bluuebunny/crossref_metadata_2025 huggingface dataset:
Polar coded spatial modulation
Authors: Akuon Peter , Xu Hongjun
Published: May 2014

A scheme is proposed, called polar coded spatial modulation (PCSM), to provide both detection/decoding of the transmitted symbol and the transmit antenna index in multiple‐input–multiple‐output (MIMO) antenna systems. Based on the free polar set and the frozen polar set in polar codes, the proposed PCSM scheme maps the transmitted information data in the free polar set and the transmit antenna index bits in the frozen polar set whose positions are known at the receiver. This has the advantage that the bits that identify the transmit antenna are not transmitted to the receiver and do not need to be detected as is the case in conventional spatial modulation (SM). Thus, PCSM presents a spectrally efficient and a power‐efficient system. For the simulations, MIMO channels with transmission over independent and identically distributed flat fading characteristics are exploited. Firstly, capacity results for coded SM which is a requirement for the construction of the codes are presented. Consequently, the bit error rate performances of the M‐ary quadrature amplitude modulation SM are analysed for various MIMO architectures after which the desirable MIMO architecture is proposed for the PCSM. In addition, the upper and lower bounds on probability of frame error for the transmitted symbol information, under successive cancellation decoding are derived and the PCSM scheme suits the bounds for the suiting architecture.
Energy efficient cognitive radio network based on multiband sensing and spectrum sharing
Authors: Shi Zhiping , Tan Tian , Teh Kah Chan , Hung Li Kwok
Published: May 2014

The authors consider the problem of energy consumption in a multiband cognitive radio network, in which a secondary user can sense multiple frequency bands authorised to the primary user (PU) before it decides to access some frequency bands and keep the interference introduced to the PU under a certain threshold. The sensing time and power allocation need to be designed carefully to reduce the energy consumption. Therefore they identify the optimal sensing time and accessing power to minimise the energy consumption of the cognitive radio that simultaneously senses and accesses multiple bands under the multiband sensing‐based spectrum sharing scheme. To obtain the optimal solution, they transform the original problem formulated as the ratio of two functions into another parametric formulation. The interference power is considered as one of constraints in the author's scheme in order to protect the PU. The algorithm of optimal sensing time and power allocation is proposed for the multiband cognitive radio system. Furthermore, they discuss the effect of channel number, interference power and gain estimation of channels on energy consumption and optimal sensing time and validate their schemes and analysis by simulation results.
Considerations on the multiplexing and diversity tradeoff in IEEE 802.11 networks
Authors: Babich Fulvio , Comisso Massimiliano , Crismani Alessandro
Published: May 2014

Multiple‐input multiple‐output (MIMO) techniques have received a considerable attention from the research community for their promising performance in faded environments, and particular interest has been given to the physical (PHY) layer implications of the tradeoff between multiplexing and diversity. This study discusses this tradeoff extending the analysis to the medium access control (MAC) layer. To this purpose, a theoretical model for assessing the performance of an 802.11 network that relies on a MIMO‐enabled PHY layer is presented. The proposed model characterises the different MIMO systems in terms of their multiplexing gain and bit error rate performance, considering both the diversity gain of the specific MIMO scheme and the impact of the spatial distribution of the nodes. The results compare, from a MAC layer perspective, the benefits of multiplexing and diversity, providing some analytic insights on the tradeoff between increasing the system's reliability and enhancing the data rate of the single link.
Complexity scalable intra‐prediction mode decision algorithm for mobile video applications
Authors: Song Yun , Long Jizhen , Yang Kun , Yang Gaobo
Published: May 2014

The full search scheme employed in H.264/AVC significantly improves the coding performance, but it also introduces a very high computational complexity which limits the applications in resource‐constrained mobile devices. In this study, the authors firstly present a discretisation total variation and orientation gradient‐based hierarchical intra‐prediction mode decision method for mobile video applications. By shrinking the candidate mode set in the rate–distortion optimisation (RDO) process, the proposed algorithm reduces the computational complexity and power consumption of the encoder. Furthermore, they extend the hierarchical algorithm to a complexity scalable version in which the coding complexity is measured on five levels by reserving various numbers of modes for RDO. Experimental results demonstrate that the proposed mode decision algorithm reduces the coding complexity significantly with negligible performance degradation and the proposed complexity scalable algorithm is effective and efficient for mobile video application.
On ML‐decoders in a two user interference channel with slow flat fading
Authors: Zhang Fuhong , Li Lin , Zhao Zhijin , Wang Haiquan
Published: May 2014

In this study, according to whether the receiver has the channel state information (CSI) and knows the co‐user's codebook or not, different maximum‐likelihood (ML)‐decoders are designed for a two user interference channel with slow flat fading. For each of the proposed ML‐decoders, performance analysis based on pair‐wise error probability is given. Although the importance of the CSI to the receiver is well investigated, these analyses reveal the fact that it also has much impact on the performance if the co‐user's codebook is known to the receiver. The analyses also tell us that to decode out interference signals is not only unnecessary, but also reduces the performance, although it has been shown that the method of decoding out the interference signal first and then subtracting it from the received signal is an efficient way to achieve the capacity region of the Gaussian interference channel under some conditions and also is applied into practical systems.
Fault detection for discrete systems based on a descriptor system method
Authors: Zhu Xiaodan , Xia Yuanqing
Published: May 2014

