bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic voltage restorer based on multilevel inverter with adjustable dc‐link voltage
Authors: Babaei Ebrahim , Kangarlu Mohammad Farhadi , Sabahi Mehran
Published: September 2013

Dynamic voltage restorer (DVR) is a power electronic converter‐based custom power device used to compensate for voltage variations. The inverter used in the DVR structure can have different topologies. Multilevel inverters are a good candidate to be used in the DVR structure especially in higher voltage level. This study proposes a new scheme for DVR based on a multilevel inverter. In the proposed DVR, a dc–dc converter is attached to the multilevel inverter. The dc‐link voltage is regulated by the dc–dc converter considering the voltage sag magnitude. In this way, the output voltage of the multilevel inverter has always its maximum possible number of levels. This results in better quality of output voltage in both deep and shallow voltage sags. It is important to emphasise that the existing inverter‐based DVR topologies do not have this capability. Also, in the proposed DVR, there is no need for an output filter. Moreover, the fundamental frequency control method for the multilevel inverter can be used instead of pulse width modulation‐based methods. This can result in lower switching losses and lower switching stresses. The mathematical analysis of the operation range of the proposed DVR is given in detail. The simulation results using Power System Computer Aided Design/Electromagnetic Transient including DC (PSCAD/EMTDC) as well as the experimental results from a laboratory prototype verify the proposed DVR scheme.
Unified algebraic synthesis of generalised Fibonacci switched capacitor converters
Authors: Kushnerov Alexander , Ben‐Yaakov Shmuel (Sam)
Published: September 2013

A unified algebraic approach to the synthesis of generalised Fibonacci switched capacitor converters (SCC) has been developed. The proposed approach reduces the power losses by increasing the number of target voltages. It is shown that the binary and Fibonacci SCC are special cases of the proposed approach. Furthermore, the proposed generalised SCC is built around the same switch network as the binary and Fibonacci SCC. This feature is extremely beneficial, since it provides the option of switching between the different target voltages, thereby increasing the resolution of attainable conversion ratios. In the case of three flying capacitors, six new conversion ratios were introduced, in addition to the 13 that had already been realised. The theoretical results were verified experimentally.
Flicker mitigation strategy for a doubly fed induction generator by torque control
Authors: Zhang Yunqian , Hu Weihao , Chen Zhe , Cheng Ming , Hu Yanting
Published: September 2013

Owing to the rotational sampling of turbulence, wind shear and tower shadow effects grid connected variable speed wind turbines could lead to the power fluctuations which may produce flicker during continuous operation. A model of an megawatt (MW)‐level variable speed wind turbine with a doubly fed induction generator is presented to investigate the flicker mitigation. Taking advantage of the large inertia of the wind turbine rotor, a generator torque control (GTC) strategy is proposed, so that the power oscillation is stored as the kinetic energy of the wind turbine rotor, thus the flicker emission could be reduced. The GTC scheme is proposed and designed according to the generator rotational speed. The simulations are performed on the national renewable energy laboratory 1.5 MW upwind reference wind turbine model. Simulation results show that damping the generator active power by GTC is an effective means for flicker mitigation of variable speed wind turbines during continuous operation.
Automated control of doubly fed induction generator integrating sensorless parameter estimation and grid synchronisation
Authors: Susperregui Ana , Jugo Josu , Lizarraga Ibone , Tapia Gerardo
Published: September 2013

This study proposes a parameter estimation method, together with a grid synchronisation algorithm, for wind turbine‐driven doubly fed induction generators (DFIGs). Aiming at achieving an automated control procedure, their integration with a previously published power control strategy is also addressed. During a normal operation mode, the DFIG is grid‐connected and generated power is commanded by combining a sliding‐mode control (SMC) scheme, which provides high dynamic performance and robust behaviour, with a model reference adaptive system observer, estimating both rotor position and speed without the use of mechanical sensors. In order to preserve performance during start‐up and grid connection without the additional requirement of an encoder, the proposed parameter estimation and grid synchronisation schemes are both sensorless. Moreover, the same SMC structure of the power control strategy is also adopted for the grid synchronisation algorithm, which facilitates transfer between synchronisation and power controllers at the instant of grid connection. Thereby, a global sensorless SMC configuration result, which is self‐matched by the parameter estimation process. The resulting scheme has been applied to a hardware‐in‐the‐loop‐based DFIG virtual prototype under realistic wind conditions, obtaining satisfactory results.
Adaptive position‐domain carrier‐smoothed code filter based on innovation sequences
Authors: Lee Je Young , Kim Hee Sung , Choi Kwang Ho , Cho Jeongho , Lee Hyung Keun
Published: September 2013

