bluuebunny/crossref_metadata_2025 huggingface dataset:
Inefficient Encoding as an Explanation for Age-Related Deficits in Recollection-Based Processing
Authors: Friedman David , Johnson Ray
Published: September 2014

A cardinal feature of aging is a decline in episodic memory (EM). Nevertheless, there is evidence that some older adults may be able to “compensate” for failures in recollection-based processing by recruiting brain regions and cognitive processes not normally recruited by the young. We review the evidence suggesting that age-related declines in EM performance and recollection-related brain activity (left-parietal EM effect; LPEM) are due to altered processing at encoding. We describe results from our laboratory on differences in encoding- and retrieval-related activity between young and older adults. We then show that, relative to the young, in older adults brain activity at encoding is reduced over a brain region believed to be crucial for successful semantic elaboration in a 400–1,400-ms interval (left inferior prefrontal cortex, LIPFC; Johnson, Nessler, & Friedman, 2013 ; Nessler, Friedman, Johnson, & Bersick, 2007 ; Nessler, Johnson, Bersick, & Friedman, 2006 ). This reduced brain activity is associated with diminished subsequent recognition-memory performance and the LPEM at retrieval. We provide evidence for this premise by demonstrating that disrupting encoding-related processes during this 400–1,400-ms interval in young adults affords causal support for the hypothesis that the reduction over LIPFC during encoding produces the hallmarks of an age-related EM deficit: normal semantic retrieval at encoding, reduced subsequent episodic recognition accuracy, free recall, and the LPEM. Finally, we show that the reduced LPEM in young adults is associated with “additional” brain activity over similar brain areas as those activated when older adults show deficient retrieval. Hence, rather than supporting the compensation hypothesis, these data are more consistent with the scaffolding hypothesis, in which the recruitment of additional cognitive processes is an adaptive response across the life span in the face of momentary increases in task demand due to poorly-encoded episodic memories.
Rapid Mental Fatigue Amplifies Age-Related Attentional Deficits
Authors: Wascher Edmund , Getzmann Stephan
Published: September 2014

Deficient information processing with increasing age has been assigned to reduced efficiency in frontal executive control functions. Dopamine has been assumed to play a central role for this decline. Dopamine, however, is also essential for the maintenance of motivation for a longer period of time and is therefore a core factor for mental fatigue. Combining these two findings, we tested to what degree older adults are more prone to performance loss due to increasing time on task than younger adults. Twelve younger and twelve older participants performed an inhibition of return task for 80 min. Performance declined in the older participants but not in the young. Event-related potentials (ERPs) of the EEG, however, showed distinct changes with time on task primarily for young participants. The dissociation between behavioral and ERP results indicates that changes in ERPs of the young participants could reflect adaptations to the task rather than fatigue. This is evident from very distinct changes of the posterior N1 component in this group. The failing (or rather unspecific) adaptation to the task in older adults might have been a consequence of lacking frontal executive control functions reflected in a massive reduction of the N2 component of the ERP, relative to the young participants.
Real space pseudopotential calculations for size trends in Ga- and Al-doped zinc oxide nanocrystals with wurtzite and zincblende structures
Authors: Bobbitt N. Scott , Sai Na , Marom Noa , Kim Minjung , Chelikowsky James R.
Published: September 2014

Zinc oxide is often used as a popular inexpensive transparent conducting oxide. Here, we employ density functional theory and local density approximation to examine the effects of quantum confinement in doped nanocrystals of this material. Specifically, we examine the addition of Ga and Al dopants to ZnO nanocrystals on the order of 1.0 nm. We find that the inclusion of these dopants is energetically less favorable in smaller particles and that the electron binding energy, which is associated with the dopant activation, decreases with the nanocrystal size. We find that the introduction of impurities does not alter significantly the Kohn-Sham eigenspectrum for small nanocrystals of ZnO. The added electron occupies the lowest existing state, i.e., no new bound state is introduced in the gap. We verify this assertion with hybrid functional calculations.
Measurements of acoustic particle velocity in a coaxial duct and its application to a traveling-wave thermoacoustic heat engine
Authors: Morii Jun , Biwa Tetsushi , Yazaki Taichi
Published: September 2014

We present theoretical solutions, based on linear acoustic theory, for axial acoustic particle velocity in an annular region of a coaxial duct. The solutions are expressed in terms of two non-dimensional parameters h/δν and R; h and δν, respectively, represent the half of the spacing between two concentric ducts and the characteristic length given by kinematic viscosity of the gas and angular frequency of acoustic oscillations, and R is the radius ratio of the ducts. The validity of the solutions was verified by direct measurements using a laser Doppler velocimeter. The present results are applied to measurements of the acoustic power distribution in a traveling wave thermoacoustic engine with a coaxial duct, which provides experimental evidence for acoustic power feedback in the coaxial duct.
Unravelling nanoconfined films of ionic liquids
Authors: Lee Alpha A. , Vella Dominic , Perkin Susan , Goriely Alain
Published: September 2014

The confinement of an ionic liquid between charged solid surfaces is treated using an exactly solvable 1D Coulomb gas model. The theory highlights the importance of two dimensionless parameters: the fugacity of the ionic liquid, and the electrostatic interaction energy of ions at closest approach, in determining how the disjoining pressure exerted on the walls depends on the geometrical confinement. Our theory reveals that thermodynamic fluctuations play a vital role in the “squeezing out” of charged layers as the confinement is increased. The model shows good qualitative agreement with previous experimental data, with all parameters independently estimated without fitting.
Broad-angle and efficient unidirectional excitations of surface plasmons with dielectric-coated subwavelength metallic periodic nanoslits
Authors: Lu Fan , Sun Lin , Wang Jia , Li Kun , Xu Anshi
Published: September 2014

