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Brain capacity limits online data growth (Vol. 43 No. 4)

image The human brain limits global information load

Study of internet file sizes shows that information growth is self-limited by the human mind. It is found here that it is the capacity of the human brain to process and record information –and not economic constraints – that may constitute the dominant limiting factor for the overall growth of globally stored information.

The authors first looked at the distribution of 633 public internet files by plotting the number of videos, audio and image files against the size of the files. They chose to focus on files hosted on domains pointing from the online encyclopaedia Wikipedia and the open web directory dmoz.

The absence of exponential tails for the graph representing the number of files indicates that economic costs were not the limiting factors for data production. Instead, it appears that underlying neurophysiological processes influence the brain’s ability to handle information. For example, when the individual attributes a subjective resolution to an image, their perception of the quality of that image matter. Their perception of the amount of information gained when increasing the resolution of a low-quality image is substantially higher then when increasing the resolution of a high-quality photo by the same degree.

The analysis shows that this relation, known as the Weber-Fechner law, is also obeyed by file-size distributions. This means that the total amount of information cannot grow faster than our ability to digest or handle it.

Neuropsychological constraints to human data production on a global scale
C. Gros, G. Kaczor and D. Marković, Eur. Phys. J. B, 85, 28 (2012)
[Abstract]

Brain learning simulated via electronic replica memory (Vol. 46 No. 4)

Typical current-voltage (i-v) characteristics of a memristor; the pinched hysteresis loop is due to the nonlinear relationship between the memristance current and voltage.

A new study shows how a new way of controlling electronic systems endowed with a memory can provide insights into the way associative memories are formed by mimicking synapses.

Scientists are attempting to mimic the memory and learning functions of neurons found in the human brain. To do so, they investigated the electronic equivalent of the synapse, the bridge, making it possible for neurons to communicate with each other. Specifically, they rely on an electronic circuit simulating neural networks using memory resistors. Such devices, dubbed memristor, are well-suited to the task because they display a resistance, which depends on their past states, thus producing a kind of electronic memory. The authors have developed a novel adaptive-control approach for such neural networks, presented in this study. Potential applications are in pattern recognition as well as fields such as associative memories and associative learning.

H. Zhao, L. Li, H. Peng, J. Kurths, J. Xiao and Y. Yang, Anti-synchronization for stochastic memristor-based neural networks with non-modeled dynamics via adaptive control approach, Eur. Phys. J. B 88, 109 (2015)
[Abstract]

Breaking up: a convoluted drama at nuclear scale, too (Vol. 48 No. 1)

Schematic distribution of the breakup

Regardless of the scenario, breaking up is dramatic. Take for example the case of carbon (12C) splitting into three nuclei of helium. Until now, due to the poor quality of data and limited detection capabilities, physicists did not know whether the helium fragments were the object of a direct breakup in multiple fragments up front or were formed in a sequence of successive fragmentations. The question has been puzzling physicists for some time. Now, the authors have used a state-of-the-art detector capable of measuring, for the first time, the precise disintegration of the 12C into three helium nuclei. Their findings, released in a study published recently, reveal a sequence of fragmentations, relevant to developing a specific kind of fusion reactions and in astrophysics. Their findings could have applications in devising an alternative to neutron-producing fusion reactions, a process called aneutronic fusion. In addition, they could help to improve our theoretical understanding of an extremely important reaction in astrophysics: the time-reversed process involving the fusion of three helium nuclei into 12C.

