bluuebunny/crossref_metadata_2025 huggingface dataset:
Two relay control robustification by continuous switched integral sliding modes
Authors: Velázquez‐Velázquez Juan‐Eduardo , Galván‐Guerra Rosalba , Fridman Leonid , Iriarte Rafael
Published: December 2018

Robust generation of self‐oscillation for mechanical systems in the presence of matched uncertainties/perturbations based on a two‐relay controller, which naturally has a switched structure, is presented. Two scenarios are considered: the case when all the system states are available and the case when only output information is measured. In both scenarios, a continuous switched integral sliding modes controller is implemented to guarantee theoretically exact compensation of matched uncertainties/perturbations before the first switching. The chattering attenuation in the presence of fast parasitic dynamics can be realised by a switched gain strategy of the super‐twisting algorithm. In the output‐based scenario, the observer and the controller are initiated sequentially. A super twisting‐based observer is used, guaranteeing theoretically exact reconstruction of the states before the controller is activated. The observer gains are also switched to diminish the chattering. Once the observer has converged, the reconstructed state is used in the controller to achieve the control objective. The observer and controller are designed to attain convergence before the first switching.
Distributed fault estimation design of interconnected systems with external disturbances
Authors: Zhang Ke , Jiang Bin , Shi Peng , Pan Jeng‐Shyang
Published: December 2018

In this study, a new distributed fault estimation observer (DFEO) design method is proposed based on unknown input observer (UIO) for interconnected systems with external disturbances. The coupling terms among interconnected subsystems are utilised to construct DFEO. At the same time, according to the characteristics of UIO, external interference is completely decoupled to improve the robustness of fault estimation. Furthermore, the authors propose a multi‐constraint design with robust and regional pole configurations to analyse and design gain matrices of DFEO, which can be calculated using linear matrix inequalities. Furthermore, asymptotic estimation of sensor faults is discussed with the help of DFEO. Finally, a simulation of the interconnected system is provided to illustrate the effectiveness of the proposed technique.
Input‐to‐state stability for non‐linear switched stochastic delayed systems with asynchronous switching
Authors: Zhang Meng , Zhu Quanxin
Published: December 2018

In this study, the input‐to‐state stability (ISS), stochastic‐ISS and integral‐ISS problems for a class of switched stochastic systems with time delays are studied. A continuously differentiable Lyapunov–Krasovskii function with an indefinite derivative is employed to derive the ISS‐type properties of the systems. Two cases are considered: (i) synchronous switching, i.e. candidate controllers coincide with the switching of the system mode; (ii) asynchronous switching, i.e. the candidate controllers have a lag to the switching of the system modes. Furthermore, for asynchronous switching, the authors allow the Lyapunov–Krasovskii function to be time‐varying and increasing, respectively, during the time when the active subsystem and the controller match each other. Then, by means of the average dwell‐time method together with the Lyapunov–Krasovskii function, they can get the desired ISS‐type results. Finally, two examples are given to show the validity of the results.
Speech enhancement for in‐vehicle voice control systems using wavelet analysis and blind source separation
Authors: Lei Peng , Chen Meiling , Wang Jun
Published: December 2018

Multiple sources of interference and low signal‐to‐interference ratio are two major challenges to speech‐based intelligent driver assistant systems. They will have a serious impact on the performance of voice control commands. To solve this problem, this study proposes a speech enhancement method based on wavelet analysis and blind source separation in a complicated automobile environment. Firstly, according to the characteristics of typical speech signals, an automatic selection method of optimal wavelet basis is given to optimise the signal denoising performance. Secondly, the mixed signals are separated by a complex fast‐independent component analysis (ICA) algorithm, and then the inverse short‐time Fourier transform is utilised to obtain the separated signals in time domain. Finally, experiments are carried out to demonstrate the effectiveness of the proposed method. Results show that its performance in terms of a correlation coefficient can be improved by about 7% compared with that of the conventional method only using fast‐ICA.
Multi‐stage approach for the transshipment of import containers at maritime container terminals
Authors: Expósito‐Izquierdo Christopher , de Armas Jesica , Lalla‐Ruiz Eduardo , Melián‐Batista Belen , Moreno‐Vega José Marcos
Published: December 2018

The management of container flows is one of the most challenging tasks for terminal managers. In this regard, the freights inside the containers have to be transported towards their requesting companies. This delivery is subject to many factors such as the vessel berthing time, yard assignment, time windows of the companies, availability of internal vehicles etc. Therefore, the time a given company waits for its requested containers is highly dependent on the management of the technical resources at the container terminal. To appropriately address the coordination of involved operations, a multi‐stage approach is proposed. It is aimed at providing a complete schedule of all the involved processes and supporting the operational decisions related to the technical terminal resources in an integrated way, from the berth to the delivery of the freights inside containers to the requiring companies. The computational results indicate that this solution approach provides a suitable solution in all cases and is appropriate for supporting terminal managers when addressing strategic decisions involving the technical equipment.
Time‐of‐day breakpoints optimisation through recursive time series partitioning
Authors: Ma Dongfang , Li Wenjing , Song Xiang , Wang Yinhai , Zhang Weibin
Published: December 2018