We experimentally demonstrate a mechanism of broad-angle and efficient unidirectional excitations of surface plasmon polaritons (SPPs). By combining the plasmonic critical angle phenomenon and grating effects, unidirectional excitation of SPPs with broad incident angular width up to 25° and high extinction ratio better than 10 dB was experimentally demonstrated. A peak extinction ratio of 17 dB was achieved. The proposed structure was also numerically simulated showing good agreement with experimental measurement. The operation principle was numerically and experimentally clarified through compare and analysis.
Impact of Maxwell rigidity transitions on resistance drift phenomena in GexTe1−x glasses
Authors: Luckas J. , Olk A. , Jost P. , Volker H. , Alvarez J. , Jaffré A. , Zalden P. , Piarristeguy A. , Pradel A. , Longeaud C. , Wuttig M.
Published: September 2014

Amorphous chalcogenides usually exhibit a resistivity, which increases with age following a power law ρ ∼ tα. Existing theories link this change in amorphous state resistivity to structural relaxation. Here, the impact of fundamental glass properties on resistance drift phenomena in amorphous GexTe1−x networks is studied. Employing Raman spectroscopy, the Maxwell rigidity transition from flexible to stressed rigid is determined to occur in the compositional range 0.250 < xc < 0.265. Stressed rigid glasses (x > 0.265) exhibit rather strong resistance drift, where the drift parameters increase steadily from α = 0.13 for amorphous GeTe to α = 0.29 for compositions near the stiffness threshold xc. On the other hand, the drift parameter in flexible glasses (x < 0.25) decreases with decreasing Ge content x to values as low as α = 0.05. These findings illustrate the strong impact of the stiffness threshold on resistance drift phenomena in chalcogenides.
Influence of strain and metal thickness on metal-MoS2 contacts
Authors: Saidi Wissam A.
Published: September 2014

MoS2 and other transition metal dichalcogenides are considered as potential materials in many applications including future electronics. A prerequisite for these applications is to understand the nature of the MoS2 contact with different metals. We use semi-local density functional theory in conjunction with dispersion corrections to study the heterostructures composed of Pd and Pt monolayers with (111) orientation grown pseudomorphically on MoS2(001). The interface properties are mapped as a function of the number of deposited overlayers, as well as a function of tensile and compressive strains. Although we show that the dependence of the contacts on strain can be fully explained using the d-band model, we find that their evolution with the number of deposited metal layers is markedly different between Pd and Pt, and at variance with the d-band model. Specifically, the Pt/MoS2 heterostructures show an anomalous large stability with the deposition of two metal monolayers for all investigated strains, while Pd/MoS2 exhibits a similar behavior only for compressive strains. It is shown that the results can be rationalized by accounting for second-nearest-neighbor effect that couples MoS2 with the subsurface metal layers. The underpinnings of this behavior are attributed to the larger polarizability and cohesive energy of Pt compared to Pd, that leads to a larger charge-response in the subsurface layers.
Grain boundary and triple junction diffusion in nanocrystalline copper
Authors: Wegner M. , Leuthold J. , Peterlechner M. , Song X. , Divinski S. V. , Wilde G.
Published: September 2014

Grain boundary and triple junction diffusion in nanocrystalline Cu samples with grain sizes, 〈d〉, of ∼35 and ∼44 nm produced by spark plasma sintering were investigated by the radiotracer method using the 63Ni isotope. The measured diffusivities, Deff, are comparable with those determined previously for Ni grain boundary diffusion in well-annealed, high purity, coarse grained, polycrystalline copper, substantiating the absence of a grain size effect on the kinetic properties of grain boundaries in a nanocrystalline material at grain sizes d ≥ 35 nm. Simultaneously, the analysis predicts that if triple junction diffusion of Ni in Cu is enhanced with respect to the corresponding grain boundary diffusion rate, it is still less than 500⋅Dgb within the temperature interval from 420 K to 470 K.
Nonlinear dielectric effect in supercritical diethyl ether
Authors: Drozd-Rzoska Aleksandra , Rzoska Sylwester J. , Martinez-Garcia Julio Cesar
Published: September 2014

Nonlinear dielectric effect (NDE) describes changes of dielectric permittivity induced by a strong electric field in a liquid dielectric. The most classical finding related to this magnitude is the negative sign of NDE in liquid diethyl ether (DEE), recalled by Peter Debye in his Nobel Prize lecture. This article shows that the positive sign of NDE in DEE is also possible, in the supercritical domain. Moreover, NDE on approaching the gas-liquid critical point exhibits a unique critical effect described by the critical exponent ψ ≈ 0.4 close to critical temperature (TC) and ψ ≈ 0.6 remote from TC. This can be linked to the emergence of the mean-field behavior in the immediate vicinity of TC, contrary to the typical pattern observed for critical phenomena. The multi-frequency mode of NDE measurements made it possible to estimate the evolution of lifetime of critical fluctuations. The new way of data analysis made it possible to describe the critical effect without a knowledge of the non-critical background contribution in prior.
Edge Thomson scattering diagnostic on COMPASS tokamak: Installation, calibration, operation, improvements
Authors: Bohm P. , Aftanas M. , Bilkova P. , Stefanikova E. , Mikulin O. , Melich R. , Janky F. , Havlicek J. , Sestak D. , Weinzettl V. , Stockel J. , Hron M. , Panek R. , Scannell R. , Frassinetti L. , Fassina A. , Naylor G. , Walsh M. J.
Published: September 2014

