bluuebunny/crossref_metadata_2025 huggingface dataset:
Conserved residues that modulate proteintrans-splicing ofNpuDnaE split intein
Authors: Wu Qin , Gao Zengqiang , Wei Yong , Ma Guolin , Zheng Yuchuan , Dong Yuhui , Liu Yangzhong
Published: April 2014

The first crystal trans-structure of a naturally occurring split intein has been determined for the Npu (Nostoc punctiforme PCC73102) DnaE split intein. Guided by this structure, the residues NArg50 and CSer35, well conserved in DnaE split inteins, are identified to be critical in the trans-splicing of Npu DnaE split intein. An in vitro splicing assay demonstrates that NArg50 and CSer35 play synergistic roles in modulating its intein activity. The C-terminal CAsn36 exhibits two orientations of its side chain and interacts with both NArg50 and CSer35 through hydrogen bonding. These interactions likely facilitate the cyclization of asparagine in the course of protein splicing. The mutation of either residue reduces intein activity, and correlates with the low activity of the Ssp (Cyanobacterium synechocystis sp. strain PCC6803) DnaE split intein. On the other hand, NArg50 also forms a hydrogen bond with the highly conserved F-block CAsp17, thus influencing the N–S acyl shift during N-terminal cleavage. Sequence alignments show that residues NArg50 and CSer35 are rather conserved in those split inteins that lack a penultimate histidine residue. The conserved non-catalytic residues of split inteins modulate the efficiency of protein trans-splicing by hydrogen-bond interactions with the catalytic residues at the splice junction.
A 30 mK, 13.5 T scanning tunneling microscope with two independent tips
Authors: Roychowdhury Anita , Gubrud M. A. , Dana R. , Anderson J. R. , Lobb C. J. , Wellstood F. C. , Dreyer M.
Published: April 2014

We describe the design, construction, and performance of an ultra-low temperature, high-field scanning tunneling microscope (STM) with two independent tips. The STM is mounted on a dilution refrigerator and operates at a base temperature of 30 mK with magnetic fields of up to 13.5 T. We focus on the design of the two-tip STM head, as well as the sample transfer mechanism, which allows in situ transfer from an ultra high vacuum preparation chamber while the STM is at 1.5 K. Other design details such as the vibration isolation and rf-filtered wiring are also described. Their effectiveness is demonstrated via spectral current noise characteristics and the root mean square roughness of atomic resolution images. The high-field capability is shown by the magnetic field dependence of the superconducting gap of CuxBi2Se3. Finally, we present images and spectroscopy taken with superconducting Nb tips with the refrigerator at 35 mK that indicate that the effective temperature of our tips/sample is approximately 184 mK, corresponding to an energy resolution of 16 μeV.
Generalized constructive tree weights
Authors: Rivasseau Vincent , Tanasa Adrian
Published: April 2014

The Loop Vertex Expansion (LVE) is a quantum field theory (QFT) method which explicitly computes the Borel sum of Feynman perturbation series. This LVE relies in a crucial way on symmetric tree weights which define a measure on the set of spanning trees of any connected graph. In this paper we generalize this method by defining new tree weights. They depend on the choice of a partition of a set of vertices of the graph, and when the partition is non-trivial, they are no longer symmetric under permutation of vertices. Nevertheless we prove they have the required positivity property to lead to a convergent LVE; in fact we formulate this positivity property precisely for the first time. Our generalized tree weights are inspired by the Brydges-Battle-Federbush work on cluster expansions and could be particularly suited to the computation of connected functions in QFT. Several concrete examples are explicitly given.
The SU(1, 1) Perelomov number coherent states and the non-degenerate parametric amplifier
Authors: Ojeda-Guillén D. , Mota R. D. , Granados V. D.
Published: April 2014

We construct the Perelomov number coherent states for an arbitrary su(1, 1) group operation and study some of their properties. We introduce three operators which act on Perelomov number coherent states and close the su(1, 1) Lie algebra. By using the tilting transformation we apply our results to obtain the energy spectrum and eigenfunctions of the non-degenerate parametric amplifier. We show that these eigenfunctions are the Perelomov number coherent states of the two-dimensional harmonic oscillator.
The effect of the Basset history force on particle clustering in homogeneous and isotropic turbulence
Authors: Olivieri S. , Picano F. , Sardina G. , Iudicone D. , Brandt L.
Published: April 2014

We study the effect of the Basset history force on the dynamics of small particles transported in homogeneous and isotropic turbulence and show that this term, often neglected in previous numerical studies, reduces the small-scale clustering typical of inertial particles. The contribution of this force to the total particle acceleration is, on average, responsible for about 10% of the total acceleration and particularly relevant during rare strong events. At moderate density ratios, i.e., sand or metal powder in water, its presence alters the balance of forces determining the particle acceleration.
Geometric uncertainty relation for mixed quantum states
Authors: Andersson Ole , Heydari Hoshang
Published: April 2014

In this paper we use symplectic reduction in an Uhlmann bundle to construct a principal fiber bundle over a general space of unitarily equivalent mixed quantum states. The bundle, which generalizes the Hopf bundle for pure states, gives in a canonical way rise to a Riemannian metric and a symplectic structure on the base space. With these we derive a geometric uncertainty relation for observables acting on quantum systems in mixed states. We also give a geometric proof of the classical Robertson-Schrödinger uncertainty relation, and we compare the two. They turn out not to be equivalent, because of the multiple dimensions of the gauge group for general mixed states. We give examples of observables for which the geometric relation provides a stronger estimate than that of Robertson and Schrödinger, and vice versa.
Research Update: Physical and electrical characteristics of lead halide perovskites for solar cell applications
Authors: Bretschneider Simon A. , Weickert Jonas , Dorman James A. , Schmidt-Mende Lukas
Published: April 2014

