The power of light-matter coupling (Vol. 46 No. 2)

A theoretical study shows that strong ties between light and organic matter at the nanoscale open the door to modifying these coupled systems’ optical, electronic or chemical properties.

Light and matter can be so strongly linked that their characteristics become indistinguishable. These light-matter couplings are referred to as polaritons. Their energy oscillates continuously between both systems, giving rise to attractive new physical phenomena. Now, the authors have explained why such polaritons can remain for an unusual long time at the lowest energy levels, in such a way that alters the microscopic and macroscopic characteristics of their constituting matter. These new results are in agreement with experimental results. These findings thus pave the way for optical, electronic and chemical applications.

A. Canaguier-Durand, C. Genet, A. Lambrecht, T. W. Ebbesen, and S. Reynaud, “Non-Markovian polariton dynamics in organic strong coupling”, Eur. Phys. J. D 69, 24 (2015)
[Abstract]

The power of resolution in charge-exchange reactions (Vol. 50, No. 1)

This review highlights the extraordinary power of the hadronic charge-exchange reactions at intermediate energies and at highest spectral resolution, as exemplified by the (n,p)-type (d,²He) and the (p,n)-type (³He,t) reactions. The review shows how areas of nuclear physics, astrophysics and particle physics alike benefit from such enhanced resolution. A major part of this review focuses on weak interaction processes in nuclei, especially on those, where neutrinos play a pivotal role like in solar neutrino induced reactions or in ββ decay. Unexpected and even surprising new features of nuclear structure are being unveiled as a result of high resolution. (See figure).

High resolution proves to be of equally high importance in areas where this would not immediately be expected. This is outlined in the chapters dealing with the neutron-neutron scattering length, with the properties of halo-nuclei or with the explosion dynamics of supernovae. Finally, the review portrays how high-resolution charge-exchange reactions connect to the symmetry energy and the nuclear equation-of-state or to processes involving ordinary capture of muons by nuclei. Clearly, the insight into the physics, which is made possible with high-resolution charge-exchange reactions, could not possibly be more diverse.

D. Frekers and M. Alanssari, Charge-exchange reactions and the quest for resolution, Eur. Phys. J. A 54, 177 (2018)
[Abstract]

The relationship between quality and quantity in research (Vol. 41, No. 5)

The quality of research groups plotted against the quantity of group members in physics

The extensive nature of group quality
R. Kenna and B. Berche, EPL, 90, 58002 (2010)
[Abstract]

The secret to improving liquid crystal's mechanical performance (Vol. 48, No. 5-6)

Better lubricating properties of lamellar liquid crystals could stem from changing the mobility of their structural dislocations by adding nanoparticles

By deliberately interrupting the order of materials—by introducing different atoms in metal or nanoparticles in liquid crystals—we can induce new qualities. For example, metallic alloys like duralumin, which is composed of 95% of aluminium and 5% copper, are usually harder than the pure metals. This is due to an elastic interaction between the defects of the crystal, called dislocations, and the solute atoms, which form what are referred to as Cottrell clouds around them. In such clouds, the concentration of solute atoms is higher than the mean concentration in the material. In a paper published recently, the authors have now theoretically calculated the static and dynamical properties of the Cottrell clouds, which form around edge dislocations in lamellar liquid crystals of the smectic A variety decorated with nanoparticles. In this study, they demonstrate a formula previously used to approximate the mobility of dislocations in the presence of Cottrell clouds. They then perform a numerical simulation of the problem to study how the Cottrell cloud erodes when the dislocation moves at high speed. This work could be important, for example, in the context of improving the lubricating performance of such liquid crystals.

P. Oswald and L. Lejček, Drag of a Cottrell atmosphere by an edge dislocation in a smectic-A liquid crystal, Eur. Phys. J. E 40, 84 (2017)
[Abstract]

The Soreq Applied Research Accelerator Facility (SARAF) (Vol. 49 No.4)

The Soreq Applied Research Accelerator Facility (SARAF) is under construction in the Soreq Nuclear Research Center at Yavne, Israel. Phase I of SARAF (SARAF-I) is already in operation, generating scientific results in several fields of interest, especially the astrophysical s-process. When completed at the beginning of the next decade, SARAF-II will be a user facility for basic and applied nuclear physics, based on a 40 MeV, 5 mA CW proton/deuteron superconducting linear accelerator. This review presents first a technical overview of SARAF-I and II, including a description of the accelerator and its irradiation targets, and provides a survey of existing research programs at SARAF-I. It then describes in some detail the research potential at the completed facility. SARAF-II’s cutting-edge specifications, with its unique liquid lithium target technology, will enable world-competitive research plans in several disciplines: precision studies of beyond-Standard-Model effects by trapping light exotic radioisotopes (including meaningful studies already at SARAF-I); extended nuclear astrophysics research with higher-energy neutrons, including generation and studies of exotic neutron-rich isotopes relevant to the astrophysical r-process; nuclear structure of exotic isotopes; high-energy neutron cross sections for basic nuclear physics and material science research, including neutron-induced radiation damage; neutron-based imaging with an imaging plane flux similar to that of a 5 MW research reactor; accelerator-based neutron therapy; and, last but not least, novel radiopharmaceuticals development and production.

