bluuebunny/crossref_metadata_2025 huggingface dataset:
Information Retention and Overload in First-Time Hearing Aid Users: An Interactive Multimedia Educational Solution
Authors: Ferguson Melanie , Brandreth Marian , Brassington William , Wharrad Heather
Published: August 2015

Purpose

An educational intervention to improve knowledge of hearing aids and communication in first-time hearing aid users was assessed. This intervention was based on the concept of reusable learning objects (RLOs).

Method

A randomized controlled trial was conducted. One group received the educational intervention, and the other acted as a control group. RLOs were delivered online and through DVD for television and personal computer. Knowledge of both practical and psychosocial aspects of hearing aids and communication was assessed using a free-recall method 6 weeks postfitting.

Results

Knowledge of both practical and psychosocial issues was significantly higher in the group that received the RLOs than in the control group. Moderate to large effect sizes indicated that these differences were clinically significant.

Conclusion

An educational intervention that supplements clinical practice results in improved knowledge in first-time hearing aid users.
Improving isolation of slot‐coupled directional couplers with weak and tight couplings
Authors: Moradian Mahdi
Published: August 2015

A suitable method for improving the isolation of slot‐coupled directional couplers with elliptical‐shaped slot and patches is introduced. It is shown that the even‐ and odd‐mode phase velocities depend on the width of the patches and slot of the slot‐coupled directional couplers. For couplers with tight couplings, the even‐ and odd‐mode phase velocities can be effectively equalised by cutting some parallel slots into the patches, while for couplers with weak couplings, the even‐ and odd‐mode phase velocities can be equalised by cutting some teeth into exterior part of the slot in the common ground plane. For various slot lengths and tooth depths, various design graphs are derived by sweeping some dimensions of the coupler. On the basis of the design graphs, three couplers with tight, moderate and weak couplings are designed and simulated. The designed coupler with tight coupling is also constructed and tested. The results show that by employing the proposed method, the isolation of the slot‐coupled directional couplers has improved significantly.
Current harmonics compensation with three‐phase four‐wire shunt hybrid active power filter based on modified D–Q theory
Authors: Dey Papan , Mekhilef Saad
Published: August 2015

This study presents a D–Q current control method with modified phase lock loop to generate the required reference current for shunt hybrid active filter (SHAPF) to improve the power quality. The performance of the proposed controller has been evaluated in terms of harmonic current mitigation and reactive power compensation under different grid conditions. Here, the passive elements of SHAPF have been used for compensation of lower order harmonics and the active part mitigates the higher order harmonics. Proportional–integral controller is considered here for DC‐link voltage regulation of the inverter. For verification, the proposed controller of SHAPF is compared with the conventional SHAPF controllers. Extensive simulations of the proposed technique are carried out through MATLAB–SIMULINK environment. A laboratory prototype has been built on dSPACE1104 platform to verify the feasibility of the suggested SHAPF controller. From the simulation and experimental results, the robustness of the proposed SHAPF controller is proved.
Analysis and prediction of the discharge characteristics of the lithium–ion battery based on the Grey system theory
Authors: Chen Lin , Tian Binbin , Lin Weilong , Ji Bing , Li Junzi , Pan Haihong
Published: August 2015

The capacity/state‐of‐charge (SoC) and voltage of lithium–ion batteries are of prime importance in electric vehicles (EVs), so their condition‐monitoring techniques are extensively studied. This study focuses on the application of the grey system theory to the parameters analysing and predicting behaviour during the discharge/charge cycles of the battery. First, Grey relation analysis is applied to study and analyse the relationship between capacity/SoC and various influencing factors. Second, the segment Grey prediction model is proposed in order to test and improve the accuracy of the capacity/SoC prediction. Finally, based on the ageing data from the National Aeronautics and Space Administration Prognostics Data Repository, the effects of different Grey theory models, such as the GM(1,1), the Verhulst model and the segment Grey prediction model, are investigated. The results show that: (i) the GRA is efficient in figuring out the relationship between the capacity/SoC and various influencing factors; (ii) the segment Grey prediction model is an effective mode of prediction for EV batteries, because its accuracy is more reliable than other two Grey models; and (iii) the segment Grey prediction model is suitable for predicting the capacity/SoC of batteries under various loading conditions.
Spatially resolved band alignments at Au-hexadecanethiol monolayer-GaAs(001) interfaces by ballistic electron emission microscopy
Authors: Junay A. , Guézo S. , Turban P. , Delhaye G. , Lépine B. , Tricot S. , Ababou-Girard S. , Solal F.
Published: August 2015

We study structural and electronic inhomogeneities in Metal—Organic Molecular monoLayer (OML)—semiconductor interfaces at the sub-nanometer scale by means of in situ Ballistic Electron Emission Microscopy (BEEM). BEEM imaging of Au/1-hexadecanethiols/GaAs(001) heterostructures reveals the evolution of pinholes density as a function of the thickness of the metallic top-contact. Using BEEM in spectroscopic mode in non-short-circuited areas, local electronic fingerprints (barrier height values and corresponding spectral weights) reveal a low-energy tunneling regime through the insulating organic monolayer. At higher energies, BEEM evidences new conduction channels, associated with hot-electron injection in the empty molecular orbitals of the OML. Corresponding band diagrams at buried interfaces can be thus locally described. The energy position of GaAs conduction band minimum in the heterostructure is observed to evolve as a function of the thickness of the deposited metal, and coherently with size-dependent electrostatic effects under the molecular patches. Such BEEM analysis provides a quantitative diagnosis on metallic top-contact formation on organic molecular monolayer and appears as a relevant characterization for its optimization.
Global stability and sensitivity analysis of boundary-layer flows past a hemispherical roughness element
Authors: Citro V. , Giannetti F. , Luchini P. , Auteri F.
Published: August 2015

