Vol. 49 No.2 - Highlights

Nuclear-structure studies of exotic nuclei with MINIBALL (Vol. 49, No. 2)

The MINIBALL spectrometer comprises 24 six-fold segmented, encapsulated high-purity germanium crystals. It was specially designed for highest g-ray detection efficiency which is advantageous for low-intensity radioactive ion beams. (picture courtesy CERN)

Investigations of exotic nuclei at the ISOLDE facility of CERN are pursued with reaccelerated radioactive ion beams by means of high-resolution g-ray spectroscopy. The experimental programme covers a range of topics, which are addressed with beams ranging from neutron-rich magnesium isotopes up to heavy radium isotopes. The nuclear-structure and nuclear-reaction studies provide important insights into collective properties and single particle excitations. The most important outcomes of these measurements include: discoveries of rare nuclear shapes like octupole deformation in the actinide region; the coexistence of different intrinsic nuclear shapes at low excitation energy, and within a very narrow energy range in strontium and mercury isotopes, for which nuclear shell model investigations yielded considerable discrepancies from theory when extrapolated from known stable nuclei; and the remarkable behaviour of exotic neutron-rich nuclei with the “magic” number of 20 neutrons and in the vicinity of semi-magic chains of Ni- and Sn isotopes. The article summarized results obtained with the REX-ISOLDE facility which is the precursor of the newly inaugurated HIE-ISOLDE accelerator at CERN. The new installation allows the in-beam spectroscopy programme to be continued with higher secondary-beam intensity, higher beam energy and better beam quality. The first results have been obtained after commissioning of the super-conducting accelerator.

P. A. Butler, J. Cederkall and P. Reiter, Nuclear-structure studies of exotic nuclei with MINIBALL, J. Phys. G: Nucl. Part. Phys. 44, 044012 (2017)

Ultrafast x-rays capture the electron and nuclear dance (Vol. 49, No. 2)

Experimental techniques used in ultrafast x-ray science

There has been revolutionary progress in producing ultrafast short-wavelength radiation and dreams of visualizing electronic and nuclear motion in complex systems on their natural timescales are rapidly unfolding. Accelerator-driven free-electron-laser sources of ultrafast, ultraintense x-ray pulses that open the door to nonlinear multiphoton x-ray phenomena, though rare (seven worldwide), have basically doubled their operating number in the past year. Laboratory-based ultrafast x-ray pulses based upon high harmonic radiation from infrared lasers, present and affordable at many institutions, have decreased in pulse duration from a longstanding record of 67 attoseconds to 43 attoseconds recently, and, have increased in photon energy to >1 keV.

The roadmap presents independent perspectives from 17 leading groups on further source developments and their potential impacts on atomic and molecular physics. We start with familiar processes, i.e. ultrafast photoexcited molecular dynamics followed with femtosecond x-ray pulses, then discuss phenomena enabled only by intense x-ray pulses from the accelerator-based free-electron-laser sources, i.e. multidimensional x-ray spectroscopies, nonlinear scattering and single-shot imaging, and conclude with the attosecond frontier where new source developments enable fundamental understanding of how charge migrates and how electrons are ejected.

L. Young and 26 co-authors, Roadmap of ultrafast x-ray atomic and molecular physics, J. Phys. B: At. Mol. Opt. Phys., 51, 032003 (2018)

Laser-ranged satellite measurement now accurately reflects Earth's tidal perturbations (Vol. 49, No. 2)

Lustbühel Satellite Laser Tacking. Credit: Jörg Weingrill (CC BY 2.0 [5])

The most precise ever laser satellite measurement method provides new clues to relativity

Tides on Earth have a far-reaching influence, including disturbing satellites’ measurements by affecting their motion. This disturbance can be studied using a model for the gravitational potential of the Earth, taking into account the fact that Earth’s shape is not spherical. The LAser RElativity Satellite (LARES), is the best ever relevant test particle to move in the Earth’s gravitational field. In a new study published, LARES proves its efficiency for high-precision probing of General Relativity and fundamental physics. By studying the Earth’s tidal perturbations acting on the LARES, the authors demonstrate the value of laser-range satellites for high-precision measurements.

