bluuebunny/crossref_metadata_2025 huggingface dataset:
Forest cutting and impacts on carbon in the eastern United States
Authors: Zhou Decheng , Liu Shuguang , Oeding Jennifer , Zhao Shuqing
Published: December 2013

Forest cutting is a major anthropogenic disturbance that affects forest carbon (C) storage and fluxes. Yet its characteristics and impacts on C cycling are poorly understood over large areas. Using recent annualized forest inventory data, we estimated cutting-related loss of live biomass in the eastern United States was 168 Tg C yr−1from 2002 to 2010 (with C loss per unit forest area of 1.07 Mg ha−1yr−1), which is equivalent to 70% of the total U.S. forest C sink or 11% of the national annual CO2emissions from fossil-fuel combustion over the same period. We further revealed that specific cutting-related C loss varied with cutting intensities, forest types, stand ages and geographic locations. Our results provide new insights to the characteristics of forest harvesting activities in the eastern United States and highlight the significance of partial cutting to regional and national carbon budgets.
Spontaneous transformation from micelles to vesicles associated with sequential conversions of comprising amphiphiles within assemblies
Authors: Takakura Katsuto , Yamamoto Takahiro , Kurihara Kensuke , Toyota Taro , Ohnuma Kiyoshi , Sugawara Tadashi
Published: December 2013

Dodecylamine-migration associated with the formation of double-chained amphiphilic imine induces the morphological transformation from micelles to giant vesicles.
A C-shaped p-sulfonatocalix[4]arene-based supermolecule exhibiting mutual-inclusion and bilayer insertion of dipicolinate
Authors: Husain Ahmad , Oliver Clive L.
Published: December 2013

A p-sulfonatocalix[4]arene-based, C-shaped supermolecule, [Ce3(PDA)4(C4AS)2·13H2O](NO3)·25H2O 1 was prepared and characterized by single crystal X-ray structural analysis, thermal methods (TG, DSC and hot-stage microscopy) and Hirshfeld analysis.
Recent progress in the chemical modification of syndiotactic polystyrene
Authors: Jaymand Mehdi
Published: December 2013

This review provides a snapshot of recent progress in the chemical modification of syndiotactic polystyrene.
Highly efficient visible-light driven photocatalysts: a case of zinc stannate based nanocrystal assemblies
Authors: Liu Caihong , Röder Robert , Zhang Lichun , Ren Zheng , Chen Haiyan , Zhang Zhonghua , Ronning Carsten , Gao Pu-Xian
Published: December 2013

Highly efficient visible-light driven photocatalysts are enabled by wide band gap semiconducting zinc stannate based nanocrystal assemblies through populating the defect energy states and coherent hetero-interfaces.
Optical quantum confinement in low dimensional hematite
Authors: Fondell Mattis , Jacobsson T. Jesper , Boman Mats , Edvinsson Tomas
Published: December 2013

Optical and vibrational properties of low dimensional hematite are investigated where the indirect transition essentially disappears for the thinnest films.
Combinatorial delivery of immunosuppressive factors to dendritic cells using dual-sized microspheres
Authors: Lewis Jamal S. , Roche Chris , Zhang Ying , Brusko Todd M. , Wasserfall Clive H. , Atkinson Mark , Clare-Salzler Michael J. , Keselowsky Benjamin G.
Published: December 2013

Microparticulate systems are beginning to show promise for delivery of modulatory agents for immunotherapeutic applications which modulate dendritic cell (DC) functions.
Resolvin E1 promotes resolution of inflammation in a mouse model of an acute exacerbation of allergic asthma
Authors: Flesher Rylie P. , Herbert Cristan , Kumar Rakesh K.
Published: December 2013

Endogenous mediators, such as RvE1 (resolvin E1), promote resolution of an inflammatory response and have potential as novel therapeutic agents. In the present study, we investigated the activity of RvE1 in a model of an acute exacerbation of chronic allergic asthma in mice. Animals sensitized to OVA (ovalbumin) received controlled low-level challenge with aerosolized antigen for 4 weeks, followed by a single moderate-level challenge to simulate an allergen-induced exacerbation of asthmatic inflammation. Induction of an exacerbation was associated with rapid recruitment of neutrophils, lymphocytes and eosinophils, together with increased levels of Th2 and pro-inflammatory cytokines. When administered before the final moderate-level challenge, RvE1 had only a modest effect on airway inflammation. To assess its effects when administered after induction of an exacerbation, we first characterized the cellular and molecular events associated with spontaneous resolution of airway inflammation over the following 96 h. Subsequently, we showed that administration of RvE1 at 2 and 8 h after the final challenge accelerated this process significantly. Specifically, RvE1 promoted a decline in the number of inflammatory cells, concentration of cytokines in lavage fluid and expression of mRNA for cytokines by macrophages, confirming its pro-resolution activity. In vitro, RvE1 had no apparent effect on lymphocytes, but suppressed significantly cytokine production by pulmonary macrophages, with evidence of down-regulation of the nuclear translocation of NF-κB (nuclear factor κB) p65 in these cells. The present study provides novel evidence that RvE1 can facilitate resolution of airway inflammation in a clinically relevant model of an acute exacerbation of asthma, possibly via its effects on activated pulmonary macrophages.
Effect of memory on BER in molecular communication
Authors: Kabir M.H. , Kwak K.S.
Published: December 2013

