bluuebunny/crossref_metadata_2025 huggingface dataset:
Accuracy and Precision of a Custom Camera-Based System for 2-D and 3-D Motion Tracking During Speech and Nonspeech Motor Tasks
Authors: Feng Yongqiang , Max Ludo
Published: April 2014

Purpose

Studying normal or disordered motor control requires accurate motion tracking of the effectors (e.g., orofacial structures). The cost of electromagnetic, optoelectronic, and ultrasound systems is prohibitive for many laboratories and limits clinical applications. For external movements (lips, jaw), video-based systems may be a viable alternative, provided that they offer high temporal resolution and submillimeter accuracy.

Method

The authors examined the accuracy and precision of 2-D and 3-D data recorded with a system that combines consumer-grade digital cameras capturing 60, 120, or 240 frames per second (fps), retro-reflective markers, commercially available computer software (APAS, Ariel Dynamics), and a custom calibration device.

Results

Overall root-mean-square error (RMSE) across tests was 0.15 mm for static tracking and 0.26 mm for dynamic tracking, with corresponding precision (
SD
) values of 0.11 and 0.19 mm, respectively. The effect of frame rate varied across conditions, but, generally, accuracy was reduced at 240 fps. The effect of marker size (3- vs. 6-mm diameter) was negligible at all frame rates for both 2-D and 3-D data.

Conclusion

Motion tracking with consumer-grade digital cameras and the APAS software can achieve submillimeter accuracy at frame rates that are appropriate for kinematic analyses of lip/jaw movements for both research and clinical purposes.
Webcam Delivery of the Lidcombe Program for Early Stuttering: A Phase I Clinical Trial
Authors: O’Brian Sue , Smith Kylie , Onslow Mark
Published: April 2014

Purpose

The Lidcombe Program is an operant treatment for early stuttering shown with meta-analysis to have a favorable odds ratio. However, many clients are unable to access the treatment because of distance and lifestyle factors. In this Phase I trial, we explored the potential efficacy, practicality, and viability of an Internet webcam Lidcombe Program service delivery model.

Method

Participants were 3 preschool children who stuttered and their parents, all of whom received assessment and treatment using webcam in their homes with no clinic attendance.

Results

At 6 months post–Stage 1 completion, all children were stuttering below 1.0% syllables stuttered. The webcam intervention was acceptable to the parents and appeared to be practical and viable, with only occasional audiovisual problems. At present, there is no reason to doubt that a webcam-delivered Lidcombe Program will be shown with clinical trials to have comparable efficacy with the clinic version.

Conclusion

Webcam-delivered Lidcombe Program intervention is potentially efficacious, is practical and viable, and requires further exploration with comparative clinical trials and a qualitative study of parent and caregiver experiences.
Experimental investigation of laser beam diffraction on phase step and its practical applications
Authors: Basisty E.V. , Komotskii V.A.
Published: April 2014

The change in shape of the spatial spectrum, which is a result of the interaction of a focused laser beam with a phase step structure (PSS), is investigated. As a laser beam passes through a PSS, a spatial spectrum of radiation in the form of two peaks with a deep gap in between is generated. The change in the peaks’ structure as the PSS moves relative to the optical axis of the laser beam is studied in detail. On the basis of the experimental results, a new scheme for measuring small linear and angular deviations is proposed.
Nanoscale rolled‐up InAs quantum dot tube photodetector
Authors: Dastjerdi M.H.T. , Mi Z.
Published: April 2014

The first demonstration of a rolled‐up InAs quantum dot tube photodetector is reported, which is fabricated by the selective release of self‐organised InAs/GaAs quantum dot heterostructures from the host substrate. The device exhibits a responsivity of ∼66 mA/W and an external quantum efficiency of ∼8% under 1064 nm excitation at 300 K.
Divide and conquer method for sparsity estimation within compressed sensing framework
Authors: Tian Wenbiao , Rui Guosheng , Kang Jian
Published: April 2014

A novel method for sparsity estimation by means of the divide and conquer method is presented. Also, the underestimation and overestimation criteria for signal sparsity is proposed and proven. Then the blind‐sparsity subspace pursuit (BSP) algorithm for sparse reconstruction is discussed. Based on the estimation, BSP combines the support set and inherits the backtracking refinement that attaches to compressive sampling matching pursuit (CoSaMP)/subspace pursuit (SP), whereas the pruning process of BSP is improved by introducing the weakly matching backtracking strategy. With the said improvement, there is no need for BSP to require the sparsity as an input parameter. Furthermore, experiments demonstrate that the divide and conquer method is effective for sparsity estimation when the isometry constant is known. In addition, the simulation results also validate the superior performance of the new algorithm and show that BSP is an excellent algorithm for blind sparse reconstruction and is robust when the estimate of sparsity is not perfectly accurate.
Snapback‐free reverse‐conducting IGBT with low turnoff loss
Authors: Yi Bo , Lin Zhi , Chen Xingbi
Published: April 2014