Owing to dependence on radio frequency signals, the accuracy of Global Navigation Satellite System (GNSS) is largely dependent on the receiver's surrounding environments. Accordingly, accurate and reliable GNSS positioning in various harsh environments has been one of the major problems of GNSS. With regard to improve positioning accuracy in GNSS, this study proposes an efficient covariance estimation method for position‐domain carrier‐smoothed code (CSC) filters which, differently from traditional Kalman filters, do not require a dynamics model for time propagation of system states. The exclusion of a dynamics model, however, may incur shortage of information to estimate covariance parameters. To handle this problem, the proposed method imposes minimal assumptions on covariance structures for pseudorange and carrier‐phase measurements. Performance of the proposed method is demonstrated by an experimental result with field‐collected measurements showing that the proposed covariance estimator improves the accuracy of CSC filtering considerably.
Adaptive filter of non‐linear systems with generalised unknown disturbances
Authors: Qin Yuemei , Liang Yan , Yang Yanbo , Wang Zengfu , Yang Feng
Published: September 2013

This study presents the state estimation problem of discrete‐time non‐linear stochastic system with generalised unknown disturbance (GUD) in the measurements. To the best of our knowledge, there is no research result on the filter design dealing with such estimation problem. Here, an upper‐bound filter is designed for the linear time‐varying system with the GUD existing in the measurement equation, and optimal parameters are derived so that the minimum upper‐bounds filter is obtained. The result is further extended to the non‐linear case via the iterative optimisation of joint state estimation and parameter identification (the linearised measurement matrix). The simulation about tracking a target via one biased radar and one biased electronic support measure (ESM) shows the effectiveness and robustness of the proposed filter.
High‐frequency radar cross‐sections of swell‐contaminated seas for a pulsed waveform
Authors: Shen Chengxi , Gill Eric , Huang Weimin
Published: September 2013

The first‐ and second‐order monostatic cross‐sections of swell‐contaminated seas for high‐frequency ground wave pulsed radar operation are derived from the fundamental electric field equations. In this case, the ocean surface, a mixture of both swell and wind wave components, is first represented with a Fourier series. In one of the two approaches used, the total Fourier coefficient is expanded as a linear sum of the contribution from swell and wind waves without considering the possible interaction between the two regimes; whereas in a second, more general situation, the analysis includes coupling effects between the wind waves and swell. Then, the corresponding electric fields received from the swell‐contaminated sea surface are obtained. A Fourier transform of the autocorrelation of the electric fields gives the Doppler power spectral density (PSD), and a comparison between this PSD and monostatic radar range equation yields the radar cross‐sections. Simulation shows that the assumption incorporating the coupling effects leads to results that better agree with historical field observations. Overall, the model proposed here not only lays a solid foundation for the development of future swell inversion algorithms, but also reveals the existence of non‐linear energy transfer between swell and wind waves from a new perspective.
Median matrices and their application to radar training data selection
Authors: Aubry Augusto , De Maio Antonio , Pallotta Luca , Farina Alfonso
Published: September 2013

This study deals with the problem of covariance matrix estimation for radar signal processing applications. The authors propose and analyse a class of estimators which do not require any knowledge about the probability distribution of the sample support and exploit the characteristics of the positive definite matrix space. Any estimator of the class is associated with a suitable distance in the considered space and is defined as the median matrix of some basic covariance matrix estimates obtained from the available secondary data set. Then, the new devised estimators are applied to the problem of secondary data selection and their performances are compared with those obtained using geometric barycenters. The results show that data selectors exploiting geometric medians can outperform those based on geometric barycenters but the former requires a computational complexity higher than the latter.
Robust radar waveform recognition algorithm based on random projections and sparse classification
Authors: Ma Jie , Huang GaoMing , Zuo Wei , Wu XinHui , Gao Jun
Published: September 2013

To solve the limitations existing in the feature‐based recognition method in information completeness and redundant of the representation and the noise robustness, a radar waveform recognition algorithm based on random projections and sparse classification (SC) is presented. Construction of the framework of the proposed algorithm consists of two phases. In the first phase, the compressed signals by random projections are used instead of traditional signal features to represent the original signal. In the second, the robust SC approach is investigated to the radar waveform recognition. Compared with the existing feature‐based recognition method, the random projections and sparse classification‐based algorithm can improve the information completeness, efficiency and the noise robust. The validity of the recognition algorithm is demonstrated with the analysis and simulations.
Joule heat welding using dual‐nanomanipulators inside scanning electron microscope: a method applied for manipulation and device fabrication of one‐dimensional nanomaterials
Authors: Yu Hongfei , Zhang Lijie , Zou Chao , Dong Youqing , Yang Yun , Huang Shaoming
Published: September 2013

The controllable manipulation of a single nanowire (NW) using dual‐nanomanipulators attached to a scanning electron microscope (e.g. selectively removing a single NW from the NW‐cluster to a desired substrate) is significant for device fabrication. This can only be achieved when the contact between the NW and tungsten tip equipped in the nanomanipulator is mechanically strong. Here, a Joule heat welding technique is developed to create strong contacts between the NWs (including metal and semiconductor NWs) and the tungsten tips, which can greatly improve the manipulation technology that presents great potential in device fabrication.
Fabrication and analytical evaluation of three‐dimensional microsolenoids achieved in fused silica by femtosecond‐laser‐based microsolidifying process
Authors: Liu Keyin , Yang Qing , Zhao Yulong , Chen Feng , Shan Chao , Fan Xiaole , Meng Xiangwei , Du Guangqing , Bian Hao
Published: September 2013

