bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring the Utility of a School-Age Narrative Microstructure Index: Proportion of Restricted Utterances
Authors: Jerger Sara , Thorne John C.
Published: April 2016

Purpose

This research attempted to replicate Hoffman's 2009 finding that the proportion of narrative utterances with semantic or syntactic errors (i.e., ≥ 14% “restricted utterances”) can differentiate school-age children with typical development from those with language impairment with a sensitivity of 83% and specificity of 88%.

Method

Methods similar to Hoffman (2009) were used to evaluate an existing set of narratives from 16 age-matched pairs of 8- to 9-year-old children, half with known language impairment. Transcripts were segmented into T-units; a code of [RESTRICTED] was assigned to any utterance with semantic or syntactic errors.

Results

A Welch'sttest for independent samples revealed a statistically significant difference in the mean proportion of restricted utterances between the two groups after accommodation for an outlier with typical development. A cutoff of ≥ 14% restricted utterances replicated Hoffman's (2009) sensitivity but not specificity. Post hoc analysis of specific error types found sensitivity and specificity rates similar to Hoffman's as well as a significant difference in means when using a proportion of sentence–internal morphosyntactic errors.

Conclusion

Results support further exploration of utterance-level error coding for diagnostic purposes and future development of this approach to meet clinical assessment needs.
The Map and the Territory: An Ethnographic Study of the Low Utilisation of a Global eHealth Network
Authors: Duclos Vincent
Published: April 2016

Recent years were marked by the implementation of many eHealth projects using information and communication technologies to provide health services in developing countries. While generating great expectations, these projects remain poorly documented and available data suggest high failure rates. This raises a practical question: How are such eHealth networks to be effectively designed and implemented? This paper addresses this question. Specifically, it presents an ethnographic study of the Pan-African e-Network, a project which connects many hospitals all across India and Africa, providing medical teleconsultations and distance learning services. The study investigates the low utilisation of the network, an issue undermining its potential and efficiency. Factors contributing to this situation include communication barriers, the presumed ego of doctors, poor awareness of the project, and a lack of flexibility to work with the specificities of the connected sites. Above all, these factors point towards a dichotomous approach across the project's design and implementation, and taking two distinct yet related forms: (a) an ontological divide between technical and ‘non-technical’ domains; (b) a political sorting out of what is and what is not the project, aimed at neutralising and accounting for heterogeneous processes and practices. In both cases, low utilisation reveals tensions between processes of closure and control, and the openness of a life that will not be contained. Ultimately, this paper intends to destabilise binary modes of thinking as they crystallise oppositions between design and implementation, project and context, technical and social worlds, efficacy and improvisation, mastery and unruliness, map and territory.
Low vibration high numerical aperture automated variable temperature Raman microscope
Authors: Tian Yao , Reijnders Anjan A. , Osterhoudt Gavin B. , Valmianski Ilya , Ramirez J. G. , Urban Christian , Zhong Ruidan , Schneeloch John , Gu Genda , Henslee Isaac , Burch Kenneth S.
Published: April 2016

Raman micro-spectroscopy is well suited for studying a variety of properties and has been applied to a wide range of areas. Combined with tuneable temperature, Raman spectra can offer even more insights into the properties of materials. However, previous designs of variable temperature Raman microscopes have made it extremely challenging to measure samples with low signal levels due to thermal and positional instabilities as well as low collection efficiencies. Thus contemporary Raman microscope has found limited applicability to probing the subtle physics involved in phase transitions and hysteresis. This paper describes a new design of a closed-cycle, Raman microscope with full polarization rotation. High collection efficiency, thermal stability, and mechanical stability are ensured by both deliberate optical, cryogenic, and mechanical design. Measurements on two samples, Bi2Se3 and V2O3, which are challenging due to low thermal conductivities, low signal levels, and/or hysteretic effects, are measured with previously undemonstrated temperature resolution.
A nitride-based epitaxial surface layer formed by ammonia treatment of silicene-terminated ZrB2
Authors: Wiggers F. B. , Van Bui H. , Friedlein R. , Yamada-Takamura Y. , Schmitz J. , Kovalgin A. Y. , de Jong M. P.
Published: April 2016

We present a method for the formation of an epitaxial  surface layer involving B, N, and Si atoms on a ZrB2(0001) thin film on Si(111). It has the potential to be an insulating growth template for 2D semiconductors. The chemical reaction of NH3 molecules with the silicene-terminated ZrB2  surface was characterized by synchrotron-based, high-resolution core-level photoelectron spectroscopy and low-energy electron diffraction. In particular, the dissociative chemisorption of NH3 at 400 °C leads to surface  nitridation, and subsequent annealing up to 830 °C results in a solid phase reaction with the ZrB2 subsurface layers. In this way, a new nitride-based epitaxial  surface layer is formed with hexagonal symmetry and a single in-plane crystal orientation.
Crosshatch roughness distortions on a hypersonic turbulent boundary layer
Authors: Peltier S. J. , Humble R. A. , Bowersox R. D. W.
Published: April 2016

