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Liquid Metal Energy Harvester by Acoustic Wave (Vol. 49 No.4)

Liquid Metal Energy Harvester by Acoustic Wave
Current generation by modulating the liquid metal shape with an applied acoustic wave

Application of a temperature gradient to a magnetic medium leads to the generation of a spin current referred to as the longitudinal spin Seebeck effect (LSSE). In a magnetic insulator such a current is created by a flux of thermal magnons. Using spin-dependent electron scattering processes in the adjacent normal metal this current can be converted to an electric voltage. The voltage evolution is determined by the development of the temperature gradient ∇T(x,t) and by the characteristics of the magnon’s motion.
By analysis of the time-dependent LSSE voltages in platinum-coated Yttrium Iron Garnet (YIG) ferrimagnetic films, the authors assumed that thermally-driven magnons with energies above 20 K move through the YIG layer ballistically due to their almost linear quasi-acoustic dispersion law. Consequently, the interaction processes within the ‘acoustic’ magnon mode do not change the magnon propagation velocity, while the number of magnons decays exponentially within an effective propagation length of 425nm. This length was found to be mostly independent on film thickness that proves the ballistic magnon transport scenario.

J. Jeon, S. K. Chung, J.-B. Lee, S. Joo Doo and D. Kim, Acoustic wave-driven oxidized liquid metal-based energy harvester, Eur. Phys. J. Appl. Phys. 81, 20902 (2018)
[Abstract]

Long-time behaviour of macroscopic quantum systems (Vol. 41, No. 6)

The renewed interest in the foundations of quantum statistical mechanics in recent years has led us to study John von Neumann's 1929 article on the quantum ergodic theorem (QET). We have found this almost forgotten article, which until now has been available only in German, to be a treasure chest, to be much misunderstood and very relevant to the recent discussion on the general and abstract reasons why, and the exact sense in which, an isolated macroscopic quantum system will approach thermal equilibrium from (more or less) any initial state. In his paper, von Neumann studied the long-time behaviour of macroscopic quantum systems. His main result, the QET, expresses so-called "normal typicality": for a typical finite family of commuting macroscopic observables, every initial wave function ψ(0) from a micro-canonical energy shell so evolves that for most times t in the long run, the joint probability distribution of these observables obtained from ψ(t) is close to their micro-canonical distribution.

In our commentary, we provide a gentle introduction to the QET and discuss its relevance to the approach to thermal equilibrium. There is, in fact, no consensus about the definition of thermal equilibrium for a quantum (or even a classical) system in microscopic terms; the main divide in the literature lies between the "ensemblists" who regard thermal equilibrium as a property of an ensemble (or a mixed state) and the "individualists" who regard thermal equilibrium as a property of an individual system (in a pure state). As we explain, von Neumann's concept of equilibrium is influenced by both views but mainly based on the individualist view, a view that has gained ground recently.

Long-time behaviour of macroscopic quantum systems - Commentary accompanying the English translation of John von Neumann’s 1929 article on the quantum ergodic theorem
S. Goldstein, J.L. Lebowitz, R. Tumulka and N. Zanghì, Eur. Phys. J. H 35, 173 (2010)
[Abstract]

Low-dimensional analogue of holographic baryons (Vol. 45 No.3)

A triple chain soliton solution at high density, displaying the baryonic popcorn phenomenon in the low-dimensional theory.

Gauge/gravity duality provides a method to study various features of a large class of strongly coupled quantum field theories. A significant motivating application for these ideas is the physics of non-perturbative phases of Quantum Chromodynamics (QCD) and this is the subject of holographic QCD (HQCD). Within HQCD baryons are described by collective excitations, known as solitons, and the study of nuclei and dense QCD translates into the investigation of multi-soliton physics in a curved spacetime with an additional spatial dimension (the holographic direction). However, even computing the classical multi-soliton solutions is a difficult problem that has not yet been solved.

The authors introduce a low-dimensional analogue of holographic baryons, with the advantage that numerical computation of multi-solitons and finite density solutions is tractable. They find that many of the conjectured features of soliton physics in HQCD are realized in this model, including a series of transitions at increasing density (dubbed baryonic popcorn) where the soliton crystal develops additional layers in the holographic direction: a phenomenon that is expected to play a vital role in understanding the important issue of dense HQCD.