In this study, the problem of fault detection for discrete systems is considered. For control inputs, unknown bounded disturbances and sensor faults, an observer‐based fault detection filter is designed based on a descriptor system method such that the error dynamic system is convergent, the effect of the disturbances on the residuals satisfies the H∞ performance index and the effect of the faults on the residuals satisfies the H− performance index. By a Lyapunov functional approach, a sufficient condition for the solvability of the fault detection problem is expressed in terms of linear matrix inequalities. A numerical example shows the effectiveness of the proposed method.
Global consensus of single‐integrator agents subject to saturation constraints
Authors: Wang Qingling , Peng Cheng , Gao Huijun , Basin Michael
Published: May 2014

This paper investigates the problem of leader‐following consensus of single‐integrator agents subject to saturation constraints. Global leader‐following consensus protocol is developed with proper choice of the relative coupling gain. Both the case of input saturation and the case of actuator saturation are considered. It is shown that global consensus of the multiagent system can be reached under the general undirected graph provided that its augmented graph contains a directed spanning tree. Numerical examples are provided to demonstrate the theoretical results.
Image‐based surface deformation for multi‐view three‐dimensional facial reconstruction
Authors: Dong Hongwei , Dong Shuhui
Published: May 2014

The authors present a new technique to generate highly detailed three‐dimensional facial models from the images of a human face. Unlike the traditional stereo matching‐based multi‐view geometry and statistical model‐based approaches, the key idea of the proposed approach is to deform a template model using photometric consistency metric defined by all input images. The image‐based facial deformation as a continuous optimisation problem is formulated. The objective function ensures the deformed surface model not only matches the image measurement among all the input images but also keeps the fine details of the template model. Also, an efficient gradient‐based optimisation technique is employed to find an optimal facial model that precisely matches an individual's face in input images. Template‐based deformation avoids the difficulty because of occlusion in images, and the robust estimation technique also improve the quality of facial reconstruction. The experimental results using synthetic and real images show that the proposed method provides a stable and quality facial reconstruction on wide‐baseline images.
Harmonic power compensation capacity of shunt active power filter and its relationship with design parameters
Authors: Khadem Shafiuzzaman K. , Basu Malabika , Conlon Michael F.
Published: May 2014

In this study, the equation for the reactive and harmonic power compensation of a shunt active power filter (APF) system has been derived by studying the power exchange mechanism and power tetrahedron phasor diagram. The switching dynamics of a voltage source inverter (VSI)‐based three‐phase, three‐wire (three‐leg /half‐bridge) shunt APF system with hysteresis band current control has been studied and verified by simulation. The relation between the design parameters and their effects on the active losses has also been identified. Detailed calculation and extensive simulation have been performed for a three‐phase, three‐wire shunt APF implemented in a 400VL–L distribution system, as an example, to study the effects of design parameter selection and their role in active power loss calculation. Simulated and calculated results are presented for the important design parameters for different switching frequencies together with their associated losses and kVA ratings. The procedure can be followed to design the parameters for other topologies, such as three‐phase, four‐wire or single‐phase systems.
Influence of germanium nano-inclusions on the thermoelectric power factor of bulk bismuth telluride alloy
Authors: Satyala Nikhil , Tahmasbi Rad Armin , Zamanipour Zahra , Norouzzadeh Payam , Krasinski Jerzy S. , Tayebi Lobat , Vashaee Daryoosh
Published: May 2014

Nanocomposite thermoelectric compound of bismuth telluride (Bi2Te3) with 5 at. % germanium nano-inclusions was prepared via mechanically alloying and sintering techniques. The influence of Ge nano-inclusions and long duration annealing on the thermoelectric properties of nanostructured Bi2Te3 were investigated. It was found that annealing has significant effect on the carrier concentration, Seebeck coefficient, and the power factor of the thermoelectric compound. The systematic heat treatment also reduced the density of donor type defects thereby decreasing the electron concentration. While the as-pressed nanocomposite materials showed n-type properties, it was observed that with the increase of annealing time, the nanocomposite gradually transformed to an abundantly hole-dominated (p-type) sample. The long duration annealing (∼500 h) resulted in a significantly enhanced electrical conductivity pertaining to the augmentation in the density and the structural properties of the sample. Therefore, a simultaneous enhancement in both electrical and Seebeck coefficient characteristics resulted in a remarkable increase in the thermoelectric power factor.
Motion of the plasma critical layer during relativistic-electron laser interaction with immobile and comoving ion plasma for ion acceleration
Authors: Sahai Aakash A.
Published: May 2014

