bluuebunny/crossref_metadata_2025 huggingface dataset:
A new spectrometer design for the x-ray spectroscopy of laser-produced plasmas with high (sub-ns) time resolution
Authors: Bitter M. , Hill K. W. , Efthimion P. C. , Delgado-Aparicio L. , Pablant N. , Lu Jian , Beiersdorfer P. , Chen Hui
Published: September 2014

This paper describes a new type of x-ray crystal spectrometer, which can be used in combination with gated x-ray detectors to obtain spectra from laser-produced plasmas with a high (sub-ns) time resolution. The spectrometer consists of a convex, spherically bent crystal, which images individual spectral lines as perfectly straight lines across multiple, sequentially gated, strip detectors. Since the Bragg-reflected rays are divergent, the distance between detector and crystal is arbitrary, so that this distance can be appropriately chosen to optimize the experimental arrangement with respect to the detector parameters. The spectrometer concept was verified in proof-of-principle experiments by imaging the Lβ1- and Lβ2-lines of tungsten, at 9.6735 and 9.96150 keV, from a micro-focus x-ray tube with a tungsten target onto a two-dimensional pixilated Pilatus detector, using a convex, spherically bent Si-422 crystal with a radius of curvature of 500 mm.
Thermally and photoinduced polymerization of ultrathin sexithiophene films
Authors: Sander Anke , Hammer Rene , Duncker Klaus , Förster Stefan , Widdra Wolf
Published: September 2014

The thermally-induced polymerization of α-sexithiophene (6T) molecules on Ag(001) and Au(001) gives rise to long unbranched polymer chains or branched polymer networks depending on the annealing parameters. There, the onset temperature for polymerization depends on the strength of interaction with the underlying substrate. Similar polymerization processes are also induced by ultraviolet radiation with photon energies between 3.0 and 4.2 eV. Radical formation by an electronic excitation in the 6T molecule is proposed as the driving mechanism that necessitates the interplay with the metallic substrate.
Magnetic properties of epitaxial Fe3O4 films with various crystal orientations and tunnel magnetoresistance effect at room temperature
Authors: Nagahama Taro , Matsuda Yuya , Tate Kazuya , Kawai Tomohiro , Takahashi Nozomi , Hiratani Shungo , Watanabe Yusuke , Yanase Takashi , Shimada Toshihiro
Published: September 2014

Fe3O4 is a ferrimagnetic spinel ferrite that exhibits electric conductivity at room temperature (RT). Although the material has been predicted to be a half metal according to ab-initio calculations, magnetic tunnel junctions (MTJs) with Fe3O4 electrodes have demonstrated a small tunnel magnetoresistance (TMR) effect. Not even the sign of the tunnel magnetoresistance ratio has been experimentally established. Here, we report on the magnetic properties of epitaxial Fe3O4 films with various crystal orientations. The films exhibited apparent crystal orientation dependence on hysteresis curves. In particular, Fe3O4(110) films exhibited in-plane uniaxial magnetic anisotropy. With respect to the squareness of hysteresis, Fe3O4 (111) demonstrated the largest squareness. Furthermore, we fabricated MTJs with Fe3O4(110) electrodes and obtained a TMR effect of −12% at RT. The negative TMR ratio corresponded to the negative spin polarization of Fe3O4 predicted from band calculations.
Determination of the optical properties and size dispersion of Si nanoparticles within a dielectric matrix by spectroscopic ellipsometry
Authors: Keita A.-S. , Naciri A. En , Battie Y. , Delachat F. , Carrada M. , Ferblantier G. , Slaoui A.
Published: September 2014

We report on a comparative study between dielectric functions of Si nanoparticles (Si-NPs) obtained from Bruggeman effective medium approximation (BEMA), Maxwell-Garnett (MG), and a modified Maxwell-Garnett (MMG) models. Unlike BEMA and MG, a size-distribution dependent dielectric function of Si-NPs is considered in the introduced MMG model. We show that the standard deviation σ of a size distribution can be evaluated by analyzing the imaginary part of the dielectric functions of Si-NPs extracted from BEMA and MMG. In order to demonstrate this, several samples composed of Si-NPs embedded in silicon-rich silicon nitride are investigated by spectroscopic ellipsometry over the photon energy range varying between 2 and 4 eV. Assuming a lognormal size distribution of the Si nanoparticles, it is evidenced that the parameter σ ranges between 1.15 and 1.35. The values of size dispersion deduced by this methodology are in good agreement with TEM observations.
Ab-initio calculations of electronic, transport, and structural properties of boron phosphide
Authors: Ejembi J. I. , Nwigboji I. H. , Franklin L. , Malozovsky Y. , Zhao G. L. , Bagayoko D.
Published: September 2014

We present results from ab-initio, self-consistent density functional theory calculations of electronic and related properties of zinc blende boron phosphide (zb-BP). We employed a local density approximation potential and implemented the linear combination of atomic orbitals formalism. This technique follows the Bagayoko, Zhao, and Williams method, as enhanced by the work of Ekuma and Franklin. The results include electronic energy bands, densities of states, and effective masses. The calculated band gap of 2.02 eV, for the room temperature lattice constant of a = 4.5383 Å, is in excellent agreement with the experimental value of 2.02 ± 0.05 eV. Our result for the bulk modulus, 155.7 GPa, agrees with experiment (152–155 GPa). Our predictions for the equilibrium lattice constant and the corresponding band gap, for very low temperatures, are 4.5269 Å and 2.01 eV, respectively.
Polarity of semipolar wurtzite crystals: X-ray photoelectron diffraction from GaN{101¯1} and GaN{202¯1} surfaces
Authors: Romanyuk O. , Jiříček P. , Paskova T. , Bartoš I.
Published: September 2014