A novel structure of the reverse‐conducting insulated gate bipolar transistor (RC‐IGBT) is proposed. The structure is connected anti‐parallel with a PNP and an NPN transistor, which are in a collector‐base short‐circuited configuration. Bidirectional conduction capability with no snapback can be obtained by this structure and the turnoff speed can be much improved. The structure can work in two different modes in a reverse‐conducting state: a diode mode and a thyristor mode. Two‐dimensional numerical simulation results show that the novel RC‐IGBT reduces the turnoff loss (Eoff) by 26.4 and 37.7% for the thyristor mode and the diode mode, respectively, and has no current non‐uniformity compared with the conventional RC‐IGBT.
Reconstruction of interior layout of building from through‐the‐wall radar image using MST‐based method
Authors: Chen Bo , Jin Tian , Lu Biying , Zhou Zhimin
Published: April 2014

To reconstruct the interior layout of a building from a through‐the‐wall radar image, a method based on a minimum spanning tree (MST) which comes from graph theory is proposed. The traditional MST method is introduced and the traditional method is improved by applying the MST model with restricted conditions to solve the reconstruction problem when there exist interference targets in a building. Anechoic chamber measurements are carried out to demonstrate the suitability and efficacy of the MST‐based method.
Outlier‐resistant adaptive filtering based on sparse Bayesian learning
Authors: Zhu Wei , Tang Jun , Wan Shuang , Zhu Jie‐Li
Published: April 2014

In adaptive processing applications, the design of the adaptive filter requires estimation of the unknown interference‐plus‐noise covariance matrix from secondary training data. The presence of outliers in the training data can severely degrade the performance of adaptive processing. By exploiting the sparse prior of the outliers, a Bayesian framework to develop a computationally efficient outlier‐resistant adaptive filter based on sparse Bayesian learning (SBL) is proposed. The expectation–maximisation (EM) algorithm is used therein to obtain a maximum a posteriori (MAP) estimate of the interference‐plus‐noise covariance matrix. Numerical simulations demonstrate the superiority of the proposed method over existing methods.
TFT‐based, multi‐stage, active pixel sensor for alpha particle detection
Authors: Kunnen G. , Smith J. , Chung H. , Allee D.
Published: April 2014

A multi‐stage thin film transistor (TFT)‐based active pixel sensor (APS), capable of successfully detecting small impulses of charge resulting from incident alpha particle strikes, is presented. Detection of alpha particles is important in the field of neutron detection, where fully integrated thin‐film‐based detectors are an attractive alternative to conventional 3He‐based proportional counters owing to their low‐cost and large‐area scaling capability, combined with the use of readily available materials. A typical TFT process, however, produces only N‐type devices with low electron mobilities – making high‐gain CMOS amplifier designs unfeasible. The disadvantages of using a TFT‐only APS design are mitigated by cascading multiple low‐gain TFT amplifiers, which results in a higher overall pixel gain – subsequently allowing for the successful detection and readout of alpha particle strikes. Presented is a new APS fabricated in an indium gallium zinc oxide TFT process is presented, and successful initial alpha response measurements are reported.
Unidirectional planar monopole ultra‐wideband antenna using wrench‐shaped feeding structure
Authors: Ellis M.S. , Zhao Zhiqin , Wu Jiangniu , Nie Z. , Liu Qing‐Huo
Published: April 2014

A unidirectional planar monopole ultra‐wideband (UWB) antenna is presented. To realise unidirectional radiation, a new feed structure is implemented without modifications in the ground plane or the monopole. By using a wrench‐shaped feeding structure, unidirectional radiation of the planar monopole antenna can be realised, especially at high frequencies. The antenna is built on a 20 × 30 mm FR4 substrate to cover a frequency bandwidth from 3.1 to over 14 GHz for a voltage standing wave ratio ≤2.
Scale‐free network model for template matching based on kernel histogram
Authors: Han Ri‐Sheng , Shen Shi‐Gen , Yue Guang‐Xue , Ding Hui
Published: April 2014

A novel method to build a scale‐free network model for template matching is proposed. The scale‐free network model of the template is produced by a kernel histogram. Moreover, those special points that have much larger effects than other points can be selected by a matching algorithm. Based on the scale‐free network model, the matching is implemented by minimising the sum of absolute differences. The proposed algorithm can match the potential object of varying scale in a clutter background. To the best of the authors' knowledge, this is the first template matching algorithm which uses the scale‐free complex network to model template matching.
Spectrum sensing method based on goodness of fit test using chi‐square distribution
Authors: Teguig D. , Le Nir V. , Scheers B.
Published: April 2014

In cognitive radio, spectrum sensing is a challenging task. Proposed is a new spectrum sensing method based on the goodness of fit test of the energy of the received samples with a chi‐square distribution. The test statistic is derived and the performance of the proposed method is evaluated by Monte Carlo simulations. It is shown that the proposed spectrum sensing method outperforms the conventional energy detection method without increasing the complexity of the sensing.
Fast closed‐form trivariate statistical isotonic modelling
Authors: Fiori S.
Published: April 2014

A non‐iterative, closed‐form solution to the problem of statistically modelling the monotonic relationship between a dependent variable and two independent variables through a probability conservation principle is introduced.
[011] waveguide stripe direction n‐i‐p‐n heterostructure InP optical modulator
Authors: Ogiso Y. , Ohiso Y. , Shibata Y. , Kohtoku M.
Published: April 2014