We analyze the motion of the plasma critical layer by two different processes in the relativistic-electron laser-plasma interaction regime (a0>1). The differences are highlighted when the critical layer ions are stationary in contrast to when they move with it. Controlling the speed of the plasma critical layer in this regime is essential for creating low-β traveling acceleration structures of sufficient laser-excited potential for laser ion accelerators. In Relativistically Induced Transparency Acceleration (RITA) scheme, the heavy plasma-ions are fixed and only trace-density light-ions are accelerated. The relativistic critical layer and the acceleration structure move longitudinally forward by laser inducing transparency through apparent relativistic increase in electron mass. In the Radiation Pressure Acceleration (RPA) scheme, the whole plasma is longitudinally pushed forward under the action of the laser radiation pressure, possible only when plasma ions co-propagate with the laser front. In RPA, the acceleration structure velocity critically depends upon plasma-ion mass in addition to the laser intensity and plasma density. In RITA, mass of the heavy immobile plasma-ions does not affect the speed of the critical layer. Inertia of the bared immobile ions in RITA excites the charge separation potential, whereas RPA is not possible when ions are stationary.
Interaction of epitaxial silicene with overlayers formed by exposure to Al atoms and O2 molecules
Authors: Friedlein R. , Van Bui H. , Wiggers F. B. , Yamada-Takamura Y. , Kovalgin A. Y. , de Jong M. P.
Published: May 2014

As silicene is not chemically inert, the study and exploitation of its electronic properties outside of ultrahigh vacuum environments require the use of insulating capping layers. In order to understand if aluminum oxide might be a suitable encapsulation material, we used high-resolution synchrotron photoelectron spectroscopy to study the interactions of Al atoms and O2 molecules, as well as the combination of both, with epitaxial silicene on thin ZrB2(0001) films grown on Si(111). The deposition of Al atoms onto silicene, up to the coverage of about 0.4 Al per Si atoms, has little effect on the chemical state of the Si atoms. The silicene-terminated surface is also hardly affected by exposure to O2 gas, up to a dose of 4500 L. In contrast, when Al-covered silicene is exposed to the same dose, a large fraction of the Si atoms becomes oxidized. This is attributed to dissociative chemisorption of O2 molecules by Al atoms at the surface, producing reactive atomic oxygen species that cause the oxidation. It is concluded that aluminum oxide overlayers prepared in this fashion are not suitable for encapsulation since they do not prevent but actually enhance the degradation of silicene.
Systematics of small parahydrogen clusters in two dimensions
Authors: Idowu Saheed , Boninsegni Massimo
Published: May 2014

We studied by means of computer simulations the low temperature properties of two-dimensional parahydrogen clusters comprising between N = 7 and 30 molecules. Computed energetics is in quantitative agreement with that reported in the only previous study [M. C. Gordillo and D. M. Ceperley, Phys. Rev. B 65, 174527 (2002)], but a generally stronger superfluid response is obtained here for clusters with more than ten molecules. Moreover, all the clusters, including the smallest one, display a well-defined, clearly identifiable solidlike structure; with only one possible exception, those with fewer than N = 25 molecules are (almost) entirely superfluid at the lowest temperature considered here (i.e., T = 0.25 K), and can thus be regarded as nanoscale “supersolids.” The implications of these results on a possible bulk two-dimensional superfluid phase of parahydrogen are discussed.
The charge conserving Poisson-Boltzmann equations: Existence, uniqueness, and maximum principle
Authors: Lee Chiun-Chang
Published: May 2014

The present article is concerned with the charge conserving Poisson-Boltzmann (CCPB) equation in high-dimensional bounded smooth domains. The CCPB equation is a Poisson-Boltzmann type of equation with nonlocal coefficients. First, under the Robin boundary condition, we get the existence of weak solutions to this equation. The main approach is variational, based on minimization of a logarithm-type energy functional. To deal with the regularity of weak solutions, we establish a maximum modulus estimate for the standard Poisson-Boltzmann (PB) equation to show that weak solutions of the CCPB equation are essentially bounded. Then the classical solutions follow from the elliptic regularity theorem. Second, a maximum principle for the CCPB equation is established. In particular, we show that in the case of global electroneutrality, the solution achieves both its maximum and minimum values at the boundary. However, in the case of global non-electroneutrality, the solution may attain its maximum value at an interior point. In addition, under certain conditions on the boundary, we show that the global non-electroneutrality implies pointwise non-electroneutrality.
Localization and stretching of polymer chains at the junction of two surfaces
Authors: Patra Tarak K. , Singh Jayant K.
Published: May 2014

We present a molecular dynamics study on the stretching of a linear polymer chain that is adsorbed at the junction of two intersecting flat surfaces of varying alignments. We observe a transition from a two-dimensional to one-dimensional (1D) structure of the adsorbed polymer when the alignment, i.e., the angle between the two surfaces that form a groove, θ, is below 135°. We show that the radius of gyration of the polymer chain Rg scales as Rg ∼ N3/4 with the degree of polymerization N for θ = 180° (planer substrate), and the scaling changes to Rg ∼ N1.0 for θ < 135° in good solvents. At the crossover point, θ = 135°, the exponent becomes 1.15. The 1D stretching of the polymer chain is found to be 84% of its contour length for θ ⩽ 90°. The center of mass diffusion coefficient D decreases sharply with θ. However, the diffusion coefficient scales with N as D ∼ N−1, and is independent of θ. The relaxation time τ, for the diffusive motion, scales as τ ∼ N2.5 for θ = 180° (planar substrate), which changes to τ ∼ N3.0 for θ ⩽ 90°. At the crossover point, the exponent is 3.4, which is slightly higher than the 1D value of 3.0. Further, a signature of reptation-like dynamics of the polymer chain is observed at the junction for θ ⩽ 90° due to its strong 1D localization and stretching.
Plasma wakefields driven by an incoherent combination of laser pulses: A path towards high-average power laser-plasma accelerators
Authors: Benedetti C. , Schroeder C. B. , Esarey E. , Leemans W. P.
Published: May 2014