We study the full three-dimensional instability mechanism past a hemispherical roughness element immersed in a laminar Blasius boundary layer. The inherent three-dimensional flow pattern beyond the Hopf bifurcation is characterized by coherent vortical structures usually called hairpin vortices. Direct numerical simulation results are used to analyze the formation and the shedding of hairpin vortices inside the shear layer. The first bifurcation is investigated by global-stability tools. We show the spatial structure of the linear direct and adjoint global eigenmodes of the linearized Navier-Stokes equations and use the structural-sensitivity field to locate the region where the instability mechanism acts. The core of this instability is found to be symmetric and spatially localized in the region immediately downstream of the roughness element. The effect of the variation of the ratio between the obstacle height k and the boundary layer thickness δk∗ is also considered. The resulting bifurcation scenario is found to agree well with previous experimental investigations. A limit regime for k/δk∗<1.5 is attained where the critical Reynolds number is almost constant, Rek ≈ 580. This result indicates that, in these conditions, the only important parameter identifying the bifurcation is the unperturbed (i.e., without the roughness element) velocity slope at the wall.
Near band-gap electronics properties and luminescence mechanisms of boron nitride nanotubes
Authors: Museur L. , Kanaev A.
Published: August 2015

The deep ultraviolet luminescence (hν ≥ 5 eV) of multiwall boron nitride nanotubes (BNNTs) is studied with time- and energy-resolved photoluminescence spectroscopy. Two luminescence bands are observed at 5.35 and 5.54 eV. Both emissions undergo a large blue shift of several tens of meV with a linear slope ΔElum/ΔEexc < 1 as the excitation energy Eexc increases. When Eexc≥5.8 eV, the spectral band positions become fixed, which marks the transition between the excitation of donor-acceptor pairs and creation of free charge carriers. We assign the 5.35 eV band to quasi donor-acceptor pair transitions and the band at 5.54 eV to free-bound transitions. Boron and nitrogen atoms distributed along characteristic defect lines in BNNTs should be involved in the luminescence process. The presented results permit a revision of previous assignments of electronic transitions in BNNTs.
Analysis of radial and longitudinal force of plasma wakefield generated by a chirped pulse laser
Authors: Ghasemi Leila , Afhami Saeedeh , Eslami Esmaeil
Published: August 2015

In present paper, the chirp effect of an electromagnetic pulse via an analytical model of wakefield generation is studied. Different types of chirps are employed in this study. Our results show that by the use of nonlinear chirped pulse the longitudinal wakefield and focusing force is stronger than that of linear chirped pulse. It is indicated that quadratic nonlinear chirped pulses are globally much efficient than periodic nonlinear chirped pulses. Our calculations also predict that in nonlinear chirped pulse case, the overlap of focusing and accelerating regions is broader than that achieved in linear chirped pulse.
Modified ion-acoustic solitary waves in plasmas with field-aligned shear flows
Authors: Saleem H. , Ali S. , Haque Q.
Published: August 2015

The nonlinear dynamics of ion-acoustic waves is investigated in a plasma having field-aligned shear flow. A Koeteweg-deVries-type nonlinear equation for a modified ion-acoustic wave is obtained which admits a single pulse soliton solution. The theoretical result has been applied to solar wind plasma at 1 AU for illustration.
Asymmetric diffusion of cosmic rays
Authors: Medvedev Mikhail V. , Medvedev Viktor V.
Published: August 2015

Cosmic ray propagation is diffusive because of pitch angle scattering by waves. We demonstrate that if the high-amplitude magnetohydrodynamic turbulence with B̃/〈B〉∼1 is present on top of the mean field gradient, the diffusion becomes asymmetric. As an example, we consider the vertical transport of cosmic rays in our Galaxy propagating away from a point-like source. We solve this diffusion problem analytically using a one-dimensional Markov chain analysis. We obtained that the cosmic ray density markedly differs from the standard diffusion prediction and has a sizable effect on their distribution throughout the galaxy. The equation for the continuous limit is also derived, which shows limitations of the convection-diffusion equation.
Suspensions of polymer-grafted nanoparticles with added polymers—Structure and effective pair-interactions
Authors: Chandran Sivasurender , Saw Shibu , Kandar A. K. , Dasgupta C. , Sprung M. , Basu J. K.
Published: August 2015

