bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic and dynamic studies of the Cl(2Pu) + H2O($\tilde X$X̃1A1) → HCl($\tilde X$X̃1Σ+) + OH($\tilde X$X̃2Π) reaction on an ab initio based full-dimensional global potential energy surface of the ground electronic state of ClH2O
Authors: Li Jun , Dawes Richard , Guo Hua
Published: August 2013

Extensive high-level ab initio calculations were performed on the ground electronic state of ClH2O. The barrier region for the title reaction was found to have significant multi-reference character, thus favoring the multi-reference configuration interaction (MRCI) method over single-reference methods such as coupled-cluster. A full-dimensional global potential energy surface was developed by fitting about 25 000 MRCI points using the permutation invariant polynomial method. The reaction path features a “late” barrier flanked by deep pre- and post-barrier wells. Calculated rate constants for the forward reaction are in reasonable agreement with experiment, suggesting a good representation of the forward barrier. The dynamics of the forward reaction was also investigated using a quasi-classical trajectory method at energies just above the barrier. While the OH bond is found to be a spectator, the HCl product has significant rotational excitation. The reaction proceeds via both direct rebound and stripping mechanisms, leading to backward and sideways scattering.
Surfaces of colloidal PbSe nanocrystals probed by thin-film positron annihilation spectroscopy
Authors: Chai L. , Al-Sawai W. , Gao Y. , Houtepen A. J. , Mijnarends P. E. , Barbiellini B. , Schut H. , van Schaarenburg L. C. , van Huis M. A. , Ravelli L. , Egger W. , Kaprzyk S. , Bansil A. , Eijt S. W. H.
Published: August 2013

Positron annihilation lifetime spectroscopy and positron-electron momentum density (PEMD) studies on multilayers of PbSenanocrystals (NCs),supported by transmission electron microscopy, show that positrons are strongly trapped at NC surfaces, where they provide insight into the surface composition and electronic structure of PbSeNCs. Our analysis indicates abundant annihilation of positrons with Se electrons at the NC surfaces and with O electrons of the oleic ligands bound to Pb ad-atoms at the NC surfaces, which demonstrates that positrons can be used as a sensitive probe to investigate the surface physics and chemistry of nanocrystals inside multilayers. Ab initio electronic structure calculations provide detailed insight in the valence and semi-core electron contributions to the positron-electron momentum density of PbSe. Both lifetime and PEMD are found to correlate with changes in the particle morphology characteristic of partial ligand removal.
Scaling Navier-Stokes equation in nanotubes
Authors: Gărăjeu Mihail , Gouin Henri , Saccomandi Giuseppe
Published: August 2013

On one hand, classical Monte Carlo and molecular dynamics simulations have been very useful in the study of liquids in nanotubes, enabling a wide variety of properties to be calculated in intuitive agreement with experiments. On the other hand, recent studies indicate that the theory of continuum breaks down only at the nanometer level; consequently flows through nanotubes still can be investigated with Navier-Stokes equations if we take suitable boundary conditions into account. The aim of this paper is to study the statics and dynamics of liquids in nanotubes by using methods of nonlinear continuum mechanics. We assume that the nanotube is filled with only a liquid phase; by using a second gradient theory the static profile of the liquid density in the tube is analytically obtained and compared with the profile issued from molecular dynamics simulation. Inside the tube there are two domains: a thin layer near the solid wall where the liquid density is non-uniform and a central core where the liquid density is uniform. In the dynamic case a closed form analytic solution seems to be no more possible, but by a scaling argument it is shown that, in the tube, two distinct domains connected at their frontiers still exist. The thin inhomogeneous layer near the solid wall can be interpreted in relation with the Navier length when the liquid slips on the boundary as it is expected by experiments and molecular dynamics calculations.
Numerical investigation for the effect of the liquid film volume on thermocapillary flow direction in a thin circular liquid film
Authors: Yamamoto T. , Takagi Y. , Okano Y. , Dost S.
Published: August 2013

NASA Astronaut Dr. Pettit carried out a thermocapillary flow experiment onboard the International Space Station in 2003. In this experiment a thin water film containing milk powder was formed in a stainless-steel wire ring. Heating a section of the ring by a soldering iron induced in the water film a thermocapillary flow towards the heated section of the ring (outward flow: cold to hot). This flow was in the opposite direction of the usually observed thermocapillary flows (inward flow: hot to cold). To shed light on this interesting phenomenon observed in the space experiment, we have conducted a three-dimensional numerical simulation study. Simulation results showed that the film geometry of the water film is a key factor determining flow direction and flow strength. When the liquid film free surfaces are convex, i.e., the water film volume is larger than that when the free surfaces are flat, an outward flow develops in the film as observed in the space experiment. However, when the free surfaces are concave, the simulation predicts an inward flow.
Single string based global optimizer for geometry optimization in strongly coupled finite clusters: An adaptive mutation-driven strategy
Authors: Sarkar Kanchan , Bhattacharyya S. P.
Published: August 2013

