bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the interaction of microbubbles: Effects of proximity, confinement, and excitation amplitude
Authors: Wiedemair W. , Tukovic Z. , Jasak H. , Poulikakos D. , Kurtcuoglu V.
Published: June 2014

The interaction of closely spaced microbubbles (MBs) exposed to a transient external pressure field is relevant for a variety of industrial and medical applications. We present a computational framework employing an interface tracking approach to model the transient dynamics of multiple, interacting, insonated MBs in arbitrary settings. In particular, this technique allows studying the effects of mutual proximity, confinement, and variations in excitation amplitude on the translatory motion of pairs of differently sized MBs. Domains of mutual repulsion or attraction are observed for closely spaced MBs in the investigated range of excitation frequencies. The repulsion domain widens and shifts to lower frequencies with increasing excitation pressure amplitude. When the MBs are confined in rigid tubes of decreasing diameters, we observe a shift of the translatory patterns towards lower frequencies, accompanied by a change in relative strength of the two translation modes. This effect is correlated to a decrease of the resonance frequency due to confinement which causes changes in oscillation amplitude and phase shift between the bubble vibrations. Coupling to the viscous host liquid gives rise to phenomena such as collective MB drift, non-symmetric attraction or repulsion, and reversal of translation direction. A system comprising six MBs inside a narrow tube highlights the potential of the computational framework to treat complex setups with multiple bubbles.
Dirac cones in the spectrum of bond-decorated graphenes
Authors: Van den Heuvel Willem , Soncini Alessandro
Published: June 2014

We present a two-band model based on periodic Hückel theory, which is capable of predicting the existence and position of Dirac cones in the first Brillouin zone of an infinite class of two-dimensional periodic carbon networks, obtained by systematic perturbation of the graphene connectivity by bond decoration, that is by inclusion of arbitrary π-electron Hückel networks into each of the three carbon–carbon π-bonds within the graphene unit cell. The bond decoration process can fundamentally modify the graphene unit cell and honeycomb connectivity, representing a simple and general way to describe many cases of graphene chemical functionalization of experimental interest, such as graphyne, janusgraphenes, and chlorographenes. Exact mathematical conditions for the presence of Dirac cones in the spectrum of the resulting two-dimensional π-networks are formulated in terms of the spectral properties of the decorating graphs. Our method predicts the existence of Dirac cones in experimentally characterized janusgraphenes and chlorographenes, recently speculated on the basis of density functional theory calculations. For these cases, our approach provides a proof of the existence of Dirac cones, and can be carried out at the cost of a back of the envelope calculation, bypassing any diagonalization step, even within Hückel theory.
Curvature induced phase stability of an intensely heated liquid
Authors: Sasikumar Kiran , Liang Zhi , Cahill David G. , Keblinski Pawel
Published: June 2014

We use non-equilibrium molecular dynamics simulations to study the heat transfer around intensely heated solid nanoparticles immersed in a model Lennard-Jones fluid. We focus our studies on the role of the nanoparticle curvature on the liquid phase stability under steady-state heating. For small nanoparticles we observe a stable liquid phase near the nanoparticle surface, which can be at a temperature well above the boiling point. Furthermore, for particles with radius smaller than a critical radius of 2 nm we do not observe formation of vapor even above the critical temperature. Instead, we report the existence of a stable fluid region with a density much larger than that of the vapor phase. We explain the stability in terms of the Laplace pressure associated with the formation of a vapor nanocavity and the associated effect on the Gibbs free energy.
On energetic prerequisites of attracting electrons
Authors: Sundholm Dage
Published: June 2014

The internal reorganization energy and the zero-point vibrational energy (ZPE) of fractionally charged molecules embedded in molecular materials are discussed. The theory for isolated open quantum systems is taken as the starting point. It is shown that for isolated molecules the internal reorganization-energy function and its slope, i.e., the chemical potential of an open molecular system are monotonically decreasing functions with respect to increasing amount of negative excess charge (q) in the range of q = [0, 1]. Calculations of the ZPE for fractionally charged molecules show that the ZPE may have a minimum for fractional occupation. The calculations show that the internal reorganization energy and changes in the ZPE are of the same order of magnitude with different behavior as a function of the excess charge. The sum of the contributions might favor molecules with fractional occupation of the molecular units and partial delocalization of the excess electrons in solid-state materials also when considering Coulomb repulsion between the excess electrons. The fractional electrons are then coherently distributed on many molecules of the solid-state material forming a condensate of attracting electrons, which is crucial for the superconducting state.
Wideband selective polarization conversion mediated by three-dimensional metamaterials
Authors: Li Yongfeng , Zhang Jieqiu , Qu Shaobo , Wang Jiafu , Chen Hongya , Xu Zhuo , Zhang Anxue
Published: June 2014

In this paper, we proposed to use ultra-thin 3D metamaterials to manipulate the polarization of the transmitted electromagnetic waves. As an example, we designed a 3D metamaterial to serve as an ultra-thin linear-polarization converter, which overcomes the defects of bulky volume and narrow bandwidth of conventional polarization converters. Polarization selectivity and polarization convertibility are achieved simultaneously in the single-layer metamaterial. The physical mechanism is analyzed using reflection matrix and transmission matrix in details. Simulated cross-polarization and co-polarization conversions for TE and TM incident waves verify the polarization selectivity and polarization convertibility.
Influence of contact's width on the resistance measurement and resistivity anisotropy determination method for an anisotropic circular disk
Authors: Nader A. , Kouba O.
Published: June 2014