Traffic signal control systems often operate with a fixed time strategy when practical conditions prohibit adaptive traffic control built upon real‐time traffic data. One of the most important challenges to have good performance for a fixed time strategy is to optimally identify the breakpoints that divide one day into different partitions, which is a time‐of‐day (TOD) breakpoints optimisation problem. Various solutions to this problem have been proposed based on classic clustering methods. However, these methods require empirical adjustment since they are not capable of incorporating the temporal information among traffic data. In this study, the TOD breakpoints optimisation problem is formulated as a time series data partitioning problem. A recursive algorithm is proposed to partition one day into several time periods based on the dynamic programming reformulation of the original problem. The appropriate number of partitions is determined through the elbow method. Then the authors present a case study based on the real data from Qingdao City in China that evaluates the proposed method against the existing ones. From simulation experiments, they illustrate that the proposed method is more effective in terms of operational performance measures such as maximum queue length and delay time than the existing ones.
Empty vehicle redistribution and fleet size in autonomous taxi systems
Authors: Babicheva Tatiana , Burghout Wilco , Andreasson Ingmar , Faul Nadege
Published: December 2018

This study investigates empty vehicle redistribution algorithms for personal rapid transit and autonomous taxi services. The focus is on passenger service and operator cost. A new redistribution algorithm is presented in this study: index‐based redistribution (IBR). IBR is a proactive method, meaning it takes into account both current demand and anticipated future demand, in contrast to reactive methods, which act based on current demand only. From information on currently waiting for passengers, predicted near‐future demand and projected arrival of vehicles, IBR calculates an index for each vehicle station, and redistribution is done based on this index. Seven different algorithm combinations are evaluated using a test case in Paris Saclay, France (20 stations and 100 vehicles). A combination of simple nearest neighbours and IBR is shown to be promising. Its results outperform the other methods tested in peak and off‐peak demand, in terms of average and maximum passenger waiting times as well as station queue length. The effect of vehicle fleet size on generalised cost is analysed. Waiting times, mileage and fleet size are taken into account while assessing this generalised cost.
Manoeuvre prediction and planning for automated and connected vehicles based on interaction and gaming awareness under uncertainty
Authors: Hu Manjiang , Xie Guotao , Gao Hongbo , Cao Dongpu , Li Keqiang
Published: December 2018

The complex and mixed traffic environment makes it a challenge for the widespread use of automated and connected vehicles (ACVs). It is necessary for these systems to have a better understanding of the traffic environment including interaction and gaming between multiple vehicles. In this study, a manoeuvre prediction and planning framework is proposed on the basis of game theories for complex and mixed traffic scenarios via vehicle‐to‐everything communication. In this framework, the interaction and gaming between multiple vehicles are considered by employing the extensive form game theories. In the payoff function, the risk assessment model based on trajectory prediction under uncertainty is employed to assess collision risks. Driving efficiency and preference are also combined in the payoff function. Uncertainty elements, including estimation and prediction, are considered to predict and plan by using Nash equilibrium of the extensive form game theory in mixed and behavioural strategies. Finally, this framework is applied and proved in different lane‐change scenarios. The results show that this framework could predict other vehicles’ driving manoeuvres and plan manoeuvres for ego vehicles by considering interaction and gaming between multiple vehicles, which helps ACVs understand the environment better and make the cooperative manoeuvre planning in complex traffic scenarios.
Effect of Cu doping and swift heavy ion irradiation on PbS quantum dots and their applications in solar cells
Authors: Ganguly Abhigyan , Sankar Nath Siddhartha , Choudhury Madhuchhanda
Published: December 2018

Copper ions are incorporated into the PbS quantum dots as dopants via a chemical method and an ion irradiation method. For irradiating the samples, a 100 MeV copper swift heavy ion beam is used with three different doses of 1 × 1011, 3 × 1011, and 1 × 1012 ions/cm2. The doped and irradiated samples are characterised by different techniques and introduced as a sensitising layer in a solar cell. The current density–voltage characteristics of the solar cells are studied under white light illumination conditions and the solar cell parameters such as Jsc, Voc, fill factor, and efficiency are obtained. Efficiency as high as 4.78% is obtained for irradiated quantum dots, which is significantly higher than that of pristine and doped quantum dot solar cells. However, at higher ion dosage, the solar cell efficiency degrades due to unwanted particle agglomeration in quantum dots.
Propagation coefficient spectrum based locating method for cable insulation degradation
Authors: Zhang Anan , Gao Chunlin , Yang Wei , Zhou Zhitong , Li Qian
Published: December 2018

