Europhysics News

Highlights

Elucidating biological cells’ transport mechanisms (Vol. 45 No.2)

Image of mitochondria observed by transmission electron microscopy.
Credit: K. Hayashi et al.

A new study focuses on the motion of motor proteins in living cells, applying a physicist’s tool called non-equilibrium statistical mechanics used to study diffusion.

Using an ingenious setup, the authors have, for the first time, calculated the force of molecular motors —called kinesin and dynein— acting on the inner components of biological cells, called mitochondria. These findings could contribute to elucidating the transport mechanism in biological cells by multiple motors.

The authors compared evaluations of the diffusion coefficient obtained via the so-called Einstein relation—which stems from non-equilibrium statistical mechanics—applied to both mitochondria and the random motion of beads artificially incorporated into a cell. They found that the medium’s viscosity obtained using the beads, was slightly lower than that obtained using the mitochondria motion. This means that physical laws such as the Einstein relation are not sufficient to fully describe the mitochondria’s motion, which is subjected to complex biological processes.

K. Hayashi, C. G. Pack, M. K. Sato, K. Mouri, K. Kaizu, K. Takahashi and Y. Okada, “Viscosity and drag force involved in organelle transport: Investigation of the fluctuation dissipation theorem”, Eur. Phys. J. E, 36, 136 (2013)
[Abstract]

"Spooky action at distance" in particle physics?! (Vol. 43 No. 2)

Spooky action at distance also for neutral kaons

The article summarised here presents the first conclusive test to better understand high-energy particles correlations: A proposal is devised for the first conclusive experimental test of a phenomenon known as 'Bell's nonlocality'. It is designed to reveal correlations that are stronger than any classical correlations, and to do so between high-energy particles that do not consist of ordinary matter and light. These results are relevant to the so-called 'CP violation' principle, which is used to explain the dominance of matter over antimatter.

In 1964, John Bell found that so-called local realistic hidden parameter theories imply that the relations between these high-energy particles correlations could be experimentally tested through so-called Bell tests.

In this study, the authors have succeeded in devising a new Bell test taking into account the decay property of high-energy particles systems, called kaon-antikaon systems, while ensuring that the test is conclusive - a goal that has never before been achieved - and simultaneously guaranteeing its experimental testability. Experimental testing requires equipment such as the KLOE detector at the accelerator facility DAPHNE in Italy.

Revealing "spooky action at distance" for kaon-antikaon pairs has fundamental implications for our understanding of such particles' correlations and could ultimately allow us to determine whether symmetries in particle physics and manifestations of particle correlations are linked.

Revealing Bell's Nonlocality for Unstable Systems in High Energy Physics
B. C. Hiesmayr, A. Di Domenico, C. Curceanu, A. Gabriel, M. Huber, J-Å. Larsson and P. Moskal, Eur. Phys. J. C, 72, 1856 (2012)
[Abstract]

100% renewable energy sources require overcapacity (Vol. 48 No. 2)

Germany's greenhouse gas (GHG) emissions from 2002 to 2015 and the political target for 2020 (bars)

To switch electricity supply from nuclear to wind and solar power is not so simple

Germany decided to go nuclear-free by 2022. A CO₂ -emission- free electricity supply system based on intermittent sources, such as wind and solar — or photovoltaic (PV) — power could replace nuclear power. However, these sources depend on the weather conditions. In a new study published recently, the author analysed weather conditions using 2010, 2012, 2013 and 2015 data derived from the electricity supply system itself, instead of relying on meteorological data. By scaling existing data up to a 100% supply from intermittent renewable energy sources, the author demonstrates that an average 325 GW wind and PV power are required to meet the 100% renewable energy target. This study shows the complexity of replacing the present primary energy supply with electricity from intermittent renewable sources, which would inevitably need to be supplemented by other forms of CO₂ - free energy production.

F. Wagner, Surplus from and storage of electricity generated by intermittent sources, Eur. Phys. J. Plus 131, 445 (2016)
[Abstract]

2D Raman mapping of stress and strain in Si waveguides (Vol. 43 No. 5)

Measured stress maps and lattice deformation sketches for waveguides: (a)-(b) without cladding (SOI0), (c)-(d) with tensile-stressing cladding (SOI1), (e)-(f) with SOI2). The arrows show the type of observed stress.