The field of thin-film photovoltaics has been recently enriched by the introduction of lead halide perovskites as absorber materials, which allow low-cost synthesis of solar cells with efficiencies exceeding 16%. The exact impact of the perovskite crystal structure and composition on the optoelectronic properties of the material are not fully understood. Our progress report highlights the knowledge gained about lead halide perovskites with a focus on physical and optoelectronic properties. We discuss the crystal and band structure of perovskite materials currently implemented in solar cells and the impact of the crystal properties on ferroelectricity, ambipolarity, and the properties of excitons.
Generalized conditional symmetries and related solutions of the Grad-Shafranov equation
Authors: Cimpoiasu Rodica
Published: April 2014

The generalized conditional symmetry (GCS) method is applied to a specific case of the Grad–Shafranov (GS) equation, in cylindrical geometry assuming the existence of an axial symmetry. We investigate the conditions that yield the GS equation admitting a special class of second-order GCSs. The determining system for the unknown arbitrary functions is solved in several special cases and new exact solutions, including solitary waves, different in form and structure from the ones obtained using other nonclassical symmetry methods, are pointed out. Several plots of the level sets or flux surfaces of the new solutions as well as surfaces with vanishing flow are displayed. The obtained solutions can be useful for studying plasma equilibrium, transport phenomena, and magnetohydrodynamic stability.
Catalytic activity of methanol in all-vapor subsecond clathrate-hydrate formation
Authors: Devlin J. Paul
Published: April 2014

Methanol's property as a catalyst in the formation of gas clathrate hydrates has been recognized for several years and was recently employed in a broad ranging study [K. Shin, K. A. Udachin, I. L. Moudrakovski, D. M. Leek, S. Alavi, C. I. Ratcliffe, and J. A. Ripmeester, Proc. Natl. Acad. Sci. U.S.A. 110, 8437 (2013)]. A new measure of that activity is offered here from comparative rates of formation of methanol (MeOH) clathrate hydrates within our all-vapor aerosol methodology for which tetrahydrofuran (THF) and other small ethers have set a standard for catalytic action. We have previously described numerous examples of the complete conversion of warm all-vapor mixtures to aerosols of gas clathrate hydrates on a sub-second time scale, generally with the catalyst confined primarily to the large cage of either structure-I (s-I) or structure-II (s-II) hydrates. THF has proven to be the most versatile catalyst for the complete subsecond conversion of water to s-II hydrate nanocrystals that follows pulsing of appropriate warm vapor mixtures into a cold chamber held in the 140–220 K range. Here, the comparative ability of MeOH to catalyze the formation of s-I hydrates in the presence of a small-cage help-gas, CO2 or acetylene, is examined. The surprising result is that, in the presence of either help gas, CH-formation rates appear largely unchanged by a complete replacement of THF by MeOH in the vapor mixtures for a chamber temperature of 170 K. However, as that temperature is increased, the dependence of effective catalysis by MeOH on the partial pressure of help gases also increases. Nevertheless, added MeOH is shown to markedly accelerate the s-II THF-CO2 CH formation rate at 220 K.
Phase stability limit of c-BN under hydrostatic and non-hydrostatic pressure conditions
Authors: Xiao Jianwei , Du Jinglian , Wen Bin , Melnik Roderick , Kawazoe Yoshiyuki , Zhang Xiangyi
Published: April 2014

Phase stability limit of cubic boron nitride (c-BN) has been investigated by the crystal structure search technique. It indicated that this limit is ∼1000 GPa at hydrostatic pressure condition. Above this pressure, c-BN turns into a metastable phase with respect to rocksalt type boron nitride (rs-BN). However, rs-BN cannot be retained at 0 GPa owing to its instability at pressure below 250 GPa. For non-hydrostatic pressure conditions, the phase stability limit of c-BN is substantially lower than that under hydrostatic pressure conditions and it is also dramatically different for other pressure mode.
Numerical study on microwave-sustained argon discharge under atmospheric pressure
Authors: Yang Y. , Hua W. , Guo S. Y.
Published: April 2014

A numerical study on microwave sustained argon discharge under atmospheric pressure is reported in this paper. The purpose of this study is to investigate both the process and effects of the conditions of microwave-excited gas discharge under atmospheric pressure, thereby aiding improvements in the design of the discharge system, setting the appropriate working time, and controlling the operating conditions. A 3D model is presented, which includes the physical processes of electromagnetic wave propagation, electron transport, heavy species transport, gas flow, and heat transfer. The results can be obtained by means of the fluid approximation. The maxima of the electron density and gas temperature are 4.96 × 1018 m−3 and 2514.8 K, respectively, and the gas pressure remains almost unchanged for typical operating conditions with a gas flow rate of 20 l/min, microwave power of 1000 W, and initial temperature of 473 K. In addition, the conditions (microwave power, gas flow rate, and initial temperature) of discharge are varied to obtain deeper information about the electron density and gas temperature. The results of our numerical study are valid and clearly describe both the physical process and effects of the conditions of microwave-excited argon discharge.
Effect of neutral gas heating on the wave magnetic fields of a low pressure 13.56 MHz planar coil inductively coupled argon discharge
Authors: Jayapalan Kanesh K. , Chin Oi-Hoong
Published: April 2014

