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EPJE Colloquium: Dense granular flows - fluidity revisited

Details: Published on 28 November 2015

Local shear rate ˙Γ for a system of frictional soft grains
Bouzid *et al.*

In this new EPJ E Colloquium, a group of authors from ESPCI, Univ. Paris-Diderot and Univ. P.M. Curie use the interpretive frame-work of non-locality to describe the rheology and fluidity in dense granular flows. Is a “good fitting” of the velocity profiles sufficient to demonstrate the validity of a particular model for non-locality?

EPJ E Highlight - Liquid foam: plastic, elastic and fluid

Details: Published on 27 November 2015

Snapshots of the foam at the exit of the convergent channel

What differentiates complex fluids from mere fluids? What makes them unique is that they are neither solid nor liquid. Among such complex fluids are foams. They are used as a model to understand the mechanisms underlying complex fluids flow. Now, a team of French physicists has gained new insights into predicting how complex fluids react under stretching conditions due to the interplay between elasticity, plasticity and flow. These findings were recently published in EPJ E by Benjamin Dollet and Claire Bocher from the Rennes Institute of Physics, in Brittany, France. Ultimately, potential applications include the design of new, optimised acoustic insulators based on liquid forms, or the mitigation of blast waves caused by explosions.

EPJ AP Highlight - Slowing dynamics of a supersonic beam

Details: Published on 25 November 2015

2D imaging of the slowed Ar* supersonic beam for a final velocity vF = 61 m/s. From this image, one can easily extract the beam divergence and the coherence radius with respect to the position and size of the effective source.

The present investigation of the slowing dynamics of a supersonic atom beam by a counter-propagating resonant laser light, in other words the dynamics of atoms in a so-called “Zeeman slower”, is characterized by two special features which are: (i) a close coupling between simulations and experiments using a nozzle beam of metastable argon atoms, (ii) the use in the simulations of a Monte-Carlo (MC) scheme aimed at analysing step by step (i.e. subsequent cycles of absorption-emission) the slowing process and describing in a realistic way atom random walks due to the spontaneous emission. It allows us to get calculated 2D images and radial profiles of the slowed beam, in good agreement with experiment. Other important characteristics as angular aperture, velocity spreads, coherence radius (not easy to be measured experimentally), etc. also result from the simulation. Since the 3D atomic motion within the laser field is considered, border effects can be studied, while they were not directly accessible in a simple radiative force model. It is finally shown that the experimental characteristics of the slowed beam are reproduced by the calculated ones, assuming a point- like source. In general a laser beam is an efficient tool to manipulate the atomic motion and its interaction with atoms can be accurately characterized by means of the present MC-code. Actually any configuration combining resonant light and atoms is relevant (provided that the semi-classical approximation is valid), in particular the use of a “pushing” laser to generate a slow atomic beam from a magneto-optical trap is a technique which has been successfully tested with metastable argon atoms. Here again the MC-code has been able to accurately predict the characteristics of the generated beam.

EPJ D Highlight - Bringing the chaos in light sources under control

Details: Published on 17 November 2015

Experimental reconstruction of the phase portrait of the quantum dot light emitting diode using the embedding technique.

Study investigates how best to stabilise the output of quantum dot LEDs

Noise is an issue in optical telecommunications. And findings means of controlling noise is key to physicists investigating light-emitting diodes or lasers. Now, an Italo-Iraqi team has worked on a particular type of light source, called the quantum dot light-emitting diode (QDLED). In a study published in EPJ D, Kais Al Namee from the National Institute of Optics, in Florence, Italy and colleagues, demonstrate that modulating bias current of the QDLED could lead to countering the noise. This, in turn, leads to stabilising such light sources, making them better suited for optical telecommunications.

EPJ Plus Focus Point - 3He replacement in neutron detection: Current status and perspectives

Details: Published on 17 November 2015

One of the most important issues that the neutron community is currently facing is related to the lack of ³He for detection purposes. This problem has triggered an interesting and stimulating research and development activity worldwide, with the aim of finding effective and cheap solutions for ³He replacement. With the advent of new materials, advanced electronics and more powerful real time computing tools it has now become possible to investigate novel designs of neutron detectors to be used in various fields of research and technology, and to address the needs of more sophisticated applications.

