bluuebunny/crossref_metadata_2025 huggingface dataset:
Stator flux‐oriented vector control of dual stator induction generator with time optimised 11‐zone hybrid PWM for grid connected wind energy generation system
Authors: Chatterjee Shantanu , Chatterjee Saibal
Published: September 2018

This work presents a novel stator flux‐oriented vector control (SFOVC) of a dual stator induction generator (DSIG) used for a grid connected, variable speed wind energy generation system. The DSIG consists of two stator windings electrically separated by an angle of 30° with dissimilar pole numbers, which are in the ratio of 1:3. In conventional vector control, the rotor flux is oriented along the d‐axis of the rotor winding. However, the rotor variables are not easily accessible. So, in the SFOVC, the total flux is made to be oriented along the d‐axis of the stator winding. SFOVC is advantageous as compared to conventional vector control because the stator variables are easily accessible and do not require any special arrangement for the measurement of variables which increases the robustness of the system. Here, two separate converters are used for the two stator windings of the machine and the converter switching is being controlled by a novel space vector based 11‐zone hybrid pulse‐width modulation (PWM). This special PWM results in better harmonic performance, reduced torque pulsation and minimal switching loss. The overall simulation is being performed in MATLAB Simulink environment and the simulated results are also being validated experimentally.
Controlled network splitting considering transient stability constraints
Authors: Kamali Sadegh , Amraee Turaj , Capitanescu Florin
Published: September 2018

Intentional islanding has been extensively studied recently as the last resort to prevent blackouts, mostly from the perspective of thermal static constraints satisfaction. However, as most previous studies on this topic do not address stability issues, their controlled islanding plans might fail to ensure the stability of resulted islands, thereby delaying their acceptance and adoption by utilities. This study makes progress towards addressing stability issues, proposing a controlled islanding model that ensures and improves the transient stability of the islanded system. Linear transient stability constraints are derived off‐line, based on the extended equal area criterion, to ensure the first swing transient stability of the synchronous machines, just after the controlled line switching. The islanding model with transient stability constraints is first developed as a mixed‐integer nonlinear program (MINLP). Furthermore, the MINLP model is linearised, resulting in a computationally lighter mixed‐integer linear program. The objective function of the islanding model is to minimise the generation imbalance of islands and to increase the transient stability margin of the resulting islands, and the obtained optimisation results are validated by the fully fledged dynamic simulation. The efficacy of the proposed method is validated by simulation on the IEEE 118‐bus system.
Multi‐leader–follower game theory for modelling interaction between virtual power plants and distribution company
Authors: Zangeneh Ali , Shayegan‐Rad Ali , Nazari Farshid
Published: September 2018

Virtual power plant (VPP) is an entity that aggregates generation of distributed generation units. Thus, it is important to design a competitive framework which models the participation of the VPPs in the electricity market along with their trading with distribution company (DisCo). This study proposes a bilevel programming framework using the concept of multi‐leader–follower game theory to determine the optimal contract prices of VPPs which compete against each other in the distribution network. The optimal prices are used for setting annual bilateral contracts with VPPs. The leader layer of the proposed bilevel problem includes VPPs, which try to maximise their profits, while the follower problem corresponds to the cost function of the DisCo, which aims to minimise the payments of supplying the forecasted demand. The DisCo optimisation problem is transferred by its Karush–Kuhn–Tucker optimality conditions, turning each VPP problem into an equivalent single‐level optimisation problem. Some case studies are defined and implemented to assess the performance of the proposed scheduling model.
Parameters affecting the arcing time of HVDC circuit breakers using black box arc model
Authors: Gouda Osama E. , Ibrahim Doaa Khalil , Soliman Adel
Published: September 2018

Arc interruption of high voltage direct current (HVDC) circuit breakers (CBs) is one of the main challenging factors for using HVDC grids. To evaluate the arc interrupting capability in HVDC CBs, black box arc models are used to represent the nonlinear arc conductance depending on Cassie and Mayr dynamic arc equations. Extensive simulation studies are carried out to investigate the effect of controlled and uncontrolled parameters on the CB arcing time. A real line represents a part of 500 kV electrical connection systems between Egypt and the Kingdom of Saudi Arabia is simulated to be a faulty load. It is found that the arcing time of the HVDC CB can be reduced by increasing the value of cooling power coefficient (p) and decreasing the value of arc time constant (τ). It is also deduced that the arcing time is reduced by the increase of the commutation capacitance value (C) and decreasing the commutation inductance (L) value and vice versa. Moreover, it is concluded that the arcing time is greatly affected by the fault location and the fault arc resistance () according to fault conditions.
City‐wide emissions modelling using fleet probe vehicles
Authors: Rushton Christopher , Galatioto Fabio , Wright James , Nielsen Erik , Tsotskas Christos
Published: September 2018