A new n‐i‐p‐n heterostructure InP(100) optical modulator is proposed. By utilising the crystallographic orientation dependence of the electro‐optic Pockels effect and electric field direction, the device, which is formed along the [011] waveguide stripe direction, has a lower half‐wave voltage than one formed along the [01̄1] direction. The half‐wave voltage of a [01̄1] direction phase modulator was 4.8 V, whereas that of the [011] direction was 2.9 V.
Facial expression recognition with regional hidden Markov models
Authors: Sun Y. , Akansu A.N.
Published: April 2014

A regional hidden Markov model (RHMM) for automatic facial expression recognition in video sequences is proposed. Facial action units are described by RHMMs for the states of facial regions: eyebrows, eyes and mouth registered in a video. The tracked facial feature points in the spatial domain form observation sequences that drive the classification process. It is shown that the proposed technique outperforms other methods reported in the literature for the person‐independent case tested with the extended Cohn‐Kanade database.
Zero‐pseudorandom noise training OFDM
Authors: Esmaiel H. , Jiang D.
Published: April 2014

A novel transmission scheme called zero‐pseudorandom noise training sequence orthogonal frequency division multiplexing (ZPN‐OFDM) is proposed, where the frame structure of dual‐pseudorandom noise (PN) padding time domain synchronous OFDM is modified by replacing the first PN sequence by a zero sequence. The new ZPN‐OFDM system offers better energy efficiency than previous OFDM systems. The ZPN‐OFDM system is tested for significant tap delay multipath channels. Simulation results show that ZPN‐OFDM can provide significant bit error rate improvement as well as energy efficiency improvement.
Advantages of EADFB laser for 25 Gbaud/s 4‐PAM (50 Gbit/s) modulation and 10 km single‐mode fibre transmission
Authors: Kobayashi W. , Fujisawa T. , Ito T. , Kanazawa S. , Ueda Y. , Sanjoh H.
Published: April 2014

The 25 Gbaud/s 4‐level pulse amplitude modulation (4‐PAM) of a 1.3 μm electroabsorption modulator integrated with a distributed feedback (DFB) laser is demonstrated for the first time. The linearities of the electroabsorption DFB (EADFB) laser and the directly modulated laser are evaluated to investigate the applicability of the PAM format to these devices.
Salient object detection based on multi‐scale super‐pixels and saliency propagation
Authors: Zhang Geng , Yuan Zejian , Liu Yuehu , Zheng Nanning
Published: April 2014

A novel method to detect the most salient object from an image is proposed. Saliency cues such as spatial colour distribution and the saliency prior are extended to super‐pixels and are integrated to compute the final saliency. The super‐pixels are generated in multiple scales so that the proposed method is adaptive to objects of different sizes. Moreover, to solve the problem that many saliency detection algorithms rely on local evidences, it is proposed to propagate the saliency information based on the spectral affinities of super‐pixels. Experimental results have proven that the proposed method achieves discriminative saliency maps and outperforms the state‐of‐the‐art methods.
Minimising nonlinear Raman crosstalk in future network overlays on legacy passive optical networks
Authors: Piehler D.
Published: April 2014

There is a desire to overlay future optical access networks onto legacy passive optical networks (PONs) to provide increasingly advanced services by filling empty wavelength bands of legacy gigabit rate PONs. Nonlinear Raman crosstalk from new wavelengths onto legacy RF video services (1550–1560 nm band) and onto the legacy digital downstream at 1490 nm, however, can limit the number and the launch power of new wavelengths. As an example, straightforward physical‐layer adjustments at the optical line terminal that increase the number of new, 10 Gbit/s channels launched in the 1575–1580 nm band by a factor of 16 without increasing the Raman penalty on the video signal are illustrated. A physical‐layer (RF) filter modifies the on–off‐keyed signal feeding each 10 Gbit/s transmitter, suppressing the RF Raman crosstalk on the video signal by 9 dB while incurring a power penalty on each 10 Gbit/s link of <0.5 (2.0) dB with (without) forward error correction. The previous Raman mitigation work used non‐standard line‐coding to shape the 10 Gbit/s electrical spectrum. In addition, polarisation‐interleaving of new wavelengths lowers the worst‐case RF DC crosstalk by ∼3 dB in fibres and it limits and stabilises DC crosstalk in low polarisation mode dispersion fibre links.
Investigation of LaAlO3/ZrO2/a‐InGaZnO thin‐film transistors using atmospheric pressure plasma jet
Authors: Wu Chien‐Hung , Huang Hau‐Yuan , Wang Shui‐Jinn , Chang Kow‐Ming , Hsu Hsin‐Yu
Published: April 2014

Amorphous indium–gallium–zinc‐oxide thin‐film transistors (a‐IGZO‐TFTs) with the LaAlO3/ZrO2 gate dielectric stack employing a novel atmospheric pressure plasma jet process that results in small subthreshold swing and low threshold voltage are proposed and fabricated. The influence of post‐deposition annealing (PDA) temperature on LaAlO3/ZrO2 gate dielectric stack and device performance was investigated. The equivalent oxide thickness of the LaAlO3/ZrO2 dielectric stack decreases from 11.5 nm without annealing to 7 nm after a 500°C annealing was applied. The LaAlO3/ZrO2/a‐InGaZnO TFT with a 500°C annealing exhibits a small subthreshold swing of 77 mV·dec−1, a high field‐effect mobility of 9 cm2·V−1·s−1 and an excellent current ratio of 1.8 × 107, which could be attributed to the improved gate dielectric quality by the PDA. The LaAlO3/ZrO2/a‐InGaZnO TFTs with excellent gate control ability allow the device to operate at a low operating voltage with low power consumption.
Depletion interaction between two ellipsoids
Authors: Miao Han , Li Yao , Ma Hongru
Published: April 2014

