bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultra‐high‐speed travelling wave directional protection based on electronic transformers
Authors: Wang Dong , Gao Houlei , Zou Guibin , Luo Sibei
Published: March 2017

Traditional travelling wave (TW) protection is affected by a series of factors such as fault initial angles, grounding resistances, fault locations and bus structures. Especially, limited bandwidth of traditional transformers also restricts the application of TW protection. Hence, to improve the reliability and sensibility of traditional TW protection method, the study designs an ultra‐high‐speed TW directional protection method based on the output of electronic transformers (ET). First, the study establishes models of ET including Rogowski coil‐based electronic current transformer and capacitance divided electronic voltage transformer, and studies their TW transfer characteristics. Second, based on high‐frequency band of ET’ secondary output signal, the study can identify fault direction correctly by comparing the similarity between voltage and current TW. Because similarity comparing‐based protection method can almost ignore the affection of secondary TW's amplitude, the novel protection method has high reliability and sensibility. Third, in order to test the performance of proposed protection method, a 500 kV power transmission system model in PSCAD is constructed. The simulation results show the proposed protection is not sensitive to fault locations, fault initial angles, grounding resistances and bus structures.
Enhancement of SVC performance in flicker mitigation of wind farms
Authors: Samet Haidar , Bagheri Ali Asghar
Published: March 2017

The output active and reactive powers of wind farms are highly time‐varying even in extremely short time periods which cause flicker. In many wind farms static VAr compensators (SVCs) are employed to mitigate this flicker. In this study it is shown that reactive power variations of wind farms are even faster than those which can be fully compensated by SVC. This inability of SVCs comes from the delays in the reactive power measurement and thyristor ignition circuit. To overcome this limitation, the reactive power of a wind farm is predicted for a half cycle (10 ms) ahead. Large numbers of data were recorded from the Manjil wind farm in different weather conditions. Auto regressive moving average (ARMA) models were used for the prediction, and model adequacy checking was employed to determine the best ARMA model order. To evaluate the performance of proposed method, with a novel procedure the wind farm is simulated using the actual recorded data. The instantaneous flicker sensation and short term flicker were calculated and compared for three cases; without SVC, using SVC with the traditional control method, and using SVC with the proposed prediction method. The results confirm the superiority of the proposed technique.
Correlation processing and its use to mitigate the effects of multipath and other interfering signals in antenna ranges
Authors: Parsons John David , Leather Paul S.H.
Published: March 2017

Correlation processing has previously been used in radio communication systems to measure and characterise multipath environments, but it can equally well be applied to the elimination of multipath effects. The authors review the historical development of the technique in the context of its earlier use, and the background to its implementation as a method of eliminating or at least substantially reducing, the effects of multipath in antenna ranges. Correlation processing, which can be implemented either as a one‐step, real‐time process or used as a post‐measurement option, also suppresses the effects of coherent and non‐coherent interfering signals, so that the accuracy of antenna pattern measurement is greatly improved. At centimetre and millimetre wavelengths, it is possible to make accurate measurements in a normal laboratory environment without the need for an anechoic chamber. A simple proof‐of‐concept practical system is described, and example results are presented to demonstrate the validity of the technique and to compare it with time gating.
Development of 3,5-Di-tert-butylphenol as a Model Substrate for Biomimetic Aerobic Copper Catalysis
Authors: Lumb Jean-Philip , Kwon Ohhyeon , Esguerra Kenneth , Glazerman Michael , Petitjean Laurène , Xu Yalun , Ottenwaelder Xavier
Published: March 2017

We develop 3,5-di-tert­butylphenol as a strategic substrate for the evaluation of biomimetic Cu2–O2 complexes intended to mimic the activity of tyrosinase. We describe a practical and scalable synthesis and validate its use in an aerobic ortho-oxygenation catalyzed by N,N′-di-tert-butylethylenediamine and [Cu(CH3CN)4]PF6.
Terahertz radiation generation by nonlinear mixing of two lasers in a plasma with density hill
Authors: Kumar Manoj , Lee Kitae , Hee Park Seong , Uk Jeong Young , Vinokurov Nikolay
Published: March 2017

An analytical formalism of the terahertz (THz) radiation generation by beating of two lasers in a plasma with the density hill is investigated. The lasers propagate obliquely to the density gradient, and the nonlinearity arises through the ponderomotive force. The density gradient renders the ponderomotive force driven beat frequency nonlinear current density J→NL to possess a nonzero curl (∇×J→NL≠0) when θ is finite, giving rise to the THz radiation generation. The plasma frequency peak ωpmax is below the frequency difference of the lasers (ωpmax<(ω1−ω2) cos θ, where ω1 and ω2 are the frequencies of the laser, and θ is the angle that is arrived by their propagation vectors with the density gradient) to avoid THz reflection. The THz power conversion efficiency decreases with the THz frequency, increases with the plasma frequency and electron temperature, and maximizes at an optimum angle of incidence. For our set of parameters, the radiated THz power is about 0.15 GW.
Backward Raman amplification in the long-wavelength infrared
Authors: Johnson L. A. , Gordon D. F. , Palastro J. P. , Hafizi B.
Published: March 2017