In molecular communication, some molecules stay longer in the medium and impinge on later transmissions. The bit error rate (BER) of a diffusion‐based molecular communication channel which has memory is analysed. The effect of four previous symbols on the current symbol is considered. Human insulin hormone is used as the messenger molecule and the first passage time of a molecule has been defined as the delay. Channel memory has been found to have a profound influence on the BER.
Automated on‐ramp merging control algorithm based on Internet‐connected vehicles
Authors: Wang Yunpeng , E Wenjuan , Tang Wenzhong , Tian Daxin , Lu Guangquan , Yu Guizhen
Published: December 2013

With the rapid development of Information and Communication Technologies, vehicular networks that communicate with each other will have an innovative application in traffic safety and congestion. This study describes a preliminary study on an automated on‐ramp merging control algorithm for vehicles on freeways under condition of Internet‐connected vehicles. On the basis of vehicular operation characteristics during the merging process analysis, a cooperative driving algorithm based on Internet of vehicles was designed to achieve ramp merging without collision. Then two on‐ramp merging cases, including one vehicle and two vehicles merging into the platoon on main lane, were discussed in detail. Simulation works were carried out and the results proved that the on‐ramp merging algorithm was effective, but the vehicle following the leading vehicle on ramp lane is disturbed seriously by the leading vehicle. At the same time, the simulation results also showed the scenario that merging a platoon into the two vehicles on main lane affects the traffic flow more seriously than letting each individual vehicle on ramp lane consecutively to merge in between the two vehicles in the main lane under the same initial condition.
Implementing a new power aware routing algorithm based on existing dynamic source routing protocol for mobile ad hoc networks
Authors: Shivashankar  , Varaprasad Golla , Hosahalli Narayanagowda Suresh
Published: December 2013

Energy consumption is a crucial design concern in mobile ad hoc networks (MANETs), since nodes are powered by batteries with limited energy, whereas in existing dynamic source routing (DSR) does not take the energy limitation of MANET nodes into account. In this study, the authors propose an efficient algorithm for MANETs, which maximises the network lifetime by minimising the power consumption while establishing path with the help of modified DSR. The proposed work minimises the energy consumption per packet and maximises the network lifetime. The design objective of modifying DSR is to select energy‐efficient paths. The main features of modified DSR are: (i) minimise energy consumed per packet (ii) maximise network lifetime for network and (iii) minimise maximum node cost. However, some intermediate nodes might act selfish and drop the packets for other nodes in order to save their own battery power. The proposed algorithm can find selfish nodes and deal with them by using a modified DSR protocol, which we call as an efficient DSR (EDSR). The simulation results show an increase in the packet delivery ratio in the network. The average node lifetime of proposed EDSR model is 45–60% longer than that of DSR model.
Cancellation of the ion deflection due to electron-suppression magnetic field in a negative-ion accelerator
Authors: Chitarin G. , Agostinetti P. , Aprile D. , Marconato N. , Veltri P.
Published: December 2013

A new magnetic configuration is proposed for the suppression of co-extracted electrons in a negative-ion accelerator. This configuration is produced by an arrangement of permanent magnets embedded in one accelerator grid and creates an asymmetric local magnetic field on the upstream and downstream sides of this grid. Thanks to the “concentration” of the magnetic field on the upstream side of the grid, the resulting deflection of the ions due to magnetic field can be “intrinsically” cancelled by calibrating the configuration of permanent magnets. At the same time, the suppression of co-extracted electrons can be improved.
Controlling precise magnetic field configuration around electron cyclotron resonance zone for enhancing plasma parameters and beam current
Authors: Yano Keisuke , Kurisu Yosuke , Nozaki Dai , Kimura Daiju , Imai Youta , Kumakura Sho , Sato Fuminobu , Kato Yushi , Iida Toshiyuki
Published: December 2013

Multi-charged ion source which has wide operating conditions is required in various application fields. We have constructed tandem type ECR ion source (ECRIS); one of the features of its main stage is an additional coil for controlling magnetic field distribution around the mirror bottom precisely. Here the effect of magnetic field variation caused by the additional coil is experimentally considered in terms of plasma parameters and beam current as the first investigation of the main stage plasma. Furthermore, behavior of magnetic lines of force flowing from the ECR zone is calculated, and is compared with measurement results aiming for better understanding of interrelationship between plasma production and ion beam generation on the ECRIS.
Ultrasonic wave-based structural health monitoring embedded instrument
Authors: Aranguren G. , Monje P. M. , Cokonaj Valerijan , Barrera Eduardo , Ruiz Mariano
Published: December 2013

Piezoelectric sensors and actuators are the bridge between electronic and mechanical systems in structures. This type of sensor is a key element in the integrity monitoring of aeronautic structures, bridges, pressure vessels, wind turbine blades, and gas pipelines. In this paper, an all-in-one system for Structural Health Monitoring (SHM) based on ultrasonic waves is presented, called Phased Array Monitoring for Enhanced Life Assessment. This integrated instrument is able to generate excitation signals that are sent through piezoelectric actuators, acquire the received signals in the piezoelectric sensors, and carry out signal processing to check the health of structures. To accomplish this task, the instrument uses a piezoelectric phased-array transducer that performs the actuation and sensing of the signals. The flexibility and strength of the instrument allow the user to develop and implement a substantial part of the SHM technique using Lamb waves. The entire system is controlled using configuration software and has been validated through functional, electrical loading, mechanical loading, and thermal loading resistance tests.
Polarization switching in GaN nanowire lasers
Authors: Hurtado A. , Xu H. , Wright J. B. , Liu Sheng , Li Q. , Wang G. T. , Luk T. S. , Figiel J. J. , Cross K. , Balakrishnan G. , Lester L. F. , Brener I.
Published: December 2013