Five UK cities will implement clean air zones to improve air quality (AQ), specifically in relation to oxides of nitrogen, and 253 UK local authorities have declared AQ management areas. Extended range electric vehicles can offer zero emission (ZE) operation but cities lack the ability to monitor and control when vehicles can switch from engine to battery. Project Autonomous and Connected vehicles for CleaneR Air (ACCRA) aims to develop and demonstrate a system allowing hybrid vehicle to become part of a city's urban traffic management control system; monitoring the vehicles’ location and operational state, and controlling the strategy to ensure ZE operation through geofenced zones with poor AQ. This study demonstrates a new methodology to model emissions using state‐of‐the‐art instantaneous vehicle emissions modelling, geographic information system (GIS) and a new method for capturing vehicle behaviour using global positioning system. Probe vehicles were used for the pilot study in Leeds, UK, to capture drive‐cycle data and the emissions are modelled. A GIS interface is used to match these emissions to the network. Finally, a high‐resolution emissions map is generated to be used as input for AQ dispersion models and the ACCRA decision‐making engine for the generation of geofencing AQ zones.
Using metasurface structures as signal polarisers in microstrip antennas
Authors: Paiva José Lucas da Silva , da Silva José Patrocínio , Campos Antônio Luiz Pereira de Siqueira , Dionísio de Andrade Humberto
Published: September 2018

This study analyses the influence of a metasurface coupled to a rectangular microstrip antenna. The proposed metasurface converts linearly polarised electromagnetic waves into circularly polarised electromagnetic waves. The rectangular microstrip antenna is designed to operate at 2.45 GHz. The metasurface is coupled to the antenna in order to provide a structure capable of radiating circularly polarised electromagnetic waves without the need for adjustments to the antenna feed. In this analysis, the metasurface was designed from unit cells, distributed in a periodic arrangement acting as a polariser, when coupled to the upper part of the antenna. The geometry of the unit cells and their distribution in the arrangement were calculated in order to obtain an axial ratio below 3 dB in the design frequency range. Prototypes of the microstrip antenna and the metasurface were constructed to obtain experimental results and it was possible to observe a good convergence between the simulated and measured results.
Wideband tunable mid‐infrared cross‐polarisation converter using monolayered graphene‐based metasurface over a wide angle of incidence
Authors: Yadav Vinit Singh , Ghosh Sambit Kumar , Das Santanu , Bhattacharyya Somak
Published: September 2018

In this study, the authors have designed and proposed a monolayer graphene‐based metasurface, performing as a broadband polarisation converter over a wide angle of incidence. The unit cell of the metasurface consists of split ring generated over a perforated single layer of graphene grown over metal‐backed silicon dioxide. The structure converts incident linearly polarised wave into its cross‐polarised component over a wide bandwidth with peak polarisation conversion exhibits value to unity. The plane of polarisation of the incident electromagnetic wave is rotated orthogonally on reflection from the proposed metasurface over full width at half maxima bandwidth around 72.83% compared with centre frequency of 2.16 THz, which can be maintained up to 40° incident angles under both transverse electric and transverse magnetic polarisations. The proposed structure is as thin as ∼λ/7.3 with respect to lowermost frequency and the period of the structure is about λ/10.7. The frequency band of polarisation conversion can be tuned by altering chemical doping as well as the electrostatic grating of the graphene sheet. The structure can find applications toward sensing, spectroscopy etc.
Detection of open circuit fault in battery power supply feeding permanent magnet synchronous motor
Authors: Breznik Mitja , Ambrožič Vanja , Nemec Mitja
Published: September 2018

This study presents a model‐based method for detecting an open‐circuit fault in battery supply unit feeding a permanent magnet synchronous motor. Apart from the commonly present DC voltage sensor at converter's input, no additional sensors are required. As a first step, the DC supply system is modelled as a lumped parameter electric circuit. Further, a procedure for estimation of DC supply voltage based on inverter's current and open‐circuit battery voltage is proposed. A sliding mode observer is then used to obtain the actual value of open‐circuit battery voltage, required by the modelling algorithm. Consequently, an open‐circuit fault in a DC supply circuitry is determined based on the analysis of discrepancy between the estimated and measured DC supply voltage. Detection algorithm has been tested on a laboratory setup and its functionality is confirmed by experimental results.
Mathematical modelling and stability analysis of PSS for damping LFOs of wind power system
Authors: Bhukya Jawaharlal , Mahajan Vasundhara
Published: September 2018

This study presents the impact of the doubly fed induction generator (DFIG) with power system stabiliser (PSS) on critical low‐frequency oscillations (LFOs) caused by the synchronous generators (SGs). These LFOs arise due to uncertainties in a system such as generating/loading conditions, intermittent wind power and may cause instability. To improve the stability, the PSS is added. This study studies the effect of varying wind speed, DFIG locations and its capacity with and without PSS on stability. The system is analysed by replacing SGs with DFIG. The sensitivity analysis is carried out with wind power penetration and voltage gain as sensitivity parameters. This identifies electromechanical modes of oscillations that have positive and negative impacts on the system. The transient and small‐signal stability (SSS) investigations are done using non‐linear simulation and eigenvalue analysis, respectively. The system uncertainties are modelled using inverse output additive perturbation structure to elude the mathematical difficulty. The location and selection of best local input signals for PSS are evaluated from residue method and time‐domain simulation analysis. The effectiveness and robustness of the proposed approaches are verified on IEEE 9‐bus test system. The PSS improves the transient stability and SSS of the system.
Effect of annealing temperature on the electrical properties of HfAlO thin films
Authors: Lin Hongxiao , Li Chun , He Zhiwei
Published: September 2018