The wakefield generated in a plasma by incoherently combining a large number of low energy laser pulses (i.e., without constraining the pulse phases) is studied analytically and by means of fully self-consistent particle-in-cell simulations. The structure of the wakefield has been characterized and its amplitude compared with the amplitude of the wake generated by a single (coherent) laser pulse. We show that, in spite of the incoherent nature of the wakefield within the volume occupied by the laser pulses, behind this region, the structure of the wakefield can be regular with an amplitude comparable or equal to that obtained from a single pulse with the same energy. Wake generation requires that the incoherent structures in the laser energy density produced by the combined pulses exist on a time scale short compared to the plasma period. Incoherent combination of multiple laser pulses may enable a technologically simpler path to high-repetition rate, high-average power laser-plasma accelerators, and associated applications.
Multiple-beam laser–plasma interactions in inertial confinement fusion
Authors: Myatt J. F. , Zhang J. , Short R. W. , Maximov A. V. , Seka W. , Froula D. H. , Edgell D. H. , Michel D. T. , Igumenshchev I. V. , Hinkel D. E. , Michel P. , Moody J. D.
Published: May 2014

The experimental evidence for multiple-beam laser-plasma instabilities of relevance to laser driven inertial confinement fusion at the ignition scale is reviewed, in both the indirect and direct-drive approaches. The instabilities described are cross-beam energy transfer (in both indirectly driven targets on the NIF and in direct-drive targets), multiple-beam stimulated Raman scattering (for indirect-drive), and multiple-beam two-plasmon decay instability (in direct drive). Advances in theoretical understanding and in the numerical modeling of these multiple beam instabilities are presented.
Classical mapping for Hubbard operators: Application to the double-Anderson model
Authors: Li Bin , Miller William H. , Levy Tal J. , Rabani Eran
Published: May 2014

A classical Cartesian mapping for Hubbard operators is developed to describe the nonequilibrium transport of an open quantum system with many electrons. The mapping of the Hubbard operators representing the many-body Hamiltonian is derived by using analogies from classical mappings of boson creation and annihilation operators vis-à-vis a coherent state representation. The approach provides qualitative results for a double quantum dot array (double Anderson impurity model) coupled to fermionic leads for a range of bias voltages, Coulomb couplings, and hopping terms. While the width and height of the conduction peaks show deviations from the master equation approach considered to be accurate in the limit of weak system-leads couplings and high temperatures, the Hubbard mapping captures all transport channels involving transition between many electron states, some of which are not captured by approximate nonequilibrium Green function closures.
Structural aspects of glass-formation in Ni-Nb melts
Authors: Holland-Moritz D. , Yang F. , Gegner J. , Hansen T. , Ruiz-Martín M. D. , Meyer A.
Published: May 2014

We report on investigations of the static structure factors of glass-forming Ni59.5Nb40.5 alloy melts by combination of the containerless processing technique of electrostatic levitation with neutron diffraction. By application of the isotopic substitution method, the full set of partial structure factors was determined. The short-range order in liquid Ni59.5Nb40.5 is characterized by a large nearest neighbor coordination number of ZNN = 14.3 and a chemical short-range order with an affinity for the formation of heterogeneous Nb-Ni nearest neighbors. The structure factors observed here in the liquid state closely resemble those reported for amorphous Nb-Ni solids. The comparison with earlier results on the short-range structure in Zr-based glass-forming melts suggests that a large local density of packing, chemical order, and structural frustration are, amongst others, common structural properties of these metallic glass-forming systems, which favor glass-formation.
Shape selection and multi-stability in helical ribbons
Authors: Guo Q. , Mehta A. K. , Grover M. A. , Chen W. , Lynn D. G. , Chen Z.
Published: May 2014

Helical structures, almost ubiquitous in biological systems, have inspired the design and manufacturing of helical devices with applications in nanoelecromechanical systems, morphing structures, optoelectronics, micro-robotics, and drug delivery devices. Meanwhile, multi-stable structures, represented by the Venus flytrap and slap bracelet, have attracted increasing attention due to their applications in making artificial muscles, bio-inspired robots, deployable aerospace components, and energy harvesting devices. Here we show that the mechanical anisotropy pertinent to helical deformation, together with geometric nonlinearity associated with multi-stability, can lead to a selection principle of the geometric shape and multi-stability in spontaneous helical ribbons. Simple table-top experiments were also performed to illustrate the working principle. Our work will promote understanding of spontaneous curling, twisting, wrinkling of thin objects, and their instabilities. The proposed theoretical framework can also serve as a tool for developing functional structures and devices featuring tunable, morphing geometries and smart actuation mechanisms that can be applied in a spectrum of areas.
An analytical model for ballistic diode based on asymmetric geometry
Authors: Zhang Peng , Hung Derek M. H.
Published: May 2014

This paper presents an analytical model which calculates the current rectification of an asymmetric two-dimensional ballistic constriction structure in a classical treatment. Such a ballistic diode eliminates the use of p-n junctions or electrodes of dissimilar materials. We show the conditions at which the I-V asymmetry may be maximized for various aspect ratios. The analytic theory is verified by Monte Carlo simulations.
Scattering of electromagnetic waves by vortex density structures associated with interchange instability: Analytical and large scale plasma simulation results
Authors: Sotnikov V. , Kim T. , Lundberg J. , Paraschiv I. , Mehlhorn T. A.
Published: May 2014