The polarization properties of a GaN nanowire laser are studied experimentally by direct analysis of the nanowire's end-facet emission. Linear and elliptical light polarizations are measured at different pumping strengths. Switching between these two polarization states is also observed as the optical excitation is increased. We attribute this polarization switching to a change in the transverse modes due to their different cavity losses.
Backhopping effect in magnetic tunnel junctions: Comparison between theory and experiment
Authors: Skowroński Witold , Ogrodnik Piotr , Wrona Jerzy , Stobiecki Tomasz , Świrkowicz Renata , Barnaś Józef , Reiss Günter , van Dijken Sebastiaan
Published: December 2013

We report on magnetic switching and backhopping effects due to spin-transfer-torque in magnetic tunnel junctions. Experimental data on current-induced switching in junctions with a MgO tunnel barrier reveal random back-and-forth switching between magnetization states, which appears when the current direction favors the parallel magnetic configuration. The effect depends on the barrier thickness tb and is not observed in tunnel junctions with very thin MgO tunnel barriers, tb < 0.95 nm. The switching dependence on bias voltage and barrier thickness is explained in terms of the macrospin model, with the magnetization dynamics described by the modified Landau-Lifshitz-Gilbert equation. Numerical simulations indicate that the competition between in-plane and out-of-plane torque components can result in a non-deterministic switching behavior at high bias voltages, in agreement with experimental observations. When the barrier thickness is reduced, the overall coupling between the magnetic layers across the barrier becomes ferromagnetic, which suppresses the backhopping effect.
Multiphysics simulation of corona discharge induced ionic wind
Authors: Cagnoni Davide , Agostini Francesco , Christen Thomas , Parolini Nicola , Stevanović Ivica , de Falco Carlo
Published: December 2013

Ionic wind devices or electrostatic fluid accelerators are becoming of increasing interest as tools for thermal management, in particular for semiconductor devices. In this work, we present a numerical model for predicting the performance of such devices; its main benefit is the ability to accurately predict the amount of charge injected from the corona electrode. Our multiphysics numerical model consists of a highly nonlinear, strongly coupled set of partial differential equations including the Navier-Stokes equations for fluid flow, Poisson's equation for electrostatic potential, charge continuity, and heat transfer equations. To solve this system we employ a staggered solution algorithm that generalizes Gummel's algorithm for charge transport in semiconductors. Predictions of our simulations are verified and validated by comparison with experimental measurements of integral physical quantities, which are shown to closely match.
The intrapair electron correlation in natural orbital functional theory
Authors: Piris M. , Matxain J. M. , Lopez X.
Published: December 2013

A previously proposed [M. Piris, X. Lopez, F. Ruipérez, J. M. Matxain, and J. M. Ugalde, J. Chem. Phys. 134, 164102 (2011)] formulation of the two-particle cumulant, based on an orbital-pairing scheme, is extended here for including more than two natural orbitals. This new approximation is used to reconstruct the two-particle reduced density matrix (2-RDM) constrained to the D, Q, and G positivity necessary conditions of the N-representable 2-RDM. In this way, we have derived an extended version of the Piris natural orbital functional 5 (PNOF5e). An antisymmetrized product of strongly orthogonal geminals with the expansion coefficients explicitly expressed by the occupation numbers is also used to generate the PNOF5e. The theory is applied to the homolytic dissociation of selected diatomic molecules: H2, LiH, and Li2. The Bader's theory of atoms in molecules is used to analyze the electron density and the presence of non-nuclear maxima in the case of a set of light atomic clusters: Li2, \documentclass[12pt]{minimal}\begin{document}${\rm Li}_{3}^{+}$\end{document} Li 3+, \documentclass[12pt]{minimal}\begin{document}${\rm Li}_{4}^{2+}$\end{document} Li 42+, and \documentclass[12pt]{minimal}\begin{document}${\rm H}_{3}^{+}$\end{document}H3+. The improvement of PNOF5e over PNOF5 was observed by visualizing the electron densities.
A multi-point laser Doppler vibrometer with fiber-based configuration
Authors: Yang C. , Guo M. , Liu H. , Yan K. , Xu Y. J. , Miao H. , Fu Y.
Published: December 2013

Laser Doppler vibrometer (LDV) is a non-contact optical interferometric system to measure vibrations of structures and machines with a high precision. Normal LDV can only offer a single-point measurement. Scanning LDV is usually impractical to do measurement on transient events. In this paper, a fiber-based self-synchronized multi-point LDV is proposed. The multiple laser beams with different frequency shifts are generated from one laser source. The beams are projected onto a vibrating object, reflected and interfered with a common reference beam. The signal including vibration information of multiple spatial points is captured by one single-pixel photodetector. The optical system is mainly integrated by fiber components for flexibility in measurement. Two experiments are conducted to measure a steady-state simple harmonic vibration of a cantilever beam and a transient vibration of a beam clamped at both ends. In the first measurement, a numerical interpolation is applied to reconstruct the mode shape with increased number of data points. The vibration mode obtained is compared with that from FEM simulation. In transient vibration measurement, the first five resonant frequencies are obtained. The results show the new-reported fiber-based multipoint LDV can offer a vibration measurement on various spatial points simultaneously. With the flexibility of fiber configuration, it becomes more practical for dynamic structural evaluation in industrial areas.
Development of a scanning head for laser Doppler vibrometry (LDV) using dual optical wedges
Authors: Rothberg S. J. , Tirabassi M.
Published: December 2013