H.K. Laursen, H.O.U. Fynbo, O.S. Kirsebom, K.S. Madsbøl and K. Riisager, Complete kinematical study of the 3α breakup of the 16.11 MeV State in 12C, Eur. Phys. J. A, 52, 271 (2016)
[Abstract]

Bright sparks shed new light on the dark matter riddle (Vol. 47 No. 2)

Data gathered by the detector module Lise depicted in the light yield energy plane

Highest sensitivity detector ever used for very light dark matter elementary particles

The origin of matter in the universe has puzzled physicists for generations. Today, we know that matter only accounts for 5% of our universe; another 25% is constituted of dark matter. And the remaining 70% is made up of dark energy. Dark matter itself represents an unsolved riddle. Physicists believe that such dark matter is composed of (as yet undefined) elementary particles that stick together thanks to gravitational force. In a study recently published, the authors use the so-called phonon-light technique to detect dark matter. They are the first to use a detection probe that operates with such a low trigger threshold, which yields suitable sensitivity levels to uncover the as-yet elusive particles responsible for dark matter. The asymmetric dark matter particle models are one of the candidates for a new elementary particle to explain dark matter. The experimental detection is no different from the scattering of two billiard balls, as the particle scatters on an atomic nucleus. The challenge: the lighter the dark matter particle is, the smaller the energy deposited in the crystal used for detection is. Currently, no other direct dark matter search method has a threshold for nuclear recoils as low as 0.3 keV. As such, the CRESST-II team are the first to ever probe dark matter particle masses at such low mass scale.

G. Angloher +39 co-authors, Results on light dark matter particles with a low-threshold CRESST-II Detector, Eur. Phys. J. C 76, 25 (2016)
[Abstract]

Bringing measuring accuracy to radical treatment (Vol. 44 No. 2)

Comparison of the experiment and simulation laser induced fluorescence spectrum of hydroxyl.

Significant progress made in evaluating the density of active species used in medical applications of plasma physics could improve the accuracy of treatment: this article presents the first determination of the absolute density of active substances called radicals found in a state of matter known as plasma. These findings could have important implications for medicine - for example, for stimulating tissue regeneration, or to induce a targeted antiseptic effect in vivo without affecting neighbouring tissues.

Laser fluorescence spectroscopy (LIF) is the detection method used to estimate the density of radicals in the plasma, made of charged species, active molecules such as radicals and atoms. The authors have chosen to focus on OH radicals because they are one of the most important reactive species in plasma science due to their high level of oxidation. This means that chemical reactions with OH initiate the destruction of harmful components either in the human body or in nature such as carbon monoxide, volatile organic compounds and methane.The problem is that, up to now, laser-induced fluorescent (LIF) capability to measure the absolute density of radicals has been very limited because of issues with registering and analysing the fluorescence signal.

In this study, the authors present a simplified model which takes into account energy transfer stemming from the radicals’ vibrations. It can be used to analyse the LIF signal at regular atmospheric pressure. They then confirm the validity of their model experimentally, with a plasma jet made of Argon gas mixed with water molecules.

Q. Xiong, A. Nikiforov, L. Li, P. Vanraes, N. Britun, R. Snyders, X.P. Lu and C. Leys, ‘Absolute OH density determination by laser induced fluorescence spectroscopy in an atmospheric pressure RF plasma jet’, Eur. Phys. J. D 66, 281 (2012)
[Abstract]

Bringing the chaos in light sources under control (Vol. 47 No. 1)

Study investigates how best to stabilise the output of quantum dot LEDs Noise is an issue in optical telecommunications. And findings means of controlling noise is key to physicists investigating light-emitting diodes or lasers. The authors have worked on a particular type of light source, called the quantum dot light-emitting diode (QDLED). They demonstrate that modulating bias current of the QDLED could lead to countering the noise. This, in turn, leads to stabilising such light sources, making them better suited for optical telecommunications.

Most light sources exhibit fluctuations due to the quantum nature of the process underlying the emission of light. However, experiments show that these fluctuations—often described as quantum noise—are inherently chaotic and subject to oscillations, dubbed mixed mode oscillations. The authors have developed a theoretical model, which is able to reproduce the chaotic and oscillating phenomena observed experimentally. This can help them understand the nature of such phenomena.

They found that spiking competition of quantum dots in the part of the diode that emits lights enhances the way in which the diode receives its own self-feedback in terms of the light being emitted and it also has an effect on the impact of noise perturbation. They also show that the dynamics of these fluctuations are completely determined by the variation of the injecting bias current feeding into the QDLED.