In this reported work, a femtosecond‐laser‐based microsolidifying method was employed to fabricate three‐dimensional (3D) microsolenoids by injecting liquid metal into helicalmicrochannels in fused silica and solidifying the liquid metal, and a proposed finite element method‐3D‐vector simulation approach was used to analyse the structure influence. An improved femtosecond laser irradiation followed by chemical etching technology was used to fabricate the complex 3D microchannels, in which an optimal laser power compensation strategy of tuning laser power from 7 to 12 mW was involved. Asilanisation process was carried out before the injection process to facilitate the injection of gallium. 3D numerical simulations of the microsolenoids were carried out by an electromagnetic‐coupled analysis method; and a simulation‐based co‐energy calculation method was used to evaluate the inductance of the 3D microsolenoids. 3D microsolenoids of optimised configurations were then achieved according to the analytical results.
Towards scalable parallel-in-time turbulent flow simulations
Authors: Wang Qiqi , Gomez Steven A. , Blonigan Patrick J. , Gregory Alastair L. , Qian Elizabeth Y.
Published: September 2013

We present a reformulation of unsteady turbulent flow simulations. The initial condition is relaxed and information is allowed to propagate both forward and backward in time. Simulations of chaotic dynamical systems with this reformulation can be proven to be well-conditioned time domain boundary value problems. The reformulation can enable scalable parallel-in-time simulation of turbulent flows.
Induced spin filtering in electron transmission through chiral molecular layers adsorbed on metals with strong spin-orbit coupling
Authors: Gersten Joel , Kaasbjerg Kristen , Nitzan Abraham
Published: September 2013

Recent observations of considerable spin polarization in photoemission from metal surfaces through monolayers of chiral molecules were followed by several efforts to rationalize the results as the effect of spin-orbit interaction that accompanies electronic motion on helical, or more generally strongly curved, potential surfaces. In this paper we (a) argue, using simple models, that motion in curved force-fields with the typical energies used and the characteristic geometry of DNA cannot account for such observations; (b) introduce the concept of induced spin filtering, whereupon selectivity in the transmission of the electron orbital angular momentum can induce spin selectivity in the transmission process provided there is strong spin-orbit coupling in the substrate; and (c) show that the spin polarization in the tunneling current as well as the photoemission current from gold covered by helical adsorbates can be of the observed order of magnitude. Our results can account for most of the published observations that involved gold and silver substrates; however, recent results obtained with an aluminum substrate can be rationalized within the present model only if strong spin-orbit coupling is caused by the built-in electric field at the molecule-metal interface.
An innovative band-to-band tunneling analytical model and implications in compact modeling of tunneling-based devices
Authors: De Michielis L. , Dağtekin N. , Biswas A. , Lattanzio L. , Selmi L. , Luisier M. , Riel H. , Ionescu A. M.
Published: September 2013

In this paper, an analytical band-to-band tunneling model is proposed, validated by means of drift-diffusion simulation and comparison with experimental data, implemented in Verilog-A, and finally proven with SPICE simulator through simulation of circuits featuring tunneling diodes. The p-n junction current calculation starts from a non-local Band-to-Band tunneling theory including the electron-phonon interaction and therefore it is particularly suited for indirect semiconductor materials such as silicon- or germanium-based interband tunneling devices.
Structural, electronic and vibrational properties of N,N′-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDI-FCN2) crystal
Authors: Colle Renato , Grosso Giuseppe , Cassinese Antonio , Centore Roberto
Published: September 2013

We present a theoretical and experimental investigation of the crystalline structure of N,N′-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDI-FCN2) that has been deduced combining experimental XRD data, obtained from powders, with global-optimization algorithms which allow to identify Bravais lattice, primitive cell parameters, and space group of the crystal. The XRD spectrum calculated for the proposed crystalline structure very well reproduces the measured XRD data. Our results suggest the triclinic lattice structure of spatial groups \documentclass[12pt]{minimal}\begin{document}$P\overline{1}$\end{document}P1¯ and P1, respectively, for the crystalline PDI-FCN2-1,7 and PDI-FCN2-1,6 isomers. In both cases, the primitive cell contains a single molecule. On the proposed crystalline structures, KS-DFT cell energy calculations, including van der Waals interactions, have been performed to assign the minimum energy geometrical structure and orientation of the molecule inside the corresponding primitive cell. These calculations evidence the molecular packing that characterizes the strong anisotropy of the PDI-FCN2 crystal. Electronic band-structures calculated for both isomers within the Kohn-Sham density-functional theory indicate that the crystalline \documentclass[12pt]{minimal}\begin{document}$P\overline{1}$\end{document}P1¯ structure is an indirect gap semiconductor, while the P1 structure is a direct gap semiconductor. The electronic band structure calculations on the optimized crystal geometries highlight strong anisotropy in the dispersion curves \documentclass[12pt]{minimal}\begin{document}$E(\bf k)$\end{document}E(k), which roots at the molecular packing in the crystal. Finally, the vibrational spectrum of both crystalline isomers has been calculated in the harmonic approximation and the dominant vibrational frequencies have been associated to collective motions of selected atoms in the molecules.
Effect of ion structure on conductivity in lithium-doped ionic liquid electrolytes: A molecular dynamics study
Authors: Liu Hongjun , Maginn Edward
Published: September 2013

