- Published on 26 January 2018
How magnetic force acts on charged subatomic particles near the speed of light
Current textbooks often refer to the Lorentz-Maxwell force governed by the electric charge. But they rarely refer to the extension of that theory required to explain the magnetic force on a point particle. For elementary particles, such as muons or neutrinos, the magnetic force applied to such charges is unique and immutable. However, unlike the electric charge, the magnetic force strength is not quantised. For the magnetic force to act on them, the magnetic field has to be inhomogeneous. Hence this force is more difficult to understand in the context of particles whose speed is near the speed of light. Moreover, our understanding of how a point-particle carrying a charge moves in presence of an inhomogenous magnetic field relied until now on two theories that were believed to differ. The first stems from William Gilbert's study of elementary magnetism in 16th century, while the second relies on André-Marie Ampère electric currents. In a new study just published in EPJ C, the authors Johann Rafelski and colleagues from the University of Arizona, USA, succeeded in resolving this ambiguity between Ameperian and Gilbertian forms of magnetic force. Their solution makes it possible to characterise the interaction of particles whose speed is close to the speed of light in the presence of inhomogeneous electromagnetic fields.
- Published on 26 January 2018
Understanding the dynamics of message transmission in networks leads to identification of key individuals spreading news and viruses in epidemics
Social networks, such as Twitter, thrive on key influencers spreading news. Like information, epidemics also spread from key individuals. To identify the most influential actors in such networks, many studies have, until now, focused on ranking the influence of individual nodes. But these methods are not accurate enough to single out influential spreaders because they fail to take into account the spreading dynamics. Now, Byungjoon Min from the Institute of Interdisciplinary Physics and Complex Systems, Balearic Island University, Palma de Mallorca, Spain, has calculated for the first time the expected size of epidemic outbreaks when spreading originates from a single seed. In a study published in EPJ B, Min accurately predicts the influence of spreaders in such networks. Applications include viral marketing, efficient immunisation strategies, and identifying the most influential actors in our society.
- Published on 26 January 2018
It is with great pleasure that we announce that Professor Kai Bongs from the University of Birmingham, UK, has been appointed Editor-in-Chief of EPJ Quantum Technology.
Prof. Bongs is the director of the UK National Quantum Technology Hub in Sensors and Metrology, a consortium of researchers from 11 universities, NPL and over 120 companies, which focuses in translating quantum science enabled precision measurements with cold atoms into technology and economic benefit. He has been working in the field of cold atoms for over 20 years. After studying Physics up to his PhD in the group of Prof. Wolfgang Ertmer at the University of Hannover and a postdoctoral appointment on atom interferometry in the group of Mark Kasevich at Yale University, he did his Habilitation on quantum gas mixtures working with Prof. Klaus Sengstock at the University of Hamburg. Since 2007 he holds a chair at the University of Birmingham heading the group of quantum matter and directing the Birmingham part of the Midlands Ultracold Atom Research Centre, MUARC. His research achievements have been recognised by a Royal Society Wolfson Research Merit Award.
Prof. Bongs takes on this position after the founding Editor, Prof. Gerard Milburn stepped down at the end of 2017. We take this opportunity to show our gratitude to Prof. Milburn for his role in bringing EPJ Quantum Technology to life and for his hard work and leadership in the past four years.
- Published on 23 January 2018
When colloidal particles find themselves in a temperature gradient they move in response to it, in some cases toward the hotter some toward the cooler side, depending on the specific physical chemistry of the colloid and the solvent surrounding it. This process, called thermophoresis, is generally regarded as a phoretic phenomenon: the thermal motion of a colloid is mainly driven by local hydrodynamic stresses in the surrounding liquid. However a complete and unique theoretical description of thermophoresis has been lacking.
- Published on 19 January 2018
EPJ is pleased to announce significant changes concerning the editorial structure of EPJ A. Following the continuous growth and broadening of the journal’s scope over the past few years, the theory section has now been divided into Theory I (Nuclear Physics) and Theory II (Hadron Physics and Quark Matter). Theory I is headed by Prof. Thomas Duguet, who has been newly appointed for this position, while Theory II continues to be headed by Prof. Tamás Biró. Further, and with immediate effect, Prof. Maria Jose Garcia Borge has been appointed Editor-in-Chief for the Experimental Physics section of the journal.
