

Semi-logarithmic plot of the survival probability P, vs. time t for several population sizes.

Lifetime simulation of biological populations reveals dramatic population fluctuations before extinction

Populations of endangered species reach a critical point in their life where they either survive or evolve towards extinction. Therefore, efforts to predict and even prevent the extinction of biological species require a thorough understanding of the underlying mechanisms. In a new study published in EPJ B, Hatem Barghathi and colleagues from Missouri University of Science and Technology, USA, have investigated how environmental disturbance at random times could cause strong fluctuations in the number of individuals in biological populations. This, in turn, makes extinction easier, even for large populations. They found that environmental disorder can lead to a period of slow population increase interrupted by sudden population collapses. These findings also have implications for solving the opposite problem when attempting to predict, control and eradicate population of viruses in epidemics.


EPJ Data Science Highlight - Are your tweets feeling well? Opinion and emotion in tweets change when you get sick

©Max Pixel (edited)
©Max Pixel (edited)

Can we tell if a person is physically ill by the way they tweet? On a recently published article in the journal EPJ Data Science, researchers at the Pacific Northwest National Laboratory uncover links between the health of users and the emotional tone of their social media output.

Guest post by by Svitlana Volkova, originally published on SpringerOpen blog

Any doctor or nurse knows good public health begins with prevention. Whether it’s a severe strain of the flu or mental illness, identifying the need for help early can save lives. Social media could be the game-changing solution public health workers have been looking for. Whereas traditional data from clinics may take weeks to collect, social media streams in real time. In other words, public health workers could monitor social media like a heartbeat, and take action before people visit a doctor.


EPJ H Highlight - How Einstein’s theory of gravitation experienced a Renaissance after World War II

Einstein’s General Relativity’s place in history.

Journey into the post-war transformation leading to the return of General Relativity within physics

Einstein’s 1915 theory of gravitation, also known as General Relativity, is now considered one of the pillars of modern physics. It contributes to our understanding of cosmology and of fundamental interactions between particles. But that was not always the case. Between the mid-1920s and the mid-1950s, General Relativity underwent a period of stagnation, during which the theory was mostly considered as a stepping-stone for a superior theory. In a special issue of EPJ H just published, historians of science and physicists actively working on General Relativity and closely related fields share their views on the process, during the post-World War II era, in particular, which saw the “Renaissance” of General Relativity, following progressive transformation of the theory into a bona fidae physics theory.


EPJ E Highlight - Granular media friction explained: Da Vinci would be proud

Heather Shevlin / Unsplash Caption: Physicists show how solid friction affects sand grains.

New study explains how solid friction forces affect granular materials in two or more dimensions

Leonardo Da Vinci had already noticed it. There is a very peculiar dynamics of granular matter, such as dry sand or grains of wheat. When these granular particles are left on a vibrating solid surface, they are not only subject to random vibrations, they are also under the spell of solid friction forces, like the force a dry floor would exert on a brick in contact with that floor. In a study published in EPJ E, Prasenjit Das from the Jawaharlal Nehru University, India, and colleagues extended our understanding of this problem from the well-known, one-dimensional case to multiple dimensions.


EPJ D Highlight - First aid kit in some living organisms helps fix DNA after lengthy sun exposure

Important photolyase residues for DNA binding.

New study unveils the binding mechanisms of enzymes capable of repairing DNA damaged by UV light before any risk of cellular malfunction sets in

Sunburn in living organisms is caused by ultraviolet (UV) light from the sun damaging the DNA in the cells. Many organisms, however, have an in-built mechanism for repairing the sun damage. This is possible thanks to an enzyme called DNA photolyase, which is so specialised that cryptochrome, a structurally similar molecule, is unable to do the same job. By comparing both types of molecule, physicists can understand precisely how the ability of our enzymes to repair DNA boils down to the most minute structural details. In a study published in EPJ D, Katrine Aalbæk Jepsen from the University of Southern Denmark, in Odense, and her colleague Ilia Solov'yov pinpoint the mechanism by which repair enzymes bind to the damaged site.


EPJ A Highlight - Nuclear and Quark Matter at High Temperature

Left: sample spectral densities, Right: the resulting scaled energy densities.

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.


EPJ N Highlight - TFM spatial kinetics model, towards ASTRID transient calculations

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.


EPJ C - New Editor-in-Chief for Theoretical Physics I

Dieter Zeppenfeld

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.

EPJ E Highlight - Granular material conductivity increases in mysterious ways under pressure

Image of grains of copper powder through a microscope.

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.


EPJ Data Science Highlight - Are your friends happier than you?

Photo from Pixabay, CC0 public domain.
Photo from Pixabay, CC0 public domain.

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.


G. Moutiers and A. Nicolas
ISSN: 2491-9292 (Electronic Edition)

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