It is shown in this work that the electric resistance expression for an anisotropic circular disk diverges if a finite dimension is assumed for a current contact and if the position of this contact approaches the axis of the least resistivity. Accordingly, the optimal position of the current contacts is along the axis of the highest resistivity. This expression is mainly used to determine the resistivity anisotropy; a new contacts configuration for the resistivity anisotropy determination is suggested.
How to remove the spurious resonances from ring polymer molecular dynamics
Authors: Rossi Mariana , Ceriotti Michele , Manolopoulos David E.
Published: June 2014

Two of the most successful methods that are presently available for simulating the quantum dynamics of condensed phase systems are centroid molecular dynamics (CMD) and ring polymer molecular dynamics (RPMD). Despite their conceptual differences, practical implementations of these methods differ in just two respects: the choice of the Parrinello-Rahman mass matrix and whether or not a thermostat is applied to the internal modes of the ring polymer during the dynamics. Here, we explore a method which is halfway between the two approximations: we keep the path integral bead masses equal to the physical particle masses but attach a Langevin thermostat to the internal modes of the ring polymer during the dynamics. We justify this by showing analytically that the inclusion of an internal mode thermostat does not affect any of the established features of RPMD: thermostatted RPMD is equally valid with respect to everything that has actually been proven about the method as RPMD itself. In particular, because of the choice of bead masses, the resulting method is still optimum in the short-time limit, and the transition state approximation to its reaction rate theory remains closely related to the semiclassical instanton approximation in the deep quantum tunneling regime. In effect, there is a continuous family of methods with these properties, parameterised by the strength of the Langevin friction. Here, we explore numerically how the approximation to quantum dynamics depends on this friction, with a particular emphasis on vibrational spectroscopy. We find that a broad range of frictions approaching optimal damping give similar results, and that these results are immune to both the resonance problem of RPMD and the curvature problem of CMD.
Resolving the Dirac cone on the surface of Bi2Te3 topological insulator nanowires by field-effect measurements
Authors: Gooth Johannes , Hamdou Bacel , Dorn August , Zierold Robert , Nielsch Kornelius
Published: June 2014

We validate the linear dispersion relation (Dirac cone) on the surface of a single Bi2Te3 nanowire via a combination of field-effect and magnetoresistance measurements by which we unambiguously prove the topological insulator nature of the nanowire surface states. Moreover, we show that the experimentally determined carrier concentration, mobility, and cyclotron mass of the surface states are in excellent agreement with relativistic models. Our method provides a facile way to identify topological insulators that too small for angle-resolved photoemission spectroscopy.
Rapid redox based transformation of metallic nanoparticles on photocatalytic silicon nanostructures
Authors: Jin Hyunjong , Chang Te-Wei , Liu G. Logan
Published: June 2014

The rapid transformation and synthesis of metal nanoparticles which reaction completes within 5 min by a photocatalytic nanostructured silicon (Si) surface is studied. The Si substrate provides excess electric carriers to the surface upon optical illumination, directly inducing redox reaction. Spherical silver (Ag) nanoparticles transform into prism shape in less than 5 min with only water and room light illumination. Direct synthesis of gold (Au) nanoparticles from gold chloride (AuCl3) solution is also demonstrated. The size and distribution of the Au nanoparticles are controlled primarily by the concentration of the applied gold chloride solution. The rapid direct redox reaction capability shown from the Ag and Au nanoparticle experiments opens additional applications for the proposed photocatalytic device.
InGaN/GaN quantum wells for polariton laser diodes: Role of inhomogeneous broadening
Authors: Glauser Marlene , Mounir Christian , Rossbach Georg , Feltin Eric , Carlin Jean-François , Butté Raphaël , Grandjean Nicolas
Published: June 2014

Contrary to the case of III-nitride based visible light-emitting diodes for which the inhomogeneous linewidth broadening characteristic of InGaN-based multiple quantum well (MQW) heterostructures does not appear as a detrimental parameter, such a broadening issue can prevent a microcavity (MC) system entering into the strong light-matter coupling regime (SCR). The impact of excitonic disorder in low indium content (x ∼ 0.1) InxGa1–xN/GaN MQW active regions is therefore investigated for the subsequent realization of polariton laser diodes by considering both simulations and optical characterizations. It allows deriving the requirements for such MQWs in terms of absorption, emission linewidth, and Stokes shift. Systematic absorption-like and photoluminescence (PL) spectroscopy experiments are performed on single and multiple In0.1Ga0.9N/GaN quantum wells (QWs). Micro-PL mappings reveal a low temperature PL linewidth of ∼30 meV, compatible with SCR requirements, for single QWs for which the microscopic origin responsible for this broadening is qualitatively discussed. When stacking several InGaN/GaN QWs, a departure from such a narrow linewidth value and an increase in the Stokes shift are observed. Various possible reasons for this degradation such as inhomogeneous built-in field distribution among the QWs are then identified. An alternative solution for the MC design to achieve the SCR with the InGaN alloy is briefly discussed.
Kinetic simulation of capacitively coupled plasmas driven by trapezoidal asymmetric voltage pulses
Authors: Diomede Paola , Economou Demetre J.
Published: June 2014