A new laser Doppler vibrometry scanning head is proposed based on a pair of rotating optical wedges. A comprehensive mathematical model is developed and used to demonstrate how the wedges can be configured to scan point-by-point, in a line, in a circle, and in a combination of the two such that a straight line scan could be performed on a structure during rotation. Inevitable misalignments are incorporated into the model and considered quantitatively for the circular tracking application. Certain advantages are apparent over systems based on dual mirrors and a Dove prism in terms of lower apparent velocities at low rotation orders. A scanning head design for the circular tracking application is presented, together with experimental data showing good agreement between predicted and measured apparent velocities caused by misalignments.
Multipoint vibrometry with dynamic and static holograms
Authors: Haist T. , Lingel C. , Osten W. , Winter M. , Giesen M. , Ritter F. , Sandfort K. , Rembe C. , Bendel K.
Published: December 2013

We report on two multipoint vibrometers with user-adjustable position of the measurement spots. Both systems are using holograms for beam deflection. The measurement is based on heterodyne interferometry with a frequency difference of 5 MHz between reference and object beam. One of the systems uses programmable positioning of the spots in the object volume but is limited concerning the light efficiency. The other system is based on static holograms in combination with mechanical adjustment of the measurement spots and does not have such a general efficiency restriction. Design considerations are given and we show measurement results for both systems. In addition, we analyze the sensitivity of the systems which is a major limitation compared to single point scanning systems.
Collisionless microinstabilities in stellarators. II. Numerical simulations
Authors: Proll J. H. E. , Xanthopoulos P. , Helander P.
Published: December 2013

Microinstabilities exhibit a rich variety of behavior in stellarators due to the many degrees of freedom in the magnetic geometry. It has recently been found that certain stellarators (quasi-isodynamic ones with maximum-J geometry) are partly resilient to trapped-particle instabilities, because fast-bouncing particles tend to extract energy from these modes near marginal stability. In reality, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here, the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with the National Compact Stellarator Experiment and the DIII-D tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, ion-temperature-gradient modes, trapped-electron modes, and mixed-type instabilities are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all simulations that include kinetic electrons, and the latter are indeed found to be stabilizing in the energy budget. These results suggest that imperfectly optimized stellarators can retain most of the stabilizing properties predicted for perfect maximum-J configurations.
Terahertz and direct current losses and the origin of non-Drude terahertz conductivity in the crystalline states of phase change materials
Authors: Shimakawa Koichi , Wagner Tomas , Frumar Miloslav , Kadlec Filip , Kadlec Christelle , Kasap Safa
Published: December 2013

THz and DC losses in crystalline states of GeSbTe and AgInSbTe phase-change material systems are re-examined and discussed. Although a simple free carrier transport has been assumed so far in the GeSbTe (GST) system, it is shown through recent experimental results that a series sequence of intragrain and intergrain (tunneling) transport, as recently formulated in Shimakawa et al., “The origin of non-Drude terahertz conductivity in nanomaterials,” Appl. Phys. Lett. 100, 132102 (2012) may dominate the electronic transport in the commercially utilized GST system, producing a non-Drude THz conductivity. The extracted physical parameters such as the free-carrier density and mobility are significantly different from those obtained from the Drude law. These physical parameters are consistent with those obtained from the DC loss data, and provide further support for the model. Negative temperature coefficient of resistivity is found even in the metallic state, similar to amorphous metals, when the mean free path is short. It is shown that the concept of minimum metallic conductivity, often used in the metal-insulator transition, cannot be applied to electronic transport in these materials.
Room temperature multiferroic properties of Pb(Fe0.5Nb0.5)O3–Co0.65Zn0.35Fe2O4 composites
Authors: Pradhan Dhiren K. , Puli Venkata S. , Narayan Tripathy Satya , Pradhan Dillip K. , Scott J. F. , Katiyar Ram S.
Published: December 2013

We report the crystal structure, magnetic, ferroelectric, dielectric, and magneto-dielectric properties of [Pb(Fe0.5Nb0.5)O3](1−x)[Co0.65Zn0.35Fe2O4]x: (x = 0.1, 0.2, 0.3, and 0.4) composites. Rietveld refinement results of X-ray diffraction patterns confirm the formation of these composites for all x values. All the composites show well-saturated ferroelectric and ferromagnetic hysteresis (multiferroic-composite behavior) at room temperature. With increase in Co0.65Zn0.35Fe2O4 (CZFO) content an increase in saturation magnetization, and decrease in saturation polarization, remanent polarization, and dielectric constant are observed. The ferroelectric phase transition temperature increases with increase in CZFO content. All of the compositions undergo second-order ferroelectric phase transitions, which can be explained by Landau-Devonshire theory. The recoverable energy density (∼0.20 to 0.04 J/cm3) and charge-curve energy density (∼0.84 to 0.11 J/cm3) decrease with increase in the CZFO content. The room-temperature magneto-dielectric measurements provide direct evidence of magneto-electric coupling via strain at room temperature.
Determination of transient atomic structure of laser-excited materials from time-resolved diffraction data
Authors: Giret Yvelin , Naruse Nobuyasu , Daraszewicz Szymon L. , Murooka Yoshie , Yang Jinfeng , Duffy Dorothy M. , Shluger Alexander L. , Tanimura Katsumi
Published: December 2013