We propose and implement a simple adaptive heuristic to optimize the geometries of clusters of point charges or ions with the ability to find the global minimum energy configurations. The approach uses random mutations of a single string encoding the geometry and accepts moves that decrease the energy. Mutation probability and mutation intensity are allowed to evolve adaptively on the basis of continuous evaluation of past explorations. The resulting algorithm has been called Completely Adaptive Random Mutation Hill Climbing method. We have implemented this method to search through the complex potential energy landscapes of parabolically confined 3D classical Coulomb clusters of hundreds or thousands of charges—usually found in high frequency discharge plasmas. The energy per particle (EN/N) and its first and second differences, structural features, distribution of the oscillation frequencies of normal modes, etc., are analyzed as functions of confinement strength and the number of charges in the system. Certain magic numbers are identified. In order to test the feasibility of the algorithm in cluster geometry optimization on more complex energy landscapes, we have applied the algorithm for optimizing the geometries of MgO clusters, described by Coulomb–Born-Mayer potential and finding global minimum of some Lennard-Jones clusters. The convergence behavior of the algorithm compares favorably with those of other existing global optimizers.
Kosaki-Longo index and classification of charges in 2D quantum spin models
Authors: Naaijkens Pieter
Published: August 2013

We consider charge superselection sectors of two-dimensional quantum spin models corresponding to cone localisable charges, and prove that the number of equivalence classes of such charges is bounded by the Kosaki-Longo index of an inclusion of certain observable algebras. To demonstrate the power of this result we apply the theory to the toric code on a 2D infinite lattice. For this model we can compute the index of this inclusion, and conclude that there are four distinct irreducible charges in this model, in accordance with the analysis of the toric code model on compact surfaces. We also give a sufficient criterion for the non-degeneracy of the charge sectors, in the sense that Verlinde's matrix S is invertible.
Numerical investigation on the primary breakup of an inelastic non-Newtonian liquid jet with inflow turbulence
Authors: Zhu Chengxiang , Ertl Moritz , Weigand Bernhard
Published: August 2013

Direct Numerical Simulations of the primary breakup of an inelastic non-Newtonian liquid jet with inflow turbulence are presented in this paper. The jet's structure, surface behavior, non-Newtonian characteristics as well as its specific breakup mechanism are investigated and discussed. The shear thinning viscosity of the liquid phase plays an important role during jet injection resulting in circumferential rotation of interfacial waves. Streamwise contra-rotating vortex pairs as well as triple vortex structures are observed in the liquid phase. The local Ohnesorge number, which has a branch-structure distribution in the liquid phase before disintegration, is found to be 30% smaller in regions near the nozzle exit and in the shear layer than in the jet tip, suggesting a clear non-Newtonian influence. A cavity breakup mechanism for this type of non-Newtonian jet is identified and explained, giving a new perspective for jet disintegration analysis.
Dynamics of stimulated L → H transitions
Authors: Miki K. , Diamond P. H. , Hahn S.-H. , Xiao W. W. , Gürcan Ö. D. , Tynan G. R.
Published: August 2013

We report on model studies of stimulated L → H transitions [K. Miki et al., Phys. Rev. Lett. 110, 195002 (2013)]. These studies use a reduced mesoscale model. Model studies reveal that L → H transition can be triggered by particle injection into a subcritical state (i.e., P<PThresh). Particle injection changes edge mean flow shear via changes of density and temperature gradients. The change of edge mean flow shear is critical to turbulence collapse and the subsequent stimulated transition. For low ambient heating, strong injection is predicted to trigger a transient turbulence collapse. Repetitive injection at a period less than the lifetime of the collapsed state can thus maintain the turbulence collapse and so sustain a driven H-mode-like state. The total number of particles required to induce a transition by either injection or gas puffing is estimated. Results indicate that the total number of injected particles required is much smaller than that required for a transition by gas puffing. We thus show that internal injection is more efficient than gas puffing of comparable strength. We also observe that zonal flows do not play a critical role in stimulated transitions. For spontaneous transitions, the spike of the Reynolds work of turbulence on the zonal flow precedes the spike in the mean electric field shear. In contrast, we show that the two are coincident for stimulated transitions, suggesting that there is no causal link between zonal and mean flows for stimulated transitions.
Linearly exact parallel closures for slab geometry
Authors: Ji Jeong-Young , Held Eric D. , Jhang Hogun
Published: August 2013

Parallel closures are obtained by solving a linearized kinetic equation with a model collision operator using the Fourier transform method. The closures expressed in wave number space are exact for time-dependent linear problems to within the limits of the model collision operator. In the adiabatic, collisionless limit, an inverse Fourier transform is performed to obtain integral (nonlocal) parallel closures in real space; parallel heat flow and viscosity closures for density, temperature, and flow velocity equations replace Braginskii's parallel closure relations, and parallel flow velocity and heat flow closures for density and temperature equations replace Spitzer's parallel transport relations. It is verified that the closures reproduce the exact linear response function of Hammett and Perkins [Phys. Rev. Lett. 64, 3019 (1990)] for Landau damping given a temperature gradient. In contrast to their approximate closures where the vanishing viscosity coefficient numerically gives an exact response, our closures relate the heat flow and nonvanishing viscosity to temperature and flow velocity (gradients).
Existence domains of dust-acoustic solitons and supersolitons
Authors: Maharaj S. K. , Bharuthram R. , Singh S. V. , Lakhina G. S.
Published: August 2013