S. Bolognesi and P. Sutcliffe, “A low-dimensional analogue of holographic baryons”, J. Phys. A: Math. Theor., 47, 135401 (2014)
[Abstract]

Lyman-Birge-Hopfield emissions from electron-impact excited N2 (Vol. 41, No. 5)

image Electron impact induced LBH emission cross-sections of Ajello & Shemansky [J. Geophys. Res. 90, 9845,1985] and Young et al. [J. Phys. B 43, 135201, 2010] (normalized at ∼ 200eV). Also shown is a typical auroral (secondary) electron flux distribution (at 120km altitude) from Jones et al. [Planet. Space Sci. 54, 45, 2006] scaled to illustrate the abundance of low energy electrons. Inset: strong auroral and dayglow LBH emission intensities in the terrestrial northern hemisphere [credit: NASA].

The Lyman-Birge-Hopfield (LBH) band system of N2 (a1Πg → X1Σ+,g ) is one of the most prominent emissions in Earth's upper atmosphere. LBH emissions are excited primarily through collisions with electrons, frequently produced by ionizing solar radiation and the solar wind. Strong LBH emissions also radiate from the nitrogen atmosphere of Titan, Saturn's largest moon. Space programs (NASA, ESA…) have launched numerous satellites with UV spectrometers to monitor these emissions.

Recently, LBH emissions resulting from electron impact excitation of N2 into the metastable a1Πg state were re-examined. By careful attention to numerous experimental variables, such as background signal rates and pressure dependence, more broadly reproducible cross-sections were obtained. Surprisingly, the results differ significantly from the widely accepted benchmark published 25 years ago, which was found to be in error. This new study indicates that the LBH emission cross-section changes more gradually with electron impact energy than previously thought.

The results of this experiment can now be used by aeronomers to better determine the type and energy of collisions responsible for atmospheric radiation. LBH band emissions provide a sensitive diagnostic of the glowing upper atmosphere. For instance, these emissions are used to infer the N2 density distribution and gas temperature, as well as the average energy and amount of electrons liberated by solar radiation (i.e., dayglow photoelectron flux) and auroral events. The changing spatial distribution of LBH emissions are important observables needed to model space weather, which can seriously upset or even interrupt satellite communications and disrupt power grids. These laboratory results will also improve the interpretation of Cassini-Huygens's ongoing observations of Titan.

Lyman-Birge-Hopfield emissions from electron-impact excited N2
J. A. Young, C. P. Malone, P. V. Johnson, J. M. Ajello, X. Liu and I. Kanik, J. Phys. B: At. Mol. Opt. Phys. 43 135201 (2010)
[Abstract]

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)
[Article]

Magnetic hyperthermia for tumour reduction (Vol. 44 No. 6)

Schematic diagram of the mechanisms leading to heat dissipation in magnetic nanoparticles

Magnetic hyperthermia is the process by which cycling magnetic nanoparticles in an alternating magnetic field leads to heat dissipation. It is a very attractive approach for the treatment of cancer because it generates no side effects unlike more conventional therapies such as radiotherapy or chemotherapy. The development of this therapy has been hampered by the lack of a clear understanding of the physical mechanisms leading heat generation. At the present time it is not possible for clinicians to be given details of the dosage and field conditions required for a given therapeutic outcome.

There are three mechanisms by which exposing magnetic nanoparticles to a cycling field can generate heat: susceptibility loss, hysteresis loss and viscous heating. We have found that these mechanisms are highly particle size dependent as shown schematically in the figure and will also depend upon the degree of aggregation of the particles. In experiments of magnetic nanoparticles of different sizes dispersed in solvents of varying viscosities, hysteresis heating has been shown to be the dominant mechanism. Although the contribution arising from viscous heating is significant its effects are uncontrollable and will not occur in vivo due to the high viscosity of tumour tissue.