The wealth of work in backward Raman amplification in plasma has focused on the extreme intensity limit; however, backward Raman amplification may also provide an effective and practical mechanism for generating intense, broad bandwidth, long-wavelength infrared radiation (LWIR). An electromagnetic simulation coupled with a relativistic cold fluid plasma model is used to demonstrate the generation of picosecond pulses at a wavelength of 10 μm with terawatt powers through backward Raman amplification. The effects of collisional damping, Landau damping, pump depletion, and wave breaking are examined, as well as the resulting design considerations for an LWIR Raman amplifier.
High-beta analytic equilibria in circular, elliptical, and D-shaped large aspect ratio axisymmetric configurations with poloidal and toroidal flows
Authors: López O. E. , Guazzotto L.
Published: March 2017

The Grad-Shafranov-Bernoulli system of equations is a single fluid magnetohydrodynamical description of axisymmetric equilibria with mass flows. Using a variational perturbative approach [E. Hameiri, Phys. Plasmas 20, 024504 (2013)], analytic approximations for high-beta equilibria in circular, elliptical, and D-shaped cross sections in the high aspect ratio approximation are found, which include finite toroidal and poloidal flows. Assuming a polynomial dependence of the free functions on the poloidal flux, the equilibrium problem is reduced to an inhomogeneous Helmholtz partial differential equation (PDE) subject to homogeneous Dirichlet conditions. An application of the Green's function method leads to a closed form for the circular solution and to a series solution in terms of Mathieu functions for the elliptical case, which is valid for arbitrary elongations. To extend the elliptical solution to a D-shaped domain, a boundary perturbation in terms of the triangularity is used. A comparison with the code FLOW [L. Guazzotto et al., Phys. Plasmas 11(2), 604–614 (2004)] is presented for relevant scenarios.
Experimental observation of self excited co-rotating multiple vortices in a dusty plasma with inhomogeneous plasma background
Authors: Choudhary Mangilal , Mukherjee S. , Bandyopadhyay P.
Published: March 2017

We report an experimental observation of multiple co-rotating vortices in an extended dust column in the background of an inhomogeneous diffused plasma. An inductively coupled rf discharge is initiated in the background of argon gas in the source region. This plasma was later found to diffuse into the main experimental chamber. A secondary DC glow discharge plasma is produced to introduce dust particles into the plasma volume. These micron-sized poly-disperse dust particles get charged in the background of the DC plasma and are transported by the ambipolar electric field of the diffused plasma. These transported particles are found to be confined in an electrostatic potential well, where the resultant electric field due to the diffused plasma (ambipolar E–field) and glass wall charging (sheath E–field) holds the micron–sized particles against the gravity. Multiple co-rotating (anti–clockwise) dust vortices are observed in the dust cloud for a particular discharge condition. The transition from multiple vortices to a single dust vortex is observed when input rf power is lowered. The occurrence of these vortices is explained on the basis of the charge gradient of dust particles, which is orthogonal to the ion drag force. The charge gradient is a consequence of the plasma inhomogeneity along the dust cloud length. The detailed nature and the reason for multiple vortices are still under investigation through further experiments; however, preliminary qualitative understanding is discussed based on the characteristic scale length of the dust vortex. There is a characteristic size of the vortex in the dusty plasma; therefore, multiple vortices could possibly be formed in an extended dusty plasma with inhomogeneous plasma background. The experimental results on the vortex motion of particles are compared with a theoretical model and are found to be in close agreement.
Synergy effects during current drive by two lower-hybrid waves
Authors: Yang Youlei , Xiang Nong , Hu Ye Min
Published: March 2017

In recent lower-hybrid current drive experiments on the experimental advanced superconducting tokamak, two lower-hybrid waves are launched simultaneously from different locations with different phase velocities to drive the plasma current. To understand the synergy effects of the two LH waves, the analytical expression for the electron velocity distribution is obtained based on Fuchs' model [Fuchs et al., Phys. Fluids 28(12), 3619–3628 (1985)], which is in good agreement with that obtained by solving the quasi-linear equation numerically via the CQL3D code [R. W. Harvey and M. G. McCoy, in Proceedings of IAEA Technical Committee Meeting on Advances in Simulation and Modeling of Thermonuclear Plasmas, Montreal, Canada (1992)]. The synergy factor is also obtained analytically. It is found that the existence of two resonant regions may bring more resonant electrons interacting with each wave and the perpendicular dynamics can further enhance the synergy effect by increasing the effective electron temperature, which in turn increases the number of electrons in the resonance with each wave.
Enhancing the electron acceleration by a circularly polarized laser interaction with a cone-target with an external longitudinal magnetic field
Authors: Gong J. X. , Cao L. H. , Pan K. Q. , Xiao C. Z. , Wu D. , He X. T.
Published: March 2017

The propagation of left-hand (LH-) and right-hand (RH-) circularly polarized (CP) lasers and the accompanying generation of fast electrons in a magnetized cone-target with pre-formed plasmas are investigated. In this work, the strength of external magnetic field is comparable to that of the incident laser. Theoretical analyses indicate that the cut-off density of LH-CP laser is larger than that without an external magnetic field. When the external magnetic field normalized by the laser magnetic field is larger than the relativistic factor, the RH-CP laser will keep on propagating till the laser energy is depleted. The theoretical predictions are confirmed by two-dimensional particle-in-cell simulations. Simulation results show that in the presence of external longitudinal magnetic field, the energies and yields of fast electrons are greatly enhanced for RH-CP laser. Besides, the coupling efficiency of laser energy to energetic electrons for RH-CP laser is much higher than that for LH-CP laser and without external magnetic field. Furthermore, detailed simulation results perform an enhancement of the incident laser absorption with increasing external magnetic field.
Analytical study of effects of positron density and temperature anisotropy on electrostatic ion cyclotron instability
Authors: Barati Moqadam Niyat M. , Khorashadizadeh S. M. , Niknam A. R.
Published: March 2017