Molecular dynamics simulations were performed to examine the role cation and anion structure have on the performance of ionic liquid (IL) electrolytes for lithium conduction over the temperature range of 320–450 K. Two model ionic liquids were studied: 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([bmim][Tf2N]) and 1-butyl-4-methylpyridinium pyrrolide ([bmpyr][pyl]) doped with Li[Tf2N] and Li[pyl], respectively. The results have demonstrated that the Li+ doped IL containing the planar [bmpyr] cation paired with the planar [pyl] anion significantly outperformed the [bmim][Tf2N] IL. The different coordination of Li+ with the [Tf2N]− or [pyl]− anions produces a remarkable change in IL structure with a concomitant effect on the transport of all ions. For the doped [bmim][Tf2N], each Li+ is coordinated by four oxygen atoms from [Tf2N]− anions. Formation of a rigid structure between Li+ and [Tf2N]− induces a decrease in the mobility of all ions. In contrast, for the doped [bmpyr][pyl], each Li+ is coordinated by two nitrogen atoms from [pyl]− anions. The original alternating structure cation|anion|cation in the neat [bmpyr][pyl] is replaced by another alternating structure cation|anion|Li+|anion|cation in the doped [bmpyr][pyl]. Increases of Li+ mole fraction in doped [bmpyr][pyl] affects the dynamics to a much lesser extent compared with [bmim][Tf2N] and leads to reduced diffusivities of cations and anions, but little change in the dynamics of Li+. More importantly, the calculations predict that the Li+ ion conductivity of doped [bmpyr][pyl] is comparable to that observed in organic liquid electrolytes and is about an order of magnitude higher than that of doped [bmim][Tf2N]. Such Li+ conductivity improvement suggests that this and related ILs may be promising candidates for use as electrolytes in lithium ion batteries and capacitors.
Equilibrium electro-deformation of a surfactant-laden viscous drop
Authors: Nganguia Herve , Young Y.-N. , Vlahovska Petia M. , Blawzdziewicz Jerzy , Zhang J. , Lin H.
Published: September 2013

We theoretically investigate the deformation of a viscous drop covered with non-diffusing insoluble surfactant under a uniform DC electric field. At equilibrium, surfactant immobilizes the spheroidal drop surface and completely suppresses the fluid flow. In this work we focus on the equilibrium electro-deformation of a surfactant-laden drop in the leaky dielectric framework by developing (1) a second-order small-deformation analysis and (2) a spheroidal model for a highly deformed (prolate or oblate) drop. Both models are compared against experimental data and numerical simulation results in the literature. Our analysis shows how the existence of equilibrium spheroidal drop depends on the permittivity ratio, conductivity ratio, surfactant coverage, and the elasticity number. Furthermore, the spheroidal model highlights that differences between surfactant effects, such as tip stretching and surface dilution effects, are greatly amplified at large surfactant coverage and high electric capillary number. These surfactant effects are well captured in the spheroidal model, but cannot be described in the second-order small-deformation theory.
The initial transient period of gravitationally unstable diffusive boundary layers developing in porous media
Authors: Tilton Nils , Daniel Don , Riaz Amir
Published: September 2013

Gravitationally unstable, transient, diffusive boundary layers play an important role in carbon dioxide sequestration. Though the linear stability of these layers has been studied extensively, there is wide disagreement in the results, and it is not clear which methodology best reflects the physics of the instability. We demonstrate that this disagreement stems from an inherent sensitivity of the problem to how perturbation growth is measured. During an initial transient period, the concentration and velocity fields exhibit different growth rates and these rates depend on the norm used to measure perturbation amplitude. This sensitivity decreases at late times as perturbations converge to dominant quasi-steady eigenmodes. Therefore, we characterize the linear regime by measuring the duration of the initial transient period, and we interpret the convergence process by examining the growth rates and non-orthogonality of the quasi-steady eigenmodes. To judge the relevance of various methodologies and perturbation structures to physical systems, we demonstrate that every perturbation has a maximum allowable initial amplitude above which the sum of the base-state and perturbation produces unphysical negative concentrations. We then perform direct numerical simulations to demonstrate that optimal perturbations considered in previous studies cannot support finite initial amplitudes. Consequently, convection in physical systems is more likely triggered by “sub-optimal” perturbations that support finite initial amplitudes.
Vortex breakdown in a water-spout flow
Authors: Herrada Miguel A. , Shtern Vladimir N. , López-Herrera José María
Published: September 2013