The axial and radial magnetic field profiles in a 13.56 MHz (radio frequency) laboratory 6 turn planar coil inductively coupled plasma reactor are simulated with the consideration of the effect of neutral gas heating. Spatially resolved electron densities, electron temperatures, and neutral gas temperatures were obtained for simulation using empirically fitted electron density and electron temperature and heuristically determined neutral gas temperature. Comparison between simulated results and measured fields indicates that neutral gas heating plays an important role in determining the skin depth of the magnetic fields.
E × B shear pattern formation by radial propagation of heat flux waves
Authors: Kosuga Y. , Diamond P. H. , Dif-Pradalier G. , Gürcan Ö. D.
Published: April 2014

A novel theory to describe the formation of E×B flow patterns by radially propagating heat flux waves is presented. A model for heat avalanche dynamics is extended to include a finite delay time between the instantaneous heat flux and the mean flux, based on an analogy between heat avalanche dynamics and traffic flow dynamics. The response time introduced here is an analogue of the drivers' response time in traffic dynamics. The microscopic foundation for the time delay is the time for mixing of the phase space density. The inclusion of the finite response time changes the model equation for avalanche dynamics from Burgers equation to a nonlinear telegraph equation. Based on the telegraph equation, the formation of heat flux jams is predicted. The growth rate and typical interval of jams are calculated. The connection of the jam interval to the typical step size of the E×B staircase is discussed.
Edge ambipolar potential in toroidal fusion plasmas
Authors: Spizzo G. , Vianello N. , White R. B. , Abdullaev S. S. , Agostini M. , Cavazzana R. , Ciaccio G. , Puiatti M. E. , Scarin P. , Schmitz O. , Spolaore M. , Terranova D. ,   RFX and TEXTOR Teams
Published: April 2014

A series of issues with toroidally confined fusion plasmas are related to the generation of 3D flow patterns by means of edge magnetic islands, embedded in a chaotic field and interacting with the wall. These issues include the Greenwald limit in Tokamaks and reversed-field pinches, the collisionality window for ELM mitigation with the resonant magnetic perturbations (RMPs) in Tokamaks, and edge islands interacting with the bootstrap current in stellarators. Measurements of the 2D map of the edge electric field Er(r=a,θ,ϕ) in the RFX reversed-field pinch show that Er has the same helicity of the magnetic islands generated by a m/n perturbation: in fact, defining the helical angle u=mθ−nϕ+ωt, maps show a sinusoidal dependence as a function of u, Er=Ẽrsin u. The associated E × B flow displays a huge convective cell with v(a)≠0 which, in RFX and near the Greenwald limit, determines a stagnation point for density and a reversal of the sign of Er. From a theoretical point of view, the question is how a perturbed toroidal flux of symmetry m/n gives rise to an ambipolar potential Φ=Φ̃sin u. On the basis of a model developed with the guiding center code Orbit and applied to RFX and the TEXTOR tokamak, we will show that the presence of an m/n perturbation in any kind of device breaks the toroidal symmetry with a drift proportional to the gyroradius ρ, thus larger for ions (ρi ≫ ρe). Immediately, an ambipolar potential arises to balance the drifts, with the same symmetry as the original perturbation.
Eddy current effect on the microwave permeability of Fe-based nanocrystalline flakes with different sizes
Authors: Wu Yanhui , Han Mangui , Tang Zhongkai , Deng Longjiang
Published: April 2014

The effective permeability values of composites containing Fe-Cu-Nb-Si-B nanocrystalline flakes have been studied within 0.5–10 GHz. Obvious differences in microwave permeability have been observed between large flakes (size range: 23–111 μm, average thickness: 4.5 μm) and small flakes (size range: 3–21 μm, average thickness: 1.3 μm). The initial real part of microwave permeability of large flakes is larger but it is decreasing faster. The larger flakes also show a larger magnetic loss. Taking into account the eddy current effect, the intrinsic microwave permeability values have been extracted based on the modified Maxwell-Garnet law, which have also been verified by the Acher's law. The dependences of skin depth on frequency have been calculated for both kinds of flakes. It is shown that the eddy current effect in the large flakes is significant. However, the eddy current effect can be ignored in the small flakes.
Mechanical deformations of boron nitride nanotubes in crossed junctions
Authors: Zhao Yadong , Chen Xiaoming , Park Cheol , Fay Catharine C. , Stupkiewicz Stanislaw , Ke Changhong
Published: April 2014

We present a study of the mechanical deformations of boron nitride nanotubes (BNNTs) in crossed junctions. The structure and deformation of the crossed tubes in the junction are characterized by using atomic force microscopy. Our results show that the total tube heights are reduced by 20%–33% at the crossed junctions formed by double-walled BNNTs with outer diameters in the range of 2.21–4.67 nm. The measured tube height reduction is found to be in a nearly linear relationship with the summation of the outer diameters of the two tubes forming the junction. The contact force between the two tubes in the junction is estimated based on contact mechanics theories and found to be within the range of 4.2–7.6 nN. The Young's modulus of BNNTs and their binding strengths with the substrate are quantified, based on the deformation profile of the upper tube in the junction, and are found to be 1.07 ± 0.11 TPa and 0.18–0.29 nJ/m, respectively. Finally, we perform finite element simulations on the mechanical deformations of the crossed BNNT junctions. The numerical simulation results are consistent with both the experimental measurements and the analytical analysis. The results reported in this paper contribute to a better understanding of the structural and mechanical properties of BNNTs and to the pursuit of their applications.
Strengthening and toughening metallic glasses: The elastic perspectives and opportunities
Authors: Liu Z. Q. , Zhang Z. F.
Published: April 2014