The presence of plasma turbulence can strongly influence propagation properties of electromagnetic signals used for surveillance and communication. In particular, we are interested in the generation of low frequency plasma density irregularities in the form of coherent vortex structures. Interchange or flute type density irregularities in magnetized plasma are associated with Rayleigh-Taylor type instability. These types of density irregularities play an important role in refraction and scattering of high frequency electromagnetic signals propagating in the earth ionosphere, in high energy density physics, and in many other applications. We will discuss scattering of high frequency electromagnetic waves on low frequency density irregularities due to the presence of vortex density structures associated with interchange instability. We will also present particle-in-cell simulation results of electromagnetic scattering on vortex type density structures using the large scale plasma code LSP and compare them with analytical results.
The actual scaling of a nominally third-order Reynolds stress
Authors: Krommes J. A. , Hammett G. W.
Published: May 2014

It is shown that a particular higher-order Reynolds stress arising from a term in the third-order gyrokinetic Hamiltonian is smaller than it nominally appears to be. However, it does not follow that all third-order terms are unimportant. The discussion is relevant to the ongoing debate about the importance of higher-order terms in the gyrokinetic theory of momentum transport.
Low temperature spectral dynamics of single molecules in ultrathin polymer films
Authors: Sobolev Yaroslav I. , Naumov Andrei V. , Vainer Yuri G. , Kador Lothar
Published: May 2014

We studied the spectral dynamics of single fluorescent dye molecules embedded in ultrathin films (5 – 100 nm) of the amorphous polymer polyisobutylene at cryogenic temperatures and its variation with film thickness. Noticeable portion of molecules in the ensemble shows a behavior which is inconsistent with the standard tunneling model: Their spectral lines are subject to irreversible spectral jumps, continuous shifting, and abrupt chaotic changes of the linewidth or jumping rate. In films thinner than 100 nm, the occurrence of “non-standard” spectral behavior increases with decreasing sample thickness at fixed excitation intensity. In addition, it also increases with laser intensity.
The dynamics of spontaneous hydrogen segregation in LaFe13−xSixHy
Authors: Baumfeld Oliver L. , Gercsi Zsolt , Krautz Maria , Gutfleisch Oliver , Sandeman Karl G.
Published: May 2014

By means of time- and temperature-dependent magnetization measurements, we demonstrate that the timescale of hydrogen diffusion in partially hydrogenated LaFe13−xSixHy is of the order of hours, when the material is held at temperatures close to its as-prepared Curie temperature, TC0. The diffusion constant is estimated to be D ≈ 10−15–10−16 m2 s−1 at room temperature. We examine the evolution of a magnetically phase-separated state upon annealing for 3 days at a range of temperatures around TC0 and show that the thermodynamic driving force behind hydrogen diffusion and phase segregation may be attributed to the lower free energy of hydrogen interstitials in the ferromagnetic state relative to the paramagnetic state.
Amplification and generation of terahertz plasmons in gated two-dimensional channels: Modal analysis
Authors: Sydoruk O.
Published: May 2014

A theoretical analysis is presented of plasmons in gated two-dimensional electron channels supporting dc currents. In contrast to previous treatments, the model takes into account complete mode spectra and transverse field distributions. Conditions for plasmon amplification are determined, and asymmetric plasmonic oscillators are analysed. The results are compared with the traditional treatment of the Dyakonov-Shur instability. The limitations of the traditional treatment are thus revealed. The present electrodynamically rigorous model can be used to design and analyse terahertz plasmonic oscillators.
Depolarization mechanisms of PbZr0.52Ti0.48O3 and PbZr0.95Ti0.05O3 poled ferroelectrics under high strain rate loading
Authors: Shkuratov Sergey I. , Baird Jason , Antipov Vladimir G. , Talantsev Evgueni F. , Jo Hwan R. , Valadez Juan C. , Lynch Christopher S.
Published: May 2014

Stress-induced and thermal-induced depolarization studies along with X-ray diffraction were performed on lead zirconate titanate ferroelectrics of different compositions, PbZr0.52Ti0.48O3 (PZT 52/48) and PbZr0.95Ti0.05O3 (PZT 95/5). Specimens were shock loaded perpendicular to the polarization vector. It was found that the polarity of the stress-induced charge released by PZT 52/48 and 95/5 was opposite to the polarity of the charge generated due to the piezoelectric effect. PZT 52/48 was only partially (45%) depolarized under 1.5 ± 0.1 GPa mechanical compression, as opposed to PZT 95/5 which was fully depolarized. The experimental results indicate that the stress-induced depolarization mechanisms are different for these two compositions. PZT 52/48 is transformed to a state with lower polarization, while PZT 95/5 undergoes a phase transition to a non-polar antiferroelectric phase.
Direct growth of single-layer graphene on Ni surface manipulated by Si barrier
Authors: Wang Gang , Li Jinhua , Chen Da , Zheng Li , Zheng Xiaohu , Guo Qinglei , Wei Xing , Ding Guqiao , Zhang Miao , Di Zengfeng , Liu Su
Published: May 2014