The effects of periodic crosshatch roughness (k+ = 160) on a Mach 4.9 turbulent boundary layer (Reθ = 63 000) are examined using particle image velocimetry. The roughness elements generate a series of alternating shock and expansion waves, which span the entire boundary layer, causing significant (up to +50% and −30%) variations in the Reynolds shear stress field. Evidence of the hairpin vortex organization of incompressible flows is found in the comparative smooth-wall boundary layer case (Reθ = 47 000), and can be used to explain several observations regarding the rough-wall vortex organization. In general, the rough-wall boundary layer near-wall vortices no longer appear to be well-organized into streamwise-aligned packets that straddle relatively low-speed regions like their smooth-wall counterpart; instead, they lean farther away from the wall, become more spatially compact, and their populations become altered. In the lower half of the boundary layer, the net vortex swirling strength and outer-scaled Reynolds stresses increase relative to the smooth-wall case, and actually decrease in the outer half of the boundary layer, as ejection and entrainment processes are strengthened and weakened in these two regions, respectively. A spectral analysis of the data suggests a relative homogenizing of the most energetic scales near Λ = ∼ 0.5δ across the rough-wall boundary layer.
Exploration of spin state and exchange integral of cobalt ions in stoichiometric ZnCo2O4 spinel oxides
Authors: Che Xiangli , Li Liping , Li Guangshe
Published: April 2016

This work reports on spin state and exchange integral of cobalt ions in stoichiometric ZnCo2O4 nanoparticles with varying particle size from about 24 to 105 nm. Cobalt ions in ZnCo2O4 nanoparticles are present as trivalence in mixed spin state. The effective magnetic moment is distributed in the range of 2.1 ∼ 1.31 μB at room temperature with coarsening of nanoparticles. Further, it is demonstrated that stoichiometric ZnCo2O4 undergoes a magnetic transition from paramagnetism to antiferromagnetism with decrease of temperature, showing a transition temperature of about 5 K. The standard molar entropy and enthalpy for 24 nm ZnCo2O4 are 170.6 ± 1.7 J K−1 mol−1 and 28.2 ± 0.3 kJ mol−1 at 298.15 K, respectively. Based on the heat capacity data, the exchange integral is determined to be 4.16 × 10−22 J. The results report here are really important for further understanding the magnetic and electronic properties of spinel oxides.
Transition to turbulence and noise radiation in heated coaxial jet flows
Authors: Gloor Michael , Bühler Stefan , Kleiser Leonhard
Published: April 2016

Laminar-turbulent transition and noise radiation of a parametrized set of subsonic coaxial jet flows with a hot primary (core) stream are investigated numerically by Large-Eddy Simulation (LES) and direct noise computation. This study extends our previous research on local linear stability of heated coaxial jet flows by analyzing the nonlinear evolution of initially laminar flows disturbed by a superposition of small-amplitude unstable eigenmodes. First, a baseline configuration is studied to shed light on the flow dynamics of coaxial jet flows. Subsequently, LESs are performed for a range of Mach and Reynolds numbers to systematically analyze the influences of the temperature and the velocity ratios between the primary and the secondary (bypass) stream. The results provide a basis for a detailed analysis of fundamental flow-acoustic phenomena in the considered heated coaxial jet flows. Increasing the primary-jet temperature leads to an increase of fluctuation levels and to an amplification of far-field noise, especially at low frequencies. Strong mixing between the cold bypass stream and the hot primary stream as well as the intermittent character of the flow field at the end of the potential core lead to a pronounced noise radiation at an aft angle of approximately 35∘. The velocity ratio strongly affects the shear-layer development and therefore also the noise generation mechanisms. Increasing the secondary-stream velocity amplifies the dominance of outer shear-layer perturbations while the disturbance growth rates in the inner shear layer decrease. Already for rmic > 40R1, where rmic is the distance from the end of the potential core and R1 is the core-jet radius, a perfect 1/rmic decay of the sound pressure amplitudes is observed. The potential-core length increases for higher secondary-stream velocities which leads to a shift of the center of the dominant acoustic radiation in the downstream direction.
Anomalous negative electrocaloric effect in a relaxor/normal ferroelectric polymer blend with controlled nano- and meso-dipolar couplings
Authors: Qian Xiaoshi , Yang Tiannan , Zhang Tian , Chen Long-Qing , Zhang Q. M.
Published: April 2016

In general, a dielectric material will eject (or absorb) heat when an electric field is applied and absorb (or eject) heat when the field is removed, under isothermal condition, which is known as the normal (or negative) electrocaloric (EC) effect. For some applications, it is highly desired that an EC material will absorb heat (cooling the surrounding) without subsequent heating under an electric pulse. Here, we show that such an EC material can be realized in a properly designed hybrid normal ferroelectric/relaxor ferroelectric polymer blend in which the normal ferroelectric component induces dipole ordering in the relaxor polymer in the poled state, which can be switched to a de-poled state by an external field. More importantly, the de-poled state can be maintained by the relaxor component when the de-poling field is removed. Consequently, the hybrid blend exhibits a large cooling (an isothermal entropy change ΔS = 11.5 J kg−1 K−1) without the subsequent heating upon the application of an electric pulse.
Generalized stationary phase approximations for mountain waves
Authors: Knight H. , Broutman D. , Eckermann S. D.
Published: April 2016