To solve the complexity of the conventional time‐domain reflectometry method for locating minor cable ageing degradation, a frequency domain‐based method for locating cable ageing degradation based on propagation coefficient spectrum is proposed in this study. First, the change pattern of cable input impedance spectrum in frequency‐domain reflectometry is analysed to reveal the relationship between input impedance spectrum and propagation coefficient, and thus finds out the working mechanism of ageing degradation on propagation coefficient spectrum. Then, in the experiment, a vector network analyser is used to measure propagation coefficient spectrum and the inverse discrete Fourier transform is applied to locate cable ageing degradation. Finally, kurtosis analysis is performed on locating curves of different bandwidth and the upper limit of frequency of the testing signal is decided. Within a certain limit, the method proposed in this study can locate degradation with higher accuracy and resolution than several time/frequency‐domain based methods currently adopted.
Effect of temperature on the pulse‐echo performance of ultrasonic transducers fabricated with PVDF film
Authors: Kelley Thomas
Published: December 2018

Empirical data is presented on the pulse‐echo performance of poly‐vinylidenefluoride (PVDF) ultrasound transducers monitored in‐situ at temperatures in the range 50–130°C. Measurements were performed over a 5 h period beginning at the sensors’ initial exposure to temperature. A reduction in pulse‐echo amplitude was observed at all temperatures in the range and was found to be proportional to temperature increase. Four different thicknesses of PVDF film were used for the trials and small differences in behaviour were observed between sensors constructed using each thickness. On average, the overall loss was found to increase linearly with temperature from a 16% drop in pk–pk pulse‐echo voltage observed at 60°C to a 95% drop in performance at 120°C after 5 h. Rates of signal loss were found to follow a logarithmic decay, particularly at temperatures above 70°C where significant reductions were observed in the initial seconds/minutes following exposure to temperature.
Enantioselective Synthesis of 1- and 4-Hydroxytetrahydrocarbazoles through Asymmetric Transfer Hydrogenation
Authors: Ertürk Erkan , Dilek Ömer , Patir Süleyman
Published: December 2018

Several 1- and 4-hydroxytetrahydrocarbazoles were prepared in high yields (up to 99%) and excellent enantiomeric excesses (up to >99% ee) from the corresponding 1- and 4-oxotetrahydrocarbazoles through asymmetric transfer hydrogenation by using the commercially available Noyori–Ikariya ruthenium catalyst. The immediate use of the freshly prepared catalyst and the use of a HCO2H–DABCO (11:6) mixture as the hydrogen source are crucial for achieving high activity and enantioselectivity. In this way, a tetrahydrocarbazole heterocycle fused to a lactone moiety was synthesized in 45% yield and 97% ee.
A methodology for the digital reconstruction of an interferogram, a schlieren image, or a shadowgram from a single digital holographic recording
Authors: Pavez C. , Pedreros J. , Avaria G. , Bora B. , Moreno J. , Soto L.
Published: December 2018

This study presents an optical assembly and digital reconstruction method that is based on digital holography for characterizing transparent objects. The image-plane optical setup is based on a versatile Mach-Zehnder interferometer for the formation of controlled parallel fringe patterns, of tens micrometers of separations or less. The numerical reconstruction of the propagated wavefront by the hologram is performed by the Fresnel-Kirchhoff transform, and it is used of three ways: (a) interferometric phase reconstruction (as in interferometry) in the phase object position, (b) reconstruction of the wavefront amplitude at a determined distance from the object (shadowgraph technique), and (c) a composed digital reconstruction process of the wavefront amplitude, defined by a digital optical assembly for the selection of angular deflections produced by the phase object (schlieren technique). The resolving power of holographic reconstruction methodology proposed is determined by the sensitivity of hologram for detecting the interferometric phase. The fringe pattern of the hologram defines a minimum phase shift resolution of 0.15π rad. The scope of the technique is experimentally tested for a steady-state phase object.
Thermoelectric performance of monolayer InSe improved by convergence of multivalley bands
Authors: T. Hung Nguyen , Nugraha Ahmad R. T. , Yang Teng , Zhang Zhidong , Saito Riichiro
Published: December 2018

We theoretically investigate a possibility of improving the thermoelectric performance of monolayer InSe through convergence of multivalley energy bands, in which some distinct valleys become almost degenerate. The convergence of energy bands is achieved by applying mechanical strain. We find that the thermoelectric power factor of monolayer InSe can be significantly enhanced by nearly a factor of 3 through the band convergence in both valence (p-type) and conduction (n-type) bands under a biaxial compressive stress of about 1.16 GPa. However, the maximum enhancement of the figure of merit ZT in the p-type and n-type InSe differs each other depending on how the valleys converge in each case. The optimal scenario is that the heavy valleys approach the light valleys in the band convergence, which leads to an increase in the power factor and, at the same time, a decrease in the thermal conductivity of an electron. This optimal condition can be obtained in the strained n-type InSe that gives the largest enhancement of ZT as high as 230% ZT of unstrained InSe. In contrast, the enhancement of ZT in the strained p-type InSe, which exhibits opposite valley convergence (light valleys joining heavy ones), gives only 26% ZT of unstrained InSe.
Temperature compensation in fluid density measurement using micro-electromechanical resonant sensor
Authors: Zhao Libo , Huang Linya , Hu Yingjie , Jiang Weile , Lu Dejiang , Li Zhikang , Zhou Xiangyang , Wang Jiuhong
Published: December 2018

