Vol. 50 No. 5-6 - Highlights

WONDER-2018: a workshop on nuclear data (Vol. 50, No. 5-6)

WONDER-2018: a workshop on nuclear data
By combining experimental data (left, example of experimental setup) and theoretical calculations (middle, example of theoretical calculations), it becomes possible to perform an evaluation of nuclear data (right, example of evaluated cross-sections). Those evaluated nuclear data are collected in a regularly updated international library such as JEFF (Joint Evaluated Fusion and Fission).

To describe the path of neutrons in the material but also the chain reactions that take place in a reactor and the changes in the composition of matter due to nuclear reactions, neutronics uses computer codes. These codes have also acquired such a level of performance since the last two decades that the main source of uncertainty in neutronic calculations comes today from nuclear data. In this context, the 5th edition of the International Workshop On Nuclear Data Evaluation for Reactor Applications (WONDER-2018), organized by the French Alternative Energies and Atomic Energy Commission (CEA) in collaboration with the NEA (Nuclear Energy Agency of the OECD) was held in Aix-en-Provence, France, on October 2018. The main objective was to identify future trends in the measurement, modeling and evaluation of nuclear data needed for current reactors and innovative reactor concepts. Proceedings were published in EPJ Web-of-Conferences: EPJ Web of Conferences Volume 211 (2019).

WONDER-2018 – 5th International Workshop On Nuclear Data Evaluation for Reactor applications, EPJ Web of Conferences 211 (2019)

Fragmenting ions and radiation sensitizers (Vol. 50, No. 5-6)

Fragmenting ions and radiation sensitizers
Mass spectrum of 5-fluorouracil showing ions produced by impact with high-energy electrons.

A new study using mass spectrometry is helping piece together what happens when DNA that has been sensitized by the oncology drug 5-fluorouracil is subjected to the ionising radiation used in radiotherapy.

The anti-cancer drug 5-fluorouracil (5FU) acts as a radiosensitizer: it is rapidly taken up into the DNA of cancer cells, making the cells more sensitive to radiotherapy. However, little is known about the precise mechanism through which radiation damages cells. A team of scientists have now used mass spectrometry to shed some light on this process; their work was recently published in EPJD. A full understanding of this process could ultimately lead to new ways of protecting normal tissues from the radiation damage caused by essential cancer treatments.

P.J.M. van der Burgt, M.A. Brown, J. Bockova, A. Rebelo, M. Ryszka, J-C. Poully and S. Eden, Fragmentation processes of ionized 5-fluorouracil in the gas phase and within clusters, Eur. Phys. J. D 73, 184 (2019)

Conductivity at the edges of graphene bilayers (Vol. 50, No. 5-6)

Conductivity at the edges of graphene bilayers
Intriguing properties arise in graphene bilayers.

The conductivity of dual layers of graphene greatly depends on the states of carbon atoms at their edges; a property which could have important implications for information transmissions on quantum scales.

Made from 2D sheets of carbon atoms arranged in honeycomb lattices, graphene displays a wide array of properties regarding the conduction of heat and electricity. When two layers of graphene are stacked on top of each other to form a ‘bilayer’, these properties can become even more interesting. At the edges of these bilayers, for example, atoms can sometimes exist in an exotic state of matter referred to as the ‘quantum spin Hall’ (QSH) state, depending on the nature of the interaction between their spins and their motions, referred to as their ‘spin-orbit coupling’ (SOC). While the QSH state is allowed for ‘intrinsic’ SOC, it is destroyed by ‘Rashba’ SOC. In an article recently published, the authors showed that these two types of SOC are responsible for variations in the ways in which graphene bilayers conduct electricity.

P. Sinha, and S. Basu, Study of edge states and conductivity in spin-orbit coupled bilayer graphene, Eur. Phys. J. B 92, 207 (2019)

Partial synchronization as a model for unihemispheric sleep (Vol. 50, No. 5-6)

Partial synchronization as a model for unihemispheric sleep
Brain connectivity.