Using the Sagdeev potential method, the existence of large amplitude dust-acoustic solitons and supersolitons is investigated in a plasma comprising cold negative dust, adiabatic positive dust, Boltzmann electrons, and non-thermal ions. This model supports the existence of positive potential supersolitons in a certain region in parameter space in addition to regular solitons having negative and positive potentials. The lower Mach number limit for supersolitons coincides with the occurrence of double layers whereas the upper limit is imposed by the constraint that the adiabatic positive dust number density must remain real valued. The upper Mach number limits for negative potential (positive potential) solitons coincide with limiting values of the negative (positive) potential for which the negative (positive) dust number density is real valued. Alternatively, the existence of positive potential solitons can terminate when positive potential double layers occur.
Electronic structure and electrical transport properties of LaCo1−xNixO3 (0 ≤ x ≤0.5)
Authors: Kumar Vinod , Kumar Rajesh , Shukla D. K. , Gautam Sanjeev , Hwa Chae Keun , Kumar Ravi
Published: August 2013

The structural analysis of LaCo1−xNixO3 (0 ≤ x ≤ 0.5) samples assures single phase rhombohedral structure with space-group R3¯c. Electronic structure of these samples has been studied by x-ray absorption near edge spectroscopy (XANES) at K-edge of O, Ni, Co and M5,4 edge of La. These studies confirm the trivalent state of Co/Ni and La in all the compositions. Upon substitution of the Ni at the Co site in LaCoO3, the O K-edge spectra show a feature about 1.2 eV lower than that of LaCoO3. This feature keeps on growing as the concentration of the Ni is increasing. This is consistent with our resistivity data which shows drastic decrease in resistivity with the Ni substitution. The resistivity data have been analyzed using Arrhenius and Efros-Shklovski's type variable range hopping models in different temperature ranges. The activation energy decreases and localization length increases systematically with increase in the Ni concentration. Observed features have been explained on the basis of change in charge-carrier density with substitution. The disorder-induced localization of carriers is found to govern conduction mechanism and resistivity behavior in substituted sample.
Dynamic separation of electron excitation and lattice heating during the photoinduced melting of the periodic lattice distortion in 2H-TaSe2
Authors: Zhu Pengfei , Cao J. , Zhu Y. , Geck J. , Hidaka Y. , Pjerov S. , Ritschel T. , Berger H. , Shen Y. , Tobey R. , Hill J. P. , Wang X. J.
Published: August 2013

The photoinduced structural dynamics in 2H-TaSe2 in the charge-density wave (CDW) state is investigated using MeV ultrafast electron diffraction. By simultaneously tracking both the melting of the periodic lattice distortion (PLD) associated with the CDW and the lattice heating, following an impulsive photoexcitation, the separate contributions of electronic excitation and lattice thermalization to the melting process are disentangled in the time domain. Two distinct time-constants, reflecting the corresponding individual dynamics of the subsystems, are observed. Our experimental results demonstrate that the PLD in 2H-TaSe2 is first suppressed promptly by the electronic excitation and scattering, and then subsequently by lattice thermalization through electron-phonon interaction, on a much longer time scale. This latter leads to the final, full melting of the PLD.
Amber-green light-emitting diodes using order-disorder AlxIn1−xP heterostructures
Authors: Christian Theresa M. , Beaton Daniel A. , Mukherjee Kunal , Alberi Kirstin , Fitzgerald Eugene A. , Mascarenhas Angelo
Published: August 2013

We demonstrate amber-green emission from AlxIn1–xP light-emitting diodes (LEDs) with luminescence peaked at 566 nm and 600 nm. The LEDs are metamorphically grown on GaAs substrates via a graded InyGa1–yAs buffer layer and feature electron confinement based on the control of AlxIn1–xP CuPt atomic ordering. A control sample fabricated without order-disorder carrier confinement is used to illustrate device improvement up to a factor of 3 in light output due to confinement at drive currents of 40 A/cm2. The light output at room temperature from our AlxIn1–xP LED structure emitting at 600 nm is 39% as bright as a GaxIn1–xP LED emitting at 650 nm.
Oblique ion acoustic shock waves in a magnetized plasma
Authors: Shahmansouri M. , Mamun A. A.
Published: August 2013

Ion acoustic (IA) shock waves are studied in a magnetized plasma consisting of a cold viscous ion fluid and Maxwellian electrons. The Korteweg–de Vries–Burgers equation is derived by using the reductive perturbation method. It is shown that the combined effects of external magnetic field and obliqueness significantly modify the basic properties (viz., amplitude, width, speed, etc.) of the IA shock waves. It is observed that the ion-viscosity is a source of dissipation, and is responsible for the formation of IA shock structures. The implications of our results in some space and laboratory plasma situations are discussed.
Nonlinear optical properties of Bi2O3-GeO2 glass at 800 and 532 nm
Authors: Oliveira Tâmara R. , Falcão-Filho Edilson L. , de Araújo Cid B. , da Silva Diego S. , Kassab Luciana R. P. , da Silva Davinson M.
Published: August 2013

