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Models explain changes in cooking meat (Vol. 51, No. 3)

Moisture flows in cooking meat. Temperature at 10 min. (blue), 30 min. (red) and 50 min. (yellow).

By treating meat as a network of flexible polymers surrounded by flowing moisture, computer models can accurately predict how much it will shrink when cooked.

Made up of complex networks of moisture-saturated proteins, meat displays some intriguing physical properties when it is cooked. In this work, mathematicians show that by modelling meat as a fluid-saturated matrix of elastic proteins, which are deformed as the fluid moves, cooking behaviours can be simulated precisely.

S Deyo, S Granzier-Nakajima, H Nelson, P Puente, K Tully, J Webb, A mathematical model for meat cooking, Eur. Phys. J. Plus 135, 322 (2020)
[Abstract]

Modern three-body forces make neutron stars collapse (Vol. 45 No.5-6)

Density profile of the collapsed state of 10000 neutrons in the X-Y-plane along the symmetry axis Z=0 (schematic illustration). Polarized neutrons, which interact through incorrect three-body forces, concentrate in small spheres separated by 0.9 fermi.

Nuclear systems ranging from light nuclei to massive neutron stars can be well described by nucleons interacting through two-body and three-body forces. From electrostatics we know that two identical uniformly charged spheres repel at any distance but the repulsion disappears when the spheres completely overlap. Similarly, in some modern expressions of nuclear three-body force it is assumed that the nuclear repulsion between the three nucleons is zero when they occupy the same position in space. The authors provide a mathematical proof that such form of the three-body force leads to the collapse of large neutron systems: N neutrons form a bound system with the energy growing as N3 (the effect becomes visible for N > 10000). The density of such system is illustrated in the Figure. Thus, in order to be compatible with our knowledge of neutron stars - where the constituents form dense nuclear matter with a finite energy per particle - modern expressions for three-body nuclear forces have to be carefully assessed regarding their strong repulsive core which should not vanish even when nucleon triples overlap.

D. K. Gridnev, S. Schramm, K. A. Gridnev and W. Greiner, “Nuclear interactions with modern three-body forces lead to the instability of neutron matter and neutron stars”, Eur. Phys. J. A, 50, 118 (2014)
[Abstract]

Molecular machines with continuous phase space (Vol. 43 No. 4)

image EMP for a tightly coupled motor as a function of the chemical driving force, for different values of the asymmetry. Note the regime in which the EMP exceeds 50%.

Molecular motors exploit the free energy released in the hydrolysis of energetic molecules like ATP to perform work useful for the cell. It is therefore important to know the efficiency of this process, i.e., the ratio between the performed work and the released free energy. The efficiency could reach 100% if the motor worked reversibly, i.e., infinitely slowly, but then its output power would vanish. Thus the relevant quantity is the Efficiency at Maximum Power (EMP). It has been shown that the EMP reaches 50% when the motor operates in the linear regime close to equilibrium. However, it has only recently been investigated further from equilibrium in models describing the motor as a discrete random process.

One can provide a more fundamental model of a molecular motor as a Brownian particle evolving in a two-dimensional continuous space, in which one coordinate represents its spatial position on the substrate and the other coordinate the advancement of the ATP-hydrolysis reaction, subject to a periodic “egg-carton” potential, whose tilt in the direction of the chemical coordinate expresses the free-energy imbalance. We have evaluated the EMP for such a model, with special choices of the potential, and found that it reaches the highest values when the displacements in the spatial and chemical coordinates are tightly bound: in this regime, efficiencies larger that 50% can be reached sufficiently far from equilibrium. When the binding is not tight, the EMP decreases since the motor can perform a chemical hydrolysis cycle without advancing. Our formalism thus allows us to gain a deeper insight into the connection between the mechanics and the thermodynamics of molecular motors.

Efficiency of molecular machines with continuous phase space
N. Golubeva, A. Imparato and L. Peliti, EPL, 97, 60005 (2012)
[Abstract]

Molecular motors in the rigid and crossbridge models (Vol. 42, No. 4)

image Examples of spontaneous oscillations of motor assemblies in the crossbridge model (red) and the rigid model (blue).

