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Rogue waves as negative entropy events (Vol. 49, No. 2)

Illustration of a rogue wave in the Japan Sea

It is commonly stated that oceanic rogue waves appear from nowhere and quickly disappear without a trace. A new approach to the complexity of wave surfaces could work out a thermodynamic framework to predict rogue waves. Attributing to each wave a local entropy, we find that negative values are closely linked to rogue waves and positive ones to small wave heights. Strikingly, the statistics of these entropy values altogether follow the integral fluctuation theorem. This law is known to hold for microscopic systems, and holds quite surprisingly for our macroscopic wave systems, too. We address the concrete examples of the North Sea, with no rogue waves, and of the Sea of Japan, which include a measured rogue. It is shown how these two sea states can be well distinguished by their entropy statistics. Such a comparison opens the possibility for better predicting the occurrence of rogue waves in specific ocean spots. The whole work is based on a stochastic multi-point approach unfolding a hierarchical order of height fluctuations of the wave surface, which also allow short time forecasting of rogue wave events.

A. Hadjihoseini, P. G. Lind, N. Mori, N. P. Hoffmann and J. Peinke, Rogue waves and entropy consumption, EPL 120, 30008 (2017)
[Abstract]

Rush hour metro crowd governed by people’s eagerness to go home (Vol. 49 No.4)

Rush hour crowd governed by people’s eagerness to go home
Credit: Photo by Rafael De Nadai on Unsplash

New model examines the relative role of random interactions between individuals in a crowd compared to interactions stemming from their eagerness to be on their way.

Ever found yourself crushed in a metro station at rush hour? The authors have developed a new model to study the movement of crowds exiting a metro station. In a recent study they have for the first time employed models typically used to study gases consisting of a large number of molecules that collide at random (known as thermostatted kinetic theory) to study the consequences of the different interactions occurring among pedestrians in a crowd while exiting a metro station. The authors assume that what motivates pedestrians to leave a metro station can be modelled as an external force that explains the conditions under which they leave due to the crowd pressure. Their model combines aspects representing the interactions between pedestrians and governed by thermostatted kinetic theory with the cooperation between pedestrians as intelligent and self-organised decision-makers, which is governed by game theory. Numerical simulations on the magnitude of the external force explain how internal interactions between pedestrians can be affected by an external force driving them to leave the station. What matters most is that all of the pedestrians are individually in the same hurry to exit the station and get away from the crowd.

C. Bianca, and C. Mogno, A thermostatted kinetic theory model for event-driven pedestrian dynamics, Eur. Phys. J. Plus, 133, 213 (2018)
[Abstract]

Rydberg-hydrogen collisions with surfaces: detection of electrons (Vol. 43 No. 2)

image Wavefunctions and energy levels for n = 10 hydrogen atom approaching a surface

In the Rydberg electronic states of atoms and molecules, one electron has been excited into a distant orbital and is very weakly bound, giving exotic physical and chemical characteristics. The Rydberg orbital can be easily polarized using weak electric fields, and when the Rydberg state is near a surface the electron distribution may be selected to be oriented towards, or away from, the surface (see figure). The van der Waals force between the atom and surface strongly perturbs the Rydberg electron, and at a distance of ~4 times the mean orbital radius the electron may transfer into the surface conduction band. The precise distance at which electron-transfer occurs is controllable by populating Rydberg states with different principal quantum numbers or different surface orientations.

In previous experiments this process was studied by detecting positive ions formed as the Rydberg species ionizes. In the present work electrons have been detected experimentally for the first time from the surface-interaction of both H atoms and H2 molecules in Rydberg states in the presence of a weak electric field normal to the surface. The electron flux away from the surface occurs because the surface interaction lowers the potential energy barrier on the vacuum-facing side of the atom allowing electron escape in that direction. In addition to the novel physics of the process, an important implication of the electron extraction is that it allows the positive ions to impact with the surface under extremely low (thermal) energy conditions. The collision energy is dependent on the ionization distance, which is determined by the initial Rydberg state selected. This opens opportunities to exploring novel forms of thermal ion-surface physics with a range of surfaces and adlayers.

Detection of electrons in the surface ionization of H Rydberg atoms and H2 Rydberg molecules
E. A. McCormack, E. So, M. Dethlefsen, M. S. Ford and T. P. Softley, J. Phys. B: At. Mol. Opt. Phys. 45 (2012) 015204
[Abstract]

Sb-free quantum cascade lasers (QCLs) in the 3-4 µm spectral range (Vol. 43 No. 3)

image Spectral tuning behaviour with corresponding peak optical output power of the external-cavity QCL and schematic sketch of the setup.