The nonlinear (NL) optical properties of glassy xBi2O3-(1−x) GeO2 with x = 0.72 and 0.82 were investigated. The experiments were performed with lasers at 800 nm (pulses of 150 fs) and 532 nm (pulses of 80 ps and 250 ns). Using the Kerr gate technique, we observed that the NL response of the samples at 800 nm is faster than 150 fs. NL refraction indices, |n2|≈ 5 × 10−16 cm2/W, and two-photon absorption coefficients, α2, smaller than 0.03 cm/GW, were measured at 800 nm. At 532 nm, we measured the NL transmittance of the samples. From the results obtained, we determined α2 ≈1 cm/GW and excited-state absorption cross-sections of ≈10−22 cm2 due to free-carriers.
Characterisation of a MeV Bremsstrahlung x-ray source produced from a high intensity laser for high areal density object radiography
Authors: Courtois C. , Edwards R. , Compant La Fontaine A. , Aedy C. , Bazzoli S. , Bourgade J. L. , Gazave J. , Lagrange J. M. , Landoas O. , Dain L. Le , Mastrosimone D. , Pichoff N. , Pien G. , Stoeckl C.
Published: August 2013

Results of an experiment to characterise a MeV Bremsstrahlung x-ray emission created by a short (<10 ps) pulse, high intensity (1.4 × 1019 W/cm2) laser are presented. X-ray emission is characterized using several diagnostics; nuclear activation measurements, a calibrated hard x-ray spectrometer, and dosimeters. Results from the reconstructed x-ray energy spectra are consistent with numerical simulations using the PIC and Monte Carlo codes between 0.3 and 30 MeV. The intense Bremsstrahlung x-ray source is used to radiograph an image quality indicator (IQI) heavily filtered with thick tungsten absorbers. Observations suggest that internal features of the IQI can be resolved up to an external areal density of 85 g/cm2. The x-ray source size, inferred by the radiography of a thick resolution grid, is estimated to be approximately 400 μm (full width half maximum of the x-ray source Point Spread Function).
Variation of c-axis correlation on vortex pinning by ab-plane non-superconducting layers in YBa2Cu3O7 films
Authors: Horide Tomoya , Murayama Takuto , Takata Kaoru , Matsumoto Kaname , Mele Paolo , Yoshida Yutaka , Ichino Yusuke , Awaji Satoshi
Published: August 2013

In YBa2Cu3O7 (YBCO) + BaSnO3 (BSO)/PrBa2Cu3O7 (PrBCO) multilayer films, behavior of vortices pinned by BSO nanorods was evaluated to discuss influence of ab-plane non-superconducting layers on c-axis correlated vortex pinning. Critical current density (Jc) and activation energy for thermally activated flux flow in magnetic field parallel to the c-axis were reduced by the PrBCO layers and a c-axis peak in an angular dependence of Jc became small, as YBCO + BSO layer thickness decreased or PrBCO layer thickness increased. Irreversibility temperature and trapping angle were not changed by the PrBCO layers for thick YBCO + BSO layers and thin PrBCO layers. This indicates that the ab-plane non-superconducting layers accelerated the vortex motion along the ab-plane without changing the vortex structure. Thin YBCO + BSO layers or thick PrBCO layers resulted in much more drastic degradation of the c-axis correlated vortex pinning due to two dimensional vortex nature or partially prevailed vortex structure, which decreased not only Jc and activation energy, but also irreversibility temperature and trapping angle. Thus, the c-axis correlation of vortex pinning is varied by addition of the ab-plane non-superconducting layers.
Temporal evolution and scaling of mixing in two-dimensional Rayleigh-Taylor turbulence
Authors: Zhou Quan
Published: August 2013

We report a high-resolution numerical study of two-dimensional (2D) miscible Rayleigh-Taylor (RT) incompressible turbulence with the Boussinesq approximation. An ensemble of 100 independent realizations were performed at small Atwood number and unit Prandtl number with a spatial resolution of 2048 × 8193 grid points. Our main focus is on the temporal evolution and the scaling behavior of global quantities and of small-scale turbulence properties. Our results show that the buoyancy force balances the inertial force at all scales below the integral length scale and thus validate the basic force-balance assumption of the Bolgiano-Obukhov scenario in 2D RT turbulence. It is further found that the Kolmogorov dissipation scale η(t) ∼ t1/8, the kinetic-energy dissipation rate ɛu(t) ∼ t−1/2, and the thermal dissipation rate ɛθ(t) ∼ t−1. All of these scaling properties are in excellent agreement with the theoretical predictions of the Chertkov model [“Phenomenology of Rayleigh-Taylor turbulence,” Phys. Rev. Lett. 91, 115001 (2003)]10.1103/PhysRevLett.91.115001. We further discuss the emergence of intermittency and anomalous scaling for high order moments of velocity and temperature differences. The scaling exponents \documentclass[12pt]{minimal}\begin{document}$\xi ^r_p$\end{document}ξpr of the pth-order temperature structure functions are shown to saturate to \documentclass[12pt]{minimal}\begin{document}$\xi ^r_{\infty }\simeq 0.78 \pm 0.15$\end{document}ξ∞r≃0.78±0.15 for the highest orders, p ∼ 10. The value of \documentclass[12pt]{minimal}\begin{document}$\xi ^r_{\infty }$\end{document}ξ∞r and the order at which saturation occurs are compatible with those of turbulent Rayleigh-Bénard (RB) convection [A. Celani, T. Matsumoto, A. Mazzino, and M. Vergassola, “Scaling and universality in turbulent convection,” Phys. Rev. Lett. 88, 054503 (2002)]10.1103/PhysRevLett.88.054503, supporting the scenario of universality of buoyancy-driven turbulence with respect to the different boundary conditions characterizing the RT and RB systems.
Nonlinear resonance absorption of laser in an inhomogeneous plasma
Authors: Rajouria Satish Kumar , K K Magesh Kumar , Tripathi V. K.
Published: August 2013