In cells, motor proteins use chemical energy to generate motion and forces. Motors often interact and form clusters because they are connected to a single rigid backbone. In a muscle the backbone is made by association of the motor tails. The backbone motion results from the action of all the motors, and feeds back on each motor. Previous works suggest that motor assemblies are endowed with complex dynamical properties, including dynamic instabilities and spontaneous oscillations, which may play a role in the mechanisms of heartbeat, flagellar beating, or hearing. In this paper, we study two models of motor assemblies: the rigid two-state model and the classical crossbridge model widely used in muscle physiology.

Both models predict spontaneous oscillations. In the rigid two-state model, they can have a "rectangular'' shape or a characteristic "cusp-like'' shape that resembles cardiac sarcomere and "stick-slip'' oscillations. The oscillations in the vicinity of the Hopf bifurcation threshold can be much faster than the chemical cycle. This property, not found in the crossbridge model where protein friction slows down the motion, could be important for the description of high frequency oscillations, such as insect wingbeat. Experiments based on the response of a motor assembly to a step displacement are also well described by both theories, which predict non-linear force displacement relations, delayed rise in tension and "sarcomere give''. This suggests that these effects are not directly dependent on molecular details. We also relate the collective properties of the motors to their microscopic properties accessible in single molecule experiments: we show that a three state state crossbridge model predicts the existence of instabilities even in the case of an apparent load decelerated detachment rate.

Dynamical behaviour of molecular motor assemblies in the rigid and crossbridge models
T. Guérin, J. Prost and J-F. Joanny, Eur. Phys. J. E, 34, 60 (2011)
[Abstract]

Molecular scale transporter with a twist, powered by liquid crystal defects (Vol. 48, No. 3)

Twisting effect, called chirogyral, dictated by the handedness of the fibre in a vertical magnetic field

Delivery of biochemical substances is now possible using a novel application of liquid crystal defects, forming a loop enclosing the substance travelling alongside twisted fibres.

Defects that break the symmetry of otherwise orderly material are called topological defects. In solid crystals, they are called dislocations because they interrupt the regularly structured atom lattice. In contrast, topological defects called disclinations take the form of loops in liquid crystals of the nematic variety, whose elongated molecules look like a shoal of fish. New experiments supported by a theoretical model show how defects forming loops around twisted plastic fibres dipped in liquid crystal could be used for the transport of biochemical substances, when controlled by electric and magnetic fields. These findings, published recently, have potential applications in electro-optical micromechanical and microfluidic systems. The loops have the ability to move alongside a translational motion when a magnetic field is applied in a direction oblique to the fibre. This means that by applying such a field, it is possible to control the transport of molecules trapped inside the loops, moving alongside the fibres.

M. Dazza, R. Cabeça, S. Čopar, M. H. Godinho and P. Pieranski, Action of fields on captive disclination loops, Eur. Phys. J. E 40, 28 (2017)
[Abstract]

Monodisperse magnetic nanoparticles prepared from block copolymer template (Vol. 48, No. 5-6)

SEM images of superparamagnetic nanoparticles made from self-assembled block copolymer template (a) on Si substrate, (b) after their release in solution

Magnetic nanoparticles are playing an increasing role in biomedical applications, both for diagnosis (e.g. contrast agent in MRI (Magnetic resonance imaging) or for MPI (magnetic particles imaging)) and for therapy thanks to their ability to exert forces and torques on biological species allowing for instance cancer cells destruction or oriented growth of biological tissue.

In order to fabricate magnetic nanoparticles with high monodispersity, required in particular in biomedical imaging, we have developed a new preparation method based on the use of self-assembled block copolymer template.

Such techniques have already been explored for the preparation of patterned media for ultra-high density magnetic recording. However, our requirements substantially differ from those for storage media. A sacrificial layer has to be introduced between the substrate and the diblock copolymer to allow the release of the nanoparticles in solution. For that purpose, an optimized germanium oxide layer was used. The obtained superparamagnetic particles do not agglomerate in solution. They can be made of biocompatible material (magnetite) and exhibit very narrow size dispersion (≈7%). They can be good contrast agents for medical imaging.