High‐K gate dielectric HfAlO thin films with different temperature annealing treatment have been deposited on the Si substrate by atomic layer deposition. The electrical properties of Hf‐films are analysed by measurement of high‐frequency capacitance–voltage (C –V) and leakage current density–voltage (J–V) characteristics. The electrical measurement results indicate the decrease of equivalent oxide thickness (EOT) due to the great change of microstructure and densification after high temperature annealing and the increase of permittivity. However, the interface state density increases. Moreover, the leakage current increases with the increase of annealing temperature. The HfAlO film annealed at 650°C has the best electrical parameters, such as dielectric constant, EOT and leakage current density determined through capacitance–voltage and current density–voltage measurements were 23.5, 0.84, 6.8 × 10−7 mA·cm−2, respectively.
The curious case of the companion: evidence for cold accretion onto a dwarf satellite near the isolated elliptical NGC 7796
Authors: Richtler T. , Hilker M. , Voggel K. , Puzia T. H. , Salinas R. , Gómez M. , Lane R.
Published: September 2018

Context. The isolated elliptical (IE) NGC 7796 is accompanied by an interesting early-type dwarf galaxy, named NGC 7796-DW1. It exhibits a tidal tail, very boxy isophotes, and multiple nuclei or regions (A, B, and C) that are bluer than the bulk population of the galaxy, indicating a younger age. These properties are suggestive of a dwarf–dwarf merger remnant.

Aims. Dwarf–dwarf mergers are poorly understood, but may have a high importance for dwarf galaxy evolution. We want to investigate the properties of the dwarf galaxy and its components to find more evidence for a dwarf–dwarf merger or for alternative formation scenarios.

Methods. We use the Multi-Unit Spectroscopic Explorer (MUSE) at the VLT to investigate NGC 7796-DW1. We extract characteristic spectra to which we apply the STARLIGHT population synthesis software to obtain ages and metallicities of the various population components of the galaxy. This permits us to isolate the emission lines for which fluxes and flux ratios can be measured and to which strong-line diagnostic tools can be applied.

Results. The galaxy’s main body is old and metal-poor. A surprising result is the extended line emission in the galaxy, forming a ring-like structure with a projected diameter of 2.2 kpc. The line ratios fall into the regime of HII-regions, although OB-stellar populations cannot be identified by spectral signatures. The low Hα surface brightnesses indicate unresolved star-forming substructures, which means that broad-band colours are not reliable age or metallicity indicators. Nucleus A is a relatively old (7 Gyr or older) and metalpoor super star cluster, most probably the nucleus of the dwarf, now displaced. The star-forming regions B and C show younger and distinctly more metal-rich components. The emission line ratios of regions B and C indicate an almost solar oxygen abundance, if compared with radiation models of HII regions. Oxygen abundances from empirical calibrations point to only half-solar. The ring-like Hα-structure does not exhibit signs of rotation or orbital movements.

Conclusions. NGC 7796-DW1 occupies a particular role in the group of transition-type galaxies with respect to its origin and current evolutionary state, being the companion of an IE. The dwarf–dwarf merger scenario is excluded because of the missing metal-rich merger component. A viable alternative is gas accretion from a reservoir of cold, metal-rich gas. NGC 7796 has to provide this gas within its X-ray bright halo. As illustrated by NGC 7796-DW1, cold accretion may be a general solution to the problem of extended star formation histories in transition dwarf galaxies.
Strong tidal energy dissipation in Saturn at Titan’s frequency as an explanation for Iapetus orbit
Authors: Polycarpe William , Saillenfest Melaine , Lainey Valéry , Vienne Alain , Noyelles Benoît , Rambaux Nicolas
Published: September 2018

Context. Natural satellite systems present a large variety of orbital configurations in the solar system. While some are clearly the result of known processes, others still have largely unexplained eccentricity and inclination values. Iapetus, the furthest of Saturn’s main satellites, has a still unexplained 3% orbital eccentricity and its orbital plane is tilted with respect to its local Laplace plane (8° of free inclination). On the other hand, astrometric measurements of saturnian moons have revealed high tidal migration rates, corresponding to a quality factor Q of Saturn of around 1600 for the mid-sized icy moons.

Aims. We show how a past crossing of the 5:1 mean motion resonance between Titan and Iapetus may be a plausible scenario to explain Iapetus’ orbit.

Methods. We have carried out numerical simulations of the resonance crossing using an N-body code as well as using averaged equations of motion. A large span of migration rates were explored for Titan and Iapetus was started on its local Laplace plane (15° with respect to the equatorial plane) with a circular orbit.