A formalism of nonlinear resonance absorption of p-polarized laser in a plasma with density gradient is developed. The nonlinearity is taken to arise through the relativistic mass effect. As the laser incident at an angle to the density gradient approaches the turning point, dielectric swelling leads to field enhancement, causing strong electron mass enhancement and reduction in local plasma frequency. When the critical layer is within a laser wavelength away from the turning point, the laser field is greatly enhanced at the critical layer and absorption of the laser is strongly affected by the nonlinear effect.
Nonlinear interaction of intense electromagnetic waves with a magnetoactive electron-positron-ion plasma
Authors: Khorashadizadeh S. M. , Rastbood E. , Zeinaddini Meymand H. , Niknam A. R.
Published: August 2013

The nonlinear coupling between circularly polarized electromagnetic (CPEM) waves and acoustic-like waves in a magnetoactive electron-positron-ion (e-p-i) plasma is studied, taking into account the relativistic motion of electrons and positrons. The possibility of modulational instability and its growth rate as well as the envelope soliton formation and its characteristics in such plasmas are investigated. It is found that the growth rate of modulation instability increases in the case that ωc/ω<1 (ωc and ω are the electron gyrofrequency and the CPEM wave frequency, respectively) and decreases in the case that ωc/ω>1. It is also shown that in a magnetoactive e-p-i plasma, the width of bright soliton increases/decreases in case of (ωc/ω)<1/(ωc/ω)>1 by increasing the magnetic field strength.
Integer quantum Hall effect in single-layer graphene with tilted magnetic field
Authors: Krstajić P. M.
Published: August 2013

Analytical expression for the Hall conductivity σyx in graphene is derived in more general case, in which magnetic field is not perpendicular to the plane of the sample. The derivations were carried out using Kubo-Greenwood formulism, which is more suitable when the spectrum is discrete. The results are analyzed as a function of the angle between the magnetic field vector and the normal of the graphene plane. Contrary to the previous theoretical studies, we show that the plateau levels are independent of the direction of the magnetic field. The positions of the plateaus, however, depend on the orientation of the magnetic field.
Fusion alpha-particle losses in a high-beta rippled tokamak
Authors: Bunno M. , Nakamura Y. , Suzuki Y. , Shinohara K. , Matsunaga G. , Tani K.
Published: August 2013

In tokamak plasmas, the confinement of energetic ions depends on the magnetic field structure. If the plasma pressure is finite, the equilibrium current (i.e., the Pfirsch-Schlüter current and diamagnetic current) flows in the plasma to maintain the magnetohydrodynamic (MHD) equilibrium. These plasma currents generate poloidal and toroidal magnetic field and alter the field structure. Moreover, if we consider the non-axisymmetry of magnetic field structures such as toroidal field (TF) ripples, the non-axisymmetric component of the equilibrium current can alter TF ripples themselves. When the plasma beta becomes high, the changes in the field structure due to the equilibrium current might affect the confinement of energetic ions significantly. We intend to clarify how these currents alter the field structure and affect the confinement of alpha particles in high-beta plasma. The MHD equilibrium is calculated using VMEC and the orbits of fusion alpha particles are followed by using the fully three-dimensional magnetic field orbit-following Monte Carlo code. In relatively low-beta plasma (e.g., the volume-averaged beta value ⟨β⟩≤2%), the changes in the magnetic field component due to the plasma current negligibly affect the confinement of alpha particles except for the Shafranov shift effect. However, for ⟨β⟩≥3%, the diamagnetic effect reduces the magnetic field strength and significantly increases alpha-particle losses. In these high-beta cases, the non-axisymmetric field component generated by the equilibrium current also increases these losses, but not as effectively as compared to the diamagnetic effect.
Electronic properties of graphene nanoribbons with periodically hexagonal nanoholes
Authors: Tian W. , Zeng Y. C. , Zhang Z. H.
Published: August 2013

By using the first-principles method based on the density-functional theory, electronic properties of graphene nanoribbons punched with periodic nanoholes (GNRPNHs) are studied systematically. It has been shown that the zigzag-edge GNRPNH at the nonmagnetic state is always metal regardless of neck widths, but its metallic properties is obviously weakened due to nanohole effects, and at the anti-ferromagnetic states, its spin degeneracy still remains and the energy gap has only a smaller change. While for armchair-edge GNRPNHs, the situations are complicated. As compared with the perfect AGNRs, their band gaps become smaller or larger depending on the ribbon widths satisfying W = 3p + 1, 3p, or 3p − 1. The analysis in depth shows that underlying origins are closely related to the width and edge shape (zigzag or armchair) of the neck subprime nanoribbon and edge subprime nanoribbon, which leads to the different quantum confinement effect. And also shown is the phenomenon of the odd-even oscillation for the band gap with the change of the neck width. These findings presented here provide theoretical references for experimentally punching desirable periodic nanoholes on the graphene nanoribbons to meet the special characteristics requirements of nanodevices.
Two-band k · p model for Si-(110) electron devices
Authors: Donetti Luca , Gámiz Francisco , Biel Blanca , Sampedro Carlos
Published: August 2013