The numerical study of the steady axisymmetric air-water flow in a vertical sealed cylinder, driven by the rotating top disk, describes topological transformations as the rotation intensifies. The air meridional flow (AMF) and swirl induce meridional motions of opposite directions in water. For slow (fast) rotation, the effect of AMF (swirl) dominates. For very fast rotation, large-scale regions of clockwise meridional circulation in air and water are separated by a thin layer of anticlockwise circulation adjacent to the interface in water. This pattern develops for other fluids as well. Physical reasoning behind the flow evolution is provided.
The structures and properties of Si/SiO2 core/shell quantum dots studied by density-functional tight-binding calculations
Authors: Dong Huilong , Hou Tingjun , Sun Xiaotian , Li Youyong , Lee Shuit-Tong
Published: September 2013

Si/SiO2 core/shell quantum dots (QDs) have been shown with wavelength-tunable photoluminescence in addition to their inert, nontoxic, abundant, low-cost, biocompatible advantages. Due to their big size, here, we apply density-functional tight-binding (DFTB) method to perform calculations to study their structures and properties. We systematically investigate the effects of surface passivation, thickness of SiO2 shell, and Si/O ratio on the structures and properties of Si/SiO2 core/shell quantum dots. We find that hydroxyl passivated Si/SiO2 core/shell quantum dots are able to stabilize the quantum dots compared with hydrogen passivated Si/SiO2 core/shell quantum dots. By using DFTB method, we are able to study Si/SiO2 core/shell quantum dots of big size (3 nm) and we find that, in Si/SiO2 core/shell quantum dots, there are competing effects between quantum confinement (blueshift) and oxidation (redshift) with the decrease of the size of Si core. The transition point is when Si/SiO2 ratio is around 1:1. The effect of the thickness of SiO2 on energy gap is not as significant as the effect of the size of the Si core. Our study provides theoretical basis for designing Si quantum dots with tunable photoluminescence.
Temporal structure of double plasma frequency emission of thin beam-heated plasma
Authors: Postupaev V. V. , Burdakov A. V. , Ivanov I. A. , Sklyarov V. F. , Arzhannikov A. V. , Gavrilenko D. Ye. , Kandaurov I. V. , Kasatov A. A. , Kurkuchekov V. V. , Mekler K. I. , Polosatkin S. V. , Popov S. S. , Rovenskikh A. F. , Sudnikov A. V. , Sulyaev Yu. S. , Trunev Yu. A. , Vyacheslavov L. N.
Published: September 2013

In the work presented here dynamics of spiky microwave emission of a beam-heated plasma near the double plasma frequency in ∼100 GHz band was studied. The plasma is heated by 80 keV, ∼2 MW, sub-ms electron beam that is injected into the multiple-mirror trap GOL-3. The beam-heated plasma diameter is of the order of the emitted wavelength. Modulation of individual emission spikes in the microwave radiation is found. The radiation dynamics observed can be attributed to a small number of compact emitting zones that are periodically distorted.
Very bright, near-infrared single photon emitters in diamond
Authors: Lau D. W. M. , Karle T. J. , Johnson B. C. , Gibson B. C. , Tomljenovic-Hanic S. , Greentree A. D. , Prawer S.
Published: September 2013

We demonstrate activation of bright diamond single photon emitters in the near infrared range by thermal annealing alone, i.e., without ion implantation. The activation is crucially dependent on the annealing ambient. The activation of the single photon emitters is only observed when the sample is annealed in forming gas (4% H2 in Ar) above temperatures of 1000 °C. By contrast, no emitters are activated by annealing in vacuum, oxygen, argon or deuterium. The emitters activated by annealing in forming gas exhibit very bright emission in the 730-760 nm wavelength range and have linewidths of ∼1.5-2.5 nm at room temperature.
Figure of merit of piezoelectret transducers for pulse-echo or transmit-receive systems for airborne ultrasound
Authors: Sessler G. M. , Hillenbrand J.
Published: September 2013

Piezoelectret transducers may be characterized relative to other kinds of piezoelectric transducers with respect to their combined transmit-receive performance by a figure of merit (FOM). Reasonable FOMs for the specific case of broadband (non-resonant) airborne ultrasonics are discussed in this paper. These FOMs are specifically suitable for a measuring system where low input voltage to the transmitter is desirable and where the receiver is assessed by its voltage- or charge-related signal-to-noise ratio. It is found that these FOMs depend chiefly on the piezoelectric d33- and g33-coefficients.
Comment on “Photoelectron angular distributions as a probe of alignment in a polyatomic molecule: Picosecond time- and angle-resolved photoelectron spectroscopy of S1 p-difluorobenzene” [J. Chem. Phys. 111, 1438 (1999)]
Authors: Midgley Jonathan , Davies Julia A. , Reid Katharine L.
Published: September 2013

In this Comment we submit the results of an experiment in which we use the technique of time-resolved photoelectron velocity map imaging to probe the intramolecular dynamics occurring following the preparation of the 3151 vibrational level in S1 p-difluorobenzene with a 1 ps laser pulse. The extracted photoelectron angular distributions are discussed in the context of earlier comparable measurements from our group [J. Chem. Phys. 111, 1438 (1999)], and we conclude that the specific interpretation of the earlier results was incorrect as a consequence of systematic errors that are removed in the present study.
Experimental evidence of the modulation of a plane wave to oblique perturbations and generation of rogue waves in finite water depth
Authors: Toffoli A. , Fernandez L. , Monbaliu J. , Benoit M. , Gagnaire-Renou E. , Lefèvre J. M. , Cavaleri L. , Proment D. , Pakozdi C. , Stansberg C. T. , Waseda T. , Onorato M.
Published: September 2013