Results. The resonance crossing can trigger a chaotic evolution of the eccentricity and the inclination of Iapetus. The outcome of the resonance is highly dependent on the migration rate (or equivalently on Q). For a quality factor Q of over around 2000, the chaotic evolution of Iapetus in the resonance leads in most cases to its ejection, while simulations with a quality factor between 100 and 2000 show a departure from the resonance with post-resonant eccentricities spanning from 0 up to 15%, and free inclinations capable of reaching 11°. Usually high inclinations come with high eccentricities but some simulations (less than 1%) show elements compatible with Iapetus’ current orbit

Conclusions. In the context of high tidal energy dissipation in Saturn, a quality factor between 100 and 2000 at the frequency of Titan would bring Titan and Iapetus into a 5:1 resonance, which would perturb Iapetus’ eccentricity and inclination to values observed today. Such rapid tidal migration would have avoided Iapetus’ ejection around 40–800 million years ago.
Evaluation of recombination losses in thin film solar cells using an LED sun simulator − the effect of RbF post-deposition on CIGS solar cells
Authors: Heinemann Marc Daniel , Kodalle Tim , Hages Charles , Klupsch Michael , Greiner Dieter , Korte Lars , Levcenco Sergej , Unold Thomas , Schlatmann Rutger , Kaufmann Christian A.
Published: September 2018

Distinguishing among different electrical loss mechanisms − such as interface and bulk recombination − is a common problem in thin film solar cells. In this work, we report a J–V measurement technique using different illuminating spectra to distinguish between these two recombination losses. The basic idea is to change the relative contribution of bulk recombination to the total losses of photo-generated charge carriers by generating them in different depths within the absorber layer using different spectral regions of the illuminating light. The use of modern LED sun-simulators allows an almost free design of illumination spectra at intensities close to 1 sun. The comparison of two simple J–V measurements, one recorded with illumination near the absorber's band-gap energy and one with light of higher energy, in combination with supporting measurements of the absorber properties, as well as device modeling, enables the extraction of the diffusion length and the interface recombination velocity. Using this technique, we show that in CIGS solar cells, an RbF post-deposition treatment does not only reduce interface recombination losses, as often reported, but also reduces bulk recombination in the CIGS absorber. Furthermore, we find that both cells, with and without RbF treatment, are dominantly affected by interface recombination losses.
Relations between the sensory properties and fat ingredients of lipsticks
Authors: de Clermont-Gallerande Hélène , Abidh Sarah , Lauer Alexandre , Navarro Séverine , Cuvelier Gérard , Delarue Julien
Published: September 2018

Lipstick is a key product in the make-up sector. A woman applies lipstick to feel feminine and attractive. The sensation she perceives when she applies the product plays an important role in her attachment to her lipstick. The impact of the ingredients on the sensory properties and the quality of the lipsticks needs to be understood, so that the formulation can be more effective and the sensory properties can be precisely adjusted to the target market. During this study, multidimensional correlations were made between the percentage of ingredients, their physico-chemical specifications and the sensory properties of the raw materials on their own or the lipsticks. The objective of this study is to predict the sensory properties of lipsticks from the physico-chemical specifications of the ingredients. It is in effect quicker to access the physical data than the sensory descriptions. The lipsticks were made using a simplified formula, evaluated in a sensory analysis and their physico-chemical characteristics were measured. The relationships between the sensory properties, the ingredient specifications and their percentage of use in the formula were highlighted. The results confirm the major role of the viscosity of oils and the wax used in the formula on the sensory and mechanical properties of the lipstick. It is therefore possible to modify the sensory properties, for example to adjust the shininess of a lipstick, without altering its mechanical resistance. This opens up opportunities for developing innovative sensory textures in short lead times.
Evaluation of Peak Reflux Velocities with Vector Flow Imaging and Spectral Doppler Ultrasound in Varicose Veins
Authors: Bechsgaard Thor , Hansen Kristoffer , Brandt Andreas , Moshavegh Ramin , Forman Julie , Føgh Pia , Klitfod Lotte , Bækgaard Niels , Lönn Lars , Jensen Jørgen , Nielsen Michael
Published: September 2018

Purpose Spectral Doppler ultrasound (SDUS) is used for quantifying reflux in lower extremity varicose veins. The technique is angle-dependent opposed to the new angle-independent Vector Flow Imaging (VFI) method. The aim of this study was to compare peak reflux velocities obtained with VFI and SDUS in patients with chronic venous disease, i. e., pathological retrograde blood flow caused by incompetent venous valves.

Materials and Methods 64 patients with chronic venous disease were scanned with VFI and SDUS in the great or the small saphenous vein, and reflux velocities were compared to three assessment tools for chronic venous disease. A flow rig was used to assess the accuracy and precision of the two methods.

Results The mean peak reflux velocities differed significantly (VFI: 47.4 cm/s vs. SDUS: 62.0 cm/s, p<0.001). No difference in absolute precision (p=0.18) nor relative precision (p=0.79) was found. No correlation to disease severity, according to assessment tools, was found for peak reflux velocities obtained with either method. In vitro, VFI was more accurate but equally precise when compared to SDUS.