Carrier transport in Si-(110) surfaces is a topic of growing interest because of its presence in the lateral interfaces of vertical structures, such as FinFETs or tri-gate devices. It has been shown that the parabolic effective mass model cannot explain the experimental behavior of electron mobility in Si-(110) surfaces, and the strongly non-parabolic conduction band structure obtained by more accurate (and complex) methods is needed. A simpler model that can reproduce the required non-parabolic features of conduction band structure is described by a two-band k · p Hamiltonian. In this paper, we show the analytic solution of such a model for a square-well potential and a numerical implementation in a coupled Poisson-Schrödinger solver and one-particle Monte Carlo simulator. The electron mobility calculations are in good agreement with experimental results for bulk MOSFETs and SOI devices.
Low temperature growth of ultra-high mass density carbon nanotube forests on conductive supports
Authors: Sugime Hisashi , Esconjauregui Santiago , Yang Junwei , D'Arsié Lorenzo , Oliver Rachel A. , Bhardwaj Sunil , Cepek Cinzia , Robertson John
Published: August 2013

We grow ultra-high mass density carbon nanotube forests at 450 °C on Ti-coated Cu supports using Co-Mo co-catalyst. X-ray photoelectron spectroscopy shows Mo strongly interacts with Ti and Co, suppressing both aggregation and lifting off of Co particles and, thus, promoting the root growth mechanism. The forests average a height of 0.38 μm and a mass density of 1.6 g cm−3. This mass density is the highest reported so far, even at higher temperatures or on insulators. The forests and Cu supports show ohmic conductivity (lowest resistance ∼22 kΩ), suggesting Co-Mo is useful for applications requiring forest growth on conductors.
A molecular dynamics investigation on mechanical properties of hydrogenated graphynes
Authors: Zhang Ying-Yan , Pei Qing-Xiang , Wang Chien-Ming , Cheng Yuan , Zhang Yong-Wei
Published: August 2013

Graphyne, a new type of carbon allotropes, has attracted considerable attention in recent years. Using molecular dynamics simulations, we investigate the mechanical properties of four different graphynes (α-, β-, γ-, and 6,6,12-graphynes) functionalized with hydrogen. The simulations results show that hydrogenation can greatly deteriorate the mechanical properties of the graphynes. For the different graphynes with 100% H-coverage, the reduction in fracture stress depends on the percentage of acetylenic linkages in the graphyne structures: The more the acetylenic linkages, the larger the reduction. For the same graphyne, the reduction in fracture stress depends on the hydrogenation location, distribution, and coverage. Hydrogenation on the acetylenic linkages causes a larger reduction in fracture stress than that on the hexagonal rings. A line hydrogenation perpendicular to the tensile direction leads to a larger reduction in fracture stress than that when the line hydrogenation is parallel to the tensile direction. For random hydrogenation, the fracture stress and Young's modulus decrease rapidly at low H-coverage (<10%), and then level off with increasing coverage. The reduction in the mechanical properties due to hydrogenation is found to be related to the formation of weakened out-of-plane C-C bonds, which leads to earlier breaking of those bonds and subsequent fracture of the graphynes. The present study not only offers an in-depth understanding in the mechanical properties of hydrogenated graphynes and their fracture mechanisms but it also presents an important database for the design and practical applications of hydrogenated graphynes.
Anisotropic resistivities in anisotropic-strain-controlled phase-separated La0.67Ca0.33MnO3/NdGaO3(100) films
Authors: Wang L. F. , Tan X. L. , Chen P. F. , Zhi B. W. , Sun Z. G. , Huang Z. , Gao G. Y. , Wu W. B.
Published: August 2013

The anisotropic resistivities (AR) in La0.67Ca0.33MnO3 films grown on orthorhombic NdGaO3(100) substrates were investigated. In this epitaxial system, the large anisotropic misfit strain was demonstrated to induce an antiferromagnetic insulator (AFI) phase transition near ∼250 K, leading to phase separation (PS) with the coexistence of AFI and ferromagnetic-metal (FM) phases at the temperature below. In the PS regime, the resistivity measured along the highly strained b-axis is greater than that along c-axis, giving rise to a huge AR. It can reach ∼12 500% and shows strong dependence on the amplitude and orientation of the magnetic field. We ascribed this unusual AR to the anisotropic-strain-controlled MnO6 octahedral deformations which can organize the competing AFI and FM phases into orientation-preferred PS pattern, thus resulting in the anisotropic percolative transport.
Phase transition characteristics of Al-Sb phase change materials for phase change memory application
Authors: Zhou Xilin , Wu Liangcai , Song Zhitang , Rao Feng , Ren Kun , Peng Cheng , Song Sannian , Liu Bo , Xu Ling , Feng Songlin
Published: August 2013

The crystallization behavior of Al-Sb thin films is investigated for phase change memory application. The crystallization temperature and optical band gap of the amorphous material increase with Al content. The thermal stability and randomness in atomic configuration of the films are enhanced considerably. The shift of Raman modes associated mainly with Sb upon phase transformation is observed, and the co-existence of Sb-rich crystalline regions and Al-rich amorphous matrix is confirmed, revealing the amorphous nature of most Al components. Three distinct resistance levels are achieved in the devices using Al50Sb50, suggesting the potentiality for multilevel data storage application of the materials.
In-plane magnetic field dependence of electric field-induced magnetization switching
Authors: Kanai S. , Nakatani Y. , Yamanouchi M. , Ikeda S. , Matsukura F. , Ohno H.
Published: August 2013