We present the results of combined experimental and theoretical (molecular dynamics simulations and integral equation theory) studies of the structure and effective interactions of suspensions of polymer grafted nanoparticles (PGNPs) in the presence of linear polymers. Due to the absence of systematic experimental and theoretical studies of PGNPs, it is widely believed that the structure and effective interactions in such binary mixtures would be very similar to those of an analogous soft colloidal material—star polymers. In our study, polystyrene-grafted gold nanoparticles with functionality f = 70 were mixed with linear polystyrene (PS) of two different molecular weights for obtaining two PGNP:PS size ratios, ξ = 0.14 and 2.76 (where, ξ = Mg/Mm, Mg and Mm being the molecular weights of grafting and matrix polymers, respectively). The experimental structure factor of PGNPs could be modeled with an effective potential (Model-X), which has been found to be widely applicable for star polymers. Similarly, the structure factor of the blends with ξ = 0.14 could be modeled reasonably well, while the structure of blends with ξ = 2.76 could not be captured, especially for high density of added polymers. A model (Model-Y) for effective interactions between PGNPs in a melt of matrix polymers also failed to provide good agreement with the experimental data for samples with ξ = 2.76 and high density of added polymers. We tentatively attribute this anomaly in modeling the structure factor of blends with ξ = 2.76 to the questionable assumption of Model-X in describing the added polymers as star polymers with functionality 2, which gets manifested in both polymer-polymer and polymer-PGNP interactions especially at higher fractions of added polymers. The failure of Model-Y may be due to the neglect of possible many-body interactions among PGNPs mediated by matrix polymers when the fraction of added polymers is high. These observations point to the need for a new framework to understand not only the structural behavior of PGNPs but also possibly their dynamics and thermo-mechanical properties as well.
Fast and efficient charge breeding of the Californium rare isotope breeder upgrade electron beam ion source
Authors: Ostroumov P. N. , Barcikowski A. , Dickerson C. A. , Perry A. , Pikin A. I. , Sharamentov S. I. , Vondrasek R. C. , Zinkann G. P.
Published: August 2015

The Electron Beam Ion Source (EBIS), developed to breed Californium Rare Isotope Breeder Upgrade (CARIBU) radioactive beams at Argonne Tandem Linac Accelerator System (ATLAS), is being tested off-line. A unique property of the EBIS is a combination of short breeding times, high repetition rates, and a large acceptance. Overall, we have implemented many innovative features during the design and construction of the CARIBU EBIS as compared to the existing EBIS breeders. The off-line charge breeding tests are being performed using a surface ionization source that produces singly charged cesium ions. The main goal of the off-line commissioning is to demonstrate stable operation of the EBIS at a 10 Hz repetition rate and a breeding efficiency into single charge state higher than 15%. These goals have been successfully achieved and exceeded. We have measured (20% ± 0.7%) breeding efficiency into the single charge state of 28+ cesium ions with the breeding time of 28 ms. In general, the current CARIBU EBIS operational parameters can provide charge breeding of any ions in the full mass range of periodic table with high efficiency, short breeding times, and sufficiently low charge-to-mass ratio, 1/6.3 for the heaviest masses, for further acceleration in ATLAS. In this paper, we discuss the parameters of the EBIS and the charge breeding results in a pulsed injection mode with repetition rates up to 10 Hz.
A complete description of tunnelling using direct quantum dynamics simulation: Salicylaldimine proton transfer
Authors: Polyak Iakov , Allan Charlotte S. M. , Worth Graham A.
Published: August 2015

We demonstrate here conclusively that the variational multiconfiguration Gaussian (vMCG) method converges to the grid based full quantum dynamics multiconfiguration time-dependent Hartree result for a tunnelling problem in many dimensions, using the intramolecular proton transfer in salicylaldimine as a model system. The 13-dimensional model potential energy surface was obtained from Hartree Fock energies with the 6-31G* basis set and the expectation value of the flux operator along the transition mode was used as a benchmark characteristic. As well as showing excellent convergence of the vMCG method on the model surface using a local harmonic approximation and a moderate number of basis functions, we show that the direct dynamics version of the vMCG also performs very well, usually needs the same number of Gaussians to converge, and converges to exact results if those are obtained on an accurately fitted surface. Finally, we make an important observation that the width of the Gaussian basis functions must be chosen very carefully to obtain accurate results with the use of the frozen-width approximation.
Electronic spectra of oxygen containing polycyclic hydrocarbon cations and the protonated analogues
Authors: Chakraborty Arghya , Fulara Jan , Maier John P.
Published: August 2015

The electronic transitions of 9-fluorenone FL+ and 2,3,6,7-dibenzotropone DBT+ cations were detected in 6 K neon matrices following a mass-selective deposition. The absorptions at 649.2 and 472.2 nm are assigned to the 2 2B1←X̃2A2 FL+ and 22A′←X̃2A′ DBT+ transitions. Absorption spectra of protonated 9-fluorenone H+-FL and 2,3,6,7-dibenzotropone H+-DBT have also been measured. Protonation of the oxygenated polycyclic aromatic hydrocarbons is carried out in a hot cathode source via in situ produced protonated ethanol. Vibrationally resolved absorptions commencing at 423.3 nm of H-FL+ and two band systems of H-DBT+ with origins at 502.4 and 371.5 nm are assigned to the 21A′←X̃1A′ electronic transition of 9-hydroxy-fluorenyl cation and 1 1A←X̃1A, 2 1A←X̃1A of 2,3,6,7-dibenzocycloheptenol cation. The assignments are based on vertical excitation energy calculations with time dependent density functional theory, symmetry adapted cluster configuration interaction, and MS-CASPT2 methods.
Tuning the wavelength of spoof plasmons by adjusting the impedance contrast in an array of penetrable inclusions
Authors: Cordero M. L. , Maurel A. , Mercier J.-F. , Félix S. , Barra F.
Published: August 2015