The depletion interactions between two ellipsoids in three configurations were studied by both Monte Carlo simulation with the Wang-Landau algorithm and the density functional theory in the curvature expansion approximation. Common features of the depletion interactions were found and the results were as expected. By comparing the results of the two methods, it is concluded that density functional theory under the curvature expansion approximation gave very good results to the depletion forces.
Parity-time symmetry broken by point-group symmetry
Authors: Fernández Francisco M. , Garcia Javier
Published: April 2014

We discuss a parity-time (PT) symmetric Hamiltonian with complex eigenvalues. It is based on the dimensionless Schrödinger equation for a particle in a square box with the PT-symmetric potential V(x, y) = iaxy. Perturbation theory clearly shows that some of the eigenvalues are complex for sufficiently small values of |a|. Point-group symmetry proves useful to guess if some of the eigenvalues may already be complex for all values of the coupling constant. We confirm those conclusions by means of an accurate numerical calculation based on the diagonalization method. On the other hand, the Schrödinger equation with the potential V(x, y) = iaxy2 exhibits real eigenvalues for sufficiently small values of |a|. Point group symmetry suggests that PT-symmetry may be broken in the former case and unbroken in the latter one.
Excellent oxidation endurance of boron nitride nanotube field electron emitters
Authors: Song Yenan , Sun Yuning , Hoon Shin Dong , Nam Yun Ki , Song Yoon-Ho , Milne William I. , Jin Lee Cheol
Published: April 2014

Boron nitride nanotubes (BNNTs) are considered as a promising cold electron emission material owing to their negative electron affinity. BNNT field emitters show excellent oxidation endurance after high temperature thermal annealing of 600 °C in air ambient. There is no damage to the BNNTs after thermal annealing at a temperature of 600 °C and also no degradation of field emission properties. The thermally annealed BNNTs exhibit a high maximum emission current density of 8.39 mA/cm2 and show very robust emission stability. The BNNTs can be a promising emitter material for field emission devices under harsh oxygen environments.
Swimming and pumping of rigid helical bodies in viscous fluids
Authors: Li Lei , Spagnolie Saverio E.
Published: April 2014

Rotating helical bodies of arbitrary cross-sectional profile and infinite length are explored as they swim through or transport a viscous fluid. The Stokes equations are studied in a helical coordinate system, and closed form analytical expressions for the force-free swimming speed and torque are derived in the asymptotic regime of nearly cylindrical bodies. High-order accurate expressions for the velocity field and swimming speed are derived for helical bodies of finite pitch angle through a double series expansion. The analytical predictions match well with the results of full numerical simulations, and accurately predict the optimal pitch angle for a given cross-sectional profile. This work may improve the modeling and design of helical structures used in microfluidic manipulation, synthetic microswimmer engineering, and the transport and mixing of viscous fluids.
Measurement of coherence length and incoherent source size of hard x-ray undulator beamline at Pohang Light Source-II
Authors: Park So Yeong , Hong Chung Ki , Lim Jun
Published: April 2014

We measured the spatial coherence length and incoherent source size of a hard x-ray undulator beamline at Pohang Light Source-II, the stored electron energy of which has been increased from 2.5 GeV to 3 GeV. The coherence length was determined by single-slit measurement of the visibility of the Fresnel diffraction pattern. The correlated incoherent source size was cross-checked for three different optics: the single slit, beryllium parabolic compound refractive lenses, and the Fresnel zone plate. We concluded that the undulator beamline has an effective incoherent source size (FWHM) of 540 μm (horizontal) × 50 μm (vertical).
Observing hot carrier distribution in an n-type epitaxial graphene on a SiC substrate
Authors: Someya T. , Fukidome H. , Ishida Y. , Yoshida R. , Iimori T. , Yukawa R. , Akikubo K. , Yamamoto Sh. , Yamamoto S. , Yamamoto T. , Kanai T. , Funakubo K. , Suemitsu M. , Itatani J. , Komori F. , Shin S. , Matsuda I.
Published: April 2014

Hot carrier dynamics in the Dirac band of n-type epitaxial graphene on a SiC substrate were traced in real time using femtosecond-time-resolved photoemission spectroscopy. The spectral evolution directly reflects the energetically linear density of states superimposed with a Fermi–Dirac distribution. The relaxation time is governed by the internal energy dissipation of electron–electron scattering, and the observed electronic temperature indicates cascade carrier multiplication.
Large eddy simulation requirements for the Richtmyer-Meshkov instability
Authors: Olson Britton J. , Greenough Jeff
Published: April 2014