In order to improve the measuring accuracy of micro-electromechanical system (MEMS) resonant sensor with micro-cantilever structure to measure fluid density, a temperature compensation method is presented. The elastic modulus of the micro-cantilever is calculated considering its temperature coefficient so that the working equation to measure fluid density is obtained with decreasing temperature disturbance on the measuring accuracy. The simulations and experimental measurements of several fluids with different densities were carried out by the MEMS micro-cantilever resonant sensor under different temperatures. The simulation analyses showed that the fluid densities measured by using the proposed resonant density sensor with temperature compensation were more fitted with the reference density values than those without temperature compensation. The experimental results showed that both the measuring accuracy and stability of the MEMS micro-cantilever resonant sensor in fluid density measurement were increased more than twice based on the temperature compensation method. Therefore, the proposed temperature compensation method is important to improve the measuring precision and stability of the MEMS micro-cantilever resonant sensor in fluid density detection fields.
An equation of state for abnormal expansion of shocked porous materials
Authors: Cao Xiuxia , Chen Junxiang , Yu Yin , Wu Qiang
Published: December 2018

Abnormal expansion phenomena occur in various types of shocked porous materials with relatively high porosity. In this work, we propose a way to treat the shock velocity D and particle velocity u data of shocked porous materials and then deduce a new equation of state (EOS). Validations show that this new EOS can well describe the pressure-volume data of porous materials over a wide range of porosity and pressure. In particular, the abnormal expansion is satisfactorily reproduced. Furthermore, based on the new EOS, a unified functional form of the EOS is deduced to describe the shock, isentropic, and isothermal compression of solid materials, which facilitates the mutual calculation among different kinds of compression states.
Challenges in materials and devices for resistive-switching-based neuromorphic computing
Authors: del Valle Javier , Ramírez Juan Gabriel , Rozenberg Marcelo J. , Schuller Ivan K.
Published: December 2018

This tutorial describes challenges and possible avenues for the implementation of the components of a solid-state system, which emulates a biological brain. The tutorial is devoted mostly to a charge-based (i.e. electric controlled) implementation using transition metal oxide materials, which exhibit unique properties that emulate key functionalities needed for this application. In Sec. I, we compare the main differences between a conventional computational machine, based on the Turing-von Neumann paradigm, and a neuromorphic machine, which tries to emulate important functionalities of a biological brain. We also describe the main electrical properties of biological systems, which would be useful to implement in a charge-based system. In Sec. II, we describe the main components of a possible solid-state implementation. In Sec. III, we describe a variety of Resistive Switching phenomena, which may serve as the functional basis for the implementation of key devices for neuromorphic computing. In Sec. IV, we describe why transition metal oxides are promising materials for future neuromorphic machines. Theoretical models describing different resistive switching mechanisms are discussed in Sec. V, while existing implementations are described in Sec. VI. Section VII presents applications to practical problems. We list in Sec. VIII important basic research challenges and open issues. We discuss issues related to specific implementations, novel materials, devices, and phenomena. The development of reliable, fault tolerant, energy efficient devices, their scaling, and integration into a neuromorphic computer may bring us closer to the development of a machine that rivals the brain.
Thickness effects on the epitaxial strain states and phase transformations in (001)-VO2/TiO2 thin films
Authors: Yang Yuanjun , Mao Xiaoli , Yao Yingxue , Huang Haoliang , Lu Yalin , Luo Linbao , Zhang Xingmin , Yin Guangzhi , Yang Tieying , Gao Xingyu
Published: December 2018

The thickness-dependent epitaxial strains and phase transformations of (001)-VO2/TiO2 thin films are investigated systematically in a wide thickness range (from 9 to 150 nm). Under a thickness of 18 nm, the tensile in-plane strain is maintained, owing to the good lattice and the symmetry matching between the VO2 thin film and the TiO2 substrate, but the compressive out-of-plane epitaxial strain is gradually relaxed. The epitaxial strains co-stabilize the rutile phase (R phase) in this thickness range. Beyond a thickness of 18 nm, the out-of-plane lattice c exhibits a sudden elongation and reaches the bulk level of 2.8528 Å at a thickness of 20 nm, which indicates a structural phase transition (SPT). A further increase of the film thickness results in another new phase (tetragonal-like or T-like) with lattice distortion, which maintains the tetragonal symmetry in the thickness range of 20 to 55 nm. From a thickness of 60 nm, the monoclinic phase (M1 phase) appears, which indicates another SPT from T-like to the monoclinic M1 phase. This SPT is more favorable energetically, owing to the assistance of the strain relaxation in the thicker films. Additionally, the metal-insulator transition temperature positively increases as a function of the out-of-plane strain. This result is consistent with the fact that the tensile strain along the cR axis (V-V atom chain) is conducive for the stabilized insulating phase. This work highlights strain engineering as a crucial avenue for manipulating the phase transformations and properties in the correlated electron system.
Effects of polymeric filler on polarization fatigue of 1-3 0.74Pb(Mg1/3Nb2/3)O3-0.26PbTiO3 single crystal/polymer composites
Authors: Wang Chunying , Lan Yu , Cao Wenwu
Published: December 2018