Polarity of semipolar GaN(101¯1) (101¯1¯) and GaN(202¯1) (202¯1¯) surfaces was determined with X-ray photoelectron diffraction (XPD) using a standard MgKα source. The photoelectron emission from N 1s core level measured in the a-plane of the crystals shows significant differences for the two crystal orientations within the polar angle range of 80–100° from the 〈0001〉 normal. It was demonstrated that XPD polar plots recorded in the a-plane are similar for each polarity of the GaN{101¯1} and GaN{202¯1} crystals if referred to 〈0001〉 crystal axes. For polarity determinations of all important GaN{h0h¯l} semipolar surfaces, the above given polar angle range is suitable.
Damping of lower hybrid waves in large spectral gap configurations
Authors: Decker J. , Peysson Y. , Artaud J.-F. , Nilsson E. , Ekedahl A. , Goniche M. , Hillairet J. , Mazon D.
Published: September 2014

Extensive experimental data support reliable power deposition and current drive by lower-hybrid (LH) waves in conditions where a large spectral gap exists between the nominal parallel index of refraction prescribed by the antenna characteristics and phasing, and that required for significant Landau damping to take place. We argue that only a significant modification of the initial spectrum at the plasma edge could explain experimental observations. Based on this assumption, a new prescription for reliable simulations of LH current drive using ray-tracing and Fokker-Planck modelling is proposed. A remarkable agreement between experimental observations in the Tore Supra tokamak and simulations is obtained for relevant parametric scans, including electron density and LH waveguide phasing. In an effort to investigate the possible role of fluctuations, it is shown that the spectral gap can be bridged dynamically in the presence of a fluctuating LH spectrum.
A novel torsion testing technique for micro-scale specimens based on electromagnetism
Authors: Huan Yong , Dai Yujing , Shao Yaqi , Peng Guangjian , Feng Yihui , Zhang Taihua
Published: September 2014

A novel torsion apparatus for micro-scale specimens is developed based on electromagnetism, in which a coil-magnet component is used for actuating and torque measuring. When the current gets through the coil, the torque, produced by Ampere force, can be easily measured by recording the current. A laser displacement sensor is applied to measure the rotation angle. The torque is calibrated using Sartorius BP211D balance. The calibration results demonstrate there is a perfect linear relationship between the torque and the current. The torque capacity is 4.0 × 10−4 N m with noise-floor of less than 10−8 N m. The rotation angle capacity is 60° with noise-floor of less than 0.02°. Two sets of copper wire specimens, with diameter of 100 μm and 140 μm, are tested using this apparatus. Experimental results, with good resolution and repeatability, successfully demonstrate the effectiveness of the torsion testing technique for micro-scale specimens.
Evaluation of observed blast loading effects on NIF x-ray diagnostic collimators
Authors: Masters N. D. , Fisher A. , Kalantar D. , Prasad R. , Stölken J. S. , Wlodarczyk C.
Published: September 2014

We present the “debris wind” models used to estimate the impulsive load to which x-ray diagnostics and other structures are subject during National Ignition Facility experiments. These models are used as part of the engineering design process. Isotropic models, based on simulations or simplified “expanding shell” models, are augmented by debris wind multipliers to account for directional anisotropy. We present improvements to these multipliers based on measurements of the permanent deflections of diagnostic components: 4× for the polar direction and 2× within the equatorial plane—the latter relaxing the previous heuristic debris wind multiplier.
Effect of counterions on the charging mechanisms of a macromolecule in aqueous nanodrops
Authors: Sharawy Mahmoud , Consta Styliani
Published: September 2014

We report the first molecular dynamics study of the effect of counterions on the charging mechanisms of a macromolecule found in an aqueous droplet that contains excess charge. To investigate the principles of the charging mechanisms of a macromolecule in a droplet, we simulate aqueous droplets that contain a poly(ethylene glycol) (PEG) molecule, sodium, and chloride ions. We study the effect of counterions by varying the concentration of the chloride ions and the temperature of the droplets. We find that the size of the droplet from which the macromolecule is released is determined by the competition between the counterions and the macromolecule for capturing the sodium ions. In droplets with radii in the range of 4 nm and smaller, \documentclass[12pt]{minimal}\begin{document}$\rm [Na_2Cl]^+$\end{document}[ Na 2 Cl ]+ ion complexes and sodium chloride aggregates are formed. The smaller the droplet the more pronounced is the formation of the NaCl aggregates. At very high temperature, in the larger droplets the \documentclass[12pt]{minimal}\begin{document}$\rm Na^+$\end{document} Na + ions are distributed throughout the entire droplet. Therefore, the sodiated PEG is released with a higher average charge than from droplets with no counterions because it has access to a higher concentration of \documentclass[12pt]{minimal}\begin{document}$\rm Na^+$\end{document} Na + ions. At moderately high temperature, the NaCl aggregates do not affect the final charge state of the macromolecule relative to the no-counterion droplets. We also report that regardless of the concentration of the counterions, the temperature plays a critical role in determining the nature of the droplet shape fluctuations that are responsible for the charging of a macromolecule and its extrusion from a droplet. At high temperature the macromolecule is released by the formation of a Taylor cone that transports ions onto the macromolecule. Differently, at lower temperature the Taylor cones are absent or have subsided. These findings provide insight into the mechanisms that macromolecules acquire their charge in droplets produced in electrospray ionization experiments.
Construction of the noncommutative complex ball
Authors: Wang Zhituo
Published: September 2014