There exist general conflicts between strength and toughness in crystalline engineering materials, and various strengthening and toughening strategies have been developed from the dislocation motion perspectives. Metallic glasses (MGs) have demonstrated great potentials owing to their unique properties; however, their structural applications are strictly limited. One of the key problems is that the traditional strengthening and toughening strategies and mechanisms are not applicable in MGs due to the absence of dislocations and crystalline microstructures. Here, we show that the strength and toughness, or equivalently the shear modulus and Poisson's ratio, are invariably mutually exclusive in MGs. Accordingly, the MGs can be categorized into four groups with different levels of integrated mechanical properties. It is further revealed that the conflicts originate fundamentally from the atomic bonding structures and the levels of strength-toughness combinations are indeed dominated by the bulk modulus. Moreover, we propose novel strategies for optimizing the mechanical properties of MGs from the elastic perspectives. We emphasize the significance of developing high bulk modulus MGs to achieve simultaneously both high strength and good toughness and highlight the elastic opportunities for strengthening and toughening materials.
Phase transformation of ZnMoO4 by localized thermal spike
Authors: Agarwal D. C. , Avasthi D. K. , Varma S. , Kremer Felipe , Ridgway M. C. , Kabiraj D.
Published: April 2014

We show that ZnMoO4 remains in stable phase under thermal annealing up to 1000 °C, whereas it decomposes to ZnO and MoO3 under transient thermal spike induced by 100 MeV Ag irradiation. The transformation is evidenced by X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Thin films of ZnMoO4 were synthesized by thermal evaporation and subsequent annealing in oxygen ambient at 600 °C for 4 h. XRD results show that as the irradiation fluence increases, the peak related to ZnMoO4 decreases gradually and eventually disappear, whereas peaks related to ZnO grow steadily up to fluence of 3 × 1012 ions/cm2 and thereafter remain stable till highest fluence. This indicates that polycrystalline ZnMoO4 film has transformed to polycrystalline ZnO thin film. The Raman lines related to ZnMoO4 are observed to have disappeared with increasing irradiation fluence. XPS results show modification in bonding and depletion of Mo from near surface region after the ion irradiation. Cross-sectional transmission electron microscopy result shows the formation of ion track of diameter 12–16 nm. These results demonstrate that ion beam methods provide the means to control phase splitting of ZnMoO4 to ZnO and MoO3 within nanometric dimension along the ion track. The observation of phase splitting and Mo loss are explained in the framework of ion beam induced thermal spike formalism.
Taylor-Couette flow of unmagnetized plasma
Authors: Collins C. , Clark M. , Cooper C. M. , Flanagan K. , Khalzov I. V. , Nornberg M. D. , Seidlitz B. , Wallace J. , Forest C. B.
Published: April 2014

Differentially rotating flows of unmagnetized, highly conducting plasmas have been created in the Plasma Couette Experiment. Previously, hot-cathodes have been used to control plasma rotation by a stirring technique [C. Collins et al., Phys. Rev. Lett. 108, 115001 (2012)] on the outer cylindrical boundary—these plasmas were nearly rigid rotors, modified only by the presence of a neutral particle drag. Experiments have now been extended to include stirring from an inner boundary, allowing for generalized circular Couette flow and opening a path for both hydrodynamic and magnetohydrodynamic experiments, as well as fundamental studies of plasma viscosity. Plasma is confined in a cylindrical, axisymmetric, multicusp magnetic field, with Te < 10 eV, Ti < 1 eV, and ne<1011 cm−3. Azimuthal flows (up to 12 km/s, M = V∕cs ∼ 0.7) are driven by edge J × B torques in helium, neon, argon, and xenon plasmas, and the experiment has already achieved Rm ∼ 65 and Pm∼0.2−12. We present measurements of a self-consistent, rotation-induced, species-dependent radial electric field, which acts together with pressure gradient to provide the centripetal acceleration for the ions. The maximum flow speeds scale with the Alfvén critical ionization velocity, which occurs in partially ionized plasma. A hydrodynamic stability analysis in the context of the experimental geometry and achievable parameters is also explored.
Enhanced dielectric nonlinearity in epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 thin films
Authors: Ma Chunrui , Ma Beihai , Mi Shao-Bo , Liu Ming , Wu Judy
Published: April 2014

High quality c-axis oriented epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 films were fabricated using pulsed laser deposition on (001) LaAlO3 substrates with conductive LaNiO3 buffers. Besides confirmation of the in-plane and out-of-plane orientations using X-ray diffraction, transmission electron microscopy study has revealed columnar structure across the film thickness with column width around 100 nm. Characterization of ferroelectric properties was carried out in comparison with polycrystalline Pb0.92La0.08Zr0.52Ti0.48O3 films to extract the effect of epitaxial growth. It is found that the ratio between the irreversible Rayleigh parameter and reversible parameter increased up to 0.028 cm/kV at 1 kHz on epitaxial samples, which is more than twice of that on their polycrystalline counterparts. While this ratio decreased to 0.022 cm/kV with increasing frequency to100 kHz, a much less frequency dependence was observed as compared to the polycrystalline case. The epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 films exhibited a higher mobility of domain wall and the higher extrinsic contribution to the dielectric properties, as well as reduced density of defects, indicating that it is promising for tunable and low power consumption devices.
Controlled synthesis and decoupling of monolayer graphene on SiC(0001)
Authors: Oida S. , Hannon J. B. , Tromp R. M.
Published: April 2014