The core Thomson scattering diagnostic (TS) on the COMPASS tokamak was put in operation and reported earlier. Implementation of edge TS, with spatial resolution along the laser beam up to ∼1/100 of the tokamak minor radius, is presented now. The procedure for spatial calibration and alignment of both core and edge systems is described. Several further upgrades of the TS system, like a triggering unit and piezo motor driven vacuum window shutter, are introduced as well. The edge TS system, together with the core TS, is now in routine operation and provides electron temperature and density profiles.
A technique for measuring dynamic friction coefficient under impact loading
Authors: Lin Y. L. , Qin J. G. , Chen R. , Zhao P. D. , Lu F. Y.
Published: September 2014

We develop a novel setup based on the split Hopkinson pressure bar technique to test the dynamic friction coefficient under impact loading. In the setup, the major improvement is that the end of the incident bar near the specimen is wedge-shaped, which results in a combined compressive and shear loading applied to the specimen. In fact, the shear loading is caused by the interfacial friction between specimen and bars. Therefore, when the two loading force histories are measured, the friction coefficient histories can be calculated without any assumptions and theoretical derivations. The geometry of the friction pairs is simple, and can be either cuboid or cylindrical. Regarding the measurements, two quartz transducers are used to directly record the force histories, and an optical apparatus is designed to test the interfacial slip movement. By using the setup, the dynamic friction coefficient of PTFE/aluminum 7075 friction pairs was tested. The time resolved dynamic friction coefficient and slip movement histories were achieved. The results show that the friction coefficient changes during the loading process, the average data of the relatively stable flat plateau section of the friction coefficient curves is 0.137, the maximum normal pressure is 52 MPa, the maximum relative slip velocity is 1.5 m/s, and the acceleration is 8400 m2/s. Furthermore, the friction test was simulated using an explicit FEM code LS-DYNA. The simulation results showed that the constant pressure and slip velocity can both be obtained with a wide flat plateau incident pulse. For some special friction pairs, normal pressure up to a few hundred MPa, interfacial slip velocities up to 10 m/s, and slip movement up to centimeter-level can be expected.
Hall probe measurements of the poloidal magnetic field in Compact Toroidal Hybrid plasmas
Authors: Stevenson B. A. , Knowlton S. F. , Hartwell G. J. , Hanson J. D. , Maurer D. A.
Published: September 2014

A linear array of 16 Hall effect sensors has been developed to directly measure the poloidal magnetic field inside the boundary of a non-axisymmetric hybrid torsatron/tokamak plasma. The array consists of miniature gallium arsenide Hall sensor elements mounted 8 mm apart on a narrow, rotatable printed circuit board inserted into a re-entrant stainless steel tube sheathed in boron nitride. The sensors are calibrated on the bench and in situ to provide accurate local measurements of the magnetic field to aid in reconstructing the equilibrium plasma current density profiles in fully three-dimensional plasmas. Calibrations show that the sensor sensitivities agree with the nominal manufacturers specifications of 1.46 V/T. Poloidal fields measured with the Hall sensor array are found to be within 5% of poloidal fields modeled with a Biot-Savart code.
Experimentally proven liquid-liquid critical point of dilute glycerol-water solution at 150 K
Authors: Suzuki Yoshiharu , Mishima Osamu
Published: September 2014

The experimental and theoretical studies of supercooled liquid water strongly suggest that the two liquid waters and their liquid-liquid critical point (LLCP) exist at low temperature. However, the decisive experimental evidence of the LLCP has not been obtained because of the rapid crystallization of liquid water in the “no-man's land.” Here, we observed experimentally the pressure-induced polyamorphic transition in the dilute glycerol-water solution which relates to the water polyamorphism. We examined the effect of the glycerol concentration on the liquid-liquid transition, and found its LLCP around 0.12–0.15 mole fraction, 0.03–0.05 GPa, and ∼150 K. A 150 K was above, or around, the recently recognized glass transition temperatures of amorphous ices, and the crystallization did not occur, indicating that the direct observation of LLCP is feasible. The low-temperature LLCP has implication to the argument of the relation between the interaction potential of water molecule and the polyamorphic phase diagram.
Recombination dynamics of excitons with low non-radiative component in semi-polar (10-11)-oriented GaN/AlGaN multiple quantum wells
Authors: Rosales D. , Gil B. , Bretagnon T. , Guizal B. , Izyumskaya N. , Monavarian M. , Zhang F. , Okur S. , Avrutin V. , Özgür Ü. , Morkoç H.
Published: September 2014