We describe the construction of the noncommutative complex ball whose commutative analog is the Hermitian symmetric space D = SU(m, 1)/U(m), with the method of coherent state quantization. In the commutative limit, we obtain the standard manifold. We also consider a quantum field theory model on the noncommutative manifold.
Activation energy and excess conductivity analysis of (Ag)x/CuTl-1223 nano-superconductor composites
Authors: Hussain Ghulam , Jabbar Abdul , Qasim Irfan , Mumtaz M. , Nadeem K. , Zubair M. , Abbas S. Qamar , Khurram A. A.
Published: September 2014

Silver (Ag) nanoparticles were added into (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (CuTl-1223) high Tc superconducting matrix to get (Ag)x/CuTl-1223, x = 0, 0.5, 1.0, 2.0, and 4 wt. %, nano-superconductor composites. The activation energy {U (eV)} and zero resistivity critical temperature {Tc (0)} were increased with increasing contents of Ag nanoparticles in (CuTl-1223) phase up to x = 2.0 wt. %. The increase of activation energy is most probably due to interaction of carriers with the metallic Ag nanoparticles present at grain boundaries of the host CuTl-1223 superconducting matrix. The systematic increase in Tc (0) and gradual decrease in normal state resistivity {ρ300 K (Ω cm)} may be due to improved inter-grains coupling by filling up the voids and pores with the inclusion of metallic Ag nanoparticles at the grain-boundaries. There are two possible mechanisms associated with the inclusion of Ag nanoparticles, one is the formation of non-superconducting regions causing the increase of activation energy and other (dominating) is the improved inter-grains connectivity promoting Tc (0). The microscopic parameters (i.e., zero temperature coherence length along c-axis {ξc (0)}, inter-layer coupling (J), inter-grain coupling (α), etc.) deduced from the fluctuation induced conductivity analysis reasonably explained the experimental findings.
Second shock ejecta measurements with an explosively driven two-shockwave drive
Authors: Buttler W. T. , Oró D. M. , Olson R. T. , Cherne F. J. , Hammerberg J. E. , Hixson R. S. , Monfared S. K. , Pack C. L. , Rigg P. A. , Stone J. B. , Terrones G.
Published: September 2014

We develop and apply an explosively driven two-shockwave tool in material damage experiments on Sn. The two shockwave tool allows the variation of the first shockwave amplitude over range 18.5 to 26.4 GPa, with a time interval variation between the first and second shock of 5 to 7 μs. Simulations imply that the second shock amplitude can be varied as well and we briefly describe how to achieve such a variation. Our interest is to measure ejecta masses from twice shocked metals. In our application of the two-shockwave tool, we observed second shock ejected areal masses of about 4 ± 1 mg/cm2, a value we attribute to unstable Richtmyer-Meshkov impulse phenomena. We also observed an additional mass ejection process caused by the abrupt recompression of the local spallation or cavitation of the twice shocked Sn.
Effect of recording condition on the diffraction efficiency of magnetic hologram with magnetic garnet films
Authors: Nakamura Yuichi , Takagi Hiroyuki , Lim Pang Boey , Inoue Mitsuteru
Published: September 2014

A holographic memory has been attracting attention as recording media with high recording density and high data transfer rate. We have studied the magnetic garnets as a rewritable and long life media for magnetic holography. However, since the signal intensity of reconstructed image was relatively low, the effects of recording conditions on the diffraction efficiency of magnetic hologram were investigated with experiments and the numerical simulation using COMSOL multi-physics. The diffraction efficiency tends to decrease as increasing the spatial frequency, and the use of short pulse laser with the pulse width of 50 ps was found to be effective to achieve high diffraction efficiency. This suggests that the formation of clear magnetic fringe similar to interference pattern can be obtained by the use of short pulse laser since undesirable heat diffusion during radiation does not occur. On the other hand, the diffraction efficiency increased as increasing the film thickness up to 3.1 μm but was saturated in the garnet film thicker than 3.1 μm in the case of spatial frequency of 1500 line pair/mm. The numerical simulation showed that the effective depth of magnetic fringe was limited about 1.8 μm irrespective of the garnet film thickness because the fringes were connected by thermal diffusion near the surface of the film, and the effective depth is limited due to this connection of the magnetic fringe. Avoiding this fringe connection, much higher diffraction efficiency will be achieved.
Band structures of bilayer radial phononic crystal plate with crystal gliding
Authors: Ma Ting , Chen Tianning , Wang Xiaopeng , Li Yinggang , Wang Peng
Published: September 2014