G. Vallejo-Fernandez, O. Whear, A. G. Roca, S. Hussain, J. Timmis, V. Patel and K. O’Grady, ‘Mechanisms of hyperthermia in magnetic nanoparticles’, J. Phys. D: Appl. Phys. 46, 312001 (2013)
[Abstract]

Magnetic nanoparticles can 'burn' cancer cells (Vol. 50, No. 3)

Magnetic nanoparticles can 'burn' cancer cells
Caption: “The specific absorption rate.”Fig. 8 (graph right below).

Magnetic hyperthermia is still a highly experimental cancer treatment, but new research shows that the therapy is tunable.

Unfortunately, cancer isn’t simply a single disease, and some types, like pancreas, brain or liver tumours, are still difficult to treat with chemotherapy, radiation therapy or surgery, leading to low survival rates for patients. Thankfully, new therapies are emerging, like therapeutic hyperthermia, which heats tumours by firing nanoparticles into tumour cells. In a new study published recently, the authors show that tumour cells’ specific absorption rate of destructive heat depends on the diameter of the nanoparticles and the composition of the magnetic material used to deliver the heat to the tumour. The authors show that the tumour absorption rate greatly depends on the diameter of the nanoparticles. Surprisingly, the absorption rate increases as particle diameter increases, as long as the level of doping of the material is sufficiently high and the diameter doesn’t exceed a set maximum value (max. 14 nanometres for cobalt doping, 16 nm for copper).

A. Apostolov, I. Apostolova and J. Wesselinowa, Specific absorption rate in Zn-doped ferrites for self-controlled magnetic hyperthermia, Eur. Phys. J. B 92, 58 (2019)
[Abstract]

Magnetite or maghemite? There is a simple answer. (Vol. 48, No. 5-6)

Correlation between δRT, the ‘centre of gravity’ of the room temperature 57Fe Mössbauer spectrum of a magnetite/maghemite sample vs. the fraction of 57Fe atoms present in magnetite, α.

The composition or stoichiometry of magnetite (Fe3O4) and maghemite (γ-Fe2O3) mixtures or solid solutions is important for the physical, geological and material sciences. It is also significant in biomedical science, where magnetic nanoparticles are used both in vitro and clinically, and where both ferrous and ferric iron ions play active roles in the production of reactive oxygen species. However, the accurate determination of the composition/stoichiometry can be tricky, as it requires either well-crystallised samples suitable for x-ray diffraction, or it relies on chemical dissolution methods that, depending on the nature of the sample, are often either unfeasible or inappropriate.

However, there is a simple answer, in the form of the recently proposed 57Fe Mössbauer spectroscopic ‘centre of gravity method’. The COG method is non-destructive and determines the composition/stoichiometry from the mean isomer shift, ¬δRT. It is well suited to nanomaterials, is simple and straightforward, and as long as appropriate measures and protocols are observed – all of which are explained in the paper – even inexperienced users will find little difficulty in its implementation.

J. Fock, L. K. Bogart, D. González-Alonso, J. I. Espeso, M. F. Hansen, M. Varón, C. Frandsen and Q. A. Pankhurst, On the ‘centre of gravity’ method for measuring the composition of magnetite/ maghemite mixtures, or the stoichiometry of magnetite-maghemite solid solutions, via 57Fe Mössbauer spectroscopy, J. Phys. D: Appl. Phys. 50, 265005 (2017)
[Abstract]

Make or break for cellular tissues (Vol. 43 No. 4)

image Active, living cells remain governed by the law of physics: image after 1300s.

Models developed to study liquids are used to investigate the mechanics of cellular tissues, which could further our understanding of embryonic development and cancer.

The present study demonstrates that the behaviour of a thin layer of cells in contact with an unfavourable substrate is akin to that of thin fluid or elastic films. Understanding the mechanism by which a thin layer of cells splits into disjointed patches, thus breaking the layer’s structural integrity, bears great significance because the human tissue, or epithelium, covering organs can only fulfil its role if here are no holes or gaps between the cells.

Thanks to the analogy between the cellular layer examined and the well-understood behaviour of thin liquid films, the authors devised a model of the layer’s evolution. They considered it as an active, amorphous material made of a continuum of cells. Because it is subject to a constant competition between neighbouring cell-cell and cell-substrate adhesion, it can either maintain its contiguous structure or break.