Pure Ni film is the first metal catalyst that can generate graphene with small domains and variable thickness across the film. The lack of control over layer number is attributed to the high carbon solubility of Ni. We designed a combinatorial Ni/Si system, which enables the direct growth of monolayer graphene via chemical vapor deposition method. In this system, Si was introduced as the carbon diffusion barriers to prevent carbon diffusing into Ni film. The designed system fully overcomes the fundamental limitations of Ni and provides a facile and effective strategy to yield homogenous monolayer graphene over large area. The field effect transistors were fabricated and characterized to determine the electrical properties of the synthesized graphene film. Furthermore, this technique can utilize standard equipments available in semiconductor technology.
Dislocation-related trap levels in nitride-based light emitting diodes
Authors: Venturi Giulia , Castaldini Antonio , Cavallini Anna , Meneghini Matteo , Zanoni Enrico , Zhu Dandan , Humphreys Colin
Published: May 2014

Deep level transient spectroscopy was performed on InGaN/GaN multiple quantum well light emitting diodes (LEDs) in order to determine the effect of the dislocation density on the deep intragap electronic levels. The LEDs were grown by metalorganic vapor phase epitaxy on GaN templates with a high dislocation density of 8 × 109 cm−2 and a low dislocation density of 3 × 108 cm−2. Three trapping levels for electrons were revealed, named A, A1, and B, with energies EA ≈ 0.04 eV, EA1 ≈ 0.13 eV, and EB ≈ 0.54 eV, respectively. The trapping level A has a much higher concentration in the LEDs grown on the template with a high density of dislocations. The logarithmic dependence of the peak amplitude on the bias pulse width for traps A and A1 identifies the defects responsible for these traps as associated with linearly arranged defects. We conclude that traps A and A1 are dislocation-related intragap energy levels.
Ab initio density functional theory study of non-polar (101¯), (112¯) and semipolar {202¯1} GaN surfaces
Authors: Mutombo P. , Romanyuk O.
Published: May 2014

The atomic structures of non-polar GaN(101¯0), (112¯0) and semipolar GaN(202¯1), (202¯1¯) surfaces were studied using ab initio calculations within density functional theory. The bulk-like truncated (1 × 1) structure with buckled Ga-N or Ga-Ga dimers was found stable on the non-polar GaN(101¯0) surface in agreement with previous works. Ga-N heterodimers were found energetically stable on the GaN(112¯0)-(1 × 1) surface. The formation of vacancies and substitution site defects was found unfavorable for non-polar GaN surfaces. Semipolar GaN{202¯1}-(1 × 1) surface unit cells consist of non-polar {101¯0} and semipolar {101¯1} nano-facets. The {101¯1} nano-facets consist of two-fold coordinated atoms, which form N-N dimers within a (2 × 1) surface unit cell on a GaN(202¯1) surface. Dimers are not formed on the GaN(202¯1¯) surface. The stability of the surfaces with single {101¯0} or {101¯1} nano-facets was analyzed. A single non-polar {101¯0}-(1 × 1) nano-facet was found stable on the GaN(202¯1) surface, but unstable on the GaN(202¯1¯) surface. A single {101¯1} nano-facet was found unstable. Semipolar GaN surfaces with (202¯1) and (202¯1¯) polarity can be stabilized with a Ga overlayer at Ga-rich experimental conditions.
Rheological properties of bi-dispersed magnetorheological fluids based on plate-like iron particles with application to a small-sized damper
Authors: Shah Kruti , Xuan Phu Do , Choi Seung-Bok
Published: May 2014

In this study, the rheological properties and an application of bi-dispersed magnetorheological fluid (MRF) based on plate-like iron particles are experimentally investigated. A bi-dispersed MR Fluid is prepared using two different micron-scale sizes of plate-like iron particles. In the absence of a magnetic field, the properties of the fluid are isotropic. Upon the application of a magnetic field, the magnetized particles form a chain aligned in the direction of the field, which promotes the appearance of a yield stress. The reversible transition from solid to liquid is the basic requirement of MR applications. Due to the anisotropy in the shape and formation of a less compact structure in the iron plate-like particles, weak sedimentation and good redispersibility of the proposed MR fluid are created. The physical properties of the proposed MR fluids are evaluated and applied to the design of a small-sized controllable MR vibration damper, which can be used for vibration control of a washing machine. The MR damper is a semi-active device that dissipates energy during vibration motion to increase the stability of the application system. Three different weight fractions of the bi-dispersed MR fluids are prepared, and their rheological properties are presented and discussed. Based on their rheological properties, the figures of merit of the proposed MR fluids are derived. A comparison of these figures of merit gives the nominal behavior of the MR fluids, which are important in the design of the application device. A stability test is also performed to check the settling rate of MR fluids per day. The change in damping force due to the problem of particles settling in the MRF and the field-dependent damping force are measured with the MR damper operated just after filling the MRF and with the MR damper operated after waiting for 48 h after filling. With basic rheological properties and outstanding mechanical properties, it is clearly demonstrated that the proposed MR fluid which has a precise weight fraction can be applicable to controllable MR damper for vibration control.
Peculiarities of laser phase behavior associated with the accelerated electron in a chirped laser pulse
Authors: Song Q. , Wu X. Y. , Wang J. X. , Kawata S. , Wang P. X.
Published: May 2014