The shock induced mixing of two gases separated by a perturbed interface is investigated through Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS). In a simulation, physical dissipation of the velocity field and species mass fraction often compete with numerical dissipation arising from the errors of the numerical method. In a DNS, the computational mesh resolves all physical gradients of the flow and the relative effect of numerical dissipation is small. In LES, unresolved scales are present and numerical dissipation can have a large impact on the flow, depending on the computational mesh. A suite of simulations explores the space between these two extremes by studying the effects of grid resolution, Reynolds number, and numerical method on the mixing process. Results from a DNS are shown using two different codes that use a high- and low-order numerical method and show convergence in the temporal and spectral dependent quantities associated with mixing. Data from an unresolved, high Reynolds number LES are also presented and include a grid convergence study. A model for an effective viscosity is proposed which allows for an a posteriori analysis of the simulation database that is agnostic to the LES model, numerics, and the physical Reynolds number of the simulation. An analogous approximation for an effective species diffusivity is also presented. This framework is then used to estimate the effective Reynolds number and Schmidt number of future simulations, elucidate the impact of numerical dissipation on the mixing process for an arbitrary numerical method, and provide guidance for resolution requirements of future calculations in this flow regime.
Nanowires enabling strained photovoltaics
Authors: Greil J. , Birner S. , Bertagnolli E. , Lugstein A.
Published: April 2014

Photovoltaic nano-devices have largely been relying on charge separation in conventional p-n junctions. Junction formation via doping, however, imposes major challenges in process control. Here, we report on a concept for photovoltaic energy conversion at the nano scale without the need for intentional doping. Our approach relies on charge carrier separation in inhomogeneously strained germanium nanowires (Ge NWs). This concept utilizes the strain-induced gradient in bandgap along tapered NWs. Experimental data confirms the feasibility of strain-induced charge separation in individual vapor-liquid-solid grown Ge NW devices with an internal quantum efficiency of ∼5%. The charge separation mechanism, though, is not inherently limited to a distinct material. Our work establishes a class of photovoltaic nano-devices with its opto-electronic properties engineered by size, shape, and applied strain.
Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme
Authors: Theophilou Iris , Tassi M. , Thanos S.
Published: April 2014

Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initiomethods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations.
Sustainable energy at the 100 W level for scientific sites on the Antarctic Plateau: Lessons learned from the Polar Experiment Network for Geospace Upper atmosphere Investigations-Automatic Geophysical Observatory project
Authors: Melville R. , Stillinger A. , Gerrard A. , Weatherwax A.
Published: April 2014

The need to provide power to unmanned instrumentation over the course of an entire year on the Antarctic plateau presents a large number of engineering and logistical challenges. Designs formulated in ideal laboratory environments often fail in the Antarctic due to the harsh operating conditions, and field experience is necessary to achieve year-round operation in the 100 W power range. In this paper we present our current power design for the Automatic Geophysical Observatories; a design based on over two decades of experience on the ice and allows for relatively continuous operation at the aforementioned power level. We also discuss our various implementation methods, both failures and successes, in an effort assist other unmanned deployments on the ice.
Homogeneous states in driven granular mixtures: Enskog kinetic theory versus molecular dynamics simulations
Authors: Khalil Nagi , Garzó Vicente
Published: April 2014

The homogeneous state of a binary mixture of smooth inelastic hard disks or spheres is analyzed. The mixture is driven by a thermostat composed by two terms: a stochastic force and a drag force proportional to the particle velocity. The combined action of both forces attempts to model the interaction of the mixture with a bath or surrounding fluid. The problem is studied by means of two independent and complementary routes. First, the Enskog kinetic equation with a Fokker-Planck term describing interactions of particles with thermostat is derived. Then, a scaling solution to the Enskog kinetic equation is proposed where the dependence of the scaled distributions φi of each species on the granular temperature occurs not only through the dimensionless velocity c = v/v0 (v0 being the thermal velocity) but also through the dimensionless driving force parameters. Approximate forms for φi are constructed by considering the leading order in a Sonine polynomial expansion. The ratio of kinetic temperatures T1/T2 and the fourth-degree velocity moments λ1 and λ2 (which measure non-Gaussian properties of φ1 and φ2, respectively) are explicitly determined as a function of the mass ratio, size ratio, composition, density, and coefficients of restitution. Second, to assess the reliability of the theoretical results, molecular dynamics simulations of a binary granular mixture of spheres are performed for two values of the coefficient of restitution (α = 0.9 and 0.8) and three different solid volume fractions (ϕ = 0.00785, 0.1, and 0.2). Comparison between kinetic theory and computer simulations for the temperature ratio shows excellent agreement, even for moderate densities and strong dissipation. In the case of the cumulants λ1 and λ2, good agreement is found for the lower densities although significant discrepancies between theory and simulation are observed with increasing density.
Role of point defects in bipolar fatigue behavior of Bi(Mg1/2Ti1/2)O3 modified (Bi1/2K1/2)TiO3-(Bi1/2Na1/2)TiO3 relaxor ceramics
Authors: Kumar Nitish , Ansell Troy Y. , Cann David P.
Published: April 2014