The time evolution of the Bragg peaks of photo-excited gold nanofilms is measured using transmission ultrafast electron diffraction (UED) with 3.0 MeV electron pulses and the corresponding structure evolution is calculated using two-temperature molecular dynamics (2T-MD). The good agreement obtained between the measured and calculated Bragg peaks, over the full experimental timescale, enables the lattice temperature effects and the structural changes to be disentangled for the first time. The agreement demonstrates that 2T-MD is a reliable method for solving the inverse problem of structure determination of laser irradiated metals in UED measurements.
Optical microcavities and enhanced electroluminescence from electroformed Al-Al2O3-Ag diodes
Authors: Hickmott T. W.
Published: December 2013

Electroluminescence (EL) and electron emission into vacuum (EM) occur when a non-destructive dielectric breakdown of Al-Al2O3-Ag diodes, electroforming, results in the development of a filamentary region in which current-voltage (I-V) characteristics exhibit voltage-controlled negative resistance. The temperature dependence of I-V curves, EM, and, particularly, EL of Al-Al2O3-Ag diodes with anodic Al2O3 thicknesses between 12 nm and 30 nm, has been studied. Two filters, a long-pass (LP) filter with transmission of photons with energies less than 3.0 eV and a short-pass (SP) filter with photon transmission between 3.0 and 4.0 eV, have been used to characterize EL. The voltage threshold for EL with the LP filter, VLP, is ∼1.5 V. VLP is nearly independent of Al2O3 thickness and of temperature and is 0.3–0.6 V less than the threshold voltage for EL for the SP filter, VSP. EL intensity is primarily between 1.8 and 3.0 eV when the bias voltage, VS ≲ 7 V. EL in the thinnest diodes is enhanced compared to EL in thicker diodes. For increasing VS, for diodes with the smallest Al2O3 thicknesses, there is a maximum EL intensity, LMX, at a voltage, VLMX, followed by a decrease to a plateau. LMX and EL intensity at 4.0 V in the plateau region depend exponentially on Al2O3 thickness. The ratio of LMX at 295 K for a diode with 12 nm of Al2O3 to LMX for a diode with 25 nm of Al2O3 is ∼140. The ratio of EL intensity with the LP filter to EL intensity with the SP filter, LP/SP, varies between ∼3 and ∼35; it depends on Al2O3 thickness and VS. Enhanced EL is attributed to the increase of the spontaneous emission rate of a dipole in a non-resonant optical microcavity. EL photons interact with the Ag and Al films to create surface plasmon polaritons (SPPs) at the metal-Al2O3 interfaces. SPPs generate large electromagnetic fields in the filamentary region of the electroformed Al-Al2O3-Ag diode, which then acts as an optical microcavity. A model is proposed for electronic processes in electroformed Al-Al2O3-Ag diodes.
Excimer emission from pulsed microhollow cathode discharges in xenon
Authors: Lee B.-J. , Rahaman H. , Nam S. H. , Iberler M. , Jacoby J. , Frank K.
Published: December 2013

Direct current (dc) microhollow cathode discharge (MHCD) is an intense source for excimer radiation in vacuum ultraviolet at a wavelength of 172 nm in a high pressure xenon (Xe) gas. The concentration of precursors for the excimer formation, i.e., excited and ionized gas atoms, increases significantly by applying high voltage pulse onto the dc MHCD over the pulse duration range from 20 to 100 ns. The intensity of the excimer emission for the voltage pulse of 20 ns duration exceeds that of the emission intensity obtained from the same MHCD operated only in the dc mode, by one order of magnitude. In addition, the emission intensity increases by one order of magnitude over the pulse duration range from 20 to 100 ns. It can be assumed that the emission intensity of the MHCD source increases as long as the duration of the high voltage pulse is shorter than the electron relaxation time. For the high voltage pulse of 100 ns duration, the emission intensity has been found to be further enhanced by a factor of three when the gas pressure is increased from 200 to 800 mbar.
The Cr-substitution concentration dependence of the structural, electric and magnetic behaviors for Aurivillius Bi5Ti3FeO15 multiferroic ceramics
Authors: Liu Jia , Bai Wei , Yang Jing , Xu Wenfei , Zhang Yuanyuan , Lin Tie , Meng Xiangjian , Duan Chun-Gang , Tang Xiaodong , Chu Junhao
Published: December 2013