While spoof plasmons have been proposed in periodic arrays of sound-hard inclusions, we show that they also exist when inclusions are penetrable. Moreover, we show that their wavelength can be tuned by the impedance mismatch between the inclusion material and the surrounding medium, beyond the usual effect of filling fraction in the array. It is demonstrated that sound-soft materials increase the efficiency in the generation of sub-wavelength plasmons, with much lower wavelengths than sound-hard materials and than a homogeneous slab. An application to the generation of acoustic spoof plasmons by an ultra compact array of air/polydimethylsiloxane inclusions in water is proposed with plasmon wavelength tunable up to deep sub-wavelength scales.
A gigawatt level repetitive rate adjustable magnetic pulse compressor
Authors: Li Song , Gao Jing-Ming , Yang Han-Wu , Qian Bao-Liang , Li Ze-Xin
Published: August 2015

In this paper, a gigawatt level repetitive rate adjustable magnetic pulse compressor is investigated both numerically and experimentally. The device has advantages of high power level, high repetitive rate achievability, and long lifetime reliability. Importantly, dominate parameters including the saturation time, the peak voltage, and even the compression ratio can be potentially adjusted continuously and reliably, which significantly expands the applicable area of the device and generators based on it. Specifically, a two-stage adjustable magnetic pulse compressor, utilized for charging the pulse forming network of a high power pulse generator, is designed with different compression ratios of 25 and 18 through an optimized design process. Equivalent circuit analysis shows that the modification of compression ratio can be achieved by just changing the turn number of the winding. At the same time, increasing inductance of the grounded inductor will decrease the peak voltage and delay the charging process. Based on these analyses, an adjustable compressor was built and studied experimentally in both the single shot mode and repetitive rate mode. Pulses with peak voltage of 60 kV and energy per pulse of 360 J were obtained in the experiment. The rise times of the pulses were compressed from 25 μs to 1 μs and from 18 μs to 1 μs, respectively, at repetitive rate of 20 Hz with good repeatability. Experimental results show reasonable agreement with analyses.
Greater Philadelphia and Tianjin Economic Development Area EcoPartnership on urban clean energy infrastructure
Authors: Cooke Merritt T.
Published: August 2015

The Greater Philadelphia (PHL)-Tianjin Economic-technological Development Area (TEDA) collaboration joined the U.S.-China EcoPartnerships program in July 2014 to jumpstart innovative “Urban Clean Energy Infrastructure” solutions in both regions. This unique combination of real-world technology demonstrations and product showcases will get viable new infrastructure breakthroughs quickly into Chinese and U.S. markets once the EcoPartnership is fully underway. The past year has been spent down-selecting priority technologies and demonstration sites, and the partnership is getting ready to initiate its initial three pilot projects. Urban clean energy infrastructure is a sizable, and yet largely untapped opportunity. The PHL-TEDA EcoPartnership can serve as an important sub-national resource to assist municipalities integrate, at the practical level, their U.S.-China Sustainable City planning efforts with commercially relevant, on-the-ground urban infrastructure project experience.
W-band EPR studies of high-spin nitrenes with large spin-orbit contribution to zero-field splitting
Authors: Akimov Alexander , Masitov Artem , Korchagin Denis , Chapyshev Sergei , Misochko Eugenii , Savitsky Anton
Published: August 2015

First W-band 94 GHz EPR spectra of randomly oriented triplet, quintet, and septet nitrenes formed during the photolysis of 1,3,5-triazido-2,4,6-tribromobenzene in cryogenic matrices are reported. In comparison with conventional X-band 9 GHz electron paramagnetic resonance (EPR) spectroscopy, W-band EPR spectroscopy allows the detection and complete spectroscopic characterization of all paramagnetic species formed at different stages of the photolysis of aromatic polyazides. This type of spectroscopy is of paramount importance for experimental determination of the sign of the zero-field splitting (ZFS) parameters of high-spin molecules with large spin-orbit contribution to the ZFS, caused by the effect of heavy atoms. The study shows that triplet 1,3-diazido-2,4,6-tribromo-5-nitrenobenzene (T1) has DT = 1.369 cm−1, ET = 0.093 cm−1, and g = 2.0033, quintet 1-azido-2,4,6-tribromo-3,5-dinitrenobenzene (Q1) shows DQ = − 0.306 cm−1, EQ = 0.0137 cm−1, and g = 2.0070, and septet 2,4,6-tribromo-1,3,5-trinitrenobenzene (S1) has DS = − 0.203 cm−1, ES = 0, and g = 2.0073. The experimental ZFS parameters agree well with the results of density functional theory calculations at the PBE/Ahlrichs-DZ level of theory, showing that such calculations adequately describe the magnetic properties of bromine-containing high-spin nitrenes. Both experimental and theoretical data indicate that, in contrast to all known to date quintet dinitrenes, dinitrene Q1 has the negative sign of magnetic anisotropy due to the “heavy atom effect.” This dinitrene along with septet trinitrene S1 possess the largest negative value of D among all known quintet and septet organic polyradicals.
Predictive energy landscapes for folding membrane protein assemblies
Authors: Truong Ha H. , Kim Bobby L. , Schafer Nicholas P. , Wolynes Peter G.
Published: August 2015