We present a laboratory experiment in a large directional wave basin to discuss the instability of a plane wave to oblique side band perturbations in finite water depth. Experimental observations, with the support of numerical simulations, confirm that a carrier wave becomes modulationally unstable even for relative water depths k0h < 1.36 (with k the wavenumber of the plane wave and h the water depth), when it is perturbed by appropriate oblique disturbances. Results corroborate that the underlying mechanism is still a plausible explanation for the generation of rogue waves in finite water depth.
Mode II electromigration failure mechanism in Sn-based Pb-free solder joints with Ni under-bump metallization
Authors: Wang Yiwei , Ho Paul S.
Published: September 2013

Early electromigration (EM) failure mechanism, also known as Mode II EM failure in Sn-based Pb-free solder joints with Ni under-bump metallization (UBM) is studied. A numerical model was built to incorporate interdiffusion and EM, and to investigate the effect of Sn crystal orientation. Results show that when the c axis of Sn has a close alignment to the current direction, intermetallic compound (IMC) growth is enhanced by both EM and extremely fast interstitial diffusion of Ni in the solder. The combined process results in IMC dissolution from the cathode side of the solder joint and causes EM failure by UBM depletion. Theoretical predictions are consistent with experimental observations.
Wide range equation of state for fluid hydrogen from density functional theory
Authors: Wang Cong , Zhang Ping
Published: September 2013

Wide range equation of state (EOS) for liquid hydrogen is ultimately obtained by combining two kinds of density functional theory (DFT) molecular dynamics simulations, namely, first-principles molecular dynamics simulations and orbital-free molecular dynamics simulations. Specially, the present introduction of short cutoff radius pseudopotentials enables the EOS to be available in the range from 9.82 × 10−4 to 1.347 × 103 g/cm3 and up to 5 × 107 K. By comprehensively comparing with various attainable experimental and theoretical data, we derive the conclusion that our DFT-EOS can be readily and reliably applied to hydrodynamic simulations of the inertial confinement fusion.
Tuning the properties of VO2 thin films through growth temperature for infrared and terahertz modulation applications
Authors: Zhao Yong , Chen Changhong , Pan Xuan , Zhu Yanhan , Holtz Mark , Bernussi Ayrton , Fan Zhaoyang
Published: September 2013

Results are reported on tuning the electrical and optical properties of sputter-deposited vanadium dioxide (VO2) thin films through control of substrate growth temperature (Ts). As Ts increases from 550 to 700 °C, the morphology changes from granular to smooth film and finally to rough film. X-ray diffraction shows the presence of VO2 along with additional weak features related to the presence of non-stoichiometric phases. Electrical measurements show the phase transition to change from abrupt to gradual as both the below- and above-transition resistivities vary with Ts. The transition and hysteresis dependences observed in electrical resistivity are similarly observed in infrared transmission. Terahertz transmission measurements show that high conductivity above the phase transition is more important in achieving high modulation depth than obtaining high resistivity below the transition. We attribute changes in the electrical and optical properties to the formation of V and O vacancies, which result in diverse valence states from the ideal V4+ of VO2. Low Ts produces material with V5+ states resulting in higher resistivity in both the insulating and metallic phases. Alternatively, high Ts introduces material with V3+ states leading to lower resistivity in the insulating phase but slightly higher resistivity in the metallic phase.
High voltage characteristics of junctionless poly-silicon thin film transistors
Authors: Cheng Ya-Chi , Wu Yung-Chun , Chen Hung-Bin , Han Ming-Hung , Lu Nan-Heng , Su Jun-Ji , Chang Chun-Yen
Published: September 2013

The breakdown voltage (VBD) and breakdown mechanism of junctionless (JL) poly-Si thin film transistor (TFT) were compared to the conventional inversion-mode (IM) TFT using fabricated devices and 3D quantum-corrected hydrodynamic transport device simulation. The simulated results are correspondent with experimental ones. The analyses of electric field distributions in on-state show that the channel of JL devices can equally share the voltage like a resistor, because there are no junctions formed between channel and source/drain. The JL TFT shows excellent breakdown characteristics; the off-state VBD of 53.4 V is several times larger than VBD of 9.5 V in IM TFT with same device size. JL devices have large potential for high voltage power metal-oxide-semiconductor devices and circuit applications.
Assortative mixing in functional brain networks during epileptic seizures
Authors: Bialonski Stephan , Lehnertz Klaus
Published: September 2013