A kinetic Particle-In-Cell simulation with Monte Carlo Collisions was performed of a geometrically symmetric capacitively coupled, parallel-plate discharge in argon, driven by trapezoidal asymmetric voltage pulses with a period of 200 ns. The discharge was electrically asymmetric, making the ion energy distributions at the two electrodes different from one another. The fraction of the period (α), during which the voltage was kept at a constant (top-flat) positive value, was a critical control parameter. For the parameter range investigated, as α increased, the mean ion energy on the grounded electrode increased and the ions became more directional, whereas the opposite was found for the ions striking the powered electrode. The absolute value of the DC self-bias voltage decreased as α increased. Plasma instabilities, promoted by local double layers and electric field reversals during the time of the positive voltage excursion, were characterized by electron plasma waves launched from the sheath edge.
Patterned silicon substrates: A common platform for room temperature GaN and ZnO polariton lasers
Authors: Zuniga-Perez J. , Mallet E. , Hahe R. , Rashid M. J. , Bouchoule S. , Brimont C. , Disseix P. , Duboz J. Y. , Gommé G. , Guillet T. , Jamadi O. , Lafosse X. , Leroux M. , Leymarie J. , Li Feng , Réveret F. , Semond F.
Published: June 2014

A platform for fabricating polariton lasers operating at room temperature is introduced: nitride-based distributed Bragg reflectors epitaxially grown on patterned silicon substrates. The patterning allows for an enhanced strain relaxation, thereby enabling to stack a large number of crack-free AlN/AlGaN pairs and achieve cavity quality factors of several thousands with a large spatial homogeneity. GaN and ZnO active regions are epitaxially grown thereon, and the cavities are completed with top dielectric Bragg reflectors. The two structures display strong-coupling and polariton lasing at room temperature and constitute an intermediate step in the way towards integrated polariton devices.
Phase modulation in pulsed dual-frequency capacitively coupled plasmas
Authors: Wen De-Qi , Zhang Quan-Zhi , Jiang Wei , Song Yuan-Hong , Bogaerts Annemie , Wang You-Nian
Published: June 2014

Particle-in-cell/Monte Carlo collision simulations, coupled with an external circuit, are used to investigate the behavior of pulsed dual-frequency (DF) capacitively coupled plasmas (CCPs). It is found that the phase shift θ between the high (or low) frequency source and the pulse modulation has a great influence on the ion density and the ionization rate. By pulsing the high frequency source, the time-averaged ion density shows a maximum when θ = 90∘. The time-averaged ion energy distribution functions (IEDFs) at the driven electrode, however, keep almost unchanged, illustrating the potential of pulsed DF-CCP for independent control of ion density (and flux) and ion energy. A detailed investigation of the temporal evolution of the plasma characteristics indicates that several high frequency harmonics can be excited at the initial stage of a pulse period by tuning the phase shift θ, and this gives rise to strong sheath oscillations, and therefore high ionization rates. For comparison, the pulsing of the low frequency source is also studied. In this case, the ion density changes slightly as a function of time, and the time-averaged ion density shows the same trend as in the HF modulation for different phase shifts θ. Moreover, the time-averaged IEDFs at the driven electrode can be modulated, showing the potential to reduce the maximum ion bombardment energy.
Polarization-insensitive optical gain characteristics of highly stacked InAs/GaAs quantum dots
Authors: Kita Takashi , Suwa Masaya , Kaizu Toshiyuki , Harada Yukihiro
Published: June 2014

The polarized optical gain characteristics of highly stacked InAs/GaAs quantum dots (QDs) with a thin spacer layer fabricated on an n+-GaAs (001) substrate were studied in the sub-threshold gain region. Using a 4.0-nm-thick spacer layer, we realized an electronically coupled QD superlattice structure along the stacking direction, which enabled the enhancement of the optical gain of the [001] transverse-magnetic (TM) polarization component. We systematically studied the polarized electroluminescence properties of laser devices containing 30 and 40 stacked InAs/GaAs QDs. The net modal gain was analyzed using the Hakki-Paoli method. Owing to the in-plane shape anisotropy of QDs, the polarization sensitivity of the gain depends on the waveguide direction. The gain showing polarization isotropy between the TM and transverse-electric polarization components is high for the [110] waveguide structure, which occurs for higher amounts of stacked QDs. Conversely, the isotropy of the [−110] waveguide is easily achieved even if the stacking is relatively low, although the gain is small.
Large magnetocaloric effect with a wide working temperature span in the R2CoGa3 (R = Gd, Dy, and Ho) compounds
Authors: Wang L. C. , Cui L. , Dong Q. Y. , Mo Z. J. , Xu Z. Y. , Hu F. X. , Sun J. R. , Shen B. G.
Published: June 2014