Electric field-induced magnetization switching through magnetization precession is investigated as a function of in-plane component of external magnetic field for a CoFeB/MgO-based magnetic tunnel junction with perpendicular easy axis. The switching probability is an oscillatory function of the duration of voltage pulses and its magnitude and period depend on the magnitude of in-plane magnetic field. Experimental results are compared with simulated ones by using Landau-Lifshitz-Gilbert-Langevin equation, and possible factors determining the probability are discussed.
Enhanced microwave shielding effectiveness of ultrathin pyrolytic carbon films
Authors: Batrakov K. , Kuzhir P. , Maksimenko S. , Paddubskaya A. , Voronovich S. , Kaplas T. , Svirko Yu.
Published: August 2013

Electromagnetic properties of pyrolytic carbon (PyC) films with thickness from 5 to 241 nm are studied experimentally and numerically at 28 GHz. We observe experimentally that PyC films are capable to absorb up to 50% of microwave power in the Ka-band. By using boundary conditions in the rectangular waveguide, we demonstrate theoretically that 50% of microwave power can be absorbed in a conductive film with thickness much smaller than the skin depth. The results of modelling for PyC films on silica substrate are in excellent coincidence with the experimental data.
Fluctuations from edge defects in superconducting resonators
Authors: Neill C. , Megrant A. , Barends R. , Chen Yu , Chiaro B. , Kelly J. , Mutus J. Y. , O'Malley P. J. J. , Sank D. , Wenner J. , White T. C. , Yin Yi , Cleland A. N. , Martinis John M.
Published: August 2013

Superconducting resonators, used in astronomy and quantum computation, couple strongly to microscopic two-level defects. We monitor the microwave response of superconducting resonators and observe fluctuations in dissipation and resonance frequency. We present a unified model where the observed dissipative and dispersive effects can be explained as originating from a bath of fluctuating two-level systems. From these measurements, we quantify the number and distribution of the defects.
Large-scale molecular dynamics simulations of wear in diamond-like carbon at the nanoscale
Authors: Sha Zhen-Dong , Sorkin Viacheslav , Branicio Paulo S. , Pei Qing-Xiang , Zhang Yong-Wei , Srolovitz David J.
Published: August 2013

We perform large-scale molecular dynamics simulations on diamond-like carbon to study wear mechanism and law at the nanoscale. Our simulations show that material loss during sliding varies linearly with normal load and sliding distance, consistent with Archard's law. Our simulations also show that the number of chemical bonds across the contact interface during sliding correlates well with friction force, but not with material loss, indicating that friction and wear follow different mechanisms. Our analysis reveals the following wear mechanism: the shear traction causes mass accumulation at the trailing end of contact, which is then lost by a cluster detachment process.
Flat lens for pulse focusing of elastic waves in thin plates
Authors: Dubois M. , Farhat M. , Bossy E. , Enoch S. , Guenneau S. , Sebbah P.
Published: August 2013

The ability of left-handed materials to overcome the diffraction limit was first considered as one of the most exciting and challenging outcomes of the negative refraction concept. Flat lens focusing of elastic waves is, however, a challenge. We demonstrate broadband focusing of elastic waves at 10 kHz carrier frequency, below the first stop band, in a 45°-tilted square array of circular air holes perforated in a Duraluminium thin plate. By adjusting the relative thickness of the outer plate we achieve large-angle negative refraction with diffraction-limited lateral resolution. We find good agreement with a simple beam-lattice model and finite-difference time-domain simulations.
Communication: Electronic UV-Vis transient spectra of the ·OH reaction products of uracil, thymine, cytosine, and 5,6-dihydrouracil by using the complete active space self-consistent field second-order perturbation (CASPT2//CASSCF) theory
Authors: Francés-Monerris Antonio , Merchán Manuela , Roca-Sanjuán Daniel
Published: August 2013

Addition of ·OH radicals to pyrimidine nucleobases is a common reaction in DNA/RNA damage by reactive oxygen species. Among several experimental techniques, transient absorption spectroscopy has been during the last decades used to characterize such compounds. Discrepancies have however appeared in the assignment of the adduct or adducts responsible for the reported transient absorption UV-Vis spectra. In order to get an accurate assignment of the transient spectra and a unified description of the absorption properties of the ·OH reaction products of pyrimidines, a systematic complete active space self-consistent field second-order perturbation (CASPT2//CASSCF) theory study has been carried out on the uracil, thymine, and cytosine ·OH addition adducts, as well as on the 5,6-dihydrouracil hydrogen abstraction products. With the obtained findings, the C5OH contributions to the lowest-energy band can be finally discarded. Instead, a bright 2(π2) state of the C6OH adducts is determined to be the main responsible in all compounds for the absorption band in the Vis range.
Communication: Infrared spectroscopy of protonated allyl-trimethylsilane: Evidence for the β-silyl effect
Authors: Chiavarino Barbara , Crestoni Maria Elisa , Lemaire Joel , Maitre Philippe , Fornarini Simonetta
Published: August 2013