Conclusion Both VFI and SDUS detected the pathologic retrograde flow in varicose veins but measured different reflux velocities with equal precision. VFI may play a role in evaluating venous disease in the future.
Dimethylisosorbide (DMI) as a Bio-Derived Solvent for Pd-Catalyzed Cross-Coupling Reactions
Authors: Watson Allan , Wilson Kirsty , Murray Jane , Sneddon Helen , Jamieson Craig
Published: September 2018

Palladium-catalyzed bond-forming reactions, such as the ­Suzuki–Miyaura and Mizoroki–Heck reactions, are some of the most broadly utilized reactions within the chemical industry. These reactions frequently employ hazardous solvents; however, to adhere to increasing sustainability pressures and restrictions regarding the use of such solvents, alternatives are highly sought after. Here we demonstrate the utility of dimethyl isosorbide (DMI) as a bio-derived solvent in several benchmark Pd-catalyzed reactions: Suzuki–Miyaura (13 examples, 62–100% yield), Mizoroki–Heck (13 examples, 47–91% yield), and Sonogashira (12 examples, 65–98% yield).
Completion of the Ablowitz-Kaup-Newell-Segur integrable coupling
Authors: Shen Shoufeng , Li Chunxia , Jin Yongyang , Ma Wen-Xiu
Published: September 2018

Integrable couplings are associated with non-semisimple Lie algebras. In this paper, we propose a new method to generate new integrable systems through making perturbation in matrix spectral problems for integrable couplings, which is called the “completion process of integrable couplings.” As an example, the idea of construction is applied to the Ablowitz-Kaup-Newell-Segur integrable coupling. Each equation in the resulting hierarchy has a bi-Hamiltonian structure furnished by the component-trace identity.
Reactive flow modeling of the polymer bonded explosive LX-17 double shock experiments
Authors: Rehagen Thomas J. , Vitello Peter , Bastea Sorin , Fried Laurence E.
Published: September 2018

Overdriven double shock experiments provide a measurement of the properties of the reaction product states of the 1-3-5-triamino-2-4-6trinitrobenzene-based explosive LX-17. These experiments used two flyer materials mounted on the end of a projectile to send an initial shock through the LX-17, followed by a second shock of a higher magnitude into the detonation products. Here, the experimental results are compared to 2D reactive flow modeling. A reactive flow model that describes only the kinetics of the LX-17 decomposition fails to accurately reproduce the decay of the first shock or the curvature or strength of the second shock. A new model is proposed in which the carbon condensate produced in the reaction zone is controlled by a kinetic rate. This allows the carbon condensate to be initially out of chemical equilibrium with the product gas. This new model reproduces the initial detonation peak and decay and matches the curvature of the second shock; however, it still over-predicts the strength of the second shock.
Temperature and carrier density dependence of electron effective mass and bandgap in semiconductor carbon nanotubes at elevated temperature: Analytical calculations
Authors: Van Tan Le , Vy Nguyen Duy , Cao Huy Thien
Published: September 2018

The effects of temperature and carrier density on the self-energy of electrons in semiconductor carbon nanotubes (CNTs) are theoretically studied by using the Matsubara Green’s function approach. We show that the bandgap is slightly changed whereas the electron effective mass is strongly affected by the temperature and electron density. Furthermore, an interesting discrepancy between the results obtained from the screening dynamical approximation and that from the Hartree-Fock approximation is shown. Specifically, the calculated quantities are compared to the results obtained in a recent experiment, and a good agreement for the energy shift is seen. These results could help to clarify the role of the Coulomb interaction and the correlation and exchange energy on the optical properties of CNTs in a wide range of temperature and density.
Thomson scattering measurements on DIII-D using in-vessel laser mirrors and lenses to diagnose a new divertor location
Authors: Carlstrom T. N. , Glass F. , Du D. , McLean A. G. , Taussig D. , Boivin R.
Published: September 2018

Translatable in-vessel mirrors have enabled the DIII-D Thomson scattering system to diagnose the divertor plasma in high triangularity shaped plasmas. Previous divertor Thomson scattering measurements in DIII-D were restricted to spatial locations along a Nd:YAG laser beam that was directed through a vertical port. This only allowed measurements to be made in low triangularity shaped plasmas. The new mirrors re-route the laser underneath floor tiles to a position of smaller major radius as necessary for high triangularity plasmas. New in-vessel collection optics transmit scattered light from regions inaccessible to external lenses. Damage to mirrors and high stray light levels are challenges that were overcome to successfully make these measurements. Through the careful use of baffles and light shields, stray light leakage into polychromator detector channels was reduced to negligible levels, allowing temperature measurements below 1 eV. The system is described and the initial results presented.
Neutron emission spectroscopy of D plasmas at JET with a compact liquid scintillating neutron spectrometer
Authors: Giacomelli L. , Belli F. , Binda F. , Conroy S. W. , Eriksson J. , Milocco A. , Popovicev S. , Syme D. B. ,   JET Contributors
Published: September 2018

Neutron emission spectroscopy is a diagnostic technique that allows for energy measurements of neutrons born in nuclear reactions. The JET tokamak fusion experiment (Culham, UK) has a special role in this respect as advanced spectrometers for 2.5 MeV and 14 MeV neutrons have been developed here for the first time for measurements of the neutron emission spectrum from D and DT plasmas with unprecedented accuracy. Twin liquid scintillating neutron spectrometers were built and calibrated at the Physikalisch-Technische Bundesanstalt (PTB) (Braunschweig, Germany) and installed on JET in the recent years with tangential-equatorial (KM12) and vertical-radial (KM13) view lines, with the latter only recently operational. This article reports on the performance of KM12 and on the development of the data analysis methods in order to extract physics information upon D ions kinematics in JET auxiliary-heated D plasmas from 2.5 MeV neutron measurements. The comparison of these results with the correspondents from other JET neutron spectrometers is also presented: their agreement allows for JET unique capability of multi-lines of sight neutron spectroscopy and for benchmarking other 14 MeV neutron spectrometers installed on the same lines of sight in preparation for the DT experimental campaign at JET.
Measurement of density fluctuation propagation direction via the far-forward collective scattering diagnostic based on polarimeter-interferometer
Authors: Shi P. , Qiu Q. S. , Zhuang G. , Gao L. , Zhou Y. N. , Zhou C. X.
Published: September 2018