The authors investigated the layer’s stability when subjected to chemical and physical disturbances. In particular, they scrutinised how the cellular layer reacted to a non-adhesive substrate with little chemical affinity with the cells. They also subjected the cell to a physical disturbance by laying them in substrates with low stiffness, such as soft gels.

So, the so-called de-wetting phenomenon has been observed, whereby the cellular layer is ruptured leading to islands of cells interspersed with dry patches. The de-wetting phenomenon is therefore due to the cells' distinctive sensitivity to the nature of its substrate, particularly to its decreased stiffness.

De-wetting of cellular monolayers
S. Douezan and F. Brochard-Wyart, Eur. Phys. J. E, 35, 34 (2012)
[Abstract]

Making oxygen on Mars thanks to plasma technology (Vol. 49, No. 1)

A pulsed plasma induces a higher vibrational excitation on Mars

Sending a manned mission to Mars is one of the next major steps in space exploration. Creating a breathable environment, however, is a substantial challenge. Plasma technology could hold the key to creating a sustainable oxygen supply on the red planet, by converting carbon dioxide directly from the Martian atmosphere.

Low-temperature plasmas are one of the best media for CO2 decomposition, both by direct electron impact and by transferring electron energy into vibrational excitation. It is shown that Mars has excellent conditions for In-Situ Resource Utilisation (ISRU) by plasma. Indeed, the pressure and temperature ranges in the Martian atmosphere mean non-thermal plasmas can be used to produce oxygen efficiently. Besides the 96% carbon dioxide atmosphere, the cold surrounding atmosphere may induce a stronger vibrational effect than that achievable on Earth.

The method offers a twofold solution for a manned mission to Mars. Not only would it provide a stable, reliable supply of oxygen, but a source of fuel as well, as oxygen and carbon monoxide have been proposed to be used as a propellant mixture in rocket vehicles.

V. Guerra and 8 co-authors, The case for in situ resource utilisation for oxygen production on Mars by non-equilibrium plasmas, Plasma Sources Sci. Technol. 26, 11LT01 (2017)
[Abstract]

Making plasma medicine available for in-body applications (Vol. 50, No. 1)

Endoscope tip without and with Neon plasma

Ever since non-thermal plasmas showed efficacy in decontamination and wound healing, the idea of deploying plasma medical therapy within the human body emerges. Besides the need for flexibility, small dimensions and biological effectiveness, also a minimal plasma-caused applicator erosion as well as an electrically safe operation mode are necessary. Of course, the endoscopic plasma source must also operate inside hollow cavities independent of the environmental conditions present. Since all requirements need to be fulfilled at the same time, the development task is quite complex.

The present paper tackles those requirements and sets special focus on new approaches for reducing leakage current, increasing the bactericidal efficacy and avoiding material erosion simultaneously. The jet-like plasma at the tube tip is maintained by a capacitively coupled discharge configuration. An additional shielding gas surrounds the jet in order to assure reproducible environmental conditions inside the body. Finally, it is found that a combination of Neon feed gas, CO2 shielding gas and a current limited high voltage supply gives the best bactericidal results and, at the same time, reduces material erosion as well as patient leakage current.

J. Winter, Th. M. C. Nishime, R. Bansemer , M. Balazinski, K. Wende and K.-D. Weltmann, Enhanced atmospheric pressure plasma jet setup for endoscopic applications, J. Phys. D: Appl. Phys. 52, 024005 (2019)
[Abstract]

Making the most of carbon nanotube-liquid crystal combos (Vol. 45 No.3)

Dispersed multi-wall carbon nanotubes on a glass surface. Credit: Yakemseva et al.

This work focuses on the influence of temperature and nanotube concentration on the physical properties of such combined materials. These findings could have implications for optimizing these combinations for non-display applications, such as sensors or externally stimulated switches, and novel materials that are responsive to electric, magnetic, mechanical or even optical fields.

In this study, the authors focused on the electro-optic and dielectric properties of ferroelectric liquid crystal-multiwall carbon nanotube combinations. Specifically, they studied the influence of temperature on the compound material’s main physical properties. They found that all dispersions exhibit the expected temperature dependencies with regard to their physical properties.