Optical properties of GaN/Al0.2Ga0.8N multiple quantum wells grown with semi-polar (10-11) orientation on patterned 7°-off Si (001) substrates have been investigated. Studies performed at 8 K reveal the in-plane anisotropic behavior of the QW photoluminescence (PL) intensity for this semi-polar orientation. The time resolved PL measurements were carried out in the temperature range from 8 to 295 K to deduce the effective recombination decay times, with respective radiative and non-radiative contributions. The non-radiative component remains relatively weak with increasing temperature, indicative of high crystalline quality. The radiative decay time is a consequence of contribution from both localized and free excitons. We report an effective density of interfacial defects of 2.3 × 1012 cm−2 and a radiative recombination time of τloc = 355 ps for the localized excitons. This latter value is significantly larger than those reported for the non-polar structures, which we attribute to the presence of a weak residual electric field in the semi-polar QW layers.
High electron mobility thin-film transistors based on Ga2O3 grown by atmospheric ultrasonic spray pyrolysis at low temperatures
Authors: Thomas Stuart R. , Adamopoulos George , Lin Yen-Hung , Faber Hendrik , Sygellou Labrini , Stratakis Emmanuel , Pliatsikas Nikos , Patsalas Panos A. , Anthopoulos Thomas D.
Published: September 2014

We report on thin-film transistors based on Ga2O3 films grown by ultrasonic spray pyrolysis in ambient atmosphere at 400–450 °C. The elemental, electronic, optical, morphological, structural, and electrical properties of the films and devices were investigated using a range of complementary characterisation techniques, whilst the effects of post deposition annealing at higher temperature (700 °C) were also investigated. Both as-grown and post-deposition annealed Ga2O3 films are found to be slightly oxygen deficient, exceptionally smooth and exhibit a wide energy bandgap of ∼4.9 eV. Transistors based on as-deposited Ga2O3 films show n-type conductivity with the maximum electron mobility of ∼2 cm2/V s.
Glow discharge based device for solving mazes
Authors: Dubinov Alexander E. , Maksimov Artem N. , Mironenko Maxim S. , Pylayev Nikolay A. , Selemir Victor D.
Published: September 2014

A glow discharge based device for solving mazes has been designed and tested. The device consists of a gas discharge chamber and maze-transformer of radial-azimuth type. It allows changing of the maze pattern in a short period of time (within several minutes). The device has been tested with low pressure air. Once switched on, a glow discharge has been shown to find the shortest way through the maze from the very first attempt, even if there is a section with potential barrier for electrons on the way. It has been found that ionization waves (striations) can be excited in the maze along the length of the plasma channel. The dependancy of discharge voltage on the length of the optimal path through the maze has been measured. A reduction in discharge voltage with one or two potential barriers present has been found and explained. The dependency of the magnitude of discharge ignition voltage on the length of the optimal path through the maze has been measured. The reduction of the ignition voltage with the presence of one or two potential barriers has been observed and explained.
Statistical analysis of the dynamics of secondary electrons in the flare of a high-voltage beam-type discharge
Authors: Demkin V. P. , Mel'nichuk S. V.
Published: September 2014

In the present work, results of investigations into the dynamics of secondary electrons with helium atoms in the presence of the reverse electric field arising in the flare of a high-voltage pulsed beam-type discharge and leading to degradation of the primary electron beam are presented. The electric field in the discharge of this type at moderate pressures can reach several hundred V/cm and leads to considerable changes in the kinetics of secondary electrons created in the process of propagation of the electron beam generated in the accelerating gap with a grid anode. Moving in the accelerating electric field toward the anode, secondary electrons create the so-called compensating current to the anode. The character of electron motion and the compensating current itself are determined by the ratio of the field strength to the concentration of atoms (Е/n). The energy and angular spectra of secondary electrons are calculated by the Monte Carlo method for different ratios E/n of the electric field strength to the helium atom concentration. The motion of secondary electrons with threshold energy is studied for inelastic collisions of helium atoms and differential analysis is carried out of the collisional processes causing energy losses of electrons in helium for different E/n values. The mechanism of creation and accumulation of slow electrons as a result of inelastic collisions of secondary electrons with helium atoms and selective population of metastable states of helium atoms is considered. It is demonstrated that in a wide range of E/n values the motion of secondary electrons in the beam-type discharge flare has the character of drift. At E/n values characteristic for the discharge of the given type, the drift velocity of these electrons is calculated and compared with the available experimental data.
Theoretical description based on general and exact nonextensive dispersion relations of plasma oscillation data and verification of new acoustic plasma waves
Authors: Ebrahimi V. , Esfandyari-Kalejahi A.
Published: September 2014

In this paper, first we represent the differences between spatial and temporal dispersions and their dependence on the measurement techniques for electrostatic waves in unmagnetized collisionless plasma. Then, three different experimental data are compared to the solutions of exact nonextensive dispersion relations for electron-ion and pair plasma. The results confirm the existence of new acoustic plasma waves. Furthermore, these comparisons yield a Maxwellian and a nonextensive plasma with nonextensive parameter q larger than one, and a Maxwellian plasma with some abnormal dispersion properties.
The hydrogen atom in plasmas with an external electric field
Authors: Bahar M. K. , Soylu A.
Published: September 2014