Lamb wave propagation in bilayer radial phononic crystal plate with crystal gliding is investigated. Axial symmetric model in cylindrical coordinate is applied to the bilayer radial phononic crystal plate for band structure calculation and transmission spectra. Gliding in radial direction and direction vertical to plate thickness is analyzed to modulate band gaps. Physical mechanism of gliding effects on radial phononic crystal plate is also studied with displacement fields of super cells. Numerical results show that crystal gliding both in radial direction and direction vertical to plate thickness can significantly tune omnidirectional band gaps. New lower band gaps occur and attenuation areas in transmission spectra are in good agreement with gaps of band structure calculation. Band structure evolution together with eigenmodes indicate that gliding effect converts lamb wave modes resulting in separations or interactions of adjacent bands to open new gaps or close the original ones. In addition, band gaps' sensitivity to crystal gliding is also investigated. Higher gaps are more sensitive to crystal gliding in thickness direction, and lowest gap extends in the map. Crystal gliding in radial direction can open new lowest order gap and open or close another two higher gaps, while the fourth gap is insensitive to it. The omnidirectional band gaps properties have potential application in acoustic device with isotropic gap characters.
Identification and design of novel polymer-based mechanical transducers: A nano-structural model for thin film indentation
Authors: Villanueva Joshua , Huang Qian , Sirbuly Donald J.
Published: September 2014

Mechanical characterization is important for understanding small-scale systems and developing devices, particularly at the interface of biology, medicine, and nanotechnology. Yet, monitoring sub-surface forces is challenging with current technologies like atomic force microscopes (AFMs) or optical tweezers due to their probe sizes and sophisticated feedback mechanisms. An alternative transducer design relying on the indentation mechanics of a compressible thin polymer would be an ideal system for more compact and versatile probes, facilitating measurements in situ or in vivo. However, application-specific tuning of a polymer's mechanical properties can be burdensome via experimental optimization. Therefore, efficient transducer design requires a fundamental understanding of how synthetic parameters such as the molecular weight and grafting density influence the bulk material properties that determine the force response. In this work, we apply molecular-level polymer scaling laws to a first order elastic foundation model, relating the conformational state of individual polymer chains to the macroscopic compression of thin film systems. A parameter sweep analysis was conducted to observe predicted model trends under various system conditions and to understand how nano-structural elements influence the material stiffness. We validate the model by comparing predicted force profiles to experimental AFM curves for a real polymer system and show that it has reasonable predictive power for initial estimates of the force response, displaying excellent agreement with experimental force curves. We also present an analysis of the force sensitivity of an example transducer system to demonstrate identification of synthetic protocols based on desired mechanical properties. These results highlight the usefulness of this simple model as an aid for the design of a new class of compact and tunable nanomechanical force transducers.
Effect of physical aging on Johari-Goldstein relaxation in La-based bulk metallic glass
Authors: Qiao Jichao , Casalini Riccardo , Pelletier Jean-Marc
Published: September 2014

The influence of physical aging on the β relaxation in La60Ni15Al25 bulk metallic glass has been investigated by mechanical spectroscopy. The amplitude of the β relaxation (ΔG″) decreases while its relaxation time (τβ) increases during aging. We find that, as in organic glasses, the changes of ln (τβ) and ln (ΔGmax ) are linearly correlated with ln (τβ) = b − a ln $(G_{\rm max}^{\prime\prime})$(G max ″). This behavior is discussed in term of the asymmetric double-well potential (ADWP) model, with U and Δ the energies characterizing the ADWP. It is suggested that during aging the ratio U/Δ remains approximately constant, with a value close to the coefficient describing the linear correlation between ln (τβ) and ln $(G_{\rm max}^{\prime\prime})$(G max ″)(U/Δ ∼ a). Moreover, the evolution versus aging time of ΔGmax  can be described by a simple stretched exponential equation giving values of τaging consistent with tan(δ) measurements during aging. The very similar behavior of the β relaxation during aging in metallic glasses and organic material strongly suggests a common nature for this relaxation.
Quantum coherent transport in SnTe topological crystalline insulator thin films
Authors: Assaf B. A. , Katmis F. , Wei P. , Satpati B. , Zhang Z. , Bennett S. P. , Harris V. G. , Moodera J. S. , Heiman D.
Published: September 2014

Topological crystalline insulators (TCI) are unique systems where a band inversion that is protected by crystalline mirror symmetry leads to a multiplicity of topological surface states. Binary SnTe is an attractive lead-free TCI compound; the present work on high-quality thin films provides a route for increasing the mobility and reducing the carrier density of SnTe without chemical doping. Results of quantum coherent magnetotransport measurements reveal a multiplicity of Dirac surface states that are unique to TCI. Modeling of the weak antilocalization shows variations in the extracted number of carrier valleys that reflect the role of coherent intervalley scattering in coupling different Dirac states on the degenerate TCI surface.
Metrics for evaluation of the author's writing styles: Who is the best?
Authors: Darooneh Amir H. , Shariati Ashrafosadat
Published: September 2014

Studying the complexity of language has attracted the physicist's attention recently. The methods borrowed from the statistical mechanics; namely, the complex network theory, can be used for exploring the regularities as a characteristic of complexity of language. In this paper, we focus on the authorship identification by using the complex network approach. We introduce three metrics which enable us for comparison the author's writing styles. This approach was previously used by us for finding the author of unknown book among collection of thirty six books written by five Persian poets. Here, we select a collection of one hundred and one books of nine English writers and quantify their writing styles according to our metrics. In our experiment, Shakespeare appears as the best author who follows a unique writing style in all of his works.
Adding flexibility to the “particles-on-a-sphere” model for large-amplitude motion: POSflex force field for protonated methane
Authors: Uhl Felix , Walewski Łukasz , Forbert Harald , Marx Dominik
Published: September 2014