Lead-free Bi(Mg1/2Ti1/2)O3-(Bi1/2K1/2)TiO3-(Bi1/2Na1/2)TiO3 (BMT-BKT-BNT) ceramics have been shown to exhibit large electromechanical strains under high electric fields along with negligible fatigue under strong electric fields. To investigate the role of point defects on the fatigue characteristics, the composition 5BMT-40BKT-55BNT was doped to incorporate acceptor and donor defects on the A and B sites by adjusting the Bi/Na and Ti/Mg stoichiometries. All samples had pseudo-cubic symmetries based on x-ray diffraction, typical of relaxors. Dielectric measurements showed that the high and low temperature phase transitions were largely unaffected by doping. Acceptor doping resulted in the observation of a typical ferroelectric-like polarization with a remnant polarization and strain hysteresis loops with significant negative strain. Donor-doped compositions exhibited characteristics that were indicative of an ergodic relaxor phase. Fatigue measurements were carried out on all of the compositions. While the A-site acceptor-doped composition showed a small degradation in maximum strain after 106 cycles, the other compositions were essentially fatigue free. Impedance measurements were used to identify the important conduction mechanisms in these compositions. As expected, the presence of defects did not strongly influence the fatigue behavior in donor-doped compositions owing to the nature of their reversible field-induced phase transformation. Even for the acceptor-doped compositions, which had stable domains in the absence of an electric field at room temperature, there was negligible degradation in the maximum strain due to fatigue. This suggests that either the defects introduced through stoichiometric variations do not play a prominent role in fatigue in these systems or it is compensated by factors like decrease in coercive field, an increase in ergodicity, symmetry change, or other factors.
Towards a better understanding of dielectric barrier discharges in ferroelectrets: Paschen breakdown fields in micrometer sized voids
Authors: Harris Scott , Mellinger Axel
Published: April 2014

Charged cellular polypropylene foams (i.e., ferro- or piezoelectrets) demonstrate high piezoelectric activity upon being electrically charged. When an external electric field is applied, dielectric barrier discharges (DBDs) occur, resulting in a separation of charges which are subsequently deposited on dielectric surfaces of internal micrometer sized voids. This deposited space charge is responsible for the piezoelectric activity of the material. Previous studies have indicated charging fields larger than predicted by Townsend's model of Paschen breakdown applied to a multilayered electromechanical model; a discrepancy which prompted the present study. The actual breakdown fields for micrometer sized voids were determined by constructing single cell voids using polypropylene spacers with heights ranging from 8 to 75 μm, “sandwiched” between two polypropylene dielectric barriers and glass slides with semi-transparent electrodes. Subsequently, a bipolar triangular charging waveform with a peak voltage of 6 kV was applied to the samples. The breakdown fields were determined by monitoring the emission of light due to the onset of DBDs using an electron multiplying CCD camera. The breakdown fields at absolute pressures from 101 to 251 kPa were found to be in good agreement with the standard Paschen curves. Additionally, the magnitude of the light emission was found to scale linearly with the amount of gas, i.e., the height of the voids. Emissions were homogeneous over the observed regions of the voids for voids with heights of 25 μm or less and increasingly inhomogeneous for void heights greater than 40 μm at high electric fields.
Skin explosion of double-layer conductors in fast-rising high magnetic fields
Authors: Chaikovsky S. A. , Oreshkin V. I. , Datsko I. M. , Labetskaya N. A. , Ratakhin N. A.
Published: April 2014

An experiment has been performed to study the electrical explosion of thick cylindrical conductors using the MIG pulsed power generator capable of producing a peak current of 2.5 MA within 100 ns rise time. The experimental goal was to compare the skin explosion of a solid conductor with that of a double-layer conductor whose outer layer had a lower conductivity than the inner one. It has been shown that in magnetic fields of peak induction up to 300 T and average induction rise rate 3 × 109 T/s, the double-layer structure of a conductor makes it possible to achieve higher magnetic induction at the conductor surface before it explodes. This can be accounted for, in particular, by the reduction of the ratio of the Joule heat density to the energy density of the magnetic field at the surface of a double-layer conductor due to redistribution of the current density over the conductor cross section.
Indirect-drive ablative Rayleigh-Taylor growth experiments on the Shenguang-II laser facility
Authors: Wu J. F. , Miao W. Y. , Wang L. F. , Yuan Y. T. , Cao Z. R. , Ye W. H. , Fan Z. F. , Deng B. , Zheng W. D. , Wang M. , Pei W. B. , Zhu S. P. , Jiang S. E. , Liu S. Y. , Ding Y. K. , Zhang W. Y. , He X. T.
Published: April 2014

In this research, a series of single-mode, indirect-drive, ablative Rayleigh-Taylor (RT) instability experiments performed on the Shenguang-II laser facility [X. T. He and W. Y. Zhang, Eur. Phys. J. D 44, 227 (2007)] using planar target is reported. The simulation results from the one-dimensional hydrocode for the planar foil trajectory experiment indicate that the energy flux at the hohlraum wall is obviously less than that at the laser entrance hole. Furthermore, the non-Planckian spectra of x-ray source can strikingly affect the dynamics of the foil flight and the perturbation growth. Clear images recorded by an x-ray framing camera for the RT growth initiated by small- and large-amplitude perturbations are obtained. The observed onset of harmonic generation and transition from linear to nonlinear growth regime is well predicted by two-dimensional hydrocode simulations.
Properties of high-angle Fe(Se,Te) bicrystal grain boundary junctions
Authors: Sarnelli E. , Adamo M. , Nappi C. , Braccini V. , Kawale S. , Bellingeri E. , Ferdeghini C.
Published: April 2014