We describe a process for the growth of a single, electronically decoupled graphene layer on SiC(0001). The method involves annealing in disilane to (1) prepare flat, clean substrates, (2) grow a single graphene layer, and (3) electronically decouple the graphene from the substrate. This approach uses a single process gas, at μTorr pressures, with modest substrate temperatures, thus affecting a drastic simplification over other processes described in the literature.
Non-local piezoresponse of LaAlO3/SrTiO3 heterostructures
Authors: Huang Mengchen , Bi Feng , Bark Chung-Wung , Ryu Sangwoo , Cho Kwang-Hwan , Eom Chang-Beom , Levy Jeremy
Published: April 2014

The hysteretic piezoelectric response in LaAlO3/SrTiO3 heterostructures can provide important insights into the mechanism for interfacial conductance and its metastability under various conditions. We perform piezoresponse force microscopy experiments on 3 unit cell LaAlO3/SrTiO3 heterostructures. A hysteretic piezoresponse is observed under a variety of non-local environmental and driving conditions. The hysteresis is suppressed when either the sample is placed in vacuum or the interface is electrically grounded. We also find the hysteresis can be affected by the presence of ions. A simple physical model related to surface adsorbates is presented to account for the observed phenomena.
Comparative study of voltage oriented and frequency coordinated control of grid connected doubly fed induction generator
Authors: Elhassan Zakieldeen , Yi Tang , Yang Li
Published: April 2014

In this paper, a comparative study between voltage oriented control (VOC) and frequency coordinated control (FCC) of grid connected doubly fed induction generator (DFIG) is presented. The two method controls are deeply done on DFIG converter sides, grid side converter (GSC), and rotor side converter (RSC). The VOC method permanently maintains the DFIG reactive power to zero values to achieve stable voltage. This control is implemented by regulating the rotor direct axis reference current in RSC using grid reactive power. On the other hand, the FCC has employed the active power obtaining from the system frequency deviation to control the rotor quadrature axis reference current in the RSC. The GSC is the same in two studies, and its applied vector controlled method. The comparison study between the two methods is conducted at a steady and dynamic state under constant and variable wind speeds. The simulation results are carried out by using PSCAD/EMTDC electromagnetic transient program to validate the comparison study between two methods control of DFIG. The outcomes of the simulation show that the VOC is very convenient when the DFIG operated at transient mode and variable wind speeds while the FCC is feasible and effective for steady-state mode applications. Furthermore, the FCC method has an ability to reduce the active and reactive powers ripples as well as decreasing torque harmonics. Both of two methods had fewer transient recovery values of output parameters, which ensure safety dynamic response of DFIG and power system. This study contributes significantly to choose the suitable control of the DFIG converters according to electrical grid operation conditions. In addition, if a joint control has been applied to these two methods, the wind power gained strong and flexible control of the frequency and voltage for different operating conditions.
Polarization controlled deep sub-wavelength periodic features written by femtosecond laser on nanodiamond thin film surface
Authors: Kumar Kuntumalla Mohan , Rajamudili Kuladeep , Rao Desai Narayana , Srikanth Vadali V. S. S.
Published: April 2014

Deep sub-wavelength (Λ/λ = ∼0.22) periodic features are induced uniformly on a nanodiamond (ND) thin film surface using femtosecond (fs) laser irradiation (pulse duration = ∼110 fs and central wavelength of ∼800 nm). The topography of the surface features is controlled by the laser polarization. Orientation of features is perpendicular to laser polarization. Periodicity (spatial periodicity of < λ/4) of the surface features is less than the laser wavelength. This work gives an experimental proof of polarization controlled surface plasmon-fs laser coupling mechanism prompting the interaction between fs laser and solid matter (here ND thin film) which in turn is resulting in the periodic surface features. Scanning electron microscopy in conjunction with micro Raman scattering, X-ray diffraction, and atomic force microscopy are carried out to extract surface morphology and phase information of the laser irradiated regions. This work demonstrates an easy and efficient surface fabrication technique.
Study of the electric-pulse-induced resistive switching effects at Pt/PrBa2Cu3Ox interfaces by multi-electrode method
Authors: Yue Ruihong , Sun Xianwen , Wei Ling , Yin Yanfeng , Yin Jiangtao , Zhang Weifeng
Published: April 2014

Polycrystalline PrBa2Cu3Ox (PBCO) ceramic is prepared using the conventional solid-state reaction method and then Pt/PBCO/Pt plane structure device is fabricated. A reversible, non-volatile, and bipolar electric-pulse-induced resistance (EPIR) effect are found in the Pt/PBCO/Pt device. In order to determine the key role that controls the EPIR effect, the electrical properties of the Pt/PBCO interfaces and the temperature dependence of the PBCO bulk resistance are investigated by multi-electrode method. The results indicate that the EPIR effect is mainly induced and dominated by the Pt/PBCO interfaces, rather than the PBCO bulk. By analyzing the I–V characteristics of the contact interfaces, the carrier injection model is inferred to explain the EPIR effect.
Study on copper phthalocyanine and perylene-based ambipolar organic light-emitting field-effect transistors produced using neutral beam deposition method
Authors: Kim Dae-Kyu , Oh Jeong-Do , Shin Eun-Sol , Seo Hoon-Seok , Choi Jong-Ho
Published: April 2014