Aurivillius Bi5Ti3FeO15 (BTFO) multiferroic ceramics with different Cr-doped concentrations have been synthesized by the conventional solid state reaction method. The influences of Cr-doping concentrations on the structural, magnetic, dielectric, and ferroelectric properties of BTFO ceramics are investigated in detail. All these sintered Cr-substituted BTFO ceramics are determined to be layered perovskite Aurivillius structure by X-ray diffraction, as well as the lattice parameters a, b, and c are in good accordance with Vegard's law along with the Cr-doping concentration. The lattice distortion a/b for Aurivillius family decreases with increasing Cr-doping concentration. Moreover, Cr-doping can promote greatly the grain growth of BTFO samples confirmed from field emission scanning electron microscopy characterization. However, no obvious signs of the improvement in ferroelectric properties are found in Cr-doped BTFO ceramics, and abnormal ferroelectric polarization versus electric field (P-E) loops are observed as Cr-doping content is beyond 0.1. Similar ε (tanδ) versus frequency plots to those of the BTFO sample are exhibited when Cr-doping concentration is less than 0.1. Nevertheless, obvious dielectric dispersion phenomena are shown as the Cr-doping concentration is beyond 0.1, and this dispersion behavior becomes strong with further increasing Cr-doping concentration, which are clearly indicated by the appearance of dielectric loss relaxation peaks in the measurement frequency from 102 Hz to 106 Hz. In addition, the corresponding frequency to relaxation peak shifts towards high frequencies with the Cr-doping concentration. Finally, the same magnetic orderings for all these Cr-doped BTFO ceramics as those of the BTFO one, i.e., superparamagnetic state dominated with antiferromagnetic interaction, are unambiguously found, signifying that the predicted Fe3+-O-Cr3+ 180° ferromagnetic superexchange interaction based on the Goodenough-Kanamori (G-K) rule might not be achieved in BTFO ceramics through Cr substitution by the conventional solid state reaction.
Design of titania nanotube structures by focused laser beam direct writing
Authors: Enachi Mihai , Stevens-Kalceff Marion A. , Sarua Andrei , Ursaki Veaceslav , Tiginyanu Ion
Published: December 2013

In this work, we report on electrochemical fabrication of titania films consisting of nanotubes (NTs) and their treatment by focused laser beam. The results of sample characterization by optical and scanning electron microscopy, cathodoluminescence imaging, and Raman scattering scanning spectroscopy are compared to those inherent to specimens subjected to thermal treatment in a furnace. The obtained data demonstrate possibilities for controlling crystallographic structure of TiO2 NTs by focused laser beam direct writing. These findings open new prospects for the design and fabrication of spatial architectures based on titania nanotubes.
Analysis of laser remote fusion cutting based on a mathematical model
Authors: Matti R. S. , Ilar T. , Kaplan A. F. H.
Published: December 2013

Laser remote fusion cutting is analyzed by the aid of a semi-analytical mathematical model of the processing front. By local calculation of the energy balance between the absorbed laser beam and the heat losses, the three-dimensional vaporization front can be calculated. Based on an empirical model for the melt flow field, from a mass balance, the melt film and the melting front can be derived, however only in a simplified manner and for quasi-steady state conditions. Front waviness and multiple reflections are not modelled. The model enables to compare the similarities, differences, and limits between laser remote fusion cutting, laser remote ablation cutting, and even laser keyhole welding. In contrast to the upper part of the vaporization front, the major part only slightly varies with respect to heat flux, laser power density, absorptivity, and angle of front inclination. Statistical analysis shows that for high cutting speed, the domains of high laser power density contribute much more to the formation of the front than for low speed. The semi-analytical modelling approach offers flexibility to simplify part of the process physics while, for example, sophisticated modelling of the complex focused fibre-guided laser beam is taken into account to enable deeper analysis of the beam interaction. Mechanisms like recast layer generation, absorptivity at a wavy processing front, and melt film formation are studied too.
Surface-enhanced Raman scattering of amorphous TiO2 thin films by gold nanostructures: Revealing first layer effect with thickness variation
Authors: Degioanni S. , Jurdyc A.-M. , Bessueille F. , Coulm J. , Champagnon B. , Vouagner D.
Published: December 2013

In this paper, amorphous titanium dioxide (TiO2) thin films have been deposited on a commercially available Klarite substrate using the sol-gel process to produce surface-enhanced Raman scattering (SERS). The substrate consists of square arrays of micrometer-sized pyramidal pits in silicon with a gold coating. Several thin TiO2 layers have been deposited on the surface to study the influence of film thickness. Ultimately, we obtained information on SERS of an amorphous TiO2 layer by gold nanostructures, whose range is less than a few nanometers. Mechanisms responsible for the enhancement are the product of concomitant chemical and electromagnetic effects with an important contribution from plasmon-induced charge transfer.
Dimpling in critical current density vs. magnetic field angle in YBa2Cu3O7 films irradiated with 3-MeV gold ions
Authors: Matsui H. , Ogiso H. , Yamasaki H. , Sohma M. , Yamaguchi I. , Kumagai T. , Manabe T.
Published: December 2013

Magnetic-field-angle θ dependence of critical current density Jc was measured in YBa2Cu3O7 films irradiated with 3-MeV gold ions. Such films were recently found to show large pinning force arising from point-like irradiation defects. A dimpled line-shape of Jc(θ) and its variation with magnetic field strength were revealed that could be well described by a simple model based on flux-lattice shear and Blatter scaling. Our results strongly suggest that vortex elasticity and electron-mass anisotropy coordinately produce the characteristic Jc anisotropy, called “shoulders,” in cuprate and iron-pnictide films.
Modeling operation of electric vehicles aggregator in reserve services market by using game theory method
Authors: Khanekehdani Habibalah Kh. , Tafreshi Masoud M. , Khosravi Marzieh
Published: December 2013