We investigate magnetic properties and magnetocaloric effects of R2CoGa3 (R = Gd, Dy, and Ho) compounds. It is found that all the compounds are ferromagnetic with the Curie temperatures of TC = 50, 17, and 10 K for R = Gd, Dy, and Ho, respectively. The R2CoGa3 have large magnetic entropy change (ΔS) that arise from the second-order ferromagnetic-to-paramagnetic phase transition. The maximum values of ΔS are found to be −12.6, −10.8, and −13.8 J/kg K with corresponding refrigerant capacity values of 382, 252, and 287 J/kg for a magnetic field change of 0–50 kOe, respectively. The large ΔS values with little or no hysteresis losses as well as wide working temperature spans imply that the R2CoGa3 compounds may serve as promising candidates for magnetic refrigeration.
Hamiltonian structures and conservation laws of the Belov-Chaltikian lattice hierarchy
Authors: Xu Songhe , Xue Bo
Published: June 2014

A hierarchy of nonlinear differential-difference equations associated with a 3 × 3 matrix spectral problem is proposed through discrete zero curvature equations. One of the nontrivial equations in this hierarchy is the famous Belov-Chaltikian lattice equation. It is shown that the hierarchy possesses infinitely many conservation laws. Hamiltonian structures for this hierarchy are constructed with the aid of the trace identity.
Note: Design and initial results of a multi-pulsed intense electron beam source
Authors: Xia L. , Zhang H. , Yang A. , Shen Y. , Wang W. , Wen L. , Zhang K. , Shi J. , Zhang L. , Deng J.
Published: June 2014

A multi-pulsed intense electron beam source is introduced, including the design and the initial experimental results. The source can generate a burst of three pulses of intense electron beams with energy of 2–3 MeV and beam intensities of around 2.5 kA. An inductive adder is chosen to generate the pulsed diode voltages and a dispenser cathode is chosen to emit electron beams. The test results indicate that the design of the source is reliable. The multi-pulsed diode voltage is up to 2.5 MV and the beam intensities are more than 2 kA at the exit of the source with small variation.
Plasma phenomenology in astrophysical systems: Radio-sources and jets
Authors: Montani Giovanni , Petitta Jacopo
Published: June 2014

We review the plasma phenomenology in the astrophysical sources which show appreciable radio emissions, namely Radio-Jets from Pulsars, Microquasars, Quasars, and Radio-Active Galaxies. A description of their basic features is presented, then we discuss in some details the links between their morphology and the mechanisms that lead to the different radio-emissions, investigating especially the role played by the plasma configurations surrounding compact objects (Neutron Stars, Black Holes). For the sake of completeness, we briefly mention observational techniques and detectors, whose structure set them apart from other astrophysical instruments. The fundamental ideas concerning angular momentum transport across plasma accretion disks—together with the disk-source-jet coupling problem—are discussed, by stressing their successes and their shortcomings. An alternative scenario is then inferred, based on a parallelism between astrophysical and laboratory plasma configurations, where small-scale structures can be found. We will focus our attention on the morphology of the radio-jets, on their coupling with the accretion disks and on the possible triggering phenomena, viewed as profiles of plasma instabilities.
Multilevel resistive switching effect in sillenite structure Bi12TiO20 thin films
Authors: Chen Ruqi , Hu Wei , Zou Lilan , Xie Wei , Li Baojun , Bao Dinghua
Published: June 2014

Multilevel resistive switching effect has been demonstrated in Pt/Bi12TiO20/Pt structures, in which the sillenite structure Bi12TiO20 thin films were prepared by a chemical solution deposition method. The non-volatile multilevel resistive switching can be easily realized by changing either the compliance current during set process or reset voltage during reset process. The Pt/Bi12TiO20/Pt devices show excellent switching parameters such as reproducible switching effect, low set/reset voltage, high cell yield, good endurance, and long retention time (up to 104 s). The dominated conduction mechanisms were Ohmic conduction in low resistance state (LRS) and lower voltage region of high resistance state (HRS), and Schottky emission in higher voltage region of HRS. In the reset process, the switching from LRS to HRS consists of two parts: an abrupt transition due to thermal effect and a gradual transition owing to electric field-induced migration of oxygen vacancies. On the basis of the measurements of the resistance-temperature dependence in different resistance states and analysis of current-voltage characteristics, we explained the resistive switching behavior using a conductive filament-related model.
Spin-resolved Fano resonances induced large spin Seebeck effects in graphene-carbon-chain junctions
Authors: Liu Yu-Shen , Zhang Xue , Feng Jin-Fu , Wang Xue-Feng
Published: June 2014

We propose a high-efficiency thermospin device constructed by a carbon atomic chain sandwiched between two ferromagnetic (FM) zigzag graphene nanoribbon electrodes. In the low-temperature regime, the magnitude of the spin figure of merit is nearly equal to that of the corresponding charge figure of merit. This is attributed to the appearances of spin-resolved Fano resonances in the linear conductance spectrum resulting from the quantum interference effects between the localized states and the expanded states. The spin-dependent Seebeck effect is obviously enhanced near these Fano resonances with the same spin index; meanwhile, the Seebeck effect of the other spin component has a smaller value due to the smooth changing of the linear conductance with the spin index. Thus, a large spin Seebeck effect is achieved, and the magnitude of the spin figure of merit can reach 1.2 at T = 25 K. Our results indicate that the FM graphene-carbon-chain junctions can be used to design the high-efficiency thermospin devices.
Deconvolution of mixed magnetism in multilayer graphene
Authors: Swain Akshaya Kumar , Bahadur Dhirendra
Published: June 2014