I. Mardor and 28 co-authors, The Soreq Applied Research Accelerator Facility (SARAF): Overview, research programs and future plans, Eur. Phys. J. A 54, 91 (2018)
[Abstract]

The twin paradox in a cosmological context (Vol. 42, No. 5)

The twin paradox in a cosmological context
∅. Grøn and S. Braeck, Eur. Phys. J. Plus, 126, 79 (2011)
[Abstract]

The unsuspected synergistic mechanism of the human heart (Vol. 49, No. 2)

3D simulations reveals that every part of the human heart works in combination with the others, while all parts influence each other’s dynamics, giving clues to help prevent cardiac conditions.

Did you know that the left side of the heart is the most vulnerable to cardiac problems? Particularly the left ventricle, which has to withstand intense pressure differences, is under the greatest strain. As a result, people often suffer from valve failure or impairment of the myocardium. This is why it is important to fully understand how the blood flow within this part of the heart affects its workings. In a new study the authors introduce a novel model that examines, for the first time with this approach, the mutual interaction of the blood flow with the individual components of the heart. Their work stands out by offering a more holistic and accurate picture of the dynamics of blow flow in the left ventricle. Until now, most cardiac models have considered separate components of the heart, either the ventricle or the mitral valve. But they have never approached the whole combination as a synergistic system. Another key shortcoming of previous models was their failure to take into account either the interaction between the blood and the heart structure, which can lead to deformation of the heart, or the structure of the heart chambers under the load of the passing blood flow. The authors also perform some experimental validations of their model.

V. Meschini, M. D. de Tullio and R. Verzicco, Effects of mitral chordae tendineae on the flow in the left heart ventricle, Eur. Phys. J. E 41, 11634 (2018).
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The “inertia of heat” concept revisited (Vol. 43 No. 5)

M. Smerlak, ‘On the inertia of heat’, Eur. Phys. J. Plus (2012) 127, 72
[Abstract]

Thermodiffusion in weightlessness (Vol. 46 No. 1)

Thermodiffusion, also called the Soret effect, is a mechanism by which an imposed temperature difference establishes a concentration difference within a mixture. Two recent studies provide a better understanding of such effects. They build on recent experimental results from the IVIDIL—Influence Vibration on Diffusion in Liquids—research project performed on the International Space Station under microgravity to avoid motion in the liquids.

In the first study, using a mathematical model the authors set out to identify how vibrations applied to a binary liquid mixture change the temperature and concentration fields over a long time scale. Their findings—if extended to ternary mixtures—have implications for models used to evaluate the economic value of oil reservoirs.

The second paper use numerical models to study the establishment of the concentration field near the critical region, where diffusion strongly diminishes. Surprisingly, the authors demonstrate that the component separation through the Soret effect is saturated and not infinite, and is reached surprisingly rapidly. The findings of this study may help determine whether the Soret effect could lead to a very large accumulation of sulfur dioxide and hydrogen sulphide capable of creating a leak in the cap-rock of a reservoir, during the process of capturing CO2 and reinjecting it in supercritical state in such a reservoir.

Y. Gaponenko, A. Mialdun and V. Shevtsova, “Experimental and numerical analysis of mass transfer in a binary mixture with Soret effect in the presence of weak convection”, Eur. Phys. J. E 37, 90, (2014)
[Abstract]

J.C. Legros, Yu. Gaponenko, T. Lyubimova and V. Shevtsova, “Soret separation in a binary liquid mixture near its critical temperature”, Eur. Phys. J. E 37, 89 (2014)
[Abstract]

Tiling pattern governs quasicrystals' magnetism (Vol. 43 No. 3)

The five-fold symmetry of the Penrose tiling

The Heisenberg antiferromagnetic model in two dimensional quasicrystals
A. Jagannathan, Eur. Phys. J. B, 85, 68 (2012)
[Abstract]

Time shift in the OPERA setup with muons in the LVD and OPERA detectors (Vol. 43 No. 5)

Distribution of the δt = t_LVD − t*_OPERA for corrected events. All the events of each year are grouped into one single point with the exception of 2008, which is subdivided into three periods.