Polarization fatigue tests have been conducted on both bulk Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystals and two 1-3 PMN-xPT/polymer composites with both “soft” and “hard” epoxy fillers, respectively. The variations of remnant polarization, coercive electric field, and micro-crack morphology under 10 Hz cyclic electric loading were studied. It was found that the magnitude of coercive field for both composites was higher compared to that of single crystals. However, as the number of cycles increases, the degradation ratio of remnant polarization and the increased portion of coercive field for both composites were lower than that of single crystals; the sequence is PMN-0.26PT bulk single crystal > 1-3 PMN-0.26PT/soft epoxy composites > 1-3 PMN-0.26PT/hard epoxy composites. In addition, the observed micro-crack propagation morphology shows that 1-3 PMN-0.26PT/hard epoxy composites can substantially improve fatigue-resistance owing to the lower stretching strain benefiting from the polymeric filler. Our results indicated that 1-3 PMN-0.26PT/polymer composites present much better electric polarization stability.
Systematic analysis for electrical conductivity of network of conducting rods by Kirchhoff's laws and block matrices
Authors: Kim Dongjae , Nam Jaewook
Published: December 2018

In recent years, high-aspect-ratio materials, such as metallic nanowires and carbon nanotubes, have become attractive alternatives for the next generation of transparent conductive films. The functionality of the films is represented by their opto-electric performance, which is primarily affected by the nano- or micro-structures inside the films. In this study, we focus on the analysis of the electrical conductivity of two-dimensional networks of conducting rods by treating parts of the networks as a linear circuit system. For the analysis, multi-nodal representation is used to assign the nodes and edges of the circuit. Based on Kirchhoff's laws, the relation between the current and electrical potential is formulated using a block matrix equation. After a series of block-matrix manipulations, the equation can be reduced to yield several simple equations expressed in terms of the incidence matrices and the weighted graph Laplacians. Among these, the equation representing the Ohm's-law-like relation between the total current and the bias voltage can be used to derive the explicit expression for the normalized conductivity, which can quantify the effect of the network. During the analysis, we also deduce the normalized number of edges, that is, the combination of variables used in the system. The normalized number of edges can be related to the reduced number density of rods by using a proper statistical model. Moreover, we found the direct relation between the normalized number of edges and the backbone fraction, which is a representative quantity related with the electrical conductivity.
Optimal palmate leaf-like conductive network for cooling a heat-generating volume
Authors: Hu Liguo , Wang Dantong , Fan Tongxiang
Published: December 2018

With the development of high-density integration and the miniaturization of electronic devices, extracting the heat generated in electronic devices has become a major issue. Conductive cooling is an effective method to extract the heat generated by electronic devices. The fundamental “volume-to-point” problem was first put forward and solved by Bejan by using a constructal theory, that is, how to construct the efficient conductive network with high thermal conductivity to cool a heat-generating volume with low thermal conductivity. In the present study, we use a palmate leaf-like conductive network to cool a heat-generating volume. We first analytically optimize the conductive network structure and then implement numerical simulations to validate the analytical result. The numerical results indicate that the optimal palmate leaf-like conductive network greatly reduces the maximum temperature difference between heat sinks and the volume. Furthermore, we show numerically that the optimal palmate leaf-like conductive network has a greater tolerance for network channel damage and effectively increases network robustness.
Plasma dynamics in the initial stage of a laser-triggered discharge-plasma
Authors: Xie Zhuo , Wu Jiazhi , Dou Yinping , Lin Jingquan , Tomie Toshihisa
Published: December 2018