Electric vehicles aggregator is in fact an intermediate between electric vehicle (EV) and operator of power grid. The EVs aggregator is responsible for the management of EVs in order to supply the owners with their orders and also for maximizing the profits of power grid in electricity market. In this study, a model was developed for the operation of EVs aggregator in the reserve services market of distribution network. In the proposed model, the reserve services market was formed after termination of the energy market. In this paper, the markets were created 24 h earlier. Pricing in the energy market and reserve services was implemented based on game theory according to the price in ISO market. Meanwhile, genetic algorithm was utilized for optimization of the proposed model.
Micromagnetic simulations of magnetic normal modes in elliptical nanomagnets with a vortex state
Authors: Lv Gang , Zhang Hong , Cao Xuecheng , Gao Feng , Liu Yaowen
Published: December 2013

Combined methods of micromagnetic simulation and Fourier analysis are employed to study the gyrotropic magnetic excitations triggered by a short in-plane Gaussian field pulse in ellipse-shaped Permalloy elements with a vortex state. We observed a series of vortex-core azimuthal magnetic normal modes. The frequency of gyrotropic mode increases with the element thickness up to 40 nm, and then a dip appears in the frequency for thickness varying from 40 to 60 nm.
Resonant behavior in heat transfer across weak molecular interfaces
Authors: Sklan Sophia R. , Alex Greaney P. , Grossman Jeffrey C.
Published: December 2013

Molecular dynamics (MD) simulations are used to study, in detail, the transfer of thermal (vibrational) energy between objects with discrete vibrational spectra to those with a semi-continuum of spectra. The transfer of energy is stochastic and strongly dependent on the instantaneous separation between the bodies. The insight from the MD simulations can be captured with a simple classical model that agrees well with quantum models. This model can be used to optimize systems for efficient frequency selective energy transfer, which can be used in designing a chemical sensor through nanomechanical resonance spectroscopy.
Terahertz generation by tilted-front laser pulses in weakly and strongly nonlinear regimes
Authors: Bodrov Sergey B. , Murzanev Aleksey A. , Sergeev Yury A. , Malkov Yury A. , Stepanov Andrey N.
Published: December 2013

Terahertz generation by femtosecond laser pulses with tilted intensity front in room-temperature and cryogenically cooled LiNbO3 crystals was investigated. The role of the interaction length and pump pulse duration was studied for weak and strong laser pump. It was shown that the optical-to-terahertz conversion efficiency is saturated as a result of the Kerr self-phase modulation of the optical pump.
Efficient light trapping in low aspect-ratio honeycomb nanobowl surface texturing for crystalline silicon solar cell applications
Authors: Gao Pingqi , Wang Hongzhe , Sun Zixu , Han Weiqiang , Li Junshuai , Ye Jichun
Published: December 2013

We report a significant reflection reduction over a broadband light spectrum in crystalline silicon via introduction of low aspect-ratio honeycomb nanobowl front surface textures. A restructuration technique is developed to shape nanopores into nanobowls, enabling excellent impedance matching and efficient mode coupling. As a result, an overall reflection down to 2% in the spectrum range of 400–1 100 nm wavelength is achieved. In comparison to nanopores-structured light-trapping configurations, the nanobowls-textures have much smaller parasitic surface area, which mitigates the surface recombination losses. The texturing technique offers a promising approach to high efficiency c-Si thin-film solar cells.
Toward stimulated interaction of surface phonon polaritons
Authors: Kong B. D. , Trew R. J. , Kim K. W.
Published: December 2013

Thermal emission spectra mediated by surface phonon polariton are examined by using a theoretical model that accounts for generation processes. Specifically, the acoustic phonon fusion mechanism is introduced to remedy theoretical deficiencies of the near thermal equilibrium treatments. The model clarifies the thermal excitation mechanism of surface phonon polaritons and the energy transfer path under non-zero energy flow. When applied to GaAs and SiC semi-infinite surfaces, the nonequilibrium model predicts that the temperature dependence of the quasi-monochromatic peak can exhibit distinctly different characteristics of either sharp increase or slow saturation depending on the materials, which is in direct contrast with the estimate made by the near-equilibrium model. The proposed theoretical tool can accurately analyze the nonequilibrium steady states, potentially paving a pathway to demonstrate stimulated interaction/emission of thermally excited surface phonon polaritons.
The effect of mode excitations on the absorption enhancement for silicon thin film solar cells
Authors: Lin Albert , Zhong Yan-Kai , Fu Ssu-Ming
Published: December 2013

Periodic gratings on solar cell back reflectors are an alternative to randomly textured surfaces to provide absorption enhancement. Theoretically, it is impossible to excite quasi-guided modes at every wavelength for a given grating geometry and the broad band enhancement can only be achieved by strong absorption peaks at several wavelengths. Therefore, the critical issue is how to maximize the short circuit current using a limited number of discrete quasi-guided modes. In this work, a common dielectric-semiconductor-dielectric-metal solar cell structure is investigated. It is found that although the number of guided mode peaks has pronounced effect on the solar cell short circuit current, the geometry resulting in the highest short circuit current does not coincide with the geometry leading to the most supported modes. It is also found that high-Q modes are always resulted from global optimization for TE incidence, while low-Q modes are resulted for TM incidence on one-dimensional gratings without a dielectric spacer. Besides, a properly designed and configured dielectric spacer can provide >40% improvement in short circuit current. It is therefore suggested for solar cells with metallic back reflectors, dielectric spacer should be included, and the texture should be formed on the dielectric spacer itself rather than on the metal. Finally, the optimization of the mode quality is proved to be critical in all cases, in addition to the number of supported modes.
Interferometric direction finding with a metamaterial detector
Authors: Venkatesh Suresh , Shrekenhamer David , Xu Wangren , Sonkusale Sameer , Padilla Willie , Schurig David
Published: December 2013