The neutral cluster beam deposition (NCBD) method has been applied to the production and characterization of ambipolar, heterojunction-based organic light-emitting field-effect transistors (OLEFETs) with a top-contact, multi-digitated, long-channel geometry. Organic thin films of n-type N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide and p-type copper phthalocyanine were successively deposited on the hydroxyl-free polymethyl-methacrylate (PMMA)-coated SiO2 dielectrics using the NCBD method. Characterization of the morphological and structural properties of the organic active layers was performed using atomic force microscopy and X-ray diffraction. Various device parameters such as hole- and electron-carrier mobilities, threshold voltages, and electroluminescence (EL) were derived from the fits of the observed current-voltage and current-voltage-light emission characteristics of OLEFETs. The OLEFETs demonstrated good field-effect characteristics, well-balanced ambipolarity, and substantial EL under ambient conditions. The device performance, which is strongly correlated with the surface morphology and the structural properties of the organic active layers, is discussed along with the operating conduction mechanism.
Degradation of AlGaN/GaN high-electron mobility transistors in the current-controlled off-state breakdown
Authors: Kuzmik J. , Jurkovič M. , Gregušová D. , Ťapajna M. , Brunner F. , Cho M. , Meneghesso G. , Würfl J.
Published: April 2014

We investigate degradation mechanisms in AlGaN/GaN HEMTs which were repeatedly driven into the current-controlled off-state breakdown or subject to 60 s voltage- or current-controlled off state stresses. The current-controlled sweep in to the breakdown allows the sustainability of breakdown that can not be observed in the voltage controlled sweep. Only temporal changes were observed in the HEMT dc performance after repetitive sweeps, which were explained by charging/discharging of the HEMT surface at the gate-to-drain access region and in the GaN buffer below the gate. Similar changes were observed also if high-voltage stress has been applied on the drain; however, permanent degradation appears after 60 s current-controlled breakdown stress. In this case, the drain leakage current, as well as the breakdown current, increases significantly. On the other hand, the breakdown voltage, as well as the gate characteristics, remains unaltered. We suggest that the avalanche-injection process is governing the off-state breakdown event with a dominant role of the potential barrier at the channel-buffer interface.
Charging and exciton-mediated decharging of metal nanoparticles in organic semiconductor matrices
Authors: Ligorio Giovanni , Vittorio Nardi Marco , Christodoulou Christos , Florea Ileana , Monteiro Nicolas-Crespo , Ersen Ovidiu , Brinkmann Martin , Koch Norbert
Published: April 2014

Gold nanoparticles (Au-NPs) were deposited on the surface of n- and p-type organic semiconductors to form defined model systems for charge storage based electrically addressable memory elements. We used ultraviolet photoelectron spectroscopy to study the electronic properties and found that the Au-NPs become positively charged because of photoelectron emission, evidenced by spectral shifts to higher binding energy. Upon illumination with light that can be absorbed by the organic semiconductors, dynamic charge neutrality of the Au-NPs could be re-established through electron transfer from excitons. The light-controlled charge state of the Au-NPs could add optical addressability to memory elements.
Control of ions energy distribution in dual-frequency magnetron sputtering discharges
Authors: Ye Chao , He Haijie , Huang Fupei , Liu Yi , Wang Xiangying
Published: April 2014

The ion energy distributions (IEDs) in the dual-frequency magnetron sputtering discharges were investigated by retarding field energy analyzer. Increasing power ratio of 2 MHz to 13.56 (27.12 or 60) MHz led to the evolution of IEDs from a uni-modal distribution towards a uni-modal distribution with high-energy peak shoulder and a bi-modal distribution. While increasing power ratio of 13.56 MHz to 27.12 MHz and 27.12 MHz to 60 MHz, led to the increase of peak energy. The evolution of IEDs shape and the increase of peak energy are due to the change of ions responding to the average field of high-frequency period towards the instantaneous sheath potential of low-frequency period.
Experimental investigation of terahertz quantum cascade laser with variable barrier heights
Authors: Jiang Aiting , Matyas Alpar , Vijayraghavan Karun , Jirauschek Christian , Wasilewski Zbig R. , Belkin Mikhail A.
Published: April 2014

We report an experimental study of terahertz quantum cascade lasers with variable barrier heights based on the AlxGa1–xAs/GaAs material system. Two new designs are developed based on semiclassical ensemble Monte Carlo simulations using state-of-the-art Al0.15Ga0.85As/GaAs three-quantum-well resonant phonon depopulation active region design as a reference. The new designs achieved maximum lasing temperatures of 188 K and 172 K, as compared to the maximum lasing temperature of 191 K for the reference structure. These results demonstrate that terahertz quantum cascade laser designs with variable barrier heights provide a viable alternative to the traditional active region designs with fixed barrier composition. Additional design space offered by using variable barriers may lead to future improvements in the terahertz quantum cascade laser performance.
Energy band line-up of atomic layer deposited Al2O3 on β-Ga2O3
Authors: Hung Ting-Hsiang , Sasaki Kohei , Kuramata Akito , Nath Digbijoy N. , Sung Park Pil , Polchinski Craig , Rajan Siddharth
Published: April 2014