The use of any solid material as a fuel and the discharge stability make a laser triggered discharge-produced-plasma (LT-DPP) an attractive light source. Density, size, uniformity, and so on of a fuel control the pinch process by a Lorentz force, and understanding the plasma dynamics in the initial stage is the most important in the LT-DPP study. This work reports how a material for a pinch is supplied and how a laser-produced-plasma (LPP) generated on the electrode behaves before the main discharge current. Our study revealed that the material of a pinch plasma is mainly supplied by laser ablation of a cathode not by current heating of the electrodes. The delay time of a discharge is determined by the velocity of an LPP generated on the cathode, and the traveling velocity of about 1 × 105 m/s of LPP is determined by two factors: the pressure of LPP and acceleration by the electric field. Before the main discharge current starts to flow, two X-ray pulses are generated. The first X-ray pulse is generated on the cathode where a laser is irradiated. The second X-ray pulse is generated on the anode when the LPP generated on the cathode arrives, and the arrival of the LPP triggers the main discharge current. The material for the pinch is not the LPP, but supplied by laser ablation. A faintly bright region appears between electrodes several tens of ns after the start of the main discharge current and this region is slowly imploded and a pinch plasma is formed at the current peak.
Effect of annealing on magnetic properties in ferrimagnetic GdCo alloy films with bulk perpendicular magnetic anisotropy
Authors: Ueda Kohei , Tan Aik Jun , Beach Geoffrey S. D.
Published: December 2018

Magnetic properties in ferrimagnetic GdCo alloy films with bulk perpendicular magnetic anisotropy (PMA) are investigated as a function of annealing temperature (Tanneal) and annealing time for several capping layers. Magnetic properties in films capped by TaOx vary markedly with Tanneal; the saturation magnetization and coercivity vary progressively with increasing Tanneal up to 300°C, and above that temperature, PMA is lost abruptly. By comparing the annealing temperature dependence for Co-dominated and Gd-dominated compositions close to the magnetization compensation point, the data are readily explained by preferential oxidation of Gd during annealing. When films are capped by a Ta/Pt bilayer, the film properties are stable up Tanneal = 300 °C, indicating that oxidation at high temperatures is effectively blocked, but the abrupt loss of PMA for Tanneal > 300 °C is still observed. X-ray diffraction measurement reveals that the amorphous structure of the films remains the same after high-temperature annealing that is sufficient to remove PMA, indicating that crystallization from the amorphous phase is not responsible for the lack of PMA. Instead, our results suggest that high annealing temperatures may cause segregation of Co and Gd atoms in the films, which reduces anisotropic pair-pair correlations responsible for the observed bulk PMA in the as-grown state.
Quantum Monte Carlo study of the electron binding energies and aromaticity of small neutral and charged boron clusters
Authors: Isaac Moreira E. M. , Brito B. G. A. , Higino Damasceno J. , Teixeira Rabelo J. N. , Hai G.-Q. , Cândido L.
Published: December 2018

The valence electron binding energies and the aromaticity of neutral and charged small boron clusters with three and four atoms are investigated using a combination of the fixed-node diffusion quantum Monte Carlo (FN-DMC) method, the density functional theory, and the Hartree-Fock approximation. The obtained electron binding energies such as the adiabatic detachment energy, vertical detachment energy, adiabatic ionization potential, and the vertical ionization potential are in excellent agreement with available experimental measurements. Their decomposition into three physical components such as the electrostatic potential and exchange interaction, the relaxation energy, and the electronic correlation effects has allowed us to determine that the neutral boron clusters are stabilized by the electrostatic and exchange interactions, while the anionic ones are stabilized by the relaxation and correlation effects. The aromaticity is studied based on electronic structure principles descriptor and on the resonance energy. The FN-DMC results from the electronic structure principles of the energy, hardness, and eletrophilicity have supported the aromaticity of B3−, B4−, and B4 and partially supported the aromaticity of the clusters B3, B3+, and B4+. The obtained values for the resonance energy of the clusters B3−, B3, B3+, B4, B4+, and B4− are 55.1(7), 54.2(8), 33.9(7), 84(1), 67(1), and 58(1) kcal/mol, respectively. Therefore, the order of decreasing stability of the trimer is B3− > B3 > B3+, while for the tetramer it is B4 > B4+ > B4−, which is in agreement with the results from the molecular orbital analysis.
The Stokes-Einstein relation for simple fluids: From hard-sphere to Lennard-Jones via WCA potentials
Authors: Ohtori Norikazu , Uchiyama Hikaru , Ishii Yoshiki
Published: December 2018

The Stokes-Einstein (SE) relation is examined for hard-sphere (HS) and Weeks-Chandler-Andersen (WCA) fluids by the molecular dynamics method on temperatures and densities corresponding to the saturated vapor line of Lennard-Jones (LJ) liquids. While the self-diffusion coefficient, D, and shear viscosity, ηsv, increases and decreases, respectively, with increasing steepness in interaction potentials, the same SE relation holds for HS and WCA fluids as that obtained for LJ liquids, i.e., Dηsv = (kBT/C)(N/V)1/3, where kB is the Boltzmann constant, T is the temperature, and N is the particle number included in the system volume V. The coefficient C is almost constant at about 6 to 2π for η > 0.3, where η is the packing fraction. The results show that the SE relation for simple liquids and fluids does not need to bear any concepts of both the hydrodynamic particle size and the boundary condition. In light of this SE relation, the Enskog, Eyring-Ree, and Zwanzig theories are quantitatively tested. In addition, the cause of deviation from unity of the exponent in the fractional SE relation for simple fluids is clearly accounted for. The present results show that applying both the original and the fractional SE relations to simple liquids and fluids does not lead to any meaningful discussions.
Competing adsorption mechanisms of pyridine on Cu, Ag, Au, and Pt(110) surfaces
Authors: Malone Walter , von der Heyde Johnathan , Kara Abdelkader
Published: December 2018