The effects of the positron concentration and ion temperature anisotropy on the electrostatic ion cyclotron instability are studied analytically, in a magnetized electron-positron-ion plasma with temperature anisotropy, using the linear kinetic theory. Positrons and electrons are supposed to drift either in the same direction or in opposite directions relative to singly ionized stationary ions and parallel to the magnetic field. The dispersion relation of the electrostatic ion cyclotron waves is derived, and then the conditions for exciting the instability of the waves are investigated. Moreover, the condition for the marginally stable state is also studied. It is found that as the positron concentration and perpendicular ion temperature increase, the growth rate of the electrostatic ion cyclotron instability decreases, whereas the critical drift velocity increases. It is also found that for the chosen set of parameters, with electrons and positrons drifting in the same direction, the instability in the plasma is stronger than when the electrons and positrons drift in opposite directions. In addition, a comparison is made to the normal electron-ion plasma.
Ion heat pinch due to the magnetic drift resonance with the ion temperature gradient instability in a rotating plasma
Authors: Zhang Debing , Xu Yingfeng , Wang Shaojie
Published: March 2017

The ion heat pinch due to the magnetic drift resonance with the ion temperature gradient instability is investigated by using the Lie-transform method. In a tokamak plasma with an equilibrium parallel flow, the total heat flux is found to direct inward with a strong flow shear. The proposed heat pinch can provide possible explanations for some experimental observations.
Increased luminescence and improved decay kinetics in lithium and cerium co-doped yttrium aluminum garnet scintillators grown by the Czochralski method
Authors: Dickens Peter T. , Haven Drew T. , Friedrich Stephan , Saleh Muad , Lynn Kelvin G.
Published: March 2017

In this study, four yttrium aluminum garnet single crystals co-doped with cerium and lithium were produced by the Czochralski method and the scintillation and defect properties were investigated. Our results demonstrated an increase in luminescence with Li co-doping as well as elimination of longer decay times. Surprisingly, although Li is monovalent, no oxidation of cerium from Ce3+ to Ce4+ was found as would be expected to maintain charge neutrality. Additionally, thermoluminescence results indicated a reduction in the trapping of charge carriers by shallow and deep traps, and room temperature photoluminescence measurements showed an improvement in the Ce3+ 5d to 4f transition efficiency.
Fully kinetic simulations of collisionless, mesothermal plasma emission: Macroscopic plume structure and microscopic electron characteristics
Authors: Hu Yuan , Wang Joseph
Published: March 2017

This paper presents a fully kinetic particle particle-in-cell simulation study on the emission of a collisionless plasma plume consisting of cold beam ions and thermal electrons. Results are presented for both the two-dimensional macroscopic plume structure and the microscopic electron kinetic characteristics. We find that the macroscopic plume structure exhibits several distinctive regions, including an undisturbed core region, an electron cooling expansion region, and an electron isothermal expansion region. The properties of each region are determined by microscopic electron kinetic characteristics. The division between the undisturbed region and the cooling expansion region approximately matches the Mach line generated at the edge of the emission surface, and that between the cooling expansion region and the isothermal expansion region approximately matches the potential well established in the beam. The interactions between electrons and the potential well lead to a new, near-equilibrium state different from the initial distribution for the electrons in the isothermal expansion region. The electron kinetic characteristics in the plume are also very anisotropic. As the electron expansion process is mostly non-equilibrium and anisotropic, the commonly used assumption that the electrons in a collisionless, mesothermal plasma plume may be treated as a single equilibrium fluid in general is not valid.
Zonal flow generation in parallel flow shear driven turbulence
Authors: Kosuga Y. , Itoh S.-I. , Itoh K.
Published: March 2017

Generation of zonal flow in parallel flow shear driven turbulence is discussed. Nonlinear dynamics is formulated by calculating energy transfer in the wave number space. It is shown that zonal flows can be generated (gain energy) from the primary mode which is driven by parallel flow shear. As a result, helical flow pattern can develop in turbulent plasmas. Our results imply that zonal flow can be generated in 3D parallel flow shear driven turbulence, which indicates that zonal flows are ubiquitous in turbulent plasmas, either 2D or 3D. Implications for turbulent momentum transport in laboratory and astrophysical plasmas are discussed.
Simulation study of overtaking of ion-acoustic solitons in the fully kinetic regime
Authors: Hosseini Jenab S. M. , Spanier F.
Published: March 2017