Large altitude asymptotic approximations are derived for vertical displacements due to mountain waves generated by hydrostatic wind flow over arbitrary topography. This leads to new asymptotic analytic expressions for wave-induced vertical displacement for mountains with an elliptical Gaussian shape and with the major axis oriented at any angle relative to the background wind. The motivation is to understand local maxima in vertical displacement amplitude at a given height for elliptical mountains aligned at oblique angles to the wind direction, as identified in Eckermann et al. [“Effects of horizontal geometrical spreading on the parameterization of orographic gravity-wave drag. Part 1: Numerical transform solutions,” J. Atmos. Sci. 72, 2330–2347 (2015)]. The standard stationary phase method reproduces one type of local amplitude maximum that migrates downwind with increasing altitude. Another type of local amplitude maximum stays close to the vertical axis over the center of the mountain, and a new generalized stationary phase method is developed to describe this other type of local amplitude maximum and the horizontal variation of wave-induced vertical displacement near the vertical axis of the mountain in the large altitude limit. The new generalized stationary phase method describes the asymptotic behavior of integrals where the asymptotic parameter is raised to two different powers (1/2 and 1) rather than just one power as in the standard stationary phase method. The vertical displacement formulas are initially derived assuming a uniform background wind but are extended to accommodate both vertical shear with a fixed wind direction and vertical variations in the buoyancy frequency.
Impact of domain size and statistical errors in simulations of homogeneous decaying turbulence and the Richtmyer-Meshkov instability
Authors: Thornber B.
Published: April 2016

Both experiments and computations are naturally constrained by boundary conditions. In fundamental problems such as homogeneous decaying turbulence (HDT) or shock-induced mixing layers, a size constraint naturally limits the growth of the large scales in the problem, modifying the physics observed. This paper explores through Large Eddy Simulation (LES) the integral properties using computations from 1283 to 10243 for HDT and 1283 to 5123 for the Richtmyer-Meshkov instability (RMI). Kinetic energy decay rates in both cases are shown to be relatively insensitive to the domain size until the spectral peak is at the first wave number. The integral length is significantly more sensitive, showing substantial discrepancies once it is greater than 10% of the domain size. However, the key error is shown to be due to a lack of statistical averaging once the integral length is greater than 5% of the box size, thus appearing earlier than the length scale saturation. This highlights that a single computation at modest grid resolution (≤2563) may not reproduce the correct physics and that at this resolution, numericists need to embrace the practice of using multiple independent realisations to reduce the statistical error, as is the norm for the experimentalist. Finally, an update on the physics of HDT and RMI as predicted through LES computations is presented.
Effect of stress voltage on the dynamic buffer response of GaN-on-silicon transistors
Authors: Yacoub H. , Fahle D. , Eickelkamp M. , Wille A. , Mauder C. , Heuken M. , Kalisch H. , Vescan A.
Published: April 2016

Back-gated measurements on conductive silicon substrates have been performed to investigate the effect of stress voltage on the dynamic behaviour of GaN-on-silicon (GaN-on-Si) transistors. Two comparable samples were studied with the only difference being the vertical dislocation density. Results show a clear correlation between dislocation density and the ability of the GaN buffer to dynamically discharge under high stress conditions.
Electron quantum dynamics in atom-ion interaction
Authors: Sabzyan H. , Jenabi M. J.
Published: April 2016

Electron transfer (ET) process and its dependence on the system parameters are investigated by solving two-dimensional time-dependent Schrödinger equation numerically using split operator technique. Evolution of the electron wavepacket occurs from the one-electron species hydrogen atom to another bare nucleus of charge Z > 1. This evolution is quantified by partitioning the simulation box and defining regional densities belonging to the two nuclei of the system. It is found that the functional form of the time-variations of these regional densities and the extent of ET process depend strongly on the inter-nuclear distance and relative values of the nuclear charges, which define the potential energy surface governing the electron wavepacket evolution. Also, the initial electronic state of the single-electron atom has critical effect on this evolution and its consequent (partial) electron transfer depending on its spreading extent and orientation with respect to the inter-nuclear axis.
Chemical kinetics and relaxation of non-equilibrium air plasma generated by energetic photon and electron beams
Authors: Maulois Melissa , Ribière Maxime , Eichwald Olivier , Yousfi Mohammed , Azaïs Bruno
Published: April 2016

The comprehension of electromagnetic perturbations of electronic devices, due to air plasma-induced electromagnetic field, requires a thorough study on air plasma. In the aim to understand the phenomena at the origin of the formation of non-equilibrium air plasma, we simulate, using a volume average chemical kinetics model (0D model), the time evolution of a non-equilibrium air plasma generated by an energetic X-ray flash. The simulation is undertaken in synthetic air (80% N2 and 20% O2) at ambient temperature and atmospheric pressure. When the X-ray flash crosses the gas, non-relativistic Compton electrons (low energy) and a relativistic Compton electron beam (high energy) are simultaneously generated and interact with the gas. The considered chemical kinetics scheme involves 26 influent species (electrons, positive ions, negative ions, and neutral atoms and molecules in their ground or metastable excited states) reacting following 164 selected reactions. The kinetics model describing the plasma chemistry was coupled to the conservation equation of the electron mean energy, in order to calculate at each time step of the non-equilibrium plasma evolution, the coefficients of reactions involving electrons while the energy of the heavy species (positive and negative ions and neutral atoms and molecules) is assumed remaining close to ambient temperature. It has been shown that it is the relativistic Compton electron beam directly created by the X-ray flash which is mainly responsible for the non-equilibrium plasma formation. Indeed, the low energy electrons (i.e., the non-relativistic ones) directly ejected from molecules by Compton collisions contribute to less than 1% on the creation of electrons in the plasma. In our simulation conditions, a non-equilibrium plasma with a low electron mean energy close to 1 eV and a concentration of charged species close to 1013 cm−3 is formed a few nanoseconds after the peak of X-ray flash intensity. 200 ns after the flash application, the electrons are thermalized and their concentration has decreased from about 1013 cm−3 down to about 1012 cm−3 leaving positive and negative ionised species and atomic radicals whose recombination characteristic times are much longer.
Electrochemical and structural properties of the electrical double layer of two-component electrolytes in response to varied electrode potential
Authors: Kiyohara Kenji , Yamagata Masaki , Ishikawa Masashi
Published: April 2016