Electrical properties of atomic layer deposited Al2O3/β-Ga2O3 interface were investigated. We determined the conduction band offset and interface charge density of Al2O3/β-Ga2O3 interface by analyzing the capacitance-voltage characteristics. The conduction band offset at the Al2O3/β-Ga2O3 interface was found to be 1.7 eV. A large positive sheet charge density of 3.6 × 1012 cm−2 is induced at the Al2O3/β-Ga2O3 interface, which caused a non-zero field of 0.7 MV/cm in the Al2O3 under flat-band conditions in the β-Ga2O3. The forward current-voltage characteristics were found to be related to trap-assisted tunneling.
Stories of vicarious experience in speeches by Barack Obama
Authors: Norrick Neal R.
Published: April 2014

Stories of personal experience have been a staple of research on narrative, while stories of vicarious experience have remained largely ignored, though they offer special insights into issues of epistemic authority and telling rights, coherence and evaluation, contextualization and stance-taking. This article investigates the largely unexplored matters of why conversationalists tell stories about other people, how they establish their authority to tell these stories, how they relate these stories to their current conversational context, and how they participant design these stories and shape them for purposes of identity construction in interaction. Speeches by Barack Obama provide a rich resource for investigating narratives of vicarious experience, illustrating a wide range of forms contextualized in complex ways, and told for a variety of purposes.
Discourse markers, structure, and emotionality in oral narratives
Authors: Romano Manuela , Cuenca Maria Josep
Published: April 2014

This paper presents a comparative analysis structure and frequency of discourse markers in two kinds of oral narratives: objective, emotionally neutral ones on the one side, and highly emotional, spontaneous ones on the other. The results prove that emotionality plays a crucial role in the structuring of oral narratives as well as in the type of discourse markers employed in them. Objective oral narratives show a higher number of discourse markers, whereas highly emotional ones present a higher variety of discourse markers, as well as a higher frequency of other pragmatic markers, in order to guide the listener through the multiplicity of side stories and the broken structure they show. In short, this work highlights the relationship between linguistic activity (language in context or use) and linguistic form.
Constraints on climate forcing by sulphate aerosols from seasonal changes in Earth's spin
Authors: Sottili Gianluca
Published: April 2014

Angular momentum exchanges between atmosphere and solid Earth are strongly modulated by variations in global atmospheric circulation. Geodetically determined length-of-day (LOD) fluctuations provide an independent resource to investigate climate changes. Here, I evaluate the effects of volcanic and anthropogenic sulphate aerosols on Earth's rotational energy variations. The period analysed, 1980–2002, shows that the strongest seasonal LOD variations are related to sulphate peak concentrations from the El-Chichón 1982, and Pinatubo and Cerro Hudson 1991 volcanic eruptions. The Earth's rotational energy budget implies that radiative forcing alone cannot produce the observed LOD anomalies. Rather, the required amount of atmospheric kinetic energy can be explained only by a strong influence of sulphate aerosols on energy partitioning into the atmosphere, for example, as sulphate aerosols affect latent heat release and transport during condensation–evaporation–freezing cycles. Overall, the effects of sulphate aerosols on Earth's spin changes are faster than those produced by greenhouse gases.
Magnetic fields in fully convective M-dwarfs: oscillatory dynamos versus bistability
Authors: Kitchatinov L. L. , Moss D. , Sokoloff D.
Published: April 2014

M-dwarfs demonstrate two types of activity: (1) strong (kilogauss) almost axisymmetric poloidal magnetic fields; and (2) considerably weaker non-axisymmetric fields, sometimes including a substantial toroidal component. Dynamo bistability has been proposed as an explanation. However, it is not straightforward to obtain such a bistability in dynamo models. On the other hand, the solar magnetic dipole at times of magnetic field inversion becomes transverse to the rotation axis, while the magnetic field becomes weaker at times far from that of inversion. Thus, the Sun resembles a star with the second type of activity. We suggest that M-dwarfs can have magnetic cycles, and that M-dwarfs with the second type of activity can just be stars observed at times of magnetic field inversion. Then the relative number of M-dwarfs with the second type of activity can be used in the framework of this model to determine parameters of stellar convection near the surface.
Multiple Imputation for Continuous and Categorical Data: Comparing Joint Multivariate Normal and Conditional Approaches
Authors: Kropko Jonathan , Goodrich Ben , Gelman Andrew , Hill Jennifer
Published: April 2014

We consider the relative performance of two common approaches to multiple imputation (MI): joint multivariate normal (MVN) MI, in which the data are modeled as a sample from a joint MVN distribution; and conditional MI, in which each variable is modeled conditionally on all the others. In order to use the multivariate normal distribution, implementations of joint MVN MI typically assume that categories of discrete variables are probabilistically constructed from continuous values. We use simulations to examine the implications of these assumptions. For each approach, we assess (1) the accuracy of the imputed values; and (2) the accuracy of coefficients and fitted values from a model fit to completed data sets. These simulations consider continuous, binary, ordinal, and unordered-categorical variables. One set of simulations uses multivariate normal data, and one set uses data from the 2008 American National Election Studies. We implement a less restrictive approach than is typical when evaluating methods using simulations in the missing data literature: in each case, missing values are generated by carefully following the conditions necessary for missingness to be “missing at random” (MAR). We find that in these situations conditional MI is more accurate than joint MVN MI whenever the data include categorical variables.
Effect of Elevated Carbon Dioxide Concentration on Rice Quality: Nutritive Value, Color, Milling, Cooking, and Eating Qualities
Authors: Goufo Piebiep , Falco Virgilio , Brites Carla , Wessel Dulcineia F. , Kratz Sylvia , Rosa Eduardo A. S. , Carranca Corina , Trindade Henrique
Published: April 2014