We present measurements and analysis demonstrating useful direction finding of sources in the S band (2–4 GHz) using a metamaterial detector. An augmented metamaterial absorber that supports magnitude and phase measurement of the incident electric field, within each unit cell, is described. The metamaterial is implemented in a commercial printed circuit board process with off-board back-end electronics. We also discuss on-board back-end implementation strategies. Direction finding performance is analyzed for the fabricated metamaterial detector using simulated data and the standard algorithm, MUtiple SIgnal Classification. The performance of this complete system is characterized by its angular resolution as a function of radiation density at the detector. Sources with power outputs typical of mobile communication devices can be resolved at kilometer distances with sub-degree resolution and high frame rates.
Dynamical properties of three terminal magnetic tunnel junctions: Spintronics meets spin-orbitronics
Authors: Tomasello R. , Carpentieri M. , Finocchio G.
Published: December 2013

This Letter introduces a micromagnetic model able to characterize the magnetization dynamics in three terminal magnetic tunnel junctions, where the effects of spin-transfer torque and spin-orbit torque are taken into account. Our results predict that the possibility to separate electrically those two torque sources is very promising from a technological point of view for both next generation of nanoscale spintronic oscillators and microwave detectors. A scalable synchronization scheme based on the parallel connection of those three terminal devices is also proposed.
Doping and hysteretic switching of polymer-encapsulated graphene field effect devices
Authors: Sundararajan Abhishek , Boland Mathias J. , Patrick Hunley D. , Strachan Douglas R.
Published: December 2013

The effects of encapsulating graphene with poly(methyl methacrylate) (PMMA) polymer are determined through in situ electrical transport measurements. After regenerating graphene devices in dry-nitrogen environments, PMMA is applied to their surfaces. Low-temperature annealing decreases the overall doping level, suggesting that residual solvent plays an important role in the doping. For few-layer graphene devices, we even observe stable n-doping through annealing. Application of solvent onto encapsulated devices demonstrates enhanced hysteric switching between p and n-doped states. The stability and ubiquitous use of PMMA in nanolithography make this polymer a potentially useful localized doping agent for graphene and other two-dimensional materials.
Precessional magnetization induced spin current from CoFeB into Ta
Authors: Jamali Mahdi , Klemm Angeline , Wang Jian-Ping
Published: December 2013

The spin dynamics at the interface between the CoFeB and Ta layer has been studied using spin pumping and spin wave characterizations. The spin pumping driven by the ferromagnetic resonance in the CoFeB layer injects a spin current into Ta layer which results in an electromotive force across the Ta layer due to the inverse spin Hall effect. Upon changing the polarity of the bias magnetic field, the polarity of the output voltage inverts and the output voltage increases linearly in respect to the microwave signal power which are consistent with the spin pumping characteristics. The effect of the in-plane magnetization angle on the output voltage has been studied. Furthermore, it is found that the frequency spectrum of the spin Hall voltage is modified by the annealing temperature and the full width at half maximum of the spin pumping increases by more than 40% with the increase of the annealing temperature from 200 °C to 300 °C. The spin Hall angle at the Ta-CoFeB interface is determined to be 0.014, and the damping constant of the CoFeB increases from 0.006 in pure CoFeB to 0.015 in Ta/CoFeB film.
Probing the electronic structure of graphene sheets with various thicknesses by scanning transmission X-ray microscopy
Authors: Bai Lili , Liu Jinyin , Zhao Guanqi , Gao Jing , Sun Xuhui , Zhong Jun
Published: December 2013

The electronic structure of an aggregation of graphene sheets with various thicknesses was probed by scanning transmission X-ray microscopy. A uniform oxidation of the graphene sheets in the flat area was observed regardless of the thickness, while in the folded area the result could be strongly affected by the geometry. Moreover, thick parts of the aggregation showed strong angle-dependence to the incident X-ray, while thin parts showed less angle-dependence, which might be related to the surface wrinkles and ripples. The electronic structure differences due to the geometry and thickness suggest a complicated situation in the aggregation of graphene sheets.
Sustainable Development and the Making and Unmaking of a Developing World
Authors: Perkins Richard
Published: December 2013

The idea of a group of developing countries with shared characteristics, challenges, and needs, distinct from those of developed countries, has been central to sustainable development discourse and policy for decades. However, in the years since the original Rio conference it has become increasingly apparent that it is difficult to sustain this notion of a single developing world. Within the context of unfolding diversity, a central claim of the present paper is that lumping all countries together under the expansive category of ‘developing’ risks obfuscating the complex challenges, solutions, and fragmented geopolitics of sustainable development. Instead, it is necessary to use the terms developing country, countries, or world far more selectively, mindful that they may conceal just about as much as they reveal. In the paper I proceed to consider a number of alternative national, subnational, and transnational spatial categorisations which might be deployed to better describe and/or analyse the evolving nature, effective governance, and politics of sustainable development challenges across space.