V.G. Gurzadyan, I. Ciufolini, H.G. Khachatryan, S. Mirzoyan, A. Paolozzi, and G. Sindoni, On the Earth’s tidal perturbations for the LARES satellite, Eur. Phys. J. Plus 132, 548 (2017)

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)

Nanosecond high-voltage pulses for air purification (Vol. 49, No. 2)

NO removal (and by-product formation) with fast high voltage pulses

Transient plasmas generated by high-voltage pulses have been widely studied and used for industrial and environmental applications for more than 100 years. The highly reactive species that are generated in these plasmas can react with particles in polluted gas and water streams. We focus on plasma for environmental applications and developed a new, very fast high-voltage pulse source for this purpose (0.5-10 ns pulse duration, 200 ps rise time and 50 kV amplitude). We showed that with this pulse source, we can achieve extremely high energy yields in ozone generation (typically used for water decontamination) and nitrogen oxide (NO) removal (a typical exhaust gas for diesel engines). Interestingly, the pulse duration, a figure of merit that has long been claimed as the key success in high-yield plasma processing (the shorter the better), had no significant influence on our yields. It appears that the key to these high yields is the very fast rise time of our high-voltage pulses. They are so fast that the complete electric field is applied to the gas while the plasma is still developing, which results in higher electron densities and ultimately in more reactive species.

T. Huiskamp, W. F. L. M. Hoeben, F. J. C. M. Beckers, E. J. M. van Heesch and A. J. M. Pemen , (Sub)nanosecond transient plasma for atmospheric plasma processing experiments: application to ozone generation and NO removal, J. Phys. D: Appl. Phys. 50, 405201 (2017)

Biological rhythms—what sets their amplitude? (Vol. 49, No. 2)

Analytical amplitude bounds constrain the oscillation minima and maxima for different types of biochemical oscillator systems

Living organisms rely on internal biological timers to ensure their proper development and functioning during adult life; examples are the formation of repetitive embryonic patterns or the entrainment of activity cycles to the day-night cycle. Such timers are typically embodied as biochemical oscillators, i.e., genetic regulatory networks that generate oscillations in the concentration of gene products within cells via a delayed negative feedback. Theoretical descriptions of these oscillators often rely on nonlinear rate equations that describe how the interactions between different gene products can give rise to stable limit-cycle oscillations. For a large class of such models, we here derive a method to construct analytical bounds for the minima and maxima of the oscillations, one of their functional key features besides their period. Numerical simulations of different example systems show that the oscillations saturate the bounds as the feedback delay becomes large. The results shed light on which details of the nonlinear feedback are responsible for constraining the oscillation amplitude and can be readily generalised to similar oscillator systems.

D. J. Jörg, Amplitude bounds for for biochemical oscillators, EPL 119, 58004 (2017)

Quantifying electrocaloric effects in multilayer capacitors (Vol. 49, No. 2)

“(a) Schematic cross-section of an MLC. (b) Photograph of three MLCs based on 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3, with active area per layer of 0.12, 0.29 and 0.42 cm2 within dashed lines. (c) Temperature change |ΔTj| measured directly using a thermocouple (solid circles) versus the ratio of active volume Vactive to total volume Vtotal. Multiplying by the ‘correction’ factor (solid squares) that would have been hitherto assumed elsewhere overestimates |ΔTj| (open circles)

Multilayer capacitors (MLCs) are now being exploited in prototype cooling devices because they show large voltage-driven changes of temperature that can be used to pump large amounts of heat. However, accurate quantification of these electrically driven temperature changes is challenging because only the core is electrocalorically active.

In a recent study, the authors investigated electrocaloric MLCs with different geometries. By increasing the active volume of the core with respect to the inactive surround, the authors were able to identify the temperature changes that could be driven in the core without thermalization due to the surround. This improves upon previous works, in which partial thermalization was assumed to be complete, leading to overestimates of temperature change.

T. Usui, S. Hirose, A. Ando, S. Crossley, B. Nair, X. Moya, and N. D. Mathur, Effect of inactive volume on thermocouple measurements of electrocaloric temperature change in multilayer capacitors of 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3, J. Phys. D: Appl. Phys. 50, 424002 (2017).

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

3D simulations of the heart mechanisms

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).

Relativity Matters: Two opposing views of the magnetic force reconciled (Vol. 49, No. 2)

Gilbertian - magnetic dipole

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 inhomogeneous 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, the authors succeeded in resolving this ambiguity between Amperian 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.

J. Rafelski, M. Formanek, and A. Steinmetz, Relativistic Dynamics of Point Magnetic Moment, Eur. Phys. J. C 78, 6 (2018)