We numerically solve the Schrödinger equation, using a more general exponential cosine screened Coulomb (MGECSC) potential with an electric field, in order to investigate the screening and weak external electric field effects on the hydrogen atom in plasmas. The MGECSC potential is examined for four different cases, corresponding to different screening parameters of the potential and the external electric field. The influences of the different screening parameters and the weak external electric field on the energy eigenvalues are determined by solving the corresponding equations using the asymptotic iteration method (AIM). It is found that the corresponding energy values shift when a weak external electric field is applied to the hydrogen atom in a plasma. This study shows that a more general exponential cosine screened Coulomb potential allows the influence of an applied, weak, external electric field on the hydrogen atom to be investigated in detail, for both Debye and quantum plasmas simultaneously. This suggests that such a potential would be useful in modeling similar effects in other applications of plasma physics, and that AIM is an appropriate method for solving the Schrödinger equation, the solution of which becomes more complex due to the use of the MGECSC potential with an applied external electric field.
Turbulence in the cylindrical slab
Authors: Gentle K. W. , Rowan W. L. , Williams C. B. , Brookman M. W.
Published: September 2014

The cylindrical slab was the first and simplest model of intrinsically unstable microturbulence. The Helimak is an experimental realization of this model. Although finite, it is sufficiently large to escape boundary effects, with dimensionless parameters similar to those of a tokamak edge or scrape off layer. The essential drive is interchange-like, a pressure gradient with unfavorable magnetic curvature, leading to a non-linearly saturated state of large-amplitude turbulence, Δnrms/n ∼ 0.5. The nonlinear processes governing this saturation are unique, unlike any of those posited for the much weaker turbulence typical of confined plasma, e.g., in a tokamak. Neither linear stability theory, quasi-linear theory, zonal flows, nor flow shear stabilization is consistent with the observations. The mechanisms determining the non-linearly saturated state constitute an important challenge to our understanding of strongly nonlinear systems.
Forces acting on a particle in a concentration gradient under an externally applied oscillating electric field
Authors: Luo Yuan , Yobas Levent
Published: September 2014

We report a force field on a particle in a concentration (conductivity) gradient under an externally applied oscillating electric field. The conductivity gradient was established through integrated microcapillaries bridging high- and low-conductivity streams in dedicated microchannels. Particles in low-conductivity electrolyte were observed to experience a strong force with the application of an oscillating field and pulled to the microcapillary openings where they were held against the flow. Particle trapping was accompanied by a concurrent electrolyte injection from high- to low-conductivity channel, triggered with the externally applied field and further contributed to the conductivity gradient near the trapping sites. We experimentally evaluated the force dependence on the magnitude and frequency of the excitation field for 10 μm polystyrene particles immersed at various conductivity levels. The experiments suggest that the observed force cannot be simply explained by dielectrophoresis or diffusiophoresis alone and further requires the consideration of a so-called concentration polarization force. This force has been rather recently postulated based on a theoretical treatment and yet to be experimentally validated. Using the theoretical treatment of this force, together with fluidic drag and diffusiophoresis, we correctly predicted trapping trajectories of particles based on a simultaneous solution of Poisson-Nernst-Planck and Stokes equations. The predicted and measured trapping velocities were found in reasonable agreement (within a factor of <1.6), suggesting that the consideration of the concentration polarization force is necessary for describing the observed particle behavior.
Stress and field contactless sensor based on the scattering of electromagnetic waves by a single ferromagnetic microwire
Authors: Herrero-Gómez C. , Aragón A. M. , Hernando-Rydings M. , Marín P. , Hernando A.
Published: September 2014

In this paper, we report an experimental study on the microwave modulated scattering intensity for a single Fe2.25Co72.75Si10B15 amorphous metallic microwire. The modulation is driven by applying a bias magnetic field that tunes the magnetic permeability of the ferromagnetic microwire. Furthermore, by using a magnetostrictive microwire, we also demonstrate that the microwave scattering is sensitive to mechanical stresses. In fact, we present a wireless microwave controlled stress sensor, suitable for biological applications, as a possible use of this effect. In addition, a first order theoretical approximation accounts for the observed influence of the magnetic permeability on the scattering coefficients. That model leads to predictions in good agreement with the experimental results.
Epitaxial growth and electronic properties of well ordered phthalocyanine heterojunctions MnPc/F16CoPc
Authors: Lindner Susi , Mahns Benjamin , Treske Uwe , Vilkov Oleg , Haidu Francisc , Fronk Michael , Zahn Dietrich R. T. , Knupfer Martin
Published: September 2014

We have prepared phthalocyanine heterojunctions out of MnPc and F16CoPc, which were studied by means of X-ray absorption spectroscopy. This heterojunction is characterized by a charge transfer at the interface, resulting in charged MnPcδ + and F16CoPcδ − species. Our data reveal that the molecules are well ordered and oriented parallel to the substrate surface. Furthermore, we demonstrate the filling of the Co 3\documentclass[12pt]{minimal}\begin{document}$d_{z^2}$\end{document}dz2 orbital due to the charge transfer, which supports the explanation of the density functional theory, that the charge transfer is local and affects the metal centers only.
Effect of oxygen incorporation on the structure and elasticity of Ti-Al-O-N coatings synthesized by cathodic arc and high power pulsed magnetron sputtering
Authors: Hans M. , to Baben M. , Music D. , Ebenhöch J. , Primetzhofer D. , Kurapov D. , Arndt M. , Rudigier H. , Schneider J. M.
Published: September 2014