The so-called “particles-on-a-sphere” (POS) model has been introduced a while ago in order to describe in simple terms large-amplitude motion of polyatomic hydrides, XHn. The POS model of protonated methane, \documentclass[12pt]{minimal}\begin{document}${\rm CH}_5^+$\end{document} CH 5+, has been shown to capture well the essence of the fluxional nature of this enigmatic floppy molecule. Here, we extend this model to the POSflex force field by adding flexibility to the C–H bonds, which are constrained to a common fixed bond length in the original model. This makes the present model extremely efficient for computer simulation, including path integral molecular dynamics in order to assess the crucial quantum effects on nuclear motion at low temperatures. Moreover, the POSflex force field can be conveniently used to study microsolvation effects upon combining it with intermolecular pair potentials to account for solute-solvent interactions. Upon computing static properties as well as thermal and quantum fluctuation effects at ambient and low temperatures, respectively, it is shown that the POSflex model is very well suited to describe the structural properties of bare \documentclass[12pt]{minimal}\begin{document}${\rm CH}_5^+$\end{document} CH 5+, including hydrogen scrambling and thus fluxionality in the first place. The far- to mid-infrared spectrum up to the bending band is roughly described, whereas the model fails to account for the well-structured stretching band by construction.
Generation of the sedimentation potential by rapid deceleration of a fluid jet
Authors: Park Han Jung , Tang Ziyao , Diebold Gerald J.
Published: September 2014

The sedimentation potential refers to the generation of a voltage in an ionic or colloidal solution as a result of motion of the ions or colloidal particles relative to the surrounding fluid. In the case of colloidal suspensions, where the density of the colloidal particles differs from that of the fluid, the effect of a body force on the suspension, generated typically either in a centrifuge or the earth's gravitational field, is to give different motion to the charged particles and the fluid, producing a distortion of the normally spherical counter charge distribution around the colloidal particles. As a result of the opposing charges attached to the particles and in the double layer in the surrounding fluid, dipoles are generated at the sites of the particles, which add to give a macroscopic voltage in the fluid. Experiments reported here show that the sedimentation potential can be generated by the rapid deceleration of a jet of colloid at a rigid surface where, again, the differential acceleration of the particles and fluid gives rise to a voltage. The voltages between a conducting surface and a metallic tube used to form the jet are found to have large signal-to-noise ratios.
High temperature optical absorption edge of CdTe single crystal
Authors: Belas E. , Uxa Š. , Grill R. , Hlídek P. , Šedivý L. , Bugár M.
Published: September 2014

The optical absorption edge of bulk CdTe single crystal was measured by infrared transmission under saturated Cd pressure in the temperature interval 295–1223 K. The absorption coefficient was directly determined up to the value of 100 cm−1. For higher values, it was estimated by extrapolating the spectra according to the Urbach exponential rule. It was observed that the common temperature-independent intersection of extrapolated Urbach absorption edge, the “Urbach focus,” does not exist in CdTe. The temperature dependence of band-gap energy Eg defined by Eg(300 K) = 1.518 eV and dEg/dT = − 4.4 × 10−4 eV/K was established, postulating linear temperature dependence of Eg by fitting the temperature dependent absorption coefficient at the band edge αg(T) = 6600 – 4T (K) (cm−1).
Dynamic spreading on pillar-arrayed surfaces: Viscous resistance versus molecular friction
Authors: Yuan Quanzi , Huang Xianfu , Zhao Ya-Pu
Published: September 2014

The dynamic spreading of a liquid droplet on micropillar-arrayed surfaces is experimentally investigated. A theoretical model is proposed to include energy dissipations raised from both the viscous resistance at mesoscale and the molecular friction at microscale in the triple-phase region. The scaling laws and spreading shape of the droplet change with the variation of the liquid viscosity because of the competition between these two mechanisms of energy dissipations at the moving contact line. The Laplace pressures at the interior corner and at the wavy contact line are the answers to the excess driving energy and the superwetting on pillar-arrayed surfaces. The formation and evolution of the bulk and the fringe are also analyzed in detail. Our results may help to understand the wetting dynamics on microtextured surfaces and assist the future design of engineered surfaces in practical applications.
Magnetic turbulence and pressure gradient feedback effect of the 1/2 mode soft-hard magnetohydrodynamic limit in large helical device
Authors: Varela J. , Watanabe K. Y. , Ohdachi S. , Narushima Y.
Published: September 2014

The aim of this study was to analyze the feedback process between the magnetic turbulence and the pressure gradients in Large Helical Device (LHD) inward-shifted configurations as well as its role in the transition between the soft-hard magnetohydrodynamic (MHD) regimes for instabilities driven by the mode 1/2 in the middle plasma. In the present paper, we summarize the results of two simulations with different Lundquist numbers, S=2.5×105 and 106, assuming a plasma in the slow reconnection regime. The results for the high Lundquist number simulation show that the magnetic turbulence and the pressure gradient in the middle plasma region of LHD are below the critical value to drive the transition to the hard MHD regime, therefore only relaxations in the soft MHD limit are triggered (1/2 sawtooth-like events) [Phys. Plasmas 19, 082512 (2012)]. In the case of the simulation with low Lundquist number, the system reaches the hard MHD limit and a plasma collapse is observed.
Higher harmonics generation in relativistic electron beam with virtual cathode
Authors: Kurkin S. A. , Badarin A. A. , Koronovskii A. A. , Hramov A. E.
Published: September 2014