Previously, the 17-channel three-wave polarimeter-interferometer system (POLARIS) on the J-TEXT tokamak has been implemented to measure far-forward collective scattering (FFCS) from electron density fluctuations. Recently, this system has been exploited to measure the propagation direction of density fluctuation. After considering the refraction of the laser probe beam passing through plasma, the ray tracing result shows that the detector of POLARIS may receive asymmetric far-forward scattering beams. Thus, the heterodyne detection of FFCS is available to identify the propagation direction of density fluctuation by resolving the asymmetric scattering spectrum. Experimentally, the transform of the heterodyne scattering spectrum from symmetry to asymmetry has been observed, while the refraction effect becomes strong demonstrating the capacity of measuring the propagation direction of fluctuation. Furthermore, by changing the plasma potential through the use of an applied positive electrode biasing, the reverse of frequency shift for the heterodyne scattering spectrum is identified, confirming the validity of direction discrimination of density fluctuation.
Magnetic response of random lasing modes in a ZnO nanoparticle film deposited on a NiFe thin film
Authors: Fujiwara Hideki , Kaiju Hideo , Nishii Junji , Sasaki Keiji
Published: September 2018

This study experimentally demonstrates lasing mode switching within a ZnO nanoparticle film coated onto a magnetic thin film of NiFe alloy. When a neodymium magnet is brought close to or moved away from the film, switching behavior is observed in the lasing modes, although such change is not induced in a ZnO nanoparticle film on a glass substrate. Our results suggest that the observed changes in lasing modes are because of a magneto-optical effect at the surface of the NiFe thin film. The magneto-optical effect would be enhanced by localized fields near the surface, inducing suppression or enhancement of the lasing modes in response to the surrounding environments, and accounting for the lasing mode switching.
Entrapping of a vortex pair interacting with a fixed point vortex revisited. I. Point vortices
Authors: Koshel Konstantin V. , Reinaud Jean N. , Riccardi Giorgio , Ryzhov Eugene A.
Published: September 2018

The problem of a pair of point vortices impinging on a fixed point vortex of arbitrary strengths [E. Ryzhov and K. Koshel, “Dynamics of a vortex pair interacting with a fixed point vortex,” Europhys. Lett. 102, 44004 (2013)] is revisited and investigated comprehensively. Although the motion of a pair of point vortices is established to be regular, the model presents a plethora of possible bounded and unbounded solutions with complicated vortex trajectories. The initial classification [E. Ryzhov and K. Koshel, “Dynamics of a vortex pair interacting with a fixed point vortex,” Europhys. Lett. 102, 44004 (2013)] revealed that a pair could be compelled to perform bounded or unbounded motion without giving a full classification of either of those dynamical regimes. The present work capitalizes upon the previous results and introduces a finer classification with a multitude of possible regimes of motion. The regimes of bounded motion for the vortex pair entrapped near the fixed vortex or of unbounded motion, when the vortex pair moves away from the fixed vortex, can be categorized by varying the two governing parameters: (i) the ratio of the distances between the pair’s vortices and the fixed vortex and (ii) the ratio of the strengths of the vortices of the pair and the strength of the fixed vortex. In particular, a bounded motion regime where one of the pair’s vortices does not rotate about the fixed vortex is revealed. In this case, only one of the pair’s vortices rotates about the fixed vortex, while the other oscillates at a certain distance. Extending the results obtained with the point-vortex model to an equivalent model of finite size vortices is the focus of Paper II [J. N. Reinaud et al., “Entrapping of a vortex pair interacting with a fixed point vortex revisited. II. Finite size vortices and the effect of deformation,” Phys. Fluids 30, 096604 (2018)].
Phase diagram of the SU(2) Kondo lattice
Authors: Abele Miguel , Riseborough P. S.
Published: September 2018

We examine the SU(2) Kondo Lattice Model, for simple cubic lattices with various magnitudes of the localized spins j and numbers of conduction electrons, nc. For j=1/2, the system undergoes transitions from the paramagnetic to magnetically ordered states. The sequence of low-temperature magnetic states found on increasing nc is symmetric about half-filling and exhibits a preference for commensurate phases over incommensurate phases. On increasing nc from small values, the sequence of magnetic orderings consists of: ferromagnetic phases, planes of ferromagnetically spins which are sequentially twisted by nc-dependent angles, ferromagnetic planes of spins that are aligned antiferromagnetically, antiferromagnetic planes of spins in which the Neel order parameters are twisted through incommensurate angles. Neel order is most stable around half-filling. Magnetic ordered phases are found to be more stable than the Kondo phase for j=1/2, but larger j values may stabilize the Kondo phase. For j=3/2 the sequence of magnetic ordering with increasing nc is the same but, depending on the value of the strength of the Kondo interaction, the Kondo phase may be stabilized in a window 4 ≥ nc ≥ 2. In accordance with Nozieres’s arguments, we find that magnetic ordering is dominant for almost filled and almost empty bands.
Two-photon-excited, three-dimensional photoluminescence imaging and dislocation-line analysis of threading dislocations in 4H-SiC
Authors: Tanuma R. , Kamata I. , Hadorn J. P. , Tsuchida H.
Published: September 2018