In 27, 085009 (2012)this work, we characterized the mechanical stress of strained silicon waveguides by micro-Raman spectroscopy. We performed accurate measurements on the waveguide facet by using a confocal Raman microscope. The silicon-on-insulator waveguide is strained by depositing thin stressing silicon nitride (SiN) overlayers. The applied stress is varied by using different deposition techniques. By investigating the waveguides facets and modeling the measured Raman shifts, the local stress and strain are extracted. Thus, two-dimensional maps of stress distribution as a function of SiN deposition parameters are drawn showing different strain distributions depending on the deposition technique. Moreover, the results show a relevant role played by the buried oxide layer, which strongly affects the waveguides final stress. Hence, the combined actions of SiN and buried oxide layers deform the whole silicon core layer and cause an inhomogeneous strain distribution in the waveguides.

The strain inhomogeneity is fundamental to enable second order nonlinear optical devices because it breaks the silicon centro-symmetry yielding a huge second order nonlinear susceptibility (χ(2)). As we demonstrate in Nature Mater. 11 148-154 (2012), a χ(2) of several tens of picometers per volt is observed and a relation between the χ(2) values and the strain inhomogeneity and magnitude is revealed. Particularly, the largest conversion efficiency is observed in the waveguides where the micro-Raman spectroscopy shows the highest deformation. Currently, no explicit theory relating the strain with the χ(2) exists. Thus, the two-dimensional micro-Raman maps could be a valuable tool for experimental confirmation of future theories.

F. Bianco, K. Fedus, F. Enrichi, R. Pierobon, M. Cazzanelli, M. Ghulinyan, G. Pucker and L. Pavesi, ‘Two-dimensional micro-Raman mapping of stress and strain distributions in strained silicon waveguides which show second order optical nonlinearities‘, Semicond. Sci. Technol. (2012) 27, 085009
[Abstract]

3D virtual slicing of an antique violin reveals ancient varnishing methods (Vol. 50, No. 2)

Volume rendering of the wood with the coating system on it

Physicists and chemists use 3D scanning to unlock the forgotten secrets of the multi-layered coating methods that give violins their exceptional tone and look.

Italian violin-making masters of the distant past developed varnishing techniques that lent their instruments both an excellent musical tone and impressive appearance. Few records from this era have survived, as techniques were most often passed down orally to apprentices; only scarce information is available on the original methods used for finishing the instruments. In a new study published recently, the authors use the Elettra synchrotron facility in Trieste to develop a non-invasive 3D-scanning approach, using the Synchrotron Radiation micro-Computed Tomography (SR-micro-CT), that yields insights into the main morphological features of the overlapping finishing layers used on violins. In turn, the morphological images can be used to determine the chemical nature of the coating. This newly developed method could help scientists rediscover the procedures and materials used, and reproduce the multi-layered coating methods of the ancient masters.

They first use the X-ray beam to scan two sets of mock-ups, prepared in their lab to mimic the finishing layers on the historical instruments. Using the mock-ups, they then optimise the 3D scanning settings, boost the spatial resolution and define the parameters required for 3D reconstruction. They then focus on a large fragment removed from a damaged cello made by the 17th-century Italian luthier Andrea Guarneri. Lastly, they compare their findings with those produced by micro-invasive analyses of the varnish to evaluate the merits of the reconstructed volumes and virtual slicing in terms of investigating such layered, complex structures.

G. Fiocco, T. Rovetta, M. Malagodi, M. Licchelli, M. Gulmini, G. Lanzafame, F. Zanini, A. Lo Giudice, and A. Re, Synchrotron radiation micro-computed tomography for the investigation of finishing treatments in historical bowed string instruments: issues and perspectives, Eur. Phys. J. Plus 133, 525 (2018)
[Abstract]

A customized THz quantum-cascade laser (Vol. 44 No. 3)

Frequency tuning using the applied current and beam profile of the local oscillator. The gray horizontal solid line indicates the frequency of the oxygen line.

Quantum-cascade lasers for the terahertz spectral region are promising light sources for several spectroscopic applications, despite currently only operating at cryogenic temperatures. The authors developed a local oscillator to be used in an airborne heterodyne receiver for the investigation of interstellar atomic oxygen. The challenge for the design consists in the simultaneous fulfilment of demanding specifications for a set of operating parameters.

The developed laser emits a single mode with an optical power of about 0.5 mW and an almost Gaussian beam shape. The laser mode can be tuned using the applied current to cover about 5 GHz in the vicinity of 4.745 THz. The local oscillator, which is based on a distributed-feedback laser combining a quantum-cascade laser with a single-plasmon waveguide and a lateral first-order grating, can be operated in a cryogen-free cooler in continuous-wave mode. The developed quantum-cascade laser exhibits large wall-plug efficiency over a wide range of current densities with a negligible spectral shift of the gain maximum in order to achieve the required tuning range.