Ti-Al-O-N coatings were synthesized by cathodic arc and high power pulsed magnetron sputtering. The chemical composition of the coatings was determined by means of elastic recoil detection analysis and energy dispersive X-ray spectroscopy. The effect of oxygen incorporation on the stress-free lattice parameters and Young's moduli of Ti-Al-O-N coatings was investigated by X-ray diffraction and nanoindentation, respectively. As nitrogen is substituted by oxygen, implications for the charge balance may be expected. A reduction in equilibrium volume with increasing O concentration is identified by X-ray diffraction and density functional theory calculations of Ti-Al-O-N supercells reveal the concomitant formation of metal vacancies. Hence, the oxygen incorporation-induced formation of metal vacancies enables charge balancing. Furthermore, nanoindentation experiments reveal a decrease in elastic modulus with increasing O concentration. Based on ab initio data, two causes can be identified for this: First, the metal vacancy-induced reduction in elasticity; and second, the formation of, compared to the corresponding metal nitride bonds, relatively weak Ti-O and Al-O bonds.
Impact of pseudo-gap states on the pinning energy and irreversibility field of high temperature superconductors
Authors: Deutscher Guy
Published: September 2014

The existence of pseudo-gap states at energies larger than the coherence energy scale is shown to be at the origin of the difficulties encountered in achieving strong vortex pinning in the high Tc cuprates. Reduction or elimination of the pseudo-gap states by overdoping is effective in increasing the condensation energy and the irreversibility field. In YBa2Cu3O7, a full BCS state, with a single energy scale, can be restored, leading to the highest known irreversibility field and pinning strength. In the bismuthates, the detrimental effect of the pseudo-gap states can only be mitigated to some extent by overdoping.
High performance magnesium anode in paper-based microfluidic battery, powering on-chip fluorescence assay
Authors: Koo Youngmi , Sankar Jagannathan , Yun Yeoheung
Published: September 2014

A high power density and long-lasting stable/disposable magnesium battery anode was explored for a paper-based fluidic battery to power on-chip functions of various Point of Care (POC) devices. The single galvanic cell with magnesium foil anode and silver foil cathode in Origami cellulose chip provided open circuit potential, 2.2 V, and power density, 3.0 mW/cm2. A paper-based fluidic galvanic cell was operated with one drop of water (80 μl) and continued to run until it was dry. To prove the concept about powering on-chip POC devices, two-serial galvanic cells are developed and incorporated with a UV-light emitting diode (λ = 365 nm) and fluorescence assay for alkaline phosphatase reaction. Further, detection using smart phones was performed for quantitative measurement of fluorescent density. To conclude, a magnesium-based fluidic battery paper chip was extremely low-cost, required minute sample volumes, was easy to dispose of, light weight, easy to stack, store and transport, easy to fabricate, scalable, and has faster analysis times.
Graphene-based tunable metamaterial terahertz filters
Authors: Yang Kai , Liu Shuchang , Arezoomandan Sara , Nahata Ajay , Sensale-Rodriguez Berardi
Published: September 2014

We propose and describe a micro-machined tunable metamaterial terahertz filter based on graphene. The device structure consists of periodic metallic rings with several gaps where tunable graphene stripes are located. We demonstrate that the filter resonance frequency can be adjusted easily by varying the conductivity of graphene and implement this by changing the number of stacked graphene layers. Moreover, the proposed design is scalable, in the sense that the resonance frequency tuning can be controlled by scaling the inner and outer radius of the metal rings. Using numerical simulations and terahertz time-domain spectroscopy measurements of the fabricated samples, we show that the resonance frequency of the structure can be altered by 40% (i.e., from ∼0.2 THz to ∼0.12 THz) by simply tuning the conductivity of graphene. Importantly, the active area of the device is ≪0.1% of the total unit cell area, which can boost the device speed upon electrostatic actuation.
The effects of Si-doped prelayers on the optical properties of InGaN/GaN single quantum well structures
Authors: Davies M. J. , Dawson P. , Massabuau F. C.-P. , Oliver R. A. , Kappers M. J. , Humphreys C. J.
Published: September 2014

In this paper, we report on the effects of including Si-doped (In)GaN prelayers on the low temperature optical properties of a blue-light emitting InGaN/GaN single quantum well. We observed a large blue shift of the photoluminescence peak emission energy and significant increases in the radiative recombination rate for the quantum well structures that incorporated Si-doped prelayers. Simulations of the variation of the conduction and valence band energies show that a strong modification of the band profile occurs for the quantum wells on Si-doped prelayers due to an increase in strength of the surface polarization field. The enhanced surface polarization field opposes the built-in field across the quantum well and thus reduces this built-in electric field. This reduction of the electric field across the quantum well reduces the Quantum Confined Stark Effect and is responsible for the observed blue shift and the change in the recombination dynamics.
Refractive index of r-cut sapphire under shock pressure range 5 to 65 GPa
Authors: Cao Xiuxia , Li Jiabo , Li Jun , Li Xuhai , Xu Liang , Wang Yuan , Zhu Wenjun , Meng Chuanmin , Zhou Xianming
Published: September 2014

High-pressure refractive index of optical window materials not only can provide information on electronic polarizability and band-gap structure, but also is important for velocity correction in particle-velocity measurement with laser interferometers. In this work, the refractive index of r-cut sapphire window at 1550 nm wavelength was measured under shock pressures of 5–65 GPa. The refractive index (n) decreases linearly with increasing shock density (ρ) for shock stress above the Hugoniot elastic limit (HEL): n = 2.0485 (± 0.0197) − 0.0729 (± 0.0043)ρ, while n remains nearly a constant for elastic shocks. This behavior is attributed to the transition from elastic (below HEL) to heterogeneous plastic deformation (above HEL). Based on the obtained refractive index-density relationship, polarizability of the shocked sapphire was also obtained.
Note: A method for minimizing oxide formation during elevated temperature nanoindentation
Authors: Cheng I. C. , Garcia-Sanchez E. , Hodge A. M.
Published: September 2014