This paper describes the three-dimensional imaging of threading edge dislocations (TEDs), pure c threading screw dislocations (TSDs), and c + a threading mixed dislocations (TMDs) in 4H silicon carbide (4H-SiC) epilayers by two-photon-excited photoluminescence (2PPL), where inclinations of dislocations in epilayers with different offcut angles are investigated. A numerical model based on carrier diffusion explains the mechanism of the dark-contrast 2PPL imaging provided by band edge emission. More than 450 threading dislocations in 4H-SiC epilayers are visualized three-dimensionally and are classified into six -type TEDs, two -type TSDs, and twelve -type TMDs according to the directions of extra half-planes and the chiral geometries (right- or left-handed screw). The 2PPL images reveal that all threading dislocation types incline in the step-flow direction, the extent of which is more prominent for a larger offcut angle. The TEDs also incline in the directions of their extra half-planes. The inclinations of TSDs perpendicular to the step-flow direction are influenced by chirality, while those of TMDs are influenced by both the directions of the extra half-planes and the chirality. The origins of the dislocation inclinations are discussed taking into account the kinetic interactions between the dislocations and the advancing steps on the growing surface.
Two-fluid MHD regime of resistive drift-wave instability
Authors: Yang Shangchuan , Zhu Ping , Xie Jinlin , Liu Wandong
Published: September 2018

Drift instabilities contribute to the formation of edge turbulence and zonal flows and thus the anomalous transport in tokamaks. Experiments often found micro-scale turbulence strongly coupled with large-scale magnetohydrodynamic (MHD) processes, whereas a general framework has been lacking that can cover both regimes, in particular, their coupling. In this paper, the linear resistive drift wave instability is investigated using a full 2-fluid MHD model, as well as its numerical implementation in the NIMROD code. Both analytical and numerical analyses reveal a macro-scale global drift wave eigenmode coupled with MHD dynamics and illustrate a non-monotonic dispersion relation with respect to both perpendicular and parallel wavenumbers. NIMROD results also reveal an edge-localized behavior in the radial mode structure as the azimuthal mode number increases, implying the dependence of the 2-fluid effects due to the inhomogeneous density profile. The edge-localization introduces a non-trivial dependence of the effective perpendicular wavenumber to the perpendicular mode number, which may explain the quantitative difference between the global dispersion relation and its local approximation from the conventional local theory.
Biological applications of ferroelectric materials
Authors: Blázquez-Castro A. , García-Cabañes A. , Carrascosa M.
Published: September 2018

The study and applications of ferroelectric materials in the biomedical and biotechnological fields is a novel and very promising scientific area that spans roughly one decade. However, some groups have already provided experimental proof of very interesting biological modulation when living systems are exposed to different ferroelectrics and excitation mechanisms. These materials should offer several advantages in the field of bioelectricity, such as no need of an external electric power source or circuits, scalable size of the electroactive regions, flexible and reconfigurable “virtual electrodes,” or fully proved biocompatibility. In this focused review, we provide the underlying physics of ferroelectric activity and a recount of the research reports already published, along with some tentative biophysical mechanisms that can explain the observed results. More specifically, we focus on the biological actions of domain ferroelectrics and ferroelectrics excited by the bulk photovoltaic effect or the pyroelectric effect. It is our goal to provide a comprehensive account of the published material so far and to set the stage for a vigorous expansion of the field, with envisioned applications that span from cell biology and signaling to cell and tissue regeneration, antitumoral action, or cell bioengineering to name a few.
Electron-trapping and energy localization in insulating materials. Technological impact of space charge electron-beam characterization
Authors: Blaise G. , Le Gressus C.
Published: September 2018

The microscopic processes of fracture or breakdown are unknown, the models are contradicted or leave unexplained several observations, the suspected relationships between the electrical properties, the mechanical properties and the charge properties of the dielectrics are not confirmed by characterization of space charges and we do not know how to relate the results to the reliability of the materials. To overcome these difficulties: (1) we apply the energy localization principle used in mechanics and detonics, (2) we replace by electron traps that localize polarization energy, the defects imagined by Griffith in mechanics and dislocations used in detonation to explain the hot spot formation, (3) the effect of strain rates is taken into account because the localized energy is of the order of the binding energies and the trapping and detrapping characteristic times are of the order of the atomic polarization time (10-9 s). We can thus explain by multiphonon processes the transfer of the localized energy towards the bounds and explain the observations which occur when the strain rates are very high, (4) we develop an electron beam technique to measure the extension of the electron trapping domain and the localized energy beyond which a total discharge of the material occurs. These measurements characterize the space charges in the dielectric interfaces where the hot spots are formed. This technique makes it possible to reproduce most of the observations that remained unexplained and to link the measurements made to the properties and reliability of the insulators.
Low-frequency charge trapping and bistable domain switching in Mg-doped LiNbO3 single crystal films
Authors: Zhang Yan , Jiang An Quan
Published: September 2018