The mid-IR spectral range is a region of great interest for numerous scientific and industrial applications such as environmental sensing, metrology and clinical diagnosis. In particular the first atmospheric window between 3-5µm is crucial where a large number of gases e.g. methane, nitric oxide, carbon mono-/dioxide or formaldehyde can be detected. The presence of very strong fundamental stretching modes of O-H, C-H and N-H bonds that can be orders of magnitude stronger than the overtones in the near-IR, brings the detection limits down to sub-ppb concentrations.

The unique feature of QCLs to tailor the emission wavelength makes them appealing sources for this kind of applications. Unfortunately the realization of QCLs in the first atmospheric window is especially challenging because a large conduction band discontinuity is needed to obtain high-energy photons. This is solved by using antimony in the lasing material. However, the growth of Sb-containing devices can be difficult and the fabrication techniques used for high performance QCLs lack compatibility.

Therefore the ETH team has focused on developing a Sb-free system by using strain-compensated InGaAs/InAlAs-AlAs on InP. In pulsed-operation watt-level emission at 3.3µm was obtained at room temperature, and lasing above 350 K could be observed. The laser performance is comparable to Sb-containing QCLs. Tunable single-mode emission between 3.15-3.4µm (Figure 1) was observed in a Littrow external-cavity configuration. The team has begun to develop buried heterostructure QCLs to obtain continuous wave operation. By incorporating first-order distributed feedback gratings, for the first time in this spectral range single-mode emitting buried heterostructure QCLs could be realized.

Sb-free quantum cascade lasers (QCLs) in the 3-4 µm spectral range
A. Bismuto, S. Riedi, B. Hinkov, M. Beck and J. Faist, Semicond. Sci. Technol. 27, 045013 (2012)
[Abstract]

Scaling up renewable energy (Vol. 45 No.3)

Power increments of the grid measured every 15 minutes, against the initial grid power for solar power

A new study focuses on the feasibility of scaling up renewable energy to cover the needs of a country the size of Germany.

Can renewable energy adequately supply the power grid, despite its intermittent nature? This is the key question in a new study presented in this work. It outlines the key issues associated with the use of renewable energy on a large scale.

The author scaled the 2012 German national grid data—including wind (8%) and solar sources (4.8%) contributions—in such a way that renewable energy constitutes a larger than actual share of electricity production, reaching up to 100%, thus covering the country’s yearly electricity needs. The power infrastructure would have to deliver three times the energy load at peak use.

This leads to excess power production, sometimes incurring negative demand-led prices when supply significantly exceeds demand. This setup still requires backup power from thermal power plants to cover periods of low wind and solar energy production.

F. Wagner, “Electricity by intermittent sources: An analysis based on the German situation 2012”, Eur. Phys. J. Plus, 129, 20 (2014)
[Abstract]

School on Energy (Vol. 52, No. 1)

Participants of the school at the Villa Monastero in Varenna, Lake Como, Italy

Since 2012, the European Physical Society and the Italian Physical Society jointly organise a biennal International School on Energy as part the training of young scientists working in the energy sector or intending to do so. The proceedings of the 5th Course with the title ‘Energy: where we stand and where we go’ are published in the EPJ Web of Conferences. Editors of the proceedings are L. Cifarelli and F. Wagner.

EPJ/WoS, Volume 246 (2020)

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)
[Article]

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)
[Article]

Science reveals improvements in Roman building techniques (Vol. 51, No. 1)

The Atrium Vestae in Rome from © Carole Raddato from Frankfurt, Germany [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)]

A variety of scientific techniques have been combined to highlight improvements in the technologies employed by the Romans in successive modifications to the Atrium Vestae in Rome.

The Romans were some of the most sophisticated builders of the ancient world. Over the centuries, they adopted an increasingly advanced set of materials and technologies to create their famous structures. To distinguish the time periods over which these improvements took place, historians and archaeologists typically measure the colours, shapes and consistencies of the bricks and mortar used by the Romans, along with historical sources. In new research published in EPJ Plus, Francesca Rosi and colleagues at the Italian National Research Council improved on these techniques through scientific analysis of the materials used to build the Roman Forum’s Atrium Vestae. They found that successive phases of modification to the building saw improvements including higher quality raw materials, higher brick firing temperatures, and better ratios between carbonate and silicate building materials.