L. Schrottke, M. Wienold, R. Sharma, X. Lü, K. Biermann, R. Hey, A. Tahraoui, H. Richter, H.-W. Hübers, and H. T. Grahn, ‘Quantum-cascade lasers as local oscillators for heterodyne spectrometers in the spectral range around 4.745 THz’, Semicond. Sci. Technol. 28, 035011 (2013).
[Abstract]

A description of the jamming transition in soft particulate matter (Vol. 41, No. 6)

This paper illustrates how the tools of equilibrium statistical mechanics can help explain a different set of natural phenomena-- the physics of systems far-from-equilibrium, such as the jamming transition in granular matter. When S. F. Edwards from Cambridge University proposed a thermodynamic formulation for grains, the community of statistical physics received it as attractive and innovative. However, since there are no first principle justifications of Edwards’s ideas they were also viewed with some degree of scepticism. Since the publication of Edwards’ original work over 20 years ago, the scientific community has debated the possibility of its validity.

Edwards’ ideas consist of proposing a statistical ensemble of volume and stress fluctuations through the thermodynamic notion of entropy, compactivity and angoricity (two temperature-like variables). We find that Edwards’ thermodynamics correctly describes our numerical and theoretical study of the jamming transition (J-point).

Using the ensemble formalism we elucidate two questions regarding the jamming transition: (i) The thermodynamic approach predicts the order of the jamming phase transition by showing the absence of critical fluctuations at jamming in observables like pressure and volume. (ii) We also show that the thermodynamic viewpoint allows one to calculate the physical observables near jamming providing a characterization of jammed solids at the J-Point.

The fact that a simple set of thermodynamics postulates gives rise to the correct results for the case of granular materials driven through the jamming transition may have implications in other fields where out of equilibrium systems are the norm.

Angoricity and compactivity describe the jamming transition in soft particulate matter
Kun Wang, Chaoming Song, Ping Wang and H.A. Makse, EPL, 91, 68001 (2010)
[Abstract]

A Fokker-Planck Model for Wealth Inequality Dynamics (Vol. 48, No. 5-6)

Model comparison with data. Overall trend is well captured as well as some short-term details.

The growing wealth inequality in most western countries during the past several decades led to an increased interest in the nature of wealth inequality dynamics – particularly, what has driven wealth inequality upwards? Statistical mechanics can be used for addressing this question. We present a simple stochastic model for wealth and income and derive from it a Fokker-Planck equation – a standard tool in non-equilibrium statistical mechanics for studying the evolution of a distribution. Using this equation we are able to calculate the joint wealth-income distribution and its dynamics. Our analysis supports empirical findings on the dynamics of wealth inequality. We find that wealth inequality inevitably tends to increase in the long run. However, even if inequality eventually goes up, we find a criterion for its possible short run decrease. This criterion is most likely to be fulfilled if the correlation between wealth and income is very low. The conditions for such a decrease are found to be met at several points during the 20th century, coinciding indeed with an observed decrease in wealth inequality.

Y. Berman, Y. Shapira and M. Schwartz, A Fokker-Planck model for wealth inequality dynamics, EPL 118, 38004 (2017)
[Abstract]

A happy marriage between critical phenomena and spintronics (Vol. 49, No. 3)

Schematic drawing of the spin Seebeck effect near the magnetic phase transition

Spintronics is a technology that aims to use spin in information processing for practical application, whereas critical phenomena belong to an academic subject that deals with phase transition. These two seemingly different subfields meet at the interface between a magnetic insulator and a paramagnetic metal. The thermal spin injection from an insulating magnet into the adjacent heavy metal is referred to as spin Seebeck effect. Since its discovery in 2008, this phenomenon has attracted much attention as a simple and versatile means for generating spin current that is needed to drive the functionality of spintronic devices. The spin Seebeck effect has been investigated extensively over the last few years, but only a little is known about its behaviour near the magnetic phase transition.

Using a stochastic model established through the study of dynamic critical phenomena, the authors have investigated the behavior of the spin Seebeck effect near the Curie temperature Tc of a simple ferromagnet which is composed of a single sublattice such as EuO. They have clarified theoretically that the spin Seebeck signal scales with the magnetization, i.e., ~(T-Tc)^1/2. Because no corresponding experiments have been reported so far, the theoretical prediction awaits experimental proof.