The study of the microwave generation regimes with intense higher harmonics taking place in a high-power vircator consisting of a relativistic electron beam with a virtual cathode has been made. The characteristics of these regimes, in particular, the typical spectra and their variations with the change of the system parameters (beam current, the induction of external magnetic field) as well as physical processes occurring in the system have been analyzed by means of 3D electromagnetic simulation. It has been shown that the system under study demonstrates the tendency to the sufficient growth of the amplitudes of higher harmonics in the spectrum of current oscillations in the VC region with the increase of beam current. The obtained results allow us to consider virtual cathode oscillators as promising high power mmw-to-THz sources.
Kinetic study of ion-acoustic plasma vortices
Authors: Khan S. A. , Aman-ur-Rehman  , Mendonca J. T.
Published: September 2014

The kinetic theory of electron plasma waves with finite orbital angular momentum has recently been introduced by Mendonca. This model shows possibility of new kind of plasma waves and instabilities. We have extended the theory to ion-acoustic plasma vortices carrying orbital angular momentum. The dispersion equation is derived under paraxial approximation which exhibits a kind of linear vortices and their Landau damping. The numerical solutions are obtained and compared with analytical results which are in good agreement. The physical interpretation of the ion-acoustic plasma vortices and their Landau resonance conditions are given for typical case of Maxwellian plasmas.
Carrier transfer from InAs quantum dots to ErAs metal nanoparticles
Authors: Haughn C. R. , Steenbergen E. H. , Bissell L. J. , Chen E. Y. , Eyink K. G. , Zide J. M. O. , Doty M. F.
Published: September 2014

Erbium arsenide (ErAs) is a semi-metallic material that self-assembles into nanoparticles when grown in GaAs via molecular beam epitaxy. We use steady-state and time-resolved photoluminescence to examine the mechanism of carrier transfer between indium arsenide (InAs) quantum dots and ErAs nanoparticles in a GaAs host. We probe the electronic structure of the ErAs metal nanoparticles (MNPs) and the optoelectronic properties of the nanocomposite and show that the carrier transfer rates are independent of pump intensity. This result suggests that the ErAs MNPs have a continuous density of states and effectively act as traps. The absence of a temperature dependence tells us that carrier transfer from the InAs quantum dots to ErAs MNPs is not phonon assisted. We show that the measured photoluminescence decay rates are consistent with a carrier tunneling model.
Dynamics of the fully stripped ion-hydrogen atom charge exchange process in dense quantum plasmas
Authors: Zhang Ling-yu , Zhao Xiao-ying , Wan Jiang-feng , Xiao Guo-qing , Duan Wen-shan , Qi Xin , Yang Lei
Published: September 2014

The plasma screening effects of dense quantum plasmas on charge exchange processes of a fully stripped ion colliding with a hydrogen atom are studied by the classical trajectory Monte Carlo method. The inter-particle interactions are described by the exponential cosine-screened Coulomb potentials. It is found that in weak screening conditions, cross sections increase with the increase of the ionic charge Z. However, in strong screening conditions, the dependence of cross sections on the ionic charge is related to the incident particle energy. At high energies, cross sections show a linear increase with the increase of Z, whereas at low energies, cross sections for Z≥4 become approximately the same. The He2+ and C6+ impacting charge exchange cross sections in dense quantum plasmas are also compared with those in weakly coupled plasmas. The interactions are described by the static screened Coulomb potential. It is found that for both He2+ and C6+, the oscillatory screening effects of dense quantum plasmas are almost negligible in weak screening conditions. However, in strong screening conditions, the oscillatory screening effects enhance the screening effects of dense quantum plasmas, and the enhancement becomes more and more significant with the increase of the screening parameter and the ionic charge.
Hydration shells of proteins probed by depolarized light scattering and dielectric spectroscopy: Orientational structure is significant, positional structure is not
Authors: Martin Daniel R. , Matyushov Dmitry V.
Published: September 2014

Water interfacing hydrated proteins carry properties distinct from those of the bulk and is often described as a separate entity, a “biological water.” We address here the question of which dynamical and structural properties of hydration water deserve this distinction. The study focuses on different aspects of the density and orientational fluctuations of hydration water and the ability to separate them experimentally by combining depolarized light scattering with dielectric spectroscopy. We show that the dynamics of the density fluctuations of the hydration shells reflect the coupled dynamics of the solute and solvent and do not require a special distinction as “biological water.” The orientations of shell water molecules carry dramatically different physics and do require a separation into a sub-ensemble. Depending on the property considered, the perturbation of water's orientational structure induced by the protein propagates 3–5 hydration shells into the bulk at normal temperature.
High resolution transmission electron microscopic in-situ observations of plastic deformation of compressed nanocrystalline gold
Authors: Wang Guoyong , Lian Jianshe , Jiang Qing , Sun Sheng , Zhang Tong-Yi
Published: September 2014