- Published on 09 January 2018
Study of the dynamic properties of biological membranes reveals new anomalous behaviour under specific circumstances
How biological membranes - such as the plasma membrane of animal cells or the inner membrane of bacteria - fluctuate over time is not easy to understand, partly because at the sub-cellular scale, temperature-related agitation makes the membranes fluctuate constantly; and partly because they are in contact with complex media, such as the cells’ structuring element, the cytoskeleton, or the extra-cellular matrix. Previous experimental work described the dynamics of artificial, self-assembled polymer-membrane complexes, embedded in structured fluids. For the first time, Rony Granek from Ben-Gurion University of The Negev, and Haim Diamant from Tel Aviv University, both in Israel, propose a new theory elucidating the dynamics of such membranes when they are embedded in polymer networks. In a new study published in EPJ E, the authors demonstrate that the dynamics of membrane undulations inside such a structured medium are governed by distinctive, anomalous power laws.
- Published on 21 December 2017
New study shows that two seemingly diverging theories of ever-increasing disorder, known as entropy, can be tested against each other experimentally in the smallest possible systems
Have you ever tried turning the spoon back after stirring jam into a rice pudding? It never brings the jam back into the spoon. This ever-increasing disorder is linked to a notion called entropy. Entropy is of interest to physicists studying the evolution of systems made up of multiple identical elements, like gas. Yet, how the states in such systems should be counted is a bone of contention. The traditional view developed by one of the fathers of statistical mechanics, Ludwig Boltzmann - who worked on a very large number of elements - is opposed to the seemingly disjointed theoretical perspective of another founding scientists of the discipline, Willard Gibbs, who describes systems with a very small number of elements. In a new study published in EPJ Plus, Loris Ferrari from the University of Bologna, Italy, demystifies this clash between theories by analysing the practical consequences of Gibbs’ definition in two systems of a well-defined size. Ferrari speculates about the possibility that, for certain quantities, the differences resulting from Boltzmann's and Gibbs' approach can be measured experimentally.
- Published on 21 December 2017
Atomic Spin Squeezing: not the Olympic sport of your dreams, but a way of enhancing measurement reliability at the quantum scale
Noise: it affects us all by distracting us. Noise also occurs at the quantum scale and can e.g. interfere with the measurements of atomic fountain clocks or with quantum information processing. This is because at that scale, there are effects that don't exist at larger scales. As such, finding ways to reduce quantum noise can enhance the precision of measurement in the examples given above. Now a team of physicists including Aranya Bhattacherjee from Jawaharlal Nehru University, New Delhi, India and colleagues are investigating ways of improving the analysis of quantum noise measurement in the case of spectroscopic investigations; their preliminary findings were released in a study in EPJ D. This method, called atomic spin squeezing, works by redistributing the uncertainty unevenly between two components of spin in these measurements systems, which operate at the quantum scale. The spin represents a degree of freedom of the quantum particles involved. Thus, the spin component with reduced uncertainty becomes more precise in delivering its measurement - as the two are inversely correlated. Potential applications include the development of future quantum networks.
- Published on 20 December 2017
Plastic scintillators consist in one or several fluorescent probes embedded in a polymer matrix. They are able to produce light while interacting with a radioactive source. Recently, their technology has been modified by making them denser to improve their absorption while limiting the fluorescence quenching, leading to make them usable as pseudo-gamma spectrometers.
This is just an example of the numerous advances reported in a review based on four editions of the ANIMMA conferences (www.animma.com). This review is organized according to the measurement methodologies: neutronic, photonic, thermal, acoustic and optical, and includes medical imaging as well as progress in data acquisition and electronic hardening. Applications involve many fields like fundamental physics, fission and fusion reactors, medical imaging, environmental protection and homeland security, radioactive wastes measurement and control.
EPJ C Highlight - Combining experimental data to test models of new physics that explain dark matter
- Published on 19 December 2017
The most statistically consistent and versatile tool to date is designed to gain insights into dark matter from models that extend the standard model of particle physics, rigorously comparing them with the latest experimental data
In chess, a gambit refers to a move in which a player risks one piece to gain an advantage. The quest to explain dark matter, a missing ingredient from the minimal model that can describe the fundamental particles we have observed (referred to as the standard model of particle physics), has left many physicists eager to gain an advantage when comparing theoretical models to as many experiments as possible. In particular, maintaining calculation speed without sacrificing the number of parameters involved is a priority. Now the GAMBIT collaboration, an international group of physicists, has just published a series of papers in EPJ C that offer the most promising approach to date to understanding dark matter.