The overtaking collisions of ion-acoustic solitons in the presence of trapping effects of electrons are studied based on a fully kinetic simulation approach. The method is able to provide all the kinetic details of the process alongside the fluid-level quantities self consistently. Solitons are produced naturally by utilizing the chain formation phenomenon, and then are arranged in a new simulation box to test the different scenarios of overtaking collisions. Three achievements are reported here. First, simulations prove the long-time life span of the ion-acoustic solitons in the presence of trapping effect of electrons (kinetic effects), which serves as the benchmark of the simulation code. Second, their stability against overtaking mutual collisions is established by creating collisions between solitons with different number and shapes of trapped electrons, i.e., different trapping parameter. Finally, details of solitons during collisions for both ions and electrons are provided on both fluid and kinetic levels. These results show that on the kinetic level, trapped electron population accompanying each of the solitons are exchanged between the solitons during the collision. Furthermore, the behavior of electron holes accompanying solitons contradicts the theory about the electron holes interaction developed based on kinetic theory. They also show behaviors much different from other electron holes witnessed in processes such as nonlinear Landau damping (Bernstein-Greene-Kruskal -BGK- modes) or beam-plasma interaction (like two-beam instability).
Magnetosonic wave in pair-ion electron collisional plasmas
Authors: Hussain S. , Hasnain H.
Published: March 2017

Low frequency magnetosonic waves in positive and negative ions of equal mass and opposite charges in the presence of electrons in collisional plasmas are studied. The collisions of ions and electrons with neutrals are taken into account. The nonlinearities in the plasma system arise due to ion and electrons flux, Lorentz forces, and plasma current densities. The reductive perturbation method is applied to derive the Damped Korteweg de Vries (DKdV) equation. The time dependent solution of DKdV is presented. The effects of variations of different plasma parameters on propagation characteristics of magnetosonic waves in pair-ion electron plasma in the context of laboratory plasmas are discussed.
High-energy (>70 keV) x-ray conversion efficiency measurement on the ARC laser at the National Ignition Facility
Authors: Chen Hui , Hermann M. R. , Kalantar D. H. , Martinez D. A. , Di Nicola P. , Tommasini R. , Landen O. L. , Alessi D. , Bowers M. , Browning D. , Brunton G. , Budge T. , Crane J. , Di Nicola J.-M. , Döppner T. , Dixit S. , Erbert G. , Fishler B. , Halpin J. , Hamamoto M. , Heebner J. , Hernandez V. J. , Hohenberger M. , Homoelle D. , Honig J. , Hsing W. , Izumi N. , Khan S. , LaFortune K. , Lawson J. , Nagel S. R. , Negres R. A. , Novikova L. , Orth C. , Pelz L. , Prantil M. , Rushford M. , Shaw M. , Sherlock M. , Sigurdsson R. , Wegner P. , Widmayer C. , Williams G. J. , Williams W. , Whitman P. , Yang S.
Published: March 2017

The Advanced Radiographic Capability (ARC) laser system at the National Ignition Facility (NIF) is designed to ultimately provide eight beamlets with a pulse duration adjustable from 1 to 30 ps, and energies up to 1.5 kJ per beamlet. Currently, four beamlets have been commissioned. In the first set of 6 commissioning target experiments, the individual beamlets were fired onto gold foil targets with energy up to 1 kJ per beamlet at 20–30 ps pulse length. The x-ray energy distribution and pulse duration were measured, yielding energy conversion efficiencies of 4–9 × 10−4 for x-rays with energies greater than 70 keV. With greater than 3 J of such x-rays, ARC provides a high-precision x-ray backlighting capability for upcoming inertial confinement fusion and high-energy-density physics experiments on NIF.
Filamentation in the pinched column of the dense plasma focus
Authors: Kubes P. , Paduch M. , Cikhardt J. , Cikhardtova B. , Klir D. , Kravarik J. , Rezac K. , Zielinska E. , Sadowski M. J. , Szymaszek A. , Tomaszewski K. , Zaloga D.
Published: March 2017

The paper describes the filamentary structure observed in the high-energy ultraviolet radiation for discharges performed at the hydrogen- or deuterium-filling and at the puffing of hydrogen, deuterium or helium, in a mega-ampere dense plasma-focus facility. The lifetime of this structure overcomes 50 ns. These filaments connect the surface of a pinched column with internal plasmoids formed at different combinations of filling and puffing gases and they should transport some current and plasma. During all the investigated deuterium shots, the fusion-produced neutrons were recorded. Therefore, deuterons should be present in the region of their acceleration, independent of the applied puffing of the gas. Simultaneously with the observed filaments, inside the dense plasma column small plasma-balls of mm-dimensions were observed, which had a similar lifetime (longer than the relaxation time) and quasi-stationary positions in the discharge volume. The observed filaments and balls might be a manifestation of the (i) discrete spatial structure of the current flowing through and around the dense plasma column and (ii) transport of the plasma from external layers to the central region. Their formation and visualization were easier due to the application of air admixtures in the puffed gas.
Initial experimental demonstration of the principles of a xenon gas shield designed to protect optical components from soft x-ray induced opacity (blanking) in high energy density experiments
Authors: Swadling G. F. , Ross J. S. , Manha D. , Galbraith J. , Datte P. , Sorce C. , Katz J. , Froula D. H. , Widmann K. , Jones O. S. , Divol L. , Landen O. L. , Kilkenny J. D. , Moody J. D.
Published: March 2017