E Boccalon, F Rosi, M Vagnini, A Romani, Multitechnique approach for unveiling the technological evolution in building materials during the Roman Imperial age: the Atrium Vestae in Rome, Eur. Phys. J. Plus 134, 528 (2019)
[Abstract]

Scoping magnetic fields out for prevention (Vol. 49 No.5-6)

Magnetic field generated by a current (I) through a finite wire

A new study reveals how to best evaluate the circulation of magnetic fields around closed loops

Concerns about the effects of magnetic fields on human health require careful monitoring of our exposure to them. Mandatory exposure limits have been defined for electric and hybrid vehicle architectures, in domestic and work environments, or simply to shelter sensitive devices from unintended sources of magnetic disturbance. In a new study published recently, the authors develop a method for deriving an approximate value of the circulation around a loop of the magnetic field generated by the flow of electric current in an arbitrarily-shaped wire of a given length. In this study, the authors set out to adapt Biot-Savart’s law, which describes the magnetic field generated by finite wires, to evaluate the circulation of such fields around a closed path or loop. This led the authors to a mathematical formula that, as the finite wire thickness decreases to zero, becomes identical to one of their recent research results expressing the magnetic field circulation as a function of the wire current and of the solid angles between the circulation path and each of the conducting wire’s endpoints.

J. M. Ferreira and J. Anacleto, The magnetic field circulation counterpart to Biot-Savart’s law, Eur. Phys. J. Plus 133, 234 (2018)
[Abstract]

Scrutinising the tip of molecular probes (Vol. 47 No. 2)

The solid lines indicate the temperature range used to estimate the amount of molecules loaded onto the probe

Nature of interaction of probe molecules on the surface of oxide particles elucidated

Studies of molecules confined to nano- or micropores are of considerable interest to physicists. That’s because they can manipulate or stabilise molecules in unstable states or obtain new materials with special properties. In a new study published recently the authors have discovered the properties of the surface layer in probe molecules on the surface of oxide particles. These properties depend on the interaction at the interface. In this particular study, probes are formed by adsorption of rod-like cyanophenyl derivates on the surface of oxide particles. The authors found that their surface layers behave like glass-forming liquids.

They used data from infrared spectroscopy and thermogravimetry to identify the strength of the interaction between the probe and the oxide surface, which also helped them determine the type of bonding to the surface. The study shows that the value of the surface density can be used to divide the composites into several groups. This helps to determine that the probe molecules applied to the surface of a given group can display similar interactions, as observed in surfaces of the same family.

S. Frunza, L. Frunza, C. P. Ganea, I. Zgura, A. R. Brás and A. Schönhals, Rod-like cyanophenyl probe molecules nanoconfined to oxide particles: Density of adsorbed surface species, Eur. Phys. J. Plus 131, 27 (2016)
[Abstract]

Self-extension model of slime mold’s allorecognition behaviour (Vol. 49 No.5-6)

Two typical encounter cases of Physarum rigidum (plasmodium). They can recognize an encounter as self or non-self and decide to fuse (a) or avoid (b) allogeneic individuals.

When slime molds encounter an allogeneic individual, they judge whether to fuse or avoid it. This decision can be made without coming in contact with each other.

Slime molds move, feed, and grow during single-celled amoeboid stage—plasmodium. They can divide into multiple individuals and fuse. In this study on Physarum rigidum, an interesting behaviour was observed when they encountered an allogeneic individual. The plasmodia stopped their movement, came in contact with each other at the cell membrane surface, and then decided their actions. If they judge the encounter can become “self”, they fused, and if they recognize it as “non-self”, they avoided each other. This allorecognition behaviour can sometimes take several hours. More importantly, this behaviour can occur without contact between cell membranes. It is impressive to observe plasmodia stay apart from each other and decide their behaviour. In our study, we clarified that this behaviour, i.e., non-contact allorecognition, occurs with the spread of slime sheath, which is hyaline mucus secreted by plasmodium. Plasmodium diffuses slime sheath as an information substance of “self” to the environment, and it can be called "self-extension".

M. Masui, S. Satoh and K. Seto, Allorecognition behaviour of slime mold plasmodium—Physarum rigidum slime sheath-mediated self-extension model, J. Phys. D: Appl. Phys. 51, 284001 (2018)
[Abstract]

Self-imaging process at the near field of cylindrical convex gratings (Vol. 46 No. 4)

Self-imaging process at the near field of cylindrical convex gratings
Experimental set-up used to obtain the near field diffraction pattern.

Diffraction gratings have become one of the most used optical elements. Their behaviour has been extensively analysed from many diverse points of view. From a general sight, diffraction gratings produce diffraction orders at the far field and self-images at the near field. The applicability of diffraction gratings is quite extensive. They can be found as fundamental parts of many different devices such as telescopes, spectrometers, optical encoders, etc.

One particular kind of optical encoder uses cylindrical convex gratings. The authors show the near-field diffraction of cylindrical convex gratings illuminated by a general source that can be punctual or finite, monochromatic or polychromatic. They analyse how the size and polychromatism of the source affect the self-imaging process of cylindrical convex gratings. A decrease in the self-images contrast is produced for finite non-punctual sources. On the other hand, polychromaticity of the source produces quasi-continuous diffraction fringes from a certain distance forward.

All the results have been proven by experiments and could be helpful in applications that include convex diffraction gratings.