We study the energy landscapes for membrane protein oligomerization using the Associative memory, Water mediated, Structure and Energy Model with an implicit membrane potential (AWSEM-membrane), a coarse-grained molecular dynamics model previously optimized under the assumption that the energy landscapes for folding α-helical membrane protein monomers are funneled once their native topology within the membrane is established. In this study we show that the AWSEM-membrane force field is able to sample near native binding interfaces of several oligomeric systems. By predicting candidate structures using simulated annealing, we further show that degeneracies in predicting structures of membrane protein monomers are generally resolved in the folding of the higher order assemblies as is the case in the assemblies of both nicotinic acetylcholine receptor and V-type Na+-ATPase dimers. The physics of the phenomenon resembles domain swapping, which is consistent with the landscape following the principle of minimal frustration. We revisit also the classic Khorana study of the reconstitution of bacteriorhodopsin from its fragments, which is the close analogue of the early Anfinsen experiment on globular proteins. Here, we show the retinal cofactor likely plays a major role in selecting the final functional assembly.
Efficient and low cost inverted hybrid bulk heterojunction solar cells
Authors: Ikram Muhammad , Imran Muhammad , Nunzi J. M. , Bobbara S. R. , Ali Salamat , Islah-u-din
Published: August 2015

In this study, hybrid bulk heterojunction solar cells with an inverted architecture were fabricated using solution processing techniques. ZnO and TiO2 nanoparticles were then incorporated to the active layer which primarily consists of poly (3-hexylthiophene) (P3HT) and [6,6] phenyl-C61-butyric acid methyl ester (PCBM). The devices were prepared with varying ratios of PCBM to nanostructured inorganic oxides (ZnO and TiO2) while keeping a fixed amount of P3HT. Various characterization techniques were used to understand the effect of metal oxide nanoparticles on structure, morphology, and performance of resulting devices. It was observed that incorporating an optimum amount of nanoparticles to the active layer increased charge carrier mobility, surface roughness of the active layer, and absorption in visible region leading to a significant increase in power conversion efficiency. However, a significant agglomeration of nanoparticles was observed as their ratio relative to PCBM increased and they completely agglomerated in the absence of the fullerene derivative.
Super-stretchable metallic interconnects on polymer with a linear strain of up to 100%
Authors: Arafat Yeasir , Dutta Indranath , Panat Rahul
Published: August 2015

Metal interconnects in flexible and wearable devices are heterogeneous metal-polymer systems that are expected to sustain large deformation without failure. The principal strategy to make strain tolerant interconnect lines on flexible substrates has comprised of creating serpentine structures of metal films with either in-plane or out-of-plane waves, using porous substrates, or using highly ductile materials such as gold. The wavy and helical serpentine patterns preclude high-density packing of interconnect lines on devices, while ductile materials such as Au are cost prohibitive for real world applications. Ductile copper films can be stretched if bonded to the substrate, but show high level of cracking beyond few tens of % strain. In this paper, we demonstrate a material system consisting of Indium metal film over an elastomer (PDMS) with a discontinuous Cr layer such that the metal interconnect can be stretched to extremely high linear strain (up to 100%) without any visible cracks. Such linear strain in metal interconnects exceeds that reported in literature and is obtained without the use of any geometrical manipulations or porous substrates. Systematic experimentation is carried out to explain the mechanisms that allow the Indium film to sustain the high strain level without failure. The islands forming the discontinuous Cr layer are shown to move apart from each other during stretching without delamination, providing strong adhesion to the Indium film while accommodating the large strain in the system. The Indium film is shown to form surface wrinkles upon release from the large strain, confirming its strong adhesion to PDMS. A model is proposed based upon the observations that can explain the high level of stretch-ability of the Indium metal film over the PDMS substrate.
Observation and interpretation of energy efficient, diffuse direct current glow discharge at atmospheric pressure
Authors: Tang Jie , Jiang Weiman , Li Jing , Wang Yishan , Zhao Wei , Duan Yixiang
Published: August 2015

A diffuse direct-current glow discharge was realized with low energy consumption and high energy utilization efficiency at atmospheric pressure. The formation of diffuse discharge was demonstrated by examining and comparing the electrical properties and optical emissions of plasmas. In combination with theoretical derivation and calculation, we draw guidelines that appearance of nitrogen ions at low electron density is crucial to enhance the ambipolar diffusion for the expansion of discharge channel and the increasing ambipolar diffusion near the cathode plays a key role in the onset of diffuse discharge. An individual-discharge-channel expansion model is proposed to explain the diffuse discharge formation.
Digital operation and eye diagrams in spin-lasers
Authors: Wasner Evan , Bearden Sean , Lee Jeongsu , Žutić Igor
Published: August 2015