Nanocrystalline (nc) metals possess extremely high strength, while their capability to deform plastically has been debated for decades. Low ductility has hitherto been considered an intrinsic behavior for most nc metals, due to the lack of five independent slip systems actively operating during deformation in each nanograin. Here we report in situ high resolution transmission electron microscopic (HRTEM) observations of deformation process of nc gold under compression, showing the excellent ductility of individual and aggregate nanograins. Compression causes permanent change in the profile of individual nanograins, which is mediated by dislocation slip and grain rotation. The high rate of grain boundary sliding and large extent of widely exited grain rotation may meet the boundary compatibility requirements during plastic deformation. The in situ HRTEM observations suggest that nc gold is not intrinsically brittle under compressive loading.
Short range polar state transitions and deviation from Rayleigh-type behaviour in Bi0.5Na0.5TiO3-based perovskites
Authors: Viola Giuseppe , Tan Yongqiang , McKinnon Ruth Agnes , Wei Xiaoyong , Yan Haixue , Reece Michael John
Published: September 2014

The polarization response of 0.95[0.94(Bi0.5Na(0.45)Li0.05)TiO3-0.06BaTiO3]-0.05CaTiO3 ceramics was studied under weak applied cyclic electric fields with different amplitudes and frequency. The analysis of the polarization signals showed that in the ferroelectric phase the non-linearity is dominated by a Rayleigh-type dynamics, while in the ergodic relaxor phase the polarization response deviates from the Rayleigh-type behaviour due to the occurrence of short range electric field-induced transitions, evidenced by the presence of four distinct frequency independent current broad peaks in the current-electric field loops, which gives rise to a characteristic non-linear polarization-electric field loop with reduced hysteresis and weak frequency dependence.
Phase segregation of polymerizable lipids to construct filters for separating lipid-membrane-embedded species
Authors: Hu Shu-Kai , Chen Ya-Ming , Chao Ling
Published: September 2014

Supported lipid bilayer (SLB) platforms have been developed to transport and separate membrane-embedded species in the species' native bilayer environment. In this study, we used the phase segregation phenomenon of lipid mixtures containing a polymerizable diacetylene phospholipid, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DiynePC), and a nonpolymerizable phospholipid, 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), to create filter barrier structures in SLBs. Upon exposing the phase segregated samples to UV light, the DiynePC-rich domains could become crosslinked and remain fixed on the surface of the support, while the DOPC-rich regions, where no crosslinking could happen, could be removed later by detergent washing, and thus became the void regions in the filter. During the filter fabrication process, we used the laminar flow configuration in a microfluidic channel to control the spatial locations of the feed region and filter region in the SLB. The flow in a microfluidic channel was also used to apply a strong hydrodynamic shear stress to the SLB to transport the membrane-embedded species from the feed region to the filter region. We varied the DiynePC/DOPC molar ratio from 60/40 to 80/20 to adjust the cutoff size of the filter barriers and used two model membrane-embedded species of different sizes to examine the filtering capability. One of the model species, Texas Red 1,2-dihexa-decanoyl-sn-glycero-3-phosphoethanolamine triethylammonium salt (Texas Red DHPE), had a single-lipid size, and the other species, cholera toxin subunit B-GM1 complex, had a multilipid size. When the DiynePC/DOPC molar ratio was 60/40, both species had high penetration ratios in the filter region. However, when the ratio was increased to 70/30, only the Texas Red DHPE, which was the smaller of the two model species, could penetrate the filter to a considerable extent. When the ratio was increased to 80/20, neither of the model species could penetrate the filter region. The results showed the possibility of using phase segregation of a mixture containing a polymerizable lipid and a nonpolymerizable lipid to fabricate filter barrier structures with tunable cutoff sizes in SLBs.
Tuning exchange bias by Co doping in Mn50Ni41−xSn9Cox melt-spun ribbons
Authors: Zhao D. W. , Li G. K. , Wang S. Q. , Ma L. , Zhen C. M. , Hou D. L. , Wang W. H. , Liu E. K. , Chen J. L. , Wu G. H.
Published: September 2014

In Mn50Ni41−xSn9Cox ribbons, the exchange bias field is very sensitive to the Co content. Based on both theoretical and experimental studies, it has been found that with increasing Co content, the pinned phase (ferromagnetic phase) remains almost unchanged while the pinning phase is changed from a canonical spin glass to a cluster spin glass and finally to a ferromagnetic phase. Changing the Co content in Mn50Ni41−xSn9Cox alloys has been proven to be an effective way of tuning the magnetic anisotropy and the phase structure of the pinning phase. With different Co contents, a continuous tuning of the exchange bias field from 345 Oe to 3154 Oe is realized.
Effect of polarization fatigue on the Rayleigh coefficients of ferroelectric lead zirconate titanate thin films: Experimental evidence and implications
Authors: Lou X. J. , Zhang H. J. , Luo Z. D. , Zhang F. P. , Liu Y. , Liu Q. D. , Fang A. P. , Dkhil B. , Zhang M. , Ren X. B. , He H. L.
Published: September 2014

The effect of polarization fatigue on the Rayleigh coefficients of ferroelectric lead zirconate titanate (PZT) thin film was systematically investigated. It was found that electrical fatigue strongly affects the Rayleigh behaviour of the PZT film. Both the reversible and irreversible Rayleigh coefficients decrease with increasing the number of switching cycles. This phenomenon is attributed to the growth of an interfacial degraded layer between the electrode and the film during electrical cycling. The methodology used in this work could serve as an alternative way for evaluating the fatigue endurance and degradation in dielectric properties of ferroelectric thin-film devices during applications.
Q-switched Nd:YAG channel waveguide laser through evanescent field interaction with surface coated graphene
Authors: Tan Yang , He Ruiyun , Macdonald John , Kar Ajoy Kumar , Chen Feng
Published: September 2014