The electrochemical and structural properties of the electrical double layers for two-component electrolytes were studied by Monte Carlo simulations using simple models. When the electrolyte contains two species of cations that have different diameters, the capacitance on the cathode dramatically increases as a large negative potential is applied. This behavior is qualitatively similar to the one reported in an experimental work that has used Li-containing ionic liquid as the electrolyte [M. Yamagata et al., Electrochim. Acta 110, 181-190 (2013)], in which it has also been reported that addition of Li ions to the electrolyte enhances the potential window to the negative side. The analysis of the ionic structure showed that the electrical double layer on the cathode is dominantly formed by the larger cations under small negative potentials, while they are replaced by the smaller cations under large negative potentials. This transition of the ionic structure with electrode potential is also consistent with the enhancement of the potential window that was found in the experimental work, which suggests that the organic cations are expelled from the electrical double layer under large negative potentials and the chance of decomposition is reduced.
The structure of liquid water up to 360 MPa from x-ray diffraction measurements using a high Q-range and from molecular simulation
Authors: Skinner L. B. , Galib M. , Fulton J. L. , Mundy C. J. , Parise J. B. , Pham V.-T. , Schenter G. K. , Benmore C. J.
Published: April 2016

X-ray diffraction measurements of liquid water are reported at pressures up to 360 MPa corresponding to a density of 0.0373 molecules per Å3. The measurements were conducted at a spatial resolution corresponding to Qmax = 16 Å−1. The method of data analysis and measurement in this study follows the earlier benchmark results reported for water under ambient conditions having a density of 0.0333 molecules per Å3 and Qmax = 20 Å−1 [J. Chem. Phys. 138, 074506 (2013)] and at 70 °C having a density of 0.0327 molecules per Å3 and Qmax = 20 Å−1 [J. Chem. Phys. 141, 214507 (2014)]. The structure of water is very different at these three different T and P state points and thus they provide the basis for evaluating the fidelity of molecular simulation. Measurements show that at 360 MPa, the 4 waters residing in the region between 2.3 and 3 Å are nearly unchanged: the peak position, shape, and coordination number are nearly identical to their values under ambient conditions. However, in the region above 3 Å, large structural changes occur with the collapse of the well-defined 2nd shell and shifting of higher shells to shorter distances. The measured structure is compared to simulated structure using intermolecular potentials described by both first-principles methods (revPBE-D3) and classical potentials (TIP4P/2005, MB-pol, and mW). The DFT-based, revPBE-D3, method and the many-body empirical potential model, MB-pol, provide the best overall representation of the ambient, high-temperature, and high-pressure data. The revPBE-D3, MB-pol, and the TIP4P/2005 models capture the densification mechanism, whereby the non-bonded 5th nearest neighbor molecule, which partially encroaches the 1st shell at ambient pressure, is pushed further into the local tetrahedral arrangement at higher pressures by the more distant molecules filling the void space in the network between the 1st and 2nd shells.
Ferroelectric molecular field-switch based on double proton transfer process: Static and dynamical simulations
Authors: Rode Michał F. , Jankowska Joanna , Sobolewski Andrzej L.
Published: April 2016

In this work, we present a reversible ferroelectric molecular switch controlled by an external electric field. The studied (2Z)-1-(6-((Z)-2-hydroxy-2-phenylvinyl)pyridin-3-yl)-2-(pyridin-2(1H)-ylidene)ethanone (DSA) molecule is polarized by two uniaxial intramolecular hydrogen bonds. Two protons can be transferred along hydrogen bonds upon an electric field applied along the main molecular axis. The process results in reversion of the dipole moment of the system. Static ab initio and on-the-fly dynamical simulations of the DSA molecule placed in an external electric field give insight into the mechanism of the double proton transfer (DPT) in the system and allow for estimation of the time scale of this process. The results indicate that with increasing strength of the electric field, the step-wise mechanism of DPT changes into the downhill barrierless process in which the synchronous and asynchronous DPTs compete with each other.
An improved grey neural network forecasting method based on genetic algorithm for oil consumption of China
Authors: Yang Yi , Chen Yanhua , Shi Jun , Liu Mingfei , Li Caihong , Li Lian
Published: April 2016