Digital operation of lasers with injected spin-polarized carriers provides an improved operation over their conventional counterparts with spin-unpolarized carriers. Such spin-lasers can attain much higher bit rates, crucial for optical communication systems. The overall quality of a digital signal in these two types of lasers is compared using eye diagrams and quantified by improved Q-factors and bit-error-rates in spin-lasers. Surprisingly, an optimal performance of spin-lasers requires finite, not infinite, spin-relaxation times, giving a guidance for the design of future spin-lasers.
Highly efficient blazed gratings based on gradient-comb-like units
Authors: Tang Kun , Qiu Chunyin , Lu Jiuyang , Ke Manzhu , Liu Zhengyou
Published: August 2015

Here we propose a multi-scaled reflective grating with excellent blazed performance (nearly perfect blazed effect at the well-predicted frequency and orientation). The blazed grating consists of a periodical array of metallic super-cells, each made of several equal-distant subwavelength slits with linearly reduced depth. A simple model based on Huygens-Fresnel principle is established to forecast the microwave response for the incidence of different polarizations: for transverse-electric polarization, the structure provides only the ordinary total reflection (i.e., without orientation deflected); for transverse-magnetic (TM) polarization, the waves are deflected to specific orientation due to the linear phase delay of the slit exits. Similar design route can be extended to acoustic systems, considering the mathematic similarity between the acoustic wave and the electromagnetic wave of TM-polarization.
Strain in epitaxial Bi2Se3 grown on GaN and graphene substrates: A reflection high-energy electron diffraction study
Authors: Li Bin , Guo Xin , Ho Wingkin , Xie Maohai
Published: August 2015

Topological insulator (TI) has been one of the focus research themes in condensed matter physics in recent years. Due to the relatively large energy bandgap, Bi2Se3 has been identified as one of the most promising three-dimensional TIs with application potentials. Epitaxial Bi2Se3 by molecular-beam epitaxy has been reported by many groups using different substrates. A common feature is that Bi2Se3 grows readily along the c-axis direction irrespective of the type and condition of the substrate. Because of the weak van deer Waals interaction between Bi2Se3 quintuple layers, the grown films are reported to be strain-free, taking the lattice constant of the bulk crystal. At the very initial stage of Bi2Se3 deposition, however, strain may still exist depending on the substrate. Strain may bring some drastic effects to the properties of the TIs and so achieving strained TIs can be of great fundamental interests as well as practical relevance. In this work, we employ reflection high-energy electron diffraction to follow the lattice constant evolution of Bi2Se3 during initial stage depositions on GaN and graphene, two very different substrates. We reveal that epitaxial Bi2Se3 is tensile strained on GaN but strain-free on graphene. Strain relaxation on GaN is gradual.
Electric field and space charge distribution measurement in transformer oil struck by impulsive high voltage
Authors: Sima Wenxia , Guo Hongda , Yang Qing , Song He , Yang Ming , Yu Fei
Published: August 2015

Transformer oil is widely used in power systems because of its excellent insulation properties. The accurate measurement of electric field and space charge distribution in transformer oil under high voltage impulse has important theoretical and practical significance, but still remains challenging to date because of its low Kerr constant. In this study, the continuous electric field and space charge distribution over time between parallel-plate electrodes in high-voltage pulsed transformer oil based on the Kerr effect is directly measured using a linear array photoelectrical detector. Experimental results demonstrate the applicability and reliability of this method. This study provides a feasible approach to further study the space charge effects and breakdown mechanisms in transformer oil.
A thin film active-lens with translational control for dynamically programmable optical zoom
Authors: Yun Sungryul , Park Suntak , Park Bongje , Nam Saekwang , Park Seung Koo , Kyung Ki-Uk
Published: August 2015

We demonstrate a thin film active-lens for rapidly and dynamically controllable optical zoom. The active-lens is composed of a convex hemispherical polydimethylsiloxane (PDMS) lens structure working as an aperture and a dielectric elastomer (DE) membrane actuator, which is a combination of a thin DE layer made with PDMS and a compliant electrode pattern using silver-nanowires. The active-lens is capable of dynamically changing focal point of the soft aperture as high as 18.4% through its translational movement in vertical direction responding to electrically induced bulged-up deformation of the DE membrane actuator. Under operation with various sinusoidal voltage signals, the movement responses are fairly consistent with those estimated from numerical simulation. The responses are not only fast, fairly reversible, and highly durable during continuous cyclic operations, but also large enough to impart dynamic focus tunability for optical zoom in microscopic imaging devices with a light-weight and ultra-slim configuration.
Giant magnetoelectric coupling interaction in BaTiO3/BiFeO3/BaTiO3 trilayer multiferroic heterostructures
Authors: Kotnala R. K. , Gupta Rekha , Chaudhary Sujeet
Published: August 2015