F. J. Torcal-Milla, L. M. Sanchez-Brea and E. Bernabeu,, Near field diffraction of cylindrical convex gratings, J. Opt., 17, 035601 (2015)
[Abstract]

Self-organized plasma jet at atmospheric pressure (Vol. 42, No. 1)

image The photograph of the capillary jet in the self-organized regime (four filaments, axial view, diameter 4 mm, exposure 1 ms).

Miniaturized non-thermal jet plasmas belong to the class of microplasmas characterized by dimensions below 1 mm. They represent an emerging technique for local surface treatment at atmospheric pressure such as surface modification and the deposition of thin functional coatings (for corrosion protection or gas diffusion barrier). The deposition of films with controlled quality requires the knowledge of the basic mechanisms, both plasma kinetics and flow dynamics that sustain and stabilize the gas discharge. This calls for a measure of the plasma parameters, validated by a suitable model. The plasma source studied here is a capacitive coupled capillary jet (27.12 MHz) operating in a distinctive regime where self-organized discharge patterns develop (Fig.: time averaged top view). This discharge regime along with the plasma source geometry puts the device in a prime position for a coating process at atmospheric pressure. The paper describes a first step towards a thorough plasma physical description of the discharge dynamics and the energy transport by determining the electron concentration in the active discharge zone. Two independent approaches were used, spectroscopic measurements of the broadening of Balmer Hβ and Hγ lines and a time-dependent, 2D fluid model of a single discharge filament. Electron concentrations between 2.2 and 3.3×1014cm-3 have been obtained after separating the relevant spectral line broadening effects. The fluid model has confirmed these results. The relatively high electron concentration in the active jet zone can be explained by the contraction of the discharge into single filaments. The self-organization makes these filaments deterministic but not stochastic. Their steady behaviour furthermore supports the establishment of a larger concentration of excited atoms, especially metastable atoms, leading to enhanced ionization.

On plasma parameters of a self-organized plasma jet at atmospheric pressure
J. Schäfer, F. Sigeneger, R. Foest, D. Loffhagen, and K.-D. Weltmann, Eur. Phys. J. D 60, 531-538 (2010)
[Abstract] | [PDF]

Self-passivation of vacancies in α-PbO (Vol. 44 No. 5)

Migration of oxygen vacancy towards lead vacancy followed by pair formation

Polycrystalline Lead Oxide (PbO) is one of the most promising materials for application in radiation medical imaging. At the current stage of technology, electronic grade PbO is not achievable because of large defect concentration. Defects act as traps for x-ray generated charge carriers during their transit across PbO layers: average distance drifted before trapping is smaller than layer thickness. Therefore, suppression of the effect of defects on carrier transport is an important challenge in PbO technology.

In metal oxides, vacancies are the main source of traps. The authors have shown that in thermally deposited PbO layers both Pb and O vacancies appear primarily in charged states of opposite sign. As a result, neighbouring vacancies can form neutral pair, which is no longer act as trapping centre. This finding offers a practical way to improve the transport properties. The post-growth annealing would initiate migration of the O vacancies towards Pb vacancies and facilitate their merging and neutral pair formation. The reduction in an amount of ionized centres increases carrier mobility and suppresses recombination thus improving x-ray generated charge collection.

J. Berashevich, J. A. Rowlands and A. Reznik, ‘Self-passivation of vacancies in α-PbO’, EPL, 102 (2013) 47002
[Abstract]

Semiclassical propagation up to the Heisenberg time (Vol. 44 No. 6)

Long time propagation of a resonance in the hyperbola billiard. The Ehrenfest time is 2.2, and the Heisenberg time is 35.3

Semiclassical propagation of waves is a fruitful approach to understand and evaluate a wide set of physical processes. This is performed by associating quantum states with Lagrangian manifolds in phase space, and the propagation is accomplished by the evolution of manifolds. However, long time propagation in Hamiltonian systems with chaotic dynamics is a longstanding unsolved problem; the reason being that Lagrangian manifolds evolve into very complex objects.

Recently, we have shown that by using the stable and unstable manifolds of periodic orbits, the propagation is simplified enormously. For this reason, in this paper we study in detail the manifolds of a periodic orbit of the hyperbola billiard, finding that they are organized by a simple tree structure. Then, we compute a complete set of homoclinic orbits (resulting from the intersection of the manifolds), which is required to evaluate the autocorrelation function of a quantum state constructed in the neighborhood of the periodic orbit (resonance). Finally, we compare the quantum and semiclassical autocorrelation up to the Heisenberg time, finding a relative error of the order of the Planck constant.

E. G. Vergini, ‘Semiclassical propagation up to the Heisenberg time’, EPL, 103, 20003 (2013)
[Abstract]

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