Energy, especially oil, plays a special and irreplaceable role in the economic development, modern civilization, and social progress. With the rapid growth over the past few decades, China has gradually become a big power in oil consumption. In order to solve the contradiction between supply and demand as well as minimize social costs, it is necessary and useful to forecast the trend of China's oil consumption. In addition, reasonable and effective oil production and scheduling through forecasting progress also makes an important impact on the health economic development, social stability, and sustainable development. However, it is a challenging task to carry out such a forecasting because oil consumption is influenced by a number of factors, such as technology development, economic level, government policy, natural disaster, unexpected politic events, and so on. Therefore, it is difficult to forecast such a complex system with a single traditional model. This paper proposes an improved hybrid method known as GGNN, which combined the grey models, the back propagation (BP) neural network, and the genetic algorithm (GA) to take the advantages of linear model, nonlinear model, and swarm intelligence optimization, respectively. GM (1, 1) and improved grey models including an unbiased GM (1, 1), initial correction GM (1, 1), p value GM (1, 1), and background value GM (1, 1)are applied to capture the linear information. BP is widely used due to its nonlinear mapping capability; in this paper, it is used to capture the nonlinear information. Moreover, the GA is also applied to obtain the optimum weights and thresholds of the GGNN which is made up of all grey models and BP neural model. The superiority of this proposed method is examined by using the historical data of China's oil consumption. Assessment results demonstrate that the proposed method GGNN can improve the forecasting accuracy compared with some other existing methods.
Core–shell interaction and its impact on the optical absorption of pure and doped core-shell CdSe/ZnSe nanoclusters
Authors: Wang Xinqin , Cui Yingqi , Yu Shengping , Zeng Qun , Yang Mingli
Published: April 2016

The structural, electronic, and optical properties of core-shell nanoclusters, (CdSe)x@(CdSe)y and their Zn-substituted complexes of x = 2–4 and y = 16–28, were studied with density functional theory calculations. The substitution was applied in the cores, the shells, and/or the whole clusters. All these clusters are characterized by their core-shell structures in which the core-shell interaction was found different from those in core or in shell, as reflected by their bondlengths, volumes, and binding energies. Moreover, the core and shell combine together to compose a new cluster with electronic and optical properties different from those of separated individuals, as reflected by their HOMO-LUMO gaps and optical absorptions. With the substitution of Cd by Zn, the structural, electronic, and optical properties of clusters change regularly. The binding energy increases with Zn content, attributed to the strong Zn–Se bonding. For the same core/shell, the structure with a CdSe shell/core has a narrower gap than that with a ZnSe shell/core. The optical absorption spectra also change accordingly with Zn substitution. The peaks blueshift with increasing Zn concentration, accompanying with shape variations in case large number of Cd atoms are substituted. Our calculations reveal the core-shell interaction and its influence on the electronic and optical properties of the core-shell clusters, suggesting a composition–structure–property relationship for the design of core-shell CdSe and ZnSe nanoclusters.
Structure and collective dynamics of hydrated anti-freeze protein type III from 180 K to 298 K by X-ray diffraction and inelastic X-ray scattering
Authors: Yoshida Koji , Baron Alfred Q. R. , Uchiyama Hiroshi , Tsutsui Satoshi , Yamaguchi Toshio
Published: April 2016

We investigated hydrated antifreeze protein type III (AFP III) powder with a hydration level h (=mass of water/mass of protein) of 0.4 in the temperature range between 180 K and 298 K using X-ray diffraction and inelastic X-ray scattering (IXS). The X-ray diffraction data showed smooth, largely monotonic changes between 180 K and 298 K without freezing water. Meanwhile, the collective dynamics observed by IXS showed a strong change in the sound velocity at 180 K, after being largely temperature independent at higher temperatures (298–220 K). We interpret this change in terms of the dynamic transition previously discussed using other probes including THz IR absorption spectroscopy and incoherent elastic and quasi-elastic neutron scattering. This finding suggests that the dynamic transition of hydrated proteins is observable on the subpicosecond time scale as well as nano- and pico-second scales, both in collective dynamics from IXS and single particle dynamics from neutron scattering. Moreover, it is most likely that the dynamic transition of hydrated AFP III is not directly correlated with its hydration structure.
BiGlobal linear stability analysis on low-Re flow past an airfoil at high angle of attack
Authors: Zhang Wei , Samtaney Ravi
Published: April 2016

We perform BiGlobal linear stability analysis on flow past a NACA0012 airfoil at 16° angle of attack and Reynolds number ranging from 400 to 1000. The steady-state two-dimensional base flows are computed using a well-tested finite difference code in combination with the selective frequency damping method. The base flow is characterized by two asymmetric recirculation bubbles downstream of the airfoil whose streamwise extent and the maximum reverse flow velocity increase with the Reynolds number. The stability analysis of the flow past the airfoil is carried out under very small spanwise wavenumber β = 10−4 to approximate the two-dimensional perturbation, and medium and large spanwise wavenumbers (β = 1–8) to account for the three-dimensional perturbation. Numerical results reveal that under small spanwise wavenumber, there are at most two oscillatory unstable modes corresponding to the near wake and far wake instabilities; the growth rate and frequency of the perturbation agree well with the two-dimensional direct numerical simulation results under all Reynolds numbers. For a larger spanwise wavenumber β = 1, there is only one oscillatory unstable mode associated with the wake instability at Re = 400 and 600, while at Re = 800 and 1000 there are two oscillatory unstable modes for the near wake and far wake instabilities, and one stationary unstable mode for the monotonically growing perturbation within the recirculation bubble via the centrifugal instability mechanism. All the unstable modes are weakened or even suppressed as the spanwise wavenumber further increases, among which the stationary mode persists until β = 4.
Calculation of the thermal conductivity of low-density CH4–N2 gas mixtures using an improved kinetic theory approach
Authors: Hellmann Robert , Bich Eckard , Vesovic Velisa
Published: April 2016