H. Adachi, Y. Yamamoto and M. Ichioka, Spin Seebeck effect in a simple ferromagnet near Tc: a Ginzburg–Landau approach, J. Phys. D: Appl. Phys. 51, 144001 (2018)
[Abstract]

A LHC first: proton-proton cross-section at 7 TeV (Vol. 43 No. 1)

The TOTEM measurement of the total cross-section of the proton at the 7 TeV centre-of-mass energy of 98 ± 3 mbarn is shown together with results from previous measurements and from cosmic rays.

The proton, one of the basic building blocks of the atomic nuclei, is a dynamic and complex system: its sub-components and their interactions keep it together in a very dynamic way. The inner structure of protons can be studied by observing how they interact with each other, which implies measuring the total cross-section of the proton-proton interactions. To measure it, the TOTEM experiment uses the fact that the total cross-section can be related to the elastic forward scattering amplitude.

Due to the tiny scattering angles the protons have to be measured very close to the CERN LHC beams, requiring custom-designed silicon detectors with full efficiency up to the physical edge. The measurement was performed in a dedicated run with special beam optics that made the angular beam spread in the interaction point small compared to the scattering angles.

The TOTEM experiment has confirmed the increase with energy of the proton-proton total cross-section by a (98± 3) mbarn result at the so far unexplored energy of the LHC. This phenomenon was expected from previous measurements performed at energies 100 times smaller at the CERN ISR in 1972. It is remarkable that the early indirect cosmic ray measurements are in good agreement with the new precise TOTEM value.

First measurement of the total proton-proton cross section at the LHC energy of Vs =7 TeV
The TOTEM collaboration: G. Antchev et al. (73 co-authors), EPL, 96, 21002 (2011)
[Abstract]

A Liquid-Lithium Target for Nuclear Physics (Vol. 50, No. 3)

A liquid-lithium target (LiLiT) bombarded by a 1.5 mA, 1.92 MeV proton beam from the SARAF superconducting linac acts as a ~30 keV quasi-Maxwellian neutron source via the ⁷Li(p,n) reaction with the highest intensity (5×10¹⁰ neutrons/s) available to date. We activate samples relevant to stellar nucleosynthesis by slow neutron capture (s-process). Activation products are detected by α, β or γ spectrometry or by direct atom counting (accelerator mass spectrometry, atom-trap trace analysis). The neutron capture cross sections, corrected for systematic effects using detailed simulations of neutron production and transport, lead to experimental astrophysical Maxwellian averaged cross sections (MACS). A parallel effort to develop a LiLiT-based neutron source for cancer therapy is ongoing, taking advantage of the neutron spectrum suitability for Boron Neutron Capture Therapy (BNCT) and the high neutron yield available.

M. Paul and 16 co-authors, Reactions along the astrophysical s-process path and prospects for neutron radiotherapy with the Liquid-Lithium Target (LiLiT) at the Soreq Applied Research Accelerator Facility (SARAF), Eur. Phys. J. A 55, 44 (2019)
[Abstract]

A meta-diffraction-grating for visible light (Vol. 44 No. 5)

Intensities diffracted into first diffraction order. Inset: SEM image of the planar meta-grating mimicking a bulk blazed grating profile.

Metamaterials — artificially engineered structures with building blocks smaller than the wavelength of light — have delivered a new way to design and make materials with exotic electromagnetic properties. The current challenge is to make these metamaterials into meta-devices that convert the promising research into practical applications. Nanotechnology has made it possible to fabricate ultrathin metamaterials – less than a 15^th of the wavelength – shrinking conventional optical devices into planar form. In the coming years, research in metamaterials, plasmonics and nanofabrication will revolutionize device form and function throughout the electromagnetic spectrum.

This paper reports experimental demonstration of a planar ultrathin (50 nm) gold diffraction grating, mimicking the function of a bulk dielectric grating but tens of times thinner. It uses the resonant properties of individual sub-wavelength meta-atoms to change the phase of the light passing through it, in the same way as a blazed diffraction grating. It functions throughout the visible region of the spectrum (400 – 900 nm), with peak efficiency at 736 nm, and exhibits asymmetric diffraction, sending 25 times more light to the left than the right.

T. Roy, A.E. Nikolaenko and E.T.F. Rogers, ‘A meta-diffraction-grating for visible light’, J. Opt. 15, 085101 (2013)
[Abstract]

A more efficient plasma sterilizer for medical devices (Vol. 41, No. 5)

B. atrophaeus spore survival curves under four operating protocols: afterglow exposure (AE) at 12 °C; preheating at 52 °C followed, 3 h after, by AE at 12 °C; AE at 12 °C followed, 3 h after, by heating at 52 °C; AE at 52 °C.