Magnetic properties of graphite modified at the edges by KCl and exfoliated graphite in the form of twisted multilayered graphene (<4 layers) are analyzed to understand the evolution of magnetic behavior in the absence of any magnetic impurities. The mixed magnetism in multilayer graphene is deconvoluted using Low field-high field hysteresis loops at different temperatures. In addition to temperature and the applied magnetic field, the density of edge state spins and the interaction between them decides the nature of the magnetic state. By virtue of magnetometry and electron spin resonance studies, we demonstrate that ferromagnetism is intrinsic and is due to the interactions among various paramagnetic centers. The strength of these magnetic correlations can be controlled by modifying the structure.
Channel cracks in atomic-layer and molecular-layer deposited multilayer thin film coatings
Authors: Long Rong , Dunn Martin L.
Published: June 2014

Metal oxide thin film coatings produced by atomic layer deposition have been shown to be an effective permeation barrier. The primary failure mode of such coatings under tensile loads is the propagation of channel cracks that penetrate vertically into the coating films. Recently, multi-layer structures that combine the metal oxide material with relatively soft polymeric layers produced by molecular layer deposition have been proposed to create composite thin films with desired properties, including potentially enhanced resistance to fracture. In this paper, we study the effects of layer geometry and material properties on the critical strain for channel crack propagation in the multi-layer composite films. Using finite element simulations and a thin-film fracture mechanics formalism, we show that if the fracture energy of the polymeric layer is lower than that of the metal oxide layer, the channel crack tends to penetrate through the entire composite film, and dividing the metal oxide and polymeric materials into thinner layers leads to a smaller critical strain. However, if the fracture energy of the polymeric material is high so that cracks only run through the metal oxide layers, more layers can result in a larger critical strain. For intermediate fracture energy of the polymer material, we developed a design map that identifies the optimal structure for given fracture energies and thicknesses of the metal oxide and polymeric layers. These results can facilitate the design of mechanically robust permeation barriers, an important component for the development of flexible electronics.
Time-resolved interference unveils nanoscale surface dynamics in evaporating sessile droplet
Authors: Verma Gopal , Singh Kamal P.
Published: June 2014

We report a simple optical technique to measure time-resolved nanoscale surface profile of an evaporating sessile fluid droplet. By analyzing the high contrast Newton-ring like dynamical fringes formed by interfering Fresnel reflections, we demonstrated λ/100 ≈ 5 nm sensitivity in surface height (at 0.01–160 nm/s rate) of an evaporating water drop. The remarkably high sensitivity allowed us to precisely measure its transient surface dynamics during contact-line slips, weak perturbations on the evaporation due to external magnetic field and partial confinement of the drop. Further, we measured evaporation dynamics of a sessile water drop on soft deformable surface to demonstrate wide applicability of this technique.
In situ X-ray ptychography imaging of high-temperature CO2 acceptor particle agglomerates
Authors: Høydalsvik Kristin , Bø Fløystad Jostein , Zhao Tiejun , Esmaeili Morteza , Diaz Ana , Andreasen Jens W. , Mathiesen Ragnvald H. , Rønning Magnus , Breiby Dag W.
Published: June 2014

Imaging nanoparticles under relevant reaction conditions of high temperature and gas pressure is difficult because conventional imaging techniques, like transmission electron microscopy, cannot be used. Here we demonstrate that the coherent diffractive imaging technique of X-ray ptychography can be used for in situ phase contrast imaging in structure studies at atmospheric pressure and elevated temperatures. Lithium zirconate, a candidate CO2 capture material, was studied at a pressure of one atmosphere in air and in CO2, at temperatures exceeding 600 °C. Images with a spatial resolution better than 200 nm were retrieved, and possibilities for improving the experiment are described.
Time-dependent response of hydrogels under constrained swelling
Authors: Drozdov A. D. , Sommer-Larsen P. , Christiansen J. deClaville , Sanporean C.-G.
Published: June 2014

Constitutive equations are developed for the viscoplastic behavior of covalently cross-linked hydrogels subjected to swelling. The ability of the model to describe the time-dependent response is confirmed by comparison of results of simulation with observations on partially swollen poly(2-hydroxyethyl methacrylate) gel specimens in uniaxial tensile tests with a constant strain rate and tensile relaxation tests. The stress–strain relations are applied to study the kinetics of unconstrained and constrained swelling. The following conclusions are drawn from numerical analysis: (i) maximum water uptake under constrained swelling a viscoplastic hydrogel is lower than that for unconstrained swelling of its elastic counterpart and exceeds maximum water uptake under constrained swelling of the elastic gel, (ii) when the rate of water diffusion exceeds the rate of plastic flow in a polymer network, swelling curves (mass uptake versus time) for viscoplastic gels under constraints demonstrate characteristic features of non-Fickian diffusion.
Growth of InGaAs/GaAsP multiple quantum well solar cells on mis-orientated GaAs substrates
Authors: Sodabanlu Hassanet , Wang Yunpeng , Watanabe Kentaroh , Sugiyama Masakazu , Nakano Yoshiaki
Published: June 2014