Human brains exhibit a slight structural asymmetry of their two hemispheres (see Figure). We have investigated the dynamical asymmetry arising from this natural structural difference in healthy human subjects, using a minimum model which elucidates the modalities of unihemispheric sleep in human brain, where one hemisphere sleeps while the other remains awake. In fact, this state is common among migratory birds and mammals like aquatic species.

By choosing appropriate coupling parameters in a network of FitzHugh-Nagumo oscillators with empirical structural connectivity, we have observed that our brain model exhibits spontaneous symmetry breaking and bistability, where each hemisphere may engage into either of two dynamical states, characterized by a relatively high and low degree of synchronization. However, a high degree of synchronization in one of the hemispheres always coincides with a low degree of synchronization in the other. This dynamical asymmetry can be even enhanced by tuning the inter-hemispheric coupling strength. These results are in accordance with the assumption that unihemispheric sleep requires a certain degree of inter-hemispheric separation.

The structural asymmetry in the brain allows for partial synchronization dynamics, which may be used to model unihemispheric sleep or explain the mechanism of the first-night effect in human sleep.

L. Ramlow, J. Sawicki, A. Zakharova, J. Hlinka, J. Ch. Claussen and E. Schöll, Partial synchronization in empirical brain networks as a model for unihemispheric sleep, EPL 126, 50007 (2019)

Delocalization of edge states in topological phases (Vol. 50, No. 5-6)

Delocalization of edge states in topological phases
Dispersions in a topological system with positive indirect gap and edge states (left); negative indirect gap and no edge states (right).

Topological properties are a hot topic currently. If the bulk of a system is topologically non-trivial (Chern number), the bulk-boundary correspondence predicts in-gap states in finite samples. These states close the energy gap between bands of different topology so that it can change at boundaries. Conventionally, the in-gap states are localized at these boundaries so that they are edge states. We show, however, that this localization only occurs for positive indirect gap. Generically, without indirect gap the in-gap states become extended by mixing with bulk states despite . This is illustrated for two fundamental lattice models (Haldane and checkerboard model) by adding terms to the Hamiltonians proportional to the identity in momentum space. Thus, the dispersions change while the topology remains unchanged. These terms can close the indirect gap and lead to delocalization of edge states in finite geometries. Thus, discrete topological invariants may exist without localized edge modes. This underlines the vital significance of indirect gaps for the existence of topological edge states and puts the bulk-boundary into perspective.

M. Malki and G. S. Uhrich, Delocalization of edge states in topological phases, EPL 127, 27001 (2019)

Chemotherapy drugs react differently to radiation while in water (Vol. 50, No. 5-6)

Chemotherapy drugs react differently to radiation while in water
Chemotherapy medication reacts to radiation.

A new study looked at the way certain molecules found in chemotherapy drugs react to radiation while in water, which is more similar to in the body, compared to previous research that studied them in gas.

Cancer treatment often involves a combination of chemotherapy and radiotherapy. Chemotherapy uses medication to stop cancer cells reproducing, but the medication affects the entire body. Radiotherapy uses radiation to kill the cancer cells, and it is targeted to the tumour site. In a recent study, published in the journal EPJD, the authors studied selected molecules of relevance in this context. They wanted to see how these molecules were individually affected by radiation similar to that used in radiotherapy.

S. E. Huber and A. Mauracher, Electron impact ionisation cross sections of fluoro-substituted nucleosides, Eur. Phys. J. D 73, 137 (2019)

Optimising structures within complex arrangements of bubbles (Vol. 50, No. 5-6)

Optimising structures within complex arrangements of bubbles
Optimising an arrangement of five bubbles.

Computer simulations reveal the secret to stronger, cheaper structures shaped like bubbly foams.

While structures which emulate foam-like arrangements of bubbles are lightweight and cheap to build, they are also remarkably stable. The bubbles which cover the iconic Beijing Aquatics Centre, for example, each have the same volume, but are arranged in a way which minimises the total area of the structure – optimising the building’s construction. The mathematics underlying this behaviour is now well understood, but if the areas of the bubbles are not equal, the situation becomes more complicated. Ultimately, this makes it harder to make general statements about how the total surface area or, in 2D, edge length, or ‘perimeter’, can be minimised to optimise structural stability. In new research published recently, the authors explore how different numbers of 2D bubbles of two different areas can be arranged within circular discs, in ways which minimise their perimeters.