The thermal conductivity of low-density CH4–N2 gas mixtures has been calculated by means of the classical trajectory method using state-of-the-art intermolecular potential energy surfaces for the CH4–CH4, N2–N2, and CH4–N2 interactions. Results are reported in the temperature range from 70 K to 1200 K. Since the thermal conductivity is influenced by the vibrational degrees of freedom of the molecules, which are not included in the rigid-rotor classical trajectory computations, a new correction scheme to account for vibrational degrees of freedom in a dilute gas mixture is presented. The calculations show that the vibrational contribution at the highest temperature studied amounts to 46% of the total thermal conductivity of an equimolar mixture compared to 13% for pure nitrogen and 58% for pure methane. The agreement with the available experimental thermal conductivity data at room temperature is good, within ±1.4%, whereas at higher temperatures, larger deviations up to 4.5% are observed, which can be tentatively attributed to deteriorating performance of the measuring technique employed. Results are also reported for the magnitude and temperature dependence of the rotational collision number, Zrot, for CH4 relaxing in collisions with N2 and for N2 relaxing in collisions with CH4. Both collision numbers increase with temperature, with the former being consistently about twice the value of the latter.
Photo-electrical and transport properties of hydrothermal ZnO
Authors: Onufrijevs P. , Ščajev P. , Jarašiūnas K. , Medvid A. , Korsaks V. , Mironova-Ulmane N. , Zubkins M. , Mimura H.
Published: April 2016

We performed the studies of optical, photoelectric, and transport properties of a hydrothermal bulk n-type ZnO crystal by using the contactless optical techniques: photoluminescence, light-induced transient grating, and differential reflectivity. Optical studies revealed bound exciton and defect-related transitions between the donor states (at ∼60 meV and ∼240 meV below the conduction band) and the deep acceptor states (at 0.52 eV above the valence band). The acceptor state was ascribed to VZn, and its thermal activation energy of 0.43 eV was determined. A low value of carrier diffusion coefficient (∼0.1 cm2/s) at low excitations and temperatures up to 800 K was attributed to impact the recharged deep acceptors. Electron and hole mobilities of 140 and ∼80 cm2/Vs, correspondently, were determined at room temperature. The decrease of carrier lifetime with excitation was ascribed to increasing rate of radiative recombination at low temperatures and nonradiative recombination above the room temperature.
Thermoelectric properties of n-type Nb-doped Ag8SnSe6
Authors: Zhang Xiao , Zhang Cheng-Long , Lin Siqi , Lu Hong , Pei Yanzhong , Jia Shuang
Published: April 2016

Electrical and thermoelectric (TE) properties for n-type Ag8SnSe6 and (Ag1−xNbx)8SnSe6 are investigated. Ag8SnSe6 has the thermoelectric figure of merit (ZT) close to 1.1 at 803 K due to its intrinsic ultralow thermal conductivity ∼0.3 Wm−1K−1, relatively low resistivity ∼0.01 Ω cm, and high Seebeck coefficient ∼−200 μV∕K. The ZT for pure Ag8SnSe6 drops to 0.02 at room temperature due to its large resistivity. Niobium doping increases the carrier concentration nearly 10 times and thus enhances its ZT to 0.11 at room temperature. Ag8SnSe6 is a promising n-type candidate of TE materials which needs further elaborations.
Time-resolved scanning electron microscopy with polarization analysis
Authors: Frömter Robert , Kloodt Fabian , Rößler Stefan , Frauen Axel , Staeck Philipp , Cavicchia Demetrio R. , Bocklage Lars , Röbisch Volker , Quandt Eckhard , Oepen Hans Peter
Published: April 2016

We demonstrate the feasibility of investigating periodically driven magnetization dynamics in a scanning electron microscope with polarization analysis based on spin-polarized low-energy electron diffraction. With the present setup, analyzing the time structure of the scattering events, we obtain a temporal resolution of 700 ps, which is demonstrated by means of imaging the field-driven 100 MHz gyration of the vortex in a soft-magnetic FeCoSiB square. Owing to the efficient intrinsic timing scheme, high-quality movies, giving two components of the magnetization simultaneously, can be recorded on the time scale of hours.
Large bandgap blueshifts in the InGaP/InAlGaP laser structure using novel strain-induced quantum well intermixing
Authors: Al-Jabr A. A. , Majid M. A. , Alias M. S. , Anjum D. H. , Ng T. K. , Ooi B. S.
Published: April 2016