In this paper, we qualitatively analyzed peculiarities of laser phase behavior associated with the accelerated electron in a chirped laser pulse. We unveiled the relationship between the changes in the orientation of the electron trajectory and the cusps in magnitude of the phase velocity of the optical field along the electron trajectory in a chirped laser pulse. We also explained how the chirp effect induced the singular point of the phase velocity. Finally, we discussed the phase velocity and phase witnessed by the electron in the particle's moving instantaneous frame.
Stochastic modeling and performance monitoring of wind farm power production
Authors: Milan Patrick , Wächter Matthias , Peinke Joachim
Published: May 2014

We present a new stochastic approach to describe and remodel the conversion process of a wind farm at a sampling frequency of 1 Hz. The method is trained on data measured on one onshore wind farm for an equivalent time period of 55 days. Three global variables are defined for the wind farm: the 1-Hz wind speed u(t) and 10-min average direction ϕ¯ both averaged over all wind turbines, as well as the cumulative 1-Hz power output P(t). When conditioning on various wind direction sectors, the dynamics of the conversion process u(t) → P(t) appear as a fluctuating trajectory around an average IEC-like power curve. Our approach is to consider the wind farm as a dynamical system that can be described as a stochastic drift/diffusion model, where a drift coefficient describes the attraction towards the power curve and a diffusion coefficient quantifies additional turbulent fluctuations. These stochastic coefficients are inserted into a Langevin equation that, once properly adapted to our particular system, models a synthetic signal of power output for any given wind speed/direction signals. When combined with a pre-model for turbulent wind fluctuations, the stochastic approach models the power output of the wind farm at a sampling frequency of 1 Hz using only 10-min average values of wind speed and directions. The stochastic signals generated are compared to the measured signal, and show a good statistical agreement, including a proper reproduction of the intermittent, gusty features measured. In parallel, a second application for performance monitoring is introduced. The drift coefficient can be used as a sensitive measure of the global wind farm performance. When monitoring the wind farm as a whole, the drift coefficient registers some significant deviation from normal operation if one of twelve wind turbines is shut down during less than 4% of the time. Also, intermittent anomalies can be detected more rapidly than when using 10-min averaging methods. Finally, a probabilistic description of the conversion process is proposed and modeled, which can in turn be used to further improve the estimation of the stochastic coefficients.
Gallium ion implantation greatly reduces thermal conductivity and enhances electronic one of ZnO nanowires
Authors: Xia Minggang , Cheng Zhaofang , Han Jinyun , Zheng Minrui , Sow Chorng-Haur , Thong John T. L. , Zhang Shengli , Li Baowen
Published: May 2014

The electrical and thermal conductivities are measured for individual zinc oxide (ZnO) nanowires with and without gallium ion (Ga+) implantation at room temperature. Our results show that Ga+ implantation enhances electrical conductivity by one order of magnitude from 1.01 × 103 Ω−1m−1 to 1.46 × 104 Ω−1m−1 and reduces its thermal conductivity by one order of magnitude from 12.7 Wm−1K−1 to 1.22 Wm−1K−1 for ZnO nanowires of 100 nm in diameter. The measured thermal conductivities are in good agreement with those in theoretical simulation. The increase of electrical conductivity origins in electron donor doping by Ga+ implantation and the decrease of thermal conductivity is due to the longitudinal and transverse acoustic phonons scattering by Ga+ point scattering. For pristine ZnO nanowires, the thermal conductivity decreases only two times when its diameter reduces from 100 nm to 46 nm. Therefore, Ga+-implantation may be a more effective method than diameter reduction in improving thermoelectric performance.
Role of electron carriers on local surface plasmon resonances in doped oxide semiconductor nanocrystals
Authors: Matsui Hiroaki , Furuta Shinya , Tabata Hitoshi
Published: May 2014

Optical properties of carrier-dependent local surface plasmons (LSPs) were studied using dopant-controlled In2O3:Sn nanocrystals (NCs). From a systematic correlation between LSP excitations and electron carriers, electron-impurity scattering contributed towards plasmon damping as one of a factor that is absent in metal NCs. A threshold electron density (ne) from a damping dominated regime to a quenched damping regime appeared at around 1020 cm−3. The validity of Mie theory failed in ITO NCs with high ne greater than 1020 cm−3 since the role of electron carriers could enhance LSPs with simultaneous damped plasmonic excitations, which is valuable information for optical applications.
Impact of organisational characteristics on turnover intention among care workers in nursing homes in Korea: a structural equation model
Authors: Ha Jong Goon , Man Kim Ji , Hwang Won Ju , Lee Sang Gyu
Published: May 2014

Objective
The aim of the present study was to analyse the impact of organisational characteristics on the turnover intention of care workers working at nursing homes in Korea.

Methods
Study participants included 504 care workers working at 14 nursing homes in Korea. The variables measured were: high-performance work practices, consisting of five subfactors (official training, employment stability, autonomy, employee participation and group-based payment); organisational commitment, consisting of three subfactors (affective, normative and continuance commitment); organisational support; and turnover intention. The inter-relationship between high-performance work practices, organisational support, organisational commitment and turnover intention and the fit of the hypothetical model were analysed using structural equation modelling.

Results
According to our analysis, high-performance work practices not only had a direct effect on turnover intention, but also an indirect effect by mediating organisational support and commitment. The factor having the largest direct influence on turnover intention was organisational commitment.