Lithium niobate single-crystal films are interesting for the integration of optoelectronic and surface acoustic wave devices. However, the domains have the preferred orientations, which limit their application in non-volatile memory devices. Here, we fabricated 5% Mg-doped LiNbO3 single-crystal films by ion-slicing of surface layers of bulk lithium niobate single-crystals. The Mg doping can improve the electrical performance of the films with the appearance of a definitive coercive voltage irrespective of applied voltages in polarization-voltage (P-V) hysteresis loops, unlike the undoped films where the apparent coercive voltages in P-V hysteresis loops equal the maximum applied voltages. Subsequent unipolar pulse stressing shows comprehensive charge injection into the films to occur at repetitive periodicities below 0.5 s that can symmetrize P-V hysteresis loops along the voltage axis. The injected charge in contradiction to an internal imprint field can change domain switching dynamics that can be described by the model of a non-ferroelectric passive layer in series with an ideal ferroelectric layer. The dielectric permittivities at low frequencies show the Maxwell-Wager relaxation of the injected charge with the broad distribution of relaxation times. As the periodicity is above 2 s, the injected charge within each cycle can be driven out of the film during intermittent time by the imprint field. This study shows the possibility of charge injection in stabilization of bipolar domain orientations in LiNbO3 single-crystal films.
Transition from minority to majority spin transport in iron-manganese nitride Fe4−xMnxN films with increasing x
Authors: Anzai Akihito , Gushi Toshiki , Komori Taro , Honda Syuta , Isogami Shinji , Suemasu Takashi
Published: September 2018

Herein, 30 nm-thick Fe4−xMnxN (x = 0, 1, 2, 3, and 4) epitaxial films were grown on MgO(001) substrates by molecular beam epitaxy, and the anisotropic magnetoresistance (AMR) properties were measured at temperatures (T) between 10 and 300 K. A negative AMR effect was observed in the Fe4N and FeMn3N films at T ≤ 300 K and in the Mn4N film at T ≤ 100 K. In contrast, a positive AMR effect was observed in the Fe3MnN and Fe2Mn2N films at T ≤ 300 K. Using the relationship between the AMR ratio, the spin polarization of the density of states at the Fermi level, and the spin polarization of the electrical conductivity (Pσ), we derived the sign of Pσ to be negative in Fe4N, Fe3MnN, and Fe2Mn2N and to be positive in FeMn3N and Mn4N. These results show that the minority spin transport is dominant in Fe4−xMnxN for x = 0, 1, and 2 at lower temperatures, whereas the majority spin transport is dominant with increasing x in Fe4−xMnxN for x = 3 and 4.
DNA demethylase ROS1 negatively regulates the imprinting of
DOGL4
and seed dormancy in
Arabidopsis thaliana
Authors: Zhu Haifeng , Xie Wenxiang , Xu Dachao , Miki Daisuke , Tang Kai , Huang Chao-Feng , Zhu Jian-Kang
Published: September 2018

Significance

Genomic imprinting is a form of epigenetic regulation causing parent-of-origin differential expression of maternally or paternally inherited alleles. The DNA demethylase DME regulates the imprinting of many genes in the
Arabidopsis
endosperm. It is not known whether and how other DNA demethylases may also regulate imprinting. Here, we discovered that the DNA demethylase ROS1 negatively regulates
DOGL4
imprinting via demethylation of the
DOGL4
promoter on the paternal allele. Additionally, we found that
DOGL4
negatively regulates seed dormancy and abscisic acid (ABA) response and that ROS1 regulates seed dormancy and ABA response by controlling
DOGL4
expression. Our results thus suggest a different mechanism of regulation of gene imprinting and reveal important roles of ROS1 in the regulation of seed dormancy and ABA response.
Teacher transformation of textbook tasks in Vietnamese EFL high school classrooms
Authors: Thi Nguyen Bao Trang , Newton Jonathan , Crabbe David
Published: September 2018

The study reported in this chapter investigated how and why the EFL teachers in a Vietnamese high school diverged from the tasks set in the textbooks provided as part of a task-based curriculum. Over a two-and-a-half-month period, nine teachers (all Vietnamese nationals) were observed teaching a sequence of five lessons covering one textbook unit; a total of 45 observed lessons. The lessons were audio and video recorded, and the teachers and selected students were interviewed. The teachers also took part in stimulated recall sessions. Results of an analysis of the features of the textbook tasks and of the observed lessons showed the teachers frequently adapt or replace textbook tasks, opting to change closed tasks into more open-ended tasks (open, divergent and input-independent) and to modify what they perceived as inauthentic tasks so they were not just ‘real world’, but ‘real’ to students. As to why teachers made these choices, interview data revealed a set of clearly articulated and shared beliefs among the teachers about the nature of teaching and learning, based in part on their experience of experimenting with different types of tasks. Prominent in their stated beliefs was a strong orientation toward the social and affective dimensions of task-based learning which prioritized learner engagement and well-being. This study provides insights into teacher decision making in task based teaching and addresses the pressing call for a ‘researched pedagogy’ which insists that “the use of tasks in classrooms must be an essential focus” (Bygate, 2011).