A standardized method to protect metallic samples and minimize oxide formation during elevated-temperature nanoindentation was adapted to a commercial instrument. Nanoindentation was performed on Al (100), Cu (100), and W (100) single crystals submerged in vacuum oil at 200 °C, while the surface morphology and oxidation was carefully monitored using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The results were compared to room temperature and 200 °C nanoindentation tests performed without oil, in order to evaluate the feasibility of using the oil as a protective medium. Extensive surface characterization demonstrated that this methodology is effective for nanoscale testing.
Raman and photoluminescence mapping of InxGa1−xN (x ∼ 0.4) at high pressure: Optical determination of composition and stress
Authors: Gkrana V. , Filintoglou K. , Arvanitidis J. , Christofilos D. , Bazioti C. , Dimitrakopulos G. P. , Katsikini M. , Ves S. , Kourouklis G. A. , Zoumakis N. , Georgakilas A. , Iliopoulos E.
Published: September 2014

The pressure response of a polar wurtzite InxGa1−xN (x = 0.37) film epitaxially grown on a GaN/sapphire template was studied by means of combined Raman and photoluminescence (PL) mappings. The pressure slopes of the Raman peaks (∂ω/∂P ∼ 4.7 cm−1·GPa−1) of the studied alloy are indicative of its intermediate stiffness between the end members of the InxGa1−xN system. The data analysis suggests that in our experiments the obtained slopes have marginal contribution, if any, from the substrate. Furthermore, the similarity of the ambient pressure value of the PL peak energy (∼1.97 eV) and its pressure slope (∂EPL/∂P ∼ 30 meV·GPa−1) with those obtained by absorption measurements implies that PL can be used to follow the pressure evolution of the energy bandgap. Finally, we demonstrate that all-optical characterization of the composition and residual stress of InxGa1−xN samples is feasible.
High power all-metal spin torque oscillator using full Heusler Co2(Fe,Mn)Si
Authors: Seki Takeshi , Sakuraba Yuya , Arai Hiroko , Ueda Masaki , Okura Ryo , Imamura Hiroshi , Takanashi Koki
Published: September 2014

We showed the high rf power (Pout) emission from an all-metal spin torque oscillator (STO) with a Co2Fe0.4Mn0.6Si (CFMS)/Ag/CFMS giant magnetoresistance (GMR) stack, which was attributable to the large GMR effect thanks to the highly spin-polarized CFMS. The oscillation spectra were measured by varying the magnetic field direction, and the perpendicular magnetic field was effective to increase Pout and the Q factor. We simultaneously achieved a high output efficiency of 0.013%, a high Q of 1124, and large frequency tunability. CFMS-based all-metal STO is promising for overcoming the difficulties that conventional STOs are confronted with.
Magnetization reversal driven by a spin torque oscillator
Authors: Sbiaa R.
Published: September 2014

Magnetization reversal of a magnetic free layer under spin transfer torque (STT) effect from a magnetic hard layer with a fixed magnetization direction and an oscillating layer is investigated. By including STT from the oscillating layer with in-plane anisotropy and orthogonal polarizer, magnetization-time dependence of free layer is determined. The results show that the frequency and amplitude of oscillations can be varied by adjusting the current density and magnetic properties. For an optimal oscillation frequency (fopt), a reduction of the switching time (t0) of the free layer is observed. Both fopt and t0 increase with the anisotropy field of the free layer.
Dynamic selective switching in antiferromagnetically-coupled bilayers close to the spin reorientation transition
Authors: Fernández-Pacheco A. , Ummelen F. C. , Mansell R. , Petit D. , Lee J. H. , Swagten H. J. M. , Cowburn R. P.
Published: September 2014

We have designed a bilayer synthetic antiferromagnet where the order of layer reversal can be selected by varying the sweep rate of the applied magnetic field. The system is formed by two ultra-thin ferromagnetic layers with different proximities to the spin reorientation transition, coupled antiferromagnetically using Ruderman-Kittel-Kasuya-Yosida interactions. The different dynamic magnetic reversal behavior of both layers produces a crossover in their switching fields for field rates in the kOe/s range. This effect is due to the different effective anisotropy of both layers, added to an appropriate asymmetric antiferromagnetic coupling between them. Field-rate controlled selective switching of perpendicular magnetic anisotropy layers as shown here can be exploited in sensing and memory applications.
Unambiguous separation of the inverse spin Hall and anomalous Nernst effects within a ferromagnetic metal using the spin Seebeck effect
Authors: Wu Stephen M. , Hoffman Jason , Pearson John E. , Bhattacharya Anand
Published: September 2014