M. Morcrette, G. Ortiz, S. Tallegas, H. Joisten, R. Tiron, T. Baron, Y. Hou, S. Lequien, A. Bsiesy and B. Dieny, Fabrication of monodisperse magnetic nanoparticles released in solution using a block copolymer template, J. Phys. D: Appl. Phys. 50, 295001 (2017)
[Abstract]

More than one brain behind E=mc2 (Vol. 44 No. 2)

Friedrich Hasenöhrl found proportionality between energy and its mass in a cavity filled with radiation. (Source: Österreichische Zentralbibliothek fuer Physik)

The present article reveals the contribution of a little known Austrian physicist, Friedrich Hasenöhrl, to uncovering a precursor to Einstein famous equation in establishing the proportionality between the energy (E) of a quantity of matter with its mass (m) in a cavity filled with radiation.

The author argues how Hasenöhrl’s work, for which he now receives little credit, may have contributed to the famous equation E=mc2. He believes the notion that mass and energy should be related did not originate solely with Hasenöhrl. Nor did it suddenly emerge in 1905, when Einstein published his paper, as popular mythology would have it.

Given the lack of recognition for Hasenöhrl’s contribution, his original work on blackbody radiation in a cavity with perfectly reflective walls is examined. This study seeks to identify the blackbody’s mass changes when the cavity is moving relative to the observer.

The reason why the Austrian physicist arrived at an energy/mass correlation with the wrong factor, namely at the equation: E = (3/8) mc2, are then explored. Hasenöhrl’s error would stem from failing to account for the mass lost by blackbody while radiating.

Before Hasenöhrl focused on cavity radiation, other physicists including French mathematician Henri Poincaré and German physicist Max Abraham, showed the existence of an inertial mass associated with electromagnetic energy. In 1905, Einstein gave the correct relationship between inertial mass and electromagnetic energy, E=mc2. Nevertheless, it was not until 1911 that German physicist Max von Laue generalised it to include all forms of energy.

S. Boughn, ‘Fritz Hasenöhrl and E=mc2’, Eur. Phys. J. H 38, 261 (2013)
[Abstract]

Multifractal analysis of breast cancer IR thermograms (Vol. 45 No.2)

Multifractal analysis of temperature time-series (A-C) of the cancerous (red) and intact (black) breasts of a patient, and of a healthy volunteer breast (green). D(h) singularity spectra (D): the multifractal wide spectrum of healthy breasts reduces to a single point (monofractality) in the presence of a tumor.

Breast cancer is a common type of cancer among women and despite recent advances in the medical field there are still some inherent limitations in current screening techniques. The radiological interpretation of X-ray mammograms often leads to over-diagnoses and to unnecessary traumatic and painful biopsies. In this paper, the authors propose a computer-aided multifractal analysis of dynamic infrared imaging as an efficient method for preliminary screening in asymptomatic women, in order to identify those with a higher risk of breast cancer. Using a wavelet-based multi-scale method to analyze the temporal fluctuations of breast skin temperature, collected both from patients with breast cancer, and from healthy volunteers, they show that the multifractal complexity of temperature fluctuations observed in intact breasts is lost in mammary glands with a malignant tumor. Besides potential clinical application, these results underline the informative content of physiological changes that may precede anatomical alterations in breast cancer development.

E. Gerasimova, B. Audit, S.-G. Roux, A. Khalil, F. Argoul, O. Naimark and A. Arneodo, "Multifractal analysis of dynamic infrared imaging of breast cancer", EPL 104, 68001 (2013)
[Abstract]

Multilayer Memristive/Memcapacitive Devices (Vol. 44 No. 6)

Device 1 is the conventional memristor design: electrodes are separated by a single ionic conductor insulator. Device 2 utilizes the multi-layer design, which forms a quasi-uniform conduction front. The simulated resistive switching of the multilayer memristor occurs largely within the linear regions where tuning can occur.