Increase in the atmospheric carbon dioxide concentration ([CO2]) enhanced the concentration of carbohydrates in rice grains, according to results of a previous study. However, its impact on other quality traits is little known. To investigate the effect of CO2 levels (375 and 550 μmol/mol) on rice quality, a field experiment was conducted with open‐top chambers. Elevated [CO2] affected several nutritional parameters of the grain. Whereas the concentration of α‐linolenic acid increased, that of linoleic and γ‐linolenic acids decreased. For example, reductions of 9 and 28% were observed for linoleic acid in the brown rice and for γ‐linolenic acid in the husk, respectively. Phytic acid concentration and zinc bioavailability were unaffected. Whereas iron bioavailability decreased in the brown rice (22%), calcium bioavailability increased in the bran and husk (5–11%). The concentrations of essential amino acids were also reduced; for example, the amount of isoleucine in the white rice, tyrosine in the brown rice, and phenylalanine in the bran decreased by 40, 57, and 23%, respectively. In contrast, elevated [CO2] resulted in improved grain whiteness (3%) and starch viscosity (11%), with no effect on the milling quality. These data indicate that increased [CO2] has both positive and negative effects on quality, depending on the specific end use of the rice grain.
Positive and Negative Roles for Soybean MPK6 in Regulating Defense Responses
Authors: Liu Jian-Zhong , Braun Edward , Qiu Wen-li , Shi Ya-Fei , Marcelino-Guimarães Francismar C. , Navarre Duroy , Hill John H. , Whitham Steven A.
Published: April 2014

It has been well established that MPK6 is a positive regulator of defense responses in model plants such as Arabidopsis and tobacco. However, the functional importance of soybean MPK6 in disease resistance has not been investigated. Here, we showed that silencing of GmMPK6 in soybean using virus-induced gene silencing mediated by Bean pod mottle virus (BPMV) caused stunted growth and spontaneous cell death on the leaves, a typical phenotype of activated defense responses. Consistent with this phenotype, expression of pathogenesis-related (PR) genes and the conjugated form of salicylic acid were significantly increased in GmMPK6-silenced plants. As expected, GmMPK6-silenced plants were more resistant to downy mildew and Soybean mosaic virus compared with vector control plants, indicating a negative role of GmMPK6 in disease resistance. Interestingly, overexpression of GmMPK6, either transiently in Nicotiana benthamiana or stably in Arabidopsis, resulted in hypersensitive response (HR)-like cell death. The HR-like cell death was accompanied by increased PR gene expression, suggesting that GmMPK6, like its counterpart in other plant species, also plays a positive role in cell death induction and defense response. Using bimolecular fluorescence complementation analysis, we determined that GmMKK4 might function upstream of GmMPK6 and GmMKK4 could interact with GmMPK6 independent of its phosphorylation status. Taken together, our results indicate that GmMPK6 functions as both repressor and activator in defense responses of soybean.
Provider Awareness Alone Does Not Improve Transition Readiness Skills in Adolescent Patients With Inflammatory Bowel Disease
Authors: Fishman Laurie N. , Ziniel Sonja I. , Adrichem Max E. , Fernandes Susan M. , Arnold Janis
Published: April 2014

Objective:

Adolescent patients with chronic health conditions must gradually assume responsibility for their health. Self‐management skills are needed for a successful transfer from adolescent to adult health care, but the development of these skills could be resource intensive. Pediatric providers are already instrumental in teaching patients about their health and may improve these skills. The aim of the study was to evaluate whether informal education of pediatric providers regarding transition improves inflammatory bowel disease (IBD) patient self‐management skills.

Methods:

Consecutive patients with IBD older than 10 years who presented to the outpatient setting were administered a survey regarding self‐management behaviors in 2008 and 2011. During this time, several conferences on transition were presented to the providers.

Results:

In 2008, 294 patients completed the survey (82%) compared with 121 patients (89%) in 2011. The patient groups were comparable with respect to sex (boys 50% vs 42%), mean age (16.7 vs 16.2 years), and type of IBD (Crohn 68% vs 66%). The 13‐ to 15‐year‐olds reported calling in refills (11%, 8%, respectively), scheduling clinic appointment (0, 1%), preparing questions (13%, 5%), and taking the main role in talking during clinic visits (15%, 24%). The 16‐ to 18‐year‐olds reported calling in refills (13%, 27%), scheduling clinic appointments (9%, 6%), preparing questions (9%, 16%), and taking the main role in talking in clinic visits (36%, 45%). Responsibility for behaviors gradually increases with age, but did not differ significantly between 2008 and 2011.

Conclusions:

Increasing awareness around transition readiness for pediatric providers had an insignificant effect on the self‐management skills of patients with IBD. A more formal or structured approach is likely required to improve transition skills in adolescent patients.