We report on the characterization of Fe(Se,Te) grain boundary junctions fabricated on a 45° tilt symmetric bicrystal substrate. The junctions show critical current densities of the order of 104 A/cm2, showing a decay of about one order of magnitude with respect to the critical current density of the film, which is very promising for applications. The current-voltage characteristics show resistively shunted junction-like behaviors, with very low normal-state resistance values, typical of superconducting/normal-metal/superconducting junctions. The magnetic field dependences of the critical currents show the typical behaviors of large Josephson junctions. Nevertheless, the critical current is uniformly distributed across the barrier. We present a simplified theoretical model accounting for this effect. The small influence of faceting along the grain boundary on the electrical parameters may be consistent with an s-wave symmetry of the order parameter.
Vacuum ultraviolet field emission lamp utilizing KMgF3 thin film phosphor
Authors: Yanagihara Masahiro , Yusop Mohd Zamri , Tanemura Masaki , Ono Shingo , Nagami Tomohito , Fukuda Kentaro , Suyama Toshihisa , Yokota Yuui , Yanagida Takayuki , Yoshikawa Akira
Published: April 2014

We demonstrated a field emission lamp by employing a KMgF3 thin film as a solid-state vacuum ultraviolet phosphor. The output power of the lamp was 2 μW at an extraction voltage of 800 V and acceleration voltage of 1800 V, and it operated at wavelengths 140–220 nm, which is the shortest wavelength reported for solid-state phosphor lamps. The thin film was grown on MgF2 substrate by pulsed laser deposition. Its conversion efficiency was almost equivalent to a single KMgF3 crystal, and it had emission peaks of 155 and 180 nm in wavelength. These peaks are attributed to transitions from the valence anion band to the outermost core cation band and correspond well with emission peaks previously reported from the crystal. Additionally, we obtained a thermal-free and low-power consumption lamp by employing carbon nanofibres (CNFs) as a field emitter. A CNF emitter was easily grown at room temperature and can be grown on flexible materials.
Effect of Mg doping on the structural and free-charge carrier properties of InN films
Authors: Xie M.-Y. , Ben Sedrine N. , Schöche S. , Hofmann T. , Schubert M. , Hung L. , Monemar B. , Wang X. , Yoshikawa A. , Wang K. , Araki T. , Nanishi Y. , Darakchieva V.
Published: April 2014

We present a comprehensive study of free-charge carrier and structural properties of two sets of InN films grown by molecular beam epitaxy and systematically doped with Mg from 1.0 × 1018 cm−3 to 3.9 × 1021 cm−3. The free electron and hole concentration, mobility, and plasmon broadening parameters are determined by infrared spectroscopic ellipsometry. The lattice parameters, microstructure, and surface morphology are determined by high-resolution X-ray diffraction and atomic force microscopy. Consistent results on the free-charge carrier type are found in the two sets of InN films and it is inferred that p-type conductivity could be achieved for 1.0 × 1018 cm−3 ≲ [Mg] ≲ 9.0 × 1019 cm−3. The systematic change of free-charge carrier properties with Mg concentration is discussed in relation to the evolution of extended defect density and growth mode. A comparison between the structural characteristics and free electron concentrations in the films provides insights in the role of extended and point defects for the n-type conductivity in InN. It further allows to suggest pathways for achieving compensated InN material with relatively high electron mobility and low defect densities. The critical values of Mg concentration for which polarity inversion and formation of zinc-blende InN occurred are determined. Finally, the effect of Mg doping on the lattice parameters is established and different contributions to the strain in the films are discussed.
Photoluminescence properties and crystallization of silicon quantum dots in hydrogenated amorphous Si-rich silicon carbide films
Authors: Wen Guozhi , Zeng Xiangbin , Wen Xixin , Liao Wugang
Published: April 2014

Silicon quantum dots (QDs) embedded in hydrogenated amorphous Si-rich silicon carbide (α-SiC:H) thin films were realized by plasma-enhanced chemical vapor deposition process and post-annealing. Fluorescence spectroscopy was used to characterize the room-temperature photoluminescence properties. X-ray photoelectron spectroscopy was used to analyze the element compositions and bonding configurations. Ultraviolet visible spectroscopy, Raman scattering, and high-resolution transmission electron microscopy were used to display the microstructural properties. Photoluminescence measurements reveal that there are six emission sub-bands, which behave in different ways. The peak wavelengths of sub-bands P1, P2, P3, and P6 are pinned at about 425.0, 437.3, 465.0, and 591.0 nm, respectively. Other two sub-bands, P4 is red-shifted from 494.6 to 512.4 nm and P5 from 570.2 to 587.8 nm with temperature increasing from 600 to 900 °C. But then are both blue-shifted, P4 to 500.2 nm and P5 to 573.8 nm from 900 to 1200 °C. The X-ray photoelectron spectroscopy analysis shows that the samples are in Si-rich nature, Si-O and Si-N bonds consumed some silicon atoms. The structure characterization displays that a separation between silicon phase and SiC phase happened; amorphous and crystalline silicon QDs synthesized with increasing the annealing temperature. P1, P2, P3, and P6 sub-bands are explained in terms of defect-related emission, while P4 and P5 sub-bands are explained in terms of quantum confinement effect. A correlation between the peak wavelength shift, as well as the integral intensity of the spectrum and crystallization of silicon QDs is supposed. These results help clarify the probable luminescence mechanisms and provide the possibility to optimize the optical properties of silicon QDs in Si-rich α-SiC: H materials.
Communication: On the origin of the surface term in the Ewald formula
Authors: Ballenegger V.
Published: April 2014