We report on a novel quantum well intermixing (QWI) technique that induces a large degree of bandgap blueshift in the InGaP/InAlGaP laser structure. In this technique, high external compressive strain induced by a thick layer of SiO2 cap with a thickness ≥1 μm was used to enhance QWI in the tensile-strained InGaP/InAlGaP quantum well layer. A bandgap blueshift as large as 200 meV was observed in samples capped with 1-μm SiO2 and annealed at 1000 °C for 120 s. To further enhance the degree of QWI, cycles of annealing steps were applied to the SiO2 cap. Using this method, wavelength tunability over the range of 640 nm to 565 nm (∼250 meV) was demonstrated. Light-emitting diodes emitting at red (628 nm), orange (602 nm), and yellow (585 nm) wavelengths were successfully fabricated on the intermixed samples. Our results show that this new QWI method technique may pave the way for the realization of high-efficiency orange and yellow light-emitting devices based on the InGaP/InAlGaP material system.
High sensitivity measurement system for the direct-current, capacitance-voltage, and gate-drain low frequency noise characterization of field effect transistors
Authors: Giusi G. , Giordano O. , Scandurra G. , Rapisarda M. , Calvi S. , Ciofi C.
Published: April 2016

Measurements of current fluctuations originating in electron devices have been largely used to understand the electrical properties of materials and ultimate device performances. In this work, we propose a high-sensitivity measurement setup topology suitable for the automatic and programmable Direct-Current (DC), Capacitance-Voltage (CV), and gate-drain low frequency noise characterization of field effect transistors at wafer level. Automatic and programmable operation is particularly useful when the device characteristics relax or degrade with time due to optical, bias, or temperature stress. The noise sensitivity of the proposed topology is in the order of fA/Hz1/2, while DC performances are limited only by the source and measurement units used to bias the device under test. DC, CV, and NOISE measurements, down to 1 pA of DC gate and drain bias currents, in organic thin film transistors are reported to demonstrate system operation and performances.
Coherent turbulent structures at the mixing-interface of a square open-channel lateral cavity
Authors: Mignot Emmanuel , Cai Wei , Launay Gaby , Riviere Nicolas , Escauriaza Cristián
Published: April 2016

The self-sustained turbulent shear or mixing layer that develops at the interface between a channel and a lateral cavity is the leading mechanism that drives the transfer of momentum and mass in these open-channel flows. Therefore, quantifying the interactions between large-scale vortical structures and the enhanced velocity fluctuations at the interface is critical to understand the physical processes which control the exchanges between the cavity and the main channel. In this investigation, we carry out hydrodynamic experiments in a straight, rectangular channel with a lateral square cavity. We measure the velocity field in a horizontal plane using particle image velocimetry to study the dynamics and statistics of the mixing layer, including the effects of the adverse pressure gradient at the downstream corner. By combining proper-orthogonal decomposition with a vortex identification technique, we investigate the motion of coherent structures and calculate the histograms of their trajectories, capturing also additional phenomena such as the vortex splitting, and the interaction of the mixing layer with inner vortices formed inside the cavity. We finally quantify the mass transport capacity of the mixing layer, from the statistics of the transverse velocity at the interface.
Communication: A difference density picture for the self-consistent field ansatz
Authors: Parrish Robert M. , Liu Fang , Martínez Todd J.
Published: April 2016

We formulate self-consistent field (SCF) theory in terms of an interaction picture where the working variable is the difference density matrix between the true system and a corresponding superposition of atomic densities. As the difference density matrix directly represents the electronic deformations inherent in chemical bonding, this “difference self-consistent field (dSCF)” picture provides a number of significant conceptual and computational advantages. We show that this allows for a stable and efficient dSCF iterative procedure with wholly single-precision Coulomb and exchange matrix builds. We also show that the dSCF iterative procedure can be performed with aggressive screening of the pair space. These approximations are tested and found to be accurate for systems with up to 1860 atoms and >10 000 basis functions, providing for immediate overall speedups of up to 70% in the heavily optimized TeraChem SCF implementation.
Development of an optical time-resolved measurement system under high-pressure and low-temperature with a piston-cylinder pressure cell
Authors: Tsuchiya Satoshi , Kino Yohei , Nakagawa Koichi , Nakagawa Daisuke , Yamada Jun-ichi , Toda Yasunori
Published: April 2016

To perform the femtosecond pump-probe spectroscopy under high pressure and low temperature, we constructed a measurement system with a piston cylinder type pressure cell installing an optical fiber bundle. The applied pressure was achieved to 6 kbar and the cell was cooled down to 15 K. Several demonstrations revealed that broadening and change of polarization of pulse (duration of ∼120 fs) owing to the dispersions in the fiber bundle are much small indicating that those have little influence on the measurement of carrier relaxation dynamics. In the measurements of κ-(BEDT-TTF)2Cu(NCS)2 under 1.3 kbar at 43 K, we have successfully detected the polarization anisotropy of the carrier relaxation dynamics and estimated the decay time in the same way as the normal measurement.
Photoconductivity of ultra-thin Ge(GeSn) layers grown in Si by low-temperature molecular beam epitaxy
Authors: Talochkin A. B. , Chistokhin I. B. , Mashanov V. I.
Published: April 2016