As a result, that fluctuations can be brought under control by changing the bias current. The next step in their research will involve focusing on synchronisation phenomena in QDLED arrays for using this source in optical telecommunications. Other potential applications could include quantum dot-enhanced LED-backlighting of LCD televisions.

K. Al Naimee, H. Al Husseini, S.F. Abdalah, A. Al Khursan, A. H. Khedir, R. Meucci and F.T. Arecchi, Complex dynamics in Quantum Dot Light Emitting Diodes, Eur. Phys. J. D 69, 257 (2015)
[Abstract]

Broad-band Coupling Transducers for Magneto-Inductive Cables (Vol. 41, No. 5)

image Flexible MI cable with 50 W coaxial connector.

Magneto-inductive (MI) waveguides are periodic structures that operate by magnetic coupling between a set of L-C resonators. A current in one element will create a magnetic field, which then induces a voltage in a neighbouring element. This voltage in turn sets up a new current, which creates a new field. In this way, current waves can propagate along a chain of coupled resonators. Magneto-inductive waves have been observed in arrays of elements formed from discrete capacitors and inductors, and also in split ring resonators. More recently, a flexible cable has been introduced, which allows the inductors and capacitors to be printed, by patterning copper layers on either side of a thin polyimide substrate. MI waveguides allow band-pass propagation at frequencies ranging from MHz to GHz, for applications ranging from data cables to safety-critical interconnects. Other applications include near field lenses, field concentrators and detectors for magnetic resonance imaging.

The performance of MI waveguides is steadily improving, Propagation losses have been reduced, and flexible cables allow bends with low reflection. However, a full range of components is needed before useful systems may be built. A key requirement is a simple method of connecting magneto-inductive and conventional systems. Since the characteristic impedance of a MI waveguide is both frequency-dependent and complex, this is not an easy task. This paper describes a very simple broadband resonant transducer capable of low-loss coupling between magneto-inductive waveguides and systems with real impedance. The transducer may even be formed automatically when a cable is cut, allowing MI waveguides to be spliced to conventional systems. This development should open up the new possibilities for practical applications of MI waves.

Broad-band Coupling Transducers for Magneto-Inductive Cables
R.R.A.Syms, L.Solymar and I.R.Young, J. Phys. D: Appl. Phys. 43, 285003 (2010)
[Abstract]

Calculation of the connective constant for self-avoiding walks (Vol. 44 No. 5)

A typical self-avoiding walk of 100 million steps on the square lattice, generated using the pivot algorithm.

Self-avoiding walks are walks on a lattice, which are not allowed to self-intersect. Despite the apparent simplicity of the self-avoiding walk model, it is an important model of polymers, and over the past 60 years it has resisted all attempts to find an exact solution.

One of the basic features of self-avoiding walks is the number of walks for a given number of steps. The number of walks grows exponentially with length, and the rate of exponential growth, called the connective constant, is a quantity of fundamental interest.

Using a novel divide and conquer Monte Carlo algorithm, the number of self-avoiding walks on the simple cubic lattice for selected lengths of up to 38 million steps were estimated to high precision. For instance, the number of walks with 606 207 steps is 7.7 × 10406 535! Using these estimates the connective constant was found to be 4.684 039 931 ± 0.000 000 027, which is significantly more accurate than estimates obtained via alternative methods.

A key open question is whether similarly powerful enumeration methods can be found for other models in statistical mechanics.

Nathan Clisby, ‘Calculation of the connective constant for self-avoiding walks via the pivot algorithm’, J. Phys. A: Math. Theor. 46, 245001 (2013)
[Abstract]

Can quarantine do more than just “flatten the curve”? (Vol. 52, No. 1)

The fraction of susceptible (main figure) and infected individuals (inset) for a single-phase soft quarantine and a two-phase quarantine.

Our modeling of the epidemic shows that compared to a single-phase soft quarantine, a quarantine composed of a strict phase followed by a softer one results in a smaller overall number of infected individuals. This occurs if individuals with anomalously-many connections such as essential workers or store cashiers become immune before all others are allowed to come out of the strict quarantine. In this case, the most “socially connected” individuals, once recovered, act as efficient breaks in the network of disease transmission.