A transparent derivation of the Ewald formula for the electrostatic energy of a periodic three-dimensional system of point charges is presented. The problem of the conditional convergence of the lattice sum is dealt with by separating off, in a physically natural and mathematically simple way, long-range non-absolutely integrable contributions in the series. The general expression, for any summation order, of the surface (or dipole) term emerges very directly from those long-range contributions.
Effect of interfacial layer on the crystal structure of InAs/AlAs0.16Sb0.84/AlSb quantum wells
Authors: Lin Y. M. , Chen C. H. , Lee C. P.
Published: April 2014

Ion channeling technique using MeV C2+ ions and high resolution X-ray diffraction were used to study the crystal quality of an InAs/AlSb-based quantum wells. We found that the InAs quality has a strong dependence on the type of the interface used. With the addition of the InSb-like interface, the crystal quality of the InAs channel was greatly improved. The InAs lattice was fully strained and aligned with the lattice of the buffer layer without any lattice relaxation. On the other hand, if the interface was of the AlAs type, the lattice of the InAs quantum well was relaxed and the crystal quality was poor. This explains why a superior InAs quantum well with high electron mobility and good surface morphology can be achieved with the use of the InSb interface.
Understanding the deposition mechanism of pulsed laser deposited B-C films using dual-targets
Authors: Zhang Song , He Zhiqiang , Ji Xiaoli , Lu Wenzhong , Wang Chuanbin , Shen Qiang , Zhang Lianmeng
Published: April 2014

Boron carbide thin films with stoichiometry (boron-carbon atomic ratio) range of 0.1 ∼ 8.9 were fabricated via pulsed laser deposition by using boron-carbon dual-targets. However, this experimental data on stoichiometry were smaller than the computer simulation values. The discrepancy was investigated by studies on composition and microstructure of the thin films and targets by scanning electron microscopy, excitation laser Raman spectroscopy, and X-ray photoelectron spectroscopy. The results indicate that the boron liquid droplets were formed by phase explosion after laser irradiation on boron sector. Part of the boron droplets would be lost via ejection in the direction of laser beam, which is tilted 45° to the surface of substrate.
Magnetic Purcell factor in wire metamaterials
Authors: Slobozhanyuk A. P. , Poddubny A. N. , Krasnok A. E. , Belov P. A.
Published: April 2014

We present an experimental study of the magnetic Purcell effect in finite arrays of the wire metamaterial. By directly measuring the spatial-frequency map of the Purcell factor, we explicitly demonstrate how the Purcell factor is enhanced at the Fabry-Pérot resonances of the wire metamaterial block in microwave frequency range. The experimental results are in a good agreement with theoretical and numerical estimations.
Phonon blocking by two dimensional electron gas in polar CdTe/PbTe heterojunctions
Authors: Zhang Bingpo , Cai Chunfeng , Zhu He , Wu Feifei , Ye Zhenyu , Chen Yongyue , Li Ruifeng , Kong Weiguang , Wu Huizhen
Published: April 2014

Narrow-gap lead telluride crystal is an important thermoelectric and mid-infrared material in which phonon functionality is a critical issue to be explored. In this Letter, efficient phonon blockage by forming a polar CdTe/PbTe heterojunction is explicitly observed by Raman scattering. The unique phonon screening effect can be interpreted by recent discovery of high-density two dimensional electrons at the polar CdTe/PbTe(111) interface which paves a way for design and fabrication of thermoelectric devices.
A radio-frequency sheath model for complex waveforms
Authors: Turner M. M. , Chabert P.
Published: April 2014

Plasma sheaths driven by radio-frequency voltages occur in contexts ranging from plasma processing to magnetically confined fusion experiments. An analytical understanding of such sheaths is therefore important, both intrinsically and as an element in more elaborate theoretical structures. Radio-frequency sheaths are commonly excited by highly anharmonic waveforms, but no analytical model exists for this general case. We present a mathematically simple sheath model that is in good agreement with earlier models for single frequency excitation, yet can be solved for arbitrary excitation waveforms. As examples, we discuss dual-frequency and pulse-like waveforms. The model employs the ansatz that the time-averaged electron density is a constant fraction of the ion density. In the cases we discuss, the error introduced by this approximation is small, and in general it can be quantified through an internal consistency condition of the model. This simple and accurate model is likely to have wide application.
Lattice-matched AlInN in the initial stage of growth
Authors: Buß E. R. , Rossow U. , Bremers H. , Hangleiter A.
Published: April 2014

We investigated the dependence of the indium content of tenfold Al1−xInxN/GaN superlattice structures grown by metal organic vapor phase epitaxy on layer thickness and strain state. Growth conditions taken from a thick lattice-matched reference sample with an indium content of about 18% lead to reduced indium contents from 3% for 0.5 nm of Al1−xInxN to 16.5% for 5.0 nm, respectively. There is no evidence for dependences of the indium incorporation on the lattice mismatch between the Al1−xInxN and the subjacent layer. Additional supply of trimethylindium only shows a very slight, almost negligible influence on the indium content of these superlattice structures. Finally, we present a model explaining the behavior of the indium content of the Al1−xInxN layer assuming the growth of an indium depleted phase in the initial stage of growth.