The effects of growth temperature on the properties of InGaAs/GaAsP multiple quantum well (MQW) solar cells on various mis-orientated GaAs substrates were studied using metalorganic vapor phase epitaxy. Thickness modulation effect caused by mismatch strain of InGaAs/GaAsP could be suppressed by low growth temperature. Consequently, abrupt MQWs with strong light absorption could be deposited on mis-oriented substrates. However, degradation in crystal quality and impurity incorporation are the main drawbacks with low temperature growth because they tend to strongly degraded carrier transport and collection efficiency. MQW solar cells grown at optimized temperature showed the better conversion efficiency. The further investigation should focus on improvement of crystal quality and background impurities.
Broadband acoustic manipulation by mimicking an arbitrary potential well
Authors: Zhang Zhe , Liang Bin , Li Rui-qi , Zou Xin-ye , Yin Lei-lei , Cheng Jian-Chun
Published: June 2014

We have proposed a continuous-index system to mimic an arbitrary “potential well” for realizing versatile manipulations on acoustic waves within a broadband. An analytical description of the acoustic propagation in the system is developed, and its validity is verified by using full-wave simulation. Both the theoretical and numerical results show that by tailoring the refractive-index profile, the system either bends the incident wave like a repulsive potential, or attracts and traps the wave like an attractor. Our design may have potential implication in various situations such as medical ultrasound imaging and sound absorbing.
Benzocyclobutene barrier layer for suppressing conductance in nonlinear optical devices during electric field poling
Authors: Jin Wenwei , Johnston Peter V. , Elder Delwin L. , Tillack Andreas F. , Olbricht Benjamin C. , Song Jinsheng , Reid Philip J. , Xu Ruimin , Robinson Bruce H. , Dalton Larry R.
Published: June 2014

We measured the electro-optic (EO) coefficients (r33) of thin-film devices made from several monolithic, high number density organic EO chromophores with and without additional charge barrier layers. We found that a cross-linkable benzocyclobutene layer was very effective in suppressing unwanted, leakage current, keeping the effective poling voltage nearly identical to the applied voltage. This barrier layer proved to be superior to a titanium dioxide (TiO2) barrier layer. The suppression of the leakage current in combination with a new chromophore enabled the construction of EO devices that had r33 values in the range of 400–500 pm V−1 with poling fields ≥ 85 V μm−1.
High-dimensional chaos from self-sustained collisions of solitons
Authors: Yildirim O. Ozgur , Ham Donhee
Published: June 2014

We experimentally demonstrate chaos generation based on collisions of electrical solitons on a nonlinear transmission line. The nonlinear line creates solitons, and an amplifier connected to it provides gain to these solitons for their self-excitation and self-sustenance. Critically, the amplifier also provides a mechanism to enable and intensify collisions among solitons. These collisional interactions are of intrinsically nonlinear nature, modulating the phase and amplitude of solitons, thus causing chaos. This chaos generated by the exploitation of the nonlinear wave phenomena is inherently high-dimensional, which we also demonstrate.
Thermal vibration of a rectangular single-layered graphene sheet with quantum effects
Authors: Wang Lifeng , Hu Haiyan
Published: June 2014

The thermal vibration of a rectangular single-layered graphene sheet is investigated by using a rectangular nonlocal elastic plate model with quantum effects taken into account when the law of energy equipartition is unreliable. The relation between the temperature and the Root of Mean Squared (RMS) amplitude of vibration at any point of the rectangular single-layered graphene sheet in simply supported case is derived first from the rectangular nonlocal elastic plate model with the strain gradient of the second order taken into consideration so as to characterize the effect of microstructure of the graphene sheet. Then, the RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet simply supported on an elastic foundation is derived. The study shows that the RMS amplitude of the rectangular single-layered graphene sheet predicted from the quantum theory is lower than that predicted from the law of energy equipartition. The maximal relative difference of RMS amplitude of thermal vibration appears at the sheet corners. The microstructure of the graphene sheet has a little effect on the thermal vibrations of lower modes, but exhibits an obvious effect on the thermal vibrations of higher modes. The quantum effect is more important for the thermal vibration of higher modes in the case of smaller sides and lower temperature. The relative difference of maximal RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet decreases monotonically with an increase of temperature. The absolute difference of maximal RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet increases slowly with the rising of Winkler foundation modulus.
Photo-driven giant reduction of the Frank elastic constants in a bent-core nematic liquid crystal
Authors: Madhuri P. Lakshmi , Krishna Prasad S. , Hiremath Uma S. , Yelamaggad C. V.
Published: June 2014

We report the influence of photoisomerization on the splay (K11) and bend (K33) elastic constants in a bent-core nematic doped with a small amount of a calamitic photoactive compound. Trans-cis isomerization of the latter compound results in a large decrease (factor of ∼3 for K33) of both the moduli, and K33 becoming almost independent of temperature except near the isotropic phase. The observed variations are much larger than can be explained by order parameter changes, and are explained using an argument based on the molecular arrangement.
Contrasting size-scaling behavior of ferromagnetism in La0.67Ca0.33MnO3 films and La0.67Ca0.33MnO3/CaRuO3 multilayers
Authors: Chen B. B. , Chen P. F. , Xu H. R. , Tan X. L. , Jin F. , Guo Z. , Zhi B. W. , Wu W. B.
Published: June 2014