V. Nimmagadda, O. Kogan and E. Khain, Path-dependent course of epidemic: Are two phases of quarantine better than one?', EPL 132 (2020)
[Abstract]

Can we study the many-body localisation transition? (Vol. 51, No. 2)

Can we study the many-body localisation transition?
The timescale for delocalisation grows quickly with disorder strength.

An interacting quantum system experiencing strong disorder can undergo a transition into a non-thermalising phase: an effect known as many-body localisation (MBL).

Delocalisation transition is understood to be driven by the hybridisation of resonant many-body configurations which can only form above a certain length scale. Experimental efforts are hindered by the finite lifetimes of the system, so one cannot truly distinguish localisation from very slow dynamics. In this letter the length- and timescales required to observe thermalisation, and how they grow when approaching the MBL transition from the delocalised side are studied. The results suggest that reliably characterising the transition’s critical properties is beyond the reach of current experimental and numerical techniques.

R. K. Panda et al, Can we study the many-body localisation transition?, EPL 128 67003 (2019)
[Abstract]

Cancer risk myth debunked (Vol. 47 No. 1)

Cancer risk is not just bad luck
© tilialucida / Fotolia

Cancer risk debate laid to rest by novel calculations distinguishing population-wide risks for each organ and individual risks linked to environmental and genetic factors.

A recent study suggests that variations in terms of cancer risk among tissues from various organs in the body merely amount to pure bad luck. In other words, cancer risk is linked to random mutations arising in the normal course of DNA replication of healthy cells. It is also claimed that environmental and genetic factors play a lesser role. The scientific community has primarily reacted negatively to this interpretation and promptly refuted it with qualitative arguments and empirical evidence. Joining these voices are the authors, who uncovered the statistical fallacy at the source of the recent study's conclusion. The key is to distinguish between individual organ risks and population risks, they wrote in this work. They also contend that the role of genetic and environmental factors must not be underplayed, even if these factors cannot explain differences in cancer rates between different organs.

D. Sornette and M. Favre, Debunking mathematically the logical fallacy that cancer risk is just “bad luck”, EPJ Nonlinear Biomedical Physics 3, 10 (2015)
[Abstract]

Carbon dating uncovers forged Cubist painting (Vol. 45 No.2)

The alleged Contraste de formes, an oil on canvas from the Peggy Guggenheim Collection, Venice, was proven to be a fake.
Credit: Caforio et al.

Physicists use carbon dating to confirm alleged Fernand Léger painting was definitely a fake, thus corroborating the doubts about its authenticity previously expressed by art historians.

For the first time, it has been possible to identify a fake painting by relying on the anomalous behaviour of the concentration of 14C in the atmosphere after 1955 to date its canvas. These findings were recently obtained by the authors.

Previously, art historians called upon scientists to compare the alleged Léger painting from the Peggy Gugenheim Collection (PGC), in Venice, Italy, with an authentic painting of the ‘Contrastes de formes’ series belonging to the Solomon Guggenheim Foundation (SGF) in New York, USA. They showed that the canvas fibres and the paint pigments differed, evidence was inconclusive. Using accelerator mass spectrometry, the authors definitely proved that the canvas sample contains a level of radioactive carbon found in 1959, years after Léger’s death in 1955.

L. Caforio et al., "Discovering forgeries of modern art by the 14C Bomb Peak", Eur. Phys. J. Plus, 129, 6 (2014)
[Abstract]

Cell motility in a compressible gel (Vol. 51, No. 1)

Actomyosin droplet with superimposed velocity field.

Cell motility is crucial to biological functions ranging from wound healing to immune response. Spontaneous movement and deformation are physically driven by the cell cytoskeleton.