The design principles of a xenon gas shield device that is intended to protect optical components from x-ray induced opacity (“x-ray blanking”) have been experimentally demonstrated at the OMEGA-60 Laser Facility at the Laboratory for Laser Energetics, University of Rochester. A volume of xenon gas placed in front of an optical component absorbs the incoming soft x-ray radiation but transmits optical and ultra-violet radiation. The time-resolved optical (532 nm) transmission of samples was recorded as they were exposed to soft x-rays produced by a gold sphere source (1.5 kJ sr−1, 250–300 eV). Blanking of fused silica (SiO2) was measured to occur over a range of time-integrated soft x-ray (<3 keV) fluence from ∼0.2–2.5 J cm−2. A shield test device consisting of a 30 nm silicon nitride (Si3N4) and a 10 cm long volume of 0.04 bar xenon gas succeeded in delaying loss of transmission through a magnesium fluoride sample; optical transmission was observed over a longer period than for the unprotected sample. It is hoped that the design of this x-ray shield can be scaled in order to produce a shield device for the National Ignition Facility optical Thomson scattering collection telescope, in order to allow measurements of hohlraum plasma conditions produced in inertial confinement fusion experiments. If successful, it will also have applications in many other high energy density experiments where optical and ultra-violet measurements are desirable.
Mitigation of hot electrons from laser-plasma instabilities in high-Z, highly ionized plasmas
Authors: Fein J. R. , Holloway J. P. , Trantham M. R. , Keiter P. A. , Edgell D. H. , Froula D. H. , Haberberger D. , Frank Y. , Fraenkel M. , Raicher E. , Shvarts D. , Drake R. P.
Published: March 2017

Hard x-ray measurements are used to infer production of hot electrons in laser-irradiated planar foils of materials ranging from low- to high-Z. The fraction of laser energy converted to hot electrons, fhot, was reduced by a factor of 103 going from low-Z CH to high-Z Au, and hot electron temperatures were reduced from 40 to ∼20 keV. The reduction in fhot correlates with steepening electron density gradient length-scales inferred from plasma refraction measurements. Radiation hydrodynamic simulations predicted electron density profiles in reasonable agreement with those from measurements. Both multi-beam two-plasmon decay (TPD) and multi-beam stimulated Raman scattering (SRS) were predicted to be above threshold with linear threshold parameters that decreased with increasing Z due to steepening length-scales, as well as enhanced laser absorption and increased electron plasma wave collisional and Landau damping. The results add to the evidence that SRS may play a comparable or a greater role relative to TPD in generating hot electrons in multi-beam experiments.
Performance of extended Lagrangian schemes for molecular dynamics simulations with classical polarizable force fields and density functional theory
Authors: Vitale Valerio , Dziedzic Jacek , Albaugh Alex , Niklasson Anders M. N. , Head-Gordon Teresa , Skylaris Chris-Kriton
Published: March 2017

Iterative energy minimization with the aim of achieving self-consistency is a common feature of Born-Oppenheimer molecular dynamics (BOMD) and classical molecular dynamics with polarizable force fields. In the former, the electronic degrees of freedom are optimized, while the latter often involves an iterative determination of induced point dipoles. The computational effort of the self-consistency procedure can be reduced by re-using converged solutions from previous time steps. However, this must be done carefully, as not to break time-reversal symmetry, which negatively impacts energy conservation. Self-consistent schemes based on the extended Lagrangian formalism, where the initial guesses for the optimized quantities are treated as auxiliary degrees of freedom, constitute one elegant solution. We report on the performance of two integration schemes with the same underlying extended Lagrangian structure, which we both employ in two radically distinct regimes—in classical molecular dynamics simulations with the AMOEBA polarizable force field and in BOMD simulations with the Onetep linear-scaling density functional theory (LS-DFT) approach. Both integration schemes are found to offer significant improvements over the standard (unpropagated) molecular dynamics formulation in both the classical and LS-DFT regimes.
Effects of B and N modified interface and applied bias on the magnetoresistance in Fe/MgO/Fe magnetic tunnel junctions
Authors: Wang T. X. , Li Y. , Xia C. X. , Zhao X. , An Y. P. , Dai X. Q.
Published: March 2017

The Fe/MgO/Fe magnetic tunnel junction with B and N modified interfaces has been studied based on the first-principle density function theory method. For junctions with thin (five layers) and thick (ten layers) MgO barriers, positive and negative tunneling magnetic resistance (TMR) ratios are obtained as a function of the interface structure under finite bias voltage. The junctions with B modified interface have Δ1 channel conductance perfectly preserved. But the spin filtering effect is reduced and thus very low TMR value is resulted. N modified interface has obvious influence to the interfacial state and drastically changes the bias dependence of the TMR output, which is promising for multifunction spintronic device applications with high TMR output and optimized bias dependence. Also, the formation energy of N insertion at the interface is lower than that of B. It will be very effective to prevent B staying at the interface with N insertion.
Viscous-resistive layer in Rayleigh-Taylor instability
Authors: Silveira F. E. M. , Orlandi H. I.
Published: March 2017