Multiferroic trilayer thin films of BaTiO3/BiFeO3/BaTiO3 were prepared by RF-magnetron sputtering technique at different thicknesses of BiFeO3 layer. A pure phase polycrystalline growth of thin films was confirmed from X-ray diffraction results. The film showed maximum remnant electric polarization (2Pr) of 13.5 μC/cm2 and saturation magnetization (Ms) of 61 emu/cc at room temperature. Thermally activated charge transport dominated via oxygen vacancies as calculated by their activation energy, which was consistent with current–voltage characteristics. Magnetic field induced large change in resistance and capacitance of grain, and grain boundary was modeled by combined impedance and modulus spectroscopy in the presence of varied magnetic fields. Presence of large intrinsic magnetoelectric coupling was established by a maximum 20% increase in grain capacitance (Cg) with applied magnetic field (2 kG) on trilayer having 20 nm BiFeO3 layer. Substantially higher magnetoelectric coupling in thinner films has been observed due to bonding between Fe and Ti atoms at interface via oxygen atoms. Room temperature magnetoelectric coupling was confirmed by dynamic magnetoelectric coupling, and maximum longitudinal magnetoelectric coupling of 515 mV/cm-Oe was observed at 20 nm thickness of BiFeO3. The observed magnetoelectric properties are potentially useful for novel room temperature magnetoelectric and spintronic device applications for obtaining higher voltage at lower applied magnetic field.
Terahertz bolometric detection by thermal noise in graphene field effect transistor
Authors: Mahjoub Akram M. , Suzuki Shinichi , Ouchi Takahiro , Aoki Nobuyuki , Miyamoto Katsuhiko , Yamaguchi Tomohiro , Omatsu Takashige , Ishibashi Koji , Ochiai Yuichi
Published: August 2015

Monolayer (MLG) and bilayer (BLG) graphene devices have been fabricated with integrated antennas and have been investigated for a wideband terahertz (THz) detection at room temperature (RT). The devices show opposite (metallic vs. semiconducting, respectively) temperature coefficients of their resistance, which enable us to achieve a reproducible THz response via bolometric heating. The bolometric nature of this response is inferred by determining the spectral density of the 1/f resistance noise exhibited by the devices, as a function of the incident THz power. With increasing power, the spectral density varies in the two devices in a manner that reflects the opposite signs of their resistance temperature coefficients. The bolometric response is furthermore confirmed for both devices by the variation of their Hooge parameter as a function of the THz power. Overall, these observations confirm the capacity of graphene devices for sensitive broadband THz detection near RT.
Design of band pass filter in a modulated magnetic graphene superlattice
Authors: Lu Wei-Tao , Li Wen
Published: August 2015

Electronic transport of graphene through a modulated magnetic superlattice where the barrier heights present Gaussian profile is studied. It is found that the incident electron could be completely transmitted in the miniband regions and be completely reflected in the bandgap regions. The results suggest an application of the structure as an effectively band pass filter, which can be controlled by the structural parameters. It is concluded that the positions of miniband and bandgap are robust to the Gaussian variation of barrier heights. The effect of this modulated magnetic superlattice is also available for the conventional electrons described by Schrödinger equation.
In situ plasma enhanced atomic layer deposition half cycle study of Al2O3 on AlGaN/GaN high electron mobility transistors
Authors: Qin Xiaoye , Wallace Robert M.
Published: August 2015

A half cycle study of plasma enhanced atomic layer deposited (PEALD) Al2O3 on AlGaN is investigated using in situ X-ray photoelectron spectroscopy, low energy ion scattering, and ex situ electrical characterizations. A faster nucleation or growth is detected from PEALD relative to purely thermal ALD using an H2O precursor. The remote O2 plasma oxidizes the AlGaN surface slightly at the initial stage, which passivates the surface and reduces the OFF-state leakage. This work demonstrates that PEALD is a useful strategy for Al2O3 growth on AlGaN/GaN devices.
Mixed convective heat transfer to Sisko fluid over a radially stretching sheet in the presence of convective boundary conditions
Authors: Khan Masood , Malik Rabia , Munir Asif
Published: August 2015

In this article, the mixed convective heat transfer to Sisko fluid over a radially stretching surface in the presence of convective boundary conditions is investigated. The viscous dissipation and thermal radiation effects are also taken into account. The suitable transformations are applied to convert the governing partial differential equations into a set of nonlinear coupled ordinary differential equations. The analytical solution of the governing problem is obtained by using the homotopy analysis method (HAM). Additionally, these analytical results are compared with the numerical results obtained by the shooting technique. The obtained results for the velocity and temperature are analyzed graphically for several physical parameters for the assisting and opposing flows. It is found that the effect of buoyancy parameter is more prominent in case of the assisting flow as compared to the opposing flow. Further, in tabular form the numerical values are given for the local skin friction coefficient and local Nusselt number. A remarkable agreement is noticed by comparing the present results with the results reported in the literature as a special case.
Direct fiber-coupled single photon source based on a photonic crystal waveguide
Authors: Ahn Byeong-Hyeon , Lee Chang-Min , Lim Hee-Jin , Schlereth Thomas W. , Kamp Martin , Höfling Sven , Lee Yong-Hee
Published: August 2015

A single photon source plays a key role in quantum applications such as quantum computers and quantum communications. Epitaxially grown quantum dots are one of the promising platforms to implement a good single photon source. However, it is challenging to realize an efficient single photon source based on semiconductor materials due to their high refractive index. Here we demonstrate a direct fiber coupled single photon source with high collection efficiency by employing a photonic crystal (PhC) waveguide and a tapered micro-fiber. To confirm the single photon nature, the second-order correlation function g(2)(τ) is measured with a Hanbury Brown-Twiss setup. The measured g(2)(0) value is 0.15, and we can estimate 24% direct collection efficiency from a quantum dot to the fiber.
Atomic transport during solid-phase epitaxial recrystallization of amorphous germanium
Authors: Radek M. , Bracht H. , Johnson B. C. , McCallum J. C. , Posselt M. , Liedke B.
Published: August 2015