The longitudinal spin Seebeck effect is measured on the ferromagnetic insulator Fe3O4 with the ferromagnetic metal Co0.2Fe0.6B0.2 (CoFeB) as the spin detector. By using a non-magnetic spacer material between the two materials (Ti), it is possible to decouple the two ferromagnetic materials and directly observe pure spin flow from Fe3O4 into CoFeB. It is shown that in a single ferromagnetic metal, the inverse spin Hall effect (ISHE) and anomalous Nernst effect (ANE) can occur simultaneously with opposite polarity. Using this and the large difference in the coercive fields between the two magnets, it is possible to unambiguously separate the contributions of the spin Seebeck effect from the ANE and observe the degree to which each effect contributes to the total response. These experiments show conclusively that the ISHE and ANE in CoFeB are separate phenomena with different origins and can coexist in the same material with opposite response to a thermal gradient.
Brillouin frequency shift hopping in polymer optical fiber
Authors: Hayashi Neisei , Minakawa Kazunari , Mizuno Yosuke , Nakamura Kentaro
Published: September 2014

We investigated the Brillouin gain spectrum dependence on large strain of up to 60% in a polymer optical fiber (POF) at 1.55 μm, and found that the Brillouin frequency shift (BFS) abruptly changes from ∼2.7 GHz to ∼3.2 GHz. We named this phenomenon “BFS hopping,” and found it to originate from the varied acoustic velocity induced by the stepwise change in the core diameter of the POF. This is because of the yielding of the overcladding layer composed of polycarbonate. After the occurrence of BFS hopping phenomenon, the BFS dependence coefficients on strain and temperature in the POF were measured to be −65.6 MHz/% and −4.04 MHz/K respectively. These values indicate that, compared to an unstrained POF, further higher-precision temperature sensing with lower strain sensitivity is feasible.
Magnetocaloric effect in Fe-Zr-B-M (M = Ni, Co, Al, and Ti) amorphous alloys
Authors: Li Xingzhou , Pan Ye
Published: September 2014

The amorphous soft magnetic Fe-Zr-B-M (M = Ni, Co, Al, and Ti) ribbons have been successfully fabricated and their magnetocaloric effect was investigated through the measurements of magnetization in this work. The magnetocaloric effect, both the maximum entropy change and the refrigerant capacity, of the precursor material Fe88Zr8B4 amorphous alloy is enhanced with microalloying addition. The Curie temperature increases with the addition of Co but decreases with the addition of Al and Ti. The field dependence of the entropy change was studied. All specimens show the same power law to the field, which is in agreement with the reported amorphous alloys. The specimen containing 1 at. %Co, whose Curie temperature is 295 K and entropy change reaches 1.48 J kg−1 K−1 at an applied field of 1.5 T, is suitable for a magnetic refrigerant at room temperature. On the other hand, the specimen containing 1 at. %Ti with Curie temperature of 270 K and refrigerant capacity of 183.5 J kg−1 is a proper work material for a magnetic refrigerant at subroom temperature.
Giant magnetoimpedance effect enhanced by thermoplastic drawing
Authors: Qiang Jian , Estevez Diana , Dong Yaqiang , Man Qikui , Chang Chuntao , Wang Xinmin , Li Run-Wei
Published: September 2014

We performed thermoplastic forming (TPF) on FeCoNbB metallic glass ribbons with a supercooled liquid region exceeding 100 K, and found the sample after TPF is still completely amorphous. More importantly, the giant magnetoimpedance (GMI) effect was improved after the forming process: the maximum GMI ratio and sensitivity increased from 41% to 12.3%/Oe in the case of as-cast sample to 280% and 358.2%/Oe in the case of resulting sample after TPF, respectively. The hysteresis loops and domain patterns were subsequently studied, which revealed that the primary factor leading to the improvement of the GMI effect was the enhanced longitudinal magnetic anisotropy induced by the TPF process. We therefore assume that TPF is an effective way that improves the GMI effect, which differs from conventional annealing methods.
Observation of negative magneto-resistance in SrFe1−xTixO3−δ (x = 0 to 0.3) systems
Authors: Sendil Kumar A. , Srinath S.
Published: September 2014

Resistance and magneto-resistance of nanocrystalline SrFe1−xTixO3−δ (x = 0 to 0.3) systems are investigated. Substitution of non magnetic Ti4+ stabilizes the single phase tetragonal crystal structure with I4/mmm space group and Ti introduces bond disorder as well as site disorder. With increase in Ti content, the disorder increase leading to localization and large change in resistivity is observed in all the systems. In undoped system, the increase in resistivity is associated with the magnetic transition. All the Ti doped samples show large change in resistivity much above the magnetic ordering temperature and three dimensional Variable Range Hopping mechanism seems to explain the transport and magneto-transport behavior in these systems.
Local charge transport properties of hydrazine reduced monolayer graphene oxide sheets prepared under pressure condition
Authors: Ryuzaki Sou , Meyer Jakob A. S. , Petersen Søren , Nørgaard Kasper , Hassenkam Tue , Laursen Bo W.
Published: September 2014

Charge transport properties of chemically reduced graphene oxide (RGO) sheets prepared by treatment with hydrazine were examined using conductive atomic force microscopy. The current-voltage (I-V) characteristics of monolayer RGO sheets prepared under atmospheric pressure followed an exponentially increase due to 2D variable-range hopping conduction through small graphene domains in an RGO sheet containing defect regions of residual sp3 carbon clusters bonded to oxygen groups, whereas RGO sheets prepared in a closed container under moderate pressure showed linear I-V characteristics with a conductivity of 267.2−537.5 S/m. It was found that the chemical reduction under pressure results in larger graphene domains (sp2 networks) in the RGO sheets when compared to that prepared under atmospheric pressure, indicating that the present reduction of GO sheets under the pressure is one of the effective methods to make well-reduced GO sheets.