Memristive devices are reshaping computing paradigms as one of the leading candidates for the future of computer memory. In conventional memristors, metallic filaments form and extend stochastically under applied electrical bias, producing a highly non-uniform conduction front. This produces devices with large variations in electrical properties that are difficult to tune.

Here, we introduce and simulate a specialized multi-layered device structure with alternating ionic conductor layers that enables the development of a quasi-uniform conduction front. This reduces catastrophic switching (Fig. 1b) in which devices rapidly exit the linear-tuning region and switch state. In our simulations of a single layer memristor, the majority of the resistance change during a switching event occurs catastrophically, while in the multilayer device the majority of switching occurs in the linear tuning region. This ability to fine-tune switching events in devices is an important property for multi-bit memory and neuromorphic computing applications.

P. R. Mickel and C. D. James, ‘Multilayer Memristive/Memcapacitive devices with engineered conduction fronts’, Eur. Phys. J. Appl. Phys., 62, 30102 (2013)
[Abstract]

Multimodal microscope enables structural and functional cellular imaging (Vol. 50, No. 2)

Answering cell physiology and pharmacology research questions often requires structural and functional information to be obtained from a network of cells. The authors have developed a multi-modal imaging system based on surface plasmon resonance (SPR) that combines several additional imaging modalities including bright-field, epifluorescence, total internal reflection microscopy and SPR fluorescence microscopy. The microscope features a wide field of view that can study ~40 cells simultaneously with subcellular resolution.

SPR is the collective oscillation of free electrons in a metal excited by polarized light. The resonance condition is highly dependent upon the refractive index of the media. Exploiting this allows the detection of both spatial and temporal variations in refractive index (RI) label-free.

In this work the authors describe a detailed design of the microscopy platform including standard tests for characterization of spatial resolution and sensitivity. Using SPR for imaging requires that the cell of interest is closely adhered to the surface. The spatial variation of refractive index was shown to be reasonably homogenous from a cultured neuron. Finally, a prototypical functional imaging experiment is reported where spatiotemporal cellular functions of stem cell-derived cardiomyocytes have been realised by detecting localized contractions.

C. L. Howe, K. F. Webb, S.A. Abayzeed, D. J. Anderson, C. Denning and N. A. Russell, Surface plasmon resonance imaging of excitable cells, J. Phys. D: Appl. Phys. 52, 104001 (2019)
[Abstract]

Multiple magnon modes in a magnetic Weyl semimetal (Vol. 51, No. 1)

dV/dI spikes’ positions, which demonstrate several magnon branches with the linear field dependence.

An area of interest in condensed matter physics is topological Weyl semimetals (WSMs). There are only a few candidates of magnetically ordered materials for the realisation of WSMs, like the kagome-lattice ferromagnet Co3Sn2S2.

Novel magnon branches are predicted in magnetic Weyl semimetals, which can be understood as a result of the coupling between two magnetic moments mediated by Weyl fermions. Here, we experimentally investigate electron transport in the kagome-lattice ferromagnet Co3Sn2S2, which is regarded as a time-reversal symmetry broken Weyl semimetal candidate. We demonstrate dV/I(I) curves with pronounced asymmetric dV/dI spikes, similar to those attributed to current-induced spin-wave excitations in ferromagnetic multilayers. In contrast to multilayers, we observe several dV /dI spikes’ sequences at low, ≈104 A/cm2 , current densities for a thick single-crystal Co3Sn2S2 flake in the regime of fully spin-polarised bulk. The spikes at low current densities can be attributed to novel magnon branches in magnetic Weyl semimetals, which are predicted due to the coupling between two magnetic moments mediated by Weyl fermions. The presence of spin-transfer effects at low current densities in Co3Sn2S2 makes the material attractive for applications in spintronics.

O. O. Shvetsov et al, Multiple magnon modes in the Co3Sn2S2Weyl semimetal candidate, EPL 127, 57002 (2019)
[Abstract]

Mutual extinction of light (Vol. 51, No. 4)

Calculated total extinction in a setup with two beams incident on a rectangular box containing many scatterers, plotted versus the angle between the two beams.