N.Yu. Agafonova plus 19 co-authors from LVD collaboration and 70 from OPERA collaboration, ‘Determination of a time shift in the OPERA setup using high-energy horizontal muons in the LVD and OPERA detectors’, Eur. Phys. J. Plus (2012) 127, 71
[Abstract]

Timeless thoughts on the definition of time (Vol. 47 No. 3)

On the evolution of how we have defined time, time interval and frequency since antiquity.

The earliest definitions of time and time-interval quantities were based on observed astronomical phenomena, such as apparent solar or lunar time, and as such, time as measured by clocks, and frequency, as measured by devices were derived quantities. In contrast, time is now based on the properties of atoms, making time and time intervals themselves derived quantities. Today’s definition of time uses a combination of atomic and astronomical time. However, their connection could be modified in the future to reconcile the divergence between the astronomic and atomic definitions. These are some of the observations made by the author of this riveting work published recently, which provides unprecedented insights into the nature of time and its historical evolution.

J. Levine, The history of time and frequency from antiquity to the present day, Eur. Phys. J. H 41, 1 (2016)
[Abstract]

Topological Insulator in an Atomic Liquid (Vol. 50, No. 4)

Topological insulators are a new class of materials whose electronic states are characterized by global topological invariants. Due to their nontrivial topology, these materials are able to conduct electricity on the surface despite being insulating in the bulk. Moreover, the metallic surface is robust against disorder and other imperfections, making topological insulators strong candidates for the building blocks of next-generation electronics technology. Although almost all known topological insulators are crystals, it has recently been shown that topological insulators and superconductors can also exist in the amorphous or glass states, as long as the relevant symmetries are maintained.

This work further generalizes the notion of topological materials by theoretically demonstrating an atomic liquid phase that supports topologically nontrivial electronic structure. Using quantum molecular dynamics simulations, it is shown that by melting a topological crystalline state with elevated temperatures, the resultant liquid phase inherits the nontrivial topology that is characterized by a nonzero Bott index, named after the famous topologist Raoul Bott. This work points to a new systematic approach for searching topological phases in amorphous and liquid systems.

G.-W. Chern, Topological insulator in an atomic liquid, EPL 126, 37002 (2019)
[Abstract]

Topological quantum phase transitions (Vol. 45 No.3)

Transformation of edge states upon increasing the exchange field. For (b), it is a new type of topological insulator, where the QSH and QAH effect appear simultaneously.

The study of novel topological phases is the focus of intensive research efforts. Some theoretical works have recently been devoted to the understanding of the effect of staggered magnetic fluxes (SMFs) on the topological quantum phase transitions (TQPTs).

In the paper we investigate topological phases and corresponding TQPTs by introducing SMFs into the quantum spin Hall (QSH) systems. By varying the flux parameters, we find a rich variety of TQPTs between topological phases with a different number of edge states. Interestingly, some topological phases with high Chern numbers or spin Chern numbers may also appear with spin-orbit couplings.

We consider in particular the effect of exchange field and its role in driving TQPTs. It is shown that the system becomes a new type of topological insulator in a certain parameter region, where the QSH and quantum anomalous Hall (QAH) phases coexist. It is hoped that this work will deepen the understanding of topological phases and motivate further developments in this exciting and rapidly developing field.

Y. Yang, Y. F. Zhang, L. Sheng and D. Y. Xing, "Topological quantum phase transitions in a spin-orbit coupled electron system with staggered magnetic fluxes", EPL, 105, 27005 (2014)
[Abstract]

Topology and Onsager symmetry: How Linear Networks become Exciting (Vol. 46 No. 4)

Oscillator networks are omnipresent; they occur, e.g., in electric devices, in mechanical systems, and in biochemistry. However, purely linear networks have limited capabilities. Diode-like, monodirectional transport is usually impossible. Also, maximum power can not be transmitted with an efficiency larger than 1/2. Therefore, engineered networks often contain active or non-linear elements such as transistors. As a possible alternative, the authors investigated purely linear networks containing Lorentz-force-like couplings that break time-reversal symmetry. These networks allow to construct linear diodes with frequency-independent isolation properties. Also, the efficiency at maximum power can approach unity. We show that this surprising system behaviour requires a combination of network loops with magnetic time-reversal symmetry breaking.

B. Sabass, Network topology with broken Onsager symmetry allows directional and highly efficient energy transfer, EPL, 110, 20002 (2015)
[Abstract]