Using La0.67Ca0.33MnO3 (LCMO) and CaRuO3 (CRO) as components, the single-layer films, bilayers, trilayers, and superlattices were fabricated on NdGaO3 (110) substrates. These epitaxial structures show quite different Curie temperature (TC) depending on the LCMO layer thickness (x), especially in the low x region. For LCMO films, TC dramatically decreases with x and disappears below 3.2 nm, as previously reported. For LCMO/CRO (CRO/LCMO) bilayers, however, a smooth decline of TC was observed, retaining a TC near 50 K at 1.6 nm. More strikingly, for the multilayers with LCMO sandwiched between CRO, TC is stabilized at ∼250 K even at x of 1.6 nm, before decreasing to 200 K at 0.8 nm. We ascribed these distinct behaviors to the LCMO/CRO interfaces, and a possible charge transfer from CRO to LCMO was suggested to play a vital role in stabilizing the ferromagnetism in ultrathin LCMO. This finding would shed some lights on the dead layer formation in ultrathin manganites and be significant in improving the performance of the related spintronic devices.
Early detection of cell activation events by means of attenuated total reflection Fourier transform infrared spectroscopy
Authors: Titus Jitto , Filfili Chadi , Hilliard Julia K. , Ward John A. , Unil Perera A. G.
Published: June 2014

Activation of Jurkat T-cells in culture following treatment with anti-CD3 (Cluster of Differentiation 3) antibody is detectable by interrogating the treated T-cells using the Attenuated Total Reflection–Fourier Transform Infrared (ATR-FTIR) Spectroscopy technique. Cell activation was detected within 75 min after the cells encountered specific immunoglobulin molecules. Spectral markers noted following ligation of the CD3 receptor with anti CD3 antibody provides proof-of-concept that ATR-FTIR spectroscopy is a sensitive measure of molecular events subsequent to cells interacting with anti-CD3 Immunoglobulin G. The resultant ligation of the CD3 receptor results in the initiation of well defined, specific signaling pathways that parallel the measurable molecular events detected using ATR-FTIR. Paired t-test with post-hoc Bonferroni corrections for multiple comparisons has resulted in the identification of statistically significant spectral markers (p < 0.02) at 1367 and 1358 cm−1. Together, these data demonstrate that early treatment-specific cellular events can be measured by ATR-FTIR and that this technique can be used to identify specific agents via the responses of the cell biosensor at different time points postexposure.
Temperature dependent spin transport properties of platinum inferred from spin Hall magnetoresistance measurements
Authors: Meyer Sibylle , Althammer Matthias , Geprägs Stephan , Opel Matthias , Gross Rudolf , Goennenwein Sebastian T. B.
Published: June 2014

We study the temperature dependence of the spin Hall magnetoresistance (SMR) in yttrium iron garnet/platinum hybrid structures via magnetization orientation dependent magnetoresistance measurements. Our experiments show a decrease of the SMR magnitude with decreasing temperature. Using the sensitivity of the SMR to the spin transport properties of the normal metal, we interpret our data in terms of a decrease of the spin Hall angle in platinum from 0.11 at room temperature to 0.075 at 10 K, while the spin diffusion length and the spin mixing conductance of the ferrimagnetic insulator/normal metal interface remain almost constant.
Auger electron nanoscale mapping and x-ray photoelectron spectroscopy combined with gas cluster ion beam sputtering to study an organic bulk heterojunction
Authors: Heon Kim Seong , Heo Sung , Ihn Soo-Ghang , Yun Sungyoung , Hwan Park Jong , Chung Yeonji , Lee Eunha , Park Gyeongsu , Yun Dong-Jin
Published: June 2014

The lateral and vertical distributions of organic p/n bulk heterojunctions for an organic solar cell device are, respectively, investigated using nanometer-scale Auger electron mapping and using X-ray photoelectron spectroscopy (XPS) with Ar gas cluster ion beam (GCIB) sputtering. The concentration of sulfur, present only in the p-type material, is traced to verify the distribution of p-type (donor) and n-type (acceptor) materials in the blended structure. In the vertical direction, a considerable change in atomic sulfur concentration is observed using XPS depth profiling with Ar GCIB sputtering. In addition, Auger electron mapping of sulfur reveals the lateral 2-dimensional distribution of p- and n-type materials. The combination of Auger electron mapping with Ar GCIB sputtering should thereby allow the construction of 3-dimensional distributions of p- and n-type materials in organic photovoltaic cells.
Modelling of photovoltaic array temperature in a tropical site using generalized extreme value distribution
Authors: Ya'acob M. Effendy , Hizam Hashim , Khatib Tamer , Radzi M. Amran M. , Gomes Chandima , Bakri A. M. , Marhaban M. Hamiruce , Elmenreich Wilfried
Published: June 2014