F. Headley, and S. Cox, Least-perimeter partition of the disc into N bubbles of two different areas, Eur. Phys. J. E 42, 92 (2019)

Improving heat recycling with the thermodiffusion effect (Vol. 50, No. 5-6)

Improving heat recycling with the thermodiffusion effect
Recycling heat using falling films.

Numerical simulations of the thermodiffusion effect within falling film absorbers reveal that thin films composed of liquid mixtures with negative thermodiffusion coefficients enhance the efficiency of heat recycling.

Absorption heat transformers can effectively reuse the waste heat generated in various industries. In these devices, specialised liquids form thin films as they flow downward due to gravity. These liquid films can absorb vapour, and the heat is then extracted by a coolant so that it can be used in future processes. So far, however, there has been little research into how the performance of these films is influenced by the thermodiffusion effect – a behaviour seen in mixtures, where different types of mixture respond differently to the same temperature gradient. In a study recently published, researchers from the Fluid Mechanics group at Mondragon University and Tecnalia, pooled their expertise in transport phenomena and absorption technology. Together, they explored for the first time the influence of the thermodiffusion property on the absorption, temperature and concentration profiles of falling films.

P. Fernandez de Arroiabe, A. Martinez-Urrutia, X Peña, M. Martinez-Agirre, M. M. Bou-Ali, On the thermodiffusion effect in vertical plate heat exchangers, Eur. Phys. J. E 42, 85 (2019)

New insights into the early stages of creep deformation (Vol. 50, No. 5-6)

New insights into the early stages of creep deformation
Varying strain patterns during creep deformation.

Computer simulations show that the evolution of material structures during creep deformation can modify material properties.

The properties of many materials can change permanently when they are pushed beyond their limits. When a given material is subjected to a force, or ‘load’, which is stronger than a certain limit, it can become so deformed that it won’t return to its original shape, even after the load is removed. However, heavy loads aren’t strictly necessary to deform materials irreversibly; this can also occur if they are subjected to lighter loads over long periods of time, allowing a slow process called ‘creep’ to take place. Physicists have understood for some time that this behaviour involves sequences of small, sudden deformations, but until now, they have lacked a full understanding of how creep deformation affects material properties over time. In new research published recently, the authors analysed the characteristic ways in which material structures evolve during the early stages of creep deformation.

D.Fernandez Castellanos, and M. Zaiser, Statistical dynamics of early creep stages in disordered materials, Eur. Phys. J. B 92, 139 (2019)

Fractal agglomerates fragment into dissimilar fragments (Vol. 50, No. 5-6)

Fractal agglomerates fragment into dissimilar fragments
A fragmentation event and the distribution of fragment sizes upon random bond removal in a Diffusion Limited Cluster Aggregation (DLCA) cluster

Fragmentation occurs everywhere in nature: polymers degrade, soot particles break up, cells divide, volcanic ash fragments, droplets break up in turbulent flow, lung fluid fragments to generate droplets. Nevertheless, little is known about the distribution of fragment sizes when a fractal agglomerate breaks up. The fragment-size distribution upon random bond removal in a linear chain composed of identical units is uniform. How does the distribution change as the morphology of the fragmenting structure changes?

More generally, fragmentation kernels, which depend on the size distribution and the fragmentation rate, have been extensively used in population balance equations. Usually, their analytical form is dictated by homogeneity requirements (as suggested by coagulation kernels) or physical arguments. In this work, the morphology-dependent fragment-size distribution is determined from numerical simulations of fragmenting in silico fractal-like agglomerates. The overarching idea is to map the agglomerate onto a graph via the adjacency matrix, the matrix that specifies the monomer-monomer bonds. Fragmentation occurs via random bond removal. The simulations showed that the distribution is U-shaped, fragmentation into dissimilar fragments, accurately reproduced by a symmetric beta distribution.