We investigate assortativity of functional brain networks before, during, and after one-hundred epileptic seizures with different anatomical onset locations. We construct binary functional networks from multi-channel electroencephalographic data recorded from 60 epilepsy patients; and from time-resolved estimates of the assortativity coefficient, we conclude that positive degree-degree correlations are inherent to seizure dynamics. While seizures evolve, an increasing assortativity indicates a segregation of the underlying functional network into groups of brain regions that are only sparsely interconnected, if at all. Interestingly, assortativity decreases already prior to seizure end. Together with previous observations of characteristic temporal evolutions of global statistical properties and synchronizability of epileptic brain networks, our findings may help to gain deeper insights into the complicated dynamics underlying generation, propagation, and termination of seizures.
Atomic mass dependent electrostatic diagnostics of colliding laser plasma plumes
Authors: Yeates P. , Fallon C. , Kennedy E. T. , Costello J. T.
Published: September 2013

The behaviours of colliding laser plasma plumes (Cp) compared with single plasma plumes (Sp) are investigated for 14 different atomic mass targets. A Faraday cup, situated at the end of a drift tube (L = 0.99 m), is employed to record the time-of-flight (TOF) current traces for all elements and both plume configurations, for a fixed laser intensity of Ip = 4.2 × 1010 W cm−2 (F = 0.25 kJ cm−2). The ratio of the peak current from the Cp relative to twice that from the Sp is designated as the peak current ratio while the ratio of the integrated charge yield from the Cp relative to twice that from the Sp is designated as the charge yield ratio. Variation of the position of the Faraday cup within the drift tube (L = 0.33, 0.55, and 0.99 m) in conjunction with a lower laser fluence (F = 0.14 kJ cm−2) facilitated direct comparison of the changing TOF traces from both plasma configurations for the five lightest elements studied (C, Al, Si, Ti, and Mn). The results are discussed in the frame of laser plasma hydrodynamic modelling to approximate the critical recombination distance LCR. The dynamics of colliding laser plasma plumes and the atomic mass dependence trends observed are presented and discussed.
Chirality-induced negative refraction in magnetized plasma
Authors: Guo B.
Published: September 2013

Characteristic equations in magnetized plasma with chirality are derived in simple formulations and the dispersion relations for propagation parallel and perpendicular to the external magnetic field are studied in detail. With the help of the dispersion relations of each eigenwave, the author explores chirality-induced negative refraction in magnetized plasma and investigates the effects of parameters (i.e., chirality degree, external magnetic field, etc.) on the negative refraction. The results show that the chirality is the necessary and only one factor which leads to negative refraction without manipulating electrical permittivity and magnetic permeability. Both increasing the degree of chirality and reducing the external magnetic field can result in greater range negative refraction. Parameter dependence of the effects is calculated and discussed.
The heterogeneous structure of metallic glasses revealed by superconducting transitions
Authors: Huang B. , Bai H. Y. , Wen P. , Ding D. W. , Zhao D. Q. , Pan M. X. , Wang W. H.
Published: September 2013

It has been postulated that metallic glasses, in contrast to their crystalline counterparts, exhibit nano-scale structural heterogeneity which is crucial for understanding the long-standing issues of relaxations and deformation of glasses. We fabricate micrometer scale metallic glassy fibers (MGFs) with different diameters and structural configurations, and find that the thinner MGFs cooled down with faster cooling rates have smaller superconducting transition temperatures and wider transition widths. We show that the superconducting properties correlate with the heterogeneous microstructure of metallic glasses and can be used as a novel way to experimentally characterize the structural heterogeneity of metallic glasses.
Ultrafast fabrication of solid phosphor based white light emitting diodes: From powder synthesis to devices
Authors: Shen Lu , Li Yang , Huang Qing
Published: September 2013

We here present our state of art spark plasma sintering technology in ultrafast fabricating transparent Ce:YAG@MgAl2O4 composite ceramics based white light emitting diodes directly from powder synthesis to final devices. The total heat processing time is less than 3 h. The optical properties of the sintered transparent composite can be easily adjusted by internal and external modifications to satisfy specific requirement. This method is also fit for fabricating multi-phosphor composites for improved color rendering index.
Growth and characterization of germanium epitaxial film on silicon (001) with germane precursor in metal organic chemical vapour deposition (MOCVD) chamber
Authors: Lee Kwang Hong , Jandl Adam , Tan Yew Heng , Fitzgerald Eugene A. , Tan Chuan Seng
Published: September 2013

The quality of germanium (Ge) epitaxial film grown directly on a silicon (Si) (001) substrate with 6° off-cut using conventional germane precursor in a metal organic chemical vapour deposition (MOCVD) system is studied. The growth sequence consists of several steps at low temperature (LT) at 400 °C, intermediate temperature ramp (LT-HT) of ∼10 °C/min and high temperature (HT) at 600 °C. This is followed by post-growth annealing in hydrogen at temperature ranging from 650 to 825 °C. The Ge epitaxial film of thickness ∼ 1 μm experiences thermally induced tensile strain of 0.11 % with a treading dislocation density (TDD) of ∼107/cm2 and the root-mean-square (RMS) roughness of ∼ 0.75 nm. The benefit of growing Ge epitaxial film using MOCVD is that the subsequent III-V materials can be grown in-situ without the need of breaking the vacuum hence it is manufacturing worthy.
Light extraction improvement of InGaN light-emitting diodes with large-area highly ordered ITO nanobowls photonic crystal via self-assembled nanosphere lithography
Authors: Wu Kui , Zhang Yiyun , Wei Tongbo , Lan Ding , Sun Bo , Zheng Haiyang , Lu Hongxi , Chen Yu , Wang Junxi , Luo Yi , Li Jinmin
Published: September 2013