We explore the adsorption of pyridine on Cu, Ag, Au, and Pt(110) surfaces using density functional theory. To account for the van der Waals interaction, we use the optB86b-vdW, optB88-vdW, optPBE-vdW, revPBE-vdW, and rPW86-vdW2 functionals. For comparison, we also run calculations using the generalized gradient approximation-PBE (Perdew–Burke–Ernzerhof) functional. We find the most stable adsorption site to depend on both metal and functional, with two energetically favorable adsorption sites, namely, a vertically oriented site and a flat pyridine site. We calculate that every functional predicts pyridine to lie in the vertical configuration on the coinage metals at a low coverage. On Pt(110), by contrast, we calculate all the functionals—except rPW86-vdW2—to predict pyridine to lie flat at a low coverage. By analyzing these differences for these adsorption configurations, along with various geometric and electronic properties of the adsorbate/substrate system, we access in detail the performance of the 6 functionals we use. We also characterize the nature of the bonding of pyridine on the coinage metals from weak to strong physisorption, depending on the functional used. On Pt(110), we characterize the nature of the bonding of pyridine as ranging from strong physisorption to strong chemisorption depending again on the functional used, illustrating both the importance of the van der Waals interaction to this system and that this system can make a stringent test for computational methods.
Surface relief gratings in azo-polymers revisited
Authors: Moujdi S. , Rahmouni A. , Mahfoud T. , Nesterenko D. V. , Halim M. , Sekkat Z.
Published: December 2018

We use the concept of vectorial photochemical tweezing to rationalize the experimental observations of surface relief gratings in azo-polymers, e.g., the photochemically induced motion of the polymer in a one-dimensional intensity gradient produced by two-laser beam interference. Vectorial motion of matter occurs when photochemically active, polarization sensitive molecules are photo-selected in a gradient of light intensity. Directional motion is imposed parallel to the gradient vector with an efficiency that depends on the respective orientations of the vectors of light polarization and intensity gradient. Different combinations of polarizations of the interfering beams leading to differing efficiencies of matter motion are revisited and discussed. We show that the magnitude of photoisomerization force dictates the efficiency of the observed matter motion. We also show that the spatial distribution of the photo-moved matter is Gaussian, the height and width of which exhibit an intensity dependence which is predicted by the theory of photochemical vectorial tweezing; both theory and experiments indicate that the photoisomerization force, which acts on thin films of azo-polymers, is in the mN range.
Bi nanowires modified by 400 keV and 1 MeV Au ions
Authors: Guerra D. B. , Müller S. , Oliveira M. P. , Fichtner P. F. P. , Papaléo R. M.
Published: December 2018

We report on the modification of the structure and morphology of Bi nanowires of two different diameters (80 or 130 nm) exposed to beams of 400 keV and 1 MeV Au+ until complete wire degradation. For fluences up to ∼1 ion/nm2, the main effect was a slight roughening of the originally smooth surface and the appearance of a damaged zone at the wire edges. After an exposure to ∼2 ions/nm2, shallow (∼5-7 nm deep) but wide (up to 120nm) depressions are seen, giving the wires a “wavy” morphology. At the largest fluence tested (10 ions/nm2), the thickest nanowires present an amorphized structure containing an embedded dispersion of small spherical metallic crystallites, while the thinner wires collapse into large (∼50nm) nanoparticles composed of a crystalline core surrounded by a disordered oxidized shell. The observed morphologic modifications are discussed considering sputtering and radiation induced surface diffusion effects.
Tunable near-infrared perfect absorber based on the hybridization of phase-change material and nanocross-shaped resonators
Authors: Li Ce , Zhu Wei , Liu Zhe , Yan Shi , Pan Ruhao , Du Shuo , Li Junjie , Gu Changzhi
Published: December 2018

Ge2Sb2Te5 (GST) is a kind of non-volatile chalcogenide phase-change material, which has a significant difference in permittivity between its amorphous and crystalline states in the infrared range. On account of this remarkable property, the combination of GST and metamaterials has great potential in tunable meta-devices. In this paper, a perfect absorber based on a nanocross-resonator array stacked above a GST spacer layer and an Au mirror (i.e., a metal-dielectric-metal configuration) is designed and experimentally demonstrated. A thin indium tin oxide (ITO) protective layer is inserted between the GST spacer and the Au resonator to avoid heat-induced oxidation of the GST layer during phase transition. We found that the ITO layer not only can protect the GST layer from deterioration, but also allows a significant blue shift in the absorption peak from 1.808 μm to 1.559 μm by optimizing the thickness of the two dielectric layers without scaling down the size of the metal structure, which provides a more feasible idea in pushing the absorption peak to higher frequency. The LC circuit model is presented to explain this blue-shift phenomenon, which is mainly attributed to the engineering of the dielectric environment of the parallel plate capacitance. In addition, such good performance in dynamitic modulation makes this perfect absorber a robust candidate for optical switching and modulating in various situations.
Inflection point in the Debye relaxation time of 2-butyl-1-octanol
Authors: Thoms Erik , Kołodziej Sławomir , Wikarek Michał , Klotz Stefan , Pawlus Sebastian , Paluch Marian
Published: December 2018