Y. DrossinoS, A. D. Melas, M. Kostoglou and L. Isella, Morphology-dependent random binary fragmentation of in silico fractal-like agglomerates, EPL 127, 46002 (2019)

Machine Learning for Characterization and Control of Non-equilibrium Plasmas (Vol. 50, No. 5-6)

Recent breakthroughs in machine learning and artificial intelligence have created cross-disciplinary research opportunities in the field of non-equilibrium plasma (NEP) treatment of complex surfaces in applications such as plasma medicine, plasma catalysis, and materials processing. Machine learning can potentially transform modeling and simulation, diagnostics, and control of NEP. Machine learning can aid in the development of predictive models for plasma-surface interactions and plasma induced surface responses from experiments, especially when there is a lack of comprehensive theoretical models for the fundamental plasma-surface interaction mechanisms. Machine learning also holds promise for extracting the latent and often multivariate information of on-line plasma diagnostics. This can facilitate real-time inference of physical and chemical properties of NEP as well as complex surfaces interacting with NEP. Learning-based approaches to feedback control is another promising research area for NEP applications, especially when the plasma interacts with complex surfaces with time-varying and uncertain characteristics that in turn would lead to unpredictable plasma behaviour and surface responses. Learning-based process control and artificial intelligence is expected to become indispensable for reliable, flexible, and effective NEP treatment of complex surfaces in the future.

A. Mesbah and D. B. Graves, Machine learning for modeling, diagnostics and control of non-equilibrium plasmas, J. Phys. D: Appl. Phys. 52, 30LT02 (2019)

Improving the signal-to-noise ratio in quantum chromodynamics simulations (Vol. 50, No. 5-6)

Improving the signal-to-noise ratio in quantum chromodynamics simulations
Fermions - the class of particle that this technique can be used to model- include the particles that make up 'ordinary' matter (protons, neutrons and electrons).

A new Monte Carlo based simulation method enables more precise simulation for ensembles of elementary particles.

Over the last few decades, the exponential increase in computer power and accompanying increase in the quality of algorithms has enabled theoretical and particle physicists to perform more complex and precise simulations of fundamental particles and their interactions. If you increase the number of lattice points in a simulation, it becomes harder to tell the difference between the observed result of the simulation and the surrounding noise. A new study recently published in EPJ Plus, describes a technique for simulating particle ensembles that are 'large' (at least by the standards of particle physics). This improves the signal-to-noise ratio and thus the precision of the simulation; crucially, it also can be used to model ensembles of baryons: a category of elementary particles that includes the protons and neutrons that make up atomic nuclei.

M. Cè, Locality and multi-level sampling with fermions. Eur. Phys. J. Plus 134, 299 (2019)

Science puts historical claims to the test (Vol. 50, No. 5-6)

Science puts historical claims to the test
Science provides valuable dating tools for artefacts

The latest analytical techniques available to scientists can confirm the validity of historical sources in some cases, and suggest a need for reconsideration in others.

As any historian will tell you, we can rarely take the claims made by our ancestors at face value. The authenticity of many of the artefacts which shape our understanding of the past have been hotly debated for centuries, with little consensus amongst researchers. Now, many of these disputes are being resolved through scientific research, including two studies recently published in EPJ Plus. The first of these, led by Diego Armando Badillo-Sanchez at the University of Évora in Portugal, analysed an artefact named ‘Francisco Pizarro’s Banner of Arms’ – believed to have been carried by the Spanish conquistador during his conquest of the Inca Empire in the 16th century. The second team, headed by Armida Sodo at Roma Tre University in Italy, investigated a colour print of Charlemagne – the medieval ruler who united much of Western Europe – assumed to be from the 16th century.

D. A. Badillo-Sanchez, C. B. Dias, A. Manhita, and N. Schiavon, The National Museum of Colombia’s “Francisco Pizarro’s Banner of Arms”: a multianalytical approach to help uncovering its history, Eur. Phys. J. Plus 134, 224 (2019)

A. Sodo, L. Ruggiero, S. Ridolfi, E. Savage, L. Valbonetti, and M.A. Ricci, Dating of a unique six-colour relief print by historical and archaeometric methods, Eur. Phys. J. Plus 134, 276 (2019)