The InGaN multiple quantum well light-emitting diodes (LEDs) with different sizes of indium-tin-oxide (ITO) nanobowl photonic crystal (PhC) structure has been fabricated using self-assembled monolayer nanosphere lithography. The light output power (LOP) of PhC LEDs (at 350 mA) has been enhanced by 63.5% and the emission divergence exhibits a 28.8° reduction compared to conventional LEDs without PhC structure. Current-Voltage curves have shown that these PhC structures on ITO layer will not degrade the LED electrical properties. The finite-difference time-domain simulation (FDTD) has also been performed for light extraction and emission characteristics, which is consistent with the experimental results.
Effect of grain-boundaries on electrical properties of n-ZnO:Al/p-Si heterojunction diodes
Authors: Kumar Mohit , Kanjilal Aloke , Som Tapobrata
Published: September 2013

We report on room temperature diode characteristics of ZnO:Al (AZO)/Si heterostructures by current-voltage measurements. In this study, with increasing AZO film thickness, systematic reduction in the turn-on potential (from 3.16 to 1.80 V) and the film stress are observed. Complementary capacitance-voltage studies reveal a decreasing trend in barrier height at the junction with increasing AZO film thickness. A gradual decrease in resistivity takes place with increasing AZO film thickness. Above observations are explained in the framework of AZO thickness dependent variation in grain size and in turn trap density at the grain boundaries influencing carrier transport across the adjacent grains.
Lung epithelial branching program antagonizes alveolar differentiation
Authors: Chang Daniel R. , Martinez Alanis Denise , Miller Rachel K. , Ji Hong , Akiyama Haruhiko , McCrea Pierre D. , Chen Jichao
Published: September 2013

Significance

Mammalian organs, including the lung and the kidney, often use a branched design to maximize their functional capacity and efficiency. Lung formation requires two developmental processes: branching morphogenesis to build a treelike tubular network, and alveolar differentiation to generate specialized epithelial cells for gas exchange. Although each process has been extensively studied, much less is known about whether and how the two processes are coordinated. We show that an epithelial branching morphogenesis program antagonizes alveolar differentiation in the mouse lung. Our findings may provide fresh insights to lung immaturity in preterm neonates and the increase in organ complexity during evolution.
Intersubjectivity in human–agent interaction
Authors: Cassell Justine , Tartaro Andrea
Published: September 2013

What is the hallmark of success in human–agent interaction? In animation and robotics, many have concentrated on the looks of the agent — whether the appearance is realistic or lifelike. We present an alternative benchmark that lies in the dyad and not the agent alone: Does the agent’s behavior evoke intersubjectivity from the user? That is, in both conscious and unconscious communication, do users react to behaviorally realistic agents in the same way they react to other humans? Do users appear to attribute similar thoughts and actions? We discuss why we distinguish between appearance and behavior, why we use the benchmark of intersubjectivity, our methodology for applying this benchmark to embodied conversational agents (ECAs), and why we believe this benchmark should be applied to human–robot interaction.
What is the teacher’s role in robot programming by demonstration?
Authors: Calinon Sylvain , Billard Aude G.
Published: September 2013

Robot programming by demonstration (RPD) covers methods by which a robot learns new skills through human guidance. We present an interactive, multimodal RPD framework using active teaching methods that places the human teacher in the robot’s learning loop. Two experiments are presented in which observational learning is ﬁrst used to demonstrate a manipulation skill to a HOAP–3 humanoid robot by using motion sensors attached to the teacher’s body. Then, putting the robot through the motion, the teacher incrementally reﬁnes the robot’s skill by moving its arms manually, providing the appropriate scaffolds to reproduce the action. An incremental teaching scenario is proposed based on insights from various ﬁelds addressing developmental, psychological, and social issues related to teaching mechanisms in humans. Based on this analysis, different benchmarks are suggested to evaluate the setup further.
Authenticity in the age of digital companions
Authors: Turkle Sherry
Published: September 2013

The first generation of children to grow up with electronic toys and games saw computers as our “nearest neighbors.” They spoke of computers as rational machines and of people as emotional machines, a fragile formulation destined to be challenged. By the mid-1990s, computational creatures, including robots, were presenting themselves as “relational artifacts,” beings with feelings and needs. One consequence of this development is a crisis in authenticity in many quarters. In an increasing number of situations, people behave as though they no longer place value on living things and authentic emotion. This paper examines watershed moments in the history of human–machine interaction, focusing on the pertinence of relational artifacts to our collective perception of aliveness, life’s purposes, and the implications of relational artifacts for relationships. For now, the exploration of human–robot encounters leads us to questions about the morality of creating believable digital companions that are evocative but not authentic.