The atomic mixing of matrix atoms during solid-phase epitaxy (SPE) is studied by means of isotopically enriched germanium (Ge) multilayer structures that were amorphized by Ge ion implantation up to a depth of 1.5 μm. Recrystallization of the amorphous structure is performed at temperatures between 350 °C and 450 °C. Secondary-ion-mass-spectrometry is used to determine the concentration-depth profiles of the Ge isotope before and after SPE. An upper limit of 0.5 nm is deduced for the displacement length of the Ge matrix atoms by the SPE process. This small displacement length is consistent with theoretical models and atomistic simulations of SPE, indicating that the SPE mechanism consists of bond-switching with nearest-neighbours across the amorphous-crystalline (a/c) interface.
First results of radiation-driven, layered deuterium-tritium implosions with a 3-shock adiabat-shaped drive at the National Ignition Facility
Authors: Smalyuk V. A. , Robey H. F. , Döppner T. , Jones O. S. , Milovich J. L. , Bachmann B. , Baker K. L. , Berzak Hopkins L. F. , Bond E. , Callahan D. A. , Casey D. T. , Celliers P. M. , Cerjan C. , Clark D. S. , Dixit S. N. , Edwards M. J. , Giraldez E. , Haan S. W. , Hamza A. V. , Hohenberger M. , Hoover D. , Hurricane O. A. , Jancaitis K. S. , Kroll J. J. , Lafortune K. N. , Landen O. L. , MacGowan B. J. , MacPhee A. G. , Nikroo A. , Pak A. , Patel P. K. , Peterson J. L. , Weber C. R. , Widmayer C. C. , Yeamans C.
Published: August 2015

Radiation-driven, layered deuterium-tritium plastic capsule implosions were carried out using a new, 3-shock “adiabat-shaped” drive on the National Ignition Facility. The purpose of adiabat shaping is to use a stronger first shock, reducing hydrodynamic instability growth in the ablator. The shock can decay before reaching the deuterium-tritium fuel leaving it on a low adiabat and allowing higher fuel compression. The fuel areal density was improved by ∼25% with this new drive compared to similar “high-foot” implosions, while neutron yield was improved by more than 4 times, compared to “low-foot” implosions driven at the same compression and implosion velocity.
Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods
Authors: Alnoor Hatim , Chey Chan Oeurn , Pozina Galia , Liu Xianjie , Khranovskyy Volodymyr , Willander Magnus , Nur Omer
Published: August 2015

Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 °C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (μ-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.
Dependence of optimal spacing on applied field in ungated field emitter arrays
Authors: Harris J. R. , Jensen K. L. , Shiffler D. A.
Published: August 2015

In ungated field emitter arrays, the field enhancement factor β of each emitter tip is reduced below the value it would have in isolation due to the presence of adjacent emitters, an effect known as shielding or screening. Reducing the distance b between emitters increases the density of emission sites, but also reduces the emission per site, leading to the existence of an optimal spacing that maximizes the array current. Most researchers have identified that this optimal spacing is comparable to the emitter height h, although there is disagreement about the exact optimization. Here, we develop a procedure to determine the dependence of this optimal spacing on the applied electric field. It is shown that the nature of this dependence is governed by the shape of the β(b) curve, and that for typical curves, the optimal value of the emitter spacing b decreases as the applied field increases.
Phylogenetics and phylogeography of a long-legged harvestman (Arachnida : Opiliones) in the Brazilian Atlantic Rain Forest reveals poor dispersal, low diversity and extensive mitochondrial introgression
Authors: Bragagnolo Cibele , Pinto-da-Rocha Ricardo , Antunes Manuel , Clouse Ronald M.
Published: August 2015

We used DNA sequence data to test the morphology-based taxonomy and examine the biogeography of the Brazilian Atlantic Rain Forest genus Promitobates. Most species are well differentiated morphologically, and a previous morphological phylogeny recovered the genus as monophyletic. However, some of these species have overlapping geographical distributions and considerable intraspecific variation, perhaps representing a species complex. Mitochondrial (12S rRNA and COI) and nuclear (ITS2 and 28S) genes were sequenced from 132 specimens collected from 27 localities. The results are consistent with significant mitochondrial introgression among the species P. ornatus, P. hatschbachi, P. lager, P. bellus and P. intermedius (the ‘P. ornatus species complex’), with one specimen identified as a hybrid between P. nigripes and this complex. A phylogeographic study of the complex was conducted using mitochondrial haplotypes. This revealed remarkably poor dispersal among populations, with only one case of a shared haplotype, and very low genetic diversity. The phylogeny showed a clear break between populations on either side of a narrow region of forest, suggesting an important historical event separated these lineages in the genus. The analyses also pointed to population breaks that date back several millions of years or extremely small effective population sizes, depending on the mutation rate.