The aim of this issue is to present an up-to-date, although not exhaustive, review on the R&D activities on ³He-free neutron detectors, with the aim of generating further discussions and activities on the subject, stimulate synergies between groups with different expertise, and show examples of existing neutron sources where new detectors and techniques can be tested and validated. This EPJ Plus Focus Point addresses all aspects related to the design of an innovative ³He-free neutron detector, from the development of new detection concepts and active material, to fast front-end electronics and acquisition systems, to the availability of neutron beams of suitable energy for detector characterization.

EPJ B Colloquium: Hierarchy of scales in language dynamics

Details: Published on 12 November 2015

Language is a collective phenomenon, shared by a group of speakers, and originating from interactions between individual group members. This dimension has captured the interest of statistical physicists who have applied their methods to study how languages change and differentiate themselves from one another over time.

EPJ E Highlight - Zooplankton: not-so-passive motion in turbulence

Details: Published on 10 November 2015

Physicists show that despite their limited swimming abilities, zooplankton called calanoid copepods display active, energetic behaviour in turbulent flows

Imagine a species that is only one millimetre long and has only a limited swimming ability. Yet, its mobility is sufficient for moving, feeding and reproducing in freshwater and seawater. That’s exactly what a type of zooplankton of the crustaceans family - namely the calanoid copepods - does. In a study published in EPJ E, physicists shed new light on how these zooplankton steer large-scale collective motion under strong turbulence. To do so, the authors study the zooplankton’s small-scale motion mechanisms when subjected to background flow motion. These findings are the work of François-Gaël Michalec from the Institute of Environmental Engineering, ETH Zurich, Switzerland, and European colleagues. Ecological applications in the field of zooplankton behaviour ecology include, for example, modelling the feeding efficiency of their predator, fish larvae.

EPJ H Highlight - May the 5th force be with you

Details: Published on 27 October 2015

alt — Ephraim Fischbach, Purdue University Physics Professor
© Purdue University

Ephraim Fischbach revisits the wealth of research emerging from the quest for the fifth force, which he hypothesised in the 1980s as being a new fundamental force in nature

Discovering possible new forces in nature is no mean task. The discovery of gravity linked to Newton’s arguably apocryphal apple experiment has remained anchored in popular culture. In January 1986, Ephraim Fischbach, Physics Professor from Purdue University in West Lafayette, Indiana, had his own chance to leave his mark on collective memory. His work made the front page of the New York Times after he and his co-authors published a study uncovering the tantalising possibility of the existence of a fifth force in the universe. In an article published in EPJ H, Fischbach gives a personal account of how the existence of the gravity-style fifth force has stimulated an unprecedented amount of research in gravitational physics - even though its existence, as initially formulated, has not been confirmed by experiment.

EPJ A Review - Melting hadrons, boiling quarks

Details: Published on 27 October 2015

In the context of the Hagedorn temperature half-centenary our understanding of the hot phases of hadronic matter both below and above the Hagedorn temperature is reviewed. The first part of this review paper just published in EPJ A addresses many frequently posed questions about properties of hadronic matter in different phases, phase transition and the exploration of quark-gluon plasma (QGP). The historical context of the discovery of QGP is described and the role of strangeness and strange antibaryon signature of QGP illustrated. In the second part the corresponding theoretical ideas and how experimental results can be used to describe the properties of QGP at hadronization are described.

EPJ Data Science Highlight - Using patients’ trail of digital crumbs for public health surveillance

Details: Published on 20 October 2015

Patients' digital crumbs could be used to complement existing disease surveillance mechanisms.
© bakhtiarzein / Fotolia

Public health agencies could capitalise on streams of data related to patients on the internet but only once interpretation methods have been validated.

Data is ubiquitous. In the area of heath, there are growing data streams directly initiated by patients through their activities on the internet and on social networks and other related ones such as electronic medical records and pharmacy sales data. These so-called Novel Data Streams (NDS) are very appealing to public health surveillance officials due to their ease of collection. A new paper published in EPJ Data Science evaluates the currently available NDS surveillance papers before outlining a conceptual framework for integrating such data into current public health surveillance systems. The authors, who hail from public health agencies, academia, and the private sector, highlight the need for future rigorous evaluation and validation of standards before NDS can effectively reinforce existing public health surveillance systems.