We demonstrate a compact passively Q-switched channel waveguide laser based on the interaction of the evanescent-field and the graphene coated surface. The graphene layer is transferred onto the surface of a femtosecond laser inscribed Nd:YAG surface waveguide for a simple integration of the saturable absorber and waveguide structure. The passive Q-switching configuration is based on the evanescent-field interaction with graphene. A 1064 nm pulsed waveguide laser with a maximum repetition rate of 10.4 MHz has been achieved, reaching an output power of 48 mW. The shortest pulse duration of the channel waveguide laser is 52 ns.
X ray photoelectron analysis of oxide-semiconductor interface after breakdown in Al2O3/InGaAs stacks
Authors: Shekhter P. , Palumbo F. , Cohen Weinfeld K. , Eizenberg M.
Published: September 2014

In this work, the post-breakdown characteristics of metal gate/Al2O3/InGaAs structures were studied using surface analysis by x ray photoelectron spectroscopy. The results show that for dielectric breakdown under positive bias, localized filaments consisting of oxidized substrate atoms (In, Ga and As) were formed, while following breakdown under negative bias, a decrease of oxidized substrate atoms was observed. Such differences in the microstructure at the oxide-semiconductor interface after breakdown for positive and negative voltages are explained by atomic diffusion of the contact atoms into the gate dielectric in the region of the breakdown spot by the current induced electro-migration effect. These findings show a major difference between Al2O3/InGaAs and SiO2/Si interfaces, opening the way to a better understanding of the breakdown characteristics of III-V complementary-metal-oxide-semiconductor technology.
The quantum mechanics of ion-enhanced field emission and how it influences microscale gas breakdown
Authors: Li Yingjie , Go David B.
Published: September 2014

The presence of a positive gas ion can enhance cold electron field emission by deforming the potential barrier and increasing the tunneling probability of electrons—a process known as ion-enhanced field emission. In microscale gas discharges, ion-enhanced field emission produces additional emission from the cathode and effectively reduces the voltage required to breakdown a gaseous medium at the microscale (<10 μm). In this work, we enhance classic field emission theory by determining the impact of a gaseous ion on electron tunneling and compute the effect of ion-enhanced field emission on the breakdown voltage. We reveal that the current density for ion-enhanced field emission retains the same scaling as vacuum cold field emission and that this leads to deviations from traditional breakdown theory at microscale dimensions.
Absolute calibration of a charge-coupled device camera with twin beams
Authors: Meda A. , Ruo-Berchera I. , Degiovanni I. P. , Brida G. , Rastello M. L. , Genovese M.
Published: September 2014

We report on the absolute calibration of a Charge-Coupled Device (CCD) camera by exploiting quantum correlation. This method exploits a certain number of spatial pairwise quantum correlated modes produced by spontaneous parametric-down-conversion. We develop a measurement model accounting for all the uncertainty contributions, and we reach the relative uncertainty of 0.3% in low photon flux regime. This represents a significant step forward for the characterization of (scientific) CCDs used in mesoscopic light regime.
Probing bismuth ferrite nanoparticles by hard x-ray photoemission: Anomalous occurrence of metallic bismuth
Authors: Chaturvedi Smita , Sarkar Indranil , Shirolkar Mandar M. , Jeng U-Ser , Yeh Yi-Qi , Rajendra Ranguwar , Ballav Nirmalya , Kulkarni Sulabha
Published: September 2014

We have investigated bismuth ferrite nanoparticles (∼75 nm and ∼155 nm) synthesized by a chemical method, using soft X-ray (1253.6 eV) and hard X-ray (3500, 5500, and 7500 eV) photoelectron spectroscopy. This provided an evidence for the variation of chemical state of bismuth in crystalline, phase pure nanoparticles. X-ray photoelectron spectroscopy analysis using Mg Kα (1253.6 eV) source showed that iron and bismuth were present in both Fe3+ and Bi3+ valence states as expected for bismuth ferrite. However, hard X-ray photoelectron spectroscopy analysis of the bismuth ferrite nanoparticles using variable photon energies unexpectedly showed the presence of Bi0 valence state below the surface region, indicating that bismuth ferrite nanoparticles are chemically inhomogeneous in the radial direction. Consistently, small-angle X-ray scattering reveals a core-shell structure for these radial inhomogeneous nanoparticles.
Spin-dependent terahertz oscillator based on hybrid graphene superlattices
Authors: Díaz E. , Miralles K. , Domínguez-Adame F. , Gaul C.
Published: September 2014

We theoretically study the occurrence of Bloch oscillations in biased hybrid graphene systems with spin-dependent superlattices. The spin-dependent potential is realized by a set of ferromagnetic insulator strips deposited on top of a gapped graphene nanoribbon, which induce a proximity exchange splitting of the electronic states in the graphene monolayer. We numerically solve the Dirac equation and study Bloch oscillations in the lowest conduction band of the spin-dependent superlattice. While the Bloch frequency is the same for both spins, we find the Bloch amplitude to be spin dependent. This difference results in a spin-polarized ac electric current in the THz range.