They also investigated the dependence of physical characteristics on nanotube concentration, which is still the subject of several contradicting reports. For increasing nanotube concentration, they observed a decrease in tilt angle, but an increase in spontaneous polarisation.

M. Yakemseva, I. Dierking, N. Kapernaum, N. Usoltseva and F. Giesselmann, “Dispersions of Multi-wall Carbon Nanotubes in Ferroelectric Liquid Crystals”, Eur. Phys. J. E, 37, 7 (2014)
[Abstract]

Many-body localisation in generalized Kondo lattice with disorder (Vol. 51, No. 3)

Schematic demonstrations of the decoherent state (left panel) and the localised state (right panel).

Many-body localisation (MBL) has gained widespread attentions in theoretical and experimental physics, the scenario of which is essentially different with that of the Anderson’s localization (AL).

In this work, we study the MBL transition in a generalised Kondo lattice, where a one-dimensional Hubbard chain with disordered spin-orbit coupling couples to a fixed impurity of spin 1/2. Based on exact diagonalisation, we calculate various quantities that can distinguish an MBL state from either an AL state or a thermal state. The model can be implemented in ultra-cold Fermi gases of alkaline-earth-like atoms in one-dimensional optical lattices and Raman-assisted spin-orbit coupling.

Reference

Ye Cao and Wei Zhang, Many-body localisation in generalized Kondo lattice with disorder, EPL 129 2000 (2020)
[Abstract]

Market crashes and the financial data fractal landscape (Vol. 45 No.5-6)

Graph of the normalized empirically found distribution of the American Dow Jones Industrial Average index, DJIA (red squares), and European Euro Stoxx 50 (blue circles) index data with prices recorded every minute data along with the Standard Normal curve for comparison.
Credit: Green et al.

Analyzing the adequation of financial data structure with its expected fractal scaling could help early detection of extreme financial events because these represent a scaling irregularity.

New research shows that the most extreme events in financial data dynamics—reflected in very large price moves—are incompatible with multi-fractal scaling. These findings have been published by the authors. Understanding the multi-fractal structure of financially sound markets could, ultimately, help in identifying structural signs of impending extreme events.

In this study, the authors performed multi-fractal testing on two sets of financial data: the Dow Jones Industrial Average (DJIA) index and the Euro Stoxx 50 indexes. They demonstrate that the extreme events which make up the heavy tails of the distribution of the Euro Stoxx 50 logarithmic graph of financial returns distort the scaling in the data set. This means that most extreme events adversely affect fractal scaling. These results contrast with previous findings that extreme events contribute to multi-fractality.

E. Green, W. Hanan and D. Heffernan, “The origins of multifractality in financial time series and the effect of extreme events”, Eur. Phys. J. B 87, 129 (2014)
[Abstract]

Martingale theory for housekeeping heat (Vol. 50, No. 2)

Traces of fluctuating housekeeping heat (grey lines) behave like downtrend stocks. Our work investigates statistics of extrema (black arrows) against the average tendency

Which universal thermodynamic properties emerge in a nonequilibrium process, in isothermal conditions at temperature T, that result from the violation of detailed balance, and how they may be quantified? The housekeeping heat is the fluctuating heat exchanged between a mesoscopic system and its environment due to the violation of detailed balance. Using the framework of martingale theory widely used in probability theory and finance, we derive a number of universal equalities and inequalities for extreme-value and stopping-time statistics of the housekeeping heat. Our theory provides a quantitative link between minimal models of gambling and financial markets (martingales) and heat fluctuations. The housekeeping heat behaves like a gambler’s fortune in a casino: its expected value in the future is always smaller or equal regardless of its past values. The super-martingale structure of the housekeeping heat implies that certain statistical properties of the housekeeping heat are system-independent, i.e. universal. A particular result of our theory is that the average value of the maximum housekeeping heat that a system absorbs from its environment cannot exceed kB T, with kB Boltzmann’s constant.

R. Chétrite, S. Gupta, I. Neri and E. Roldán, Martingale theory for housekeeping heat, EPL 124, 60006 (2018),
[Abstract]

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