The cytoskeleton consists of protein filaments and motors which constantly consume chemical energy (ATP) and convert it to work. In particular, actin filaments interact with myosin motors to generate contraction forces in the cell, which drive cell motion and division. Most of the research has focused, both experimentally and theoretically, on cell migration on a two-dimensional substrate (crawling), providing a detailed outline of some basic migration mechanisms. However, some cells, such as breast tumor cells, can also “swim” in a straight line inside a 3D tissue or a polymeric fluid, in the absence of substrates. The authors present a minimal model for pattern formation within a compressible actomyosin gel, which is numerically solved both in 2D and 3D. Contractility leads to the emergence of an actomyosin droplet within a low-density background. This droplet then becomes self-motile for sufficiently large motor contractility. Simulations also show that compressibility has the effect to facilitate motility, as it decreases the value of the isotropic contractile stress beyond which the droplet starts to move.

G. Negro et al, Hydrodynamics of contraction-based motility in a compressible active fluid, EPL 127, 58001 (2019)
[Abstract]

Charge and spin density in helical Luttinger liquids (Vol. 47 No. 3)

Planar spin helix, pinned by an impurity

Often an electron confined to one spatial dimension does not have many options. It can have spin up or down and it can go right or left. In helical systems the possibilities are further reduced: the spin projection is tied to the direction of motion. This phenomenon is called spin-momentum locking and takes place at the edges of two-dimensional topological insulators. Its consequences are exciting for spintronics: since spin up and down electrons counter-propagate, spin transport can be easily generated by charge currents. In our work, we identify peculiar properties of the weakly interacting helical Luttinger liquid. We address the interesting question: Are the charge density and spin correlations influenced by spin-momentum locking? While for strong interactions the system becomes a Wigner crystal of fractional charges e/2 built on a strongly anisotropic spin wave (which we have shown in a previous publication), in this work, we demonstrate that, for weak interactions, density correlations are featureless, i.e. the density is not affected by impurities. However, spin correlations are well represented by a planar spin helix that can be pinned by magnetic impurities.

N. Traverso Ziani, C. Fleckenstein, F. Crépin and B. Trauzettel, Charge and spin density in the helical Luttinger liquid, EPL 113, 37002 (2016)
[Abstract]

Charge transfer measurements in low-energy ion-atom collisions (Vol. 44 No. 1)

We have used a radio frequency ion trap to study two charge transfer reactions:

(1) Resonant charge transfer: 3He2+ + 4He (1s2) → 3He + 4He2+,

(2) Single electron charge transfer: 3He2+ + 4He (1s2) → 3He+ + 4He+.

We have determined the resonant charge transfer (RCT) rate coefficient of 3He2+ with para -4He (1s2) at energies below 1 eV (reaction (1)). The rate coefficient is measured to be 5.9±0.6×10-10 cm3s-1 at an equivalent temperature of 1200K and is in reasonable agreement with recent calculations. This measurement extends our knowledge to a lower energy region thus adding to our understanding of the charge transfer process of 3He2+, α-particles, with He encountered in astrophysics and fusion research.

While this measurement extends the experimental results below eV energies for the first time, it however provides an interesting observation. The rate coefficient for resonant two electrons transfer (reaction (1)) is orders of magnitude larger than the rate coefficient for single electron transfer (reaction (2)) at comparable temperature reported in the literature. This may lead to the following fundamental questions. The electron spin in para-He is anti-parallel. The spatial wave function that represents the two electrons is symmetric. The probability density for the two electrons close together is finite. Can the proximity of the two electrons account for this relatively large two electrons resonant charge transfer rate coefficient? Is it possible that the two anti-parallel electrons couple to form a loosely bound electron pair that is responsible for this relatively fast two-electron transfer? Can we gain some physical insight by measuring the rate coefficient of the resonant charge transfer of 3He2+ with ortho-4He (1s2s) (metastable helium (23S1)) where the two electron spins are parallel?

C. Kyriakides, B.S. Clarke, W. M. O'Donnell, B. Zygelman and V.H.S. Kwong, ‘Resonant charge transfer of 3He2+ with 4He(1s2) at energies below 1 eV’, J. Phys. B: At. Mol. Opt. Phys. 45 235701 (2012)
[Abstract]

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