Bacterial endospores, the most resistant microorganisms, can be inactivated by exposure to UV photons of the outflow of an N₂-O₂ discharge at reduced pressure (5 Torr). These photons are formed through N and O atom collisions in the discharge afterglow, which generate NO_γ excited molecules emitting in the 180-270 nm range (UV-C). Some of these N and O atoms can diffuse prior to combining into NO molecules, ensuring, contrary to UV lamps, inactivation within holes and crevices. These photons create lethal damage to the spore DNA, at a rate that increases with the spore-deposit temperature. At 68 °C, the number of survivors of B. atrophaeus spores after a 30 min exposure is one log less compared to 28 °C, hence a shorter sterilization process. Such behaviour occurs only when heat is applied, neither before nor after, but simultaneously with UV photons (figure): inactivation does not result from the addition of sub-lethal damage caused independently by UV radiation and by heat.

Heat provides the energy required to surmount the (small) potential barrier(s) encountered as the chemical reaction leading to the DNA lesion, once initiated by photon excitation, proceeds. The energy barrier corresponds to molecular (conformation) rearrangements, as the reaction develops to reach the final chemical state on the DNA strand. Assuming Arrhenius-law dependence on temperature, the activation energy supplied by heat is 54 kJ/mol compared to that by photoexcitation, estimated ∼ 440-460 kJ/mol, as for many chemical reactions. To the authors' knowledge, it is the first time that such a genuine synergy effect is demonstrated.

Synergy effect of heat and UV photons on bacterial-spore inactivation in an N₂-O₂ plasma-afterglow sterilizer
M. K. Boudam and M. Moisan, J. Phys. D: Appl. Phys. 43 295202 (2010)
[Abstract]

A multi-object spectral imaging instrument (Vol. 44 No. 6)

Fluorescent microbeads are tracked using a camera. A series of slits displayed on a DMD deflect light into a spectrometer and are updated to follow the microbeads. Spectra are obtained in real time from a CCD image of the slits after dispersion from a prism.

Imaging spectrometers acquire three-dimensional spectral data cubes (x, y, λ) to enable chemical imaging in fields ranging from microscopy and biomedicine to remote sensing. Traditional systems, employing time-sequential recording of the complete data cube, cannot record time-varying phenomena and are optically highly inefficient. Our technique enables spectra to be recorded in real time from a programmable sparse array of spots within a microscope sample. Real-time computer-controlled manipulation of the spot array enables tracking and video-rate spectroscopy of these points with the very high optical efficiency. This is achieved with a digital micro-mirror device (DMD) that deflects light from the sparse multiple points in the sample into a slitless spectrometer consisting of a dispersive prism and CCD camera. We demonstrate real-time spectra of multiple fluorescent microbeads in aqueous solution as they diffuse in the sample.

G. M. Gibson, M. Dienerowitz, P. A. Kelleher, A. R. Harvey and M. J. Padgett, ‘A multi-object spectral Imaging Instrument’, J. Opt. 15, 085302 (2013)
[Abstract]

A new generation of chiral nuclear forces (Vol. 46 No. 4)

Chiral effective field theory provides a systematically improvable perturbative approach to deriving nuclear forces in harmony with the symmetries of Quantum Chromodynamics. Combined with modern few- and many-body methods, this framework represents a commonly accepted procedure for ab initio studies of nuclear structure and reactions.

In this work, the authors introduce a new generation of nucleon-nucleon forces up to fourth order in the chiral expansion. By employing an appropriate regularization in coordinate space, which maintains the analytic structure of the amplitude, the authors succeed in significantly reducing the amount of finite-cutoff artefacts. In addition, a simple approach to estimating the theoretical uncertainty in few- and many-nucleon calculations from the truncation of the chiral expansion is formulated. By calculating various two-nucleon scattering and bound-state observables, the authors verify that the results at different chiral orders and for different values of the regulator are indeed consistent with each other and with the experimental data. The new generation of chiral nuclear forces is expected to provide an excellent starting point for applications in nuclear physics.

E. Epelbaum, H. Krebs and U.-G. Meißner, Improved chiral nucleon-nucleon potential up to next-to-next-to-next-to-leading order, Eur. Phys. J. A, 51, 53 (2015)
[Abstract]

Subcategories

Page 1 of 39

Start
Prev
1
2
3
4
5
6
7
8
9
10
Next
End