We report a striking anomaly in the pressure dependent Debye-relaxation time of the branched monohydroxy alcohol 2-butyl-1-octanol. Evidence of a crossover from slower to faster than exponential pressure dependency was obtained at different temperatures via high pressure broadband dielectric spectroscopy. At the same time, viscosity measurements reveal similar behavior in the viscosity, respectively, the structural relaxation time, indicating a similar origin of the phenomena.
Abscisic acid and its metabolites are involved in drought tolerance in four native species of Patagonian semiarid shrublands (Argentina)
Authors: Cenzano Ana M. , Reginato Mariana , Varela M. Celeste , Luna M. Virginia
Published: December 2018

Drought is the main stress that affects growth of native species of Patagonian Monte. Physiological and biochemical traits with functional roles in adaptation to drought are still scarce in native species. The aim of this study was to evaluate changes in dry matter content and abscisic acid (ABA) and its metabolites (phaseic acid-PA, dihydrophaseic acid-DPA, ABA conjugated with glucose-ABA-GE) level in green leaves and fine roots of four native species during contrasting seasons regarding water availability. Results show that grasses had higher leaf dry matter content (LDMC) and root dry matter content (RDMC) than Lycium chilense shrub and LDMC decreased during autumn in Larrea divaricata. In green leaves, there was an interaction between species and seasons for ABA and PA contents. L. divaricata had high ABA content during spring and low ABA content during autumn; while L. chilense showed the opposite pattern. During spring, drought tolerant species had high PA content while drought avoidant species had low PA content, and during autumn these species showed the opposite pattern. ABA-GE content was highest in L. chilense green leaves. In fine roots, ABA content was highest in L. divaricata and during spring PA was higher in L. divaricata than P. ligularis and L. chilense. PA was the only metabolite that decreased in L. divaricata during autumn. Results showed that ABA homeostasis maintains the functioning of different life forms with different drought resistance strategies in Patagonia semiarid shrublands. In green leaves of the drought avoidant L. chilense shrub, the ABA conjugation pathway was active in both seasons. During spring, the most drought tolerant L. divaricata showed highest activation of ABA synthesis and ABA oxidation pathways. During autumn L. chilense showed highest activation of ABA synthesis and together with P. ligularis showed active the ABA oxidation pathway.
Variations in body-size spectra of periphytic ciliates at different depths: a case study in coastal waters of the Yellow Sea
Authors: Abdullah Al Mamun , Xu Guangjian , Sikder Mohammad Nurul Azim , Warren Alan , Xu Henglong
Published: December 2018

Body-size spectra are inherent characteristics of organisms that can be used to summarise the functional structure of a community and thus be used in both ecological studies and biomonitoring programs. In order to determine the effect of water depth on body-size spectra of marine periphytic ciliate communities, a 1-month baseline survey was conducted at four depths (1, 2, 3.5 and 5m) in coastal waters of the Yellow Sea, northern China. Based on equivalent spherical diameters (ESD), 50 species were categorised into seven body-size ranks: S1, 2–17μm; S2, 22–27μm; S3, 29–36μm; S4, 37–49μm; S5, 53–71μm; S6, 84–92μm; S7, 127–153μm. These seven body-size ranks were composed of four trophic functional groups: algivores (A), bacterivores (B), predators (R) and non-selectives (N). Body-size rank S1 was composed primarily of the B functional group; S2 was composed of the N and R functional groups, S3 and S4 were composed of the A, B and N functional groups, S5 and S6 were composed of the A functional group and S7 was composed of the R functional group. The medium body-size ranks (S4 and S5) were dominant at 1 and 2m, whereas the smallest body-size rank (S1) was dominant at 3.5 and 5m. Canonical analysis of principal coordinates revealed a clear vertical variation in body-size spectra at the four depths. Body-size diversity indices peaked at 2–3.5m and fell sharply at 5m. Body-size diversity indices peaked at 2–3.5m and fell sharply at 5m. Body-size distinctness, as measured by the paired-index (ellipse) test, showed an increasing trend of departure from the expected pattern from surface to deeper layers. These results suggest that the body-size spectra of periphytic ciliates may be significantly shaped by water depth and thus may be used as bioindicators of the ecological integrity and quality of water at different depths in marine ecosystems.