In this work, new scaling laws of the time growth rate γ of the Rayleigh-Taylor instability with the plasma resistivity η, kinematic viscosity ν, and electron number density ne are derived. A viscosity scale is defined in terms of the time decay of the perturbative fluid flow perpendicular to the equilibrium magnetic field, at the quasi-static approximation. Such a scale provides the identification of a viscous layer that can be combined with the resistive layer to produce a viscous-resistive layer. The latter, in turn, is found to satisfy an algebraic biquadratic equation. When viscous effects are negligible, it is shown that the viscous-resistive layer is given by the resistive layer. Somewhat surprisingly, when viscous effects cannot be neglected, it is shown that the viscous-resistive layer is given by the geometric mean of the resistive and viscous layers. A dispersion relation for the time growth rate is derived in terms of the viscous-resistive layer. When viscous effects cannot be neglected, two new scaling laws are found. At the quasi-static approximation, it is shown that γ ∼ (ην)1∕4. However, on account of a finite electron mass, it is shown that γ∼(ν/ne)1/3. Further developments of our formulation are addressed in connection with a finite compressibility in the perturbative flow.
Effect of partitioning on the convergence properties of the Rayleigh-Schrödinger perturbation series
Authors: Mihálka Zsuzsanna É. , Szabados Ágnes , Surján Péter R.
Published: March 2017

Convergence features of the Rayleigh-Schrödinger perturbation theory (PT) strongly depend on the partitioning applied. We investigate the large order behavior of the Møller-Plesset and Epstein Nesbet partitionings in comparison with a less known partitioning obtained by level shift parameters minimizing the norm of operator Q^W^, with W^ being the perturbation operator while Q standing for the reduced resolvent of the zero order Hamiltonian H^0. Numerical results, presented for molecular systems for the first time, indicate that it is possible to find level shift parameters in this way which convert divergent perturbation expansions to convergent ones in some cases. Besides numerical calculations of high-order PT terms, convergence radii of the corresponding perturbation expansions are also estimated using quadratic Padé approximants.
Heat transfer at the convex fluid-solid interface
Authors: Dinler Ali
Published: March 2017

Interfacial heat transfer across curved surfaces has not been understood sufficiently well. The present study reports a significant decrease in heat transfer at a convex fluid-solid interface. Effects of curvature on the Kapitza length and the thermal accommodation coefficient are investigated for both gas and liquid phases to understand the occurrence of large temperature jumps. The study also examines the penetration depth of non-equilibrium effects into gas from the convex surface theoretically and reveals the expansion of the Knudsen layer at convex surfaces.
Two-photon-absorption line strengths for nitric oxide: Comparison of theory and sub-Doppler, laser-induced fluorescence measurements
Authors: Kulatilaka Waruna D. , Lucht Robert P.
Published: March 2017

We discuss the results of high-resolution, sub-Doppler two-photon-absorption laser-induced fluorescence (TPALIF) spectroscopy of nitric oxide at low pressure and room temperature. The measurements were performed using the single-longitudinal mode output of a diode-laser-seeded optical parametric generator (OPG) system with a measured frequency bandwidth of 220 MHz. The measurements were performed using a counter-propagating pump beam geometry, resulting in sub-Doppler TPALIF spectra of NO for various rotational transitions in the (0,0) vibrational band of the A2Σ+ − X2Π electronic transition. The experimental results are compared with the results of a perturbative treatment of the rotational line strengths for the 20 different rotational branches of the X2Π(v″ = 0) → A2Σ+(v′ = 0) two-photon absorption band. In the derivation of the expressions for the two-photon transition absorption strength, the closure relation is used for rotational states in the intermediate levels of the two-photon transition in analogy with the Placzek treatment of Raman transitions. The theoretical treatment of the effect of angular momentum coupling on the two-photon rotational line strengths features the use of irreducible spherical tensors and 3j symbols. The final results are expressed in terms of the Hund’s case (a) coupling coefficients aJ and bJ for the X2Π(v″ = 0) rotational level wavefunctions, which are intermediate between Hund’s case (a) and case (b). Considerable physical insight is provided by this final form of the equations for the rotational line strengths. Corrections to the two-photon absorption rotational line strength for higher order effects such as centrifugal stretching can be included in a straightforward fashion in the analysis by incorporating higher order terms in these coupling coefficients aJ and bJ, although these corrections are essentially negligible for J < 50. The theoretical calculations of relative line intensities are in good agreement both with our experiment and with published experimental results. In addition, the calculated line shapes and relative intensities for closely spaced main branch and satellite transitions are in excellent agreement with our experimental measurements.
Development of an excited-state calculation method for large systems using dynamical polarizability: A divide-and-conquer approach at the time-dependent density functional level
Authors: Nakai Hiromi , Yoshikawa Takeshi
Published: March 2017

In this study, we developed an excited-state calculation method for large systems using dynamical polarizabilities at the time-dependent density functional theory level. Three equivalent theories, namely, coupled-perturbed self-consistent field (CPSCF), random phase approximation (RPA), and Green function (GF), were extended to linear-scaling methods using the divide-and-conquer (DC) technique. The implementations of the standard and DC-based CPSCF, RPA, and GF methods are described. Numerical applications of these methods to polyene chains, single-wall carbon nanotubes, and water clusters confirmed the accuracy and efficiency of the DC-based methods, especially DC-GF.
Auto-correlation function and frequency spectrum due to a super-position of uncorrelated exponential pulses
Authors: Garcia O. E. , Theodorsen A.
Published: March 2017