The standard approach of assessing the efficiency of a solar cell is strongly depending on the cell temperature (Tc). The value of Tc is calculated based on solar radiation and ambient temperature values as well as the nominal operating cell temperature (NOCT). NOCT is defined as the temperature element in a solar cell exposed at 800 W/m2 of solar radiation, 20 °C of ambient temperature, and a wind speed of 1 m/s. However, these conditions may vary depending on the climate zone nature. In this research, a new condition called tropical field operation cell temperature (tFOCT) is introduced based on the maximum daily standard climatic parameters under tropical field conditions. These parameters are calculated and justified using generalized extreme value distribution based on the transient conditions of the tropical weather as a unique approach of field value adaptation. The results show that the suitable weather conditions for measuring the tFOCT are 886 W/m2 of solar radiation, 34 °C of ambient temperature, and a wind speed of 3.2 m/s. In addition to that, it is concluded that the recommended tFOCT value is 52.5 °C. Based on these conditions, an enhanced Tc model is proposed and it is found that this model has higher accuracy than the standard model.
Chapter 2. Study abroad and formal instruction contrasted
Authors: Pérez-Vidal Carmen
Published: June 2014

This chapter presents the Study Abroad and Language Acquisition (SALA) research Project in detail, as an introduction to the empirical studies reported on in Part II of this volume, each dealing with a specific objective of the project in relation to a domain of learners’ progress achieved in Study Abroad (SA) and Formal Instruction (FI) contexts of acquisition. It begins by establishing the project’s general goal. This leads to a review of current findings in SA research, followed by a presentation of the specific objectives and the research questions of the empirical SALA studies. Then the methods, the participants, the design, the data collection instruments, the procedures and the tests used in the studies are described. Finally results are pulled together and discussed, and conclusions are reached.
Chapter 4. Oral accuracy growth after formal instruction and study abroad
Authors: Juan-Garau Maria
Published: June 2014

The present study examines the effects on oral accuracy of a three-month Study Abroad (SA) period on forty-three advanced-level L3 English learners. It analyses the gains accrued in the SA context in the light of the gains derived from the preceding and subsequent Formal Instruction (FI) environment as well as the impact of contact during SA. It also compares native and non-native performance and examines whether students with a lower or higher pre-departure level make most progress in accuracy abroad. In so doing, this chapter contributes to answering the first research question in the SALA Project. Results show an advantage for the SA context, where learners become more target-like, with long-lasting effects. Students with lower pre-departure levels benefit the most from SA. Some contact variables associated with accuracy development are identified.
Chapter 9. Comparing progress in academic writing after formal instruction and study abroad
Authors: Pérez-Vidal Carmen , Barquin Elisa
Published: June 2014

In this chapter, we consider progress in the domain of academic writing by 73 advanced-level EFL learners within the SALA Project. We compare their essays before and after a 6-month period of Formal Instruction at home (FI/AH), a 3-month period of Study Abroad (SA), and 15 months after SA. We seek to throw light onto one of the objectives in SALA, namely, to what extent writing improves with the practice and instruction received during FI/AH, in contrast with allegedly some practice done but none or little instruction received during SA. We also aim at contributing to an under-researched area in SA studies (but see Sasaki 2004, 2007, 2011). Progress in writing is measured via quantitative measures in the domains of complexity, accuracy, and fluency (CAF), building upon previous work (see Pérez-Vidal & Juan-Garau 2009, 2011, and Pérez-Vidal, Juan-Garau, & Mora 2012). After the SA, but not after the FI context, significant gains were found in the domains of fluency and complexity, but not in the domain of accuracy, and these gains were maintained 15 months after returning from abroad.
Establishing coherence in schoolbook texts
Authors: van Silfhout Gerdineke , Evers-Vermeul Jacqueline , Sanders Ted J.M.
Published: June 2014

This article focuses on the influence of connectives (because, so) and layout (continuous
placement of sentences versus each sentence beginning on a new line) on the quality of students’ mental representations. By using
multiple comprehension tasks, we found that cohesive text features have different effects on each facet of deeper text
comprehension. On local comprehension tasks (i.e. bridging inference questions), all students performed better after reading
history texts containing connectives than after reading texts without these markers. On global comprehension tasks (i.e. sorting
tasks), pre-vocational students performed better when coherence relations were marked, regardless of layout, while pre-un iversity
students did not need connectives as long as texts were presented in a natural, continuous way. These findings indicate that
connectives are an important factor in creating comprehensible texts, in particular for pre-vocational students. Finally, we
conclude there is a mismatch between these findings and the current practice in designing optimal educational texts, at least in
the Netherlands.
Does instruction about phonological correspondences contribute to the intelligibility of a related language?
Authors: Bergsma Fenna , Swarte Femke , Gooskens Charlotte
Published: June 2014

This paper investigates whether instruction about phonological correspondences between the native and a closely related language contributes to the intelligibility of this closely related language. Previous research has shown that closely related languages can be mutually intelligible to a certain degree (cf. Gooskens, 2007). Little is known about methods for improving the intelligibility of a closely related language. In this paper we focus on improving the intelligibility of spoken Frisian for Dutch speakers. In a 50-minute instruction session, participants got information about the most frequent sound correspondences between Dutch and Frisian, e.g. /sk/ in Frisian is often /sx/ in Dutch. The results of the intelligibility test show no significant improvement, neither at the text level, nor at the word level. Further research could focus on other language combinations, but also on a longer time span of intervention and other linguistic factors, such as unknown vowels.