Photoconductivity (PC) spectra of Si/Ge(GeSn)/Si structures with the ultra-thin (1.0–2.3 nm) Ge and GeSn alloy layers grown by the low-temperature (T = 100 °C) molecular beam epitaxy are studied. Photoresponse in the range of 1.2–0.4 eV related to light absorption in the buried Ge(GeSn) layer is observed. It is shown that in case of lateral PC, a simple diffusion model can be used to determine the absorption coefficient of this layer α ∼ 105 cm−1. This value is 100 times larger than that of a single Ge quantum dot layer and is reached significantly above the band gap of most bulk semiconductors. The observed absorption is caused by optical transitions between electron and hole states localized at the interfaces. The anomalous high value of α can be explained by the unusual state of Ge(GeSn) layer with high concentration of dangling bonds, the optical properties of which have been predicted theoretically by Knief and von Niessen (Phys. Rev. B 59, 12940 (1999)).
Nanograin-enhanced in-plane thermoelectric figure of merit in n-type SiGe thin films
Authors: Lu Jianbiao , Guo Ruiqiang , Huang Baoling
Published: April 2016

SiGe thin films are desirable candidates for many thermoelectric applications because of their low cost, low toxicity, and high compatibility with microelectronics fabrications. Currently, their applications are limited by their very poor thermoelectric performance. In this study, phosphorus-doped SiGe thin films with improved thermoelectric properties were grown using low pressure chemical vapor deposition, and the effects of different annealing treatments, doping concentration, composition, and temperature on their thermoelectric properties were explored. It is found that the segregation of phosphorus dopants plays an important role in grain growth and thermoelectric transport properties. The improved thermoelectric performance is mainly attributed to the significantly reduced in-plane thermal conductivity by the naturally formed nanograins. By adjusting the growth conditions, doping and post treatments, an in-plane ZT ∼ 0.16 at 300 K was obtained for the optimized n-type samples, which is even ∼50% higher than the record of bulk SiGe.
Honeycomb-like nanofiber based triboelectric nanogenerator using self-assembled electrospun poly(vinylidene fluoride-co-trifluoroethylene) nanofibers
Authors: Jang Shin , Kim Hyounjin , Kim Yeongjun , Kang Byung Ju , Oh Je Hoon
Published: April 2016

In this study, a honeycomb-like nanofiber based triboelectric nanogenerator (HN-TENG) is presented. In order to fabricate the honeycomb-like nanofiber, we utilized self-assembly of electrospun poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) nanofibers. The honeycomb-like P(VDF-TrFE) nanofiber network was directly produced via electrospinning without any additional processing. The HN-TENG showed a maximum voltage, current, and power density of 160 V, 17 μA, and 1.6 W/m2, respectively. The power density was enhanced more than twofold as compared with a typical flat nanofiber network based TENG due to the large surface area and high surface roughness of the honeycomb structure. Finally, we verified that HN-TENG has the potential to be used for practical applications by driving 100 light emitting diodes and charging capacitors.
Determination of the electronic, dielectric, and optical properties of sillenite Bi12TiO20 and perovskite-like Bi4Ti3O12 materials from hybrid first-principle calculations
Authors: Lardhi Sheikha , Noureldine Dalal , Harb Moussab , Ziani Ahmed , Cavallo Luigi , Takanabe Kazuhiro
Published: April 2016

Density functional theory calculation was conducted to determine the optoelectronic properties of bismuth titanate sillenite (Bi12TiO20) and perovskite-like (Bi4Ti3O12) structures. The lattice parameters were experimentally obtained from Rietveld analysis. The density functional perturbation theory approach was used with the standard Perdew–Burke–Ernzerhof functional and screened Coulomb hybrid Heyd–Scuseria–Ernzerhof functional to investigate the electronic structure and absorption coefficient. Both compounds have good carrier transport properties, low effective hole and electron masses, high dielectric constant, and low exciton binding energy.
Parametric analysis of a solid oxide fuel cell auxiliary power unit operating on syngas produced by autothermal reforming of hydrocarbon fuels
Authors: Dong Jun , Xu Xinhai , Xu Ben , Zhang Shuyang
Published: April 2016

A 1 kWe integrated auxiliary power unit (APU) system consisting of an autothermal reformer and a solid oxide fuel cell (SOFC) unit, as well as balance-of-plant components, was designed and analyzed. A relatively easy-to-approach SOFC model was developed in order to conveniently calculate V-I and P-I curves and the system's net efficiency at different operating conditions. The effects of steam to carbon and oxygen to carbon ratios in the reactants, channel dimensions of the SOFC unit, and hydrocarbon fuel types on the integrated APU system's performance were discussed. Five hydrocarbon fuels including diesel, Jet-A, gasoline, ethanol, and methanol were studied as fuel sources for the APU system. The system's net efficiency around 35% is possible for all the tested fuels in the current density range of 100–400 mA/cm2. The APU system was also verified to be thermally self-sustainable in the steady state operation by a thermal management analysis.
Liquid evaporation-driven folding of graphene sheets
Authors: Liu Qingchang , Gao Yuan , Xu Baoxing
Published: April 2016

We propose a theory of folding graphene sheets from rapid evaporation of its liquid suspension. Using an energy criterion that contains the competition among bending energy of graphene sheets, surface energy of graphene sheets and liquid and their interfacial energy, and binding energy of folded graphene sheets, we are able to quantitatively correlate folded three-dimensional (3D) graphene structures with both geometric size and surface wettability of original graphene sheets. Theoretical predictions of folded 3D graphene patterns and sizes agree well with the parallel molecular dynamics simulations. Our theory is of immediate interest to the study of crumpling/folding original two-dimensional structures to 3D shapes through evaporation of a liquid suspension.