Conclusions
The results of the present study suggest that to improve health conditions for frail elderly patients at nursing homes, as well as the efficiency of nursing homes through the continuance of nursing service and enhancement of quality of service, long-term care facilities should reduce the turnover intention of care workers by increasing their organisational commitment by actively implementing high-performance work practices.

What is known about the topic?
Considerable studies have shown that the adoption of high-performance work practices is related to an organisation’s performance and job satisfaction. In addition, previous studies found that job satisfaction is inversely related to the turnover intention of employees.

What does this paper add?
This paper identified that high-performance work practices are closely related to the turnover intention of care workers in nursing homes. These findings could improve our understanding of the factors that impact on labour management in nursing homes.

What are the implications for practitioners?
The turnover of care workers is one of the major managerial challenges for nursing home managers. The findings of this study suggest that managers should be focused on high-performance work practices to improve the efficiency of their organisations.
Development of Novel Guanidine–Bisurea Bifunctional Organocatalysts and their Application to Asymmetric α-Hydroxylation of Tetralone-derived β-Keto Esters
Authors: Odagi Minami , Takayama Kan , Furukori Kota , Watanabe Tatsuya , Nagasawa Kazuo
Published: May 2014

A series of guanidine–bisurea bifunctional organocatalysts 4, with chiral centres located outside the urea groups, were synthesized. The novel catalyst 4 is conformationally more flexible than the original catalyst 1. In α-hydroxylation of tetralone- derived β-keto esters, 4 afforded the corresponding alcohols in high yields with moderate enantioselectivity.
Open pulled straw vitrification and slow freezing of sheep IVF embryos using different cryoprotectants
Authors: Bhat M. H. , Sharma V. , Khan F. A. , Naykoo N. A. , Yaqoob S. H. , Vajta G. , Khan H. M. , Fazili M. R. , Ganai N. A. , Shah R. A.
Published: May 2014

The aim of the present study was to evaluate the post-thaw survival and hatching rates of sheep blastocysts using different cryoprotectants. In Experiment 1, Day 6 sheep embryos were cryopreserved by a slow freezing protocol using 10% ethylene glycol (EG), 10% dimethyl sulfoxide (DMSO) or a mixture of 5% EG and 5% DMSO. Hatching rates were higher in the 10% EG group than in the 10% DMSO or EG + DMSO groups (30% vs 18% and 20%, respectively). In Experiment 2, embryos were cryopreserved by open pulled straw (OPS) vitrification using either 33% EG, 33% DMSO or a mixture of 16.5% EG + 16.5% DMSO. Re-expansion and hatching rates in the EG + DMSO group (79.16% and 52.74%, respectively) were higher than those in the EG group (64.28% and 30.02%, respectively), whereas the outcomes for the DMSO group were the lowest (45.18% and 8.6%, respectively). In Experiment 3, embryos were cryopreserved by OPS vitrification using either 40% EG, 40% DMSO or a mixture of 20% EG + 20% DMSO. Re-expansion and hatching rates were highest in the EG group than in the EG + DMSO and DMSO groups (92.16% vs 76.30% and 55.84% re-expansion, respectively; and 65.78% vs 45.55% and 14.46% hatching, respectively). In conclusion, OPS vitrification was found to be more efficient for cryopreservation of in vitro-developed sheep embryos than traditional freezing.
Control of catalytic efficiency by a coevolving network of catalytic and noncatalytic residues
Authors: McMurrough Thomas A. , Dickson Russell J. , Thibert Stephanie M. F. , Gloor Gregory B. , Edgell David R.
Published: May 2014

Significance

Maximizing structural and functional information from multiple sequence alignments is difficult for protein families that exhibit extreme sequence variation. We addressed this issue by identifying covarying positions within the sequence alignment to predict networks of coevolving amino acid residues in LAGLIDADG homing endonucleases, enzymes used for genome-engineering applications. Intriguingly, the predicted coevolving network with the highest score includes the active-site metal-binding residues and adjacent residues. We were able to modulate catalytic efficiency ∼100-fold by substitution of residues in the network. Our data show that the evolutionary trajectory and fitness landscape of LAGLIDADG active sites is constrained by a barrier of coevolving residues and imply that generating an optimal coevolving network is an important consideration when engineering these endonucleases.
Visualizing synaptic vesicle turnover and pool refilling driven by calcium nanodomains at presynaptic active zones of ribbon synapses
Authors: Vaithianathan Thirumalini , Matthews Gary
Published: May 2014

Significance

Sensory synapses in the retina are characterized by special structures at the site of neurotransmitter release called synaptic ribbons, which transmit information about both sustained and rapidly changing visual stimuli. Because rapid signaling is important for detecting spatial and temporal contrast, we investigated the mechanism of fast neurotransmitter release at ribbon synapses, using high-resolution imaging of synaptic vesicle turnover and calcium responses. We find that nanodomains of high calcium at ribbons drive exocytosis of membrane-associated synaptic vesicles within milliseconds, accounting for the rapid component of neurotransmitter release, whereas replacement of lost vesicles occurs at membrane-distal sites on the ribbon. The results provide insight into synaptic mechanisms that enhance detection of contrast, a fundamental aspect of visual processing.