The auto-correlation function and the frequency power spectral density due to a super-position of uncorrelated exponential pulses are considered. These are shown to be independent of the degree of pulse overlap and thereby the intermittency of the stochastic process. For constant pulse duration and a one-sided exponential pulse shape, the power spectral density has a Lorentzian shape which is flat for low frequencies and a power law at high frequencies. The algebraic tail is demonstrated to result from the discontinuity in the pulse function. For a strongly asymmetric two-sided exponential pulse shape, the frequency spectrum is a broken power law with two scaling regions. In the case of a symmetric pulse shape, the power spectral density is the square of a Lorentzian function. The steep algebraic tail at high frequencies in these cases is demonstrated to follow from the discontinuity in the derivative of the pulse function. A random distribution of pulse durations is shown to result in apparently longer correlation times but has no influence on the asymptotic power law tail of the frequency spectrum. The effect of additional random noise is also discussed, leading to a flat spectrum for high frequencies. The probability density function for the fluctuations is shown to be independent of the distribution of pulse durations. The predictions of this model describe the variety of auto-correlation functions and power spectral densities reported from experimental measurements in the scrape-off layer of magnetically confined plasmas.
Negative viscosity from negative compressibility and axial flow shear stiffness in a straight magnetic field
Authors: Li J. C. , Diamond P. H.
Published: March 2017

Negative compressibility ion temperature gradient (ITG) turbulence in a linear plasma device controlled shear de-correlation experiment can induce a negative viscosity increment. However, even with this negative increment, we show that the total axial viscosity remains positive definite, i.e., no intrinsic axial flow can be generated by pure ITG turbulence in a straight magnetic field. This differs from the case of electron drift wave turbulence, where the total viscosity can turn negative, at least transiently. When the flow gradient is steepened by any drive mechanism, so that the parallel shear flow instability (PSFI) exceeds the ITG drive, the flow profile saturates at a level close to the value above which PSFI becomes dominant. This saturated flow gradient exceeds the PSFI linear threshold, and grows with ∇Ti0 as |∇V∥|/|k∥cs|∼|∇Ti0|2/3/(k∥Ti0)2/3. This scaling trend characterizes the effective stiffness of the parallel flow gradient.
Fast sensitive amplifier for two-probe conductance measurements in single molecule break junctions
Authors: Johnson Tyler K. , Ivie Jeffrey A. , Jaruvang Jason , Monti Oliver L. A.
Published: March 2017

We demonstrate an amplifier based on the Wheatstone bridge designed specifically for use in single molecule break junctions. This amplifier exhibits superior performance due to its large bandwidth, flat frequency response, and high sensitivity. The amplifier is capable of measuring conductance values from 102 to 10−6G0 (G0 = 2e2/h), while maintaining a bandwidth in excess of 20 kHz, and shows remarkable resolution in the molecular conductance regime of 10−2 to 10−5 G0.
The impact of local structure variation on thermal quenching of luminescence in Ca3MoxW1−xO6:Eu3+ solid solution phosphors
Authors: Wang Chunhao , Ye Shi , Li Ye , Zhang Qinyuan
Published: March 2017

Near-ultraviolet (NUV, 365–410 nm) excitable white light emitting diodes require intense absorption in the NUV region for the tri-color phosphors (red, green, and blue). Optional red phosphor Ca3MoO6:Eu3+ meets the requirement of NUV absorption but suffers from severe quenching, while Ca3WO6:Eu3+ has good resistance to thermal quenching but could not absorb NUV light efficiently. It is requisite to investigate the candidate Ca3MoxW1−xO6:Eu3+ to balance the both effects. Results indicate that thermal quenching turns to be worse with an increase in Mo contents in the solid solutions with inevitable distortions or defects, especially when exciting the charge transfer band of WO6 and MoO6 groups. Temperature-dependent Raman spectroscopy is utilized to reveal the impact of structural variation in the quenching process since the variations influence the energy transfer between WO6/MoO6 groups and Eu3+ ions or among Eu3+ ions. Results show that the tilting or distortion of the Ca/W/MoO6 octahedral framework and weakened Eu3+-O bonds have large impacts on thermal quenching performance of Eu3+ luminescence in the solid solutions. The research would benefit the design of novel red phosphors.
X-ray micro-CT measurement of large parts at very low temperature
Authors: Koutecký T. , Zikmund T. , Glittová D. , Paloušek D. , Živčák J. , Kaiser J.
Published: March 2017

At present, the automotive industry, along with other industries, has increasing demands on accuracy of produced parts and assemblies. Besides the regular dimensional and geometrical inspection, in some cases, also a verification at very low temperatures is required. X-ray computed tomography (CT), as a tool for non-destructive testing, is able to examine samples and then determine dimensions for strictly stable temperature conditions necessary for the stability of the CT system. Until now, no system that allows scanning of samples larger than a few millimeters at temperatures much below 0 °C has been presented. This paper presents a cooling system for CT imaging of parts with length up to 300 mm at the extreme temperature conditions of −40 °C, which are based on automotive industry requests. It describes the equipment and conditions under which it is possible to achieve a temperature stability of samples at low temperatures, while keeping an independent temperature regulation of the CT system. The presented system uses a standard industrial CT device and a newly designed cooling stage with passive cooling based on phase-change material. The system is demonstrated on the measurement of plastic part (car door handle) at temperatures of −40 °C and 20 °C. The paper also presents the method of how to interpret the thermal changes using tools of the commercial software VGStudio MAX (Volume Graphics GmbH, Germany).
Conservative discretization of the Landau collision integral
Authors: Hirvijoki E. , Adams M. F.
Published: March 2017