β-trimethylsilyl-2-propyl cation has been formed by the gas phase protonation of allyl-trimethylsilane and characterized by infrared multiple photon dissociation spectroscopy. The experimental Cβ-Cα+ stretching feature at 1586 cm−1, remarkably blue-shifted with respect to a C−C single bond stretching mode, is indicative of high double bond character, a signature of β-stabilizing effect due to hyperconjugation of the trimethylsilyl group in the β-position with respect to the positively charged carbon. Density functional theory calculations at the B3LYP/6-311++G(2df,2p) level yield the optimized geometries and IR spectra for candidate isomeric cations and for neutral and charged reference species.
Optical properties of monoclinic HfO2 studied by first-principles local density approximation + U approach
Authors: Li Jinping , Han Jiecai , Meng Songhe , Lu Hantao , Tohyama Takami
Published: August 2013

The band structures and optical properties of monoclinic HfO2 are investigated by the local density approximation + U approach. With the on-site Coulomb interaction being introduced to 5d orbitals of Hf atom and 2p orbitals of O atom, the experimental band gap is reproduced. The imaginary part of the complex dielectric function shows a small shoulder at the edge of the band gap, coinciding with the experiments. This intrinsic property of crystallized monoclinic HfO2, which is absent in both the tetragonal phase and cubic phase, can be understood as a consequence of the reconstruction of the electronic states near the band edge following the adjustment of the crystal structure. The existence of a similar shoulder-like-structure in the monoclinic phase of ZrO2 is predicted.
Hydrodynamic analysis of laser-driven cylindrical implosions
Authors: Ramis R.
Published: August 2013

Three-dimensional hydrodynamic simulations are performed to study laser-driven cylindrical implosions in the context of experiments (F. Perez et al., Plasma Phys. Controlled Fusion 51, 124035 (2009)) carried out at the Rutherford Appleton Laboratory in the framework of the HiPER project. The analysis is carried out by using the 3D version of the hydrocode MULTI (R. Ramis et al., Comput. Phys. Commun. 49, 475-505 (1988)). The influence of the main laser parameters on implosion performance and symmetry is consistently studied and compared with the results of 2D analysis. Furthermore, the effects of uncertainties in laser irradiation (pointing, focusing, power balance, and time jitter) on implosion performance (average peak density and temperature) are studied by means of statistical analysis.
Spintronics in a magnetic quantum dot
Authors: Ghosh Angsula , Frota H. O.
Published: August 2013

Spintronics or spin electronics has been a growing area of research based on the active control and manipulation of spin degrees of freedom. In this work, we study the thermoelectric properties of a quantum dot using the Anderson model in presence of the repulsive Coulomb interaction within the mean-field formalism. The temperature difference applied across the dot drives a spin current which depends on the temperature and chemical potential. We demonstrate that the quantum dot in presence of the Coulomb interaction behaves as a spin filter for selected values of the chemical potential and is able to filter electrons by their spin orientation. The spin thermopower has also been studied where the effects of the impurity energy level, temperature and also the Coulomb term have been observed.
Pressure-induced transformation and superhard phase in fullerenes: The effect of solvent intercalation
Authors: Yao Mingguang , Cui Wen , Xiao Junping , Chen Shuanglong , Cui Jinxing , Liu Ran , Cui Tian , Zou Bo , Liu Bingbing , Sundqvist Bertil
Published: August 2013

We studied the behavior of solvated and desolvated C60 crystals under pressure by in situ Raman spectroscopy. The pressure-induced bonding change and structural transformation of C60s are similar in the two samples, both undergoing deformation and amorphization. Nevertheless, the high pressure phases of solvated C60 can indent diamond anvils while that of desolvated C60s cannot. Further experiments suggest that the solvents in the solvated C60 act as both spacers and bridges by forming covalent bonds with neighbors in 3D network at high pressure, and thus, a fraction of fullerenes may preserve the periodic arrangement in spite of their amorphization.
Hot spot runaway in thin film photovoltaics and related structures
Authors: Karpov V. G. , Vasko A. , Vijh A.
Published: August 2013

We show that thin film diode structures, such as photovoltaics and light emitting arrays, can undergo zero threshold localized thermal runaway leading to thermal and electrical nonuniformities spontaneously emerging in originally uniform systems. The linear stability analysis is developed for a system of thermally and electrically coupled two discrete diodes, and for a distributed system. These results are verified with numerical modeling that is not limited to small fluctuations. The discovered instability negatively affects the device performance and reliability. It follows that these problems can be mitigated by properly designing the device geometry and thermal insulation.
Experimental study of optimized surface-plasmon-mediated tunneling in metal-dielectric multilayers
Authors: Zhang M. C. , Allen T. W. , DeCorby R. G.
Published: August 2013

We describe experimental work on the optimization of surface-plasmon-mediated tunneling through symmetric dielectric-metal-dielectric multilayers. Samples were deposited using an electron-beam evaporator, and optical characterization was performed using a custom-built prism-coupler setup. Experimental results are in good agreement with theoretical predictions. Samples containing ∼120 nm total thickness of silver, equivalent to ∼10 skin depths, exhibit peak transmittance ∼0.7 at the 632 nm design wavelength. The results point to the practical utility of admittance-matching techniques and potential transmittance theory, and provide insights for research on plasmonics, metamaterials, and superlenses.