In many branches of the natural sciences Nature is interrogated by performing wave scattering experiments. An incident wave impinges on a sample, and characteristics of the scattered and transmitted waves are analysed to find detailed information about the target.

When a single light wave is incident on a complex scattering medium, the transmitted intensity differs from the incident one due to extinction. We introduce the new concept of mutual extinction, which occurs when more than one light wave is incident and propose new experiments to observe mutual extinction and transparency in two-beam experiments with either elastic and absorbing scatterers.

A. Lagendijk et al., Mutual extinction and transparency of multiple incident light waves, EPL 130, 34002 (2020)
[Abstract]

Nano amorphous Interfaces in phase-change memory materials (Vol. 51, No. 2)

Model of nano interface between amorphous and crystalline phases in a PCM material.

Phase-change memory (PCM) is an emerging non-volatile memory technology. It encodes data through the rapid and reversible transition between amorphous and crystalline states of PCM materials.

In this work the effects of three kinds of nano amorphous interfaces in PCM materials are summarised, i.e. interfaces could either enhance phase stability (the amorphous Si/amorphous Sb2Te3 interface and the amorphous GeTe/cubic Sb2Te3 interface) or promote crystallization (the amorphous/crystalline GeSbTe interface). Therefore, these nano interfaces can be used to enhance data-retention ability or accelerate data-encoding speed.

X.-P. Wang, Y.-T. Liu, Y.-J. Chen, N.-K. Chen and X.-B. Li, Nanoscale amorphous interfaces in phase-change memory materials: structure, properties and design, J. Phys. D: Appl. Phys. 53, 114002 (2020)
[Abstract]

Nanoparticles hitchhiking their way along strands of hair (Vol. 48 No. 1)

Corrugated hair surface

Massaging hair can help more quickly deliver nanoparticle-based treatment to the roots

In shampoo ads, hair always looks like a shiny, smooth surface. But for physicists peering into microscopes, the hair surface looks much more rugged, as it is made of saw-tooth, ratchet-like scales. In a new theoretical study published recently, the authors have demonstrated that massaging hair can help to apply drug treatment—encapsulated in nanoparticles trapped in the channels formed around individual hairs—to the hair roots. This is because the oscillatory movement of the massaging directs the way these particles are transported. This phenomenon was previously discovered in experiments on pork skin samples, which were conducted by Jürgen Lademann, dermatologist at the Charité clinic in Berlin, Germany, and his team. It is also relevant at the microscopic scale, in the transport on microtubules taking place in two directions between the cells within our bodies. By constrast, these findings could also help find ways of preventing harmful nanoparticles from being transported along hairs into the wrong places.

M. Radtke and R. R. Netz, Ratchet effect for two-dimensional nanoparticle motion in a corrugated oscillating channel, Eur. Phys. J. E 39, 116 (2016)
[Abstract]

Nanoscale heat flow predictions (Vol. 45 No.4)

Snapshot of the final configuration of a nc-Si sample. Credit: Melis et al.

A new study predicts that heat flow in novel nanomaterials could contribute to creating environmentally friendly and cost-effective nanometric-scale energy devices.

Physicists are now designing novel materials with physical properties tailored to meet specific energy consumption needs. Before these so-called materials-by-design can be applied, it is essential to understand their characteristics, such as heat flow. Now, the authors have developed a predictive theoretical model for heat flux in these materials, using atom-scale calculations. These findings could have implications for optimizing the thermal budget of nanoelectronic devices or in the production of energy through thermoelectric effects in novel nanomaterials.

The authors adopted a method called approach equilibrium molecular dynamics (AEMD), which is robust and suitable for representing large systems to deliver trustworthy predictions on thermal transport. Ultimately, the model could be applied to semiconductors used as high-efficiency thermoelectrics, and to graphene nanoribbons used as heat sinks for so-called ultra large scale integration devices, such as computer microprocessors.

C. Melis, R. Dettori, S. Vandermeulen and L. Colombo, “Calculating thermal conductivity in a transient conduction regime: theory and implementation”, Eur. Phys. J. B, 87, 96 (2014)
[Abstract]

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