We describe a density-, momentum-, and energy-conserving discretization of the nonlinear Landau collision integral. The method is suitable for both the finite-element and discontinuous Galerkin methods and does not require structured meshes. The conservation laws for the discretization are proven algebraically and demonstrated numerically for an axially symmetric nonlinear relaxation problem using a finite-element implementation.
Magnetosonic hump and dip solitons in a quantum plasma with Bohm potential effect
Authors: Hussain S. , Mahmood S.
Published: March 2017

Low frequency nonlinear magnetosonic wave propagation is investigated in magnetized electron ion quantum plasmas. A two fluid quantum magnetohydrodynamic model is employed for a magnetized dense plasma. The quantum effects like Bohm potential (due to wave nature of the particles) and Fermi pressure (due to spin 1/2 particles) for degenerate electrons are taken in the model. The electron inertia is also included in the momentum equation of degenerate electrons, which gives the magnetosonic wave dispersion effects on electron inertial length scale in the linear wave analysis. The Korteweg de Vries (KdV) equation is derived for studying low amplitude magnetosonic solitons in a magnetized quantum plasma by employing a reductive perturbation method. It is found that in the presence of Bohm potential force in quantum plasma model both plasma hump and dip soliton structures of magnetosonic waves are formed. The magnetosonic soliton hump structures moves with super magnetosonic wave speed, while dip magnetosonic wave structures have sub magnetosonic wave speed. The effects of varying plasma parameters such as plasma density and magnetic field intensity on nonlinear structures are discussed and illustrated numerically in the context of astrophysical plasma conditions existing in compact stars.
Development of an inertial confinement fusion platform to study charged-particle-producing nuclear reactions relevant to nuclear astrophysics
Authors: Gatu Johnson M. , Zylstra A. B. , Bacher A. , Brune C. R. , Casey D. T. , Forrest C. , Herrmann H. W. , Hohenberger M. , Sayre D. B. , Bionta R. M. , Bourgade J.-L. , Caggiano J. A. , Cerjan C. , Craxton R. S. , Dearborn D. , Farrell M. , Frenje J. A. , Garcia E. M. , Glebov V. Yu. , Hale G. , Hartouni E. P. , Hatarik R. , Hohensee M. , Holunga D. M. , Hoppe M. , Janezic R. , Khan S. F. , Kilkenny J. D. , Kim Y. H. , Knauer J. P. , Kohut T. R. , Lahmann B. , Landoas O. , Li C. K. , Marshall F. J. , Masse L. , McEvoy A. , McKenty P. , McNabb D. P. , Nikroo A. , Parham T. G. , Paris M. , Petrasso R. D. , Pino J. , Radha P. B. , Remington B. , Rinderknecht H. G. , Robey H. , Rosenberg M. J. , Rosse B. , Rubery M. , Sangster T. C. , Sanchez J. , Schmitt M. , Schoff M. , Séguin F. H. , Seka W. , Sio H. , Stoeckl C. , Tipton R. E.
Published: March 2017

This paper describes the development of a platform to study astrophysically relevant nuclear reactions using inertial-confinement fusion implosions on the OMEGA and National Ignition Facility laser facilities, with a particular focus on optimizing the implosions to study charged-particle-producing reactions. Primary requirements on the platform are high yield, for high statistics in the fusion product measurements, combined with low areal density, to allow the charged fusion products to escape. This is optimally achieved with direct-drive exploding pusher implosions using thin-glass-shell capsules. Mitigation strategies to eliminate a possible target sheath potential which would accelerate the emitted ions are discussed. The potential impact of kinetic effects on the implosions is also considered. The platform is initially employed to study the complementary T(t,2n)α, T(3He,np)α and 3He(3He,2p)α reactions. Proof-of-principle results from the first experiments demonstrating the ability to accurately measure the energy and yields of charged particles are presented. Lessons learned from these experiments will be used in studies of other reactions. The goals are to explore thermonuclear reaction rates and fundamental nuclear physics in stellar-like plasma environments, and to push this new frontier of nuclear astrophysics into unique regimes not reachable through existing platforms, with thermal ion velocity distributions, plasma screening, and low reactant energies.
H and Au diffusion in high mobility a-InGaZnO thin-film transistors via low temperature KrF excimer laser annealing
Authors: Bermundo Juan Paolo S. , Ishikawa Yasuaki , Fujii Mami N. , Ikenoue Hiroshi , Uraoka Yukiharu
Published: March 2017

We report the fabrication of high mobility amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) irradiated by a single shot of a 248 nm KrF excimer laser. Very high mobilities (μ) of up to 43.5 cm2/V s were obtained after the low temperature excimer laser annealing (ELA) process. ELA induces high temperatures primarily in the upper layers and maintains very low temperatures of less than 50 °C in the substrate region. Scanning Transmission Electron micrographs show no laser induced damage and clear interfaces after the laser irradiation. In addition, several characterization studies were performed to determine the μ improvement mechanism. The analysis of Secondary Ion Mass Spectrometry and X-ray Photoelectron Spectroscopy suggests incorporation of H mainly from the hybrid passivation layer into the channel. Moreover, Energy-dispersive X-ray Spectroscopy results show that Au diffused into the channel after ELA. Both KrF ELA-induced H and Au diffusion contributed to the higher μ. These results demonstrate that ELA can greatly enhance the electrical properties of a-IGZO TFTs for promising applications in large area, transparent, and flexible electronics.